JP2000045851A - Failure determination device for water temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely discriminate failure of a water temperature sensor irrespective of engine operation conditions. SOLUTION: Limit time Tlmt required for cooling water temperature WT of an internal combustion engine at the time of cooling reaching a specified value WF/B is set based on a quantity of heat estimated by an intake air amount senseds by an air flow sensor. Failure is determined when the sensed value by the water temperature sensor does not reach the specified value WF/B within the time Tlmt, that is, the sensed value is slowly increased. It is thus possible to precisely determine failure since the determination is executed while considering quantity of heat fluctuated according to an operation condition of the internal combustion engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine (hereinafter referred to as "internal combustion engine").
(Referred to as an engine).

[0002]

2. Description of the Related Art As is well known, information detected by a water temperature sensor is used for various controls for engine operation such as fuel injection and ignition timing. If this information is incorrect, control is performed appropriately. Instead, it may lead to an increase in harmful components in the exhaust gas. Therefore, in the United States and other countries, the provision of a water temperature sensor failure judgment function is required by law,
At the time of failure determination, measures such as turning on a warning light in the driver's seat are taken.

[0003] This type of water temperature sensor comprising a thermistor or the like outputs the cooling water temperature as a resistance value. When the detected value is fixed (disconnection), conversely when the detected value is fixed in a region below the practical region (short), and when the detected value changes by showing a sudden drop in water temperature within a practical region, that is, Assuming three types of situations (drift) when there is a decrease in the detection value that should not be possible even during the operation of the engine, a failure judgment is made when any of the situations is met.

[0004]

When the output of another sensor is mixed with the output of the water temperature sensor due to, for example, a connection error, the output of the water temperature sensor changes slowly due to the influence of the output of the other sensor. In some cases. In addition, if the above-described disconnection or short circuit occurs under such circumstances, the detection value of the water temperature sensor, which should originally be fixed outside the practical range, may be fixed within the practical range due to the output of other sensors. Become. In these cases, it should be determined as a sensor failure.However, for example, even in an operation state in which the amount of heat generated by the engine is extremely small while traveling downhill, the same output state is obtained, and the conventional failure determination device cannot distinguish between the two. However, there has been a problem that failure determination cannot be performed accurately.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a water temperature sensor failure judging device which can reliably identify an original water temperature sensor failure irrespective of operating conditions.

[0006]

To achieve the above object, according to the present invention, a water temperature sensor is determined by a judging means based on a parameter correlated with a calorific value of the internal combustion engine detected by a correlation parameter detecting means. Is configured to perform the failure determination. As described above, since the determination is made in consideration of the heat generation amount that fluctuates according to the operation state of the internal combustion engine, accurate failure determination can be performed.

According to the second aspect of the present invention, the time limit required for the cooling water temperature of the internal combustion engine to reach a predetermined value when the engine is cold is limited based on the heat value estimated from the parameter detected by the correlation parameter detecting means. It is set by the time setting means, and when the detection value of the water temperature sensor does not reach the predetermined value within the time limit, a failure judgment is made by the judging means. As described above, since the determination is made in consideration of the heat generation amount that fluctuates according to the operation state of the internal combustion engine when the engine is cold, accurate failure determination can be performed.

According to the third aspect of the present invention, the internal combustion engine is in an operating state that can affect the cooling water temperature during warm-up, based on a parameter correlated with the calorific value of the internal combustion engine detected by the correlation parameter detecting means. Whether or not this is the case is determined by the operating state determining means, and a failure determination is made by the determining means when the detection value of the water temperature sensor does not fluctuate despite the operating state that can affect the cooling water temperature. As described above, since the determination is made in consideration of the heat generation amount that fluctuates according to the operation state of the internal combustion engine at the time of warm-up, accurate failure determination can be performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a water temperature sensor failure judging device embodying the present invention will be described below.

As shown in FIG. 1, an engine 1 to which the failure determination device of the present embodiment is applied is configured as an in-line four-cylinder gasoline engine. The combustion chamber 2 of the engine 1 is connected to an air cleaner 7 via an intake port 3, an intake manifold 4, a surge tank 5, and an intake passage 6, and the flow rate of intake air introduced from the air cleaner 7 is adjusted by a throttle valve 8. After that, the fuel is mixed with the fuel injected from the fuel injection valve 9 and is drawn into the combustion chamber 2 as an air-fuel mixture with the opening of the intake valve 10. An ignition plug 11 is provided in the combustion chamber 2, and the air-fuel mixture is
The engine 1 is ignited and burns, and pushes down the piston 12 to generate engine torque. The combustion chamber 2 has an exhaust port 13,
The exhaust gas after combustion is connected to a muffler (not shown) via the exhaust manifold 14, the exhaust passage 15, and the catalytic converter 16, and is discharged from the combustion chamber 2 with the opening of the exhaust valve 17, so that the catalytic converter 16 After the harmful components have been purified, they are discharged into the atmosphere.

In the passenger compartment, an input / output device (not shown), storage devices (ROM, RAM, BURAM, etc.) for storing control programs and control maps, etc., and a central processing unit (C
An ECU (engine control unit) 21 provided with a PU (Pull Input / Output Unit), a timer counter, and the like is installed to perform comprehensive control of the engine 1. On the input side of the ECU 21, an air flow sensor 22 as a correlation parameter detecting means for detecting an intake air amount Q, a water temperature sensor 23 for detecting a cooling water temperature WT of the engine 1, and an O ₂ sensor 24 for detecting an oxygen concentration in exhaust gas The output side is connected to the fuel injection valve 9, the ignition plug 11, a warning light 25 provided in the driver's seat of the vehicle, and the like. The ECU 70 determines the fuel injection amount, the ignition timing, and the like based on the detection information from each sensor, controls the driving of the fuel injection valve 9 and the ignition plug 11, and executes a failure determination process for the water temperature sensor 23, which will be described later. At the time of failure determination, the warning lamp 25 is turned on.

Next, the engine 1 configured as described above
The operation of the failure determination device for the water temperature sensor 23 will be described.

The ECU 21 executes a failure determination routine shown in FIGS. 2 and 3 at predetermined time intervals. The ECU 21 determines whether or not the start of the engine 1 has been completed in step S2,
When the start is completed, the cooling water temperature WT detected by the water temperature sensor 23 is read in step S4, and it is determined in step S6 whether the cooling water temperature WT is equal to or higher than the F / B starting water temperature WF / B. As is well known, the ECU 21 controls the fuel injection amount by an open loop while performing correction such as a warm-up increase during a cold start or the like, and when the cooling water temperature WT reaches the F / B start water temperature, O ₂ The control is switched to the normal feedback control based on the output of the sensor 24. That is, in step S6, it is determined whether the engine 1 is in a cold state or a warm-up state, and the subsequent failure determination processing is different. still,
The F / B start water temperature WF / B is a unique value of the engine 1, and is generally set in a range of about 7 to 30 ° C.

If the determination in step S6 is NO (No) and the engine 1 is cold, the ECU 21 proceeds to step S8.
Then, the intake air amount Q is calculated based on the output of the air flow sensor 22. In this embodiment, the airflow sensor 2
As 2, a Karman vortex sensor that counts a vortex street generated on the downstream side of the strut 22a provided in the intake passage 6 is employed, so that an output of a frequency corresponding to the vortex generation cycle is obtained from the airflow sensor 22. Then, in step S8, the output frequency is converted into the intake air amount Q. The intake air amount Q may be estimated based on, for example, the engine rotation speed and the pressure in the intake manifold, or the engine rotation speed and the volumetric efficiency, instead of being directly detected by the airflow sensor 22 as described above. Next, in step S10, it is determined whether or not the intake air amount Q is equal to or larger than a preset lower limit air amount Qa, and the processes of step S8 and step S10 are repeated until a determination of YES (affirmative) is made.

The change in the cooling water temperature WT is caused by a change in the calorific value of the engine 1. In this embodiment, as will be described in detail later, the intake air amount Q is used as a parameter for estimating the actual calorific value. The threshold value (limit time limit Tlmt) for failure determination based on the rise of the cooling water temperature WT is switched according to the intake air amount Q. However, in the operation state where the intake air amount Q is extremely small, the cooling water temperature WT
Since the rise of the air flow is slow and cannot be determined, the boundary at which the determination can be made is determined by the lower limit air amount Qa (in this embodiment, the air flow sensor 2).
This is set as 20 Hz in the frequency conversion of 2, and the determination is made in step S10.

If the determination in step S10 is YES,
In step S12, the current cooling water temperature WT is read, and in step S14, a time limit Tlmt is set from the intake air amount Q and the cooling water temperature WT according to the map of FIG. 4 (time limit setting means). As is clear from the map, the time limit Tlmt is set substantially in inverse proportion to the cooling water temperature WT. However, even when the cooling water temperature WT is the same, when the intake air amount Q is large at the boundary of 70 Hz in frequency conversion, When the time limit Tlmt is short and the amount of intake air Q is small, the time limit Tlm
t is set long. Note that the time limit Tlmt may be set so as to change steplessly in accordance with, for example, the intake air amount Q without switching to the two steps as described above.

Next, at step S16, a timer T is started, and at step S18, the cooling water temperature WT is adjusted to the above-mentioned F / F.
In step S20, it is determined whether or not the timer T is equal to or more than a time limit Tlmt. And
Before the time limit Tlmt elapses, the cooling water temperature WT reaches the F / B start water temperature WF / B, and the determination in step S18 is YES.
Then, a normality determination is made in step S22, and the warning lamp 25 is kept in the off state. Also, the cooling water temperature WT is F / B
If the time limit Tlmt has elapsed without reaching the start water temperature WF / B and the determination in step S20 is YES, a failure determination is made in step S24, and the warning lamp 25 is held in a lighting state (determination means). Then, the timer T is reset in step S26, and this routine ends. Although the F / B start water temperature WF / B is used in the determination in step S18, the F / B start water temperature WF / B is not necessarily required, and another value may be used.

The processing status of the above-described failure judgment at the time of cooling will be described with reference to FIG. Note that a curve H in the figure shows a case where the running is started after the start and the cooling water temperature WT rises at a certain speed, and a curve L is a case where the cooling water temperature WT is slowly increased due to being left in idle operation after the start. When
In any case, the failure determination process is started immediately after the start.

In the case of a curve H representing a running time, since the engine 1 is operated with a certain load, the intake air amount Q
The limit time Tlmt is set short based on Q ≧ 70 Hz, and in the case of the curve L representing the idling operation, since the intake air amount Q is small, the limit time Tlmt is set long based on Q <70 Hz. You.

That is, the fuel injection amount is basically the intake air amount Q
The amount of heat generated by the engine depends on the amount of fuel injection (that is, the amount of fuel used for combustion). Therefore, since the engine calorific value is large in the region where the intake air amount Q is large, the determination is made with a short time limit Tlmt on the assumption that the cooling water temperature WT reaches the F / B start water temperature WF / B in a short time. On the other hand, in a region where the intake air amount Q is small, the heat value of the engine is small.
Assuming that it takes a long time to reach the start water temperature WF / B, the determination is made with a long time limit Tlmt. In any case, before the time limit Tlmt elapses, the water temperature sensor 2
Since the cooling water temperature WT detected at 3 reaches the F / B start water temperature WF / B, a normality determination is made.

The situation where the sensor detection value rises slowly as indicated by the curve L may be caused by a connection error or the like, as described in the prior art, even if the intake air amount Q is large, in addition to the output of the water temperature sensor 23. Occurs when the output of the sensor is mixed. At this time, a short time limit Tlmt is set.
Since the sensor detection value does not reach the F / B start water temperature WF / B even after mt has elapsed, a failure determination is made.

Thus, when the rise of the detected value is slow, it is possible to reliably determine whether the cause is the operating state of the engine 1 or the failure of the water temperature sensor 23. It is possible to prevent a situation in which engine control such as fuel injection and ignition timing is performed based on the water temperature WT.

On the other hand, if the determination in step S6 is YES and the engine 1 is warmed up, the ECU 21 proceeds to step S3.
+ 0.5 ° C. with the value of −0.5 ° C. as the lower limit temperature WT1 based on the cooling water temperature WT detected by the water temperature sensor 23 in 2
Is set as the upper limit temperature WT2. Next, in step S34, the intake air amount Q is calculated based on the output of the air flow sensor 22 as in step S8, and in step S36, it is determined whether the intake air amount Q is equal to or larger than the lower limit air amount Qb (operating state). Determination means).

The cooling water temperature WT, which has been gradually increased during operation in the cold state, shifts to an equilibrium state when the warm-up is completed, and is maintained at a substantially constant temperature inherent to the engine. In this state, when the operating condition of the engine 1 changes and the amount of generated heat increases or decreases, the cooling water temperature WT changes in accordance with the direction of the increase or decrease. As will be described in detail later, the failure is determined based on the fluctuation of the cooling water temperature WT at this time.
As in the case of a, in an operation state where the intake air amount Q is extremely small, the cooling water temperature WT is not affected by an increase or decrease in the amount of heat generation. Therefore, the lower limit air amount is used as the intake air amount Q in an operating state that can affect the cooling water temperature WT. Qb is determined, and consideration is given to performing a failure determination only when the air amount is equal to or more than the lower limit air amount Qb.

If the determination in step S36 is YES, the timer T is started in step S38, and step S4
0, the cooling water temperature WT detected by the water temperature sensor 23 is within the range between the lower limit temperature WT1 and the upper limit temperature WT2 (set water temperature range).
Is determined in step S42, and in step S42, it is determined whether or not 300 seconds, which is the sampling period, has elapsed based on the timer T. If the determination of YES is made in step S40 assuming that the cooling water temperature WT is within the range, and the determination of NO is made in step S42 that 300 seconds have not yet elapsed, the process returns to step S34 and the subsequent processing is repeated. At this time, if the intake air amount Q is less than the lower limit air amount Qa in step S36 and the determination is NO, the timer T is temporarily stopped in step S44 during that time. That is, when the operation state is such that the intake air amount Q is minimal and does not affect the cooling water temperature WT, the failure determination in step S40 is interrupted, and the counting of the sampling period in step S42 is also interrupted.

If the cooling water temperature WT is out of the range between the lower limit temperature WT1 and the upper limit temperature WT2 before 300 seconds elapse, and the determination in step S40 becomes NO, a normality determination is made in step S46 and a warning light is issued. 25 is kept off. Further, 300 seconds have elapsed without the cooling water temperature WT falling out of the region, and the determination in step S42 is YES.
When S is reached, a failure determination is made in step S48, and the warning lamp 25 is kept in the lighting state (determination means). After that, the timer T is reset in step S50, and this routine ends.

The processing status of the above-described failure judgment at the time of warm-up will be described with reference to FIG. In the figure, the water temperature sensor 23
The normal time is indicated by a solid line, and the time when the water temperature sensor 23 has failed is indicated by an alternate long and short dash line.

When the failure determination is started, a region (shown by hatching) having a width of 1 ° C. centered on the cooling water temperature WT is determined by the lower limit temperature WT1 and the upper limit temperature WT2, and the cooling water temperature WT
Sampling is started. As described above, the sampling is interrupted when the intake air amount Q is minimum, so that it can be considered that the engine 1 is operating with a certain amount of heat generation during the sampling period. And 300sec
If the calorific value slightly increases or decreases during the sampling period according to the operating condition, the cooling water temperature WT changes as shown by the solid line under the influence of the change, and goes out of the hatched area. That is, since this state means that the detection value of the water temperature sensor 23 has changed in response to the fluctuation of the cooling water temperature WT, normality is determined.

On the other hand, as described in the prior art, the occurrence of disconnection or short-circuit overlaps with a connection error or the like, and the water temperature sensor 23
If the detected value of is stuck in the practical range, the cooling water temperature W
T hardly fluctuates as shown by the dashed line, and is always kept in the hatched area during the sampling period.
Since it is not normally conceivable that an operating condition in which the calorific value is stable enough to cause a water temperature fluctuation of 1 ° C. to continue for a sampling period of 300 sec, it is actually impossible to consider the cooling water temperature WT
Is determined to be undetectable by the water temperature sensor 23 although it has fluctuated.

Thus, if the detected value is fixed and almost constant, it is possible to reliably determine whether the cause is the operating state of the engine 1 or the failure of the water temperature sensor 23, and an erroneous detection is made. It is possible to prevent a situation in which engine control such as fuel injection and ignition timing is performed based on the cooling water temperature WT.

The description of the embodiment has been completed above, but the embodiments of the present invention are not limited to this embodiment. For example,
In the above embodiment, the intake air amount Q detected by the airflow sensor 22 is used as a parameter correlated with the heat generation amount of the engine 1, and the time limit Tlmt is set based on the intake air amount Q (when the engine is cold). , It was determined whether or not the operating state could affect the cooling water temperature WT (at warm-up),
It is not always necessary to use the intake air amount Q. Instead, the fuel injection amount may be used, or the heat generation amount of the engine 1 may be directly detected by the high temperature sensor.

[0032]

As described above, according to the water temperature sensor failure judging device according to the first aspect of the present invention, the failure is judged based on a parameter correlated with the heat generation amount of the internal combustion engine. Is determined, the failure of the original water temperature sensor can be reliably identified regardless of the operating state.

According to the water temperature sensor failure judging device according to the second aspect of the present invention, the time limit is set from a parameter correlated with the calorific value of the internal combustion engine, and based on the time limit, the rise of the cooling water temperature at the time of cooling is determined. Since the determination is made, a determination is made in consideration of the amount of heat generation, so that a failure of the water temperature sensor at the time of cooling can be reliably identified.

According to the third aspect of the present invention, the failure is determined when the detected value of the water temperature sensor does not fluctuate even though the internal combustion engine is in an operating state affecting the cooling water temperature. As a result, a determination is made in consideration of the amount of heat generation, and a failure of the water temperature sensor during warm-up can be reliably identified.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram illustrating a failure determination device for a water temperature sensor according to an embodiment.

FIG. 2 is a flowchart illustrating a failure determination routine executed by an ECU.

FIG. 3 is a flowchart illustrating a failure determination routine executed by an ECU.

FIG. 4 is a map for setting a time limit Tlmt.

FIG. 5 is a time chart showing a failure determination situation at the time of cooling.

FIG. 6 is a time chart showing a failure determination situation during warm-up.

[Explanation of symbols]

Reference Signs List 1 engine (internal combustion engine) 21 ECU (judgment means, time limit setting means, operation state judgment means) 22 air flow sensor (correlation parameter detection means) 23 water temperature sensor Q intake air amount (correlation parameter) WT cooling water temperature Tlmt time limit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuhiro Miyake 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Takuya Matsumoto 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi 3G084 CA02 DA27 EA07 EA11 EB08 EC04 FA07 FA20

Claims (3)

[Claims] 1. Correlation parameter detection means for detecting a parameter correlated with the heat value of an internal combustion engine, and determination means for performing a failure determination of a water temperature sensor based on the parameter detected by the correlation parameter detection means. A failure determination device for a water temperature sensor. 2. A limit time required for the cooling water temperature of the internal combustion engine to reach a predetermined value in a cold state is set based on a heat value estimated from a parameter detected by the correlation parameter detecting means. Time limit setting means for performing a failure determination when the detection value of the water temperature sensor does not reach a predetermined value within the time limit set by the time limit setting means. The failure determination device for a water temperature sensor according to claim 1. 3. An operating state determining means for determining whether or not the internal combustion engine at the time of warming-up is in an operating state that can affect the cooling water temperature based on the parameters detected by the correlation parameter detecting means. Then, the determination unit determines that the detection value of the water temperature sensor exceeds the set water temperature range for a predetermined time, even though the operation state determination unit determines that the operation state may affect the cooling water temperature. The failure determination device for a water temperature sensor according to claim 1, wherein the failure determination is performed when the temperature does not fluctuate.