Automotive Engineering - April 2021 - 24

Optimizing hybrids

FOR COST AND
EFFICIENCY
48V Hybrid

Dimensions

ICE Variant
ICE Power Density

High Power
100kW/1

Very High Power
120kW/1

NA
45 - 55kW/1

Mid Power
80kW/1

Miller
WG-TC

Miller + VVL + VCS
VGT TC

Miller + VVL + VCS
Electric boosted TC

NA Atkinson
>40% efficiency

Miller
TC

Bore x Stroke

Common long-stroke layout

Key Dimensions
Crankcase

Bore pitch, Block height, skirt depth,
Valve diameters and positions, Cylinder head height, inlet and exhaust flanges

Casting
Machining

Components

Cylinder
Head

Table 2: Engine
component
commonality.

400V Hybrid

Mid Power
70-80kW/1

Reduced MB dia
NA Port, IEM

TC Port & Chamber, IEM

Casting

TC Port & Chamber, IEM

Machining

Crankshaft

Standard

Pin width & Oil Supply for VCS

Friction reduced
(smaller bearings)

Conrod

Standard

VCS / Variable Compression System

Lightweight

Piston

High CR

CR Variable

High CR, lightweight,
min. friction rings

Valve train module

DOHC DVVT

2-step intake VVL

DOHC DVVT

Oil pump

Mechanical

Mechanical + Electric-VCS

Mechanical

water pump

Mechanical

Electric

Electric

FEAD

Standard

Standard

Beltless - electric A/C and Vacuum

Crankcase and cranktrain
The crankcase structure must address both mechanical and thermal
loads considering gasoline engines with high power density and hence
high thermal load as well as peak firing pressure requirements of 150
bar (2,176 psi) for future knock-free combustion. Due to the significant
weight advantage, aluminum is proposed with and open deck structure.
For engine variants with variable compression ratio, the conventional connecting rod is replaced by the VCS variable conrod. In this
case, adaptation of the crankshaft (conrod journal width) is required
as well as the addition of the hydraulic control system including electric booster oil pump and pressure accumulator as shown in Figure 6.

Figure 8: The 100 kW/L performance variant of the modular
engine includes variable compression ratio and variablegeometry turbocharging.
In addition to these concept features, further measures that could be incorporated with minimal changes to the production and assembly lines, even for existing production facilities, including:
*	 electronically controlled thermostat/coolant temperature-management module
*	 second-order mass balancing shafts with roller
bearings (Figure 5)
*	 friction reducing coatings (piston rings, piston pins)
*	 camshaft roller bearings (1st bearing)
*	 switchable high performance water pump (lowfriction seal, efficiency-optimized impeller)
24 April 2021

A modular architecture with compact base cylinder head and separate cam carrier module permits the standardization of the main interfaces such as cylinder head height or camshaft positions. This approach, while also saving costs and weight, provides flexibility for the
application of different variability of the valvetrain systems (Figure 7)
without modifying the cylinder head itself. The base cylinder head
with combustion chamber, gas exchange ports and cooling jacket has
a cooled, integrated exhaust gas manifold with compact routing.
Cylinder head cooling for turbocharged engines with higher power
density requires special attention. A top-down cooling concept developed specifically for 4-valve cylinder heads features two cooling
jackets in the cylinder head, joined by efficient cooling jets between
the exhaust valves of each cylinder.
The base variants of the represented engine family possess switchable water pumps with map-controlled thermostat. A fully variable
thermo-management module allowing zero flow at low, part-load
operation is mandatory for future high efficiency concepts.
For electrification variants with 48V, an electric water pump becomes an attractive alternative, providing true on-demand flow and
AUTOMOTIVE ENGINEERING

BOTH IMAGES: AVL

Cylinder head, valvetrain and cooling



Automotive Engineering - April 2021

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