FIELD

The present disclosure relates to a power transmission device that appropriately transmits or cuts off rotational power of an input member to an output member.

BACKGROUND

In general, a motorcycle has a power transmission device for appropriately transmitting or cutting off driving power of an engine to a transmission and a driving wheel. The power transmission device includes an input member coupled to the engine side. An output member is coupled to the transmission and driving wheel side. A clutch member is coupled to the output member. A pressure member presses clutch plates, drive-side clutch plates and driven-side clutch plates, against each other or releases a press-contact force. The power transmission device is configured to transmit power by pressing the drive-side clutch plates and the driven-side clutch plates against each other. This cuts off power by releasing the press-contact force.

For example, in a power transmission device disclosed in WO2016/024557, a receiving member is attached to the pressure member. A clutch spring, urging means, contained in the receiving member to urge the pressure member in a direction so that the drive-side clutch plates and driven-side clutch plates are pressed against each other. One cam surface is formed in the receiving member. The other cam surface, which faces the one cam surface, is formed in the clutch member. These cam surfaces constitute a back-torque limiting cam that reduces the press-contact force between the drive-side clutch plates and the driven-side clutch plates. The pressure member and the clutch member rotate relative to each other when the rotation speed of the output member exceeds the rotation speed of the input member.

That is, if the pressure member and the clutch member rotate relative to each other when the rotation speed of the output member exceeds the rotation speed of the input member, the one cam surface and the other cam surface slide over each other. The back-torque limiting cam functions to move the receiving member in the axial direction relative to the pressure member. The urging force of the clutch spring applied to the pressure member decreases. Thus, the press-contact force between the drive-side clutch plates and the driven-side clutch plates is reduced.

SUMMARY

However, in the existing power transmission device described above, when the entire device, including the pressure member and the clutch member, rotates at a high speed, the receiving member is pressed against the clutch member, which is positioned radially outside, by a generated centrifugal force. The sliding resistance of the receiving member may become larger than expected. In this case, when a driver operates a clutch lever or the like to separate the pressure member from the clutch member to disengage the clutch, release the press-contact force between the clutch plates, and subsequently reengages the clutch, to press the clutch plates against each other, movement of the receiving member is slowed due to excessive sliding resistance. Thus, a problem arises in that the response, when engaging the clutch, becomes dull and the driver experiences an unpleasant sensation in operability due to feeling of idle driving.

The present disclosure is designed to overcome the background deficiencies described above. It provides a power transmission device that can improve responsiveness when engaging a clutch. This improves operability by reducing the sliding resistance of a receiving member.

According to the disclosure, a power transmission device comprises a clutch housing that rotates together with rotation of an input member. A plurality of drive-side clutch plates are attached to the clutch housing. A clutch member has a plurality of driven-side clutch plates alternately formed with the drive-side clutch plates of the clutch housing. They are attached with an output member. A pressure member is attached to the clutch member. The pressure member presses the drive-side clutch plates and the driven-side clutch plates against each other or releases a press-contact force in accordance with relative movement to the clutch member in an axial direction. An urging member moves the pressure member in a direction such that the drive-side clutch plates and the driven-side clutch plates are pressed against each other. A receiving member, constituted by a separate member, is attached to the pressure member. The receiving member receives an urging force of the urging member on the pressure member side. It transmits the urging force to the pressure member. A back-torque limiting cam, constituted by a pair of cam surfaces, reduces a press-contact force between the drive-side clutch plates and the driven-side clutch plates. The pressure member and the clutch member rotate relative to each other when a rotation speed of the output member exceeds a rotation speed of the input member. One of the cam surfaces is formed in the receiving member. The other cam surface is formed in the clutch member. The power transmission device transmits or cuts off rotational power input to the input member to the output member by pressing the drive-side clutch plates and the driven-side clutch plates against each other or releasing the press-contact force. The power transmission device includes a radially-outside restricting portion that restricts radially-outward movement of the receiving member relative to the pressure member. Also, it maintains a clearance between a side surface of the receiving member and the clutch member.

In the power transmission device, the radially-outside restricting portion includes a flange portion formed on an opening side of the receiving member. A contact portion is formed in the pressure member. The contact portion restricts the radially-outward movement of the receiving member by making contact with the flange portion.

In the power transmission device, the contact portion is a wall surface extending in a rotation axis direction of the pressure member. It conformably makes contact with a side surface of the flange portion.

In the power transmission device, the contact portion, in plan view, has a conforming shape to an outer peripheral shape of the flange portion.

In the power transmission device, an attachment hole, for attaching the receiving member, is formed in the pressure member. The radially-outside restricting portion is a radially-outside opening of the attachment hole. It restricts the radially-outward movement by contacting the receiving member.

In the power transmission device, the receiving member has a contact surface with a shape conforming to the radially-outside opening of the attachment hole. The contact surface contacts with the radially-outside opening.

The power transmission device has the radially-outside restricting portion that restricts radially-outward movement of the receiving member relative to the pressure member. Thus, it maintains the clearance between the side surface of the receiving member and the clutch member. This makes it possible to improve responsiveness when engaging the clutch. Also, it improves operability by reducing the sliding resistance of the receiving member.

The radially-outside restricting portion includes the flange portion. The flange portion is formed on the opening side of the receiving member. The contact portion is formed in the pressure member. It restricts radially-outward movement of the receiving member by making contact with the flange portion. Thus, it is possible to restrict the radially-outward movement by using the flange portion of the receiving member. It is also possible to reliably reduce the sliding resistance of the receiving member.

The contact portion is the wall surface extending in the rotation axis direction of the pressure member. The contact portion contacts the side surface of the flange portion. Thus, it is possible to cause the flange portion to stably contact with the contact portion. It is also possible to more reliably reduce the sliding resistance of the receiving member.

The contact portion, in plan view, has a shape conforming to the outer peripheral shape of the flange portion. Thus, it is possible to cause the flange portion to contact the contact portion. It is also possible to further reliably reduce the sliding resistance of the receiving member.

The attachment hole, for attaching the receiving member, is formed in the pressure member. The radially-outside restricting portion is the radially-outside opening of the attachment hole. It restricts the radially-outward movement by contacting the receiving member. Thus, is possible to restrict radially-outward movement of the receiving member by using the radially-outside opening of the attachment hole. It is also possible to reliably reduce the sliding resistance of the receiving member.

The receiving member has the contact surface conforming to the radially-outside opening of the attachment hole. The contact surface contacts the radially-outside opening. Thus, it is possible to cause the receiving member to stably contact the radially-outside opening, It is also possible to more reliably reduce the sliding resistance of the receiving member.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

