DE102008046315A1 - Method for starting internal combustion engine, involves pivoting piston and spraying fuel in combustion chamber, where air is sucked from suction track by intake stroke of piston, and fuel-air-mixture is ignited at ignition point - Google Patents

Abstract

The method involves pivoting a piston and spraying fuel in a combustion chamber. The air is sucked from a suction track by an intake stroke of the piston. A fuel-air-mixture is ignited (S20) in a mixture ratio at an ignition point, where the internal combustion engine is switched directly from a starting mode to a dry run mode in which a mixture ratio is adjusted (S12).

Description

The The invention relates to a method for the sequential start of an internal combustion engine in the stop-start mode according to the preamble of claim 1.

During the so-called stop-start operation of a motor vehicle engine is stopped automatically for reasons of fuel economy of the engine at a standstill of the motor vehicle. If the driver of the motor vehicle signals a start-up request, for example by actuating an accelerator pedal or by engaging a gear, the engine is automatically restarted. Such a method for operating a motor vehicle is in the DE 196 21 950 C2 disclosed.

One Such a so-called sequential start of the engine is different from its conditions from a normal start from a cold Condition of the engine. Usually, the engine goes on the next start immediately from its starting operating condition to an idle operating condition. For direct fuel injection engines, this corresponds to idling mode a so-called homogeneous operation of the engine. So fuel is injected only during the suction stroke of a piston of the engine, so that the injected fuel optimally with the sucked Air mixed and the combustion chamber of the engine homogeneous with fuel-air mixture is filled. In such a homogeneous operation occur disadvantageously charge exchange losses. By this means Man filling losses of the combustion air or the mixture on the way to the cylinder through resistances in the intake system. So there are higher pressures necessary to the gas column to transport to the cylinder. This will be an increased Intake and Ausschiebearbeit necessary, which is the overall result the charging of the engine deteriorate and the combustion reliability to reduce.

The DE 10 2004 029 378 A1 discloses a method for starting an internal combustion engine in which a first amount of fuel is injected into the combustion chamber during the intake stroke and a second amount of fuel is injected into the combustion chamber during the compression stroke of the piston. This corresponds to the so-called homogeneous split operation, in which an inhomogeneity of the mixture distribution in the combustion chamber is consciously accepted in order to improve the combustion reliability by the second injection in the compression stroke. Again, the desired combustion reliability and fuel economy is not achieved due to the warm engine at the next start.

Of the The invention is therefore based on the object, a method for the next start to provide an internal combustion engine in the stop-start mode, which the startup behavior of the internal combustion engine in the following start improved and fuel efficiency during the next start optimized.

These The object is achieved by a method having the features of the patent claim 1 solved. The internal combustion engine to be started points at least one combustion chamber in which a piston is movable is arranged and in which fuel is injected. in this connection Air is taken from an intake during a suction stroke sucked the piston and during a compression stroke of the piston in the combustion chamber compressed. At a given ignition timing eventually becomes the resulting fuel-air mixture ignited. According to the invention, it is now provided that from a start operating state of the internal combustion engine directly is transferred to an idle operating state, in which set a lean mixture ratio in the combustion chamber becomes. By targeted leaning of the mixture, so by adjusting a lambda value> 1, Charge change losses in the idle mode after the Sequence start reduced. The fuel economy also improves idle after the stop-start sequencer start.

to further improve combustion reliability and Fuel economy at the next start sees the invention three injection times before, which are selected alternatively or together can. Possible injection times are included the suction stroke of the piston, the compression stroke of the piston and the Ignition itself. An injection during the suction stroke corresponds to the already mentioned homogeneous operation the internal combustion engine. A combination of injection during the suction stroke and the compression stroke of the piston is also already equivalent Homogeneous split or shift operation. Especially preferred However, the combination of the three injection times mentioned above selected. This will make an even bigger Inhomogeneity of the mixture distribution at the ignition point achieved. It is a so-called expanded one Homogeneous split operation, in which a last fuel quantity only injected immediately before the ignition into the combustion chamber becomes. In combination with the invention lean mixture setting results so a particularly good combustion reliability at particularly low charge cycle losses of the internal combustion engine. The combination of the three injection times thus achieves the Combustion reliability of a homogeneous operation at stoichiometric or rich mixture setting and at the same time the fuel economy of a lean mixture setting.

In a further embodiment of the invention, an exact control of the mixture ratio is provided in dependence on an engine temperature. Thus, the degree of leanness of the mixture in the idle mode can be adapted to the current circumstances. So it would be conceivable, for example, to choose a slightly richer mixture at a follow-up start with a relatively cold engine than with a follow-up start when the engine is completely warm. Further fine adjustments of the mixture ratio can be carried out according to methods known per se for operating internal combustion engines. For example, an optimization of the mixture ratio depending on the fuel quality used is known.

In A further embodiment of the invention is intended the idle mode after a predetermined period of time terminate and move to another operating state, in which is a stoichiometric or rich mixture ratio is set. This serves to transfer the operating state the internal combustion engine in its normal operation, for example at Acceleration of the vehicle.

In This further operating state are in turn two injection times alternatively or together possible. So can during the further operating state of fuel during the compression stroke or injected during the suction stroke of the piston. An injection during the suction stroke again corresponds the already mentioned homogeneous operation of the internal combustion engine. This is particularly advantageous in full load operation of the internal combustion engine use. In a partial load operation of the internal combustion engine is in contrast, the combination of the two injection times mentioned advantageous. Fuel is thus both during the suction as well as during the compression stroke of the piston in the Combustion chamber of the internal combustion engine injected. This again corresponds the already mentioned homogeneous split or shift operation. hereby is at a part load operation of the internal combustion engine advantageously a Improved efficiency achieved.

in the Following is the invention and its embodiments will be explained in more detail with reference to the drawing. The only figure shows a flow chart of an embodiment the method according to the invention.

in the Stop-start operation of a motor vehicle is at vehicle standstill For the purpose of saving fuel, the engine of the Automobile stopped automatically. Gives the driver of the motor vehicle a start request, for example by pressing a Accelerator pedal or engaging a gear, to recognize, so in the first Step S10 automatically restarts the engine. With the summarized in the Fig. Block B10 process steps At the end of the starting phase, the engine becomes idling brought. For this purpose, first in step S12 set a lean mixture ratio. The relationship between injected fuel quantity and combustion air lambda is therefore greater than 1.

The Method is further characterized by a specific injection pattern out. First, in step S14, during a Suction strokes of the piston injected a first amount of fuel. These are mixed with the air drawn in from the intake tract in the intake stroke, so that a homogeneous filling of a cylinder of the Engine with fuel-air mixture yields. Through a second injection during the compression stroke of the piston in step S16 becomes a first inhomogeneity in the distribution of the fuel-air mixture introduced in the cylinder. Up to this point, the procedure is the same the known layer or Homogensplitbetrieb with additional Emaciation of the injection ratio. After completion the compression stroke thus near the top dead center of the piston In addition, in method step S18, a third fuel quantity is added injected, so the inhomogeneity of the fuel distribution to emphasize further. Immediately after the third injection takes place in the Process step S20 the ignition of the mixture, which the piston in step S22 along its expansion stroke of a conveyed upper to the bottom dead center of the cylinder. The burned mixture is subsequently injected by the exhaust stroke in step S24 of the piston into an exhaust tract of the engine.

After completion of this complete four-stroke cycle, it is checked whether predetermined criteria for a transition of the engine are met in its normal operation. This may be the case, for example, after a predetermined time, when a predetermined engine temperature is reached, or when the driver wants to accelerate, that is to say when depressing an accelerator pedal. If the criteria are not met, the four-stroke cycle begins again with step S14, without changing the mixture ratio. If the above criteria are met, then a stoichiometric or rich mixture is set, the ratio lambda is thus ≤ 1. The engine is now in its normal operating condition, whereby an injection timing can be selected according to the engine load. If the engine is in part-load operation, a fuel-saving shift or homogeneous split operation with injection during the intake stroke and the compression stroke can be selected. In full-load operation of the engine, in contrast, to promote the power output, a homogeneous operation, ie an operation with fuel injection selected only during the suction stroke of the piston. This operating mode is maintained until the automatic stop-start system again detects idling or stoppage of the motor vehicle and from these Reasons the engine turns off. At the next sequential start, the process is started anew starting from step S10.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 19621950 C2 [0002]
• DE 102004029378 A1 [0004]

Claims (8)

A method for the sequential start in a stop-start operation of an internal combustion engine with at least one combustion chamber in which a piston is movably arranged and in which fuel is injected, wherein air is sucked from an intake during an intake stroke of the piston and compressed during a compression stroke of the piston is, and wherein at a predetermined ignition timing, a fuel-air mixture is ignited in a certain mixture ratio, characterized in that is transferred from a start operating state of the internal combustion engine directly in an idle operating state in which a lean mixture ratio is set. Method according to claim 1, characterized in that in the idling mode, fuel at the ignition timing is injected. Method according to claim 1 or 2, characterized that in the idle mode fuel during the suction stroke is injected. Method according to one of the preceding claims, characterized in that in the idling mode fuel during the compression stroke is injected. Method according to one of the preceding claims, characterized in that the mixture ratio depending a motor temperature is set. Method according to one of the preceding claims, characterized in that from the idle mode after a predetermined period in a further operating condition passed in which a stoichiometric or rich mixture ratio is set. Method according to Claim 6, characterized that at a partial load operation of the internal combustion engine in the other Operating condition Fuel during the compression stroke is injected. Method according to Claim 6, characterized that at a full load operation of the internal combustion engine in the other Operating state Fuel injected during the suction stroke becomes.