Electro-hydraulic Power Steering Research Articles

A Comparison of Hydraulic and Electro-Hydraulic Power Steering Control Systems for Increasing Energy Efficiency

A Comparison of Hydraulic and Electro-Hydraulic Power Steering Control Systems for Increasing Energy Efficiency

Parameters optimization of electro-hydraulic power steering system based on multi-objective collaborative method

Electro-hydraulic power steering (EHPS) systems are widely used in commercial vehicles due to their adjustable power assist and energy-saving advantages. In this paper, a dynamic model of the EHPS system is developed, and quantitative expressions for three evaluation indexes, steering road feel, steering sensibility and steering energy loss, are derived for the first time. A multi-objective collaborative optimization model of the EHPS system is then established, which consists of one total system and three parallel subsystems, based on collaborative optimization theory. Considering the coupled variables of each subsystem, the total system is optimized by a multi-objective algorithm, while the subsystems are optimized by a single-objective algorithm. The optimization results demonstrate that the average frequency domain energy of the steering road feel is increased by 69.1%, the average frequency domain energy of steering sensitivity is reduced by 19.2%, and steering energy consumption is reduced by 10.8% compared to the initial value. The non-dominated sorting genetic algorithm-II (NSGA-II) shows superior comprehensive performance compared to the other two multi-objective algorithms, and the optimization performance can be further improved by setting appropriate algorithm parameters.

Design and implementation of human driving data-based lane-keeping assistance system for electric bus

This paper describes design, implementation, and evaluation of human driving data-based Lane Keeping Assistance System (LKAS) for electric bus equipped with a hybrid electric power steering system. The hybrid electric-power steering system used in this study means a steering system in which an Electric Power Steering (EPS) system and an Electro-Hydraulic Power Steering (EHPS) system are integrated into a ball-nut. A dynamic model of hybrid EPS system including EHPS system and EPS system has been developed to generate EPS torque and EHPS force corresponding to the input torque. In order to determine proper timing of LKAS intervention, driving data of electric bus drivers were collected and driving patterns were analyzed using a 2-D normal distribution probability density function. Lane information necessary for the lane-keeping assistance system is obtained from a vision camera mounted on the electric bus. Sliding mode control is used to get a Steering Wheel Angle (SWA) required for LKAS. A Proportional–Integral (PI) control is used to obtain an overlay torque required to track the target SWA. A proposed DLC threshold has been validated using vehicle simulation software, TruckSim, and MATLAB/Simulink. It is shown that the proposed DLC threshold shows good performance in both cases of slow lane departure and fast lane departure. The proposed algorithm has been successfully implemented on the electric bus and evaluated via real-world driving tests. Test scenario setting and the evaluation of performance were carried out by ISO 11270 criteria. It is shown that the algorithm successfully prevented the electric bus from unintended lane departure satisfying ISO 11270 criteria.

Robustness Analysis of an Electrohydraulic Steering Control System Based on the Estimated Uncertainty Model

The impossibility of replacing hydraulic drives with other type drives in heavy duty machinery is the main reason for the development of a system for controlling hydraulic power steering. Moreover, the need for remote automatic control of the steering in specific types of mobile machinery leads to significant scientific interest in the design of embedded systems for controlling electro-hydraulic steering units. This article introduces an approach, which has been developed by authors, for robust stability and robust performance analysis of two embedded systems for controlling electro-hydraulic power steering in mobile machinery. It is based on the suggested new more realistic “black box” SIMO model with output multiplicative uncertainty. The uncertainty is obtained by parameters confidence interval and Gauss approximation formula. The embedded control systems used a linear-quadratic Gaussian (LQG) controller and H∞ controller. The synthesis of the controllers was performed on the basis of a nominal part of an uncertainty model. Robust stability and robust performance analyses were performed in the framework of a so-called structured singular value, μ. The obtained theoretical results were experimentally approved by real experiments with both of the developed control systems, which were physically realized as a laboratory test rig.

Robust μ-Controller for Hydraulic Spool Valve, Pilot Operated with Switching Micro Valves

Hydraulic spool valve, pilot operated with bi-state switching micro valves is a low-cost alternative to the conventional proportional and high-response valves. However, high-frequency switching causes variations in the control flow which limits achievable spool tracking error. This paper presents the design of a robust μ-controller for the spool position reference tracking synthesized with D-K iterative procedure. Furthermore, in order to reduce wind-up effects in the closed-loop, the μ-controller is decomposed to a canonical observer and state feedback components which allows explicit introduction of the saturated control signal in the controller equations. The uncertainty model required for the μ-synthesis is inferred from the nonlinear hydraulic model by identification of a Box–Jenkins model set characterized by its parameter covariance matrix. The regulator is implemented in a 32-bit programmable logic controller (PLC) and its performance is experimentally verified on a laboratory test bench of electro-hydraulic power steering system.

Testing and optimization of noise of an electrohydraulic power steering pump

Testing and optimization of noise of an electrohydraulic power steering pump

GA-tuning of Multivariable PID Controller for Electrohydraulic Load-Sensing Servo System

The main purpose of this article is to present the design, optimal setting and experimental study of a multivariable PID controller supposed for electrohydraulic power steering system with load-sensing function. The set of the controller is performed through an optimization procedure based on a genetic algorithm. The PID controller is embedded into a microcontroller for mobile machinery used in laboratory test rig for investigation of an electrohydraulic servo steering system. Results obtained in conditions of physical experiment and numerical simulation with the optimally tuned PID controller are presented. An analysis of the control performance, as well as some features of the used method for setting the PID controller.

Study on tie rod force characteristics in electro-hydraulic power steering system for heavy vehicle

The tie rod is one of the key components affecting the steering stability and reliability in the steering system of heavy vehicles. In order to meet the heavy load steering requirements of heavy vehicles, the steering system is universally the electro-hydraulic power steering system (EHPSS). The hydraulic actuators used in the EHPSS are double hydraulic cylinders, which are connected in series and symmetrically installed in this study. The hydraulic drive system in the steering system will affect the steering mechanism of stress state, leading to the tension of the tie rod in most working conditions. The tie rod be compressed only in extremely unequal loading of dual-tires. The tie rod force model is established based on Lagrange equation and verified by the tie rod test platform. Three key parameters describing the force rule of tie rod are obtained by adopting quasi-steady state analysis method, including pump pressure, difference value and sum value of left and right tires steering resistance torque. Pump pressure is the key factor affecting the tie rod force. The higher the pump pressure is, the greater the pull force of tie rod is. The steering resistance torque will further affect the variation law of the tie rod force. In the analysis when the tire at middle position, with the increase of difference value of steering resistance torque, the tie rod force offset between loading conditions and no-load conditions increases. When the tire turns from the middle to both sides, the increase of sum value of steering resistance torque will result in the rising of tie rod force change rate. This study reveals the variation law and key parameters of the tie rod force of heavy vehicles. It can provide basis for stability and reliability design of steering system.

Integral Sliding-Mode Tracking Control for Heavy Vehicle Electrohydraulic Power Steering System

Since heavy vehicles need all-terrain adaptability and large load drive capability, the dual hydraulic cylinders symmetrically arranged and connected in series are widely used in their steering system, which is quite different from the traditional electrohydraulic power steering systems. Accurate steering control for this dual hydraulic system is challenged due to its complicated structure and a wide range of steering loads. To solve this issue, an improved integral sliding-mode control (ISMC) is presented in this article. Specifically, a hyperbolic tangent function is integrated into the controller to mitigate the chattering caused by the sliding mode. A stability analysis is then conducted based on the finite-time Lyapunov stability theory, revealing the proposed controller's capability of achieving the asymptotic convergence of the tracking error within a finite time. A test bench is also established to experimentally validate the controller's effectiveness through multiple test scenarios, including various tire loads, supply pressures, and command signals frequencies. The results show that the tracking error of ISMC is kept within 0.5°, which is significantly superior to PID control. In addition, the ISMC can achieve high-precision control under lower supply pressure, showing the energy-saving potential of nonlinear control for the steering system in heavy vehicles.

Coordinated control strategy for vehicle electro-hydraulic compound steering system

In order to reduce steering energy consumption and improve steering feeling of heavy commercial vehicle, a novel electro-hydraulic compound steering system is proposed, which combines the function of electro-hydraulic power steering and electric power steering. The electro-hydraulic compound steering system dynamic model is established and the coordinated control strategy of dual actuators is proposed by analyzing the structure and dynamic characteristics of electro-hydraulic compound steering system. The genetic algorithm is used to optimize the steering assist torque distribution, and an Elman neural network predictive controller with fuzzy compensation is designed to solve the nonlinear problem of the electro-hydraulic compound system. Finally, the simulation is carried out by using Amesim/Simulink. The simulation results show that the coordinated control strategy designed in this paper enables the electro-hydraulic compound steering system significantly better than the traditional electro-hydraulic power steering system in steering feeling and energy consumption.

Advanced Embedded Control of Electrohydraulic Power Steering System

Abstract The article presents a developed embedded system for control of electrohydraulic power steering based on multivariable uncertain plant model and advanced control techniques. The plant model is obtained by identification procedure via “black box” system identification and takes into account the deviations of the parameters that characterize the way that the control signal acts on the state of the model. Three types of controller are designed: Linear-Quadratic Gaussian (LQG) controller, H∞ controller and μ-controller. The main result is a performed comparative analysis of time and frequency domain properties of control systems. The results show the better performance of systems based on µ-controllers. Also the robust stability and robust performance are investigated. All three systems achieved robust stability which guarantees their workability, but only the system with µ-controller has robust performance against prescribed uncertainties. The control algorithms are implemented in specialized 32-bit microcontroller. A number of real world experiments have been executed, which confirm the quality of the electrohydraulic power steering control system.

Optimal three-loop cascade PI-P-PI controller for electro-hydraulic power steering system

The present paper presents an optimally tuned proportional integral differential (PID) system which calculates the driving signal for the switching valves in order to achieve steering trajectory tracking. The designed cascade control algorithm consists of three PID controllers respectively for the spool valve position, for the effective flow rate and for the steering cylinder position. The stages of the cascade control algorithm synthesis are presented. The goals of control algorithm are to achieve fast transients with minimal overshot and steady state error. Controllers’ are tuned consequently by starting from the innermost loop based on an identified single-input multiple output (SIMO) model of the steering system by optimization algorithm with a quadratic cost. After one of the controllers is successfully tuned the model of the corresponding closed loop system is approximated and employed in the optimization procedure for the next control loop from the cascade system. The developed control algorithm is programmed into a specialized vehicle microcontroller and tested on a steering system test bench in the laboratory.

Energy analysis and optimization design of vehicle electro-hydraulic compound steering system

In order to reduce the vehicle steering energy consumption and improve the steering road feeling, this work proposes an electro-hydraulic compound steering (EHCS) system, which combines the functions of electric power steering (EPS) and electro-hydraulic power steering (EHPS). For this novel steering system, there is a complex mechanical-electro-hydraulic coupling relationship that affects the steering performance. Thus, how to choose the appropriate parameters to ensure the system of good energy-saving characteristics and steering road feeling is one of the key issues. The power flow of mechanical, electrical and hydraulic subsystems is used to test the coupling relationship between the parameters of the motor, hydraulic pipe, hydraulic valve, power cylinder, and mechanical steering structure, and analyze their influence on the steering energy consumption. According to the results of energy consumption sensitivity analysis, the main coupling parameters are selected as design variables, and the steering energy consumption, steering road feeling and steering wheel return error are taken as optimization objectives. To add population diversity and accelerate convergence velocity, the improved competitive multi-objective particle swarm optimization (CMOPSO) algorithm is proposed and used for optimization. The optimization results illustrate that the CMOPSO has better convergence compared with the basic MOPSO, and the EHCS system optimized by CMOPSO has a better steering economy, with better steering road feeling and smaller steering wheel return error. To verify the comprehensive steering performance, the optimized EHCS system is installed on the vehicle for an on-field road test. Compared with original EHPS, the road test results show that the energy consumption of the modified vehicle under the steering condition significantly decreases, and can also meet the steering assistance and driver road feeling requirements. Furthermore, the real road traffic scene around Nanjing University of Aeronautics and Astronautics is reconstructed to analyze the relationship between the whole vehicle energy consumption and energy characteristics of the EHCS system in the intelligent traffic environments, which verifies the steering energy consumption is reduced by 51.7% under the 15 km test road.

Adaptive fuzzy radial basis function neural network integral sliding mode tracking control for heavy vehicle electro-hydraulic power steering systems

Due to parametric uncertainties, unknown nonlinearities, and dynamic external disturbances, it is a challenging and valuable task for heavy vehicle electro-hydraulic power steering systems to realize high-precision tracking control. To cope with this complex nonlinear tracking control problem, the integral sliding mode control is an extremely potential control method, which has strong robustness to model uncertainties and unknown disturbances, and can effectively reduce the steady-state error in tracking control process. However, the inherent chattering phenomenon of integral sliding mode control seriously affects its control performance. In order to suppress the chattering while ensuring robustness, adaptive fuzzy technique is adopted as an effective auxiliary means, which can not only deal with the inherent chattering problem of integral sliding mode control and a priori knowledge of the disturbance upper bound in controller design but also dynamically adjust the parameters in the fuzzy rules. Moreover, the designed adaptive fuzzy–integral sliding mode control scheme still needs the precise mathematical models of the control systems. But it is difficult to obtain the model for heavy vehicle electro-hydraulic power steering systems with highly complex and coupling properties. Therefore, to further improve the method, this paper presents a novel adaptive fuzzy–radial basis function neural network–integral sliding mode control method for the complex systems to achieve timely and accurate steering angle tracking control. In addition to the advantages of adaptive fuzzy–integral sliding mode control, the modified controller no longer requires the precise mathematical models of heavy vehicle electro-hydraulic power steering systems and realizes the continuous adaptive updating of weights. Finally, the effectiveness and superiority of the proposed control scheme is illustrated by comparisons and extensive simulations.

Adaptive Robust Control of Multi-Axle Vehicle Electro-Hydraulic Power Steering System With Uncertain Tire Steering Resistance Moment

To investigate the unknown (uncertain) tire steering resistance moment and model uncertainties in a multi-axle vehicle electro-hydraulic power steering system (EHPSS), including the steering mechanisms, valve-controlled double hydraulic actuators, and heavy-duty tires, an adaptive robust control algorithm is developed to estimate the tire steering resistance moment online and compensate for the model uncertainties of EHPSS. The proposed control strategy consists of an adaptive control law and a robust controller which are based on a Lyapunov function. The adaptive control law is employed to update estimated values of the (unknown) tire steering resistance moment and parameter uncertainties in the EHPSS, whereas complicated nonlinearities are addressed by the robust controller. All adaptive laws of the EHPSS and controller, which can impede parametric uncertainties and stabilize the EHPSS, are synthesized by backstepping techniques. The comparative simulation results demonstrate that the proposed adaptive robust control scheme can achieve the desired performance for feasible tracking trajectories despite the existence of an uncertain tire steering resistance moment and external disturbance in the EHPSS.

An investigation on the energy-saving effect of a hybrid electric-power steering system for commercial vehicles

This article describes an investigation on the energy consumption of an alternative hybrid electric power steering system. The conventional hydraulic power steering system that is widely used in commercial vehicles can provide high steering-feel and reliability performances. However, since the combustion engine drives the pump, the hydraulic power steering system is energetically inefficient. To cope with this disadvantage of the hydraulic power steering system and to provide a technical base for the steering-related advanced driver assistance system, the Hybrid electric power steering system offers a solution for heavy commercial vehicles. The “Hybrid” of the title means that, for heavy commercial vehicles, the electric power steering system and electro-hydraulic power steering system are integrated in a ball-nut steering system. In this paper, to verify the energy-saving effect of the Hybrid electric power steering system, a dynamic model of the Hybrid electric power steering system was developed to estimate the energy consumption in the steering system. Furthermore, the fuel-efficiency test for the Hybrid electric power steering system were conducted while replacing the two steering systems (the conventional hydraulic power steering and Hybrid electric power steering system) in one vehicle on the chassis dynamometer for the proposed driving cycle. The driving cycle including the steering-angle profile has been developed to clearly investigate the effect on the energy-saving potential by the types of the steering system (hydraulic power steering and Hybrid electric power steering). The simulation results of the energy-consumption estimation showed that the hybrid electric power steering system can reduce the steering-system energy consumption by more than 50% under the proposed driving cycle. Also, the vehicle testing of the chassis dynamometer revealed that the Hybrid electric power steering system can improve the fuel efficiency of the vehicle by 1% for the specified driving cycle.

Modeling, simulation, and experimental validation of electro-hydraulic power steering system in multi-axle vehicles

An accurate electro-hydraulic power steering system (EHPSS) model is essential to analyze dynamic steering performance and advanced nonlinear control. The main obstacle to establish an accurate model is the complex structure, including steering mechanism, valve controlled dual hydraulic-actuator, and heavy duty tires. This paper constructs a suitable model incorporating these parts, based on a Lagrange equation describing the steering trapezoid mechanism and dual cylinder hydraulic dynamics, regarding steering resisting moment as an external load. A simplified tire model is used to represent the tire basic steering load characteristics. Due to the complexity of the kinematic relationship in the model, several expressions are fitted using back propagation neural networks to significantly reduce calculation difficulty. Experimental measurements and simulation using Matlab/Simulink and experiment are realized for the case of in situ steering, and the results validate the proposed model accuracy. Thus, the proposed model is suitable to analyze the system and design advanced controllers.

Study on Speed Sensor-less Vector Control of Induction Motors Based on AMEsim-Matlab/Simulink Simulation

Abstract The model of speed sensor-less vector control system of induction motors has been built on the AMEsim and Matlab/Simulink platform, AMEsim and Simulink can be connected by creating an S-function interface. The results of Co-simulation indicate that the algorithms of model reference adaptive system (MRAS) based on counter electromotive force (EMF) can estimate the speed with some accuracy in static and dynamic conditions and make the electro-hydraulic power steering (EHPS) system offer the assist force as quickly as the sensor-based system. So the proposed model and control algorithms are correct and have reached the expectation.

Extended state observer based control scheme for the A-EHPS with load pressure estimation

The accumulative electro-hydraulic power steering system (A-EHPS) is essentially an electro-hydraulic servo system with high parametric uncertainties and nonlinearities that are caused by the characteristics of the hydraulic system. The throttle structure in the steering gear and the on-way resistance increase the control difficulty of the plant. This paper reports the construction of a mathematical model that contains the throttle structure and the on-way resistance for the A-EHPS system. Furthermore, an extended state observer and a sliding mode controller are synthesized to estimate uncertain nonlinear components and improve the quality of control in the A-EHPS. The uncertain nonlinear parts contain important information on the high-pressure chamber’s load pressure, which cannot be directly measured. That is, the proposed control scheme can be used to estimate steering resistance, which is essential for the top-layer control strategy. Simulations are performed to validate the control performance and the parameter design principle of the proposed extended state observer scheme. The scheme is then implemented in an actual system, and its robustness advantages over traditional controllers are verified.

The Simulation for the Electro-Hydraulic Power Steering Assisted Control System of Electric Motor Coach

With its energy-saving and green & non-pollution feature, the electric motor coach has been become the focus of public attention, but it also brought the new challenge for the steering system and the matching assisted control system. In this paper it made the introduction for the principle and structure of electro-hydraulic power steering control system, and also carried out the modeling and simulation for the assist characteristic, motor model, steering control valve and assisted control system of the electro-hydraulic power steering assisted control system, finally established the EHPS model and its assisted control system model by using MATLAB/Simulink, to build the practical foundation of the electro-hydraulic power steering assisted control system in the car.