GB1597031A

GB1597031A - Load-dependant brake force regulator

Info

Publication number: GB1597031A
Application number: GB236578A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-01-21
Filing date: 1978-01-20
Publication date: 1981-09-03
Also published as: DE2702346A1; DE2702346C2; IT1143841B

Description

(54) LOAD-DEPENDENT BRAKE FORCE REGULATOR tut71) We, WABCO FAHRZEUGBREMSEN Gg!.m.b.H. (formerly Wabco Westinghouse G.m.b.H.), a company organised according to the laws of the Federal Republic of Ger many, of 3000 Hannover 91, Postfach 9112 80, 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 load-dependent brake force regulator for a pressure medium operated motor vehicle or trailer vehicle brake system.

In the EEC guidelines for bringing into conformity the legal requirements of member states regarding the brake systems of motor vehicles and their trailers, regulations were made which stipulate the characteristic curves of brake systems within certain braking ranges in so-called distribution or braking bands. That is to say the brake systems must be so constructed that the characteristic curves of braking for the individual axles of the vehicle in dependence on the pressure in the brake line are within the range of the distributor bands.

To comply with these regulations, at least one axle of the vehicle, that is the rear axle, must be subject to load-dependent brake force control. This is achieved by installing an automatic load-dependent brake force regulator in the connecting line between the motor vehicle brake valve and the wheel brake cylinders, so that the level of pressure introduced into the brake cylinders from the motor vehicle brake valve is regulated in dependence on the load and hence on the reflexion of the vehicle springs or, in the case of vehicles having pneumatic springs, in dependence on the pressure in the pneumatic spring bellows.

Brake force regulators and automatic load-dependent brake force regulators are already known by way of German Patent Specification 1 231 584, 1 655 766 and 1 934 784, and one has also been described in British Patent Application No. 38345/77 (Serial No. 1 584 598) the latter in particular, being designed for a load/empty control ratio of 1:1 to 4:1. The distribution bands specified for both the unladen and the laden vehicle can be complied with by means of the characteristic curves of the regulators.

In the case of vehicles whose automatic load-dependent brake force control is effected only by controlling the rear axle it can arise, when braking in an unladen or partially laden state, that the brake cylinders of the rear axle are acted on by a relatively low brake pressure, in accordance with the rear axle load, whereas full brake pressure is introduced into the brake cylinders of the uncontrolled front axle, and this may result in the front wheels becoming locked. This disadvantage can be eliminated by a pilot valve device, which is arranged in the housing of the regulator to provide what may be called a "threshold brake force regulator".

The main purpose of the threshold in the regulator is to make the wear of the brake linings, in unladen and partially laden vehicles, uniform at the front and rear axle.

The regulator described in the abovementioned Application No. 38345/77 (Serial No. 1 584 598) includes such a pilot valve device and functions to provide a loaddependent control of the vehicle rear axle only after a certain pressurethe pilot or threshold pressure-has been reached. In the initial stage of braking or in the case of a slight partial braking, the front and rear axle brake cylinders are acted on by unregulated pressure until, at the pilot braking pressure, the load-dependent control cuts in, in accordance with the setting of the regulator.

There is a demand on the part of vehicle manufactures for an automatic load-dependent brake force regulator which, for the development of a new generation of vehicles, will solve the problems of load-dependent control in an optimum, economical manner and proceeds from values which, at a threshold in an order of magnitude of 1 bar and at an output pressure of 1-5 bar at 7-5 bar input pressure, lie in the control position "empty", which means a control ratio of 13:1.

To meet this demand using the design of regulator which is known at present and which has a control ratio of 4:1 could be done only with considerable difficulty since it would involve, at least, a substantial increase in the diameter of the regulator and substantial expense.

The present invention provides a loaddependent brake force regulating device for use in pressure medium-operated brake systems, which device has a brake pressure control piston assembly exposed to the pressure at an inlet of the regulating device, a brake pressure control valve which is operable by the brake pressure control piston assembly in dependence on the adjustment of a load-controlled relating member, and a brake pressure pilot valve operable to apply a pllot pressure to the control piston assembly to load the said assembly in the same direction as the said inlet pressure, the pilot valve being responsive to the said inlet pressure whereby, as the inlet pressure increases, the pilot pressure increases over a pre-determined initial range and then decreases, the brake pressure control valve and the brake pressure pilot valve being arranged co-axially in a common housing.

The construction and operation of an automatic load-dependent brake force regulator constructed according to the invention will now be described, by way of example, in more detail with the aid of the accompanying drawings, in which Fig. 1 shows a section through the regulator, and Fig. 2 illustrates the variation of control pressure with input brake pressure in the regulator.The regulator has a housing 1 in which there is arranged a brake pressure control piston consisting of a piston 2 and a diaphragm 3, and, inside the piston 5 a double valve member 6 tensioned by a spring 4 and guided in a guide 5, which valve member, together with a valve seat 7 positioned at the inner wall of the piston 2, forms an inlet valve 6, 7 and, together with a valve seat 8 provided by the end face of a valve push rod 9 positioned beneath the double valve member 6, forms an outlet valve 6, 8. Joined to the piston 2 there is a number of radial fins 10 of which the faces 1Oa which face the diaphragm 3 form parts of a tapered casing.

In the housing 1 there is provided a number of radial and stationary fins 11 into the interspaces of which the fins 10 mesh without contact and of which the faces 1 la which face the diaphragm form an opposite tapered casing.

The diaphragm 3 is attached by its outer edge to the housing 1 and by its inner edge to the piston 2, thereby forming the brake pressure control piston 2, 3 the upper operating surface 12 of which is invariable and the lower operating surface 15 of which is variable with the Ç ment of the control piston 2, 3. The upper surface 12 of the control piston is part of a control chamber 13, located above the piston 2, which is connected to a compressed air connection 14 leading to the motor vehicle, or trailer vehicle, brake, valve; and the lower surface 15 of the control piston is part of a chamber 16, located beneath the diaphragm 3, which is connected to a connection 17 wflich leads to the brake cylinders.

In a central bore of the housing 1 there is guided the partially hollow valve push rod 9, the upper end face of which, as has already been mentioned, forms the outlet valve seat 8 and from the cavity 18 of which air can be exhausted through a chamber 19 and an outlet 20. The valve push rod 9 is in operational connection with a ball pivot 21 of a lever 22, this ball pivot being supported on a pivot of a shaft 23. The shaft 23 is connected to the axle of the vehicle by means of a lever 24 with the interconnection of rods (not shown) and a resilient member (not shown). A relieving piston 25 is arranged in the housing coaxial to the valve push rod 9, the upper end of which piston supports the ball pivot 21 from below thereby equalising the forces acting on the ball pivot from above.

A chamber 26 located beneath the relieving piston 25 is connected to the chamber 13 by a connecting pipe 28.

A braking pressure pilot device is arranged in the upper portion of the housing 1 and consists of a pilot piston 29, constructed as a step piston and, arranged beneath this pilot piston, a valve member 31 also guided in the above-mentioned guide 5 and tensioned in an upwards direction by a spring 30. This valve member 31, together with a valve seat 32 fixed in the housing forms an inlet valve 31, 32 and, together with a valve seat 33 provided by the lower face of the piston 29, forms an outlet valve 31, 33.

Two chambers pilot chamber 35 and a graduating chamber 36-formed by the stepped pilot piston 29 and the housing 1 and separated from one another in a pressureproof manner, are connected to the connection 14 leading to the motor vehicle brake valve. The pilot chamber 35 can be acted on by compressed air from the connection 14 by way of the chamber 13 and the inlet valve 31, 32, and the graduating chamber 36 can be acted on by compressed air from connection 14 by way of a bore 37.

The pilot chamber 35 is, furthermore, directly connected by way of a bore 38 to the chamber 3a located above the diaphragm 3 and air is exhausted from it by way of outlet 18, 19, 20 when the outlet valve 31, 33 is open. The pilot piston 29 is tensioned by a spring 39 with the aid of which the "threshold" may be adjusted by means of an adjusting screw 40.

The following is a general description of the operation of the automatic load-dependent brake force regulator and, in connection with this description, the pilot device will be discussed in more detail.

In the empty (unladen) state of the vehicle, the distance between the axle and the brake force regulator is at its greatest, and the lever 24 is in its lowest position, which means that the brake pressure coming from the motor vehicle brake valve or from the trailer vehicle control valve is transmitted at its lowest level to the brake cylinders.

If the vehicle is laden, the distance between the brake force regulator and the axle decreases and the lever 24 is there by pivoted upwards in the direction of greater effect.

A horizontal position of the lever 24 roughly corresponds to a brake force for a halfladen vehicle. In its uppermost position the brake pressure coming from the motor vehicle brake valve or from the trailer vehicle control valve is transmitted in full to the brake cylinders.

During braking, a brake pressure coming from the motor vehicle brake valve or from the trailer vehicle control valve passes through connection 14 into the chamber 13 and presses the piston 2 downwards. In so doing, the valve push rod 9 is similarly pressed downwards by the double valve member 6 until it comes to rest on the ball pivot 21 and, as the piston 2 descends further, the valve 6, 7 opens. Compressed air is then able to flow through connection 17 into the brake cylinders as well as into chamber 16 beneath the diaphragm 3.

By means of the connecting pipe 28 the compressed air introduced into the regulator passes simultaneously into the chamber 26 beneath the piston 25.

During the downward movement of the piston 2, the diaphragm 3 detaches itself from the fins 11 arranged in the regulator housing 1 and rests increasingly against the fins 10 of the piston 2. The effective surface area of the diaphragm is thus steadily increased until is exceeds the surface area of the upper side of the piston. As a result, the piston 2 is raised again and the valve 6, 7 is closed. Full braking has now been achieved, and the pressure prevailing in the brake cylinders corresponds to the pressure controlled in dependence on the weight of the load.

After the brake pressure has been removed, the compressed air in the brake cylinders pushes the piston 2 into its upper end position (opening the outlet valve 6, 8) and escapes to the atmosphere by way of the outlet valve 6, 8 through the bore 18 of the valve push rod 9 and by way of the chamber 19 through the outlet 20.

The operation of the pressure pilot valve is as follows: The brake pressure arriving by way of connection 14 passes simultaneously by way of chamber 13 and the pilot-inlet valve 31, 32 into the pilot chamber 35 and further acts by way of the bore 38 on the diaphragm 3, and it also passes directly from the connection 14 into the graduating chamber 35 by way of the bore 37. At a-specific 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 closes the inlet valve 31, 32.The compressed air that flows on to the upper side of the diaphragm 3 until the inlet valve 31, 32 closes, counteracts the brake cylinder pressure that has built up on the lower side of the diaphragm and removes the load-dependent control in this range-up to 1 bar input pressure in our example-,that is to say a correspondingly higher pressure builds up in the chamber 16 beneath the diaphragm 3.

When a brake pressure in excess of l bar is passed out of the motor vehicle brake valve, pressure continues to build up only in the chamber 36--because the inlet valve 31, 32 is closed-and moves the piston 29 upwards again, which opens the outlet valve 31, 33 and, in so doing, exhausts air from chamber 35 and at the same time the pressure above the diaphragm 3 falls to 0 bar.

The continuous characteristic curve 1 shown in Figure 2 represents the operation of the pilot valve, that is, corresponding to the example given here, the threshold of 1 bar and the fall in pressure above diaphragm 3 (the control pressure) from 1 bar to 0 at an increase in pressure from the vehicle brake valve from 1 to 7-5 bar. The dotted characteristic curve 2 in Figure 2 represents the operation of the regulator described in Application No. 38345/77 (Serial No.

1584598), that is, a threshold of 1 bar and the control pressure of 1 bar remaining unchanged at a pressure increase from the vehicle brake valve from 1 to 7.5 bar.

The automatic load-dependent brake force regulator described above makes it possible to meet specific demands on the part of vehicle manufacturers for a regulator, the values of which, related to the so-called "threshold," start from an order of magnitude which, at a threshold in an order to magnitude of 1 bar and at an output pressure of 1-5 bar at 7.5 bar input pressure, lies in the regulator position "empty" without having to increase substantially the dimensions of the installation or take costly measures.

These demands are met by so designating the surface area ratios of the pilot step piston 29 that the total surface area effects a closing of the brake pressure pilot valve 31, 32 at 1 bar and that during the further build-up of presssure from 1 to 7-5 bar in the ring area 12 of the step piston 2, pressure on the substantially larger inner surface (the upper surface of the diaphragm 3) is reduced from 1 bar to 0 bar.

The pressure pilot device of the regulator described above furthermore has a very important safety feature, which is not present in the pressure pilot device of the regulator previously described in Application No.

38345/77 (Serial No. 1584598). If, in that previously described regulator, leakage occurs in the threshold valve or the pilot valve, the full pressure of 1:1 is always transmitted, regardless of the position of the regulator, that is to say, full brake pressure is used for braking even for the unladen vehicle, whereas if a leak occurs in the pilot valve of the regulator described above, both the pilot function of the brake force regulator and the normal load-dependent control function is maintained.

In addition, as a result of the co-axial arrangement of the brake pressure pilot valve and the brake pressure control valve in the regulator described above-in contrast to the lateral arrangement of the brake pressure pilot valve described in Application 38345/77 (Serial No. 1584598)-there are other important advantages to be derived.

These advantages mainly relate to finishing techniques as regards the machining of the housing 1 of the regulator and the arrangement of the air inlet and outlet bores and also to the possiblity of a smaller construction offered by the coaxial arrangement of the two valves.

The resulting simplification means that one and the same guide member 5 may be used both for guiding the double valve member 6 of the brake pressure control valve and for guiding the double valve member 31 of the brake pressure pilot valve.

Another important feature of the regulator described above is that air is removed from the breathing chamber 29a above the pilot piston, the pilot valve and the control valve by means of a common outlet system 18, 19, 20.

WHAT WE CLAIM IS: 1. A load-dependent brake force regulating device for use in pressure mediumoperated brake systems which device has a brake pressure control piston assembly exposed to the pressure at an inlet of the regulating device, a brake pressure control valve which is operable by the brake pressure control piston assembly in dependence on the adjustment of a load-controlled regulating member, and a brake pressure pilot valve operable 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 pilot valve being responsive to the said inlet pressure whereby, as the inletipresssure increases, the pilot pressure increases over a predetermined initial range and then decreases, the brake pressure control valve and the brake pressure pilot valve being arranged co-axially in a common housing.

2. A device according to claim 1, in which the pilot valve comprises an inlet valve for applying pressure medium to the control piston assembly over the said initial range of inlet pressure, and an outlet valve for allowing pressure medium applied to the control piston assembly to escape as inlet pressure increases further.

3. A device according to claim 1 or claim 2, in which the brake pressure control valve and the brake pressure pilot valve each include a respective double valve member, and in which the double valve members are arranged so that they engage one within another through an annular housing wall or are separated from one another by an annular wall which is fixed to the housing.

4. A device according to claim 3, in which the separating housing wall of the double valve members acts as a common guide member.

5. A device according to claim 2, in which the pilot valve comprises, for the inlet valve and the outlet valve, a common, double valve member, and a pilot piston that may be exposed on one side to the pressure at the said inlet and on the other side of which is a breathing chamber.

6. A device according to claim 5, in which, for the removal of air pressure medium from the breathing chamber, the brake pressure pilot valve, and the brake pressure control valve, there is provided a common device outlet system.

7. A device according to claim 5 or claim 6, in which the common double valve member, together with a valve seat fixed in a housing of the device forms the pilot inlet valve and, together with a valve seat provided by the pilot piston forms the pilot outlet valve.

8. A device according to any one of claims 5 to 7, in which the pilot piston is constructed as a step piston.

9. A device according to claim 8, in which the pilot piston, together with a housing, forms, on the said one side of the pilot piston, a pilot chamber and a graduating chamber separated from one another in a pressure-proof manner.

10. A device according to claim 9, in which pressure medium form the said inlet may be passed into the pilot chamber by way of the pilot inlet valve and may be passed directly into the graduating chamber by way of a bore.

11. A device according to any one of the preceding claims in which the brake pressure control piston is a differential piston com

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

Claims

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

12 of the step piston 2, pressure on the substantially larger inner surface (the upper surface of the diaphragm 3) is reduced from 1 bar to 0 bar.

The pressure pilot device of the regulator described above furthermore has a very important safety feature, which is not present in the pressure pilot device of the regulator previously described in Application No.

38345/77 (Serial No. 1584598). If, in that previously described regulator, leakage occurs in the threshold valve or the pilot valve, the full pressure of 1:1 is always transmitted, regardless of the position of the regulator, that is to say, full brake pressure is used for braking even for the unladen vehicle, whereas if a leak occurs in the pilot valve of the regulator described above, both the pilot function of the brake force regulator and the normal load-dependent control function is maintained.

In addition, as a result of the co-axial arrangement of the brake pressure pilot valve and the brake pressure control valve in the regulator described above-in contrast to the lateral arrangement of the brake pressure pilot valve described in Application 38345/77 (Serial No. 1584598)-there are other important advantages to be derived.

These advantages mainly relate to finishing techniques as regards the machining of the housing 1 of the regulator and the arrangement of the air inlet and outlet bores and also to the possiblity of a smaller construction offered by the coaxial arrangement of the two valves.

The resulting simplification means that one and the same guide member 5 may be used both for guiding the double valve member 6 of the brake pressure control valve and for guiding the double valve member 31 of the brake pressure pilot valve.

Another important feature of the regulator described above is that air is removed from the breathing chamber 29a above the pilot piston, the pilot valve and the control valve by means of a common outlet system 18, 19, 20.

WHAT WE CLAIM IS: 1. A load-dependent brake force regulating device for use in pressure mediumoperated brake systems which device has a brake pressure control piston assembly exposed to the pressure at an inlet of the regulating device, a brake pressure control valve which is operable by the brake pressure control piston assembly in dependence on the adjustment of a load-controlled regulating member, and a brake pressure pilot valve operable 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 pilot valve being responsive to the said inlet pressure whereby, as the inletipresssure increases, the pilot pressure increases over a predetermined initial range and then decreases, the brake pressure control valve and the brake pressure pilot valve being arranged co-axially in a common housing.
2. A device according to claim 1, in which the pilot valve comprises an inlet valve for applying pressure medium to the control piston assembly over the said initial range of inlet pressure, and an outlet valve for allowing pressure medium applied to the control piston assembly to escape as inlet pressure increases further.
3. A device according to claim 1 or claim 2, in which the brake pressure control valve and the brake pressure pilot valve each include a respective double valve member, and in which the double valve members are arranged so that they engage one within another through an annular housing wall or are separated from one another by an annular wall which is fixed to the housing.
4. A device according to claim 3, in which the separating housing wall of the double valve members acts as a common guide member.
5. A device according to claim 2, in which the pilot valve comprises, for the inlet valve and the outlet valve, a common, double valve member, and a pilot piston that may be exposed on one side to the pressure at the said inlet and on the other side of which is a breathing chamber.
6. A device according to claim 5, in which, for the removal of air pressure medium from the breathing chamber, the brake pressure pilot valve, and the brake pressure control valve, there is provided a common device outlet system.
7. A device according to claim 5 or claim 6, in which the common double valve member, together with a valve seat fixed in a housing of the device forms the pilot inlet valve and, together with a valve seat provided by the pilot piston forms the pilot outlet valve.
8. A device according to any one of claims 5 to 7, in which the pilot piston is constructed as a step piston.
9. A device according to claim 8, in which the pilot piston, together with a housing, forms, on the said one side of the pilot piston, a pilot chamber and a graduating chamber separated from one another in a pressure-proof manner.
10. A device according to claim 9, in which pressure medium form the said inlet may be passed into the pilot chamber by way of the pilot inlet valve and may be passed directly into the graduating chamber by way of a bore.
11. A device according to any one of the preceding claims in which the brake pressure control piston is a differential piston com

prising a rigid piston exposed to the pressurat the said inlet and a diaphragm piston exposed to the pilot pressure.
12. A device according to claim 11, when appendant to claim 9 or claim 10, in which the diaphragm piston is exposed to the pressure in a control chamber which is connnected directly to the pilot chamber.
13. A device according to claim 9, in which the pilot piston is loaded against the direction of pressure in the pilot and graduating chambers.
14. A device according to claim 13, in which the loading of the pilot piston is adjustable.
15. A device according to claim 5, in which the double valve member is loaded in the direction of closing of the pilot outlet valve.
16. A load-dependent brake force regulating device for use in pressure mediumoperated brake systems the device being substantially as described herein with reference to, and as shown in, Fig. 1 of the accompanying drawings.