EP1679438A1 - Method for starting a combustion engine - Google Patents

Abstract

A direct-injection internal combustion engine equipped with an engine management system and having more than one cylinder in which pistons oscillate in the cylinders between a top-dead-center position and a bottom-dead-center position is started. Fuel is injected into a cylinder of an internal combustion engine before the internal combustion engine is rotated, the cylinder being in a compression phase. The engine is rotated by engaging an engine starting device after the start of fuel injection. The fuel is combusted in the cylinder while the starting device is engaged. An independent claim is included for a system for starting an internal combustion engine.

Description

The invention relates to a method for starting a equipped with an engine control direct injection internal combustion engine with a crankshaft and n cylinders, in which n piston between a top dead center (TDC) and a bottom dead center (UT) oscillate.

Due to the limited resources of fossil fuels, in particular due to the limited mineral oil reserves as a raw material for the production of fuels for the operation of internal combustion engines, the development of internal combustion engines is constantly striving to minimize fuel consumption. On the one hand, the improved i.e. more effective combustion in the forefront of the effort. On the other hand, certain strategies with regard to the basic operation of the internal combustion engine can also be effective.

One concept for improving the fuel consumption of a vehicle is, for example, to switch off the internal combustion engine - instead of continuing to run it in the leelauf - when there is no momentary power requirement. In practice, this means that at least when the vehicle is stationary, the internal combustion engine is turned off. One application is the stop-and-go traffic, as it sets, for example, in traffic jams on highways and highways. In inner-city traffic, stop-and-go traffic is no longer the exception, but the rule, as a result of the existing and non-coordinated traffic lights. Other applications provide limited level crossings and the like.

The problem with the concepts, which turn off the engine in case of lack of demand to improve fuel economy, is the need to restart the engine. Restarting causes problems among other things, because with uncontrolled stopping of the internal combustion engine, the crankshaft and the camshaft in any and in addition Unknown position come to a halt. Consequently, the position of the pistons in the individual cylinders of the internal combustion engine is also not known and left to chance. However, this information is essential for an uncomplicated and as fast as possible and thus fuel-saving restart.

In an internal combustion engine equipped with an electronically controlled ignition and / or an electronically controlled injection, markers arranged on the crankshaft and / or the camshaft provide signals about the crank angle position to sensors connected to the engine control unit for controlling ignition and injection timing. But to generate these signals, it is first necessary to put the crankshaft in rotation. At the beginning of a start, there is generally a lack of clarity about the correct injection and ignition timing, so that a run-in phase for synchronizing the crank angle position on the one hand and the engine operating parameters on the other hand is required.

The knowledge of the position of the individual cylinders d. H. the knowledge of the position of the individual pistons of an internal combustion engine is required so that the injection of the fuel and the initiation of the ignition of the fuel-air mixture in the individual cylinders targeted. can be done at defined crankshaft angles, so as to ensure optimum combustion with the lowest possible fuel consumption and the lowest possible emissions. Furthermore, a targeted injection and ignition is necessary to prevent the auto-ignition of mixture components - the so-called knocking - and a round as possible. ensure uniform running of the internal combustion engine, which is characterized by a minimum of torsional vibrations of the crankshaft and thus by a minimum of speed fluctuations. The task of controlling the injection and ignition usually takes over a motor control.

According to the prior art, the position of the individual cylinders of an internal combustion engine by means of camshaft sensor and crankshaft sensor, which is also referred to as a crank angle sensor, determined.

The fixed, arranged on the internal combustion engine crankshaft sensor detects signals from a ring or ring gear, which rotates with the crankshaft and can be provided for example on the flywheel. The signal generated by the crankshaft sensor is required by the engine controller to calculate the speed and angular position of the crankshaft. This data requires engine control to calculate ignition timing, fuel injection, and fuel quantity under all engine operating conditions, with knowledge of the crankshaft speed and angular position being the most important information generated by the crankshaft sensor.

Although the speed and angular position can basically be determined by means of camshaft sensor. However, the speed should be determined as accurately as possible to ensure proper and optimal operation of the engine, which is why the crankshaft sensor is still used for this purpose in the prior art, since the crankshaft rotates at twice the speed of the camshaft and thus a signal with a much higher resolution. A higher resolution can also be generated by means of crankshaft sensor because the arranged on the crankshaft flywheel can accommodate a variety of teeth or other signal generators due to its relatively large diameter.

In addition, the piston position with the aid of the evaluation of a crankshaft signal is much more accurately determined by means of a camshaft signal, since the camshaft via a relatively soft drive (usually belt or chain drive) is connected to the crankshaft for the purpose of driving. Therefore, the camshaft can not follow the movements of the crankshaft synchronously. There are deviations of the camshaft signal relative to the crank angle signal.

The camshaft sensor is needed to make a statement about whether the cylinder or the piston in the combustion cycle - compressing and expanding - or in the charge cycle - pushing out and sucking - located. The crankshaft sensor determines only the position of the piston in a crank angle window of 360 °. Based on the information of the crankshaft sensor, for example, the statement can be made whether the piston is at top dead center (TDC) or bottom dead center (UT). Since in a four-stroke internal combustion engine, a working cycle, consisting of compression, expansion, ejection and suction, but 720 ° crankshaft angle (KWW) includes, it is necessary to know whether a piston located at top dead center (TDC) in the so-called combustion -OT (VOT) or at top dead center during the charge cycle (LOT). This information is provided by the camshaft sensor, so that the piston position can be determined unambiguously in the interaction between camshaft sensor and crankshaft sensor.

In practice, the position of only a single cylinder of the internal combustion engine is usually determined by means of said sensors, whereby the position of the remaining cylinders is fixed. With knowledge of the position of a single cylinder, the engine controller can calculate the ignition timing and injection timing of that one cylinder. With the information stored in the engine control information regarding the firing order of the internal combustion engine, the ignition times and the injection times of the remaining cylinders then arise.

In this case, a distinction must be made between the terms injection angle and ignition angle, which are based on the position of the crankshaft, and the terms ignition timing and injection timing. For example, an injection angle could be 15 ° CA before TDC, whereas the injection timing is understood to mean that the engine controller, knowing the position of the piston and the speed, calculates the time to inject.

The method, which uses the two sensors, namely the camshaft sensor and the crankshaft sensor to determine the cylinder position, requires in principle that the internal combustion engine is in operation and the camshaft and the crankshaft rotate sufficiently fast, so that the sensors send a signal to the Motor control can deliver.

To simplify the restart, various concepts are proposed in the prior art.

The German patent application DE 42 30 616 proposes, for example, to store the angular position of the crankshaft, which is registered at shutdown, and to use for the restart, so that the appropriate ignition timing and injection times are immediately available. Should this stored information about the last position of the cylinder no longer exist when restarting, because it has been lost, for example, when removing the battery and thus lacking power to the engine control is injected and ignited according to the prior art when starting at any time, wherein the internal combustion engine adjusts itself with the help of the engine control within a few working cycles to the desired operating point. But even with existing power supply has been shown in practice that the angular position of the stationary crankshaft can be detected only very inaccurate with the conventional sensors. Problems prepares in this context, that the crankshaft at the end of the discharge process also backwards d. H. can rotate counter to their actual direction of rotation, since the compressed gases located in individual cylinders are anxious to relax.

Other approaches prefer methods for controlled shutdown and starting of the internal combustion engine. Controlled parking consists in deliberately approaching certain crank angle positions - so-called preferred positions - when the internal combustion engine is switched off. The end position of the crankshaft is no longer left to chance and more or less accurately registered, but it will be specifically brought about for the restart advantageous crank angle positions.

Another disadvantage of the proposed strategy, in which the internal combustion engine is shut down in the absence of need to improve fuel consumption, is the fact that increase the requirements of the starting device by the stop-and-go operation. On the one hand, the number of starts increases when the internal combustion engine is switched off more frequently, which is a corresponding d. H. the rugged requirements adapted robust starting device requires. On the other hand, the starting process, which can take up to one second, worsens the driving dynamics and driving comfort due to the starting noise.

In a conventional internal combustion engine having a conventional starting device such as a starter or the like capable of forcibly rotating the crankshaft, such as an electric motor, for starting the engine, the starting device is activated and the crankshaft is rotated added. In this case, the starting device is used as long as the forced drive of the crankshaft until the engine control is synchronized and the internal combustion engine by Einspritzug of fuel and ignition of the fuel-air mixture can maintain the rotation of the crankshaft without starting device.

During the entire synchronization and beyond until idling, about 700 rpm, due to the combustion processes in the individual cylinders, the starting device remains activated. In particular, the time-consuming synchronization is responsible for the long start times of conventional methods for starting an internal combustion engine.

In order to operate an internal combustion engine, in particular with regard to the increasing stop-and-go traffic, as needed d. H. in the absence of need, it is therefore necessary to simplify the reboot, i. faster and more fuel-efficient. The prior art suggests various concepts for achieving this goal.

German Offenlegungsschrift DE 198 08 472 A1 describes a method for starting a direct-injection internal combustion engine, in which the crankshaft is rotated by means of a drive at a slow speed in a position in which the piston of a cylinder in the upper Dead center (TDC) is located. As a result of one below introduced first ignition command, the crankshaft undergoes another small rotational movement, whereby the expansion stroke is initiated. During the subsequent expansion phase, fuel is injected into the at least one cylinder and ignited in the cylinder fuel-air mixture, whereby the actual starting process is initiated or initiated.

DE 198 08 472 A1 has for its object to provide a method for starting the engine, which manages with a much lower amperage. The background is that the starting of an internal combustion engine requires much higher currents than the normal drive or the normal operation of the internal combustion engine, which is why the design of an on-board battery as a compromise solution must take into account both load cases.

The initial rotation of the crankshaft and positioning of a piston at top dead center (TDC) is intended to bring the piston of a cylinder into a stable position in which the piston is driven neither by a relaxing cylinder charge nor a reverse rotation due to the reversal of an incomplete and incomplete one Compression takes place.

Deviating from DE 198 08 472 A1 proposes alternatively a method in which the piston of a cylinder is brought by turning the crankshaft by means of a drive in a position shortly after the TDC position.

The generated by a drive rotational movement of the crankshaft at the beginning of the process is not comparable to the initiated by a starter forced rotation of the crankshaft, which is already part of the actual starting process, while positioning the piston according to DE 198 08 472 A1 only as a start preparation must be considered.

At a suitable position of the stationary crankshaft, in which a piston is already in top dead center (TDC) or shortly after top dead center (TDC), then even a restart from standstill without starter is possible. This fuel is directly into the combustion chamber of the corresponding cylinder of the stationary Internal combustion engine is injected and ignited by means of a spark plug, so that the explosion of the air-fuel mixture brings the pistons in motion, whereby the crankshaft is rotated.

A similar method for starting an internal combustion engine describes the German patent application DE 100 24 438 A1. Also in this process, the crankshaft for d. H. brought before each start of an electric machine in a so-called positioning phase in a start position, this start position is characterized in that the piston is brought at least one cylinder in a position before top dead center (TDC).

In the subsequent starting phase, in the at least one cylinder, which is in the compression phase, a first combustion with reduced compression and reduced filling level is triggered, this combustion is to support the attacking in the starting phase on the crankshaft torque of the electric machine.

A disadvantage of the two described methods according to the prior art is that a positioning phase is required before each start, in which the piston of at least one cylinder is brought into a position advantageous or necessary for the actual starting process. This positioning requires additional time and prolongs the startup process considerably. As stated earlier, increasing start-up time adversely affects vehicle dynamics and ride comfort.

For this reason, DE 198 08 472 A1 even proposes to initiate the positioning, that is to say the turning of the crankshaft, by remote control of the door lock in order to avoid the loss of time caused by the positioning required before each starting operation. Due to the principle, this variant is only suitable for a restart of the internal combustion engine after leaving the vehicle and not for the inner-city stop-and-go traffic, in which a large number of restarts within a short period of time are required.

Against this background, it is the object of the present invention to provide a method for starting an internal combustion engine according to the preamble of claim 1, with which the known disadvantages of the prior art are overcome, in particular, a shortening of the start times to be achieved.

• ■ ausgehend von einer der Motorsteuerung bekannten Stop-Position der Kurbelwelle,
• ■ zum Starten der Brennkraftmaschine eine Startvorrichtung aktiviert wird, mit der die Kurbelwelle in Drehung versetzt wird, und
• ■ bei noch stillstehender Kurbelwelle mindestens in einen Zylinder, der sich in der Kompressionsphase befindet, Kraftstoff eingespritzt wird und das sich in diesem mindestens einen Zylinder befindliche Kraftstoff-Luft-Gemisch gezündet wird, wodurch die Startvorrichtung unterstützt wird.

This object is achieved by a method for starting a equipped with an engine control direct injection internal combustion engine with n cylinders in which n piston between a top dead center (TDC) and a bottom dead center (UT) oscillate, and a crankshaft, which is characterized in that

• ■ starting from a stop position of the crankshaft known to the engine control,
• ■ For starting the internal combustion engine, a starting device is activated, with which the crankshaft is rotated, and
• ■ When the crankshaft is still stationary at least in a cylinder which is in the compression phase, fuel is injected and that in this at least one cylinder located fuel-air mixture is ignited, whereby the starting device is supported.

In contrast to the methods known from the prior art, a positioning phase is dispensed with in the method according to the invention. The initiation of the starting device supporting combustion processes is carried out in the form of a fuel injection in at least one cylinder with still stationary crankshaft.

Ie. the injection takes place before activation of the starting device or at the latest simultaneously with activation of the starting device. In this case, starting from a known stop position of the crankshaft is injected into the cylinder, which is in the compression phase on the way to top dead center (TDC), wherein - if there are several cylinders in the compression phase - injected into more than one cylinder can be. This will be advantageous as well This is because the combustion gases expanding in the combustion chamber of each cylinder contribute proportionately to the drive torque exerted by the gas forces on the crankshaft, and the starting time is shortened with an increasing number of cylinders.

The omission of the positioning significantly shortens the starting process, with the elimination of the positioning and the energy required for positioning is saved, which improves the overall efficiency of the internal combustion engine. According to the invention initiated in the cylinders combustion processes and the starting device mutually support, wherein the two torques, namely on the one hand exerted by the starting device on the crankshaft torque and on the other hand, the result of the combustion processes of the gas forces on the crankshaft torque applied to a common drive torque overlay or add.

The method proposed according to the invention enables a rapid and, in particular, fuel-saving restart, as a result of which the quantities of pollutants generated during the startup procedure are also reduced. In a favorable scenario, the support of the starting process by applying an external torque by means of the starting device - for example, a starter or a starter generator - already at or shortly after the first time the top dead center (ZOT) are terminated. In a four-cylinder in-line engine, this is generally about a quarter turn of the crankshaft. By shortening the start time, the driving dynamics and in particular the ride comfort is improved due to the lower noise emissions. Since the position of the crankshaft is known at the beginning of the restart, there is clarity about the correct injection timing and ignition timing, so that an entry phase for the synchronization of the engine operating parameters is not or only to a very limited extent required. The different possibilities of determining the crankshaft position at the start of the start will be discussed below in connection with the preferred embodiments of the method.

With the method according to the invention, the object underlying the invention is thus achieved, namely to show a method with which the known disadvantages of the prior art are overcome, in particular a shortening of the start times is achieved.

Further advantageous embodiments of the method are discussed in connection with the subclaims.

• ■ die bekannte Stop-Position der Kurbelwelle eine vorbestimmbare Position ist, die nach Abschalten der Brennkraftmaschine kontrolliert angefahren wird, indem nach Abschalten der Zündung und/oder der Kraftstoffzufuhr die von der Brennkraftmaschine bis zu ihrem Stillstand abgegebene Energie kontrolliert in der Weise verbraucht wird, daß die Kurbelwelle in dieser vorbestimmbaren Stop-Position angehalten wird.

Advantageous embodiments of the method, in which

• ■ the known stop position of the crankshaft is a predeterminable position, which is started in a controlled manner after switching off the engine by the energy emitted by the internal combustion engine to its standstill is consumed in a controlled manner after switching off the ignition and / or fuel supply that the crankshaft is stopped in this predeterminable stop position.

This embodiment of the method is advantageous because the approaching of a predeterminable position, in particular a preferred position, is favorable for a restart, in particular shortens the starting time and thus significantly contributes to the solution of the object underlying the invention.

Such a method allows, for example, in internal combustion engines with direct injection even starting without starter or without activation of the starter, for which only fuel injected into the combustion chambers of the stationary engine and must be ignited by means of a spark plug, so that the explosion of the air-fuel mixture, the piston in Moving, whereby the crankshaft is rotated.

However, this type of starting or restarting requires compliance with certain boundary conditions. In particular, as already mentioned, the crankshaft must be in a specific position or in a specific crank angle range. In this respect, especially for internal combustion engines with direct injection method for controlled parking targets.

A method for the controlled shutdown of an internal combustion engine is disclosed, for example, in WO 01/48373. WO 01/48373 teaches the use of a method in which after switching off d. H. after completion of the regular operation of the internal combustion engine, an adjusting device is activated and controlled, with which the crankshaft and / or the camshaft is moved into a predefinable advantageous angular position. Both active and passive adjustment devices can be used.

As an active adjusting device can serve an electric motor which transmits a torque to the crankshaft and this rotates after switching off the internal combustion engine in the desired position, which is then maintained until the restart of the internal combustion engine.

Passive adjusting devices but can also be used according to WO 01/48373, said passive adjusting after the normal operation of the internal combustion engine exploit the still existing in the wake of the crankshaft rotary motion and influence in the way that the crankshaft in the predetermined advantageous crankshaft position to a standstill comes. As a passive adjustment means are proposed, for example, include a gas exchange valve control, which transmits a suitable braking brake torque to the engine or crankshaft, so that the delay of the shaft and thus its end position is controllable.

Compared to the active adjustment devices, the passive adjustment devices offer the advantage that their energy consumption is generally lower and also of acceptable value in terms of the underlying task - fuel-saving restart - since the passive adjustment devices do not initiate a rotational movement of the crankshaft, but inherently delay only an existing rotational movement of the crankshaft in a suitable manner.

A method for the outlet control of an internal combustion engine, in which the gas exchange valves of the internal combustion engine are used specifically for controlling the preferred positions, is described in WO 01/44636 A2. By suitable control d. H. by suitably opening and closing the gas exchange valves, influence is exerted on the combustion chamber pressure and thus on the torque exerted by the gas forces on the piston and the connecting rod on the crankshaft. However, this method requires an internal combustion engine which has an at least partially variable valve control.

However, in order to precisely approach a certain preferred position of the crankshaft, but a lot of information is necessary. In this case, all data already measured and / or derived for the usual engine control can be used, in particular the engine speed, the crankshaft angle, the engine temperature or a temperature correlated therewith, such as the coolant temperature and / or the intake pressure in the intake manifold. Experience has shown that the variables mentioned have the strongest influence on the outflow movement of the internal combustion engine or the crankshaft.

In connection with the approach of a predeterminable position, it is necessary to determine how much energy is present after switching off the internal combustion engine in the drive train and must be reduced during the discharge process.

A model for the discharge movement of the internal combustion engine is described for example in the European patent application with the application number 03101379.0. This model takes into account the actual kinetic energy of the drive train, the friction losses and / or the compression and expansion processes in the cylinders of the internal combustion engine. Such a model can be obtained on the basis of theoretical considerations and implemented in the form of mathematical equations. Preferably, however, the model is obtained entirely or at least partially empirically, ie by observing the Motor behavior and processing of the measured data obtained (eg as a lookup table).

• ■ die Zündung des in dem mindestens einen Zylinder befindlichen Kraftstoff-Luft-Gemisches im oberen Totpunkt (OT) des Kolbens oder in der sich anschließenden Expansionsphase erfolgt, nachdem der Kolben des mindestens einen Zylinders den oberen Totpunkt (OT) durchschritten hat.

Advantageous embodiments of the method, in which

• The ignition of the fuel-air mixture in the at least one cylinder is performed at top dead center (TDC) of the piston or in the subsequent expansion phase after the piston of the at least one cylinder has passed top dead center (TDC).

In this way, the piston is prevented from being moved and accelerated in the direction of the bottom dead center (UT) by the gas pressure which builds up as a result of the combustion of the fuel-air mixture, before it has passed top dead center (TDC). As a result, the crankshaft would receive a wrong sense of rotation contrary to their actual direction of rotation, which would make the starting process difficult, in particular prolonging. The initiated combustion would not support the starting device, but counteract the torque exerted by the starting device on the crankshaft, which would be counterproductive.

The proposed variant of the method is particularly advantageous if it is taken into account that the speed of the crankshaft is very low at the beginning of the starting process and the inertia of the system in motion together with the starting device may not be sufficiently large to the piston of at least one cylinder at ignition initiated before top dead center (TDC), move further towards top dead center (TDC) and beyond top dead center.

• ■ die Brennkraftmaschine mit einem Absolutwinkelsensor ausgestattet wird, der auch ohne Drehung der Kurbelwelle Informationen über die absolute Stellung der Kurbelwelle an die Motorsteuerung liefert, so daß die Stellung der stillstehenden Kurbelwelle als bekannte Stop-Position während eines Abschaltvorganges für den Neustart der Brennkraftmaschine weder erfaßt noch gespeichert zu werden braucht.

Also advantageous are embodiments of the method in which

• ■ The internal combustion engine is equipped with an absolute angle sensor, which provides information about the absolute position of the crankshaft to the engine control without rotation of the crankshaft, so that the position of the stationary crankshaft as a known stop position during a shutdown for the restart of the internal combustion engine neither detected nor needs to be stored.

The absolute angle sensor detects at the beginning of the starting process, the crankshaft position and supplies this information to the engine control, which controls starting from this then known stop position of the crankshaft, the method for starting the internal combustion engine. In this context, the term "absolute" means that the position of a piston is uniquely determined, i. its position on the circumference of the crankshaft in a crank angle window of 360 ° and also whether the piston is in the charge cycle or in the combustion loop. According to the prior art, this takes place - as already stated above - in an interaction of camshaft sensor and crankshaft sensor.

In contrast to the sensors commonly used in the prior art, which were discussed in detail in the introduction to the description, the absolute angle sensor also detects the position of the stationary crankshaft. This can be achieved, for example, by arranging on the camshaft a ring or sprocket which has non-uniform markings on its circumference, which provide information about the angular position of the camshaft and thus of the crankshaft. The target may be, for example, a sprocket, in which the distributed on the circumference of the teeth have a different width or different sized interdental spaces.

The corresponding sensor then not only picks up signals from the revolving sprocket, but sees the position of the crankshaft when the sprocket is stationary. A synchronization of injection timing and ignition timing is not required or significantly shortened. Furthermore, it is harmless if the stored in the engine control information or data on the crank angle position - lost - for example in case of power failure.

• ■ die Brennkraftmaschine mit einem Absolutwinkelsensor ausgestattet wird, der bei umlaufender Kurbelwelle bis zum Stillstand der Kurbelwelle Informationen über die absolute Stellung der Kurbelwelle an die Motorsteuerung liefert, und
• ■ die Stellung der stillstehenden Kurbelwelle von der Motorsteuerung als bekannte Stopp-Position der Kurbelwelle für den Neustart der Brennkraftmaschine gespeichert wird.

But are also advantageous embodiments of the method in which

• ■ The internal combustion engine is equipped with an absolute angle sensor that provides information about the absolute position of the crankshaft to the engine control with rotating crankshaft to the standstill of the crankshaft, and
• ■ The position of the stationary crankshaft is stored by the engine control as a known stop position of the crankshaft for the restart of the internal combustion engine.

The sensor used must be able to track or detect the position of the crankshaft to the standstill of the crankshaft. Therefore, it must also have the ability to detect reverse rotational movements, as they may result at the end of the phasing of the crankshaft. Only in this way it is ensured that the position of the crankshaft is detected with sufficient accuracy and this crank angle position is available for a later start or restart as a known stop position.

• ■ die Startvorrichtung während der ersten Expansionsphase des mindestens einen Zylinders deaktiviert wird d.h. nachdem der Kolben des mindestens einen Zylinders den oberen Totpunkt (OT) durchschritten hat und bevor der Kolben des mindestens einen Zylinders den unteren Totpunkt (UT) erreicht.

Advantageous embodiments of the method, in which

• The starting device is deactivated during the first expansion phase of the at least one cylinder, ie after the piston of the at least one cylinder has passed top dead center (TDC) and before the piston of the at least one cylinder reaches bottom dead center (TDC).

The internal combustion engine is raised in the context of this process variant after the comparatively early deactivation of the starting device solely by the combustion processes initiated in the combustion chambers of the cylinder combustion processes to the idle speed of about 700 U / min. The early deactivation of the starting device on the one hand reduces the energy consumed by the starting device and on the other hand the noise emitted by the starting device, which basically contributes to the solution of the object underlying the invention, namely to ensure a fuel-efficient, quiet and comfortable restart.

However, embodiments of the method in which the starting device remains activated for at least one revolution of the crankshaft are also advantageous. This will ensure that the boot process completes successfully.

Embodiments of the method in which the starting device is deactivated only when a predeterminable minimum rotational speed is reached are also advantageous. This variant also has the goal of ensuring a safe start of the internal combustion engine.

Also advantageous are embodiments of the method in which a starter is used as starting device. If a starter is used as starting device, the method is also suitable for retrofitting already on the market and equipped with a starter internal combustion engines or vehicles, since then only changes in the control programs of the engine control must be made to the engine when starting according to the to be able to operate the process according to the invention. If necessary, an absolute angle encoder must be provided in order to be able to determine the absolute position of the crankshaft required for the starting process.

Also advantageous are embodiments of the method in which a starter generator is used as starting device. A so-called starter generator combines the functions of a conventional starter and a generator or an alternator.

Advantageous is a combined starter generator on the one hand in terms of the stop-and-go traffic, which requires a start-stop operation and thus a correspondingly high number of restarts, and on the other hand in view of the increased demand for electrical energy as a result of the increasing vehicle comfort and thus additionally necessary electrical systems.

In generator mode, the starter-generator in the lower speed range, preferably with the interposition of a transmission with power generation sufficiently high speeds driven by the internal combustion engine and used for power generation, whereas when starting the starter-generator, the internal combustion engine with small speeds and high torque forcibly set in rotation ie drives.

For use so-called integrated starter generators (ISG) may come, but also so-called ISAD starter generators (Integrated Starter Alternator Damper) or the like. The ISAD, also referred to as a crankshaft starter generator, combines the functions of a starter, the alternator and a vibration absorber in itself. The system comprises an electric machine which engages around the crankshaft instead of the flywheel between the engine and the transmission.

• ■ die zumindest teilweise variable Ventilsteuerung in der Art gesteuert wird, daß zumindest das erste Arbeitsspiel des mindestens einen Zylinders mit verminderter Kompression durchgeführt wird.

In internal combustion engines, which are equipped with an at least partially variable valve control, embodiments of the method are advantageous in which

• ■ the at least partially variable valve control is controlled in such a way that at least the first working cycle of the at least one cylinder is carried out with reduced compression.

A reduced compression can be realized by suitable timing of the valves. For example, can be reduced by an early closing of the intake valve, the fresh cylinder charge, resulting in the compression phase to a lower pressure in the combustion chamber. Another possibility is to increase the valve overlap or to close the intake valves late with the aim of re-expelling part of the fresh intake charge without taking part in the combustion. Also, this approach leads to a reduced cylinder pressure in the compression phase during startup.

Regardless of the chosen manner, a reduced compression, ie a reduced cylinder pressure, leads to a reduction of the necessary drive torque which must be applied for a successful start of the internal combustion engine. Consequently, this procedure also leads to a fuel economy in the context of the starting process.

• ■ die Kompression des mindestens einen Zylinders während des Startvorganges in mehreren Schritten gesteigert wird.

In this case, embodiments of the method are advantageous in which

• ■ the compression of the at least one cylinder is increased during the starting process in several steps.

• Vorteilhaft sind Ausführungsformen des Verfahren, bei denen
• ■ zur Unterstützung des Startvorganges bei noch stillstehender Kurbelwelle in mindestens einen Zylinder, der sich in der Expansionsphase befindet, Kraftstoff eingespritzt wird und das sich in diesem mindestens einen Zylinder befindliche Kraftstoff-Luft-Gemisch gezündet wird, wodurch der Startvorgang unterstützt wird.

This variant of the method takes into account the fact that - a deactivated starting device vorrausgesetzt - win a rotating crankshaft and its hinged components with increasing speed and inertia and with progressive rotation of the crankshaft, the number of cylinders in which combustion processes are initiated and thus the Support startup process increases. Therefore, with increasing speed and progressive rotational movement of the crankshaft and an increasing fresh cylinder charge can be compressed without the risk of reverse rotation of the crankshaft would be feared. For this reason, a gradual increase in the compression, that is, the cylinder pressure or the fresh cylinder charge is preferable.

• Advantageous embodiments of the method, in which
• ■ To assist the starting process with still stationary crankshaft in at least one cylinder, which is in the expansion phase, fuel is injected and is ignited in this at least one cylinder located fuel-air mixture, whereby the starting process is assisted.

Fig. 1

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer ersten Ausführungsform des Verfahrens aufgetragen über °KW,

Fig. 2

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer zweiten Ausführungsform des Verfahrens aufgetragen über °KW,

Fig. 3

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer dritten Ausführungsform des Verfahrens aufgetragen über °KW,

Fig.4

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer vierten Ausführungsform des Verfahrens aufgetragen über °KW,

Fig. 5

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer fünften Ausführungsform des Verfahrens aufgetragen über °KW, und

Fig. 6

in einer chronologischen Abfolge die einzelnen Verfahrensschritte einer sechsten Ausführungsform des Verfahrens aufgetragen über °KW.

In the following the invention will be described in more detail with reference to six embodiments according to Figures 1 to 6. Hereby shows:

Fig. 1

in a chronological sequence, the individual method steps of a first embodiment of the method plotted over ° CA,

Fig. 2

in a chronological sequence the individual process steps of a second embodiment of the method plotted over ° CA,

Fig. 3

in a chronological sequence the individual process steps of a third embodiment of the method plotted over ° CA,

Figure 4

in a chronological sequence the individual process steps of a fourth embodiment of the method plotted over ° CA,

Fig. 5

in a chronological sequence the individual process steps of a fifth embodiment of the method plotted on ° KW, and

Fig. 6

in a chronological sequence, the individual process steps of a sixth embodiment of the method plotted over ° CA.

FIG. 1 shows, in a chronological sequence, the individual method steps of a first embodiment of the method plotted over ° CA.

Starting from a stop position of the crankshaft, which is known to the engine control and in which at least one cylinder of the internal combustion engine is in the compression phase, fuel is injected into these at least one cylinder while the crankshaft is still stationary. In this case, the piston of the at least one cylinder is located between the bottom dead center (UT) and the top dead center (ZOT) of the ignition.

Simultaneously with the initiation of the injection process, the starting device is activated, which is to transmit a drive torque to the crankshaft in addition to the initiated combustion processes. In the process variant shown in FIG. 1, the injection process is terminated or completed before the top dead center (ZOT) has been reached. The crank angle range in which the injection is carried out bears the reference numeral 2.

The ignition of the located in the at least one cylinder fuel-air mixture takes place in the expansion phase after the piston has passed the top dead center (ZOT). The ignition is indicated by the reference numeral 3.

The phase in which the starting device is activated and supports the starting process is indicated by the reference numeral 1. The starting device is already deactivated in the first subsequent expansion phase of the at least one cylinder. In the further course of the engine is ramped up exclusively by means of combustion processes initiated in the cylinders to the idle speed

FIG. 2 shows, in a chronological sequence, the individual method steps of a second embodiment of the method plotted over ° CA. Only the differences from the method variant shown in FIG. 1 will be discussed, for which reason reference is otherwise made to FIG. 1. The same reference numerals have been used.

In contrast to the exemplary embodiment according to FIG. 1, in the method variant according to FIG. 2, the ignition of the fuel-air mixture in the at least one cylinder takes place already in the compression phase before the piston passes through top dead center (ZOT).

FIG. 3 shows, in a chronological sequence, the individual method steps of a third embodiment of the method plotted over ° CA. Only the differences from the method variant shown in FIG. 2 will be discussed, for which reason reference is otherwise made to FIG. 2. The same reference numerals have been used.

In contrast to the exemplary embodiment according to FIG. 2, in the variant of the method according to FIG. 3 the starting device is not already deactivated in the first expansion phase of the at least one cylinder, but is further used to support the starting process. In this case, the starting device remains activated until reaching a predefinable minimum speed at which a successful starting procedure or attempt can be assumed.

FIG. 4 shows, in a chronological sequence, the individual method steps of a fourth embodiment of the method plotted over ° CA. Only the differences from the method variant shown in FIG. 1 will be discussed, for which reason reference is otherwise made to FIG. 1. The same reference numerals have been used.

In contrast to the exemplary embodiment according to FIG. 1, the injection process in the method variant according to FIG. 4 is already initiated before the starting device is activated. Ie. the two measures which are to force the crankshaft to rotate as part of the starting process, namely the activation of the starting device and the initiation of combustion processes, are not initiated simultaneously but with a time offset.

The ignition of the located in the at least one cylinder fuel-air mixture takes place at top dead center (TDC).

FIG. 5 shows, in a chronological sequence, the individual method steps of a fifth embodiment of the method plotted over ° CA. Only the differences from the method variant shown in FIG. 1 will be discussed, for which reason reference is otherwise made to FIG. 1. The same reference numerals have been used.

In contrast to the exemplary embodiment according to FIG. 1, the starting device in the method variant according to FIG. 5 is already deactivated when the top dead center (ZOT) is reached before the cylinder moves from the compression phase into the expansion phase. Ie. during the expansion phase, the crankshaft is forcibly rotated as part of the starting process solely by the initiation of combustion processes.

FIG. 6 shows, in a chronological sequence, the individual method steps of a sixth embodiment of the method plotted over ° CA. Only the differences from the method variant shown in FIG. 2 will be discussed, For that reason, reference is otherwise made to FIG. 2. The same reference numerals have been used.

In contrast to the exemplary embodiment according to FIG. 2 and analogously to the previously described method variant according to FIG. 5, the starting device in the method variant according to FIG. 6 is already deactivated when the top dead center (ZOT) is reached before the cylinder moves from the compression phase into the expansion phase. As has already been explained in more detail in connection with FIG. 5, consequently the crankshaft is forcibly rotated during the expansion phase during the starting process solely by the initiation of combustion processes.

reference numeral

1

Crank angle range in which the starting device is activated

2

Crank angle range in which the injection is performed

3

ignition

KW

crankshaft angle

LOT

top dead center during the charge change

OT

Top Dead Center

UT

bottom dead center

ZOT

top dead center during combustion or ignition

Claims (11)

A method of starting a direct injection internal combustion engine equipped with an engine control with n cylinders in which n pistons oscillate between a top dead center (TDC) and a bottom dead center (TDC) and a crankshaft,
characterized in that ■ starting from a crankshaft stop position known to the engine control, ■ For starting the internal combustion engine, a starting device is activated, with which the crankshaft is rotated, and ■ When the crankshaft is still stationary at least in a cylinder which is in the compression phase, fuel is injected and that in this at least one cylinder located fuel-air mixture is ignited, whereby the starting device is supported. Method according to claim 1,
characterized in that The known stop position of the crankshaft is a predeterminable position, which is started in a controlled manner after the internal combustion engine has been switched off, by consuming the energy emitted by the internal combustion engine to a standstill, after switching off the ignition and / or the fuel supply, in such a way that the crankshaft is stopped in this predeterminable stop position. Method according to claim 1 or 2,
characterized in that The ignition of the fuel-air mixture in the at least one cylinder is performed at top dead center (TDC) of the piston or in the subsequent expansion phase after the piston of the at least one cylinder has passed top dead center (TDC). Method according to one of the preceding claims,
characterized in that ■ The internal combustion engine is equipped with an absolute angle sensor, which provides information about the absolute position of the crankshaft to the engine control even without rotation of the crankshaft, so that the position of the stationary crankshaft as a known stop position during a shutdown for the restart of the internal combustion engine neither detected nor needs to be stored. Method according to one of claims 1 to 3,
characterized in that ■ The internal combustion engine is equipped with an absolute angle sensor that provides information about the absolute position of the crankshaft to the engine control with rotating crankshaft to the standstill of the crankshaft, and ■ The position of the stationary crankshaft is stored by the engine control as a known stop position of the crankshaft for the restart of the internal combustion engine. Method according to one of the preceding claims,
characterized in that The starting device is deactivated during the first expansion phase of the at least one cylinder, ie after the piston of the at least one cylinder has passed top dead center (TDC) and before the piston of the at least one cylinder reaches bottom dead center (TDC). Method according to one of the preceding claims,
characterized in that ■ The starter is a starter. Method according to one of claims 1 to 6,
characterized in that ■ The starter generator is used as starting device. Method according to one of the preceding claims for starting an internal combustion engine, which is equipped with an at least partially variable valve control,
characterized in that ■ the at least partially variable valve control is controlled in such a way that at least the first working cycle of the at least one cylinder is carried out with reduced compression. Method according to claim 9,
characterized in that ■ the compression of the at least one cylinder is increased during the starting process in several steps. Method according to one of the preceding claims,
characterized in that ■ To assist the starting process with still stationary crankshaft in at least one cylinder, which is in the expansion phase, fuel is injected and is ignited in this at least one cylinder located fuel-air mixture, whereby the starting process is assisted.

Images