Plasma,thermal sprayed coatings for use in electric,hybrid systems
Whether we like it or not, hybrid systems – where we recover some of the waste energy generated when we burn fuel – are part of our future, whether this they be in our passenger cars or our racecars. Motorsport, certainly at the highest levels, has a choice as to whether it leads or follows. However, if it does neither, it will be isolated and will lose manufacturer support.
I have had some involvement in motorsport hybrid systems over the past 15 years, some of it on the Panoz Q9, some of it on the KERS systems in Formula One, and some on the early development phases of the current Formula One energy recovery systems. The march of technology has been relentless and impressive, with each iteration showing an increase in performance or a decrease in size; it’s just a shame that those ‘outside the box’ aren’t able to get an appreciation for the dramatic progress which has taken place. As with personal computing, for example, hybrid systems benefit from the miniaturisation and tighter packaging of components.
The problem with the increasingly tight packaging of high-voltage components though comes when we have components working at different voltages getting too close together. The effects of creepage and clearance have been discussed previously in respect of fasteners, but there are other components that absolutely must be metallic if they are to function correctly: one example here might be shields to prevent the effects of electromagnetic interference. In the same way that the ‘Faraday cage’ effect that shields the occupants of a car from lightning, EMC (electro-magnetic compatibility) shielding protects electronics from the effects of interference which might, for instance, be the result of having electronics packaged close to powerful electric motors, where fields are being created and then collapsing rapidly as the motor is used to generate torque or harvest energy.
Plasma and thermal spray processes can be used to help create effective shields. One way to do this is to spray an electrically conducting shield (commonly sheet metal) with an insulating material. The insulation means the shield can then be placed very close to conductors without providing a path to earth or between two other components working at different voltages.
Another approach, which can work out much lighter, is to use an electrical insulator as the substrate for a shield, with the shield being formed by a sprayed coating of a metal – typically something like aluminium, which itself can be over-sprayed with an insulating ceramic or polymer. In order to provide the necessary shielding, very little thickness of aluminium is required, and the substrate can easily be made stiff, especially if it is a moulded composite component. If we try to produce the same effect with a metallic shield, we need to resort to expensive press tooling to form a stiff shape, whereas a simple machined mould for a composite tool can be made pretty quickly these days.
It is possible to incorporate EMC shielding based on thermal/plasma sprayed coatings into composite outer cases rather than using separate shields. Again, a thin metallic coating is sprayed directly onto the casing, and this may or may not be over-sprayed with an insulator.
Written by Wayne Ward