JP2006046179A - Failure diagnosis device for air fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discover a failure of an air-fuel ratio sensor at an early stage by forcedly performing air-fuel ratio feed back control when the air-fuel ratio sensor fails from start of an engine for shortening period of a state that exhaust gas noxious component increases. <P>SOLUTION: In a failure diagnosis device for the air-fuel ratio sensor provided with the air-fuel ratio sensor detecting oxygen concentration in exhaust gas in an exhaust gas passage of the engine and provided with an air-fuel ratio feedback control means performing air-fuel ratio feedback control with using the air-fuel ratio sensor, a determination means determining a failure of the air-fuel ratio sensor if output voltage of the air-fuel ratio sensor never exceeds rich lean determination voltage after predetermined time passes from start of air-fuel ratio feedback control is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio sensor failure diagnosis apparatus, and in particular, even when an air-fuel ratio sensor has failed since engine startup, the air-fuel ratio sensor is forcibly detected by forcibly performing air-fuel ratio feedback control. The present invention relates to a failure diagnosis apparatus for an air-fuel ratio sensor that can be found in

  An engine mounted on a vehicle is provided with an O2 sensor as an air-fuel ratio sensor for detecting an oxygen concentration in exhaust gas in an exhaust passage, and an air-fuel ratio feedback is made so that the air-fuel ratio becomes a target value using an output voltage of the O2 sensor. Some have air-fuel ratio feedback control means for performing fuel control by control. The engine uses air-fuel ratio feedback control to optimize the air-fuel ratio to improve combustibility, improve the exhaust gas purification efficiency by the catalyst, and reduce exhaust exhaust harmful components.

  In the air-fuel ratio feedback control, if the O2 sensor fails, the air-fuel ratio feedback control is distorted, and the air-fuel ratio becomes inappropriate, causing an engine malfunction. Therefore, a failure diagnosis device that determines the failure of the O2 sensor has been proposed. Yes.

In the conventional failure diagnosis device for an air-fuel ratio sensor, the output voltage is detected before the activation of the O2 sensor, which is an air-fuel ratio sensor, and the abnormality determination of the O2 sensor is performed according to the abnormality determination condition. Some make a diagnosis.
Japanese Patent Laid-Open No. 2001-17396

Further, in the conventional air-fuel ratio sensor failure diagnosis apparatus, the O2 sensor is disconnected when the output value of the O2 sensor, which is an air-fuel ratio sensor, does not satisfy the first condition until a predetermined time or more has elapsed after the engine is started. If the output value of the O2 sensor does not satisfy the second condition, it is determined that the O2 sensor is disconnected or inactive.
JP-A-5-65840

  Recently, exhaust gas regulations for engines mounted on vehicles have become stricter, and the need for O2 sensor failure diagnosis with higher accuracy and various failure patterns has increased. It is required to prevent the vehicle from running for a long time and a state in which harmful exhaust components increase increases for a long time.

  Conventionally, the fuel control for controlling the air-fuel ratio at the start of the engine is an open loop control, and then the output voltage of the O2 sensor changes the rich lean determination voltage from one of the low side and the high side to the other side. If it is determined that the O2 sensor is activated by exceeding, the fuel control is set to the closed loop control (air-fuel ratio feedback control) state, and the failure of the O2 sensor is determined in the closed loop control state.

  However, as shown in FIG. 6, it is determined that the O2 sensor has failed since the start of the engine, the output voltage of the O2 sensor does not exceed the rich lean determination voltage, and the O2 sensor is not activated, and the air-fuel ratio is controlled. In the case where the fuel control continues in the open loop control state, the failure of the O2 sensor could not be determined because of the open loop control state. In such a case, since the fuel control does not become a closed loop control state, the failure determination of the O2 sensor is delayed, and there is a problem that it takes a long time to travel in a state where exhaust harmful components increase. It was.

  The present invention provides a malfunction of an air-fuel ratio sensor provided with an air-fuel ratio feedback control means for providing an air-fuel ratio sensor for detecting an oxygen concentration in exhaust gas in an exhaust passage of an engine and performing air-fuel ratio feedback control using the air-fuel ratio sensor. In the diagnostic device, if the output voltage of the air-fuel ratio sensor has never exceeded the rich lean determination voltage after a set time has elapsed after starting the air-fuel ratio feedback control, the air-fuel ratio sensor has failed. It is characterized in that determination means for determining is provided.

  According to the present invention, when the set time has elapsed after the air-fuel ratio feedback control is started by the determination means, the air-fuel ratio sensor fails if the output voltage of the air-fuel ratio sensor has never exceeded the rich / lean determination voltage. Even if the air-fuel ratio sensor has failed since the start of the engine, the air-fuel ratio sensor can be detected early by forcibly performing the air-fuel ratio feedback control. In addition, the time during which exhaust harmful components are increased can be shortened.

According to the air-fuel ratio sensor failure diagnosis apparatus of the present invention, in order to detect the air-fuel ratio sensor failure at an early stage, the output voltage of the air-fuel ratio sensor is once even when the set time has elapsed after starting the air-fuel ratio feedback control. When the rich lean determination voltage is not exceeded, it is determined that the air-fuel ratio sensor has failed.
Embodiments of the present invention will be described below with reference to the drawings.

  1 to 5 show an embodiment of the present invention. In FIG. 5, 2 is an engine mounted on a vehicle (not shown), 4 is an intake passage, and 6 is an exhaust passage. The engine 2 is a V-type engine, and is configured by arranging a first cylinder bank 8-1 on one side and a second cylinder bank 8-2 on the other side in a V shape.

  The intake passage 4 is provided with an air cleaner 10 at the upstream end, a throttle valve 12 is provided in the middle, and the downstream side branches into two first and second branch intake passages 4-1 and 4-2, and the first branch. The downstream end of the intake passage 4-1 is connected to a combustion chamber (not shown) on the first cylinder bank 8-1 side, and the downstream end of the second branch intake passage 4-2 is connected to the second cylinder bank 8-2 side. To a combustion chamber (not shown).

  The intake passage 4 is provided with a bypass air passage 14 that bypasses the throttle valve 12 and communicates the upstream side and the downstream side. An idle control valve 16 capable of adjusting the flow rate of idle air flowing through the bypass air passage 14 is provided in the middle of the bypass air passage 14. The idle control valve 16 is connected to an air-fuel ratio feedback control means 68 described later.

  The exhaust passage 6 branches on the upstream side into two first and second branch exhaust passages 6-1 and 6-2, and the upstream end of the first branch exhaust passage 6-1 serves as the first cylinder bank 8-1. And the upstream end of the second branch exhaust passage 6-2 communicates with the combustion chamber on the second cylinder bank 8-2 side, and the first and second branch exhaust passages 6-1 and 6- 2 downstream ends meet.

  The first branch exhaust passage 6-1 is provided with a first three-way catalyst 18-1, and a first front O2 sensor 20-1 which is an air-fuel ratio sensor upstream of the first three-way catalyst 18-1. And a first rear O2 sensor 22-1 is provided at a downstream side of the first three-way catalyst 18-1.

  The second branch exhaust passage 6-2 is provided with a second three-way catalyst 18-2, and a second front O2 sensor 20-2, which is an air-fuel ratio sensor, is located upstream of the second three-way catalyst 18-2. And a second rear O2 sensor 22-2 is provided downstream of the second three-way catalyst 18-2.

  The first and second front O2 sensors 20-1 and 20-2 detect the oxygen concentration in the exhaust gas in the first and second branch exhaust passages 6-1 and 6-2, and are rich signals that are inverted as output voltages. And a lean signal. The first and second rear O2 sensors 22-1 and 22-2 are connected to the first and second branch exhaust passages 6-1 and 6-2 on the downstream side of the first and second three-way catalysts 18-1 and 18-2. The oxygen concentration in the exhaust gas is detected, and a rich signal and a lean signal that are inverted as output voltages are output. A three-way catalyst 24 is provided in the exhaust passage 6 on the downstream side of the joining portion of the first and second branch exhaust passages 6-1 and 6-2.

  The engine 2 is provided with first and second fuel injection valves 26-1 and 26-2 on each side so as to be directed to the combustion chambers of the first and second cylinder banks 8-1 and 8-2. . The first and second fuel injection valves 26-1 and 26-2 are connected to the fuel tank 30 through the fuel supply passage 28. The fuel in the fuel tank 30 is pumped to the fuel supply passage 28 by the fuel pump 32, dust is removed by the fuel filter 34, and the fuel is supplied to the first and second fuel injection valves 26-1 and 26-2.

  In the middle of the fuel supply passage 28, a fuel pressure adjusting section 36 for adjusting the fuel pressure is provided. The fuel pressure adjusting unit 36 adjusts the fuel pressure to a predetermined value by the intake pipe pressure introduced from the pressure guiding passage 38 communicating with the intake passage 4, and returns excess fuel to the fuel tank 30 through the fuel return passage 40.

  The fuel tank 30 communicates with a canister 44 through an evaporation passage 42. In the middle of the evaporation passage 42, a tank pressure control valve 46 is provided. The tank pressure control valve 46 is controlled to be opened and closed by adjusting an intake pipe pressure introduced from a pressure passage 48 communicating with the intake passage 4 by a tank pressure control solenoid valve 50. The canister 44 communicates with the intake passage 4 on the downstream side of the throttle valve 12 by a purge passage 52. A purge control valve 54 is provided in the middle of the purge passage 52. Further, the canister 44 is provided with an atmospheric valve 56 for adjusting the atmosphere to be introduced.

  The engine 2 includes a second branch exhaust passage 6-2 upstream of the second front O2 sensor 20-2 constituting the exhaust system and a first and second branch intake passage 4- constituting the intake system. An EGR passage 58 that communicates with the merging portion of 1 · 4-2 is provided. An EGR control valve 60 is provided in the middle of the EGR passage 58. The EGR control valve 60 adjusts the EGR amount of the exhaust gas recirculated from the exhaust system to the intake system.

  Further, the engine 2 includes first and second ignition coils 62 on each side for causing spark plugs (not shown) provided in the combustion chambers of the first and second cylinder banks 8-1 and 8-2 to fly. -1 and 62-2 are provided, and the PCV valve 64 is provided in the second cylinder bank 8-2.

  The idle control valve 16, the first and second front O2 sensors 20-1 and 20-2, the first and second rear O2 sensors 22-1 and 22-2, and the first and second fuel injection valves 26. -1, 26-2, fuel pump 32, purge control valve 54, EGR control valve 60, and first and second ignition coils 62-1 and 62-2 are the first and second front O2 sensors. 20-1 and 20-2 (hereinafter referred to as “O2 sensor 20”) are connected to an air-fuel ratio feedback control means 68 constituting a failure diagnosis device 66.

  The air-fuel ratio feedback control means 68 includes an intake air temperature sensor 70 that detects the intake air temperature, an intake air amount sensor 72 that detects the intake air amount, a throttle opening sensor 74 that detects the throttle opening, and a cam angle. A cam angle sensor 76 that detects the intake pipe pressure, a water temperature sensor 80 that detects the coolant temperature of the engine 2, and a crank angle of the engine 2 that also functions as an engine speed sensor. A crank angle sensor 82, a fuel level sensor 84 for detecting the fuel level in the fuel tank 30, and a pressure sensor 86 for detecting the pressure in the fuel tank 30 are connected.

  The air-fuel ratio feedback control means 68 includes a display lamp 88, an electric load 90, a power steering pressure switch 92, a heater blower fan switch 94, a vehicle speed sensor 96, a combination meter 98, and a cruise control module 100. The main relay 102, the ignition switch 104, and the battery 106 are connected.

  The air-fuel ratio feedback control means 68 uses the output voltage of the O2 sensors 20 and 22 for detecting the oxygen concentration in the exhaust gas provided in the exhaust passage 6 of the engine 2 so that the air-fuel ratio becomes the target value. Fuel control is performed to improve the combustibility by optimizing the air-fuel ratio, improve the exhaust purification efficiency by the catalysts 18 and 24, and reduce exhaust harmful components to be discharged.

  The failure diagnosis device 66 for the O2 sensor 20 includes a determination unit 108 in the air-fuel ratio feedback control unit 68. As shown in FIG. 2, after the engine 2 is started, the determination unit 108 performs open loop control of fuel control after the coolant temperature reaches a set water temperature (for example, 20 degrees Celsius) for a set time (for example, 60 seconds). Is passed, the closed-loop control (air-fuel ratio feedback control) is forcibly started assuming that the O2 sensor 20 is active. Then, when the set time has elapsed after the air-fuel ratio feedback control is started, the determination unit 108 has failed the O2 sensor 20 when the output voltage of the O2 sensor 20 has never exceeded the rich lean determination voltage. It is determined.

  Next, the operation of this embodiment will be described.

  As shown in FIG. 3, the failure diagnosis device 66 for the O2 sensor 20 starts the engine 2 and performs fuel control for open loop control. When a program for forcibly closing loop control starts (202), It is determined whether the cooling water temperature Wt 2 is equal to or higher than the set water temperature Wts (for example, 20 degrees Celsius) (204).

  If this determination (204) is YES, it is determined whether a fuel cut is being executed (206).

  If this determination (206) is YES, it is determined whether a high load increase of the fuel is being executed (208).

  If this determination (208) is YES, it is determined whether the O2 sensor 20 is active (210).

  As shown in FIG. 4, when the program for determining the activation of the O2 sensor 20 is started (210-2), the output voltage V of the O2 sensor 20 increases the rich lean determination voltage Vt as shown in FIG. It is judged whether it has exceeded from the side to the low side or from the low side to the high side (210-4).

  If this determination (210-4) is YES, it is determined that the O2 sensor 20 is active (210-6), and the process returns to determination (210).

  If the determination (210-4) is NO, it is determined whether the coolant temperature Wt of the engine 2 is equal to or higher than the set water temperature Wts (for example, 20 degrees Celsius) (210-8).

  If this determination (210-8) is YES, it is determined whether the execution time Top of the open loop control is equal to or longer than a set time Tops (for example, 60 seconds) (210-10).

  If this determination (210-10) is YES, it is determined that the O2 sensor 20 is active (210-6), and the process returns to determination (210).

  On the other hand, if the determinations (210-8) and (210-10) are NO, the process returns to determination (210-4).

  If the determination (210) is YES according to the result of the activation determination of the O2 sensor 20, the open loop control of the fuel control is terminated and the closed loop control is forcibly executed (212).

  On the other hand, if the determinations (204) to (210) are NO, the process returns to determination (204).

That is, the failure diagnosis device 66 of the O2 sensor 20 performs the open loop control after the engine 2 is started.
(1) No fuel cut or high load increase (2) Cooling water temperature is higher than set water temperature (3), O2 sensor 20 is active (3-1), O2 sensor 20 output voltage is rich Lean judgment voltage exceeded or
(3-2) When the cooling water temperature is equal to or higher than the set water temperature and the open loop control determines that the set time or longer is an execution condition of the closed loop control, and when these conditions are satisfied, the closed loop control (air-fuel ratio feedback control is forcibly performed) ) Is started (see FIG. 2).

  As shown in FIG. 1, the failure diagnosis device 66 of the O2 sensor 20 starts the failure diagnosis program when the closed loop control is forcibly performed after the engine 2 is started (302). It is determined whether Wt is not less than a first set water temperature Wts1 (for example, 10 degrees Celsius) and not more than a second set water temperature Wts2 (for example, 110 degrees Celsius) (304).

  If this determination (304) is YES, it is determined whether the heater integrated time Ht of the sensor heater (not shown) provided in the O2 sensor 20 is equal to or longer than a set time Hts (for example, 24 seconds) (306). .

  If this determination (306) is YES, it is determined whether a fuel cut is being executed (308).

  If this determination (308) is YES, it is determined whether the execution time Tcl of the closed loop control of the fuel control is equal to or longer than the set time Tcls (for example, 30 seconds) (310).

  If this determination (310) is YES, it is determined whether the output voltage V of the O2 sensor 20 never exceeds the rich lean determination voltage Vs (for example, 0.45 V) (312).

  If this determination (312) is YES, it is determined that the O2 sensor 20 has failed (314).

  On the other hand, if the determinations (304) to (312) are NO, the process returns to determination (304).

That is, the failure diagnosis device 66 of the O2 sensor 20 performs the forced closed loop control after the engine 2 is started.
(1) The forced closed-loop control (air-fuel ratio feedback control) has passed the set time (2), and the failure determination condition of the O2 sensor 20 is that the output voltage of the O2 sensor 20 never exceeds the rich lean determination voltage. If these conditions are determined and these conditions are satisfied, it is determined that the O2 sensor 20 has failed.

  As described above, the failure diagnosis device 66 for the O2 sensor 20 activates the O2 sensor 20 when the open loop control of the fuel control after the coolant temperature reaches the set water temperature after the engine 2 is started passes the set time. The closed-loop control (air-fuel ratio feedback control) is forcibly started. Then, the failure diagnosis device 66 for the O2 sensor 20 starts the air-fuel ratio feedback control, and when the set voltage has elapsed and the output voltage of the O2 sensor 20 has never exceeded the rich / lean determination voltage, the O2 sensor 20 It is determined that 20 has failed.

  As a result, the failure diagnosis device 66 for the O2 sensor 20 performs the air-fuel ratio feedback control forcibly, even when the O2 sensor 20 has failed since the engine 2 is started, to thereby prevent the failure of the O2 sensor 20. It can be detected at an early stage, and the time during which exhaust harmful components increase can be shortened.

  In the above-described embodiment, the output voltage of the O2 sensor 20 has never exceeded the rich / lean determination voltage from the low side to the high side once the set time has elapsed after the start of the air-fuel ratio feedback control (output). The voltage is fixed to a state below the rich / lean determination voltage), but when the set time after the start of the air-fuel ratio feedback control has elapsed, the output voltage of the O2 sensor 20 is once rich / lean determination voltage. Is not exceeded from the high side to the low side (fixed in a state where the output voltage exceeds the rich / lean determination voltage), it is similarly determined that the O2 sensor 20 has failed.

  In the above embodiment, the closed loop control is forcibly started from the open loop control after the engine 2 is started, and the failure is determined by the output voltage of the O2 sensor 20 during the air-fuel ratio feedback control. Even during operation, on the condition that the open-loop control is changed to the closed-loop control, the output voltage of the O2 sensor 20 is once rich / lean determined when the set time elapses after starting the air-fuel ratio feedback control. When the voltage does not exceed, by determining that the O2 sensor 20 has failed, the present invention can be applied not only to the start of the engine 2 but also to the failure diagnosis of the O2 sensor 20 during operation of the engine 2. In this embodiment, the air-fuel ratio sensor is described as the O2 sensor. However, the same applies to various air-fuel ratio sensors (for example, an air-fuel ratio sensor that directly detects the air-fuel ratio of exhaust gas) provided in the exhaust system. Control is possible.

  The air-fuel ratio sensor failure diagnosis apparatus according to the present invention can detect a failure of the air-fuel ratio sensor at an early stage, and therefore can shorten the time during which the vehicle travels in a state where the air-fuel ratio sensor has failed.

It is a flowchart of failure diagnosis of the failure diagnosis apparatus showing an embodiment. It is a timing chart of failure diagnosis. It is a flowchart of closed loop control implementation. It is a flowchart of active determination. It is a system block diagram of a failure diagnosis apparatus. It is a timing chart of conventional failure diagnosis.

Explanation of symbols

2 Engine 4 Intake passage 6 Exhaust passage 20-1 First front O2 sensor 20-2 Second front O2 sensor 66 Failure diagnosis device 68 Air-fuel ratio feedback control means 80 Water temperature sensor 108 Determination means

Claims (1)

  In an air-fuel ratio sensor failure diagnosis apparatus comprising an air-fuel ratio sensor for detecting an oxygen concentration in exhaust gas in an exhaust passage of an engine, and an air-fuel ratio feedback control means for performing air-fuel ratio feedback control using the air-fuel ratio sensor, Judgment that the air-fuel ratio sensor has failed when the output voltage of the air-fuel ratio sensor has never exceeded the rich lean determination voltage after a set time has elapsed after the air-fuel ratio feedback control has started. A fault diagnosis apparatus for an air-fuel ratio sensor, characterized in that means is provided.

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