ams launches automotive-grade certified capacitive sensor to simplify design and reduce assembly costs

ams, a supplier of high-performance sensor solutions, has launched an automotive-grade certified capacitive sensor, the AS8579, which enhances the safety of automated driving assistance systems. The AS8579 performs hands-on detection on the steering wheel rather than on the steering column, making it more reliable and economical. By introducing the AS8579 capacitive sensor, automakers are better able to comply with the European 2021 Safety Regulation (UN Regulation 79), which requires that all cars sold in Europe with lane keeping assist systems (LKAS) must include hands-on detection in the steering wheel from April 1, 2021.

The AS8579 uses a new capacitive sensing technology that separates the resistive and capacitive parts (quantity/share/ratio) of the impedance measured by the sensor element. Compared to the charge-discharge method of capacitive sensing used in today's cars, this technology can more reliably detect whether the driver's hands are on the steering wheel - even when wearing gloves or in wet conditions. This means that the AS8579 helps automakers improve the safety of advanced driver assistance systems (ADAS) while reducing the cost of manual driving detection systems: the AS8579 can sense the impedance of the steering wheel heater element, while similar capacitive sensing systems for manual driving detection require dedicated metal sensor elements built into the steering wheel.

“More sophisticated ADAS functionality and, in the future, fully or partially automated driving systems will bring huge benefits to car users and society as a whole, such as reducing traffic congestion, reducing the number of accidents caused by driver error and making road travel more pleasant,” said Alexander Rensink, Business Unit Manager for Position Sensors at ams. “ADAS was originally designed to keep vehicles and people safe, and by introducing the first anti-spoofing hands-on detection system for all driving conditions, ams is making a significant contribution to the safety of the next generation of cars equipped with ADAS.”

Improved ams capacitive sensing technology addresses ADAS safety concerns

Developing a reliable method to detect whether a driver's hands are on the steering wheel could remove a significant barrier to large-scale deployment of ADAS in passenger and commercial vehicles. Automakers are implementing increasingly complex automated driving features, including features such as adaptive cruise control, traffic jam stop-start systems, and LKAS. All of these features require the driver to be ready to take back control of the vehicle immediately if the vehicle system fails to detect a safety threat, and manual driving detection is a critical part of any system used to monitor driver readiness.

Torque sensors have been used in the past to detect the continuous, small deflections caused by the driver's grip on the steering wheel, but this form of hands-on driving detection can be easily fooled (illegally), posing risks to the driver and other road users.

The trend in the automotive industry is now to use capacitive sensing for hands-on driving detection as this technology is more reliable for human contact and is simpler and less expensive to design and build than other options.

The charge and discharge method of capacitive sensing is well understood and has been used for years in products such as touch screens and touch-sensitive buttons. However, detection fails when the driver is wearing gloves, and water or moisture can also produce false detection signals, undermining the safety performance of manual driving detection based on this capacitive sensing method.

By implementing reliable capacitive sensing based on I/Q demodulation, the AS8579 capacitive sensor from ams enables car manufacturers to achieve extremely high safety standards in the more complex autonomous driving and driver assistance features currently under development.

The AS8579’s safety credentials also include the provision of multiple on-chip diagnostic features, ensuring support for ISO 26262 functional safety standards up to ASIL B. The sensor is AEC-Q100 Grade 1 qualified. The AS8579 operates at four selectable driver output frequencies (45.45kHz, 71.43kHz, 100kHz or 125kHz) and offers excellent immunity to electromagnetic interference.

The sensor is packaged in SSOP24 and operates on a 5V supply voltage.