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Recent years have brought an exponential increase in the number of electronic gadgets and sensors used in automobile design. This will only continue as the sector continues to shift to e-mobility and autonomous driving. At the same time, with electrification, the application of these technologies will change accordingly. With the need for responsive electrical current and temperature control in their charging and drivetrain circuits, hybrid and battery-driven designs (xEVs) are opening new opportunities for sensor deployment. As external sensors and connectivity drive xEVs’ growing autonomy, new emphasis will be placed on the sensor applications and technologies enhancing the in-vehicle experience.
Closed-loop feedback mechanisms are used to monitor and manage mechanical, electronic or electromechanical processes within a car. Here, sensors play a pivotal role in producing the input to such systems, delivering information on the process they are watching. For example, this information may take the form of rotational data in the case of wheels, axles and motors. Engineers look for angle sensors with low-power requirements, excellent angular precision and few temperature fluctuations. Originally discovered in 1975, tunnel magnetoresistance (TMR) sensor technology fulfills this role.
Figure 1 shows the three layers that make up the TMR element’s fundamental structure: a fixed magnetic layer, a free layer and a barrier layer comprised of a thin insulator. The external magnetic field that the free layer is exposed to affects how magnetized it is. The element has a low electrical resistance when the magnetic fields of the two layers are aligned. When the magnetic field of the two layers is in opposition, the resistance is high.
In contrast to TMR sensors, Hall sensors, commonly used in electronic switches, are ideal for cost-sensitive applications or for detecting much stronger magnetic fields. They provide indirect measurements of elements, including rotation, speed, distance, angle and fluid levels. These components pick up the resulting voltage variations that flow within the semiconductor when a magnetic field is applied perpendicularly to it. The measured magnetic field strength is compared to a preset level or a level that can be programmed in the sensor. The output of the sensor changes when this threshold is reached (the switching point).
The effects of electrification on sensors
The area of deployment that sensors occupy inside electric vehicles is growing as automakers shift away from the internal-combustion engine toward xEVs. IHS Markit predicts that by 2030, there will be 800 xEV models, up from roughly 335 today.
Thermal management is essential for batteries, charging circuits, and drivetrain components in xEVs. One ongoing challenge is the prevention of thermal runaway and the consequent fire risk. Engineers need precision-temperature sensors to closely monitor hotspots in these locations and act swiftly in response. Due to the large currents involved in operating or charging an xEV, even a little increase in contact resistance within a connection can result in a catastrophic temperature rise (Pv = I2R). The connector between the vehicle battery and motor inverters is a particular hotspot where there is a high current flow.
To correct the above challenge, designers tend to choose high-voltage–resistant negative-temperature–coefficient (NTC) sensors in these hotspots, as they feature a high operating temperature and high electrical insulation. Moreover, because NTC sensors can be placed directly on the hotspot, they can quickly detect any temperature changes. Data from these sensors is used to restrict the currents that pass through these charging or drivetrain circuits, reducing the temperature back to where it should be.
Equally essential components in the xEV battery management system (BMS) are pressure sensors, which are used to measure the pressure within the lithium-ion cells. They monitor operating pressures and alert the BMS to any unusual pressure rises. Faster than temperature sensors alone, the response times of these sensors can detect and report pressure spikes that result from thermal events inside a cell.
Advancing toward autonomous driving
In addition to the seismic changes in automobile design that the shift to e-mobility represents, advanced driver-assistance systems (ADAS) are evolving toward increasing levels of driving autonomy. To provide a complete picture of the environment around a vehicle, engineers tend to use LiDAR, radar and cameras in combination, working together identified as sensor fusion. But these imaging systems are negatively affected by vehicle vibration, which distorts their outputs. One way of stabilizing the outputs of these imaging sensors is to use six-axis inertial measurement units (IMUs). The approach is to capture the image data and IMU data and apply software techniques to compensate for any distortions caused by the movement.
IMUs are also useful for engineers developing navigation systems to supplement for when the GPS signal is unavailable or unreliable. The gyroscope and accelerometer outputs are fused to determine the vehicle’s position, known as dead reckoning. This technique helps address any gaps in GPS availability and reliability, such as going through a tunnel or working in urban and GNSS-denied environments.
The digital cockpit
The occupants’ comfort, security and safety are all improved by the use of sensors and electronics within the cockpit. When it starts to rain, the wipers and lights automatically turn on, and seats may be programmed to adjust for different drivers. Reversing camera images are stabilized by IMUs, which increases ADAS accuracy and enhances the driving experience. By reducing distractions, each of these cutting-edge sensor-based systems helps improve driver concentration.
The user interface is likewise evolving. In the digital cockpit, voice commands, gesture control and haptic responses form part of this new interface. As we advance to higher levels of autonomy, new technologies drive alternative notification and control mechanisms. For instance, engineers are adopting MEMS-based microphones to increase the reliability of voice-activated devices by removing road noise using Road-noise Active Noise Control (RANC).
Piezo actuators are increasingly employed in the vehicle’s touch displays. They provide drivers with tactile sensations, often known as haptic feedback. In addition to touch tactile feedback, new technology development in MEMS ultrasonic sensors can be used for gesture control.