JPS59128981A - Blown-off detecting method of diesel engine glow plug - Google Patents

Abstract

PURPOSE:To prevent previously progressing blown-off and to block power supply to remaining glow plugs by comparing the voltage drop across a glow resistor with referential voltage equivalent with gradient of voltage drop thus detecting blown-off of glow plug. CONSTITUTION:In a system where a plurality of glow plugs RG provided for each cylinder in Deisel engine are connected in parallel to supply preheating current through a common glow resistor RR, the voltage drop across said resistor RR is compared with referential voltage equivalent with the gradient of said voltage drop to detect blown-off of glow plug RG.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting disconnection of a glow plug that preheats the inside of an engine cylinder when starting a diesel engine.

Diesel engine cars have poor starting performance compared to gasoline engine cars, so a glow plug (heater) is used to preheat the inside of the cylinder to improve the ignition of the fuel. Passenger cars in particular require startability comparable to gasoline cars, so glow plugs with a rapid temperature rise are used to ensure instantaneous preheating.

Since a large current (approximately 60 A) is applied to this type of glow plug, there is a high possibility of disconnection.

One glow plug is used for each cylinder, and in multi-cylinder engines, the same number of glow plugs are connected in parallel. Figure 1 is an equivalent circuit diagram of a glow plug.
RG is a glow plug, RS is a current sensor, SW is a switch (engine key), and B is a battery. A resistor having a positive temperature coefficient is used in the glow plug RG. Therefore, the temperature of the glow plug is detected using this characteristic. For this purpose, a several milliohm (mΩ) Karen] sensor RS is connected in series with the glow plug.

If battery B is connected in this state, the temperature of glow plug RG will rise due to the current. At this time, current sensor R
Since the current flowing through 5 becomes smaller as the temperature of the glow plug increases, the voltage drop occurring across the current sensor becomes smaller as the temperature of the glow plug increases.

Figure 2 shows this characteristic diagram, where TG is the glow plug temperature and VS
is the voltage across the current sensor. If the voltage drop of this current sensor is detected, the temperature of the glow plug is detected. Then, the power switch is controlled on and off by the voltage vS across the current sensor, and the glow plug temperature T
Control is performed so that G does not exceed a set value (for example, 900°C).

The above is a temperature control method during rapid heating before starting the engine, in which the engine key SW is turned on and voltage is applied directly from the battery B to the glow plug RG. 4 glow plugs RG
It holds true that all of them are Masatomi. vB is the voltage of battery B. Here, VB=10V, R6=10mΩ, 90
If the glow plug resistance at 0°C is R(, = 0.5Ω, then the detection voltage s at 900°C will be. Therefore, monitor Vs, and if it drops to 0.8V, the glow plug temperature will reach 900°C. It determines that the glow plug has risen and automatically turns off the switch SW to prevent thermal damage to the glow plug.

By the way, if one of the glow plugs breaks for some reason, Vs=0 at a temperature much lower than 900℃.
．． It becomes 8V. In other words, there are three glow plugs (resistance R
The glow plug resistance value RG' when Vs=0.8V at RG' = 0.37
It is Ω. Therefore, since RG=0.5Ω is 900°C, RG'=0.37Ω is approximately. According to this, after one glow plug is disconnected, when the temperature rises to 660° C., the switch SW is turned off to prevent further temperature rise, thereby preventing chain disconnections. However, since it is not possible to distinguish how many glow plugs the value of the detection voltage Vs is caused by, this cannot be used for disconnection detection. However, in this case, since the glow plug temperature does not exceed 900', there is no need to detect disconnection.

Figure 3 shows an example of the glow plug temperature detection circuit and switch control circuit, where RY is a relay replacing switch SW, and CP
is a comparator for determining the voltage VS generated at the current sensor R9, and TRa to 'I'Rc are relay drive transistors.

Glow plugs can also be used temporarily after the engine has started (usually 2
minutes) is used. This is called stable preheating, and as shown in FIG. 4, a series resistor RR called a glow resistor is inserted between the battery B and the glow plug RG to divide the voltage Va. In other words, the resistance value of the current sensor R5 of the first FyJ is about 1/100 of the composite value of R, but the resistance value of the glow resistor RR in Fig. 4 is approximately equal to the composite value of RG, so vB=14v. Glow resistor RR if available
Since 7v, which is half of that, is applied to the glow plug RG,
7VL is not applied to. For this reason, the glow plug temperature TG can be adjusted to 9.5 degrees without controlling the power switch on and off.
The temperature is kept below 00℃.

By the way, if one of the glow plugs breaks for some reason in this stable preheating state, there is a strong possibility that the remaining glow plugs will also break in a chain reaction. In other words, if all four glow plugs are true lightning and RR#RG/4, the power PG consumed by the glow plugs is expressed by the following equation.

Here, if R at 900°C is 0.5Ω and VB = 14V, PG = 392W, and a stable preheating state that maintains the glow plug below 900°C with this power continues (.

However, when one glow plug is disconnected, the combined resistance of the remaining glow plugs increases, so that the power distribution of the glow resistor RR and glow plug RG is biased toward the glow plug side. For example, in the power distribution of the glow plug and glow resistor when the glow plug is at 900 degrees Celsius, it is assumed that the resistance value of the glow resistor does not change significantly, and when the glow resistor has a current of 11, which is = 56 (A) under normal conditions. The voltage drop is 56
If AxO is 125Ω-7■, the power consumption per glow plug during normal operation is 392(W)X~=98
It is W. However, if one glow plug breaks, the power consumption per glow plug becomes large compared to normal power consumption.

As a result, the glow plug temperature TG rises by 900'C or more, resulting in a chain of disconnections.Therefore, in this case, it is necessary to detect disconnections.

In order to prevent the above-described chain of disconnections, the present invention detects the disconnection of one glow plug and notifies the user of the disconnection, or cuts off the power to the remaining glow plugs. It is something to do.

The present invention provides a system in which a plurality of glow plugs provided for each cylinder of a diesel engine are connected in parallel and a preheating current is supplied to them through a common glow resistor. The present invention is characterized in that disconnection of the cough glow plug is detected by comparing it with a reference voltage equivalent to the 1st slope of the voltage drop, and this will be explained in detail below with reference to the illustrated embodiment.

When a glow plug is disconnected, the voltage of the glow resistor changes depending on the number of glow plugs (total weight, one or more disconnected). In the present invention, disconnection is detected by detecting this change. For example, if glow plugs have a resistance value of 0°5Ω when the temperature reaches boo°C,
When the four glow plugs are normal and the condition is set to RRζRG/4, the voltage applied to the glow plugs and the voltage applied to the glow resistor are VB = 14V,
It is divided into 7v each. However, when one glow plug is disconnected at 906° C., the combined resistance of the remaining three glow plugs becomes Rc/3−0.167Ω, and the voltage division ratio between the glow plug and the glow resistor changes.

FIG. 5 is an explanatory diagram of this. Assuming that the resistance value of each glow plug at 900° C. is 0.5Ω, the voltage ■R applied to the glow resistor RR during normal operation is as follows. On the other hand, when one glow plug R is disconnected, the voltage vR applied to the glow resistor RR decreases to . Therefore vR>vR
According to the relationship ′, disconnection of the glow plug in a stable preheating state can be detected.

FIG. 6 shows a disconnection detection circuit showing an embodiment of the present invention.
N is the reference voltage VREF generation circuit, cp is the reference voltage VR
This is a comparator that compares EF with the voltage vR generated in the glow resistor RR. When the battery voltage vB is derived from an automobile battery, its value varies greatly depending on the conditions on the vehicle side. Therefore, it is required that disconnection detection be possible over most of the battery voltage range. Figure 10 shows an example of the characteristics when four glow plugs are used.As shown in this graph, the voltage drop that occurs across the glow resistor vR is in the range 1v, 1v when all four glow plugs are heavy.
The voltage drop vR changes depending on the number of glow plugs, as in region (1) when a main wire is broken, region (2) when two wires are broken, and region I when three wires are broken. Further, when the battery voltage (applied voltage) vB changes in the state of each glow plug, the voltage across the glow resistor also changes proportionally in accordance with the battery voltage vB. When the glow plug reaches 900°C with the resistor energized as shown by the solid line ε in Figure 10, the two-dot chain line indicates that the glow plug reaches 900°C.
When the resistor is at product temperature at 00°C, the broken line is when the glow plug is at 750°C and the resistor is at room temperature.

Here, a reference voltage VREF is set between the region (2) and the region (2), and disconnection detection is performed by comparing VREP and vR. To set the reference voltage VREF, use the battery voltage vB.
It is necessary to have a condition such that the point of inflection is near IOV.

This is because glow plugs and glow resistors are heating elements, so when the battery voltage changes, the voltage drop that occurs in the glow plugs is different depending on when all four glow plugs are normal and when one is broken, and is proportional to the change in battery voltage. This is due to the fact that there is no parallel movement. FIG. 8 shows the inflection point (1) of VREF with emphasis.

The reference voltage generation circuit GEN sets the voltage vREF with the (+) side of the battery voltage vB as a reference, as shown in FIG. Specifically, a current IREF is caused to flow through the resistor R1 and the reference voltage VRE is
Generate F. In the circuit of this example, the diode D is connected until the battery voltage VB changes from OV to Vl as shown in Figure 8.
I, D2. No current flows through the D3 circuit. Therefore, in this region, the voltage drop across R+ is
Assuming that the current amplification factor (h FE ) of is larger than that of fluorine (more than 100), IREP # I C= IB = VB /RI+Ra
Therefore, VREF is determined by VREP = IREF XR+ #IB xR+. In other words, for a change in battery voltage vB, VR
EF changes by R+/(R+fR4).

Next, when VB reaches Vl, IER4+VBE=VDI +VD2 +VD3, and the diodes DI, D2. Current begins to flow through D3. Here, VBB is the base-emitter voltage of the transistor TR, and VD1 to VD3 are the forward voltages of the diodes DI and D2 and the Zener voltage of the Zener diode D3. In this state, the base voltage of the transistor TR is fixed to the diode voltage VDI''VD:24-Vo3, so the emitter current IE does not change even if the battery voltage vB changes.

Therefore, the voltage drop V'REF generated by R+4 becomes XR1, and the amount of change in V'REF with respect to a change in battery voltage vB is smaller than in the region of vB and 1 or less.

FIG. 9 shows a circuit in which a power cutoff function and an alarm display function are added to the glow plug disconnection detection function. comparator c
p corresponds to that in Figure 6, and under normal conditions (VR>VREF
), the output Vo is at L (low) level, and the transistor '
"R2 is turned off. Therefore, the stable preheating circuit PRE
The l transistor TRI is driven by the output of the relay RY.
and resistor RR to energize glow plug RG. On the other hand, if even one of the glow plugs R is disconnected, VR<VREF, so the output Vo of the comparator CP becomes H.
(high) level. As a result, transistor TR2
turns on and forces the base of transistor TRI to ground. Therefore, the transistor TR1 is connected to the circuit PRE.
It turns off regardless of the output (maintains H level for 120 seconds after rapid heating) and turns off relay RY. At the same time V
When o=H, the oscillation circuit O3C starts, and the transistor TR3
to make the indicator lamp L blink.

FIG. 11 is a characteristic diagram of the reference voltage VREF and the N source voltage VB when each constant of the reference voltage generating circuit GEH is set as shown. Although disconnection cannot be detected in area A, the temperature of the glow plug never exceeds 900°C.

As described above, according to the present invention, disconnection of a glow plug that preheats the inside of a cylinder of a diesel engine can be detected, so that a chain disconnection of glow plugs can be prevented.

Furthermore, the resistance value of the glow resistor RR#l';! There is no particular need for G/4. Furthermore, VREF can be determined to a different value by changing R1, R2° and R4. Furthermore, this detection method can also be applied to overload detection of motors, etc.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the temperature control method during rapid heating using a glow plug, Figure 2 is its characteristic diagram, Figure 3 is a configuration diagram showing an example of the temperature control circuit, Figures 4 and 5. is an explanatory diagram of stable preheating using a glow plug, FIG. 6 is a configuration diagram showing an embodiment of the present invention, FIG. 7 is a detailed diagram of the reference voltage generation circuit, FIG. 8 is its characteristic diagram, and FIG. 9 is a circuit diagram showing an application example of FIG. 6, and FIGS. 10 and 11 are explanatory diagrams of the optimum reference voltage. In the figure, RG is a glow plug, RR is a glow resistor, and B
GEN is a reference voltage generation circuit, and CP is a comparator. Applicant Fujitsu Ten Ltd. (and 1 other person) Representative Patent Attorney Minoru Aoyagi

Claims (1)

[Claims] (11) In a system in which a plurality of glow plugs provided for each cylinder of a diesel engine are connected in parallel and a preheating current is supplied through a common glow resistor, the voltage generated in the glow resistor. A method for detecting disconnection of a glow plug for a diesel engine, characterized in that disconnection of the glow plug is detected by comparing the drop with a reference voltage equivalent to the slope of the voltage drop. (2) Disconnection of a glow plug for a diesel engine. A method for detecting disconnection of a glow plug for a diesel engine according to claim 1, characterized in that when the disconnection is detected, an indicator lamp is blinked to display the disconnection.