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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). Copyright © 2010 SAE International. Source

Ki Y.-H.,Kookmin University | Ahn H.-S.,Kookmin University | Cheon J.S.,MOBIS
SAE Technical Papers | Year: 2012

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. The validity and the effectiveness of the proposed fault-tolerant control for an EMB are shown by using EMB hardware-in-the-loop simulations (HILS), so that fault tolerance is guaranteed for a scenario of sensor failures. The HILS consists of an EMB set, a TriCore-based actuator Electronic Control Unit (ECU), a host PC, and a CAN monitoring tool. Copyright © 2012 SAE International. Source

Lee K.-J.,Kookmin University | Kwon J.-M.,Kookmin University | Cheon J.S.,MOBIS | Ahn H.-S.,Kookmin University
SAE Technical Papers | Year: 2014

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. Copyright © 2014 SAE International. Source

Lee K.-J.,Kookmin University | Ki Y.-H.,Kookmin University | Ahn H.-S.,Kookmin University | Hwang G.,Infineon Technologies | Cheon J.S.,MOBIS
SAE International Journal of Passenger Cars - Mechanical Systems | Year: 2013

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. Based on hazard analysis and risk assessment according to ISO26262, the EMB system should be ASIL-D compliant, the highest ASIL level. To this end, an external signature watchdog and an Infineon 32-bit microcontroller TriCore are used to reduce risks considering common-cause failure. Moreover, a software design method is introduced for implementing functional safety oriented monitoring functions based on an asymmetric dual core architecture considering redundancy and diversity. The validity of the proposed ECU design approach is verified by using the EMB hardware-in-the-loop simulation (HILS). Furthermore, it is shown that the existing sensor fault tolerant control system can be used more effectively for mitigating the effects of hardware and software faults by applying the proposed functional safety oriented ECU design method. Copyright © 2013 SAE International. Source

Kim J.,MOBIS | Jo C.,MOBIS | Kwon Y.,MOBIS | Cheon J.S.,MOBIS | Park S.J.,MOBIS
SAE International Journal of Passenger Cars - Mechanical Systems | Year: 2014

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. Although the EMB 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[1] and additional mechanical backup measures[2] in this regard.Although the EMB is conventionally thought of as a solution for oil-free braking system[3-4], the EMB system introduced in the current paper includes a hydraulic piston to make several functions possible. First, the hydraulic system allows for a mechanical back-up mechanism that leads to increased reliability. Second, the clamping force for braking control can be measured with a pressure sensor. And finally, the dual piston structure proposed in the current paper, which leads to amplification of the force transmission, allows for the design of lower specification and higher cost effective motor and gear components.This new concept of EMB is termed the hEMB (hybrid EMB) in this paper. This study proposes to use a combined system of front hEMB and rear hydraulic caliper. This type of system has the potential of providing many advanced braking functions without the high cost associated with fully electric four wheel brake by wire systems. Prototypes of hEMB actuators were made and attached in a test vehicle. Results of bench and vehicle tests will be given to show the functionality of the system. Copyright © 2014 SAE International. Source

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