JP2014066179A - Electric oil pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric oil pump capable of restraining unbalance of a magnetic attraction force.SOLUTION: An electric oil pump comprises: a motor part 9 having a motor rotor 7 and a stator 8; a rotor driving shaft 15 connected to the motor rotor 7; a pump part 6 that includes a pump rotor 4 on the outer periphery of which outer teeth are formed and that is driven by the rotor driving shaft 15 and an outer rotor 5 on the inner periphery of which inner teeth meshed with the outer teeth are formed, and that continuously changes capacities of plural pump chambers formed between the outer teeth and the inner teeth by rotation of the rotor driving shaft 15 to increase or decrease the capacities; a suction port 10b opened in a region in which the capacity of the pump chamber increases; an emission port 10c opened in a region in which the capacity of the pump chamber decreases; a center housing 10 housing the motor part 9 and the pump part 6; and a bearing part 16 supporting the rotor driving shaft 15 rotatably to the center housing 10. A center axial line Os of the stator 8 is offset arranged on the emission port 10c side with respect to a center axial line Od of the rotor driving shaft 15.

Description

  The present invention relates to an electric oil pump.

  Patent Document 1 discloses an electric oil pump in which a drive shaft of an electric motor is rotatably supported by a single bearing at a position between a motor rotor and a pump rotor.

JP 2010-112328 A

However, in the above prior art, when the pump rotor is pushed from the discharge port side to the suction port side by the load due to the discharge pressure, the motor rotor is inclined according to the amount of play between the rotating shaft and the bearing. There is a problem that the air gap with the stator is large and small in the rotational direction, and the magnetic attraction force is unbalanced. Since it is considered that the unbalance of the magnetic attractive force can increase vibration during operation and cause abnormal wear of the bearing portion, it is preferable to make it as small as possible.
The objective of this invention is providing the electric oil pump which can suppress the imbalance of a magnetic attraction force.

  In order to achieve the above object, in the present invention, the center axis of the stator is offset from the center axis of the drive shaft on the discharge port side.

  Therefore, the size difference of the air gap when the motor rotor is inclined can be suppressed, and the unbalance of the magnetic attractive force can be suppressed.

1 is a longitudinal sectional view of an electric oil pump 1 according to Embodiment 1. FIG. It is a schematic diagram of the motor part which shows the change of the air gap at the time of the motor rotor inclination resulting from discharge pressure. It is a figure which shows the tendency of the operation sound with respect to the deviation | shift amount from a reference position. FIG. 5 is a schematic diagram of a motor unit 9 showing an effect of suppressing an unbalance of magnetic attractive force according to the first embodiment.

[Example 1]
FIG. 1 is a longitudinal sectional view of the electric oil pump 1 of the first embodiment.
The electric oil pump 1 according to the first embodiment is a pump mounted for an automatic transmission of a vehicle having a function of stopping an engine when the vehicle is stopped. The automatic transmission has a separate main (mechanism) pump that is driven by rotational input from the engine and motor. However, when the engine is stopped, the mechanical pump does not operate, so hydraulic pressure cannot be generated. If the hydraulic pressure decreases due to a factor inside the transmission, it takes time to secure the hydraulic pressure necessary for restarting, so it is assumed that the drivability is reduced. Therefore, in addition to the mechanical pump, an electric oil pump 1 that can discharge the hydraulic pressure regardless of the operating state of the engine is provided, and the required hydraulic pressure is secured to improve the drivability of engine restart and restart.
The electric oil pump 1 is, for example, an electromechanically integrated electric oil pump in which an oil pump 2 and an inverter 3 are integrally provided.

[Configuration of oil pump 2]
The oil pump 2 includes a pump unit 6 including a pump rotor 4 having external teeth and an outer rotor 5 having internal teeth, and a motor unit 9 including a motor rotor 7 and a stator 8. The pump rotor 4 and the motor rotor 7 are connected by a rotor drive shaft 15.
The pump unit 6 and the motor unit 9 are accommodated in one center housing 10. The center housing 10 is formed of aluminum die casting. The center housing 10 has an opening at both ends in the axial direction (horizontal direction in FIG. 1), and has a cylindrical shape in which a pump element accommodating portion 11 for rotatably housing the outer rotor 5 is formed on one inner periphery of the opening. A pump housing portion 12 is formed, and a motor housing portion 13 is formed in the inner periphery (motor chamber) for housing the motor rotor and the like, and is further axially outer than the motor housing portion 13. Is formed with a bracket 14 for attachment to the automatic transmission.

  The motor rotor 7 includes a rotor core 71 connected to the rotor drive shaft 15 and a permanent magnet 72 embedded in the outer periphery of the rotor core 71. The stator 8 includes a stator core 55 and a coil 56. Stator core 55 is formed by laminating electromagnetic steel plates and has a plurality of teeth. The coil 56 is obtained by winding a coil wire around a tooth. A resin insulator is mounted between the core body and the wound coil, and the electrical insulation between the stator core 55 and the coil 56 is maintained. The motor unit 9 of the first embodiment is a three-phase brushless motor, and the stator core 55 and the coil 56 are provided in multiples of the U, V, and W phases.

Inside the center housing 10 is a bearing portion 16 that rotatably supports the rotor drive shaft 15, and the bearing portion 16 is connected to the inner periphery of the center housing 10 and between the pump housing portion 12 and the motor housing portion 13. A partition wall 10a is defined. The bearing portion 16 is, for example, a sliding bearing formed by machining the center housing 10. A seal member that rotatably supports the rotor drive shaft 15 at the inner periphery of the bearing portion 16 and seals between the rotor drive shaft 15 and the inner periphery of the bearing portion 16 at the end on the motor housing portion 13 side. 17 is provided.
The pump cover 18 includes a discharge portion 19 that extends in a cylindrical shape that communicates with the discharge region of the pump element, and a suction portion 20 that communicates with the suction region of the pump element. A seal ring groove 22 to which the seal ring 21 is attached is formed on the outer periphery of the distal end of the discharge unit 19. A bolt hole 23 is formed in the pump cover 18, and the bolt hole 24 formed in the center housing 10 is fastened and fixed by a bolt 25.

[Configuration of inverter 3]
The inverter 3 includes an inverter housing 26, a control board 27, and a heat sink 28.
The inverter housing 26 includes a resin-made closing portion 29 that closes the motor housing portion 13, a cylindrical standing portion 30 that is erected from the closing portion 29 and inserted into the inner wall of the motor housing portion 13, and a flange surface of the bracket 14. And a flange surface 34 provided with a through hole 33 through which the bolt 32 penetrates while pressing the seal member 31. Thereby, the inside of the motor housing portion 13 (motor chamber) is configured as a drying chamber, and the inside of the pump housing portion 12 (pump chamber) and the outer periphery of the pump are configured as wet chambers.
The control board 27 is accommodated in the inverter housing 26 and fastened by a plurality of bolts 35, for example. On the control board 27, an FET 36, a CPU (not shown) and the like are surface-mounted, and a capacitor 37 and an inductor 38 are attached. A flat heat radiation sheet 39 is provided between the control board 27 and the heat sink 28 at a position corresponding to the FET 36.
The heat sink 28 is attached to the inverter housing 26 so as to close the inverter housing 26.
The inverter 3 sequentially supplies a DC current supplied from a battery (not shown) via the connector 40 to the U, V, and W phases of the coil 56 by switching the FET. The electrical connection structure between the control board 27 and the coil wire 53 will be described later. The coil wire 53 is provided for each of U, V, and W phases.

The electric oil pump 1 according to the first embodiment is housed in a pump housing hole 42 formed in the housing 41 of the automatic transmission. A discharge passage 43 for supplying hydraulic pressure and a suction passage 44 communicating with an oil suction opening that opens in an oil pan (not shown) are opened in the pump housing hole 42. The discharge passage 43 is formed with an enlarged diameter portion 45 facing the pump accommodation hole 42, and the discharge portion 19 of the pump cover 18 is fitted and supported by the enlarged diameter portion 45 by insertion. A seal ring 21 seals between the discharge channel 43 and the pump accommodation hole 42. The discharge flow path 43 and the discharge area of the pump element communicate with each other through a discharge port 46 formed in the discharge unit 19.
A suction port 10b and a discharge port 10c are provided in a concave groove shape in the pump housing part 12 of the partition wall 10a. The suction port 10b and the discharge port 10c are disposed at positions facing each other when viewed from the axial direction of the rotor drive shaft 15. The suction port 10b communicates with the suction part 20, and the discharge port 10c communicates with the discharge part 19.
In the first embodiment, as shown in FIG. 1, the center axis Os of the stator 8 is offset from the center axis Od of the rotor drive shaft 15 by a predetermined amount L1 on the discharge port 10c side.

Next, the operation will be described.
[Unbalance of magnetic attractive force]
Conventional electric oil pumps have a structure having bearings at positions between the motor rotor and the pump rotor, instead of a structure having bearings at both ends of the rotor drive shaft, considering layout feasibility and cost reduction. When the motor is required to output a larger torque within a limited life range and cost, it is necessary to increase the amount of magnetic flux passing through the air gap between the motor rotor (permanent magnet) and the stator. Then, in order to increase the amount of magnetic flux, a device such as reducing the air gap is required.
However, an increase in the amount of magnetic flux also increases the mutual magnetic attraction force, which is more strongly affected by the deviation of the air gap between the motor rotor and the stator. The size of the air gap is caused by various factors such as a coaxial shift of the rotating shaft, dimensional tolerance of each component, assembly accuracy, inclination of the motor rotor, and a stator holding structure.

  The dimensional tolerance and assembly accuracy of each component have appropriate accuracy for general purposes in consideration of cost and productivity. Further, the motor rotor can be inclined by an amount determined geometrically depending on the clearance and length of the bearing, but when the pump is operated, as shown in FIG. Will tilt in the direction. When the direction of the inclination due to the discharge pressure and the coaxial shift or inclination related to the accuracy of each part overlap in the same direction, the influence of the size of the air gap between the motor rotor and the stator becomes more susceptible.

Therefore, the conventional electric oil pump has the following problems.
Electric oil pumps often operate when the engine is stopped or when the engine is running at low speed, and quietness is one of the important functions, while the air gap associated with the inclination of the motor rotor Eccentricity is one factor of vibration during operation and tends to affect the operating sound. In particular, when torque is required, it is greatly affected.
When there is no margin in the layout, it must be a specification that receives rotation only with the bearing provided between the motor rotor and pump rotor, but the pump rotor receives the load mainly due to the discharge pressure of the oil pump, The motor rotor tilts within the bearing clearance range.
Furthermore, the coaxial deviation between the motor rotor and the stator teeth occurs due to the dimensional accuracy of each component, dimensional variations caused by assembly, and the like.
On the other hand, the method of suppressing the inclination and eccentricity by setting the bearing structure at both ends of the drive shaft has an effect on the layout feasibility and cost.

[Relationship between operating noise and deviation]
Ideally, the distance between the motor rotor and the stator = air gap (magnetic resistance) is uniform in the circumferential direction. However, actually, even when all the dimensions are nominal (design reference values), there is a clearance between the rotor drive shaft and the bearing, and the motor rotor has a geometrically predetermined inclination. When the pump is operated, since the pump rotor receives a load due to the discharge pressure in the pump, the rotor drive shaft is inclined in a substantially constant direction. As a result, the air gap (minimum value) between the motor rotor and the stator becomes L shown in FIG. The value of L is further increased by taking into account tolerances such as the coaxiality of the bearing hole, stator, etc., and this fluctuation is defined as the amount of deviation from the air gap reference position.
FIG. 3 shows the operation sound evaluation, the decomposition and measurement results of the product, and it has been found that the greater the “deviation amount” and the smaller the value of L, the greater the operation sound.

[Relationship between deviation and noise]
The mechanism by which the air gap correlates with the operating noise is estimated as follows.
First, the air gap between the motor rotor and the stator may vary among individuals depending on the positional accuracy and inclination of the motor rotor.
1. Reason why the air gap is not uniform: The motor rotor tilts within the geometrically acceptable range.
(a) Dimensional accuracy of the structure (coaxial deviation, shaft clearance difference, etc.)
(b) Unbalance of magnetic attractive force due to the size of the air gap
(c) Load applied to pump rotor by discharge pressure
2.Effects of motor rotor tilt
(a) Since the motor rotor is inclined, a slight angular deviation occurs between the rotation surfaces of the pump rotor and the outer rotor.
(b) Because the magnetic attractive force (proportional to the square of the air gap) increases on the side where the air gap becomes smaller due to the inclination, the torque fluctuation increases.
3.Estimation Based on 2 above, depending on the amount of tilt, there will be a difference in the way of contact (angle and energy) between the pump rotor and outer rotor.
Since the pump rotor and the outer rotor come into contact with each other by meshing during rotation, an operation noise is generated. It can be estimated that the noise generated in the pump section is sensitive to the motor rotor inclination and the torque fluctuation, that is, the air gap between the motor rotor and the stator.
As a supplement, in the state where there is no discharge pressure, the direction in which the air gap is small will change if the stator is switched on while the air gap is biased. On the other hand, there is discharge pressure. In the state, the pump rotor and the outer rotor are urged by the discharge pressure, so that a constant inclination cannot always be maintained, and the posture during rotation may change.

[An unbalance suppression effect of magnetic attractive force]
In contrast, in the first embodiment, the center axis Os of the stator 8 is offset from the center axis Od of the rotor drive shaft 15 by a predetermined amount L1 on the discharge port 10c side. In other words, the center axis Od of the rotor drive shaft 15 is offset from the center axis Os of the stator 8 by a predetermined amount L1 on the suction port 10b side. In other words, the position of the stator 8 is shifted in advance in the direction of inclination of the rotor drive shaft 15 with respect to the rotor drive shaft 15 so that a predetermined amount of the minimum value L of the air gap between the motor rotor and the stator can be secured initially. doing.
For this reason, as shown in FIG. 4, when the pump rotor 4 receives a load due to the discharge pressure from the discharge side to the suction side and the rotor drive shaft 15 tilts during pump operation, the minimum value of the air gap between the motor rotor and the stator L can be increased by a predetermined amount L1 with respect to the prior art shown in FIG. Furthermore, since the amount of deviation from the reference position of the rotor drive shaft 15 due to the discharge pressure can be obtained in advance by experiments or the like, the predetermined amount L1 is the amount of deviation from the reference position of the rotor drive shaft 15 due to the discharge pressure. By keeping them in agreement, the size of the air gap due to the discharge pressure can be suppressed.

Therefore, in the electric oil pump 1 of the first embodiment, in addition to the inclination of the motor rotor 7 caused by the discharge pressure, the influence of the air gap size due to the accuracy of each part, that is, the influence of the magnitude of the magnetic attractive force can be minimized.
Therefore, the imbalance in the circumferential direction of the magnetic attraction force between the motor rotor and the stator due to the inclination of the motor rotor 7 and the accuracy of each part with respect to the conventional structure can be suppressed, and the effect of reducing the operating noise can be obtained.
Further, in the case where the air gap between the motor rotor and the stator becomes too small, the allowable surface pressure of the bearing is exceeded. For example, when the bearing is formed as a machined aluminum body, abnormal wear of the bearing may occur. However, this risk can be reduced.
Furthermore, since there is only one bearing portion 16, there is no need for a bearing structure that holds both ends of the drive shaft, which is advantageous in terms of layout, and at the same time, it is possible to suppress the additional cost and magnetic attraction force that affects operating noise. With respect to the unbalance, it is possible to obtain an effect while minimizing the influence on layout and cost.
In addition, by forming the bearing portion 16 by directly machining the center housing 10 having the functions of the pump accommodating portion 12 and the motor accommodating portion 13, in order to form the bearing, for example, press-fitting of another member costs Compared to a conventional structure that leads to an increase in cost, it can also be expected to have a cost-saving effect.

The electric oil pump 1 according to the first embodiment has the following effects.
(1) A motor unit 9 having a motor rotor 7 and a stator 8, a rotor drive shaft 15 connected to the motor rotor 7, a pump rotor 4 formed on the outer periphery and driven by the rotor drive shaft 15, and an inner periphery A pump having an outer rotor 5 formed with internal teeth that mesh with the external teeth, and continuously increasing or decreasing the volume of a plurality of pump chambers formed between the external teeth and the internal teeth by the rotation of the rotor drive shaft 15 Part 6, a suction port 10b that opens to a region where the volume of the pump chamber increases, a discharge port 10c that opens to a region where the volume of the pump chamber decreases, and a center housing 10 that houses the motor unit 9 and the pump unit 6 And a bearing portion 16 that rotatably supports the rotor drive shaft 15 with respect to the center housing 10, and the center axis Os of the stator 8 is offset from the center axis Od of the rotor drive shaft 15 on the discharge port 10c side. .
Thereby, the magnitude difference of an air gap can be suppressed and the imbalance of magnetic attraction force can be suppressed.
(2) Since one bearing portion 16 is provided at a position between the motor rotor 7 and the pump rotor 4, it is advantageous in terms of layout establishment and cost reduction.
(3) To form the bearing by forming the bearing portion 16 by direct shaving on the center housing 10 having the functions of the pump housing portion 12 and the motor housing portion 13, for example, press fitting with another member is costly Compared to a conventional structure that leads to an increase in cost, it can also be expected to have a cost-saving effect.

[Other Examples]
Although the present invention has been described based on the embodiments, the specific configuration of each invention is not limited to the embodiments, and even if there is a design change or the like without departing from the scope of the invention, Included in the invention.
For example, in the embodiment, an example in which one bearing portion is provided between the motor rotor and the pump rotor as a bearing for supporting the drive shaft is shown, but a configuration in which bearing portions are provided at both ends of the drive shaft may be employed. Even if the drive shaft is supported at both ends, an inclination caused by the discharge pressure occurs, and therefore, by applying the present invention, it is possible to obtain the same effect as the embodiment.

1 Electric oil pump
2 Oil pump
3 Inverter
4 Pump rotor
5 Outer rotor
6 Pump part
7 Motor rotor
8 Stator
9 Motor part
10 Center housing (housing)
10b Suction port
10c Discharge port
15 Rotor drive shaft (drive shaft)
16 Bearing part (bearing)

Claims (3)

A motor unit having a motor rotor and a stator;
A drive shaft connected to the motor rotor;
A pump rotor driven by the drive shaft with outer teeth formed on the outer periphery and an outer rotor formed with inner teeth meshing with the outer teeth on the inner periphery; and by rotating the drive shaft, the outer teeth and the inner teeth A pump unit that continuously increases or decreases the volume of a plurality of pump chambers formed between
A suction port that opens into a region where the volume of the pump chamber increases;
A discharge port that opens into an area where the volume of the pump chamber decreases;
A housing for housing the motor unit and the pump unit;
A bearing that rotatably supports the drive shaft with respect to the housing;
With
An electric oil pump characterized in that a center axis of the stator is offset from the center axis of the drive shaft toward the discharge port. The electric oil pump according to claim 1,
An electric oil pump, wherein one bearing is provided at a position between the motor rotor and the pump rotor. In the electric oil pump according to claim 1 or 2,
An electric oil pump, wherein the bearing is formed by cutting the housing.

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