Position sensors drive automobile innovation

Measurement of the angular and linear position of various automobile components opens the way to innovative solutions to enhance driving pleasure, safety and performance while reducing fuel consumption, emissions and cost. With more than 25 years of experience in the field, Electricfil Automotive has the necessary know-how in all the leading sensor technologies to provide optimum position-sensing solutions for any engine, clutch, transmission, body or chassis application.

With the increasing use of electronic control systems in automobiles, position sensors have become a key component in the automotive industry. They provide control systems with the information they need to optimize engine, clutch, transmission and other vehicle functions.

Engine management

Today's automobile engines are increasingly controlled by electronic control units (ECU). To optimize engine performance while reducing fuel consumption and emissions, these closed loop control systems require information on the position of a number of components.

For instance, to optimize ignition and injection system timing, the ECU needs to know the exact position of the crankshaft. The crank sensor is used together with a similar camshaft position sensor to monitor the relationship between the pistons and the valves. This is particularly important for engines with variable valve lift (VVL) designed to optimize the air/fuel mixture ratio and temperature, pumping losses, swirl effect and other important parameters.

For fast synchronization and reduced engine emissions on starting, the camshaft position must be provided by a sensor with a True Power On (TPO) function to determine the absolute position of the shaft as soon as the sensor is switched on.

These position sensors help improve engine performance with better torque ratios when starting, higher torque at low RPMs, more power and lower pollution and fuel consumption.

Other engine management applications include new stop/start systems that automatically switch the engine off when the vehicle stops at traffic lights or in traffic jams. To calculate optimum injection and ignition parameters for each restart, a position sensor provides the exact position and direction of rotation of the crankshaft. In this way, position sensors once again contribute to lower fuel consumption and CO2 emissions.

In another application, the throttle is controlled by an electronic system rather than directly by the accelerator pedal. The ECU takes various performance factors such as air/fuel ratio and pumping losses into account when determining the optimum throttle position. A throttle position sensor is required by the ECU to allow closed loop control of the throttle actuator.

Other position sensors are used on exhaust gas recirculation (EGR) systems designed to keep vehicles in line with emission regulations. The electronic control systems uses the information provided by the EGR valve position sensor to monitor the recirculation flowrate and maintain optimum engine performance and emission control.

Finally, turbochargers require position sensors to monitor the position of the actuators controlling the turbocharger wastegate and variable geometry functions.

Transmissions

In manual, automated manual (AMT) and dual clutch (DCT) transmissions, gear shifting is made possible by hydraulic or electric actuators that release the clutch or move a shifting fork. These actuators are either controlled automatically in dual clutch (DCT) and automated manual (AMT) transmissions or by a clutch pedal in manual transmissions (MT). Whatever the system, electronic clutch control and driver assistance functions improve driving comfort and extend the service life of clutch components.

For example, hill-holder functions make starting on even the steepest hill easy on both the driver and the clutch. Safety lock-outs prevent shifting into wrong gear, starting the engine with the clutch engaged or downshifting on slippery roads. The parking brake can be automatically released when the clutch is engaged. Other clutch-related functions include torque limiting, cruise-control switch-off, stop & start, anti-stall systems, clutch-riding alarms and clutch position indication. And the list is growing continuously.

With electronic transmissions such as AMTs and increasingly popular DCTs, the driver no longer needs to press a pedal and manually shift gears. The electronic control system determines the right time to operate the actuators for optimum clutch control. This decreases fuel consumption and increases comfort and driving pleasure through smoother shifting without any driver intervention, explaining the bright future for these solutions, particularly in Europe.

To implement these functions, sensors are required to determine the clutch position or status and send the information to the electronic control system. Depending on the type of transmission, this information is generally monitored via the position of the master and/or slave cylinder, the clutch release bearing or the clutch pedal.

In addition, with the new dual clutch transmissions (DCT), optimized gear shifting requires information on the position of the shift fork to synchronize transfers between the two clutches.

And finally, in today's automatic transmissions, an electronic module controls the torque converter and electro-hydraulic actuators to change gears smoothly and efficiently. To do this, it needs to know the current drive mode (P,R,N,D,L), supplied by the transmission range sensor (TRS). A position switch is used to identify Park position for shift-by-wire safety functions.

Vehicle systems

Electronic control systems used to adjust vehicle suspension or level headlights also require position sensors. They use non-contact technology and must be compact and accurate.

New electric braking systems (e-braking) and electric parking brake systems (e-parking) need position sensors to provide information on the position of the brake caliper. This is also true for the regenerative braking systems that already equip today's hybrid vehicles.

Accelerator pedal position sensors provide information required by the ECU to control the throttle valve. Clutch pedal position sensors are used for various driver assistance functions already described above in the section dealing with transmissions. Position sensors are also used on the brake pedal to control the brake light switch.

Sensor clusters and mechatronic modules

To offer more functions with higher reliability and lower cost, carmakers are looking for higher levels of integration for their control systems. Various types of sensors can be combined in sensor clusters or in mechatronic modules that include power, actuation and communication functions. For instance, in today's electronic transmissions, sensors, actuators and the transmission control unit (TCU) can be combined in a single module installed inside the gearbox and immersed in oil. Advantages include simplified wiring, connection and sealing, easy assembly and improved quality and process control. Successful integration requires critical know-how in interconnection and sealing technologies, over and above basic sensing expertise. The right level of integration is a trade-off between cost, quality and production volume considerations. Opposing needs related to multiple transmission architectures and high-volume production often lead to a compromise between full integration in a single module and modular integration within sensor clusters.

The right technology for every application

Most position sensors used in the automotive industry used to be potentiometric sensors, offering simple design and low cost. However this kind of sensor has a number of important drawbacks. First, it requires mechanical contact that leads to high wear and failure rates that are no longer compatible with the quality standards of today's car makers. Another problem is the difficult integration of such sensors in multi-sensor and mechatronic modules. For this reason, new powertrain and vehicle applications are better served by compact non-contact technologies, compatible with harsh environments. Requirements related to accuracy, cost, airgap, dimensions or the electrical interface are different depending on the case. Electricfil therefore carries out continuous research and development on a wide range of technologies in order to provide the best solution for every application.

Hall effect
Electricfil used its extensive experience and know-how in Hall effect technology to develop innovative and flexible position measurement solutions. 1D Hall devices with optimized magnetic configurations can be used to measure continuous displacement over a 1-40 mm stroke. 2D Hall sensors can be used for 360° angular measurements as well as linear displacements. Hall sensing elements can also be used in position switches that produce a binary output signal identifying two positions rather than a continuous analog signal.

GMR
Giant Magneto-Resistive (GMR) technology offers position sensing characteristics similar to those of Hall sensors but with a higher sensitivity.

LVDT
LVDT (Linear Variable Differential Transformer) position sensing solutions are based on a well-known inductive principle (see box). They are suitable for strokes up to 100 mm and can withstand temperatures up to 180°C.

Eddy-current
Another position sensor that Electricfil is presently developing is based on eddy-current technology. Suitable for strokes up to 50 mm, this technology requires no magnets and is totally insensitivity to external magnetic fields.

Position sensors for today's automotive applications must satisfy stringent reliability, performance, size and cost requirements. The reliability criterion imposes a non-contact technology to eliminate mechanical wear. Among the many non-contact designs now available, Electricfil offers its LVDT proven core technology and ASIC for position-sensing solutions that optimize performance, size and cost to perfectly match the needs of each customer application.

Technology

An LVDT (linear variable differential transformer) position sensor delivers a signal proportional to the linear displacement of a magnet fixed to a moving part. A primary coil is energized to create a magnetic field that is coupled into two secondary coils. The difference between the resulting voltages induced in the two secondary coils varies with the position of the magnet and provides the basic position signal. An ASIC is used to condition the signal. The complete sensor can be located outside the housing of the part in a less severe environment, providing non-contact measurement of displacement through aluminum walls, or the sensing component can be located inside the housing with the electronics outside. Electricfil has developed an original patented sensor design with its own application specific integrated circuit (ASIC).

Characteristics

• stroke up to 100 mm
• temperatures up to 180°C
• typical accuracy: ± 2%
• response time: 1 ms
• air gap up to 4.5 mm
• size: stroke length + 30 mm
• integrated diagnostics
• insensitive to rotation (with cylindrical magnet)
• non-contact sensing
• through-wall detection for non-magnetic materials
• integrated or remote electronics
• low sensitivity to external magnetic fields
• high mounting tolerances

Electricfil LVDT know-how

• integration in sensor clusters or mechatronic modules
• wide range of packages and interfaces
• fully programmable sensors
• proven core technology including ASIC
• PWM or analog mode

Applications

Electricfil's LVDT technology is now available for cost-effective solutions to many position-sensing needs in engine, transmission, body or chassis applications. For example, mass production of an LVDT sensor for a dual clutch transmission (DCT) to be used by a leading sportscar manufacturer will begin in 2008. The sensor measures the position of the shift fork to synchronize transfers between the two clutches. Electricfil can supply LVDT sensors as individual components or included in sensor clusters or mechatronic modules. The new Technopole R&D center, its talented engineering staff and state-of-the-art resources are at you disposal to develop optimum LVDT solutions for your position-sensing needs.

Automotive requirements for position sensors

Position sensors must meet the usual requirements of automotive applications including vibration immunity, temperature ranges of up to -40 to +160°C and sealing against fluids like ATF. In addition, they are often integrated in systems that affect the safety of the driver and passengers. In such a case the sensor is part of an overall safety strategy that must be implemented at system level. For this reason, Electricfil can build redundancy and diagnostic capabilities into its position sensors.

Electricfil experience

Mass production of the first non-contact position sensor for detection of the gearstick position in automatic transmissions began in 2001 and involved encoded Hall Effect technology. This innovative sensor solution is also used in CVT, 6-speed automatic and hybrid transmissions from several car makers in Europe and the USA.

Since then, Electricfil has gone on to supply a growing number of automakers and OEMs with position sensor solutions designed to meet their individual needs. Today it has expanded its proven core technologies to include LVDT position sensing, featuring an ASIC for a multitude of signal treatment and programming possibilities to ensure fast delivery of custom sensing solutions. For example, mass production of an LVDT sensor for a dual clutch transmission (DCT) to be used by a leading sportscar manufacturer will begin in 2008. The sensor measures the position of the shift fork to synchronize transfers between the two clutches. Upcoming technologies include Eddy-current linear position sensing to satisfy needs for higher sensitivity to moving targets and total insensitivity to external magnetic fields.

Sensor solutions currently represent 75% of Electricfil’s sales, with applications in transmission systems, engine management and vehicle systems. These solutions help customers enhance engine performance, reduce fuel consumption and emissions and improve passenger comfort and safety while at the same time cutting costs. More than 100 engineers work in the new Technopole R&D center or on customer sites around the world, applying proven core technologies to produce sensor solutions that fit customer needs for individual sensors, sensor clusters or mechatronic modules. Electricfil Automotive has unequalled expertise in the field of optimized engine performance and a capacity for innovation that places the group among the key players in automotive electronic and electromagnetic systems. With 1200 employees, Electricfil Automotive produces 30 million sensors and develops more than 25 new solutions every year.

Electricfil knowhow

Sensor solutions currently represent 75% of Electricfil’s sales, with applications in transmission systems, engine management and vehicle systems. These solutions help customers enhance engine performance, reduce fuel consumption and emissions and improve passenger comfort and safety while at the same time cutting costs. More than 100 engineers work in the new Technopole R&D center or on customer sites around the world, applying proven core technologies to produce sensor solutions that fit customer needs for individual sensors, sensor clusters or mechatronic modules. Innovation is an ongoing process at Electricfil, and car manufacturers and automotive suppliers alike can count on them to keep pace with their sensor needs.

and a capacity for innovation that places the group among the key players in automotive electronic and electromagnetic systems. With 1200 employees, Electricfil Automotive produces 30 million sensors and develops more than 25 new solutions every year. More than 150 million engine speed sensors designed and produced by Electricfil are currently on the road worldwide.