Feature Sensors & sensing systems
Sensors gain position in the automotive industry
In the automotive industry, position sensors need to offer the highest levels of reliability, despite having to withstand punishing environmental conditions including wide variations in temperature, shock, vibration and exposure to liquid. Graham Pattison, Variohm EuroSensor’s sales director, gives us an overview of the technologies and trends from the industry
T
he automotive industry constantly challenges sensor manufacturers to provide position measurement products that help to enhance levels of vehicle performance, economy and safety at increasingly competitive costs. With typical temperature variations beyond -40°C to +150°C, high levels of shock and vibration, plus exposure to water, salts and automotive fluids, position sensors placed close to the engine, gearbox and transmission systems face very tough environmental conditions. However, they must, of course, perform with absolute 'no- compromise' levels of reliability. In the past the sensor technology favoured for most automotive mea- surement applications has been the traditional potentiometer types that rely on the contact between a conductive plastic material and metal wipers. These sensors have an excel- lent price-performance ratio and can yield extremely long life, excellent durability and high reliability. However, new and emerging application areas that will replace traditional mechanical linkage sys- tems with electronic closed loop servo controls, for mission critical processes such as steering and engine management, have called for non- contact sensor technologies which meet the higher service life and relia- bility requirements that are now being called for by the industry. Variohm EuroSensor's distribution
partner, the German manufacturer Novotechnik, manufactures both poten- tiometric and non-contact position sensors for angular and linear position measurement. The non-contact tech- nologies include Hall Effect principles for rotary measurement and magne- tostrictive linear position sensors.
Reliable solutions
The non-contact sensors provide a typical life of up to 350 million movements and are available in two form factors. The first type, termed by Novotechnik as ‘Non-contacting' is similar in design to potentiometric
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contact and with no bearing system to wear, provide the ultimate life and reliability, and are being used for the most demanding applications.
Proving the technology
Novotechnik's position sensors for automotive applications have often had a proving ground in other demand- ing industries – such as agricultural machinery and mobile construction equipment – where, arguably, the environmental conditions are even more extreme.
Contactless magnetic rotary sensors for use in harsh environments
types in that the two sensor compo- nents are housed in casings with precision bearings that support the rotating or linear displacement ele- ments. The second ‘Touchless’ design sees the sensing elements supplied individually and mounted within the application using an external bearing or support system to maintain the correct gap between the components. With a typical measuring resolution of over 14 bits and linearity values of better than 0.1%, these technologies more than fulfil the specification requirements for automotive position measuring applications. Across Novotechnik’s comprehen- sive range of contacting and non- contacting sensors, measurement angles below 360˚ to multi-turn devices are available for rotary models, and stroke lengths between 5mm and 5000mm are offered for linear sensors. Housing designs vary from lightweight moulded polycarbonates to heavy duty aluminium, fully sealed up to IP69K. Touchless versions may include indi- vidual encapsulation of components that can provide total isolation from harsh environments. Most sensor types are fully available in redundant ver- sions for complete safety assurance. Touchless versions, with no sensor
One such emerging area is four-wheel steering where front and rear wheels are synchronised in the same direction to allow improved traction stability at high speeds, and synchronised in opposite directions for parking manoeu- vrability at low speeds. This concept is now being used for some high-end luxury cars and off-road vehicles but was first developed to optimise agricul- tural tasks like seed drilling as well as allowing for mobile machinery, such as road laying equipment, to operate much more flexibly. The concept basically involves linear or rotary position sensors mounted on the driver’s wheel or steered axle, combined with a servo controlled actuator with additional feedback sensors driving the rear axle. Some of the most exciting develop- ments in which position sensors are playing an important role are steer- by-wire and throttle-by-wire. Similar in principle to fly-by-wire in aviation, these systems effectively replace existing mechanical linkages with closed loop electronic servo systems to provide space saving and weight reduction advantages, remove the potential for wear, and reduce service intervals and parts replacement. Perhaps most importantly, they allow significantly increased efficiency and enhance safety when used in combina- tion with advanced control systems. The steer-by-wire system includes two position and angular measuring devices, one sensor for detecting the steering angle and one that detects the actual value of the steering
MARCH 2011 Design Solutions
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