One of the bug bears of driving in city traffic – apart from the time delays – is the often deplorable fuel consumption of stop-start driving. To help overcome this, the new Mazda3 2.0 Sport comes with iStop technology which pauses the engine (rather than stopping it), which the company says delivers increased fuel economy while reducing CO2 emissions.
In everyday city driving, when the vehicle first comes to a standstill and the driver depresses the clutch to engage neutral, the engine shuts down automatically. A green indicator lamp in the instrument cluster shows that the start-stop system has initiated engine cut-off as planned. The car doesn’t use any fuel when it’s stationary. To continue driving, the driver depresses the clutch and the engine starts up again automatically.
The Mazda system uses combustion energy to restart the engine quickly with only a little help from the starter motor in certain situations and a small amount of fuel. Mazda i-stop ‘pauses’ the engine, rather than stops it, so it is poised on ‘stand-by’ for a rapid restart in just 0.35 seconds because the combusted fuel mix is stored, ready to be ignited as soon as the driver depresses the clutch.
Initial ignition, combined with an impulse to the crankshaft, is able to restart the engine in a smooth and fuel-efficient way – twice as fast as conventional start-stop systems.
To do this, the pistons and crankshaft, valve opening and direct petrol injection are precisely tuned with one another. Mazda says that by adopting this unique approach to restart, which is says is quicker than conventional start-stop systems, i-stop also adds to a feel of quality in having a minimal impact on both noise and vibration levels.
The i-stop system is activated when the car is started – although there is a ‘deactivate’ switch on the dashboard. According to Mazda, the fully automatic system is non-intrusive and not noticeable when driving after initial start-up.
The system capitalizes on the advantages of direct-injection technology to restart the engine after stopping. Once the 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 – putting the engine in an ideal restart position. One cylinder remains in the combustion-stroke position and 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.
To ensure all aspects of the car remain functional during engine shut-off, the Mazda3 2.0 has two batteries. The main battery delivers the general energy supply, while the sub battery is used exclusively for starting the engine, this ensures that the electric system, audio, climate control and lights continue to work. Only the air conditioner is slightly interrupted during restart.
The i-stop system does not operate until the engine has warmed up sufficiently, nor does it operate on steep inclines, for safety reasons.
The all-new Mazda3 range is billed as having a “more powerful and emotional” bodystyle and comes in hatchback and saloon models.
The comapany says the 2.0 Sport delivers 16 percent fuel economy savings (mpg, combined cycle) over the outgoing model, with CO2 emissions reduced up to 19 percent.
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