Drive train innovations for a lighter gearshift
18 December 2012
Lightweight vehicle designs are quickly becoming fundamental to future sustainable mobility, not only for conventional drive systems, but also for electric vehicle concepts. One key area in which developers are currently focusing their efforts is in the optimisation of vehicle drive systems in order to contribute to the overall weight saving. Tier Two automotive supplier, Schaeffler has achieved notable successes in the development of shift masses, transmission selector hubs and gearshift forks.
Reductions in weight and design space can be achieved using shift masses, while simultaneously enabling improvements in driver handling and comfort. Conventional shift masses comprise a steel component with a relatively high mass. These generate mass inertia, which balances out force peaks and vibrations that occur during gearshift operations.
Here, Schaeffler offers two optimised mass solutions. The mass of Schaeffler’s i2 shift mass module has been reduced by up to 70 per cent compared with that of conventional components. However, the lower inertia level of the i2 shift mass module is increased using a gearbox. At the core of the gearshift module is a two-stage planetary gearbox that enables very high ratios. A slipping clutch reduces the load on the plastic gear teeth during overloading, which helps to ensure a long operating life.
Schaeffler’s lightweight shift mass also utilises a different approach to more conventional shift masses, which improves the distribution of weight. Fitting the actual mass on the outer end of the lightweight carrier ensures optimum utilisation of the lever action provided. The lightweight carrier is made of aluminium or plastic, combined with a steel gearshift lever for transmitting the gearshift forces.
Selector hubs and gearshift forks
With its new selector hub made from sheet metal, Schaeffler can now facilitate reductions in weight of up to 25 per cent compared with conventional solid sintered metal versions. The new two-part design comprises geometrically compatible sheet metal half shells, which, after the design optimisation process, can transmit a higher torque than sintered components.
In manual transmissions, intelligent use of mixed designs is key to opening up further potential efficiency improvements. For example, Schaeffler’s new hybrid gearshift forks with aluminium bodies can replace more traditional, conventional steel versions. The striker jaw is a high precision sheet metal blanked component. During assembly, this is precisely aligned with the screw mounting axis and joined to the gearshift fork, compensating for single component tolerances.
Unlike conventional aluminium gearshift forks, costly recasting or complex reworking are not necessary. This mixed design not only reduces the weight of the component, but also makes it more compact, which in turn, reduces the design envelope. Moreover, this simplified assembly process enables the hybrid design to be manufactured anywhere in the world. Schaeffler’s Pascal Kohtes summarises:
“Our new lightweight concepts enable reductions in weight of up to 1.2 kg for transmissions. Often, lightweight designs not only have a positive effect on the components themselves, but also initiate significant positive secondary effects on the vehicle as a whole. These range from advantages in driving dynamics and weight reductions, to cutting fuel consumption and CO2 emissions. Lightweight designs are therefore a specialist area with a strategic focus that will dominate mobility into the future.”
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