Speed-Variable Switched Differential Pump System for Direct Operation of Hydraulic Cylinders

Schmidt, Lasse; Roemer, Daniel Beck; Pedersen, Henrik C.; Andersen, Torben Ole

doi:10.1115/fpmc2015-9575

Cited by 19 publications

(19 citation statements)

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“…To avoid low-pressure operation, which is an inherent feature of the double pump configuration [77,78] added a third pump which is only active in the forward direction, see Figure 6c. Using advanced control functionality, it is possible to control the pressure level (i.e., the minimum chamber pressure) and thus the drive stiffness during motion.…”

Section: Class B-variable-speed Single Prime Mover With Multiple Pumpsmentioning

confidence: 99%

Classification and Review of Pump-Controlled Differential Cylinder Drives

et al. 2019

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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.

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Section: Class B-variable-speed Single Prime Mover With Multiple Pumpsmentioning

confidence: 99%

Classification and Review of Pump-Controlled Differential Cylinder Drives

et al. 2019

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“…The only difference from the formulation given in Equation 15is about the flow area that depends on the valve command. Then, the flow rate of both the CVs and the RVs is computed according to Equation (19). The evoked parameters are the valve flow gain (kv,i), the cracking pressure (pc,i), the inlet pressure (pIn,i), and the outlet pressure (pOut,i).…”

Section: The Dynamic Modeling Of the Systemmentioning

confidence: 99%

Section: The Dynamic Modeling Of the Systemmentioning

confidence: 99%

“…It is based on multiple fixed-displacement pumps/motors driven by a common variable-speed prime mover. Alternatives with two hydraulic units [6,[16][17][18] or with three hydraulic units [19][20][21] exist.…”

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confidence: 99%

“…Table 1 provides a synthesis of these options. [6,[16][17][18][19][20][21]46] Additionally, limited researches addressed passive load-holding capabilities for SCCs. This feature serves the purpose of maintaining a given actuator position without supplying any power to the system.…”

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A Self-Contained Electro-Hydraulic Cylinder with Passive Load-Holding Capability

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Self-contained electro-hydraulic cylinders have the potential to replace both conventional hydraulic systems and the electro-mechanical counterparts enhancing energy efficiency, plug-and-play installation, and reduced maintenance. Current commercial solutions of this technology are limited and typically tailor-made, whereas the research emphasis is primarily on cost efficiency and power applications below five [kW]. Therefore, there is the need of developing more flexible systems adaptable to multiple applications. This research paper offers a contribution in this regard. It presents an electro-hydraulic self-contained single-rod cylinder with passive load-holding capability, sealed tank, capable of recovering energy, and scalable up to about eighty [kW]. The system implementation on a single-boom crane confirms its feasibility: The position tracking error remains well within ±2 [mm], oscillations are limited, and the overall energy efficiency is about 60 [%] during actuation. Concerning the passive load-holding devices, it is shown that both vented and non-vented pilot-operated check valves achieve the desired functioning and can hold the actuator position without consuming energy. Additional observations about the size and the arrangement of the load-holding valves are also provided. In conclusion, this paper demonstrates that the proposed self-contained cylinder can be successfully extended to several practical applications, especially to those characterized by overrunning external loads and the need of securing the actuator position.

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