Classification and Review of Pump-Controlled Differential Cylinder Drives

Abstract

Pump-controlled hydraulic cylinder drives may offer improved energy efficiency, compactness, and plug-and-play installation compared to conventional valve-controlled hydraulic systems and thus have the potential of replacing conventional hydraulic systems as well as electro-mechanical alternatives. Since the late 1980s, research into how to configure the hydraulic circuit of pump-controlled cylinder drives has been ongoing, especially in terms of compensating the uneven flow requirements required by a differential cylinder. Recently, research has also focused on other aspects such as replacing a vented oil tank with a small-volume pressurized accumulator including the consequences of this in terms of thermal behavior. Numerous references describe the advantages and shortcomings of pump-controlled cylinder drives compared to conventional hydraulic systems or electro-mechanical drives. This paper presents a throughout literature review starting from the earliest concepts based on variable-displacement hydraulic pumps and vented reservoirs to newer concepts based on variable-speed electric drives and sealed reservoirs. By classifying these drives into several proposed classes it is found that the architectures considered in the literature reduce to a few basic layouts. Finally, the paper compares the advantages and shortcomings of each drive class and seek to predict future research tasks related to pump-controlled cylinder drives. IntroductionWith an increased industrial focus on energy efficiency, plug-and-play installation, and compactness, conventional valve-controlled hydraulic cylinder drives are increasingly being replaced by electro-mechanical alternatives, such as roller or ball screws [1], especially for small power classes. This happens despite the well-known advantages of hydraulic linear actuation such as large force/power densities, reliability, and robustness. Hydraulic actuation is, however, still the preferred solution for many applications such as industrial presses, large mobile machinery, crane manipulators, primary aircraft control etc. [2][3][4]. Among other reasons this is due to certain limitations for the electro-mechanical alternatives, such as limited reliability (e.g., shock loads damage), the difficulties of implementing overload/failure protection and/or limited force capabilities [5][6][7]. To strengthen the position regarding these applications and to make hydraulic cylinder drives competitive with electro-mechanical drives for low power applications, there is a need to enhance both the energy efficiency and the overall flexibility of hydraulic cylinder drives.The flexibility of a hydraulic system may be related to how power is being distributed between the prime mover and the actuator(s). As illustrated in Figure 1, at least three different power distribution topologies exist: hydraulic, mechanical, and electrical distribution.

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

“…which are numbered here as one through five and defined as: (1) : the external force, (2) , : forces from commanded accelerations by adjusting the velocity command sent to the electric motor, (3) : frictional forces, (4) : forces arising from transient pressure changes as a result of a previous valve switch, (5) , : forces due to oscillations of the mass . The analysis presented here was conducted using an abrupt change in the external force.…”

“…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.…”

A Comparison Study of a Novel Self-Contained Electro-Hydraulic Cylinder versus a Conventional Valve-Controlled Actuator—Part 1: Motion Control

“…Current commercial solutions of the SCC technology are limited and typically tailor-made [8], especially the ones developed for load-carrying applications that are required to contain passive load-holding devices, according to the safety regulations (e.g., ISO 17096 and DNVGL-ST-0378). Then, the research emphasis is primarily on different electro-hydraulic configurations [10][11][12][13], for low-power servo applications [14][15][16][17]. There is, therefore, a lack of experimental studies comparing state-of-the-art, valve-controlled technology for load-carrying applications to self-contained hydraulic cylinders in the technical literature, both in terms of motion performance and energy efficiency.…”

Enabling Energy Savings in Offshore Mechatronic Systems by using Self-Contained Cylinders

“…An alternative solution to the inefficient VCC is a "valve-less" pump controlled (electro-hydraulic) cylinder drive. Pump-controlled concepts using standard differential cylinders are classified and reviewed in Ketelsen et al (2019). In literature, research related to compact electro-hydraulic cylinders is primarily on cost efficiency and low power applications (less than 5 [kW ]).…”