IN HYBRID MODE AT 300 AN HOUR
FROM THE ENGINE TO THE WHEELS
Integrated sportiness, ecology and efficiency: this is the promise made by the new Hybrid AMT
THE MOST DIFFICULT CHALLENGES are the best ones to beat and this is also true in the field of technology.
For example, how to combine hybrid traction (with energy recovery when braking and zero emissions) with speeds of around 300 km/h and gearshifts of a few milliseconds that are demanded by sporty supercars?
The solution has two names: Graziano and Oerlikon. The former, pure Italian, is practically a synonym for transmissions, gears and gearshifts. The Graziano name may not be very well-known to the general public but sector operators are fully aware that the company has enormous experience – it opened in 1951 – of transmissions for all types of vehicles, with an array of applications ranging from the Fiat Panda to urban buses to the legendary Aston Martin, Ferrari and Lamborghini supercars.
When it became part of the Oerlikon Group in 2007, Graziano’s expertise grew and, amongst other things, it was able to expand its knowledge of hybrid and electric traction.
Before discussing this special gearbox, a brief parenthesis about the pros and cons of the various types of gearboxes currently in use.
Layouts, differences, pros and cons
The “American-style” automatic transmission (with torque converter) is famous for its smoothness but it is also a notorious energy guzzler because it is fairly inefficient and heavy. Its bulimia is due mainly to slipping and dragging in the torque converter, the reason that more modern devices block the converter in the higher gears.
The dual-clutch transmission is very similar to the conventional type except that it has three shafts instead of the classic two. In practice, it has two parallel gearboxes, one for the even gears and one for the odd gears. The shafts have their own clutch, which means that changing gear is very fast because the next gear – third, for example – can be engaged while the previous gear is still inserted. The change is made by “opening” one clutch and “closing” the other, without interrupting the flow of torque from the engine thanks to precise control by modern electronics. However, this layout is more complicated and heavier and causes more friction than the layout with two manual shafts that is still a champion of efficiency and lightness.
The benefits of automated transmission are similar to those of manual transmission (simplicity, lightness and performance) and it is easy to understand why: it is has two shafts in which gear selection and clutch engagement are performed by servomechanisms. Its conceptual closeness to manual transmission means that it has also inherited the “gap” when the torque is interrupted to allow the gear change to be completed.
The Oerlikon Graziano proposal, which will begin road tests in a few months, is called Hybrid AMT (Automated Manual Transmission) and has an automated unit which has many of the benefits of the dual-clutch transmission without inheriting its defects thanks to the combination of an electric motor and sophisticated electronics.
One of the most important tasks that have to be performed by an electric car is to fill the ”gap” in torque that is felt when the clutch is engaged to change gear. The Hybrid AMT “knows” when the clutch will be engaged and activates the electric motor that performs the Torque Infill mechanism to make gear changing practically imperceptible.
The multi-purpose hybrid
The compact but efficient electric motor – 120 kW and 200 Nm maximum torque – is coupled to a clutch and a two-speed planetary reducer, the presence of which has well-founded technical and performance reasons.
Electric motors have a great aptitude for high revs given that the rotor is circular and can be balanced perfectly and is an advantage that is even more developed in brushless units.
This characteristic means that in many cases they can be connected to the wheels with a simple fixed reduction ratio gearbox.
If the vehicle reaches very high speeds a single reduction ratio might not be enough and this is why the Hybrid AMT places the above-mentioned two-speed planetary reducer between the electric motor (which in any case reaches 14,000 rpm) and the differential.
The electric motor coupled to the 6-speed transmission also performs other important tasks, such as recovering energy when braking and activating the KERS function, which can be achieved by storing surplus acceleration in super-capacitors for use by the electric motor when coming out of a corner.
It is interesting to know that the auxiliary shaft and reverse gears can be eliminated in an electric motor (it can easily reverse its direction of rotation), which produces zero emissions and can recharge the battery.
The strong torque generated quickly and very flexibly by the electric motor also means that it can be fully and optimally exploited by “nippy” sports engines, even with just 6-speed transmission
The electric motor also intervenes to limit thermal loads on the clutch, keeping them within acceptable limits even when used extensively.
We can also assume that the versatility of this “electric” transmission will enable various modes of operation (sport, eco, rain and so on) by selecting different command maps. Apropos of this, we should mention the contribution made by Vocis, a group company that specializes in electro-hydraulic integration, control systems and software.
The Oerlikon Graziano Hybrid AMT is not only a concentrate of technology and inventiveness, it also embodies a more evolved trend in the current automotive panorama: the all-round use of electric motors in hybrid traction. In fact they will not be used just to recover energy or keep emissions at zero levels, but will also increase the comfort and performance of ICEs by flexibly improving generation and use characteristics.