GB1578752A

GB1578752A - Vehicle braking apparatus

Info

Publication number: GB1578752A
Application number: GB796576A
Authority: GB
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1976-02-28
Filing date: 1976-02-28
Publication date: 1980-11-12
Also published as: NL182134B; IT1071582B; SE7702095L; SE429631B; FR2342192A1; NL7701918A; NL182134C; FR2342192B1; BE851909A

Description

(54) VEHICLE BRAKING APPARATUS (71) We, THE BENDIX CORPORATION, of 401 Bendix Drive, South Bend, Indiana 46620, The United States of America, a corporation organised and ,existing under the laws of the State of Delaware, U.S.A., 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: This invention relates to fluid pressure operable vehicle braking systems.

A fluid pressure operable braking system may include an actuator which applies an increasing braking force with an increasing applied fluid pressure or an actuator which applies an increasing braking force with a decreasing applied fluid pressure.

In more specific forms of such a system service braking and parking braking actuators are incorporated in a combined spring applied parking brake actuator and airapplied service brake actuator. The spring applied actuator may act through the service brake actuator. One such actuator is illustrated in the Specification of U.K.

Patent No. 956195.

In a typical vehicle braking system such dual actuators may be provided to operate rear wheel brakes and single actuators may be provided to operate front wheel brakes.

In the interests of safety and reliability it is also known to control the front and rear service brake pressure circuits from separate reservoirs through discrete portions of a dual foot valve.

One object of the present invention is to provide means for improving still further upon such a system.

According to the present invention there is provided a fluid pressure operable vehicle braking system including a first fluid pressure operable braking circuit controllable by a brake presure control valve to control first brake actuator means, a second fluid pressure-operable braking circuit the pressure output of which to a second actuator means is graduable by a relay valve in dependence upon a first pressure signal derived from the first braking circuit, said relay valve having first pressure-responsive means responsive to the presence of a predetermined second signal pressure derived from a third brake circuit to render said relay valve normally graduably unresponsive to the first pressure signal and said relay valve having further pressure-responsive meansresponsive to à pressure output of a parking brake control valve to switch the relay valve to a condition in which regardless of said first and second signal pressures, the second actuator means apply parking brake force.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example, with reference to the accompanying drawings in which: Fig. 1 illustrates in simplified diagrammatical form relevant parts of a fluid pressure operable braking system in accordance with the present invention and Fig. 2 illustrates an elaboration of a system according to the present invention.

Referring to Fig. 1 of the drawings, the apparatus includes three compressed air reservoirs denoted by references 1, 2 and 3 which are charged from a compressor through suitable protection valves not shown. The reservoir 1 is a parking brake reservoir and this is connected to a parking brake control valve, denoted by reference 4, the output of which is applied as a parking brake input to a relay valve denoted generally by the reference 5. This relay valve is a valve of the type generally known as a self-lapping valve and is supplied from tbe reservoir 1 via a supply port 6, the output of the valve being derived from an output port 7 and being applied to the spring brake portion of each of a pair of rear actuators for the brakes of the vehicle.

One such actuator is shown at 8 and this includes a spring brake parking section 9 and a fluid pressure operable service portion 10. The spring brake and service portion are arranged in tandem such that the force exerted by the spring brake when release air is released therefrom is transmitted through the service portion 10 to the brake rigging to apply the vehicle rear brakes. The reservoir 2 is the rear service reservoir and this supplies the dual foot valve which is denoted by reference 11 and having an output applied to the service portion 10 of the rear brakes. A further and parallel output from 11 is applied to the other actuator of the rear brakes on the other side of the vehicle.

The reservoir 3 is the front brake service reservoir and this supplies the second portion of the dual foot valve 11, the output of this being applied to a normal single diaphragm service actuator as shown at 12 for operating the front brakes of the vehicle, a similar actuator being provided for the other side of the vehicle.

Referring now in greater detail to the relay valve 5, this operates in the manner of a differential relay valve and in the position shown it is effectively rendered inoperative by the fact that no air is present at the input 13 from the parking brake valve 4. The relay valve comprises a central plunger 14 having formed thereon three different effective piston areas, the area on top of a piston 15, the area beneath piston 15 and the area of a piston 16. The pistons 15 and 16 are sealingly slideable within respective cylindrical portions in the body of the valve. The plunger has a downwardly extending spigot 17, the end of which forms an exhaust valve closure member which bears against an input valve closure member 18 which is resiliently urged upwards towards the closed position shown.

The member 18 is sealingly slideable within the main housing of the valve and an exhaust passage 19 passes therethrough to at ionosphere. The relay valve has first and second pressure signal input ports 21 and 20, the port 20 communicating with a region above the piston 15 and the port 21 communicating with a region between the pistons 15 and 16 of different area. In addition, the plunger is continually urged downwards by a spring 22 which is captive between a slideable piston 23 and-the upper side of the piston 15. The piston 23 has an area which is several times the area of piston 15 or 16 and this in turn is urged upwards by a further spring 24 captive between the under side thereof and the housing.An upward extension of the plunger passes sealingly and slideably through a central bore of the piston 23 and is provided with an end stop 25 so that upward movement of the piston 23 from its lower stop 26 carries the plunger and pistons 15 and 16 with it to effectively disable the relay valve with regard to operation in response to signal pressures at ports 20 and 21.

In normal, fault-free service operation of the apparatus, the relay valve is essentially inactive except for parking operation.

Thus in normal running the parking brake 4 is operated to a brake-release position which pressurises the input port 13 from the reservoir 1 and urges the large piston 23 downwardly against the abutment 26 thereby urging the plunger downwards by virtue of the thrust on the spring 22 assisted by the presure at port 20. This holds closed the exhaust valve passage 19 and holds unseated the inlet valve 18 to provide a communication between the park reservoir 1 and the spring brake 9 via the ports 6 and 7 of the relay valve. The spring brakes are thus pressurised and set to the release condition. The pressure applied to 9 with no presure at port 20 and with pressure at 13 is that which is attained beneath piston 16 and which is sufficient to lap off the valve 18 by raising 16.In a subsequent service braking operation, the foot valve 11 is operated and substantially equal output pressures are normally derived from the two service braking circuits and applied to actuator 10 and 12. Rear brake service reservoir pressure is still applied to the control input port 20 and front service circuit output pressure is now applied also at port 21 of the relay valve but this nevertheless results in no deflection of the relay valve from its adopted position.

Consider now the effect of a failure of the third or rear service circut associated with the rear service reservoir 2 and which has an input connected to the second input port 20. Such a fault will result in the air pressure being reduced at the port 20 and air above the valve member 18 is now effective to a greater extent on the plunger by acting beneath the piston 16. The valve 18 now laps - off at a lower presure which is applied to the spring brakes. However the spring 22 is sufficient to maintain such air pressure in the spring brakes as to hold the spring brakes off. With a service application under these conditions, the front service brake pressure being again applied to the control port 21 now acts differentially on the plunger between the pistons 15 and 16, and is able to cause air to be further released from- the spring brakes until a fresh equilibrium lapping condition of the self-lapping valve is established which is now within the control range of the spring of the spring brake. This control range is the range of pressures within which a small decrement of applied pressure results in a corresponding increment of brake force.

Thus in the event of a rear service brake failure, the rear braking is supplemented by a spring brake pressure which is approximately inversely proportional to the level of braking pressure applied to the front service brakes.

In order to render the relay valve the more reliable in the event of such failure, in the light of the fact that as described, the upward extending stem of the plunger only moves relative to the piston 23 under failure conditions, it may be desirable to employ suitable nylon guides in the upward extending stem of the plunger. Additionally or alternatively, a stop may be provided in the body of the valve below the plunger in such a position that when the valve is released from a parking condition by the application of full park reservoir pressure to the chamber above the piston 23, contacts this stop before the piston 23 becomes seated on abutment 26. In this way the stem of the plunger is foroed to move relative to piston 23 at each operation of the parking brake to park the vehicle.

In an alternative embodiment of the relay valve of Fig. 1, the end stop 25 of the stem may be slideably enclosed within an annular space provided in the piston 23, the top of the bore through this piston being covered by a cap such as to avoid the necessity for the slideable seal between piston 23 and plunger stem.

In the foregoing, the system described is one in which spring brakes are provided solely on the rear axles of the vehicle. If spring brakes are provided on the front axles, the system may alternatively be arranged to be responsive to failure in the front wheel service circuit to cause the spring brakes associated with the front wheels to be operated in accordance with the required degree of braking. This may be achieved by a relay valve as described with reference to Fig. 1, the input port 20 being supplied with a pressure signal derived from the service reservoir and the input port 21 being supplied with a pressure signal from the rear service portion of the foot valve 11.

In yet another possible adaption of the system employing the invention as illustrated in diagrammatical form in Fig. 2, spring brakes (of a said fourth and second circuits respectively) are assumed to be provided on front and rear axles of the vehicle. In Fig. 2, the reference used are those which correspond to the references used in Fig. 1, but with the prefix 3, and it will be seen that two such relay valves are now provided, one to compensate for rear service circuit failure and one to compensate for front service circuit failure.

The relay valve which compensates for rear service failure is denoted by reference 35R and the relay valve which compensates for front service pressure failure is denoted by reference 35F. Additionally, the spring brake portions of the front and rear actuators of the vehicle are denoted by references 39F and 39R respectively.

The operation of the system of Fig. 2 will be clear from the above description of the system of Fig. 1, considered in relation to either the front or rear spring brake actuators. As in the case moreover of the single relay valve of Fig. 1, both relay valves of Fig. 2 are operable for parking.

WHAT WE CLAIM IS: - 1. A fluid pressure operable vehicle braking system including a first fluid pressure operable braking circuit controllable by a brake pressure control valve to control first brake actuator means, a second fluid pressure operable braking circuit the pressure output of which to a second actuator means is graduable by a relay valve independence upon a first pressure signal derived from the first braking circuit, said relay valve having first pressure-responsive means responsive to the presence of a predetermined second signal pressure derived from a third brake circuit to render said relay valve normally graduably unresponsive to the first pressure signal and said relay valve having further pressure-responsive means responsive to a pressure output of a parking brake control valve to switch the relay valve to a condition in which regardless of said first and second signal pressures, the second actuator means apply parking brake force.

2. A vehicle braking system as claimed in Claim 1, said second circuit being a spring brake circuit.

3. A vehicle braking system as claimed in Claim 1 or 2, said first and third circuits being the circuits of dual circuit service brakes.

4. A vehicle braking system as claimed in Claims 1, 2, or 3, said relay valve comprising a self-lapping relay valve.

5. A vehicle braking system as claimed in Claims 1, 2, 3 or 4, the presure signal derived from the third circuit being a supply pressure to the third circuit.

6. A vehicle braking system as claimed in Claims 1, 2, 3, 4 or 5, said first pressureresponsive means being spring biassed to provide in the absence of the pressure output signal from the parking brake control valve, a sufficient output pressure from the relay valve to just hold the spring brake in the released condition, a said pressure signal from the third circuit further biassing the spring brake out of the control

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the range of pressures within which a small decrement of applied pressure results in a corresponding increment of brake force. Thus in the event of a rear service brake failure, the rear braking is supplemented by a spring brake pressure which is approximately inversely proportional to the level of braking pressure applied to the front service brakes. In order to render the relay valve the more reliable in the event of such failure, in the light of the fact that as described, the upward extending stem of the plunger only moves relative to the piston 23 under failure conditions, it may be desirable to employ suitable nylon guides in the upward extending stem of the plunger. Additionally or alternatively, a stop may be provided in the body of the valve below the plunger in such a position that when the valve is released from a parking condition by the application of full park reservoir pressure to the chamber above the piston 23, contacts this stop before the piston 23 becomes seated on abutment 26. In this way the stem of the plunger is foroed to move relative to piston 23 at each operation of the parking brake to park the vehicle. In an alternative embodiment of the relay valve of Fig. 1, the end stop 25 of the stem may be slideably enclosed within an annular space provided in the piston 23, the top of the bore through this piston being covered by a cap such as to avoid the necessity for the slideable seal between piston 23 and plunger stem. In the foregoing, the system described is one in which spring brakes are provided solely on the rear axles of the vehicle. If spring brakes are provided on the front axles, the system may alternatively be arranged to be responsive to failure in the front wheel service circuit to cause the spring brakes associated with the front wheels to be operated in accordance with the required degree of braking. This may be achieved by a relay valve as described with reference to Fig. 1, the input port 20 being supplied with a pressure signal derived from the service reservoir and the input port 21 being supplied with a pressure signal from the rear service portion of the foot valve 11. In yet another possible adaption of the system employing the invention as illustrated in diagrammatical form in Fig. 2, spring brakes (of a said fourth and second circuits respectively) are assumed to be provided on front and rear axles of the vehicle. In Fig. 2, the reference used are those which correspond to the references used in Fig. 1, but with the prefix 3, and it will be seen that two such relay valves are now provided, one to compensate for rear service circuit failure and one to compensate for front service circuit failure. The relay valve which compensates for rear service failure is denoted by reference 35R and the relay valve which compensates for front service pressure failure is denoted by reference 35F. Additionally, the spring brake portions of the front and rear actuators of the vehicle are denoted by references 39F and 39R respectively. The operation of the system of Fig. 2 will be clear from the above description of the system of Fig. 1, considered in relation to either the front or rear spring brake actuators. As in the case moreover of the single relay valve of Fig. 1, both relay valves of Fig. 2 are operable for parking. WHAT WE CLAIM IS: -

1. A fluid pressure operable vehicle braking system including a first fluid pressure operable braking circuit controllable by a brake pressure control valve to control first brake actuator means, a second fluid pressure operable braking circuit the pressure output of which to a second actuator means is graduable by a relay valve independence upon a first pressure signal derived from the first braking circuit, said relay valve having first pressure-responsive means responsive to the presence of a predetermined second signal pressure derived from a third brake circuit to render said relay valve normally graduably unresponsive to the first pressure signal and said relay valve having further pressure-responsive means responsive to a pressure output of a parking brake control valve to switch the relay valve to a condition in which regardless of said first and second signal pressures, the second actuator means apply parking brake force.

range of the spring brake.

7. A vehicle braking system as claimed in Claim 6, including a fourth fluid pressure-operable braking circuit the pressure output of which to a further spring brake actuator means is graduable by a further self-lapping relay valve in dependence upon a pressure signal derived from the second braking circuit, said relay valve having first pressure-responsive means responsive to the presence of a predetermined signal pressure derived from the first brake circuit to render said relay valve normally graduably unresponsive to the latter said signal from the second circuit and said second relay valve also having further pressure-responsive means responsive to the pressure output of the parking brake control valve to switch the relay valve to a condition in which, regardless of the said signal pressures applied to it, the further spring brake actuator means also apply a parking brake force.

8. A self-lapping relay valve for use in a system as claimed in any preceding claim, said relay valve comprising a double valve controlling communication between an output-port and input port or exhaust, respectively, said double valve being controlled by a spring-loaded plunger having pressureresponsive areas to be responsive in a like sense to the pressures at said output port and a port for connection to the first circuit and a pressure-responsive area to be responsive in an opposing sense to a pressure of the third circuit, a further port for connection to the parking brake control valve and a further presure responsive member having an area subject to the pressure at the further port which area is sufficiently large to overpower the spring load force exerted on the plunger and override any combination of the pressures on the other said pressure responsive areas even though the pressure at the further port may be no greater than any said other pressure.

9. A vehicle braking system substantially as described herein with reference to Fig. 1 or Fig. 2 of the accompanying drawings.