U.S. patent application number 09/726612 was filed with the patent office on 2001-04-19 for control apparatus for automatic transmission.
Invention is credited to IlJima, Makoto.
Application Number | 20010000338 09/726612 |
Document ID | / |
Family ID | 11575825 |
Filed Date | 2001-04-19 |
United States Patent
Application |
20010000338 |
Kind Code |
A1 |
IlJima, Makoto |
April 19, 2001 |
Control apparatus for automatic transmission
Abstract
A control apparatus for an automatic transmission of a vehicle
having a forward friction element for engaging or disengaging a
turbine shaft with the automatic transmission in a forward running
direction and a lock-up clutch for directly transmitting a rotation
of an engine to the turbine shaft, comprises an abrupt deceleration
control means for disengaging the forward engagement element and
the lock-up clutch when an abrupt deceleration of the vehicle is
detected, and a restoring means for canceling the abrupt
deceleration control means and for restoring the forward friction
element to an engagement state when an accelerator pedal is
depressed for acceleration.
Inventors: |
IlJima, Makoto; (Tokyo-To,
JP) |
Correspondence
Address: |
SMITH GAMBRELL & RUSSELL, L.L.P.
The Beveridge DeGrandi Weilacher & Young
Intellectual Property Group
1850 M Street, N.W., Suite 800
Washington
DC
20036
US
|
Family ID: |
11575825 |
Appl. No.: |
09/726612 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09726612 |
Dec 1, 2000 |
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09477361 |
Jan 4, 2000 |
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6183391 |
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Current U.S.
Class: |
477/62 ; 477/168;
477/171; 477/74 |
Current CPC
Class: |
F16H 59/48 20130101;
F16H 61/14 20130101; F16H 61/662 20130101; F16H 2061/6608
20130101 |
Class at
Publication: |
477/62 ; 477/74;
477/168; 477/171 |
International
Class: |
B60K 041/02; B60K
041/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 1999 |
JP |
4116/1999 |
Claims
d sensor 92, whether or not the vehicle is in an abrupt
deceleration. Based on output signals from the drive range judging
section 83, the lock-up engagement judging section 84 and the
deceleration judging section 85, a forward clutch and lock-up
clutch control section 86 outputs control signals to a switching
section 87 and a duty ratio establishing section 88. The switching
section 87 outputs ON-OFF signals to the solenoid 57a of the
electromagnetic valve 57 and the duty ratio establishing section 88
outputs duty signals to the solenoid 69a of the electromagnetic
valve 69. That is, the clutch control unit 72 outputs ON-OFF
signals to the electromagnetic valve 57 so as to engage or
disengage the lock-up clutch 11 and also outputs duty signals to
the electromagnetic valve 69 so as to control the hydraulic
pressure for actuating the forward clutch 42. Thus, when the
vehicle is abruptly decelerated, a signal for setting the pilot
pressure of the pilot passage 68 at zero is outputted to the
solenoid 69a of the electromagnetic valve 69, and at the same time,
an OFF signal for setting the pilot pressure of the pilot passage
55a at zero is outputted to the solenoid 57a of the electromagnetic
valve 57. As a result, the forward clutch 42 and the lock-up clutch
11 are disengaged, thereby an occurrence of the engine stall can be
prevented. Further, when the accelerator pedal is depressed
immediately after the abrupt acceleration, since the forward clutch
42 is engaged again, an overrun of the engine can be prevented. In
this embodiment, whether the vehicle is in an abrupt acceleration
is judged based on a signal from the secondary pulley rotational
speed sensor 76, however the judgment of an abrupt acceleration may
be performed by an ABS operation signal. In this case, as shown in
FIG. 3, the deceleration judging section 85 receives signals from a
front wheel speed sensor 91 and a rear wheel speed sensor 92,
respectively and judges an abrupt acceleration of the vehicle.
Next, an operation of the control apparatus will be described with
reference to a flowchart in FIG. 4. First, at a step S1, it is
judged whether or not the vehicle is in a running mode, namely, the
selector lever is positioned at "D" or "Ds" range. If it is judged
that the vehicle is in a running mode, at a step S2 a hydraulic
pressure P.sub.c1 is supplied to the hydraulic piston 43 of the
forward clutch 42 to engage the forward clutch 42. The hydraulic
pressure P.sub.c1 is controlled according to a duty ratio of
electric current supplied from the clutch control unit 72 to the
solenoid 69a of the electromagnetic valve 69. Then, at a step S3,
it is judged whether or not a lock-up condition, that is, a running
condition under which the lock-up clutch 11 is engaged, is
satisfied. If the lock-up condition is satisfied, at a step S4 the
lock-up clutch 11 is engaged. Generally, the lock-up condition is
satisfied when the vehicle speed is larger than a specified value
and the changing rate of the engine speed is smaller than a
specified value. Thus, a signal is sent to the solenoid 57 of the
electromagnetic valve 57 to change the switch valve 56 from a
position indicated in FIG. 2 to another position. As a result, a
hydraulic pressure P.sub.c is fed to the apply chamber 11. On the
other hand, when the engagement condition is not satisfied, at a
step S5 the switch valve 56 is set at a position where the lock-up
clutch 11 is disengaged, namely, is set in a released condition. At
a step S6, it is judged whether or not an abrupt deceleration
control condition, that is, a running condition under which an
abrupt deceleration control is operated, is satisfied. If the
abrupt deceleration control condition is satisfied, at a step S7
the forward clutch 42 is released and at a step S8 the lock-up
clutch 11 is also released. The condition under which the abrupt
deceleration control is operated is that the brake switch 82 is
turned ON, the throttle opening angle sensor 77 detects a fully
closed throttle and the deceleration of the vehicle is larger than
a specified value V.sub.B. In case of a vehicle employing the
continuously variable transmission 13, since the vehicle speed can
be detected by a signal from the secondary pulley rotational speed
sensor 76, it can be detected whether the deceleration of the
vehicle is larger than the specified value V.sub.B or not, by
detecting a revolution number N.sub.s of the secondary pulley. For
example, the abrupt deceleration condition can be judged by
detecting that a differential of N.sub.s with respect to time has
exceeded the specified value V.sub.B, or a rate of change of the
vehicle speed has exceeded a certain value. Accordingly, when the
brake is operated, a signal is sent from the brake switch 82 to the
clutch control unit 72, a deceleration (dN.sub.s/dt) of the vehicle
is calculated based on a Ns signal from the secondary pulley
rotational speed sensor 76, and it is judged that the deceleration
is larger than the specified value V.sub.B (abrupt deceleration),
the electromagnetic valve 57 is deenergized and at the same time a
control signal of 100% duty ratio is sent to the electromagnetic
valve 69 for the slip pressure control. Thus, the forward clutch 42
is released and further the hydraulic pressure in the apply chamber
11a of the lock-up clutch 11 is drained outside through the oil
cooler 59, thereby an occurrence of the engine stall can be
prevented. The condition for performing the abrupt deceleration
control can be considered otherwise than described before. For
example, in case where the decrement of the engine speed N.sub.e
becomes larger than a specified value N.sub.B while the lock-up
clutch 11 is in an engagement condition, that is, in case of
dN.sub.e/dt>N.sub.B, the sudden deceleration control may be
performed. Further, in this case, the abrupt deceleration control
may be suspended when the engine speed N.sub.e is higher than a
specified value in consideration of the effect of engine brake. A
step S9 is for checking a restoring condition for canceling the
abrupt deceleration control and for restoring the engagement of the
forward clutch 42. While the condition is not satisfied, both
forward clutch and 42 and lock-up clutch 11 continue to be released
to prevent an engine stall. If the condition is satisfied, the
program returns to the step S1 and when the accelerator pedal is
depressed for acceleration immediately after the abrupt
deceleration, the forward clutch 42 is engaged again to prevent an
engine overrun. The abrupt deceleration control is canceled, when
either of the following conditions is satisfied; a case where the
throttle opening angle sensor 77 detects a depression of the
accelerator pedal, a case where the vehicle acceleration is larger
than a specified value, a case where the engine speed is larger
than a specified value, a case where a specified time (for example,
0.2 to 1 second) has elapsed after releasing the lock-up clutch 11
or a case where a difference between the engine speed N.sub.e and
the turbine speed N.sub.t is larger than a specified value, for
example N.sub.t/N.sub.p is 60 to 80%. The construction of the
forward and reverse changeover apparatus 12 is not limited to the
one shown in the embodiment of the present invention. Further, in
this embodiment, the automatic transmission is formed by a
continuously variable transmission but the control apparatus
according to the present invention can be applied to other types of
automatic transmissions. While the presently preferred embodiment
of the present invention has been shown and described, it is to be
understood that this disclosure is for the purpose of illustration
and that various changes and modifications may be made without
departing from the scope of the invention as set forth in the
appended claims. What is claimed is:
1. A control apparatus for an automatic transmission of a vehicle
having an engine, a torque converter, a turbine shaft, a forward
friction element for engaging or disengaging said turbine shaft
with said automatic transmission in a forward running direction and
a lock-up clutch for directly transmitting a rotation of said
engine to said turbine shaft, comprising: an abrupt deceleration
control means for disengaging said forward engagement element and
said lock-up clutch when an abrupt deceleration control condition
is satisfied; and a restoring means for canceling said abrupt
deceleration control means and for restoring said forward friction
element to an engagement state when a restoring condition is
satisfied.
2. The control apparatus according to claim 1, wherein said abrupt
deceleration control condition includes at least a condition in
which said vehicle is braked and a deceleration of said vehicle is
larger than a specified value.
3. The control apparatus according to claim 1, wherein said
restoring condition includes at least a condition in which said
engine is in an acceleration state.
Description
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
2. The present invention relates to a control apparatus for
controlling an operation of an automatic transmission for a
vehicle, and more particularly, to a control apparatus for
disengaging a lock-up clutch when an abrupt brake is applied in
order to prevent an engine stall.
3. 2. Background Art
4. Japanese Patent Application Laid-open No. Toku Kai-Hei 2-227342
discloses a drive system having a torque converter with a lock-up
clutch, a planetary gear type forward and reverse changeover
apparatus and a continuously variable transmission (CVT). The drive
system is designed to disengage the lock-up clutch of the torque
converter when an anti-lock brake (ABS) operates, that is, when the
wheel slip is properly controlled, so that an engine stall is
prevented.
5. However, particularly when a vehicle is abruptly braked on a
road surface having low friction coefficient, even if the vehicle
is equipped with ABS, depending upon braking conditions, there is a
possibility that a wheel is locked to stop the rotation before the
lock-up clutch is released and as a result an engine stall
occurs.
6. In order to solve this problem, Japanese Patent Application
Laid-open No. Toku-Kai-Hei 4-357357 proposes a drive system in
which both forward clutch and reverse brake of the forward and
reverse changeover apparatus are set to a disengagement condition.
However, releasing both of the forward clutch and reverse brake may
cause an overrun of the engine, in case where a driver depresses an
accelerator pedal to accelerate the vehicle immediately after an
abrupt braking.
SUMMARY OF THE INVENTION
7. It is an object of the present invention to provide a control
apparatus of an automatic transmission capable of preventing an
engine stall when an abrupt brake is applied and also capable of
preventing an overrun of the engine when an accelerator pedal is
depressed after the abrupt brake is applied. In order to attain the
object, the control apparatus for an automatic transmission of a
vehicle having a forward friction element for engaging or
disengaging a turbine shaft with the automatic transmission in a
forward running direction and a lock-up clutch for directly
transmitting a rotation of an engine to the turbine shaft,
comprises an abrupt deceleration control means for disengaging the
forward engagement element and the lock-up clutch when an abrupt
deceleration of the vehicle is detected, and a restoring means for
canceling the abrupt deceleration control means and for restoring
the forward friction element to an engagement state when an
accelerator pedal is depressed for acceleration.
BRIEF DESCRIPTION OF THE DRAWINGS
8. FIG. 1 is a skeleton diagram showing a drive system of an
automatic transmission having a torque converter with a lock-up
clutch;
9. FIG. 2 is a circuit diagram showing a hydraulic control circuit
for controlling the drive system of FIG. 1;
10. FIG. 3 is a block diagram showing control processes in a CVT
control unit and a clutch control unit; and
11. FIG. 4 is a flowchart showing a flow of control in a control
apparatus of an automatic transmission.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
12. Referring now to FIG. 1, reference numeral 1 denotes an engine
of which a crankshaft 2 is connected with a converter case 4 of a
torque converter 3 through a drive plate 5 and reference numeral 4a
denotes a pump impeller provided in the converter case 4. Reference
numeral 6 denotes a turbine runner disposed opposite to the pump
impeller 4a and connected with a turbine shaft 7. A stator 8 is
disposed between the pump impeller 4a and the turbine runner 6 and
is supported by an one-way clutch 10 attached to a stator
supporting shaft 9. A lock-up clutch 11 mounted on the turbine
shaft 7 is designed to engage or disengage with the drive plate 5.
The driving force of the engine 1 is transmitted to the turbine
shaft 7 through the torque converter 3 or the lock-up clutch
11.
13. An apply chamber 11a is provided on one side of the lock-up
clutch 11 and a release chamber 11b is provided on the other side
of the lock-up clutch 11. The torque converter is operative when
hydraulic pressure is supplied to the release chamber 11b and
circulated through the apply chamber 11a. On the other hand, the
lock-up clutch is engaged when hydraulic pressure is supplied to
the apply chamber 11a and hydraulic pressure of the release chamber
11b is reduced. Further, it is possible to apply a slip control to
the lock-up clutch 11 by regulating a pressure of the release
chamber 11a so as to cause a slip in the lock-up clutch 11.
14. The driving force of the turbine shaft 7 is transferred to a
primary shaft 14 of a continuously variable transmission 13 through
a forward and reverse changeover apparatus 12. The primary shaft 14
is connected with a primary pulley 15 which comprises a fixed
sheave 15a fixed to the primary shaft 14 and a moving sheave 15b
provided opposite to the fixed sheave 15a and moving slidably in
the axial direction on the primary shaft 14 through a ball spline
so as to vary the groove width of the pulley 15.
15. A secondary pulley 17 is mounted on a secondary shaft 16
provided in parallel with the primary pulley 14. The secondary
pulley 17 has a fixed sheave 17a fixed to the secondary shaft 16
and a moving sheave 17b moving slidably in the axial direction on
the secondary shaft 16 so as to vary the groove width of the pulley
17.
16. A drive belt 18 is looped over the primary and secondary
pulleys 15, 17 so as to transmit the driving force from the primary
pulley 15 to the secondary pulley 17. The rotating speed of the
secondary pulley 16 is continuously varied by means of changing the
winding radius of the respective pulleys 15, 17 by changing the
groove widths of both pulleys 15, 17.
17. In order to vary the groove width of the primary pulley 15, a
cylinder 22 is mounted on the primary shaft 14 so that a primary
oil chamber 21 is formed between the moving sheave 15b and the
cylinder 22, and in order to vary the groove width of the secondary
pulley 17, a plunger 24 is mounted on the secondary shaft 16 so
that a secondary oil chamber 23 is formed between the moving sheave
17b and the plunger 24.
18. The secondary shaft 16 is connected to an intermediate shaft
26a through gears 25a, 25b, a gear 26b mounted on the intermediate
shaft 26a meshes with a final reduction gear 28 of a differential
27 and the final reduction gear 28 drives wheels 30a and 30b
through the differential 27 and axles 29a and 29b.
19. Numeral 12 denotes a forward and reverse changeover apparatus,
which comprises a sun gear 31 secured to the turbine shaft 7, a
carrier 33 connected with the primary shaft 14, a pair of planetary
pinions 34, 35 rotatably mounted on the carrier 33 and meshing with
the sun gear 31 and a ring gear 32 provided around the planetary
pinions 34, 35 and meshing therewith. There is provided a reverse
brake 37 between a brake cylinder 36 fixed to a housing of the
forward and reverse changeover apparatus 12 and the ring gear 32
and the reverse brake 37 is actuated by a hydraulic piston 38.
20. The turbine shaft 7 is connected with a clutch drum 41 and a
forward clutch 42 is provided between the clutch drum 41 and the
carrier 33. Further, a hydraulic piston 43 is slidably mounted on
the clutch drum 41 to actuate the forward clutch 42. When a
hydraulic pressure is supplied to the hydraulic piston 43 to engage
the forward clutch 42, the rotation force of the turbine shaft 7 is
transmitted to the primary shaft 14 through the carrier 33 to
rotate the turbine shaft 14 in the same direction of the turbine
shaft 7. At this moment, since no hydraulic pressure is supplied to
the hydraulic piston 38, the reverse brake 37 is disengaged.
21. On the other hand, when a hydraulic pressure is supplied to the
hydraulic piston 38 under the condition of the forward clutch 42
disengaged, the reverse brake 37 is engaged to restrict the
rotation of the ring gear 32. Therefore, the rotation of the
turbine shaft 7 is transmitted to the carrier 33 through the pair
of planetary pinions 34, 35. Then, since the ring gear 32 is fixed,
the carrier 33 and the primary shaft 14 connected therewith rotate
in a reverse direction to that of the turbine shaft 7.
22. Further, an oil pump 44 is driven by the converter case 4 to
actuate hydraulic devices such as the primary pulley 15, the
secondary pulley 17, the reverse brake 37, the forward clutch 42
and the like.
23. Referring to FIG. 2, the oil pump 44 sucks oil from an oil pan
45 and discharges a hydraulic pressure from a discharge port. The
discharge port is connected through a secondary pressure passage 46
to the secondary oil chamber 23 for actuating the moving sheave 17b
of the secondary pulley 17 and is connected to a secondary pressure
port of a line pressure control valve 47. The line pressure control
valve 47 regulates a secondary pressure Ps supplied to the
secondary oil chamber 23 to a value corresponding to a driving
force of the drive belt 18. That is, when the engine output is
large, for example when a vehicle travels on an uphill grade or
makes a sharp acceleration, the secondary pressure P.sub.s is
raised to prevent a slip of the drive belt 18. When the engine
output is small, the secondary pressure P.sub.s is reduced so as to
save a loss of the oil pump 44.
24. The secondary pressure passage 46 is connected with a secondary
pressure port of a shift control valve 48. A primary pressure
passage 49 connected to a control pressure port of the shift
control valve 48 is connected to the primary oil chamber 21 for
actuating the moving sheave 15b of the primary pulley 15. A primary
pressure P.sub.p regulated by the shift control valve 48 is
supplied to the primary oil chamber 21. Since the regulated primary
pressure P.sub.p is obtained by reducing the secondary pressure
P.sub.s, it does not exceed the secondary pressure P.sub.s.
However, since the pressure receiving area of the primary oil
chamber 21 is designed to be larger than that of the secondary oil
chamber 23, the clamping force of the drive belt 18 is larger on
the primary pulley 15 side than on the secondary pulley 17 side.
Accordingly, the speed ratio can be varied continuously by changing
the groove width of the primary pulley 15 by means of controlling
the primary pressure so that the primary pressure becomes a value
corresponding to a target speed ratio and a target shift speed.
25. A selector lever 50 provided in the passenger compartment is
interconnected with a manual valve 51 and a reverse signal valve 52
to change over driving modes. A driver operates the selector lever
50 to select either of five ranges, "P" (parking) range, "R"
(reverse) range, "N" (neutral) range, "D" (drive) range and "Ds"
(sports drive). In coordination with the operation of the selector
lever 50, those valves 51, 52 take corresponding positions.
26. The secondary pressure passage 46 is connected to a clutch
pressure passage 54 through a clutch pressure control valve 53.
When the selector lever 50 is positioned at either of "N", "D" and
"Ds" ranges, the clutch pressure passage 54 communicates with a
pilot pressure passage 55 through the reverse signal valve 52.
Further, the pilot pressure passage 55 is connected to a pilot
chamber 56p of a switch valve 56 through a branch pressure passage
55a and an electromagnetic valve 57 and the switch valve 56 is
operated by energizing the electromagnetic valve 57.
27. The switch valve 56 has a lock-up changeover section 56a, an
oil cooler changeover section 56b and a lock-up release changeover
section 56c and these are constructed so as to operate
concurrently. FIG. 2 indicates a condition where no hydraulic
pressure is supplied to the pilot chamber 56p of the switch valve
56. When a hydraulic pressure is supplied to the pilot chamber 56p,
the switch valve 56 is changed over to other positions.
28. The lock-up changeover section 56a has two positions, one for
connecting an apply pressure passage 60 communicating with the
apply chamber 11a with an oil cooler 59 through a cooling passage
58, another for connecting the apply pressure passage 60 with the
clutch pressure passage 54. The oil cooler changeover section 56b
has two positions, one for connecting the cooling passage 58 with
the apply pressure passage 60, another for connecting a lubrication
oil pressure passage 61 communicating with a lubrication oil
pressure port of the line pressure control valve 47 with the
cooling passage 58. The lock-up release changeover section 56c has
two positions, one for connecting a release pressure passage 62
communicating with the release chamber 11b with the lubrication oil
pressure passage 61, another for connecting the release pressure
passage 62 with the clutch pressure passage 54 through a slip
pressure passage 63. The forward and reverse changeover section 56d
has two positions, one for connecting a changeover passage 64 with
the slip pressure passage 63, another for connecting the changeover
pressure passage 64 with the clutch pressure passage 54.
29. The hydraulic piston 38 of the reverse brake 37 is connected
with a brake activation pressure passage 65 and the hydraulic
piston 43 of the forward clutch 42 is connected with a clutch
activation pressure passage 66. The slip pressure passage 63 is
provided with a slip pressure control valve 67 for regulating a
slip pressure supplied to the slip pressure passage 63 to a desired
pressure in accordance with an outside pilot pressure fed to an
outside pilot chamber.
30. Further, in order to supply the outside pilot pressure to the
slip pressure control valve 67, there is provided a pilot pressure
passage 68 between an pilot port of the slip pressure control valve
67 and the clutch pressure passage 54. Further, there is provided
an electromagnetic valve 69 in the pilot pressure passage 68 in
order to control the pilot pressure. The electromagnetic valve 69
employs a duty solenoid valve in which the pilot pressure is
adjusted by varying duty ratios of electric current supplied to a
solenoid 69a. In this case, in place of the duty solenoid valve, a
proportional type electromagnetic relief valve may be used.
31. The slip control of the lock-up clutch 11 is performed in the
following manner:
32. When a signal is sent to the electromagnetic valve 57 to feed a
hydraulic pressure to the pilot chamber 56p of the switch valve 56,
the release chamber 11b of the lock-up clutch 11 communicates with
the slip pressure 63. Then, the pressure of the release chamber 11b
is adjusted through the slip pressure passage 63 by varying the
duty ratio between 0% and 100%.
33. When the manual valve 51 is positioned at "D" range or "Ds"
range by operating the selector lever 50, the changeover pressure
passage 64 communicates with the clutch activation pressure passage
66 and as a result the forward clutch 42 is engaged by a hydraulic
pressure from the clutch pressure passage 54. On the other hand,
the manual valve is positioned at "R" range, the changeover
pressure passage 64 communicates with the brake activation pressure
passage 65 and as a result the reverse brake 37 is engaged by a
hydraulic pressure from the clutch pressure passage 54.
34. When the manual valve 51 is positioned at other ranges, both
forward clutch 42 and reverse brake 37 are disengaged.
35. As shown in FIG. 2, since a clutch pressure P.sub.c is supplied
to the electromagnetic valve 57 at respective ranges "N", "D" and
"Ds", under the ranges "D" and "Ds", the switch valve 56 is changed
over by sending a signal to the electromagnetic valve 57 and as a
result the clutch pressure P.sub.c is supplied to the apply chamber
11a of the torque converter. Further, a hydraulic pressure from the
slip pressure control valve 67 communicates with the release
pressure passage 62 and the slip pressure reduced by the
electromagnetic valve 69 brings the lock-up clutch 11 into a
lock-up condition. At this moment, the pilot pressure activates the
clutch pressure control valve 53 through the pilot pressure passage
55 to generate a hydraulic pressure P.sub.c1 for activating the
forward clutch 42. This hydraulic pressure P.sub.c1 is supplied to
the forward clutch 42 through the clutch activation pressure
passage 66.
36. At "R" or "P" range, no hydraulic pressure is supplied to the
pilot pressure passage 55. Under this condition, the clutch
pressure control valve 53 generates a hydraulic pressure P.sub.c2
to be supplied to the reverse brake 37. The hydraulic pressure
P.sub.c2 is established at a higher pressure than the pressure
P.sub.c1 to be supplied to the forward clutch 42
(P.sub.c1<P.sub.c2). Thus, at reverse range, a high brake
pressure can be secured.
37. Reference numeral 71 denotes a CVT control unit for sending
control signals to the line pressure control valve 47 and the shift
control valve 48 and reference numeral 72 denotes a clutch control
unit for sending control signals to the electromagnetic valves 57,
69. These control units 71, 72 are included in a TCU (transmission
control unit) 73 integrally.
38. Referring to FIG. 3, the CVT control unit 71 includes a
micro-computer which is connected to miscellaneous sensors such as
an engine speed sensor 74, a primary pulley rotational speed sensor
75, a secondary pulley rotational speed sensor 76 and a throttle
opening angle sensor 77. Signals from these sensors are sent to a
continuously variable transmission control section 78 from which
control signals are sent to respective solenoids of the line
pressure control valve 47 and the shift control valve 48 through
respective duty ratio establishing sections 79a, 79b.
39. The clutch control unit 72 includes a micro-computer which is
connected with miscellaneous sensors, in addition to the aforesaid
sensors 74 to 77, such as a selector lever position sensor 81, and
a brake switch 82. In a drive range judging section 83, the current
drive range is judged based on signals from the selector lever
position sensor 81. In a lock-up engagement judging section 84, it
is judged based on the signals from the aforesaid sensors 74 to 77
whether or not the lock-up clutch 11 should be engaged. Further, in
a deceleration judging section 85, it is judged based on the
signals from the aforesaid sensors 74, 76, 77 and signals from the
brake switch 82, the front wheel speed sensor 91 and the rear wheel
speed sensor 92, whether or not the vehicle is in an abrupt
deceleration.
40. Based on output signals from the drive range judging section
83, the lock-up engagement judging section 84 and the deceleration
judging section 85, a forward clutch and lock-up clutch control
section 86 outputs control signals to a switching section 87 and a
duty ratio establishing section 88. The switching section 87
outputs ON-OFF signals to the solenoid 57a of the electromagnetic
valve 57 and the duty ratio establishing section 88 outputs duty
signals to the solenoid 69a of the electromagnetic valve 69.
41. That is, the clutch control unit 72 outputs ON-OFF signals to
the electromagnetic valve 57 so as to engage or disengage the
lock-up clutch 11 and also outputs duty signals to the
electromagnetic valve 69 so as to control the hydraulic pressure
for actuating the forward clutch 42.
42. Thus, when the vehicle is abruptly decelerated, a signal for
setting the pilot pressure of the pilot passage 68 at zero is
outputted to the solenoid 69a of the electromagnetic valve 69, and
at the same time, an OFF signal for setting the pilot pressure of
the pilot passage 55a at zero is outputted to the solenoid 57a of
the electromagnetic valve 57. As a result, the forward clutch 42
and the lock-up clutch 11 are disengaged, thereby an occurrence of
the engine stall can be prevented. Further, when the accelerator
pedal is depressed immediately after the abrupt acceleration, since
the forward clutch 42 is engaged again, an overrun of the engine
can be prevented.
43. In this embodiment, whether the vehicle is in an abrupt
acceleration is judged based on a signal from the secondary pulley
rotational speed sensor 76, however the judgment of an abrupt
acceleration may be performed by an ABS operation signal. In this
case, as shown in FIG. 3, the deceleration judging section 85
receives signals from a front wheel speed sensor 91 and a rear
wheel speed sensor 92, respectively and judges an abrupt
acceleration of the vehicle.
44. Next, an operation of the control apparatus will be described
with reference to a flowchart in FIG. 4.
45. First, at a step S1, it is judged whether or not the vehicle is
in a running mode, namely, the selector lever is positioned at "D"
or "Ds" range. If it is judged that the vehicle is in a running
mode, at a step S2 a hydraulic pressure P.sub.c1 is supplied to the
hydraulic piston 43 of the forward clutch 42 to engage the forward
clutch 42. The hydraulic pressure P.sub.c1 is controlled according
to a duty ratio of electric current supplied from the clutch
control unit 72 to the solenoid 69a of the electromagnetic valve
69.
46. Then, at a step S3, it is judged whether or not a lock-up
condition, that is, a running condition under which the lock-up
clutch 11 is engaged, is satisfied. If the lock-up condition is
satisfied, at a step S4 the lock-up clutch 11 is engaged.
Generally, the lock-up condition is satisfied when the vehicle
speed is larger than a specified value and the changing rate of the
engine speed is smaller than a specified value.
47. Thus, a signal is sent to the solenoid 57 of the
electromagnetic valve 57 to change the switch valve 56 from a
position indicated in FIG. 2 to another position. As a result, a
hydraulic pressure P.sub.c is fed to the apply chamber 11. On the
other hand, when the engagement condition is not satisfied, at a
step S5 the switch valve 56 is set at a position where the lock-up
clutch 11 is disengaged, namely, is set in a released
condition.
48. At a step S6, it is judged whether or not an abrupt
deceleration control condition, that is, a running condition under
which an abrupt deceleration control is operated, is satisfied. If
the abrupt deceleration control condition is satisfied, at a step
S7 the forward clutch 42 is released and at a step S8 the lock-up
clutch 11 is also released.
49. The condition under which the abrupt deceleration control is
operated is that the brake switch 82 is turned ON, the throttle
opening angle sensor 77 detects a fully closed throttle and the
deceleration of the vehicle is larger than a specified value
V.sub.B.
50. In case of a vehicle employing the continuously variable
transmission 13, since the vehicle speed can be detected by a
signal from the secondary pulley rotational speed sensor 76, it can
be detected whether the deceleration of the vehicle is larger than
the specified value V.sub.B or not, by detecting a revolution
number N.sub.s of the secondary pulley. For example, the abrupt
deceleration condition can be judged by detecting that a
differential of N.sub.s with respect to time has exceeded the
specified value V.sub.B, or a rate of change of the vehicle speed
has exceeded a certain value.
51. Accordingly, when the brake is operated, a signal is sent from
the brake switch 82 to the clutch control unit 72, a deceleration
(dN.sub.s/dt) of the vehicle is calculated based on a Ns signal
from the secondary pulley rotational speed sensor 76, and it is
judged that the deceleration is larger than the specified value
V.sub.B (abrupt deceleration), the electromagnetic valve 57 is
deenergized and at the same time a control signal of 100% duty
ratio is sent to the electromagnetic valve 69 for the slip pressure
control. Thus, the forward clutch 42 is released and further the
hydraulic pressure in the apply chamber 11a of the lock-up clutch
11 is drained outside through the oil cooler 59, thereby an
occurrence of the engine stall can be prevented.
52. The condition for performing the abrupt deceleration control
can be considered otherwise than described before. For example, in
case where the decrement of the engine speed N.sub.e becomes larger
than a specified value N.sub.B while the lock-up clutch 11 is in an
engagement condition, that is, in case of dN.sub.e/dt>N.sub.B,
the sudden deceleration control may be performed. Further, in this
case, the abrupt deceleration control may be suspended when the
engine speed N.sub.e is higher than a specified value in
consideration of the effect of engine brake.
53. A step S9 is for checking a restoring condition for canceling
the abrupt deceleration control and for restoring the engagement of
the forward clutch 42. While the condition is not satisfied, both
forward clutch and 42 and lock-up clutch 11 continue to be released
to prevent an engine stall. If the condition is satisfied, the
program returns to the step S1 and when the accelerator pedal is
depressed for acceleration immediately after the abrupt
deceleration, the forward clutch 42 is engaged again to prevent an
engine overrun.
54. The abrupt deceleration control is canceled, when either of the
following conditions is satisfied; a case where the throttle
opening angle sensor 77 detects a depression of the accelerator
pedal, a case where the vehicle acceleration is larger than a
specified value, a case where the engine speed is larger than a
specified value, a case where a specified time (for example, 0.2 to
1 second) has elapsed after releasing the lock-up clutch 11 or a
case where a difference between the engine speed N.sub.e and the
turbine speed N.sub.t is larger than a specified value, for example
N.sub.t/N.sub.p is 60 to 80%.
55. The construction of the forward and reverse changeover
apparatus 12 is not limited to the one shown in the embodiment of
the present invention. Further, in this embodiment, the automatic
transmission is formed by a continuously variable transmission but
the control apparatus according to the present invention can be
applied to other types of automatic transmissions.
56. While the presently preferred embodiment of the present
invention has been shown and described, it is to be understood that
this disclosure is for the purpose of illustration and that various
changes and modifications may be made without departing from the
scope of the invention as set forth in the appended claims.
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