A Sensor Fusion Approach to Estimate Clamp Force in Brake-bYy-Wire Systems S. Saric, A. Bab-Hadiashar and R. Hoseinnezhad Swinburne University of Technology Victoria 3122, Australia Abstract- Elimination of a clamp force sensor from brake-by- wire system designs is strongly demanded due to implementation difficulties and cost issues. In this paper a new method is presented to estimate clamp force based on other sensory information. The proposed estimator fuses the outputs of two models to optimise the root mean square error (RMSE) of estimation. Experimental results show that the estimator can accurately track the true clamp force for high speed cases as demanded by anti-lock braking system (ABS) controls. A training strategy has been used to ensure that the estimator can successfully adapt to frictional variations within the reduction gearing. This paper is concluded with a discussion on the reliability of the developed clamp force estimator. I. INTRODUCTION Design and implementation of electromechanical braking (EMB) systems for drive-by-wire has been focused upon by researchers and industry experts [1-3]. In EMB systems an electric motor drive is coupled to reduction gearing that provides brake control to a wheel. The motor is typically of a permanent magnet brushless DC type. The reduction gearing generally consists of a planetary gear-train connected to a ball-screw that can generate clamp forces of up to 50 kN. Generally EMB calipers utilise a clamp force sensor to close a loop for the purpose of controlling caliper dynamic performance. The control of an EMB with an internal clamp force sensor can be achieved using a standard motion control architecture adopted for servo motors (cascaded position, velocity and current control loops) that is slightly modified to suit the application at hand. Line et al. [4] replace the position control loop with a force control loop to control an EMB. This architecture is shown in Fig. 1. The implementation of this overall control system requires the use of a displacement sensor and three motor current sensors for the three-phase brushless DC motor. The former is realised by a resolver. A clamp force sensor is a relatively expensive component in an EMB caliper. The cost is derived from its high unit value from a supplier, as well as its relatively high production cost that emanates from the complex assembly procedures dealing with small tolerances, as well as on-line calibration for performance variability from one clamp force sensor to another. The successful use of a clamp force sensor in an EMB system poses a challenging engineering task. If a clamp force sensor is placed close to a brake pad, then it will be subjected to severe temperature conditions reaching up to 800 °C that will challenge its mechanical integrity. Also temperature drifts must be compensated for. This situation can be avoided by embedding a clamp force sensor deep within the caliper, i.e. at the near end of the ball-screw. Schwarz et al. [5] show that embedding this sensor leads to hysteresis that is influenced by friction between the clamp force sensor and the point of contact of an inner pad with the rotor. This hysteresis prevents a true clamp force to be measured. Due to the cost issues and engineering challenges involved with including the clamp force sensor, it is highly desirable to eliminate this component from the EMB system. A potential opportunity to achieve this presents itself in a sensor fusion approach at signal level. That is, to accurately estimate the clamp force based on alternative EMB sensory measurements leading to the omission of a clamp force sensor. The idea of eliminating a clamp force sensor using other sensory information has been the subject of past work and will be detailed ahead. Figure 1. EMB system control architecture. Crown Copyright 2006 3007