GB2235513A

GB2235513A - Clutch control valve

Info

Publication number: GB2235513A
Application number: GB8913036A
Authority: GB
Inventors: William Stuart Jennins
Original assignee: Electro Hydraulic Technology Ltd
Current assignee: Electro Hydraulic Technology Ltd
Priority date: 1989-06-07
Filing date: 1989-06-07
Publication date: 1991-03-06
Also published as: GB8913036D0

Abstract

An electrically controlled clutch control valve which provides both hydraulic flow and hydraulic pressure control to the clutch cylinder comprises a valve body 11 containing a spool 12 maintained in contact with the drive pin 13 of the electrical actuator 14 by a spring 20. Port 16 is in communication with the clutch cylinder and when an increase in pressure is required, spool 12 is pushed by actuator 14 to allow additional fluid to flow from the pump port 17. When pressure is higher than required, the spool is moved to allow port 16 to communicate with the tank port 18. To control flow, positional feedback with respect to the spool is provided by a displacement detector 19 and the spool is moved to known positions (FIGS 3 and 4). When a position of maximum pressure is reached a further displacement detector on the clutch cylinder instructs the control circuit not to increase the pressure further. Gear changing is permitted when the ports 17, 18 are isolated from port 16 and the clutch is disengaged. <IMAGE>

Description

CLUTCH CONTROL VALVE This invention relates to a valve for the hydraulic control of a clutch for a semi-automatic gearbox, for use in vehicles, particularly motor vehicles,which valve is hereinafter referred to for convenience as a "clutch control valve", and to control system which comprises the valve.

A friction plate clutch is often used to transmit the drive from the engine to the gearbox of a vehicle. The gear ratios in the gearbox are changed whilst the clutch is disengaged, and the smooth transition from one gear to another is dependent on the manner in which the clutch is disengaged, and particularly on the manner in which it is re-engaged. Within a typical clutch assembly, the friction plate is clamped to the driven member by means of a spring loaded plate, typically a diaphragm spring plate. The movement of this diaphragm spring plate is controlled by a hydraulic clutch cylinder. Typically a manually operated clutch is controlled by hydraulic flow and pressure control of this cylinder are used to control the clutch operation.

We have now devised an electrically controlled clutch control valve which provides both hydraulic flow and pressure control to the clutch cylinder.

It can provide numerous rates of clutch engagement, each rate to be selected according to the requirements of the vehicle's transmission at the time of engagement as is more fully hereinafter described.

According to the first aspect of the present invention, there is provided a clutch control valve which comprises (a) a spool working within a valve housing, (b) an electrical actuator for operating the spool, and (c) a first displacement detector adapted to provide a feed back of the position of the spool.

The spool diameter, the spool length and the travel would be readily determined by a man skilled in the art. Typically the spool diameter would be between 2 mm and 12 mm.

A dual diameter spool is preferred, but an alternative design can be used utilising a single diameter spool. The valve housing would typically be cylindrical in shape, containing the spool therein and with the electrical actuator mounted on one end thereof.

The clutch control valve according to the present invention is used in conjunction with a second displacement detector fitted to the clutch cylinder and with electronic controls, typically a micro-processor.

Typically the functions of this micro-processor would include the selection of the rate of engagement appropriate to the vehicle's transmission at the time of clutch engagement. The selection would determine the time taken for the decay of pressure as the clutch moves towards the fully engaged position. We do not exclude the possibility of other means of selection being used, for example the driver of the vehicle may select the rate of engagement to be used.

According to the second aspect of the present invention there is provided a clutch control system comprising a clutch control valve according to the first aspect, a second displacement detector and electronic controls.

The aformentioned displacement detectors would typically be either a potentiometer or a linear variable differential transformer (LVDT), but we do not exclude the possibility of the use of an other type of displacement detector.

The electrical actuator would typically be a proportional solenoid, or an alternative electrical actuator as may considered appropriate by a man skilled in the art. The displacement detector would typically be fitted to the electrical actuator, at the end furthest from the spool.

To allow the valve to control flow rather than pressure, the spool has to moved to known positions, and the positional feedback is by means of the displacement detector. For the flow through the valve to be stopped, the spool has to be moved to a certain first position as is more fully illustrated hereinafter in Figure 3. In this manner, the clutch cylinder will be held in the position required to have the clutch disengaged, thereby permitting the changing of gear ratios in the gearbox. To permit a specific flow rate from the clutch to the tank port, the spool will be moved to a certain second position as is more fully illustrated hereinafter in Figure 4.

The present invention will be further described by reference to the accompanying drawings, which show by example only, one embodiment of a clutch control valve according to the present invention.

Figure 1 illustrates, in graphical form, the hydraulic pressures required to operate the clutch during the movement of the said clutch, together with the controls provided by the clutch control valve.

Figure 2 illustrates the clutch control valve, partly in longitudinal section.

Figures 3 and 4 illustrate the clutch control valve in two different working modes, partly in longitudinal section.

Referring firstly to Figure 1, in which the pressure control phases are shown in full lines, and the flow control phases are represented by broken lines. Clutch travel from position 1 on the graph to position 2 is at an increasing pressure, to a maximum pressure reached at position 2. The pressure increase may be uniform, or otherwise, and it will be appreciated that the pressure will be greater than that required to move the clutch cylinder against the spring force in the clutch assembly. When this position 2 is reached, the signal from the second displacement detector on the clutch cylinder will instruct the control circuit not to increase the pressure any further, and the pressure will remain constant for the remainder of the stroke, i. e. until position 3 is reached. At this position, the valve will close as described hereinafter.The relative position of the clutch will remain constant until the clutch is to be re-engaged, when the valve will be moved to a partially open position, as described hereinafter, allowing fluid to flow from the clutch cylinder to tank. The clutch will then move towards the engaged position, position 5 on the graph. At this position, the pressure control will resume, and the pressure will then decay as the clutch travels towards the fully engaged position. The time taken for this pressure decay will vary according the speed at which the clutch is to be engaged, as hereinbefore described.

Line 7 in Figure 1 indicates the pressure required to move the clutch cylinder against the spring force in the clutch assembly.Typically, the pressure required will be between 25 bar and 100 bar, and the clutch travel will be between 2 mm and 20 mm.

Referring now to Figure 2, which illustrates the valve having a valve body (11), in which is disposed a spool (12), which is maintained in contact with drive pin (13) of the electrical actuator (14) by the spring (20). The first displacement detector (19) is mechanically linked to drive pin (13), and is used to indicate the spool position. Port (16) is in fluid flow connection with the clutch cylinder. The spool slides along the bore of the valve body (11), according to the force applied to the the spool by the drive pin (13) of the electrical actuator (14). When the valve is running in the pressure control mode, the pressure generated in chamber (15) is proportional to the force generated by the electrical actuator (14). When an increase in pressure is required, the spool (12) is pushed by the electrical actuator (14) in order to allow additional fluid from the pump port (17).When the pressure is higher than that required, the spool will move along the bore to allow the clutch cylinder port (16) to become in fluid flow connection with the tank port (18).

Referring now to Figures 3 and 4. To allow the valve to control flow rather than pressure, the spool has to moved to known positions, and the positional feedback is by means of the displacement detector (19), shown in Figure 2. For the flow through the valve to be substantially stopped, the spool is moved to the position shown in Figure 3, wherein both the tank port (18) and pump port (17) are isolated from the clutch cylinder port (16). When the spool is in the position shown in Figure 3, the clutch cylinder will be held in the position corresponding to having the clutch disengaged, thereby permitting the changing of gear ratios in the gearbox.

To permit a specific flow rate of hydraulic fluid from the clutch cylinder via clutch port (16) to tank via the tank port (18), the spool will be moved to the position shown in Figure 4, wherein the flow can occur from clutch port (16) to tank port (18).

When the valve is in the positions shown in Figures 3 and 4, the current required to drive the electrical actuator will relates to the pressure in chamber (15). By this means, the pressure in chamber (15) can be determined by the electronic controls (not shown) when position 5 in Figure 1 is reached. This information is used to determine the start point of the pressure decay phase, position 6 in Figure 1.

Claims

1. A clutch control valve suitable for a semi-automatic gearbox, comprising;- (a) a spool working within a valve housing, (b) an electrical actuator, and (c) a displacement detector to provide a feed back of the spool position, characterised in that the aforementioned constituent parts are adapted and arranged such that they control both pressure and flow of hydraulic fluid.

2. A clutch control valve as claimed in claim 1 wherein (i) the spool controls the pressure and (ii) the spool, in conjunction with the displacement detector, controls flow by moving to pre-determined positions.

3. A clutch control valve as claimed in claim 2 wherein the spool is a dual diameter.

4. A clutch control system comprising (i) a clutch control valve as claimed in any one of claims 1 to 3, (ii) a second displacement -detector and (iii) electronic controls.