GB2111613A - Controlling gearbox and clutch of a power transmission - Google Patents

Abstract

A control system for a power transmission system which incorporates a multi-range gearbox and a clutch, comprises a clutch operating lever (4), a fluid-pressure operated servo cylinder (7) for disengaging the clutch and operable in response to movement of the clutch operating lever (4), a double acting fluid-pressure-operated actuator (10) for changing gear ranges in the gearbox, a selector valve (11) for selectively directing pressurised fluid (normally air) in opposite directions to the actuator, and valve means such as a relay valve (20) or a pressure regulating valve for transmitting pressurised fluid to the selector valve (11) to move the actuator (10) during or after disengagement of the clutch, the valve means (20) being operable by changes in fluid pressure e.g. in an hydraulic circuit (5,6,7) or a pneumatic circuit (8), resulting from movement of the clutch operating lever (4). <IMAGE>

Description

SPECIFICATION Power transmission control system This invention relates to control systems for power transmission systems which incorporate a multi-range gearbox and a clutch, such as those which are frequently incorporated in trucks.

One known system of this type comprises a clutch operating lever, a fluid-pressure operated servo cylinder for disengaging the clutch and operable in response to movement of the clutch operating lever, a double acting fluid-pressure operated actuator for effecting changes in gear ranges within the multi-range gearbox, a selector valve for selectively directing pressurised fluid in opposite directions to the said actuator to move it in opposite directions, and a control valve for transmitting fluid to the selector valve to effect movement of the actuator during or immediately after disengagement of the clutch. (In this specification the term "fluid" includes both gases and liquids and therefor encompasses pneumatic and hydraulic systems).

The control valve of this known system comprises a two position valve which, in its open position effects communication between a source of fluid pressure and the selector valve. The control valve is opened and closed by direct mechanical actuation by means of an actuating mechanism connected to the clutch pedal or the clutch actuating lever.

The mechanical connection between the control valve and the clutch pedal has a number of disadvantages. First, it requires that the control valve be positioned physically close to the clutch pedal, which in turn requires fluid supply lines to be led to the front of the vehicle and into the vehicle cab, both of which can be difficult to provide in the limited available space. Moreover, the discharge of compressed gases into the confined space of a vehicle cab is undesirable.

Secondly, the interaction between the clutch pedal and the valve can be felt by the driver during actuation of the clutch and can be disconcerting.

Thirdly, the mechanical connection may require adjustment during the life of the vehicle due to misalignment of the actuating rod and the control valve as the clutch wears. Fourthly, the additional moving parts required by the system add to the assembly and maintenance costs of the system.

According to the present invention there is provided a control system for a power transmission system which incorporates a multirange gearbox and a clutch, the control system comprising a clutch operating lever, a fluidpressure operated servo cylinder for disengaging the clutch and operable in response to movement of the clutch operating lever, a double acting fluid-pressure-operated actuator for effecting changes in gear ranges within the multi-range gearbox, a selector valve for selectively directing pressurised fluid in opposite directions to the said actuator, to move the actuator in opposite directions and valve means operable in response to movement of the clutch pedal for transmitting pressurised fluid to the selector valve to effect movement of the actuator during or after disengagement of the clutch, characterised in that the valve means is operated by changes in fluid pressure resulting from movement of the clutch operating lever.

By arranging the valve means to be operated by changes in fluid pressure resulting from movement of the clutch pedal, it is no longer necessary to position the valve means adjacent the clutch pedal. As a result, all the disadvantages mentioned above can be avoided.

The valve means may be in any convenient form. For example, it may comprise a pressure regulator valve for transmitting fluid pressure between the servo cylinder and the selector valve when the pressure in the servo cylinder exceeds a predetermined level, following actuation of the clutch pedal.

Alternatively, the valve means may comprise a relay valve having an open position, for effecting communication between the selector valve and a source of fluid pressure, and a closed position, for preventing such communication. Any convenient means may be adopted for operating the relay valve. For example, where the clutch operating lever operates an hydraulic circuit between a master cylinder and a slave cylinder for operating the servo cylinder, the relay valve may be operable in response to changes in the hydraulic fluid pressure in the hydraulic circuit. Alternatively, the relay valve may be operable in response to changes in fluid pressure in the servo cylinder.

The system may be hydraulically or pneumatically operated. Where the system is used in trucks however, the servo cylinder, actuator, selector valve and valve means are preferably pneumatic.

Three specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a first embodiment of a control system in accordance with the invention; Figure 2 is a circuit diagram of a second embodiment of a control system in accordance with the invention; and Figure 3 is a circuit diagram of a third embodiment of a control system in accordance with the invention.

In the drawings, similar components are identified by like reference numerals.

Referring to Figure 1, a control system for a power transmission system is illustrated. The power transmission system comprises a multirange gearbox (not shown) in which the ranges of gears are selected by means of a selector rod 1, which is movable between two positions, individual gears within each range being selected .by means of a gear shift lever (not shown). The power transmission system also includes a clutch (not shown) operated by a clutch actuating rod 3.

The control system for the power transmission system comprises a clutch operating lever, or pedal, 4 which is connected to an hydraulic master cylinder 5. The master cylinder 5 is connected by means of an hydraulic line 6 to a slave cylinder 7 which operates a pneumatic servo cylinder 8. The servo cylinder is connected to the clutch operating lever 3 and to one port 9 of an air supply block (not shown) which provides a source of compressed air when the vehicle is in use. The combined hydraulic/pneumatic slave and booster cylinder assembly 7,8 is of conventional construction.

The selector rod 1 is movable between its two positions by a double-acting pneumatically operated actuator 10 which is controlled by a pneumatic selector valve 11. The selector valve 11 is a two-position spool valve operable manually by the vehicle driver and having an inlet port 12, a vent port 13, and two outlet ports, 15, 16. When the spool 1 7 of the selector valve 11 is in its first position (illustrated), the inlet port 12 is in communication with the first outlet port 1 5, and the second outlet port 1 6 is in communication with the vent port 13. In the second position, the inlet port 1 2 communicates with the second outlet port 16 and the first outlet port 1 5 communicates with the vent port 13.

The two outlet ports 1 5, 16 of the selector valve are connected to the head-and rod-ends respectively of the actuator 10 so that, when fluid pressure is present in the inlet port 12, the actuator will extend when the selector valve 11 is in its first position and retract when the selector valve 11 is in its second position thereby enabling the selector rod 1 to be moved between its two positions.

The supply of pneumatic pressure to the selector valve 11 is controlled by a relay valve 20.

The relay valve 20 has a valve member 21 movable between an open position (not shown) in which another outlet port 22 in the air supply block is placed in communication with the inlet port 12 of the relay valve 11, and a closed position (illustrated) in which the line from the outlet port 22 is closed, and the inlet port 12 of the relay valve 11 is vented. The valve member 21 is biased into the closed position by a spring 23 and is movable into the open position by air pressure applied to the relay valve 11 along an air line 24.

The air line 24 is connected to the servo cylinder 8 and transmits the air pressure therein to the relay valve 20.

The operation of the control system is as follows: When the vehicle is in use the servo cylinder will normally be unpressurised, so that the relay valve 20 is in its closed position, illustrated. The outlet port 1 2 of the selector valve 11 is therefore vented, and both sides of the actuator 10 are at atmospheric pressure.

If the driver wishes to change gear without changing the gear range of the gearbox, he depresses the clutch operating lever 4, thereby pressurising the master and slave cylinders 5 and 7. When the pressure in the slave cylinder 7 exceeds a predetermined minimum, pneumatic pressure from the outlet port 9 of the air block is applied to the servo cylinder 8. The pressure in the servo cylinder 8 is transmitted to the relay valve 20 and when this pressure exceeds that of the spring 23 the relay valve opens thereby placing the further outlet 22 in the air supply block in communication with the inlet port 12 of the selector valve. The actuator 10 will therefore tend to extend downwardly as seen in the drawings.

However, since the actuator 10 is already in its fully extended position, no further movement will occur, and the selector rod 1 will not move. The driver can then change gear and release the lever 4, thereby depressurising the master and slave cylinders. The pressure in the servo cylinder 8 will then be vented to atmosphere, allowing the clutch to engage again, and the relay valve to return to its closed position.

If the driver wishes to select a different gear range, he will position the selector valve in its second position so that the inlet port 1 2 is placed in communication with the second outlet port 1 6 and the first outlet port is vented. When the clutch operating lever 4 is depressed the system will operate as described above, except that the pneumatic pressure applied via the relay valve 20 will be communicated by the selection valve 11 to the rod end of the actuator 1 0, the head end being vented to atmosphere. The actuator 10 will therefore move the selector rod 1 into its other position, causing a different gear range to be selected in the gearbox.

In orderto ensure that the selector rod has travelled fully into its other position during or immediately after disengagement of the clutch, the rating of the spring 23 is so chosen that the relay valve 20 moves into the open position after the pressure in the servo cylinder has reached a level sufficient to initiate disengagement of the clutch.

Referring now to Figure 2, an alternative control system is illustrated. This system is identical to that of Figure 1, except that the relay valve 20 is operable in response to changes in hydraulic fluid pressure in the hydraulic circuit between the master and slave cylinders 5 and 7. The operation of the system is as described with reference to Figure 1 except that the valve of the spring 23 will be so chosen in relation to the changes in hydraulic pressure in the line 6 that the relay valve 20 opens whilst the servo cylinder 8 disengages the clutch or immediately thereafter.

Referring now to Figure 3, a further alternative control system is illustrated. This system is identical to that of Figure 1, except that the relay valve 20 is replaced by a pressure regulator valve 30. This valve transmits the pressure in the servo cylinder 8 directly to the inlet port 1 2 of the selector valve 11 and therefore eliminates the connection to the further port 22 of the air supply block. The pressure regulator valve includes a pilot passage 31 and a variable-rating spring 32. When the pressure in the servo cylinder 8 exceeds the pressure of the spring 32, the pressure applied to the regulator valve 30 via its pilot passage 31 opens the valve 30 which communicates the air pressure in the servo cylinder 8 with the inlet port 12 of the selector valve 11. Again, the rating of the spring 32 is selected so that the regulator valve 30 opens after the pressure in the servo cylinder 8 is sufficient to initiate disengagement of the clutch.

In all the control systems described above, the relay and pressure regulating valves controlling the supply of pressure to the selector valve 11 are operated by fluid pressure. They can consequently be positioned at any convenient location in the vehicle and can be remote from the clutch operating lever 4. Since there is no mechanical connection between these valves and the lever 4, the driver will be unable to feel the operation of the valves as the lever 4 is depressed. Moreover, the operation of the valves will be unaffected by changes in the initial position of the clutch actuating rod which occur as the clutch wears.

Claims (7)

1. A control system for a power transmission system which incorporates a multi-range gearbox and a clutch, the control system comprising a clutch operating lever, a fluid-pressure operated servo cylinder for disengaging the clutch and operable in response to movement of the clutch operating lever, a double acting fluid-pressure-operated actuator for effecting changes in gear changes within the multi-range gearbox, a selector valve for selectively directing pressurised fluid in opposite directions to the said actuator, to move the actuator in opposite directions and valve means operable in response to movement of the clutch pedal for transmitting pressurised fluid to the selector valve to effect movement of the actuator during or after disengagement of the clutch, characterised in that the valve means is operated by changes in fluid pressure resulting from movement of the clutch operating lever.

2. A system according to Claim 1 wherein the valve means comprises a relay valve having an open position, for effecting communication between the selector valve and a source of fluid pressure, and a closed position, for preventing such communication.

3. A system according to Claim 2 wherein the clutch pedal operates an hydraulic circuit between a master cylinder and a slave cylinder, for operating the servo cylinder and the relay valve is operable in response to changes in the hydraulic fluid pressure in the hydraulic circuit.

4. A system according to Claim 2 wherein the relay valve is operable in response to changes in the fluid pressure in the servo cylinder.

5. A system according to Claim 1 wherein the valve means comprises a pressure regulator valve for transmitting fluid pressure between the servo cylinder and the selector valve when the pressure in the servo cylinder exceeds a predetermined level.

6. A system according to any one of Claims 1 to 5 wherein the servo cylinder, the actuator, the selector valve and the valve means are pneumatic.

7. A control system for a power transmission system substantially as hereinbefore described with reference to Figures 1, 2 or 3 of the accompanying drawings.