GB1602711A

GB1602711A - Motor-vehicle brake valve with control means for an auxiliary brake

Info

Publication number: GB1602711A
Application number: GB24895/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-10-29
Filing date: 1978-05-31
Publication date: 1981-11-18
Also published as: SE7809851L; NL187842C; DE2748671B2; NL7810570A; IT7869485A0; FR2407106A1; SE437245B; DE2748671C3; NL187842B; FR2407106B1; DE2748671A1; IT1203205B

Description

(54) MOTOR VEHICLE BRAKE VALVE WITH CONTROL MEANS FOR AN AUXILIARY BRAKE (71) We, WABCO FAHRZENGBREMSEN GMBH (Formerly WABCO WESTINGHOUSE GMBG), 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 motor-vehicle brake valve assembly for controlling actuation of a brake system actuated by a pressurized medium and also of a multi-stage auxiliary brake system.

The automatic switching-in of an auxiliary brake, upon actuation of the motor-vehicle brake valve of a pressure medium-operation system, by means of a brake pedal or foot-plate is disclosed in German Patent Specification 1122 850. The auxiliary brake, in accordance with this Patent, is switched in by slightly depressing the brake pedal, although the switching action does not occur in stages. As the brake pedal is depressed, air is first admitted to the operating cylinder of the auxiliary brake by way of an air inlet valve, and when the brake pedal is further depressed, air is also admitted to the operating cylinder of the friction brake, i.e. of the service brake.

Control arrangements for motor-vehicle brake valves are also known which switch in an auxiliary brake in a plurality of braking stages, use being made for the auxiliary brake, particularly when the system is used on omnibuses, of what are called retarders having three switching stages. In the known arrangements, these three braking stages are controlled by means of electrically or pressure-medium-actuated switches, the first two braking stages of the retarder usually being switched in by means of electric switches prior to the friction brake, and a third stage being switched in by means of pressurized-medium switches shortly after the friction brake has come into use.

However, the three braking stages of the retarder are controlled by a piston of the motorvehicle brake and this suffers from some disadvantages which are objected to, particularly, by the operators of transport businesses. Thus, a rubber element, serving as a transmission element, is usually arranged between the brake pedal and the brake valve piston and leads to an undesirable travel hysteresis when the braking stages are reversed or switched off, and upon recovery of the rubber element following the relaxation of pressure on the brake pedal, this hysteresis being increased at the third stage by the hysteresis of the pressurized medium.

Occasionally the second stage has been switched back whereas the third stage has continued to be switched in because of the total hysteresis caused by the rubber element and the pressurized medium.

A further disadvantage that has been found to exist is that the switching of the first two braking stages, which takes place during the idling stroke of the brake valve piston, i.e. prior to the pressurized medium effecting control, is completed without any indication in the form of a detectable mechanical transition point, so that an unnoticed switching from the first to the second stage causes undesirable rather sudden braking, and in some instances this can have unpleasant consequences for the following traffic and for passengers standing in the omnibus.

Motor-vehicle brake valves in which the above-described disadvantages do not exist, have been disclosed and include the arrangement of detectable mechanical transition points in the brake-pedal unit.

However, in the case of vehicles whose brake valves, for technical reasons, do not form a component integral with the brake-pedal unit, i.e. wherein the operation of the brake valve is started off by the pedal unit by way of rod connexions, problems arise as regards co-ordination between the setting of the braking stages of an auxiliary brake on the brake unit and the setting of the opening time of the brake valve. This problem of co-ordinating the settings is particularly great when use is made of pedal units and brake valves produced by different manufacturers.

It has also been proposed that, in addition to the transition point settings in the pedal, a further transition point unit should be provided in the brake valve body itself. This proposal provides the possibility of corrlating the transition point settings to the brake valve-opening times in one and the sasme piece of equipment.

However, the disadvantage exists that, although the driver senses the transition point on the brake pedal, thereafter no detectable resistance is offered to the brake pedal, so that the driver may accidentally move the brake pedal into the next braking stage and thus cause undesirable fairly sudden braking.Furthermore, the arrangement is subject to heavy wear, The present invention provides a brake valve assembly for controlling actuation of a pressure medium-operated brake system and also of a multi-stage auxiliary brake, the assembly including: an electrical switching arrangement operable to cause switching from one auxiliary braking stage to another; a valve actuation stem movable to actuate a brake valve of the pressure mediumoperated brake system and also to operate the switching arrangement, and a transition point device including at least one compression spring arranged around the valve stem and co-operable therewith whereby a switch from one auxiliary braking stage to another is associated with a change in the resilient bias on the valve stem.

The construction and mode of operation of an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a motor-vehicle brake valve assembly, the upper casing part of which together with the transition point device is shown in section, Figure 2 shows the arrangement of the three electrical switching stages of Figure 1.

Figure 3 illustrates the electrical switching stages seen in the direction indicated by the arrow X of Figure 2, Figure 4 is a diagrammatic illustration of the three-stage electric switch, and Figure 5 is a graph in which pressure points and switching points of the brake valve are plotted against the stroke of the valve stem and the force acting on the valve stem.

In the motor-vehicle brake valve assembly 1, illustrated in Figure 1, details of the piston and valve arrangement in the lower part 2 of the casing are not shown, since it is not necessary, for the purpose of explaining the invention, to describe the actual mode of operation of the motorvehicle brake valve for actuating a two-circuit service valve unit. the invention being concerned with the stem actuation system provided in the upper part 3 of the casing.

That portion of the actuating means that is arranged in the part 3 of the casing consists of a pressure stem 4 having an inclined face 5 which, upon downward movement of the stem 4, actuates in turn three spring-loaded actuating elements 6, 7 and 8 of an electric switch assembly 12 consisting of three switches 9, 10 and 11 (see Figures 2 to 4) and so switches-in the three braking stages I, II and III of an auxiliary brake in succession.

Figures 1 and 4 show the stem 4 in the unactuated braking position, i.e. none of the three braking stages I, II and III of the electric stepswitch assembly 12 is switched in.

The switches 9, 10 and 11 are adjustable so that the switching stages, illustrated individually in figure 4, can be set to suit the use to which the vehicle is to be put, i.e. to suit the braking conditions. since adjustment to suit the opening strokes of the brake valve 1 can be carried out on the same piece of equipment, the complete valve unit can be set at the works of the manufacturer.

To create a detectable transition point before the second braking stage of the auxiliary brake is switched-in, a compression spring 13, fitted in the casing part 3 around the pressure stem 4, is held between a lower spring support 14, firmly connected to the casing 3, and an upper spring support 15, which is designed to act as a guide for the spring 13 and is slidably guided on a slide element 16 of the stem 4. When the brake is released, a flange 3a integral with the casing 3 forms an upper abutment for the spring support 15. An abutment 17 on the stem 4 defines the actual detectable transition point, and serves to drive the upper support ring 15 during downward movement of the stem 4 caused by depressing the brake pedal (not shown).

To create a second detectable transition point prior to switching in the third braking stage, a second shorter compression spring 18 is fitted in the casing 3 around the first compression spring 13, the support 14 for the spring 13 serving as a lower abutment, and the upper support for the spring 18 being formed by a ring 18a secured to the upper end of the spring 18 and co-operating with an abutment 19 integral with the casing. In conjunction with the ring 18a on the spring 18, an extended downwardly directed formation 15a of the supper spring-support ring 15 forms an abutment (and thus defines the second detectable transition point) when the stem 4 continues its downward movement.

The mode of operation of the transition point device in providing two transition points in coordination with the switching-in of the three auxiliary braking stages is as follows: When the brake pedal, not illustrated, is actuated, the pressure stem 4 moves downwards; the spring-biased actuating element 6 of the switch 9 follows the inclined face 5 and switchesin the auxiliary braking stage I. Further depression of the brake pedal causes the stem 4 to continue its downward movement so that the abutment 17 on the stem 4 moves into contct with the upper support ring 15 for the spring 13, and the first transition point can be detected. Only after this pressure point has been overcome will the auxiliary braking stage II be switched in by means of the inclined face 5 of the stem 4 engaging the actuating element 7 of the switch 10.

Then, with continued pressure on the brake pedal and the downward movement of the stem 4 caused thereby, the actual functioning of the motor-vehicle brake valve in the lower part 2 of the casing in Figure 1 becomes effective, i.e. air is admitted to the friction brake or the service brake, and only thereafter, as shown in the graph of Figure 5, does the actuating element 8 of the switch 11 switch-in auxiliary braking stage III of the third brake by way of the inclined face 5 after the second transition point has previously been overcome this second transition point is set when the drive element 15a of the upper spring-support ring 15 encounters the ring 18a of the second spring 18.

The transition point arrangement can also be used for foot-board brake valves, i.e. for brake valves hasving a pedal fitted directly on the valve.

The brake valve described above provides a switching arrangement for an auxiliary brake that is integrated with the motor-vehicle brake valve, and whose transition point means is contained in the valve body, while the transition points for the various auxiliary braking stages cannot be unintentionally overriden by the driver, the components used in the arrangement being capable of resisting wear.

WHAT WE CLAIM IS: 1. A brake valve assembly for controlling actuation of a pressure medium-operated brake system and also of a multi-stage auxiliary brake, the assembly including: an electrical switching arrangement operable to cause switching from one auxiliary braking stage to another; a valve acutating stem movable to actuate a brake valve of the pressure medium-operated brake system and also to operate the switching arrangement, and a transition point device including at least one compression spring arranged around the valve stem and co-operable therewith whereby a switch from one auxiliary braking stage to another is associated with a change in the resiliant bias on the valve stem.

2. A brake valve assembly according to claim 1, in which the spring is supported, at one end, on a guide member movable in the same direction as the stem.

3. A brake valve assembly according to claim 2, in which the guide member is arranged to slide on the stem.

4. A brake valve assembly according to claim 2 or claim 3, in which the guide member is movable by engagement with an abutment on the stem.

5. A brake valve assembly according to any one of the preceding claims, in which the transition point devices includes two compression springs each arranged around the valve stem and co-operable therewith whereby a switch from each of two auxiliary braking stages is associated with a respective change in the resilient bias on the valve stem.

6. A brake valve assembly according to claim 5 when appendant to any one of claims 2 to 4, in which the second spring is supported, at one end, on a guide member movable by engagement by the guide member of the first spring.

7. A brake valve assembly according to any one of claims 2 to 4 or claim 6, in which movement of the, or each guide member under the biasing force of the respective spring is limited by a stop.

8. A brake valve assembly substantially as described herein with reference to, and as illustrated by, the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. switch 11 switch-in auxiliary braking stage III of the third brake by way of the inclined face 5 after the second transition point has previously been overcome this second transition point is set when the drive element 15a of the upper spring-support ring 15 encounters the ring 18a of the second spring 18. The transition point arrangement can also be used for foot-board brake valves, i.e. for brake valves hasving a pedal fitted directly on the valve. The brake valve described above provides a switching arrangement for an auxiliary brake that is integrated with the motor-vehicle brake valve, and whose transition point means is contained in the valve body, while the transition points for the various auxiliary braking stages cannot be unintentionally overriden by the driver, the components used in the arrangement being capable of resisting wear. WHAT WE CLAIM IS:

1. A brake valve assembly for controlling actuation of a pressure medium-operated brake system and also of a multi-stage auxiliary brake, the assembly including: an electrical switching arrangement operable to cause switching from one auxiliary braking stage to another; a valve acutating stem movable to actuate a brake valve of the pressure medium-operated brake system and also to operate the switching arrangement, and a transition point device including at least one compression spring arranged around the valve stem and co-operable therewith whereby a switch from one auxiliary braking stage to another is associated with a change in the resiliant bias on the valve stem.