JPS585476A - Controller for quick-heating glow plug - Google Patents

Abstract

PURPOSE:To release the thermal stress by temporarily stopping the quick-heating when the heating temperature will reach to the predetermined temperature prior to the setting temperature then heating again after the difference between the inner temperature and the outer temperature has been decreased. CONSTITUTION:Upon closing of a key switch 12, the glow plug 11 is heated quickly through a relay contact (re) to increase the resistance Rg of the heating coil. When the potential (a) of the first bridge circuit increases and the plug temperature will reach to TM prior to the setting temperature Ts, the timer 13 is set by a comparator C1 to open the relay contact rl for the predetermined time through OR gate 14, delay circuit 15 and a relay drive 16 to stop the quick- heating temporarily. When the power is conducted again after elapsing of the timer to increase the temperature, the differential potential is produced across the points (a), (b) of the second bridge circuit while when the plug temperature will reach to the setting Ts of preheating of the combustion chamber, the contact rl is opened for predetermined time by the comparator C2 through OR gate 14 similarly with C1 thus to stop the heating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a glow plug, which is a starting assist device for a diesel engine.

In order to improve the startability of a diesel engine, the inside of the combustion chamber is heated, and it is known to use a rounded glow plug for heating.

FIG. 1 shows a cross-sectional view of a glow plug. 1 is a glow plug main body, and 2 is a heating coil.

Conventionally, with such a glow plug, as shown in Figure 2a, the preheat setting temperature [Ts (approximately ton degrees Celsius)] is 5 to
However, for drivers who are accustomed to gasoline-fueled engines, the preheating time is too long for drivers who are accustomed to gasoline-fueled engines.
It is desirable to shorten the preheating time tbo's by rapid heating as shown in Figure bK. However, when such rapid heating is performed, a sudden temperature difference is created between the heating coil 2 and the outer surface of the glow plug body 1, and a thermal gradient resulting from the ζosit difference and thermal stress are generated. , which does not occur when the preheating time is 5 to 7 seconds and is due to good thermal stress. Problems such as cracks in the glow plug main body and disconnection or melting of the heating coil due to high temperature heating occur.

Therefore, an object of the present invention is to provide a glow plug control device that alleviates the thermal stress near the heating coil that occurs when the glow plug is heated in a short time, and that does not require complicated operations during startup. shall be.

Next, the present invention will be explained in detail with reference to the drawings.

As mentioned above, cracks in the glow plug and thermal stress caused by the heating coil are the cause of the problem, and the problem can be solved by alleviating this thermal stress. The round part includes the heating coil part, the glow plug body and 1m outside! It is necessary to make the temperature difference between El as small as possible.

Therefore, in the present invention, as shown in Figure C, the glow plug is rapidly heated, and the heating temperature is set before the set temperature J The rapid heating is stopped, and after the internal and external temperatures have reached a certain level, heating is performed again in an attempt to alleviate the thermal stress that occurs. According to this two-stage heating,
As shown in Figure 5, the difference between the temperature of the heating coil section (internal temperature) and the temperature of the outer surface of the glow plug body (external temperature) decreases.

FIG. 4 is a circuit diagram of a glow plug control device according to the present invention. In Figure 4, Bo is the power source, which includes the battery for the wheels. 12 is a key switch, r. is a relay contact, and B. is a glow plug current detection resistor having a value less than the normal temperature resistance value tD'/1° of the glow plug.

11 is a glow plug, and is the resistance of the heating coil of the 'ELK glow plug. The heating current of the glow plug will flow through the circuit: power supply) Co 4 life switch 12 → relay swing point r → current detection resistor 8 → glow plug 11 → power supply 1o @ R1, R,, Rse Ra is a resistor, resistors R1, &, a current detection resistor 8 of the glow plug, and a resistor Rg of the glow plug's heating coil constitute a first bridge circuit, and resistors R1, R4 and resistors R, R-
@C1e C1 is a comparator and is connected to terminal a, @ of the bridge circuit of C breather 1,
cm is the terminal of the second bridge route, aKil is connected.

13 is a timer connected to the output terminal of the comparator CIC.

14 is ``ORIg circuit comparison 1! Its input terminal is connected to the output terminal of Ct*Cs. 15 is a signal delay circuit which is applied to the output terminal of the OR circuit. Reference numeral 16 is a relay drive circuit, and the relay is connected to the output terminal of the signal delay circuit, which is connected to the output terminal of the signal delay circuit. R.L.
is a relay coil with one end of its terminal connected to the output terminal of the drive circuit and the other end grounded.

Next, the control circuit of the skeleton glow plug will be explained with reference to the time chart of FIG. First, key switch 1-'l
When the power is turned on, the current is the power supply E as mentioned above.

The flow flows from the key switch 12, the relay contact r., the temperature detection resistor 8., the glow plug 11, and the power source Eo, and the heat generating coil of the glow plug is heated and its temperature rises. As the temperature rises, the value of the resistance Rg of the heating coil also increases, and the first
The potential at terminal a of the bridge circuit increases, breaking the balance of the bridge circuit. When the temperature of the glow plug is set in the middle of the set temperature fTa in the combustion chamber and reaches 9TM, the voltage across asj of the I11 bridge circuit will not exceed the set value of comparator C1, and comparator C will output the signal. is sent to timer 1jS. The timer 15 receives the output signal from the comparator CI and sends the output signal to the OR circuit during the window opening time t''dt+tmO.

The dead output signal passes through the OR circuit 14 and is input to the signal delay circuit, and the dead delay circuit sends an output signal to the relay drive circuit 16 after a short time dt. Relay coil RL is energized by the output of this relay drive circuit. The operation of the relay opens the relay contact rt and cuts off the current flowing to the glow plug. Rapid heating is stopped from this point K, and the time tm
During this period, heat is radiated from the heating coil section. After the current of timer 15 Hiro glow plug is 1111T for t3 time,
Since the signal is stopped, the activation signal is not sent to the relay drive circuit 16, and therefore the time delay is delayed.
% will be de-energized, the relay will return and the contact rA will close again. When contact rt closes, the glow plug is energized again and rapid heating begins.

When rapid heating starts and the temperature rises, a potential difference occurs between terminals a and blljlK of the second bridge circuit, and this potential difference also depends on the resistance value Rg of the heating coil due to heating of the glow plug, so the temperature of the glow plug increases When the temperature rises to the room preheating set temperature Ts, the potential between terminals a and b becomes Comparison 1.
! When the set value of Cs is exceeded, the comparator C outputs an output signal. dt,
After that, the relay drive circuit 16 is activated, and the relay contact rtK
The heating current circuit is cut off for a period of time ts. - After a certain period of time, the relay returns to its normal state, and the same heating current flows through the contact rt again. The same operation is repeated and the glow plug is warmed up.
L will be maintained at the combustion chamber preheating set temperature 1 [Ts.

As described above in detail, the glow plug control device according to the present invention can alleviate the thermal stress caused by rapid heating of the glow plug, can prevent the electrical components and heating coil of the glow plug from breaking or fusing, and can Since the plug is heated instantly, it has the excellent effect of eliminating complicated operations during startup.

do.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the glow plug, Figure 2m is a diagram showing the temperature characteristics of the glow plug, Figure 5 is the temperature f4I of the glow plug.
FIG. 4 is a control circuit diagram according to the present invention, and FIG. 5 is a time chart showing the operational relationship of the control device according to the same invention. Eo...power supply, 11...glow plug, R...
Current detection resistor, Rs * & e Rs * Ra・
...resistance, c,,c,...ratio aS. 13...Timer, 14...011 circuit, 15...
Delay circuit, 16... Relay drive circuit, RL-... Relay coil, rA... Relay contact. Patent applicant: Isuso Jidosha Co., Ltd. Patent attorney: Tsuji Sanagai (2 persons) Figure 1 Figure 2 (1) Figure 4

Claims (1)

[Claims] A glow plug with a heating element whose resistance value changes according to changes in heating temperature, a current detection resistor, and a normally closed current control element whose circuit is opened when a signal is applied are connected in series to the power supply. In the heating circuit for a glow plug, the heating circuit comprises: first and second calculation devices that calculate the resistance value of the heating element based on the voltage t generated across the current detection resistor;
A drive circuit that drives the current control element; and a first comparator that outputs an output signal and operates the drive circuit when the calculation result of the calculation device of iris 1 reaches a preset value before the preheating set temperature. and a second comparator which outputs a death output signal when the calculation result of the second calculation device reaches the preheating set temperature J[K and operates the drive circuit. .