Endless belt power transmission systems or components – Control for variable input to output speed-ratio – Including belt shiftable axially from one to another surface...
Reexamination Certificate
1999-12-10
2001-09-25
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Control for variable input to output speed-ratio
Including belt shiftable axially from one to another surface...
C474S070000
Reexamination Certificate
active
06293882
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to control devices for bicycle transmissions and, more particularly, to an apparatus that compensates for return spring and other forces applied by the bicycle transmission to a motor drive used to operate the bicycle transmission.
There are two major types of bicycle transmissions currently marketed. One type of bicycle transmission uses a derailleur to shift a chain from one sprocket to another to change the drive ratio, and the other type uses a planetary gear mechanism disposed inside a rotating hub such as a wheel hub to change the drive ratio. In either case, an operating member such as a lever, push rod or rotatable ring is moved to operate the transmission, and the operating member is connected to a transmission actuating member such as a control wire or link that is pulled or released by the rider to cause the desired movement of the operating member. To facilitate the operation of the transmission in a pull and release manner, a return spring commonly is used to bias the operating member to an initial state. The transmission then is operated by moving the operating member against the progressively increasing force of the return spring and the natural resistance by the transmission to changing gears. When the resistance of the return spring is added to the natural resistance by the transmission to changing gears, the force that must be applied to the transmission actuating member can become quite large.
Motor-driven bicycle transmissions are becoming more common. Such motor-driven bicycle transmissions relieve the rider of the task of manually pulling and releasing the transmission actuating member. Of course, the motor used to cause the pulling and releasing of the transmission actuating member must be designed to withstand the forces noted above. This sometimes makes it necessary to use a relatively large motor which increases the cost, size and weight of the transmission operating mechanism. The larger motor also creates significantly more current drain on the battery used to operate the motor, thus resulting in short battery life. Consequently, motor-driven transmissions usually are not used when the size, cost or weight of the bicycle is an important factor, such as in racing environments.
SUMMARY OF THE INVENTION
The present invention is directed to an operating force compensating apparatus for a bicycle transmission that reduces the force required to operate the bicycle transmission and hence allows the use of a small motor to operate the transmission. In one embodiment of the present invention, a motor drive apparatus for a bicycle transmission includes a support; an interface member for coupling to a transmission actuating member that exerts a first force having a first force component in a first direction, wherein the interface member is mounted to the support for rotation around a rotational axis; a motor for coupling to the interface member; and a biasing mechanism for exerting a second force on the interface member having a second force component in a second direction opposite the first direction.
In a more specific embodiment, a cam having a cam surface varies the second force applied to the interface member by the biasing mechanism. In the typical situation where the biasing mechanism exerts the second force at a force applying location on the interface member, the cam usually varies the force applying location relative to the rotational axis. More specifically, the interface member may have the shape of a lever with an actuating member connector for connecting to the transmission actuating member, wherein the actuating member connector is radially spaced apart from the rotational axis. The interface member includes a cam follower for engaging the cam surface, wherein the cam follower is located at an intermediate portion of the lever between the actuating member connector and the rotational axis. Thus, the force applying location rotates around the rotational axis when the interface member rotates around the rotational axis. A first axis extending between the rotational axis and the force applying location is inclined relative to a second axis extending between the rotational axis and the cam follower. If the biasing mechanism comprises a spring having a first end coupled to the support and a second end coupled to the force applying location for applying the second force along a spring axis, then rotation of the interface member varies the distance between the spring axis and the rotational axis, thus varying the torque applied to the interface member to compensate for the resistance exerted by the transmission.
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Fujii Kazuhiro
Kitamura Satoshi
Bucci David A.
Deland James A.
Johnson Vicky A.
Shimano Inc.
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