Friction Braking Torque Research Articles

Integrated control of braking-yaw-roll stability under steering-braking conditions

Sharp steering-braking at a high speed exposes sport utility vehicles with high gravity centers and narrow wheel tracks to the risks of tire locking, sideslip and rollover. To avoid these risks and ensure braking safety, yaw stability and roll stability upon steering-braking, a braking-yaw-roll stability integrated control strategy was proposed, which consists of a supervisor, an upper and a lower controller for the front and rear axle independent drive electric vehicle. In the supervisor, a nonlinear vehicle predictive model was constructed and four control modes were proposed according to the vehicle status and rollover indexes. The weight coefficients between braking force, yaw stability and roll stability are determined dynamically by the control mode and output to the upper controller. The upper controller used a nonlinear model predictive control to determine the longitudinal braking force distribution of the four wheels. And in the lower controller, the regenerative braking torque and friction braking torque of each wheel were distributed. Finally, simulation verifications were carried out on the high and low adhesion roads. The results show that the control strategy proposed in this study can effectively prevent the vehicle from rollover while ensuring braking safety and yaw stability.

Integrated Regenerative Braking System and Anti-Lock Braking System for Hybrid Electric Vehicles & Battery Electric Vehicles

<div class="section abstract"><div class="htmlview paragraph">This paper describes development of an integrated regenerative braking system and anti-lock brake system (ABS) control during an ABS event for hybrid and electric vehicles with drivelines containing a single electric motor connected to the axle shaft through an open differential. The control objectives are to recuperate the maximum amount of kinetic energy during an ABS event, and to provide no degraded anti-lock control behavior as seen in vehicles with regenerative braking disabled. The paper first presents a detailed control system analysis to reveal the inherent property of non-zero regenerative braking torque control during ABS event and explain the reason why regenerative braking torque can increase the wheel slip during ABS event with existing regenerative braking control strategies. Then, the regenerative brake control problem during ABS events is formulated with a unified control system architecture where the regenerative braking torque is coordinated with the friction braking torque of ABS system. An integrated closed loop based wheel slip control including both regenerative braking control loop and friction braking control loop during ABS event, referred to as RBS-ABS event control, is developed. The maximum regenerative braking is achieved and optimal vehicle braking performances and vehicle stability are maintained during ABS event. Finally, simulation tests are provided to illustrate RBS-ABS event control as an effective solution to satisfy desired wheel slip with the same level of stop distance in comparison with that of ABS control only while performing energy recuperation.</div></div>

Impact of regenerative braking torque blend-out characteristics on electrified heavy road vehicle braking performance

Electric and hybrid vehicles use a co-operative brake system that consists of regenerative brake and friction brake with different dynamic characteristics to obtain adequate deceleration during braking. Hence, the mechanism of braking blend-out (that is the mechanism of switching off regenerative braking) may affect the vehicle braking performance. This work focusses on the development of various co-operative braking strategies (series and parallel) for electrified heavy road vehicles by considering instantaneous braking blend-out and ramp down braking blend-out characteristics. The developed co-operative braking strategies were evaluated in a Hardware-in-Loop experimental setup equipped with TruckMaker® software. The results showed that instantaneous braking blend-out has more impact on vehicle braking performance in terms of momentary magnitude change in the longitudinal deceleration, pitch angle and suspension deflection for a laden vehicle compared with an unladen vehicle on both dry and icy road surfaces. Ramp down braking blend-out reduced these momentary magnitude changes and thereby improved vehicle’s braking performance in terms of stopping distance and ride comfort. The results of this study indicate that ramp down braking blend-out is expected to improve the vehicle dynamic performance during active braking control due to the smooth transition between friction braking torque and regenerative braking torque.

Design of a frictional–electromagnetic compound disk brake for automotives

According to the disadvantages of serious wear and heat fade of friction pad in frequent and high speed braking of friction brakes, and the insufficient power of electromagnetic brakes in low speed braking, a novel frictional-electromagnetic compound disk brake which combines both of these two brake principles is proposed for automotives in this paper. The excitation coils are designed based on the Zhang Yicheng theory model, and the compound brake prototype is manufactured based on the self-made magnetic brake pads and existing automotive brakes. The magnetic field and dynamic of the brake are simulated by using COMSOL Multiphysics software. The frictional–electromagnetic compound brake tests are implemented on the reconstructive disk brake simulation test bench. The experimental results show that the friction braking torque accounts for more than 90% of the compound braking torque in the process of compound braking, and the trend of the change is the same as that of the compound braking torque. When the initial braking speed exceeds 75 km/h, the electromagnetic braking torque does not increase with the increase in speed, instead, it decreases slightly because of demagnetization. The designed frictional–electromagnetic compound disk brake has good braking performance.

Development of a Cooperative Braking System for Front-Wheel Drive Electric Vehicles

Most electric vehicles adopt cooperative braking systems that can blend friction braking torque with regenerative braking torque to achieve higher energy efficiency while maintaining a certain braking performance and driving safety. This paper presented a new cooperative regenerative braking system that contained a fully-decoupled hydraulic braking mechanism based on a modified electric stability control system. The pressure control algorithm and brake force distribution strategy were also discussed. Dynamic models of a front wheel drive electric car equipped with this system and a simulation platform with a driver model and driving cycles were established. Tests to evaluate the braking performance and energy regeneration were simulated and analyzed on this platform and the simulation results showed the feasibility and effectiveness of this system.

Hierarchical Braking Torque Control of In-Wheel-Motor-Driven Electric Vehicles Over CAN

This paper proposes a hierarchical braking torque control system design over controller area network (CAN) for electric vehicle with four in-wheel motors. Based on nonlinear tyre-road friction estimation, an adaptive braking torque control scheme is devised in the upper level controller to simultaneously regulate the wheel slip ratio for both front and rear wheels. While in the lower-level controller, a frequency-depended braking torque allocator is developed to dynamically distribute the braking torques command from upper level controller into friction braking torque and regenerative braking torque. A braking supervisor is established to enable or disable proposed hierarchical braking controller according to wheel slip ratio as well as vehicle speed condition. To avoid undesired discontinuities in braking torque signal when proposed braking controller is enabled abruptly, an initial value of the estimated tyre-road friction is rescaled additionally. Dedicated CAN bus module is built by using SimEvent toolbox, by which vehicle states as well as control signals can be transmitted and shared. Co-simulation by using MATLAB/Simulink and CarSim is conducted to demonstrate the effectiveness of the proposed hierarchical braking torque controller. Random CAN-induced delays are considered in the braking control process, by which the robustness of the proposed hierarchical braking controller is further verified.

Cooperative control of regenerative braking and friction braking in the transient process of anti-lock braking activation in electric vehicles

Regenerative braking significantly improves the energy efficiency in electric vehicles. Cooperative control between regenerative braking and friction braking during anti-lock braking control is a critical issue in brake system coupling. For safety concerns, regenerative braking is often terminated at the beginning of anti-lock braking control. Oscillations between activation of an anti-lock braking system and exit from anti-lock braking system control may occur under poorly matched control parameters. To solve these problems, we propose an index that indicates the possibility of activation of an anti-lock braking system. It is derived by a fuzzy logic algorithm which is based on the estimated regenerative braking torque, the estimated friction braking torque and other vehicle state variables. Regenerative braking can be adjusted on the basis of the index to ensure that such braking is of a low level when an anti-lock braking system is activated. Simulations and experiments are carried out to evaluate the effectiveness of the index. The results show that regenerative braking decreases as the index increases, thereby improving the braking safety and the driving comfort during the transient process of activation of an anti-lock braking system.

Cooperative control for friction and regenerative braking systems considering dynamic characteristic and temperature condition

The braking system of hybrid electric vehicle (HEV) is composed of friction and regenerative braking system, meaning that braking torque is generated by the collaboration of the friction and regenerative braking system. With the attributes, there are two problems in the HEV braking system. First, rapid deceleration occurs due to dynamic characteristic difference when shifting the friction and regenerative braking systems. Second, the friction braking torque alters with temperature because the friction coefficient changes with the temperature. These problems cause the vehicle to be unstable. In this paper, the concurrence control and compensation control were proposed to solve these problems. And also, the concurrence control and compensation control were combined for the stability of the braking system. In order to confirm the effect of these control algorithms, the experiment and simulation were conducted. Consequently, it was confirmed that the control algorithm of this study improved the vehicle safety and stability.

Cooperative Control Algorithm for Friction and Regenerative Braking Systems Considering Temperature Characteristics

In a hybrid electric vehicle (HEV), the braking system is composed of friction braking and regenerative braking. When a driver presses the brake pedal, each braking system collaborates and applies braking torque. The friction brake is a hydraulic system which has a slow response time and the regenerative brake is an electric system which responds quickly. Such characteristics bring a control problem, especially transient characteristic of shifts between regenerative brake and friction brake, because the hydraulic system cannot follow the response time of the electric system. The friction braking torque is also governed by the friction coefficient which changes with temperature. This causes the braking torque to be generated differently with the demanded braking torque, without considering the temperature. Due to these problems, the driver would feel uncomfortable and the vehicle would be unstable resulting from the difference in response time and variance of the friction coefficient when pressing the brake pedal. Hence, it is essential to coincide the settling time of friction and regenerative braking system regarding the temperature. To solve these problems, the hydraulic system was mathematically modelled using the flow and continuity equations and the electric system was modelled using the d-q transformation and voltage equation. The temperature estimation model of the brake components was developed using the heat transfer methods which are conduction, convection and semi-infinite solid. The brake temperature was calculated by the finite difference method (FDM). With the mathematical model of hydraulic and electric systems, the coincidence control for the settling time of both systems was established. It was also possible to find the friction coefficient and calculate the braking torque by using the temperature estimator. In this paper, the numerical simulation was carried out to verify these control algorithms. The difference in response time between friction and regenerative braking system was reduced and the transient characteristic was improved. Also, the braking torque was compensated with the temperature, and the difference between demanded and actual braking torque lessen using the algorithms.

Performance Evaluation of an Anti-Lock Braking System for Electric Vehicles with a Fuzzy Sliding Mode Controller

Traditional friction braking torque and motor braking torque can be used in braking for electric vehicles (EVs). A sliding mode controller (SMC) based on the exponential reaching law for the anti-lock braking system (ABS) is developed to maintain the optimal slip value. Parameter optimizing is applied to the reaching law by fuzzy logic control (FLC). A regenerative braking algorithm, in which the motor torque is taken full advantage of, is adopted to distribute the braking force between the motor braking and the hydraulic braking. Simulations were carried out with Matlab/Simulink. By comparing with a conventional Bang-bang ABS controller, braking stability and passenger comfort is improved with the proposed SMC controller, and the chatting phenomenon is reduced effectively with the parameter optimizing by FLC. With the increasing proportion of the motor braking torque, the tracking of the slip ratio is more rapid and accurate. Furthermore, the braking distance is shortened and the conversion energy is enhanced.

Speed control experiments for heavy duty vehicles with coordinated friction and engine compression brakes

In this paper we describe the development and experimental validation of a coordination scheme between friction and engine compression brakes for a Class 8 Freightliner truck used as a development platform in the California PATH program. The coordination scheme maintains the speed tracking performance of the nominal PID controller, which was originally designed for the case of friction brakes only. Through the coordination scheme, the command of the nominal PID controller is interpreted as a braking torque demand and split into a friction brake command and compression brake command. The split is based on the models for the compression braking torque and friction braking torque developed and identified from open-loop experiments. The results of closed-loop experiments show that the integration of the compression brake into the speed control framework reduces the usage and therefore the wear of the conventional friction brakes.

A study on regenerative braking for a parallel hybrid electric vehicle

In this paper, a regenerative braking algorithm is presented and performance of a hybrid electric vehicle (HEV) is investigated. The regenerative braking algorithm calculates the available regenerative braking torque by considering the motor characteristics, the battery SOC and the CVT speed ratio. When the regenerative braking and the friction braking are applied simultaneously, the friction braking torque corresponding to the regenerative braking should be reduced by decreasing the hydraulic pressure at the front wheel. To implement the regenerative braking algorithm, a hydraulic braking module is designed. In addition, the HEV powertrain models including the internal combustion engine, electric motor, battery, CVT and the regenerative braking system are obtained using AMESim, and the regenerative braking performance is investigated by the simulation. Simulation results show that the proposed regenerative braking algorithm contributes to increasing the battery SOC which results in the improved fuel economy. To verify the regenerative braking algorithm, an experimental study is performed. It is found from the experimental results that the regenerative braking hydraulic module developed in this study generates the desired front wheel hydraulic pressure specified by the regenerative braking control algorithm.