GB2343929A

GB2343929A - Hydraulic clutch actuation system with electrically operated valve

Info

Publication number: GB2343929A
Application number: GB9924292A
Authority: GB
Inventors: Michael Neil Basnett
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-11-07
Filing date: 1999-10-15
Publication date: 2000-05-24
Also published as: GB9824362D0; GB9924292D0

Abstract

A clutch actuation system comprises a master cylinder 11 and a slave cylinder 12 connected via a hydraulic pipe 16 having an electrically operable valve, eg solenoid valve 20, controlled by an electronic control unit 15 that receives signal from an engine speed sensor 21, transmission speed sensor 22, gear lever sensor 23 and road wheel speed sensor 24. When a gear is engaged and the signals from the engine sensor 21 and transmission sensor 22 received by the control init 15 indicate that a speed difference is greater than a predetermined amount solenoid valve 20 is operated to restrict flow between cylinders 11, 12 thereby engaging the clutch gradually without shock. In a first and a second embodiment of valve 20 flow is switched between an unrestricted flow and a restricted flow (see figs 2 and 3), while in a third embodiment of valve 20 the restricted flow is variable (see fig 4).

Description

A Motor Vehicle and a Clutch Actuation Svstem Therefor This invention relates to a motor vehicle and in particular to a system to control the clutch engagement of a motor vehicle.

It is well known to provide a motor vehicle with a clutch to engage and disengage drive between an engine and a transmission of the motor vehicle.

The most common means of engaging and disengaging such a clutch is by means of a hydraulically operable actuator system comprising a driver operable master cylinder connected to a hydraulic slave cylinder linked to the clutch. By operating a lever associated with the master cylinder a driver of the motor vehicle can increase or decrease the hydraulic pressure in the system thereby causing the slave cylinder to move an actuating linkage between the slave cylinder and the clutch. In this way the driver is able to control engagement and disengagement of the clutch.

It is a problem with such a prior art arrangement that there are circumstances when rapid clutch engagement can result in damage to the transmission. For example, if the engine is operating at a high rotational speed and the transmission is stationery a large shock load will be transmitted to the transmission if the clutch is rapidly engaged with the transmission in gear. Similarly, if the vehicle is traversing down a hill in gear with the clutch disengaged but the engine idling then the converse situation will arise. The transmission will be rotating at a relatively high rotational speed relative to the engine and once again sudden and rapid engagement of the clutch will produce shock loadings in the transmission and the engine which are both undesirable and can lead to premature failure of these components.

It has previously been proposed to introduce a flow restrictor between the master cylinder and the slave cylinder to restrict the rate at which fluid can flow from the slave cylinder to the master cylinder while not restricting the flow from the master cylinder to the slave cylinder. However, such systems have been found to be unsatisfactory. It will be understood that these flow restrictor systems to be effective unnecessarily restrict the speed of engagement of the clutch during normal gear changes. This will normally produce rapid clutch wear due to the considerable amount of clutch slippage that occurs during such a slow engagement of the clutch.

It is an object of this invention to overcome the problems associated with the prior art.

According to the invention there is provided a motor vehicle having an engine, a transmission driven by the engine, a clutch interposed between the engine and the transmission to selectively connect the engine to the transmission and clutch control system to effect engagement and disengagement of the clutch, the clutch control system comprising a hydraulic master cylinder to provide a source of hydraulic fluid at pressure, a slave cylinder connected to the master cylinder and having an output member in engagement with the clutch to effect engagement and disengagement of the clutch, an electrically operable valve interposed between the master cylinder and the slave cylinder and an electronic control unit to control the electrically operable valve, the electronic control unit being arranged to receive signals indicative of engine and transmission rotational speeds wherein the electronic control unit is operable to proportionally restrict the rate of engagement of the clutch by controlling the flow of hydraulic fluid through the electrically operable valve when a speed difference greater than a predetermined amount is sensed to exist between the engine and the transmission.

The master cylinder may be operable by a driver operable lever.

The engine may have a speed sensor associated therewith to provide a signal indicative of the rotational speed of the engine to the electronic control unit.

The transmission may have an input shaft driven by the clutch, the rotational speed of which may be measured by a transmission speed sensor used to provide a signal indicative of transmission speed to the electronic control unit.

The electrically operable valve may have a valve member moveable between a first unrestricted flow position and a second flow restricting position by a solenoid.

The valve member may be biased into the first unrestricted flow position by a spring.

The solenoid when energised by the electronic control unit may move the valve member against the action of the spring into the second flow restricting position.

The electrically operable valve may have a first port for connection to the master cylinder and a second port for connection to the slave cylinder interconnected by one or more conduits formed as part of the electrically operable valve, the valve member being operable to change the effective cross-sectional area of the conduits from a relatively large cross-sectional area in said first unrestricted flow position to a relatively small crosssectional area in said second flow restricting position.

The electrically operable valve may alternatively have a first port for connection to the master cylinder and a second port for connection to the slave cylinder interconnected by one or more conduits formed as part of the electrically operable valve and a valve member operable to vary the effective cross-sectional area of the conduits between a relatively large crosssectional area to a relatively small cross-sectional area.

The valve member may be moveable by a solenoid to vary the crosssectional area of the conduits.

The valve member may be biased towards a position providing the maximum cross-sectional area by a spring and may be moved away from the position of maximum cross-sectional area by the solenoid.

The invention will now be described by way of example with reference to the accompanying drawing of which : Fig. 1 is a schematic representation of a clutch actuation system forming part of a motor vehicle according to the invention; Fig. 2 is a cross-section through a first embodiment of an electrically operable valve forming part of the clutch actuation system shown in Fig. l ; Fig. 3 is a cross-section through a second embodiment of an electrically operable valve forming part of the clutch actuation system shown in Fig. l ; and Fig. 4 is a cross-section through a third embodiment of an electrically operable valve forming part of the clutch actuation system shown in Fig. 1.

With reference to Figs. 1 and 2 there is shown an engine 2 forming part of a motor vehicle, the engine being arranged to drive a transmission in the form of a gearbox 4 through a clutch 13 mounted upon a flywheel 3 of the engine 2. The gearbox 4 has an input shaft 5 driven by the clutch 13 and an output shaft 6 to provide drive to one or more driven wheels of the motor vehicle. The gearbox 4 has a number of geartrains therein to vary the ratio between the input shaft 5 and the output shaft 6. A change speed mechanism controlled by a gear lever 7 is used to effect a ratio change within the gearbox 4.

Engagement and disengagement of the clutch 13 is effected by a clutch control system in the form of a hydraulic clutch actuation system.

The clutch actuation system comprises a hydraulic master cylinder 11 connected to a slave cylinder 12 by a hydraulic pipe 16, an electrically operable valve 20 controlled by an electronic control unit 15 and a driver operable lever 17 to effect pressurisation of the fluid within the master cylinder 11 by means of a push rod 18.

The driver operable lever in the form of the clutch pedal 17 is pivotally connected by means of a pivot pin 19 at its upper end to part of the body structure 8 of the motor vehicle.

Movement of the clutch pedal 17 by a motor vehicle operator will effect motion of the push rod 18 into or out from the master cylinder 11 in which it co-operates with an end face of a hydraulic piston (not shown). Movement of the push rod 18 into the master cylinder will cause hydraulic fluid to be displaced from the master cylinder along the pipe 16 into the slave cylinder 12. This will cause a piston (not shown) supported by the slave cylinder 12 to be displaced thereby moving an output member connected to the slave cylinder 12 in the form of an actuation lever 14.

The actuation lever 14 is arranged at the opposite end to its position of connection to the slave cylinder 12 to co-operate with a release bearing (not shown) used to release and engage the clutch 13.

The electronic control unit 15 is arranged to receive a signal indicative of engine rotational speed from an engine speed sensor 21, a signal indicative of transmission rotational speed from a transmission speed sensor 22, a signal indicative of gear lever position from a gear lever sensor 23 and a signal indicative of road wheel speed from a road wheel speed sensor 24 associated with a road wheel 9 of the motor vehicle.

With particular reference to Fig. 2 there is shown an electrically operable valve 20 having a body defining a number of conduits 33,34. The valve member 20 has a first port 32 for connection to the master cylinder 11 and a second port 31 to connect the valve member 20 to the slave cylinder 12 by means of the pipe 16.

The first and second ports 32,31 are connected within the body of the valve member 20 by the conduits 33,34.

An orifice plate 35 having a first orifice 36 of large cross-sectional area and a second orifice 37 of relatively smaller cross-sectional area is interposed between the conduits 33,34. A valve member 38 is biased away from the orifice plate 35 by a helical spring 39, the helical spring acting against a spring abutment 40 formed on one end of the valve member 38 and an abutment surface formed within the body of the valve 20.

A solenoid 41 is connected to the electronic control unit 15 by means of two wires W. When the solenoid 41 is not energised by the electronic control unit 15 the valve member 38 adopts the position as shown in Fig. 2 due to the biasing effect of the spring 39. When the solenoid 41 is energised by the electronic control unit 15 the valve member 38 is urged away from the solenoid 41 until it abuts the orifice plate 35. When the valve member 38 is in this second position it closes off the large orifice 36 so that the only connection between the conduit 33 and the conduit 34 is via the small orifice 37.

The electrically operable valve 20 is therefore operable in two states. A first state in which the large orifice 36 is uncovered and a virtually unrestricted flow through the valve 20 between the first and second ports 32,31 is possible and a second state in which the valve member 38 obscures the large orifice 36 so that flow between the first and second ports 32,31 is restricted by the relatively small cross-sectional area of the small orifice 37.

The cross-sectional area of the large orifice 36 is substantially the same as or greater than the conduits 33,34 whereas the cross-sectional area of the small orifice 37 is relatively small compared to the cross-sectional area of the conduits 33,34.

Operation of the clutch actuating system is as follows. During normal operation the solenoid 41 is not energised by the electronic control unit 15 and so the flow between the master cylinder 11 and the slave cylinder 12 is unrestricted and very rapid engagement of the clutch 13 can be achieved.

However, when the signals from the engine sensor 21 and the transmission sensor 22 received by the electronic control unit 15 indicate that a speed difference greater than a predetermined amount is sensed to exist between the engine 2 and the gearbox 4 the electronic control unit is operable to energise the solenoid 41. This causes the valve member 38 to close off the large orifice 38 in the orifice plate 35 thereby restricting flow between the master cylinder 11 and the slave cylinder 12 in either direction.

However, as a significant speed difference can only occur when the clutch 13 is disengaged the principal effect of this closure of the large orifice 36 is to restrict the rate at which hydraulic fluid can return from the slave cylinder 12 to the master cylinder 11 thereby restricting the rate at which the clutch 13 can be engaged. Even if the driver suddenly removes their foot from the clutch pedal 17 the restriction due to the presence of the small orifice 37 is such that the clutch 13 will not be rapidly engaged but will engage gradually thereby preventing the transfer of a sudden shock loading to the gearbox 4.

To reduce the duration for which the solenoid 41 is energised the electronic control unit 15 is arranged to only energise the solenoid 41 when the signal from the gear lever sensor 23 indicates that the gearbox is in one of its driving gear ratios.

With particular reference to Fig. 3 there is shown an electrically operable valve 120 which is an alternative to the valve 20 previously described.

The electrically operable valve 120 has a first port 132 connected to a second port 131 by two conduits 133,134, the flow through which is controlled by a valve member 138.

The valve member 138 has an orifice plate 135 attached to one end and a spring abutment plate 140 attached to the opposite end. The spring abutment plate 140 is acted upon by a spring 139 biasing the valve member 138 away from a solenoid 141.

The orifice plate 135 has a number of flow orifices 136 around its circumference and a central control orifice 137 located in the centre of the orifice plate 135. The orifice plate 135 is biased against the end of the valve member 138 by a spring 146 thereby maintaining contact at all times between the orifice plate 135 and the valve member 138.

The control orifice 137 in the aperture plate 135 co-operates with a central bore 142 in the valve member 138. The bore 142 communicates with the conduit 133 by means of a cross-drilling 143. The outer surface of the valve member 138 has a number of flats thereon which form clearance passageways between the valve member and the body 150 of the electrically operable valve 120. This allows fluid to flow through the flow orifices 136 from the conduit 134 past the valve member 138 into the conduit 133. The cross-sectional area of the flow orifices 136 is substantially the same as the cross-sectional area of the conduits 133,134. Similarly, the clearance between the valve member 138 and the body 150 is such that it represents a cross-sectional area similar to that of the conduits 133,134.

The cross-sectional area of the control orifice 137, the bore 142 and the cross-drilling 143 are all considerably less than the cross-sectional area of the conduits 133,134. Therefore, when the valve member 138 is moved towards the solenoid 141 causing the orifice plate 135 to contact an abutment surface 145 formed in the body 150 a considerable restriction to flow through the electrically operable valve 120 is achieved.

Normally, the valve member 138 and the orifice plate 135 are in the positions shown in Fig. 3 and are only moved into the flow restricting position when the solenoid 141 is energised by the electronic control unit 15.

With reference to Fig. 4 there is shown a third embodiment of an electrically operable valve 220 which is different from the two valves previously described in that it is able to vary the restriction to flow rather than just switch the restriction between two predetermined levels. The electrically operable valve 220 has a first port 232 and a second port 231 interconnected by means of conduits 233,344 and a valve member in the form of a spool valve 238 moveable by a solenoid 241. The spool valve 238 is biased as shown in Fig. 4 by a spring 239 into a position where it provides minimal restriction to flow between the first and second ports 232,231. The spool valve 238 has two control diameters 236,237 which are moved into the conduits 233,234 to provide a varying restriction to flow. The spool valve 238 has an end plate 240 which is acted upon by the electro-magnetic forces produced by the solenoid 241. The electronic control unit 15 not only controls whether the solenoid 241 is energised or not but also varies the energising current to the solenoid thereby effecting the position of the spool valve 238 in the conduits 233,234. In this way, the cross-sectional area of the conduits 233,234 is varied between a condition in which flow through the conduits 233,234 is virtually unrestricted to a condition in which the larger diameter 237 of the spool valve 238 virtually obscures the conduits 233,234 thereby greatly restricting flow through the electrically operable valve 220.

Claims

CLAIMS 1. A motor vehicle having an engine, a transmission driven by the engine, a clutch interposed between the engine and the transmission to selectively connect the engine to the transmission and a clutch control system to effect engagement and dis-engagement of the clutch, the clutch control system comprising a hydraulic master cylinder to provide a source of hydraulic fluid at pressure, a slave cylinder connected to the master cylinder and having an output member in engagement with the clutch to effect engagement and dis-engagement of the clutch, an electrically operable valve interposed between the master cylinder and the slave cylinder and an electronic control unit to control the electrically operable valve, the electronic control unit being arranged to receive signals indicative of engine and transmission rotational speeds wherein the electronic control unit is operable to proportionally restrict the rate of engagement of the clutch by controlling the flow of hydraulic fluid to the electrically operable valve when a speed difference greater than a predetermined amount is sensed to exist between the engine and the transmission.
2. A motor vehicle as claimed in Claim 1 in which the master cylinder is operable by a driver operable lever.
3. A motor vehicle as claimed in Claim 1 or in Claim 2 in which the engine has a speed sensor associated therewith to provide a signal indicative of the rotational speed of the engine to the electronic control unit.
4. A motor vehicle as claimed in any of Claims 1 to 3 in which the transmission has an input shaft driven by the clutch, the rotational speed of which is measured by a transmission speed sensor used to provide a signal indicative of transmission speed to the electronic control unit.
5. A motor vehicle as claimed in any of Claims 1 to 4 in which the electrically operable valve has a valve member moveable between a first unrestricted flow position and a second flow restricting position by a solenoid.
6. A motor vehicle as claimed in Claim 5 in which the valve member is biased into the first unrestricted flow position by a spring.
7. A motor vehicle as claimed in Claim 6 in which the solenoid when energised by the electronic control unit moves the valve member against the action of the spring into the second flow restricting position.
8. A motor vehicle as claimed in any of Claims 5 to 7 in which the electrically operable valve has a first port for connection to the master cylinder and a second port for connection to the slave cylinder interconnected by one or more conduits formed as part of the electrically operable valve, the valve member being operable to change the effective cross-sectional area of the conduits from a relatively large cross sectional area in said first unrestricted flow position to a relatively small cross-sectional area in said second flow restricting position.
9. A motor vehicle as claimed in any of Claims 1 to 4 in which the electrically operable valve has a port for connection to the master cylinder and second port for connection to the slave cylinder interconnected by one or more conduits formed as part of the electrically operable valve and a valve member operable to vary the effective cross sectional area of the conduits between a relatively large cross-sectional area to a relatively small cross-sectional area.
10. A motor vehicle as claimed in Claim 9 in which the valve member is moveable by a solenoid to vary the cross-sectional area of the conduits.
11. A motor vehicle as claimed in Claim 10 in which the valve member is biased towards a position providing the maximum cross-sectional area by a spring.
12. A motor vehicle as claimed in Claim 11 in which the valve member is moved away from the position of maximum cross-sectional area by the solenoid.
13. A motor vehicle substantially as described herein with reference to the accompanying drawing.