GB1598607A

GB1598607A - Spring brake control system

Info

Publication number: GB1598607A
Application number: GB2401278A
Authority: GB
Original assignee: Bendix Westinghouse Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-09-23

Description

(54) SPRING BRAKE CONTROL SYSTEM (71) We, BENDIX WESTINGHOUSE LIM ITED, a Company incorporated under the Laws of Great Britain, of Douglas Road, Kingswood, Bristol, England, 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 spring brake control systems and relates to an improvement in or modification of the spring brake control system claimed in the Specification of U.K. Patent No. 1470377.

In the specification of U.K. Patent No.

1470377, there is described and claimed a vehicle spring brake parking system including a spring brake actuator connected to act as a parking brake when controlling fluid pressure is removed therefrom and which is held in the off condition by the application thereto of a controlling hold-off pressure characterised by the hold-off pressure to the actuator being derived from a relay valve, said relay valve being controlled by a service or secondary brake control pressure applied to the relay valve via check valve means.

According to the present invention there is provided an improvement in or modification to the invention claimed in Patent No.

1470377 and comprising a tractor vehicle spring brake parking system including a spring brake actuator connected to act as a parking brake on rear wheels of a tractor vehicle when a controlling hold off fluid pressure is removed therefrom characterised by the hold-off pressure being derivable from an on/off relay valve having two input chambers one said chamber being arranged to receive an upright graduable trailer secondary brake pressure signal and the other said chamber being arranged to receive an inverse graduable tractor secondary spring brake control pressure signal said on/off relay valve having a characteristic whereby it is thereby normally held in its on condition for all but a parking condition in which both said pressure signals are below a prescribed value.

In order that the present 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 of which: Fig. 1 illustrates part of a tractor vehicle braking system employing one embodiment of the invention Fig. 2 illustrates pressures in the system of Fig. 1 during operation.

Referring to Fig. 1, there is illustrated part of a system suitable for a tractor vehicle in a tractor/trailer combination. A normal service braking system is preferably provided additionally to the secondary and parking system illustrated.

The front brakes of the tractor are provided with a spring brake actuator 1 and the rear brakes of the vehicle are provided with a spring brake actuator 2. These actuators 1 and 2 also include service brake chambers for applying service brakes via the normal foot-operated service brake valve of the vehicle. It will be understood moreover that for the respective front and rear axles further actuators are normally provided as necessary connected to the same front and rear fluid pressure lines. The pressure source for operating the tractor/trailer secondary system comprises a reservoir 3 and the braking is controlled by a control lever in the drivers cab of the tractor vehicle, this lever being that of a manual secondary/park control valve 4.The control valve 4 has two outputs, one which for a tractor front wheel secondary application is an inverse output is applied to a relay valve 6 and the other, which for a trailer secondary brake application is an upright pressure, is applied to a relay valve 5.

Both these relay valves are graduating relay valves which therefore produce output pressures which are variable proportionally as the input pressures from the valve 4. The inverse output pressure signal of the relay valve 6 is applied to the front secondary/ park spring brake as shown and the upright output of the relay valve 5 is applied to the trailer secondary braking control line 8.

These two outputs are also applied as inputs to an on-off relay valve denoted by reference 9 which is fed with fluid pressure input from the reservoir 3 and provides an output pressure to the tractor rear axle parking spring brake 2.

The on/off relay valve 9 is a relay valve which has two input chambers pressure in either of which when at more than a prescribed level will render the valve to its on condition. In the absence of either or both pressures at said level, the valve reverts to its off condition.

In operation of the arrangement of Fig. 1, it will be appreciated from the foregoing that in the event of the driver's brake control lever being placed in a full application condition, the secondary trailer brake connection 8 is fully pressurised to control the trailer brakes to adopt a full braking condition and also the inverse pressure which appears at the output of the relay valve 6 in these conditions is so low as to permit release of the spring in each of the front spring brake actuators such as 1 to an extent as to permit a full secondary brake application. Under these conditions, the pressure applied to the relay valve 9 from the line 7 is sufficient to turn the relay valve 9 on and thereby maintain a controlling holdoff pressure to the rear spring brakes of the tractor vehicle.In such circumstances therefore, even with a hurried application of the secondary brakes as, for example, in the case of a driver who suddenly realizes he has no service braking, the rear spring brakes of the tractor are prevented from being operated and thereby a risk of a jack-knifing effect of the combination which could otherwise be caused by application of rear spring brakes may be avoided.

In the event that the position of the handle of the valve 4 is moved backwards such as to reduce the value of the upright pressure in the line 7, a corresponding increase of the pressure in the line 10 occurs up to a crossover point which is above the level at which the on-off relay valve 9 is switched on accordingly. For the whole of the secondary brake application range for the valve 4, the spring brakes 2 are maintained in the release condition.

In the event of the handle 4 being placed in the park condition, the output pressures are released both from line 7 and 10 and the relay valve 9 is thereby switched to the off condition and the rear spring brakes 2 is vented together with the front secondary spring brakes 1 to provide parking of the tractor vehicle.

Referring to Fig. 2, this shows in diagrammatical form the operating output characteristics of the valve 4, the pressures on lines 7 and 10 being shown crossing over at an intermediate point which is at a higher pressure than the operating level L9 above which the relay valve 9 switches to the on oaFdition to maintain a hold-off pressure to * wear spring brakes of the tractor vehicle WHAT WE CLAIM IS: 1.A tractor vehicle spring brake parking system including a spring brake actuator connected to act as a parking brake on rear wheels of a tractor vehicle when a controlling hold-off fluid pressure is removed therefrom characterised by the hold off pressure being derivable from an on/off relay valve'having two input chambers one said chamber being arranged to receive an upright graduable trailer secondary brake pressure signal and the other said chamber being arranged to receive an inverse graduable tractor secondary spring brake control pressure signal said on/off relay valve having a characteristic whereby it is thereby normally held in its on condition for all but a parking condition in which both said pressure signals are below a prescribed value.

2. A tractor vehicle spring brake parking system substantially as described herein with reference to Fig. 1 and Fig. 2 of the accompanying drawings.

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Claims

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

the reservoir 3 and provides an output pressure to the tractor rear axle parking spring brake 2.

The on/off relay valve 9 is a relay valve which has two input chambers pressure in either of which when at more than a prescribed level will render the valve to its on condition. In the absence of either or both pressures at said level, the valve reverts to its off condition.

In operation of the arrangement of Fig. 1, it will be appreciated from the foregoing that in the event of the driver's brake control lever being placed in a full application condition, the secondary trailer brake connection 8 is fully pressurised to control the trailer brakes to adopt a full braking condition and also the inverse pressure which appears at the output of the relay valve 6 in these conditions is so low as to permit release of the spring in each of the front spring brake actuators such as 1 to an extent as to permit a full secondary brake application. Under these conditions, the pressure applied to the relay valve 9 from the line 7 is sufficient to turn the relay valve 9 on and thereby maintain a controlling holdoff pressure to the rear spring brakes of the tractor vehicle.In such circumstances therefore, even with a hurried application of the secondary brakes as, for example, in the case of a driver who suddenly realizes he has no service braking, the rear spring brakes of the tractor are prevented from being operated and thereby a risk of a jack-knifing effect of the combination which could otherwise be caused by application of rear spring brakes may be avoided.

In the event that the position of the handle of the valve 4 is moved backwards such as to reduce the value of the upright pressure in the line 7, a corresponding increase of the pressure in the line 10 occurs up to a crossover point which is above the level at which the on-off relay valve 9 is switched on accordingly. For the whole of the secondary brake application range for the valve 4, the spring brakes 2 are maintained in the release condition.

In the event of the handle 4 being placed in the park condition, the output pressures are released both from line 7 and 10 and the relay valve 9 is thereby switched to the off condition and the rear spring brakes 2 is vented together with the front secondary spring brakes 1 to provide parking of the tractor vehicle.

Referring to Fig. 2, this shows in diagrammatical form the operating output characteristics of the valve 4, the pressures on lines 7 and 10 being shown crossing over at an intermediate point which is at a higher pressure than the operating level L9 above which the relay valve 9 switches to the on oaFdition to maintain a hold-off pressure to * wear spring brakes of the tractor vehicle WHAT WE CLAIM IS: 1.A tractor vehicle spring brake parking system including a spring brake actuator connected to act as a parking brake on rear wheels of a tractor vehicle when a controlling hold-off fluid pressure is removed therefrom characterised by the hold off pressure being derivable from an on/off relay valve'having two input chambers one said chamber being arranged to receive an upright graduable trailer secondary brake pressure signal and the other said chamber being arranged to receive an inverse graduable tractor secondary spring brake control pressure signal said on/off relay valve having a characteristic whereby it is thereby normally held in its on condition for all but a parking condition in which both said pressure signals are below a prescribed value.
2. A tractor vehicle spring brake parking system substantially as described herein with reference to Fig. 1 and Fig. 2 of the accompanying drawings.