GB2049082A - Load-responsive braking systems - Google Patents

Abstract

A two-circuit brake system, in which the circuits control, respectively, the front brakes 20 and rear brakes 17 of a vehicle, has an automatic load- dependent brake force regulator 15 connected in the rear axle brake circuit 13. With a view to matching the braking forces of both axles to the total vehicle loading, the regulator has load-dependent control inputs 22, 23 from a front suspension unit 30 on one side of the vehicle and from a rear suspension unit 28 on the other side of the vehicle. The brake valve 11 which controls the brake circuits has an input 19 from the regulator output whereby the front axle brake circuit is controlled in dependence on the regulated brake pressure of the rear axle circuit. <IMAGE>

Description

SPECIFICATION Pressure medium-actuated brake systems The invention relates to pressure medium actuated brake systems and, in particuiar, to twocircuit systems incorporating automatic loaddependent regulation of the braking force.

Automatically load-controlled braking force regulators used in order to match the brake pressure in the brake cylinders to the current loading of the vehicle. The matching occurs automatically in that a control pressure which is dependent on the axle loading is used to adjust, by way of the braking force regulator, the level of the brake pressure produced by the brake valve.

In most cases, only the braking force of the rear axle of the vehicle is regulated, and the control pressure necessary for the braking force regulator is taken from one of the two rear axle pneumatic springs or from one of the two rear axle hydraulic equalising devices. This has the disadvantage in certain circumstances, however, that either the front wheel brakes or the rear wheel brakes of the vehicle depending on the weight distribution are overbraked or underbraked.

It is a known procedure also to regulate the braking force on the front axle by means of a separate valve controlled by the load-controlled regulating valve of the rear axle. In this case, however, the dependence on the loading of the rear axle remains a great disadvantage. Equal retarding of the vehicle at any loading with optimum distribution of the braking force and with the same pedal travel can only be achieved by means of heavy expenditure on automatically load-controlled braking force regulation on all axles.

Some concrete examples are given below of vehicies in which the front wheel or rear wheel brakes are constantly over- or underbrake because of the special conditions in which the vehicle is used.

In the case of buses which are used as public transport in town traffic, there is a constant change in the loading of the vehicle, and in an extreme case the driver brings the empty vehicle a standstill at a bus-stop with a light pressure on the pedal and then, after a large number of passengers has entered through the door at the front - this is a bus with one-man operation and stopped mainly in the front half of the bus, i.e.

predominantly loading the front axle, the driver has to apply a great deal of pressure to the pedal in order to brake the vehicle. The reason for this is that, because the regulated rear axle is not so heavily loaded, a relatively low pressure is produced in the brake cylinders by way of the braking force regulator: as a result, the rear wheels do not brake strongly enough in reiation to the total weight of the vehicle and the driver is forced to achieve an adequate braking effect by way of the front wheel brakes by applying a high pedal pressure, resulting in considerable wear on the brake linings due to constant overbraking of the front wheel brakes.

In the case illustrated here, therefore, there are two disadvantageous features, namely the excessive wear on the brake linings of the front wheel brakes and the constant change in the brake pedal forces to be applied by the driver.

The opposite applies in the case of town buses which have the passenger entry door at the rear and in which the passengers, according to experience, mainly stop in the rear section of the bus. When braking takes place in this case, because of the high loading on the regulated rear axle, a high pressure corresponding to the rear axle loading is produced in the brake cylinders by way of the braking force regulator. The front wheels of the unregulated front axle which is not heavily loaded may lock during this braking operation as a result of the low friction resistance.

In both the cases illustrated, emergency braking of the empty vehicle may lead to locking of the front wheels, since the wheels of the regulated rear axle are braked in accordance with the low load, whilst the full brake pressure is produced in the brake cylinders of the unregulated front axle.

The problem with which the present invention is concerned is that of matching the braking forces of both axles to the total loading, by comparatively simple means, in order to prevent excessive wear on the brake linings, locking of the front wheels, and constant changes in the brake pedal forces to be applied by the driver.

The present invention provides a pressure medium-actuated brake system for a vehicle, including two brake circuits for respective vehicle axles; a brake valve assembly including a first brake valve means operable upon actuation of the valve assembly to control a first one of the brake circuits, and a second brake valve means operable to control the second brake circuit; the first circuit including a braking force regulator the output of which is connected to operate the second brake valve means, and the regulator being operable as a function of the loading of one of the axles on one side of the vehicle and also of the other axle on the opposite side of the vehicle.

An embodiment of the invention is explained in greater detail hereinafter, by way of example, with reference to the accompanying drawing, in which: Fig. 1 shows a diagram of a pressure mediumoperated two-circuit, two-line brake systems, and Fig. 2 shows, diagrammatically a two-circuit brake valve suitable for use in the system of Fig. 1.

According to Fig. 1 , the compressed air required to operate the brake system and produced by an air compressor 1 is led to supply tanks 5 and 6 by way of a safety valve 2 and lines 3 and 4. From the tanks 5 and 6, lines 7 and 8 lead to supply connections 9 and 10 of a twocircuit motor vehicle brake valve 1 The brake circuit I of the brake valve 11 is connected by an outlet connection 12 and a line 13 to an input connection 14 of an automatic load-controlled braking force regulator 15, the control connection 1 6 of which is connected to the operating brake cylinders 1 7 of the rear axle.The control connection 1 6 of the braking force regulator 1 5 is also connected by way of a line 1 8 to a relay connection 1 9 provided on the brake valve 11.

Between the brake circuit li of the brake valve 11 and the operating brake cylinders 20 of the front axle there is a direct connection by way of an outlet connection 21 of the brake valve.

Connections 22 and 23 of the braking force regulator 1 5 are connected, respectively, by way of a line 27 to the pneumatic spring 28 of the rear axle of one side of the vehicle and by way of a line 29 to the pneumatic spring 30 of the front axle of the other side of the vehicle.

For the sake of completeness, the diagram also shows brake apparatus which are involved with the operation of the trailer brake system and the hand or auxiliary brake system but, since they are unrelated to the system according to the invention, they are not referred to in the present description.

A suitable form of the motor vehicle brake valve 11 is illustrated in Fig. 2: this valve corresponds to the two-circuit control valve described in German Patent No. 1,505,371, but with modifications which it has been necessary to make for the system of Fig. 1. These modifications are explained in the following description which is confined, with regard to construction and operation, to those functions directly associated with the system of Fig. 1.

The brake valve housing 31 accommodates the brake circuit I in the upper section and the brake circuit II in the lower section, and each circuit contains valve elements to regulate the flow of pressure medium between the corresponding inlet and outlet openings.

In the upper part of the housing 31 an inlet chamber 32 and a brake air chamber 33 are arranged, and the two chambers 32 and 33 are separated by means of a fixed inlet valve seat 34.

When the brake is not actuated, the inlet valve seat 34 is closed by a combined inlet and outlet valve element 35. The valve element 35 is accommodated by the radial flange 36 on the upper end of a valve sleeve 37 which is movably arranged in an annular sealing ring 38. The crosspiece of this sealing ring supports the lower end of a spring 39, the upper end of which engages with the radial flange 36 of the valve sleeve 37 in order to force the valve element 35 into engagement with the valve seat 34 to produce a seal.

A stepping piston 42 which is movably supported in the brake air chamber 33 is nonpositively connected to a brake pedal 40 by way of a spring member 41. When the brake is not actuated, the piston 42 is held in the upper position by means of a spring 43 which is arranged between the floor of the chamber 33 and the lower surface of the piston 42. When the stepping piston 42 moves downwards, an outlet valve seat 34a on the piston comes into engagement with the valve element 35; this closes the outlet valve 34a, 35, producing a seal, and opens the inlet valve 34, 35 to establish a connection between inlet chamber 32 and brake air chamber 33 so that pressure medium can flow to the braking force regulator 1 5 by way of the outlet connection 12.

In the lower part of the valve housing 31 a relay chamber 44 is separated from a second brake air chamber 45 by means of a relay piston. The relay piston consists of an outer piston section 46 and an inner piston section 47 which are arranged to move with respect to each other. When the brake is not actuated, the inner piston section 47 is pushed by means of a spring 48 into engagement with an annular surface on the outer piston section 46 so that when pressure fluid is fed to the relay chamber 44 by way of the reiay connection 19 the piston sections 46 and 47 are moved downwards as a single unit.When the lower end 50a of the piston 47 (constituting an outlet valve seat) engages with a lower combined inlet and outlet valve element 49, the latter is moved away from the inlet valve seat 50 so that inlet valve 49, 50 is opened in order to link the supply connection 10 to the outlet connection 21.

The operation of the motor vehicle brake valve when connected in the brake system of Fig. 1 is briefly described in the following: When the brake pedal 40 is actuated, the stepping piston 42 is moved downwards by way of the spring member 41, closing the outlet 34a and opening the inlet 34. Depending on how strongly the brake is actuated, the brake cylinders 1 7 of the first (rear axle) circuit are thereby partly or completely filled with air from the supply connection 9 by way of the chambers 32 and 33 and the outlet connection 1 2 of the brake valve, and the regulator 1 5.

At the same time the pressure flowing into the brake valve, by way of the relay connection 1 9 and regulated as a function of the load by the regulator 15, builds up in the chamber 44 above the relay piston 46 of the second (front axle) circuit. The relay piston section 46 moves downwards and carries the piston section 47 along with it against the force of the spring 48: the outlet 50a is thereby closed and the inlet 50 opened.

Compressed air flows from the supply connection 10 by way of the outlet connection 21 of the brake valve into the brake cylinders 20 of the second (front axle) circuit, which are thus supplied with air to correspond to the load-controlled pressure in the chamber 44.

The pressure building up in the chamber 33 of the rear axle circuit acts on the underside of the stepping piston 42, which is thereby moved upwards against the force of the spring member 41 until the forces on either side of the piston 42 are equalised. In this position the inlet 34 and the outlet 34a are closed (terminal position). In the same way the pistons 46 and 47, under the influence of the increasing pressure in the chamber 45 of the front axle circuit, move upwards until a similar terminal position is reached, i.e., until the inlet 50 and the outlet 50a are closed.

No detailed description of the operation of the two-circuit-controlled braking force regulator 1 5 of Fig. 1 need be given since suitable forms of regulators are already known. The regulator may, for example, be as described in the German Offenlegungsschrift No. 24 57 008.

The arrangement described above with reference to Figs. 1 and 2 provides a way of matching the braking forces of the front and rear axles to the total vehicle loading without incurring the reiatively high costs which would be associated with individual regulation of each axle, i.e. by fitting each axle with an automatically loadcontrolled braking force regulator. The matching is achieved through the use of the braking force regulator 1 5 which is controlled by an average value from the two pneumatic springs 28, 30 but is used for load-controlled regulation of only one vehicle brake circuit -- the rear axle brake circuit with regulation of the front axle brake circuit being effected via the brake valve 11 by means of the regulated rear axle brake pressure.

Claims (9)

1. A pressure medium-actuated brake system for a vehicle, including two brake circuits for respective vehicle axles; a brake valve assembly including a first brake valve means operable upon actuation of the valve assembly to control a first one of the brake circuits, and a second brake valve means operable to control the second brake circuit; the first circuit including a braking force regulator the output of which is connected to operate the second brake valve means, and the regulator being operable as a function of the loading of one of the axles on one side of the vehicle and also of the other axle on the opposite side of the vehicle.

2. A system as claimed in claim 1, in which the first and second circuits are, respectively, for the rear and front axles of the vehicles.

3. A system as claimed in claim 1 or claim 2, in which the regualtor is operable as a function of the average of the said loading of the axles.

4. A system as claimed in any one of the preceding claims, in which the regulator has control connections from pneumatic springs or hydraulic equalizing devices of the axles to operate the regulator as a function of the said loading of the axles.

5. A system as claimed in any one of the preceding claims, in which the brake valve assembly includes, for each brake circuit, a pressure-medium inlet chamber and a brake chamber separated by the respective brake valve means, the brake chamber of the first circuit having a connection to the regulator inlet.

6. A system as claimed in any one of the preceding claims, in which the brake valve assembly includes, for each valve means, a respective pressure-responsive, valve-operating member, the valve-operating member of the second brake valve means being exposed to the output brake pressure of the regulator.

7. A system as claimed in claim 6, in which the valve-opernting member of the second brake valve means is exposed to the pressure in a relay chamber having a connection from the regulator output.

8. A system as claimed in any one of the preceding claims, in which the brake valve assembly is substantially as described herein with reference to, and as illustrated, Fig. 2 of the accompanying drawings.

9. A pressure medium-actuated brake system substantially as described herein with reference to, and as illustrated by, the accompanying drawings.