Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2003-01-31
2004-11-02
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S058000, C474S028000
Reexamination Certificate
active
06813551
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a control apparatus for a continuously variable transmission, and more particularly, to an apparatus for controlling the gear ratio of the continuously variable transmission by use of a flow control unit.
b) Description on the Related Art
Continuously variable transmissions have hitherto been used as transmissions for automobiles and so on. With a belt type continuously variable transmission, a V belt is passed around the primary pulley on the engine side and the secondary pulley on the wheel side, thus continuously changing the gear ratio by changing the groove widths of the primary and secondary pulleys.
Driving force required to change the gear ratio of this transmission is generally produced by hydraulic pressure from a hydraulic actuator. The flow control unit as shown, for example, in Japanese Patent Laid-open publication No. Hei11-182667 is employed as a hydraulic actuator. The flow control unit shown in Japanese Patent Laid-open publication No. Hei11-182667 comprises a shift-up flow control valve and a shift-down flow control valve which are separate from each other and further comprises shift-up and shift-down solenoid valves designed respectively to control the shift-up and shift-down flow control valves.
During shift up, duty control is performed in which the shift up shift-up flow control valve is turned on and off repeatedly, thus allowing operating fluid to flow from the shift-up flow control valve to the primary pulley's fluid chamber. This causes the turning radius of the portion of the primary pulley around which the V belt is passed to increase, thus allowing shift up. During shift down, on the other hand, duty control is performed in which the shift-down flow control valve is turned on and off repeatedly, thus allowing operating fluid to flow from the shift-down flow control valve through the primary pulley's fluid chamber. This causes the turning radius of the portion of the primary pulley around which the V belt is passed to decrease, thus allowing shift down. Here, the orifice area within the flow control valves is determined based on the duty ratio of the solenoid valves. A characteristic of the duty ratio with respect to the orifice area is stored in advance in an electronic control unit, and the duty ratio of the solenoid valves is calculated based on this characteristic.
Since manufacturing variation occurs in flow control and solenoid valves, variation also occurs in that characteristic of the duty ratio with respect to the orifice area. Consequently, the characteristic of the duty ratio with respect to the orifice area stored in the electronic control unit does not necessarily agree with the actual characteristic of the flow control unit for the duty ratio with respect to the orifice area, thus resulting in difference in characteristic between the two. Consequently, an error occurs between the desired and actual flow rates, thus aggravating the ability of actual gear ratio to follow desired gear ratio.
Additionally, a continuously variable transmission achieves change gear control by determining target input rotation speed based, for example, on required amount of driving force such as an accelerator opening amount and driving conditions such as vehicle speed or operation by the driver and by controlling gear ratio such that actual input rotation speed agrees with target input rotation speed. A change gear control device which controls the gear ratio of a continuously variable transmission such that actual input rotation speed agrees with target input rotation speed is included in Japanese Patent Laid-Open Publication No. Hei 7-4508. With this conventional technology, feedforward and feedback manipulated variables are added, a control value appropriate for manipulated variable is treated as a shift actuator manipulated variable, a feedback manipulated variable which provides a near-zero deviation of actual input rotation speed from target speed is stored as a correction manipulated variable and this correction manipulated variable is added to feedforward and feedback manipulated variables. This allows learning and correction of changes in feedforward characteristic caused by individual differences between continuously variable transmissions and deterioration over time.
With conventional continuously variable transmissions, however, there has been a problem of shift characteristic aggravation as a result of variation in control value if the feedforward manipulated variable is reflected in an actuator manipulated variable before learning of actuator manipulated variable is complete.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above problems, and an advantage of the present invention is that it provides a control apparatus for a continuously variable transmission which improves the ability of the actual gear ratio to follow a desired gear ratio.
Another advantage of the present invention is that it provides a control apparatus for a continuously variable transmission which ensures reduced variation in change gear control value before learning of actuator manipulated variable is complete.
In order to achieve the advantages, according to a first aspect of the present invention there is provided a control apparatus for a continuously variable transmission which controls the gear ratio by using an operating fluid supply and discharge device to change the flow rate of operating fluid entering and leaving a gear change mechanism, the control apparatus comprising a hydraulic control signal calculation device which calculates a hydraulic control signal output to the operating fluid supply and discharge device, a fluid volume detection device which detects a change in operating fluid volume within the gear change mechanism over a predetermined period of time during which a gear change operation is in progress, a fluid volume estimation device which estimates a change in operating fluid volume within the gear change mechanism over the predetermined period of time, based on the hydraulic control signal, and a correction device which corrects the hydraulic control signal to flow control output characteristic map, based on the deviation of the value detected by the fluid volume detection device from the value estimated by the fluid volume estimation device.
According to the present invention, since the hydraulic control signal to flow control output characteristic map for the operating fluid supply and discharge device is corrected based on the deviation of the value detected by the fluid volume detection device from the value estimated by the fluid volume estimation device, it is possible to accurately learn and correct any difference between the characteristic map stored in the electronic control unit and the actual characteristic of the operating fluid supply and discharge device. Consequently, error between desired and actual flow rates can be minimized, thus providing improved ability of actual gear ratio to follow desired gear ratio.
In the present invention, the fluid volume estimation device may include a differential pressure detection device which detects the difference between operating fluid pressures anterior and posterior to the operating fluid supply and discharge device, the fluid volume estimation device estimating a change in operating fluid volume within the gear change mechanism, based on the hydraulic control signal and on the value detected by the differential pressure detection device. The fluid volume estimation device may estimate a change in operating fluid volume within the gear change mechanism, based on the hydraulic control signal, on the value detected by the differential pressure detection device and on a dynamic characteristic model for the hydraulic control signal with respect to the flow control output.
By estimating change in operating fluid volume within the gear change mechanism based on the dynamic characteristic model for the hydraulic control signal and the flow control output, it is possible to c
Kondo Hiroki
Kono Katsumi
Matsuo Kenji
Taniguchi Hiroji
Terashima Masato
Nguyen Tan Q.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Tran Dalena
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