Drive device for electric vehicle

Abstract

To suppress frictional resistance between a predetermined rotating shaft of a power transmission path from a motor shaft to a driving wheel and a sliding contact member and abrasion of the sliding contact member.SOLUTION: A drive device for an electric vehicle is provided with a sliding contact device having a sliding contact member which is in sliding contact with a predetermined rotating shaft in a power transmission path from a motor shaft to drive wheels, and a drive section which separates the sliding contact member from the predetermined rotating shaft when the rotational speed of the motor is higher than the predetermined rotational speed. The predetermined rotation shaft and the case are electrically connected to each other via the slide contact member when the slide contact member is in slide contact with the predetermined rotation shaft, and are electrically disconnected from each other via the slide contact member when the slide contact member is separated from the predetermined rotation shaft.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a drive device for an electric vehicle. [Background technology]

[0002] A conventional drive device for an electric vehicle of this type includes a motor having a rotor and a stator attached to the motor shaft, and an inverter that drives the motor by switching switching elements (see, for example, Patent Document 1). In this device, the metal motor housing and the motor shaft are electrically connected by conductive means (sliding contact members, guide case, spring). This allows electromagnetic noise induced in the motor shaft to escape to the motor housing, preventing it from leaking to external devices such as the drive shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-244180 Summary of the Invention [Problem to be solved by the invention]

[0004] In the electric vehicle drive device described above, a sliding contact member is constantly in sliding contact with a predetermined rotating shaft (e.g., motor shaft) in the power transmission path from the motor shaft to the drive wheels, electrically connecting the motor housing and the motor shaft, thereby suppressing discharge of the shaft voltage of the motor shaft. However, frictional resistance between the predetermined rotating shaft and the sliding contact member and wear of the sliding contact member can be issues, so there is a need to address these issues in areas where discharge of the shaft voltage of the motor shaft is unlikely to occur. The electric vehicle drive device disclosed herein primarily aims to suppress frictional resistance between the predetermined rotating shaft and the sliding contact member in the power transmission path from the motor shaft to the drive wheels, and wear of the sliding contact member. [Means for solving the problem]

[0005] The electric vehicle drive device of the present disclosure employs the following measures to achieve the above-mentioned primary object. The electric vehicle drive device of the present disclosure is an electric vehicle drive device including a motor having a rotor attached to a motor shaft and a stator around which a motor coil is wound, and a bearing provided between the motor shaft and a case, and further including a sliding contact device having a sliding contact member that is in sliding contact with a predetermined rotating shaft in a power transmission path from the motor shaft to a drive wheel, and a drive unit that separates the sliding contact member from the predetermined rotating shaft when the rotation speed of the motor is higher than a predetermined rotation speed, wherein electrical conduction is established between the predetermined rotating shaft and the case via the sliding contact member when the sliding contact member is in sliding contact with the predetermined rotating shaft, and electrical conduction via the sliding contact member is released when the sliding contact member is separated from the predetermined rotating shaft.

[0006] The electric vehicle drive device disclosed herein includes a sliding contact device having a sliding contact member that is in sliding contact with a predetermined rotating shaft in a power transmission path from the motor shaft to the drive wheels, and a drive unit that separates the sliding contact member from the predetermined rotating shaft when the motor rotation speed is higher than the predetermined rotation speed. The predetermined rotating shaft and the case are electrically connected via the sliding contact member when the sliding contact member is in sliding contact with the predetermined rotating shaft, and the electrical connection via the sliding contact member is broken when the sliding contact member is separated from the predetermined rotating shaft. The inventors have confirmed through experiments and analysis that, without the sliding contact member, shaft voltage discharge from the motor shaft occurs when current flows to the case via the bearing, and that as the motor rotation speed increases, the oil film thickness around the bearing increases, making shaft voltage discharge less likely. Based on this, by separating the sliding contact member from the predetermined rotating shaft when the motor rotation speed is higher than the predetermined rotation speed, frictional resistance between the predetermined rotating shaft and the sliding contact member and wear of the sliding contact member can be reduced in the range of high motor rotation speed (the range where shaft voltage discharge is less likely to occur). [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic configuration diagram of an electric vehicle 20 equipped with an electric vehicle drive device according to an embodiment of the present disclosure. [Figure 2] 4 is an explanatory diagram showing an example of the relationship between the rotation speed Nm of the motor 22 (motor shaft 25) and the supplied hydraulic pressure. FIG. [Figure 3] 10 is a flowchart illustrating an example of a processing routine. DETAILED DESCRIPTION OF THE INVENTION

[0008] A mode (embodiment) for carrying out the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic configuration diagram of an electric vehicle 20 equipped with an electric vehicle drive device according to an embodiment of the present disclosure. As shown in the figure, the electric vehicle 20 according to the embodiment includes a motor 22, a gear mechanism 30, a differential gear 40, drive shafts 42a, 42b, a sliding contact device 50, an inverter 60, a battery 66, and an electronic control unit (hereinafter referred to as "ECU") 70. The motor 22, gear mechanism 30, differential gear 40, drive shafts 42a and 42b, and bearings 25a, 25b, 31a, 31b, 44a, and 44b (described later) are made of metal (conductive material), and the motor 22, gear mechanism 30, differential gear 40, portions of the drive shafts 42a and 42b (portions on the differential gear 40 side), and bearings 25a, 25b, 31a, 31b, 44a, and 44b are housed in a case (housing) 46. The case 46 is fixed to the vehicle body. Lubricating oil is supplied to the motor 22, gear mechanism 30, differential gear 40, drive shafts 42a and 42b, and bearings 25a, 25b, 31a, 31b, 44a, and 44b through a hydraulic circuit (not shown).

[0009] The motor 22 is configured as a synchronous generator motor and includes a rotor 23 with a permanent magnet embedded in a rotor core and a stator 24 with three-phase (U-phase, V-phase, and W-phase) coils wound around a stator core. The rotor 23 is attached to a motor shaft 25. The motor shaft 25 is rotatably supported by a case 46 via bearings 25a and 25b. The gear mechanism 30 includes a counter shaft 31 coaxially connected to the motor shaft 25 by spline fitting or the like, a counter gear 32 attached to the counter shaft 31, and a final gear (differential ring gear) 33 meshing with the counter gear 32 and connected to a differential gear 40. The counter shaft 31 is connected to the motor shaft 25 by spline fitting or the like and rotatably supported by the case 46 via bearings 31a and 31b. The differential gear 40 is connected to drive wheels DWa and DWb via drive shafts 42a and 42b. The drive shafts 42a and 42b are rotatably supported by a case 46 via bearings 44a and 44b, respectively. Choke coils 46a and 46b are attached to the drive shafts 42a and 42b, respectively.

[0010] The sliding contact device 50 is configured as a device that brings the spool 54 into sliding contact with the motor shaft 25 and releases that sliding contact, and includes, in addition to the spool 54, a mechanical oil pump 51, a sleeve 53, an oil seal (seal ring) 55, and a spring 56. The mechanical oil pump 51 is attached to the motor shaft 25. Hydraulic oil (hydraulic pressure) from the mechanical oil pump 51 is supplied to an oil chamber in the spool 54 via a hydraulic circuit (not shown). The sleeve 53 and the spool 54 are made of metal (conductive material). The sleeve 53 is formed into a cylindrical shape with a bottom that opens toward the motor shaft 25. The spool 54 is slidably disposed within the sleeve 53, with one end (on the motor shaft 25 side) protruding from the sleeve 53. The spool 54 is biased toward the motor shaft 52 by a spring 56 disposed between the bottom of the sleeve 53 and the other end of the spool 54. An oil chamber is formed within the spool 54, and the spool 54 is biased away from the motor shaft 52 by the supply hydraulic pressure supplied to the oil chamber from the mechanical oil pump 51. When the biasing force caused by the supply hydraulic pressure (hereinafter referred to as the "hydraulic biasing force") is equal to or less than the biasing force of the spring 56, the spool 54 slides against the motor shaft 52. When the hydraulic biasing force exceeds the biasing force of the spring 56, the spool 54 moves away from the motor shaft 52, and the sliding contact with the motor shaft 52 is released. Therefore, it can be considered that the sleeve 53 and the spool 54 form a brush with a variable length structure, and that the brush is activated (operated) by the oil supply from the mechanical oil pump 51. FIG. 2 is an explanatory diagram showing an example of the relationship between the rotation speed Nm of the motor 22 (motor shaft 25) and the supplied hydraulic pressure. As shown in the figure, the supplied hydraulic pressure increases as the rotation speed Nm of the motor 22 (motor shaft 25) increases. In the figure, the predetermined rotation speed Nm1 and the predetermined oil pressure Po1 are the rotation speed Nm of the motor 22 (motor shaft 25) and the supplied oil pressure when the hydraulic biasing force becomes equal to the biasing force of the spring 56. The sliding contact device 50 may further include a relief valve for draining the hydraulic oil from the oil chamber in the spool 54.

[0011] The inverter 60 is connected to a power line 64. The inverter 60 includes six transistors as switching elements and six diodes connected in parallel to each of the six transistors. The six transistors are arranged in pairs, two of them on the source side and two on the sink side of the positive and negative lines of the power line 64. The connection points of two of the six transistors that make up a pair are connected to the three-phase (U-phase, V-phase, W-phase) coils of the motor 22. The battery 66 is configured as, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery with a rated voltage of several hundred volts, and is connected to the power line 64.

[0012] The ECU 70 includes a microcomputer having a CPU, ROM, RAM, flash memory, input / output ports, and communication ports, as well as various drive circuits and logic ICs. The ECU 70 receives signals from various sensors. Examples of the various sensors include a rotational position sensor 22a that detects the rotational position θm of the rotor of the motor 22, and current sensors 22u, 22v, and 22w that detect phase currents Iu, Iv, and Iw flowing through the respective phases (U, V, and W) of the motor 22. Although not shown, other sensors include a shift position sensor that detects a shift position SP of the shift lever, an accelerator pedal position sensor that detects an accelerator opening Acc that indicates the amount of depression of the accelerator pedal, a brake pedal position sensor that detects a brake pedal position BP that indicates the amount of depression of the brake pedal, and a vehicle speed sensor that detects the vehicle speed V. The ECU 70 controls the switching of transistors T11 to T16 of the inverter 60. The ECU 70 calculates the rotation speed Nm of the motor 22 (motor shaft 25) based on the rotation position θm of the rotor 23 of the motor 22.

[0013] In the electric vehicle 20 of this embodiment, the ECU 70 sets the required torque Td* required for driving based on the accelerator opening Acc and the vehicle speed V, sets the torque command Tm* for the motor 22 so that the vehicle drives at the set required torque Td*, and controls the switching of the six transistors of the inverter 60 so that the motor 22 is driven at the torque command Tm*.

[0014] If electric vehicle 20 of the embodiment were not equipped with sliding contact device 50, discharge of the shaft voltage of motor shaft 25 would occur due to current flowing from the power transmission path from motor shaft 25 to drive wheels DWa, DWb to case 46 via bearings 25a, 25b, 31a, 31b, etc. (for example, from motor shaft 25 via bearings 25a, 25b), and this discharge would sometimes transmit a relatively large amount of electromagnetic noise to drive wheels DWa, DWb via the power transmission path. In contrast, by providing sliding contact device 50, in the low vehicle speed range (a vehicle speed range in which the rotation speed of motor shaft 25 (rotation speed of motor 22) is equal to or lower than predetermined rotation speed Nm1), spool 54 comes into sliding contact with motor shaft 25, electrically connecting motor shaft 25 and case 46 (vehicle body) via spool 54 and sleeve 53, thereby earthing motor shaft 25 to case 46 (vehicle body), and suppressing discharge of the shaft voltage of motor shaft 25. Furthermore, in the high vehicle speed range (a vehicle speed range in which the rotational speed of motor shaft 25 is higher than predetermined rotational speed Nm1), spool 54 moves away from motor shaft 25, thereby suppressing frictional resistance and wear of spool 54 due to sliding contact between motor shaft 25 and spool 54. The inventors have confirmed through experiments, analysis, etc. that as the rotational speed of motor shaft 25 (motor 22) and countershaft 31 increases, the oil film thickness in bearings 25a, 25b, 31a, 31b, etc. increases, making it difficult for shaft voltage discharge to occur in motor shaft 25. In the embodiment, the specifications of sliding contact device 50 are designed so that the upper limit of the rotational speed range in which shaft voltage discharge in motor shaft 25 is a concern is the above-mentioned predetermined rotational speed Nm1. For example, for each rotation speed Nm of motor 22, the minimum oil film thickness of bearings 25a, 25b, 31a, 31b can be estimated based on the specifications (particulars) of bearings 25a, 25b, 31a, 31b and the amount of oil supplied to bearings 25a, 25b, 31a, 31b, the breakdown voltage can be estimated based on this minimum oil film thickness, the presence or absence of shaft voltage discharge can be determined based on the estimated breakdown voltage, and the above-mentioned predetermined rotation speed Nm1 can be set based on the determination result for each rotation speed Nm of motor 22. Note that when setting the predetermined rotation speed Nm1, the torque of motor 22 can also be taken into consideration.

[0015] The electric vehicle drive device of the embodiment described above includes a sliding contact device 50 having a mechanical oil pump 51, a metal sleeve 53 and spool 54, and a spring 56. At vehicle speeds where the rotational speed Nm of the motor 22 (motor shaft 25) is equal to or less than a predetermined rotational speed Nm1, the spool 54 comes into sliding contact with the motor shaft 25, electrically connecting the motor shaft 25 and the case 46 via the spool 54 and the sleeve 53 and grounding the motor shaft 25 to the case 46 (vehicle body), thereby suppressing discharge of the shaft voltage of the motor shaft 25. Furthermore, at vehicle speeds where the rotational speed Nm1 of the motor 22 is higher than the predetermined rotational speed Nm1, the spool 54 moves away from the motor shaft 25, thereby suppressing frictional resistance and wear of the spool 54 due to sliding contact between the motor shaft 25 and the spool 54.

[0016] In the above-described embodiment, the sliding contact device 50 includes the mechanical oil pump 51. However, instead, the sliding contact device 50 may include an electric oil pump. In this case, the ECU 70 may execute the processing routine of FIG. 3. In this routine, the ECU 70 determines whether the rotation speed Nm of the motor 22 (motor shaft 25) is equal to or less than the predetermined rotation speed Nm1 (step S100). If it is determined that the rotation speed Nm of the motor 22 is equal to or less than the predetermined rotation speed Nm1, the ECU 70 stops driving the electric pump (step S110) and ends this routine. In this case, the spool 54 comes into sliding contact with the motor shaft 25. On the other hand, if it is determined that the rotation speed Nm of the motor 22 is higher than the predetermined rotation speed Nm1, the ECU 70 drives the electric pump in a predetermined manner (step S120) and ends this routine. In the predetermined driving, the electric pump is driven so that the supplied hydraulic pressure is higher than the predetermined hydraulic pressure Po1, i.e., so that the hydraulic biasing force is greater than the biasing force of the spring 56. In this case, the spool 54 moves away from the motor shaft 25. This control provides the same effects as those of the above-described embodiment.

[0017] In the above-described embodiment, the spool 54 of the sliding contact device 50 is in sliding contact with the motor shaft 25, but this is not limiting and the sliding contact device may be in sliding contact with a predetermined rotating shaft in the power transmission path from the motor shaft to the drive wheels. For example, the spool 54 may be in sliding contact with the counter shaft 31.

[0018] In the above-described embodiment, the sliding contact device 50 uses hydraulic oil (hydraulic fluid) from the mechanical oil pump 51 to operate the spool 54, thereby bringing the spool 54 into sliding contact with the motor shaft 25 or releasing the sliding contact, but the present invention is not limited to this and may be any device having a sliding contact member that comes into sliding contact with a predetermined rotating shaft in the power transmission path from the motor shaft to the drive wheels, and a drive unit that separates the sliding contact member from the predetermined rotating shaft when the rotation speed of the motor is higher than the predetermined rotation speed. For example, the sliding contact member may be brought into sliding contact with the predetermined rotating shaft or released from sliding contact by moving the sliding contact member using electromagnetic force or power from a motor or the like.

[0019] The correspondence between the main elements of the embodiment and the main elements of the invention described in the "Means for Solving the Problem" section will be explained below. In the embodiment, the motor shaft 25 corresponds to the "motor shaft," the motor 22 corresponds to the "motor," the bearings 25a and 25b correspond to the "bearings," and the sliding contact device 50 corresponds to the "sliding contact device."

[0020] The correspondence between the main elements of the embodiments and the main elements of the invention described in the "Means for Solving the Problem" section does not limit the elements of the invention described in the "Means for Solving the Problem" section, since the embodiments are examples for specifically explaining the mode for implementing the invention described in the "Means for Solving the Problem" section. In other words, the interpretation of the invention described in the "Means for Solving the Problem" section should be based on the description in that section, and the embodiments are merely specific examples of the invention described in the "Means for Solving the Problem" section.

[0021] The above describes the forms for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms within the scope that does not deviate from the gist of the present disclosure. [Industrial Applicability]

[0022] The present disclosure is applicable to industries such as the manufacturing industry of drive devices for electric vehicles. [Explanation of symbols]

[0023] 20 Electric vehicle, 22 Motor, 23 Rotor, 24 Stator, 25 Motor shaft, 25a, 25b, 31a, 31b, 44a, 44b Bearing, 30 Gear mechanism, 46 Case, 50 Sliding contact device, 51 Mechanical oil pump, 53 Sleeve, 54 Spool, 55 Oil seal, 56 Spring, 60 Inverter, 70 ECU.

Claims

[Claim 1] A drive device for an electric vehicle, comprising: a motor having a rotor attached to a motor shaft and a stator around which a motor coil is wound; and a bearing provided between the motor shaft and a case, a sliding contact device including a sliding contact member that is in sliding contact with a predetermined rotating shaft in a power transmission path from the motor shaft to a drive wheel, and a drive unit that separates the sliding contact member from the predetermined rotating shaft when the rotation speed of the motor is higher than a predetermined rotation speed, When the sliding contact member is in sliding contact with the predetermined rotating shaft, electrical conduction is established between the predetermined rotating shaft and the case via the sliding contact member, and when the sliding contact member is separated from the predetermined rotating shaft, electrical conduction via the sliding contact member is released. A drive device for an electric vehicle comprising:

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