2012-28-0004

Trelleborg Innovative Solutions for Growing Problems of High-Frequency Noise and Vibration

Enrico Kruse Advanced Engineering Manager – Trelleborg Automotive Europe

Bruno Carré Dpty VP Global Engineering – Trelleborg Automotive

ABSTRACT

In this paper, we will present a wide variety of Solutions to manage growing problems of high-frequency noise and vibration. These solutions go from very simple and cost-efficient design features requiring very accurate simulation and testing capabilities, to more sophisticated products such a Active Vibration Control components.

INTRODUCTION

The Global Automotive Industry is requesting years after years Continuous Improvements in Vehicle Noise Vibration and Harshness Performance. Therefore the demand for better performances for Power Train Mounting System is constantly increasing and is more and more focused on to High-Frequency Issues. In this paper, we will present several cases related to High-Frequency Issues that Trelleborg had to manage and we will see that Trelleborg can deliver very Simple and Cost-Efficient Solutions as well as Very Performing Innovative Technology such as Active-Vibration Control. MAIN SECTION

1ST CASE – DOBLE-ISOLATION

The 1 st case is related to an European Top 3 OEM. The concerned engine is a 6 Cylinders Engine with Transversal Installation. The issue is 21st and 42nd order Chain Whine Noise, during 2nd Gear Wide Open Throttle. In below chart we can see 21st and 42 th order Contribution to Interior Noise (dB(A) vs rpm / Hz).

We can see that the 21st order has a contribution from 500 Hz to above 2.000 Hz. The dynamic stiffness measurements completed on the Trelleborg part show a resonance peak at 1.000 Hz.

This resonance peak and dynamic stiffness increase after 1.800 Hz will couple with engine excitations and therefore generate High Interior Noise as we could see in the 1st picture. We can see below the coupling frequency range between Engine Excitation and the Left-Hand Side Dynamic Stiffness.

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In order to decrease significantly this coupling between excitation an LHS Mount response, Trelleborg proposed to re-design the part using a Double-Isolation Concept. This concept is to add to the Rubber Main Spring – the 1st isolation layer – a 2nd isolation of the entire component. Therefore the component is assembled to the car body through rubber grommets which are press-fitted into the Trelleborg part (see below picture).

With this Double-Isolation device, the entire component has a vertical bounce mode close to 500 Hz.

The Dynamic Stiffness of the Part is now as shown in the curve below. After 500 Hz – vertical bounce mode – we can see a significant reduction of the dynamic stiffness which means a significantly reduced transmissibility.

The same Interior Noise Test shows consequently a very important Interior Noise Reduction of up tp 8 dBA.

2ND CASE – “RUBBER FLAPS”

The 2nd case is related to a European Top 3 OEM. The concerned engine is a 6 Cylinder engine with longitudinal i.e. North South installation. The target was to improve the overall NVH Vehicle performance through better gearbox mount dynamic stiffness. We conducted joint technical workshop with the OEM for Idea Generation and Knowledge Sharing. The X-direction dynamic performance for original design is shown in the attached picture.

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Dynamic Stiffness curve shows a peak value at 1.250 Hz and the curve starts increasing after 900 Hz. The basic idea to improve the X-direction Dynamic Performance of Trelleborg parts is to add to the original design some very simple additional rubber mass – “Rubber Flaps “ - on the shear element (refer to attached picture).

These “Rubber Flaps” behave as small Dynamic Dampers and their shape can be tuned easily by FEA Simulation to get targeted improvement for the mount dynamic stiffness. The Trelleborg FEA team could model and analyse – with Abaqus Software - the “Rubber Flaps” behaviour as shown below.

When we look at the “Rubber Flaps” 1st Modal Shape, we can see their contribution in X-direction. Therefore we achieve a new design w delivering a X-direction dynamic stiffness with a significant improvement starting at 800 Hz.

This improvement above 800 Hz far out-weights the higher dynamic stiffness from 400 Hz to 800 Hz and provides better overall vehicle NVH performance. This design principle has been jointly patented by the OEM and Trelleborg and it is applicable and applied on a wide variety of PTMS. This example and the following one demonstrate that with some grams of rubber we can significantly improve our part dynamic performance and that we can tune our Design by FEA to meet customer expectations.

3RD CASE – “RUBBER RING”

The 3 rd case is related to an European Top 3 OEM. The concerned engine is a 4 Cylinder Engine with transversal installation. The PTMS is a 4 Point System with Left-Hand Side (LHS), Lower Torque Rod (LTR), a Right-Hand Side (RHS) and an Upper Torque Rod (UTR). The issue was to improve the overall vehicle NVH performances through better radial dynamic stiffness of the Trelleborg Part. The Technical Issue was a potential modal alignment between the RHS and the UTR.

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The X-direction dynamic stiffness – fore-aft in the vehicle - shows a main spring mode close to 800 Hz with a potential modal alignment with the UTR mode in that direction. The target was to separate these modes from each other top prevent modal coupling. Therefore we added a rubber ring to the main spring to shift the natural frequency of 1st main spring mode. The attached picture shows the effect of increasing this additional mass in two steps, thus lowering the resonance frequency.

We can see at component level that we eliminated the modal alignment risk and we were able to confirm this with a Body-In-White measurement. The next pictures shows the BIW measurement set-up with Upper Torque Rod (blue) and Right-Hand Side (red). We measured the ratio between BIW Acceleration and Engine Bracket acceleration. This measurement is representative of the RHS mount transmissibility.

We can see that we improved the transmissibility between 700 Hz and 1.700 Hz and therefore improved the total car NVH performance using a very simple cost-efficient feature with some additional grams of rubber. This 3rd case was showing the improvements we can manage on a Hydromount to improve its transmissibility. To support this we must have a) an accurate FEA simulation process for Hydromount including glycol contribution b) suitable test equipment to be able to measure up to 2.000 Hz which is higher frequency than standard test equipments available on the market can achieve and c) Full-Capabilities for Vehicle NVH Measurement. Trelleborg developed a FEA simulation process based on Abaqus Software to calculate dynamic stiffness up-to 2.000 Hz with good accuracy as we can see in below correlation plot.

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Trelleborg also developed and built its own test equipment for high-frequency dynamic stiffness measurement up-to 2.000 Hz with or w/o preload.

Trelleborg has also full-capabilities for vehicle NVH measurement including an anechoic chamber with a dyno, a 2-post shaker and all necessary hardware and software to measure and process vibration and noise including sound quality.

4TH CASE – ANTI-VIBRATION CONTROL

All these examples presented were using simple, cost-efficient design features to manage high-frequency issues. Trelleborg also developed a state-of-the-art technology to manage Specific Vibration Issues at a Specific Car Point across a Broad rpm Range. We call it Active Vibration Control.

It enables us to improve Driver and Passenger Comfort by reducing Various Customer Inputs such as

- Seat Track Vibrations - Steering Wheel Vibrations - Global Interior Sound Level

AVC can also be potentially used for active tuning of vehicle sound quality. AVC produces controlled vibrations – either with Open-Loop or Closed-Loop Control - which target to cancel engine vibrations (see attached scheme). Therefore we can minimize Interior Noise and Vibrations without any NVH compromise.

The AVC includes a) an Actuator Assembly b) an Electronic Unit c) an Error Sensor in case of the Closed-Loop System.

The AVC Control System has the following characteristics. It can be integrated in the AVC Component or be stand-alone.

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The basic components and force output of the AVC Actuator are described in the next pictures. It should be noted the design is completely scalable for a perfect balance between NVH requirements, cost weight and size.

Recently Trelleborg worked with a US OEM on a demonstrator vehicle to quantify the global NVH improvement we can achieve by using a Trelleborg AVC System. In the picture below, we can see that we can improve Interior Noise by 5 to 20 dB(A) depending on engine rpm range. This is a significant improvement which contributes to better comfort for the driver and the passengers.

CONCLUSION

The Automotive Markets faces growing problems of High-Frequency Noises and Vibrations as OEMs target to improve overall car NVH Performances. To manage these issues Trelleborg developed and validated a variety of Tools and Processes to Design-to-High-Frequency and can propose a complete portfolio of Solutions from Simple Cost-Efficient Design with Additional Rubber Masses working as Dynamic Dampers to more Sophisticated Products such as Active Vibration Control Systems.

REFERENCES

NA. CONTACT

Enrico Kruse Advanced Engineering Manager Trelleborg Automotive Europe Mob +49 1511 2232 550 enrico.kruse@trelleborg.com www.trelleborg.com ADDITIONAL SOURCES

NA

DEFINITIONS, ACRONYMS, ABBREVIATIONS LHS Mount : Left-Hand Side Mount RHS Mount : Right-Hand Side Mount UTR : Upper Torque Rod LTR : Lower Torque Rod NVH : Noise Vibration & Harshness OEM : Original Equipment Manufacturer FEA : Finite Element Analysis BIW : Body-in-Whire AVC : Active Vibration Control

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