RU2613362C1 - Control device for internal combustion engine - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: invention refers to the control device for an internal combustion engine, particularly, to troubleshooting. The control device for an internal combustion engine with an air-fuel ratio gauge and a control unit of supplied electric potential to the air-fuel ratio gauge. The device performs control of a fuel supply cut-off for stopping fuel supply into the combustion chamber and troubleshooting control for the purpose of failure diagnostics in the air-fuel ratio gauge based on a current output signal of the air-fuel ratio gauge after completion of control of the fuel supply cut-off. The air-fuel ratio gauge is performed so that its output current increases, when the determined air-fuel ratio of exhaust gases increases and the maximum value of the output current increases, when electric potential supplied to the air-fuel ratio gauge increases. The control unit of supplied electric potential makes electric potential supplied to the air-fuel ratio gauge equal to that of the fuel supply cut-off and different to normal electric potential, which is supplied, when the control of the fuel supply cut-off is not performed, during performing of control of the fuel supply cut-off, and until completion of troubleshooting control after completion of control of the fuel supply cut-off, and changes electric potential supplied to the air-fuel ratio gauge from electric potential of the fuel supply cut-off to normal one after completion of troubleshooting control.

EFFECT: invention allows controlling wear troubleshooting for diagnostics of operation performance reduction of the air-fuel ratio gauge.

13 cl, 13 dwg

Description

FIELD OF THE INVENTION

[0001] The invention relates to a control device for an internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] The internal combustion engine is conventionally known which has an exhaust channel provided with an air-fuel ratio sensor and which is adapted to control the amount of fuel supplied to the internal combustion engine based on the output signal of this air-fuel ratio sensor.

[0003] As this air-fuel ratio sensor, a sensor equipped with a first electrode that is exposed to exhaust gases flowing in the exhaust channel, a second electrode that is exposed to the atmosphere, and a solid electrolyte layer of zirconium oxide, etc., is used, which is located between the first electrode and the second electrode. When determining the air-fuel ratio of exhaust gases (hereinafter referred to as the “air-fuel ratio in exhaust gases”) by this air-fuel ratio sensor, a certain voltage (for example, 0.45 V) is supplied between these electrodes and the current flowing between these electrodes , is defined as the output current. Further, the air-fuel ratio in the exhaust gas is calculated based on this output current.

[0004] On the other hand, in an internal combustion engine that is equipped with this air-fuel ratio sensor, control of the fuel cut-off to stop the fuel supply to the combustion chamber or to reduce the amount of fuel supplied to the combustion chamber can be performed with the internal combustion engine operating (with a rotating crankshaft) during braking of an internal combustion engine, etc. When this control is performed by the fuel cut-off, the atmospheric gas supplied to the combustion chamber flows directly to the exhaust channel. Therefore, a gas similar to atmospheric gas flows over the surface of the air-fuel ratio sensor, which is located in the exhaust channel. It should be noted here that the output current of the air-fuel ratio sensor increases when the air-fuel ratio in the exhaust gas rises (i.e., as the degree of depletion increases). In this regard, when a gas similar to atmospheric gas flows over the surface of the air-fuel ratio sensor, an excessive output current is generated.

[0005] Thus, it has been proposed to limit the voltage supplied to the air-fuel ratio sensor during the execution of the fuel cut-off control (for example, Patent Document 1). According to Patent Document 1, when the supply voltage is thus limited, the output current decreases even during the execution of the fuel cut-off control, and thus, the generation of excess output current can be prevented.

Reference Technical Documents

Patent documents

[0006] Patent Document 1: Publication of Japanese Patent Application No. 2004-316553 (JP 2004-316553 A)

Patent Document 2: Publication of Japanese Patent Application No. 2005-351096 (JP 2005-351096 A)

Patent Document 3: Publication of Japanese Patent Application No. 2000-356618 (JP 2000-356618 A)

Patent Document 4: Publication of Japanese Patent Application No. 5-240829 (JP 5-240829 A)

SUMMARY OF THE INVENTION

The problem solved by the invention

[0007] In this case, the air-fuel ratio sensor that is used for this internal combustion engine gradually wears out during its use. This wear and tear can be seen, for example, in a deterioration in responsiveness, that is, a phenomenon in which the output current of the air-fuel ratio sensor changes later than the current air-fuel ratio, etc. When the air-fuel ratio sensor wears out in this manner, this prevents the various types of control performed by the control device for the internal combustion engine.

[0008] Therefore, it is proposed to perform wear diagnosis management to diagnose a reduction in the performance of the air-fuel ratio sensor as a malfunction. More specifically, for example, when the actual air-fuel ratio changes, a response time that elapses before the output parameter of the air-fuel ratio sensor changes is determined, and a fault diagnosis in the air-fuel ratio sensor is performed based on this response time. During this fault diagnosis, the diagnosis can be carried out with accuracy, which increases with increasing degree of change in the current air-fuel ratio.

[0009] As described above, when the fuel cut-off control is performed, a gas similar to atmospheric gas flows over the surface of the air-fuel ratio sensor, so that gas with an air-fuel ratio is extremely high. After that, when the normal control starts after the control of the fuel cut-off ends, the air-fuel ratio of exhaust gases usually becomes closer to the theoretical air-fuel ratio. In this regard, during the end of the fuel cut-off control, the air-fuel ratio near the air-fuel ratio sensor may change significantly. Therefore, when the troubleshooting control of the air-fuel ratio sensor is performed at the end of the fuel cut-off control, a malfunction in the air-fuel ratio sensor can be accurately diagnosed.

[0010] In this case, when the voltage supplied to the air-fuel ratio sensor varies greatly, noise is temporarily generated in the air-fuel ratio sensor. Therefore, when the supplied voltage is reduced to, for example, 0 V during execution of the fuel cut-off control, and then rapidly changes to a normal voltage (voltage that is supplied while the fuel cut-off control is not performed, and which amounts to, for example, 0.45 V), at the end of the fuel cut-off control, as in the aforementioned patent document 1, noise is generated in the output current of the air-fuel ratio sensor after the end of the fuel cut-off control. In this regard, when the troubleshooting control of the air-fuel ratio sensor is performed during the end of the fuel cut-off control, the malfunction in the air-fuel ratio sensor cannot be accurately diagnosed.

[0011] Thus, in view of the aforementioned problem, an object of the invention is to provide a control device for an internal combustion engine that can make the voltage supplied to the air-fuel ratio sensor different from the normal voltage for the duration of the fuel cut-off control, and which can accurately diagnose a malfunction in the air-fuel ratio sensor even when the applied voltage changes to normal voltage after the end of control th fuel supply.

Means of solving the problem

[0012] In order to solve the above problem, the first invention provides a control device for an internal combustion engine. This control device includes an air-fuel ratio sensor, which is located in the exhaust channel of the internal combustion engine, and a voltage supply control unit that controls the voltage supplied to the air-fuel ratio sensor. The control device controls the fuel cut-off to stop the fuel supply to the combustion chamber or reduce the amount of fuel supplied to the combustion chamber during operation of the internal combustion engine, and control fault diagnosis to diagnose a malfunction of the air-fuel ratio sensor based on the current output of the air-fuel sensor fuel ratio after the end of the fuel cutoff control. The air-fuel ratio sensor is configured so that its output current increases when the detected air-fuel ratio of the exhaust gas rises, and the maximum value of the output current increases when the voltage supplied to the air-fuel ratio sensor rises. The voltage supply control unit makes the voltage supplied to the air-fuel ratio sensor equal to the fuel cut-off voltage different from the normal voltage that is supplied when the fuel cut-off control is not performed, during the fuel cut-off control and before the fault diagnosis control is performed after the end of the fuel cut-off control, and changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to normal voltage after the end of the fault diagnosis management.

[0013] The second invention is obtained by modifying the first invention as follows. The internal combustion engine further comprises an exhaust gas purification catalyst that is located in an exhaust channel of the engine. The exhaust air-fuel ratio sensor is located on the exhaust side of the exhaust gas purification catalyst in the direction of exhaust gas flow. The enrichment control after restoring the fuel supply to bring the air-fuel ratio of exhaust gases flowing to the exhaust gas purification catalyst to a rich air-fuel ratio, which is richer than the theoretical air-fuel ratio after the end of the fuel cut-off control, is performed by the internal engine control device combustion.

[0014] A third invention is obtained by modifying the second invention as follows. The voltage supply control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after the later of the following time points: the time when the control of fault diagnosis is completed and the time when the control of enrichment after restoration is completed fuel supply.

[0015] A fourth invention is obtained by modifying the third invention as follows. The voltage supply control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage before the output current of the air-fuel ratio sensor becomes less than the value corresponding to the theoretical air-fuel ratio again after the end of the enrichment control after restoration of fuel supply.

[0016] The fifth invention is obtained by modifying the third or fourth invention as follows. The enrichment control after restoration of the fuel supply ends when the output current of the air-fuel ratio sensor becomes equal to or less than the current at the end of the determination, corresponding to the air-fuel ratio at the end of the determination, which is richer than the theoretical air-fuel ratio.

[0017] The sixth invention is obtained by modifying the fifth invention as follows. The supply voltage control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after the end of the enrichment control after restoring the fuel supply and before the output current of the air-fuel ratio sensor changes from a current that is equal to or less than current at the end of the determination, to the current corresponding to the theoretical air-fuel ratio.

[0018] The seventh invention is obtained by modifying the second invention as follows. The enrichment control after restoration of the fuel supply ends on the basis of another parameter, regardless of the output current of the air-fuel ratio sensor. The supply voltage control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after the end of the fault diagnosis control and before the end of the enrichment control after restoring the fuel supply.

[0019] The eighth invention is obtained by modifying the seventh invention as follows. The control of the fault diagnosis is not performed even after the end of the control of the fuel cutoff, when the condition for the control of the diagnosis of faults is not fulfilled at the time of the end of the control of the fuel cutoff. The enrichment control after restoring the fuel supply ends after the output current of the air-fuel ratio sensor becomes equal to the value corresponding to the air-fuel ratio at the end of the determination determined in advance for the first time from the start of the enrichment control after restoring the fuel supply when the fault diagnosis control is not performed after the end of the fuel cutoff control. The enrichment control after restoring the fuel supply ends on the basis of another parameter, regardless of the output current of the air-fuel ratio sensor, when a fault diagnosis control is performed after the end of the fuel cutoff control.

[0020] The ninth invention is obtained by modifying any of the first to eighth inventions as follows. The control of the fault diagnosis is not performed even after the end of the control of the fuel cutoff, when the condition for the control of the diagnosis of faults is not fulfilled at the time of the end of the control of the fuel cutoff. The supply voltage control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage as soon as the output current of the air-fuel ratio sensor becomes equal to or less than the value determined in advance after the end of the fuel cut-off control when the fault diagnosis control is not performed after the end of the fuel cut-off control.

[0021] A tenth invention is obtained by modifying any of the first to ninth inventions as follows. The fuel cut-off voltage is less than the normal voltage.

[0022] The eleventh invention is obtained by modifying the tenth invention as follows. The fuel cut-off voltage is higher than the lower limit of the voltage range of the current limit of the air-fuel ratio sensor at the time when the air-fuel ratio sensor is exposed to a gas having a theoretical air-fuel ratio.

[1223] The twelfth invention is obtained by modifying the tenth or eleventh invention as follows. The control of the fault diagnosis is not performed even after the end of the control of the fuel cutoff, when the condition for the control of the diagnosis of faults is not fulfilled at the time of the end of the control of the fuel cutoff. The fuel cut-off voltage is higher than the lower limit of the voltage range of the current limit of the air-fuel ratio sensor at a time when the air-fuel ratio sensor is exposed to a gas having a predetermined lean air-fuel ratio. The voltage supply control unit changes the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage as soon as the output current of the air-fuel ratio sensor becomes equal to or less than the value corresponding to the given lean air-fuel ratio when Diagnostic fault management is not performed after the end of the fuel cutoff control.

[0024] The thirteenth invention is obtained by modifying any of the first to twelfth inventions as follows. An internal combustion engine comprises an exhaust gas purification catalyst that is located in an exhaust channel of an engine. The air-fuel ratio sensor is located on the outlet side of the exhaust gas purification catalyst in the direction of the exhaust gas flow and is configured as a bowl-shaped air-fuel ratio sensor with a current limit. Additionally, an air-fuel ratio inlet sensor is provided which is located in the exhaust channel of the exhaust gas purification catalyst on the inlet side and which is configured as a multilayer air-fuel ratio sensor with a current limit.

Result of invention

[0025] The invention can make the voltage supplied to the air-fuel ratio sensor different from the normal voltage during the fuel cut-off control, and can accurately diagnose a malfunction in the air-fuel ratio sensor even when the supplied voltage changes to normal voltage after the end of the fuel cutoff control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a view schematically showing an internal combustion engine in which a control device according to the invention is applied.

FIG. 2 is a schematic sectional view of a multilayer air-fuel ratio sensor.

FIG. 3 is a graph showing the relationship between the voltage supplied to the sensor and the output current for each air-fuel ratio in the exhaust gas.

FIG. 4 is a view showing the relationship between the air-fuel ratio in exhaust gases and the output current I at a time when the applied voltage is constant.

FIG. 5 is a timing chart of the output current of the intake sensor, the output current of the exhaust sensor, etc., before and after controlling the fuel cut-off.

FIG. 6 is a timing chart of an output current from an inlet sensor, an output current of an exhaust sensor, etc., before and after controlling a fuel cut-off.

FIG. 7 is a timing chart of an output current from an intake sensor, an output current of an exhaust sensor, etc., before and after controlling a fuel cut-off.

FIG. 8 is a flowchart showing a procedure for controlling the voltage supplied to the exhaust air-fuel ratio sensor.

FIG. 9 is a timing chart of an output current from an inlet sensor, an output current of an exhaust sensor, etc., before and after controlling the fuel cut-off.

FIG. 10 is a timing chart of an output current from an inlet sensor, an output current of an exhaust sensor, etc., before and after controlling a fuel cut-off.

FIG. 11 is a timing chart of an output current from an inlet sensor, an output current of an exhaust sensor, etc., before and after controlling the fuel cut-off.

FIG. 12 is a flowchart showing a procedure for controlling the voltage supplied to the exhaust air-fuel ratio sensor and enrichment control after restoring the fuel supply.

FIG. 13 is a view schematically showing the structure of a bowl-shaped air-fuel ratio sensor.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Next, a diagnostic device for an internal combustion engine according to the invention will be described in detail with reference to the drawings. Moreover, in the following description, the same components are denoted by the same reference position. FIG. 1 is a view schematically showing an internal combustion engine on which a diagnostic device according to a first embodiment of the invention is applied.

[0028] General Description of an Internal Combustion Engine

As can be seen from FIG. 1, engine housing, cylinder block, piston, cylinder head, combustion chamber, inlet valve, inlet, exhaust valve, exhaust outlet are designated respectively as 1, 2, 3, 4, 5, 6, 7, 8, and 9. Piston 3 makes a reciprocating movement inside the block of 2 cylinders. The cylinder head 4 is attached to the cylinder block 2. A combustion chamber 5 is formed between the piston 3 and the cylinder head 4. The inlet valve 6 opens and closes the inlet 7, while the exhaust valve 8 opens and closes the outlet 9.

[0029] As shown in FIG. 1, the spark plug 10 is located in the central part of the surface of the inner wall of the cylinder head 4, while the fuel injection valve 11 is located on the side of the surface of the inner wall of the cylinder head 4. The spark plug 10 is configured to generate a spark in accordance with the ignition signal. In addition, the fuel injection valve 11 injects a predetermined amount of fuel into the combustion chamber 5 in accordance with the injection signal. In this case, the fuel injection valve AND can also be positioned to inject fuel into the inlet 7. In addition, in the present embodiment, gasoline having a theoretical air-fuel ratio of 14.6 is used as fuel. However, other fuels can be used in an internal combustion engine to which a diagnostic device according to the invention is applied.

[0030] The inlet 7 of each cylinder is connected to the expansion tank 14 through the corresponding inlet branch pipes 13. The expansion tank 14 is connected to the air purifier 16 through the inlet pipe 15. The inlet channels 7, the inlet branch pipes 13, the expansion tank 14 and the inlet pipe 15 form intake duct. In addition, a throttle valve 18 is located inside the inlet pipe 15, which is actuated by a throttle valve actuator 17. The throttle valve 18 can be actuated by the throttle valve actuator 17, which leads to a change in the opening area of the inlet channel.

[0031] On the other hand, the exhaust openings 9 of the respective cylinders are connected to the exhaust manifold 19. The exhaust manifold 19 has a plurality of branch sections that are connected to the outlet openings 9, respectively, and a common section where all the branch sections are connected. A common portion of the exhaust manifold 19 is connected to the inlet casing 21, which has a built-in inlet exhaust gas purification catalyst 20. The inlet casing 21 is connected to the exhaust casing 23, which has a built-in exhaust catalyst for cleaning the exhaust gases 24, through the exhaust pipe 22. The exhaust openings 9, the exhaust manifold 19, the inlet casing 21, the exhaust pipe 22 and the exhaust casing 23 form an exhaust channel.

[0032] The electronic control unit (ECU) 31 is a digital computer and is equipped with RAM (random access memory) 33, ROM (read-only memory) 34, a microprocessor (CPU) 35, input port 36 and output port 37, which are connected together by bi-directional bus 32. An air flow meter 39 is located in the intake pipe 15 to determine the flow rate of air flowing through the intake pipe 15. The output signal of this air flow meter 39 is supplied through a corresponding analog-to-digital converter (ADC) 38 to inlet port 36. In addition, there is an air-fuel ratio inlet sensor 40 that senses an air-fuel ratio in exhaust gases flowing inside the exhaust manifold 19 (i.e., exhaust gases flowing in the exhaust gas purification inlet catalyst 20) located in common section of the exhaust manifold 19. In addition, in the exhaust pipe 22 is located the exhaust sensor 41 air-fuel ratio, which determines the air-fuel ratio in the exhaust gases flowing inside the exhaust pipe 22 (i.e. exhaust gases flowing from the inlet catalyst 20 for exhaust gas purification and flowing to the exhaust catalyst 24 for exhaust gas purification). The output signals of these air-fuel ratio sensors 40 and 41 are also supplied via the respective ADC 38 to the input port 36. The configurations of these air-fuel ratio sensors 40 and 41 will be explained below.

[0033] In addition, the load sensor 43, which generates an output voltage proportional to the force applied to the accelerator pedal 42, is connected to the accelerator pedal 42, and the output of the load sensor 43 is supplied to the input port 36 through the corresponding ADC 38. The crankshaft angle sensor 44 generates an output pulse every time, for example, the crankshaft rotates 15 degrees, and this output pulse is supplied to the input port 36. In the CPU 35, the engine speed is calculated based on the output pulse of this angle sensor 44 to lenvala. On the other hand, the output port 37 is connected via an appropriate drive circuit 45 to a spark plug 10, a fuel injector 11, and a throttle valve actuator 17.

[0034] Both the inlet exhaust gas purification catalyst 20 and the exhaust gas purification catalyst 24 are a three component catalyst that has the ability to adsorb oxygen. More specifically, each exhaust gas purification catalyst 20 and 24 is formed from a ceramic support on which a precious metal is deposited that has a catalytic effect (e.g., platinum (Pt)) and a substance that has the ability to adsorb oxygen (e.g., cerium oxide ( CeO ₂ )). Upon reaching a predetermined activation temperature, the exhaust gas purification catalysts 20 and 24 exhibit, in addition to the catalytic effect, the ability to adsorb oxygen while removing unburned gases (HC, CO, etc.) and nitrogen oxides (NO _x ).

[0035] In accordance with the oxygen adsorption ability of the exhaust gas purification catalysts 20 and 24, the exhaust gas purification catalysts 20 and 24 accumulate oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in the exhaust purification catalysts 20 and 24 gas, poorer than the theoretical air-fuel ratio, and is hereinafter referred to as the "poor air-fuel ratio". On the other hand, the exhaust gas purification catalysts 20 and 24 release oxygen accumulated therein when the air-fuel ratio of the exhaust gases flowing therein is richer than this theoretical air-fuel ratio, and is hereinafter referred to as “rich air-fuel ratio”. As a result, while oxygen adsorption ability of the exhaust gas purification catalysts 20 and 24 is maintained, the air-fuel ratio of exhaust gases flowing from the exhaust gas purification catalysts 20 and 24 is approximately equal to the theoretical air-fuel ratio, regardless of the air-fuel ratio of exhaust gases flowing into the exhaust gas purification catalysts 20 and 24.

[0036] In this case, the "air-fuel ratio of exhaust gases" means the ratio of the mass of fuel to the mass of air that enter before the exhaust gas is created, and usually this means the ratio of the mass of fuel to the mass of air that enter the combustion chamber at the time of exhaust . In the present description, the air-fuel ratio of exhaust gases is referred to as the "air-fuel ratio of exhaust gases" in some cases.

[0037] Description of the air-fuel ratio sensors

In the present embodiment, a multilayer current-limit air-fuel ratio sensor is applied as each of the air-fuel ratio sensors 40 and 41. The design of the air-fuel ratio sensors 40 and 41 will be specifically described using FIG. 2. Each of the air-fuel ratio sensors 40 and 41 comprises a solid electrolyte layer 51, an exhaust side electrode 52, which is located on one side surface of the solid electrolyte layer 51, an atmosphere side electrode 53, which is located on the other side surface a solid electrolyte layer 51, a diffusion rate limiting layer 54 that limits the diffusion rate of the exhaust gas passage, a protective layer 55 that protects the diffusion rate limiting layer 54 and a heating section 56 that th heats the sensors 40 and 41 of the air-fuel ratio.

[0038] The solid electrolyte layer 51 is formed from a sintered compact of oxides with ionic oxygen conductivity, which are obtained by applying CaO, MgO, Y ₂ O ₃ , Yb ₂ O _3, and the like. as a stabilizer on ZrO ₂ (zirconia), HfO ₂ , ThO ₂ , Bi ₂ O ₃ or the like. In addition, the diffusion rate limiting layer 54 is formed of a porous sintered compact of heat-resistant inorganic substances such as alumina, magnesium oxide, quartzite, spinel, mullite, or others. In addition, both the exhaust side electrode 52 and the atmosphere side electrode 53 are formed of a noble metal with high catalytic activity such as platinum or the like.

[0039] In addition, the voltage V supplied to the sensor is supplied between the electrode on the exhaust side and the electrode on the atmosphere by the voltage supply control unit 60, which is installed in the ECU 31. In addition, the ECU 31 contains a current sensing device 61 that determines current I flowing between these electrodes 52 and 53 through the solid electrolyte layer when voltage is supplied to the sensor. The current detected by this current sensing device 61 is the output current of each of the air-fuel ratio sensors 40 and 41.

[0040] Each of the air-fuel ratio sensors 40 and 41 thus configured has a current-voltage characteristic (VI) as shown in FIG. 3. As can be seen from FIG. 3, the output current I increases when the air-fuel ratio in the exhaust gas rises (shifts to the poor side). In addition, in curve VI, for each air-fuel ratio in the exhaust gases, there is a range parallel to the V axis, namely, a range where the output current barely changes even when the voltage supplied to the sensor changes. This voltage range is referred to as the limiting current range, and the current at this time is referred to as the limiting current. In FIG. 3, the range of the limiting current and the limiting current at a time when the air-fuel ratio in the exhaust gases is 18 are indicated by W ₁₈ and Ι _18, respectively.

[0041] On the other hand, in the range where the voltage supplied to the sensor is less than the current limit range, the output current changes substantially in proportion to the voltage supplied to the sensor. This range is called the proportional range. The slope here is determined by the resistance of the DC element of the solid electrolyte layer 51. In addition, in the range where the voltage supplied to the sensor is higher than the current limit range, the output current also increases when the voltage supplied to the sensor increases. In this range, the output voltage changes when the voltage supplied to the sensor changes due to the decomposition of moisture contained in the exhaust gases, etc. on the electrode 52 from the exhaust side.

[0042] FIG. 4 is a graph showing the relationship between the air-fuel ratio in exhaust gases and the output current I at a time when the supply voltage is set to a constant value of about 0.45 V. As can be seen from FIG. 4 for the sensors 40 and 41 of the air-fuel ratio, the output current I from each of the sensors 40 and 41 of the air-fuel ratio increases when the air-fuel ratio in the exhaust gas rises (i.e., shifts to the poor side). In addition, each of the air-fuel ratio sensors 40 and 41 is configured such that the output current I is zero when the air-fuel ratio in the exhaust gas is equal to the theoretical air-fuel ratio. In addition, when the air-fuel ratio in the exhaust gas becomes equal to or greater than a certain value, or becomes equal to or less than a certain value, the ratio of the change in the output current to the change in the air-fuel ratio in the exhaust gas decreases.

[0043] In this case, in the above example, the current limit air-fuel ratio sensor configured as shown in FIG. 2, is applied as each of the air-fuel ratio sensors 40 and 41. However, provided that the output parameter changes smoothly when the air-fuel ratio in the exhaust gas changes, at least in the immediate vicinity of the theoretical air-fuel ratio, any air-fuel ratio sensor can be used instead of the air-fuel sensor relationship with current limit, for example, air-fuel ratio sensor without current limit, etc.

[0044] Basic management

With the internal combustion engine configured in this way, the amount of fuel injection from the fuel injection valve 11 is set so that the air-fuel ratio of the exhaust gases flowing to the inlet exhaust gas purification catalyst 20 becomes equal to the optimal air-fuel ratio based on the operating state of the engine, based on the output signals of the air-fuel ratio inlet sensor 40 and the air-fuel ratio output sensor 41. As a method for setting this fuel injection value, a control execution method can be mentioned in which the air-fuel ratio of exhaust gases flowing to the inlet exhaust gas purification catalyst 20 becomes equal to the target air-fuel ratio based on the output signal of the air-fuel inlet sensor 40 the ratio and correction of the output signal of the inlet sensor 40 of the air-fuel ratio or a change in the target air-fuel ratio based on the output signal of the exhaust The sensors 41 of the air-fuel ratio.

[0045] Furthermore, with the internal combustion engine according to an embodiment of the invention, controlling the fuel cut-off to stop the fuel injection from the fuel injection valve 11 or substantially reduce the amount of fuel injected from the valve AND fuel injection to stop the fuel supply to the chamber 5, substantially reducing the amount of fuel supplied to the combustion chamber 5 during operation of the internal combustion engine, is performed during deceleration, and the like. a vehicle equipped with an internal combustion engine. This control of the fuel cut-off, for example, is performed when the amount of pressing the accelerator pedal 42 is zero or almost zero (i.e., the engine load is zero or almost zero), and the engine speed is equal to or higher than the set speed, which is higher than rpm during idle.

[0046] When the fuel cut-off control is performed, atmospheric gas (air) or gas similar to atmospheric gas is discharged from the internal combustion engine. Therefore, both air-fuel ratio sensors 40 and 41 are exposed to a gas having an extremely high air-fuel ratio (i.e., an extremely high depletion ratio).

[0047] In addition, during the fuel cut-off control, a large amount of oxygen flows into the exhaust gas inlet catalyst 20, and the oxygen adsorption amount of the exhaust gas inlet catalyst 20 reaches an upper adsorption limit. In this regard, when using the internal combustion engine according to the present embodiment, enrichment control after recovering the fuel supply to make rich the air-fuel ratio of exhaust gases flowing to the exhaust gas purification inlet catalyst 20 is performed immediately after the fuel cut-off control is completed, so as to release oxygen accumulated by the inlet exhaust gas purification catalyst 20 while controlling the fuel cut-off. This is shown in FIG. 5.

[0048] FIG. 5 is a timing chart of the output current of the air-fuel ratio inlet sensor 40, the oxygen adsorption amount of the exhaust gas inlet catalyst 20, and the output current of the air-fuel ratio exhaust sensor 41 at a time when the fuel cut-off control is performed. The output current of each of the air-fuel ratio sensors 40 and 41 is zero when the air-fuel ratio in the exhaust gas is equal to the theoretical air-fuel ratio, and increases when the air-fuel ratio in the exhaust gas is shifted to the poor side. In the example shown in the figure, the control of the fuel cut-off starts at time t ₁ and the control of the fuel cut-off ends at time t ₃ .

[0049] In the example shown in the figure, when the fuel shut-off control starts at time t ₁ , exhaust gases whose air-fuel ratio is poor are discharged from the engine body 1, and the output current of the air-fuel ratio intake sensor 40 increases respectively. At this time, oxygen in the exhaust gases flowing to the intake exhaust gas purification catalyst 20 is accumulated by the exhaust exhaust gas purification catalyst 20. Therefore, the oxygen adsorption amount of the intake exhaust purification catalyst 20 increases. On the other hand, the output current of the exhaust air-fuel ratio sensor 41 remains zero (corresponding to the theoretical air-fuel ratio).

[0050] After this, when the oxygen adsorption amount of the inlet exhaust gas purification catalyst 20 reaches a maximum adsorption value (Cmax) at time t ₂ , the inlet exhaust gas purification catalyst 20 can no longer accumulate oxygen. Therefore, after time t ₂ , the output current of the exhaust air-fuel ratio sensor 41 becomes greater than 0.

[0051] When the control of the fuel cut-off ends at time t ₃ , the enrichment control after restoring the fuel supply is performed to release oxygen accumulated by the exhaust purification inlet catalyst 20 during the control of the fuel cut-off. When controlling enrichment after restoring the fuel supply, exhaust gases whose air-fuel ratio is richer than the theoretical air-fuel ratio are discharged from the engine housing 1. As a result, the output current of the intake air-fuel ratio inlet sensor 40 becomes less than 0, and the oxygen adsorption amount of the intake exhaust purification catalyst 20 is gradually reduced. At this time, even when the exhaust gas, in which the air-fuel ratio is rich, is forced to flow into the inlet exhaust gas purification catalyst 20, the oxygen accumulated by the inlet exhaust gas purification catalyst 20 reacts with unburned exhaust gases, thus , the air-fuel ratio of exhaust gases discharged from the inlet exhaust gas purification catalyst 20 is approximately equal to the theoretical air-fuel ratio. Therefore, the output air-fuel ratio of the exhaust air-fuel ratio sensor 41 is approximately zero.

[0052] After an ongoing decrease, the amount of oxygen adsorption eventually becomes approximately zero, and unburned gases flow from the inlet exhaust gas purification catalyst 20. Thus, at time t ₄ , the air-fuel ratio in the exhaust gas detected by the exhaust air-fuel ratio sensor 41 drops to the air-fuel ratio at the end of the determination, which is richer than the theoretical air-fuel ratio. Thus, when the output current of the exhaust air-fuel ratio sensor 41 reaches the current at the end of the determination (which corresponds to the air-fuel ratio at the end of the determination), which is slightly less than zero for the first time from the start of enrichment control after restoring the fuel supply, enrichment control after restoring the supply fuel runs out. After this, normal air-fuel ratio control begins. In the example shown in the figure, the air-fuel ratio of exhaust gases discharged from the engine housing is controlled to correspond to the theoretical air-fuel ratio.

[0053] In this case, the condition for ending the enrichment control after restoring the fuel supply is not absolutely necessary for determining the rich air-fuel ratio by the exhaust air-fuel ratio sensor 41. For example, enrichment control after restoration of the fuel supply can be completed under another condition, when it expires some time after the total intake air reaches a certain value, etc., after the end of the fuel cut-off control.

[0054] Failure Diagnostics Management

As described above, in the case where the amount of injected fuel is set based on the signals of each of the sensors 40 and 41 of the air-fuel ratio, when a malfunction occurs in each of the sensors 40 and 41 of the air-fuel ratio and the accuracy of the output signal of each of the sensors 40 and 41 air-fuel ratio is deteriorating, the amount of fuel injected cannot be set optimally. This leads to a deterioration in the properties of exhaust emissions and a deterioration in fuel economy. Therefore, in many internal combustion engines, a fault diagnosis control is performed to self-diagnose faults in each of the air-fuel ratio sensors 40 and 41.

[0055] As such a fault diagnosis control, for example, mention may be made, for example, of a control that is performed based on the output of each of the air-fuel ratio sensors 40 and 41 immediately after the end of the fuel cut-off control. As an example of such a fault diagnosis control, a fault diagnosis control will be described for diagnosing a slowdown in the response of the exhaust air-fuel ratio sensor 41 (i.e., deterioration related to a delay in the output of the air-fuel ratio sensor in response to a change in the air-fuel ratio near the air-fuel ratio sensor), as an example of a malfunction.

[0056] FIG. 6 is a timing chart of the output current of the air-fuel ratio inlet sensor (inlet output current), the output current of the air-fuel ratio exhaust sensor on the side (exhaust output current), and the value of the diagnostic end indicator before and after the fuel cut-off control is performed. In the example shown in the figure, the control of the fuel cut-off starts at time t ₁ and the control of the fuel cut-off ends at time t ₃ . When the fuel cut-off control ends, exhaust gases in which the air-fuel ratio is rich are forced to flow into the exhaust gas purification inlet catalyst 20 through the enrichment control after the fuel supply is restored. It should be noted, however, that since a large amount of oxygen is accumulated by the inlet exhaust gas purification catalyst 20, the air-fuel ratio of exhaust gases discharged from the inlet exhaust gas purification catalyst 20 is equal to the theoretical air-fuel ratio.

[0057] In the event that there is no malfunction consisting in slowing down the response in the exhaust air-fuel ratio sensor 41, the output current of the air-fuel ratio sensor 41 is changed as shown by the solid line A in FIG. 6. That is, after the end of the fuel cut-off control, the output current of the exhaust air-fuel ratio sensor 41 starts to fall with some delay from the end of the fuel cut-off control, because there is some distance from the engine casing 1 to the exhaust air-fuel ratio sensor 41 . In addition, the air-fuel ratio of exhaust gases flowing from the intake catalyst 20 for purification of exhaust gases at this time is approximately equal to the theoretical air-fuel ratio. Therefore, the output current of the exhaust air-fuel ratio sensor 41 becomes zero.

[0058] On the other hand, in the event that there is a malfunction in slowing down the response of the exhaust air-fuel ratio sensor 41, the output current of the air-fuel ratio exhaust sensor 41 changes as shown by broken line B in FIG. 6. That is, the speed at which the output current drops is less when there is no deceleration in the response of the exhaust air-fuel ratio sensor 41 (as shown by solid line A). Thus, the speed at which the output current of the exhaust air-fuel ratio sensor 41 drops depends on whether there is a slowdown in the response of the air-fuel ratio sensor 41. Therefore, by calculating this fall rate, it becomes possible to diagnose whether or not there is a slowdown in the response of the exhaust air-fuel ratio sensor 41.

[0059] Thus, in the example shown in the figure, the rate at which the output current changes (hereinafter referred to as the "rate of change of the detection current") at a time when the output current value of the exhaust air-fuel ratio sensor 41 is within a predetermined current range X (hereinafter "the current detection range") between a value (I ₁₈₎ corresponding to the air-fuel ratio of approximately 18 and the value (I ₁₆₎ corresponding to the air-fuel ratio of about 16 is calculated during the exercise enrichment phenomenon after restoring the fuel supply after the fuel cutoff control. In the present embodiment, in particular, the time ΔΤ during which the output current changes from the upper limit (i.e., I ₁₈ ) of the determination current range to the lower limit (i.e., I ₁₆ ) of the determination current range is used as parameter indicating the rate of change of the current detection. It is understood that with a decrease in the rate of change in the detection current, this time ΔΤ of change in the determination current increases. In this case, the time ΔΤ of the change in the determination current in FIG. 1 is a parameter indicating the rate of change of the air-fuel ratio of the determination shown by the solid line A, and the time ΔΤ _{2 of the} change in the determination current in FIG. 1 is a parameter indicating a rate of change of the air-fuel ratio of the determination shown by dashed line B.

[0060] Further, in the present embodiment, a malfunction in the exhaust air-fuel ratio sensor 41 is diagnosed based on the determination current change time ΔΤ calculated in this way. More specifically, when the determination current change time ΔΤ is longer than the control current change time during a malfunction (e.g., ΔΤ ₂ ), that is, when the determination current change rate is less than the control determination current change speed during the malfunction, it is determined that there is a malfunction expressed in slowing down the response of the exhaust air-fuel ratio sensor 41. On the contrary, when the current change time ΔΤ is less than the control current change time in the event of a malfunction (for example, ΔΤ ₁ ), that is, when the determination current change rate is higher than the control current change speed in the event of a malfunction, it is determined that there is no malfunction expressed in deceleration the response of the exhaust sensor 41 air-fuel ratio. Moreover, the control time of the current change in the event of a malfunction can be a value determined in advance, or a value that changes in accordance with the operating parameter, for example, engine speed, engine load, or the like during enrichment control after recovery of fuel supply.

[0061] Further, when the output current of the exhaust air-fuel ratio exhaust sensor 41 falls below the lower limit (ie, Ι ₁₆ ) of the detection current range (at time t ₅ ), the value of the diagnostic end indicator changes to 1 under the assumption that fault diagnosis in the exhaust air-fuel ratio sensor 41. This diagnostic end indicator is a flag that is reset to 0 when the ignition key is turned off to turn off a vehicle system equipped with an internal combustion engine, and which is set to 1 when a fault diagnosis is made after starting the internal combustion engine.

[0062] As described above, in the management of the fault diagnosis, the fault diagnosis is performed when the air-fuel ratio of exhaust gases passing near the exhaust air-fuel ratio sensor 41 changes to the theoretical air-fuel ratio from the state where the fuel cut-off control is performed namely, the state where the air-fuel ratio of exhaust gases passing near the exhaust air-fuel ratio sensor 41 is extremely high (the degree of depletion ya is extremely high). Thus, by performing a fault diagnosis, when the air-fuel ratio of exhaust gases passing near the exhaust air-fuel ratio sensor 41 changes significantly, it becomes possible to increase the accuracy in performing the fault diagnosis.

[0063] However, in the present embodiment, in the vehicle equipped with the internal combustion engine, the indicator lamp lights up when the diagnostic device determines that there is a malfunction in the exhaust air-fuel ratio exhaust sensor 41 from the exhaust side.

[0064] Furthermore, the control of the fault diagnosis is not always performed after the end of each control of the fuel cut-off, and is performed when a certain execution condition is fulfilled. As such a fulfillment condition, it can be mentioned, for example, that when the temperature of the exhaust air-fuel ratio sensor 41 rises so that it becomes equal to or higher than the activation temperature, the fault diagnosis control is not performed a predetermined number of times since the start of the vehicle system equipped with the internal engine combustion, etc.

[0065] In this case, in the above example, a fault diagnosis control for diagnosing a malfunction of a response slowdown of the exhaust air-fuel ratio sensor 41 is performed after the end of the fuel cut-off control. However, according to the invention, any type of fault diagnosis control can be performed, provided that this fault diagnosis is performed based on the output signal of each of the air-fuel ratio sensors 40 and 41 after the end of the fuel cut-off control.

[0066] Supply voltage control

In particular, in the present embodiment, the voltage supplied to the air-fuel ratio exhaust sensor 41 is about 0.45 V during normal operation (when the fuel cut-off control is not performed). Thus, as can be seen from FIG. 3, the air-fuel ratio in the exhaust gas can be appropriately determined in the immediate vicinity of the theoretical air-fuel ratio.

[0067] However, if the voltage supplied to the exhaust air-fuel ratio sensor 41 is maintained at 0.45 V during the fuel cut-off control, the output current of the air-fuel ratio exhaust sensor 41 is extremely large (see I _{0, 45AIR} in Fig. 3). When this excessively large output current occurs, the electrical circuit to which the output current of the air-fuel ratio exhaust sensor 41 is supplied must also have a large capacitance. As a result, the manufacturing cost of this electrical circuit increases. On the other hand, during the fuel shutoff control, the injection from the fuel injection valve 11 is not performed, so it is not necessary to determine the air-fuel ratio of the exhaust gas by the air-fuel ratio exhaust sensor 41.

[0068] FIG. 7 is a timing chart of the output current of the air-fuel ratio inlet sensor (inlet output current), the output current of the air-fuel ratio output sensor (exhaust output current), the voltage supplied to the air-fuel ratio output sensor 41, and the diagnostic end indicator value to and after completing the fuel shutoff control. As can be seen from FIG. 7, in the present embodiment, the voltage supplied to the air-fuel ratio exhaust sensor 41 is reduced to 0.2 V during execution of the fuel cut-off control. In the example shown in FIG. 7, in particular, when the output current of the exhaust air-fuel ratio sensor 41 reaches Ι ₁₈ , the voltage supplied to the air-fuel ratio exhaust sensor 41 decreases from 0.45 V to 0.2 V.

[0069] As can be seen from FIG. 3, the maximum value that the output current can receive increases when the voltage supplied to the output air-fuel ratio sensor 41 rises. Therefore, in the case when the voltage supplied to the exhaust air-fuel ratio exhaust sensor 41 is set to 0.2 V, an output current equal to or greater than I _0.2AIR (a value less than I _0.45AIR ) in the exhaust sensor 41 does not occur. air-fuel ratio, even when a gas similar to atmospheric gas (atmospheric gas in FIG. 3) flows over the surface of the exhaust air-fuel ratio sensor 41. As a result, the creation of an extremely large output current from the exhaust air-fuel ratio sensor 41 can be prevented.

[0070] Further, in the present embodiment, when the above-mentioned fault diagnosis control is not performed during the end of the fuel cut-off control, the supplied voltage rises from 0.2 V to 0.45 V when the output current of the air-fuel exhaust sensor 41 the ratio drops to Ι ₁₈ (at time t ₆ in FIG. 6), as shown by the dashed line in FIG. 7.

[0071] It should be noted here that, as can be seen from FIG. 3, the air-fuel ratio can be defined in a certain interval as a rich air-fuel ratio and as a poor air-fuel ratio compared to the theoretical air-fuel ratio when the voltage supplied to the exhaust air-fuel ratio sensor 41 is set to 0 , 45 V. On the other hand, when the voltage supplied to the exhaust air-fuel ratio sensor 41 is set to 0.2 V, the air-fuel ratio can be determined in a certain range as god air-fuel ratio, which makes it impossible to separate an air-fuel ratio equal to or greater than about 18 from a poorer air-fuel ratio. That is, when the voltage supplied to the exhaust air-fuel ratio sensor 41 decreases to 0.2 V, the interval in which the air-fuel ratio can be determined becomes unacceptable. Thus, by increasing the supplied voltage to 0.45 V after the end of the fuel cut-off control, the air-fuel ratio can be determined in a certain interval compared to the theoretical air-fuel ratio during normal operation. As a result, the air-fuel ratio within the interval that is needed during normal operation can be determined after the end of the fuel cutoff control.

[0072] In the present embodiment, in particular, the supplied voltage rises after the output current of the exhaust air-fuel ratio sensor 41 drops to I ₁₈ . It should be noted here that when the supply voltage rises before the output current of the exhaust air-fuel ratio sensor 41 drops to Ι ₁₈ , the output current of the air-fuel ratio exhaust sensor 41 rises above I _0.2AIR when the supply voltage rises. As a result, an excessively large output current flows into an electrical circuit that is connected to the exhaust air-fuel ratio sensor 41. In the case where the capacitance of the applied electrical circuit is small, the electrical circuit is damaged. In contrast, according to the present embodiment, the supplied voltage rises after the output current of the air-fuel ratio exhaust sensor 41 drops to I ₁₈ . Therefore, the appearance of an excessively large output current of the exhaust air-fuel ratio sensor 41 can be prevented.

[0073] In addition, as will be described later, when the voltage supplied to the exhaust air-fuel ratio sensor 41 does not change in a stepwise manner, noise is temporarily generated in the output current of the air-fuel ratio exhaust sensor 41. Therefore, immediately after the applied voltage changes, the air-fuel ratio of exhaust gases flowing over the surface of the exhaust air-fuel ratio sensor 41 cannot be determined with accuracy. In the present embodiment, the supplied voltage changes when the output current of the exhaust air-fuel ratio exhaust sensor 41 from the exhaust side drops to I ₁₈ . The applied voltage changes smoothly, and the occurrence of an excessively large output current is prevented. In some cases, therefore, noise resulting from a change in the supplied voltage can be stopped before the output current of the exhaust air-fuel ratio sensor 41 reaches zero, which corresponds to the theoretical air-fuel ratio.

[0074] Moreover, in the above example, the normal voltage, i.e. the supplied voltage during normal operation is assumed to be 0.45 V, and the fuel cut-off voltage, i.e. the supplied voltage during the control of the fuel cut-off is assumed to be 0.2 V. However, the normal voltage and voltage of the fuel cut-off are not necessary for an appropriate assessment of these values.

[0075] It should be noted, however, that the fuel cut-off voltage should be less than the normal voltage in the present embodiment. In addition, the fuel cut-off voltage is such a voltage at which the output current of the exhaust air-fuel ratio sensor 41 becomes equal to or less than the maximum allowable current of the electric circuit, even when gas similar to atmospheric gas flows over the surface of the exhaust sensor 41 air -fuel relations. In addition, the fuel cut-off voltage is a voltage that is higher than the lower limit voltage (V _LOW in FIG. 3) of the limit current range at a time when the exhaust air-fuel ratio sensor 41 is exposed to exhaust gases whose air-fuel ratio is theoretical air-fuel ratio.

[0076] More preferably, the fuel cutoff voltage is a voltage that is higher than the minimum voltage of the current limiting range of the air-fuel ratio sensor while the exhaust air-fuel ratio sensor 41 is exposed to gases whose air-fuel ratio is a predetermined poor air-fuel ratio (e.g., an air-fuel ratio of 18). In this case, the voltage supplied to the exhaust air-fuel ratio sensor 41 rises from the fuel cut-off voltage to the normal voltage when the output current of the air-fuel ratio exhaust sensor 41 becomes equal to or less than a value (e.g., I ₁₈ ), corresponding to this predetermined poor air-fuel ratio (e.g., an air-fuel ratio of 18).

[0077] In addition, the time point of the voltage increase applied to the exhaust air-fuel ratio sensor 41 after the fuel cut-off control has ended does not have to coincide with the time when the output current of the air-fuel ratio exhaust sensor 41 drops to become equal or less than Ι ₁₈ corresponding to an air-fuel ratio of approximately 18. Accordingly, this point in time may coincide with the point in time when the output current of the exhaust air-fuel sensor 41 o the ratio becomes equal to or less than a predetermined value (the value is greater than zero), with the exception of I ₁₈ . It should be noted, however, that the output current at a time when the voltage supplied to the exhaust side air-fuel ratio exhaust sensor 41 rises is preferably a limiting current.

[0078] Supply voltage control during fault diagnosis control

Moreover, as described above, when the voltage supplied to the exhaust air-fuel ratio sensor 41 changes stepwise, noise is temporarily generated in the output current of the air-fuel ratio exhaust sensor 41. Therefore, when the fault diagnosis control is performed immediately after the end of the fuel cut-off control, as described above, noise is generated in the output current of the exhaust air-fuel ratio sensor 41 during the execution of the fault diagnosis control. When noise thus arises in the output current of the exhaust air-fuel ratio sensor 41 during the fault diagnosis control, a malfunction in the air-fuel ratio exhaust sensor 41 cannot be accurately determined.

[0079] Further, in the present embodiment, as described above, when the output current of the exhaust air-fuel ratio sensor 41 reaches a current at the end of the determination that is slightly less than zero, which corresponds to the theoretical air-fuel ratio, enrichment control after supply recovery fuel runs out. That is, in the present embodiment, when the oxygen adsorption amount of the inlet exhaust gas purification catalyst 20 becomes approximately zero, and unburned gases begin to flow out of the inlet exhaust gas purification catalyst 20, enrichment control after the fuel supply is restored. However, when noise is generated in the output current of the exhaust air-fuel ratio exhaust sensor 41, when unburned gases start to flow from the inlet exhaust gas purification catalyst 20, the outflow of unburned gases cannot be accurately determined.

[0080] Thus, in the present embodiment, the voltage supplied to the air-fuel ratio exhaust sensor 41 rises after the fuel cut-off control is completed after a later of the following time points: the time at which the fault diagnosis control ends and the moment the time at which the output current of the exhaust air-fuel ratio sensor 41 reaches the current at the end of the determination. That is, in the present embodiment, the supplied voltage rises after a later of the following time points: the time at which the fault diagnosis control ends and the time at which the enrichment control ends after the fuel supply is restored. In the example indicated by the solid line in FIG. 7, the fault diagnosis control ends at time t ₅ , and the output current of the exhaust air-fuel ratio sensor 41 reaches the current at the end of determination at time t ₄ , which arrives later than time t ₅ . Therefore, in the example shown in the figure, the voltage supplied to the exhaust air-fuel ratio sensor 41 rises from 0.2 V to 0.45 V at time t ₄ .

[0081] By increasing the applied voltage at this point in time, it becomes possible to prevent noise in the output current when the voltage supplied to the exhaust air-fuel ratio sensor 41 changes during the execution of the fault diagnosis control. In addition, the timing of the flow of unburned gases from the intake catalyst 20 for purifying exhaust gases can be accurately determined.

[0082] In this case, in the aforementioned embodiment of the invention, the fault diagnosis control ends before the output current of the exhaust air-fuel ratio sensor 41 reaches the current at the end of the determination. However, in the case when the fault diagnosis control is performed in a specific mode, the fault diagnosis control is performed after the output current of the exhaust air-fuel ratio sensor 41 reaches the current at the end of the determination. In this case, the voltage supplied to the exhaust air-fuel ratio sensor 41 rises after performing the fault diagnosis control.

[0083] Further, in the aforementioned embodiment, the applied voltage rises after a later of the following time points: the time at which the fault diagnosis control ends and the time when the enrichment control ends after the fuel supply is restored. However, when the applied voltage rises late, the period in which the interval providing determination of the air-fuel ratio is unsuitable is lengthened accordingly. Accordingly, it is preferable that the supplied voltage rises before the output current of the exhaust air-fuel ratio sensor 41 becomes less than zero again after a temporary zeroing (i.e., before the exhaust gases in which the air-fuel ratio is rich flow out from the inlet catalyst 20 for purification of exhaust gases) or before the output current of the exhaust air-fuel ratio sensor 41 becomes greater than zero again after a temporary zeroing (i.e., before the exhaust gases in which air but the fuel ratio is poor, will flow from the inlet catalyst 20 exhaust gas purification), after the end of the enrichment control after restoring the fuel supply. Alternatively, the applied voltage may be raised before the output current of the exhaust air-fuel ratio sensor 41 becomes zero from a value equal to less than the current at the end of the determination (which corresponds to the theoretical air-fuel ratio) (during the period indicated by M on Fig. 7) after the end of the enrichment control after restoring the fuel supply.

[0084] In addition, the supplied voltage can be raised before the output current of the exhaust air-fuel ratio sensor 41 changes from a value in the immediate vicinity of zero after converting to zero (which corresponds to a theoretical air-fuel ratio) from a value equal to or less current at the end of the determination, after the end of the enrichment control after restoring the fuel supply. Thus, the supplied voltage rises when the output signal of the exhaust air-fuel ratio sensor 41 barely changes.

[0085] Block diagram

FIG. 8 is a flowchart showing a procedure for controlling the voltage supplied to the air-fuel ratio exhaust sensor 41. The control procedure shown in the figure is performed through interruption at intervals of some time.

[0086] First, in step S11, it is determined whether or not the voltage drop indicator Fv is set to 1. The voltage drop indicator Fv is a flag that is set to 1 when the voltage supplied to the air-fuel ratio output sensor 41 decreases, and which is set to 0 otherwise. If it is determined in step S11 that the voltage drop indicator is set to 0, proceeds to step S12. At step S12, it is determined whether or not the fuel cut-off control is started. If it is determined that the fuel shutoff control has not started, the control procedure ends. On the other hand, if it is determined in step S12 that control of the fuel cut-off has been started, the transition to step S13 is performed. In step S13, the voltage supplied to the exhaust air-fuel ratio sensor 41 is reduced to 0.2 V. In the next step S14, the voltage drop indicator Fv is set to 1, and the control procedure ends.

[0087] Further, in the control procedure in step S11, it is determined that the voltage drop indicator Fv is set to 1, and the transition to step S15 is performed. At step S15, it is determined whether or not the fuel shutoff control is complete. If it is determined that the fuel shutoff control is not completed, the control procedure ends. As a result, the voltage supplied to the exhaust air-fuel ratio sensor 41 is kept at 0.2 V. On the other hand, if it is determined in step S15 that the fuel cut-off control has been completed, proceeds to step S16. At step S16, it is determined whether or not the fault diagnosis control is complete. If it is determined that the fault diagnosis management has not been completed, the control procedure ends. As a result, the voltage supplied to the exhaust air-fuel ratio sensor 41 is kept at 0.2 V.

[0088] On the other hand, if it is determined in step S16 that the fault diagnosis control has been completed, proceeds to step S17. At step S17, it is determined whether or not the output current of the exhaust air-fuel ratio sensor 41 is equal to or less than the current Iref at the end of the determination. If it is determined that the output current of the exhaust air-fuel ratio sensor 41 is greater than the Iref current at the end of the determination, the control procedure ends. In this case, also, the voltage supplied to the exhaust air-fuel ratio sensor 41 is maintained equal to 0.2 V. On the other hand, if it is determined in step S17 that the output current of the air-fuel ratio exhaust sensor 41 is equal to or less than current Iref at the end of the determination, proceeds to step S18. In step S18, the voltage supplied to the exhaust air-fuel ratio sensor 41 rises to 0.45 V. In a subsequent step S19, the voltage drop indicator Fv is set to 0, and the control program ends.

[0089] In this case, in the aforementioned embodiment of the invention, the voltage supplied to the exhaust air-fuel ratio sensor 41 is described. However, the voltage supplied to the air-fuel ratio inlet sensor 40 can also be controlled in a similar manner. It should be noted, however, that the air-fuel ratio inlet sensor 40 is not used to determine that unburned gases leaked from the inlet exhaust gas purification catalyst 20 to end enrichment control after restoring the fuel supply in this case. Accordingly, in the case where the fault diagnosis control is performed, the voltage supplied to the air-fuel ratio inlet sensor 40 rises when the fault diagnosis control is performed. On the other hand, in the case where the fault diagnosis control is not performed, the voltage supplied to the air-fuel ratio inlet sensor 40 rises when the output current of the air-fuel ratio inlet sensor 40 drops to Ι ₁₈ , as in the case of the exhaust sensor 41 air-fuel ratio.

[0090] Second Embodiment

Next, a second embodiment of the invention will be described with reference to FIG. 9. The control device for the internal combustion engine is generally identical to the configuration, etc. of the control device according to the first embodiment of the invention. However, while in the first embodiment, the enrichment control after recovery of the fuel supply ends when the output current of the exhaust air-fuel ratio exhaust sensor 41 reaches the current at the end of the determination, in the second embodiment, the enrichment control after restoration of the fuel supply ends independently from the output current of the exhaust air-fuel ratio sensor 41.

[0091] More specifically, in the present embodiment, enrichment control after fuel recovery is completed based on the integrated flow rate of past exhaust gases that have passed to the exhaust gas purification inlet catalyst 20 from the end of the fuel cut-off control, namely, from the beginning enrichment control after restoration of fuel supply. In this case, the integrated flow rate of past exhaust gases that have passed to the inlet exhaust gas purification catalyst 20 is estimated based on, for example, the output signal of the air flow meter 39 and the like.

[0092] FIG. 9 is a timing diagram similar to FIG. 7 showing an inlet output current or the like. before and after completing the fuel shutoff control. As can be seen from FIG. 9, in the present embodiment, the integration of the exhaust gas flow rate that has passed into the exhaust gas purification inlet catalyst 20 starts at the end of the fuel cut-off control, namely, at the beginning of the enrichment control after the fuel supply is restored (at time t ₃ ) . Further, when the integrated flow rate of the exhaust gases that have passed to the inlet exhaust gas purification catalyst 20 reaches the value ∑Vref determined in advance at time t ₇ , the enrichment control after restoring the fuel supply ends. As a result, the output current of the inlet sensor 40 of the air-fuel ratio rises to zero (which corresponds to the theoretical air-fuel ratio).

[0093] Even in the case where the enrichment control after restoring the fuel supply ends based on the integrated exhaust gas flow rate, when the fault diagnosis control is not performed after the end of the fuel cut-off control, the voltage supplied to the air-fuel ratio exhaust sensor 41 rises from 0.2 V to 0.45 V after falling to I ₁₈ , as in the case of the aforementioned first embodiment.

[0094] On the other hand, when the enrichment control after the recovery of the fuel supply ends in this way based on the integrated exhaust flow rate, the output current of the exhaust air-fuel ratio sensor 41 is not used to determine the end time of the enrichment control after the restoration of the fuel supply. Therefore, there is no need to accurately determine the moment when the output current of the exhaust air-fuel ratio sensor 41 becomes equal to the current at the end of the determination using the air-fuel ratio exhaust sensor 41 after the enrichment control has been started after the fuel supply has been restored. Thus, in the present embodiment, in the case where the fault diagnosis control is performed after the end of the fuel cut-off control is completed, the voltage supplied to the air-fuel ratio exhaust sensor 41 rises from 0.2 V to 0.45 V when the diagnostic control malfunctioning ends at time t ₄ time. Thus, the interval of the air-fuel ratio, in which it can be determined by the exhaust air-fuel ratio sensor 41, can smoothly change to a suitable interval after the end of the fuel cutoff control.

[0095] Moreover, the voltage supplied to the exhaust air-fuel ratio exhaust sensor 41 from the exhaust side may not necessarily increase simultaneously with the end of the fault diagnosis control, provided that the fault diagnosis control is completed. It should be noted, however, that when the time moment for increasing the applied voltage is delayed, the period in which the interval providing the determination of the air-fuel ratio is unsuitable, accordingly lengthens. Accordingly, it is preferable that the applied voltage be raised before the end of the enrichment control after restoring the fuel supply.

[0096] Further, in the aforementioned embodiment, the end of the enrichment control after the recovery of the fuel supply is determined based on the integrated flow rate of the exhaust gases that have passed to the inlet exhaust gas purification catalyst 20. However, the end of the enrichment control after restoring the fuel supply can be determined based on another parameter, provided that this parameter is not the output current of the exhaust air-fuel ratio sensor 41. As such a parameter, we can mention, for example, the time elapsed since the start of enrichment control after restoring the fuel supply, the integrated amount of injected fuel from the beginning of enrichment control after restoring the fuel supply, etc.

[0097] Third Embodiment

Next, a third embodiment of the invention will be described with reference to FIG. 10. The control device for the internal combustion engine is generally identical in configuration and the like to the control device according to the first embodiment of the invention and the control device according to the second embodiment of the invention. However, in the aforementioned embodiment of the invention, the end time of the enrichment control after restoring the fuel supply remains unchanged, regardless of whether a fault diagnosis control is performed. In contrast, according to the present embodiment, the end time of the enrichment control after restoring the fuel supply changes depending on whether or not the fault diagnosis control is performed.

[0098] More specifically, in the present embodiment, in the case where the fault diagnosis control is not performed after the end of the fuel cut-off control, the enrichment control after restoring the fuel supply ends when the output current of the air-fuel ratio exhaust sensor 41 drops to the current at the end determination (at time t4 in FIG. 10), as shown in FIG. 10. Accordingly, exhaust gases in which the air-fuel ratio is rich flow into the inlet exhaust gas purification catalyst 20 until time t ₄ , while the output current of the air-fuel ratio inlet sensor 40 is zeroed after time t ₄ . In this case, as in the case of the above embodiment, the voltage supplied to the exhaust air-fuel ratio sensor 41 rises from 0.2 V to 0.45 V at time t ₆ (when the output current of the exhaust sensor 41 is air -fuel ratio drops to I ₁₈ ).

[0099] On the other hand, in the case that a fault diagnosis control is performed after the end of the fuel cut-off control, the end time of the enrichment control after the fuel supply is restored is determined based on the integrated exhaust gas flow rate that has passed to the exhaust gas purification inlet catalyst 20, as shown in FIG. 11. Accordingly, the enrichment control after restoration of the fuel supply ends when the integrated exhaust flow rate reaches ∑Vref determined in advance (at time t ₇ ).

[0100] Furthermore, in the present embodiment, when the fault diagnosis control is performed, the voltage supplied to the air-fuel ratio output sensor 41 rises from 0.2 V to 0.45 V when the fault diagnosis control ends time t ₅ , as in the case of the second embodiment of the invention.

[0101] According to the present embodiment, in the case where the fault diagnosis control is not performed, the enrichment control after the recovery of the fuel supply ends after the output current of the exhaust air-fuel ratio sensor 41 drops to the current at the end of the determination. In this regard, enrichment control after recovery of the fuel supply can be performed until all of the oxygen accumulated by the intake exhaust gas purification catalyst 20 is exhausted. Thus, the oxygen adsorption capacity of the inlet exhaust gas purification catalyst 20 can be increased. On the other hand, in the case that a fault diagnosis control is performed, the enrichment control after the fuel supply is restored ends independently of the output current of the exhaust air-fuel ratio sensor 41. Therefore, noise arising from a change in voltage supplied to the exhaust air-fuel ratio exhaust sensor 41 may not affect the determination of when the fault diagnosis control is completed.

[0102] Block diagram

FIG. 12 is a flowchart showing a procedure for controlling the voltage supplied to the air-fuel ratio exhaust sensor 41 and for enrichment control after restoring the fuel supply. The control procedure shown in the figure is performed through interruption at intervals of some time. Meanwhile, steps S21 to S25 are the same as steps S11 to S15 of FIG. 8 respectively, therefore, their description will be omitted.

[0103] If it is determined in step S25 that the fuel cut-off control is completed, proceeds to step S26. At step S26, it is determined whether or not the enrichment indicator Fr after restoring the fuel supply is 1. The enrichment indicator Fr after restoring the fuel supply is a flag that is 1 when the enrichment control after restoring the fuel supply is performed, and which is 0 otherwise . If the enrichment control after the restoration of the fuel supply has not yet started, it is determined in step S25 that the enrichment indicator Fr after the restoration of the fuel supply is not equal to 1, and the transition to step S27 is performed. In step S27, enrichment control is started after the fuel supply is restored. Subsequently, in step S28, the enrichment indicator Fr after restoring the fuel supply is 1, and the control procedure ends.

[0104] In the subsequent control procedure in step S26, it is determined that the enrichment indicator Fr after restoring the fuel supply is 1 and the transition to step S29 is performed. At step S29, it is determined whether or not the fault diagnosis control is performed after the end of the fuel cutoff control. If it is determined that the fault diagnosis control has been performed, proceeds to step S30. At step S30, it is determined whether or not the fault diagnosis control is complete. If it is determined that the fault diagnosis management has not been completed, the control procedure ends. As a result, the voltage supplied to the exhaust air-fuel ratio sensor 41 is maintained at 0.2 V and the enrichment control after the fuel supply is restored continues. After that, when the fault diagnosis control is performed, the transition from step S30 to step S31 in the subsequent control procedure is performed, and the voltage supplied to the exhaust air-fuel ratio sensor 41 rises to 0.45 V. Then, in step S32, the recovery control after recovery fuel supply is running out. In step S33, the voltage drop indicator Fv becomes 0. In step S34, the enrichment indicator Fr after restoring the fuel supply is set to 0, and the control procedure ends.

[0105] On the other hand, if it is determined in step S29 that the control of the fault diagnosis has not been performed after the end of the fuel cut-off control, proceeds to step S35. At step S35, it is determined whether or not the output current I of the exhaust air-fuel ratio sensor 41 is equal to or less than I ₁₈ (a value corresponding to the air-fuel ratio 18). If it is determined that the output current I of the exhaust air-fuel ratio sensor 41 is greater than Ι ₁₈ , the control procedure ends. As a result, the voltage supplied to the air-fuel ratio exhaust sensor 41 is maintained at 0.2 V, and enrichment control after the fuel supply is restored. After that, when the output current I of the exhaust air-fuel ratio sensor 41 drops to become equal to or less than I ₁₈ , a transition is made from step S35 to step S31 in the control procedure. Next, steps S31 to S34 are performed and the control procedure ends.

[0106] Type of air-fuel ratio sensors

Moreover, in the aforementioned embodiment, in the invention, both the air-fuel ratio inlet sensor 40 and the air-fuel ratio output sensor 41 are a multilayer air-fuel ratio sensor with a current limit as shown in FIG. 2. Each of these air-fuel ratio sensors may be a bowl-shaped air-fuel ratio sensor with a current limit.

[0107] FIG. 13 is a view schematically showing the structure of each of the bowl-shaped air-fuel ratio sensors 40 ′ and 41 ′. As shown in FIG. 13, each bowl-shaped air-fuel ratio sensor 40 'and 41' comprises a solid electrolyte layer 51 ', which is in the form of a cup (cylinder), an exhaust side electrode 52', which is located on the outer surface of the solid electrolyte layer 51 ', an atmosphere-side electrode 53, which is located on the inner surface of the solid electrolyte layer 51 ′, a diffusion rate limiting layer 54 ′ that limits the diffusion rate of the exhaust gas passage, and a heating portion 56 ′ that heats each sensor 40 ′, and 41 'air-fuel ratio. As can be seen from FIG. 13, the diffusion rate limiting layer 54 ′ has a cup shape configured to cover the outer surface of the solid electrolyte layer 51 ′. In addition, the heating section 56 'is located inside the solid electrolyte layer 51'.

[0108] When each bowl-shaped air-fuel ratio sensor 40 'and 41' is configured in this manner, the entire outer peripheral surface of the diffusion rate limiting layer 54 'is exposed to exhaust gases. As a result, the flow rate of the exhaust gases reaching the electrode 52 from the exhaust side 'is large, and a large current arises between the electrodes. Therefore, the output current of the cup-shaped air-fuel ratio sensor is greater than the output current of the multilayer air-fuel ratio sensor, while the load supplied to the electric circuit of the cup-shaped air-fuel ratio sensor increases. Therefore, when a bowl-shaped air-fuel ratio sensor is used, the load supplied to the electric circuit can be more effectively reduced by performing control with the aforementioned embodiment of the invention. Moreover, the types of the intake air-fuel ratio sensor and the exhaust air-fuel ratio sensor need not be the same. For example, the air-fuel ratio inlet sensor may be a multilayer air-fuel ratio sensor, and the air-fuel ratio exhaust sensor may be a bowl-shaped air-fuel ratio sensor.

Description of Reference Positions

[0109]

1 ENGINE HOUSING

5 COMBUSTION CHAMBER

7 INLET HOLE

9 OUTLET

19 EXHAUST MANIFOLD

20 EXHAUST GAS INLET CATALYST

24 EXHAUST GAS CLEANING EXHAUST CATALYST

31 ECU

40 INLET SENSOR AIR FUEL RELATIONS

41 OUTLET SENSOR AIR FUEL RELATIONS

Claims (42)

1. The control device for an internal combustion engine, which is characterized in that it contains an air-fuel ratio sensor located in an exhaust channel of an internal combustion engine; and an electronic control unit configured to control the voltage supplied to the air-fuel ratio sensor, wherein the electronic control unit is configured to control the fuel cut-off to stop the fuel supply to the combustion chamber or to reduce the amount of fuel supplied to the combustion chamber during operation of the internal combustion engine, the electronic control unit is configured to diagnose a malfunction in the air-fuel ratio sensor based on the current output of the air-fuel ratio sensor after the end of the fuel cut-off control, the air-fuel ratio sensor is configured so that the output current of the air-fuel ratio sensor increases when the detected air-fuel ratio of the exhaust gas increases, and the air-fuel ratio sensor is configured so that the maximum value of the output current increases when the voltage supplied to the sensor air-fuel ratio rises, and the electronic control unit is configured to make the voltage supplied to the air-fuel ratio sensor equal to the fuel cut-off voltage different from the normal voltage that is supplied when the fuel cut-off control is not performed, during the fuel cut-off control and until diagnostic fault management after the end of the fuel cut-off control, as well as the electronic control unit is configured to change the voltage supplied to tchiku air-fuel ratio from the fuel supply cut-off voltage to the normal voltage after closure defect diagnosis control. 2. The control device according to claim 1, in which the internal combustion engine contains an exhaust gas purification catalyst, an exhaust gas purification catalyst is located in an exhaust channel of an internal combustion engine, an air-fuel ratio sensor is located on the outlet side of the exhaust gas purification catalyst in the direction of the exhaust gas flow, and the electronic control unit is configured to perform enrichment control after restoring the fuel supply to bring the air-fuel ratio of exhaust gases flowing to the exhaust gas purification catalyst to a rich air-fuel ratio after the end of the fuel cut-off control, while the rich air-fuel ratio is richer than theoretical air-fuel ratio. 3. The control device according to claim 2, in which the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after a later of the following times: the time when the control of fault diagnosis is completed and the time when the enrichment control is completed after restoration of fuel supply. 4. The control device according to claim 3, in which the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage before the output current of the air-fuel ratio sensor becomes less than the value corresponding to the theoretical air-fuel ratio again after the end of control enrichment after restoration of fuel supply. 5. The control device according to claim 3 or 4, in which the electronic control unit is configured to complete enrichment control after restoring the fuel supply when the output current of the air-fuel ratio sensor becomes equal to or less than the current at the end of the determination, corresponding to the air-fuel ratio at the end of the determination, which is richer than the theoretical air-fuel ratio . 6. The control device according to claim 5, in which the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after the end of the enrichment control after restoring the fuel supply and before changing the output current of the air-fuel ratio sensor from a current that is equal to or less, than the current at the end of the determination, to the current corresponding to the theoretical air-fuel ratio. 7. The control device according to claim 2, in which the electronic control unit is configured to complete enrichment control after restoring the fuel supply based on a different parameter regardless of the output current of the air-fuel ratio sensor, and the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage after the end of the fault diagnosis control and before the end of the enrichment control after restoring the fuel supply. 8. The control device according to claim 7, in which the electronic control unit is configured so that the control of the fault diagnosis is not performed even after the end of the fuel cutoff control, when the condition for performing the control of the fault diagnosis is not fulfilled at the time of the end of the fuel cutoff control, the electronic control unit is configured to complete enrichment control after restoring the fuel supply after the output current of the air-fuel ratio sensor becomes equal to the value corresponding to the air-fuel ratio at the end of determination and determined in advance for the first time from the start of enrichment control after restoring the fuel supply, when the fault diagnosis control is not performed after the end of the fuel cut-off control, and the electronic control unit is configured to complete the enrichment control after restoring the fuel supply based on another parameter, regardless of the output current of the air-fuel ratio sensor, when a fault diagnosis control is performed after the fuel cut-off control is completed. 9. The control device according to any one of paragraphs. 1-4 or 6-8, in which the electronic control unit is configured so that the control of the fault diagnosis is not performed even after the end of the fuel cutoff control, when the condition for performing the control of the fault diagnosis is not fulfilled at the time of the end of the fuel cutoff control, and the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage as soon as the output current of the air-fuel ratio sensor becomes equal to or less than a value determined in advance after the end of the fuel cut-off control when the fault diagnosis control is not performed after the end of the fuel cut-off control. 10. The control device according to any one of paragraphs. 1-4 or 6-8, in which fuel cut-off voltage is less than normal voltage. 11. The control device according to claim 10, in which the cutoff voltage of the supply fuel is higher than the lower limit of the voltage range of the current limit of the air-fuel ratio sensor at a time when the air-fuel ratio sensor is exposed to a gas having a theoretical air-fuel ratio. 12. The control device according to claim 10, in which the electronic control unit is configured so that the control of the fault diagnosis is not performed even after the end of the fuel cut-off control, when the condition for performing the control of the fault diagnosis is not fulfilled at the time of the end of the control of the fuel cut-off, the fuel cut-off voltage is higher than the lower limit of the voltage range of the current limit of the air-fuel ratio sensor at the time when the air-fuel ratio sensor is exposed to a gas having a predetermined lean air-fuel ratio, and the electronic control unit is configured to change the voltage supplied to the air-fuel ratio sensor from the fuel cut-off voltage to the normal voltage as soon as the output current of the air-fuel ratio sensor becomes equal to or less than a value corresponding to a predetermined lean air-fuel ratio, when the fault diagnosis control is not performed after the end of the fuel cut-off control. 13. The control device according to any one of paragraphs. 1-4 or 6-8, in which the internal combustion engine contains an exhaust gas purification catalyst, an exhaust gas purification catalyst is located in an exhaust channel of an internal combustion engine, the air-fuel ratio sensor is located on the outlet side of the exhaust gas purification catalyst in the direction of the exhaust gas flow and the air-fuel ratio sensor is a bowl-shaped air-fuel ratio sensor with a current limit, and the control device further comprises the air-fuel ratio inlet sensor located in the exhaust channel of the exhaust gas purification catalyst on the inlet side and the air-fuel ratio inlet sensor is configured as a multilayer air-fuel ratio sensor with a current limit.

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