JPS59203877A - Glow plug conduction controlling device - Google Patents

Abstract

PURPOSE:To control the temperature of a glow plug without being affected by an electric source voltage by a method wherein the charging and discharging of a capacitor is effected by a current proportional to the square of an impressing voltage upon quick heating of the glow plug while the quick heating is interrupted by this terminal voltage. CONSTITUTION:When a key switch 2 is closed, the positive side input of a comparator 22 is increased, transistors 24, 23 are put ON, a main relay 4 is closed and a voltage is impressed on the glow plugs 3a-3d. This voltage of a positive terminal 7 is inputted into a voltage square-law circuit 8 and the output thereof is inputted into a current exchanging circuit 14. A constant current, proportional to an input voltage, flows into the output 14b of the circuit 14 and a capacitor 16 is charged by the constant current in accordance with the voltage. The conducting time of the glow plugs 3a-3d is controlled in accordance with the terminal voltage of the capacitor 16 whereby the control of quick heating of the glow plugs may be effected without being affected by the electric source voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to temperature control of a glow plug, and is intended to maintain a stable temperature after a rapid temperature rise without using a current detection resistor.

Conventionally, a voltage higher than the rated voltage is applied to the glow plug to rapidly heat it, and once the specified temperature is reached, the voltage applied to the plug is lowered using a dropping resistor, etc., or the overvoltage is switched to intermittent energization to maintain a stable temperature. is widely used, and as a means of detecting whether a predetermined temperature has been reached, a microresistance is often inserted in series with the glow plug, and the voltage division ratio between the glow plug and the plug is determined. It cannot be used unless the plug has a relatively large resistance temperature coefficient. On the other hand, JP-A-54-6522
Although it is known to simulate the glow plug temperature using a CR circuit as seen in Japanese Patent No. 5, there is a problem in that controllability deteriorates unless changes in the applied voltage are sufficiently taken into consideration.

The present invention provides a first means for outputting a voltage approximately proportional to the square of the voltage applied to the glow plug during rapid heating of the glow plug, and a second means for outputting a current proportional to the output voltage of the first means. By providing the second means with means for interrupting the rapid heating of the glow plug when the terminal voltage of the capacitor being charged or discharged reaches a predetermined value, the applied voltage can be maintained without being affected by fluctuations in the power supply voltage due to cranking, etc. The object of the present invention is to provide a glow plug energization control device that rapidly heats a glow plug to a certain temperature in a time corresponding to the voltage.

The present invention will be explained below with reference to embodiments shown in the drawings.

In FIG. 1, 1 is a 12V rated battery, 2 is a key switch, and 3a to 3d are glow plugs connected in parallel, the rated voltage of which is approximately 1/2 or less of the battery rated voltage. 4 is a main relay that opens and closes the direct application of battery voltage to the glow plugs 3a to 3d; 5 is a sub-relay to apply voltage to the glow plugs 3a to 3d via a dropping resistor 6; the dropping resistor 6 is the glow plug This resistor divides a portion of the battery voltage so that the voltage is close to the glow plug rated voltage. 7 is a positive terminal of the glow plugs 3a to 3d, and 8 is a voltage squaring circuit which inputs the voltage of terminal 7 and outputs a voltage approximately proportional to the square of the input voltage at its output 8a. , 9 is 5, IV Zener diode, 1o
is a resistance of IKΩ, and 11 is a resistance of 3.3Ω. As shown in FIG. 2, the input/output characteristics of the voltage square circuit 8 are approximately as shown by curve b with respect to ideal square curve a.

12.13 is a resistor that divides the voltage of the output 8a of the voltage square circuit, 12 is 6.2Ω, and 13 is 2Ω, dividing the voltage of 8a to about 1/4 °C. Reference numeral 14 denotes a well-known voltage-current conversion circuit which draws a constant current proportional to the voltage applied to its input terminal 14a at its output terminal 14b, and its input/output characteristics are, for example, a directly proportional straight line as shown in FIG.

15 is a three-terminal regulator that outputs a constant voltage of 5V to its output 15a, and 16 is a capacitor connected from a constant voltage of 5V to the output 14b of the voltage-current conversion circuit 150, and its capacitance is 100μI? I'm keeping it to a certain extent. 17 is a resistor that allows the capacitor 16 to slowly discharge the charge stored in the capacitor 16 when no external voltage is applied, and has a resistance of about 10 OKΩ. Diode 19 is a comparison circuit to prevent discharge through the comparator 22.
The negative input of the resistor 20.21 divides the voltage (5■) of the output 5a of the three-terminal regulator 15 and sets it to 2.5■, and the positive input is connected to the cathode of the diode 18. When the terminal voltage of the capacitor 16 becomes high (then the output of the comparator 22 becomes low level.2
3 is a transistor for driving the main relay 4;
4 is the transistor 2 according to the output of the comparator 22.
Transistor that drives 3. 25 is comparator 22
This is a transistor that turns on when the output of transistor 25 becomes low level, and when transistor 25 turns on, comparator
The voltage level of the negative side input of 2 becomes high. 26 is a transistor for driving sub-relay 5, 27 is transistor 2
A transistor 28 drives the key switch 2 for a certain period of time (e.g., 2 minutes) from the time when the key switch 2 is closed, or when the water temperature of a diesel engine (not shown) reaches a predetermined value (e.g., 40°C).
This is an afterglow timer circuit that outputs a high level to its output 28a until the voltage rises to .

Next, the operation of the above configuration will be explained. When the key switch 2 is closed, the battery voltage fluctuates over a wide range of 6 to 16 V due to cranking, etc., but the output voltage of the 3-terminal regulator 15 is constant at 5V, so the negative input of the comparator 22 is 1V. It is 2.5■ of /2. Here, since the terminal voltage of the capacitor 16 is 0.sup., the voltage on the plus side input of the comparator 22 becomes higher than the voltage on the minus side input, and the output of the comparator 22 becomes high level. Then, since the transistors 24 and 23 are turned on in sequence, the main relay 4 closes its contacts and the battery voltage is applied to the glow plugs 3a to 3d. In this way, the glow plugs 3a to 3d start to rapidly heat up, but the voltages at the positive terminals 7 of the glow plugs 3a to 3d are input to the voltage square circuit 8, and the output 8a is approximately expressed as shown in Figure 2. The voltage characteristic is a square function, and the voltage of the output 8a of the voltage square circuit 8 is divided to about 1/4 by the resistor 12.13 and input to the input 14a of the current conversion circuit 14. A constant current proportional to the input voltage as shown in FIG. 3 flows into the output 14b of the voltage-current conversion circuit 14. Therefore, the capacitor 16 is charged with a constant current according to the voltage of the output 14a of the voltage-current conversion circuit 14, and as shown in FIG.
The voltage at b decreases linearly with a slope inversely proportional to the voltage at input 14a. Therefore, the voltage of output 14b changes from 5■ to 2.5
The time required for the voltage to drop to (2) is also inversely proportional to the voltage of the human power 14a. Therefore, the output of comparator 22 is
After closing the output 14b, the voltage at the output 14b becomes 5 as shown in Figure 4.
The time required to drop from ■ to 2.5■ becomes a high level. This means that the output of the comparator 22 becomes high level for a time inversely proportional to the input voltage of the voltage square circuit 8, that is, the square of the voltage of the positive terminal 7 of the glow plugs 3a to 3d, and finally the main relay 4 is activated for a time t. The contacts are closed and the glow plugs 3a to 3d are energized for L time. When the capacitor 16 is charged with a constant current and the voltage of the positive side of the comparator 22 becomes low, the output of the comparator 22 is inverted to a low level. Then, the transistors 24 and 23 are sequentially turned off, the contacts of the main relay 4 are opened, and the glow plugs 3a to 3d are switched to stable heating at the rated voltage via the sub relay 5 and the dropping resistor 6. At the same time, the transistor 25 is turned on, and the output 15a of the three-terminal regulator 15 is connected to the negative input of the comparator 22, thereby maintaining the output of the comparator 22 at the U-level.

Now, the fact that the time during which the battery voltage is directly applied via the main relay 4 after closing the key switch 2 is inversely proportional to the square of the voltage applied to the glow plugs 3a to 3d means that the overvoltage glow plug 3a
During the period when ~3d is rapidly heated, glow plugs 3a~3
Regardless of the voltage applied to d, current is applied until a constant temperature is reached. This is because, in general, the temperature rise when heating a heating element by applying energy is proportional to the energy loss due to radiation, conduction, or convection, or, if the energy loss is small, to the amount of energy applied, compared to the energy applied during the application of energy. The temperature reached by the glow plug is expressed as 1"oc(V2,'R)xt, where the resistance of the glow plug is R1, the applied voltage is ■, and the energization time is t.Therefore, the energization time t is the square of the applied voltage (■). By making it inversely proportional to , the reached temperature T of the glow plugs 3a to 3d can be made constant regardless of the applied voltage.After the main relay 4 is turned off, the sub relay 5 whose contacts are closed from the moment the key switch 2 is closed A voltage near the rated voltage of the glow plug is applied through the dropping resistor 6 to maintain a stable temperature, and when the afterglow timer circuit 28 outputs 28a after a predetermined time period has passed, the output 28a becomes low level. The contact of the sub-relay 2 is opened and the energization by the battery 1 is completely terminated.

In addition, if the key switch 2 is opened and the key switch 2 is closed again before the main relay 4 opens the contact by closing the key switch 2, the voltage across the capacitor 16 will change because the discharge resistor 17 has a high resistance. , since it does not drop rapidly,
Start rapid heating again from the beginning and install glow plug 3a~
3d can be prevented from overheating.

In addition, there are the following as other embodiments of the present invention.

The voltage squaring circuit 8 may be constructed by combining an i+11 Zener diode 9 and a resistor 10.11, or may generate a voltage proportional to the square of the voltage applied to the glow plugs 3a to 3d. Any other method may be used. Also voltage type/j! i conversion II! The l path 14 is also not limited to the circuit of the embodiment, and may be any circuit as long as it flows out or draws in a constant current proportional to the input terminal.

The capacitor 16 is charged after the key switch 2 is closed, but it is charged to a constant voltage immediately after the key switch 2 is closed, or it is already charged to a constant voltage when the key switch 2 is opened. You may also use a method of constant current discharge from a state where the

As described above, according to the present invention, the first means outputs a voltage approximately proportional to the square of the voltage applied to the glow plug, and the first means outputs a current proportional to the output voltage of the first means. By providing a means for charging or discharging the capacitor by the second means and interrupting the rapid heating of the glow plug when the terminal voltage of the capacitor reaches a predetermined value, the temperature of the glow plug can be raised to a certain temperature during rapid heating. Since the rapid heating is interrupted by detecting the terminal voltage of the capacitor, which changes as it is charged or discharged with a constant current, the temperature reached by the glow plug remains constant, regardless of fluctuations in the power supply caused by cranking, etc. There is an excellent effect that can be done.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram of the voltage square circuit 8, Fig. 3 is a characteristic diagram of the voltage-current conversion circuit 14, and Fig. 4 is a capacitor during rapid heating. 16 is a constant current charging characteristic diagram, and FIG. 5 is a characteristic diagram of applied voltage and energization time of the glow plug. 2...Key switch, 3a-3d...Glow plug, 4...Main relay, 5...Sub relay, 6...
・Dropping resistor, 8... Voltage square circuit, 14...
・Voltage-current conversion circuit, 15...3 terminal regulator,
16... Capacitor, 28... Afterglow timer circuit. Representative Patent Attorney Takashi Okabe

Claims (1)

[Claims] a first means for outputting a voltage approximately proportional to the square of the voltage applied to the glow plug; a second means for outputting a current proportional to the output voltage of the first means; and a second means for outputting a current proportional to the output voltage of the first means. 1. A glow plug energization control device comprising: a capacitor that is charged or discharged; and means for interrupting rapid heating of the glow plug when a terminal voltage of the capacitor reaches a predetermined value.