Desperately seeking driveline silence: Veri-Tek works to reduce drivetrain NVH

Automotive Industries,  Feb, 2003  by Rob Wilson

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Silencing noise and vibration harshness in the driveline is becoming more and more important as consumers demand increasingly greater comfort and performance levels in their vehicles. The thinking is that if they pay for an up market sound or entertainment system, they certainly want the ability to appreciate what they've bought.

Axle and driveshaft NVH is a big part of the quest for improved acoustics. "Drivetrain NVH was very elusive as little as six years ago because there were fewer known ways of measuring, reducing and isolating noise and vibration sources within the powertrain," says Jim Juranitch, CEO of Veri-Tek Inc. Wixom, Mich. 'Customers' expectations were less, and the vehicles of the time were louder overall, which effectively masked many component NVH sins.

Today we have several patented means of measuring either acceleration (G forces) or velocity (mm/sec) in the powertrain system and then tracking the order of noise and isolating it to the component source. This is done both in the vehicle, and on the production line, at production line speeds."

From isolation of NVH sources to building near perfect driveshaft and axle assemblies, here's how the progression of advances developed.

Signature analysis based in-process verification (IPV) systems are Veri-Tek's specialty. Its proprietary software, VT-1000, was integrated with cells for testing axles and subassemblies for NVH as well as for functional tests such as gear ratio, limited slip, anti-lock components, breakaway and running torque, wheel stud alignment and oil fill.

Out of this came the Veri-Tek Energy Testing and Analyses for Gears (VETAG) test cells. These have now proven themselves on more than 5 million axles on numerous vehicles. On the new Ford Thunderbird, the implementation of VETAG technology has played a role in the vehicle achieving zero warranty returns for axle NVH complaints with over 25,000 axles produced.

The VETAG test machine measures the overall noise level of each axle assembly and discriminates between good and bad axle assemblies. The rating is correlated to subjective, and objective, road test data through the use of calibration axles. As part of the test cycle the machine simulates coast as well as drive conditions in order to verify NVH compliance from both sides of the ring and pinion gear.

Essentially, the VETAG makes sure bad assemblies are not shipped to the customer and it provides "Root Cause" feedback for manufacturing quality improvement, cost reduction and higher first pass production yield. This detailed technical feedback from the VETAG, and the ability of the customer to use it to improve first pass production yield, is a significant part of the system's value.

"The success with the axle test cells led to exploring new methods for testing driveshafts; however, logic said 'why not look at a new approach to manufacturing at the same time?" says Juranitch. "Let's not make bad assemblies. Let's try to achieve best in class results with six-sigma quality and outstanding results eliminating NVH issues. And let's do it all for less cost."

Reinventing driveshaft production proved to be an undertaking and several more patent pending developments overhang the advance. A number of separate machines were developed that are put together in complete manufacturing cells with integrated IPV.

First in the process is a Synchrowelder machine that welds drive shaft components onto both driveshaft tube ends simultaneously using a hybrid friction welding principle. Uniquely, during the welding process the tube is rotated while the ends are held stationary.

From welding, the driveshaft proceeds to a Truing Machine which aligns the tube on a mass center related to the vehicle's true running center. The entire surface of the driveshaft is dynamically straightened. Conventional methods of straightening make a pretzel with dips and bumps that add to NVH issues, whereas the truing method eliminates them.

Next comes the True Vehicle Running Center (TVRC) assembly machine. It places the Cardan joint at the center of the yoke before roll staking the snap rings in place.

A fourth machine, an Articulation Torque Tester, verifies the integrity of the rolling process by dynamically measuring the torque to rotate each of the four joints. And each of these machines has one or more patent pending design features.

Also of interest are half-shaft testers developed by Veri-Tek. These are automatically cycled and conduct a barrage of tests to quantify external grease leakage, spline characteristics, snap ring or ring groove presence, half shaft joint lash, and articulation torque.

"With the right planning," says Juranitch, "it is reasonable to expect a zero-defect launch while also realizing reduced cycle times, and component costs. It is also possible to produce hundreds of thousands of shafts with no NVH, or other warranty issues. We have, in fact, recently accomplished just that with a new drive shaft cell installation.