Gerotor pumps

Abstract: A gerotor pump comprises the usual lobed annulus 30 containing the lobed rotor (not shown in Figure 2) which is journalled on cylindrical boss 36. The boss is free to turn on the eccentric pin 38 between positions controlled by limit pin 42 encountering end abutments. This enables the pump to automatically adjust to the variable direction of drive of the annulus - in this case via coupling 32 - so as to be unidirectional in fluid output via flow passages 16 18.

Description: This invention relates to pumps of the kind comprising a male rotor with n lobes which is located internally of and meshed with a female annulus having n+1 lobes. These two form a gerotor set which is driven either from the annulus or the rotor and the two turn relative to one another and about parallel axes. A series of chambers is formed between the lobes and each chamber extends between two lines of contact between the rotor and annulus. These lines lie generally on the peaks, or maximum radius portions of the rotor lobes, and move along the annulus as the parts rotate at different speed. Hence the chambers increase in size as they proceed from a position adjacent a plane containing both axes and adjacent the point of full mesh between a male lobe and a female recess between lobes (or vice versa) towards a diametrically opposite position at a place where only the crests (maximum radius portions) of the lobes of both rotor and annulus meet. This travel is the induction stroke and fluid is sucked into the chambers as they follow this path from an inlet port at an axial end of the chambers. Similarly, as the chambers continue in their travel on the opposite side of said plane returning to the start point, they diminish and expel fluid through a second port or outlet. As stated, pumps of the kind mentioned in the foregoing two paragraphs are well known and exist in many variations. With internal combustion engines the direction of rotation of the main shaft (e.g. the crank shaft of the engine) is usually unidirectional because of valve timing and ignition timing requirements, and hence a pump of this kind e.g. used as the lubrication oil pump and driven from such a crankshaft is also unidirectional. But with certain rotary machines for example some kind of compressors, the direction of rotation is unimportant and may vary from one cycle of operation to another. If a gerotor pump is used with such a machine, the effect on the pump of changing the direction of rotation is to expel fluid through the inlet and suck through the outlet: usually this is unacceptable. It is therefore known in the prior art to provide means for shifting the eccentricity of one axis of the gerotor relative to the other, according to the direction in which the annulus or rotor is driven. Usually the shift is through 180 degrees in said reversal that is from one side of the stationary axis to the other. This enables the inlet and outlet to remain unchanged and give unidirectional flow through the pump irrespective of reversible drive direction. Many different schemes have been put forward to cause the automatic shift. Thus it is known to mount the annulus in an eccentric ring which is itself angularly movable in a pump body cavity, and to dispose a blade spring between the annulus and the eccentric so as to create a frictional drag between the two. When the annulus turns in one direction, this drags the eccentric ring to one position against the stop and hence fixes the position of the axes. When the drive direction is reversed, the spring drags the eccentric in the opposite direction and hence changes the axis positions. Difficulties with this design are power loss caused by the frictional drag, which is effective during the whole of the operation although only needed at the start-up point, and the additional space required to accommodate the additional component, i.e. the eccentric ring. Another approach has located the annulus in a carrier ring which is freely pivoted, and use the carrier ring to shift the position of the parts with respect to a drive shaft so as to bring about the required result, but again extra components and additional volume are required and the operation is not found reliable. FR 1 149 821 shows a gear pump of the kind having a slipper located between the male toothed rotor and the female toothed annulus, in which the slipper is made integral with a carrier which journals the rotor, so that as the rotor axis is shifted for flow reversal, the slipper moves with it. Finally, in GB-1 095 923-A, which is the closest prior art, it is proposed to journal the rotor on a tubular bush arranged for through flow as part of the fluid circulation path from an inlet to an outlet which are effectively disposed at opposite ends of the gerotor set, and having an external surface concentric with the rotor axis so that the rotor runs on the bush. The bush is provided with a cylindrical extension which is concentric with the annulus and hence eccentric to the rotor. Pin and stop means are provided to limit angular travel of the bush between two extreme positions. When the direction of rotation changes, the bush automatically turns in the same direction as that of rotation, to take the eccentricity from one side of the annulus axis to the other. The problem with this automatically reversing arrangement is that in order to avoid throttling the flow of working fluid in any angular position, the extension from the bush has to be of large diameter in order to provide an adequate flow passage through the bush. In fact the extension is of larger diameter than the bush itself. The extension must be of a certain length related to its diameter to afford adequate journal surface against the loads applied in the pump, which amount to a lateral load on this bush at the highest pressure zone in the pump and which tend to tilt the bush and extension about their axes. So this diameter and length make the complete pump construction unduly large as well as complicating manufacture and hence making the pump expensive. The object of the invention is to solve this problem. According to the invention, a pump in accordance with the features of claim 1 is provided. By making the fluid flow connections external of the pump the bush can be made small and the axial dimensions remain compact, so that manufacture is simplified and cost reduced. The invention is now more particularly described with reference to the accompanying drawings wherein: Figure 1 is an end elevation of a pump body to house a gerotor pump set; Figure 2 is a sectional elevation of the same but with parts removed for clarity; Figure 3 is an alternative embodiment ; and Figure 4 is a perspective view of an eccentric used in the various embodiments. Turning first to Figure 1, this shows the inlet and outlet ports 10, 12 relative to the circular chamber bounded by the line 14 which in use contains the annulus (not shown) of the gerotor set. These ports are communicated to flow passages which may lead for example to an inlet port 16 and an outlet port 18. Also indicated is central axis 20 which is concentric to the surface 14, and a cut-away 22 extending arcuately over about 180° about the centre 20. In Figure 2, the pump set annulus 30 is shown, which is internally lobed with n+1 lobes and is connected for drive by means of co-axial projection 32 which may for example be engaged with the end of a crankshaft 34 by means of flats or a key and keyway. The rotor, not shown, having n lobes is located internally of the annulus and has a concentric bore journalled on boss 36. The boss is cylindrical and has a main axis. Hence the rotor turns about that axis when the annulus is driven. The boss 36 (see also Figure 4) is, in Figure 2, journalled on the fulcrum pin 38 which is eccentric of the boss main axis, and this pin may be fast, for example a drive fit, in a bore in the end wall of the annulus and/or in the parallel face of the cover component 40. The limit pin 42 is carried by the boss 36. In operation, the annulus is driven, and this transmits drive to the rotor albeit at a different speed, so that the rotor turns on the boss 36. The pressure difference between one side of the pump and the other due to the direction of turning causes the boss 36 to pivot on the fulcrum 38 until the limit pin 42 reaches one or other end of the recess 22 according to the direction of the pressure difference. When the direction of rotation of the annulus changes, the boss 36 automatically moves around to re-position the rotor and take the limit pin 42 from one end to the other of the recess. The arrangement in Figure 3 differs only in that the boss 36 is journalled on pivot pin 48 which has a head 50 and in that the annulus has drive means 52 engaging with the crankshaft or like. It will be appreciated by those skilled in the art that the pin 38 could be made integral with the boss 36 for example by a powder moulding technique. So could the pin 42. Alternative annulus drive means may be used, for example by providing the annulus with external gear teeth and transmitting drive from a pinion train.

Claims: A gerotor pump having an annulus (30) provided with n+1 internal lobes and a male lobed rotor with n lobes located internally of the annulus, said annulus being contained and journalled in a circular chamber in a pump cover component (40), means for transmitting drive to the annulus, said rotor having a bore concentric of the rotor, a boss (36) which is cylindrical about a main axis and journalled in said rotor bore so that when the annulus is driven to rotate in the circular chamber the rotor is also driven to rotate about said main axis which is eccentric to the axis of the circular chamber and effect pumping action from an inlet port in the cover component to an outlet port in the body, a fulcrum pin (38) on the boss (36) which fulcrum pin is eccentric of said main axis and is journalled in said pump cover component (40), and limit pin (42) and abutment carried by the cover component and boss for limiting pivoting of the boss in the direction of rotation of the annulus and rotor so that when said direction of rotation changes the boss pivots by 180° to take the eccentricity of the boss from one side of the axis of rotation of the annulus to the opposite side thereof, whereby the pumping action will continue from inlet to outlet despite the reversal of rotational direction, characterised in that said inlet and outlet ports in the cover component open to flow passages (16,18) through the cover component and said fulcrum pin (38) extends into a bore in the pump cover component. A pump as claimed in Claim 1 wherein the fulcrum pin (38) is a drive fit in the pump cover component. A pump as claimed in Claim 1 wherein the fulcrum pin (38) is made integral with the boss by powder metallurgy techniques.

Inventors: HODGE STEVE, HODGE, STEVE
Applicants: CONCENTRIC PUMPS LTD, CONCENTRIC PUMPS LIMITED
Application year: 1991
Main classification: F04C15
IPC codes: F04C2, F04C11, F04C14, F04D17, B23F15