U.S. patent application number 09/986891 was filed with the patent office on 2002-07-04 for driving force control apparatus.
Invention is credited to Kadota, Keiji, Shimizu, Kouichi.
Application Number | 20020087252 09/986891 |
Document ID | / |
Family ID | 27345184 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020087252 |
Kind Code |
A1 |
Shimizu, Kouichi ; et
al. |
July 4, 2002 |
Driving force control apparatus
Abstract
A driving force control apparatus is provided to optimize the
acceleration performance and improve the energy efficiency of a
vehicle. Preferably, the front wheels are driven by the internal
combustion engine, while the rear wheels are driven by the electric
motor. The electric motor is driven by electrical power generated
by the generator. The generator is driven by the engine. When
acceleration slippage occurs in the front wheels, the generator is
controlled so as to produce a generation load torque corresponding
to the acceleration slippage magnitude.
Inventors: |
Shimizu, Kouichi;
(Sagamihara-shi, JP) ; Kadota, Keiji; (Tokyo,
JP) |
Correspondence
Address: |
SHINJYU GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Family ID: |
27345184 |
Appl. No.: |
09/986891 |
Filed: |
November 13, 2001 |
Current U.S.
Class: |
701/84 ; 701/69;
701/90; 903/916 |
Current CPC
Class: |
B60W 20/10 20130101;
B60W 30/18027 20130101; B60W 10/06 20130101; Y02T 10/62 20130101;
B60W 10/08 20130101; B60K 17/356 20130101; B60K 28/16 20130101;
B60K 6/52 20130101; B60W 2520/263 20130101; B60W 20/00 20130101;
B60W 2552/40 20200201; B60K 6/44 20130101; Y10S 903/916
20130101 |
Class at
Publication: |
701/84 ; 701/69;
701/90 |
International
Class: |
G06F 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2000 |
JP |
2000-346287 |
Nov 14, 2000 |
JP |
2000-346288 |
Jul 25, 2001 |
JP |
2001-225144 |
Claims
What is claimed is:
1. A driving force control apparatus for a vehicle having front and
rear wheels with at least one of the front and rear wheels being a
drive wheel driven by an internal combustion engine that drives a
generator, said driving force control apparatus comprising: a drive
wheel slippage estimating section configured to estimate if
acceleration slippage is occurring in the drive wheel; and a
generator control section configured to control a generation load
torque of the generator to substantially correspond to an
acceleration slippage magnitude of the drive wheel, when said drive
wheel slippage estimating section estimates acceleration slippage
occurring in the drive wheel.
2. The driving force control apparatus as recited in claim 1,
wherein said drive wheel slippage estimating section estimates if
acceleration slippage is occurring based on a speed differential
between the front wheels and the rear wheels.
3. The driving force control apparatus as recited in claim 1,
wherein said drive wheel slippage estimating section estimates if
acceleration slippage is occurring from a comparison between a
drive torque transferred from the internal combustion engine to the
drive wheel and a road surface reaction force limit torque of the
drive wheel.
4. The driving force control apparatus as recited in claim 1,
wherein said generator control section includes a generation load
torque adjusting section configured to adjust the generation load
torque of the generator, a surplus torque computing section
configured to compute a surplus torque that substantially
corresponds to a difference magnitude by which a drive torque
transferred from the internal combustion engine to the drive wheel
exceeds a road surface reaction force limit torque of the drive
wheel, and a generation load torque control section operatively
coupled to said generation load torque adjusting section to control
the generation load torque of the generator to a torque value based
on said surplus torque computed by said surplus torque computing
section.
5. The driving force control apparatus as recited in claim 4,
wherein said surplus torque computing section determines said
surplus torque based on the acceleration slippage magnitude of the
drive wheel and the generation load torque of the generator.
6. The driving force control apparatus as recited in claim 4,
wherein said surplus torque computing section includes a drive
wheel limit torque computing section configured to compute a
current road surface reaction force limit torque of the drive
wheel, and said surplus torque computing section determines said
surplus torque based on a difference between the current road
surface reaction force limit torque computed by said drive wheel
limit torque computing section and the drive torque transferred
from the internal combustion engine to the drive wheel.
7. The driving force control apparatus as recited in claim 1,
further comprising an electric motor operatively driven by
electrical power generated by said generator, said electric motor
being arranged to operatively drive at least one of the front and
rear wheels which is a subordinate drive wheel that not driven by
said internal combustion engine which is a main drive wheel.
8. The driving force control apparatus as recited in claim 7,
further comprising a load torque computing section configured to
compute a magnitude of an engine load torque imposed on the
internal combustion engine by the generator due to power generation
of the generator; a deviation torque computing section configured
to compute a deviation torque obtained by subtracting a minimum
allowed torque for which the internal combustion engine will not
stop from an output torque of the internal combustion engine; and
an internal combustion engine output control section configured to
control a lower limit of the output torque of the internal
combustion engine such that the deviation torque is larger than the
engine load torque imposed on the internal combustion engine by the
generator due to power generation of the generator.
9. The driving force control apparatus as recited in claim 8,
wherein said internal combustion engine output control section is
configured to start when the deviation torque is smaller than the
engine load torque, and to control the output torque of the
internal combustion engine in accordance with a magnitude of a
value obtained by subtracting the deviation torque from the engine
load torque regardless of an acceleration operation on the internal
combustion engine.
10. The driving force control apparatus as recited in claim 7,
further comprising a load torque computing section configured to
compute a magnitude of an engine load torque imposed on the
internal combustion engine by the generator due to power generation
of the generator; a deviation torque computing section configured
to compute a deviation torque obtained by subtracting a minimum
allowed torque for which the internal combustion engine will not
stop from an output torque of the internal combustion engine; and a
load torque control section configured to control a maximum value
of the generation load torque from the generator so as to be less
than or equal to the deviation torque.
11. The driving force control apparatus as recited in claim 7,
wherein said drive wheel limit torque computing section includes a
limit torque calculating section configured to repeatedly calculate
the road surface reaction force limit torque of the main drive
wheel; a limit torque maximum value updating section configured to
compare the road surface reaction force limit torque and a
predetermined limit torque, set the larger of the current road
surface reaction force limit torque and the predetermined limit
torque as a maximum limit torque value, and set the maximum limit
torque value as a road surface reaction force limit torque value;
and a limit torque reset section configured to start upon
determining that a driving force of the subordinate drive wheel
should be increased, and resets the maximum limit torque value to
an updated maximum limit torque value.
12. The driving force control apparatus as recited in claim 11,
wherein said limit torque reset section determines that the driving
force of the subordinate drive wheel should be increased when a
speed differential occurs between the front and rear wheels that is
greater than or equal to a prescribed value.
13. The driving force control apparatus as recited in claim 11,
further comprising a wheel grip limit estimating section configured
to compute a wheel grip limit estimation value for the main drive
wheel, and said limit torque reset section determining that the
driving force of the subordinate drive wheel should be increased
upon determining that the wheel grip limit estimation value of the
main drive wheel is at least close to a detected wheel grip
limit.
14. The driving force control apparatus as recited in claim 11,
further comprising a poor road estimating section configured to
estimate if detected road conditions are within a prescribed poor
road range, said limit torque reset section determining that the
driving force of the subordinate drive wheel should be increased
upon said poor road estimating section determining that the vehicle
is traveling on a road within the prescribed poor road range.
15. The driving force control apparatus as recited in claim 11,
further comprising an ascending road estimating section configured
to estimate if the vehicle is traveling on an ascending road, said
limit torque reset section determining that the driving force of
the subordinate drive wheel should be increased upon said ascending
road estimating section determining that the vehicle is traveling
on an ascending road.
16. The driving force control apparatus as recited in claim 11,
further comprising a running resistance detecting section
configured to detect a running resistance of the vehicle, and said
limit torque reset section determining that the driving force of
the subordinate drive wheel should be increased upon said running
resistance detecting section determining that the running
resistance is greater than or equal to a prescribed value.
17. The driving force control apparatus as recited in claim 11,
wherein said limit torque reset section resets the maximum limit
torque value to a prescribed value only when the current road
surface reaction force limit torque is smaller than a previous road
surface reaction force limit torque.
18. The driving force control apparatus as recited in claim 11,
wherein said limit torque reset section resets the maximum limit
torque value to the predetermined maximum limit torque when the
vehicle is stopped.
19. The driving force control apparatus as recited in claim 11,
wherein the predetermined maximum limit torque is the current road
surface reaction force limit torque calculated by said limit torque
calculating section.
20. The driving force control apparatus as recited in claim 7,
further comprising: an acceleration slippage apprehension
estimating section configured to estimate if road surface
conditions are such that there is an apprehension of acceleration
slippage occurring in said main drive wheel; a requested torque
detecting section configured to detect a requested driving torque
inputted to said internal combustion engine; and an additional
generator control section configured to control an additional
generation load torque of said generator that is established in
accordance with the requested driving torque when said acceleration
slippage apprehension estimating section estimates that the road
conditions are such that there is an apprehension of acceleration
slippage occurring in the main drive wheel.
21. The driving force control apparatus as recited in claim 7,
further comprising an acceleration slippage apprehension estimating
section configured to estimate if road surface conditions are such
that there is an apprehension of acceleration slippage occurring in
said main drive wheel; and an additional generator control section
configured to control an additional generation load torque of said
generator that is a prescribed percentage of an output torque of
said internal combustion engine, when the acceleration slippage
apprehension estimating section estimates that the road conditions
are such that there is an apprehension of acceleration
slippage.
22. The driving force control apparatus as recited in claim 7,
further comprising an acceleration slippage apprehension estimating
section configured to estimate if road surface conditions are such
that there is an apprehension of acceleration slippage occurring in
the main drive wheel; and an additional generator control section
configured to control the torque of said generator to match a
generation load torque when the acceleration slippage apprehension
estimating section estimates that there is an apprehension of
acceleration slippage, the generation load torque being determined
in accordance with a difference between the current road surface
reaction force limit torque and a previously-calculated high-.mu.
road surface reaction force limit torque.
23. The driving force control apparatus as recited in claim 20,
further comprising a wheel grip limit estimating section configured
to compute a wheel grip limit estimation value for said main drive
wheel, and said acceleration slippage apprehension estimating
section estimating if there is an apprehension of acceleration
slippage occurring based on an estimation made by said wheel grip
limit estimating section.
24. The driving force control apparatus as recited in claim 20,
further comprising a poor road estimating section configured to
estimate if road conditions is within a prescribed poor road range,
said acceleration slippage apprehension estimating section
estimating there is an apprehension of acceleration slippage
occurring based on an estimation made by said poor road estimating
section.
25. The driving force control apparatus as recited in claim 20,
further comprising an ascending road estimating section configured
to estimate if the vehicle is traveling on an ascending road, said
acceleration slippage apprehension estimating section determining
there is an apprehension of acceleration slippage occurring based
on an estimation made by said ascending road estimating
section.
26. The driving force control apparatus as recited in claim 20,
further comprising a running resistance detecting section
configured to detect a running resistance of the vehicle, and said
acceleration slippage apprehension estimating section determining
if there is an apprehension of acceleration slippage occurring
based on the detection made by said running resistance detecting
section.
27. The driving force control apparatus as recited in claim 7,
further comprising: a requested torque detecting section configured
to detect a requested driving torque inputted to said internal
combustion engine; a low speed condition determining section
configured to determine if a traveling speed of the vehicle is less
than or equal to a prescribed speed; and a first low speed control
section configured to control the torque of the generator to match
a generation load torque determined in accordance with the
requested driving torque detected by said requested torque
detecting section when said low speed condition determining section
determines that the vehicle is in a low speed condition, said first
low speed control section being configured to start when said low
speed condition determining section determines that the vehicle is
in a low speed condition, and starts said generator control section
when said low speed condition determining section determines that
the vehicle is not in a low speed condition.
28. The driving force control apparatus as recited in claim 7,
further comprising: a requested torque detecting section configured
to detect a requested driving torque inputted to said internal
combustion engine; and a low speed condition determining section
configured to determine if a traveling speed of the vehicle is less
than or equal to a prescribed speed, said generator control section
calculates a first generation load torque accordance with the
acceleration slippage magnitude of said main drive wheel when
acceleration slippage of said main drive wheel is estimated to be
occurring and when said low speed condition determining section
determines that the vehicle is in a low speed condition, and
calculates a second generation load torque in accordance with the
requested driving torque detected by said requested torque
detecting section, and controls the torque of said generator to
substantially correspond to the larger of the first and second
generation load torques.
29. The driving force control apparatus as recited in claim 20,
wherein said requested torque detecting section determines said
requested driving torque based on an operation amount of an
accelerator.
30. The driving force control apparatus as recited in claim 7,
further comprising: a weight distribution determining section
configured to determine a front and rear weight distribution of the
vehicle; a low speed condition determining section configured to
determine if a traveling speed of the vehicle is less than or equal
to a prescribed speed; and a second low speed control section
configured to control the torque of the generator to match a
generation load torque determined in accordance with the front and
rear weight distribution determined by said determining section
when said low speed condition determining section determines that
the vehicle is in a low speed condition, said second low speed
control section starts when said low speed condition determining
section determines that the vehicle is in a low speed condition,
and starts said generator control section when the vehicle is not
in the low speed condition.
31. The driving force control apparatus as recited in claim 7,
further comprising: a weight distribution determining section
configured to determine the front and rear weight distribution of
the vehicle; and a low speed condition determining section
configured to determine if a traveling speed of the vehicle is less
than or equal to a prescribed speed, said generator control section
calculates a first generation load torque in accordance with the
acceleration slippage magnitude of said main drive wheel when
acceleration slippage of said main drive wheel is estimated to be
occurring acceleration slippage and when said low speed condition
determining section determines that the vehicle is in a low speed
condition, calculates a second generation load torque in accordance
with the front and rear weight distribution determined by said
weight distribution determining section, and controls the torque of
the generator to match the larger of the first and second
generation load torques.
32. The driving force control apparatus as recited in claim 7,
further comprising: a subordinate drive wheel slippage estimating
section configured to estimate acceleration slippage occurring in
the subordinate drive wheel; and an electric motor torque limiting
section configured to starts when said subordinate drive wheel
slippage estimating section determines that acceleration slippage
is occurring in the subordinate drive wheel, said electric motor
torque limiting section limiting the torque of the generator by
adjusting a field current of said electric motor such that torque
transferred to the subordinate drive wheel from said electric motor
does not exceed the road surface reaction force limit torque of the
subordinate drive wheel.
33. The driving force control apparatus as recited in claim 7,
further comprising: a battery; a subordinate drive wheel slippage
estimating section configured to estimate acceleration slippage
occurring in the subordinate drive wheel; and an electrical power
distributing section configured to distribute to said battery a
portion of the electrical power supplied to said electric motor
from said generator when said subordinate drive wheel slippage
estimating section determines that acceleration slippage is
occurring in the subordinate drive wheel.
34. The driving force control apparatus as recited in claim 7,
further comprising: a slippage condition estimating section
configured to estimate a slippage condition of the subordinate
drive wheel; and an internal combustion engine output control
section configured to lower an output torque of said internal
combustion engine in accordance with an acceleration slippage
magnitude of the slippage condition detected by said slippage
condition detecting section torque regardless of an acceleration
operation on said internal combustion engine.
35. The driving force control apparatus as recited in claim 7,
further comprising: a slippage condition detecting section
configured to detect a slippage condition of the subordinate drive
wheel; a clutch section configured to transfer torque to the
subordinate drive wheel from said electric motor; and a transfer
torque section configured to adjust a torque transferred to the
subordinate drive wheel by said clutch section in accordance with
an acceleration slippage magnitude of the slippage condition
detected by said slippage condition detecting section.
36. The driving force control apparatus as recited in claim 7,
further comprising: an internal combustion engine output limiting
section configured to start when said surplus torque computed by
said surplus torque computing section exceeds a load capacity of
the generator, and said internal combustion engine output limiting
section lowering an engine output torque of the internal combustion
engine based on a magnitude of a value obtained by subtracting a
torque determined based on the load capacity of the generator from
said surplus torque regardless of an acceleration operation on said
internal combustion engine.
37. The driving force control apparatus as recited in claim 36,
further comprising: a battery configured to supply electrical power
to an electric motor; a supply power adjusting section that adjusts
the magnitude of electrical power supplied from said battery to
said electric motor; an acceleration request detecting section
configured to detect an acceleration request operation; an
acceleration condition detecting section configured to detect the
acceleration condition of the vehicle; and a battery power
increasing section that starts upon determining that said internal
combustion engine output limiting section has started, said battery
power increasing section increasing, via said supply power
adjusting section, the magnitude of electrical power supplied to
said electric motor from said battery by a magnitude in accordance
with the magnitude by which said internal combustion engine output
limiting section reduced said output torque, upon determining that
the rotational speed of the subordinate drive wheel is being
controlled proportionally to an acceleration request based on the
detection values of said acceleration request detecting section and
said acceleration condition detecting section.
38. The driving force control apparatus as recited in claim 37,
wherein said acceleration request detecting section determines if
the rotational speed of the subordinate drive wheel is being
controlled proportionally to said acceleration request based on the
acceleration request indication quantity caused by a driver and the
elapsed time of said acceleration request indication.
39. The driving force control apparatus as recited in claim 37,
wherein said acceleration condition detecting section detects the
acceleration condition of the vehicle based on at least one of the
wheel speed of the subordinate drive wheel, the wheel acceleration
of the subordinate drive wheel, and the longitudinal acceleration
of the vehicle.
40. A driving force control apparatus for a vehicle having front
and rear wheels with at least one of the front and rear wheels
being a drive wheel driven by an internal combustion engine that
drives a generator, said driving force control apparatus
comprising: drive wheel slippage estimating means for estimating if
acceleration slippage is occurring in the drive wheel driven by the
internal combustion engine; and generator control means for
controlling a generation load torque of the generator to
substantially correspond to an acceleration slippage magnitude of
the drive wheel, when said drive wheel slippage estimating means
estimates acceleration slippage occurring in the drive wheel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a vehicle driving
force control apparatus in which at least one wheel from among the
front and rear wheels is driven by an internal combustion engine.
More specifically, the present invention relates to a drive control
apparatus that is useful in a four-wheel drive vehicle in which one
pair of wheels from among the front wheels and rear wheels is
driven by an internal combustion engine and the other pair of
wheels is driven by an electric motor.
[0003] 2. Background Information
[0004] Four-wheel drive control apparatuses in which one pair of
wheels from among the front wheels and rear wheels is driven by an
engine and the other pair of wheels is driven by an electric motor
are disclosed in Japanese Laid-Open Patent Publication Nos.
7-231508 and 8-300965.
[0005] In the drive control apparatus presented in Japanese
Laid-Open Patent Publication No. 7-231508, the engine drives a
generator and the electric energy generated by the generator drives
the electric motor. The drive control apparatus controls the
electric energy supplied from the generator to the electric motor
based on the condition of the vehicle. As a result, a large
capacity battery is not necessary, and thus, the weight of the
vehicle can be reduced.
[0006] In the drive control apparatus presented in Japanese
Laid-Open Patent Publication No. 8-300965, an engine drives one
pair of wheels and an electric motor drives the other pair of
wheels. The electric motor is driven by electric energy from a
battery. The drive control apparatus estimates the road surface
friction coefficient .mu.. When the estimated road surface friction
coefficient .mu. is low, the drive control apparatus controls the
electric motor to an output torque based on the detected road
surface friction coefficient .mu.. In short, the drive control
apparatus attempts to prevent acceleration slippage of the wheels
driven by the engine by adjusting the output torque of the electric
motor in accordance with the detected road surface friction
coefficient .mu..
[0007] In view of the above, there exists a need for an improved
vehicle driving force control apparatus that optimises the
acceleration performance of the vehicle while also improving the
fuel consumption and other energy efficiencies. This invention
addresses this need in the art as well as other needs, which will
become apparent to those skilled in the art from this
disclosure.
SUMMARY OF THE INVENTION
[0008] It has been discovered that in the apparatus described in
Japanese Laid-Open Patent Publication No. 7-231508, the
acceleration slippage of the wheels driven by the engine cannot be
directly suppressed. Specifically, acceleration cannot be directly
suppressed slippage because the four-wheel drive is accomplished by
driving the electric motor based on the deviation of the front
wheel rotational speed and the rear wheel rotational speed from a
standard rotational speed that corresponds to the accelerator
position and the deviation between the front wheel rotational speed
and the rear wheel rotational speed.
[0009] Meanwhile, in the apparatus described in Japanese Laid-Open
Patent Publication No. 8-300965, the electric motor is driven and
the motor torque is controlled only under certain conditions.
Specifically, the electric motor is driven and the motor torque is
controlled only when the brakes are not being operated, the gear
shift is in a position other than neutral, the accelerator is being
depressed, the vehicle is travelling at or below a prescribed
speed, and the road surface friction coefficient .mu. is equal to
or below a prescribed value. However, acceleration slippage of the
wheels driven by the engine cannot be directly suppressed.
[0010] In short, in both of these drive control apparatuses, there
is the possibility that, in situations where the accelerator is
excessively depressed, the wheels driven by the engine will
experience more acceleration slippage than necessary and sufficient
acceleration performance and travelling stability will not be
attainable.
[0011] The present invention focuses on this kind of problem and
aims to provide a vehicle driving force control apparatus that
optimises the acceleration performance of the vehicle while also
improving the fuel consumption and other energy efficiencies.
[0012] The present invention can be basically carried out by
providing for a vehicle having front and rear wheels with at least
one of the front and rear wheels being a drive wheel driven by an
internal combustion engine that drives a generator. The driving
force control apparatus basically comprises a drive wheel slippage
estimating section, and a generator control section. The drive
wheel slippage estimating section is configured to estimate if
acceleration slippage is occurring in the main drive wheels. The
generator control section is configured to control a generation
load torque of the generator to substantially correspond to an
acceleration slippage magnitude of the main drive wheels, when the
drive wheel slippage estimating section estimates acceleration
slippage occurring in the main drive wheels.
[0013] With the present invention, the portion of the output torque
from the internal combustion engine that is surplus torque
corresponding to the magnitude of the acceleration slippage of the
driving wheels, i.e., corresponding to the torque that cannot be
used effectively by the drive wheels, is converted to electric
energy. Therefore, the acceleration slippage of the drive wheels
driven by the power of the internal combustion engine is suppressed
and the necessary acceleration performance can be obtained in such
situations as when the vehicle is starting to move.
[0014] These and other objects, features, aspects and advantages of
the present invention will become apparent to those skilled in the
art from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses a preferred
embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Referring now to the attached drawings which form a part of
this original disclosure:
[0016] FIG. 1 is a schematic block diagram of a vehicle equipped
with a vehicle driving force control apparatus in accordance with a
first embodiment of the present invention;
[0017] FIG. 2 is a block diagram of a control system for the
vehicle driving force control apparatus in accordance with the
first embodiment of the present invention;
[0018] FIG. 3 is a block diagram illustrating the 4WD controller
for the vehicle driving force control apparatus in accordance with
the first embodiment of the present invention;
[0019] FIG. 4 is a flow chart showing the processing procedure
executed by the 4WD controller for the vehicle driving force
control apparatus of the first embodiment of the present
invention;
[0020] FIG. 5 is a flow chart showing the processing executed by
the surplus torque computing section for the vehicle driving force
control apparatus of the first embodiment of the present
invention;
[0021] FIG. 6 is a flow chart showing the processing executed by
the road surface estimating section for the vehicle driving force
control apparatus of the first embodiment of the present
invention;
[0022] FIG. 7 is a graph showing the wheel speed waveforms when at
the slippage limit;
[0023] FIG. 8 is a graph showing the wheel speed waveforms when
travelling on a poor road;
[0024] FIG. 9 is a graph showing the relationship between
distribution ratio and the accelerator position;
[0025] FIG. 10 is a flow chart showing the processing executed by
the target torque limiting section for the vehicle driving force
control apparatus of the first embodiment of the present
invention;
[0026] FIG. 11 is a flow chart showing the processing executed by
the surplus torque converting section for the vehicle driving force
control apparatus of the first embodiment of the present
invention;
[0027] FIG. 12 shows exemplary time charts for the surplus torque
converting section for the vehicle driving force control apparatus
of the first embodiment of the present invention;
[0028] FIG. 13 shows exemplary time charts for another surplus
torque converting section for the vehicle driving force control
apparatus of the first embodiment of the present invention;
[0029] FIG. 14 is a flow chart showing the processing executed by
the surplus torque computing section for the vehicle driving force
control apparatus of the second embodiment of the present
invention;
[0030] FIG. 15 is an example of an engine output torque
characteristic map for in computing the engine output torque based
on signals from the engine speed sensor and a throttle sensor;
[0031] FIG. 16 is a flow chart showing the processing executed by
the maximum value updating section for the vehicle driving force
control apparatus of the second embodiment of the present
invention;
[0032] FIG. 17 shows exemplary time charts based on the vehicle
driving force control apparatus of the first embodiment of the
present invention;
[0033] FIG. 18 shows exemplary time charts based on the vehicle
driving force control apparatus of the second embodiment of the
present invention;
[0034] FIG. 19 shows exemplary time charts for a case where the
maximum torque limit value is not updated;
[0035] FIG. 20 shows exemplary time charts for a case where the
maximum torque limit value is updated;
[0036] FIG. 21 shows alternative exemplary time charts for a case
where the maximum torque limit value is updated;
[0037] FIG. 22 shows exemplary time charts for resetting the
maximum torque limit value update;
[0038] FIG. 23 is a flow chart used for explaining a variation of
the processing executed by the surplus torque computing section of
the second embodiment of the present invention;
[0039] FIG. 24 shows exemplary time charts illustrating an example
of the maximum limit torque computation;
[0040] FIG. 25 shows exemplary time charts illustrating an example
of the generation load torque computation;
[0041] FIG. 26 is a flow chart showing the processing executed by
the motor torque limit computing section for the vehicle driving
force control apparatus of the third embodiment of the present
invention;
[0042] FIG. 27 is a flow chart showing the processing executed by
the field current converting for the vehicle driving force control
apparatus of the third embodiment of the present invention;
[0043] FIG. 28 is a schematic block diagram of a vehicle equipped
with a vehicle driving force control apparatus in accordance with
the fourth embodiment of the present invention;
[0044] FIG. 29 is a flow chart showing the processing executed by
the distributing device control section for the vehicle driving
force control apparatus of the fourth embodiment of the present
invention;
[0045] FIG. 30 is a flow chart showing the processing executed by
the clutch control limiting section for the vehicle driving force
control apparatus of the fifth embodiment of the present
invention;
[0046] FIG. 31 is a flow chart showing the processing executed by
the internal combustion engine output control section for the
vehicle driving force control apparatus of the sixth embodiment of
the present invention;
[0047] FIG. 32 is a schematic block diagram of a vehicle equipped
with a vehicle driving force control apparatus in accordance with
the seventh embodiment of the present invention;
[0048] FIG. 33 is a flow chart showing the target torque limiting
section for the vehicle driving force control apparatus in
accordance with the seventh embodiment of the present
invention;
[0049] FIG. 34 shows a map used for acceleration request
determination in the vehicle driving force control apparatus in
accordance with the seventh embodiment of the present
invention;
[0050] FIG. 35 is a flow chart showing the processing executed by
the battery control for the vehicle driving force control apparatus
of the seventh embodiment of the present invention;
[0051] FIG. 36 is a block diagram illustrating a 4WD controller in
accordance with the eighth embodiment;
[0052] FIG. 37 is a flowchart showing a processing procedure in
accordance with the eighth embodiment;
[0053] FIG. 38 is a flowchart showing a processing procedure
executed by a surplus torque calculator of the eighth
embodiment;
[0054] FIG. 39 is a flowchart showing a processing procedure
executed by a target torque controller of the eighth
embodiment;
[0055] FIG. 40 shows exemplary time charts illustrating the
relationship between deviation torque and target generation load
torque; and
[0056] FIG. 41 is a flowchart showing a target torque controller in
accordance with a ninth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] Selected embodiments of the present invention will now be
explained with reference to the drawings. It will be apparent to
those skilled in the art from this disclosure that the following
description of the embodiments of the present invention is provided
for illustration only, and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
[0058] Referring initially to FIG. 1, an example of a four-wheel
drive vehicle is illustrated to explain a first embodiment of the
present invention. The vehicle is capable of four-wheel drive in
which the left and right front wheels 1L and 1R are driven by an
internal combustion engine 2 and the left and right rear wheels 3L
and 3R are driven by an electric motor 4. As shown in the FIG. 1,
the engine output torque Te of the internal combustion engine 2 is
transferred to the left and right front wheels 1L and 1R through a
transmission and a differential gear 5. A portion of the engine
output torque Te of the engine 2 is transferred to a generator 7
using an endless belt drive 6.
[0059] The generator 7 rotates at rotational speed Nh, which is the
product of the rotational speed Ne of the engine 2 and the pulley
ratio of the endless belt drive 6. The load placed on the engine 2
by the generator 7 due to the field current Ifh is adjusted by the
4WD controller 8 to generate a voltage corresponding to the load
torque. The voltage generated by the generator 7 can be supplied to
the electric motor 4 through the electrical line 9. A junction box
10 is provided at an intermediate point in the electrical line 9
between the electric motor 4 and the generator 7. The drive shaft
of the electric motor 4 can be connected to the rear wheels 3L and
3R via a reduction gear 11, a clutch 12 and a. differential 13.
[0060] A main throttle valve 15 and a sub throttle valve 16 are
disposed inside the intake passage 14 (e.g., an intake manifold) of
the engine 2. The throttle opening of the main throttle valve 15 is
adjusted/controlled in accordance with the amount of depression of
the accelerator pedal 17, which also functions as a throttle
opening indicating device or section. In order to adjust the
throttle opening of the main throttle valve 15, the main throttle
valve 15 is either mechanically linked to the depression amount of
the accelerator pedal 17, or adjusted/controlled electrically by
the engine controller 18 in accordance with the depression amount
detection value from an accelerator sensor 17a that detects the
depression amount of the accelerator pedal 17. The depression
amount detection value of the accelerator sensor 17a is outputted
to the 4WD controller 8. The accelerator sensor 17a constitutes a
requested torque detecting section configured to detect a requested
driving torque inputted to the internal combustion engine 2.
[0061] The sub throttle valve 16 uses a stepper motor 19 as an
actuator for adjusting its throttle opening. Specifically, the
throttle opening of the sub throttle valve 16 is
adjusted/controlled by the rotational angle of the stepper motor
19, which corresponds to the step count. The rotational angle of
the stepper motor 19 is adjusted/controlled by a drive signal from
the motor controller 20. The sub throttle valve 16 is provided with
a throttle sensor. The step count of the stepper motor 19 is
feedback-controlled based on the throttle opening detection value
detected by this throttle sensor. In this embodiment, the output
torque of the engine 2 can be controlled (reduced) independently of
the operation of the accelerator pedal by the driver by adjusting
the throttle opening of the sub throttle valve 16 so as to be
smaller than the throttle opening of the main throttle valve
15.
[0062] The apparatus is also equipped with an engine speed
detection sensor 21 that detects the rotational speed of the engine
2. The engine speed detection sensor 21 outputs its detected signal
to the 4WD controller 8.
[0063] As shown in FIG. 2, the generator 7 is equipped with a
voltage adjusting device 22 (regulator) for adjusting the output
voltage V. The generation load torque Th against the engine 2 and
the generated voltage V are controlled by the adjustment of field
current Ifh executed by the 4WD controller 8. The voltage adjusting
device 22 receives a generator control command (field current
value) from the 4WD controller 8 and adjusts the field current Ifh
of the generator 7 to a value corresponding to the generator
control command. It is also capable of detecting the output voltage
V of the generator 7 and outputting the detected voltage value to
the 4WD controller 8. Additionally, the rotational speed Nh of the
generator 7 can be computed based on the rotational speed Ne of the
engine 2 and the pulley ratio of the endless belt drive 6.
[0064] A current sensor 23 is provided inside junction box 10. The
current sensor 23 detects the current value Ia of the electrical
power supplied from the generator 7 to the electric motor 4 and
outputs the detected armature current signal to the 4WD controller
8. The voltage across the electric motor 4 is detected by the 4WD
controller 8 to provide a voltage value across the electrical line
9. A relay 24 shuts off or connects the voltage (current) supplied
to the electric motor 4 in accordance with a command received from
the 4WD controller 8.
[0065] A command from the 4WD controller 8 controls the field
current Ifm of the electric motor 4 and the adjustment of the field
current Ifm adjusts the drive torque Tm. A thermistor 25 measures
the temperature of the electric motor 4. The apparatus is also
equipped with a motor speed sensor 26 that detects the rotational
speed Nm of the drive shaft of the electric motor 4. The motor
speed sensor 26 outputs a signal for the detected rotational speed
of the electric motor 4 to the 4WD controller 8.
[0066] The clutch 12 is a hydraulic clutch or electric clutch and
transmits torque at a torque transfer rate corresponding to a
clutch control command from the 4WD controller 8.
[0067] The wheel speed sensors 27FL, 27FR, 27RL, and 27RR are
provided on wheels 1L, 1R, 3L and 3R, respectively. Each speed
sensor 27FL, 27FR, 27RL, and 27RR outputs a pulse signal
corresponding to the rotational speed of the respective wheel 1L,
1R, 3L and 3R to the 4WD controller 8. Each of the pulse signals
serves as a wheel speed detection value.
[0068] As shown in FIG. 3, the 4WD controller 8 is equipped with a
generator control section 8A, a relay control section 8B, a motor
control section 8C, a clutch control section 8D, a surplus torque
computing section 8E, a target torque limiting section 8F, and a
surplus torque converting section 8G. FIG. 3 also shows control
blocks that are used by embodiments that will be discussed
later.
[0069] The 4WD controller 8 is a control unit that preferably
includes a microcomputer with a 4WD control program that is
operatively coupled to the internal combustion engine 2 and the
electric motor 4 to control the torque applied to the left and
right front wheels 1L and 1R by the internal combustion engine 2
and the torque applied to the left and right rear wheels 3L and 3R
by an electric motor 4 as discussed below. The 4WD controller 8 can
also include other conventional components such as an input
interface circuit, an output interface circuit, and storage devices
such as a ROM (Read Only Memory) device and a RAM (Random Access
Memory) device. The memory circuit stores processing results and
control programs. The RAM of the 4WD controller 8 stores statuses
of operational flags and various control data for the control
program. The ROM of the 4WD controller 8 stores various operations
for the control program. The 4WD controller 8 is capable of
selectively controlling any of the components of the driving force
control apparatus in accordance with the control program. It will
be apparent to those skilled in the art from this disclosure that
the precise structure and algorithms for 4WD controller 8 can be
any combination of hardware and software that will carry out the
functions of the present invention. In other words, "means plus
function" clauses as utilized in the claims should include any
structure including, but not limited to, hardware and/or algorithm
or software that can be utilized to carry out the function of the
"means plus function" clause. Moreover, the terms "device" and
"section" as utilized in the claims should include any structure,
i.e., hardware alone, software alone, or combination of hardware
and software.
[0070] Through the voltage adjusting device 22, the generator
control section 8A monitors the generated voltage V of the
generator 7 and adjusts the generated voltage V of the generator 7
to the required voltage by adjusting the field current Ifh of the
generator 7. Thus, the generator control section 8A includes a
generation load torque adjusting section as discussed below. The
relay control section 8B controls shutting off and connecting the
power supply from the generator 7 to the electric motor 4. The
monitor control section 8C adjusts the field current Ifm of the
electric motor 4 in order to adjust the torque of the electric
motor 4 to the required value.
[0071] As shown in FIG. 4, at a prescribed sampling time cycle, the
processing is conducted in sequence by the surplus torque computing
section 8E, the target torque limiting section 8F, and the surplus
torque converting section 8G based on the input signals.
[0072] First, the processing shown in FIG. 5 is conducted by the
surplus torque computing section 8E which includes second and third
load torque computing sections as discussed below. The surplus
torque computing section 8E is configured to compute a surplus
torque that substantially corresponds to a difference magnitude by
which a drive torque transferred from the internal combustion
engine 2 to the front drive wheels 1L and 1R exceeds a road surface
reaction force limit torque of the front drive wheels 1L and
1R.
[0073] At step S10, the wheel speeds computed based on the signals
from the wheel speed sensors 27FL, 27FR, 27RL, and 27RR are used to
subtract the wheel speed of the rear wheels 3L and 3R (subordinate
drive wheels) from the wheel speed of the front wheels 1L and 1R
(main drive wheels) and find the slippage speed .DELTA.VF, which is
the magnitude of the acceleration slippage of the front wheels 1L
and 1R. Then processing proceeds to step S20.
[0074] The slippage speed .DELTA.VF can be calculated as follows.
The average front wheel speed VWf (which is the average of the left
and right wheel speeds for the front wheels 1L and 1R) and the
average rear wheel speed VWr (which is the average of the left and
right wheel speeds for the rear wheels 3L and 3R) are calculated
using the following two equations: VWf=(VWfl+VWfr)/2 and
VWr=(VWrl+VWrr)/2.
[0075] Now, the slippage speed (acceleration slippage magnitude)
.DELTA.VF of the front or main drive wheels 1L and 1R is calculated
by the differential between the average front wheel speed VWf and
the average rear wheel speed VWr, i.e., .DELTA.VF=VWf-VWr.
[0076] In step S20, the control program determines whether or not
the calculated slippage speed .DELTA.VF exceeds a prescribed value,
such as zero. If slippage speed .DELTA.VF is determined to be zero
or below, it is estimated that the front wheels 1L and 1R are not
experiencing acceleration slippage and processing proceeds to step
S60. Conversely, if in step S20 slippage speed .DELTA.VF is
determined to be larger than zero, it is estimated that the front
wheels 1L and 1R are experiencing acceleration slippage and thus
control proceeds to step S30. In step S30, the absorption torque
T.DELTA.VF required for suppressing the acceleration slippage of
the front wheels 1L and 1R is calculated using the equation below
and processing proceeds to step S40. The absorption torque
T.DELTA.VF is an amount that is proportional to the acceleration
slippage magnitude as set forth in the equation
T.DELTA.VF=K1.times..DELT- A.VF, where K1 is a gain that is found
through experimentation or the like.
[0077] In step S40, the current load torque TG of the generator 7
is calculated based on the equation below, and then processing
proceeds to step S50. 1 TG = K2 V .times. Ia K3 .times. Nh where :
V : voltage of the generator 7 , Ia : armature current of the
generator 7 , Nh : rotational speed of the generator 7 , K3 :
efficiency , and K2 : coefficient .
[0078] In step S50, the surplus torque, i.e., the target generation
load torque Th that the generator 7 should carry, is found based on
the above equation: Th=TG+T.DELTA.VF. Thus, the surplus torque
computing section 8E (steps S30-S50) determines the surplus torque
based on the acceleration slippage magnitude of the front wheels 1L
and 1R and the generation load torque of the generator 7. Then,
processing proceeds to step S100.
[0079] Meanwhile, if the main drive wheels 1L and 1R are determined
not to be experiencing acceleration slippage in step S20, then
processing proceeds to step S60 where the road surface estimating
section 60 is started and an estimation is executed of whether or
not the road surface is such that there is an apprehension of
acceleration slippage occurring. Then, processing proceeds to step
S70.
[0080] In step S70, processing is directed to step S80 when, based
on the estimation of the road surface estimating section 60, the
AS-FLG is ON, i.e., it was determined that the road surface is such
that there is an apprehension of acceleration slippage occurring.
Meanwhile, processing is directed to step 90 when the AS-FLG is
OFF, i.e., it was determined that there is no apprehension of
acceleration slippage. Zero is assigned as the target generation
load torque Th and processing proceeds to step S80.
[0081] In step S80, the second target load torque computing section
starts and calculates the target generation load torque Th for
making the drive torque of the subordinate drive wheels 3L and 3R
the required value. Then, processing proceeds to step S100.
[0082] In step S100, the control program determines whether or not
the vehicle speed is at or below a prescribed vehicle speed, e.g.,
at or below 3 km. Thus, step S100 constitutes a low speed condition
determining section. If the control program determines that the
vehicle speed is at or below the prescribed speed, then processing
proceeds to step S110. If the vehicle speed is determined to be
faster than the prescribed speed, then processing ends and returns
to the beginning of the control program to repeat the control
program after a prescribed sampling time cycle has expired.
[0083] Thus, the generator control device 8 includes a first
generator load torque generator control section in steps S10-S50
that calculates a first target generation load torque Th of the
generator 7 in accordance with the acceleration slippage magnitude
of the main drive wheels 1L and 1R when acceleration slippage of
the main drive wheel 1L and 1R is estimated to be occurring
acceleration slippage and when the low speed condition determining
section (step S100) determines that the vehicle is in a low speed
condition. Then, after step S110 discussed below in more detail,
the processing proceeds to step S120.
[0084] In step S120, the target generation load torque Th
corresponding to the acceleration slippage and the second target
generation load torque Th2 are compared. If second target
generation load torque Th2 is determined to be larger, then the
value of Th2 is assigned to Th in step S130 and processing returns.
Otherwise, processing ends and returns to the beginning of the
control program to repeat the control program after a prescribed
sampling time cycle has expired.
[0085] In this embodiment, the larger of the target generation load
torque Th (which corresponds to the acceleration slippage) and the
second target generation load torque Th2 (which is based on a low
speed condition at or below a prescribed speed) is selected, but it
is also acceptable to assign second target generation load torque
Th2 to target generation load torque Th unconditionally when under
low speed conditions at or below a prescribed speed.
[0086] Next, the processing of the road surface estimating section
60 will be explained using FIG. 6. The road surface estimating
section 60 is configured to form an acceleration slippage
apprehension estimating device or section. The road surface
estimating section 60 is configured to compute road surface
condition including, but not limited to, a poor road condition
estimate to determine if detected road conditions are within a
prescribed poor road range, a wheel grip limit estimation value for
the front drive wheel 1L and 1R, an ascending road estimate to
determine if the vehicle is traveling on an ascending road, and a
running resistance of the vehicle.
[0087] In step S150, the road surface estimating section 60
estimates whether or not the current road surface condition is
poor. In other words, the road surface estimating section 60 acts
as a poor road estimating section that is configured to estimate if
detected road conditions are within a prescribed poor road range.
If the road is estimated to be a poor road, then processing
proceeds to step S175 where the limit torque reset section 67
determining that the driving force of the subordinate drive wheels
3L and 3R should be increased upon the poor road estimating section
determining that the vehicle is traveling on a road within the
prescribed poor road range. If the road was not estimated to be a
poor road, then processing proceeds to step S 155 where it is
estimated whether or not the road surface condition is in the
vicinity of the wheel grip limit. If it is estimated that the road
surface condition is in the vicinity of the wheel grip limit, then
processing proceeds to step S175, where the limit torque reset
section 67 determines that the driving force of the subordinate
drive wheels 3L and 3R should be increased upon determining that
the wheel grip limit estimation value of the main drive wheel 1L
and 1R is at least close to a detected wheel grip limit. If not,
then processing proceeds to step S160 where it is estimated whether
or not the vehicle is travelling on an ascending road whose grade
exceeds a prescribed grade. If the road is estimated to be an
ascending road whose grade exceeds a prescribed grade, then
processing proceeds to step S175 where the limit torque reset
section 67 determines that the driving force of the subordinate
wheels 3L and 3R should be increased upon the ascending road
estimating section determining that the vehicle is traveling on an
ascending road. If not, then processing proceeds to step S165. If
the control program determines that the running resistance exceeds
a prescribed resistance due to travelling on sandy terrain, a snowy
road surface, or the like, then processing proceeds to step S175
where the limit torque reset section 67 determining that the
driving force of the subordinate wheels 3L and 3R should be
increased upon the running resistance detecting section determining
that the running resistance is greater than or equal to a
prescribed value. If not, then processing proceeds to step
S170.
[0088] In step S175, the AS-FLG, which indicates that the road
surface is such that there is an apprehension of acceleration
slippage, is turned ON because the road surface is in the vicinity
of the wheel grip limit, is an ascending road, or has a running
resistance that exceeds a prescribed resistance.
[0089] In step S170, the AS-FLG is turned OFF because the road
surface condition does not fit into any of the above
categories.
[0090] While the preceding explanation described determining if the
road conditions matched any one of four different types, it is also
acceptable to estimate other road conditions for which there is the
apprehension of acceleration slippage occurring or to estimate only
a portion of the aforementioned four types of road condition.
[0091] In this embodiment, the estimations for poor road and road
surface in the vicinity of the wheel grip limit are conducted as
follows. The wheel speed waveform shown in FIG. 7 is used when
travelling on a road surface that is in the vicinity of the grip
limit, while the wheel speed waveform shown in FIG. 8 is used when
travelling on a poor road. According to these waveforms, the wheel
speed shows an oscillation with a frequency of approximately 8 Hz
when the vehicle is travelling on a road surface in the grip limit
vicinity and approximately 11 Hz when the vehicle is travelling on
a poor road. Although these frequencies have a variance of .+-.2
Hz, they are unique to the vehicle. Therefore, by experimentally
measuring the frequency when at the grip limit and the frequency
when travelling on a poor road for the particular vehicle, it can
be determined when the vehicle is travelling at the grip limit or
on a poor road by focusing on these frequency bands. Technologies
for determining the travelling condition of a vehicle based on a
specified frequency band are presented in Japanese Laid-Open Patent
Publication No. 2000-233739, etc. The threshold value of the
oscillation level used for making the determination should be a
value that sufficiently avoids the background noise level in a case
of either of the two road surface conditions. Therefore, the same
degree of frequency band should be used for both the grip limit
determination and the poor road determination. Additionally,
instead of finding the oscillation frequency when at the grip limit
and the oscillation frequency when travelling on a poor road for
the particular vehicle experimentally, the unsprung resonance
frequency of the drive shaft .+-.2 Hz can be used as the
oscillation frequency for the grip limit and the unsprung resonance
frequency of the suspension .+-.2 Hz can be used as the frequency
band for travelling on a poor road.
[0092] Therefore, based on the facts just presented, the
determination of whether the vehicle is travelling on a poor road
or on a road surface that is at the grip limit is accomplished by
passing the wheel speeds through a band pass filter,
differentiating the same with a differentiator, and determining if
the absolute value is greater than or equal to a prescribed
threshold value (e.g., 2G). The following frequency bands should be
used as the band region of the aforementioned band pass filter in
the cases shown in FIGS. 7 and 8, for example: the frequency band
from 6 to 10 Hz should be used for detecting a grip limit road
surface; the frequency band from 9 to 13 Hz should be used for
detecting a poor road; and the frequency band from 6 to 13 Hz
should be used when detecting both.
[0093] Furthermore, the determination of whether or not the vehicle
is on an ascending road can be accomplished based on the ascent
resistance. More specifically, it can be determined if the road is
ascending at a grade that exceeds a prescribed grade by installing
a G sensor that measures the acceleration force that acts on the
vehicle in the vertical direction with respect to the road surface
and estimating the grade of the road surface based on the output Gv
from this G sensor. In this case, Gv=g.times.cos .theta. (where g
is the acceleration due to gravity and .theta. is the road surface
grade) and ascent resistance R=g.times.sin .theta..
[0094] An ascending road can also be estimated based on the actual
slant of the vehicle body. The estimation of whether or not the
running resistance is greater than or equal to a prescribed value
can be accomplished using a known technology, such as that
disclosed in Japanese Laid-Open Patent Publication No. 2000-168405.
For example, the estimation can be conducted as follows. First, the
acceleration Ar of the subordinate drive wheels 3L and 3R is
calculated and then the product of the acceleration Ar and the
vehicle weight W is calculated to obtain the vehicle acceleration
part driving force Fa (=Ar.times.W). Meanwhile, the four-wheel
driving force Fw (sum of driving force of main drive wheels 1L and
1R and driving force of subordinate drive wheels 3L and 3R) is
calculated. Then it can be estimated if the running resistance
exceeds a prescribed value by determining if the running resistance
force Fs, which is the difference between the vehicle acceleration
part driving force Fa and the four-wheel driving force Fw, exceeds
a prescribed threshold value (e.g., 980 N).
[0095] Now, the processing executed by the second target load
torque computing section will be explained. First, the torque
(accelerator position) requested by the driver is calculated based
on the accelerator pedal operation amount. The distribution ratio
.alpha.1 for the generation load, which is proportional to the
estimated request torque, is determined based on a map such as
shown in FIG. 9. The upper limit is set to, for example, 30%. The
engine torque Te is found based on engine speed sensor 21, a
throttle sensor, etc., and the target generation load torque Th is
calculated by multiplying the engine torque Te by distribution
ratio .alpha.1. The distribution ratio .alpha.1 takes a value of
0.1 or the like, where a value of 1 corresponds to the entire
engine torque.
[0096] Although here the distribution ratio .alpha.1 is set so as
to vary in accordance with the requested torque of the driver, it
is also acceptable to keep the ratio fixed or to vary it in a
stepwise manner. Furthermore, it is also acceptable to find the
road surface limit reaction force for a high-.mu. road (e.g., a
road surface with a friction coefficient .mu. value between 0.7 and
1) in advance by experimentation and vary the distribution ratio
.alpha.1 in accordance with the difference between the
aforementioned road surface limit reaction force and the current
road surface limit reaction force at the main drive wheels 1L and
1R. Thus, the second generator control section is configured to
control the torque of the generator 7 to match a generation load
torque when the acceleration slippage apprehension estimating
section estimates that there is an apprehension of acceleration
slippage, the generation load torque being determined in accordance
with a difference between the current road surface reaction force
limit torque and a previously-calculated high-.mu. road surface
reaction force limit torque.
[0097] A low speed condition determining section is configured to
determine if a traveling speed of the vehicle is less than or equal
to a prescribed speed. A first low speed control section is
configured to control the torque of the generator 7 to match a
generation load torque determined in accordance with the requested
driving torque detected by the requested torque detecting section
when the low speed condition determining section determines that
the vehicle is in a low speed condition.
[0098] The first low speed control section is configured to start
when the low speed condition determining section determines that
the vehicle is in a low speed condition. The first low speed
control section starts the generator control section 8 when the low
speed condition determining section determines that the vehicle is
not in a low speed condition.
[0099] The generator control section 8 calculates a first
generation load torque accordance with the acceleration slippage
magnitude of the main drive wheel 1L and 1R when acceleration
slippage of the main drive wheel 1L and 1R is estimated to be
occurring and when the low speed condition determining section
determines that the vehicle is in a low speed condition. The
generator control section 8 also calculates a second generation
load torque in accordance with the requested driving torque
detected by the requested torque detecting section, and controls
the torque of the generator 7 to substantially correspond to the
larger of the first and second generation load torques.
[0100] Next, the operation of the above-described apparatus will be
explained. When the torque transferred from the engine 2 to the
front wheels 1L and 1R is larger than the road surface reaction
force limit torque, i.e., when acceleration slippage occurs in the
front wheels 1L and 1R (which are the main drive wheels 1L and 1R),
due to the road surface friction coefficient .mu. being small or
the driver depressing the accelerator pedal 17 too deeply, the
drive torque transferred to the front wheels 1L and 1R is
controlled so as to approach the road surface reaction force limit
torque of the front wheels 1L and 1R by having the generator 7
generate at a generation load torque Th corresponding to the
magnitude of the acceleration slippage. As a result, acceleration
slippage of the front wheels 1L and 1R (which are the main drive
wheels) is suppressed.
[0101] Next, the processing executed by the third target load
torque computing section (step S110) will be explained. First, the
torque (accelerator position) requested by the driver is calculated
based on the accelerator pedal operation amount. The distribution
ratio .alpha.2 for the generation load, which is proportional to
the estimated request torque, is determined. The upper limit is set
to, for example, 20%. The engine torque Te is found and the second
target generation load torque Th2 is calculated by multiplying the
engine torque Te by distribution ratio .alpha.2. The distribution
ratio .alpha.2 takes a value of 0.2 or the like, where a value of 1
corresponds to the entire engine torque. Although here the
distribution ratio .alpha.2 is set so as to vary in accordance with
the requested torque of the driver, it is also acceptable to keep
the ratio fixed.
[0102] Furthermore, the invention is not limited to determining
distribution ratio .alpha.2 in accordance with the driver requested
torque. For example, it is also acceptable to calculate the second
target generation load torque Th2 using .alpha.2 as the weight
distribution of the subordinate drive wheels 3L and 3R based on the
front-rear weight distribution of the vehicle. Thus, the third
target load torque computing section (step S110) includes weight
distribution determining section configured to determine a front
and rear weight distribution of the vehicle based on inputs from
weight distribution sensors such as strain gauges. As previously
mentioned, the low speed condition determining section (step S100)
determines if a traveling speed of the vehicle is less than or
equal to a prescribed speed. A second low speed control device or
section is configured to control the torque of the generator 7 to
match a generation load torque determined in accordance with the
front and rear weight distribution determined by the low speed
condition determining section when the low speed condition
determining section (step S100) determines that the vehicle is in a
low speed condition. The second low speed control device or section
starts the generator control device 8 when the vehicle is not in
the low speed condition.
[0103] Next, the processing executed by the target torque limiting
section 8F will be explained based on FIG. 10. First, in step S200,
the control program determines whether or not the target generation
load torque Th is larger than the maximum load capacity HQ of the
generator 7. Processing proceeds to the beginning of the control
program to repeat the control program after a prescribed sampling
time cycle has expired, if the control program determines that
target generation load torque Th is less than or equal to the
maximum load capacity HQ of the generator 7. Conversely, processing
proceeds to step S210 if the control program determines that target
generation load torque Th is larger than the maximum load capacity
HQ of the generator 7.
[0104] In step S210, the excess or surplus torque .DELTA.Tb, which
is the portion of target generation load torque Th that exceeds the
maximum load capacity HQ, is found according to the following
equation: .DELTA.Tb=Th-HQ. Then, processing proceeds to step
S220.
[0105] In step S220, the current engine torque Te is computed based
on the signals from the engine speed detection sensor 21 and the
throttle sensor. Then, processing proceeds to step S230.
[0106] In step S230, the engine torque upper limit value TeM is
calculated by subtracting the aforementioned excess or surplus
torque .DELTA.Tb from the aforementioned engine torque Te, as set
forth in the equation TeM=Te-.DELTA.Tb. After the engine torque
upper limit value TeM is outputted to the engine controller 18,
processing proceeds to step S240.
[0107] Without relation to operation of the accelerator pedal 17 by
the driver, the engine controller 18 limits the engine torque Te
such that the inputted engine torque upper limit value TeM becomes
the upper limit value of engine torque Te. The processing from step
S210 to this point comprises an internal combustion engine output
limiting device or section.
[0108] In step S240, the maximum load capacity HQ is assigned as
the target generation load torque Th and then processing returns to
the beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired.
[0109] Next, the processing executed by the surplus torque
converting section 8G will be explained based on FIG. 11. The
surplus torque converting section 8G forms a generation load torque
control section that is operatively coupled to the generation load
torque adjusting section of the generator control section 8A to
control the generation load torque of the generator 7 to a torque
value based on the surplus torque computed by the surplus torque
computing section 8E.
[0110] First, in step S600, the control program determines if Th is
larger than 0. If Th is determined to be larger than 0, processing
proceeds to step S610 because one of the following is occurring:
the front wheels 1L and 1R are experiencing acceleration slippage;
the conditions are such that there is an apprehension of
acceleration slippage occurring; or the vehicle is in a low speed
state at or below a prescribed speed. If the control program
determines that Th is less than or equal to 0, then processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has expired
without executing the subsequent steps because the vehicle is in a
state in which the front wheels 1L and 1R are not experiencing
acceleration slippage or other comparable state.
[0111] In step S610, the rotational speed Nm of the electric motor
4 detected by motor speed sensor 21 is received as input. The
target motor field current Ifm corresponding to the rotational
speed Nm of the electric motor 4 is calculated and the target motor
field current Ifm is outputted to the motor control section 8C.
Then, processing proceeds to step S620.
[0112] In this embodiment, the target motor field current Ifm
corresponding to the rotational speed Nm of the electric motor 4 is
held to a fixed prescribed current value when rotational speed Nm
is below a prescribed rotational speed and the field current Ifm of
the electric motor 4 is reduced by a known weak magnetic field
control method when the electric motor 4 is rotating above a
prescribed rotational speed (see FIG. 12). In short, when the
electric motor 4 rotates at a high speed the motor torque decreases
due to the rise in the motor induced voltage E. Therefore, as
discussed earlier, when the rotational speed Nm of the electric
motor 4 reaches or exceeds a prescribed value, the current flowing
to the electric motor 4 is increased and the required motor torque
Tm is obtained by reducing the field current Ifm of the electric
motor 4 and lowering the induced voltage E. As a result, even if
the electric motor 4 rotates at a high speed, the required motor
torque Tm can be obtained because the motor induced voltage E is
kept from rising and the motor torque is prevented from decreasing.
Also, the price of the electronic control circuit can be reduced in
comparison with continuous field current control because the motor
field current Ifm is controlled in two stages: a stage for when the
rotational speed is below a prescribed value and another stage for
when the rotational speed is at or above a prescribed value.
[0113] It is also acceptable to provide a motor torque correcting
section that continuously corrects the required motor torque Tm by
adjusting the field current Ifm in accordance with the rotational
speed Nm of the electric motor 4. That is, instead of switching
between two stages, the field current Ifm of the electric motor 4
can be adjusted in accordance with the motor rotational speed Nm.
As a result, even if the electric motor 4 rotates at a high speed,
the required motor torque Tm can be obtained because the motor
induced voltage E is kept from rising and the motor torque is
prevented from decreasing. Furthermore, since a smooth motor torque
characteristic can be obtained, the vehicle can travel with better
stability than in the case of two-stage control and the vehicle can
always be kept in a state where the motor driving efficiency is
good.
[0114] In step S620, the induction current E of the electric motor
4 is calculated based on the target motor field current Ifm and the
rotational speed Nm of the electric motor 4. Then, processing
proceeds to step S630.
[0115] In step S630, the corresponding target motor torque TM is
calculated based on the generation load torque Th computed by
surplus torque computing section 8E. Then, processing proceeds to
step S640.
[0116] In step S640, the corresponding target armature current Ia
is calculated using the target motor torque TM and the target motor
field current Ifm as variables. Then, processing proceeds to step
S650.
[0117] In step S650, the equation V=Ia.times.R+E is used to
calculate the target voltage V of the generator 7 from the target
armature current Ia, resistance R, and the induced voltage E.
Processing returns to the beginning of the control program to
repeat the control program after a prescribed sampling time cycle
has expired after the target voltage V of the generator 7 is
outputted to the generator control section 8A. The resistance R is
the resistance of the electrical line 9 and the resistance of the
coil of the electric motor 4.
[0118] Although here the surplus torque converting section 8G takes
into account control of the motor when it calculates the target
voltage V at the generator 7 that corresponds to the target
generation load torque Th, it is also acceptable to calculate the
voltage value V that achieves the target generation load torque Th
directly from target generation load torque Th.
[0119] FIG. 12 shows an example of a time chart for the processing
described above. In this embodiment, the steps S10 and S20
constitute a main drive wheel slippage estimating device or
section. The generator control section 8A, which controls field
current Ifh, constitutes a generation load torque adjusting device
or section. The steps S30 to S50 constitute a surplus torque
computing device or section. The surplus torque converting section
8G constitutes a generator load torque control device or
section.
[0120] Furthermore, the acceleration performance of the vehicle is
improved because the surplus power generated by the generator 7 is
used to drive the electric motor 4, which drives the rear wheels 3L
and 3R (which are the subordinate drive wheels).
[0121] At the same time, the electric motor 4 is driven by the
surplus torque beyond the road surface reaction force limit torque
of the subordinate drive wheels 3L and 3R. Consequently, the energy
efficiency is improved, which leads to improved fuel
consumption.
[0122] In this embodiment, if the rear wheels 3L and 3R were always
driven, several energy conversions (mechanical
energy.fwdarw.electrical energy.fwdarw.mechanical energy, etc.)
take place and energy losses occur in accordance with the
conversion efficiencies. Therefore, the acceleration performance of
the vehicle would decline in comparison with a case where only the
front wheels 1L and 1R were driven. Consequently, it is generally
preferred that driving of the rear wheels 3L and 3R be suppressed.
Conversely, this embodiment takes into consideration the fact that
when travelling on a slippery road surface or the like, even if all
of the output torque Te of the engine 2 is transferred to the front
wheels 1L and 1R, not all of the torque will be used as driving
force. The driving force that cannot be utilized efficiently by the
front wheels 1L and 1R is outputted to the rear wheels 3L and 3R
and the acceleration performance is improved.
[0123] Furthermore, in the present embodiment, even if the front
wheels 1L and 1R (which are the main drive wheels) are not
experiencing acceleration slippage but the road surface condition
is estimated to be such that there is an apprehension of
acceleration slippage occurring, a generation load torque is
produced in advance and the vehicle is put into a four-wheel drive
state to an extent that the vehicle remains stable. As a result,
travel stability can be obtained reliably and the stability and
response of the vehicle with respect to acceleration slippage are
improved.
[0124] When the vehicle is starting to move or is otherwise in a
low speed condition at or below a prescribed speed, there is the
danger that the estimation of acceleration slippage will not be
conducted appropriately regardless of whether the acceleration
slippage is estimated using the difference in speed .DELTA.V
between the front and rear wheels or using the road surface
reaction force limit torque. In other words, the precision of the
acceleration slippage detection degrades when the speed is low
because the precision of the wheel speed detection performed by
rotary sensors and the like degrades and the road surface reaction
force is too small due to the small acceleration of the vehicle.
Thus, it is possible to have a situation where vehicle does not go
into a four-wheel drive state even though acceleration slippage is
actually occurring. Meanwhile, if acceleration slippage of the main
drive wheels 1L and 1R occurs when on sandy terrain or a snowy road
surface, the road surface contacted by the main drive wheels 1L and
1R will change and travelling conditions will worsen (e.g., road
surface friction coefficient .mu. will decline and running
resistance will increase). The lower the speed of the vehicle is,
the larger the effect of the change in the road surface caused by
the vehicle will be. In short, when the vehicle is starting to move
or otherwise travelling at a very low speed, the occurrence of
slippage will worsen the road surface condition and afterwards it
will be difficult to start moving even if the vehicle goes into
four-wheel drive.
[0125] With the present embodiment, when the vehicle is starting to
move or otherwise in a low speed state at or below a prescribed
speed, the subordinate drive wheels 3L and 3R are driven in advance
with a drive torque corresponding to the requested drive torque
(acceleration request or the like) of the driver even before
acceleration slippage occurs. As a result, stable starting and
stable travel at low speeds can be achieved even when travelling on
sandy terrain or other road surface for which acceleration slippage
occurs easily.
[0126] In step S630, in the surplus torque converting section 8G,
the target motor torque TM is calculated based on the generation
load torque Th. When the vehicle is in a low speed state at or
below a prescribed speed and Th2 is selected as Th, it is also
acceptable to calculate target motor torque TM based on the
accelerator position.
[0127] FIG. 13 a time chart for a case where the load torque of the
generator 7 is output-controlled even when in a low speed state at
or below a prescribed speed. In this example, the low speed state
at or below a prescribed speed is defined to be when the rear wheel
speed is 5 km/h or less.
[0128] This embodiment demonstrates a case where, under certain
conditions, the generator 7 is placed in a loaded state even when
acceleration slippage is not occurring, but it is also acceptable
to place the generator 7 in a loaded state only when acceleration
slippage is occurring.
[0129] This embodiment furthermore demonstrates a case where the
voltage generated by the generator 7 is used to drive the electric
motor 4, thus achieving a four-wheel drive arrangement, but the
invention is not limited to such an arrangement. It is also
acceptable for the electrical power generated by the generator 7 to
be supplied to another load device and consumed by the other load
device.
[0130] This embodiment also describes using throttle control as the
internal combustion engine output limiting device or section, but
the invention is not limited to such a method. The output can be
limited by using one or more of the following methods: retarding
the ignition timing of the internal combustion engine, cutting the
ignition, reducing or stopping the fuel, or throttle control.
Second Embodiment
[0131] Referring now to FIGS. 14-25, a driving force control
apparatus in accordance with a second embodiment will now be
explained. The basic construction of this embodiment is the same as
that of the first embodiment, except that the surplus torque
computing section 8E is different. In view of the similarity
between the first and second embodiments, the parts of the second
embodiment that are identical to the parts of the first embodiment
will be given the same reference numerals as the parts of the first
embodiment. Moreover, the descriptions of the parts of the second
embodiment that are identical to the parts of the first embodiment
may be omitted for the sake of brevity.
[0132] The processing executed by the surplus torque computing
section 8E is shown in FIG. 14. The surplus torque computing
section 8E includes a drive wheel limit torque computing section
that is configured to compute a current road surface reaction force
limit torque of the drive wheel. Basically, the surplus torque
computing section 8E determines the surplus torque based on a
difference between the current road surface reaction force limit
torque computed by the drive wheel limit torque computing section
(step S730) and the drive torque transferred from the internal
combustion engine (2) to the drive wheels 1L and 1R.
[0133] First, in step S700, the output torque Te of the engine 2 is
computed based on signals from the engine speed sensor 21 and a
throttle sensor using, for example, a map like that shown in FIG.
15. Then, processing proceeds to step S710.
[0134] In step S710, the current torque TG of the generator 7 is
computed based on the voltage V of the generator 7, the armature
current Ia, and the rotational speed Nh of the generator 7 in the
same manner as in step S40 of the previous embodiment. Then
processing proceeds to step S720.
[0135] In step S720, the drive train acceleration torque Tif is
computed using the equation shown below. Then processing proceeds
to step S730.
Tif=(drive train inertia[including gear ratio]).times.angular
acceleration
[0136] In this embodiment, the angular acceleration is found based
on the wheel speed of the front wheels 1L and 1R.
[0137] In step S730, the equation Ff=(Te-TG).times.TR.times.G-Tif
is used to calculate the road surface reaction force Ff of front
wheels 1L and 1R, where Tr is the torque converter multiplication
ratio and G is the gear ratio of transmission. In this equation,
the output torque Te of the engine 2 is multiplied by TR.times.G in
order to convert it to the driving torque transferred to the front
wheels 1L and 1R. Naturally, the TG is zero when the generator 7 is
not operating. After this calculation, processing proceeds to step
S740.
[0138] The target torque limiting section 8F includes a limit
torque calculating section that is configured to repeatedly
calculate the road surface reaction force limit torque of the main
drive wheel 1L and 1R. The limit torque maximum value updating
section 63 is configured to compare the road surface reaction force
limit torque and a predetermined limit torque. The limit torque
maximum value updating section 63 set the larger of the current
road surface reaction force limit torque and the predetermined
limit torque as a maximum limit torque value, and set the maximum
limit torque value as a road surface reaction force limit torque
value. The limit torque reset section 67 is configured to start
upon determining that a driving force of the subordinate drive
wheels 3L and 3R should be increased, and resets the maximum limit
torque value to an updated maximum limit torque value. The limit
torque reset section 67 is further configured to determines that
the driving force of the subordinate drive wheel 3L and 3R should
be increased when a speed differential occurs between the front and
rear wheels that is greater than or equal to a prescribed value
(see step S820). The limit torque reset section 67 resets the
maximum limit torque value to a prescribed value only when the
current road surface reaction force limit torque is smaller than a
previous road surface reaction force limit torque. The limit torque
reset section 67 also resets the maximum limit torque value to the
predetermined maximum limit torque when the vehicle is stopped. The
predetermined maximum limit torque is the current road surface
reaction force limit torque calculated by the limit torque
calculating section.
[0139] In step S740, the maximum value updating section 63 starts
and updates the maximum value of the road surface reaction force.
Then, processing proceeds to step S750.
[0140] In step S750, the equation Te>Ffm.div.TR.div.G is used to
determine if there is any surplus torque in the engine torque Te.
If there is no surplus in the engine torque Te, i.e., the output
torque Te is smaller, then processing proceeds to step S780.
Conversely, if there is a surplus in torque Te, i.e., the output
torque Te is larger, then processing proceeds to step S770.
[0141] In step S770, the equation Th=Te-(Ffm.div.TR.div.G) is used
to calculate the surplus torque, i.e., the target generation load
torque Th, which is the portion of the engine torque Te that is in
excess of the maximum road surface reaction force limit torque Ffm
of the front wheels 1L and 1R.
[0142] In this embodiment, steps S700 to S750 constitute a main
drive wheel estimating device or section, with step S770
constituting a surplus torque computing device or section, and step
S730 constituting a main drive wheel limit torque computing device
or section.
[0143] Meanwhile, if in step S750, the control program determines
that the main drive wheels 1L, and 1R are not experiencing
acceleration slippage, then processing proceeds to step S780, in
which road surface estimating section 60 starts and estimates if
the road surface is such that there is the apprehension of
acceleration slippage occurring. Then, processing proceeds to step
S790.
[0144] In step S790, processing is directed to step S800 if the
control program determines that the road surface is such that there
is the apprehension of acceleration slippage based on the
estimation executed by road surface estimating section 60.
Otherwise, if the control program determines that the road surface
does not pose the apprehension of acceleration slippage, processing
is directed to step S810, in which processing is directed to step
S820 after zero is assigned as the target generation load torque
Th.
[0145] In step S800, the second target load torque computing device
or section starts and finds the target generation load torque Th
for making the drive torque of the subordinate drive wheels 3L and
3R the required value. Then, processing proceeds to step S820.
[0146] In step S820, the control program determines whether or not
the vehicle speed is at or below a prescribed vehicle speed, e.g.,
at or below 5 km. If the control program determines that the
vehicle speed is at or below the prescribed speed, then processing
proceeds to step S830. If the vehicle speed is determined to be
faster than the prescribed speed, processing ends and returns to
the beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired.
[0147] In step S830, the third load torque calculating section
starts and finds second generation load torque Th2. Then,
processing proceeds to step S840.
[0148] In step S840, the target generation load torque Th (which
corresponds to the acceleration slippage) and the second target
generation load torque Th2 are compared. If the second target
generation load torque Th2 is determined to be larger, then
processing proceeds to step S850, where the value of Th2 is
assigned to Th and then processing returns to the beginning of the
control program to repeat the control program after a prescribed
sampling time cycle has expired. If the second target generation
load torque is not larger, then processing ends and returns to the
beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired.
[0149] In this embodiment, the larger of target generation load
torque Th (which corresponds to the acceleration slippage) and the
second target generation load torque Th2 (which is based on a low
speed condition at or below a prescribed speed) is selected, but it
is also acceptable to assign the value of second target generation
load torque Th2 to target generation load torque Th unconditionally
when under low speed conditions at or below a prescribed speed.
[0150] Next, the processing executed by the maximum value
processing section 63 will be explained in reference to FIG. 16.
First, in step S900, the control program determines if the speed of
the subordinate drive wheels is less than or equal to a prescribed
threshold value, i.e., if the vehicle is substantially in a stopped
condition. If the control program determines that the vehicle is in
a stopped condition, then processing proceeds to step S960 where
zero is assigned to the maximum limit torque Ffm, i.e., maximum
limit torque Ffm is reset. Conversely, if the control program
determines that the vehicle is not in a stopped state, then
processing proceeds to step S910.
[0151] In step S910, the speed difference .DELTA.VF between the
front and rear wheels is found. If speed difference .DELTA.VF is
determined to be greater than or equal to a prescribed threshold
value, then acceleration slippage is actually occurring and
processing proceeds to step S940. Meanwhile, if the speed
difference is below the prescribed threshold value, i.e., if the
control program determines that acceleration slippage is not
occurring, then processing proceeds to step S920, where maximum
value updating processing is executed. The prescribed threshold
value is a value with enough leeway that error does not occur
during turning or the like.
[0152] In step S920, the present (the current) road surface
reaction torque Ff and the maximum limit torque Ffm are compared.
If the present road surface reaction torque Ff is larger, then
processing proceeds to step S930. Otherwise, processing ends and
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has
expired.
[0153] In step S930, the maximum limit torque Ffm is updated to the
present (current) road surface reaction torque Ff.
[0154] In step S940, the once previous (i.e., previously computed)
road surface reaction force Ffs is compared with the road surface
reaction torque Ff. If the road surface reaction torque Ff is
smaller, then processing proceeds to step S950. Otherwise,
processing moves to step S920 without resetting the maximum limit
torque.
[0155] In step S950, the maximum limit torque Ffm is reset to the
current road surface reaction torque Ff.
[0156] Next, the operation of the apparatus of this second
embodiment will be explained. In this embodiment, the actual
acceleration slippage (i.e., the speed difference .DELTA.V between
front and rear wheels) of front wheels 1L and 1R is not detected
directly. Rather, when the output torque Te of the engine 2 exceeds
the road surface reaction force limit torque Ff, the excess portion
of the output torque Te of the engine 2 is absorbed by the
generator 7. As a result, acceleration slippage of the front wheels
1L and 1R is suppressed and a similar operational effect to that of
the first embodiment is achieved.
[0157] Unlike the first embodiment, in the second embodiment, the
generator 7 generates power and the generation load is produced so
long as the output torque Te of the engine 2 exceeds the road
surface reaction force limit torque Ff of the main drive wheels 1L
and 1R, even if the actual speed difference .DELTA.V between the
front and rear wheels is zero.
[0158] If, as in the first embodiment, the load of the generator 7
is controlled using the speed difference .DELTA.V between the front
and rear wheels, when speed difference .DELTA.V is close to zero
hunting will occur and there is the danger that vibration will be
worsened and the ride will be degraded. Since the speed difference
.DELTA.V does not converge to zero, the front wheels 1L and 1R will
continue to have a small amount of acceleration slippage and there
is the apprehension that the vehicle behaviour will become
unstable.
[0159] Conversely, in the second embodiment, even if the actual
speed difference .DELTA.V between the front and rear wheels is
zero, the generator 7 generates power so long as the output torque
Te of the engine 2 exceeds the road surface reaction force limit
torque Ff of the main drive wheels 1L and 1R. Therefore, the
aforementioned hunting is suppressed and unforeseen vibrations can
be prevented. Also, the speed difference .DELTA.V between the front
and rear wheels can be made to converge to zero in a stable
manner.
[0160] FIG. 17 shows a time chart illustrating the behaviour of the
first embodiment. Hunting occurs easily because the torque absorbed
by the generator 7 is computed to a size that is proportional to
the change in the slippage speed .DELTA.VF of the front wheels 1L
and 1R. In particular, as the gain K1 is increased, the response
improves but hunting occurs more easily. It is also acceptable to
use the PI control or the PID control based on the temporal changes
in the slippage speed .DELTA.VF.
[0161] Conversely, FIG. 18 shows a time chart illustrating the
behavior of the second embodiment. Even if the actual wheel speed
difference goes to zero, there is an estimation value for the
portion of the output torque of the engine 2 that exceeds the road
surface reaction force limit torque. Therefore, the control program
determines that there is a torque to be absorbed by the generator
7. As a result, the wheel speed difference converges readily
without the occurrence of hunting.
[0162] In this second embodiment, when the vehicle starts and
begins to travel, the output torque requested of the vehicle will
gradually decrease due to gear shifting and the decrease in the
torque multiplication ratio of the torque converter. Consequently,
unless the road surface conditions change greatly, the output
torque of subordinate drive wheels 3L and 3R will not be
particularly necessary. By updating the maximum value as is done in
this embodiment, excessive output torque from the subordinate drive
wheels 3L and 3R is eliminated and energy losses can be reduced.
This arrangement is also preferable in view of the service life of
the electric motor 4 because it does not require frequent starting
and stopping of the electric motor 4.
[0163] Meanwhile, FIG. 19 shows a case where the maximum value
updating of the road surface reaction force limit torque used for
the aforementioned estimation is unconditionally continued. In this
embodiment, acceleration slippage cannot be detected even when the
road surface condition changes such that an increase in the driving
torque of subordinate drive wheels 3L and 3R is necessary, such as
when the road surface reaction force decreases due to travelling on
a road surface with a low road surface friction coefficient .mu..
Conversely, in the present embodiment, the maximum limit torque Ffm
(which was being updated) is reset when the control program
determines that the conditions require increasing the drive torque
of the subordinate wheels 3L and 3R. Thus, as shown in FIG. 20,
even if maximum value updating is executed, the required driving
performance can be ensured by producing the drive torque at the
subordinate wheels 3L and 3R to an appropriate degree. FIG. 20
illustrates a case where the reset determination is based on
whether nor not the actual wheel speed difference .DELTA.VF exceeds
a prescribed threshold value.
[0164] Furthermore, since the subordinate drive wheels 3L and 3R
are producing driving torque (there is a generation load), the
maximum limit torque, which serves as a reference, decreases even
when the maximum value updating is reset. As a result, the driving
torque of the subordinate drive wheels 3L and 3R increases.
[0165] When the reset determination is conducted based on the
actual speed difference .DELTA.V between the main drive wheels 1L
and 1R and the subordinate drive wheels 3L and 3R, it is necessary
to use a threshold value that has a certain degree of leeway in
order to prevent errors caused by wheel speed differences during
turning. Therefore, even if the road surface has a low limit, the
maximum limit torque Ffm will not be reset so long as slipping that
exceeds the threshold value does not occur.
[0166] Conversely, consider a case where the reset is conducted
based on an estimation of a poor road or the wheel grip limit and
changes in the road surface are detected by observing the frequency
characteristic of the speed difference .DELTA.V instead of
detecting slippage directly from the speed difference .DELTA.V. As
shown in FIG. 21, even when the speed difference .DELTA.V does not
exceed the threshold value, it can be determined if the road
surface is such that the driving force is required from the
subordinate drive wheels 3L and 3R. Therefore, it is easier for the
subordinate drive wheels 3L and 3R to output the driving torque
before acceleration slippage occurs in cases where the conditions
are such that acceleration slippage can occur easily.
[0167] Furthermore, by resetting when the road is poor, it is
easier for the subordinate drive wheels 3L and 3R to output the
driving torque while the vehicle is stable before acceleration
slippage occurs and the poor road driving performance is
improved.
[0168] When on an ascending road, the shift in weight tends to
cause the weight distribution to be such that the weight born by
the rear wheels increases and, consequently, acceleration slippage
more readily occurs in the main drive wheels 1L and 1R. In short,
such a road surface condition calls for increasing the driving
force of the subordinate drive wheels 3L and 3R. Therefore, by
resetting when it is estimated that the road is ascending,
acceleration slippage of main drive wheels 1L and 1R can be
appropriately suppressed because the main drive wheels 1L and 1R
are the front wheels.
[0169] Furthermore, by resetting when the running resistance is
large, e.g., when travelling on sandy terrain or a snowy road,
acceleration slippage of the main drive wheels 1L and 1R is
suppressed and the driving performance is improved by being in a
four-wheel drive state.
[0170] In this second embodiment, as indicated by A in FIG. 22,
cases of resetting unnecessarily in accordance with a change in the
road condition can be reduced by resetting only in cases where the
road surface reaction force limit torque grows smaller as the
vehicle travels.
[0171] In view of the fact that acceleration slippage occurs
readily when the vehicle is starting to move, acceleration slippage
of main drive wheels 1L and 1R when the vehicle is starting to move
can be appropriately suppressed by resetting when the vehicle is
stopped.
[0172] In this second embodiment, acceleration slippage can be
suppressed appropriately in accordance with the current road
condition because the maximum limit torque is reset to the current
(actual) road surface reaction force limit torque Ff at the time of
resetting. However, the invention is not limited to resetting
maximum limit torque Ffm to the current value. For example, it is
also acceptable to prepare a plurality of pre-set values and select
a pre-set value based on the current road surface.
[0173] Also, the processing executed by the surplus torque
computing section 8E in steps S750 and S770 can be replaced by a
computation of the motor torque or the drive torque of subordinate
drive wheels 3L and 3R. For example, as shown in FIG. 23, steps
S750 and S770 might be replaced by steps S771 to S775. In step
S771, the maximum road surface limit torque Ffm is multiplied by
the gain (0.9) to calculate Flim; in step S772, the driving torque
Fd of main drive wheels 1L and 1R is calculated; and in step S773
the surplus torque is calculated. At step S774, processing proceeds
to the aforementioned step S780 of there is no surplus torque. If
there is a surplus torque, processing proceeds to step S775, where
the generation load torque Th is calculated and then processing
proceeds to step S820. An example of the maximum limit torque Ffm
computation performed in this processing is shown in FIG. 24 and an
example of the generation load torque computation is shown in FIG.
25. With this processing, the maximum limit torque Ffm can be
provided with some leeway. In FIG. 25, the crosshatching indicates
the corresponding the subordinate drive wheel torque.
Third Embodiment
[0174] Referring now to FIGS. 26 and 27, a driving force control
apparatus in accordance with a third embodiment will now be
explained. The basic construction of this embodiment is the same as
that of the first embodiment, except that the 4WD controller 8 is
provided with a motor torque limit computing section 8H and a field
current converting section 8J. In view of the similarity between
the first and third embodiments, the parts of the third embodiment
that are identical to the parts of the first embodiment will be
given the same reference numerals as the parts of the first
embodiment. Moreover, the descriptions of the parts of the second
embodiment that are identical to the parts of the first embodiment
may be omitted for the sake of brevity.
[0175] The motor torque limit computing section 8H is accessed
after the processing executed by the aforementioned surplus torque
converting section 8G is completed, and field current converting
section 8J is accessed after the processing executed by the motor
torque limit computing section 8H is completed.
[0176] The processing executed by the motor torque limit computing
section 8H is illustrated in FIG. 26. First, in step 1000, the
estimated vehicle speed VS is estimated and then processing
proceeds to step S1010. The estimated vehicle speed VS can be
estimated by using, for example, the detection value of a
longitudinal G sensor.
[0177] In step S1010, the rear wheel speed VR' for a case where
acceleration slippage of the rear wheels 3L and 3R is assumed not
be occurring is calculated based on the estimated vehicle speed VS,
the tire diameter, etc. Then, processing proceeds to step
S1020.
[0178] In step S1020, the wheel speed VR of the rear wheels 3L and
3R are received from the wheel speed sensors 27RL and 27RR of the
rear wheels 3L and 3R and the equation .DELTA.VR=VR-VR' is used to
calculate the acceleration slippage magnitude .DELTA.VR for the
rear wheels 3L and 3R. The wheel speed VR is the average value for
the left and right wheels. Then, processing proceeds to step
S1030.
[0179] In step S1030, the acceleration slippage magnitude .DELTA.VR
is used to determine whether or not the rear wheels 3L and 3R are
experiencing acceleration slippage. If the control program
determines that the acceleration slippage magnitude .DELTA.VR is
less than or equal to a prescribed value (e.g., the acceleration
slippage magnitude .DELTA.VR is less than or equal to 0), i.e., if
the control program determines that the rear wheels 3L and 3R are
not experiencing acceleration slippage, then processing proceeds to
step S1040 where 0 is assigned to flag FR.
[0180] On the other hand, if the acceleration slippage magnitude
.DELTA.VR is determined to be larger than 0 in step S1030, i.e., if
the rear wheels 3L and 3R are determined to be experiencing
acceleration slippage, then processing proceeds to step S1050.
[0181] In step S1050, the limiting torque T.DELTA.VR corresponding
to the acceleration slippage magnitude .DELTA.VR of the rear wheels
3L and 3R is computed using the equation
T.DELTA.VR=K4.times..DELTA.VR. Then, processing proceeds to step
S1060.
[0182] In step S1060, the current motor torque Tm is computed using
the equation Tm=K5.times.Ia.times.Ifm, where K4 and K5 are gain
constants. Then processing proceeds to step S1070.
[0183] In step S1070, the target motor torque TM, which is limited
by limiting torque T.DELTA.VR, is found using the equation
TM=Tm-T.DELTA.VR. Then processing proceeds to step S1080.
[0184] In step S1080, the flag FR is assigned 1, which indicates
target motor torque TM has been calculated. Then, processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has
expired.
[0185] The field current converting section 8J executes the
processing shown in FIG. 27. In step S1200, the control program
determines whether or not the target motor torque TM has been
computed. Processing proceeds to step S1210 if FR is 1, i.e., if
the control program determines that the target motor torque TM has
been changed. Meanwhile, processing returns directly to the
beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired, if FR is 0,
i.e., if the control program determines that the target motor
torque TM has not been changed.
[0186] In step S1210, the motor field current Ifm, which determines
the target motor torque TM after changing, is calculated based on
the rotational speed Nm of the electric motor 4, the armature
current Ia, and the induction current E of the electric motor 4.
The calculated motor field current Ifm is outputted to the motor
control section 8C and the processing returns to the beginning of
the control program to repeat the control program after a
prescribed sampling time cycle has expired.
[0187] In this embodiment, steps S1000 to S1030 constitute a
subordinate drive wheel slippage estimating device or section and
steps S1040 to S1080, S1200, and S1210 constitute an electric motor
torque limiting device or section.
[0188] In this embodiment, when acceleration slippage occurs in the
rear wheels 3L and 3R (subordinate drive wheels), which are driven
by the electric motor 4, the motor field current Ifm becomes
smaller and the motor efficiency declines. As a result, the
acceleration slippage of the rear wheels 3L and 3R is suppressed
and the driving stability of the vehicle is improved further.
[0189] Instead of controlling the motor field current Ifm in
accordance with the target motor torque TM, it is also acceptable
to control the motor field current Ifm in direct correspondence to
.DELTA.VR such that .DELTA.VR goes to zero or below.
Fourth Embodiment
[0190] Referring now to FIGS. 28 and 29, a driving force control
apparatus in accordance with a fourth embodiment will now be
explained. The basic construction of this embodiment is the same as
that of the first embodiment, except that as shown in FIG. 28, it
is provided a battery 30 and an electrical power distributing
device or section 31 that distributes a portion of the electrical
power generated by the generator 7 to the battery 30. In view of
the similarity between the first and fourth embodiments, the parts
of the fourth embodiment that are identical to the parts of the
first embodiment will be given the same reference numerals as the
parts of the first embodiment. Moreover, the descriptions of the
parts of the fourth embodiment that are identical to the parts of
the first embodiment may be omitted for the sake of brevity.
[0191] Thus, in this embodiment, the electrical power distributing
device 31 constitutes an electrical power distributing device or
section that is disposed along the electrical line 9. The
electrical power distributing device 31 is configured such that the
distribution ratios with respect to the electric motor 4 and the
battery 30 can be changed by adjusting the resistance value of the
variable resistor 31a. The distribution ratio can be changed by a
command from the 4WD controller 8. A voltage transformer 32
converts the voltage of the electrical power supplied thereto into
a voltage that can be used to charge the battery 30 (e.g., converts
42 volts to 12 volts).
[0192] The 4WD controller 8 is equipped with a distributing device
control section 8K that constitutes an electrical power
distributing device or section. The distributing device control
section 8K is accessed after the processing executed by motor
torque limit computing section 8H or the processing executed by
field current converting section 8J.
[0193] The processing executed by the distributing device control
section 8K is as shown in FIG. 29. In step S1300, the control
program determines whether or not the rear wheels 3L and 3R are
experiencing acceleration slippage using speed sensors 27FL, 27FR,
27RL, 27RR. If the control program determines that the rear wheels
3L and 3R are not experiencing acceleration slippage, then
processing proceeds to step S1320. If the control program
determines that the rear wheels 3L and 3R are experiencing
acceleration slippage, processing proceeds to step S1310.
[0194] In this embodiment, the determination of whether or not
acceleration slippage is occurring can be accomplished based on the
result of the processing executed in the aforementioned steps S1000
to S1020, which constitute a subordinate drive wheel slippage
estimating device or section.
[0195] In step S1310, a command for distributing a portion of the
voltage V generated by the generator 7 to the battery 30 at a
predetermined distribution ratio is issued to the electrical power
distributing device 31. The electrical power distributing device 31
is configured to distribute to the battery 30 a portion of the
electrical power supplied to the electric motor 4 from the
generator 7) when the subordinate drive wheel slippage estimating
device or section determines that acceleration slippage is
occurring in the subordinate drive wheels 3L and 3R. Then
processing returns to the beginning of the control program to
repeat the control program after a prescribed sampling time cycle
has expired.
[0196] In step S1320, the supply of electrical power to the battery
30 is stopped and a command for supplying electrical power only to
the motor is issued to the distributing device 31. Then processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has
expired.
[0197] Additionally, in step 1310, it is also acceptable to vary
the distribution ratio of the distributing device 31 in accordance
with the slippage rate so that the acceleration slippage of the
rear wheels is suppressed.
[0198] When the slippage magnitude .DELTA.VR is found based on the
difference between the rear wheel speed VR and the wheel speed VR'
calculated from the estimated vehicle speed VS, the equation shown
below is used to calculate the aforementioned slippage rate A. 2 A
= VR VR '
[0199] When the presence or absence of acceleration slippage is
determined by computing the surplus torque based on the road
surface limit grip amount and the motor torque Tm, the slippage
rate A is calculated as shown below. 3 A = Tm Tm
[0200] In the present embodiment, when acceleration slippage occurs
in the rear wheels 3L and 3R, the driving force of the rear wheels
3L and 3R is decreased by lowering the voltage supplied to the
electric motor 4, which drives the rear wheels 3L and 3R. As a
result, the acceleration slippage of the rear wheels 3L and 3R is
suppressed and similar an operational effect to that of the
previously described embodiment is achieved.
[0201] Since a portion of the voltage not supplied to the electric
motor 4 is stored in the battery 30, the voltage not supplied to
the electric motor 4 can be utilized effectively for another
purpose.
Fifth Embodiment
[0202] Referring now to FIG. 30, a driving force control apparatus
in accordance with a fifth embodiment will now be explained. The
basic construction of this embodiment is the same as that of the
first embodiment, except that acceleration slippage of the rear
wheels 3L and 3R is suppressed by providing a clutch control
limiting section 8L that limits the torque transfer rate of the
clutch 12. The clutch control limiting section 8L and the clutch 12
constitutes a clutch device or section. Clutch control limiting
section 8L constitutes a transfer torque control device or section.
In view of the similarity between the first and fifth embodiments,
the parts of the fifth embodiment that are identical to the parts
of the first embodiment will be given the same reference numerals
as the parts of the first embodiment. Moreover, the descriptions of
the parts of the fifth embodiment that are identical to the parts
of the first embodiment may be omitted for the sake of brevity.
[0203] The processing executed by clutch control limiting section
8L is as shown in FIG. 30. In step S1400, the control program
determines whether or not the rear wheels 3L and 3R are
experiencing acceleration slippage using speed sensors 27FL, 27FR,
27RL, 27RR. If the control program determines that the rear wheels
3L and 3R are not experiencing acceleration slippage, then
processing proceeds to step S 1420. If the control program
determines that the rear wheels 3L and 3R are experiencing
acceleration slippage, then processing proceeds to step S1410.
[0204] In this embodiment, the determination of whether or not
acceleration slippage is occurring can be accomplished based on the
result of the processing executed in the aforementioned steps S1000
to S1030, which constitute a slippage condition detecting device or
section.
[0205] In step S1410, the reducing torque corresponding to the
acceleration slippage magnitude of the rear wheels 3L and 3R is
computed. The reducing torque .DELTA.TR or .DELTA.TM and the
current motor output torque are used to compute the maximum torque
transfer rate of the clutch 12. After the maximum torque transfer
rate KD is outputted to the clutch control section 8D, processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has
expired.
[0206] Meanwhile, in step S1420, the maximum torque transfer rate
KD is assigned 100 (which indicates 100%). The maximum torque
transfer rate KD is outputted to clutch control section 8D. Then
processing returns to the beginning of the control program to
repeat the control program after a prescribed sampling time cycle
has expired.
[0207] The clutch control section 8D limits in such a manner that
the upper limit of the torque transfer rate of the clutch 12
becomes the maximum torque transfer rate KD inputted from the
clutch control limiting section 8L. Thus, in the present
embodiment, when acceleration slippage occurs in the rear wheels 3L
and 3R, the upper limit of the transfer rate for the driving force
transferred to the rear wheels 3L and 3R from the clutch 12 is
suppressed. Consequently, the driving force actually transferred to
the rear wheels 3L and 3R decreases and the acceleration slippage
of the rear wheels 3L and 3R is suppressed. As a result, an
operational effect similar to those of the previously described
embodiments is achieved.
Sixth Embodiment
[0208] Referring now to FIG. 31, a driving force control apparatus
in accordance with a sixth embodiment will now be explained. The
basic construction of this embodiment is the same as that of the
first embodiment, except that the 4WD controller 8 is equipped with
an internal combustion engine output control section 8M. The
internal combustion engine output control section 8M constitutes an
internal combustion engine output control device or section. The
internal combustion engine output control section 8M is accessed
after the processing of motor torque limit computing section 8H or
after the processing of field current converting section 8J in
place of the aforementioned clutch control limiting section 8L and
distributing device control section 8K. In view of the similarity
between the first and sixth embodiments, the parts of the sixth
embodiment that are identical to the parts of the first embodiment
will be given the same reference numerals as the parts of the first
embodiment. Moreover, the descriptions of the parts of the sixth
embodiment that are identical to the parts of the first embodiment
may be omitted for the sake of brevity.
[0209] The processing executed by internal combustion engine output
control section 8M is as shown in FIG. 31. In step S1500, the
control program determines whether or not the rear wheels 3L and 3R
are experiencing acceleration slippage. If the control program
determines that the rear wheels 3L and 3R are not experiencing
acceleration slippage, then processing proceeds to step S1510. In
S1510, a command for opening the throttle opening of the sub
throttle valve 16 is issued to the motor controller 20 such that
the throttle opening of the sub throttle valve 16 is greater than
or equal to the opening of main throttle value 15. Then, processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has expired.
Meanwhile, if the control program determines that the rear wheels
3L and 3R are experiencing acceleration slippage, then the control
program proceeds to step S1520.
[0210] In step S1520, the slippage rate of the rear wheels 3L and
3R is computed and processing proceeds to step S1530. When the
slippage magnitude .DELTA.VR is found based on the difference
between the rear wheel speed VR and the wheel speed VR' calculated
from the estimated vehicle speed VS, then the equation shown below
is used to calculate the aforementioned slippage rate A. 4 A = VR
VR '
[0211] However, when the presence or absence of acceleration
slippage is determined by computing the surplus torque based on the
road surface limit grip amount and the motor torque Tm, the
slippage rate A is calculated as shown below. 5 A = Tm Tm
[0212] In step S1530, the throttle opening with respect to the
closing direction corresponding to the magnitude of the
acceleration slippage is computed. For example, the throttle
opening is calculated using the equation .theta.=K6.times.A, where,
K6 is a gain constant. Gain K6 can also be modified based on such
factors as the difference between the previous slippage rate and
the current slippage rate. A command for the computed opening is
issued to the motor controller 20. Then processing returns to the
beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired.
[0213] In the present embodiment, the output of the engine 2 is
controlled so as to decrease without relation to the driver's
operation of the accelerator by adjusting the sub throttle 16 in
the closing direction by an amount corresponding to slippage rate
A, which is the slippage condition detection value for the rear
wheels 3L and 3R. As a result, the generation load of the generator
7 becomes smaller, i.e., the driving torque transferred from the
electric motor 4 to the rear wheels 3L and 3R becomes smaller, and
the acceleration slippage of the rear wheels 3L and 3R is reduced
and suppressed.
[0214] As a result, acceleration slippage of the rear wheels 3L and
3R, too, is suppressed and the driving stability improves. At the
same time, the energy efficiency improves, which leads to improved
fuel consumption, because the output torque of the engine 2 is
suppressed.
Seventh Embodiment
[0215] Referring now to FIGS. 32-35, a driving force control
apparatus in accordance with a seventh embodiment will now be
explained. The basic construction of this embodiment is the same as
that of the first and second embodiments except that, as shown in
FIG. 32, a motor driving battery 49 is provided. The electrical
power from the generator 7 and the electrical power from the motor
driving battery 49 are supplied to the electric motor 4 via
inverter 50. The battery 49 has a relay (not shown) for shutting
off the supply of electrical power. In view of the similarity
between the prior embodiments and the seventh embodiments, the
parts of the seventh embodiment that are identical to the parts of
the first and second embodiments will be given the same reference
numerals as the parts of the first and second embodiments
embodiment. Moreover, the descriptions of the parts of the seventh
embodiment that are identical to the parts of the first embodiment
may be omitted for the sake of brevity.
[0216] The inverter 50 converts the electrical power supplied from
battery 49 to alternating current and combines it with the
electrical power supplied from the generator 7 before outputting
the resultant to the electric motor 4. The amount of electrical
power supplied from battery 49 to the electric motor 4 is adjusted
by commands from controller 8.
[0217] The target torque limiting section 8F of the present
invention will be explained using FIG. 33. In step S300, the
control program determines whether or not the aforementioned target
generation load torque Th is larger than the maximum load capacity
HQ of the generator 7. If target generation load torque Th is
determined to be less than or equal to the maximum load capacity HQ
of the generator 7, then processing proceeds to step S400 where
zero is assigned to Bh. Then, in step S410, the battery control
section 65 starts and processing returns to the beginning of the
control program to repeat the control program after a prescribed
sampling time cycle has expired.
[0218] On the other hand, if target generation load torque Th is
determined to be larger than the maximum load capacity HQ of the
generator 7 in step S300, processing proceeds to step S310. In step
S310, the excess or surplus torque Th, which is the portion of the
target generation load torque Th in excess of the maximum load
capacity HQ, is found using the equation .DELTA.Tb=Th-HQ. Then
processing proceeds to step S320.
[0219] In step 320, the current engine torque Te is computed based
on the signals from the engine speed detection sensor 21 and the
throttle sensor. Then processing proceeds to step S330.
[0220] In step S330, the engine torque upper limit value TeM, which
is obtained by subtracting the excess or surplus torque .DELTA.Tb
from the engine torque Te, is computed according to the equation
TeM=Te-.DELTA.Tb. The computed engine torque upper limit value TeM
is outputted to the engine controller 18. Then processing proceeds
to step S340.
[0221] In this embodiment, the engine controller 18 limits the
engine torque Te such that the received engine torque upper limit
value TeM becomes the upper limit value of the engine torque Te
regardless of the driver's operation of the accelerator pedal 17.
The processing from step S310 to this point constitutes an internal
combustion engine output limiting device or section.
[0222] In step 340, the control program determines whether or not
there is an acceleration request based on the accelerator pedal
operation amount. The processing step S340 and/or sensor 17a
constitute an acceleration request detecting device or section that
is configured to detect an acceleration request operation. The
acceleration request detecting device or section determines if the
rotational speeds of the subordinate drive wheel 3L and 3R are
being controlled proportionally to the acceleration request based
on the acceleration request indication quantity caused by a driver
and the elapsed time of the acceleration request indication. If
there is no acceleration request greater than or equal to a
prescribed acceleration, processing proceeds to step S420.
Meanwhile, if there is an acceleration request greater than or
equal to a prescribed acceleration, processing proceeds to step
S350.
[0223] The aforementioned determination of whether or not there is
an acceleration request greater than or equal to a prescribed value
is accomplished by determining if the accelerator operation falls
at a position in the crosshatched area of the map shown in FIG. 34.
That is, the control program determines that an acceleration
request occurred when an accelerator position that is greater than
or equal to a prescribed accelerator position continues for a
prescribed amount of time. The reason the continuance over a
prescribed amount of time is used is to make it possible to
reliably detect a condition in which the vehicle is stuck.
[0224] In step S350, the control program determines whether or not
the speed of subordinate drive wheels 3L and 3R is less than or
equal to a prescribed value, i.e., whether or not the vehicle is in
a stuck condition in which the speed of the subordinate drive
wheels 3L and 3R is suppressed compared to the acceleration
request. The processing step S350 constitutes an acceleration
condition detecting device or section that is configured to detect
the acceleration condition of the vehicle based on at least one of
the wheel speed of the subordinate drive wheels 3L and 3R, the
wheel acceleration of the subordinate drive wheels 3L and 3R, and
the longitudinal acceleration of the vehicle. Processing proceeds
to step S360 if the control program determines that the vehicle is
in a stuck condition. Conversely, processing proceeds to step S420
if the control program determines that the vehicle is not in a
stuck condition.
[0225] In step S360, the excess or surplus torque .DELTA.Tb is
assigned to Bh. In step S370, the battery control section 65 starts
and adjusts the amount of electrical power supplied from the
battery. The battery control section 65 constitutes supply power
adjusting device or section (65) that adjusts the magnitude of
electrical power supplied from the battery 49 to the electric motor
4. Then, processing proceeds to step S420.
[0226] In step 420, the generation load torque Th is limited to the
maximum load capacity HQ of the generator 7 and then processing
returns to the beginning of the control program to repeat the
control program after a prescribed sampling time cycle has
expired.
[0227] Next, the battery control section 65 is discussed using FIG.
35. In step S500, the control program determines whether or not Bh
is zero. If it is zero, processing proceeds to step S530 and the
power supply from battery 49 is stopped. If Bh is not zero,
processing proceeds to step S510.
[0228] In step S510, the supply amount from the battery 49 is
computed using the equation BP=K7.times.Bh, where K7 is a gain
constant. Then processing proceeds to step S520.
[0229] In step S520, a signal determined based on BP is fed to
inverter 50 and then processing returns to the beginning of the
control program to repeat the control program after a prescribed
sampling time cycle has expired. The step S520 constitutes a
battery power increasing device or section that starts upon
determining that the internal combustion engine output limiting
device or section (steps S310-330) has started. The battery power
increasing device or section increases the magnitude of electrical
power supplied to the electric motor 4 from the battery 49 by a
magnitude in accordance with the magnitude by which the internal
combustion engine output limiting device or section reduced the
output torque, upon determining that the rotational speed of the
subordinate drive wheel (3L, 3R) is being controlled proportionally
to an acceleration request based on the detection values of the
acceleration request detecting device or section (step S340) and
the acceleration condition detecting device or section (step
S350).
[0230] In step S530, a power stop command is sent to battery 49 and
inverter 50 and then processing returns to the beginning of the
control program to repeat the control program after a prescribed
sampling time cycle has expired.
[0231] Next, the operation and effects of the present embodiment
are described. When the surplus torque becomes larger and exceeds
or is in danger or exceeding the load capacity of the generator,
the output torque of the engine 2 is reduced in accordance with the
excess or surplus torque. As a result, it is not absolutely
necessary to have a large generator with a large load capacity.
This is advantageous in terms of cost and such installability
factors as the space occupied by the generator.
[0232] Additionally, when the internal combustion engine output
limiting device or section limits the output torque of the engine 2
in view of the load capacity of the generator and the main drive
wheels 1L and 1R are spinning (i.e., the vehicle is stuck), the
amount of power supplied to the electric motor 4 from battery 49 is
increased in accordance with the amount by which the output torque
of the engine 2 was reduced if the control program determines that
the driving force of the subordinate drive wheels 3L and 3R will
decline in comparison to the acceleration request. As a result,
when the vehicle is stuck, even if the output torque of the engine
2 is reduced in order to suppress acceleration slippage of main
drive wheels 1L and 1R, the driving torque of subordinate drive
wheels 3L and 3R is increased by a corresponding amount and the
total driving force of the vehicle remains equal. Therefore, the
ability to escape from a stuck condition is improved.
Eighth Embodiment
[0233] Referring now to FIGS. 2-4 and 36-40, a driving force
control apparatus in accordance with an eighth embodiment will now
be explained. The basic construction of this embodiment is the same
as that of the first embodiment, except that the driving force
control apparatus as been modified in accordance with the following
explanation. In view of the similarity between the first and eighth
embodiments, the parts of the eighth embodiment that are identical
to the parts of the first embodiment will be given the same
reference numerals as the parts of the first embodiment. Moreover,
the descriptions of the parts of the eighth embodiment that are
identical to the parts of the first embodiment may be omitted for
the sake of brevity. Also, the definitions of terms and
abbreviations of the terms defined in the following explanation of
this eighth embodiment have the same definition as in the first
embodiment, if the abbreviations and/or terms are redundantly used
in the following explanation.
[0234] An example of a four-wheel drive vehicle is illustrated in
FIG. 36 to explain this eighth embodiment of the present invention.
The vehicle is capable of four-wheel drive in which the left and
right front wheels 1L and 1R are driven by the internal combustion
engine 2 and the left and right rear wheels 3L and 3R are driven by
the electric motor 4. As shown in the FIG. 1, the engine output
torque Te of the internal combustion engine 2 is transferred to the
left and right front wheels 1L and 1R through the transmission and
the differential gear 5. The portion of the engine output torque Te
of the engine 2 is transferred to a generator 7 using an endless
belt drive 6.
[0235] The generator 7 rotates at rotational speed Nh, which is the
product of the rotational speed Ne of the engine 2 and the pulley
ratio of the endless belt drive 6. The load placed on the engine 2
by the generator 7 due to the field current Ifh is adjusted by the
4WD controller 8 to generate a voltage corresponding to the load
torque. The voltage generated by the generator 7 can be supplied to
the electric motor 4 through the electrical line 9. A junction box
10 is provided at an intermediate point in the electrical line 9
between the electric motor 4 and the generator 7. The drive shaft
of the electric motor 4 can be connected to the rear wheels 3L and
3R via a reduction gear 11, a clutch 12 and a. differential 13.
[0236] The main throttle valve 15 is disposed inside the intake
passage 14 (e.g., an intake manifold) of the engine 2. The throttle
opening of the main throttle valve 15 is adjusted/controlled in
accordance with the amount of depression of the accelerator pedal
17, which also functions as a throttle opening indicating device or
section. The main throttle valve 15 is either mechanically linked
to the depression amount of the accelerator pedal 17, or
adjusted/controlled electrically by the engine controller 18 in
accordance with the depression amount detection value from an
accelerator sensor that detects the depression amount of the
accelerator pedal 17. The depression amount detection value of the
accelerator sensor is outputted to the 4WD controller 8. The main
throttle valve 15 preferably uses a stepper motor 19 as an actuator
for adjusting its throttle opening. Specifically, the throttle
opening of the main throttle valve 15 is adjusted/controlled by the
rotational angle of the stepper motor 19, which corresponds to the
step count. The rotational angle of the stepper motor 19 is
adjusted/controlled by a drive signal from the motor controller 20.
The main throttle valve 15 is provided with a throttle sensor. The
step count of the stepper motor 19 is feedback-controlled based on
the throttle opening detection value detected by this throttle
sensor.
[0237] The apparatus is also equipped with an engine speed
detection sensor 21 that detects the rotational speed of the engine
2. The engine speed detection sensor 21 outputs its detected signal
to the 4WD controller 8.
[0238] As shown in FIG. 2, the generator 7 is equipped with a
voltage adjusting device 22 (regulator) for adjusting the output
voltage V. The generation load torque Th against the engine 2 and
the generated voltage V are controlled by the adjustment of field
current Ifh executed by the 4WD controller 8. The voltage adjusting
device 22 receives a generator control command (field current
value) from the 4WD controller 8 and adjusts the field current Ifh
of the generator 7 to a value corresponding to the generator
control command. It is also capable of detecting the output voltage
V of the generator 7 and outputting the detected voltage value to
the 4WD controller 8. Additionally, the rotational speed Nh of the
generator 7 can be computed based on the rotational speed Ne of the
engine 2 and the pulley ratio of the endless belt drive 6.
[0239] The current sensor 23 is provided inside junction box 10.
The current sensor 23 detects the current value Ia of the
electrical power supplied from the generator 7 to the electric
motor 4 and outputs the detected armature current signal to the 4WD
controller 8. The voltage across the electric motor 4 is detected
by the 4WD controller 8 to provide a voltage value across the
electrical line 9. A relay 24 shuts off or connects the voltage
(current) supplied to the electric motor 4 in accordance with a
command received from the 4WD controller 8.
[0240] The command from the 4WD controller 8 controls the field
current Ifm of the electric motor 4 and the adjustment of the field
current Ifm adjusts the drive torque Tm. A thermistor 25 measures
the temperature of the electric motor 4. The apparatus is also
equipped with a motor speed sensor 26 that detects the rotational
speed Nm of the drive shaft of the electric motor 4. The motor
speed sensor 26 outputs a signal for the detected rotational speed
of the electric motor 4 to the 4WD controller 8. The clutch 12 is a
hydraulic clutch or electric clutch and transmits torque at a
torque transfer rate corresponding to a clutch control command from
the 4WD controller 8.
[0241] The wheel speed sensors 27FL, 27FR, 27RL, and 27RR are
provided on wheels 1L, 1R, 3L and 3R, respectively. Each speed
sensor 27FL, 27FR, 27RL, and 27RR outputs a pulse signal
corresponding to the rotational speed of the respective wheel 1L,
1R, 3L and 3R to the 4WD controller 8. Each of the pulse signals
serves as a wheel speed detection value.
[0242] The 4WD controller 8 is a control unit that preferably
includes a microcomputer with a 4WD control program that is
operatively coupled to the internal combustion engine 2 and the
electric motor 4 to control the torque applied to the left and
right front wheels 1L and 1R by the internal combustion engine 2
and the torque applied to the left and right rear wheels 3L and 3R
by the electric motor 4 as discussed below.
[0243] Referring now to FIG. 3, in this eighth embodiment of the
present invention, the 4WD controller 8 is equipped with a
generator control section 8A, a relay control section 8B, a motor
control section 8C, a clutch control section 8D, a surplus torque
computing section 8E, a target torque limiting section 8F, and a
surplus torque converting section 8G. The remaining control blocks
shown in FIG. 3 are used by other embodiments discussed herein.
[0244] Referring back to FIG. 4, in this eighth embodiment of the
present invention, at a prescribed sampling time cycle, the
processing is conducted in sequence by the surplus torque computing
section 8E, the target torque limiting section 8F, and the surplus
torque converting section 8G based on the input signals.
[0245] According to the eighth embodiment, the engine controller 18
executes the following processes as shown in FIG. 37, depending
upon signals inputted in each of predetermined sampling intervals
(as shown in FIG. 4). In step S2040, a target engine torque value
TeN requested by a driver is calculated depending upon a detected
signal from the motor controller 20 that controls the main throttle
valve 15. Then, processing proceeds to step S2041.
[0246] In step S2041, the control program determines if an engine
torque upper limited value TeM is outputted from the 4WD controller
8. If the signal is outputted, then the program proceeds to step
S2042. If the signal is not outputted, the program proceeds to step
S2044.
[0247] In step S2042, the control program compares the engine
torque upper limited value TeM with the target engine torque value
TeN. If the engine torque upper limited value TeM is larger, the
program proceeds to step S2043. If the engine torque upper limited
value TeM is equal to or smaller than the target engine torque
value TeN, the program proceeds to step S2044.
[0248] In step S2043, the engine torque upper limited value TeM is
substituted for the target engine torque value TeN so that the
target engine torque value TeN is enlarged. Then, the program
proceeds to step S2044.
[0249] In step 2044, an engine torque Te is calculated depending
upon a throttle opening signal, an engine rotation speed, and etc.
Then, the program proceeds to step S2045.
[0250] In step S2045, a deviation .DELTA.Te' of the target engine
torque value TeN to the engine torque Te is computed by the
following equation: .DELTA.Te'=TeN-Te. Then, the program proceeds
to step S2046.
[0251] In step S2046, a deviation .DELTA..theta. of a degree of
throttle opening is calculated depending upon the deviation
.DELTA.Te, and an opening degree signal corresponding to the
deviation .DELTA..theta. is outputted to the stepper motor 19.
[0252] Referring back to FIG. 3, the generator control section 8A
monitors a generated voltage V of the generator 7 through the
voltage adjusting device 22, and it controls the field current Ifm
of the generator 7, so that it controls the generated voltage V of
the generator 7 for a predetermined voltage.
[0253] The relay control section 8B turns on/off the power supply
from the generator 7 to the motor 4. The motor control section 8C
controls the torque of the motor 4 for a predetermined value by
controlling the field current Ifm of the motor 4.
[0254] Referring to FIG. 4, a cycle of control is performed by
surplus torque computing section 8E, the target torque limiting
section 8F and the surplus torque converting section 8G depending
on inputted signals in predetermined sampling time intervals.
[0255] Referring to FIG. 38, the surplus torque computing section
8E executes the following processing for computing a load
torque.
[0256] In step S2001, the speed values of the front wheels or
driving wheels 1L and 1R and the rear wheels or subordinate wheels
3L and 3 are obtained depending upon signals from the sensors 27FL,
27FR, 27RL and 27RR. By subtracting the speed value of the rear
wheel 3L and 3R from the speed value of the front wheels 1L and 1R,
a slip speed .DELTA.VF is calculated as an acceleration slip amount
of the front wheels 1L and 1R. Then, the program proceeds to step
S2002.
[0257] In step S2002, the program compares the slip speed .DELTA.VF
with zero. If the slip speed .DELTA.VF equals or is smaller than
zero, the program assumes the front wheels 1L and 1R are not
slipping and proceeds to step S2003. In step S2003, zero is
substituted for the variable Th.
[0258] If the slip speed .DELTA.VF is larger than zero in step
S2002, the program assumes that the front wheels 1L and 1R are
slipping. Then, the program proceeds to step S2004. In step S2004,
an absorbing torque T.DELTA.VF is calculated for preventing the
acceleration slip of the front wheels 1L and 1R. Then, the program
proceeds to step S2005.
[0259] In step S2005, a current load torque TG of the generator 7
is calculated by the following equation. Then, the program proceeds
to step S2006. 6 TG = K2 .times. V .times. Ia K3 .times. Nh where V
: voltage of the generator 7 , Ia : armature current of the
generator 7 , Nh : rotational speed of the generator 7 , K3 :
efficiency , and K2 : coefficient .
[0260] In step S2006, calculated is a target generation load torque
Th that is an additional torque that should be loaded to the
generator 7, by the equation: Th=TG+T.DELTA.VF.
[0261] Referring to FIG. 40, the processing of the target torque
limiting section 8F will now be explained. In step S2011, the
program compares the target generation load torque Th with a
maximum load capacity HQ of the generator 7. If the target
generation load torque Th equals or is smaller than the maximum
load capacity HQ, the program proceeds to step S2013. If the target
generation load torque Th is larger than the maximum load capacity
HQ, then the program proceeds to step S2012.
[0262] In step S2012, the maximum load capacity HQ is substituted
for the target generation load torque Th as shown in the following
equation: Th=HQ. Then, the program proceeds to step S2013.
[0263] In step S2013, the current engine torque Te is calculated
depending upon signals from the engine speed detection sensor 21
and the throttle sensor. Then, the program proceeds to step S2014.
In step S2014, a minimum allowed torque Tk for which the engine 2
will not stop is calculated depending upon a rotational speed Ne
and etc. Then, the program proceeds to step S2015. However, a
predetermined value may be used as the minimum allowed torque Tk
instead of calculating the torque Tk.
[0264] In step S2015, a deviation torque .DELTA.Te is calculated by
using the following equation: .DELTA.Te=Te-Tk. Then the program
proceeds to step S2016. Therein, steps S2013-S2015 constitute a
deviation torque computing device or section.
[0265] In step S2016, the program compares the deviation torque
.DELTA.Te with the target generation load torque Th. If the
deviation torque .DELTA.Te is smaller than the target generation
load torque Th, the program proceeds to step S2017.
[0266] In step S2017, an engine torque upper limited value TeM is
calculated by the following equation TeM=Te+(Th-.DELTA.Te)+.alpha.,
where .alpha. is a value for safety. Then, the engine torque upper
limited value TeM is outputted to the engine controller 18.
[0267] However, the engine speed Ne of the engine 2 cannot vary
quickly because of the rotational inertia of the entire driving
system when the throttle valve 15 is ordered to quickly open or
close. In other words, the output power response speed of the
engine 2 cannot be very fast. Accordingly, .alpha. may be zero. In
case that .alpha. is set as a relatively large value, the target
torque of the engine 2 may be controlled to be immediately large
when the deviation torque .DELTA.Te is smaller than the generator
load torque Th.
[0268] Therein, steps S2041-S2043, step S2016 and step S2017
constitute controlling an internal combustion engine output control
device or section.
[0269] Next, the processing executed by the surplus torque
converting section 8G will be explained based on FIG. 11. First, in
step S600, the control program determines if Th is larger than 0.
If Th is determined to be larger than 0, processing proceeds to
step S610 because one of the following is occurring: the front
wheels 1L and 1R are experiencing acceleration slippage; the
conditions are such that there is an apprehension of acceleration
slippage occurring; or the vehicle is in a low speed state at or
below a prescribed speed. If the control program determines that Th
is less than or equal to 0, then processing returns to the
beginning of the control program to repeat the control program
after a prescribed sampling time cycle has expired without
executing the subsequent steps because the vehicle is in a state in
which the front wheels 1L and 1R are not experiencing acceleration
slippage or other comparable state.
[0270] In step S610, the rotational speed Nm of the electric motor
4 detected by motor speed sensor 21 is received as input. The
target motor field current Ifm corresponding to the rotational
speed Nm of the electric motor 4 is calculated and the target motor
field current Ifm is outputted to the motor control section 8C.
Then, processing proceeds to step S620.
[0271] In this embodiment, the target motor field current Ifm
corresponding to the rotational speed Nm of the electric motor 4 is
held to a fixed prescribed current value when rotational speed Nm
is below a prescribed rotational speed and the field current Ifm of
the electric motor 4 is reduced by a known weak magnetic field
control method when the electric motor 4 is rotating above a
prescribed rotational speed (see FIG. 12). In short, when the
electric motor 4 rotates at a high speed the motor torque decreases
due to the rise in the motor induced voltage E. Therefore, as
discussed earlier, when the rotational speed Nm of the electric
motor 4 reaches or exceeds a prescribed value, the current flowing
to the electric motor 4 is increased and the required motor torque
Tm is obtained by reducing the field current Ifm of the electric
motor 4 and lowering the induced voltage E. As a result, even if
the electric motor 4 rotates at a high speed, the required motor
torque Tm can be obtained because the motor induced voltage E is
kept from rising and the motor torque is prevented from decreasing.
Also, the price of the electronic control circuit can be reduced in
comparison with continuous field current control because the motor
field current Ifm is controlled in two stages: a stage for when the
rotational speed is below a prescribed value and another stage for
when the rotational speed is at or above a prescribed value.
[0272] It is also acceptable to provide a motor torque correcting
section that continuously corrects the required motor torque Tm by
adjusting the field current Ifm in accordance with the rotational
speed Nm of the electric motor 4. That is, instead of switching
between two stages, the field current Ifm of the electric motor 4
can be adjusted in accordance with the motor rotational speed Nm.
As a result, even if the electric motor 4 rotates at a high speed,
the required motor torque Tm can be obtained because the motor
induced voltage E is kept from rising and the motor torque is
prevented from decreasing. Furthermore, since a smooth motor torque
characteristic can be obtained, the vehicle can travel with better
stability than in the case of two-stage control and the vehicle can
always be kept in a state where the motor driving efficiency is
good.
[0273] In step S620, the induction current E of the electric motor
4 is calculated based on the target motor field current Ifm and the
rotational speed Nm of the electric motor 4. Then, processing
proceeds to step S630.
[0274] In step S630, the corresponding target motor torque TM is
calculated based on the generation load torque Th computed by
surplus torque computing section 8E. Then, processing proceeds to
step S640.
[0275] In step S640, the corresponding target armature current Ia
is calculated using the target motor torque TM and the target motor
field current Ifm as variables. Then, processing proceeds to step
S650.
[0276] In step S650, the equation V=Ia.times.R+E is used to
calculate the target voltage V of the generator 7 from the target
armature current Ia, resistance R, and the induced voltage E.
Processing returns to the beginning of the control program to
repeat the control program after a prescribed sampling time cycle
has expired after the target voltage V of the generator 7 is
outputted to the generator control section 8A. The resistance R is
the resistance of the electrical line 9 and the resistance of the
coil of the electric motor 4.
[0277] Although here the surplus torque converting section 8G takes
into account control of the motor when it calculates the target
voltage V at the generator 7 that corresponds to the target
generation load torque Th, it is also acceptable to calculate the
voltage value V that achieves the target generation load torque Th
directly from target generation load torque Th. FIG. 12 shows an
example of a time chart for the processing described above.
[0278] Referring back to FIG. 3, in this eighth embodiment, the
generator control section 8A constitutes a generator load torque
computing device or section, and the surplus torque converting
section 8G constitutes a generator load torque control device or
section. Referring again to FIG. 38, step S2001 and step S2002
constitutes a drive wheel slippage estimating device or section.
The steps S2004-S2006 constitute a deviation torque computing
device or section.
[0279] Next, the operation of the apparatus of this eighth
embodiment will be explained. A torque delivered from the engine 2
to the front wheels 1L and 1R may be greater than the road grip
limit torque. In such a case, the front wheels or the driving
wheels 1L and 1R may slip. The amount of the slip makes the
generator 7 to generate a power at the generator load torque Th.
Thus, the driving torque delivered to the front wheels 1L and 1R is
controlled toward the road surface reaction limit torque, so that
the front wheels 1L and 1R are kept away from the acceleration
slippage. Meanwhile, the acceleration ability of the automobile is
improved because the surplus power generated by the generator 7 is
supplied to the motor 4 that drives the rear wheels 3L and 3R.
Furthermore, the energy efficiency is improved and fuel efficiency
is improved because the motor 4 is driven by the surplus torque
from the driving wheels.
[0280] The acceleration ability is also improved by the surplus
power which cannot be used by the front wheels 1L and 1R, but which
can be used by the rear wheels 3L and 3R only when the automobile
is on a slippery road. This is better than the driving system which
always distributes the driving force not only to the front wheels
1L and 1R but also to the rear wheels 3L and 3R because the driving
energy has to be converted some times.
[0281] When the output torque Te of the engine 2 is set to equal to
the engine torque upper limited value TeM, the engine 2 is kept
away from getting too much load torque of the generator 7.
[0282] In FIG. 40, graph (a) shows an example of variation of the
deviation torque .DELTA.Te. When a target generation load torque Th
that is going to be used by the generator 7 varies as shown in
graph (b) of FIG. 40, a deviation torque .DELTA.TeM is calculated
as shown in graph (c) of FIG. 40. Thus, the engine torque is
controlled to be greater than the current engine torque Te by the
deviation torque .DELTA.TeM.
[0283] The surplus power generated by the generator 7 can be
consumed by a load such as an air conditioner other than by the
motor 4.
[0284] The subject invention is not limited to the structure in
which a load torque is determined depending upon a slippage amount
of the front wheels 1L and 1R compared to that of the rear wheels
3L and 3R, and the amount of electric power generated by the
generator 7 is defined corresponding to the load torque. However, a
driving torque that is required by the rear wheels 3L and 3R can be
calculated by a different way. The driving torque can define the
generated power amount of the generator 7, so that a preferable
load torque is created by the generator 7. The structure in which
the engine torque upper limited value TeM is outputted from the 4WD
controller 8 to the engine controller 18 can be replaced with
another structure. In such a structure, the engine torque deviation
.DELTA.TeM can be supplied to the engine controller 18, and the
engine controller 18 can calculate the degree of the throttle
opening corresponding to the engine controller 18.
Ninth Embodiment
[0285] Referring now to FIG. 41, a driving force control apparatus
in accordance with a ninth embodiment will now be explained. This
ninth embodiment is most identical to the eighth embodiment, except
for the construction pertinent to the flowchart shown in FIG. 41.
Thus, the basic construction of this embodiment also relies on the
basic construction of the first embodiment. In view of the
similarity between ninth and eighth embodiments, the descriptions
of the parts of the ninth embodiment that are identical to the
parts of the prior embodiment have been omitted for the sake of
brevity. Also, the definitions of terms and abbreviations of the
terms defined in the following explanation of this eighth
embodiment have the same definition as in the first and eighth
embodiment, if the abbreviations and/or terms are redundantly used
in the following explanation.
[0286] Referring to FIG. 41, a flow chart for a special processing
program is illustrated in accordance with the ninth embodiment.
This program compares the target generation load torque Th with the
maximum load capacity HQ of the generator 7 in step S2061. If the
target generation load torque Th equals to or is smaller than the
maximum load capacity HQ, the program proceeds to step S2063. If
the torque Th is smaller than the capacity HQ, the program proceeds
to step S2062.
[0287] In step S2062, the maximum load capacity HQ is substituted
for the target generation load torque Th as shown in the following
equation: Th=HQ. Then the program proceeds to step S2063.
[0288] In step S2063, a current engine torque Te is calculated
depending upon signals from the engine rotational speed detection
sensor 21 and the throttle sensor. Then, the program proceeds to
step S2064.
[0289] In step S2064, a minimum allowed torque Tk for which the
engine 2 will not stop is calculated depending upon the current
engine rotational speed and etc. Then the program proceeds to step
S2065.
[0290] In step S2065, a deviation torque .DELTA.Te is calculated by
using the following equation: .DELTA.Te=Te-Tk. Then, the program
proceeds to step S2066.
[0291] In step S2066, the program compares the deviation torque
.DELTA.Te with the target generation load torque Th. If the torque
.DELTA.Te is smaller than the torque Th, the program proceeds to
step S2067.
[0292] In step S2067, the target generation load torque Th is
reduced toward the deviation torque .DELTA.Te by using the
following equation: Th=.DELTA.Te-.alpha., where .alpha. is a
coefficient for safety and .alpha. can be zero. Therein, steps
S2066 and S2067 constitute a load torque control device or
section.
[0293] The engine 2 is kept away from obtaining too much generator
load torque by controlling the generation load by the deviation
torque .DELTA.Te.
[0294] Although the above embodiments were explained using an
example of a vehicle capable of four-wheel drive, the invention can
be applied to any vehicle with two or more wheels in which a
portion of the wheels are driven by an internal combustion engine
and another portion or the entire remainder of wheels are driven by
a motor 4.
[0295] The term "acceleration slippage" as used in this invention
refers to slippage of the wheels when the vehicle is
accelerating.
[0296] As used herein, the following directional terms "forward,
rearward, above, downward, vertical, horizontal, below and
transverse" as well as any other similar directional terms refer to
those directions of a vehicle equipped with the present invention.
Accordingly, these terms, as utilized to describe the present
invention should be interpreted relative to a vehicle equipped with
the present invention.
[0297] The term "configured" as used herein to describe a
component, section or part of a device includes hardware and/or
software that is constructed and/or programmed to carry out the
desired function. Moreover, terms that are expressed as "means-plus
function" in the claims should include any structure that can be
utilized to carry out the function of that part of the present
invention.
[0298] The terms of degree such as "substantially", "about" and
"approximately" as used herein mean a reasonable amount of
deviation of the modified term such that the end result is not
significantly changed. For example, these terms can be construed as
including a deviation of at least .+-.5% of the modified term if
this deviation would not negate the meaning of the word it
modifies.
[0299] This application claims priority to Japanese Patent
Application Nos. 2000-346287, 2000-346288 and 2001-225144. The
entire disclosures of Japanese Patent Application Nos. 2000-346287,
2000-346288 and 2001-225144 are each hereby incorporated herein by
reference.
[0300] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing description of the embodiments according to the
present invention are provided for illustration only, and not for
the purpose of limiting the invention as defined by the appended
claims and their equivalents. Thus, the scope of the invention is
not limited to the disclosed embodiments.
* * * * *