DuPont™ Vespel® polyimide rectangular rings provide reliable sealing for John Deere’s pioneering tractor dual-clutch transmission
Geneva, 29 November 2016 — John Deere, Mannheim/Germany, makes use of the excellent friction and wear behaviour of sealing rings made of DuPont™ Vespel® in its pioneering dual-clutch DirectDrive Transmission (DDT) with eight powershift speeds. These rings provide a low-leakage seal against oil pressure of up to 20 bar at oil temperatures of between -30 °C and 80 °C with transient peaks of up to 110 °C over the entire service life of the transmission. John Deere, one of the world’s largest agricultural machinery manufacturers, is offering this particularly efficient and energy-saving DDT system, which permits direct gear shifts without any interruption in traction, in its 6R series of six cylinder tractors.
Dual-clutch transmissions which can be shifted under load with no interruption in traction are available as an option on John Deere’s 6R series of tractors. Rectangular rings made from Vespel®, with its particularly low friction and wear, help to provide a durable, reliable seal against the oil pressure which builds up during speed shift cycles. Photo: DuPont
In John Deere’s DirectDrive transmissions, the Vespel® rectangular sealing rings are located at the wet clutch pressure oil transfer points on the shafts of the two sub-transmissions. As a specialist from John Deere’s Power Train Engineering explains: “When the clutches are hydraulically actuated, the rings provide a reliable seal for these pressure oil transfer points. As this happens, the conditions change at the sealing points. When the clutch is disengaged, the rings are exposed to low relative speeds between the shaft of hardened and ground 20MnCr5 and the clutch housing with no pressure. When the clutch is engaged, the relative speed is zero, while the differential pressure is at its highest. In both cases, the material’s very low friction and very low wear help to ensure low-maintenance operation of the transmission. Moreover, DuPont’s recommended ring design minimises leakage.”
DuPont and John Deere have closely worked together in order to select the grade of material and tailor the the dimensions of the groove and the rectangular cross-section of the rings. The DuPont development team selected a Vespel® grade with a low coefficient of thermal expansion to provide a consistently high sealing action over the entire temperature range. With its very high creep resistance and excellent friction and wear behaviour, it contributes to the particularly low-maintenance operation of the transmission.
Peter Bergmann, European Transportation Market Segment Leader, DuPont™ Vespel® & Kalrez®, adds: “This successful collaboration with John Deere is another demonstration of how companies can benefit from DuPont being a one-stop-shop able not only to manufacture the basic material Vespel® but also to mass-produce high-quality parts. As a result, we are particularly flexible in responding to specific customer requirements and in recommending the most suitable material from our range of grades which are specifically tailored for dynamic applications. Once the material has been selected, we can relatively quickly provide samples for customer testing and for component investigations in our lubricated wear and friction Center Of Excellence , so helping to ensure short development times.”
DuPont manufactures the sealing rings, maintaining very tight tolerances, using its proprietary direct-forming process. The design of the butt joint geometry provides low leakage over a wide operating range and facilitates assembly. Without compromising on reliability, rings of this kind help to save on costs, installation space and weight in comparison with metal components in numerous transmission applications.
Background: dual-clutch transmissions …
… basically consist of two independent sub-transmissions, each connected to the engine via a clutch. One sub-transmission contains the uneven speeds (1, 3, 5 etc.), while the other contains the even speeds (2, 4, 6 etc.). On shifting, the next speed in the passive sub-transmission is firstly preselected via synchronised switch points and then the load is transferred between the two clutches. This takes place very quickly without any interruption in traction, meaning the corresponding speeds can be power-shifted. The clutches may in principle also be used as starting elements.
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