Vehicle Center Of Gravity Research Articles

Development and control of a new AUV platform

This paper presents an architecture of a newly developed autonomous underwater vehicle (AUV) platform, named KAUV-1, which is designed as a torpedo with very light weight and small size, suitable for use in marine exploration and monitoring. The KAUV-1 has a unique ducted propeller lo- cated at the aft end with yawing actuation acting as a rudder. For depth motion, the KAUV-1 is de- signed to have a mass shifter mechanism inside to change the vehicle center of gravity and to control its pitch angle and depth motion. The paper also presents an analysis on the equations of motion of the KAUV-1 with mass shifter mechanism and a new depth control strategy for the KAUV-1. The feasi- bility of the proposed control strategy is validated through simulation and experiment of performance of the vehicle.

Road friction effect on the optimal vehicle control strategy in two critical manoeuvres

This paper presents a research study on the optimal way to negotiate safety-critical vehicle manoeuvres depending on the available actuators and road friction level. The motive is to provide viable knowledge of the limitations of vehicle capability under the presence of environmental preview sensors. In this paper, an optimal path is found by optimising the sequence of actuator requests during the manoeuvres. Particular attention is paid to how the vehicle control strategy depends on friction. This study shows that the actuation of all the forces and torques on and around the vehicle centre of gravity is approximately scaled with friction, whereas at individual wheel level, the optimal force allocation will differ under different friction conditions. A lower friction level leads to lower velocities and load transfer, which influences the individual wheels’ tyre force constraints. However, the actuator response compared to the whole system is increased at a lower friction level.

Center of gravity height real-time estimation for lightweight vehicles using tire instant effective radius

Center of gravity (CG) height is an important parameter for lightweight vehicles (LWVs). Because of the inherently smaller weight and size, a LWV's CG height is more easily affected by loading conditions compared with conventional vehicles. This paper proposes a novel tire instant effective radius (TIER) method for real-time estimation of the CG height for LWVs. The method utilizes the mathematical correlation between the tire vertical load transfer that is proportional to the CG height, and the TIER variation. A Kalman filter based estimator is designed to simultaneously identify the vehicle CG height as well as the unknown nominal tire effective radius. To verify the performance of the proposed estimator, simulation results are first provided for several vehicles with different CG heights, and then road test results obtained on a lightweight electric ground vehicle (EGV) equipped with an advanced measurement system are given. Both simulation and experimental results show that the developed estimator is capable of providing an accurate estimation of the vehicle CG height in real-time.

Prediction of a vehicle maximum forward speed to pass double lane change manoeuvre

In this study, a simple method is proposed to predict the maximum speed for a vehicle to pass a double lane change (DLC) test manoeuvre. This method utilises a simple roll plane model with only four parameters to predict the vehicle centre of gravity (CG) lateral acceleration limit. Then the allowed minimum curvature radius of the vehicle CG trajectory during all possible DLC manoeuvres is maximised using an optimisation approach. The vehicle CG lateral acceleration predicted by the simplified roll plane model is compared with that predicted by a well-correlated full vehicle multi-body ADAMS model; the maximum speed passing DLC manoeuvre predicted by the proposed method is then further compared and validated with field test data from the same vehicle.

Study on the Time Lag between Steering Input and Vehicle Lateral Acceleration Response under Different Key Vehicle Parameters

A passively suspended road vehicle rolls outwards under the influence of lateral acceleration when cornering, which is very dangerous under large lateral acceleration. In this paper, time lag between steering input and vehicle lateral acceleration response is systematically studied to implement the active roll control algorithm from the viewpoint of vehicle system dynamics. A 3 DOF yaw-roll vehicle model is established based on vehicle lateral, roll and yaw dynamics. Vehicle parameters of a 1997 Jeep Cherokee is used for parametric study, where the influences of vehicle velocity, steering frequency, mass, length, roll, yaw moment of inertia, position of vehicle centre of gravity, and tyre cornering stiffness are studied via numerical simulation. The analysis results will help improve the real time rollover warning/control algorithm design for vehicle safety.

Comparison of various double-lane change manoeuvre specifications

One of the commonly used performance measures to quantify a vehicle's handling transient dynamics is the maximum forward speed (MFS) while passing a certain specified double-lane change (DLC) manoeuvre without violating the boundary and tyre lift-off. The MFS is directly associated with the minimum curvature radius (MCR) of the vehicle centre of gravity (CG) trajectory controlled by the driver during the manoeuvre. The MCR is further affected by the vehicle dimensions to meet the boundary condition. In this study, a single heavy vehicle CG trajectory is assumed to be a combination of three straight lines and two third-order spline curves. A heavy vehicle multi-body system model established with ADAMS/Car is correlated with test data for step-steer and constant radius cornering events, and then the model is used to demonstrate that the assumptions considered in the formulation applied in this paper are valid for this specific vehicle category. The MCRs of four heavy vehicles are maximised among all the possible choices of the vehicle CG trajectory during each of five specific DLC manoeuvres, including North Atlantic Treaty Organization (Allied Vehicle Testing Publication 03-160W), International Organization for Standardization (ISO) 3888-1, ISO 3888-2, Consumer Union Short Course and Test Operations Procedure 2-2-609. The maximised MCR (MMCR), considered as the best possible choice of vehicle CG trajectories, is further solved as a function of the vehicle width and length. The results will show the sensitivity of the MMCR to the vehicle length and width, thus the impact on the vehicle transient handling dynamics. Finally, the comparison of five DLC specifications may help users to correlate a vehicle's MFS from one specification to others.

Control performance of a road vehicle with four independent single-wheel electric motors and steer-by-wire system

This article presents a motion controller for a road vehicle equipped with a steer-by-wire system and four independent electric rim-mounted drives. The motion controller separates the control law from the specific actuator setup by the usage of virtual global control variables acting on the vehicle centre of gravity. A control allocation algorithm distributes the virtual control variables to the available actuators. An approximation of the real actuator dynamics is used to analyse the performance of different motion controller types in the linear and nonlinear driving regions. In addition, a vehicle state observer consisting of a traction force observer and an unscented Kalman filter is discussed to analyse the control behaviour in the case of a real sensor setup.

203 低重心型平行二輪ビークルの搭乗者を含む重心位置制御システムの構築(トレーニング・制御)

In this paper, structure design and modeling of novel seating-type two wheel vehicle with lower position of gravity center is proposed. The vehicle's gravity center is assigned at the lower position than that of the wheel axis, whose vehicle has the structure of the pendulum. Therefore, it enables the passenger to always keep the stable posture, even if the vehicle is in the power-off or control-off state. Then, the gravity center position's adjustment system is installed inside the vehicle body. Swing of the vehicle body generated by the bias of the passenger's gravity center position is controlled by the proposed seat positioning system. As a result, alignment of pitch angle of the vehicle body is possible by a seat positioning system that has been proposed.

Key Factors Effect on Vehicle Braking Performance Based on Nonlinear 3DOF Vehicle Dynamic Model

3DOF nonlinear braking dynamic model considering tire-road adhesion characteristics was established, and non-dimensional equations were gained from the above mathematic models by using braking torque coefficient, front and rear axle equivalent inertia coefficients and braking force distribution coefficient. Based on the numerical calculation in Matlab-Simulink software, the effect of key factors, (including vehicle mass and vehicle gravity center position variation, frontal and rear braking force distribution coefficient, and frontal and rear axle inertial variation caused by driven mode) on vehicle braking performance, such as braking distance and wheel lockup status, was investigated and summarized. Several 3D visualizations of the simulation results show that variation of vehicle center of gravity, vehicle mass, braking moment distribution, wheel equivalent inertia due to driveline, can cause quite complex effect. It can be assumed that the gained results in this study can help to improve vehicle braking performance and enhance braking stability.

Steering/Braking Control of Articulated Vehicle for Small Turning

A wheel loaders is a kind of articulated-frame steered vehicles and is used in narrow workspaces such as livestock barns. Its small-radius turning performance is important for improving operating efficiency in narrow workspaces. An integral steering/braking control system for small-radius turning was developed in this study. In this system, braking force acts on the inside tires to make a yaw-moment around the vehicle centre of gravity. The braking force acting on the inside tires is controlled by a feedback control system of hydraulic pressure using an electro-magnetic relief valve. The relief valve is controlled by pulse width modulation to produce a desired hydraulic pressure. The control of braking force is only active when the articulation angle and vehicle speed are appropriate. Experimental results showed that the yaw-moment control allowed the articulated vehicle to turn in a smaller radius. The turning radius by the steering system with the yaw-moment control became at least 1.2 m smaller than the normal system on the wet unpaved road.

On fractional control method for four-wheel-steering vehicle

Four-wheel-steering (4WS) system can enhance vehicle cornering ability by steering the rear wheels in accordance with the front wheels steering and vehicle status. With such steering control system, it becomes possible to improve the lateral stability and handling performance. In this paper, a new control method for 4WS vehicle is proposed, its rear wheels steering angle is in accordance with the angle of front wheels steering and vehicle yaw rate, and the effects of front wheels steering angle velocity are considered by adopting the fractional derivative theory. Some design specifications for control law are also given. The effects of the control method are verified by a kind of numerical scheme presented in this paper. The dynamic characteristics such as the side-slip angle and the yaw angle velocity of the vehicle gravity center are compared among three kinds of vehicles with different control methods. And the kinematics characteristics such as turning radius between 4WS and 2WS are also discussed. Numerical simulation shows that the control method presented can improve the transient response and reduce the turning radius of 4WS vehicle.

Precision Gravity Center Position Measurement System for Heavy Vehicles

Knowledge of a vehicle’s inertial parameters is essential for safety research and accident reconstruction. A precision measure system is proposed to determine the weight and gravity center for heavy vehicles. Based on a static gravity measuring principle with three measuring points, a hydraulically driven 2-DOF motion platform is developed. The transfer function model is derived for the hydraulically driven system. By means of a degree-of-freedom control scheme, the platform can realize accurate positioning to construct two intersected planes and work out the three-dimensional coordinates of the vehicle gravity center. Experiments demonstrate that the system has less than 0.3% measurement error in weight, and is able to measure the gravity centre accurately with deviation ≤3mm in X and Y direction, and ≤5mm in Z direction.

Virtual rollover tests

A simulation of an FMVSS 208 rollover dolly test of a generic pickup truck model was performed using PAM-CRASH. Data from published real-world rollover dolly tests of large passenger cars were used to validate the simulations. The pickup truck model used in the simulation had properties similar to that of the cars used by other researchers in their rollover tests. The initial conditions input into the simulation were similar to actual vehicles subjected to FMVSS 208 rollover dolly tests. The vehicle dynamic responses during the rollovers and the simulation were analysed; the results were compared with published test data, namely rotational velocity, energy loss, vertical and horizontal acceleration, velocity and displacement of vehicle centre of gravity.

Vehicle and Course Characterization Process for Indoor Tire Wear Simulation

Abstract An empirical methodology is described for separately characterizing vehicles and road courses for subsequent combination to predict tire force histories in tire use or testing. By building a library of vehicle and wear course characterizations, indoor wear test simulations can be selectively constructed by using any combination of “virtual” test vehicles and wear courses. A reliable transient record of vertical, lateral and fore-aft forces and inclination angles can be generated and supplied to drive the indoor wear tire loading fixture. Vehicle characterization involves mapping the basic dynamic load transfer behavior over a range of acceleration, deceleration and cornering maneuvers. A unique indoor vehicle test facility is described for efficiently capturing the tire forces and inclination angles during various maneuvers. All four tire positions can be characterized. Vehicle center of gravity (CG) accelerations and speeds are also recorded during indoor testing. An alternative to experimental measurements is the use of a vehicle computer model for mapping the basic dynamic load transfer behavior. Empirical equations relating vehicle kinematics to tire forces and inclination angles have been developed and are presented. A method of utilizing these equations together with outdoor wear course measurements for predicting transient tire force histories is presented. The method is demonstrated and validated with several vehicle case studies. The tire force component of a wear course can be characterized by measurement of a few parameters: the vehicle CG accelerations and the longitudinal velocity. Course characterization is illustrated using the Department of Transportation's Uniform Tire Quality Grading wear course in the San Angelo, TX area. The full 650 km course was characterized and combined with the laboratory characterization of a 1997 Pontiac Grand Am. Four 650 km drive files were created, one for each tire position, for an indoor wear machine. These consisted of five time-based parameters: radial load, lateral force, wheel torque (acceleration, deceleration forces), inclination angle, and velocity. By sequencing a tire through these four drive files, it was “rotated” as it would have been on the actual vehicle. Examples of tire wear rates and irregular wear are shown for a number of tire constructions, comparing the indoor to the outdoor results. Good correlation was achieved. This simulation technique permits the tire force spectrum of quite complex and lengthy routes to be accurately reproduced in the precisely controlled environment of the laboratory. Each cornering maneuver, each braking and acceleration event, every hill and town can be reproduced in real-time. Only by combining the specific vehicle dynamics of a given vehicle with that of a specific wear route can tire wear be accurately simulated. This tire-vehicle system simulation methodology is referred to as a TS-Sim model.

Influences of the load centre of gravity on heavy vehicle acceleration

The aim of this paper is to analyse the influence of the load centre of gravity on heavy vehicle acceleration. This analysis is done through a method in which a vehicle centre of gravity map is used. A model for the driving force is presented for bus, truck and tractor-semitrailer combinations. The proposed model takes into consideration the resistance forces (drag, rolling resistance, translation and rotation acceleration, climbing resistance) and the 4 X 2 traction system. The positions of the vehicle centre of gravity as a function of the position of the load centre of gravity are determined. The vehicle acceleration is calculated based on the position of the load centre of gravity. This study analyses the acceleration of one of the Mercedes-Benz do Brasil tractor-semitrailer vehicle. A comparison of the acceleration for different maximum adhesion coefficients and ramps are presented, showing new results. An example showing the variations of the load centre of gravity position with the acceleration time and distance is provided. The load centre of gravity position is important for vehicle safety and the efficiency and economy in the transportation of the load.

Study on automatic path tracking using virtual point regulator

This study discusses a vehicle path tracking strategy using a virtual point ahead of the vehicle to trace the desired path. Although the vehicle center of gravity can also be employed for the tracking, it is impossible to design the yaw control independently from the controlled lateral motion. By contrast, the yaw motion, as well as the lateral motion, can be controlled to obtain its own desired performance when the virtual point is used for the tracking, although this applies with certain reservations. Additionally, employing the virtual point also secures good robust stability and disturbance suppression performance of the control system.

Land Vehicle Roll/Yaw Product of Inertia Measurement

This paper focuses on the measurement of the roll/yaw product of inertia of a vehicle and describes a four-degree-of-freedom lumped-parameter ADAMS model used to simulate the test configuration. The measurement is performed by oscillating the vehicle in yaw and monitoring the resulting yaw acceleration and roll torque. The product of inertia is calculated from equations representing the motion of a rigid body relative to a nonmoving reference frame modified to accommodate for the misalignment of the vehicle center of gravity and the test apparatus yaw axis, and to approximate the compliant behavior between the test device and vehicle. The effects of the vehicle center of gravity misalignment from the test apparatus’ yaw axis and the compliance between the test vehicle and test device are studied. The measurement uncertainty is found using the law of propagation of uncertainty.

Electric Vehicle Related Technologies. Motion Control of Electric Vehicles by Distribution Control of Traction Forces.

This paper proposes a new method to improve the handling and stability of electric vehicles by controlling the yaw moment generated by driving/braking forces. Yaw moment is controlled by the feedforward compensation of steering angle (and steering velocity) to minimize the side slip angle at the vehicle center of gravity. To realize this kind of yaw moment control, the right and left driving/braking forces should be controlled independently. Theoretical analysis and computer simulation are carried out to show the effectiveness of this control system. The results show that the handling and stability are improved significantly compared to those of the conventional two-wheel-steering vehicles, and that a 4WS-equivalent vehicle performance is obtained. This control effectiveness is also verified by experimental results using a downsized vehicle model on a moving belt tester.

Motion Control of Front-Wheel-Steering Vehicles by Yaw Moment Compensation. Comparison with 4WS Performance.

This paper proposes a new method to improve the handling and stability of vehicles by controlling the yaw moment generated by driving/braking forces. Yaw moment is controlled by the feedforward compensation of steering angle (and steering velocity) to minimize the side slip angle at the vehicle center of gravity. To realize this kind of yaw moment control, the right and left driving/braking forces should be controlled independently. Theoretical analysis and computer simulation are carried out to show the effectiveness of this control system. The results show that the handling and stability are improved significantly compared to those of the conventional two-wheel-steering vehicles, and that a 4WS-equivalent vehicle performance is obtained. This control effectiveness is also verified by experimental results using a downsized vehicle model on a moving belt tester.

Gross thrust coefficient - Turbofan engines

QL = CS(h ± X6 (2) The plenum pneumatic capacitances are based on isentropic compressibility. The pressure rates associated with the inner circular skirt plenums and the inskirt plenum, which lies between the inner circular skirts and the outer peripheral skirt, vary with vehicle motion in pitch and heave where dP/dt = (kP/V)[2Q + A(dZ/dt ± xd8/dt)] (3) The equations of vehicle motion in pitch and heave represent a rigid craft operating over a nondeforming surface with zero forward speed and are simplified by limiting the motion to small perturbations. A body-fixed coordinate system is used with the origin fixed at the vehicle center of gravity. A further simplification is realized due to symmetry about the x-z and y-z planes of the vehicle. The equation of motion in heave for the multiple-skirt ACV is 2 = 9 ~