DE10260169B4 - Method for operating an internal combustion engine - Google Patents

Abstract

A method for operating an internal combustion engine with several cylinders, with fuel being injected directly into the respective combustion chambers of the cylinders, characterized in that, in the case of partial load operation and a homogeneous fuel-air mixture with lambda equal to 1, the fuel injection is switched off for at least one cylinder and the valve actuation for the deactivated cylinder and at the same time a throttling of the internal combustion engine is reduced in such a way that, despite the deactivation of the fuel injection for at least one cylinder, a torque generated by the internal combustion engine with the remaining cylinders that have not been deactivated and into which fuel continues to be injected constantly corresponds to the currently requested torque, wherein a fresh air flow conveyed by the deactivated cylinders due to the maintenance of the valve actuation is guided and separated separately from an exhaust gas flow ejected from the non-deactivated cylinders th first units is fed to an exhaust gas aftertreatment device and that the cylinders of the internal combustion engine are arranged in a row, with every second cylinder being switched off in the ignition sequence and that a gas flow emerging from cylinders 1 and 4 ...

Description

The invention relates to a method for operating an internal combustion engine, in particular gasoline engine, in particular of a motor vehicle, with a plurality of cylinders, wherein fuel is injected directly into respective combustion chambers of the cylinder, according to the preamble of claim 1.

In petrol engines with stoichiometric combustion (lambda = 1), an amount of fresh air for combustion is adapted to the currently used fuel quantity. This means that in a part-load operation, a smaller amount of air is needed than in full-load operation. In conventional gasoline engines to a throttle valve is provided in the intake manifold, which lowers an intake manifold as far as necessary, so that the desired amount of fresh air is supplied according to the current operating state of the internal combustion engine. Since the engine must suck in the partial load operation during the intake stroke against a negative pressure, resulting in this part-load operation correspondingly large gas exchange losses.

For multi-cylinder gasoline engines with intake manifold injection, it is for example from the DE 44 21 257 A1 It is known that cylinder deactivation at part-load operation results in a fuel economy benefit. By decoupling the intake and exhaust valves from the valve train at selected cylinders and switching off the injection to these cylinders, the remaining cylinder for a constant torque on a clutch each have to apply a higher power. This means that the intake manifold pressure must rise. The engine is thus throttled by the cylinder deactivation.

Typical of an indirectly injecting gasoline engine is the formation of a wall film of fuel in the region of the intake manifold between injection valve and intake valve. If the injection is blanked out, this wall film will still give off a certain amount of fuel. This amount of fuel, which is too small to safely collapse a safe ignition in the cylinder, must not be unburned with the exhaust gas to the environment. Therefore, a shutdown of the inlet and outlet valves is required. However, this creates a great mechanical effort. Another disadvantage of this decoupling of the intake and exhaust valves of the deactivated cylinders is that these deactivated cylinders compress and expand another, namely lower, mass than the fired cylinders. The trapped air mass is additionally reduced via blow-by. This uneven ratio of the compressed masses in the compression stroke of deactivated and fired cylinders leads to an inequality in Vedichtungs- and expansion work of the cylinder, resulting in engines with few, for example, four cylinders to a high degree of turbulence, which is why the cylinder deactivation is not used in such engines.

JP 55049549 A describes a method of operating an internal combustion engine, with six cylinders, wherein fuel is directly injected into respective combustion chambers of the cylinders. In the method, the fuel supply via cylinder groups (1-3) or (4-6) is optionally carried out with a lower load, so that a partial load operation takes place via this change between the two cylinder groups.

The US 44 34 767 discloses a method wherein the cylinders of the internal combustion engine are arranged in a row and wherein in the firing order every second cylinder is switched off.

The DE 199 25 021 A1 discloses a method, wherein in an internal combustion engine for the purpose of exhaust gas control, the exhaust pipes of the cylinders 1 and 4 and 2 and 3 are interconnected.

The invention has for its object to provide a method of the type mentioned above for low-cylinder engines available.

This object is achieved by a method of o. G. Art solved with the features characterized in claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

For this purpose, it is provided according to the invention that at partial load operation and homogeneous fuel-air mixture with lambda equal to 1 at least for one cylinder, the fuel injection is switched off, maintaining the valve actuation for the deactivated cylinder while throttling the internal combustion engine is reduced such that despite switching off the fuel injection for at least one cylinder, a torque produced by the internal combustion engine with the remaining non-deactivated cylinders to which fuel continues to be injected is constantly equal to the currently requested torque, a fresh air flow delivered by the deactivated cylinders being kept separate from any one of them due to the maintenance of the valve actuation exhaust gas flow discharged separately from cylinders which have not been switched off and is supplied to separate first units of an exhaust gas aftertreatment device.

This has the advantage that, without additional mechanical effort and without the need for a shutdown function on the valve actuation, lower consumption is achieved by reduced throttling of the internal combustion engine during partial load operation due to reduced charge exchange losses, while at the same time maintaining a desired smoothness of the internal combustion engine.

For example, the separate first units of the exhaust gas aftertreatment device are separate precatalysts.

After the first units of the exhaust gas aftertreatment device, the exhaust gas flow and the fresh air flow are expediently brought together again and fed to a second unit of the exhaust gas aftertreatment device, for example a main catalytic converter.

In a particularly preferred embodiment for an internal combustion engine, in which the cylinders are arranged next to one another in a row, every second cylinder is switched off in the ignition sequence.

Further features, advantages and advantageous embodiments of the invention will become apparent from the dependent claims, as well as from the following description of the invention.

The invention is illustrated below with reference to an Otto engine with four cylinders arranged in series. However, this is merely exemplary and the invention is not limited to four-cylinder internal combustion engines. In this internal combustion engine, the firing order is usually 1-3-4-2. Both for full-load torque as well as for running quiet reasons in cylinder deactivation, the exhaust gases from the cylinders 1 and 4 on the one hand and from the cylinders 2 and 3 on the other hand each derived together, for example, in each case a "2-in-1" manifold, and one each Pre-catalyst supplied. In other words, the gas streams from the cylinders 1 and 4 are passed together and fed to a first precatalyst. Separately, the gas streams from the cylinders 2 and 3 are passed together and fed to a second precatalyst separate from the first precatalyst. This avoids that cylinders burning directly one after the other influence each other. If cylinders 1 and 4 or 2 and 3 are switched off at partial load, one of the pre-catalysts is exposed to combustion exhaust gases. The corresponding other pre-catalyst receives fresh air from the deactivated cylinders. This ensures that the exhaust gas cleaning is maintained independently of the cylinder deactivation. After the two precatalysts, the previously separate gas streams are recirculated together and fed to a common main catalyst. Since this is needed only at higher loads, where no cylinder shutdown takes place, this is not a problem.

Thus, although the deactivated cylinders feed fresh air into the exhaust system, thereby rendering the exhaust gas "lean" as a whole, the exhaust gas purification is not adversely affected by the separation of gas flows from fired and deactivated cylinders.

The cylinder deactivation in gasoline engines with direct injection thus enables economical and clean part-load operation, especially in 4-cylinder engines with "2 in 1" exhaust manifold. Since an initially mentioned wall film of fuel in the intake manifold does not occur in engines with direct injection, can be dispensed with the additional design effort for a cylinder-individual deactivation of the valve actuation. Thus, the inventive method can be implemented without mechanical change to the base engine. The deactivated cylinders inevitably compress the same amount of air as the fired cylinders, which ensures good running smoothness even on engines with few cylinders (typically 4).

Claims (4)

A method of operating an internal combustion engine, having a plurality of cylinders, wherein fuel is injected directly into respective combustion chambers of the cylinder, characterized in that at partial load operation and homogeneous fuel-air mixture with lambda equal to 1 at least for one cylinder, the fuel injection off, the valve actuation for maintaining deactivated cylinder and at the same time throttling of the internal combustion engine is reduced so that despite switching off the fuel injection for at least one cylinder from the internal combustion engine with the remaining, not switched off cylinders, in which further fuel is injected, torque is constantly equal to the currently requested torque wherein a fresh air flow delivered by the deactivated cylinders due to the maintenance of the valve actuation is separated and separated from an exhaust gas flow discharged from the non-deactivated cylinders; Each of the cylinders of the internal combustion engine is arranged in a row, wherein in the firing order every second cylinder is switched off and that one of the cylinders 1 and 4 leaving the gas stream together in a first exhaust pipe and a gas stream from the Cylinders 2 and 3 are discharged together in a separate from the first exhaust pipe second exhaust pipe. A method according to claim 1, characterized in that the separate first units of the exhaust gas aftertreatment device are separate pre-catalysts. Method according to at least one of the preceding claims, characterized in that after the first units of the exhaust gas aftertreatment device, the exhaust gas flow and the fresh air flow are brought together again and fed to a second unit of the exhaust gas aftertreatment device. A method according to claim 3, characterized in that the second unit of the exhaust gas aftertreatment device is a main catalyst.