Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1998-12-01
2001-03-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C477S031000, C477S034000, C477S037000, C477S116000, C477S117000, C477S156000, C475S031000, C192S003510
Reexamination Certificate
active
06202015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic control system of an automatic transmission of a motor vehicle.
2. Description of the Prior Art
A known example of hydraulic control system of an automatic transmission is disclosed in Japanese laid-open Patent Publication No. 62-18336. In this hydraulic control system, a creep preventive device controls a solenoid for neutral control when the position of the select lever is changed from a neutral range to one of forward-drive ranges, so that the line pressure is supplied as it is to a start clutch (forward-drive friction engaging element) until a piston stroke is completed. After the piston stroke is completed, the clutch engaging pressure supplied to the start clutch is reduced or the supply of the pressure is temporarily stopped, so that the pressure of the start clutch is controlled to a low level at which the clutch does not have an engaging capacity.
With this arrangement, the vehicle is prevented from creeping while it is in one of drive ranges, and the supply of the line pressure can always be finished at a point of time when the start clutch is placed in the same engaging condition, thereby preventing an engaging shock and racing of the engine.
In the known hydraulic control device of the automatic transmission, however, the completion of the piston stroke is determined when a difference between the engine rotating speed and the turbine rotating speed detected at a certain moment becomes larger than a predetermined value after the range is changed. If the engine speed (Ne) changes due to an increase in the idling speed (idle up) during the piston stroke, therefore, it is possible that the piston stroke of the forward-drive friction engaging element (FWD/C) is judged by mistake as being finished at a point of time when the difference between the engine speed and the turbine speed (Nt) is increased, as shown in
FIG. 4
, even though the real piston stroke is not finished yet. In this case, the supply of the pressure to the start clutch is stopped or reduced. If the driver tries to start the vehicle at the time when the judgement is made by such mistake, an engaging shock or racing of the engine occurs due to a delay in engagement of the forward-drive friction engaging element, and the vehicle may not be smoothly or readily started.
SUMMARY OF THE INVENTION
The present invention was developed so as to solve the above-described problem, by relating detection of the piston stroke, only with the turbine speed. Namely, the present invention provides a hydraulic control system of an automatic transmission of a motor vehicle, which includes a friction element (
15
) that is engaged when the vehicle is in a forward-drive range, and detecting means (forward-drive friction element piston stroke detecting means) (
22
) for detecting a stroke of a piston of the friction element (
15
) from a first position for releasing the friction element, to a second position for engaging the friction element, when the range of the automatic transmission is changed from a neutral range to the forward-drive range. The hydraulic control system further includes control means (forward-drive friction element control means (
18
)) that controls a hydraulic pressure supplied to the piston of the friction element (
15
), to a first level lower than a given level at which the friction element (
15
) has an engaging capacity, while the vehicle in the forward-drive range is being stopped. Further, the detecting means (
22
) for detecting the stroke of the piston of the friction element (
15
) generates a stroke completion signal (S) to the control means (
18
) when a difference between a turbine speed (TbnREV
0
) of the automatic transmission detected upon a change of the range, and a current turbine speed (TbnREV), is larger than a predetermined value (TbnREV
1
). The control means (
18
) supplies a hydraulic pressure having a second level that is higher than the first level, to the piston of the friction element (
15
), until the control means (
18
) receives the stroke completion signal (S).
The reference numerals in parentheses are those of corresponding elements in one embodiment of the present invention as described later.
If the idling speed of the engine is increased (idle up) during the stroke of the piston of the friction element from the releasing position to the engaging position when the vehicle is changed from the neutral range to the forward drive range, the turbine rotating speed is temporarily increased with a delay, following an increase of the engine speed, but the turbine speed is gradually lowered if the piston is in the middle of the stroke.
By judging completion of the stroke only based on the turbine speed, therefore, a misjudgement on completion of the piston stroke based on the increase of the engine speed due to idle up can be prevented, and the completion of the piston stroke can be more accurately detected. Thus, the hydraulic control system of the present invention can surely avoid engaging shocks and racing of the engine while preventing the vehicle from creeping when the position of the select lever is changed from the neutral range to the forward-drive range.
REFERENCES:
patent: 4730708 (1988-03-01), Hamono et al.
patent: 5411451 (1995-05-01), Ando et al.
patent: 5813943 (1998-09-01), Kousaka et al.
Beaulieu Yonel
Cuchlinski Jr. William A.
Jatco Corporation
Rossi & Associates
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