Method for processing an electrical signal, and control device for a camshaft adjuster or internal combustion engine for carrying out the method

Abstract

The invention relates to a method for processing an electrical signal (S) that is generated continuously over time and based on measurement values from a sensor (23, 24, 25) and is transmitted via a line (20, 22) that is subject to disturbance variables, having the following features: establishing a scanning rate interval (T), establishing quantization levels (Q1, Q2), assigning the electrical signal to a quantization level (Q1, Q2), determining the number of changes in the quantization level (Q1, Q2) in the scanning rate interval (T), rejecting all even-numbered changes in the quantization level (Q1, Q2) within the scanning rate interval (T). The invention also relates to a control device (17, 21) for a camshaft adjuster (7, 8) or for an internal combustion engine (1), which carries out a method of this kind.

Description

[0001] Method for processing an electrical signal and control unit for a camshaft adjuster or internal combustion engine for carrying out the method

[0002] The invention relates to a method for processing an electrical signal which is generated continuously over time and based on measured values ​​of a sensor and is transmitted via a conductor subject to disturbances.

[0003] Furthermore, the invention relates to a control unit for an internal combustion engine or a camshaft adjuster.

[0004] Various operating procedures for camshaft adjusters are described in documents DE 102 59 133 A1 and DE 102 42 659 A1. These documents particularly address the interaction of an engine control unit with the camshaft adjustment system. Swashplate gears, which function as three-shaft gears, are used as the actuating gears for the camshaft adjusters.

[0005] DE 10 2012 219 297 A1 describes a method for operating a motor vehicle that includes an engine control unit and a camshaft adjustment control unit. A CAN bus is provided for data transmission. The camshaft adjustment control unit can be started before the engine control unit has completed booting.

[0006] WO 2006 / 122665 A1 describes a topology for generating a control signal for an electrically operated camshaft adjuster. A control unit is integrated into a control unit. Hall sensors are provided to detect the states of the camshaft adjuster.

[0007] DE 10 2004 041 232 B4 describes a method for operating a camshaft adjuster, which may include an electric or hydraulic actuating device. In each case, reference and / or base values ​​relating to the condition of the camshaft adjuster are obtained within the scope of the operating method by averaging temporally separated values.

[0008] In electric camshaft adjusters, like engine control units, the electrical signals are evaluated by sensors from the crankshaft and camshaft trigger wheels. Unlike engine control units, the cables between the control units and the sensors are comparatively long. These cables are exposed to a variety of interference in the engine compartment.

[0009] Ground shifts due to high current loads and the irradiation of electromagnetic waves cause voltage spikes and signal noise in the desired signal. With increasing electrification in vehicles, the number of interference sources is also increasing, meaning reliable signal transmission over long cables is no longer guaranteed.

[0010] Signal evaluation is therefore generally difficult and more complex than with engine control units.

[0011] Object of the invention

[0012] The invention is based on the object of avoiding the disadvantages of the prior art and in particular of processing an electrical signal that has been exposed to electrical interference.

[0013] This object is achieved according to the invention by a method for processing an electrical signal according to claim 1. The object is likewise achieved by a control unit having the features of claim 10. Configurations and advantages of the invention explained below in connection with the control unit also apply mutatis mutandis to the method, and vice versa. The method according to the invention is based on the finding that the voltage peaks and signal noise components radiated into many useful signals have a different temporal duration than their average change. If the temporal and / or absolute change in the useful signal is approximately known in advance, the proposed method opens up a simple way of eliminating interference without having to resort to a computationally intensive Fourier transformation unit.

[0014] The method according to the invention is suitable, for example, for signals whose value changes continuously. Continuous change is to be understood in the mathematical sense that there are no sudden changes in the signal. This applies, for example, to signals that are measured values ​​of continuously changing quantities.

[0015] The method is also well suited for signals whose value changes abruptly if the time of the change is predictable within certain limits, especially if the changes occur periodically.

[0016] It is particularly well-suited for digital signals or analog signals with pronounced edges. For example, a Hall sensor can detect the rotational speed of a shaft using a trigger wheel. Trigger wheels have gears that are easy to detect with magnetic detection because the proportionality of the induced voltage to the first derivative of the field change creates an edge peak. This does not need to be recorded in its absolute value, but can simply be registered as present / absent and thus only needs to be counted.

[0017] A prerequisite for the method is the ability to select a suitable sampling rate interval. This requirement is easily met for many applications, since a measurement can be based on previously measured values, for example, and many physical quantities do not change suddenly. If no historical measured values ​​are available that can be reasonably used, assumptions can be made plausible. For example, for a stationary motor, the speed of its motor shaft can be assumed to be zero.

[0018] The sampling rate interval can be set to a fixed value. For example, it can be hardware-encoded or set once at the start of the process without subsequent changes. Alternatively, the sampling rate interval can be set in a controlled or regulated manner. Resetting can occur after each measurement or be linked to predetermined time periods, measured values, and / or external conditions.

[0019] Quantization levels are also specified for the method. Their number and size depend on the application; for digital signals, two quantization levels are sufficient.

[0020] According to the inventive method, the number of changes in the quantization level is determined. A measured value change only occurs when a certain threshold is exceeded, so that the measured value is assigned to a different quantization level. This reliably eliminates noise components and random fluctuations.

[0021] In many applications, interference that affects the electrical signal is due to long cables. Interference is usually reflected in the signal curve through the first derivative of the interference, which is why voltage spikes occur. The invention takes advantage of the fact that these voltage spikes are comparatively short and cause no or a double change in the quantization interval. If the sampling rate interval is chosen to be significantly larger, for example, an order of magnitude larger, than the duration of the average voltage spikes caused by interference radiation, a double change in the quantization level can be reliably attributed to interference. The method according to the invention therefore rejects all even-numbered changes in a quantization level within the sampling interval.In a further development, if an odd number of changes in the quantization level occur within a sampling rate interval, all changes in the quantization levels following the first change within the sampling rate interval are discarded. Thus, only whether an odd or even number of changes in the quantization levels occur within the sampling rate interval is determined. As a result, it is irrelevant whether a voltage peak due to interference occurs before or after the change in the desired signal.

[0022] The proposed method is particularly suitable for digital signals. However, it is also suitable for analog signals that are quantized into two or more quantization levels after transmission through the conductor.

[0023] Due to its high robustness, the method according to the invention enables the use of comparatively long cables without requiring additional shielding requirements. This also opens up possibilities for placing a control unit that evaluates the signals further away, allowing for more flexible installation locations in an internal combustion engine, thus reducing the control unit's exposure to heat and enabling better packaging.

[0024] In addition to the voltage spikes caused by EMC interference, noise also complicates the evaluation of edge peaks. The quality of the signal can be further improved by prior filtering. A low-pass filter, for example, is provided for this purpose. Furthermore, the hysteresis can be processed using a logic filter that evaluates the individual edge patterns.

[0025] In a further development, if two sampling rate intervals with odd-numbered changes in the quantization level follow one another, the number of changes in the quantization level in the current and previous sampling rate interval is set to zero. This is based on the consideration that the measured value either fluctuates around the threshold separating the quantization levels or that the two edges of a disturbance are randomly distributed across two different sampling intervals.

[0026] The proposed method is particularly suitable for a control unit of an electric or hydraulic camshaft adjuster of an internal combustion engine that executes the method steps. The internal combustion engine is designed as a reciprocating piston engine and, in a known basic structure, comprises a crankshaft and at least one camshaft. An electromechanically adjustable actuating gear is provided for adjusting the camshaft, which may be, for example, a three-shaft gear, in particular a wave gear. The camshaft adjuster can be operated as follows:

[0027] - The angular position of the crankshaft is determined continuously, with an incremental detection of angular changes starting from a detected reference angular position;

[0028] - a reference position of the camshaft is detected, in particular by means of a trigger disc;

[0029] - the current angular position of the camshaft and crankshaft is calculated from the recorded angular changes of the rotor;

[0030] - the difference between the two angular positions mentioned, i.e. the phase difference between the crankshaft and the camshaft, is calculated and used to control the electric motor driving the adjustment shaft.

[0031] The camshaft's reference position is detected, and the corresponding signal is usually provided to the combustion engine's control unit anyway. This signal contains edge peaks that can be counted.

[0032] In an advantageous embodiment, the angular changes of the crankshaft are recorded with a finer resolution than the angular changes of the electric motor rotor, which is non-rotatably coupled to the adjusting shaft of the actuating gear. Due to the positive or negative reduction ratio of the actuating gear, a very fine resolution of the angular position of the camshaft is possible.

[0033] In a preferred method, angular positions of both the crankshaft and the rotor of the electric motor, which lie between two positions that can be discretely distinguished from one another using sensor signals, are approximately determined mathematically by temporal extrapolation. This assumes that the shaft in question, i.e., the motor shaft of the electric motor or the crankshaft, rotates at a virtually constant speed during the period to which the interpolation refers.

[0034] The internal combustion engine comprises a crankshaft, at least one camshaft which is adjustable electromechanically via an actuating gear, in particular a wave gear, an engine control unit and a camshaft control unit provided for controlling an actuating motor, namely an electric motor, which actuates the actuating gear, wherein the engine control unit is linked to a device for detecting the angular position of the crankshaft and the camshaft control unit is linked to the engine control unit,and wherein the only means for detecting the angular position of the camshaft are a device for detecting a reference position of the camshaft to be adjusted and a device for detecting the angular position of the shaft of the servomotor, and the camshaft control unit is designed to determine the phase position of the camshaft in relation to the crankshaft on the basis of the information provided by these devices in combination with the detected angular position of the crankshaft and the transmission ratio of the servo gear.

[0035] The electric actuator of the camshaft adjuster, for example, is designed as a permanent magnet synchronous motor. The electric motor has, for example, four or six pole pairs. Changes in the angular position of the electric motor's rotor can be detected using Hall sensors, for example.

[0036] According to one possible embodiment, the engine control unit includes a memory that stores the edges of a crankshaft trigger wheel detected during crankshaft rotation. By detecting both rising and falling edges, not only can a higher resolution be achieved compared to detecting only similar edges, but a verification mechanism can also be implemented to ensure that the recorded data is free of logical contradictions. This type of signal processing is also feasible in the camshaft control unit. Similarly, the camshaft control unit includes a memory.

[0037] Within the sampling rate interval, a maximum of one pulse is evaluated; all others are discarded. The following applies: If an even number of pulses occurs (e.g., rising-falling, falling-rising, falling-rising-falling-rising...), then this is considered a disturbance, and these pulses are completely ignored. If an odd number of pulses occurs (e.g., rising, rising-falling-rising, rising-falling-rising-falling-rising, falling-rising-falling-rising-falling...), then only the first edge in the direction in which it occurs is evaluated; subsequent edges are discarded.

[0038] The evaluation of edge patterns from the wanted signal and the suppression of edge peaks attributable to disturbances work particularly reliably when the sampling rate interval is not selected as a constant, but rather is adjusted to the expected signal sequence. Therefore, a further development provides for the sampling rate interval to be dependent on the rotational speed of the shaft to be measured. The sampling rate interval must be selected so that it is shorter than the expected minimum duration between two wanted pulses and longer than the typical duration of a disturbance.

[0039] The evaluation, which is easy to perform in the control unit by counting pulses, frees up computing capacity that can be used for other tasks. For example, a multiple edge angle calculation of the camshaft and crankshaft can be performed to enable a fallback calculation in the event of a loss of the crankshaft sensor signal or one of the Hall signals. For this purpose, a further development proposes performing a calculation for several cam edges (rising and falling) and / or a partial selection of the signals (e.g., using only every second or third value). For example, in the case of brief interference, this increases the chance of determining a plausible measured value.

[0040] Example

[0041] The invention is explained in more detail below using an exemplary embodiment.

[0042] The embodiment relates to a control unit for an electric camshaft adjuster and is illustrated schematically in the figures. Shown are:

[0043] Fig. 1 Components of an internal combustion engine with electromechanical camshaft adjustment in an overview,

[0044] Fig. 2 the interaction between an engine control unit and a camshaft control unit of the combustion engine,

[0045] Fig. 3 the relationship between measurements on the crankshaft and a camshaft of the internal combustion engine,

[0046] Fig. 4a a schematic, analogue useful signal with interference signals,

[0047] Fig. 4b a schematic, digital useful signal with interference signals,

[0048] Fig. 5a-h show various possible signal patterns that can occur within a sampling rate interval. An internal combustion engine, designated overall by reference numeral 1 in Figure 1, constructed as an inline engine comprises a crankshaft 2 and two camshafts 3, 4, namely an intake camshaft 3 and an exhaust camshaft 4. Deviating from the illustrated embodiment, the internal combustion engine could also be a reciprocating piston engine of a different design, for example, a V-engine, which has two intake and two exhaust camshafts.

[0049] The camshafts 3, 4 are driven by the crankshaft 2 via chain drives 5, 6. Each camshaft 3, 4 is adjustable by means of an electromechanical camshaft adjuster 7, 8. The camshaft adjuster 7, 8 each has a three-shaft gear constructed as a wave gear as the adjusting gear 9, 10. An input-side shaft of the adjusting gear 9, 10 is driven by the chain drive 5, 6. The output-side shaft of the adjusting gear 9, 10 is connected in a rotationally fixed manner to the camshaft 3, 4 to be adjusted. A third shaft of each adjusting gear 9, 10 can be driven by an electric motor 11, 12 assigned to the respective camshaft adjuster 7, 8. Here, the motor shaft of the electric motor 11, 12, designated 29 (Figure 2), on which a rotor 28 is fastened, is coupled in a rotationally fixed manner, optionally via a compensating coupling, to the third shaft of the actuating gear 9, 10.In the exemplary embodiment, the so-called third shaft is an inner ring of a wave generator of the actuating gear 9, 10 designed as a wave gear.

[0050] The electric motors 11, 12 are connected to a camshaft control unit 17 via connecting lines 13 and signal lines 14. Plug connections of the electric motor 11, 12 for the connecting lines 13 are designated 15, and plug connections for the signal lines 14 are designated 16. The aforementioned lines 13, 14 are connected to a plug connection 18 of the camshaft control unit 17. Hall signals are transmitted via the signal lines 14. These signals are acquired with the aid of Hall sensors (not shown) and provide information about changes in the angular position of the rotor 28. The Hall sensors are part of a rotor position detection device designated overall by 44. The camshaft control unit 17 is connected to the engine control unit, designated 21, of the internal combustion engine 1 via a data bus 19, namely the CAN bus, and a signal line 20. A crankshaft sensor 23 is connected to the engine control unit 21 via a crankshaft line 22.The crankshaft sensor 23 senses a crankshaft trigger wheel 27, which is rigidly connected to the crankshaft 2. Furthermore, sensors 24, 25 are connected to the engine control unit 21, each of which interacts with a trigger disc 26, which is connected to a camshaft 3, 4.

[0051] Figure 2 illustrates data processing operations in the engine control unit 21 (left) and the camshaft control unit 17 (right). As can be seen from the illustration, the signal generated by the trigger disk 26 is processed within the engine control unit 21. In the exemplary embodiment, the trigger disk 26 schematically has a single elevation 32. One flank of the elevation 32 is designated 33. A camshaft trigger is provided by the flank 33 of the trigger disk 26 in a conventional manner. A logical connection is established between the camshaft trigger and the scanning of the crankshaft trigger wheel 27.

[0052] The crankshaft trigger wheel 27 has teeth 35, which, together with an adjacent gap located between two teeth 35, each cover an angle of 6°. By omitting two teeth, a recess 36 is formed, with the first tooth 35 bordering the recess 36 representing a reference marking 34. The signal detected with the aid of the reference marking 34 is also referred to as a TD signal. A copy of this TD signal, to which a further marking may be added, is sent from the engine control unit 21 via the signal line 20 to the camshaft control unit 17. Within the camshaft control unit 17, the TD signal, which indicates a reference angular position of the crankshaft, is logically linked to features of the electric motor 11, 12.

[0053] Figure 2 shows permanent magnets 30 and windings 31 of the electric motor 11, 12. A possible pattern of Hall signals HSA, HSB, HSC, which provide information about changes in the angular position of the rotor 28, is shown schematically in . Each combination of the Hall signals HSA, HSB, HSC corresponds to a bit pattern, in the exemplary embodiment, the bit patterns 010, 011, 001, 101, 100, and 110.

[0054] As Figure 3 shows, each tooth 35 provides a rising flank Fs and a falling flank Ff. It can be assumed with good approximation that the crankshaft speed does not change during further rotation by one tooth 35. Thus, the time interval, which indicates a partial period during the further rotation of the crankshaft 2 from one tooth 35 to the next tooth 35, can be used to calculate any angular position of the crankshaft 2 lying between two teeth 35. In this way, the camshaft reference position, i.e., the angular position of the camshaft 3, 4 at which the flank 33 is detected, can also be assigned to an exact angular position of the crankshaft 2.

[0055] In a similar manner, the angular positions of the camshaft 3, 4 are extrapolated using bit patterns generated during operation of the electric motor 11, 12. This calculation also assumes that the motor shaft 29 rotates at an approximately constant angular velocity within the relevant angular range.

[0056] Figure 4a shows a signal S that is received and processed by one of the control units 17, 21. The applied voltage is plotted over time. The signal S consists of a useful signal 45, which is superimposed with interference pulses 46a to 46h. Due to the short duration of the interference signals, they induce voltages that appear as peaks.

[0057] The electrical signal S is analog and is first transformed into a digital signal S'. Two quantization levels Qi, Q2, also designated low and high, are provided for the digital signal. Assignment to one of the quantization levels is as follows: If the signal voltage is above an upper threshold value U2, assignment to quantization level Q2 is made regardless of the actual level. Similarly, if the signal voltage is below a lower threshold value U1, assignment to quantization level Q1 is made. This means that interference pulses 46b and 46h, for example, have no influence on assignment to quantization level Q1.

[0058] The range between thresholds U1 and U2 defines a transition range. If the voltage exceeds or falls below one of the thresholds over time and thus reaches the transition range, but without exceeding or falling below the other threshold, no reassignment of the quantization stage Qi, Q2 occurs. The interference pulse 46e therefore does not cause a reassignment because the voltage exceeds the lower threshold U1 but then falls below it again without first reaching the level of the upper threshold U2.

[0059] All other interference pulses 46a, 46c, 46d, 46f and 46g are included in the digital signal S'.

[0060] In the next step, the number of changes in the quantization level Qi, Q2 in the respective sampling rate interval T is determined. All even-numbered changes in the quantization level Qi, Q2 in the sampling rate interval T are discarded, so that only the first change is considered. As described below, this eliminates the noise pulses.

[0061] The interference pulse 46a, which occurs in the first sampling rate interval T, is shown in more detail in Figure 5d. It forms a double edge and thus a double change in the quantization level Qi, Q2, and is therefore not counted. The same applies to the interference pulses 46d and 46f, which are shown enlarged in Figure 5c. They also form a double edge and are therefore not counted.

[0062] The interference pulse 46c is located in the range in which the useful signal 45 changes from the quantization level Q2 to the quantization level Qi. The relevant sampling rate interval T is shown in Fig. 5a. There is an odd number of edges, so that the first edge is counted as a change in the quantization level from Q2 to Qi. The same applies to the reverse transition, which in Figure 4a is provided with a flatter signal rise and the two interference pulses 46f, 46g. The corresponding sampling rate interval is shown in Figure 5g. The five edges again form an odd number, so that they count as a change in the quantization level Qi, Q2.

[0063] The reduction of interference pulses 46a to 46h thus achieved frees up computing power in the control unit 17, 21, which is available for other calculations. Figure 3 shows a trigger disk 26 that differs from the one in Figure 2 in that calculations are performed on three flanks. Using the values ​​shown there, the phase angle is calculated in the case of

[0064] Arrow 1 to 2 x 0° - 0° = 0°,

[0065] Arrow 2 to 2 x 15° - 30° = 0°,

[0066] Arrow 3 to 2 x 90° - 160° = -20°.

[0067] This allows redundancy to be achieved and also makes a control loop more stable.

[0068] List of reference symbols Combustion engine Crankshaft Camshaft Camshaft Chain drive Chain drive Camshaft adjuster Camshaft adjuster Actuating gear Actuating gear Electric motor Electric motor Connecting cable Signal cable Plug connection for connecting cables Plug connection for signal cables Camshaft control unit Plug connection of the camshaft control unit Data bus Signal cable Engine control unit Crankshaft cable Crankshaft sensor Sensor Sensor Trigger disc Crankshaft trigger wheel Rotor Motor shaft Permanent magnet 31 Winding

[0069] 32 Survey

[0070] 33 flank

[0071] 34 Reference mark

[0072] 35 teeth

[0073] 36 recess

[0074] 37 Evaluation unit

[0075] 38 Ring buffer of the camshaft control unit

[0076] 39 Memory area

[0077] 40 memory area

[0078] 41 Ring buffer of the engine control unit

[0079] 42 memory area

[0080] 43 Memory area

[0081] 44 Rotor position detection device

[0082] 45 useful signal

[0083] 46a - 46h Interference pulses

[0084] Ff falling edge

[0085] Fs rising edge

[0086] HSA Hall signal

[0087] HSB Hall signal

[0088] HSC Hall signal

[0089] S Signal

[0090] S' digital signal

[0091] T sampling rate interval

[0092] TD TD signal

[0093] P1 Arrow 1

[0094] P2 Arrow 2

[0095] P3 Arrow 3

Claims

Patent claims 1 . Method for processing an electrical signal (S) which is generated continuously over time and based on measured values from a sensor (23, 24, 25) and is transmitted via a line (20, 22) subject to disturbances, with the following features: a) setting a sampling rate interval (T), b) setting quantization levels (Qi, Q2), c) assigning the electrical signal to a quantization level (Qi, Q2), d) determining the number of changes in the quantization level (Qi, Q2) in the sampling rate interval (T), e) discarding all even-numbered changes in the quantization level (Qi, Q2) within the sampling rate interval (T).

2. Method according to claim 1, characterized in that if there is an odd number of changes in the quantization level (Qi, Q2) within a sampling rate interval (T), all changes in the quantization level (Qi, Q2) in the sampling rate interval (T) following the first change are discarded.

3. Method according to claim 1 or 2, characterized in that the electrical signal (S) is a digital signal or an analog signal which, after transmission through the line (20, 22), is quantized in exactly two quantization levels (Qi, Q2).

4. Method according to one of the preceding claims, characterized in that the electrical signal (S) is filtered.

5. Method according to one of the preceding claims, characterized in that in the case of two consecutive sampling rate intervals (T) with odd-numbered changes of the quantization level (Qi, Q2), the number of changes of the quantization level (Qi, Q2) in the current and previous outgoing sampling rate interval (T) is set to zero.

6. Method according to one of the preceding claims, characterized in that the sensor (23, 24, 25) measures a continuously changing quantity.

7. Method according to claim 6, characterized in that the sensor (23, 24, 25) scans a trigger wheel of a camshaft (3, 4) or a crankshaft (2).

8. Method according to one of the preceding claims, characterized in that the sampling rate interval (T) is controlled or regulated by the measured values.

9. Method according to one of the preceding claims, characterized in that the sampling rate interval (T) is less than 50ps.

10. Control unit (17, 21) for a camshaft adjuster (7, 8) or for an internal combustion engine (1), which carries out a method according to one of the preceding claims.

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