Automotive Engineering - April 2021 - 20

Optimizing hybrids

COVER STORY

FOR COST AND
EFFICIENCY

Table 1: Power
targets of the
modular ICE
variants with and
without variable
compression-ratio
technology.

Powertrain and ICE power range

20 April 2021

PO 12 kW 48V
Belt Starter-Generator
replacing alternator

P2 20 kW 48V
Module between ICE and Transmission
with parallel-axis e-Motor and
reduction gearbox [8]

P2 20 kW 48V
Direct Hybrid Transmission with
parallel-axis E-Motor integrated
in Transmission [9]

Figure 3: 48V electrification locations: P0, P2 and Hybrid Transmission.
140

VCR: Variable Compression Ratio
VVL: Variable Valve Lift
IEM: integrated exhaust manifold
UHPI: ultra high pressure injection

[kW/1]
120

Maximum specific power
at stolchlometric AFR

100

80

60

40
240
35% 36%

[g/kWh]
230
37%

220

210

38% 39% 40% 41%

42%

200

190

180

170

43% 44%

45%

46% 47%

48% 49%

160
50%

Best point specific consumption and Brake Thermal efficiency

Figure 4: Tradeoff between engine brake thermal efficiency and specific power.

Engine tech packages for high combustion
and performance
Future emission requirements including more highly-loaded emissions certification cycles can be achieved with an aftertreatment
package consisting of a 3-way catalyst for gaseous emissions and a
AUTOMOTIVE ENGINEERING

ALL IMAGES: AVL

A boundary condition for electrified powertrain variants is the achievement of at least the same vehicle
performance compared to the conventional versions,
but at lower fuel consumption. Typically, the demanded power for this segment is in the range from 140 kW
up to 240 kW for the main vehicle variants, though
specific top-performance versions may be higher.
The increasing electrification range (Figure 2) will
include 48V-P0 micro-hybrids, more or less replacing
the 12V systems as the new standard, as well as parallel hybrids in 48V-P2 or P4 configurations, high-voltage full hybrids both without and increasingly with
plug-in functionality and finally, serial hybrids.
The first level of hybrid system (P0 position) uses a
48V belt starter-generator (BSG) system, substituting
the more powerful alternator for the 12V machine, in
the same belt-drive layout. The 48V supply is a prerequisite for the e-supercharger, respectively e-turbocharger, used in the higher-performance engine variants, as well as a limited electric driving range. The
electric power is around 12kW.
The next level in powertrain electrification is a P2
configuration, remaining at the 48V level and delivering around 20kW electric power. The arrangement as
shown in Figure 3 with the e-machine packaged parallel to the gearbox allows the integration in transverse
installations, usually very sensitive regarding overall
powertrain length.
The configurations with further increased electrical
performance support extended recuperation capability, torque assist, load-point shifting of the ICE and full
electric drive. Integrating the e-motor into the transmission architecture allows integration of electrical
and mechanical functions in P2 or P2.5 architectures
(Figure 3, right). A modular hybrid transmission family
( " Direct Hybrid Transmission " ), allowing the integration of 48V as well as high-voltage e-motors is the
basis for the 400V variants. The power of the electric
motor is increased to around 120kW.



Automotive Engineering - April 2021

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