Rapid manufacturing aids hybrid sports car project
26 October 2010
Westfield Sportscars recently approached Warwick Manufacturing Group research engineer, Stephen Lambert improve the acceleration performance of its Sport Turbo 1600 model. The project is being funded jointly by Warwick Innovative Manufacturing Research Centre and Potenza Technology, a specialist in hybrid and electric vehicle systems. The car’s 1.6litre 200bhp petrol has now been supplemented by two electric motors, each rated at 75kW to give the vehicle a four wheel drive boost for up to three minutes during a race. F1-style inboard suspension was added to drive the front wheels independently. The motors are brought into play by the driver pulling a pair of ‘push to pass’ paddles behind the steering wheel, the torque applied depending on throttle position.
Maximising the power and duration of the electric drive to the front wheels had one major limiting factor: excessive heating of the 396 lithium ion phosphate that provide its power. This was a challenge, as the only space available for the batteries was in an enclosure beneath the driver's seat.
Initially, Mr Lambert stored the cells in rows, side by side, in two battery boxes machined from solid plastic, one for each motor. However, an alternative solution was proposed by engineers from the rapid prototyping machine manufacturer, EOS, which is currently involved with the Formula Student project at Warwick. Instead of open battery boxes, two arrays of eleven plastic modules were designed so that each cell could be retained in its own cylindrical cavity, 18 per module.
Rapid manufacturing in an EOSINT P-series laser-sintering machine, driven by data from the CAD model of the new battery box, was used to produce the modules from layers of fused EOS PA 2200 polyamide powder. The flexibility of design afforded by this technique allowed air channels to be created between each cell cylinder and between adjacent modules as they are bolted together – very difficult, if not impossible, to create using any other production method.
These rapidly manufactured parts have significantly enhanced cell cooling at maximum current draw, enabling Westfield to obtain maximum performance from the electric motor boosters. From a standing start, the Westfield Hybrid in four wheel drive mode now achieves 60mph in 3.5 seconds, compared with 5.5 seconds when only the rear wheels are driven.
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