Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2001-07-20
2002-11-26
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S046000, C474S011000, C474S028000
Reexamination Certificate
active
06485392
ABSTRACT:
RELATED APPLICATIONS
This application claims the priorities of Japanese Patent Application No.2000-223684 filed on Jul. 25, 2000, and No.2000-222453 filed on Jul. 24, 2000, which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates generally to a belt-type continuously variable transmission comprising a V belt wound around drive and driven pulleys whose widths are variable, and particularly to a shift control system which controls thrusts directed axially onto the drive and driven pulleys for the speed ratio change of the belt-type continuously variable transmission.
BACKGROUND OF THE INVENTION
Many types of such transmissions and shift control systems have been proposed, and some are now in practical use. A typical belt-type continuously variable transmission comprises a drive-side actuator, which is used for adjusting the width of the drive pulley (in axial thrust control), and a driven-side actuator, which is used for adjusting the width of the driven pulley (in axial thrust control). In the speed ratio change of the transmission, these actuators are controlled to act on the respective pulleys axially with thrusts that are appropriate for the drive and driven pulleys to achieve their proper pulley widths.
For the purpose of achieving automatic speed ratio change, various belt-type automatic transmissions have been proposed with shift control systems that are designed to control the thrusts of such actuators in correspondence to the driving condition of the vehicle. For example, such a belt-type automatic transmission is disclosed in Japanese Laid-Open Patent Publication No. H9(1997)-72397. In this transmission, for the speed ratio change, the axial thrust of one pulley is controlled to a target thrust value while the thrust of the other pulley is adjusted to a value that is a product of the target thrust value and a pulley thrust ratio or to a value that is the sum of a value which corresponds to the ratio and a value which corresponds to the deviation of the rotational speed of the engine.
Various apparatus or devices and methods have been also proposed to control the speed ratio change of respective belt-type continuously variable transmissions. However, these prior-art systems and methods have experienced problems of inferior responsivity and convergency because of constant gains seen in control feedbacks for both upshifts and downshifts or of inappropriate parameters set as feedback.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a shift control system which can control the axial thrusts of the pulleys to optimal values for the speed ratio change of a belt-type continuously variable transmission.
It is another object of the present invention to provide a shift control system which can control the axial thrust of the pulleys to least values necessary for the speed ratio change of a belt-type continuously variable transmission.
To achieve these objectives, the present invention provides a shift control system which controls the axial thrusts generated by drive-side and driven-side actuators (for example, the drive-side cylinder chamber
6
and the driven-side cylinder chamber
9
described in the following preferred embodiment), respectively, to vary the widths of the drive and driven pulleys for achieving a shift to a target speed change ratio. The shift control system comprises contact-circle enlarging pulley determination means (for example, refer to Step S
51
described in the following embodiment) and additional thrust calculation means (for example, refer to Step S
5
described in the following embodiment). The contact-circle enlarging pulley determination means determines which pulley, i.e., the drive pulley or the driven pulley, is to be the contact-circle enlarging pulley whose diameter of the belt-contact circle is enlarged during the shift, and the additional thrust calculation means calculates a shifting additional thrust which is added for the contact-circle enlarging pulley to shift the transmission to the target speed change ratio. Preferably, the shifting additional thrust is set inversely proportional to the running speed of the V belt.
While the speed of the V belt is high, if the pulley widths were varied quickly, then the resulting shift would be too rapid. However, if the speed of the shift is controlled in inverse proportion to the running speeds of the V belt, then a shift control appropriate for comfortable travelling is possible. Therefore, the shift control system according to the present invention sets the shifting additional thrust inversely proportional to the running speed of the V belt and realizes a good shift control.
Furthermore, it is preferable that the shifting additional thrust be set proportional to the difference between the diameter of the contact circle of the contact-circle enlarging pulley at present and the diameter of the contact circle of the contact-circle enlarging pulley after the shift to the target speed change ratio. The larger the diameter difference between the belt-contact circles of the contact-circle enlarging pulley before and after the shift, faster the speed of the shift being required. If the speed of the shift is controlled proportionally to the diameter difference between the belt-contact circles, then a shift control appropriate for comfortable travelling is possible. Therefore, the shift control system according to the present invention sets the shifting additional thrust proportional to the diameter difference between the belt-contact circles and realizes a better shift control.
The shift control system can also comprise belt-speed calculation means, which calculates the running speed of the V belt, and first gain coefficient calculation means, which calculates a first gain coefficient in inverse proportion to the running speed of the V belt. In this case, the additional thrust calculation means uses the first gain coefficient for calculating the shifting additional thrust.
Furthermore, the shift control system may comprise belt-speed calculation means, which calculates the running speed of the V belt, and first gain coefficient calculation means, which calculates a first gain coefficient in inverse proportion to the running speed of the V belt, from the rotational speed of the drive pulley and the current speed change ratio. Then, the additional thrust calculation means uses the first gain coefficient for calculating the shifting additional thrust.
According to the present invention, the shifting additional thrust, which is added for the contact-circle enlarging pulley to achieve a shift to a target speed change ratio, can be set proportional to the difference between the diameter of the contact circle of the contact-circle enlarging pulley at present and the diameter of the contact circle of the contact-circle enlarging pulley after the shift to the target speed change ratio.
While the diameter difference between the belt-contact circles of the contact-circle enlarging pulley before and after a shift is relatively large, then the shift needs to be carried out comparatively fast. However, if the speed of the shift is controlled proportionally to the diameter difference, then the shift control can be executed smoothly. Therefore, the shift control system according to the present invention sets the shifting additional thrust proportional to the diameter difference and realizes a good shift operation.
Also, the shift control system may comprise diameter-change calculation means, which calculates the difference between the diameters of the contact circles of the contact-circle enlarging pulley at present and after a shift, and second gain coefficient calculation means, which calculates a second gain coefficient in proportion to the difference between the diameters of the contact circles. In this case, the additional thrust calculation means uses the second gain coefficient for calculating the shifting additional thrust.
It is preferable that the difference between the diameters of the contact circles of the contact-circle enlarging pulley at
Kanehara Shigeru
Koyama Hideo
Miyazaki Tetsushi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Estremsky Sherry
Honda Giken Kogyo Kabushiki Kaisha
Lewis Tisha D.
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