Demonstration of Efficient Energy Recovery Systems Using Digital Displacement® Hydraulics

Abstract

Heavy off-road vehicles using conventional hydraulic systems waste significant energy through the throttling of fluid to control the motion of their actuators. This paper demonstrates how Digital Displacement® Pump Motors (DDPMs) can be used to enable efficient hydraulic energy recovery systems for these vehicles by controlling the motion of actuators directly without the need of throttling. Experiments were carried out on a test rig consisting of a 10 tonne boom supported by a hydraulic ram designed to mimic the setup of a heavy off-road vehicle. In order to demonstrate the DDPM’s potential for energy recovery systems the round-trip efficiency was measured by lifting and lowering the boom. The round-trip efficiency was taken to be the ratio of the mechanical energy output from the DDPM, when motoring to lower the boom, to the mechanical energy input to the DDPM, when pumping to raise the boom, over a known ram extension. The results showed measured round-trip efficiencies of between 63% and 87% over a range of pressures, shaft speeds and displacement fractions. Measured data obtained during the test was used to simulate the test using different system architectures and components to determine the energy efficiency. Both load sense and displacement controlled systems were simulated using both swashplate and Digital Displacement pumps. Comparison showed that the Digital Displacement systems used between 1.1 and 10.8 times less energy than the equivalent swashplate based systems. This work forms the basis for further development of energy recovery system architectures using DDPMs. Future challenges include development of the actuator control valves and transformers required to implement such systems.

Experimental Investigations of Partially Valve-, Partially Displacement-Controlled Electrified Telehandler Implements

“…In studies that focus on dynamic performance, very often a similar setup can be found with only one cylinder that applies the power-train concept of interest that has a mechanical load structure installed that involves realistic inertia and kinematic chains as on the real HDMM. In [16], for example, the original stick mechanism of a backhoe is incorporated into the test rig, and in [17], the full-size boom structure of a 16-tonne excavator is installed on a stationary rig for testing the lift cylinder. Still, those test rigs involve only one actuator, while the interest in this paper is on the interplay of multiple implement actuators.…”

“…Furthermore, the efficiency or consumption of the whole implement system with all major actuators is of interest; thus, boom, tilt, and telescope cylinders should be present in the setup connected by the real kinematic chains. Accordingly, setting up a test rig for a single actuator as in [14][15][16][17], would not be effective. Instead, an existing conventional nine-tonne telehandler has been chosen as the test platform, which can be seen in Figure 1, to incorporate the original kinematic chains, inertia, and control interface.…”

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“…Recent tests at Danfoss using a DDPM with a loaded linear actuator have shown that between 78%-88% of the energy originating from the prime mover can be recovered. 36…”

Simulation Analysis of a Novel Digital Pump with Direct Recycling of Hydraulic Energy

“…John Hutcheson et al utilized the digital displacement pump motor as a controlling element to directly control the motion of the actuator. Without throttling loss, the digital displacement system saved 1.1-10.8 times of energy through the comparison of their simulation outcomes [25]. Jill Macpherson et al carried out a backwardfacing simulation on an 18-ton excavator with the bus system architecture.…”