JP2943573B2 - Air-fuel ratio sensor temperature control circuit failure detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio sensor for detecting an air-fuel ratio of an internal combustion engine, and more particularly, to a failure related to a temperature control (temperature control) circuit including a heater of an air-fuel ratio sensor with a heater. The present invention relates to a failure detection device for detecting a failure.

[0002]

2. Description of the Related Art Conventionally, in the air-fuel ratio control of an internal combustion engine, an air-fuel ratio sensor provided in an exhaust passage is used. Then, based on the air-fuel ratio detected by the air-fuel ratio sensor, the actual fuel-air ratio is controlled to the target air-fuel ratio by feedback-controlling the target fuel amount to be supplied to the internal combustion engine. Here, a heater-equipped air-fuel ratio sensor including a heater is used in order to stably maintain the temperature of a sensor element constituting the air-fuel ratio sensor at a predetermined activation temperature. When the air-fuel ratio sensor with a heater is used, the heater is controlled by a temperature control (temperature control) circuit because the temperature of the exhaust gas slightly varies depending on the operating conditions of the internal combustion engine and the position of the exhaust passage. Thus, the temperature of the air-fuel ratio sensor is appropriately controlled according to the conditions.

[0003] In the air-fuel ratio sensor with a heater in the past, there was no way to detect a failure such as disconnection in a temperature control circuit including a heater and a wire harness. Therefore, when a failure occurs in the temperature control circuit, the air-fuel ratio sensor detects the air-fuel ratio on the assumption that the temperature adjustment of the air-fuel ratio sensor is appropriately performed. As a result, the actual air-fuel ratio to be obtained by the air-fuel ratio control may deviate from the target air-fuel ratio, which may deteriorate the exhaust emission.

Accordingly, Japanese Utility Model Laid-Open Publication No. Sho 62-44272 proposes an apparatus for detecting a disconnection of a temperature control circuit including a heater with respect to an air-fuel ratio sensor with a heater. In this device, when the vehicle is provided with a failure diagnosis system, the presence or absence of a failure such as a disconnection is set as one of the diagnostic items, and the driver is promptly warned of the diagnosis result.

That is, in the conventional temperature control circuit, a heater and its drive circuit are connected in series to a power supply to form a heater energizing circuit. Then, the temperature of the air-fuel ratio sensor is adjusted by opening and closing the heater energizing circuit according to the operating conditions of the internal combustion engine and the difference in the position of the air-fuel ratio sensor in the exhaust passage. In such a heater energizing circuit, a failure such as disconnection is detected. Specifically, a resistor is connected in series in the middle of a heater energizing circuit including a heater, a voltage drop by the resistor is compared with a reference voltage, and when there is no voltage drop, a voltage of a predetermined level is output. . Then, when the condition for energizing the heater is satisfied and the output of the voltage drop in the temperature control circuit is at a predetermined level, a signal indicating that the failure is due to disconnection or the like is output.

[0006]

However, the above-mentioned prior art is based on the premise that the system has only one air-fuel ratio sensor with heater in the exhaust passage. Therefore, when a plurality of heater-equipped air-fuel ratio sensors are provided in the exhaust passage and a system for individually controlling the temperature of each heater is configured, failure of each heater energizing circuit including each heater according to the number of heaters may occur. A circuit for detecting each is required. For example, when the internal combustion engine is a V-type engine, or when the system is a double air-fuel ratio sensor in which an air-fuel ratio sensor with a heater is provided upstream and downstream of the catalytic converter, respectively, the air-fuel ratio sensor with a heater is used. Accordingly, a plurality of fault detection circuits are required, which not only complicates the circuit configuration but also increases the number of components.

The present invention has been made in view of the above-mentioned circumstances, and a first object of the present invention is to detect a failure of each heater of a plurality of air-fuel ratio sensors with a heater using one circuit. An object of the present invention is to provide a failure detection device for an air-fuel ratio sensor temperature control circuit that is made possible. A second object of the present invention is to provide a failure detection device for an air-fuel ratio sensor temperature control circuit, which can specify which of a plurality of heaters has a failure.

[0008]

Means for Solving the Problems In order to achieve the first object, in the first invention, as shown in FIG.
A plurality of air-fuel ratio sensors M3 provided in the exhaust passage M2 of the internal combustion engine M1 and having temperature characteristics, and a plurality of energized heat-generation type sensors provided in each of the air-fuel ratio sensors M3 for heating the respective air-fuel ratio sensors M3. A heater M4 for controlling the energization of each heater M4 in accordance with the operating conditions of the internal combustion engine M1 and the temperature conditions of the exhaust passage M2.
In the air-fuel ratio sensor temperature adjustment circuit M5 configured to adjust the heat generation amount of each of the air-fuel ratio sensors M3, a current value flowing through each heater M4 or a voltage drop in each heater M4 is compared with a reference value. For this purpose, a comparator M having one end of all heaters M4 connected in parallel to one input terminal
6, an energized state determining means M7 for judging whether or not all heaters M4 are energized, and when the energized state determining means M7 determines that all heaters M4 are energized, It is intended to include a failure determination means M8 for determining a failure of each heater M4 based on the output result of the comparator M6 obtained by comparing the current value or the voltage drop with the reference value.

In order to achieve the second object, according to a second aspect of the present invention, as shown in FIG. 2, in the apparatus for detecting a temperature of an air-fuel ratio sensor according to the first aspect of the present invention, a fault judging means M8 is provided. When the failure of each heater M4 is determined, the non-energization of one heater M4 and the energization of all the remaining heaters M4 performed simultaneously with the non-energization are sequentially and forcibly performed on all the heaters M4. Power supply means M9, and when the heaters M4 are successively de-energized and energized by the forced power supply means M9, all the heaters M based on the output result of the comparator M6.
4 includes a failure specifying means M10 for specifying a heater M4 in which a failure has occurred.

[0010]

According to the structure of the first aspect of the invention, as shown in FIG. 1, the air-fuel ratio sensor M3 is controlled by the air-fuel ratio sensor temperature adjusting circuit M5 in accordance with the operating condition of the internal combustion engine and the temperature condition of the exhaust passage. By controlling the energization of each of the heaters M4 provided in, the amount of heat generated by each of the heaters M4 is adjusted, and the temperature of each of the air-fuel ratio sensors M4 is adjusted.

Here, when the energization state judgment means M7 judges that all the heaters M4 are energized, the current value flowing through all the heaters M4 or the voltage drop in all the heaters M4 is compared with the comparator. In M6, it is compared with a reference value. Then, the failure determination means M8 determines the failure of each heater M4 based on the output result of the comparator M6 at that time. For example, if any one of the heaters M4 is broken due to disconnection or the like, the current value or the voltage drop to be compared with the reference value in the comparator M6 changes, and the failure determination unit M8 determines that the failure has occurred. Is determined.

Therefore, it is not necessary to provide a failure determination circuit for each of the plurality of heaters M4. According to the configuration of the second aspect of the present invention, as shown in FIG. 2, when the failure determination means M8 determines that each heater M4 has failed, the forced energization means M9 de-energizes one heater M4, The energization to all the remaining heaters M4 performed simultaneously with the non-energization is performed for all the heaters M4.
4 forcibly. When the heaters M4 are sequentially de-energized and energized, the fault specifying means M10 specifies the heater M4 having a fault among all the heaters M4 based on the output result of the comparator M6. Is done. For example, when the output result of the comparator M6 is at a low level, one non-energized heater M4 is identified as having failed due to disconnection or the like.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a failure detecting device for an air-fuel ratio sensor temperature control circuit according to the first and second aspects of the present invention will be described in detail with reference to FIGS.

FIG. 3 is a schematic configuration diagram showing a gasoline engine system in this embodiment. In an engine body 1 constituting a V-type engine as an internal combustion engine mounted on an automobile, each cylinder is formed by being divided into a left bank 2 and a right bank 3. The left and right banks 2 and 3 are connected to intake manifolds 4L and 4R and exhaust manifolds 5L and 5R, respectively.

Each of the intake manifolds 4L and 4R is connected to a common surge tank 6 and a common intake pipe 7.
An air cleaner 8 is provided on the inlet side of the air cleaner. The intake manifolds 4L and 4R, the surge tank 6, the intake pipe 7, and the like constitute an intake passage. Then, the air taken into the intake pipe 7 from the outside from the air cleaner 8 passes through the surge tank 6 to each of the intake manifolds 4L, 4L.
Guided to R. The air guided to the intake manifolds 4L, 4R is supplied to the combustion chambers 2 in the left and right banks 2, 3 at the timing when the intake valves 9L, 9R are opened.
a, 3a.

In the middle of the intake pipe 7, each of the combustion chambers 2a, 3a
Is provided with a throttle valve 10 for adjusting the intake air amount Q introduced into the engine. The throttle valve 10 is opened and closed in conjunction with operation of an accelerator pedal (not shown).
Each intake manifold 4L, 4R is provided with a fuel injection injector 11L, 11R corresponding to each cylinder. The left and right banks 2 and 3 are provided with spark plugs 12L and 12R respectively corresponding to the cylinders. As is well known, each of the injectors 11L and 11R is opened by energization, and when the valve is opened, fuel pumped from a fuel tank (not shown) through a fuel pump is injected into each of the intake manifolds 4L and 4R. Is done. Further, the fuel injected from each of the injectors 11L and 11R becomes a mixture with air and is introduced into each of the combustion chambers 2a and 3a. Further, in each of the combustion chambers 2a and 3a, the introduced air-fuel mixture is exploded and burned by the operation of the ignition plugs 12L and 12R.

On the other hand, each of the exhaust manifolds 5L and 5R constitutes a part of an exhaust passage, and each of the exhaust manifolds 5L and 5R constitutes an exhaust passage.
At L and 5R, at the timing when the exhaust valves 13L and 13R are opened, the exhaust gas after combustion is led out from the combustion chambers 2a and 3a. Then, in order to purify the derived exhaust gas and discharge it to the atmosphere, each exhaust manifold 5L, 5L
Three-way catalytic converters 14L and 14R are connected to R, respectively. Also, each three-way catalytic converter 14L, 1
Exhaust pipes 15L and 15R are respectively connected to the downstream side of 4R, and one common exhaust pipe 16 is connected to the downstream side of each exhaust pipe 15L and 15R. As is well known, each of the three-way catalytic converters 14L and 14R oxidizes hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas and purifies exhaust gas by reducing nitrogen oxide (NOx). .

Each spark plug 12 of each of the left and right banks 2 and 3
L, 12R have separate distributors 17L, 1
The ignition signal distributed at 7R is applied. Each distributor 17L, 17R is a separate igniter 18
L, 18R to the crankshaft 1
9 and is distributed to each of the spark plugs 12L and 12R in synchronization with the rotation of No. 9. The ignition timing of each of the ignition plugs 12L, 12R is determined by the high voltage output timing from each of the igniters 18L, 18R.

The engine body 1 is provided with a rotation speed sensor 31 for detecting the rotation speed of the crankshaft 19 as the engine rotation speed NE. A first cylinder discriminating sensor 32 and a second cylinder discriminating sensor for detecting the cylinder angle and the crank angle reference positions G1 and G2 such as the top dead center position are provided in the left and right banks 2 and 3 of the engine body 1, respectively. Each of the sensors 33 is provided. The cylinder discriminating sensors 32 and 33 detect the crank angle reference positions G1 and G2 based on the rotation of the camshafts 20L and 20R interlocked with the crankshaft 19.

An air flow meter 34 is mounted downstream of the air cleaner 8. The air flow meter 34 detects the amount of intake air Q taken into each of the combustion chambers 2a and 3a of the engine body 1 through the intake pipe 7 and the like. In the vicinity of the air flow meter 34, an intake air temperature sensor 3
5 is attached. The intake air temperature sensor 35 detects the temperature of air taken into the intake pipe 7, that is, the intake air temperature THA. A throttle sensor 36 is provided near the throttle valve 10. The throttle sensor 36 detects the opening of the throttle valve 10, that is, the throttle opening TA. In addition, a water temperature sensor 37 is attached to the engine body 1. The coolant temperature sensor 37 detects the temperature of the coolant in the engine body 1, that is, the coolant temperature THW.

On the other hand, a first air-fuel ratio sensor 38 and a second air-fuel ratio sensor 39 are provided in the middle of the exhaust passage and upstream and downstream of the three-way catalytic converter 14L, respectively. Similarly, a third air-fuel ratio sensor 40 and a fourth air-fuel ratio sensor 4 are provided in the middle of the exhaust passage and upstream and downstream of the other three-way catalytic converter 14R.
1 are provided. Each of these air-fuel ratio sensors 3
From 8 to 41, the oxygen concentration Ox in the exhaust gas is detected. Each of the air-fuel ratio sensors 38 to 41 includes a sensor element having a temperature characteristic. The first heater 38a and the second heater 38a for heating the sensor element for controlling the temperature of the sensor element. The heater 39a, the third heater 40a, and the fourth heater 41a are provided for each of the air-fuel ratio sensors 38 to 41, respectively.

The transmission 21 drivingly connected to the engine body 1 is provided with a vehicle speed sensor 42. The vehicle speed sensor 42 detects the speed of the vehicle, that is, the vehicle speed SPD.

In addition, the intake passage of this embodiment is provided with a bypass passage 22 which bypasses the throttle valve 10 and communicates the intake pipe 7 on the upstream side of the throttle valve and the surge tank 6 on the downstream side thereof. I have. This bypass passage 22
Is provided with a well-known linear solenoid type idle speed control valve (ISCV) 23. The opening of the ISCV 23 is controlled to stabilize the idling of the engine when the throttle valve 10 is fully closed when the engine is idling. Therefore, by controlling the opening of the ISCV 23 during idling, that is, by performing the ISC control,
The amount of air flowing through the bypass passage 23 is adjusted, and the amount of intake air Q to each of the combustion chambers 2a and 3a in each of the left and right banks is adjusted.

On the other hand, in this embodiment, a warning lamp 24 is provided on an instrument panel of a driver seat (not shown), and one lead of the warning lamp 24 is connected to a plus terminal of a battery 25. The warning lamp 24 is turned on to notify the driver when a failure related to the heaters 38a to 41a of the air-fuel ratio sensors 38 to 41 is detected.

In this embodiment, each injector 11L,
11R, each igniter 18L, 18R, ISCV23,
The warning lamp 24 and each heater 38a, 39a, 40a,
41a are electronic control units (hereinafter simply referred to as “ECUs”).
). For that, EC
U51 includes injectors 11L and 11R, igniters 18L and 18R, ISCV 23, warning lamp 24, battery 25, and heaters 38a, 39a, 40a and 41.
a are electrically connected to each other. Also, the ECU 51
Includes a rotation speed sensor 31 and respective cylinder discrimination sensors 32 and 3.
3, air flow meter 34, intake air temperature sensor 35, throttle sensor 36, water temperature sensor 37, air-fuel ratio sensors 38 to
41 and the vehicle speed sensor 42 are electrically connected to each other. Then, the ECU 51 determines that each of the sensors 31 to 3
3, 35 to 42 and various calculation and judgment processes are performed based on various signals from the air flow meter 34. As a result, the injectors 11L, 11R, the igniters 18L, 18R, the ISCV 23, the warning lamp 24, and the heaters 38a, 39a, 40a, 41a are suitably controlled.

FIG. 4 is a block diagram showing the electrical configuration and the like of the ECU 51. The ECU 51 is a central processing unit (CPU)
52, a read-only memory (ROM) 53 in which a predetermined control program and the like are stored in advance, and a random access memory (RAM) 5 for temporarily storing the calculation results and the like of the CPU 52
4. Backup RA for storing pre-stored data
M55 and so on. The ECU 51 is a logical operation circuit in which these units 52 to 55, an analog / digital converter (A / D converter) 56 with a multiplexer, an input / output unit 57 with a buffer, and the like are connected by a bus 58. Is configured as

The A / D converter 56 is connected to the air flow meter 34, the intake air temperature sensor 35, the water temperature sensor 37, the air-fuel ratio sensors 38 to 41, the battery 25, and the like. Further, a current detection circuit 59 described later is connected to the A / D converter 56. The input / output unit 57 includes the above-described rotation speed sensor 31 and each of the cylinder discrimination sensors 3.
2, 33, a throttle sensor 36, a vehicle speed sensor 42, and the like are connected to each other. The ISCV 23, the injectors 11L and 11R,
The igniters 18L and 18R, the warning lamp 24 and the like are connected respectively. Further, the above-described heaters 38 a to 41 a are connected to the input / output unit 57 via the drive circuit 60. In addition, the input / output unit 57 is connected to a voltage drop detection circuit 61 described later.

Then, the CPU 52 controls each of the sensors 31 to 3.
Various signals from 3, 35 to 42 and the air flow meter 34 are read as input values via the A / D converter 56 and the input / output device 57. Similarly, the CPU 52 reads a signal from the current detection circuit 59 via the A / D converter 56 as an input value. Further, the CPU 52 includes a voltage drop detection circuit 6.
1 is read as an input value via the input / output device 57. Further, based on these input values, the CPU 52 outputs the ISCV 23 and the injectors 11 via the input / output unit 57.
L, 11R, the igniters 18L, 18R, the warning lamp 24 and the like are suitably controlled. Similarly, the CPU 52 suitably controls energization to the heaters 38a to 41a via the input / output unit 57 and the drive circuit 60 based on the input value.

Here, the above-described current detection circuit 59, drive circuit 60, and voltage drop detection circuit 61 are included in the ECU 51, and the ECU 51 including these circuits and the like adjusts the temperature of each heater 38a to 41a ( Temperature control circuit) and its failure detection device.

That is, FIG. 5 is a connection diagram showing the relationship between each heater energizing circuit including each heater 38a to 41a and its drive circuit 60, current detection circuit 59, voltage drop detection circuit 61, and the like. In the figure, each heater 38a
To 41a are connected in parallel to the above-described battery 25 via an input terminal 62. And each heater 3
8a to 41a, the driving circuit 60,
The current detection circuit 59 and the voltage drop detection circuit 61 are connected.

The drive circuit 60 includes heaters 38a to 41a.
, A power MOS-type first transistor 63, a second transistor 64, a third transistor 65, and a fourth transistor 66.
The input terminals of the transistors 63 to 66 are connected to the input / output unit 5
7 is connected to the CPU 52. The emitter terminals of the transistors 63 to 66 are connected to the heaters 38a to 38a.
1a. Then, by inputting a command signal from the CPU 52 to each input terminal of each of the transistors 63 to 66, each of the transistors 63 to 66 is turned on, and each heater energizing circuit including each of the heaters 38a to 41a is closed.

The current detection circuit 59 includes a transistor 63
Through heater terminals 38a to 41a
, Four resistors 67, 68, 6 connected in series, respectively.
9, 70, and an operational amplifier 71 and other eight resistors 7
2, 73, 74, 75, 76, 77, 78, 79. One end of each of the resistors 67 to 70 connected to the collector terminal of each of the transistors 63 to 66 is grounded. One end of each of the resistors 72 to 75 is connected between each of the resistors 67 to 70 and each of the transistors 63 to 66. The non-inverting input terminal of the operational amplifier 71 is connected between the resistor 76 and the resistor 77. The other end of each of the resistors 72 to 75 is connected to the inverting input terminal of the operational amplifier 71. Further, a resistor 78 is connected between the inverting input terminal and the output terminal of the operational amplifier 71, and an output terminal of the operational amplifier 71 is connected to the A / D converter 56 via the resistor 79.

The current detection circuit 59 thus configured
When one of the heaters 38a to 41a is specified and driven, the resistances 67 to 70 and the resistances 72 to 75
Is amplified by the operational amplifier 71 and input to the A / D converter 56. And
The current value is A / D converted by the A / D converter 56 and then input to the CPU 52. The CPU 52 detects an abnormality in the current value based on a predetermined current detection program.

The voltage drop detection circuit 61 includes one comparator 80
, Four diodes 81, 82, 83, 84 and one resistor 85. Each diode 81-8
The anode terminal 4 is connected between each heater 38a-41a and each transistor 63-66. The cathode terminals of the diodes 81 to 84 and the resistor 8
One end of the resistor 5 is connected to the non-inverting input terminal of the comparator 80, and the other end of the resistor 85 is grounded. The output terminal of the comparator 80 is connected to the CPU 52 via the input / output unit 57. In addition, one end of a resistor 86 is connected to the output terminal of the comparator 80. The highest voltage (smallest voltage drop) among the emitter terminals of the transistors 63 to 66 is input to the non-inverting input terminal of the comparator 80. The reference voltage VB is input to the inverting input terminal of the comparator 80. Then, the comparator 80 compares the voltage drop with the reference voltage VB, and the result of the comparison is input from the output terminal to the CPU 52 via the input / output device 57. The CPU 52 detects a voltage drop abnormality based on a predetermined voltage drop determination program. Here, when the output of the comparator 80 is at a high level, that is, when the voltage is high (the voltage drop is small) when all the heaters 38a to 41a are in the energized state, the CPU 52 detects an abnormality in the voltage drop.

In this embodiment, the ECU 51 comprises a temperature control circuit, an energization state judging unit, a failure judging unit, a forced energizing unit and a failure specifying unit. Then, during operation of the engine, the ECU 51 drives and controls each of the injectors 11L and 11R to execute fuel injection control.
Further, the ECU 51 controls the driving of each of the igniters 18L and 181R to execute the fuel injection timing control. Furthermore, EC
U51 is based on a signal from each of the air-fuel ratio sensors 38 to 41 and the like, and based on the air-fuel ratio feedback control of the engine (FB control)
Execute At this time, the ECU 51 sets each air-fuel ratio sensor 38
In addition to controlling the driving of the heaters 38a to 41a in order to adjust the temperature of the heaters 41 to 41, failure detection and the like of the heater energizing circuits including the sensors 38a to 41a are executed.

Next, in the gasoline engine system configured as described above, the ECU 5
A description will now be given of the contents of the processing operation for adjusting the temperature of the air-fuel ratio sensor and detecting the failure of the heater, which is performed by the first embodiment.

The flowcharts of FIGS.
Is a process routine for adjusting the temperature of the air-fuel ratio sensor and detecting a failure of the heater, which is executed by the routine shown in FIG.

When the processing of this routine is started, first, at step 100, the rotation speed sensor 31, the air flow meter 34, the throttle sensor 36 and the water temperature sensor 3
7 based on each detection signal from the engine speed NE,
Operation states such as the intake air amount Q, the throttle opening TA, and the cooling water temperature THW are read. Here, the voltage level of the battery 25 is also read.

Then, in step 110, energization control for each heater 38a-41a of each air-fuel ratio sensor 38-41 is executed. That is, the engine operating conditions are determined based on the engine speed NE, the intake air amount Q, the throttle opening TA, the cooling water temperature THW, and the like read this time. or,
The determined engine operating conditions are compared with heater energizing conditions preset according to the installation positions of the air-fuel ratio sensors 38 to 41, and if the energizing conditions are satisfied,
Each transistor 63 in the drive circuit 60 in a well-known manner
To 66 are subjected to switching control. By opening and closing each heater energizing circuit by this switching control, energization to each of the heaters 38a to 41a is controlled, so that the temperature of the sensor elements in each of the air-fuel ratio sensors 38 to 41 is adjusted.

Subsequently, in step 200, in a state where the heaters 38a to 41a are energized,
It is determined whether or not all the heaters 38a to 41a are energized. Here, all heaters 38a to 41
If “a” is not in the energized state, step 400
Move to. If all the heaters 38a to 41a are in the energized state, the process proceeds to step 210.

In step 210, it is determined whether or not the output of the comparator 80 in the voltage drop detection circuit 61 is at a low level. That is, when all the heaters 38a to 41a are energized without any trouble, a desired voltage drop occurs in each heater energizing circuit. Then, a low-level voltage is input to the non-inverting input terminal of the comparator 80 of the voltage drop detection circuit 61, and this voltage is lower than the reference voltage VB of the inverting input terminal. Is output. Therefore, when the output of the comparator 80 is at a low level, each of the heaters 38a to 41a
The process proceeds to step 400 assuming that the voltage drop in each heater energizing circuit including is normal. If the output of the comparator 80 is not at a low level, it is determined that a failure such as a disconnection has occurred in the heater energizing circuit, and the process proceeds to step 300 to identify which heater energizing circuit has a failure. Transition.

In step 300, in order to specify which of the heater energizing circuits has an abnormal voltage drop,
Executes voltage drop abnormality determination. More specifically, as shown in FIG.
In order to make all heaters 39a, 40a, and 41a other than 8a energize, each transistor 63 to
66 is subjected to switching control.

Subsequently, in step 302, it is determined whether or not the output of the comparator 80 at that time is low. Here, when the output of the comparator 80 is at a low level, it is determined that the first heater 38a is abnormal, and the process proceeds to step 303. Then, in step 303, the abnormality flag H1XA for indicating that the first heater 38a is abnormal due to disconnection or the like is set to "1", and the routine proceeds to step 304. If the output of the comparator 80 is not low, it is determined that any of the heaters 39a, 40a, and 41a other than the first heater 38a is abnormal, and the process proceeds to step 304.

Then, in step 304, all the heaters 38a, 40a, except for the second heater 39a,
The switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to make the 41a conductive.

Subsequently, in step 305, it is determined whether or not the output of the comparator 80 at that time is at a low level. Here, when the output of the comparator 80 is at a low level, it is determined that the second heater 39a is abnormal, and the process proceeds to step 306. Then, in step 306, an abnormality flag H2XA for indicating that the second heater 39a is abnormal due to disconnection or the like is set to “1”, and the routine proceeds to step 307. If the output of the comparator 80 is not low, the first and second heaters 3
It is determined that one of the heaters 40a and 41a other than the heaters 8a and 39a is abnormal, and the process proceeds to step 307.

Then, in step 307, all heaters 38a, 39a, except for the third heater 40a,
The switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to make the 41a conductive.

Subsequently, in step 308, it is determined whether or not the output of the comparator 80 at that time is at a low level. Here, when the output of the comparator 80 is at a low level, it is determined that the third heater 40a is abnormal, and the process proceeds to step 309. Then, in step 309, an abnormality flag H3XA for indicating that the third heater 40a is abnormal due to disconnection or the like is set to "1", and the routine proceeds to step 310. If the output of the comparator 80 is not low, the remaining fourth heater 41
Assuming that a is abnormal, the process proceeds to step 310.

Then, in step 310, all the heaters 38a, 39a, except for the fourth heater 41a,
The switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to make the 40a conductive.

Subsequently, in step 311, it is determined whether or not the output of the comparator 80 at that time is at a low level. Here, when the output of the comparator 80 is at a low level, it is determined that the fourth heater 41a is abnormal, and the process proceeds to step 312. Then, in step 312, an abnormality flag H4XA for indicating that the fourth heater 41a is abnormal due to disconnection or the like is set to "1". If the output of the comparator 80 is not at a low level, it is determined that all the heaters 38a to 41a are not abnormal, and a series of processing regarding the abnormality determination is ended.

As described above, after the process of determining a voltage drop abnormality in step 300 is performed, the process proceeds to step 400 in the flowchart of FIG. In the flowchart of FIG.
Alternatively, after step 300, in step 400, it is determined whether or not the output result of the operational amplifier 71 in the current detection circuit 59 is in an overcurrent state. This determination is made by comparing the output level of the operational amplifier 71 with a predetermined value corresponding to the number of heaters 38a to 41a that are energized at each time. When the output level of the operational amplifier 71 is higher than a predetermined value, it is determined that an overcurrent state has occurred. Here, if the output of the operational amplifier 71 is not in an overcurrent state, step 6 is executed to execute the next abnormality determination.
Move to 00. If the output of the operational amplifier 71 is in an overcurrent state, step 50 is executed to execute the next abnormality determination.
Move to 0.

In step 500, an overcurrent abnormality determination is performed to specify which of the heater energizing circuits including the heaters 38a to 41a is in an overcurrent state. Specifically, as shown in FIG. 8, first, in step 501, the transistors 63 to 66 of the drive circuit 60 are subjected to switching control so as to forcibly energize only the first heater 38a. At this time, the other heaters 39a to 41a
Is not energized, the only input to the operational amplifier 71 of the current detection circuit 59 is the current value flowing through the heater energization circuit including the first heater 38a. Then, an output current value corresponding to the input current value is output from the current detection circuit 59 as a detection current Is, and the current value is input to the CPU 52 via the A / D converter 56.

Subsequently, at step 502, it is determined whether or not the value of the detected current Is at that time is larger than a predetermined value α. Here, if the value of the detection current Is is not larger than the predetermined value α, it is determined that the heater energizing circuit including the first heater 38a is not in an overcurrent state, and the step 5 is performed.
Move to 04. When the value of the detection current Is is larger than the predetermined value α, the process proceeds to step 503. Then, in step 503, the abnormality flag H1XB for indicating that the heater energizing circuit including the first heater 38a is abnormal in the overcurrent state is set to "1", and the routine proceeds to step 504.

In step 504, switching control is performed on the transistors 63 to 66 of the drive circuit 60 so as to forcibly energize only the second heater 39a. Subsequently, at step 505, the detected current I
It is determined whether or not the value of s is greater than a predetermined value α. Here, when the value of the detection current Is is not larger than the predetermined value α, it is determined that the heater energizing circuit including the second heater 39a is not in an overcurrent state, and the process proceeds to step 507. If the value of the detection current Is is larger than the predetermined value α, the process proceeds to step 506. And step 50
At 6, the abnormal flag H2XB for indicating that the heater energizing circuit including the second heater 39a is abnormal in the overcurrent state is set to "1", and the routine proceeds to step 507.

In step 507, the switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to forcibly energize only the third heater 40a. Subsequently, in step 508, the detected current I
It is determined whether or not the value of s is greater than a predetermined value α. Here, if the value of the detection current Is is larger than the predetermined value α, it is determined that the heater energizing circuit including the third heater 40a is not in an overcurrent state, and the process proceeds to step 510.
If the value of the detection current Is is larger than the predetermined value α, the process proceeds to step 509. Then, in step 509, an abnormal flag H for indicating that the heater energizing circuit including the third heater 40a is abnormal in an overcurrent state is set.
3XB is set to "1", and the routine goes to Step 510.

In step 510, the transistors 63 to 66 of the drive circuit 60 are switched so as to forcibly energize only the fourth heater 41a. Subsequently, at step 511, the detected current I
It is determined whether or not the value of s is greater than a predetermined value α. Here, when the value of the detection current Is is not larger than the predetermined value α, it is determined that the heater energizing circuit including the fourth heater 41a is not in an overcurrent state, and the process proceeds to step 513. If the value of the detection current Is is larger than the predetermined value α, the process proceeds to step 512. And step 51
In 2, the abnormality flag H4XB for instructing that the heater energizing circuit including the fourth heater 41a is abnormal in the overcurrent state is set to "1", and the routine proceeds to step 513.

In step 513, the transistors 63 to 66 of the drive circuit 60 are switched so as to forcibly turn off all the heaters 38a to 41a.

Subsequently, in step 514, it is determined whether or not the value of the detected current Is at that time is larger than a predetermined value β (β <α). If the value of the detection current Is is not larger than the predetermined value β, all the heaters 38a to 38a
It is assumed that all heater energizing circuits including 41a are not in an overcurrent state. If the value of the detection current Is is larger than the predetermined value β, the process proceeds to step 515. Then, in step 515, an abnormal flag HAXB for instructing that all the heater energizing circuits including all the heaters 38a to 41a are abnormal in an overcurrent state is set to "1".

As described above, after the process of determining an abnormality related to overcurrent is performed in step 500, the process is performed as shown in FIG.
The process moves to step 600 in the flowchart of FIG. In step 600, each of the heaters 38a-38
It is determined whether or not a predetermined operating condition for performing a performance degradation abnormality determination (failure determination) according to a is satisfied. This determination is based on the currently read engine speed NE, intake air amount Q,
The determination is performed based on the throttle opening TA, the vehicle speed SPD, the voltage level of the battery 25, and the like. That is, the predetermined time has elapsed since the engine started, the vehicle speed SPD is lower than the predetermined value, the voltage level of the battery 25 is within the predetermined range, and the engine load (the intake air amount Q and the throttle opening degree TA) is lower. Within a predetermined range, the air-fuel ratio sensors 38-4
It is presumed that the predetermined operating condition is that the element temperature of the first element is within a predetermined temperature range (for example, 500 to 900 ° C.) in which the element is not deactivated. When the predetermined operating condition is satisfied, the process proceeds to step 700 on the assumption that an abnormality determination relating to the performance degradation of each of the heaters 38a to 41a is to be performed. If the predetermined operating condition is not satisfied, the process directly proceeds to step 800.

In step 700, each heater 38
The abnormality determination of the performance degradation according to a to 41a is executed. Specifically, as shown in FIG. 9, first, in step 701, all the transistors 63 to 66 of the drive circuit 60 are turned off for a predetermined time in order to forcibly turn off all the heaters 38a to 41a for a predetermined time. Let it. here,
When all the heaters 38a to 41a are de-energized for a predetermined time, the temperature of each of the heaters 38a to 41a itself decreases during that time. In this example,
The heaters 38a to 41a are de-energized only for "about 10 seconds".

As a result, the temperature of each of the heaters 38a to 41a is lowered from the high temperature state to the same temperature state as the sensor element. If the heaters 38a to 41a are not energized for only about 10 seconds, the decrease in the element temperature of each of the air-fuel ratio sensors 38 to 41 is about 50 ° C., and each of the air-fuel ratio sensors 38 to 41 is normal. "4.
00 ° C ”or less.

Next, at step 702, the drive circuit 6 is driven to forcibly energize only the first heater 38a.
The switching control of each of the 0 transistors 63 to 66 is performed. Subsequently, in step 703, the value of the detected current Is at that time is set to a predetermined value γ (γ <β <α) as a reference value.
It is determined whether it is smaller than. Here, the detection current Is
Is not smaller than the predetermined value γ, it is determined that the performance of the first heater 38a is not degraded, and the process proceeds to step 7
Move to 05. If the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 704. Then, in step 704, the abnormality flag H1 for indicating that the performance of the first heater 38a is degraded is abnormal.
XC is set to "1", and the routine goes to Step 705.

In step 705, the switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to forcibly energize only the second heater 39a. Subsequently, at step 706, the detected current I
It is determined whether the value of s is smaller than a predetermined value γ. Here, if the value of the detection current Is is not smaller than the predetermined value γ, the process proceeds to step 708 on the assumption that the performance of the second heater 39a is not degraded. If the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 707. Then, in step 707, the abnormality flag H2XC for instructing that the performance of the second heater 39a is degraded is set to “1”, and the process proceeds to step 708.

In step 708, the switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to forcibly energize only the third heater 40a. Subsequently, at step 709, the detected current I
It is determined whether the value of s is smaller than a predetermined value γ. Here, when the value of the detection current Is is not smaller than the predetermined value γ, the process proceeds to step 711 on the assumption that the performance of the third heater 40a is not degraded. If the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 710. Then, in step 710, an abnormality flag H3XC for instructing that the performance degradation of the third heater 40a is abnormal is set to “1”, and the process proceeds to step 711.

In step 711, the switching of each of the transistors 63 to 66 of the drive circuit 60 is controlled so as to forcibly energize only the fourth heater 41a. Subsequently, at step 712, the detected current I
It is determined whether the value of s is smaller than a predetermined value γ. Here, when the value of the detection current Is is not smaller than the predetermined value γ, it is assumed that the performance of the fourth heater 41a does not decrease. If the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 713. And step 71
In 3, the abnormality flag H4XC for indicating that the performance of the fourth heater 41a is abnormal is set to "1".

As described above, after the processing of the abnormality determination (failure determination) relating to the performance degradation of each of the heaters 38a to 41a is performed in step 700, the processing shifts to step 800 in the flowchart of FIG.

In step 800, each heater 38
It is determined whether there is an abnormality in the heater energizing circuit including a to 41a. That is, each of the abnormality flags H1XA to H4XA, H
It is determined whether any one of 1XB to H4XB, HAXB, H1XC to H4XC is "1". Here, when there is no abnormality, it is determined that there is no failure in each heater energizing circuit including each of the heaters 38a to 41a, and the process proceeds to step 810. Then, in step 810, the warning lamp 24 is turned off, and the subsequent processing ends once. If there is an abnormality, it is determined that there is a failure in each heater energizing circuit including each of the heaters 38a to 41a, and the process proceeds to step 820. Then, in step 820, the warning lamp 24 is turned on to warn the driver of a failure of each heater energizing circuit including each of the heaters 38a to 41a.

Subsequently, in step 830, a diagnostic code indicating that a failure has occurred in the heater energizing circuit including the heaters 38a to 41a is stored in the backup RA.
It is stored in M55. In this case, each abnormality flag H1XA
~ H4XA, H1XB ~ H4XB, HAXB, H1XC
-H4XC, each heater 38a-41a related to the failure
Are specifically specified and stored in the backup RAM 55. The diagnostic code stored in the backup RAM 55 is
If all other faults do not occur during the 40 warm-up cycles, they are erased. Then, after the processing of step 830 is completed, the subsequent processing is temporarily ended.

As described above, according to this embodiment, the heaters 38a to 41a of the air-fuel ratio sensors 38 to 41 are energized and controlled by the ECU 51 in accordance with the engine operating conditions and the exhaust passage temperature conditions. You. With this control, the amount of heat generated by each of the heaters 38a to 41a is adjusted, and the temperature of the sensor elements in each of the air-fuel ratio sensors 38 to 41 is adjusted.

In this embodiment, all the heaters 3
8a to 41a are connected in parallel to one input terminal of a comparator 80 in the voltage drop detection circuit 61. The comparator 80 compares the voltage drop in all the heaters 38a to 41a with the value of the reference voltage VB. When the heaters 38a to 41a are energized,
When the ECU 51 determines that all the heaters 38a to 41a are in the energized state, the failure caused by the disconnection or the like of each heater energizing circuit including the heaters 38a to 41a is determined based on the output result of the comparator 80. Is determined. For example,
If any one of the heaters 38a to 41a is broken due to disconnection or the like, the voltage drop of all heater energizing circuits that are compared with the value of the reference voltage VB in the comparator 80 will change, The ECU 51 determines that one of the heater energizing circuits is faulty due to disconnection or the like.

Therefore, in this embodiment, one comparator 8
Since the failure such as disconnection of each of the heaters 38a to 41a is determined only by using 0, a plurality of heaters 38a to 38a to 41a are determined.
It is not necessary to separately provide a circuit and the like for failure determination for each of the 41a. As a result, it is possible to detect a failure such as a disconnection of each of the heaters 38a to 41a by using only the voltage drop detection circuit 61 including one comparator 80. Therefore, it is not necessary to provide a plurality of failure detection circuits for the heaters 38a to 41a in accordance with the number of the heaters 38a to 41a, thereby simplifying the circuit configuration and suppressing an increase in the number of parts. Can be.

Further, in this embodiment, each heater 38a
When it is determined that a failure such as disconnection of the heaters 38a to 41a has occurred, the non-energization of one of the heaters 38a to 41a and the energization of all the remaining heaters 38a to 41a performed simultaneously with the non-energization are performed for all the heaters 38a to 41a are forcibly performed sequentially. And each heater 3
When de-energization and energization of the heaters 8a to 41a are sequentially performed, the ECU 51 based on the output result of the comparator 80 outputs a failed heater energization circuit among the heater energization circuits including the heaters 38a to 41a. Is specified.
For example, when the output of the comparator 80 is low when the first heater 38a is not energized and the other heaters 39a to 41a are energized,
At this time, it is specified that the heater energizing circuit including the first heater 38a that has been de-energized has failed. That is, assuming that the heater energizing circuit including the first heater 38a has failed due to disconnection or the like, the abnormality flag H1XA is set to “1”.
Is set to Therefore, one heater energizing circuit in which a failure such as disconnection has occurred is specified from the plurality of heater energizing circuits. As a result, a plurality of heater-equipped air-fuel ratio sensors 3
It is possible to specifically specify which of the heaters 38a to 41a has a failure such as disconnection corresponding to 8 to 41.

In addition, in this embodiment, each heater 38a
To 41a are energized, each heater 3 based on the output result of the operational amplifier 71 in the current detection circuit 59.
The overcurrent state in 8a to 41a is determined by the ECU 51. If it is determined that each of the heaters 38a to 41a is in the overcurrent state,
a is forcibly energized sequentially, and when the energization is performed, the ECU 51
Thus, the heaters 38a to 41a in the overcurrent state are specified based on the output result of the operational amplifier 71. For example, the first
If the output result of the operational amplifier 71 is larger than the predetermined value α when the heater 38a is forcibly energized, it is specified that the first heater 38a is in an overcurrent state. That is, the abnormality flag H1XB is set to “1” assuming that the first heater 38a has failed in the overcurrent state. Accordingly, one of the heaters 38a to 41a which has failed in the overcurrent state is selected from the plurality of heaters 38a to 41a.
a to 41a are specified. As a result, which of the heaters 38a to 38a-4 corresponds to the plurality of air-fuel ratio sensors with heaters 38 to 41.
It is possible to specifically specify whether or not a failure has occurred in the overcurrent state in 1a.

Further, in this embodiment, when the predetermined operation condition is satisfied, all the heaters 38a to 41a are forcibly de-energized, and then the heaters 38a to 41a are forcibly energized in sequence. Failures related to those performance degradations are determined. Then, among the plurality of heaters 38a to 41a, the heaters 38a to 41a having the failure related to the performance degradation are specifically specified. As a result, it is possible to specifically specify which of the heaters 38a to 41a has a performance degradation failure corresponding to the plurality of heater-equipped air-fuel ratio sensors 38 to 41.

That is, in this embodiment, each heater 38a
The current value in each heater energization circuit including the heater currents 41a to 41a is detected as the detection current Is, and based on the detection current Is, the overcurrent and the performance degradation failure of the heaters 38a to 41a are specified. Therefore, by using both the identification of the fault caused by the overcurrent and the performance degradation performed based on the current value and the identification of the failure caused by the disconnection and the like performed based on the above-described voltage drop, each heater can be used. 38
The failures related to a to 41a can be more specifically specified with high accuracy.

In this embodiment, the heaters 38a to 38a-4
When the failure related to 1a is detected, the warning lamp 24 is turned on, so that the driver can be immediately notified of the failure related to each of the heaters 38a to 41a. Further, since the failure detection data relating to each of the heaters 38a to 41a is stored in the backup RAM 55, the data relating to each of the heaters 38a to 41a is read out by reading the data in the backup RAM 55 during periodic inspection of the engine or the like. Presence / absence, type of the failure, and heater 38a related to the failure
To 41a can be specifically confirmed.

It should be noted that the present invention is not limited to the above-described embodiment, but may be carried out as follows by appropriately changing a part of the configuration without departing from the spirit of the invention. (1) In the above embodiment, a total of four upstream and downstream three-way catalytic converters 14L and 14R arranged in parallel corresponding to the exhaust passages of the left and right banks 2 and 3 of the V-type engine. This is embodied when the air-fuel ratio sensors with heaters 38 to 41 are provided. On the other hand, the present invention can be embodied in a case where the air-fuel ratio sensors with heaters are respectively arranged on the upstream side and the downstream side of the three-way catalytic converter arranged in the exhaust passage of the series engine.

(2) In the above embodiment, the comparator 80 of the voltage drop detection circuit 61 compares the voltage drop in each of the heaters 38a to 41a with the value of the reference voltage VB. On the other hand, the comparator may be configured to compare a current value flowing through each heater with a reference value.

(3) In the above embodiment, both the voltage drop detection circuit 61 including the comparator 80 and the current detection circuit 59 are provided, and the voltage drop in each of the heaters 38 a to 41 a and each of the heaters 38 a to 38 a
41a based on both of the current values flowing through the heaters 38a
To 41a are determined. On the other hand, only a voltage drop detection circuit including a comparator may be provided, and the failure of each heater may be determined based on only the voltage drop at each heater.

[0079]

As described above in detail, according to the first aspect of the invention, the current value flowing through each heater or the voltage drop at each heater is compared with the reference value by the comparator. One end of each heater is connected in parallel to the input terminal. Then, when it is determined that all the heaters are energized, the failure of each heater is determined based on the output result of the comparator. Therefore, it is not necessary to separately provide a failure determination circuit corresponding to each of the plurality of heaters. As a result, an excellent effect is achieved in that a failure relating to each heater of the plurality of air-fuel ratio sensors with heaters can be detected using one circuit.

According to the second aspect of the present invention, when a failure of each heater is determined, non-energization of one heater and energization of all remaining heaters performed simultaneously with the non-energization are performed for all heaters. The heaters are sequentially and forcibly performed. When the heaters are sequentially de-energized and energized, the heater in which a failure has occurred among all the heaters is specified based on the output result of the comparator. As a result, an excellent effect that it is possible to specifically identify which of the plurality of heaters has failed is exhibited.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram showing a basic conceptual configuration of the first invention.

FIG. 2 is a conceptual configuration diagram showing a basic conceptual configuration of the second invention.

FIG. 3 is a schematic configuration diagram showing a gasoline engine system according to an embodiment that embodies the first and second inventions.

FIG. 4 is a block diagram showing a configuration of an ECU and the like in one embodiment.

FIG. 5 is a connection diagram showing a relationship between each heater energizing circuit including each heater, its drive circuit, current detection circuit, voltage drop detection circuit, and the like in one embodiment.

FIG. 6 is a flowchart showing a processing routine for air-fuel ratio sensor temperature adjustment and heater failure detection executed by an ECU in one embodiment.

FIG. 7 is a flowchart detailing a portion of the flowchart of FIG. 6 in one embodiment.

FIG. 8 is a flowchart detailing a part of the flowchart of FIG. 6 in one embodiment.

FIG. 9 is a flowchart showing a part of the flowchart of FIG. 6 in detail in one embodiment.

[Explanation of symbols]

1 ... engine body as internal combustion engine, 5L, 5R ... exhaust manifold, 15L, 15R, 16 ... exhaust pipe (5L, 5
R, 15L, 15R, and 16 constitute an exhaust passage), 38: first air-fuel ratio sensor, 39: second air-fuel ratio sensor, 40: third air-fuel ratio sensor, 41: fourth air Fuel ratio sensor, 38a: first heater, 39a: second heater, 40a: third heater, 41a: fourth heater,
51 ... ECU (a temperature control circuit, an energization state determination unit, a failure determination unit, a forced energization unit, and a failure identification unit are configured by 51), 80 ... Comparators.

Continuation of the front page (56) References JP-A-3-189350 (JP, A) JP-A-53-19888 (JP, A) JP-A-62-44272 (JP, U) JP-A-62-153556 (JP, A) , U) Hikaru 4-130463 (JP, U) (58) Fields studied (Int. Cl. ⁶ , DB name) G01N 27/26 391 G01N 27/409

Claims (2)

(57) [Claims] 1. A plurality of air-fuel ratio sensors provided in an exhaust passage of an internal combustion engine and having a temperature characteristic, and a plurality of energized heat-generation types provided in each of the air-fuel ratio sensors for heating the air-fuel ratio sensors. A heater for controlling the energization of each heater in accordance with the operating conditions of the internal combustion engine and the temperature condition of the exhaust passage, thereby adjusting the amount of heat generated by each heater and adjusting the temperature of each air-fuel ratio sensor. In the air-fuel ratio sensor temperature adjustment circuit, one end of all the heaters is connected in parallel to one input terminal in order to compare a current value flowing through each heater or a voltage drop in each heater with a reference value. A comparator connected to the heater; an energization state determination unit for determining whether all the heaters are energized; and an energization state of the heaters by the energization state determination unit. When it is determined that, based on the output result of the comparator obtained by comparing the current value or the voltage drop and the reference value, failure determination means for determining failure of each heater A fault detection device for an air-fuel ratio sensor temperature control circuit, comprising: 2. The failure detection device for an air-fuel ratio sensor temperature adjustment circuit according to claim 1, wherein when the failure determination means determines that each of the heaters has failed, the one heater is de-energized and the non-energization is performed. The energization to all the remaining heaters performed at the same time
Forcibly energizing means for sequentially forcing all heaters sequentially, and when de-energization and energization of the heaters are sequentially performed by the forcible energizing means, all of the heaters are based on the output result of the comparator. And a failure identification unit for identifying a heater in which a failure has occurred among the heaters.