Tech Insider / CZINGER 21C THE 21C IS BOTH A TESTBED AND A CUSTOMER-READY CAR ORIGINS The 21C was initially created to be a technology demonstrator for Divergent’s technology. Originally called the Blade, the car was “an in-house project to practice and develop the techniques, which would produce something marketable to demonstrate the technology”, says Czinger’s Ewan Baldry. The project served this purpose well and Divergent now has several OEM customers. However, a private showing of the car at the Pebble Beach Concours d’Elegance in 2019 sparked such a positive reaction that the project morphed from a concept into a bona fide, homologated production car, and the Czinger brand was created. Despite the motorsport background of many of the team members and the clear performance intent of the car, it was decided not to use the transmission as a stressed chassis part because the impact on NVH would have been unacceptable. However, the stiffness and strength of the casing was still of utmost importance, for example, the dynamic stiffness of the casing under load affects its installation in the vehicle and the design and operation of the gears within. Baldry explains, “Our optimization engine allows us to use dynamic stiffness as one of the requirements. If you look at the other structures on the car, internally there are lots of weird and wonderful geometries that are driven by this dynamic stiffness requirement.” Any displacement of the shafts within the casing under load has an impact on how the gears mesh. Bolton recalls, “The dynamic stiffness plays a role in the way the gears are cut. The involute profiles and microgeometries used account for any variation in the casing stiffness. Usually [with a cast casing], the stiffness is just what it is, and you need to compensate for it in the gear geometry. Whereas we were able to say, ‘What gear geometry would you like? We’ll target the stiffness to match that’.” One of AM’s most appealing party tricks is the ability We’re already to incorporate internal geometries within solid parts exceeding that cannot be created using the mechanical traditional manufacturing techniques. For example, the properties of typical 21C transmission features a cast materials” sump-based oil system that relies on a pair of pumps to keep the transmission lubricated. “The pump manifold is manufactured with all of the internal passageways already incorporated,” says Bolton. “There is no need for machining and they can take crazy routes that perfectly match the flow rates and pressure drop we need. They even run following the curved surface of the casing, rather than having to take straight lines. We have also printed in all the oil galleries throughout the main case.” Returning to the topic of NVH, Bolton says that with a variety of thin wall features within the case, there was potential for resonances to occur, particularly in the integrated oil tank, which has a 2mm wall thickness. “What we did there is add a Voroni lattice pattern to stiffen those walls up, otherwise they would have definitely resonated,” he explains. ITERATION Castings such as transmission casings are long lead time parts, and every detail needs to be baked in before committing to pattern making and production. Not so with AM, where it is possible to make design changes on the fly, from print to print. At the time of writing, Czinger had printed three iterations of the casing. ADVANCED CAPABILITES Divergent has a host of in-house capabilites for both building and testing AM-manufactured parts 8 Transmission Technology International / 2023