GB2115093A - Brake pressure regulator for an hydraulic vehicle braking system - Google Patents

Abstract

The present specification discloses a brake pressure regulator comprising a housing (10), within which a compensating piston (52) is disposed between a first and a second outlet chamber (30,42) which are connected to a wheel-brake cylinder (RzI and RzII respectively) of a rear wheel each. In an intermediate area of the length of the compensating piston (52) a first inlet chamber (26) is formed which is connected to a first master cylinder (HzI) and communicated via a first valve (86, 88) with the first outlet chamber (30). This valve (86, 88) is disposed in a first stepped piston (64) which is in turn disposed in the compensating piston (52) and closes the valve (86, 88) when the pressure in the first outlet chamber (30) increases. A second inlet chamber (38) is also formed which is connected to a second master cylinder (HzII) and communicates with the second outlet chamber (42) via a second valve (104, 106) which responds to the deceleration of the vehicle (Fig 1) or the vehicle load (Fig 2). <IMAGE>

Description

SPECIFICATION Brake pressure regulator for an hydraulic vehicle braking system The present invention relates to a brake pressure regulatorforan hydraulic vehicle braking system.

More particularly the present invention relates to a brake pressure regulatorforan hydraulic vehicle braking system comprising a housing in which first and second inlet chambers and first and second outlet chambers for a first and a second brake circuit respectively are formed, the two outlet chambers are separated from each other by a compensating piston, between the first inlet and outlet chambers a stepped piston is disposed which bounds the first outlet chamber with its larger face and which is loaded by a spring towards a reduction in size of said outlet chamber, between the first inlet and outlet chambers, a pressure-conscious valve is also disposed which is controlled by the position of the stepped piston in relation to the compensating piston, and between the second inlet and outlet chambers, a further controlled valve is disposed.

Brake pressure regulators of this kind are provided above all for diagonally split vehicle braking systems in which the two brake circuits are each connected to a front wheel and its diagonally opposite rear wheel.

In such vehicle brake systems, the brake pressure regulator has the task of reducing the rise in pressure at the rear-wheel brakes in comparison to the rise in pressure at the front wheel brakes, as soon as the pressure at the rear wheel brakes has reached a certain level and, as the case may be, the vehicle has achieved a certain deceleration.

In the case of a known brake pressure regulator (DE-OS 28 20 768) of the type described, the stepped piston is disposed axially adjacent to the compensating piston. Both pistons are hollow and each contains a valve body and a spring which loads the corresponding valve body in the direction of a valve seat formed in the piston concerned. Both valve bodies each have an extension which projects axially outwards. In the inoperative position, the valve body disposed in the stepped piston supports itself by means of its extension on the compensating piston and the valve body disposed in the compensating piston supports itself by means of its extension on the housing.As a result, when inoperative, both valves are kept open so that the first inlet chamber is connected with the first outlet chamber through the stepped piston and the second inlet chamber is connected with the second outlet chamber through the compensating piston. The second inlet chamber is connected to the second outlet chamber additionally via canals which by-pass the valve disposed in the compensating piston and contain a valve controlled by means of it being deceleration-conscious.

The deceleration-conscious valve comprises a ball valve which is movable within a bore in the housing, said bore being displaced in an axial direction from the two pistons, and a valve seat which is formed on a cap, said cap closing said bore.

If in this known brake pressure regulator, during a braking action, the pressure in the first outlet chamber exceeds a certain level, the stepped piston is displaced against the force of the spring, loading it in a direction away from the compensating piston and having the tendency to enlarge the first outlet chamber. The compensating piston follows the stepped piston and thereby maintains the pressure equilibrium between the two outlet chambers. As a result of the movement of the compensating piston, the valve disposed therein closes so that the pressure in the second outlet chamber can only increase under the condition that the deceleration-conscious valve is still open.On further displacement of the stepped piston, the valve disposed therein also closes and thereafter, the pressure in the two outlet chambers can only increase to a lesser proportion than the pressure in the two inlet chambers, said proportion being dependent on the aspect ratio of the two faces of the stepped piston.

If the first brake circuit of the vehicle brake system connected to the known brake pressure regulator fails, then the compensating piston works without the aid of the stepped piston against the spring loading the said stepped piston. As a result, a limitation of pressure in the second outlet chamber occurs only at a pressure level at which it must be expected that the rear wheel connected to the second brake circuit will lock.If on the other hand, the second brake circuit fails, then the valve contained in the stepped piston will close prematurely as, in this case, the compensating piston will not follow the stepped piston As a result, the pressure in the first outlet chamber will be prematurely reduced in relation to the pressure in the first inlet chamber, which is also undesirable, as this results in the braking action of the rear wheel connected to the still intact first brake circuit being weaker than under the normal condition of both brake circuits.

The aim of the present invention is to lessen the effect of the failure of a brake circuit in a brake pressure regulator of the above-described type on the pressure distribution in the outlet chamber of the other brake circuit and to construct the brake pressure regulator in an altogether more simple and space-saving manner.

According to the present invention there is provided a brake pressure regulator for an hydraulic vehicle braking system, comprising a housing in which first and second inlet chambers and first and second outlet chambers for a first and second brake circuit respectively are formed, the two outlet chambers being separated from each other by a compensating piston and a stepped piston being disposed between the first inlet and outlet chambers, said stepped piston bounding the first outlet chamber with its larger face and being loaded by a spring towards a reduction in size of said outlet chamber, a pressure-conscious valve being also disposed between the first inlet and outlet chambers, said valve being controlled by the position of the stepped piston in relation to the compensating piston, and a further controlled valve being disposed between the second inlet and outlet chambers, the stepped piston together with the spring loading said stepped piston and the pressure-conscious valve, being disposed in the compensating piston, and the pressureconscious valve being controlled by the stepped piston, independent of the position of the compensating piston in relation to the housing.

The brake pressure regulator according to the invention thus comprises only one pressureconscious valve and this is disposed together with the stepped piston which controls it within the compensating piston in a space-saving manner. The effect of this valve is independent of all movements of the compensating piston in relation to the housing; as a result, the pressure-conscious valve always changes over at the same pressure as long as the first brake circuit is intact, independent of whether the second brake circuit is likewise intact or not. The second brake circuit, on the other hand, comprises only the additional controlled valve; as a result, it is impossible after closure of this valve that the pressure in the second outlet chamber should still increase undiminished.

The compensating piston is advantageously situated between two identical springs with flat spring rates which are supported on the housing.

A preferred embodiment of the present invention has its origins in a feature of the known brake pressure regulator of this type, namely that the additional valve is controlled by means of it being deceleration-conscious. In this case, in keeping with the invention, a second stepped piston is disposed between the second inlet and outlet chambers, coaxial with the compensating piston and movable independently thereof, said second stepped piston having a valve seat for the deceleration-conscious valve on its smaller face, which bounds the second inlet chamber, and said second stepped piston assuming an end position when inoperative in which the volume of the second inlet chamber is at its smallest.

Thus, the additional advantage is achieved that the deceleration-conscious valve disposed in the second brake circuit does not act as a pressure limiting valve but as a pressure-reducing valve and in so far is comparable to the pressure-conscious valve belonging to the first brake circuit. After closure of both valves, the compensating piston would actually effect a pressure equalisation between the two outlet chambers even if only the pressure-conscious valve were developed as pressure-reducing valve and the deceleration-conscious valve, on the other hand, as pressure limiting valve; however, the development of both valves as pressure-reducing valves has the advantage that a pressure equalisation between both outlet chambers is possible after the closure of both valves, with or without very slight movement of the compensating piston.

The present invention will now be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial section of one embodiment of a brake pressure regulator according to the invention; and Figure 2 is an axial section of a brake pressure regulator modified from Figure 1.

The brake pressure regulator represented in Figure 1 has a housing 10 made of simple profile steel being quadrilateral in cross section and having a stepped bore, the axis of which is referred to hereinafter as longitudinal axis 12. The brake pressure regulator is intended to be mounted in a motor vehicle such that the longitudinal axis 12, in a vertical longitudinal plane of the vehicle, is inclined at approximately 30 to the horizontal and is so disposed that the left end of the housing in Figure 1 lies at the front and higher than the right rear end. A bolt (not shown) is provided for this mounting of the regulator and extends through a transverse bore 14 in the housing 10.

The stepped bore extends through the housing 10 along the longitudinal axis 12 from the front, and comprises a front threaded portion 18 closed by a screw cap 16, a front cylinder portion 20 joining up therewith, whose diameter is only marginally smaller than the inner diameter of the threaded portion 20, an intermediate cylinder portion 22 of medium diameter, and a rear cylinder portion 24 of smaller diameter.

The middle area of the front cylinder section 20 forms a first inlet chamber 26 which is adapted to be connected via main cylinder connection 28 to a first main cylinder Hzl - indicated by an arrow only. The front area of the front cylinder portion 20 forms a first outlet chamber 30 which is adapted to be connected via a brake connection 32 to a first wheel-brake cylinder Rzl - likewise indicated only by an arrow on a rear wheel. A ventilation chamber 34 is provided near the rear end of the front cylinder section 20 and this is connected to atmosphere via a dust filter 36.

On the rear end of the rear cylinder portion 24, a second inlet chamber 38 is formed which is adapted to be connected via a second main cylinder connection 40 to a second main cylinder Hzll, once again indicated by an arrow only. Furthermore, the front end of the intermediate cylinder portion 22 forms a second outlet chamber 42 together with the rear end of the front cylinder portion 20, said second outlet chamber 42 being adapted to be connected via a second brake connection 44 to a second wheel brake cylinder Rzll- once again indicated by an arrow only on the second rear wheel of the vehicle.

In the front cylinder portion 20, two weak springs 46 and 48 are disposed, the front one of which is supported on the cap 16 and the rear one on a perforated plate 50 situated between the cylinder portions 20 and 22. A compensating piston 52 with low axial initial bias is disposed between the two springs 46 and 48. The two springs 46 and 48 are, for example, shaped as cross-shaped leaf springs with flat spring rates. This means that, in the case of axial deviations, the springs only exert minor restoring forces on the compensating piston 52 which floats between them and these restoring forces are just sufficient to return the compensating piston 52 after each brake actuation to its depicted intermediate position.

On its outer surface, the compensating piston 52 has three annular seals 54, 56 and 58 which separate the first inlet chamber 26 from the first outlet chamber 30 or ventilation chamber 34 respectively, or the latter from the second outlet chamber 42. The compensating piston 52 is hollow and comprises a bush 60 which is fixed at its front end within the piston 52, and which has an axial bore 62. Afirst stepped piston 64 has a front end portion where the piston diameter is at its largest and where said piston is guided in said bore 62. In the rear part of the compensating piston 52, which is closed to the rear, a bore 66 is formed which has a smaller diameter than the bore 62 and which receives a corresponding rear section of the stepped piston 64. The stepped piston 64 is sealed against both bores 62 and 66 with, in each case, an annular seal 68 and 70 respectively.Furthermore, the bush 60 is sealed against the compensating piston 52 with an annular seal 80. The area of the bore 66 which lies behind the annular seal 70 is connected to atmosphere via the ventilation chamber 34 and the filter 36.

Within the compensating piston 52 and around the first stepped piston 64, a coiled pressure spring 82 is disposed. This spring 82 is conical at the front and cylindrical atthe rear, the rear end being supported on the compensating piston 52 and the front end on the stepped piston 64. The spring 82 thus tends to keep said stepped piston 64 resting against a perforated front plate 84 of the bush 60.At the front end of the stepped piston 64, an annular valve seat 86 made of an elastomeric material is fixed and this, together with a valve body 88 which is carried in the stepped piston 64 so as to be axially slidable, forms a pressure-conscious valve 86, 88. The valve body 88 is biased towards the front by a coiled pressure spring 90 situated inside the stepped piston 64 and has a front extension 92 which, in the illustrated inoperative position, pushes against the front plate 84 and keeps the valve body 88 lifted from the valve seat 86.

In the intermediate cylinder portion 22 and in the rear cylinder portion 24, a second stepped piston 94 is disposed which is sealed in each case with an annular seal 96 and 98 respectively. The front face 100 of the second stepped piston 94, together with the compensating piston 52, bounds the second outlet chamber 42. The rear face 102, which has a smaller surface area than that of the front face 100, bounds the second inlet chamber 38. On this rear face 102, an annular valve seat 104 made of an elastomeric material is fixed and, together with a valve body 106, forms a deceleration-conscious valve 104,106. In the example given in Figure 1,the valve body 106 is a sphere which is carried in a cage 108 fixed to the second stepped piston 94 and is adapted to be axially movable.

The second stepped piston 94 has a continuous axial canal 110 which opens out inside the valve seat 104 and contains a pin 112. The pin 112 rests on the perforated plate 50 and does not quite reach to the valve seat 104 when the second stepped piston 94 assumes its depicated inoperative position, in which it is supported on an annular shoulder 114 between the cylinder portions 22 and 24. A relief bore 116 leads from the shoulder 114 into the open.

In the following description of the mode of operation of the brake pressure regulator as represented in Figure 1, it is assumed at the outset that both brake circuits Hzl-Rzl and Hzll-Rzll are in order and that the vehicle is carrying a light load, upon actuation of the two main cylinders Hzl and Hzll (which are normally disposed in a common housing), the pressure-conscious valve 86,88 and the deceleration-conscious valve 104, 106 are both open.

The pressure gradually increasing in the inlet chambers 26 and 38 is therefore transferred to the outlet chamber 30 and 42 undiminished.

At a certain increase in pressure, the vehicle achieves deceleration which causes the spherical valve body 106 inside the cage 108 to roll forwards and upwards and to rest against the valve seat 104 so that the deceleration-conscious valve 104,106 closes. The spring rate of the spring 82 is selected such that the increase in pressure in the outlet chamber 30 reached by this time pushes the stepped piston sufficiently far to the rear that the valve seat 86 lies against the valve body 88 and, as a result, the pressure-conscious valve 86,88 closes at approximately the same time as the deceleration-conscious valve 104,106 in an unladen vehicle. If one of the two valves were to close before the other, then a movement of the compensating piston 52 would prevent a variation in the pressure in both outlet chambers 30 and 42 occurring.

Upon further increase in pressure in the two inlet chambers 26 and 38, the pressure-conscious valve 86,88 acts together with the first stepped piston 64 as pressure-reducing valve which lets the pressure in the outlet chamber 30 increase only to an extent which is reduced in comparison to the pressure increase in the inlet chamber 28 at the ratio of the operative faces of the first stepped piston 64. The deceleration-conscious valve 104, 106 operates in corresponding manner together with the second stepped piston 94 as a pressure-reducing valve which allows the pressure in the second outlet chamber 42 to increase only to an extent which is reduced in comparison to the pressure in the second inlet chamber 38 at the ratio of the operative faces 100 and 102 of the second stepped piston 94.

In the case of a heavily-laden vehicle, the increase in pressure in the outlet chambers 30 and 42, at which the first stepped piston 64 is pushed to the rear and the pressure-conscious valve 86, 88 closes, cannot yet decelerate the vehicle sharply enough to cause the deceleration-conscious valve 104,106 to also close. As a result, the continuously increasing pressure of the second main cylinder Hzll is transferred undiminished into the outlet chamber 42 and the forwards-movement of the compensating piston 52 caused thereby lets the pressure in the outlet chamber 30 increase to the same extent as in the outlet chamber 42.Both wheel-brake cylinders Rzl and Rzll, therefore, are supplied with a continuously increasing pressure until finally deceleration of the vehicle is achieved, at which point the decelerationconscious valve 104,106 closes and only permits further increases in pressure in the outlet chamber 42 and, due to the mobility of the compensating piston 52, also in the outlet chamber 30, at a reduced rate of increase in proportion to the further increase of pressure in the inlet chambers 26 and 38.

If the first brake circuit Hzl-Rzl fails, then the compensating piston 52 moves to its forward end position defined by the cap 16 on every brake actuation, so that the outlet chamber 42 receives appropriately more brake field and the driver notices the failure of the first brake circuit from the fact that the brake pedal requires great depression. The deceleration conscious valve 104,106 closes upon the deceleration which has been selected by the adjustment of the inclination of the longitudinal axis 12 in comparison to the horizontal.The second stepped piston 94, however, is displaced more rapidly upon further increase in pressure in the inlet chamber 38 than in the case of an intact first brake circuit Hzl-Rzl and, as a result, the pin 112 lifts the valve body 106 from the valve seat 104 so that the pressure in the outlet chamber 42 is adapted to that in the inlet chamber 38 again and the rear wheel to which the wheel-brake cylinder Rzll is assigned is brake appropriately more sharply than in the case of an intact first brake circuit.

If, on the other hand, the second brake circuit Hzll-Rzll fails, then the compensating piston 52 moves at each brake actuation into its rear end position, at the right of the drawing, this end position being defined by the perforated plate 50; the pressure-conscious valve 86, 88, however, operates normally.

The modified brake pressure regulator represented in Figure 2 differs from that in Figure 1 only by details in the rear area to the right of the perforated plate 50. The cylinder portion 22 extends in this case further to the rear and in the housing 10 a bush 118 is firmly fixed at its rear end region, said bush having an inner diameter which issmallerthan that of the cylinder portion 22. In cylinder portion 22 and in the bush 118, a stepped piston 120 is carried which conforms in structure and dimensions with the stepped piston 64.While the stepped piston 64 in Figure 2, in conformity with Figure 1, represents a connection between the first inlet chamber 26 and the first outlet chamber 30 controlled by the pressure-conscious valve 86,88, the stepped piston 120 forms a connection between the second inlet chamber 38 and the second outlet chamber 42, controlled by a pressure-conscious valve 122,124. To the valve 122,124 belong an annular valve seat 122 fixed to the front end of the stepped piston 120, and a valve body 124 which is carried in the stepped piston 120 so as to be axially displaced, said valve body being loaded by a spring 126 which is also situated in the stepped piston 120, in the direction of the valve seat 122 and having a front extension 128.In the inoperative position as depicted, the extension 128 is supported on the perforated plate 50 so that it keeps the valve body 124 lifted from the valve seat 122.

On the rear end of the housing 10, a lever 132 is positioned on a bearing pin 130 which extends transversely of and at a distance from the longitudinal axis 12, and at the end of the lever a spring, indicated by an arrow 134, is attached. The said spring 134 is connected in a manner known perseto an axis of the vehicle arranged such that the lever 132 is adjusted, in the case of increasing strain, in the direction of the arrow 134. An adjusting screw 136 secured by a lock nut 138 is screwed into the lever 132, basically coaxially with the longitudinal axis 12.

The adjusting screw 136 is sealed by a sleeve 140 against the housing 10 and the bush 118, and its end rests against the rearward face of the stepped piston 120. The lever 132, and thus the adjusting screw 136, are shown in a position which corresponds to the vehicle when lightly laden.

If, during braking action, the pressure in the second inlet chamber 38 (as in the first inlet chamber 26) increases only moderately, then it is transferred through the open valve 122,124 into the second outlet chamber 42. If the pressure in the outlet chamber 42 exceeds a level predetermined by the adjustment of the spring 134, then the stepped piston 120 is displaced by the pressure differential occurring in it against the resistance of the spring 134 to the rear, that is, in Figure 2, to the right, so that the valve seat 122 rests against the valve body 124 and the connection between the second inlet chamber 38 and the second outlet chamber 42 is interrupted.In the case of further increases in pressure in the inlet chamber 38, the stepped piston 120 is displaced again slightly in a forwards direction so that the valve 122,124 is temporarily opened and the pressure in the outlet chamber 42 increases at a proportion to the increasing pressure in the inlet chamber 38 which corresponds to the proportion of the operative faces of the stepped piston 120.

If, however, the vehicle is heavily laden and the spring 134 is thus more highly loaded, said spring holds the lever 132 in a position which deviates by several degrees in clockwise direction from the depicted position. The stepped piston 120 therefore assumes an initial position when the brakes are not in actuation which deviates slightly towards the front from the depicted position, that is to the left in Figure 2. When the brakes are actuated and the pressure in the inlet chamber 38 and the outlet chamber 42 increases, a very marked increase in pressure is required to push the stepped piston 120 so far back to the rear that the valve seat 122 reaches the valve body 124. In the case of the vehicle being more heavily laden, the valve 122,124, thus only closes when a very high pressure level in the outlet chamber 42 is reached. The valve 122,124 is therefore conscious of the load of the vehicle and replaces the valve 104,106 depicted in Figure 1 which is conscious of the deceleration of the vehicle.

Claims (4)

1. A brake pressure regulator for an hydraulic vehicle braking system, comprising a housing in which first and second inlet chambers and first and second outlet chambers for a first and second brake circuit respectively are formed, the two outlet chambers being separated from each other by a compensating piston, and a stepped piston being disposed between the first inlet and outlet chambers, said stepped piston bounding the first outlet chamber with its larger face and being loaded by a spring towards a reduction in size of said outlet chamber, a pressure-conscious valve being also disposed between the first inlet and outlet chambers, said valve being controlled by the position of the stepped piston in relation to the compensating piston, and a further controlled valve being disposed between the second inlet and outlet chambers, the stepped piston together with the spring loading said stepped piston and the pressure-conscious valve being disposed in the compensating piston, and the pressureconscious valve being controlled by the stepped piston, independent of the position of the compensating piston in relation to the housing.

2. A brake pressure regulator as claimed in claim 1, in which the compensating piston is disposed between two identical springs which are supported on the housing and have flat spring rates.

3. A brake pressure regulator as claimed in claims 1 or 2, in which the valve disposed between the second inlet and outlet chambers is a deceleration-conscious valve and in which between the second inlet and outlet chambers a second stepped piston is disposed which is coaxial with the compensating piston and can be moved independently thereof, said stepped piston having on its smaller face, which bounds the second inlet chamber, a valve seat for the deceleration-conscious valve and assuming an end position when inoperative at which the volume of the second inlet chamber is at its smallest.

4. A brake pressure regulator for an hydraulic vehicle braking system, constructed and arranged substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.