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Efficient, Controllable, Digital

Digital Displacement Technology is based on a simple fundamental idea: Only use the cylinders that are required to meet the demand.

Through development of this concept, Digital Displacement hydraulic machines represent a true leap forward in hydraulic machine control and energy efficiency.  Adopting the radial piston format and providing each piston with its own individually controlled solenoid valve, idle losses are minimised and high bandwidth control is available through switching on the cylinders on a cycle by cycle basis.

Pump idle - 12ms - 320x320

All six cylinders of one bank of a pump idling. The low-pressure valves above the cylinders are open and oil moves into and out of the cylinders at low pressure.  No work is done on the fluid and this is true even if the system pressure is at 420 bar.

Pump enabled - 12ms - 320x320

When commanded to pump, the low-pressure valve above each cylinder closes as its respective piston reaches bottom-dead-centre.  This initiates the pumping stroke and the high-pressure valve opens to deliver oil to the external circuit.

Efficiency can be thought of as how much useful work gets done in comparison to the work wasted to machine losses.  Digital Displacement pumps reduce pressurised losses by selectively enabling cylinders to meet load demand.  In comparison to the swashplate mechanism, which cannot offload cylinders but instead reduces the stroke to reduce output, losses in the DD machine scale almost linearly with the amount of flow being produced.  In a swashplate pump, leakage and frictional losses cannot be avoided and a common method of improving efficiency is to reduce the shaft speed using a costly variable frequency drive.  Digital Displacement pumps achieve similar savings in terms of energy consumption but using conventional motors.

DDP 200 bar pressurised idle

Digital Displacement Pump 200 bar pressurised idle

Swash plate pump 200 bar pressurised idle

Swash plate pump 200 bar pressurised idle

Efficiency comparison of DDP and common swash-plate industrial pump

Through the use of a solenoid valve on each piston, high bandwidth control over the pump output can be achieved.  The decision to use a cylinder is made on a shaft turn by shaft turn basis in order to meet the pressure demand set in the pump controller.

Digital Displacement introduces a new concept to hydraulic pump control in the form of true pressurised idle.  With the shaft spinning and no demand to produce flow, all pistons are isolated from any line pressure and therefor incur minimal losses.  From the idle state, full flow can be achieved within 30ms independantly of working pressure.

Conventional hydraulic machines suffer from high radiated noise caused by port plate depressurisation.

This noise is pervasive and excludes hydraulics from some application areas such automotive or noise critital production or test environments.

Digital Displacement pumps don’t contain a port plate and compression energy in the cylinder is fully recovered before the low pressure valve poppet opens.

    • Digital Displacement reduces losses by approximately 90% in comparison to a similarly sized axial piston pump

 

    • 30ms response time to demand, independent of pressure

 

    • Low investment in prime mover – induction motor plus soft starter / DOL

 

    • Reduction in fluid cooling requirement

 

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