Electric vehicle drive unit

Abstract

To provide a drive system for an electric vehicle, which is of a type having a pair of right and left drive devices independently driving right and left drive wheels, and which can suppress fluctuating noise when the vehicle turningly travels.SOLUTION: A predetermined gear in a gear mechanism constituting a first reducer 20 and a gear at a location corresponding to the predetermined gear in a gear mechanism constituting a second reducer 24 have tooth surface errors different from each other. As a result, a sound pressure of gear noise generated from the predetermined gear mutually differs from a sound pressure of gear noise generated from the gear at the location corresponding to the predetermined gear, and even when a rotation difference occurs between the right and left drive wheels when the vehicle turningly travels, the difference in noise level between the right and left noises is large, and therefore, fluctuating noise whose amplitude fluctuates periodically is suppressed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drive unit for an electric vehicle in which left and right drive units independently drive left and right drive wheels, and in particular to a technology for suppressing fluctuating noise caused by a shift in frequency of noise due to rotating bodies generated by the left and right drive units during turning, etc. [Background technology]

[0002] There is known a drive device for an electric vehicle in which one of a pair of left and right drive devices is composed of a first electric motor and a first reducer, and the other is composed of a second electric motor and a second reducer, and the first electric motor and first reducer and the second electric motor and second reducer are arranged symmetrically on the left and right. For example, the drive device for an electric vehicle described in Patent Document 1 is such an example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-100318

[0004] According to the drive device for an electric vehicle described in Patent Document 1, a pair of left and right first and second drive wheels are independently driven by a pair of left and right first and second electric motors, respectively. As a result, if a malfunction occurs in one of the pair of left and right first and second electric motors, the other electric motor can drive the other drive wheel, so the vehicle will not become unable to travel. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the drive device for the electric vehicle in Cited Document 1, the frequencies of noises such as gear noise generated by the gear mechanism in the first reduction gear and the gear mechanism in the second reduction gear shift when the vehicle is turning, and as a result, a fluctuating sound (humming sound, beat sound) whose amplitude fluctuates periodically is generated due to the frequency shift, which causes the inconvenience of impairing the comfort and sensory satisfaction of the vehicle occupants.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a drive unit for an electric vehicle in which a pair of left and right drive units independently drive left and right drive wheels, which can suppress fluctuating noise when the vehicle is cornering. [Means for solving the problem]

[0007] The gist of the present invention is (a) a drive device for an electric vehicle that includes a first drive device having a first electric motor and a first reducer, and a second drive device having a second electric motor and a second reducer, on the left and right sides, and (b) a predetermined gear in a gear mechanism that constitutes the first reducer and a gear at a position corresponding to the predetermined gear in the gear mechanism that constitutes the second reducer have different tooth surface errors. [Effects of the Invention]

[0008] According to the drive device for an electric vehicle of the present invention, a predetermined gear in the gear mechanism constituting the first reduction gear and a gear in a position corresponding to the predetermined gear in the gear mechanism constituting the second reduction gear have different tooth flank errors. This changes the tooth contact position, causing the sound pressure of the gear noise generated from the predetermined gear to differ from the sound pressure of the gear noise generated from the gear in the position corresponding to the predetermined gear. Even when there is a rotational difference between the left and right drive wheels when the vehicle is cornering, the difference in noise levels between the left and right noises is large, and fluctuating noise with periodically fluctuating amplitude is suppressed.

[0009] Preferably, the tooth surface accuracy is a crowning that forms a bulge in the tooth trace direction, and one of the specified gear and the gear corresponding to the specified gear has a crowning ratio of 1.6 or more times that of the other. This suppresses the large difference in noise levels between the left and right noises and the fluctuating noise whose amplitude fluctuates periodically, even when a rotational difference occurs between the left and right drive wheels when the vehicle is cornering.

[0010] Preferably, the force (intensity) of the gear noise generated from the first drive unit and the second drive unit is represented by a meshing transmission error (dB), and the difference between the meshing transmission error of the first drive unit and the meshing transmission error of the second drive unit is 6 dB or more. As a result, even when a rotational difference occurs between the left and right drive wheels when the vehicle is cornering, the difference in noise levels between the left and right noises is large, and fluctuating noise with periodically fluctuating amplitude is suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a drive device for an electric vehicle according to an embodiment of the present invention; [Figure 2] 2 is a diagram illustrating crowning (shape error) intentionally formed on the tooth surface of a predetermined gear in a gear mechanism that constitutes a reducer provided in the electric vehicle of FIG. 1. FIG. [Figure 3] 2 is a diagram illustrating a bias (shape error) intentionally formed on the tooth surface of a predetermined gear in a gear mechanism that constitutes a reducer provided in the electric vehicle of FIG. 1. FIG. [Figure 4] 2 is a diagram illustrating a pressure angle error and a torsion angle error (posture error) that are intentionally formed on the tooth surface of a predetermined gear in a gear mechanism that constitutes a reducer provided in the electric vehicle of FIG. 1. FIG. [Figure 5] 3 is a diagram showing the relationship between the output torque of the electric motor and the meshing transmission error, with the crowning magnification, which indicates the magnitude of the crowning in FIG. 2, as a parameter. FIG. [Figure 6] FIG. 3 is a diagram showing the relationship between the crowning magnification, which indicates the size of crowning on the tooth surface of the gear in FIG. 2 on the side where crowning is actively increased, and the average level of meshing transmission error. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0013] FIG. 1 is a diagram illustrating a drive unit 12 of an electric vehicle 10 according to one embodiment of the present invention, showing a first rotor shaft 40, a second rotor shaft 46, a first countershaft 56, a second countershaft 64, a first output shaft 58, and a second output shaft 66, which are developed on a plane. In FIG. 1, the drive unit 12 includes a first drive unit 14 and a second drive unit 16 housed in a case 18, at positions symmetrical with respect to a center line CL passing through the center of the electric vehicle 10 in the width direction. The first drive unit 14 includes a first electric motor MG1 and a first reduction gear 20, and drives one of the first drive wheels 22 located on the left side in FIG. 1. The second drive unit 16 includes a second electric motor MG2 having the same output as the first electric motor MG1 and a second reduction gear 24, and drives the other of the second drive wheels 26 located on the right side in FIG. 1.

[0014] The case 18 preferably includes a central partition wall 28 along a center line CL that passes through the center in the width direction of the electric vehicle 10. The interior of the case 18 is divided symmetrically about the center line CL by the central partition wall 28 into a first motor chamber 30 that houses the first electric motor MG1 and a first reducer chamber 32 that houses the first reducer 20, and a second motor chamber 34 that houses the second electric motor MG2 and a second reducer chamber 36 that houses the second reducer 24. The first electric motor MG1 and the second electric motor MG2, and the first reducer 20 and the second reducer 24 are arranged in line-symmetric positions about the center line CL. The power transmission components of the gear mechanism that constitutes the first reducer 20 and the power transmission components of the gear mechanism that constitutes the second reducer 24 are also arranged symmetrically and in line-symmetric positions about the center line CL.

[0015] The first electric motor MG1 has a fixed, cylindrical first stator 38 and a first rotor 42 located concentrically on the inner periphery of the first stator 38 and rotatably supported by a first rotor shaft 40. The second electric motor MG2 has a fixed, cylindrical second stator 44 and a second rotor 48 located concentrically on the inner periphery of the second stator 44 and rotatably supported by a second rotor shaft 46. The first rotor shaft 40 and the second rotor shaft 46 are rotatable about axes perpendicular to the center line CL in FIG. 1. That is, the first rotor shaft 40 and the second rotor shaft 46 are rotatably supported by the case 18 via a pair of bearings 50 and a pair of bearings 52, respectively.

[0016] The first reduction gear 20 includes a first input shaft 54 ​​that is concentrically connected to the first rotor shaft 40 and supports an input gear 54a, a first counter shaft 56 that is arranged parallel to the first input shaft 54 ​​and supports a large-diameter gear 56a that meshes with the input gear 54a and a small-diameter gear 56b that is smaller in diameter than the large-diameter gear 56a, and a first output shaft 58 that is arranged parallel to the first counter shaft 56 and supports an output gear 58a that meshes with the small-diameter gear 56b. The first output shaft 58 is connected to the first drive wheel 22 via a first axle 60. The input gear 54a and the large-diameter gear 56a that meshes with it, and the output gear 58a that meshes with the small-diameter gear 56b each constitute a reduction gear pair.

[0017] Similarly, the second reducer 24 includes a second input shaft 62 that is concentrically connected to the second rotor shaft 46 and supports an input gear 62a, a second counter shaft 64 that is disposed parallel to the second input shaft 62 and supports a large-diameter gear 64a that meshes with the input gear 62a and a small-diameter gear 64b that is smaller in diameter than the large-diameter gear 64a, and a second output shaft 66 that is disposed parallel to the second counter shaft 64 and supports an output gear 66a that meshes with the small-diameter gear 64b. The second output shaft 66 is connected to the second drive wheels 26 via a second axle 68. The input gear 62a and the large-diameter gear 64a that meshes with it, and the output gear 66a that meshes with the small-diameter gear 64b each constitute a reduction gear pair.

[0018] In the first reducer 20, the input gear 54a has fewer teeth than the large-diameter gear 56a, and the small-diameter gear 56b has fewer teeth than the output gear 58a. Similarly, in the second reducer 24, the input gear 62a has fewer teeth than the large-diameter gear 64a, and the small-diameter gear 64b has fewer teeth than the output gear 66a. The input gear 54a, the large-diameter gear 56a, and the output gear 58a have the same number of teeth as the input gear 62a, the large-diameter gear 64a, and the output gear 66a, and the first reducer 20 and the second reducer 24 have the same reduction ratio.

[0019] In the gear mechanism of the first reducer 20 and the gear mechanism of the second reducer 24, the first input shaft 54 ​​supporting the input gear 54a, the second input shaft 62 supporting the input gear 62a, the first counter shaft 56 supporting the large-diameter gear 56a and the small-diameter gear 56b, the second counter shaft 64 supporting the large-diameter gear 64a and the small-diameter gear 64b, and the first output shaft 58 supporting the output gear 58a and the second output shaft 66 supporting the output gear 66a are common parts with each other except for tooth surface errors.

[0020] A different tooth flank error or tooth flank accuracy is intentionally provided between at least one of a predetermined gear in the gear mechanism constituting the first reducer 20, for example, at least one of the input gear 54a and the large-diameter gear 56a meshing therewith, or the small-diameter gear 56b and the output gear 58a meshing therewith, and a gear in a position corresponding to the at least one gear in the gear mechanism constituting the second reducer 24. The different tooth flank error means that the sound pressure of the gear noise generated by the first reducer 20 and the sound pressure of the gear noise generated by the second reducer 24 differ to an extent that the fluctuating sound (beat sound) generated by the combination of the gear noises is not noticeable. The different tooth flank error changes the sound pressure resulting from the meshing state.

[0021] Tooth flank error is something that changes the tooth contact position between the tooth flanks and changes the gear noise level. For example, it is the crowning and waveform rounding of the tooth flank shown in the form error in Figure 2, the bias of the tooth flank shown in the form error in Figure 3, and the pressure angle error and helix angle error of the tooth flank shown in the attitude error in Figure 4.

[0022] Figure 5 shows the meshing transmission error (dB) versus the output torque Tmg of the first electric motor MG1 or the second electric motor MG2, with the crowning magnification as a parameter, obtained when the crowning in Figure 2 is used as the tooth surface error. Meshing transmission error is a value expressed as a rotation angle error that represents the rotational fluctuation that occurs in one gear when the other gear is rotated at a constant speed while meshing with the other gear, and is expressed as the maximum lead / lag angle of the other gear.

[0023] The force, or intensity, of gear noise is represented by the meshing transmission error TE. The crowning magnification is the ratio of the crowning of the gear with increased crowning to the crowning of the other gear with increased crowning, when the crowning magnification of one of the left and right gears (original) that has not been increased is set to 1.0.

[0024] FIG. 5 shows that in a region where the output torque Tmg of the electric motor is relatively large, the meshing transmission error TE increases as the crowning magnification ratio increases. For example, the meshing transmission error TE increases as the crowning magnification ratio of a predetermined gear in the gear mechanism constituting the first reduction gear 20 and a gear at a position corresponding to the predetermined gear in the gear mechanism constituting the second reduction gear 24, i.e., the more actively the crowning ratio of one of the left and right gears is increased relative to the other.

[0025] Figure 6 shows the relationship between the crowning magnification, which indicates the size of the crowning on the tooth surface of the other gear that has been actively increased, and the average level of the transmission error (TE), and experimentally shows the range in which the noise level of the fluctuating sound, which is a composite sound of the left and right gear noises, is effectively suppressed. This range is the range in which the crowning magnification is 1.6 or more, and in which the transmission error (TE) is +6 dB or more higher than the original level when the crowning magnification is 1.0.

[0026] According to the drive unit 12 of this embodiment, a predetermined gear in the gear mechanism constituting the first reduction gear 20 and a gear in a position corresponding to the predetermined gear in the gear mechanism constituting the second reduction gear 24 have different tooth surface errors. As a result, the sound pressure of the gear noise generated from the predetermined gear differs from the sound pressure of the gear noise generated from the gear in a position corresponding to the predetermined gear, and even when there is a difference in rotation between the left and right drive wheels when the vehicle is cornering, the difference in noise levels between the left and right noises is large, and fluctuating noise with periodically fluctuating amplitude is suppressed.

[0027] Furthermore, according to the drive unit 12 of this embodiment, the tooth surface accuracy is a crowning that forms a bulge in the tooth trace direction, and one of the specified gear and the gear corresponding to the specified gear has a crowning ratio of 1.6 or more times that of the other. As a result, even when a rotational speed difference occurs between the left and right drive wheels 22, 26 while the vehicle 10 is cornering, the difference in noise levels between the left and right noises is large, and fluctuating noise with periodically fluctuating amplitude is suppressed.

[0028] Furthermore, according to the drive unit 12 of this embodiment, the force (strength) of the gear noise generated from the first drive unit 14 and the second drive unit 16 is represented by the meshing transmission error (dB), and the difference between the meshing transmission error of a predetermined gear of the first drive unit 14 and the meshing transmission error of the gear at a location corresponding to the predetermined gear of the second drive unit 16 is 6 dB or more. As a result, even when a rotational difference occurs between the left and right drive wheels 22, 26 while the vehicle 10 is cornering, the difference in noise levels between the left and right noises is large, and fluctuating noise with periodically fluctuating amplitude is suppressed.

[0029] Although one embodiment of the present invention has been described above with reference to the drawings, the present invention can be embodied in other ways.

[0030] For example, all of the gears of the gear mechanism constituting the first reducer 20 of the first driving device 14 and all of the gears of the gear mechanism constituting the second reducer 24 of the second driving device 16 may have different tooth surface errors, or some of the gears of the gear mechanism constituting the first reducer 20 of the first driving device 14 and some of the gears of the gear mechanism constituting the second reducer 24 of the second driving device 16 may have different tooth surface errors.

[0031] Furthermore, the tooth surface error in the above-described embodiment is formed by crowning, but instead of this, a shape error such as bias, or an attitude error such as a pressure angle error or helix angle error may be used.

[0032] Furthermore, the reduction mechanism constituting the first reducer 20 and the reduction mechanism constituting the second reducer 24 are arranged at positions symmetrical with respect to the center line CL, but they do not necessarily have to be arranged at positions symmetrical with respect to the axis.

[0033] Furthermore, the input gear 54a, the large diameter gear 56a, and the output gear 58a, and the input gear 62a, the large diameter gear 64a, and the output gear 66a may be helical gears or spur gears.

[0034] It should be noted that the above is merely one example of the present invention, and various modifications can be made to the present invention without departing from the spirit of the present invention. [Explanation of symbols]

[0035] 10: electric vehicle, 12: drive unit, 14: first drive unit, 16: second drive unit, 18: case, 20: first reducer, 22: first drive wheel, 24: second reducer, 26: second drive wheel, 28: central partition, 30: first motor chamber, 32: first reducer chamber, 34: second motor chamber, 36: second reducer chamber, 38: first stator, 40: first rotor shaft, 42: first rotor, 44: second stator, 46: second Rotor shaft, 48: second rotor, 50: bearing, 52: bearing, 54: first input shaft, 54a: input gear, 56: first counter shaft, 56a: large diameter gear, 56b: small diameter gear, 58: first output shaft, 58a: output gear, 60: first axle, 62: second input shaft, 62a: input gear, 64: second counter shaft, 64a: large diameter gear, 64b: small diameter gear, 66: second output shaft, 66a: output gear, 68: second axle

Claims

[Claim 1] A drive device for an electric vehicle, the drive device including a first drive device having a first electric motor and a first reduction gear, and a second drive device having a second electric motor and a second reduction gear, on the left and right sides, A predetermined first gear in the gear mechanism constituting the first reducer and a second gear at a position corresponding to the first gear in the gear mechanism constituting the second reducer have different tooth surface errors. A drive device for an electric vehicle.

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