Digital Displacement® (DD) technology is a fundamental advance in fluid power.
Conventionally, hydraulic pumps and motors are controlled varying the stroke of the pistons with an adjustable mechanism. They are robust, compact and low cost, but suffer from poor energy efficiency over typical duty cycles and suffer from the delay and inaccuracy of analog control. Despite these drawbacks, hydrostatic power transmission is used in applications where the benefits outweigh the drawbacks, such as mobile work vehicles and industrial machinery. However, large markets such as automotive transmissions and wind turbines are ruled out by the poor overall efficiency.
Digital Displacement® is a fundamental advance. Instead of varying the stroke mechanically, the output is controlled by digitally enabling individual cylinders on a stroke-by-stroke basis. Each cylinder is provided with electronically-controlled digital valves, capable to change state in few milliseconds. Each cylinder may be switched from idle, motoring or pumping cycles once every shaft revolution, in a pattern determined by an embedded controller. This results in much faster and more accurate control response compared to variable-stroke machines.
DD machines exhibit superior part-load efficiency, because cylinders which are not needed for the present demand will default to an “idle” state, in which they have very little parasitic energy loss. Conventional machines pressurise all cylinders on every stroke, suffering high fixed losses from bearing loads, leakage and oil compressibility, leading to poor part-load efficiency.
A comparison of the efficiency and energy losses of the E-dyn 96 Digital Displacement® pump with a conventional 70cc/rev swash plate pump is shown below. The measured loss results of the 70cc/rev swash plate pump are normalised to 96cc/rev to be directly comparable to E-dyn96.
Over a typical duty cycle, DD machines show a quarter of the energy losses of conventional machines. This translates into significant energy costs savings, as well as reducing oil heating.
For a fixed industrial application, the figure below shows the calculated electrical energy cost reduction of a 96cc/rev DDP compared to a swashplate pump, on the basis of continuous operation.
At the 1.6MW scale for wind turbines, the machines are even more efficient: AIP has demonstrated the most efficient hydraulic transmission ever built, with 93.5% peak efficiency from shaft-to-shaft, and a wide range of efficient operation even at part load. Working with MHI, we have built 7MW transmissions for offshore wind application.
Making such machines has required development by AIP of multiple technology areas:
* Ultra-fast digitally-controlled valves, exhibiting low pressure drop and high reliability;
* Design of machines from the scale of a few kW to multi-megawatt
* Embedded control electronics
* Simulation models predicting energy efficiency and dynamic response;
* Novel system architectures and control systems
AIP keeps all core development in-house, mixing mechanical, electronic, software and simulation engineers in a single creative environment including design, workshop, prototype build and test rigs up to 4MW capacity.
In the process, AIP has filed over 50 patent families, and dozens more with partner companies. AIP’s innovation has been recognised with innovation awards from the IET, Rushlight and The Carbon Trust.
Contact us to find out how Digital Displacement® technology can enhance your product.