The Volkswagen Group is one of the world’s leading automobile manufacturers, and the largest carmaker in Europe, delivering almost 10 million cars to customers each year. This corresponds to a market share of the world passenger car market of almost 13%. Employing over 15,000 people, Volkswagen’s primary transmission site at Kassel supplies almost four million manual and automatic transmissions every year, and includes Europe’s largest light-alloy foundry to produce aluminum and magnesium housing components. The Kassel plant also reconditions old engines and gearboxes, and manufactures 3.5 million exhaust systems each year.
Volkswagen engineers at Kassel have used RomaxDESIGNER software to support transmission manufacturing for more than four years. “It’s important for the effective manufacture of gearboxes that you use a process that is not too costly” says Juri Kniss, calculations engineer at Volkswagen. “Some parameters are cheap to control, others are expensive. We want to look at all these parameters and examine the influence of variations in the production process. Romax provides the ability to look at the whole system, rather than individual components alone.”
At its Kassel plant, Volkswagen engineers use RomaxDESIGNER on a range of standard and non-standard investigations to support the effective production of manufactured gearboxes and to ensure the required quality has been achieved.
“We’ve used RomaxDESIGNER for more than four years,” says Kniss. “As a factory site, our focus is not to design gear sets, it’s to ensure the gearboxes we manufacture are consistently of the required quality. With RomaxDESIGNER we can assess the effects of gear manufacturing variability within a fast and accurate simulation.” He describes RomaxDESIGNER as “an important element in a ‘tool chain’ that includes other less specialized CAE packages.” In this case, engineers at Kassel use RomaxDESIGNER to analyze existing designs and assess how the tolerance variability of gear micro-geometry will impact on the NVH of the finished gearbox. “Romax allows us to do this by integrating rapid modeling and analysis of gears, shafts, bearings and housings within a single gearbox model to predict how components interact with each other.”
“We have also recently used RomaxDESIGNER to predict bearing preloads required for a new EV gearbox, which we achieved by calculating the interaction between three shafts and the electric motor,” Kniss explains, “and to look at which rings to mount in the factory. The housing hasn’t a great degree of stiffness, leading to complex interactions. So we want to change the bearing preloads and see the effects, to identify the correct settings to use when manufacturing the gearbox. To validate the methodology we set up a test rig to compare results and were able to see that Romax provided a good validation.”
As part of the same project, RomaxDESIGNER was also used to analyze the fit between the motor stator and the gearbox housing, to predict any housing deformations and the resulting effects on the gears and bearings.
During the gearbox assembly the stator is fitted into the housing. This results in an interference fit and a degree of deformation of the housing, which causes some displacement of the gearbox bearings. The interference fit was modeled externally and the bearing displacements then applied as preloads to the Romax model. “In this case, we had a highly detailed model that we could apply to all of the bearings, to examine the effects of the interference fit,” Kniss says, “with different shaft misalignment predictions being evident along with different contact patterns for most of the gear sets.”
“We took the Romax misalignment predictions and passed them to our colleagues in Wolfsburg to support optimization of the gears, so they could apply this to calculate new micro geometry, to reduce noise and improve durability and so on,” states Kniss.
Summarizing their analysis work to date, Kniss adds, “The main benefit of using RomaxDESIGNER at the Kassel transmission plant is that we can build complex models that reflect the whole system, and we get good results. We can build several models if needed and use Romax to predict the effects of different tolerances so we can work out which ones we should focus on.”