GB2087017A

GB2087017A - Hydraulic braking system

Info

Publication number: GB2087017A
Application number: GB8131818A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1980-11-03
Filing date: 1981-10-22
Publication date: 1982-05-19
Also published as: IT8124825A0; DE3041247A1; GB2087017B; IT1139678B; DE3041247C2; FR2493425B2; FR2493425A2

Abstract

A hydraulic brake booster has a pressure chamber which is (17) bounded by a working piston (2) and (13) can be connected via an inlet valve to a pressure fluid source or via a discharge valve (18, 27) to an unpressurized reservoir. Both valves have valve seats arranged in parallel in the working piston, the outlet valve being operated directly by a control piston (3) and the inlet valve by a lever (21) pivoted on the power piston by the central piston. During operation of the valves by the control piston, there is an overlapping stroke range during which both valves are closed. <IMAGE>

Description

SPECIFICATION Hydraulic braking system The present invention relates to a hydraulic brakiny system and in particular to a hydraulic power booster, of the kind wherein a pressure chamber between a working piston and a control piston in a housing is connectible via an inlet valve with a pressure fluid source and via a discharge valve with a supply reservoir, wherein both valves are designed as seat valves having axes in parallel to the pistons' axes and wherein the seats of the discharge valve and of the inlet valve are supported by the working piston, the closure member of the discharge valve being located on the side of the seat close to the pressure chamber and the closure member of the inlet valve being located on the side of the seat remote from the pressure chamber, and wherein the closure members are operatively connected to the control piston until attainment of the closing position and the connecting pieces between the control piston and each one of the closure members is so dimensioned that an overlapping stroke will be the result in the event of a relative movement of control piston and working piston during which both valves are closed.

German patent application P 29 09 685.3 describes a hydraulic power booster which accommodates a working piston in a largerdiameter bore and a control piston in a smallerdiameter bore. A pressure chamber is formed between the working piston and the control piston which is unpressurized in the inactive position of the power booster. The arrangement includes an inlet valve and a discharge valve providing the possibility of connecting the pressure chamber with a pressure fluid source upon actuation of the brake and with an unpressurized return line in the release position of the brake.

When the brake is applied, the control piston will be moved axially in the direction of the working piston, with the closure member of the discharge valve which communicates with the control piston being first of all in abutment with the seat of the discharge valve, as a result whereof the connection between the pressure chamber and the unpressurized return reservoir will be interrupted. If the control piston continues to move, a connecting piece which is formed at the control piston will abut at the closure member of the inlet valve thereby establishing a connection between the pressure chamber and the pressure fluid source. The pressure fluid metered into the pressure chamber will cause displacement of the working piston in the actuating direction until the closure member of the inlet valve will be in abutment with the seat.As both valves have an overlapping stroke, they will remain closed with the force acting on the control piston unchanged.

When the force acting on the control piston decreases, the working piston will be restored by spring force to its initial position in which the pressure fluid metered into the pressure chamber is permitted to flow back to the unpressurized fluid reservoir.

The power booster described is characterized in particular by a short overall length. All flow channels for the valves are arranged for in the working piston. If the brake is applied extremely slowly, the pushing open of the inlet valve may be felt in the accelerator pedal, since the closure member assigned to the inlet valve is acted upon by the accumulator pressure and will be pressurebalanced after the latter valve is opened. This may slightly impair the driving comfort.

It is, therefore, an object of the present invention to improve a hydraulic power booster of the kind referred to in such a way that, while maintaining a short overall length and a straightforward structure of the control piston, a reaction on the brake pedal when opening the inlet valve will be avoided to the greatest possible extent.

According to the invention in its broadest aspect a hydraulic power booster of the kind referred to is characterized in that a lever is supported at the working piston which is capable of swivelling substantially vertically to the piston's axis, in that the free end of the lever abuts at the control piston carrying the closure member of the discharge valve and in that the lever is adapted to abut at the closure member of the inlet valve in the area of the point of su-pport.

It has to be regarded as particularly favourable in such an embodiment if there is a lever transmission between the control piston and the closure member of the inlet valve. As in this arrangement a lower force is sufficient to open the inlet valve, also the force reaction occurring when the closure member of the inlet valve lifts will be reduced correspondingly. An improvement of the driving comfort will thus be attained.

If the lever is preloaded in the direction of the control piston, by means of a compression spring a well-defined inactive position of the lever will be the result.

It is particularly advantageous to have the valve seat and the closure member of the discharge valve spaced from each other in the inactive position, since in this case a complete discharge of pressure will take place in the pressure chamber.

An expedient embodiment will result when arranging for the closure member of the inlet valve to be subjected to the force of a compression spring in the direction of the pressure chamber.

This compensates in a simple way for manufacturing tolerances of the device, since the closure member of the discharge valve is radially displaceable to a slight degree with relation to the piston axis.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing.

In the drawing, reference numeral 1 designates a housing, 2 a working piston and 3 a control piston. The working piston 2 is guided slidably in a larger-diameter bore 4, while the control piston 3 is guided slidably in a smaller-diameter bore 5. A push rod 6 is formed at the working piston 2 which extends in the (non-illustrated) area out of the housing 1 in a sealed relationship thereto and which actuates with its free end for instance the piston of a master cylinder of a brake unit. The inactive position of the working piston 2 is determined by a compression spring 7.

The periphery of the working piston 2 has a recess 8 so that an annular chamber 9 is formed.

The annular chamber 9 is, on the one hand, in communication with a pressure fluid inlet port 10 and on the other hand, with a radial bore of the working piston. An axial bore 12 extends from the radial bore 11 to an inlet valve 13 which is composed substantially of a valve seat 14 and a closure member 1 6 loaded by a compression spring 1 5. A connection between the pressure fluid inlet port 10 and a pressure chamber 1 7 can be established via the inlet valve 13, the pressure chamber being limited by parts of the working piston 2 and of the control piston 3.

In addition, an axial bore 1 9 encompassed by a valve seat 1 8 ends in the pressure chamber 1 7 and is in communication via a channel 20 with the end surface of the working piston 2 remote from the pressure chamber 17. In the area of this chamber not shown, there is furthermore disposed a pressure fluid discharge port having a return reservoir connected thereto.

A lever 21 which is capable of swivelling substantially vertically relative to the piston's axis is supported in the working piston 2. The lever 21 includes a pin 23 in the area of the point of support 22 which pin will strike the closure member 16 of the inlet valve 13 in the event of a sufficiently great swivelling movement and will shift the closure member 1 6 back in opposition to the force of the compression spring 1 5. The free end of the lever 21 is in abutment with an extension 24 of the control piston 3 and is maintained in this position by a compression spring 25 on the side remote from the control piston.

The area of the control piston 3 lying opposite to the bore 19 includes a recess 26 having a closure member 27 supported therein such that it is spaced from the valve seat 1 8 in the inactive position shown. The closure member 27 bears against a stop edge 28 of the control piston 3 and is held there by means of a compression spring 29. The closure member 27 combines with the valve seat 1 8 to form the discharge valve. The control piston 3 is sealingly guided in a hollow cylindrical element 30. The end surface of the control piston 3 remote from the pressure chamber 1 7 is in communication with an actuating rod 31, the latter being in its turn axially siidable by a brake pedal (not shown).

The Mode of operation of the illustrated device will now be described in more detail in the following starting from the inactive position shown in the drawing. When an actuating force F acts on the actuating rod 31, the control piston 3 will be displaced to the left, as seen in the drawing. This movement causes the lever 21 to swivel clockwise in opposition to the force of the compression spring 25 until the closure member 27 moves in abutment with the valve seat 1 8 and the connection will be interrupted between the pressure chamber 1 7 and the return reservoir (not shown). With the displacement of the control piston 3 to the left being continued, the compression spring 29, on which the closure member 27 is supported will be compressed, while the lever 21 will be caused to swivel further.

In this state, the inlet valve 13 and the discharge valve comprising the valve seat 1 8 and the closure member 27 are closed.

The swivelling movement of the lever 21 will be continued until the pin 23 strikes the closure member 16 of the inlet valve 13 and the closure member 1 6 lifts from the valve seat 14. Now there is a connection between the pressure fluid inlet port 10 and the pressure chamber 17 allowing pressure fluid to flow into the pressure chamber 1 7. As a result, the working piston 2 moves with the lever 21 shaped thereat to the left, as seen in the drawing, until the lever 21 has swivelled back so far that the pin 23 lifts from the closure member 1 6 and the inlet valve 13 is closed. This produces a new state of balance wherein inlet valve and discharge valve are closed and either the working piston 2 or the push rod 6 coupled thereto has covered a distance which corresponds to the actuating force F. Upon removal of the actuating force F, the actuating rod 31 will be moved to the right, as seen in the drawing, by a spring system (not shown) so that the lever 21 swivels back to its inactive position and the closure member 27 lifts from the valve seat 1 8.

The pressure fluid metered into the pressure chamber 1 7 will now propagate through the bore 19 and the channel 20 back to the pressure fluid reservoir until the pressure in the pressure chamber 1 7 has been completely discharged.

Claims

1. A hydraulic power booster of the kind wherein a pressure chamber between a working piston and a control piston in a housing is connectible via an inlet valve with a pressure fluid source and via a discharge valve with a supply reservoir, wherein both valves are designed as seat valves having axes in parallel to the pistons' axes and wherein the seats of the discharge valve and of the inlet valve are supported by the working piston, the closure member of the discharge valve being located on the side of the seat close to the pressure chamber and the closure member of the inlet valve being located on the side of the seat remote from the pressure chamber, and wherein the closure members are operatively connected to the control piston until attainment of the closing position and the connecting pieces between the control piston and each one of the closure members is so dimensioned that an overlapping stroke will be the result in the event of a relative movement of control piston and working piston during which both valves are closed, characterized in that a lever (21) is supported at the working piston (2) which is capable of swivelling substantially vertically to the piston's axis, in that the free end of the lever (21) abuts at the control piston (3) carrying the closure member (27) of the discharge valve (18, 27) and in that the lever (21) is adapted to abut at the closure member (16) of the inlet valve (13) in the area of the point of support (22).

2. A hydraulic power booster as claimed in claim 1, characterized in that lever (21) is preloaded in the direction of the control piston (3) by means of a compression spring (25).

3. A hydraulic power booster as claimed in claim 1, characterized in that the valve seat (18) and the closure member (27) of the discharge valve are spaced from each other in the inactive position.

4. A hydraulic power booster as claimed in claim 1, characterized in that the closure member (27) of the discharge valve (18,27) is subjected to the force of a compression spring (29) in the direction of the pressure chamber (17).

5. A hydraulic power booster substantially as described with reference to the accompanving drawing .