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Faster than conventional start-stop technology
MZR 2.0 DISI joins the new Mazda3 compact family
With direct fuel injection and exclusive "i-stop" system

2010 Mazda3, driving shot with two graphic inserts.

Direct injection, i-stop, aerodynamics and other measures reduce fuel consumption by up to 14% in the combined cycle.

APN

27 June 2009.

 i-Stop - brief
 i-Stop - economy
 i-Stop - details

 2.0 DISI specs

 Modifications

 Batteries

 Single-nanotech

 Main dimensions

 Mazda3 EU specs

 Mazda3 US specs

 

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... about?

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).

  i-Stop: briefly

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.

New Mazda3 5-door at red traffic light, rear shot.

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 the restart.

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 start-stop system.

  Power / Economy

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.

Driver cluster with i-stop indicator lamp.

Driver cluster 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).

  How it works

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 driving.

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 automatically.

Mazda3 i-stop graphic: engine STOP phase.

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.

Mazda3 i-stop graphic: engine START phase.

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 conventional systems.

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.

  Modifications

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.

  Batteries

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: Single-nanotechnology catalyst

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 petrol engines.

Mazda Single-nanotechnology catalyst graphic.

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.

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