Hydraulic control circuit for a continuously variable transmission

• US 20040171457A1
• Filed: 12/03/2003
• Published: 09/02/2004
• Est. Priority Date: 06/04/2001
• Status: Active Grant

• Current Assignee: Torotrak Limited (Torotrak Plc)
• Original Assignee: Torotrak Limited (Torotrak Plc)
• Inventors: Fuller, John William Edward
• Granted Patent: US 7,056,261 B2
• Time in Patent Office: Days
• US Class Current: 477/37
• CPC Class Codes: F16H 2061/6605 Control for completing downshift at hard braking
• CPC Class Codes: F16H 61/6648 controlling of shifting being influenced by a signal derived from the engine and the main coupling

Abstract

A hydraulic control circuit is disclosed for a continuously variable transmission having a continuously variable transmission unit (“variator”) in which the position of at least one ratio determining element (e.g. A roller 28 of a toroidal race rolling traction type variator) is influenced by means of a hydraulic actuator (100, 100′, 100″). The control circuit comprises a flow line (106) through which hydraulic fluid is fed to and from the actuator means (eg. A control valve 116 disposed in the flow line) for adjusting pressure in the flow line, and a first valve (125) connected to the flow line so that opening of the first valve diverts flow of fluid to/from the flow line.

Claims

1. A hydraulic circuit for a continuously variable transmission comprising a continuously variable ratio unit (“

variator”

) which is controllable by means of at least one hydraulic actuator acting on a movable torque transmission element of the variator, the actuator having opposed first and second working chambers and the circuit comprising first and second flow lines both connected to respective actuator working chambers for feeding fluid thereto and therefrom and means for supplying fluid flow through both of the flow lines, variable control valve means being incorporated in both flow lines for generating an adjustable back pressure therein and a further valve being connected between the two flow lines, upstream of the variable control valve means, whereby opening of the further valve enables flow of fluid from one flow line to the other in order to reduce pressure difference between the lines.

2. A hydraulic control circuit as claimed in claim 1, provided with an electronic control unit (ECU) whereby the state of the further valve is determined in dependence on measured transmission and/or vehicle operating conditions.

3. A hydraulic control circuit as claimed in claim 2 wherein the further valve has a variable opening.

4. A hydraulic control circuit as claimed in claim 2 or claim 3 wherein the further valve is a flow control valve.

5. A hydraulic control circuit as claimed in claims 2 to 4 wherein the ECU is arranged to detect a requirement for rapid ratio change and to open the further valve in response.

6. A hydraulic control circuit as claimed in any of claims 2 to 5 wherein the ECU is arranged to monitor vehicle acceleration and to control the further valve in dependence thereupon.

7. A hydraulic control circuit as claimed in any of claims 2 to 6 wherein the ECU is arranged to monitor transmission ratio and to control the further valve in dependence thereupon.

8. A hydraulic control circuit as claimed in any of claims 1 to 7 for a continuously variable transmission operable in low and high regimes, the ECU being arranged to monitor transmission regime and to open the further valve fully only in low regime.

9. A hydraulic control circuit as claimed in any preceding claim for a continuously variable transmission having geared neutral, wherein the ECU is arranged such that after opening the further valve during deceleration, it progressively closes the further valve as the transmission approaches geared neutral.

10. A continuously variable transmission comprising a toroidal race, rolling traction variator and a hydraulic circuit as claimed in any preceding claim.

11. A continuously variable transmission as claimed in claim 10 wherein the variator is a torque control variator.