Sense Of Control
All the electronic gadgets and driver aids you find in cars these days are largely attributed to the emergence of high-performance computers. The real stars, however, are those tiny devices we call sensors, because these things have evolved to become smaller, more accurate and immensely more robust. This means that they can be installed in tight spaces where conditions may be harsh (hot, high vibration, extreme pressure) and still supply the computer with accurate and timely data. Despite having grown smaller, the sensor’s role in the electronic management of the modern vehicle’s performance has never been bigger. Every car manufactured today needs sensors in the engine, while at the high end, cars like the BMW 7 Series and Lexus LS rely on a bewildering array of sensors for the control of engine performance, gearbox activity, braking, body/chassis dynamics, traction, air-con …
and the list goes on.
To perform its job, a sensor must firstly be able to detect a change in its assigned parameter (e.g. temperature, pressure, body roll, et al). Each is unique, being designed for a specific function. So a temperature sensor cannot be used as a pressure sensor and vice versa. In addition, a variety of scientific principles (magnetism, photo-electricity, piezo-electricitiy, et al) form the basis of a sensing device’s function. But regardless of the form or function, all these sensors have one thing in common: the nature of their feedback signal. Whatever a sensor detects – pressure, temperature, air flow, vibration – it converts the measurement into an electrical form (usually a voltage of between 0 and 5 volts) to send into the ECU (electronic control unit) where the analogue voltage is converted into a digital input.
The current generation of ECUs rely on a combination of information from a multitude of sensors to control one parameter. In a vehicle stability system, for example, the ECU compares yaw rate (rotation about the vertical axis of the car) measured by a g-sensor with information from a position sensor for steering wheel angle and computes the slip angle. The result determines if the car is in a state of understeer, oversteer or neutrality. Both the wheel speed and throttle position sensors further help to evaluate if the cause of instability is excessive speed. Within fractions of a second, the ECU concludes its findings and sends the right dose of electrical pulses to a hydraulic servo valve to modulate pressure to one or more wheel brakes and a throttle control motor to gradually reduce throttle opening. Since the monitoring is continuous, the ECU will restore driver priority immediately once stability is established. Electronic stability systems are an extremely effective means of idiot-proofing vehicle dynamics, thanks to the relevant sensors’ performance and reliability.
The simple-looking sensor is, in fact, a complex yet compact piece of hardware that is also a key element in the car’s electronic control network. Microprocessors are now powerful enough to both send and receive a multitude of signals simultaneously, so it is just as well that micro-engineering has produced miniaturized sensors that tell the tale with accuracy and consistency. This is an important factor, since the ECU’s precision in ultimately controlling an actuator is limited by the accuracy of the measured signal.
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