Case Studies

Getrag Ford

Getrag Ford Transmissions GmbH was founded in 2001 as a joint venture between the automobile manufacturer, Ford, and the transmissions specialist, Getrag, to combine the strengths of the two partners in developing and manufacturing automobile transmissions. The company develops and manufactures manual and automated manual transmissions as well as dual-clutch transmissions for all Ford brands as well as for other OEMs. It employs a workforce of 4,240, not counting the 2,300 people employed by Getrag (Jiangxi) Transmission Co. Ltd. – a joint venture founded by the Getrag Corporate Group and the Jiangling Motors Company Group.

Transmission specialist reinvents the dual clutch
Dual-clutch transmissions provide an excellent example of how long it takes to bring some innovations to the mass market. Although the dual-clutch transmission without any interruption in tractive force was first patented in 1940, it was not until the 1980s that it achieved practical success in the Porsche 962 Group C racing car and subsequently in the Audi S1 rally version driven by Walter Röhrl. At that time, the technology was too expensive to allow series production. It was not until the start of the new millennium that VW revisited the PDK (Porsche dual-clutch) transmission and made it suitable for series production. The experts at Getrag Ford Transmissions are now contributing their knowledge in the field of transmission technology to the further development of this product.

Soon, Getrag Ford Transmissions will launch a new generation of dual-clutch transmissions that allow automatic gear shifting without any loss of power flow. In these transmissions, the oil does not just act as a lubricant but also provides the hydraulic control. Using computer simulation, engineers were able to ensure proper oil circulation under all operating conditions.

Oil quantity demands balance
The biggest problem in the development of a dual-clutch transmission is how to place two clutches together with all the associated hydraulic and electronic components in a space no larger than that required for a conventional transmission box. “To transfer maximum torque using a clutch that is only half the normal size, we use wet clutch systems that operate in an oil bath for high performance engines,” explains the company’s head of CAD Product Development, Rüdiger Muth. “This means that oil circulation through the complex internal mechanism must be guaranteed under all operating conditions.”

Engineers want to know as early as possible how much oil they must put into the transmission to reach a given oil level, and how this level changes when the vehicle accelerates, brakes hard or corners at speed. This issue of oil quantity is by no means a trivial one, as Ronald Engel, technical specialist for pump and lubricant technology in dual-clutch transmissions at Getrag Ford Transmissions, explains: “The financial people and the experts responsible for transmission efficiency want to have as little oil as possible in the transmission, whereas the people responsible for durability want as much as possible. And, if possible, we want to guarantee that the customer can drive 150,000 miles without having the transmission system serviced. All this must be calculated up front in order to find the right balance.”

In the past, engineers used a graduated breaker to fill prototypes with a given quantity of oil. There was a certain amount of spillage, but even more expensive and time-consuming were examinations of the oil level under driving conditions. This not only requires a tilting test rig but also requires the production of a transparent housing − a cost item of about 100,000 euros. In an effort to avoid these costs, and to obtain this information earlier in the development cycle, engineers tried using mathematical fill level simulation. Ford's engine development department had such a tool but it turned out to be unsuitable for transmission development since a gearbox, unlike an engine sump, consists of hundreds of individual parts. The various assemblies had to be painstakingly simplified and the parts fused in order to calculate the enclosed volume. That operation alone took nearly four weeks.

Reliable data early in the process
Since no commercial software could be found to determine oil levels digitally, Getrag Ford Transmissions’ PLM partner, Siemens PLM Software, offered to develop a solution. The solution, based on the NX™ digital product development system, allows the calculation of volumes enclosed by multiple individual parts. Now commercially available as the SpaceFinder function in NX, it performs a type of mathematical filling simulation that is suitable not only for digital oil level measurements but, in principle, for all applications where engineers must calculate complex design spaces surrounded by a variety of individual components. These include, for example, the calculation of trunk space or an analysis of design spaces involving models from different CAD systems – wherever it is necessary to analyze spaces that are not really mathematically closed, which are frequently found in real-life situations.

Using SpaceFinder, it takes only a few seconds to calculate an oil fill level. The fill simulation provides the user with a model of the “frozen” oil, which is then used as a basis for further analyses. “For example, I can specify an oil level that I need for optimal transmission operation and the software determines the corresponding volume,” says Engel. “This optimization takes into account a minimum level for lubrication and a maximum amount that is dictated by price and efficiency considerations,” he notes.

SpaceFinder not only calculates the fill level but also provides the relationship between the volume and the fill level as a graph. Ideally, this should be as linear as possible since shoulders in the graph indicate dead space in the transmission that takes up unnecessary amounts of oil. In such cases, the user can examine the shoulders in more detail and, if necessary, define sections to identify unused spaces, and then make the necessary design changes to eliminate these from the housing geometry.

Ready for use
The results delivered by digital oil level measurement offer a satisfactory level of precision, as tests have shown. While the programmers were using the software to calculate the oil levels for various transmissions, Engel was studying these levels on a physical model to compare the measured values with the results obtained from the simulation. The discrepancy was less than 3.5 ounces and was therefore well within the predefined tolerance. “At first, I was very wary of the software results,” Engel says. “But the sample measurements we took at the test bench convinced me that we could trust its predictions.”

Getrag Ford Transmissions currently uses SpaceFinder as a standalone solution that is not yet integrated in the existing CAD and PLM environment. (The company's CAD system is NX I-deas™.) This is because this C3P data management environment, which consists of a number of decentralized data management systems, is being replaced by a central PLM backbone based on Teamcenter® digital lifecycle management software. Muth says this will provide the ideal platform for integrating SpaceFinder into the development process.

Engel is convinced that the use of this new CAE tool will make many measurements in physical transmission systems unnecessary, saving a lot of time and effort, not to mention the long lead times for the production of a physical prototype. “To perform a basic transmission measurement, we need at least a week in the lab,” he explains. “We perform the measurements a number of times to ensure that statistical errors are kept well under control. And if important geometrical dimensions such as the diameter of the gears change during development, we have to check the measurement results again. I can imagine that in the future we will be able to establish all of this faster and more efficiently in the CAD system prior to producing the prototypes.”

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