JPH0356417B2 - - Google Patents

Description

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

2. Description of the Related Art One method of controlling the operating state of an internal combustion engine (hereinafter simply referred to as an engine) of an automobile or the like is to control the amount of fuel injected into the engine. In this system, the absolute pressure P _BA in the intake pipe downstream of the throttle valve is detected by a pressure sensor, and the engine speed is detected by a rotation sensor, the detection output of this sensor is used to determine the basic fuel injection time Ti, and the engine cooling water temperature
Corresponds to the required fuel injection amount by multiplying the above basic fuel injection time Ti by an increase or decrease correction coefficient according to other engine operating parameters such as T _W and intake temperature T _A or transient changes in the engine. The fuel injection time Tout is calculated.

The above-mentioned cooling water temperature T _W and intake air temperature T _A are detected by a temperature sensor such as a thermistor, but in this temperature sensor, the temperature signal is set to be a high voltage at low temperature, and the temperature signal is set to be a high voltage at low temperature. In many cases, a thermistor and a resistor are combined so that the temperature signal saturates in the temperature range. This is because the rate of change of the temperature signal is required to be large in a region where it is desired to precisely control the engine according to the temperature.

In the past, in order to determine whether there was an abnormality in the temperature sensor, a predetermined determination value was set to a value slightly larger than the saturated voltage, and the determination was made at the same time as the engine was started. In this case, a temperature signal larger than the predetermined determination value may be instantaneously output, and an abnormality may be mistakenly recognized at the initial stage of starting the engine.

The present invention has been made to solve these conventional drawbacks, and an object of the present invention is to provide a temperature sensor abnormality determination method that eliminates misidentification at the initial stage of engine startup and can always accurately determine abnormality.

The temperature sensor abnormality determination method according to the present invention is to determine the magnitude of the output value of the temperature sensor and a predetermined discrimination value after a predetermined time has elapsed from the start of the engine, and when the discrimination result is the same for a second predetermined time, Determine it as abnormal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In Fig. 1, reference numeral 1 denotes an air filter, and intake air that has passed through the filter 1 is supplied to the engine 3 through an intake pipe 2, and the amount of air is controlled by a throttle valve 4 provided in the intake pipe 2. adjusted. 5
6 is a throttle opening sensor that is composed of, for example, a potentiometer and generates an output voltage at a level that corresponds to the opening of the throttle valve 4, and 6 is a level that corresponds to the absolute pressure P _BA downstream of the throttle valve 4 in the intake pipe 2. 7 is a cooling water temperature sensor that generates an output voltage at a level corresponding to the cooling water temperature of the engine 3; 8 is a sensor that determines the rotation angle of the crankshaft (not shown) of the engine 3; Center (TDC)
9 is a crank angle sensor that generates a pulse signal (TDC signal) when 11 is an exhaust pipe, and 12 is a three-way catalyst. 13 is an injector, which is an intake valve of engine 3 (not shown)
It is provided in a nearby intake pipe 2 and is configured to inject and supply fuel to the engine 3 in an amount corresponding to the input pulse period. Throttle opening sensor 5, intake absolute pressure sensor 6, cooling water temperature sensor 7, crank angle sensor 8, intake temperature sensor 9, and oxygen concentration sensor 10
Each output voltage is input to the control circuit 14.

The control circuit 14 is composed of a so-called microprocessor such as a microcomputer, and controls the basic fuel injection time according to a predetermined program.
A calculation process is performed for a fuel injection time Tout corresponding to the actual fuel injection amount obtained by multiplying Ti and the basic fuel injection time Ti by an increase or decrease correction coefficient.

FIG. 2 is a block diagram showing a specific configuration of the control circuit 14. In FIG. 2, a control circuit 14 performs digital arithmetic processing according to a program.
It has a CPU (central processing circuit) 15. CPU1
The input/output bus 16 is connected to the input/output bus 1.
Data signals or address signals are input/output to/from the CPU 15 via the CPU 15. The input/output bus is connected to an A/D converter 17, an MPX (multiplexer) 18, a counter 19, a ROM (read-on memory) 20, a RAM (random access memory) 21, and a drive circuit 22 for the injector 13. has been done. MPX18 is a CPU
This is a switch that selectively relays and supplies any one of the output signals of the sensors 5 to 7, 9, and 10 to the A/D converter 17 via the level conversion circuit 23 in response to a command from the sensor 15. The counter 19 measures the generation cycle of output pulses from the crank angle sensor 8 supplied via the waveform shaping circuit 24 .

The cooling water temperature sensor 7 consists of a thermistor 7a that is supplied with power from the power supply +Vcc, and is connected in series with a resistor _R1 between the power supply +Vcc and ground so that the temperature signal is saturated in the low temperature range in which the engine 3 is operated. , outputs a temperature signal from the connection point between thermistor 7a and resistor _R1 . Similarly, the intake temperature sensor 9
It consists of a thermistor 9a and a resistor _R2 connected in series between the power supply +Vcc and ground. Thermistor 7
Although a and 9a are resistive elements (PTC: POSISTOR) having a positive temperature coefficient, they may have a negative temperature coefficient if the connection with the resistor is reversed.

Next, the procedure of the method for determining an abnormality in a temperature sensor according to the present invention will be explained, for example, in the case of the intake temperature sensor 9, according to the flowchart shown in FIG.

First, in the initialization (step 1) of the control circuit 14, a predetermined temperature _TAO is set as the temperature _TA of the intake air in the intake pipe 2, and then the temperature TAO of the intake air in the intake pipe 2 is set.
It is determined whether a first predetermined time _t1 has elapsed since the start of the engine (step 2). If the predetermined time _t1 has elapsed, the output value V _TA of the intake temperature sensor 9 is read (step 3), and the magnitude of the output value V _TA of the intake temperature sensor 9 and the predetermined judgment value V _TAH is determined (step 3). 4). Here, the first predetermined time t ₁ is set to a time sufficient to warm up the engine 3 such that the output value V _TA of the intake air temperature sensor 9 falls below the determination value V _TAH , for example, about 10 minutes.

When the output value V _TA of the intake air temperature sensor 9 is larger than the determination value V _TAH , it is determined whether the state of V _TA >T _TAH continues beyond a second predetermined time t ₂ (step 5). , if it continues beyond time _t2 , it is determined as an abnormality and an alarm is issued and stored (step 6).
Thereafter, an F/S (fail safe) action is taken (step 7). On the other hand, if the duration of the state of V _TA > T _TAH is within the second predetermined time t ₂ , the previously read value is set as the output value V _TA of the intake air temperature sensor 9 (step 8).

In step 4, the output value of the intake air temperature sensor 9
After determining that V _TA is less than or equal to the discrimination value V _TAH , or after completing step 8, the process returns to step 3 through step 9, in which all other tasks such as abnormality determination of other sensors are performed, and the above series of operations is performed. is repeated in synchronization with the TDC signal.

Note that in the above embodiment, the intake air temperature sensor 9
Although the abnormality determination of the cooling water temperature sensor 7 has been described, the abnormality determination of the cooling water temperature sensor 7 is also performed in exactly the same manner. Further, the temperature sensor is not limited to the cooling water temperature sensor 7 and the intake temperature sensor 9, but any sensor that detects the temperature related to the engine 3 may be used.

As explained above, according to the present invention, after a predetermined time period has elapsed since the start of the engine to allow the engine to warm up sufficiently, the output value of the temperature sensor and the predetermined judgment value are judged in magnitude, and the judgment result is used as the second judgment value. Since it is determined that it is abnormal when it is the same for a predetermined period of time,
In addition to eliminating misidentification during the initial stage of engine startup,
It is possible to avoid erroneous temperature abnormality detection that occurs instantaneously, and accurate abnormality determination can be made at all times.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an electronically controlled fuel supply system to which the temperature sensor abnormality determination method according to the present invention is applied, FIG. 2 is a block diagram showing a specific configuration of the control circuit in FIG. 1, and FIG. The figure is a flowchart showing the procedure of a method for determining abnormality in a temperature sensor according to the present invention. Explanation of symbols of main parts, 2... Intake pipe, 3...
Engine, 5... Throttle opening sensor, 6...
Intake absolute pressure sensor, 7...Cooling water temperature sensor, 8...
...Crank angle sensor, 9...Intake temperature sensor.

Claims (1)

[Scope of Claims] 1. A method for determining an abnormality in a temperature sensor used to control an internal combustion engine, which comprises determining whether the output value of the temperature sensor and a predetermined determination value are large or small after a first predetermined time has elapsed from the start of the internal combustion engine. Abnormality determination of a temperature sensor, characterized in that when the output value of the temperature sensor continuously exists on one side of the predetermined determination value exceeds a second predetermined time, it is determined to be abnormal. Method. 2. The temperature sensor abnormality determination method according to claim 1, wherein the temperature sensor has a characteristic that its output is saturated in a low temperature range in which the internal combustion engine is operated. 3. The method for determining an abnormality in a temperature sensor according to claim 1 or 2, characterized in that the value of the temperature signal is set to a predetermined value within the first predetermined time from the start of the internal combustion engine. 4. If the time during which the output value of the temperature sensor continues to be on one side with respect to the predetermined discrimination value is within the second predetermined time, the value of the temperature signal is the output value of the temperature sensor read last time. A method for determining an abnormality in a temperature sensor according to claim 1, 2, or 3, characterized in that: