Abstract: In a stepwise automatic transmission, a mass is concentrated in a longitudinal direction thereof. The stepwise automatic transmission includes an input shaft, an intermediate shaft, an output shaft, a first clutch which is connected and disconnected in accordance with a rotation speed of the input shaft, first and second power transmission mechanisms, and a second clutch which is connected and disconnected in accordance with rotation speed of the intermediate shaft. The intermediate shaft is disposed rearward of the input shaft. When the first clutch is connected, the first power transmission mechanism transmits rotation of the input shaft to the intermediate shaft. The second clutch is provided on the intermediate shaft. When the second clutch is connected, the second power transmission mechanism transmits rotation of the intermediate shaft to the output shaft. A front end of the second clutch is located forward of a rear end of the first clutch as viewed from an axial direction of the input shaft.

Abstract: A motorcycle having high durability and a large space below a seat includes an internal space at least a portion of which is located between an engine unit and a seat provided in a cover member. The engine unit is pivotally suspended on a body frame. A center axis of a cylinder extends obliquely upward from a crankcase and forwardly. Oil reservoirs and provided in a bottom of a crank chamber and a bottom of a portion of a transmission chamber located in a front portion of a transmission case, respectively. The oil reservoirs are communicated with each other by a communication path. A bottom surface of the transmission chamber in the portion in which portion the oil reservoir is provided is located downward of the bottom surface of the portion rearward of the oil reservoir of the transmission chamber.

Abstract: A downsized power unit equipped with a clutch operation-assisting device that reduces operation force of a clutch lever. The clutch operation-assisting device includes a push shaft and a first rotation plate that is rotatably supported by a support plate and connected to a clutch wire, and slides the push shaft by rotation. The first rotation plate and a second rotation plate are connected by gear. The second rotation plate is rotatably supported by a bearing member fixed to the support plate. A spring unit that provides assisting force in a direction to disengage a friction clutch is connected to the second rotation plate by pin. The spring unit, as seen from a shaft direction of the push shaft, is disposed so that an extension direction of an auxiliary spring does not pass through a rotation center of a pressure plate.

Abstract: In a stepwise automatic transmission, a mass is concentrated in a longitudinal direction thereof. The stepwise automatic transmission includes an input shaft, an intermediate shaft, an output shaft, a first clutch which is connected and disconnected in accordance with a rotation speed of the input shaft, first and second power transmission mechanisms, and a second clutch which is connected and disconnected in accordance with rotation speed of the intermediate shaft. The intermediate shaft is disposed rearward of the input shaft. When the first clutch is connected, the first power transmission mechanism transmits rotation of the input shaft to the intermediate shaft. The second clutch is provided on the intermediate shaft. When the second clutch is connected, the second power transmission mechanism transmits rotation of the intermediate shaft to the output shaft. A front end of the second clutch is located forward of a rear end of the first clutch as viewed from an axial direction of the input shaft.

Abstract: To centrifugal clutch with reduced size, which facilitates reduced width of a straddle type vehicle, includes a clutch housing on which an outer plate is mounted, and a clutch boss on which an inner plate is mounted. A roller weight is provided between the clutch housing and a rightmost outer plate. A cam surface formed on the clutch housing guides the roller weight in a direction such that the outer plate and the inner plate are press-fitted together when the roller weight moves outward in a radial direction of a secondary sheave shaft. A cam surface formed on the rightmost outer plate guides the roller weight outward in the radial direction and toward the cam surface with respect to an axial direction when the roller weight moves outward in the radial direction of the secondary sheave shaft.

Abstract: An actuation force transmission mechanism is provided that can be interposed between a shift actuator and a shift shaft. The mechanism can include: first and second coupling parts that can be coupled for movement relative to each other in sliding directions; a biasing mechanism that can be configured for urging the first and second coupling parts toward a neutral position; and a stopper mechanism that can be configured for stopping relative movement of one of the first and second coupling parts when moved relatively from the neutral position against an urging force of the biasing mechanism. When the shift actuator is stroked by a predetermined amount, the first coupling part can move relative to the second coupling part against the urging force until the first coupling part is stopped by the stopper mechanism, at which point, the first and second coupling parts can move together.

Abstract: A motorcycle having high durability and a large space below a seat includes an internal space at least a portion of which is located between an engine unit and a seat provided in a cover member. The engine unit is pivotally suspended on a body frame. A center axis of a cylinder extends obliquely upward from a crankcase and forwardly. Oil reservoirs are provided in a bottom of a crank chamber and a bottom of a portion of a transmission chamber located in a front portion of a transmission case, respectively. The oil reservoirs are communicated with each other by a communication path. A bottom surface of the transmission chamber in the portion in which portion the oil reservoir is provided is located downward of the bottom surface of the portion rearward of the oil reservoir of the transmission chamber.

Abstract: In a motorcycle having a V-belt type continuously variable transmission, a resin washer made of a nylon resin is interposed between a boss fixed to a moving sheave half of a secondary sheave and a spring bearing member. The boss contacts the spring bearing member through the resin washer, whereby the moving sheave half is restricted to a Top position, in which a spacing between it and a stationary sheave half becomes maximum. In this manner, the maximum speed is not changed by exchange of the V-belt, the V-belt does not slip or become considerably abraded or deteriorated, and noise generation is suppressed.

Abstract: Abrasion of a V-belt in a belt type continuously variable transmission accommodated in an engine unit of a motorcycle is suppressed. A V-belt wound around and contacting a primary sheave and a secondary sheave 72 is at least partially formed from a resin. A plurality of grooves aligned at a predetermined pitch in a radial direction are formed on sheave surfaces of the primary and secondary sheaves. The average pitch P(mm) of the grooves is P??0.08K×10?3+0.18, where K(Hv) indicates surface hardness of the sheave surfaces.

Abstract: A transmission mechanism is provide that can be interposed between a shift actuator and a shift shaft. The mechanism can include first and second coupling parts that can be coupled for movement relative to each other; a biasing mechanism that can be configured for urging the first and second coupling parts toward a neutral position; and a stopper mechanism that can be configured for stopping the relative movement of one of the first and second coupling parts when moved relatively from the neutral position against urging force of the biasing mechanism. When the shift actuator is stroked by a predetermined amount, a dog can be compulsorily disengaged as the first and second coupling parts are moved together by the stopper mechanism, and engaged as one of the first and second coupling parts moves relatively against the urging force, for allowing smooth shift change.

Abstract: A clutching system comprises a lever mechanism portion and a clutch mechanism portion. The lever mechanism portion comprises a push lever. The push lever comprises a cam surface. The clutch mechanism portion comprises a push rod. The push rod comprises a cam follower. A Belleville spring functions as a clutch spring. The cam surface and the cam follower are formed such that a lever ratio of the push lever at a pivot start position is larger than a lever ratio of the push lever at a pivot finish position. The Belleville spring is formed such that a force required to move the push lever at the pivot finish position is smaller than a force required to move to the push lever at the pivot start position.

Abstract: A belt-type continuously variable transmission that is easily manufactured includes a belt wound around a primary sheave and a secondary sheave. The primary sheave includes a fixed sheave member, a movable sheave member, a cam plate, and a roller weight. The movable sheave member has a guide rib extending toward the cam plate. The cam plate has a slider having a guide groove. The position of the radially outer portion of an end surface of the slider is shifted toward the right in the rotation axis extending direction from the position of the radially inner portion of the end surface.

Abstract: In order to reduce the influences of engine heat and vibration on a shift actuator, a shift actuator is disposed apart from the engine and the transmission on a vehicle. In particular a straddle-type vehicle, the vehicle includes a head pipe and a body frame including a main frame that extends rearward from the head pipe. The engine is suspended by the body frame 2 and a transmission is disposed next to the engine. The transmission includes a shift mechanism having a multiple-step speed change gear and a clutch mechanism that interrupts the transmission of rotation at the switching of the speed change gear of the transmission 40. An automatic transmission control unit operates the clutch mechanism and switches the speed change gear of the transmission automatically.

Abstract: A downsized power unit equipped with a clutch operation-assisting device that reduces operation force of a clutch lever. The clutch operation-assisting device includes a push shaft and a first rotation plate that is rotatably supported by a support plate and connected to a clutch wire, and slides the push shaft by rotation. The first rotation plate and a second rotation plate are connected by gear. The second rotation plate is rotatably supported by a bearing member fixed to the support plate. A spring unit that provides assisting force in a direction to disengage a friction clutch is connected to the second rotation plate by pin. The spring unit, as seen from a shaft direction of the push shaft, is disposed so that an extension direction of an auxiliary spring does not pass through a rotation center of a pressure plate.

Abstract: To centrifugal clutch with reduced size, which facilitates reduced width of a straddle type vehicle, includes a clutch housing on which an outer plate is mounted, and a clutch boss on which an inner plate is mounted. A roller weight is provided between the clutch housing and a rightmost outer plate. A cam surface formed on the clutch housing guides the roller weight in a direction such that the outer plate and the inner plate are press-fitted together when the roller weight moves outward in a radial direction of a secondary sheave shaft. A cam surface formed on the rightmost outer plate guides the roller weight outward in the radial direction and toward the cam surface with respect to an axial direction when the roller weight moves outward in the radial direction of the secondary sheave shaft.

Abstract: A belt-type continuously variable transmission that is easily manufactured includes a belt wound around a primary sheave and a secondary sheave. The primary sheave includes a fixed sheave member, a movable sheave member, a cam plate, and a roller weight. The movable sheave member has a guide rib extending toward the cam plate. The cam plate has a slider having a guide groove. The position of the radially outer portion of an end surface of the slider is shifted toward the right in the rotation axis extending direction from the position of the radially inner portion of the end surface.

Abstract: A transmission mechanism is provide that can be interposed between a shift actuator and a shift shaft. The mechanism can include first and second coupling parts that can be coupled for movement relative to each other; a biasing mechanism that can be configured for urging the first and second coupling parts toward a neutral position; and a stopper mechanism that can be configured for stopping the relative movement of one of the first and second coupling parts when moved relatively from the neutral position against urging force of the biasing mechanism. When the shift actuator is stroked by a predetermined amount, a dog can be compulsorily disengaged as the first and second coupling parts are moved together by the stopper mechanism, and engaged as one of the first and second coupling parts moves relatively against the urging force, for allowing smooth shift change.

Abstract: Abrasion of a V-belt in a belt type continuously variable transmission accommodated in an engine unit of a motorcycle is suppressed. A V-belt wound around and contacting a primary sheave and a secondary sheave 72 is at least partially formed from a resin. A plurality of grooves aligned at a predetermined pitch in a radial direction are formed on sheave surfaces of the primary and secondary sheaves. The average pitch P(mm) of the grooves is P??0.08K×10?3+0.18, where K(Hv) indicates surface hardness of the sheave surfaces.

Abstract: An actuation force transmission mechanism is provided that can be interposed between a shift actuator and a shift shaft. The mechanism can include: first and second coupling parts that can be coupled for movement relative to each other in sliding directions; a biasing mechanism that can be configured for urging the first and second coupling parts toward a neutral position; and a stopper mechanism that can be configured for stopping relative movement of one of the first and second coupling parts when moved relatively from the neutral position against an urging force of the biasing mechanism. When the shift actuator is stroked by a predetermined amount, the first coupling part can move relative to the second coupling part against the urging force until the first coupling part is stopped by the stopper mechanism, at which point, the first and second coupling parts can move together.

Abstract: A clutching system comprises a lever mechanism portion and a clutch mechanism portion. The lever mechanism portion comprises a push lever. The push lever comprises a cam surface. The clutch mechanism portion comprises a push rod. The push rod comprises a cam follower. A Belleville spring functions as a clutch spring. The cam surface and the cam follower are formed such that a lever ratio of the push lever at a pivot start position is larger than a lever ratio of the push lever at a pivot finish position. The Belleville spring is formed such that a force required to move the push lever at the pivot finish position is smaller than a force required to move to the push lever at the pivot start position.