The miniature sensors that control automobile performance are made in a specific way to work properly when mounted directly on automobile tires. They must be able to detect measurements in motion and withstand the elements.
The most important aspect of automobile performance is tire pressure. Tires will take the shape they were designed to when inflated at the right pressure. The tires require more energy to move as the air pressure drops. In the daily driving routine from one place to the next, drivers can forget to keep their tires inflated. Sometimes punctures can happen and go unnoticed. It is important to have an onboard sensor that informs the driver when more air is needed. These sensors require careful design considerations. Simulation provides the tools to help you find the perfect design.
Tire Pressure Sensors Create Driving Experience
Low tire pressure can lead to a reduction in fuel economy. Low tires can also contribute tons of greenhouse gases to our atmosphere. Low tire pressure can make it difficult for vehicles to stop or slip on wet surfaces. Automotive manufacturers must install pressure monitoring sensors on wheels to inform drivers if the tire pressure drops below the desired pressure. Schrader Electronics is the current market leader in tire pressure monitoring technology.
Schrader Electronics produces 45 million sensors each year and supplies sensors to top automotive companies like GM, Ford and Mercedes. Reliability and durability are essential for a sensor’s ability to withstand road conditions over the entire life of a vehicle. When designing the required functions, geometry, or materials, it is important to consider shock, vibrations, pressure, humidity and temperature. Christabel Evans is an engineer in the Schrader Electronics mechanical team. She has used multiphysics simulation and finite element analysis to create efficient, reliable tire sensors for all types of vehicles.
Designing better sensors with FEA
Schrader’s Hi-Speed Snap-In Tire Pressure Monitoring sensor, as shown in Figure 1, is a commonly-used product. It mounts directly to the wheel assembly and measures the tire pressure–even while the car is moving. The sensor will sound a warning when the tire pressure drops too low. This alerts the driver to pull over and re-inflate the tires.
Figure 1. Figure 1. Bottom: Ten-fold amplification of stress/deformation on the transmitter housing due to the centrifugal load caused by the wheel’s spin.
Schrader Electronics has been producing sensors for nearly 20 years. Christabel Evans and her coworkers wanted to find a more efficient way to design and test products. The team used FEA to simulate their designs and then iterated the process. This allowed them to reduce experimental costs and evaluate design performance throughout development. Schrader Electronics discovered that the FEA software options available were too expensive to be used by their entire team. They decided to use the COMSOL Multiphysics(r) Structural Mechanics Module and the CAD Import module of COMSOL Multiphysics(r). They began by running a series of tests, comparing standard samples with simulations to validate and improve the software’s results.
Improve Sensitivity & Durability With Better Simulation Tools
The researchers started to incorporate more biological parameters into their simulations over time. These included dynamic loads like centrifugal force and environmental stresses like temperature change. They also began to include static factors like pressure and crush load. The Hi-Speed Snap-ITM TPMS is a transmitter consisting of a circuit enclosed in an enclosure attached to a stem and cap. The valve stem connects with the tire rim, allowing airflow. The Hi-Speed TPMS valve geometry has a rib to help keep the assembly in place.
Figure 1 shows how Schrader Electronics measured stress on the enclosure due to outside forces such as shock, vibration, tire fitment or vibration, and how the device deforms when loaded under these conditions. Figure 2 shows a component that a spin-test machine can spin at high speed. The material selection was tested to ensure that it could withstand the loads.
Figure 2. Figure 2.
Evans and her team could find the best model and improve their design by simultaneously analyzing several models. They tested different materials and load scenarios.
Schrader researchers could learn COMSOL Multiphysics software faster than other simulation packages. Additionally, deployment was much easier due to flexible licensing options. Evans says that COMSOL Multiphysics software is easy to use and is quick to learn. Engineers were able to pick it up immediately.
Schrader intends to focus their attention on design and growth at the moment with a little emphasis on failure analysis. However, they are hoping to improve their development-focused approach through simulation tools. Each new design aims to improve driver comfort, safety, and environmental impact.
Many engineers use COMSOL across many teams in the Mechanical Engineering Department of Schrader Electronics. From left to right: Sam Guest (left), Andrew Herron (right), Adam Wright, Christabel Evans and Russell McKee.