Mirror Bore Coating
Reducing drag inside the engine and improving fuel consumption and power
Engine energy efficiency is a major influence on fuel consumption and engine performance. There are several factors that lower energy efficiency; one is mechanical loss. Energy efficiency drops due to the friction that arises from mechanical parts rubbing against each other. Mirror bore coating is a technology that raises energy efficiency by reducing the friction inside the engine.
Technology Functionality
Many
engines
today
use
lightweight
aluminum
materials
for
the
cylinder
block.
In
the
cylinder
block
there
is
a
cylindrical
space
inside
which
the
piston
moves
up
and
down.
However,
since
aluminum
cannot
endure
the
friction
and
heat
that
arises,
designs
also
use
a
cast
iron
cylinder
liner.
Rather
than
inserting
a
cylinder
liner,
though,
mirror
bore
coating
technology
sprays
molten
iron
onto
the
surface
of
the
cylinder
bore
and
forms
an
iron
coating
layer
on
the
walls
inside.
By
giving
this
a
mirror-like
finish,
the
drag
that
arises
when
the
piston
is
operating
can
be
reduced.
The
main
purpose
of
this
technology
is
to
reduce
drag,
though
there
are
other
merits
as
well.
Firstly,
by
removing
the
cylinder
liner
the
design
realizes
a
lighter
engine.
Moreover,
compared
to
the
roughly
2mm-thick
cylinder
liner,
the
0.2mm
mirror
bore
coating
is
extremely
thin,
making
for
better
heat
conduction.
This
results
in
better
cooling
performance
and
less
engine
knocking,
and
the
efficiency
of
the
engine
as
a
whole
is
improved.
The
leeway
gained
can
go
towards
increasing
fuel
economy
and
engine
power.
Mirror
bore
coating
is
able
to
improve
the
fundamental
performance
of
the
engine
without
the
need
for
a
special
device.
Technology Configuration
Technology for coating the inside of the cylinder bore has existed for a long time. However, the technology was very labor-intensive and so was only utilized for racing cars or high-end sports cars. Nissan was able to apply the technology for its GT-R vehicle. Through unique technology that pretreats the aluminum surface by spraying molten iron, Nissan could achieve a large reduction in the cost of the technology. This meant that the technology could be employed in mass-produced engines without an increase in cost.
(Left) A cast iron liner and conventional four-cylinder engine. (Right) A new type of four-cylinder engine with mirror bore coating.