Model based wheel slip control via constrained optimal algorithm

In a near future, it is imminent that passenger vehicles will soon be introduced with a new revolutionary brake by wire system which replaces all the mechanical linkages and the conventional hydraulic brake systems with complete 'dry' electrical components. One of the many potential benefits of a brake by wire system is the increased brake dynamic performances due to a more accurate and continuous operation of the EMB actuators which leads to the increased amount of possibilities for control in antilock brake system. The main focus of this thesis is on the application of a model predictive control (MPC) method to devise an antilock brake control system for a brake by wire vehicle. Unlike the traditional ABS control algorithms which are based on a trial and error method, the MPC based ABS algorithm aims to utilizes the behaviour of the model to optimize the wheel slip dynamics su bject to system constraints. The final implementation of the wheel slip controller embraces decentralized control architecture to independently control the brake torque at each four wheel. Performance of the wheel slip controller is validated through Software-in-the-Loop and Hardware-in-the-Loop simulation. In order to support the high demands of the computational power and the real time constraints of the Hardware-in-the-Loop simulation, a novel multi processor real-time simulation system is developed using the reflective memory network and the off-the-shelf hardware components

Magnetically Actuated Hybrid Brake for Autonomous, Electrified Vehicles

Autonomous driving, the electrification of the powertrain and the reduction of emissions are three major development trends in today’s automotive industry. New mobility solutions such as electrified, autonomous shuttles for transporting people and goods in cities are being conceived and require a change of view in development, not only on the software level but also on chassis components. For braking systems, there are changes in the requirements for these vehicles. Existing test specifications for the performance of wheel brakes for passenger cars are primarily designed for the worst-case scenarios that can be caused by a human driver. Based on a stakeholder analysis as well as a use-case consideration new requirements are generated and new test specifications are developed, which are tailored to autonomous shuttles. Especially the restriction of the Operational Design Domain of the autonomous shuttle results in significantly lower thermal requirements for the wheel brake compared to conventional passenger cars. Nevertheless, high braking torques are still required due to high vehicle masses and the scenario of non-availability of the regenerative brake. Based on the identified requirements and development goals from the analysis, the solution space of braking systems in the state of the art is considered and the suitability of different brake concepts is discussed. Although current hydraulic concepts for passenger cars meet the dynamic and thermal requirements, they have little potential for reducing emissions and tend to corrode due to the increasing duration between actuations when regenerative brakes are in use. As an alternative, the focus of development lies on electromechanical concepts for individual wheel brake modules with electromotive actuation, which in the event of a fault only leads to the failure of one of four wheel brakes. Previous concepts of electromotively actuated brakes show a development conflict in the fact that many gear stages are necessary due to the high transmission ratios, which show a high efficiency variance over temperature due to their lubricants. In the concept space of electromechanical actuators, electromagnets can be found in addition to electric motors. However, only a few concept studies have been published regarding the state of the art and research, although electromagnetic actuation promises some advantages over electromotive actuation. These include less complex actuation, smaller installation space, and less mechanical complexity. Due to the revealed gap in the state of the art, an electro-magnetic concept is selected to be investigated for its suitability as a wheel brake for an autonomous shuttle. For this purpose, either holding magnets or solenoids can be used as actuators, with holding magnets promising significantly higher magnetic forces at small air gaps. For the investigations, a first design of a drum brake actuated by a holding magnet is prototypically realized. The concept comprises a combination of a magnetically actuated solid disc brake with a downstream duplex drum brake. The interconnection of the two brakes promises the utilization of the wheel rotation angle for actuation of the drum brake and a redundant actuator design through the use of two excitation coils in the mag-netic disc brake. To evaluate the suitability of the concept, actuator forces, dynamics, total torques and disc brake torques are measured in operation. The largest deviations from the design considerations occur in the torque curve of the brake over speed, which are investigated in more detail using a hypothesis- and test-based approach. In addition to investigations into the influence of magnetic field weakening effects, such as eddy currents, the coefficient of friction of the friction partners on the holding magnet actuator is also determined and identified as the main cause of the torque drop. A dependence on both the velocity and the axial force is examined. The investigation of the torque hysteresis of the overall braking system shows the difficulty in setting small torques, since the magnet has a high current demand to pass the initial air gap, which then generates medium torques when it hits the disc. A proposal for control by means of a current pre-control is also being tested and evaluated. Through the investigations carried out, the development conflict in the use of a holding-magnetic actuator concept for the actuation of a wheel brake is recorded, and through the hypothesis-based approach the causal effect of the torque drop is identified. The realized magnetic actuator concept fulfills the requirements for dynamics and the wish for low-emission, compact braking concepts, but does not achieve the required braking torques over the entire operating range of an autonomous shuttle. In the outlook a proposed conceptual solution of actuation by means of solenoid actuators is discussed, which promises to solve the described development conflict, but in turn requires a higher transmission ratio due to the lower force potential

Simulation method and laboratory brake friction dynamometer for tribology studies, A

Department Head: Allan Thomson Kirkpatrick.Includes bibliographical references (pages 113-116).Two of the most important parameters of brake system design are the frictional and wear capabilities of the rotor and pad materials. These parameters must meet minimum design requirements in an effort to enhance friction and reduce wear to improve the performance and life of brake system components. The frictional and wear performance of the rotor and pad materials can be assessed through laboratory brake dynamometer testing and evaluation. In the current study, a wear testing simulation and an inertia laboratory brake dynamometer were developed to resolve differences in wear rates of brake materials. Dynamometer testing was conducted to verify the logic of the simulation and the functionality of the dynamometer by measuring wear rates of brake rotor material samples, some of which were subjected to cryogenic heat treatment to modify their wear rates, at varying brake application pressures. Dynamometer testing established that the wear simulation and inertia laboratory brake dynamometer developed during the current study could function together as a suitable tribological experimental apparatus. Specifically, dynamometer testing demonstrated the ability of the experimental apparatus to resolve differences in wear rates of brake materials due to variations in brake application pressure at relatively short test durations; however, dynamometer test results did not show conclusive evidence to suggest an advantage in subjecting the rotor materials used in the current study to cryogenic treatment to lower the rotor or pad wear rates

Implementation of Automatic DC Motor Braking PID Control System on (Disc Brakes)

The vital role of an automated braking system in ensuring the safety of motorized vehicles and their passengers cannot be overstated. It simplifies the braking process during driving, enhancing control and reducing the chances of accidents. This study is centered on the design of an automatic braking device for DC motors utilizing disc brakes. The instrument employed in this study was designed to accelerate the vehicle in two primary scenarios - before the collision with an obstacle and upon crossing the safety threshold. It achieves this by implementing the Proportional Integral Derivative (PID) control method. A significant part of this system comprises ultrasonic sensors, used for detecting the distance to obstructions, and rotary encoder sensors, which are utilized to measure the motor's rotational speed. These distance and speed readings serve as essential reference points for the braking process. The system is engineered to initiate braking when the distance value equals or falls below 60cm or when the speed surpasses 8000rpm. During such events, the disc brake is activated to reduce the motor's rotary motion. The suppression of the disc brake lever is executed pneumatically, informed by the sensor readings. Applying the PID method to the automatic braking system improved braking outcomes compared to a system without the PID method. This was proven by more effective braking results when the sensors detected specific distance and speed values. Numerous PID tuning tests achieved optimal results with K_p = 5, K_i = 1, and K_d = 3. These values can be integrated into automatic braking systems for improved performance. The PID method yielded more responsive braking outcomes when applied in distance testing. On the contrary, the braking results were largely unchanged in the absence of PID. Regarding speed testing, the PID method significantly improved the slowing down of the motor speed when it exceeded the maximum speed limit of 8000 rpm. This eliminates the possibility of sudden braking, thus maintaining the system within a safe threshold. The average time taken by the system to apply braking was 01.09 seconds, an indication of its quick responsiveness. This research is a valuable addition to control science, applying the PID control method to automatic DC motor braking. It provides valuable insights and concrete applications of PID control to complex mechatronic systems. It is also noteworthy for its development and optimization of suitable PID parameters to achieve responsive and stable braking. The study, therefore, offers a profound understanding of how PID control can be employed to manage braking systems on automatic DC motors, thereby advancing knowledge and application of control in control science and mechatronics

Vehicle dynamics with brake hysteresis

This paper studies hysteresis of vehicle brakes and its influence on the vehicle dynamics. The experimental investigation clearly shows the non-linear and asymmetric characteristics of hysteresis of the disk brakes in passenger cars. A computational model of the brake mechanism with hysteretic elements, based on the Bouc–Wen method, is developed and verified with experimental data. Using the developed model, the influence of hysteresis on the vehicle dynamics during straight-line braking with an anti-lock braking system is analysed. It is also observed that the variations in the hysteresis parameters have important influences on the main vehicle brake characteristics such as the stopping (brake) distance, the time of braking and the average deceleration. A comparative analysis of the simulation results is also given for braking with zero hysteresis or with hysteresis represented as a signal delay and linear function

Robust control of brake systems with decoupled architecture

Modern brake systems have the tendency to decoupled brake system design involving electric and/or electrohydraulic brake actuators. In this thesis, a corresponding brake control architecture applicable for electric and automated vehicles is proposed and includes (i) base braking, (ii) brake blending and (iii) wheel slip control functions. Main focus has been given to the robustness of continuous wheel slip control during emergency braking in high and low road friction conditions. As the solution, several control laws were designed and experimentally validated during road tests. Results obtained for three vehicle prototypes with individual on-board and in-wheel electric motors and electrohydraulic brake-by-wire system present significant improvement in braking performance and ride quality compared to the conventional wheel slip control strategies.Moderne Bremssysteme tendieren zur entkoppelten Konstruktion mit involvierten elektrischen und/oder elektrohydraulischen Aktuatoren. In der vorliegenden Arbeit ist die entsprechende Bremsregelungsarchitektur für die elektrischen und automatisierten Fahrzeuge vorgeschlagen, die beinhaltet Funktionen zur (i) primären Bremsung, (ii) gemischten Bremsung und (iii) Radschlupfregelung. Der Schwerpunkt dieser Arbeit ist auf die Robustheit der kontinuierlichen Radschlupfregelung während einer Notbremsung bei hoher und niedriger Fahrbahnreibung gelegt. Als die Lösung sind mehrere Regelungsstrategien entwickelt und experimentell validiert. Die Ergebnisse für drei Fahrzeugprototypen mit individuellen Board- und Radnabemotoren und einem elektrohydraulischen Brake-by-Wire System demonstrieren wesentliche Verbesserung der Bremsleistung und Fahrqualität im Vergleich zu den konventionellen Strategien der Radschlupfregelung

Collaboratively Navigating Autonomous Systems

The objective of this project is to focus on technologies for enabling heterogeneous networks of autonomous vehicles to cooperate together on a specific task. The prototyped test bed consists of a retrofitted electric golf cart and a quadrotor designed to perform distributed information gathering to guide decision making across the entire test bed. The system prototype demonstrates several aspects of this technology and lays the groundwork for future projects in this area

Control strategies for blended braking in road vehicles. A study of control strategies for blended friction and regenerative braking in road vehicles based on maximising energy recovery while always meeting the driver demand.

In HEV and EV, higher fuel economy is achieved by operating the ICE and electric motor in the most efficient region and by using regenerative braking. Such a braking system converts, transfers, stores and reuses kinetic energy which would otherwise be dissipated as heat through friction brakes to the environment. This research investigates the control of braking for a mixed-mode braking system in a these vehicles based on the proportion of braking energy that can be stored. Achieving mixed-mode braking requires the ‘blending’ of the two systems (regenerative and friction), and in brake blending, the electric motor/generator (M/G) and the hydraulic actuation pressure are controlled together to meet the driver’s braking demand. The research presented here has established a new robust dynamic modelling procedure for the design of combined regenerative and hydraulic braking systems. Direct torque control and pressure control were selected as the control criteria in both brakes. Two simulation models have been developed in Matlab/Simulink to generate analysis the performance of the control strategy in the blended braking system. Integration of the regenerative braking system with ABS has also been completed, based on two conditions, with and without the deactivation of the regenerative braking. Verification of the models is presented, based on experimental work on two EVs manufactured by TATA Motors; the ACE light commercial vehicle and the VISTA small passenger car. It is concluded that braking demand and vehicle speed determine the operating point of the motor/generator and hence the regenerative braking ratio

The 29th Aerospace Mechanisms Symposium

The proceedings of the 29th Aerospace Mechanisms Symposium, which was hosted by NASA Johnson Space Center and held at the South Shore Harbour Conference Facility on May 17-19, 1995, are reported. Technological areas covered include actuators, aerospace mechanism applications for ground support equipment, lubricants, pointing mechanisms joints, bearings, release devices, booms, robotic mechanisms, and other mechanisms for spacecraft

A New Self-Contained Electro-Hydraulic Brake System

The automotive brake system plays a significant role not only in the deceleration and stopping process, but also in many stability control strategies. To overcome the limitations of conventional brake systems and to improve vehicle control strategies such as traction control, and differential braking, a new generation of brake systems called the brake-by-wire system has been introduced to the vehicle industry. This generation of brake systems combines electrical, mechanical and, in some cases, hydraulic components. Although different types of brake-by-wire mechanisms have been developed in the past two decades, there still exist demands for further improvement and developing new brake mechanisms in the automotive industry due to the ever increasing demand for better safety and performance. This research proposes a novel brake-by-wire system based on cam actuation. This system is a combination of electrical, mechanical and hydraulic components. The unique feature of the cam actuation brake system proposed in this research is that the characteristics of the motor torque amplification can be optimized by careful design of the cam shape. The compactness and self-contained characteristic of the design allow the brake system to be installed on each wheel enabling fully independent control of each wheel for better stability control. Moreover, the cam actuated brake has a fail-safe advantage by keeping the direct connection between the driver and the brake calipers in case of any system failure. In this work, different subsystems of the brake system and their components are explained, the dynamic model of the system is found and the design parameters are optimized. Specifically, the optimal design problem has been formulated by taking the geometry of the cam as the optimization variable and the open-loop response time of the brake system as the objective function to be minimized. The solution to this problem is then obtained by the multi-layer design optimization process using the genetic algorithm (GA). Various control algorithms are applied to the developed cam actuated brake system to investigate their performance in terms of tracking a desired braking pressure