A Class of Energy Efficient Self-Contained Electro-Hydraulic Drives with Self-Locking Capability

Abstract

Pump controlled and self-contained electro-hydraulic cylinder drives may improve energy efficiency and reduce installation space compared to conventional valve solutions, while being in line with the trend of electrification. The topic has gained increasing interest in industry as well as in academia in recent years. However, this technology has failed to break through in industry on a broad scale, with the reason assumed to be lack of meeting industry requirements. These requirements include high drive stiffness enabling a large application range, and the ability to maintain cooling and filtration in required ranges, enabling proper reliability and durability. Furthermore, at this point the cost of realization of such drives is comparable only to high end valve drive solutions, while not providing dynamics on a similar level. An initiative to improve this technology in terms of a class of drives evolving around a hydraulic cylinder locking mechanism is proposed. The resulting class of drives generally rely on separate cylinder forward and return flow paths, allowing for fluid cooling and filtration as well as control of the drive stiffness. The proposed class of drives is analyzed regarding energy loss and recovery potential, a basic model based control design is realized, and the industrial feasibility of the drive class is considered. It is found that the proposed class of drives may be realized with standard components maintained in their design ranges at competitive costs compared to conventional valve solutions. Furthermore, it is found that pressure levels may be controlled in a proper way, allowing to produce either highly efficient operation or a high drive stiffness.

A Novel Solution for the Elimination of Mode Switching in Pump-Controlled Single-Rod Cylinders

“…Assuming p 1 > p 3 before the switch, p 1 must decrease to p 3 after the valves switch, whereas p 2 must increase to fulfill Equation (8). During this transition, from the SSL and the definition of the hydraulic force, the valves will switch a second time if p 2 < p − 2 , with p − 2 defined as:…”

“…This results in different flows into, and out of, the cylinder, which must be handled for proper operation of the actuator. Several solutions exist, involving either, the use of multiple pumps or auxiliary valves [5][6][7][8]. Conceptually, the simplest solution involves a switching valve arrangement that connects one of the cylinder chambers to a hydraulic reservoir, displacing the differential flow to and from the reservoir as the actuator is operated.…”

“…Under certain operating conditions, the switching valve arrangement may oscillate, reversing its connections rapidly, even for a constant input (i.e., constant velocity of the electric motor, or displacement of the pump). This results in oscillations of the pressures and velocity of the actuator, which may lead to reduced performance and loss of control over the actuator [8][9][10]. This phenomenon is commonly referred to as mode switching, first described by Williamson and Ivantysynova [12].…”

Energy-Efficient Robust Control for Direct Drive and Energy Recuperation Hydraulic Servo System

“…However, the existing literatures regarding the hydraulic servo system usually concentrated on the improvement of tracking performance due to the difficulties result from the highly nonlinear nature of the plant. Actually, the energy consumption is also a big issue that needs to be dealt with [14][15][16][17]. To achieve the two targets simultaneously, both the control law and the hardware configuration should be taken into account.…”

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 2: Energy Efficiency

“…SCCs can in fact enhance energy efficiency, modular design, plug-and-play installation, and reduced maintenance [12]. Current commercial solutions of the SCC technology are limited and typically tailor-made, whereas the research emphasis is primarily on different electro-hydraulic configurations [13][14][15][16], energy-efficiency [17][18][19][20][21], thermal analysis [22][23][24], and low-power servo applications [25]. According to the survey presented in [10], compact and self-contained solutions comprising passive load-holding devices, able to operate in four quadrants, and suitable for power levels above 5 kW are missing, both on the market and four quadrants, and suitable for power levels above 5 kW are missing, both on the market and in the technical literature.…”