Walk behind mower

1. A walk behind mower including a driven wheel rotatably supported by a body frame, a power source for selectively driving the driven wheel, a dog clutch provided in a power transmission path between the power source and the driven wheel, and a clutch actuating mechanism interposed between the power source and the dog clutch for selectively disengaging the dog clutch;

wherein the dog clutch includes an input end consisting of a first clutch half provided with teeth, an output end consisting of a second clutch half provided with teeth configured to selectively mesh with the teeth of the first clutch half, and a spring member interposed between the first clutch half and the second clutch half to normally urge the two clutch halves away from each other;

wherein the clutch actuating mechanism is configured to displace the two clutch halves toward each other against a biasing force of the spring member by using a drive force transmitted from the power source to the clutch actuating mechanism;

wherein the walk behind mower further includes a centrifugal rotary clutch interposed between the power source and the clutch actuating mechanism;

wherein the walk behind mower further includes an axle shaft rotatably supported by the body frame and having a pair of driven wheels fixedly attached to either end thereof, a driven bevel gear rotatably supported by an intermediate part of the axle shaft, a drive bevel gear fixedly supported by a driven shaft extending vertically, the drive bevel gear being connected to an output end of the centrifugal rotary clutch via the driven shaft and meshing with the driven bevel gear;

wherein the dog clutch is coaxially mounted on the axle shaft in such a manner that the second clutch half is fixedly secured to the axle shaft and the first clutch half is rotatably supported on the axle shaft; and

wherein the clutch actuating mechanism comprises a cam mechanism formed between the driven bevel gear and the first clutch half in such a manner that the first clutch half is displaced toward the second clutch half against a biasing force of the spring member when the drive force is transmitted from the power source to the driven bevel gear via the centrifugal rotary clutch and the drive bevel gear, and wherein the first clutch half is disengaged from the second clutch half under the biasing force of the spring member when the drive force is not transmitted from the power source to the driven bevel gear.

2. The walk behind mower according to claim 1 ,

wherein the clutch actuating mechanism comprises at least one projection projecting from one of the first clutch half and the driven bevel gear, and at least one recess provided in the other of the first clutch half and the driven bevel gear, the cam mechanism being formed between the projection and the recess.

3. The walk behind mower according to claim 2 , wherein the cam mechanism includes a ramp surface formed in the at least one projection.

4. The walk behind mower according to claim 1 , wherein the teeth of the first clutch half project axially toward the second clutch half, and the teeth of the second clutch half project axially toward the first clutch half, the spring member comprises a compression coil spring wound around a part of the axle shaft located between the two clutch halves to urge the two clutch halves away from each other.

5. The walk behind mower according to claim 1 , further comprising a drive clutch interposed between the power source and an input end of the centrifugal rotary clutch, wherein the drive clutch is configured to be selectively engaged according to an operation by an operator.