Closed Loop Controlled Electronic Carburation System 2010-32-0115
The China III stage today represents the most stringent motorcycle emission rule in the world, mixing the European standards for tailpipe emissions with the United States rules for durability and evaporative emissions. On the other hand Chinese vehicles are based on small engines that ask for affordable, compact and simply solutions. This scenario drove Dell'Orto to develop a tailored engine management system, leading to a new generation of the existing electronic carburation system ECS, that features an oxygen sensor closed-loop control as well as a throttle contactless linear sensor.
This paper presents the development of the second generation ECS for two- and three-wheeler Chinese vehicle application. System conceptualization, components design, control strategies, experimental development and durability testing are shown for a single cylinder air cooled engine application.
According to the operating condition and the driver demand, the air to fuel ratio AFR is pre-set by means of a proportional control electrovalve. A closed coupled oxygen switching sensor then detects the resulting AFR. According to this feedback signal the electronic control unit ECU adjusts the driving signal of the AFR control electrovalve, in order to match the stoichiometric conditions. This allows to miximize the three-way catalytic converter efficiency, without using secondary air system. The closed coupled oxygen sensor doesn't need a heating circuit, since it uses the hot exhaust gases to heat up itself quickly. The oxygen sensor feed-back control is used also during the transient operation of the emission test cycle, improving the catalyst performance. Moreover the ECS closed-loop control technique allows to bias from stoichiometric AFR, enhancing the emissions, driveability and fuel economy trade-off.
Regarding the durability issue, the closed loop control self compensates engine ageing, keeping the AFR at its target level. A new linear throttle sensor, with contactless technology, assure a robust and durable behavior. The throttle sensor auto-zeroing strategy is implemented to compensate the idle deviation during engine lifetime. Embedded recovery strategies allow engine operation in case of sensors or actuators failures, flashing the malfunction indicator lamp for easy service diagnosis. Thanks to the closed-loop control, the ECS can compensate not only engine ageing but also production variability as well as different fuels, filter clogging, environmental condition, etcetera.
The aim of closed-loop ECS is to simply replace the existing carburetors and ignition modules, with no need to re-design the engine. The electronic carburetor is interchangeable with the previous one, while the ECU replaces the ignition control module. Existing flywheel generators can be used since the electric absorption of the ECU and the AFR control electrovalve is very low. Compared to a fuel injection system the ECS gives the same performance without electric fuel pump and toothed flywheel. Furthermore the ECS is compatible with kick-start as well as battery-less application, concept that can be interesting for many other small engine applications rather than two- and three- wheeler.
