Clutch device

1 . A clutch device to allow or block transfer of a rotation driving force of an input shaft to an output shaft, the clutch device comprising:

a clutch center housed in a clutch housing holding a plurality of input-side rotating plates rotationally drivable by rotational driving of the input shaft, the clutch center being rotationally drivable together with the output shaft;

a pressure plate movable toward, or away from, and to be rotatable with respect to, the clutch center, the pressure plate holding one or more of a plurality of output-side rotating plates arranged alternately with the plurality of input-side rotating plates, the pressure plate being configured to press the plurality of input-side rotating plates and the plurality of output-side rotating plates;

a clutch spring to urge the pressure plate in a first direction where the first direction is a direction in which the pressure plate moves toward the clutch center and a second direction is a direction in which the pressure plate moves away from the clutch center; and

a stopper plate secured to the clutch center to limit movement of the pressure plate away from the clutch center in the second direction by a predetermined distance or longer; wherein

an end, on the side of the first direction, of the clutch spring is in contact with the pressure plate, and an end, on the side of the second direction, of the clutch spring is in contact with the stopper plate;

the clutch center includes:

a center-side assist cam surface to generate a force in a direction from the pressure plate toward the clutch center, in order to increase a pressing force between the plurality of input-side rotating plates and the plurality of output-side rotating plates, when the clutch center rotates with respect to the pressure plate;

the pressure plate includes:

a pressure-side assist cam surface configured to be contactable with the center-side assist cam surface, and to generate a force in a direction from the pressure plate toward the clutch center in order to increase the pressing force between the plurality of input-side rotating plates and the plurality of output-side rotating plates, when the pressure plate rotates with respect to the clutch center; and

a housing portion located to the side of the pressure-side assist cam surface in a rotation direction of the pressure plate, the housing portion housing the clutch spring; and

the clutch device includes a reducer to reduce a restoring force of the clutch spring in a direction from the clutch spring toward the pressure-side assist cam surface during a time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction.

2 . The clutch device according to claim 1 , wherein the clutch center is configured to hold the plurality of output-side rotating plates.

3 . The clutch device according to claim 1 , wherein during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, the reducer is configured to restrict inclination of the clutch spring, housed in the housing portion, in the rotation direction.

4 . The clutch device according to claim 3 , wherein

the reducer includes a partition wall defining the housing portion; and

the clutch spring is in contact with an inner circumferential surface of the partition wall in an entirety of the partition wall.

5 . The clutch device according to claim 4 , wherein

the housing portion has an inner diameter that is increased in the second direction from the side of the first direction; and

the clutch spring has a truncated cone shape.

6 . The clutch device according to claim 1 , wherein

during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, the reducer is configured to restrict movement of the end, on the side of the first direction, of the clutch spring with respect to the pressure plate in the rotation direction and restrict movement of the end, on the side of the second direction, of the clutch spring with respect to the stopper plate in the rotation direction; and

during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, an axis of the clutch spring inclines in a direction from the pressure-side assist cam surface toward the clutch spring as extending in the second direction from the side of the first direction, or is parallel or substantially parallel to a straight line extending in a moving direction in which the pressure plate moves.

7 . The clutch device according to claim 6 , wherein the reducer is configured to secure the end, on the side of the first direction, of the clutch spring to the pressure plate, and secure the end, on the side of the second direction, of the clutch spring to the stopper plate.

8 . The clutch device according to claim 7 , wherein the reducer includes:

a first holding groove in the pressure plate, recessed in the first direction from the side of the second direction, and configured to hold the end, on the side of the first direction, of the clutch spring; and

a second holding groove in the stopper plate, recessed in the second direction from the side of the first direction, and configured to hold the end, on the side of the second direction, of the clutch spring.

9 . A clutch device to allow or block transfer of a rotation driving force of an input shaft to an output shaft, the clutch device comprising:

a clutch center housed in a clutch housing holding a plurality of input-side rotating plates rotationally drivable by rotational driving of the input shaft, the clutch center being rotationally drivable together with the output shaft;

a pressure plate movable toward, or away from, and to be rotatable with respect to, the clutch center, the pressure plate being configured to hold one or more of a plurality of output-side rotating plates alternately arranged with the plurality of input-side rotating plates, the pressure plate being configured to press the plurality of input-side rotating plates and the plurality of output-side rotating plates;

a clutch spring to urge the pressure plate in a first direction where the first direction is a direction in which the pressure plate moves toward the clutch center and a second direction is a direction in which the pressure plate moves away from the clutch center; and

a lifter plate secured to the pressure plate to restrict movement of the pressure plate away from the clutch center in the second direction by a predetermined distance or longer; wherein

an end, on the side of the first direction, of the clutch spring is in contact with the lifter plate, and an end, on the side of the second direction, of the clutch spring is in contact with the clutch center;

the clutch center includes:

a center-side assist cam surface to generate a force in a direction from the pressure plate toward the clutch center, in order to increase a pressing force between the plurality of input-side rotating plates and the plurality of output-side rotating plates, when the clutch center rotates with respect to the pressure plate; and

a housing portion located to the side of the center-side assist cam surface in a rotation direction of the clutch center, the housing portion housing the clutch spring;

the pressure plate includes:

a pressure-side assist cam surface configured to be contactable with the center-side assist cam surface, and to generate a force in a direction from the pressure plate toward the clutch center in order to increase the pressing force between the plurality of input-side rotating plates and the plurality of output-side rotating plates, when the pressure plate rotates with respect to the clutch center; and

the clutch device includes a reducer to reduce a restoring force of the clutch spring in a direction from the clutch spring toward the center-side assist cam surface during a time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction.

10 . The clutch device according to claim 9 , wherein the clutch center is configured to hold the plurality of output-side rotating plates.

11 . The clutch device according to claim 9 , wherein during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, the reducer is configured to restrict inclination of the clutch spring, housed in the housing portion, in the rotation direction.

12 . The clutch device according to claim 11 , wherein:

the reducer includes a partition wall defining the housing portion; and

the clutch spring is in contact with an inner circumferential surface of the partition wall in an entirety of the partition wall.

13 . The clutch device according to claim 9 , wherein

during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, the reducer is configured to restrict movement of the end, on the side of the first direction, of the clutch spring with respect to the lifter plate in the rotation direction and restrict movement of the end, on the side of the second direction, of the clutch spring with respect to the clutch center in the rotation direction; and

during the time period until the center-side assist cam surface and the pressure-side assist cam surface approach and contact each other from a state of being spaced apart from each other in the rotation direction, an axis of the clutch spring inclines in a direction from the center-side assist cam surface toward the clutch spring as extending in the first direction from the side of the second direction, or is parallel or substantially parallel to a straight line extending in a moving direction in which the pressure plate moves.