Hydrostatic transmission

Hydrostatic/hydraulic

• Reduced efficiency. Gears are one of the most efficient methods of mechanical power transmission, with efficiencies as high as 90 percent in many cases. In contrast, few hydrostatic transmission systems achieve more than about 65 percent efficiency. This is due to a combination of internal losses in the pump and motor(s), and losses in the piping and valves.
• Higher cost. For a given level of power-transmitting capacity, a hydrostatic CVT will be more expensive to produce than an equivalent geared transmission. In addition to the pump and motor(s), a hydrostatic system requires the use of an oil reservoir, piping and in many applications, an oil cooler, this last item being necessary to dissipate the waste heat that results from hydrostatic power transmission's relatively low efficiency.
• Greater weight. Due to the high oil pressure at which a hydrostatic CVT operates, the pump and motor(s) are under considerable mechanical stress, especially when maximum power and loading is being applied. Hence these items must be very robust in construction, typically resulting in heavy components. Additional weight will be found in the oil reservoir and its oil load, as well as the piping and valving.