GB2295435A

GB2295435A - Hydraulic control system for clutches has valve controling filling of cylinder

Info

Publication number: GB2295435A
Application number: GB9524070A
Authority: GB
Inventors: Heinz Ruhmer
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1994-11-25
Filing date: 1995-11-24
Publication date: 1996-05-29
Anticipated expiration: 2015-11-24
Also published as: GB9524070D0; FR2727476B1; JPH08226405A; GB2295435B; DE19542766B4; FR2727476A1; DE19542766A1

Abstract

The present invention relates to a working cylinder assembly having a piston (1) which slides in a working cylinder in a housing (2) and which divides the housing into two working chambers (3, 4) containing a hydraulic fluid, one of the working chambers (3) being capable of being loaded by a hydraulic control device (6) via a control line (5). The other hydraulic chamber (4) forms a closed system with a fluid connection to a valve (7) which connects the other hydraulic chamber (4) to a filling device (8) during a filling operation and which, after the termination of the filling operation, connects the other hydraulic chamber (4) to the hydraulic control device (6) for the purpose of compensating fluid losses. <IMAGE>

Description

DESCRIPTION A WORKING CYLINDER ASSEMBLY The present invention relates to a working cylinder assembly.

More particularly the present invention relates to a working cylinder assembly having a piston which slides in a housing and which divides the housing into two working chambers containing a hydraulic fluid, one of the working chambers being capable of being loaded hydraulically with a pressure-supply device by a control device via a control line.

German Patent Application DE 4,407,648 not previously published, discloses an apparatus for recording the position of an actuating element in a slave cylinder. The actuating element is in this case connected via a control line and hydraulic directional valves to a controllable pressure-supply device of a hydraulic control device. For recording the instantaneous position of the actuating element in the slave cylinder, there is arranged in its hydraulic control line a measuring piston which is pretensioned into a rest position and which divides a housing into a primary chamber connected to the control line and a secondary chamber connected to the slave cylinder.

For arranging the measuring device, the piston has two interconnected part pistons enclosing a pressure relieved measuring chamber which is connected to a tank or a compensating reservoir via a connecting bore. In the rest position, that is to say in the pressureless state of the measuring piston, the secondary chamber likewise has a connection to the compensating reservoir, so that changes in volume of the hydraulic fluid as a result of fluctuations in wear or in temperature can be compensated. Moreover, a filling of the closed system of secondary chamber, pressureless chamber and slave cylinder with hydraulic fluid takes place via these hydraulic connections.

while the measuring piston is sliding in its housing, fluid losses from the pressureless measuring chamber into the primary chamber occur, so that the fluid level falls in the compensating reservoir and rises in the pressure-supply device of the hydraulic control device. This finally leads to a failure of the apparatus.

The aim of the present invention is to develop further a working cylinder assembly of the relevant generic type, in such a way that losses of hydraulic fluid in the closed system can be compensated and a filling of the closed system by means of conventional filling devices is possible.

According to the present invention there is provided a working cylinder assembly comprising a piston which subdivides a working cylinder into two hydraulic chambers which, in use, contain a hydraulic fluid, one of the hydraulic chambers when in use, being capable of being loaded hydraulically by a control device via a control line, characterized in that there is provided a valve which is adapted to connect the other hydraulic chamber which is not, in use, connected to the hydraulic control line, to a filling device during a filling operation and which, after the termination of the filling operation, is arranged to connect the other hydraulic chamber to the hydraulic control device for the purpose of compensating fluid losses.

By virtue of the present invention the said valve, in use, connects the hydraulic chambers not hydraulically loadable via the control line, to a filling device during a filling or bleeding operation and, after the termination of a filling operation, connects the hydraulic chambers to the pressure-supply delce for the purpose of compensating fluid losses.

During operation, that is to say after the termination cf t filling or bleeding operation, the connection from the hydraulic chambers to the filing device is preferably closed.

coording to one embsailer.t of the ore sent invention, the valve has a valve piston whIch slides in a valve housing and which, for a first operation of filling the hydraulic chambers not connected to the control line, is fixed by a holding element in such a way that the connection between the filling device and the hydraulic chamber is opened, with the result that a pressureless inlet for the hydraulic fluid is possible. The holding force of the holding element is such that, when the working cylinder is commissioned, that is to say when the control line is loaded for the first time, the holding element is released and the valve piston can slide in the valve housing. The control of the valve piston takes place, further, via an appropriate pressure loading.A renewed filling or a bleeding of the secondary chamber takes place under pressure, in such a way that the connection to the filling device is restored as a result of a loading of the valve piston with hydraulic fluid.

One possibility for using the working cylinder assembly according to the present invention is to arranged it in a control line of a hydraulically loadable actuating element, a primary chamber being connected to the hydraulic control device and a secondary chamber to the housing receiving the actuating element. The hydraulic connection between the working cylinder and the housing of the actuating element forms, at the same time, a hydraulic rod, by means of which the fluid volume is pushed to and fro.

The measuring piston sliding in the working cylinder serves, at the same time, as a measuring device for monitoring the position of the actuating element.

Such an arrangement of the working cylinder assembly is advantageous especially when a direct arrangement of a position or path transducer presents problems for reasons of space or on account of the necessary electrical leads on the actuating element.

In a development of the present invention, the piston of the working cylinder assembly is formed from a first and a second part piston which slide on the inner wall of the working cylinder and between which a pressure-relieved chamber is formed. The pressurerelieved chamber has a passage which can be controlled by the valve in such a way that the chamber is likewise connected to the filling device during the filling operation and, after the termination of the filling operation, is connected to the pressure-supply device of the hydraulic control device.

The present invention can advantageously be employed in the control arrangement of a friction clutch of a motor vehicle.

The valve ensures that the closed system comprising the said secondary chamber, pressureless chamber and/or housing of the actuating element is connected to the filling device during a first filling and a combined vacuum/pressure-filling operation can thus take place. When the working cylinder assembly is commissioned, the valve changes over automatically, so that entrained oil losses can be compensated via the hydraulic control device. A renewed filling which becomes necessary during a service takes place under pressure, the connection to the filling device being opened again as a result of the design of the valve.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows an apparatus for actuating a friction clutch incorporating a working cylinder assembly constructed according to the present invention; and Fig. 2 shows a representation of a valve for use in the present invention for controlling the connections to the secondary chamber, filling device and secondary chamber, hydraulic control device.

The apparatus illustrated in Fig. 1 comprises a friction clutch 17 which connects an internalcombustion engine of a motor vehicle to a transmission (not shown) in dependence on specific operating states or on transitions between individual operating states.

The friction clutch can be engaged and disengaged by an activating mechanism 18. The activating mechanism 18 is itself activated via an actuating element 16 which slides in a slave cylinder 19. The slave cylinder 19 is connected to a hydraulic control device 6 via a control line 5 and a directional valve 20.

The hydraulic control device 6 has a pressure-medium pump 22 which can be driven via a motor 21 eg the internal combustion engine and which is connected to a pressure-supply device (fluid reservoir) 23 and loads the slave cylinder 19 via the directional valve 20.

Moreover, a non-return valve 24 and a pressure accumulator 26 are provided in the pressure-medium circuit between the pressure-medium pump 22 and the directional valve 20. The pressure accumulator 26 can be such that, when the motor vehicle is commissioned, at least one first uncoupling without the supply of energy is possible. Consequently, no special motor is required for the pressure-medium pump 22, and during driving the pressure accumulator 26 is then supplied by the pressure-medium pump 22 driven via the internal-combustion engine 21.

To regulate the frictional engagement of the friction clutch 17, there is provided an electronic control device 27 which transmits a regulating variable for clutch activation to the directional valve 20 in dependence on sensed or predetermined quantities. The sensed quantities are, inter alia, the engine speed, the throttle-flap position and the clutch activation travel or clutch engagement state.

For determining the clutch activation travel, a hydraulic working cylinder 2 designed as a sensor cylinder is arranged in the control line 5 of the slave cylinder 19. A part 5a of the control line 5 constitutes a hydraulic rod which displaces the fluid volume between the slave cylinder 19 and the working cylinder 2.

The working cylinder 2 consists of a cylindrical housing which a composite piston 1 subdivides into a primary chamber 3 and a secondary chamber 4. Both the primary chamber 3 and the secondary chamber 4 are connected in the flow path between the control device 6 and the slave cylinder 19, the primary chamber 3 being connected via the directional valve 20 to the hydraulic control device 6 and the secondary chamber 4 being connected to the slave cylinder 19. The composite piston 1 is pretensioned into its position of rest via a compression spring (not shown) counter to the pressure-medium loading by the hydraulic control device 6. The composite piston 1 consists of two part pistons 12 and 13 which slide sealingly on the inner wall of the housing 2. Between the part pistons 12 and 13, a measuring rod 32 having a measuring scale is fixedly connected to the part pistons 12, 13.By transfer means 33 engaging into the measuring scale of the measuring rod 32, the translational movement of the composite piston 1 is converted into a rotational movement and is transmitted in a known way to a rotary potentiometer (not shown), the rotary potentiometer generating an electrical output signal which is proportional and therefore linear to the path covered by the actuating element 16.

The volume in working cylinder 2 between part pistons 12 and 13, and surrounding measuring rod 32, forms a pressure-relieved measuring chamber 14 which is connected to a valve 7 via a hydraulic line 34 as in secondary chamber 4 when the composite piston 1 is in its position of rest, so that, after the clutch has been fitted the hydraulic line 34 is connected for a first filling operation, to a combined vacuum/pressure-filling device 8. In the illustrated embodiment, the first filling operation takes place via a brake compensating reservoir 31 and a valve 7.

This is because a filling of the closed system formed by the secondary chamber 4, the pressureless measuring chamber 14 and slave cylinder 19, via the pressuresupply device (fluid reservoir) 23 of the hydraulic control device 6 presents problems in many cases, since the reservoir 23 cannot always be arranged accessibly in a motor vehicle and cannot be used for a combined vacuum/pressure filling without changes in construction. After filling has been terminated, during the initial commissioning of the friction clutch 17, a holding element 11 in valve 7 is released and the valve piston 10 is displaced by the pressure in the hydraulic line 30 which is equal to the hydraulic pressure of the control line 5.The valve 7 then connects the hydraulic line 34 to the line 35, so that changes in volume in the secondary chamber 4 and in the pressureless measuring chamber 14 as a result of entrained oil losses which occur, can be compensated. A bleeding and filling of the closed system 4, 14, 19 which becomes necessary during a service takes place under pressure, the pressure being such that is exceeds the pressure in the hydraulic line 35 and the valve piston 10 opens the connection between the filling device 8 and the hydraulic line 34.

Fig. 2 shows a possible embodiment of the valve 7. In this construction the stepped valve piston 10 slides in the valve housing 9 via seals 36 and 37 and subdivides the housing into three valve chambers 39, 40, 41. In the installed state, the valve piston 10 is firmly fixed by the holding element 11, for example a spring ring adhering by frictional connection, in an end position in which the connection between the brake compensating reservoir 31 and the filling device 8 and the hydraulic line 34 to the secondary chamber 4 and the pressureless measuring chamber 14 is open, even when a vacuum is applied at the brake compensating reservoir 31, so that pressureless filling can take place. After the filling operation and the loading of end face 38 (first clutch activation) by the pressurized hydraulic fluid of the primary circuit, the holding element 11 is released and the valve piston 10 is pushed out of its fixed end position into the opposite end position, so that the hydraulic line 34 is connected to the line 35. A renewed filling operation takes place under pressure, so that a force is applied to the opposite end face 42, the said force pushing the valve piston 10 into an end position in which the connection between the brake compensating reservoir 31 and the hydraulic line 34 is opened.

Within the scope of the present invention the valve 7 can be designed as a separate component or as a component forming a constructional unit with the working cylinder 2.

Claims

1. A working cylinder assembly comprising a piston which subdivides a working cylinder into two hydraulic chambers which, in use, contain a hydraulic fluid, one of the hydraulic chambers when in use, being capable of being loaded hydraulically by a control device via a control line, characterized in that there is provided a valve which is adapted to connect the other hydraulic chamber which is not, in use, connected to the hydraulic control line, to a filling device during a filling operation and which, after the termination of the filling operation, is arranged to connect the other hydraulic chamber to the hydraulic control device for the purpose of compensating fluid losses.

2. A working cylinder assembly as claimed in claim 1, in which, after the termination of the fillIng operation, the valve is arranged to disconnect the hydraulic chamber from the filling device.

3. A working cylinder assembly as claimed in claim 1 or 2, in which the valve has a valve piston arranged to slide in a valve housing and which, for rst filling operation, is held by a holding element in a fixed end position in which the connection between the filling device and the hydraulic chamber is opened, the holding force of the holding element being such that the holding element is released when the valve piston is loaded for the first time with a system pressure generated by the hydraulic control device.

4. A working cylinder assembly as claimed in any one of claims 1 to 3, in which the piston consists of a first and a second part piston which are interconnected and slide sealingly on the inner wall of the working cylinder a pressure-relieved chamber being formed between the part pistons, and having a passage which can be controlled by the valve in such a way that the chamber is connected to the filling device during a filling operation and to a fluid reservoir of the hydraulic control device after the filling operation.

5. A working cylinder assembly as claimed in any one of claims 1 to 4, in which the valve forms a constructional unit with the working cylinder.

6. A device for controlling an actuating element loadable hydraulically via a control line, characterized in that there is arranged in the control line a working cylinder assembly as claimed in any one of claims 1 to 5, in which the position in the working cylinder can be recorded as a measure of the positions of the actuating element.

7. A friction clutch for a motor vehicle, characterized in that a device as claimed in claim 6 is provided.

8. A working cylinder assembly constructed and arranged substantially as hereinbefore described with reference to and is illustrated in the accompanying drawings.

9. A device for controlling an actuating element, incorporating a working cylinder as claimed in claim 8.

10. A friction clutch for a motor vehicle, incorporating a device as claimed in claim 9.