GB2400423A

GB2400423A - Hydraulic braking pump having a bypass within

Info

Publication number: GB2400423A
Application number: GB0308131A
Authority: GB
Inventors: Robert George Uzzell
Original assignee: TRW Ltd
Current assignee: TRW Ltd
Priority date: 2003-04-09
Filing date: 2003-04-09
Publication date: 2004-10-13
Anticipated expiration: 2023-04-09
Also published as: GB0308131D0; GB2400423B

Abstract

An electrohydraulic braking (EHB) system comprising a reservoir 10 for storing brake fluid, a pump 14 connected to the reservoir 10 for producing a supply of pressurized brake fluid, an accumulator 12 coupled to the pump 14 for storing pressurized brake fluid and a valve arrangement 28,30 for selectively controlling the supply of pressurized brake fluid from the accumulator 12 to the vehicle brakes 26 . In order to enable the accumulator pressure to be selective discharged for servicing purposes, an additional flow path (A) can be opened mechanically via the pump 14 which allows the flow of brake fluid from the accumulator 12 back to the reservoir 10. The additional flow path (A) may be established by selective displacement of a part of the pump 14 within its housing.

Description

DESCRIPTION

ELECTROHYDRAULIC BRAKING

SYSTEMS FOR VEHICLES

The present invention relates to electrohydraulic braking systems for road vehicles.

It is conventional practice for electrohydraulic braking (EHB) systems to comprise a reservoir for storing brake fluid, a pump connected to the reservoir for producing a supply of pressurized brake fluid, an accumulator coupled to the pump for storing pressurized brake fluid and a valve arrangement for controlling the supply of pressurized brake fluid from the accumulator to the vehicle brakes.

The pump is usually configured such that brake fluid can flow only in one direction through it, namely from the reservoir to the accumulator. The valve arrangement typically comprises a normally closed valve disposed between the accumulator and the brake actuators (ie. brake fluid flows from the accumulator to the brake actuators only during braking demands), so that brake fluid is stored under pressure in the accumulator when the EHB system is in its default mode (ie.

non-braking mode).

For service work to the EHB system, it is required that the accumulator can be 2 1 discharged of pressurized brake fluid, particularly if the accumulator needs replacing. Conventional techniques for discharging the accumulator can lead to a loss of brake fluid.

It is an object of the present invention to provide a convenient means of discharging the pressurized accumulator and allowing brake fluid to return to the reservoir.

In accordance with the present invention, in order to enable the accumulator pressure to be selectively discharged for servicing purposes, an additional flow path can be opened mechanically via the pump which allows the flow of brake fluid from the accumulator back to the reservoir.

Advantageously, the additional flow path is established by selective displacement of a part of the pump within a pump housing bore.

The pump preferably comprises a pump piston disposed reciprocally within a surrounding sleeve, the position of said sleeve within the housing bore being adjustable for opening said additional flow path.

The sleeve preferably has a peripheral surface region which is caused to be normally held in abutment with a surface region on the housing to close said additional flow path, the sleeve being selectably displaceable whereby to separate the said abutting surface regions of the sleeve and housing to thereby open said additional flow path.

Advantageously, said peripheral surface region of the sleeve comprises a peripheral flange and said surface region of the housing comprises a shoulder, said flange and shoulder co-operating to form a seal which closes said additional flow path during normal operation of the system but which opens said additional flow path when the shoulder and flange are caused to be separated.

Preferably said selective displacement of the sleeve is achieved by means of a rotatable plug which is received in said housing bore and which serves to hold the pump in place within the bore, the plug being coupled mechanically to the sleeve whereby partial withdrawal of the plug from the housing bore causes sufficient axial displacement of the sleeve to open said additional flow path around said peripheral flange.

In one embodiment, the plug is a unitary member coupled to the sleeve so that the plug and sleeve are constrained to move, at least in an axial sense.

In another embodiment, the plug comprises a first, inboard component coupled to the sleeve and freely displaceable within the housing bore, a second, outboard component screw-threadedly fixed within the housing bore, and a spring biassing means effective between said first and second components to normally hold them apart, the arrangement being such that if the pressure in the accumulator exceeds a predetermined upper level, the biassing effect of the spring means is overcome and the first component is moved towards the second component, the sleeve coupled to the first component thereby moving correspondingly to open said additional flow path and thereby provide automatic pressure relief for the accumulator.

In order to enable the biassing effect of the spring means to be overcome and the first component to be moved towards the second component, the first plug member can be of greater diameter than the sleeve whereby accumulator pressure above said predetermined level is effective to cause the spring biassing means to be compressed.

In the latter embodiment, partial withdrawal of the second component enables the first components to be displaced to open said additional flow path.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of part of an electrohydraulic braking system in accordance with a first embodiment of the present invention; Fig. 2 is a longitudinal section through the pump of the system of Fig. 1; Figs. 3 and 4 are schematic representations of part of an electrohydraulic braking system in accordance with a second embodiment of the present invention, shown in two different operating positions.

Referring first to Figure 1, a brake fluid reservoir l O is connected to an accumulator 12 via a pump 14. The pump 14 comprises a longitudinally displaceable piston 16 which is engaged by an engine-rotated cam 18 for pumping brake fluid from the reservoir 10, via conduits 20, 22, to the accumulator 12. The internal valving arrangement in the pump 14 is such that fluid can normally flow through the pump in one direction only, ie. from the reservoir l O to the accumulator 12.

The accumulator 12 is coupled to a brake actuator 24 of a disc brake 26 via a first solenoid valve 28, the brake actuator 24 also being connected to the reservoir l O via a second solenoid valve 30. The solenoid valves 28, 30 are controlled by an ECU (not shown) of the EHB system such that the valve 28 is opened and the valve 30 is closed during a brake apply operation and the valve 28 is closed and the valve 30 opened during a brake release condition. A bypass line 32 containing a pressure relief valve 34 connects the accumulator 12 with the reservoir 10 for limiting the maximum pressure in the accumulator.

The piston 16 is slidably guided in a generally cylindrical sleeve 36 which is itself received in a bore 38 of a housing 40 of the pump 14. The sleeve 36 has an annular peripheral flange 42 which is normally held in abutment with a stepped shoulder 44 in the bore 38 by means of a screwthreaded pump retaining plug 46 which is received in an end region 48 of the bore 38 having a correspondingly screw-threaded portion adjacent its mouth. The plug 46 and sleeve 36 are mechanically hooked together by a plurality of axially extending fingers 50 on the inboard end of the plug so that any movement of the plug to the left as viewed in the Figures is followed by the sleeve 36. Fluid flow via the piston 16 passes around the fingers 50 on the right hand end of the plug 46, as viewed in Fig. 1, into the conduit 22 during normal operation to charge the accumulator 12. An 0 ring seal 52 prevents fluid flow around the periphery of the plug 46.

With this arrangement, in order to enable the pressure in the accumulator 10 to be selectively released, partial unscrewing of the plug 46 (without fully releasing it from the housing bore 38) causes the sleeve 36 to be drawn by a corresponding small amount to the left, as viewed in Figs. I and 2, so that it assumes the position shown in Fig. 2 wherein the annular flange 42 is displaced axially from the shoulder 44 to thereby open a fluid drain passage extending around the flange 42 and back to the reservoir 10 via the clearance between the bore 38 and the sleeve 36.

To assist in enabling the plug 46 to be screwed in/out of the bore 38, it can be provided with a keyed recess 54.

Thus, release of the accumulator pressure and return of brake fluid to the reservoir l O can be achieved simply by partial unscrewing of the plug 46 by, for example, a few turns. In view of the presence of the O- ring seal 52, no brake fluid is lost during this operation.

The embodiment of Figs.3 and 4 uses a similar piston 16 and sleeve 36 but has a modified plug construction which includes an automatic pressure relief arrangement, enabling the conventional pressure relief valve 34 of Fig. 1 to be dispensed with.

The essentially unitary plug 46 of Figs. 1 and 2 is replaced in the embodiment of Figs.3 and 4 by a multi-part plug comprising a first, unthreaded member 56 of solid, generally cylindrical configuration which is received displaceable within the bore 38 and a second, threaded cap member 58 which is received in a correspondingly threaded portion at the mouth region of the bore 38. Normally, the member 56 is axially spaced by a small amount from the threaded cap member 58 as a result of the biassing effect of a pair of Belleville washers 60 acting between a shoulder 62 on said first member 58 and the inboard side of the second threaded member 58. In this condition the flange 44 on the pump sleeve 36 is urged into abutment with the shoulder 42 in the bore 38 as shown in Fig. 3, for the normal charging operation of the accumulator by the pump.

As shown in Figs.3 and 4, the displaceable member 56 has a greater diameter than that of the sleeve 36 and is received in a larger diameter region 38a of the bore 38, whereby the member 56 presents a greater area to the pressurized brake fluid than that presented by the sleeve 36. In consequence, should the accumulator pressure exceed a predetermined level, the Belleville washers 60 are compressed sufficiently to cause the displaceable member 56 to be moved to the left as viewed in Figs.3 and 4. Since the sleeve 36 remains coupled to the member 56 by the fingers 50, the sleeve 36 is caused to follow the displacement of the member 56 and thereby opens up the discharge path back to the reservoir around the flange 44, in a similar manner to that described in connection with the first embodiment and illustrated in Fig. 2 For release of the accumulator pressure for servicing purposes, the screw threaded plug portion 58 is partially unscrewed as in the case of the first embodiment to allow the plug member 56 and sleeve 36 to be displaced to the left to open up the flow path back to the reservoir around the flange 44.

With the above described construction, the advantage is obtained that the additional flow path for selectively discharging the accumulator pressure is integrated within the pump assembly so that neither additional external components nor installation space are required.

Claims

An electrohydraulic (EHB) braking system comprising a reservoir for storing brake fluid, a pump connected to the reservoir for producing a supply of pressurized brake fluid, an accumulator coupled to the pump for storing pressurized brake fluid and a valve arrangement for selectively controlling the supply of pressurized brake fluid from the accumulator to the vehicle brakes, and wherein, in order to enable the accumulator pressure to be selectively discharged for servicing purposes, an additional flow path can be opened mechanically via the pump which allows the flow of brake fluid from the accumulator back to the reservoir.
2. An EHB system as claimed in claim 1, wherein the additional flow path is established by selective displacement of a part of the pump within a pump housing bore.
3. An EHB system as claimed in claim 2, wherein the pump comprises a pump piston disposed reciprocally within a surrounding sleeve, the position of said sleeve within the housing bore being adjustable for opening said additional flow path.
4. An EHB system as claimed in claim 3, wherein the sleeve has a peripheral surface region which is caused to be nonnally held in abutment with a surface region on the housing to close said additional flow path, the sleeve being selectably displaceable whereby to separate the said abutting surface regions of the sleeve and housing to thereby open said additional flow path.
5. An EHB system as claimed in claim 4, wherein said peripheral surface region of the sleeve comprises a peripheral flange and said surface region of the housing comprises a shoulder said flange and shoulder co- operating to form a seal which closes said additional flow path during normal operation of the system but which opens said additional flow path when the shoulder and flange are caused to be separated.
6. An EHB system as claimed in claim S. wherein said selective displacement of the sleeve is achieved by means of a rotatable plug which is received in said housing bore and which serves to hold the pump in place within the bore, the plug being coupled mechanically to the sleeve whereby partial withdrawal of the plug from the housing bore causes sufficient axial displacement of the sleeve to the open said additional flow path around said peripheral flange.
7. An EHB system as claimed in claim 5, wherein the plug is a unitary member coupled to the sleeve so that the plug and sleeve are constrained to move together, at least in an axial sense.

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8. An EHB system as claimed in claim 5, wherein the plug comprises a first, inboard component coupled to the sleeve and freely displaceable within the housing bore, a second outboard component screw-threadedly fixed within the housing bore, and a spring biassing means effective between said first and second components to normally hold them apart, the arrangement being such that if the pressure in the accumulator exceeds a predetermined upper level, the biassing effect of the spring means is overcome and the first component is moved towards the second component, the sleeve coupled to the first component thereby moving correspondingly to the open said additional then path and thereby provide automatic pressure relief for the accumulator.
9. An EHB system as claimed in claim 8, wherein in order to enable the biassing effect of the spring means to be overcome and the first component to be moved towards the second component the first plug member is of greater diameter than the sleeve whereby accumulator pressure above said predetermined level is effective to cause the spring biassing means to be compressed.
10. An EHB system as claimed in claims 8 and 9, wherein partial withdrawal of the second component enables the first component to be displaced to open said additional then path.
11. An EHB system substantially as hereinbefore described, with reference to and as illutrated in the accompanying drawings