Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1998-07-06
2001-03-20
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S052000, C701S095000, C477S015000, C477S047000
Reexamination Certificate
active
06205387
ABSTRACT:
The contents of Tokugan Hei. 9-179271, with a filing date of Jul. 4, 1997 in Japan, are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates to control of a continuously variable transmission for a vehicle, and in particular to speed change control when a driver releases his/her foot from the accelerator pedal of the vehicle.
BACKGROUND OF THE INVENTION
In a V-belt or toroidal continuously variable transmission, a target speed change ratio is generally fixed according to a load and a vehicle speed of an engine, and a real speed change ratio is controlled to follow the target speed change ratio under predetermined response characteristics.
In this type of control, when a driver depresses an accelerator pedal to accelerate, the target speed change ratio tends to vary in the increasing direction, as the engine rotation speed increases, so as to maintain the vehicle speed. As a result, the continuously variable transmission shifts down so as to reach the increased target speed change ratio.
Conversely, when the driver releases his/her foot from the accelerator pedal, the target speed change ratio varies in the decreasing direction, as the engine rotation speed decreases, so as to maintain the vehicle speed. As a result, the continuously variable transmission shifts up so as to reach the decreased target speed change ratio.
When the driver releases his/her foot from the accelerator pedal, the accelerator pedal rapidly returns to the state wherein it is not depressed. Consequently, the target speed change ratio also rapidly falls, and the engine rotation speed sharply falls for the same vehicle speed.
Some of the recent vehicles incorporate a fuel cut mechanism so that during coasting of the vehicle when the accelerator pedal is not depressed, fuel supply to the engine is cut in order to improve fuel-cost performance. When the rotation speed drops to a fuel recovery rotation speed due to fuel cut, fuel supply is resumed in order to prevent the engine from stalling.
When the above-mentioned speed change control is combined with such an engine, the engine rotation speed tends to fall to less than the fuel recovery rotation speed when the driver releases his/her foot from the accelerator pedal, and as fuel supply is immediately resumed in order to prevent the engine from stalling, improvement of fuel cost-performance due to fuel cut becomes difficult. Moreover to improve fuel cost-performance, it is desirable to prolong fuel cut time during coasting, and to lock up to the torque converter interposed between the engine and the continuously variable transmission. When fuel supply is resumed in this state, the output torque of the engine rapidly increases. This is transmitted to the vehicle as a shock, and the driver experiences a sense of discomfort.
To resolve this problem, Tokkai Hei 7-301297 for example, published by the Japanese Patent Office in 1995, discloses a method of decreasing the speed change control response sensitivity only when the driver releases his/her foot from the accelerator pedal.
SUMMARY OF THE INVENTION
However, under such a speed change control, the response of the engine is blunted when the driver releases his/her foot from the accelerator pedal, and may still give an uncomfortable sensation to the driver.
It is therefore an object of this invention to prevent engine rotation speed from falling more than necessary while maintaining engine response when depression of an accelerator pedal is released.
In order to achieve the above object, this invention provides a control device for a continuously variable transmission for a vehicle. The vehicle comprises an engine for driving the vehicle, a throttle for varying a rotation output of the engine according to an opening thereof, and an accelerator pedal for varying the opening of the throttle according to a depression thereof. The continuously variable transmission varies the rotation output of the engine to a specified speed change ratio.
The control device comprises a sensor for detecting a degree of the depression of the accelerator pedal, and a microprocessor for controlling the transmission. The microprocessor is programmed to calculate a target speed change ratio according to the degree of the depression of the accelerator pedal, vary the specified speed change ratio of the transmission to the target speed change ratio at a predetermined response sensitivity, determine if the accelerator pedal has been released from the depression from the degree of the depression of the accelerator pedal, and decrease the response sensitivity during a process of changing over of the target speed change ratios before and after the accelerator pedal is released from the depression.
The accelerator pedal depression degree sensor may comprise a sensor for detecting the opening of the throttle. In this case, the microprocessor is further programmed to determine that the accelerator pedal has been released from the depression when the opening of the throttle has become a minimum opening.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.
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Arthur Gertrude
Cuchlinski Jr. William A.
Foley & Lardner
Nissan Motor Co,. Ltd.
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