In a power transmission apparatus, a centrifugal clutch includes a holder, a press, and springs to urge masses from a radially outer position to a radially inner position. The masses are each housed in an associated one of housing portions arranged in a circumferential direction of the holder such that the masses are radially movable. More than one spring is provided in the circumferential direction between an inner peripheral wall surface of each of the housing portions and an associated one of the masses to urge the associated mass from the radially outer position to the radially inner position.

A power transmission apparatus a centrifugal clutch including a holder and a press. The holder and the press are each circumferentially provided with protrusions fitted and attached to cut-outs of a clutch housing. The holder is an integrated assembly into which a mass that is being held is integrated. The integrated assembly and the press are non-connected separate components and are independently movable toward or away from each other.

In a power transmission apparatus, a centrifugal clutch includes a holder, a press, a first spherical 14bodv that is partially protruded from a first opening and in contact with a rolling contact surface of the press so as to be rollable thereon, and a second spherical body that is partially protruded from a second opening and in contact with a rolling contact surface of the holder so as to be rollable thereon. A through hole has a tapered shape from the first opening to the second opening. Disconnection of the first spherical body is prevented by an outer peripheral edge of one of the first opening and the second opening that has a smaller diameter.

During movement of a mass of a centrifugal clutch a radially inner position to a radially outer position and a resulting increase in torque transmitted from an input gear to an output shaft, a power transmission apparatus includes a first torque region where the apparatus restricts operation of a pressing assist cam and a second torque region where the apparatus allows operation of the pressing assist cam.

A centrifugal clutch includes an input part, an output part, a centrifugally engageable and disengageable friction unit, and a shifting apparatus. The friction unit has first frictional elements connected to the input part, and second frictional elements connected to the output part and layered alternately with the first frictional elements. The shifting apparatus is for frictionally engaging the first frictional elements and the second frictional elements to engage the clutch. The shifting apparatus has a centrifugal mass and a brake spring. When the centrifugal mass moves from a disengaged position to an engaged position, the brake spring is arranged to apply a first braking force contrary to a first direction of motion of the centrifugal mass. The brake spring is also arranged to apply a second braking force contrary to a second direction of motion of the centrifugal mass. The first braking force is greater than the second braking force.

A centrifugal clutch includes an input part, an output part, a centrifugally engageable and disengageable friction unit, and a shifting apparatus. The friction unit has first frictional elements connected to the input part, and second frictional elements connected to the output part and layered alternately with the first frictional elements. The shifting apparatus is for frictionally engaging the first frictional elements and the second frictional elements to engage the clutch. The shifting apparatus has a centrifugal mass and a brake spring. When the centrifugal mass moves from a disengaged position to an engaged position, the brake spring is arranged to apply a first braking force contrary to a first direction of motion of the centrifugal mass. The brake spring is also arranged to apply a second braking force contrary to a second direction of motion of the centrifugal mass. The first braking force is greater than the second braking force.

An agricultural header includes: a header frame; at least one cutting unit carried by the header frame and including a cutting element and a driveshaft coupled to the cutting element; and a gearbox configured to drive the cutting element. The gearbox includes a gearbox output rotatably coupled to the driveshaft; and a clutch including an intermediate shaft and at least one clutch shoe rotatably coupled to the intermediate shaft and displaceable between a non-engaging position where the at least one clutch shoe does not engage the gearbox output and an engaging position where the at least one clutch shoe engages the gearbox output. The clutch is configured such that the at least one clutch shoe displaces to the engaging position when a rotational speed of the intermediate shaft reaches a threshold value.

An agricultural header includes: a header frame; at least one cutting unit carried by the header frame and including a cutting element and a driveshaft coupled to the cutting element; and a gearbox configured to drive the cutting element. The gearbox includes a gearbox output rotatably coupled to the driveshaft; and a clutch including an intermediate shaft and at least one clutch shoe rotatably coupled to the intermediate shaft and displaceable between a non-engaging position where the at least one clutch shoe does not engage the gearbox output and an engaging position where the at least one clutch shoe engages the gearbox output. The clutch is configured such that the at least one clutch shoe displaces to the engaging position when a rotational speed of the intermediate shaft reaches a threshold value.

An electromagnetic clutch of a brushless control-by-wire centrifugal ball arm engagement device includes a brushless electromagnet, a thrust pressing disc, a driven inner-spline hub, a control-by-wire drive disc, a centrifugal ball arm hollow disc, centrifugal ball arm pins, centrifugal ball arms, centrifugal balls, a magnetic conductive force transmitting disk, a drive shaft; once the brushless electromagnet is energized, the centrifugal ball arms and the centrifugal balls each make a circular motion around the centrifugal ball arm pin outwardly along the smooth surface of the thrust pressing disc by the action of centrifugal force produced by them when rotating with high speed. The component of the centrifugal force in the direction of the central axis of the centrifugal ball arm hollow disc drives the thrust pressing disc to compress the outer-spline-groove steel sheets and the inner-spline-groove friction discs with each other, which makes the clutch engaged.

A one way clutch comprises an outer race including a radially outer first annular part to which rotation is input from outside and a radially inner second annular part capable of rotating when receiving rotation from the first annular part, an inner race provided radially inside the outer race and rotatable relative to the outer race, a plurality of torque transmission members provided between the outer race and the inner race to transmit torque between the outer race and the inner race, and a coupling mechanism that couples the first annular part and the second annular part together to make them integrally rotatable when the speed of rotation input from outside is lower than a specific speed and decouples them when the speed of rotation exceeds the specific speed.