JP2709921B2 - Waveform shaping circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping circuit used in a crankshaft rotation angle detecting circuit used in an electronic control unit for controlling fuel injection and ignition timing of an internal combustion engine. is there. [Prior art] Conventionally, technologies in such a field include, for example, Japanese Patent Application Laid-Open
There is a signal processing circuit described in Japanese Patent Application Laid-open No. -69202. In the signal processing circuit, in a waveform shaping circuit that shapes a waveform of an output signal of an electromagnetic pickup and generates a pulse signal, a waveform shaping pulse having the same phase as the electromagnetic pickup signal Since the voltage is differentiated and the differentiated signal is superimposed on the signal of the electromagnetic pickup, the detection malfunction due to the mechanical vibration noise can be prevented. FIG. 2 is a circuit diagram showing an embodiment of the waveform shaping circuit disclosed in the above document. In FIG. 2, IC ₁ is a comparator (open collector type), Tr ₁ is a PNP transistor, D ₁ and D ₂ are diodes for clamping the signal of the electromagnetic pickup 13 to the common mode input voltage range of the comparator IC ₁ , and C ₁ is A noise canceling capacitor, R ₁ is a current limiting resistor for applying a bias to the diode D ₁ , a capacitor C ₂ and a resistor R ₈ differentiate the signal amplified by the transistor Tr ₁ and calculate the differentiated waveform voltage. Differentiating circuit for applying to the signal of the electromagnetic pickup 13, R ₃ and
R ₄ is a resistor for providing a threshold level of the comparator IC _1. FIG. 3 is a waveform diagram showing an operation state of the circuit shown in FIG. 2 when mechanical vibration noise is superimposed on the rotation angle signal of the electromagnetic pickup 13. In the figure, (A) is an input signal from the electromagnetic pickup 13 and (B) is a comparator IC1.
(C) shows each waveform of the voltage of the negative input terminal of the comparator IC1. Differential voltage at time t ₁ noise at time t ₂ is duplicated electromagnetic pickup signal is pulled down below the threshold level SL of comparator IC _1, malfunction due to noise can be prevented. Normally, the engine speed at which noise is a problem is often 30 to 400 rpm, and the noise level has been found to be about 50 to 200 mVpp in terms of peak value.
It is necessary to the determine the time constant of the output voltage characteristic of the circuit shown in FIG. 2 while considering capacitor C ₂ and a resistor R _8. FIG. 4 also shows a circuit for waveform shaping the output signal of the conventional electromagnetic pickup 13, and it is said that this circuit can also prevent malfunction due to noise. [Problems to be Solved by the Invention] However, the magnitude of the output voltage of the electromagnetic pickup 13 normally has a characteristic that is proportional to the engine rotation speed. The output voltage is large during rotation, and naturally the noise voltage due to mechanical vibration also increases when the engine is rotating at high speed.
Therefore, in the circuit having the configuration shown in FIG. 2, the output signal of the electromagnetic pickup 13 is shaped in order to remove mechanical vibration noise, and the shaped pulse signal having the same phase as the obtained signal of the electromagnetic pickup 13 is differentiated. Although applied to the signal of the electromagnetic pickup 13 is positively fed back signal, since the feedback amount is constant (the circuit shown in FIG. 2 and the feedback amount resistor R ₂ resistor R ₈
It is difficult for the engine to remove mechanical vibration noise from low speed rotation to high speed rotation. For example, if the feedback amount is determined to remove mechanical vibration noise at low speed rotation, the feedback amount is small and mechanical vibration noise at high speed rotation with large amplitude cannot be removed. Further, if the feedback amount is determined to remove mechanical vibration noise at high speed rotation, the feedback amount becomes large, and the signal of the electromagnetic pickup 13 at low speed rotation with a small signal level cannot be detected. Further, in the circuit having the above-described configuration, as shown in FIG.
Diode D ₁ is required to clamp the signal of the electromagnetic pickup 13 to the common mode input voltage range of the comparator IC _1, the signal of the electromagnetic pickup 13 will float from the ground GND level, on the various electrical loads in motor vehicles There is a drawback that noise generated when turning off is easily induced. Further, in the circuit configuration shown in FIG. 4, there is no problem of noise induced as described above so one side of the electromagnetic pickup 13 is in the ground GND, a zero cross signal of the electromagnetic pickup 13 of the transistor Tr ₂ base because the emitter is detected by utilizing the闘値, it requires a diode D ₃ for correcting the level shift by the闘値the base of the transistor Tr _2, the transistor Tr ₂ base-emitter闘値and diode It has a drawback that can not be detected accurately zero crossing by the deviation of the variation and temperature characteristics of the forward voltage of the D _3. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is possible to eliminate the above-described problems and eliminate mechanical vibration noise that is proportional to the engine speed superimposed on an electromagnetic pickup signal, and accurately eliminate the zero of the electromagnetic pickup signal. An object of the present invention is to provide a waveform shaping circuit which can detect a cross and hardly induce noise. Means for Solving the Problems In order to solve the above problems, the present invention comprises an electromagnetic pickup for detecting the rotation angle of an internal combustion engine, a comparator having an input signal terminal and a reference potential terminal, and A waveform shaping circuit that receives the output signal of the electromagnetic pickup at a terminal and shapes the waveform with the comparator, differentiates the output signal shaped by the comparator, absorbs the differentiated falling differential signal, and outputs a rising differential signal. A differentiating circuit, and a rising differential signal from the differentiating circuit is fed back to the input signal terminal side of the comparator, and is provided in parallel with the differentiating circuit, and an output signal from the comparator is fed back to an input signal terminal of the comparator via a resistor. And a feedback circuit that changes the threshold level when detecting the falling of the comparator. The waveform shaping circuit was configured by connecting the reference potential terminal of the comparator and the ground side of the electromagnetic pickup to a common ground. [Operation] By configuring the waveform shaping circuit as described above, the amount of feedback changes according to the magnitude of the amplitude of the electromagnetic pickup signal. That is, the threshold voltage of the electromagnetic pickup signal is small when the engine is rotating at a low speed and becomes large when the engine is rotating at a high speed. Therefore, the feedback amount is small when the rotating speed of the engine is low, and is large when the engine is rotating at high speed. For this reason, it is possible to remove a mechanism vibration noise having a magnitude that changes in proportion to the rotation speed of the engine superimposed on the electromagnetic pickup signal. Also, since the differentiating circuit absorbs the falling differential signal of the shaped waveform output signal and makes the feedback amount zero, the zero cross point of the accurate electromagnetic pickup signal, that is, the signal waveform of the electromagnetic pickup 13 changes from-potential to + potential. (In the case of a car engine, for example, coincides with the top dead center), and the comparator reference potential terminal and the ground terminal of the electromagnetic pickup are connected to a common ground, so noise is induced. It becomes a difficult configuration. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a waveform shaping circuit according to the present invention. In the figure, a terminal a of the electromagnetic pickup 13 is connected to the ground, a terminal b is connected to the resistor 1, and further connected to the + input terminal of the comparator 7 through the resistors 3 and 6. The negative input terminal of the comparator 7 is connected to the ground, and its output is connected to the power supply + Vcc through the resistor 12.
And to the output terminal c. The output terminal c of the comparator 7 is connected to one end of the resistor 8 and one end of the capacitor 11. The other end of the resistor 8 is connected to the resistor 1
The other end of the capacitor 11 is connected through a resistor 9 to the connection point between the resistor 3 and the resistor 6, and the connection point between the capacitor 11 and the resistor 9 is connected to the anode side. The cathode of the diode 10 connected to the ground is connected. One end of the connection point between the resistor 1 and the resistor 3 is connected to the ground, and the capacitor 2 is connected to the ground.
Further, an anode of the diode 4 and a cathode of the diode 5 are connected to a connection point of the resistor 3 and the resistor 6, and a cathode of the diode 4 and an anode of the diode 5 are connected to the ground. In the circuit shown in FIG. 1, reference numeral 2 denotes a capacitor for removing noise, and diodes 4 and 5 and a resistor 6 are diodes and resistors for protecting the comparator 7 from overvoltage and overcurrent inputs. The resistor 12 is a pull-up resistor of the comparator 7 of the oven collector output type. The capacitor 11 and the resistor 9 are differentiating circuits for differentiating the output pulse of the comparator 7, and 10 is a diode for allowing the differentiating circuit to perform only the rising differentiation and absorb the falling differentiation signal. The resistor 1, the resistor 3, the resistor 8, and the resistor 9 are resistors for determining a feedback amount for positively feeding back the voltage of the output signal of the comparator 7 or the differential voltage of the output signal. 5 and 6 are waveform diagrams showing the operation of the circuit shown in FIG. 1. FIG. 5 is a waveform diagram in which a part of the circuit when the engine is running at a low speed is omitted, and FIG. FIG. 9 is a waveform diagram in the case. FIGS. 5A and 6A show the output signal waveforms of the electromagnetic pickup 13. When the engine shown in FIG. 6A rotates at a high speed, it is compared with the case when the engine rotates at a low speed shown in FIG. 5A. As a result, the output signal voltage value of the electromagnetic pickup 13 is large, and mechanical vibration noise is also large. An output signal waveform diagram of FIG. 5 and FIG. 6 (B) in the comparator 7, the output signal of the electromagnetic pickup 13 in FIG. (A) drops below V _TL, the output voltage of the comparator 7 becomes 0V When the output signal of the electromagnetic pickup 13 rises to 0 V or more, the output voltage of the comparator 7 becomes Vcc. FIGS. 5 and 6 (C) show differential waveforms at the connection point of the capacitor 11 and the resistor 9. The falling differential signal of the output signal of the comparator 7 in FIG. 5 (B) is absorbed by the diode 10 and almost appears. Instead, only the rising differential signal of the output signal of the comparator 7 appears. The time constant of this rising differential signal is
Almost determined by 11 and resistor 9. The cycle of the output signal of the electromagnetic pickup 13 is inversely proportional to the engine speed, that is, the cycle is long (large) when the engine speed is low (small), and short (small) when the engine speed is high (large). ) (Ie, the frequency is directly proportional to the engine speed). Therefore, the discharge voltage Vd of the rising differential signal of the output signal of the comparator 7 increases as the engine speed increases and decreases as the engine speed decreases. That is, the feedback amount of positive feedback by the differential signal of the output signal of the comparator 7 increases as the engine speed increases. Accordingly, as shown in (A) of FIG. 5 and FIG. 6, the threshold voltage V _TL at which the output signal of the electromagnetic pickup 13 is lowered is larger at high engine speed, low engine speed Time gets smaller. For this reason, it is possible to remove mechanical vibration noise proportional to the engine rotation speed. This will be described in more detail below. The comparator 7 has hysteresis in the threshold voltage and has two threshold voltages in order to prevent malfunction due to noise. The lower threshold voltage is V _TL and the higher threshold voltage is zero cross (0
V). The difference between these two threshold voltages is called the hysteresis voltage. Considering the case where the input changes from a positive potential to a negative potential, at this time, the output voltage of the comparator 7 is Vcc, and the + input terminal of the comparator 7 is a feedback voltage from the output (for example, +2 V, hereinafter, this numerical value is an example). )
Is biased. The reference voltage of the comparator 7 is the ground potential (0 V) of the negative input terminal. When the input voltage gradually decreases and reaches the threshold voltage V _TL (−2 V), the potential of the + input terminal voltage of the comparator 7 cancels the bias to become 0 V, so that the output changes from Vcc to 0 V, and the bias becomes 0 V. next, the threshold voltage V _TL is made to 0V from -2V. Therefore, even if noise is superimposed on the input voltage (at this point, it is lower than −2 V), no output change occurs unless the input voltage exceeds 0 V (no noise of 2 V or more).
That is, the hysteresis improves noise immunity. The range of the hysteresis voltage is a dead zone. In the circuit of FIG. 1, since the feedback voltage changes by the action of the capacitor 11, the threshold voltage V _TL
Also changes in proportion to the engine speed. That is, the hysteresis voltage of the comparator 7 also changes, and becomes smaller when the engine speed is low, and becomes larger when the engine speed is high. The noise resistance is proportional to the engine speed. On the other hand, the output signal voltage of the electromagnetic pickup 13 changes in proportion to the engine speed, and the noise voltage due to mechanical vibration also changes in proportion to the engine speed. Therefore,
When the output signal of the electromagnetic pickup 13 is input to the circuit of FIG. 1 set to an appropriate circuit constant, when the engine speed is high and the output signal voltage and noise of the electromagnetic pickup 13 are large, the hysteresis voltage of the comparator 7 is reduced. Since it becomes large, it operates without malfunction even with large noise. Also, even when the engine speed is low, the hysteresis voltage is automatically reduced, so that small noises can be properly removed and the electromagnetic pickup signal is not missed. The threshold voltage _VTL is represented by the following equation (1). V _TL ≒ − (R ₁ / R ₈ ) · V _cc − ｛(R1 + R3) / R9｝ · V
_d (1) Here, R ₁ , R ₃ , R ₈ , and R ₉ are the resistance values of the resistor 1, the resistor 3, the resistor 8, and the resistor 9, respectively, and R ₉ >> R ₁ , R ₁₂ (Resistor
12 is the resistance value). In the above equation (1), the first term on the right side is a fixed threshold component by the resistor 8, and the second term on the right side is a threshold component of the rotation speed response. In the above equation (1)
V _d is represented by the following equation (2). V _d ≒ V _cc · Exp ｛-t / (C ₁₁ · R ₉ )｝ (2) Here, C ₁₁ is the capacitance of the capacitor 11, and t may be about the period of the output signal of the electromagnetic pickup 13. . FIG. 7 shows that in the circuit shown in FIG. ₁ , R ₁ = 3.9 KΩ,
_{R 3 = 270KΩ, R 6 =} 220Ω, R 8 = 100KΩ, R 9 = 330KΩ, R 12
This graph shows the characteristics of the engine rotation speed (rpm) and the threshold voltage (v) when = 1 KΩ, C ₂ = 1000 pF, and C ₁₀ = 0.022 μF. Further, as shown in FIG. 5C and FIG. 6C, the falling differential signal of the output signal of the comparator 7 is absorbed by the diode 10 and clamped at 0 V, so that the positive feedback Since the amount becomes 0, the comparison reference voltage of the comparator 7 (-input potential of the comparator 7) is connected to the ground (0V), and the end a of the electromagnetic pickup 13 is also connected to the ground (0V). The cross can be detected, that is, the signal waveform of the electromagnetic pickup 13 changes from − potential to +
A point that crosses 0 V when changing to a potential (in the case of an automobile engine, for example, coincides with top dead center) can be accurately detected. In addition, since one end of the comparator 7 which is the reference potential is directly connected to the ground, the reference potential is stable, and the output signal voltage and noise of the electromagnetic pickup 13 are high due to the high engine speed as described above. Is large, the hysteresis voltage of the comparator 7 becomes large, so that there is an effect that noise is hardly induced. Further, the diode 10 has a function of removing a negative voltage portion of a differential waveform of the output voltage of the comparator 7 due to the capacitor 11 of the capacitor, and ideally clamping the output voltage to 0V.
Actually, the forward voltage component of the diode 10 appears as a residual voltage, but is discharged in a short time to 0 V, so that there is usually no problem. As described above, according to the above embodiment, the output signal of the comparator 7, that is, the rising differential signal of the differentiating circuit including the resistor 9, the capacitor 11, and the diode 10 for differentiating the rising of the output signal of the electromagnetic pickup 13 is input to the comparator 7. And the output signal of the comparator 7 is fed back to the input side of the comparator 7 via the resistor 8, so that the feedback amount changes according to the engine speed, and the threshold of the output signal of the electromagnetic pickup 13 is changed. Since the drive voltage is low when the engine speed is low and high when the engine speed is high, it is possible to remove mechanical vibration noise superimposed on the output signal of the electromagnetic pickup 13 and proportional to the engine speed. Further, the waveform shaping circuit of the above embodiment is
The differentiating circuit absorbs the falling differential signal of the waveform shaping output signal by the diode 10 to reduce the amount of feedback to zero, and the reference potential terminal of the comparator 7 which is a main component of the waveform shaping circuit is connected to (−
Since the terminal and the ground side of the electromagnetic pickup 13 are connected to a common ground, accurate zero-cross detection can be performed and noise is hardly induced. [Effects of the Invention] As described above, according to the present invention, a differentiation circuit that differentiates an output signal shaped by a comparator, absorbs the differentiated falling differential signal, and outputs a rising differential signal, and the differentiation circuit Is fed back to the input signal terminal side of the comparator, and is provided in parallel with the differentiating circuit, and the output signal from the comparator is fed back to the input signal terminal of the comparator via a resistor, so that the falling of the comparator is obtained. Since a feedback circuit for changing a threshold level at the time of detection is provided, and the reference potential terminal of the comparator and the ground side of the electromagnetic pickup are connected to a common ground, the following excellent effects can be obtained. Since the feedback amount changes according to the amplitude of the output signal of the electromagnetic pickup, the waveform of the crankshaft rotation angle detection circuit that uses the waveform shaping circuit of the present invention for electronic control for controlling fuel injection and ignition of the internal combustion engine If applied to the shaping circuit, the threshold voltage of the electromagnetic pickup signal is small when the rotation speed of the internal combustion engine is low, and becomes large when the rotation speed is high, so that the threshold voltage is proportional to the rotation speed of the internal combustion engine superimposed on the electromagnetic pickup signal. It is possible to remove mechanical vibration noise of which magnitude changes. Further, since the differentiating circuit absorbs the falling differentiating circuit and makes the feedback amount zero, it is possible to accurately detect the zero cross of the electromagnetic pickup signal. In addition, by connecting the comparator reference potential terminal and the ground terminal of the electromagnetic pickup to a common ground, noise is less likely to be induced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a waveform shaping circuit configuration according to the present invention;
2 is a circuit diagram showing an example of a conventional waveform shaping circuit, FIG. 3 is a waveform diagram showing an operation state of the circuit shown in FIG. 2, FIG. 4 is a circuit diagram showing an example of a conventional waveform shaping circuit, FIG. 5 and FIG.
FIG. 7 is a waveform diagram showing the operation of the circuit shown in FIG. 1, and FIG. 7 is a diagram showing characteristics of the rotation speed (rpm) of the engine and the threshold voltage (Vd) in the circuit shown in FIG.
In the figure, 1,3,6,8,9,12 …… resistor, 2,11 …… capacitor,
4, 5, 10: Diode, 7: Comparator, 13: Electromagnetic pickup.

Claims (1)

(57) [Claims] An electromagnetic pickup for detecting a rotation angle of the internal combustion engine,
A waveform shaping circuit that includes a comparator having an input signal terminal and a reference potential terminal, receives an output signal of the electromagnetic pickup at the input signal terminal, and shapes the waveform by the comparator; differentiating the output signal shaped by the comparator A differentiating circuit for absorbing the differentiated falling differential signal and outputting a rising differential signal, and a rising differential signal from the differentiating circuit being fed back to the input signal terminal side of the comparator, and being provided in parallel with the differentiating circuit; A feedback circuit that changes a threshold level when detecting a fall of the comparator by feeding back an output signal from the comparator to an input signal terminal of the comparator via a resistor; and Connect the reference potential terminal and the ground side of the electromagnetic pickup to a common ground Waveform shaping circuit, characterized in that connected.