Displacement machine in which the geometric displacement per cycle can be changed. For design-based reasons, this is only possible for vane and piston constructions.
Variable pumps can be adjusted from the maximum to zero or through zero to the maximum negative (reversing pump), while for variable motors the range from maximum to zero is sufficient.
The advantage of a variable pump is its low power loss, as it only transports as much as is required in the respective case (pump control, primary control).
Variable motors are needed for hydrostatic transmissions with secondary adjustment or primary-secondary adjustment as well as for secondary control .
Variable motor