GB2057607A - Arrangement for Blocking a Vehicle Clutch - Google Patents

Abstract

An arrangement for holding a vehicle clutch in a position disengaging torque transmission between an engine and a gearbox, a hydraulic circuit being arranged for clutch operation to transfer movements between an operating means (7, 9) and at least one means (11, 14) actuating the clutch. A blocking valve (21), incorporated in the hydraulic circuit, has a non-return valve function regulated by a gear position sensor (24, 36) to allow flow of hydraulic medium in a direction from the operating means (7, 9) to the actuating means (11, 14) and to block the passage of hydraulic fluid in the opposite direction when a gear is not engaged in the gearbox. The operating means can be a clutch pedal (7) and the activating means a servo unit (11), the clutch pedal being articulatedly connected to a hydraulic piston (8) in a hydraulic cylinder, which in turn is articulatedly connected via the blocking valve to a hydraulic- pneumatic servo unit (11) attached to the vehicle and adapted to perform the actual disengagement work on being activated. The blocking valve comprises pressure-medium regulated control means (37, 53) by means of which the holding function of the blocking valve (21) can be disengaged when a gear is not engaged in the gearbox. In Figure 1 a gear selector 3 controls the movement of a shaft 19 on which a selector fork is mounted. A switch 5 is provided for disconnecting the driving wheels for use when the vehicle is stationary and is required to power ancillary equipment. <IMAGE>

Description

SPECIFICATION Arrangement for Blocking a Vehicle Clutch The present invention relates to an arrangement for holding a vehicle clutch in a position disengaging torque transmission between an engine and a gearbox, a hydraulic circuit being arranged for the operation of the clutch to transfer movements between an operating means and at least one means actuating the clutch.

In vehicle technology, gearboxes of the split type are used, especially with heavy vehicles, said gearboxes comprising a main gearbox and an auxiliary gearbox connected one after the other and individually operable. The auxiliary gearbox can be formed as a planetary gearing with two speeds. As a rule, the operation of such an auxiliary gearbox takes place half-automatically, signifying that the driver pre-selects a desired gear, e.g. by means of a gear selector switch, whereafter the gear change is triggered by a manual disengagement, usually by pushing down the clutch pedal of the vehicle. Such a gear change process results in that the driver does not have the same possibility as with a manual change to decide when the changing sequence is completed and when the clutch pedal can once again be released.This causes the risk that the engagement movement will not be completed during gear selection and that the teeth in the transmissions only partly mesh and thereby give cause for gear tooth damage.

A plurality of arrangements are known for eliminating this disadvantage, to ensure by blocking that the clutch between engine and gearbox will remain disengaged until the gearchanging sequence is completely executed. In these known arrangements a lever actuating the clutch is connected to a piston in a compressedair cylinder. When the clutch pedal is pressed down, the compressed-air cylinder is energized, the piston in it carrying out the de-clutching work proper. The piston is here adapted to coact with blocking means which, irrespective of whether the clutch pedal is released too early, holds the clutch in its disengaged position until the gearchanging sequence is completed.The blocking means comprise a blocking valve placed in the compressed-air pipe to the compressed-air cylinder and a sensing means which senses the gear position and in response thereto controls the blocking valve. When a gear is engaged, the blocking valve assumes an air-bleed position, and the compressed air in the compressed-air cylinder is released freely to the surroundings, simultaneously as communication with the vehicle compressed-air system is closed. During the gear-changing sequence, the blocking valve assumes a position which allows communication between the compressed-air system of the vehicle and the compressed-air cylinder, whereby the cylinder is completely filled with compressed air giving its piston maximum stroke and holding the clutch in a disengaged position during the gear-changing sequence.

Such known arrangements with clutch blocking in a compressed-air circuit are preferably suitable for clutch systems with manual adjustment of the clutch clearance as clutch plate wear takes place.

In heavy vehicles it is however becoming more and more usual to use servo units for clutch operation, having automatic adjustment of the clutch clearance in response to clutch plate wear.

Such a servo unit comprises a compressed-air cylinder, the piston of which is connected to the clutch lever via a push rod. When the servo unit is energized, the piston executes a movement with a stroke corresponding to the stroke of the clutch pedal. After energizing, the piston returns to a rest position under the action of spring force. Said rest position for the piston will be moved as the clutch plates wear, although on the other hand the stroke of the piston on operating the clutch pedal will be unaltered. This results in that the compressed-air cylinder must be formed with a stroke which is considerably greater than a maximum pedal travel.

When using such a servo unit, holding a clutch by the supply of compressed air to the compressed-air cylinder is not possible. The stroke the piston would have to execute would be larger than the movement of the clutch pedal, and this would cause clutch break-down. With regard to this, it has not been possible to utilize the advantages of a clearance-adjusting servo unit in gearboxes equipped with a holding device, and one has had to resort to the use of manual adjustment of the clutch plates.

The present invention hás the object of eliminating the last-mentioned disadvantages and relates to an arrangement for holding a clutch, which can also be used together with servo units having automatic adjustment of the clearance between the clutch plates. For clutch operation there is thus arranged a hydraulic circuit to transfer movements between an operating means and at least one actuating means for the clutch, the invention substantially being distinguished in that in the hydraulic circuit there is incorporated a blocking valve with a non-return function regulated by a gear position sensor to allow flow of hydraulic fluid in a direction from the operating means to the actuating means and to block the flow of hydraulic fluid in the opposite direction when a gear is not engaged in the gearbox.

The invention is further distinguished in that the gear position sensor comprises a piston displaceably mounted in the blocking valve, the outer end of said piston being adapted to engage against the cylindrical surface of an operating shaft displaceably mounted in the gearbox and adapted to engage in a recess formed in said shaft when a gear is not engaged.

In an advantageous embodiment of the inventive arrangement, the operating means is a clutch pedal and the actuating means is a servo unit. The clutch pedal is thus articulatedly connected to a hydraulic piston in a hydraulic cylinder, the latter being articulatedly connected via the blocking valve with a hydropneumatic servo unit attached to the vehicle, the servo unit being adapted for carrying out the actual disengagement work on being activated.

The invention will now be described with respect to the last-mentioned embodiment with reference to the appended drawings, in which Fig. 1 schematically illustrates an inventive arrangement for blocking a vehicle clutch, and Fig. 2 is a cross section of a blocking valve incorporated in this arrangement.

The arrangement in accordance with Fig. 1 is intended for a heavy vehicle, e.g. a lorry or a truck, provided with a so-called split gearbox which comprises a main gearbox (not shown) and an auxiliary gearbox 1 connected in series. The main gearbox is a conventional vehicle gearbox with a plurality of speeds, and the auxiliary gearbox 1 is a planetary gearing with two speeds.

Conduits from a compressed-air source 2 in the vehicle are connected conventionally to the auxiliary gearbox 1. Electrical wires from a gear selector 3 are also connected to the auxiliary gearbox 1, the gear selector comprising an electric switch by means of which the gear selector 3 can be caused to assume one of two positions corresponding to the two speeds of the gearbox 1. The gear selector 3 is connected to the vehicle current supply source 6 via a clutch pedal switch 4 and a switch 5 for disconnecting the drive on the vehicle wheels, the switch 5 in its initial position connecting the clutch pedal switch 4 with the current supply source 6.

The vehicle clutch is operated by a clutch pedal 7 which is articulatedly connected to a piston 8 in a stationary hydraulic cylinder 9. The latter is in turn connected to a servo unit 11 via a conduit 10, said servo unit being adapted for carrying out the actual declutching work. The servo unit 11 is conventionally attached to the vehicle and comprises a hydraulic piston 13 displaceable in a hydraulic cylinder 12, the piston being connected via a push rod 14 to a lever 1 5 intended for operating the clutch. The push rod 14 in the servo unit 11 also engages in a compressed-air cylinder 16 in which a displaceably mounted compressedair piston 1 7 is connected to the push rod 14 and via the latter can cause the lever 1 5 to pivot to operate the clutch.The supply of compressed air to the compressedair cylinder 1 6 is regulated by a valve 1 8 controlled by the hydraulic oil pressure in the hydraulic oil conduit 10, so that the compressed-air supply will be proportional to the hydraulic oil pressure.

The servo unit 11 is conventionally formed to automaticaily adjust the clutch clearance as wear takes place on the clutch plates, whereby the clearance remains substantially constant. The hydraulic piston 1 3 and the compressed-air piston 1 7 therefore have a greater stroke than is otherwise justified for operating the clutch.

The auxiliary gearbox 1 comprises an axially displaceable operating shaft 19 which conventionally carries a gear-change fork (not shown) for actuating gear-changing discs (not shown) and for engaging a desired gear. The operating shaft 19 is thereby controlled by pneumatic piston-cylinder units (not shown) which are controlled by solenoid valves (not shown) which in turn are controlled by the gear selector 3. In Fig. 1 there is only shown a part of this operating shaft 19, which is provided at its outer end with a radial recess 20 of limited axial extent.

In the hydraulic oil conduit 10 between the clutch pedal hydraulic cylinder 9 and the servo unit 11 there is connected a blocking valve 21 the structural form of which is described later on. This valve 21 has two positions, a blocking position 22 in which the valve acts as a non-return valve and only allows the passage of oil from the hydraulic cylinder 9 to the servo unit 11, and an open position 23 in which the valve 21 acts as an open communication allowing the passage of oil in both directions. The blocking valve 21 is provided with a sensing means 24 adapted for sensing which gear is engaged in the gearbox 1. When no gear is engaged, the sensing means 24 engages the recess 20 of the operating shaft 1 9, but otherwise engages the cylindrical surface 25 of the shaft 19 at one side of said recess 20.The blocking valve 21 thereby assumes the open position 23 when a gear is engaged, while it assumes the closed or blocking position 22 during the actual gear-changing process when no gear is engaged.

The blocking valve 21 is also connected to the vehicle compressed-air source 2 via a solenoid valve 26. Said valve 26 is controlled by means of the switch 5 for disconnecting the driving wheels.

When said switch is operated, the valve 26 assumes an open position 27, compressed air being fed to the blocking valve 21 which then assumes its open position 23. Simultaneously therewith, compressed air will also be supplied to the control means for the gearbox 1, to put the gearbox into neutral in a conventional manner.

When the valve 26 is not actuated, the valve connection 28 from the compressed-air source 2 is blocked and the valve connection 29 to the blocking valve 21 is thereby open to the surroundings for air bleeding.

The switch 5 for disconnecting the driving wheels is intended to be actuated when it is desired to use a power take-off on the vehicle gearbox, e.g. for ancillary equipment, when the vehicle is stationary, i.e. in such cases where no power transmission to the vehicle driving wheels can take place. In such a case, the clutch blocking means must be by-passed, and the auxiliary gearbox 1 must be caused to assume a neutral position. This is provided conventionally by suppiying compressed air via the valve 26 and a compressed-air conduit 30 to control means (not shown) intended for the purpose and provided in the gearbox 1.

The construction of the blocking valve 21 is illustrated in Fig. 2. It will be seen that a valve housing 31 is formed with a connection chamber 32 for a conduit from the hydraulic cylinder 9 of the clutch pedal 7, a connection chamber 33 for a conduit from the valve 26 for disengaging the driving wheels, and a connection chamber 34 for a conduit in communication with the servo unit 11. The valve housing 31 is formed with a cylindrical bottom hole 35 accommodating and constituting guidance for a lower piston 36 and an upper piston 37. An upwardly open bottom hole is made in the latter, said hole accommodating a compression spring 38.The spring 38 thereby bears against the bottom plane 39 of the cylindrical hole 35 and presses the upper piston 37 into engagement against the upper side of the lower piston 36, which in turn is pressed into engagement against the operating shaft 19, thereby acting as the sensing means 24 of the blocking valve 21.

The two pistons 36, 37 are chamfered on their mutually opposing sides, an annular space 40 thus being formed between them. This space 40 is in communication with the connection chamber 33 via a duct 41. The cylindrical surfaces of the two pistons 36, 37 are conventionally provided with seals 42 in the form of O-rings, sealing the space 40 between the pistons 36, 37. To enable evacuation of air enclosed in the cylinder hole 35, an air-bleed hole 43 is provided in the valve housing 31 and opens out at the bottom plane 39 of the cylindrical hole.

A non-return valve 44 is also incorporated in the valve housing 31. For this reason the valve housing 31 is formed with an upper shouldered cylindrical recess 50 in which the valve components are accommodated. The outer part of the recess 50 is provided with a thread in which an assembly plug 51 is screwed. A blind hole in the inside of the plug 51 accommodates a compression spring 46 urging a valve ball 45 into engagement against a valve seat 47, the latter being pressed into the recess 50 and into engagement against a shoulder. The valve seat 47 is designed such as to form an inlet chamber 48 in the non-return valve 44, said chamber 48 being in communication via the connecting chamber 32 with the hydraulic cylinder 9, and an outlet chamber 49 which, via the connecting chamber 34, is in communication with the servo unit.A concentric smaller hole 52 is provided at the bottom of the recess 50, eccentrically opening out into the bottom plane 39 of the cylindrical hole 35. In said hole 52 there is mounted an axially displaceable push pin 53, engaging with its downward end against the upper piston 37 and with its upper end urging the valve ball 45 away from the valve seat 47. The push pin 53 is sealed with a seal 54 in the form of an O-ring.

A blocking valve 21 made in the way described will operate as a non-return valve when the lower piston 36 of the valve 21 is in a lower position, thereby engaging against the bottom of the recess 20 of the operating shaft 1 9, as shown in Fig. 2. Said position is assumed when no gear is engaged. Providing that the driving wheel disconnection valve 26 assumes an unenergized position, the upper piston 37 will engage against the lower piston 36, and the ball 45 of the nonreturn valve 44 can thereby sealingly engage against the valve seat 47.

Actuation of the blocking valve 21 can take place in two different ways. The one occurs when the gearbox 1 has a gear engaged and the other occurs when the driving wheel disconnection valve 26 is energized. In the first case the operating shaft 1 9 will be displaced axially during gear positioning, the lower piston 36 being actuated to assume an upper position with engagement against the portion 25 of the operating shaft 1 9 not having a recess. This results in that the upper piston 37 is pressed upwards and that it urges the valve ball 45 via the push pin 53 to leave the valve seat 47, the valve 21 then allowing passage of hydraulic oil in both directions.

When actuating the valve in accordance with the second alternative, compressed air is led into the space 40 between the pistons 36, 37. This results in that the upper piston 37 is pressed upwards and in an analogous manner actuates the push pin 53 and valve ball 45.

A gear change in the auxiliary gearbox 1 carried out when the vehicle is in motion is usually started by a desired gear being selected by means of the gear selector 3. When the clutch pedal 7 is depressed, the switch 4 is closed and the gear selector 3 is supplied with current via the driving wheel disconnection switch 5 from the current supply source 6. The depression. of the clutch pedal 7 also results in that hydraulic oil in the hydraulic cylinder 9 is supplied via the hydraulic-oil conduit 10 to the servo unit 11, which ensures with the aid of compressed air that disengagement of the connection between the vehicle engine and the gearbox is carried out.

In the auxiliary gearbox 1 a gear change is conventionally carried out by means of means intended for the purpose. The gearbox operating shaft 1 9 is thereby displaced, the blocking valve 21 with its sensing means against the bottom plane of the recess 20 functioning as a non-return valve during the gearchanging sequence when no gear is engaged. If actuation of the clutch pedal 7 ceases before said sequence is completely executed, the blocking valve 21 will ensure that both clutch and clutch pedal 7 are held in a position of disengagement until said sequence is carried out entirely, subsequent to which said means automatically return to their unenergized positions.

The present invention is not limited to the described embodiment but can be modified into alternative embodiments within the scope of the accompanying patent claims.

Claims (6)

Claims

1. An arrangement for holding a vehicle clutch in a position disengaging torque transmission between an engine and a gearbox, a hydraulic circuit being arranged for the operation of the clutch to transfer movements between an operating means and at least one actuating means for the clutch, characterized in that a blocking valve is incorporated in the hydraulic circuit, said valve having a non-return valve function regulated by a gear position sensor to allow flow of hydraulic fluid in a direction from the operating means to the actuating means and to block the passage of hydraulic fluid in the opposite direction when a gear is not engaged in the gearbox.

2. An arrangement as claimed in claim 1, characterized in that the blocking valve comprises pressure-medium regulated control means by means of which the holding function of the blocking valve can be disengaged when a gear is not engaged in the gearbox.

3. An arrangement as claimed in claim 2, characterized in that the gear position sensor comprises a piston displaceably mounted in the blocking valve, the outer end of said piston being adapted for engagement against the cylindrical surface of an operating shaft mounted displaceably in the gearbox and adapted to engage in a recess formed in the operating shaft when a gear is not engaged.

4. An arrangement as claimed in claim 3, characterized in that the gear position sensing piston is acted on by a spring-loaded inner piston which urges the piston into engagement against the operating shaft and which, on pressuremedium supply to a side space between the piston, releases the holding function of the blocking valve.

5. An arrangement as claimed in any one of the preceding claims, wherein the operating means is a clutch pedal and the actuating means is a servo unit, characterized in that the clutch pedal is articulatedly connected to a hydraulic piston in a hydraulic cylinder, and that the hydraulic cylinder, via the blocking valve, is in communication with a hydraulic-pneumatic servo unit attached to the vehicle and adapted for carrying out the actual disengagement work on being activated.

6. An arrangement substantially as hereinbefore described with reference to and as shown in the accompanying drawings.