GB2187801A - Lubricating compressors - Google Patents

Abstract

A single cylinder air compressor is provided with a valve arrangement in the crankcase which impedes breathing of the crankcase during induction strokes to create crankcase pressure elevations to expel lubricating oil from a low point of the crankcase via the small passage 18. This is achieved by using the crankweb counterweight 21 as a blocking means for breather passage 19. The face 20 of the counterweight obscures passage 19 during inductor, thus raising the crankcase pressure. This restricts the oil accumulating in the crankcase to the level of the inner end of passage 18. <IMAGE>

Description

GB 2 187 801 A 1

SPECIFICATION dance with the invention and,

Figure 2 illustrates a side view thereof.

Gas compressors Referring to Fig. 1 a single cylinder piston compressor shown in sectional form therein This invention relates to gas compressors and 70 comprises a cylinder and crankcase casting 1 relates more particularly to gas compressors provided with a valve plate 2 and a cylinder which utilise a reciprocating piston in a cylin- head 3. The casting 1 has a cylinder bore 4 der. within which a piston 5 is reciprocated by A common form of gas compressor relies means of a crankshaft 6 connected to the upon one or more reciprocating pistons in a 75 piston via a connecting rod 7 and a gudgeon cylinder. Such gas compressors are used to pin 8. The crankshaft is rotatable in respective charge reservoirs of compressed air braking bearings 9 and 10 which are pressure fed systems of heavy road vehicles. The of such from the right-hand end of the crankcase compressors are usually lubricated by oil un- wherein an oil pressure chamber 11 is pro der pressure from the vehicle engine lubrica- 80 vided, this chamber being pressure fed with tion system and one problem encountered is oil from an engine onto which the compressor that accumulation of oil drained into the com- is mounted onto a suitable flange 12. The pressor crankcase from the bearings can inner end 13 of the crankshaft is suitably pro cause over-lubrication of the cylinder bores vided with a drive pinnion (not shown) en and resultant oil carry-over into the system 85 gageable with a suitable gear train in the can be excessive. Such oil carry-over can be crankcase of the engine.

detrimental to the system and is preferably to The oil ways providing connection between be removed or prevented. One obvious way the oil chamber 11 and the big- end bearing to reduce such oil carry-over is to limit the and the left hand main bearing are denoted by flow of oil to the compressor bearings but 90 broken outlines 14 and 15, and it will be ap this can seriously impair the working life of preciated that in operation oil flow leakage will the compressor. run down into the lower part of the crankcase The present invention seeks to provide an which is shown to be closed by a suitable improved gas compressor wherein oil carry- cover plate 16 and as shown in Fig. 1 (also over can be substantially reduced without un- 95 as a dotted outline in Fig. 2), there is pro desirably reducing the oil flow to the bearings. vided a small upwardly directed oil flow pas According to the present invention there is sage 18 communicating with the sump in the provided a gas compressor comprising a lower part of the crankcase at a low level.

crankcase and cylinder assembly having a ro- Furthermore, at an appreciably higher point in tatable crankshaft with a crankpin connected 100 the crankcase there is provided a somewhat to a piston for reciprocating a piston in the larger air breather passage denoted by refer cylinder for alternatively effecting induction ence 19 and shown dotted in Fig. 1. The and compression strokes said crankshaft rotat- angular position of this air passage 19 in rela ing in bearings which are supplied with lubri- tion to the crankshaft rotation is chosen so cation under pressure from a source of lubri- 105 that it is substantially obscure by an outer cant and characterised by said crankcase be- face 20 of the crankweb counterweight 21 ing provided with a valve which closes during during induction strokes of the crankshaft and induction strokes to create pressure elevations piston assembly. Since passages 18 and 19 in the crankcase to scavenge surplus lubricant are the only breathing passages for the therefrom via a lubricant outlet passage. 110 crankcase the inner end of the passage 19 In accordance with one example of the in- and outer face 20 of the crankcase comprise vention the valve which closes during induc- a valve which can impede breathing of the tion strokes may comprise a check valve ar- crankcase.

ranged to freely permit air flow into the As shown in Fig 2 the direction of rotation crankcase during compression strokes but 115 of the crankshaft is denoted by an arrow 22, closing during induction strokes. Furthermore, the crankweb 21 being shown in dotted out said check valve may have a restricted flow line. It is seen moreover that a suitable angu by-pass to limit the pressure elevations which lar position moving away from top dead may be produced in the crankcase. centre after completion of a compression In a further or preferred embodiment of the 120 stroke the surface 20 of the counterweight of invention the valve may comprise a passage the crankweb is about to obscure the inner which is obscured by a part of the crankshaft end of the passage 19. The effect of this is over a part of the induction stroke. to immediately impede the formerly free flow In order that the invention may be more of air into and out of the crankcase so that clearly understood and readily carried into ef- 125 the downward movement of the piston is able fect the same will be further described by to create a suitable pressure elevation which way of example with reference to the accom- acts in a sense, to drive oil above the plate panying drawings of which 16 out into the gear housing upwards via the Figure 1 illustrates a part-sectional view of a small passage 18. By such means, the level of piston and cylinder air compressor in accordrained out oil in the crankcase of the corn- 2 GB2187801A 2 pressor is positively limited to a level deter- ing provided with a valve which closes during mined by the ineer end of the passage 18. induction strokes to create pressure elevations The size of the passage 18 and the larger in the crankcase to scavenge surplus lubricant passage 19 are selected along with the range therefrom via a lubricant outlet passage.

of angular positions of the crankshaft for 70 2. A gas compressor as claimed in claim which the passage 19 is closed during induc- 1, said valve comprising a check valve ar tion strokes, to ensure that any tendency for ranged to permit air flow outwardly of the oil build-up in the crankcase is prevented. On crankcase but not inwardly of the crankcase.

the other hand, it is undesirable to create 3. A gas compressor as claimed in claim 2 more than a minimal pressure elevation in the 75 said check valve being provided with a bypass crankcase because this can not only reduce passage to limit pressure elevations in the the efficiency of the compressor but it may crankcase.

also be counter effected in that it will tend to 4. A gas compressor as claimed in claim drive lubricant upwards past the piston rings 1, said valve being formed by a part of the into the compression chamber -of the com- 80 crankshaft of the compressor obscuring a pressor. breather passage during said induction As mentioned in the foregoing, an alterna- strokes.

tive method of achieving the same result as 5. A gas compressor as claimed in claim 4 that described above with reference to Figs. 1 said part comprising a crankweb counter- and 2, would comprise the provision of a suit- 85 weight portion of the crankshaft.

able check valve in a passage such as 19 but 6. A gas compressor substantially as de- it may be appreciated that without careful sescribed herein with reference to Figs. 1 and 2 lection of the check valve characteristics and of the accompanying drawings.

the provision of a possible by-pass path Printed for Her Majesty's Stationery Office around it, unacceptably high crankcase pres- by Burgess & Son (Abingdon) Lid, Dd 8991685, 1987.

sure elevations may occur during operation Published at The Patent Office, 25 Southampton Buildings, and these are undesirable for reasons already London, WC2A l AY, from which copies may be obtained.

given above.

With a compressor such as described with reference to Figs. 1 and 2, it may be appreciated that the correct functioning of the invention is dependent upon the compressor always being mounted at an attitude for which it is designed having regards to the invention.

In order to provide for positioning at a range of different but predetermined attitudes the crankcase may be provided with a plurality of passages such as 18 all but the lowest of which for the selected attitude, being plugged- off as required.

It will be appreciated that the present invention relies upon the production of an acceptable crankcase pressure to drive out surplus oil. In the case of a single cylinder compres- sor this is effected by closing a valve during an induction stroke but in the case of multiple cylinders with a common crankcase volume it may be necessary to arrange the relative cyclic positions of the pistons such that there is an interval of net reducing crankcase volume and to arrange for the valve device to close during that particular interval. This will inevitably still occur during an induction stroke of at least one such cylinder.

Claims (1)

1. A gas compressor comprising a crankcase and cylinder assembly having a rotatable crankshaft with a crankpin connected to a piston for reciprocating a piston in the cylinder for alternatively effecting induction and compression strokes said crankshaft rotating in bearings which are supplied with lubrication under pressure from a source of lubricant and characterised by said crankcase be-