Energy Saving Potential in Knuckle Boom Cranes using a Novel Pump Controlled Cylinder Drive

This paper is considering the application of a novel pump controlled cylinder drive, the so-called Speed-variable Switched Differential Pump (SvSDP), for knuckle boom crane actuation. Especially the control system for the SvSDP drive is considered, and aiming on improving energy efficiency a refinement of the existing control structure is proposed. An energy efficient sizing algorithm for the SvSDP drive is developed, and fundamental differences between the achievable operating range for the SvSDP drive compared to a conventional valve-cylinder drive are discussed. A case study is conducted with knuckle boom crane actuation, and compared to a conventional valve actuation. Simulation results show that the motion tracking performance is on a similar level compared to the valve actuation approach, while the energy consumption is drastically decreased. For the given test trajectory the valve actuation system consumes 0.79 kWh of electrical energy, while the SvSDP drive consume 0.06 kWh, if ideal energy recovery and storage is assumed

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

This paper presents a self-contained pump-controlled hydraulic linear drive including an innovative load holding sub-circuit. For safety critical applications such as crane manipulators, locking valves or load holding valves are enforced by legislation, but the load holding functionality may also be used actively to decrease the energy consumption for applications where the load is kept stationary for longer periods of time. The system proposed in this paper is based on a simple hydraulic architecture using two variable-speed electric motors each connected to a fixed-displacement pump. This architecture is well-known in academic literature, but in this paper a novel load holding sub-circuit has been included. To control this load holding functionality, the low chamber pressure needs to be controlled accurately, while still being able to control the motion of the cylinder piston as well. Due to strong cross-couplings between cylinder piston motion and chamber pressures this task is non-trivial. The control for opening the locking valves is indirect in the sense that it is controlled via the chamber pressures, which are actively controlled. The fundamental control strategy presented in this paper is based on transforming the highly coupled physical states to virtual states, significantly reducing cross-couplings.publishedVersio

Bootstrap reservoir concepts for electro-hydraulic compact cylinder drives

This paper presents a conceptual study aiming to improve the compactness of electro-hydraulic compact drives (ECD ). In most current ECD architectures, gas accumulators are used as volume compensators for the flow imbalance emerging whenever asymmetric single rod cylinders are used. To stay within a required reservoir pressure range typically from two to four bar, a large gas volume is required, compromising system compactness. Combining conventional ECD architectures with a bootstrap reservoir offers a greater degree of freedom in system design, which enables downsizing or avoidance of the gas volume. Another potential benefit by including a bootstrap reservoir is the possibility of elevating the backpressure of the ECD thus enhancing drive stiffness, expanding the application range and market acceptance. Based on an open analysis of the solution space occurring when introducing a bootstrap reservoir, three system architectures are selected for a conceptual study. The results show that the downsizing potential is strongly dependent on the maximum friction force and the area ratio of the bootstrap reservoir pistons, while a linear analysis reveals that for some system architectures the bootstrap reservoir may severely influence the system dynamics. Simulation results confirm the functionality of the proposed system architectures, and show that a potential for downsizing/avoiding the gas volume, as well as increasing the ECD stiffness is present

Thermo-Hydraulic Modelling and Experimental Validation of an Electro-Hydraulic Compact Drive

Electro-hydraulic compact drives (ECDs) are an emerging technology for linear actuation in a wide range of applications. Especially within the low power range of 5–10 kW, the plug-and-play capability, good energy efficiency and small space requirements of ECDs render this technology a promising alternative to replace conventional valve-controlled linear drive solutions. In this power range, ECDs generally rely on passive cooling to keep oil and system temperatures within the tolerated range. When expanding the application range to larger power classes, passive cooling may not be sufficient. Research investigating the thermal behaviour of ECDs is limited but indeed required for a successful expansion of the application range. In order to obtain valuable insights into the thermal behaviour of ECDs, thermo-hydraulic simulation is an important tool. This may enable system design engineers to simulate thermal behaviour and thus develop proper thermal designs during the early design phase, especially if such models contain few parameters that can be determined with limited information available. Our paper presents a lumped thermo-hydraulic model derived from the conservation of mass and energy. The derived model was experimentally validated based on experimental data from an ECD prototype. Results show good accuracy between measured and simulated temperatures. Even a simple thermal model containing only a few thermal resistances may be sufficient to predict steady-state and transient temperatures with reasonable accuracy. The presented model may be used for further investigations into the thermal behaviour of ECDs and thus toward proper thermal designs required to expand the application range.publishedVersio

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

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