With Romano Albesiano and Piero Soatti (respectively Aprilia’s Technical Division Director and the technical manager of the SL 750 Shiver project) we’ll learn all about the new technological components packed into the latest naked from Aprilia, about to hit the 2-wheeler market.
What are the most important and innovative contents of the brand-new Aprilia 750cc propulsor with liquid cooling? With this engine, Aprilia enters into the medium sector with a cylinder that was previously missing from its range. By creating this new propulsor, we introduced a layout level with completely state-of-the-art technological components for a 4-valve distribution per cylinder with a camshaft at the top and a “triple” distribution system, therefore, mixed gears and chains. This choice was adopted for two reasons: a reduction of bulk and improved noise reduction and upkeep. We began the project with another idea that consisted of a single loop of the chain, only to switch over to the final system halfway through the project. Proceeding with the propulsor, we have a head with an integrated bobbin that was developed specifically for this project and friction from the multi-disc hydraulic command that is bathed in oil. Even in this case, the same line of reasoning applies as we experimented with various solutions before arriving at this choice that proved to be better in respect to other systems and in its exemplary functioning. Lastly is the truly innovative aspect of the engine’s hardware, the famous “ride by wire” system.
Aprilia SL 750 Shiver
What is the ride-by-wire system composed of, how does it function, and what advantages does it offer? This system offers numerous advantages, but let’s first look at its composition. The throttle opening is not controlled mechanically with the accelerator cable (like in the majority of bikes), but instead by the rotation of the accelerator that is transferred by a component called a “demand sensor” with an electrical signal to the central-line that also functions with other factors (principally the engine’s revolutions while in gear, among others). This way, the throttle is better managed to satisfy the user’s desire, interpreted by the movement of the accelerator. This technology was initially introduced by the automotive sector and has since been adapted to the world of two wheels, named as “top riding” in the many enthusiastic comments recently written up in industry press. In fact, besides the optimal riding and improvement in conditions that typically risk being critical in traditional systems (such as the opening-closure or the opening in the first outing), the ride-by-wire system also has advantages in the management of resistant torque while stopping, executed either by an anti-skipping system or throttle control, not to mention limiting emissions and consumption. What were the principal criticisms you encountered during development of the motorcycle’s technical layout? As often happens with naked bikes, and especially with this one, the greatest challenge was making everything fit. In the Shiver, we have a more refined engine control system that, due to its evolution, is more complex. To compensate, we used peculiar solutions such as the layout of the under-tank area that was arranged so that the air box has a function beyond simply acting as the box filter. It also contains the throttle bodies, the central-line, and the pressure sensors: everything is contained inside the box filter. This opened up a lot of space and enabled us to compact the weight, making the general aesthetic cleaner which is always difficult with a naked. Another solution along those same lines is the position of the shock absorber. It was inserted laterally without the need for leverage which, besides giving us an exciting aesthetic, also allowed the exhaust to develop in a more linear manner inside the swing arm, allowing us to gain significant space.
What are the technical reasons for the choice of a composite frame and the lateral placement of the mono-shock absorber? That placement of the shock absorber was unthinkable just a few years ago, but this type of layout works well today because the technology for controlling the shock absorbers’ lowering has evolved greatly and, even without leverage, is equal to that of traditional systems. The composite frame was chosen for many reasons. However, it primarily enforces the trademark family-feeling of Aprilia off road motorcycles. To see this fused aluminum-steel frame is quite nice and with current technology (even the FEM calculation), you are able to create a product with a weight-rigidity ratio that is certainly suitable for this type of motorcycle. Speaking more generally, this type of layout has advantages in terms of standardization. You can essentially use a technical base that links the fixed-aluminum parts (that last for the life of the engine in multiple models) and modify some elements, such as the short tube, making everything more flexible.
How was the research on the tonality of the Shiver’s exhaust articulated? On this project we did one thing that at least I, personally, haven’t done before. When an exhaust is developed, there are two fundamental aspects that, at times, seem to be contrasting: guarantee satisfactory engine performance and remain within legal emission limits. In this case, we added a third objective: obtain an enjoyable sound, searching to reduce the high frequencies as much as possible and emphasize the lower ones. To accomplish this during the project (that had already been started), we mixed things up and performed simulations with computerized codes with the collaboration of our partners, in this case, the automotive Alfa Romeo company. We again looked at the overall layout of the silencer so that we could create the most voluminous, expanding anti-chamber, thus creating a silencer capable of eliminating the whistles and high frequencies, resulting in a larger voice.