JP2002174121A - Thermostat diagnosis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermostat diagnosis device capable of accurately diagnosing whether a thermostat is malfunctioned or not by finding the estimated temperature of a cooling medium, sequentially changed, closely corresponding to a change in combustion condition of an engine and comparing it with a temperature detected by equipment including a sensor. SOLUTION: An electronic control device 51 estimates the newest cooling temperature by averaging processing (annealing processing) of the temperature of a cooling medium (a cooling water temperature) estimated in the past and a cooling water temperature newly estimated in accordance with the operated condition of the engine 1 during combustion in the engine 1 after started while estimating and calculating the newest cooling water temperature by adding a predetermined addition number to the cooling water temperature estimated in the past without performing annealing processing during fuel cut. The cooling water temperature estimated in this way is compared with the cooling water temperature actually measured by a water temperature sensor 41 for diagnosis of whether the thermostat is malfunctioned or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermostat diagnostic device which is provided in a cooling medium circulation passage for cooling an engine and detects an abnormal operation of a thermostat which regulates the temperature of the cooling medium by opening and closing the passage.

[0002]

2. Description of the Related Art Generally, in a cooling system provided in a water-cooled engine, a cooling medium (cooling water) temporarily absorbs heat generated by an engine body and radiates the heat to the outside through a radiator provided separately from the engine body. The cooling water after the heat release is returned to the engine body again, and the process of absorbing heat from the engine body is repeated. In order to cause the cooling water to repeat the heat absorbing action and the heat releasing action, a circulation passage for circulating the cooling water is provided between the engine body and the radiator. Further, a thermostat is provided in the middle of the circulation passage. The thermostat is a control valve that opens and closes mechanically according to the temperature of the cooling water in the circulation passage, and maintains the cooling water temperature at an appropriate temperature by allowing or restricting the flow of the cooling water in the circulation passage.

[0003] For example, immediately after the start of the engine, if the cooling water temperature is equal to or lower than a predetermined temperature (hereinafter, referred to as a set temperature), in other words, before the engine warm-up is completed, the thermostat keeps the valve closed. Under such conditions, the cooling water is not circulated between the engine body and the radiator, and the temperature of the engine rises efficiently. Thereafter, when the warming-up of the engine is completed and the cooling water temperature exceeds the set temperature, the thermostat opens to allow the flow of the cooling water in the circulation passage. That is, heat generated from the engine body is radiated to the outside through the radiator, and the engine is efficiently cooled. Further, once the warm-up of the engine is completed and the cooling water temperature reaches the set temperature once, as apparent from the above-described characteristics, the thermostat repeatedly opens and closes appropriately at a state where the cooling water temperature is at the set temperature. That is, the temperature of the cooling water in the circulation passage, and thus the temperature of the engine main body, are generally maintained at the set temperature.

[0004] In the cooling system of the engine configured as described above, the thermostat sometimes sticks in the valve open state. In such a case, regardless of whether the warm-up of the engine has been completed or not, the heat of the cooling water is constantly radiated through the radiator, so that the engine is in a supercooled state. The warm-up completion time will be delayed. Particularly in an engine equipped with an internal combustion engine, during warm-up operation, a so-called warm-up increase that normally increases the supply amount of fuel provided for engine combustion is normally performed. , Worsening fuel economy and emissions.

Therefore, in order to take appropriate measures against such abnormalities of the thermostat, for example, Japanese Patent Laid-Open Publication No. 2000-2000.
In the thermostat diagnostic apparatus described in Japanese Patent Application Laid-Open No. 104549, the cooling water temperature estimated to be reached if the thermostat is functioning normally at some point after the engine is started is determined by the cooling water temperature at the time of starting the engine and the starting time of the engine. In addition to the elapsed time since the start of the engine, the estimation is performed based on various parameters related to the heat balance of the cooling water, such as the operating state of the engine. Then, the estimated cooling water temperature (estimated water temperature) and the cooling water temperature actually measured by a sensor or the like (actually measured water temperature)
At a certain time after the start of the engine to detect an abnormality in the thermostat.

[0006] When detecting an abnormality in the thermostat by comparing the estimated water temperature with the actually measured water temperature as in the apparatus described in the above publication, various parameters related to the heat balance of the cooling water are different from the estimated water temperature. The more accurately the error is reflected, the higher the reliability of the abnormality detection (diagnosis).

For example, until an arbitrary time, the instantaneous heat balance of the cooling water between the engine body and the radiator at each time is cumulatively calculated, and based on the result, the cooling water temperature near the thermostat at the arbitrary time is calculated. Consider the case of estimating. At this time, it is more accurate to take into account not only the instantaneous heat value of the engine at each time but also the time required for heat to be transferred from the engine body to the cooling water (time delay due to heat conduction). This is preferable for obtaining the estimated water temperature.

As a method of taking such a time lag into account when estimating the cooling water temperature near the thermostat, a calculation method using averaging processing (smoothing processing) can be considered.
For example, the amount of heat newly absorbed by the cooling water (the amount of temperature rise of the cooling water) is obtained based on the operating state of the engine, and this amount of temperature rise is added to the previously obtained cooling water temperature (previous value) to obtain the current cooling. Water temperature (estimated water temperature raw value) will be obtained.
In the arithmetic method applying the smoothing process, the raw value obtained here is averaged with the previous value, and this is adopted as the cooling water temperature estimated this time (estimated water temperature processing value). By performing such an annealing process when estimating the cooling water temperature, it is possible to correct a time delay (error) caused by the heat conduction, the transfer of the cooling water, and the like.

[0009]

By the way, the estimated water temperature treatment value is determined when the estimated water temperature raw value rises or falls monotonically or changes relatively slowly even if it rises and falls repeatedly. Changes basically following the same water temperature value while maintaining a predetermined difference from the estimated water temperature raw value. If such tracking is performed accurately, an estimated water temperature (process value) obtained by subtracting only the error (time delay, etc.) from the raw value of the cooling water temperature obtained based on the operating state of the engine can be obtained sequentially with high accuracy. become. In this regard, since the cooling water temperature generally tends to rise monotonically during the period from the start of the engine to the completion of warm-up, the estimated water temperature processing value is smaller than the estimated water temperature raw value. To meet the condition of accurately following while maintaining the predetermined difference.

However, when the combustion of the internal combustion engine provided in the engine is temporarily stopped in the process of increasing the temperature of the engine, for example, when the fuel cut is executed, the calorific value of the engine is reduced. Decreases rapidly. Under such a condition, the estimated water temperature treatment value continues to increase despite the estimated water temperature raw value falling. In other words, the transition mode of the estimated coolant temperature processing value deviates from the transition mode of the estimated raw water temperature value approximating the transition mode of the actual cooling water temperature.

The estimated water temperature processing value corresponds to a criterion for determining whether an abnormality has occurred in the thermostat. Therefore, the transition mode of the estimated water temperature processing value and the transition mode of the estimated water temperature raw value (the transition mode of the actual cooling water temperature)
The deviation from the above causes a concern that an erroneous determination is made as to whether or not an abnormality has occurred in the thermostat.
That is, the reliability of the diagnosis regarding the operation state of the thermostat is reduced.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an estimated temperature that precisely corresponds to a change in the combustion state of an engine with respect to a temperature of a cooling medium that changes sequentially. It is an object of the present invention to provide a thermostat diagnostic device capable of accurately diagnosing the presence or absence of an abnormality in a thermostat by calculating the temperature and comparing the temperature with a temperature detected by a device such as a sensor.

[0013]

To achieve the above object, the present invention relates to a thermostat for opening and closing a passage for circulating a cooling medium between an engine and a radiator in accordance with the temperature of the cooling medium. In a thermostat diagnostic device for detecting the temperature of the cooling medium, the temperature estimating means for estimating the temperature of the cooling medium, the temperature estimating means for estimating the temperature of the cooling medium, when the calorific value of the engine exceeds a predetermined amount The latest temperature is estimated by averaging the temperature of the cooling medium estimated in the past and the temperature of the cooling medium newly estimated based on the operating state of the engine, while the heat generation of the engine is performed. If the amount is equal to or less than the predetermined amount, temperature estimating means for estimating the latest temperature without performing the averaging process; and And summarized in that and a diagnosis means for detecting an abnormality of the thermostat based on a relationship between the temperature issued.

The temperature estimating means recognizes that when the engine is performing engine combustion, the calorific value of the engine exceeds the predetermined amount, and the engine stops engine combustion. In such a case, it may be recognized that the calorific value of the engine is equal to or less than the predetermined amount.

[0015] The temperature estimating means may recognize that the calorific value of the engine is equal to or less than the predetermined amount when the engine is performing a fuel cut.

[0016] The diagnostic means may be arranged such that, when the estimated latest temperature exceeds a predetermined temperature, if the detected temperature is equal to or lower than the latest temperature or a predetermined judgment temperature, May be diagnosed as abnormal.

The diagnostic means detects an abnormality of the thermostat based on a relationship between the estimated latest temperature and the detected temperature when a predetermined period has elapsed from the start of the engine. You may.

According to each of the above configurations, during the period in which the engine is performing engine combustion (during the period in which heat generation (radiation) is exerted on the cooling medium), heat transfer from the engine to the cooling medium, etc. While the temperature of the cooling medium is successively estimated while taking into account the time delay factor caused by the engine sufficiently accurately, during the period when the engine stops the engine combustion (during the period when the cooling medium is not generating heat). Thus, the temperature of the cooling water can be estimated by considering only the amount of heat radiation from the cooling medium. Therefore, irrespective of whether the engine is performing engine combustion or not, the temperature of the cooling medium can be always accurately estimated, and the abnormality of the thermostat can be detected based on the estimated temperature. It becomes possible to make a highly reliable diagnosis of the operating state of the thermostat.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermostat diagnostic apparatus according to the present invention will be described as a water-cooled vehicle-mounted internal combustion engine (engine).
An embodiment applied to the cooling system will be described with reference to the drawings.

As shown in FIG. 1, a four-cylinder engine 1
Are provided with a cylinder 3, a piston 4, a crankshaft 5, a connecting rod 6 for connecting the piston 4 and the crankshaft 5, a water jacket 7 surrounding the cylinder 3, and an internal space provided outside the engine body and communicating with the water jacket 7. Radiator 8, cooling fan 9, water pump 10 and the like.

In the combustion chamber 11 of each cylinder 3, the air-fuel mixture explodes and burns, so that the piston 4 moves up and down, and this up-and-down movement is converted into the rotational driving force of the crankshaft 5 via the connecting rod 6. Further, the supply of the air-fuel mixture and the discharge of the combustion gas are performed via an intake / exhaust port (not shown). The water jacket 7 serving as a space for circulating cooling water cools the cylinder head 12 and the cylinder block 13 heated by the explosion and combustion of the air-fuel mixture as necessary, or maintains the cylinder 3 at a constant temperature.
It is configured to surround the outer periphery of.

The radiator 8 and the cooling water circulation path of the water jacket 7 are connected by upper and lower communication passages 14 and 15. A thermostat 16 is provided in the middle of the lower communication passage 15. Thermostat 1
Reference numeral 6 denotes a valve that opens and closes mechanically according to the water temperature. In the present embodiment, when the water temperature is 80 ° C. or less, the valve 6 closes to close the communication passage 14 and the water temperature exceeds 80 ° C. Then, the valve is opened and the passage 14 is opened.

A water temperature sensor 41 provided on the inner wall of the water jacket 7 detects the temperature of the cooling water (cooling water temperature) T
A detection signal corresponding to the HW is output and the electronic control unit (EC
U) Send to 51. Next, an electronic control unit (ECU) 51 that controls and diagnoses (detects an abnormality) each part of the engine including the thermostat 16 based on the operating state of the engine 1.
Will be described.

As shown in the block diagram of FIG.
1 is a central processing unit (CPU) 52, a read-only memory (ROM) 53, a random access memory (RAM) 5
4, a backup RAM 55, a timer counter 56, and the like. The ECU 51 constitutes a logical operation circuit formed by connecting these components to the external input circuit 57 and the external output circuit 58 via a bus 59. Here, the ROM 53 stores in advance programs related to various kinds of operation control of the engine 1, diagnosis of various members constituting the engine 1, and the like. RAM
54 temporarily stores the calculation result of the CPU 52 and the like. The backup RAM 55 is a non-volatile memory that stores data even after the engine stops. The timer counter 56 can perform a plurality of timing operations simultaneously. The external input circuit 57 includes a buffer, a waveform circuit, a hard filter (a circuit including an electric resistor and a capacitor), an A / D converter, and the like. The external input circuit 57 includes a drive circuit and the like.
As described above, the water temperature sensor 41 outputs a detection signal corresponding to the cooling water temperature THW in the water jacket 7.
The throttle sensor 42 outputs a detection signal corresponding to the throttle valve opening TA corresponding to the depression amount of an accelerator pedal (not shown). The rotation speed sensor 43 outputs a detection signal corresponding to the rotation speed of the crankshaft 5, that is, the engine rotation speed NE. The oxygen sensor 44 outputs a detection signal according to the oxygen concentration in the exhaust gas. Intake air amount sensor 45
Outputs a detection signal corresponding to the intake air amount Ga. Vehicle speed sensor 46 outputs a detection signal according to vehicle speed SPD. The intake air temperature sensor 47 outputs a detection signal corresponding to the temperature (intake air temperature) THA of the intake air introduced into the air cleaner. The CPU 52 reads detection signals of the various sensors 41 to 47 input via the external input circuit 57 as input values. The CPU 52 (ECU 51) executes, for example, control of the fuel injection amount and fuel injection timing by the injector 48, diagnosis of various members constituting the engine 1, and the like based on the input values.

Next, among the various controls executed by the ECU 51, diagnosis of the thermostat 16 (diagnosis control) will be described.

The ECU 51 performs a diagnosis for detecting an abnormality when the thermostat 16 is stuck in the open state during the period from the start of the engine 1 until the warm-up is completed. In the diagnosis, the ECU 51 calculates two kinds of parameters such as a raw value ecthw and a processing value ecthwsm regarding a cooling water temperature (hereinafter referred to as an estimated water temperature) estimated to be observed when the thermostat 16 is functioning normally. .

First, the estimated water temperature raw value ecthw is a cooling water temperature (estimated value) which is basically obtained by taking into account only the heat balance of the cooling water such as the operating state of the engine 1 or the like. on the other hand,
The estimated water temperature treatment value eththwsm is calculated by
Is a basic amount, and is an estimated water temperature obtained in consideration of a time required for heat to be transferred from the engine 1 to the cooling water (a time delay element caused by heat conduction), a determination error, and the like. Corresponds to the lower limit value of the cooling water temperature THW observed when the cooling water temperature is functioning.

Estimated water temperature raw value ectw and processing value ect
hwsm is obtained, for example, according to the following arithmetic expressions (I) and (II), and is periodically updated.

Ecthw (i) = ecthw (i−1) + Δecthw (I) ecthwsm (i) = ecthwsm (i−1) + (ecthw (i) −ecthws m (i−1)) / (average rate) ) ... (II) where ethw (i): current obtained ethw ethw (i-1): last obtained ecthw Δecthw: additional amount of ethw obtained by referring to a map or the like based on the operating state of the engine 1 ecthwsm (i) : Ethwsms obtained this time ethwsms (i-1): averaging rate of ethwsmsm obtained last time: numerical value larger than "1" (for example, 2
Constant is set to ⁵⁾ ECU 51 after the start of the engine 1, these two parameters Ecthwsm, we intend updated every predetermined time Ecthw, estimated water processed value Ecthwsm predetermined judgment temperature (in this embodiment Then set to 75 ° C.)
Is reached, it is determined whether or not an abnormality (sticking in the valve open state) has occurred in the thermostat 16. At the time of this determination, an actually measured value of the cooling water temperature (hereinafter simply referred to as cooling water temperature) TH obtained based on the detection signal of the water temperature sensor 41
W is compared with the determination temperature. And the cooling water temperature THW
If the temperature is below the determination temperature,
6 is functioning normally ", and the cooling water temperature T
If the HW is equal to or higher than the determination temperature, the "thermostat 1
No. 6 function has failed (thermostat 16
Is stuck in the open state). "

FIG. 3 shows that the estimated water temperature raw value ecthw and the processed value ecthwsm, which are sequentially calculated, and the thermostat 16 are abnormal during the period from the start of the engine 1 to the completion of warm-up. 5 is a time chart showing an example of a change in cooling water temperature THW.

As shown in FIG. 3, when the engine 1 is started at the time t0, as long as the operation state of the engine represented by the fuel injection amount, the engine load, and the like is in a substantially steady state, the estimated water temperature raw value ecthw is obtained. (Dashed line) and processing value ecthw
The sm (solid line) indicates a tendency to monotonically increase. Estimated raw water temperature value eththw and processing value ec at an arbitrary time
The deviation d between thwsm converges to a predetermined value (about 5 ° C. in the present embodiment) after the engine start time t0, and thereafter keeps a substantially constant difference (see also FIG. 4).

If the thermostat 16 is stuck in the valve open state, the cooling water circulates between the engine 1 and the radiator 8 even before the warm-up is completed, and the engine 1
Is in a supercooled state, and the cooling water temperature THW grasped based on the detection signal of the water temperature sensor 41 falls below the estimated water temperature processing value eththwsm for almost the entire period from the start of the engine 1 to the completion of the warm-up. Become. In the present embodiment, for example, as shown by a two-dot chain line in FIG. 3, at a time tx at which the estimated coolant temperature processing value ectwsms reaches the determination temperature, the cooling water temperature THW changes the estimated coolant temperature processing value ectwsmsm (determination temperature). By recognizing that the temperature is lower, the abnormality of the thermostat is detected.

As described above, the estimated raw water temperature value ethw and the estimated processed water temperature value eththwsm are determined as long as the operating state (combustion state) of the engine represented by the fuel injection amount, engine load, and the like is in a substantially steady state. Shows a monotonically increasing tendency. Also, the deviation d between the two is the engine 1
After the start, the value converges to a predetermined value, and thereafter, a substantially constant difference is maintained.

On the other hand, when the fuel cut (control) is performed, the temperature of the engine 1 and the temperature of the cooling water in the water jacket 7 may fall even during the warm-up period. Here, the fuel cut is a part of the operation control performed by the ECU 51. For example, when the engine speed NE exceeds a predetermined number set in advance according to the operation state of the engine 1,
This refers to control for temporarily reducing the load on the engine 1 by temporarily stopping the supply of fuel (fuel injection) to the combustion chamber 11, preventing heating of an exhaust purification catalyst (not shown), or improving fuel efficiency. During the fuel cut period, the engine 1 misfires (combustion of the engine stops), and generates little heat. Since the parameters reflected in the calculation of the estimated raw water temperature value eththw include the loss of heat generation due to the execution of the fuel cut,
Even under such conditions, the estimated raw water temperature value ecthw
The transition mode substantially coincides with the transition mode of the cooling water temperature that decreases due to the execution of the fuel cut.

However, the estimated water temperature processing value eththwsm
Is to apply an averaging process (smoothing process) to the addition amount added to the previous value ectwsmsm (i-1) when calculating the latest value ethwswsm (i) (see the arithmetic expression (II)). For this reason, the latest value ecthwsm (i)
In calculating (updating) the time delay element caused by heat conduction from the engine 1 to the cooling water, etc., is accurately reflected, but under conditions where the calorific value of the engine 1 fluctuates rapidly, It is difficult to accurately follow the change (fluctuation) of the actual cooling water temperature.

Therefore, in the thermostat diagnostic apparatus according to the present embodiment, when the thermostat 16 is diagnosed, the smoothing process is interrupted during the fuel cut period, and the above equation (II) is replaced. For example, based on the following equation (III), the latest value ecth of the estimated water temperature processing value
Find wsm (i).

Ecthwsm (i) = ecthwsm (i−1) + Δecthw (III) That is, the addition amount Δecthw that is uniquely obtained by referring to a map or the like based on the operating state of the engine 1 is calculated as the estimated water temperature processing value ecthwsm ( It will be applied directly as the addition amount of i-1).

For example, FIG. 5 shows an estimated water temperature raw value ectw and a processed value ectw which are obtained when a fuel cut is performed during a predetermined period from the start of the engine 1 to the completion of warm-up.
6 is a time chart showing transition of m.

As shown in FIG. 5, when the fuel cut is performed during the warm-up process of the engine 1, the estimated raw water temperature value ethth is obtained.
The value of w temporarily decreases, and then increases again when the fuel cut is completed (when the fuel supply is restarted) (dotted line). At this time, if the “smoothing process” is continued in updating the estimated water temperature processing value eththwsm, it becomes difficult to follow the transition of the estimated water temperature raw value eththw (broken line),
The deviation d between the estimated raw water temperature value eththw and the processing value ecthwsm is temporarily reduced. On the other hand, in the diagnostic control according to the present embodiment, the “smoothing process” is not performed during the fuel cut period, and the estimated water temperature processing value ectwsmsm is uniquely updated based on, for example, the operating state of the engine 1. Is applied, and the smoothing process is restarted with the end of the fuel cut. By applying such a control structure, not only can the deviation d be maintained at a constant value during or after the execution of the fuel cut, but also as a whole, During the implementation, in calculating the estimated water temperature treatment value eththwsm, a time delay element caused by heat conduction from the engine 1 to the cooling water or the like can be sufficiently accurately reflected.

Next, with respect to the diagnostic control of the thermostat 16, a specific diagnostic procedure by the ECU 51 will be described with reference to a flowchart.

FIGS. 7 and 8 show that after the engine 1 is started,
9 shows a “thermostat diagnosis routine” for diagnosing the operation state of the thermostat 16 during the warm-up period. ECU
Reference numeral 51 denotes a ROM for storing a program related to this routine in advance.
53, and an ignition switch (not shown)
Is turned "ON", basically, until it is determined that "the thermostat 16 is functioning normally" or "the thermostat is abnormal".
Execute repeatedly every second.

When the processing of the ECU 51 shifts to this routine, the ECU 51 first determines in step S101 (FIG. 7) whether or not a condition for executing diagnosis is satisfied. The diagnosis execution condition is satisfied when the following conditions (1), (2), and (3) are all satisfied when this routine is first executed, in other words, when the engine 1 is started. (1) The cooling water temperature THW is -10 ° C or more and 35 ° C or less. (2) The intake air temperature THA is -10 ° C or more and 35 ° C or less. (3) The difference between the cooling water temperature THW and the intake air temperature THA at the time of starting is −15 ° C. or more and 7 ° C. or less.

When all of the conditions (1) to (3) are satisfied, the ECU 51 determines that the diagnosis execution condition is satisfied, and shifts the processing to step S102.
On the other hand, if any one of these conditions (1) to (3) is not satisfied, the processing in this routine ends. The above conditions (1) to (3) correspond to temperature conditions necessary and sufficient to obtain a highly reliable diagnosis result. If at least one of these conditions is not satisfied, it is erroneously determined whether the thermostat 16 is abnormal. Considering that there is a possibility of making a judgment, postponing the execution of the diagnosis. Also,
If the diagnosis has already been performed due to the interruption before the previous routine, the execution is stopped.

In step S102, it is determined whether or not the starting recognition flag F is set to "1".
The start-time recognition flag F is initialized to “0” when an ignition switch (not shown) of the engine 1 is turned “ON”. Therefore, after the engine 1 is started, the ECU 5
1 shifts to this routine for the first time, and the determination made in step S102 is necessarily negative. Step S1
If the determination in step 02 is negative, the initial condition is set only once after the engine 1 is started.
A series of processes from S104, S105a and S105b are performed. On the other hand, if the determination in step S102 is affirmative, the process jumps to step S106.

In step S103, the ECU 51
The current cooling water temperature THW is stored as the starting cooling water temperature THWst, and the current intake air temperature THA is stored as the starting intake air temperature THAst. In step S104, the starting cooling water temperature T
HWst and the intake air temperature at start THast are compared, and “TH
If it is determined that “Wst ≦ THast”, the process proceeds to step S105a, where the estimated water temperature processing value ecth
wsm and the initial value of the estimated raw water temperature ecthw as TH
Wst is adopted. On the other hand, if it is determined in step S104 that “THWst> THAst”, the process proceeds to step S105b, and THAst is adopted as the initial value of the estimated water temperature processing value ectthwsm and the estimated water temperature raw value eththw.

That is, the above steps S103 and S10
4, through the processing in S105a and S105b, the EC
U51 is the cooling water temperature THW at the start and the intake air temperature (outside air temperature)
Compare with THA and estimate lower temperature Estimated water temperature treatment value ec
thwsm and the estimated raw water temperature value eththw are selected as initial values. For example, when the intake air temperature THA is lower than the cooling water temperature THW, the cooling water temperature THW hardly increases. However, by performing the above selection, the initial value of the estimated water temperature processing value ectwwsm is set to be low, and the processing value ectwwsm is determined as the determination value ( (See FIG. 3) is delayed. As a result, the possibility of erroneous determination of the estimated water temperature decreases, and the diagnostic accuracy increases.

After the processing in step S105a or S105b, the start-time recognition flag F is set to "1" in step S106.

In the following step S107, the values ectwsm (i) and ecthw (i) stored as the latest values of the estimated water temperature processing value and the estimated water temperature raw value are respectively replaced with the previous values ethwsmsm (i-1), stored as ecthw (i-1).

In step S108, the previous value echwsm (i-1) of the estimated water temperature processing value and the minimum value of the intake air temperature (hereinafter, referred to as
A deviation α from the ethamin (referred to as a minimum intake air temperature) is calculated. Here, the intake air temperature minimum value ethamin is the minimum value of the intake air temperature THA that has been observed up to now since the start of the engine 1, and corresponds to a substitute value of the outside air temperature. That is, since the intake air temperature sensor 41 is installed in an engine room (not shown), the intake air temperature THA obtained based on the detection signal tends to be higher than the outside air temperature. Therefore, in the present embodiment, the minimum value of the intake air temperature THA observed after the start of the engine 1 is regarded as a value closest to the outside air temperature, and this is adopted as a substitute value of the outside air temperature. Also, the previous value of the estimated water temperature treatment value, echwsm (i-1)
And the minimum value of the intake air temperature (hereinafter referred to as the minimum intake air temperature) et
is used as a parameter for calculating an addition amount Δecthw (see arithmetic expression (I)) of the estimated raw water temperature value ecthw applied in this routine. A method for calculating the addition amount Δecthw will be described later.

Note that the deviation α calculated in step S108 is set so as not to fall below “0”. That is, in the subsequent step S109, the ECU 51 determines whether or not the deviation α is equal to or greater than “0”. If the determination is affirmative, the process proceeds to step S111 while storing the value of the deviation α calculated in step S108,
If the determination is negative, the deviation α is set to “0” (step S110), and the process proceeds to step S111 (FIG. 8).

In step S111, the engine 1
It is determined whether or not the vehicle equipped with is currently running. Such a determination is made for the following reason.

The greater the amount of air that has passed through the radiator, the higher the cooling capacity of the radiator and the more the heat radiation of the cooling water is promoted.
That is, as the vehicle speed increases, the amount of air passing through the radiator increases, and the influence on the heat radiation of the cooling water increases. Further, as the vehicle speed increases, the vehicle speed wind introduced into the engine room increases, and the vehicle speed wind efficiently cools the engine 1, so that the heat absorption amount of the cooling water decreases. Therefore, the behavior of the cooling water temperature THW is essentially different during traveling and during non-traveling (idling).

In step S111, it is determined whether the vehicle is traveling or idle. If the vehicle is traveling, the process proceeds to step S112. If the vehicle is idle, the process proceeds to step S113a. The engine 1
The determination as to whether or not the vehicle equipped with the vehicle is traveling may be made based on the vehicle speed SPD obtained from the detection signal of the vehicle speed sensor 46, for example.

In step S112, it is determined whether or not a fuel cut is currently being performed. If the determination is affirmative, the process proceeds to step S113b, and if the determination is negative, the process proceeds to step S113c. During the fuel cut, the heat value of the engine is almost “0”. Therefore, as a factor affecting the cooling water temperature, the addition amount Δecthw only taking into account the heat radiation amount of the cooling water is considered.
Ask for. On the other hand, during fuel supply (during fuel injection), as a factor affecting the cooling water temperature, the estimated water temperature raw value ecth is sufficiently considered, taking into account the effect of the heat generated by the engine 1 on the cooling water temperature.
The addition amount Δecthw of w is obtained. That is, for example, even if the difference between the cooling water temperature and the outside air temperature is equal,
The behavior (change) of the cooling water temperature differs depending on whether or not the fuel cut is performed.

Therefore, the ECU 51 determines in step S11
1 and S112, which are different from each other according to the three operating states (“idle”, “running and performing fuel cut”, and “running and supplying fuel”) classified based on the series of determinations. Map MP1 (Step S113)
a), MP2 (step S113b), or MP3
Estimated raw water temperature value ect with reference to (Step S113c)
An addition amount Δecthw of hw is obtained. Note that the addition amount Δe
Each map MP1, MP2, and M for obtaining cthw
P3 varies depending on the characteristics of the vehicle or engine to be applied or the cooling system thereof. However, basically, the previous value of the estimated water temperature treatment value echws
The difference α (see steps S108 to S110) between m (i-1) and the minimum intake air temperature ethamin, and parameters related to the operating state of the engine 1 such as the intake air amount Ga (particularly, those reflecting the calorific value) are used as variables. The amount Δecthw can be easily set by an experiment or the like so as to be obtained. Further, on all the maps MP1 to MP3, the larger the deviation α, the smaller the addition amount Δecthw tends to be. In addition, as the addition amount Δecthw obtained from each map, among the positive, negative, and “0”,
Any numerical value belonging to the range can be applied.

After the processing in any of steps S113a, S113b and S113c, the ECU 51
Shifts the processing to step S114, and calculates the current estimated raw water temperature value eththw by adding the currently calculated addition amount Δecthw to the estimated raw water temperature value eththw (i-1).

In step S115, the fuel cut is being performed, and the addition amount Δecthw is equal to the predetermined value β.
(However, β <0) is determined.
If the determination is negative, the process proceeds to step S116, and if the determination is affirmative, the process proceeds to step S117. In step S116, the previous operation expression (II)
The estimated water temperature processing value eththwsm is calculated according to the following. On the other hand, in step S117, the estimated water temperature processing value eththwsm is calculated in accordance with the above-mentioned arithmetic expression (III). In calculating the estimated water temperature treatment value eththwsm, the above-mentioned arithmetic expressions (II) and (III) are applied alternatively, so that the deviation d (FIGS. 3 to 6) can be obtained during or after the fuel cut. ) Can be maintained at a constant difference. In general, during the execution of the diagnostic control, when calculating the estimated water temperature processing value ectwsmsm,
As described above, the time delay factor caused by the heat conduction from the engine 1 to the cooling water is sufficiently accurately reflected.

After calculating the estimated water temperature processing value ethwsmsm in either of steps S116 and S117, the ECU 51 shifts the processing to step S118.

In step S118, it is determined whether the estimated water temperature treatment value eththwsm is lower than the determination temperature of 75 ° C. And if the judgment is affirmative, EC
U51 shifts the processing to step S119, and if the judgment is negative, shifts the processing to step S120b.

In step S120b, it is determined that the thermostat is abnormal (the thermostat 16 is stuck in the open state), and a warning light is turned on for the driver of the vehicle equipped with the engine 1 or the like. Give a warning through such as. After the same step S120b,
The ECU 51 terminates the processing of this routine and prohibits the interruption of the routine from being executed again.

On the other hand, in step S119, it is determined whether or not the cooling water temperature THW exceeds a determination temperature of 75 ° C. If the determination is negative, the process exits this routine and repeats a series of processes in this routine at the next interrupt timing. That is,
The determination as to whether or not the thermostat 16 has an abnormality is left to the next and subsequent routines. If the determination in step S119 is affirmative, the process proceeds to step S120a, and a determination is made that "thermostat 16 is functioning normally", followed by terminating the present routine. That is, as described above with reference to FIG. 3, before the estimated coolant temperature processing value eththwsm estimated from the calorific value of the engine 1 rises and reaches the determination temperature 75 ° C., the actual cooling water temperature THW falls to the determination temperature 75 ° C. This is because the thermostat 16 is functioning normally and the cooling water temperature THW is considered to have risen appropriately. When the processing in this routine ends after the normality is determined in step S120a, the ECU 51 prohibits the execution of the interrupt to this routine again.

Based on the above diagnosis procedure, this routine
After the engine 1 is started, an estimated water temperature raw value ectw which directly reflects the temperature of the cooling water to be observed when the thermostat 16 is functioning normally, and an estimated water temperature obtained by subjecting the estimated water temperature raw value to predetermined processing The processing value ethwsmsm is
It is updated every predetermined time. And the estimated water temperature treatment value e
cthwsm is a predetermined determination temperature (75 in the present embodiment).
Set to ° C. ) Is reached, the actual measurement value (hereinafter, simply referred to as cooling water temperature) THW of the cooling water temperature obtained based on the detection signal of the water temperature sensor 41 is compared with the determination temperature, so that the thermostat 16 is abnormal (the valve is open). Is determined.

According to such a control structure, during the execution of the diagnostic control, the calculation of the estimated water temperature treatment value eththwsm generally takes into account a sufficient time delay element caused by heat conduction from the engine 1 to the cooling water. While it can be accurately reflected, the deviation d between the two parameters ecthw and ecthsm can be kept constant during or after the fuel cut.

Therefore, regardless of the fluctuation of the combustion state of the engine 1 which significantly affects the fluctuation of the cooling water temperature, it is possible to ensure high accuracy and reliability in the thermostat diagnosis.

The determination temperature of 75 ° C. to be applied in the “thermostat diagnosis routine” of the present embodiment.
Indicates that the valve opening temperature of the normally functioning thermostat 16 is 8
When the temperature is set to about 0 ° C., it is only a numerical value that can secure sufficient reliability for the diagnosis. Therefore, it may be appropriately changed according to the characteristics of the thermostat, the engine, and the like to be applied.

In the “thermostat diagnosis routine” of the present embodiment, a predetermined type of judgment temperature (75 ° C.) is used to determine the timing of diagnosing (determining) an abnormality of the thermostat 16. In addition to being applied as a reference value, it is also applied as a reference value for determining the presence or absence of abnormality of the thermostat 16 by comparing with the cooling water temperature THW. On the other hand, for example, when the estimated water temperature processing value eththwsm reaches the predetermined determination temperature A, if the cooling water temperature THW is equal to or lower than another determination temperature B different from the determination temperature A, an abnormality occurs in the thermostat. It is also possible to apply a control structure such as "determining that the operation is performed."

Further, after a predetermined time has elapsed after the start of the engine 1, the estimated water temperature processing value ect at that time is determined.
If the cooling water temperature THW has not reached the predetermined determination temperature C determined based on the hwsm, the thermostat 16
It is also possible to perform a determination that an abnormality has occurred.

In the "thermostat diagnosis routine" of the present embodiment, only when the fuel cut is performed and the addition amount Δecthw is smaller than a predetermined value β (where β <0), “ Without performing the “smoothing process” (according to the above equation (III)),
It was decided to update wsm. On the other hand, if the fuel cut is performed, a control structure that does not perform the “smoothing process” regardless of the value of the addition amount Δecthw may be applied. Regardless of whether or not the fuel cut is performed, in a state where the addition amount Δ is less than a predetermined value in a range of less than “0” (a state where the heat generation amount of the engine 1 is lower than the predetermined amount). By applying a control structure that does not perform the “smoothing process”, effects equivalent to or equivalent to the present embodiment can be achieved.

In the “thermostat diagnosis routine” of the present embodiment, when the estimated water temperature processing value ectwsmsm is updated during the fuel cut-off period,
It is determined that the estimated water temperature processing value ectwsmsm is updated without performing the “annealing process” (according to the above-described arithmetic expression (III)). On the other hand, during the period when the fuel cut is being performed, the estimated water temperature processing value ectwsmsm is updated,
A constant (negative numerical value) set in advance for each predetermined period may be simply added. Also, not only during fuel cut,
Even if misfire has occurred for some reason or under other conditions in which the amount of heat released to the outside is greater than the amount of heat absorbed from the engine 1 for the cooling water, the "smoothing process" is not appropriately performed. Alternatively, a control structure may be applied in which the estimated water temperature processing value ectwsmsm is updated by adding a separately set addition amount (negative numerical value).

Further, in the cooling system for the engine 1 according to the present embodiment, the passage 15 through which the cooling water flows from the radiator 8 toward the water jacket 7 of the engine 1.
The configuration in which the thermostat 16 is provided in the middle is adopted. However, the present invention is not limited to this. For example, a configuration may be adopted in which a thermostat 16 is provided in the passage 14 for flowing the cooling water from the water jacket 7 of the engine 1 toward the radiator 8. In short, if it is in the middle of a passage that circulates cooling water between the engine and a radiator that dissipates the heat of the cooling water for cooling the engine to the outside,
Regardless of the configuration in which the thermostat is provided in any part, an effect equivalent to or equivalent to that of the present embodiment can be obtained.

The engine 1 according to the present embodiment
Is an engine that generates output only from a four-cylinder internal combustion engine. However, the present invention can also be applied to, for example, a hybrid engine that combines an internal combustion engine and an electric motor.

[0072]

As described above, according to the present invention,
Regardless of whether the engine to be applied is performing engine combustion or not, the temperature of the cooling medium can always be accurately estimated, and the abnormality of the thermostat can be detected based on the estimated temperature. Thus, a highly reliable diagnosis of the operation state of the thermostat can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a cooling system for a vehicle-mounted engine to which a thermostat diagnostic device according to an embodiment of the present invention is applied.

FIG. 2 is an exemplary block diagram showing an electric configuration of the electronic control device according to the embodiment;

FIG. 3 is a time chart showing changes in an estimated raw water temperature value, an estimated water temperature processing value, and the like from the start of the engine to the completion of warm-up.

FIG. 4 is a time chart showing a transition of a difference between an estimated raw water temperature value and an estimated water temperature processing value.

FIG. 5 is a time chart showing transition of an estimated water temperature raw value and an estimated water temperature processing value observed when a fuel cut is performed during a predetermined period from the start of the engine to the completion of warm-up.

FIG. 6 is a time chart showing a transition of a difference between an estimated raw water temperature value and an estimated water temperature processing value.

FIG. 7 is an exemplary flowchart showing a procedure for diagnosing the thermostat according to the embodiment;

FIG. 8 is a flowchart showing a procedure for diagnosing the thermostat according to the embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Cylinder 4 Piston 5 Crankshaft 6 Connecting rod 7 Water jacket 8 Radiator 11 Combustion chamber 12 Cylinder head 13 Cylinder block 14, 15 Communication passage 16 Thermostat 41 Water temperature sensor 42 Throttle sensor 43 Speed sensor 44 Oxygen sensor 45 Intake amount sensor 46 Vehicle speed sensor 47 Intake air temperature sensor 48 Injector 56 Timer counter 57 External input circuit 59 Bus

Claims (4)

[Claims] 1. A thermostat diagnostic device for detecting an abnormality in a thermostat that opens and closes a passage for circulating a cooling medium between an engine and a radiator in accordance with the temperature of the cooling medium, wherein the temperature of the cooling medium is detected. Temperature detecting means, and a temperature estimating means for estimating the temperature of the cooling medium,
If the calorific value of the engine exceeds a predetermined amount, averaging processing is performed on the temperature of the cooling medium estimated in the past and the temperature of the cooling medium newly estimated based on the operating state of the engine. Temperature estimating means for estimating the latest temperature without performing the averaging process when the calorific value of the engine is equal to or less than the predetermined amount. A diagnostic device for a thermostat, comprising: diagnostic means for detecting an abnormality of the thermostat based on a relationship between a temperature and the detected temperature. 2. The temperature estimating means recognizes that when the engine is performing engine combustion, the calorific value of the engine exceeds the predetermined amount, and the engine stops engine combustion. 2. The method according to claim 1, wherein the control unit recognizes that a heat value of the engine is equal to or less than the predetermined value.
A thermostat diagnostic device as described. 3. The thermostat according to claim 1, wherein the detected temperature is lower than the latest temperature or a predetermined determination temperature when the estimated latest temperature exceeds a predetermined temperature. The abnormality diagnosis device for a thermostat according to claim 1, wherein the diagnosis is performed to determine that the abnormality is abnormal. 4. A diagnosing means for detecting an abnormality of the thermostat based on a relationship between the estimated latest temperature and the detected temperature when a predetermined period has elapsed from the start of the engine. 2. The method according to claim 1, wherein
Or the diagnostic device for a thermostat according to 2.