With the increasing requirements of Advanced Driver-Assistance Systems (ADAS) and autonomous driving, more sensors will be necessary to address safety concerns proactively. Wheel-mounted sensors relay the tire data to the driving safety systems in the form of an electrical signal. Instead of relying on embedded batteries, TDK Corp. has unveiled an energy harvesting module that converts mechanical vibration energy from the vehicle’s rotating tire into electricity.
At CES 2021, TDK has introduced InWheelSense, an energy harvesting and sensing module that converts the force of tire rotation into piezoelectric power and enables battery-less sensing, data collection and transmission from the wheel.
“A massive digital transformation and electrification wave is going on, and the automotive industry is poised to completely transform the way smart mobility is thought through,” said Rakesh Sethi, vice president & deputy general manager, Advanced Product Development for Sensors and Actuators, at TDK, at a CES 2021 press conference. “The wheel is the last part of the car that has not been digitized or electrified. This module provides perpetual power to any sensor system or electronic embedded system.”
From perception sensors to non-perception sensors
ADAS and autonomous vehicles need sensors such as LIDAR, radar, image and infrared cameras to see their surroundings and provide critical decision making information. These perception sensors can see through difficult environments and generate valuable data, but the challenges of false positives and false negatives remain. For enhanced sensing performance in adverse weather or all terrain conditions, Sethi said non-perception sensors (e.g. piezoelectric, inertial measurement unit, ultrasound, and strain gauges) embedded in the tire or the wheel do a better job digitizing and classifying driving and road conditions.
“Currently, many companies that have joined this electrification bandwagon are experiencing not great success with the perception-based sensors because some of the extreme corner cases can’t be caught by the perception sensors,” Sethi explained. “Perception-based sensing for autonomous driving is spearheaded by various companies, but they need sensor fusion data to improve the quality and reduce the failures.”
Tire-pressure monitoring systems or TPMS are used in vehicles to notify the driver when his or her vehicle’s tire pressure is low or going flat. Direct and indirect TPMS systems are, however, inadequate for a measure of tire and road surfaces under all conditions. It is also not easy to replace or recharge the batteries of a monitoring system.
The power available from ambient mechanical vibrations is seen as a promising alternative, and piezoelectric energy harvesting systems have emerged as a reliable solution for powering remote sensor systems.
Energy harvesting and sensing
With InWheelSense, TDK proposes a piezoelectric energy harvester for rotating automating wheels. The module is placed in the bead area, at the boundary between the tire and the wheel, “which happens to be the maximum power generation area,” said Sethi. It uses the force received from the road surface to generate electricity.
TDK claims the inWheelSense module enables scalable power generation according to the load of the driving system by allowing multiple device connections along the wheel’s circumference, and reports an average continuous power of 1mW when driving at 105 km/h. When asked about the technology scalability, Sethi said, “We expect the power to go up by 40 percent every 15 to 18 months.”
Here, TDK has “a dual strategy”, said Sethi. “Not only does this module act as a harvesting power generation module, but it is also a sensor” that captures various driving conditions by the changes in electromotive force characteristics. “When the car is in motion, the module creates a heartbeat signal that actually reflects the performance of the car and the mobility itself. By looking at this signal quality, we are able to infer several traction, road conditions, tire conditions, sidewall temperature, pressure, etc.”
This “heartbeat signal”, or waveforms from the piezoelectric effect, is output when the tires contact the road surface. “Whether the car is moving in a straight direction, stopping, turning right or left, going at high speed, accelerating, decelerating, the unique heartbeat signal is almost a real time streaming of data at the edge, where we can judge on the fly in the extremely low latency […] the imbalance of the wheel or the rolling resistance.”
The InWheelSense module, which can be installed on existing wheels, collects real time data from additional wheel sensors such as accelerometers, barometric pressure and temperature. Data can be stored and/or processed through an inference engine in the control module, powered by an edge application processor. Decisions can be made in real time with no dependency on the cloud in case of adverse weather conditions.
“This kind of real time streaming actionable data at the edge is what we are providing to our customers so that they can develop their systems and integrate these modules where necessary, whether embedded in tire, whether embedded in rim, or whether it’s just in the space between the tire and the wheel,” commented Sethi.
From automotive to ocean robots
Sold both as a harvester and a sensor, TDK’s module has a Bluetooth connectivity and a power management circuit “where we can deliver the real-time experience with the power we generate with a single module.” Wiring multiple modules is possible for customers planning to run extremely high compute cycles in the wheel itself, Sethi said.
Targeting ADAS and autonomous driving applications, TDK’s module can also be integrated in connected transportation infrastructures (e.g. smart bridges, traffic controls) “where we can, without battery, derive information and understand the vibration and the dynamic response of the motions and the structural stresses.” In wind farms, the module could be integrated in the blades to improve the maintenance cycles and productivity. Finally, algorithms on the edge on battery-less devices could run where power is unavailable, for instance in submersibles and autonomous ocean robots.
With this module, which allows for stable power generation in the wheel, enables non-perception sensing of the vehicle and road conditions in real time and streams data as needed, Sethi said TDK intends to “enhance the business of TPMS customers and embedded tire module customers.” He added, “here’s an opportunity for many new market players to come in and provide technology as a service or add features for robotaxis.”
Available now, the reference kit design and samples for investigational are being used by various OEMs, including top four car OEMs, tier twos, and tire makers, said Sethi. The early production is expected early 2023, and the volume production in 2025.
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