GB2045882A

GB2045882A - Hydraulic power booster

Info

Publication number: GB2045882A
Application number: GB8007305A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1979-03-12
Filing date: 1980-03-04
Publication date: 1980-11-05
Also published as: IT8020514A0; IT1129622B; DE2909685C2; FR2451483B1; FR2451483A1; GB2045882B; DE2909685A1

Abstract

An hydraulic power booster e.g. for a vehicle brake system includes a housing 1 containing a working piston 5 a control piston 6, the two pistons defining a pressure chamber therebetween, fluid being admitted to the chamber via an inlet valve 16 and released via an outlet valve 20, characterised in that the valves are mounted in the control piston and have a common valve operating member 24 whereby, when the control piston is operated, the outlet valve is closed prior to the opening of the inlet valve. <IMAGE>

Description

SPECIFICATION Hydraulic power booster This invention relates to hydraulic power boosters such as are employed in vehicle braking systems.

One form of hydraulic brake booster of this type is described in Germany printed patent application 19 37317. In this arrangement the control piston is operated by the brake pedal while the working piston is connected in one piece with the piston of the master cylinder. Co-axially to the valve seat of the discharge valve the seat for the inlet valve is designed at the control piston. Both valves close in the same direction. Their valve poppets are rigidly connected with one another and are loaded by a common valve spring. When, with the operation of the control piston, the discharge valve closes the inlet valve opens and vice versa. With a modified form of design the valve poppet of the discharge valve is connected to the control piston by a rubber disc.The rubber disc is deformed to such an extent when the discharge valve closes that the inlet valve, which is equipped with a seat in the control piston, opens. In both cases the result of vibrations of the vehicle may be that inspite of an unchanged position of the control piston the pressure chamber between the control piston and the working piston is repeatedly alternately connected to the pressure fluid source and the reservoir. Furthermore this results in an overall length not to be remained under, as both valves are spatially connected one behind the other and the control piston must be surrounded by an inlet-circumferential groove over a sufficient axial length.

Furthermore a brake booster is known (German printed patent apaplication 2461 295) wherein a slide valve is used instead of the two set valves. In this brake booster there is a sufficiently long idle path between the closing of the one valve and the opening of the other valve, which excludes the fact that as a result of vehicle vibrations an alternate opening and closing of both valves occurs. With a slide valve however, the closing effect is not as good as with a seat valve because of the unavoidable circumferential split. The necessary careful treatment results in high production costs. Furthermore here too a predetermined overall length is not to be remained under.

According to the present invention there is provided An hydraulic power booster, including a housing within which a pressure chamber between a working piston and a control piston is connectable via an inlet valve with a pressure fluid source and via a discharge valve with a reservoir, wherein both valves comprise seat valves whose axes are sub- stantially parallel to the piston axes, wherein the seat of the discharge valve is supported by the working piston and the valve poppet of the discharge valve is arranged on the side of the seat facing the pressure chamber, and said valve poppet is, until the closedposition is reached, coupled non-positively with the control poston, wherein the seat of the inlet valve is supported by the working piston, wherein the valve poppet of the inlet valve is arranged on the side of the seat opposite the pressure chamber and is, until the closed position is reached, non-positively coupled with the control piston and wherein the connecting parts between the control piston and each of the valve poppets are dimensioned such that during relative movement between the control piston and working piston there is an over overlapping stroke range during which both valves are closed.

With this construction the opening of the inlet valve is not effected directly following the closing of the discharge valve. By dimensioning the connecting parts between control piston and the respective valve poppet one can provide for an idle path or overlapping stroke area, during which both valves are closed. The flow channels which are assigned to the valves are provided only in the working piston, but not in the control piston. Therefore only one of the pistons must be treated accordingly, thus saving costs. Since neither a long slide valve must be provided nor a seat valve must be placed in the control piston the overall length may be kept shorter than it formerly was the case.

The overlapping stroke area amounts to 1,0 - 1,5 mm. One the one hand this idle path is short enough not to cause any difficulties during the application of the brakes. On the other hand the idle path is long enough to prevent alternate opening and closing of the valves in case of vehicle vibrations.

Furthermore it is advatageous when closing springs supported by the working piston are assigned to the valve poppets of both valves and when the one end of the inlet valve-connecting piece is rigidly connected to the control piston, the one end of the discharge valve-connecting piece is rigidly connected to the valve poppet of the discharge valve and the other ends of the inlet valve connecting piece and the discharge connecting piece provide non-positive coupling with the valve poppet of the inlet valve of the control piston respectively. In their closed position the valve poppets are always adjacent the seat by a power exerted by their spring.

The non-positive coupling with the control piston is effected in each case only at the beginning of the opening movement.

An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure shows a longitudinal section through a power booster.

Referring to the drawing, the booster includes a housing 1 in which a large bore 2 with a final section 3 and a small bore 4 are provided. In the large bore a working piston 5 is slidable, in the small bore a control piston 6. In the area of the enlargement 3 the large bore is closed by an end piece 7, which carries a seal by which a push-rod 9, actuated by the working piston 5, projects therethrough and is sealingly guided therein. This push-rod can, with its free end, e.g. operate the piston of a master cylinder of a brake system. A supporting sleeve 10 is inserted in the end piece 7 by which the push-rod 9 is guided.

A spring 11 keeps the working piston 5 in a pressureless condition in the illustrated position.

The control piston 6 has a bearing piece 12 in which a push-rod 13 engages, which is connected to e.g. a brake pedal. A spring 14 urges the control piston 6 to the right side if no pedal power is acting. A pressure chamber is defined between the working piston 5 and the control piston 6. The pressure acting in the pressure chamber multiplied with the sectional area of the working piston 5 results in the power which can be passed on via the push-rod 9.

In the working piston 5 an inlet valve 16 with valve seat 17, valve poppet 18 and valve spring 19 as well as discharge valve 20 with seat 21, valve poppet 22 and valve spring 23 are provided. A cross rail 24, at which an inlet valve-connecting piece (25) is fixed and which has a slot 26, through which a discharge valve-connecting piece 27, fixed at the valve poppet 22, extends, which carries a head at its free end, is connected to the control piston 6. The working piston 5 has a circumferential groove 29, which communicates with the inlet valve 16 via a radial bore 30 and which is connected with a connecting line 31, leading to a pressure fluid source, such as a pump or accumulator, in the housing 1 during the total stroke of the working piston 5. The inlet direction is indicated by the arrow Z.The discharge valve 20 is in contact with a bore chamber 33 in front of the front of the piston 5 via an axial bore 32. This bore chamber is connected to a reservoir by means of a connecting line 35 equipped with a connecting sleeve 34. The discharge direction corresponds to the arrow A. Besides the bore chamber is equipped with a discharge bore 37 closed by a screw 36.

During the operation the control piston 6 is pushed to the left side by operation of the push rod 13. First the closure of the discharge valve 20 is effected. As a result of this the pressure chamber 15, which so far was under atmospheric pressure, separated from the reservoir. during further movement of the control piston 6 an idle path or overlapping stroke range is effected, during which both valves 16 and 20 are closed. Only then is opening of the inlet valve 16 effected. The pressure chamber 15 is filled with pressure fluid and the working piston 5 is shifted to the left side, until the control piston 6 reaches the end of its travel. Subsequently the inlet valve 16 closes when the working piston 5 has moved a little further. The discharge valve 20 however remains closed because of the idle path. The position of the working piston 5, which is achieved in this way, therefore is kept. When the pressure onto the push rod 13 reiaxes the control piston moves to the right under the influence of the hydraulic pressure, and the spring 11. Hereby the discharge valve 20 opens.

The working piston follows the control piston to the right under the influence of the spring 11 with simultaneous displacement of the pressure fluid out of the pressure chamber 15 via the bore chamber 33 to the reservoir.

Claims

1. An hydraulic power booster, including a housing within which a pressure chamber between a working piston and a control piston is connectable via an inlet valve with a pressure fluid source and via a discharge valve with a reservoir, wherein both valves comprise seat valves whose axes are substantially parallel to the piston axes, wherein the seat of the discharge valve is supported by the working piston and the valve poppet of the discharge valve is arranged on the side of the seat facing the pressure chamber, and said valve poppet is, until the closed position is reached, coupled non-positively with the control piston, wherein the seat of the inlet valve is supported by the working piston, wherein the valve poppet of the inlet valve is arranged on the side of the seat opposite the pressure chamber and is, until the closed position is reached, non-positively coupled with the control piston and wherein the connecting parts between the control piston and each of the valve poppets are dimensioned such that during relative movement between the control piston and working piston there is an overlapping stroke range during which both valves are closed.

2. A power booster according to claim 1, wherein the overlapping stroke range is 1,0 - 1,5 mm.

3. A power booster according to claim 1 or 2, wherein the working piston has a circumferential groove the axial length of which corresponds to the maximum stroke of the working piston, wherein the side of the valve seat, which is opposite the pressure chamber communicates with the circumferential groove and the side of the other valve seat which is opposite the pressure chamber is connected to the front end of the working piston opposite the pressure chamber, and wherein the housing in the area of the circumferential groove and in the area in front of the working piston-front end having connecting lines each, leading to the pressure fluid source or the reservoir respectively.

4. A power booster according to any one of claims 1 to 3, wherein closing springs, which are supported by the working piston, are assigned to the valve poppets of both valves, wherein one end of an inlet valve-connecting piece is rigidly connected to the control piston, whereon one end of a discharge valve connection piece is rigidly connected to the valve poppet of the discharge valve and wherein the other end of the inlet valve connecting piece and the discharge valve connecting piece provide for nonpositive coupling with the valve poppet of the inlet valve or the control piston respectively.

5. An hydraulic power booster, including a housing having a cylindrical bore in which a working piston is slidably located, a reduced diameter bore portion communicating with a co-axial with the cylindrical bore and in which a control piston is slidably located, the space between the control piston and the working piston defining a pressure chamber, first valve means mounted in the control piston for supplying a pressure fluid to the chamber, second valve means mounted in the control piston for releasing pressure fluid from the chamber, said valves having a common valve operating means, said operating means being so arranged that, when the control opening is operating, said outlet valve is closed prior to opening of the inlet valve to release pressure fluid into the chamber.

6. An hydraulic power booster substantially as described herein with reference to the accompanying drawing.

7. A vehicle fitted with one or more hydraulic power booster as claimed in any one of claims 1 to 6.