From multi-axis micro electromechanical systems (MEMS) to vision and radar sensors, and from exotic to well-established or mature technologies, sensors initiate the control system process. Advanced packaging, sensor interfaces, combined sensors and advanced system concepts are among the latest improvements that sensor and sensor-based system suppliers are developing to achieve increased control as well as reduce costs in safety systems.

Multi-sensor Packaging

According to the recent iSuppli report “Multi-sensor Packages Come into Vogue,” the use of multi-sensor MEMS packages in automotive Electronic Stability Control (ESC) systems will begin in 2010. Initially offered in systems from companies like Bosch and Continental, these multi-sensor products will increase to 25.9 million units in 2014 and address more than 50% of the market.

The reasons for the increasing popularity of multi-sensor packages or combo sensors that include an accelerometer and gyroscope are rather straightforward. “Combo sensors save costs through fewer packages and probably in later versions through a shared ASIC,” says Richard Dixon, senior analyst for MEMS at iSuppli. The package-level integration also allows carmakers to reduce the number of modules inside vehicles.

Based on the U.S. National Highway Traffic Safety Administration’s (NHTSA) requirement for electronic stability control systems on all passenger vehicles under 10,000 pounds by the 2012 model year, ESC will be a widely deployed system. ESC has been phased into U.S vehicles to meet the Federal requirement since 2009 models. However, ESC was already implemented in 80% of the registered vehicles in Germany and will be required for all new vehicles by the end of 2014. By comparing the driver’s request (input) with actual vehicle motion from accelerometers, gyroscopes and wheel speed sensors, an ESC system helps the driver detect and minimize skidding.

One of the MEMS sensor manufacturers offering a gyro-accelerometer combo sensor is VTI Technologies. Packaged in an 18.65 mm x 8.5 mm x 4.53 mm leadframe-based package, the SCC1300-D02 is a ±100º/s x-axis and ±2 g 3-axis design, and the SCC1300-D04 is ±300º/s x-axis and ±6 g 3-axis unit (see Fig. 1). The three-axis accelerometer and single-axis gyro combo are based on VTI's 3D MEMS manufacturing technology, which enables the company to produce extremely robust, stable and low-noise sensors.

The System Dictates the Sensor(s)

System requirements shape the specifications for the sensor or sensors used in the system and ultimately determine which sensor technology meets those requirements. Electric power steering (EPS) provides a good case in point. EPS is one of the energy saving measures being implemented by carmakers.

With the capability to reduce fuel consumption by as much as 4%, EPS is gaining in popularity. According to an article in The Detroit News, Ford Motor Co. has said that 90% of its vehicles will have EPS by 2012. Nexteer Automotive, a Saginaw, Mich., company, expects full-size pickup trucks to begin using electric power steering within the next three years.

EPS is also an essential feature for other advanced features such as automatic parking assist, adaptive cruise control (ACC), hybrid vehicles and vehicles with stop-start systems. EPS could also be part of future collision avoidance systems.

In an EPS system, a sensor indicates the driver's steering requirements, so a microcontroller can actuate an electric motor on the steering column or the steering rack. Hall-Effect devices, one of the elder statesmen of semiconductor sensors, continue to improve for EPS and other motion control applications. Two suppliers have taken rather different approaches to using Hall-Effect technology for EPS systems.

Melexis designed its second generation of automotive Hall-Effect latch sensors as a successor to its USx88x series. The initial product, the MLX92211, operates from 2.7 to 24V and provides latching magnetic behavior. South and North magnetic fields applied perpendicular to the package top cause the open drain output to switch ON and OFF. Rotary applications such as electric power steering commonly use shaft-mounted multi-pole ring magnets for this purpose.

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