Design and testing of a multi-cylinder piezo pump for hydraulic actuation

Hydraulic actuation systems are widely used in industries such as aerospace, marine, off-highway vehicles, and manufacturing. There is a move away from hydraulic distribution of power from a centralised supply to electrical power distribution, to reduce maintenance requirements and weight, and to improve efficiency. However, hydraulic actuators have many advantages, such is power density, durability and contollability, and so the ability to locally convert electrical to hydraulic power to drive an actuator is important. Traditional hydraulic pumps are inefficient and unsuitable for low power application, and so piezopumps offer a promising alternative for converting electrical to hydraulic power in the sub-100W range. Currently, the use of piezopumps is severely limited by their maximum power (typically a few watts or less) and low flows which can be provided. This paper details the design, simulation and testing of a multi-cylinder piezopump which is intended to push the envelope of possible power output. Simulation results demonstate that pumps with 2 or 3 cylinders show increasing benefits in terms of hydraulic and electrical performance due to reduced flow and current ripple compared to a single cylinder pump. Experimental results from a two cylinder pump confirm this, and the effect of the phase relationship between the drive signals is investigated in detail. The experimental pump exhibits fast-acting disc-style reed non-return valves allowing piezostack drive frequencies upto 1.4kHz to be used. Custom power electronics tailored to the pump requirements were developed in unison. These features were critical in demonstrating the potential for multicylinder piezopumps to play an important role as a future actuation solution.