GB2098755A - Air compressor systems - Google Patents

Abstract

In an air compressor system for the brakes of a vehicle an individually operable changeover valve 13 is provided which is operable only when the vehicle parking brake is applied but automatically reset upon release of the parking brake, the changeover valve 13 providing a control pressure to a cut-off valve 7 to isolate the air compressor from a reservoir and to open the valve 19 to vent a portion of line to present pressure signals to governor A which would otherwise cause the compressor to be unloaded. A pressure take-off 21 for tyre inflation being provided upstream of the cut-off valve and thereby being able to be pressurised to an higher pressure than normally by operation of valve 13. <IMAGE>

Description

SPECIFICATION Air compressor systems This invention relates to air compressor system and relates especially to air compressor system for vehicle braking apparatus.

In certain types of wheeled vehicle, especially off-road vehicles with large pneumatic tyres, it is considered desirable to adapt the air compressor system which normally operates to charge storage reservoirs for the vehicle braking system, for easy use in reinflating the pneumatic tyres. A problem exists however in achieving tyre inflation from the braking system without signficantly overcharging the braking system because the latter is usually arranged to operate with air pressures (typically 120 p.s.i.) which are appreciably less than the pressure (typically 160 p.s.i.) required for tyre inflation of such vehicles.

The present invention has the object of reducing the said problem.

According to the present invention there is provided an air compressor system including an air compressor with a connection for charging a reservoir a governor device operable in response to a pressure signal indicative of a predetermined reservoir pressure to switch the compressor between a charging mode and a non-charging mode.

Where the system is employed on a vehicle which is provided with a parking brake said means may be arranged to be resettable by release of the parking brake. In particular, if the parking brake includes spring brakes, the spring brake hold-off pressure may be employed to effect the setting of said means.

In the foregoing, it is to be understood that the governor device operable to switch the compressor in and out of operation may either operate to condition the compressor to operate off load or alternatively may operate to switch a purge valve in an air dryer in the system.

In order that the invention may be more fully understood the same will be further described by way of example with reference to the accompanying drawing which illustrates in diagrammatical form a compressor system in accordance with the invention adapted to being utilisable for tyre inflation in addition to its main object of supplying compressed air to reservoirs of a vehicle braking system.

Referring to the drawing a compressor denoted by reference 1 has a safety valve 2 and a connection 3 feeds compresed air from the compressor to an air dryer 4 the output of which is fed via an output check valve 4a of the air dryer and a connection 5 to a sensing tank capacity 6 and then via a cut-off valve 7 to the input of a multi-circuit protection valve 8 with outputs 9, 10, 11 and 12. The outputs 9, 10 and 11 are intended for charging three reservoirs of a braking system on the vehicle and the output 12 is an auxillary output which is connected to a manually operable push-pull changeover valve 13 which in normal operation presents a block to the output 12 from the multi-circuit protection valve.The valve 13 also has a switching pressure input on line 14 intended for connection to a spring brake circuit and a normally vented output 15 connected on the one hand as a control input to cut off valve 7 and on the other hand as a controlling input to an on-off relay valve 19 which when signalled with air via end 12 and valve 13 is operable to vent the input connection of the multi-circuit valve 8. This input connection is also used to signal a governor device 17 for controlling a purge valve 18 provided at the bottom of the air dryer 4.

In normal operation of the system for vehicle braking purposes the compressor 1 operates to supply air under pressure to the air dryer and the output via the air dryer check valve is applied via a sensing tank 6 and cut off valve 7 to the multi-circuit protection valve 8 for charging reservoirs connected to outputs 9, 10 and 11. When the pressure at the output of the cut off valve 7 attains a predetermined pressure the governor 17 operates to open the purge valve 18, the air dryer is purged and the compressor operates off load for as long as the preset pressure to reservoirs 9, 10 and 11 is attained in sensing tank 6. If the pressure in one or other of the multi-circuit valve outputs 9, 10 and 11 falls, the compressor comes back onto load after closure of the vent valve 18.

In the event of the apparatus being required to be employed for tyre inflation, the pressure required may be greater than is provided for by the setting of the governor 17. A connection 21 between the sensing tank 6 and the cut off valve 7 is utilisable to supply pressure to the tyres after manual operation of the valve 13. With the type of valve envisaged for 13, this is only possible after venting of a spring brake pressure line 14 on parking of the vehicle. By such operation of the valve 13, the auxilliary output 12 is connected through valve 13 to the line 15 so as to provide a pressure signal to the cut-off valve 7 and on/off valve 19.

Referring briefly to Figure 2, this shows a diaphragm cut-off valve which is seen to have a relatively large area 'A' which is subject to the output pressure and a relatively smaller area 'a' which is subject (when seated) to the input pressure. Furthermore, a control port 22 being now provided via 13 with a pressure equivalent to approximately the full charged reservoir pressure for the system, and assisted also by a spring 23 causes the diaphragm 24 to seat to enclose the smaller area (a) thereby disconnecting the sensing tank 6 from the output of cut off valve 7 and from the governor 17. Since the output 15 is also connected to the on/off relay valve 19, this valve switches to a venting condition in which it vents the input to the multi circuit protection valve thereby preventing the governor receiving any pressure signal.As result of this, the compressor 1 is now allowed to operate up to a higher pressure limited either by the safety valve 2 or by the pressure at which the cut-off valve reopens, the latter pressure normally being intended to be higher than the safety valve opening pressure. In view of this, an appreciably elevated pressure is achievable in the connection 21 without being inhibited by operation of the governor 17. The facility of tyre inflation is therefore readily available without significant overchanging of the brake reservoirs connected to 9, 10 and 11.

In order that the system may reset automatically in the event of the vehicle being required to be operated the line 14 is connected as aforementioned to a spring brake control circuit of the vehicle such that when pressure is applied to the spring brakes to release them from a parked condition, a pressure responsive plunger in the valve 13 operates to reset valve 13 to close off the auxilliary connection 12 and vent the pipe 15. The cut-off valve 7 therefore is immediately opened by the excess pressure in the sensing tank 6 and the on/off relay valve 19 switches to its normal operation condition, the result of both these factors being that the pressure in sensing tank 6 is immediately shared with the remainder of the system downstream of the cut-off valve 7 and the governor is enabled to revert to normal operation.

In a case where a system does not include an air dryer such as 4, it will be usually desirable to provide a wet tank with a suitable automatic drain valve and in this case, the sensing tank 6 would not be expected to be required owing to the capacity of the wet tank. Thus the output 21 would be taken from the connection between the wet tank and the cut-off valve 7, the output of the cut-off valve 7 again being connected to the governor which would then operate to control an unloader mechanism on the compressor itself. The manner of operation of the system is essentially identical to that described for Figure 1.

The push-pull valve 13 may be any suitable commercialiy available valve such for example as a push-pull control valve PP-5 marketed by Bendix Corporation of the United States.

Whilsttheforegoing system has been described with reference to a particular embodiment of a compressor system for a vehicle braking system it is not limited thereto and moreover further variations or modification of the invention may readily be apparent to persons skilled in the art of air compressor systems and especially vehicle braking systems.

Claims (6)

1. An air compressor system including an air compressorwith a connection for charging a reservoir a governor device operable in response to a pressure signal indicative of a predetermined reservoir pressure to switch the compressor between a charging mode and a non-charging mode.

A cut off valve operable to isolate the compressor from the reservoir and a vent valve operable to vent the pressure signal and a pressure take-off connection upstream of the cut-offvalveto deliver a pressure output which is higher than said predetermined pressure.

2. An air compressor system as claimed in claim 1, said cut-off valve and said vent valve being operable by a pressure output from a changeover valve.

3. An air compressor system as claimed in claim 1 installed on a vehicle said changeover valve including means whereby it is resettable as a consequence of release of a parking brake of the vehicle.

4. An air compressor system as claimed in claim 3 said changeover valve being a manually operable valve and including means for preventing operation thereof to enable delivery of said higher pressure in the event of a parking brake not being applied.

5. A system as claimed in any preceeding claim wherein said cut-off valve has a spring biassed pressure reponsivevalve closure member which in the closed position presents part of its effective area to the pressure at an input port and part of its effective area to the pressure at an output port, said pre-determined pressure being such as to hold the closure member open and a third port for receiving a pressure output from a change over valve to assist the spring bias and effect closure of the cut-off valve.

6. A system substantially as described herein with reference to Figure 1 or Figures 1 and 2 of the accompanying drawings.