Shift control system for an automatic transmission

A shift control system for an automatic transmission of a vehicle controls the output of the engine according to the running condition of the vehicle when gear-shifting operation of the automatic transmission is detected. A shifting condition signal representing an actual value of the running condition during a gear-shifting operation is compared with a reference value signal representing a reference value of the running condition during the gear-shifting operation, and a correction signal is output on the basis of the result of the comparison. The controlled variable of the engine output power is corrected on the basis of the correction signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a shift control system for an automatic 
transmission. 
2. Description of the Prior Art 
An automatic transmission generally comprises a torque converter and a 
multi-gear ratio transmission gear mechanism connected to the torque 
converter. The transmission gear mechanism is provided with hydraulic 
frictional elements which are selectively applied and released in order to 
shift transmission gear ratios. 
When the shift-time taken to shift one gear ratio to another is too long, 
the driver feels uncomfortable and the running performance of the vehicle 
deteriorates. On the other hand, when the shift-time is too short, shift 
shock occurs. Accordingly, the shift-time should be carefully controlled. 
In the shift control system disclosed in U.S. Pat. No. 4,283,970, the line 
pressure is controlled in order to adjust the shift-time. That is, in the 
shift control system, the basis line pressure is corrected depending on 
the length of the shift-time. 
In the shift control system disclosed in Japanese Unexamined Patent 
Publication No. 61(1986)-104128, the engine output power is reduced for a 
predetermined time when the transmission shifts in order to suppress shift 
shock. 
Though the system which corrects the basic line pressure is advantageous in 
view of the suppression of the shift shock, it needs additional line 
pressure control means such as solenoids, which results in substantial 
cost increases. Further, the system which reduces the engine output power 
is for suppressing fluctuation in torque during the gear-shifting and does 
not control the shift-time, and is not satisfactory in view of an optimal 
shift control. 
SUMMARY OF THE INVENTION 
In view of the foregoing observations and description, the primary object 
of the present invention is to provide a shift control system for an 
automatic transmission in which the shift-time can be controlled to an 
optimal value without increasing the cost. 
The present invention provides a shift control system for an automatic 
transmission of a vehicle which controls the output of the engine 
according to the running condition of the vehicle when a gear-shifting 
operation of the automatic transmission is detected. In the present 
invention, a signal is generated representing an actual value of the 
running condition of the vehicle during a gear-shifting operation. In 
addition, a reference signal is output which represents a target value 
signal of the running condition during the gear-shifting operation. A 
correction signal is then output based on a comparison of the shifting 
condition signal and the target value signal. The engine output power is 
accordingly corrected, by correction of the controlled variable of the 
engine output power on the basis of a correction signal.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, a front-engine front-drive vehicle is provided with a shift 
control system in accordance with an embodiment of the present invention. 
An engine 1 has four cylinders 2 into which air-fuel mixture is fed 
through an intake passage 4. The intake passage 4 is provided with a 
throttle valve 3. Reference numerals 5 to 8 respectively denote spark 
plugs, a distributor, an ignition coil and an ignition controller which 
form an ignition system. Reference numeral 9 denotes an exhaust passage. 
The output power of the engine 1 is transmitted to an automatic 
transmission 10 through a crankshaft or the output shaft of the engine 1. 
The engine output torque thus transmitted to the automatic transmission 10 
is further transmitted to front wheels 13 through a differential gear unit 
11 and an axle 12. 
The automatic transmission 10 has a torque converter 14, a multi-gear ratio 
transmission gear mechanism 20 and a hydraulic circuit 30 which provides 
hydraulic pressure to the torque converter 14 and the transmission gear 
mechanism 20. The transmission gear mechanism 20 has planetary-gear sets 
and provides four forward speeds and one reverse. 
Further the vehicle is provided with an engine control unit 100 and a shift 
control unit 200. 
Into the engine control unit 100, an engine speed sensor 51 inputs an 
engine speed signal Sn, a crank angle sensor 52 inputs a crank angle 
signal Sc, a water temperature sensor 53 provided on a cylinder block 1b 
inputs a water temperature signal Sw which represents the temperature of 
engine cooling water Tw, a knock sensor 54 inputs a knock signal Sk which 
represents the intensity of engine knock, a throttle position sensor 55 
inputs a throttle opening signal St and an intake vacuum sensor 56 
provided in the intake passage 4 downstream of the throttle valve 3 inputs 
an intake vacuum signal Sb. Further other signals Sx required for control 
of the engine 1 are input into the engine control unit 100. The engine 
control unit 100 sets an effective ignition advance angle according to 
those signals and shift-related ignition retardation pulse signal Pj and a 
shift information signal Cs which are input from the shift control unit 
200, and outputs an ignition timing control signal Cq to the ignition 
controller 8 at the time which corresponds to the effective ignition 
advance angle. The secondary winding of the ignition coil 7 sends a 
high-voltage surge to the spark plugs 5 through the distributor 6 at the 
time corresponding to the ignition timing control signal Cq. 
The shift control unit 200 receives the water temperature signal Sw from 
the water temperature sensor 53, the throttle opening signal St from the 
throttle position sensor 55, a turbine speed signal Su from a turbine 
speed sensor 57, a vehicle speed signal Sv from a vehicle speed sensor 58, 
and a range signal Ss representing th position of the shift lever from the 
shift position sensor 59. The shift control unit 200 further receives 
other signals Sy required for control of the automatic transmission 10. 
The shift control unit 200 develops drive signals Ca, Cb, Cc and Cd on the 
basis of those signals and selectively outputs the drive signals to 
solenoid valves 61, 62, 63 and 64 which regulate the hydraulic pressures 
applied to various clutches and brakes in the transmission gear mechanism 
20, thereby causing the automatic transmission 10 to shift to a desired 
gear speed. Further the shift control unit 200 develops a drive signal Ce 
and selectively outputs it to a solenoid valve 65 which applies and 
releases hydraulic pressure to and from a lockup clutch. 
The shift control unit 200 has a built-in memory and a shift pattern map 
shown in FIG. 2 is stored in the built-in memory. The shift control unit 
200 refers the throttle opening Th and the vehicle speed V as respectively 
represented by the signals St and Sv to shift lines a, b, c, d, e and f, 
and determines whether the upshifting condition or the downshifting 
condition is satisfied. Further, the shift control unit 200 outputs to the 
engine control unit 100 the shift information signal Cs which represents 
the gear-speed to which the automatic transmission 10 is to shift and the 
final engine output torque reduction T by which the engine output torque 
is to be reduced. The shift lines a, b and c are 1-2, 2-3 and 3-4 upshift 
lines, respectively. The shift lines d, e and f are 2-1, 3-2 and 4-3 
downshift lines, respectively. 
The engine control unit 100 sets the basic ignition advance angle on the 
basis of the engine speed and the intake vacuum as represented by the 
signals Sn and Sb. Further, when the shift-related ignition retardation 
pulse signal Pj is fed to the engine control unit 100 from the shift 
control unit 200, the engine control unit 100 sets a shift-related 
correction value for retarding the ignition timing from the basic ignition 
timing which corresponds to the basic ignition advance angle, thereby 
suppressing shift shock which occurs in response to gear-shifting 
operation of the automatic transmission 10. Further, the engine control 
unit 100 determines a shift completion time correction value on the basis 
of the final engine output torque reduction T which is a correction signal 
obtained from the shift information signal output from the shift control 
unit 200, the shift completion time correction value being for correcting 
the shift-related correction value and thereby correcting the completion 
time of the gear-shifting operation. That is, the effective ignition 
advance angle is determined on the basis of the basic ignition advance 
angle, the shift-related correction value and the shift completion time 
correction value, and the completion time of the gear-shifting operation 
is adjusted according to the shift completion time correction value which 
is determined on the basis of the final engine output torque reduction T. 
As will be described later, the final engine output torque reduction T is 
determined on the basis of a basic engine output torque reduction T.sub.B 
and a final learning value .DELTA.T1. The term learning value is utilized 
since the learning values are modified or adjusted according to whether 
the present engine output torque is too large or too small so that the 
final engine output torque T is optimally set. The basic engine output 
torque reduction T.sub.B is corrected according to the rate of change of 
the engine speed at the time a predetermined time after the start of the 
gear-shifting operation. This point will be described in more detail with 
reference to FIG. 4. In FIG. 3, curves .alpha., .beta., .epsilon. 
represent different manners of change of the engine speed after a 1-2 
upshift command signal is generated. 
When it is assumed that a 1-2 upshift command signal is selectively output 
to the solenoids 61, 62, 63 and 64 at time t1, due to the delay in 
response, the rate of change of the engine speed does not substantially 
change for a certain time after the time t1. At time t2, switching of the 
friction elements in the transmission gear mechanism 20 is actually 
started, that is, gear-shifting operation is actually started, and at the 
time t2, the engine speed which has been increasing begins to decrease. 
Aiter the time t2, the switching of the friction elements progresses and 
the engine speed continues to decrease. The switching of the friction 
elements is completed at time t3, when the engine speed which has been 
decreasing comes to increase. 
In this particular embodiment, the predetermined time, which determines the 
time the rate of change of the engine speed which is used for correcting 
the basic engine output torque reduction T.sub.B, is 0.7 seconds. That is, 
in this particular embodiment, the basic engine output torque reduction Ts 
is corrected according to the rate of change of the engine speed at the 
time 0.7 seconds after the start of the gear-shifting operation (the time 
t2 in FIG. 3). The basic engine output torque reduction T.sub.B is 
corrected so that the switching of the friction elements is completed just 
at the time 0.7 seconds after the start of the gear-shifting operation. 
From this viewpoint, the curves .alpha., .beta., .gamma. are regarded as 
follows. The curve u indicates that the gear-shifting has been effected in 
an optimal manner. That is, the gear-shifting operation is completed at 
the time t4 and the rate of change of the engine speed becomes 
substantially 0 at the time t4. In other words, when the final engine 
output torque reduction T is optimally set, the engine speed changes in 
the manner shown by the curve .alpha.. On the other hand, the curve .beta. 
indicates that the gear-shifting operation is prematurely completed before 
the time t4. In this case, the engine output torque is so small and slip 
of the friction elements is so small that the shift-time becomes too 
short. Accordingly, in this case, the basic engine output torque reduction 
T.sub.B is corrected so that the final engine output torque reduction T 
becomes smaller. The curve .gamma. indicates that the gear-shifting 
operation is competed after the time t4. In this case, the engine output 
torque is so large and slip of the friction elements is so large that the 
shift-time becomes too long. Accordingly, in this case, the basic engine 
output torque reduction T.sub.B is corrected so that the final engine 
output torque reduction T becomes larger. 
That the gear-shifting operation is effected in which of the manners shown 
by the curves .alpha., .beta., .gamma. can be known by detecting the rate 
of change of the engine speed at the time t4. That is, that the rate of 
change of the engine speed at the time t4 is substantially 0 indicates 
that the gear-shifting is effected in the manner shown by the curve 
.alpha., which is the best. That the rate of change of the engine speed at 
the time t4 is of a positive value larger than a predetermined value 
indicates that the gear-shifting is prematurely completed (in the manner 
shown by the curve .beta.), and that the rate of change of the engine 
speed at the time t4 is of a negative value smaller than a predetermined 
value indicates that the gear-shifting is completed too late (in the 
manner shown by the curve .gamma.). 
The operation of the shift control unit 200 will be described with 
reference to t-e flow charts shown in FIGS. 4 and 5, hereinbelow. 
In step S1, the shift control unit 200 reads the signals from the sensors. 
Then he shift control unit 200 determines the basic engine output torque 
reduction T.sub.B according to the map stored therein on the basis of the 
throttle opening Th and the engine speed N. (step S2). 
In the next step S3, the shift control unit 200 corrects a basic learning 
value .DELTA.To (determined in the manner described later) according to 
the manner of gear-shifting operation and the throttle opening Th and 
determines the final learning value .DELTA.Tl. The basic learning value 
.DELTA.To is determined on the basis of the manners of gear-shifting 
operation in 1-2 upshift at a predetermined throttle opening Th (35 to 40% 
as will be described later), and in the case of the gear-shifting 
operations under other conditions, the basic learning value .DELTA.To is 
corrected by a correction coefficient (or a correction value) which is 
picked from a correction coefficient map stored in the shift control unit 
200 in advance. 
In step S4, the shift control unit 200 adds together the basic engine 
output torque reduction T.sub.B obtained in step S2 and the final learning 
value .DELTA.T1 obtained in step S3 and calculates the final engine output 
torque reduction T. Then the shift control unit 200 outputs the final 
engine output torque reduction T to the engine control unit 100 in step 
S5. The engine control unit 100 determines the effective ignition advance 
angle on the basis of the final engine output torque reduction T upon 
receipt thereof. 
In step S6, the shift control unit 200 determines whether the automatic 
transmission 10 is to be caused to shift according to the shift pattern 
map shown in FIG. 2. Then according to the result of the determination, 
the shift control unit 200 selectively outputs a shift command signal to 
the solenoid valves 61, 62, 63 and 64 in step S7. 
In step S8, the shift control unit 200 determines whether 1-2 upshift is to 
be effected. When the answer to this question is NO, the shift control 
unit 200 directly returns to step S1, and otherwise the shift control unit 
200 determines the basic learning value .DELTA.To in step S9. 
FIG. 5 is the flow chart illustrating in detail the operation of the shift 
control unit 200 for determining the basic learning value .DELTA.To in 
step S9. First the shift control unit 200 determines in step S21 whether 
the throttle opening Th is in the range of 35 to 40%, and when the 
throttle opening Th is in the range of 35 to 40%, the shift control unit 
200 detects in step S22 the time t2 (FIG. 3) at which the gear-shifting 
operation is actually started. Then the shift control unit 200 determines 
0.7 seconds after the time t2 (at the time t4 in FIG. 3) whether the 
change of the throttle opening Th at that time is substantially 0. (steps 
S22 and S23) In this particular embodiment, when the change of the 
throttle opening Th is no more than 3 to 4%, it is considered that the 
change of the throttle opening Th is substantially 0. 
When the answer to the question in step S24 is YES, the shift control unit 
200 calculates the rate of change X1 of the engine speed N at the time t4, 
and determines whether the rate of change X1 is within a predetermined 
range (A.ltoreq.X1.ltoreq.b, a&lt;0, b&gt;0).) (steps S25 and S26) When the rate 
of change X1 is within the predetermined range, it is considered that the 
rate of change X1 is substantially 0. 
When it is determined in step S26 that the rate of change X1 is not within 
the predetermined range, the shift control unit 200 further determines in 
step S27 whether the rate of change X1 is larger than the value b. That 
the answer to the question in step S27 is YES means that the gear-shifting 
operation is done in the manner represented by the curve .beta. and the 
present engine output torque is too small. Accordingly, when the answer to 
the question in step S27 is YES, the shift control unit 200 subtracts a 
predetermined correction value d (d&gt;0) from the present learning value 
.DELTA.To so that the final engine output torque reduction ratio T is 
reduced. (step S28) On the other hand, that the answer to the question in 
step S27 is NO means that the gear-shifting operation is done in the 
manner represented by the curve .gamma. and the present engine output 
torque is too large. Accordingly, when the answer to the question in step 
S27 is NO, the shift control unit 200 adds the predetermined correction 
value d (d&gt;0) to the present learning value .DELTA.To so that the final 
engine output torque reduction T is increased. (step S29) 
The learning value .DELTA.To determined in step S28 or S29 is substituted 
for the current learning value and stored in step S30. The learning value 
.DELTA.To stored in step S30 is used for determining the final learning 
value .DELTA.T1 in step S3 in FIG. 4. 
That the answer to the question in step S26 is YES means that the present 
engine output torque is optimal. Accordingly, in this case, the shift 
control unit 200 directly returns as indicated in FIG. 4, ready for 
reading the next set of data signals from the sensors in subsequent 
shifting operations. When the answer to the question in step S21 or S24 is 
NO, the learning condition has not been satisfied, and accordingly, the 
shift control unit 200 returns to the position indicated in FIG. 4, 
without executing the learning steps. 
Though, in the embodiment described above, the engine output power is 
adjusted by controlling the ignition advance angle in order to control the 
completion time of gear-shifting operation, the engine output power may be 
adjusted by controlling one or more of the quantity of fuel to be fed to 
the engine, the supercharging pressure and the quantity of intake air. 
FIG. 6 shows a modification of the steps for determining the learning value 
.DELTA.To (steps S26 to S30 in FIG. 5). In the flow chart shown in FIG. 6, 
the learning value .DELTA.To is corrected by steps including steps S41, 
S42 and S43 when it is determined that the gear-shifting operation is done 
in the manner represented by the curve .beta.. On the other hand, when it 
is determined that the gear-shifting operation is done in the manner 
represented by the curve .gamma., the learning value .DELTA.To is 
corrected on the basis of the rate of change X2 of the engine speed at the 
time 0.3 seconds after the time t4 (time t5 FIG. 3). This is because the 
manner of gear-shifting can be like that represented by the curve .gamma. 
when the vehicle ascends a steep slope even if the line pressure is 
proper. That is, when it is determined that the gear-shifting operation is 
done in the manner represented by the curve .gamma., the shift control 
unit 200 calculates the rate of change X2 of the engine speed after 0.3 
seconds lapses after the time t4 when the rate of change of the throttle 
opening Th is substantially 0. (steps S44, S45 and S46) Then the shift 
control unit 200 determines in step S47 whether the value obtained by 
subtracting the rate of change X2 of the engine speed at the time t5 from 
the rate of change X1 at the time t4 is larger than a predetermined value 
c. That is, in step S47, the shift control unit 200 determines whether the 
engine speed has not fallen between the time t4 and the time t5. When it 
is determined in step S47 that the value obtained by subtracting the rate 
of change X2 of the engine speed at the time t5 from the rate of change X1 
at the time t4 is larger than the predetermined value c, the shift control 
unit 200 determines the vehicle is ascending a slope and directly returns 
without determining the learning value .DELTA.To. 
When it is determined in step S47 that the value obtained by subtracting 
the rate of change X2 of the engine speed at the time t5 from the rate of 
change X1 at the time t4 is not larger than the predetermined value c, the 
shift control unit 200 determines in step S48 whether the remainder is 
smaller than 0. (In the case represented by the curve .gamma., the rate of 
change X1 is negative and the rate of change X2 is positive.) When the 
answer to the question in step S48 is YES, the shift control unit 200 sets 
the learning value .DELTA.To to the value obtained by adding the 
predetermined correction value d (d&gt;0) to the present learning value 
.DELTA.To. (step S49) The learning value .DELTA.To determined in step S49 
is stored in step S50. 
As can be understood from the description above, in accordance with this 
embodiment, the time to be watched by a timer can be a predetermined 
particular time interval, e.g., a predetermined time interval after the 
start of gear-shifting operation, and accordingly, load on the control is 
minimized. Further, the engine speed sensor 51 for detecting the engine 
speed is normally provided in the automatic transmission, and accordingly 
additional detecting means is not required. 
Though in the embodiment described above, said predetermined time is 
determined on the basis of the time at which the engine speed actually 
begins to change after the shift command signal is generated, the 
predetermined time may be determined on the basis of the time at which the 
shift command signal is generated. In such a case the predetermined time 
should be determined taking into account the delay in response. 
Further instead of detecting the engine speed, other rotational speeds such 
as the rotational speed of the output shaft of the torque converter 14 may 
be detected.