Let the Sparks Fly

The evolution of electrical systems – from the spark plug to the CAN bus

Article and Images Graeme Morpeth

Last time (see The Star, November-December, 2017), we explored the first electrical system in the automobile – the ignition system developed by Bosch and used in Mercedes racing cars in 1905 – that generated and controlled the timing of the sparks that ignited the fuel/air mixture in the cylinders.

The next major innovation in electrical systems was the introduction of the practical electric self-starter by Charles Kettering, who adapted it from an electric motor he had developed for cash registers. The electric self-starter, used in combination with a generator and battery, was first installed on the 1912 Cadillac and was rapidly adopted by nearly all other automobile manufacturers, replacing the quirky and dangerous crank starter employed on earlier cars. This single innovation is credited as the major reason that the gasoline-powered automobile replaced the horse and buggy.

With a reliable supply of electricity available, automobile engineers soon started adding other electrical components for safety, reliability, comfort and convenience, including lights, windscreen wipers, heaters, radios, and gauges to monitor car speed and engine condition. By 1955, automobile wiring diagrams – the W198 300SL Gullwing’s is shown here (Figure 1) – had become a complex maze of multicolored wires and connections sufficient to cause the layman to stare in disbelief.

Wiring systems became more complex with the addition of other conveniences: Air-conditioning systems, as introduced in the W100 600 Grosser Mercedes in 1963, for example, needed their own separate wiring circuit and electrical system (Figure 2). The entire climate-control and comfort systems were all electronically controlled, even offering separate controls for each position in the cabin.

Similarly, the radios that were once considered luxury options gave way to audio systems that are today considered a necessity: Current models have the Comand system that integrates entertainment, communication and navigation systems with one – or two, depending upon the model – display screens for both information and control.

In the late 1960s, the entry of semiconductor electronics into the automotive-engineering world changed everything.

The electronic circuits, computer sensing and control systems made possible using  integrated circuits spawned a whole new world of development. Fuel-injection systems, previously mechanically operated, were now computer controlled, first as single-point injection, then multipoint, then direct injection into individual cylinders, combined with multiple injections and multiple sparks per ignition stroke.

Anti-lock braking systems, which used sensors on each wheel to monitor individual wheel rotation, could be used to actuate the brakes on specific wheels to control skidding and loss of control. Based on these systems, a plethora of driving aids became possible, including electronic stability control, early tire-pressure monitoring systems, brake-assist and traction-control systems.

From an owner’s perspective, these systems are a joy to behold and use; from an engineer’s perspective, they are a nightmare, requiring complicated and heavy wiring. Part of the solution has come from the introduction of Controller Area Network (CAN) database systems, robust vehicle “bus” systems that allow all the micro-processors and other electronic control devices on a vehicle to communicate without the need for a central host computer (Figure 3). Originally developed by Robert Bosch GmbH, the CAN bus was formally introduced at the 1986 Society of Automotive Engineers conference in Detroit, Michigan.

The CAN bus is message-based, with small-wattage multiplex fiber-optic signal systems controlling components and just the power circuits using larger and heavier cables, thus saving on materials, complexity and weight. The latest “D2B” (Domestic Digital Bus) transmission can transmit data at the speed of light (3 x 105 km/sec) at a rate of 5.6 x 106 bips, up to 60 times faster than the equivalent copper-cable system. A modern automobile may have as many as 70 interlinked and interrelated systems that communicate with each other to control engine output, suspension, brakes and steering, as well as comfort, convenience, information and entertainment.

But there is more to come. In our next installment, we’ll discuss 48-volt direct-current systems, which are now being introduced on advanced hybrid and fully electric vehicles, such as the next-generation CLS to be launched in 2018.