U.S. patent number RE37,598 [Application Number 09/517,704] was granted by the patent office on 2002-03-19 for continuously variable transmission control apparatus.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Tadayuki Akiyama, Takayoshi Nabeta, Shojiro Sato, Nobusuke Toukura.
United States Patent |
RE37,598 |
Toukura , et al. |
March 19, 2002 |
Continuously variable transmission control apparatus
Abstract
An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle. The transmission
is operable at a variable speed ratio for transmitting a drive from
its input shaft to its output shaft. A target value for the speed
of rotation of the input shaft of the transmission is calculated
based on the sensed vehicle operating conditions including vehicle
acceleration. A correction factor per predetermined unit time is
calculated based on the sensed vehicle acceleration when the sensed
vehicle acceleration exceeds a threshold value with the accelerator
pedal released. The correction factor is added to the target input
shaft speed value to correct the target input shaft speed value in
an increasing direction at intervals of the predetermined unit
time. The threshold value is decreased as the vehicle speed
increases. The speed ratio is controlled to bring the input shaft
speed into coincidence with the corrected target value.
Inventors: |
Toukura; Nobusuke (Yokosuka,
JP), Sato; Shojiro (Yokohama, JP), Nabeta;
Takayoshi (Yokosuka, JP), Akiyama; Tadayuki
(Fuji, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
27335271 |
Appl.
No.: |
09/517,704 |
Filed: |
March 2, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
727086 |
Oct 8, 1996 |
05722500 |
Mar 3, 1998 |
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Foreign Application Priority Data
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Oct 12, 1995 [JP] |
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7-264087 |
Oct 12, 1995 [JP] |
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7-264088 |
Oct 16, 1995 [JP] |
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7-267295 |
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Current U.S.
Class: |
477/40;
477/47 |
Current CPC
Class: |
F16H
61/66254 (20130101); F16H 59/22 (20130101); F16H
59/24 (20130101); F16H 59/42 (20130101); Y10T
477/621 (20150115); F16H 59/48 (20130101); Y10T
477/62423 (20150115); F16H 59/44 (20130101) |
Current International
Class: |
F16H
61/66 (20060101); F16H 61/662 (20060101); F16H
59/24 (20060101); F16H 59/42 (20060101); F16H
59/44 (20060101); F16H 59/22 (20060101); F16H
59/48 (20060101); F16H 59/18 (20060101); F16H
059/48 () |
Field of
Search: |
;477/40,47 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wright; Dirk
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input and output
shaft, the transmission being operable at a variable speed ratio
for transmitting a drive from the input shaft to the output shaft,
comprising:
means for sensing vehicle operating conditions including vehicle
acceleration and vehicle speed;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for calculating a correction factor per predetermined unit
time based on the sensed vehicle acceleration when the sensed
vehicle acceleration exceeds a threshold value in the presence of
the released accelerator pedal indicative signal;
means for adding the correction factor to the target input shaft
speed value to correct the target input shaft speed value in an
increasing direction at intervals of the predetermined unit
time;
means for decreasing the threshold value as the vehicle speed
increases; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value.
2. A continuously variable transmission control apparatus as
claimed in claim 1, further including means for setting the
threshold value at a predetermined value greater than zero when the
vehicle speed is equal to or higher than a first predetermined
value and a predetermined value less than zero when the vehicle
speed is equal to or higher than a second predetermined value,
reducing the correction factor substantially to zero when the
vehicle acceleration is equal to or less than a predetermined value
less than the first predetermined value.
3. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input and output
shaft, the transmission being operable at a variable speed ratio
for transmitting a drive from the input shaft to the output shaft,
comprising:
means for sensing vehicle operating conditions including vehicle
acceleration and vehicle speed;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for calculating a correction factor per predetermined unit
time based on the sensed vehicle acceleration when the sensed
vehicle acceleration is less than a threshold value in the presence
of the released accelerator pedal indicative signal;
means for subtracting the correction factor from the target input
shaft speed value to correct the target input shaft speed value in
a decreasing direction at intervals of the predetermined unit
time;
means for decreasing the threshold value as the vehicle speed
increases; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected, target value.
4. A continuously variable transmission control apparatus as
claimed in claim 3, further including means for setting the
threshold value at a predetermined value less than zero and close
to zero when the vehicle speed is equal to or lower than a
predetermined value.
5. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input and output
shaft, the transmission being operable at a variable speed ratio
for transmitting a drive from the input shaft to the output shaft,
comprising:
means for sensing vehicle operating conditions including vehicle
acceleration;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for producing a brake application indicative signal in
response to application of braking to the vehicle;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for calculating a correction factor per predetermined unit
time based on the sensed vehicle acceleration to bring the vehicle
acceleration into a predetermined range in the presence of the
released accelerator pedal indicative signal;
means for adding the correction factor to the target input shaft
speed value to correct the target input shaft speed value at
intervals of the predetermined unit time;
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value; and
means for retaining the correction factor in the presence of the
brake application indicative signal.
6. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input and output
shaft, the transmission being operable at a variable speed ratio
for transmitting a drive from the input shaft to the output shaft,
comprising:
means for sensing vehicle operating conditions including vehicle
acceleration;
means for sensing an operator's demand for vehicle cruising;
means for sensing an operator's demand for vehicle
acceleration;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means responsive to the sensed operator's demand for vehicle
cruising for correcting the calculated target input shaft speed
value to bring the vehicle acceleration into a predetermined
range;
means responsive to the operator's demand for vehicle acceleration
sensed during the target input shaft speed value correction for
changing the target input shaft speed value at a predetermined rate
toward the calculated target value; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value.
7. A continuously variable transmission control apparatus as
claimed in claim 6, wherein the means for correcting the calculated
target input shaft speed value includes means for subtracting a
predetermined value from the corrected target value at uniform time
intervals when the corrected target value is equal to or greater
than the calculated target value.
8. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input and output
shaft, the transmission being operable at a variable speed ratio
for transmitting a drive from the input shaft to the output shaft,
comprising:
means for sensing vehicle operating conditions including vehicle
acceleration;
means for sensing a degree to which the accelerator pedal is
depressed;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for correcting the calculated target input shaft speed value
to bring the vehicle acceleration into a predetermined range when
the sensed degree indicates the accelerator pedal released;
means for changing the target input shaft speed value at a
predetermined rate toward the calculated target value when the
sensed degree indicate the accelerator pedal depressed during the
target input shaft speed value correction; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value.
9. A continuously variable transmission control apparatus as
claimed in claim 8, wherein the means for correcting the calculated
target input shaft speed value includes means for subtracting a
predetermined value from the corrected target value at uniform time
intervals when the corrected target value is equal to or greater
than the calculated target value..Iadd.
10. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input shaft and an
output shaft, the transmission being operable at a variable speed
ratio for transmitting a drive from the input shaft to the output
shaft, comprising:
means for sensing vehicle operating conditions including vehicle
speed;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for determining a vehicle acceleration;
means for calculating a correction factor per predetermined unit
time based on the determined vehicle acceleration when the
determined vehicle acceleration exceeds a threshold value in the
presence of the released accelerator pedal indicative signal;
means for adding the correction factor to the target input shaft
speed value to correct the target input shaft speed value in an
increasing direction at intervals of the predetermined unit
time;
means for decreasing the threshold value as the vehicle speed
increases; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target
value..Iaddend..Iadd.
11. A continuously variable transmission control apparatus as
claimed in claim 10, further including means for setting the
threshold value at a predetermined value greater than zero when the
vehicle speed is equal to or higher than a first predetermined
value and a predetermined value less than zero when the vehicle
speed is equal to or higher than a second predetermined value,
reducing the correction factor substantially to zero when the
vehicle acceleration is equal to or less than a predetermined value
less than the first predetermined value..Iaddend..Iadd.
12. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input shaft and an
output shaft, the transmission being operable at a variable speed
ratio for transmitting a drive from the input shaft to the output
shaft, comprising:
means for sensing vehicle operating conditions including vehicle
speed;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for determining a vehicle acceleration;
means for calculating a correction factor per predetermined unit
time based on the determined vehicle acceleration when the
determined vehicle acceleration is less than a threshold value in
the presence of the released accelerator pedal indicative
signal;
means for subtracting the correction factor from the target input
shaft speed value to correct the target input shaft speed value in
a decreasing direction at intervals of the predetermined time
unit;
means for decreasing the threshold value as the vehicle speed
increases; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target
value..Iaddend..Iadd.
13. A continuously variable transmission control apparatus as
claimed in claim 12, further including means for setting the
threshold value at a predetermined value less than zero and close
to zero when the vehicle speed is equal to or lower than a
predetermined value..Iaddend..Iadd.
14. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input shaft and an
output shaft, the transmission being operable at a variable speed
ratio for transmitting a drive from the input shaft to the output
shaft, comprising:
means for sensing vehicle operating conditions including vehicle
speed;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for producing a released accelerator pedal indicative signal
when the accelerator pedal is released;
means for producing a brake application indicative signal in
response to application of braking to the vehicle;
means for determining a vehicle acceleration;
means for calculating a correction factor per predetermined unit
time based on the determined vehicle acceleration to bring the
vehicle acceleration into a predetermined range in the presence of
the released accelerator pedal indicative signal;
means for adding the correction factor to the target input shaft
speed value to correct the target input shaft speed value at
intervals of the predetermined unit time;
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value; and
means for retaining the correction factor in the presence of the
brake application indicative signal..Iaddend..Iadd.
15. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input shaft and an
output shaft, the transmission being operable at a variable speed
ratio for transmitting a drive from the input shaft to the output
shaft, comprising:
means for sensing vehicle operating conditions including vehicle
speed;
means for sensing an operator's demand for vehicle cruising;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for sensing an operator's demand for vehicle
acceleration;
means for determining a vehicle acceleration;
means responsive to the sensed operator's demand for vehicle
cruising for correcting the calculated target input shaft speed
value to bring the vehicle acceleration into a predetermined
range;
means responsive to the operator's demand for vehicle acceleration
sensed during the target input shaft speed value correction for
changing the target input shaft speed value at a predetermined rate
toward the calculated target value; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target
value..Iaddend..Iadd.
16. A continuously variable transmission control apparatus as
claimed in claim 15, wherein the means for correcting the
calculated target input shaft speed value includes means for
subtracting a predetermined value from the corrected target value
at uniform time intervals when the corrected target value is equal
to or greater than the calculated target value..Iaddend..Iadd.
17. An apparatus for controlling a continuously variable
transmission for use with an automotive vehicle including an
accelerator pedal, the transmission having an input shaft and an
output shaft, the transmission being operable at a variable speed
ratio for transmitting a drive from the input shaft to the output
shaft, said apparatus comprising:
means for sensing vehicle operating conditions including vehicle
speed;
means for calculating a target value for the speed of rotation of
the input shaft based on the sensed vehicle operating
conditions;
means for sensing a degree to which the accelerator pedal is
depressed;
means for determining a vehicle acceleration;
means for correcting the calculated target input shaft speed value
to bring the vehicle acceleration into a predetermined range when
the sensed degree indicates the accelerator pedal released;
means for changing the target input shaft speed value at a
predetermined rate toward the calculated target value when the
sensed degree indicate the accelerator pedal depressed during the
target input shaft speed value correction; and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target
value..Iaddend..Iadd.
18. A continuously variable transmission control apparatus as
claimed in claim 17, wherein the means for correcting the
calculated target input shaft speed value includes means for
subtracting a predetermined value from the corrected target value
at uniform time intervals when the corrected target value is equal
to or greater than the calculated target value..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for controlling a
continuously variable transmission for use with an automotive
vehicle to change the engine brake force when the vehicle is
coasting.
Some automotive vehicles employ a continuously variable
transmission having an input shaft coupled to the engine and an
output shaft coupled to the drive shaft for transmitting a drive
from the engine to the drive shaft. Such a continuously variable
transmission operates with a speed ratio controlled in a manner to
bring the speed of rotation of the input shaft into coincidence
with a target value calculated as a function of engine throttle
position (or accelerator pedal position) and vehicle speed. It is
the current practice to decrease the target input shaft speed value
as the throttle position decreases. If the vehicle is coasting on a
downhill slope, the operator will release the accelerator pedal.
This causes the throttle position to decrease so that the target
input shaft speed value is changed (decreased) in a direction to
weaken the engine brake. As a result, the operator would feel an
excessive degree of vehicle acceleration in spite of the fact that
the accelerator pedal is released and increase the frequency at
which the operator depresses the brake pedal.
For example, Japanese Patent Kokai No. 6-81932 discloses a
continuously variable transmission control apparatus intended to
reduce the frequency at which the operator depresses the brake
pedal when the vehicle is coasting on a downhill slope by
increasing the lower limit for the target input shaft speed value
as the absolute value of the vehicle weight gradient resistance
increases to perform aggressive operate engine brake operations.
With such a conventional apparatus, however, the target input shaft
speed value changes frequently to provide a sense of
incompatibility to the operator with changes in the gradient of the
slope.
SUMMARY OF THE INVENTION
It is a main object of the invention to provide an improved
continuously variable transmission control which can provide a
smooth engine brake force change to meet the operator's expectation
therefor when the vehicle is coasting with the accelerator pedal
being released.
There is provided, in accordance with the invention, an apparatus
for controlling a continuously variable transmission for use with
an automotive vehicle including an accelerator pedal. The
transmission has an input and output shaft. The transmission is
operable at a variable speed ratio for transmitting a drive from
the input shaft to the output shaft. The continuously variable
transmission control apparatus comprises means for sensing vehicle
operating conditions including vehicle acceleration and vehicle
speed, means for producing a released accelerator pedal indicative
signal when the accelerator pedal is released, means for
calculating a target value for the speed of rotation of the input
shaft based on the sensed vehicle operating conditions, means for
calculating a correction factor per predetermined unit time based
on the sensed vehicle acceleration when the sensed vehicle
acceleration exceeds a threshold value in the presence of the
released accelerator pedal indicative signal, means for adding the
correction factor to the target input shaft speed value to correct
the target input shaft speed value in an increasing direction at
intervals of the predetermined unit time, means for decreasing the
threshold value as the vehicle speed increases, and means for
controlling the speed ratio to bring the input shaft speed into
coincidence with the corrected target value.
In another aspect of the invention, the continuously variable
transmission control apparatus comprises means for sensing vehicle
operating conditions including vehicle acceleration and vehicle
speed, means for producing a released accelerator pedal indicative
signal when the accelerator pedal is released, means for
calculating a target value for the speed of rotation of the input
shaft based on the sensed vehicle operating conditions, means for
calculating a correction factor per predetermined unit time based
on the sensed vehicle acceleration when the sensed vehicle
acceleration is less than a threshold value in the presence of the
released accelerator pedal indicative signal, means for subtracting
the correction factor from the target input shaft speed value to
correct the target input shaft speed value in a decreasing
direction at intervals of the predetermined unit time, means for
decreasing the threshold value as the vehicle speed increases, and
means for controlling the speed ratio to bring the input shaft
speed into coincidence with the corrected target value.
In another aspect of the invention, the continuously variable
transmission control apparatus comprises means for sensing vehicle
operating conditions including vehicle acceleration, means for
producing a released accelerator pedal indicative signal when the
accelerator pedal is released, means for producing a brake
application indicative signal in response to application of braking
to the vehicle, means for calculating a target value for the speed
of rotation of the input shaft based on the sensed vehicle
operating conditions, means for calculating a correction factor per
predetermined unit time based on the sensed vehicle acceleration to
bring the vehicle acceleration into a predetermined range in the
presence of the released accelerator pedal indicative signal, means
for adding the correction factor to the target input shaft speed
value to correct the target input shaft speed value at intervals of
the predetermined unit time, means for controlling the speed ratio
to bring the input shaft speed into coincidence with the corrected
target value, and means for retaining the correction factor in the
presence of the brake application indicative signal.
In another aspect of the invention, the continuously variable
transmission control apparatus comprises means for sensing vehicle
operating conditions including vehicle acceleration, means for
sensing an operator's demand for vehicle cruising, means for
sensing an operator's demand for vehicle acceleration, means for
calculating a target value for the speed of rotation of the input
shaft based on the sensed vehicle operating conditions, means
responsive to the sensed operator's demand for vehicle cruising for
correcting the calculated target input shaft speed value to bring
the vehicle acceleration into a predetermined range, means
responsive to the operator's demand for vehicle acceleration sensed
during the target input shaft speed value correction for changing
the target input shaft speed value at a predetermined rate toward
the calculated target value, and means for controlling the speed
ratio to bring the input shaft speed into coincidence with the
corrected target value.
In still another aspect of the invention, the continuously variable
transmission control apparatus comprises means for sensing vehicle
operating conditions including vehicle acceleration, means for
sensing a degree to which the accelerator pedal is depressed, means
for calculating a target value for the speed of rotation of the
input shaft based on the sensed vehicle operating conditions, means
for correcting the calculated target input shaft speed value to
bring the vehicle acceleration into a predetermined range when the
sensed degree indicates the accelerator pedal released, means for
changing the target input shaft speed value at a predetermined rate
toward the calculated target value when the sensed degree indicate
the accelerator pedal depressed during the target input shaft speed
value correction, and means for controlling the speed ratio to
bring the input shaft speed into coincidence with the corrected
target value.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail by reference to
the following description taken in connection with the accompanying
drawings, in which:
FIG. 1 is a block diagram showing one embodiment of a continuously
variable transmission control apparatus made in accordance with the
invention;
FIG. 2 is an overall flow diagram showing the operation of the
digital computer used for the continuously variable transmission
control;
FIG. 3 is a detailed flow diagram showing the programming of the
digital computer as it is used for target input shaft speed
calculation;
FIGS. 4 to 10 are detailed flow diagrams showing the programming of
the digital computer as it is used for target input shaft speed
calculation;
FIG. 11 is a graph of vehicle speed versus input shaft speed;
FIG. 12 is a graph of vehicle speed versus vehicle acceleration;
FIG. 13 is a graph of vehicle acceleration versus input shaft speed
correction factor;
FIG. 14 is a graph of vehicle speed versus operator's expected
deceleration;
FIG. 15 is a graph of vehicle speed versus operator's expected
deceleration used in explaining the target vehicle acceleration
range;
FIG. 16 is a graph of vehicle speed versus vehicle
acceleration;
FIGS. 17A to 17F are graphs used in explaining the behaviors of the
vehicle coasting on a downhill slope in connection with application
of brake to the vehicle; and
FIG. 18A is a graph showing corrected target input shaft speed
value changes with time when changes up are required to resume the
normal control without target input shaft speed value correction;
and
FIG. 18B is a graph showing corrected target input shaft speed
value changes with time when changes down are required to resume
the normal control without target input shaft speed value
correction.
DETAILED DESCRIPTION OF THE INVENTION
With reference to the drawings, and in particular to FIG. 1, there
is shown a continuously variable transmission control apparatus for
use with an automotive vehicle having an internal combustion engine
1. The engine 1 operates on command from an engine control unit 6
which controls the amount of fuel metered to the engine 1, the
fuel-injection timing and the ignition-system spark-timing. For
example, the amount of fuel metered to the engine, this being
determined by the width of the electrical pulses applied to the
fuel injector 4, is repetitively determined from calculations
performed in the engine control unit 6 based on various conditions
of the engine that are sensed during its operation. These sensed
conditions include cylinder-head coolant temperature, ambient
temperature, throttle position, engine load, engine speed, etc. The
calculated value for the fuel-injection pulse-width is transferred
to set the fuel injector 4 according to the calculated value
therefor. A drive from the engine 1 is transmitted to a drive shaft
3 through a continuously variable transmission 2. The continuously
variable transmission 2 has an input shaft coupled to an internal
combustion engine 1 and an output shaft coupled to the drive shaft
3. The continuously variable transmission 2 may be of the V-belt or
troidal type.
The continuously variable transmission 2 operates on command
applied to a speed ratio control unit 5 from a transmission control
unit 7. The transmission control unit 7 determines a target input
shaft speed DSRREV repetitively from calculations performed therein
based on various conditions of the automotive vehicle that are
sensed during its operation. These sensed conditions include
vehicle speed VSP, throttle position TVO, transmission input shaft
speed Ni, driven road wheel speed, brake pedal position,
transmission output shaft speed No, vehicle longitudinal
acceleration G and accelerator pedal position. Thus, a vehicle
speed sensor 8, a throttle position sensor 9, an engine speed
sensor 10, a driven road wheel speed sensor 11, a brake switch 12,
a transmission output shaft speed sensor 13, a vehicle acceleration
sensor 14 and an idle switch 15 are connected to the transmission
control unit 7. The vehicle speed sensor is provided to sense the
speed VSP of traveling of the automotive vehicle. The throttle
position sensor 9 may be a potentiometer associated with the
throttle valve situated in the induction passage of the engine and
connected in a voltage divider circuit for supplying a voltage
proportional to the degree TVO of opening of the throttle valve.
The engine speed sensor 10 is provided for producing a pulse signal
having a repetition rate proportional to the speed Ne of rotation
of the engine. The driven road wheel speed sensor 11 is located for
producing a pulse signal having a repetition rate proportional to
the speed of rotation of the driven road wheels. The brake switch
12 is responsive to the application of braking to the automotive
vehicle to close to supply current from the engine battery to the
transmission control unit 7. The transmission output shaft speed
sensor 13 is located for producing a pulse signal of a repetition
rate proportional to the speed of rotation of the transmission
output shaft. The vehicle acceleration sensor 14 is provided for
producing a signal indicative of the longitudinal acceleration G of
the automotive vehicle. The idle switch 15 closes to supply current
from the engine battery to the transmission control unit 7 when the
throttle position is at an angle less than a predetermined value,
that is, the accelerator pedal is released. The continuously
variable transmission is shown as having an input shaft directly
coupled to the engine 1. In this case, the speed Ni of rotation of
the transmission input shaft is equal to the engine speed Ne. It is
to be understood, of course, that the transmission input shaft may
be coupled to the engine 1 through a reduction gear unit or torque
converter. In this case, another speed sensor is provided to
produce a signal indicative of the speed Ni of rotation of the
transmission input shaft. The transmission control unit 7 also
communicates with the engine control unit 6 for synchronized engine
and transmission control. The transmission control unit 7. The
determined target input shaft speed DSRREV is converted into a
corresponding target speed ratio DSRRTO (=Ni/No) which is
transferred to the speed ratio control unit 5 to bring the input
shaft speed Ni into coincidence with the target input shaft speed
DSRREV.
The transmission control unit 7 may employ a digital computer which
includes a central processing unit (CPU) a central processing unit
(CPU), a read only memory (ROM), a random access memory (RAM) and
an input/output interface unit (I/O). The central processing unit
communicates with the rest of the computer. The input/output
interface unit includes an analog-to-digital converter which
receives analog signals from the throttle position sensor 9 and
other sensors and converts them into digital form for application
to the central processing unit. The input/output interface unit
also includes counters which count the pulses fed thereto from the
speed sensors 10, 11 and 13 and convert the counts into
corresponding speed indication digital signals for application to
the central processing unit. The read only memory contains the
programs for operating the central processing unit and further
contains appropriate data in look-up tables used in calculating
appropriate values for the speed ratio control.
FIG. 2 is a flow diagram illustrating the programming of the
digital computer as it is used to control the continuously variable
transmission 2. The computer program is entered at the point 102 at
uniform intervals of time, for example 5 msec. At the point 104 in
the program, the sensor signals fed to the transmission control
unit 7 from various sensors 8 to 15 are read into the computer
memory. At the point 106, a target value DSRREV for the speed Ni of
rotation of the transmission input shaft is calculated from a speed
change map programmed into the computer. The speed change map
defines the target input shaft speed DSRREV as a function of
throttle position TVO and vehicle speed VSP, as shown in FIG. 11.
At the point 108, the calculated target input shaft speed value
DSRREV is corrected for engine brake operation. This correction is
made based on the vehicle longitudinal acceleration G as described
later in greater detail. At the point 110 in the program, a target
speed ratio DSRRTO is calculated to bring the transmission input
shaft speed Ni in coincidence with the corrected target value
DSRREV. At the point 112, the calculated target speed ratio value
DSRRTO is transferred to the input/output interface unit which
converts it into a corresponding control signal. This control
signal is applied to the speed ratio control unit 5 which thereby
operates the transmission 2 with a speed ratio corresponding to the
calculated value DSRRTO.
FIG. 3 is a flow diagram illustrating the above correction of the
target transmission input shaft speed value DSRREV. At the point
120 in FIG. 3, which corresponds to the point 108 of FIG. 2, the
computer program is entered. At the point 122, an acceptable
correction range where the speed Ni of the input shaft of the
continuously variable transmission 2 can be corrected is determined
based on the target input shaft speed DSRREV calculated at the
point 106 of FIG. 2. At the point 124, a threshold value of the
vehicle longitudinal acceleration G is calculated. At the point
126, the vehicle acceleration G is compared with the calculated
threshold value for a determination as to whether or not a stronger
or weaker engine brake is required. At the point 128, the rate of
change of the engine brake force, that is, a correction factor by
which the target input shaft speed is to be corrected per unit
time, is calculated according to the vehicle longitudinal
acceleration G. At the point 130, the correction factor calculated
at the point 128 is used to correct the target input shaft speed
DSRREV so as to produce an engine brake force corresponding to the
vehicle longitudinal acceleration. At the point 132, the corrected
target input shaft speed DSRENBR is set as a new target input shaft
speed DSRREV. The new target input shaft speed DSRREV is outputted
to calculate a target speed ratio DSRRTO. Following this, the
program proceeds to the point 134 where the program returns to the
entry point 120.
Referring to FIGS. 4 to 10, the details of the above correction of
the target transmission input shaft speed value DSRREV will be
described. At the point 140 in FIG. 4, which corresponds to the
point 122 of FIG. 3, the computer program is entered. At the point
142 in the program, an upper limit DSRHLMT of the acceptable
correction range for the input shaft speed Ni is calculated from
the map of FIG. 11 which defines the upper limit DSRHLMT as a
function of vehicle speed VSP. At the point 144, a lower limit
DSRLLMT of the acceptable correction range for the input shaft
speed Ni is calculated from the map of FIG. 11 which defines the
lower limit DSRLLMT as a function of vehicle speed VSP. At the
point 146, an acceleration side threshold value VSPOVLM is
calculated from a map programmed into the computer. This map
defines the acceleration side threshold value VSPOVIM as a function
of vehicle speed VSP, as shown in FIG. 12. At the point 148, a
deceleration side threshold value VSPUDLM is calculated from the
map of FIG. 12. The map may be obtained experimentally from
accelerations the operator expects when the accelerator pedal is
released, this being detected when the idle switch 15 is turned on.
The operator bodily senses vehicle acceleration in an accelerated
motion range (AMR) defined above the acceleration side threshold
value VSPOVLM and vehicle deceleration in a decelerated motion
range (DMR) defined below the deceleration side threshold value
VSPUDLM.
Upon completion of the step at the point 148 in the program of FIG.
4, the program proceeds to the point 150 of FIG. 5 which
corresponds to the point 126 of FIG. 3. At the point 152, a
determination is made as to whether or not the vehicle speed VSP is
equal to or less than a predetermined value, for example, 10 Km/h.
If the answer to this question is "yes", then it means that the
vehicle speed is in a predetermined low speed range and the program
proceeds to the point 154 where the vehicle acceleration TKRAMS6 is
set at 0 and then to the point 166. Otherwise, the program proceeds
to the point 156 where the vehicle acceleration (or deceleration)
TKRAMS6 is calculated based on the difference between the vehicle
speed VSP read in this cycle of execution of this program and the
vehicle speed VSP.sub.-5 read before a predetermined number of (in
this case 5) cycles of execution of this program. Although the
vehicle acceleration TKRAMS6 is calculated as the rate of change of
the vehicle speed VSP, it is to be understood, of course, that it
may be the sensed value of the vehicle acceleration sensor 14. At
the point 158, a determination is made as to whether or not the
vehicle acceleration TKRAMS6 is greater than the acceleration side
threshold value VSPOVLM calculated at the point 146 of FIG. 4. If
the answer to this question is "yes", then the program proceeds to
the point 16 where an accelerated motion flag VSPMNS is set to
indicate that the vehicle acceleration is in the accelerated motion
range so that a stronger engine brake is required and then to the
point 168. Otherwise, the program proceeds to another determination
step at the point 162. This determination is as to whether or not
the vehicle acceleration TKRAMS6 is smaller than the deceleration
side threshold value VSPUDLM calculated at the point 148 of FIG. 4.
If the answer to this question is "yes", then the program proceeds
to the point 164 where a decelerated motion flag VSPMNS is set to
indicate that the vehicle acceleration is in the decelerated motion
range requiring a weaker engine brake force and then to the point
168. Otherwise, the program proceeds to the point 166 where a
uniform motion flag VSPEOS is set to indicate that the vehicle
acceleration is in the uniform motion range so that the existing
engine brake is to be retained.
Following this, the program proceeds to the point 168 of FIG. 6
which corresponds to the point 128 of FIG. 3. At the points 170 and
172 in the program, a down- or up-shift correction factor DDSRDN or
DDSRUP by which the target input shaft speed DSRREV is to be
corrected per unit time is calculated from a map programmed into
the computer. This map specifies this correction factor DDSRDN or
DDSRUP as a function of vehicle acceleration TKRAMS6, as shown in
FIG. 13. This map may be obtained experimentally, as described
later. The downshift correction factor DDSRDN is calculated in a
direction to increase the target input shaft speed value DSRREV so
as to increase the engine brake force when the vehicle acceleration
TKRAMS6 has a positive sign and the upshift correction factor
DDSRUP is calculated in a direction to decrease the target input
shaft speed value DSRREV so as to decrease the engine brake force
when the vehicle acceleration TKRAMS6 has a negative sign. In the
illustrated case, the unit time corresponds to the time interval (5
msec) of execution of this program.
At the point 174 in the program, a determination is made as to
whether or not a flag OLDIDLR, which was set to 1 if the idle
switch 15 is off in the last cycle of execution of this program, is
0. If the answer to this question is "yes", then the accelerator
pedal was depressed and the program proceeds to another
determination step at the point 176. This determination is as to
whether or not a flag IDLE, which has been set to 1 if the idle
switch 15 is off in the present cycle of execution of this program,
is 0. If the answer to this question is "yes", then it means that
the accelerator pedal remains depressed and the program proceeds to
the point 220 of FIG. 8. Otherwise, it means that the accelerator
pedal is released from its depressed position and the program
proceeds to the point 178 where the flag OLDIDLE is set to 1 and
then the program proceeds to the point 240 of FIG. 9.
If the answer to the question inputted at the point 174 is "no",
then it means that the accelerator pedal was released and the
program proceeds to another determination step at the point 180.
This determination is as to whether or not the flag IDLE is 0. If
the answer to this question is "no", then it means that the
accelerator pedal remains released and the program proceeds to the
point 200 of FIG. 7. Otherwise, it means that the accelerator pedal
is depressed from its released position and the program proceeds to
the point 182 where the flag OLDIDLE is cleared to 0 and then to
the point 220 of FIG. 8.
FIG. 7 is a flow diagram illustrating the correction of the target
input shaft speed value DSRREV when the accelerator pedal remains
released. At the point 202 in the program, a determination is made
as to whether or not the accelerated motion flag VSPPLS (FIG. 5)
has been set at 1. If the answer to this question is "yes", then it
means that the vehicle acceleration is in the accelerated motion
range (FIG. 12) and the program proceeds to the point 204 where the
central processing unit increase the target input shaft speed value
DSRREV by adding the downshift correction factor DDSRDN calculated
at the point 170 of FIG. 6 to the last corrected target input shaft
speed value DSRENBR (DSRENBR=DSRENBR.sub.-1 +DDSRDN where
DSRENBR.sub.-1 is the corrected target input shaft speed value
obtained in the last cycle of execution of this program) in order
to increase the engine brake force so as to bring the vehicle
acceleration from the accelerated motion range into the uniform
motion range. At the point 206, a correction flag NOWCNT is set at
1 to indicate that the target input shaft speed value DSRREV is
being corrected. Following this, the program proceed to the point
250 of FIG. 10.
If the answer to the question inputted at the point 202 is "no",
then the program proceeds to another determination step at the
point 208. This determination is as to whether or not the
correction flag NOWCNT has been set. If the answer to this question
is "no", then it means that no correction is required for the
target input shaft speed value DSRREV and the program proceeds to
the point 210 where the target input shaft speed value DSRREV
calculated at the point 106 of FIG. 2 is set for the corrected
target input shaft speed value DSRENBR. Following this, the program
proceeds to the point 250 of FIG. 10.
If the answer to the question inputted at the point 208 is "no",
then the program proceeds to another determination step at the
point 212. This determination is as to whether or not the
decelerated motion flag VSPMNS (FIG. 5) has been set. If the answer
to this question is "yes", then it means that the vehicle
acceleration is in the decelerated motion range and the program
proceeds to the point 214. Otherwise, the program proceeds to the
point 250 of FIG. 10. At the point 214, a determination is made as
to whether or not the brake pedal is released. This determination
is made based on the signal BRK fed from the brake switch 12. If
the answer to this question is "yes" (BRK=0), then the program
proceeds to the point 216 where the central processing unit
decreases the target input shaft speed value DSRREV gradually by
adding the upshift correction factor DDSRUP (negative value)
calculated at the point 172 of FIG. 6 to the last corrected target
input shaft speed value DSRENBR (DSRENBR=DSRENBR.sub.-1 +DDSRUP
where DSRENBR.sub.-1 is the corrected target input shaft speed
value DSRENBR obtained in the last cycle of execution of this
program). Following this, the program proceeds to the point 250 of
FIG. 10. If the answer to the question inputted at the point 214 is
"no", then the program proceeds to the point 250 of FIG. 10. That
is, the operator's braking operation is given top priority by
preventing the target input shaft speed value DSRREV from being
corrected to a smaller value even though the vehicle acceleration
is in the decelerated motion range where the engine brake should be
weakened.
FIG. 8 is a flow diagram illustrating the correction of the target
input shaft speed value DSRREV when the accelerator pedal is
depressed or remains depressed. At the point 222 in the program, a
determination is made as to whether or not the correction flag
NOWCNT has been set at 1. If the answer to this question is "yes",
then it means that the target input shaft speed value DSRREV is
being corrected and the program proceeds to the point 228.
Otherwise, the program proceeds to the point 224 where the
correction flag NOWCNT is cleared to 0 and then to the point 226
where the target input shaft speed value DSRREV calculated at the
point 106 of FIG. 2 is set for the corrected target input shaft
speed value DSRENBR. Following this, the program proceeds to the
point 270 of FIG. 10.
At the point 228 in the program, a determination is made as to
whether or not the target input shaft speed value DSRREV calculated
at the point 106 of FIG. 2 is equal to or less than the corrected
target input shaft speed value DSRENBR.sub.-1 obtained in the last
cycle of execution of this program. If the answer to this question
is "yes", then the program proceeds to the point 230. Otherwise,
the program proceeds to the point 224. At the point 230, the
corrected target input shaft speed value DSRENBR is calculated by
subtracting a predetermined value (in the illustrated case 1 rmp)
from the last corrected target input shaft speed value
DSRENBR.sub.-1 (DSRENBR=DSRENBR.sub.-1 -1). Following this, the
program proceeds to the point 270 of FIG. 10.
FIG. 9 is a flow diagram illustrating the correction of the target
input shaft speed value DSRREV when the accelerator pedal is
released. At the point 242 in the program, a determination is made
as to whether or not the last corrected target input shaft speed
value DSRENBR.sub.1- is greater than the upper limit DSRHLMT for
the input shaft speed calculated at the point 142 of FIG. 4. If the
answer to this question is "yes", then the program proceeds to the
point 244 where the upper limit DSRHLMT is set for the corrected
target input shaft speed DSRENBR and then to the point 250 of FIG.
10. Otherwise, the program proceeds to another determination step
at the point 246. This determination is as to whether or not the
correction flag NOWCNT has been set at 1. If the answer to this
question is "yes", then it means that the target input shaft speed
value DSRREV is being corrected and the program proceeds to the
point 250 of FIG. 10. Otherwise, the program proceeds to the point
228 where the target input shaft speed value DSRREV calculated at
the point 106 of FIG. 2 is set for the corrected target input shaft
speed value DSRENBR. Following this, the program proceeds to the
point 250 of FIG. 10.
At the point 252 in the program of FIG. 10, a determination is made
as to whether or not the corrected target input shaft speed value
DSRENB is equal to or less than the lower limit DSRLLIT calculated
at the point 144 of FIG. 4. If the answer to this question is
"yes", then the program proceeds to the point 254 where the lower
limit DSRLLMT is set for the corrected target input shaft speed
value DSRENBR. At the point 256, the correction flag is cleared to
zero. Following this, the program proceeds to the point 272.
If the answer to the question inputted at the point 254 is "no",
then the program proceeds to another determination step at the
point 258. This determination is as to whether or not the corrected
target input shaft speed value DSRENBR is greater than the upper
limit DSRHLMT calculated at the point 142 of FIG. 4. If the answer
to this question is "yes", then the program proceeds to the point
266. Otherwise, the program proceeds to the point 272. At the point
266, the upper limit DSRHLMT is set for the corrected target input
shaft speed value DSRENBR. Upon completion of the step at the point
266, the program proceeds to the point 272. The program proceeds
from the point 270 to the point 272.
At the point 272, the corrected target input shaft speed value
DSRENBR is set for the new target input shaft speed value DSRREV.
Following this, the program proceeds to the point 274 where the
program returns to the entry point 102 of FIG. 2. The calculated
new target input shaft speed value DSRREV is transferred to the
input/output interface unit which converts it into a corresponding
target speed ratio and produces a control signal causing the speed
ratio control unit 5 to set the continuously variable transmission
2 according to the target speed ratio. As a result, the vehicle
acceleration is converged into the uniform motion range of FIG. 12,
that is, the vehicle acceleration is controlled continuously to
bring the engine brake force toward a value the operator expects
according to the vehicle speed VSP.
The target input shaft speed value DSRREV is corrected at uniform
time intervals based on a correction factor calculated from the map
of FIG. 13 when the vehicle acceleration comes out of the uniform
motion range of FIG. 12 with the vehicle being coasting, that is,
with the accelerator pedal being released. The map of FIG. 12 is
prepared through our experiments performed on a given automotive
vehicle coasting down hills with the accelerator pedal being
released. It has been discovered through the experiments that the
degree of deceleration the operator expects when the accelerator
pedal is released remains about 0.06 G (acceleration=-0.06 G) and
it is almost independent on the vehicle speed VSP, as shown in FIG.
14. According to the invention, the target input shaft speed value
is controlled to converge the deceleration resulting from the
engine brake into a target acceleration range .DELTA. G having a
predetermined width around about -0.06 G, as indicated by the
hatched area of FIG. 15, regardless of the vehicle speed VSP when
the vehicle is coasting with the accelerator pedal released. If the
vehicle acceleration is smaller than the target acceleration range
.DELTA. G as indicated by the point G2, the target input shaft
speed value is corrected to decrease so as to weaken the engine
brake force. If the vehicle acceleration is greater than the target
accelerating range .DELTA. G as indicated by the point G1, the
target input shaft speed value is corrected to increase so as to
provide a greater engine brake force.
If the target acceleration range .DELTA. G is set around about
-0.06 G regardless of vehicle speed, however, the operator will
bodily sense a stronger engine brake force at certain low vehicle
speeds (about 20 km/h) and an insufficient engine brake force at
certain high vehicle speeds (100 km/h or more). It has been
discovered that the deceleration the operator expects when the
accelerator pedal is released at such low or high vehicle speeds
varies according to the vehicle speed VSP. For this reason, it is
desirable to provide an engine brake force the operator expects
when the accelerator pedal is released over the entire vehicle
speed range by defining the uniform motion range corresponding to a
predetermined acceleration range .DELTA. G between upper and lower
limits VSPOVLM and VSPUDLM which increase with respect to the
reference acceleration value Gc (-0.06 G) as the vehicle speed VSP
decreases and decreases with respect to the reference acceleration
value Gc as the vehicle speed VSP increases, as shown in FIG.
16.
Description will be described further to the upper and lower limits
VSPOVLM and VSPUDLM of the uniform motion range. The upper limit,
that is, the acceleration side threshold value VSPOVLM of FIG. 12
used to determine whether the engine brake force is to be
intensified, decreases as the vehicle speed VSP increases. This is
effective to provide aggressive rapid engine brake application so
as to meet the operator's expectation for a stronger deceleration
when the accelerator pedal is released at a high vehicle speed. It
is preferable to increase the engine brake force even with a small
acceleration increase when the accelerator pedal is released at a
very high vehicle speed by setting the the acceleration side
threshold value VSPOVLM at a value equal substantially to zero or
at a value less than zero when the vehicle speed VSP is in a very
high range greater than a first predetermined value (for example,
100 km/h), as indicated by the broken lines of FIG. 16. When the
vehicle speed VSP is in a very low vehicle speed range less than a
predetermined second value (for example, 20 km/h), the operator
expects almost no engine brake application even with the
accelerator pedal being released. In such a very low vehicle speed
range, the acceleration side threshold value VSPUDLM is set a
value, for example 0.1 G or more, much greater than zero so as to
avoid engine brake application even when the vehicle acceleration
increases. In the range between the very-high and -low vehicle
speed ranges, the acceleration side threshold value VSPOVIM is set
to decrease as the vehicle speed VSP increases, as shown in FIGS.
12 and 16.
The upper limit, that is, the deceleration side threshold value
VSPUDLM of FIG. 12 used to determine whether the engine brake force
is to be weakened, decreases as the vehicle speed VSP increases.
For example, the deceleration side threshold value VSPUDLM is set
at a value greater than the reference value -0.06 G and smaller
than zero in a low vehicle speed range. The deceleration side
threshold value VSPUDLM is set at a value, for example, -0.1 G or
less, smallr than the reference value -0.0 G in a high vehicle
speed. Since the deceleration side threshold value VSPULM is
sufficiently small when the vehicle is coasting at a high vehicle
speed on a downhill slope with the accelerator pedal being
released, the vehicle acceleration is held in the uniform motion
range and the vehicle can coast to meet the operator's expectation
without excessive target input shaft speed changes regardless of
small slope gradient variations. When the vehicle speed VSP is in a
very low vehicle speed range less than a predetermined second value
(for example, 20 km/h), the operator expects almost no engine brake
application even with the accelerator pedal being released. In such
a very low vehicle speed range, thus, the acceleration side
threshold value VSPUDLM is set at a value, for example, -0.03 G,
somewhat smaller than zero so that the target input shaft speed
value is corrected to decrease when the vehicle acceleration comes
into the decelerated motion range. This is effective to avoid
engine brake application so as to prevent the vehicle from being
decelerated. Similarly, in the range between the high and low
vehicle speed ranges, the deceleration side threshold value VSUD LM
is set to decrease as the vehicle speed VSP increases, as shown in
FIGS. 12 and 16.
The operation of the continuously variable transmission control
apparatus of the invention will be described in connection with
changes in the acceleration and deceleration side threshold values
VSPOVLM and VSPUD LM defining the uniform motion range of FIG. 12.
The acceleration TKRA MS 6 is monitored to determine whether the
vehicle acceleration is in the uniform motion range of FIG. 12.
This determination is made by comparison with the vehicle
acceleration with the acceleration and deceleration side threshold
values VSPOVLM and VSPUDLM (points 158 and 162). The vehicle
acceleration is in the accelerated motion range if the vehicle
acceleration is greater than the acceleration side threshold value
VSPOVLM (point 160) and in the decelerated motion range if the
vehicle acceleration is less than the acceleration side threshold
value VSPUDLM (point 164). The operator's intention for vehicle
deceleration is determined based on the operation of the
accelerator pedal (points 174 to 182). When the vehicle is coasting
with the accelerator pedal held released (point 200), the
continuously variable transmission control apparatus increases the
engine brake force by adding the downshift correction factor DDSRDN
calculated from the map of FIG. 13 to the corrected target input
shaft speed value DSRENB so as to correct the target input shaft
speed in an increasing direction if the vehicle acceleration is in
the accelerated motion range (points 202 and 204) and it weakens
the engine brake force by adding the upshift correction factor
DDSRUP to the corrected target input shaft speed value DSRENBR so
as to correct the target input shaft speed value in a decreasing
direction if the vehicle acceleration is in the decelerated motion
range (points 212 and 214). That is, the continuously variable
transmission control apparatus corrects the corrected target input
shaft speed value DSRENBR to control the engine braking force so as
to converge the vehicle acceleration into the uniform motion range
of FIG. 12.
When the vehicle starts coasting with the accelerator pedal being
released, the engine brake force the operator expects is dependent
upon the vehicle speed VSP. If the continuously variable
transmission 2 is controlled merely by bringing the input shaft
speed into the target value DSRREV when the vehicle is coasting, a
sudden and great engine brake force change will occur in response
to a small slope gradient or road surface change. The invention
permits a smooth and continuous engine brake change without such a
sudden and great engine brake force change with the occurrence of a
slope gradient or road surface change by controlling the engine
brake force in a manner to bring the vehicle acceleration into the
uniform motion range. The invention also can provide a smooth and
continuous engine brake control in response to an engine load
change.
Since the threshold values VSPOVLM and VSPUDLM used to determine
the vehicle acceleration is in the uniform motion range of FIG. 12
is dependent on the vehicle speed VSP, the uniform motion range can
be changed according to the status of the road on which the vehicle
is operating, i.e., whether the road is a highway or superhighway
or whether the road is less or much congested with traffic. It is,
therefore, possible to provide a vehicle deceleration feel the
operator expects without any sense of incompatibility.
The operation of the continuously variable transmission control
apparatus of the invention will be described in connection with
operator's brake pedal operation. The engine brake force correction
starts upon the occurrence of two conditions, that is, when the
vehicle acceleration TKRAMS6 comes out of the uniform motion range
into the accelerated or decelerated motion range of FIG. 12 (points
158 and 162) and when the accelerator pedal remains released
(points 200 et seq.). It is now assumed that the vehicle is
coasting on a downhill slope with the accelerator pedal remaining
released. When the vehicle acceleration comes into the accelerated
or decelerated motion range of FIG. 12, determined based on the
vehicle speed VSP, (points 160 and 164), the down- or up-shift
correction factor DDSRDN or DSRUP is used to change the corrected
target input shaft speed value DSRENBR and, thus, the engine brake
force continuously at uniform time intervals. This is effective to
provide smooth engine brake force changes in a direction to
converge the vehicle acceleration into the uniform motion range of
FIG. 12 according to the gradient of the downhill slope so as to
realize a feel of vehicle deceleration the operator expects.
When the gradient of the downhill slope on which the vehicle is
coasting with the accelerator held released increases, the vehicle
acceleration increases into the accelerated motion range (FIG. 12)
so as to increase the vehicle speed VSP since the target input
shaft speed value has been set for a more gentle gradient of the
downhill slope. For this reason, it is required to intensify the
engine brake force. According to the invention, a downshift
correction factor DDSRDN is calculated, from the map of FIG. 13, as
a function of vehicle acceleration when the vehicle acceleration
comes into the accelerated motion range (FIG. 12). The downshift
correction factor DDSRDN is added to the last value of the
corrected target input shaft speed value DSRENBR to change the
target speed ratio value DSRRTO. The downshift correction factor
DDSP, DN is calculated, at uniform intervals of time (in the
illustrated case 5 msec) according to the existing vehicle
acceleration. This is effective to provide smooth target input
shaft speed value changes and thus smooth engine brake force
changes in a direction to converge the vehicle acceleration into
the uniform motion range (FIG. 12) according to the increase of the
gradient of the downhill slope so as to realize a feel of vehicle
deceleration the operator expects.
When the gradient of the downhill slope on which the vehicle is
coasting with the accelerator held released decreases, the vehicle
acceleration decreases into the decelerated motion range (FIG. 12)
so as to decrease the vehicle speed VSP since the target input
shaft speed value has been set for a more steep gradient of the
downhill slope. For this reason, it is required to weaken the
engine brake force. According to the invention, an upshift
correction factor DDSRUP is calculated, from the map of FIG. 13, as
a function of vehicle acceleration when the vehicle acceleration
comes into the decelerated motion range (FIG. 12). The upshift
correction factor DDSRDN (which has a negative value) is added to
the last value of the corrected target input shaft speed value
DSRENBR to change the target speed ratio value DSRRTO. The upshift
correction factor DDSRUP is calculated, at uniform intervals of
time (in the illustrated case 5 msec) according to the existing
vehicle acceleration. This is effective to provide smooth target
input shaft speed value changes and thus smooth engine brake force
changes in a direction to converge the vehicle acceleration into
the uniform motion range (FIG. 12) according to the decrease of the
gradient of the downhill slope so as to realize a feel of vehicle
deceleration the operator expects.
It is now assumed that the brake pedal is depressed to initiate
braking at time t1, for decreasing the vehicle speed to 40 km/h or
less, when the vehicle coasting at 60 km/h on a downhill slope
comes close to the front vehicle running at 40 km/h. Since the
vehicle is coasting on a downhill slope in this case, the engine
brake force correction (points 200 et seq.) continues (NOWCNT=1 at
the point 208). Because of braking, however, the vehicle
deceleration increases so that the vehicle acceleration comes into
the decelerated motion range (FIG. 12). As a result, the
deceleration flag VSPMNS is set at 1 and then the control is
performed to weaken the engine brake force from the point 212.
Since the brake flag BRK is set at 1 to indicate the brake pedal is
depressed, the corrected input shaft speed DSRENBR remains at the
last value therefor.
During the interval between the times t1 at which the brake pedal
is depressed and the time t2 at which the brake pedal is released,
the vehicle speed VSP decreases causing a decrease in the speed No
of rotate on of the output shaft of the transmission 2. On the
other hand, the corrected target input shaft speed value DSRENBR
(=target input shaft speed DSRREV) remains at the value calculated
at the time t1 when braking is initiated. For this reason, the
speed ratio DSRRTO increases to intensify the engine brake force
continuously so as to permit raid vehicle deceleration.
After the time t2, the engine brake force control proceeds from the
point 200 to retain the target input shaft speed value at the value
calculated at the time t2 at which the brake pedal is released. It
is, therefore, possible to prevent the vehicle from being
accelerated to come close to the front vehicle again. This is
effective to avoid frequent operator's brake pedal operations.
The operation of the continuously variable transmission control
apparatus of the invention will be described in connection with
operator's accelerator pedal operation. The engine brake force
correction starts upon the occurrence of two conditions, that is,
when the vehicle acceleration TKRAMS6 comes out of the uniform
motion range into the accelerated or decelerated motion range of
FIG. 12 (points 158 and 162) and when the accelerator pedal remains
released (points 200 et seq.). It is now assumed that the vehicle
is coasting on a downhill slope with the accelerator pedal
remaining released. When the vehicle acceleration comes into the
accelerated or decelerated motion range of FIG. 12, determined
based on the vehicle speed VSP, (points 160 and 164), the down- or
up-shift correction factor DDSRDN or DSRUP is used to control the
rate at which the corrected target input shaft speed value DSRENBR
is changed. This is effective to provide smooth engine brake force
changes in a direction to converge the vehicle acceleration into
the uniform motion range of FIG. 12 so as to realize a feel of
vehicle deceleration the operator expects.
When the operator depresses the accelerator pedal during the
vehicle coasting, the control proceeds to the points 220 et seq. so
as to terminate the engine brake force correction. In this case, if
the target input shaft speed value DSRREV calculated from the map
of FIG. 11 is equal to or greater than the last value
DSRENBR.sub.-1 of the corrected target input shaft speed (point
228), it means that changes up are required to initiate the normal
speed change control without the engine brake force correction and
the target input shaft speed is increased gradually from the last
corrected target input shaft speed value DSRENBR.sub.-1 to the
calculated target input shaft speed value DSRREV, as shown in FIG.
18A, by decreasing a predetermined value (for example, 1 rpm) from
the last value DSRENBR.sub.-1 of the corrected target input shaft
speed (point 230) so as to avoid shocks resulting from great
vehicle acceleration changes. On the other hand, if the target
input shaft speed value DSRREV calculated from the map of FIG. 11
is less than the last value DSRENBR.sub.-1 of the corrected target
input shaft speed (point 228), it means that changes down are
required to initiate the normal speed change control without the
engine brake force correction and the target input shaft speed is
set at the value calculated from the map of FIG. 11.
Preferably, the corrected target input shaft speed value DSRENBR is
changed at a predetermined constant value (in the illustrated case
1 rpm) at uniform intervals of time (in the illustrated case 5 msec
corresponding to each cycle of execution of the program). This
permits the operator to easily grasp the vehicle behavior changes
resulting from accelerator pedal operation regardless of changes in
vehicle operating conditions such as downhill slope gradient. While
the start of vehicle coasting is judged when the accelerator pedal
is released, it is to be understood that the engine brake force
correction may be initiated upon the operation of the deceleration
command switch associated with a cruise control unit or in response
to a deceleration command produced from the cruise control unit.
While the termination of the engine brake force correction is
judged when the accelerator pedal is depressed, it is to be
understood that the engine brake force correction may be terminated
upon the operation of the acceleration command switch associated
with a cruise control unit or in response to an acceleration
command produced from the cruise control unit.
* * * * *