Electric oil pump

A drive rotation shaft is rotatably supported by a first slide bearing between a rotor part and a pump rotor, and is rotatably supported by a second slide bearing on its distal end side of a pump rotor fixing part of the drive rotation shaft. Working oil is supplied to the first slide bearing and the second slide bearing. According to this configuration, since the distal end side of the drive rotation part is rotatably supported by the second slide bearing, inclination of the drive rotation shaft is restricted by an inner peripheral surface of the second slide bearing, thereby suppressing occurrence of noise.

TECHNICAL FIELD

The present invention relates to an electric oil pump, and particularly to an electric oil pump in which working oil is supplied from a discharge part to a bearing part bearing a pump drive rotation shaft.

BACKGROUND ART

In recent years, with increasing demand for lowering fuel consumption of automotive vehicles, automotive vehicles provided with idle stop functions and hybrid vehicles have become commercially practical. Such a vehicle requires a pump drive source in addition to an internal combustion engine, because various pumps driven by the internal combustion engine are at rest when the internal combustion engine is at rest. Especially, in cases of automotive vehicles provided with idle stop functions and hybrid vehicles, an oil pump is required to ensure oil pressure of a hydraulic mechanism controlling a transmission. In view of the foregoing, an electric oil pump, which applies a torque to a pump rotor by an electric motor, tends to be in increasing use.

Conventionally, as an electric oil pump mounted in a transmission of an automotive vehicle, a trochoid type internal gear pump is frequently adopted. The internal gear pump is a pump in which a pump rotor is rotated by a drive rotation shaft driven by an electric motor, and an outer rotor having internal teeth meshing with external teeth of the pump rotor is thereby rotated, so that a plurality of chambers formed between the internal teeth of the outer rotor and the external teeth of the pump rotor continuously vary in volume, and thereby suck and discharge working oil. Such an electric oil pump is described in JP 2012-207638 A (patent document 1), for example.

An electric oil pump includes: a drive control section for controlling energization to an electric motor; a stator part including a winding and an iron core for generating a magnetomotive force by energization from the drive control section; a rotor part in a space inside the stator part, including a permanent magnet, and configured to be rotated by the magnetomotive force; a drive rotation shaft fixed by press fitting or the like to the rotor part, and configured to rotate integrally with the rotor part; and a pump rotor part fixed by press fitting or the like to the drive rotation shaft, and configured to rotate integrally with the drive rotation shaft. A bearing part for the drive rotation shaft is formed with an oil groove for introducing working oil from a discharge part, and thereby forming an oil film on a rotation slide surface of the drive rotation shaft.

PRIOR ART DOCUMENT(S)

Patent Document 1: JP 2012-207638 A

SUMMARY OF THE INVENTION

As described above, in an automotive vehicle provided with an idle stop function or a hybrid vehicle, an electric oil pump is operating under a condition in which an internal combustion engine is at rest. Since the internal combustion engine causes no operation sound under that condition, an operation sound caused by the electric oil pump is noisy to a passenger in a vehicle interior. Accordingly, it is desired to minimize the operation sound of the electric oil pump.

The present inventor and others made studies and revealed that inclination of the drive rotation shaft was a factor for causing the operation sound of the electric oil pump. Specifically, as in patent document 1, the drive rotation shaft is rotatably supported by an one-side slide bearing, so that the drive rotation shaft is inclined in a clearance between an inner peripheral surface of the slide bearing and an outer peripheral surface of the drive rotation shaft, and unevenness occurs in a clearance (air gap) between the stator part and the rotor part, and it causes a disturbance in a spatial magnetic flux wave, and thereby causes harmonic components. The harmonic components become a factor for increasing an electromagnetic exciting force in a radial direction and causing vibration, and thereby cause noise.

In order to reduce inclination of the drive rotation shaft, it is conceivable to minimize the clearance between the inner peripheral surface of the slide bearing and the outer peripheral surface of the drive rotation shaft. However, it causes a new problem that because of the slide bearing, excessive reduction of the clearance causes shortage of supply of lubricating oil, and thereby causes seizing, or increasing a manufacturing cost (by employment of precision machining). On the other hand, in a case where the drive rotation shaft is rotatably supported by a ball bearing, it is possible to suppress inclination of the drive rotation shaft to some extent, but the use of the ball bearing causes a new problem of causing an increase in the number of parts, and an increase in the parts cost, and a necessity to ensure a space where the ball bearing is mounted for the drive rotation shaft. Moreover, rotation of the ball bearing may cause a noise called cry.

It is an object of the present invention to provide a new electric oil pump in which inclination of a drive rotation shaft is suppressed by a simple configuration so that noise is small.

The present invention is characterized in that a drive rotation shaft is rotatably supported by a first slide bearing between a rotor part and a pump rotor, and is rotatably supported by a second slide bearing on its distal end side of a pump rotor fixing part of the drive rotation shaft, and working oil is supplied to the first slide bearing and the second slide bearing.

According to the present invention, the feature that the distal end side of the drive rotation shaft is rotatably supported by the second slide bearing serves to restrict inclination of the drive rotation shaft by an inner peripheral surface of the second slide bearing, and thereby suppress the occurrence of noise. Additionally, since the provision of the slide bearing is sufficient, the configuration becomes simple.

MODE(S) FOR CARRYING OUT THE INVENTION

Although the following describes embodiment(s) of the present invention in detail with reference to drawings, the present invention is not limited to the following embodiment(s), but includes various modifications and applications within a technical concept of the present invention.

The following describes an electric oil pump according to an embodiment of the present invention with reference to the drawings. For example, the electric oil pump is a pump mounted for an automatic transmission of a vehicle provided with an idle stop function. The automatic transmission is a belt-type continuously variable transmission, and a mechanical pump is additionally provided which is driven by an engine.

When the engine is at rest under idle stop control, it is impossible to ensure oil pressure by the mechanical pump. When oil pressure becomes lower due to leakage or the like from frictional engagement elements and pulleys in the belt-type continuously variable transmission, it takes time to provide oil pressure required for restarting, thereby degrading the drivability. Accordingly, in addition to the mechanical pump, the electric oil pump is provided to discharge oil pressure irrespective of operating state of the engine, and thereby ensure oil pressure for compensation for leakage from the frictional engagement elements and pulleys, and thereby enhance the drivability when the engine is restarted and when the vehicle is restarted.

FIG. 1is a perspective view of whole configuration of the electric oil pump.FIG. 2is an exploded perspective view of the electric oil pump. Electric oil pump10includes: an electric motor section10A; a drive control section10B next to and fixed to electric motor section10A; a pump section10C configured to be driven by electric motor section10A.

As shown inFIG. 2, electric motor section10A includes at least a rotor part16and a stator part18. Electric motor section10A is housed in an electric motor section housing part24formed in one side of a housing20made of metal such as aluminum alloy.

The other side of housing20is formed with a pump section housing part22housing the pump section10C. Pump section10C includes at least a pump rotor12having external teeth, and an outer rotor14having internal teeth. Pump rotor12and outer rotor14are housed in pump section housing part22formed in the other side of housing20. Drive control section10B includes at least: a cabinet44; a control board46housed in cabinet44; a cover48fixed to cabinet44to house the control board46.

The following further describes the structure of electric oil pump10in detail with reference toFIG. 3. Electric oil pump10includes: pump section10C including pump rotor12having external teeth and outer rotor14having internal teeth; and electric motor section10A including rotor part16coupled to pump rotor12, and stator part18. A winding18A is wounded around stator part18, and is put into drive control circuit (or drive control section)42.

The pump section10C and electric motor section10A are housed respectively in pump section housing part22formed in a first end surface of housing20, and in electric motor section housing part24formed in a second end surface of housing20. Namely, housing20is formed with pump section housing part22on the first end surface side, which houses outer rotor14therein rotatably, and is formed with electric motor section housing part24on the second end surface side, which fixes stator part18inside of an opening, and is formed further with a bracket26outside of electric motor section housing part24in the axial direction, for attachment to the automatic transmission.

Moreover, a first bearing part30is formed in housing20for supporting rotatably the drive rotation shaft28that couples pump rotor12and rotor part16to each other. First bearing part30is configured so that its inner peripheral surface rotatably supports an outer peripheral surface of an intermediate portion of drive rotation shaft28. The “intermediate portion” means a portion between pump rotor12and rotor part16, and is not limited to the center of drive rotation shaft28.

First bearing part30is formed in a separation wall31that separates pump section housing part22and electric motor section housing part24from each other. First bearing part30is a slide bearing, wherein a first clearance having a specific distance is formed between the inner peripheral surface of first bearing part30and the outer peripheral surface of drive rotation shaft28, wherein working oil is introduced to the first clearance via a first oil introduction passage33from the discharge side high in pressure. In addition, a seal member32is provided above drive rotation shaft28and first bearing part30for sealing the drive rotation shaft28.

Pump cover34includes: a discharge port36extending in the form of a cylindrical tube communicating with a discharge opening of pump section10C; and a suction port38communicating with a suction opening of pump section10C. A seal ring40is attached to an outer periphery of a distal end of discharge port36.

A land portion39separates discharge port36and suction port38from each other in pump cover34, and is formed with a second bearing part41. Second bearing portion41rotatably supports a distal end portion29of drive rotation shaft28that is located on a distal side of a fixing portion to which pump rotor12is fixed. The second bearing part41is a slide bearing, wherein a second clearance having a predetermined distance is formed between an inner peripheral surface of second bearing part41and an outer peripheral surface of drive rotation shaft28, wherein working oil is introduced to the second clearance via a second oil introduction passage not shown from a suction side. InFIG. 3, an A-part circled by a broken elliptic line is a major part of the present embodiment, which is described further in detail below with reference toFIG. 4.

Cabinet44constituting the drive control section42is fixed to electric motor section housing part24of housing20to tightly seal the electric motor section housing part24. Incidentally, drive control section10B shown inFIGS. 1 and 2is identical to drive control section42shown inFIG. 3. Drive control section42includes: cabinet44made of synthetic resin, and fixed to housing20; control board46housed in cabinet44; and cover48made of synthetic resin, and fixed to cabinet44to cover the control board46. An inverter circuit is mounted to control board46for supplying a controlled electric current to winding18A wounded around stator part18of electric motor section10A. A connector terminal50is disposed between cabinet44and cover48, and configured to supply electric power to control board46.

In electric oil pump10described above, a winding beginning portion and a winding ending portion of winding18A wounded around stator part18constituting the electric motor section10A are connected to an input terminal not shown and a neutral terminal not shown, which are formed in cabinet44, via insertion holes not shown formed in cabinet44of drive control section42that is next to and fixed to electric motor section housing part24. Accordingly, a drive signal is controlled by the inverter circuit and supplied to winding18A, to cause the rotor part16of electric motor section10A to rotate, and finally cause the pump rotor12to rotate to perform a pumping action.

The following describes detailed configuration of the A-part shown inFIG. 3and its operation with reference toFIG. 4. As shown inFIG. 3, a part of separation wall31of housing20is formed with first bearing part30. First bearing part30is located between pump rotor12and rotor part16constituting the electric motor section10A, and rotatably supports drive rotation shaft28at this position, wherein drive rotation shaft28couples pump rotor12and rotor part16to each other. First bearing part30is a slide bearing, wherein the inner peripheral surface of first bearing part30and the outer peripheral surface of drive rotation shaft28are configured to slide relative to each other with first clearance G1. The first clearance G1is supplied with working oil from first oil introduction passage33in communication with discharge port36. The inner peripheral surface of first bearing part (slide bearing)30is formed with an oil groove30A along drive rotation shaft28. The oil groove30A is supplied with working oil from first oil introduction passage33. Thereby, an oil film is formed in first clearance G1, to enable a function of slide bearing.

The land portion39that separates discharge port36and suction port38from each other in pump cover34is formed with second bearing part41that rotatably supports distal end portion29of drive rotation shaft28. Second bearing part41is in the form of a circular recess, in which distal end portion29of drive rotation shaft28is inserted and disposed. Second bearing part41is a slide bearing, wherein a second clearance G2having a predetermined distance is formed between the inner peripheral surface of second bearing part41and the outer peripheral surface of drive rotation shaft28. Working oil is introduced to the second clearance G2from a suction port side via second oil introduction passage43. The inner peripheral surface of second bearing part (slide bearing)41is formed with an oil groove41A that is supplied with working oil from second oil introduction passage43. Thereby, an oil film is formed in second clearance G2, to enable a function of slide bearing.

Moreover, a third clearance G3is formed between a distal end surface of distal end portion29of drive rotation shaft28and a side end surface of the circular recess of second bearing part41, and is supplied with working oil from the suction port side.

In this way, in the configuration of the present embodiment, drive rotation shaft28is rotatably supported at two places, i.e. the intermediate portion and distal end portion29of drive rotation shaft28by bearing parts30and41as slide bearings. Accordingly, when drive rotation shaft28is inclined around a proximity of first bearing part30, the distal end portion29of drive rotation shaft28contacts the inner peripheral surface of second bearing part41so that the inclination of drive rotation shaft28is restricted. This serves to reduce variation (unevenness) of an air gap between stator part18and rotor part16as compared to the conventional configuration, and thereby suppress an increase of an electromagnetic exciting force in a radial direction, and thereby suppress the occurrence of noise.

Additionally, since the forming of two bearing parts30,41implemented by slide bearings is sufficient, the configuration can be simplified. It is also possible to suppress the number of parts and the parts cost as compared to cases where ball bearings or the like are employed, and thereby suppress the price per product in addition to the simplification of the configuration.

The following describes a difference in inclination of drive rotation shaft28between the electric oil pump described in patent document 1 and the electric oil pump according to the present embodiment, with reference toFIGS. 5 and 6. In this comparison, an inner diameter d1and a bearing length L1of the slide bearing between pump rotor12and rotor part16, and an outer diameter ds of drive rotation shaft28, and an outer diameter dm of rotor part16, and an inner diameter dc of stator part18are the same therebetween. Moreover, the slide bearing constituting the second bearing part41in the present embodiment is assumed to have an inner diameter d2and a bearing length L2. Herein, the inner diameters of both slide bearings are set equal to each other (d1=d2). Additionally, the interval distance between both slide bearings (where the pump rotor is arranged) is represented by L3.

FIG. 5shows the case of the electric oil pump of patent document 1. Inclination θ1of drive rotation shaft28is determined by the following equation (1).
θ1=tan−1(C/L1)  (1)
where C represents a clearance distance between drive rotation shaft28and the slide bearing, namely, C=d1−d2.

On the other hand,FIG. 6shows the case of the electric oil pump of the present embodiment. Inclination θ2of drive rotation shaft28is determined by the following equation (2).
θ2=tan−1(C/(L1+L2+L3))  (2)

As understood from the above, in the present embodiment, since two slide bearings are employed, the bearing length is virtually equal to (L1+L2+L3), and thereby greater than bearing length L1of the conventional example shown inFIG. 5. Accordingly, with regard to the inclination of drive rotation shaft28, θ2<θ1is satisfied so that the inclination is restricted to be smaller in the present embodiment.

Based on inclinations θ1, θ2, a minimum value of the air gap between stator part18and rotor part16, AGmin, is determined as follows.

In the case of the electric oil pump shown inFIG. 5, an air gap minimum value AG1min is determined by the following equation (3).
AG1min=(dc−dm)/2+C−(CLs/L1−dm(1−cos θ1))   (3)

On the other hand, in the case of the electric oil pump shown inFIG. 6, an air gap minimum value AG2min is determined by the following equation (4).
AG2min=(dc−dm)/2+C−(CLs/(L1+L2+L3)−dm(1−cos θ2))  (4)

When δ1=CLs/L1−dm(1−cos θ1) and δ2=CLs/(L1+L2+L3)−dm(1−cos θ2) are defined, δ1>δ2results in AG1min<AG2min so that variation of the air gap is smaller in the present embodiment. Therefore, this makes it possible to suppress the unevenness of the air gap as a factor for generating the operation sound, and thereby reduce the operation sound resulting from the unevenness of the air gap.

Incidentally, it is conceivable to reduce the inclination of drive rotation shaft28by increasing the bearing length of the slide bearing shown inFIG. 5, but it causes a new problem that the length between stator part18and pump rotor12increases, and thereby causes the axial size of the whole electric oil pump to increase. This is disadvantageous in consideration that the electric oil pump is housed in an engine room in which a space for layout is limited.

In the present embodiment, by using the part L3, to which pump rotor12of drive rotation shaft28is fixed, virtually as a bearing length, the bearing length can be increased without increase of the size of the whole electric oil pump. Accordingly, as shown inFIG. 6, the inclination of drive rotation shaft28can be reduced, and as a result, variation of the air gap between rotor part16and stator part18can be reduced.

In this way, in the present embodiment, two portions of drive rotation shaft28, namely, the intermediate portion and the distal end portion29of drive rotation shaft28, which sandwich pump rotor12, are rotatably supported by the slide bearings of bearing parts30,41, so that the bearing length is virtually increased. When drive rotation shaft28is inclined around the proximity of first bearing part30, the distal end portion29of drive rotation shaft28contacts the inner peripheral surface of second bearing part41so that the inclination of drive rotation shaft28is restricted to be small. This serves to reduce variation (unevenness) of the air gap between stator part18and rotor part16as compared to the conventional configuration, and thereby suppress increase of the electromagnetic exciting force in the radial direction, and thereby suppress the occurrence of noise.

The following describes fluctuations of the electromagnetic force caused by variation of the air gap between stator part18and rotor part16.FIG. 7shows a cross-section of stator part18and rotor part16, and shows a state in which rotor part16is eccentric.

The iron core18B constituting the stator part18is made of layered silicon steel plates or the like, and includes nine salient pole parts18C extending radially inwardly. Around the salient pole part, a bobbin part is formed of insulating synthetic resin. The bobbin part has a function to ensure insulation between salient pole part18C and winding18A wound around itself.

The winding18A of each phase is wounded around the bobbin part covering the salient pole part18C, and each bobbin part is therefore usually arranged in the order of the U-phase, the V-phase, and the W-phase. In the present embodiment, since the winding of each phase is divided into three, nine salient pole parts18C are formed in iron core18B, and arranged next to each other.

Rotor part16is disposed inside of salient pole parts18C, wherein a permanent magnet16B is disposed inside a back yoke16A.FIG. 7shows a situation where inclination of drive rotation shaft28causes back yoke16A of rotor part16to be eccentric in an X direction among salient pole parts18C of stator part18, and thus causes unevenness of the air gap.

In that situation, when rotor part16rotates, the electromagnetic forces in the X direction and the Y direction fluctuate with the rotation angle (mechanical angle).

FIG. 8shows fluctuations of the electromagnetic force in the X direction during one rotation of rotor part16. As compared to the case of eccentricity=0, the electromagnetic force fluctuates significantly in the conventional configuration ofFIG. 5. On the other hand, the fluctuation of the electromagnetic force is smaller in the configuration of the present embodiment shown inFIG. 6. The fluctuation of the electromagnetic force in the X direction causes a rotational primary vibration, and thereby increases the sound.

FIG. 9shows fluctuations of the electromagnetic force in the Y direction during one rotation of rotor part16. As compared to the case of eccentricity=0, the electromagnetic force fluctuates significantly in the conventional configuration ofFIG. 5. On the other hand, the fluctuation of the electromagnetic force is smaller in the configuration of the present embodiment shown inFIG. 6. The fluctuation of the electromagnetic force in the Y direction causes a rotational secondary vibration, and thereby increases the sound. In this way, if the eccentricity of rotor part16can be reduced, the fluctuation of the electromagnetic force can be reduced, and as a result, the operation sound can be suppressed.

As described above, in the present embodiment, two portions of drive rotation shaft28, namely, the intermediate portion and the distal end portion29of drive rotation shaft28, which sandwich pump rotor12, are rotatably supported by the slide bearings of bearing parts30,41. When drive rotation shaft28is inclined around the proximity of first bearing part30, the distal end portion29of drive rotation shaft28contacts the inner peripheral surface of second bearing part41, so that the inclination of drive rotation shaft28is restricted. This serves to reduce variation (unevenness) of the air gap between stator part18and rotor part16as compared to the conventional configuration, and thereby suppress increase of the electromagnetic vibration in the radial direction, and thereby suppress the occurrence of noise.

In the present embodiment, as shown inFIG. 6, by using the part L3, to which pump rotor12of drive rotation shaft28is fixed, virtually as a bearing length, the bearing length can be increased without increase of the size of the whole electric oil pump.

Additionally, since the forming of bearing parts30,41implemented by slide bearings is sufficient, the configuration can be simplified. It is also possible to suppress the number of parts and the parts cost as compared to cases where ball bearings or the like are used, and thereby suppress the price per product in addition to the simplification of the configuration.

In the present embodiment, the inner diameter of the second bearing part41formed in land portion39of pump cover34is set equal to the inner diameter of first bearing part30formed in separation wall31of housing20, However, if the inner diameter of second bearing part41is set smaller, the distance of second clearance G2becomes smaller so that the inclination of drive rotation shaft28can be further reduced.

Moreover, the feature that second bearing part41is in the form of the circular recess serves to promote rise of the temperature of working oil. This allows to reduce the viscosity of working oil, and makes it easy for working oil to flow even in a narrow passage. This configuration is advantageous when the inner diameter of second bearing part41is set smaller so that the distance of second clearance G2is set shorter.

Furthermore, the feature that drive rotation shaft28is rotatably supported by first bearing part30and second bearing part41serves to reduce the load to the bearings. This is an effect by the extension of the bearing length, whereby it is possible to employ a metal material that is lower in hardness and lower in cost. Thus, it is possible to broaden the degree of freedom of material selection. Thereby, it can be expected that the unit price of the electric oil pump is suppressed to be low.

Next, the following describes configuration for positioning the pump cover34and housing20relative to each other. In the present embodiment, first bearing part30is formed in housing20, whereas pump cover34is formed in pump cover34. Accordingly, if the position of first bearing part30and second bearing part41relative to each other is deviated, drive rotation shaft28may be assembled under a condition that drive rotation shaft28is inclined. The inclination of drive rotation shaft28causes a phenomenon in which the operation sound gets larger. Therefore, it is important to assemble pump cover34and housing20in a normal state. The following describes this positioning mechanism.

FIG. 10shows an example in which a positioning projecting portion51in the form of a circular projection is formed in a surface of pump cover34in contact with housing20. The positioning projecting portion51in the form of a circular projection is contacted to and fitted by spigot fitting with a wall surface of a circular positioning hole52formed in pump section housing part22in which outer rotor14of housing20is housed, thereby serving as a positioning mechanism for positioning the pump cover34and housing20relative to each other. This configuration serves to prevent the position of first bearing part30and second bearing part41from deviating from each other, and prevent drive rotation shaft28from being assembled with inclination.

FIG. 11shows an example in which at least two positioning pins53are formed in a surface of pump cover34in contact with housing20. The positioning pins53are inserted into two positioning holes54formed in a surface of housing20in contact with pump cover34, and thereby serves as a positioning mechanism to position pump cover34and housing20relative to each other. This configuration serves to prevent the position of first bearing part30and second bearing part41from deviating from each other, and prevent drive rotation shaft28from being assembled with inclination. Moreover, although the example ofFIG. 10requires to increase the size of pump section housing part22in the axial direction for the spigot fitting, the example ofFIG. 11does not require to increase the size of pump section housing part22in the axial direction, and does not require to change the axial length of the electric oil pump.

FIG. 12shows an example in which at least two positioning holes55are formed in a surface of pump cover34in contact with housing20. The positioning holes55receive insertion of two positioning pins56formed in a surface of housing20in contact with pump cover34, and thereby serves as a positioning mechanism to position pump cover34and housing20relative to each other. This configuration serves to prevent the position of first bearing part30and second bearing part41from deviating from each other, and prevent drive rotation shaft28from being assembled with inclination. Moreover, similar to the example ofFIG. 11, this example does not require to increase the size of pump section housing part22in the axial direction, and does not require to change the axial length of the electric oil pump.

In summary, the present invention is characterized in that the drive rotation shaft is rotatably supported by the first slide bearing between the rotor part and the pump rotor, and is rotatably supported by the second slide bearing on its distal end side of the pump rotor fixing part of the drive rotation shaft. Working oil is supplied to the first slide bearing and the second slide bearing.

According to this configuration, since the distal end side of the drive rotation part is rotatably supported by the second slide bearing, inclination of the drive rotation shaft is restricted by the inner peripheral surface of the second slide bearing, thereby suppressing occurrence of noise. Moreover, the configuration can be simplified, because it only requires that each of the housing and the pump cover is formed with a slide bearing.