JPS63243437A - Trouble discriminating method for cooling water temperature sensor in internal combustion engine air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To prevent the misdiscrimination from occurring, by discriminating whether an output level of a water temperature sensor is out of the range of both upper and lower limit values or not, and making a control circuit perform trouble discrimination of the water temperature sensor, in case a fact that suction air temperature is other than a high suction air temperature state of more than the specified temperature is detected. CONSTITUTION:When an engine 5 is driven, a control circuit 20 controls a linear type solenoid valve 9 on the basis of each output of various driving state detecting devices including a water temperature sensor 12, and it also controls an air-fuel ratio of mixture. In this case, at a water temperature sensor trouble discriminating routine to be processed by the control circuit 20, first suction air temperature TA by a suction air temperature sensor 13 is compared with a high temperature state discriminating temperature TA1, and when TA<TA1 is the case, cooling water temperature TW by the water temperature sensor 12 is compared with upper limit temperature TWH and lower limit temperature TWL. And, when a state of TW>TWH, TW<TWL is continued as long as the specified time, it is so discriminated that the water temperature sensor 12 is out of order. On the other hand, when TA>=TA1 is the case, the said trouble discrimination is prohibited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining abnormality in an internal combustion engine cooling water temperature sensor.

Kudan Nii I In order to purify the exhaust gas of in-vehicle internal combustion engines, improve fuel efficiency, etc., the concentration of exhaust components such as oxygen concentration in the exhaust gas is detected by an exhaust component concentration sensor, and the amount of air in the mixture supplied to the engine is measured. For example, an air-fuel ratio control device that feedback-controls the air-fuel ratio of a supplied air-fuel mixture by adjusting fuel according to a value detected by an exhaust component concentration sensor was developed in the 1970s.
It is known from Japanese Patent No. 5-3533.

In such an air-fuel ratio control device, a plurality of engine operating parameters other than the exhaust component concentration are detected by various sensors. One of the sensors is a water temperature sensor that detects the internal combustion engine cooling water temperature. For example, since the engine combustion state is unstable before the warm-up of the internal combustion engine is completed, air-fuel ratio oven loop control is performed that performs air-fuel ratio feedback control, so the completion of warm-up is detected from the output level of the water temperature sensor. Fuel ratio feedback control has started.

Incidentally, an abnormal state may occur in which the water temperature sensor cannot accurately detect the cooling water temperature due to deterioration or failure of the water temperature sensor. Inconveniences arise, such as vacuum-fuel ratio oven loop control of the water temperature sensor or air-fuel ratio feedback control when air-fuel ratio oven loop control should be performed. Therefore, a method is generally used in which it is determined that the water temperature sensor is abnormal when the output level of the water temperature sensor becomes a value outside a predetermined normal operating range (for example, -30° C. to 120° C.).

However, for example, in an idling state immediately after a long period of high-speed driving, the internal combustion engine is in a high temperature state, and in such a state, even if the water temperature sensor is normal, the output level from the water temperature sensor that is above the normal operating range may be exceeded. Therefore, it may be erroneously determined that the water temperature sensor is in an abnormal state.

Therefore, it is an object of the present invention to provide a method for determining an abnormality in an internal combustion engine cooling water temperature sensor, which prevents erroneous determination of abnormality in the water temperature sensor when the engine is in a high temperature state.

The abnormality determination method for an internal combustion engine cooling water temperature sensor according to the present invention detects that the intake temperature of the internal combustion engine is not in a high intake temperature state equal to or higher than a predetermined temperature, and when the intake temperature is not in the high intake temperature state, the output level of the water wetness sensor is The water temperature sensor is characterized in that it is determined that the water temperature sensor is abnormal when it is detected that the water temperature sensor is outside the range of the upper limit value and the lower limit value.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, practical examples of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an air-fuel ratio control device to which the abnormality determination method of the present invention is applied. In this air-fuel ratio control device, the intake manifold 4 downstream of the throttle valve 3 of the carburetor 1 and the vicinity of the air discharge port of the air cleaner 2 are connected to the intake secondary air supply passage 8.
communicated by. A so-called linear solenoid valve 9 is provided in the intake secondary air supply passage 8 . The opening degree of the N11 valve 9 changes in proportion to the current value supplied to the solenoid 9a.

A negative pressure detection boat 6 is provided on the inner wall surface of the carburetor 1 near the throttle valve 3. The negative pressure detection boat 6 is located upstream of the throttle valve 3 when the opening of the throttle valve 3 is less than a predetermined opening, and is located downstream of the throttle valve 3 when the opening is larger than the predetermined opening. Negative pressure Pc in negative pressure detection boat 6 is supplied to negative pressure switch 7 via negative pressure passage 6a. The negative pressure switch 7 is provided to detect the closed state of the throttle valve 3, and is turned on when the negative pressure in the negative pressure detection boat 6 is, for example, 30a+mH or less.

On the other hand, the absolute pressure sensor 10 is installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure PEA in the intake manifold 4, and the crank angle sensor 11 is connected to the crankshaft of the internal combustion engine (hereinafter simply referred to as the engine) 5. (
The cooling water temperature sensor 12 generates an output at a level corresponding to the cooling water ITw of the engine 5, and the intake air temperature sensor 13 generates a pulse synchronized with the rotation of the engine 5 (not shown), for example, a TDC pulse. Generates an output voltage according to
The oxygen concentration sensor 14 is provided as an exhaust component concentration sensor in the exhaust manifold 15 of the engine 5, and generates an output voltage according to the oxygen concentration in the exhaust gas. Oxygen concentration sensor 1
4 is, for example, λ where the output voltage suddenly changes at the stoichiometric air-fuel ratio.
=1 type sensor. A catalytic converter 34 is installed in the exhaust manifold 15 downstream of the oxygen concentration sensor 14 in order to promote the reduction of harmful components in the exhaust gas.
is provided. Negative pressure switch 7, absolute pressure sensor 10
, the crank angle sensor 11, the water temperature sensor 12, the intake temperature sensor 13, and the oxygen concentration sensor 14.
0. The control circuit 20 further includes a vehicle speed sensor 16 that generates an output at a level corresponding to the speed V of the vehicle, an atmospheric pressure sensor 17 that generates an output according to the atmospheric pressure PA, and a clutch pedal (not shown) that is depressed. and a clutch switch 18 that is turned off. The negative pressure switch 7 and the clutch switch 18 generate a low level output when turned off, and generate a high level output of voltage 8 when turned on.

The control circuit 20 includes an absolute pressure sensor 10, as shown in FIG.
Water temperature sensor 12, intake temperature sensor 13, oxygen concentration sensor 1
4. A level conversion circuit 21 that converts each output level of the vehicle speed sensor 16 and the atmospheric pressure sensor 17; and a level conversion circuit 21.
A multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the multiplexer 22, and an A/D converter 23 that converts the signal output from the multiplexer 22 into a digital signal.
A waveform shaping circuit 24 shapes the output signal of the crank angle sensor 11, and the generation interval of the output pulses of the waveform shaping circuit 24 is measured by the number of clock pulses output from a clock pulse generation circuit (not shown) to rotate the engine. Number N
A counter 25 that outputs e data, a level conversion circuit 26 that converts the output levels of the negative pressure switch 7 and clutch switch 18, a digital input camosulator 27 that converts the converted output into digital data, and an opening drive for the solenoid valve 9. a driving circuit 28 and a light emitting diode 19 for alarm.
It consists of a drive circuit 33 for lighting and driving, a CPU (central processing unit) 29 for performing digital calculations according to a program, a ROM 30 in which various processing programs and data are written in advance, and a RAM 31. Solenoid valve 9
The solenoid 9a is connected in series with a drive transistor and an N-flow detection resistor (both not shown) of the drive circuit 28, and a power supply voltage is supplied across the series circuit. Multiplexer 22, A/D converter 23, counter 25, digital input camosulator 27, drive circuits 28, 33, C
PU29, ROM30 and RAM31 are input/output bus 32
are connected to each other by. Note that the CPU 29 has a built-in timer A (not shown), and the RAM 31 is nonvolatile.

In this configuration, the A/D converter 23 inputs the absolute pressure Pa A % in the intake manifold 4, the cooling water temperature TW, the intake air temperature TA, the oxygen concentration in the exhaust gas, the vehicle speed V, and the atmospheric pressure P.
Alternatively, the information A is sent to the counter 25, information representing the engine speed Ne, and the digital input camosulator 27 sends on/off information of the negative pressure switch 7 and clutch switch 18 to the CPU 29 via the input/output bus 32. Supplied. When the ignition switch (not shown) is turned on, the CPU 29 repeatedly processes one air-fuel ratio control routine of the program in response to clock pulses, reads the above-mentioned information, and performs air-fuel ratio feedback based on the information. Determine whether to control or air/fuel ratio oven loop 61110. In the case of air-fuel ratio feedback control, for example, an air-fuel ratio control reference value is determined from the engine speed Ne and absolute pressure PBA, and the air-fuel ratio control reference value is corrected according to the output of the oxygen concentration sensor 14 and the electromagnetic valve 9 The air-fuel ratio control output value AFOUT representing the current value supplied to the solenoid 9a is calculated as data, and the calculated output value AFOUT is supplied to the drive circuit 28.

The drive circuit 28 performs closed loop control on the current value flowing through the solenoid 9a so that the current value flowing through the solenoid 9a becomes the output value AFOUT. The solenoid valve 9 opens in proportion to the current value flowing through the solenoid 9a, so the output is 1i! 1AFo
An amount of intake secondary air corresponding to UV is supplied into the intake manifold 4, and the air-fuel ratio of the supplied air-fuel mixture is feedback-controlled toward the stoichiometric air-fuel ratio. In addition, in the case of open loop control, the output value AFOU is set regardless of the output of the oxygen concentration sensor 14, so the opening degree of the solenoid valve 9 is determined according to engine parameters other than the oxygen concentration in the exhaust gas. , or the valve is closed and the supply of intake secondary air is stopped.

Next, the procedure of the method for determining an abnormality in a cooling water temperature sensor for an internal combustion engine according to the present invention will be explained according to the water temperature sensor abnormality determining routine shown in FIG. 3 as an operation flow diagram of the CPU 29. Note that this abnormality determination routine is processed every time the above-described air-fuel ratio control routine is processed or by interruption at every predetermined time.

In this procedure, first, it is determined whether the abnormality determination flag nFS is equal to 6 (step 51). flag 77
FS is a flag to indicate whether various sensors including the water wetness sensor 12 are normal or abnormal, and in the case of 72FS-6, it indicates that the water temperature sensor 12 has been determined to be abnormal in this water temperature sensor abnormality determination routine. . Step 51
If nFs is 46, the water temperature sensor 12 is not determined to be abnormal after the flag nFs is initialized, so the intake air 21TA is read and the intake air ITA is smaller than the high temperature state determination temperature TAI (for example, 60°C). It is determined whether or not (step 52). If TA<TAI, it is not a high intake temperature state, so the coolant temperature Tw is read and it is determined whether or not the coolant ITw is higher than the upper limit temperature Tw+ (for example, 140°C) (step 53), Tw≦T.
If w+-+, it is determined whether the cooling water temperature Tw is lower than the lower limit temperature TwL (for example, -60° C.) (step 54). If Tw≧TWL, it is determined that the water temperature sensor 12 is operating normally, and a predetermined time t^ (for example, 30 SeC) is set in the timer A to start down measurement (step 55). On the other hand, Tw>Tw+1 or Tw
If TwL, the water temperature Tw is outside the normal operating range detected by the water temperature sensor 12, so it is determined whether the measured value TTW of timer A has reached 0 (step 56). After the temperature outside the normal operating range of the water temperature sensor 12 is detected until this state continues for a predetermined time tA,
That is, if TTW>O, the water temperature sensor 12 is not considered to be abnormal because it is possible that the temperature momentarily became outside the normal operating range due to the influence of noise or the like. However, if TT w-0, the state remains for a predetermined time tA after the temperature outside the normal operating range of the water temperature sensor 12 is detected.
Since the above continues, it is determined that the water temperature sensor 12 is abnormal and the abnormality determination flag nFs is set equal to 6 (step 5).
7).

Therefore, when the flag 77FS is set to 6, in the next processing cycle, after the determination in step 51, a lighting command is issued to the drive circuit 33 to light the light emitting diode 19, and sensor abnormalities such as prohibition of air-fuel ratio feedback control are detected. Processing is performed (step 58).

On the other hand, in step 52, if T^≧TA+, it is a high intake temperature state, so the temperature of the engine 5 is actually higher than the normal operating range of the water temperature sensor 12, that is, the upper limit temperature Tv.
z-+ and the water temperature sensor 12 is normal, its output may be outside the normal operating range. Step 55 is executed to end the current water wetness sensor abnormality determination routine processing.

As described above, in the internal combustion engine cooling water temperature sensor abnormality determination method of the present invention, the abnormality determination of the water temperature sensor is prohibited when the engine intake temperature is high, regardless of the output level of the water temperature sensor. Even if the water temperature sensor output exceeds the normal operating range depending on the state, it is possible to prevent the water temperature sensor from erroneously determining that it is abnormal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an outline of an air-fuel ratio control device to which the abnormality determination method of the present invention is applied, FIG. 2 is a block diagram showing a specific configuration of a control circuit in the device in FIG. 1, and FIG. FIG. 3 is an operation flow diagram showing the procedure of the abnormality determination method of the present invention. Explanation of symbols for main parts 1... Carburetor 2... Air cleaner 3... Throttle valve 4... Intake manifold 7... Negative pressure Switch 8...Intake secondary air supply passage 9...Linear type solenoid valve 10...Absolute pressure sensor 11...Crank angle sensor 12... ... Cooling water temperature sensor 14 ... Oxygen concentration sensor 15 ... Exhaust manifold 16 ... Vehicle speed sensor 17 ... Atmospheric pressure sensor

Claims (1)

[Claims] A method for determining an abnormality in a cooling water temperature sensor of an air-fuel ratio control device that controls an air-fuel ratio of a supplied air-fuel mixture based on engine operating parameters including a cooling water temperature of the internal combustion engine, the method comprising: When detecting that the intake temperature is other than the high intake temperature state and detecting that the output level of the water temperature sensor is outside the range of the upper limit value and the lower limit value when the intake temperature state is other than the high intake temperature state, it is determined that the water temperature sensor is abnormal. An abnormality determination method characterized by: