Automotive Engineering - April 2021 - 23

COVER STORY

be significantly tightened. For the next step towards 50% brake thermal efficiency, a new generation of technology packages is in development, including pre-chamber spark ignition and ultra-high-pressure
injection. The aim is to allow high compression ratio in the whole map
while suppressing knock. One approach to achieve that is a reduction
of the charge-air temperature close to ambient temperature, by use of
a two-stage e-supercharger with dual intercooling.
A modular charging concept including electrified components such
as e-superchargers and e-turbos enables optimized use of electric
energy in the hybrid powertrain. For acceleration utilizing the thermodynamic amplification (electric energy is utilized to compress air
and/or spin up the TC) rather than direct electric power, the battery
can be reduced in size without loss of vehicle performance.
With an electrified powertrain supplementing engine torque at low
engine speed, the exhaust-gas turbocharger systems can be rematched with focus on the high-speed area. This extends the potential application of each charging technology towards higher specific
power, leading to a more cost-effective overall package.
Table 1 shows variants in each power class based on current-production TGDI technology base and the potential for efficiency improvement with application of the above technologies. By applying
the above-mentioned technology elements, the full range of ICE
power can be covered by an engine family based on a turbocharged
in-line 4-cylinder with about 2.0L displacement and specific power
ratings from 70 to 120kW/L.

Modular ICE technology packages
An ICE engine family with modular components is proposed to avoid developing a dedicated base engine for
each application. As well as a significant cost advantage
due to higher component production volumes, this approach gives high flexibility considering uncertain future
volume distributions. This approach has been proposed
before and implemented by several OEMs in production. The concept is now adapted and extended to include variation based on the degree of electrification.
The basic engine architecture has been laid out from the
outset to minimize mechanical losses of the base engine:
*	 long stroke (Stroke/Bore > 1.2)
*	 crankshaft offset 12~15% of stroke
*	 long conrod (L/r > 3.3)
*	 minimization of bore distortion by structural
*	 optimization and shape honing
*	 valvetrain with low friction (RFF+HLA)
*	 minimized diameter of main bearings
*	 demand-controlled piston cooling jets
*	 split cooling (separate cooling circuits for cylinder
head and block)
*	 chain-driven oil pump, pressure and volume flow is
demand-controlled

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April 2021 23


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Automotive Engineering - April 2021

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