Smart sensors deliver in-cabin comfort by canceling road noise

Imagine yourself sitting in your car, driving along the highway and on small country roads. What noises do you hear? The answer probably depends on whether you have an electric vehicle or a car with a conventional combustion engine. What many people don’t know is that without the sound of a combustion engine, noise coming from the tires becomes much more noticeable for the driver and the passengers. Road noise cancellation reduces in-cabin noise coming from the tires. This significantly increases driving comfort in electric cars, especially if you want to listen to music or have a conversation.

Most electric vehicles are therefore equipped with noise dampening material. This, however, comes with additional weight. The SMA380 from Bosch follows a much more advanced approach: The small sensor measures the sound waves coming from the tires on the road surface. This vibration data makes it possible to calculate and emit corresponding inverse sound waves that cancel out the noise via the vehicle’s speaker system before it reaches driver and passengers. Let’s take a closer look at this fascinating technology.

Latency is one of the key parameters for active noise cancelling in automotive applications. This is where Bosch’s SMA380 3-axis acceleration sensor with low latency comes into play. The sensor efficiently measures the noise level by registering the sound waves close to the wheels and providing the data to corresponding systems. These can then calculate the overall frequency of the noise and emit the inverted frequency at exactly the same time the road noise reaches the vehicle cabin.

The SMA380 accurately measures low-g vibrations with a latency of about 100 µs. This latency allows the system to transmit acoustic data from all four wheels very fast and helps send the necessary counter-frequency just in time. Besides its low latency, the SMA380 comes with a small footprint of only 2.3x2.8 square millimeters, which provides for easy integration into the vehicle, and features a high temperature stability of -40–125°C.

Thanks to its bandwidth, the acceleration sensor is able to measure vibrations across a broad frequency range, which makes it suitable for further NVH (Noise, Vibration, Harshness) applications or monitoring tasks in the vehicle. One such application is condition monitoring: Additionally to road noise, the sensor can monitor vibrations coming from the engine, where a change in the typical frequencies could mean that something is wrong.

Active road noise cancellation makes it possible not only to save weight, but also space which can be used for other components. So, it’s no surprise that this emerging technology is being increasingly adopted by EV-manufacturers, especially for premium and mid-range models. Since four sensors are needed per car – one close to each wheel – availability and reliability is a major concern for manufacturers. Here, Bosch’s experience and production capability are key.

1. Road noise has become one of the key challenges for driving comfort in electric vehicles. Active road noise cancellation is a new possibility to efficiently reduce road noise in the passenger cabin and provide a comfortable driving experience.

2. With a latency of about 100 µs, the SMA380 is fast enough for noise cancellation systems to emit inverted sound waves in the exact moment the road noise reaches the cabin.

3. The sensor comes with a broad frequency range and can for instance measure vibrations coming from the power train to be used in condition monitoring.

4. Bosch has the experience and production capacities to reliably supply large numbers of high-quality MEMS sensors like the SMA380.