Oil pump apparatus

Abstract: An oil pump apparatus (100) comprising a housing (10), an outer rotor (22) having a substantially cylindrical outer periphery rotatably received in a substantially cylindrical recess (11s) in the housing (10). A plurality of circumferentially equally spaced gear teeth (22a) are formed on the inner peripheral surface of the outer rotor (22). The oil pump apparatus (100) further comprises an inner rotor (21), on the outer peripheral surface of which is disposed a plurality of gear teeth (21a). The gear teeth (21a) on the inner rotor (21) are in partial meshing engagement with the gear teeth (22a) on the outer rotor (22) so as to define a plurality of working chambers (R) therebetween. The inner rotor (21) is driven by a drive shaft (32), and a plurality of mounting lands are disposed on the inner periphery of the inner rotor (21) for contact with the drive shaft (32).

Description: Field of the Invention The present invention generally relates to an oil pump apparatus. More particularly, the present invention relates to an oil pump apparatus including an inner and outer rotor which are disposed in a housing, with a shaft rotatably connected to the inner rotor which in turn rotates the outer rotor. Background of the Invention An oil pump apparatus is described in Japanese unexamined Patent Publication No. Shou. 63-223382. This apparatus includes an inner rotor, an outer rotor, a housing and a crank shaft. The inner rotor is substantially cylindrical in shape, and rotational force is transmitted thereto from the crank shaft. Furthermore, the inner rotor includes a journal portion at its inner periphery. The inner peripheral surface of the inner rotor extends along the outer peripheral surface of the crank shaft. The housing includes a receiving portion which receives the journal portion of the inner rotor so as to maintain the inner rotor in a set position. This arrangement is quite complex and is susceptible to low levels of tolerance. Therefore, precise manufacturing of the inner rotor and the housing is required. As the journal portion of the inner rotor is forced against the housing, a rotational resistance between the journal portion and the receiving portion is established. This rotational friction enduces premature wearing of the receiving portion of the housing. An example of an internal gear oil pump without a journal portion of the inner rotor is disclosed in US 5215165A, on which the preamble of claim 1 is based. SUMMARY OF THE INVENTION The present invention provides an oil pump apparatus comprising: a housing; an outer rotor having a substantially cylindrical outer periphery rotatably received in a substantially cylindrical recess in the housing, and a toothed inner periphery; an inner rotor having a toothed outer periphery partially in mesh with the teeth on the outer rotor; the inner rotor being mounted on a drive shaft rotatably mounted in the housing and being drivingly connected to the drive shaft; the inner and outer rotors having their axes offset one from the other to create a plurality of working chambers between the teeth of the inner and outer rotors to convey hydraulic fluid from an inlet port in the housing to an outlet port in the housing as the inner rotor rotates, driving the outer rotor; wherein the mounting of the inner rotor on the drive shaft is through a circular array of discrete spaced mounting lands defining axially extending zones of contact between the inner rotor and the drive shaft, those zones of contact being separated by axially extending oil passages between the inner rotor and the drive shaft. BRIEF DESCRIPTION OF THE DRAWINGS Additional detailed features of the present invention will become apparent from the following description and from the following detailed drawings wherein: Fig. 1 is a front view of an oil pump apparatus in accordance with the preferred embodiment of the present invention; Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1; Fig. 3 is a front view of an inner rotor in accordance with the preferred embodiment of the present invention; and Fig. 4 is a cross-sectional view taken along line IV-IV of Fig. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention will be explained below based on the drawings. Figs. 1 and 2 show a structure of an oil pump apparatus 100. Fig. 1 is a front view of the oil pump apparatus 100. The oil pump apparatus 100 includes a housing 10, an inner rotor 21 and an outer rotor 22. The housing 10 includes a body 11 and a cover 12. The body 11 has a cylindrical concaved portion 11s. The inner rotor 21 and the outer rotor 22 are disposed into the cylindrical concaved portion 11s of the housing 10. As shown in Fig. 2, the oil pump apparatus 100 is located on the side end of an engine block 31 and is rotatably driven by a crank shaft 32. An oil seal 33 is located between the outer peripheral surface of the crank shaft 32 and the body 11 of the housing 10. At the end of the crank shaft 32, a crank pulley 34 is attached. The crank pulley 34 drives a timing belt 35, which in turn drives a cam shaft and a water pump apparatus (not shown). The cover 12 is fixed to the body 11 by ten flat-head screws 13. The body 11 and the cover 12 have holes 11a and 12a, respectively. The crank shaft 32 is rotatably received within the holes 11a and 12a of the housing 10. The body 11 has two attaching holes 11b and 11k into which pins (not shown) on the engine block 31 are inserted, and has nine installing holes 11c, 11d, 11e, 11f, 11g, 11h, 11i, 11j, 11m into which bolts (not shown) are inserted for connecting the body 11 of the housing 10 to the engine block 31. The body 11 also has a hole 11n into which an installing bolt (not shown) is inserted for attaching an auxiliary apparatus such as a water pump, an alternator or a pump for power steering (not shown). The cylindrical concaved portion 11s of the body 11 includes a suction port 11p and a discharge port 11q. As shown in Fig. 1 and Fig. 3, the inner rotor 21 has ten external gear teeth 21a on the outer peripheral surface thereof and an inner hole 21b. The inner hole 21b includes four projections 21c for supporting the outer surface of the crank shaft 32. Each projection 21c extends radially towards the centre of the crank shaft 32. The projections 21c are equidistantly located on the inside circumference of the inner rotor 21. Thereby, oil passages S1 are formed between the outer peripheral surface of the crank shaft 32 and the inner peripheral surface of the inner rotor 21, as shown in Fig. 3. The oil passages S1 have a width of about 0.2 millimeter. Further, the inner hole 21b has a pair of projectional members 21d and 21e, which engage with a pair of plane surfaces 32a and 32b on the outer surface of the crank shaft 32 so as to prevent circumferential sliding of the inner rotor 21 on the crank shaft 32. As shown in Fig. 3, the projectional member 21d has a concaved ditch 21h and the projectional member 21e has a concaved ditch 21j. The clearance S2 between the concaved ditch 21h and the plane surface 32b is provided as an oil passage. The clearance S3 between the concaved ditch 21j and the plane surface 32a is provided as another oil passage. As shown in Fig. 2, the side surface 21f of the inner rotor 21 slidably contacts a bottom surface 11r of the cylindrical concaved portion 11s of the body 11 and the side surface 21g of the inner rotor 21 slidably contacts an internal surface 12b of the cover 12. The outer rotor 22 is located in the cylindrical concaved portion 11s of the body 11. The centre axis of the outer rotor 22 and the centre axis of the inner rotor 21 are displaced with a predetermined distance. The outer rotor 22 has eleven internal gear teeth 22a on its inner peripheral surface. These internal gear teeth 22a engage the external gear teeth 21a of the inner rotor 21 so as to form a plurality of pump chambers R. The external gear teeth 21a of the inner rotor 21 and the internal gear teeth 22a of the outer rotor 22 are designed to be trochoid curves. There is a clearance L between the outer peripheral surface of the outer rotor 22 and the inner peripheral surface of the cylindrical concaved portion 11s. The clearance L is about 0.3 millimeter. This clearance L absorbs the rotational vibration of the crank shaft 32. The operation of the oil pump apparatus discussed above will be hereinafter described. The inner rotor 21 is connected to the crank shaft 32, and is rotated together with the crank shaft 32. The inner rotor 21 is rotated in the direction of the arrow Y as indicated in Fig. 1. As the inner rotor 21 is rotated, the external gear teeth 21a of the inner rotor 21 engage with the internal gear teeth 22a of the outer rotor 22 sequentially. Accordingly, the outer rotor 22 is rotated in the same direction. Between the internal gear teeth 22a and the external gear teeth 21a, chambers R are formed as shown in Fig. 1. The chambers R suck the hydraulic oil from the suction port 11p and discharge the hydraulic oil to the discharge port 11q, when both the inner rotor 21 and the outer rotor 22 are rotated. The crank shaft 32, the inner rotor 21 and the outer rotor 22 are prone to vibration when rotated. A reason for this is the crank shaft 32 may not be perfectly straight or the oil pump apparatus 100 itself may not be located correctly or the crank shaft 32 may not be located correctly. However, the clearance L absorbs this vibration. In addition, when both the inner rotor 21 and the outer rotor 22 are rotated, hydraulic oil may leak from the chambers R through the clearance between the side surface 21f of the inner rotor 21 and bottom surface 11r of the cylindrical concaved portion 11s of the body 11, or the clearance between the side surface 21g of the inner rotor 21 and inside surface 12b of the cover 12. Hydraulic oil leaked in this manner is returned into the engine block 31 through the passages S1, S2 and S3.

Claims: An oil pump apparatus comprising: a housing (10); an outer rotor (22) having a substantially cylindrical outer periphery rotatably received in a substantially cylindrical recess (115) in the housing (10), and a toothed (22a) inner periphery; an inner rotor (21) having a toothed (21a) outer periphery partially in mesh with the teeth (22a) on the outer rotor (22); the inner rotor (21) being mounted on a drive shaft (32) rotatably mounted in the housing (10) and being drivingly connected to the drive shaft (32); the inner and outer rotors (21,22) having their axes offset one from the other to create a plurality of working chambers R between the teeth (21a,22a) of the inner and outer rotors (21,22) to convey hydraulic fluid from an inlet port (11p) in the housing (10) to an outlet port (11a) in the housing as the inner rotor (21) rotates, driving the outer rotor (22); CHARACTERISED IN THAT : the mounting of the inner rotor (21) on the drive shaft (32) is through a circular array of discrete spaced mounting lands (21c) of the inner rotor (21) contacting a cylindrical outer peripheral portion of the drive shaft (32) to mount the inner rotor (21) concentrically on the drive shaft (32), the mounting lands (21c) defining axially extending zones of contact between the inner rotor (21) and the drive shaft (32) equidistantly spaced around the inner peripheral surface (21b) of the inner rotor (21), which zones of contact are separated by axially extending oil passages (51) between the inner rotor (21) and the drive shaft (32). An oil pump apparatus according to claim 1, wherein the mounting lands (21c) comprise the radially inner extremities of a circular array of projections (21c) extending radially inward from the inner peripheral surface (21b) of the inner rotor (21). An oil pump apparatus according to claim 1 or claim 2, wherein the axially extending oil passages (S1) formed between the inner rotor (21) and the drive shaft (32) extend from one end face (21f; 21g) of the inner rotor (21) to the other (21g; 21f). An oil pump apparatus according to any preceding claim, wherein four mounting lands (21c) at 90° spacings are disposed between the inner rotor (21) and the drive shaft (32). An oil pump apparatus according to any preceding claim, wherein at least one drive flat (21d, 21e) is disposed on the inner peripheral surface (21b) of the inner rotor (21) to engage with at least one plane surface (32a, 32b) on the drive shaft (32). An oil pump apparatus according to claim 5, wherein an axial concave portion (21h, 21j) is formed on the radially inner surface of the or each drive flat (21d, 21e), thereby providing one or more further oil passages (S2, S3).

Inventors: MIURA YOSHINORI, MIURA, YOSHINORI
Applicants: AISIN SEIKI, AISIN SEIKI KABUSHIKI KAISHA
Application year: 1998
Main classification: F04C2
IPC codes: F04C2, F04C15