Mazda continues to follow its ‘Sustainable Zoom-Zoom’ strategy. With the launch of a Mazda unique and highly efficient start-stop system called ‘i-stop’ in the new Mazda3 MZR 2.0 DISI, the company takes another step down this path. This innovative system paired with direct-injection petrol technology in the new Mazda3, delivers an impressive mix of driving fun and environmental compatibility.

The unique system uses combustion energy to restart the engine quickly with only a little help by the starter motor and without using much fuel. To accomplish this, the positioning of the pistons and crankshaft, valve opening and direct petrol injection are precisely tuned with one another. The support of the electric starter motor is only required at the very beginning of restart. Initial ignition combined with an impulse to the crankshaft is able to restart the engine in an extremely smooth and fuel-efficient way, and twice as fast as conventional start-stop systems.

Combined with the direct-injection petrol engine, aerodynamic optimisation of the exterior and further measures, the new i-stop system reduces the fuel consumption of the all-new Mazda3 2.0 DISI by 14 percent in a combined cycle, compared to the first-generationMazda3 with conventional 2.0-litre petrol.

The Mazda i-stop System

When Mazda developing engineers started working to renew the entire model range, they adhered to a simple logic : cars that are not moving should produce no emissions. This has resulted in the introduction of a Mazda-developed start-stop system, which makes its European debut in the new 2.0-litre DISI four cylinder engine in the new Mazda3.

The i-stop system of the new Mazda3 2.0-litre direct-injection petrol is activated automatically when the car is started. If the driver chooses, he can deactivate the system with a switch on the dashboard. The system is not noticeable when driving after initial start-up. Only when the vehicle first comes to a standstill and the driver pushes down the clutch to idle the car, does the engine shut down automatically.

A green indicator lamp in the driver cluster shows that the start-stop system has initiated engine cut-off as planned. When the car is stationary, no fuel is used. To continue driving, the driver pushes the clutch and the engine starts up again automatically.

With i-stop, Mazda is not introducing a variation of other systems currently on the market. In fact, it is a completely unique solution developed solely by Mazda that needs an electric motor only during the initial phase of restart. Basically, i-stop capitalizes on the advantages of direct-injection technology to restart the engine after stopping. And it is exactly this ability that makes Mazda’s i-stop system so unique.

Once the new Mazda3 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. 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 causes the piston to move down. At the same moment, the starter motor applies a small amount of additional momentum to the crankshaft. Both these events together initiate an extremely quick restart of the engine.

The decision to not use engine combustion power alone for restart was made after Mazda development engineers carefully measured how much fuel is needed for re-ignition. They recognized that using combustion power alone to restart would not only require a careful analysis of piston positioning prior to engine cut-off, it would also require 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. By supporting restart with an electric motor, this could be avoided.

Coordinating this type of re-ignition mechanism with the electric impulse at restart requires extremely sensitive sensors and engine control. The Mazda i-stop system monitors the piston position of each cylinder and calculates in a fraction of a second prior to engine cut-off exactly which cylinders will be most efficient for restarting later. 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. The Mazda system, on the other hand, initiates engine restart immediately with a measured restart time of just 0.35 seconds, twice as fast as conventional systems.

This is also the reason why the new Mazda3 2.0-litre DISI petrol engine is so smooth and quiet upon restart. As the use of an electric starter is limited to a minimum, the engine restarts without a loss in reaction time, without vibration and noise. With this new engine, Mazda introduces the first piston engine that restarts as spontaneously as if turning on a switch.

The new Mazda3 2.0 i-stop uses only 6.8 l/100 km of fuel (combined), 14 percent less than the conventional 2.0-litre petrol engine with intake-manifold injection in the previous-generation Mazda3. It emits 159 g/km of CO2 and meets Euro Stage V emission standards. Nevertheless, with a maximum power of 111 kW/151 PS at 6,200 rpm and maximum torque of 191 at 4,500 rpm and a six-speed manual gearbox, it delivers sporty driving performance.

Adapting i-stop to an existing engine concept required only a few modifications. Besides adapting the engine management system, it requires a unique crank-angle position sensor, which is more precise. With the help of this sensor, i-stop is able 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 reliable electric energy supply at all times, particularly during engine shut-off and restart, the Mazda3 2.0 i-stop has two batteries. The 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 is still 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.

The i-stop system does not initiate engine cut-off during the warm-up phase, helping 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.