JPS6135715Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current control circuit for an electromagnetic switching device such as an electromagnetic fuel injection valve for an internal combustion engine.

BACKGROUND ART Electromagnetic switching devices such as relays, solenoids, and electromagnetic fuel injection valves for internal combustion engines require a large drive current when starting to operate because they do not operate unless the drive current reaches a predetermined level. However, if this large drive current continues to flow throughout the operation of the electromagnetic switching device, there will be problems such as heat generation in the excitation winding or increased power loss. For this reason, a current control circuit is used that supplies a large current when the electromagnetic switching device is driven, and after the switching device operates, supplies a small current that is sufficient to maintain the operating state, that is, a holding current. It is being Another advantage is that the recovery time can be shortened by supplying the holding current to the switching device after operation.

FIG. 1 shows a block diagram of a conventional example of a current control circuit for an electromagnetic switching device. In the figure,
Reference numeral 1 designates a solenoid valve for fuel injection in an internal combustion engine as an electromagnetic switching device, which is driven by a drive circuit 2 . A fuel injection control pulse t _i as shown in FIG. 2a is applied to the input terminal 3, having a pulse width approximately determined by engine operating parameters such as the intake air amount and the instantaneous rotational speed of the internal combustion engine. This control pulse _ti is applied to the input terminal of the drive circuit 2 via the inverter 4 and the NOR circuit 5. The drive circuit 2 is turned on to drive the solenoid valve 1 by applying the control pulse t _i . The current flowing through the electromagnetic valve 1 is detected by a current detection circuit 6 and supplied to a switching circuit 7 at the next stage. The switching circuit 7 is
A first comparison circuit 8 generates an output as shown in FIG. 2d to determine the maximum value _I1 of the current flowing through the solenoid valve 1.
and a second comparator circuit 9 that operates on and off in response to the maximum value _I2 and minimum value _I3 of the holding current flowing through the solenoid valve 1 to generate an output as shown in FIG. 2e. , the respective outputs are supplied to one input terminal of the NOR circuit 5 via the NOR circuit 10 in the form of a pulse signal as shown in FIG. 2(f). Therefore, the drive circuit 2
The current flowing through the solenoid valve 1 changes as shown in FIG. 2c to perform on/off operation in response to the output signal of the NOR circuit 5 (FIG. 2g).

Further, when the current of the electromagnetic valve 1 is controlled by switching as described above, a back electromotive force is generated in the electromagnetic valve 1, so a back electromotive force absorption circuit 11 is provided to absorb the back electromotive force. This back electromotive force absorption circuit 11 has a flywheel circuit 12 configured from a transistor and the like connected in parallel to the solenoid valve 1. When the flywheel circuit 12 is in the on state, the current flowing through the electromagnetic valve 1 decreases more slowly when the drive circuit 2 is turned off than when the flywheel circuit 12 is in the off state. Therefore, the flywheel circuit 12 is connected to the solenoid valve 1.
In order to improve the responsiveness to the control pulse t _i , it is desirable to turn on the solenoid valve 1 within its switching region (FIG. 2A). Therefore, the first comparison circuit 8
As shown in FIG. 2i, a delay circuit 13 that delays the output of Δt by Δt, and a control circuit 14 that turns on the flywheel circuit 12 in accordance with the output of the delay circuit 13 are provided.

In the back electromotive force absorption circuit 11 in the current control circuit of such an electromagnetic switching device, the back electromotive force of the solenoid valve 1 passes through the elements constituting the flywheel circuit 12, so that it has excellent peak voltage and peak current resistance. Although it is necessary to use an element, such an element generally has a high power resistance, so an element with a larger capacity than necessary is used, which has the disadvantage of increasing costs. In addition, in order to match the turn-on of the flywheel circuit 12 with the starting point of the switching region A of the solenoid valve 1 in FIG.
3 is used, but it has the disadvantage that it is very difficult to achieve synchronization and that it is necessary to adjust the delay time Δt.

An object of the present invention is to provide a current control circuit for an electromagnetic switching device that eliminates the above-mentioned drawbacks.

Hereinafter, the present invention will be explained in detail with reference to FIGS. 3 to 5.

FIG. 3 is a block diagram of an embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals. In the figure, back electromotive force absorption circuit 1
The circuit configuration other than 1 is the same as that in FIG. 1. This back electromotive force absorption circuit 11 includes a thyristor (SCR) connected in parallel to the electromagnetic valve 1 and in a forward direction with respect to the back electromotive force, and a thyristor (SCR) connected in parallel to the solenoid valve 1 and in a forward direction with respect to the back electromotive force. The control means includes, for example, an inverter 15, a differentiating circuit 16, a diode D1 _, etc., for supplying an ignition current to the gate of the SCR. Note that _D2 is a diode for protecting the gate of the SCR, and prevents the potential of the gate from becoming more negative than that of the cathode.

FIG. 4 is a circuit diagram showing a specific configuration of the embodiment shown in FIG. 3, in which components equivalent to those in FIG. 3 are surrounded by broken lines and designated by the same reference numerals. In the figure, a control pulse t applied to input terminal 3
The phase of _i is inverted by an inverter 4 consisting of an operational amplifier OP ₁ and a resistor R ₁ and then supplied to a NOR circuit 5 .
The NOR circuit 5 is composed of resistors R ₂ to R ₅ and a transistor Q ₁ , and its output is sent to the next stage drive circuit 2.
supplied to The drive circuit 2 consists of resistors R ₆ , R ₇ and a transistor Q ₂ , and the collector of the transistor Q ₂ is connected to the solenoid valve 1 whose one end is connected to the positive potential line 17 .
connected to the other end. Also, transistor
A resistor _R8 serving as a current detection circuit 6 is connected between the emitter of transistor _Q2 and the negative potential line 18, and a connection point _P1 between the emitter of transistor _Q2 and resistor _R8 is connected.
A voltage corresponding to the current flowing through the solenoid valve 1 is generated.

The switching circuit 7 includes an operational amplifier OP ₂ forming a first comparison circuit 8 and an operational amplifier OP ₃ forming a second comparison circuit 9 . Operational amplifier OP ₂
The potential at point _P1 , which changes according to the current fluctuation of the solenoid valve 1, is applied to the inverting input terminal of _OP3 , and the output terminal of each is connected to the positive potential line 17 via resistors _R9 and _R10 . has been done. The operational amplifier OP ₂ has a first reference potential at a point P 3, which is obtained by dividing the potential at a point P ₂ by a voltage divider circuit consisting of resistors R ₁₁ and R ₁₂ , applied to the non-inverting input terminal, and the first reference potential at a point P ₃ is applied to the non _- inverting input terminal.
That is, when the potential of the inverting input terminal becomes higher than the first reference potential, a negative potential output is generated as shown in FIG. 5d. In addition, the maximum value of current I ₁ of solenoid valve 1
is determined by the value of the first reference potential at the non-inverting input terminal of the operational amplifier OP ₂ , ie the ratio of the resistors R ₁₁ and R ₁₂ . On the other hand, a second reference potential at point _P4 , which is obtained by dividing the potential at point _P2 by a voltage dividing circuit including resistors _R14 and _R15 , is applied to _the non-inverting input terminal of operational amplifier OP3.
Furthermore, since a resistor _R16 is connected between the non-inverting input terminal and the output terminal of the operational amplifier _OP3 , the second reference potential is used to maintain the solenoid valve 1 in accordance with the output potential of the operational amplifier _OP3 . It changes to two reference potentials that determine the local maximum value I ₂ and local minimum value I ₃ of the current. In addition, the resistance R ₁₆
The width between the local maximum value I ₂ and the local minimum value I ₃ is determined.
Furthermore, the reference potential at point _P5 , which is obtained by dividing the potential at point _P2 by a voltage dividing circuit consisting of resistors _R17 and _R18 , is the non-inverting input terminal of operational amplifier _OP1 and the inverting input terminal of operational amplifier _OP4 , which will be described later. are applied to each. In addition, the point
The potential of P ₂ is the resistor R ₁₉ and the Zener diode ZD ₁
determined by The output of operational amplifier OP ₂ (Fig. 5 d) and the output of operational amplifier OP ₃ (Fig. 5 e) are:
The signal is supplied to a NOR circuit 10 composed of resistors _R20 to _R23 and a transistor _Q3 , and is applied to the input resistor _R3 of the NOR circuit 5 as an output as shown in FIG. 5f. Further, the output of the operational amplifier OP ₃ is supplied to the back electromotive force absorption circuit 11 at the next stage.

As described above, the back electromotive force absorption circuit 11 has a control means for supplying an ignition current to the gate of the SCR in accordance with the output of the second comparison circuit 9 in the switching circuit ₇ , that is, the output of the operational amplifier OP3. .
The output of the operational amplifier OP ₃ is inverted by an inverter ₁₅ consisting of resistors R ₂₄ to R ₂₆ and a transistor _{Q 4} and outputted as a signal as shown in FIG. It is differentiated in circuit 16 (FIG. 5j). Since the cathode side of the SCR is fixed at potential U _B , the gate trigger pulse requires a peak value exceeding U _B. For this,
_R27 is connected to the U _B side in order to level shift the zero potential of the differential waveform to U _B. In addition, the operational amplifier OP ₄ connected to the output terminal of the differentiating circuit 16 is a resistor.
This is to limit the level shift by R ₂₇ to the section of the control pulse t _i so that no trigger pulse is generated at the falling edge of the control pulse t _i . Differential circuit 16
The output of (Fig. 5j) is connected to diode D ₁ as shown in Fig. 5k.
It is converted into the waveform shown in and applied to the SCR gate.

Since the SCR is not forward biased unless the anode potential exceeds U _B , it remains off even if a trigger pulse is applied to the gate, and the anode potential exceeds U _B , which means that the back electromotive force (Fig. 5 l) It is turned on only when the trigger pulse is applied to the gate. In addition, due to the self-holding characteristic of SCR, while back electromotive force is generated, if it is triggered at the beginning when the back electromotive force is generated, it will continue to maintain the on state even if the trigger pulse disappears, and the back electromotive force will disappears, the on-current becomes less than the holding current of the SCR, and the SCR is turned off. Therefore, the trigger pulse turns the SCR into an on state while a back electromotive force is generated in the switching region A, and discharges the back electromotive force to the positive potential line 17. Also, since the SCR is in the OFF state, the back electromotive force generated outside the switching area A is connected to the other end of the solenoid valve 1 and the transistor.
It is discharged as the base current of the transistor Q ₂ by the Zener diode ZD ₂ connected between the base of Q 2 and the base of Q ₂ . This is to improve the responsiveness of the current of the solenoid valve 1 to the control pulse _ti .

As detailed above, according to the current control circuit of the electromagnetic switching device according to the present invention, reliability can be improved and costs can be reduced because SCR is used which has high peak voltage and peak current resistance. Also, SCR
Since it is small, the circuit can be configured compactly. Furthermore, since the timing of turning on the SCR is synchronized with the back electromotive force generated in the switching region, a delay circuit can be omitted and its adjustment is not required.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional current control circuit, FIG. 2 is a waveform diagram at each part of FIG. 1, FIG. 3 is a block diagram of an embodiment of the current control circuit according to the present invention, and FIG. A specific circuit diagram of the embodiment shown in the figure,
FIG. 5 is a waveform chart at each part of FIG. 4. Explanation of symbols of main parts, 1... Solenoid valve, 2...
Drive circuit, 5, 10...NOR circuit, 6... Current detection circuit, 7... Switching circuit, 11... Back electromotive force absorption circuit, 16... Differential circuit.

Claims (1)

[Claims for Utility Model Registration] (1) An electromagnetic switching device, a current detection circuit that detects the current flowing through the electromagnetic switching device, and a switching device that operates on and off according to the current value detected by the current detection circuit. an electromagnetic switching circuit, a driving circuit that drives the electromagnetic switching device in response to a predetermined input signal or an output signal of the switching circuit, and a back electromotive force absorption circuit that absorbs a back electromotive force generated in the electromagnetic switching device. In the current control circuit of the type switching device, the back electromotive force absorption circuit is
A thyristor connected in parallel to the electromagnetic switching device and in a forward direction with respect to the back electromotive force, and a control means for supplying an ignition current to the gate of the thyristor in response to an output signal of the switching circuit. A current control circuit for an electromagnetic switching device characterized by: (2) The control means includes a differentiation circuit that differentiates the output signal of the switching circuit and shifts the level to a predetermined level, and a unidirectional element connected between the output terminal of the differentiation circuit and the gate of the thyristor. A current control circuit for an electromagnetic switching device according to claim 1, characterized in that it has the following. (3) The current control circuit for an electromagnetic switching device according to claim 2, wherein a unidirectional element is connected between the gate and cathode of the thyristor.