JPS6016756Y2 - Failure alarm device for air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to a device for detecting and warning abnormalities in the control device.

Recently, as a method for reducing harmful exhaust gases from automobiles, a feedback type air-fuel ratio control device that controls the air-fuel ratio based on information regarding engine exhaust gas components has been proposed.

In this method, for example, as shown in FIG. A deviation signal between the output signal and the reference value Vs (for example, a value corresponding to the set air-fuel ratio) is detected by the deviation detection circuit 4 (differential amplifier, comparator, etc.), and the control circuit 5 generates a control signal according to the deviation signal. (For example, a proportional signal proportional to the deviation signal, an integral signal obtained by integrating the deviation signal, or a signal obtained by adding these two signals, etc.) is generated, and the fuel metering device 6 (carburizer fuel injection device, etc.) is controlled based on the control signal. By additionally controlling the fuel supply amount and air supply amount (the fuel metering device is of course also controlled by other factors such as the operator operating the throttle valve), the mixture supplied to the engine body 1 is The air-fuel ratio is maintained at a set air-fuel ratio.

If this set air-fuel ratio is set, for example, to the optimum operating point of the exhaust purification device 7 (catalyst device, reactor device, etc.), harmful components in the exhaust gas can be efficiently reduced under various operating conditions.

For example, as an exhaust purification device, CO and HC oxidation and NOx
When using a three-way catalytic device that simultaneously performs the reduction of the air-fuel ratio, the set air-fuel ratio is set to a value close to the stoichiometric air-fuel ratio.

In the above control device, if the device fails, it will have a negative effect on exhaust purification, fuel efficiency, drivability, etc., so it is very important to detect the failure and issue an alarm.

A method for determining whether the control device is malfunctioning is to detect a control signal, a deviation signal, an exhaust sensor output signal, etc., and output the signal, as shown in, for example, Japanese Unexamined Patent Publication No. 10842 of Showa 4CR. One possibility is to check the status (no change for a long time, no signal at all, etc.).

However, the characteristics of the exhaust sensor used in the above air-fuel ratio control device usually change depending on the temperature.

For example, in the case of a commonly used zirconia oxygen concentration meter, its electrical equivalent circuit is as shown in Figure 2, consisting of a battery whose electromotive force e changes depending on the oxygen concentration, and a resistance value ρ which changes depending on the sensor temperature. It is expressed as a series circuit with a changing internal resistance.

Since the value of the internal resistance ρ has a temperature characteristic as shown in FIG. 3, the internal resistance ρ becomes large at low temperatures, and almost no electromotive force e can be extracted.

For this reason, even if the control device itself is normal, if the temperature is low, the electromotive force cannot be extracted from the exhaust sensor, so there is a problem that it may be incorrectly determined to be malfunctioning.

In addition, in engines, fuel correction is generally performed during operating conditions that affect the air-fuel ratio feedback control system based on the output of the exhaust sensor, such as sudden acceleration or sudden decrease. There is a risk of erroneously determining that the control device is malfunctioning.

In order to solve these problems, if the above-mentioned judgment is made in consideration of the above-mentioned operating conditions and the temperature of the exhaust sensor, accurate failure judgment can be made.

However, fuel correction conditions outside the feedback control system, such as sudden acceleration and deceleration, have already been detected in some way when controlling the engine, or can be easily detected, and the detected signal may be used as one of the conditions for the above determination, but at the same time it is necessary to consider the temperature condition of the exhaust sensor.

However, in order to take this temperature condition into consideration, a new temperature sensor is installed near the exhaust sensor, and the temperature is detected when the internal resistance ρ of the exhaust sensor becomes small and the electromotive force e can be sufficiently extracted. However, there are major problems such as maintenance problems such as heat resistance and durability of the temperature sensor, and high production costs, making it difficult to put it into practical use.

In order to solve all of the above-mentioned problems, the present invention is intended to solve all of the above problems. For example, when the output state of the control signal continues to be biased to one side, in addition to the above-mentioned operating state, the throttle valve of the engine remains open more than the predetermined degree for a predetermined period of time. An object of the present invention is to provide a device that issues a failure alarm for an air-fuel ratio control device when the air-fuel ratio control device is maintained.

However, it is also possible to issue a failure alarm even when the throttle valve of the engine changes instantaneously, for example when overtaking.

The present invention will be explained below based on the drawings.

FIG. 4 shows an embodiment of the present invention.

In Fig. 4, 8 is a throttle valve opening signal generator, which outputs a high level signal when the opening is above a certain level, and a low level signal when the opening is above a certain level. (It may be possible to output a low-level signal in the above manner).

The signal is input to an integral discriminator 9, where the direction of integration is changed depending on the low level signal and high level signal, the signal is integrated, and it is determined whether the integrated value reaches a predetermined value,
For example, if the integrated value is above a predetermined value, a high level signal is output, and if it is below a predetermined value, a low level signal is output.

That is, when the integral discriminator 9 outputs a high-level signal, it indicates that the throttle valve opening is small and the temperature of the exhaust sensor 3 is low, and when the integral discriminator 9 outputs a low-level signal, it indicates that the throttle valve opening is small and the temperature of the exhaust sensor 3 is low. When the throttle valve opening is small, the time when the throttle valve opening is large is longer than the time when the opening is small, and the exhaust sensor 3
This indicates that the temperature is higher than a predetermined value.

The throttle valve opening signal generator 8 and the integral discriminator 9 form a throttle valve opening state discriminator.

Reference numeral 10 denotes an engine control state discriminator that detects abnormalities in the feedback type air-fuel ratio control device itself, such as during sudden acceleration (when increasing fuel), when fuel is cut, or when the feedback control system is set to open loop control. It detects a control state of the engine that affects the control system by forcibly changing the amount of fuel supplied to the engine regardless of a failure, and outputs a signal.

For example, it is configured to output a high level signal when the above control state is detected.

Further, 11 is an exhaust signal which inputs the output signal Se of the exhaust sensor 3, deviation detection circuit 4 or control circuit 5 explained in FIG. 1, and outputs a signal when the signal does not change continuously for a predetermined period of time. The discriminator outputs, for example, a low level signal when the signal Se does not continuously change.

Reference numeral 12 denotes an alarm signal generator, into which the output signals of the integral discriminator 9, engine control state discriminator 10 and exhaust signal discriminator 11 are input, and the integral discriminator 9 and engine control state discriminator 10 detect low level signals. and when the exhaust signal discriminator 11 outputs a low level signal, a signal for activating the alarm 13 is output.

In other words, there is a control state in which the throttle valve opening is increased for more time than it is decreased, the temperature of the exhaust sensor exceeds a predetermined value, and the amount of fuel in the engine is forcibly increased or decreased. For example, when the output signal of the exhaust sensor does not change continuously for a predetermined period of time, a signal for activating the alarm 13 is output.

Note that a check device 14 may be provided as shown by the broken line, and a signal may be sent to the alarm signal generator 12 and/or the alarm device 13 when the engine is started to check for abnormalities in the alarm device 13.

FIG. 5 shows a specific embodiment of the present invention, and the same reference numerals as in FIGS. 1 and 4 indicate the same parts.

In FIG. 5, B is a power supply circuit. The throttle valve opening signal generator 8 includes a resistor, a transistor, and a throttle valve that outputs a low-level voltage signal when the opening is above a predetermined opening, and outputs a high-level voltage signal when the opening is below a predetermined opening. Therefore, a high-level voltage signal is output to point P when the throttle valve opening becomes more than a predetermined opening, and a low-level voltage signal is output when the throttle valve opening becomes less than a predetermined opening. Output.

The integral discriminator 9 is composed of a resistor, a diode, a capacitor, and an operational amplifier, and a voltage signal obtained by integrating the high-level and low-level voltage signals of the throttle valve opening signal generator 8 is output at the Q point (operational amplifier OP1 When the output level of the throttle valve opening signal generator input to the 1-Y terminal of the amplifier OP1 is higher than the voltage level applied to the 1-Yo terminal of the amplifier OP1, the output level decreases. When it is small, integrate in the increasing direction).

Note that the output level of the voltage signal has upper and lower limits set by a circuit consisting of resistors R□, R2 and diodes D□, D2.

In addition, 8 points, that is, the output terminal of the operational amplifier OP2 has a voltage level of 1+ higher than the voltage level input to the r-J terminal of the amplifier OP2.
If the voltage level of the Q point input to the Y terminal is large, a high level voltage signal is output, and in the opposite case, a low level voltage signal is output.

Next, the engine control state discriminator 10 includes a fuel increase detection switch 10a that outputs a high level voltage signal when detecting a full fuel increase (full throttle) and a fuel increase detection switch 10a that outputs a high level voltage signal when the feedback control is set to open loop control. It is composed of an open control detection switch 10b and a diode that outputs a high-level voltage signal, and outputs a high-level signal at point T at least when full increase operation or open control operation occurs.

(In this embodiment, the above switches 10a and 10b are used, but a switch that outputs a high-level voltage signal by detecting the fuel cut time may be added.) The exhaust signal discriminator 11 includes a resistor and a diode. , capacitor,
Consists of transistors and operational amplifiers.

U, V, and W in this exhaust signal discriminator 11. The voltage waveform applied to point X is shown in FIG.

In FIG. 6, U represents an output signal when the control circuit 5 of FIG. 1 includes a proportional circuit and an integral circuit.

A dashed-dotted line V' indicates a threshold level for turning on the transistor Tr1, and a dashed-dotted line W' indicates a divided voltage level obtained by dividing the voltage from the power supply B by the resistors B3vR4.

Therefore, when the signal from the control circuit 5 does not continuously change (it always changes when the feedback control system is operating normally), the output signal at point
Conversely, when the signal from the control circuit 5 is continuously changing, it becomes high level.

The alarm signal generator 12 is composed of a resistor, a diode, and an operational amplifier, and at least one of the integral discriminator 9 and the engine control state discriminator 10 input to the 1,000-yield terminal of the operational amplifier OP3 receives a high-level voltage signal. When outputting, the operational amplifier OP3 outputs a high level voltage signal to point E, and the operational amplifier OP outputs a low level voltage signal to point F.

Further, when the integral discriminator 9 and the engine control state discriminator 10 output a low level voltage signal, a low level voltage signal is output at point E.
Outputs a high level voltage signal to point F.

Therefore, when point E and point F are at high level and low level, respectively, diode D3. D becomes conductive, and a signal obtained by dividing the voltage signal at points E and F by resistors R3 and R4 is output at point Y. Conversely, when points E and F become low and high levels, respectively, the diode D3. D becomes non-conductive and Y
The point is no longer affected by the voltage signals at points E and F.

Furthermore, the operational amplifier OP5 and the resistors R5 to R7 constitute a comparator with hysteresis, and the operational amplifier OP5
If the signal at the point If it is larger than the divided voltage, a low level signal is output to point G.

In this circuit, once a high-level signal is output at point G, even if the voltage signal input to the rJ terminal of operational amplifier OP5 rises a little, that is, operational amplifier OP3. Even if OP4 is ON or OFF, the X of exhaust signal discriminator 11
A high level signal is output unless the voltage signal at the point reaches a high level.

That is, it has a hysteresis characteristic. The alarm device 13 is composed of a resistor and a light emitting diode, and the alarm signal generator 1
When 2 outputs a high level voltage signal, the light emitting diode L
Make D emit light.

To briefly summarize the operation above, when the throttle valve maintains a predetermined opening degree or more on average for a predetermined period of time, when the feedback control is not open, and when the fuel is fully increased, the alarm signal generator 12 point becomes low level and point F becomes high level. At this time, if the feedback control system fails and the output signal of the control circuit 5 stops changing, the exhaust signal discriminator 11 outputs a low level signal and the alarm 13 is activated. The light emitting diode LD emits light.

In addition, even if the exhaust signal/compulsion discriminator 11 outputs a low level signal, the above point E will be high if the throttle valve is continuously closed, the feedback control is open, or the fuel is fully increased. level, F point becomes low level, Y point has E point and F point.
Since a voltage signal obtained by dividing the voltage at the point is output, the output of the operational amplifier OP5 is kept at a low level, and the light emitting diode LD of the alarm 13 does not emit light.

Note that a normal lamp or buzzer may be used instead of the light emitting diode.

The check device 14 is composed of a starting switch 14a that outputs a high-level voltage signal when the engine is started (when the key switch is in the starting position), and a diode.
Each time the engine is started, the light emitting diode LD emits light and its function is inspected.

As explained above, according to the present invention, the exhaust sensor output, control signal, etc. do not change continuously for a predetermined period of time or more, the throttle valve opening maintains a predetermined opening or more on average over time, and normal feedback is achieved. Since the configuration is configured to issue a failure alarm when the three conditions that control is being performed are satisfied, there is no need to install a new temperature sensor near the exhaust sensor, and there is no malfunction due to operating conditions. , a failure in the feedback control system can be accurately detected and an alarm can be issued, and the failure can be quickly corrected, allowing the vehicle to be operated in a normal state at all times.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a feedback type air-fuel ratio control device, Figure 2 is an electrical equivalent circuit diagram of an exhaust sensor, Figure 3 is a diagram of the relationship between temperature and internal resistance of the exhaust sensor, and Figure 4 is a diagram of the present invention. FIG. 5 is a specific circuit diagram of the block diagram shown in FIG. 4, and FIG. 6 is an output waveform diagram of FIG. 5. Explanation of symbols: 1... Engine body, 2... Bent exhaust pipe, 3... Exhaust sensor, 4... Deviation detection circuit, 5... Open control circuit, 6 ... Fuel metering device, 7 ... Exhaust purification device, 8 ... Throttle valve opening signal generator, 9 ... Integral discriminator, 10.・
...Engine control state discriminator, 11. Song/exhaust signal discriminator, 12. Song/alarm signal generator, 13.....Alarm device, 14. Song/check device.

Claims (1)

[Scope of utility model registration request] an exhaust sensor that detects the concentration of engine exhaust gas components;
A deviation detection circuit outputs a deviation signal between the output of the exhaust sensor and a reference value, and a control circuit outputs a control signal corresponding to the deviation signal. An air-fuel ratio control device that performs feedback control based on an exhaust signal discriminator that outputs a first signal when the exhaust sensor output, deviation signal, or control signal does not change continuously for a predetermined time or more, and an engine throttle valve. a throttle valve opening state discriminator that outputs a second signal when the throttle valve opening degree is maintained at a predetermined opening degree or more on average for a predetermined period of time;
An engine control state discriminator that detects the control state that changes the fuel supply amount and outputs a third signal separately from the feedback control system, and an exhaust signal discriminator that outputs the first signal and detects the throttle valve opening. A failure alarm device for an air-fuel ratio control device, comprising: a warning device that issues an alarm when a state discriminator outputs a second signal and an engine control state discriminator does not output a third signal.