JPH0632534Y2 - Solenoid valve drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a solenoid valve drive circuit, and more particularly to a solenoid valve drive circuit applied to a fuel injection valve of an internal combustion engine.

(Prior Art) As a drive circuit of an electromagnetic valve for fuel injection of an internal combustion engine, a so-called peak hold type drive for separately controlling a current at the time of opening a needle and a current at the time of holding in order to improve responsiveness The circuit is known.

FIG. 3 shows a conventional drive circuit in which the output valves 2 and 3 are connected across the solenoid valve coil 1.

The outline of the operation will be described below.

First, when a drive signal is applied to the input terminal 4, the output transistors 2 and 3 are turned on and a current flows through the solenoid valve coil 1. This current flows into the current detection resistor 5 and is converted into a voltage, which is input to the peak current detection circuit 6 and the hold current detection circuit 7 , respectively.

When the input current reaches the maximum value here, the peak current detection circuit
6 operates to bring the output to the “H” level and turns off the output transistor 2. When the output transistor 2 is turned off, the current from the power supply is turned off, and the electric energy accumulated in the solenoid valve coil 1 is transferred to the solenoid valve coil 1 → output transistor 3 → current detection resistor 5 → flywheel diode D.
Flowing through.

When the current becomes equal to or lower than a predetermined value due to this discharge, the hold current detection circuit 7 operates to bring the output to the “L” level and turns on the output transistor 2.

After that, ON / OFF is repeated with the hold current value as a boundary, and the current value within the predetermined range is continued only during the period when the drive signal exists.

Fig. 4 shows this state as a waveform diagram. Fig. 4 (a) shows the drive signal, and Fig. 4 (b) shows the solenoid valve coil 1.
Is the current flowing to.

(Problems to be Solved by the Invention) In the conventional device having the above configuration, it takes a long time from the peak current to the hold current. This is because the current flowing from the solenoid valve coil 1 after the peak current value is detected and the output transistor 2 is turned off is only due to the discharge through the output transistor 3.

This means that when the end of the drive waveform is a small pulse width such that it is at an intermediate position between the peak current and the hold current,
This means that the pulse width causes a difference in the current value at the end of the drive waveform, and as a result, the needle fall time of the solenoid valve is not constant, which adversely affects the solenoid valve characteristics.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic valve drive circuit capable of obtaining stability when the needle is closed when the drive time is short.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, a flip-flop circuit is connected to the output stage of the peak current detection circuit and the hold current detection circuit, and this output is connected to this output. The output transistor is controlled to be turned on and off, and the current detection resistor is connected to the surge absorbing zener diode circuit connected to one end of the solenoid valve coil.

(Operation) When the peak current detection circuit detects the current flowing in the solenoid valve coil, the output transistor is turned off via the flip-flop circuit, and during this period the current from the solenoid valve coil is forced to the Zener diode circuit to force the limit. Shed.

The current after the current limit is set to the hold current value by the hold current detection circuit.

(Examples) Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a solenoid valve drive circuit according to the present invention.

In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. F and F are flip-flop circuits, the CLK terminal is the output terminal of the peak current detection circuit 6 ,
The CLR terminal is connected to the output terminal of the hold current detection circuit 7 .

And the terminal is connected to one of the AND2 circuits, and
The drive signal end is connected to the other input end of the D2 circuit, and the output end of the AND2 circuit is connected to the (+) input end of the operational amplifier A ₂ .

Further, the terminal of the Zener diode circuit ZD for surge absorption connected to one end of the solenoid valve coil 1 is connected to the current detection resistor 5.

Other configurations are the same as those in FIG. Note that FIG. 2 is a waveform diagram for explaining the operation.

Next, the operation will be described with reference to FIGS. 1 and 2.

First, when a drive signal arrives at the input terminal 4, the output transistors 2 and 3 are turned on and a current flows through the solenoid valve coil 1. This current is converted into a voltage by the current detection resistor 5,
It is input to each of the current detection circuits 6 and 7 .

Here, when the coil current reaches the peak value, the output of the peak current detection circuit 6 becomes the “H” level, and the C of the F and F circuits is
It is input to the LK terminal, and as a result, the output terminal becomes "L" level and the output transistors 2 and 3 are turned off.

When the output transistor 3 is turned off, the energy (back electromotive force) accumulated in the solenoid valve coil 1 is
Zener diode ZD → current detection resistor 5 → flywheel diode D flows and falls sharply.

The Zener voltage is set to about 2/3 of the breakdown voltage of the output transistor.

If the current falls below the lower limit of the hold current in this state, the output of the hold current detection circuit 7 becomes "L" level and the ▲ ▼ terminals of F and F become "L", so the output becomes "H" level. And the output transistor 3 is turned on.

That is, the ON period of the output transistor 3 is from the peak detection of the current to the detection of the lower limit value of the hold current, and the current is limited during this period to shorten the time.

After that, the output transistor 2 is repeatedly turned on and off by the output of the hold current detection circuit 7 so that the solenoid valve coil current goes up and down the upper and lower limit values of the hold current.

At this time, the output transistor 3 is on, and when the output transistor 2 is off, the current flows through the flywheel diode D and the current falls gently. For this reason, the current is limited to a constant width.

According to the above-described embodiment, the fall time of the solenoid valve coil can be shortened, and therefore the characteristics when the needle is closed can be stabilized.

[Effect of the Invention] As described above, according to the present invention, after the current flowing through the solenoid valve coil reaches the peak current, the current is made to fall sharply until it reaches the hold current. A solenoid valve drive circuit with improved fuel flow stability can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a solenoid valve drive circuit according to the present invention, FIG. 2 is a waveform diagram for explaining the operation, FIG. 3 is a conventional solenoid valve drive circuit diagram, and FIG. It is a waveform diagram of. 1 ... Solenoid valve coil 2, 3 ... Output transistor, 4 ... Input terminal 5 ... Current detection resistor 6 ... Peak current detection circuit 7 ... Hold current detection circuit F, F ... Flip-flop circuit ZD ... … Zener diode D …… Flywheel diode

Claims (1)

[Scope of utility model registration request] 1. Two output transistors are connected to each other with a solenoid valve coil interposed therebetween, and a current flowing through the solenoid valve coil is introduced into a peak current detection circuit and a hold current detection circuit via a current detection resistor, In a solenoid valve drive circuit for an internal combustion engine that controls a current flowing in a solenoid valve coil according to an output state of each circuit, a flip-flop circuit is connected to an output stage of the peak current detection circuit and the hold current detection circuit, This output controls ON / OFF of the output transistor, and the other end of the surge absorbing zener diode connected to one end of the solenoid valve coil is connected to the current detection resistor. Valve drive circuit.