JPS60204971A - Ignitor for diesel engine - Google Patents

Abstract

PURPOSE:To permit the certain electrical-discharge operation of a spark plug by installing a means which permits a plural times of electrical-discharge operation of the spark plug continuously and an electrical-discharge timing setting means which carries-out the electrical-discharge operation of the spark plug for a specific time. CONSTITUTION:Each output of a start switch 8, idle switch 9, and a crank-angle sensor 10 is input into a control circuit 7. An oscillating circuit 18 permits a plural times of electrical discharge of a spark plug continuously. The electrical-discharge operation of the spark plug is permitted with a crank-angle sensor 10, counter 17, and a flip-flop circuit 16 over the range from before the start of fuel injection to after the injection. Thus, the spark plug can be certainly put into electric discharge even in the cylinder having a high-pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an improvement in an ignition device that promotes ignition and combustion of fuel injected into the cylinders of a diesel engine.

<Background Art> An ignition device that includes a spark plug provided together with a fuel injection valve in a cylinder of a Diesel/I-engine and promotes ignition and combustion of fuel injected from the fuel injection valve by spark discharge at the spark plug has been conventionally known. Various proposals have been made. In such a conventional ignition device, for example, Japanese Patent Application Laid-Open No. 58-7005
As shown in Japanese Patent No. 3, the spark plug is activated to discharge at a predetermined timing after the start of fuel injection. Here, since the fuel injection timing is 10 degrees before compression top dead center during startup and about 50 degrees before compression top dead center during idling, the discharge operation of the ignition plug is performed approximately near compression top dead center.

However, in diesel engines, the compression ratio is set high in order to increase the compression air temperature dust during fuel injection, and for this reason, the cylinder pressure near the compression top dead center is as shown in Figure 1 in the case of a Ganlin engine. very expensive in comparison. As shown in Figure 2, the relationship between the discharge voltage at the spark plug and the internal pressure is such that the discharge voltage increases as the cylinder pressure increases. 70-80K to discharge
A high voltage of V [when the gap between the electrodes of the spark plug is lsm] is required.

In order to generate a high-voltage discharge of 70 to 80 KV using a spark plug with a gap length of 1 harmonic, it is necessary to increase the voltage resistance of the ignition coil, cable, etc., and to have a powerful power supply, which requires technical and technical problems. This caused problems in terms of cost. These problems can be avoided by reducing the discharge voltage by reducing the gap length between the electrodes of the spark plug, but it is said that reducing the gap length worsens the ignitability of the fuel injected into the cylinder. This would have caused new inconveniences.

<Object of the invention> The present invention has been made with attention to such problems,
An object of the present invention is to provide an ignition device that can reliably discharge a spark plug in a high-pressure cylinder without reducing the gap length between the spark plug electrode and the spark plug electrode using a power source that generates a very high voltage. .

<Summary of the Invention> To this end, the present invention focuses on the phenomenon that the voltage required for the discharge operation decreases when the discharge operation of the spark plug is repeated continuously at a high frequency, and the following ignition device is constructed. . That is, a means for discharging the spark plug continuously multiple times, and a discharging operation timing setting means for causing the discharging operation of the spark plug by the means to be performed from before to after the start of fuel injection are provided. The above object is achieved by starting the discharging operation before fuel injection when the cylinder pressure is low and the discharge voltage is low, so that even after the fuel injection when the cylinder pressure increases, the spark plug is discharged by the low discharge voltage. This is what we aim to do.

<Example> The present invention will be described below based on an example shown in FIG. 3.4. Here, the basic configuration as an ignition device is the third
As shown in the figure, it is almost the same as the ignition system for gasoline engines. In other words, the output voltage of the battery 1 is the ignition coil 20
Pressure is input to the primary side, and high pressure generated on the secondary side of the ignition coil 2 is applied via the distributor 3 to spark plugs 48 to 4d arranged for each cylinder of the four-cylinder diesel engine. . Here, the connection between the secondary side of the ignition coil 2 and the distributor 3 and the connection between the distributor 3 and the spark plugs 48-4d are made by high-tensile cables 58-5e.

The primary side circuit of the ignition coil 20 is controlled to open and close by a switching power transistor 6, and the power transistor 6 is turned on and off by a signal issued from the control circuit γ.

The outputs of a start switch 8, an idle switch 9, and a crank angle sensor 10 are input to the control circuit 7, and the circuit configuration thereof is shown in FIG.

To explain this, the outputs of the start switch 8, which detects when the engine is cranking and outputs a high signal, and the idle switch 9, which detects when the engine is idling and outputs a high signal, are input to the OR gate 11. .

In addition, a signal emitted every 180 degrees of crank rotation angle from a crank angle sensor 1o that detects the crank rotation angle position of the engine is input to a monostable multivibrator circuit (hereinafter abbreviated as monostable multi) 12 of a positive edge trigger. The output of the monostable multi 12 is the OR gate 11.
It is inputted to the AND gate 13 together with the output of .

Here, the output of the monostable multi 12 is also input to the second monostable multi 14 of the negative edge trigger, and the output of the second monostable multi 14 is also input to the third monostable multi 15 of the negative edge trigger. and the third
The output of the monostable multi 15 is input to the set terminal of the RSS flip-flop circuit 16.

On the other hand, the crank rotation angle of the crank angle sensor 10 is 2°.
The signal generated each time is input to the count input terminal of a presettable counter 1γ. Furthermore, this counter 1
The preset input terminal 7 is configured to receive a signal from the crank angle sensor 10 every 180 degrees of crank rotation angle, and the output of the counter 17 is input to the reset terminal of the clip prop circuit 16.

The Q output of the flip-flop circuit 16 is combined with a pulse signal of a predetermined frequency which is the output of the oscillation circuit 18 to perform a second AND operation.
The output of the AND gate 19 is input to the second OR gate 20 along with the output of the first AND gate 13. The output of the OR gate 20 is input to the amplifier circuit 21 and amplified, and then output to the base terminal of the power transistor 6.

Here, as will become clear from the description of the operation below, the oscillation circuit 18 constitutes the main part of the means for discharging the spark plug multiple times in succession, and the crank angle sensor 10. Counter 17. The flip-flop circuit 16 constitutes a main part of a discharge operation timing setting means for discharging the spark plug from before to after the start of fuel injection.

Next, the operation will be explained with reference to the time chart of signal waveforms of each part shown in FIG.

First, when cranking or idling is detected and the start switch 8 or idle switch 9 begins to output a high signal, the output of the OR gate 11 becomes high level (see FIG. 5 (4)). As a result, conditions are set for performing the spark plug discharge operation during engine startup and idling, when the spark plug discharge operation is most needed.

On the other hand, when the 180° signal of the crank angle sensor 10 is output at a preset crank rotation angle position (for example, a crank rotation angle position where the piston is 80' before the compression top dead center) (see Fig. 5 (B)). ), the monostable multi 12 is triggered and outputs a pulse signal having a pulse width equal to the time required to conduct the primary current in the ignition coil 2 (see FIG. 5(C)). At the negative edge of the output pulse of this monostable multi 12, the second monostable multi 14
is triggered and outputs a pulse signal with a pulse width narrower than the output pulse width of the first monostable multi 12.

The negative edge of this pulse signal triggers the third monostable multi 15, which outputs a pulse signal with a width sufficient to set the flip-flop circuit 16 (see FIG. reference). The flip-flop circuit 16 is set by this pulse signal, and a high signal is output from the Q output (Fig. 5 (G)).
reference).

On the other hand, the 180° signal emitted from the crank angle sensor 10 is also input as a trigger signal to the preset terminal of the counter 1γ, and presets the value of the crank rotation angle corresponding to the period in which the spark plug is caused to perform multiple discharge operations. Here, the 2° signal of the crank angle sensor 10 (the fifth
(see figure (g))) is always input to the count input terminal of the counter 17, and the counter 1T counts the number of input pulses, and when the count value reaches the preset value, outputs a carry signal ( 5(G) The Q output of the flip-flop circuit 16 changes from a high signal to a low signal (see FIG. 5, 0).The output of this flip-flop circuit 16 is the output of the oscillation circuit 18 (see FIG. 5, 0). ) is input to the AND gate 19. In other words, the period during which the Q output of the flip-flop circuit 16 outputs a high signal (this period corresponds to the crank rotation angle preset to operate the spark plug in continuous discharge operation) is input to the AND gate 19. The output of the AND gate 19 outputs a high signal in accordance with the output of the oscillation circuit 18 (see FIG. 5(I)).

The output of this AND gate 19 and the output of the first AND gate 13 are inputted to an OR gate 20, and the OR gate of Ryokawa
is taken, and its output signal is amplified to an output level sufficient to drive the power transistor 6 (see Fig. 5 (J
)reference).

The power transistor 6 is turned on and off by the pulse train generated in this way, and the current on the primary side of the ignition coil 2 is interrupted (see FIG. (see Figure 0), the spark plug is continuously discharged.

At this time, if the crank rotation angle counted by counter 1T is 80" (40 pulses of 2° signal), the fuel injection timing is 10° at compression top dead center at startup and 1 at idling.
If the setting is set to be just before compression top dead center, multiple discharge operations of the spark plug will occur from an early stage before compression top dead center until the compression top dead center position with the fuel injection timing in between. .

In this way, by repeating the discharge after the full discharge (this discharge is easy because it is carried out when the cylinder pressure is low), the ions from the previous discharge remain between the spark plug electrodes. The required discharge voltage for the second and subsequent discharges can be lowered. Therefore, even if the crank rotates and the piston approaches the compression top dead center and the pressure in the cylinder during discharge increases, the required discharge voltage will not rise suddenly, preventing discharge cut-off due to the increase in pressure in the cylinder, and after fuel injection. Even when the pressure inside the cylinder becomes high near the compression top dead center of the cylinder, it is possible to perform the discharge operation reliably without applying a high voltage, and the ignition and combustion of the injected fuel can be promoted.

In this embodiment, the spark plug is discharged only during engine startup and idling, when ignition and combustion by the spark plug are most needed, but the spark plug may be operated in other operating states as well.

<Effect of simplicity> As explained above, Honbaro uses multiple spark plugs installed in the cylinder of a diesel engine continuously from an early period before compression top dead center, when the cylinder pressure is low, to after the start of fuel injection. It is now activated by multiple discharges. Therefore, the ions generated by the discharge when the cylinder pressure is low facilitates the discharge operation of the spark plug when the cylinder pressure is high after fuel injection, and the power supply device generates high pressure even when the cylinder pressure is high. The spark plug discharge operation is performed simply and reliably without the use of other devices, and the ignition and combustion of fuel injected when the cylinder pressure is high is promoted, and starting performance is improved and idle noise is reduced. Become.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between cylinder pressure and crank rotation angle, Fig. 2 is a graph showing the relationship between cylinder pressure and discharge voltage, Fig. 3.4 is a diagram of the present invention, and Fig. 5 is a graph showing the relationship between cylinder pressure and discharge voltage. FIG. 3 is a time chart showing signal waveforms at points 8 to 8 in FIGS. 3 and 4. FIG. 2...Ignition coil 4a-4d...Spark plug 6.
...Power transistor T...Control circuit 10...
Crank angle sensor 16...Flip 7 4g circuit
1γ...Counter 18...Allowed during oscillation circuit
Applicant Fujio Sasajima, patent attorney representing Nissan Motor Co., Ltd. Figure 1 7 Years old in Funk IfJh I- Figure 2

Claims (1)

[Claims] A spark plug disposed in a cylinder of a diesel engine together with a fuel injection valve, and a control device for controlling a discharge operation of the spark plug, and a control device for controlling a discharge operation of the spark plug. The ignition device for a diesel engine assists the ignition and combustion of fuel injected into the fuel injection valve, the ignition device includes means for discharging the spark plug a plurality of times in succession; 1. An ignition device for a diesel engine, comprising means for setting a discharge operation timing from before to after a valve is started.