Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
1997-09-15
2001-02-20
Cuchlinski, Jr., William A (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S061000, C475S186000, C475S192000
Reexamination Certificate
active
06192306
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control of a continuously variable transmission.
BACKGROUND OF THE INVENTION
A toroidal type continuously variable transmission for use with a vehicle is disclosed, for example, in Tokkai Hei 3-89066 published by the Japanese Patent Office in 1991. In this controller, a pair of power rollers are gripped between input/output cone disks on the same rotation axis, and a speed change ratio is continuously varied according to a tilt of these power rollers.
The power rollers are supported by a trunnion, and their inclination is varied by displacing the trunnion in specified directions respectively at right angles to the rotation axes of the rollers and the disks. Such an assembly is disclosed for example in SAE Technical Paper No. 901761 published by the Engineering Society For Advancing Mobility in 1990.
Each trunnion is associated with an oil pressure piston, and hydraulic pressure is supplied to the oil pressure piston via a control valve comprising a spool and a sleeve linked to a stepping motor. The stepping motor rotates according to a speed change command value or a step number input from a controller comprising a microprocessor.
An offset amount from a neutral position of the trunnion in the aforesaid specified direction is mechanically fed back to the spool of the control valve via a cam or a link. Due to this feedback, the trunnion offset amount is controlled so as to obtain a power roller gyration angle depending on the command value.
As the offset of the trunnion is only of the order of several millimeters, when part of the trunnion deforms due to the transmitting torque of the power roller, an error arises between a target speed change ratio and a real speed change ratio.
One way of reducing this error would be to use an electronic feedback system wherein the real speed change ratio is measured using a sensor, and the controller controls the stepping motor such that the real speed change ratio coincides with the target speed change ratio.
In this electronic feedback system, it is desirable to perform PID (Proportional Integral Differential) control according to the characteristics of a speed change target value depending on engine running conditions.
In PID control, when a discrepancy arises between a target value and a measured value, a direct proportional output P is first generated, and then an integral control output I, which is an integral value, is generated.
In this case, when the variation of the discrepancy exceeds a stepping motor operating speed limit (response speed limit), a target step number given to the stepping motor and real step number accomplished by the stepping motor do not coincide, and as a result the discrepancy is not eliminated. Hence the direct proportional output P does not disappear, and an integral cumulative value of an integral control output value also increases.
At some point, when the real speed change ratio coincides with the target speed change ratio, the direct proportional control output P disappears, however the integral control output I still remains due to the drive speed lit of the step motor and it continues to accumulate. As a result, the real speed change ratio overshoots the target speed change ratio. In a vehicle transmission, this overshoot of the speed change ratio causes the drivability of the vehicle to be impaired.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to suppress overshoot of a speed change ratio in speed change control of a continuously variable transmission comprising an electronic feedback system.
It is a further object of this invention to suppress overshoot of a speed change ratio even in case the characteristics of the continuously variable transmission have deteriorated with time.
In order to achieve the above objects, this invention provides a speed change controller for use with a continuously variable transmission of a vehicle, this transmission having an actuator for continuously varying a speed change ratio. The controller comprises a sensor for detecting a real speed change ratio of the transmission and a control circuit. The control circuit is configured to set a target speed change ratio of the transmission according to a running state of the vehicle, calculate a proportional value which is directly proportional to a difference between the target speed change ratio and the real speed change ratio, calculate an integral value which is the integral of the difference between the target speed change ratio and the real speed change ratio, correct the integral value to a value within a preset range when the integral value does not lie within the preset range, and drive the actuator based on the sum total of the proportional value and the integral value.
It is preferable that the control circuit is further configured to expand the preset range by a predetermined first minute amount when the integral value does not lie within the preset range.
It is further preferable that the control circuit is further configured to narrow the preset range by a predetermined second minute amount less than the first minute amount when the integral value lies within the preset range.
It is also preferable that the controller further comprises a device for detecting a running state of the transmission, wherein the control circuit is further configured to set the preset range according to the running state of the transmission.
In this case, it is further preferable that the detecting device comprises a sensor for detecting a temperature of lubricating oil of the transmission and a sensor for detecting a pressure thereof.
According to another aspect of this invention, the control circuit is configured to set a target speed change ratio of the transmission according to a running state of the vehicle, calculate a proportional value which is directly proportional to a difference between the target speed change ratio and the real speed change ratio, calculate an integral value which is the integral of the difference between the target speed change ratio and the real speed change ratio, calculate a command value to be output to the actuator based on the proportional value and the integral value, calculate a variation rate of the command value, stop calculating the integral value when the variation rate exceeds a predetermined variation rate, and drive the actuator by outputting the command value thereto.
It is preferable that the predetermined variation rate is set based on an operating speed limit of the actuator.
It is also preferable that the controller further comprises a device for detecting a running state of the transmission, wherein the control circuit is further configured to determine the predetermined variation rate according to the running state of the transmission.
It is further preferable that the detecting device comprises a sensor for detecting a temperature of lubricating oil of the transmission and a sensor for detecting a pressure thereof.
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: 4718012 (1988-01-01), Oshiage
M. Nakano et al., Dynamic Characteristics of Speed Ratio Control of the Halt Toroidal CVT for Passenger SAE Technical Paper Series, Sep. 1990, p. 24-32.
Kidokoro Hitoshi
Muramoto Itsuro
Cuchlinski, Jr. William A
Donnelly Arthur
Foley & Lardner
Nissan Motor Co,. Ltd.
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