Advanced synchronizers from Oerlikon Graziano provide fuel savings and easier gear shifting on heavy trucks
|New generation synchronizers from Oerlikon Graziano featuring integrated activation system with optimized clearances to give smoother shifting and reduce drag. Click to enlarge.|
Oerlikon Graziano has developed a family of advanced synchronizers for heavy-duty truck transmissions. The first application of the technology, on new 9-speed and 14-speed premium gearboxes, has contributed to transmission efficiency improvement, helping to fuel saving and emission reduction.
The new synchronizers save fuel in two ways: by optimizing the shift to minimize torque interruption and by reducing steady-state drag torque in the transmission. They combine the high durability and high performance of Oerlikon Graziano’s existing Long Life synchronizers with a new internal activation system, the use of optimized clearances and lubricant paths for higher efficiency.
|During a gearshift, synchronizers manage the speed difference between the previous gear selected and the next one, to ensure a smooth, quiet shift. In a typical transmission, all the gears are in constant mesh but only one pair is driving because in each pair, one of the gears freewheels until connected to its shaft by a synchronizer.|
|The hub of the synchronizer is splined to the shaft and carries three equi-spaced struts around its perimeter, on which the selector sleeve rides. In order to connect the synchronizer hub to the gear and engage the chosen ratio, the sleeve is moved towards the selected gear when the driver operates the gearshift lever.|
|Fine internal teeth on the synchronizer sleeve connect with opposing external teeth on the side of the gear to transmit power. But the sleeve cannot simply engage with the gear because they are rotating at different speeds. To prevent grinding or crashing of the synchronizer teeth, two further elements are carried between the hub and the gear: a synchronizer ring and one or more cone clutches.|
|The synchronizer, or blocker, ring carries fine external teeth matching those of the sleeve and the gear. It blocks the sleeve from travelling into full engagement until the speeds have been synchronized. The cones provide the necessary friction to adjust the rotating speed of the gear until it matches that of the shaft. At this point, the friction on the synchronizer ring decays and the ring’s external teeth line up with the sliding sleeve, allowing it to complete its travel and fully engage the teeth of the selected gear.|
The new synchronizers are configured in single and double cone arrangements, each with the same external geometry to allow flexibility in transmission design. In all, four different synchronizer specifications are used on the 14-speed transmission and three on the 9-speed.
The synchronizers have exceptionally high torque capacity—up to 18,000 N·m (13,276 lb-ft) in the first applications—and use molybdenum-coated steel cones for high durability with optimum friction. Future developments include the potential for carbon coating. A key feature of the new technology is the integrated activation system which provides outstanding durability and ease of assembly.
By increasing the speed of a manual shift, Oerlikon Graziano has been able to reduce the torque interruption, keeping the engine at optimum efficiency for longer and reducing engine transients to save fuel.
Whichever gear is selected, large differences in rotating speed can exist across the other synchronizers. With a conventional design this leads to significant drag losses which impair efficiency, but the new synchronizers greatly reduce this effect to further improve fuel economy.
The new synchronizers improve the shift process during three distinct phases. Prior to synchronization, the integrated activation system provides optimized load characteristics to give improved consistency and outstanding durability, compared to a standard design.
The second phase, synchronization, has been shortened by the use of multi-cone technology, best-in-class friction materials and the optimization of geometries and tribological properties.
The third phase, from synchronization to engagement, has been improved by incorporating new internal features allowing smoother travel of the sliding sleeve, avoiding blocking problems and providing a more friendly engagement feel to the driver, and finally making this solution even more attractive in applications which are usually manual shift with air assistance, so any shift problems can immediately become obvious to the driver. The new system ensures a fast, smooth and reliable shift under all conditions, making it an attractive alternative to a powershift system as it packages into a much smaller space.