GB2367590A

GB2367590A - Internal pump with dissimilar rotor materials

Info

Publication number: GB2367590A
Application number: GB0120842A
Authority: GB
Inventors: Jun Yoshioka
Original assignee: Dana Inc
Current assignee: Dana Inc
Priority date: 2000-08-28
Filing date: 2001-08-28
Publication date: 2002-04-10
Also published as: DE10141863A1; JP2002106475A; GB0120842D0

Abstract

An internal gear pump or a gerotor pump is provided, wherein the inner (10) and outer (20) rotors are made of different materials having different coefficients of thermal expansion to thereby vary the tip clearance therebetween according to temperature change. With this arrangement, the internal pump with dissimilar rotor materials provides a thermal/viscosity compensation mechanism that reduces the temperature effect in the pump efficiency.

Description

2367590 Internal Pump With Dissimilar Rotor Materials

BACKGROUND OF THE NVENTION

1. Field of the Invention'

5 This invention concerns hydraulic devices and more particularly relates to a hydraulic PUMP that provides efficient operation when used with fluids at extremely cold temperatures and at extremely hot temperatures and at tenperatures therebetween.

2. Description of Related Art

10 Internal gear pumps and gerotor pumps are positive displacement fluid pumps the design of which is based on the use of a gear with teeth around the outer prirneter of an inner rotor engaged by the gear teeth around the inner perimeter of a larger ring- shaped rotor. The axes of rotation of the two rotors are displaced one from the other by a distance. equal to the difference between the pitch radfi of the two gears or rotors. In addition, the axes of rotation of thetwo 15 rotors are maintained by the inner rotor being mounted to a bearing supported shaft and the outer rotor supported within a cylindrical bore that is rigidly located relative to the center of rotation of the shaft of the inner rotor.

As is conventional, the outer rotor of the internal gear pump and the outer rotor of the gerotor pump each rotate within the cylindrical bore of the pump housing. In the presence of the 20 fluid being pumped, the outer cylindrical surface of the rotating outer rotor and the stationary housing cylindrical bore act as a hydrodynamic journal bearing. Thus, when the pump is used to pump fluids such as oils having high lubricity and viscosity a "bearing effect" is realized, i.e. the fam. of oil between the peripheral surface of the rotating outer rotor and the inner surface of the stationary cylindrical bore serves to reduce friction and bear loads without wear. The effectiveness of the "bearing effect" depends upon many factors not the least of which is the lubricity and the viscosity of the fluid being pumped vis-a-vis the relative speed of the parts and the load applied to the film of the fluid. As in the case of most hydrodynamic journal be 5 designs, it is generally considered a necessity that the outer rotor and the housing be made of different materials because of a tendency for the affinity of like materials to experience some molecular bonding and material transfer.when in contact under load.

However, the conventional design does not account for leakage and changes that occur between the tip and lobes of the inner and outer rotor as a result-of extreme temperatures. When 10 using an internal pump to create hydraulic pressure in conditions where temperatures vary, the effect of viscosity change with temperature (i.e., viscosity reduction as temperature increases) reduces the pump efficiency due to an increase in the internal leakage at the tip between'the inner and outer rotor/gerotor. The prior art fails to address these deficiencies and drawbacks inherent in the prior art.

15 Accordingly, there is a need for pumps of the above-described type to be made so as to efficiently and durably pump fluids at widely varying temperatures and/or viscosities and/or lubricates without wear, with low friction and with high and constant efficiency.

SLT&04ARY OF THE MVENTION 20 The present invention contemplates a gear pump, such as an internal gear pump or a gerotor pump, wherein the inner and outer rotors are of different materials of different coefficient of thermal expansion to thereby vary the tip clearance according to temperature change. With 2 this arrangement, the internal pump with dissimilar rotor materials provides a thermal/vis cosity compensation mechanism that reduces the temperature effect in the pump efficiency.

Accordingly, one object of the present invention is to provide a new and improved positive displacement hydraulic pump for use with super-cooled. and super-heated fluids and for 5 use with fluids at a temperature between the temperatures of the super- cooled and superheated fluids.

A further object of the present invention is to provide a new and improved gear-type positive displacement hydraulic pump having an inner rotor and an outer rotor with the inner rotor having at least one less tooth than the outer rotor and has its centerline positioned at a fixed M eccentricity from the centerline of the outer rotor and in which the outer rotor is supported for rotation by a plurality of cylindrical roller bearings interposed between a support housing and the outer rotor and in which the rotors are made. of a different material and have different coefficient of thermal expansion.

is BREEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and features of the present invention will be apparent from the following detailed description when taken with the drawings in which:

FIGS. I a-11 are schematic views showing the operation ofan internal (gerotor-type) hydraulic pump made in accordance with the present invention; 20 FIG. 2 is a cross section of the internal hydraulic pump shown in Fig. l a shown the fluid inlet and discharge ports.

FIGS. 3a and 3b are sectional views showing the t ip clearance between the inner and outer gerotors impacted by the principle concepts of this invention.

3 DETAILED DESCRIPTION OF PREFERRED ENMODINENT

Refening to the drawings and more particularly FIGS. I a- I I and 2 thereof, the gerotor illustrated is a positive displacement pumping unit consisting ofj.ust two elements - an inner 5 rotor 10 and an outer rotor 20. The pumping unit of this invention is suitable for a variety of applications including but not limited to a clutch system for a drive train and/or a differential assembly.

With reference to FIG. I a, the inner r6tor 10 has one less tooth 10' that the outer rotor 20 and has its centerline 12 positioned at a fixed eccentricity from the centerline 22 of the outer 10 element 20. Although gerotor pumps come in a variety of geometric configurations, materials and sizes, all share the same basic principal of having one less tooth on the inner driving element. Conjugately-generated tooth profiles maintain continuous fluid tight contact during operation.

As the gerotor revolves, liquid is drawn from the inlet (see FIG. 2) into the enlarging 15 chamber to a maximum volume equal to that of the missing tooth on the inner element The liquid is forced out as the teeth.mesh, decreasing the chamber volume. As the input shaft (and mner rotor) begins to rotate (see FIGS. 1 a- 1 e), the gap between the inner and outer rotor roots 14, 24 increases in volume, creating a vacuum, causing fluid to be drawn into the chamber 50 through the inlet 30 (see FIG. 2). In FIG. If, the chamber 50 has reached its maximum volume.

20 At this point, the tips 16 and lobes 26 seal the chamber 50 from both the inlet 30 Oow pressure) and the outlet or discharge 40 (high pressure).

Further shaft rotation as depicted in FIGS. Ig through 11 causes the chamber 50 to become connected to the discharge port 40, and as additional rotation occurs, the chamber's 4 volume becomes smaller, forcing fluid out -until the chamber 50 is substantially empty. The foregoing process occurs constantly for each chamber, thus providing a smooth pumping action.

As aforementioned, a design parameter that must be controlled carefully in pumps of the above-described type in order that the efficiency of the pumps be. kept as high as possible is the 5 tip-cleamce because it represents a leak path from the high pressure cavity to the low pressure cavity of the pump. In this case, the tip- clearance of e' ach stage of the gerotor fuel pump is partly controlled by carefully selecting the materials for the inner and outer rotors taking into account their coefficients of thermal expansion.

The essence of this invention consists of making the inniT and outer rotor with material 10 having different coefficients of thermal expansion so that by varying the temperature, the tip clearance would also vary. For example, by making the inner gerotpr of aluminum and the outer gerotor of steel, the tip clearance would reduce as temperature increases due to the different coefficient of thermal expansion. Making the outer gerotor of aluminum and the inner gerotor of steel would have an opposite effect.

15 Alffiough this disclosure will provide an exhaustive analysis of gerotor geometry, the principles of this invention are set forth in the following -example and one skilled in the art would be enabled to generate the complex computations, e.g., FEA thermal analysis, associated with a model embodying this invention.

In this example to estimate the reduction of clearance between two thin cylinder coaxial to each other, the outer cylinder is made of steel with a coefficient of thermal expansion of K=1 1.5 times 10-6, and the inner cylinder is made of aluminum with a coefficient of thermal expansion of K=22 times 10-6. At 296K, the radial clearance between the two cylinders when both are eccentric to each other is (4.000" - 3.900'/2 --0.050". 5 Increasing the temperature by I 00'Y, would change the dimensions for the cylinders by the following amount:

Steel cylinder diameter = 4.00011 + (4.000" Kst - I OOK) = 4.0046" Aluminum cylinder diameter= 3.900" + (3.900" - Kw - I POK) = 3.9086" 5 The clearance at 396K is (4-0046" - 3.9086')/2 = 0.048" which is a reduction of 0,002" for an increase of I 00M.

This example uses steel and aluminum but any material can be selected to provide a desired compensation of the tip clearance with the increase or decrease in temperature. See FIGSAa and 3b showing tip clearance."IF for a tooth and lob,6 arrangement 10 Accordingly, from the above it can be concluded that because the effect of the temperature change on the gerotor pump made according to the present invention can be controlled and nianipulated, the pump can be manufactured to design operating tip-clearance dimensions based on viscosity of the hydraulic fluid utilized by the pump and the associated tip clearance changes associated with the thermal conditions of the pump.

15 Various changes and modifications can be made in the construction of the gerotor pu mp described above without departing from the spirit of the invention. Such changes and modifications are contemplated by the inventors and they do not wish to be limited except by the scope of the appended claims.

6

Claims

Claimsi

1. A positive displacement hydraulic pump comprising:

an inner rotor having a plurality of external teet formed thereon, a ring-shaped outer rotor having a plurality of internal teeth and being formed with an 5 outer cylindrical surface, said external teeth of said inner rotor in meshing engagement with said internal teeth of said outer rotor, said external teeth formed on said inner rotor being at least one less in number han the number of internal teeth formed on saidbuter rotor, said inner rotor having its axis of rottion positioned at a fixed eccentricity from th e axis of rotation of said outer rotor and said external teeth of said inn6rrotor and said internal teeth of 10 said outer rotor having generated tooth profiles adapted to maintain a continuous fluid tight contact during rotation of said inner and outer rotors, wherein said inner rotor is made of a first material having a first coefficient of thermal expansion and said outer rotor is made of a second material having a second coefficient of therm al expansion, said first coefficient of friction being different than said second coefficient of 15 f1detion to compensate for changes in viscosity based on a tip clearance between said inner and outer rotors.

2. The hydraulic pump according to claim 1, wherein said. first coefficient is larger than said second coefficient.

3. The hydraulic pump according to. claim 1, wherein said first coefficient is smaller than said second coefficient.

7

4. The hydraulic pump according to claim 1, said internal teeth of said outer rotor have generated tooth profiles for maintaining continuous fluid tight contact during rotation of said inner and outer rotors within a wide range of temperatures.

5. The hydraulic pump according to claim 1, wherein a tip clearance between said external teeth of said inner rotor and said internal teeth of said outer rotor varies in proportion to a viscosity change of said hydraulic fluid based on temperature.

6. The hydraulic pump according to claim 1, further comprising a ringshaped stationary 10 support housing for said inner and outer rotors, an inner cylindrical surface formed in said support housing.

7. The hydraulic pump 'according to claim 6, finther comprising a plurality of roller bearings interposed between and in direct contact with said inner cylindrical surface of said 15 support housing and the outer cylindrical surface of said outer rotor.

8. The hydraulic pump according to claim 7, firther comprising a pair of end plates fixed to said support housing and cooperating with the latter to enclose.said inner and outer rotors, a drive shaft extending through said pair of end plates for driving connection with said inner rotor, 20 one of said pair of end plates having a fluid inlet port formed therein and the other of said pair of end plates having a fluid outlet port formed therein, said inlet port and said outlet port being located relative to said inner and outer rotors so that rotation of said inner rotor and said outer rotor creates an expanding chamber adjacent said inlet port for drawing fluid therein while 8 simultaneously creating a contracting chamber adjacent said outlet port for forcing the fluid through said outlet port at a high pressure.

9. A method of compensating for the effects of viscosity change resulting from temperatures in a positive displacement hydraulic pump, said method comprising the steps of. providing an inner rotor having a plurality of external teeth formed thereon made of a fir-st material having a first coefficient of thermal expansion, providing a ring-shaped outer rotor having a plurdlity of internal teeth made of a second material having a second coefficient ofthermal. expansion diffeient than said first coefficient of thermal expansion, positioning said inner rotor to have its axis of rotation positioned at a fixed eccentricity from the axis of rotation of said outer rotor, said external teeth of said inner rotor in meshing engagement with said internal teeth of said outer roto r, wherein said external teeth formed on said inner rotor being at least one less in number than the number of internal teeth formed on said outer rotor, providing a hydraulic fluid. to said inner and outer rotors via inlet and discharge ports, choosing said first and second coefficients of thermal expansion to provide a continuous fluid tight contact between said external teeth of said inner rotor and said internal teeth of said outer rotor during rotation of said inner and outer rotors taking into account a change in viscosity of said hydraulic fluid.

9

10. The method according to claim 9, wherein a tip clearance between said external teeth of said inner rotor and said internal teeth of said outer rotor varies with temperature in proportion to a viscosity of said hydraulic fluid.

5

11. A hydraulic pump substantially as described herein with reference to, and as shown in, the accompanying drawings.