JP2002013461A - Glow plug failure diagnostic device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems of a conventional failure diagnostic method for a multiple cylinder diesel engine, where glow plugs are connected in parallel, being performed by checking the voltage generated in the both ends of the glow plug parallel connection body 12, however, the temperature of the glow plug is greatly varied according to the time and conditions and the electric resistance value is also greatly changed so that it is impossible to automatically diagnose the failure by an ECU 21. SOLUTION: Right after completing the energization to the glow plug parallel connection body 12 via a grow plug relay 3, a failure diagnostic switch element 9 provided in another path for diagnosing the failure is turned on for an extremely short time not to cause the temperature rise in the glow plug and a battery voltage is impressed on the glow plug parallel connection body 12. The voltage V generated in its both ends is compared with a decision voltage prescribed in a decision voltage part 20 by a diagnostic processing part 19 to diagnose whether it is failure or not. The temperature right after completing the energization to the glow plug is almost same in cooling or restarting so that the failure can be diagnosed without affected by the temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug failure diagnosis apparatus and method for diagnosing a failure such as disconnection of a glow plug in a diesel engine.

[0002]

2. Description of the Related Art In a diesel engine, ignition of spray fuel at the time of engine start is promoted to improve startability, and to prevent generation of white smoke (deterioration of exhaust emission) at an early stage of start. A glow plug for preheating the combustion chamber is used. The glow plug is essentially constituted by an electric resistance, and a current is supplied from the battery to the glow plug to generate heat. One glow plug is provided for one cylinder. When the engine is a multi-cylinder engine, all glow plugs are connected in parallel.

One of the glow plugs connected in parallel is
If the glow plug of one cylinder is disconnected, the following problem occurs. The exhaust emission of the disconnected cylinder deteriorates, and white smoke is generated. Since the glow plugs of the other cylinders are energized to generate heat and generate heat, the start is performed, but the combustion noise is generated between the cylinder in which the glow plug is disconnected and the healthy cylinder, so that the vibration noise increases. As the startability deteriorates, the battery consumption by the starter motor increases, causing the battery to run down. The current flowing through the glow plugs of the other cylinders becomes large, and accelerates the deterioration of the glow plugs of the other cylinders. Also, if a certain glow plug is short-circuited or a short-circuit accident occurs on the way to the glow plug, current from the battery flows intensively there and hardly flows to the glow plugs of other cylinders. Therefore, starting becomes difficult. In addition, the short-circuited glow plug will eventually burn out (disconnect).

[0004] In view of the above, it is desired to diagnose the glow plug as soon as possible and to repair or replace the glow plug as soon as possible.
It is needless to say that it is most certain that a worker applies a voltage to each of the glow plugs and diagnoses whether or not the wire is broken at a vehicle maintenance shop. However, this is time-consuming and costly, and cannot be diagnosed during vehicle operation. Therefore, it has been required to automatically diagnose by a failure diagnosis device. In such a failure diagnosis, a voltage generated at both ends of a parallel connection of glow plugs is detected, and the detected value is detected. I checked the size and diagnosed it.

For example, if a glow plug having a resistance value R is disposed in N cylinders, the N glow plugs are connected in parallel.
/ N. However, if one wire is broken, (N-1) parallel connections are made, so the combined resistance value of the parallel connection body is R /
(N-1), which is a higher resistance value than before the disconnection.
Therefore, the divided voltage generated at both ends of the parallel-connected body after the disconnection is larger than that before the disconnection. Therefore, a voltage that is higher than the voltage in a normal state and lower than the voltage in the case of a single disconnection is determined in advance as a determination voltage, and the voltage at both ends of the parallel-connected body is detected. If so, he was diagnosed as having a break.

[0006] As a conventional document relating to such a glow plug failure diagnosing method and device, Japanese Utility Model Publication No.
JP-A-41255 (in which the glow plug disconnection detecting operation is stopped during engine start operation to prevent erroneous determination), and JP-A-11-182400 (disconnection is detected using an engine control unit (ECU)). And so on).

[0007]

(Problems to be Solved) However, in the above-mentioned conventional glow plug failure diagnosis, the resistance value of the glow plug differs greatly depending on the time or situation to be diagnosed, and the detected voltage also varies greatly accordingly. Therefore, it is extremely difficult to properly set a determination voltage as a reference for diagnosis, and there has been a problem that it is not possible to appropriately perform a fault diagnosis automatically by an engine control unit (ECU) or the like.

(Explanation of Problems) There are the following circumstances that make it difficult to properly set the judgment voltage. (1) The resistance change due to the temperature change of the glow plug is large In general, the electric resistance changes so that it increases when the temperature is high and decreases when the temperature is low. However, since the glow plug is disposed in the combustion chamber of the engine as desired, the temperature of the glow plug varies greatly depending on time and conditions. For example, the temperature is below freezing before a cold start in a cold region, and reaches as high as 350 degrees Celsius at the full combustion load. Even with the same glow plug, the resistance value differs greatly at each temperature. Therefore, the combined resistance value of the parallel-connected glow plugs greatly differs depending on the temperature.

(2) The change in the combined resistance value at the time of disconnection is small On the other hand, the change in the combined resistance value when one of the glow plugs connected in parallel is disconnected is not so large. For example, when three glow plugs each having a resistance value of 1.5Ω are connected in parallel, the combined resistance value without disconnection is equal to 0.1.
5Ω, and the combined resistance value when one wire is broken is 0.75Ω
Therefore, the change at the time of disconnection is (0.75-0.5)
= 0.25Ω, not so large. In order to detect disconnection, it is necessary to detect a voltage change due to this slight change in resistance. It is very difficult as a practical matter to overcome the above circumstances and to accurately determine the judgment voltage for diagnosing whether the voltage generated at both ends of the parallel connection of the glow plugs is normal. Was. The present invention
It is an object to solve the above problems.

[0010]

In order to solve the above-mentioned problems, a glow plug failure diagnosis apparatus according to the present invention provides a glow plug parallel connection body to which a battery voltage is applied through a first path including a glow relay. In order to apply a battery voltage at the time of diagnosis, a second path including a failure diagnosis switch element provided separately from the first path and the failure diagnosis switch element are turned on immediately after the energization of the glow relay is completed. In addition, a control diagnosis unit for detecting a voltage between both ends of the glow plug parallel-connected body caused by the turning on and comparing the detected voltage with a predetermined determination voltage to perform a failure diagnosis is provided.

Further, in the glow plug failure diagnosis method of the present invention, the battery voltage is applied to the glow plug parallel-connected body to which the battery voltage is applied through the first path including the glow relay at the time of failure diagnosis. A second path including a switch element is provided separately from the first path. Immediately after energization of the glow relay is completed, the failure diagnosis switch element is turned on to detect a voltage between both ends of the glow plug parallel connection body. The failure diagnosis is performed by comparing the voltage with a predetermined determination voltage. The judgment voltage in the glow plug failure diagnosis device and method includes a voltage for judging a disconnection of the glow plug, and the voltage may be a value determined according to the battery voltage at the time of judgment.

(Summary of operation to be solved) Immediately after the power supply to the glow plug is terminated, a battery voltage is applied through another path provided for failure diagnosis, and a voltage generated at both ends of the parallel connection of the glow plugs is detected. The detected voltage is compared with a predetermined judgment voltage to determine whether or not a failure has occurred. Glow plug failure diagnosis is performed by examining the change in the combined resistance value of the glow plug parallel connection,
The electric resistance value of the glow plug changes greatly depending on the temperature. However, the temperature immediately after the end of energization of the glow plug is
Since the temperature is substantially the same at the time of cold and at the time of restart, it is possible to diagnose a failure without being affected by the temperature change.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a glow plug failure diagnosis device of the present invention. In FIG. 1, 1 is a battery, 2 is an ignition switch, 3 is a glow relay, 3A is a relay contact, 3B is a relay coil, 4 is a diode, 5 is a glow plug control switch element, 6, 7 are resistors, 8 is a terminal, 9 is a fault diagnostic switch element, 10 is a resistor, 11 is a terminal, 12 is a glow plug parallel connection body, 12
A is a collective connection point, 13 is a capacitor, 14 is a smoothing circuit, 15 is a terminal, 16 is a glow-on time map, 17 is a glow-on signal generator, 18 is a failure diagnostic signal generator, 1
9 is a diagnosis processing unit, 20 is a judgment voltage unit, 21 is an ECU (engine control unit), and 22 is a water temperature sensor. The water temperature sensor 21 is a sensor that detects the temperature of an engine (not shown), and the diode 4 is a diode for preventing backflow.

As the glow plug parallel connection body 12, 3
An example is shown in which glow plugs are connected in parallel. One end of the glow plug parallel connection body 12 is connected to ground (engine body ground). A collective connection point 12A at the other end is connected to the battery 1 via the relay contact 3A of the glow relay 3, and is connected to the smoothing circuit 14, the terminal 15
Is connected to the diagnostic processing unit 19 via the. The glow plug control switch element 5 is a relay coil 3 of the glow relay 3.
B is a switch element for determining whether or not a current flows.
When a current is applied to the relay coil 3B, the relay contact 3A
Turns on. The glow plug control switch element 5 is turned on by the glow-on signal generated by the glow-on signal generation unit 17. The glow-on signal can be generated with reference to a glow-on time map 16 (described later with reference to FIG. 2).

The failure diagnosis switch element 9 is a switch element for applying a battery voltage to the glow plug parallel connection body 12 when performing a failure diagnosis of the glow plug.
The failure diagnosis switch element 9 is turned on by an extremely short failure diagnosis signal generated by the failure diagnosis signal generator 18. When the battery voltage is applied when the failure diagnosis switch element 9 is turned on, a voltage V generated between the collective connection point 12A and the ground is detected from the terminal 15 and is compared with the judgment voltage of the judgment voltage section 20 for diagnosis. In the determination voltage section 20, a required determination voltage is prepared in advance according to the type of the fault to be diagnosed. The capacitor 13 and the smoothing circuit 14 are connected to remove noise from the detection voltage V.

When the ignition switch 2 is turned on, operating power is supplied to the ECU 21 via the relay coil 3B (at this stage, a current large enough to turn on the relay contact 3A has not yet flowed). Is started. As soon as the ECU 21 is started, a glow-on signal is generated by the glow-on signal generation unit 17,
The glow plug control switch element 5 is turned on, and the relay contact 3A is turned on. The glow plug control switch element 5, the failure diagnostic switch element 9, the capacitor 13, the smoothing circuit 14, and the like are incorporated in the ECU 21.
The ECU 21 is configured as a computer having a CPU, a memory, a clock, and the like, and also performs fuel injection control, engine control, and the like (in FIG. 1, those control parts are omitted). We also perform control and diagnosis related to the invention. Therefore, the ECU 21 includes the control diagnosis unit according to the present invention.

Next, a glow plug failure diagnosis method according to the present invention will be described. First, an outline will be described. When the ignition switch 2 is turned on and the glow plug control switch element 5 is turned on, the relay contact 3A is turned on, the voltage of the battery 1 is applied to the glow plug parallel connection body 12, the glow plug generates heat, and the engine burns. Preheat the room. Immediately after the glow plug control switch element 5 is turned off,
The failure diagnosis switch element 9 is turned on, and the voltage of the battery 1 is applied to the glow plug parallel connection body 12 via the failure diagnosis switch element 9 this time. The voltage between both ends of the glow plug parallel connection body 12 is detected from the terminal 15 and is compared with the determination voltage to perform failure diagnosis.

Next, the glow plug failure diagnosis method of the present invention will be described in detail. FIG. 3 is a flowchart for explaining this, and FIG. 4 is a time chart in the fault diagnosis of the present invention. Hereinafter, description will be made in accordance with the steps of FIG. 3 with reference to FIGS. Step 1: When the ignition switch 2 of FIG. 1 is turned on, the operating power is supplied to the ECU 21 and the ECU 21
Is started. Immediately upon activation, a glow-on signal is generated, and the glow-plug control switch element 5 is turned on by the signal, and the glow-plug parallel connection body 12 is energized. In addition, variables used for failure diagnosis (for example, a value _Vref of a reference ground voltage (engine body voltage) as a reference for voltage measurement and a value _{Vglow of a} glow voltage at the time of energizing a diagnosis) are initialized (to a value of 0). set). Note that (1) in FIG. 4 is a switch signal according to the ignition switch 2 is turned on at time t _1, it is set to be the start at t _3.

The glow-on signal for turning on the glow plug can be composed of three signals: a start standby mode signal, a start start mode signal, and a post-combustion mode signal. These are generated with reference to the glow-on time map 16. Next, these will be described. While (2) 4 is a start standby mode signal, which is from time t ₁ to the ignition switch 2 is turned on, is generated as a signal which lasts time A. Time A to keep this on
Is determined according to the temperature of the engine at that time (the temperature detected by the water temperature sensor 21) according to FIG. FIG. 2 is a diagram (glow-on time map) showing the relationship between the on-time of the start standby mode signal and the engine temperature, where the horizontal axis represents the engine temperature and the vertical axis represents the on-time. As shown
For example, if the detected engine temperature is T, the ON time is determined to be _AT , so that a signal of the ON time _AT is generated as the start standby mode signal at this time.

The start start mode signal is turned on when a start signal is issued by the ignition switch 2 and is generated as a signal that continues for a time B. The post-complete explosion mode signal is generated as a signal that is turned on when the engine completely explodes and enters the engine RUN state, and that continues for a time C. These on-durations B and C are also determined by a diagram (glow-on time map) similar to that of FIG. 2 that is predetermined in advance for generating the start-start mode signal and the after-combustion mode signal. The above three mode signals are continuously output while being partially overlapped. While any one of them is output, the glow plug is turned on, so that the glow-on signal eventually becomes (5) in FIG. As shown in FIG. 4, from the start (t ₁ ) of the start standby mode signal of (2) in FIG.
This is a signal that continues until the end (t ₇ ) of the post-combustion mode signal of (4) in FIG.

Step 2: Check whether or not the current supply to the glow plug has been completed. As mentioned in Step 1, the energization to the glow plug in parallel connection body 12 is started from the time t _1, and ends at time t _7. FIG. 4 (6) shows the current supplied to the glow plug, and FIG. 4 (8) shows the glow temperature. At the beginning of the current supply, the temperature of the glow plug is low.
Since the electric resistance value is small, the current value is large (FIG. 4).
'S I _P indicates the peak value). Since the current value is large, the calorific value is also large, and the glow temperature rises rapidly. However, as the temperature rises due to the heat generated by energization, the electrical resistance value also increases, so that the glow current decreases and the temperature rises slowly. Then, when the temperature rise due to the energization and the increase in the electrical resistance value due to the temperature rise are balanced (time t ₂ ), the glow current and the glow temperature are stabilized (glow current = I _S , glow temperature = T _S ).
Thus, in steady state, it is expected to start the engine is performed, the complete combustion state is also achieved, although Guroon signal as then greet the end time t ₇ of Guroon signal is not being generated , This step 2
Then, it waits until the end of the glow-on signal.

Step 3: In order to confirm whether or not the glow relay 3 is physically turned off, it is checked whether or not a predetermined delay time T _D has elapsed. The fact that the glow relay 3 is physically turned off means that the relay contact 3A is turned off, but the relay contact 3A is not necessarily turned off at the same time as the glow-on signal is turned off. By the time the relay contact 3A is physically turned off,
Since the glow-on signal is turned off, the glow plug control switch element 5 is turned off, the relay coil 3B is deenergized, and the relay contact 3A is turned off, there is some time delay from the time when the glow-on signal is turned off. Usually, it is checked how long the time delay is, and a time slightly longer than that is set in advance as the delay time T _D. that way,
When Guroon signal has passed the delay time T _D from the off, relay contact 3A is surely turned off.

Step 4: After the delay time T _D has elapsed from the time when the glow-on signal is turned off (time t ₇ ) (in other words, after it is assured that the relay contact 3A has been physically turned off) ), The voltage appearing at the collective connection point 12A is detected from the terminal 15, and this is detected as the reference ground voltage V _ref.
And Note that, in order to increase the reliability of the value of the reference ground voltage _Vref , it is desirable to perform this detection a plurality of times (eg, eight times) and take the average. Step 5 ... soon finished the detection of the reference ground voltage (time t _8), turns on the failure diagnosis switching element 9. This is performed by applying the failure diagnosis signal of (7) in FIG. Thereby, the voltage of the battery 1 is applied to the glow plug parallel connection body 12 through the failure diagnosis switch element 9. The ON continuation time of the failure diagnosis switch element 9 is an extremely short time that does not cause a rise in the temperature of the glow plug. In (7) of FIG. 4, time t ₇ ~
between t ₉ is the extremely short time in practice, but are drawn enlarged for illustration clarity.

Step 6: It is checked whether or not the time required for stabilizing the ON state of the failure diagnosis switch element 9 has elapsed. Step 7: After reaching the stable state, a voltage appearing at the collective connection point 12A is detected from the terminal 15, and this is set as a diagnostic energizing glow voltage V _glow . In order to increase the reliability of the value of the glow voltage V _glow during the energization of the diagnosis, this detection is also performed a plurality of times (eg,
8) and it is desirable to take the average. As can be understood by referring to (7) and (8) of FIG. 4 in correspondence with each other, the glow temperature is maintained when the reference ground voltage _Vref is detected and when the glow voltage _Vglow at the time of diagnosis energization is detected. Similarly, the temperature T _S is stable. That is, at the same temperature, the reference ground voltage V _ref and the glow voltage V _glow during diagnosis energization are detected, so that there is no difference between the two voltages due to a change in the electrical resistance of the glow plug due to a temperature change.

Step 8: Turn off the failure diagnosis signal (time t)
₉ ), the failure diagnosis switch element 9 is turned off. Step 9: The difference between the glow voltage V _glow at diagnosis energization and the reference ground voltage V _ref (V _glow −
V _ref ) is calculated, and this is set as the fault diagnosis voltage V _valid . Step 10: It is determined whether or not the battery is short-circuited (the wires supplied from the battery are in electrical contact → being in a parallel connection state with the load of the wire). Otherwise, go to step 14. The determination of whether or not the battery is short-circuited is performed by the voltage V _SB for determining the short-circuit.
Is determined in advance in the determination voltage unit 20, and when the failure diagnosis voltage V _valid is equal to or higher than that (V _valid ≧ _VSB ), it is determined that the battery is short-circuited.

Step 11: It is determined whether or not the ground is short-circuited (the wiring on the battery side from the parallel connection of the glow plugs is electrically in contact with the engine body). Goes to step 14. To determine whether or not ground short-circuit occurs, a voltage V _SG for determining the short-circuit is determined in advance in the determination voltage unit 20, and the fault diagnosis voltage V _SG is determined.
_{If valid} is less than that (V _valid ≤ V _SG ), it is determined that the ground is short-circuited. Step 12: It is determined whether or not the glow plug is disconnected. If the glow plug is disconnected, the process proceeds to step 13, and if not, the process proceeds to step 14. In order to determine whether or not the wire is disconnected, a voltage V _GO for determining the disconnection is determined in advance in the determination voltage unit 20, and when the failure diagnosis voltage V _valid is equal to or higher than that (V _valid ≧ V _GO ). It is determined that the wire is disconnected. Step 13: A diagnosis of failure is issued. Step 14: A diagnosis of normality is issued.

The voltage detected at the terminal 15 is detected as a voltage division of the voltage of the battery 1 and depends on the battery voltage. However, since the voltage value of the battery 1 is not always the same and changes with the passage of time,
Strictly speaking, it is desirable that the determination voltage also changes according to the change in the battery voltage. The failure diagnosis according to the present invention is performed as described above, and the reference ground voltage V _ref and the glow voltage V _glow at the time of diagnosis energization used for the failure diagnosis are all glow plugs which are turned on for starting the engine. Is detected immediately after is turned off. At the time of this detection, the glow plug is intentionally heated to a predetermined temperature regardless of the condition of the outside air. Since the engine load has not risen and the temperature in the combustion chamber has little change since the engine has just started, the temperature is stable even when the engine is cold or when the engine is restarted immediately after the operation is stopped. In the present invention,
Since the failure diagnosis is performed based on the voltage detected in such a situation, the failure diagnosis can be performed without being affected by a change in electric resistance due to a change in temperature.

[0028]

As described above, according to the glow plug failure diagnosing apparatus and method of the present invention, immediately after the completion of energization of the glow plug, the temperature is substantially the same at the time of cold or restart. Since the battery voltage is applied for a very short time through a separate path provided for fault diagnosis and the voltage generated at both ends of the parallel connection of the glow plugs is detected for fault diagnosis, the fault diagnosis is not affected by temperature changes. You can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing a glow plug failure diagnosis device of the present invention.

FIG. 2 is a diagram illustrating a relationship between an on-time of a start standby mode signal and an engine temperature;

FIG. 3 is a flowchart showing a glow plug failure diagnosis method according to the present invention.

FIG. 4 is a time chart in the failure diagnosis of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery, 2 ... Ignition switch, 3 ... Glow relay, 3A ... Relay contact, 3B ... Relay coil, 4
... Diode, 5 ... Glow plug control switch element,
6, 7: resistor, 8: terminal, 9: fault diagnostic switch element,
10: resistor, 11: terminal, 12: glow plug, 13 ...
Capacitor, 14 smoothing circuit, 15 terminal, 16 glow-on time map, 17 glow-on signal generator, 1
8: Failure diagnosis signal generator, 19: Diagnosis processor, 20: Determination voltage unit, 21: ECU (engine control unit), 22: Water temperature sensor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiromi Sato 8 Dosana, Fujisawa City, Isuzu Motors Corporation Fujisawa Plant (72) Inventor Katsushi Shimizu 8 Dosana, Fujisawa City, Isuzu Motors Fujisawa Plant

Claims (4)

[Claims] 1. A glow plug connected to a glow plug to which a battery voltage is applied in a first path including a glow relay is provided separately from the first path to apply the battery voltage at the time of failure diagnosis. A second path including the failure diagnosis switch element, and turning on the failure diagnosis switch element immediately after the end of energization of the glow relay, and detecting a voltage between both ends of the glow plug parallel-connected body caused by the turning on of the failure diagnosis switch element. A glow plug failure diagnosis device, comprising: a control diagnosis unit that performs a failure diagnosis by comparing the voltage with a predetermined determination voltage. 2. The glow plug failure according to claim 1, wherein the judgment voltage includes a voltage for judging a disconnection of the glow plug, and the voltage is a value determined according to a battery voltage at the time of the judgment. Diagnostic device. 3. A second path including a fault diagnosis switch element for applying a battery voltage at the time of fault diagnosis to a parallel connection of glow plugs to which a battery voltage is applied via a first path including a glow relay. Provided separately from the first path, the failure diagnosis switch element is turned on immediately after the end of energization of the glow relay to detect a voltage across the glow plug parallel-connected body, and compares the voltage with a predetermined determination voltage. A glow plug failure diagnosis method characterized by performing a failure diagnosis. 4. The glow plug according to claim 3, wherein the judgment voltage includes a voltage for judging a disconnection of the glow plug, and the voltage is a value determined according to a battery voltage at the time of the judgment. Failure diagnosis method.