Patent Application
20150367720
The present invention relates to electric vehicle drive units for driving wheels of, e.g., electric vehicles.
JP-A-2007-224979 (Patent Literature 1) discloses a conventional electric vehicle drive unit which includes a plurality of drive-motor units in a vehicle body, for driving a left and a right wheels individually of each other.
If a plurality of drive-motor units are fixed to the vehicle body, transmission members are required in order to transmit driving forces of the drive-motor units to respective wheel hubs.
Conventionally, these transmission members are provided by constant-velocity joints. The constant-velocity joint is spline-fitted to a wheel-side rotation member of a speed reducer in the drive-motor unit.
Patent Literature 1: JP-A-2007-224979
If a spline fitting is utilized to connect the constant-velocity joint and the wheel-side rotation member of the speed reducer in the drive-motor unit, the spline connection requires a disconnection prevention member.
Another problem when a plurality of drive-motor units are fixed to the vehicle body is that for a small vehicle, the drive-motor units will occupy a considerable amount of space with respect to the vehicle body, and on the contrary, the space for the constant-velocity joints has to be small. This leads to an increased operation angle between an input shaft and an output shaft of the constant-velocity joint as the joint is assembled, which can shorten the life of constant-velocity joint.
The operation angle of the constant-velocity joint can be decreased by lowering the fixing position of the drive-motor unit on the vehicle body; however, this decreases a distance between the drive-motor unit and the ground surface, resulting in increased risk that the drive-motor unit will be hit by a flying rock and be damaged.
It is therefore an object of the present invention to provide an improved connection structure between the constant-velocity joint and the drive-motor unit, and provide an improved fixing structure for the drive-motor unit to be fixed to the vehicle body at a decreased operation angle of the constant-velocity joint.
The present invention provides an electric vehicle drive unit which includes a plurality of drive-motor units for individually driving left and right wheels. The drive-motor units are installed in a vehicle body via a sub-frame, and driving forces from the drive-motor units are transmitted to left and right wheel hubs via power transmission members.
The left wheel and the right wheel are driven by two of the drive-motor units: the drive-motor units may be integrated with each other by a common casing.
Also, the two drive-motor units which drive the left and the right wheels may have individual casings. The two drive-motor units may be fixed back-to-back in the sub-frame, with the drive-motor units' respective output shafts having their rotation axis slanted so as to make the power transmission members, which are provided by constant-velocity joints, have their operation angles within a tolerable angle.
It is desirable that the electric vehicle drive unit further includes anti-vibration members disposed at least between the drive-motor unit and the sub-frame or between the sub-frame and the vehicle body. The anti-vibration members may be provided by rubber bushings.
The output shaft of the drive-motor unit may have a flange member, to which the power transmission member is bolted.
The flange member may be supported rotatably with respect to the casing of the drive-motor unit, being spline-fitted with a speed reducer output shaft of the drive-motor unit.
According to the present invention, a plurality of drive-motor units for individually driving a left and a right wheels are installed in a vehicle body via a sub-frame, and driving forces from the drive-motor units are transmitted to left and right wheel hubs via power transmission members. The arrangement makes it possible to dispose an input shaft and an output shaft of the power transmission members within a small operation angle. This improves life of the power transmission members.
Hereinafter, description will be made for an electric vehicle drive unit 20 according to an embodiment of the present invention, with reference to the drawings.
As shown in
The sub-frame 13, in which the drive-motor units 20a, 20b are installed, is fixed to the chassis 12 via anti-vibration members 14 provided by rubber bushings for example.
In an embodiment shown in
In the embodiment shown in
The embodiment shown in
As shown in
In the embodiment shown in
In the embodiment shown in
Next, reference will be made to
The drive-motor unit 20a includes a motor 21, which is a radial gap motor having: a stator 24 fixed to the casing 41; a rotor 23 disposed on an inner side of the stator 24 with a radial gap; and a motor rotation shaft 22 which is fitted to an inner side of the rotor 23 and rotates integrally with the rotor 23.
The speed reducer section 31 includes: a speed reducer section input shaft 32 which has eccentric sections 32a, 32b; cycloid discs 33, 34 which are held by the eccentric sections 32a, 32b rotatably via rolling bearings 33a, 34a and working as revolving members; a plurality of outer pins 35 held at fixed positions on the casing and working as outer circumferential engagers for engagement with outer circumferential portions of the cycloid discs 33, 34; a motion conversion mechanism which transmits rotational movement of the cycloid discs 33, 34 to the wheel-side rotation member 38; and counterweights 36a, 36b.
The motor-side rotation member 30 is constituted by spline-fitting the motor rotation shaft 22, which is a cylindrical member rotated by the motor 21, around the speed reducer section input shaft 32 which has an outer diameter surface disposed to fit to an inner diameter surface of the motor rotation shaft 22. The motor-side rotation member 30 is supported rotatably by rolling bearings 30a, 30b at two ends of the motor 21, and at a left end of the speed reducer section 31.
As shown in
The outer pins 35 are disposed equidistantly on a circular track which centers around the rotational center of the motor-side rotation member 30. They are located on revolution tracks of the cycloid discs 33, 34. As the cycloid discs 33, 34 make their revolutions, the wavy curves and the outer pins 35 engage with each other and generate rotational movement of the cycloid discs 33, 34.
The counterweights 36a, 36b are half-disc-like, each having a through-hole at a place away from its center for fitting to the speed reducer section input shaft 32, and are disposed on outer sides of the eccentric sections 32a, 32b respectively, at a 180-degree phase difference therefrom in order to cancel inertial moment caused by the rotation of the cycloid discs 33, 34.
The motion conversion mechanism is constituted by a plurality of inner pins 37 held by the wheel-side rotation member 38 and the through-holes 33b, 34b formed in the cycloid discs 33, 34. The inner pins 37 are disposed equidistantly on a circular track which centers around the rotational center of the wheel-side rotation member 38. In order to reduce frictional resistance with the cycloid discs 33, 34, needle roller bearings are provided to make contact with inner wall surfaces of the through-holes 33b, 34b of the cycloid discs 33, 34. On the other hand, the through-holes 33b, 34b are formed correspondingly to the plurality of inner pins 37. The through-holes 33b, 34b have their inside diameter formed larger than an outside diameter of the inner pins 37 (maximum outer diameter including that of the needle roller bearing) by a predetermined dimension.
The wheel-side rotation member 38 includes: a flange section 38a which has holes in its end surface for holding the inner pins 37; and an output shaft 38 for connection with the power transmission members 15a or 15b.
The output shaft 38 has a shaft section 38b and a cylindrical section 38c which is spline-connected around an outer diameter surface of the shaft section 38b. The cylindrical section 38c is rotatably supported on its outer diameter surface, by the casing 42 of the speed reducer section 31 via double-row rolling bearing 39a, 39b.
A flange member 38d is formed on an outboard side of the cylindrical section 38c of the output shaft 38 of the speed reducer section 31, integrally therewith.
From an outboard side of the flange member 38d of the speed reducer section 31, an outer ring of the constant-velocity joint 15c of the power transmission member 15a is bolted.
Desirably, the casings 41, 42 of the motor portion 21 and the speed reducer section 31 are made from a light-metal material (e.g., aluminum alloy).
In order to prevent oil leak, an oil seal 43 is disposed at an end of the cylindrical section 38c of the output shaft 38 of the speed reducer section 31, and at an outboard end of the casing 42 of the speed reducer section 31.
In all of the embodiments thus far, the two drive-motor units 20a, 20b have their casings individually from each other; however, the two drive-motor units 20a, 20b may be integrated in a common casing.
Operation details of the first driving device 20a, which has the arrangement described above, will be covered hereafter.
In the motor 21, coils in the stator 24, are externally supplied with an AC current, for example, to generate an electromagnetic force, which in turn rotates the rotor 23 which includes permanent magnets or DC magnets. If the frequency of the voltage which is supplied to the coil is increased, the rotor 23 rotates at an increased speed accordingly.
As the rotor 23 rotates, the motor-side rotation member 30 connected thereto rotates, which then causes the cycloid discs 33, 34 to make their revolutions around the rotation center of the motor-side rotation member 30. In this process, the outer pins 35 come into engagement with the curvy wave patterns of the cycloid discs 33, 34 to cause the cycloid discs 33, 34 to rotate in the opposite direction from the rotating direction of motor-side rotation member 30.
As the cycloid discs 33, 34 makes their rotational movements, the inner pins 37 which are inserted through the through-holes 33b, 34b make contact with inner wall surfaces of the through-holes 33b, 34b, and the revolutionary movements of the cycloid discs 33, 34 is transmitted to the wheel-side rotation member 38, and then to the power transmission member 15a. Since the through-holes 33b, 34b have their inside diameter made larger than the outside diameter of the inner pins 37, the inner pins 37 and the inner wall surfaces of the through-holes 33b, 34b make contact and then move apart from each other, and repeat this while keeping their mutual movement. Consequently, revolutionary movements of the cycloid discs 33, 34 are not transmitted to the inner pins 37 and only the rotational movements of the cycloid discs 33, 34 are transmitted to the wheel-side rotation member 38.
It should be noted here that the speed reducer section 31 of the configuration described above has a speed reduction ratio which can be calculated as (ZA−ZB)/ZB, where ZA represents the number of the outer pins 35, and ZB represents the number of wave patterns in the cycloid discs 33, 34.
As understood, a compact drive-motor unit having a high speed-reduction ratio can be obtained by utilizing a cycloid reduction gear system which can provide a large speed reduction ratio without requiring a multi-stage configuration. The needle roller bearings are used at places where the inner pins 37 make contact with the cycloid discs 33, 34. This decreases contact resistance and therefore increases transmission efficiency of the speed reducer section 31.
Each embodiment described thus far makes use of a radial gap motor in which there is a radial gap between the stator and the rotor. The present invention is not limited to this, however, and whatsoever types of motor may be utilized. For example, use of an axial gap motor in which there is an axial gap between the stator and the rotor will allow the electric vehicle drive unit to be compact in the axial direction.
Further, in each embodiment described above, the motor-side rotation member is provided by an assembly of a motor rotation shaft and a speed reducer section input shaft which are spline-connected to each other. This makes it possible to simplify the shape of each component, leading to improved assemblability. However, this does not constitute any limitation, either. The motor-side rotation member may be a one-piece member, also.
Thus far, embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to these illustrated embodiments. Any of these embodiments illustrated thus far may be modified or changed in many ways within the scope or within the equivalence of the present invention.
The present invention can be utilized advantageously in drive-motor unit for electric vehicles, etc.
11 Electric Vehicle
12 Chassis
13 Sub-Frame
13
a,
13
b Front Wheels
14
a,
14
b Rear Wheels
14 Anti-Vibration Member
15
a,
15
b Power Transmission Member
15
c Constant-Velocity Joint
15
d Shaft Section
20
a,
20
b Drive-Motor Unit
38
d Flange Member
41, 42 Casing
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-013914 | Jan 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/083478 | 12/13/2013 | WO | 00 |
