injection, i-stop, aerodynamics and other measures reduce
fuel consumption by up to 14% in the combined cycle.
How about reducing the fuel budget of your compact
car to the point of driving more than 50 days a year for free, without any
voucher from anyone?
Well, if you translate the 14 percent reduction of the combined
fuel consumption (fuel consumption depends to a large extend on
driving styles and other factors) in the all-new Mazda3, with its MZR 2.0
DISI engine and i-stop system (compared to the 2.0-litre petrol engine
with intake-manifold in the previous Mazda3), and convert it then into
US$, euros or any other currency, it would mean reducing, for instance, a
1500 euros annual fuel budget to 1290 euros.
The 210 euros economy of this example amounts to
driving 51 days of the year... for free.
But first, what is this Mazda3 2.0 DISI i-stop...
After the new compact Mazda3
sedan was presented in the USA
last November, then in Europe last spring in both 4-door
sedan (saloon) and 5-door hatchback body styles, the time has come for
the Japanese brand to present its new i-stop system which makes its
European debut with the new MZR 2.0 DISI (for Direct-Injection Spark
Ignition) four cylinder petrol engine in the new Mazda3 2.0 Sport.
In the UK, the hatchback and saloon (sedan) versions of
the Mazda3 2.0 Sport are priced from £18,025 (on-the-road price,
that's including 15% VAT, number plates, delivery, 12 months road fund
licence, first registration fee, 3 year or 60,000 mile warranty and 3
years European Roadside Assistance). In France, prices (TTC, all taxes
included) start from euros 22,200 (also with 3 year or 100,000 km warranty
and 3 years European Roadside Assistance).
Start-Stop systems are getting more and more popular in
many cars. What makes Mazda's own i-stop system different from other one?
All Start-Stop systems have the key function of
cutting-off the engine to reduce fuel consumption at specific times, such
as the red traffic lights, and then to restart it automatically when the
driver wants to move on again.
However, Mazda says that the main differentiating point
of its system is that it's the world’s only start-stop system that uses combustion
energy for restart, giving a fast response to pedal input and
comparatively high potential for saving fuel.
Mazda indicates that its i-stop system restarts the MZR
2.0 DISI engine in about 0.35 seconds, which is slightly over a third of
one second, and... twice as fast as conventional start-stop systems.
The i-stop system
restarts the engine in about 0.35 seconds.
How does Mazda's i-stop make that difference?
It's partly in the i-stop itself, but in a no less
important part of the new direct-injection petrol engine itself.
The Mazda-developed system uses combustion energy to
restart the engine, with a little help by the starter motor, without using
much fuel. To accomplish this (diagrams below),
the positioning of the pistons and crankshaft, valve opening and direct
petrol injection are precisely tuned with one another, so that the support
of the electric starter motor is only required at the very beginning of
Mazda indicates that the combination of the initial
ignition with an impulse to the crankshaft is able to restart the engine
in a smooth and fuel-efficient way, and twice as fast as a conventional
Reducing fuel consumption was never the exclusivity of
one particular technology, no matter how important this technology can be.
In the case of the all-new Mazda3 2.0 DISI system, the
combination of direct petrol injection with aerodynamic optimisation of
the exterior and other measures, all help the new i-stop system reduce the
fuel consumption by 14 percent in a combined cycle, compared to the
conventional 2.0-litre petrol engine with intake-manifold injection
(indirect injection) in the previous-generation Mazda3.
with i-stop indicator lamp.
According to the manufacturer's figures, the new Mazda3
2.0 DISI i-stop gives a combined fuel consumption of 6.8 l/100
km (that makes 14.71 km per litre, 34.5 US mpg, or 41.5 UK mpg).
With the fuel tank capacity of 55 litres, this consumption average
provides an autonomy of 808 km, or 502 miles. It emits 159 g/km of
CO2 and meets Euro Stage V emission standards.
The Mazda3 2.0 DISI has a maximum power of 111
kW/151 PS (149 bhp) at 6,200 rpm and maximum torque of 191 Nm (141
lb-ft, 26.4 kg-m) at 4,500 rpm, and is paired to a six-speed manual
gearbox (More at: Mazda3
2.0 DISI specifications).
In more details, the i-stop system is activated
automatically when the car is started (it can be deactivated from a switch
on the dashboard). When active, the system is not noticeable while
When the vehicle comes to a standstill and the driver
pushes down the clutch pedal to idle the car, the engine shuts down
automatically. An indicator lamp in the driver cluster shows that the
start-stop system has initiated engine cut-off as planned. To resume
driving, the driver pushes the clutch and the engine starts up again
Mazda says that its i-stop is unique in the fact that
it needs an electric motor only during the initial phase of restart.
Once the car comes to a halt, the engine’s control
module does not cut-off the engine until the cylinder air volume of the
compression-stroke and the expansion-stroke pistons are equal (see the
"Piston Stop Position" rectangles and arrows, to the
right of each of the two opposite images). The driver does not notice
this, because it takes only a fraction of a second, and it puts the engine
in an ideal restart position.
During this process, one cylinder remains in the combustion-stroke
position. The restart process begins when fuel is injected directly
into this cylinder, atomized then ignited, which pushes the piston down (left
cylinder in the opposite image), while at the same moment, the starter
motor applies a small amount of additional momentum (bottom left circle
with the arrow in the opposite image) to the crankshaft and... the
engine is running again. Both these events together initiate an very quick
restart of the engine.
Why is the engine combustion power not used alone to
initiate the restart, without the brief electric starter motor
assistance? Mazda says that it would require a careful analysis of
piston positioning prior to each engine cut-off, as well as a complete
scavenging of unburned gases from the combustion chambers. This would mean
letting the engine continue to run a bit longer before engine cut-off,
which would cost additional fuel. Having measured how much fuel is needed
for re-ignition, Mazda's engineers preferred the solution of restarting
the engine with an electric motor.
Mazda explains that coordinating this type of
re-ignition mechanism with the electric impulse at restart requires
extremely sensitive sensors and engine control. That is why the i-stop
system monitors the piston position of each cylinder and calculates in a
fraction of a second prior to engine cut-off, which cylinders will be most
efficient for restarting later.
On the other hand, conventional systems identify which
cylinder is in combustion-stroke position after the crankshaft is turned
by an electric starter, which requires additional energy and slows down
restart. Mazda specifies that i-stop initiates engine restart immediately
with a measured restart time of 0.35 seconds, twice as fast as
Mazda adds that the use of the electric starter is
limited to a minimum, helping the engine to restart without vibration,
noise or loss in reaction time. With this new engine, Mazda claims that it
introduces the first piston engine that restarts as spontaneously as if
turning on a switch.
Adapting i-stop to an existing engine concept needed a
few modifications. Besides adapting the engine management system, it
requires a more precise crank-angle position sensor allowing to stop the
crankshaft in the ideal restart position by cutting fuel injection,
closing the throttle valve and using alternator load as a brake.
To ensure reliability and electric supply at all times,
particularly during engine shut-off and restart, the Mazda3 MZR 2.0 DISI i-stop
has two batteries. One main battery delivers the general energy supply,
while the sub battery is used exclusively for starting the engine.
When i-stop shuts off the engine, illumination, audio
system and all other electric consumers continue to work. Even the climate
control remains operating as usual, as long as the driver does not require
the full cooling capability of the system. In this case i-stop recognizes
the need to restart the engine and initiates it accordingly. The function
of all systems is not interrupted during engine restart.
Also, i-stop does not initiate engine cut-off during
the warm-up phase, to allow the exhaust-gas treatment system to reach its
optimal operating temperature quickly and minimize emissions. The same
goes for stopping on a slope. If the car is on a hill with a grade of more
than 14 percent, the engine continues to run for safety reasons.
|World first from Mazda:
The new Mazda3’s
MZR 2.0 DISI petrol engine uses a new under-floor
catalyst with single-nanotechnology, a global first.
This new Mazda technology helps reduce quantities of
precious metals to make catalytic converters for
Precious metals are used in
catalysts because they cause chemical reactions on
their surfaces that purify exhaust gasses. But
exposure to high exhaust gas heat can cause these
particles to move and combine into larger particles.
Large amounts of precious metals have always been
used to counteract this.
To solve the problem, Mazda says
it developed a new catalyst material structure that
allows precious metal particles smaller than 5
nanometres (nm) in diameter to be embedded in it.
These so-called “Single-nano
particles“ remain fixed in their original
positions when exposed to hot exhaust gasses,
instead of moving and forming larger particles.
Their surface area is preserved, even when the
particles endure natural degradation over years.
As result, Mazda says that the
three-way catalyst used on the new
Mazda3 MZR 2.0-litre petrol has up to 90 percent
less precious metals in it – from 0.55 g/litre to
only 0.15 g/ litre – while it delivers minimal
deterioration in purifying performance over a long
period of time.