Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1998-09-23
2001-05-01
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S066000, C701S060000, C701S061000, C701S065000, C701S066000, C701S071000, C701S072000, C701S074000, C701S078000, C701S082000, C701S083000, C701S084000, C477S045000, C477S097000, C180S197000
Reexamination Certificate
active
06226583
ABSTRACT:
The contents of Tokugan Hei 9-260068, with a filing date of Sep. 25, 1997 in Japan, are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates to a drive ratio control for a continuously variable transmission of a vehicle. More particularly, it relates to the control of the drive ratio during traction control accompanying braking.
BACKGROUND OF THE INVENTION
In a toroidal continuously variable transmission for a vehicle such as that disclosed in U.S. Pat. No. 5,542,890, there is a tendency for the real drive ratio to diverge from the target drive ratio depending on the direction or size of transmitted torque, due to slackness of the bearings supporting the power rollers or the elastic deformation of the trunnions. Specifically, a deviation towards upshift tends to occur when the input torque is decreasing and a deviation towards downshift tends to occur when the input torque is increasing. These deviations, that is to say, the drive ratio error is large when the input torque is large.
In this context, Tokkai Hei 8-338490 published in 1996 by the Japanese Patent Office discloses the feedback correction of drive ratio error on the basis of the correction value TS
1
calculated from a target drive ratio RTO and an input torque Tin to the transmission.
The target torque RTO is obtained from the vehicle speed VSP and throttle opening TVO of the engine.
However this type of drive ratio control creates the following problems when applied to vehicles provided with a traction control device which accompanies braking.
A traction control device which accompanies braking decreases the engine output corresponding to the slip of the drive wheel and operates braking of the vehicle wheels so that grip is not lost with respect to the road surface. The basis of such a device lies in the application of the braking if drive wheel slip is detected even when the vehicle is accelerating due to depression of the accelerator pedal.
Hence for example if traction control is applied during acceleration and the braking is applied, the rotation speed of the drive wheels will temporarily decrease. As a result, the toroidal continuously variable transmission will temporarily vary the drive ratio in the direction of downshift in a similar way to when there has been an increase in engine torque.
Since this is not a result of an actual loss of vehicle speed, the variation of the drive ratio is either totally unnecessary or leads to so called hunting in which the drive ratio oscillates until it finally falls to an appropriate value.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to suppress the variation of the drive ratio when braking is applied by traction control or the like.
In order to achieve the above object, this invention provides a transmission control device for use with such a vehicle that has a continuously variable transmission which arbitrarily varies a drive ratio between an input axis and an output axis and has a braking operation device which performs braking corresponding to a braking condition irrespective of a depression of an accelerator pedal.
The transmission control device comprises a sensor for detecting whether or not the braking is being performed, and a microprocessor programmed to calculate a vehicle speed from a rotation speed of the output axis, control the drive ratio depending on the vehicle speed, and correct the drive ratio in the direction of upshift when the braking is being performed.
It is preferable that the microprocessor is further programmed to calculate a target drive ratio from the vehicle speed, calculate a basic value of the drive ratio control depending on the target drive ratio, calculate a correction value based on the target drive ratio and the torque input to the input axis, control the drive ratio of the continuously variable transmission based on the sum of the correction value and the basic value, and modify the compensating value in the upshift direction when the braking is being performed.
It is further preferable that the sensor comprises a sensor which detects a brake pressure applied by the braking operation device, and the microprocessor is further programmed to modify the correction amount in the direction of upshift in response to an increase in the braking pressure.
The braking operation device may comprise a traction control device which performs braking and reduces engine output in response to a slip of a drive wheel of the vehicle.
The braking operation device may comprise an anti-lock braking device which performs braking depending in response to a slip of a drive wheel of the vehicle.
The braking operation device may comprise a lateral slip prevention device which performs braking in response to understeering or oversteering of the vehicle.
When the brake operation device comprises a brake actuator and a controller which outputs a pressure increasing signal and a pressure decreasing signal to the brake actuator so as to increase and decrease a pressure which the brake actuator generates, the microprocessor may be programmed to estimate a brake pressure applied by the brake actuator based on a duration period of the pressure increasing signal and a duration period of the pressure decreasing signal, instead of detecting the brake pressure by the sensor.
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.
REFERENCES:
patent: Re. 36186 (1999-04-01), White et al.
patent: 5127501 (1992-07-01), Arikawa
patent: 5519617 (1996-05-01), Hughes et al.
patent: 5788599 (1998-08-01), Adachi et al.
patent: 5873802 (1999-02-01), Tabata et al.
patent: 6009967 (2000-01-01), Hrovat
patent: 6059688 (2000-05-01), Nozaki et al.
patent: 6077190 (2000-06-01), Tabata et al.
patent: 0443591 (1991-08-01), None
patent: 8-338490 (1996-12-01), None
Cuchlinski Jr. William A.
Foley & Lardner
Mancho Ronnie
Nissan Motor Co,. Ltd.
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