Abstract
There is growing interest in using electric motors as prime movers in mobile hydraulic systems. This increases the interest in so-called pump-controlled systems, where each actuator has its own drive unit. Such architectures are primarily appealing in applications where energy efficiency is important and electric recuperation is relevant. An issue with pump-controlled systems is, however, mode-switch oscillations which can appear when the pressure levels in the system are close to the switching condition. In this paper, the mode-switching behavior of different generalized closed and open circuit configurations is investigated. The results show that the choice of where to sense the pressures has a huge impact on the behavior. They also show that, if the pressure sensing components are properly placed, closed and open circuits can perform very similarly, but that mode-switch oscillations still can occur in all circuits. Active hysteresis control is suggested as a solution and its effectiveness is analyzed. The outcome from the analysis shows that active hysteresis control can reduce the risk for mode-switch oscillations significantly.
Highlights
This paper is about the control of asymmetric hydraulic actuators with individual drive units
All flow to the cylinder will pass the orifice, and larger valves or higher reservoir pressure compared to closed circuits, where only the differential flow between the cylinder chambers passes through the orifice, is required
To build in hysteresis in an electronic control unit that controls valve positions and motor speed can be considered as the most flexible and straightforward approach. This is the method that is used in the simulations presented in Section 5 and what is meant when it later is refereed to active hysteresis
Summary
This paper is about the control of asymmetric hydraulic actuators with individual drive units. The study presented in this paper is limited to system architectures based on one conventional two-port pump where valves are used to handle the differential flow from the cylinder. Such systems are highly interesting since they only require one hydraulic machine, and they can be assumed to be less costly and more compact than most other systems. The general problem with these systems is, oscillatory switching behavior between pump and motor mode This problem is the focus of this paper
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