Ahead of Automotive Testing Expo North America 2015 (October 20-22), Volvo Cars attribute leader Torgny Ljungberg talks about how the company is developing its skills in virtual validation of squeak and rattle
Please tell us the background to your presentation.
As an attribute leader at Volvo Cars I’m responsible for solidity. One of my main tasks is to prevent squeak and rattle (S&R) from occurring on future car models. We have started to develop our skills in virtual S&R verification, which includes both dynamic as well as static S&R. In the very early vehicle development phase we go through all the concepts and give our input to the responsible design engineer and project managers before the final concept is chosen.
When a project starts and virtual CAD and CAE models are available, we start our detailed work going through all critical interfaces and ensure that they are robust enough to minimize the risk of S&R issues. We perform both static and dynamic CAE calculations in areas where we have difficult interfaces, such as in the instrument panel and door panel.
The relative movement together with the general process tolerances (GD&T) will show if there is a risk of S&R for each interface either due to contact, which causes a ‘rattling’ noise, or tangential movement when parts are in contact due to pretension, which could cause a ‘squeak’ noise. For squeaking noise Volvo has a big material database for different material pairs and their stick-slip behavior. If pretension and relative movement is found, the material pair is located in the database which will show ‘red’ or ‘green’ stick slip behavior. The database also includes results for different climate and contact force.
For dynamic CAE calculations we use the E-line method where it’s possible to see the relative movement between two parts in the critical interfaces, such as in split lines where the risk of S&R is greater. The relative movement together with the general process tolerances will show if there is a risk of S&R for each interface, either due to contact, which causes a rattling noise, or big movement, which could cause a squeak noise.
How have companies typically performed S&R verification?
Historically, S&R verification is performed on expensive physical prototypes early in the development process. Later pre-series cars in the factory are used to verify the manufacturing process as well as the suppliers of all included parts. Currently, many issues are found late in development when it’s expensive or impossible to change the design.
Why is your method more accurate?
E-line uses normal road load and the result is an absolute movement in millimeters. Current analysis, for example Eigen Frequency/Modal analysis, is based more on several years of experience and it’s difficult to know exactly where the limit for OK/NOK is.
August 20, 2015