Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2001-04-20
2003-01-28
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S037000, C477S065000, C477S154000
Reexamination Certificate
active
06512971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to lock-up control apparatus in an automatic transmission of a vehicle having a torque converter between an engine and a transmission mechanism.
2. Description of Related Art
Japanese Patent Laid-Open Publication No. HEI 7-279700 discloses a control apparatus for an automatic transmission of an automobile with a torque converter between the engine and transmission, which control apparatus determines a coasting state, in which the engine is driven by the transmission, based on an index related to engine torque, and when the coasting state is detected, the engine speed is increased when the lock-up clutch is engaged. With this arrangement, it is possible to engage the lock-up clutch to secure the engine brake even in a low speed coasting state.
In the above-described control apparatus, as a method for detecting the coasting state, an accelerator OFF is judged by the index related to the engine torque, i.e., by a signal from a throttle sensor.
However, there is a problem, in terms of detection precision, in judging the coasting state using a signal from the throttle sensor or a signal from the accelerator as an index related to the engine torque, or a signal directly from the engine. Even if the coasting state is judged only when the accelerator opening is 0, in actual operation, the coasting state is established even when the accelerator opening is other than 0 in some cases.
For example, a coasting state may be established when a vehicle runs on a steep downhill, the accelerator pedal is slightly depressed and the vehicle speed is increasing. In such a case, although the vehicle is actually in a the coasting state in which the engine is driven by the transmission, since the accelerator pedal is depressed, the coasting state can not be detected, and the torque-up control can not be effected. Therefore, the lock-up clutch can not be reliably engaged, and the engine brake can not be applied in some cases.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a lock-up control apparatus in an automatic transmission capable of reliably engaging a lock-up clutch in any vehicle state, and capable of applying an engine brake.
According to a first aspect, the present invention provides a lock-up control apparatus in an automatic transmission having a torque converter between the engine and transmission, in which the torque converter includes a lock-up clutch capable of directly coupling an output shaft of the engine and an input shaft of the transmission. The lock-up control apparatus includes a lock-up clutch drive capable of engaging the lock-up clutch by hydraulic pressure in a state in which the engine speed is lower than the speed of the input shaft of the transmission mechanism. The lock-up control apparatus further includes speed difference detecting means for detecting a difference between the rotational speeds of the engine and the transmission input shaft; and engine speed control means for increasing the engine speed if the difference in rotational speeds detected by the speed difference detecting means exceeds a predetermined limit when the lock-up clutch is engaged.
Accordingly, if the rotational speed difference between the engine and the transmission input shaft detected by the speed difference detecting means exceeds the predetermined limit, when the lock-up clutch is engaged, the engine speed is increased to reduce the difference between the engine speed and the speed of the input shaft of the transmission. At that time, the speed difference detected by the speed difference detecting means can precisely indicate an actual coasting state of the vehicle. Thus, in any vehicle state, e.g., even when the throttle is slightly open on a steep downhill, it is possible to reliably engage the lock-up clutch, and to secure the engine brake. With such a control, the engine speed approaches the input shaft speed. In this manner, when the lock-up clutch is engaged, the speed difference between the engine and the transmission input shaft, to be absorbed by the lock-up clutch, is reduced. Therefore, even with the engaging hydraulic pressure of the lock-up clutch smoothly increased, the engagement can be completed within a short time, and the gear shift time can be shortened. The shift shock due to the difference in speeds between the engine and the input shaft of the transmission can also be prevented.
In a preferred embodiment, the engine speed control means includes engine control means for directly controlling the engine so that it becomes easy to control the engine speed. According to another preferred embodiment, the engine speed control means further increases output torque of the engine as the difference between the engine speed and the speed of the input shaft of the transmission becomes greater.
In the above-described preferred embodiment, it is possible to cause the actual speed difference to converge within a predetermined speed difference, irrespective of the magnitude of the speed difference. Further, if the speed difference is reduced, the engine torque can be set smaller and, thus, it is possible to prevent the engine speed from exceeding the input shaft speed, so as not to give the driver an unpleasant sensation. With such a control, when the lock-up clutch is released during gear shifting, even if the input shaft speed changes, the torque can be increased without time lag.
According to still another preferred embodiment, when the difference between the engine speed and the speed of the input shaft of the transmission remains unchanged, the engine speed control means reduces the engine output torque as the speed of the input shaft of the transmission mechanism increases. In this preferred form, it is possible to provide the desired control while taking the characteristics of the torque converter into consideration.
According to yet another preferred embodiment, when the difference between the engine speed and the speed of the input shaft of the transmission converges within a predetermined range, the engine speed control means maintains the output torque constant for a predetermined time (e.g., until the operation of engaging the lock-up clutch is completed). By maintaining the output torque constant, the engine speed can be maintained constant, and the operation of engaging the lock-up clutch can be smoothly effected.
According to yet another preferred embodiment of the invention, when the difference between the engine speed and the speed of the input shaft of the transmission converges within the predetermined range, if the output torque of the engine is positive, the engine speed control means maintains the output torque at 0. With this preferred form, when the output torque of the engine is positive, the engine drives the transmission mechanism. Therefore, by maintaining the output torque at 0, it is possible to prevent the engine speed from exceeding the input shaft speed, and to prevent the speed difference therebetween from increasing, whereby the lock-up clutch can be engaged smoothly.
According to another preferred embodiment, when the difference between the engine speed and the speed of the input shaft of the transmission mechanism converges within the predetermined range, if the output torque of the engine is negative, the engine speed control means maintains the output torque at that obtained when the difference converged within the predetermined range. In this preferred embodiment, when the output torque of the engine is negative, by maintaining the output torque at that obtained when the difference converged within the predetermined range, it is possible to maintain the difference between the engine speed and the input shaft speed within the predetermined range, and the lock-up clutch can be engaged smoothly.
According to still another preferred embodiment, when the lock-up clutch is engaged, the lock-up clutch drive sweeps up the engaging hydraulic pressure at a predetermined gradient to execute engagement. The sweep up is continued for a prede
Koumura Kazuo
Kusafuka Muneo
Kuwata Masayuki
Saitou Masao
Aisin AW Co. Ltd.
Lorusso & Loud
Nguyen Tan
Tran Dalena
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