A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. A mechanical torque transfer arrangement transfers torque between the first shaft of the first hydraulic unit and a rotatable housing of the second hydraulic unit. One of the first and second hydraulic units operates as a hydraulic pump and the other operates as a hydraulic motor, and both of the first and second hydraulic units have variable displacement.

In a transmission of the present invention, a transmission case has a peripheral wall with an opening sized to allow an HST to be other than a main plate of the HST. The HST has the main plate and a sub-plate sandwiching members out of a center section, a pump-side holder and a motor-side holder that face to each other with the pump main body and the motor main body being arranged between the members. The sub-plate has an engaging portion, and the transmission case has a mounting seat with which the engaging portion is engaged in a slidable manner so that the HST is guided until an installation position.

In a transmission of the present invention, a transmission case has a peripheral wall with an opening sized to allow an HST to be other than a main plate of the HST. The HST has the main plate and a sub-plate sandwiching members out of a center section, a pump-side holder and a motor-side holder that face to each other with the pump main body and the motor main body being arranged between the members. The sub-plate has an engaging portion, and the transmission case has a mounting seat with which the engaging portion is engaged in a slidable manner so that the HST is guided until an installation position.

A hydrostatic transmission includes a pump running surface and a motor running surface connected by internal porting formed in a housing member. A valve is disposed in the housing and connects a sump formed by the housing and the internal porting. A trunnion includes a first arm engaged to a swash plate to rotate the swash plate to vary the output of the pump, and a second arm which rotates with the first arm, the second arm having an operative end that is capable of opening the valve to permit a hydraulic connection between the internal porting and the sump through the valve bore when the trunnion is rotated to a predetermined position.

A hydrostatic transmission includes a pump running surface and a motor running surface connected by internal porting formed in a housing member. A valve is disposed in the housing and connects a sump formed by the housing and the internal porting. A trunnion includes a first arm engaged to a swash plate to rotate the swash plate to vary the output of the pump, and a second arm which rotates with the first arm, the second arm having an operative end that is capable of opening the valve to permit a hydraulic connection between the internal porting and the sump through the valve bore when the trunnion is rotated to a predetermined position.

In a transmission of the present invention, a transmission case has a peripheral wall with an opening sized to allow an HST to be other than a main plate of the HST. The HST has the main plate and a sub-plate sandwiching members out of a center section, a pump-side holder and a motor-side holder that face to each other with the pump main body and the motor main body being arranged between the members. The sub-plate has an engaging portion, and the transmission case has a mounting seat with which the engaging portion is engaged in a slidable manner so that the HST is guided until an installation position.

In a transmission of the present invention, a transmission case has a peripheral wall with an opening sized to allow an HST to be other than a main plate of the HST. The HST has the main plate and a sub-plate sandwiching members out of a center section, a pump-side holder and a motor-side holder that face to each other with the pump main body and the motor main body being arranged between the members. The sub-plate has an engaging portion, and the transmission case has a mounting seat with which the engaging portion is engaged in a slidable manner so that the HST is guided until an installation position.