GB1598838A

GB1598838A - Load-dependent brake force regulator

Info

Publication number: GB1598838A
Application number: GB3170/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-01-31
Filing date: 1978-01-26
Publication date: 1981-09-23
Also published as: DE2703945B1; IT1203165B; IT7867180A0; DE2703945C2

Description

(54) LOAD-DEPENDENT BRAKE FORCE REGULATOR (71) We, WABCO FAHRZEUGBREM SEN GmbH, (formerly WABCO WESTING HOUSE GmbH) a German Company of, Am Lindener Hafen 21, 3000 Hannover 91, 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 load-dependent brake force regulator for a pressure medium operated brake system for a motor vehicle or trailer vehicle.

British Patent Application No. 38345/77 Serial No. 1584598 describes a brake force regulator which permits a load-dependent control of the rear axle of a vehicle only after a certain pilot braking pressure, determined by a pilot valve, has been reached. In the initial stage of braking or in the case of slight partial braking, uncontrolled pressure acts on the front and rear brake cylinders until the load-dependent control cuts in, corresponding to the setting of the regulator. The regulator described in this earlier Application is designed for a relatively low load/empty control ratio (1 : 1 to 4 : 1).

Some types of vehicle, particularly with a view to their future development, require a greater control ratio, for example 10:1. For this reason, a load-dependent brake force regulator has already been proposed in our British Patent Application No. 2365/78Se- rial No. 1597031 (WP4/77) in which the pilot valve is integrated into the regulator in such a manner that the number of extra parts is negligible and the dimensions of the installation are only slightly larger than those of the regulator mentioned previously.

Such brake force regulators equipped with a pilot valve are known as "threshold brake force regulators". "Threshold" or "threshold pressure" is the term used for the adjustable pilot pressure of the pilot valve, from which pressure the loaddependent control takes place.

It is a disadvantage that different brake force regulators must be manufactured and kept in stock for different types of vehicle because it is not possible, or is possible only at considerably increased cost, to convert existing regulators having a small control ratio into regulators having a large control ratio and vice versa).

To avoid the necessity of having two different regulators with different control ratios, it is also known to use only a regulator with the larger control ratio and to make use of only a small portion of the control range when smaller control ratios are required. The great disadvantage with this, however, is that the accuracy of control is considerably impaired.

The problem with which the present invention is concerned is to make it possible, with a single regulator, to achieve both a large and a small control ratio while involving only comparatively negligible alterations to the regulator and no alterations to the cast components thereof.

The present invention provides a loaddependent brake force regulator for use in pressure medium-operated brake systems, the regulator having a brake pressure control piston assembly exposed to the pressure at an inlet of the regulator; a brake pressure control valve operable by the brake pressure control piston assembly in depedence on the adjustment of a load-controlled regulating member, and a brake pressure pilot valve comprising: a pilot piston on one side of which are defined a pilot chamber and a graduating chamber, and which is responsive to the pressure in those chambers to control operation of a pilot inlet valve and a pilot outlet valve; the pilot chamber being connected to receive pressure medium from the regulator inlet through the inlet valve, when open, to apply a pilot pressure to the control piston assembly to load the said assembly in the same direction as the said inlet pressure; the outlet valve, when open, connecting the pilot chamber to an outlet bore; and the graduating chamber having an inlet from a supply bore which is connected to receive pressure medium from the regulating inlet; a removable sealing member being positioned to close one of the said bores of the pilot valve whereby removal of the scaling member from that position modifies the operating characteristic of the regulator.

In one embodiment, the sealing member is located in the outlet bore, and the pilot chamber is sealed from the graduating chamber.

As an alternative to the outlet bore being sealed, in another embodiment, the outlet bore is open and the graduating chamber is relieved of pressure, the sealing member being -located in the supply bore. As a further alternative, the outlet bore is open, and the graduating chamber and the pilot chamber are connected to one another, the sealing member being located in the supply bore.

The invention will now be described in more detail with the aid of the attached drawing illustrating, by way of example, embodiments of the invention.

Figure 1 shows a section through a brake force regulator constructed according fo the invention; Figures 2 to 5 each illustrated a modification of the regulator according to Figure 1, each representing in section only the pressure pilot valve, and Figure 6 shows a graph of the characteristic curves which may be obtained with a brake force regulator according to the invention, showing the pressure Pe introduced into the brake cylinders as a function of the pressure Pa leaving the brake valve.

The regulator shown in Figure 1 has a housing 1 with a brake pressure control piston (comprising a piston 2 and a flexible diaphragm 3) and a double valve 6, 7 and 8.

The double valve is formed by a double valve member 6, a valve seat 7 arranged at the inner wall of the piston 2 and another valve seat 8 which is constructed at the upper end face of a valve push rod 9 arranged below the double valve member 6.

A number of radial ribs 10 are joined to the piston 2, which ribs engage in a contactfree manner with the corresponding ribs 11 arranged in the housing 1. The end faces 10a and lia facing the diaphragm 3, of the radials ribs 10 and 11 respectively, form parts of a tapered casing and, in the position shown in the drawing, the diaphragm 3 rests against the end faces 11a. The brake pressure control piston 2,3 formed by the piston diaphragm has an upper active face 12 and a lower active face 15. The upper active face 12 is of constant area and is connected by way of a control chamber 13 to a compressed air connection 14, which leads to a motor vehicle brake valve or a trailer brake valve.

The area of the lower active face 15 of the diaphragm varies with the movement of the graduating piston 2, 3 and is connected to a connection 17 which leads to the brake cylinders.

The valve push rod 9 is connected to a ball pivot 21 of a lever 22 which is mounted on the pivot of a shaft 23 connected by a lever 24, with the interposition of a rod and a spring member, not shown, to the axle of the vehicle. The valve push rod 9 has a hollow space 18 from which air can be removed by way of a chamber 19 and outlet 20. A relieving piston 25 is arranged in the housing co-axial to the valve push rod 9, the upper end of which piston supports the ball pivot 21 from below and so equalises the forces acting from above on the ball pivot.

A chamber 26 loacted under the relieving piston 25 is connected by a connecting tube 28 to the control chamber 13.

A braking pressure pilot device is arranged in the upper portion of the housing 1. The pilot device consists of a pilot piston 29 constructed as a step piston; an inlet valve 31, 32, and an outlet valve 31, 33. The inlet valve 31, 32 is formed by a valve member 31 and a valve seat 32 fixed to the housing, and the outlet valve is formed by a valve member 31 and a valve seat 33 constructed on the pilot piston 29. Between the pilot piston 29 and the housing 1 there are provided a pilot chamber 35 and a graduating chamber 36 which are separated from one another in terms of pressure. The graduating chamber 36 is connected by a bore 37 to the connection 14, while the pilot chamber 35 is connected by way of the inlet valve 31, 32 and the chamber 13 to the connection 14. The pilot chamber 35 is also connected by a bore 38 directly to the chamber 3a located above the diaphragm 3 and, when the outlet valve 31, 33 is open, air is removed from the pilot chamber by way of an outlet channel 42 and the outlet 18, 19, 20. The pilot piston 29 is biased by a spring 39, with the aid of which the so-called "threshold" may be set by means of an adjusting screw 40.

The operation of the load-dependent regulator is briefly described below.

When braking, brake pressure passes from the motor vehicle brake valve or the trailer brake valve through the connection 14 into the chamber 13 and presses the piston 2 downwards. The double valve member 6 follows this movement and, in so doing, closes valve 6, 8 and depresses the valve push rod 9 until it comes to rest on the ball pivot 21. The valve 6, 7 then opens as the piston 2 continues to descend and compressed air can now flow through connection 17 into the brake cylinders and into the chamber 16 beneath the diaphragm 3.

As the piston 2 descends, the diaphragm 3 detaches itself from the ribs 11 provided in the regulator housing and rests increasingly against the ribs 10 of the piston 2. The active surface area of the diaphragm 3 is thus continuously enlarged until it exceeds the surface area of the upper end of the piston.

As a result of this, the piston is raised again and the valve 6, 7 is closed again. Consequently, full braking is achieved and the pressure prevailing in the brake cylinders corresponds to the pressure controlled in dependence on the weight of the load.

The compressed air introduced into the device is fed simultaneously into the chamber 26 below the piston 25, through the connection tube 28. After the brake pressure has been removed, the compressed air pressure prevailing in the brake cylinders pushes the piston 2 into its upper end position, opening the valve 6,8, and escapes to the atmosphere through the open valve, the bore 18 of the valve push rod 9, the chamber 19 and the outlet 20.

In the description of the load-dependent regulator thus far, the operation of the pressure pilot valve has not been considered. The operation of the pressure pilot valve is as follows, imagining for the present that the sealing components 44 and 46 in the outlet channel 42 are absent. The brake pressure entering through the connection 14 simultaneously passes through the chamber 13 and the pilot-inlet valve 31, 32 into the pilot chamber 35 and then acts by way of the bore 38 on the diaphragm 3, and it also passes directly from the connection 14 into the graduating chamber 36 through the bore 37. At a certain input pressure acting on the total surface area of the piston of both chambers 35 and 36, the pilot piston 29 moves upwards against the force of the spring 39, allowing the valve member 31 to move upwards and thereby closing the inlet valve 31, 32.The compressed air that flows over the upper side of the diaphragm 3 until the inlet valve 31, 32 closes, opposes the brake cylinder pressure building up on the lower side of the diaphragm and removes the load-dependent control in this region, i.e. a correspondingly higher pressure builds up in the chamber 16 beneath the diaphragm 3.

If the brake pressure supplied by the motor vehicle brake valve exceeds the certain pressure level, the pressure increases still further only in the chamber 36, as a result of the inlet valve 31, 32 being closed, and causes the piston 29 to move further upwards, which opens the outlet valve 31, 33, thus allowing air out of the chamber 35, and consequently, at the same time, the control pressure above the diaphragm 3 decreases in steps to zero. In Figure 6, the characteristic curve of the regulator produced in this manner is represented by the lines a and b. The point A corresponds to the "threshold pressure" and the point B to the full brake pressure in the regulator position "empty".

Figure 1 will now be considered again as well as Figures 2 to 6, for the purpose of describing different ways of cutting out the operation of the pressure pilot piston 29 in order to achieve smaller control ratios.

In Figure 1, this is achieved by closing the outlet channel 42 between the piston 29 and the valve member with the aid of sealing members 44 and 46. The pilot device then still functions, initially, as already described in that, after the valve seat 33, constructed at the pilot piston 29, has been lifted from the valve member 31 following the build-up of a sufficiently high pressure in the pilot chamber 35, the inlet valve 31, 32 is dosed and the pilot piston is caused to move further upwards after a further increase in pressure as a result of the pressure acting in the graduating chamber 36, so opening the outlet valve 31, 33.Now, however, air cannot escape from the chamber 35 since the channel 42 is blocked, with the result that the control pressure introduced through the inlet valve 31, 32 into chamber 3a acting on the upper side of the diaphragm 3 is kept constant. This results in a characteristic curve represented by the lines a and c in Figure 6.

To achieve the same result, according to Figure 2, the bore 37 is closed with the aid of a sealing member 48 and the graduating chamber 36 is relieved of pressure by being connected to the outlet. This relief of pressure can be achieved, as shown, simply by omitting the upper O-ring 50 of the pilot piston 29 (cf.Figure 1). In the arrangement according to Figure 2, when operating the brake valve, pressure is first introduced through the connection 14, the control chamber 13, the inlet valve 31, 32 and the pilot chamber 35 and then through the bore 38 into the chamber 3a above the diaphragm 3 (cf. Figure 1). Starting at a certain pressure, the pilot piston 29 moves upwards and closes the inlet valve 31, 32.Further operation of the pilot piston even in the case of a further increase in pressure is not possible because the bore 37 is closed and the graduating chamber 36 is relieved of pressure, as a result of which the outlet valve 31, 33 cannot open and the control pressure on the upper side of the diaphragm is kept constant.

In order to achieve the same result, in Figure 3, the bore 37 is again closed with the aid of a sealing member 52 and the pilot chamber 35 is also connected to the graduat ing chamber 36. This connection can be made simply by omitting the lower O-ring 54 of the pilot piston 29 (cf. Figure 1). By means of this measure, it is possible, as in the case of the embodiment according to Figure 2. for the inlet valve 31, 32 to adopt its closed position while the outlet valve 31, 33, however, cannot open, as a result of which the control pressure introduced into the chamber 3a above the diaphragm 3 is kept constant.

Figure 4 shows a further embodiment for achieving the same effect as the embodiments according to Figures 1 to 3. In this embodiment, the bore 37 is again closed by a sealing member 56 and the pilot chamber 35, as a modification of the embodiment according to Figure 3, is connected to the graduating chamber 36 by a channel 58 so that the O-rings 50 and 54 (cf. also Figure 1) may be left in place.

Figure 5 shows an embodiment of the invention which is generally similar to that shown in Figure 1 except that the pilot valve member 68 (corresponding to the valve member 31 of Figure 1) is permanently closed (that is to say, it has no outlet bore corresponding to the bore 62 of Figure 1).

However, a removable sealing member 70 is still provided in the outlet bore 62 of the pilot piston 66 and, with this form of the regulator, a comparatively small control ratio can be achieved. To modify the operating characteristic of this regulator to obtain a larger control ratio, the sealing member 70 is removed whereupon, when the pilot outlet valve opens, air is removed from the pilot chamber 60 (corresponding to chamber 35 of Figure 1), and the control pressure in the space above the diaphragm 3, to which the line 61 leads, is relieved in steps by way of the outlet bore 62 (from which the sealing member 70 is no omitted) and the hollow space 64 of the pilot piston 66.

It will be understood from the above description that a characteristic curve (6f.

Figure 6) consisting of the lines a and c, i.e.

a relatively small control ratio, can also be achieved with the aid of the embodiments according to Figures 2 to 5 as well as with the embodiment of Figure 1.

So that the brake force regulators according to Figures 1 to 5 may easily be reconverted for large control ratios, the sea ling members may be detachable, for example in the form of suitably sealed grub screws. This construction can also be used to open or, if desired, to close the channel 58 of Figure 4.

As a further alternative, in the case of the embodiment of Figure 4, a double shut-off mechanism with two possible positions may be provided. In the first position, the bore 37 between the inlet connection 14 and the graduating chamber 36 is open and the connecting channel 58 between the pressure graduating chamber 36 and the pilot chamber 35 is closed. In the second position, the bore 37 is closed and the connecting channel 58 is open. To facilitate its use, for each position of the double shut-off mechanism, the particular control ratio may be shown on the device: alternatively, the particular modification reference number of the device that can be obtained by switching over may be shown. This solution is especially advantageous because the storage of spare parts is substantially made easier.Only one spare device need be stocked in spare parts stores for both modifications of the device.

In each of the alternative embodiments of the invention described above, a cut-out of part of the operation of the pilot piston of the pilot valve is effected. This is achieved by virtue of the fact that, following the threshold (point A in Figure 6) the control pressure which acts in chamber 3a on one side of the control piston 2,3, is maintained constant, thus producing a small control ratio, because a reduction of the threshold pressure or the pressure acting on that side of the control piston can no longer take place. Conversion from a small to a larger control ratio and vice versa can be effected without having to alter the size and shape of the components.When the intended use of a regulator is known, conversion to the required control ratio can be made in a simple manner by closing the appropriate bore of the pilot valve and opening the necessary pressure release connections before installation in the vehicle.

WHAT WE CLAIM IS: 1. A load-dependent brake force regulator for use in pressure medium-operated brake systems, the regulator having a brake pressure control piston assembly exposed to the pressure at an inlet of the regulator; a brake pressure control valve operable by the brake pressure control piston assembly in dependence on the adjustment of a loadcontrolled regulating member, and a brake pressure pilot valve comprising: a pilot piston on one side of which are defined a pilot chamber and a graduating chamber, and which is responsive to the pressure in those chambers to control operation of a pilot inlet valve and a pilot outlet valve; the pilot chamber being connected to receive pressure medium from the regulator inlet through the inlet valve, when open, to apply a pilot pressure to the control piston assembly to load the said assembly in the same direction as the said inlet pressure; the outlet valve, when open, connecting the pilot chamber to an outlet bore; and the graduating chamber having an inlet from a supply bore which is connected to receive pressure medium from the regulating inlet: a removable sealing member being posi

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Claims

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ing chamber 36. This connection can be made simply by omitting the lower O-ring 54 of the pilot piston 29 (cf. Figure 1). By means of this measure, it is possible, as in the case of the embodiment according to Figure 2. for the inlet valve 31, 32 to adopt its closed position while the outlet valve 31, 33, however, cannot open, as a result of which the control pressure introduced into the chamber 3a above the diaphragm 3 is kept constant.

Figure 4 shows a further embodiment for achieving the same effect as the embodiments according to Figures 1 to 3. In this embodiment, the bore 37 is again closed by a sealing member 56 and the pilot chamber 35, as a modification of the embodiment according to Figure 3, is connected to the graduating chamber 36 by a channel 58 so that the O-rings 50 and 54 (cf. also Figure 1) may be left in place.

Figure 5 shows an embodiment of the invention which is generally similar to that shown in Figure 1 except that the pilot valve member 68 (corresponding to the valve member 31 of Figure 1) is permanently closed (that is to say, it has no outlet bore corresponding to the bore 62 of Figure 1).

However, a removable sealing member 70 is still provided in the outlet bore 62 of the pilot piston 66 and, with this form of the regulator, a comparatively small control ratio can be achieved. To modify the operating characteristic of this regulator to obtain a larger control ratio, the sealing member 70 is removed whereupon, when the pilot outlet valve opens, air is removed from the pilot chamber 60 (corresponding to chamber 35 of Figure 1), and the control pressure in the space above the diaphragm 3, to which the line 61 leads, is relieved in steps by way of the outlet bore 62 (from which the sealing member 70 is no omitted) and the hollow space 64 of the pilot piston 66.

It will be understood from the above description that a characteristic curve (6f.

Figure 6) consisting of the lines a and c, i.e.

a relatively small control ratio, can also be achieved with the aid of the embodiments according to Figures 2 to 5 as well as with the embodiment of Figure 1.

So that the brake force regulators according to Figures 1 to 5 may easily be reconverted for large control ratios, the sea ling members may be detachable, for example in the form of suitably sealed grub screws. This construction can also be used to open or, if desired, to close the channel 58 of Figure 4.

As a further alternative, in the case of the embodiment of Figure 4, a double shut-off mechanism with two possible positions may be provided. In the first position, the bore

37 between the inlet connection 14 and the graduating chamber 36 is open and the connecting channel 58 between the pressure graduating chamber 36 and the pilot chamber 35 is closed. In the second position, the bore 37 is closed and the connecting channel 58 is open. To facilitate its use, for each position of the double shut-off mechanism, the particular control ratio may be shown on the device: alternatively, the particular modification reference number of the device that can be obtained by switching over may be shown. This solution is especially advantageous because the storage of spare parts is substantially made easier.Only one spare device need be stocked in spare parts stores for both modifications of the device.

In each of the alternative embodiments of the invention described above, a cut-out of part of the operation of the pilot piston of the pilot valve is effected. This is achieved by virtue of the fact that, following the threshold (point A in Figure 6) the control pressure which acts in chamber 3a on one side of the control piston 2,3, is maintained constant, thus producing a small control ratio, because a reduction of the threshold pressure or the pressure acting on that side of the control piston can no longer take place. Conversion from a small to a larger control ratio and vice versa can be effected without having to alter the size and shape of the components.When the intended use of a regulator is known, conversion to the required control ratio can be made in a simple manner by closing the appropriate bore of the pilot valve and opening the necessary pressure release connections before installation in the vehicle.

WHAT WE CLAIM IS: 1. A load-dependent brake force regulator for use in pressure medium-operated brake systems, the regulator having a brake pressure control piston assembly exposed to the pressure at an inlet of the regulator; a brake pressure control valve operable by the brake pressure control piston assembly in dependence on the adjustment of a loadcontrolled regulating member, and a brake pressure pilot valve comprising: a pilot piston on one side of which are defined a pilot chamber and a graduating chamber, and which is responsive to the pressure in those chambers to control operation of a pilot inlet valve and a pilot outlet valve; the pilot chamber being connected to receive pressure medium from the regulator inlet through the inlet valve, when open, to apply a pilot pressure to the control piston assembly to load the said assembly in the same direction as the said inlet pressure; the outlet valve, when open, connecting the pilot chamber to an outlet bore; and the graduating chamber having an inlet from a supply bore which is connected to receive pressure medium from the regulating inlet: a removable sealing member being posi

tioned to close one of the said bores of the pilot valve whereby removal of the sealing member from that position modifies the operating characteristic of the regulator.
2. A regulator as claimed in claim 1, in which the sealing member is located in the outlet bore, and the pilot chamber is sealed from the graduating chamber.
3. A regulator as claimed in claim 1, in which the outlet bore is open to allow pressure medium therein to escape, and the graduating chamber is relieved of pressure, the sealing member being located in the supply bore.
4. A regulator as claimed in claim 1, in which the outlet bore is open to allow pressure medium therein to escape, and the graduating chamber and the pilot chamber are connected to one another, the sealing member being located in the supply bore.
5. A regulator as claimed in claim 1, in which a connecting channel is provided between the graduating chamber and the pilot chamber, and further removable sealing member is positioned to close the connecting channel whereby removal of the further sealing member from that position modifies the operating characteristic of the regulator.
6. A regulator as claimed in any one of the preceding claims, in which the, or each, removable sealing member is a grub screw.
7. A regulator as claimed in claim 4, in which a connecting channel is provided between the graduating chamber and the pilot chamber and in which the sealing member is a two-position valve which is positioned to close the supply bore and open the connecting channel and is movable to open the supply bore and close the connecting channel.
8. A load-dependent brake force regulator for use in pressure medium-operated brake systems, the regulator being substantially as described herein with reference to and as shown in Figure 1 or Figure 1 as modified by any one of Figures 2 to 5 of the accompanying drawings.