Since 1994, the development
of advanced hydraulic machines has been led by our spin-out company
Artemis Intelligent Power Ltd
Most hydraulic system
loads need variable flow for their proper operation. Conventionally
this can be achieved in three ways. One is through flow control
valves which alter the flow at the expense of energy loss. Variable
swash-plate axial-piston machines are frequently employed for hydrostatic
drives where energy becomes a consideration. Less commonly, a fixed
displacement pump can be driven by a variable speed prime-mover.
A new technique, originally developed for the power-take-off for
the Duck, provides yet another way of controllably transferring
energy between mechanical and fluid power. This technology is now
referred to as 'Digital Displacement®'.
is a registered trademark of Artemis Intelligent Power Ltd
The basic structure of
these new machines is similar to that of tthe conventional reciprocating
machine, with poppet valves connecting to the low and high-pressure
manifolds of each cylinder. But, instead of being self-acting, each
of the poppet valves is equipped with an electro-magnetic actuator.
The valves are operated by a micro-controller at precise times,
near the ends of the stroke, in order to establish fluid connection
between the moving piston and the appropriate manifold. This control
allows cylinders to behave in any of the three ways, they can pump
or motor - adding or subtracting fluid from the high pressure manifold
- or they can be disabled. The function of each cylinder can be
changed at each end of each stroke. As the valves are actuated at
times in the cycle when there is almost no pressure difference across
them, the actuators can be compact and use little power. Either
permanent magnets or springs are used to maintain the disabled poppets
at default positions. A micro-controller controls the valves from
its output port via a bank of power semiconductors. The figure below
shows the cylinder head arrangement of a single cylinder Digital
Displacement® pump-motor which can be
run under pressure-control, flow-control or ternary-mode of cylinder
head of single-cylinder pump-motor
Rampen bending girders
- Fast response
: These machines are capable of attaining either full
or zero output from any starting condition, in less than a single
with micro-processor : The compatibility with micro-processors
allow the use of advanced control logic. Also the same machine
can be used as a pump, a motor or both.
- Higher efficiency
: As disabled cylinders are not pressurised, losses are
reduced in comparison with swash-plate machines leading to higher
efficiency, especially at part load.
of pump-motors : Unlike conventional machines banks of
radial pump-motors can be combined along a common shaft and used
as a summing junction of both torque and power whilst providing
isolation between services. Accumulators may be used in conjunction
with some of the banks to transfer power in or out of the system.
The radial configuration provides good force balancing and gives
optimal space for the mechanical components like valves and bearings.