In-wheel Motor Electric Vehicle Research Articles

Energy saving control based on motor efficiency map for electric vehicleswith four-wheel independently driven in-wheel motors

For four-wheel independently driven in-wheel motor electric vehicles, the four-wheel drive/braking torque can be controlled independently. Therefore, it has an advantage that energy saving control can be applied effectively. This article studies several energy saving control methods from two levels of driving and braking for four-wheel independently driven in-wheel motor electric vehicles under urban conditions based on the motor efficiency map. First, the energy saving control logic and the evaluation index were proposed in the article. The four-wheel drive torque was online optimized in real time through drive energy saving control, in order to improve the driving efficiency in the driving process of electric vehicles. According to the theory of ideal braking force distribution and Economic Commission of Europe braking regulations, the parallel regenerative braking control method based on the motor efficiency map was then studied. The parallel regenerative braking control method was applied to four-wheel independently driven in-wheel motor electric vehicles. The simulation analysis under typical urban driving cycle conditions was carried out to determine the braking intensity of the parallel brake front axle separate regenerative braking, and finally the braking energy recovery rate of electric vehicle can be improved in the low speed and low braking torque. Finally, simulation experiments have been carried out to verify the researched method under the NEDC, UDDS, and J1015 urban driving cycles. The simulation results show that the energy saving control methods have an obvious effect on energy saving under the urban driving cycle conditions.

A stochastic power management strategy with skid avoidance for improving energy efficiency of in-wheel motor electric vehicles

In this study, a stochastic power management strategy for in-wheel motor electric vehicles is proposed to reduce the energy consumption and increase the driving range, considering the unpredictable nature of the driving power demand. A stochastic dynamic programming approach, policy iteration algorithm, is used to create an infinite horizon problem formulation to calculate optimal power distribution policies for the vehicle. The developed stochastic dynamic programming strategy distributes the demanded power, Pdem between the front and rear in-wheel motors by considering states of the vehicle, including the vehicle speed and the front and the rear wheels’ slip ratios. In addition, a skid avoidance rule is added to the power management strategy to maintain the wheels’ slip ratios within the desired values. Undesirable slip ratios cause poor brake and traction control performances and therefore should be avoided. The resulting strategy consists of a time-invariant, rule-based controller which is fast enough for real time implementations, and additionally, it is not expensive to be launched since the future power demand is approximated without a need to vehicle communication systems or telemetric capability. A high-fidelity model of an in-wheel motor electric vehicle is developed in the Autonomie/Simulink environment for evaluating the proposed strategy. The simulation results show that the proposed stochastic dynamic programming strategy is more efficient in comparison to some benchmark strategies, such as an equal power distribution and generalized rule-based dynamic programming. The simulation results of different driving scenarios for the considered in-wheel motor electric vehicle show the proposed power management strategy leads to 3% energy consumption reduction in average, at no additional cost. If the resulting energy savings is considered for the total annual trips for the vehicle and also the total number of electric vehicles in the country, the proposed power management strategy has a significant impact.

Simulation analysis and optimization of ride quality of in-wheel motor electric vehicle

In order to evaluate the influence of unsprung mass on ride comfort for an in-wheel motor electric vehicle, an improved genetic algorithm based on fitness evaluation was proposed to optimize the suspension system. The simulation model was established in ADAMS software for the target sports utility vehicle with front McPherson and rear unequal length double arm suspension systems. The ride comfort of the target vehicle was analyzed by the developed simulation model. The stiffness and damping of the suspensions were optimized by the root mean square values of the vehicle weighted vertical acceleration and the pitching angle acceleration with the help of the multi-disciplinary and multi-objective optimization software, ISIGHT. The results show that, the proposed multi-objective optimization algorithm is helpful to achieve the ride comfort improvement and the computation time reduction.

A Piecewise Affine Robust Yaw Stability Control Method for In-wheel Motor Electric Vehicle

Considering the nonlinear tire force and suspension K&C characteristic, this paper presents a piecewise affine robust yaw stability control method for the in-wheel motor electric vehicle. Using the piecewise linear to approximate front and rear tire force, and additional steering angle to describe the suspension K&C characteristic, a piecewise affine lateral dynamics model with uncertainty disturbance is firstly established. And then, by means of analysis of the dynamic behavior of front and rear tire force, the unreachable piecewise partition is neglected such that the lateral dynamics model is simplified. By using LMI technique, the yaw stability controller which can guarantee the closed-loop stability and Hinf disturbance rejection is obtained. Simulation results show that the yaw stability control method proposed in this paper is feasible and effective.

Robust Yaw Stability Control for In-Wheel Motor Electric Vehicles

This study investigated robust yaw moment control for motion stabilization in four-wheel electric vehicles. A two-degree-of-freedom direct yaw moment control scheme is proposed. An engineering weighting function with embedded engineering specifications is included in the proposed approach. The controller was synthesized and its corresponding properties were studied. A rear-wheel drive in-wheel motor electric vehicle was employed for a practical evaluation of the scheme. Because of the robust control framework, the presented system can overcome model uncertainties, side wind disturbances, and parameter variation problems. Experiments were conducted to illustrate the feasibility and effectiveness of the proposed controller.

Vertical Vibration Simulation Analysis of In-wheel Motor Electric Vehicle Suspension

To analyze the vertical vibration characteristics of in-wheel motor electric vehicle suspension, through MATLAB/ Simulink for simulation and analysis, a vertical kinetic model of 1/4 vehicle is built. Without changing the original premise of vehicle suspension parameters, vehicle vertical vibration acceleration 􀝕􁈷 of in-wheel motor as unsprung mass and wheel dynamic load 􀜨􀯧 are in turn to be simulated, to study the influence of the increase of the unsprung mass on the vertical vibration of the suspension because of the introduction of in-wheel motor. The research results provide a reference for improving the NVH characteristics of in-wheel motor electric vehicle.

Influences Analysis of In-wheel Motor on EV Vibration Performance

To analyse the influence of the increased unsprung mass on electric vehicle vibration performance as in-wheel motor embedded within the hub, Using one-quarter vehicle system with two degree-of-freedom, the vibration model of in-wheel motor electric vehicle is established, and the vibration performance indexes are presented. The frequency response characteristics and statistical characteristics of vibration response quantity are built by the method of frequency domain analysis. The influence of the increased unsprung mass on the vibration performance of electric vehicle is analysed based on B-level road and urban driving condition. The results show that vehicle speed variation has greater impact on the vibration response varibles of in-wheel motor electric vehicle; and the increased unsprung mass of in-wheel motor electric vehicle exerts a little influence on body acceleration and wheel displacement, but has a serious impact on wheel acceleration and an evident influence on relative dynamic load of wheel, as well as a certain influence on suspension deflection.

Electric vehicles with in-wheel switched reluctance motors: Coupling effects between road excitation and the unbalanced radial force

The switched reluctance motor (SRM) has great application potential in in-wheel motor electric vehicle (IWM-EV) due to its advantages, such as a high starting torque for initial acceleration, a wide operating speed range and high efficiency to extend the battery service life. However, these advantages are overshadowed by its inherent vibration and noise due to the unbalanced radial force. For the vehicle vibration system, the vertical component of SRM unbalanced radial force, namely SRM vertical force, is one of the major concerns. This paper analytically investigates the coupling effect of SRM vertical force and road excitation on IWM-EV vibration. First, the system dynamics model of IWM-EV and IWM driving EV controller are proposed to include SRM vertical force; then the analytical models are solved to predict the vehicle dynamic responses at different speeds on periodic and stochastic road inputs with various amplitudes and coherence functions between left- and right-sides of the vehicle. It is concluded that SRM vertical force is highly coupled with road excitation and SRM airgap eccentricity, and such coupling effects yield a great impact on vehicle vertical vibration dynamics.

Dynamic motion stabilization for front-wheel drive in-wheel motor electric vehicles

This article presents a new dynamic motion stabilization approach to front-wheel drive in-wheel motor electric vehicles. The approach includes functions such as traction control system, electronic differential system, and electronic stability control. The presented electric vehicle was endowed with anti-skid performance in longitudinal accelerated start; smooth turning with less tire scrubbing; and safe driving experience in two-dimensional steering. The analysis of the presented system is given in numerical derivations. For practical verifications, this article employed a hands-on electric vehicle named Corsa-electric vehicle to carry out the tests. The presented approach contains an integrated scheme which can achieve the mentioned functions in a single microprocessor. The experimental results demonstrated the effectiveness and feasibility of the presented methodology.

Composite Control and Co-Simulation in In-Wheel Motor Electric Vehicle Suspension

An in-wheel motor electric vehicle has high unsprung mass because of its in-wheel motor, which decreases vehicle ride comfort and vehicle safety. This paper presents a controllable suspension employing an optimal design hybrid damping control strategy based on ideal skyhook and groundhook as a reference. A sliding mode controller is designed to make the plant track the ideal reference model. The exponent reaching law based on fraction order calculus is used to improve the dynamic quality of the sliding mode motion. Moreover, a dynamics model of in-wheel motor electric vehicle suspension is established in Adams. The joint simulation of Adams and Matlab prove that the designed controller can reduce tire dynamic load effectively, maintain better ride comfort, and suppress vibration better than the integer order exponential reaching law. Furthermore, the proposed controller has better composite performance than the general hybrid damping control strategy.

Differential Drive Assisted Steering Control for an In-wheel Motor Electric Vehicle

Differential Drive Assisted Steering Control for an In-wheel Motor Electric Vehicle

Effect of the unbalanced vertical force of a switched reluctance motor on the stability and the comfort of an in-wheel motor electric vehicle

Switched reluctance motors are well suited to in-wheel-motor-driven electric vehicles because of their numerous advantages, such as a high torque density, a high operating efficiency and excellent power–speed characteristics. However, these advantages are overshadowed by their inherent high torque ripple and vibrations. The unbalanced radial force of the switched reluctance motor is one of the main reasons for vibrations of the switched reluctance motor but has attracted less attention for in-wheel motor applications according to previous research. In this paper, the vertical component of the residual unbalanced radial force of the switched reluctance motor, i.e. the vertical force of the switched reluctance motor, is taken into account in the stability and comfort analysis for in-wheel-motor-driven electric vehicles. The results in this paper indicate that the vertical force of the switched reluctance motor has a great effect on the lateral and anti-rollover stabilities of the vehicle. The direct cause of this phenomenon is that the vertical force of the switched reluctance motor is directly applied on the wheels, which will result in a significant variation in the tyre load, and the tyre can easily jump off the ground. Furthermore, the frequency of the vertical force of the switched reluctance motor covers a wide bandwidth which involves the resonance frequencies of the vehicle body’s vibrations and the wheel bounce. As a result, the comfort of the vehicle is greatly harmed. Therefore, the effect of the vertical force of the switched reluctance motor on the the comfort of the vehicle is also considerable in some resonance situations. The conclusion is that the vertical force of the switched reluctance motor not only causes the stability of the vehicle to deteriorate but also has a considerable effect on the the comfort of the vehicle, and an appropriate control method for the switched reluctance motor is desired.

In-wheel motor electric vehicle state estimation by using unscented particle filter

Vehicle state parameters are essential for active safety stability control and very valuable in chassis design evaluation. In this paper, a method for vehicle state parameters estimation is developed for in–wheel motor (IWM) electric vehicle (EV). The observer is based on information fusion combining standard sensor suite in today's typical vehicle and feedback signals from IWM. This paper utilise unscented particle filter (UPF) for tyre lateral force, longitudinal velocity, lateral velocity and yaw rate estimation, which is based on a numerically efficient nonlinear stochastic estimation technique. Planar vehicle model and dynamic tyre model are developed to describe behaviour of IWM EV. Detailed simulation verifies the validation and robustness of proposed estimation algorithm.

Vibration effect and control of In-Wheel Switched Reluctance Motor for electric vehicle

The Switched Reluctance Motor (SRM) processes favorable driving capacity and great application potential in In-Wheel Motor (IWM) Electric Vehicle (EV). However vibration and noise problems are always the disadvantages of SRM. This paper investigates the vibration and noise issues and corresponding control methodology for the IWM application of SRM. By utilizing the analytical Fourier fitting method, a convenience method for modeling In-Wheel Switched Reluctance Motor (IW SRM) is proposed and the characteristics of the unbalanced residual lateral force related to vibration excitation are analyzed. Then the dynamic negative effect of IW SRM on vehicle is analyzed with a quarter driving and vibration vehicle model. It is found that the vertical shock occurs under the vehicle starting condition and high frequency force excitation exists under the constant speed condition. To address these issues, corresponding control methods are proposed, modified and compared. The proposed combined vibration feedback control of current chopping with PWM can effectively reduce the SRM residual force and ensure the required vehicle speed, though some slight low frequency forces are induced.

Active approach to Electronic Stability Control for front-wheel drive in-wheel motor electric vehicles

Recently, motion control for electric vehicles has gradually gained respect in automotive society due to increased strictness of vehicle safety evaluation over time. Electronic Stability Control (ESC) is the kernel technology, which refers to two-dimensional motion stabilization. Many investigations have demonstrated that Direct Yaw-moment Control (DYC) is an effective and practical way to carry out the ESC of electric vehicles. However, based on the drive train of conventional steering, conventional approaches are using braking to achieve the DYC. This paper proposes a new ESC based on the construction of DYC. The presented approach is based on a core of individual traction control measures for propulsion wheels. This approach not only constrain the longitudinal slip, but also ensure the performance and the effectiveness of two-dimensional motion control. With a proper control, the vehicle can be maintained to a nearly neutral-steering under high speed turning. Hence, the vehicle’s dynamic stability can be enhanced under aggressive driving by yaw-moment control. Evaluation of the entire control system is performed by well-acknowledged software, which demonstrates that the vehicle’s dynamic stability can be enhanced under aggressive driving by the proposed approach.

A reduced-order nonlinear sliding mode observer for vehicle slip angle and tyre forces

In this paper, a reduced-order sliding mode observer (RO-SMO) is developed for vehicle state estimation. Several improvements are achieved in this paper. First, the reference model accuracy is improved by considering vehicle load transfers and using a precise nonlinear tyre model ‘UniTire’. Second, without the reference model accuracy degraded, the computing burden of the state observer is decreased by a reduced-order approach. Third, nonlinear system damping is integrated into the SMO to speed convergence and reduce chattering. The proposed RO-SMO is evaluated through simulation and experiments based on an in-wheel motor electric vehicle. The results show that the proposed observer accurately predicts the vehicle states.

State Estimation for 4WD In-Wheel Motor Electric Vehicle

This article proposed a Double Extended Kalman Filters (Double EKFs) observer to estimate states of 4WD in-wheel motor electric vehicle. One EKF observer was used to estimate vehicle longitudinal velocity. The other EKF observer was employed to estimate vehicle sideslip angle. The structure has two benefits: Firstly, two EKFs reduce the order of the wholly state observer, so that calculation load could be lower. Secondly, the two EKFs could be adjusted easier and more independently. The paper investigates the feasibility of this observer in two vehicle test conditions. The test results indicate the effectiveness of the Double EKFs State estimation.

Optimization of Double Pivot Suspension Kingpin Axis during Steering

A double pivot suspension used for in-wheel motor electric vehicle was designed, and the virtual prototype model of the suspension assembly was build. The suspension parameters changed greatly during steering. In order to solve this problem, this paper proposed a non-linear response surface model to fit the relationship of suspension parameters and design variables. An optimization scheme was designed based on the response surface model. The suspension performance was improved significantly using optimized variables.

Wheel Dynamic Load Optimization of In-Wheel Motorelectric Vehicle Based on Response Surface Method

A multi-body dynamic rigid-flexible coupling model of an in-wheel motor vehicle is built. This vehicle is based on a particular class-A car. An overall investigation of the influence of unsprung mass on vehicle ride comfort is conducted. With the increment of unsprung mass, overall vehicle ride comfort is decreased. The degradation of wheel dynamic load performance is most obvious. Suspension parameters are optimized based on the multi-body dynamic model of the vehicle and Response Surface Method. The suspension deflection and wheel dynamic load of the vehicle using optimized suspension parameters are improved significantly, while the body vertical acceleration increased slightly.

Integrated control of in-wheel motor electric vehicles using a triple-step nonlinear method

To improve the vehicle stability of an electric vehicle with four in-wheel motors, an integrated control scheme with active front wheel steering and direct yaw moment is proposed using a triple-step nonlinear method. The method handles the nonlinear tire characteristics explicitly and actualizes a decoupling control for the considered two-input two-output nonlinear system, in the sense that the closed-loop error dynamics evolve independently. The design procedure is formalized as a triple-step deduction, and the derived controller consists of three parts: steady-state-like control, feedforward control considering reference variations, and state-dependent error feedback control. Finally, the designed controller is evaluated in a realistic seven DOF vehicle model and results are satisfying.