Two-stage Fluid Pump

Abstract

A two-stage pump assembly in which one of the pumping elements is a Gerotor pump and the other pumping element is a radial piston pump. The Gerotor pump acts to charge the radial piston pump and also acts as a first stage high-flow pump. Both pumps can operate together to produce a combined flow, and the Gerotor pump can be unloaded to divert its flow and thereby permitting the radial piston pump to act as a first stage pumping unit. Individual and replaceable pump bodies are provided for the piston type pump.

Description

BACKGROUND OF THE INVENTION

This invention pertains to fluid pumps of the type having two stages of flow and in which two separate pumps are used to provide these stages of flow. One type of prior art, two-stage hydraulic pump is shown in U.S. Pat. No. 3,053,186, issued Sept. 11, 1962 to Gondek. That patent discloses a gear-type pump which feeds into and supercharges an axial-piston-type pumping unit. Such a two-stage pump is not only expensive to manufacture because of its cylinder body machining requirements and because of its numerous parts, particularly in regard to its valving arrangement, but it also is not particularly compact.

SUMMARY OF THE INVENTION

The present invention provides a two-stage fluid pump having a Gerotor pump as the first stage pumping unit, and which Gerotor pump can act simultaneously with and supercharge a second pump of the radially arranged piston type.

A more specific object of the present invention relates to the use of individual piston blocks for each of the radial-type pistons, whereby an economically produced pump is provided. That is to say, the individual pump body can be fashioned from selected and ideal heat treated material and the critical machining required is only necessary on relatively small areas. Therefore, a very satisfactory pump body is provided for each of the individual pumping pistons and a minimum amount of machining is required to provide these accurately formed pump bodies. In addition, various pump bodies of different bores can be interchanged to permit changing of the capacity of the individual pumping units.

Another aspect of the present invention relates to a particularly compact and efficient two-stage pump, which is quiet in operation and in which the load is evenly distributed on the cam shaft due to the use of radially disposed pistons.

Generally, the present invention provides a two-stage fluid pump which is small and compact and has low pulsations, exceptionally well lubricated, quiet in operation, and economical to manufacture. A quiet pump has been provided with good life, and one which can provide high-flow at low pressure.

These and other objects of the present invention will appear hereinafter as this disclosure progresses, reference being had to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a portion of a two-stage pump embodying the present invention in which certain portions of the pump are shown as broken away and in section for clarity in the drawings;

FIG. 2 is a bottom view of the pump together with the unloading valve and relief valve, but on a reduced scale;

FIG. 3 is an elevational view, in section, of one of the piston blocks;

FIG. 4 is another view of the piston block shown in FIG. 3, the view being taken generally along the line 4--4 in FIG. 3;

FIG. 5 is another view of the piston block taken generally along line 5--5 of FIG. 3;

FIG. 6 is a view of the race for the pistons, the view being taken generally along line 6--6 in FIG. 1, but on a reduced scale;

FIG. 7 is a view of the plate shown in FIG. 1, the view being taken generally along line 7--7 thereof;

FIG. 8 is a view of the Gerotor pumping units, the view being taken generally along the line 8--8 in FIG. 1;

FIG. 9 is a longitudinal cross-sectional view of the shaft assembly of the pump shown in FIG. 1; and

FIG. 10 is a flow diagram for the pump assembly.

DESCRIPTION OF A PREFERRED EMBODIMENT

The general arrangement of the present two-stage fluid pump includes a source of power, such as for example, an electric motor 1 having a drive shaft 2 to which is keyed or otherwise fixed the shaft 3. Shafts 2 and 3 form a drive shaft means which drive the Gerotor pump 4. The shaft means also furnishes the driving power to the radial piston pump 5. The Gerotor pump 4 can provide pressurized fluid to the radial piston pump 5 via passages to be referred to, so as to supercharge the radial-piston-type pump. An unloading valve 8 and a one-way check valve 9 are provided in the assembly and in this manner depending on the pressure setting of the valve 8, the Gerotor pump can ordinarily pump pressure fluid past the check valve 9 and into the delivery conduit 10 of the assembly, along with the discharge of the radial piston pump 5 from passage 11. Alternatively, the discharge from the Gerotor pump can be dumped via the unloading valve 8 when the pressure setting valve 8 is reduced, and under these circumstances, it is only the radial piston pump 5 that provides fluid pressure discharge. Thus, the two pumps 4 and 5 can act in unison, or alternatively the pump 5 can act by itself, being fed by the Gerotor pump.

The assembly includes a pump housing H which is secured by cap screws 12 to the motor base, and a top housing 13 is secured by cap screws 14 to the housing H. The tubular shaft 3 is journaled on needle bearings 15 located in the top housing 13, and a suitable shaft seal 16 is located between the top housing 13 and the upper end of the shaft 3.

The top housing defines an outer rotor 20 having a pumping chamber 18, in which inner rotor 21 of the Gerotor pump is located. The inner rotor 21 has one tooth less than the outer rotor, and is eccentric thereto, and is detachably connected to the shaft 3 by means of the ball 22 which is engaged in detents in the inner rotor 21 and on the periphery of the shaft 3. The two rotors act as a positive displacement gear-type pump in the known manner, the inner rotor being driven by the shaft 3. This pump may be of the type manufactured by W. H. Nichols Company of Waltham, Mass. The pressure fluid from the Gerotor pump can be delivered via outlet 24 and conduit 24a (see FIGS. 1, 2 and 10) directly to the discharge line 10.

In addition, pressure fluid from the Gerotor unit is discharged via passage means 23 to the annular groove 25 (FIG. 1) in the housing H, from which it passes through ports 26 in the plate 27 and then via passageway 28 in the pump body B, past the check ball 29 and into the pumping chamber 30 of the piston pump 5. A piston 31 reciprocates within the bore 32 which forms the pumping chamber 30, to thereby provide suction and discharge strokes for each of the pistons.

The pistons are reciprocated by the action of the cam portion 33 formed on the shaft 3 and more particularly, the race 34 (see FIG. 6) is journaled on needle bearings 36 around the shaft 3, and the inner, large end 37 of the pistons bear against the race 34. It will be noted that the race 34 has a flat surface 40 on which one of the inner ends of the pistons rest. By having this flat surface on the race, the race remains stationary as the shaft 3 rotates.

It has been found particularly desirable to make this race out of a good bearing material, such as cast iron or bronze. These materials have been found desirable because, with the flat surface 40 provided for one of the pistons, the other two pistons act on the periphery of the race to also form their own seat by each forcing a permanent deformation on the race after less than 1 hour of operation at full load. Thus, area contact is established between race 34 and individual piston ends resulting in smooth bearing action.

It will also be noted that a second set of needle bearings 42 is provided between the inner end of shaft 3 and the housing H. The Gerotor pump provided insures that good lubrication is furnished to the needle bearings 42 via the passage 44 between the housing H and the shaft 3. Fluid leakage past this annular space 44 acts to lubricate the entire piston-type pump, which results in a particularly quiet and reliable pumping arrangement.

The use of needle bearings 15, 36 and 42 contributes to a compact design. Three pistons equally and radially disposed have been found to result in a very even thrust applying force on the cam surface of the shaft 3.

Referring now to FIGS. 3, 4 and 5 which show a pump body for each of the pistons 31, it will be seen that only a relatively small body is required for each of the pistons, thereby reducing the amount of machining required. These bodies can be heat treated with particular nicety and to a fine degree of finish and can be readily repaired or replaced. Also, bodies of different sized pumping chambers can be provided for pistons of similar size so that pump capacity can be readily varied.

Long screws 50 extend through the port plate 51, pump bodies B and are threadably engaged in the housing H to removably hold the assembly together.

The discharge from the pump 5 is via passage 11 to the conduit 11a where it communicates with conduit 10 leading past relief valves RV.

Claims

We claim:

1. A two-stage fluid pump comprising,

a source of power having a drive shaft means,

a positive displacement Gerotor pump having an outer rotor and an inner rotor drivingly connected to said shaft means

a radially piston pump mounted on said Gerotor pump and having radially extending pumping chambers, said Gerotor pump having a fluid delivery communication with said pumping chambers for supercharging said piston pump,

said Gerotor pump also having a second fluid discharge outlet separate from said communication for separate discharge of pressure fluid from said pump,

said piston pump having a plurality of replaceable and individual pump bodies defining said pumping chambers and including means for controlling fluid flow to and from said chambers,

a pumping piston in each of said chambers,

said shaft means having an eccentric portion,

a race rotatably mounted around said eccentric portion, said race abutting against one end of said pistons to radially reciprocate said pistons in pumping and discharge strokes,

a flat surface on the outer periphery of said race positioned to engage one of said pistons to prevent rotary motion of said race,

and a port plate connected to said pump bodies and defining a discharge passage from said chambers.