GB2125114A - Air compressor and air pressure system - Google Patents

Abstract

An air compressor has a piston (3) operable to compress air within a cylinder (2), the piston being driven by a drive shaft (10) via a clutch (13). The clutch is normally held lightly in engagement by a spring device (17a) reinforced by the compressor output supplied to chamber (A). When a charged load reaches a predetermined pressure, this is fed to chamber (B), acting on piston (18) to overcome the combined effects of spring device (17a) and pressure in chamber (a) to disengage the clutch and thereby interrupt drive to the piston (3). <IMAGE>

Description

SPECIFICATION Air compressor and air pressure system This invention relates to an air compressor, primarily for use in a vehicle air-actuated braking system, and being of the kind having at least one compressor element operable by drive means to effect compression of air within a space, the compressed air usually being fed, in use, to a reservoir and thence on demand to the braking system for actuation of the latter.

The driving of such a compressor consumes a significant amount of power and thus adversely affects the fuel consumption of the driving power source which, when the compressor is used to pressurise a vehicle braking system, is usually the main vehicle engine. It is therefore desirable to drive the compressor for the minimum time required to maintain the system pressure at an acceptable level. One proposal for achieving this is to transmit drive from the drive means to the compressor element via a spring-engaged clutch and to use the compressor output pressure to overcome the spring force and disengage the clutch when said pressure attains a predetermined value, in order to interrupt drive to the compressor until the pressure falls to another predetermined value at which the spring force prevails to reengage the clutch and re-establish drive to the compressor.

It has been found difficult with such an arrangement to arrive at a satisfactory balance in terms of minimising shock loading of the compressor components upon clutch reengagement whilst providing for a desired degree of heat dissipation by the clutch. An object of the present invention is to provide an air compressor in which the compressor element is driven via a clutch and which is capable of being operated in such a manner that the aforesaid problems are alleviated or avoided.

According to the present invention, an air compressor comprises at least one compressor element operable by drive means to effect compression of air within a space, a clutch for transmitting drive from the drive means to the compressor element when compression is required, a first device operable in response to the compressor output pressure to provide a force urging the clutch into engagement in correspondence with said output pressure, thrust means for urging the clutch lightly into engagement in the absence of compressor output pressure, and a second device operable upon the attainment of a predetermined load pressure to effect disengagement of the clutch and thereby interrupt the drive in said compressor element.

Preferably, said first device is a first piston movable in a chamber to which the compressor output pressure is applied and said means for urging the clutch lightly into engagement is a spring, conveniently in the form of a stack of Belleville washers, acting on said piston and conveniently disposed within said chamber.

In a convenient practical arrangement, the second device is in the form of a second piston acting in a direction opposite to the first piston and preferably coupled to the first piston so as to move the latter in a direction to disengage the clutch upon the attainment of said predetermined load pressure.

From another aspect of the invention, an air pressure system comprises an air compressor of the invention, a reservoir connected to the compressor for charging with air under pressure therefrom via a one-way valve, a feed-back line connected to the compressor output upstream of the one-way valve and to said first device, and a governor valve connected between the reservoir and said second device and operable to apply reservoir pressure to said second device upon the attainment of said predetermined load pressure in order to disengage the clutch against the combined action of said first device and thrust means.

This manner of using the compressor of the invention is particularly advantageous in overcoming the problems discussed previously because the fact that the feed-back line is connected to the compressor output upstream of the one-way valve means that said first device is responsive to the compressor output pressure as distinct from the reservoir pressure. This enables full engagement of the clutch to occur progressively once driving of the compressor element commences by slipping engagement of the clutch under the action of said thrust means.

Prolonged clutch slip under load and consequent energy dissipation is thereby avoided, and excessive shock loading of the compressor components is also prevented.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side view, partly in cross section, of one form of the compressor of the invention, and Figure 2 is a view similar to Figure 1 of an alternative form of the compressor of the invention.

The compressor illustrated in the drawing is primarily intended for use with a vehicle airactuated braking system and comprises a housing 1 defining a cylinder 2 within which reciprocates a piston 3 coupled by a connecting rod 4 to a crankshaft 5 supported in bearings 6 mounted in the housing. As indicated by the arrows, air enters the cylinder during the induction stroke of the piston via an inlet port 7 and leaves the cylinder via an exhaust port 8, the ports being controlled by reed valves in conventional manner.

The crankshaft 5 rotatably supports one end of a drive input shaft 10, supported at its other end in a bearing 11 carried in an end cap 12 of the housing 1.

The crankshaft is driven via a multiplate clutch 13, which may be dry or oil immersed, and which includes a plurality of fixed clutch plates 1 3A nonrotatably attached to an axially extending annular portion 1 4A of a clutch member 14 fast for rotation with the crankshaft 5, the plates 1 3A being axially slidable relative to the portion 14A.

The clutch further includes a plurality of driven plates 1 3B mounted on the shaft 10 by way of splines 1 OA so as to be rotatable with the shaft 10 and axially slidable thereon.

A clutch engagement force is provided by a stack of Belleville washers 1 5 mounted within an annular space A defined partly by a fixed member 1 6 and partly by a piston 1 7 slidable within the member 16, the Belleville washers 15 acting between the member 1 6 and piston 1 7 to apply clutch engaging force to the clutch plates via a thrust bearing 9 and a specially formed end clutch plate 13AA which has an axially extending flange 1 3a upon which is mounted the thrust bearing 9.

The Belleville washers 1 5 are located around an axially extending flange 1 7a of the piston 17, the flange 1 7a surrounding a boss 1 6a of the member 1 6 which affords additional guidance for the piston 1 7. An annular piston 18 is disposed at the opposite side of the member 1 6 to the piston 17 and is carried on the shaft 10 by way of an axially extending portion 18a of the piston. A circlip 19 disposed towards the free end of the portion 1 8a couples the piston 1 8 axially to the piston 1 7 for the purpose to be described.

The drawing illustrates part of a vehicle airactuated braking system which includes a reservoir 20 coupled to the output of the compressor by a line 21. The reservoir is connected via 3 line 22 to a governor valve 23 which is in turn connected by line 24 to a chamber B within the housing 1. A branch 26 of the line 21 forms a feedback loop connected to the chamber A. The shaft 10 is continuously rotated by a power source, such as the engine of a vehicle in which the system is installed. The reservoir 20 is designed to accept a predetermined maximum safe pressure, which may typically be 11 bar.The Belleville washers 1 5 are strong enough to apply a light clutch engaging force to the clutch plates to maintain the clutch in at least slipping engagement and when the system is started up with the reservoir at substantially atmospheric pressure, the piston will be reciprocated at first relatively slowly which will have the effect of pressurising the reservoir, line 26 and chamber A so that the pressure acting on the piston 1 7 increases the clutch engaging force and thus the speed of the piston. At a predetermined pressure, the pressure in the chamber A combined with the effect of the Belleville washers 1 5 is sufficient to fully engage the clutch without slip, whereupon the crankshaft 5 is driven at the speed of the shaft 10 and the piston works at maximum effect to pressurise the reservoir 20.

When the pressure within the reservoir reaches a predetermined value, referred to as the cut-out pressure, the governor valve 23, which is responsive to the reservoir pressure, operates to apply the reservoir pressure along line 24 to the chamber B and thus to the piston 1 8. The pressure receiving surface of the piston 1 8 is large enough to provide a force sufficient to overcome the force of the Belleville washers 1 5 combined with that generated by the pressure applied via line 26 to the piston 1 7, which is of relatively small area, and the piston 1 8 exerts a pull on the piston 1 7 via the circlip 19, thereby relieving the clutch 13 of all the clutch engaging force.

Reciprocation of the piston 3 ceases and the pressure in line 26 decays, either through clearances present in the system, or through a bleed valve which may be provided in line 26 for this purpose.

Unwanted decay of pressure from the reservoir 20 is prevented by a check valve 27, but usage of the braking system will ultimately reduce the pressure in the reservoir to a predetermined cut-in pressure, at which point the governor valve operates to exhaust the pressure from the line 24 and chamber B, once more enabling light clutch engaging pressure to be applied by the Belleville washers 1 5 which is reinforced by air pressure in the feedback line 26 as rotation of the crank commences. The clutch will be fully re-engaged once more when sufficient pressure exists in chamber A, which will conveniently occur near to the cut-in pressure, since this optimises the balance obtained in terms of minimising shock loading of the compressor components whilst permitting a desired degree of heat dissipation by the clutch.

During normal operation of a vehicle in which the system is installed, the cycle will be repeated to maintain the pressure in the reservoir 20 between the cut-in and cut-out pressures.

The alternative form of the compressor of the invention shown in Figure 2 comprises a housing 100 defining a cylinder 101 within which slides a piston 103 coupled by a connecting rod 104 to a bearing 105 surrounding an accentric portion 106 of a first shaft, indicated generally at 107, whereby rotation of the shaft 107 effects reciprocal movement of the piston 103 within the cylinder. The shaft 107 is rotatable within bearings 108 of the housing 100 and an end portion of the shaft 107 forms or has secured thereto a first clutch part 109 having a partconical clutch face 110.

A second shaft 111 extends through the first shaft 107 in coaxial relationship with the rotary axis of the latter and protrudes from the shaft 107 at either end thereof. The left hand end portion of the second shaft 111, as seen in the drawing, is connected to drive means in the form of a drive input member 112 in a manner so as to be fast for rotation with the latter, the member 112 being provided with splines 113 to permit the application of input drive from a power source to the shaft 111 and also, when required, to the shaft 107 via a part-conical clutch face 11 4 complementary with the clutch face 110 and carried by a radially outwardly projecting flange 11 5 of the drive member which forms a second clutch part.

A spring 123 is disposed between one face of the piston and an opposed face of the body 100, and urges the shaft 111 to the right so as thereby to load the clutch parts 109 and 115 lightly but sufficiently firmly into engagement to enable drive to be transmitted to the piston 103. Since the shaft 111 is fast for rotation with the drive input member 112, the shaft 111 is rotated continuously, irrespective of the operative condition of the clutch and can be used to provide a continuous drive to an item of auxiliary equipment of a vehicle, such as a power steering pump for example. For this purpose, it is provided at its left hand end with a driving formation, shown as a tongue 128.By passing the second shaft 111 through the first shaft 107, not only is a compact arrangement provided by locating the clutch and piston 11 8 respectively at either end of the shaft, but it means that since the shaft 111 is supported within the shaft 107 it is effectively supported, together with the clutch assembly, by the main bearings 108 of the compressor which support the shaft 1 07. This avoids the provision of additional bearings which also contributes to compactness as well as economy of manufacture.

The right-hand end portion of the shaft 111 extends through a pressure chamber 11 6 formed in a surrounding part 117 of the body, the pressure chamber containing a piston 11 8 which is slidably mounted on the shaft 111 by way of oppositely extending axially projecting portions 119 and 120 which form bearing bushes. The shaft 111 is provided with a radial flange 121 beyond the right-hand end of the piston 116 and a thrust bearing 1 22 permits rotation of the shaft 111 whilst it is under thrust from the piston 11 8.

With the compressor installed in a braking system similar to that illustrated in Figure 1, reservoir pressure is applied via a port 1 24 into the chamber 11 6 at the left-hand side of the piston 118 and a build-up in reservoir pressure has the effect of loading the piston in a direction towards the right and thereby adding to the force of the spring 123 to urge the clutch faces more firmly into engagement. The governor valve is connected to the chamber 11 6 at the right-hand side of the piston via a port 125 and when the predetermined maximum pressure is obtained in the reservoir, the governor valve is actuated to apply reservoir pressure to the right-hand side of the piston via the port 125. The areas over which pressure is applied at the right and left hand sides respectively of the piston 118 are chosen such that application of pressure to the right-hand side of the piston is sufficient to overcome the combined forces of the pressure at the left-hand side of the piston and the spring so that the clutch faces are no longer urged firmly into engagement and drive to the shaft 7 is interrupted. When the reservoir pressure falls below its minimum permitted value, the governor valve exhausts the right-hand side of the piston, enabling the spring 27 to re-engage the clutch and the cycle recommences.

Claims (14)

1. An air compressor comprising at least one compressor element operable by drive means to effect compression of air within a space, a clutch for transmitting drive from the drive means to the compressor element when compression is required, a first device operable in response to the compressor output pressure to provide a force urging the clutch into engagement in correspondence with said output pressure, thrust means for urging the clutch lightly into engagement in the absence of compressor output pressure, and a second device operable upon the attainment of a predetermined load pressure to effect disengagement of the clutch and thereby interrupt the drive to said compressor element.

2. An air compressor according to Claim 1 wherein said first device is a first piston movable in a chamber to which the compressor output pressure is applied.

3. An air compressor according to Claim 2 wherein said means for urging the clutch lightly into engagement is a spring acting on said first piston.

4. An air compressor according to Claim 3 wherein the spring is disposed within said chamber.

5. An air compressor according to any one of the preceding claims wherein the second device is in the form of a second piston acting in a direction opposite to the first piston.

6. An air compressor according to Claim 5 wherein the second piston is coupled to the first piston so as to move the latter in a direction to disengage the clutch upon the attainment of said predetermined load pressure.

7. An air compressor according to Claim 5 or Claim 6 wherein the driven portion of the clutch is drivingly connected to a drive input shaft, and the second piston is of annular form with an axial hollow boss which serves to mount the piston on the shaft passing freely rotatably therethrough, the axial extent of the boss being such as to permit the coupling thereof to the first piston axially spaced therefrom.

8. An air compressor according to Claim 1 wherein the first and second devices are pistons which partially define respective chambers for reception of pressure fluid to actuate the associated piston, the chamber partially defined by the first piston containing a spring acting to urge the clutch lightly into engagement and the action of the spring being reinforced by the application of pressure fluid from the compressor output to the chamber partially defined by the first piston.

9. An air compressor according to Claim 8 wherein the operational area of the second piston is larger than that of the first piston by an extent such that application of said load derived pressure to the second piston is sufficient to overcome the opposing combined effects of the spring and first piston so as to move the first piston to clutchdisengagement position.

10. An air compressor according to any one of the preceding claims wherein the clutch is a multiplate friction clutch.

11. An air compressor according to Claim 1 wherein said first and second devices are oppositely facing surfaces of a common piston member each partially defining a respective pressure chamber, one of said faces being of smaller effective area than the other and acting, under pressure applied to the chamber which it partially defines, to reinforce the action of said thrust means the other face being of larger area than said one face such that load pressure applied thereto overcomes the action of the thrust means reinforced by the action of said one face.

12. An air compressor according to Claim 11 wherein the compressor element is driven by a first shaft which is fast for rotation with a first clutch part, a second clutch part is driven by a drive input shaft, the drive input shaft driving a third shaft which is arranged to be rotated continuously by the drive input shaft irrespective of whether or not the clutch is engaged.

13. An air compressor according to Claim 12 wherein the third shaft extends through the first shaft and acts as an axial force transmission member between said piston member and the clutch disposed respectively at opposite sides of the compressor element.

14. An air compressor substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

1 5. An air pressure system comprising a compressor according to any one of the preceding claims, a reservoir connected to the compressor for charging with air under pressure therefrom via a one-way valve, a feed-back line connected to the compressor output upstream of the one-way valve and to said first device, and a governor valve connected between the reservoir and said second device and operable to apply reservoir pressure to said second device upon the attainment of said predetermined load pressure in order to disengage the clutch against the combined action of said first device and thrust means.