Dana Corporation Purchases Comprehensive In-Line Axle Testing Technology
Since the end of 2003 when Dana Corporation in Toledo, Ohio, began manufacturing front and rear differential assemblies for the BMW X5 sports activity vehicle (SAV), each differential has undergone extensive testing in what is one of the world's most advanced production test stands. Designed and built by Burke Porter Machinery, the equipment does not rely on subjective analysis by the operator, but in less than one minute performs objective noise, vibration and harshness (NVH) tests at the end of the production line before the differential is shipped.
Full NVH testing of vehicle transmission components is becoming more common in response to higher levels of expectation from drivers. What sets the Dana test stand apart is the first ever use in production of a new system, the details of which are undisclosed, whereby the vibrations of the input and output shafts are measured as the pinion gear engages with the crown wheel, allowing the quality of gear meshing to be determined more accurately.
The new stand was designed to test differentials manufactured for X5 SAVs built at BMW's Spartanburg factory in South Carolina. Batches of differentials on assembly pallets reach the end of the production line where the test stand recognises the differential model and serial number by scanning a barcode on the differential housing. Both the assembly and pallet are loaded automatically into a fixture and the assembly is clamped at in-vehicle mounting points so that the geometry is not affected during testing. The input shaft of the test stand that simulates the drive from the engine is engaged and so also are the two output shafts that will, when the differential is in the car, be connected to the back wheels.
At the same time, the differential is filled with temperature-controlled oil. Double metering is used to ensure that the correct amount enters the unit, as it will be shipped in this condition and it is important that it is neither overfilled nor underfilled.
As the oil fill cycle finishes the shafts start to rotate, taking the assembly through a sequence of tests at different speeds. Dana configures the tests themselves to suit the vehicle model and to accommodate future types of differentials that may be produced. Typically, the input ramps up through various speeds to 6,000 rpm, representing about 100 mph on the road after 4 to 1 reduction through the differential.
Test scenarios include varying the speed at constant torque, varying the torque from positive to negative at constant speed, and combining the two. In this way, the gear set is monitored for NVH under heavy load in both directions and also when the gears are only lightly meshing. The speed of the two output shafts is synchronised so that only straight line driving is simulated; the differential gears are not included in the tests as noise is more of an issue when cruising rather than when cornering. On completion of the test, the differential is automatically placed back onto its pallet and returned to the production line for final, pre-delivery processing.
Following successful pre-production trials of the test stand in Toledo, Ohio, Dana ordered a second stand. Installed early in 2004, the production stand in Birmingham performs NVH tests on four variants of front and rear differentials for another car manufacturer. The cell recognises the type of assembly by data handshake over a local network and in this case robotically loads not only the differential, but also the appropriate fixture needed to clamp it. So that there is minimal lost time due to load / unload, a rotary turntable with two fixturing positions allows the next unit to be loaded while the previous one is undergoing tests.
The latest test stand for Dana was installed in Austria at the end of 2004, again for testing differentials. It is similar to the Birmingham test stand except that loading of the units is carried out manually rather than by robot. The machine integrates the output torque transducer measurements to the NVH analysis. In this way, instead of just the mean torque being available, high-speed data capture and analysis allows peak-to-trough measurements to be made resulting from the torque fluctuations from the gear meshing. The quality of the gear set is therefore indicated more precisely.
The design function for all these test stands was supported by eight seats of SolidWorks CAD, enabling a short lead-time from date of order to commissioning at the user’s premises. System control software writing and programming was carried out in-house at Gosport, minimising reliance on third parties and facilitating the setting up of internet links for remote troubleshooting.
Test stand for production line testing of BMW X5 differentials at Dana Corporation.