【正文】 Research on the system configuration and energy control strategy for parallel hydraulic hybrid loaderSun Hui, , Jing JunqingJiangsu Xuzhou Construction Machinery Research Institute, Jiangsu, ChinaAccepted 30 October 2009. Available online 22 November 2009., How to Cite or Link Using DOIPermissions amp。 ReprintsAbstractAimed at the frequent starts/stops operation characteristics of the loader, an energy saving scheme with parallel hydraulic hybrid system is proposed to regenerate and reuse the braking energy normally lost in a conventional loader. Hydraulic hybrid system is designed and sized to capture braking energy from normal–moderate braking operating modes while ensures hybrid system working in higher efficiency region. According to the higher power density characteristic of hydraulic hybrid system, the regenerative braking strategy and energy reuse strategy are designed to coordinate all the powertrain ponents in an optimal manner while satisfying performance constraints of loader. Energy controller using logic threshold approach is built up to control the dynamic transitions among the various operation modes. Simulation and experimental results show the parallel hydraulic hybrid loader (PHHL effectively recovered and reused the braking energy, improved the working performance of loader and effectively reduced the fuel consumption.KeywordsLoader。 Hydraulic hybrid system。 Braking energy regeneration。 Energy management。 Hydraulic pump/motor1. IntroductionWith the rising concern in a global scale environmental issue, energy saving in automobiles is a very important subject [1]and[2]. Offroad vehicles have been paid much attention in the field of energy saving and environment protection, for the reason of their large application quantities, high fuel consumption and bad emissions [3]. Loader has the characteristics of frequent starts/stops and larger vehicle weight which generated significant amounts of braking energy. Usually, this part of energy is wasted by the frictional braking system which caused the energy loss and heat generation in the system. Therefore, the braking energy recovery and reuse is a promising way to improve fuel economy and working performance of offroad vehicles [4]and[5]. There is a wealth of literature focused on hybrid electric engineering vehicles, but the publications devoted to hydraulic propulsion options are relatively scarce [6]and[7].A parallel hydraulic hybrid loader is one that contains two sources of power, with one source being an internal bustion engine. The other power source is hydraulic pump/motor and accumulators. One feature of PHHL is the ability to recover energy normally lost during braking and store the energy in a hydraulic accumulator. The stored energy is used to provide the total mand power during loader launching or provide auxiliary traction power during shoveling operation mode, which avoids the engine working in the regions of low efficiency and significant emissions. In this paper, an energy saving scheme with parallel hydraulic hybrid system is proposed to capture the braking energy normally lost to friction brakes. Hydraulic hybrid system is designed and sized to capture braking energy from normalmoderate braking operating modes while ensures hybrid system working in higher efficiency region. According to the advantage of high power density for hydraulic accumulator and the operation characteristics of loader (stopandgo duty cycles, the regenerative braking strategy and energy reuse strategy are designed to coordinate all the powertrain ponents in an optimal manner while satisfying performance constraints. Energy control strategy is built up around the concept of multilevel hierarchic control system. PHHL simulation model and the control system simulation model based on the proposed energy control strategy are developed in Matlab/Simulink environment. Experimental results and simulation results demonstrate that PHHL with proposed control strategy effectively improves the fuel economy and working performance.2. Configuration of the PHHL. Operating principle of PHHLFig.1 presents the configuration of proposed PHHL, which consists primarily of an engine, hydraulic torque converter, boom tanks, dump tanks, a high pressure accumulator, a hydraulic reservoir, a variable displacement hydraulic pump, and a variable displacement hydraulic pump/motor unit, clutch, transmission, torque coupler and differential. The hydraulic pump/motor is coupled to the propeller shaft via a torque coupler. Engine is the power source of the loader, one part of the engine power is used to drive the loader through hydraulic torque converter and transmission, the remainder part of engine power is used to realize the shifting and loading functions by means of hydraulic cylinders. Hydraulic regenerative system, which consists of a hydraulic pump/motor, hydraulic accumulator, hydraulic reservoir and hydraulic relief valve, et al. drives the loader together with the engine. During deceleration, the hydraulic pump/motor decelerates the loader while operating as a pump to capture the energy normally lost to friction brakes in a conventional loader. Also, when the vehicle brake is applied, the hydraulic pump/motor uses the braking energy to charge the hydraulic fluid from a low pressure hydraulic accumulator into a highpressure accumulator, increasing the pressure of the nitrogen gas in the high pressure accumulator. The high pressure hydraulic fluid is used by the hydraulic pump/motor unit to generate torque during the next acceleration [8]and[9]. Hydraulic pump/motor is designed and sized to capture braking energy from normal, moderate braking events and is supplemented by friction brakes for aggressive braking. While shoveling and digging, the hydraulic pump/motor works in motor mode to provide auxiliary traction power for the loader which ensures the engine working in better fuel economy region and reducing the overflow losses of hydraulic system.Fig.