Hydraulic Hybrid System Research Articles

ON THE DYNAMIC BEHAVIOR OF SERIES HYDRAULIC HYBRID VEHICLE

High Stopping frequency of heavy vehicles such as refuse trucks produces a large amount of energy which is generated by driving engine during vehicle acceleration. Most of this energy is wasted in form of heat to the environment when the vehicle brakes. This wasted energy normally lost during braking is significant especially in repeated stopping vehicles. This research presents a concept for the hydraulic hybrid system design using automation studio software to build the suggested hydraulic circuit. The classical mechanical traction in traditional vehicle can be replaced by this system without lowering vehicle performance and other satisfaction criteria in addition to achieving the main target from hybridization; regenerate energy which is always lost during vehicle braking and reuse to accelerate it again. It also includes the hydro- mechanical system architecture (which is called SHHS) and its component specification after changes in traditional vehicle structure. The switching matrix for control unit also illustrated. In this paper, the dynamics model for the SHHS (Series hydraulic hybrid vehicle) is constructed by MATLAB/SIMULINK package. The vehicle performance is investigated during various modes of operation at different condition.

Review of Different Energy Saving Strategies Applicable To Hydraulic Hybrid Systems Used In Heavy Vehicles

The paper reviews the different methods to improve the performance of a hydraulic system. Facing the environment problem, the efficient hydraulic hybrid system is highly demanded. Depending on the energy storage and controlling strategy of heavy vehicles the consumption of energy, emission of exhaust takes place. This paper first analyses the recent development of energy savings of the hydraulic powered heavy vehicle. The construction machinery and the automobiles use the same hybrid power system. An efficient process is designed to store the excess energy and use the same as and when demanded by the system having frequent start-stop characteristics. In the conventional method, heavy vehicles work on the lesser amount of fuel efficiency. Some of the state-of-the-art technical skills required to improve the overall efficiency and hence the fuel economy are surveyed in this article. Also, some challenges faced by the researchers and the manufacturers in this field are discussed.

Conceptual design of hydraulic hybrid test rig for engine performance enhancement

A large amount of torque is needed in moving heavy duty vehicle and machinery to achieve high acceleration speed or to perform activities at any off-road condition or rough terrain in a short time. This additional torque can be harness from hydraulic hybrid system. Hydraulic hybrid has been considered as an alternative to fulfil the increased demands on higher efficiency and better systems, components and functionality of a vehicle. In this paper, a conceptual design of hydraulic hybrid test rig for engine performance enhancement was proposed using a dynamometer test setup. A differential gear mechanism was identified as the vital component of the transmission system to couple both power generated from engine and hydraulic hybrid system.

Control strategies and optimization analyses of front-mounted parallel system

In order to recover and use the vehicle’s own braking energy as much as possible to improve fuel economy, reducing greenhouse gas emissions, this paper analyzes the braking characteristics of a certain type of heavy vehicle in the driving condition of the city, according to the structure characteristics of hydraulic hybrid system, the control strategies and processes of three working modes are proposed. By establishing the vehicle dynamic model, the simulation model was established on AMESim software, and the effect of control strategies on the performance of the whole machine were analyzed and optimized. The hardware and software system of the controller based on MATLAB/Simulink and dSPACE were developed, and the correctness of the control strategies and simulation analyses were verified by the road condition tests on the experimental prototype vehicle which was converted from a primitive heavy vehicle. Simulation and experimental results show that the proposed control policy parameters are reasonable. The hydraulic regenerative braking control strategies can reasonably distribute the ratio of hydraulic regenerative braking torque and the traditional friction torques, under the premise to ensure braking safety, the kinetic energy of the brake can be recovered and utilized efficiently, and it has good ride comfort.

Conceptual design of the hybrid hydraulic system based on adjacency matrices operations

This paper presents a new method to describe the selection design of directional control valves in the form of matrix. The directional control valves in hybrid are the basic units to implement the distribution of flow in the hydraulic system. Both the design requirements of the hybrid hydraulic system and the basic units are expressed by the adjacency matrices. Therefore, the selection design of directional control valves is the process to decompose the adjacency matrix of the system into a series of sub-matrices according to the decomposition rules. The defined rules of adjacency matrices are obtained according with the composite physical model of several valves. For obtaining easily the selection design of directional control valves, the library of basic units is established. The style of directional control valves is obtained by matching the sub-matrices with the matrices of basic units. Through configuring the others components, a thorough conceptual design process of the hydraulic system is established. Example is given to illustrate the whole design process in detail.

Development of Small Hydraulic Downhole Motors for Well Drilling Applications

Further development of the well drilling technologies becomes possible due to the improvement of rock cutting tools and hydraulic downhole motors. When developing a new hydraulic motor, it is highly important to eliminate rotor vibrations and reduce motor size. There are two main trends in further improvement of hydraulic motors: The upgrade of the downhole screw motors currently in use and the development of new reliable geared turbodrills. Besides, the R&D works are underway to construct a roller vane motor for downhole drilling. The experts of Gubkin Russian State University of Oil and Gas have launched a new R&D programme aiming at developing a hybrid hydraulic system combining the best features of a screw motor and a roller vane motor. The hybrid hydraulic system could be a radical solution to the problem of rotor vibrations in a hydraulic motor. The R&D activities conducted by Gubkin Russian State University of Oil and Gas are intended to create an advanced downhole drilling motor for the cutting tools with high-torque bits rotating at a speed of 240 to 450 rpm. The main area of application of the hybrid hydraulic motor is horizontal drilling of oil and gas fields. Yet, some R&D findings can be used for performing other production tasks, e.g., designing the pumping facilities for oil and gas extraction and pumping.

Different Rule-based Control Schemes for a Series Hydraulic Hybrid Vehicle

In a hybrid hydraulic vehicle, the hydraulic accumulator is used as the secondary power source in addition to the engine to propel the vehicle. Since the accumulator is a passive power source, it will be only used to compensate the difference between the power demand and the power delivery by the engine. Obviously, the main energy consumption is the engine. Hence a straightforward strategy to improve the fuel economy is to reduce the engine operating period. In contrast, because of the low energy density characteristic, the accumulator can only afford the required power in a short period. As a consequence, the hydraulic hybrid vehicle has been concluded only suitable for start-stop-and-go driving pattern. This paper present different rule-based control schemes for a 3.5- ton series hydraulic hybrid truck. The simulation results indicate that by applying suitable control scheme, the proposed series hydraulic hybrid system offers improvements of fuel economy for both urban and highway driving condition. The improvement is of 42.67% and 36.56% for urban and highway driving conditions, respectively in comparison with the corresponding conventional vehicle.

Optimal Power Management of Hydraulic Hybrid Mobile Machines—Part I: Theoretical Studies, Modeling and Simulation

Recent demands on improved system efficiency and reduced system emissions have driven improvements in hydraulic system architectures as well as system supervisory control strategies employed in mobile multi-actuator machinery. Valve-controlled (VC) architectures have been in use for several decades and have seen moderate improvements in terms of system efficiency. Further, throttle-less concepts such as displacement-controlled (DC) actuation have been recently proposed and successfully demonstrated efficiency improvements in numerous prototypes (wheel-loaders, excavators, and skid-steer loaders) of different sizes. The combination of electric or hydraulic hybrid systems for energy recovery (for a single actuator) with VC actuation for the rest of the actuators has also been recently deployed by original equipment manufacturers (OEMs) on some excavator models. The combination of DC actuation together with a series hydraulic hybrid actuator for the swing drive has been previously proposed and implemented as part of this work, on a mini-excavator. This combination of highly efficient DC actuation with hydraulic hybrid configuration allows drastic engine downsizing and efficiency improvements of more than 50% compared to modern-day VC-actuated systems. With a conservative, suboptimal supervisory control, it was previously demonstrated that over 50% energy savings with a 50% downsized engine over the standard load-sensing (LS) architecture for a 5-t excavator application. The problem of achieving maximum system efficiency through near-optimal supervisory control (or system power management) is a theoretically challenging problem, and has been tackled for the first time in this work for DC hydraulic hybrid machines, through a two-part publication. In Part I, the theoretical aspects of this problem are outlined, supported by simulations of the theoretically optimal supervisory control as well as an implementable, near-optimal rule-based supervisory control strategy that included a detailed system model of the DC hybrid hydraulic excavator. In Part II, the world's first prototype DC hydraulic hybrid excavator is detailed, together with machine implementation of the novel supervisory control strategy proposed in Part I. The main contributions of Part I are summarized below. Dynamic programming (DP) was employed to solve the optimal supervisory problem, and benchmark implementable strategies. Importantly, the patterns in optimal state trajectories and control histories obtained from DP were analyzed and identified for different working cycles, and a common pattern was found for engine speed and DC unit displacements across different working cycles. A rule-based strategy was employed to achieve near-optimal system efficiency, with the design of the strategy guided by optimal patterns. It was found that the strategy replicates optimal system behavior with the same rule for controlling engine speed for different cycles, but different rules for the primary unit (of the series-hybrid swing drive) for different cycles. Thus, in terms of practical implementation of a rule-based approach, the operator is to be provided with a family of controllers from which one can be chosen so as to have near-optimal system behavior under all kinds of cyclical operation.

State of Charge Estimator Design for a Gas Charged Hydraulic Accumulator

The gas charged hydraulic accumulators under consideration are used as energy storage devices in automotive hydraulic hybrid systems. The knowledge of the state of charge (SOC) is of utmost importance for an efficient energy management of the hybrid drive-train. Since the direct measurement of the SOC is difficult and costly, an SOC estimator design is presented based on a mathematical model of the gas charged hydraulic accumulator. Two different SOC estimation strategies, a signal-based approach and an Extended Kalman-filter, are presented and compared with each other. The performance of the estimators is validated by means of measurement results of a test driving cycle.

Development and Analysis of Small Scale Water Accumulator by Using Piston Type

An accumulator is an auxiliary component in a hydraulic system as it stores the energy and avoids the pump from running continuously through the system which can reduce the pumps life. The accumulator is also used as the power source in the hydraulic hybrid system to accelerate the vehicle. A common hydraulic system uses the hydraulic oil as their working medium, but there is an application using water due to the high accessibility and environmental concern. In this paper, an accumulator is developed by using weighing method to increase the pressure in the system. This system uses water as a medium to provide clean environment as well as safe for mobile purpose. The system includes electric motor, water pump, directional control valve, pressure control valve and motor hydraulic. The performance of the accumulator is obtained by measuring the ratio of output and input pressure. The source of electricity is varied by using an inverter to control the frequency and the power of the pump. From the experiment, the pressure output and flow rate decreased with the increasing of the loads on top of the accumulator, while the pressure loss increased with the number of load. The operational frequency is optimal at a low reading compared to a higher frequency.

Analysis of the Wheel Loader Hydraulic Hybrid System Based on Braking Energy Recovery

The wheel loader will release a lot of energy in the process of reducing the speed and braking. In the paper it introduced the types and features of the loader hydraulic hybrid system, analyzed configuration, energy saving scheme and working state of the loader parallel hydraulic hybrid system. The results show that the parallel hydraulic hybrid system is applied to the loader, not only it can efficiently recovery braking energy, but also it can improve the dynamic performance of the loader, so the engine can work in the optimal fuel economy area, improve fuel economy.

Implementable Strategy Research of Brake Energy Recovery Based on Dynamic Programming Algorithm for a Parallel Hydraulic Hybrid Bus

The purpose of this paper is to develop an implementable strategy of brake energy recovery for a parallel hydraulic hybrid bus. Based on brake process analysis, a dynamic programming algorithm of brake energy recovery is established. And then an implementable strategy of brake energy recovery is proposed by the constraint variable trajectories analysis of the dynamic programming algorithm in the typical urban bus cycle. The simulation results indicate the brake energy recovery efficiency of the accumulator can reach 60% in the dynamic programming algorithm. And the hydraulic hybrid system can output braking torque as much as possible. Moreover, the accumulator has almost equal efficiency of brake energy recovery between the implementable strategy and the dynamic programming algorithm. Therefore, the implementable strategy is very effective in improving the efficiency of brake energy recovery. The road tests show the fuel economy of the hydraulic hybrid bus improves by 22.6% compared with the conventional bus.

Dynamic Analysis and Design Optimization of Series Hydraulic Hybrid System through Power Bond Graph Approach

The availability of natural gas and crude oil resources has been declining over the years. In automobile sector, the consumption of crude oil is 63% of total crude oil production in the world. Hence, automobile industries are placing more emphasis on energy efficient hydraulic hybrid systems, which can replace their conventional transmission systems. Series hydraulic hybrid system (SHHS) is a multidomain mechatronics system with two distinct power sources that includes prime mover and hydropneumatic accumulator. It replaces the conventional transmission system to drive the vehicle. The sizing of the subsystems in SHHS plays a major role in improving the energy efficiency of the vehicle. In this paper, a power bond graph approach is used to model the dynamics of the SHHS. The obtained simulation results indicate the energy flow during various modes of operations. It also includes the dynamic response of hydropneumatic accumulator, prime mover, and system output speed. Further, design optimization of the system is carried out to optimize the process parameters for maximizing the system energy efficiency. This leads to increase in fuel economy and environmentally friendly vehicle.

Modeling, Simulation and Design Optimization of a Series Hydraulic Hybrid Vehicle

Crude oil resources in the world continue to diminish; automobile, agricultural machinery and construction machinery manufacturing companies are placing more emphasis on energy efficient series hydraulic hybrid systems which can replace their conventional transmission systems. Series hydraulic hybrid system is a mechatronics system with two source of power (that includes prime mover and hydro-pneumatic accumulator) which drives the vehicle. Even though, it has been proven as an energy efficient system, sizing of the components or sub-system for automobiles has got a major influence on energy efficiency of vehicle. In this paper, a power bond graph approach is used to model the dynamics of series hydraulic hybrid system and simulation results elucidate various modes of operations. It also shows the dynamic response of hydro-pneumatic accumulator, prime-mover and system output speed. Further, design optimization of system is carried out to optimize the physical /process parameters for the maximum system's output energy that, leads to increase in energy efficiency and environmental friendly vehicle.

Experiment for a Parallel Hydraulic Hybrid Terminal Tractor

Hydraulic hybrid technology of vehicle has the potential to significantly improve fuel economy and reduce emission, and increasingly aroused the attention of the research institutions and automotive manufacturers all over the world. The main of this work is to design a parallel hydraulic hybrid system for a heavy terminal tractor. Firstly, overall scheme design, construction design, and hydraulic regenerative braking system (HRBS) for terminal tractor are designed. Furthermore, the hydraulic hybrid terminal tractor is refitted successfully. The test results show that the sample vehicle is credible and in good operation, a fuel economy improvement of the new scheme is 38.1%~61.6% more than conventional baseline. Experimental study has very important value in the hydraulic hybrid terminal tractor real application.

Logic Threshold Based Energy Control Strategy for Parallel Hydraulic Hybrid Vehicles

To improve the performance of a Parallel Hydraulic Hybrid Vehicle (PHHV), the operation of components in the hydraulic hybrid system of the vehicle should be well coordinated. This study introduces an energy control strategy based on the logic threshold methodology for PHHVs. The energy distribution of the PHHV can be controlled in real-time and the operation modes of the PHHV can be changed dynamically by means of this energy control strategy. A simulation model for the analysis of the whole vehicle dynamic performance is developed using the Simulink in MATLAB. The multi-objective Genetic Algorithm (GA) optimization method is employed to get the optimal working modes, the best energy distribution in different drive cycles and the optimal parameters of the control strategy. In this optimization, maximum fuel economy is the objective and the difference of engine optimal torque and active pressure torque and the pressure limit are the variables of the GA optimization. The simulation results show that the fuel economy of the PHHV can be improved and in addition, the dynamic performance of the vehicle can be enhanced with the proposed energy control strategy.

Vehicle Hydraulic Brake Energy Storage System Design

Simple description the background of hydraulic hybrid technology, scope of application. Put forward the idea of hybrid hydraulic system design based on the car's braking performance, the main elements parameter calculation. Simulation results show that the braking process is smooth, brake energy recovery, the system design and parameter calculation of reasonable.

Theoretical investigations on the effect of system parameters in series hydraulic hybrid system with hydrostatic regenerative braking

As gasoline prices rise and the green movement grows, more fluid power companies are working to develop hydraulic hybrid drive trains for large trucks to passenger cars and wind turbines. The hydraulic hybrid drive system is more effective and efficient than traditional hybrid systems because the quantum of recuperation energy generated is comparatively very high. Series hydraulic hybrid system specially designed for stop-and-go vehicles captures energy as the vehicle brakes and puts the vehicle in motion, when the vehicle is restarted. Then the engine kicks in, once the energy captured gets depleted. The kinetic energy lost as heat energy during mechanical friction braking is recovered and stored in the hydraulic accumulator as potential energy during hydrostatic regenerative braking. This paper gives an insight in to the dynamic simulation results obtained using LMS AMESim tool and effect of various system parameters like pre-charge pressure and hydraulic pump/motor maximum displacement on system output power. Varying the pre-charge pressure of the accumulator and controlling the hydraulic pump/motor maximum displacement show significant improvement in the system output power. Maximizing the system output power indirectly leads to less fuel consumption and pollution reduction in hybrid vehicles.

The Study on Optimal Matching of Power System of Hybrid Hydraulic TLT

According to the running characteristic of an aircraft tractor and the specificity of serve target, the hybrid hydraulic system program is proposed. In the use of Adopting Simulated Annealing Genetic Algorithm, for the demand of aircraft tractor’s system, the multi-objective is transformed to a single objective function of the automobile’s dynamic performance and fuel economy performance by using the linear weighted method. Then the mathematical optimizing model of the powertrain is established, through calculating, reasonable parameters are gotten. The analysis of the simulation results shows that the comprehensive performance of the automobile has been remarkably promoted. On the basis of previous work, the system pressure of different weight aircraft models of traction has been optimized in order to give full play to the vehicle's performance. The research has important reference value for the theory analysis of hybrid systems and engineering applications.

Research on the system configuration and energy control strategy for parallel hydraulic hybrid loader

Aimed 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 components 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.