Energy harvesting and sensing modules for automotive wheels in ADAS applications

InWheelSense™ is a multi-faceted power generation and sensing solution that can be installed on the wheels of a car, converting the force of the tire's rotation into piezoelectric power, and performing battery-free sensing and data acquisition and transmission in harsh environments such as wheels where power supply is very difficult. The module can sense road conditions, wheel alignment, tire pressure and other conditions in real time, and can connect to roadside infrastructure to help achieve smart mobility. InWheelSense is a self-sufficient, all-inclusive technology platform with power, sensing and connectivity capabilities, all included in the wheel, which will help improve the safety and comfort of the next generation of autonomous vehicles and smart transportation scenarios.

To date, environmental sensing for ADAS features has been driven primarily by perception sensors such as LiDAR, radar, and image and infrared cameras. While these sensors provide valuable data for ADAS operations, challenges with false positives and false negatives remain. To improve sensing performance in adverse weather conditions or on all terrains, non-perception sensors embedded in tires or wheels, such as piezoelectric, inertial measurement units (IMUs), ultrasonic, and strain gauges, can more accurately digitize and classify driving and road conditions.

Figures 1 and 2 The top picture shows the InWheelSense energy harvesting module. The bottom picture shows the module installed on the rim of a car.

Harvesting energy with piezoelectric elements

The InWheelSense energy harvesting module uses piezoelectric elements to generate electrical energy from mechanical movement or force. Placed at the boundary between the tire and the wheel, the module can generate electricity using the force generated by the road surface as the tire rotates. Connecting multiple devices around the wheel, the module enables scalable power generation based on the load of the drive system, achieving an average continuous power output of 1mW when driving at 65mph/105km/h. This permanent power source is ideal for digitizing driving, road and tire conditions using a range of non-perceptual sensing technologies.

Using piezoelectric elements for road condition and environmental sensing

Since changes in speed, turns, and other operating conditions cause changes in the device's electromotive force characteristics, the InWheelSense module can sense various driving conditions by analyzing the waveforms generated by the piezoelectric effect and using these power changes. The tire outputs a waveform when it contacts the road, so when the car starts to move, the waveform is continuously generated. As the speed of the vehicle increases, the frequency of waveform generation increases, and when the direction of travel changes, the load on the tire will also change, resulting in different waveforms that reflect the driving characteristics at the time. Since a waveform is output for each revolution of the wheel, the InWheelSense module can not only detect the speed during driving, but also detect the road surface condition based on the shape of the output waveform.

Figure 3 The InWheelSense module can sense various driving conditions by analyzing the waveform of the piezoelectric effect; different waveforms are generated to reflect the driving characteristics at the time.

The InWheelSense platform also allows real-time collection of data from other wheel sensors (including accelerometers, air pressure and temperature) to an onboard computing unit. The control module platform includes power management, digital computing capabilities and low-power data transmission using BLE. Data can be stored and/or processed by an inference engine in the control module, which is powered by an edge application processor that enables algorithms to make meaningful inferences instantly. This enables low-latency control responses in severe weather conditions without relying on the cloud. The energy harvesting generator provides all the power required for data acquisition, processing and operation (transmission).

InWheelSense's piezoelectric-based energy harvesting and sensing modules are powerful and reliable power sources and high dynamic range sensing devices for tire and driving conditions, improving the safety of smart mobility vehicles. These non-sensing sensors can work with connected transportation infrastructure (such as smart bridges, traffic control and signage), transmit real-time data, and support vehicle-pedestrian networks, vehicle-infrastructure networks, and vehicle-vehicle networks.

InWheelSense also offers an evaluation kit designed to allow for a simple evaluation of the energy harvesting module as a prototype that attaches to an existing wheel. The kit can wirelessly collect data from the device output and generate electricity without the need for additional equipment.