Title of Invention

A METHOD FOR KNOCK DETECTION IN AN INTERNAL COMBUSTION ENGINE

Abstract

A method for detecting knocking in an internal combustion engine is disclosed, in which method the output signal of at least one knocking sensor which is assigned to the internal combustion engine is evaluated using a downstream evaluation device. Here, knocking is detected if the conditioned output signal of the knocking sensor exceeds a predefinable reference value. The input signal of the reference value adjustments calculated as a funtion of whether or not the internal combustion engine is in a dynamic operating state, in which case measure values which have been determined when knocking has been detected are also used to calculate the reference value in the case of dynamics.

Full Text

The invention relates to a method for detecting knocking in an internal combustion engine of the generic type of Claim 1. Prior Art It is known that in internal combustion engines with a knocking control knocking sensors are used which emit output signals which make it possible to detect whether or not knocking combustion is occurring. Solid-borne sound sensors, for example, are used for knocking detection, there being embodiments with a single knocking sensor, with two knocking sensors which are mounted at predefinable points on the engine block or with one knocking sensor for each cylinder. The problem when evaluating the signals supplied by the knocking sensors is the separation of the signal caused by the knocking from the signals generated by the other noises. Because both the knocking signal and the background signal depend on various operating conditions of the internal combustion engine, it is already known to carry out the knocking evaluation as a function of the rotational speed of the internal combustion engine. In a device for detecting knocking which is known from DE-P 43 32 711, there is a description of how the output signals of two knocking sensors are processed for detecting knocking. Here, reference levels which are compared with the current output signal which corresponds to a conditioned knocking sensor signal are formed in a microprocessor from preceding knocking signals. If the signal exceeds the reference level, knocking is detected and the corresponding actuation, for example of the ignition, is carried out, ensuring that knocking no longer occurs during the following combustion- So that the dependence of the background signal and of the knocking signal on the rotational speed is taken into account and optimum detection of knocking can be carried out, the reference level is changed as a function of the rotational speed, in which case the reference level is also raised as the rotational speed increases. Advantages of the Invention The method according to the invention for detecting knocking having the features of Claim 1 has the advantage that reliable detection of knocking is possible independently of the intensity of the noise over the entire operating range of the internal combustion engine. This advantage is achieved in that, in addition to the customary adjustment of the reference level, improved adjustment of the reference level in the case of dynamics is carried out in particular for internal combustion engines with a severe increase in noise. Even in engines with above average generation of noise or in regions with above average increase in noise, there is no erroneous detection of knocking because in this case the reference level is also advantageously adapted. Further advantages of the invention are achieved by ueans of the measures disclosed in the subclaims. It is particularly advantageous here that the improved icijustment of the reference level in the case of iynamics permits more rapid adjustment of the reference .evel. This rapid adjustment is maintained by reducing the associated factor in the case of dynamics in comparison with the normal case. Drawing The invention is illustrated in the drawing and will be explained in more detail in the following description. In particular, Figure 1 shows a possible way of implementing a device for detecting knocking, with which device the methods according to the invention for detecting knocking can be carried out. Figures 2 and 3 illustrate two knocking detection methods according to the invention as flowcharts, and Figure 4 shows various reference level profiles. Description In the embodiment of a device for detecting knocking in an internal combustion engine which is illustrated in Figure 1, two knocking sensors 10,11, for example solid-borne sound sensors are arranged at predefinable points on the engine block 12 of the internal combustion engine. The knocking sensors 10,11 emit signals S1,S2 which depend both on the engine noise and on interference noise which may be present and knocking noise which may be present. In order to detect knocking reliably, the signal elements must be separated. To do :his, the signals SI and S2 of the knocking sensors 10,11 are suitably further processed in the evaluation ievice 13 and a signal S3 which makes it possible to ietect whether or not knocking is occurring is jenerated at the output of the evaluation unit 13. "he evaluation device 13 may be embodied as a discrete ircuit or may be a component of a microcomputer. The valuation circuit 13 is integrated, for example, in he control unit of the internal combustion engine. A icrocomputer 14 which further processes the signals S3 of the evaluation device 13 is, for example, a microprocessor of the control unit. As a function of the signal S3 which makes it possible to detect whether or not knocking is occurring, the microcomputer 14 controls ignition devices 15 and/or injection devices 16 and thus regulates the combustion process in the individual cylinders of the internal combustion engine. In order to regulate the internal combustion engine in an optimum way, the microprocessor 14 is provided with further signals which are supplied, for example, by a sensor 17, for example a throttle valve signal transmitter. Of course, it is possible to have any desired number of sensors whose output signals are fed to the microcomputer after appropriate conditioning and processed by said microcomputer. In the exemplary embodiment according to Figure 1, the signals are supplied in each case via inputs which are designated as El and E2, and the outputs are represented as outputs Al, A2 and A3. The actual detection of knocking takes place in the evaluation device 13. In the selected exemplary embodiment, the evaluation device 13 comprises at least one amplifier 18 which has an adjustable gain and to which the output signals SI and S2 which are supplied by the knocking sensors 10 and 11 are fed. Here, in each case the output signal of the cylinder which is assigned by means of software to the cylinder in which combustion is currently taking place is fed in. In an adjoining bandpass filter 19, the amplified signals are filtered in such a way that the signal elements with frequencies which are typical of knocking are preferred. The bandpass filter is adjoined by a demodulation circuit 20, for example a rectifier. The signals which are emitted by the demodulation circuit 20 are integrated in the integrator 21 and the integrated signals KI are applied to a first input of the comparator 22 . A reference signal or a reference level Ref of a [lacuna] using, for example, a lowpass filter 23 by averaging knocking sensor signals conditioned in a predefinable way is formed [lacuna] to the other input of the comparator 22. The way in which the actual values of the reference level are formed and the values which they assume comprises the core of the invention and is described in more detail below. The precise structure of the individual elements for the evaluation device 13 is not essential to understanding the invention and is therefore not disclosed in more detail. The evaluation device 13 can also be implemented completely as a digital evaluation device, for example as a microprocessor. The detection of knocking occurs as follows using the device illustrated in Figure 1: the knocking sensors 10,11 register the noise caused by the internal combustion engine and output corresponding signals SI and S2 to the evaluation device 13. These signals are filtered and amplified in a suitable way. The comparison of the integrated knocking signals Kl with the reference level Ref yields the signal S3 which makes it possible to detect whether knocking has occurred. The precise procedure during the detection of knocking in internal combustion engines which have knocking sensors operating as solid-borne sound sensors can be sxplained, for example, using the flowchart illustrated in Figure 2. In this exemplary embodiment, the noise Lkr of the current combustion is determined in a first ;tep SCH1. From the noise ikr, the ratio virkr of the loise ikr to the current combustion and the noise iveraged over a plurality of combustions of the same :ylinder to the so-called reference level rkr is formed n a step SCH3, the reference level rkr(old) being reviously read in in the step SCH2. The ratio virkr calculated in step SCH3 is investigated in step SCH4 to determine whether it is greater than the knocking detection threshold ke. If the ratio virkr = ikr/rkrfold) exceeds the knocking detection threshold ke, knocking is detected and a signal KL is output. The following also applies: if ikr is greater than rkr(old)*ke knocking is detected and a corresponding signal KL is output. The calculation of the reference level rkr(old) during knocking-free operation therefore takes place if it is recursively detected in step SCH4 that vikr is not greater than ke in step SCH5, in accordance with the formula: rkr(new) = (1-1/KRFTP)*rkrfold) + l/KRFTF*ikr. The variable KRFTP is referred to as a so-called adjustment factor. The adjustment factor can be suitably adapted in accordance with the specific internal combustion engine. The new reference level rkr(new) which is formed in this way represents the basic noise of the internal combustion engine without knocking. In the next program run, the reference level rkr(new) calculated in step SCH5 is taken into account in step SCH6 as reference level rkr(old) and used for the next calculation of the ratio virkr. If combustion is detected as being knocking in step SCH4, the noise ikr which is measured for this combustion is not completely included in the calculations for the reference level rkr. The way in which the calculations are carried out in the case of knocking depends on whether or not dynamics are present. For this purpose, it is checked in step SCH7 whether the internal combustion engine is in a dynamic operating state. For the detection of dynamics it is possible to check, for example, whether the rotational speed changes significantly. If it: is not a case of dynamics, the calculation of the measured noise ikr is effected by dividing said noise ikr by the factor ke in order to avoid a rise in the reference level rkr as a result of the knocking noise. In this case the new value for the reference level rkr (new) is calculated in step SCH8 according to the formula rkr(new) = (1-1/KRFTP)*rkr(old) + 1/KRFTP*(ikr/ke) . In theory it is not possible to dispense with the inclusion of the calculation of knocking combustions because in the case of dynamics the noise also includes the natural increase in noise of the internal combustion engine and must be appropriately included. So that incorrect detection should not occur when there is a rapid and strong increase in the basic noise in the case of dynamics (step SCH7 shows that dynamics are present), that is to say so that suddenly louder combustions are not erroneously detected as knocking, two measures are taken for the duration of the dynamics: the reference level adj ustment is accelerated by selecting a smaller factor KRFTP and the knocking detection threshold is increased. Despite these countermeasures to guard against erroneous detection of knocking, incorrect detections may occur in the internal combustion engines or engines with above average rise in noise, for example as a consequence of piston gouging. However, combustion which is erroneously detected as knocking leads to unjustified deceleration of the adjustment of the calculated basic noise rkr owing to the weighting, described above, of the noise of the current combustion ikr by the factor ke when including it in the calculations of the reference level rkr. This discrepancy between the actual basic noise and the calculated basic noise can result in further incorrect detections. Because any detection of knocking ultimately brings about an adjustment of the ignition angle in the retarded direction, erroneously detected knocking can lead to corresponding reductions in performance and efficiency which are completely unnecessary in the case of the incorrect detections. For this reason, according to the invention the calculation of the reference level which has been described hitherto in the case of dynamics detected in step SCH7 is carried out according to another method, as a result of which incorrect detections are reduced and at the same time detection of actual knocking continues to be ensured. Depending on whether or not a dynamic case is present, the new reference level value is carried out either according to the formula given in step SCH8 or according to the formula given in step SCH9. In step SCH6, the old value of the reference level rkr(old) is then respectively replaced by the new value rkr(new) and this is used again in step SCH3 for forming ratios. The method described thus results in a calculation for the reference level rkr(new) in a dynamic case according to a modified formula where knocking is detected, when there is actual knocking or incorrect detection, so that the following applies: rkr(new) = (1-1/KRFTP)*rkr(old) + l/KRFTP*rkr(old)*ke. Here, the variable rkr(old)*ke corresponds precisely to the noise level which has not yet been detected as knocking. In contrast to a method in which no distinction is made between dynamics and non-dynamics, a higher value is therefore included in the calculations for the adjustment of the reference level, nut said higher level is defined from the averaged loise level. This method for determining a reference level prevents erroneous detection of knocking and thus unnecessary reductions in performance and efficiency. Figure 3 illustrates a further exemplary embodiment of the invention which takes into account adjustment of the reference level in the case of dynamics. This method differs from the one illustrated in Figure 2 only in the additional step SCH10 which includes an additional threshold value interrogation. If knocking is detected in step SCH4 and dynamics are detected in step SCH7 (either the actual presence of knocking or incorrect detections), the step SCH10 is subsequently carried out. Here, the value virkr is compared with a threshold ke*(KRRPN*(ke-1) +1) , the factor KRRPN being able to assume a value range (0.1) lying between ke and ke£. If this value is not exceeded, the reference level is calculated with the formula given in step SCH9, and the following applies: rkr(new) = (1-1/KRFTP)*rkrfold} + 1/KRFTP*(rkr(old)*ke). If, on the other hand, this threshold value is also exceeded by the ratio virkr, the formula given in step SCH8 is used for the calculation of the new reference value, said formula corresponding to the formula used hitherto when knocking was detected. This formula is as follows: rkr(new) = (1-1/KRFTP)*rkr(old) + 1/KRFTP*(ikr/ke). The introduction of this further variable threshold enables the previous behaviour of the reference level adjustment to be implemented with KRRPN=0; on the other hand with KRRPN = 1 adj ustment of the reference level is achieved with maximum speed, as is desirable in internal combustion engines or engines with a rapid rise in noise during rotational speed dynamics, with the result that the probability of incorrect detections during dynamics over a relatively long time period and the associated reductions in performance and efficiency are made smaller. In Figure 4, examples which are determined for the profile of the variables by means of simulation are plotted: virkr_P: ratio of the noise ikr of the current combustion to the average value of the noise of the last combustion of the same cylinder, kekref: knocking detection threshold rkrref: reference level = sliding average value for the last combustions inputnew: value which is used for calculation of the current reference level and ikrref: noise of the current combustion, in each case a value of 0 (Figure 4a), 0.5 (Figure 4b) and 1.0 {Figure 4c) having been selected for the factor KRRPN. B_kl specifies whether knocking is detected (high level) or not {low level). WE CLAIM: 1. A method for knock detection in an internal combustion engine, having at least one knock sensor and an evaluation device connected to said at least one knock sensor, wherein said evaluation device includes at least one comparison means which compares an output signal of the knock sensor to a variable reference level, wherein said variable reference level is produced as a function of preceding output signals of the knock sensor, wherein the variable reference level is supplied to the comparison means via a low-pass filter and the comparison means detects knocking depending on a comparison result, characterized in that tracking of the reference level takes place according to at least three different methods, wherein a first method is selected when no knock is detected, a second method is selected when knock is detected and a dynamic threshold is not exceeded and a third method is selected when knock is detected and a the dynamic threshold is exceeded. 2. The method for knock detection according to claim 1, wherein the reference value rkr(new) is produced with the equations: 1: rkr(new)=(l - l/KRFTP)*rkr(old)+l/KRFTP*ikr, for the first method 2: rkr(new)=(l - l/KRFTP)*rkr(old)+l/KRFTP*(ikr/ke) for the second method or 3:rkr(new)=(l - l/KRFTP)*rkr(old)+l/KRFTP*(rkr(old)*(ke), for the third method wherein rkr(old) is the previous reference value, KRFTP is the tracking factor, ikr is the noise of the current combustion, and ke is a factor. 3. The method for knock detection according to claim 2, wherein knocking is detected when the proportion virkr, which is produced from the current knock value ikr and preceding reference level rkr(old), exceeds a predeterminable value ke. 4. The method for knock detection according to claim 1, wherein output signals of the knock sensor, which were determined when knocking was detected, are also taken into account in the determination of a new reference value. 5. The method for knock detection according to claim 3, wherein with production of a reference level rkr, consideration is also given as to whether a proportion virkr is greater than a threshold value ke*(KRRPN*(ke-l)+l), wherein ke is a knock detection threshold and KRRPN is a factor with a value between 0 and 1, wherein KRRPN is selected to be 1 for rapid reference level tracking and lower than 1 for less rapid reference level tracking.

Documents:

in-pct-2001-0750-che abstract.pdf

in-pct-2001-0750-che claims.pdf

in-pct-2001-0750-che correspondence others.pdf

in-pct-2001-0750-che correspondence po.pdf

in-pct-2001-0750-che description (complete).pdf

in-pct-2001-0750-che drawings.pdf

in-pct-2001-0750-che form-1.pdf

in-pct-2001-0750-che form-19.pdf

in-pct-2001-0750-che form-26.pdf

in-pct-2001-0750-che form-3.pdf

in-pct-2001-0750-che form-5.pdf

in-pct-2001-0750-che petition.pdf