Renault Cleon, near Rouen, France, is a gearbox manufacturer supplying assemblies not only to Renault cars, but also to external customers such as Volvo and Mitsubishi. The Meshing and Acoustics Test Unit have always been interested in the vibration generated by the meshing of cogs, and have developed specialized indices (derived from order measurements) to act as a quality indicator. Tests are carried out on every prototype and units statistically chosen from the production floor. However, the traditional testing process was manually intensive, sometimes requiring more than 2 days to complete one test. To increase productivity and measurement capabilities, a new test bench was designed, and the LMS System Integration Group called in to develop a more automated procedure.
During a test the gearbox is mounted on a rig and driven through a pre-defined series of run-ups and run-downs by an electrical motor. To fully characterize the gearbox and to simulate a real working environment, a second motor acts as a brake - to apply different loads, and the oil temperature is also systematically varied. The same sequence is then repeated for each gear ratio.
Multiple accelerometers are mounted on the gear casing, and data acquired from 800 rpm to 5200 rpm as speed is changed at 50 rpm per second. The processing calculates specified order levels for each run and generates a spectral map. A vibration level check is performed by ‘placing’ a 12dB/octave line at a tangent to the highest peak in each order track over a given rpm range: the quality indicator level is the value of the line at 3000 rpm. Reports are then automatically generated to a specified template, and the result table exported to Microsoft Excel.
The LMS software is designed for use by technicians - a bar-code readout on the gearbox is used to identify the gearbox to the system, the operator selects one test from a given list and presses ‘start’. Everything else is fully automated from the front-end arming to the print-out of the report. Extensive customized database tools are also provided for easy recall and analysis of selected gearboxes at a later date. Because the operator is restricted to following a designated process, errors are eliminated and so high quality data are guaranteed. Furthermore, training is minimized and overall productivity is far better. In effect each system is not a general purpose tool, but a process-centric application - however the underlying technology is the same as that used by the high performance LMS CADA-X system.
M. Sébastien Petit, Manager of the Meshing and Acoustics Test Unit stated “LMS delivered the special development on time and to budget. Since installation the test time has been reduced to less than half a day per gearbox, including the mounting procedure, I am very satisfied.”
