Transmission for an electric bicycle

[0002] 1. Field of the Invention

[0003] The present invention is related to an electrical bicycle, and more particularly to a transmission for an electrical bicycle.

[0004] 2. Description of Related Art

[0005] A conventional transmission for an electric bicycle utilizes a planet gear assembly to transmit power from cranks. The structure of the planet gear is complex and requires a high manufacturing precision, so the cost of the planet gear is high. When the required velocity rate for different bicycles varies, the transmission needs to be replaced with another planet gear assembly. This also increases the manufacturing cost. Moreover, it is inconvenient for a manufacture to change a relative angle between the motor and a crank axle of the bicycle, because other elements must be redesigned in this situation.

[0006] Therefore, the invention provides a transmission for an electric bicycle to mitigate and/or obviate the aforementioned problems.

[0007] A main objective of the invention is to provide a transmission for an electric bicycle which has a simple and compact structure with a low cost.

[0008] Another objective of the invention is to provide a transmission for an electric bicycle which is able to change a relative angle between a motor and a crank axle.

[0009] Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0010] FIG. 1 is a front view of a transmission for an electric bicycle in accordance with the invention;

[0011] FIG. 2 is a side cross sectional view of FIG. 1 taken the line “2—2”;

[0012] FIG. 3 is a front sectional view of the transmission;

[0013] FIG. 4 is a perspective view of a seat assembled in the transmission;

[0014] FIG. 5 is a side cross sectional view of a second embodiment of the transmission; and

[0015] FIG. 6 is a side cross sectional view of FIG. 3 taken along the line “6—6”.

[0016] Referring to FIGS. 1 and 2, a transmission for an electrical bicycle in accordance with the present invention has a housing (10) coupled with a motor (20). The housing (10) is composed of two symmetrical semi-housings—a first semi-housing (101) and a second semi-housing (102) assembled with each other. For simplicity of description, only the first semi-housing (101) is described in detail. The second semi-housing (102) is completely symmetrical to the first one.

[0017] The first semi-housing (101) has a chamber (11) and a plurality of holes (13) defined at edges thereof. Via bolts inserted through these holes (13), the first semi-housing (101) and the second semi-housing (102) are combined to form the housing (10).

[0018] The motor (20) has an output axle (21) inserted in the housing (10) and a driving gear (22) is secured on the output axle (21). In this embodiment, the driving gear (22) is a spiral gear shaft with two teeth. The driving gear (22) is engaged with an idler (23).

[0019] A crank axle (30) transversally extends between the first semi-housing (101) and the second semi-housing (102) and is parallel to the output axle (21) of the motor (20). A pair of cranks (62) is assembled on two ends of the crank axle (30). A first bearing (31) is provided at a first end of the of the crank axle (30). A stepped sleeve (32) is provided on the first bearing (31) and is rotatable about the crank axle (30). The stepped sleeve (32) is also rotatable about the housing (10) by means of a second bearing (not numbered) provided between the stepped sleeve (32) and the housing (10). A first end of the stepped sleeve (32) extends out from the housing (10) and has a chain wheel (60) secured thereon.

[0020] A driven gear (34) is provided on a second end of the stepped sleeve (32) and separate from the second bearing on the stepped sleeve (32) by a distance sleeve (33). The driven gear (34) is engaged with the idler (23) and has a first non-return means (35) such as a non-return bearing or a ratchet wheel fitted between the stepped sleeve (32) and the driven gear (34). The stepped sleeve (32) further has a recess (321) defined at the second end thereof and has a second non-return means (36) fitted therein.

[0021] The crank axle (30) further is inserted through a seat (41) received in the housing (10). Referring to FIGS. 2, 4 and 6, the seat (41) is composed of a connecting portion (42) and three arms (43, 431, 432) disposed perpendicular to the connecting portion (42), wherein the first arm (43), the second arm (431) and the third arm (432) are parallel to each other, and a distance between the first arm (43) and the second arm (431) is smaller than that between the first arm (43) and the third arm (432). Two bushes (45) are respectively provided between the crank axle (30) and the first arm (43) and the second arm (431), and maintenance-free bearings (not numbered) are respectively provided between the bushes (45) and the crank axle (30). A first gear (46) is assembled on the bush (45) in the second arm (431) and outside the second arm (431) and is rotatable about the crank axle (30). The first gear further has a step (not numbered) engaged in the second non-return means (36). A second gear (47) is provided between the first arm (43) and the second arm (431) and secured on the crank axle (30) by a key (not numbered) received in a slot (not numbered) in the crank axle (30). Thus, the second gear (47) is rotated with the crank axle (30) when the crank axle (30) is turned. A duplicate gear (48) is provided between the first arm (43) and the third arm (432), and is composed of a third gear (481) engaged with the first gear (46) and a fourth gear (482) engaged with the second gear (47). A shaft (49) is inserted through the duplicate gear (48) and secured on the first arm (43) and the third arm (432). A fastener (491) is assembled on the third arm (432) by screws for securing the shaft (49).

[0022] The seat (41) further has a nose (50) provided on the connecting portion (42) and abuts a force sensor (55) secured on a side wall of the housing (10), as shown in FIG. 3. The force sensor (55) is electrically connected with a control circuit (not shown or numbered). A flexible sheet (56) is assembled beside the force sensor (55) and has an upper end pushing against the connecting portion (42). Furthermore, a speed sensor (53) is assembled on the housing (10) and extends into the chamber (101).

[0023] Referring back to FIGS. 2 and 6, when a user propels the bicycle without using electric power, the crank axle (30) is turned by the user's feet and drives the second gear (47) to rotate. The fourth gear (482) then is driven by the second gear (47) to rotate about the shaft (49). Thus, the third gear (481) integrated with the fourth gear (482) drives the first gear (46) to rotate about the crank axle (30). The second non-return means (36) is rotated with the first gear (46) and drives the stepped sleeve (32) to rotate, and the stepped sleeve (32) drives the chain wheel (60) to rotate, and thus the bicycle moves forward. In this case, the first non-return means (35) and the driven gear (34) are unable to be rotated.

[0024] When the user utilizes the electric power as an auxiliary power, the motor (20), which is controlled by the control circuit cooperated with the force sensor (55) and the speed sensor (53), provides suitable power to drive the crank axle (30).

[0025] Referring to FIG. 3, when the user pedals the crank (62) to rotate the crank axle (30), there is a counterforce perpendicular to the crank axle (30) on the second gear (47). Therefore, the seat (41) has a trend to pivot about the crank axle (30), but the seat (41) is unable to be pivoted because of the nose (50) blocked by the force sensor (55). Thus, under the counterforce, the seat (41) as well as the nose (50) has only a little displacement. At the same time, the force sensor has a deformation corresponding to the displacement of the nose (50), and sends a signal to the control circuit to actuate the motor (20). The output power of the motor (20) is corresponding to the counterforce on the crank axle (30). The seat (41) and the nose (50) are able to return to their original positions under the force of the flexible sheet (56) when the counterforce is eliminated.

[0026] The output power of the motor (20) is transmitted by the driving gear (22), then from the idler (23) to the driven gear (34), and in turn drives the stepped sleeve (32) to rotate via the first non-return means (35). Then, the stepped sleeve (32) drives the chain wheel (60) to rotate. Because of the high rotational speed of the motor (20), the rotational speed of the first non-return means (35) is higher than that of the second non-return means (36). In this case, the stepped sleeve (32) is completely driven by the motor (20), and the user need not pedal the crank (62).

[0027] Furthermore, the speed sensor (53) is able to detect the rotational speed of the second gear (47) and is cooperated with the force sensor (55) to change the output power of the motor (20).

[0028] In a second embodiment of the invention, referring to FIG. 5, the output axle (21a) is perpendicular to the crank axle (30). A cone driving gear (83) is provided on the output axle (21). An idler (85) is composed of a gear shaft (86) and a cone gear (87) secured on the gear shaft (86). The cone driving gear (83) is engaged with the cone gear (87), and the gear shaft (86) is engaged with the driven gear (34).

[0029] From the above description, it is noted that the invention has the following advantages:

[0030] 1. Because the transmission utilizes the gears (46, 47) engaged with the duplicate gear (48) to transmit the power from the crank, the structure is simpler than the conventional one with a planet gear and the manufacturing cost is low.

[0031] 2. In the situation where the output axle (21) is parallel to the crank axle (30), the efficiency of the transmission is highest

[0032] 3. The driving gear (22)'s tooth quantity is two, so it is easy to manufacture the driving gear, and it facilitates achievement of a large velocity rate for the transmission.

[0033] 4. When a user pedals the crank to drive the bicycle without using electric power, the rotation of the stepped sleeve (32) does not drive the driven gear (34) and the output axle (22) of the motor because of the action of the first non-return means (35). Then the user does not waste strength to drive the driven gear (34) and the motor.

[0034] 5. The motor (20) can be arranged with the output axle (21a) perpendicular to the crank axle (30), and other elements in the transmission need not be redesigned.

[0035] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.