Revolutionising Road Safety: How Next-Gen Inertial Sensors Tackle OEM Challenges in the Automotive Industry

In the rapidly advancing automotive industry, car manufacturers face many challenges as they strive to integrate the latest sensor technologies into their vehicles. The quest for enhanced safety, improved performance and regulatory compliance drives the need for more sophisticated inertial measurement units (IMUs). However, the journey towards achieving these goals is fraught with technical complexities and cost-related hurdles.

Steering towards precision
Modern cars are already equipped with various ADAS functions, such as lane departure warnings, assisted parking, and automated braking. While incredibly useful, these systems still require the driver’s constant attention.

To achieve full autonomy, there must be absolute confidence in the vehicle’s ability to continue safely and precisely under any condition – be it inclement weather or challenging road conditions – while ensuring the well-being of passengers, pedestrians, and vulnerable road users. This level of trust hinges on sophisticated guidance and navigation technologies that maintain safe operation, even when vehicle perception sensors like LiDAR, radar, or cameras are compromised or when atmospheric conditions, terrain, or urban environments obstruct GNSS satellite signals.

Still, the dawn of self-driving vehicles is upon us. Rapid development in advanced positioning sensor technologies help them drive increasingly safer and more accurately. Statistically speaking, the accident ratio of self-driving vehicles is already lower in comparison to non-autonomous vehicles controlled solely by humans.

At the heart of this vehicle sensing technology lies the IMU sensor. Grounded in the principles of gravity and physics rather than external variables, the IMU provides a continuous stream of data, enabling the vehicle to stay on course. In the event of perception sensor failure, the IMU sensor ensures that the vehicle can safely maintain its course until it can either safely stop or resume normal navigation once the primary systems are restored.

A typical six-degrees-of-freedom (6DoF) IMU sensor includes a three-axis accelerometer and a three-axis gyroscope. In the automotive industry these are typically based on micro-electromechanical systems (MEMS) due to their cost to performance ratio and small size. Accelerometers measure linear acceleration across three orthogonal axes, and by integrating this acceleration data over time, you can deduce velocity. Further integration of velocity over time yields positional changes. Gyroscopes, on the other hand, gauge the rate of rotation around three orthogonal axes. By integrating these angular rates over time, changes in the vehicle's roll, pitch, and yaw can be established.

Sensor integration challenges
Cost concerns are ever-present in the OEM landscape. The total cost of ownership (TCO), which encompasses the initial investment in technology, as well as ongoing maintenance and potential upgrades, is a critical factor in the decision-making process.

Advanced ADAS and autonomous driving applications impose stringent requirements on sensor accuracy and stability, but defining what is considered ‘good enough’ is a fairly complicated task. No matter how much is invested in hardware and software development, it is impossible to account for every single driving scenario. The challenge lies in connecting component selection to real-world situations, as prioritising cost over performance can increase the risk of an accident in a rare, unpredictable corner case. OEMs must balance pursuing cutting-edge technology with the imperative to maintain affordability and profitability, all while taking into account both actual safety and the driver’s perception of it.

Furthermore, OEMs must navigate the complex terrain of regulatory compliance. For instance, the United Nations Economic Commission for Europe (UNECE) headlight leveling regulation stipulates stringent requirements for vehicle lighting systems, necessitating high-performance sensors to ensure that headlights are kept levelled, thereby improving road safety and reducing glare-related accidents. The traditional method of using height sensors is both expensive and inconvenient as the bulky sensors and lengthy cables make it difficult to utilize the same design over car models. The next generation MEMS sensors offer the VAVE (Value analysis/Value engineering) many OEMs might wish for.

A clear design trend is dividing the architecture to Zonal control units. Due to the nature of IMUs, their placement within the vehicle is in general less restricted than with other parts and mounting in any angle or even away from the vehicle's mass center point can be managed with a few algorithm tweaks. IMUs can thus widely and effectively enhance the different vehicle functions from GNSS integration, chassis control and In-vehicle infotainment (IVI) to camera and headlight alignment regardless of which zone the IMU signal originates from. As vehicle architectures rapidly evolve, ongoing design efforts present the opportunity to address both cost and performance optimization simultaneously. Investing in a high-performance IMU and effectively utilizing its signals throughout the vehicle can enable superior performance while also reducing overall costs. However, each vehicle function is still widely developed in their respective silos and cross-functional co-operation is not yet standard.

Combined gyro and accelerometer
The automotive industry seeks solutions that can offer high-quality signal output, even in harsh environmental conditions, while providing a high degree of integration and built-in safety features. Engineers also value MEMS sensors that incorporate various system-level time synchronization features, ensuring its output can be easily harnessed across the entire vehicle.

Representing an evolution in sensor technology, the SCH1633-D01 MEMS sensor from Murata aims to address these OEM challenges. Production of the new, automotive qualified and validated sensor has started, and the first car models fitted with Murata’s flagship IMU sensor are ready and waiting to be delivered.

The sensors’ SafeSPI 2.0 interface boasts a 20-bit data frame for an extremely smooth and high-resolution output. The data-ready timestamp index and SYNC functions enable various subsystems, such as GNSS integration, chassis control, and vehicle attitude sensing (camera and headlight alignment), to use its measurements.

The unique 24-pin SOIC housing measuring 11.8mm x 13.4 mm x 2.9mm (lwh) is designed to offer flexibility in design and robustness to withstand PCB strain.

Furthermore, the extensive self-diagnostics features utilize over 200 monitoring signals to ensure the output is always trustworthy. It features AEC-Q100 grade 1 qualification to guarantee reliable use throughout the component's lifetime. It is ISO 26262 compliant with an ASIL-B+ rating (up to ASIL-D via system integration) for exceptional built-in functional safety. Moreover, Murata handles the calibration of the orthogonality of the measurement axes, a process typically performed by system integrators, which can significantly reduce the time and expense involved in bringing a vehicle to market.

The road ahead
As OEMs continue to push the boundaries of what is possible in automotive technology, the need for sensors that can keep pace with these demands grows ever more critical. The industry's response, through innovations like the SCH1633-D01 MEMS sensor, is a testament to the ongoing commitment to overcome these challenges and drive the future of automotive design and safety.