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An Electrical Parking Brake (EPB) system is a device that operates to park the vehicle automatically with the push of a button instead of using conventional hand or foot levers which in some ways makes it the first by wire type of brake system. As such, it is being considered in some vehicle architectures as an automatic redundant backup for vacuum-less brake systems or autonomous cars. The EPB system is generally divided into cable puller and motor on caliper (MOC) types. Recently, the MOC type EPB is being more widely applied in the global market due to product competitiveness and cost effectiveness. The MOC type EPB is composed of the caliper body, torque member, pad assembly, nut assembly and actuator. Among them, the caliper body and torque member play a main role in the robustness of the EPB system and occupy more than 80% of the total weight.

EMB (Electro-Mechanical Brake) which converts electrical motor power to brake clamping force at each wheel is a system that has been investigated and developed by various automotive part suppliers through the years. In particular, as the number of electrically powered vehicles, such as hybrid electric vehicles, electric vehicles and fuel cell electric vehicles, has expanded, the EMB has received increased interest due to its fast response that is much suited for effective cooperative control with regenerative braking. However, issues such as cost competitiveness, reliability and regulations need to be solved for commercialization [1-2]. A new concept, the hybrid Electro-Mechanical Brake (hEMB) is characterized by a dual piston structure linked by hydraulics inside of the caliper. It is possible to reduce the required motor power and increase the level of emergency back-up braking through the amplification effect of the dual piston mechanism [3].

This paper proposes a design approach for the network configuration of brake-by-wire (BBW) systems using the FlexRay communication protocol. Owing to the absence of mechanical or hydraulic back-ups, the BBW system needs to be highly reliable and fault-tolerant. The FlexRay network is shown to be very effective for such requirements of BBW systems by using hardware in-the-loop simulation (HILS), which allows developing and testing various algorithms and faithfully reproduces the actual system. The FlexRay protocols are designed using the FIBEX configuration tool appropriately for the control of BBW systems, and they are analyzed using the FlexRay communication monitoring tool. The results of HILS illustrate that the braking performance of a controller area network (CAN)-based network and that of a FlexRay-based network for BBW systems are very similar, however, the FlexRay-based network system is more reliable and ensures better fault diagnosis by monitoring more variables.

Electro-Mechanical Brake (EMB) is the brake system that is actuated by electrical energy and has a similar design with the Electric Parking Brake (EPB). It uses motor power and gears to provide the necessary torque and a screw & nut mechanism is used to convert the rotational movement into a translational one. The main difference of EMB compared with EPB is that the functional requirements of components are much higher to provide the necessary performance for service braking such as response time. Such highly responsive and independent brake actuators at each wheel lead to enhanced controllability which should result in not only better basic braking performance, but also improvements in various active braking functions such as integrated chassis control, driver assistance systems, or cooperative regenerative braking.

In this paper, we propose a hardware and a software design method considering functional safety for an electro-mechanical brake (EMB) control system which is used as a brake actuator in a brake-by-wire (BBW) system. A BBW system is usually composed of electro-mechanical calipers, a pedal simulator, and a control system. This simple by-wire structure eliminates the majority of bulky hydraulic brake devices such as boosters and master cylinders. The other benefit of a BBW system is its direct and independent response; this leads to enhanced controllability, thus resulting in not only improved basic braking performance but also considerably easier cooperative regenerative braking in hybrid, fuel-cell, and electric cars. The importance of a functional safety based approach to EMB electronic control unit (ECU) design has been emphasized because of its safety critical functions, which are executed with the aid of many electric actuators, sensors, and application software.

A Brake By Wire (BBW) system is generally composed of electro-mechanical calipers at each wheel, a pedal simulator and a central controller. The brake demand is processed by the pedal and the central controller commands the brake distribution for each brake actuator. The highly responsive and independent brake actuators lead to enhanced controllability which should result in not only better basic braking performance, but also improvements in various active braking functions such as integrated chassis control, driver assistance systems, or cooperative regenerative braking. Although the BBW system has the potential for numerous advantages and innovations in braking, it has yet to be successfully introduced in series production mainly due to safety and cost concerns. Recent studies have been made to investigate the functional safety aspects and additional mechanical backup measures in this regard.

In this paper, for the fault-tolerant control of electro-mechanical brakes (EMBs), we continuously estimate several system variables and utilize these estimates to detect faulty sensor outputs. The clamping force is estimated by using the motor position and hysteresis phenomenon during clamping and releasing. Current sensor faults can be easily derived from the characteristics of a three-phase balanced circuit, and the motor position is estimated by applying different methods in low-speed and high-speed regions where a model-based approach is adopted. Using the proposed fault-tolerant logic, we can detect which sensor has a fault during driving or braking. Then, we use a bumpless transfer technique so that the control performance does not deteriorate when the estimated values are substituted for the measured values.

Brake-By-Wire (BBW) is a term used to describe next generation brake systems that rely on motor driven electro-mechanical calipers in place of conventional hydraulic components such as the booster, master cylinder, hydraulic unit, and parking brake. Instead the system configuration is simplified to a pedal simulator, electro-mechanical calipers that require no boosting, and electric control units. The active, highly-responsive, and independent control of the brake actuators at each wheel allows for great control flexibility and improved brake performance. It is also very well-suited for easy integration with cooperative regenerative braking and driver assistance functions. Although such potential and innovations have driven the interest and research into BBW systems through the years, it has yet to be successfully introduced in series production mainly due to the underlying perception of the lack of reliability of electronic components and overall cost concerns.

In regenerative braking, the kinetic energy of the vehicle is stored in a battery as the electric energy that is otherwise being dissipated as heat by friction, so that the stored energy is recuperated to drive the vehicle. In general, another independent braking mechanism, such as hydraulic brakes, needs to be used in cooperation with regenerative braking in order to meet the total braking force demand. The smart booster system, which uses a permanent magnet synchronous motor to replace the conventional vacuum booster, is proposed in this paper as an active braking system which is well suited for such regenerative cooperative braking applications in environment friendly vehicles. A pressure feedback control is used with a nested current control loop using pressure and current sensors, respectively.

The importance of functional safety design has recently grown with the increasing widespread application of electric/electronic (E/E) systems in today's automotive industry. Such E/E systems, usually composed of mechatronic actuators, various sensors, and electronic control units (ECU), have become too complex to be handled in the conventional quality management manner that was used for most predominantly mechanical applications. ISO/DIS 26262, an adaptation of the pre-existing IEC 61508 requirements specifically for the automotive industry, has been prepared as the global standard to meet such demands for a more structured and systematic approach to functional safety design. The functional safety concept design includes a hazard analysis and risk assessment phase that is based on ASIL (Automotive Safety Integrity Level) categorization. ASIL has four levels, A, B, C, and D, where A has the lowest risk and D has the highest.

A dry Brake-By-Wire (BBW) system is one in which the existing hydraulic system is replaced by motor driven electro-mechanical calipers. Although it has yet to be introduced into series production, the attractive benefits of BBW have kept it in the mainstream of brake research for a number of years. In the current investigation, the BBW system is configured with electric wedge brakes in the front axle where high braking forces are required, while conventional electro-mechanical brakes are used in the rear axles. This paper will examine the feasibility of the current BBW system configuration through lab and vehicle performance tests including ABS (anti-lock braking system).

The main classification of Electric Parking Brakes (EPB) can be made into cable puller and caliper integrated types. In this paper, the main design considerations that need to be made for each type of system will be examined. In terms of mechanical design, actuator design factors including target capacity, system size, and vehicle mounting will be briefly discussed. In terms of software, a unified software structure that can incorporate both types of EPBs will be introduced. This unified approach, made up of fixed and variable modules, allows for more efficient software development for both types of EPB systems. The fixed modules are related to the identical target functions regardless of EPB type, while the variable modules are made up of the different considerations that need to be made depending on the EPB type in order to meet such targets. Finally, some test results of target functions for both types of EPB systems will be given.