Putz, M., Wunsch, C., Schiffer, M., and Peternel, J., "Test Results of A Sensor-Less, Highly Nonlinear Electro-Mechanical Brake," SAE Technical Paper 2014-01-2541, 2014, doi:10.4271/2014-01-2541.
The electro-mechanical brake (EMB) of Vienna Engineering (VE) uses a highly non-linear mechanism to create the high pressing force of the pad. The advantage is that the pad moves very fast when the pad pressing force is low and moves slower with increasing pressing force.The normal force in EMBs is often controlled by observing mechanical deformation to conclude to stress or force, commonly using strain gauges. It causes costs of the gauge itself and attaching them to e.g. the caliper and a sensitive amplifier. The full gauge equipment goes into the safety-related brake control system. The faintest damage (e.g. stone impacts, heat) gets the vehicle to the repair shop making expensive replacement necessary.To avoid the costs of the force measurement in the safety related system VE took the electrical motor measurements from the very beginning of the brake development for EMB control. These electrical values (position, rpm, current, voltage) are already present to operate the brushless DC motor and need no additional parts.In this paper a comparison is done between the effort to use force measurement and the sensor-less approach of VE. Safety concepts with gauges and without (using motor data) are discussed as well as long- and short term accuracy. With the constant torque of the non-linear VE EMB the motor current does not directly represent the force on the pad. In this paper it is discussed how normal force can be calculated in the non-linear brake.The theory is compared with test stand results. The potential of improved algorithm for calculation is discussed.