A conventional bicycle hub assembly generally includes a hub, an axle, a rotatable unit and a gear disk so as to position the axle and to allow the wheel to rotate. According to practical needs, a tubular portion and a derailleur device are equipped. The hub assembly can transmit torque in one direction or in two directions, the one-direction transmission means that the hub rotates in the forward direction to move the bicycle move forward, and the reverse direction cannot move the bicycle. The two-direction transmission means that the hub can transmit torque in both directions. The ratchet mechanism for the one-direction transmission hub can be engaged in radial direction or in axial direction. The radial engagement means that the hub includes teeth in the radial direction and the teeth are engaged with radial ratchet blocks. The axial engagement means that the hub includes teeth in the axial direction and the teeth are engaged with axial ratchet blocks.
When in action, the one-direction transmission ratchet device generates a linear movement between the ratchet device and the hub so as to generate a gap to disengage the ratchet device and the hub. Therefore, the hub cannot transmit torque. The linear movement between the ratchet device and the hub can be two-side linear movement and single-side linear movement.
Taiwan Patent No. 088117780 discloses an axle, a hub co-axially connected with the axle, at last one bearing device which includes at least two bearings located between the hub and the axle, so that the hub is rotatable relative to the axle. A rotor is rotatable about the axle and has at least gear connected to the rotor. A free wheel which is located between the rotor and the hub, and has two plates and each plate has a toothed surface. The two toothed surfaces are pushes toward each other by a tension device. The two plates are co-axial with the axle and located on a plane that is perpendicular to the axis of the axle when the wheel is in stopped status. The plates are kept to be inclined relative to the plane perpendicular to the axis of the axle. The two plates are installed consecutively and a spring pushes the two plates toward each other.
Taiwan Utility Patent No. 096219278 discloses a collar made by metal and multiple teeth are defined in an inner periphery of the collar. The teeth extend axially. A ratchet block is made by magnetic material and includes two end surfaces. The shape of the ratchet block is axially and slidably engaged with the teeth of the collar. One end surface has an annular teeth and a fly wheel has another annular teeth which is engaged with the annular teeth of the end surface in one direction. A permanent magnet is connected to the other end surface that does not have the annular teeth.
The hub of the first example includes an annular threaded portion on the right end thereof and the annular threaded portion has teeth which are engaged with one of the plates in radial direction and can be moved linearly relative to the plate. The rotor has teeth which are engaged with the other plate in radial direction, so that linear movements can be made in two directions. The two respective facing surfaces of the two plates have teeth engaged with each other. The annular threaded portion, the two plates and the spring are cooperated to form a free wheel mechanism. The two plates can be moved linearly in two directions. When the pedals are treaded forward, the teeth between the two plates are pushed to each other to transmit torque. When the pedals are treaded backward, the teeth between the two plates slide over each other, and the sliding action is cooperated with the linear movement in two directions, the two plates are separated from each other so that the hub is rotated without torque being output.
The hub of the second example has annular ratchet teeth on the inside of the fly wheel and the ratchet block facing the fly wheel has annular ratchet teeth so as to be engaged with the end of the fly wheel. The ratchet block is attracted by the permanent magnet so as to be normally located in the collar. The ratchet block is moved linearly relative to the collar. The annular ratchet teeth on the other side of the fly wheel are fixed so as to form the linear movement in one direction between the ratchet block and the hub. This also achieves the purpose that the hub transmits torque in only one direction.
However, the teeth in the two examples are composed of an inclined surface and a vertical surface. Therefore, the teeth have a pre-set height and there is a difference in height between the next tooth. During the interactive linear movement between the plates or the ratchet blocks, the inclined surface is too large so that no gap is formed and this causes wearing by friction between the teeth. The friction generates resistance to slow down the linear movement. Besides, the difference of height between the vertical surfaces of the teeth affects the smooth actions between the ratchet teeth. The plates and the ratchet blocks cannot be quickly engaged again and the sensitivity of the transmission is reduced. Besides, the linear movement of the second example, the fly wheel h as an annular ratchet gear connected to one side thereof and this arrangement is difficult to be manufactured the annular ratchet gear is difficult to be machined precisely. Furthermore, there is a gap between the plates and the spring, between the ratchet block and the permanent magnet, and between the hub and the axle. The spring or the permanent magnet is simply mounted to the axle and the two ends of the spring or the permanent magnet are not well positioned so that the parts tend to be inclined or tilt when operation. This affects the transmission of the ratchet mechanism.
The present invention intends to provide a hub assembly to mitigate the shortcomings of the conventional hub assemblies.