JPS632613Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an overspeed prevention device for an internal combustion engine, and in particular, it uses a CR time constant circuit to delay the operation of a thyristor that controls current supply to an ignition coil. This relates to something that delays the ignition timing.

That is, the present invention detects the positive voltage induced in the generating coil during high-speed rotation and turns on the switching transistor based on the terminal voltage of a time constant circuit connected in series to the generating coil via the switching transistor. None, despite the subsequent negative voltage induced in the generator coil, the discharge of the discharge capacitor connected in series with the ignition coil to the ignition coil is delayed according to the above time constant characteristics by the discharge control thyristor. The ignition speed, that is, the overspeed of the internal combustion engine is reliably prevented.

The present applicant has already provided the above-mentioned overspeed prevention device as Japanese Patent Application Laid-Open No. 57-41467.

The present invention relates to an improvement of the above-mentioned device, and is characterized by reducing the number of electronic components, lowering costs, and making the device smaller and lighter.

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a specific configuration of the present invention. Reference numeral 1 denotes a power generation coil, and a flywheel with a permanent magnet embedded around it is provided.By rotating this flywheel in synchronization with the engine's crankshaft, a voltage corresponding to the rotational speed of the engine is applied to the power generation coil. It induces A resistor 2, a resistor 3, and the base and collector of a switching transistor 5 are connected in series to this generating coil 1.
A first capacitor 4 is connected in parallel between the connection midpoint of the resistors 2 and 3 and the emitter of the switching transistor 5. The first capacitor 4 is used to charge the positive induced voltage of the generator coil 1, and the resistor 3 and the base-emitter of the switching transistor 5 charge the first capacitor 4 at a predetermined time. It constitutes a discharge circuit that discharges at a constant rate. Therefore, the switching transistor 5 is made conductive when the charge in the first capacitor 4 is discharged by the discharge circuit. Further, 6 is a first thyristor connected in parallel to the first capacitor 4, and a Zener diode 7 is connected between the gate and anode of the first thyristor 6.
A resistor 8 is connected between the cathode and gate of the thyristor 6.
is connected. That is, the Zener diode 7 becomes conductive when the charging voltage of the first capacitor 4 reaches a set level, and the first thyristor 6 becomes conductive when the Zener diode 7 is conductive, giving priority to the discharge circuit. Thus, the charge in the first capacitor 4 is discharged in a short time.

Further, a reverse diode 9 is connected between one end of the generator coil 1 and the emitter of the switching transistor 5, and when the switching transistor 5 is conductive, it connects to a second thyristor 1, which will be described later.
4 trigger voltage is bypassed. Further, the cathode side of the diode 9 is connected to one end of the primary winding 12a of the ignition coil 12 via a forward diode 10 and a second capacitor 11, and the other end of this primary winding 12a is connected to the power generating coil 1. connected to the other end. In addition,
The second capacitor 11 is used to charge the positive induced voltage of the generator coil 1. On the other hand, the positive potential side of the second capacitor 11 is connected to the anode of the reverse diode 9 via a Zener diode 13 in the forward direction and a second thyristor 14 in the reverse direction. This second thyristor 1
The gate of the second thyristor 14 is connected to the other end of the generator coil 1, and a diode 15 and a resistor 17 are connected between the gate and the cathode of the second thyristor 14, respectively. Further, a diode 16 is connected between the gate and anode of the second thyristor 14. Therefore, the second thyristor 1
4 becomes conductive in response to a trigger voltage based on the negative induced voltage of the generator coil 1, and is connected to the second capacitor 11.
The charging charge is transferred to the primary winding 12 of the ignition coil.
It is designed to cause discharge through a. Further, 18 is a spark plug connected to the secondary winding 12b of the ignition coil 12.

Next, the operation of the above circuit will be described.

First, when the flywheel in which a permanent magnet is embedded is rotated, an induced voltage Ve as shown in FIG. 2 is obtained at both ends of the generating coil 1 in the vicinity thereof. The positive voltage of this voltage Ve passes through the resistor 2 to the first capacitor 4, and the diode 1
0 to the second capacitor 11 for charging. Figure 3 shows the charging voltage V _c4 of capacitor 4 and the charging voltage V _c11 of capacitor 11.
FIG. According to this, during low speed rotation and overspeed, such as when starting the engine, each charging voltage V _c4 , V _c11
It can be seen that there is a tendency for the value to decrease.

Now, when the engine speed has not risen sufficiently, such as when the engine is started, the voltage of the generator coil 1 is equal to the Zener voltage of the Zener diode 7 V _B0
However, this Zener diode 7 is in an off state. Therefore, the thyristor 6 is also in a non-conductive state. On the other hand, the first capacitor 4
The charging voltage increases and the terminal voltage of this capacitor 4 reaches a predetermined level, but the charging voltage is discharged through the resistor 3 and between the base and emitter of the switching transistor 5, and the switching transistor 5 is turned on. . Here, the discharge time constant determined by the values of the resistor 3 and the first capacitor 4 is set shorter than the positive half period of the voltage waveform, so as shown in FIG. The switching transistor 5 can be turned off before a half-cycle voltage is generated. Thus, depending on the negative half-cycle voltage, diode 9, the anode of thyristor 14 and Zener diode 1
3. Each circuit connecting the resistor 17 and the gate of the thyristor 14 becomes conductive, and the resistor 17 connects the thyristor 14.
A potential difference is generated between the gate and cathode of the thyristor 14, and the thyristor 14 becomes conductive. In this way, the charge accumulated in the capacitor 11 is passed through the thyristor 14 and the diode 15 to the primary winding 12a of the ignition coil 12, and is transferred to the secondary winding 12b.
induces high voltage in Therefore, a sufficiently large spark is generated in the ignition plug 18 and ignites the air-fuel mixture.

Next, a case will be described in which the engine rotation is at a medium speed. In this case, the voltage induced in the generator coil 1 increases, and the charging voltage of the capacitor 4 increases.
V _c4 also rises as shown in Figure 3. Furthermore, when the induced voltage becomes sufficiently higher than the Zener voltage V _B0 of the Zener diode 7, the Zener diode 7
becomes conductive and the thyristor 6 is turned on. Therefore, the charge in the capacitor 4 is discharged by the thyristor 6, and the base potential of the transistor 5 decreases, making the transistor 5 inoperable. Therefore, when a negative half-cycle voltage is obtained, the thyristor 14 is triggered in the same way as above, and the capacitor 1
1 charge to the primary winding 1 of the ignition coil 12
2a, and generates a high voltage in the secondary winding 12b at regular ignition timing.

Subsequently, when the engine enters the high-speed overspeed region, the charging voltage of capacitor 4 decreases as shown in Figure 3.
V _c4 becomes below the Zener voltage V _B0 . Therefore, the Zener diode 7 is turned off, the thyristor 6 is prohibited from conducting, and the voltage charged in the capacitor 4 causes the transistor 5 to operate according to the discharge time constant determined by the capacitor 4 and the resistor 3.

In this case, the induced voltage of the generator coil 1
Since the frequency of Ve' is higher as shown in FIG. 5 compared to when the speed is low, the discharge time of the capacitor 4 also extends to the negative half cycle of the induced voltage Ve'. Therefore, even when there is a negative induced voltage, the transistor 5 is operated by the capacitor 4 and the resistor 3, so the negative voltage is bypassed through the transistor 5, and the gate of the thyristor 14 is connected to the gate of the thyristor 14 when the transistor 5 is inoperative. The ignition start signal is not received until the ignition timing is reached, and as a result, the ignition timing is delayed. FIG. 6 shows this state. When the charging voltage of the capacitor 4 becomes less than the breakover voltage V _B0 of the Zener diode 7, the discharge time determined by the capacitor 4 and the resistor 3 is extended to the negative half cycle of the induced voltage. As a result, there will be a sudden delay. In addition, by arbitrarily selecting the time constants of the capacitor 4 and resistor 3, or by adding another time constant circuit to them, it is possible to adjust the voltage as shown in FIG. 7 in proportion to the voltage exceeding the Zener voltage V _B0 . It is possible to obtain excellent retardation operating characteristics.

In addition, Fig. 6 shows that when the charging voltage of the capacitor 4 is just below the breakover voltage V _B0 of the Zener diode 7 in the high-speed rotation region of the engine, the discharge time determined by the capacitor 4 and the resistor 3 is This figure shows the retard control characteristics when the time constant is set so as to extend to the middle of a half cycle. In addition, Fig. 7 shows that when the charging voltage of the capacitor 4 just drops below the breakover voltage V _B0 of the Zener diode 7 in the high-speed rotation region of the engine, the discharge time determined by the capacitor 4 and the resistor 3 reaches the negative side of the induced voltage. This figure shows the retard angle control characteristics when the time constant is set so that the delay starts to extend to half a cycle.

In this manner, the overspeed prevention device of the present invention can retard the ignition timing of the spark plug 18 by a predetermined time constant width by discharging the capacitor 4 in the overspeed range of the engine, thereby stabilizing the rotational speed of the internal combustion engine. This can prevent engine damage, shaft breakage, or seizure due to overspeeding.

Note that during manufacturing, the structural dimensions, especially the dimensions of the air gap between the generator coil 1 and the flywheel in which the permanent magnet is embedded, will vary, but the air gap will normally vary in the direction of widening from a predetermined value. It is designed to As a result, the induced voltage in the generator coil 1 may become slightly smaller, but in the present invention, the retard control is started from the point when the charging voltage V _C4 of the first capacitor 4 falls below the breakover voltage V _B0 of the Zener diode 7. As a result, the number of revolutions subject to retard control tends to decrease, and desired over-rotation can always be reliably prevented.

As explained above, according to the present invention, a generator coil that induces a voltage according to the rotational speed of an internal combustion engine,
A first capacitor and a second capacitor that charge the positive induced voltage are electrically connected in response to a trigger voltage based on the negative induced voltage of the generator coil, and the charge of the second capacitor is transferred to the ignition coil. a second thyristor for discharging via the primary winding; a discharging circuit for discharging the charge charged in the first capacitor at a predetermined time constant; and conduction when the discharge circuit discharges the charge charged in the first capacitor. a switching transistor that bypasses the trigger voltage of the second thyristor;
a Zener diode that becomes conductive when the charging voltage of the capacitor reaches a set level; and a first Zener diode that becomes conductive when the Zener diode is conductive and discharges the charge of the first capacitor in a short time with priority over the discharge circuit. By having a configuration equipped with a thyristor, the spark plug 18 is activated when the engine overspeeds.
It is possible to delay the ignition of the air-fuel mixture and slow down the rotation of the engine. Further, the above time constant can be selected to be arbitrarily large, and thereby the ignition timing can be retarded arbitrarily, and when compared with the prior invention of the applicant mentioned above, It is possible to reduce the number of resistors and diodes used to determine the operating voltage, thereby reducing costs, and also making it possible to reduce the size and weight of portable machines such as chainsaws and lawn mowers. be. Furthermore, according to the present invention, even if variations occur in the structural dimensions, particularly in the air gap between the generating coil and the flywheel, during manufacturing, the desired over-speed can always be reliably prevented.

[Brief explanation of drawings]

Fig. 1 is a specific circuit diagram of the overspeed prevention device according to the present invention, Fig. 2 is a voltage waveform diagram of the generating coil, and Fig. 3 is the terminal voltage characteristics of the first capacitor and the second capacitor with respect to the engine speed. , Figure 4 is a discharge voltage characteristic diagram of the first capacitor when the engine is running at low speed, Figure 5 is a discharge voltage characteristic diagram of the first capacitor when the engine is running at high speed, and Figures 6 and 7 are the discharge voltage characteristic diagram of the first capacitor when the engine is running at high speed. FIG. 3 is a timing retard control characteristic diagram. 1... Generator coil, 3... Resistor, 4... First capacitor, 5... Switching transistor,
6...First thyristor, 7...Zener diode, 14...Second thyristor, 11...Second
Capacitor, 12...Ignition, 18...
spark plug.

Claims (1)

[Scope of utility model registration request] A generator coil that induces a voltage according to the rotational speed of the internal combustion engine, a first capacitor and a second capacitor that charge the positive induced voltage, and a trigger voltage that receives a trigger voltage based on the negative induced voltage of the generator coil. a second thyristor that is electrically conductive and discharges the charge charged in the second capacitor via the primary winding of the ignition coil; a discharge circuit that discharges the charge charged in the first capacitor at a predetermined time constant;
a switching transistor that becomes conductive when the charge charged in the first capacitor is discharged by the discharge circuit and bypasses the trigger voltage of the second thyristor; and a zener that becomes conductive when the charge voltage of the first capacitor reaches a set level. An internal combustion engine comprising: a diode; and a first thyristor that is conductive when the Zener diode is conductive and discharges the charge in the first capacitor in a short time in priority to the discharge circuit. Overspeed prevention device.