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In this study, a novel hydraulic energy-regenerative system was presented from its proposal through model-ing to its control. The system was based on a closed-loop hydrostatic transmission and used a hydraulic ac-cumulator as the energy storage system fabricated in a novel configuration to recover the kinetic energywithout any reversion of the fluid flow. 50734
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The displacement variation in the secondary unit was reduced, in-creasing the uses of several types of hydraulic pump/motors. The proposed system was modeled based onits physical attributes. A hierarchal control system was implemented and focused on the design of an adap-tive fuzzy sliding mode control for speed control of the secondary unit. The energy utilization and the influ-ences on the energy-recovery potential of the system were analyzed. Simulation and experiments wereperformed to evaluate the validity of the employed mathematical model and the effectiveness of the controlsystem. The experimental results indicated that the designed system was effective and that the round trip re-covery efficiency varied from 22% to 59% for the test bench. 1. IntroductionEnergy conservation has become increasingly important due to in-creases in fuel prices and environmental pollution. Energy-saving sys-tems based on hybrid concepts have been studied to reduce energyconsumption and exhaust emissions from cars, trucks [1–6], earthmovers and construction machines (i.e.,. wheel loaders, excavators,harvesters) [7–9]. Energy-saving systems may be classified into anumber of types: electric, mechanical, and hydraulic systems use bat-teries, flywheels, and hydraulic accumulators, respectively. The struc-ture, characteristics and applicability of these energy-saving systemswere previously summarized and analyzed [10]. Hydraulic energy-saving systems are promising technologies because of their high re-covery efficiency and high specific power.Two main types of loads are handled by construction equip-ment, linear motion and rotational motion loads. Most studies ofenergy conservation in construction machinery concentrate on re-ducing the energy consumption of hydraulic linear actuators[7–9]. In contrast, rotational loads such as winch systems or trav-elers on wheel loaders or excavators have very high energy regen-erative potentials [8]. Previous studies have not addressed theenergy regeneration of rotational loads, but analyzed structure,control strategy and energy management of hydraulic hybrid sys-tems. The hydraulic systems evaluated in previous studies were of the flowcoupling type, andmost of the energy savings resulted fromre-duced losses via throttling control, engine control or recovered energyfrom the potentials of the loads or the arms源!自`优尔'文"论/文`网[www.youerw.com of excavators [11–15].In this study, we developed a closed-loop hydraulic energy-regenerative system for use in rotational motion load systems.Rotational motion load hydraulic systems, constant pressure sys-tems (CPS),
secondary control systems with two common rails(CPR), and electro-hydraulic actuators (EHA) have been consideredas energy-regenerative systems. The CPS systems employ a fly-wheel with an auxiliary hydraulic pump/motor so that they areable to recover the kinetic energy of the load and reuse the recov-ered energy. However, if the efficiency of one component waslow, which often occurred for the flywheel pump/motor, the over-all round-trip efficiency was very low [3]. The EHA systems havebeen proven high recovery efficiency and good performance. How-ever, the cost and the low specific power for the EHA systems usingbatteries or the low specific energy for the EHA systems using supercapacitors are the drawbacks of the EHA systems [2].Moreover,inpractice, the primary power source is usually a combustion enginebecause the addition of electric motors, generators, and batteries ina limited space is not a viable solution. The CPR system includestwo common rails: a high-pressure line connected with high-pressure accumulators and a low-pressure line connected directlyto a tank, resulting in an appearance similar to that of an electricnetwork. Thus several secondary units could be used both simulta-neously and independently. Pumps were used to control the pres-sure, while the speeds of the loads were controlled by adjustingthe displacements of the secondary units. CPR systems have beenshown to have good performance and energy-saving potentials inseveral applications [16]. However, the low efficiency of the secondary unit, its influence on other units, and fluid inertia aredisadvantages of such systems [4–6].The proposed system is a novel closed-loop hydrostatic transmis-sion (HST) system with two hydraulic accumulators. The system hadenergy recovery potential and good performance.