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01/11/2004
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Even before Delphi’s radical twin-disc maximum torque brake (MTB) has been launched on a vehicle, engineers are working on an even more advanced 14V mechatronic development of the technology, writes Roger Bishop. It could be ready for production by 2010.
In June last year European Automotive Design reported on the original system with two fully floating disc rotors and friction pads facing all surfaces. These are acted on by a hydraulic piston and reacted by the brake body. The piston action clamps the rotors and the pads together providing four braking surfaces and two effective radii for the same size of piston. It is expected to be on a production vehicle by 2006.
Even allowing for inevitable efficiency losses, braking torque is 1.9 times that of a single-disc system. In the mechatronic version—called the Electric Maximum Torque Brake (EMTB)—torque output for a given current is therefore effectively doubled, providing terrific braking performance with little power usage. For example 140W is all it would take to stop a Renault Laguna at 1g on a high µ surface.
Such performance could change conventional thinking on electric front braking systems, which until now has assumed that 42V is required to stop a reasonable sized car. A 14V EMTB is said to be good for vehicle masses of between 2500 and 3000kg—greatly simplifying the system and eliminating high voltage connectors and the expensive DC-DC converters needed to run dual voltage on the same car.
Instead of an hydraulic actuator, a brushless permanent magnet DC motor with a reduction gear drives a ballscrew to translate rotary into linear motion. Actuation takes place in just 6ms—fast enough to achieve full ABS and chassis control strategy performance. A prototype was on display at the Mondial de l’Automobile. Nick Jones, chief engineer at Delphi’s Innovation Centre, Paris, said the project emerged from knowledge gained in developing Delphi’s hybrid (front hydraulic/rear electric) braking system. The key was the robustness of the actuators and their ability to operate over a wide range of non-optimum states (temperature, moisture, age etc). “If you achieve that it reverses the complexity spiral and simplifies the rest of the system requirements,” he said.
The main challenges centred on power supply and redundancy. “Having two or three independent power systems was too costly, too complex and ultimately self-defeating,” said Jones. “Our alternative approach is redundant computing—duplicating the computing power around the vehicle with a fault-tolerant power system. You still need a dependable power system with a small back-up battery and the ability to monitor the power source, but essentially each braking corner is calculating what it should do and what the others should do.” He believes there will be a legislative requirement for the power system and the battery state-of-health monitoring.
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Author
Roger Bishop
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