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Research activities
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Hybrid mobile hydraulics for excavators
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0D models of axial piston pumps/motors
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CFD studies on conical poppet valves
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CFD analysis of gerotor pumps
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Lumped parameter models of crescent pumps
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Lumped parameter models of vane pumps
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Lumped parameter models of gerotor pumps
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Coupled simulation of telehandler hydraulics
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Modelling of brake booster vacuum pumps
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Absorbed energy in ICE lubricating pumps
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Multi-body simulation of axial piston pumps
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Development of variable flow lubricating pumps
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Optimization of ICE lubrication gerotor pumps
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Publications
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Research projects
Energy analysis of hybrid energy-efficient mobile hydraulics for excavators
Improving energy efficiency in mobile hydraulics is critical for environmental and economic reasons. A promising trend suggests the electrification of machines, in which electric motors drive hydraulic pumps coupled to actuators. This approach removes the flow control valves and allows energy recovery. However, the entire power managed by the hydraulic linear actuators must pass through the electric machines. This feature is not feasible for medium-high power applications as they require electric motors with high power and large generation of electricity on board. Therefore, this study applies to a hydraulic excavator arm the idea of splitting the power transferred to/from the actuator between the hydraulic and electrical domains (i.e., a centralized hydraulic power supply is involved). The goal is to reduce the power rating of the electrical components while maintaining the high power of the hydraulic actuator.
The reference vehicle used for this study is a 9-ton commercial excavator with an installed power of approximately 50 kW. The hydraulic circuit powers five linear actuators shown in Figure 1 and three hydraulic motors for the two tracks and the cabin swing. The hydraulic circuit is based on the principle of load sensing with flow sharing. The simulations were carried out in the Simcenter Amesim® version 2021.1 environment. The arm kinematics was simulated using the 2D Mechanical library.
In Figure 1 the view of the main actuators in the excavator is shown.
Figure 1
The excavator reference model has been validated through experimental tests. The test cycles consisted of individually supplying each directional control valve with the maximum positive and negative command signal for the movement of the related actuator. The delivery pressure and the delivered flow rate of the pump have been measured. Engine speed was also recorded.
In the new hybrid circuit (figure 2), the internal combustion engine drives an electric generator and a fixed displacement pump PU1. The generator is used to charge a supercapacitor battery which, in turn, powers four electric motors. One drives the cabin rotation directly (swing supercomponent), while the other three drive a respective motor-pump connected to an actuator (electro-hydraulic modules EH1, EH2, EH3). The fixed displacement pump, together with a gas-charged hydraulic accumulator, maintains the pressure in the common rail line within a range, so that the hydraulic circuit is supplied with an approximately fixed supply pressure. Depending on the load on the respective actuator, the motor-pump can act as a pump or motor by exchanging energy both with the hydraulic circuit and on the electric circuit.
Figure 2
Different architectures were evaluated in a digging cycle based on the JCMAS standard.
The results have shown the expected system operation and efficiency benefits: depending on the layout, fuel savings from 28% to 38% compared to the original excavator. Almost 60% of the energy is transferred to the actuators hydraulically minimizing the power rating of the electric machines in favor of the cost and compactness of the system. Finally, the proposed hybrid design also has a general validity being modular, scalable and applicable to different hydraulic machines.
In Figure 3 the cumulative energy managed by the electro-hydraulic modules EH in the digging cycle is shown. Positive energy is supplied to the actuators, negative is received by the actuators.
Figure 3
More analyses and details are available in:
PADOVANI D, RUNDO M, ALTARE G, 2020: The Working Hydraulics of Valve-Controlled Mobile Machines: ...
ALTARE G, PADOVANI D, NERVEGNA N, 2013: A Close-up View of a Load Sensing "Hybrid" PDCV