Method for monitoring a knock control, and device for knock control of an internal combustion engine

A method for monitoring a knock control and a device for knock control of an internal combustion engine are provided, in which digital knock data are obtained for the knock control in that the acquisition of data of a knock sensor, converted from analog to digital, is started at a start angle of the internal combustion engine and ended at an end angle. The digital knock data are evaluated so as to detect a malfunction in the acquisition of the digital knock data.

BACKGROUND INFORMATION

German Patent Application No. DE 100 22 815 describes a device in which the signal of a knock sensor is converted from analog to digital and the further processing of the knock data is then implemented on the basis of these digital data. Monitoring of the knock control is provided as well, which is based on the feeding of test signals and a check as to whether a corresponding knock level that matches these test signals is produced. Evaluation of the digital knock data for monitoring purposes is not provided.

SUMMARY OF THE INVENTION

The method according to the present invention for monitoring a knock control, and the device according to the present invention for knock control of an internal combustion engine have the advantage over the related art that monitoring of the knock control is implemented by direct evaluation of the digital knock data. In this manner monitoring of the knock control is able to be carried out during continuous operation of the internal combustion engines, without interrupting the knock control, by the application of test signals. Thus, the operational reliability of the internal combustion engine is improved.

The start and the end of the data acquisition are implemented by a comparison unit, which compares an instantaneous angle information with previously calculated start angles and end angles for the data acquisition. In addition to the angle information, the calculation of a data quantity requires knowledge of a rotational speed of the internal combustion engine. With the aid of this information, a length of time for the acquisition of the data is first calculated in an especially simple manner and the data quantity then calculated therefrom. It is also possible to use an average value for the rotational speed as engine-speed information. As additional monitoring, a counter may be modified upon each start or end of the data acquisition. This counter will then be checked independently of an angle information, i.e., at specified time intervals. Such a type of monitoring is independent of a device that supplies the instantaneous angle information of the internal combustion engine and consequently can also not be affected by a faulty determination of the angle information. As a further form of monitoring, a check may additionally be carried out upon the occurrence of an end angle as to whether a start angle of a subsequent cylinder of the internal combustion engine lies after the end angle.

DETAILED DESCRIPTION

FIG. 1shows an internal combustion engine and a control device1assigned to the internal combustion engine in highly schematized form. The internal combustion engine is represented by a cylinder100inside which a piston101is disposed. A combustion in cylinder100causes a pressure increase, which effects a displacement of piston101. A connecting rod (not shown further) converts this motion of piston101into a motion of a crankshaft102. A sensor ring103on which individual marking teeth104have been provided is rigidly connected to crankshaft102.FIG. 1schematically shows eight teeth. However, as a rule, sensor rings103have thirty or sixty teeth, one or two of these teeth not being embodied in order to mark a fixed reference point that corresponds to a permanently specified angle position of crankshaft102.

The control of the internal combustion engine is performed by control device1, which actuates actuators for the control of the internal combustion engine and reads in the signals from sensors that supply information regarding states of the internal combustion engine. A control line105, by which control device1controls an actuator106on top of cylinder100is shown inFIG. 1as one example. Such an actuator106may be a spark plug or a fuel injector, for instance, by which either an ignition of the air-fuel mixture already carried into cylinder100is implemented, or by which a corresponding quantity of fuel is injected. Furthermore, two different sensors are shown inFIG. 1as examples.

A knock sensor108on the outside of cylinder100records corresponding vibration signals in cylinder100and forwards them via a data line107to control device1. With the aid of these knock signals, a so-called knock control is realized, i.e., an operation of the internal combustion engine in direct proximity to the knock limit, thereby allowing an especially economical operation of the internal combustion engine.

With the aid of engine-speed sensor109, a sliding of marking teeth104along engine-speed sensor109is detected, and signals, which are proportional to the particular position of crankshaft102, are thereby provided in control device1via data line110. This information allows internal combustion engine1to carry out interventions in an angle-synchronous manner, i.e., to implement actuating interventions at the actuators at specific positions of the crankshaft of the internal combustion engine. Only one cylinder100has been illustrated schematically inFIG. 1. However, conventional internal combustion engines usually have a plurality of cylinders100, in particular four cylinders100.

FIG. 2elucidates the signal processing of a knock control in greater detail. The signals from two knock sensors108, which are assigned to a plurality of cylinders of an internal combustion engine, are routed via a multiplexer10, which always switches through one sensor signal only. This is possible because the knock signals in the cylinders of an internal combustion engine do not occur at the same time and thus do not overlap in time. Multiplexer10forwards the data flow of the knock sensors combined in this manner to a filter11. This filter11has an anti-aliasing function in order to prevent the occurrence of interference effects caused by sampling at a limited frequency. An additional signal amplification takes place in amplifier stage12downstream from this filter11, and this amplified signal is forwarded to an analog-digital converter. The analog knock signal is then sampled in this analog/digital converter, and corresponding sampling values are stored in a buffer memory14. The storing in memory14is implemented by a direct-memory access module19(DMA). The sampling values of the knock signal stored in buffer memory14thereupon are processed in blocks in an evaluator15; in particular, it is determined in this manner whether or not a knocking combustion is taking place at a specific combustion in one of the cylinders to which knock sensors108have been assigned. A corresponding output signal is then also made available at an output line16.

The relevant measuring window in which the analog/digital conversion by analog/digital converter13takes place, is specified by a window generator17. This window generator17is connected to analog/digital converter13via a corresponding control line18. In response to a corresponding signal from window generator17, analog/digital converter13begins with the analog/digital conversion, and each of the sampling values of the knock signal from knock sensors108generated in this manner is stored in buffer memory14. If the data acquisition then is no longer to take place, window generator17stops the analog/digital conversion by analog/digital converter13. The corresponding signals from window generator17are also forwarded to a monitoring unit20, which monitors the entire knock control. Furthermore, monitoring unit20also has the data of buffer memory14or the data of evaluation unit15in readiness.

FIG. 2shows the means for processing the knock signals and the monitoring units as individual, separate functional blocks. However, these individual functional blocks may also be grouped together with control device1in a housing, and they may also be partially realized by a corresponding program, which is executed by a multifunction controller of control device1. In particular the functional blocks that are post-connected to analog/digital converter13are preferably realized by corresponding program modules which are processed by a multifunction controller of a control device1.

Control device1is designed to process angle-controlled and time-controlled processes. Angle-controlled processes are processes that are meant to occur at a particular angular position of crankshaft102of the internal combustion engine. To this end, control device1analyzes the signal from engine-speed sensor109. Assuming sixty teeth on a ring sensor103, an angular resolution of 6° crankshaft angle may be realized in this way. Since the rotational speed of an internal combustion engine does not change randomly within 6°, intermediate values are able to be calculated in a corresponding manner, based on an instantaneous engine-speed signal and the occurrence of a tooth104. For instance, an angle counter by which an angular resolution of below 1°, such as 0.75°, arc of crankshaft rotation is realized within control device1is normal. A corresponding program module checks for each of these angles whether an activation of components of the internal combustion engine or control device1is to be implemented in connection with the angle. In this manner the functionality of window generator17is produced, in that an angle information is provided for the start of the data acquisition and an angle information for the end of the data acquisition of the signals from knock sensors108. This calculation is normally carried out in conjunction with the calculation of the ignition angle since a useful acquisition of knock data is meaningful within a particular angle window following ignition. Thus, in addition to the ignition angle, a start angle and an end angle is calculated for each ignition event for the acquisition of knock data. The window generator receives values for this start angle and end angle and the information regarding the instantaneous position of crankshaft102of the internal combustion engine, i.e., the instantaneous angle information, within control device1. If window generator17determines that the instantaneous angle corresponds to the start angle, then the analog/digital converter is turned on, and if the window generator subsequently determines that the end angle is reached, then the analog/digital conversion by analog/digital converter13is stopped again. As an alternative, analog/digital converter13may also be operated continuously and only the storing in buffer memory14be controlled by window generator17. In this case, DMA19evaluates the control signals of window generator17. InFIG. 2, control line18is connected both to analog/digital converter13and to DMA19. Depending on which module is being used to generate the measuring windows, one of the two lines is not required.

Monitoring unit20then checks whether the analog/digital conversion by analog/digital converter13was successful and whether correct storing into buffer memory14is taking place. An additional device is provided for this purpose, in particular an additional program module, which is triggered independently of the start angle or the end angle of the acquisition of the data. For monitoring the knock-data acquisition, monitoring unit20may utilize both signals from window generator17and buffer memory14or evaluator15. At any rate, monitoring unit20has access to the digital knock data stored in buffer memory14and analyzes these data directly in order to detect a malfunction in the acquisition of the digital knock data. Due to the direct evaluation of the data converted from analog to digital, monitoring parallel to the continuous operation of the knock control is possible. It is not necessary to use test signals and thereby interrupt the continuous knock control or knock detection. However, this requires that the evaluation be performed directly on the basis of the digital data.

In a first monitoring by monitoring unit20, the data quantity stored in buffer memory14is evaluated. A specific minimum quantity of data must be stored in buffer memory14for each knock event in order to allow a meaningful analysis to be carried out to begin with. A first simple evaluation consists of checking the data quantity generated in buffer memory14with regard to a specific measuring window. Furthermore, it may also be considered in this context whether these measured values have sufficient signal height and whether sufficient variations of the digital knock data are present.

In conjunction with an engine speed information, the expected data quantity of a particular knock window is able to be calculated with good approximation. This is accomplished in an especially uncomplicated manner if, starting from the start angle and end angle and the rotational speed of the internal combustion engine, a length of time is calculated that is available for the analog/digital conversion. Along with the known sampling frequency of analog/digital converter13, it is then possible to calculate as a good approximation the size of the data block that is stored in buffer memory14in connection with the knock window. The more precise the consideration of the rotational speed information, the more precise the calculation of the size of the data block in buffer memory14. For instance, it is useful to utilize the rotational speed at the start angle and the end angle for the calculation of an average value of the rotational speed, and to use the rotational speed, averaged in this manner, to calculate the data quantity. Excessive deviations from the data quantity calculated in this manner then allow inferences regarding malfunctions of either window generator17or analog/digital converter13. The advantage of this monitoring method is that is may be carried out in parallel to the normal evaluation of the knock data. It is not necessary to apply a test signal to the signal-processing chain, since no knock detection is possible during such a test phase and thus no knock control either. It is especially advantageous for the monitoring if the triggering of this monitoring within the control device occurs independently of window generator17. This may be accomplished by calculating not only the start angle and end angle, but a monitoring angle as well, for which the monitoring unit then implements a check of the data in buffer memory14. As an alternative, monitoring unit20may also be activated in a time-controlled manner, i.e., a monitoring routine, which then checks the individual data quantity of the measuring window that occurred immediately previously, is checked at fixedly defined time intervals.

A special form of the time-controlled monitoring by monitoring unit20may consist of window generator17incrementing a start-angle counter at each start angle or an end-angle counter at each end angle. Monitoring unit20is activated at regular time intervals, these time intervals being selected in such a way that at least one evaluation window must have occurred since the last call-up of monitoring unit20at each meaningful rotational speed of the internal combustion engine. Given longer time periods, a correspondingly larger number of measuring windows that must have occurred since the last call-up of this monitoring routine may also be provided. Only if an appropriate number of counter values of the start-angle counter or the end-angle counter are found in the monitoring routine triggered in a time-controlled manner, will the knock detection be evaluated as fault-free.

Further monitoring may be performed together with the end angle. In the process, monitoring unit20checks whether, upon the occurrence of an end angle, a start angle that has a subsequent angle value with regard to the instantaneous end angle, is already stored in window generator17for the next measuring window. In particular in the case of 4-cylinder internal combustion engines, on overlap of the measuring windows of individual combustion processes in the cylinders is impossible. A check as to whether the end angles and start angles of successive combustion processes are plausible with regard to each other thus constitutes a check of the calculations of window generator17.

A further evaluation by monitoring unit20provides that the end result, which was calculated by evaluator15and output via line16, is forwarded to monitoring unit20as well. In a real internal combustion engine this output signal always has a certain minimum height if the entire evaluation chain is functioning properly. By checking whether the output value is lying within a certain signal window, it is therefore possible to determine whether a complete malfunction of a component or an interruption of a connection line has occurred.

A further check is performed by checking DMA19with the aid of a self-test. DMA19checks the storage process into memory14, in particular whether DMA19was able to perform a memory access to memory14before a new digital value was made available by analog/digital converter13. If a fault occurs in the process, then the DMA will set a corresponding fault bit. By checking this fault bit, monitoring unit20is able to determine whether the acquisition (and storing) of the knock data is being carried out correctly. If the other components of the evaluation chain, such as multiplexer10, anti-aliasing filter11, or analog/digital converter13are equipped with self-testing as well, then the results of these self-tests may also be used to detect fault in the acquisition of the knock data, like in the case of DMA19.

Further monitoring is performed in that the activity of analog/digital converter13and/or DMA19is monitored with regard to an activity between the measuring windows. For no data are allowed to be written into memory14between the measuring windows. Monitoring unit20therefore checks whether analog/digital converter13is at rest following the end of a measuring window (variant including window formation by control of analog/digital converter13), or whether DMA19is at rest (variant including window formation by control of DMA19).