The effect of half-shaft torsion dynamics on the performance of a traction control system for electric vehicles

This article deals with the dynamic properties of individual wheel electric powertrains for fully electric vehicles, characterised by an in-board location of the motor and transmission, connected to the wheel through half-shafts. Such a layout is applicable to vehicles characterised by significant power and torque requirements where the adoption of in-wheel electric powertrains is not feasible because of packaging constraints. However, the dynamic performance of in-board electric powertrains, especially if adopted for anti-lock braking or traction control, can be affected by the torsional dynamics of the half-shafts. This article presents the dynamic analysis of in-board electric powertrains in both the time domain and the frequency domain. A feedback control system, incorporating state estimation through an extended Kalman filter, is implemented in order to compensate for the effect of the half-shaft dynamics. The effectiveness of the new controller is demonstrated through analysis of the improvement in the performance of the traction control system

Drivability analysis of through-the-road-parallel hybrid vehicles

In the last decade, Hybrid Electric Vehicles (HEVs) have spread worldwide due to their capability to reduce fuel consumption. Several studies focused on the optimisation of the energy management system of hybrid vehicles are available in literature, whilst there are few articles dealing with the drivability and the dynamics of these new powertrain systems. In this paper a ‘Through-the-Road-Parallel HEV' is analysed. This architecture is composed of an internal combustion engine mounted on the front axle and an electric motor powering the rear one. These two powertrains are not directly connected to each other, as the parallel configuration is implemented through the road-tyre force interaction. The main purpose of this paper is the drivability analysis of this layout of HEVs, using linearised mathematical models in both time (i.e. vehicle response during tip-in tests) and frequency domain (i.e. frequency response functions), considering the effect of the engaged gear ratio. The differences from a traditional Front-Wheel-Drive (FWD) configuration are subsequently highlighted. Furthermore, the authors compare different linearised dynamic models, with an increasing number of degrees of freedom, in order to assess which model represents the best compromise between complexity and quality of the results. Finally, a sensitivity analysis of the influence of the torque distribution between the front (thermal) and rear (electric) axles on vehicle drivability is carried out and presented in detai

The effect of the front-to-rear wheel torque distribution on vehicle handling: an experimental assessment

The front-to-rear wheel torque distribution influences vehicle handling and, ulti-mately, it affects key factors such as vehicle safety and performance. At a glance, due to part of the available tire-road friction being used for traction at the driven axle, a Front-Wheel-Drive (FWD) vehicle would be expected to be more understeering than a Rear-Wheel-Drive (RWD) vehicle. However, such effect may be counterbalanced, or even reversed, mainly due to the yaw moment caused by the lateral contribution of the traction forces at the front wheels. This paper proposes an experimental assessment, carried out on a fully electric vehicle with multiple mo-tors, allowing different front-to-rear wheel torque distributions. The results confirm that the yaw moment effect discussed is considerable, especially at low vehicle speeds and high steering an-gles. In particular, the RWD vehicle resulted more understeering than the FWD one at 30 km/h

Energy efficient torque vectoring control

Tire forces are at the heart of the dynamic qualities of vehicles. With the advent of electric vehicles the precise and accurate control of the traction and braking forces at the individual wheel becomes a possibility and a reality outside test labs and virtual proving grounds. Benefits of individual wheel torque control, or torque-vectoring, in terms of vehicle dynamics behavior have been well documented in the literature. However, very few studies exist which analyze the individual wheel torque control integrated with vehicle efficiency considerations. This paper focuses on this aspect and discusses the possibilities and benefits of integrated, energy efficient torque vectoring control. Experiments with a four-wheel-drive electric vehicle show that considerable energy savings can be achieved by considering drivetrain and tire power losses through energy efficient torque vectoring control

Understeer characteristics for energy-efficient fully electric vehicles with multiple motors

Electric vehicles with multiple motors allow torque-vectoring, which generates a yaw moment by assigning different motor torques at the left and right wheels. This permits designing the steady-state cornering response according to several vehicle handling quality targets. For example, as widely discussed in the literature, to make the vehicle more sports-oriented, it is possible to reduce the understeer gradient and increase the maximum lateral acceleration with respect to the same vehicle without torque-vectoring. This paper focuses on the novel experimentally-based design of a reference vehicle understeer characteristic providing energy efficiency enhancement over the whole range of achievable lateral accelerations. Experiments show that an appropriate tuning of the reference understeer characteristic, i.e., the reference yaw rate of the torque-vectoring controller, can bring energy savings of up to ~11% for a case study four-wheel-drive electric vehicle demonstrator. Moreover, during constant speed cornering, it is more efficient to significantly reduce the level of vehicle understeer, with respect to the same vehicle with even torque distribution on the left and right wheels

Nonlinear Model Predictive Control for Integrated Energy-Efficient Torque-Vectoring and Anti-Roll Moment Distribution

This study applies nonlinear model predictive control (NMPC) to the torque-vectoring (TV) and front-to-total anti-roll moment distribution control of a four-wheel-drive electric vehicle with in-wheel-motors, a brake-by-wire system, and active suspension actuators. The NMPC cost function formulation is based on energy efficiency criteria, and strives to minimize the power losses caused by the longitudinal and lateral tire slips, friction brakes, and electric powertrains, while enhancing the vehicle cornering response in steady-state and transient conditions. The controller is assessed through simulations using an experimentally validated high-fidelity vehicle model, along ramp steer and multiple step steer maneuvers, including and excluding the direct yaw moment and active anti-roll moment distribution actuations. The results show: 1) the substantial enhancement of energy saving and vehicle stabilization performance brought by the integration of the active suspension contribution and TV; 2) the significance of the power loss terms of the NMPC formulation on the results; and 3) the effectiveness of the NMPC with respect to the benchmarking feedback and rule based controllers

On the handling performance of a vehicle with different front-to-rear wheel torque distributions

The handling characteristic is a classical topic of vehicle dynamics. Usually, vehicle handling is studied through the analysis of the understeer coe�cient in quasi-steady-state maneuvers. In this paper, experimental tests are performed on an electric vehicle with four independent mo- tors, which is able to reproduce front-wheel-drive, rear-wheel-drive and all-wheel-drive (FWD, RWD and AWD, respectively) architectures. The handling characteristics of each architecture are inferred through classical and new concepts. More speci�cally, the study presents a pro- cedure to compute the longitudinal and lateral tire forces, which is based on a �rst estimate and a subsequent correction of the tire forces that guarantee the equilibrium. A yaw moment analysis is then performed to identify the contributions of the longitudinal and lateral forces. The results show a good agreement between the classical and new formulations of the un- dersteer coe�cient, and allow to infer a relationship between the understeer coe�cient and the yaw moment analysis. The handling characteristics for the considered maneuvers vary with the vehicle speed and front-to-rear wheel torque distribution. In particular, an apparently surprising result arises at low speed, where the RWD architecture is the most understeering con�guration. This outcome is discussed through the yaw moment analysis, highlighting the yaw moment caused by the longitudinal forces of the front tires, which is signi�cant for high values of lateral acceleration and steering angle

On the model-based design of front-to-total anti-roll moment distribution controllers for yaw rate tracking

In passenger cars active suspensions have been traditionally used to enhance comfort through body control, and handling through the reduction of the tyre load variations induced by road irregularities. However, active suspensions can also be designed to track a desired yaw rate profile through the control of the anti-roll moment distribution between the front and rear axles. The effect of the anti-roll moment distribution relates to the nonlinearity of tyre behaviour, which is difficult to capture in the linearised vehicle models normally used for control design. Hence, the tuning of anti-roll moment distribution controllers is usually based on heuristics. This paper includes an analysis of the effect of the lateral load transfer on the lateral axle force and cornering stiffness. A linearised axle force formulation is presented, and compared with a formulation from the literature, based on a quadratic relationship between cornering stiffness and load transfer. Multiple linearised vehicle models for control design are assessed in the frequency domain, and the respective controllers are tuned through optimisation routines. Simulation results from a nonlinear vehicle model are discussed to analyse the performance of the controllers, and show the importance of employing accurate models of the lateral load transfer effect during control design

Energy consumption analysis of a novel four-speed dual motor drivetrain for electric vehicles

The electric vehicle is becoming increasingly prevalent as a viable option to replace hydrocarbon fuelled vehicles, and as such the development of high efficiency fully electric drivetrains is a particularly relevant research topic. The drivetrain topology is one of the main focuses of research on fully electric drivetrains, because of the variety of available options. For example, the adoption of multiple-speed mechanical transmissions can improve both the performance and energy consumption when compared to a single-speed transmission. A four-speed, dual motor drivetrain design is presented in this article which works on the principle of two double-speed transmissions, each driven by a separate motor linked through a sole secondary shaft. This drivetrain architecture provides increased flexibility of the electric motor operating points, theoretically being beneficial to the overall efficiency of the system for any driving condition. This paper presents the design of the transmission, its governing equations and the method adopted to optimize the state selection map and electric motor torque distribution. A backward-facing energy consumption model is used to compare the results of the four-speed transmission with those of single- and double-speed transmissions for four case study vehicles. © 2012 IEEE