U.S. patent application number 09/849256 was filed with the patent office on 2001-11-22 for shift control system for continuously variable transmission.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Inoue, Daisuke, Kondo, Hiroki, Kono, Katsumi, Kubota, Hirofumi, Mashiki, Zenichiro, Matsuo, Kenji, Mitani, Shinichi, Takagi, Isao, Tamura, Tadashi, Tanaka, Hiroya, Taniguchi, Hiroji, Yamamoto, Yoshiaki, Yasue, Hideki.
Application Number | 20010044358 09/849256 |
Document ID | / |
Family ID | 18654995 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010044358 |
Kind Code |
A1 |
Taniguchi, Hiroji ; et
al. |
November 22, 2001 |
Shift control system for continuously variable transmission
Abstract
A speed change control system for a continuously variable
transmission, for controlling a gear ratio by deciding an abrupt
acceleration demand of a driver, to effect an abrupt speed change
when it is decided that the driver demands an abrupt acceleration.
The speed change control system comprises: a drive state decider
for deciding that the vehicle has changed from a driven state to a
drive state, when said abrupt acceleration is demanded at the
driven state; and a speed change controller for controlling said
continuously variable transmission to effect said abrupt speed
change, after said drive state decider decides that the vehicle has
changed from the driven state to the drive state.
Inventors: |
Taniguchi, Hiroji;
(Okazaki-shi, JP) ; Kono, Katsumi; (Toyota-shi,
JP) ; Matsuo, Kenji; (Toyota-shi, JP) ; Yasue,
Hideki; (Toyota-shi, JP) ; Tamura, Tadashi;
(Nishikamo-gun, JP) ; Inoue, Daisuke; (Toyota-shi,
JP) ; Yamamoto, Yoshiaki; (Toyota-shi, JP) ;
Kondo, Hiroki; (Toyota-shi, JP) ; Takagi, Isao;
(Okazaki-shi, JP) ; Mashiki, Zenichiro;
(Nisshin-shi, JP) ; Kubota, Hirofumi;
(Mishima-shi, JP) ; Tanaka, Hiroya;
(Nishikamo-gun, JP) ; Mitani, Shinichi;
(Toyota-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
18654995 |
Appl. No.: |
09/849256 |
Filed: |
May 7, 2001 |
Current U.S.
Class: |
477/44 |
Current CPC
Class: |
F16H 2061/6611 20130101;
F16H 61/66254 20130101; F16H 61/6648 20130101 |
Class at
Publication: |
477/44 |
International
Class: |
F16H 059/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2000 |
JP |
2000-149084 |
Claims
What is claimed is:
1. A speed change control system for a continuously variable
transmission, for controlling a gear ratio to effect an abrupt
speed change when it is decided that a driver demands an abrupt
acceleration, comprising: drive state deciding means for deciding
that the vehicle has changed from a driven state to a drive state,
in response to the demand of said abrupt acceleration when the
vehicle is in the driven state; and speed change control means for
controlling said continuously variable transmission to effect said
abrupt speed change, after said drive state deciding means decides
that the vehicle has changed from the driven state to the drive
state.
2. A speed change control system according to claim 1, wherein said
speed change control means includes means for controlling the
continuously variable transmission to interrupt a speed change for
a time period from the decision of said abrupt acceleration demand
to the change of the vehicle to the drive state, when said abrupt
acceleration is demanded at the driven state of the vehicle.
3. A speed change control system according to claim 1, wherein said
speed change control means includes means for controlling the
continuously variable transmission to perform the abrupt speed
change when said abrupt acceleration demand is decided, when said
abrupt acceleration is demanded at the drive state of the
vehicle.
4. A speed change control system according to claim 1, wherein said
speed change control means includes means for controlling the gear
ratio of the continuously variable transmission so that an input
speed may be a target input speed set on the basis of a running
state of the vehicle, and for making an increase amount of the
target input speed larger than an increase amount at a speed change
other than the abrupt speed change when the abrupt speed change is
to be performed.
5. A speed change control system according to claim 3, wherein said
speed change control means includes means for controlling the gear
ratio of the continuously variable transmission so that an input
speed may be a target input speed set on the basis of a running
state of the vehicle, and for making an increase amount of the
target input speed larger than an increase amount at a speed change
other than the abrupt speed change when the abrupt speed change is
to be performed.
6. A speed change control system according to claim 1, further
comprising: output control means for executing a rounding control
to relax an increase of an output of a prime mover mounted on the
vehicle, when the abrupt acceleration is demanded.
7. A speed change control system according to claim 1, wherein said
speed change control means includes means for controlling the
continuously variable transmission to lower a speed changing rate
to a value as low as zero for a time period from the decision of
said abrupt acceleration demand to the change of the vehicle to the
drive state, when said abrupt acceleration is demanded at the
driven state of the vehicle.
8. A speed change control system according to claim 1, further
comprising: means for deciding that the abrupt acceleration is
demanded, on the basis of a changing rate of an accelerator
depression.
9. A speed change control system according to claim 1, wherein said
drive state deciding means includes means for deciding that the
vehicle has changed from the driven state to the drive state, on
the basis of a lapse time period from an instant when a prime mover
mounted on the vehicle changes from an idling state to a non-idling
state.
10. A speed change control system according to claim 1, wherein
said drive state deciding means includes: means for estimating a
driving force of the vehicle; and means for deciding that the
vehicle has changed to the drive state, when the estimated driving
force is higher than a road load.
11. A speed change control system for a continuously variable
transmission, for controlling a gear ratio to effect an abrupt
speed change when it is decided that a driver demands an abrupt
acceleration, comprising: a controller for deciding that the
vehicle has changed from a driven state to a drive state in
response to the demand of said abrupt acceleration when the vehicle
is in the driven state; and for controlling said continuously
variable transmission to effect said abrupt speed change after said
drive state deciding means decides that the vehicle has changed
from the driven state to the drive state.
12. A speed change control system according to claim 11, wherein
said controller includes a judging device for judging that the
vehicle has changed from a driven state to a drive state in
response to the demand of said abrupt acceleration when the vehicle
is in the driven state; and a shift controller for controlling said
continuously variable transmission to effect said abrupt speed
change after said judging device judges that the vehicle has
changed from the driven state to the drive state.
13. A speed change control system according to claim 12, wherein
said shift controller includes a device for controlling the
continuously variable transmission to interrupt a speed change for
a time period from the judge of said abrupt acceleration demand to
the change of the vehicle to the drive state, when said abrupt
acceleration is demanded at the driven state of the vehicle.
14. A speed change control system according to claim 12, wherein
said shift controller includes a device for controlling the
continuously variable transmission to perform the abrupt speed
change when said abrupt acceleration demand is judged, when said
abrupt acceleration is demanded at the drive state of the
vehicle.
15. A speed change control system according to claim 12, wherein
said shift controller includes a device for controlling the gear
ratio of the continuously variable transmission so that an input
speed may be a target input speed set on the basis of a running
state of the vehicle, and for making an increase amount of the
target input speed larger than an increase amount at a speed change
other than the abrupt speed change when the abrupt speed change is
to be performed.
16. A speed change control system according to claim 14, wherein
said shift controller includes a device for controlling the gear
ratio of the continuously variable transmission so that an input
speed may be a target input speed set on the basis of a running
state of the vehicle, and for making an increase amount of the
target input speed larger than an increase amount at a speed change
other than the abrupt speed change when the abrupt speed change is
to be performed.
17. A speed change control system according to claim 12, further
comprising: output controller for executing a rounding control to
relax an increase of an output of a prime mover mounted on the
vehicle, when the abrupt acceleration is demanded.
18. A speed change control system according to claim 12, wherein
said shift controller includes a device for controlling the
continuously variable transmission to lower a speed changing rate
to a value as low as zero for a time period from the decision of
said abrupt acceleration demand to the change of the vehicle to the
drive state, when said abrupt acceleration is demanded at the
driven state of the vehicle.
19. A speed change control system according to claim 12, further
comprising: a device for deciding that the abrupt acceleration is
demanded, on the basis of a changing rate of an accelerator
depression.
20. A speed change control system according to claim 12, wherein
said judging device includes a device for judging that the vehicle
has changed from the driven state to the drive state, on the basis
of a lapse time period from an instant when a prime mover mounted
on the vehicle changes from an idling state to a non-idling
state.
21. A speed change control system according to claim 12, wherein
said judging device includes: a device for estimating a driving
force of the vehicle; and deciding device for deciding that the
vehicle has changed to the drive state, when the estimated driving
force is higher than a road load.
22. A speed change control method for a continuously variable
transmission, for controlling a gear ratio to effect an abrupt
speed change when it is decided that a driver demands an abrupt
acceleration, comprising: a step for judging that the vehicle has
changed from a driven state to a drive state, in response to the
demand of said abrupt acceleration when the vehicle is in the
driven state; and a step for controlling said continuously variable
transmission to effect said abrupt speed change, after it is judged
that the vehicle has changed from the driven state to the drive
state.
23. A speed change control method according to claim 22, wherein
said step for controlling said continuously variable transmission
includes a step for controlling the continuously variable
transmission to interrupt a speed change for a time period from the
judge of said abrupt acceleration demand to the change of the
vehicle to the drive state, when said abrupt acceleration is
demanded at the driven state of the vehicle.
24. A speed change control method according to claim 22, wherein
said step for controlling said continuously variable transmission
includes a step for controlling the continuously variable
transmission to perform the abrupt speed change when said abrupt
acceleration demand is decided, when said abrupt acceleration is
demanded at the drive state of the vehicle.
25. A speed change control method according to claim 22, wherein
said step for controlling said continuously variable transmission
includes a step for controlling the gear ratio of the continuously
variable transmission so that an input speed may be a target input
speed set on the basis of a running state of the vehicle, and for
making an increase amount of the target input speed larger than an
increase amount at a speed change other than the abrupt speed
change when the abrupt speed change is to be performed.
26. A speed change control system according to claim 24, wherein
said step for controlling said continuously variable transmission
includes a step for controlling the gear ratio of the continuously
variable transmission so that an input speed may be a target input
speed set on the basis of a running state of the vehicle, and for
making an increase amount of the target input speed larger than an
increase amount at a speed change other than the abrupt speed
change when the abrupt speed change is to be performed.
27. A speed change control method according to claim 22, further
comprising: a step for executing a rounding control to relax an
increase of an output of a prime mover mounted on the vehicle, when
the abrupt acceleration is demanded.
28. A speed change control method according to claim 22, wherein
said step for controlling said continuously variable transmission
includes a step for controlling the continuously variable
transmission to lower a speed changing rate to a value as low as
zero for a time period from the decision of said abrupt
acceleration demand to the change of the vehicle to the drive
state, when said abrupt acceleration is demanded at the driven
state of the vehicle.
29. A speed change control method according to claim 22, further
comprising: a step for judging that the abrupt acceleration is
demanded, on the basis of a changing rate of an accelerator
depression.
30. A speed change control method according to claim 22, wherein
said step for judging includes a step for judging that the vehicle
has changed from the driven state to the drive state, on the basis
of a lapse time period from an instant when a prime mover mounted
on the vehicle changes from an idling state to a non-idling
state.
31. A speed change control method according to claim 22, wherein
said step for judging includes: a step for estimating a driving
force of the vehicle; and a step for deciding that the vehicle has
changed to the drive state, when the estimated driving force is
higher than a road load.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a system for controlling a
gear ratio of a continuously variable transmission and, more
particularly, to a system for performing a speed change control
when a driver demands an abrupt acceleration.
[0003] 2. Related Art
[0004] The speed change control in the continuously variable
transmission is executed by determining a target input speed on the
basis of running conditions such as a demand for a driving force,
e.g., an accelerator opening (or depression), or the vehicle speed
or on the basis of a manual selection by the driver, and by
controlling the gear ratio so that the actual input speed may be
equal to the target input speed. For this speed change control, the
intended target input speed is finally achieved not by changing the
gear ratio so that the actual input speed may be instantly equal to
its target value, but by setting a transient target input speed
determined from the target input value, by feedback-controlling the
gear ratio of the continuously variable transmission so that the
actual input speed may be equal to the transient target input
speed, and by updating the transient target input speed
sequentially. As a result, the speed changing rate is determined on
how to set the transient target input speed. Therefore, the
ordinary speed change is executed by setting the transient target
input speed delayed by first-order time lag from the target input
speed so that it is executed at such a rate as to raise neither any
shock or the delay feel of the speed change.
[0005] With this setting of the speed changing rate at all times,
however, a demanded acceleration feel may not be obtained due to
the delay in the speed change when an abrupt acceleration is
demanded by depressing the accelerator pedal abruptly and deeply.
In order to eliminate this disadvantage, in the invention disclosed
in Japanese Patent Application Laid-Open No. 63-68426, a downshift
of a high speed changing rate is executed by changing the target
input speed of the continuously variable transmission stepwise on
the basis of the decision of an abrupt acceleration, if this abrupt
acceleration is manually effected by the driver in a vehicle having
the continuously variable transmission mounted thereon. When the
gear ratio of the continuously variable transmission is to be
feedback-controlled, more specifically, the amount of control is
increased the more for the larger deviation between the present
value and the target value so that the speed changing rate becomes
the higher. Therefore, the increase amount of the transient target
input speed is enlarged or changed stepwise so that the speed
changing rate is raised to improve the acceleration response to the
abrupt acceleration demand.
[0006] In the prior art, the abrupt speed change described above
for increasing the target input speed stepwise is executed when the
decision of the abrupt acceleration is held by the operation of the
drive for the abrupt acceleration, as effected by the abrupt and
deep depression of the accelerator pedal by the driver. Therefore,
a serious longitudinal vibration (or a surging) or a resulting
shock may occur when an abrupt speed change is executed in the
driven state where a decelerating manipulation is made by returning
the accelerator pedal to drive the engine forcibly by the running
inertial force.
[0007] When the abrupt acceleration is manipulated for the engine
in the driven state, more specifically, the output shaft torque
changes from the state of a negative torque to the state of a
positive torque so that the looseness of the drive line is reduced
to reverse the twist of the elastic line. As a result, there occurs
the so-called "longitudinal vibration (or the surging)" to cause
the pitching or rocking of the vehicle body in a back and forth
direction. In order to prevent this pitching or rocking, the
so-called "rounding control" for raising the engine torque gently
is executed for the abrupt acceleration in the driven state.
[0008] On the other hand, the gear ratio control of the
continuously variable transmission, accompanying the manipulation
for the abrupt acceleration, is performed by raising the transient
target input speed stepwise to raise the gear ratio abruptly. With
the gear ratio being thus controlled, the inertial force
accompanying the rise in the gear ratio acts as a negative torque
on the engine.
[0009] When the rounding control of the engine torque and the
abrupt speed change control of the continuously variable
transmission progress simultaneously as the decision of the abrupt
acceleration is held, these two controls interfere with each other
to delay the rise in the engine torque. As a result, the engine is
still in the driven state at the instant when the rounding control
of the engine torque is ended, so that the engine torque is
abruptly raised from that state. After all, even if the rounding
control is executed for raising the engine torque, the changing
rate (or the changing gradient) of the torque is raised at the
instant when the vehicle changes from the driven state to the drive
state, that is, when the output shaft torque of the engine is
switched from the negative torque to the positive torque, thereby
to cause the serious surging and the resulting shock.
SUMMARY OF THE INVENTION
[0010] A main object of the invention is to provide a speed change
control system which can prevent the surging or the shock even if
an abrupt acceleration is manipulated when a prime mover is in the
driven state, without deteriorating the acceleration
responsibility.
[0011] Therefore, the speed change control system of the invention
is characterized in that the abrupt speed change control of the
continuously variable transmission is executed after the vehicle
was changed from the driven state to the drive state. According to
an aspect of the invention, more specifically, there is provided a
controller for effecting an abrupt speed change by judging an
abrupt acceleration demand of the driver, when it is judged that
the driver demands the abrupt acceleration. Moreover, the
controller comprises: drive state deciding means or a judging
device for judging, when said abrupt acceleration demand is one
from the driven state of the vehicle, that the vehicle has changed
from the driven state to the drive state; and speed change control
means or a shift controller for controlling said continuously
variable transmission to effect said abrupt speed change, after it
is judged that the vehicle has changed from the driven state to the
drive state.
[0012] In this invention, therefore, if the vehicle is in the
driven state when the abrupt acceleration is demanded, it is
decided by the drive state deciding means that the vehicle has
changed from the driven state to the drive state. If it is decided
that the vehicle has changed from the driven state to the drive
state, moreover, the abrupt speed change control is executed in the
continuously variable transmission. Even if the rounding control of
the output torque of the prime mover is executed in response to the
abrupt acceleration demand, therefore, the interference between the
two controls and the resulting delay in the change to the drive
state are avoided because the abrupt speed change control of the
continuously variable transmission is not executed yet at that
instant of execution. Moreover, the abrupt speed change control of
the continuously variable transmission is executed after the change
of the vehicle into the drive state so that the changing rate (or
the changing gradient) of the torque at the switching time from the
driven state to the drive state is relaxed to prevent or suppress
the surging and the resulting shock.
[0013] Said speed change control means or the shift controller in
the invention may be constructed to control the continuously
variable transmission to interrupt the speed change in the
continuously variable transmission, if said abrupt acceleration
demand is one from the driven state of the vehicle, for the time
period from the decision of said abrupt acceleration demand to the
change of the vehicle to the drive state.
[0014] With this construction, the speed change control of the
continuously variable transmission is not executed after the
decision of the abrupt acceleration demand was held and before the
change from the driven state to the drive state. In this time
period, therefore, it is possible to execute the control the prime
mover on the basis of the abrupt acceleration demand, such as the
rounding control of the output torque solely. As a result, the
prime mover can be controlled easily and precisely, and the timing
for starting the abrupt speed change control in the continuously
variable transmission can be properly set.
[0015] Moreover, said speed change control means or the shift
controller in the invention may be constructed to control the
continuously variable transmission to perform the abrupt speed
change in the continuously variable transmission, if said abrupt
acceleration demand is one from the drive state of the vehicle,
when said abrupt acceleration demand is decided.
[0016] With this construction, the abrupt speed change control of
the continuously variable transmission is executed instantly in
response to the abrupt acceleration demand, if any in the drive
state, so that the shock is not deteriorated to improve the
acceleration responsibility.
[0017] Moreover, said speed change control means or the shift
controller in the invention may be constructed to control the gear
ratio of the continuously variable transmission so that an input
speed may be a target input speed set on the basis of the running
state of the vehicle, and to make an increase amount of the target
input speed larger than that at a speed change other than the
abrupt speed change when the abrupt speed change is to be
performed.
[0018] With this construction, in the case of an abrupt speed
change, the target input speed is drastically raised to raise the
speed changing rate so that a speed change according to a demand
can be made.
[0019] The above and further objects and novel features of the
invention will more fully appear from the following detailed
description when the same is read with reference to the
accompanying drawings. It is to be expressly understood, however,
that the drawings are for the purpose of illustrations only and are
not intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a flow chart showing an example of a control to be
executed by a control system according to the invention;
[0021] FIG. 2 is a time chart illustrating one example of a change
in the output shaft torque of the case in which the control of FIG.
1 is executed;
[0022] FIG. 3 is a flow chart for explaining a control example for
deciding a change from a driven state to a drive state for
executing an abrupt speed change;
[0023] FIG. 4 is a block diagram schematically showing a drive
system of a vehicle, to which the invention is directed, and a
control system for the drive system; and
[0024] FIG. 5 is a diagram showing one example of a continuously
variable transmission of the drive system schematically.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The invention will be specifically described in connection
with its embodiments. First of all, here will be described one
example of a power transmission line of a vehicle, to which the
invention is directed. In FIG. 4, a prime mover 1 is connected to a
transmission mechanism 2, of which the output shaft 3 is connected
through a differential 4 to right and left drive wheels 5. Here,
the prime mover 1 includes a variety of prime movers to be employed
in the vehicle, such as an internal combustion engine, e.g., a
gasoline engine or Diesel engine, an electric motor or a unit
combining those internal combustion engine and electric motor. In
the following description, the prime mover 1 is exemplified either
by the so-called "direct injection gasoline engine" which can
perform a homogeneous combustion or a stratified combustion by
directly injecting fuel in a cylinder and controlling its injecting
rate and a timing, or by the gasoline engine which is equipped with
an electronic throttle valve capable of controlling the throttle
opening electrically freely.
[0026] This engine 1 is so constructed that it can be electrically
controlled, and is equipped with an electronic control unit (E-ECU)
6 constructed mainly of a microcomputer for the electric control.
This electronic control unit 6 is constructed to control at least
the output of the engine 1, and this control includes the rounding
control for relaxing the rise of the engine torque when demanded
drive quantity is high. On the other hand, the electronic control
unit 6 is fed with an output shaft speed (or an engine speed) NE
and the demanded drive quantity such as an accelerator pedal
depression or opening PA as the data for their controls.
[0027] These demanded drive quantities are, in short, signals for
increasing/decreasing the output of the engine 1, and can adopt
either a manipulation signal of an accelerating/decelerating
manipulation unit 7 such as an accelerator pedal to be manipulated
by the driver, or a signal generated by processing the manipulation
electrically. In addition, there is adopted a demanded drive
quantity signal which comes from the (not-shown) cruise control
system for keeping the vehicle speed at a set value.
[0028] On the other hand, the transmission mechanism 2 is
constructed to include a fluid coupling mechanism 8, a
forward/backward switching mechanism 9 and a continuously variable
transmission (CVT) 10. The fluid coupling mechanism 8 is, in short,
a device which is constructed to transmit the torque through a
fluid or oil between a member on the input side and a member on the
output side. This device is exemplified by a torque converter which
is adopted in the ordinary vehicle. On the other hand, this fluid
coupling mechanism 8 is provided with a lock-up clutch 11. This
lock-up clutch 11 is the clutch which is constructed to couple the
input side member and the output side member directly through
mechanical means such as the friction discs, and is equipped with a
damper 12 made of an elastic member such as a shock-absorbing coil
spring. When the fluid coupling mechanism 8 is provided for driving
the engine 1 continuously even on a stopped vehicle, an automatic
clutch to be automatically applied/released on the basis of the
state of the vehicle can be employed in place of the aforementioned
fluid coupling mechanism 8.
[0029] The fluid coupling mechanism 8 is connected at its input
member to the output member of the engine 1 and at its output
member to the input member of the forward/backward switching
mechanism 9. This forward/backward switching mechanism 9 is
constructed of a double-pinion type planetary gear mechanism, for
example, which is composed of (not shown): an input element of one
of a sun gear and a carrier; an output element of the other; brake
means for fixing a ring gear selectively; and clutch means for
connecting any two rotary elements of the three elements of the sun
gear, the carrier and the ring gear selectively to integrate the
entire planetary gear mechanism. In short, the forward/backward
switching mechanism 9 is constructed to set the forward state by
applying the clutch means and to set the backward state by applying
the brake means.
[0030] The continuously variable transmission 10, as shown in FIG.
4, is a mechanism capable of changing the ratio between the speed
of a member on its input side and the speed of a member on its
output side, i.e., a gear ratio steplessly (or continuously), and
can adopt the belt-type continuously variable transmission or the
toroidal-type (or traction-type) continuously variable
transmission. One example of the belt-type continuously variable
transmission 10 will be briefly described with reference to FIG. 5.
This mechanism 10 is constructed to include: a driving pulley (or
primary pulley) 20; a driven pulley (or secondary pulley) 21; and a
belt 22 made to run on those pulleys 20 and 21. These pulleys 20
and 21 are individually composed of: stationary sheaves 23 and 24;
movable sheaves 25 and 26 for moving toward and away from the
stationary sheaves 23 and 24; and hydraulic actuators 27 and 28 for
pushing the movable sheaves 25 and 26 toward the stationary sheaves
23 and 24.
[0031] The driving pulley 20 is mounted on an input shaft 29, and
the driven pulley 21 is mounted on an output shaft 30 arranged in
parallel with the input shaft 29. To the hydraulic actuator 28 in
the driven pulley 21, moreover, there is fed the oil pressure which
accords to the demanded drive quantity represented by the
accelerator depression PA so that the belt 22 is given the tension
necessary for transmitting the torque. To the hydraulic actuator 27
of the driving pulley 20, on the other hand, there is fed working
oil for establishing the gear ratio to equalize the speed of the
input shaft 29 to the target input value. In short, by changing the
widths of grooves (i.e., the gaps between the stationary sheaves 23
and 24 and the movable sheaves 25 and 26) in the individual pulleys
20 and 21, the winding radii of the belt 22 on the individual
pulleys 20 and 21 are changed to larger and smaller values to
execute the speed change. By feedback-controlling the quantity of
the working oil on the driving pulley 20 on the basis of the
deviation between the actual input speed and the target input
speed, more specifically, the speed change is executed so that the
changing rate is the higher for the larger deviation.
[0032] In the continuously variable transmission 10 shown in FIG.
5, therefore, a gear ratio on the lowest side (i.e., a maximum gear
ratio) .sub.ax is set when the winding radius of the belt 22 on the
driving pulley 20 is the minimum and when the winding radius of the
belt 22 on the driven pulley 21 is the maximum. On the contrary, a
gear ratio on the highest side (i.e., a minimum gear ratio) .sub.in
is set when the winding radius of the belt 22 on the driving pulley
20 is the maximum and when the winding radius of the belt 22 on the
driven pulley 21 is the minimum.
[0033] The controls of the individual states of the
application/release and the slipping half-application of the
lock-up clutch 11 in the transmission mechanism 2 and the controls
of the forward/backward switching actions of the mechanism 9 and
the gear ratio in the continuously variable transmission 10 are
basically made on the basis of the running state of the vehicle.
For these controls, there is provided an electronic control unit
(T-ECU) 13 which is constructed mainly of a microcomputer.
[0034] This electronic control unit 13 is connected in a data
communicating manner with the aforementioned electronic control
unit 6 for the engine, and is fed with control data including a
vehicle speed SPD, and the output speed No and the input speed NIN
of the transmission mechanism 2. With the electronic control unit
13, there is electrically connected a shift unit 14 for selecting
the individual states (or positions) for the transmission mechanism
2, which include: a stop state (or a parking position: P); a
backward state (or a reverse position: R); a neutral state (or a
neutral position: N); an automatic forward state (or a drive
position: D) in which a gear ratio is automatically set according
to running states of the vehicle to make an ordinary run; a state
of adopting the pumping loss of the engine 1 as a braking force (or
a brake position: B); and a state of inhibiting the setting of the
gear ratio on a higher speed side than a predetermined value (or a
SD position).
[0035] The gear ratio of the continuously variable transmission 10
thus far described is controlled by determining the target input
speed on the basis of the demanded drive quantity so that the
actual input speed may be equal to its target value. However, the
magnitude of the speed changing rate affects not only the magnitude
of the inertial force of the rotary members including the engine 1
but also the shift shock or the surging. In the ordinary speed
change, therefore, the gear ratio of the continuously variable
transmission 10 is controlled, for example, by setting a transient
target input speed of a first-order lag for the target input speed
so that the actual input speed may change following the change of
that transient target value. When a demand for abrupt acceleration
is made by depressing the accelerator pedal abruptly, on the other
hand, a control is executed to change the transient target input
speed stepwise, i.e., with a large increase amount so as to improve
the acceleration responsibility.
[0036] The control system according to the invention is constructed
to execute the abrupt speed change for changing the transient
target input speed stepwise, differently according to the
drive/driven states of the vehicle (or the engine 1). FIG. 1 is a
flow chart for explaining an example of the controls, in which the
routine is repeatedly executed at a predetermined short time
interval.
[0037] First of all, as shown in FIG. 1, there are read in (at Step
S1) the vehicle speed SPD, the actual input speed NIN and the
accelerator depression PA as the demanded drive quantity. Next, an
accelerator depression changing rate DPA is computed (at Step S2).
In other words, there is computed the changing rate of the
accelerator depression for a unit time period.
[0038] Then, it is decided (at Step S3) whether or not a flag
XTRNSFT is set at "1". This flag XTRNSFT is set to "1" when the
decision of the abrupt acceleration demand is made, and is
initially set at "0". Therefore, the answer of Step S3 is NO at the
time when the decision of the abrupt acceleration demand is not
made. When the answer of Step S3 is NO, it is decided (at Step S4)
whether or not the accelerator depression changing rate DPA
computed at Step S2 is higher than a reference changing rate . This
reference changing rate presents a reference for discriminating the
abrupt acceleration demand and a gentler acceleration and has a
predetermined value. Here, the reference changing rate may be a
fixed value or a value changing with other conditions such as the
vehicle speed.
[0039] The routine shown in FIG. 1 is provided for controlling the
transient speed change when the abrupt acceleration is demanded.
Therefore, this routine is ended without any control, in the
absence of the abrupt acceleration demand, that is, when the answer
of Step S4 is NO because the changing rate DPA of the accelerator
depression PA, if changed, is less than the reference changing rate
. When the answer of Step S4 is YES in the presence of the abrupt
acceleration demand, on the contrary, both the flag (i.e., the
abrupt acceleration demand flag) XTRNSFT indicating that the abrupt
acceleration has been demanded, and a flag (i.e., an abrupt speed
change flag) XSTEP indicating the execution of the abrupt speed
change control for changing the target input speed stepwise are
individually set to "1" (at Step S5).
[0040] On the other hand, the initial value NINTST of a target
input speed NINT is set (at Step S6) to the actual input speed NIN
at that setting instant. Therefore, the speed change control is
executed with reference to the actual input speed NIN at the
instant when the decision of the abrupt acceleration demand is
held. On the other hand, the target input speed NINT at this time
is sequentially set at the transient time of the speed change until
the target input speed determined according to the running state of
the vehicle such as the vehicle speed or the accelerator depression
is reached, and is a transient one for dictating the speed changing
rate, for example.
[0041] Next, it is decided (at Step S7) whether or not a lapse time
CTIDL from the instant when the idle contact is switched from ON to
OFF has exceeded a reference time period T0. This reference time
period T0 is equal to or longer than a time for which the rounding
control is made for relaxing the rise of the output shaft torque
and for preventing the surging. The reference time period T0 is set
to a value for the vehicle to change from the driven state to the
drive state, or a larger value than that, and is either set to a
predetermined fixed value or varied according to the running state
of the vehicle such as the vehicle speed.
[0042] If the lapse time period CTIDL has failed to reach the
reference time period T0, the answer of Step S7 is NO. Then, the
target input speed NINT is computed (at Step S8) by adding a
predetermined value STEP1 to the target input speed initial value
NINTST. This predetermined value STEP1 is a sum either for
inhibiting the initial speed change or for suppressing the speed
changing rate. In the former case, the predetermined value STEP1 is
set to "0". In the latter case, the predetermined value STEP1 is
set to such a small value that the inertial force by the downshift
in the continuously variable transmission 10 may not excessively
suppress the rise of the output shaft torque of the engine 1.
[0043] After the target input speed NINT was thus computed, it is
decided (at Step S9) whether or not the abrupt speed change (or the
stepwise speed change) according to the abrupt acceleration demand
has been ended. This decision is made upon whether or not the
actual input speed NIN approaches the target input value NINT so
close that their deviation is less than a predetermined value, by
increasing the target input speed NINT stepwise and by keeping the
value temporarily. When the predetermined value to be added to the
target input speed initial value NINTST is "0" or an approximate
small value STEP1, therefore, the abrupt speed change control is
continued. As a result, the answer of Step S9 is NO, and the
control leaves this routine.
[0044] If the routine of FIG. 1 is executed again in this state,
the abrupt acceleration demand flag XTRNSFT has already been set at
"1", and the answer of Step S3 is YES. As a result, the routine
advances to Step S10, at which it is decided whether or not the
abrupt speed change flag XSTEP is at "1". This abrupt speed change
flag XSTEP has also been set at "1" because the decision of the
abrupt acceleration demand is held. Therefore, the answer of Step
S10 is YES, and the routine advances to Step S7.
[0045] If this answer of Step S7 is NO because the lapse time
period CTIDL from the instant when the idle contact was switched
from ON to OFF has not reached the reference time period T0, the
routine advances to Step S8, at which the speed change is inhibited
or executed at a low rate. If the time period for finishing the
rounding control to prevent the surging has elapsed so that the
answer of Step S7 is YES, that is, if it is decided that the
vehicle has changed from the driven state to the drive state, the
routine advances not to Step S8 but to Step S11, at which the
target input speed NINT is computed by adding a predetermined value
STEP2 to the target input speed initial value NINTST. This
predetermined value STEP2 is one for setting the target input speed
to a higher value for raising the speed changing rate when the
continuously variable transmission 10 is to be feedback-controlled
to equalize the actual input speed to the target value. The value
STEP2 is set according to the target input speed which is
calculated on the basis of the running state of the vehicle or the
demanded drive quantity.
[0046] When the control for raising the gear ratio of the
continuously variable transmission 10 little by little while the
rounding control of the engine output is being made for preventing
the surging, that is, when the predetermined value STEP1 at Step S8
is set to a value larger than "0", the target input speed NINT may
be computed at Step S11 by adding the predetermined value STEP2 to
the target value NINT at the setting time.
[0047] When the target input speed NINT is thus increased stepwise,
the feedback deviation for controlling the gear ratio of the
continuously variable transmission 10 is enlarged to raise the
changing rate of the gear ratio, i.e., the speed changing rate.
[0048] Thus, for the time period or longer from the switching-OFF
of the idle contact to the end of the rounding control for
preventing the surging, the speed change is inhibited or executed
at a low rate. For this period, therefore, the negative torque
accompanying the speed change exerts no action on the engine 1, or
the rise of the output shaft torque is not obstructed. By the
rounding control, moreover, the output shaft torque is gently
raised so that the engine 1 is switched from the driven state to
the drive state. Therefore, this change from the driven state to
the drive state is gently done so that the surging is prevented or
suppressed. If the speed change in the continuously variable
transmission 10 is inhibited in that case, the output shaft torque
of the engine 1 can be controlled without any especial
consideration to the negative torque accompanying the speed change.
For this control, moreover, the constant or coefficient for the
control can be set to simplify the control and to facilitate the
design.
[0049] Thus, after the engine 1 was switched to the drive state,
the abrupt speed change in the continuously variable transmission
10, i.e., the speed change, in which the target input speed NINT is
stepwise increased, is executed to progress the speed change
abruptly. As a result, when the actual input speed NIN comes close
to the range of a predetermined value of the target input speed
NINT stepwise increased, the decision of the end of the stepwise
speed change is held to affirm the answer at Step S9. In this case,
the abrupt speed change flag XSTEP is reset to zero (at Step S12),
and a flag (or a speed changing rate fixing control flag) XKOTEI
indicating the execution of the speed changing rate fixing control
is set to "1" (at Step S13). This routine is then ended.
[0050] In this speed changing rate fixing control, the actual input
speed is increased at a constant changing rate when it is equalized
to the engine speed (i.e., the target input speed) for establishing
at an optimum fuel consumption both the demanded drive quantity and
the demand output, as computed on the basis of the running state of
the vehicle such as the accelerator depression or the vehicle
speed.
[0051] When the routine of FIG. 1 is thus restarted, the answer of
Step S3 is YES, but the answer of Step S10 is NO. Therefore, the
routine advances to Step S14, at which it is decided whether or not
the speed changing rate fixing control flag XKOTEI is at "1". When
the aforementioned stepwise speed change was ended so that the
speed change for fixing the speed changing rate at a constant value
is started, the answer of Step S14 is YES because the speed
changing rate fixing control flag XKOTEI is set at "1" at Step
S13.
[0052] And, the target input speed NINT is increased by a constant
value (at Step S15). Namely, the following computation is
executed:
NINT(i)=NINT(i-1)+DNINHLD.
[0053] Next, it is decided (at Step S16) whether or not the speed
changing rate fixing control is ended. If this control is not
ended, this routine is ended to continue the foregoing control. If
the speed changing rate fixing control is ended so that the answer
of Step S16 is YES, on the contrary, the speed changing rate fixing
control flag XKOTEI and the abrupt acceleration demand flag XTRNSFT
are individually set to zero (at Step S17 and Step S18). Then, this
routine is ended. Instantly as the answer of Step S14 is NO, this
routine is ended because the speed changing rate fixing control has
already been ended.
[0054] At the end of this speed changing rate fixing control, the
actual input speed NIN is equal within a predetermined deviation
range to the target input value which is determined by the
vehicular running state such as the vehicle speed or the
accelerator depression, so that the end can be decided on the basis
of the difference between the target input speed and the actual
input speed NIN. If this decision is held, moreover, the speed
change on the basis of the abrupt acceleration demand is ended so
that the individual flags of Steps S17 and S18 are reset to
zero.
[0055] The variation of the output shaft torque of the case in
which the aforementioned control is executed is illustrated in FIG.
2. When the accelerator pedal is deeply depressed at time t0 midway
of the case in which the vehicle is running in the driven state
with the zero accelerator depression, the lapse time CTIDL from
time to is counted. If the decision of the abrupt acceleration
demand is held at time t1 because the accelerator depression
changing rate DPA exceeds the reference changing rate , moreover,
the degree of opening of an throttle valve (e.g., an electronic
throttle valve) is gradually increased, and the abrupt acceleration
demand flag XTRNSFT and the abrupt speed change flag XSTEP are
individually set to "1".
[0056] The throttle opening is so controlled that it may not be
instantly set to the opening based on the acceleration demand but
the output shaft torque may be varied at a relatively gentle
gradient by the so-called "rounding control". This variation is
illustrated by a solid line in FIG. 2.
[0057] In the case of an abrupt acceleration demand from the driven
state, that is, in case the lapse time CTIDL from the time t0 of
switching the idle contact from ON to OFF has not reached the
reference time period T0, on the other hand, the control of the
gear ratio of the continuously variable transmission 10 is executed
by employing the summed speed of the predetermined STEP1 and the
actual input speed NIN at the time t0 when the decision of the
abrupt acceleration demand is held, as the target input speed NINT.
The predetermined value STEP1 is zero or as small as zero so that
the speed change in the continuously variable transmission 10 is
inhibited or executed at a low rate. The variation of the target
input speed NINT is illustrated by a solid line in FIG. 2.
[0058] As a result, the inertial force, as caused by the speed
change in the continuously variable transmission 10, does not act
as a negative torque on the output shaft of the engine 1 so that
the output shaft torque rises with a relatively low gradient
according to the rounding control. When the rounding control is
ended after the change from the driven state to the drive state,
moreover, the throttle opening is increased in response to the
abrupt acceleration demand so that the output shaft torque rises
accordingly abruptly.
[0059] By thus substantially inhibiting the speed change in the
continuously variable transmission 10 or keeping an approximate
state, the output shaft torque varies from a negative torque to a
positive torque during the rounding control thereby to reduce the
torque changing rate at the changing time from the driven state to
the drive state. As a result, the surging or the resulting shock is
prevented or relaxed even if the power transmission line for
transmitting the power to the wheels 5 loses its play or looseness
or if the elastic line reverses its twist.
[0060] When the aforementioned lapse time CTIDL reaches the
reference time period T0, moreover, the stepwise speed change of
the gear ratio of the continuously variable transmission 10 is
started at time t2. Specifically, the target input speed NINT is
set to the sum of the actual input speed NINTST at the time when
the decision of the abrupt acceleration demand is held and the
predetermined value STEP2, so that it is stepwise increased. As a
result, the feedback deviation for controlling the gear ratio
increases so that the speed change is executed at a high rate.
Accordingly, the driving force of the vehicle rises to improve the
acceleration responsibility.
[0061] As an abrupt speed change at a high changing rate is thus
executed so that the actual input speed NIN approaches the stepwise
varied target value NINT, the end of the stepwise speed change is
decided. At time t3, the abrupt speed change flag XSTEP is reset to
zero, and the speed changing rate fixing control flag XKOTEI is set
to "1". After this, there is executed the speed changing rate
fixing control for increasing the target input speed NINT by
predetermined values. The speed changing rate at this time is lower
than that at the time of the aforementioned stepwise speed
change.
[0062] If the actual input speed NIN is substantially equalized, as
a result of executing the speed changing rate fixing control, to
the target input value which is determined on the basis of the
running state of the vehicle, the end of the speed changing rate
fixing control is decided. At time t4, both the abrupt acceleration
demand flag XTRNSFT and the speed changing rate fixing control flag
XKOTEI are reset to zero.
[0063] When the abrupt speed change in the continuously variable
transmission is executed simultaneously with the holding of the
decision of the abrupt acceleration demand, on the contrary, the
output shaft torque varies, as indicated by a broken line in FIG.
2. When the abrupt speed change in the continuously variable
transmission is executed simultaneously with the rounding control
of the output shaft torque, more specifically, a negative torque
accompanying the speed change acts on the output shaft of the
engine so that the state does not change from the driven to drive
states in the rounding control. At the end of the abrupt speed
change in the continuously variable transmission, moreover, the
negative torque having acted on the output shaft of the engine is
lightened or released so that the output shaft torque of the engine
abruptly rises in response to the abrupt acceleration demand. As a
result, the varying gradient of the torque at the changing time
from the driven state to the drive state rises to cause the surging
and the resulting shock.
[0064] If an abrupt acceleration demand is made in the
aforementioned control when the vehicle is in the drive state, that
is, if the lapse time CTIDL reaches the reference time period T0
when the decision of the abrupt acceleration demand is held, the
answer of Step S7 is affirmative, and the routine advances to Step
S11, at which the stepwise speed change is instantly started. At
this time, therefore, the acceleration responsibility is
improved.
[0065] Here in the specific embodiment thus far described, it is
decided, on the basis of the reach to the reference time period T0
by the lapse time CTIDL from the switched time of the idle contact
from ON to OFF, that the vehicle has changed from the driven state
to the drive state. In order to improve the acceleration
responsibility, however, it is desired to decide the change to the
drive state as early as possible. In order to satisfy such desire,
the driving force may be estimated to decide on the basis of the
estimated driving force that the vehicle has changed from the
driven state to the drive state.
[0066] One example is shown in FIG. 3. FIG. 3 is a flow chart
showing a series of operations to be done in place of that of Step
S7 of FIG. 1. In other words, the operations of this flow chart is
executed after the operation of Step S6 or Step S10 of FIG. 1.
First of all, from the throttle opening or the like set by the
aforementioned rounding control, the predicted load ratio (i.e.,
the ratio of the load to the whole load) of the engine 1 is
computed, and the engine torque is estimated (at Step S31) from the
map of the predicted load ratio computed and the engine speed.
Next, an estimated driving force is computed (at Step S32) on the
basis of the estimated engine torque, the gear ratio, the reduction
ratio (or the differential ratio) of the differential 4, and the
effective radius of tires. Next, it is decided (at Step S33)
whether or not the estimated driving force is higher than the sum
of the road load and a predetermined value.
[0067] If the rounding control is made for preventing the shock in
the course of the control to raise the output shaft torque on the
basis of the abrupt acceleration demand, it takes a considerable
time period to change into the drive state in the case of an
acceleration from the driven state, thereby to establish a state in
which the estimated driving force is at or lower the road load. If
the estimated driving force exceeds the road load, moreover, the
vehicle is switched to the drive state.
[0068] If the answer of Step S33 is negative, therefore, the
estimated driving force is still low so that the vehicle is in the
driven state. Therefore, the routine advances to Step S8 of FIG. 1,
at which the speed change is inhibited or executed (slowly) at a
low rate. If the answer of Step S33 is affirmative, on the
contrary, the vehicle has been switched to the drive state.
Therefore, the routine advances to Step S11 of FIG. 1 thereby to
execute the abrupt speed change for increasing the target input
speed NINT stepwise.
[0069] By this control, too, the abrupt speed change is executed
instantly as the vehicle is changed from the driven state to the
drive state, so that the acceleration responsibility is
improved.
[0070] Here will be briefly described the relations between the
specific embodiment thus far described and the invention. The means
for executing the operation of Step S7 shown in FIG. 1 and the
operation of Step S33 of FIG. 3 corresponds to drive state deciding
means of the invention, and the means for executing the operations
of Steps S8 and S11 of FIG. 1 corresponds to speed change control
means.
[0071] Here, in the specific embodiment described above, the abrupt
speed change is executed by increasing the target input speed
stepwise. In short, however, the abrupt speed change in this
embodiment may be raised in its changing rate as high as possible,
and the means therefor should not be limited to the means for
raising the target input speed stepwise.
[0072] On the other hand, the decision on the change from the
driven state to the drive state should not be limited to the means
exemplified in the foregoing specific embodiment but can be made by
suitable means, if necessary. For the operation to compute the
target driving force from the accelerator depression or the like so
that the engine torque may be controlled to achieve the target
driving force computed, the means can be embodied as one for
deciding that the vehicle has been changed from the driven state to
the drive state, by measuring the lapse time period after the
target drive force exceeds the sum of the road load and a
predetermined value and on the basis of the arrival of the measured
lapse time period at the reference time period.
[0073] Here will be synthetically described the advantages to be
obtained from the invention. According to the invention, if the
vehicle is in the driven state when the abrupt acceleration demand
is made, it is decided that the vehicle has been changed from the
driven state to the drive state. After this decision is held, the
abrupt speed change control is executed in the continuously
variable transmission. Even if the rounding control of the output
torque of the prime mover is executed in response to the abrupt
acceleration demand, therefore, the abrupt speed change control of
the continuously variable transmission is not executed at the time.
It is, therefore, possible to avoid the interference between the
controls of the two or the time lag, as caused by the interference,
in the change to the drive state. On the other hand, the abrupt
speed change control of the continuously variable transmission is
executed after the vehicle was changed to the drive state, so that
the changing rate (or the changing gradient) of the torque at the
changing instant from the driven state to the drive state can be
relaxed to prevent or suppress the surging and the resulting
shock.
[0074] According to the invention, on the other hand, the speed
change control of the continuously variable transmission is not
executed, until the change from the driven state to the drive state
after the decision of the abrupt acceleration demand is held. For
this time period, therefore, it is possible to execute the control
of the prime mover such as the rounding control of the output
torque solely on the basis of the abrupt acceleration demand.
Therefore, the prime mover can be controlled easily and precisely
to set more proper timing of the start of the abrupt speed change
control in the continuously variable transmission.
[0075] According to the invention, moreover, the abrupt speed
change control of the continuously variable transmission can be
executed instantly in response to the abrupt acceleration demand,
if from the drive state, so that the acceleration responsibility
can be improved without deteriorating the shock.
[0076] According to the invention, moreover, the target input speed
can be drastically increased for the abrupt speed change so that
the speed changing rate can be raised to perform a speed change in
response to the demand.
* * * * *