Method for evaluating a knock sensor signal

Abstract

Method for evaluating a knock sensor signal (1) of a vehicle powered by an internal combustion engine, wherein the knock sensor signal (1) is composed of at least an engine background noise, a knock noise and an injector noise (4), wherein the influence of the injector noise (4) on the knock sensor signal (1) is estimated. - by comparing an injection position and a knock detection window position and - by determining in which frequency range the injector noise (4) occurs.

Description

[0001] The present invention relates to a method for evaluating a knock sensor signal of a vehicle driven by an internal combustion engine.

[0002] Knocking noises occur during the uncontrolled combustion of fuel in gasoline engines. The sudden increase in temperature and pressure places significant stress on the pistons, bearings, cylinder head, and valves, which can cause damage. Therefore, a knock sensor, designed as a structure-borne sound sensor, is usually provided to monitor the occurrence of knocking. The combustion engine can then be controlled so that knocking no longer occurs.

[0003] However, the combustion noise recorded by the knock sensor may contain noise components, particularly those caused by injection pulses. Previously, some attempts were made to avoid overlap between the injection window and the knock detection window. However, with the trend toward multiple injection pulses aimed at optimizing fuel consumption and emissions, this is often not possible.

[0004] Some attempts are made to correct for noise signals from the knock sensor signal. Such an approach is known from DE 101 54 422 A1. However, such noise correction is either very complex, as it requires precise knowledge of the noise, or relatively inaccurate if such knowledge is not available. Furthermore, both the basic engine noise and the noise can change over the running time and service life of an engine. Furthermore, tolerances in the engine design cause noise differences.

[0005] Furthermore, document DE 10 2011 103 427 A1 discloses a method for knock control in internal combustion engines. Knock control uses a PID controller in which a setpoint and an actual value are compared in a closed control loop. Self-adaptation of the setpoint enables stable knock control with high control quality.

[0006] Document DE 10 2011 083 511 A1 also discloses a knock control device in which erroneous knock detection can be suppressed. A knock window setting device sets a knock detection period in advance during which vibration due to knocking occurs. In an interpolation period, the knock window setting device multiplies the processing result by a digital signal processing device by a linear interpolation value between an open gain and a predetermined interpolation gain.

[0007] It is therefore an object of the present invention to provide a method for evaluating a knock sensor signal which enables good knock detection with manageable effort.

[0008] This problem is solved by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0009] According to one aspect of the invention, a method is provided for evaluating a knock sensor signal of a vehicle powered by an internal combustion engine, wherein the knock sensor signal is composed of at least a basic engine noise, a knocking noise, and an injector noise. Not all components contribute to the knock sensor signal at all times. The knocking noise and the injector noise each occur only temporarily. The sum of the basic engine noise and the injector noise is also referred to here as the basic noise.

[0010] The influence of the injector noise on the knock sensor signal is estimated by comparing an injection position with a knock detection window position and by determining the frequency range in which the injector noise occurs and, if necessary, correcting this frequency range by factorially weighting the noise with respect to the respective dominant frequencies of the noise.

[0011] By comparing an injection position with a knock detection window position, it is assessed whether both positions overlap in terms of crank angle. This is possible because the point in time during combustion at which knock is most likely to occur is known. The injection positions are also known. If there is no overlap, the injector noise has little influence on the knock detection. If the positions overlap, possibly significantly, a significant influence of the injector noise can be expected.

[0012] To evaluate the knock sensor signal, typically defined frequency bands are evaluated, for example three frequency bands whose position depends on the cylinder diameter.

[0013] The distinction between knocking noise and injector noise in a frequency range can be made by comparing the frequency patterns at a constant operating point with and without injector noise.

[0014] The method has the advantage of allowing an estimate of the extent and location of the injector noise affecting the knock sensor signal. The method does not require the precise detection of the noise in order to subtract it from the knock sensor signal. The method is therefore relatively inexpensive and applicable throughout the entire service life of the engine.

[0015] According to one embodiment, the knock sensor signal is averaged over a time interval Δt, wherein the time interval Δt is shortened when a significant change in the knock sensor signal is detected.

[0016] This design has the advantage of allowing the knock detection to adapt to a changing engine background noise or background noise. If a significant change in the knock sensor signal is detected, the filtering of the knock sensor signal is modified and made less sluggish, allowing the change to be detected more accurately and quickly.

[0017] A significant change in the knock sensor signal is understood to be, for example, a change that is greater than the amplitude of the knocking noise.

[0018] According to one embodiment, a changed background noise can then be learned. The faster filtering makes it possible to learn and use the changed background noise very quickly to ensure reliable knock detection as quickly as possible, even after a significant change in the knock sensor signal.

[0019] A change in the background noise is detected by comparing the injector noise position with the knock window, i.e., the angular range in which knocking is expected. If the start and / or end of injection lies entirely or partially within the knock window, the noise increase can be attributed to the injector noise. If one or more knock events occur, their signal increase can be treated as knock noise, regardless of whether the injector noise is present or not.

[0020] According to one embodiment, a knock detection threshold is adapted to the changed background noise.

[0021] According to one aspect of the invention, a computer program product is provided, comprising instructions which, when the program is executed by a computer, for example a control unit, cause the computer to carry out the described method.

[0022] According to a further aspect of the invention, a computer-readable medium is provided, comprising instructions which, when executed by a computer, cause the computer to carry out the described method.

[0023] Embodiments of the invention are described below by way of example with reference to schematic drawings. Fig. 1 shows a diagram of a knock sensor signal according to a prior art method, Fig. Figure 2 shows a diagram of a knock sensor noise in a method according to an embodiment of the invention and Fig. 3 shows a diagram of a knock sensor noise in a method according to another embodiment of the invention.

[0024] Fig. Figure 1 shows a knock sensor signal 1 plotted over time. The knock sensor signal 1 was recorded using a structure-borne sound sensor on the combustion engine. The knock sensor signal 1 includes a basic engine noise, a knocking noise, and an interference noise generated primarily by the injection processes. Multiple injections occur in time interval I, resulting in injector interference noise that significantly influences the knock sensor signal 1. The knock sensor signal 1 exhibits an upward offset in time interval I.

[0025] Furthermore, in the diagram according to Fig. 1 shows a knock detection threshold 2, which is normally above the knock sensor signal 1. Knocking of the combustion engine is detected when the knock sensor signal 1 is above the knock detection threshold 2.

[0026] In time interval I, the offset of the knock sensor signal 1 caused by the injector noise is so large that the knock sensor signal 1 is above the knock detection threshold 2. Even if no knocking occurs in time interval I, knocking would therefore be detected.

[0027] Fig. Figure 2 shows a diagram of a knock sensor signal 1 plotted over time according to an embodiment of the invention. According to this embodiment, it is provided that a changed background noise 3, which in Fig. 2 is shown only schematically, is learned when a significant change in the knock sensor signal 1 is detected.

[0028] Such a significant change is detected at the beginning of time interval I. This is due to a change in the background noise 3, caused by the occurrence of an injector noise. The knock detection threshold 2 is raised accordingly in interval I.

[0029] At the beginning of time interval I and immediately after the end of time interval I, there are transitions in which knock detection is not entirely reliable. The reason for this is that the new background noise 3 is not learned immediately, but requires some time. Therefore, during transition Ü, there is a risk of false detections in both directions.

[0030] Fig. Figure 3 shows a diagram of the knock sensor signal 1 according to another embodiment of the invention. Here, the Fig. The procedure explained in section 2 is further supplemented by faster learning of the new background noise 3 in the transitions Ü. In particular, this can be achieved by shortening the temporal averaging of the knock sensor signal in the transitions Ü in order to detect the knock sensor signal 1 less slowly, i.e., the period over which the averaging is performed is shortened. This significantly shortens the duration of the transitions Ü and thus the period during which reliable knock detection is not possible.

[0031] Fig. Figure 3 thus illustrates an embodiment in which improved knock detection is also possible in the area of ​​the transitions Ü. This is achieved by quickly learning the background noise, which is altered by the injector noise 4 in interval I. Curve 4 schematically illustrates the period in which the injector noise occurs. Precise knowledge of the noise is not necessary for the method, since it is not intended to be subtracted from the knock sensor signal.

[0032] Instead, the background noise 3, which has been altered by the injector noise 4, is detected, and the knock detection threshold 2 is raised accordingly. During the transitions Ü, the temporal averaging of the knock sensor signal 1 is shortened for faster adaptation to the changed background noise 3.

[0033] Signal 5 is a counter that determines how long the applied correction for the transitions Ü should be active.

[0034] The procedure according to Fig. 3 thus provides reliable knock detection over practically the entire time period, even in a time interval I in which multiple injections take place and thus injector noise is present. List of reference symbols 1 knock sensor signal 2 Knock detection threshold 3 Background noise 4 Injector noise 5 Signal

Claims

[1] Method for evaluating a knock sensor signal (1) of a vehicle operated by an internal combustion engine, wherein the knock sensor signal (1) is composed of at least a basic engine noise, a knock noise and an injector noise (4), wherein the influence of the injector noise (4) on the knock sensor signal (1) is estimated - by comparing an injection position with a knock detection window position and - by determining the frequency range in which the injector noise (4) occurs. [2] Method according to claim 1, wherein the knock sensor signal (1) is averaged over a time interval Δt, wherein the time interval Δt is shortened when a significant change in the knock sensor signal (1) is detected. [3] Method according to claim 2, wherein a changed background noise (3) is learned when a significant change in the knock sensor signal (1) is detected. [4] Method according to claim 3, wherein a knock detection threshold (2) is adapted to the changed background noise (3). [5] Method according to one of claims 1 to 4, wherein an injector noise (4) simulated on the test bench is subtracted from the knock sensor signal (1). [6] A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 5. [7] A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 5.

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