JPH0320539Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement of a diesel engine stop fuel cutoff circuit used for stopping a diesel engine.

<Prior Art> In various automobiles equipped with a diesel engine, when the diesel engine is stopped, the fuel is cut off when the key switch is placed in the OFF position. It has a built-in timer, so it won't run for an unnecessarily long time.
I try not to keep the fuel cut off.

This type of fuel cutoff circuit closes the fuel valve by supplying current to the solenoid coil from the vehicle's battery, so while the key switch is off,
Keeping the fuel shut off at all times means that current must continue to be supplied to the solenoid that keeps the fuel valve in the shut off position, which can easily be disconnected in a very short period of time. This is because the battery installed in the vehicle will increase.

As a result, the conventional configuration of such diesel engine stop fuel cutoff circuits is typically
It is as shown in the figure.

When the key switch KS is turned on, a current from the vehicle-mounted battery BT passes through a resistor R1 and a diode D1, and then is supplied as a base current to the transistor Q1 through a voltage divider circuit consisting of resistors R2 and R3. On the other hand, charging of the capacitor C1 is started, which determines the fuel cutoff time when the key switch is cut off, as will be described later.

When transistor Q1 turns on, transistor Q2 also turns on, and therefore resistors R4 and R5
Current is also supplied to the series circuit.

However, in the voltage divider circuit consisting of the series circuit of the resistors R4 and R5, the resistor R5 is the resistor R5.
6. As a result of receiving the base current from the voltage divider circuit of R7, the power transistor is short-circuited by the transistor Q3 which is turned on, and therefore receives the divided voltage output of the voltage divider circuit of resistors R4 and R5 as its base. Tp remains off, thus solenoid coil SR to close the fuel valve (not shown)
is not energized and fuel is supplied to the diesel engine.

When the driver turns off the key switch KS to stop the diesel engine, transistor Q3 immediately turns off. This means that the short circuit of the resistor R5 is released.

Under these conditions, on the other hand, even if the key switch is turned off, transistor Q1 will continue to discharge until the fully charged capacitor C1 is discharged below the base threshold voltage through resistors R2 and R3. During this period, the current supplied from the transistor Q2 is exchanged and divided by the resistors R4 and R5, and a divided voltage is supplied to the base of the power transistor Tp, turning it on.

Therefore, solenoid coil SR is energized,
A fuel valve (not shown) is closed.

After turning off the key switch KS, the time that this fuel cut-off state is maintained depends mainly on the capacitor C1.
The time constant is determined by the capacitance value of R2 and the resistance value of resistor R2, and in actual products, it is set to about 10 seconds.

Therefore, after the set time has elapsed, as capacitor C1 discharges, transistors Q1 and Q
2. The power transistor Tp also returns to the off state,
The system returns to the initial state described in this explanation and waits for the next key switch to be turned on.

In such a circuit, it is usually necessary to place a flywheel diode Df in parallel with the solenoid coil SR to absorb surges, and also to protect the power transistor Tp, a flywheel diode Df is placed in parallel with the power supply. A diode Dp connected in the opposite direction is provided.

<Problems to be solved by the invention> The problem with the conventional fuel cutoff circuit for stopping a diesel engine as described above is that if the battery BT is accidentally connected in reverse, the expensive power transistor Tp, Or the built-in or external diode Dp parallel to it can be easily destroyed.

Generally, batteries installed in vehicles are normally replaced periodically every few years. On the other hand, in recent years, it has become increasingly common for users to replace batteries themselves, rather than leaving it to a specialist. Therefore, it is common for the positive and negative terminals of batteries to be connected incorrectly.

If such a connection is made incorrectly, the diode connected in parallel with the power transistor Tp will first be damaged.
With respect to this diode, Dp is likely to be destroyed by a large inrush current in the forward direction, and furthermore, the power transistor Tp is likely to be destroyed subsequently.

As a countermeasure to this problem, a proposal has been made to omit the flywheel diode Df.
However, in that case, it is true that the solenoid coil will be affected by the large inrush current caused by the reverse connection of the battery.
Since SR exhibits high impedance, it has the ability to limit the large current that attempts to flow through the diode Dp or power transistor Tp to a smaller value, but the absorption function, which is necessary for the flywheel diode in the first place, is lost, and the solenoid A new fear has arisen that the power transistor Tp may be destroyed by the surge generated in the coil SR.

The present invention was developed in view of these conventional circumstances, and provides a fuel cutoff circuit for stopping a diesel engine that takes sufficient measures against reverse battery connection without compromising the functions previously required. That is.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a fuel cutoff circuit for stopping a diesel engine having the following configuration.

From the moment the key switch is turned off, the power transistor is turned on for a period of time determined by a timer, a solenoid coil connected in series with the power transistor is energized by battery current, and the fuel valve is closed. A flywheel diode for surge absorption is connected in parallel to the solenoid coil in a direction opposite to the polarity of the battery, and a flywheel diode for surge absorption is connected in parallel to the power transistor to protect the battery. A fuel cutoff circuit for stopping a diesel engine in which a diode is connected in a direction opposite to the polarity; a Zener diode is connected in series with the flywheel diode and in a forward direction with respect to the battery polarity; A fuel cutoff circuit for stopping a diesel engine, characterized in that a series circuit of a diode and the Zener diode is connected in parallel to the solenoid coil.

<Functions and Effects> When the Zener diode is connected in series with the flywheel diode as in the present invention,
The zener voltage of the zener diode exhibits resistance to the inrush current that occurs at the moment when the battery is connected in the reverse direction, and works to bypass the initial large current to the solenoid coil while reducing its value. Since the magnitude of the directional current can also be suppressed, it is possible to effectively protect the power transistor from destruction without changing the power transistor or the diode connected in parallel with the power transistor or the diode built in or externally connected to the power transistor.

Nevertheless, on the one hand, the surge absorption function necessary for the flywheel diode can be performed as expected without being impaired.

In other words, the present invention is extremely significant for this type of circuit because it can provide a large reverse current resistance to an existing circuit system without any inconvenience by simply adding a Zener diode.

<Embodiment> FIG. 1 shows an embodiment of a fuel cutoff circuit for stopping a diesel engine constructed in accordance with the present invention. This embodiment is an improvement of the conventional example explained with reference to FIG. 2, and therefore, components that may be the same as those in FIG. 2 are given the same reference numerals in FIG. are doing.

In fact, in accordance with the idea of the present invention, in this embodiment, the only improvement to the circuit shown in the second diagram is the addition of a Zener diode ZD.

In other words, for both ends of solenoid coil SR,
In addition to the existing flywheel diode Df, a Zener diode ZD which is in the forward direction with respect to the polarity of the battery BT is provided in series, and these series circuits are connected.

The normal operation of the fuel cutoff circuit for stopping the diesel engine in this embodiment is as already described in connection with the conventional example, and there is no difference, so a re-explanation will be omitted here. When replacing a BT, if you accidentally connect the battery BT with the polarity opposite to the illustrated polarity, this circuit will reduce the zener voltage of the zener diode ZD against the large inrush current that flows at the moment of connection. The power transistor Tp and its built-in It is possible to effectively protect the diodes Dp, etc. that are connected in parallel or externally from being destroyed, without changing them.

Nevertheless, on the other hand, the surge absorption function necessary for the flywheel diode Df can be performed as expected without being impaired.

Note that the specific circuit to which the present invention can be applied is not limited to the one shown in the drawings. The power transistor is turned on, and the solenoid coil connected in series with the power transistor is excited by the battery current to close the fuel valve. At the same time, a flywheel diode for surge absorption is connected in parallel to the solenoid coil to change the polarity of the battery. Any fuel cutoff circuit for stopping a diesel engine that is connected in the opposite direction to the fuel cutoff circuit can be equally improved by the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a preferred embodiment of a fuel cutoff circuit for stopping a diesel engine constructed according to the present invention, and FIG. 2 is a schematic diagram of a typical conventional fuel cutoff circuit for stopping a diesel engine. . In the figure, BT is a battery, Q1, Q2, Q3 are transistors, Tp is a power transistor, Dp is a diode built into the power transistor or externally connected in parallel, SR is a solenoid coil, Df is a flywheel diode, ZD
is a zener diode, KS is a key switch, D1
are diodes, R1, R2, R3, R4, R5,
R6 and R7 are resistors, and C1 is a capacitor for setting the timer setting time.

Claims (1)

[Claim for Utility Model Registration] From the moment the key switch is turned off, a power transistor is turned on for a period of time determined by a timer, and a solenoid coil connected in series with the power transistor is excited by battery current. A flywheel diode for surge absorption is connected in parallel with the solenoid coil in a direction opposite to the polarity of the battery, and a flywheel diode is connected in parallel with the power transistor to close the fuel valve. A diesel engine stop fuel cutoff circuit in which a diode for power transistor protection is connected in a direction opposite to the polarity of the battery; A fuel cutoff circuit for stopping a diesel engine, characterized in that a series circuit of the flywheel diode and the Zener diode is connected in parallel to the solenoid coil.