A hydrostatic differential transmission, comprising:
- a hollow, cylindrical input housing having opposing forward and rearward ends and a cylindrical side wall;
- an input drive shaft extending through an aperture in the forward wall of said input housing with a rearward end disposed within the interior of the input housing,
- said input shaft connected coaxially with said input housing for rotation therewith;
- an output shaft extending through an aperture in the rearward end of the input housing with a forward end disposed within the interior of the input housing, said output shaft freely rotatable in the rearward end aperture, coaxial with the input shaft;
- a generally disk-shaped differential coaxially mounted on the forward end of the output shaft and the rearward end of the input shaft, for free rotation on said shafts;
- a plurality of pinion gears rotatably mounted uniformly around a circumferential surface of the differential for free rotation about axes extending radially from the differential;
- a forward ring gear mounted on the interior of said input housing side wall for rotation therewith and in operable engagement with said pinion gears;
- an output housing coaxially mounted on the rearward end of said output shaft within the interior of the input housing, for rotation with said output shaft;
- said output housing including a generally disk-shaped base portion and a forwardly projecting cylindrical side wall;
- a rearward ring gear mounted on a forward edge of said output housing side wall for rotation therewith and in operable engagement with said pinion gears;
- a forward hydraulic pump rotatably mounted on said input shaft for free rotation thereon between a forward valve plate and a rearward surface of the input housing forward end;
- said forward pump presenting a plurality of bores extending therethrough parallel to said input shaft and arranged uniformly around a circle concentric to said input shaft;
- pistons disposed for reciprocating movement in the respective bores of said forward pump to displace hydraulic fluid therein;
- a forward swash plate adjustable connected to the input housing for interaction with said forward pump pistons to effect reciprocating movement thereof;
- a rearward hydraulic pump rotatably mounted on said output shaft for free rotation thereon between a rearward valve plate and the base of said output housing;
- said rearward pump presenting a plurality of bores extending therethrough and arranged with passageways through the valve plates and differential in a substantially closed hydraulic circuit with said forward pump bores, whereby fluid displaced in each pump is directed to the other pump;
- pistons disposed for reciprocating movement in the respective bores of the rearward pump to displace hydraulic fluid therein;
- a rearward fixed swash plate formed on a forward surface of the output housing base for interaction with said rearward pump pistons to effect reciprocating movement thereof;
- said rearward swash plate having a planar surface in contact with said rearward pump pistons, said surface oriented in a plane offset at a predetermined angle from perpendicular to the axis of the output shaft;
- said forward swash plate adjustable mounted for selective pivotal movement from a neutral position within a plane oriented at the same angle from perpendicular to the input shaft axis as the fixed swash plate, to a direct-drive position within a plane oriented perpendicular to the axis of the input shaft;
- said forward and rearward pumps connected to said differential for rotation therewith;
- and
- control means connected between said input housing and said forward swash plate, for selective adjustment of the forward swash plate between the neutral and direct-drive positions;
- whereby rotation of the input shaft with the forward swash plate in the neutral position will cause a transfer of fluid between corresponding bores of said forward and rearward pumps;
- and
- whereby rotation of the input shaft with the forward swash plate in the direct drive position will prevent reciprocation of the forward pump pistons, thereby preventing flow of hydraulic fluid and locking the input and output shafts at substantially identical velocity.