By Karsten Köhler, Business Development Manager at TDK-Micronas
The auto industry is amid two transformative trends: the gradual transition from internal combustion engines (ICE) to electric motors and drivetrains and the ongoing development of driver assistance and self-driving features. Sensor technology is famously integral to both trends, but electrification and assisted driving account for only some application areas where sensors are integrated into modern automobiles.
Some consider cars to be computers on wheels, but the fact is that cars will always be complex electromechanical systems with many moving parts — everything from wheels, braking systems, and suspension systems to valves in conduits for various fluids and gases.
As monitoring and control become more precise, they become more efficient and safer. The positions of moving parts must be detected and controlled, and fluid reserves and the status of multiple automotive subsystems must also be monitored.
Electric vehicles (EVs) have motors, batteries, and charging systems that must be managed carefully. Each system has a specific temperature range within which it should operate, requiring sophisticated thermal management. This is equally true of all of the distinct EV types: battery-powered EVs, hybrid EVs, mild hybrid EVs, and plug-in hybrid EVs (xEV).
All of this is accomplished using sensors. Our intent here is to provide an overview of how rich modern automobiles are in sensors, including brief explanations of some of those sensors. We will also survey some of the use cases discussed less frequently than electrification or self-driving.
The sensor-rich automobile
The number of sensors in each automobile rolling off a production line today is estimated to be anywhere from 50 to 200 or more. That range might seem wide, but the requirements for sensors vary from one automaker to the next and are subject to driveline type and vehicle segment. Furthermore, feature-rich vehicles will have many more sensors than modestly priced cars.
Analysts generally agree that the average number of sensors that different automakers use to monitor and control a vehicle’s drivetrain is about 30. That estimate applies whether the car has a gas engine or an electric motor, though the lineup of sensors will be different.
On the one hand, ICE vehicles will have sensors that monitor the position of mechanical parts, including throttles, camshafts, and turbochargers. They will also include airflow and pressure sensors (inside the intake manifold, for example). EV powertrains, on the other hand, require sensors to measure electrical parameters, including currents, voltages, and the state of the battery, known as SoX, with “X” representing “charge” or “health.”
Estimates are that another 20 or 30 sensors in a car are dedicated to driver-assist and automated self-driving features. These estimates generally focus on the various combinations of optical, radar, ultrasound, and lidar sensors auto OEMs elect to use to detect other vehicles, pedestrians, and objects.
A sensor-rich environment
While much attention has been focused on the EV transformation and self-driving capabilities, modern vehicles also incorporate many sensors in almost every function performed by and in a modern car.
Several sensor types suit that purpose, including Hall sensors, tunneling magnetoresistance (TMR) sensors, inertial measurement units (IMU), temperature sensors, pressure sensors, microphones, and others.
Though Hall and TMR sensors are magnetic sensors, they operate on different magnetic properties, each featuring specific sweet-spot applications. Both technologies are excellent for detecting the position of mechanical elements, and the selection among the two is defined by requirements such as sensitivity, signal-to-noise, stray field robustness, or space claim.
TMR is typically suitable for detecting smaller and quicker movements in tight environments, such as the position of the rotor of small motors. In contrast, Hall, a decade-proven technology, is often considered for covering larger movements in harsher environments, such as the pedal’s stroke or the position of a valve. A common use case of magnetic sensors is current sensing in the drivetrain.
Design engineers will thoroughly understand the needs of the specific application they are working on and know how to consider the differences when selecting between them.
That said, TMR versus Hall is not always an either/or proposition. They are often used in tandem to provide a solution for mission-critical applications with high functional safety requirements, as they offer sought-after “heterogenous redundancy.”
IMUs, meanwhile, are sensors that combine a magnetometer and an accelerometer to provide 6-axis motion detection. They accurately detect vehicle dynamics in real time, feeding reliable data to decision-making algorithms, including safety-critical applications like airbag deployment.
Braking and steering
The most direct driving experience for most people, besides acceleration, is through steering and braking.
For example, automakers frequently use Hall sensors in their steering systems to measure angle, torque, and axle position. In contrast, TMRs detect the position of the electric power steering (EPS) motor. Precise determinations are crucial for driver safety, improving vehicle performance, and supporting advanced driver assistance systems.
When it comes to both electromechanical and electrohydraulic brakes (EMB and EHB, respectively), automakers use sensors to extract data in real time for precise control of braking force. Automakers use a combination of Hall and TMR sensors for precise brake-by-wire, to drive actuation motors (e.g., the e-motor boosting brake pressure, or for direct actuation of the pads), to detect the position of brake calipers in a feedback loop, and to measure brake fluid levels. Using these sensors helps ensure the ranking systems’ safety, efficiency, and responsiveness.
In EVs, Hall and TMR sensors can also be used, for example, in the e-axle to transmit the transmission position, as a parking lock sensor, or to measure the rotor position. Rotor-position sensing is a highly dynamic process, as the sensor needs to keep track of the fast-spinning rotor to adapt precisely to what the driver intends to do. The more accurate the rotor position sensor, the more responsive the vehicle will feel, and the more economically the motor can be operated.
Driver assist
Again, the most celebrated advanced driver assistance system (ADAS) features are those that perform object detection, a capability that relies on cameras, radar, lidar, and ultrasound. What is sometimes skipped over is that some of these sensors rely on other sensors (Hall, TMR, IMU) for image stabilization. The incessant vibration that motor vehicles experience on the road renders any image detection close to useless without stabilization.
But there are other essential ADAS functions. These include dynamic suspension, headlight leveling, electronic/roll stability control (ESC/RSC), and drive-by-wire (DbW). These also require the precise control of mechanical elements, and detecting their position is critical for passenger safety. IMUs are frequently used for these applications.
Thermal management systems
Thermal management is as much an issue for xEVs as it is for ICE vehicles. Where ICE cars have engines that cannot be allowed to overheat, xEVs have batteries, charge systems, power inverters, and motors that must be similarly cooled. Still, unlike ICE vehicles, they also sometimes need to be heated. That applies especially to the battery. Lithium-ion chemistries used in today’s xEVs operate best (charging and discharging) in a temperature window between 30 and 60°C.
All systems in an xEV must operate efficiently from a single power source—the battery. Ensuring that the entire system operates optimally requires complex thermal management systems. The fact that each of the EV subsystems (battery, motor, charger, etc.) has its distinct temperature range complicates the thermal management task.
Of course, that requires thermal sensors as well as Hall and/or TMR sensors, all working in conjunction with high-voltage controllers to drive actuators in valves and pumps (usually 12V but up to 48V; both values are high in this context).
Position sensors are critical to ensuring that the pumps, valves, and vents used to keep all these subsystems within their respective optimal temperature ranges are used precisely and efficiently.
Coolant valves are a representative example of increasing complexity. Some automakers are now using 8-way valves. Sensor makers are devising sensors that can monitor such complexity and are adopting sophisticated controllers with enough flash memory to contain the necessary software.
Mentioning pumps and valves brings up a corollary issue. Every vehicle has multiple reservoirs for coolants, anti-freeze solutions, windshield cleaners, and other fluids. Sensors monitor fill levels. Once again, magnetic position sensors are commonly used for size, cost, and functional safety reasons. Magnetic-level sensors have replaced other technologies (capacitive sensors, ultrasound) in many applications.
Sensors that measure pressure and meter flow ensure that conduits for gases (e.g., refrigerants) are sound and operating optimally.
xEV manufacturers are now deliberately using vehicle grilles for cooling purposes, carefully managing how open or closed they are and using them to direct airflow where needed — another task for position sensors and motor drivers. These systems are more sophisticated than one might guess because they must be capable of stall detection; this allows them to avoid damage should the grille get clogged by dirt, snow, or road debris.
Unified HVAC
Throughout most of the history of ICE vehicles, the passenger cabin has been treated almost as an entirely separate domain. After all, there was little reason to integrate the engine with in-cabin comfort functions (with a few exceptions, such as siphoning heat from the engine for warming and relying on the engine to drive power for compressors). This approach led to growth in the number of more-or-less independent subsystems within every vehicle, a proliferation that eventually became unwieldy. Now, automakers are competing to find new efficiencies, and combining multiple systems with similar functions has been a fruitful avenue toward that goal.
A prime example of this is the thermal management system of modern xEVs. Suppose you need a sophisticated heating, air conditioning, and ventilation (HVAC) system for the motor and battery, and you already have one for the passenger cabin. In that case, it is inefficient to keep them separate. Automotive OEMs have begun treating new vehicles as a unified HVAC system capable of both heating and refrigeration. Again, this necessitates temperature sensors, along with all the positional sensors, actuators, and controllers for all of the active elements in the overall HVAC system.
Auto OEMs continue to outfit automobile cabins with new features and amenities, and sensors play a role here. Consider a modern luxury car seat: it is vented and provides massage, which would be impossible without modern sensors and drivers.
It is beneficial to monitor and provide precise control of seats, windows, sunroofs, doors, windshield wipers, and other exterior and interior systems for both comfort and safety. Depending on the application, this relies on a mix of Hall and TMR positional sensors, along with IMUs. Infotainment systems, meanwhile, are increasingly voice-activated, necessitating the inclusion of microphones.
Conclusion
We have been talking about precision in monitoring and control, but it is important to note that automotive manufacturers continue to innovate and that innovation often comes with more complexity. This puts pressure on sensor manufacturers to be innovative, too.
We have been focusing on sensors here today, but it is important to note that sensors must work in conjunction with actuators and controllers. Here, too, experienced automotive engineers are practiced at selecting sensors, actuators, and controllers designed to work together, making it much easier to comply with the strict standards and regulations adopted by the automotive industry to ensure the safety of drivers, passengers, and bystanders.
