JPS6252145B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an overspeed prevention device for an internal combustion engine.

Conventionally, current-interrupting type non-contact ignition devices have been widely used in engine spark ignition systems. This uses a main switching control element using a power transistor and a sub-switching element using a signal transistor or thyristor to control this main switching control element, and is based on the level of the induced voltage on the primary side of the ignition coil. The primary coil conducts or cuts off the short-circuit current, and intermittently generates high-energy ignition sparks at the spark plug connected to the secondary coil.

However, in this type of ignition system, since the ignition timing is not controlled, the engine's appropriate ignition timing is approximately constant at normal and high speeds, resulting in good fuel efficiency, and furthermore, the engine output increases and overspeeding occurs. This often occurs, resulting in seizure and damage to the crankshaft, and accidents in which the flywheel rotor falls off or is blown away, resulting in problems such as reduced durability and personal injury.

Therefore, in an attempt to solve these problems, various overspeed prevention devices have been provided to prevent overspeed.

However, such an ignition system detects the voltage level of the voltage induced in the ignition coil, etc., and uses this to directly determine the engine control speed, retards the ignition timing, or stops the ignition (misfire). This was to prevent rotation. For this reason, in such devices, large variations in the engine control speed occur due to dimensional variations such as the magnetic force of the rotor and the air gap between the ignition coil and the rotor, and as a result, the engine speed actually reaches the overspeed range. Despite this, there were cases in which actions such as retarding the ignition timing or stopping the ignition were not performed, making it impossible to reliably prevent engine overspeed.

An object of the present invention is to provide an overspeed prevention device for an internal combustion engine that reliably prevents the engine from overspeeding despite variations in the magnetic force of the rotor, air gap, etc. Embodiments of the invention will be specifically described with reference to the drawings.

FIG. 1 is a circuit diagram specifically showing the overspeed prevention device of the present invention, in which 1 is an ignition coil, 2
is a spark plug connected to this ignition coil 1, 3 is a first capacitor connected in series to the primary coil of ignition coil 1 via diodes 4 and 5, and 6 and 7 are connected to the primary coil of ignition coil 1. A resistor and a third capacitor connected in series, 8 a resistor connected in parallel to the capacitor 7, 9,
A thermistor and a resistor 10 are connected in series, and are connected in parallel to a resistor 8. Reference numeral 11 denotes a transistor whose base is connected to the midpoint between the resistor 6 and the capacitor 7, and the collector and emitter of this transistor 11 are connected to the line _l1 connecting the ignition coil 1 and the diode 4 via the resistor 12. They are each directly connected to the line _l2 connecting the ignition coil 1 and the diode 5. 13
is a transistor whose base is connected to the collector of transistor 11, and the collector and emitter of transistor 13 are connected via resistor 14 to line _l1 and directly to line _l2 , respectively. 15
is a PNP type transistor whose base is connected to the collector of transistor 13, its emitter is connected to line _l1 , and its collector is connected to the collector of transistor 1.
It is connected to the base of 6. Further, the collector of the transistor 16 is connected to the line _l1 , and the emitter is connected to the line _l2 . The transistors 11, 13, 15, and 16 constitute a switching circuit that controls the timing of the primary short-circuit current to the ignition coil 1.

On the other hand, the anode/cathode of the thyristor 17 and a second capacitor 18 are connected between the connection midpoint of the resistor 6 and capacitor 7 and the line _l2 , and the connection midpoint of the thyristor 17 and the capacitor 3 and the diode There is a resistor 1 between the connection center point of 5
9 and 20 are connected in series, and these constitute a discharge circuit in which the charge in the capacitor 3 is discharged at a predetermined time constant. Note that the resistor 20 includes resistors 22 and 23 and a thermistor 2, as shown in FIG.
This is a temperature compensation circuit for the thyristor 17, which is composed of 4. The gate of a thyristor 17, which is a switching element, is connected to the midpoint between these resistors 19 and 20. 21 is a capacitor connected in parallel to the resistor 20.

Next, the operation of this over-rotation prevention device will be described.

Now, in the primary coil of ignition coil 1,
When the voltage shown in Figure 3a is induced by the rotation of the rotor, current flows through the series circuit of resistor 6 and capacitor 7 during the half cycle in which the potential of line _l1 becomes positive. The base potential of the transistor 11 gradually increases based on the charging circuit time constant of the series circuit. During this time, since the transistor 11 is still off, the base potential of the transistor 13 rises to a predetermined potential, which turns on and its collector potential drops. Therefore, the base potential of the transistor 15 decreases,
By passing a current between its emitter and base, this transistor 15 is also turned on, and the transistor 16 connected in cascade thereto is also immediately turned on. Therefore, a large current flows between the collector and emitter of this transistor 16.

On the other hand, the capacitor 7 is gradually charged, and when its terminal voltage reaches a predetermined potential, a current begins to flow between the base and emitter of the transistor 11, which turns on. Along with this, the transistors 13 and 1 which were in the on state as described above
5 and 16 are all inverted to the OFF state, and by interrupting the large current flowing through the transistor 16, a high voltage is generated in the secondary coil of the ignition coil 1, and a spark is generated in the ignition plug.

Incidentally, the charging/discharging voltage of the capacitor 3 is as shown in FIG. be done. Note that the trigger level of this thyristor 17 is shown as T.L. However, at this time, the anode side of the thyristor 17 is not positive and the cathode side is not negative, and in particular, the potential of the anode is not positive, so that positive charging is not performed when the thyristor 17 is in the on state. That is, the thyristor is in an off state. Therefore, the capacitor 18 is not charged, and the transistor 11 is controlled to be turned on by the charging time constant of the resistor 6 and capacitor 7.

On the other hand, when the rotational speed of the rotor exceeds the normal rotational speed depending on the engine speed, the capacitor 3 is charged in the same negative half cycle as described above, and the charging pressure of the capacitor 3 changes between positive and negative due to the time constant. They overlap, and a predetermined trigger current is input to the thyristor 17. In addition, in the positive half cycle of the induced voltage of the ignition coil 1, the discharge time constant of the discharge circuit consisting of the capacitor 3 and the resistors 19 and 20 is sufficiently decreased as shown in Fig. 3c, compared to when the engine speed is low. Since the trigger current is increasing, the trigger current continues to flow during the positive half cycle according to its discharge time constant, and the thyristor 17 remains on. Therefore, the capacitor 18 connected to the thyristor 17 is charged with a positive voltage, and the base of the transistor 11 is newly connected to increase the capacity of the transistor 18, so that the overall charging circuit time constant is increase,
The timing at which this transistor 11 turns on is delayed. Therefore, transistors 13, 15, 1
The timing of turning off the ignition coil 1 is also delayed, and the timing of cutting off the short circuit current flowing through the primary side coil of the ignition coil 1 is also delayed. FIG. 4 shows the primary breaking current waveform in this case.

As a result, the ignition timing is delayed by a time _t1 at a predetermined normal rotational speed, that is, when the thyristor 17 is turned on, as shown in FIG. 18 and the resistor 6, the charging time is continuously delayed at an appropriate slope.

In this manner, when the engine speed exceeds the set value, by delaying the supply of high voltage to the spark plug, overspeeding of the engine can be effectively prevented. The present invention does not detect the voltage level of the induced voltage of the ignition coil and directly determine the engine control speed based on the voltage level as in the conventional ignition system described above, and performs ignition timing retard control, etc. As mentioned above, once the negative induced voltage of the ignition coil is
Since the engine control speed is determined by charging the capacitor and using the discharge time, even if the magnitude of the induced voltage in the ignition coil that occurs at the same engine speed varies, The variation in the controlled rotational speed is significantly smaller than that of the conventional ignition device. Therefore, even if the air gap between the rotor and the ignition coil varies, over-rotation can be prevented reliably and the engine can be operated safely.

As explained in detail above, according to the present invention, there is provided an ignition coil that induces a voltage according to engine rotation, and an ignition coil that is connected to the ignition coil and that is charged during the negative half cycle of the voltage induced therein. a first capacitor, a discharge circuit for discharging the charge of the first capacitor at a predetermined time constant; and a discharge circuit connected to the ignition coil, during a positive half cycle of the induced voltage,
a switching element that is turned on when the first capacitor is discharged; a second capacitor connected in series to this switching element; and a switching element connected in parallel to a circuit in which the second capacitor and the switching element are connected in series, and A third capacitor is charged during the positive half cycle and is turned on at a set level based on a charging time constant of a charging circuit including these second capacitors and a third capacitor to the ignition coil. and a switching circuit that controls the cutoff timing of the primary short-circuit current, so that when the engine speed exceeds the set rotation speed, a second capacitor is added to the third capacitor during the positive half cycle. By making the charging time constant large, the primary short-circuit current of the ignition coil caused by the switching circuit can be cut off with a delay. As a result, the ignition timing is also delayed.
Therefore, the engine speed can be maintained at the set control speed. In this way, over-speeding of the engine can be reliably prevented regardless of variations in structural dimensions, etc., magnetic force of the rotor, etc. Further, as shown in FIGS. 6a, b, and c, it can also be used with other current interrupt type non-contact ignition devices, and can perform overspeed prevention control of the internal combustion engine.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram specifically explaining the overspeed prevention device of the present invention, FIG. 2 is a detailed diagram of a thyristor temperature compensation circuit, and FIGS. 3 a, b, and c are for each operating state shown in FIG. Signal waveform diagrams for each part of the circuit, Figure 4 is a primary breaking current waveform diagram, Figure 5 is an ignition timing characteristic diagram,
FIGS. 6a, 6b, and 6c are circuit diagrams showing other usage examples of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Ignition coil, 2... Spark plug, 3... First capacitor, 7... Third capacitor, 11, 13, 15, 16... Switching circuit transistor, 17... Switching element, 18 ...Second capacitor.

Claims (1)

[Claims] 1. An ignition coil that induces a voltage according to engine rotation, a first capacitor connected to the ignition coil and charged during a negative half cycle of the voltage induced therein, and the first capacitor. a discharge circuit that discharges the charged charge at a predetermined time constant; and a switching circuit that is connected to the ignition coil and is turned on during a positive half cycle of the induced voltage and when the first capacitor is discharged. a second capacitor connected in series to the switching element; and a third capacitor connected in parallel to the circuit in which the second capacitor and the switching element are connected in series and charged during the positive half cycle. and a switching circuit that turns on at a set level to control the timing of cutting off the primary short-circuit current to the ignition coil based on the charging time constant of the charging circuit including the second capacitor and the third capacitor. An overspeed prevention device for an internal combustion engine, comprising: