In today’s cars, electronics and computers have replaced many mechanical components, taking over control of crucial systems. Many of these changes are intended to improve safety, but has their complexity introduced new and unnecessary risks? Â鶹´«Ă˝ assesses the electronic systems found in modern cars and the ways in which they can fail
Cruise control
Cruise control systems use an electronic control module (ECM) to maintain a speed set by the driver. The ECM sends signals to an actuator to open or close the throttle. Several manufacturers have recalled models over cruise control problems, such as drivers being unable to disengage the control. Newer “adaptive” cruise control systems add feedback from in-car radar to stay a safe distance from the car in front.
“Manufacturers have recalled several models over problems with cruise control”
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Anti-lock brakes
The electronic anti-lock braking systems introduced by Chrysler and General Motors in 1971 represented the first technical advance that took direct control from drivers and handed it over to electronics built into the car. By modulating the braking force during an emergency stop, ABS ensures the wheels do not lock, and so prevents the car entering an uncontrollable skid. If one wheel is rotating much more slowly than the others, an electronic control unit activates valves in the hydraulic braking systems to lessen the braking force on that wheel. A study by the US National Highway Traffic Safety Administration of crashes between 1995 and 2007 concluded that ABS reduced the number of non-fatal car crashes by 6 per cent; no change was found in the number of fatal crashes.
Engine control module
Controlling the engine is the most complex job in a modern car, so the engine control module (ECM) is the most powerful computer in a vehicle. It gathers information such as the amount of oxygen in the exhaust gases and the temperature of the engine from dozens of sensors, and uses these measurements to calculate how much fuel should be injected into the engine at each stroke and when, so that it ignites at precisely the right moment. The overall aim is to optimise performance while producing the lowest possible emissions and the best possible fuel economy. Problems with the ECM can result in the engine failing to work at all.
Door locks
The door locks on most new cars can be operated by a remote control that also deactivates the alarm. The radio frequencies these devices operate on are close to those used by communications systems operated by the military, radio amateurs and emergency services, including the Tetra system used by UK police forces. In February this year, hundreds of British motorists in Windermere, Cumbria, reported being unable to lock or unlock their cars. The problem was traced to interference from hand-held wireless devices used at a nearby restaurant to take orders.
Power steering
First introduced by Honda in 1990, electronically controlled power-assisted steering uses sensors in the steering column to send information on the motion of the steering wheel to an electronic control unit. This sends control signals to operate electric motors that reduce the physical effort required from the driver. The amount of assistance provided depends on driving speed and road conditions. This year, General Motors recalled 1.3 million vehicles in North America to fix a power steering problem that caused cars to veer off-course. And in February, Toyota confirmed it had received reports of power steering problems in some of its Corolla cars sold in the US.
Electronic throttle control
Mechanical throttles use a flexible, sheathed cable, known as a Bowden cable, to transmit movement of the accelerator pedal to the engine’s throttle valve. Electronic throttles rely on sensors which monitor the position of the pedal. An electronic control unit then takes into account other inputs, such as engine and vehicle speed to set the position of the throttle valve.
There are allegations that systems of this kind have contributed to incidents in which cars from Honda, Ford, Audi and most recently Toyota have accelerated out of control, but no clear link with the electronic throttle has ever been established. Some manufacturers have blamed these incidents on a floor mat jamming the pedal mechanism, or on worn pedal components. Others have blamed driver error.
Vehicle data bus
Electronic control units, sensors and actuators communicate via a digital network called the “vehicle bus”. Most modern cars use the CAN-bus standard, which operates at up to 1 megabit per second. The format of the data sent across the network enables different modules to rapidly decide whether the information is relevant to the functions they control. Brian Kirk of software design group Robinson Associates, based near Stroud, Gloucestershire, UK, has that CAN-bus messages can be corrupted – possibly as a result of corrosion or electromagnetic interference – and that modules receiving bad data packets may not be able to detect this corruption, potentially leading to malfunctions and accidents. Manufacturers deny these claims.
“Consumers will want reassurance that software will not jeopardise safety”
Too complicated to understand
During the 1980s, drivers of Mercedes-Benz cars with anti-lock brakes (ABS) reported that their brakes were failing on a section of autobahn in the Saarland region of Germany. The problem, caused by electromagnetic interference (EMI) from a nearby radio transmitter, was solved by putting up a giant wire mesh by the side of the road to shield traffic from its radio transmissions.
Ever since, there has been a plethora of court cases claiming that EMI has caused cars’ electronic systems to malfunction – and in some cases that cars have crashed as a result. Cellphones, radar, and military and emergency services’ radios – and even the cars’ own electronic systems – have all come under suspicion as the source of the EMI.
Manufacturers deny that EMI is a problem, claiming that electronic shielding and duplication of key components keep cars operating properly. Last month Toyota released a report it had commissioned from California engineering consultancy Exponent which concluded that cars were protected from EMI because they incorporated multiple sensors to perform each function.
Another area highlighted as a risk factor is the sheer complexity of the software in modern cars. Ford and Toyota have recently issued updates to fix glitches in the software used to control the braking systems in some of their hybrid models. Other manufacturers have at various times reported problems with automatic transmission systems, engine control modules and the software that controls the deployment of airbags.
While computer users accept software updates as routine, the prospect may be more disconcerting for car owners, says Krishnasami Rajagopalan, an analyst at international business consultancy Frost & Sullivan. He predicts that consumers will in future want reassurance that the increased use of electronics does not jeopardise safety.
Validating computer code is always a complex business. Last year researchers at the Australian research institute NICTA and the University of New South Wales thought it worthy of note that they had been able to show mathematically that 7500 lines of code for an operating system they had written was secure. The code in systems controlling modern cars runs to hundreds of millions of lines.
