JPH0743336A - Detecting device for failure of circuit for adjusting temperatur of air/fuel ratio sensor - Google Patents

Abstract

PURPOSE:To detect failure related to each heater of a plurality of air/fuel ratio sensors with heater using one circuit. CONSTITUTION:Each air/fuel ratio sensor with heater is provided at the upstream and downstream sides of each ternary catalyst converter corresponding to each of left and right banks of an V-type engine. Heaters 38a-41a of each air/fuel ratio sensor with heater are subjected to conduction control according to the operating conditions of engines and the temperature conditions of exhaust path, thus performing temperature control of each air/fuel ratio sensor. For comparing the voltage drop in the heaters 38a-41a with a reference value, one edge of all heaters 38a-41a is connected in parallel to one input terminal of a comparator 80 in a voltage effect detection circuit 61. Then, when all of heaters 38a-41a are in a conduction state, a CPU 52 judges whether the heaters 38a-41a failed or not according to the output result of the comparator 80. This configuration eliminates the need for providing a circuit for judging failure corresponding to each of a plurality of heaters 38a-41a individually.

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 of a 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 fault.

[0002]

2. Description of the Related Art Conventionally, in 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 target fuel amount to be supplied to the internal combustion engine is feedback-controlled, so that the actual air-fuel ratio is controlled to the target air-fuel ratio. Here, in order to stably maintain the temperature of the sensor element forming the air-fuel ratio sensor at a predetermined activation temperature, a heater-equipped air-fuel ratio sensor including a heater is used. Since the temperature of the exhaust gas is slightly different depending on the operating conditions of the internal combustion engine and the position of the exhaust passage, when the air-fuel ratio sensor with a heater is used, the heater is controlled by the temperature adjustment (temperature adjustment) circuit. As a result, the temperature of the air-fuel ratio sensor is preferably controlled according to the conditions.

By the way, in the previous air-fuel ratio sensor with a heater, there is 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 adjustment 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, which should be obtained by the air-fuel ratio control, deviates from the target air-fuel ratio that is the target, and there is a risk that exhaust emission may be deteriorated.

Therefore, Japanese Utility Model Application Laid-Open No. 62-44272 proposes a device for an air-fuel ratio sensor with a heater, which detects disconnection of a temperature control circuit including the heater. In this device, when a vehicle is equipped with a failure diagnosis system, the presence or absence of a failure such as a disconnection is one of the diagnosis items, and the driver is promptly alerted to the diagnosis result.

That is, in the temperature control circuit according to this prior art, the heater and its drive circuit are connected in series to the power source to form a heater energizing circuit. 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 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, and a voltage drop due to the resistor is compared with a reference voltage. 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 adjustment circuit is at a predetermined level, it is determined that there is a failure such as disconnection, and a signal indicating that is output.

[0006]

However, the above-mentioned prior art is premised on a system in which only one heater-equipped air-fuel ratio sensor is provided in the exhaust passage. Therefore, when a system is provided in which a plurality of air-fuel ratio sensors with heaters are provided in the exhaust passage and the temperature of each heater is individually adjusted, failure of each heater energizing circuit including each heater depending on the number of heaters may occur. Each detection circuit is required. For example, in the case where the internal combustion engine is a V-type engine, or in the case of a double air-fuel ratio sensor system in which heater-equipped air-fuel ratio sensors are provided on the upstream side and the downstream side of the catalytic converter, respectively, the heater-equipped air-fuel ratio sensors Therefore, a plurality of failure detection circuits are required, which not only complicates the circuit configuration but also causes an increase in the number of parts.

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

[0008]

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 energization heat generation type heaters provided in each of the air-fuel ratio sensors M3 for heating each air-fuel ratio sensor M3. A heater M4 is provided, and each heater M4 is controlled by energizing the heater M4 according to 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 in which the temperature of each air-fuel ratio sensor M3 is adjusted by adjusting the amount of heat generated by the heater, the current value flowing through each heater M4 or the voltage drop in each heater M4 is compared with a reference value. Therefore, one of the input terminals of all the heaters M4 is connected in parallel to the comparator M.
6, an energized state determination means M7 for determining whether all the heaters M4 are energized, and an energized state determination means M7 determines that all the 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 amount with the reference value.

In order to achieve the second object, in the second invention, as shown in FIG. 2, in the failure detecting device for the air-fuel ratio sensor temperature adjusting circuit according to claim 1, the failure determining means M8. When the failure of each heater M4 is determined by, the non-energization for one heater M4 and the energization for all the remaining heaters M4 simultaneously with the non-energization are sequentially and forcibly performed for all the heaters M4. For energizing each of the heaters M4 based on the output result of the comparator M6 while the energization means M9 for
4 is provided with a failure identifying means M10 for identifying the 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 temperature adjusting circuit M5 allows the air-fuel ratio sensors M3 to operate in accordance with the operating conditions of the internal combustion engine and the exhaust passage temperature conditions. By controlling the energization of each of the heaters M4 provided in the, the amount of heat generated by each of the heaters M4 is adjusted and the temperature of each air-fuel ratio sensor M4 is adjusted.

Here, since the energization state determination means M7 determines that all the heaters M4 are in the energized state, the current value flowing through all the heaters M4 or the voltage drop in all the heaters M4 is determined by the comparator. It is compared with the reference value at M6. 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 of the heaters M4 is out of order due to disconnection or the like, the current value or the voltage drop amount that is compared with the reference value in the comparator M6 will change, and the failure determination means M8 will determine that there is a failure. To be judged.

Therefore, it is not necessary to individually provide a failure determination circuit for each of the plurality of heaters M4. According to the configuration of the second invention, as shown in FIG. 2, when the failure determination means M8 determines a failure of each heater M4, the forced energization means M9 deenergizes one heater M4 and its Energization of all the remaining heaters M4 performed at the same time as de-energization is performed by all the heaters M4.
Forcibly performed for 4 sequentially. Then, when the heater M4 is sequentially de-energized and energized, the failure identifying unit M10 identifies the heater M4 having a failure among all the heaters M4 based on the output result of the comparator M6. To be done. For example, when the output result of the comparator M6 is at a low level, one heater M4 that is not energized is identified as having a failure due to disconnection or the like.

[0013]

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

FIG. 3 is a schematic diagram showing the gasoline engine system in this embodiment. In an engine body 1 that constitutes a V-type engine as an internal combustion engine mounted on a vehicle, each cylinder is divided into a left bank 2 and a right bank 3. Intake manifolds 4L and 4R and exhaust manifolds 5L and 5R are connected to the left and right banks 2 and 3, respectively.

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

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

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

Each spark plug 12 of the left and right banks 2 and 3
L and 12R have separate distributors 17L and 1
The ignition signal distributed at 7R is applied. Each distributor 17L, 17R is a separate igniter 18
The high voltage output from L, 18R is applied to the crankshaft 1
It is distributed to each spark plug 12L, 12R in synchronism with the rotation of 9. The ignition timing of each spark plug 12L, 12R is determined by the high voltage output timing from each igniter 18L, 18R.

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

An air flow meter 34 is attached downstream of the air cleaner 8. The air flow meter 34 detects the amount Q of intake air taken into the combustion chambers 2a, 3a of the engine body 1 through the intake pipe 7 and the like. The intake air temperature sensor 3 is provided near the air flow meter 34.
5 is attached. The intake air temperature sensor 35 detects the temperature of the 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 water temperature sensor 37 detects the temperature of the cooling water in the engine body 1, that is, the cooling water temperature THW.

On the other hand, a first air-fuel ratio sensor 38 and a second air-fuel ratio sensor 39 are provided on the upstream side and the downstream side of the one-way three-way catalytic converter 14L in the middle of the exhaust passage. Similarly, the third air-fuel ratio sensor 40 and the 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 respectively. Each of these air-fuel ratio sensors 3
The oxygen concentration Ox in the exhaust gas is detected from 8 to 41. Each of the air-fuel ratio sensors 38 to 41 is provided with a sensor element having a temperature characteristic, and a first heater 38a of an electric heating type for heating the sensor element for adjusting the temperature of each of the sensor elements, and a second heater. The heater 39a, the third heater 40a, and the fourth heater 41a are provided in each of the air-fuel ratio sensors 38 to 41.

A vehicle speed sensor 42 is provided on the transmission 21 drivingly connected to the engine body 1. The vehicle speed sensor 42 detects the vehicle speed, 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 connects the intake pipe 7 on the upstream side of the valve and the surge tank 6 on the downstream side to each other. There is. This bypass passage 22
A well-known linear solenoid type idle speed control valve (ISCV) 23 is provided midway. The opening of the ISCV 23 is controlled to stabilize the idling of the engine when the throttle valve 10 is fully closed. 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 Q of intake air into the combustion chambers 2a, 3a of the left and right banks is adjusted.

On the other hand, in this embodiment, a warning lamp 24 is provided on the instrument panel of the driver's seat (not shown), and one lead of the warning lamp 24 is connected to the positive terminal of the 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 described above is detected.

In this embodiment, each injector 11L,
11R, each igniter 18L, 18R, ISCV23,
The warning lamp 24 and the heaters 38a, 39a, 40a,
Each of 41a is an electronic control unit (hereinafter simply referred to as "ECU").
The drive is controlled by the (51). Therefore, EC
In U51, each injector 11L, 11R, each igniter 18L, 18R, ISCV23, warning lamp 24, battery 25 and each heater 38a, 39a, 40a, 41.
a are electrically connected to each other. In addition, the ECU 51
Includes a rotation speed sensor 31, cylinder identification sensors 32, 3
3, air flow meter 34, intake air temperature sensor 35, throttle sensor 36, water temperature sensor 37, each air-fuel ratio sensor 38-
41 and the vehicle speed sensor 42 are electrically connected to each other. Then, the ECU 51 uses the sensors 31 to 3
Various calculation and judgment processes are executed based on various signals from 3, 35 to 42 and the air flow meter 34. As a result, the injectors 11L and 11R, the igniters 18L and 18R, the ISCV 23, the warning lamp 24, and the heaters 38a, 39a, 40a, and 41a are preferably driven and controlled.

FIG. 4 is a block diagram showing the electrical configuration of the ECU 51. ECU 51 is a central processing unit (CPU)
52, a read-only memory (ROM) 53 that stores a predetermined control program and the like in advance, and a random access memory (RAM) 5 that temporarily stores the calculation result of the CPU 52 and the like.
4. Backup RA that saves pre-stored data
Equipped with M55 etc. 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 device 57 with a buffer, etc. are connected by a bus 58. Is configured as.

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, etc. are connected to the A / D converter 56, respectively. A current detection circuit 59 described later is connected to the A / D converter 56. The input / output unit 57 includes the rotation speed sensor 31, the cylinder discrimination sensor 3 described above.
2, 33, a throttle sensor 36, a vehicle speed sensor 42, etc. are respectively connected. Further, the I / O device 57 includes the above-mentioned ISCV 23, each injector 11L, 11R,
The igniters 18L and 18R, the warning lamp 24, and the like are connected to each other. Further, the above-mentioned heaters 38 a to 41 a are connected to the input / output device 57 via the drive circuit 60. In addition, a voltage drop detection circuit 61, which will be described later, is connected to the input / output device 57.

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

The current detection circuit 59, the drive circuit 60, and the voltage drop detection circuit 61 described above are included in the ECU 51. The ECU 51 including these circuits and the like uses the ECU 51 to adjust the temperature of the heaters 38a to 41a. A temperature control circuit) and its failure detection device are configured.

That is, FIG. 5 is a connection diagram showing the relationship between each heater energizing circuit including the heaters 38a to 41a and its driving circuit 60, the current detecting circuit 59, the voltage drop detecting circuit 61 and the like. In the figure, each heater 38a
One end of each of 41a to 41a is connected in parallel to the battery 25 described above via the input terminal 62. And each heater 3
Between the other end of 8a to 41a and the ground side, the drive 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.
It is composed of a power MOS type first transistor 63, a second transistor 64, a third transistor 65 and a fourth transistor 66 provided corresponding to the above.
The input terminals of the transistors 63 to 66 are connected to the input / output unit 5
It is connected to the CPU 52 via 7. The emitter terminals of the transistors 63 to 66 are heaters 38a to 4a, respectively.
1a, respectively. Then, by inputting a command signal from the CPU 52 to each input terminal of each transistor 63 to 66, each transistor 63 to 66 is turned on, and each heater energizing circuit including each heater 38a to 41a is closed.

The current detection circuit 59 includes transistors 63
To heaters 38a to 41a via collector terminals of
4 resistors 67, 68, 6 connected in series to
9, 70, operational amplifier 71 and other eight resistors 7
2, 73, 74, 75, 76, 77, 78, 79. One ends of the resistors 67 to 70 connected to the collector terminals of the transistors 63 to 66 are grounded. One ends of the resistors 72 to 75 are connected between the resistors 67 to 70 and the transistors 63 to 66, respectively. The non-inverting input terminal of the operational amplifier 71 is connected between the resistors 76 and 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 the 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 resistors 67 to 70 and the resistors 72 to 75 are
The current value detected by the combination of and 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. In the CPU 52, the current value abnormality is detected based on a predetermined current detection program.

The voltage drop detection circuit 61 includes one comparator 80.
It is composed of four diodes 81, 82, 83, 84 and one resistor 85. Each diode 81-8
The anode terminals of No. 4 are connected between the heaters 38a to 41a and the transistors 63 to 66, respectively. The cathode terminal of each of the diodes 81 to 84 and the resistor 8
One end of 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 device 57. In addition, one end of the resistor 86 is connected to the output terminal of the comparator 80. Then, the highest voltage (the smallest voltage drop) in 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 drops with the reference voltage VB, and the comparison result is input to the CPU 52 from the output terminal via the input / output unit 57. The CPU 52 performs voltage drop abnormality detection based on a predetermined voltage drop determination program. Here, when all the heaters 38a to 41a are in the energized state and the output of the comparator 80 is at a high level, that is, the voltage is high (the voltage drop is small), the CPU 52 detects the voltage drop abnormality.

In this embodiment, the ECU 51 comprises a temperature control circuit, an energization state determination means, a failure determination means, a forced energization means, and a failure identification means. Then, when the engine is in operation, the ECU 51 drives and controls the injectors 11L and 11R to execute the fuel injection control.
Further, the ECU 51 drives and controls the igniters 18L and 181R so as to execute the fuel injection timing control. Furthermore, EC
U51 is an air-fuel ratio feedback control (FB control) of the engine based on signals from the air-fuel ratio sensors 38 to 41.
To execute. At this time, the ECU 51 controls the air-fuel ratio sensor 38
The heaters 38a to 41a are driven and controlled in order to adjust the temperatures of the sensors to 41, and the failure detection of the heater energizing circuits including the sensors 38a to 41a is executed.

Next, in the gasoline engine system configured as described above, the ECU 5 is operated when the engine is operating.
The contents of the processing operation for adjusting the temperature of the air-fuel ratio sensor and detecting the failure of the heater, which are executed by No. 1, will be described.

The flow charts shown in FIGS. 6 to 9 are EC
U51 is a processing routine for adjusting the temperature of the air-fuel ratio sensor and detecting a heater failure, which is periodically executed at intervals of "several ms" during engine operation.

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 37.
Based on the detection signals from the vehicle speed sensor 42 and the like, the engine speed NE, the intake air amount Q, the throttle opening TA, the cooling water temperature THW, the vehicle speed SPD and the like are read. The voltage level of the battery 25 is also read here.

Then, in step 110, energization control for the heaters 38a-41a of the air-fuel ratio sensors 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, etc. which are read this time.
When the energization condition is satisfied according to the determined engine operating condition and the installation positions of the air-fuel ratio sensors 38 to 41, the transistors 63 to 63 in the drive circuit 60 are connected in a known manner. 66 is switching-controlled. By opening / closing each heater energization circuit by this switching control, energization to each heater 38a-41a is controlled, and thus the temperature of the sensor element in each air-fuel ratio sensor 38-41 is adjusted.

Then, in step 200, in a state where the heaters 38a to 41a are energized and controlled,
It is determined whether all the heaters 38a to 41a are in the energized state. Here, all the heaters 38a to 41
If all of a are not in the energized state, the subsequent processing is terminated as it is. When all the heaters 38a to 41a are all in the energized state, the process proceeds to step 210.

In step 210, it is determined whether the output of the comparator 80 in the voltage drop detection circuit 61 is 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, and the non-inverting input terminal of the comparator 80 of the voltage drop detecting circuit 61 is connected. The low-level voltage is input, and the comparator 80 outputs the low-level voltage. Therefore, when the output of the comparator 80 is at a low level, it is determined that the voltage drop in each heater energizing circuit including the heaters 38a to 41a is normal, and the process proceeds to step 400. If the output of the comparator 80 is not at a low level, it is determined that each heater energizing circuit has a failure such as disconnection, and in order to identify which heater energizing circuit has a failure, step 30 is performed.
Move to 0.

In step 300, in order to specify which of the heater energization circuits has an abnormal voltage drop,
Execute the voltage drop abnormality judgment. Specifically, as shown in FIG. 7, first, in step 301, the first heater 3
In order to energize all the heaters 39a, 40a, 41a other than 8a, each transistor 63 to
66 is switching-controlled.

Then, in step 302, it is judged 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 first heater 38a is abnormal, and the process proceeds to step 303. Then, in step 303, the abnormality flag H1XA for instructing 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 at the low level, it is determined that any of the heaters 39a, 40a, 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 other than the second heater 39a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled to energize 41a.

Then, in step 305, it is judged 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, the abnormality flag H2XA for instructing that the second heater 39a is abnormal due to a disconnection or the like is set to "1", and the process proceeds to step 307. When the output of the comparator 80 is not low level, the first and second heaters 3
If any of the heaters 40a and 41a other than 8a and 39a is abnormal, the process proceeds to step 307.

Then, in step 307, all the heaters 38a, 39a, other than the third heater 40a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled to energize 41a.

Then, in step 308, it is judged 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, the abnormality flag H3XA for instructing that the third heater 40a is abnormal due to disconnection or the like is set to "1", and the process proceeds to step 310. When the output of the comparator 80 is not low level, 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, other than the fourth heater 41a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled so that 40a is energized.

Then, in step 311, it is judged 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, the abnormality flag H4XA for instructing 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 the series of processes regarding abnormality determination is ended.

In this way, after the processing of the abnormality determination of the voltage drop in step 300 is executed, the processing shifts to step 400 in the flowchart of FIG. In the flowchart of FIG. 6, the process proceeds from step 210 or step 300 to step 400, and it is determined whether or not the output result of the operational amplifier 71 in the current detection circuit 59 is the overcurrent state. This determination is made by comparing the output level of the obe amplifier 71 with a predetermined value corresponding to the number of heaters 38a to 41a that are energized at each time. Then, when the output level of the operational amplifier 71 is higher than a predetermined value, it is determined that the overcurrent state.
Here, if the output of the operational amplifier 71 is not in the overcurrent state, the next abnormality determination is not executed, and step 80 is performed.
Move to 0. If the output of the operational amplifier 71 is in the overcurrent state, step 500 is executed to execute the next abnormality determination.
Move to.

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

Subsequently, in 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 detected 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 the overcurrent state, and step 5
Move to 04. When the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 503. Then, in step 503, the abnormality flag H1XB for instructing that the heater energization circuit including the first heater 38a is abnormal in the overcurrent state is set to "1", and the process proceeds to step 504.

In step 504, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the second heater 39a is forcibly energized. Then, in step 505, the detected current I at that time is detected.
It is determined whether the value of s is larger than the predetermined value α. Here, when the value of the detected 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 the overcurrent state, and the process proceeds to step 507. If the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 506. And step 50
6, the abnormality flag H2XB for instructing that the heater energization 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 transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the third heater 40a is forcibly energized. Then, in step 508, the detection current I at that time is detected.
It is determined whether the value of s is larger than the predetermined value α. Here, when the value of the detected 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 the overcurrent state, and the process proceeds to step 510.
If the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 509. Then, in step 509, an abnormality flag H for instructing that the heater energizing circuit including the third heater 40a is abnormal in the overcurrent state.
3XB is set to "1" and the process proceeds to step 510.

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

Then, in step 513, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that all the heaters 38a to 41a are forcibly aligned and not energized.

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). Here, when the value of the detected current Is is not larger than the predetermined value β, all the heaters 38a to 38a.
It is assumed that all the heater energizing circuits including 41a are not in the overcurrent state. If the value of the detected current Is is larger than the predetermined value β, the process proceeds to step 515. Then, in step 515, the abnormality flag HAXB for instructing that all the heater energizing circuits including all the heaters 38a to 41a are abnormal in the overcurrent state is set to "1".

As described above, after the process of the abnormality determination regarding the overcurrent is executed 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 heater 38a-41
It is determined whether or not the diagnosis execution condition for performing the abnormality determination of the performance deterioration related to a is satisfied. This determination is made based on the engine speed NE, the vehicle speed SPD, the voltage level of the battery 25, and the like that are read this time. That is, the execution condition is satisfied with the execution condition that a predetermined time has elapsed after the engine is started, the vehicle speed SPD is lower than a predetermined value, and the voltage level of the battery 25 is within a predetermined range. Is judged. Then, if the diagnosis execution condition is not satisfied, the process proceeds to step 800 without executing the abnormality determination of performance degradation. If the diagnosis execution condition is satisfied, the process proceeds to step 700 in order to execute the abnormality determination of performance degradation.

In step 700, in order to specify which of the heaters 38a to 41a has a performance deterioration abnormality, an abnormality determination relating to the heater performance deterioration is executed. For details, as shown in FIG. 9, first, step 701.
At, in order to forcibly energize only the first heater 38a, the transistors 63 to 66 of the drive circuit 60 are switching-controlled.

Subsequently, in step 702, it is determined whether or not the value of the detected current Is at that time is smaller than a predetermined value γ (γ <β <α). Here, when the value of the detected current Is is not smaller than the predetermined value γ, the first heater 38
Assuming that there is no performance deterioration related to a, the process proceeds to step 704. When the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 703. Then, in step 703, the abnormality flag H1XC for instructing that the performance deterioration of the first heater 38a is abnormal is set to "1", and the process proceeds to step 704.

In step 704, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the second heater 39a is forcibly energized. Then, in step 705, the detected current I at that time is detected.
It is determined whether the value of s is smaller than the predetermined value γ. Here, when the value of the detected current Is is not smaller than the predetermined value γ, it is determined that the performance of the second heater 39a is not deteriorated, and the process proceeds to step 707. When the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 706. Then, in step 706, the abnormality flag H2XC for instructing that the performance deterioration of the second heater 39a is abnormal is set to "1", and the process proceeds to step 707. In step 707, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the third heater 40a is forcibly energized.

Subsequently, in step 708, it is determined whether or not the value of the detected current Is at that time is smaller than the predetermined value γ. Here, if the value of the detected current Is is not smaller than the predetermined value γ, it is determined that the performance of the third heater 40a is not deteriorated, and the process proceeds to step 710. If the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 709. Then, in step 709, the abnormality flag H3XC for instructing that the performance deterioration of the third heater 40a is abnormal is set to "1", and the process proceeds to step 710.

In step 710, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the fourth heater 41a is forcibly energized. Then, in step 711, the detected current I at that time is detected.
It is determined whether the value of s is smaller than the predetermined value γ. Here, if the value of the detected current Is is not smaller than the predetermined value γ, it is assumed that the performance of the fourth heater 41a does not deteriorate. If the value of the detected current Is is smaller than the predetermined value γ, the process proceeds to step 712. And step 71
In 2, the abnormality flag H4XC for instructing that the performance deterioration of the fourth heater 41a is abnormal is set to "1".

As described above, after the abnormality determination processing relating to performance degradation is executed in step 700, the processing shifts to step 800 in the flowchart of FIG. In step 800, each heater 38a-41
It is determined whether or not the heater energizing circuit including a is abnormal. That is, each abnormality flag H1XA to H4XA, H1XB
.About.H4XB, HAXB, H1XC to H4XC is determined to be "1". Here, if there is no abnormality, it is determined that there is no failure in each heater energization circuit including each heater 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 is temporarily terminated. If there is an abnormality, it is assumed that there is a failure in each heater energizing circuit including each heater 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 the failure of each heater energizing circuit including the heaters 38a to 41a.

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

As described above, according to this embodiment, the ECU 51 controls the energization of the heaters 38a-41a of the air-fuel ratio sensors 38-41 in accordance with the engine operating conditions and the exhaust passage temperature conditions. It By this control, the heat generation amount of each of the heaters 38a to 41a is adjusted and the temperature of the sensor element 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 the comparator 80 in the voltage drop detection circuit 61. Further, the comparator 80 compares the voltage drop in all the heaters 38a to 41a with the value of the reference voltage VB. Then, 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 due to the disconnection of each heater energization circuit including the heaters 38a to 41a is determined based on the output result of the comparator 80. To be judged. For example,
When any of the heaters 38a to 41a has a failure due to disconnection or the like, the voltage drop amount related to all the heater energizing circuits that is compared with the value of the reference voltage VB in the comparator 80 changes. The ECU 51 determines that any one of the heater energizing circuits has a failure due to a disconnection or the like.

Therefore, in this embodiment, one comparator 8
Since a failure such as disconnection of each of the heaters 38a to 41a is determined only by using 0, a plurality of heaters 38a to
It is not necessary to individually provide a circuit or the like for failure determination for each of 41a. As a result, it is possible to detect a failure such as disconnection of each of the heaters 38a to 41a only by using the voltage drop detection circuit 61 including one comparator 80. Therefore, it is not necessary to provide a plurality of failure detection circuits related to the heaters 38a to 41a according to the number of the heaters 38a to 41a, and the circuit configuration can be simplified and the increase in the number of parts can be suppressed. You can

Moreover, in this embodiment, each heater 38a is
When a failure such as disconnection of any one of the heaters 38a to 41a is determined, deenergization of one of the heaters 38a to 41a and energization of all the remaining heaters 38a to 41a performed simultaneously with the deenergization of all the heaters 38a to 41a are performed. 41a is sequentially and compulsorily performed. And each heater 3
8A to 41a are sequentially de-energized and energized, the ECU 51 causes the heater energization circuit in which a failure occurs in each heater energization circuit including the heaters 38a to 41a based on the output result of the comparator 80. Is specified.
For example, when the output result of the comparator 80 is at a low level when the first heater 38a is not energized and the other heaters 39a to 41a are energized,
At that time, it is specified that the heater energizing circuit including the first heater 38a that is not energized is out of order. That is, it is determined that the heater energizing circuit including the first heater 38a has failed due to a disconnection or the like, and the abnormality flag H1XA is "1".
Is set to. Therefore, one heater energizing circuit in which a failure such as disconnection has occurred is specified from among the plurality of heater energizing circuits. As a result, a plurality of heater-equipped air-fuel ratio sensors 3
Corresponding to Nos. 8 to 41, it is possible to specifically specify which heater 38a to 41a has a failure such as disconnection.

In addition, in this embodiment, each heater 38a is
~ 41a is energized, based on the output result of the operational amplifier 71 in the current detection circuit 59, each heater 3
The ECU 51 determines the overcurrent state in 8a to 41a. When it is determined that the heaters 38a to 41a are in the overcurrent state, the heaters 38a to 41a are
a is sequentially forcibly energized, and 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
When the output result of the operational amplifier 71 is larger than the predetermined value α when the heater 38a of 1 is forcibly energized, the first heater 38a is specified to be in the overcurrent state. That is, the abnormality flag H1XB is set to "1" because the first heater 38a has failed in the overcurrent state. Therefore, one of the plurality of heaters 38a to 41a that has a failure due to an overcurrent state
a to 41a are specified. As a result, which of the heaters 38a-4 is associated with the plurality of heater-equipped air-fuel ratio sensors 38-41.
It is possible to specifically specify whether or not 1a has a failure due to an overcurrent state.

Similarly, when the diagnosis execution condition is satisfied,
Each of the heaters 38a to 41a is forcibly energized in sequence, and based on the output result of the operational amplifier 71, each of the heaters 38a to 41a.
A failure due to the performance degradation of a is determined. And ...
From the plurality of heaters 38a to 41a, the heaters 38a to 41a that are causing a failure due to performance degradation are specifically specified. As a result, a plurality of heater-equipped air-fuel ratio sensors 3
Corresponding to Nos. 8 to 41, it is possible to specifically specify which of the heaters 38a to 41a has a performance deterioration failure.

That is, in this embodiment, each heater 38a is
Current value in each heater energizing circuit including each heater 38a to 41a is detected, and each heater 38a to
The overcurrent and performance degradation failures associated with 41a are identified.
Therefore, by using together the identification of the fault caused by the overcurrent and the performance deterioration performed based on the current value and the identification of the fault caused by the disconnection performed based on the voltage drop, the heaters The failure related to 38a to 41a can be specified more specifically with high accuracy.

Further, in this embodiment, each heater 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 heater 38a to 41a is stored in the backup RAM 55, the failure relating to each heater 38a to 41a is read by reading the data in the backup RAM 55 at the time of periodical inspection of the engine. Presence / absence, the type of the failure, and the heater 38a related to the failure
~ 41a can be specifically confirmed.

The present invention is not limited to the above-described embodiments, but may be implemented as follows with a part of the configuration appropriately modified without departing from the spirit of the invention. (1) In the above embodiment, a total of four upstream and downstream sides of the 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 heater-equipped air-fuel ratio sensors 38 to 41 are provided. On the other hand, the present invention can be embodied in the case where the heater-equipped air-fuel ratio sensors are simply arranged on the upstream side and the downstream side of the three-way catalytic converter arranged in the exhaust passage of the in-line 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 the 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 heater 38a to 41a and the current flowing through each heater 38a to 41a. The failure related to each of the heaters 38a to 41a is determined based on both the values. On the other hand, only the voltage drop detection circuit including the comparator may be provided to determine the failure of each heater based on only the voltage drop in each heater.

[0077]

As described in detail above, according to the first aspect of the present invention, one of the comparators is used to compare the current value flowing in each heater or the voltage drop in each heater with the reference value. One end of every heater is connected in parallel to the input terminal. When it is determined that all the heaters are in the energized state, the failure of each heater is determined based on the output result of the comparator. Therefore, it is not necessary to individually provide a failure determination circuit for each of the plurality of heaters. As a result, the excellent effect of being able to detect a failure related to each heater of the plurality of heater-equipped air-fuel ratio sensors is achieved by using one circuit.

Further, according to the second invention, when the failure of each heater is determined, the non-energization of one heater and the energization of all the remaining heaters simultaneously with the non-energization are all performed. The heaters are forcibly operated sequentially. Then, when non-energization and energization are sequentially performed to each heater, the heater having the failure is specified among all the heaters based on the output result of the comparator. As a result, it is possible to specifically specify which of the plurality of heaters is out of order, which is an excellent effect.

[Brief description of drawings]

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

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

FIG. 3 is a schematic configuration diagram showing a gasoline engine system in an embodiment embodying 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 and its driving circuit, current detection circuit, voltage drop detection circuit, and the like in one embodiment.

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

FIG. 7 is a flowchart showing a part of the flowchart of FIG. 6 in detail according to an embodiment.

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

FIG. 9 is a flowchart showing in detail a part of the flowchart of FIG. 6 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, 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 (51 comprises a temperature control circuit, energization state determination means, failure determination means, forced energization means and failure identification means), 80 ... comparator.

[Procedure amendment]

[Submission date] November 16, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Failure detection device for air-fuel ratio sensor temperature control circuit

[Claims]

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 of a 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 fault.

[0002]

2. Description of the Related Art Conventionally, in 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 target fuel amount to be supplied to the internal combustion engine is feedback-controlled, so that the actual air-fuel ratio is controlled to the target air-fuel ratio. Here, in order to stably maintain the temperature of the sensor element forming the air-fuel ratio sensor at a predetermined activation temperature, a heater-equipped air-fuel ratio sensor including a heater is used. Since the temperature of the exhaust gas is slightly different depending on the operating conditions of the internal combustion engine and the position of the exhaust passage, when the air-fuel ratio sensor with a heater is used, the heater is controlled by the temperature adjustment (temperature adjustment) circuit. As a result, the temperature of the air-fuel ratio sensor is preferably controlled according to the conditions.

By the way, in the previous air-fuel ratio sensor with a heater, there is 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 adjustment 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, which should be obtained by the air-fuel ratio control, deviates from the target air-fuel ratio that is the target, and there is a risk that exhaust emission may be deteriorated.

Therefore, Japanese Utility Model Application Laid-Open No. 62-44272 proposes a device for an air-fuel ratio sensor with a heater, which detects disconnection of a temperature control circuit including the heater. In this device, when a vehicle is equipped with a failure diagnosis system, the presence or absence of a failure such as a disconnection is one of the diagnosis items, and the driver is promptly alerted to the diagnosis result.

That is, in the temperature control circuit according to this prior art, the heater and its drive circuit are connected in series to the power source to form a heater energizing circuit. 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 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, and a voltage drop due to the resistor is compared with a reference voltage. 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 adjustment circuit is at a predetermined level, it is determined that there is a failure such as disconnection, and a signal indicating that is output.

[0006]

However, the above-mentioned prior art is premised on a system in which only one heater-equipped air-fuel ratio sensor is provided in the exhaust passage. Therefore, when a system is provided in which a plurality of air-fuel ratio sensors with heaters are provided in the exhaust passage and the temperature of each heater is individually adjusted, failure of each heater energizing circuit including each heater depending on the number of heaters may occur. Each detection circuit is required. For example, in the case where the internal combustion engine is a V-type engine, or in the case of a double air-fuel ratio sensor system in which heater-equipped air-fuel ratio sensors are provided on the upstream side and the downstream side of the catalytic converter, respectively, the heater-equipped air-fuel ratio sensors Therefore, a plurality of failure detection circuits are required, which not only complicates the circuit configuration but also causes an increase in the number of parts.

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

[0008]

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 energization heat generation type heaters provided in each of the air-fuel ratio sensors M3 for heating each air-fuel ratio sensor M3. A heater M4 is provided, and each heater M4 is controlled by energizing the heater M4 according to 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 in which the temperature of each air-fuel ratio sensor M3 is adjusted by adjusting the amount of heat generated by the heater, the current value flowing through each heater M4 or the voltage drop in each heater M4 is compared with a reference value. Therefore, one of the input terminals of all the heaters M4 is connected in parallel to the comparator M.
6, an energized state determination means M7 for determining whether all the heaters M4 are energized, and an energized state determination means M7 determines that all the 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 amount with the reference value.

In order to achieve the second object, in the second invention, as shown in FIG. 2, in the failure detecting device for the air-fuel ratio sensor temperature adjusting circuit according to claim 1, the failure determining means M8. When the failure of each heater M4 is determined by, the non-energization for one heater M4 and the energization for all the remaining heaters M4 simultaneously with the non-energization are sequentially and forcibly performed for all the heaters M4. For energizing each of the heaters M4 based on the output result of the comparator M6 while the energization means M9 for
4 is provided with a failure identifying means M10 for identifying the 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 temperature adjusting circuit M5 allows the air-fuel ratio sensors M3 to operate in accordance with the operating conditions of the internal combustion engine and the exhaust passage temperature conditions. By controlling the energization of each of the heaters M4 provided in the, the amount of heat generated by each of the heaters M4 is adjusted and the temperature of each air-fuel ratio sensor M4 is adjusted.

Here, since the energization state determination means M7 determines that all the heaters M4 are in the energized state, the current value flowing through all the heaters M4 or the voltage drop in all the heaters M4 is determined by the comparator. It is compared with the reference value at M6. 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 of the heaters M4 is out of order due to disconnection or the like, the current value or the voltage drop amount that is compared with the reference value in the comparator M6 will change, and the failure determination means M8 will determine that there is a failure. To be judged.

Therefore, it is not necessary to individually provide a failure determination circuit for each of the plurality of heaters M4. According to the configuration of the second invention, as shown in FIG. 2, when the failure determination means M8 determines a failure of each heater M4, the forced energization means M9 deenergizes one heater M4 and its The energization of all the remaining heaters M4 performed simultaneously with the non-energization of
Forcibly performed for 4 sequentially. Then, when the heater M4 is sequentially de-energized and energized, the failure identifying unit M10 identifies the heater M4 having a failure among all the heaters M4 based on the output result of the comparator M6. To be done. For example, when the output result of the comparator M6 is at a low level, one heater M4 that is not energized is identified as having a failure due to disconnection or the like.

[0013]

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

FIG. 3 is a schematic diagram showing the gasoline engine system in this embodiment. In an engine body 1 that constitutes a V-type engine as an internal combustion engine mounted on a vehicle, each cylinder is divided into a left bank 2 and a right bank 3. Intake manifolds 4L and 4R and exhaust manifolds 5L and 5R are connected to the left and right banks 2 and 3, respectively.

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

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

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

Each spark plug 12 of the left and right banks 2 and 3
L and 12R have separate distributors 17L and 1
The ignition signal distributed at 7R is applied. Each distributor 17L, 17R is a separate igniter 18
The high voltage output from L, 18R is applied to the crankshaft 1
It is distributed to each spark plug 12L, 12R in synchronism with the rotation of 9. The ignition timing of each spark plug 12L, 12R is determined by the high voltage output timing from each igniter 18L, 18R.

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

An air flow meter 34 is attached downstream of the air cleaner 8. The air flow meter 34 detects the amount Q of intake air taken into the combustion chambers 2a, 3a of the engine body 1 through the intake pipe 7 and the like. The intake air temperature sensor 3 is provided near the air flow meter 34.
5 is attached. The intake air temperature sensor 35 detects the temperature of the 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 water temperature sensor 37 detects the temperature of the cooling water in the engine body 1, that is, the cooling water temperature THW.

On the other hand, a first air-fuel ratio sensor 38 and a second air-fuel ratio sensor 39 are provided on the upstream side and the downstream side of the one-way three-way catalytic converter 14L in the middle of the exhaust passage. Similarly, the third air-fuel ratio sensor 40 and the 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 respectively. Each of these air-fuel ratio sensors 3
The oxygen concentration Ox in the exhaust gas is detected from 8 to 41. Each of the air-fuel ratio sensors 38 to 41 is provided with a sensor element having a temperature characteristic, and a first heater 38a of an electric heating type for heating the sensor element for adjusting the temperature of each of the sensor elements, and a second heater. The heater 39a, the third heater 40a, and the fourth heater 41a are provided in each of the air-fuel ratio sensors 38 to 41.

A vehicle speed sensor 42 is provided on the transmission 21 drivingly connected to the engine body 1. The vehicle speed sensor 42 detects the vehicle speed, 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 connects the intake pipe 7 on the upstream side of the valve and the surge tank 6 on the downstream side to each other. There is. This bypass passage 22
A well-known linear solenoid type idle speed control valve (ISCV) 23 is provided midway. The opening of the ISCV 23 is controlled to stabilize the idling of the engine when the throttle valve 10 is fully closed. 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 Q of intake air into the combustion chambers 2a, 3a of the left and right banks is adjusted.

On the other hand, in this embodiment, a warning lamp 24 is provided on the instrument panel of the driver's seat (not shown), and one lead of the warning lamp 24 is connected to the positive terminal of the 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 described above is detected.

In this embodiment, each injector 11L,
11R, each igniter 18L, 18R, ISCV23,
The warning lamp 24 and the heaters 38a, 39a, 40a,
Each of 41a is an electronic control unit (hereinafter simply referred to as "ECU").
The drive is controlled by the (51). Therefore, EC
In U51, each injector 11L, 11R, each igniter 18L, 18R, ISCV23, warning lamp 24, battery 25 and each heater 38a, 39a, 40a, 41.
a are electrically connected to each other. In addition, the ECU 51
Includes a rotation speed sensor 31, cylinder identification sensors 32, 3
3, air flow meter 34, intake air temperature sensor 35, throttle sensor 36, water temperature sensor 37, each air-fuel ratio sensor 38-
41 and the vehicle speed sensor 42 are electrically connected to each other. Then, the ECU 51 uses the sensors 31 to 3
Various calculation and judgment processes are executed based on various signals from 3, 35 to 42 and the air flow meter 34. As a result, the injectors 11L and 11R, the igniters 18L and 18R, the ISCV 23, the warning lamp 24, and the heaters 38a, 39a, 40a, and 41a are preferably driven and controlled.

FIG. 4 is a block diagram showing the electrical configuration of the ECU 51. ECU 51 is a central processing unit (CPU)
52, a read-only memory (ROM) 53 that stores a predetermined control program and the like in advance, and a random access memory (RAM) 5 that temporarily stores the calculation result of the CPU 52 and the like.
4. Backup RA that saves pre-stored data
Equipped with M55 etc. 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 device 57 with a buffer, etc. are connected by a bus 58. Is configured as.

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, etc. are connected to the A / D converter 56, respectively. A current detection circuit 59 described later is connected to the A / D converter 56. The input / output unit 57 includes the rotation speed sensor 31, the cylinder discrimination sensor 3 described above.
2, 33, a throttle sensor 36, a vehicle speed sensor 42, etc. are respectively connected. Further, the I / O device 57 includes the above-mentioned ISCV 23, each injector 11L, 11R,
The igniters 18L and 18R, the warning lamp 24, and the like are connected to each other. Further, the above-mentioned heaters 38 a to 41 a are connected to the input / output device 57 via the drive circuit 60. In addition, a voltage drop detection circuit 61, which will be described later, is connected to the input / output device 57.

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

The current detection circuit 59, the drive circuit 60, and the voltage drop detection circuit 61 described above are included in the ECU 51. The ECU 51 including these circuits and the like uses the ECU 51 to adjust the temperature of the heaters 38a to 41a. A temperature control circuit) and its failure detection device are configured.

That is, FIG. 5 is a connection diagram showing the relationship between each heater energizing circuit including the heaters 38a to 41a and its driving circuit 60, the current detecting circuit 59, the voltage drop detecting circuit 61 and the like. In the figure, each heater 38a
One end of each of 41a to 41a is connected in parallel to the battery 25 described above via the input terminal 62. And each heater 3
Between the other end of 8a to 41a and the ground side, the drive 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.
It is composed of a power MOS type first transistor 63, a second transistor 64, a third transistor 65 and a fourth transistor 66 provided corresponding to the above.
The input terminals of the transistors 63 to 66 are connected to the input / output unit 5
It is connected to the CPU 52 via 7. The emitter terminals of the transistors 63 to 66 are heaters 38a to 4a, respectively.
1a, respectively. Then, by inputting a command signal from the CPU 52 to each input terminal of each transistor 63 to 66, each transistor 63 to 66 is turned on, and each heater energizing circuit including each heater 38a to 41a is closed.

The current detection circuit 59 includes transistors 63
To heaters 38a to 41a via collector terminals of
4 resistors 67, 68, 6 connected in series to
9, 70, operational amplifier 71 and other eight resistors 7
2, 73, 74, 75, 76, 77, 78, 79. One ends of the resistors 67 to 70 connected to the collector terminals of the transistors 63 to 66 are grounded. One ends of the resistors 72 to 75 are connected between the resistors 67 to 70 and the transistors 63 to 66, respectively. The non-inverting input terminal of the operational amplifier 71 is connected between the resistors 76 and 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 the 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 resistors 67 to 70 and the resistors 72 to 75 are
The current value detected by the combination of and 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. In the CPU 52, the current value abnormality is detected based on a predetermined current detection program.

The voltage drop detection circuit 61 includes one comparator 80.
It is composed of four diodes 81, 82, 83, 84 and one resistor 85. Each diode 81-8
The anode terminals of No. 4 are connected between the heaters 38a to 41a and the transistors 63 to 66, respectively. The cathode terminal of each of the diodes 81 to 84 and the resistor 8
One end of 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 device 57. In addition, one end of the resistor 86 is connected to the output terminal of the comparator 80. Then, the highest voltage (the smallest voltage drop) in 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 drops with the reference voltage VB, and the comparison result is input to the CPU 52 from the output terminal via the input / output unit 57. The CPU 52 performs voltage drop abnormality detection based on a predetermined voltage drop determination program. Here, when all the heaters 38a to 41a are in the energized state and the output of the comparator 80 is at a high level, that is, the voltage is high (the voltage drop is small), the CPU 52 detects the voltage drop abnormality.

In this embodiment, the ECU 51 comprises a temperature control circuit, an energization state determination means, a failure determination means, a forced energization means, and a failure identification means. Then, when the engine is in operation, the ECU 51 drives and controls the injectors 11L and 11R to execute the fuel injection control.
Further, the ECU 51 drives and controls the igniters 18L and 181R so as to execute the fuel injection timing control. Furthermore, EC
U51 is an air-fuel ratio feedback control (FB control) of the engine based on signals from the air-fuel ratio sensors 38 to 41.
To execute. At this time, the ECU 51 controls the air-fuel ratio sensor 38
The heaters 38a to 41a are driven and controlled in order to adjust the temperatures of the sensors to 41, and the failure detection of the heater energizing circuits including the sensors 38a to 41a is executed.

Next, in the gasoline engine system configured as described above, the ECU 5 is operated when the engine is operating.
The contents of the processing operation for adjusting the temperature of the air-fuel ratio sensor and detecting the failure of the heater, which are executed by No. 1, will be described.

The flow charts of FIGS. 6 to 9 show the ECU 51.
The processing routine for adjusting the temperature of the air-fuel ratio sensor and detecting the failure of the heater, which is executed by, is periodically executed at intervals of "several ms" during engine operation.

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 are detected.
Based on each detection signal from 7 etc., the engine speed NE,
The operating states such as the intake air amount Q, the throttle opening TA and the cooling water temperature THW are read. In addition, the voltage level of the battery 25 is also read here.

Then, in step 110, energization control for the heaters 38a-41a of the air-fuel ratio sensors 38-41 is executed. That is, the engine operating condition is calculated based on the engine speed NE, the intake air amount Q, the throttle opening TA, the cooling water temperature THW, etc. which are read this time. or,
The calculated 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 when the energizing conditions are satisfied,
Each transistor 63 in the drive circuit 60 in a known manner
The switching control of 66 is performed. By opening and closing each heater energizing circuit by this switching control, energization to each heater 38a to 41a is controlled, and thus the temperature of the sensor element in each air-fuel ratio sensor 38 to 41 is adjusted.

Then, in step 200, in a state where the heaters 38a to 41a are energized and controlled,
It is determined whether all the heaters 38a to 41a are in the energized state. Here, all the heaters 38a to 41
If all of a are not energized, step 400
Move to. When all the heaters 38a to 41a are all in the energized state, the process proceeds to step 210.

In step 210, it is determined whether the output of the comparator 80 in the voltage drop detection circuit 61 is low level. That is, when all the heaters 38a to 41a are energized without any problem, 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 since this voltage is lower than the reference voltage VB of the inverting input terminal, the low-level voltage is output from the comparator 80. Will be output. Therefore, when the output of the comparator 80 is at a low level, each of the heaters 38a to 41a is
Assuming that the voltage drop in each heater energizing circuit including is normal, the process proceeds to step 400. If the output of the comparator 80 is not at a low level, it is determined that the heater energization circuit has a failure such as disconnection, and in order to identify which of the heater energization circuits has a failure, go to step 300. Transition.

In step 300, in order to specify which of the heater energization circuits has an abnormal voltage drop,
Execute the voltage drop abnormality judgment. Specifically, as shown in FIG. 7, first, in step 301, the first heater 3
In order to energize all the heaters 39a, 40a, 41a other than 8a, each transistor 63 to
66 is switching-controlled.

Then, in step 302, it is judged 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 first heater 38a is abnormal, and the process proceeds to step 303. Then, in step 303, the abnormality flag H1XA for instructing 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 at the low level, it is determined that any of the heaters 39a, 40a, 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 other than the second heater 39a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled to energize 41a.

Then, in step 305, it is judged 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, the abnormality flag H2XA for instructing that the second heater 39a is abnormal due to a disconnection or the like is set to "1", and the process proceeds to step 307. When the output of the comparator 80 is not low level, the first and second heaters 3
If any of the heaters 40a and 41a other than 8a and 39a is abnormal, the process proceeds to step 307.

Then, in step 307, all the heaters 38a, 39a, other than the third heater 40a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled to energize 41a.

Then, in step 308, it is judged 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, the abnormality flag H3XA for instructing that the third heater 40a is abnormal due to disconnection or the like is set to "1", and the process proceeds to step 310. When the output of the comparator 80 is not low level, 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, other than the fourth heater 41a,
The transistors 63 to 66 of the drive circuit 60 are switching-controlled so that 40a is energized.

Then, in step 311, it is judged 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, the abnormality flag H4XA for instructing 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 the series of processes regarding abnormality determination is ended.

In this way, after the processing of the abnormality determination of the voltage drop in step 300 is executed, the processing shifts to step 400 in the flowchart of FIG. In the flowchart of FIG. 6, steps 200 and 210
Alternatively, in step 400 after shifting from step 300, it is determined whether or not the output result of the operational amplifier 71 in the current detection circuit 59 is in the 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. Then, when the output level of the operational amplifier 71 is higher than a predetermined value, it is determined that the overcurrent state. Here, if the output of the operational amplifier 71 is not in the 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 the overcurrent state, step 50 is executed to execute the next abnormality determination.
Move to 0.

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

Subsequently, in 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 detected 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 the overcurrent state, and step 5
Move to 04. When the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 503. Then, in step 503, the abnormality flag H1XB for instructing that the heater energization circuit including the first heater 38a is abnormal in the overcurrent state is set to "1", and the process proceeds to step 504.

In step 504, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the second heater 39a is forcibly energized. Then, in step 505, the detected current I at that time is detected.
It is determined whether the value of s is larger than the predetermined value α. Here, when the value of the detected 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 the overcurrent state, and the process proceeds to step 507. If the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 506. And step 50
6, the abnormality flag H2XB for instructing that the heater energization 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 transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the third heater 40a is forcibly energized. Then, in step 508, the detection current I at that time is detected.
It is determined whether the value of s is larger than the predetermined value α. Here, when the value of the detected 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 the overcurrent state, and the process proceeds to step 510.
If the value of the detected current Is is larger than the predetermined value α, the process proceeds to step 509. Then, in step 509, an abnormality flag H for instructing that the heater energizing circuit including the third heater 40a is abnormal in the overcurrent state.
3XB is set to "1" and the process proceeds to step 510.

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

Then, in step 513, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that all the heaters 38a to 41a are forcibly aligned and not energized.

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). Here, when the value of the detected current Is is not larger than the predetermined value β, all the heaters 38a to 38a.
It is assumed that all the heater energizing circuits including 41a are not in the overcurrent state. If the value of the detected current Is is larger than the predetermined value β, the process proceeds to step 515. Then, in step 515, the abnormality flag HAXB for instructing that all the heater energizing circuits including all the heaters 38a to 41a are abnormal in the overcurrent state is set to "1".

As described above, after the process of the abnormality determination regarding the overcurrent is executed 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 heater 38a-41
It is determined whether or not a predetermined operating condition for performing an abnormality determination (fault determination) of performance degradation related to a is satisfied. This judgment is made by reading the engine speed NE, intake air amount Q,
It is performed based on the throttle opening TA, the vehicle speed SPD, the voltage level of the battery 25, and the like. That is, a predetermined time has elapsed since the engine was started, the vehicle speed SPD is lower than a predetermined value, the voltage level of the battery 25 is within a predetermined range, and the engine load (the intake air amount Q or the throttle opening TA) is Within a predetermined range, air-fuel ratio sensors 38-4
It is estimated as a predetermined operating condition that the element temperature of No. 1 is within a preset predetermined temperature range (for example, 500 to 900 ° C.) that does not become inactive. Then, if the predetermined operating condition is satisfied, it is determined that the abnormality determination regarding the performance deterioration of each of the heaters 38a to 41a is executed, and the process proceeds to step 700. If the predetermined operation condition is not satisfied, the process directly proceeds to step 800.

In step 700, each heater 38
The abnormality determination of the performance deterioration related 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 here,
By deenergizing all the heaters 38a to 41a 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 heater 38a-41a itself is lowered from the high temperature state to the same temperature state as the sensor element. Further, if the heaters 38a to 41a are simply de-energized for about 10 seconds, the decrease in the element temperature of the air-fuel ratio sensors 38 to 41 is about "50 ° C", and the air-fuel ratio sensors 38 to 41 are normal. Should operate in "4
It does not fall below 00 ° C ".

Next, in step 702, the drive circuit 6 is forced to energize only the first heater 38a.
Switching control is performed on each of the zero transistors 63 to 66. Then, in step 703, the value of the detected current Is at that time is a predetermined value γ (γ <β <α) as a reference value.
Is less than or equal to. Here, the detection current Is
If the value of is not smaller than the predetermined value γ, it is determined that there is no performance deterioration related to the first heater 38a, and step 7
Move to 05. When the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 704. Then, in step 704, an abnormality flag H1 for instructing that the performance deterioration of the first heater 38a is abnormal.
XC is set to "1" and the process proceeds to step 705.

In step 705, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the second heater 39a is forcibly energized. Then, in step 706, the detected current I at that time is detected.
It is determined whether the value of s is smaller than the predetermined value γ. Here, if the value of the detected current Is is not smaller than the predetermined value γ, it is determined that the performance of the second heater 39a is not deteriorated, and the process proceeds to step 708. If the value of the detected 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 deterioration of the second heater 39a is abnormal is set to "1", and the process proceeds to step 708.

In step 708, the transistors 63 to 66 of the drive circuit 60 are switching-controlled to forcibly energize only the third heater 40a. Then, in step 709, the detected current I at that time is detected.
It is determined whether the value of s is smaller than the predetermined value γ. Here, when the value of the detected current Is is not smaller than the predetermined value γ, it is determined that the performance of the third heater 40a is not deteriorated, and the process proceeds to step 711. When the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 710. Then, in step 710, the abnormality flag H3XC for instructing that the performance deterioration of the third heater 40a is abnormal is set to "1", and the process proceeds to step 711.

At step 711, the transistors 63 to 66 of the drive circuit 60 are switching-controlled so that only the fourth heater 41a is forcibly energized. Then, in step 712, the detected current I at that time is detected.
It is determined whether the value of s is smaller than the predetermined value γ. Here, if the value of the detected current Is is not smaller than the predetermined value γ, it is assumed that the performance of the fourth heater 41a does not deteriorate. When the value of the detection current Is is smaller than the predetermined value γ, the process proceeds to step 713. And step 71
3, the abnormality flag H4XC for instructing that the performance deterioration of the fourth heater 41a is abnormal is set to "1".

In this way, after the processing of the abnormality determination (fault determination) relating to the performance deterioration of each of the heaters 38a to 41a is executed in step 700, the processing shifts to step 800 in the flowchart of FIG.

In step 800, each heater 38
It is determined whether or not there is an abnormality in the heater energizing circuit including a to 41a. That is, each abnormality flag H1XA to H4XA, H
It is determined whether or not any of 1XB to H4XB, HAXB, and H1XC to H4XC is "1". Here, if there is no abnormality, it is determined that there is no failure in each heater energization circuit including each heater 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 is temporarily terminated. If there is an abnormality, it is assumed that there is a failure in each heater energizing circuit including each heater 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 the failure of each heater energizing circuit including the heaters 38a to 41a.

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

As described above, according to this embodiment, the ECU 51 controls the energization of the heaters 38a-41a of the air-fuel ratio sensors 38-41 in accordance with the engine operating conditions and the exhaust passage temperature conditions. It By this control, the heat generation amount of each of the heaters 38a to 41a is adjusted and the temperature of the sensor element 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 the comparator 80 in the voltage drop detection circuit 61. Further, the comparator 80 compares the voltage drop in all the heaters 38a to 41a with the value of the reference voltage VB. Then, 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 due to the disconnection of each heater energization circuit including the heaters 38a to 41a is determined based on the output result of the comparator 80. To be judged. For example,
When any of the heaters 38a to 41a has a failure due to disconnection or the like, the voltage drop amount related to all the heater energizing circuits that is compared with the value of the reference voltage VB in the comparator 80 changes. The ECU 51 determines that any one of the heater energizing circuits has a failure due to a disconnection or the like.

Therefore, in this embodiment, one comparator 8
Since a failure such as disconnection of each of the heaters 38a to 41a is determined only by using 0, a plurality of heaters 38a to
It is not necessary to individually provide a circuit or the like for failure determination for each of 41a. As a result, it is possible to detect a failure such as disconnection of each of the heaters 38a to 41a only by using the voltage drop detection circuit 61 including one comparator 80. Therefore, it is not necessary to provide a plurality of failure detection circuits related to the heaters 38a to 41a according to the number of the heaters 38a to 41a, and the circuit configuration can be simplified and the increase in the number of parts can be suppressed. You can

Moreover, in this embodiment, each heater 38a is
When a failure such as disconnection of any one of the heaters 38a to 41a is determined, deenergization of one of the heaters 38a to 41a and energization of all the remaining heaters 38a to 41a performed simultaneously with the deenergization of all the heaters 38a to 41a are performed. 41a is sequentially and compulsorily performed. And each heater 3
8A to 41a are sequentially de-energized and energized, the ECU 51 causes the heater energization circuit in which a failure occurs in each heater energization circuit including the heaters 38a to 41a based on the output result of the comparator 80. Is specified.
For example, when the output result of the comparator 80 is at a low level when the first heater 38a is not energized and the other heaters 39a to 41a are energized,
At that time, it is specified that the heater energizing circuit including the first heater 38a that is not energized is out of order. That is, it is determined that the heater energizing circuit including the first heater 38a has failed due to a disconnection or the like, and the abnormality flag H1XA is "1".
Is set to. Therefore, one heater energizing circuit in which a failure such as disconnection has occurred is specified from among the plurality of heater energizing circuits. As a result, a plurality of heater-equipped air-fuel ratio sensors 3
Corresponding to Nos. 8 to 41, it is possible to specifically specify which heater 38a to 41a has a failure such as disconnection.

In addition, in this embodiment, each heater 38a is
~ 41a is energized, based on the output result of the operational amplifier 71 in the current detection circuit 59, each heater 3
The ECU 51 determines the overcurrent state in 8a to 41a. When it is determined that the heaters 38a to 41a are in the overcurrent state, the heaters 38a to 41a are
a is sequentially forcibly energized, and 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
When the output result of the operational amplifier 71 is larger than the predetermined value α when the heater 38a of 1 is forcibly energized, the first heater 38a is specified to be in the overcurrent state. That is, the abnormality flag H1XB is set to "1" because the first heater 38a has failed in the overcurrent state. Therefore, one of the plurality of heaters 38a to 41a that has a failure due to an overcurrent state
a to 41a are specified. As a result, which of the heaters 38a-4 is associated with the plurality of heater-equipped air-fuel ratio sensors 38-41.
It is possible to specifically specify whether or not 1a has a failure due to an overcurrent state.

Further, in this embodiment, when the predetermined operating condition is satisfied, all the heaters 38a to 41a are forcibly de-energized, and then the heaters 38a to 41a are forcibly energized one after another, Failures associated with those performance degradations are determined. Then, among the plurality of heaters 38a to 41a, the heaters 38a to 41a that have caused the failure related to the performance deterioration are specifically specified. As a result, it is possible to specifically specify which of the heaters 38a to 41a has a performance deterioration failure corresponding to the plurality of heater-equipped air-fuel ratio sensors 38 to 41.

That is, in this embodiment, each heater 38a is
Current values in the heater energizing circuits including the heaters 41a to 41a are detected as the detected current Is, and the overcurrent and the performance deterioration failure of each of the heaters 38a to 41a is specified based on the detected current Is. Therefore, by using together the identification of the failure caused by the overcurrent and the performance deterioration performed based on the current value and the identification of the failure caused by the disconnection performed based on the above voltage drop, each heater is 38
The failure related to a to 41a can be specified more specifically with high accuracy.

Further, in this embodiment, the heaters 38a-4a are used.
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 heater 38a to 41a is stored in the backup RAM 55, the failure relating to each heater 38a to 41a is read by reading the data in the backup RAM 55 at the time of periodical inspection of the engine. Presence / absence, the type of the failure, and the heater 38a related to the failure
~ 41a can be specifically confirmed.

The present invention is not limited to the above-described embodiment, but may be implemented as follows with a part of the configuration appropriately changed without departing from the spirit of the invention. (1) In the above embodiment, a total of four upstream and downstream sides of the 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 heater-equipped air-fuel ratio sensors 38 to 41 are provided. On the other hand, the present invention can be embodied in the case where the heater-equipped air-fuel ratio sensors are simply arranged on the upstream side and the downstream side of the three-way catalytic converter arranged in the exhaust passage of the in-line engine.

(2) In the above embodiment, the comparator 80 of the voltage drop detecting 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 the 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 heater 38a to 41a and the current flowing through each heater 38a to 41a. The failure related to each of the heaters 38a to 41a is determined based on both the values. On the other hand, only the voltage drop detection circuit including the comparator may be provided to determine the failure of each heater based on only the voltage drop in each heater.

[0079]

As described in detail above, according to the first aspect of the present invention, one of the comparators is used to compare the current value flowing in each heater or the voltage drop in each heater with the reference value. One end of every heater is connected in parallel to the input terminal. When it is determined that all the heaters are in the energized state, the failure of each heater is determined based on the output result of the comparator. Therefore, it is not necessary to individually provide a failure determination circuit for each of the plurality of heaters. As a result, the excellent effect of being able to detect a failure related to each heater of the plurality of heater-equipped air-fuel ratio sensors is achieved by using one circuit.

Further, according to the second invention, when the failure of each heater is determined, the non-energization of one heater and the energization of all the remaining heaters simultaneously with the non-energization are all performed. The heaters are forcibly operated sequentially. Then, when non-energization and energization are sequentially performed to each heater, the heater having the failure is specified among all the heaters based on the output result of the comparator. As a result, it is possible to specifically specify which of the plurality of heaters is out of order, which is an excellent effect.

[Brief description of drawings]

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

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

FIG. 3 is a schematic configuration diagram showing a gasoline engine system in an embodiment embodying 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 and its driving circuit, current detection circuit, voltage drop detection circuit, and the like in one embodiment.

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

FIG. 7 is a flowchart showing a part of the flowchart of FIG. 6 in detail according to an embodiment.

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

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

[Description of Reference Signs] 1 ... Engine body as internal combustion engine, 5L, 5R ... Exhaust manifold, 15L, 15R, 16 ... Exhaust pipe (5L, 5
R, 15L, 15R, 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 (51 comprises a temperature control circuit, energization state determination means, failure determination means, forced energization means and failure identification means), 80 ... comparator.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

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[Figure 9]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication G01N 27/409

Claims (2)

[Claims] 1. A plurality of air-fuel ratio sensors provided in an exhaust passage of an internal combustion engine and having temperature characteristics, and a plurality of energization heat-generation type sensors provided in each of the air-fuel ratio sensors for heating the air-fuel ratio sensors. And controlling the energization of each heater according to the operating condition of the internal combustion engine and the temperature condition of the exhaust passage to adjust the heat generation amount of each heater to adjust the temperature of each air-fuel ratio sensor. In the air-fuel ratio sensor temperature control circuit configured to perform the above, in order to compare the current value flowing through each heater or the voltage drop in each heater with a reference value, one input terminal is connected in parallel with one end of all the heaters. A comparator connected to the power source, an energization state determination means for determining whether or not all the heaters are energized, and an energization state determination means for energizing all the heaters. 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 the failure of each heater A failure detection device for an air-fuel ratio sensor temperature control circuit, comprising: 2. A failure detection device for an air-fuel ratio sensor temperature control circuit according to claim 1, wherein when one of the heaters has a failure determined by the failure determination means, one heater is de-energized and its de-energized. At the same time, energizing all the remaining heaters,
Based on the output result of the comparator, when the energization means for sequentially and compulsorily performing all the heaters and the non-energization and the energization of the heaters are sequentially performed by the force energization means, Failure detection device for an air-fuel ratio sensor temperature control circuit, comprising: failure specifying means for specifying a heater having a failure in the heater.