JPH0734951A - Rotation signal detecting circuit - Google Patents

Abstract

PURPOSE:To detect the zero-cross point of a rotation signal by a magnetic pickup type sensor with high accuracy by changing a detected voltage (slice level) depending on the rotation signal and the magnitude of its peak voltage, and setting the slice level at the time when hysteresis operates, in a specific range. CONSTITUTION:With a rotation signal detecting circuit 3, the signal level of a rotation signal 2a outputted from an engine-rotation detecting machine 2 is voltage-divided by respective resistors 7 to 9, and is inputted to a minus input terminal of a comparator 21. On the other hand, the slice level 23a which is voltage-divided by resistors 16, 17 and determined by the voltage biased by resistor 18, is inputted to a plus terminal of the comparator 21. Then, the inputs of the respective terminals are compared with each other. As a result, when a voltage-divided signal of the rotation signal 2a is, for example, higher than the slice level 23a, the output of the comparator 21 is reduced to a low level. Then, when the output of the comparator 21 is changed, a comparation voltage is changed, and hysteresis is given to the reference voltage. By setting the comparation voltage in the range 5 to 10mV, malfunction can be prevented, and the detecting accuracy can also be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to engine rotation detection for engine control, and more particularly to a magnetic pickup coil signal input circuit.

[0002]

2. Description of the Related Art A magnetic pickup type rotation sensor is a sensor which detects that a magnetic flux generated from the sensor itself has changed due to an external factor and outputs an electric signal according to the amount of change in the magnetic flux. To detect the engine rotation, the above-mentioned change in magnetic flux is generated by the protrusion provided on the sensor plate that rotates in synchronization with the rotation axis of the engine. If the engine speed is low, the change in the magnetic flux is small and the output voltage from the sensor is low. On the contrary, when the engine speed is high, the change in the magnetic flux is large, so that the output from the sensor is also large. On the other hand, the sensor output may be changed according to the above-described principle due to the plate notch or distortion generated in the manufacturing process in addition to the rotation detection protrusion on the sensor plate. The signal generated by this causes noise as a cause of engine control malfunction. Therefore, when processing the signal of the magnetic pickup type rotation sensor, a circuit for distinguishing the voltage of the normal signal from the noise is necessary. Especially, the voltage (slice level) that distinguishes the signal from the noise is the rotation speed of the engine. Alternatively, it needs to be changed according to the output voltage of the sensor signal.

As described above, in order to detect the signal from the sensor, the technique for changing the slice level is disclosed in the open technical report 88-.
An input circuit as described in No. 11199 is used.

[0004]

In the above-mentioned prior art, when a sensor signal higher than the slice level is detected, the output of the input circuit is inverted, and at the same time, the hysteresis is provided to lower the slice level to the ground level. This is configured as described above in order to detect the zero cross when the sensor signal shifts from the + voltage to the − voltage, that is, the zero cross. The engine control device controls fuel and ignition with reference to this zero-cross point. Here, in engine control in recent years, more precise fuel and ignition control is required due to stricter exhaust gas regulations and the like, and therefore, higher precision is also required in the positional accuracy at which the rotation signal is generated. The accuracy of the rotation detection signal is related to the slice level voltage of the input circuit as well as the position accuracy of the protrusions provided on the sensor plate. That is, the slice level is lowered to around 0 V due to hysteresis, but if the voltage becomes high to some extent, an error will occur in the detection of the zero cross point,
It affects the accuracy of engine control. The above-mentioned prior art does not consider such accuracy.

On the other hand, as a method of detecting the zero-cross point with high accuracy, a method of completely setting the slice level to 0 V is conceivable, but in order to realize this method, an input circuit is operated- (minus) power source is required. Therefore, the circuit becomes very expensive. An object of the present invention is to provide an input circuit that inexpensively and highly accurately shapes a signal output from a magnetic pickup type rotation sensor.

[0006]

[Means for Solving the Problems] The above problem is caused when a voltage comparator (comparator) for comparing a sensor signal and a slice level is used for an input circuit for one power supply (only + power supply is used), and hysteresis occurs. This can be solved by setting the slice level voltage of 1 to 5 mV to 10 mV.

[0007]

Since the offset voltage of the comparator used in the input circuit is 5 mV, the slice level is set to 5
If it is set to mV or more, no malfunction of the circuit is caused. Further, by setting the slice level to 10 mV or less, the detection of the signal becomes closer to 0 V, so the detection accuracy is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the rotation signal detecting means in the engine control system. Reference numeral 1 is a sensor plate for detecting engine rotation, which is connected to a rotation shaft of the engine, 2 is a magnetic pickup type rotation detector, 3 is a rotation signal detection circuit, and 4 is a CPU. Although not shown, the sensor plate 1 has a protrusion 5 for detecting a control reference position that serves as a reference for fuel injection and ignition control. By the protrusion 5,
When the sensor plate 1 rotates, the gap G between the sensor plate 1 and the rotation detector 2 changes. At this time, a change occurs in the magnetic flux generated between the sensor plate 1 and the rotation detector 2, and a potential difference is generated at both ends of the coil in the rotation detector 2 and output from the rotation detector 2 as a rotation signal 2a. To be done. The above-mentioned signal is input to the rotation signal detection circuit 3, waveform-shaped, and input to the CPU 4.

FIG. 2 is a timing chart showing the operation when the engine speed is low. When the engine speed is low,
The peak voltage Vp of the rotation signal 2a output from the rotation detector 2 is a relatively low voltage. Rotation signal detection circuit 3
Then, when the rotation signal 2a becomes higher than a certain voltage, the rotation detection signal 3a is changed from the high level to the low level, and when the rotation signal 2a becomes lower than a predetermined voltage, the rotation detection signal 3a is changed from the low level to the high level. Such a signal is output to the CPU 4. At this time, if the sensor plate 1 is damaged or distorted, noise is generated at a timing other than the signal as shown in FIG. The rotation signal detection circuit 3 needs to be a circuit that does not erroneously detect this noise.

FIG. 3 is a timing chart showing the operation when the engine speed is high. When the engine speed is high, the rate of change of the magnetic flux with respect to the time between the sensor plate 1 and the rotation detector 2 is large, so the peak voltage Vp of the signal becomes a higher voltage than when the speed is low. Similarly, the voltage of noise that enters the rotation signal 2a also increases. Therefore, the rotation signal detection circuit 3 needs to be a circuit that does not detect the noise that changes the generated voltage according to the rotation of the engine.

As shown in FIG. 2 or FIG. 3, the rotation signal 2
The rotation detection signal 3a having the waveform shaped a is input to the CPU 4, and this signal is used as a reference for controlling fuel injection and ignition. In particular, the time point (zero cross point) at which the rotation signal 2a changes from + voltage to −voltage is used as a reference. This is because the zero cross point when the output waveform of the rotation detector 2 shifts from the + voltage to the − voltage has a constant generation position (angle) regardless of whether the engine speed is high or low. Therefore, the rotation signal detection circuit 3 must be configured to detect this zero-cross point as well.

FIG. 4 shows a detailed circuit of the rotation signal detecting circuit 3. 6 is a Zener diode that clamps the input voltage when the rotation signal 2a is equal to or higher than a predetermined voltage, 7, 8 and 9 are resistors for voltage division, 10 is a transistor that operates when the rotation signal 2a is equal to or higher than the predetermined voltage, and 11 is A capacitor for holding a voltage according to the peak value of the rotation signal 2a, 12
Is a resistor that gives the discharge time constant of the capacitor 11, 1
Reference numerals 3 and 14 denote transistors for biasing the voltage charged in the capacitor 11 to the slice level 23a, and 15
Is a resistor for applying a voltage to the emitter of the transistor 13, 16 and 17 are resistors for providing an initial value of the slice level 23a, 18 is a resistor for biasing the voltage given from the transistor 14, and 19 is a hysteresis for the slice level 23a of the comparator 21. Resistor to give, 20 is a pull-up resistor of the output of the comparator 21, 21 is the rotation signal 2
It is a comparator that compares the voltage magnitudes of a and the slice level 23a. The rotation signal 2a shown in FIG. 2 or 3 is input to the rotation signal detection circuit 3 from the rotation detector 2.
In the rotation signal detection circuit 3, first, the signal levels of the rotation signal 2a are divided by the resistors 7, 8 and 9 and input to the negative input terminal of the comparator 21. The + input terminal of the comparator 21 has a slice level 23a which is divided by the resistors 16 and 17 and is determined by the voltage biased from the resistor 18.
Is input and the magnitude of the rotation signal 2a is compared with the divided signal. If the divided voltage signal of the rotation signal 2a is higher than the slice level 23a, the output of the comparator 21 becomes Low level. High if the voltage comparison results are reversed
Is output. On the other hand, similarly to the above, the signal divided by the resistors 7, 8 and 9 is applied to the base of the transistor 10,
When the rotation signal 2a becomes higher than the predetermined voltage, the transistor is turned on. When the transistor 10 is turned on, a current flows from Vcc, which is a constant voltage (for example, 5V), to the emitter of the transistor 10 and the capacitor 11 is charged. At this time, as the capacitor 10 is charged, the emitter potential of the transistor 10 rises, and when the voltage input to the base of the transistor 10 decreases by V _BE , the transistor 10 is kept on. Can not be. Therefore, the voltage charged in the capacitor 11 is the peak voltage V of the rotation signal 2a.
It becomes a voltage according to p. Next, when the peak of the rotation signal 2a passes and becomes −voltage or 0 V, the electric charge charged in the capacitor 11 is discharged through the resistor 12. On the other hand, the charging voltage of the capacitor 11 is given to the base of the transistor 13, and the transistor 13 is turned on. At this time, the emitter potential of the transistor 13 becomes higher than the base voltage by V _BE . Similarly, the transistor 14 is also turned on because the base potential is applied, and the emitter potential at that time becomes lower than the base potential by V _BE . That is, the emitter potential of the transistor 14 and the charging voltage of the capacitor 11 are substantially equal to each other. The voltage generated at the emitter of the transistor 14 is applied to the slice level 23 via the resistor 18.
The slice level 23a changes depending on the magnitude of the bias voltage. According to the above-mentioned principle, the slice level 23a changes according to the magnitude of the peak voltage of the rotation signal 2a, and also changes according to time by discharging the capacitor 11 until the next signal is input.

As described above, when the comparator 21 compares the slice level 23a with the divided voltage signal of the rotation signal 2a and detects the signal to set the output of the comparator 21 to Low, the emitter of the transistor 13 is changed from the resistor 15 to the resistor 15. Since the voltage is supplied, the emitter potential becomes almost 0V, the transistor 14 is turned off, and the bias voltage via the resistor 18 is not applied. Since the output side of the comparator 21 of the resistor 19 is also approximately 0V, the slice level 23a becomes a voltage divided by the combined resistance of the resistors 17 and 19 and the resistor 16. Therefore, when the output of the comparator 21 outputs Low, there is hysteresis and the slice level 23a becomes a low voltage.

FIG. 5 is a timing chart showing the operation of the rotation detection circuit 3. When the rotation signal 2a is input and becomes higher than the slice level 23a, the rotation signal detection circuit 3
The rotation detection signal 3a, which is the output of, becomes low level. At this time, the slice level 23a is 0 V due to hysteresis.
It decreases to the vicinity. When the rotation signal 2a drops in voltage and becomes lower than the slice level 23a, the rotation detection signal 3
a becomes High level, and at the same time, the slice level 23a rises to a level according to the peak voltage Vp of the input rotation signal 2a, and then decreases according to the discharge characteristic of the capacitor 11. At this time, even if noise is generated in the rotation signal 2a, if it is equal to or lower than the voltage of the slice level 23a, it is not detected as a signal.

Although the rotation signal is detected as described above, it is necessary to improve the detection accuracy of the position where the rotation signal 2a is generated in order to strengthen regulations on exhaust gas and improve fuel economy in recent years. As an example, FIG. 6 shows the operation timing of the ignition control. The ignition control outputs the ignition signal by counting the time or angle to the ignition position with reference to the rising of the rotation detection signal 3a. Here, since the zero cross point of the rotation signal 2a is the control reference, the rotation detection signal 3a is preferably a signal that rises at the zero cross point of the rotation signal 2a. In this case, accurate ignition control can be performed as shown in A of FIG. However, if the rotation detection signal 3a rises at a timing different from the zero-cross point as shown in FIG. 6B, the ignition timing will shift by the amount of the shift, and accurate ignition control will not be possible. there is a possibility. Therefore, it is necessary to make the signal detection timing of the rotation signal detection circuit 3 accurate. For that purpose, the slice level 23a at the time of hysteresis should be set as close to 0V as possible.

FIG. 7 is a timing chart showing the relationship between the slice level 23a and the detection timing. FIG. 7A shows a waveform shaping state when the slice level V _SL is high when hysteresis is applied. At this time, a deviation t _D occurs between the zero cross point of the rotation signal 2a and the rotation detection signal 3a. This is because the rotation signal 2a is not a square wave but a waveform close to a sine wave. Therefore, the higher the slice level V _{SL, the} larger t _D becomes. Conversely, slice level 2
If 3a is low, the deviation t _D between the zero cross point of the rotation signal 2a and the rotation detection signal 3a becomes small as shown in FIG. 7B.

FIG. 8 is a graph showing the relationship between the slice level V _SL and the signal detection deviation t _D when the above hysteresis is applied. The higher the slice level V _SL , the larger the deviation t _D becomes exponentially. Therefore, the rotation signal 2
In order to detect the zero cross point of a with high accuracy, it is necessary to set V _SL to a predetermined value or less. It can be seen from the graph of FIG. 8 that V _SL can be set to 10 mV or less in order to minimize the deviation at the time of signal detection, especially when considering the engine from high rotation to low rotation. From the above, if V _{SL is set} to 10 mV or less, the zero-cross point of the rotation signal 2a can be accurately detected.

If V _{SL is set} to 0 V, the rotation signal 2a
It is possible to detect the zero-cross point of
However, it is difficult to realize with the comparator 21 used in the rotation signal detection circuit 3 shown in FIG. That is, the power source of the comparator 21 is supplied from the battery voltage V _B, and the ground of the comparator 21 is connected to the ground of the entire rotation signal detection circuit 3 and becomes 0V. At this time, when the input terminal of the comparator 21 is set to 0V, the comparator 21 may malfunction. FIG. 9 shows a waveform when the malfunction occurs. When the rotation signal 2a is generated and becomes higher than the slice level 23a, the rotation detection signal 3a becomes Low, and at the same time, the slice level 23a becomes 0V.
However, when the potential difference between the ground of the comparator 21 and the input terminal falls within a voltage within which the characteristics of the comparator 21 can be achieved, the comparator 21 may not operate normally. When the rotation signal 2a has a negative voltage, the voltage of the negative input terminal of the comparator 21 is originally lower than the voltage of the negative input terminal of the comparator 21, so that the rotation detection signal 3a may be high, but may remain low. Therefore, when using a single power supply type comparator, the voltage of the slice level 23a cannot be made lower than a predetermined voltage. In order to realize the slice level = 0V, it is necessary to use a device that detects 0V, that is, a dual power supply type comparator of + and − for the comparator 21. Therefore, in addition to the rotation signal detection circuit 3, it is necessary to provide a minus power supply, resulting in a very expensive circuit. In order to make the circuit inexpensive and prevent malfunction, it is necessary to set the slice level to a predetermined voltage or higher.
Since the input voltage for the comparator 21 to normally operate is generally set to 5 mV or higher, the slice level V _SL when hysteresis operates needs to be 5 mV or higher.

From the above, by setting the slice level when hysteresis acts to 5 mV or more and 10 mV or less, it is possible to construct a rotation signal detection circuit that is inexpensive and has good detection accuracy.

[0021]

As described above, there is an effect that a rotation signal detecting circuit that can inexpensively detect the zero-cross point of the rotation signal with high accuracy can be supplied to the magnetic pickup type rotation detector.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a rotation detection method in an engine control system.

FIG. 2 is a timing chart showing the operation of a rotation signal and a rotation detection signal when the engine speed is low.

FIG. 3 is a timing chart showing the operation of a rotation signal and a rotation detection signal when the engine speed is high.

FIG. 4 is a detailed circuit diagram of a rotation signal detection circuit.

FIG. 5 is a timing diagram illustrating the operation of the rotation signal detection circuit.

FIG. 6 is a timing chart for explaining the influence on the control when the detected position of the rotation signal is deviated.

FIG. 7 is a timing diagram illustrating a relationship between a slice level and signal detection accuracy.

FIG. 8 is a graph showing a relationship between a slice level and a signal detection deviation.

FIG. 9 is a timing chart when a circuit malfunction occurs when the slice level is too low.

[Explanation of symbols]

1 ... Sensor plate, 2 ... Rotation detector, 2a ... Rotation signal, 3 ... Rotation signal detection circuit, 3a ... Rotation detection signal, 4 ...
CPU, 5 ... protrusion, 6 ... Zener diode, 7, 8,
9, 12, 15, 16, 17, 18, 19, 20, ... Resistance, 10, 13, 14 ... Transistor, 11 ... Capacitor, 21 ... Comparator, 23a ... Slice level.

Claims (1)

[Claims] 1. An engine having a plurality of cylinders, a plate connected to a rotating shaft of the engine for detecting rotation of the engine, a magnetic pickup type rotation detector for detecting engine rotation from the plate, First voltage dividing means for dividing the signal from the rotation detector at a predetermined ratio,
A voltage comparator for inputting a signal divided by the first voltage dividing means to a first input terminal; a second voltage dividing means for dividing the signal at a rate different from that of the first voltage dividing means; 2 means for holding the maximum voltage of the voltage output from the voltage dividing means, comparison voltage generating means for dividing the power supply voltage that generates a constant power supply voltage regardless of the battery voltage, and the holding means for holding the comparison voltage. Means for biasing the voltage from the first voltage divider means and the biased comparison voltage to the second input terminal of the voltage comparator to detect the magnitude relationship with the signal from the first voltage dividing means. Means for varying the output from the comparator,
In a rotation signal detection circuit having means for decreasing the held voltage with a predetermined time constant, the rotation signal detection circuit has means for changing the comparison voltage when the output of the voltage comparator changes and for giving a hysteresis to the comparison voltage. , The comparison voltage when the comparison voltage has hysteresis is 5 mV or more 1
A rotation signal detection circuit characterized by being set to 0 mV or less.