GB1593713A

GB1593713A - Pressure reducer for brake assemblies

Info

Publication number: GB1593713A
Application number: GB8174/78A
Authority: GB
Original assignee: Graubremse GmbH
Current assignee: Graubremse GmbH
Priority date: 1977-03-02
Filing date: 1978-03-01
Publication date: 1981-07-22
Also published as: DE2708941A1; FR2382358A1; IT7820772A0; IT1092891B; FR2382358B1

Description

(54) PRESSURE REDUCER FOR BRAKE ASSEMBLIES (71) We, GRAUBREMSE GmbH, a Company organised and existing under the laws of the Federal Republic of Germany, of Eppelheimer Strasse 76, 6900 Heidelberg, Federal Republic of Germany, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:: The invention relates to a pressure reducer for motor vehicle brake assemblies, which can be actuated by a pressure medium, having a differential piston, subjected to the control pressure on one of its partial action surfaces, and a balance space provided on the other side of the differential piston, as well as an overflow valve assembly which has an inlet chamber and an outlet chamber and which is supported by an adjustable spring and has, a partial action surface which is subjected in use to the overflowed pressure medium.

A pressure reducer of this type has been disclosed in DT-AS 1,680,087. In this case, the overflow valve is inserted into a by-pass line which is connected to the inlet control pressure and which leads to the second partial action surface on the inflow side of the differential piston. Otherwise, the differential piston has on its other side only a single action surface which is delimited by the braking and balance chamber so that the modulated pressure acts against this action surface. This pressure reducer gives a characteristic in which a lower pressure range and an upper pressure range can be distinguished. A pressure reduction takes place in the lower pressure range. This pressure reduction is suppressed in the upper pressure range.

German Patent Specification 1,231,584 also shows a pressure reducer designed as an automatically load-dependent regulator of the braking force. Valves of this type have a constant reduction over the entire pressure range - relative to a defined mechanical position. The action surface of the differential piston is variable via the mechanical control impulse. Here also, the braking chamber and the balance chamber are designed as identical chambers.

A further reducer, designed as an automatically load-dependent regulator for the braking force, has been disclosed in German Utility Model 6,602,230, the action surface, subjected to the modulated pressure in the braking chamber, here being designed not to be variable. This pressure reducer, however, already has a lower pressure range and an upper pressure range. In the lower pressure range, a reduction of 1:1 is carried out. In the upper pressure range, the reduction is smaller. The transition from the lower pressure range to the upper pressure range is adjustable. Nevertheless, a family of characteristics of equal slope results. In the transition zone, relatively large deviations from the final gearing occur in this case, and these are disadvantageous in some respects.

US Patent Specification 2,980,469 shows a trailer-braking valve having an overflow valve which is inserted into a by-pass line on the rear side of the control piston. A pressure reduction, however, cannot be achieved with this trailer-braking valve.

Two pressure ranges are provided. Pressure gearing takes place in the lower pressure range. In the upper pressure range, pressure gearing of 1 : 1 results. The control piston employed in this case is not regarded as a differential piston. Although it has a balance chamber, it has no braking chamber.

It is the object of the invention to design the pressure reducer of the type initially set forth in such a way that the characteristics shown in Figures 1 and 2 can be achieved.

This means that, in a lower pressure range, the pressure reduction should be relatively small as compared with the maximum press urc reduction. In the adjacent upper pressure range, the pressure ratio of the modulated pressure to the control pressure should steadily fall. The transition between the two pressure ranges should here be adjustable. Furthermore, it should be possi blc freely to set the slope of the characteristic in the upper pressure range.

According to the invention, this is achieved in the pressure reducer of the type initially set forth, when the balance space is sealed from the braking chamber, the braking chamber communicates with the inlet chamber of the overflow valve and the outlet chamber of the overflow valve communicates with the balance space. Hence, a relatively high modulated pressure, which is useful for overcoming the response thrcsholds of devices which are downstream in the braking assembly, is obtained in the lower pressure range. In particular, however, over-braking in the transition zone is avoided. The transition zone is adjustable by means of the variable spring of the overflow valve so that there is scope for setting this transition zone at a relatively low valuc.It is even possible to envisage a reduction smaller than I 1 in the lower pressure range by selecting the size of the partial action surface which is associated with the modulated pressure in the braking chamber.

Two partial action surfaces which. as a rulc. are subjected to different pressures, are formed on the other side of the differential piston by the seal separating the balance space from the braking chamber. As a result. a reduced pressure which in every case is smaller than the modulated pressure in the braking chamber, is exerted on a partial action surface of the differential piston. In the limiting case, that is to say when the overflow valve is in the open position, these two pressures are equal.

The invention can be applied both in a valve with through control (i.e. where the pressure medium is released on opening the valve) and in a valve designed as a releay. In a through valve the partial action surface subjected to the control pressure on one side of the differential piston is larger than or equal to the partial action surface, on the differential piston, subjected to the modulated pressure of the braking chamber, in order to attain a reduction of I . I in the lower pressure range. ln a valve designed as a relay, however, the partial action surfaces must be of equal size in order to achieve the same purpose.However, when a reduction, which is smaller than 1 . 1, is rcached in the lower pressure range, then the partial action surface subjected to the control pressure on one side of thc differential piston is smaller than the partial action surfacc, on the differential piston, subjected to the modulated pressure of the braking chamber.

This applies to both valves with fully advanced control and valves designed as a relay.

The partial action surface, associated with the balance space, on the differential piston can be designed to be variable. This results in an adjustable pressure reducer. If the partial action surface is designed to be adjustable during operation. as a function of the loading state of the vehicle, this makes an automatically load-dependent regulator of the braking force possible.

The partial action surface, subjected to the overflowed pressure medium, of the overflow valve is designed to be smaller than the seat area of the overflow valve so that. with rising pressure, the pressure difference falls up to the open position. The overflow valve is provided with a non-return valve so that the loaded partial action surface on the differential pressure piston can be vented again.

The concept of the invention is shown by means of some preferred illustrative embodiments and described further in the following text. In the drawings: Figure I shows a diagram of the modulated pressure versus the inlet control pressure, as a function of the adjustable spring force on the overflow valve, Figure 2 shows a similar diagram, where it is possible to vary the slope of the characteristics in the upper pressure range, Figure 3 shows a similar diagram, as a function of the magnitude of the balance area on the differential piston, Figure 4 shows a further diagram, where a pressure reduction which is smaller than 1 1, is possible in the lower pressure range, Figure 5 shows a cross-section through the pressure reducer together with the overflow valve.

Figure 6 shows a corresponding pressure reducer designed as a relay and Figure 7 shows a pressure reducer as an automatically load-dependent regulator of the braking force.

In Figures 1 to 4, diagrams are represented. On the abscissa. the control pressure P1 is plotted, such as can be passed onto a partial action surface on one side of the differential piston. On the ordinate, the modulated pressure P2 is plotted, specifically the pressure which acts in the braking chamber and which is hence also transmitted to the brake cylinders. In all four diagrams, the 45" line has been drawn in, which corrcsponds to a reduction ratio of 1 1. It can be seen at once that this line is not exceeded in any of the diagrams. Gearingup thus does not take place.

Figure 1 shows the course of a characteristic, which results for a certain geometrically fixed overflow valve having a seat area Fs and a certain fixed partial action surface AFK. The ratio of these two action surfaces represents a constant, it being understood that the partial action surface on the rear side is smaller than the seat area Fs so that this constant is smaller than 1. The diagram is now shown with the characteristics for different spring forces K1, K2 and K3. The spring force on the overflow valve is adjustable. The transition between the lower pressure range having a reduction of 1 . 1 and the upper pressure range having a lower reduction is displaced depending on the adjustment of this spring force. At the same time, the limit reduction is thus also set or adjusted.

Figure 2 shows a diagram for a constant spring force K, but with the different area ratios. As a result of the constant spring force K, the transition point between the lower and the upper pressure range is fixed.

The slope of the characteristic in the second pressure range, and hence the course of the reduction in this second pressure range, can be selected by the choice of different area ratios. The smaller the ratio of the partial action surface on the rear side to the seat area, the flatter is the course of the characteristic.

It is to be understood that the diagrams of Figures 1 and 2 have been drawn separately only for the sake of clarity.

Figure 3 applies to an automatically loaddependent regulator of the braking force or to an adjustable pressure reducer. Of course, the parameters from Figures 1 and 2 here also apply. With respect to the characteristics, there is also an additional superposition by the external parameter depending on the state of loading. The mass ratio of the vehicle in the empty state and in the loaded state is designated as m.

The characteristic shown in Figure 4 is intended to clarify that, in the lower pressure range, it is also possible to achieve a reduction which is smaller than 1 1, in order to avoid over-braking in every case.

For this purpose, the partial action surface S, which is subjected to the control pressure on the inlet side of the differential piston, must be smaller than the partial action surface B which is subjected, on the outlet side of the differential piston, to the pressure in the braking chamber. This partial action surface B must be appropriately chosen in the design. Again, the diagram applies to a spring force, set to be constant, on the overflow valve and to a constant area ratio on the valve body of the overflow valve.

The pressure reducer 1 shown in Figure 5 comprises a casing 2 in which the differential piston 3 is located and guided so that it has a sealing action. This is a pressure reducer 1 of the through control type. The control pressure is led via the line 4 to the pressure reducer 1 and reaches the space 5 on the inlet side.

As a result of the design of the differential piston and the arrangement of the seal 6, two partial action surfaces are formed on the inlet side on the differential piston 3, specifically one partial action surface S, which in this case is a circular area and is subjected on the inlet side to the control pressure via the space 5. The second partial action surface 7 which is located on the inlet side, that is to say on one side of the differential piston 3, is an annular area which is under the action of atmospheric pressure via the bore 8.

On the other side of the differential piston 3, two partial action surfaces are likewise provided or formed, which are separated from one another by the seal 9. Via the braking chamber 10, the partial action surface B is subjected in particular to the modulated pressure which also becomes effective via the lines 12 and 13 in the braking chamber 11. The second partial action surface 14 on the other side or rear side of the differential piston 3 adjoins the balance space 15 which does not communicate with the braking chamber 10, and is divided off by the seal 9.

The twin-valve body 16 is suspended in the differential piston 3, and this is customarily effected by means of a spring which is not shown here. The inlet valve 16, 17 is formed by the rim 17 drawn inwards on the differential piston 3. The outlet valve 16, 18 is formed by the outlet seat 18 on the casing side. The vent bore 20 leads to atmosphere.

The overflow valve 21 which is here shown in a construction separate from the pressure reducer 1, can of course also be integral, as Figures 6 and 7 show. The overflow valve 21 comprises a casing 22 in which the valve body 23 is guided, so that it has a sealing action, with the aid of the seal 24. The valve body 23 is backed up on the casing side via the spring 25, the force K of which is adjustable by means of the setting screw 26. The valve body 23 interacts with a seat 27 which is on the casing side and which includes the seat area F5 and the inlet chamber 28. The inlet chamber communicates via the lines 29 and 12 with the braking chamber 10 of the pressure reducer 1. On the rear side, that is to say the side which is subjected to the overflowed pressure medium, of the valve body 23, the partial action surface AFK is formed by the seal 24.

The pressure in the outlet chamber 30 of the overflow valve 21 acts on this partial action surface AFK, which outlet chamber communicates via the line 31 with the balance space 15 of the pressure reducer 1. For the purpose of venting the balance space 15, the valve body 23 of the overflow valve 21 has a bore 32 which, by means of the rubber plate 33 on the valve body 23, is designed in the manncr of a non-return valve opening in the direction of the inlet chamber 2X. The circular partial action surface. enclosed by the seal 24, in the spring space 34 communicites via the bore 35 with the atmosphere.

The mode of action of the pressure reducer according to Figure 5 corresponds to the diagrams of Figures 1 and 2. In the initial position shown, the inlet valve 16, 17 of the pressure reducer 1 is closed, whilst the outlet valve 1(, 18 is opened, so that the brake cylinder I I is vented and the remaindex of the systeni also is under atmospheric pressure. On braking, control air is passed via the line 4 into Ihe space 5 of the pressure reducer 1, and This acts on the partial action surf;ice S.As a result, the differential piston 3 moves downwillds so that the outlet valve lh. 18 is closed alld the inlet valve 16, 17 is opened. The eolllplessed air flows via the open inlet valve If', 17 into the braking chamber 10 and from there via the lines 12 and 13 into the braking cylinder 11 where braking is initiated. It can be seen that the seals 6 and 9 are oii identical diameters so that the partial action surfaces S and B are designed to have the same size.Conse quently a gearing of I I is achieved in this lower pressure range. and this corresponds to the curve seFnlcnt on the 45" line in Figures 1 and 2. Although the pressure modulated by the braking chamber 10 also passes via the line 2') into the inlet chamber 28. the overflow valve 21 remains closed as long as the force of the spring 25 has not yet been overcome by this pressure via the seat area Fs, so that the pressure of the braking chamber 10 cannot yet become active in the balance space 15. The inlet valve 23, 27 of the overflow valve 21 opens only when the force K of the spring 25 is reached on the inlet side of the overflow valve 21 by the rising pressure - this corresponds to the corner point on the 45" line - so that a reduced pressure is passed via the outer chamber and the line 31 into the balance space 15 and hence onto the partial action surface 14 of the differential piston 3. At this point in time, the upper pressure range has been reached. The pressure reducer 1 moves into a closure position in which both the inlet valve 16, 17 and the outlet valve 16, 18 are closed.The pressure reduction corresponds to the flatter curve segments in Figures 1 and 2.

At the end of braking. the line 4 is connected to atmosphere so that the equilibrium of forces on the differential piston 3 is upset. As a result. the outlet valve 16, 18 opens so that the brake cylinder 13 is vented. Simultaneously, the inlet chamber 28, the outlet chamber 3() and hence also the balance space 15 are vented. After the inlet valve 23, 27 has closed, the further venting of the balance space 15 down to atmospheric pressure takes place via the non-return valve 32, 33.

It can be seen from the illustrative embodiment of Figure 5 in conjunction with Figures 1 and 2 that the position of the corner point in Figure 1 can be varied at once by adjusting the force K of the spring 25. The slope of the straight line in the second pressure range according to Figure 2 can be selected by the constructional choice of the area ratio of the partial action surface AFK to the seat area F,,.

The illustrative embodiment of Figure 6 shows a pressure reducer designed as a relay, in which the same corresponding parts, or the corresponding parts have the same function, are designated analogously to Figure 5. As the only difference from the illustrative embodiment according to Figure 5, it must be noted here that the control pressure medium does not in this case, pass through the valve. The medium acts via the line 4. At the inlet valve 16, 17, the space 36 is under the pressure of compressed air from a compressed air reservoir. The supply of compressed air to this space 36 is not shown and is effected in a known manner. The valve body 16 is here backed up on the casing side via the spring 19 in a somewhat different manner.

Furthermore, it is evident that the partial action surface B which is subjected to the modulated pressure in the braking chamber 10, is designed to be larger than the partial action surface S on the inlet side of the differential piston 3. This results in a pressure reduction in the lower pressure range, corresponding to the given area ratio. The result is thus the mode of action represented in Figure 4. In this case, an additional peculiarity is the result that the partial action surface AFK which is subjected to the overflowed pressure of the valve body 23 of the overflow valve 21, is located on the other side of the valve body, that is to say it carries a negative sign. Otherwise, the mode of action is also analogous.

The illustrative embodiment of Figure 7 now shows a pressure reducer designed as an automatic load-dependent regulator of the braking force, which regulator is subjected in a known manner to a drive shown only in part and which adjusts automatically in accordance with the load on the vehicle.

The height of the outlet valve 16, 18. that is to say its position relative to the inlet valve 16, 17, is adjusted in a known manner via this drive. This causes the diaphragm 3 to contact the housing to reduce its effective surface area. In this illustrative embodiment also, the braking chamber 10 is separated from the balance space 15 by the seal 9. The balance space 15 can be put under load only via the overflow valve 21. Since the diameters of the seals 6 and 9 are of the same size, a gearing of 1:1 here also results in the lower pressure range. In the upper pressure range, a pressure reduction takes place, specifically in accordance with the lines in Figure 3, that is to say as a function of the loading state of the vehicle.

WHAT WE CLAIM IS: 1. Pressure reducer for motor vehicle brake assemblies, which can be actuated by a pressure medium, the pressure reducer comprising a differential piston, subjected, in use, to the control pressure on one of its partial action surfaces, a balance space provided on the other side of the differential piston, an overflow valve assembly which has an inlet chamber and an outlet chamber and whose valve is supported by an adjustable spring and has a partial action surface which is subjected, in use, to the overflowed pressure medium, a braking chamber sealed from the balance space, the braking chamber communicating with the inlet chamber of the overflow valve assembly and the outlet chamber of the overflow valve assembly communicating with the balance space.

2. Pressure reducer according to Claim 1, wherein two partial action surfaces are formed on said other side of the differential piston by the seal separating the balance space from the braking chamber.

3. Pressure reducer according to Claim 1 or 2, wherein the partial action surface subjected to the control pressure on said one side of the differential piston is larger than or equal to the partial action surface on the differential piston subjected to the modulated pressure of the braking chamber.

4. Pressure reducer according to Claim 1 or 2, wherein the partial action surface subjected to the control pressure on said one side of the differential piston is smaller than the partial action surface, on the differential piston, subjected to the modulated pressure of the braking chamber, in order to attain a reduction, which is smaller than 1 . 1, in the lower pressure range.

5. Pressure reducer according to Claim 1 or 2, operating as a relay, wherein the partial action surface subjected to the control pressure on said one side of the differential piston is equal to the partial action surface, on the differential piston, subjected to the modulated pressure of the braking chamber.

6. Pressure reducer according to Claim 1 or 2, wherein the partial action surface, associated with the balance space, on the differential piston is variable.

7. Pressure reducer according to Claim 6, wherein the partial action surface is adjustable during operation, as a function of the loading state of the vehicle.

8. Pressure reducer according to any one of the preceding Claims, wherein the partial action surface subjected to the overflowed pressure medium, on the overflow valve is smaller than the seat area of the overflow valve.

9. Pressure reducer according to Claim 8, wherein the overflow valve is provided with a non-return valve.

10. Pressure reducer constructed substantially as herein described with particular reference to figure 5, 6 or 7 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. balance space 15 can be put under load only via the overflow valve 21. Since the diameters of the seals 6 and 9 are of the same size, a gearing of 1:1 here also results in the lower pressure range. In the upper pressure range, a pressure reduction takes place, specifically in accordance with the lines in Figure 3, that is to say as a function of the loading state of the vehicle. WHAT WE CLAIM IS:

1. Pressure reducer for motor vehicle brake assemblies, which can be actuated by a pressure medium, the pressure reducer comprising a differential piston, subjected, in use, to the control pressure on one of its partial action surfaces, a balance space provided on the other side of the differential piston, an overflow valve assembly which has an inlet chamber and an outlet chamber and whose valve is supported by an adjustable spring and has a partial action surface which is subjected, in use, to the overflowed pressure medium, a braking chamber sealed from the balance space, the braking chamber communicating with the inlet chamber of the overflow valve assembly and the outlet chamber of the overflow valve assembly communicating with the balance space.