Vehicle testing evolves to match new legislation and technologies
PCB Piezotronics has unveiled an Automotive Sensors division dedicated to providing vehicle-testing services.
Greg Reed, Contributing Editor -- Test & Measurement World, 11/9/2007 2:20:00 PM
PCB Piezotronics recently established a new Automotive Sensors division and opened a technical support facility in Novi, MI. Dedicated to the vehicle testing market, the new division will offer technical sales and applications engineering support in North America, Europe, and Asia.
Jeffrey Case, a 15-year veteran of the automotive industry and the director of sales and marketing for the PCB Automotive Sensors division, took some time to discuss some of the challenges involved in vehicle test and explained how test needs have changed in the face of recent legislation.
Q: How do you satisfy customers across multiple test environments?
A: Our customer's test requirements are very application focused. Whether requirements are for modal and structural analysis, powertrain testing, or vehicle durability, our main objective is to help the customer to perform a test as efficiently and as accurately as possible. These very specific application requirements might require a sensor technology from any of our traditional product groups or might call for multiple products to be used across several different groups.
For example, a customer executing a vehicle brake performance test would require a brake pedal force sensor to measure pedal effort, a DC accelerometer to measure vehicle deceleration, several brake line pressure sensors to measure brake system performance, accelerometers to measure harshness, and microphones to measure any brake noise phenomenon.
Q: What role do modal and structural analysis and transducer electronic data sheet (TEDS) sensors play in ensuring the overall safety of vehicles?
A: The structural behavior of a vehicle is a critical parameter to how a vehicle performs on the road under various conditions, particularly evasive maneuvers. In order for both active and passive vehicle systems to perform consistently under these conditions, the vehicle structure needs to be as stiff as possible (minimal compliance at the suspension inputs) with its flexural modes distanced from any low frequency road or vehicle system input.
Modal mapping is performed early on in the design stage to ensure a solid vehicle structure that allows active and passive suspension systems to function consistently and efficiently through all operating conditions. These modal tests are best performed with multichannel data-acquisition systems and TEDS sensors. TEDS-capable systems, when used properly, allow for quicker set-up times and reduced errors in channel identification. Our company offers a complete range of modal testing equipment and TEDS-capable sensors, including shakers, modal hammers, load cells, and accelerometers.
Q: How has noise, vibration, and harshness (NVH) testing evolved over the last few years?
A: NVH testing has evolved over the last few decades from a highly specialized field to a more commodity based test and development environment. Methods employed in today's NVH testing have not changed much in the last few years. However, our customers are looking for ways to increase efficiency and speed in their setup and testing.
With increases in computing power, online multiple-channel acquisition systems are growing in size and in numbers. The introduction of TEDS into sensors and data-acquisition equipment have allowed these large acquisition systems to become more manageable, in terms of shortened setup time and increased accuracy of sensor identification.
In the US, we are seeing fewer vehicle modals, as OEMs are producing fewer physical prototypes across shared platforms. A more common, current approach is to perform an operating modal analysis to understand vehicle and system dynamic behavior in its operating environment. Vehicles have become much quieter over the past 20 years, mainly due to an increase in customer awareness and expectations, and increased legislation regarding interior and exterior noise.
For example, European directive 70/157/EEC, established in 1975, limited exterior pass-by noise to 82 dBA. Since then, this number has been reduced to the current limit of 74 dBA under directive 92/97/EEC, established in 1996, and enforced today. As a result of decreasing noise levels, more of our customers are requiring larger dynamic ranges for their microphones.
Product development cycles are getting shorter. Although the number of physical tests is decreasing, the complexity of each test has actually increased, as our customers try to gain more information in a shorter timeframe. This often means "piggy-backing" an NVH test with a vehicle performance test, which requires reliable, robust instrumentation and cabling, and leaves little margin for setup and other errors.
Q: Which test technologies have been developed to respond to recent legislation and safety requirements?
A: Increased customer awareness for automotive safety and government mandated testing continue to be the driving force behind current automotive safety testing. Computer-aided engineering (CAE) is being used extensively in barrier and vehicle impact, seat-belt load, and vehicle rollover testing to validate a design before commitment to a certified test.
There have also been a few changes in test technologies in recent years. Until recently, a rollover propensity test was strictly a static test of a vehicle's center of gravity. This test is now a highly evasive vehicle test maneuver, requiring a steering robot to ensure test repeatability. This test will measure the effectiveness of a soon-to-be mandatory electronic stability control, which is something a static test simply cannot do.
Although current roof crush tests require a static load product application, there is an industry wide push to make it more representative of a dynamic loading event, similar to the actual physical changes to a structure during an actual rollover scenario. Dynamic test technologies are increasing, as they are a better representation of a real-world event.
Q: What are some challenges associated with powertrain test?
A: One of the biggest challenges in any powertrain test is the ability to consistently and accurately measure sensor data under engine operation. The requirement for a sensor in this application, whether acceleration, sound, pressure, force, or torque, is usually extreme. The harsh environment of a powertrain test includes contaminants, high temperature, moving parts, and limited space.
Measuring and combining these external signals and information gleaned off the controller-area network (CAN) bus can be a challenge if the correct signal-conditioning and data-acquisition systems are not chosen or correctly configured. With the introduction and ever increasing use of hybrid technology in today's powertrains, we are seeing issues with electrical noise. The electrical machines found in today's electric hybrid powertrains induce electrical noise, which can be picked up by external sensors. Though quite challenging, we work with customers to custom tailor sensor solutions for virtually any diesel, gas, or hybrid powertrain test application.
Q: What are some future trends within automotive testing?
A: Wireless sensing technology is a growing discussion topic within automotive testing circles. This technology currently exists and is used in industrial monitoring solutions, but does not currently meet requirements of a typical automotive test. From my experience, I see this technology about five years away having significant impact and practical usage within the automotive test world. Issues with size and synchronization need to be worked out before this happens.
Because of shortened product development cycles, automotive engineers may be asked to combine several types of measurements into one test. This could mean taking NVH measurements during a vehicle powertrain performance test, two areas of test which traditionally have been separately maintained. This strong trend will require better integration of sensors and a very versatile data-acquisition system.
The number of physical tests per vehicle will continue to decrease, as virtual methods for product development are refined. However, these physical tests will increase in complexity to satisfy requirements of virtual vehicle correlation and vehicle attribute confirmation. Component and vehicle durability is one physical test that will not be replaced by virtual methods in the near future. Durability tests will continue to be accelerated, both in severity and type of input. Three axis component automotive durability testing will also increase in the near future, as results have been indicative of real-world issues in a shorter time window, whereas single axis testing could not provide such outcomes.
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