Method for controlling charge adjustment devices

The invention relates to a control process for charge flow management devices mainly as fitted in direct-injection internal combustion engines wherein such charge flow management devices are arranged in intake ports.

In direct-injection internal combustion engines, but also in port-injection type internal combustion engines having intake ports into which no fuel is injected, undesirable fouling of the intake valves will occur due to accumulations of unburnt fuel, combustion gas constituents, and lubricating oil residue. Such fouling is at least in part attributable to the charge flow management devices which, depending on the engine's operating regime, restrict the fresh-air intake flow or, where multiple intake ports are provided per cyclinder, close off individual ports either partially or fully for the purpose of permitting or optimizing a combustion process in the combustion chamber.

As the engine's operating regime changes from power output to overrun, the charge flow management devices are placed into their idle position in which they cause the fresh-air supply to be almost fully shut off. For an intake valve arranged in an intake port equipped with a charge flow management device, this constitutes a highly unfavorable operating condition. Upon a load alteration from power output to overrunning, the hot intake valve will be suddenly cut off from its fresh air supply and will cool down but slowly as a result. With the engine on overrun, this throttling effect produces a negative pressure in intake ports equipped with charge flow management devices. This causes more lubricating oil to be drawn into the engine via the valve guides, resulting in increased fouling on the hot valves. Due to the backflow of combustion gases that takes place during the last firing cycle, unburnt fuel, combustion gas constituents and lubricating oil residue will be present in the intake ports. As the charge flow management device closes, this residue is trapped in the intake port for an extended period of time, causing additional fouling.

It is the object of the invention, therefore, to provide a control method for charge flow management devices mainly as fitted in direct-injection internal combustion engines that reduces the amount of intake valve fouling due to unburnt fuels, combustion cast constituents, and lubricating oil residue.

According to the invention this is achieved by keeping the charge flow management devices open when the internal combustion engine operates on overrun. As soon as the engine enters into overrun mode, all charge flow management devices are opened and fresh air can flow into the combustion chamber without restriction. This takes place regardless of whether the engine was previously running at full, partial or idle load.

This process can be applied to all internal combustion engines comprising intake ports with charge flow management devices and wherein all or some of the intake ports merely serve to take in air without any admixture of fuel.

This control method has the following benefits from the viewpoint of preventing intake valve fouling:

All intake valves will cool down very quickly when the engine is on overrun, and will therefore quickly reach a favorable “low-temperature range” in which the valves are cleaned by the lubricating oil passing along their surface, so that fouling will be prevented.

Since there is no flow restriction, the build-up of negative pressure in intake ports fitted with charge flow management devices is eliminated. As a result, less lubricating oil will be drawn into the cylinder via the valve guides and can contribute to additional fouling when the valves are hot than would be the case with the charge flow management device closed.

Since the charge flow management is open, the unburnt fuel, combustion gas constituents and lubricating oil residue forced back into the intake port will not remain trapped therein for an extended period of time and can therefore not cause additional fouling.