GB2188682A 1
SPECIFICATION decrease the volume of a compression chamber 6 of which the piston 2 forms one wall. Improvements relating to gas compressors The compressor is also conveniently provided with a valve plate 7 carrying a delivery reed 5 This invention relates to gas compressors and 70 valve 8 and an inlet reed valve 9. The delivery relates more especially to air compressors reed valve 8 provides one way communication fitted with unloader valves which when sig- from the compression chamber 6 through the nalled operates to connect a compression valve plate to a delivery port 10 of a cylinder chamber to atmosphere. head 11 and the inlet valve 9 provides one
In air compressors of a type fitted to and 75 way communication between a induction or driven by heavy vehicle engines for supplying inlet chamber 12 through a passage 13 in the compressed air to reservoirs of compressed valve plate. The cylinder head and valve plate air braking systems, it is common to fit an are assembled to the cylinder by conventional unloader valve signalled in response to a de- bolts denoted by ref. 14. The cylinder head is sired reservoir pressure being attained for confurther provided with an unloader valve illus- necting the compression chamber to atmos- trated on a larger scale in Fig. 2 and compris phere. Typically, such a valve is fitted in the ing a valve member 15 sealingly slideable in a cylinder head of a piston and cylinder com- bore 16 to open and close a passage 17 pressor and arranged to open when signalled between the compression chamber 6 and the to connect the compression chamber to the 85 inlet chamber 12. This valve member has an inlet chamber so as to interrupt supply of annular pressure responsive area 23 wubject compressed air to a delivery port to the reser- to control pressure at a control port 27 acting voirs. In such compressors it has been found in a sense to overcome the bias of a spring that undue heating has occurred and the ob18 when a desired reservoir pressure is at ject of the present invention is to reduce such 90 tained. Additionally, the pressure responsive heating. member is provided with an internal passage According to the present invention there is way 19 which communicates with a further provided a gas compressor comprising a reci- area 20 located to act in a sense to enhance procating member forming a movable wall of the bias of spring 18 in the presence of pres a compression chamber for cycliely increasing 95 sure in the chamber 6. The whole assembly and decreasing the volume thereof to induce of the unloader valve is held together by a and deliver compressed gas to a delivery port, vented closure member 21 located in the cyl an unloader valve having a biassed valve inder head by an internal circlip 22. The clo member acting in a sense to close a vent sure member 21 being provided with a spigot aperture communicating with said chamber 100 25 having an annular seal 23 upon which the said unloader valve being operable by a fluid valve member is sealingly slideable.
pressure signal acting on a pressure respon- Considering the operation of the compressor sive area in a sense to counteract the bias and the included unloader valve when the and having a further area subject to the pres- pressure in the reservoir or reservoirs being sure in said chamber acting in a sense to 105 supplied via the delivery port 10 has attained enhance the bias. a desired pressure value this pressure applied In a preferred embodiment of the invention to the control port 27 and acting on the pres said further pressure area is at least as large sure responsive annular control area 24 of the as the area presented to the pressure in said unloader valve is sufficient to lift the valve chamber by the valve member in the closed 110 member 15 against the bias of spring 18. The position thereof. vent passage 17 is therefore uncovered and In order that the invention may be more the compression chamber 6 is connected to clearly understood and readily carried into ef- the inlet chamber 12 which is at approxi fect the same will be further described by mately atmospheric pressure. On a downward way of example with reference to the accom- 115 stroke of the piston 2 whilst air induced via panying drawing of which, the inlet valve on the next compression stroke Figure 1 illustrates a part sectional perspec- of the piston 2 this air is expelled with mini tive view of a single cylinder piston air com- mum energy absorption via the open passage pressor and, 17.
Figure 2 illustrates an unloader valve on an 120 Ignoring for the present the inner area 20 enlarged scale. which assists the bias by being connected to Referring to Fig. 1, this illustrates the upper the compression chamber, and assuming a part of a single cylinder piston-type air com- small control signal pressure drop occurs at pressor, with the crankcase and crankshaft as- the control port 27, the unloader valve tends sembly not shown. The crankshaft is commu- 125 to close during induction strokes but to par- nicated via a connecting rod, the upper end of tially open on compression strokes, such which is indicated by reference 1, pivotally opening being caused by recovering reservoir connected to a piston 2 via a gudgeon pin 3. pressure enhanced by compression chamber The piston 2 is thereby reciprocable in a bore pressure acting on the valve closure area of 4 of a cylinder 5 alternatively to increase and 130 17. The result of this partial opening can be_ 2 GB2188682A 2 substantial energy dissipation and over heating. By including the additional area subject to the compression chamber pressure and effective in a sense to enhance the bias on the unloader valve, such over heating can be appreciably reduced or prevented. Preferably the additional area 20 is at least as large as the area of the valve member covering the vent passage 17 which is subject to compres- sion chamber pressure in the closed position thereof.
1. A gas compressor comprising a recipro- cating member forming a movable wall of a compression chamber for cyclicly increasing and decreasing the volume thereof to induce and deliver compressed gas to a delivery port, an unloader valve having a biassed valve member acting in a sense to close a vent aperture communicating with said chamber said unloader valve being operable by a fluid pressure signal acting on a pressure responsive area in a sense to counteract the bias and having a further area subject to the pressure in said chamber acting in a sense to enhance the bias.
2. A gas compressor as claimed in claim 1 wherein said further area is at least as large as the area presented by the valve member to the pressure in said chamber in the closed position thereof.
3. A gas compressor substantially as described herein with reference to Fig. 1 and Fig. 2 of the accompanying drawing.
Frinted for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained.