Neutral Steer Research Articles

Electric Car Conversion

One of the directions for making cleaner and more economic vehicles is to adopt electric vehicle concept. Therefore, an internal combustion powered engine Nissan Micra Vehicle was converted into battery powered electric vehicle. The power train of the car was redesigned to use DC electric motor in replacement of the existing internal combustion engine and to give the gear ratios possibility of a normal car. The power rating of the motor was determined by considering the rolling, gradient and aerodynamic resistances which gave a total tractive effort of 12190.84 N. The designed power rating was then determined to be 8 kW and this value was used to select the number of batteries that gave the required current to reach an adequate range of operation. To balance the weight of the car, the battery rack was located behind the center of gravity to give the developed vehicle a neutral steer characteristic. After installation of electric motor, inverter and the batteries, then the batteries were connected in series and parallel to the inverter with cable wire via variable frequency drive to ac motor and potentiometer. The vehicle was then evaluated and the voltage produced was able to move the vehicle at 6.24 m/s and the maximum frequency obtained was fifty megahertz (50 MHz).

Modelling and Simulation of Skid Prediction in a Passenger Car

The vehicle handling is defined as the responsiveness of a vehicle to the driver input. The driver and vehicle is a closed loop system where the driver observes the direction or position of the vehicle in order to correct his input to achieve the desired motion. It is required for the driver to safely ride the vehicle particularly during cornering, acceleration and braking in order to avoid skidding. The skid occurring in a vehicle is a condition in automobile handling where one or more tyres slip relative to the road and the overall vehicle handling gets affected. Tire slip and related slip angle describe the performance of an individual tire. The cornering behaviour of a vehicle is one of the important modes in handling. In this project, a mathematical model is build using MATLAB-SIMULINK for a passenger car undergoing cornering. The steer angles for various speeds and radius of turns are determined and the results are displayed in the form of graphs. An app is designed using the MATLAB app designer which predicts the type of skid- under steer, over steer or neutral steer while the vehicle is undergoing cornering. This system is then simulated in the real time environment with the help of IPG Carmaker and driving scenario designer app in MATLAB and the corresponding results are noted

Handling performance optimisation for formula vehicle using multi-objectives evolutionary algorithms

A method based on constraint multi-objective evolutionary algorithms approach is proposed to optimise the handling performance of a race car dynamic. This involves a software-in-the-loop optimisation (SiLO) between a high-fidelity model of a formula vehicle modelled in VI-Grade and MATLAB for hosting the optimisation algorithms. The optimisation process involves the tuning of the suspension design variables, i.e. spring stiffness, anti-roll bar stiffness, damper coefficient, toe angle, and camber angle for both front and rear suspensions against eight objectives functions, i.e. sideslip overshoot, yaw rate overshoot, linear understeer gradient, limit understeer gradient, maximum lateral acceleration, yaw rate phase delay and lateral acceleration phase delay. A custom constraint function was introduced to improve the convergence speed of the optimisation process. The optimised result showed a promising increase in handling performances, i.e. the maximum achievable lateral acceleration has increased by 8.9% whilst maintaining the stability of the vehicle close to neutral steer behaviour. The sideslip angle was well controlled under 1 deg at 95% of maximum lateral acceleration, and slip angle overshoot has improved by 1.65% in step steer manoeuvre. Additionally, the skid-pad events and autocross event laps time were reduced by 5.19% and 1.71%, respectively.

Direct yaw moment control for distributed drive electric vehicle handling performance improvement

For a distributed drive electric vehicle (DDEV) driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. And direct yaw-moment control (DYC) has been widely studied and applied to vehicle stability control. Good vehicle handling performance: quick yaw rate transient response, small overshoot, high steady yaw rate gain, etc, is required by drivers under normal conditions, which is less concerned, however. Based on the hierarchical control methodology, a novel control system using direct yaw moment control for improving handling performance of a distributed drive electric vehicle especially under normal driving conditions has been proposed. The upper-loop control system consists of two parts: a state feedback controller, which aims to realize the ideal transient response of yaw rate, with a vehicle sideslip angle observer; and a steering wheel angle feedforward controller designed to achieve a desired yaw rate steady gain. Under the restriction of the effect of poles and zeros in the closed-loop transfer function on the system response and the capacity of in-wheel motors, the integrated time and absolute error (ITAE) function is utilized as the cost function in the optimal control to calculate the ideal eigen frequency and damper coefficient of the system and obtain optimal feedback matrix and feedforward matrix. Simulations and experiments with a DDEV under multiple maneuvers are carried out and show the effectiveness of the proposed method: yaw rate rising time is reduced, steady yaw rate gain is increased, vehicle steering characteristic is close to neutral steer and drivers burdens are also reduced. The control system improves vehicle handling performance under normal conditions in both transient and steady response. State feedback control instead of model following control is introduced in the control system so that the sense of control intervention to drivers is relieved.

Steady-state characteristics of skid steering for wheeled vehicles

Skid steering has been applied to various electric vehicles and unmanned vehicles because of its advantages in mobility and layout flexibility. This paper proposes an analytical lateral dynamic model of skid steering for a wheeled vehicle that could be applied to its design and control. The model is described by second-order ordinary differential equations in an explicit form. The steady-state characteristics of skid steering for wheeled vehicles are analysed on the basis of differential equations. The results of the steady-state analysis show that the steady-state response of the skid-steered wheeled vehicle is determined by the stability factor. When the vehicle has a neutral steer property, the neutral yaw rate gain is positively related to the velocity difference, and the neutral turning radius is inversely related to the velocity difference rate.

Electronic differential for high-performance electric vehicles with independent driving motors

This paper presents a novel electronic differential design for high performance electric vehicles (EVs) with independent driving motors. The aim of this design is to achieve neutral–steer in intense driving scenarios. The proposed method employs a closed–loop control system that constantly regulates the torque commands sent to the independent driving motors. These commands are generated to tune the torque difference between left and right driving motors at the amount that leads to neutral–steer. Real vehicle parameters and real tyre testing data are employed in extensive simulations. Simulation results demonstrate that the new electronic differential works in principle and can endow the EV with a close–to–neutral steer characteristic, which is of great significance to high–performance vehicles in challenging driving conditions. Also, comparative simulations demonstrate how the proposed method can outperform competing methods in terms of steering performance in various scenarios, while maintaining the dynamic stability of the vehicle.

Research for the Turning Vehicles ESP Control Performances on the Yaw Elastic Restriction Vehicle System

Project the structure of the yaw elastic restriction vehicle system, and set up the system dynamic model. Establish yaw elastic restriction vehicle dynamics simulation system based on Matlab/Simulink aimed at Chery A3 sedan. Adopting the brake driving integration ESP control strategy, analyze and verify the stability control performance of independent vehicle systems and yaw elastic restriction vehicle system respectively in neutral steer, understeer and oversteer three test conditions. The results of the study show that the stability control performance of yaw elastic restriction vehicle system and independent vehicle systems has remarkable consistency. This provides a basis for vehicle driving stability control test.

Performance Enhancement of Road Vehicles Using Active Independent Front Steering (AIFS)

Technological developments in road vehicles over the last two decades have received considerable attention towards pushing the safe performance limits to their ultimate levels. Towards this goal, Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) systems have been widely investigated. AFS systems introduce corrective steering angles to conventional system in order to realize target handling response for a given speed and steering input. It is thus expected that such an action under severe maneuvers may cause one tire to reach saturation while the other tire may be capable of developing more force. This study, therefore, proposes an Active Independent Front Steering (AIFS) system capable of controlling a wheel independently. At low speeds, the proposed AIFS system will modify the steer angle with speeds while maintaining pro-ackerman geometry similar to an AFS system. In doing so, it will realize a target response defined as one provided by a neutral steer system. However, in a severe maneuver, as the inner tire approaches the saturation limit, the AIFS system controller will only increase the angle of the outer tire, effectively introducing an anti-ackerman geometry. The study is carried out using a comprehensive 4-wheel handling model with AIFS capability. A PI controller with ability to detect and control the outer wheel independently is incorporated to examine the handling performances of an understeer vehicle under a ramp-step and sinusoidal steering inputs. In general, the results demonstrate that AIFS can perform as well as AFS in realizing target response while AIFS can provide performance enhancement beyond the limits of AFS. The control approach of AIFS is also shown to be effective for split-μ condition. Language: en

Towards neutral steer and sideslip reduction for four-wheeled electric vehicles

This paper proposes an approach to achieving both neutral steer and sideslip reduction for four-wheeled electric vehicles. The control problem is reduced to constructing a servo system tracking appropriate reference input, where the tracking is realized in the framework of H ∞ control. To deal with time-varying vehicle velocity for practical purpose, a gain scheduling strategy is developed to obtain the controller, where the lower and upper bounds of the velocity are used to obtain a polytopic range for the parameters in the system coefficient matrices. A numerical example is given to show validity of the proposed approach.

Handling enhancement of a sliding-mode control assisted four-wheel steer vehicle

This paper is an investigation of the role of the robust control strategy of the rear wheel steer system to improve handling. To establish an accurate model of the vehicle, a nine degree-of-freedom (DOF) model is considered. The model’s degrees of freedom consist of three angular motions (roll, pitch, and yaw) of the sprung mass, spin of the wheels, and two translational motions (forward and side travel) of the unsprung mass. Also, the environment and geometric effects, such as aerodynamic forces, tyre–ground interaction, body roll versus camber relation, steering command saturation, and roll axis inclination, are taken into account. The front and rear suspensions are assumed to be a MacPherson strut and semi-trailing arm respectively. Cornering behaviour of the vehicle is studied and compared for a manual two-wheel steer (2WS) and a sliding-mode control assisted four-wheel steer (4WS) vehicle. A 3-DOF vehicle model is used to make a fast state estimation. The yaw rate is used as the reference signal for the control system, to ensure that the desired handling is obtained. The results show that during the standard cornering manoeuvres, the sliding-mode control provides significant tracking performance and lower sensitivity to vehicle velocity, road condition, and roll axis inclination compared to the 2WS. Also lane tracking and cornering behaviour of the steering system is enhanced towards the neutral steer.

STEADY-STATE CHARACTERISTICS ANALYSIS OF DEEP-SEA RUNNING MECHANISM WITH PLANETARY GEAR WHEEL BASED ON ARTICULATED STEERING RADIUS

Steady-state characteristics analysis for the deep-sea running mechanism with planetary gear train which is designed to adapt to complex terrain in the deep-sea hydrothermal sulfide and rich-cobalt incrustation survey area is based on articulated steering radius. The articulated steering radius formula of the deep-sea running mechanism is derived from the geometric relationship, considering the wheel side slip angle. Based on the formula, three types of steering steady-state characteristic analysis, understeer, neutral steer and oversteer, are made for the mechanism. Steering simulation analysis of the running mechanism with planetary gear is conducted in ADAMS software with different speed. In the process of steering, the side slip angle increases first, then gradually decreases and finally tends to be stable. The side slip angle of the front wheels is greater than that of the rear wheels. While the speed of steering turns to be faster, wheel side slip angle and steering radius increase. The mechanism is understeer, and performs good handling stability characteristic.

Using GPS with a model-based estimator to estimate critical vehicle states

This paper demonstrates a method to estimate the vehicle states sideslip, yaw rate, and heading using GPS and yaw rate gyroscope measurements in a model-based estimator. The model-based estimator using GPS measurements provides accurate and observable estimates of sideslip, yaw rate, and heading even if the vehicle model is in neutral steer or if the gyro fails. This method also reduces estimation errors introduced by gyroscope errors such as the gyro bias and gyro scale factor. The GPS and Inertial Navigation System measurements are combined using a Kalman filter to generate estimates of the vehicle states. The residuals of the Kalman filter provide insight to determine if the estimator model is correct and therefore providing accurate state estimates. Additionally, a method to predict the estimation error due to errors in the estimator model is presented. The algorithms are tested in simulation with a correct and incorrect model as well as with sensor errors. Finally, the estimation scheme is tested with experimental data using a 2000 Chevrolet Blazer to further validate the algorithms.

The application of understeer gradient in stability analysis of articulated vehicles

This paper introduces the generalised algebraic formula for understeer gradient (Ku) of articulated vehicles. This formula plays a similar role as that for a single vehicle system. The articulated vehicle is understeer if Ku is positive, neutral steer if it is equal to zero, and oversteer if it is negative. It is not stable in the yaw plane if it is oversteer and driven above the critical speed. The algebraic solutions are validated numerically and compared to experimental data measured from an 18-wheel tractor semi-trailer system. The impedance concept is introduced to facilitate the process of the algebraic analysis of articulated vehicles. This allows Ku and critical speed equations to be expressed in a compact systematic form.

左右独立駆動制御による前輪タイヤ余裕度向上(自動車・二輪車の運動と制御(1),OS2 交通・物流機械のダイナミクス(振動,制御を含む))

This paper investigates the improvement of front tire grip margin by using Direct Yaw-moment Control (DYC) which is designed from the viewpoint of tire force usage. The micro-scale electric vehicle 'NOVEL' is equipped with two in-wheel-motors at rear axle and their motor torques can be controlled independently to achieve the DYC. In this paper, the DYC, which control objective is determined as Neutral-Steer(NS) characteristics, is designed with the application of yaw moment following control. Finally, the effect of the DYC on improvement of front tire grip margin is proved by NOVEL on J-turn test.

Lateral Dynamics and Stability of Two Full Vehicles in Tandem

The lateral dynamics and stability of two full vehicles in tandem are investigated. The nonlinear differential equations of motion of this four-axle articulated vehicle system are presented in matrix form and then linearized. The critical forward velocity of the steady state for oversteering conditions is derived in a closed form, and the criteria for understeer, neutral steer, or oversteer are given. Uncertainty of the critical forward velocity and its sensitivity to errors in the system parameters are evaluated using the root mean square method. Conditions for nonoscillatory and oscillatory instabilities of the linearized vehicle system are given. Effects of the critical system parameters (mainly the mass distribution) on the stability are investigated.

Static Turning Analysis of Vehicles Subject to Externally Applied Forces - A Moment Arm Ratio Formulation

SUMMARY A formulation for representing the static turning response of a two-axle vehicle due to applied external or control forces is expressed in terms of a simple ratio of two distances along the vehicle longitudinal axis. The two distancescoincide with points on the vehicle at which externally applied/ control forces and their reactive inertial forces act with respect to the vehicle neutral steer point. The resulting formulation is equivalent to the rotational equilibrium equation written with respect to the neutral steer point. The method allows a simple “visual analysis” of the steady turning process by showing how key forces and associated moment arms can change with respect to one another due to vehicle modifications or different operatingconditions, thereby affecting the static turning response of the vehicle.