DE10151678B4 - Method for determining a current engine speed - Google Patents

Abstract

A method of determining the current engine speed, comprising: a sensor sensing a gear connected to the crankshaft of the engine having on its surface a plurality of regularly spaced teeth which generate a signal corresponding to the surface of the gear as the sensor passes; is evaluated by the control unit of the engine for determining the rotational speed, wherein the speed is determined from the time interval of predeterminable signal edges, characterized in that the determination of the rotational speed for rotational speeds which are greater than a predefinable threshold value according to a first method and for rotational speeds, which are below this threshold value or a second threshold value, according to a second method, wherein the second method comprises calculating the rotational speed in a predefinable time grid, the first method comprising evaluating SYNCHRO pulses which are offset by a predefinable crankshaft angle spaced apart, which is dependent on the number of cylinders of the engine.

Description

The invention is based on a method for determining a current engine speed according to the preamble of the main claim.

State of the art

The engine speed is a very important factor in engine control because the engine speed is calculated from different engine operating variables. In today's engines, the calculation of the engine operating magnitudes and the engine control output quantities, which are calculated by the engine control based on the speed information available to it, from the current engine speed in different time grids, for example, every 10 ms, 20 ms, 50 ms and in a angle synchronous grid instead. This angle-synchronous grid (SYNCHRO) is calculated once for each combustion, four times for a 4-cylinder engine within a working cycle of 720 ° crankshaft angle. The angular distance between two SYNCHROs (SYNCHRO distance) thus amounts to 180 ° crankshaft in a 4-cylinder engine and is commonly referred to as segment spacing.

The engine speed nmot is obtained from angle information. The calculation of the engine speed nmot takes place, for example, at the beginning of a SYNCHRO. The engine speed is determined from the time interval to the previous SYNCHRO start. This determination of the engine speed is currently averaged for the respective SYNCHRO timing, but over 180 ° crankshaft angle (for a 4-cylinder engine).

This determined engine speed value will be used for all calculations requiring engine speed until a new engine speed is calculated again at the next SYNCHRO. At low speeds, especially in the starting phase of the engine, the course of the actual engine speed has a strong momentum. The size nmot calculated at the beginning of the SYNCHRO is therefore not up-to-date enough for a very precise motor control.

The DE 199 26 982 A1 shows an engine speed calculation device that allows the calculation process of the engine speed, without this being influenced by rotary pulsing in the low speed range of the engine. For this purpose, in the low-speed range of the engine, a predetermined value is divided by a time required for rotation by an angle equal to a multiple of a predetermined angle. In the high speed range of the engine, the predetermined value is divided by the value equal to the multiple of the time required for rotation by the predetermined angle.

From the US 4,972,333 a device for measuring a time interval and a method for operating a speed sensor is known. It is proposed to use a correction coefficient to correct an error of a measured angle, which is determined as a function of a currently existing angle of rotation.

From the DE 3824713 A1 is a speed sensor known. It is provided to analyze both falling and rising edges of a donor wheel in areas of low speed for calculating the speed. In the range of higher speeds is provided to analyze either rising or falling edges of a donor wheel.

Object of the invention

The object of the present invention is therefore to provide a method for determining a current engine speed, which delivers especially in the starting phase of the engine at low speeds more recent engine speeds, which are taken into account for the control of the engine. In this case, no additional Zahnzeitvermessung be performed to spare the resources of the processor or computer. This object is achieved by an inventive method with the features of claim 1.

In today's engines, the engine speed is usually determined by means of a crankshaft connected to the gear wheel, which is scanned by a sensor. The gear wheel has on its surface 60 minus 2 teeth. The two missing teeth lie next to each other and form the so-called reference mark, which is needed to determine the absolute position of the gear and thus the crankshaft. When the gear wheel rotates, the teeth run past a stationary sensor. The sensor, for example, an inductive sensor, therefore provides an output signal, which is present after suitable preparation as a rectangular signal whose course depends on the surface of the gear. This square wave signal is evaluated by the engine control unit to determine the angular position of the crankshaft and to determine the engine speed. Such a system is for example in the DE-OS 44 34 833 shown.

When evaluating such a speed-dependent rectangular signal, the timings of each edge or predeterminable edges of the rectangular signal are stored in a drum memory via a mechanism of the microcontroller of the control unit. So that the microcontroller of the control unit is not overloaded too much and to limit speed fluctuations in their effect is not in current systems from each signal edge of the square wave signal of Sensor calculates a speed. The current procedure is explained below.

Advantages of the invention

The inventive method for calculating a current engine speed with the features of claim 1 has the advantage that even at low speeds, a current value of the engine speed nmot is present, which can be used for the further calculations of speed-dependent large. This is particularly advantageous because the speed dynamics, especially in the starting phase so that no negative impact on the calculations of other operating variables of the engine, which is based on the engine speed directly or indirectly, has. All time slots that require engine speed as the arithmetic unit can thus resort to significantly more recent engine rpm nmot values than current systems.

This advantage is achieved by using current angle information for speed calculation. It is particularly advantageous that the speed information which is present anyway in a drum or ring memory of the control unit in current engines is used for the speed calculation and any necessary corrections in the speed calculation are taken into account. By using a suitable evaluation algorithm, therefore, only the rotational speed information, which already exists in the drum memory, is advantageously evaluated better.

It is particularly advantageous that it is easy to switch back and forth between the previously used calculation algorithm, which can be maintained at higher speeds, and the new algorithm used for low speeds.

Further advantages of the invention are achieved by the measures specified in the dependent claims.

drawing

An embodiment of the invention is illustrated in the drawing and will be explained in more detail in the following description. In detail shows 1 a speed detection system in which the method according to the invention can proceed. The 2 and 3 show waveforms for 200 or 1000 revolutions per minute and 4 shows the relative engine speed as a function of time.

description

In 1 an embodiment of an engine speed detection is shown, with which also the inventive method can be performed. A gear 1 For example, a 60 minus 2 tooth gear, with the crankshaft 6 is connected by a fixed sensor 5 , For example, scanned an inductive sensor. To define a preferred position that has fixed to the crankshaft 6 connected gear 1 a reference mark 2 For example, two missing teeth on. Teeth of a gear wheel 1 are with 3 denotes the tooth flanks bear the reference numeral 4 , Turns the gear 1 , the teeth move on the sensor 5a over and in the sensor 5a a voltage is induced. With the help of a suitable signal shaping circuit 5b a pulse train S1 is output of the sensor 5a get the surface of the gear 1 reflects.

The output signal S1 of the signal shaping circuit 5b gets the processor 17 fed, which carries out the evaluation. It is from the signal S1 by means of an interruption device 8th derive a sync signal SYNCHRO whose pulse intervals are angularly equidistant and dependent on the number of cylinders of the engine. Furthermore, speed-dependent time values are formed from the signal S1, for example in the time switch 9 that over the switch 10 a ring buffer 11 , for example, part of the processor 17 is to be fed. The ring buffer 11 includes a predeterminable number of memory elements. The restoring takes place in each case by activation of the switch 14 ,

From the content of predefinable ring buffer elements, via switches 15 and 16 the arithmetic unit 18 of the processor 17 is fed, calculates the arithmetic unit 18 according to a predefinable method, the current engine speed. Under certain predeterminable conditions, the arithmetic unit 18 also calculate the speed from the time intervals of the SYNCHRO pulses.

With the in 1 The apparatus according to the invention described below can be realized. To understand these procedures, first in 2 illustrated signal waveforms S (t) explained. In 2 For example, a number of rasters are shown on a first timeline for the example of a 4-cylinder engine that rotates at 200 revolutions per minute. The SYNCHRO is started every 180 ° crankshaft revolution in such an engine. The successive SYNCHROs are in the 2 denoted by A, B, C and D. The time interval between two SYNCHROs or two synchro-pulses, z. B. between A and B is in this example 150 ms. Between the SYNCHROs are the pulses generated by the edges of the sensor signal. The distance between two SYNCHROs is 30 teeth, the area of the missing teeth (the reference mark) is not shown. In this area, pulses can be generated for example by a so-called tooth simulation.

By a mechanism in the microcontroller used who entered the times of each tooth pulse in a drum memory. For the normal speed calculation, however, only the entries from the current SYNCHRO start and from the previous SYNCHRO start are evaluated.

For example, two calculation grids are plotted on the second time axis, a 10 ms raster and a 50 ms raster. The 50 ms rasters are numbered from 50/1 to 50/9.

At the beginning of each SYNCHRO signal A, B, C and D, the engine speed nmot is recalculated. For example, with SYNCHRO B, the speed nmot, B is determined by evaluating the time elapsed between A and B. This speed nmot, B is used in the subsequent 50 ms calculations and also in all 10 ms calculations between B and C. In SYNCHRO C, the engine speed nmot, C is recalculated and then used for all subsequent time grids. Again 2 can be seen, is at too much changing engine speed too long with old values of nmot expected because no recalculation has been done, although many new sensor signal pulses and thus also speed information is available.

Again 2 can also be seen, represents the speed nmot, which is calculated from the time interval between two SYNCHROs, the mean value of the speed over the last 30 teeth, or associated square wave signals, is at speed dynamics, both with increasing and decreasing speed The average nmot, averaged over 30 teeth, is approximately equal to the actual speed in the middle of the interval between two synchronizing pulses SYNCHRO.

The speed nmot, B is calculated as described above at the beginning of the SYNCHRO pulse B and corresponds in speed dynamics approximately the current speed at time 50 (2) This speed is used until provided in SYNCHRO C, the new size nmot, C provided becomes. In grid 50 (6), the speed information is approximately 200 ms old. The same applies to every 10 ms raster. In the 10 ms grid just before SYNCHRO C, the speed information nmot, B then used is even older than 200 ms.

In 3 are further signal curves S (t) and some calculation grid shown for the example of a 4-cylinder engine at 1000 revolutions per minute. The SYNCHRO distance, z. B. the distance between A and B is in this case 30 ms. It can be seen that at this higher speed the large nmot calculated at the SYNCHRO start is not very up to date. Thus, the large nmot, B in the arithmetic grid 50 (2) is about 40 ms old. With the method according to the invention for determining a current rotational speed, a significantly more up-to-date rotational speed is determined, in particular at low rotational speeds, which is then available in each case for the calculations supplied by the control unit based on rotational speed information.

According to the invention, various different options are used for both the calculation time for the current speed and for the type of calculation, which will be explained in more detail below.

Time of calculation

• a) Die Berechnung erfolgt nur im Zeitraster, beispielsweise alle 10 ms oder
• b) Die Berechnung erfolgt nur zu SYNCHRO-Beginn oder
• c) Es wird sowohl im Zeitraster, beispielsweise 10 ms, als auch im SYNCHRO-Beginn berechnet.

In the inventive method, the speed nmot under certain predeterminable conditions, for example, at low speed is no longer calculated at the SYNCHRO start with the previous algorithm, but with one of the new calculation algorithms to be described. Possible times for the calculation are:

• a) The calculation takes place only in the time frame, for example every 10 ms or
• b) The calculation is done only at SYNCHRO start or
• c) It is calculated both in the time frame, for example 10 ms, and in the SYNCHRO start.

The calculation of the rotational speed nmot according to one of the methods specified under a to c can, for example, be clipped to specific conditions. A condition can be chosen depending on the engine speed, which is calculated, for example, at low engine speed according to a first method and, if the engine speed is greater than a threshold, possibly with hysteresis, is calculated by another method, in particular will then again the usual method and the speed calculated from the time interval between successive SYNCHROs. If necessary, other conditions can also be taken into account.

The determination of the switching condition for the speed calculation can be done in the same or in a different time grid as the speed calculation.

calculation

When calculating the engine speed in the time grid, no independent determination of tooth times is necessary. Rather, the information already available in the drum memory about the last times of the teeth, or about the last times of specifiable signal distances, is used. In addition to the drum memory with the teeth times, there is a pointer to the position in the drum memory on which the next entry is to be stored. This pointer is evaluated with. He gives information about the last entry in this drum store. If, taking into account further entries in the drum memory, the beginning of the drum store is reached, the entries in front of it are at the end of the drum store. Since they have not been overridden, they are still available and can be read out at this point.

When evaluating the entries of the drum memory, one or more of the algorithms described below can be used. All algorithms have in common that the speed is calculated from the time interval between two entries in the drum memory and the angular distance of these entries.

In a method according to the invention, the time between the last two teeth is evaluated. The last two entries in the drum memory are evaluated. In another method, the time between the last and the n teeth tooth is evaluated. For this purpose, the last entry and the entry with n positions (n = 2 to 29 with a segment length of 30 teeth) are evaluated.

Another evaluation method makes use of the time between the last tooth and the tooth which is one segment long. The last entry in the drum memory and the entry located one segment long are then evaluated. This older entry was in the same place in the drum memory, but has just been overwritten by the last entry. When using a second drum memory, access to older entries is also possible. This second drum memory can either be described in the speed detection by always written alternately in one of these two drum memory, or it is the second drum memory described by the time frame from. The advantage of this type of calculation is that influences are eliminated by a non-circular engine run, because at any time an engine speed is averaged over a SYNCHRO length. With this algorithm, the SYNCHRO does not have any more up-to-date speed information, because the speed is also averaged over a segment length.

In a further method according to the invention, the time between predefinable fixed teeth is evaluated to determine the current speed, for example between tooth 2 and tooth 6 or between tooth 17 and tooth 21, depending on which difference is more current. With this method, the non-circular engine run is taken into account. In the compression phase of the engine, the speed will be less than the average over a segment length or a SYNCHRO distance, in contrast, larger in the combustion phase. If the speed is plotted in a graph over the time of 180 ° crankshaft, a speed curve is observed, which is similar to the solid curve in 4 behaves.

In 4 the relative engine speed is plotted as a function of time between two SYNCHRO marks or pulses. The runout of the speed curve can be seen from the solid line. There are areas in which the engine speed nmot is greater than the average speed or as the average value of the speed. These areas are labeled B1 and B5. In a range with nmot less than the average speed (B3) and in areas in transition with nmot approximately equal to the average speed (B2, B4). If only these last-mentioned ranges are evaluated, the rotational speed thus determined is approximately equal to the mean value of the rotational speed. In 4 the dashed arrows indicate which 10 ms rasters evaluate which of the two possible tooth time information B2 or B4.

In a further method according to the invention, a corrected time between the last two teeth is used to determine the engine speed. The corrected time between the last two teeth, corrected with a factor that describes the unevenness of the engine revolution, is evaluated. In the relative engine speed is shown as a function of time as a solid curve. If the speed is determined at a time when the relative engine speed is system-related 1.1 times the average, then this factor must be divided by 1.1, or multiplied by a factor of 1 / 1.1, so that the correct mean engine speed can be calculated. All tooth sides are therefore multiplied by a value from a characteristic, depending on the tooth number from SYNCHRO beginning.

The reciprocals of in 4 shown function included. The average speed is thus calculated according to the formula: nmot, medium = nmot, last two teeth factor

The factor is a function of the number of the tooth in question. The factor as a function of the tooth number can be determined by first setting it to a constant of 1.0. If the engine speed nmot is measured over a segment length or a distance between two SYNCHROs in the time grid of 10 ms, the result is a speed curve that corresponds to the solid curve in 4 equivalent. From this the factor can be calculated as a function of the tooth number. The rotational speed values determined by a method according to the invention can additionally be averaged and / or filtered.

Furthermore, it is possible to make even a change limitation. In an extended evaluation process, the result is still plausible. The speed nmot, 10 ms, which is calculated in the time grid, may for example have a maximum deviation from the large nmot, SYNCHRO calculated in the SYNCHRO. If the speed nmot, 10 ms leaves the specified tolerance band by nmot, SYNCHRO, a predefinable limitation takes place. The tolerance band can be represented, for example, by: 0.5 nmot, SYNCHRO <nmot, 10 ms ≤ 1.5 nmot, SYNCHRO.

It may optionally be made smaller and smaller to avoid a speed jump this tolerance band shortly before reaching the switching speed. This results in a continuous transition from the new speed calculation described here to the original speed calculation, which, as already mentioned, evaluates the distance between two SYNCHRO pulses for speed determination.

Each of the above-described methods for determining the speed of a motor provides a more recent result for the speed at low speeds than the method that relies on determining the speed from the distance between two SYNCHROs. It is essential in each case that at low speeds, the determination or the calculation of the speed is done in a fast time grid, while at higher speeds, especially at higher speeds than a predetermined speed threshold is switched to the speed determination in the SYNCHRO distance.

Claims (10)

A method of determining the current engine speed, comprising: a sensor sensing a gear connected to the crankshaft of the engine having on its surface a plurality of regularly spaced teeth which generate a signal corresponding to the surface of the gear as the sensor passes; is evaluated by the control unit of the engine for determining the rotational speed, wherein the speed is determined from the time interval of predeterminable signal edges, characterized in that the determination of the rotational speed for rotational speeds which are greater than a predefinable threshold value according to a first method and for rotational speeds, which are below this threshold value or a second threshold value, according to a second method, wherein the second method comprises calculating the rotational speed in a predefinable time grid, the first method comprising evaluating SYNCHRO pulses which are offset by a predefinable crankshaft angle spaced apart, which is dependent on the number of cylinders of the engine. Method for determining the current engine speed according to claim 1, characterized in that at engine speeds which are smaller than the threshold value, the speed is determined from each signal edge or from predeterminable signal edges. A method for determining the current engine speed according to one of the preceding claims, characterized in that the control device comprises a drum memory, with a predetermined number of memory locations that the time value of each signal edge is written into the drum memory and that for determining the current speed at low speeds the Time value difference between predeterminable signal edges is evaluated from the drum memory. Method for determining the current engine speed according to one of the preceding claims, characterized in that the respective last two entries are evaluated in the memory for speed calculation. Method for determining the current engine speed according to one of the preceding claims, characterized in that the time between the last and the nth past entries in the memory for speed calculation is evaluated. Method for determining the current engine speed according to one of the preceding claims, characterized in that the calculation times for the speed are determined according to specifiable criteria. Method for determining the current engine speed according to one of the preceding claims, characterized in that in the calculation of the speed corrections and / or Compensations are carried out that take into account system-related irregularities in the speed curve. Method for determining the current engine speed according to one of the preceding claims, characterized in that the values obtained for the current engine speed (nmot) are additionally averaged and / or filtered and / or limited in the maximum change. Method for determining the current engine speed according to one of the preceding claims, characterized in that the rotational speeds calculated according to different methods are related to one another and a plausibility check is carried out by means of variable tolerance bands. Device for determining the current engine speed, comprising a computing device, in particular the engine control unit, to which the signals supplied by the sensor are supplied, characterized in that at least one of the methods according to one of the preceding claims expires in the device.

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