JPH0452461Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a solenoid drive device for an automatic engine yoke that operates the engine yoke during an engine starting operation.

PRIOR ART In general, in the case of a solenoid drive device that drives an electromagnetic solenoid for an autochoke when starting an engine, for example, a switching transistor is turned on and off in response to commands to energize and de-energize the solenoid.
The solenoid is connected in series with the solenoid in the event of a short circuit such as a short circuit where part of the solenoid winding is shorted. It is necessary to protect the switched switching transistor from overcurrent.

FIG. 2 shows, as an example, a specific circuit configuration of an autochoke solenoid drive device in a conventional general-purpose engine.

Here, we will introduce a switch that works in conjunction with the engine start switch and closes its contacts when the engine is started.
Solenoid 1 and thermoswitch 2 are connected in series to power supply 3 via SW and fuse F, and when the engine warms up to a predetermined temperature, thermoswitch 2 turns off and stops energizing solenoid 1. It's becoming like that. In addition, a switching transistor is connected in parallel with the thermo switch 2.
Tr1 is connected to its base side, and a transistor Tr1 is connected to the base side of the transistor Tr1 in order to make the engine work for a short time to facilitate starting the engine when the engine is warm (thermo switch 2 is in the OFF state). A timer circuit 4 for turning on is provided.

As the timer circuit 4, the power supply voltage is connected to the resistor R1,
Potential V1 at point a divided by R2 and switch
It consists of a comparator CMP that compares the terminal voltage V2 of the capacitor C charged through the resistor R3 when the switch SW is turned on. Depending on the comparison result, the transistor Tr1 is turned on at the beginning when the switch SW is closed, and then for a certain period of time. With the passage of time, the transistor Tr1 is turned off.

But with something like this, the transistor
If solenoid 1 is short-circuited when solenoid 1 is energized by turning on Tr1, fuse F will melt and protect transistor Tr1 from overcurrent.
It is necessary to set the current capacity of the transistor Tr1 large relative to the fuse capacity so that the fuse F blows out within the time that the transistor Tr1 is within the ASO (safe operating area). Also, if the fuse is mistakenly replaced with one with a larger fuse capacity than the specified one, transistor Tr1
There may be cases where protection is not properly provided.

On the other hand, as shown in FIG. 3, an overcurrent protection circuit detects the overcurrent flowing through the transistor Tr1 and forcibly turns off the transistor Tr1 via the comparator CMP in the timer circuit 4 without using any fuses. It is also conceivable to provide 5.

As the overcurrent protection circuit 5, a transistor
The overcurrent flowing through Tr1 is detected by the resistor R5, and the control transistor Tr2 is turned on, and the capacitor C in the timer circuit 4 is rapidly charged through the resistor R6.
The configuration is such that the output of the CMP is forcibly brought to a low level to turn off the transistor Tr1.

But with something like this, the transistor
Although overcurrent protection for Tr1 can be performed quickly, a relatively large power capacity is required for the resistor R5 for overcurrent detection, and the power loss when driving solenoid 1 in normal conditions becomes large. 1's drive voltage drops. Normally, this type of solenoid 1 has a narrow operating voltage range, and when the voltage of the power supply 3 drops, the drop in the driving voltage of the solenoid 1 due to the power loss of the resistor R5 is normal. Can't be ignored.

Purpose This invention was made taking the above points into consideration.
In a device in which the solenoid is driven via a switching transistor for a certain period of time only when the thermoswitch is off, the fuse It is possible to quickly and reliably provide overcurrent protection for the transistor without separately installing a circuit or disconnection element for responding to overcurrents, and it also does not affect the drive voltage of the solenoid during normal operation. This invention provides a solenoid drive device for auto-choke.

Structure In order to achieve the objective, the present invention includes a solenoid drive device for an automatic yoke in which a thermoswitch for driving the solenoid is connected in series with the solenoid, and a transistor that is turned on for a certain period of time after an engine starting operation is connected in parallel with the thermoswitch. In addition, a switch control circuit is provided to detect an unsaturated voltage generated in the transistor when the solenoid is short-circuited and forcibly turn off the transistor.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG.
As in the previous case, a switch linked to the engine start switch connected in series to power supply 3
A circuit consisting of a SW, a solenoid 1, and a thermoswitch 2, a switching transistor Tr1 connected in parallel with the thermoswitch 2, and a timer circuit 4 provided on the base side of the transistor Tr1.
Furthermore, a switch control circuit 6 is provided which detects the unsaturated voltage generated on the collector side of the transistor Tr1 when the solenoid 1 is short-circuited and forcibly turns off the transistor Tr1 via the comparator CMP in the timer circuit 4. That's what I do.

As for the switch control circuit 6, the transistor Tr1 is in an unsaturated operating state when the potential at the resistance dividing point b of the resistors R7 and R8 provided between the collector and emitter of the transistor Tr1 increases beyond a predetermined value. is detected and turns on the control transistor Tr2, thereby rapidly charging the capacitor C in the timer circuit 4 through the resistor R6, forcing the output of the comparator CMP to a low level and turning off the transistor Tr1. ing.

With this configuration, under normal conditions, when the engine is started when the engine is cold (thermo switch 2 is on) and the switch SW is turned on, the Solenoid 1 is energized and the check yoke is activated, and then when the engine is in operation and the engine has warmed up to a predetermined temperature, the thermo switch 2 is turned off and solenoid 1 is deenergized, and the current yoke operation is restored. The condition is canceled.

Also, when the switch SW is turned on while the engine is warm (thermo switch 2 is off), the capacitor C in the timer circuit 4
During a preset time (for example, 3 seconds) by the time constant formed by the resistor R3, V2≧V1 and the output of the comparator CMP becomes high level, during which the transistor Tr1 is turned on and the solenoid 1 is connected. force to activate the chiyoke. When the capacitor C is charged over time and becomes V2<V1, the output of the comparator CMP is inverted to low level, the transistor Tr1 is turned off, and the solenoid 1 is deenergized.

Now, if the solenoid 1 causes a short circuit such as a short circuit while the switching transistor Tr1 is in the on state, the collector current of the transistor Tr1 increases, which increases the voltage between the collector and the emitter of the transistor Tr1.
1 falls into an unsaturated operating state.

When the transistor Tr1 falls into an unsaturated operating state, the unsaturated voltage generated on the collector side of the transistor Tr1 is detected by the switch control circuit 6, and the capacitor C is forcibly charged as described above. Transistor Tr1 will be forced off to protect it from overcurrent.

At this time, the detected value of the unsaturated voltage can be set appropriately according to the values of the resistors R7 and R8, and the base bias resistor R4 of the transistor Tr1 can be set appropriately.
The collector current of the transistor Tr1 when the solenoid 1 is short-circuited can be limited by the value of . Furthermore, due to the time constant determined by the capacitor C and the resistor R6, the transistor Tr1
detects the unsaturated voltage of the transistor Tr1
The turn-off time can be set to fall within that ASO.

The engine stop operation is performed and the switch is turned off.
When SW is opened, capacitor C is connected to resistor R1,
It is discharged through R2 and diode D1, and timer circuit 4 is reset.

Effects As described above, in the solenoid drive device for an autochute yoke according to the present invention, the solenoid is driven via the switching transistor for a certain period of time only when the thermoswitch is off. When overcurrent protection is applied to a transistor due to a short circuit, the switch control circuit detects the unsaturated voltage generated on the collector side of the transistor and forcibly closes the transistor, without using a fuse or other overcurrent-responsive circuit breakage or disconnection element. This allows the transistor to be turned off quickly and reliably, and the transistor can be easily turned off in the ASO, and the switch control circuit can be turned off. It has the excellent advantage that the power loss is small and does not affect the driving voltage of the solenoid during normal operation.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the solenoid drive device for an autochoke according to the present invention, and FIG.
3 and 3 are electrical circuit diagrams respectively showing a conventional solenoid drive device for an automatic yoke. 1...Solenoid, 2...Thermo switch, 3
...Power supply, 4...Timer circuit, 5...Overcurrent protection circuit, 6...Switch control circuit, Tr1...Switching transistor, CMP...Comparator, F...Fuse.

Claims (1)

[Scope of utility model registration request] In a solenoid drive device for an automatic engine yoke in which a thermoswitch for driving the solenoid is connected in series with the solenoid, a transistor that is turned on for a certain period of time after an engine starting operation is connected in parallel with the thermoswitch, and an unsaturated voltage of the transistor is detected. A solenoid drive device for an automatic yoke, characterized in that it is provided with a switch control circuit that forcibly turns off the transistor.