Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2000-07-12
2001-11-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S061000, C701S067000, C701S079000, C474S011000, C474S018000, C477S046000
Reexamination Certificate
active
06317672
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control of an infinite speed ratio transmission for vehicles.
BACKGROUND OF THE INVENTION
Tokkai Sho 63-219956 published by the Japanese Patent Office in 1988 discloses an infinite speed ratio transmission (referred to hereafter as IVT) which permits a speed ratio to be varied up to infinity by combining a reduction gear unit and planetary gear set with a toroidal continuously variable transmission (referred to hereafter as CVT).
The rotation of an engine is input to the CVT having a continuously variable speed ratio, and to the reduction gear unit which has a fixed speed ratio. The output shaft of the CVT is joined to a sun gear of the planetary gear set, and the rotation output of the reduction gear unit is joined to a planet carrier of the planetary gear set. A ring gear of the planetary gear set is joined to a final output shaft of the IVT. The planet carrier supports the center of plural planet gears held between the sun gear and ring gear.
An output shaft of the reduction gear unit and a planet carrier are joined via a power recirculation clutch. The output shaft of the CVT is also joined to the final output shaft via a direct clutch.
In a direct mode wherein the power recirculation clutch is disengaged and the direct clutch is engaged, the rotation of the CVT output shaft is directly output to the final output shaft, so the speed ratio li of the IVT is equal to a speed ratio lc of the CVT.
On the other hand, a power recirculation mode where the power recirculation clutch is engaged and the direct clutch is disengaged, the direction and speed of the output rotation of the final output shaft vary according to the difference between the speed ratio lc of the CVT and the speed ratio of the reduction gear unit. The speed ratio li of the IVT, i.e., the ratio of the rotation speed of the input shaft and the rotation speed of the final output shaft, varies from a negative value to a positive value. At the point where the rotation direction of the final output shaft changes, the speed ratio li of the IVT becomes infinite, and the final output shaft is stationary. This point is referred to as the geared neutral point (GNP).
SUMMARY OF THE INVENTION
When the IVT is used for the transmission device of a vehicle, at the geared neutral point GNP, the vehicle remains at rest. If the CVT speed ratio lc is increased from the GNP, the vehicle moves forward, and if it is decreased, the vehicle reverses. Therefore, the IVT does not require a torque converter as was required in prior art automatic transmissions. At the GNP, the transmission torque of the CVT is 0.
A toroidal CVT varies the speed ratio according to a gyration angle of power rollers gripped between an input disk and output disk. Due to this construction, in a toroidal CVT, a torque shift may also occur wherein the speed ratio varies due to fluctuations of input torque or looseness of component elements.
Due to this torque shift, hysteresis occurs in the relation between the input torque and gyration angle of the power rollers which corresponds to the CVT speed ratio. As a result, it may occur that the gyration angle of the power rollers fluctuates in a certain range centered on the GNP even if the step number of a step motor which varies the gyration angle of the power rollers is precisely set.
If a fluctuation of the speed ratio of the CVT occurs in the vicinity of the geared neutral point GNP, a shock may be produced due to the difference between the rotation speed of the CVT output shaft corresponding to the GNP and the real rotation speed of the CVT output shaft in the instant when the power recirculation clutch is engaged.
Further, if the CVT speed ratio varies in the reverse direction to the forward direction intended by the driver, a creep torque may act on the drive wheels in the reverse direction to the forward direction immediately after the power recirculation clutch is engaged, and the driver may therefore experience an uncomfortable feeling.
It is therefore an object of this invention to prevent a shock due to drift of CVT speed ratio in the vicinity of the GNP, and prevent the driver from experiencing an uncomfortable feeling, in an infinite speed ratio transmission.
In order to achieve the above object, this invention provides a speed change controller for an infinite speed ratio transmission for a vehicle. The infinite speed ratio transmission comprises an input shaft, a continuously variable transmission which transmits a rotation speed of the input shaft to a first output shaft at an arbitrary speed ratio, a fixed speed ratio transmission which transmits the rotation speed of the input shaft to a second output shaft at a fixed speed ratio, a planetary gear set comprising a first rotation element joined to the first output shaft, a second rotation element, and a third rotation element which varies a rotation direction and a rotation speed according to a difference of a rotation speed of the first rotation element and a rotation speed of the second rotation element, and a clutch joining the second output shaft and second rotation element.
The controller comprises a selector lever which selects one of a stationary range, forward motion range and reverse motion range, a sensor which detects a range selected by the selector lever, an actuator which varies the speed ratio of the continuously variable transmission according to an operating position, and a microprocessor programmed. The microprocessor is programmed to determine whether or not the range selected by the selector lever has changed from the stationary range to one of the forward motion range and the reverse motion range, change the operation position of the actuator to a predetermined position when the range selected by the selector lever has changed from the stationary range to one of the forward motion range and the reverse motion range, and change the operation position of the actuator from the predetermined position to the position corresponding to a geared neutral point which a rotation speed of the third rotation element becomes zero. The predetermined position is set so as to be different from the position corresponding to the geared neutral point.
The operating position of the actuator has a hysteresis region with respect to the speed ratio of the continuously variable transmission according to a transmission torque of the continuously variable transmission.
So the microprocessor may be programmed to disengage the clutch when the range selected by the selector lever is the stationary range, maintain the actuator at an operating position corresponding to a geared neutral point at which the rotation speed of the third rotation element is zero, when the range selected by the selector lever is the stationary range, determine whether or not the range selected by the selector lever has changed from the stationary range to one of the forward motion range and the reverse range, change the operation position of the actuator from the operating position corresponding to the geared neutral point to a first position when the range selected by the selector lever has changed from the stationary range to one of the forward motion range and reverse motion range, and change the operation position of the actuator from the first position to a second position. The second position corresponds to an operating position of the actuator which is displaced from the operating position corresponding to the geared neutral point in a direction represented by the range selected by the selector lever, and which realizes the geared neutral point when the clutch is engaged. The first position corresponds to an operating position of the actuator which is further displaced from the second position in the direction represented by the range selected by the selector lever.
The microprocessor may also be programed to disengage the clutch when the range selected by the selector lever is the stationary range, determine whether or not the range selected by the selector lever has changed from the stationary range to one of the forward motio
Abe Manzaburou
Kuramoto Hiroaki
Nagato Tatsuya
Narita Yasushi
Nishio Motoharu
Arthur Gertrude
Cuchlinski Jr. William A.
Foley & Lardner
Nissan Motor Co,. Ltd.
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