An ever-increasing level of electrical equipment in cars is posing difficulties for vehicle makers.
Complex wiring carrying high currents in the vicinity of the steering column brings the associated risk of a short-circuit in a crash. Bigger holes needed in bulkheads to accommodate the large wiring harnesses to supply power to equipment, such as electric power steering, weaken the structure. And the problem of shielding equipment against electro-magnetic interference becomes increasingly difficult.
There are also implications for fuel consumption. Reducing the weight of a vehicle by 100kg is estimated to save 0.34litres of fuel per km. Cutting demand for electrical power by 100W can save 0.17 litres/km. Potentially, reducing a vehicle’s electrical load is an easier way for designers to cut fuel consumption.
Delphi, the components arm of General Motors, has developed a system to simplify the electrical installation and reduce the power demand. It combines the idea of a databus linking the car’s electrics with the concept of intelligent load management.
Communications buses have been used to link the electronic modules scattered around a modern car before, but it is expensive and has been limited to luxury vehicles. Delphi says its system should be cheap enough to fit to mass market models.
Instead of a complex wiring loom, only four wires are needed: a positive and negative feed plus two data cables.
There are three key components: a steering column module, an instrument cluster module, and a computer. The steering column module consists of a printed circuit board incorporating microswitches (known as a bussed electrical centre) for controlling functions such as indicators, immobiliser, airbag and power steering. The switches are connected by a serial databus using the Canbus standard to each component, eliminating most of the wiring in the steering column.
The computer integrates the functions of all the electronic modules currently distributed around the car, says Peter Stradler, Delphi systems engineer. This integration is the key to making the system economic to fit in mass market cars.
But it also makes possible intelligent load management – a process by which the central computer monitors the electrical load and flattens out peaks in demand.
Equipment such as electric power steering causes a dramatic increase in power demand while it is being used, but only for a few seconds at a time. The management system compensates for this by momentarily reducing power to other, non-essential functions, such as electric windows.
Benefits of the bus system include greater design flexibility, reduced weight, and simplified manufacture.
Also, the use of intelligent load management should reduce fuel consumption by eliminating power peaks and allowing the use of a smaller, more efficient generator, claims Delphi.