Oil pump

An oil pump has a pump body, an outer rotor, and an inner rotor. The pump body includes a rotor chamber, an inlet port and an outlet port formed in the rotor chamber, an inlet passage communicating with the inlet port, an outlet passage communicating with the outlet port, a relief valve, a relief chamber formed on a discharge side of the relief valve, and an oil return passage formed from the relief chamber to the inlet passage. The outer rotor is supported by the inner circumferential support wall of the rotor chamber. The oil return passage is formed in the inner circumferential support wall as a groove-like recess and opens along an outer circumferential surface of the outer rotor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a configuration of an oil pump that can achieve a size reduction of the entire pump, reduction in wear of the rotor during operation and that can also achieve longer pump life and reduction in production cost.

2. Description of the Related Art

There are, as conventionally known, internal gear oil pumps with a relief valve. Japanese Patent Application Laid-open No. S63-246482 discloses a specific configuration of such an oil pump. The pump according to Japanese Patent Application Laid-open No. S63-246482 has in general a configuration, in which a circular recess6in which inner and outer rotors are arranged has a smooth cover attachment surface22therearound to attach a cover24, and a plurality of bolt holes23drilled at suitable locations for fastening the cover24.

An oil return passage26is formed in the cover attachment surface22in the form of a groove from near a discharge chamber11toward an inlet chamber10. One end of this oil return passage26opens to an inlet passage12, while the other end extends as far as to a portion adjacent the discharge chamber11. The cover attachment surface22is thus divided into a pump chamber-side portion22athat surrounds the circular recess6, and an outer portion22b.

A side hole27a, which is drilled in a middle position of a relief passage27that opens to an outlet passage14, opens to the oil return passage26. A known relief valve28is mounted in the relief passage27, so that lubricating oil under excess pressure is discharged into the oil return passage26through the side hole27ato flow back to the inlet chamber10when the pressure of discharged oil exceeds a predetermined value.

SUMMARY OF THE INVENTION

According to Japanese Patent Application Laid-open No. S63-246482, the pump chamber-side portion22ais provided between the oil return passage26and the circular recess6so as to separate the oil return passage26and the circular recess6. Accordingly, the pump casing5is increased in size radially outward by the width of the pump chamber-side portion22a.

The oil return passage26is formed independently of and located away from the circular recess6. The pump casing5has a complex shape because of such a configuration, which causes high production cost. The flow path of the relief oil is long since the oil return passage26is formed at a position away from the circular recess6, because of which the relief oil may not flow smoothly and it is highly likely that the pressure relief action may not be performed properly.

The technical solutions (objects) of the present invention are to achieve: efficient return of relief oil to the inlet side by a relief valve to ensure a favorable pressure relief action; retardation of wear of the rotor mounted in the pump body to increase pump life; a very compact design; and simple production.

Through vigorous research, the inventors have achieved the above objects by providing an oil pump, which, according to a first aspect of the present invention, includes: a pump body; an outer rotor; and an inner rotor, the pump body including a rotor chamber having an inner circumferential support wall on an inner circumferential side, an inlet port and an outlet port formed in the rotor chamber, an inlet passage communicating with the inlet port, an outlet passage communicating with the outlet port, a relief valve allowing oil to flow from the outlet passage to the inlet passage by relieving pressure, a relief chamber formed on a discharge side of the relief valve, and an oil return passage formed from the relief chamber to the inlet passage; the outer rotor being supported by the inner circumferential support wall of the rotor chamber; and the inner rotor being arranged on an inner side of the outer rotor. The oil return passage is formed in the inner circumferential support wall as a groove-like recess and opens along an outer circumferential surface of the outer rotor.

According to a second aspect of the present invention, in the oil pump according to the first aspect, the oil return passage is formed at and around a symmetric point of a maximum partition part located between a trailing end of the inlet port and a leading end of the outlet port relative to a center point of the rotor chamber, whereby the above objects were achieved. According to a third aspect of the present invention, in the oil pump according to the first aspect, the oil return passage is formed at an upper end portion in a depth direction of the inner circumferential support wall and opened in a surface portion of the rotor chamber, whereby the above objects were achieved. According to a fourth aspect of the present invention, in the oil pump according to the third aspect, the oil return passage is formed to a depth from a surface of the rotor chamber less than half a thickness in an axial direction of the outer rotor, whereby the above objects were achieved.

The above objects were achieved by providing an oil pump, which, according to a fifth aspect of the present invention, includes: a pump body; an outer rotor; and an inner rotor, the pump body including a rotor chamber having an inner circumferential support wall on an inner side, an inlet port and an outlet port formed in the rotor chamber, an inlet passage communicating with the inlet port, an outlet passage communicating with the outlet port, a relief valve allowing oil to flow from the outlet passage to the inlet passage by relieving pressure, a relief chamber formed on a discharge side of the relief valve, and an oil return passage formed from the relief chamber to the inlet passage; the outer rotor being supported by the inner circumferential support wall of the rotor chamber; and the inner rotor being arranged on an inner side of the outer rotor. The oil return passage is formed as a gap extending to a same depth in an axial direction as a depth of the rotor chamber between a body wall portion, located between the relief chamber and the inlet passage, and an outer circumferential surface of the outer rotor.

According to a sixth aspect of the present invention, in the oil pump according to the first aspect, the oil return passage is formed by a gap formed in an upper portion of the inner circumferential support wall and by a deep groove formed on a radially outer side of the inner circumferential support wall in close proximity thereto, so as to communicate the relief chamber with the inlet passage, the deep groove communicating with the gap, whereby the above objects were achieved.

According to the present invention, the oil return passage is formed in the inner circumferential support wall from the relief chamber to the inlet passage as a groove-like recess that opens along an outer circumferential surface of the outer rotor. In this configuration, the outer circumferential surface of the outer rotor forms part of the wall of the oil return passage.

Therefore, the oil return passage of the present invention is not a separate groove-like recess formed at a position away from the rotor chamber of the pump body as seen in conventional pumps, but rather, it forms a groove together with the outer circumferential surface of the outer rotor. Accordingly, the oil pump of the present invention can be made smaller and more lightweight than conventional counterparts.

Moreover, the portion of the inner circumferential support wall of the rotor chamber where the oil return passage is formed does not contact the outer circumferential surface of the outer rotor. Therefore, the area of surface where the rotor chamber and the outer rotor substantially contact each other is reduced, and the smaller contact area leads to lower friction resistance, whereby drive loss is reduced and fuel economy is increased.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The oil pump according to the present invention is generally comprised of a pump body A, an outer rotor91, and an inner rotor92(seeFIG. 1). The pump body A is comprised of a rotor chamber11, an inlet port14, an outlet port15, and a relief valve2(seeFIG. 2).

The outer rotor91and inner rotor92are trochoid or substantially trochoid gears. The outer rotor91has a plurality of inner teeth91gformed on the inner periphery, while the inner rotor92has a plurality of outer teeth92g. The inner rotor92has one fewer number of outer teeth92gthan the number of inner teeth91gof the outer rotor91, so that there are formed a plurality of interteeth spaces S between the inner teeth91gof the outer rotor91and the outer teeth92gof the inner rotor92.

The rotor chamber11is made up of an inner circumferential support wall11aand a bottom11b. In the present invention, a pump cover B may be provided to the pump body A, and they are both mounted at predetermined locations on an engine housing of a car or the like. The pump body A has a body wall portion1aat the outer periphery. The distal end of the body wall portion1ais formed flat. Suitably spaced bolt holes1bare formed in the body wall portion1afor fixedly attaching the body to the pump cover B with fastening means such as bolts.

A shaft hole12is formed in the bottom11bof the rotor chamber11for a drive shaft8to pass through (seeFIG. 1). Also formed in the bottom11bare the inlet port14and the outlet port15. Between the trailing end14tof the inlet port14and the leading end15fof the outlet port15is formed a maximum partition part16, while, between the trailing end15tof the outlet port15and the leading end14fof the inlet port14is formed a minimum partition part17(seeFIG. 2).

An inlet passage14acommunicates with the inlet port14. The inlet passage14acommunicates with the outside of the pump body A and allows oil to flow in from a lubrication circuit outside the pump body A. An outlet passage15acommunicates with the outlet port15. The outlet passage15aallows oil to flow out to the lubrication circuit outside the pump body A.

The inner circumferential support wall11aof the rotor chamber11is a portion that holds and rotatably supports the outer rotor91. The inner circumferential support wall11aforms a cylindrical inner wall surface, which is non-continuous at portions where it intersects with the inlet port14and the outlet port15(seeFIG. 2A). Namely, the inner circumferential support wall11aof the rotor chamber11is formed from a plurality of wall parts, which hold the outer circumferential surface91aof the outer rotor91(seeFIG. 3A).

The relief valve2is provided between the inlet port14and the outlet port15, and serves to return oil from the outlet port15side to the inlet port14side when the pressure of discharged oil exceeds a predetermined value. A valve member passage21ais formed inside a valve housing21, and a relief passage21bis formed at one end in the longitudinal direction of the valve member passage21ato communicate with the outlet passage15a. Part of the oil flowing through the outlet passage15aenters the valve member passage21athrough the relief passage21bas relief oil.

A relief drain hole21cis formed in the valve housing21, so that the valve member passage21ainside the valve housing21communicates with the outside. The relief drain hole21cis opened and closed by a valve member22to be described later. The relief drain hole21cis opened to relieve pressure (seeFIG. 3A).

The valve member22and a resilient member23are arranged inside the valve member passage21asuch that the resilient member23resiliently presses the valve member22to close the relief passage21b. More specifically, a coil spring is used as the resilient member23. A relief chamber18is formed around a portion where the relief drain hole21cis formed in the valve housing21(seeFIG. 1A,FIG. 2A,FIG. 3A, and others). The relief chamber18is a cavity (space) that communicates the relief drain hole21cwith the inlet port14. The relief chamber18serves to deliver the oil drained from the relief drain hole21cinto the inlet port14.

Next, an oil return passage3in the first embodiment of the present invention will be described. The oil return passage3is formed in a suitable region of the inner circumferential support wall11aof the rotor chamber11. The oil return passage3is formed at a location opposite from the maximum partition part16, with the rotation center Pa of the outer rotor91being in the middle as a center point, i.e., at a symmetrical point (seeFIG. 2A). This location includes the surrounding region. The oil return passage3is formed in the inner circumferential support wall11abetween the relief chamber18and the inlet passage14a.

The oil return passage3is formed as a substantially arcuate recess extending along the circumferential direction of the rotor chamber11in a suitable region of the inner circumferential support wall11a(seeFIG. 2). The oil return passage3is formed to have a substantially L-shaped cross-sectional shape in a section orthogonal to the circumferential direction from the upper end face to the inner side face of the inner circumferential support wall11a. The corner of the oil return passage3with a substantially L-shaped cross-sectional shape may either be rounded or orthogonal.

The inner circumferential support wall11ais shaped like the rest thereof below the oil return passage3in the depth direction so as to support the outer circumferential surface91aof the outer rotor91housed in the rotor chamber11(seeFIG. 1BandFIG. 2B). Therefore, the outer rotor91is prevented from moving in radial directions by parts of the inner circumferential support wall11asupporting the outer circumferential surface91aof the outer rotor91. As radial rocking movement of the outer rotor91is reduced, knocking noise produced by the outer rotor91colliding the rotor chamber11, or damage to the outer rotor91, can be reduced.

Part of the outer circumferential surface91aof the outer rotor91that passes the region of the oil return passage3forms the substantially groove-like recess together with the oil return passage3. The oil return passage3is a fluid passage that communicates the relief chamber18with the inlet passage14aand allows the relief oil to return from the relief chamber18back to the inlet passage14athrough the oil return passage3(seeFIG. 2A).

The relief oil flowing through the oil return passage3thus makes direct contact with the outer circumferential surface91aof the outer rotor91, so that, as the outer rotor91rotates inside the rotor chamber11, oil can be distributed between the outer circumferential surface91aof the outer rotor91and the inner circumferential support wall11a(seeFIG. 3AandFIG. 3B).

Since the oil return passage3is formed along the outer circumferential surface91aof the outer rotor91, the pump body A can be made smaller as compared to the conventional pump that has the oil passage at a position away from the rotor chamber11. The contact area between the inner circumferential support wall11aand the outer circumferential surface91aof the outer rotor91is reduced in the region where the oil return passage3is formed (seeFIG. 1B), so that the friction resistance between the outer rotor91and the rotor chamber11is reduced. Drive loss is accordingly reduced, and fuel economy is improved.

Moreover, since the oil return passage3is located on the opposite side from the maximum partition part16between the trailing end14tof the inlet port14and the leading end15fof the outlet port15, with the rotation center Pa of the outer rotor91being in the middle (at the symmetric point), oil that flows from the relief chamber18back to the inlet passage14apasses through the oil return passage3(seeFIG. 3).

Since the pressure of oil flowing through the oil return passage3is negative, the outer rotor91is pulled from the side of the maximum partition part16toward the oil return passage3by the force of negative pressure f (seeFIG. 3B). The direction in which the outer rotor91is pulled by the force of negative pressure f is indicated by arrow Q inFIG. 3AandFIG. 3C.

Therefore, the tip clearance t between the inner teeth of the outer rotor91and the outer teeth of the inner rotor92on the maximum partition part16(seeFIG. 3C) is reduced. That is, the seal tightness of the interteeth spaces S between the outer rotor91and the inner rotor92on the maximum partition part16is increased, so that leakage from the outlet side to the inlet side is reduced, and the volume efficiency (ratio of actual discharge to theoretical discharge) can be increased.

Moreover, the oil flowing through the oil return passage3can be delivered to the gap between the inner circumferential support wall11aof the rotor chamber11and the outer circumferential surface91aof the outer rotor91and serves as lubricating oil to allow smooth rotation of the outer rotor91(seeFIG. 4A).

Next, the relationship between the depth of the oil return passage3and the length in the thickness direction of the outer rotor91will be explained. One half the length in the depth direction of the rotor chamber11is denoted as Db, while the length in the depth direction of the oil return passage3is denoted as Da (seeFIG. 4B). The imaginary line L in the drawing indicates the centerline in the thickness direction of the outer rotor. The depth direction of the rotor chamber11and the thickness direction of the outer rotor91are the same. The depth Da of the oil return passage3is set smaller than half the length in the depth direction Db of the rotor chamber11.

Therefore, in the region where the oil return passage3is formed, the inner circumferential support wall11aextends from the bottom11bof the rotor chamber11in the height direction to a point beyond half the depth of the rotor chamber11. Accordingly, even if there is created a rotational force M that causes the outer rotor91to swing and tilt relative to the rotor chamber11around the contact point P1between the lower end in the depth direction of the oil return passage3and the outer circumferential surface91aof the outer rotor91, the outer circumferential surface91aof the outer rotor91is supported by part of the inner circumferential support wall11aup to a point higher than half the thickness of the outer rotor.

That is, the outer rotor91is supported by the inner circumferential support wall11aover a range that extends beyond the center of gravity in the axial direction of the outer circumferential surface91a(midpoint of the thickness of the outer rotor91). Therefore, the reaction force F from the contact point P1against the outer rotor91abutting the contact point P1acts on a point higher than the midpoint of the thickness of the outer rotor91(seeFIG. 4B). This configuration makes it difficult for the outer rotor91to tilt inside the rotor chamber11and thus the outer rotor91is prevented from abutting the inner circumferential support wall11aobliquely, and possible damage to the outer rotor91is reduced.

In a second embodiment of the present invention, the oil return passage3is formed substantially at a midpoint in the depth direction of the inner circumferential support wall11aof the rotor chamber11(seeFIG. 5AandFIG. 5B). In this embodiment, the outer circumferential surface91aof the outer rotor91passing the oil return passage3is supported stably by both upper and lower portions of the inner circumferential support wall11aon both sides of the oil return passage3.

In a third embodiment of the present invention, the oil return passage3is formed at the lowermost position in the depth direction of the inner circumferential support wall11aof the rotor chamber11(seeFIG. 5CandFIG. 5D). In the third embodiment, as the oil return passage3is formed at the lowermost position in the depth direction, i.e., at the lower end of the inner circumferential support wall11aand surrounded by the bottom11aof the rotor chamber11and the outer circumferential surface91aof the outer rotor91, it is substantially tubular so that it can deliver relief oil from the relief chamber to the inlet port most stably.

In a fourth embodiment of the present invention, the oil return passage3is not formed in the inner circumferential support wall11aof the rotor chamber11but on the inner side of the body wall portion1a(seeFIG. 6). In this embodiment, the oil return passage3extends axially all along the outer circumferential surface91aof the outer rotor91.

Therefore, in this embodiment, the outer circumferential surface91aof the outer rotor91passing the region where the oil return passage3is formed does not make contact with the inner circumferential support wall11a. The oil return passage3has a large volume so that it can deliver a large amount of relief oil from the relief chamber18to the inlet passage14a.

Next, an oil return passage3in a fifth embodiment of the present invention will be described. The oil return passage3of the fifth embodiment is substantially an embodiment of a narrower concept of the first embodiment described in the foregoing. The oil return passage3of the first embodiment is formed as a groove-like recess in the inner circumferential support wall11aand opens along the outer circumferential surface91aof the outer rotor91. In contrast, the oil return passage3of the fifth embodiment is made up of two parts, a gap31and a deep groove32. The gap31and the deep groove32both extend between the relief chamber18and the inlet passage14aand communicate with each other.

The gap31is formed by cutting away an upper portion of the inner circumferential support wall11aalong the circumferential direction of the wall11a(seeFIG. 7C). In other words, the upper end of the inner circumferential support wall11ais lower in the region where the oil return passage3is formed than other portions of the inner circumferential support wall11a. The top of the inner circumferential support wall11awhere the gap31is formed is flat, and the height is constant. The gap31formed above the inner circumferential support wall11aopens along the outer circumferential surface91aof the outer rotor91(seeFIG. 7C).

The deep groove32is formed on a radially outer side of the inner circumferential support wall11ain close proximity thereto (seeFIG. 7BandFIG. 7C). The deep groove32is a fluid passage that is arcuate similarly to the inner circumferential support wall11a. The deep groove32is formed in communication with and between the relief chamber18and the inlet passage14aas mentioned above, the upper part of the deep groove32communicating with the gap31.

The deep groove32has a rectangular cross-sectional shape, and its bottom may be deeper, or shallower than, or equal to the bottom of the rotor chamber11. The deep groove32should preferably be located closest possible to the inner circumferential support wall11a. The oil return passage3formed by such deep groove32and gap31has a substantially inverted L-shaped cross-sectional shape in a section orthogonal to the circumferential direction of the inner circumferential support wall11a(seeFIG. 7C).

Part of the inner circumferential support wall11astands as an upright wall portion beside the deep groove32. In the fifth embodiment, in this way, the gap31that forms part of the oil return passage3extends along the circumferential direction of the inner circumferential support wall11a, so that the oil return passage3is open along the outer circumferential surface91aof the outer rotor91through the gap31(seeFIG. 7AandFIG. 7B).

According to the fifth embodiment, the oil return passage3formed by the gap31and the deep groove32can return a large amount of relief oil from the relief chamber18to the inlet passage14a, so that the pressure relief action can be performed most favorably. The gap31allows part of the oil being returned to be distributed between the inner circumferential support wall11abelow the gap31and the outer circumferential surface91aof the outer rotor91, so that the outer rotor91can rotate very smoothly.

Similarly to the first to fourth embodiments, the oil return passage3in the fifth embodiment should preferably be formed at or around a location opposite from the maximum partition part16, with the rotation center Pa of the outer rotor91being in the middle as a center point, i.e., at a symmetric point.

According to the second aspect of the invention, the oil return passage is located opposite from the maximum partition part between the trailing end of the inlet port and the leading end of the outlet port, with the rotation center of the outer rotor being in the middle. Namely, the oil return passage is located at or around a symmetric point of the maximum partition part relative to the rotation center of the outer rotor as the point of symmetry.

Relief oil flowing back from the relief chamber to the inlet passage flows through the oil return passage formed at such a position. Since a negative pressure is created by the relief oil flowing through the oil return passage, the outer rotor is pulled from the maximum partition part toward the oil return passage.

The tip clearance between the inner rotor and the outer rotor is reduced on the maximum partition part, or both rotors almost abut each other, so that airtight interteeth spaces are formed between the outer rotor and the inner rotor. Leakage to the inlet side is thus reduced, and the volume efficiency (actual discharge to theoretical discharge) can be improved.

According to the third aspect of the invention, the oil return passage is formed at an upper end portion in the depth direction of the inner circumferential support wall and opened to a surface portion of the rotor chamber. It is therefore provided as a recess in the thickness direction of the outer rotor, with a support portion that partially supports the outer circumference of the outer rotor. That is, the inner circumferential support wall exists in the region of the rotor chamber where the oil return passage is formed.

Since the outer circumferential surface of the outer rotor is supported by the remaining inner circumferential support wall in the region where the oil return passage is formed, the outer rotor is prevented from moving in radial directions. As radial rocking movement of the outer rotor is reduced, knocking noise produced by the outer rotor colliding the pump body or inner circumferential support wall, or damage to the outer rotor, can be reduced.

Since the oil return passage is formed at the upper end portion in the depth direction of the inner circumferential support wall and opened to a surface portion of the rotor chamber, it can be formed by casting in which the casting with holes is removed from the mold, i.e., there is no need of post-processing such as machining or welding but the groove can be formed from the beginning by casting, so that the production cost can be reduced. Other effects of the present invention as described herein are likewise achieved.

According to the fourth aspect of the invention, the oil return passage is formed to a depth from the surface of the rotor chamber less than half the thickness in the axial direction of the outer rotor. That is, the outer rotor is supported by the inner circumferential support wall at the center of gravity in the axial direction of the outer circumferential surface (midpoint of the thickness of the outer rotor), so that it is difficult for the outer rotor to tilt, and thus the outer rotor is prevented from tilting and abutting the inner circumferential support wall of the oil pump body obliquely, and possible damage to the outer rotor is reduced.

According to the fifth aspect of the invention, the oil return passage is formed as a gap between a body wall portion located between the relief chamber and the inlet passage and the outer circumferential surface of the outer rotor. As there is no inner circumferential support wall in the region where the oil return passage is formed in the rotor chamber, the outer circumferential surface of the outer rotor does not contact the inner circumferential support wall there, so that friction resistance is reduced, whereby drive loss is reduced and fuel economy is improved. The oil return passage has a large volume so that it can deliver a large amount of relief oil from the relief chamber to the inlet passage and ensure a favorable pressure relief action. Moreover, the shape of the pump body is made simple, so that molds for casting the pump body can be made simple.

According to the sixth aspect of the invention, the oil return passage is formed as a gap formed in an upper portion of the inner circumferential support wall and a deep groove formed on the radially outer side of the inner circumferential support wall in close proximity thereto, such as to communicate the relief chamber with the inlet passage. The deep groove communicates with the gap so that the gap and the deep groove together can return a large amount of relief oil from the relief chamber to the inlet passage, whereby the pressure relief action can be performed most favorably. The gap allows part of the oil being returned to be distributed between the inner circumferential support wall below the gap and the outer circumferential surface of the outer rotor, so that the outer rotor can rotate very smoothly.