DE102015202207B4 - Method for synchronization when starting a spark-ignited multi-cylinder internal combustion engine - Google Patents

Abstract

Method of synchronization when starting a spark-ignited multi-cylinder internal combustion engine with
- At least two cylinders (x ≥ 2), each cylinder comprises a connected to a crankshaft and a rotating crankshaft between a bottom dead center (UT) and a top dead center (TDC) oscillating piston and at least one first cylinder (x = 1) with a pressure sensor for metrological detection of a cylinder pressure in a cylinder-associated piston is formed with cylinder-associated combustion chamber, and
- A starting device with which the crankshaft when starting forcibly set in rotation, in which for the purpose of starting the internal combustion engine
the starting device is activated to set the crankshaft in rotation, characterized in that
- _{By the} pressure sensor, the time T _{N1u is} detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) exceeds a predetermined pressure threshold p _N , and a pressure gradient dp ₁ = p _{cyl, 1} (t ₂ ) - p _{cyl , 1} (t ₁ ) / (t ₂ -t ₁ ) is determined to verify that the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) is an increasing pressure with dp ₁ > 0 and the first cylinder is located in the compression stroke,
- The time T _{N1d is} detected by means of pressure sensor, to which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) again _{falls below} the predetermined pressure _threshold p _N , wherein a compression time T _comp = (T _N1d - T _N1u ) / 2 determined is, which requires the cylinder-related piston after exceeding the predetermined pressure threshold p _N to reach the top dead center (TDC), and
- The position of the piston of at least one cylinder x at top dead center (TDC) is determined using the compression time T _comp and the cylinder associated time T _Nxu to which the cylinder pressure p _{cyl, x} in cylinder x exceeds the predetermined pressure _threshold p _N , where at least one cylinder x is fired to take the internal combustion engine into operation.

Description

• - mindestens zwei Zylindern (x ≥ 2), wobei jeder Zylinder einen mit einer Kurbelwelle verbundenen und bei rotierender Kurbelwelle zwischen einem unteren Totpunkt (UT) und einem oberen Totpunkt (OT) oszillierenden Kolben umfasst und mindestens ein erster Zylinder (x = 1) mit einem Drucksensor zur messtechnischen Erfassung eines Zylinderdrucks in einem vom zylinderzugehörigen Kolben mit ausgebildeten zylinderzugehörigen Brennraum ausgestattet ist, und
• - einer Startvorrichtung, mit der die Kurbelwelle beim Starten zwangsweise in Drehung versetzbar ist,

bei dem zwecks Starten der Brennkraftmaschine

• - die Startvorrichtung aktiviert wird, um die Kurbelwelle in Drehung zu versetzen.

The invention relates to a method for synchronization when starting a spark-ignited multi-cylinder internal combustion engine with

• - At least two cylinders (x ≥ 2), each cylinder comprises a connected to a crankshaft and a rotating crankshaft between a bottom dead center (UT) and a top dead center (TDC) oscillating piston and at least one first cylinder (x = 1) with a pressure sensor for metrological detection of a cylinder pressure in a cylinder-associated piston is formed with cylinder-associated combustion chamber, and
• a starting device with which the crankshaft is forcibly set in rotation during starting,

in the purpose of starting the internal combustion engine

• - The starting device is activated to enable the crankshaft in rotation.

In the context of the present invention, the term internal combustion engine comprises gasoline engines, but also hybrid internal combustion engines that use a hybrid combustion process, as well as hybrid drives, which in addition to the internal combustion engine include an electric motor which can be connected to the engine, which receives power from the internal combustion engine or as switchable Auxiliary drive additionally delivers power.

The German patent application DE 41 14 797 A1 describes a method and a device for working stroke detection in a four-stroke engine. The cylinder identification at engine start is carried out using a cylinder pressure sensor, wherein the crankshaft is rotated by means of a starter. For detecting the power stroke, a threshold value for the cylinder pressure is set and used. The determination and detection of the top dead centers is carried out by measuring the maximum cylinder pressures and the referencing or assignment to the crankshaft angle.

The German disclosure documents DE 101 13 194 A1 and DE 37 211 62 A1 also describe methods for detecting the working cycles of a cylinder of an internal combustion engine or for determining the top dead centers using a metrologically detected by means of sensor cylinder pressure, this information is used in each case for a quick synchronization when starting the internal combustion engine.

The knowledge of the position of each cylinder, 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 or the initiation of the ignition of the fuel-air mixture targeted, d. H. can be done at defined crankshaft angles (KW), so as to ensure optimized combustion in the individual cylinders with the lowest possible fuel consumption and the lowest possible emissions.

Furthermore, a targeted injection or ignition is necessary in order to prevent the unwanted self-ignition of mixture parts - the so-called knocking - and to ensure a uniform possible running of the internal combustion engine, which is characterized by a minimum of torsional vibrations of the crankshaft and thus by a minimum characterized in 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 German patent application DE 40 02 228 A1 describes a method for working stroke detection in a four-stroke engine using a crankshaft sensor.

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 engine speed being the primary information generated by the crankshaft sensor.

Although the speed can basically be determined by means of camshaft sensor. The speed should, however, be determined as accurately as possible to ensure proper and optimal operation of the engine, which is why the crankshaft sensor is preferably used in the prior art, since the crankshaft rotates at twice the speed of the camshaft and thus a signal with a delivers 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.

The camshaft sensor is needed to make a statement as to whether the cylinder, ie the piston, is in the combustion cycle comprising compressing and expanding or in the charge cycle including exhaustion and suction. The crankshaft sensor determines only the position of the piston in a crank angle window of 360 ° KW. Based on the information of the crankshaft sensor, for example, the statement can be made whether the piston at top dead center ( OT ) or at bottom dead center ( UT ) stands. Since in a four-stroke internal combustion engine a working cycle consisting of compressing, expanding, pushing out and suction, 720 ° crankshaft angle (KW) includes, it is necessary to know whether a top dead center ( OT ) located at the top dead center of the combustion cycle or at top dead center of the charge cycle. This information is supplied by the camshaft sensor, so that the piston position can be determined unambiguously in the interaction of camshaft sensor and crankshaft sensor.

In practice, usually the position of only a single cylinder of the internal combustion engine, the so-called reference cylinder, 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.

The restarting and thus the synchronization of a multi-cylinder internal combustion engine is becoming increasingly important, since it is constantly trying to minimize fuel consumption in the development of internal combustion engines, and a concept for reducing fuel consumption is to shut down the internal combustion engine, if no current power requirement instead of idling it (start-stop strategy). 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 existing and inconsistent traffic lights and increased traffic volumes. Other applications provide limited level crossings and the like.

The problem with the concepts, which turn off the engine in the absence of demand to reduce fuel consumption, is the need to restart the engine. In an uncontrolled shutdown of the internal combustion engine, the crankshaft and the camshaft come to an arbitrary, unknown position to a halt. The position of the pistons in the individual cylinders of the internal combustion engine is then unknown and left to chance. However, this information is essential for an uncomplicated and as fast as possible and thus fuel-efficient restart.

So that the necessary information about the cylinder position is present at the start of the internal combustion engine, the last position of the cylinder can be stored in the engine control when switching off the engine so that a basis for the calculation of the ignition timing and the injection time is available when restarting without sensor signal.

If this stored information on the last position of the cylinder is no longer present when restarting, because it has been lost, for example, when removing the battery and the lack of power to the engine control, a method for determining the cylinder position is required. Starting procedure, in which injected and ignited uncontrollably at any time and the internal combustion engine adjusts itself with the help of the engine control within a few working cycles to the desired operating point, are in a start-stop strategy due to the high number of startup processes not expedient, there would be significant disadvantages in terms of fuel consumption and emissions behavior would be contrary to the basic objective of switching off in the absence of power requirement. In addition, each startup would take a relatively long time, d. H. need a few crankshaft revolutions for synchronization.

The method described above, 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 or rotate the camshaft and the crankshaft sufficiently fast, so that the sensors can provide a signal to the engine control, which is why a starting device is provided with which the crankshaft can be forcibly set in rotation at start or is. If a cylinder is used as the reference cylinder, as described above, at least 720 ° CA, i. H. two crankshaft revolutions needed for synchronization.

Disadvantages are, in particular, the high costs for the device for carrying out this method, namely the need to provide two sensors.

Against this background, it is the object of the present invention to provide a method for synchronization when starting a multi-cylinder internal combustion engine according to the preamble of claim 1, with which the disadvantages known in the prior art are overcome and which includes both a crankshaft sensor and a camshaft sensor dispensable.

• - mindestens zwei Zylindern (x ≥ 2), wobei jeder Zylinder einen mit einer Kurbelwelle verbundenen und bei rotierender Kurbelwelle zwischen einem unteren Totpunkt (UT) und einem oberen Totpunkt (OT) oszillierenden Kolben umfasst und mindestens ein erster Zylinder (x = 1) mit einem Drucksensor zur messtechnischen Erfassung eines Zylinderdrucks in einem vom zylinderzugehörigen Kolben mit ausgebildeten zylinderzugehörigen Brennraum ausgestattet ist, und
• - einer Startvorrichtung, mit der die Kurbelwelle beim Starten zwangsweise in Drehung versetzbar ist,

bei dem zwecks Starten der Brennkraftmaschine

• - die Startvorrichtung aktiviert wird, um die Kurbelwelle in Drehung zu versetzen,

das dadurch gekennzeichnet ist, dass

• - mittels Drucksensor der Zeitpunkt T_N1u detektiert wird, zu dem der Zylinderdruck p_cyl,1 im ersten Zylinder (x = 1) eine vorgebbare Druckschwelle p_N übersteigt, und ein Druckgradient dp₁ = p_cyl,1(t₂) - p_cyl,1(t₁) / (t₂-t₁) ermittelt wird, um zu verifizieren, dass der Zylinderdruck p_cyl,1 im ersten Zylinder (x = 1) ein ansteigender Druck mit dp > 0 ist und sich der erste Zylinder im Kompressionstakt befindet,
• - mittels Drucksensor der Zeitpunkt T_N1d detektiert wird, zu dem der Zylinderdruck p_cyl,1 im ersten Zylinder (x = 1) die vorgegebene Druckschwelle p_N wieder unterschreitet, wobei eine Kompressionszeit T_comp = (T_N1d - T_N1u) / 2 ermittelt wird, welche der zylinderzugehörige Kolben nach Übersteigen der vorgegebenen Druckschwelle p_N bis zum Erreichen des oberen Totpunktes (OT) benötigt, und
• - die Stellung des Kolbens mindestens eines Zylinders x im oberen Totpunkt (OT) ermittelt wird unter Verwendung der Kompressionszeit T_comp und dem zylinderzugehörigen Zeitpunkt T_Nxu , zu dem der Zylinderdruck p_cyl,x im Zylinder x die vorgegebene Druckschwelle p_N übersteigt, wobei dieser mindestens eine Zylinder x befeuert wird, um die Brennkraftmaschine in Betrieb zu nehmen.

This object is achieved by a method for synchronization when starting a spark-ignited multi-cylinder internal combustion engine with

• at least two cylinders (x ≥ 2), each cylinder having a crankshaft connected thereto and a crankshaft rotating between a bottom dead center (FIG. UT ) and a top dead center ( OT ) comprises oscillating piston and at least one first cylinder (x = 1) is equipped with a pressure sensor for metrological detection of a cylinder pressure in a cylinder-associated piston formed by the cylinder-associated combustion chamber, and
• a starting device with which the crankshaft is forcibly set in rotation during starting,

in the purpose of starting the internal combustion engine

• the starting device is activated in order to set the crankshaft in rotation,

which is characterized in that

• - By means of pressure sensor the time T _N1u is detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) a predefinable pressure threshold p _N is exceeded, and a pressure gradient dp ₁ = p _{cyl, 1} (t ₂ ) - p _{cyl, 1} (t ₁ ) / (t ₂ -t ₁ ) is determined to verify that the cylinder pressure p _{cyl, 1} in the first cylinder ( x = 1) is an increasing pressure with dp> 0 and the first cylinder is in the compression stroke,
• - By means of pressure sensor the time T _N1d is detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) the predetermined pressure threshold p _N again _falls below, wherein a compression time T _comp = (T _N1d - T _N1u ) / 2 is determined, which the cylinder-associated piston after exceeding the predetermined pressure _threshold p _N until reaching top dead center ( OT ), and
• - The position of the piston of at least one cylinder x at top dead center ( OT ) is determined using the compression time T _comp and the cylinder related time T _Nxu to which the cylinder pressure p _{cyl, x} in the cylinder x the predetermined pressure threshold p _N exceeds, with this at least one cylinder x is fired to put the internal combustion engine into operation.

The method according to the invention makes it possible to dispense with equipping the internal combustion engine with a crankshaft sensor and a camshaft sensor.

Rather, the internal combustion engine for carrying out the method according to the invention is equipped with at least one pressure sensor. In this case, at least one cylinder is provided with a pressure sensor with which the cylinder pressure in the combustion chamber of this cylinder can be detected by measurement. This at least one cylinder is referred to in the context of the present invention as the first cylinder or reference cylinder, even if this cylinder according to the DIN standard has a different numbering, for example, in an in-line four-cylinder engine is an internal cylinder.

In a first method step, the starting device is activated and the crankshaft forcibly rotated.

Using the pressure sensor, in a second method step, the cylinder pressure p _{cyl, 1} monitored in the first cylinder to determine if and when the first cylinder is in the compression stroke. This is a pressure threshold p _N predetermined, which exceeds only one cylinder located in the compression stroke, so that it can be safely ruled out that the first cylinder is in another stroke, ie in the expansion stroke, the exhaust stroke or in the intake stroke. The pressure threshold p _N is to be set sufficiently high according to the above objective. Exceeds the cylinder pressure p _{cyl, 1} in the first cylinder, the predetermined pressure threshold p _N will be the time T _N1u to which this happens detected and below a pressure gradient dp ₁ determined to verify that the cylinder pressure p _{cyl, 1} in the first cylinder is actually a continuously increasing pressure. At the end of the second process step, it is known whether or that the first cylinder is in the compression stroke and the time T _N1u to which the pressure in the first cylinder is the threshold pressure p _N has exceeded.

In a third method step, the time is determined by means of a pressure sensor T _N1d detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder, the predetermined pressure threshold p _N falls below again. The determined times T _N1u and T _N1d serve to calculate the so-called compression time T _comp , The compressed air from the piston during the compression stroke expands after passing through the top dead center in the subsequent expansion stroke again, for simplicity it is assumed that the pressure curve in the first cylinder is symmetrical. Half of the time (T _N1d - T _N1u ), which between the exceeding and again _{below the pressure threshold} p _N elapsed, is the time that the piston of the first cylinder after exceeding the predetermined pressure threshold p _N until reaching top dead center ( OT ), namely the compression time T _comp ,

With the help of the determined in the third step compression time T _comp can now with every cylinder x equipped with a pressure sensor, the position of the cylinder associated piston at top dead center, ie, the position of the top dead center, are determined, which is why this cylinder is fired, ie spark-ignited, to take the internal combustion engine in operation.

For this purpose, in a fourth method step by means of a pressure sensor, the cylinder-associated time T _Nxu detected, to which the cylinder pressure p _{cyl, x} in the cylinder x the predetermined pressure threshold p _N exceeds. As a result of the third process step, it is known how much time after exceeding the predetermined pressure threshold p _N must pass until the piston reaches the top dead center, simplifying it is assumed that the speed of the crankshaft n _mot is approximately constant. The latter can be readily assumed, since the crankshaft is still forcibly set in rotation by means of starting device at this time.

Which cylinder or cylinders within the next two crankshaft revolutions using the compression time T _comp put into operation, ie supplied with fuel and ignited or will depend on the specific case, namely on which cylinders are equipped with a pressure sensor. If only one single cylinder, ie the first cylinder, is equipped with a pressure sensor, this first cylinder is, as a matter of principle, the cylinder that is fired first.

If several cylinders are equipped with a pressure sensor, it is particularly advantageous to fire the cylinder which follows and is closest to the first cylinder in the firing order. In a four-cylinder inline engine whose cylinders are operated with the ignition sequence 1 - 3 - 4 - 2 and in which the first and fourth cylinders are equipped with a pressure sensor, it makes sense, for example, the first cylinder determined compression time T _comp to use to fire the fourth cylinder one crankshaft revolution later. This significantly shortens the start time, particularly as compared to a procedure in which the first cylinder makes two crankshaft revolutions later using the compression time T _comp is put into operation.

With the method according to the invention, the object underlying the invention is achieved, namely a method for synchronization when starting a spark-ignited multi-cylinder internal combustion engine according to the preamble of claim 1, with which both a crankshaft sensor and a camshaft sensor is unnecessary.

Further advantages of the method according to the invention are explained in connection with the preferred embodiments of the method which emerge from the subclaims.

Advantageous embodiments of the method, in which the speed n _mot the crankshaft is determined using two determined times T _Nxd or T _Nxu by which an elapsed time between them is measured, and an associated crank angle window which is swept over in the elapsed time period. If two cylinders are used to determine the rotational speed, the thermodynamic offset of the cylinders belonging to the determined times must be taken into account for determining the associated crank angle window, which is determined by the ignition sequence of the at least two cylinders of the internal combustion engine and the number x the cylinder results.

According to the above embodiment, timings are determined T _Nxd or T _Nxu a cylinder or two cylinders determines the speed of the crankshaft. For example, if the first cylinder of a four-cylinder in-line engine equipped with a pressure sensor, the time T _N1u ( t ₁ ) are detected, to which the cylinder pressure in the first cylinder, the pressure threshold p _N first time passes, and two crankshaft revolutions later may be the time T _N1u ( t ₂ ) are detected, to which the cylinder pressure in the first cylinder, the pressure threshold p _N for the second time, ie again exceeds.

The elapsed time period [T _N1u (t ₂ ) _{-T N1u} (t ₁ )] can be assigned to an associated crank angle window, namely 720 ° _CA. This results in the speed, because in the elapsed time, the crankshaft has rotated twice.

If several cylinders are equipped with a pressure sensor, for example in the case of a four-cylinder in-line engine whose cylinders are operated with the ignition sequence 1 - 3 - 4 - 2, the first and fourth cylinders, the time can be determined by means of a pressure sensor T _N1u ( t ₁ ) are detected, to which the cylinder pressure in the first cylinder, the pressure threshold p _N first time exceeds, and a crankshaft revolution later may be the time T _N4u ( t ₂ ) are detected, to which the cylinder pressure in the fourth cylinder, the pressure threshold p _N exceeds for the first time.

The associated crank angle window corresponds to the thermodynamic offset of the cylinders belonging to the determined times, namely the offset of the first and fourth cylinders. For the firing sequence selected above, the offset is 360 ° KW.

The accuracy in determining the speed n _mot increases when two cylinders are used and the offset of these two cylinders is chosen as small as possible or cylinders are used with the smallest possible offset. In a four-cylinder in-line engine in which each cylinder is equipped with a pressure sensor, it is particularly advantageous to use two successive cylinders in the firing order.

In a multi-cylinder internal combustion engine, in which only a first cylinder (x = 1) is equipped with a pressure sensor for metrological detection of the cylinder pressure, process variants are advantageous in which the position of the piston of the first cylinder at top dead center ( OT ) is determined as soon as this first cylinder is again in the compression stroke, using the compression time T _comp and the cylinder related time T _N1u to which the cylinder pressure p _{cyl, 1} in the first cylinder, the predetermined pressure threshold p _N exceeds, wherein this first cylinder is fired to take the internal combustion engine in operation.

The above method variant relates to internal combustion engines, in which a single cylinder is used to carry out the method, d. H. equipped with a pressure sensor. In the present case, this first cylinder is also the cylinder which is fired first and used to determine the rotational speed of the crankshaft.

Even if each cylinder of an internal combustion engine is equipped with a pressure sensor for metrological detection of the cylinder pressure, the method according to the invention for synchronization can focus on a cylinder, namely the first cylinder according to the invention, i. H. restrict.

In multi-cylinder internal combustion engines, in which each cylinder is equipped with a pressure sensor for metrological detection of the cylinder pressure, therefore, process variants may be advantageous, which are characterized in that the position of the piston of the first cylinder at top dead center ( OT ) is determined as soon as this first cylinder is again in the compression stroke, using the compression time T _comp and the cylinder related time T _N1u to which the cylinder pressure p _{cyl, 1} in the first cylinder, the predetermined pressure threshold p _N exceeds, wherein this first cylinder is fired to take the internal combustion engine in operation.

As in the previous method variant, embodiments of the method may also be advantageous in the above variant of the method, in which the rotational speed n _mot the crankshaft is determined using two determined times T _N1d or T _N1u of the first cylinder, through which an elapsed time interval is measured, and an associated crank angle window of 720 ° KW, which is swept over in the elapsed time.

Advantageously, in the embodiment in question, in which each cylinder is equipped with a pressure sensor, but also be process variants, which are characterized in that the rotational speed n _mot the crankshaft is determined using two determined times T _Nxd or T _Nxu two successive cylinders in the firing order, by which an interval of time elapsed therebetween is measured, and an associated crank angle window, which is swept in the elapsed time and corresponds to a thermodynamic offset of the two cylinders belonging to the determined times, which is the number x the cylinder determines.

In multi-cylinder internal combustion engines with four cylinders process variants are advantageous in this context, which are characterized in that the speed n _mot the crankshaft is determined using two determined times T _Nxd or T _Nxu two successive cylinders in the firing order, by which an interval of time elapsed therebetween is measured, and an associated crank angle window of 180 ° KW, which is swept over in the elapsed time period.

For the synchronization of a multi-cylinder internal combustion engine, in which each cylinder is equipped with a pressure sensor for metrological detection of the cylinder pressure, also variants of the method may be advantageous, which are characterized in that the position of the piston of the cylinder following the first cylinder in the firing order x at top dead center ( OT ) is determined using the compression time T _comp and the cylinder related time T _Nxu to which the cylinder pressure p _{cyl, x} in the cylinder x the predetermined pressure threshold p _N exceeds, with this cylinder x is fired to put the internal combustion engine into operation.

The cylinder preceding in the firing order is used to estimate the compression time T _comp to determine. The cylinder following in the firing order then becomes using this compression time T _comp and the cylinder related time T _Nxu determines the position of the piston at top dead center.

This procedure speeds up the commissioning of the internal combustion engine considerably. If each cylinder of the internal combustion engine is equipped with a pressure sensor for detecting the cylinder pressure, two consecutive cylinders in the firing sequence can be used for synchronization and be sufficient. In a four-cylinder in-line engine then already sufficient 180 ° KW for synchronization of the internal combustion engine.

Advantageous in this context are process variants in which the rotational speed n _mot the crankshaft is determined using a detected time T _Nxd or T _Nxu of the first cylinder and a determined time T _Nxd or T _Nxu of the cylinder following in the firing order x by which an interval of time elapsed therebetween is measured and an associated crank angle window which is swept in the elapsed time and the thermodynamic displacement of the first cylinder and the cylinder following in the firing order x equals, resulting from the number x the cylinder determines.

Advantageous are process variants in which the predetermined pressure threshold p _N in the context of the synchronization and the determination of the position at top dead center ( OT ) is set high with p _{N, high} ≥ 15bar.

Also advantageous are process variants in which the predetermined pressure threshold p _N in the context of the synchronization and the determination of the position at top dead center ( OT ) is set high with p _{N, high} ≥ 20bar.

The pressure threshold p _N should be set sufficiently high so that it can be safely assumed that the first cylinder is in the compression stroke.

Advantageous are process variants in which the predetermined pressure threshold p _N as part of the determination of the speed n _mot the crankshaft is lowered to p _{N, low} ≤p _{N, high} .

In this context, process variants in which the predetermined pressure threshold is advantageous are advantageous p _N as part of the determination of the speed n _mot the crankshaft p _{N, low} is lowered with 1.5bar≤p _{N, low} ≤10bar, preferably with 3.5bar≤p _{N, low} ≤7bar.

Advantageous are process variants in which a cylinder x the internal combustion engine is fired by fuel supplied to this cylinder and a spark ignition is initiated. This variant relates, for example, direct-injection gasoline engines.

• 1 schematisch die Druckverläufe p_cyl,x in den Zylindern einer fremdgezündeten Vierzylinder-Brennkraftmaschine beim Starten.

In the following the invention is based on an embodiment according to the 1 described in more detail. Hereby shows:

• 1 schematically the pressure curves p _{cyl, x} in the cylinders of a spark-ignited four-cylinder internal combustion engine when starting.

1 shows to illustrate the basic principle of the method according to the invention, the pressure gradients p _{cyl, x} in the four cylinders of a spark-ignited four-cylinder inline engine when starting.

At the in 1 each cylinder is equipped with a pressure sensor, wherein the cylinders are ignited in the firing order 1 - 3 - 4 - 2 shown four-cylinder in-line engine.

When starting the crankshaft is first forcibly rotated by means of starting device in rotation, resulting in the pressure curves shown p _{cyl, x} would result or would result. Using a pressure sensor, the cylinder pressure in the first cylinder becomes p _{cyl, 1} supervised. Will be a predetermined pressure threshold p _N exceeded, this is an indication that the first cylinder is in the compression stroke, and the time T _N1u to which the cylinder pressure p _{cyl, 1} the pressure threshold p _N reached is detected. In the following, a pressure gradient dp ₁ = p _{cyl, 1} (t ₂ ) - p _{cyl, 1} (t ₁ ) / (t ₂ -t ₁ ) is determined in order to verify that the cylinder pressure p _{cyl, 1} in the first cylinder actually a continuously increasing pressure is with dp ₁ > 0 and the first cylinder is in the compression stroke.

In a further method step, the time is determined by means of a pressure sensor T _N1d detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder, the predetermined pressure threshold p _N falls below again. The determined times T _N1u and T _N1d serve to calculate the so-called compression time T _comp , The compressed by the piston during the compression stroke air expands after passing through the top dead center ( TDC ₁ ) in the subsequent expansion stroke again, which simplifies it is assumed that the pressure curve is symmetrical and the speed n _mot is constant. Half of the time (T _N1d - T _N1u ), which between the exceeding and again _{below the pressure threshold} p _N elapsed, is the time that the piston of the first cylinder after exceeding the predetermined pressure threshold p _N until reaching top dead center ( TDC ₁ ), ie the compression time T _comp ,

Using the compression time T _comp can now with every cylinder x equipped with a pressure sensor, the position of the cylinder-associated piston at top dead center ( TDC _x ), ie the position of the top dead center, are determined.

In order to accelerate the commissioning of the internal combustion engine, ie to shorten the starting process, it is particularly advantageous here, the position of the piston of the third cylinder in the firing order following third cylinder (x = 3) at top dead center (TDC ₃ ) using the compression time T _comp and the cylinder related time T _N3u to which the cylinder pressure p _{cyl, 3} in the third cylinder, the predetermined pressure threshold p _N exceeds to determine. The third cylinder is then first fired, ie, fueled and ignited, to operate the engine.

In the present case, only half a crankshaft revolution is needed for the synchronization of the four-cylinder in-line engine, d. H. 180 ° KW.

The speed n _mot the crankshaft can be calculated using the two determined times T _N1u and T _N3u of the two successive cylinders in the firing order, ie the elapsed time (T _N3u -T _N1u ) and the associated crank angle _window of 180 ° KW, which is swept in the elapsed time period.

LIST OF REFERENCE NUMBERS

dp ₁

Pressure gradient in the first cylinder

KW

crank angle

° CA

Degree crank angle

n _mot

Speed of the crankshaft, speed of the internal combustion engine

OT

Top Dead Center

p _{cyl, x}

Cylinder pressure in cylinder x

p _{cyl, 1} (t ₁ )

Cylinder pressure in the first cylinder at the time t ₁

p _{cyl, 1} (t ₂ )

Cylinder pressure in the first cylinder at the time t ₂

p _N

predetermined or predefinable pressure threshold

T _comp

compression time

t

Time

T _N1d

Time at which the pressure in the first cylinder is the pressure threshold p _N below

T _N1u

Time at which the pressure in the first cylinder is the pressure threshold p _N exceeds

T _Nxd

Time at which the cylinder pressure in the cylinder x the pressure threshold p _N below

T _Nxu

Time at which the cylinder pressure in the cylinder x the pressure threshold p _N exceeds

TDC _x

top dead center of compression in the first cylinder x

UT

bottom dead center

x

Number of cylinders, number of the respective cylinder

Claims (14)

Method for synchronization when starting a spark ignited multi-cylinder internal combustion engine with - at least two cylinders (x ≥ 2), each cylinder comprises a connected to a crankshaft and a rotating crankshaft between a bottom dead center (UT) and a top dead center (TDC) oscillating piston and at least one first cylinder (x = 1) is equipped with a pressure sensor for metrologically detecting a cylinder pressure in a cylinder-associated combustion chamber formed by the cylinder-associated piston, and a starting device with which the crankshaft is forcibly set in rotation at start-up in the case of Starting the internal combustion engine - the starting device is activated to set the crankshaft in rotation, characterized in that - by means of pressure sensor the time T _{N1u is} detected, to which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) a predetermined pressure threshold p exceeds _N , and a pressure gradient dp ₁ = p _{cyl, 1} (t ₂ ) - p _{cyl, 1} (t ₁ ) / (t ₂ -t ₁ ) is determined to verify that the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1 ) is an increasing pressure with dp ₁ > 0 and the first cylinder is in the compression stroke, - is detected by pressure sensor the time T _N1d , at which the cylinder pressure p _{cyl, 1} in the first cylinder (x = 1) the predetermined pressure _threshold p _N again _falls below, wherein a compression time T _comp = (T _N1d - T _N1u ) / 2 is determined, which the cylinder-associated piston after exceeding the predetermined pressure threshold p _{N is} required until top dead center (TDC) is reached, and the position of the piston of at least one cylinder x at top dead center (TDC) is determined using the compression time T _comp and the cylinder- _related time T _Nxu , at which the cylinder pressure p _{cyl, x} in the cylinder x exceeds the predetermined pressure _threshold p _N , wherein this at least one cylinder x is fired to take the internal combustion engine into operation. Method according to Claim 1 characterized in that the speed n _{mot of} the crankshaft is determined using two detected times T _Nxd or T _Nxu , by which an elapsed time interval is measured, and an associated crank angle _window swept over in the elapsed time period. Method according to Claim 1 or 2 for synchronization when starting a multi-cylinder internal combustion engine, in which only a first cylinder (x = 1) is equipped with a pressure sensor for metrological detection of the cylinder pressure, characterized in that the position of the piston of the first cylinder at top dead center (TDC) is determined as soon as this first cylinder is again in the compression stroke, using the compression time T _comp and the cylinder- _related time T _N1u to which the cylinder pressure p _{cyl, 1} in the first cylinder exceeds the predetermined pressure _threshold p _N , this first cylinder is fired to put the internal combustion engine into operation. Method according to Claim 1 or 2 for synchronization when starting a multi-cylinder internal combustion engine, wherein each cylinder is equipped with a pressure sensor for metrological detection of the cylinder pressure, characterized in that the position of the piston of the first cylinder at top dead center (TDC) is determined as soon as this first cylinder again in the compression stroke, using the compression time T _comp and the cylinder- _related time T _N1u , at which the cylinder pressure p _{cyl, 1} in the first cylinder exceeds the predetermined pressure _threshold p _N , this first cylinder being fired to start up the internal combustion engine. Method according to Claim 3 or 4 characterized in that the rotational speed n _{mot of} the crankshaft is determined using two determined times T _N1d or T _{N1u of} the first cylinder, through which an elapsed time interval is measured, and an associated crank angle window of 720 ° KW, which is in the elapsed one Time span is covered. Method according to Claim 4 characterized in that the speed n _{mot of} the crankshaft is determined using two detected times T _Nxd or T _{Nxu of} two successive cylinders in the firing order, by which an elapsed time interval is measured, and an associated crank angle window, which is in the elapsed time is swept and corresponds to a thermodynamic offset of belonging to the determined times two cylinders, which is determined by the number x of cylinders. Method according to Claim 6 for synchronizing a multi-cylinder internal combustion engine with four cylinders, characterized in that the speed n _{mot of} the crankshaft is determined using two determined times T _Nxd or T _{Nxu of} two cylinders following each other in the firing order, by which an interval of time elapsed is measured, and an associated crank angle window of 180 ° KW, which is covered in the elapsed time period. Method according to Claim 1 or 2 for synchronization when starting a multi-cylinder internal combustion engine, wherein each cylinder is equipped with a pressure sensor for metrological detection of the cylinder pressure, characterized in that the position of the piston of the first cylinder in the firing order following cylinder x at top dead center (TDC) is determined using the compression time T _comp and the cylinder- _related time T _Nxu , at which the cylinder pressure p _{cyl, x} in the cylinder x exceeds the predetermined pressure _threshold p _N , this cylinder x being fired in order to start up the internal combustion engine. Method according to Claim 8 characterized in that the rotational speed n _{mot of} the crankshaft is determined using a detected time T _Nxd or T _{Nxu of} the first cylinder and a detected time T _Nxd or T _Nxu of the cylinder following in the firing order, through which an elapsed time elapsed between them and an associated crank angle window which is swept in the elapsed time and corresponds to the thermodynamic displacement of the first cylinder and the following cylinder x in the firing order, which is determined by the number x of cylinders. Method according to one of the preceding claims, characterized in that the predetermined pressure threshold p _N in the context of synchronization and determining the position at top dead center (TDC) is set high with p _{N, high} ≥ 15 bar. Method according to one of the preceding claims, characterized in that the predetermined pressure threshold p _N in the context of synchronization and the determination of the position at top dead center (TDC) is set high with p _{N, high} ≥ 20bar. Method according to Claim 10 or 11 , characterized in that the predetermined pressure threshold p _N in the context of determining the speed n _{mot of} the crankshaft to p _{N, low} ≤ p _{N, high is} lowered. Method according to Claim 12 , characterized in that the predetermined pressure threshold p _N in the context of determining the rotational speed n _{mot of} the crankshaft is reduced to p _{N, low} with 1.5bar ≤ p _{N, low} ≤ 10bar. Method according to one of the preceding claims, characterized in that a cylinder x of the internal combustion engine is fired by the fact that fuel supplied to this cylinder and a spark ignition is initiated.

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