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23/05/2008
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An innovative idea could lead to greatly improved power transmission in automotive applications – and beyond. Tom Shelley reports
A former French naval engineer has latched on to latest developments in powder metallurgy based magnets to come up with a magnetic clutch that could open the way to a novel automotive kinetic energy storage system.
Engineering consultant Jacques Clausin says the scheme is an adaptation of very large active shock absorbers he came up with to remove vibrations generated by the propeller of nuclear submarines. The clutch uses a new ferromagnetic material called Somaloy, an iron powder agglomerate that is mildly electrifcally conductive.
Made by the Swedish company Höganäs, this is a soft magnetic composite powder material with low eddy current losses at high frequencies, allowing magnetic circuits to be made smaller and lighter. Conventional magnetic machines and devices use magnetic circuits made up of stacked sheets. However, magnetic fields then have to be located in the planes of the sheets, otherwise eddy currents would be induced in them (insulation between sheets prevents the induction of eddy currents in other directions).
If the magnetic iron consists of insulated particles, though, magnetic fields can circulate in any direction, without inducing eddy currents that would absorb energy. This is particularly relevant in a machine such as the proposed clutch, since its purpose is to transmit torque in cases where there will be a significant mismatch between the speed of the vehicle transmission and that of the flywheel. This is because, in any kinetic energy storage system, the flywheel must be spun up from a slow speed when the vehicle is going fast and needs to brake; but when the flywheel is going at full speed, it will be required to assist vehicle acceleration from rest or a slow speed.
Clausin’s intention was to devise a clutch that could be put in a Peugeot 406 and allow torque to be transferred to and from a flywheel in a completely controllable way, using the air gap in the clutch to control the amount of torque being transferred at any moment. The machine design has a planar squirrel cage on the vehicle transmission side and permanent magnets on the flywheel, which would weigh about 20kg.
The clutch has not actually been made yet, but the design has been modelled and evaluated by Peugeot. According to Clausin, it was to have been developed and prototyped by ZF (Germany).
“Unhappily, no financial agreement occurred between ZF and Peugeot, and my project stopped,” he adds.
He estimates that response time would be about 6 milliseconds. “This very short response time is used to ensure a controlled slip at low rpms of 600 to 1,000, in order to filter the torsion vibrations coming from the diesel engine.”
The design parameters were: nominal transmitted torque, 300Nm, diameter 240mm, and width 60mm, similar to the dimensions of a conventional clutch.
Several patents protect the intellectual property.
Pointers
* In the clutch, torque is transmitted across a small air gap only about 1mm across, which spacing can be precisely varied
* Powder metallurgy magnetic circuits are used to eliminate eddy currents
* Size would be about the same as that of a conventional clutch
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Author
Tom Shelley
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