GB1602808A

GB1602808A - Load-dependent brake force regulation

Info

Publication number: GB1602808A
Application number: GB22839/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-06-11
Filing date: 1978-05-25
Publication date: 1981-11-18
Also published as: IT1203182B; SE445105B; DE2726520C2; IT7868146A0; SE7804423L; DE2726520A1

Description

(54) LOAD-DEPENDENT BRAKE FORCE REGULATION (71) We, WABCO FAHRZEUG BREMSEN GmbH (formerly Wabco Westinghouse 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 regulating device.

The installation of load-dependent brake force regulators in pressure medium brake systems of road vehicles produces a brake force control dependent on the weight of the load of the vehicle, in which the brake forces on the axles and the braking are so co-ordinated that the maximum frictional engagement on the wheels is approximately equal.

The regulation included in a supplement to the EEC guide-lines, regarding the compliance with friction curves specified in so-called distribution bands, these friction curves representing the relation between braking and stiction value, stipulates that at least one axle of the vehicle, i.e. the rear axle or one of the rear axles, must be subject to load-dependent control.

Brake force regulators and automatic load-dependent brake force regulators, the latter in particular being designed for a load/empty ratio of 1:1 to 4:1, have become known by way of German Patent Specifications 12 31 584, 16 55766 and 1934 784 and one is also described in British Patent Application No. 38345/77, Serial No.

1584598. The characteristics curve of the latter regulator both in the unladen and the laden state complies with the values stipulated in the distribution bands.

The adverse effect, on the front axle, of rear axle brake force control during braking in unladen or partially laden vehicles can be prevented by the pilot valve device described in detail in the above-mentioned Patent Application No. 38345/77.

Vehicle manufacturers, concerned with the development of a new generation of vehicles, have called for a load-dependent control according to a control ratio far in excess of the normal value of approximately 4.7:1, and load-dependent brake force regulators have been proposed which have made it possible to provide a control ratio up to a value of 13:1 (see, for example, Application No. 2365/78). Serial No.

1597631.

Since brake force regulators having the normal control ratio of approximately 4.7:1 and those regulators, planned for the future, having the high control ratio of up to 13:1 may differ from each other as regards their manufacture, consideration has been given to developing regulators to provide normal control and high control ratios, which are alike as far as manufacturing is concerned.

One solution to this problem has been proposed in Patent Application No. 3170/78 Serial No. 1598838, which discloses brake force regulators which can be installed in various types of vehicle without the use of additional components, these regulators having an upper control ratio up to the maximum value that can be obtained and not less than 4.7:1.

There is still the disadvantage, however, that for many types of vehicles which, because of their design or the conditions of their use require brake force regulators having a control ratio of < 4.7:1, different brake force regulators must continue to be manufactured and kept in stock.

The problem remains, therefore of constructing a regulator through which it is possible, with a single device, to obtain both a control ratio of ,4.7:1 and a control ratio of < 4.7:1 as a result of practically negligible alterations to the components, it being possible, in particular, to alter the control ratio without making alterations to the cast components of the regulator.

The present invention provides a loaddependent brake force regulator for 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 is defined a pilot chamber and on the other side of which is defined 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 regulator inlet.

The construction and operation of an automatic load-dependent brake force regulator in accordance with the invention, will be explained below with reference to the accompanying drawings in which: Figure la shows a section through the brake force regulator, Figure 1 b shows a section through a modified form of the pilot valve of the regulator of Fig. la, Figure Ic shows a section through another modified form of the pilot valve of the regulator of Fig. la, and Figure 2 is a graph of the characteristic curves that can be obtained with the brake force regulators illustrated in Figs. la to c in which the pressure pi introduced into the brake cylinders is shown as a function of the pressure P0 leaving the brake valve.

The regulator shown in Figure la has a housing I with a control piston 2, 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 provided at the inner wall of the piston 2, and a further valve seat 8 constructed on the upper end face of a valve push rod 9 arranged beneath the double valve member 6. A number of radial ribs 10 are joined to the piston 2, which ribs engage in a contact-free manner between corresponding ribs 11 arranged on the housing 1. The faces 10a and l la, facing the diaphragm 3, of the radial ribs 10 and 11 respectively, form parts of a tapered casing.

In the position shown in the diagram the diaphragm 3 rests against the faces 1 la. The graduating piston 2, 3 formed by the control piston and the diaphragm has an upper active face 12 and a lower active face 15.

The upper active face 12 is constant and is connected via a control chamber 13 to a compressed air connection 14 leading to the motor vehicle brake valve or the trailer brake valve. The lower active face 15 varies with the movement of the graduating piston 2, 3 and is connected to a connection 17 leading to the brake cylinders.

The valve push rod 9 is connected to a ball pivot 21 of a lever 22, which lever is mounted on the pivot of a shaft 23 connected to the vehicle axle by means of a lever 24 with the interconnection of rods, not shown, and a resilient member. The valve push rod 9 has a cavity 18 from which air escapes via a chamber 19 and an outlet 20. A relieving piston 25 is arranged in the housing, co-axial to the valve push rod 9, the upper end of which relieving piston supports the ball pivot 21 from below thereby equalising the forces acting-on the ball pivot 21 from above. A chamber 26 located beneath the relieving piston 25 is connected via a connecting pipe 28 to the control chamber 13.

A pressure pilot device is arranged in the upper portion of the housing 1 of the control valve. It consists of a pilot piston 29 which is biased by a spring 39 supported at the valve housing cover la, the bias of which spring is adjustable by means of a screw 40 arranged in the cover la, and also of 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 in the housing and the outlet valve is formed by the valve member 31 and a valve seat 33 constructed on the pilot piston 29. Between the pilot piston 29 and the housing 1, a pilot chamber 35 and a graduating chamber 36a are provided which are separated from one another in terms of pressure.The graduating chamber 36a is connected to the connection 14 by means of a bore 37 and a chamber 36 which is formed on the underside of the pilot piston 29 and with which the chamber 36a communicates by virtue of the absence of a seal in the grooves B of the piston. The pilot chamber 35 is connected to the connection 14 by means of the inlet valve 31, 32 and the chamber 13, and is also connected directly to the chamber 3a above the diaphragm 3 by means of a bore 38. When the outlet valve 31, 33 is open, air is allowed to escape from the pilot chamber through an outlet channel 18 and the outlet 19, 20. Air is allowed to escape from a breathing space 29a above the pilot piston likewise through the outlet 18, 19, 20.

The following is a brief description of the operation of the load-dependent control valve.

When the brakes are applied, brake pressure passes from the motor vehicle brake valve and the trailer control valve respectively via the connection 14 into the chamber 13 and depresses the piston 2. At the same time, the valve push rod 9 is similarly depressed by the double valve member 6 until it comes to rest on the ball pivot 21 and opens the valve 6, 7 as it continues to descend. Compressed air can then flow via connection 17 into the brake cylinders and also into the chamber 16 beneath the diaphragm 3.

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

As a result of this, the piston 2 is raised again and the valve 6, 7 is closed again.

Consequently, a closed position of the brakes is achieved. The pressure then prevailing in the brake cylinders corresponds to the pressure regulated in dependence on the weight of the load.

By means of connecting pipe 28 the compressed air introduced into the device passes simultaneously into the chamber 26 beneath the piston 25, the piston 25 supporting the ball pivot 21.

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

In the description of the load-dependent regulating valve thus far with reference to Figure la, the operation of the pressure pilot valve has not been considered. The brake pressure entering 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 bore 38 on the diaphragm 3 and also passes directly into the graduating chamber 36a by way of bore 37.

At a specific input pressure acting on the underside of the piston 29 in the chamber 35 the pilot piston 29 moves upwards against the force of the spring 39 and against the force of the pressure prevailing in graduating chamber 36a and acting on a ring area of the pilot piston 29 in the direction of bias of the spring. This upward movement of piston 29 closes the inlet valve 31, 32. The compressed air flowing onto the upper side of the diaphragm 3 before the inlet valve 31, 32 closes counteracts the brake cylinder pressure building up on the underside of the diaphragm and cancels the load-dependent control in this region, i.e. a correspondingly higher pressure builds up in chamber 16 beneath the diaphragm 3.

When a brake pressure in excess of a specific pressure level is supplied by the motor vehicle brake valve, pressure continues to build up only in the chamber 36a (because the inlet valve 31, 32 is closed) and moves the piston 29 downwards again which results in the re-opening of the inlet valve 31, 32 and allows compressed air to act on the diaphragm 3 via bore 38. The above-mentioned closing of the inlet valve 31, 32 then takes place again and, with the subsequent further increase in pressure in the chamber 36a, the inlet valve 31, 32 reopens. The characteristic curve of the regulator, produced in this manner, is shown in Figure 2 by the lines a and b, this curve corresponding to a control ratio of < 4.7:1. The point A corresponds to the "threshold pressure" and the point B corresponds to the full brake pressure.

A brake force regulator having a control ratio of > 4.7:1 can be produced from the brake force regulator first described without altering the components and by simple measures, that is merely by removing an O-ring from a groove A of the cover la and inserting it into a groove B of the pilot piston 29, as shown in Figure 1 b. This modification, which takes the regulator outside the scope of the present invention, prevents the build-up of pressure in chaniber 36a and allows a pressure opposing the bias of the spring 39 to build up instead in the chamber 36 on the other side of the pilot piston thus creating the necessary conditions for a control ratio of > 4.7:1 described in Application No. 2365/78.The characteristic curve of a regular produced in this manner is represented by the lines a and d in Figure 2, point A here also corresponding to the "threshold pressure" and point B3 corresponding to the full brake pressure.

To produce a regulator having a control ratio of 4.7:1, it is necessary only to seal the bore 37 as indicated at 37a in Fig. Ic. This modification, which also takes the regulator outside the scope of the present invention, means that the installation of O-rings in the ring grooves A and B can be dispensed with.

The lines a and e in Figure 2 show the gradient of this characteristic curve, the full brake pressure being indicated by the point B2.

WHAT WE CLAIM IS: 1. A load-dependent brake force regulator for 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

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. respectively via the connection 14 into the chamber 13 and depresses the piston 2. At the same time, the valve push rod 9 is similarly depressed by the double valve member 6 until it comes to rest on the ball pivot 21 and opens the valve 6, 7 as it continues to descend. Compressed air can then flow via connection 17 into the brake cylinders and also into the chamber 16 beneath the diaphragm 3. As the piston 2 descends, the diaphragm 3 detaches itself from the ribs 11 arranged in the regulator housing and rests increasingly against the ribs 10 of the piston 2. The active surface area of the diaphragm is thus steadily increased until it exceeds the surface area of the upper side of the piston. As a result of this, the piston 2 is raised again and the valve 6, 7 is closed again. Consequently, a closed position of the brakes is achieved. The pressure then prevailing in the brake cylinders corresponds to the pressure regulated in dependence on the weight of the load. By means of connecting pipe 28 the compressed air introduced into the device passes simultaneously into the chamber 26 beneath the piston 25, the piston 25 supporting the ball pivot 21. After the brake pressure has been removed the compressed air prevailing in the brake cylinders pushes the piston 2 into its upper end position and escapes to the atmosphere through the outlet valve 6, 8, the bore 18 of the valve push rod 9, through the chamber 19 and the outlet 20. In the description of the load-dependent regulating valve thus far with reference to Figure la, the operation of the pressure pilot valve has not been considered. The brake pressure entering 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 bore 38 on the diaphragm 3 and also passes directly into the graduating chamber 36a by way of bore 37. At a specific input pressure acting on the underside of the piston 29 in the chamber 35 the pilot piston 29 moves upwards against the force of the spring 39 and against the force of the pressure prevailing in graduating chamber 36a and acting on a ring area of the pilot piston 29 in the direction of bias of the spring. This upward movement of piston 29 closes the inlet valve 31, 32. The compressed air flowing onto the upper side of the diaphragm 3 before the inlet valve 31, 32 closes counteracts the brake cylinder pressure building up on the underside of the diaphragm and cancels the load-dependent control in this region, i.e. a correspondingly higher pressure builds up in chamber 16 beneath the diaphragm 3. When a brake pressure in excess of a specific pressure level is supplied by the motor vehicle brake valve, pressure continues to build up only in the chamber 36a (because the inlet valve 31, 32 is closed) and moves the piston 29 downwards again which results in the re-opening of the inlet valve 31, 32 and allows compressed air to act on the diaphragm 3 via bore 38. The above-mentioned closing of the inlet valve 31, 32 then takes place again and, with the subsequent further increase in pressure in the chamber 36a, the inlet valve 31, 32 reopens. The characteristic curve of the regulator, produced in this manner, is shown in Figure 2 by the lines a and b, this curve corresponding to a control ratio of < 4.7:1. The point A corresponds to the "threshold pressure" and the point B corresponds to the full brake pressure. A brake force regulator having a control ratio of > 4.7:1 can be produced from the brake force regulator first described without altering the components and by simple measures, that is merely by removing an O-ring from a groove A of the cover la and inserting it into a groove B of the pilot piston 29, as shown in Figure 1 b. This modification, which takes the regulator outside the scope of the present invention, prevents the build-up of pressure in chaniber 36a and allows a pressure opposing the bias of the spring 39 to build up instead in the chamber 36 on the other side of the pilot piston thus creating the necessary conditions for a control ratio of > 4.7:1 described in Application No. 2365/78.The characteristic curve of a regular produced in this manner is represented by the lines a and d in Figure 2, point A here also corresponding to the "threshold pressure" and point B3 corresponding to the full brake pressure. To produce a regulator having a control ratio of 4.7:1, it is necessary only to seal the bore 37 as indicated at 37a in Fig. Ic. This modification, which also takes the regulator outside the scope of the present invention, means that the installation of O-rings in the ring grooves A and B can be dispensed with. The lines a and e in Figure 2 show the gradient of this characteristic curve, the full brake pressure being indicated by the point B2. WHAT WE CLAIM IS:

1. A load-dependent brake force regulator for 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 is defined a pilot chamber and on the other side of which is defined 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 regulator inlet.

2. A regulator according to claim 1, including a breathing chamber which is also located on the said other side of the pilot piston and which is connected to an outlet bore, the breathing chamber and the graduating chamber being sealed from each other.

3. A regulator according to claim 2, in which the seal between the breathing chamber and the graduating chamber is removable.

4. A load-dependent brake force regulator for pressure medium-operated brake systems, the regulator being substantially as described herein with reference to, and as shown in, Fig. la of the accompanying drawings.