JPS63205446A - Fuel injection controller - Google Patents

Abstract

PURPOSE:To achieve a good pilot injection by controlling the potential to negative value upon discharge of a piezoelectric actuator, thereby lowering threshold voltage and preventing creeping discharge of the piezoelectric actuator. CONSTITUTION:Main section of fuel injection controller comprises a ceramic actuator 9 arranged in high pressure chamber 10 of an injection pump 8, a drive circuit 13 and a timing circuit 14. The drive circuit 13 comprises a power source 7, first switch element 1 and inductor 2, second switch element 3 and inductor 4, and a negative potential control circuit comprised of Zener diode 5 and a diode 6. Here. the first switch element 1 is conducted in the direction from the power source 7 toward the first inductor 2 when it is turned ON by a timing signal. The second switch element 3 is conducted in such direction as the plus terminal of the ceramic actuator 9 is grounded through the second inductor 4 when it is turned ON by the timing signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel injection system using a piezoelectric ceramic actuator that performs pilot injection prior to main injection of fuel in order to reduce noise and vibration in a diesel engine. Regarding a control device.

[Conventional technology]

A conventional fuel injection control device using a piezoelectric actuator is shown in FIG. 5 (see Japanese Patent Laid-Open No. 138859/1983). This device includes a ceramic actuator 21, a capacitor 22 for storing electric charge generated by the actuator 21, and a switch element 23.
and 24, and inductors 25 and 26. The voltage generated by the ceramic actuator 21 is the capacitor 2.
2, and transfers this charge to the ceramic actuator 2.
1, thereby increasing the threshold voltage of the actuator. When the switch element 23 is turned on, the electric charge of the actuator is discharged in the loop of the positive side of the ceramic actuator 21, the inductor 25, the switch element 23, and the capacitor 22. Switch element 2
4 is turned on, charge is supplied through the loop of the negative side of the ceramic actuator 21 → capacitor 22 → switch element 24 → inductor 26.

When the ceramic actuator shown in FIG. 2 is used (see Japanese Unexamined Patent Publication No. 60-4279), there is a risk of creeping discharge due to the creeping discharge withstand voltage of the actuator element, so the applied voltage is limited.

The voltage across the ceramic actuator 21 in the device of FIG. 5 is shown in FIG. 4(a). For example, if 1 in FIG. 4(a) is the creeping discharge withstand voltage, this device does not completely discharge to 0 volts during discharge, so PZT is small in response to potential changes in the actuator. Furthermore, since it is possible to discharge only to close to 0 volts, the threshold voltage must be increased in order to increase pilot performance. Therefore, there is a risk of creeping discharge in the actuator element, and if this is not taken into consideration, there is a problem that the injection rate of the injector cannot be controlled.

[Problem that the invention seeks to solve]

In view of the above-mentioned problems, an object of the present invention is to lower the threshold voltage by setting the potential after discharge to a negative value, thereby preventing creeping discharge in the piezoelectric actuator and obtaining good pilot injection performance. It is in.

[Means for solving problems]

In the present invention, a piezoelectric actuator, a first switch element, a first inductor, a second inductor, a first inductor, a first switch element, a first inductor, a second inductor, and a piezoelectric actuator are arranged in a high pressure chamber of a fuel injection pump of an internal combustion engine and are used to control sub-injection of the fuel injection pump. A fuel injection control device is provided that includes two switch elements and a negative potential control circuit. In this device, charging is started from the voltage supply means to the piezoelectric actuator via the first switch element and the first inductor that are turned on at the first time,
A series circuit of a second inductor and a second switch element is connected in parallel with the piezoelectric actuator, and a negative potential control circuit is further connected in parallel with the piezoelectric actuator.

The second switch element is turned on at a second time to discharge the charge of the piezoelectric actuator. The first period and the second period are different from each other, and the period thereof is equal to the period of the main injection of the fuel injection pump. The negative potential control circuit is composed of, for example, a series circuit of a Zener diode and a diode or a series circuit of a varistor and a diode.

[For production]

If the above-mentioned device is used, the voltage of the piezoelectric actuator will be as shown in Fig. 4 (b), and the potential after discharge will be a negative potential, and even though the actuator potential change ΔPZTO value is the same, the threshold voltage will be changed to the position of ■2. It is also possible to increase the value of ΔPZT within the creeping discharge breakdown voltage, and it is possible to bring out greater pilot performance even under adverse conditions.

〔Example〕

A circuit diagram of a fuel injection control device as an embodiment of the present invention is shown in FIG. This device is a high pressure chamber 10 of an injection pump 8.
Ceramic actuator 9 and drive circuit 1 arranged in
3 and a timing circuit 14. Drive circuit 1
3 is a power supply 7 as a voltage supply means, a switch element (thyristor) as a first switch element, an inductor 2 as a first inductor, an inductor 4 as a second inductor, and a switch as a second switch element. It includes an element (thyristor) 3, a Zener diode 5 and a diode 6 as a negative potential control circuit. The timing circuit 14 supplies a timing signal (TRIGl) for turning on (conducting) the switch element 1 and a timing signal (TRIG2) for turning on the switch element 3.

The ceramic actuator 9 is a piezoelectric element laminate 40 as shown in FIG. 2, and includes several tens of PZT elements 41.
are alternately stacked with electrode plates 42. This piezoelectric element laminate has a piezoelectric effect and an inverse piezoelectric effect, and when used as a drive source for an actuator, it has a response on the order of several tens of microseconds (10-6 seconds) and a large pressing force. This is advantageous for actuators in fuel injection systems.

The aforementioned ceramic actuator 9 is connected to the fuel injection pump 8.
It is attached to the front part of the high pressure chamber and controlled by the drive circuit 13. The drive circuit 13 changes the amount of charge on the ceramic actuator 9 to expand and contract the actuator element, thereby changing the pressure in the high pressure chamber 10 to perform pilot injection. The drive circuit 13 is configured and connected as follows. The voltage supplied from the power supply 7 is supplied to the positive terminal of the ceramic actuator 9 via a series circuit of the switch element 1 and the inductor 2.

The negative terminal of the ceramic actuator 9 is grounded. A series circuit of an inductor 4 and a switch element 3 is connected in parallel to the ceramic actuator 9, and further a Zener diode 5 and a diode.

A series circuit of Doro is connected in parallel to the ceramic actuator 9. The anode side of the Zener diode 5 is connected to the positive side terminal of the ceramic actuator 9, and the cathode side is connected to the cathode of the diode 6. The anode of the diode 6 is connected to the negative terminal of the ceramic actuator 9. When the switching element 1 is turned on by the timing signal TRIG 1, it conducts from the power source 7 to the inductor 2. When the switch element 3 is turned on by the timing signal TRIG 2, it conducts in the direction in which the positive terminal of the ceramic actuator 9 is grounded via the inductor 4.

The operation of the drive circuit 13 will be explained with reference to the timing chart of FIG. FIG. 3(a) shows the lifted state of the plunger 11 of the fuel injection pump 8. As shown in FIG. 3(f), as the plunger 11 lifts, the high pressure chamber pressure increases, and when it exceeds the opening pressure of the nozzle 12, the injection rate waveform shown in FIG. 3(g) Injection begins. Further, as the pressure in the high pressure chamber increases, charges are generated in the ceramic actuator 9 due to the piezoelectric effect, as shown in FIG. 3(b), and the voltage increases. Thereafter, the timing signal TRIG 2 is generated from the timing circuit 14 as shown in FIG. It is possible to discharge the battery until the potential on the negative side becomes higher than on the positive side. As a result of this driving, the potential of the ceramic actuator 9 becomes negative as shown in FIG. 3(b). In order to control the value of this negative potential, a Zener diode 5 is connected in parallel with the ceramic actuator 9.

Further, a diode 6 is connected in series with the Zener diode 5 in order to maintain the charge on the ceramic actuator 9 that is generated as the pressure in the high pressure chamber increases. The ceramic actuator 9 contracts due to electric discharge, and the pressure in the high pressure chamber reaches the third level.
The pressure decreases as shown in Figure (f), fuel injection temporarily stops, and pilot injection is performed. After that, plunger 11
By lifting, injection (main injection) is started again.

Next, when fuel is spilled by the governor mechanism, the pressure in the high pressure chamber decreases, and one injection ends. Next, the pressure in the high pressure chamber decreases, and the timing circuit 14 generates the timing signal TRIG 1 as shown in FIG. 3(C) at a location unrelated to fuel injection, and the switch element 1 in FIG. 1 is turned on. . When the switch element 1 is turned on, a current flows from the power supply 7 through the switch element 1 to the inductor 2 and the ceramic actuator 9 as shown in FIG. 3(e), and the ceramic actuator 9 is charged. This timing signal TRIG1
Charging the ceramic actuator 9 when the timing signal TRIG2 is applied increases the width of change in the voltage across the ceramic actuator 9 (ΔPZT in FIG. 4) when the timing signal TRIG2 is applied, and also serves to prevent polarization deterioration due to reverse potential. ing. Further, the inductor 2 efficiently supplies energy to the ceramic actuator 9 and reduces the peak value of the current flowing through the circuit.

In this embodiment, a thyristor is used as a switching element, but a transistor can also be used instead. When a transistor is used, an inexpensive circuit configuration can be obtained because it can be easily turned on and off in drive control.

Further, in this embodiment, a Zener diode is used to control the negative potential of the ceramic actuator, but a varistor may be used instead of the Zener diode 5. As a modification, it is also possible to control the negative potential by providing a resistor in series with the inductor 4 instead of the Zener diode 5 and the diode 6, and by matching the drive circuit and the ceramic actuator.

Furthermore, the power supply 7 as a voltage supply means in this embodiment
For this purpose, a voltage booster circuit, a voltage booster, or the like can be used.

〔Effect of the invention〕

According to the present invention, the potential after discharge of the piezoelectric actuator is lowered to a negative potential, the threshold voltage is lowered, and the possibility of creeping discharge of the actuator is reduced, or the short potential is reduced within the withstand voltage of creeping discharge. The change can be increased, and the pilot performance in fuel injection of an internal combustion engine can be improved.

[Brief explanation of the drawing]

1 is a circuit diagram of a fuel injection control device as an embodiment of the present invention, FIG. 2 is an exploded perspective view of a piezoelectric element laminate of a ceramic actuator used in the device of FIG. 1, and FIG. 3 is a diagram of the structure shown in FIG. FIG. 4 is a waveform diagram comparing the ceramic actuator voltage in the conventional device with the ceramic actuator voltage in the device in FIG. 1, and FIG. 5 is a timing chart explaining the operation of the conventional device. FIG. 2 is a circuit diagram of a fuel injection control device. (Explanation of symbols) 1... Switch element, 2... Inductor, 3... Switch element, 4... Inductor, 5... Zener diode, 6... Diode, 7... Power supply, 8... Fuel injection pump, 9... Ceramic actuator, 10... High pressure chamber, 11... Plunger, 12... Nozzle, 13... Drive circuit, 14... Timing circuit, 40... ... Piezoelectric element laminate, 21... Ceramic actuator, 22... Capacitor, 23, 24... Switch element, 25, 26... Inductor, 27... Diode. Fig. 3 Vl--1-- 21...Ceramic actuator 22...Capacitor 27...Diode

Claims (5)

[Claims] 1. a piezoelectric actuator disposed in a high pressure chamber of a fuel injection pump of an internal combustion engine for controlling sub-injection of the fuel injection pump; a first switch element receiving voltage from a voltage supply means; a first inductor with one end connected to the voltage supply means and the other end connected to the piezoelectric actuator; a second inductor with one end connected between the first inductor and the piezoelectric actuator; , a second switch element connected in series with the second inductor at its other end and whose series circuit is connected in parallel with the piezoelectric actuator; and a negative potential connected in parallel with the piezoelectric actuator. A control circuit is provided, wherein the first switch element is conductive at a first period having the same period as the main injection period of the fuel injection pump, and the second switch element is conductive at a first period having the same period as the main injection period of the fuel injection pump. conduction at a second period different from the first period in the same cycle, charging of the piezoelectric actuator is started from the first period, and the electric charge of the piezoelectric actuator is discharged at the second period. A fuel injection control device designed to 2. The fuel injection control device according to claim 1, wherein the first switch element and the second switch element are thyristors. 3. The fuel injection control device according to claim 1, wherein the first switch element and the second switch element are transistors. 4. 2. The fuel injection control device according to claim 1, wherein said negative potential control circuit is constituted by a series circuit of a Zener diode and a diode. 5. 2. The fuel injection control device according to claim 1, wherein said negative potential control circuit is comprised of a series circuit of a varistor and a diode.