Optimal Control and Energy-Saving Analysis of Common Pressure Rail Architectures: HHEA and STEAM

In recent years several novel hydraulic architectures have been proposed with the intention of significantly increasing system efficiency. Two of these architectures, Steigerung der Energieefflzienz in der Arbeitshydraulik mobiler Arbeitsmaschinen (STEAM), and the Hybrid Hydraulic-Electric Architecture (HHEA), use a system of multiple common pressure rails (CPRs) to serve the multiple degrees-of-freedom of the machine. The key difference is that STEAM throttles hydraulic power from these rails while HHEA combines electric and hydraulic power to meet actuator demands. As a throttle-less architecture, HHEA is expected to save more energy than STEAM at the expense of added complexity. Therefore, it is useful to quantify this additional energy saving. Both systems have discrete operational choices corresponding to how the CPRs are utilized for each actuator. It is necessary to determine optimal operation for each of these architectures for analysis and fair comparison. Techniques for optimal operation of the HHEA have been developed previously from the Langrange multiplier method. Applying the same optimal control method to STEAM encountered some technical challenge leading to the optimal control algorithm not being able to satisfy certain constraints. The issue is analyzed and solved by adding noise to the optimization. Using this proposed algorithm, case studies are performed to compare the energy-saving potentials of STEAM and HHEA for two sizes of excavators and a wheel-loader performing representative duty cycles. The baseline is a standard load-sensing architecture. Results show that STEAM and HHEA can reduce energy consumption between 35–65% and 50–80% respectively.

Pressure characteristics of a novel double rotor hydraulic transformer

The hydraulic transformer is the core component when it works with the common pressure rail system, which integrates the functions of the pump and the motor, and thus possesses sensitive pressure characteristics. The rotating speed has significant influence on the pressure characteristics of a hydraulic transformer while it has not been considered previously. In this study, aimed at improving the working performance, a novel double rotor hydraulic transformer is proposed and a comprehensive mathematical model considering the dynamic characteristics of the cylinder block is established. At the same time, a prototype is made and the experiment is conducted. The test results show that the robust rotor structure enables a larger pressure range, and the numerical results exhibit a good match with the test results. The parameter sensitivity study shows that the delivery pressure is mainly subject to the valve plate control angle δ and, under the effects of the resistance torques, pressure loss will occur especially under a large control angle and a high rotating speed. The magnitude of the instantaneous angular velocity fluctuation increases sharply when the speed is lower than 400 r/min, which is the main reason for the serious pressure pulsation at a low speed. As a result of the improved low-speed stability and output flow uniformity, the pressure pulsation rate of the double rotor hydraulic transformer is greatly reduced. However, the pulsation rate is still high at an extremely low speed. In addition, when the rotating speed exceeds the capability of the damping grooves, the pressure undershoot becomes serious at the A-T transition region around the control angle of −30°. Consequently, from the perspective of pressure characteristics, the limitation on the rotating speed under small control angles is suggested for the design of the double rotor hydraulic transformer controller.

Robust controller design for the excavator swing system under the active regulating common pressure rail

In this paper, a new kind of rule called Active Regulating Common Pressure Rail (ARCPR) for hydraulic system is presented. Especially, the main focus is to improve the control performance for the swing hydraulic system with the parametric uncertainties and time delay effect caused by employing ARCPR. Firstly, the traditional CPR is introduced and the energy saving potential is analyzed. Then, the mathematical model of the displacement regulating system and swing driving system is presented. Moreover, the displacement regulating system model is simplified by considering the parametric uncertainties and time delay condition. Furthermore, a robust controller is designed to meet the system requirements. Finally, a simulation based on standard working condition is conducted and the result shows the control performance can meet the practical requirement well.

Passivity Based Backstepping Control for Trajectory Tracking Using a Hydraulic Transformer

Throttling loss is a major contributor to the low system efficiency in hydraulic systems. Hydraulic transformers can potentially be an energy efficient, throttle-less control approach for multi-actuators systems powered by a common pressure rail (CPR). The transformer transforms the input CPR pressure to the desired pressure of the actuator instead of throttling it. Regenerative energy can also be captured. For transformers to be useful, they must also have good control performance. This paper presents a a passivity based trajectory tracking controller for a hydraulic actuator driven by a transformer consisting of two mechanically coupled variable displacement pump/motors. In addition to controlling the motion of the actuator, the transformer speed can also be regulated at the most efficient operating speed. The nonlinear controller is designed using a Lyapunov function that is based upon a recently discovered natural energy storage function for hydraulic actuators. Experimental results validate the efficacy of this controller.

Parameter Matching Analysis of Hydraulic Hybrid Excavators Based on Dynamic Programming Algorithm

In order to meet the energy saving requirement of the excavator, hybrid excavators are becoming the hot spot for researchers. The initial problem is to match the parameter of each component, because the system is tending to be more complicated due to the introduction of the accumulator. In this paper, firstly, a new architecture is presented which is hydraulic hybrid excavator based on common pressure rail combined switched function (HHES). Secondly, the general principle of dynamic programming algorithm (DPA) is explained. Then, the method by using DPA for parameter matching of HHES is described in detail. Furthermore, the DPA is translated into the M language for simulation. Finally, the calculation results are analyzed, and the optimal matching group is obtained.

Observer-Based Robust Control for Hydraulic Velocity Control System

This paper investigates the problems of robust stabilization and robust control for the secondary component speed control system with parameters uncertainty and load disturbance. The aim is to enhance the control performance of hydraulic system based on Common Pressure Rail (CPR). Firstly, a mathematical model is presented to describe the hydraulic control system. Then a novel observer is proposed, and an observed-based control strategy is designed such that the closed-loop system is asymptotically stable and satisfies the disturbance attenuation level. The condition for the existence of the developed controller can by efficiently solved by using the MATLAB software. Finally, simulation results are provided to demonstrate the effectiveness of the proposed method.

Energy-Saving Analysis of Hydraulic Hybrid Excavator Based on Common Pressure Rail

Energy-saving research of excavators is becoming one hot topic due to the increasing energy crisis and environmental deterioration recently. Hydraulic hybrid excavator based on common pressure rail (HHEC) provides an alternative with electric hybrid excavator because it has high power density and environment friendly and easy to modify based on the existing manufacture process. This paper is focused on the fuel consumption of HHEC and the actuator dynamic response to assure that the new system can save energy without sacrificing performance. Firstly, we introduce the basic principle of HHEC; then, the sizing process is presented; furthermore, the modeling period which combined mathematical analysis and experiment identification is listed. Finally, simulation results show that HHEC has a fast dynamic response which can be accepted in engineering and the fuel consumption can be reduced 21% to compare the original LS excavator and even 32% after adopting another smaller engine.

Dual-Pump Hydraulic Hybrid Excavator with Combined Common Pressure Rail and Valve-Controlled System

To solve the low efficiency problem of hydraulic excavator, one type of Dual-Pump hydraulic architecture with combined Common Pressure Rail (CPR) and traditional valve controlled system is presented. Firstly, we analyze the energy consumption of excavator during one cycle to know the energy distribution among each actuator. Then, the Dual-Pump system is explained to design an easy to modify, cost efficient hydraulic hybrid excavator. Moreover, we focus on the boom system and construct the model. Finally, a simulation is created and the results illustrate that the proposed system can satisfy the design requirement.