U.S. patent application number 09/734542 was filed with the patent office on 2001-06-28 for driving force control system for four-wheel drive vehicles.
This patent application is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Hirakawa, Mitsuaki, Kitano, Kazuhiko, Nakasako, Toru, Taguchi, Satoshi, Uchiyama, Naoki, Yamamoto, Akihiro.
Application Number | 20010005704 09/734542 |
Document ID | / |
Family ID | 18488058 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005704 |
Kind Code |
A1 |
Kitano, Kazuhiko ; et
al. |
June 28, 2001 |
Driving force control system for four-wheel drive vehicles
Abstract
A four-wheel drive vehicle is provided in which the main driven
wheels are driven by an engine via a torque converter and the
auxiliary driven wheels are driven by an electric motor. The
response of the vehicle to the operation of the accelerator is
improved by suppressing in advance the slip of the main driven
wheels due to an excess output of the engine. The main driven
wheels are driven by an engine via a torque converter and auxiliary
driven wheels are driven by an electric motor. The vehicle is
started by the output of the electric motor in the region in which
the speed ratio of the torque converter is small (that is to say,
the region in which the efficiency is low) such as when the vehicle
is starting, and when it enters the region in which the speed ratio
of the torque converter exceeds 0.8 and the efficiency exceeds 85%
the drive of the electric motor is stopped or suspended and the
vehicle is made to travel by means of the output of the engine.
Inventors: |
Kitano, Kazuhiko; (Wako-shi,
JP) ; Nakasako, Toru; (Wako-shi, JP) ;
Yamamoto, Akihiro; (Wako-shi, JP) ; Uchiyama,
Naoki; (Wako-shi, JP) ; Hirakawa, Mitsuaki;
(Wako-shi, JP) ; Taguchi, Satoshi; (Wako-shi,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
1050 Cnnecticut Avenue, N.W., Suite 600
Washington
DC
20036-5339
US
|
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha
|
Family ID: |
18488058 |
Appl. No.: |
09/734542 |
Filed: |
December 13, 2000 |
Current U.S.
Class: |
477/107 ;
180/65.27; 180/65.28; 180/65.285; 477/156; 903/903; 903/916 |
Current CPC
Class: |
B60W 2540/10 20130101;
Y02T 10/40 20130101; F16H 2059/467 20130101; B60W 2520/10 20130101;
Y02T 10/62 20130101; B60W 10/08 20130101; B60W 20/10 20130101; Y10S
903/903 20130101; B60W 2710/086 20130101; B60W 10/06 20130101; B60K
28/165 20130101; B60K 6/52 20130101; B60W 2520/26 20130101; B60K
17/354 20130101; B60W 20/00 20130101; Y10S 903/916 20130101; B60K
17/356 20130101; B60K 23/0808 20130101; B60W 2710/0677 20130101;
B60W 30/18027 20130101 |
Class at
Publication: |
477/107 ;
477/156 |
International
Class: |
B60K 041/04; F16H
061/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
11-366934 |
Claims
1. A driving force control system for a four-wheel drive vehicle
comprising main driven wheels driven by an engine via a torque
converter, speed ratio detecting means for detecting the speed
ratio of said torque converter and auxiliary driven wheels driven
by an electric motor independently from the engine, the control
system comprising a control means coupled to said speed ratio
detecting means for controlling the distribution ratio of the
output generated by the engine and the output generated by the
electric motor according to the speed ratio of said torque
converter.
2. A driving force control system for a four-wheel drive vehicle
according to claim 1, wherein the speed ratio of said torque
converter at which the drive of the electric motor is stopped is
different from the speed ratio of said torque converter at which
the drive of the electric motor is started.
3. A driving force control system for a four-wheel drive vehicle
according to claim 1, wherein main driven wheel speed detecting
means and auxiliary driven speed detecting means are coupled to
said control means and wherein said control means determines the
state of slip of said main driven wheels and said control means
changes the maximum output of said electric motor according to the
state of slip of said main driven wheels .
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a driving force control
system for four-wheel drive vehicles comprising main driven wheels
which are driven by an engine via a torque converter and auxiliary
driven wheels which are driven by an electric motor independently
from the engine.
[0003] 2. Description of the Prior Art
[0004] Hybrid type four-wheel drive vehicles in which a pair of
front or rear main driven wheels are driven by an engine and
another pair of front or rear auxiliary driven wheels are driven by
an electric motor which is connected to a battery are known in, for
example, Japanese Patent Application Laid-open No. 5-8639 and
Japanese Patent Application Laid-open No. 6-225403. Such four-wheel
drive vehicles attempt to economize on fuel consumption and improve
the ground covering properties on poor condition roads by switching
over between a two-wheel drive state in which the vehicle travels
using the engine alone and a four-wheel drive state in which the
vehicle travels using the engine and the electric motor on the
basis of a switch-over pattern which is predetermined using the
engine load and the vehicle speed as parameters.
[0005] In the case of front-wheel drive vehicles in which the
engine is mounted on the front section, since the percentage torque
amplification is large in the region in which the speed ratio of
the torque converter is small, such as when starting to travel. The
front wheels, which are the main driven wheels, easily slip on
slippery road surfaces such as roads with snow. It is therefore
possible to suppress in advance the slip of the front wheels by
distributing the driving force to the rear wheels which are
auxiliary driven wheels. Moreover, the response of the vehicle to
depression of the accelerator pedal can be enhanced by applying
assistance from an electric motor in the region in which the speed
ratio of the torque converter, which employs the transmission of a
fluid, is small. The efficiency .eta. of the torque converter is a
function of the speed ratio e (output rotational rate/input
rotational rate). The efficiency .eta. is low in the region where
the speed ratio e is small such as when the vehicle is starting to
travel, and the efficiency .eta. is high in the region where the
speed ratio e is large such as when the vehicle is cruising.
Therefore, if the engine is assisted by accurately operating the
electric motor in the region where the speed ratio e of the torque
converter is small such as when the vehicle is starting, it can
contribute to economizing the fuel consumption of the engine.
SUMMARY OF THE INVENTION
[0006] The present invention has been made in view of the
above-mentioned circumstances and, with regard to a four-wheel
drive vehicle whose main driven wheels are driven by an engine via
a torque converter and whose auxiliary driven wheels are driven by
an electric motor. It is an objective of the present invention to
improve the response of the vehicle to the operation of the
accelerator by suppressing the slip of the main driven wheels when
starting to travel, etc.
[0007] In order to achieve this object, a driving force control
system for a four-wheel drive vehicle is provided which comprises
main driven wheels driven by an engine via a torque converter,
speed ratio detecting means for detecting the speed ratio of the
torque converter and auxiliary driven wheels driven by an electric
motor independently from the engine. A control means controls the
distribution ratio of the output generated by the engine and the
output generated by the electric motor according to the speed ratio
of the torque converter.
[0008] Since the output generated by the engine and the output
generated by the electric motor are distributed according to the
speed ratio of the torque converter, by reducing the output of the
engine for driving the main driven wheels and increasing the output
of the electric motor for driving the auxiliary driven wheels in
the region in which the speed ratio of the torque converter is low
and the percentage torque amplification is high when the vehicle is
starting, the driving force can be distributed among the four
wheels so as to suppress the slip of the main driven wheels and
improve the response of the vehicle to the operation of the
accelerator. By assisting the output of the engine by means of the
output of the electric motor so as to compensate for the reduction
in the torque converter efficiency .eta. in the region in which the
speed ratio is low, it can be anticipated that the effect will be
to reduce the fuel consumption.
[0009] Furthermore, a driving force control system for a four-wheel
drive vehicle is proposed wherein the speed ratio of the torque
converter at which the drive of the electric motor is suspended,
different from the speed ratio of the torque converter at which the
drive of the electric motor is started.
[0010] Since the speed ratio at which the drive of the electric
motor is suspended is made different from the speed ratio at which
the drive of the electric motor is started, it is possible to
prevent frequent switch-over between driving and stopping or
suspending the drive of the electric motor when the speed ratio
changes slightly.
[0011] Still further, a driving force control system for a
four-wheel drive vehicle is proposed wherein the maximum output of
the electric motor changes according to the state of slip of the
main driven wheels.
[0012] Since the maximum output of the electric motor is changed
according to the state of slip of the main driven wheels, it is
possible to effectively suppress the slip of the main driven wheels
on a road surface having a low coefficient of friction when the
vehicle is starting, etc. thereby enhancing the ground covering
properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 to FIG. 6 illustrate an embodiment of the present
invention.
[0014] FIG. 1 is a diagram showing the entire structure of a hybrid
four-wheel drive vehicle.
[0015] FIG. 2 is a graph showing the characteristics of a torque
converter.
[0016] FIG. 3 is a flow chart of the main routine.
[0017] FIG. 4 is a flow chart showing a routine for determining the
possibility of slip in the main driven wheels.
[0018] FIG. 5 is a flow chart of a routine for determining the
maximum output of an electric motor.
[0019] FIG. 6 is a flow chart of a routine for determining the
output of the electric motor and the output of an engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] FIG. 1 shows a hybrid four-wheel drive vehicle which
comprises right and left main driven wheels Wf, Wf (front wheels)
which are driven by an engine E via a transmission T and a front
differential gear Df, and right and left auxiliary driven wheels
Wr, Wr (rear wheels) which are driven by an electric motor M
connected to a battery B via a rear differential gear Dr.
[0021] A known torque converter C is provided between the
crankshaft of the engine E and the main shaft of the transmission
T, and the speed ratio e (output rotational rate/input rotational
rate) of the torque converter C is detected by a torque converter
speed ratio detecting means Sa. The degree of opening .theta.AP of
an accelerator which is operated by the driver is detected by an
accelerator degree of opening detecting means Sb. Right and left
main driven wheel speeds VfR, VfL are detected by main driven wheel
speed detecting means ScR, ScL, and right and left auxiliary driven
wheel speeds VrR, VrL are detected by auxiliary driven wheel speed
detecting means SdR, SdL.
[0022] The speed ratio e of the torque converter C, degree of
opening .theta.AP of the accelerator, main driven wheel speeds VfR,
VfL and auxiliary driven wheel speeds VrR, VrL are input into an
electronic control unit U which forms the control means of the
present invention. An electronic control unit U controls the output
of the engine E via a throttle valve TV as well as the output of
the electric motor M via a motor driver MD.
[0023] FIG. 2 shows the characteristics of the standard torque
converter C. The abscissa denotes the speed ratio e (output
rotational rate / input rotational rate) and the ordinate denotes
the efficiency .eta. and the torque ratio t. As is clear from the
figure, the efficiency .eta. increases up to a maximum value of 85%
in the region of the converter in which the speed ratio e is in the
range from 0.0 to 0.8. The torque ratio t linearly decreases from
2.2 to 1.0 in the region of the converter in which the speed ratio
e is in the range from 0.0 to 0.8, and it is maintained at a
constant value of 1.0 in a coupling region in which the speed ratio
e exceeds 0.8.
[0024] When the vehicle starts to travel the engine E drives the
main driven wheels Wf, Wf and the speed ratio e of the torque
converter C gradually increases from 0.0, but in the region of the
converter prior to the coupling region in which the speed ratio e
exceeds 0.8, the torque ratio is 1.0 or more so that a torque
amplification effect is exhibited. By reducing the output of the
engine E during this period and driving the auxiliary driven wheels
Wr, Wr by means of the electric motor M so as to assist the
reduction, the vehicle is put in a four-wheel drive state so as to
enhance the starting performance on road surfaces having a low
coefficient of friction, while effectively preventing the main
driven wheels Wf, Wf from slipping. In particular, since the
electric motor M can drive the auxiliary driven wheels Wr, Wr
without any of the time delay that is an intrinsic characteristic
of a fluid transmission, the starting response of the vehicle can
be enhanced.
[0025] In addition, since the efficiency .eta. of the torque
converter C is as low as 85% or less in the coupling region in
which the speed ratio e is 0.8 or below, by driving the auxiliary
driven wheels Wr, Wr by means of the electric motor M in this
region to assist the engine E, the load applied to the engine E can
be lightened in the region in which the efficiency .eta. of the
torque converter C is low, and thus it is anticipated that the
effect will be to suppress an increase in the fuel consumption.
[0026] Next, details of the control of the engine E and the
electric motor M are explained by reference to the flow charts
shown in FIG. 3 to FIG. 6.
[0027] In Step S1 of the main routine shown in FIG. 3, a
determination is made as to whether or not the main driven wheels
Wf, Wf (front wheels) which are driven by the engine E, are
slipping. In the case where the main driven wheels Wf, Wf have
slipped, in order to increase the ground covering properties rather
than economize on fuel consumption, the auxiliary driven wheels Wr,
Wr are driven by the electric motor M to put the vehicle in a
four-wheel drive state.
[0028] In the subsequent Step S2, the maximum output of the
electric motor M is determined. The maximum output of the electric
motor M may be set at three levels of 4 kW, 8 kW and 12 kW. The
maximum output of the electric motor M is set at the lowest level
of 4 kW in a state in which the main driven wheels Wf, Wf are not
slipping, the maximum output of the electric motor M is set at the
middle level of 8 kW in a state in which the main driven wheels Wf,
Wf are slipping and the degree of opening .theta.AP of the
accelerator is comparatively low, and the maximum output of the
electric motor M is set at the highest level of 12 kW in a state in
which the main driven wheels Wf, Wf are slipping to a great extent
and the degree of opening .theta.AP of the accelerator is
comparatively high. Since the maximum output of the electric motor
M is thus changed according to the state of slip of the main driven
wheels Wf, Wf, it is possible to effectively suppress the slip of
the main driven wheels Wf, Wf according to the coefficient of
friction of the road surface, etc. thus enhancing the ground
covering properties.
[0029] In the subsequent Step S3, the output of the electric motor
M and the output of the engine E are determined in relation to each
other to obtain a total output which is determined by the degree of
opening .theta.AP of the accelerator.
[0030] Next, the subroutine of Step S1 is explained by reference to
the flow chart shown in FIG. 4.
[0031] First of all, the difference between the front and rear
wheel speeds is calculated by subtracting the auxiliary driven
wheel speeds VfR, VrL which are detected by the auxiliary driven
wheel speed detecting means SdR, SdL from the main driven wheel
speeds VfR, VfL which are detected by the main driven wheel speed
detecting means ScR, ScL. In Step S12 if there was no slip of the
main driven wheels Wf, Wf during the previous cycle, the routine
moves on to Step S13, and in Step S13 (1) if the wheel speed
difference exceeds a predetermined wheel speed difference 1; or (2)
if the speed ratio e of the torque converter C is at a
predetermined speed ratio or below and the rate of change of the
speed ratio e exceeds a predetermined rate of change of the speed
ratio, it is determined in Step S14 that the main driven wheels Wf,
Wf are slipping.
[0032] On the other hand, in Step S12 if the main driven wheels Wf,
Wf had slipped during the previous cycle, the routine moves on to
Step S15, and in Step S15 (1) if the required engine output is less
than the engine output limit value or (2) if the wheel speed
difference is less than a predetermined wheel speed difference 2,
it is determined in Step S16 that the main driven wheels Wf, Wf are
not slipping.
[0033] As hereinbefore described, when a determination is made
using the flow chart shown in FIG. 4 as to whether or not the main
driven wheels Wf, Wf are slipping, the routine moves on to the flow
chart shown in FIG. 5.
[0034] First of all, in Step S21 if there was an increase in the
output of the electric motor M during the previous cycle, the
routine moves on to Step S22, and in Step S22 if (1) the vehicle
speed exceeds a predetermined vehicle speed or (2) the accelerator
is `OFF`, the output of the electric motor M is not increased in
Step S23 and the maximum output of the electric motor M is set at
the lowest level `1` (4 kW) in Step S24. This is because there is
no need to strongly assist the engine by means of the electric
motor M after the vehicle has started and is in a cruising state or
when the vehicle is decelerating.
[0035] In Step S21 if there was no increase in the output of the
electric motor M during the previous cycle, the routine moves on to
Step S25, and if the main driven wheels Wf, Wf are not slipping,
the maximum output of the electric motor M is set at the lowest
level `1` (4 kW) in Step S26. This is because in the case in which
the main driven wheels Wf, Wf are not slipping there is no need to
drive the auxiliary driven wheels Wr, Wr strongly to enhance the
starting performance on a road surface having a low coefficient of
friction.
[0036] In the Step S25 if the main driven wheels Wf, Wf are
slipping, the routine moves on to Step S27 and the output of the
electric motor M is increased, in the subsequent Step S28 the
degree of opening .theta.AP of the accelerator which is detected by
the accelerator degree of opening detecting means Sb, is compared
with a predetermined degree of opening of the accelerator and if
the degree of opening .theta.AP of the accelerator is not higher
than the predetermined degree of opening of the accelerator, it is
determined that the degree to which the main driven wheels Wf, Wf
are slipping is small, and in Step S29 the maximum output of the
electric motor M is set at the middle level `2` (8 kW) in order to
eliminate the slip of the main driven wheels Wf, Wf. If the degree
of opening .theta.AP of the accelerator exceeds the predetermined
degree of opening of the accelerator in Step S28 it is determined
that the degree to which the main driven wheels Wf, Wf are
slipping, is large, and the maximum output of the electric motor M
is set at the highest level `3` (12 kW) in Step S30 in order to
promptly eliminate the slip of the main driven wheels Wf, Wf.
[0037] As hereinbefore described, when the maximum output of the
electric motor M for driving the auxiliary driven wheels Wr, Wr is
determined using the flow chart shown in FIG. 5, the routine moves
on to the flow chart shown in FIG. 6.
[0038] First of all, in Step S31 if the electric motor M was in
action during the previous cycle, the routine moves on to Step S32
and in Step S32 the speed ratio e of the torque converter C which
is detected by the torque converter speed ratio detecting means Sa,
is compared with a predetermined first threshold of 0.8. If the
speed ratio e is 0.8 or more it is determined that the efficiency
.eta. of the torque converter C is in a high region of 85% or more,
and in Step S33 the operation of the electric motor M is stopped,
as to suspend the assistance from the electric motor M. On the
other hand, in Step S31 if the electric motor M was suspended, in
Step S34 the speed ratio e of the torque converter C is compared
with a predetermined second threshold of 0.75. If the speed ratio e
is 0.75 or below, it is determined that the efficiency .eta. of the
torque converter C is in a low region of less than 85%, and it is
determined that it is necessary to assist the output of the engine
E by driving the auxiliary driven wheels Wr, Wr, and in Step S35
the electric motor M is operated to assist the engine E by means of
the electric motor M.
[0039] Since a hysteresis is thus introduced so that the assistance
from the electric motor M is suspended when the speed ratio e of
the torque converter C becomes 0.8 or more and the assistance from
the electric motor M is started when the speed ratio becomes 0.75
or less, it is possible to prevent frequent switch-over between
driving and suspending the drive of the electric motor M.
[0040] In the subsequent Step S36 if the electric motor is
operating and moreover in Step S37 if the maximum output of the
electric motor M exceeds the required output, in Step S38 the
output of the electric motor M is reduced to the required output
and the output of the engine E is made zero so the required output
is met by means of the output of the electric motor M alone. On the
other hand, in the Step S37 if the maximum output of the electric
motor M is not higher than the required output, in Step S39 the
output of the electric motor M is set at its maximum output and the
shortfall is provided from the output of the engine E. In the Step
S36 if the electric motor M is suspended in Step S40, the output of
the engine E is increased step by step in accordance with the
decrease in the output of the electric motor M so that the output
of the engine E coincides with the required output when the output
of the electric motor M becomes zero.
[0041] In addition, since the load applied to the engine E
increases while the vehicle is ascending, in Step S34 of the flow
chart shown in FIG. 6 the speed ratio e of the torque converter C
becomes 0.75 or less or the main driven wheels Wf, Wf slip and, as
a result, the electric motor M is operated in Step S35 and the
output of the engine E can be assisted.
[0042] As hereinbefore described, since the output of the engine E
for driving the main driven wheels Wf, Wf is reduced and the output
of the electric motor M for driving the auxiliary driven wheels Wr,
Wr is increased in the region in which the speed ratio e of the
torque converter C is low and the percentage of torque
amplification is high when the vehicle is starting, the driving
force is distributed among the front right, front left, rear right
and rear left wheels to suppress the slip of the main driven wheels
Wf, Wf and the response of the vehicle to the operation of the
accelerator can be improved by driving the auxiliary driven wheels
Wr, Wr by means of the electric motor M which does not have the
time delay that is an intrinsic characteristic of a fluid
transmission.
[0043] Although the output of the engine E is made zero in Step S38
of the flow chart shown in FIG. 6, it is desirable for the main
driven wheels Wf, Wf to have a some degree of output on roads
having a low coefficient of friction. Therefore, it is possible to
set the output of the engine E so as to be about 0.3 times the
required output instead of zero in Step S38.
[0044] As hereinbefore described, since the output generated by the
engine and the output generated by the electric motor are
distributed according to the speed ratio of the torque converter,
by reducing the output of the engine for driving the main driven
wheels and increasing the output of the electric motor for driving
the auxiliary driven wheels in the region in which the speed ratio
of the torque converter is low and the torque amplification
efficiency is high when the vehicle is starting, the driving force
can be distributed among the four wheels to suppress the slip of
the main driven wheels and improve the response of the vehicle to
the operation of the accelerator. Above all, by assisting the
output of the engine by means of the output of the electric motor
to compensate for the reduction in the torque converter efficiency
.eta. in the region in which the speed ratio is low, it can be
anticipated that the effect will be to reduce the fuel
consumption.
[0045] Since the speed ratio at which the drive of the electric
motor is suspended, is made different from the speed ratio at which
the drive of the electric motor is started, it is possible to
prevent frequent switch-over between driving and suspending the
drive of the electric motor when the speed ratio changes
slightly.
[0046] Further, since the maximum output of the electric motor is
changed according to the state of slip of the main driven wheels,
it is possible to effectively suppress the slip of the main driven
wheels on a road surface having a low coefficient of friction when
the vehicle is starting, etc. thus enhancing the ground covering
properties.
[0047] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. The presently disclosed embodiments are
therefore to be considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims, rather than the foregoing description, and all
changes which come within the meaning and range of equivalency of
the claims are, therefore, to be embraced therein.
* * * * *