Bicycle transmission device

1. A bicycle transmission device comprising:

an input rotational shaft;

an output part;

a transmission mechanism configured to accelerate a rotational input from the input rotational shaft and output the rotation input to the output part;

a switching mechanism configured to selectively switch between a first state, in which the output part and the input rotational shaft are operatively coupled together to transmit the rotational input via the transmission mechanism from the input rotational shaft to the output part through a first rotating body, a second rotating body, a third rotating body and a fourth rotating body, and a second state, in which the output part and the input rotational shaft are operatively coupled together without transmitting the rotational input from the input rotational shaft to the output part via the transmission mechanism; and

an assist motor configured to transmit torque to the second rotating body or the output part,

the transmission mechanism comprising:

the first rotating body integrally rotatable with the input rotational shaft;

the second rotating body rotatable around a center axis, a position of the center axis does not change with respect to the input rotational shaft, and the torque of the first rotating body being transmitted to the second rotating body;

the third rotating body rotates with the second rotating body as a single unit when the switching mechanism is in the first state; and

the fourth rotating body to which the torque of the third rotating body is transmitted and that is integrally rotatable with the output part.

2. The bicycle transmission device as recited in claim 1 , wherein

the switching mechanism, while in the first state, transmits torque in between the input rotational shaft and the first rotating body, between the first rotating body and the second rotating body, between the second rotating body and the third rotating body, between the third rotating body and the fourth rotating body, and between the fourth rotating body and the output part; and

the switching mechanism, while in the second state, does not transmits torque between one of the input rotational shaft and the first rotating body, the first rotating body and the second rotating body, the second rotating body and the third rotating body, the third rotating body and the fourth rotating body, and the fourth rotating body and the output part.

3. The bicycle transmission device as recited in claim 1 , wherein

the transmission mechanism comprises a transmission shaft that supports the second rotating body and the third rotating body.

4. The bicycle transmission device as recited in claim 3 , wherein

the transmission shaft integrally rotates with at least one of the second rotating body and the third rotating body.

5. The bicycle transmission device as recited in claim 3 , wherein

the switching mechanism comprises a switching unit, at least a part of which is disposed between the transmission shaft and the second rotating body, between the transmission shaft and the third rotating body, or between the fourth rotating body and the output part.

6. The bicycle transmission device as recited in claim 5 , wherein

the switching unit comprises a coupling member, at least a part of which is disposed between the transmission shaft and the third rotating body and that can couple the transmission shaft and the third rotating body, and a control member that uncouples the coupling member from the transmission shaft or the third rotating body.

7. The bicycle transmission device as recited in claim 6 , wherein

the coupling member comprises a pawl that is provided on the outer periphery of the transmission shaft and movable between a position either protruding from a groove or being separated from the groove, which is formed on an inner periphery of the third rotating body.

8. The bicycle transmission device as recited in claim 6 , wherein

the control member is movably arranged in an axial direction of the transmission shaft.

9. The bicycle transmission device as recited in claim 1 , wherein

the transmission mechanism is accelerated by the first rotating body and the second rotating body and is decelerated by the third rotating body and the fourth rotating body.

10. The bicycle transmission device as recited in claim 1 , further comprising

an assist motor that transmits torque to the second rotating body or the output part.

11. The bicycle transmission device as recited in claim 1 , wherein

the transmission mechanism further comprises a transmission body that joins the input rotational shaft and the first rotating body, and

a torque sensor is attached to the transmission body.

12. The bicycle transmission device as recited in claim 1 , wherein

the input rotational shaft is a crankshaft that is configured to receive a manual drive force as an input.

13. The bicycle transmission device as recited in claim 1 , wherein

the output part comprises an attaching portion to which a sprocket can be attached.

14. A The bicycle transmission device comprising:

an input rotational shaft;

an output part;

a transmission mechanism configured to accelerate a rotational input from the input rotational shaft and output the rotation input to the output part; and

a switching mechanism configured to selectively switch between a first state, in which the output part and the input rotational shaft are operatively coupled together to transmit the rotational input via the transmission mechanism from the input rotational shaft to the output part through a first rotating body, a second rotating body, a third rotating body and a fourth rotating body, and a second state, in which the output part and the input rotational shaft are operatively coupled together without transmitting the rotational input from the input rotational shaft to the output part via the transmission mechanism,

the transmission mechanism comprising:

the first rotating body integrally rotatable with the input rotational shaft;

the second rotating body rotatable around a center axis, a position of the center axis does not change with respect to the input rotational shaft, and the torque of the first rotating body being transmitted to the second rotating body;

the third rotating body rotates with the second rotating body as a single unit when the switching mechanism is in the first state; and

the fourth rotating body to which the torque of the third rotating body is transmitted and that is integrally rotatable with the output part,

the switching mechanism further comprising a one-way clutch that rotates the input rotational shaft and the output part as a single unit when a rotational speed of the input rotational shaft in one direction is equal to or greater than a rotational speed of the output part in the one direction, and that permits a relative rotation between the input rotational shaft and the output part when the rotational speed of the input rotational shaft in the one direction is less than the rotational speed of the output part in the one direction.

15. The bicycle transmission device as recited in claim 14 , wherein

the one-way clutch is a roller clutch.

16. The bicycle transmission device as recited in claim 14 , further comprising:

a transmission body that joins the input rotational shaft and the first rotating body,

the transmission body having a tubular shape that partially covers a section of the output part, and

the one-way clutch being disposed between an inner periphery of the transmission body and an outer periphery of the output part.

17. The bicycle transmission device as recited in claim 16 , wherein

the transmission body and the first rotating body are integrally formed as a one-piece member.