Rotary Pump With Pressure Relief

Abstract

A rotary pump includes a housing, rotors, an inlet chamber, an outlet chamber and pressure relief means. The pressure relief means includes a movable wall normally resiliently biased into engagement with one of said rotors and exposed to fluid pressure at said outlet chamber. At a predetermined maximum pressure, the fluid pressure force acting upon the wall will overcome the resilient bias and move the wall away from said rotors to a degree sufficient to interconnect said outlet and said inlet chambers in fluid communication and allow fluid to flow therebetween and thereby disrupt the pumping action of the rotors. The movable wall pressure relief contacts only one of the rotors.

Description

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a pressure relief for a rotary pump, and more particularly, to a pressure relief of the sliding wall type wherein the resiliently biased, slidable wall is in fluid communication with the pumping chambers of the pump.

2. Discussion of the Prior Art

It has been necessary to provide rotary pumps of the type having inner and outer rotors with eccentric axes for rotation, such as those used in lubrication pumps for internal combustion engines, with an effective pressure relief valve. For those pumps utilized as lubrication pumps, the pressure differentials between running and shut-off pressure is often quite small, 105 p.s.i. running pressure with 110 p.s.i. shut-off pressure. For those pumps, a very sensitive pressure relief valve must be provided.

Heretofore, pressure relief valves of the sliding wall type have been inadequate for pumps wherein sensitivities of the magnitude mentioned above were required. For this reason, sliding wall valves with the cost advantage thereof, were usable only in those applications having a relatively large on-off pressure differential.

SUMMARY OF INVENTION

The present invention provides a more sensitive sliding wall type pressure relief than heretofore possible, by providing means whereby the wall contacts only one of a pair of rotors. By contacting only one of the rotors an increased surface area of slidable wall is exposed to the generated pump pressure and thus the generated fluid force acting on the wall, namely that force which equals the exposed slidable wall area times pressure, will be proportionally increased. Thus, for any given pressure a force signal of greater magnitude is generated, allowing applicant's pressure relief to be capable of much more sensitive operation than has heretofor been possible with sliding wall pressure relief devices.

The biasing force on the wall is sufficient to permit the pump to generate fluid pressure up to a predetermined, desirable maximum pressure, at which point the fluid pressure force on the wall will overcome the bias and said wall will be moved away from the rotors to the extent that the pumping chambers are put into fluid communication with each other so that the fluid flows between the outlet chamber and the inlet chamber thereby disrupting the pumping action of the rotors beyond the predetermined pressure. As the fluid pressure drops to an acceptable level, the biasing force will again urge the movable wall into a position whereby the outlet and inlet chambers of the pump are again sealed from each other and normal pumping will resume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a hydraulic pump, illustrating certain features of the present invention.

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of a hydraulic pump illustrating an alternate embodiment of the present invention.

FIG. 4 is a partial, cross-sectional view of an alternate embodiment of the present invention.

FIG. 5 is a plane view of one element of FIG. 4.

FIG. 6 is a cross-sectional view of the pump of FIG. 1 in a second operating condition.

FIG. 6a is a force diagram illustrating the hydraulic forces acting on a certain portion of the pump of FIG. 1.

FIG. 7 is a cross-sectional view illustrating a prior art device.

FIG. 7a is a force diagram illustrating the hydraulic forces acting on a certain portion of the pump of FIG. 7.

DETAILED DESCRIPTION OF INVENTION

Referring now more specifically to the drawings and more specially to FIGS. 1 and 2, a rotary pump may generally be seen at 10. The pump 10 includes a housing 12 with a fluid inlet 14 and fluid outlet 15. Housing 12 has a cylindrical cavity 16 defined by cylindrical wall 18 and wall 20 which is transverse to the axis 22 of said cylindrical cavity 16. As is well-known in the art, ports communicating with low pressure inlet 14 and high pressure fluid outlet 15 are formed in the upper wall 20.

Mounted for eccentric rotation within cavity 16 is an outer rotor 30 having teeth 32 inter-engaged with teeth 34 of an inner rotor 36. It will be noted that axis 38 of inner rotor 36 is parallel to and off-set from axis 22 of outer rotor 30. The parallel but off-set axis of rotation results in eccentric rotational pumping action as is well-known in the art when inner rotor 36 is driven and may be more fully understood by reference to U.S. Pat. No. 2,792,788. Fixedly mounted to inner rotor 36 is a rotary shaft 39 which is provided with splines 42 for attachment to an external driving means (not shown).

Sealing the opposite end of cavity 16 is a slidable wall 40 which is movable, under certain conditions, along axis 22 while maintaining its sealing relation to cylindrical wall 18. Mounted to housing 12 by a snap ring 42 is a resilient biasing means 44 which resiliently urges wall 40 in a generally upwards direction in FIG. 1. The present resilient biasing means 44 has the embodiment of a Belleville spring.

Wall 40 is formed with a raised boss 46 which will contact the lower end of rotor 36 when said wall is resiliently urged into upward position. It should be noted that due to raised boss 46, a lower surface 48 of wall 40 will not in any position contact outer rotor 30. A clearance 50 is thus formed between surface 48 and the lower end of outer rotor 30 which clearance is of the magnitude of 0.0005 inch which due to the effect of hydrostatic filling will not adversely affect the normal pumping action of rotary pump 10.

Reference to FIG. 3 will indicate a modified form of rotary pump 110 wherein a flat slidable wall 140 is utilized with an elongated inner rotor 136. The effect is identical with that described in the above paragraph, with a clearance 50' of the magnitude of 0.0005 inch being formed between the outer rotor 130 and slidable wall 140. As the operation of pumps 10 and 110 are identical the operation of pump 110 will not be described in detail.

FIGS. 4 and 5 illustrate a further modification of the present invention. In FIGS. 4 and 5 a modified Belleville spring 60 is provided. Modified Belleville spring 60 has a radial slot 62 and two small holes 64 adjacent the radial slot. Utilizing a tool, such as the well-known snap-ring pliers, the holes 64 may be forced closer together, thus decreasing the outer diameter of spring 60 so as to permit insertion thereof into the cavity 16 and retention thereof in the cavity 16 by cooperation of the spring 60 with a groove 69 in the wall 18. Thus, the modified Belleville spring 60 may be utilized as a self-mounting fastening device to retain the movable wall 240 in the cavity 16 and to resiliently bias the movable wall 240 into engagement with the inner rotor 236 thereby eliminating the need for snap rings or other means of retaining the resilient biasing means in place.

The operation of pumps 10, 110 and 210 of FIGS. 1, 3 and 5 respectively is identical and therefore will be described in detail for pump 10 only. In operation, fluid enters pump 10 through inlet 14 from which it is communicated through the inlet port in upper wall 20 to a pumping chamber 70. Pumping chamber 70 is formed by teeth 32 and 34 of inner and outer rotors 30 and 36 respectively together with the upper wall 20 and slidable wall 40. As shaft 39 is rotated in either direction, the chamber 70 is rotated toward outlet 15 and is reduced in size; and the fluid entrapped therein is forced under pressure out the high pressure outlet 15. When pump 10 is generating fluid pressures below the predetermined maximum, biasing means 44 is sufficient to urge slidable wall 40, upward into contact with inner rotor 36 and maintain clearance 50 at a magnitude so as not to interfere with the pumping action. As the generated fluid pressure exceeds a predetermined maximum, the generated pressure force acting upon surface 48 will overcome resilient biasing spring 44 and wall 40 will move away from rotors 30 and 36. As is seen in FIG. 6, this will create an enlarged clearance 50' between wall 40 and outer rotor 30 and a clearance 150 between the inner rotor 36 and the raised boss 46. The clearances 50' and 150 will allow fluid to flow from chamber to chamber and effectively destroy the pumping and pressure creating action of the eccentrically rotating rotors. As the pressure drops to an acceptable level, the slidable wall 40 will be urged upward by resilient means 44 towards the rotors, and clearances 50' and 150 will be closed allowing pumping action to resume.

For comparative purposes, FIG. 7 will illustrate a prior art device 310 in which slidable wall 340 contacts both inner rotor 346 and outer rotor 330. The upper surface of wall 340 has been divided into surfaces 301, 302, 303, 304 and 305 for illustrative purposes.

It should be noted, the reaction force generated by the fluid pressure, of that force which will tend to overcome the bias, is equal to generated fluid pressure times wall area in contact with the fluid. It may easily be seen by reference to FIGS. 6a and 7a that the area of the present invention in contact with fluid pressure, namely 101 and 103, far exceeds that contact area of the prior art device, namely 302 and 304. Thus, for any given generated fluid pressure, the resulting generated reaction force will be greater in the present invention than in the prior art device. By increasing the force generated by any given pressure it is possible to design a pressure relief sensitive to smaller increments of pressure differentials.

Applicant's novel arrangement of slidable wall 40 and rotors 30 and 36 has the effect of amplifying the pressure relief reaction to any given pressure differential.

It should also be noted that the clearance 50' required to crack the pumping chambers and allow fluid to flow between the rotors is partially formed by the gap 50. Therefore, the movable wall has a lesser distance to move away from the rotors to effect a pressure relief and thus has a faster response than the prior art devices.

By providing a sliding wall type pressure relief that has a larger reaction to a given pressure than does the prior art devices, applicant has invented a more sensitive, quicker acting and therefore more usable device than has been heretofore available.

Claims

Having thus described my invention, I now claim:

1. A rotary pump comprising:

a housing having a cylindrical cavity therein;

inner and outer rotors with inter-engaging teeth forming pumping chambers mounted for eccentric rotational motion within said cavity;

a slidable wall sealing one side of said cavity, said wall being slidable in an axial direction of said cavity and forming a wall for said pumping chambers when said wall is within a predetermined axial distance of said rotors;

resilient biasing means mounted to said housing for resiliently urging said slidable wall into engagement with only one of said rotors, said biasing means permitting said slidable wall to move a distance greater than the predetermined axial distance away from said rotors when said pump generates a pressure greater than a predetermined maximum.

2. The rotary pump of claim 1 wherein said resilient biasing means is a Belleville spring.

3. The rotary pump of claim 2 wherein said Belleville spring has one radial slot and at least one hole proximate each side of said slot.

4. The rotary pump of claim 1 wherein said resilient biasing means is a C-shaped Belleville spring including means permitting gripping of said Belleville spring and tangentially compression thereof.

5. The rotary pump of claim 1 wherein only the inner rotor is contacted by said slidable wall.

6. The rotary pump of claim 1 wherein said slidable wall is formed with a substantially centrally located raised boss so as to contact the inner rotor only.

7. The rotary pump of claim 1 wherein said inner rotor extends to a position beyond said outer rotor so as said slidable wall will contact said inner rotor only.

8. A rotary pump comprising:

a housing having a substantially cylindrical cavity therein;

inner and outer rotors having inter-engaging teeth forming the side walls of pumping chambers mounted for eccentric rotation within said cavity;

a slidable wall sealing one end of said cavity, said slidable wall additionally forming one wall of said pumping chambers when said slidable wall is within a predetermined distance of said rotors, said slidable wall being formed so as to contact only one of said rotors; and

a resilient biasing means mounted in said housing for resiliently urging said slidable wall in a direction towards said rotors, into an engagement with said one of said rotors and to within a predetermined distance of the other of said rotors, said biasing means allowing said slidable wall to move a distance greater than the predetermined distance from said rotors when said pump generates greater than a predetermined maximum pressure.

9. A rotary pump comprising:

a housing having a substantially cylindrical cavity containing eccentrically rotating inner and outer rotors;

a wall slidable within and sealing one end of said cavity, said wall interacting with said rotors to form pumping chambers when said wall is located within a predetermined axial distance of one of said rotors and in contact with the other of said rotors: and

biasing means mounted to said housing for locating said wall within the predetermined axial distance from said one of said rotors and biasing said wall into engagement with the other of said rotors provided the pump generated pressure does not exceed a predetermined maximum pressure.

10. The combination of claim 9 wherein said wall is formed with a centrally raised boss.

11. The combination of claim 9 wherein the inner rotor is longer than the outer rotor, thereby exposing a larger area of said wall to pump generated pressure.

12. The combination of claim 9 wherein said biasing means is a C-shaped, self-retaining Belleville spring.