Experimental and numerical approach to investigate tire and ABS combined influence on wet braking performance of passenger cars.

This PhD activity is mainly focused on the study of the emergency braking test, where the tire behaviour can be influenced by the ABS system during such manoeuvre on wet roads. The main goal is to investigate and optimize the optimal shape of the longitudinal force characteristics of the tire in order to reduce the braking distance. The only evaluation of the μ-peak could not be sufficient for reliable assessments but the whole shape of the longitudinal curve should be considered. Nowadays, the Wet Grip Index (WGI) is the parameter with which it is possible to classify the quality of a tire in wet conditions in the EU tire label and it is mainly based on maximum grip that a tire can perform interacting with the wet road. Understanding the optimal shape of the curve could also mean to understand if the WGI approach can give a complete evaluation of tire performance during the braking, or there could be something more to take into account. A numerical approach was considered and a ABS logic has been modelled with the aim to replicate the fundamental strategies of a passenger car. A half vehicle model has been considered for this research work. A more physical approach on ABS modelling is proposed in this thesis, with the aim to estimate the optimal working range of the logic without any pre-set information. Regarding the implemented tire model, the focuses were on trying to find a method to characterize the tire in wet conditions and understand how the longitudinal relaxation length can influence the ABS work in simulation environment. A method is proposed to get a possible estimation of the longitudinal relaxation length of the tire from vehicle measurements. Moreover, a study about the relaxation length evaluation with respect to the excitation frequency coming from the longitudinal slippage will be described in this thesis. The emergency braking model was used to optimize the reference curve in order to reduce the braking distance. The analysis is focused on three parameters that can identify the longitudinal characteristics of the tire: the braking stiffness, μ-peak and drop down of the grip after the peak condition. The main outcome of the simulation results shows that the μ-peak could not be considered as the only critical parameter to evaluate the braking performance of the tire and that the drop-down of the grip seems to play a very important role to reduce braking distances

Adaptive optimal slip ratio estimator for effective braking on a non-uniform condition road

In this paper, an adaptive algorithm is developed which senses the road condition change and estimates a (time-varying) optimal braking slip ratio. This is conducted by two on-line simultaneously operating tire-road friction-curve slope calculators: one based on the accelerometer output and the other based on the wheel speed. The required vehicle speed is estimated using a robust sliding-mode observer. Enforcement of the online optimal braking reference is left to an adaptive sliding mode controller to cope with the system strong nonlinearity, time dependency and the speed and friction-coefficient estimation errors. The algorithm is applied to a half model car and the braking performance is examined. The results indicate that the proposed algorithm substantially reduces the stopping time and distance. The performance of the algorithm is verified using different vehicle initial speeds and especially non-uniform road condition where 8% improvement versus the nonadaptive optimal slip ratio algorithm is recorded

Sliding Mode Measurement Feedback Control for Antilock Braking Systems

We describe a nonlinear observer-based design for control of vehicle traction that is important in providing safety and obtaining desired longitudinal vehicle motion. First, a robust sliding mode controller is designed to maintain the wheel slip at any given value. Simulations show that longitudinal traction controller is capable of controlling the vehicle with parameter deviations and disturbances. The direct state feedback is then replaced with nonlinear observers to estimate the vehicle velocity from the output of the system (i.e., wheel velocity). The nonlinear model of the system is shown locally observable. The effects and drawbacks of the extended Kalman filters and sliding observers are shown via simulations. The sliding observer is found promising while the extended Kalman filter is unsatisfactory due to unpredictable changes in the road condition

Brake Strategy Analysis for Industrial Normal-closed Brake Based on Rotational Inertia Test and Simulation

Industrial brakes pose the dilemma of weighing brake capability against brake impact since the brake torque cannot be adjusted. On the one hand, the brake torque may be insufficient to stop the movement within a limited distance or parking position. On the other hand, the brake torque may be so high it can damage the transmission chain. In this study, the traditional brake strategy and the field oriented control (FOC) brake strategy were compared through simulation and a rotational inertia test. The influence of the rated brake torque and the open-closed ratio were obtained. Based on the test and simulation results, a semi-empirical formula that defines the relationship between relative brake capability and open-closed ratio was developed. Additional simulations were performed to analyze the performance of the brake in a flexible transmission chain. As an industrial application example, the benefits and the cost of a 'smart brake' based on the FOC brake strategy were analyzed. The results indicate that the equivalent brake torque with the FOC brake strategy is a function of the real-time controllable input and open-closed ratio, which can be conducted during the braking procedure. This can be an efficient way to solve the above problems

Discrete-time slip control algorithms for a hybrid electric vehicle

This thesis develops a discrete-time sliding mode control scheme for a slip control of a hybrid electric vehicle. In order to handle different road conditions, fuzzy logic technique is employed to develop control of slip ratio. A discrete-time Sliding mode observer is also designed to estimate the vehicle velocity online. Furthermore, in order to cope up with changing slip dynamic for varying road conditions an Adaptive sliding mode control has been designed by employing Lyapunov theory. The performances of developed adaptive sliding mode control, Sliding mode control and Fuzzy logic control for slip ratio are compared through extensive Matlab simulation and it is observed that the discrete time Fuzzy adaptive sliding mode control perform effectively

Intelligent Sliding Mode Scheme for Regenerative Braking Control

Controller design for an Anti-Lock Braking System (ABS) of a Hybrid Electric Vehicle (HEV) or Electric Vehicle (EV) is a challenging task because of the trade-off between braking efficiency and energy recuperation efficiency. In hybrid vehicles, the brake torque demand is met by both the conventional friction braking system and an electric Regenerative Braking System (RBS). Hence, an effective ABS controller is required to achieve high braking efficiency without losing energy recuperation efficiency. This paper presents an Intelligent Sliding Mode Scheme (ISMS) to retain high energy recuperation efficiency as well as good braking efficiency of an EV with a unique braking configuration. The ISMS has a supervisory logic based motor torque limiter and slip controller. The slip controller is designed based on a two-wheeled model which has a hydraulic unit at the front producing frictional braking cooperating with a regenerative braking system with a brake-by-wire unit at the rear wheels. The slip controller is designed considering the hydraulics and motor actuator dynamics and the complete Magic Formula (MF) is used for tyre force estimation. The logic-based torque limiter not only regulates the brake torque to follow an assigned brake force distribution but also ensures that the battery is not overcharged

Blended Antilock Braking System Control Method for All-Wheel Drive Electric Sport Utility Vehicle

At least two different actuators work in cooperation in regenerative braking for electric and hybrid vehicles. Torque blending is an important area, which is responsible for better manoeuvrability, reduced braking distance, improved riding comfort, etc. In this paper, a control method for electric vehicle blended antilock braking system based on fuzzy logic is promoted. The principle prioritizes usage of electric motor actuators to maximize recuperation energy during deceleration process. Moreover, for supreme efficiency it considers the batteryâs state of charge for switching between electric motor and conventional electrohydraulic brakes. To demonstrate the functionality of the controller under changing dynamic conditions, a hardware-in-the-loop simulation with real electrohydraulic brakes test bed is utilized. In particular, the experiment is designed to exceed the state-of-charge threshold during braking operation, what leads to immediate switch between regenerative and friction brake modes. Document type: Part of book or chapter of boo

Research and Implement of PMSM Regenerative Braking Control for Electric Vehicle

As the society pays more and more attention to the environment pollution and energy crisis, the electric vehicle (EV) development also entered in a new era. With the development of motor speed control technology and the improvement of motor performance, although the dynamic performance and economical cost of EVs are both better than the internal-combustion engine vehicle (ICEV), the driving range limit and charging station distribution are two major problems which limit the popularization of EVs. In order to extend driving range for EVs, regenerative braking (RB) emerges which is able to recover energy during the braking process to improve the energy efficiency. This thesis aims to investigate the RB based pure electric braking system and its implementation. There are many forms of RB system such as fully electrified braking system and blended braking system (BBS) which is equipped both electric RB system and hydraulic braking (HB) system. In this thesis the main research objective is the RB based fully electrified braking system, however, RB system cannot satisfy all braking situation only by itself. Because the regenerating electromagnetic torque may be too small to meet the braking intention of the driver when the vehicle speed is very low and the regenerating electromagnetic torque may be not enough to stop the vehicle as soon as possible in the case of emergency braking. So, in order to ensure braking safety and braking performance, braking torque should be provided with different forms regarding different braking situation and different braking intention. In this thesis, braking torque is classified into three types. First one is normal reverse current braking when the vehicle speed is too low to have enough RB torque. Second one is RB torque which could recover kinetic energy by regenerating electricity and collecting electric energy into battery packs. The last braking situation is emergency where the braking torque is provided by motor plugging braking based on the optimal slip ratio braking control strategy. Considering two indicators of the RB system which are regenerative efficiency and braking safety, a trade-off point should be found and the corresponding control strategy should be designed. In this thesis, the maximum regenerative efficiency is obtained by a braking torque distribution strategy between front wheel and rear wheel based on a maximum available RB torque estimation method and ECE-R13 regulation. And the emergency braking performance is ensured by a novel fractional-order integral sliding mode control (FOISMC) and numerical simulations show that the control performance is better than the conventional sliding mode controller