Axial tapered piston bent axis piston A2F6.1 quantitative structure with fixed displacement, hydrostatic drive is used as a pump or motor in open or closed loop. When used as a quantitative piston pump, flow proportional to the drive speed and displacement. When the quantitative piston pump as a motor, the output proportional to the flow speed and inversely proportional to the displacement. Quantitative piston pump with the pressure drop between the output torque of the high pressure side and low pressure side and increased.