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Editor: John Mortimer
Thursday, 27 August 2015
I4 engine with the performance of a V8
A research programme in the
US is pulling together various technologies to create a four-cylinder engine
with the performance of a V8.
The programme, expected to be complete
by the end of 2017 and funded by the Department of Energy, is making use of variable
compression ratio, variable valve timing, supercharging and compacted graphite
Project lead is in the hands of Envera
LLC of Los Angeles, California with Eaton Corporation acting as a joint partner
contributing relevant advanced technology R&D as a cost-share partner.
The researchers are expecting to
achieve an output of 283kW from the 2.4-litre engine which is equivalent to
118kW/litre and a brake specific fuel consumption of 234g/kWh. A torque of
440Nm is claimed.
The high efficiency VCR engine funded
by the US Department of Energy is worth $2,784,127, is due to be completed in
31 December 2017.
The engine uses variable compression
ratio from 8.5 to 1 to 18.1, variable valve timing to cater for Atkinson cycle
and various supercharging settings and advanced supercharging to create high ‘launch’
torque and pow standby losses.
The aim is to achieve a 25 per cent
improvement in fuel economy over a standard spark ignition engine and 40 per
cent better “mileage” than a V8 powered van or pickup truck without compromising
performance, based on a GMC Sierra 1500 vehicle.
Final engine assembly is penciled in to
take place in the first quarter of 2016.
The engine uses a new cooled
supercharger, Eaton’s VVA technology which was introduced on 2.5-litre GM
four-cylinder engines in MY 2014. In the Envera engine, late intake valve
closing is used to achieve the Atkinson cycle. And analysis by Eaton of its VVA
mechanism suggests the Envera cam settings for efficiency, power and torque are
attainable with the Eaton VVA mechanism.
Envera describes the VCR engine as “supercharged
to attain 360 bhp (268kW) and V8-like driving responsiveness”. It is
supercharged through a clutch
Envera puts forward two versions of its
variable compression ratio design – VCR 1.0 and VCR 2.0. In VCR 1.0 the crankshaft
is mounted in a ‘crankshaft cradle’ with the crankshaft axis and cradle axis
offset by 13.5mm.
Pivoting the cradle 32 degrees varies
the compression ratio from 8.5 to 18.6 to 1 according to Envera claims.
In the VCR 2.0 version, the research
team puts forward the notion of a pre-assembled control shaft that slides in
bearing sockets formed in the crankcase and what Envera calls a “cylinder jug”.
Each cylinder gives the appearance of being a “jug” with the pre-assembled control
shaft passing through the “handle” of the “jug”.
The control shaft is assembled by press
fitting a steel eccentric onto the steel shaft, followed by sliding on an
eccentric bronze bushing which is followed by another steel eccentric until the
camshaft is fully assembled.
Envera proposes making the cylinder block
of CGI material and mounting this in an aluminium crankcase.
Envera says: “CGI gives more robust cylinder
walls and deck than stock aluminium crankcase with steel liners”.
The researchers claim the entire VCR
2.0 engine uses a stock cylinder head with Eaton VVL and Atkinson cycle cams, a
nitrile curtain bonded to steel flanges giving a bond that os stronger than the
curtain, and finally a stock bedplate and crankshaft for the bottom end of the
Envera claims the VCR mechanism does
not add mass to the cranktrain. High engine speeds and loads are allegedly
attainable with conventional and reliable cranktrain technology.
Whether anything will come of the
research programme remains to be seen, as OEMs appear reluctant to add too much complex (and costly) technology to their gasoline engines to gain extra performance. But Eaton is likely to gain mileage,
possibly from the cooled supercharger (it is cooled by air from the
intercooler) which uses an Eaton TVS 1320 rotor set. Envera claims that “with
the new cooling technology, the supercharger can deliver higher pressures
Of course, the situation can be viewed
from the other end of the telescope: because of the higher pressures generated,
the supercharger needs to be cooled!
Whatever, GTPower power modelling
points to projected values for the engine: 234g/kWh fuel economy; 440Nm torque at
2,500 rev/min, and 118kW/litre at 6,000 rev/min. All of this while with a
200kW/litre load capacity and a “near-stock engine length”. For further details see...