Mazda Motors has just released details about its new and more efficient variation on the conventional idle-shutoff system that it claims can boost fuel economy by up to 10 percent in urban driving modes where stop-and-go traffic conditions dominate. Due to roll out in production vehicles starting in 2009, the Smart Idle Stop System (SISS) is designed to operate on direct-injection engines. Unlike conventional setups that use the starter motor to bring the engine back to life, the "enlightened" SISS accomplishes the task by combustion.
Several elements contribute to making the SISS package function properly. First of all, it's capable of terminating the engine's rotation process on shutdown so that the pistons stop in a precise orientation that creates a proper amount of air volume in each cylinder. Immediately prior to restart, the SISS indexes each of the piston positions and then injects an appropriate fuel charge. At that point, the spark plug fires and the force generated by the combustion process restarts the engine. As an added benefit, SISS manages to complete the stop-to-start transition in 0.35 second, about half the time of a traditional idle-shutdown design that relies on the starter motor. No word yet as to when or even if SISS will be introduced to the American market, but Mazda's extensive use of direct-injection engine designs makes it fairly likely this innovation will become part of the firm's overall mileage-maxxing toolkit here at some point.