This paper presents a novel approach to digital pumps and motors with electronic controlled valves for each working chamber in positive displacement machines. The approach is focused on low speed operation of hydraulic pumps and motors.
When applied to High Torque Low Speed radial piston units with eccentric shaft it offers increased efficiency, increased power capacity, more compact design, displacement control and a number of other control features.
The proposed valve system has out-wards opening poppet-type valves on both the high- and low pressure side. This solution allows for a symmetric valve arrangement, enabling the units to operate as traditional motors/pumps with traditional distributor valves as well as to be used in simplified system layouts where full advantage is taken of the technology.
This is opposed to current solutions having poppet type valves opening inwards on the low-pressure side and outwards on the high-pressure side, requiring dedicated high- and low pressure ports, also on motors.
New opportunities and challenges are discussed, among which are four quadrant operation, displacement variation, start and stop, valve timing, overpressure protection and valve actuators.