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On Electro-Mechanical Brakes (EMB) spring-support can be necessary for releasing the brake without electrical energy. Advantageous brake-configurations can make use of the spring over the whole actuation range during engage and release. Such optimized spring support is known as “energy-swing. Under loss-less conditions the spring force could be in permanent equilibrium with the force required to press the pad, i.e. the brake could be controlled without actuation energy. In reality this will not be fully achievable as actuation losses and different operational conditions need to be covered. Still, significant advantages can be gained. The EMB of Vienna Engineering (VE) fulfills a key condition for energy-swing as it facilitates using the spring for engage- and release-support. Car brakes must release automatically when power is off. Consequently, spring-induced engage-support must always be smaller than release-forces and release-support must ensure overcoming mechanical resistance.

Since more than eight years Vienna Engineering (VE) is working on an electro-mechanical brake (EMB) actuated by eccentrics and a highly non-linear actuation mechanism. The principle allows full braking in approx. 70 milliseconds (including air gap) and only approx. 3 A RMS actuator current at 12 V for classical ABS with oscillations. This EMB reached an elaborated state. Versions for passenger cars, elevators, railway and commercial vehicles (CVs) were derived. Now, as the EMB is going to road tests, it is necessary to fulfill safety requirements closely. What are these safety requirements and how can they be fulfilled? The properties of the overall system, of the mechanics and electronics of the single brake are discussed in this paper. The overall brake system for EMBs needs a truly redundant power supply, a safe control bus and a safe brake pedal. The mechanics of a single brake can be required to release when power is off and it must not get mechanically stuck.

At first glance a friction brake should be controlled by normal force to produce predictable brake force. Controlling an actuator (and hence brake pad) position basically seems to introduce uncertainties to normal force and brake force, because at first view the position tells little about actual normal force. The electro-mechanical brake (EMB) of Vienna Engineering (VE) can be operated by position-control, either without force sensor (saving costs) or even with a true brake torque sensor. For position control a relation between actuator position and normal force is used. When pad wear is correctly adjusted a certain actuator position produces a given deformation and at known elasticity the deformation produces a defined normal force. In the VE-EMB this relation uses a three-dimensional curve and includes temperature influence of the coefficient of friction, thermal expansion and thermal elasticity change.

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.

With linear actuated brakes the actuation force (or torque) rises linearly from 0 to the full actuation force at full braking. This means that the actuation must be designed for the rare case of full-braking. The parts must be designed for this peak load (e.g. motor, gear) and the transmission ratio is determined by the full-braking actuation torque, which causes the highest transmission ratio and hence determines slow actuation dynamic. Ideally the actuation should make the fastest travel at low normal force and turn to slow movement and high force at the highest pad force. Mathematically the torque transmission ratio should optimally be an exact representation of the actuation characteristics (actuation torque over actuation movement), creating the highest torque-transmission ratio at highest force and the fastest movement at low pad force.

The VE-brake is an electromechanical disc brake with very low actuation force, actuated by a small electro motor. It was originally conceived as a vehicle brake but is equally applicable to wind turbines and other equipment. It has been highly successful in extreme dynamometer tests and is now being installed in test vehicles. As a foot-brake the VE-brake releases automatically at power-off and can be actuated to a parking position, which stays at power-off. The auto-release function can be inverted so that it brakes automatically at power-off as an emergency brake for wind turbines and rolling stock. A considerable amount of electricity is required to keep conventional windmill-brakes released. In light wind, the VE brake enhances yield by permitting the turbine a lower start-up speed, and in gusty or higher wind speeds, the graduated activation enables the turbine to continue functioning in demand-braked mode, rather than switching to emergency shut-down mode.

Conventional brakes commence with given brake torque distribution and abruptly change to wheel individual torque corrections when ABS-ESP intervenes. This leads to less than optimal braking, firstly around the transition from “given distribution” to individual ABS-ESP control and secondly when ABS-ESP switches from “locked” to “rotating”. Neither of these states offers the optimal deceleration. The VE mechatronic brake (EMB, electro mechanical brake) is designed to apply wheel individual braking with wheel optimized torques that give the best braking and stability from initial input to maximum deceleration, without sudden transition to ABS-ESP. With electric drive motors, a very rapid adjustable part of wheel individual torque can be combined with the individually controllable VE brakes.

Scientists at the Austrian Institute of Technology (AIT), formerly Austrian Research Center, focused on investigating electro mechanical brakes (EMB) for automobiles. Research showed that EMBs can address brake distribution with regenerative and friction braking ("blending") at hybrid and electric cars due to the ability of the EMBs to be actuated as required (and do not automatically produce brake force at pedal activation). The target was to develop an EMB with low actuation force and energy that is simple and reliable, rolls back to disengage when power is off and acts as a parking brake. Several solutions were considered (with and without self-amplification). A pivotal mechanism with very high transmission ratio using eccentricity emerged as a favorable solution. Vienna Engineering (VE) took over and assumed the research during 2010. VE revealed that non-linear behavior facilitated low actuation forces at high braking torque and can use a controlled amount of self-amplification.