Chapter 6 - Brake system layout design

Electric vehicles (EVs) have the advantage of using both regenerative braking and mechanical braking to produce the necessary braking torque. Currently, vehicles use Anti-lock Braking Systems (ABS) which provide intermittent braking torque to the vehicle and thereby prevents skidding or slipping of the vehicle by ensuring pure rolling of the wheels. Regenerative braking on the other hand generates the necessary braking torque by converting the kinetic energy of the vehicle to electrical energy via the motor(s). To coordinate both braking systems, the conventional method involves the use of crisp logic controllers that depend on lookup tables containing the data about various aspects of the vehicle such as battery state of charge (SoC), brake pedal input etc., to enable co-operative control of both systems. This paper presents a combined implementation of both braking systems in electric vehicles using separate fuzzy controllers for both ABS and regenerative braking. The control scheme is implemented such that when regenerative braking is not capable of providing enough braking torque, braking will be one by ABS. Two fuzzy logic controllers have been used, one to implement regenerative braking and the other to implement mechanical braking via ABS. If such a control algorithm is used, the driver will not have to manually adjust the level of regenerative braking in the vehicle and such an approach ensures that the braking process of an EV is smooth, safe and efficient. It also reduces the wear and tear of the brake pads thereby extending their life and reducing the cost of maintenance and by extension the total cost of ownership of the vehicle. The results demonstrate that the controllers for both ABS and regenerative braking can coordinate efficiently and reliably to produce proper and safe braking of the vehicle.

Regenerative braking is one of the most important features of a hybrid vehicle. Currently used regenerative braking systems add a considerable cost to the vehicle due to the electronics involved. The author presents here a novel method for implementing a regenerative brake strategy without changing the mechanical brake system, i.e., without adding complex electronic systems like ABS, of a low cost conventional vehicle which is converted to a low-cost HEV (hybrid electric vehicle) for front axle applications. The electric braking force is additional to the mechanical braking force applied by friction brakes under normal conditions. In a previous study, a similar strategy was discussed but for application on the rear axle only. This strategy pertains to the regenerative brake force being applied on the front axle of a rear wheel drive vehicle. The strategy is simulated over urban drivecycles and results are compared with NEDC drivecycle. The results show a potential of 30% of brake energy recuperation with the proposed strategy. The study also illustrates the relevance of the strategy to high traffic volume markets with low vehicle speeds.

In recent years, more use of narrow lanes as a temporary traffic management scheme (TTMS) on UK motorway roadwork sections has been made. The rationale is to free up carriageway space, especially for sites with high traffic demands needing repairs. What remains to be determined is the impact of this work on traffic operation. This is important due to the need to manage traffic operational turbulence which could affect the capacity as well as safety levels in roadwork sections. Site observations (mainly using camcorders from overhead bridges) were made which uncovered two discernible patterns of driving behaviour where narrow lanes are implemented at roadworks, especially when heavy goods vehicles (HGVs) are present: (i) “avoiding” passing/overtaking HGVs travelling in the adjacent lanes and (ii) lane “repositioning” while passing/overtaking which might cause some turbulence to traffic operation. From one site, almost half of the passenger car drivers (including small vans) who were following a HGV on the adjacent lanes were avoiding passing that HGV. Also, nearly three quarters of the observed passenger cars, the passenger car drivers tried to position their vehicles as far away as possible, laterally, from the adjacent HGV while passing/overtaking that HGV in order to widen the lateral gap between their vehicles and the HGV. This resulted in driving too close to the edge of the road markings of their current lane away from the HGV. Therefore, this paper aims to report on the “avoiding” and lane “repositioning” behaviours to help inform traffic management teams/designers using narrow lanes as TTMS and make them aware of such behaviours (especially for motorway sections carrying high percentages of HGVs). Also, the finding from these observations were used in the development of a new micro-simulation model in order to evaluate the effect of such turbulence.

Traffic Modeling and Safety Analysis on Motorway Ramps

This paper presents a model-based fault detection method for an electrohydraulic braking system with cooperative regenerative braking management. The regenerative braking system can save energy and improve endurance in electric vehicles. However, failure of the regenerative system may result in the system being unable to fully convert the recovered energy into stored electrical energy, with a large portion of the energy being dissipated as heat. Meanwhile, the motor braking torque output is limited, and the range of battery state of charge is affected. In this paper, a Carsim/Simulink co-simulation was developed to model the operating conditions and failure modes of the regenerative braking system in an electric vehicle. A three-stage dynamic equation was derived to model the piston movement in the wheel cylinder of the electrohydraulic braking system. A vector control using coordinate transformation was developed for the permanent magnet synchronous motor to control the current and torque. Since various system components have been built, the advantage of model-based methods can perform predictive maintenance compared with the current corrective and preventive maintenance. Therefore, this paper proposed a three-layer systematic model (torque distribution layer, execution layer, and actuation layer) of electric vehicle regenerative braking system to detect and diagnose various fault conditions. Various parameters were compared with the normal braking mode in order to provide systematic guidance on fault detection.

With the development of the global automotive industry, environmental pollution and driving safety have been major problems. This paper focuses on a novel integrated cooperative antilock braking system (ABS) controller, which is used for antilock regenerative braking systems (ARBS) and antilock mechanical braking systems (AMBS) for hybrid electric vehicles (HEV) driving on different road surfaces. An intelligent tire system is utilized to detect varying road surfaces to obtain friction information and optimal operation slip ratio. In addition, the HEV eight‐degree‐of‐freedom dynamics model is developed for ABS control, which includes the LuGre tire model. Adaptive backstepping and finite state machine controllers are explored to maintain optimal wheel slip and regenerate energy, based on wheel slip, battery state of charge (SOC), motor capability torque, and vehicle velocity, and to develop the switching rules of regenerative and mechanical braking systems. In order to evaluate the performance of regenerative and mechanical braking systems on harvesting energy and driving safety, the HEV and LuGre dynamic tire models are developed in MATLAB SIMULINK /SimDriveline. The estimation results of different road surfaces and slip controller effects are tested via the experiments and simulations, finding good braking performances and high regenerative efficiency in different maneuvers.

<div class="section abstract"><div class="htmlview paragraph">A novel type of regenerative braking system for electric vehicles is proposed in this paper. Four pressure-difference-limit valves, two relief valves and two brake pedal simulators, are added to the layout of a conventional four-channel hydraulic modulator. The cooperation of relief valves and hydraulic pumps provides a stabilized high-pressure source. Pressure-difference-limit valves ensure that the pressure in each wheel cylinder can be modulated separately at a high precision. Besides, the functions of anti-lock braking system and electronic stability program are integrated in this regenerative braking system. The models of regenerative braking controller and vehicle dynamics are built in MATLAB/Simulink. Hydraulic brake model is built in AMESim through a parameterized and modularized method. Meanwhile, the control strategy of hydraulic brake modulation and brake force distribution are designed. Simulations are conducted via co-simulation interface between MATLAB and AMESim under scenarios of typical braking and ECE driving cycle. Simulation results show that regenerative and hydraulic braking forces are coordinated well during typical braking process, verifying the feasibility and effectiveness of the models built and strategies proposed. Under an ECE driving cycle, the proposed RBS can recover more than 75% of the total recoverable braking energy, which lengthen the vehicle’s driving range by more than 24%.</div></div>

In recent years, most road traffic accidents were caused by commercial vehicles, the main reason being the bad conditions of brake systems. In this paper, based on the statistical data of the accidents caused by commercial vehicles, symptoms and mechanisms of the accidents are analyzed; the main factors of the accidents were discovered. Then, using multi-sensor technology, WinCE 5.0 and distributed data acquisition technology, a software and hardware platform for data acquisition of the commercial vehicle brake system running parameters was built. By using the platform, the vehicle’s brake system performance parameters can be collected in real-time to recognize dangerous brake systems.

Vehicle electrification aims at improving energy efficiency and reducing pollutant emissions. It also creates opportunities to enhance active safety systems with the use of electric machines (EM) as regenerative braking actuators to support the friction brake system. Vehicle energy efficiency can be improved by integrating regenerative braking (RBS) and friction brakes to enable more frequent energy recuperation activations especially during high deceleration demands. This study aims at designing and implementing a new torque allocation strategy for wheel slip control in a four-wheel-drive (4WD) hybrid electric vehicle (HEV) with a single EM. The antilock braking system (ABS) is designed using sliding mode control, which offers robustness against tyre force nonlinearity. A brake torque blending algorithm is developed to distribute torques between electric and friction brake actuators based on a pre-defined energy recuperation priority. The challenge of allocating brake torques at each of the four wheels with brake-by-wire (BBW) and a centralized EM is particularly addressed in this study. Simulation analyses using a hardware-in-the-loop (HIL) test rig are conducted to verify the proposed control algorithms.

Braking systems are undergoing major changes to meet new safety and environmental requirements. As a safety component, the braking system is capable of assisting the driver or intervening autonomously when the stability of the car compromised, or when the driver wants to avoid collisions or limit the consequences of an accident by reducing relative speed at impact. With the brake system actions, the goal of reducing road fatalities is being achieved, and this cannot be without reducing human error as well. New brake-by-wire systems were developed in the automotive industry to improve strategies such as traction control. These systems provide distributed braking forces, regenerative braking, and traction control. It combines electronic, mechanical and hydraulic components and is constantly evolving since human beings are concerned with safety and performance.

This paper summarises the measured emergency braking performance of a tri-axle heavy goods vehicle semitrailer fitted with a novel pneumatic slip control braking system developed by the Cambridge Vehicle Dynamics Consortium. Straight-line braking tests were carried out from 40 km/h in order to compare a commercially electro-pneumatic available anti-lock braking system and the Cambridge Vehicle Dynamics Consortium system, which has bi-stable valves coupled with a sliding-mode slip controller. On average, the Cambridge Vehicle Dynamics Consortium system reduced the stopping distance and the air use by 15% and 22% respectively compared with those for the conventional anti-lock braking system. The most significant improvements were seen on a wet basalt-tile surface (with similar friction properties to ice) where the stopping distance and the air use were improved by 17% and 30% respectively. A third performance metric, namely the mean absolute slip error, is introduced to quantify the ability of each braking system to track a wheel slip demand. Using this metric, the bi-stable valve system is shown to improve the wheel slip demand tracking by 62% compared with that of the conventional anti-lock braking system. This improvement potentially allows more accurate control of the wheel forces during extreme manoeuvres, providing scope for the future development of advanced stability control systems.

A new cooperative braking control strategy (CBCS) is proposed for a parallel hybrid electric vehicle (HEV) with both a regenerative braking system and an antilock braking system (ABS) to achieve improved braking performance and energy regeneration. The braking system of the vehicle is based on a new method of HEV braking torque distribution that makes the antilock braking system work together with the regenerative braking system harmoniously. In the cooperative braking control strategy, a sliding mode controller (SMC) for ABS is designed to maintain the wheel slip within an optimal range by adjusting the hydraulic braking torque continuously; to reduce the chattering in SMC, a boundary-layer method with moderate tuning of a saturation function is also investigated; based on the wheel slip ratio, battery state of charge (SOC), and the motor speed, a fuzzy logic control strategy (FLC) is applied to adjust the regenerative braking torque dynamically. In order to evaluate the performance of the cooperative braking control strategy, the braking system model of a hybrid electric vehicle is built in MATLAB/SIMULINK. It is found from the simulation that the cooperative braking control strategy suggested in this paper provides satisfactory braking performance, passenger comfort, and high regenerative efficiency.

<div class="section abstract"><div class="htmlview paragraph">The driving range of the electric vehicle (EV) greatly restricts the development of EVs. The vehicles waste plenty of energy on account of automobiles frequently braking under the city cycle. The regenerative braking system can convert the braking kinetic energy into the electrical energy and then returns to the battery, so the energy regeneration could prolong theregenerative braking system. According to the characteristics of robustness in regenerative braking, both regenerative braking and friction braking based on fuzzy logic are assigned after the front-rear axle’s braking force is distributed to meet the requirement of braking security and high-efficient braking energy regeneration. Among the model, the vehicle model and the mechanical braking system is built by the CRUISE software. The paper applies the MATLAB/SIMULINK to establish a regenerative braking model, and then selects the UEDC city cycle for model co-simulation analysis. Finally, the feasibility of the proposed control strategy is demonstrated by the simulation results. It shows that the driving range of the EV could be effectively increased on the premise of satisfying the demand of the driver braking force.</div></div>

The paper focuses on issues related to selected automotive brakes with the aim of applying the proposed methodology to other structural systems of this type. The main aim of the paper is to identify the factors that differentiate the course of wear and occurrence of a fault in brake system components of passenger cars and light commercial vehicles during the warranty service period. The following methods were used in this study: systematic literature review, process analysis, and descriptive and inferential statistics, including analysis of variance and multiple classification analysis. As a result of an analysis of 295 brake system repairs, six differentiating factors that allowed for ex post analysis of the repairs were identified. An analysis of the interaction of these factors made it possible to distinguish three groups of motor vehicles depending on the cause of failure of the braking system. Based on the data generated in the warranty process, it is possible to determine the factors that differentiate the occurrence of a fault and the course of brake disc and pad wear.

Active safety systems for Heavy Goods Vehicles (HGVs), like passenger cars, often require an accurate estimate of sideslip angle. However, very little research has been published on HGV sideslip estimation in low friction conditions. This paper proposes three nonlinear Kalman Filters to estimate the tractor sideslip angle of a tractor-semitrailer combination. Performance is compared in simulation to a linear Kalman Filter in both high and low friction conditions. An Unscented Kalman Filter using a yaw-roll vehicle model and nonlinear tire model is found to accurately estimate sideslip in all maneuvers simulated, significantly outperforming the linear Kalman Filter.