GB2320750A

GB2320750A - Master cylinder device

Info

Publication number: GB2320750A
Application number: GB9726553A
Authority: GB
Inventors: Thomas Riess
Original assignee: Mannesmann Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1996-12-20
Filing date: 1997-12-16
Publication date: 1998-07-01
Anticipated expiration: 2017-12-16
Also published as: GB2320750B; ES2157705A1; GB9726553D0; FR2757577B1; ES2157705B1; DE19653270A1; FR2757577A1; DE19653270B4

Abstract

A master cylinder device has a sleeve-like piston 5 arranged to slide axially in piston chamber 16, a pressure connection 18 opening into the piston chamber 16, and a connection 12 defining a passage 14 linking the chamber to a top-up reservoir 11. A plunger 15 and a sealing gasket 13 together form a closure member for opening and closing the passage 14, and the plunger 15 is engaged by the piston 5 to close the passage when sufficient pressure has built up in the chamber 16. The piston 5 is coupled to a piston rod 7 by means of a clamping sleeve 6, a resilient member 9, and an oscillation damper 8.

Description

1 2320750 MASTER CYLINDER DEVICE The invention relates to a master

cylinder device for hydraulic actuating systems usable in particular in motor vehicles.

Known forms of master cylinder devices are described for example in DE 31 11 411 C2 and DE 44 04 859 Al. Such devices have a piston chamber formed in a housing with a piston arranged to slide axially therein and a pressure connection opening into the piston chamber. Such devices serve as the main cylinder for actuating hydraulic brakes or clutches. In order that a compensation of volume of the hydraulic fluid may take place in the piston chamber, which is necessary for example due to temperature fluctuations or due to wear on the actuating members (brake or clutch linings), the piston chamber formed in the master cylinder is connected to a top-up reservoir filled with hydraulic fluid. In order that pressure can be built-up in the piston chamber, in the pressure build-up phase, the top-up reservoir must be cut off from the piston chamber. For this purpose the known master cylinders are provided with a primary and a secondary chamber. The primary chamber serves for the buildup of pressure while the secondary chamber is connected to the top-up reservoir during the pressure build-up phase. The secondary chamber is formed by an annular gap between the piston and housing wall, which in the axial direction is defined by two gaskets or packings. If the piston is actuated for the buildup of pressure, the front piston packing travels beyond a breather bore producing the connection between the secondary piston chamber and topup reservoir and thus separates the latter from the primary chamber.

On account of the provision of the secondary chamber, master cylinders of this type have a somewhat bulky and long construction. Furthermore, there is always the danger that the piston packing travelling over the breather bore will be 2 damaged, and this could lead to a failure of the master cylinder. Very high demands are therefore made of the manufacturing quality. The increasing optimization of vehicles with a simultaneous increase in the equipment of a motor vehicle means that ever decreasing space is available in the engine compartment for the individual components. All components therefore require the most compact possible construction.

It is an object of the invention to provide an improved master lo cylinder device constructed so that its size can be kept as compact as possible.

According to the invention there is provided a master cylinder device for a hydraulic actuating system; said device comprising a piston chamber formed in a housing, a piston arranged to slide axially in the chamber, a pressure connection opening into the piston chamber, a connection for connecting the piston chamber to a top-up reservoir, and a closure member able to be actuated by way of the piston, which closes the connection between the top-up reservoir and the piston chamber, when a pre-determined pressure has built up in the piston chamber.

Due to this construction, the previously known secondary chamber in the master cylinder can be dispensed with and the overall dimensions of the housing can hence be reduced. Also, one of the dual packings can be omitted. Furthermore the frictional forces can be reduced, which leads not only to a lower necessary displacement force, but acoustically a possible source of noise is eliminated.

Preferably the closure member is a plunger disposed in an inlet channel formed radially in the housing, which plunger projects into the piston chamber in the open position and acts on a sealing member, such as a gasket in the closed position. The 3 separation of the inlet channel from the piston chamber takes place by way of this gasket. The plunger is preferably made from synthetic material. Due to this the weight can be reduced.

Furthermore damage to the piston is avoided. The piston, on actuation, comes into contact with the plunger and pushes the latter in the radial direction into the inlet channel. The plunger then takes over the function of a control piston.

The gasket closing off the inlet channel preferably has two 10 regions whereof the crosssection is in the shape of a circular ring and the radially outer region is provided with a plurality of ribs projecting axially in both directions. The ribs are preferably uniformly distributed over the periphery of the radially outer region. Channels or passages are formed by these ribs. These channels ensure the passage of hydraulic fluid from the topup reservoir into the piston chamber, when the plunger is in its open position. Due to this the manufacturing tolerance may be kept very low. The axial gap between the plunger and the sealing seat of the gasket may have a correspondingly small construction, so that the plunger need carry out only short strokes in order to pass from the open into the closed position.

In order to provide a reliable actuation and to prevent tilting of the plunger, its end projecting into the piston chamber preferably has a spherical construction.

The plunger is preferably T-shaped in crosssection and in particular preferably comprises at least one axial bore located radially on the outside or a groove extending in the axial direction, by which a connection can be made between the top-up 4 reservoir and the piston chamber. Due to this construction, the plunger may be inserted with an exact fit in the inlet or connecting channel, so that radial support is always guaranteed and tilting of the plunger is avoided at the time of shifting by the piston. The more bores or axial grooves that are provided, the quicker a compensation of volume may take place.

An embodiment of the invention will be described in detail hereafter, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 is a cross-sectional view of a master cylinder device constructed in accordance with the invention; Figure 2 is an axial section through the sealing member used in the device; and Figure 2a is a plan view of the sealing member shown in Figure 2.

The master cylinder device shown in Figure 1 consists essentially of a housing 1, a piston 5 arranged to move axially in a chamber 16 in the housing 1, a pressure medium connection 18 connected to the piston chamber 16 by way of a channel 17 and a compensating reservoir 11 connected by way of a channel 14 and a connection 12 to the pressure chamber 16.

The piston 5 is constructed in the form of a sleeve. A piston rod 7 is mounted to move by its front end inside the piston 5 in the radial direction, so that it can carry out slight tilting movements. An oscillation damper 10 is located between the base of the piston and the piston rod 7. By way of a resilient member 9, which is pressed by a clamping sleeve 6 against a plunger portion (not shown in detail here) of the piston rod 7, the piston rod 7 is supported against the oscillation damper 10 and the oscillation damper 10 is placed under pre-tension. The piston 5 is mounted in a guide sleeve 4, which is engaged by snap action in known manner by its lugs 4a distributed over the periphery, in recesses 3 provided in the housing 1. A seal between the piston 5 and housing 1 takes the form of a grooved ring 10. The housing 1 is provided with a radial projection, on the end of which the connection 12, which is connected to the top-up reservoir 11, is located. The connection 12 is provided with a central bore 12a, which opens into the inlet channel 14 in the projection of the housing 1. The inlet channel 14 constructed as a stepped bore terminates in the piston chamber 16.

Inserted in the inlet channel 14 is a closure member which takes the form of a plunger 15 of T-shaped cross-section. The plunger 15 has an inner end of spherical construction which projects into the piston chamber 16. On the side facing the plunger 15, the connection 12 is provided with an axial recess, so that the bore 12a widens out in the form of a step. The enlargement in bore diameter corresponding approximately to the larger diameter of the inlet channel 14. A gasket 13 is inserted in this enlarged region. In its radially outer peripheral surface, the plunger 15 comprises a plurality of bores or grooves extending in the axial direction (or on a leg extending in the radial direction), which form channels 15a.

The gasket 13 comprises two regions 13b, 13c of annular crosssection, which are connected to each other by way of a disc- shaped web 13d. The radially inner region 13b has a thicker construction than the radially outer region 13c. Distributed uniformly over the periphery, the radially outer region 13c is provided with a plurality of ribs 13a, which extend in both axial directions. In the open position of the plunger 15, these 6 ribs 13a lie on the upper surface of the plunger 15 and on the stop face 12b in the connection 12. The hydraulic medium is able to flow by way of the gaps thus formed.

Figure 1 shows the master cylinder device in its basic position. The topup reservoir 11 is connected by way of the bore 12a, the inlet channel 14 and the channels 15a in the plunger 15 to the piston chamber 16. At the time of actuation of the piston rod 7, the piston 5 moves downwardly in the drawing. Thus it pushes the plunger 15 in the direction of the connection 12 and thus presses the gasket 13 against the stop face 12b. The bore 12a is in this case closed- off with respect to the bore 14, so that the top-up reservoir 11 is separated from the piston chamber 16.

Now, upon further movement of the piston 5, pressure is able to 15 buildup in the piston chamber 16, which passes by way of the channel 17 to the slave cylinder not shown here in detail and connected to the pressure connection 18. When the load on the piston rod 7 is removed, the piston 5 travels back again. When the piston 5 releases the plunger 15, on account of its inherent elasticity provided by the material, the gasket 14 springs back and pushes the plunger 15 into the piston chamber 16, due to which the connection to the top-up reservoir 11 is reestablished.

To increase the operational reliability, it is advantageous if the master cylinder device is installed in the vehicle so that the opening of the plunger 15 is assisted by the force of gravity.

7 List of reference numerals 1 Housing 2 Grooved ring 3 Recess 4 Guide sleeve 4a Lug Piston 6 Clamping sleeve 7 Piston rod 8 Rubber disc 9 Oscillation damper Grooved ring 11 Top-up reservoir 12 Connection 12a Bore/groove/channel 12b Stop face 13 Gasket 13a Axial rib 13b Annular region 13c Annular region 13d Web 14 Inlet channel 15 Closing member/plunger 16 Piston chamber 17 Channel 18 Pressure connection 8

Claims

1. A master cylinder device for a hydraulic actuating system, in particular in motor vehicles,said device comprising a piston chamber (16) formed in a housing (1) a piston (15) arranged to slide axially therein, a pressure connection (18) opening into the piston chamber (16) a connection (12) for connecting the piston chamber (16) to a top-up reservoir (11), and a closure member (15) able to be actuated by way of the piston (5), which closes the connection between the top-up reservoir (11) and the piston chamber (16), when sufficient pressure has built up in the piston chamber (16).

2. A device according to Claim 1, wherein the closure member (15) is a plunger arranged in an inlet channel (14) formed in the housing (1), which plunger projects in the open position into the piston chamber (16) and in the closed position acts on a sealing member (13).

3. A device according to Claim 2, wherein the sealing member (13) comprises two regions (13b, 13c) whereof the cross-section is in the shape of a circular ring and the radially outer region (13c) is provided with a plurality of ribs (13a) projecting axially in both directions.

4. A device according to Claim 3, wherein the ribs (13a) are distributed uniformly over the periphery of the gasket (13).

5. A device according to Claim 2, 3 or 4, wherein the end region of the plunger (15) projecting into the piston chamber (16) has a spherical construction.

9

6. A device according to Claim 2, 3, 4 or 5, wherein the plunger (15) is provided with at least one axial bore lying radially on the outside or an axial groove (15a), by which a connection can be established between the top-up reservoir (11) and piston chamber (16).

7. A device according to any one of Claims 2 to 6, wherein the plunger (15) has a T-shaped cross-section.

8. A master cylinder device substantially as described with reference to and as illustrated in any one or more of the Figures of the accompanying drawings.