GB2044365A

GB2044365A - Cylinder Head for Multi-stage Air Compressor

Info

Publication number: GB2044365A
Application number: GB8005197A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1979-02-15
Filing date: 1980-02-15
Publication date: 1980-10-15
Also published as: GB2044365B; FR2449211A1; DE2905720A1; FR2449211B1

Abstract

A cylinder head for a compressor having a pre-compression stage 23 and a high pressure stage 24 has a pressure chamber 5 for receiving pressurized fluid from the pre- compression stage and delivering it to the high pressure stage and, to cool down the pressurized fluid before it enters the high pressure stage, a coolant space 2, 3 surrounds the pressure chamber 5. Advantageously, parallel paths are provided for the flow of coolant through the coolant space. <IMAGE>

Description

SPECIFICATION Cylinder Head for Multi-stage Air Compressor The invention relates to compressors and, in particular to a cylinder head for a multi-stage compressor.

The ever-increasing demand for compressed air in vehicle air brake systems and also for socalled secondary users (i.e. sudsidiary systems using the same compressed air supply) necessitates a correspondingly greater volume for the compressed air tanks. However, since the installation of more or larger compressed air tanks is limited by the amount of space available in a vehicle it has been necessary to consider reducing the volume of the tanks by incrnasingthe delivery pressure and to reduce the size of brake cylinders by raising the brake operating pressure.

Experiments showed that, in the case of a conventional braking system with a delivery pressure of approx. 8 bar, increasing the delivery pressure to approx. 1 8 bar with the same output capacity enables tank volume to be reduced to 50 to 60% of its original size or, in other terms, the output capacity of an existing conventional system with a given tank volume can be increased by making a changeover to a high pressure system. This is of particular use if a large storage capacity is required, e.g. in the case of vehicles which have to carry out lifting and lowering operations with pneumatic spring systems in order to change skips or, as a further example, when buses with a high compressed air consumption for secondary users are equipped with a blocking protection system.

At present, delivery pressures of approx. 18 bar are obtained with single-stage single-cylinder air compressors but, with a high delivery pressure, high temperature in the pressure pipes is also reached. If it is required to use delivery pressures which exceed this figure (for example because of the special working conditions of a vehicle) or if it is required to reduce the pressure pipe temperature or to raise the volumetric efficiency, then the use of multi-stage air compressors become necessary.

For vehicle braking systems and the secondary users in the vehicle, it is generally sufficient to provide 2-stage air compressors which consist of a pre-compressor stage and a high pressure stage. The air which is pre-compressed to an intermediate pressure in the first stage is led into the compression chamber of the second stage and there compressed to the required final pressure.

It is absolutely essential, in order to avoid high pressure pipe temperatures, that the precompressed air (which will be at a very high temperature) is cooled down before entering the compression chamber of the second stage, and this makes it necessary to provide an intermediate cooling system. The provision of a cooling system of this type may, however, raise certian difficulties since the cost of parts and fitting is correspondingly high and also, as mentioned at the beginning, the amount of space available in vehicles is severly limited.

German Patent No. 867,894 describes intermediate cooling systems for multi-stage air compressors in which cooling elements consisting of tubular coils are arranged in a waterjacket surrounding the cylinder. This solution is comparatively complex and expensive and increases considerably the dimensions of the air compressor. In addition, access for cleaning and repairs is very difficult, and the cooling effect in the region of the cylinder is not optimun.

Furthermore, arrangements such as those described for example in German Patent No. 11 89 673 are known, being equipped with a special, very extensive cooling system consisting of cooling tubes, which has to be built in front of the cylinder housing of the air compressor, screwed to the latter and connected by means of pipelines. This solution is also costly and takes up a great deal of space, and this also applies to aircooled tubular coils which are also arranged outside the air compressor and connected by means of pipelines.

The problem with which the present invention is concerned is that of creating an intermediate cooling system which, utilising an existing cooling source, can be so arranged that little or no addition space is taken up; which need not entail substantial cost; which can be comparatively easy to repair and/or maintain, and which enables intensive cooling to be provided.

The present invention provides a cylinder head for a multi-stage compressor having at least a pre-compression stage and a high pressure stage; the cylinder head having intake and output chambers for the compressor, coolant space for the pre-compression and high pressure stages, and a pressure chamber for receiving pressurized fluid from the precompression stage and delivering pressurized fluid to the high pressure stage; the pressure chamber extending over substantially the whole width of the cylinder head and being surrounded by the coolant space, with the outer surface of the wall of the pressure chamber being in direct contact with the coolant space to transfer heat to the coolant space from pressurized fluid in the pressure chamber.

Advantageously, parallel paths are provided for the flow of coolant through the coolant space.

By way of example a cylinder head constructed according to the invention for a 2-stage air compressor is described hereinafter with reference to the attached Figures, in which: Fig. 1 shows a cross-section through the cylinder head, along the line B-B shown in Figs.

2 and 3; Fig. 2 shows a longitudinal section through the 1 st compression stage (low pressure) of the cylinder head, along the line A-A in Fig. 1; and Fig. 3 shows a longitudinal section through the 2nd compression stage (high pressure) of the cylinder head, along the line C-C in Fig. 1.

The cylinder head 1 is divided up into a coolant space 2 and 3, and an air space consisting of an intake chamber 4, a pressure chamber 5 and a high pressure output chamber 6.

The coolant space 2 and 3 is connected by way of connections 7 and 8 to a cooling system, for example the cooling system of the engine, and the coolant flow within the cylinder head from the inlet connection is divided up into two parallel streams by means of a throttle or diaphragm 9.

The coolant employed may be water, oil, air or any other suitable substance.

An air intake connection 10 of the intake chamber 4 produces the connection to the atmosphere and the users are provided with compressed air by way of a pressure connection 11 of the output chamber 6. A valve plate 1 5 is arranged between the cylinder housing 14 and the cylinder head 1, and intake holes 12 and pressure holes 1 3 in the valve plate, with associated multi-plate intake valve 1 6 and multiplate pressure valve 1 7 respectively, provide a path from the air intake chamber 4 to the pressure chamber 5 via the cylinder of the first compression stage.The pressure chamber 5 extends over the full width of the cylinder head, and a path from the pressure chamber 5 to the output chamber 6 via the cylinder of the second compression stage is produced by way of intake holes 18 and pressure holes 19 in the valve plate 1 5 with associated plate valves 20 and 21, respectively.

The intermediate cooling arrangement for the air pre-compressed in the low pressure stage extends over the full width of the cylinder head 1 and comprises the coolant space 2 and 3 which surrounds the entire pressure chamber 5 and simultaneously serves to cool the cylinder head.

The entire outer surface of the wall 25 of the chamber 5 is in direct contact with the coolant space and, in addition, heat dissipation is considerably assisted by means of ribs 22 projecting into the pressure chamber 5 (Figs. 2 and 3).

The method of operation of the 2-stage air compressor with the cylinder head described above is as follows: By way of a filter which is not shown, air is taken in from the atmosphere and passes by way of the connection into the intake chamber 4. When the piston 23 in the cylinder of the first compression stage moves downwards, air is drawn in by way of the intake holes 1 2 through the opening multiplate intake valve 1 6 and when the piston moves upwards the air is compressed in the compression chamber between the top of the piston and the underside of the valve plate 1 5 and then forced into the pressure chamber 5 by way of the pressure holes 13 and the opening multi-plate pressure valve 1 7. The multi-plate intake valve 1 6 which closes itself automatically prevents the compressed air from flowing back into the atmosphere. In the pressure chamber 5 which extends over the full width of the cylinder head, a heat exchange now takes place by way of the walls and the cooling ribs 22 with the coolant in the space 2 and 3 which surrounds the pressure chamber 5 over the whole width of the cylinder head.

Downward movement of the piston 24 in the cylinder of the second compression stage draws the pre-compressed and intermediately cooled air through the intake holes 1 8 and the opening plate valve 20 into the compression chamber which lies between the piston 24 and the valve plate 15. The air is then compressed to its final pressure by upward movement of the piston 24 and is forced, by way of the pressure holes 19 and the opening plate valve 21 into the output chamber 6, with the plate valve 20 closing itself to prevent the compressed air from flowing back into the pressure chamber 5. By way of the connection 11, the air compressed at a high pressure passes to the users or to one or more compressed air tanks (not shown).

The cooling arrangement of the cylinder head described above enables intensive cooling to be achieved. This is due to the fact that the highest component temperatures are produced in the cylinder head in the region of the low pressure chamber 5 and there is, therefore, a high At (temperature differential) between component temperature and coolant temperature. A high At results in good heat dissipation.

In addition, the flow of coolant round the pressure chamber 5 is veryintensive. This is made possible by the fact that although there is only one coolant inlet and one coolant outlet, two parallel coolant flows are provided within the cylinder head space.

Preferably, all the channels conducting the coolant are arranged in such a way that they rise towards the coolant outiet; in this way, when using fluid coolants, any air which may be present is eliminated.

Claims

1. A cylinder head for a multi-stage compressor having at least a pre-compression stage and a high pressure stage; the cylinder head having intake and output chambers for the compressor, coolant space for the precompression and high pressure stages, and a pressure chamber for receiving pressurized fluid from the pre-compression stage and delivering pressurized fluid to the high pressure stage; the pressure chamber extending over substantially the whole width of the cylinder head and being surrounded by the coolant space, with the outer surface of the wall of the pressure chamber being in direct contact with the coolant space to transfer heat to the coolant space from pressurized fluid in the pressure chamber.

2. A cylinder head as claimed in claim 1, in which the intake and output chambers and coolant space are defined by walls of the cylinder head.

3. A cylinder head as claimed in claim 1 or claim 2, in which the intake and output chambers and/or coolant space are defined by walls of the cylinder head and the valve plate.

4. A cylinder head as claimed in any one of the preceding claims in which the wall of the pressure chamber is provided with ribs projecting into the pressure chamber.

5. A cylinder head as claimed in any one of the preceding claims, in which parallel paths are provided for the flow of coolant through the coolant space.

6. A cylinder head as claimed in claim 5, in which, to produce the parallel paths, a diaphragm or throttle is arranged in the coolant space.

7. A cylinder head for a compressor, the cylinder head being substantially as described herein with reference to, and as shown in, the accompanying drawings.