GB2160596A - Pump - Google Patents

Abstract

A pump 1 for hydraulic fluid, pump comprises a plurality of radially arranged pistons 9, with an eccentric rotor 4, 5 provided with a non-rotatable collar 7 having a plurality of external bearing surfaces 8 appropriate to the number of pistons 9, and extending orthogonally with respect to the axis of reciprocation of the pistons. There are means 10, 11 to convey fluid to be pumped to the pistons 9 to urge the latter towards their respective bearing surfaces 8, and means such as plunger 14 acting on the collar 7, to prevent rotational movement of same, in circumstances where, after a failure of supply fluid, the pump 1 adopts a free wheelig condition because the pistons 9 are no longer being urged towards their respective bearig surfaces 8. In a second embodiment the plunger is concentric with the piston. <IMAGE>

Description

SPECIFICATION Pump This invention reiates to a pump, of the radial piston kind, comprising a plurality of radially arranged pistons associated with an eccentric rotor, the latter being drivable by a power source e.g. an electric motor.

Although radial piston pumps may be pro- vided with a source of fluid to be pumped at minimal or zero pressure, the pump of the invention is particularly concerned with an arrangement whereby the supply of fluid is already at a substantial pressure e.g. 1 50 p.s.i., with the pump serving to boost this pressure to e.g. 1 500 p.s.i. With such an arrangement the supply fluid may be used advantageously to to urge the pistons constantly into engagement with the rotor, as a means of avoiding the incorporation of compression springs to achieve this engagement, and consequently avoiding cavitation and pump seal damage which invariably occurs with spring urged pistons, upon failure, for whatever reason, of the supply fluid and with the pump continuing to be driven.Thus, with fluid urged pistons, lack of fluid results in the pistons no longer being in contact with the rotor, so that, with the pump continuing to be driven e.g. until fluid supply failure is appreciated, the pump in effect freewheels with the pistons no longer reciprocated by rotation of the rotor, and consequently with the pump not attempting to deliver non-existent fluid The nature of the supply fluid could be oil, water, an oil-water emulsion, etc.

Furthermore, in relatively slow speed hydraulic motors, in contrast to pumps, a rotor arrangement is known whereby the rotor is provided with an interposed, non-rotatable collar having a plurality of tangential bearing surfaces appropriate to the number of pistons involved. Thus, a five cylinder motor would incorporate a pentagonally profiled collar.

However, when incorporating a tangentially profiled collar in a pump in which piston compression springs are avoided, failure of the fluid supply and the resulting effect of the pistons no longer being in contact with the rotor provides for the possibility of disadvantageous rotor spin, due to friction i.e. drag in the bearings supporting the rotor, whereby the tangential surfaces of the rotor are no longer orthogonal or generally so, with respect to the line of reciprocation of the associated piston, resulting in the pump being unable to pump efficiently, if at all.

According to the present invention there is provided a pump for hydraulic fluid, the pump comprising a plurality of radially arranged pistons, an eccentric rotor provided with a non-rotatable collar having a plurality of external bearing surfaces appropriate to the number of pistons and extending orthogonally with respect to the axis of reciprocation of the pistons, means to convey fluid to be pumped to the pistons to urge the latter towards respective bearing surfaces, and means acting on the collar, to constrain rotational movement of same, in circumstances of a failure of supply fluid where the pump adopts a free wheeling condition, due to the pistons no longer being urged towards respective bearing surfaces.

With the pump of the invention, there is ensured accurate alignment between the bearing surfaces of the collar and their associated pistons upon re-start of the pump following a failure of supply fluid, and consequently their is ensured an ability to re-start the pump immediately the fluid supply is again available. Thus, with the pump of the invention, no pump downtime is involved as the need to re-set or re-align the collar is avoided.

The pistons, conveniently located around an annular pump body, preferably engage their respective bearing surfaces via a pad of a high pressure bearing material, and piston-to-pad engagement may be direct, or indirect, the latter reducing potential impact damage to the relatively brittle pad.

Whilst the pump may be provided with any desired number of cylinders, it is preferred to provide five cylinders, which adequate hydraulic balance. Consequently, in this case, the collar would be provided with five bearing surfaces and hence have a pentagonal, or generally pentagonal outer periphery.

The means acting on the collar to constrain rotational movement of same may consist of a plunger engaging a portion of the collar periphery. Whilst engagement may be positive, e.g. by a spigot of the plunger engaging a socket of the collar, it is preferred for there to be frictional engagement, with the plunger engaging a flat surface of the collar periphery.

As indicated previously, a plurality of plunger type constraining means may be provided e.g.

five plungers in a five cylinder pump, and in accordance with a first embodiment each plunger may be located in an individual radial hole in the pump body interposed between an adjacent pair of pistons, and consequently, in this case the collar of the first embodiment would be provided with flat bearing surfaces extending orthogonally with respect to the longitudinal axis of their associated plungers, but in the case of a six cylinder pump, three plungers, located 120 apart, could be provided. Preferably, the plungers are spring loaded against their respective flat surfaces.In detail, each plunger may be slidably located towards an inner end of its radial hole, with the outer end of each hole closed by a screwin plug, with a coil compression spring located between a forward face of the plug and a rearward face of the plunger, and with a sealing ring associated with each plug. Also with this first embodiment, the pistons may bear directly on slipper pads seated on the bearing surfaces. For enhanced wear resistance a recess may be bored into the piston ends to receive a hardened steel disc, a bearing face of which is adapted to project beyond the annular end of the piston and thus to make engagement with the slipper pads.

In accordance with a second embodiment, each plunger may be housed within an associated piston, with a coil compression spring between the plunger and its piston to ensure that the plunger remains in position in circumstances where the piston moves radially outwardly upon a failure of the fluid supply occuring. The plunger is displaceable about an axis co-incident with the axis of reciprocation of the associated piston. This embodiment thus avoids the need to drill individual radial holes into the pump body as is the case with the first embodiment and, in the absence of such holes, greater freedom is provided in the pump body for porting requirements.Furthermore, this embodiment lends itself to the indirect piston-to-pad proposal referred to previously, in that the plunger may be provided at its inward end with a flange, extending radially outwards with respect to the longitudinal axis of the plunger, an outer face of the plunger flange being in permanent contact with the bearing surface, via an interposed slipper pad, and an inner, annular face of the plunger flange being engaged by an inner end face of the piston, at least in circumstances where low pressure fluid supply e.g., at 1 50 p.s.i.. is available. Furthermore, a cushioning effect on the slipper pad is achieved by the interposed plunger flange, in circumstances when the latter is struck by its piston.Also in comparison with the first embodiment, a greater bearing surface areaorresponding basically to the plunger diameter plus the plunger flange-is available for engagement with the slipper pad. With this embodiment, it is preferred for the plunger to have a hollow interior to house at least part of its coil compression spring, with oil admissible to the interior of the plunger via an axial hole in an outer head of the plunger and a radial supply port in communication with the axial hole.A throttling effect on oil being expressed from the plunger interior, and hence a dashpot effect on the inwardly moving piston, may be achieved if the hole is covered by a valve member, itself provided with a bore of smaller cross sectional area than the axial hole, engaged by the coil compression spring, the latter thus transmissing its loading to its plunger via the valve member, and, as the latter is not provided with a seal so that pressure is available to both sides, increase in fluid pressure due to piston movement will eventually lead to exhaustion of fluid from within the plunger.

The invention will now be described in greater detail by way of examples, with reference to the accompanying drawings, in which: Figure 1 is a transverse view, partly in section, of a first embodiment of pump in accordance with the invention; Figure 2 is an axial view of the pump on the line ll-ll of Fig. 1; and Figure 3 corresponds to Fig. 1 but shows a second embodiment of pump.

In both embodiments, like reference numer als are empioyed for like components.

In the drawings a pump 1 for hydraulic fluid comprises an annular pump body 2 carrying bearings 3 for rotatably supporting a shaft 4 having an eccentric 5, the shaft 4 being driven through a pinion 6 from a drive source, e.g. an electric motor. The eccentric 5 is in drivable relationship with a non-rotatable collar 7 having five external bearing surfaces 8 each extending orthogonally with respect to the axis of reciprocation of an associated, reciprocable piston 9 housed within the pump body 2.Fluid to be pumped is conveyed at a first, lower pressure, e.g. 1 50 p.s.i., to each piston 9 from a supply port 10 and conduit 11, and being returned at a higher pressure, e.g. 1 500 p.s.i., by the same port 10 and conduit 11, with control valves 12, 1 3 arranged for appropriate fluid supply and delivery, the lower fluid pressure urging the pistons 9 into engagement with their respective bearing surfaces 8.

In accordance with the first embodiment, interposed between adjacent pistons 9 are provided five plungers 14 located in individual radial holes 1 5 in the pump body 2.

Each hole 1 5 is closed at its outer end by a screwed-in plug 16, with a coil compression spring 1 7 located between a forward face of the plug 1 6 and a rearward face of the plunger 14. Each plunger 14 engages a surface 18 of the collar 7, each surface 18 extending orthogonally with respect to the longitudinal axis of the respective plunger 14 and being located between two adjacent surfaces 8, the plungers 14 and surfaces 18 constituting means to constrain rotational movement of the collar 7 in circumstances where a failure of supply of pressure fluid would result in the pistons 9 no longer being in contact with the bearing surfaces 8. A hardened steel disc 1 9 is fitted into a bore in the end of the piston 9 adjacent the collar 7, the disc 1 9 bearing on a slipper pad 20 seated on the bearing surface 8, as the disc projects slightly beyond that end of the piston 9.

In accordance with the second embodiment shown in Fig. 3, plungers 1 4A are located within pistons 9A, the latter having hollow interiors for this purpose. Such an arrangement is in contrast to being located within individual radial holes 1 5. A coil compression spring 21 is located between each plunger 1 4A and its piston 9A, and each plunger 1 4A is provided at its inward end with a flange 22 extending radially outwardly with respect to the longitudinal axis of the plunger 1 4A and the co-axial axis of reciprocation of the piston 9A, indicated by chain dotted line 23, an inner, annular face 24 of the plunger flange 22 being engaged by the piston. Each plunger 14A also has a head 25 having an axial hole 26 in communication with a radial supply port 27 in the flange 22, so that oil may be admitted to the interior of the plunger 14 and piston 9A. The coil compression spring 21 bears indirectly on the plunger 14A, via a valve member 28 which covers the hole 26 and which itself is provided with a bore 29 of smaller diameter than the hole 26, to achieve a dashpot effect.

Claims (21)

1. A pump for hydraulic fluid, the pump comprising a plurality of radially arranged pistons, an eccentric rotor provided with a non-rotatable collar having a plurality of external bearing surfaces appropriate to the number of pistons and extending orthogonally with respect to the axis of reciprocation of the pistons, means to convey fluid to be pumped to the pistons to urge the latter towards their respective bearing surfaces, and means acting on the collar, to constrain rotational movement of same, in circumstances of a failure of supply fluid where the pump adopts a free wheeling condition, due to the pistons no longer being urged towards respective bearing surfaces.

2. A pump as claimed in Claim 1, wherein the pistons are located around an annular pump body.

3. A pump as claimed in Claim 1 or Claim 2, wherein the pistons engage their respective bearing surfaces via a pad of a high pressure bearing material.

4. A pump as claimed in Claim 3, wherein piston-to-pad engagement is direct.

5. A pump as claimed in any preceding Claim, provided with five cylinders.

6. A pump as claimed in any preceding Claim, wherein the means acting on the collar to constrain rotational movement of same consists of a plunger engaging a portion of the collar periphery.

7. A pump as claimed in Claim 6, wherein the engagement is positive.

8. A pump as claimed in Claim 7, wherein the engagement is by a spigot of the plunger engaging a socket of the collar.

9. A pump as claimed in Claim 7, wherein the engagement is frictional, with the plunger engaging a flat surface of the collar periphery.

10. A pump as claimed in Claim 7 and any Claim appendant thereto, wherein a plurality of plungers are provided.

11. A pump as claimed in Claim 10, wherein each plunger is located in an individual radial hole in the pump body, the radial holes being interposed between adjacent pistons.

12. A pump as claimed in Claim 10 and any Claim appendant thereto, wherein the plungers are spring loaded against their respective surfaces.

13. A pump as claimed in Claim 10 and any Claim appendant thereto, wherein each plunger is slidably located towards an inner end of its radial hole, with the outer end of each hole closed by a screw-in plug, with a coil compression spring located between a forward face of the plug and rearward face of the plunger, and with a sealing ring associated with each plug.

14. A pump as claimed in Claim 10 and any Claim appendant thereto, wherein the plungers bear on slipper pads seated on bearing surfaces.

1 5. A pump as claimed in any one of Claims 3 to 14, wherein a recess is bored into the piston ends to receive a hardened steel disc, a bearing face of which disc projects beyond the piston to make engagement the pad.

1 6. A pump as claimed in any one of Claims 1 to 10, wherein each plunger is housed within an associated piston, with a coil compression spring between each plunger and its piston.

1 7. A pump as claimed in Claim 16, wherein each plunger is provided at its inner end with a flange, extending radially outwardly with respect to the longitudinal axis of the plunger, an outer face of the plunger flange being in permanent contact with the bearing surfaces via an interposed slipper pad, and an inner, annular face of the plunger flange being engaged by the piston.

18. A pump as claimed in Claim 16 or 17, wherein the plunger has a hollow interior to house at least a part of its coil compression spring, with oil admissible to the hollow interior to the plunger via an axial hole in an outer head of the plunger and a radial supply port in the plunger flange.

1 9. A pump as claimed in Claim 18 wherein the axial hole is covered by a valve member itself provided with a bore of smaller cross-section than the axial hole and engaged by the coil compression spring.

20. A pump for hydraulic fluid substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

21. A pump for hydraulic fluid substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.