JPS6044848B2 - Engine rotation detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an engine rotation detection circuit in an electronic circuit device for an automobile.

For example, in automobiles, electronic circuits are installed in various display devices such as vehicle speedometers and engine speed meters called tachometers.

This type of electronic circuit receives input from a transducer that converts a mechanical action into an electrical signal, and the electronic circuit is also devised in various ways depending on the characteristics of the electrical signal. In this case, waveform shaping and amplification in the input circuit are determined depending on which part of the transducer the input electrical signal is extracted from, otherwise the measurement circuit, display circuit, etc. may not operate correctly. . FIG. 1 is an explanatory diagram of the configuration of a conventionally used engine revolution meter. In the figure, the part 1 surrounded by the broken line is the electronic circuit part forming the tachometer, and the part 2
3 is a key switch that is opened and closed by a key on the driver's cab instrument panel; 4 is a ballast resistor; and 5 is a battery that converts the voltage of battery 2 from 6 to 12 volts to a high voltage of 10,000 to 150,000 volts. The ignition coil 6 for changing the voltage to a voltage is controlled on/off in synchronization with the rotation of the engine, and is a breaker point (
7 is a distributor for distributing the high voltage generated on the secondary coil side of the ignition gate coil 5 to each plug in accordance with the order of explosion of the cylinders, and 8 is a capacitor. When current is supplied from the battery 2 to the spark plug, the breaker point 6 is synchronized with the rotation of the engine, so the ground side of the primary coil of the ignition coil 5, that is, point a, is A rectangular voltage signal shown in is generated. By the way, the electronic circuit section 1 of the engine revolution meter is constructed as follows.

That is, a switching element such as the transistor 11
The base of resistor 12, diode 13, and resistor 14
It is connected to the input terminal 15 via the resistor 16, and grounded via the resistor 16. Further, a connection point between the diode 13 and the resistor 12 is grounded via a capacitor 17. The emitter of the transistor 1' is grounded, and the collector is connected to a pulse generating circuit 18, which in turn is connected to a display meter 20 via an output circuit 19. Note that 21 is a stabilized power supply. When the input signal shown in FIG.
is applied to the base of

FIG. 2b shows the voltage across the capacitor 17, and in accordance with this voltage, a trigger pulse as shown in FIG. 2c is generated as a voltage between the collector and emitter of the transistor 11. That is, when the base voltage of the transistor 11 exceeds the BE of this transistor 11, it turns on, triggers the pulse generation circuit 18, and outputs a pulse of a certain time width to the circuit 19.
send to The output circuit 19 amplifies this pulse to drive a meter 20 such as an ammeter. Therefore, the current flowing through the primary coil of the ignition coil 5 is transferred to the input terminal 15.
The meter 20 swings in proportion to the number of input signal pulses per unit time, and the engine speed can be determined. However, since the electronic circuit section 1 of the engine revolution meter extracts the input signal from the connection point between the primary coil and the breaker point 6,
20 at the moment breaker point 6 turns off as shown in
High voltages reaching 0-400 volts were occurring.

If this is repeatedly input to the electronic circuit unit 1 as an induced electromotive force of the ignition coil 5, the integrated circuit unit 1 is likely to be destroyed, or if there are devices nearby that are driven by the same power source, it may cause induced noise. There were problems such as the possibility of this occurring more easily. FIG. 3 shows a voltage waveform generated at one end b of the primary coil of the ignition coil 5 on the battery 2 side. As shown in the figure, one end b of the primary coil is separated from the induced electromotive force generated in the secondary coil, so when the breaker point 6 is turned off, the battery voltage during running, for example 14 volts, is present at point b. The noise is extremely small. Therefore, the electronic circuit section 1 of the engine revolution meter
If the input terminal 15 of the breaker point 6 is connected to this point b, the conventional problem described above will be solved, but when the breaker point 6 is turned on, the voltage at this point b is about 10 volts, and the first
The conventional circuit shown in the figure could not respond to this input signal. The present invention has been made in view of the above circumstances, and provides an engine rotation detection circuit that is less affected by noise and can obtain a pulse signal of a predetermined time width corresponding to the rotation of the engine regardless of the magnitude of the input signal voltage. is aimed at.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the embodiment shown in FIG. 4, an input signal is supplied from one end of the primary coil of the ignition coil 5 on the point b side to the input terminal 15 of the electronic circuit section 1 of the engine revolution meter.
This input signal is shown in FIG. 3 above. In FIG. 4, parts corresponding to those of the conventional device (FIG. 1) are given the same reference numerals and explanations are omitted, but the electronic circuit section 1, which is the gist of this embodiment, is constructed as follows. has been done. That is, one end of a first resistor 22 is connected to the input terminal 15, and the collector and base of an NPN transistor 23 are connected to the other end of this resistor 22. NPN formed to have the same characteristics as a pair with this transistor 23
The base and emitter of the transistor 24 are commonly connected to the transistor 23, and the commonly connected emitters are grounded. The collector of this transistor 24 is supplied with a power supply voltage from the battery 2 via a second resistor 25, and the connection point between the transistor 24 and the resistor 25 is connected to the base of a switching element, such as a transistor 26. A capacitor 27 is connected between the base and emitter of the transistor 26, and the collector outputs a trigger signal to the pulse generating circuit 18. Note that 19, 20, and 21 are an output circuit, a meter, and a stabilized power supply, respectively. The operation of generating a trigger signal in the circuit configured as described above will be explained next.

When the transistors Ql and Q2 are formed with the same characteristics as shown in FIG. 5, the base-emitter voltages VBEl and BE2
are equal, and the respective emitter currents 1E1 and E12 are also approximately equal.
Therefore, collector current 1C191C2) base current 1B1
The relationship of 91B2 is expressed by the following equation. Therefore, the relationship with the current 11 flowing from the input terminal 15 through the resistor 22 is expressed by the following equation.

Here, the current increase writing HP. , is sufficiently large for 2, then 2
Since 1hpE→0, equation (3) becomes 102−=11. By the way, the current 12 flowing from the battery 2 through the resistor 25 is divided into the base current of the transistor Q3 and the collector current 102 of the transistor Q2, but when comparing 12 and 102, if 102 is 12, the current 12 is divided into the base current of the transistor Q3 and the collector current 102 of the transistor Q2. is on. If 2≧12, turn off.

Therefore, from C2==11, the following can be said. (1) 11
When the number is 12, O is on.

(2) When 11≧12, are off.

On the other hand, the currents 11 and 12 flowing through the resistors 22 and 25 are
If the voltage at point b shown in FIG. 4 is Vb, and the voltage at point c is c (electromotive force of battery 2), it can be expressed as follows.

Rl and R2 are resistance values of resistors 22 and 25, respectively.
That is, by appropriately selecting the ratio of the resistance values Rl and R2, the transistor 26 can be turned on and off in synchronization with the opening and closing of the breaker point 6 without being affected by the magnitude of the input signal voltage or variations in the values of the resistors 22 and 25. (Q3) can be controlled on/off. For example, if the above resistance value is R1=R2, the period during which breaker point 6 is on is b<VO, so as is clear from equations (4) and (5) above, 11 times 1
2, and the transistor 26 is turned on. Also, the period when breaker point 6 is off is::Vc, so
It can be seen from the above equations (4) and (5) that 11=12 and the transistor 26 is turned off. Also, since the voltage Vc of the battery 2 is VO>VBE, the transistor 2
The input signal voltage forming the boundary where 6 is inverted between on and off is expressed by the following equation.

Therefore, in the embodiment described above, the input signal is supplied from point b, but the circuit operates reliably even if it is supplied from point a, that is, the other end of the ignition coil 5, as in the conventional circuit.
As mentioned above, the embodiment circuit of this invention! According to this, the first
By appropriately selecting the resistance value ratio of the second resistors 22 and 25, various states of the input signal can be detected and reliably responded to, resulting in a wide range of applications.

In the above embodiment, the resistors 22 and 25 may be configured in any way within an integrated semiconductor circuit as long as they function as resistance circuits and the transistor 26 functions as a switching element. Furthermore, in FIG. 4, the resistor 22 is connected to the input terminal 15, and the resistor 25 is connected to the power supply circuit.
Even if the resistor 22 is connected to the power supply circuit and the resistor 25 is connected to the input terminal 15, the same effect can be obtained by appropriately selecting the ratio of the resistors 22 and 25. Further, although the transistors Ql and Q2 have the same characteristics, they may have slightly different characteristics, and furthermore, resistors may be inserted into the emitters of Ql and Q2, respectively. Further, although the above embodiment is used as an engine revolution meter, it can also be used as an engine revolution detection circuit in other automotive electronic circuits such as a fuel injection device.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining a conventional edge rotation detection circuit, Fig. 2 is a signal waveform diagram for explaining the operation of the circuit shown in Fig. 1, and Fig. 3 is one end of the ignition coil on the point b side. FIG. 4 is a diagram for explaining an engine rotation detection circuit according to an embodiment of the present invention, and FIG. 5 is a circuit diagram used for explaining the operation of the circuit shown in FIG. 4. be. DESCRIPTION OF SYMBOLS 1... Electronic circuit section of engine revolution meter, 2... Battery (power supply), 5... Ignition coil, 6... Switch, 15... Input terminal, 18... Pulse generating circuit, 22... First resistor, 23... First transistor (Q1), 24... Second transistor (Q2)
, 25... second resistor, 26... switching element (
Q3), 27. ．． ．． capacitor.

Claims (1)

[Claims] 1. A power source, a primary coil having one end connected to one electrode of the power source, and a primary coil connected between the other end of the primary coil and the other electrode of the power source and controlled on/off in synchronization with engine rotation. As a result, there is a switch that interrupts the current flowing through the primary coil, a secondary coil whose one end is connected to the connection point between the switch and the primary coil, and which forms an ignition coil together with the primary coil; a spark plug to which a high voltage is applied; a first resistor having one end connected to the primary coil; a second resistor having one end connected to one electrode of the power supply; The first resistor has a base and a collector connected to the other end of the second resistor, and an emitter connected to the other electrode of the power supply.
a transistor, this first transistor and a base,
a second transistor whose emitters are commonly connected and whose collector is connected to the other end of the second or first resistor; a capacitor connected between the collector and emitter of the second transistor; and a switching element that is controlled on/off based on the collector voltage of the engine and provides a trigger signal to the pulse generation circuit, and obtains a pulse signal of a predetermined time width according to the rotation of the engine from the pulse generation circuit. Engine rotation detection circuit.