GB2070698A

GB2070698A - Improvements in and relating to apparatus for producing compressed air

Info

Publication number: GB2070698A
Application number: GB8100663A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1980-01-12
Filing date: 1981-01-09
Publication date: 1981-09-09
Also published as: GB2070698B; DE3001034A1; FR2473648A1

Abstract

A piston compressor 1 has an associated pressure-operated device 3 arranged to connect an additional chamber 8 to the clearance volume 11 of the compressor when a preset pressure level is reached in a reservoir 2 in order to provide pressure stabilisation. The device 3 includes a piston 5 movable by reservoir pressure against a biassing spring 16 to connect the additional chamber 8 (in the form of a groove 24, 25 in the piston 5) via a groove 9 and a pipe 12 to the clearance volume 11. <IMAGE>

Description

SPECIFICATION Improvements in and relating to apparatus for producing compressed air The invention relates to apparatus for producing compressed air which apparatus is especially suitable for use in vehicle compressed air brake systems.

The maximum pressure level in a compressed air producing apparatus is generally determined by means of the cut-off pressure of a pressure regulator or, when using a selfstabilising air compressor, by the stabilising pressure of the air compressor, with the stabilising pressure being determined by the ratio of the swept volume to the clearance space, that is, the space remaining above the piston when the latter is in its highest position.

In a brochure "From our development programme 1971" published by WABCO Fahrzeugbremsen GmbH, self-stabilising air compressors are described, and in these air compressors, a volume of air drawn in is compressed during the upward movement of a piston in the normal way, and air is supplied for as long as the compression pressure in the cylinder exceeds the counter-pressure in the system which may include an air reservoir. No air is supplied when the pressure in the system is equal to that available from the air compressor. If the compressor is now allowed to continue runnning there is no further pressure increase in the system at each compression stroke. The stabilised state or the stabilising pressure has been reached. In this state there is almost no more work performed, since the compression work is recovered on expansion.The supply pressure closes the pressure valve and the air in the cylinder is alternately expanded and compressed. Only mechanical friction energy and air losses must be made up.

A principle generally used in self-stabilising air compressors is that of controlled lengthening of the cylinder or, in general terms, reduction of the compression ratio in order to provide a selected final pressure at which air is no longer supplied to the system.

Application of this principle leads to lengthened construction of the cylinder and impairment of the delivery rate so that this measure also produces relatively long filling times. A known alternative is the installation of a pressure regulator which, when a particular pressure is reached, switches the air compressor to idle running, in which condition the counter-pressure is no longer that of a closed system, but is atmospheric pressure to which the compressor is connected intermittently.

When air delivery is switched off or switched into the atmosphere unpleasant noises are produced as a result of the release of residual pressure.

In high pressure systems there arises the problem of pressure pipe temperature rise resulting from high cut-off pressure. This problem is suitable for solution by means of self-stabilising air compressors.

Known high pressure system solutions are expensive and, when air delivery is switched off or switched into the atmosphere particularly unpleasant noises are produced. It will be evident from the above that each known compressor arrangement has at least one undesirable feature and could be improved.

It is an object of the present invention to provide improved compressed air producing apparatus.

According to the invention, apparatus for producing compressed air includes: a) piston compressor means having a piston movable in a compression chamber, b) compressed air storage means connected to the piston compressor means and, c) pressure-controlled connection means connected to the storage means arranged, when the storage means pressure reaches a preset level, to increase the clearance volume of the compression chamber.

Preferably, the pressure-controlled connection means includes a valve by way of which the clearance volume of the compression chamber is connectable to an additional volume.

Preferably, the pressure-controlled connection means includes: (a) a piston which is arranged in a cylinder housing and which has a working face communicating with a control port, (b) an internal enclosure formed by the piston and the cylinder wall, (c) an inlet port in the cylinder wall, (d) spring means arranged to bias the piston to a rest position at which the inlet port is isolated from the internal enclosure, the piston being movable by a force applied at its working face to a position at which the inlet port is connected to the internal enclosure.

Preferably, sealing rings located on the piston are arranged, in the rest position, to seal off the inlet port from the internal enclosure and from a swept space.

Preferably, the cylinder housing includes a vent port for the swept space which accommodates the spring means.

Preferably, the cylinder housing inludes a vent port arranged to be connected to the internal enclosure when the piston is in the rest position.

Preferably, in the internal enclosure, the surface which can be acted upon in the switching direction of the piston is greater than the surface lying opposite.

Preferably, the increase in the clearance volume of the air compressor means is provided by the internal enclosure and a further enclosure connectable to the internal enclosure by movement of the piston.

Preferably, the internal enclosure is annular.

Preferably, the pressure-controlled connection means is attachable to the air compressor means.

Alternatively, the pressure-controlled connection means is built into the air compressor means.

Pressure-controlled connection means, adapted to provide an increase in volume in apparatus according to the invention, is provided by the invention.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a diagram of a compressed air producing apparatus with a valve arranged to switch in a clearance volume at a predetermined pressure and, Figure 2 is a diagram of another valve arranged to switch in a volume and suitable for air producing apparatus as shown in Fig.

1.

Compressed air producing apparatus according to Fig. 1 consists of an air compressor 1 and a compressed air tank 2, between which is connected a valve 3. The valve 3 is arranged to switch in a clearance volume. A piston 5 arranged in the housing 4 of the switching valve 3 can be acted upon by the pressure of the supply tank 2 by way of a connection 7 and a pipeline 6. A waist in the piston 5 forms, with the wall of the housing 4, an annular chamber 8. When the piston 5 is in the lower position the annular chamber 8 is connected by way of a control groove 9, a connection 10 and a pipeline 1 2 to the clearance volume 11 (compression chamber) of the air compressor 1.Sealing rings 1 3 and 14 on the piston 5 seal off the chamber 8 in the direction of the connection 7, and a sealing ring 1 5 is provided as a seal between the chamber 8 and the control groove 9 and/or the connection 10. Beneath the piston 5 there is a compression spring 16, the action of which is opposed to downward movement of the piston 5.

The space 17 accommodating the spring 1 6 is provided with a venting aperture 1 8. A further sealing ring 1 9 seals off the control groove 9 and/or the connection 10 in the direction of the space 1 7 or the atmosphere.

When the required operating pressure is reached in the tank 2, this pressure, by acting upon the piston 5 at its surface 19, overcomes the spring 16. The piston 5 then moves downwards until the seal '15 comes into the region of the control groove 9. Connection then exists between the chamber 8 and the clearance volume 11 by way of the connection 10 and the pipeline 1 2. A connection 20 may be provided for this purpose.

In this way there is an increase in the air compressor 1, in the clearance volume above the piston 21 in the upper position, the result being that there is now a particular ratio of swept volume to clearance volume which determines the stabilising pressure. Air delivery is interrupted and the outlet valve or pressure valve 22 of the air compressor 1 acts as a non-return valve. If the pressure in the supply tank 2 drops, the force of the spring 1 6 pushes the piston 5 upwards again and the sealing ring 1 5 blocks the connection 9, 10, 1 2 with the air compressor 1. The chamber 8 vents into the atmosphere by way of an opening 23.

The sealing ring 1 5 is prevented from remaining in contact with the housing 4 in the region of the control groove 9 when the piston 5 is in the lower position in which the chamber 8 is connected with the clearance volume 11, because fluttering movements of the piston 5 could lead to rapid wear on the sealing ring 1 5. The annular piston surface 24 of the chamber 8 on the side of the spring 1 6 is slightly larger than the opposite annular surface 25 away from the spring 1 6, so that the pressure which builds up after the chamber 8 is connected with the clearance volume 11 moves the piston 5 further downwards against the spring 1 6 so that the contact between the sealing ring 1 5 and the housing 4 in the region of the control groove 9 is released.

The valve embodiment shown in Fig. 2 has the same reference numbers as that in Fig. 1 where the components referred to are the same in both embodiments. The components which have necessarily been changed due to the provision of an additional volume adjacent to the cylinder bore of the piston 5a are provided with a suffix a in addition to the same reference numbers.

It can be seen that an additional volume 26, formed by a separate bore in the housing, is connected by means of a housing borehole 27 with an annular chamber 8a of a piston 5a. A surface 24a of the piston 5a here forms the surface which is acted upon to release the seal 1 5 from the area of contact with the housing 3a in the region of the control groove 9.

In each case an additional clearance volume which lies outside the cylinder is switched in by the switching valve only when the operating pressure is reached. Filling of the supply tank takes place with the optimum compres-, sion ratio until this extra clearance volume is switched in. The subsequent sudden reduction of the compression ratio, which is deliberate, leads to the self-stabilising effect which is required at this point, and this is of particular advantage for high pressure systems.

Claims

1. Apparatus for producing compressed air, including: a) piston compressor means having a piston movable in a compression chamber, b) compressed air storage means con nected to the piston compressor means and, c) pressure-controlled connection means connected to the storage means arranged, when the storage means pressure reaches a preset level, to increase the clearance volume of the compression chamber.

2. Apparatus according to Claim 1, wherein the pressure-controlled connection means includes a valve by way of which the clearance volume of the compression chamber is connectable to an additional volume.

3. Apparatus according to claim 1 or 2, in which the pressure-controlled connection means includes: (a) a piston which is arranged in a cylinder housing and which has a working face communicating with a control port {b) an internal enclosure formed by the piston and the cylinder wall, (c) an inlet port in the cylinder wall, (d) spring means arranged to bias the piston to a rest position at which the inlet port is isolated from the internal enclosure, the piston being movable by a force applied at its working face to a position at which the inlet port is connected to the internal enclosure.

4. Apparatus according to claim 3, wherein sealing rings located on the piston are arranged, in the rest position, to seal off the inlet port from the internal enclosure and from a swept space.

5. Apparatus according to claim 4, wherein the cylinder housing includes a vent port for the swept space which accommodates the spring means.

6. Apparatus according to any one of claims 3 to 5, wherein the cylinder housing includes a vent port arranged to be connected to the internal enclosure when the piston is in the rest position.

7. Apparatus according to any one of claims 3 to 6, wherein, in the internal enclosure, the surface which can be acted upon in the switching direction of the piston is greater than the surface lying opposite.

8. Apparatus according to any one of the preceding claims, wherein the increase in the clearance volume of the air compressor means is provided by the internal enclosure and a further enclosure connectable to the internal enclosure by movement of the piston.

9. Apparatus according to any one of the preceding claims, wherein the internal enclosure is annular.

10. Apparatus according to any one of claims 1 to 9, wherein the pressure-controlled connection means is attachabie to the air compressor means.

11. Apparatus according to any one of claims 1 to 9, wherein the pressure-controlled connection means is built into the air compressor means.

1 2. Apparatus for producing compressed air, substantially as herein described with reference to and as illustrated by Fig. 1 of the accompanying drawings.

1 3. Pressure-controlled connection means adapted to provide an increase in volume in apparatus as claimed in any one of claims 1 to 10.

14. Pressure-controlled connections means adapted to provide an increase in volume, substantially as herein described with reference to and as illustrated by Fig. 1 of the accompanying drawings.

1 5. Pressure-controlled connection means adapted to provide an increase in volume, substantially as herein described with reference to and as illustrated by Fig. 2 of the accompanying drawings.

1 6. A vehicle including apparatus for producing compressed air as claimed in any one of claims 1 to 1 2.