As seen with EVs and autonomous vehicles, automobiles are increasingly becoming computerized, and sensors are now indispensable for purposes like detecting a vehicle’s condition and control inputs. TDK has developed a device that enables in-wheel sensing without batteries—a feat nearly impossible in the past. This will help improve the safety and comfort of next-generation autonomous vehicles.
Sensors Play a Vital Role in Improving Automotive Performance
Sensors, which detect various data in automobiles, are some of the most essential electronic components. Different types of sensors are installed to support different functions, from the power train to the steering, the brakes, navigation systems and networks. Not only do they support safe and comfortable driving, they also contribute to improved mileage and reduced electrical power consumption.
Today, a single vehicle could contain more than 50 sensors. There is a growing need for sensors that accurately detect a vehicle’s running condition, its surroundings and driver control inputs, in order to further improve the performance of autonomous vehicle control and Advanced Driver-Assistance Systems (ADAS)*1 in the future.
Detecting Running Conditions in Real Time Through In-Wheel Sensing
Although sensors are now installed in almost every part of an automobile, placing them in a moving part like the wheel was considered impractical due to power supply issues, so it never came to fruition—with exceptions like TPMS (Tire-Pressure Monitoring System)*2, which runs on a battery and detects tire pressure and temperature. However, if it were possible to accurately detect the movements and forces acting upon the four tires—which, of all auto parts, are what come into direct contact with the road after all—there is the potential to greatly improve safety and comfort. InWheelSense™ was born out of efforts to solve the challenges of supplying power and sensing within the tire.
InWheelSense is a proprietary sensing solution from TDK that utilizes a piezoelectric energy harvesting device called the EH module (energy harvesting module). It employs a unique method of power generation that takes advantage of the piezoelectric effect*3—the phenomenon where an electrical charge is produced when pressure is applied to a piezoelectric element*4—to generate electrical power using the weight of the vehicle that bears on the device every time the tire rotates. This has enabled battery-less sensing within the tire, to which supplying power used to be very difficult. Because the device’s electromotive force changes with the status of the vehicle—like changes in speed, turns, or slipping tires—it has also become possible to sense the running condition of the vehicle in real time.
Tires Coupled with Sensors Greatly Expand the Potential of Autonomous Vehicles and ADAS
The EH module generates electricity every time the tire rotates, with an average continuous output of 1 mW when the car is traveling in a straight path at 105 km/h. This amount of power generation is sufficient for sensing through a low-power microcontroller and for wireless transmission. Installing multiple EH modules in a tire will generate more power, enabling more detailed monitoring of vehicular data by supplying power to multiple sensors including temperature sensors, pneumatic pressure sensors and accelerometers, and by transmitting data to the vehicle wirelessly. TDK is offering the InWheelSense Evaluation Kit, which can easily be attached to existing wheels, facilitating evaluation of the EH module.
In the future, sensing with InWheelSense is expected to have a wide range of applications, including the detection of vehicle, road, and driving conditions which are essential to realizing autonomous vehicles, tire maintenance services, and evaluating the dynamic characteristics of tires and wheels. With new in-wheel sensing solutions, TDK will keep contributing to the evolution of next-generation automobiles.
InWheelSense, the product featured in this article, has won the Grand Prix at the CEATEC AWARD 2020 in the Digital City Planning of the New Normal Age category.
- ADAS (Advanced Driver-Assistance Systems): Advanced driving assistance systems that enhance the safety of automobiles.
- TPMS (Tire-Pressure Monitoring System): A system that detects tire pressure and temperature using sensors installed in the tire/wheel, and wirelessly transmits data to the vehicle for monitoring. Because it is battery-powered, ensuring operational stability and reliability under harsh temperature environments has been challenging.
- Piezoelectric effect: A phenomenon where an electric charge is generated in response to the mechanical stress caused by applying pressure to a piezoelectric substance.
- Piezoelectric element: An electronic component that converts the force applied to a piezoelectric substance, like crystals and specific types of ceramics, to electrical power.