Matthew Hancock

A comparison of braking and differential control of road vehicle yaw-sideslip dynamics

Abstract Two actuation mechanisms are considered for the comparison of performance capabilities in improving the yaw-sideslip handling characteristics of a road vehicle. Yaw moments are generated either by the use of single-wheel braking or via driveline torque distribution using an overdriven active rear differential. For consistency, a fixed reference vehicle system is used, and the two controllers are synthesized via a single design methodology. Performance measures relate to both open-loop and closed-loop driving demands, and include both on-centre and limit handling manoeuvres.

Yaw motion control via active differentials

The majority of vehicle dynamics control systems currently in production utilize some form of brake or throttle intervention to generate a yaw moment and control wheel slip. Such control systems can be both intrusive and inefficient. The use of active driveline technology is therefore an attractive alternative and recent advances in controlled differential technology have served to make it a potentially viable one. Using simulation results, this paper will demonstrate the power of these devices to influence vehicle dynamics by first proposing a suitable control strategy. This is then used to illustrate how, with perfect actuation, a vehicles handling characteristics may be modified. The actuator limitations imposed by the two main classes of contemporary controlled differentials are then discussed and imposed on the simulation model. Using the ideal results as a benchmark, the relative merits of each type are then assessed.

Modeling and Analysis of Active Differential Dynamics

Active differentials are used to improve the overall performance of traction control and vehicle dynamics control systems. This paper presents the development of a unified mathematical model of active differential dynamics using the bond graph modeling technique. The study includes active limited slip differential and various common types of torque vectoring differentials. Different levels of model complexity are considered, starting from, a second-order model with lumped input and output inertia toward higher-order models including the gear inertia and half-shaft compliance. The model is used for a theoretical analysis of drivability and time response characteristics of the active differential dynamics. The analysts is illustrated by simulation results.

Modelling of electromechanically actuated active differential wet-clutch dynamics

The paper presents a lumped-parameter dynamic model of an electromechanically actuated wet clutch found in an active limited slip differential. The bond graph modelling technique is used to describe the multi-physical clutch system including the clutch actuator dynamics, the axial dynamics with the fluid film squeeze effect, the thermal dynamics, and the torque development dynamics with a multi-functional clutch friction coefficient static characteristic. Different variants of the individual subsystem models are considered, ranging from first-principle models to simplified and numerically more efficient models. The proposed models are parameterized and thoroughly validated on the basis of the experimental data collected by using an active differential and clutch test rig. The modelling results are used for the purpose of analysis of the clutch steady state and transient behaviour under various operating modes.

Optimization of Global Chassis Control Variables

Abstract The paper presents a global chassis control (GCC) optimization approach using a gradient-based optimal control algorithm. The goal is to find optimal actions of various actuators such as active steering and active differential, which ensure satisfying the optimization criterion (e.g. trajectory following error minimization) subject to different equality and inequality constraints on state and control variables. The optimization algorithm is based on an exact gradient method, where the cost function gradient is calculated by using a backpropagation-through-time-like algorithm. The proposed GCC optimization approach is illustrated on an example of double lane change maneuver using rear active steering and/or rear active differential actuators.

Modeling of Active Differential Dynamics

Active differentials are increasingly being used in high-end vehicles in order to improve the overall performance of vehicle dynamics control systems. The active differentials can be divided into active limited slip differentials and torque vectoring differentials. This paper presents the development of a generalized mathematical model of active differential dynamics using the bond graph modeling technique. Different levels of model complexity are considered, starting from a second-order model with lumped input and output inertia towards high order models including the gear inertia and halfshaft compliance. The paper also presents typical model simulation results and their comparative analysis with respect to drivability and time response features.Copyright

A Linearized Vehicle Dynamics Model for Global Chassis Control

The paper presents an analytical linearized vehicle dynamics model for global chassis control. Use of the following vehicle dynamics actuators is anticipated: active front and rear steering, active rear and central differential, and drive-by-wire power plant. The linearized model takes into account the tire effects of combined slip and variable normal force. The transfer function form of the linearized model is used for an analysis of control authority of different actuators. The influence of lateral tire relaxation length is also analyzed and incorporated in the model. Characteristic features of the transfer function model with respect to yaw rate output are revealed and used for model order reduction. The presented linearized model is validated against nonlinear models of different complexity.Copyright

Modeling and Experimental Validation of Active Limited Slip Differential Clutch Dynamics

This paper deals with modeling of an Active Limited Slip Differential (ALSD) which comprises a wet clutch actuated by an electromechanical mechatronic system consisting of a DC motor and ball-ramp mechanism. The structure of the proposed ALSD model is divided in two subsystems: (i) clutch axial force development model and (ii) clutch torque development model. The former includes DC motor dynamics; gear box kinematics and backlash; ball-ramp mechanism kinematics, friction, and compliance; fluid squeeze speed dynamics; and clutch pack axial compliance and damping. The latter includes structural compliance and inertias, as well as dynamic friction effects. Each submodel has a pure physical structure. This facilitates model parameterization through a series of relatively simple experimental procedures, which are also described in the paper. The final model has been validated under various operating conditions by using an ALSD test rig. The validation results point to a good modeling accuracy.Copyright

A Closed-Loop Strategy of Active Differential Clutch Control

The paper presents experimentally supported control-oriented analysis of dynamics of an active differential wet clutch actuated by a geared DC motor. A closed-loop clutch control strategy is proposed. The strategy is based on experimentally obtained hysteresis-free clutch applied force vs. motor position curve and related closed-loop motor position control. A controller algorithm is proposed to compensate for the effect of clutch free-play variations due to clutch wear. The proposed control strategy performance is verified on a wet clutch experimental setup.© 2009 ASME

Bond Graph Modeling and Analysis of Active Differential Kinematics

This paper describes the kinematic structures of Active Limited Slip Differential (ALSD) and different concepts of Torque Vectoring Differentials (TVD) (superposition clutch concept, stationary clutch concept, and 4WD concept). The bond graph method is used to derive the models of ALSD/TVD kinematics. Based on the developed models, a comparative analysis of active differential operating modes and performance is conducted.Copyright