Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1998-07-24
2001-02-13
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S061000, C477S046000
Reexamination Certificate
active
06188946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission control system for and method of an automotive vehicle employing a continuously variable automatic transmission, and specifically to techniques for optimally controlling a speed ratio, which states the ratio of the transmission input to output speed, of an automobile continuously variable automatic transmission even under particular vehicle driving conditions, for example when restarting after the vehicle experiences wheel spin at drive road wheels during the starting period on uphill roads with wheel spin, or when restarting after the vehicle experiences wheel spin at drive wheels during the starting period on low-&mgr; roads.
2. Description of the Prior Art
Japanese Patent Provisional Publication Nos. 8-178042 and 4-54371 have disclosed a belt-type continuously variable automatic transmission, often abbreviated to “CVT”. Generally, the speed ratio of the CVT is electronically controlled in accordance with a predetermined speed-change pattern by means of an electronic transmission control unit. The predetermined speed-change pattern is pre-stored as a preprogrammed characteristic map in the memory (ROM) of the transmission control unit. A desired speed necessary for the speed-change control action is generally based on vehicle speed and engine load. As a control parameter corresponding to the vehicle speed, a rotational speed of the output shaft of the CVT (i.e., a drive-wheel speed) is generally used.
SUMMARY OF THE INVENTION
When the vehicle starts from the standstill state on low-&mgr; roads, such as wet, icy, or snow roads, particularly when starting on low frictional roads or during uphill driving, there is a tendency for wheel spin to occur. Owing to the wheel spin, the drive-wheel speed rises rapidly, while the rise of vehicle speed is not so much. In spite of such less rise of the vehicle speed, the electronic transmission control unit begins to perform the speed-change control action according to the speed-change ratio based on the engine load and the drive-wheel speed (regarded as the vehicle speed), as if the actual vehicle speed rises rapidly. That is, the transmission control unit would generate an upshift command due to the rapid rise of drive-wheel speed. As a result of this, the speed ratio tends to unreasonably shift toward the minimum speed ratio line (or the highest-speed line) in the predetermined speed-change pattern. Under these conditions, if the accelerator pedal is released by the driver to prevent the undesired wheel spin occurring at the drive road wheels, the vehicle may come to a standstill without adequate return of the speed ratio of the CVT to a relatively large value closer to the maximum speed ratio line (or the lowest-speed line). Thus, the speed ratio tends to be fixed undesiredly to a relatively small speed ratio closer to the minimum speed ratio line. Assuming that the vehicle is restarted from the standstill state with the speed-change ratio fixed to a certain small value closer to the minimum speed ratio line, the vehicle cannot be easily restarted owing to the small speed ratio.
In an electronically-controlled continuously variable automatic transmission, it is desirable to provide a satisfactory speed ratio control action even under the previously-discussed particular vehicle driving conditions, such as when restarting on the uphill roads owing to wheel spin, or when restarting on low-&mgr; roads, such as wet, icy, or snow roads, owing to wheel spin.
Accordingly, it is an object of the invention to provide a transmission control system of an automotive vehicle with a continuously variable automatic transmission which avoids the aforementioned disadvantages of the prior art.
In order to accomplish the aforementioned and other objects of the present invention, a transmission control system of an automotive vehicle with a continuously variable automatic transmission, comprises a transmission control system for an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is defined as a ratio of transmission input to output speed and is changeable continuously depending on vehicle speed and engine load, comprises a hydraulic actuator producing a regulated line pressure and a speed-change control pressure necessary to adjust the speed ratio hydraulically, and an electronic transmission control unit including a data processing section detecting an acceleration of a drive wheel of the vehicle, comparing the acceleration of the drive wheel to a predetermined acceleration value, and inhibiting an upshifting action by preventing a speed ratio of the continuously variable automatic transmission from being upshifted toward a speed ratio less than a predetermined upshift limiting threshold.
According to another aspect of the invention, a transmission control method of an automotive vehicle with a continuously variable automatic transmission whose speed-change ratio is defined as a ratio of transmission input to output speed and is changeable continuously depending on vehicle speed and engine load, comprising the steps of: detecting an acceleration of a drive wheel of the vehicle; comparing the acceleration of the drive wheel to a predetermined acceleration value; and inhibiting an upshifting action by preventing a speed ratio from being shifted toward a speed ratio less than a predetermined upshift limiting threshold.
REFERENCES:
patent: 4653006 (1987-03-01), Osanai et al.
patent: 5178044 (1993-01-01), Suzuki et al.
patent: 5362287 (1994-11-01), Tanaka et al.
patent: 5586953 (1996-12-01), Abo
patent: 5655991 (1997-08-01), Lardy et al.
patent: 5707313 (1998-01-01), Suzuki
patent: 5890991 (1999-04-01), Sakakiyama
patent: 1-79466 (1989-03-01), None
patent: 4-54371 (1992-02-01), None
patent: 8-178042 (1996-07-01), None
Asano Hiroshi
Suzuki Akito
Foley & Lardner
Nguyen Tan
Nissan Motor Co,. Ltd.
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