GB2445872A

GB2445872A - Prioritising hydraulic supply between a clutch actuating circuit and a gearshift actuating circuit of an automatic manual transmission (AMT)

Info

Publication number: GB2445872A
Application number: GB0800969A
Authority: GB
Inventors: Shaun Mepham; Diogenes Peres; Lloyd Storey
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2007-01-18
Filing date: 2008-01-18
Publication date: 2008-07-23
Also published as: GB0700974D0; GB0800969D0

Abstract

An automatic manual transmission (AMT) includes a system for prioritising the supply of hydraulic pressure between a clutch actuating circuit and a gear selector actuating circuit. A clutch pressure circuit including a clutch pressure valve 114 and a clutch actuator 112, is connected to an hydraulic source, eg pump 102, and a priority valve 110 is arranged between the source and a gearshift circuit including gearshift control valves 120 and gearshift actuator 118. The priority valve 110 is configured to switch between a first position in which the gearshift circuit and an auxiliary flow conduit 122 (which returns fluid to the hydraulic supply or feeds an auxiliary circuit e.g. an oil or clutch cooling circuit) is connected to the hydraulic supply; a second position in which the supply of flow to the gearshift circuit is maintained but the supply of flow to the auxiliary circuit is disabled, and a third position in which the supply of flow to both the gearshift circuit and the auxiliary circuit is disabled. The priority valve 110 is configured to switch in response to a drop in supply pressure below predetermined thresholds.

Description

Hydraulic circuit for the control of a twin clutch transmission The

present invention relates to the control of vehicle transmissions, more particularly, but not exclusively, to hydraulic circuits for the control of twin clutch transmissions.

Various clutch release systems and clutch engagement systems are known for operating a clutch in an automated manual transmission. For example, an hydraulically actuated clutch is provided, wherein pressure is applied to clamp the clutch and thereby provide a transmission of torque from the engine to a speed change means within the transmission. In another system, the applied pressure is used to release the clutch and thereby break the transmission of torque. It is known to utilise both pressure clamping and pressure releasing systems to operate the two clutches of a twin clutch transmission.

It is also known to use a common hydraulic supply pump for operating one or more clutches and an hydraulic speed change shifting system within a transmission. In such systems, the pump may be unable to supply a sufficient volume of hydraulic fluid to drive the clutch and speed change shifting circuits concurrently, whereby the pressure will drop, resulting in a loss of clutch apply pressure during a speed change actuation.

In order to overcome this problem, a pump of increased capacity can be employed, in order to increase the available flow and pressure. However, driving the pump would increase the demand on the vehicle engine, thereby increasing fuel consumption.

It is an object of the invention to provide an alternative solution to the above problem.

According to a first aspect of the invention, there is provided an hydraulic circuit for controlling a vehicle transmission having a common hydraulic supply pump for operating one or more clutches and an hydraulic speed change shifting system within the transmission, the circuit having means for prioritising the supply of hydraulic pressure to a clutch pressure circuit over a gearshift circuit.

According to another aspect of the invention, there is provided an hydraulic system for controlling a vehicle transmission, the system having means for prioritising the supply of hydraulic pressure between at least two hydraulic circuits of an automated manual transmission including at least one clutch actuating circuit and a gear selector actuating circuit.

Other features and aspects of the invention will be readily apparent from the claims and the following description, made by way of example only, with respect to the accompanying drawings, in which: Figure 1 is a schematic layout of a conventional hydraulic control system for a vehicle transmission; Figure 2 is a schematic layout for a modified hydraulic control system incorporating a pressure regulating priority valve; and Figure 3 is a schematic and simplified layout for an hydraulic control system for a transmission, including means for prioritising flow to a clutch pressure circuit over a gearshift circuit.

A conventional hydraulic system for a vehicle transmission is indicated at 100 in figure 1.

An hydraulic pump 102 provides pressurised fluid to multiple circuits of the transmission, including a clutch pressure feed 104, a clutch cooling feed 106 and multiple gear selector valve feeds 108.

In such arrangements, all circuits may operate concurrently, resulting in a simultaneous demand for hydraulic pressure from the pump 102. If too high a demand is placed on the pump 102, it is possible for the level of pressure in the clutch pressure feed 104 to fall to a critically low level. This would cause a loss of clutch apply' pressure (and, hence, a loss of clutch clamping force), resulting in excessive clutch slip, engine flare or uncontrolled engine racing.

Referring to Figure 2, a pressure-regulating priority valve 110 is used to prioritise the supply of hydraulic pressure from the pump 102 to the clutch pressure feed 104. In particular, priority value 110 is used to restrict or prevent the flow of hydraulic fluid from the pump 102 to the gear selector valve feeds 108.

A simplified circuit 200 is shown in Figure 3, wherein a pump 102 is used to supply hydraulic pressure to a clutch actuator 112, via a clutch pressure valve 114 in the clutch pressure feed 104. If there is sufficient flow to maintain the necessary clutch pressure, the priority value 110 (controlled by a pilot pressure control conduit 116) adopts a first position in which both a gear selector valve feed 108 (and, hence, one or more gearshift control valves and a gearshift actuator 118) and an auxiliary or excess flow conduit 122 is connected to the hydraulic supply 102. Hence, with the priority valve 110 in a first position, pressure is supplied to the clutch pressure valve 114, gearshift control valve 120 and the auxiliary flow conduit 122.

If the supply flow to the circuit 200 drops, the pressure regulating the priority valve 110 will also drop. At a predetermined threshold, the priority valve 110 adopts a second position, in which a portion B of the valve 110 is aligned with inlet and outlet ports, thereby cutting out the flow to the auxiliary flow conduit 122, whilst maintaining a supply of hydraulic fluid at sufficient pressure for the gearshift control valve 120 and the clutch pressure valve 114.

If the pressure fall below a critical threshold, the priority valve 110 adopts a third position, in which supply to the gearshift control valve 120 and the auxiliary flow conduit 122 is disabled.

The function of the priority valve 110 is to prevent a drop in pressure supply to the clutch actuator 112 resulting from demand on the hydraulic supply from other circuits within the transmission. The arrangements of Figures 1 and 2 have particular advantage in ensuring no critical loss of clutch pressure during gearshift in a DCT or AMT.

In a preferred embodiment, the auxiliary flow conduit 122 is arranged for regulating maximum circuit pressure by returning excess hydraulic flow to the feed supply for the pump 102. However, in other embodiments, the conduit 122 may connect to an auxiliary supply circuit, e.g. an oil cooling circuit, oil cleaning filter circuit, or any other non-critical circuit in the transmission.

Claims

Claims I. An automated manual transmission having an hydraulic system

for prioritising the supply of hydraulic pressure between at least two hydraulic circuits, including at least one clutch actuating circuit and at least one gear selector actuating circuit.
2. A transmission according to claim I wherein the system includes a clutch pressure circuit connected to an hydraulic source, and a priority valve arranged between the hydraulic source and a gearshift circuit.
3. A transmission according to claim 2 wherein the priority valve is configured to switch between a first position in which the gearshift circuit is operatively connected to the hydraulic source, and a second position in which the supply of flow to the gearshift circuit is disabled.
4. A transmission according to 2 or claim 3 wherein priority valve is arranged for selectively connecting the hydraulic source to a gearshift circuit and an auxiliary flow circuit.
5. A transmission according to claim 4 wherein the auxiliary flow circuit is arranged for returning excess hydraulic flow to the hydraulic source.
6. A transmission circuit according to claim 4 wherein the auxiliary flow circuit is arranged for supplying hydraulic flow to at least one of an oil cooling circuit, oil cleaning filter circuit, or any other non-critical circuit in the transmission.
7. A transmission according to any of claims 4 to 6 wherein the priority valve is configured to switch between a first position in which the gearshift circuit and auxiliary flow circuit is operatively connected to the hydraulic source, a second position in which the supply of flow to the gearshift circuit is maintained but the supply of flow to the auxiliary flow circuit is disabled, and a third position in which the supply of flow to both the gearshift circuit and the auxiliary flow circuit is disabled.
8. A transmission according to any of claims 2 to 7 wherein the priority valve is a pressure regulating valve operable to move from a first position to a second position when the supply pressure from the hydraulic source falls below a predetermined threshold.
9. An hydraulic circuit for controlling a vehicle transmission having a common hydraulic supply pump for operating one or more clutches and an hydraulic gear shift mechanism within a transmission, the circuit having means for priontising the supply of hydraulic pressure to a clutch pressure circuit over a gearshift circuit.
10. A circuit according to claim 9 wherein the circuit includes a priority valve arranged between an hydraulic supply pump and a gearshift circuit.
11. A circuit according to claim 10 wherein the priority valve is configured to switch between a first position in which the gearshift Circuit is operatively connected to the supply pump, and a second position in which the supply of flow to the gearshift circuit is disabled.
12. A circuit according to 10 or claim 11 wherein priority valve is arranged for selectively connecting the hydraulic supply pump to a gearshift circuit and an auxiliary flow circuit.
13. A circuit according to claim 12 wherein the priority valve is configured to switch between a first position in which the gearshift circuit and auxiliary flow circuit is operatively connected to the supply pump, a second position in which the supply of flow to the gearshift circuit is maintained but the supply of flow to the auxiliary flow circuit is disabled, and a third position in which the supply of flow to the gearshift circuit and the auxiliary flow circuit is disabled.
14. A circuit according to any of claims 9 to 13 wherein the priority valve is a pressure regulating valve operable to move from a first position to a second position when the supply pressure from the pump falls below a predetermined threshold.
15. A prioritising hydraulic circuit for a vehicle transmission substantially as described herein and/or as illustrated in Figure 2 or Figure 3.