JPS6111657Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a circuit that detects an abnormal voltage of a glow plug used in a diesel vehicle or the like and maintains it as it is depending on the driving condition.

Conventionally, diesel cars and the like have been equipped with glow plugs to facilitate combustion. When starting the car, the time to energize the glow plug is determined depending on the vehicle situation at that time, and the glow plug is first energized for the predetermined time. The engine is driven after the set time and the glow plug is energized under certain conditions even after the engine is running (afterglow), which is different from the energization to the glow plug before the engine is started (preglow). The voltage applied to the plug is approximately the power supply voltage.
It is set to 1/2. This is set by dividing the voltage using series resistors, but if the glow plug is disconnected, this divided voltage will increase. Normally there are 4 glow plugs, but if you use 1 glow plug,
Assume that there is a main disconnection. If the series resistance is R ₁ and the resistance of one glow plug is R ₂ , the voltage applied to the glow plug is V _P4 = R ₂ / (R ₂ + 4R ₁ ) to V _P3 =
It increases to R ₂ /(R ₂ +8R ₁ ). Therefore, the voltage applied to the glow plug becomes high, causing rapid deterioration of the glow plug and causing problems in running. Therefore, when one or more glow plugs are disconnected and the voltage applied to the glow plugs increases, measures are usually taken to detect this and cut off the power supply to the glow plugs. This method usually involves detecting whether the voltage applied to the glow plug is above or below a set voltage, and if it is above or below a set voltage, the relay that is energizing the glow plug is cut off. However, with only this method, when the relay is cut off, it is detected that the voltage is zero again, and the relay becomes conductive, but since the voltage exceeds the set value, the relay becomes cut off again, and this relay becomes conductive.・There was a drawback that the relay contacts were worn out due to repeated interruptions, resulting in a decline in quality.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional ones, and provides an abnormal voltage detection and holding circuit for glow plugs with improved quality.

An embodiment of this invention will be described below with reference to the drawings. In the figure, 1 is a battery, 2 is a key switch, 3 is a glow relay that is driven by a glow unit (not shown) during pre-glow and applies battery voltage to glow plug 4, and 5 is turned on by a signal from after-glow unit 6 during after-glow. An afterglow relay that conducts and cuts off contacts by an afterglow coil 7; 8 is a series resistor that divides the voltage applied to the glow plug 4 during afterglow; 9 is a series resistor that divides the voltage applied to the glow plug 4 during afterglow; A signal line 10 transmits the signal to the unit 6, a detection circuit 1 detecting whether the voltage of the signal line 9 is above or below the set voltage.
Reference numeral 1 denotes a holding circuit that holds the voltage when a voltage equal to or higher than the set voltage value is detected in the detection circuit 10, and includes a diode 12. 13 is a power relay that supplies power to the afterglow coil 7 under preset conditions; 14 and 15 are comparators; 16
is an inverter, and 21 is a resistor whose one end is connected to the output terminal of the inverter 16 and the other end is connected to the normally open terminal of the power relay 13.
This constitutes a function that determines whether or not it is necessary to maintain the detection state. 17 and 18 are resistors that set the detection level (hereinafter referred to as V _P ) of the comparator 14, and 19 and 20 are resistors that set the comparison voltage of the comparator 15. Note that the relationship between the battery voltage V _B , the detection level V _P of the comparator 14, and the aforementioned V _P4 and V _P3 is set so that V _B > V _P3 > V _P > V _P4 . 22 is a transistor that drives the power relay 13; 23, 24, 25, and 28 are diodes;
6 is a switch built into the generator that turns ON or OFF depending on the power generation status (hereinafter referred to as Reg/L terminal); 26a is a charge lamp; 27 is a switch that detects water temperature, etc. and determines whether afterglow is necessary; This allows afterglow to occur when the light is off.

Next, the function of this circuit will be explained. When the key switch 2 is connected to an ignition terminal (not shown), it makes the glow relay 3 conductive for the time set by the glow unit (not shown),
Apply battery voltage V _B to glow plug 4,
The temperature of the glow plug rapidly rises to a temperature at which the engine can be started. At this time, since V _B is applied to the glow plug 4, a voltage V _B higher than the detection level V _P is input to the detection circuit 10 via the signal line 9, and the output of the comparator 14 becomes "H" →
The signal is inverted to "L", and the output of the inverter 16 is turned off.

On the other hand, since afterglow is not required before the engine starts, the base drive current of transistor 22 is
The current flows to the Reg/L terminal 26 which is in the ON state, the transistor 22 turns OFF, and the power relay 13 turns OFF.
Therefore, no voltage is generated at the normally open terminal, no voltage is applied to the output terminal of the inverter 16 via the resistor, and the output of the comparator 15 becomes "L".

Next time the engine starts, glow relay 3
is turned off by a glow unit (not shown),
On the other hand, the Reg/L terminal 26 is turned OFF, and the base drive current flows to the transistor 22.
2 is turned on, the power relay 13 is turned on, the afterglow relay 5 is made conductive, and the glow plug 4 is energized through the series resistor 8, thereby performing an afterglow operation.

In this state, if all four glow plugs 4 are normal, the applied voltage V _P4 is lower than the detection voltage V _P of the detection circuit 10 as described above, the output of the comparator 14 is "H", and the output of the inverter 16 is teeth
ON, the output of the comparator 15 is in the "L" state. Next, when one or more glow plugs 4 are disconnected, the applied voltage becomes V _P3 or more than V _P3 and a voltage higher than the detection voltage V _P is input to the detection circuit 10, and the output of the comparator 14 is inverted to "L". Then, the output of the inverter 16 is turned off. Also, since the output of the comparator 14 is "L", the base current of the transistor 22 flows to the comparator 14 via the diode 23, and the transistor 22
However, the excitation current of the power relay 13 is not momentarily interrupted due to the flyhole effect caused by the diode 28, and a time lag occurs in the OFF operation of the power relay 13, and the output of the comparator 14 becomes "L".
After that, the power supply voltage remains applied to the normally open terminal for a while, and then it is turned off, the afterglow relay 5 is turned off, the power to the glow plug 4 is stopped, and the input to the detection circuit 10 is turned off. The voltage becomes zero. Therefore, a voltage is applied to the output terminal of the inverter 16 via the resistor 21 during the time lag. Here, since the comparison voltage of the comparator 15 set by the resistors 19 and 20 is set lower than the output voltage of the inverter 16, the output of the comparator 15 is inverted from "L" to "H". This output voltage is fed back to the input terminal of the comparator 14 via the diode 12, but since this voltage is set to a value higher than the detection voltage V _P of the detection circuit 10, no voltage is applied to the glow plug 4. However, the output of the comparator 14 remains at "L", and the state in which the glow plug 4 is energized is maintained.

In the above embodiment, a case has been described in which the operation delay of the power relay 13 is utilized, but the same effect can be obtained even if a time lag function is added separately. Further, the detection circuit 10 and the holding circuit 11 may be constructed of other individual electronic components without using a comparator. Moreover, it can be used not only for detecting abnormal voltage of a glow plug but also for other voltage detection and holding functions.

As described above, according to this invention, the abnormal voltage of the glow plug of a diesel car is not only detected but also held, and since the relay operation delay is used for holding, the power supply to the glow plug is stopped in the event of an abnormality. This has the effect of being able to reliably achieve this without any malfunction.

[Brief explanation of the drawing]

The figure shows an abnormal voltage detection and holding circuit for a glow plug according to an embodiment of this invention. In the figure, 4 is a glow plug, 5 is an afterglow relay, 6 is an afterglow unit, 10 is a detection circuit, 11 is a holding circuit, and 13 is a power relay.

Claims (1)

[Scope of utility model registration request] In a glow plug that heats an engine, and a constant voltage is applied to the glow plug even after the engine is driven, a detection circuit that detects when the voltage applied to the glow plug exceeds a predetermined value and outputs a predetermined signal. , turning on the relay contact that controls the output of this detection circuit and the power supply to the above glow plug,
A holding circuit receives an output that is displaced due to turning off, and maintains the detector output at the predetermined signal even if the voltage applied to the glow plug becomes smaller than the predetermined value by feeding back the output to the detection circuit. Equipped with a glow plug abnormal voltage detection and holding circuit.