Test The Limits

Carmakers burning through cash with thermal testing

By Ed Tate

April 22 2015

As part of traditional product development, car manufacturers build a fleet of pre-production vehicles in special facilities, incurring a huge level of cost – easily in excess of $1 million per prototype. These cars are transported all around the world, to be driven and tested in almost every climate from sweltering desert heat to snowy mountain tops. One important aspect of this process is looking at whether new models have any problems with heating and cooling. The trouble is, if engineers find any thermal problems, it’s then very expensive to change the design after it’s been finalised and approved. In the pre-production phase when the tooling for manufacturing is already being prepared – there really is no going back. Development teams therefore have to find other ways to fix the problem, such as adding heat shields or upgrading materials. Switching a plastic part for a metal one that will survive the heat adds cost, eating into precious profit margins. If this method doesn’t work, it is possible to change the software and actually reduce air conditioning and horsepower in certain situations. This happens with many cars, and it’s definitely something customers notice. On a hot day, for example, if a buyer is driving up a hill or accelerating away from a stop light, they may get a poor response from the engine and feel tepid, humid air from the vents. The engine’s torque is limited and the air conditioning is turned off briefly. That’s the electronic control system intruding, limiting potential damage to the vehicle. To avoid damaging and engine in high-temperature situations, the manufacturer reduces engine power 20% or more. For a high performance vehicle, the speed is reduced. For a truck towing a loaded trailer in the mountains, the maximum speed may be reduced to less than 45 mph. Naturally, manufacturers hate this, as do customers, but at the late stage of development there’s often little else they can do. Thermal development through simulation highlights potential hot spots on a computer screen before the first prototype is built. Comprehensive simulations, covering every operating and ambient condition, predict what will happen when testing anywhere in the world. This early knowledge allows inexpensive changes in the design, eliminating expensive changes later. Exa works with its customers to eliminate costly late-stage changes and reduce the need to make quite so many expensive pre-production cars. For example, in a recent project we were able to improve vehicle thermal performance using simulations to a point where only a single thermal issue was uncovered late in the design stage. Usually there are dozen or more issues found using traditional prototype/testing design approach. This is a radical change for engineers and designers to make, as it involves a whole new working process, different to how car manufacturers have traditionally engineered their products. However, it’s a change that will ultimately pay great dividends, by helping to deliver the no-compromise cars that everybody wants.