At present, six factors are shaping how sensors in general will meet the tough new challenges that electric cars and autonomous vehicles present. These factors comprise raw performance, functional safety support, higher robustness/intelligence, security, and—further out in time, to probably beyond 2030—the potential for new packaging concepts. Some of these factors, as they pertain to magnetic sensors, are discussed in further detail below.
Wheel speed sensors, an important system underpinning anti-lock braking systems (ABS) and indirect tire-pressure-monitoring, increasingly need lower jitter performance. The requirements of the car are for more accurate position information in line with future self-parking scenarios, as well as higher precision measurement overall to support an algorithm calculating tire pressure. Magnetic sensors—typically Hall effect and anisotropic magnetoresistive (AMR) devices today—are beginning to transition to AMR sensing to meet increased performance challenges.
Where functional safety is involved, increasing the number of sensors from one to two or three can lead to a higher ASIL safety rating at the system level. Applications include angle sensing in steering systems, or in pedal or throttle positions, for example.
For Big Data applications, sensors must be able to collect a greater amount of information than in the past while also keeping more of the raw signal, compared to sensors today that filter the information. And because the information collected will be vital to Big Data analysis, sensor robustness and intelligence will be a necessary attribute for all sensors, not just for magnetic ones.
What is unique to magnetic sensors, however, is their vulnerability to stray magnetic fields. To meet a rise in demand for robustness in this regard, sensors in electric vehicles will need a new level of protection against stray magnetic fields, caused by the electromagnetic fields of the large electric traction motor. Companies are required to now meet a field specification of 4000 A/m, compared to 1000 A/m in the past.
In security, sensors are already required for security applications, such as the use of motion sensors inside key fobs to mitigate hacking of the RF signal to open a car. Thus, any sensor must be considered as a potential hacking point into any system.
Lastly, both the continued proliferation of sensors and the potential new freedom in the cabin allowed by autonomous driving are two factors spurring designers to reassess sensor packaging formats. With European cars today featuring more than 150 sensors and switches, companies like GM, BMW, and VW are providing new ways for car drivers and passengers to interact with information systems in the vehicle, removing bulky knobs in favor of haptic touch or even touchless sensing. According to HIS Markit expert Dixon, car doors and other panels could be used to accommodate many functions and offer sleek new designs.
While such sensors offer solutions in the near term, flexible Hall sensors have also been demonstrated recently by Bosch and researchers from the Max Planck Institute. Jaguar Land Rover is one car company investigating at present flexible electronics to elegantly incorporate even more functionality while also maintaining an uncluttered appearance; it is likely not alone in this process. Such a development becoming commonplace may still be far in the future, but the concept represents a freedom of design not possible today, and which could prove disruptive to current semiconductor processes and infrastructure.
The dominant magnetic sensor solution today remains the Hall effect IC, a technology that serves well over 60 applications in the passenger car. Hall-effect sensors and switches in 2017 accounted for 90% of the global revenue of magnetic sensors in automotive.
Hall sensors are notable for their robust performance, small size, and low cost. These devices can be deployed at high temperatures experienced under the hood and are compatible with CMOS electronics. While Hall devices measure their fields vertically, the trend has been to extend spatial resolution in the lateral directions using magnetic field “concentrators.” Such devices are dubbed 2D and 3D Hall ICs, and in many cases, are replacing linear Hall sensors and angle sensors, e.g., for chassis height measurements and electronic throttle control in the powertrain.