WO2009000389A1 - Method for starting an internal combustion engine - Google Patents

Abstract

The invention relates to a method for starting an internal combustion engine. The temperature of the coolant of the internal combustion engine is detected by a coolant sensor. According to the coolant temperature, the starter of the internal combustion engine is brought to a certain rotational speed during the starting of same, in order to heat the combustion chamber. After a pre-determined amount of time and/or a pre-determined number of rotations of the internal combustion engine, fuel for the external mixture formation is injected in an intake stroke of the internal combustion engine by means of an injection device. The quantity of combustion air is controlled by means of a throttle flap and the fuel-air mixture taken in is ignited in the previously heated combustion chamber of the internal combustion engine by means of an ignition device. The injection of fuel is first started with a minimum amount which is then continuously increased until it reaches a cold start amount. The method according to the invention is provided for spark-ignition internal combustion engines with external mixture formation. The fuel is completely evaporated such that wetting of the spark plug is prevented.

Description

 Method for starting an internal combustion engine

The invention relates to a method for starting an internal combustion engine according to the preamble of claim 1.

The starting ability, in particular the cold start capability, of internal combustion engines depends primarily on the vapor pressure of the fuel to be injected. Alcohol, alcohol mixed and bad as well as summer fuels have a low vapor pressure, whereby the cold start capability of the internal combustion engine is reduced due to the low evaporation quality.

A method for starting an internal combustion engine is known from the published patent application DE 42 23 680 A1. The spark-ignition internal combustion engine has a

Injection device for injecting fuel into an intake tract of the internal combustion engine. The amount of the combustion air sucked by the internal combustion engine is controlled by a throttle valve. To improve the starting capability, the coolant temperature is detected before starting the internal combustion engine and depending on the fuel and / or fuel quality, the internal combustion engine initially towed by means of a starter. By doing compression work, the combustion chambers are preheated, resulting in improved evaporation of the injected fuel in the combustion chamber. After a predetermined period of towing the engine, fuel is in the intake injected and ignited from the intake tract into the combustion chamber sucked air-fuel mixture by means of an igniter. The disadvantage here is that the injection of the fuel into the intake takes place with respect to an idling amount significantly increased cold start amount, so that the injected fuel evaporates despite the preheating of the combustion chamber by towing at low temperatures or coolant temperatures only to a small extent, thus one Spark plug of the ignition device is wetted with non-vaporized or liquid fuel and the engine can not be started.

The inventive method for starting an internal combustion engine with the characterizing features of claim 1 has the advantage that the injection of fuel is first started with a comparison with a previous idle or cold start amount lowered minimum amount, then subsequently increases the minimum amount steadily up to a cold start amount becomes.

Advantageously, a complete evaporation of the injected fuel is achieved by means of the small minimum amount, so that wetting of the spark plug with non-evaporated fuel can be avoided, thereby ensuring ignition of an ignitable fuel-air mixture in the combustion chamber.

The measures listed in the dependent claims advantageous refinements and improvements of claim 1 method for starting an internal combustion engine are possible.

To improve the process with respect to the evaporation of the injected fuel, the throttle valve is closed at the beginning of the injection. Advantageously, with the complete closing of the throttle produces a suppression in the intake tract, which improves the vaporization properties of the fuel.

To further improve the method regarding the evaporation of the injected fuel, the fuel type and / or the fuel quality is determined by means of a sensor. Advantageously, the fuel type and / or the fuel quality can be determined by an adaptive detection, so that the method for starting the internal combustion engine automatically at injecting the temperatures of unmatched fuels with too low a vapor pressure, such as summer fuels, alcohol or alcohol mixed fuels and poor fuels, and / or at very low temperatures.

Further features and combinations of features result from the description and the drawings. The embodiment of the invention is shown in simplified form in the drawings and explained in more detail in the following description.

Showing:

Fig. 1 is a comparison of the time course of the amounts of injected fuel of a conventional and the inventive method for starting an internal combustion engine and

Fig. 2 is a comparison of the time courses of the

Speeds of the internal combustion engine of a conventional and the inventive method for starting an internal combustion engine.

The method is exemplary of an internal combustion engine turned off, the injection device for external mixture formation in an intake tract in the intake tract, a throttle valve for controlling the of the internal combustion engine sucked combustion air and in a combustion chamber has an ignition device for igniting a fuel-air mixture of the internal combustion engine. To start the internal combustion engine, a starter initially tows the internal combustion engine, after which fuel is injected into the intake tract after a predetermined period of time and / or a predetermined number of revolutions. The subsequently formed in the intake tract fuel-air mixture is sucked into the combustion chamber and ignited by means of a spark plug of the ignition device in the combustion chamber. Furthermore, the internal combustion engine has a coolant sensor for detecting the coolant temperature. In particular, the combustion chamber temperature should be determined in the method according to the invention with the coolant sensor.

In the figures, the time courses of the amounts of injected fuel (Fig. 1) and the rotational speeds of the internal combustion engine (Fig. 2) of a conventional method (solid line) and a method according to the invention (dashed line) for starting an internal combustion engine, especially in cold start operation , qualitatively opposed.

In a conventional method for starting an internal combustion engine, the temperature or the coolant temperature is detected. At low temperatures or coolant temperatures when starting the internal combustion engine by means of the starter at time tθ or after a predetermined period and / or a predetermined number of revolutions of the internal combustion engine with a starter speed at time tl 'with the injection of a cold start amount of fuel started. The cold start amount is significantly increased compared to an idling amount after a start end tSE and is injected in a predetermined time period or a predetermined number of revolutions of the internal combustion engine until the time t1 (FIG. By contrast, when using a fuel suitable for low temperatures, in particular a fuel with an increased vapor pressure, a time t2 (FIG. 2) is reached before the time t 1 (FIG. 1), from which the fuel-air mixture in the combustion chamber Internal combustion engine can be ignited by means of the spark plug early and the speed of the engine increases steadily from the starter speed to the end of the startup tSE and assumes a suitable idle speed after the end of the starting process tSE. In the conventional method, the amount of injected fuel is steadily lowered until a time t3 after the time t2 until finally a suitable idling amount of fuel for operating the engine at an idling speed is achieved.

With a winter fuel (DVPE class D / Dl = 60.0 - 90.0 kPa) with a compared to a summer fuel (DVPE class A = 45.0 - 60.0 kPa) increased vapor pressure, up to temperatures T of about -30 ⁰ C (according to DIN EN 228) a sufficient to start the internal combustion engine evaporation of the injected fuel can be ensured, so that the internal combustion engine can be started by the generic method.

In the conventional generic process, when injected, the temperatures of unmatched fuels having too low a vapor pressure, such as summer fuels, alcohol or alcohol blended fuels and bad fuels, and / or at very low temperatures (T << - 15 ° C) Starting behavior of the internal combustion engine significantly deteriorated. Due to the poor quality of the vaporization of the fuels and / or the very low temperatures, only a small part of the injected fuel is vaporized, so that the larger proportion of the increased cold start amount already shortly after Start tθ or tl 'unvaporized passes into the combustion chamber and wets the spark plug with fuel. By wetting with unvaporized or liquid fuel, the spark plug can not form a spark and the fuel-air mixture can not be ignited. Even with lowering of the cold start amount at the time t3 or at the start end tSE, the engine is dragged only at the starter speed beyond the time t2 to the start end tSE or a startup stop t2 '(FIG. 1).

In contrast, in the method according to the invention for starting the internal combustion engine, no fuel is injected at a predetermined time and / or a predetermined number of revolutions of the internal combustion engine until time t4 (FIG. 1). In this period until the time t4, the internal combustion engine is brought only by the starter to a starter speed, whereby the combustion chambers of the internal combustion engine by means of mechanical friction and gas exchange, in particular the compression, are heated. Advantageously, a lubricant of the internal combustion engine is circulated and heated, so that the friction losses decrease with increasing duration or number of revolutions of the internal combustion engine. Only starting from the point in time t4 does the injection of a minimum quantity of fuel begin, in which case the minimum quantity is then steadily increased up to a time t5 to a cold start quantity (FIG. 1). Advantageously, the minimum amount of fuel is significantly smaller than the cold start amount in the conventional method and / or smaller than compared to the cold start amount smaller idle amount, so that wetting of the electrodes of the spark plug with fuel, especially at the beginning of starting the internal combustion engine, by the evaporation of the small minimum amount can be reliably avoided. Due to the steadily increasing, injected fuel quantity in a time t.sub.T (FIG. 2) lying after the time t.sub.4, the combustion chamber is located in the combustion chamber Internal combustion engine for igniting a sufficient amount of ignitable fuel-air mixture before. With the beginning of the combustion of the sucked fuel-air mixture, the temperature in the combustion chamber or the cooling water increases, so that the continuously rising from the minimum amount at the time t4 to the cold start amount at time t5 injected fuel (Fig. 1) evaporates sufficiently and can be detonated. As a result, the number of revolutions of the engine increases from the starter speed at time tβ to an idling speed continuously until after the start end tSE. The cold start amount may be maintained from the time t5 to the start end tSE, or lowered steadily from a time t7 to a suitable idle amount after the start end tSE.

To further improve the atomization or evaporation of the injected fuel, the throttle valve can be completely closed, so that in the intake tract, a negative pressure, whereby the evaporation properties of the injected fuel can be improved and the fuel evaporates more easily. As soon as it comes to ignite the fuel-air mixture, the throttle valve is transferred from its closed position back into a suitable open position. In a further advantageous embodiment of the method according to the invention, the fuel type and / or the fuel quality can be determined by means of an adaptive recognition, so that the fuel properties are present even before starting the internal combustion engine. In this case, the fuel type and / or the fuel quality are detected by a sensor and processed the measured data of the detection together with the measured data of the coolant sensor in a known control unit of the internal combustion engine, whereby the inventive method also with regard to the evaporation quality of the fuel to be injected automated can be. With the method according to the invention for starting an internal combustion engine, fuels with a low vapor pressure can be injected even at low temperatures, so that the internal combustion engine can be safely started. The inventive method is also suitable for reliably starting an internal combustion engine at very low temperatures (T << - 15 ° C).

Claims

claims 1. A method for starting an internal combustion engine, wherein the coolant temperature is detected by means of a coolant sensor, whereupon, depending on the coolant temperature, the internal combustion engine is brought to a starter speed when starting by means of starters for heating their combustion chamber, whereupon after a predetermined period of time and / or a predetermined Number of revolutions of the internal combustion engine fuel is injected for external mixture formation by means of injector in an intake stroke of the internal combustion engine, wherein the amount of combustion air is controlled by a throttle and the aspirated fuel-air mixture is ignited in the previously heated combustion chamber of the internal combustion engine by means of igniter, characterized in that the injection of fuel is first started with a minimum amount and then the minimum quantity is increased steadily up to a cold start amount. 2. The method according to claim 1, characterized in that at the beginning of the injection, the throttle valve is closed. 3. The method according to any one of claims 1 or 2, characterized in that the fuel type and / or the fuel quality is determined by means of a sensor.