JPH0235155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for a sheathed glow plug installed in an internal combustion engine.

In a glow plug temperature control device that detects the voltage applied to the glow plug and controls the energization time to the glow plug, the glow plug's sheath tube surface temperature and the inside of the sheath tube, which are necessary to start the engine, are controlled. A phenomenon occurs in which the temperature difference between the glow plug and the heating element housed in the glow plug increases as the voltage applied to the glow plug becomes higher than the rated voltage of the glow plug. In other words, in so-called rapid heating type glow plugs, a large current is supplied to the glow plug to increase the rate of temperature rise, and the surface of the glow plug's sheath tube is rapidly raised to the temperature required to start the engine (for example, 900°C). When the power supply voltage is high, the temperature difference between the surface temperature and the heating element temperature becomes significantly large. On the other hand, if you simply change the temperature, the heating element will overheat and melt, which is likely to cause a failure.

An object of the present invention is to appropriately cope with the temperature difference between the surface temperature of the glow plug and the temperature of the heating element due to changes in power supply voltage, and the expansion and contraction of the energization time to the glow plug, and to reliably prevent melting of the heating element. Another object of the present invention is to provide a temperature control device for a glow plug that can quickly raise the temperature.

The present invention includes a key switch 2 having an OFF terminal 21, a preheating terminal 22, and a starter motor operation terminal 23, a rapid heating type glow plug 3, and a rapid temperature increase relay 4 for supplying a large current to the glow plug 3. , a relay 5 for energizing the glow plug 3 via a current limiting resistor 52, controlling energization of the relays 4 and 5, and controlling the energization time of the relay 4 by the applied voltage Vg of the glow plug 3. In the temperature control device for a glow plug, the first timer 6 includes a resistor R5 from a constant voltage source connected to the preheating terminal 22 and the starter motor operation terminal 23. , a first charging circuit L1 that charges the capacitor C1 via the diode D1, and the applied voltage
Vg is divided by resistors R3 and R4, and diode D2
A second charging circuit L2 that charges the capacitor C1 via the second charging circuit L2, a Zener diode that breaks down when the applied voltage Vg exceeds a set value, and a resistor R9 are connected in series, and the second charging circuit L2 is connected in parallel to the resistor R3. , and a third charging circuit L3 that charges the capacitor C1, and the resistance values of the respective resistors satisfy the following relationship: resistance R9<resistance R3<resistance R5.

Next, the present invention will be explained based on embodiments shown in the drawings.

1 is battery, 2 is key switch and OFF
It has a terminal 21, a preheating terminal 22, and a starter motor operation terminal 23. 3 is a glow plug, 4 is a first relay for supplying a large current inserted into the energizing circuit to the glow plug 3, 41 is its normally open contact, and 5 is a current limiting resistor 52 to the glow plug 3. 51 is its normally open contact; 6 is the first relay for controlling relay 4;
7 is a chopping timer that outputs a pulse to intermittently open and close the relay 4 according to the glow plug voltage during the time when the starter motor is energized; 8 is a timer for displaying the starting time; a glow lamp to be lit, 9 a complete explosion detection circuit for detecting self-operation of the engine, 10 a second timer for controlling the relay 5 and performing afterglow and keeping the glow plug 3 warm after the temperature has risen;
Reference numeral 1 denotes an OR circuit which receives the outputs of the first timer 6 and the chopping timer 7 and generates an OR output to the relay 4.

C1 to C4 are capacitors, R1 to R10 are resistors, D1 to D3 are diodes, and ZD1 to ZD3 are Zener diodes.

The first timer 6 includes a comparator 60, a capacitor C1 for determining a time constant, a constant voltage source, and a capacitor C1 connected to each other via a diode D1 and a resistor R5.
The charging circuit L1 connects the capacitor C1 via a diode D2 and a resistor R3 so that charging is performed while the charging voltage of the capacitor C1 is less than a value determined so that it is approximately a constant ratio to the glow plug applied voltage Vg. A second charging circuit L2 charges the capacitor C1, and a third charging circuit L3 charges the capacitor C1 when the glow plug applied voltage Vg exceeds a certain value via the diode D2 and the constant voltage diodes ZD2, ZD3. The charging current i1 from the charging circuit L1 and the charging current i from the charging circuit L2
2. Charged by charging current i3 from charging circuit L3. The capacitor C1 is charged by the charging circuits L1 and L2 when the voltage Vg applied to the glow plug is below the set value, and when the voltage Vg applied to the glow plug is above the set value, the charging circuit L3 is further combined.
1, L2, and L3 are all made to work.

Next, the operation of the first timer will be explained.

When the voltage Vg applied to the terminals of the glow plug 3 is low (for example, Vg < 11 volts), the capacitor C1 is charged only with the charging currents i1 and i2 of the charging circuits L1 and L2, and as the voltage Vg increases, R
9, ZD2 and ZD3 are corrected by charging current i3 from charging circuit L3 connected in series. These three charging circuits have the voltage applied to the glow plug terminal Vg, the charging voltage of C1 Vc, the reference voltage of the comparator 60 Vi, the breakdown voltage of diode D2 Vf, and the breakdown voltage of Zener diodes ZD2 and ZD3 Vz. Then, it works as follows.

(a) When Vg is high (for example, Vg > 11 volts) Vg > Vc + Vf + Vz (Vz > Vc + Vf) Vc = 1/C1∫ (i1 + i2 + i3) dt ...... (1) (b) When Vg is moderate (for example, 11 Volt>Vg
> 8 volts) Vg + Vf + Vz ≧ Vg > (R3 + R4) / R3 (Vc + Vf) Vc = 1 / C1∫ (i1 + i2) dt ...... (2) (c) When Vg is low (e.g. 8 volts > Vg)
Vg≦(R3+R4)/R3(Vc+Vf) Vc=1/C1∫i1dt ………(3) The charging voltage characteristic line in each case of (a), (b), and (c) is plotted using the graph in Figure 2. ₁ , b ₁ and c ₂ . The above equations (1) to (3) that determine the charging voltage Vc to C1 are charging characteristics when Vc is near the reference voltage Vi,
In fact, when circuit L1 works, Vc=
Since charging starts from 0, Vg, Vf, Vc, V
2, the battery is charged as shown in Figure 2. Therefore, when the power supply voltage Vg is high, initial charging is performed rapidly by charging currents i1, i2, and i3 at the beginning when the characteristic curve has an inflection point P as shown in the characteristic curve a shown in FIG. i2 to determine the inversion time of the comparator 60, that is, the energization time of the first timer 60. In addition, the inflection point S of each curve a, b, c is the charging pressure Vc = V2 - Vf = Vg × R3 /
This is the point (R3+R4)-Vf.

The charging curve for C1 is as shown in Figure 2 under each voltage condition, and based on these condition settings, the energization time to the glow plug 3 due to the output of the first timer 6 in Figure 1 is calculated from the formula, and is shown in Figure 3. The experimental values and calculated values (line) of the example are shown in the figure. The generation position of the inflection point Q on the energization time-applied voltage characteristic curve accompanying the generation of the above inflection point P is the Zener diode ZD2, ZD
By appropriately selecting the breakdown voltage value Vz according to 3, it can be freely set according to the glow plug characteristics, and the inflection point Q of the energization time-applied voltage characteristic curve
An advantageous energization time can be achieved by determining the conditions for keeping the surface temperature of the glow plug almost constant on the lower voltage side, and the condition for keeping the temperature of the internal heating element at a constant temperature close to the disconnection temperature on the higher voltage side. can be controlled.

As described above, the temperature control device for a glow plug according to the present invention has a first temperature controller whose output time constant changes depending on the input voltage.
In the glow plug temperature control device, the first timer is provided with a timer and a first relay that is provided in the energizing circuit to the glow plug and is turned on and off by the output of the first timer. As a charging circuit for the capacitor, there is a first charging circuit that is constantly energized, and a first charging circuit that performs charging while the charging voltage of the capacitor is below a value determined so that it is approximately a constant ratio to the voltage applied to the glow plug. The second charging circuit has a Zener diode and is configured to charge when the voltage applied to the glow plug exceeds a certain value. This makes it possible to appropriately increase/decrease the energization time to the glow plug, reliably prevent melting of the heating element, and moreover, enable rapid preheating and temperature rise.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the glow plug temperature control device of the present invention, Fig. 2 is a graph showing the charging characteristics of the capacitor, and Fig. 3 is the energization time of the glow plug by the first timer and the terminal voltage of the glow plug. It is a graph showing the relationship between In the figure, 4...first relay, 6...first timer, C1...capacitor for determining the time constant of the first timer, L1...first charging circuit, L2...
Second charging circuit, L3...Third charging circuit.

Claims (1)

[Claims] 1. A key switch 2 having an OFF terminal 21, a preheating terminal 22, and a starter motor operating terminal 23; a rapid heating type glow plug 3; and a rapid heating device for supplying a large current to the glow plug 3. a relay 4; a relay 5 for energizing the glow plug 3 via a current limiting resistor 52; In a glow plug temperature control device equipped with an energization control circuit having a first timer 6 for controlling time, the first timer 6 includes the preheating terminal 22 and the starter motor operating terminal 2.
a first charging circuit L1 that charges the capacitor C1 from a constant voltage source connected to the resistor R5 and the diode D1; and the applied voltage Vg is divided by the resistors R3 and R4;
A second charging circuit L2 that charges the capacitor C1 via a diode D2, a Zener diode that breaks down when the applied voltage Vg exceeds a set value, and a resistor R9 are connected in series, and the second charging circuit L2 is connected in parallel to the resistor R3. A temperature control device for a glow plug, comprising a third charging circuit L3 connected to the capacitor C1 to charge the capacitor C1, and a resistance value of each of the resistors satisfies a relationship of resistance R9<resistance R3<resistance R5.