Low-speed/high torque (LSHT) motors are widely used to drive the rotation of the wheels on large mobile machines or of hydraulic winches. The primary requirement is start from zero speed with a high torque, something that can be difficult to achieve reliably with other units.
The motors are typically built inside the winch drum or vehicle wheel units and often include the main wheel bearings and holding brakes.
LSHT motors can be either axial or radial piston units. However, the requirement to run at low speed for long periods of time means that their design needs to be significantly different from the standard pump layout, as these will not provide sufficient hydrostatic lubrication films at low speed.
One of the most common formats uses an eccentric cam in the drum which is driven by the radial pistons pushing against balls or rollers. The pistons are connected to either high or low-pressure lines by timing port connections inside the motor.
By isolating the connections to individual pistons the motor displacement can be changed, either to provide alternative speeds for a given flow, or remove all drive and allow the motors to freewheel.
LSHT motors come with a wide range of different sizes, piston numbers and numerous brake and wheel installation options.
We have not provided details of all possibilities here as they have been covered by the earlier pump and motor discussions.
Tips for operating and maintaining
As with all hydraulics, always keep the fluid clean but also pay attention to the case leakage temperatures and flows. High leakages will be a sign of early failure and bearing flushing can be added if operating temperatures inside the motors are too high.
There are also a great many electronic and hydraulic control options available depending on requirements.
LSHT motors have good low leakage and therefore high operating efficiency characteristics.
Noise levels are low.