JPS5825586A - Apparatus for helping to start diesel engine - Google Patents

Abstract

PURPOSE:To slow rate of heating a glow plug and exothermic coil for preventing them from damages by connecting a first voltage lowering resistance in series to the exothermic coil of the glow plug through a switching means when the temperature of the glow plug reaches a preset value. CONSTITUTION:Assuming that two glow plugs 1 are disconnected, two times voltage in the normal case are applied to the plug 1. When the composit resistance of the glow plug 1 exceeds a normal set value of resistance, a comparator C2 generates the output signal which is amplified by an amplifier A2 to operate a relay RL2 so that the normally closed contacts RL2 are opened. Next, a second glow plug heating circuit is opened and then a timer 3 generates the output signal after a set time of the timer 3 to operate a third relay RL3 so that the normally opened contacts rl3 are closed and thereby resistance R4 is inserted in parallel to resistance R2 forming a first bridge to halve the composite resistance. Thus, the glove plug 1 can be prevented from overheating.

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 preheated, and it is known to use a glow plug for this purpose. In conventional rapid heating systems, the preheating set temperature in the combustion chamber (approximately 900°C
)K2! It took 4 to 10 seconds to preheat until the temperature was reached. However, waiting for the preheating time of 4 to 10 seconds during operation is unbearable for drivers who are accustomed to engines that use the engine as fuel, so it is desirable to shorten the preheating time. In order to meet this demand, the heating speed is further increased and the glow plug is heated rapidly, which causes the glow plug to change from a low temperature (outside temperature) to a high temperature (approximately 900℃).
As a result, the heating coil part of the glove 2g reaches a high temperature K.

The outer periphery remains at a low temperature, which means that a large thermal gradient occurs between the heating coil and the outer periphery, which causes thermal stress, which can cause problems such as cracks in various parts of the globe lugs and disconnection of the heating element. I was awake. In order to prevent such cracks and disconnections due to the temperature difference between the heat generating part and the outer circumferential part of the gray plug, as shown in Figure 1, the heating speed is the same from the start of preheating the glow plug to the preheating set temperature T$ of the combustion chamber. It stops preheating at 200 degrees, and heats at ultra-rapid heating speed 2 until it reaches a preset constant temperature TM just before the preheating set temperature Ts, and after exceeding the set point TM, it responds to the heating of the heating coil. A method of heating by switching the rapid heating speed bK may be considered. In other words, as shown in Figure 2, heating is performed with a large initial current t from the preheating start point to the switching point (the point where the temperature reaches TM in Figure 1), and after passing the switching point g, as shown in the diagram fK. This is a method of decreasing the heating current. According to this method, the temperature difference between the heat generating coil portion and the outer peripheral portion of the glow plug is small, and failures such as cracks in the glow plug and disconnection of the heat generating coil portion can be reduced. By the way, there are normally a number of gloves for preheating the combustion chamber corresponding to the number of cylinders in the engine, and the heating coils of some of them may break for some reason. If the heating coil of the glow plug is disconnected, there is no particular problem as long as it prevents the engine from starting, even if it is just one, but normally in a 4-cylinder engine, two out of the four gummy plugs are disconnected. Even if one heating coil breaks, the engine can be started using the other two.

However, as shown in Figure 1, the heating of the glow plug was
In the method of heating in stages, the initial planned temperature T
M is performed by detecting the resistance value of the heating coil of the glow plug, so if the glow plug is disconnected, the combined resistance of the heating coil of the gummy plug will increase by the amount of disconnection of the heating coil, resulting in the glow shown in Figure 5. Switching occurs at a point where the temperature is lower than the switching point 1 shown by the solid line X, where there is no disconnection in the heating coil of the plug. The subsequent temperature rise is at point 11 in the figure.
The temperature rises as indicated by Y (the reason will be explained later).The temperature rises even if it exceeds the preheating set temperature T$, which results in overheating of the Kt Jiglow plug heating coil.Therefore, the present invention
As shown in Figure 1, in the gummy plug rapid heating control device that heats the gummy plugs in two stages, the heating coils of some of the gummy plugs were disconnected. An object of the present invention is to provide a rapid heating control device for a glow plug that can control heating without overheating the heating coil of other glow plugs that remain even if such an accident occurs.

Next, the rapid heating control device for gummy plugs according to the present invention will be explained in detail with reference to the drawings.

FIG. 4 is a circuit diagram used in the glow plug rapid heating control device according to the present invention. In the same figure, B.

is the power source, which comes from the vehicle's battery, etc. 2 is a key switch. Reference numeral 1 denotes glow plugs, which are provided according to the number of cylinders in the engine, and in this embodiment, four cylinders, that is, four gray plugs will be described, but it is natural that more or fewer gray plugs may be used. Individual glow plug IL 1bl
Each of the ICs and 1d has a heating coil, and the internal resistance of each of the heating coils is rg, and the combined resistance of the example in which four of the heating coils are connected in parallel is Rg=-r g/4. Re is the internal resistance of the four glow plugs, that is, a temperature detection resistance for detecting the temperature of the heating coil. Rle
R1# R4 is a resistor, which is connected to the temperature detection resistor Re and the gummy
A first bridge circuit is formed by the resistance Rg of the heating coil of the plug, R1, and R1, and a second bridge circuit is formed by the temperature detection resistance Re and the resistance Rg, R3, and R4 of the heating coil of the glow plug. . CI is the first comparator,
Before the set preheating temperature in Figure 1, place the gummy at the switching point TM.
It is set to emit an output signal when the resistance value of the heating coil of the plug reaches the intermediate point tf of the first bridge circuit.
Its input terminal is connected to J2m. Person 1 uses an amplifier to amplify the output signal of comparator C1, and connects the first relay R.
Comparator C emits an output signal that activates Ls.
Its input terminal is connected to the output terminal of I. Cs is a comparator for detecting disconnection of the heating coil of the glow plug, as will be described later, and its input terminal is connected to the intermediate point m1, m@K of the second bridge circuit.

A is an amplifier which amplifies the output signal of the comparator Cs and
The input terminal of the relay RL is connected to the output terminal of the comparison snow C. rLl is a normally closed contact of the 10th relay RL),
Power go.

Key switch 2, temperature detection resistor RC1 - plug 1
The series circuit with the first glow plug heating current circuit constitutes a first glow plug heating current circuit. Rdl is the voltage drop resistance % r4 is the second relay ~
It is a normally closed contact point of RL, and the power supply Eζ key switch 2
, the temperature detection resistor Re, and the glow plug 1 constitute a second glow plug heating current circuit. Rd3 is a voltage drop resistor, and a series circuit with 144 constitutes a third glow plug heating current circuit. 3 is timer, RL
s is a $5 relay.

Next, the operation of the above circuit will be explained. First.

When the key switch is closed, the group lag heats up through the 10th group 4-plug heating current circuit, that is, the normally closed contact r4 of the power supply to-+@19 relay RLt → detection resistor Re → glow plug 1 → power supply; As the temperature of the heating coil 11 increases, its resistance value (2) also increases. Now°
The relationship between the disconnection temperature of the ζ glow plug and the resistance Rg of the glow plug is as shown in Figure 5, IsA. When the temperature reaches a point 7M before the set temperature Ts, the comparator C-t issues an output signal.゛The output signal is amplified by the amplifier AI and fl
Relay RLI of El is activated, opening its normally closed contact r4. By opening the contact rA1, the first glow plug heating current circuit is opened, and the heating current flowing to the glow plug is transferred to the second glow plug heating current circuit, that is, from the power source go to the key switch to the voltage drop resistor. Rd1 → Normally closed relay contact rlH → Detection resistor →
A heating current flows through the glow plug 1 → the power source. And the voltage applied to the glow plug decreases by the voltage drop of the voltage drop resistor Rcil, and the current also decreases by the amount? Therefore, the glow plug is heated at a slower speed than the first glow plug heating current circuit. In the case where all the glow plugs are normal, but if the heating coil of the plug is disconnected in the odd and even DKZ glow plugs, the relationship between the temperature and resistance of the gas stomach to the glow plug is shown by the dotted line BK in Figure 5. As a result, the combined resistance Rgt of the glow plugs is twice the value in the case of four glow plugs, and the resistance RM that reaches the switching point also reaches the normal temperature TM) at a lower temperature Tbl, so the temperature 1 When ' is reached, the comparator C1 issues an output signal, opens its normally closed contact r4, and transfers to the second glow plug heating current circuit. However, since the two globes 2g are disconnected, the current flowing through the globe 2g also decreases, which reduces the voltage drop 4 across the voltage drop resistor, and conversely, the current flowing through the globe 2g decreases. The voltage will become higher.

That is, for now, let the resistance rg-CL of the switching point temperature of the glow plug heating coil be 1Ω, and the voltage E of the power source Eo be 12
v, voltage drop resistor Rd1. ．． ．． 12fl, if wiring resistance is ignored, the current l flowing through the glow plug after switching under normal conditions is the combined resistance of the glow plug Rg - Tg/4
== Q, 025Q Tehbka G:p,E
12 ■=□=□492 inside 926ARg 2+α025 The voltage Erg applied to both ends of globe 2g is Erg=
3E-Rdlx I (becomes u48V. However, 2
If the heating coil of the main glow plug is disconnected, the combined resistance Rg/ of the two gloves is Rgt = rg/
2 = (L Q 5 Q toner'), the power I' flowing through the plug 1 is therefore the voltage Erg/ applied to the glow plug, E
rg'=E - Rdl x 1'ki (L2?5V).

This increase in applied voltage leads to overheating of the heating coil as shown by curve Y in FIG. Therefore, in order to prevent this overheating, comparator C sets the composite resistance value Rg/of the glow plug to the set resistance value R$ when the glow plug is normal.
If the second bridge circuit and comparator C2 are set so as to reach a value R, / that exceeds 9 and generate an output signal, the group lag resistance Rg' will increase as shown at point C in Figure 5.
When the temperature reaches Rs/ (temperature at point C in Fig. S), comparator CI issues an output signal, which is amplified by amplifier A3, actuates relay RLm, and opens its normal contact rt.

By opening r41, the second glow plug heating current circuit will be opened. Then, after the time set by the timer 5 after the key switch 2 is closed, the timer emits an output signal which activates the third glue relay RL to close its normally open contact 4, thereby heating the third glow plug. Moving on to the current circuit. Therefore, the current flowing through the glow plug is limited by the voltage drop of both voltage drop resistors Rdl *Ra=, thereby preventing the glow plug heating coil from overheating.

In the above embodiment h, the timer 5 is used to operate the third relay RL, and its normally open contact is used to insert the stain pressure drop resistor into the heating current circuit of the glow plug. , timer 5, and relay RL, and install a voltage drop resistor R across the normally closed contact of the second relay RL in Figure 4.
You can connect 4 d-rows directly in parallel. Also, voltage drop resistance R
If ds and R6 are made of a heating element with the same temperature coefficient as the glow plug's heating element, and a resistor is installed in the engine cylinder in a Kfk-like manner so that the temperature changes in the same way as the glow plug, the glow plug is created. It exhibits even better effects in terms of control.

As explained in detail above, the glow plug control device according to the present invention, when starting the engine, does not heat the inside of the combustion chamber by ultra-rapid heating from the start of preheating to the preheating set temperature, but instead sets the preheating temperature. When the temperature of the glow plug reaches the preset value before reaching the value, use the switching means.

The first voltage drop resistor is connected in series with the heat generating coil of the glow plug to reduce the heating speed, which prevents cracks in the glow plug and damage to the heat generating coil due to thermal stress that occurs when heating at an opportunity with ultra-rapid heating. There is no problem of disconnection,
In addition, even if some of the multiple glow plugs are disconnected, the engine can still be started with the remaining two glow plugs.

When it is detected that the remaining glow plug approaches the preheating set temperature, a second voltage drop resistor is further connected in series with the first voltage drop resistor to prevent the remaining glow plug from overheating. This O 2 gas has an excellent repellent effect to protect the remaining gloves from overheating.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between glow plug temperature, temperature difference between inside and outside, and heating time. Figure 2 is a diagram showing the relationship between glow plug KfI current and heating time. Figure 5 is a diagram showing the relationship between glow plug temperature and heating time. The diagram showing the temperature characteristics, Figure 4, is the main product 1! FIG. 5 is a control circuit diagram of the diesel engine starting assist device according to JLK, and is a diagram showing the relationship between the power of the glove 2, the resistance of the heating coil, and the temperature. Bo...power supply, 1...glow plug, 2...
Key switch, RLt...1st relay, RL, central 2 relay, RI4...5th relay, r4erL failure
1t@...Contact of 1st relay, 2nd relay, 3rd relay, Re...Resistance for temperature detection, R4# Rx
e Rs t R4...Resistor, C1#Cri...Comparator, A1, Al...Amplifier, Rdt, Rds...
・Resistance for voltage drop. Patent applicant: Isuso Jidosha Co., Ltd. Agent Patent attorney: 2 people (2) Figure 1 Figure 2

Claims (1)

[Scope of Claims] A glow plug having a heating element whose resistance value changes according to changes in heating temperature, and a temperature detection resistor. A switching circuit that switches the current flowing through the glow plug is connected in series with the power source, and a circuit that detects the temperature of the heating element based on the voltage generated across the temperature detection resistor, and a circuit that also detects the temperature. and a disconnection detection circuit that detects disconnection of the heating element based on the voltage generated across the resistor, and when the temperature detector reaches a predetermined set value before the preheating set temperature, the switching circuit to reduce the heating current flowing to the glow plug, and
A starting assist device for a diesel engine, characterized in that when the disconnection detection circuit detects a disconnection of the heating element, the switching circuit is activated to further reduce the current flowing through the glow plug.