GB2145179A

GB2145179A - A load-responsive brake pressure regulator for vehicles

Info

Publication number: GB2145179A
Application number: GB08420881A
Authority: GB
Inventors: Leo Gilles; Helmut Heibel
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-08-16
Filing date: 1984-08-16
Publication date: 1985-03-20
Also published as: FR2550749B1; DE3329498A1; GB2145179B; FR2550749A1; GB8420881D0

Abstract

An inlet chamber (14) adapted to be connected to a brake master cylinder and an outlet chamber (44) adapted to be connected to at least one wheel brake cylinder are each defined by a respective stepped piston (18 and 48). One or each stepped piston (18, 48) is supported by an adjustment member (72) which is adjustable in response to the loading of the vehicle. The larger diameter areas (26, 56) of both stepped pistons (18, 48) define spaces which constantly communicate with each other and are connected to the inlet chamber (14) by a pressure reducing valve (34) and to the outlet chamber (44) by the pressure increasing valve (64) disposed in one each of the two stepped pistons (18,48) up to a pressure only which depends on the adjustment of the adjustment member (72). The combined effect of both stepped pistons (18, 48) and the associated valves (34, 64) permits the course of the pressure in the outlet chamber (44) as compared to the pressure in the inlet chamber (14) to be adapted largely to the ideal course of pressure which depends on the loading condition of the vehicle. The pistons and valves may be arranged in parallel bores (Figure 1 not shown). <IMAGE>

Description

SPECIFICATION A load-responsive brake pressure regulator for vehicles The invention relates to a load-responsive brake pressure regulator for vehicles, of the kind com- prising an inlet chamber adapted to be connected to a controlled pressure fluid source, an outlet chamber adapted to be connected to at least one wheel brake cylinder, two pistons, one defining the inlet chamber and the other one the outlet chamber, an adjustment member which is adjustable in response to the loading of the vehicle and supports at least one of the two pistons in load-responsive manner, and a pressure reducing valve disposed between the inlet and outlet chambers, controlled by one of the two pistons, and open in an inoperative position.

It is usual in vehicles whose rear axle is loaded only a little when the vehicle is unloaded, to have the wheel brake cylinders of the front wheels connected directly to a brake master cylinder, whilst the wheel brake cylinders of the rear wheels are connected to the brake master cylinder either by way of a common load-responsive brake pressure regulator common to both rear wheels, or by one regulator for each wheel. Normally such brake pressure regulators are so designed that the pressure in the rear wheel brake cylinders will rise up to a switchover pressure, in the same way as the pressure in the brake master cylinder rises, whereas above the switchover pressure, the pressure in the rear wheel brake cylinders will continue to rise at a certain fraction only of the pressure rise in the brake master cylinder.In this manner it is attempted to approach the ideal curve of pressure at which the pressure in the rear wheel brake cylinders, as compared to the pressure in the front wheel brake cylinders on the whole, rises approximately parabolically. With some vehicles the gradient of the ideal course of pressure is different when the vehicle is loaded than when it is unloaded. For such vehicles load-responsive brake pressure regulators of the kind set forth have been developed to reduce the pressure in the rear wheel brake cylinders as compared with the pressure in the brake master cylinder relatively less when the vehicle is laiden than with an empty vehicle.

For instance, DE-OS 30 41 879 discloses a brake pressure regulator of the kind set forth in which the two pistons defining the inlet and outlet chambers, respectively, are coupled by a rocker element whose pivot axis is adjustable in response to the loading of the vehicle by means of a linkage such that the lever arms of the two pistons vary in opposite sense with respect to the pivot axis, depending on the load condition. The pressure reducign valve is not only controlled by the piston defining the outlet chamber but is also suspended, with certain lost-motion, from a stepped piston which has two effective end faces of different areas, the smaller of which is exposed constantly to the pressure prevailing in the inlet chamber, whilst the greater is constantly exposed to the pressure in the front wheel brake circuit, through a separate connection.With an intact front wheel brake circuit the stepped piston grants the pressure reducing valve freedom to close when controlled accordingly by the respective piston which delimits the outlet chamber Upon failure of the front wheel brake circuit, however, the stepped piston holds the pressure reducing valve in a position in which it cannot close so that the pressure of the brake master cylinder will reach the rear wheel brake cylinders unreduced. Under no circumstances will it be possible to let the pressure in the rear wheel brake cylidners rise more than the pressure in the brake master cylinder. Yet such greater rise may be desired even with an intact front wheel brake circuit if the vehicle is of such design that its useful load acts predominantly on the rear axle. This may happen, for example, with passenger cars having a large trunk behind the rear axle.

According to our invention in a load-responsive brake pressure regulator of the kind set forth, at least the other one of the two pistons is a stepped piston having two effective end faces of different areas, the gerater one thereof facing the inlet chamber and the smaller one facing the outlet chamber, and a pressure increasing valve disposed in addition between the inlet and outlet chambers is controlled by the latter piston and is similarly open in the said inoperative position.

This makes the regulator more adaptable to different axle load distributions than known pressure regulators.

Load-responsive brake pressure regulators including stepped pistons and corresponding pressure increasing valves have been known for a long time, e.g. from DE-AS 1163 695. Such brake pressure regulators are disposed between a brake master cylinder and brake cylinders of front wheel brakes; they cannot reduce the pressure rise in brake cylinders of rear wheel brakes as compared to the pressure rise in the brake master cylinder, if required.

A preferred embodiment of the invention has the pressure increasing valve arranged in series with the pressure reducing valve. The order of the two valves is not decisive in this arrangement. Preferably, the pressure increasing valve together with its corresponding piston is disposed between the outlet chamber and the pressure reducing valve with its corresponding piston.

In this latter arrangement both pistons preferably comprise stepped pistons of which the end faces of larger effective areas face each other.

The pistons may be disposed beside each other, in a similar manner to the brake pressure regulator known from DE-OS 30 41 879. In another arrangement requiring very little space and involving very low manufacturing costs both pistons are arranged co-axially. In such an arrangement an intermediate piston may be provided between the two pistons and connected to the adjustment member. In such a case the adjustment member may be a cam engaging in a recess formed in the intermediate piston.

Some embodiments of our invention will be de scribed in greater detail below, with reference to diagrammatic drawings, in which: Figure 1 is an axial sectional elevation of a first brake pressure regulator; Figure 2 is a pressure diagram of the first brake pressure regulator; Figure 3 is an axial sectional elevation of a second brake pressure regulator; Figure 4 is an axial sectional elevation of a third brake pressure regulator; Figure 5 is a side elevation as seen in the direction of arrow V in Figure 4; Figure 6 is a pressure diagram of the third brake pressure regulator; and Figure 7 is an axial sectional elevation of a fourth brake pressure regulator.

The brake pressure regulator shown in Figure 1 of the drawings includes a casing 10 formed with a connecting bore 12 for a conduit coming from a brake master cylinder (not shown). The connecting bore 12 communicates with an inlet chamber 14 which is part of a first stepped bore 16 and extends all around a first stepped piston 18.

The first stepped piston 18 includes a transverse bore communicating permanantly with the inlet chamber 14 and opening into a longitudinal bore 22. The longitudinal bore 22 extends through that part of the first stepped piston 18 which has the greater diameter; it defines the inlet chamber 14 by an annular smaller end face 24 and has a greater end face 26 at its other end which is the upper end in Figure 1. Placed in the longitudinal bore 22 is an annular valve seat 28 which, together with a valve body 30 and a valve spring 32, constitute a pressure reducing valve 34. The valve spring 32 tends to urge the valve body against the valve seat 28 so as to close the pressure reducing valve 34.Yet this is counteracted in the inoperative position shown of the first stepped piston 18, by an extension 36 formed at the valve body 30, passing through the valve seat 28, and abutting against the wall of a transverse connecting passage 38.

The casing 10 is formed with another connecting bore 42 communicating with an outlet chamber 44 which is part of a second stepped bore 46. The chamber 44 annularly surrounds a second stepped piston 48 and communicates permanently through a transverse bore 50 with a longitudinal bore 52 formed in this stepped piston. The longitudinal bore 52 extends through that part of the second stepped piston 48 which has the greater diameter and defines the outlet chamber 44 by an annular smaller end face 54. Remote from the end face 54 the piston 48 has a greater end face 56.

An annular valve seat 58 is formed within the longitudinal bore 52 and co-acts with a valve body 60 and a valve spring 62 to define a pressure increasing valve 64. The valve spring 62 tends to urge the valve body 60 against the valve seat yet is prevented from accomplishing this in the inoperative position of the second stepped piston 48 shown, due to the provision of an extension 66 formed at the valve body 60 and abutting against a threaded plug 68.

The space of the second stepped bore 46 defined by the greater end face 56 of the second stepped piston 48 is sealed tightly toward the outside by the threaded plug 68 and communicates through the connecting passage 38 only with the space of the first stepped bore 16 defined by end face 26 of greater area of the first stepped piston 18. The connecting passage 38 may be opened for venting of the brake pressure regulator but, in operation, it is closed, as shown in the drawing.

A pivotal bearing 70 is formed in the casing 10, the geometrical axis thereof being located approximately in the middle between the geometrical axes of the two stepped bores 16 and 46 and extending perpendicularly to the common plate of the latter two axes. An adjustment member 27 in the form of a two-arm lever is supported in the swing bearing 70 and is connected in a manner not shown with the rear axle of a vehicle in which the brake pressure regulator is mounted. The connection is such that the adjustment member 72 adopts the position shown in continuous lines when the vehicle is unloaded, whereas its position is as indicated in dash-dot lines when the vehicle is fully loaded.

On one side of the pivotal bearing 70 a spring 74 abuts on the adjustment member 72 and the spring 74 in turn supports the first stepped piston 18. At the other side of the pivotal bearing 70 the member 72 supports a tapped 76 which is guided for displacement in the second stepped bore 46. A spring 78 is clamped between the tapped 76 and the second stepped piston 48.

The mode of operation of the brake pressure regulator shown in Figure 1 will be described below, assuming first that the respective vehicle is unloaded or loaded only lightly so that the adjustment member 72 will be in its position illustrated in continuous lines. At the beginning of a braking procedure, brake fluid will pass from the brake master cylinder through the connecting bore 12 into the inlet chamber 14, then through the open pressure reducing valve 34 into the connecting passage 38 and on through the similarly open pressure increasing valve 64 into the outlet chamber 44 and further through the connecting bore 42 into brake cylinders of the rear wheel brakes. Initially, therefore, as the brakes are applied, the pressure generated in the brake master cylinder will become effectively unreduced in the brake cylinders of the rear wheel brakes.

At the first stepped piston 18 this pressure produces a force directed away from the connecting passage 38 but not strong enough to overcome the resistance of the spring 74. During the first phase of braking, therefore, the stepped piston 18 remains in its position shown at which the pressure reducing valve 34 remains open. The same pressure is still less able to overcome the resistance of the spring 78 since this is subject to stronger bias by the adjustment member 72 than the spring 74.

Thus also the second stepped piston 48 will remain in its position shown in pressure increasing valve 64 will also remain open.

During the first phase of braking, therefore, with the vehicle unloaded, the pressure rise from zero 0 to a switchover point A takes place at a ratio of 1:1. The prevailing pressure in the outlet chamber 44 and thus also in the rear wheel brake cylinders is an outlet pressure P 44 which is equal to the inlet pressure P 14 prevailing in the inlet chamber 14. However, after the pressure has risen to the switchover point A, the resulting pressure force acting on the first stepped piston 18 will overcome the resistance of spring 74 so that the first stepped piston will be displaced away from the connecting passage 38. As a consequence the pressure reducing valve 34 will close.The pressure increasing valve 64 on the other hand will remain open as the pressure reached at the switchover point A still is not sufficient to produce a resulting force at the second stepped piston 48 which might overcome the resistance of the spring 78. Upon further increase cf the inlet pressure P 14, the outlet pressure P 44 will increase only sub-proportionally.

Consequently the course of pressure approaches the parabola-like curve indicated in a continuous line in Figure 2 and representing the ideal course of pressure at an unloaded vehicle.

When the vehicle is loaded, the adjustment member 72 is in the position indicated in dash-dot lines in Figure 1, at which position the spring 74 is under greater bias, whilst the spring 78 is subject to less bias than in the unloaded condition. As shown in Figure 2, therefore, in loaded condition the pressure rise at a ratio of 1:1 will take place only from zero 0 to a switchover point B. As soon as this is reached, the resulting pressure force acting on the second stepped piston 48 will overcome the resistance of the spring 78 so that pressure increasing valve 64 will close, whilst the pressure reducing valve 34 still remains open.Upon further increase of the inlet pressure P 14 acing on the greater end face 56 of the second stepped piston 48 the later will be displaced further away from the connecting passage 38 producing, by its smaller end face 54, an outlet pressure P 44 which is higher than the inlet pressure P 14. Thus the outlet pressure P 44 rises from the switchover point B to another switchover point C at which the inlet pressure P 14 has reached such a level that the resulting pressure force at the first stepped piston 18 will overcome the resistance of the spring 74, which is biassed more strongly with the vehicle loaded. Now, therefore, also the pressure reducing valve 34 closes. Upon further rise of the inlet pressure P 14, consequently the rise of the outlet pressure P 44 is flatter.On the whole, the course of the pressure approaches ideal course of pressure for the loaded vehicle, indicated in Figure 2 by a dashdot line which is likewise similar to a parabola.

The steepness of the further pressure increase above the switchover point C depends on the surface area ratio of the effective end faces 24 and 26 of the two stepped pistons 18 and 48, as well as 54 and 56. Depending on this ratio of areas the result may be that above the switchover point C the outlet pressure P 44 rises together with the inlet pressure P 14 either as during the first phase of the pressure increase from 0 to B at a ratio of 1:1 or even more steeply than from 0 to B yet flatter than from B to C or flatter than from 0 to B, as shown in Figure 2, but somewhat steeper still than the pressure rise above the switchover point A, with the unloaded vehicle.

As the brake pressure regulator shown in Figure 3 largely corresponds to the one shown in Figure 1, comparable structural members are marked by the same reference numerals as in Figure 1. A difference is to be seen essentially only in that the adjustment member 72 of Figure 3 acts only on the first stepped piston 18, whilst the second stepped piston 48 is supported directly on the casing 10 by means of its spring 78. As a result, only the switchover pressure of the pressure reducing valve 34 depends on the loading condition of the vehicle The pressure increasing valve 64, on the other hand, switches invariably at a certain pressure in connecting passage 38.

The brake pressure regulator shown in Figures 4 and 5 is modified still further by comparison with the embodiments of Figures 1 and 2 in that the two stepped bores 16 and 46 are arranged co-axially, merging directly into each other. An apertured intermediate wall 80 is fixed between them in casing 10 to serve as a stop for the extensions 36 and 66 of the two valve bodies 30 and 60. Accordingly, the two stepped pistons 18 and 48 are also disposed co-axially and such that their greater end faces 26 and 56 face each other. In addition to the stepped bores 16 and 46 and stepped pistons 18 and 48 received therein, as may be seen in Figure 4, the casing includes a second pair of such stepped bores and stepped pistons, entirely separate from the first. Thus two brake pressure regulators are formed, each of which may be coordinated with one of the rear wheel brakes (not shown).A common adjustment member 72 is associated with these two hydraulically separated brake pressure regulators. It is embodied by a single arm lever supported by the casing 10, as in the embodiment of Figure 3. A balance beam 82 is disposed between the adjustment member 72 and the first stepped pistons 18 of both brake pressure regulators to take care that the forces depending on the loading of the vehicle and acting at the adjustment member 72 are distributed evenly to both stepped pistons 18. These forces are transmitted by the rear axle of the vehicle, in a manner not shown, to a pressure rod 84 and from the same through a sleeve 86 and a compression spring 88 to the adjustment member 72.

With the brake pressure regulator shown in Figures 4 and 5, the end face ratios of the two stepped pistons 18 and 48 are so selected and tuned to the influence of the adjustment 72 on the stepped pistons 18, which influence depends on the loading condition, that each of the two brake pressure regulators arranged in the common casing 10 has the pressure diagram as shown in Figure 6. It may be taken from this diagram that the pressure increasing valve 64 closes independently of the loading condition of the vehicle before the pressure reducing valve 34 closes. Therefore, at any rate the pressure switchover point B will be reached after which the rise is greater in the outlet pressure P 44 than in the inlet pressure P 14.How ever, when the vehicle is unloaded, the pressure reducing valve 34 closes after only a little further pressure increase at switchover point A, whereby the outlet pressure P 44 will continue to rise only gently upon further increase of the inlet pressure P 14. When the vehicle is loaded, the steep pressure increase above the switchover point B is continued up to the switchover piont C beyond which the pressure P 44 will rise only as it does above the switchover point A when the vehicle is unloaded.

The brake pressure regulator shown in Figure 7 differs from the one shown in Figures 4 and 5 above all in that the casing 10 is divided in the middle, fully encloses both stepped pistons 18 and 48, and includes an intermediate piston 92 between the two pistons 18 and 48 instead of the immovable intermediate wail 80 shown in Figure 4.

The two stepped pistons 18 and 48 are biassed toward the intermediate piston 92 by their respective springs 74 and 78. The connecting passage 38 bypasses the intermediate piston 92, which has only a mechanical function of serving as an adjustable stop for the extensions 36 and 66 of the two valve bodies 30 and 60.

The adjustment member 72 once more is a lever supported for pivotal movement at the casing 10.

However, as shown in Figure 7, a cam 94 fixed to the adjustment member 72 is received in the casing 10 substantially without clearance within a recess 96 formed in the intermediate piston 92.

Figure 7 shows the adjustment member 72 and cam 94 in continuous lines in the position they adopt when the vehicle is unloaded. The discontinuous lines refer to the position when the vehicle is loaded.

Claims

1. A load-responsive brake pressure regulator for vehicles of the kind set forth in which at least the other one of the two pistons is a stepped piston having two effective end faces of different areas, the greater one thereof facing the inlet chamber and the smaller one facing the outlet chamber, and a pressure increasing valve disposed in addition between the inlet and outlet chambers is controlled by the latter piston and is similarly open in the inoperative position.

2. The brake pressure regulator as claimed in claim 1, in which the pressure increasing valve is arranged in series with the pressure reducing valve.

3. The brake pressure regulator as claimed in claim 2, in which the pressure increasing valve together with its corresponding piston is arranged between the outlet chamber and the pressure reducing valve with its corresponding piston.

4. The brake pressure regulator as claimed in claim 3, in which both pistons comprise stepped pistons of which the end faces of larger effective areas face each other.

5. The brake pressure regulator as claimed in one of claims 1 to 4, in which the two pistons are arranged co-axially.

6. The brake pressure regulator as claimed in claim 5, in which an intermeidate piston arranged between the two pistons is connected to the adjustment member.

7. The brake pressure regulator as claimed in claim 6, in which the adjustment member comprises a cam which engages in a recess formed in the intermediate piston.

8. A load-responsive brake pressure regulator substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

9. A load-responsive brake pressure regulator substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

10. A load-responsive brake pressure regulator substantially as described herein with reference to and as illustrated in Figures 4, 5 and 6 of the accompanying drawings.

11. A load-responsive brake pressure regulator substantially as described herein with reference to and as illustrated in Figure 7 of the accompanying drawings.