Hybridization of Powertrains
In almost all vehicle segments, electrification of the powertrain is necessary to reach the fleet consumption thresholds. At the same time, due to the relatively low energy density of the battery, the introduction of pure electric vehicles has been less dynamic than it was hoped for. In particular plug-in hybrids contribute significantly to the anticipated reductions as the CO2 emissions are determined by the electric range alone or the battery size, respectively. However, plug-in hybrid powertrains demand a massive intervention into the construction of the transmission which generates additional cost for relatively small production volumes. The manufacturers are therefore called to develop concepts which can be combined with various transmissions in a modular manner and have suicient performance for various vehicle classes. One concept to solve this conflict is the compact ePGS module, developed by FEV.
In contrast to full hybrids the main advantage of the plug-in hybrid is the possibility to drive longer distances even with higher velocity purely in electric drive mode. This however requires a higher electric performance of the electric machine of 70 to 100 kW under real operating conditions. Especially with vehicles featuring a transversely mounted engine, the higher performance of the hybrid drive – including E-motor, clutch and damper – requires additional installation space.
Common Hybridization concepts
One common hybrid topology is the so-called P2 hybrid. Here the traction machine is positioned coaxially between the combustion engine and the transmission input and can be separated from the combustion engine via a clutch for pure electric driving. The Volkswagen Golf GTE or the Audio A3 e-tron, respectively, represent one option to keep the total installation length of engine, electric machine and transmission in a P2 concept constant. In these vehicles the electric engine is fully integrated into the transmission which was reduced by one gear. Another option is the layout of the electric machine axially parallel to the gear shaft . This layout allows for a neutral length, but requires an additional transmission unit in form of a gear set or a chain between gearbox input shaft and electric engine.
FEV ePGS: compact and suitable for daily use
FEV has developed a compact alternative in the form of the ePGS, which can be combined with all common transmission variants. However, the combination with an automatic transmission is the most appropriate solution. Here the converter can be eliminated completely which allows for installation space for the ePGS module. Due to the excellent controllability of the electric motor a comparable comfort can still be achieved during take-off . Since the electric motor runs in generator mode during the take-off procedure, an additional start-up element is not necessary. At the re-start of the combustion engine from the EV mode the ePGS uses the inertia of the electric machine in addition. The electric machine is decelerated with the closing of the clutch, and the combustion engine will be accelerated directly to synchronous speed. This happens almost jolt-free when the electric machine is adequately controlled. Also, no torque reserve has to be kept for the re-start of the combustion engine in the electric machine, so that the total available performance of the electric motor can be used in the EV mode. This fact reduces the installation length of the drive as well because the machine requires up to 10 kW less performance than a P2 concept with identical driving performance in the EV mode. The suitability for daily use of the ePGS has been demonstrated with several prototypes and within a series production development project. Depending on the hybrid topology and the battery size, the CO2 emissions can be reduced by 15-50 percent.