Transmission assembly

A hydraulic drive device, comprising:

• a hydraulic pump connected to a hydraulic motor through a porting system;
• a swash plate positioned to vary the output of the hydraulic pump and being movable in an arcuate manner along a first axis of rotation;
• and
• a trunnion shaft having a proximal end connected to the swash plate and a distal end connected to a separate control arm, whereby rotation of the control arm causes arcuate motion of the swash plate to vary the output of the hydraulic pump;
• the distal end of the trunnion shaft having a plurality of tapered recesses formed thereon and spaced along the circumference of the trunnion shaft, each recess extending a distance along the trunnion shaft from the distal end;
• the control arm having a plurality of tapered ribs shaped to engage the plurality of tapered recesses on the trunnion shaft, each tapered rib fitting into one of the plurality of tapered recesses when the control arm is attached to the trunnion shaft.

A hydraulic drive device, comprising:

• a housing forming an internal sump;
• a center section mounted in the internal sump and having a first running surface located on a first surface of the center section, a second running surface located on a second surface of the center section, a hydraulic porting system disposed therein to hydraulically connect the first running surface to the second running surface, and a pair of ports formed in a second side of the center section opposite a first side to hydraulically connect the hydraulic porting system to the internal sump;
• a hydraulic pump rotatably disposed on the first running surface and a hydraulic motor disposed on the second running surface;
• a pair of check plugs disposed in the pair of ports and connected to hydraulic porting formed in the center section, each check plug having a closed position and an open position, whereby the pair of check plugs permit fluid flow from the hydraulic porting to the internal sump when in the open position;
• and
• a rotary bypass mechanism comprising:
• a shaft disposed in the housing and having a longitudinal axis;
• a pair of engagement fingers located along the longitudinal axis of the shaft, each of the pair of engagement fingers being located adjacent to one of the pair of check plugs, and
• a bypass arm engaged to one end of the shaft and disposed external to the housing, the bypass arm capable of rotating the shaft along the longitudinal axis between a first position where each of the pair of engagement fingers is not in contact with a respective one of the pair of check plugs, and a second position where each of the pair of engagement fingers is in contact with the respective one of the pair of check plugs to cause each of the pair of check plugs to move to the open position;
• the housing comprising a pair of detents formed on an external surface thereof and the bypass arm comprising a first pair of detent openings that engage the pair of detents when the bypass arm is in the first position to frictionally retain the bypass arm in the first position and a second pair of detent openings located to engage the pair of detents when the bypass arm is in the second position to functionally retain the bypass arm in the second position.

A walk-behind vehicle for control by a vehicle operator, comprising:

• a frame having a prime mover disposed thereon;
• an axle for driving at least one wheel of the vehicle, the axle having a first axis of rotation;
• a transmission housing mounted to the frame and forming an internal sump;
• a hydraulic pump and a hydraulic motor disposed in the internal sump;
• a swash plate disposed in the transmission housing and engaged to the hydraulic pump for varying the output thereof,
• a trunnion shaft having a first end engaged to one side of the swash plate and a second end disposed outride the transmission housing;
• a control arm disposed on the second end of the trunnion shaft for rotating the trunnion shaft about a second axis of rotation;
• an input shaft driven by the prime mover and rotatable about a third axis of rotation, the input shaft extending into the transmission housing and driving the hydraulic pump:
• and
• an output shaft extending from the transmission housing and engaged to and driving the axle, the output shaft driven by the hydraulic motor and rotatable about a fourth axis of rotation;
• wherein the second axis of rotation, the third axis of rotation and the fourth axis of rotation are all disposed in a single plane and the single plane is parallel to the first axis of rotation.