Hydraulic control apparatus and method for belt-type continuously-variable transmission

• US 20070232423A1
• Filed: 03/16/2007
• Published: 10/04/2007
• Est. Priority Date: 03/17/2006
• Status: Active Grant

• Current Assignee: Jatco Limited (Nissan Motor Co., Ltd.), Nissan Motor Co., Ltd.
• Original Assignee: Jatco Limited (Nissan Motor Co., Ltd.)
• Inventors: Katou, Yoshiaki, Yamazaki, Masanori
• Granted Patent: US 7,931,551 B2
• Time in Patent Office: Days
• US Class Current: 474/28
• CPC Class Codes: F16H 2061/66277 by optimising the clamping force exerted on the endless flexible member
• CPC Class Codes: F16H 2061/66286 Control for optimising pump efficiency
• CPC Class Codes: F16H 61/0021 Generation or control of line pressure
• CPC Class Codes: F16H 61/66272 characterised by means for controlling the torque transmitting capability of the gearing

Abstract

A hydraulic control apparatus includes a continuously-variable transmission; a line-pressure control section configured to produce a line pressure by adjusting a discharge pressure of an oil pump; a first hydraulic-pressure control section configured to adjust a first hydraulic pressure based on the line pressure, the first hydraulic pressure being supplied to the drive pulleys; and a second hydraulic-pressure control section configured to adjust a second hydraulic pressure based on the line pressure, the second hydraulic pressure being supplied to the driven pulleys. The continuously-variable transmission includes a pair of drive pulleys including a first movable pulley and a first fixed pulley; a pair of driven pulleys including a second movable pulley and a second fixed pulley; and a belt wound between the pair of drive pulleys and the pair of driven pulleys. The line-pressure control section is configured to adjust the line pressure to a value set by adding a margin pressure to higher one of the first hydraulic pressure and the second hydraulic-pressure, and configured to reduce the margin pressure when the first hydraulic pressure is higher than the second hydraulic pressure.

Claims

1. A hydraulic control apparatus comprising:

a continuously-variable transmission including

a pair of drive pulleys including a first movable pulley and a first fixed pulley,

a pair of driven pulleys including a second movable pulley and a second fixed pulley, and

a belt wound between the pair of drive pulleys and the pair of driven pulleys, the continuously-variable transmission being adapted to be continuously shifted by moving at least one of the first movable pulley and the second movable pulley by means of hydraulic pressure and thereby varying at least one of a groove width between the pair of drive pulleys and a groove width between the pair of driven pulleys to vary a winding radius of the belt;

a line-pressure control section configured to produce a line pressure by adjusting a discharge pressure of an oil pump;

a first hydraulic-pressure control section configured to adjust a first hydraulic pressure based on the line pressure, the first hydraulic pressure being supplied to the drive pulleys; and

a second hydraulic-pressure control section configured to adjust a second hydraulic pressure based on the line pressure, the second hydraulic pressure being supplied to the driven pulleys,

the line-pressure control section being configured

to adjust the line pressure to a value set by adding a margin pressure to higher one of the first hydraulic pressure and the second hydraulic pressure, and

to reduce the margin pressure when the first hydraulic pressure is higher than the second hydraulic pressure.

2. The hydraulic control apparatus as claimed in claim 1, wherein

the line-pressure control section is configured to reduce the margin pressure when a transmission ratio calculated by dividing the belt winding radius of driven pulleys by the belt winding radius of drive pulleys is smaller than 1.

3. The hydraulic control apparatus as claimed in claim 1, wherein

the hydraulic control apparatus further comprises an actual transmission-ratio sensing section adapted to sense an actual transmission ratio;

the first hydraulic-pressure control section

includes a first control valve adapted to adjust a communication between a line-pressure supplying oil passage and a first-hydraulic-pressure supplying oil passage for supplying the first hydraulic pressure to the drive pulleys, and

is configured to adjust the first hydraulic pressure to its value for achieving a target transmission ratio by controlling an opening of the first control valve; and

the line-pressure control section is configured to carry out a transmission-ratio feedback control to adjust the line pressure so as to achieve the target transmission ratio on the basis of the sensed actual transmission ratio, after the first hydraulic-pressure control section becomes incapable of achieving the target transmission ratio due to the reduction of the line pressure adjusted to, the value set by adding the margin pressure.

4. The hydraulic control apparatus as claimed in claim 3, wherein

the first hydraulic-pressure control section is configured to allow the line-pressure supplying oil passage to communicate with the first-hydraulic-pressure supplying oil passage by giving an offset to the opening of the first control valve while the transmission-ratio feedback control for line pressure is being carried out.

5. The hydraulic control apparatus as claimed in claim 4, wherein

the first hydraulic-pressure control section is configured to determine an amount of the offset in accordance with a level of the line pressure at the start time of the transmission-ratio feedback control.

6. The hydraulic control apparatus as claimed in claim 3, wherein

the first hydraulic-pressure control section is a mechanical feedback mechanism including

a drive source adapted to output a driving amount according to the target transmission ratio, and

a link adapted to provide the opening of the first control valve in accordance with the driving amount and the groove width between the drive pulleys;

and

the mechanical feedback mechanism is adapted to adjust the first hydraulic pressure to bring the groove width between the drive pulleys to its value for achieving the target transmission ratio.

7. The hydraulic control apparatus as claimed in claim 6, wherein when the actual transmission ratio produced by the mechanical feedback mechanism has a deviation from the target transmission ratio,

the line-pressure control section is configured

to bring the actual transmission ratio substantially equal to the target transmission ratio by correcting the driving amount, then

to reduce the line pressure adjusted to the value set by adding the margin pressure, and then

to carry out the transmission-ratio feedback control for line pressure.

8. The hydraulic control apparatus as claimed in claim 6, wherein

the drive source is a step motor adapted to output a rotational step number according to the target transmission ratio as the driving amount;

the link includes

a rod adapted to extend or contract according to the rotational step number,

a position sensor connected with the first movable pulley and adapted to extend or contract according to the groove width of drive pulleys,

a first link member connecting the rod with the position sensor, and

a second link member connecting a middle portion of the first link member with a spool of the first control valve; and

the actual transmission-ratio sensing section is the position sensor.

9. The hydraulic control apparatus as claimed in claim 3, wherein

the first control valve is an electronic control valve whose opening is directly controlled by electromagnetic force.

10. The hydraulic control apparatus as claimed in claim 3, wherein

the first control valve is a hydraulic control valve whose opening is controlled by a signal pressure outputted according to the target transmission ratio.

11. The hydraulic control apparatus as claimed in claim 10, wherein

the first hydraulic-pressure control section is configured to allow the line-pressure supplying oil passage to communicate with the first-hydraulic-pressure supplying oil passage by fixing the opening of the first control valve to its maximum during the transmission-ratio feedback control for line pressure.

12. The hydraulic control apparatus as claimed in claim 1, wherein

the line-pressure control section is configured to reduce the margin pressure when a vehicle is in a steady state where a transmission ratio is constant.

13. The hydraulic control apparatus as claimed in claim 1, wherein

the line-pressure control section is configured to reduce the margin pressure during a shift.

14. The hydraulic control apparatus as claimed in claim 13, wherein the shift is an upshift.

15. The hydraulic control apparatus as claimed in claim 13, wherein

the first hydraulic-pressure control section includes a first control valve adapted to adjust a communication between a line-pressure supplying oil passage and a first-hydraulic-pressure supplying oil passage for supplying the first hydraulic pressure to the drive pulleys;

the first hydraulic-pressure control section is configured

to adjust the first hydraulic pressure to its value for achieving a target transmission ratio by controlling an opening of the first control valve, and

to allow the line-pressure supplying oil passage to communicate with the first-hydraulic-pressure supplying oil passage by giving an offset to the opening of the first control valve, while the line-pressure control section is reducing the margin pressure; and

the line-pressure control section is configured to adjust the line pressure to bring the line pressure to a target value for first hydraulic pressure during the shift.

16. The hydraulic control apparatus as claimed in claim 13, wherein

the first hydraulic-pressure control section is a mechanical feedback mechanism including

a drive source adapted to output a driving amount according to a target transmission ratio, and

a link adapted to provide the opening of the first control valve in accordance with the driving amount and the groove width between the drive pulleys;

and

the mechanical feedback mechanism is adapted to adjust the first hydraulic pressure to bring the groove width between the drive pulleys to its value for achieving the target transmission ratio.

17. The hydraulic control apparatus as claimed in claim 16, wherein

the drive source is a step motor adapted to output a rotational step number according to the target transmission ratio as the driving amount;

and

the link includes

a rod adapted to extend or contract according to the rotational step number,

a position sensor connected with the first movable pulley and adapted to extend or contract according to the groove width of drive pulleys,

a first link member connecting the rod with the position sensor, and

a second link member connecting a middle portion of the first link member with a spool of the first control valve.

18. The hydraulic control apparatus as claimed in claim 13, wherein

the first control valve is an electronic control valve whose opening is directly controlled by electromagnetic force.

19. The hydraulic control apparatus as claimed in claim 13, wherein

the first control valve is a hydraulic control valve whose opening is controlled by a signal pressure outputted according to a target transmission ratio.

20. The hydraulic control apparatus as claimed in claim 19, wherein

the first hydraulic-pressure control section is configured to allow a line-pressure supplying oil passage to communicate with a first-hydraulic-pressure supplying oil passage by fixing the opening of the first control valve to its maximum, while the line-pressure control section is reducing the margin pressure.

21. A hydraulic control apparatus comprising:

a continuously-variable transmission including

a pair of drive pulleys including a first movable pulley and a first fixed pulley,

a pair of driven pulleys including a second movable pulley and a second fixed pulley, and

a belt wound between the pair of drive pulleys and the pair of driven pulleys, the continuously-variable transmission being adapted to be continuously shifted by moving at least one of the first movable pulley and the second movable pulley by means of hydraulic pressure and thereby varying at least one of a groove width between the pair of drive pulleys and a groove width between the pair of driven pulleys;

first means for producing a line pressure by adjusting a discharge pressure of an oil pump;

second means for adjusting a first hydraulic pressure based on the line pressure, the first hydraulic pressure being supplied to the drive pulleys; and

third means for adjusting a second hydraulic pressure based on the line pressure, the second hydraulic pressure being supplied to the driven pulleys,

the first means including

means for adjusting the line pressure to a value set by adding a margin pressure to higher one of the first hydraulic pressure and the second hydraulic-pressure, and

means for reducing the margin pressure when the first hydraulic pressure is higher than the second hydraulic pressure.

22. A hydraulic control method for a continuously-variable transmission including

a pair of drive pulleys including a first movable pulley and a first fixed pulley,

a pair of driven pulleys including a second movable pulley and a second fixed pulley, and

a belt wound between the pair of drive pulleys and the pair of driven pulleys, the continuously-variable transmission being adapted to be continuously shifted by moving at least one of the first movable pulley and the second movable pulley by means of hydraulic pressure and thereby varying at least one of a groove width between the pair of drive pulleys and a groove width between the pair of driven pulleys,

the hydraulic control method comprising:

producing a line pressure by adjusting a discharge pressure of an oil pump so as to bring the line pressure to a value set by adding a margin pressure to higher one of a target first hydraulic pressure and a target second hydraulic pressure;

adjusting a first hydraulic pressure to the target first hydraulic pressure on the basis of the line pressure, the first hydraulic pressure being supplied to the drive pulleys;

adjusting a second hydraulic pressure to the target second hydraulic pressure on the basis of the line pressure, the second hydraulic pressure being supplied to the driven pulleys; and

reducing the margin pressure when the first hydraulic pressure is higher than the second hydraulic pressure.