GB2122268A

GB2122268A - Air compressor

Info

Publication number: GB2122268A
Application number: GB08314937A
Authority: GB
Inventors: Glyn Philip Reginald Farr
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-05-28
Filing date: 1983-05-31
Publication date: 1984-01-11
Also published as: GB8314937D0; GB2122268B

Abstract

An air compressor has a piston (3) for compressing air within a cylinder (2), and a clutch of which a part (15) is driven by an input member (12) and another part (9) is fast with a shaft (7) driving the piston. The clutch is normally held in engagement by a spring device (22) which acts via a shaft (11) on the clutch part (15) clutch disengagement being effected by a piston (18) under the action of compressor output pressure applied at inlet A. The shaft 11 passes through the clutch (9, 15) and shaft (7) and is continuously rotated by the drive input member (12) irrespective of the state of engagement of the clutch. <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 fuei 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 clutch and to cause the clutch to be disengaged when said pressure attains a predetermined value, in order to interrupt drive to the compressor until the pressure falls to another predetermined valve at which the clutch is caused to re-engage and thereby re-establish drive to the compressor.The compressor is therefore driven for the minimum time necessary to maintain a desired pressure level.

However, it is common practice in motor vehicles to drive other auxiliary apparatus, such as a power steering pump, from an output shaft of the compressor, and an object of the present invention is to provide a compressor in which this facility is provided in a simple and convenient manner whilst at the same time enabling drive to the compressor element to be interrupted when not required, in order to minimise power consumption.

According to the present ihvention, 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, means to disengage the clutch in response to the compressor output pressure or a load supplied thereby, and an additional drive transmission member driven in rotation by the drive means independently of said clutch whereby the additional member continues to be driven by the drive means even when the clutch is disengaged.

Conveniently, the compressor element is rotatable by a first shaft operatively associated with a first clutch part normally in driving engagement with a second clutch part rotatable by the drive means, and the drive transmission member is an additional shaft extending through the first shaft.

Preferably, the clutch is disposed at one side of the compressor element and the clutch disengagement means at the other side of said element, the additional shaft then acting in translation to transmit clutch disengagement force from said means to the clutch, conveniently to the second clutch part.

In one typical practical arrangement, the compressor element is a piston reciprocable in a cylinder by an eccentric portion of the first shaft, the additional shaft extending through the eccentric portion and being co-axial with the rotary axis of the first shaft.

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 broken away of one form of the compressor of the invention, and Figure 2 is a view, similar to Figure 1, of an alternative embodiment of the compressor of the invention.

The compressor illustrated in Figure 1 is primarily intended for use with a vehicle airactuated braking system and comprises a housing 1 defining a cylinder 2 within which slides a piston 3 coupled by a connecting rod 4 to a bearing 5 surrounding an eccentric portion 6 of a first shaft, indicated generally at 7, whereby rotation of the shaft 7 effects reciprocal movement of the piston 3 within the cylinder. The shaft 7 is rotatable within bearings 8 of the housing 1 and an end portion of the shaft 7 forms or has secured thereto a first clutch part 9 having a part-conical clutch face 10.

A second shaft 11 extends through the first shaft 7 in co-axial relationship with the rotary axis of the latter and protrudes from the shaft 7 at either end thereof. The left hand end portion of the second shaft 11, as seen in the drawing, is connected to drive means in the form of a drive input member 12 in a manner so as to be fast for rDtation with the latter, the member 12 being provided with splines 1 3 to permit the application of input drive from a power source to the shaft 11 and also, when required, to the shaft 7 via a part conicai clutch face 14 complementary with the clutch face 10 and carried by a radially outwardly projecting flange 15 of the drive member which forms a second clutch part.

The right hand end of the shaft 11 extends through a pressure chamber 1 6 formed in a surrounding part 1 7 of the body, the pressure chamber containing a piston 1 8 which is slidably mounted on the shaft 11 by way of an axially projecting portion 1 9 which forms a bearing bush.

The shaft 11 is provided, within the chamber 16, with a radial flange 20, between which and an opposing face of the piston 1 8 is located a thrust bearing 21. A stack of Belleville washers 22 is disposed between the opposite face of the flange 20 and a further thrust bearing 23 which engages a facing end of the shaft 7, the effect of the washers being to urge the shaft 11 to the right and thereby load the clutch parts 9 and 1 5 into firm driving engagement.

The shaft 11 is continuously rotated by a power source, such as the engine of a vehicle in which the compressor is installed, via a belt and pulley applied to the splines 13, the shaft 11 being provided with a drive tongue 24, or similar means, enabling it to be connected to an item of auxiliary equipment of a vehicle which requires continuous operation, such as a power steering pump for example. When the- compressor is installed in a vehicle braking system, the cylinder 2 is connected, in a typical arrangement, to a storage reservoir, (not shown) from which actuating pressure for a braking system may be derived as required.Pumping is effected by the piston in conjunction with inlet and exhaust valves which operate in timed synchronism with the piston in known manner to permit pressure to be built-up in the cylinder and discharged to the reservoir. The reservoir is designed to accept a predetermined maximum safe pressure, which may typically be 11 bar, and is connected to a conventional governor valve (not shown) which may be of a diaphragm or piston type as will be familiar to those versed in the art.The governor valve is arranged to operate, upon the attainment of the aforesaid maximum pressure in the reservoir, to supply reservoir pressure via an inlet A to the chamber 1 6 at the right hand side of the piston 18, which is caused to move to the left compressing the Belleville washers 22 and thereby disengaging the clutch parts 9 and 1 5 to interrupt the drive from the drive input member 12 to the shaft 7 so that the piston 3 ceases to reciprocate. The inner shaft 11 continued to rotate, providing continued drive, if required, to the aforesaid auxiliary equipment via the tongue 24 or other drive means.When the reservoir pressure falls to a lower predetermined value, typically 9 bar, the governor valve operates to exhaust air from behind the piston 1 8 to atmosphere enabling the Belleville washers to reengage the clutch parts 9 and 1 5 so that the shaft 7 is once again driven from the drive means to recommence pressurising of the reservoir. This cycle is able to continue automatically as the pressure in the reservoir rises and falls.

In order to avoid applying a sudden high torque through the clutch parts upon their reengagement to drive the shaft 7, it is desirable to hold open an inlet valve of the cylinder as the cycle recommences to minimise the resistance to movement of the piston. This can be achieved by using the reservoir pressure applied to the piston 1 8 to act, via a restrictor, on a unloader valve (not shown) which acts to open the inlet valve of the cylinder to prevent compression.The restrictor would provide the necessary delay in the build-up of pressure in the unloader valve to ensure that the inlet valve is not held open until compression has ceased, and conversely to effect slow decay of pressure from the unloader valve after reservoir pressure has been removed from the piston 18, to ensure that the piston is accelerated towards its working speed before the inlet valve is allowed to close.

Figure 2 illustrates an alternative embodiment of the compressor of the invention which differs in the manner in which loading and unloading of the clutch is effected. The principal parts of the compressor are identical to those of Figure 1 and only those parts which differ are described in detaii. The shaft 11 is provided with a radial flange 25 beyond the right hand end of the piston 1 8 and a thrust bearing 26 permits rotation of the shaft 11 whilst it is under thrust from the piston 1 8. The shaft 11 is axially fast with the input member 12 and a spring 27 lightly urges the piston 18 to the right and thereby, via the shaft 11, urges the clutch faces 10 and 14 into engagement sufficiently firmly to enable drive to be transmitted to the piston 3.Reservoir pressure is applied via a port 28 into the chamber 16 at the left hand side of the piston 1 8 and a build-up in reservoir pressure has the effect of loading the piston in a direction towards the right and thereby urging the clutch faces more firmly into engagement. The governor valve is connected to the chamber 1 6 at the right hand side of the piston 18 via a port 29 and when the predetermined maximum pressure is obtained in the reservoir, the governor valve is actuated to apply reservoir pressure to the right side of the piston.The areas over which pressure is applied at the right and left hand sides respectively of the position 1 8 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.

By passing the second shaft 11 through the first shaft 7, not only is a compact arrangement provided by locating the clutch and piston 1 8 respectively at either end of the shaft, but it means that since the shaft 11 is supported within the shaft 7 it is effectively supported, together with the clutch assembly, by the main bearings 8 of the compressor which support the shaft 7. This avoids the provision of additional bearings which also contributes to compactness as weli as economy of manufacture. The invention also provides a simple and convenient means of interrupting drive to the compressor when not required whiist permitting continuous drive to be applied via the shaft 11 to auxiliary equipment.

Claims

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, means to disengage the clutch in response to the compressor output pressure or a load supplied thereby, and an additional drive transmission member driven in rotation by the drive means independently of said clutch whereby the additional member continues to be driven by the drive means even when the clutch is disengaged.

2. An air compressor according to Claim 1 wherein the compressor element is rotatable by a first shaft operatively associated with a first clutch part normally in driving engagement with a second clutch part rotatable by the drive means, and the drive transmission member is an additional shaft extending through the first shaft.

3. An air compressor according to Claim 2 wherein the clutch is disposed at one side of the compressor element and the clutch disengagement means at the other side of said element, the additional shaft then acting in translation to transmit clutch disengagement force from said means to the clutch.

4. An air compressor according to Claim 2 or Claim 3 wherein the compressor element is a piston reciprocable in a cylinder by an eccentric portion of the first shaft, the additional shaft extending through the eccentric portion and being co-axial with the rotary axis of the first shaft.

5. An air compressor according to Claim 2 wherein the clutch disengagement means is a piston and cylinder device at the side of the compressor element remote from the drive means, the additional shaft being operatively coupled to the piston and cylinder device in such a manner as to transmit clutch disengagement force in translation to the clutch whilst rotating under the action of the drive means.

6. An air compressor according to Claim 5 wherein thrust means are arranged to act on said additional shaft in opposition to said piston and cylinder device whereby the force of the thrust means is transmitted by that shaft to the clutch to maintain the clutch lightly in engagement when said piston and cylinder device is inoperative.

7. An air compressor according to Claim 5 or Claim 6 wherein the additional shaft passes through said piston and cylinder device and is provided with a radial flange, one side of which is acted upon by said thrust means and the other side by the piston and cylinder device.

8. An air compressor according to Claim 7 wherein the piston of the piston and cylinder device may be subject alternatively to pressure at either side thereof so that it either reinforces or opposes the action of said thrust means, the opposed sides of the piston being of unequal area arranged so that pressure supplied to the smaller side reinforces the action of the thrust means and the same or a similar pressure applied to the larger area is able to overcome the reinforced action of the thrust means to disengage the clutch:

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