Method for Checking a Variable Valve Lift Control of an Internal Combustion Engine

Abstract

Various embodiments include a method for checking a variable valve lift control of an internal combustion engine comprising: during operation of the internal combustion engine, detecting a rotational speed of the internal combustion engine; and measuring an intake pressure in the intake tract of the internal combustion engine corresponding to the detected rotational speed. The method further includes: defining a reference frequency dependent on the rotational speed of the internal combustion engine; defining a comparison frequency as a non-integral multiple of the reference frequency; determining amplitudes of oscillations of the intake pressure at the reference frequency and amplitudes of oscillations of the intake pressure at the comparison frequency; and evaluating a ratio of the determined amplitudes and the respective absolute values.

Claims

1. A method for checking a variable valve lift control of an internal combustion engine, the method comprising: during operation of the internal combustion engine, detecting a rotational speed of the internal combustion engine; measuring an intake pressure in the intake tract of the internal combustion engine corresponding to the detected rotational speed; defining a reference frequency dependent on the rotational speed of the internal combustion engine; defining a comparison frequency as a non-integral multiple of the reference frequency; determining amplitudes of oscillations of the intake pressure at the reference frequency and amplitudes of oscillations of the intake pressure at the comparison frequency; and evaluating a ratio of the determined amplitudes and the respective absolute values.

2. The method as claimed in claim 1, wherein the determination of amplitudes includes using a Grtzel algorithm.

3. The method as claimed in claim 1, further comprising evaluating the ratio of the determined amplitudes on the basis of criteria specific to the internal combustion engine.

4. The method as claimed in claim 1, wherein the non-integral multiple lies in a range between 1.3 and 1.7.

5. The method as claimed in claim 1, further comprising identifying a fault in the variable valve lift control if the two amplitudes have a defined ratio to each other and an absolute value of the reference amplitudes significantly greater than zero.

6. The method as claimed in claim 1, further comprising identifying the variable valve lift control as fault-free if the two amplitudes have a shared order of magnitude and both values are close to zero.

7. A device for checking a variable valve lift control of an internal combustion engine, the device comprising: a processor programmed to, during operation of the internal combustion engine: receive a first signal from a detection device indicating a rotational speed of the internal combustion engine; and receive a second signal from a measurement device indicating an intake pressure in the intake tract of the internal combustion engine; and the processor further programmed to, in a defined static behavior of the internal combustion engine, at discrete times: define a reference frequency dependent on the rotational speed of the internal combustion engine; define a comparison frequency as a non-integral multiple of the reference frequency; determine amplitudes of oscillations of the intake pressure at the reference frequency and amplitudes of oscillations of the intake pressure at the comparison frequency; and evaluate a ratio of the determined amplitudes.

8. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further features and advantages of the teachings herein are discussed below with reference to several figures. The figures show:

[0033] FIG. 1 a temporal development of an intake pressure signal of a variable valve lift control of an internal combustion engine;

[0034] FIG. 2 a temporal development of an intake pressure signal of a variable valve lift control with a fault on one cylinder of the internal combustion engine;

[0035] FIG. 3 a temporal development of an intake pressure signal of a variable valve lift control with a fault on two cylinders of the internal combustion engine;

[0036] FIG. 4 a flowchart for one embodiment of a method incorporating teachings of the present disclosure;

[0037] FIG. 5 a temporal development of an intake pressure signal of a variable valve lift control of an internal combustion engine, with both intake pressure signals evaluated using methods and/or devices incorporating teachings of the present disclosure;

[0038] FIG. 6 a block circuit diagram in principle of a device for performance of a method incorporating teachings of the present disclosure; and

[0039] FIG. 7 a flow chart of an example method for checking a variable valve lift control of an internal combustion engine incorporating teachings of the present disclosure.

DETAILED DESCRIPTION

[0040] The present disclosure describes methods and devices for monitoring a variable valve lift control, which check whether the valve switching has functioned correctly. It has already been established in advance which frequencies should be considered. The amplitudes of the intake pressure signal are evaluated at only two frequencies. As a result, this means a limited and low calculation complexity, so that the method can be implemented well in existing electronic vehicle control devices. Furthermore, the proposed system is sufficiently sensitive to also establish faults on only one cylinder, which cannot be ensured with the known methods described above.

[0041] In some embodiments, the amplitudes are determined using a Grtzel algorithm. This merely means a lower calculation complexity in comparison with a conventional classic Fourier transformation.

[0042] In some embodiments, the ratio of the determined amplitudes is evaluated on the basis of criteria specific to the internal combustion engine. In this way, the method can also be adapted very precisely to the checked internal combustion engine concerned, and thereby allows a precise conclusion about the variable valve lift control of the respective internal combustion engine.

[0043] In some embodiments, the non-integral multiple lies in a range between 1.3 and 1.7, e.g. 1.5. In this way, a suitable range of the ratio between reference frequency and comparison frequency is used, which allows a good conclusion about a state of the variable valve lift control of the internal combustion engine.

[0044] In some embodiments, in the case that the two amplitudes have a defined ratio to each other and an absolute value of the reference amplitudes defined is significantly greater than zero, a fault in the variable valve lift control is detected.

[0045] In some embodiments, in the case that the two amplitudes have the same order of magnitude and both values are close to zero, the variable valve lift control is detected as fault-free. In this way, criteria are defined by which a clear distinction can be made between a defective and a fault-free valve lift control.

[0046] FIG. 4 shows a flow chart for an example method incorporating teachings of the present disclosure. In a step 100, a reference frequency f.sub.R of the internal combustion engine is determined as a function of the rotational speed of the internal combustion engine. At the same time, the intake pressure signal P in the manifold intake tract of the internal combustion engine is measured by means of a pressure sensor. In a step 110, using the determined reference frequency f.sub.R and the intake pressure signal P, a reference amplitude Af.sub.R of the intake pressure signal P is calculated using the Grtzel algorithm.

[0047] In a step 120, a comparison frequency f.sub.V is determined which constitutes a non-integral multiple of the reference frequency f.sub.R. The intake pressure signal P together with the comparison frequency f.sub.V is used to calculate, in a step 130, the comparison amplitude A.sub.V of the oscillations of the intake pressure signal P at the comparison frequency f.sub.V.

[0048] In a step 140, the determined reference amplitude A.sub.R is compared with the comparison amplitude A.sub.V and the comparison is evaluated, wherein defined criteria of the internal combustion engine are used.

[0049] FIG. 5 shows a temporal development of the intake pressure signal P together with the temporal development of the reference amplitude A.sub.R and of the comparison amplitude A.sub.V of the intake pressure signal P at the reference frequency f.sub.R and at the comparison frequency f.sub.V respectively. It is evident that the intake pressure signal P in the left-hand portion which represents a fault-free system, and in the right-hand portion which represents a defective system, are configured differently. It is evident that the harmonic components on the intake pressure signal P in the case of a fault are substantially higher than in the fault-free case.

[0050] Said Grtzel algorithm is carried out continuously during operation of the internal combustion engine. The comparison frequency f.sub.V is the reference frequency f.sub.R multiplied by a non-integral factor. In some embodiments, the factor lies in a range between 1.3 and 1.7, e.g. 1.5.

[0051] A non-integral ratio of the comparison frequency f.sub.V to the reference frequency f.sub.R is justified in that, on a fault in one or more cylinders of the internal combustion engine (e.g. a four-cylinder engine), an integral factor would in each case influence the excitation of the intake pressure signal P. Thus a fault in the variable valve lift control in the frequency space is not reflected in a non-integral multiple of oscillations of the intake pressure P, so that a fault can easily be distinguished from a correct state of the variable valve lift control. The selected non-integral factor should be adapted to the respective internal combustion engine to be checked, which requires a specific calibration process for the respective internal combustion engine to be checked.

[0052] It must be taken into account that the closer the factor lies to an integral multiple, the smaller the deviations of the reference frequency f.sub.R from the comparison frequency f.sub.V. The aim is therefore a non-integral factor in which the deviations of the reference from the comparison frequency in the case of a fault are as small as possible. In the fault-free case (left-hand portion of FIG. 5), it is evident that the amplitudes A.sub.R, A.sub.V of the reference and comparison frequencies f.sub.R, f.sub.V are very similar, wherein peaks on the comparison amplitude A.sub.V each constitute a start of performance of the Grtzel algorithm. A permitted order of magnitude of a ratio of amplitudes A.sub.R, A.sub.V lies in a range from around 2 to around 3.

[0053] In the first matrix after the dotted centre line of the right-hand portion of FIG. 5 (fault case), the values of the reference aptitude A.sub.R and the comparison amplitude A.sub.V are not static, or have greatly increased oscillations, whereby these values are rejected and the Grtzel algorithm is not performed. In the faulty region, the reference amplitude A.sub.R shifts upward and the comparison amplitude A.sub.V shifts downward, so that as a result, the two amplitudes A.sub.R, A.sub.V differ greatly.

[0054] In some embodiments, the internal combustion engine has a steady rotational speed to a certain extent, wherein a degree of deviation is indeed permissible in a transient region; if however this region is exceeded (e.g. during a strong acceleration process), the method cannot function because in this case, the changes to the engine rotational speed and intake pressure P in the intake tract are too great (not shown in the figures). The extent of the respective transience in which the method cannot function cannot be specified generally, but must be specified for each internal combustion engine individually. In some embodiments, the real-time performance of the proposed method allows an evaluation to start afresh whenever said necessary conditions of the static state are present again.

[0055] As a result, this means that a fault detected by means of the proposed method must be confirmed or reproduced several times before a genuine fault is identified. A mathematical formula apparatus for performance of the Grtzel algorithm is as follows:

=(2/n)f

n . . . sampling or scanning rate of the method
. . . pi

Q.sub.t=2cos Q.sub.t-1Q.sub.t-2+P.sub.t+P.sub.akt

Q.sub.t . . . temporary value of intake pressure P
P.sub.t . . . actual value of intake pressure P
t . . . actual time stage

A=SQR(Q.sub.t-1.sup.2+Q.sub.t-2.sup.2Q.sub.t-1Q.sub.t-22cos )

A . . . amplitude of superposed pressure fluctuations in Pa
SQR . . . square root

[0056] Said procedure of the Grtzel algorithm should be carried out for the reference frequency f.sub.R and also for the associated comparison frequency f.sub.V.

[0057] As a result, using the method described, a reduced Fourier transformation is performed in the form of a Grtzel algorithm, by means of which pre-specified frequencies of oscillations of the intake pressure P are analysed.

[0058] In some embodiments, a reliable detection and high sensitivity can be achieved. Furthermore, no comparison with modeled values is necessary, since these are real values from real operation of the internal combustion engine. Moreover, it is also possible to check internal combustion engines with cylinder banks which are not mutually independent. Also, in comparison with conventional methods with DFT/FFT processes, merely a low calculation power is sufficient for the method.

[0059] FIG. 6 shows a block circuit diagram of a device 200 incorporating teachings of the present disclosure for checking a variable valve lift control. A detection device 200 can be seen for detecting a rotational speed of the internal combustion engine; said detection device is functionally connected to a measuring device 210 (e.g. pressure sensor) for measuring an intake pressure P in the intake tract of the internal combustion engine. A calculation device 220 is functionally connected to the measuring device 210 and is configured, in a defined static behavior of the internal combustion engine, to perform the following steps at discrete times: [0060] definition of a reference frequency f.sub.R dependent on the rotational speed of the internal combustion engine; [0061] definition of a comparison frequency f.sub.V as a non-integral multiple of the reference frequency f.sub.R; [0062] determination of amplitudes A.sub.R of oscillations of the intake pressure P in the intake tract of the internal combustion engine at the reference frequency f.sub.R, and of amplitudes of oscillations of the intake pressure P in the intake tract of the internal combustion engine at the comparison frequency f.sub.V; and [0063] defined evaluation of a ratio of the determined amplitudes A.sub.R, A.sub.V.

[0064] In some embodiments, the device 200 may be configured as an electronic engine control unit on which the method is executed as software. This supports easy adaptability of the method.

[0065] FIG. 7 shows a flowchart for an example method for checking a variable valve lift control of an internal combustion engine incorporating teachings of the present disclosure.

[0066] In a step 300, a rotational speed of the internal combustion engine is detected.

[0067] In a step 310, the intake pressure P in the intake tract of the internal combustion engine is measured.

[0068] In a step 320, a reference frequency f.sub.R is defined which is dependent on the rotational speed of the internal combustion engine, and a comparison frequency f.sub.V is defined as a non-integral multiple of the reference frequency f.sub.R.

[0069] In a step 330, determination takes place of amplitudes A.sub.R of oscillations of the intake pressure P in the intake tract of the internal combustion engine at the reference frequency f.sub.R, and of amplitudes of oscillations of the intake pressure P in the intake tract of the internal combustion engine at the comparison frequency f.sub.V.

[0070] In a defined static behavior of the internal combustion engine, the following steps are performed at discrete times: In a step 340, a defined evaluation of a ratio of the determined amplitudes A.sub.R, A.sub.V and their absolute values is performed.