JP5002858B2 - Engine tachometer - Google Patents

Description

  The present invention relates to an engine tachometer that measures an engine speed based on electromagnetic waves generated from an ignition system of an engine.

  An engine tachometer is used for a mower or a chain saw driven by an engine in order to measure an accumulated usage time from the beginning of driving of the engine. Among the engine tachometers, in an engine tachometer called a non-contact type, an electromagnetic induction coil that receives electromagnetic waves generated by the engine ignition system is housed in a case.

In addition, by attaching one end of the antenna lead to the outside of the case, the electromagnetic wave guided from the ignition system through the antenna lead is guided to the electromagnetic induction coil in the tachometer body, and further based on the pulse signal obtained from the electromagnetic wave. The engine speed is calculated (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 09-113522

  However, the conventional engine tachometer is configured to introduce electromagnetic waves generated from the ignition system of the engine into the electromagnetic induction coil installed in the case of the tachometer body through the antenna lead. The loss of electromagnetic wave energy between the part and the electromagnetic wave induction coil of the engine tachometer increases, and there is a problem that intrusion of external noise is unavoidable. In addition, depending on the length of the antenna lead, there are disadvantages such as variations in the reception level of the electromagnetic wave placed on the electromagnetic induction coil, that is, the reception sensitivity, which makes it impossible to detect and measure the engine speed with high accuracy.

  The present invention has been made paying attention to the conventional problems as described above, and is a sensor that can prevent variations in reception sensitivity due to the difference in cable length and intrusion of external noise into the cable with respect to the tachometer body. It is an object of the present invention to provide an engine tachometer that enables connection of a device and also enables continuous connection of a conventional antenna device that does not have the electromagnetic induction coil.

  To achieve the above object, an engine tachometer according to the present invention includes a signal input jack on the tachometer main body side into which the signal input plug of the first sensor device in which a signal input plug is connected to a sensor, An input circuit connected to the signal input jack and having an electromagnetic induction coil for inducing electromagnetic waves received by the first sensor device, and extracting a predetermined level of current corresponding to the electromagnetic waves, and obtained from the input circuit A waveform shaping circuit that extracts a pulse signal of a predetermined frequency that has been shaped based on an electric current, an arithmetic circuit that calculates the engine speed using the pulse signal from the waveform shaping circuit as an input, and an electromagnetic induction coil that induces electromagnetic waves received by the sensor An input circuit for extracting a current of a predetermined level corresponding to the electromagnetic wave, and a waveform shaped waveform based on the current obtained from the input circuit. A switch for switching automatically when a signal input plug of the second sensor device having a waveform shaping circuit for taking out a signal is inserted into the signal input jack on the tachometer main body side, and By switching the changeover switch, the output pulse from the waveform shaping circuit on the second sensor device side is input to the arithmetic circuit on the tachometer body side, bypassing the input circuit on the tachometer body side. It is characterized by comprising.

  With the above configuration, when the signal input plug of the first sensor device is inserted into the signal input jack of the tachometer body, the electromagnetic wave input from the first sensor device is caused by the electromagnetic induction coil on the tachometer body side. Induced, converted into a current corresponding to electromagnetic waves by an input circuit on the tachometer main body side, further converted into a pulse signal, and input to an arithmetic circuit for engine speed. On the other hand, when the signal input plug of the second sensor device is inserted into the signal input jack of the tachometer body, the electromagnetic wave input through the sensor of the second sensor device is the second sensor. It is directly guided by an electromagnetic wave induction coil installed in the device, input to the input circuit and waveform shaping circuit in the second sensor device, pulse-converted, and then input to the tachometer body for the first time. And the said pulse signal bypasses the said input circuit containing the electromagnetic wave induction coil in the said tachometer main body, and is input into the said arithmetic circuit. For this reason, when the second sensor device is connected, there is almost no influence of the variation in reception sensitivity due to the difference in cable length as in the conventional case, and the signal current based on the electromagnetic wave flowing through the cable is not affected. Since the level can be maintained at a sufficient value, the influence of external noise entering the cable can be kept relatively small.

  In the engine tachometer according to the present invention, the change-over switch may be a circuit-switching jack whose contact is automatically switched by inserting a circuit-switching plug provided in the second sensor device. Features.

  With the above configuration, the signal input plug and the circuit switching plug of the second sensor device are simultaneously inserted into the signal input jack and the circuit switching jack on the tachometer body side, respectively, so that the second through the signal input plug. The pulse signal input from the sensor device can be input to the arithmetic circuit by bypassing the input circuit including the electromagnetic wave induction coil on the tachometer main body side.

  According to the present invention, any one of the first sensor device having no electromagnetic wave induction coil and the waveform shaping circuit, and the second sensor device having an electromagnetic wave induction coil and the waveform shaping circuit. The engine speed can be calculated on the basis of the signal corresponding to the engine speed from the first, and when the second sensor device is used, the influence of variations in reception sensitivity due to the cable length can be eliminated. In addition, the influence of the external noise on the received signal can be minimized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram conceptually showing a tachometer body P of an engine tachometer according to an embodiment of the present invention. The tachometer body P includes a jack portion 1, an input circuit 2, a waveform shaping circuit 3, an arithmetic circuit 4, a display 5, and an operation switch 6.

  The jack section 1 includes a signal input jack 1a and a circuit switching jack 1b. The circuit switching jack 1b receives a signal input from a signal input plug that is simultaneously inserted into the signal input jack when a circuit switching plug provided in a second sensor device described later is inserted. 2 has a function of switching so as to bypass 2 and connect to the waveform shaping circuit 3. That is, the circuit switching jack 1b functions as a changeover switch.

  The input circuit 2 functions to inductively input an electromagnetic wave input from a first sensor device described later through a signal input jack 1a and convert the electromagnetic wave into a current signal of a predetermined level. The waveform shaping circuit 3 generates a pulse signal from the current input from the input circuit 2, performs waveform shaping, and converts it into a pulse signal suitable for calculation.

  The arithmetic circuit 4 calculates the engine speed by arithmetic processing based on a pulse signal from the waveform shaping circuit 3 based on a predetermined program. The display 5 functions to display the calculation result performed by the calculation circuit 4, that is, the engine speed.

  The operation switch 6 includes a display changeover switch and the like in addition to a power switch for starting the operation of each circuit as the tachometer body P.

  FIG. 2 shows the first sensor device Q used by being connected to the tachometer main body P, and includes a sensor 7 and a signal input plug 9 connected to the sensor 7 via a cable 8. Reference numeral 9 a denotes a pin of the signal input plug 9. The signal input plug 9 can be connected to the signal input jack 1a of the tachometer body P.

  FIG. 3 shows a second sensor device R used by being connected to the tachometer body P. The second sensor device R includes a sensor 10, an input circuit 11, a waveform shaping circuit 12, and a cable 13. A signal input plug 14 and a circuit switching plug 15. The signal input plug 14 and the circuit switching plug 15 are formed in one block body as shown in the figure for convenience of handling. Therefore, the signal input pins 14a and the signal circuit switching pins 15a corresponding to the plugs 14 and 15 are arranged in parallel.

  The pins 14a and 15a can be simultaneously inserted into the signal input jack 1a on the tachometer main body P side and the circuit switching jack 1b having a changeover switch configuration.

  FIG. 4 is a circuit diagram showing details of the tachometer main body P shown in FIG. In FIG. 4, the circuit switching jack 1b of the jack section 1 has received the signal (electromagnetic wave) input through the signal input plug 9 or 14 and the signal input jack 1a, and the circuit switching plug 9 or 14 has been inserted. Depending on whether or not, it is introduced into the electromagnetic wave induction coil 16 in the input circuit 2 through different contacts, or the input circuit 2 is bypassed and supplied to the waveform shaping circuit 3. That is, the circuit switching jack 1b performs the same function as the selector switch of the form shown in FIG.

  One end of the electromagnetic induction coil 16 is connected between the base and emitter of the transistor 17 (this emitter is grounded). The transistor 17 amplifies a current (signal) based on the electromagnetic wave induced by the electromagnetic wave induction coil 16 and outputs it to the waveform shaping circuit 3.

  Two diodes 18 and 19 connected in series between the power source and the ground, a resistor 20 and a resistor 21 also connected in series between the power source and the ground, and a connection point between these diodes 18 and 19; The resistor 22 connecting the connection point of the resistor 20 and the resistor 21 and the diode 23 connected between the connection point of the resistor 20 and the resistor 21 and the ground constitute the input circuit 2 together with the electromagnetic induction coil 16. is doing. The circuit functions to convert the output of the transistor 17 into a predetermined level of current and output it to the waveform shaping circuit 3.

  The waveform shaping circuit 3 includes a flip-flop in which two NANDs 24 and 25 are cross-coupled, two NANDs 26 and 27 connected in series on the output side of one NAND 24, and a waveform shaping connected between input and output terminals of the other NAND 25. Two resistors 28 and 29 and a capacitor 30, and a waveform shaping capacitor 31 connected between the output terminal of the NAND 27 and the ground.

  On the output side of the waveform shaping circuit 3, the arithmetic circuit 4, the display 5 and the operation switch 6 are provided in the same manner as in FIG.

  FIG. 5 shows details of the first sensor device Q shown in FIG. 2, and a signal input plug 9 is connected to a sensor 7 made of a conductive metal disc via a cable 8 as an antenna lead. Made up of.

  FIG. 6 shows details of the second sensor device R, in which an electromagnetic wave induction coil 32 provided in the input circuit 11 is connected to a sensor 10 made of a conductive metal disk. Each end of the electromagnetic induction coil 32 is connected between the base and emitter of the transistor 33 (this emitter is grounded). The transistor 33 amplifies the electromagnetic wave output (signal) induced by the electromagnetic wave induction coil 32 and outputs it to the waveform shaping circuit 12.

  Two diodes 34 and 35 connected in series between the power source and the ground, a resistor 36 and a capacitor 37 which are also connected in series between the power source and the ground, and a connection point between the diodes 34 and 35 and the resistor 36 and The resistor 38 connecting the connection point of the capacitor 37 and the diode 39 connecting the connection point of the resistor 36 and the capacitor 37 and the ground together with the electromagnetic induction coil 32 constitute the input circuit 11. The circuit functions to convert the output of the transistor 33 into a predetermined level of current and output it to the waveform shaping circuit 12.

  The waveform shaping circuit 12 includes a flip-flop obtained by cross-coupling two NANDs 40 and 41, a NAND 42 connected to the output side of one NAND 40, and two resistors 43 for waveform shaping connected between input and output terminals of the other NAND 41. , 44 and a capacitor 45.

  A signal input plug 14 is connected to the output terminal of the NAND 42 of the waveform shaping circuit 12. The circuit switching plug 15 does not constitute a part of the electric circuit, but functions to physically switch signals.

  In the engine tachometer configured as described above, one of the first and second sensor devices Q and R can be connected to the tachometer body P to measure the engine speed.

  First, the signal input plug 9 of the first sensor device Q is inserted into the signal input jack 1a of the tachometer body P, and then the operation switch 6 is operated to instruct measurement of the engine speed.

  In the above case, the electromagnetic wave generated in the ignition system of the engine is transmitted through the sensor 7, the cable 8, and the pin 9a of the plug 9 to the signal input jack 1a, the circuit switching jack 1b and the electromagnetic wave induction on the tachometer body P side. It passes through the coil 16 one after another and is guided to the electromagnetic wave induction coil 16. The current generated in the electromagnetic induction coil 16 by the induction of the electromagnetic wave is amplified by the transistor 17 and then adjusted to a predetermined current level by the adjustment circuit unit including the diodes 18 and 19, the resistors 20 and 22, and the resistor 21. Is done.

  In the waveform shaping circuit 3, a predetermined level of current from the input circuit 2 is input to a flip-flop composed of NANDs 24 and 25, and a predetermined frequency and pulse width corresponding to a time constant determined by the resistor 28.29 and the capacitor 30 are obtained. Generate a square wave pulse. This pulse signal is input to the arithmetic circuit 4 via the NANDs 26 and 27. The arithmetic circuit 4 receives the pulse signal, calculates the engine speed according to a program prepared in advance, and displays the calculation result on the display 5.

  On the other hand, instead of the first sensor device Q, the signal input plug 14 and the circuit switching plug 15 of the second sensor device R are connected to the signal input jack 1a and the circuit switching jack 1b of the tachometer body P. , Plug them in at the same time. Subsequently, the operation switch 6 is operated to instruct start of measurement of the engine tachometer.

  In the above case, the electromagnetic wave received by the sensor 10 is immediately guided to the electromagnetic wave induction coil 32 of the input circuit 11 in the second sensor device R. The current flowing through the electromagnetic wave induction coil 32 by the induction is amplified by the transistor 33 and then adjusted to a predetermined level by the adjustment circuit unit including the diodes 34 and 35, the resistors 36 and 38, the capacitor 37 and the diode 39.

  Further, in the waveform shaping circuit 12, the current obtained from the input circuit 11 is converted into a predetermined frequency and a predetermined pulse width according to a time constant determined by the resistors 43 and 44 and the capacitor 45 by a flip-flop composed of NANDs 40 and 41. Generate a square wave pulse. The pulse signal is input to the signal input plug 14 via the NAND 42.

  The pulse signal input to the signal input plug 14 is input to the signal input jack 1a into which the signal input plug 14 is inserted. At this time, the circuit switching plug 15 switches the contact connection of the circuit switching jack 1b into which the circuit switching plug 15 is inserted. For this reason, although the pulse signal input to the signal input jack 1a is passed through the circuit switching jack 1b, the main circuit of the input circuit 2 having the electromagnetic induction coil 16 is bypassed and input to the waveform shaping circuit 3. .

  The pulse input to the waveform shaping circuit 3 is used for measuring the engine speed in the arithmetic circuit 4 and the measurement result is displayed on the display 5 in the same manner as described above.

  Accordingly, since the second sensor device R itself has the input circuit 11 and the waveform shaping circuit 12 having the electromagnetic induction coil 32 and the transistor 33, the pulse signal obtained by the second sensor device R is a tachometer. The main body P can be immediately used for calculating the engine speed.

  Therefore, the pulse signal from the second sensor device R input to the signal input jack 1a can be input to the arithmetic circuit 4 while bypassing both the input circuit 2 and the waveform shaping circuit 3.

  Therefore, when the second sensor device R is used, even if the length of the cable 13 varies, the signal current flowing through the cable 13 can be hardly affected by external noise. By making the cable 13 a shield structure, the influence of external noise can be suppressed almost completely.

  As described above, in the present embodiment, the output pulse of the waveform shaping circuit 12 in the second sensor device R is changed to the input circuit 2 on the tachometer body P side by switching the circuit selector switch 1b on the tachometer body P side. Since it is configured to be bypassed and input to the arithmetic circuit 4 on the tachometer body P side, the electromagnetic wave input through the sensor 10 of the second sensor device R is induced by the electromagnetic wave in the second sensor device R. The signal current that can be directly induced by the coil 32 and is based on the electromagnetic wave is input to the input circuit 11 and the waveform shaping circuit 12 in the second sensor device R, and then input to the tachometer body P. The input circuit 2 including the electromagnetic wave induction coil 16 in P can be bypassed and input to the arithmetic circuit 4. For this reason, when the second sensor device R is connected, there is almost no influence of variations in reception sensitivity due to the cable length as in the prior art, and the level of the pulse current based on the electromagnetic wave flowing through the cable 13 Can be maintained at a sufficient value, so that the influence of external noise entering the cable 13 can be kept relatively small.

  The engine tachometer of the present invention enables connection of a second sensor device capable of preventing variations in reception sensitivity due to cable length and intrusion of external noise to the tachometer body, and electromagnetic induction to the tachometer body. This has the effect that a conventional antenna device without a coil can be continuously connected, and is useful for an engine tachometer that measures the engine speed based on electromagnetic waves generated from the ignition system of the engine.

It is a block diagram which shows the tachometer main body of the engine tachometer by embodiment of this invention. It is a block diagram of the 1st sensor apparatus connected to the engine tachometer shown in FIG. It is a block diagram of the 2nd sensor apparatus connected to the engine tachometer shown in FIG. It is a circuit diagram of the tachometer main body shown in FIG. FIG. 3 is a circuit diagram of the first sensor device shown in FIG. 2. It is a circuit diagram of the 2nd sensor apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Jack part 2, 11 Input circuit 3, 12 Waveform shaping circuit 4 Arithmetic circuit 5 Display unit 7, 10 Sensor 8, 13 Cable 9, 14 Signal input plug 15 Circuit switching plug 16, 32 Electromagnetic induction coil 17, 33 Transistor P rotation system main body Q first sensor device R second sensor device

Claims (2)

A signal input jack on the tachometer main body side into which the signal input plug of the first sensor device having a signal input plug connected to the sensor can be inserted, and the first sensor device connected to the signal input jack An input circuit for extracting a predetermined level of current corresponding to the electromagnetic wave, and a waveform shaping circuit for extracting a pulse signal of a predetermined frequency shaped based on the current obtained from the input circuit And an input circuit that has an arithmetic circuit for calculating the engine speed using the pulse signal from the waveform shaping circuit as an input, an electromagnetic induction coil for inducing electromagnetic waves received by the sensor, and for extracting a predetermined level of current corresponding to the electromagnetic waves, and Second sensor device having a waveform shaping circuit for extracting a pulse signal having a waveform shaped based on a current obtained from the input circuit A switching switch that is automatically switched when the signal input plug is inserted into the signal input jack on the tachometer main body side, and the waveform on the second sensor device side is switched by switching the switching switch. An engine tachometer configured to input an output pulse from a shaping circuit to the arithmetic circuit on the tachometer body side, bypassing the input circuit on the tachometer body side. 2. The engine rotation according to claim 1, wherein the change-over switch is a circuit change-over jack whose contact is automatically changed by inserting a circuit change-over plug provided in the second sensor device. Total.

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