EP2942512A2 - Method for determining a cranking position of a combustion engine - Google Patents

Abstract

The invention relates to a method for determining a crankshaft position of an internal combustion engine, wherein a speed curve of the crankshaft over a time is detected; wherein the crankshaft position (OT *) is determined by adjusting the speed curve with a known speed curve of a working cycle of the internal combustion engine; wherein the known speed curve has a characteristic of the crankshaft position section; wherein a signal of an electric machine coupled to the crankshaft is detected; wherein a value occurring at least once per cycle (OT ', OT ", OT"') of the signal in the determination of the crankshaft position is taken into account; and wherein the determination of the crankshaft position is effected by superposition and / or combination of the crankshaft position, as determined by adjustment with the rotational speed curve, with the crankshaft position, as determined from the value (OT ', OT ", OT"').

Description

The present invention relates to a method for determining a crankshaft position of an internal combustion engine.

State of the art

For the operation of a modern internal combustion engine, it is necessary that the electronic engine control unit information about the current engine speed are available. For this purpose, a sensor wheel mounted on the crankshaft of the internal combustion engine, the rotational speed of which is detected, for example, by means of an inductively acting sensor or Hall sensor, can be used. This registers passing metallic marks and determines the rotation speed over the time difference between two marks.

For the execution of crank angle synchronous functions beyond the absolute position of the crankshaft is detected, for example, to determine the timing of the injection and possibly ignition correctly. This is achieved via a tooth gap on the encoder wheel, which can be detected by the speed sensor and thus assigned to a defined crankshaft angle. In particular, the detection of top dead center (TDC) is of interest.

Depending on the type of internal combustion engine, other variables must be recorded via other sensors. In a four-stroke engine with a cylinder, the crankshaft performs two complete revolutions per cycle, so that the tooth slot can be used to determine the crankshaft position, but not the power stroke. Thus, for example, an upper dead center results at the end of the compression stroke and an upper dead center at the end of the Ausblastakts, which is not through the tooth gap information can be distinguished. This distinction is made in motorcycles bspw. By the evaluation of the intake manifold pressure.

In other internal combustion engines, in particular those having more than one cylinder, the position of the camshaft detected via a sensor can be evaluated in order to obtain further information about the exact position.

It is therefore desirable to provide a way to provide an accurate position of the crankshaft without additional components.

Disclosure of the invention

According to the invention, a method with the features of claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

In a method according to the invention for determining a crankshaft position, in particular a top dead center, of an internal combustion engine, a speed curve of the crankshaft (that is to say rotational speed over time) is detected. The crankshaft position is determined by adjusting the speed curve with a known speed curve of a working cycle of the internal combustion engine. Such a known speed curve can be determined, for example, on a test bench. In this case, the known speed curve has a (in particular exactly one) characteristic of the crankshaft position section, so that the crankshaft position can be determined from the occurrence of the section in the detected speed curve.

This type of cross-correlation of an already known, in particular for starting an internal combustion engine typical speed curve during a work cycle with a momentarily measured on the crankshaft speed curve allows the determination of the crankshaft position, since the speed curve during a cycle usually no repeating areas having. In particular, the important crankshaft position of the ignition top dead center (ZOT), which occurs only once per cycle, is characterized in the speed curve by a characteristic section. In general, the ZOT occurs at or shortly after a speed minimum, in particular a minimum, followed by a monotonically increasing (approximately linear) course, in which the speed increases significantly (almost to twice the value).

This makes it possible to distinguish between the two top dead centers that occur during a working cycle, which is not possible solely by the transmitter wheel with the associated sensor.

Furthermore, according to the invention, a signal of an electric machine coupled to the crankshaft is detected, taking into account a value of the signal occurring in the determination of the crankshaft position at least once per working cycle, in particular when the crankshaft position of interest is reached. This can be achieved in particular by adjusting the electric machine accordingly with respect to the crankshaft of the internal combustion engine. Since an internal combustion engine is coupled in modern vehicles with an electric machine, which is usually designed as a generator or so-called starter generator, their signals can be used in addition to more accurate determination of the crankshaft position. Signals of the electric machine provide more accurate crankshaft positions, but usually only ambiguous, since usually more of the values occur per cycle. This is due to the fact that usually multi-pole electrical machines are used. In superimposition and / or combination with the clear, but usually somewhat inaccurate determination of the crankshaft position from the rotational speed curve, it is possible to determine a specific crankshaft position very precisely.

Such a signal, preferably a voltage signal of a phase of the electric machine, allows very accurate conclusions about the exact angular position of the crankshaft. In particular, a zero crossing of a rising edge, a zero crossing of a falling edge, a minimum or a maximum be correlated as a value with a crankshaft position, for example, a top dead center by the electric machine and the crankshaft, suitably adjusted during assembly, accordingly.

Preferably, the characteristic portion of the speed curve comprises a minimum, a maximum, a slope and / or a threshold value. Depending on which crankshaft position is to be determined, different types of sections may be characteristic and / or particularly well detected.

It is advantageous if the speed curve of the crankshaft is detected by measuring a time difference between two occurrence times of the value and calculating it with an angle of the crankshaft swept over during this time difference. In this way, the rotational speed per se can be determined by means of the signals which can be tapped on the electrical machine, whereby the transmitter wheel with associated sensor is no longer necessary.

Advantageously, the crankshaft position is determined by adjusting the speed curve in an initial cycle and determines the crankshaft position in subsequent cycles by counting the occurrence of the value. Since the characteristic speed curve usually occurs when starting the internal combustion engine, in particular here the crankshaft position can be determined. In the following, it is easy to deduce the desired crankshaft position based on the number of values that occur. For example, if the value occurs three times per crankshaft revolution, the desired crankshaft position occurs after six consecutive occurrences of the value.

It is advantageous if the voltage signal of the phase is generated by a plurality of magnetic exciters of the electric machine, wherein one of the magnetic exciter is so deviated from the rest, that the section of the voltage signal generated by it exactly once per revolution of the crankshaft at the crankshaft position has the value. If the value occurs several times per crankshaft revolution, which is the case when a multi-pole electric machine is used, that of the crankshaft position corresponding value can be determined by means of adjustment with the known characteristic curve. If a corresponding magnetic exciter, ie the corresponding pole, changes something, then the section of the signal which it generates also changes in amplitude. This makes it easier to identify the value associated with the desired crankshaft position. However, this requires a change in the electrical machine, which may be undesirable.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

• FIG. 1 schematically shows a sensor wheel with sensor for speed determination according to the prior art.
• FIG. 2 shows a speed curve during a work cycle during the start of an internal combustion engine
• FIGS. 3a to 3c show an example of a single-phase electric machine with associated waveform and possible crankshaft positions.
• FIG. 4 shows an example of a waveform of a three-phase electric machine with possible crankshaft positions.

Embodiment (s) of the invention

In FIG. 1 schematically illustrated a transmitter wheel 20 and an associated inductive sensor 10, as used in the prior art for speed determination. The encoder wheel 20 is usually fixedly connected to a crankshaft of an internal combustion engine and the sensor 10 is fixedly mounted at a suitable location.

The encoder wheel 20, usually made of a ferromagnetic material, has teeth 22 which are arranged on the outside at a distance 21 between two teeth 22. At a location on the outside, the sender wheel 20 has a gap 23 in the length of a predetermined number of teeth. This gap 23 serves as a reference mark for detecting an absolute position of the encoder wheel 20th

The sensor 10 has a bar magnet 11 to which a soft magnetic pole pin 12 is attached. The pole pin 12 in turn is surrounded by an induction coil 13. When the encoder wheel 20 rotates, teeth 22 and empty spaces between each pair of teeth alternately pass the induction coil 13 of the sensor 10. Since the encoder wheel 20 and thus also the teeth 22 are made of a ferromagnetic material, during rotation in the coil induces a signal that distinguishes between a tooth 22 and an air gap.

By correlating a time difference between two teeth at an angle included by these two teeth, the angular velocity and the rotational speed, respectively, can be calculated.

At the gap 23, the induced signal in the induction coil on a different course than in the otherwise alternate with empty spaces teeth 22. In this way, an absolute position detection, but only with respect to a full crankshaft revolution, possible.

In FIG. 2 is a characteristic speed curve 60 of a crankshaft of a single-cylinder engine designed as an internal combustion engine during cranking for the duration of a cycle.

The top dead center (TDC) of the cylinder is reached twice, at 0 ° and at 360 ° (applied to the right). The ignition TDC, which is decisive for an injection time, corresponds to the TDC at 0 °. The speed curve 60 can be clearly seen that the ignition TDC at 0 ° corresponds to a characteristic of this TDC section of the speed curve 60, namely a steep, long rise to a minimum. This can be, at least to some extent, determine a crankshaft position from the speed curve. The area OT * takes into account a certain degree of uncertainty in the determination.

In FIG. 3a a designed as a single-phase generator electric machine 30 is shown, which comprises a rotor 32 with a circumferential direction 40 and a stator 33. The rotor 32 includes six poles, each formed as opposing north poles 41 and south poles 42.

The electric machine 30 is in this case connected or coupled to the crankshaft of an internal combustion engine such that the top dead center of the internal combustion engine is located at the position indicated by TDC.

In FIG. 3b the tapped on the coil at the stator 33 voltage U _{P is shown} as a voltage waveform. Since the electric machine 30 six-pole, so with three pairs of poles is formed, occur per full revolution 45 of the rotor 32 three full sine waves of the voltage, for this purpose a uniform circular motion of the rotor 32 is assumed.

The orientation of electric machine 30 and crankshaft is such that the top dead center OT is reached at a zero crossing of a rising edge of the voltage signal U _P. However, since, as already mentioned, three full sine waves per revolution occur, also three zero crossings rising edges occur.

Although such a zero crossing can be detected exactly, however, no clear assignment of one of the three zero crossings to the one top dead center OT is possible. Rather, three possible top dead centers OT ', OT ", OT'" are detected.

In Figure 3c For example, the three possible top dead centers OT ', OT ", OT'" are again shown during one revolution 45 (ie here half working game). It is assumed that this turn out the first 360 ° FIG. 2 corresponds so that in addition to OT * an uncertainty range for the desired top dead center, the ignition TDC off FIG. 2 can be drawn. A work cycle would have six possible top dead centers and an uncertainty range OT *.

By combining these two methods, a desired crankshaft position can thus be precisely determined. One condition for this is merely that the uncertainty range OT * is only so wide that only one of the possible top dead centers OT ', OT ", OT"', etc. can be assigned to it.

In FIG. 4 Voltage curves U _U , U _V , U _{W of} the three phases of a three-phase electric machine are shown. To detect the possible top dead centers OT ', OT ", OT'" one of the phases, in this case U _U , must be selected here as the so-called indicator phase. This is, for example, by individual signal lines allows the individual phases of the electric machine to an evaluating controller.

In addition, by way of example, a time difference .DELTA.t between the values OT 'and OT is entered. By detecting this time difference .DELTA.t or also subsequent time differences between the following values, the speed can be determined when offsetting with an angle of the rotor or crankshaft swept over during this time difference .DELTA.t This eliminates the need for a sensor wheel and associated sensor to increase the resolution by also using values from other phases.

Claims (13)

Method for determining a crankshaft position of an internal combustion engine,
wherein a speed curve of the crankshaft over a time is detected;
wherein the crankshaft position (OT *) is determined by adjusting the speed curve with a known speed curve (60) of a working cycle of the internal combustion engine;
wherein the known speed curve (60) has a characteristic of the crankshaft position section;
wherein a signal (U _P , U _U ) of an electric machine (30) coupled to the crankshaft is detected;
wherein a value occurring at least once per working cycle (OT ', OT ", OT"') of the signal (U _P , U _U ) is taken into account in the determination of the crankshaft position; and
wherein the determination of the crankshaft position is determined by superimposing and / or combining the crankshaft position as determined by adjustment with the speed curve (60) with the crankshaft position as determined from the value (OT ', OT ", OT"'), he follows. The method of claim 1, wherein the characteristic portion comprises a minimum, a maximum, a slope and / or a threshold. The method of claim 1 or 2, wherein the electric machine (30) is adjusted with respect to the crankshaft such that the value (OT ', OT ", OT"') per cycle occurs at least once upon reaching the crankshaft position. Method according to one of the preceding claims, wherein the signal (U _P , U _U ) comprises a voltage signal of a phase of the electrical machine (30). Method according to one of the preceding claims, wherein the value (OT ', OT ", OT'") comprises a zero crossing of a rising edge, a falling edge zero crossing, a minimum or a maximum. Method according to one of the preceding claims, wherein the speed curve of the crankshaft is detected by measuring a time difference (Δt) between two times of occurrence of the value (OT ', OT ", OT'") and with an angle swept over during this time difference (Δt) Crankshaft is charged. Method according to one of the preceding claims, wherein the crankshaft position is determined by adjusting the speed curve in an initial cycle and wherein the crankshaft position in subsequent cycles by counting the occurrence of the value (OT ', OT ", OT'") is determined. Method according to one of the preceding claims, wherein the voltage signal (U _P , U _U ) of the phase is generated by a plurality of magnetic exciters (41, 42) of the electrical machine (30) and wherein one of the magnetic exciter is so deviating from the rest, that the portion of the voltage signal generated by it has the value exactly once per revolution of the crankshaft at the crankshaft position. Method according to one of the preceding claims, wherein the crankshaft position comprises a position occurring exactly once per cycle and wherein a working cycle comprises two full revolutions of the crankshaft. Method according to one of the preceding claims, wherein the crankshaft position comprises a top dead center of the internal combustion engine. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims. A computer program that causes a computing unit to perform a method according to any one of claims 1 to 10 when executed on the computing unit. A machine-readable storage medium having a computer program stored thereon according to claim 12.

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