VEHICLE-DRIVING APPARATUS

Abstract

An object of the present invention is to decrease the size of a torque difference amplification mechanism to decrease the size and weight of a vehicle driving wheel apparatus which includes the torque difference amplification mechanism. The invention includes a gear unit 30, which is provided between electric motors (2L, 2R) each having an outer rotor (5) and left and right driving wheels and is constituted by two planetary gear mechanisms (3L, 3R) each having three elements and two degrees of freedom assembled coaxially with each other. The planetary gear mechanisms include: input outer gears (R.sub.L, R.sub.R) coupled to the outer rotors (5) of the electric motors (2L, 2R); output planetary carriers (C.sub.L, C.sub.R) coaxial with the outer gears (R.sub.L, R.sub.R); sun gears S.sub.L, S.sub.R which are coaxial with the outer gears (R.sub.L, R.sub.R); and planetary gears P.sub.L, P.sub.R serving as revolution gears. One planetary carrier (C.sub.L) of the two planetary gear mechanisms (3L, 3R) is joined to the sun gear (S.sub.R) in the other by a first joint member (31); the sun gear (S.sub.L) is joined to the planetary carrier (C.sub.R) in the other by a second joint member (32) and these joint members are disposed coaxially with each other. The planetary carriers (C.sub.L, C.sub.R) of the planetary gear mechanism (S.sub.L, S.sub.R) are coupled to output gear shafts (14L, 14R) of the driving wheels.

Claims

1. A vehicle driving apparatus comprising: two driving sources each mounted on a vehicle and controllable independently from the other; a left driving wheel and a right driving wheel; and a gear unit mounted between the two driving sources and the left and right driving wheels, the gear unit including two coaxially assembled planetary gear mechanisms each having three elements with two degrees of freedom; wherein each of the driving sources is provided by an electric motor including an outer rotor, each of the planetary gear mechanisms includes an input outer gear coupled to the outer rotor of the electric motor, an output planetary carrier provided coaxially with the outer gear, a sun gear provided coaxially with the outer gear, and planetary gears as revolutionary gears, the planetary carrier of one of the two planetary gear mechanisms is joined to the sun gear of the other by a first joint member, the sun gear of said one of the two is joined to the planetary carrier of said other by a second joint member, the two joint members are coaxial with each other, and the planetary carrier of each of the planetary gear mechanisms is coupled to an output gear shaft of the driving wheel.

2. The vehicle driving apparatus according to claim 1, wherein the outer gear which makes engagement with the planetary gears of the planetary gear mechanism, is provided in an inner diameter surface of the electric motor's outer rotor, integrally therewith.

3. The vehicle driving apparatus according to claim 1, wherein the outer gear, which makes engagement with the planetary gears of the planetary gear mechanism, is provided separately at an inner end region of the outer rotor of the electric motor.

4. The vehicle driving apparatus according to claim 1, wherein the electric motor has its stator disposed on an inner diameter side of the outer rotor, the stator being fastened to a housing which houses the vehicle driving apparatus.

5. The vehicle driving apparatus according to claim 4, wherein the planetary carrier of the planetary gear mechanism has a carrier pin for supporting the planetary gears; an outboard-side carrier flange; and an inboard-side carrier flange; the outboard-side carrier flange has a hollow shaft portion extending outboard; and the hollow shaft portion has its outer diameter supported inside of the stator of the electric motor via a rolling bearing.

6. The vehicle driving apparatus according to claim 4, wherein the inboard-side carrier flange of the planetary gear mechanism has a shaft portion extending inboard; and the shaft portion has an outer diameter surface provided with an output-side small diameter gear for engagement with a large-diameter gear serving as an output gear of the output gear shaft which is coupled to the driving wheel.

7. The vehicle driving apparatus according to claim 1, wherein the vehicle driving apparatus includes a housing having a three-piece structure constituted by a center housing, a left-side housing and a right-side housing; the center housing has a partition wall at its center for division into a left portion and a right portion; and the first joint member and the second joint member penetrate the partition wall.

8. The vehicle driving apparatus according to claim 1, wherein the joint members are double-structured, in which one of the first joint member and the second joint member is provided by a hollow shaft while the other of the joint members is provided by a shaft inserted through the hollow shaft; and coupling of each of the first joint member and the second joint member to its corresponding planetary carrier is provided by a spline fitting.

9. The vehicle driving apparatus according to claim 1, wherein the inner-diameter-side one of the first and the second joint members has an oil hole.

10. The vehicle driving apparatus according to claim 5, wherein the inboard-side carrier flange of the planetary gear mechanism has a shaft portion extending inboard; and the shaft portion has an outer diameter surface provided with an output-side small diameter gear for engagement with a large-diameter gear serving as an output gear of the output gear shaft which is coupled to the driving wheel.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0082] FIG. 1 is a cross-sectional plan view which shows an embodiment of a vehicle driving apparatus according to the present invention.

[0083] FIG. 2 is an enlarged view of a gear unit portion in the embodiment in FIG. 1.

[0084] FIG. 3 is a sectional view taken in a line A-A in FIG. 1.

[0085] FIG. 4 is a sectional view taken in a line B-B in FIG. 1.

[0086] FIG. 5 shows a gear configuration of the vehicle driving apparatus according to the embodiment in FIG. 1 in the form of skeleton diagram to explain an electric vehicle.

[0087] FIG. 6 is a velocity diagram for describing a torque difference amplification factor provided by the gear unit incorporated in the vehicle driving apparatus according to the embodiment in FIG. 1.

[0088] FIG. 7 is a cross-sectional plan view which shows another embodiment of a vehicle driving apparatus according to the present invention.

[0089] FIG. 8 is an enlarged view of a gear unit portion in the embodiment in FIG. 7.

[0090] FIG. 9 is a skeleton diagram which shows a gear configuration of a vehicle driving apparatus in a conventional technique 1.

[0091] FIG. 10 is a velocity diagram for describing a torque difference amplification factor provided by the gear unit incorporated in the vehicle driving apparatus according to the conventional technique 1.

[0092] FIG. 11 is a skeleton diagram which shows a gear configuration of a vehicle driving apparatus according to a conventional technique 2.

[0093] FIG. 12 is a velocity diagram for describing a torque difference amplification factor provided by the gear unit incorporated in the vehicle driving apparatus according to the conventional technique 2.

DESCRIPTION OF EMBODIMENTS

[0094] Hereinafter, embodiments of the present invention will be described based on the attached drawings.

[0095] FIG. 5 shows an electric vehicle AM, which is a rear-wheel drive vehicle including a chassis 60; driving wheels 61L, 61R as rear wheels; front wheels 62L, 62R; a two-motor vehicle driving apparatus 1 according to the present invention; a battery 63; an inverter 64, etc. FIG. 5 shows a gear configuration of the vehicle driving apparatus 1 as a skeleton diagram.

[0096] As shown in FIG. 1 and FIG. 3, the vehicle driving apparatus 1 includes: electric motors 2L, 2R which are mounted on the vehicle and serve as two, independently controllable drive sources; and two, i.e., left and right, planetary gear mechanisms 3L, 3R each having three elements and two degrees of freedom, provided between the left driving wheel 61L and the right driving wheel 61R between the electric motors 2L, 2R.

[0097] Driving torques from the two-motor vehicle driving apparatus 1 are transmitted, via drive shafts constituted by constant velocity joints 65a, 65b and middle shafts 65c, to the left driving wheel 61L and the right driving wheel 61R.

[0098] It should be noted here that the two-motor vehicle driving apparatus 1 is also applicable, in addition to rear wheel drive systems as shown in FIG. 5, to front wheel drive systems and four-wheel drive systems.

[0099] The left electric motor 2L and the right electric motor 2R in the two-motor vehicle driving apparatus 1 are provided by outer-rotor electric motors of the same specification, having the same maximum output.

[0100] The two-motor vehicle driving apparatus 1 is housed in a housing 4.

[0101] The housing 4 is divided into three pieces in a direction orthogonal to an axis of the planetary gear mechanisms 3L, 3R, providing a three-piece structure as shown in FIG. 1, including a center housing 4a and a left and a right side-housing 4bL, 4bR fixed to two side surfaces of the center housing 4a. The left side-housing 4bL and the right side-housing 4bR are fixed to respective openings of both sides of the center housing 4a using a plurality of bolts (not illustrated).

[0102] The left side-housing 4bL and the right side-housing 4bR house the electric motors 2L, 2R in their cylindrical portions. The cylindrical portions have their outer side surfaces provided with outer walls 4cL, 4cR for closing the cylindrical portions.

[0103] As shown in FIG. 1, the center housing 4a has a partition wall 11 at its center. The partition wall 11 divides the housing 4 into two, one on the left and the other on the right.

[0104] The electric motors 2L, 2R are provided by outer rotor motors: On an inner diameter side of the outer rotor 5, a stator 6 is provided and is fastened to the housing 4 which houses the vehicle driving apparatus.

[0105] The stator 6 includes a stator core 6a and a coil 6b. The stator core 6a is integral with the corresponding one of the outer walls 4cL, 4cR of the cylindrical portions which house the electric motors 2L, 2R.

[0106] The outer rotor 5 is disposed spaced apart aroung an outer circumference of the stator 6, with its outboard end supported rotatably by a rolling bearing 7 with respect to corresponding one of the outer walls 4cL, 4cR of the cylindrical portions which house the electric motors 2L, 2R.

[0107] The outer walls 4cL, 4cR of the cylindrical portions which house the electric motors 2L, 2R have their inner walls provided with bearing fitting projections 8 for fixing the rolling bearings 7.

[0108] Between the center partition wall 11 of the housing 4 and the left and the right electric motor 2L, 2R, the planetary gear mechanisms 3L, 3R, are housed, each having three elements and two degrees of freedom as constituent members of the gear unit 30 for receiving torques from the two electric motors 2L, 2R, amplifying and then distributing the torques to the left and the right driving wheel 61L, 61R.

[0109] The gear unit 30 is constituted by the planetary gear mechanisms 3L, 3R, which include: inputting outer gears R.sub.L, R.sub.R provided in inner diameter surfaces of cylindrical portions formed as inboard extensions of the outer rotors 5 of the electric motors 2L, 2R; sun gears S.sub.L, S.sub.R which are coaxial with their respective outer gears R.sub.L, R.sub.R; planetary gears P.sub.L, P.sub.R serving as revolution gears in engagement with the outer gears R.sub.L, R.sub.R and the sun gears S.sub.L, S.sub.R; outputting planetary carriers C.sub.L, C.sub.R coupled to the planetary gears P.sub.L, P.sub.R and are coaxial with the outer gears R.sub.L, R.sub.R; a first joint member 31 which joins one of the planetary carriers C.sub.L (on the left in FIG. 1) with the sun gear S.sub.R in the other (on the right in FIG. 1 and FIG. 2); a second joint member 32 which joins one of the sun gears S.sub.L (on the left in FIG. 1 and FIG. 2) with the planetary carrier C.sub.R in the other (on the right in FIG. 1 and FIG. 2); and output-side small diameter gears 13b which engage with output gears 14a of output gear shafts 14L, 14R. The output-side small diameter gears 13b are coupled to the planetary carriers C.sub.L, C.sub.R.

[0110] It should be noted here that in the embodiment shown in FIG. 1 and FIG. 2, the outer gears R.sub.L, R.sub.R which make engagement with the planetary gears P.sub.L, P.sub.R of the planetary gear mechanisms 3L, 3R are integral with the inner diameter surfaces of the outer rotors 5 of the electric motors 2L, 2R. In an embodiment in FIG. 7 and FIG. 8, the outer gears R.sub.L, R.sub.R which make engagement with the planetary gears P.sub.L, P.sub.R of the planetary gear mechanisms 3L, 3R are separately provided at inner ends of the outer rotors 5 of the electric motors 2L, 2R.

[0111] Also, in the embodiment in FIG. 1 and FIG. 2, the output-side small diameter gears 13b coupled to the planetary carriers C.sub.L, C.sub.R are formed integrally with the planetary carriers C.sub.L, C.sub.R, but these gears may be formed separately.

[0112] The planetary carriers C.sub.L, C.sub.R have carrier pins 33 for supporting the planetary gears P.sub.L, P.sub.R; outboard-side carrier flanges 34a coupled to outboard ends of the carrier pins 33; and inboard-side carrier flanges 34bcoupled to inboard ends of the carrier pins.

[0113] The outboard-side carrier flange 34a has a hollow shaft portion 35 extending outboard. The hollow shaft portion 35 has its outboard-side outer diameter surface supported, via a rolling bearing 20b, by a bearing fitting hole 19b which is formed in an inboard-side end surface of the stator core 6a in each of the electric motors 2L, 2R.

[0114] The inboard-side carrier flange 34b has a hollow shaft portion 36 extending inboard. The hollow shaft portion 36 has its inboard-side end supported, via a rolling bearing 20a, by a bearing fitting hole 19a which is formed in the partition wall 11 of the center housing 4a.

[0115] The output-side small diameter gear 13b is formed integrally with an outer circumferential surface of the hollow shaft portion 35 of the carrier flange 34a.

[0116] The planetary gears P.sub.L, P.sub.R are supported by the carrier pins 33 via needle roller bearings 37.

[0117] Also, between each set of counter surfaces of the carrier flanges 34a, 34b and the planetary gears P.sub.L, P.sub.R, a thrust plate 38 is inserted for smooth rotation of the planetary gears P.sub.L, P.sub.R.

[0118] Between each set of outer circumferential surfaces of the carrier flanges 34a, 34b and the outer gears R.sub.L, R.sub.R, rolling bearings 39a, 39b are disposed.

[0119] The first joint member 31 and the second joint member 32 which couple the two planetary gear mechanisms 3L, 3R that provide the gear unit 30 of the vehicle driving apparatus 1 penetrate the partition wall 11 that divides the center housing 4a of the housing 4 into the left and the right portion.

[0120] The first joint member 31 and the second joint member 32 are disposed coaxially with each other in a double structure, i.e., a structure where one of the joint members (the second joint member 32 in the embodiment shown in FIG. 1 and FIG. 2) has a hollow shaft and the other of the joint members (the first joint member 31 in the embodiment shown in FIG. 1 and FIG. 2) has a shaft inserted through the hollow shaft.

[0121] In the embodiment shown in FIG. 1 and FIG. 2, a spline 41 is formed at an end of the planetary gear mechanism 3R on the right side of the second joint member 32 which has the hollow shaft, and at the hollow shaft portion 36 of the inboard-side carrier flange 34b of the planetary carrier C.sub.R, whereby the second joint member 32 is coupled to the planetary carrier C.sub.R by means of spline fitting.

[0122] Also, in the embodiment shown in FIG. 1 and FIG. 2, a spline 42 is formed at an end of the planetary gear mechanism 3L on the left side of the first joint member 31, and at the hollow shaft portion 35 of the outboard-side carrier flange 34a of the planetary carrier C.sub.L, whereby the first joint member 31 is coupled to the planetary carrier C.sub.L by means of spline fitting.

[0123] As described, in the planetary gear mechanisms 3L, 3R, by employing the spline fitting for coupling the first joint member 31 to the planetary carrier C.sub.L, and the second joint member 32 to the planetary carrier C.sub.R, it becomes possible to separate the two planetary gear mechanisms 3L, 3R in the left-right direction, allowing these planetary gear mechanisms to be assembled together with other speed-reduction gear shafts into the housing 4 which has a three piece structure, from both left and right directions.

[0124] The second joint member 32 has an end facing the planetary carrier C.sub.L, having its outer circumferential surface formed with an external gear for engagement with the planetary gear P.sub.L of the left planetary gear mechanism 3L. This external gear constitutes the sun gear S.sub.L of the left planetary gear mechanism 3L.

[0125] As for the first joint member 31, which is inserted through the second joint member 32 that is provided by the hollow shaft, the right planetary gear mechanism 3R has its end provided with a large-diameter portion 43. The large-diameter portion 43 has its outer circumferential surface formed with an external gear for engagement with the planetary gear P.sub.R of the right planetary gear mechanism 3R. This external gear constitutes the sun gear S.sub.R of the right planetary gear mechanism.

[0126] Of the first joint member 31 and the second joint member 32, the inner-diameter-side joint member (the first joint member 31) is coupled to the sun gear S.sub.R, a maximum diameter of which is smaller than a minimum diameter of a spline hole in an inner surface of the hollow shaft portion 36 of the inboard-side carrier flange 34b of the planetary carrier C.sub.R fitted by the outer-diameter-side joint member (the second joint member 32). This makes it easy to assemble the inner-diameter-side joint member (the first joint member 31).

[0127] Between an outer circumferential surface of the inner-diameter-side joint member (the first joint member 31) and an inner circumferential surface of the outer-diameter-side joint member (the second joint member 32), a collar 44 is disposed. Needle roller bearings 45, 46 are disposed at two ends of the collar 44.

[0128] Fitting (splines 41, 42) of the first joint member 31 and the second joint member 32 with the planetary carriers C.sub.L, C.sub.R is provided by axially slidable fitting. This makes it possible to eliminate imbalanced load to the gear tooth flank caused by thrust forces from the helical gears.

[0129] As the first joint member 31 and the second joint member 32 and the planetary carriers C.sub.L, C.sub.R which are spline fitted (splines 41, 42) therewith slide axially, this movement is limited by thrust bearings 47, 48 provided at two ends of the outer-diameter-side joint member (the second joint member 32 in the embodiment in FIG. 1 and FIG. 2).

[0130] The inner-diameter-side joint member (the first joint member 31 in the embodiment in FIG. 1 and FIG. 2) in the double-structure shaft which couples the two planetary gear mechanisms 3L, 3R, is supported at an end away from the spline-fitting, between the joint member (the first joint member 31 in the embodiment in FIG. 1 and FIG. 2) and the planetary carrier (C.sub.L in the embodiment in FIG. 1 and FIG. 2), by a deep groove ball bearing 49 with respect to the other planetary carrier (C.sub.R in the embodiment in FIG. 1 and FIG. 2).

[0131] The inner-diameter-side joint member (the first joint member 31 in the embodiment in FIG. 1 and FIG. 2) in the double-structure shaft which couples the two planetary gear mechanisms 3L, 3R has an oil hole 50 through its core of the shaft.

[0132] The output gear shafts 14L, 14R, each having the large-diameter output gear 14a, are supported by bearing fitting holes 53a formed in two surfaces of the partition wall 11 of the center housing 4a and by bearing fitting holes 53b formed in each of the side housings 4bL, 4bR, via rolling bearings 54a, 54b. The bearing fitting holes 53a, 53b are stepped, with wall portions for contact by outer rings of the rolling bearings 54a, 54b.

[0133] The output gear shafts 14L, 14R have their respective outboard end portions extended from openings formed in the side housings 4bL, 4bR, out of the housing 4. These extended outboard ends of the output gear shafts 14L, 14R have their outer circumferential surfaces joined to outer joint members of the constant velocity joints 65a by means of spline coupling.

[0134] The constant velocity joints 65a joined to the output gear shafts 14L, 14R are connected to the driving wheels 61L, 61R via middle shafts 65c and the constant velocity joints 65b (FIG. 5).

[0135] Oil seals 55 are provided around outboard end portions of the output gear shafts 14L, 14R, to seal gaps in the openings formed in the side housings 4bL, 4bR, thereby to prevent lubrication oil from leaking from inside the housing 4 and to prevent muddy water and the like from making entry from outside.

[0136] The two-motor vehicle driving apparatus 1 according to the embodiment shown in FIG. 1 and FIG. 2 has a gear configuration shown in the skeleton diagram in FIG. 5.

[0137] As shown in FIG. 5, the left electric motor 2L and the right electric motor 2R are driven by electric power which is supplied from a battery 63 via an inverter 64. The electric motors 2L, 2R are controlled independently from each other by an electronic controller (not illustrated), being able to generate and output different torques.

[0138] Torques from the outer rotors 5 of the electric motors 2L, 2R are supplied to the outer gears R.sub.L, R.sub.R of the gear unit 30.

[0139] Via the gear unit 30, the output-side small diameter gears 13b in the planetary gear mechanisms 3L, 3R engage with the large-diameter output gears 14a of the output gear shafts 14L, 14R. The torques from the outer rotors 5 of the electric motors 2L, 2R are further amplified by a teeth ratio between the output-side small diameter gear 13b and the output gear 14a, and then outputted to the driving wheels 61L, 61R.

[0140] The gear unit 30 is an assembly of two identical single pinion planetary gear mechanisms 3L, 3R, each having three elements and two degrees of freedom, being coaxially arranged with the other.

[0141] The planetary gear mechanisms 3L, 3R include: the coaxially arranged sun gears S.sub.L, S.sub.R and outer gears R.sub.L, R.sub.R; the plurality of planetary gears P.sub.L, P.sub.R between the sun gears S.sub.L, S.sub.R and the outer gears R.sub.L, R.sub.R; and the planetary carriers C.sub.L, C.sub.R which support the planetary gears P.sub.L, P.sub.R rotatably and are coaxial with the sun gears S.sub.L, S.sub.R and the outer gears R.sub.L, R.sub.R. It should be noted here that, the sun gears S.sub.L, S.sub.R and the planetary gears P.sub.L, P.sub.R are external gears having their teeth on their outer circumference, while the outer gears R.sub.L, R.sub.R are internal gears having their teeth on their inner circumference. The planetary gears P.sub.L, P.sub.R engage with the sun gears S.sub.L, S.sub.R and the outer gears R.sub.L, R.sub.R.

[0142] In the planetary gear mechanisms 3L, 3R, if the planetary carriers C.sub.L, C.sub.R are fixed, the sun gears S.sub.L, S.sub.R and the outer gears R.sub.L, R.sub.R rotate in reverse directions. For this reason, in the velocity diagram shown in FIG. 6, the outer gears R.sub.L, R.sub.R and the sun gears S.sub.L, S.sub.R are disposed on opposite sides with respect to the planetary carriers C.sub.L, C.sub.R.

[0143] As described above, in the gear unit 30, a first planetary gear mechanism, i.e., the planetary gear mechanism 3L which has the sun gear S.sub.L, the planetary carrier C.sub.L, the planetary gears P.sub.L, and the outer gear R.sub.L; and a second planetary gear mechanism, i.e., the planetary gear mechanism 3R which has the sun gear S.sub.R, the planetary carrier C.sub.R, the planetary gears P.sub.R, and the outer gear R.sub.R; are assembled coaxially with each other.

[0144] With these, the planetary carrier C.sub.L of the first planetary gear mechanism 3L and the sun gear S.sub.R of the second planetary gear mechanism 3R are joined to each other to form the first joint member 31, while the sun gear S.sub.L of the first planetary gear mechanism and the planetary carrier C.sub.R of the second planetary gear mechanism 3R are joined to each other to form the second joint member 32.

[0145] A torque TM1 generated in the electric motor 2L is supplied to the outer gear R.sub.L of the first planetary gear mechanism 3L, and then the first planetary gear mechanism 3L transmits the torque to the output-side small diameter gear 13b. The output-side small diameter gear 13b engages with the output gear 14a of the output gear shaft 14L to provide one-stage speed reduction, and thus a driving torque TL is outputted from the output gear shaft 14L to the driving wheel 61L.

[0146] A torque TM2 generated in the electric motor 2R is supplied to the outer gear R.sub.R of the second planetary gear mechanism 3R, and then the second planetary gear mechanism 3R transmits the torque to the output-side small diameter gear 13b. The output-side small diameter gear 13b engages with the output gear 14a of the output gear shaft 14R to provide one-stage speed reduction, and thus a driving torque TR is outputted from the output gear shaft 14R to the driving wheel 61R.

[0147] Outputs from the electric motors 2L, 2R are supplied to respective outer gears R.sub.L, R.sub.R of the two planetary gear mechanisms 3L, 3R, and the outputs from the first joint member 31 and the second joint member 32 are supplied to the driving wheels 61L, 61R.

[0148] The second joint member 32 has a hollow shaft structure, through which the first joint member 31 is inserted. The shaft which constitute the first joint member 31 and the second joint member 32 has a double structure.

[0149] The first joint member 31, the solid shaft, has one of its ends (right end in the figure) serving as a rotation shaft of the sun gear S.sub.R, with the other end (left end in the figure) penetrating the sun gear S.sub.L and connected to the planetary carrier C.sub.L. The second joint member 32, the hollow shaft, has one of its ends (left end in the figure) serving as a rotation shaft of the sun gear S.sub.L, with the other end (right end in the figure) connected to the planetary carrier C.sub.R. The first joint member 31 and the second joint member 32 join the two planetary gear mechanisms.

[0150] Since the gear unit 30 is an assembly of the two identical single pinion planetary gear mechanisms 3L, 3R, it can be graphically represented as two velocity diagrams as shown in FIG. 6. For easy understanding, the two velocity diagrams are arranged in the up-down direction, with the upper velocity diagram representing the left planetary gear mechanism 3L, while the lower velocity diagram representing the right planetary gear mechanism 3R. In the embodiment of FIG. 1 and FIG. 2, driving torques TL, TR taken out of the gear unit 30 are amplified by a certain reduction ratio as the torques are transmitted by the output-side small diameter gears 13b engaged with the output gears 14 before being transmitted to the left and the right driving wheel 61L, 61R. For the sake of easy understanding, however, the driving torques will continue to be called TL and TR in describing the velocity diagrams in FIG. 6 and mathematical equations hereinbelow.

[0151] The two, planetary gear mechanisms 3L, 3R use identical gears having identical number of teeth: So, a distance between the outer gear R.sub.L and the planetary carrier C.sub.L is equal to a distance between the outer gear R.sub.R and the planetary carrier C.sub.R in the velocity diagrams, and this distance will be represented by a. Likewise, a distance between the sun gear S.sub.L and the carrier C.sub.L is equal to a distance between the sun gear S.sub.R and the planetary carrier C.sub.R, and this distance will be represented by b. A ratio of a distance between the planetary carriers C.sub.L, C.sub.R and the outer gears R.sub.L, R.sub.R to a distance between the planetary carriers C.sub.L, C.sub.R and the sun gears S.sub.L, S.sub.R is equal to a ratio of an inverse (1/Zr) of the number of teeth Zr of the outer gears R.sub.L, R.sub.R to an inverse (1/Zs) of the number of teeth Zs of the sun gears S.sub.L, S.sub.R. Therefore, a=(1/Zr), and b=(1/Zs).

[0152] With R.sub.R being a point of reference, a proportion of moment M yields the following equation (11), where an arrow M in FIG. 6 indicates the positive direction of the moment:

a.Math.TR+(a+b).Math.TL(b+2a).Math.TM1=0 (11)

[0153] With R.sub.L being a point of reference, a proportion of moment M yields the following equation (12):

a.Math.TL(a+b).Math.TR+(b+2a).Math.TM2=0 (12)

[0154] From Equation (11)+Equation (12), the following equation (13) is obtained:

b.Math.(TRTL)+(2a+b).Math.(TM2TM1)=0 (TRTL)=((2a+b)/b).Math.(TM2TM1) (13)

[0155] The term (2a+b)/b in Equation (13) is the torque difference amplification factor . Substitution with a=1/Zr and b=1/Zs gives =(Zr+2Zs)/Zr, and the following torque difference amplification factor is obtained:

=(Zr+2Zs)/Zr

[0156] In the present invention, inputs from the electric motors 2L, 2R are R.sub.L, R.sub.R, while outputs to the driving wheels 61L, 61R are S.sub.R+C.sub.L, S.sub.L+C.sub.R.

[0157] When the two electric motors 2L, 2R generate mutually different torques TM1, TM2 and there is an input torque difference TIN (=(TM2TM1)), the gear unit 30 amplifies the input torque difference TIN and therefore it is possible to obtain a driving torque difference .Math.TIN which is larger than the input torque difference TIN. In other words, even if the input torque difference TIN is small, it is possible with the gear unit 30 to amplify the input torque difference TIN by the above-described torque difference amplification factor (=(Zr+2Zs)/Zr), and therefore it is possible to make the driving torque difference TOUT (=.Math.(TM2TM1)) between the driving torques TL, TR larger than the input torque difference TIN before the torques are supplied to the left driving wheel 61L and the right driving wheel 61R.

[0158] In the conventional technique 1 and the conventional technique 2, the torque difference amplification mechanism which is provided by the gear unit 105 includes outer gears R in both of its left and right joint members of the two planetary gear mechanisms. Therefore, one of the joint members which connects the left or the right outer gear with a separate member must have a larger diameter than the other outer gear R.

[0159] According to the present invention, the torque difference distribution mechanism which is provided by the gear unit 30 is constituted by two planetary gear mechanisms which are connected to each other at the sun gear S.sub.L and the planetary carrier C.sub.R, and at the sun gear S.sub.R and the planetary carrier C.sub.L, so the invention does not need a connection member which has a larger diameter than the outer gears R.sub.L, R.sub.R. Hence, the present invention makes it possible to reduce the size of the torque difference distribution mechanism as compared to those in the conventional technique 1 and the conventional technique 2, and therefore to reduce the size and weight of the vehicle driving apparatus 1 for an electric vehicle which incorporates the torque difference distribution mechanism.

[0160] Reducing the size and weight of the vehicle driving apparatus 1 for electric vehicles increases degree of freedom in layout of the vehicle driving apparatus 1 on the vehicle and in layout of the other peripheral components on the vehicle.

[0161] Also, downsizing the vehicle driving apparatus 1 provides other benefits such as increased cabin space.

[0162] In the embodiments described thus far, output torques from the two planetary gear mechanisms 3L, 3R are transmitted to the output gears 14a of the output gear shafts 14L, 14R which are coupled to the driving wheels 61L, 61R; alternatively however, multi-stage gear mechanism may be used with intermediate gear shafts being provided between the two sets of the planetary gear mechanisms 3L, 3R and the output gear shafts 14L, 14R.

[0163] In the embodiment shown in FIG. 1, two drive sources provided by the electric motors 2L, 2R are electric motors of the same specification, having the same maximum output; but the two drive sources are not limited to this example.

[0164] The vehicle on which the vehicle driving apparatus 1 is mounted is not limited to electric vehicles and hybrid electric vehicles. For example, the vehicle may be a fuel cell automobile which utilize a first electric motor 2L and a second electric motor 2R as drive sources.

[0165] The present invention is not limited in any way by the embodiments described so far, and may be implemented in many ways within the scope of the present invention.

REFERENCE SIGNS LIST

[0166] 1: Vehicle Driving Apparatus

[0167] 2L, 2R: Electric Motor

[0168] 3L, 3R: Planetary Gear Mechanism

[0169] 4: Housing

[0170] 4a: Center Housing

[0171] 4bL, 4bR: Side Housing

[0172] 4cL, 4cR: Outer Wall

[0173] 5: Outer Rotor

[0174] 6: Stator

[0175] 6a: Stator Core

[0176] 6b: Coil

[0177] 7: Rolling Bearing

[0178] 8: Bearing Fitting Projection

[0179] 11: Partition Wall

[0180] 13b: Output-Side Small Diameter Gear

[0181] 14L, 14R: Output Gear Shaft

[0182] 149a: Output Gear

[0183] 19a, 19b: Bearing Fitting Hole

[0184] 20a, 20b: Rolling Bearing

[0185] 30: Gear Unit

[0186] 31: First Joint Member

[0187] 32: Second Joint Member

[0188] 33: Carrier Pin

[0189] 34a, 34b: Carrier Flange

[0190] 35, 36: Hollow Shaft Portion

[0191] 37: Needle Roller Bearing

[0192] 38: Thrust Plate

[0193] 39a, 39b: Rolling Bearing

[0194] 41, 42: Spline

[0195] 43: Large-Diameter Portion

[0196] 44: Collar

[0197] 45, 46: Needle Roller Bearing

[0198] 47, 48: Thrust Bearing

[0199] 49: Deep Groove Ball Bearing

[0200] 50: Oil Hole

[0201] 53a, 53b: Bearing Fitting Hole

[0202] 54a, 54b: Rolling Bearing

[0203] 55: Oil Seal

[0204] 60: Chassis

[0205] 61L, 61R: Driving Wheel

[0206] 62L, 62R: Front Wheel

[0207] 63: Battery

[0208] 64: Inverter

[0209] 65a, 65b: Constant Velocity Joint

[0210] 65c: Middle Shaft

[0211] AM: Electric Vehicle

[0212] C.sub.L, C.sub.R: Planetary Carrier

[0213] P.sub.L, P.sub.R: Planetary Gear

[0214] R.sub.L, R.sub.R: Outer Gear

[0215] S.sub.L, S.sub.R: Sun Gear