Interrelated power delivery controls – including engine control – Clutch control – Condition responsive control
Reexamination Certificate
1998-05-08
2001-05-15
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Clutch control
Condition responsive control
C192S003290
Reexamination Certificate
active
06231480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control system for a fluid coupling of an automatic transmission equipped with a lockup clutch, and, more particularly, to a lockup clutch control system for a fluid coupling of an automatic transmission which controls engagement of a lockup clutch during traveling downhill.
2. Description of the Related Art
Typically, a control system for an automatic transmission equipped with a fluid coupling, such as a torque converter, performs a downslope gear shift or slope control which refers to the control which causes a down shift of the automatic transmission from a higher gear, for example a fourth gear, to a lower gear, for example a third gear, to apply engine brake more effectively during traveling on a downslope.
With an automatic transmission equipped with a fluid coupling incorporating a lockup clutch, when the lockup clutch is changed in operation from a disengaged mode in which the fluid coupling is unlocked to allow relative rotation between a pump as a rotation input element and a turbine as a rotation output element of the fluid coupling to a full-engagement mode in which the pump and turbine of the fluid coupling is locked together or a slip mode in which the lockup clutch is allowed to slip for a gear shift during traveling downhill, deceleration is felt by the driver as a drawing shock due to overlapped shocks resulting from the change in operation mode of the lockup clutch and a down shift and a feeling of deceleration is intensified due to increased reverse torque transmitted to the engine from driving wheels.
There have been proposed on-slope gear shift control systems which cause a gear shift according to downslopes and upslopes. Such an on-slope gear shift control system is known from, for example, Japanese Unexamined Patent Publication No. 5-716262. Lockup clutch slip control has been known in various forms one of which is described in, for example, Japanese Unexamined Patent Publication No. 3-13060. However, there has been neither discussion regarding an enhanced and unpleasant feeling of deceleration occurring in an automatic transmission coupled with these features nor suggestion regarding how to relieve the enhanced and unpleasant feeling of deceleration.
SUMMARY OF THE INVENTION
It is an objective of the invention to provide a lockup clutch control system for a fluid coupling of an automatic transmission which prevents drawing shocks due to overlapped shocks resulting from a change in operation mode of the lockup clutch and a down shift during deceleration on a downslope and a feeling of deceleration intensified due to increased reverse torque transmitted to the engine from driving wheels.
The foregoing objects of the present invention are achieved by providing a lockup control system for controlling engagement of a lockup clutch for a fluid coupling through which driving torque is transmitted to a transmission gear mechanism of an automatic transmission from an engine such that the lockup clutch is engaged to lock an input element and an output element of the fluid coupling together when and disengaged to unlock the fluid coupling to allow relative rotation between the input element and the output element of the fluid coupling when disengaged. The lockup control system includes an engagement control means for controlling the lockup clutch to be engaged in different states including an engagement state in which the lockup clutch is completely engaged and a slip mode in which the lockup clutch is engaged but allowed to slip, a driving condition detecting means for detecting driving conditions of the vehicle including at least a slope of road on which the vehicle is traveling, a shift control means for shifting the transmission gear mechanism into desired gears according to the driving conditions, and a control means for controlling the shift control means to cause a gear shift of the transmission gear mechanism to a gear in which engine brake is more effected when a detection of a downhill slope greater than a specified slope is made by the driving condition detecting means, and controlling the engagement control means to relax engagement of the lockup clutch when the gear shift is caused resulting from the detection of a downhill slope greater than the specified slope.
The lockup control system may control the shift control means to cause a gear shift of the transmission gear mechanism to a lower gear in which engine brake is more effective than in a higher gear when the detection of a downhill slope greater than the specified slope is made while the transmission gear mechanism is in the higher gear and controls engagement control means to change engagement of the lockup clutch so as to allow relative rotation between the input element and the output element of the fluid coupling when a gear shift from the higher gear to the lower gear is caused due to a change in driving condition independent from a downhill slope greater than the specified slope and to disengage the lockup clutch when the gear shift from the higher gear to the lower gear is caused due to the detection of a downhill slope greater than the specified slope.
With the lockup control system of the invention, when the vehicle is traveling on a downslope sharper than a specified slope, the automatic transmission is shifted to a lower gear to apply engine brake more effectively and engagement of the lock up clutch is released after the down shift. As a result, the automatic transmission is prevented from suffering an overlapped shock resulting from a change in operation mode of the lockup clutch and a down shift during deceleration on a downslope and from providing enhanced deceleration due to increased reverse torque transmitted to the engine, which always lead to an enhanced and unpleasant feeling of deceleration. Further, when the automatic transmission is shifted to a lower gear, for example a third gear from a higher gear, for example a fourth gear, in which engine brake is applied more effectively while the vehicle is traveling on a downslope sharper than a specified slope, engagement of the lockup clutch is released in the lower gear. The automatic transmission is prevented from providing an enhanced feeling of deceleration due to an overlapped shock resulting from a change in operation mode of the lockup clutch and a down shift during deceleration on a downslope.
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Estremsky Sherry
Mazda Motor Corporation
Nixon & Peabody LLP
Pang Roger
Studebaker Donald R.
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