Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1999-03-18
2001-06-05
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S056000, C477S031000, C477S034000
Reexamination Certificate
active
06243637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to techniques for controlling the automatic transmission used in automobiles, and particularly to a technique for electronically controlling the working oil pressure on one or more clutches that is caused to act at the time of gear shifting.
The automatic transmission generally includes a torque converter coupled with the output shaft of engine, gear units that are connected to the output shaft of the torque converter and have a plurality of driving ranges, and at least two clutches that are acted when the automatic transmission makes gear shifting. Most of the clutches for use in automatic transmission are generally multiple-disk clutches. The gear shifting is performed during the interval in which one clutch is disengaged and the other one is engaged. The clutch is generally driven by oil pressure. Since the transfer torque is changed by the change of the working oil pressure on the engaged clutch, it is important to control the oil pressure of clutch.
A conventional example is given in U.S. Pat. No. 4,922,424 which describes an automatic transmission control for disengaging and engaging clutches by electronically controlling the working oil pressure of clutch. According to this US patent, control values for use in controlling the working oil pressure of the engaged clutch at the time of upshifting and the working oil pressure of the disengaged clutch at the time of downshifting are calculated from a predetermined functional equation based on engine speed, turbine speed and oil pump capacity coefficient of torque converter. The engine speed is the input shaft speed of torque converter, the turbine speed is the output shaft speed of torque converter, and the pump capacity coefficient is determined by the characteristics of the torque converter. The control technique in this US patent enables the working oil pressure of clutch to be correctly and precisely controlled and the transfer torque of clutch to be controlled most suitably to the driving condition of car even though the automatic transmission is changed in its performance after a long time usage.
FIG. 12A
is a signal diagram to which reference is made in explaining the controlled operation of the oil pressure type clutch that makes automatic shifting in the conventional automatic transmission. It is assumed that after the car driver depresses the accelerator pedal and makes the car reach a desired cruising speed, he keeps the accelerator pedal as it stands as shown in
FIG. 12A
by the solid line (a). Under this condition, a shift control command (at (b) in
FIG. 12A
) is generated according to a shift control program that is determined by the car's speed, and the accelerator pedal angle or throttle opening. The automatic transmission has a shift control program as, for example, shown in FIG.
12
B. The curve shown by
1
→
2
shows the position in which a shift control command to change from the first to second gear is produced. Similarly, the upshifting command curves are shown for the shifting from the second to third, and third to fourth gear. The downshifting command curves are not shown.
When a shift control command (at (b) of
FIG. 12A
) occurs at time t
1
ordering to shift from the second to third gear, the disengaged side oil pressure (not shown) that is applied from the oil pump to the disengaged clutch is reduced. At the same time, the engaged side oil pressure (at (f) of
FIG. 12A
) to be applied to the engaged clutch is increased. This engaged side oil pressure (f) is generated by a hydraulic control system according to an engaged side oil pressure command value ((e) of FIG.
12
A). When the engaged side oil pressure (f) is increased enough at time t
2
, the shifting operation is started. The interval from time t
2
to time t
5
is the target shifting time, within which the shifting operation is required to complete.
According to the conventional example mentioned above, as indicated by the solid line curves in
FIG. 12A
when the accelerator pedal is kept at a constant angle during the shifting operation, the shifting operation from the second to third gear is completed at the target time t
5
, and the turbine speed ((c) of
FIG. 12A
) is reduced to a low value. However, if the accelerator pedal is further depressed to accelerate at time t
3
in the process of the shifting operation, the shifting interval exceeds the target time to extend to time t
6
at which the shifting operation ends, as indicated by the broken line. This extension will cause the clutch to wear away or break down, and reduce the performance of the automatic transmission.
SUMMARY OF THE INVENTION
The inventors of this application have found that the delay of this shifting operation is ascribed to the delay of the response of the oil pressure system, and developed a novel control technique for automatic transmission that allows the shifting operation to complete without delay even if the oil pressure system has a response delay.
According to the prior art, the values of the engaged side oil pressure command ((e) of
FIG. 12A
) are decided by the values of the required transfer torque of clutch that are determined by the values of the actual turbine torque of torque converter (the output shaft torque of torque converter) as shown in
FIG. 12A
at (d). If the accelerator pedal is kept depressed a constant amount, the required transfer torque of clutch is not changed, and thus the actual oil pressure converges at the oil pressure command value within the target time even if there is a delay (period of time from t
1
to t
2
) with which the oil pressure system responds to the oil pressure command to provide the actual oil pressure fitted to the command.
However, when the engine torque (load) is increased by acceleration operation, the turbine torque increases, and thus the oil pressure command value is changed in accordance with the required transfer torque of clutch that is increasing. There are, however, a delay with which the actual engine torque is changed in response to the acceleration operation (operation of accelerator pedal), and a response delay of the oil pressure system. Thus, the actual oil pressure does not immediately follow a new oil pressure command value that has been determined on the basis of the increased turbine torque. When the oil pressure is not raised enough relative to the increased turbine torque, the transfer torque of clutch is insufficient, allowing unnecessary slip of clutch to occur. Therefore, the shifting time is increased as shown in
FIG. 12A
by the broken lines, and the clutches are worn down.
The oil pressure control apparatus for automatic transmission according to the invention controls at least one clutch in the automatic transmission connected to an engine output to be engaged or disengaged by oil pressure, thus making shifting operation. In this case, the output torque of engine is calculated on the basis of a parameter that represents the load on the engine, and the engine speed. In addition, the transfer torque required for the clutch is computed from at least the calculated output torque of engine and the engine speed. Then, an oil pressure command value acting on the clutch is determined in accordance with the computed transfer torque.
According to the embodiments of the invention, the parameter that represents a load on the engine may be, for example, the amount of intake air flow of the engine, rate of throttle opening, fuel injection pulse width, fundamental amount of fuel injection or a combination of these parameters. These parameters can be detected in a short time with almost no delay from the depression of the accelerator pedal. Therefore, even if the acceleration operation is made after the issue of a shift control command, an oil pressure command value for clutch is immediately determined on the basis of the amount of the accelerator pedal angle or depression stroke without waiting for the increase of the turbine torque (engine torque). Thus, the time required to change the actual working oil pressure ca
Kuroiwa Hiroshi
Minowa Toshimichi
Noda Junichi
Ochi Tatsuya
Okada Mitsuyoshi
Beaulieu Yonel
Cuchlinski Jr. William A.
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi , Ltd.
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