Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Patent
1999-03-02
2000-03-07
Marmor, Charles A.
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
477 46, 74336R, B60K 4108
Patent
active
060333383
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to transmission control systems and in particular to a transmission control system for a vehicle having a continuously variable transmission. The invention also relates to: a vehicle including such a transmission control system; a control means for such a transmission control system; and to method of controlling such a transmission control system.
BACKGROUND OF THE INVENTION
It is known to provide a vehicle with a transmission control system to control the operation of a continuously variable transmission (CVT) by varying its transmission ratio in a continuous manner. An increase in transmission ratio causes a decrease in road speed for a given engine speed and a decrease in transmission ratio causes an increase in road speed for a given engine speed.
It is a known advantage of equipping vehicles with a CVT that, by operating the prime mover at its optimum efficiency and varying the transmission ratio in a continuous manner, it is possible to achieve optimum acceleration. It is, however, a known disadvantage of such systems that on over-run, because the transmission ratio is varied in a continuous manner, there is very little engine braking to assist deceleration.
In U.S. Pat. No. 5,527,231 a system is disclosed which detects an over-run condition and provides for a continuous increase in transmission ratio while the brakes are being operated, so as to provide engine braking on over-run to reduce the stress on the service brakes.
In U.S. Pat. No. 5,527,232 a system is disclosed which detects an over-run condition and fixes the transmission ratio at the value it possessed on commencement of over-run, for example, when the accelerator pedal is released rapidly on entry to a bend. This system prevents a decrease in transmission ratio under such circumstances, which would provide little engine braking.
SUMMARY OF THE INVENTION
It is an object of this invention to provide: an improved transmission control system for a vehicle; a vehicle including such a transmission control system; a control means for such a transmission control system; and to provide a method of controlling such a transmission control system.
According to the invention there is provided a transmission control system for a vehicle, the transmission control system comprising a control means arranged in use to be capable of operation in a continuous mode in which it can vary the transmission ratio of a continuously variable transmission in a substantially continuous manner and also arranged in use to be capable of operation in a stepped mode in which it can increase said transmission ratio in steps by substantially stepped down-shifts in response to a manually operable down-shift request means, wherein the control means is further arranged in use to be capable of operation in a hybrid mode in which stepped down-shifts can be made using said manually operable down-shift request means and acceleration of the vehicle is performed in the continuous manner.
It may be possible to enter the hybrid mode only when the control means is operating in the continuous mode and, also or in the alternative, on or after selection by a user of a stepped down-shift while the control means is operating in the continuous mode.
It may also be necessary to satisfy one or more predetermined hybrid mode entry conditions, which may include one or more of: detection of a vehicle speed which is above a predetermined level; determination of a post-entry engine speed which is at least substantially equal to the pre-entry engine speed, whereby there is a reduced likelihood that the engine speed will appear to a user to fall after the hybrid mode is entered and a stepped down-shift is made; and determination of a post-entry engine speed which is below a predetermined level, that level being a level at which the control means is arranged to automatically decrease the transmission ratio, whereby there is a reduced likelihood that the system will automatically leave the hybrid mode shortly after entering it.
The control means may
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Jackson Neil David
Taylor Richard
Ho Ha
Marmor Charles A.
Rover Group Limited
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