System for detecting malfunction of internal combustion engine radiator

A system for detecting malfunction of a radiator, more precisely a thermostat (shut-off valve) in the engine cooling system. In the system, an estimated coolant temperature CTW is calculated from the temperature condition and operating condition at engine starting. When the estimated coolant temperature CTW has reached a judge malfunction value CTWJUD but the detected coolant temperature TW has not reached a judge normal value TWJUD, the thermostat 64 is discriminated to have malfunctioned, thereby enabling to detect malfunction of the radiator with high accuracy and high response.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a system for detecting or discriminating
 malfunction of an internal combustion engine radiator, more particularly
 to a system for detecting or discriminating malfunction of a thermostat in
 a cooling system of an internal combustion engine.
 2. Description of the Related Art
 The internal combustion engine of a vehicle is connected through a
 communicating passage with a radiator for cooling a coolant. A thermostat
 (a shut-off valve) is installed in the communicating passage. The
 thermostat closes the communicating passage when the coolant temperature
 is low, such as at engine starting, and opens it when the temperature
 rises so as to pass coolant into the radiator for cooling.
 The radiator is one of the on-board components of a vehicle. The ability to
 detect or discriminate radiator malfunction is therefore desirable. For
 example, Japanese Laid-open Patent Application No. Hei 6(1994)-213117,
 which relates to a radiator equipped with a thermally insulated tank for
 storing coolant heated during ordinary operation, teaches a system that
 detects the coolant temperature at engine starting and determines that the
 thermally insulated tank is out of order when the detected temperature is
 abnormally low.
 This earlier system can also determine when the thermostat is stuck closed
 or stuck open based on abnormally high or low detected coolant temperature
 during normal engine operation.
 However, the ability of this conventional system to detect thermostat
 malfunction is limited to times when the detected coolant temperature is
 abnormal. It therefore does not provide satisfactory detection accuracy
 and response.
 SUMMARY OF THE INVENTION
 The object of this invention is therefore to overcome this drawback of the
 prior art and for this to provide a system for detecting or discriminating
 malfunction of an internal combustion engine radiator, capable of
 high-accuracy, high-response detection of radiator malfunction,
 particularly of malfunction of a thermostat incorporated in a radiator.
 To achieve this object, the invention provides a system for detecting
 malfunction of an internal combustion engine radiator comprising: engine
 operating condition detecting means for detecting operating conditions of
 the engine including at least a coolant temperature; engine-start-time
 coolant temperature determining means for determining an engine-start-time
 coolant temperature at starting of the engine based on at least the
 detected coolant temperature; thermal load parameter determining means for
 determining a parameter indicative of thermal load contributing to a rise
 of the coolant temperature based on the detected engine operating
 conditions; estimated coolant temperature calculating means for
 calculating an estimated coolant temperature based on at least the
 determined engine-start-time coolant temperature and the determined
 parameter indicative of thermal load; and radiator malfunction
 discriminating means for comparing the detected coolant temperature and
 the calculated estimated coolant temperature with predetermined values
 respectively and for discriminating whether the radiator malfunctions
 based results of comparison.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 An embodiment of the invention will now be explained with reference to the
 attached drawings.
 FIG. 1 is an overall schematic view of a system for detecting or
 discriminating malfunction of an internal combustion engine radiator
 according to the invention.
 Reference numeral 10 in FIG. 1 designates a four-cylinder, four-cycle
 internal combustion engine. An air intake pipe 12 equipped with a throttle
 valve 14 is connected to the main engine unit 10a of the engine 10. A
 throttle position sensor 16 associated with the throttle valve 14 produces
 and sends to an electronic control unit (ECU) 20 an electric signal
 representing the opening .theta. TH of the throttle valve 14.
 The air intake pipe 12 is connected to an intake manifold (not shown)
 downstream of the point where the throttle valve 14 is installed. For each
 cylinder, a fuel injector 22 is provided in the intake manifold at a point
 upstream of an intake valve (not shown) of the cylinder.
 Each fuel injector 22 is mechanically connected with a fuel pump (not
 shown), that supplies it with pressurized fuel, and is also electrically
 connected with the ECU 20. The fuel injector 22 injects (supplies) the
 pressurized fuel before the intake valve during the period when it is
 controlled to be open by the ECU 20.
 A manifold absolute pressure sensor 26 is connected with the air intake
 pipe 12 through a branch pipe 24 at a point downstream of the throttle
 valve 14. The manifold absolute pressure sensor 26 outputs an electric
 signal representing the absolute manifold pressure PBA in the air intake
 pipe 12.
 An air temperature (intake air temperature) sensor 30 is installed
 downstream of the absolute pressure sensor 26 for outputting an electric
 signal representing the air temperature (intake air temperature) TA. A
 coolant temperature sensor 32 is installed near a coolant passage (not
 shown) of the engine unit 10a for outputting an electric signal
 representing the engine coolant temperature TW.
 A cylinder discrimination sensor 34 is installed in the vicinity of the
 camshaft or crankshaft (neither shown) of the engine 10 for outputting a
 cylinder discrimination signal CYL every time a piston (not shown) of a
 certain cylinder reaches a prescribed position.
 A TDC sensor 36 is installed in the vicinity of a camshaft or crankshaft
 (neither shown) for outputting a TDC signal pulse once every crank angle
 (e.g., BTDC 10 degrees) associated with the TDC (top dead center) position
 of the piston of each cylinder. A crank angle (CRK) sensor 38 is similarly
 installed for outputting CRK signal pulses at a shorter crank angle period
 (e.g., every 30 degrees) than the period of the TDC signal pulses.
 In the exhaust system of the engine 10, an air/fuel ratio (O.sub.2) sensor
 42 is installed at an appropriate portion of an exhaust pipe 40 connected
 to an exhaust manifold (not shown). The air/fuel ratio sensor 42 outputs a
 signal representing the oxygen concentration O.sub.2 of the exhaust gas. A
 three-way catalytic converter 44 is provided downstream of the air/fuel
 ratio sensor 42 for removing HC, CO and NO.sub.x components from the
 exhaust gas.
 Spark plugs 48 associated with the respective cylinder combustion chambers
 (not shown) of the engine unit 10 are electrically connected with the ECU
 20 through an ignition coil and an igniter 50.
 A knock sensor 52 is mounted on the cylinder head (not shown) of the main
 engine unit 10a for outputting a signal representing vibration of the
 engine 10. Further, a vehicle speed sensor 54 is mounted in the vicinity
 of the drive shaft (not shown) of the vehicle powered by the engine 10.
 The vehicle speed sensor 54 outputs a pulse once every unit rotation of
 the vehicle wheels.
 The outputs of these sensors are sent to the ECU 20.
 The ECU 20, which is constituted as a microcomputer, comprises an input
 circuit 20a for receiving input signals from the aforesaid sensors and
 subjecting them to wave shaping, conversion to a prescribed voltage level
 and conversion from analog to digital form, a CPU (central processing
 unit) 20b for conducting logical operations, a memory means 20c for
 storing processing programs executed by the CPU, processed data and the
 like, and an output circuit 20d.
 The output of the knock sensor 52 is sent to a detection circuit (not
 shown) in the ECU 20, where it is amplified and compared with a knock
 discrimination level. The CPU 20b uses the output of the detection circuit
 to discriminate whether knock (detonation) occurs in the combustion
 chambers. The CPU 20b also calculates the engine speed NE from the counted
 number of CRK pulses and calculates the vehicle speed VPS from the counted
 number of output pulses from the vehicle speed sensor 54.
 The CPU 20b also retrieves a basic ignition timing based on a predefined
 map (characteristic) stored in the memory means 20c using the detected
 engine speed NE and the manifold absolute pressure PBA (an engine load
 parameter) as address data, adjusts the basic ignition timing based on the
 engine coolant temperature TW and further adjusts (retards) the basic
 ignition timing if engine knock has been detected.
 The CPU 20b also determines the quantity of fuel injection in terms of
 injector open time and drives the fuel injectors 22 through the output
 circuit 20d and a drive circuit (not shown).
 A radiator 60 in the engine cooling system is connected to the engine 10.
 FIG. 2 is an explanatory side sectional view showing the details of the
 radiator 60.
 The radiator 60 is connected to the engine unit 10a through an inlet pipe
 (communicating passage) 62. A thermostat 64 is fitted in the inlet pipe
 62.
 The radiator 60 has an upper tank 66 at the top, a lower tank 68 at the
 bottom, and a honeycomb core 70 accommodated in the intervening space. The
 inlet pipe 62 is connected to the upper tank 66 and an outlet pipe 74 is
 connected to the lower tank 68. A water pump 72 pressurizes coolant in the
 coolant passage of the engine unit 10a so as to circulate it through the
 inlet pipe 62, the upper tank 66, the core 70, the outlet pipe 74 and back
 to the coolant passage of the engine unit 10a.
 As indicated by an arrow in FIG. 2, the core 70 is cooled by air flowing in
 from the direction of vehicle travel. A forced flow of cooling air is
 further produced by a fan 76 located behind the radiator.
 The thermostat 64 is a shut-off valve operated by means of a bimetallic
 strip. At engine starting, when the coolant temperature is low, the
 thermostat 64 closes the inlet pipe 62 to prevent coolant from flowing
 into the radiator 60. Then, as the coolant temperature rises, it
 progressively opens the inlet pipe 62 so that the coolant flows in contact
 with the core 70 to be cooled and is then returned to the engine coolant
 passage.
 As explained further later, the CPU 20b uses the aforesaid sensor outputs
 to estimate the temperature of the coolant in this arrangement or
 configuration and, based on the result, determines whether the thermostat
 64 has malfunctioned.
 This malfunction detection or discrimination will now be explained with
 reference to the flow chart of FIG. 3. The illustrated program is executed
 at prescribed intervals of, for example, 2 sec.
 First, in S10, it is checked whether the engine 10 is in starting mode.
 This discrimination or determination is made by first checking whether the
 starter motor (not shown) is operating and, if it is not, then checking
 whether the engine speed NE is has reached the cranking speed. If the
 result of either check is affirmative (Yes), it is determined that the
 engine 10 is in starting mode.
 When the result in S10 is Yes, next, in S12, the values of the totalized
 engine load for coolant temperature estimation TITTL, the totalized
 cooling loss CLTTL, the post-engine-starting counter ctTRM (for clocking
 time elapsed after engine starting), and the totalized vehicle speed
 VPSTTL are set to zero and the estimated coolant temperature CTW is set to
 (overwritten with) the value of an engine-start-time estimated coolant
 temperature TWINIT. These parameters will be explained later.
 When the result in S10 is No, it is checked in S14 whether the bit of a
 flag F_MONTRM is set to 1.
 The bit of this flag being set to 1 means that conditions for execution of
 thermostat malfunction detection or discrimination are established. This
 flag bit is set by checking whether conditions for execution of thermostat
 malfunction detection are established in a separate routine.
 FIG. 4 is a flow chart showing the routine for determining whether
 conditions for execution of thermostat malfunction detection are
 established. This routine is executed once every prescribed crank angle.
 In S100, it is checked whether the engine 10 is in starting mode. The
 method described regarding S10 of FIG. 3 is used.
 When the result in S100 is Yes, it is checked in S102 whether the air
 temperature (intake air temperature) TA detected by the air temperature
 sensor 30 is equal to or higher than a prescribed value TATHERML (e.g.,
 -7.degree. C.) and lower than a prescribed value TATHERMH (e.g.,
 50.degree. C.), and whether the coolant temperature TW detected by the
 coolant temperature sensor 32 is equal to or higher than a prescribed
 value TWTHERML (e.g., -7.degree. C.) and lower than a prescribed value
 TWTHERMH (e.g., 50.degree. C.).
 When the result in S102 is Yes, then, in S104, the difference between the
 detected coolant temperature TW and air temperature TA is calculated and
 it is checked whether the calculated difference is less than a prescribed
 value DTTHERM (e.g., 10.degree. C.).
 When the result in S104 is Yes, then, in S106, the detected coolant
 temperature TW is used to retrieve a coolant temperature estimation
 engine-start-time coolant temperature correction value KDCTW (explained
 later) from a table compiled based on the characteristic (curve) shown in
 FIG. 5.
 Next, in S108, the engine-start-time detected air temperature TAINIT is
 overwritten with the air temperature TA and the engine-start-time detected
 coolant temperature TWINIT is overwritten with the coolant temperature TW.
 Next, in S110, it is checked whether the engine-start-time detected air
 temperature TAINIT is lower than the engine-start-time detected coolant
 temperature TWINIT. When the result is Yes, CTAOS is overwritten with
 TAINIT in S112. When the result is No, CTAOS is overwritten with TWINIT in
 S114.
 CTAOS is the corrected engine-start-time air temperature. By these steps,
 the value of the engine-start-tine air temperature is corrected to the
 lower of the engine-start-time detected coolant temperature TWINIT and the
 engine-start-time detected air temperature TAINIT.
 Next, in S116, the bit of the flag F_MONTRM is set to 1 to indicate that
 conditions for execution of thermostat malfunction detection or
 discrimination are established.
 When the result in S102 or S104 is No, the bit of the flag F_MONTRM is
 reset to 0 in step S118 to indicate that conditions for execution of
 thermostat malfunction detection or discrimination are not established.
 When the result in S100 is No, then, in S120, the difference between the
 air temperature TA and the engine-start-time detected air temperature
 TAINIT is calculated and it is checked whether the calculated difference
 is less than a prescribed value DTATHERM, i.e., whether the decrease in
 the air temperature is large.
 When the result in S120 is Yes, the bit of the flag F_MONTRM is reset to 0
 in S122 to indicate that conditions for execution of thermostat
 malfunction detection or discrimination are not established. If the result
 is No, S122 is skipped.
 As explained further later, in this embodiment thermostat malfunction is
 discriminated based on the relationship between the detected coolant
 temperature and the estimated coolant temperature, and since the estimated
 coolant temperature is calculated from the engine-start-time detected
 coolant temperature, conditions for execution of thermostat malfunction
 detection are defined as being established when the engine 10 has cooled
 to around the air temperature and change in the air temperature is small.
 In other words, the conditions are defined as being established when the
 air temperature and the coolant temperature detected at the time of engine
 starting are within prescribed ranges (S102) and the detected air
 temperature does not exceed the detected coolant temperature by more than
 a prescribed value (S104). Therefore, when the decrease in the detected
 air temperature after starting is large (S120), it is found that the
 conditions are not established because not enough time has passed since
 the vehicle was parked or because the drop in the air temperature was
 large.
 The detection of thermostat malfunction of this embodiment will now be
 explained. The estimated coolant temperature CTW is calculated from the
 temperature condition and operating condition at engine starting (S32 in
 FIG. 3). When the estimated coolant temperature CTW has reached (i.e., is
 greater than) the judge malfunction value CTWJUD but the detected coolant
 temperature TW has not reached (i.e., is lower than) the judge normal
 value TWJUD, the thermostat 64 is discriminated to have malfunctioned
 (S300 to S308 in FIG. 13).
 In S32, the estimated coolant temperature CTW is calculated as:
 Estimated coolant temperature CTW=Engine-start-time detected coolant
 temperature TWINIT (S108 in FIG. 4)+Coolant temperature estimation basic
 value DDCTW (S30 in FIG. 3).times.Coolant temperature estimation
 engine-start-time coolant temperature correction value KDCTW (S106 in FIG.
 4).
 The coolant temperature estimation basic value DDCTW increases in
 proportion to an increase of the thermal load parameter contributing to
 coolant temperature rise (totalized engine load for coolant temperature
 estimation TITTL; S28 in FIG. 3 and S200 to S212 in FIG. 9). Based on the
 results of their studies, the inventors found that the thermal load
 parameter can be calculated from the totalized engine load TIMTTL and the
 totalized cooling loss CLTTL (cooling loss owing to passenger compartment
 heater and wind). (See S26 in FIG. 3.)
 The explanation of FIG. 3 will be continued. In S14, the bit of the flag
 determined in the subroutine of FIG. 4 is checked. When the result is
 affirmative (Yes), i.e., when it has been found that conditions for
 execution of thermostat malfunction detection or discrimination are
 established, then, in S16, a difference DCTW is calculated from the
 estimated coolant temperature in the preceding cycle CTW(k-1) and the
 corrected engine-start-time air temperature CTAOS (the lower of the
 engine-start-time detected coolant temperature and the engine-start-time
 detected air temperature, as determined in S110 to S114).
 In this specification and the drawings, the notation (k) indicates a
 sampling number in a discrete system, i.e., the interval of one activation
 cycle of the routine of FIG. 3. The notation (k-1) indicates that the
 value is that in the preceding cycle. (In the interest of simpler
 notation, (k) is not affixed to current cycle values.)
 Next, in S18, the difference DCTW is used to retrieve the heater cooling
 loss HTCL from a table compiled based on the characteristic (curve) shown
 in FIG. 6. By "heater cooling loss" is meant the loss occurring when
 high-temperature coolant is used to heat the passenger compartment.
 The heater cooling loss HTCL increases in proportion to increase of the
 difference DCTW between the estimated coolant temperature and the air
 temperature (lower of the detected coolant temperature and the detected
 air temperature). It is expressed as a value corresponding to the fuel
 injection period (quantity of fuel injection) per unit time.
 Next, in S20, the difference DCTW is used to retrieve the wind cooling loss
 WDCL from a table compiled based on the characteristic (curve) shown in
 FIG. 7.
 For any given wind speed, the wind cooling loss WDCL also increases in
 proportion to increase of the difference DCTW. It is also expressed as a
 value corresponding to the fuel injection period (quantity of fuel
 injection) per unit time.
 Next, in S22, a wind speed WDSINIT (fixed value) for a time of strong wind
 is added to the vehicle speed VPS detected by the vehicle speed sensor 54
 to calculate an estimated relative wind speed WDS.
 Next, in S24, the estimated relative wind speed WDS is used to retrieve a
 wind-speed correction value KVWD from a table compiled based on the
 characteristic (curve) shown in FIG. 8.
 Next, in S26, the totalized cooling loss CLTTL is calculated.
 Specifically, the product of the wind cooling loss WDCL and the wind-speed
 correction value KVWD is added to the calculated heater cooling loss HTCL,
 the result is added to (used to update) the preceding-cycle totalized
 cooling loss CLTTL(k-1), and the sum is defined as the current-cycle
 totalized cooling loss CLTTL.
 Next, in S28, the totalized engine load for coolant temperature estimation
 TITTL is calculated.
 This is calculated, as will be described later, based on the totalized
 engine load TIMTTL etc. The totalized engine load TIMTTL is calculated
 using the routine shown in FIG. 9, which is executed at a certain crank
 angle such as TDC.
 First, in S200, the technique explained with reference to S10 is used to
 check whether the engine 10 is in starting mode. When the result is No, it
 is checked in S202 whether the bit of the thermostat malfunction detection
 conditions established flag F_MONTRM is set to 1, i.e., whether conditions
 for execution of thermostat malfunction detection or discrimination are
 established.
 When the result in S202 is Yes, it is checked in S204 whether the bit of a
 flag F_FC is set to 1, i.e., whether fuel cutoff in effect. When the
 result is No, then, in S206, the detected engine speed NE is used to
 retrieve an engine speed correction value KNETIM from a table compiled
 based on the characteristic (curve) shown in FIG. 10.
 Next, in S208, the detected manifold absolute pressure PBA is used to
 retrieve a load correction value KPBTIM from a table compiled based on the
 characteristic (curve) shown in FIG. 11, whereafter the totalized engine
 load TIMTTL is calculated in S210.
 Specifically, the product of a multiplication correction term KPA, the
 calculated engine speed correction value KNETIM, and the load correction
 value KPBTIM and a basic fuel injection period (quantity of fuel
 injection) TIM, is added to (used to update) the preceding totalized
 engine load TIMTTL(k-1), and the sum is defined as the totalized engine
 load TIMTTL.
 When the result in S200 is Yes or the result in S202 is No, accurate
 calculation of the totalized engine load is difficult, so the value of the
 totalized engine load is set to zero in S212. When the result in S204 is
 Yes, the remaining steps are skipped because fuel is not being injected.
 The explanation of FIG. 3 will be continued. In S28, the totalized engine
 load for coolant temperature estimation TITTL is calculated based on the
 so-calculated totalized engine load.
 Specifically, the totalized cooling loss CLTTL is subtracted from the
 calculated totalized engine load TIMTTL and the difference is defined as
 the totalized engine load for coolant temperature estimation TITTL.
 Next, in S30, the calculated totalized engine load for coolant temperature
 estimation TITTL is used to retrieve the coolant temperature estimation
 basic value DDCTW from a table compiled based on the characteristic
 (curve) shown in FIG. 12, whereafter the final estimated coolant
 temperature CTW is determined in S32.
 Specifically, the product of coolant temperature estimation basic value
 DDCTW and the coolant temperature estimation engine-start-time coolant
 temperature correction value KDCTW (calculated in S106 of FIG. 4) is added
 to the engine-start-time detected coolant temperature TWINIT, and the sum
 is defined as the estimated coolant temperature CTW.
 The value of the post-engine-starting counter ctTRM is then incremented by
 1 in S34. Next, in S36, the totalized vehicle speed VPSTTL is updated by
 adding the vehicle speed VPS detected in the current cycle thereto.
 Next, in S38, a post-engine-starting average vehicle speed VPSAVE is
 calculated by dividing the updated totalized vehicle speed VPSTTL by the
 post-engine-starting counter ctTRM.
 Next, S40, it is discriminated or detected whether the thermostat 64 is
 normal or malfunctions (faulty).
 The subroutine for this is shown in FIG. 13.
 First, in S300, it is checked whether the coolant temperature TW detected
 by the coolant temperature sensor 32 is equal to or greater than the judge
 normal value TWJUD (e.g., 70.degree. C.). When the result is Yes, it is
 checked in S302 whether the average vehicle speed VPSAVE exceeds a
 reference value VPSAVTRM (e.g., 30 km/h). When the result is Yes, the
 thermostat 64 is determined to be normal in S304.
 When the result in S300 is No (in other words when TW is lower than TWJUD),
 it is checked in S306 whether the estimated coolant temperature CTW is
 greater than the judge malfunction value CTWJUD (e.g., 75.degree. C.).
 When the result in S306 is Yes, the thermostat 64 is determined to be
 faulty in S308, i.e., to have experienced a malfunction such as excessive
 leakage, too low valve opening temperature or open-state sticking.
 When the result in S306 is No, it is checked in S310 whether the difference
 obtained by subtracting the detected coolant temperature TW from the
 estimated coolant temperature CTW is equal to or less than a second judge
 malfunction value DCTWJUD (e.g., 15.degree. C.). When the result is No,
 the thermostat is determined to be faulty in S308.
 Thus, when the estimated coolant temperature reaches the judge malfunction
 value before the detected coolant temperature reaches the judge normal
 value, thermostat malfunction is determined. On the other hand, when the
 estimated coolant temperature is much higher than the detected coolant
 temperature, thermostat malfunction is determined even before the
 estimated coolant temperature reaches the prescribed value.
 When the thermostat is found to be normal, the bit of the flag F_MONTRM is
 reset to 0 in S312.
 When the result in S302 is No, i.e., when it is found that the radiator 60
 is exposed to little wind owing to low vehicle speed (average vehicle
 speed), the discrimination or detection is delayed. This is to avoid a
 discrimination or detection error that might arise because under such a
 condition the coolant temperature rises rapidly even if the thermostat 64
 is not actually faulty.
 Specifically, when the result is No in S302, a separate subroutine not
 shown in the drawings is activated in S314. In this subroutine, the fan 76
 is forcibly operated for a prescribed time period to cool the radiator 60
 and then, after elapse of the prescribed time period, the coolant
 temperature TW and the judge normal value TWJUD are compared, whereafter
 the thermostat is determined to be normal when the coolant temperature TW
 is equal to or higher than the judge normal value TWJUD and is judged to
 be faulty when the coolant temperature TW is lower than the judge normal
 value TWJUD.
 As explained in the foregoing, this embodiment is configured so that
 malfunction of the radiator is concluded to have occurred also when the
 estimated coolant temperature reaches the judge malfunction value before
 the detected coolant temperature reaches the judge normal value (or even
 before the estimated coolant temperature reaches the prescribed value if
 the estimated coolant temperature is much higher than the detected coolant
 temperature).
 Specifically, an estimated coolant temperature is calculated from the
 coolant temperature at engine starting and thermal load parameters
 simulating radiator operation or approximating the radiator behavior, the
 actual coolant temperature is detected, the estimated and actual coolant
 temperatures are compared with predetermined values, and presence/absence
 of thermostat malfunction is determined by discriminating the temperature
 rise characteristics of the two. Thermostat malfunctions such as excessive
 leakage, too low valve opening temperature and open-state sticking can
 therefore be detected with high accuracy and good response.
 This embodiment is thus configured to have a system for detecting
 malfunction of a radiator connected to an internal combustion engine (10)
 through a communicating passage (the inlet pipe 62) for cooling a coolant
 of the engine, the radiator having a thermostat (64) which closes or opens
 the communicating passage, comprising: engine operating condition
 detecting means (the crank angle sensor 38, the manifold absolute pressure
 sensor 26, the coolant temperature sensor 32, the intake air temperature
 sensor 30, the vehicle speed sensor 54, the ECU 20) for detecting
 operating conditions of the engine (i.e., the engine speed NE, the
 manifold pressure PBA, the intake air temperature TA, the vehicle speed
 VPS) including at least a coolant temperature (TW); engine-start-time
 coolant temperature determining means (ECU 20, S108-S114) for determining
 an engine-start-time coolant temperature (TWINIT, CTAOS) at starting of
 the engine based on at least the detected coolant temperature (TW);
 thermal load parameter determining means (ECU 20, S26-S28, S200-S212) for
 determining a parameter indicative of thermal load contributing to a rise
 of the coolant temperature (TITTL) based on the detected engine operating
 conditions; estimated coolant temperature calculating means (ECU 20,
 S30-S32, S200-S212 (for calculating an estimated coolant temperature (CTW)
 based on at least the determined engine-start-time coolant temperature and
 the determined parameter indicative of thermal load; and radiator
 malfunction discriminating means (ECU 20, S40, S300-S308) for comparing
 the detected coolant temperature (TW) and the calculated estimated coolant
 temperature (CTW) with predetermined values (TWJUD, CTWJUD) respectively
 and for discriminating whether the radiator (60, i.e., the thermostat 64)
 malfunctions based results of comparison.
 In the system, the thermal load parameter determining means determines the
 parameter indicative of thermal load based on at least a totalized engine
 load (TIMTTL).
 In the system, the thermal load parameter determining means determines the
 totalized engine load based on at least a quantity of fuel injection to be
 supplied to the engine (TIM.times.KPA), a speed of the engine (NE) and a
 load of the engine (PBA).
 In the system, the thermal load parameter determining means determines a
 wind cooling loss (CLTTL) and adjusts the totalized engine load by the
 determined totalized cooling loss.
 In the system, the thermal load parameter determining means determines the
 wind cooling loss based on at least air temperature (TA, i.e., CTAOS) and
 a speed of a vehicle on which the engine is mounted (VPS).
 In the system, the radiator malfunction discriminating means includes;
 detected coolant temperature comparing means for comparing the detected
 coolant temperature (TW) with a first one of the predetermined values
 (TWJUD); and calculated estimated coolant temperature comparing means for
 comparing the calculated estimated temperature (CTW) with a second one of
 the predetermined values (CTWJUD); and discriminates that the radiator
 malfunctions when the detected coolant temperature is determined to be
 lower than the first one of the predetermined values (S300) and the
 calculated estimated temperature is determined to be greater than the
 second one of the predetermined values (S306).
 In the system, the radiator malfunction discriminating means includes;
 difference calculating means (S310) for calculating a difference (CTW-TW)
 between the detected coolant temperature and the calculated estimated
 coolant temperature and difference comparing means for comparing the
 difference with a third one of the predetermined values (DCTWJUD); and
 discriminates that the radiator malfunctions when the detected coolant
 temperature is determined to be lower than the first one of the
 predetermined values (S300 and the calculated estimated temperature is
 determined to be not greater than the second one of the predetermined
 values (S306), but the difference is determined to be greater than the
 third one of the predetermined values (S310).
 The system further includes: malfunction discrimination condition detecting
 means (ECU 20, S14, S100-S122) for detecting whether conditions for
 execution of radiator malfunction discrimination are established; wherein
 the radiator malfunction discriminating means discriminates whether the
 radiator malfunctions when the conditions for execution of radiator
 malfunction discrimination are established.
 In the system, the malfunction discrimination condition detecting means
 detects that the conditions for execution of radiator malfunction
 discrimination are established when the engine is determined to be cooled
 to around an air temperature and change in the air temperature is small.
 In the system, the radiator malfunction discriminating means discriminates
 whether the thermostat (64) of the radiator malfunctions.
 Although the invention has thus been shown and described with reference to
 specific embodiments, it should be noted that the invention is in no way
 limited to the details of the described arrangements but changes and
 modifications may be made without departing from the scope of the
 invention which is defined by the appended claims.