Method of determining failure of sensors in a control device for an internal combustion engine

A method of determining failure of sensors in a control device for an internal combustion engine which comprises steps of setting a predetermined time corresponding to a warmup time of the sensors after an electric power source is activated; determining whether the predetermined time elapses from when the electric power source is activated; determining whether output signals of the sensors are in allowable ranges when the predetermined time elapses; determining the sensors as normal when the output signals of the sensors are in the allowable ranges; and determining the sensors as abnormal when the output signals of the sensors are out of the allowable ranges.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of determining the failure of sensors in 
a control device for an internal combustion engine to prevent an erroneous 
determination when an electric power is activated. 
2. Discussion of the Background 
FIG. 2 is a constitution diagram showing a general control device for an 
internal combustion engine. 
In this drawing, a numeral 1 designates a cylinder which drives an internal 
combustion engine, 2, an electromagnetic drive type injector (fuel 
injection valve) which supplies fuel, 3, an intake pipe which supplies air 
to the cylinder 1, 4, a hot wire type air-flow sensor which detects an air 
quantity sucked into the cylinder 1, 5, and intake air throttle valve 
which controls the air quantity sucked into the cylinder 1, 6, and exhaust 
pipe which discharges exhaust gas from the cylinder 1, and 7, a water 
temperature sensor which detects a temperature of the cylinder 8 based on 
that of cooling water. 
The injector 2, the air flow sensor 4, the intake air throttle valve 5, and 
the water temperature sensor 7, are respectively disposed at the intake 
pipe 3. The injector 2 and the water temperature sensor 7 are disposed 
adjacent to the cylinder 1. 
A numeral 8 designates a control device which controls, for instance, fuel 
injection quantity or the like based on signals from various sensors, 
which is equipped with an input interface 80 which receives signals, a 
microprocessor 81 which performs a calculation of input signals, a ROM 82 
which stores a calculation program or the like, a RAM 83 which temporarily 
memorizes data in calculation, and an output interface 84 which outputs a 
control signal B or the like based on a calculation result. 
A numeral 9 is an ignition device which ignites the cylinder 1 at a 
predetermined rotation angle, which also functions as a rotation sensor of 
the internal combustion engine, and which outputs an electric pulse 
corresponding to a rotation signal at every predetermined rotation angle 
as a pulse signal P. 
The opening degree signal C from the intake air throttle valve 5 and the 
temperature signal D from the water temperature sensor 7 are inputted to 
the control device 8 with output signals from other sensors, not shown. 
Next, explanation will be given to a control operation of fuel injection of 
the control device for an internal combustion shown in FIG. 2. 
In the hot wire type air-flow sensor 4, a hot wire is installed at an 
intake air passage, a supply current thereof is controlled by a feed back 
control so that a hot wire temperature is maintained at a constant value 
(for instance, 160.degree. C.), and the supply current value to the hot 
wire is converted to an electric voltage and is outputted as an air 
quantity signal A. Accordingly, when air flow quantity is large and the 
cooling effect thereof is large, since the supply current is large, the 
level of the air quantity signal A is also enhanced. On the contrary, when 
the air flow quantity is small and the cooling effect thereof is small, 
since the supply current is small, the level of the air quantity signal A 
is diminished. 
The control device 8 calculates a fuel quantity to be supplied to the 
cylinder 1 based on the air quantity signal A from the air flow sensor 4. 
At this time, a rotation pulse frequency number, that is, a rotation 
number of the internal combustion engine, is obtained based on the pulse 
signal P from the ignition device, and the fuel quantity per revolution is 
calculated. Furthermore, synchronizing with the pulse signal P, the 
control signal B having a required pulse width corresponding to a required 
fuel quantity, is applied to the injector 2. 
Furthermore, a required air fuel ratio of the internal combustion engine, 
is necessary to be set to a rich side when the temperature of the cylinder 
1 is low. The control device 8 corrects to increase the pulse width of the 
control signal B which is applied to the injector 2, based on the 
temperature signal D from the water temperature sensor 7. Furthermore, the 
control device 8 detects an acceleration state of the internal combustion 
engine based on the opening degree signal C from the intake air throttle 
valve 5, and corrects to increase the air fuel ratio to the rich side in 
the acceleration time. 
Furthermore, the control device 8 always checks whether signals from 
various sensors are in allowable ranges. The control device 8 determines 
that the sensors are out of order in case that those signals are out of 
the allowable ranges, and stops the usage of the abnormal sensors. For 
instance, an upper limit value and a lower limit value of each sensor are 
predetermined. A failure of a sensor is detected when the value of the 
output signal of the sensor is equal to, or more than the upper limit 
value, and when the value is equal to or less than lower limit value. 
However, a value of an output signal of each sensor may not be stabilized 
just after an electric power source is activated and may show an abnormal 
value. Therefore the control device 8 may perform an erroneous 
determination of a failure of the sensor. Particularly, in case of the 
air-flow sensor 4, the hot wire is cool just after the electric power 
source is activated. The hot wire must be heated by the supply current. 
Before such warmup the air quantity signal A assumes an abnormal value 
above a normal one and the possibility of an erroneous determination of 
the failure of the sensor is increased. When an erroneous determination is 
made that a sensor is in failure, the control device 8 is in the state in 
which a normally functional sensor is not utilized, which lowers the 
reliability of the control device 8. 
In the conventional method of determining a failure of a sensor in a 
control device for an internal engine, as stated above, the value of the 
output signal of the sensor is compared with an allowable range for 
determining a failure of the sensor. Therefore, there is a possibility of 
an erroneous determination of the failure by an abnormal operation of 
sensors when an electric power source is activated, which impairs the 
reliability of control. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of determining 
failure of sensors in a control device for an internal combustion engine 
capable of avoiding a failure determination based on an abnormal output 
signal of the sensor when an electric power source is activated, 
preventing an erroneous determination of the failure of the sensor, and 
enhancing a reliability in the detection of failure and the control 
thereof. 
According to an aspect of the present invention, there is provided a method 
of determining failure of sensors in a control device for an internal 
combustion engine which comprises steps of: 
setting a predetermined time corresponding to a rise time of the sensors 
when an electric power source is activated; 
determining whether the predetermined time elapses from when the electric 
power source is activated; 
determining whether output signals of the sensors are in allowable ranges 
when the predetermined time elapses; 
determining the sensors as normal when the output signals of the sensors 
are in the allowable ranges; and 
determining the sensors as abnormal when the output signals of the sensors 
are out of the allowable ranges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Explanation will be given to an embodiment of the present invention 
referring to the drawings. 
FIG. 1 is a flow chart showing an embodiment of a failure determination 
routine according to the present invention. The device to which this 
invention is applied, is as shown in FIG. 2. A part of a calculation 
program stored in the ROM 82 of the control device 8 is changed. First of 
all, a predetermined time TF is set to a counter CF which corresponds to 
the rise or warmup time of a sensor after the electric power source is 
activated (step S0). For instance, in case of the air-flow 4 the 
predetermined time TF is set to a time in which the output signal, that 
is, the air quantity signal A is stabilized (about 3 seconds). 
In this case, the counter CF is a down counter. The failure determining 
routine is a timer routine which is iterated at every constant time. 
Accordingly, the counter CF is decremented at every performing of the 
routine, and becomes zero after the predetermined time TF. 
Next, a sensor output signal (for instance, the air quantity signal A) is 
AD converted and stored in the RAM 83 (step S1). Furthermore, depending on 
whether the value of the counter CF is 0, a determination is made whether 
the predetermined time TF has elapsed from when the electric power source 
is activated (step S2). 
When the counter CF is 0, a determination is made that the predetermined 
time TF has elapsed after the electric power source is activated, and a 
determination is made whether the output signal of the sensor (sensor 
value) has a value in an allowable range. 
Accordingly, the operation determines whether the sensor value is equal to 
or more than a lower limit value L, (step S3). When the sensor value is 
equal to, or more than the lower limit value L, the operation determines 
whether the sensor value is equal to, or lower than an upper limit value H 
(step S4). When the sensor value is equal to, or lower than the upper 
limit value H, the operation regards that the sensor value is in the 
allowable range, and determines the sensor as normal (step S5). 
On the contrary, when the sensor value is lower than the lower limit value 
L, or higher than the upper limit value H, the operation regards that the 
sensor value is out of the range, and determines the sensor as abnormal 
(step S6). 
After the normality or the abnormality of the sensor is determined, the 
operation returns to the reading step S1 of the output signal of the 
sensor. Since the counter CF is 0 already, the operation goes from the 
determining step S2 of the counter CF, to the determining steps S3 and S4 
of the sensor, by which the determination of the existence of the failure 
of the sensor, is iterated. These failure determining steps S1 and S3 to 
S6, in normal time, are the same as in the conventional case. 
On the contrary, when a determination is made that the counter CF is not 0 
in step S2, since the predetermined time of TF has not elapsed from when 
the electric power source was activated, the counter CF is decremented 
(step S7). After this step, the operation bypasses through the determining 
routine of the sensor, and returns to the step S1. Accordingly, the 
failure determining routine is iterated, until the predetermined time TF, 
and the value of the counter CF, become 0. 
By this method, the failure determining treatment of the sensor is stopped 
during the predetermined time of TF just after the electric power source 
is activated, and the erroneous determination of the failure of the sensor 
is prevented. Accordingly, a sound or reliable sensor is always used in 
the control, which enhances not only the reliability of the failure 
detection but the reliability of the control. 
Furthermore, in the above embodiment, a case is shown in which an erroneous 
determination of the hot wire type air-flow sensor 4, is prevented. 
However, this invention is applicable to the other sensors with the same 
effect, when the operation of the sensor just after the electric power 
source is activated, is unstable. 
As stated above, according to the present invention, a step of setting a 
predetermined time corresponding to a rise time of a sensor when an 
electric power source is activated, a step of determining whether the 
predetermined time has elapsed after the electric power source is 
activated, a step of determining whether an output signal of the sensor is 
in an allowable range in case that the predetermined time has elapsed, a 
step of determining the sensor as normal in case that the output signal is 
in the allowable range, and a step of determining the sensor as abnormal 
in case that the output signal is out of the allowable range, are 
provided. In this invention, the failure determining treatment of the 
sensor is stopped during a certain time just after the electric power 
source is activated, and a failure determination based on an abnormal 
output signal of the sensor when the electric power source is activated, 
is avoided. Therefore, the erroneous determination of the failure of the 
sensor is prevented, and this invention has an effect in which a method of 
determining failure of the sensor in the control device for an internal 
combustion engine which enhances the reliability of the failure detection 
and the reliability of the control, is provided.