GB2168442A - Breaking pressure control unit - Google Patents

Abstract

A braking pressure control unit with a closure member, comprising a closure portion and a shaft portion, movable along an axis relative to a valve seat to control fluid flow through the valve seat opening. The closure member (22) and the shaft portion (24) are undetachably interconnected by e.g. soldering or friction-welding to facilitate ease of manufacture and assembly. In one embodiment the unit has a closure sleeve (5) which can be inserted into a housing (1) of a braking pressure generator and which incorporates a first valve assembly (21, 22) for the braking pressure control and a second valve assembly (16) to act as a non-return valve. The first valve assembly (21, 22) comprises, as a closure member, a control piston (23) slidable pressure-responsively in opposition to the force of a control spring (25) and including a closure portion (22) which cooperates with a valve seat (21) provided in a second sleeve (12) which latter is displaceable in the first sleeve (5). Owing to the slidability of the second sleeve (12), there results a reduction of the outlet pressure which commences almost simultaneously with the reduction of the inlet pressure. Due to the arrangement of the valve seat (21) at a component movable separately from the first sleeve (5), materials may be chosen for the first valve assembly (21, 22) which ensure optimum tightness and, simultaneously, insusceptibility to brake fluid and high temperatures. <IMAGE>

Description

SPECIFICATION Braking pressure control unit The present invention relates to a braking pressure control unit with a closure member composed of two parts, a closure portion and a shaft portion, the said closure member being movable along an axis relative to a valve seat with a view to controlling the flow of a medium through an opening comprising the valve seat.

A like closure member is used on the braking pressure control unit known from U.S. patent 4, 198,099. The shaft portion of the closure member includes an end portion of smaller diameter, onto which latter the substantially hemispherical closure portion containing a bore as well as a prop ring are slid until they abut on the shoulder of the step and are held by a circlip inserted into a groove of the end portion.

Said closure member which consists of a great number of components is complicated and costly both in respect of its manufacture and its assembly.

It is an object of the present invention to provide a closure member for a braking pressure control unit which affords ease of manufacture as well as ease of assembly.

The invention also relates to a braking pressure control unit comprising a sleeve which receives components of said unit and can be inserted into a housing of a braking pressure generator, which sleeve includes a pressure fluid inlet, a pressure fluid outlet and an interposed valve assembly for controlling pressure fluid passage, the said valve assembly comprising a control piston, slidable pressure-responsively in opposition to a control force and a valve seat encompassing the control piston, the control piston including a valve closure portion associated with the valve seat and a shaft portion which projects through the valve seat and by which it is sealedly guided in the sleeve, as well as comprising a second valve assembly designed as a non-return valve.

Such a braking pressure control unit is known from West German printed and published patent application 32 22 760. In this known braking pressure control unit, components are arranged in the interior of a sleeve that can be screwed into a receiving bore in a tandem master cylinder, the said bore being stepped several times, as well as at the outer periphery of the sleeve. The outwardly placed components are two seals co-operating with the wall of the receiving bore and confining an inlet pressure chamber as well as an outlet pressure chamber. It is arranged, by the positioning of the seals, that the pressure fluid is introduced radially, while it leaves the braking pressure control unit in an axial direction. To control the braking pressure, the two pressure chambers are via radial bores in communication with the valve assembly arranged centrally in the interior of the sleeve.The control piston's closing portion co-operates with a valve seat designed at a sleeve step.

By virtue of this braking pressure control unit, a specific pressure variation is achieved in the pressure-reducing phase. At first, the outlet pressure is held constant and the inlet pressure is reduced until attainment of a pressure balance when the sealing lip of the nonreturn valve is able to lift and the inlet and outlet pressures then decrease jointly.

This known braking pressure control unit does not arrange for a reduction of the outlet pressure commencing with the decrease of the inlet pressure.

It is another object of the present invention to provide a braking pressure control unit of the type initially referred to which is of straightforward design and reliable in operation, and wherein the pressure reduction of the outlet pressure commences with the decrease of the inlet pressure.

According to one aspect of the present invention there is provided a braking pressure control unit with a closure member composed of two parts, a closure portion and a shaft portion, the said closure member being movable along an axis relative to a valve seat, with a view to controlling the flow of a medium through an opening comprising the valve seat, characterised in that the closure portion and the shaft portion are undetachably interconnected.

An embodiment having a closure portion in the shape of a ball, preferably a steel ball, which is commercially available in high precision and surface quality, affords advantages in respect of the tightness of the valve which basically depends on the shape and the surface of the closure portion.

In a particularly simple and reliable embodiment, the parts of the closure member are interconnected by soldering.

Favourably, an improvement of the present invention arranges for the valve seat element comprising the valve seat to be made of polyphenylenesulphide or a polyphenylenesulphide solid solution, since thus it will be accomplished to preserve the seal-tightness of the valve in comparison to a valve in which both the valve seat and the closure portion are made of metal, even when subject to high temperatures and aggressive media, such as brake fluid, while low demands are made on the manufacturing accuracy.

When the closure portion and the shaft portion of the closing member are interconnected by a soldering action, the parts to be coupled are, however, exposed to an appreciable thermal stress. The interconnection can be effected at low costs and with little thermal stress imposed on the component parts, if they are interconnected by friction-welding. It will thus be accomplished that the heat re quired to couple these parts does not have to be furnished from the outside, but is generated by the frictional action. Favourably, thermal stress is encountered but within locally bounded areas of the components. There is no need to machine the assembled parts, since the zone of junction of the parts is not disposed in the area of the valve sealing surface.

Special advantages are obtained if a tempered steel ball is provided as closure portion.

Due to the heating occurring locally in the zone of junction of the components, the structure and the surface of the steel ball in the sealing area will not be influenced, whereby the high degree of tightness and stability of the valve which can be attained when using a tempered steel ball is maintained. A thus designed valve is particularly apt for use on a brake slip control apparatus wherein high pressures and short switch-over times occur.

In an embodiment in which the shaft portion comprises an end portion of larger diameter that is remote from the closure portion, the amount of energy required to carry out the friction-welding process can be kept low by providing for the shaft portion to have a smallest possible diameter in the zone of junction.

A minor friction-welding moment in the ini tial phase of the joining action may be accomplished in that the end face of the shaft portion to be connected with the closure portion is plane.

Furthermore, it is provided that the shaft portion can be furnished with two closure portions.

According to another aspect of the present invention there is provided a braking pressure control unit comprising a sleeve which receives components of said unit and can be inserted into a housing of a braking pressure generator, which sleeve includes a pressure fluid inlet, a pressure fluid outlet and an interposed valve assembly for controlling pressure fluid passage, the said valve assembly comprising a control piston, slidable pressure-responsively in opposition to a control force, and a valve seat encompassing the control piston, the control piston including a valve closure portion associated with the valve seat and a shaft portion which projects through the valve seat and by which it is sealedly guided in the sleeve, as well as comprising a second valve assembly designed as a non-return valve, characterised in that the valve seat is designed at a second sleeve which is sealedly slidably arranged in the sleeve.

When pressure is reduced on the inlet side, the second sleeve will be displaced which results in a volume increase in the outlet chamber. The volume increase on the outlet side brings about a pressure reduction of the outlet pressure which essentially, i.e. while neglecting influences which the friction caused by seals takes on the displacing movement of the second sleeve, is effected in conjunction with the pressure reduction on the inlet side. After both pressures have adopted the same amount, the non-return valve device will open, and inlet pressure and outlet pressure will decrease evenly. As the second sleeve is a separate component, the material of the sleeve can be chosen in a particularly favourable manner in respect of optimising the tightness and the useful life of the valve assembly. In addition, the braking pressure control unit can be replaced as a whole.There is no provision of seals sliding on the wall of the receiving bore in the braking pressure generator housing, hence there is no danger of the seals being damaged during mounting and dismounting of the braking pressure control unit.

It is provided in a favourable improvement that the second sleeve is held by a spring element in abutment on an outlet-side stop of the first sleeve. It is thus ensured that the control piston will always cover the same valve closure travel.

According to an improvement a sealing lip of a seal that is arranged betwen an outer circumferential surface of the second sleeve and an inner circumferential surface of the first sleeve forms the non-return valve. Favourably, said seal does not slide on the wall of the receiving bore during the assembly of the braking pressure control unit; hence there is no need to finely machine the receiving bore in the housing of the braking pressure generator.

To secure the ring seal to the first or the second sleeve increases the functional dependability.

A special advantage is afforded by an embodiment wherein the second sleeve is designed as a plastics component and the control piston is designed as a metal component.

Owing to this material combination, there is considerable increase of the tightness of the valve assembly in comparison to a valve assembly in which both said comnponents are made of metal.

An embodiment which, due to this separate manufacture, is particularly favourable in respect of making will be attained in that the control piston is composed of two parts and that these parts, namely the closure portion and the shaft portion, are undetachably interconnected. In this regard, it is particularly advantageous if the closure portion is designed by a customary steel ball which can be obtained in high precision and surface quality.

It is expedient to make the second sleeve of polyphenylenesulphide or a polyphenylenesulphide solid solution, since this plastic material is not attcked by the brake fluid and has high temperature stability.

The operational accuracy of the valve assembly will be improved in that the interior of the sleeve, into which the shaft portion of the control piston is slidable, is via a bore con nected with the atmosphere and is sealed relative to the receiving bore by a seal st the end surface of the sleeve.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-section through one embodiment of braking pressure control unit mounted into a housing of a braking pressure generator, Figure 2 is a cross-section through another embodiment of the braking pressure control unit, Figure 3 illustrates a braking pressure control unit with three-way/two-position seat valve with two spherical closing portions, and Figure 4 illustrates a braking pressure control unit with another spherical seat valve.

Reference numeral 1 designates the housing of a braking pressure generator designed as tandem master cylinder. Incorporated in the housing 1 is a stepped receiving bore 2 which communicates via a connecting bore 3 with a pressure fluid chamber of the tandem master cylinder (not illustrated in more detail). A braking pressure control unit 4, which is connected on the outlet side with at least one wheel brake cylinder (not shown), is screwed into the receiving bore 2 in a pressure-fluidtight fashion.

Alternatively, the arrangement of the braking pressure control unit at the tandem master cylinder can be chosen such that, for instance, only one braking pressure control unit is placed between the one pressure chamber of the tandem master cylinder and the wheel brake cylinders of the rear axle, while the wheel brake cylinders of the front axle are connected with the other pressure chamber, or that a braking pressure control unit is inserted between each of the two pressure chambers and a wheel brake cylinder of a rear wheel. In the latter case, the brakes of the rear wheels are acted upon by two separate brake circuits.

With the intermediate braking pressure control unit 4, the pressure generated by the braking pressure generator is fed to the rearwheel brake or the rear-wheel brakes in an unchanged fashion, to begin with. When a predetermined pressure is exceeded, that is the so-called change-over pressure, the braking pressure control unit will perform a predefined reduction of the pressure supplied to the rear-wheel brake or the rear-wheel brakes.

The braking pressure control unit of Figure 1 comprises an externally threaded bi-partite sleeve 5, to accommodate the components of the unit, which can be screwed into an internally threaded portion of the receiving bore 2.

Said sleeve 5 includes a cap 6 to accommodate a control spring 25. Sleeve 5 has a through-bore 7 which is stepped several times. Arranged in the portion of largest internal diameter is an end of cap 6. Said cap 6 is rigidly coupled to the other part of the sleeve 5 by means of frontal, radial projections 8 spread over its periphery and engaging into an annular groove 9 at the inner end of this sleeve portion. At this end of cap 6, a ring bearing 11 and a sealing assembly 10 which will be described in more detail hereinbelow are disposed in the interior of the cap 6.

In the inner bore portions of the sleeve 5 succeeding the portion of largest internal diameter, a second sleeve 12 is arranged and a sealedly slidably guided in a smallest diameter portion.

The second sleeve 12 is composed of two rigidly interconnected parts and substantially of bowl-shaped design and furnished with a circular opening 13. For providing a sealing between first 5 and second sleve 12, there is provision of an annular seal 15 that is inserted into an outer circumferential groove 14 in the second sleeve 12 and that includes a sealing lip 16 alongside its periphery which is close to the guide portion of the sleeve 5 and which abuts on the inner wall of the first sleeve 5.

Arranged between the end of the cap 6 and the bottom of the second sleeve 12 is a spring element 17 which keeps the second sleeve 12 in abutment on a step of the stepped inner bore 7 of the first sleeve 5.

The end portion of smallest inner diameter of the sleeve 5 communicates with a pressure fluid outlet 20 of the braking pressure control unit 4 which is provided with an internal thread into which a pressure fluid line leading to a wheel brake cylinder can be screwed.

The opening 13 provided in the second sleeve 12 forms the valve seat 21 for a closure portion 22 of a control piston 23 that is arranged in the inside of the second sleeve 12. The diameter of the valve seat 21 is chosen such as to correspond to the diameter of the portion of the inner bore 7 of the sleeve 5 which serves to guide the sleeve 12 and on which the sealing lip 16 of the seal 15 is abutting, that is the smallest diameter portion.

The control piston 23 is composed of two parts, the closure portion 22 and a shaft portion 24. A ball, which can be obtained in the trade with high surface quality, serves as the closure portion 22 and is connected to the shaft portion 24 by being soldered thereto.

The second sleeve 12 is made of a plastics material, preferably of any polyphenylenesulphide or any polyphenylenesulphide solid solution. The thus designed valve assembly is distinguished by great tightness, insusceptibility to brake fluid and a high temperature stability.

The shaft portion 24 of the control piston 23 extends through the valve seat opening, through the sealing assembly 10 located at the cap's end as well as through the ring bearing 11 into the interior of the cap 6 and is at its end acted upon by the force of a control spring 25. Said control spring 25 bears against the inner end face of the cap 6.

What is not illustrated is a thread device which allows one to inifinitely variably set the preload of the control spring. Part of the thread device is supported on the cap and on the control piston, respectively, while another part forms the adjustable support for the spring.

Disposed at the outer end face of the cap 6 is a seal 26 by which the receiving bore 2 filled with pressure fluid is sealed against the interior of the cap 6 which is connected to atmosphere via a bore 27. The sealing assembly 10 encompassing the shaft portion 24 of the control piston 23 includes two sealing lips which face away from the cap's interior, which abut on the shaft portion 24 and on the cap's inner circumference and which provide for the sealing at the cap end close to the sleeve.

The drawing displays the braking pressure control unit 4 inserted into the receiving bore 2 in its unpressurised condition, that means with the brake system not actuated. Under the action of the control spring 25, the control piston 23 abuts with its spherical closing portion 22 on spacing cams having openings 28.

The passage through the pressure fluid outlet 20 is safeguarded by the openings 28. Via the intermediary of the spacing cams, the second sleeve 12 is kept in abutment on the outlet-side stop of the first sleeve 5 by the spring element 17.

Pressure fluid is delivered from the pressure chamber of the tandem master cylinder via the connecting bore 3, the channel between the cap and the inner wall of the receiving bore 2 or, respectively, the inner wall of the first sleeve portion to the pressure fluid inlet 30 of the braking pressure control unit 4. The pressure fluid inlet is formed by the interspaces between the radial projections 8 of the cap 6.

The pressure fluid propagates further through the chamber between the sealing assembly 10 and the second sleeve 12, through the channel between shaft portion 24 and sleeve opening, through the open valve assembly 21, 22 and the openings 28 to the pressure fluid outlet 20 of the braking pressure control unit 4 and thus to one or several of the wheel brake cylinders.

When the braking pressure generator is actuated and the pressure at the pressure fluid inlet 30 increases in consequence thereof, likewise the pressure in the pressure fluid outlet 20 of the braking pressure control unit 4 will rise. In this respect, the arrows 39 and 40 characterised the direction of flow of the pressure fluid. Upon attainment of the predetermined change-over pressure, the pressure force acting on the control piston 23 to the left, when viewing the drawing, will exceed the counterforce of the control spring 25.

Subsequently, the control piston 23 moves in the closing direction and closes the valve passage until, with the pressure at the pressure fluid inlet 30 continuing to increase, such a high counterforce has developed in the opening direction that the control piston 23 opens again. Due to the ratio of surfaces chosen at the control piston, repeated opening and closing will bring about a reduction of the outlet pressure in relation to the pressure at the pressure fluid inlet 30. This way, the wheel brake cylinders of the rear wheels are actuated with less pressure than the front wheels.

As soon as the braking pressure is decreased on the inlet side, the second sleeve 12 will displace together with the seal 15, whereby the volume on the outlet side is increased and the pressure on the outlet side is decreased. On attainment of the pressure balance between inlet side and outlet side, the sealing lip 16 of the non-return valve (seal 15) will lift, and the pressure will continue to be decreased, while the second sleeve 12 will displace in the direction of the outlet opening 20 until it abuts on the first sleeve 5.

The described braking pressure control unit bears the advantage that it allows to be manufactured, adjusted and checked or only checked and re-adjusted, if need be, separately from the braking pressure generator, before it is screwed into the receiving bore 2 of the housing 1 and this way is integrated into the braking pressure generator. The separate adjustment and checking is possible both by a hydraulic test arrangement in a test housing provided for this special purpose and by mechanically applying a force on the control piston. To this end, there is merely need for a force-travel diagram, from which that force can be taken that is necessary to close the first valve assembly. In dependence on the closing force determined, the adjusting device for the spring force of the control spring is to be actuated.In comparison to a braking pressure control unit which is sealed directly towards the receiving bore, it is not required to machine the surfaces in the housing of the braking pressure generator. The seal 1 5 additionally performs the function of a non-return valve. This obviates the need for any additional non-return valve.

The braking pressure control. unit 4 comprises but few and, moreover, simple component parts. It is of very small overall size and, in addition, is accommodated in a space-saving fashion at a favourable location directly in the housing 1 of the braking pressure generator.

The receiving bore 2 need not extend transversely to the main bore, but may likewise be arranged in parallel to said, for instance, and may be connected to said by a radial channel.

The pressure control unit according to Figure 2, which may be made use of on a vehicular brake system for instance, comprises a housing 36 with a stepped bore 37 which is fluid-tightly closed at its end of largest diameter by means of a closure plug 38. Said housing 36 has an extension provided with a thread and comprising a pressure fluid inlet 41. By means of said extension, the pressure control unit can be screwed for instance into a corresponding opening of a pressure generator, e.g. a master cylinder of a brake system, or into a portion of a line connected with the master cylinder. A pressure fluid outlet 42 leading to at least one wheel brake cylinder is provided in the closure plug 38.

Starting from the closure plug 38, the housing 36 accommodates a range spacer 43, a valve seat element 35, a distance piece 44 and a cap 45, all being in abutment on one another. Inside the cap 45, there is provided a control spring 46 determining the closing of the valve, a ring bearing 47 and a sealing assembly 48 which will be described more closely hereinbelow.

The range spacer 43 having the shape of a disc includes a bulge, whereagainst a closure member 33 is bearing at a distance from the pressure fluid outlet 42, and includes openings 49 for the passage of pressure fluid.

The valve seat element 35 is of substantially bowl-shaped design and is furnished with a circular opening 50 in its bottom surface.

Serving as a sealing between the valve seat element 35 and the housing 36 is an annular seal 52 inserted into an outer circumferential groove 51 of the valve seat element 35, the said seal having along its circumference a sealing lip 53 which abuts on the inner wall of the stepped bore 37.

The cap 45 is at a radial distance from the inner wall of the stepped bore 37 in the housing 36 and comprises at its end by which it abuts on the distance piece 44 a pressure fluid passage in the shape of openings 54 which permits the propagation of pressure fluid from the pressure fluid inlet 41 to valve seat 34.

The opening 50 provided in the bottom surface of the valve seat element 35 forms the valve seat 34 for a closure portion 31 of a closure member 33 in the form of a control piston, the said closure portion being arranged in the interior of the valve seat element 35.

The said control piston is composed of two parts, the closure portion 31 and a shaft portion 32 and is with the shaft portion 32 guided in the ring bearing 47. A commercial steel ball of high surface quality which is coupled to the shaft portion 32 by being soldered thereto serves as the closure portion 31. Said shaft portion 32 contains a sphericalsegment shaped indentation in which the ball is placed. The spherical closure portion 31 is pre-centered in the valve seat element 35 by guide webs 29 and, therefore, performs only small radial movements during the closing action.

The valve seat element 35 is made as an injection-moulded part of polyphenylenesulphide or a polyphenylenesulphide solid solution. The valve assembly thus designed is distinguished by great tightness, insusceptibility to brake fluid as pressure medium, and great temperature stability. The shaft portion 32 of the control piston extends through the valve seat opening, through the sealing assembly 48 arranged at the end of the cap as well as through the ring bearing 47 into the interior of the cap 45 and is at its end acted upon by the force of a control spring 46. Said control spring 46 takes support on the inner end surface of the cap 45, on the one hand, while it bears against the shaft portion 32 via an adjusting element hving the shape of a screw 55 arranged in a spring plate, on the other hand.

The adjusting device allows to infinitely variably set the preload of the control spring. Owing to the screw 55, the force of the control spring 46 can be applied to the control piston almost precisely so that no disturbing transverse forces are allowed to occur. Furthermore it is enabled to adjust the force of the control spring from the outside. To this end, the valve is adjusted outside the housing 36 by twisting the screw 55 and by measuring the force at the control piston which is in its closing position, without there being any need for a hydraulic pressurisation.

Arranged in a bulge at the outer end surface of the cap 45 is a seal 56 by which the stepped bore 37 filled with pressure fluid is sealed towards the inner space of the cap 45 which is in communication wjth the atmosphere via a bore 57.

The sealing assembly 48 encompassing the shaft portion 32 of the closure member 33 comprises two sealing lips directed away from the cap's interior and abutting on the shaft portion 32 and on the cap's inner circumference.

The drawing (Figure 2) displays the braking pressure control unit in its unpressurised condition, i.e. with the brake system not actuated. By the action of the control spring 46, the closure member 33, that is the control piston, abuts with its spherical closure portion 31 on the range spacer 43 which is supported on the housing 36 and which establishes the passage to the pressure fluid outlet 42 by means of openings 49.

Pressure fluid propagates from the pressure chamber of the master cylinder via the pressure fluid inlet 41, the channel between cap 45 and the inner wall of the stepped bore 37 to the openings 54 at the end of the cap 45.

The pressure fluid propagates further via the chamber between the sealing assembly 48 and the valve seat element 35, via the channel between shaft portion 32 and opening 50, via the open valve sssembly and the openings 49 in the range spacer 43 to the pressure fluid outlet 42 of the pressure control unit and thus to any one or to several of the wheel brake cylinders. When the pressure generator is actuated and, consequently, the pressure increases at the pressure fluid inlet, likewise the pressure in the pressure fluid outlet 42 of the braking pressure control unit 41 will rise. The arrows 58 and 59 characterise the direction of flow of the pressure fluid.On attainment of the predetermined pressure at which pressure reduction commences, the compressive force acting to the left, when viewing in the drawing, on the control piston (closure member 33) exceeds the counterforce of the control spring 46. Subsequently, the control piston will move in the closing direction and close the valve passage at the valve seat 34, until further increase of the pressure at the pressure fluid inlet 41 will have caused development of a counterforce in the opening direction of an amount so high that the control piston opens again. On account of the employed ratio of surfaces at the control piston, repeated opening and closing brings about a reduction of the outlet pressure in relation to the pressure at the pressure fluid inlet 41.Hence it follows that the wheel brake cylinders of the rear wheels are actuated by a pressure less than the pressure generated by the master cylinder.

When the braking pressure is reduced on the inlet side, the sealing lip 53 of the seal 52 designed as non-return valve will lift on attainment of the pressure balance between inlet side and outlet side, and the outlet pressure will be reduced.

The inventively designed valve is particularly apt when used on similarly designed braking pressure control units, for instance both as valve for the pressure-reducing device and as valve for the adapting device of the braking pressure control unit proposed in West German patent application P 33 21 806. Owing to the inventive design, the diameters of the control piston can be chosen to be so large that the forces resulting from the friction caused by the sleeve seals will not take great effect on the control accuracy.

The valve illustrated in Figure 3 contains an inlet chamber 65 which, via the intermediary of an electromagnetically actuatable twoway/two-position directional control valve 68, is in communication with a pressure source 69 via a housing port 66 and a pressure line 67. The directional control valve 68 closes the connection between pressure source 69 and inlet chamber 65 in the illustrated position.

Upon corresponding actuation, the pressure source 69 will be connected to the inlet chamber 65.

In the interior of the valve, an annular piston 70 is sealedly guided and kept in abutment on a stop 72 close to the inlet by a compression spring 71. The opening in the annular piston 70 forms a valve passage between the inlet chamber 65 and an outlet chamber 73. Designed at the opening in the annular piston 70 is a first valve seat 74 which is associated with a first closure portion 61 of a valve closure member 60. The outlet chamber 73 is substantially of cylindrical shape and, at its one end face, is bounded by the annular piston 70, while at its other end face a second valve seat 75 is designed at an opening of a line leading to a return reservoir 76. Via the intermediary of a shaft portion 63 extending through the opening in the annular piston 70, a second closure portion 62 is arranged at the valve closure member 60 which co-operates with the second valve seat 75.A compression spring 77 is located between annular piston 70 and second closure portion 62 which spring normally maintains the first closure portion 61 in abutment on the first valve seat 74.

The closure portions 61 and 62 are undetachably connected with the cylindrically designed shaft portion 63 by way of frictionwelding, for example. Terminating into the outlet chamber 73 is another pressure port 78 which leads via a line to a pressure fluid user 79.

The thus designed valve is particularly favourable in use on hydraulic brake systems with slip control, for instance in a system as it is proposed in West German patent application P 34 13 626.6 In the event of a like employment, the pressure source is the pressure (booster) chamber of a hydraulic booster, while the pressure port 78 is via a pressure chamber of a tandem master cylinder arrangement in communication with a pressure fluid user 79 in the form of a wheel brake cylinder.

Depending on the commencement of a brake slip control period, the directional control valve 68 is switched to assume the open position, and a hydraulic connection is established between pressure source 69 and inlet chamber 65. Pressurisation of the inlet chamber 85 has as a consequence that, with the closure portion 61 bearing against the valve seat 74, the annular piston 70 is displaced to the right, when viewing the drawing, in opposition to the force of the spring 71 so that the second closure portion 62 finally moves into abutment on the assigned valve seat 75 and closes the connection between the outlet chamber 73 and the unpressurised return reservoir 76. Subsequently, further displacement of the annular piston 70 to the right causes the closure portion 10 to lift from the assigned valve seat 74, and pressure fluid is allowed to propagate from the pressure source 69 via the inlet chamber 65 into the outlet chamber 73 and further to the user 79.

Upon termination of a brake slip control period, the electromagnetically actuated directional control valve 68 is switched over, among others. After the valve passage in the annular piston 70 which is controlled by the closure portion 61 has been closed, lifting of the closure portion 62 from the valve seat 75 re-establishes the connection between the outlet chamber 73 and the unpressurised return reservoir. The valve will then adopt its inactive position illustrated.

The valve displayed in Figure 4 employs the same reference numerals as the Figure 3 valve for similar members and comprises a closure member composed of a shaft portion 63 and a spherical closure portion 61, the said closure member being associated with a first valve seat 74 at a valve slide element 85.

The shaft portion 63 is stepped in its diameter and, with its portion 64 of larger diameter, is held with radial clearance in a hollow bore 80 in an actuating piston 81 in an axially immovable fashion by means of a circlip 82.

With its smaller-diameter portion 83, the shaft portion 63 is connected by for example, friction-welding, with the closure portion 61 designed as a ball. Due to its ability to move radially, the closure member is able to adopt a position coaxial to the valve seat 74 irrespective of the alignment between valve seat 74 and actuating piston 81. Thus, compensation of alignment errors is ensured in a simple way.

The first valve seat 74 is designed at the end of a bore 84 in the valve slide element 85, through which bore a first chamber 86 communicating with a pressure fluid user 79 is hydraulically connectible with a chamber 87 communicating with a return reservoir 76. The valve slide element 85 is guided in a housing bore and inlcudes a conically designed closing portion 88 which is associated with a second valve seat 89 and which serves to close a pressure fluid passage 90 between a chamber 91 connected with the pressure fluid source 69 and the chamber 86 leading to the pressure fluid user 79. The pressure fluid passage 90 is formed by axial grooves at the outer periphery of the valve slide element 85.

When the actuating piston 81 is displaced to the left, when viewing the drawing, from its non-illustrated inactive position in which the pressure fluid user 79 is in communication with the return reservoir 76 via the bore 84, first the closure portion 61 will close the connection to the return reservoir 76, as is shown, the closure member displacing radially to the axis of the actuating piston 81, if necessary. Upon further displacement, the closure portion 88 lifts from the valve seat 89 and establishes a connection between the pressure source 69 and the pressure fluid user 79. When the actuating piston 81 displaces to the right, the connection to the pressure source 69 will be interrupted first, and only subsequently will the connection to the return reservoir 76 be established.

Claims (22)

1. A braking pressure control unit with a closure member composed of two parts, a closure portion and a shaft portion, the said closure member being movable along an axis relative to a valve seat, with a view to controlling the flow of a medium through an opening comprising the valve seat, characterised in that the closure portion (31) and the shaft portion (32) are undetachably interconnected.

2. A braking pressure control unit as claimed in claim 1, characterised in that the closure poriton (31) is formed by a ball.

3. A braking pressure control unit as claimed in claim 1 or 2, characterised in that the parts of the closure member (33) are interconnected by soldering.

4. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the valve seat element (35) comprising the valve seat (34) is made of polyphenylenesulphide or any polyphenylenesulphide solid solution.

5. A braking pressure control unit as claimed in claim 1, characterised in that the parts of the closure member (60) are interconnected by friction-welding.

6. A braking pressure control unit as claimed in claim 5, characterised in that a tempered steel ball is provided as the closure portion (61, 62).

7. A braking pressure control unit as claimed in claim 6, characterised in that the shaft portion (63) comprises an end portion (64) of larger diameter that is remote from the closure portion (61).

8. A braking pressure control unit as claimed in anyone of the preceding claims, characterised in that the end face of the shaft portion (63) to be connected to the closure portion (61, 62) is plane.

9. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the shaft portion (63) is connected to two closure portions (61, 62).

10. A braking pressure control unit as claimed in claim 1 and comprising a sleeve which receives components of said unit and can be inserted into a housing of a braking pressure generator, which sleeve includes a pressure fluid inlet, a pressure fluid outlet and an interposed valve assembly for controlling the pressure fluid passage, the said valve assembly including a control piston, comprising said closure member, slidable pressure-responsively in opposition to a control force and a valve seat encompassing the control piston, the control piston including tthe closure portion allocated to the valve seat and the shaft portion which projects through the valve seat and by which it is sealedly guided in the sleeve, as well as comprising a second valve assembly designed as a non-return valve, characterised in that the valve seat (21) is designed at a second sleeve (12) which is sealedly slidably arranged in the sleeve (5).

11. A braking pressure control unit as claimed in claim 10, characterised in that the closure portion (22) of the control piston is formed by a steel ball.

12. A braking pressure control unit as claimed in claim 11, characterised in that the second sleeve is made of polyphenylenesuphide or any polyphenylenesulphide solid solution.

13. A braking pressure control unit comprising a sleeve which receives components of said unit and can be inserted into a housing of a braking pressure generator, which sleeve includes a pressure fluid inlet, a pressure fluid outlet and an interposed valve assembly for controlling pressure fluid passage, the said valve assembly comprising a control piston, slidable pressure-responsively in opposition to a control force, and a valve seat encompassing the control piston, the control piston including a valve closure portion associated with the valve seat and a shaft portion which projects through the valve seat and by which it is sealedly guided in the sleeve, as well as comprising a second valve assembly designed as a non-return valve, characterised in that the valve seat (21) is designed at a second sleeve (12) which is sealedly slidably arranged in the sleeve (5).

14. A braking pressure control unit as claimed in claim 13, characterised in that the second sleeve (12) is held by a spring element (17) in abutment on a stop of the first sleeve (5) close to the outlet.

15. A braking pressure control unit as claimed in claim 13 or claim 14, characterised in that a sealing lip (16) of a seal (15) arranged between an outer circumferential surface of the second sleeve (12) and an inner circumferential surface of the first sleeve (5) forms the non-return valve.

16. A braking pressure contol unit as claimed in claim 15, characterised in that the ring seal (15) is secured to the first (5) or to the second sleeve (12).

17. A braking pressure control unit as claimed in any one of claims 13 to 16, characterised in that the second sleeve (12) is designed as a plastics component and the control piston (23) is designed as a metal component.

18. A braking pressure control unit as claimed in claim 17, characterised in that the control piston (23) is composed of two parts, comprising the closure portion (22) and the shaft portion (24), which are undetachably coupled to one another.

19. A braking pressure control unit as claimed in claim 18, characterised in that the closure portion (22) of the control piston (23) is formed by a customary steel ball.

20. A braking pressure control unit as claimed in claim 19, characterised in that the second sleeve is made of polyphenylenesuphide or any polyphenylenesulphide solid solution.

21. A braking pressure control unit as claimed in any one of claims 13 to 20, characterised in that the interior of the sleeve (5) which communicates via a bore (27) with the atmosphere and into which the shaft portion (24) of the control piston (23) is displaceable is sealed in relation to the receiving bore (2) through a seal (26) at the end face of the sleeve (5).

22. A braking pressure control unit substantially as herein described with reference to and as illustrated in Figure 1, Figure 2, Figure 3 or Figure 4 of the accompanying drawings.