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Written by Paul Weissler
The potentialmarket for an electric wheel-braking system is apparent to automotiveengineers, but none is now in vehicleproduction. Such a system adds a levelof precision to braking itself, but even more important, brake-by-wire fitsinto the engineering picture to meet the low-emissions/higher fuel economymandates in government regulation. Andit could be easier to integrate intosemi-autonomous and autonomous operation. Premium braking system supplier Brembo, in a display at NAIAS, featureda system it already has shown to many car makers. Electric foundation braking has been in development at Brembo forsome 15 years, and as Chief Technical Officer Georgio Ascanelli told AutomotiveEngineering, it has potential for considerable further development. Other electricbraking systems developed to date have poseddurability/reliability questions, Ascanelli noted. Forcontrast, he pointed to the Brembo design"s use of one central ECU and fourcorner modules. "It could operatewith a failure of the other four," he said, so there is coverage for evensimultaneous multiple failures. Someseparation of the battery supply system also would be needed to fit into thispicture. With all the failure modeanalysis normal for safety-related systems, there should be an overallconfidence level even for autonomous driving. The Brembo test system has accumulated over 500,000 km (300,000 mi) of safe operation on a sports car, Ascanelli said, and the company is completing a demonstrator to provide further evidence to vehicle OEMs. Technically, he expects the system to be ready for use well before 2020, while admitting that some OEMs consider such innovations to be risky. Brake pedal just a sensor The system beginsat the "brake pedal," in this case a spring-loaded electro-mechanical sensor (with potential forredesign/downsizing) that produces aproportional signal to the ECU. Thismodule both confirms battery system state of charge and operates a pump/motorassembly to produce a hydraulic output to the front caliper, a six-pistonunit. Doesn"t this make it anelectro-hydraulic system? For largercars, yes, because the design of the present rotor and caliper do notprovide the wheel space needed for apurely electrical system. Using thebasic architecture, an all-electric system could be produced for small cars,such as the Renault Twingo, Ascanelli explained. And with product redesign and continuousimprovement, the potential of all-electric foundation brakes for larger models can beanticipated. At its presentstate, the system response time is just 90 ms, vs. 300 ms on aconventional all-hydraulic brakingsystem with booster and anti-lock braking actuator. The fast response time means the system canprovide auto-braking improvements for both basic collision-mitigation systemsand the more demanding requirements of autonomous driving, he noted. Because the rearsystem is "dry" (i.e., fully electro-mechanical), using a motor and gearbox, it lends itself also to serving as theparking brake. Pistons positively retracted Although thesystem does use hydraulics for the frontbrakes, the overall electrical operation permits quickly and positivelyretracting pistons front and rear because the circuits are being controlledwith motors and an ECU. The retracted pistonclearance, 0.2 mm (.001-in) or more totally eliminates piston drag on the rotor friction surfaces, Ascanelli said, which he claims accounts forabout 10% of fuel consumption in city operation with a gasoline engine. The precise control of an electric braking system also permitscalibration to improve the efficiency of regenerative braking on electricvehicles and hybrids, so it boosts fueleconomy for these cars. Those twofactors no drag and improved regen braking therefore lower carbon dioxideemissions, he added. An electricbraking system does add components, but in addition to a simpler parkingbrake it eliminates the brake booster and anti-lock brakeactuator. So Ascanelli said he believesthe overall system can be lighter than a conventional one. The initial selling price to OEMs would have to becompetitive with the conventional systems in use, he admitted, even if it costs suppliers more. However, he believes suppliers can "get to a comparable price" by increasingvolume and using feedback from the market to correct the naturalover-engineering that is typical of a new design, particularly one sosafety-related.
Date written: 20-Jan-2016 10:56 EST
More of this article on the SAE International Website
ID: 1803
The potentialmarket for an electric wheel-braking system is apparent to automotiveengineers, but none is now in vehicleproduction. Such a system adds a levelof precision to braking itself, but even more important, brake-by-wire fitsinto the engineering picture to meet the low-emissions/higher fuel economymandates in government regulation. Andit could be easier to integrate intosemi-autonomous and autonomous operation. Premium braking system supplier Brembo, in a display at NAIAS, featureda system it already has shown to many car makers. Electric foundation braking has been in development at Brembo forsome 15 years, and as Chief Technical Officer Georgio Ascanelli told AutomotiveEngineering, it has potential for considerable further development. Other electricbraking systems developed to date have poseddurability/reliability questions, Ascanelli noted. Forcontrast, he pointed to the Brembo design"s use of one central ECU and fourcorner modules. "It could operatewith a failure of the other four," he said, so there is coverage for evensimultaneous multiple failures. Someseparation of the battery supply system also would be needed to fit into thispicture. With all the failure modeanalysis normal for safety-related systems, there should be an overallconfidence level even for autonomous driving. The Brembo test system has accumulated over 500,000 km (300,000 mi) of safe operation on a sports car, Ascanelli said, and the company is completing a demonstrator to provide further evidence to vehicle OEMs. Technically, he expects the system to be ready for use well before 2020, while admitting that some OEMs consider such innovations to be risky. Brake pedal just a sensor The system beginsat the "brake pedal," in this case a spring-loaded electro-mechanical sensor (with potential forredesign/downsizing) that produces aproportional signal to the ECU. Thismodule both confirms battery system state of charge and operates a pump/motorassembly to produce a hydraulic output to the front caliper, a six-pistonunit. Doesn"t this make it anelectro-hydraulic system? For largercars, yes, because the design of the present rotor and caliper do notprovide the wheel space needed for apurely electrical system. Using thebasic architecture, an all-electric system could be produced for small cars,such as the Renault Twingo, Ascanelli explained. And with product redesign and continuousimprovement, the potential of all-electric foundation brakes for larger models can beanticipated. At its presentstate, the system response time is just 90 ms, vs. 300 ms on aconventional all-hydraulic brakingsystem with booster and anti-lock braking actuator. The fast response time means the system canprovide auto-braking improvements for both basic collision-mitigation systemsand the more demanding requirements of autonomous driving, he noted. Because the rearsystem is "dry" (i.e., fully electro-mechanical), using a motor and gearbox, it lends itself also to serving as theparking brake. Pistons positively retracted Although thesystem does use hydraulics for the frontbrakes, the overall electrical operation permits quickly and positivelyretracting pistons front and rear because the circuits are being controlledwith motors and an ECU. The retracted pistonclearance, 0.2 mm (.001-in) or more totally eliminates piston drag on the rotor friction surfaces, Ascanelli said, which he claims accounts forabout 10% of fuel consumption in city operation with a gasoline engine. The precise control of an electric braking system also permitscalibration to improve the efficiency of regenerative braking on electricvehicles and hybrids, so it boosts fueleconomy for these cars. Those twofactors no drag and improved regen braking therefore lower carbon dioxideemissions, he added. An electricbraking system does add components, but in addition to a simpler parkingbrake it eliminates the brake booster and anti-lock brakeactuator. So Ascanelli said he believesthe overall system can be lighter than a conventional one. The initial selling price to OEMs would have to becompetitive with the conventional systems in use, he admitted, even if it costs suppliers more. However, he believes suppliers can "get to a comparable price" by increasingvolume and using feedback from the market to correct the naturalover-engineering that is typical of a new design, particularly one sosafety-related.
Date written: 20-Jan-2016 10:56 EST
More of this article on the SAE International Website
ID: 1803
