Electrically assisted bicycle

Abstract: An electric bicycle 1 comprises a motor powered driving assembly 20 including a flat type DC motor 26, a speed reduction mechanism 22, a control circuit 25, a pedal load sensor 24, and a pedal rotation speed sensor 23 which are integrally assembled together, the motor powered driving assembly being disposed adjacent a lower median portion of a body frame 2. Through this arrangement it is possible to provide an electric bicycle which affords ease of control and good riding comfort and has relatively low center of gravity.

Description: This invention relates to an electric bicycle capable of actuating a motor powered driving assembly according to the pedal load and, more particularly, to an electric bicycle having a motor powered driving assembly operative to detect the speed of the bicycle and assist the pedal load within predetermined limits. Hitherto, there have been proposed various electric bicycles of the type having a manually operated driving power and a motor operated driving power arranged in parallel such that the former driving power is assisted by means of an electric motor within a predetermined range which varies according to the pedal load. In such an electric bicycle, it is necessary to control the range of assistance by a motor powered driving assembly in such a manner that such assistance be 50 % of bicycle speed in the case of a bicycle speed of from 0 to 15 km/h and, within a bicycle speed range of from 15 km/h to 24 km/h, it be gradually decreased according to the bicycle speed, the assistance being reduced to 0 % when a bicycle speed of 24 km/h is reached. Therefore, the motor powered driving assembly includes a pedal load sensor for detecting a pedal load, a pedal speed sensor for detecting the rotational speed of the pedal, an electric motor, a speed reduction mechanism, and a control circuit. The control circuit controls the electric motor on the basis of information from both the pedal load sensor and pedal speed sensor so as to provide for power assistance within the predetermined range. In addition, the electric bicycle has a rechargeable battery for use as an electric energy source. Specifically, one such prior art arrangement is disclosed in Japanese Patent Application Laid-Open No. 7-40878. In this prior art arrangement, a motor powered driving assembly is set up integrally with the bicycle at a location adjacent main pipe and seat pipe members of the body frame. In fact, however, it has been difficult to arrange that all components of the assembly, including an electric motor, a speed reduction mechanism, a control circuit, a pedal load sensor, and a pedal speed sensor, are integrally mounted together beneath a pedal crank shaft. Further, components such as electric motor, speed reduction mechanism, control circuit, pedal load sensor, and pedal speed sensor are arranged in spaced apart relation, and this requires wiring for electrically interconnecting these components. Therefore, for protection of the wiring it is necessary to cover the entire assembly of such components with a resin cover. Whilst, from the standpoints of ease of riding and ease of handling, the position of gravity center of the bicycle is important. In this connection, it must be considered that the weight of the rider is considerably heavier than the weight of the bicycle, so that the center of gravity during bicycle riding is positioned considerably higher than the gravity center of the bicycle itself. Therefore, it is required that the position of gravity center of the bicycle itself be set as much low as possible and centrally between the front and rear wheels. However, with prior art electric bicycles, it is inevitable that the center of gravity of the bicycle is positioned rather high since the motor powered driving assembly is mounted in an inner space defined by bicycle frame members or above the pedal crank shaft . As such, the prior art electric bicycles have been unsatisfactory from the view points of ease of riding and ease of handling. Reference DE-A1-31 17 415 discloses an electric bicycle having a supplementary electric motor drive. The electric motor, a planetary gear and a one way clutch are disposed around a pedal crank shaft of said bicycle. DE-U1-94 07 684.7 describes an electric bicycle having a driving assembly which comprises an electric motor and a speed reduction mechanism. Said driving assembly is disposed beneath the pedal crank shaft of said bicycle wherein the motor shaft is orientated perpendicular to the pedal crank shaft. Reference EP-A1-0 743 238 is filed earlier but published later than the present invention. This document describes an assisting motor for a motor assisted bicycle wherein an electric motor positioned around the pedal crank shaft is controlled by a controlling device positioned on the rear of the main frame of said bicycle. It is the object of the present invention to provide an electric bicycle having a lower center of gravity and providing an increased riding comfort and safety. This is achieved by the teaching of claim 1. In particular, the electric bicycle in accordance with the invention comprises a motor powered driving assembly operative to assist a pedal driving assembly which is disposed in a lower median portion of a body frame constructed integrally with a front wheel, a saddle, and a rear wheel. According to such arrangement of the invention, it is possible to maintain the gravity center of the bicycle itself at a lower position without detriment to riding comfort and ease of control, because the motor powered driving assembly is incorporated in a lower median portion of the body frame. Further, the invention affords ease of mounting to the bicycle of the motor powered driving assembly. In the electric bicycle of the invention, the motor powered driving assembly may be disposed beneath a saddle pipe, with a pedal shaft of the pedal driving assembly being disposed in the motor powered driving assembly. This arrangement enables the gravity center of the bicycle to be maintained lower. In a first embodiment of the invention, the motor powered driving assembly comprises an electric motor, a speed reduction mechanism, a pedal rotation speed sensor, a pedal load sensor, and a control circuit which are integrally assembled together. According to the first embodiment, it is possible to incorporate the motor powered driving assembly into a lower median portion of the body frame. In a second embodiment of the invention, at least a portion of the motor powered driving assembly is exposed. According to the second embodiment, during a bicycle run, wind comes in direct contact with the motor powered driving assembly so that cooling of the motor powered driving assembly can be enhanced. Therefore, any heat generated from a flat type DC motor and/or the control circuit can be released without provision of any special means. In a third embodiment of the invention, the flat type DC motor is an axial hollow type motor. According to the third embodiment, the axial dimensional size of the motor, that is, thickness of the motor, can be reduced. In a fourth embodiment of the invention, a permanent magnet used in the flat type DC motor of the motor powered driving assembly is such that it is comprised of a mixture of an isotropic Nd-Fe-B magnetic powder and an anisotropic Nd-Fe-B magnetic powder which has been set into shape by Joule heated sintering. According to the fourth embodiment, by virtue of the permanent magnet with temperature characteristics allowing for the size limitation and use environment, it is possible to provide required motor characteristics. In a fifth embodiment of the invention, an armature of the flat type DC motor is a coreless armature, and an armature winding and a commutator are integrally formed by resin. According to the fifth embodiment, it is possible to enhance motor weight reduction and provide improved motor response characteristics, and thus to improve the controllability of the electric bicycle. In a sixth embodiment, the coreless armature of the flat type DC motor is formed of a resin compound containing soft magnetic powder. According the sixth embodiment, it is possible to provide higher motor power. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic side view showing an electric bicycle according to one embodiment of the invention: Fig. 2 is a sectional view showing the construction of a motor powered driving assembly according to one embodiment of the invention; and Fig. 3 is a sectional view showing the construction of a flat type DC motor employed in the motor powered driving assembly. DETAILED DESCRIPTION OF THE EMBODIMENTS One embodiment of this invention will now be described with reference to Figs. 1 to 3. Fig. 1 shows a schematic view of an electric bicycle embodying the invention, the bicycle being shown as having a body frame similar in basic construction to that of a conventional bicycle. The electric bicycle 1 includes a pedal driving assembly 10 to be driven by man-power and a motor powered driving assembly 20 which assists the pedal driving assembly. The body frame 2 of the electric bicycle 1 comprises a number of pipe elements for integrally interconnecting a front wheel 3, a rear wheel 4, and a saddle 5, the pipes being integrated together at a lower end of a saddle pipe 6 located centrally of the bicycle. The motor powered driving assembly 20, in its entirety, is mounted in a lower median portion of the body frame 2, or beneath the lower end of the saddle pipe 6 in the present case. In the case of a conventional bicycle a pedal crank shaft is disposed in aforesaid lower median portion, but in the electric bicycle 1 of the invention, a pedal crank shaft 11 of the pedal driving assembly 10 is disposed in the motor powered driving assembly 20. The position of the pedal crank shaft 11 is set so as to enable pedaling operation to be made by the rider while assuming a sitting position on the saddle 5 in substantially same way as in the case of a conventional bicycle. By virtue of this arrangement, the electric bicycle 1 can have a center of gravity maintained lower without detriment to the ease of control and riding comfort. The pedal crank shaft 11 extends through a casing 21 of the motor powered driving assembly 20, opposite ends of the crank shaft being coupled to cranks 12 which are fitted with pedals 13. A chain 16 is trained between a front sprocket 14 mounted to a crank shaft 12 and a rear sprocket 15 provided on the rear wheel 4 side. These elements 11 to 16 constitute the pedal driving assembly 10. On the rear side of the saddle pipe 6 there is provided a battery case 8 in which is housed a batter 7. Fig. 2 is a detail view showing the construction of the motor powered driving assembly 20. This motor powered driving assembly 20 is mounted below the body frame 2. The casing 21 of the motor powered driving assembly 20 comprises a box 21A, a gear cover 21B, a motor cover 21C, and a lid 21D. These members are sealed by means of gasket, so that the motor powered driving assembly 20 is of waterproof construction. Elements, such as a speed reduction mechanism 22, a pedal rotation speed sensor 23, and a pedal load torque sensor 24, are disposed within a space defined by the box 21A and the gear cover 21B in the casing 21. A control circuit 25 is provided, among others, within a space defined by the box 21A and the lid 21D. Further, a flat type DC motor 26 is disposed, among others, within a space defined by a recessed portion of the gear cover 21B and the motor cover 21 C. So disposed in the casing 21, the speed reduction mechanism 22, the control circuit 25, and the flat type DC motor 26 are integrated together, with the pedal rotation speed sensor 23 and pedal load sensor 24 incorporated in addition to them. According to such arrangement of the motor powered driving assembly 20, the rotational speed of pedaling is detected by the pedal rotation speed sensor 23 and, at the same time, relevant load torque is detected by the pedal load sensor 24. Then, on the basis of detection values (information) from them, a built-in microcomputer of the control circuit 25 determines a PWM (pulse width modulation) inverter output for actuating the flat type DC motor 26. Thus, by actuating the flat type DC motor 26 through the PWM inverter output to cooperate with man power from the pedal 13 through the intermediary of the speed reduction mechanism 22, rotation effort is transmitted from the front sprocket to the rear wheel 4 through the chain 16 and rear sprocket 15, thereby to provide propulsive power for the electric bicycle 1. Whilst, from the standpoints of controllability and riding comfort with respect to the electric bicycle 1, the motor powered driving assembly 20 is subject to limitations as to dimensions, configuration and mass effect. That is, the width is limited from pedaling consideration; the height is limited from clearance consideration relative to the ground surface; the length is limited from the consideration of possible interference with the rear wheel 4, and the mass of the assembly is limited by the total mass of the electric bicycle 1. In order to satisfy these dimensional considerations, the flat type DC motor 20 is employed as the source of power. Fig.3 shows the construction of the flat type DC motor 26 employed in the motor powered driving assembly 20. One example of such motor is an axial cavity type motor as employed for condenser cooling in automotive air conditioners. Conventionally, as a power source for electric bicycles, an electric motor using a ferrite magnet has been employed, but the problem is that the output of such a motor is insufficient. Therefore, the flat type DC motor 26 uses a new high-performance permanent magnet 27. This permanent magnet 27 is comprised of a mixture of an isotropic Nd-Fe-B magnetic powder and an anisotropic Nd-Fe-B magnetic powder which has been set into shape by Joule heated sintering. In the flat type DC motor 26, a coreless armature 28 is basically used, and an armature winding 29 and a commutator 30 are integrally formed by resin molding material. With such coreless construction, however, there involves considerable magnetic gap between the armature winding 20 and the permanent magnet 27, which makes it difficult to obtain a compact and high power motor. Therefore, the resin material for integrally forming the coreless armature 28 was blended with soft magnetic powder, and the armature winding 29 and the commutator 30 were integrally formed from the blended resin molding material. This provided for high power performance, or about 2.5 times as high as conventional motors of same size, thus contributing to size and weight reduction with respect to the motor powered driving assembly 20. The motor powered driving assembly 20 is set on the body frame 2 side through a mounting hole formed on the upper end of the casing 21. The motor powered driving assembly 20 mounted to the body frame 2 is such that the casing 21 is exposed except a part of its upper portion; therefore, during a bicycle run, wind strikes on the exposed portion so that heat generated from the flat type DC motor 26, control circuit 25, and the like is dissipated through the casing 21.

Claims: An electric bicycle (1), comprising: a pedal driving assembly (10) including a pedal crank shaft (11) and a motor powered driving assembly (20), said motor powered driving assembly (20) comprising an electric motor (26), being constructed to be able to assist the pedal driving assembly (10) and being disposed in a lower median portion of the body frame (2), characterised in that said motor powered driving assembly (20) further comprises a speed reduction mechanism (22) and a control circuit (25), said electric motor (26), said speed reduction mechanism (22) and said control circuit (25) are arranged within a casing (21) of said motor powered driving assembly (20), the motor powered driving assembly (20) being disposed at a position that the pedal crank shaft (11) is included in the motor powered driving assembly (20), said electric motor (26) together with a motor shaft being disposed closer to the rear wheel (4) than said pedal crank shaft (11), said motor shaft and said pedal crank shaft (11) being disposed in a parallel manner, and said motor shaft, said speed reduction mechanism (22) and said pedal crank shaft (11) are disposed behind each other, wherein said speed reduction mechanism (22) being disposed between the pedal crank shaft (11) and the motor shaft. An electric bicycle according to claim 1, further characterized in that said electric motor (26) is a flat type DC motor. An electric bicycle according to claim 1 or claim 2, characterized in that said motor powered driving assembly (20) further comprises a pedal rotation speed sensor (23) and a pedal load sensor (24) integrally assembled together. An electric bicycle (1) according to any of claims 1 to 3, further characterized in that said flat type DC motor (26) is an axial air gap type motor. An electric bicycle (1) according to any of claims 1 to 4, further characterized in that a permanent magnet (27) used in said flat type DC motor (26) of said motor powered driving assembly (20) is comprised of a mixture of an isotropic Nd-Fe-B magnetic powder and an anisotropic Nd-Fe-B magnetic powder which has been set into shape by Joule heated sintering. An electric bicycle (1) according to claim 4 or 5, further characterized in that a armature (28) of said flat type DC motor is coreless armature and an armature winding (29) and a commutator (30) are integrally formed by resin. An electric bicycle (1) according to claim 5 or claim 6, further characterized in that said coreless armature (28) of said flat type DC motor (26) is formed of a resin component containing soft magnetic powder.

Inventors: WADA MASAMI, WADA, MASAMI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: B62M23
IPC codes: B62M6