Hydraulic transmission

A hydraulic transmission to permit a drive engine to operate in a range of optimum fuel efficiency comprising a primary unit having a plurality of hydrostatic pumps driven by said drive engine to supply fluid from a reservoir to a pressure line, first clutch means disposed between said drive engine and at least one of said hydrostatic pumps of said primary unit, means for automatically actuating said first clutch means in response to the pressure in said pressure line, an accumulator communicating with said pressure line for accumulating fluid, a second unit connected to said pressure line having a plurality of hydrostatic machines, said secondary unit operable to provide a drive torque to a load in a first operating mode, said secondary unit further operable to provide a braking torque to said load in a second operating mode, second clutch means disposed between said load and at least one of said hydrostatic machines of said secondary unit, means for actuating said second clutch means in response to the desired torque to be delivered by said hydrostatic machines to said load, said first and said second clutch means being actuated by the pressure generated in said transmission, at least one of said hydrostatic machines comprising an axial piston type hydrostatic machine of the bent axis design having a plurality of pistons and a drive shaft, said axial piston type hydrostatic machine including, an inlet port for receiving fluid, an outlet port for delivering fluid, a conical friction clutch disposed between said drive shaft and said pistons, a swash plate cooperating with the pistons defining the drive flange of said conical friction clutch, said drive shaft defining the driven clutch member of said conical friction clutch, said conical friction clutch being automatically actuated by hydraulic pressure forces generated in said machine.