Driving system for an electric vehicle

Abstract: A driving system for an electric vehicle which drives wheels (81, 82) thereof with the aid of an AC motor (110) via an inverter (4) while a battery (1) is used as a power source is constructed such that the primary side and the secondary side of the AC motor are rotatably supported in a motor frame (141). One of the primary and the secondary sides of the AC motor is operatively connected to a power transmission shaft (811, 821) for one of a left-hand wheel (82) and a right-hand wheel (81) via a reversible type speed reducing mechanism while the direction of rotation of the power transmission shaft is reversed relative to that of the one of the primary and secondary sides. The other one of the primary and the secondary sides of the AC motor (110) is operatively connected to a power transmission shaft for the other one of the wheels via a non-reversible type speed reducing mechanism while the direction of rotation of the power transmission shaft is kept unchanged relative to that of the other one of the primary and secondary sides. Electricity from the battery (1) is fed to the coil (112) on the primary side of the AC motor via the inverter and a slip ring (151).

Description: The present invention relates generally to an electric vehicle adapted to be driven with a battery as a power source. More particularly, the present invention relates to a driving system for an electric vehicle of the foregoing type. To facilitate understanding of the present invention, two typical conventional driving systems each employable for an electric vehicle will be described below with reference to Fig. 6 and Fig. 7. Fig. 6 shows by way of schematic plan view a conventional driving system for an electric vehicle including wheels each adapted to be driven by an AC motor to which AC current is fed from an inverter with a battery as a power source. In the drawing, reference numeral 1 designates a battery, and reference numeral 4 designates an inverter for driving an AC motor 5 for driving wheels 81 and 82. Reference numeral 3 designates a protection fuse which is used as desired. In addition, reference numeral 2 designates a main switch by way of which the battery 1 is electrically connected to and disconnected from the inverter 4. An output shaft of the AC motor 5 is connected to a differential gear 7 via a speed reducing unit 6 in order to rotationally drive the wheels 81 and 82. Reference numerals 811 and 821 designate power transmission shafts which serve to transmit the rotational force generated by the AC motor 5 to the wheels 81 and 82. Reference numeral 9 designates conductors which connect the inverter 4 to the AC motor 5. As is well known, the electric vehicle is driven with the battery 1 as a power source with the aid of the driving system constructed in the above-described manner. In fact, however, the following is required for electric vehicles (hereinafter referred to simply as E-vehicle) in order to be used just as conventional internal combustion engine installed vehicles (hereinafter referred to as ICE-vehicle) are used. 1) Electric vehicles must have good drivability, that is, a. good acceleration performance, b. long distance driving on one battery charging, and c. good maneuverability. 2) Electric vehicles must have high reliability and good maintainability. To meet the foregoing requirements, it is necessary that the following further requirements are satisfactorily met. 1) A driving system for an E-vehicle exhibits the substantially same drivability and reliability as those of an ICE-vehicle. 2) The driving system is designed with small dimensions and light weight and functions at high efficiency. 3) The driving system is manufactured at low costs. In view of the requirements as mentioned above, the conventional driving system as shown in Fig. 6 is constructed such that an output from the AC motor 5 is transmitted to the wheels 81 and 82 via the speed reducing unit 6 and the differential 7 in order to rotationally drive the wheels 81 and 82. In spite of the structure employed for the conventional driving system, the following problems are left still unsolved. 1) Since the differential unit is mechanically designed and constructed, it is unavoidably manufactured at expensive costs. 2) Efficiency of the driving system is undesirably reduced mainly due to mechanical loss derived from the speed reducing unit and the differential. 3) Maintenance service should periodically be performed for a lubricant filled in the speed reducing unit and the differential unit. In contrast with the conventional driving system as mentioned above, a driving system including no mechanical differential unit is exemplified by a driving system as shown in Fig. 7. It should be noted that same components as those shown in Fig. 6 are represented by same reference numerals. The driving system shown in Fig. 7 is constructed such that a left-hand wheel 81 and a right-hand wheel 82 are rotationally driven with the aid of separate driving systems. In the figure, reference numerals 31, 41, 51 and 61 designate components constituting the driving system for the left-hand wheel 81 and reference numerals 32, 42, 52 and 62 designate components for the right-hand wheel 82. These components designated by the above reference numerals correspond to the components designated by reference numerals 3, 4, 5 and 6 in Fig. 6, respectively. The driving system shown in Fig. 7 does not require any mechanical differential because AC motors 51 and 52 exhibit a differential function corresponding to the differential 7 shown in Fig. 6. This non-mechanical driving system is entirely free from the problems inherent to the mechanical differential but the following problems are newly raised. 4) The non-mechanical differential is manufactured at expensive costs with heavy weight and large dimensions due to the necessity for mounting two sets of inverters, AC motors and speed reducing units. 5) Maneuverability of the E-vehicle including the non-mechanical differential is different from that of ICE-vehicles because the non-mechanical differential exhibits an electrical differential function. To sum up, the driving system for E-vehicles should satisfactorily meet the following requirements. 1) It has the same maneuverability as that of the ICE-vehicle. 2) It operates at high efficiency. 3) It is manufactured at low costs with light weight and small dimensions. In the circumstances as mentioned above, many requests have been hitherto raised from users for providing a practical driving system for E-vehicle which can satisfactorily meet the foregoing requirements. DE-A-30 36 465 discloses a driving system including an electric motor. The stator of the motor is fixedly arranged at a fixed housing whereas the rotor is coupled, via a planetary gear, to the output shaft. The present invention has been made in consideration of the aforementioned background. An object of the present invention is to provide a driving system for an electric vehicle which assures that maneuverability substantially equal to that of a conventional internal combustion engine driven vehicle can be obtained with the driving system. Another object of the present invention is to provide a driving system for an electric vehicle which operates at high efficiency and can be manufactured at low costs with light weight and small dimensions. According to the present invention, there is provided a driving system for an electric vehicle in accordance with claim 1. Some specific details are mentioned in the subclaims. It should be noted that "primary side" of an AC motor in the following specification represents a part of the AC motor corresponding to a stator of a conventional AC motor to which electricity is fed and "secondary side" of the same represents a part of the conventional AC motor corresponding to a rotor adapted to be rotationally driven by the stator. To favorably construct the driving system, it is recommendable that the first part (primary side) of the AC motor is fixedly secured to a cylindrical frame, while the second part (secondary side) of the AC motor is arranged inside of the primary side of the AC motor. Usually, the electricity feeding means may comprise a slip ring disposed around the outer periphery of the cylindrical frame, a brush adapted to be brought in contact with the slip ring, and a brush holder fixedly secured to the motor frame for holding the brush. To construct a power transmission system associated with the driving system, the cylindrical frame may comprise an external gear arranged around the outer periphery thereof, which external gear meshes with an internal gear operatively connected to the power transmission shaft for the other one of the left-hand wheel and the right-hand wheel. The reversible connecting means may comprise a speed reducing mechanism having a pair of spur gears meshing with each other. On the other hand, the non-reversible connecting means may comprise a speed reducing mechanism having an internal gear and an external gear to mesh with the internal gear. It is preferable that the power transmission shaft for the left-hand wheel may be arranged in alignment with the power transmission shaft for the right-hand wheel while extending along a common axis. In the present invention, the first part (primary side) and the second part (secondary side) of an AC motor are rotatably separately arranged, respectively, such that they drive left-hand and right-hand wheels via a reversible type speed reducing mechanism and a non-reversible type speed reducing mechanism, respectively. With this arrangement, a wheel driving unit itself which comprises the AC motor, the reversible type speed reducing mechanism and the non-reversible type speed reducing mechanism performs the same differential function as that of conventional mechanical type differentials. It should be understood that both the wheels are rotated in the same direction with the aid of the reversible and the non-reversible speed reducing mechanisms. According to the present invention, advantageous effects are obtained as follows: 1) Since the driving system does not require any conventional mechanical differential it can operate at high efficiency. 2) Since an AC motor, differential and speed reducing mechanisms can be constructed integrally, the driving system is manufactured at low costs with light weight and small dimensions as a whole. 3) The electric vehicle with the driving system exhibits the same maneuverability as that of conventional ICE-vehicles. The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. The present invention is illustrated in the following drawings in which: Fig. 1 is a schematic plan view of a driving system for an electric vehicle constructed according to the present invention, particularly illustrating the whole structure of the driving system; Fig. 2 is a schematic sectional view of a wheel driving unit for the driving system shown in Fig. 1 constructed according to a first embodiment of the present invention; Fig. 3 is an illustrative view of the wheel driving unit shown in Fig. 2, particularly illustrating a mode of operation of the wheel driving unit; Fig. 4 is a schematic sectional view of a wheel driving unit for the driving system shown in Fig. 1 constructed according to a second embodiment of the present invention; Fig. 5 is an illustrative view of the wheel driving unit for the driving system shown in Fig. 4, particularly illustrating a mode of operation of the wheel driving unit; Fig. 6 is an illustrative view of a conventional driving system for an electric vehicle; and Fig. 7 is an illustrative view of another conventional driving system for an electric vehicle. The present invention will now be described in detail hereinafter with reference to the accompanying drawings which illustrate preferred embodiments thereof. Fig. 1 shows by way of a schematic plan view the whole structure of a driving system for an electric vehicle (hereinafter referred to as an E-vehicle) constructed according to a first embodiment of the present invention. It should be noted that same or similar components to those of the conventional driving system described above with reference to Fig. 6 are represented by same reference numerals. In Fig. 1, reference numeral 10 designates a wheel driving unit for the driving system. The wheel driving unit 10 includes an AC motor which substantially corresponds to the AC motor 5 shown in Fig. 6. The detailed structure of the wheel driving unit 10 will be described below with reference to Fig. 2. In Fig. 2, reference numeral 110 designates an AC motor of which a first part (primary side) (corresponding to a stator of the conventional AC motor) and a second part (secondary side) (corresponding to a rotor of the same) are rotatable. As is apparent from Fig. 2, the AC motor 110 is constructed in the form of an induction motor adapted to be driven by an inverter 4. Reference numeral 111 designates a core on the primary side which includes a primary winding (coil) 112 of the AC motor 110, and reference numeral 113 designates a core on the secondary side which includes a secondary winding coil (not shown) of the AC motor 110 which serves as a rotor of the AC motor 110 generally. Reference numeral 114 designates a rotational output shaft on the secondary side of the AC motor 110 and reference numeral 115 designates a shaft which is positionally coincident with the rotation center axis of a rotary core frame 116. It should be added that the shafts 114 and 115 are arranged in the coaxial relationship relative to the rotor 113 on the secondary side of the AC motor 110. The core 111 on the primary side of the AC motor 110 is fixedly secured to the rotary core frame 116 which in turn is rotatably supported by the shaft 115 with the aid of a bearing 117. Reference numeral 120 designates a reversible type speed reducing mechanism which includes a pair of spur gears 121 and 122 constituting a single-stage speed reducing unit. The spur gear 121 is fixedly mounted on the rotational output shaft 114 on the secondary side. The spur gear 122 meshing with the spur gear 121 is fixedly mounted on a power transmission shaft 811. As shown in Fig. 2, the shafts 114 and 811 are rotatably supported by a motor frame 141 with the aid of bearings, respectively. Reference numeral 130 designates a non-reversible type speed reducing mechanism including an internal ring gear which constitutes a single-stage speed reducing unit. The non-reversible type speed reducing mechanism 130 is composed of a pair of gears 131 and 132. The gear 131 is designed in the form of an external gear which is arranged around the outer periphery of the rotary core frame 116, while the gear 132 meshing with the gear 131 is designed in the form of an internal ring gear which is generated around the inner periphery of a rotary frame 133 having an inner diameter larger than an outer diameter of the rotary core frame 116. A power transmission shaft 821 is projected from the rotary frame 133 while extending along the center axis of the latter. As shown in the figure, the power transmission shaft 821 is supported by the motor frame 141 with the aid of bearings. Both the power transmission shafts 811 and 821 are arranged in the coaxial relationship relative to the motor frame 141. The shaft 115 of the AC motor 110 is rotatably supported by a supporting member 142 at the innermost end of the latter with the aid of bearings wherein a large part of the supporting member 142 is located inside of the rotary frame 133 while extending inward of the motor frame 141. It is desirable that a speed reduction ratio of the speed reducing section 120 is set to be equal to that of the speed reducing section 130 from the viewpoint that both the left-hand and right-hand wheels 81 and 82 of the E-vehicle exhibits the same traveling performances. An AC current is fed to the primary coil 112 of the AC motor 110 via a slip ring section 150. A slip ring 151 of the slip ring section 150 is arranged around the outer periphery of the rotary core frame 116, while a brush holder 153 for holding brushes 152 is fixedly secured to the motor frame 141. In Fig. 2, reference numeral 9 designates a feed line by way of which an AC current is fed to the AC motor 110 from the inverter 4. Fig. 3 is an illustrative view of the driving system for the E-vehicle shown in Fig. 2, particularly illustrating a mode of operation of the driving system. It should be noted that same components as those shown in Fig. 2 are represented by same reference numerals. It is assumed that the magnetic flux generated by the coil 112 on the primary side of the AC motor 110 is rotated in the clockwise direction as seen from the right-hand side of Fig. 3. This causes the secondary side of the AC motor 110 to be rotated in the same clockwise direction as that of the magnetic flux but the primary side of the driving system is rotated in the counter-clockwise direction due to the reactive function derived from the rotational force generated by the secondary side of the AC motor 110. As the secondary side of the AC motor 110 is rotated, the direction of rotation of the secondary side of the driving system is reversed relative to that of the AC motor 110 because of the arrangement of the spur gears 121 and 122 in the reverse type speed reduction section 120, whereby a rotational output from the secondary side of the driving system is transmitted to the power transmission shaft 811 via the gears 121 and 122 while the secondary side of the AC motor 110 is rotated in the counter-clockwise direction. On the other hand, a rotational output from the primary side of the AC motor 110 is transmitted to the power transmission shaft 821 via the gears 131 and 132 in the non-reverse type speed reducing section 130 while the direction of rotation of the primary side of the AC motor 110 are rotated in the same direction, i.e., the primary side of the AC motor 110 is rotated in the counter-clockwise direction. Consequently, the primary side and the secondary side of the AC motor 110 are rotated in the same direction to rotationally drive the wheels 81 and 82 in the same direction. Next, the differential function of the driving system constructed according to the first embodiment of the present invention will be described below. In this embodiment, each of the primary side and the secondary side of the AC motor 110 is freely rotatable so that the power generated by the AC motor 110 is transmitted to the wheels 81 and 82 via the reversible type speed reducing section 120, the non-reversible type speed reducing section 130 and the power transmission shafts 811 and 812. In other words, the torque generated by the AC motor 110 is distributed into the primary side and the secondary side of the driving system corresponding to the rotary core frame 116 and the rotational output shaft 114. At this time, a ratio of the distribution of the torque into the primary side and the secondary side of the driving system varies depending on the load to be borne by each of the wheels 81 and 82. As is apparent from the above description, it can be concluded that the wheel driving unit 10 of the driving system exhibits the same differential function as that of the conventional mechanical type differential. Next, a driving system for an E-vehicle constructed according to a second embodiment of the present invention will be described below with reference to Fig. 4 and Fig. 5. The structure of a wheel driving unit 10A for the driving system is substantially identical with that shown in Fig. 2 with the exception that a reversible type speed reducing section 120 and a non-reversible type speed reducing unit 130 are arranged in the reversed state as seen in the transverse direction of the figures. It should be noted that same components as those shown in Fig. 2 are represented by same reference numerals. In Fig. 4, reference numeral 116A designates a rotary core frame on the primary side of an AC motor 110. The rotary core frame 116A is designed in the cylindrical configuration in the same manner as the frame 116 shown in Fig. 2. Reference numeral 134 designates a spur gear which is fixedly mounted on a rotational output shaft 114 to constitute a non-reversible type speed reducing section 130 in cooperation with an opponent gear 135 designed in the form of an internal ring gear. The internal ring gear 135 meshing with the spur gear 134 is operatively connected to a power transmission shaft 811. Reference numeral 144 designates a frame for supporting the rotational output shaft 114 extending between a rotor 113 on the secondary side of the AC motor 110 and the spur gear 134. The frame 144 is made integral with a motor frame 141. A rotational output shaft 118 having a spur gear 121 fixedly mounted thereon is connected to the rotary core frame 116A while extending along the rotational center axis of the same. Fig. 5 is an illustrative view of the driving system corresponding to Fig. 3, particularly showing a mode of operation of the driving system. An AC motor 110 shown in Fig. 5 operates in the same manner as that shown in Fig. 3 with the exception that an output from the rotational output shaft 114 is transmitted to the power transmission shaft 811 via the non-reversible type speed reducing section 130 while the power transmission shaft 811 is rotated in the same direction as that of the rotational output shaft 114. On the other hand, an output from the rotational shaft 118 connected to the rotary core frame 116A having a coil on the primary side of the AC motor 110 fixed thereto is transmitted to the power transmission shaft 821 via the reversible type speed reducing section 120 while the direction of rotation of the rotational shaft 118 is reversed relative to the rotational shaft 114 so as to rotate both the power transmission shafts 811 and 812 in the same direction. Also in this embodiment, the primary side and the secondary side of the AC motor 110 are freely rotatable so that power is transmitted to wheels 81 and 82 via the speed reducing sections 120 and 130 each comprising a pair of gears and the power transmission shafts 811 and 812. The torque generated by the AC motor 110 is distributed into a rotational shaft 118 on the primary side of the AC motor 110 and the rotational shaft 114 on the secondary side of the same in the same manner as the rotational output shafts 114 and 118 in the preceding embodiment of the present invention. At this time, a ratio of torque distributed to the rotational output shaft 114 to that of the rotational output shaft 118 varies depending on the load to be borne by each of the wheels 81 and 82. Thus, the wheel driving unit 10A constructed according to the second embodiment of the present invention exhibits the same differential function as that of the conventional mechanical type differential as mentioned above. It is desirable that a speed reduction ratio of each of the speed reducing sections 120 and 130 is selectively determined to assume an optimum value from the viewpoint of the whole structure of the driving system of the present invention. In addition, it is desirable that the power transmission shafts 811 and 812 as shown in Fig. 2 and Fig. 4 are arranged in the coaxial relationship relative to the wheel driving unit. Although the present invention has been described above with respect to the case that an induction motor is used as an AC motor for the wheel driving unit, it should be noted that the present invention should not be limited only to this case but it may equally be applied to the case that other type of AC motor is employed in place of the induction motor. It should be added that the structure employed for each of the slip ring and the bearings is not limited only to that shown in Fig. 2 and Fig. 4. The present invention has been described in detail with respect to preferred embodiments, and it will now be that changes and modifications may be made without departing from the appended claims.

Claims: A driving system for an electric vehicle, comprising an AC motor (10, 10A) which drives wheels (81, 82) of the vehicle, and a battery (1) which is used as a power source, comprising: a motor frame (141), supporting means for rotatably and separately supporting a first part which includes a primary winding (112) of said AC motor (10, 10A) and a second part which includes a secondary winding of the same, respectively, relative to said motor frame, wherein the first and second part of said AC motor are rotatable relative to each other, means (120) for reversibly operatively connecting the first or second part of said AC motor to a power transmission shaft (811; 821) for driving a left-hand wheel or a right-hand wheel, means (130) for non-reversibly operatively connecting the other of the first and second part of said AC motor to a power transmission shaft (821; 811) for the other one of said left-hand wheel and said right-hand wheel, and means (150) for feeding electricity from said battery to the first part of said AC motor. The driving system as claimed in claim 1, characterized in that the first part of said AC motor is fixedly secured to a cylindrical frame (116) while the second part of said AC motor is arranged inside of the first part of said AC motor. The driving system as claimed in claim 1 or 2, characterized in that said electricity feeding means (150) comprises a slip ring (153) disposed around the outer periphery of said cylindrical frame, a brush (152) adapted to be brought in contact with said slip ring, and a brush holder (151) fixedly secured to said motor frame for holding said brush. The driving system as claimed in claim 2, characterized in that said cylindrical frame (116) comprises an external gear (131) arranged around the outer periphery thereof, said external gear (131) meshing with an internal gear (132) operatively connected to said power transmission shaft for the other one of said left-hand wheel and said right-hand wheel. The driving system as claimed in any of claims 1 to 4, characterized in that said reversible connecting means (120) comprises a speed reducing mechanism having a pair of spur gears meshing with each other. The driving system as claimed in any of claims 1 to 5, characterized in that said non-reversible connecting means (130) comprises a speed reducing mechanism having an internal gear and an external gear to mesh with said internal gear. The driving system as claimed in any of claims 1 to 3, characterized in that said supporting means comprises: a first shaft (114) and a second shaft (115) operatively connected to the second part of said AC motor, a first bearing disposed in said motor frame to rotatably support said first shaft (114), a second bearing arranged extending inside of said motor frame to rotatably support said second shaft (115), and a third bearing (117) disposed on said second shaft to rotatably support a cylindrical frame (116) having the first part of said AC motor fixedly mounted inside thereof. The driving system as claimed in claim 7, characterized in that said cylindrical frame (116) has an external gear (131) arranged around the outer periphery thereof, said external gear meshing with an internal gear (132) operatively connected to said power transmission shaft for the other one of said left-hand wheel and said right-hand wheel, while a spur gear is disposed on said first shaft to mesh with a spur gear disposed on said power transmission shaft for one of said left-hand wheel and said right-hand wheel. The driving system as claimed in claim 1, characterized in that said supporting means comprises: a first shaft (115) and a second shaft (114) operatively connected to the second part of said AC motor, a third shaft (821) disposed along a rotational center axis of a cylindrical frame (116) having the first part of said AC motor fixedly mounted inside thereof, a first bearing arranged extending inside of said motor frame to rotatably support said first shaft, a second bearing disposed in said cylindrical frame to rotatably support said second shaft, and a third bearing disposed in said motor frame (141) to rotatably support said third shaft. The driving system as claimed in claim 9, characterized in that a spur gear is disposed on said third shaft to mesh with a spur gear disposed on said power transmission shaft for one of said left-hand wheel and said right-hand wheel, and a spur gear is disposed on said first shaft to mesh with an internal gear operatively connected to said power transmission shaft for the other one of said left-hand wheel and said right-hand wheel. The driving system as claimed in any of claims 1 to 10, characterized in that said power transmission shaft (811) for said left-hand wheel is arranged in alignment with said power transmission shaft (821) for said right-hand wheel while extending along a common axis. A driving system as claimed in any of claims 1 to 11 wherein said motor frame (141) is fixedly mounted on a vehicle body, said supporting means comprising: means for separately rotatably supporting a frame (116) to which a core (111), and said primary winding (112) of the first part of said AC motor are fixedly secured, and a rotor of the second part of said AC motor, said frame and said rotor being arranged on a common axis relative to said motor frame, means for operatively connecting said rotor to the power transmission shaft for one of a left-hand wheel and a right-hand wheel such that a rotational speed of said power transmission shaft is reduced compared to same of said rotor, means for operatively connecting said frame to the second power transmission shaft for the other one of said left-hand wheel and said right-hand wheel such that a rotational speed of said power transmission shaft is reduced compared to same of said frame, and means for feeding electricity from said battery to the said primary winding via an inverter.

Inventors: KINOSHITA SHIGENORI, KINOSHITA, SHIGENORI, KINOSHITA, SHIGENORI, C/O FUJI ELECTRIC CO., LTD.
Applicants: FUJI ELECTRIC CO LTD, FUJI ELECTRIC CO., LTD.
Application year: 1993
Main classification: B60L11
IPC codes: H02K7, B60K1, B60L9, B60K17, B60K6, B60L11, H02K16