Figure 1. New vehicle development requires extensive dynamic testing. (Image: Kistler Group)

Vehicle development would not be possible without thorough vehicle dynamics tests. They provide the data that will inform the final setup of the chassis and the characteristics of the control systems. Passing the ISO tests for stable driving behavior is the fundamental requirement for developing a distinctive driving experience and a feeling of safety while driving, both for passenger vehicles on public roads and racing cars in motorsports. At the same time, maximum passenger comfort in terms of noise and vibration is also one of the top objectives.

A common vehicle dynamics test arose 25 years ago, dubbed by a German newspaper as the “elk test.” At the time, Swedish media had demonstrated that a new car model would topple over when forced to evade a suddenly appearing elk. While elks are less of a problem in most countries, drivers may well face a situation where a child or a reversing car will unexpectedly obstruct the road ahead. The evasive maneuver which is then carried out by the driver will result in a sudden load shift. For the car to remain stable in such situations, it needs to conform to the ISO 3888-2 Standard, which requires passing the VDA lane-change test. Two further tests that need to be passed before a vehicle is safe to be put on the road are: steady-state circular driving behavior and braking on a one-sided slippery track surface while driving straight ahead. Measuring a vehicle’s performance in these tests requires technology that captures longitudinal and lateral vehicle speed. These tests enable engineers to predict the dynamic behavior of a vehicle and to optimize its balance and drivability.

Optical Measurement Technology

Figure 2. Wheel force transducers (WFT) measure the forces and moments acting on the tire contact patch by capturing three forces and moments on a rotating wheel. (Image: Kistler Group)

Kistler Group, Winterthur, Switzerland, offers the Correvit S-Motion sensor to capture all the relevant motion parameters. The optical technology measures the slip angle, longitudinal, and lateral dynamics — the lateral acceleration — to evaluate the vehicle’s behavior during steady-state circular driving as per ISO 4138. It also measures the yaw rate, roll and pitch angles, and acceleration in three axes, with advanced vehicle dynamic tests. The Correvit optical and motion sensor solution is direct, frictionless, slip-free, and suitable for harsh conditions. Correvit optical technology is combined with additional data from an in-built six degree of freedom inertial measurement unit (IMU). Its sensor fusion technology provides low noise signals. The resulting speed and slip angle data quality is due to the robust optical sensor core. Unlike Global Navigation Satellite System (GNSS) sensors, Kistler fusion technology has the benefit of being unaffected by surrounding buildings or trees, enabling accurate data to be measured under all conditions without signal dropout.

The new SF-Motion, which was developed for racing car applications, supplies this technology in a smaller package, enabling the sensor to be easily mounted to the vehicle body without bulky adaptations. It can also be fully integrated in the monocoque of a race car. The sensor can also be mounted on each wheel, allowing true tire slip measurement for fast evaluation without corrective equations and calculations. The measuring accuracy is guaranteed through factory calibration methodology and certification.

Wheel Force Transducers for Vehicle Durability Testing

Vehicle development also relies on wheel force transducers (WFT). These wheels replace the standard rim to measure the forces and moments acting on the tire contact patch. WFTs are multi-axial 6-component precision measuring systems that capture three forces and moments on a rotating wheel. They are designed for use in the development and testing of complete chassis and chassis components of different vehicles such as passenger cars, SUVs, commercial vehicles, racing cars, and industrial vehicles. The measured wheel data enables the vehicle developer to design the vehicle accurately and safely, as the sensors are installed directly at the interface between the vehicle and the road. Only the tire and the mechanical structure of the measuring wheel are located between the road and the wheel hub of the vehicle. High data accuracy is crucial because WFTs are used for the development and dimensioning of parts relevant to safety. Careful calibration procedures are therefore necessary to ensure accuracy when measuring the forces and moments and the angle and angular velocity of the rotating wheel. Kistler offers an accredited hexapod calibration bench to ensure that high quality standards are met over the long term.

Evolution of Noise, Vibration, and Harshness (NVH) Measurement for Future Mobility Solutions

Figure 3. Advanced accelerometers from Kistler perform holistic NVH tests to optimize vehicles. (Image: Kistler Group)

Vehicle design targets might be very different when considering future mobility concepts. With the introduction of e-mobility: noise, vibration, and harshness become new challenges. NVH covers all aspects of the acoustic and vibrational behavior of a vehicle. A proper design of the NVH characteristics not only influences performance, durability, and reliability of the vehicle, it also ensures conformity to customer expectations in terms of drivability, comfort, and brand image. As vehicle technology evolves, NVH testing paradigms evolve too. In the past, internal combustion engine (ICE) and powertrain applications generally required accelerometers that could withstand temperatures of up to 160 °C. At the same time, they needed to ensure a thermally stable sensitivity to avoid the need for temperature corrections. Such standards can be fulfilled by Kistler’s PiezoStar technology, which also offers higher sensitivity compared to industry-standard Quartz solutions. When shifting to the future and especially for e-motors, broader usable frequency ranges of up to 10 kHz that still provide high sensitivity are necessary. Electrical ground isolation is important to avoid measurement current loops. Last, but not least, a good acceleration sensor for automotive applications must ensure easy and flexible mounting to guarantee a quick and reliable test setup.

Measurement Data Management in Vehicle Development

Finally, the data generated in vehicle testing needs to be managed efficiently and effectively. Kistler offers MaDaM, a flexible data management system that allows users to import and store large amounts of many different types of measurement data. The data can then be visualized and analyzed using jBEAM, which is a platform-independent application that processes many different data formats and can be embedded into existing software. Evaluation methods can be configured flexibly to ensure that individual test runs are evaluated with maximum efficiency. Kistler offers special editions of jBEAM for specific application areas, including durability testing and powertrain analysis, so users can be sure they get exactly the software functions they need for their work.

As innovation cycles in the automotive industry are becoming shorter and shorter, integrated vehicle testing both on the test bench and the test course, are ever more critical. Kistler measurement solutions cover the entire measurement chain, from the sensor technology, to signal conditioning, to all common interfaces, and user-friendly software.

This article was written by Thorsten Beck, Product Manager, Vehicle Testing, Kistler Group. For more information, visit here .