Variable displacement hydraulic pumps

[wolfy3]

In online examples of variable displacement systems with swash-plate pumps, the input pump & motor are usually of equal size. When the constant RPM input pump is at full tilt (max displacement) the fixed displacement motor is at the same RPM for a 1:1 ratio, and when the pump is at no tilt (no displacement) the motor doesn't turn at all, 1:0 ratio. So, the output can reach the same speed or lower.

If a design requirement was that ratio is 1:3 at maximum displacement, would designing the input pump's pistons to be larger, moving 3 times the volume of the motor's pistons do the trick? I'm trying to design a hydrostatic system for a vehicle, but haven't seen any examples of where the output is speed can be faster than the input. Thanks in advance.

 

[gtoguy97]

Yes, designing the input pump's pistons to be larger, moving 3 times the volume of the motor's pistons would achieve your goal of a 1:3 ratio at maximum displacement. However, it is important to note that the output speed can only be increased if you also increase the input speed. This means that, for example, if you have an input pump with a constant RPM of 1000, the output motor will be able to reach a maximum of 3000 RPM if the piston size is 3 times larger.