Engine and method for diagnosing engine

Abstract

Provided are an engine and a method for diagnosing an engine with which NOx sensor failure can be diagnosed with greater accuracy.　This engine is configured such that: a NOx sensor failure diagnosis operation S103 accompanied by a DPF regeneration process, EGR stoppage, and urea water injection stoppage is performed under the control of an electronic control device; and detection data for a pair of NOx concentrations J, K detected by a pair of NOx sensors in the NOx sensor failure diagnosis operation are transmitted S105 to an engine diagnosis tool with which the failure diagnosis for the pair of NOx sensors S108 is performed on the basis of the detection data, said engine diagnosis tool being situated outside the engine. In this engine diagnosis method, the failure diagnosis for the NOx sensors S108 is performed by the engine diagnosis tool on the basis of detection data transmitted from the engine.

Description

Engine and engine diagnostic method

[0001] The present invention relates to an engine and a diagnostic method for the engine, and more particularly to an engine and a diagnostic method for the engine that can improve the accuracy of diagnosing a malfunction of a NOx sensor.

[0002] 2. Description of the Related Art Conventionally, there are engines in which a failure diagnosis of a NOx sensor is performed based on detection of the NOx concentration in the engine exhaust (see, for example, Patent Document 1).

[0003] JP 2011-241737 A (see FIG. 4)

[0004] <<Problem>> The accuracy of NOx sensor fault diagnosis may be reduced. In the engine of Patent Document 1, when the exhaust gas temperature is low, the exhaust gas flow rate is unstable, urea crystals remain in the exhaust passage, and if EGR is continued, the NOx concentration decreases, resulting in a decrease in the accuracy of the NOx concentration detection data detected by the NOx sensor. Furthermore, if urea water is injected, the NOx purification function of the SCR causes the NOx concentration detection data to change significantly. This may result in a decrease in the accuracy of NOx sensor fault diagnosis.

[0005] An object of the present invention is to provide an engine and an engine diagnostic method that can improve the accuracy of NOx sensor failure diagnosis.

[0006] The main configuration of the present invention is as follows: (Invention according to claim 1) An engine configured to perform a NOx sensor failure diagnosis operation accompanied by DPF regeneration processing, EGR stop, and urea water injection stop under the control of an electronic control unit, and to transmit detection data of a pair of NOx concentrations detected by the pair of NOx sensors during this NOx sensor failure diagnosis operation to an engine diagnostic tool external to the engine that performs a failure diagnosis of the pair of NOx sensors based on this detection data.

[0007] (Invention according to claim 3) An engine diagnostic method characterized by controlling an electronic control device to cause the engine to perform a NOx sensor fault diagnosis operation involving DPF regeneration processing, EGR stoppage, and urea water injection stoppage, and during this NOx sensor fault diagnosis operation, cause a pair of detection data of NOx concentrations detected by a pair of NOx sensors on the upstream and downstream exhaust sides of the SCR to be transmitted to an engine diagnostic tool, and cause the engine diagnostic tool to perform a fault diagnosis of the NOx sensor based on the detection data.

[0008] The invention according to claim 1 or claim 3 achieves the following effects. Effect 1: The accuracy of fault diagnosis of a pair of NOx sensors can be improved. During NOx sensor fault diagnosis operation, the DPF regeneration process raises the exhaust gas temperature, stabilizing the exhaust gas flow rate and burning off urea crystals adhering to the exhaust passage. Furthermore, EGR is stopped to increase the NOx concentration, thereby improving the accuracy of the NOx concentration detection data from the pair of NOx sensors. Furthermore, this detection data is not affected by the NOx purification function of the SCR due to the cessation of urea water injection, and is therefore less likely to change. By transmitting the pair of highly accurate and less likely to change detection data of NOx concentrations to an engine diagnostic tool in this way, the engine diagnostic tool can perform fault diagnosis of the pair of NOx sensors based on the pair of NOx concentration detection data, thereby improving the accuracy of fault diagnosis of the pair of NOx sensors.

[0009] <Effect 2> Fault diagnosis of the pair of NOx sensors can be performed while the exhaust system remains mounted on the engine. Since the detection data of the pair of NOx concentrations detected by the pair of NOx sensors during the NOx sensor fault diagnosis operation is transmitted to an engine diagnostic tool outside the engine that performs fault diagnosis of the pair of NOx sensors based on this detection data, fault diagnosis of the NOx sensors can be performed while the exhaust system remains mounted on the engine.

[0010] 1 is a schematic diagram of an engine according to an embodiment of the present invention and an engine diagnostic tool used to diagnose the engine. It is a block diagram showing the electronic control unit of the engine of FIG. 1 and peripheral components such as sensors and actuators connected to the electronic control unit. It is a flowchart of control by the electronic control unit of the engine in diagnosing an engine fault during normal operation of the engine of FIG. 1. It is a flowchart of control in a first NOx sensor fault diagnosis using the engine diagnostic tool of FIG. 1, where FIG. 4(A) is a flowchart of control by the engine diagnostic tool, and FIG. 4(B) is a flowchart of control by the engine electronic control unit. It is a flowchart of control in a second NOx sensor fault diagnosis using the engine diagnostic tool of FIG. 1, where FIG. 5(A) is a flowchart of control by the engine diagnostic tool, and FIG. 5(B) is a flowchart of control by the engine electronic control unit. It is a flowchart of control in a functional recovery diagnosis of the engine's NOx purification function after replacing the NOx sensor using the engine diagnostic tool of FIG. 1, where FIG. 6(A) is a flowchart of control by the engine diagnostic tool, and FIG. 6(B) is a flowchart of control by the engine electronic control unit.

[0011] 1 to 6 are diagrams for explaining an engine and an engine diagnostic method according to an embodiment of the present invention. In this embodiment, a vertical in-line multi-cylinder diesel engine and a diagnostic method for this engine will be explained.

[0012] As shown in FIG. 1, the engine 1 includes an electronic control unit 8, an intake system 10, a fuel supply system 11, and an exhaust system 12. An engine cooling fan 1c is disposed in front of the engine 1, and a flywheel 1d is disposed in the rear of the engine 1. The electronic control unit 8 is an engine ECU. ECU is an abbreviation for electronic control unit. The intake system 10 includes, in order from the upstream side of the intake path, an air cleaner 10a, an intake throttle valve 10b, an intake sensor 10c, and an intake manifold 10d. The timing and opening degree of the intake throttle valve 10b are controlled by the electronic control unit 8. The intake sensor 10c detects the intake air flow rate and intake air temperature. Furthermore, the intake system 10 receives exhaust gas recirculation (EGR) from the exhaust system 12 via the EGR system 5. EGR is an abbreviation for exhaust gas recirculation. The EGR device (5) comprises, in order from the upstream side of the EGR, an EGR cooler (5a) and an EGR valve (5b), and the opening and closing of the EGR valve (5b) is controlled by an electronic control device (8).

[0013] As shown in FIG. 1, the fuel supply system 11 is of a common rail type and includes a common rail 11a and a fuel injector 11b that injects fuel into each cylinder 1a. The fuel injector 11b is controlled by an electronic control unit 8, and opens at a predetermined timing for a predetermined time to inject a predetermined amount of fuel. The fuel injection amount is regulated by a governor function of the electronic control unit 8 based on the accelerator position detected by an accelerator sensor 13 and the actual engine speed detected by an engine speed sensor 14. Furthermore, under control of the electronic control unit 8, the DPF regeneration process performs a post-injection in addition to a main injection from the fuel injector 11b. An after-injection may also be performed between the main injection and the post-injection.

[0014] As shown in FIG. 1 , the exhaust system (12) includes, in order from the exhaust upstream side, an exhaust manifold (12a), a DOC (6a), a DPF (6), a urea water injector (9), an SCR (7), and an ASC (7a). The DOC (6a) and the DPF (6) are housed in a DPF case (6b), the SCR (7) and the ASC (7a) are housed in an SCR case (7b), a mixing passage (12b) is provided between the DPF case (6b) and the SCR case (7b), and a urea water injector (9) is disposed upstream of this mixing passage (12b). The urea water (9a) injected from the urea water injector (9) into the mixing passage (12b) is mixed with exhaust gas (15) and supplied to the SCR (7).

[0015] DOC is an abbreviation for diesel oxidation catalyst, which oxidizes CO (carbon monoxide) and NO (nitric oxide) in the exhaust (15), and during DPF regeneration processing, catalytically combusts after-injection fuel and post-injection fuel injected from the fuel injector (11b) to raise the temperature of the exhaust (15) and incinerate and remove PM accumulated in the DPF (6). PM is an abbreviation for particulate matter. DPF is an abbreviation for diesel particulate filter, which captures PM in the exhaust. SCR is an abbreviation for selective catalytic reduction type catalyst, which uses urea water (9a) injected into the exhaust (15) from the urea water injector (9) to adsorb ammonia to the SCR (7), which then uses this as a reducing agent to reduce NOx (nitrogen oxide) in the exhaust, and removes N ２ (nitrogen gas) and H ２ ASC is an abbreviation for ammonia purification oxidation catalyst, and NH ３ (Ammonia) to prevent slippage.

[0016] As shown in FIG. 1, the exhaust system (12) includes, from the upstream side of the exhaust gas, a DOC inlet exhaust gas temperature sensor (6c), a DPF inlet exhaust gas temperature sensor (6d), an exhaust differential pressure sensor (6e), a DPF outlet exhaust gas temperature sensor (6f), a NOx sensor (3) on the upstream exhaust side of the SCR (7), an SCR inlet exhaust gas temperature sensor (7c), and a NOx sensor (4) on the downstream exhaust side of the SCR (7). During normal engine operation, NOx reduction operation is performed using EGR and the SCR (7) with urea water injection. When the differential pressure between the inlet and outlet of the DPF (6) detected by the exhaust differential pressure sensor (6e) indicates that the amount of PM accumulation has reached the amount required to start regeneration, and the DOC (6) has reached its activation temperature due to the temperature rise caused by the exhaust gas (15), DPF regeneration processing is initiated.

[0017] 1, urea water 9a in a urea water tank 9b is pumped to the urea water injector 9 by a urea water pump 9c, and the urea water injector 9 is controlled by an electronic control device 8, and is opened for a predetermined time at a predetermined timing to inject a predetermined amount of urea water 9a into a mixing passage 12b. The injection amount of the urea water 9a is calculated by a calculation unit of the electronic control device 8 of the engine 1 based on a pair of NOx concentrations (J) and (K) detected by a pair of NOx sensors 3 and 4, an intake air flow rate detected by an intake sensor 10c, etc. A urea water level sensor (9d) and a urea water temperature sensor (9e) are arranged in the urea water tank (9b), and the electronic control device (8) of the engine (1) displays a recommendation to replenish the urea water (9a) and to prevent the urea water (9a) from freezing on the display device (1b) of the engine (1).

[0018] As shown in FIG. 1, a display device 1b for the engine 1 is connected to the electronic control device 8 for the engine 1, and this display device 1b for the engine 1 is arranged on an operation panel such as a dashboard of the engine-mounted machine, and displays an engine failure determination display (S6) (described later) in FIG. 3 and the like. The engine-mounted machine refers to a traveling or fixed-type agricultural machine or construction machine equipped with the engine 1. Traveling machines include tractors and backhoes, and fixed-type machines include engine generators. A liquid crystal display, an organic EL display, or the like can be used for the display device 1b for the engine 1. EL is an abbreviation for electroluminescence.

[0019] The engine 1 diagnosis procedure performed by the engine 1 electronic control unit 8 is outlined below: As shown in Figure 3, the engine 1 electronic control unit 8 performs a fault diagnosis (S4) of the engine 1 during normal engine operation, and when a fault determination (S5) of the engine 1 is made, the engine 1 electronic control unit 8 displays an engine fault indication (S6) on the display device 1b of the engine 1 and simultaneously displays a NOx sensor fault diagnosis recommendation. The user of the engine-mounted machine who has confirmed this display (S6) requests a service technician to perform a NOx sensor failure diagnosis. The service technician then uses the engine diagnostic tool 2 to have the engine 1's electronic control unit 8 perform a NOx sensor failure diagnosis operation (S103, S203). Based on the NOx sensor failure determination display (S110, S210) confirmed by the NOx sensor failure diagnosis (S108, S208), the service technician replaces the NOx sensor and then performs a function recovery check diagnosis (S309) of the engine's NOx purification function after the NOx sensor replacement, as shown in FIG. 6A. If a failure determination (S5) of the engine 1 is made, the engine 1's electronic control unit 8 limits the output of the engine 1, rendering the engine-mounted machine inoperable, and the user is prompted to request a NOx sensor failure diagnosis from a service technician.

[0020] As shown in FIG. 1, the engine (1) includes a DPF (6), an SCR (7), a pair of NOx sensors (3) and (4) on the exhaust upstream and downstream sides of the SCR (7), an electronic control unit (8), an EGR device (5), and a urea water injector (9).

[0021] As shown in Figure 3, in this engine 1, a fault diagnosis (S4) of the engine 1 during normal operation is performed by the electronic control unit (8) of the engine (1) based on the NOx purification rate of the SCR (7) during engine operation, and when a fault determination (S5) of the engine 1 is made, the determination result is displayed (S6) on the display device (1b) of the engine 1. Normal operation refers to operation other than the NOx sensor fault diagnosis operation (S103) (S203) shown in Figures 4(B) and 5(B) and the engine function recovery confirmation operation (S303) after NOx sensor replacement shown in Figure 6(B), and NOx reduction processing is performed during normal operation by EGR and urea water injection.

[0022] As shown in FIGS. 4(B) and 5(B), the engine 1 is configured to perform NOx sensor failure diagnosis operations (S103) (S203) that involve DPF regeneration processing, EGR stop, and urea water injection stop under the control of the electronic control unit 8, and to transmit (S105) (S205) detection data of the pair of NOx concentrations (J) (K) detected by the pair of NOx sensors 3 and 4 during the NOx sensor failure diagnosis operations (S103) (S203) to an engine diagnosis tool 2 outside the engine 1 that performs failure diagnosis (S108) (S208) of the pair of NOx sensors 3 and 4 based on the detection data.

[0023] This engine has the following advantages. During the NOx sensor failure diagnosis operations (S103) and (S203) shown in Figures 4(B) and 5(B), the DPF regeneration process raises the exhaust gas temperature, stabilizes the exhaust gas flow rate, burns off urea crystals adhering to the exhaust passage (12c), and stops the EGR to increase the NOx concentration. This improves the accuracy of the detection data of the NOx concentrations (J) and (K) obtained by the pair of NOx sensors (3) and (4). Furthermore, because the urea water injection is stopped, this detection data is not affected by the NOx purification function of the SCR (7) and is therefore less likely to change. In this way, by transmitting (S105) (S205) the pair of highly accurate and stable detection data of the NOx concentrations (J) and (K) to the engine diagnostic tool (2), as shown in FIGS. 4A and 5A, the engine diagnostic tool (2) can perform fault diagnosis (S108) (S208) of the pair of NOx sensors (3) and (4) based on the detection data of the pair of NOx concentrations (J) and (K), thereby improving the accuracy of the fault diagnosis (S108) (S208) of the pair of NOx sensors (3) and (4).

[0024] This engine also provides the following advantages: As shown in Figures 4(A) and 5(A), the detection data of the pair of NOx concentrations (J) and (K) detected by the pair of NOx sensors (3) and (4) during the NOx sensor failure diagnosis operation (S103) and (S203) is transmitted (S105) and (S205) to an engine diagnostic tool (2) outside the engine (1), which performs failure diagnosis (S108) and (S208) of the pair of NOx sensors (3) and (4) based on the detection data. Therefore, failure diagnosis of the NOx sensors (3) and (4) can be performed while the exhaust system (12) illustrated in Figure 1 remains mounted on the engine (1).

[0025] The DPF regeneration process associated with the NOx sensor failure diagnosis operation (S103) (S203) shown in Figures 4(A) and 5(A) differs from the DPF regeneration process during normal operation in that it is performed even when the PM accumulation amount has not yet reached the amount required to start regeneration. As with normal operation, this DPF regeneration process is performed by post-injecting fuel from the fuel injector (11b) after the exhaust gas temperature at the inlet side of the DOC (6a) shown in Figure 1 reaches a temperature at which the DOC (6a) can be activated. When the exhaust gas temperature at the inlet side of the DOC (6a) is low, the intake throttle valve (10b) is narrowed, the main injection fuel is increased, after-injection is performed, or other measures are taken to raise the exhaust gas temperature at the inlet side of the DOC (6a) to the temperature at which the DOC (6a) can be activated. In addition, when an exhaust pipe fuel injection valve is provided, the DPF regeneration process can also be performed by exhaust pipe injection from the exhaust pipe fuel injection valve instead of post injection from the fuel injector (11b).

[0026] As shown in FIG. 6(B), this engine is configured to perform, under the control of the electronic control device (8), a function recovery check operation (S303) for the engine's NOx purification function after the replacement of the NOx sensor, which includes DPF regeneration processing, EGR stop, and urea water injection, and to transmit (S305) detection data of the pair of NOx concentrations (J) and (K) detected by the pair of NOx sensors (3) and (4) during this function recovery check operation (S303) to the engine diagnostic tool (2), which performs a function recovery check diagnosis (S309) for the engine's NOx purification function after the replacement of the NOx sensor based on this detection data.

[0027] This engine has the following advantages. During the engine's functional recovery check operation (S303) for the NOx purification function after the replacement of the NOx sensor shown in FIG. 6B, the DPF regeneration process raises the exhaust temperature and stabilizes the exhaust flow rate. The urea crystals adhering to the exhaust passage 12c shown in FIG. 1 are burned off, and the EGR is stopped to increase the NOx concentration. This improves the accuracy of the detection data of the NOx concentrations (J) and (K) obtained by the pair of NOx sensors 3 and 4 shown in FIG. 6B. By transmitting the highly accurate pair of NOx concentrations (J) and (K) as detection data to the engine diagnostic tool 2 (S305), the engine diagnostic tool 2 can perform a functional recovery check diagnosis (S309) for the engine after the replacement of the NOx sensor based on the detection data of the pair of NOx concentrations (J) and (K), as shown in FIG. 6A. This improves the accuracy of the engine diagnostic tool 2's functional recovery check diagnosis (S309) for the NOx purification function after the replacement of the NOx sensor.

[0028] Next, a description will be given of a method for diagnosing the engine 1. The diagnosis of the engine 1 is performed in the following order: a malfunction diagnosis (S4) of the engine 1 during normal operation as shown in Figure 3; a malfunction diagnosis (S108) (S208) of the NOx sensor; replacement of the NOx sensor based on confirmation of the NOx sensor malfunction determination display (S110) (S210) as shown in Figures 4(A) and 5(A); and a functional recovery diagnosis (S309) of the engine for the NOx purification function after the NOx sensor replacement as shown in Figure 6(A).

[0029] First, as shown in FIG. 3, the electronic control device 8 of the engine 1 performs a fault diagnosis (S4) on the engine 1 during normal operation based on the NOx purification rate of the SCR 7 while the engine is running, and if a fault determination (S5) is made for the engine 1, the display device 1b of the engine 1 displays the engine fault determination (S6) and simultaneously displays a recommendation for a NOx sensor fault diagnosis.

[0030] Next, when the user confirms the display (S6) on the display device (1b) of the engine (1) and requests a service technician to perform a NOx sensor failure diagnosis, the service technician controls the electronic control device (8) to perform a NOx sensor failure diagnosis operation (S103) in the engine (1) that involves DPF regeneration processing, stopping EGR, and stopping urea water injection, as shown in FIG. 4(B). During this NOx sensor failure diagnosis operation (S103), detection data of a pair of NOx concentrations (J) and (K) detected by a pair of NOx sensors (3) and (4) located upstream and downstream of the SCR (6) is transmitted to the engine diagnostic tool (2) (S105). Based on the detection data, the engine diagnostic tool (2) performs a NOx sensor failure diagnosis (S108), as shown in FIG. 4(A).

[0031] This engine diagnostic method has the following advantages. During the NOx sensor failure diagnostic operation (S103) shown in FIG. 4B, the DPF regeneration process raises the exhaust gas temperature, stabilizing the exhaust gas flow rate and burning off urea crystals adhering to the exhaust passage 12c. Furthermore, the EGR is stopped to increase the NOx concentration, thereby improving the accuracy of the detection data of the NOx concentrations J and K obtained by the pair of NOx sensors 3 and 4. Furthermore, since the urea water injection is stopped, this detection data is not affected by the NOx purification function of the SCR 7 and is therefore less likely to change. In this way, by transmitting (S105) (S205) the pair of highly accurate and stable detection data of the NOx concentrations (J) and (K) to the engine diagnostic tool (2), as shown in FIG. 4A, the engine diagnostic tool (2) can perform a fault diagnosis (S108) of the pair of NOx sensors (3) and (4) based on the detection data of the pair of NOx concentrations (J) and (K), thereby improving the accuracy of the fault diagnosis (S108) of the pair of NOx sensors (3) and (4).

[0032] This engine diagnostic method also provides the following advantages. As shown in FIG. 4A, the detection data of the pair of NOx concentrations (J) and (K) detected by the pair of NOx sensors (3) and (4) during the NOx sensor fault diagnosis operation (S103) and (S203) is transmitted (S105) and (S205) to an engine diagnostic tool (2) outside the engine (1), which performs fault diagnosis (S108) and (S208) of the pair of NOx sensors (3) and (4) based on the detection data. Therefore, fault diagnosis (S108) and (S208) of the NOx sensors (3) and (4) can be performed without removing the exhaust system (12) shown in FIG. 1 from the engine (1).

[0033] As shown in FIG. 4A, in the engine diagnostic tool (2), if the absolute value of the difference between the pair of NOx concentrations (J) and (K) exceeds a predetermined determination threshold value (L), a failure determination (S109) of the NOx sensor is made, and if the absolute value of the difference is equal to or less than the predetermined determination threshold value (L), a normality determination (S111) of the pair of NOx sensors (3) and (4) is made.

[0034] As shown in FIG. 4A, in the engine diagnostic tool 2, in response to the NOx sensor failure determination (S109) or the normality determination (S111) of the pair of NOx sensors 3 and 4, the tool display unit 2 a of the engine diagnostic tool 2 shown in FIG. 1 displays the NOx sensor failure determination display (S110) or the normality determination display (S112) of the pair of NOx sensors 3 and 4 shown in FIG. 4A.

[0035] As shown in FIG. 4A, when a NOx sensor failure determination display (S110) is made, a display recommending replacement of one of the NOx sensors and a display recommending failure diagnosis of the NOx sensor after replacement are also made. A service technician who sees this display replaces one of the pair of NOx sensors 3, 4 with a NOx sensor that has been previously confirmed to be normal, and performs failure diagnosis of the NOx sensor after replacement (S208) shown in FIG. 5A. Furthermore, as shown in FIG. 4A, when a display showing a normality determination display (S112) of the pair of NOx sensors 3, 4 is made, a display recommending inspection of components other than the pair of NOx sensors 3, 4 is also made. A service technician who sees this display inspects sensors such as the SCR inlet exhaust gas temperature sensor 7c and actuators such as the urea water injector 9.

[0036] After the NOx sensor has been replaced in accordance with the NOx sensor failure determination (S109) shown in FIG. 4A, as shown in FIG. 5B, under the control of the electronic control device (8), a post-NOx sensor replacement NOx sensor failure diagnosis operation (S203) is performed, which involves DPF regeneration processing, stopping EGR, and stopping urea water injection. During this NOx sensor failure diagnosis operation (S203), detection data of the pair of NOx concentrations (J) and (K) detected by the pair of NOx sensors (3) and (4) including the replaced NOx sensor (3) is transmitted to the engine diagnostic tool (2) (S205). As shown in FIG. 5A, the engine diagnostic tool (2) performs a failure diagnosis (S208) of the post-NOx sensor replacement NOx sensor based on the detection data.

[0037] As shown in FIG. 5A, in the engine diagnostic tool (2), if the absolute value of the difference between the pair of NOx concentrations (J) and (K) exceeds a predetermined judgment threshold (L), a fault judgment (S209) is made for the unreplaced NOx sensor (4), and if the absolute value of the difference is equal to or less than the predetermined judgment threshold (L), a normality judgment (S211) is made for the pair of replaced and unreplaced NOx sensors (3) and (4).

[0038] As shown in FIG. 5A, in the engine diagnostic tool 2, in response to the failure determination (S209) of the unreplaced NOx sensor 4 or the normality determination (S311) of the pair of replaced and unreplaced NOx sensors 3, 4, the tool display unit 2 a of the engine diagnostic tool 2 displays the failure determination of the unreplaced NOx sensor 4 (S210) or the normality determination of the pair of replaced and unreplaced NOx sensors 3, 4 (S212).

[0039] As shown in Figure 5(A), when the NOx sensor failure determination display (S210) is made, a display recommending replacement of the other (unreplaced) NOx sensor and a display recommending diagnosis to confirm recovery of engine function after NOx sensor replacement are also made. A service technician who has confirmed this display replaces the other (unreplaced) NOx sensor with a NOx sensor that has been previously confirmed to be normal, and performs a diagnosis to confirm recovery of engine function after NOx sensor replacement, as shown in Figure 6. Also, as shown in Figure 5(A), when the normality determination display (S212) is made for the pair of NOx sensors 3 and 4, a display recommending diagnosis to confirm recovery of engine function after NOx sensor replacement is also made, and a service technician who has confirmed this display performs a diagnosis to confirm recovery of engine function after NOx sensor replacement, as shown in Figure 6.

[0040] After the NOx sensor has been replaced in accordance with the failure determination (S109) of the NOx sensor or the failure determination (S109) (S209) of the unreplaced NOx sensor (4) shown in FIG. 4(A) or FIG. 5(A), the electronic control unit (8) controls the engine (1) to perform a post-NOx sensor function recovery check operation (S303) involving DPF regeneration processing, EGR stop, and urea water injection after the NOx sensor replacement, as shown in FIG. 6(B). During this engine function recovery check operation (S303), the detection data of the pair of NOx concentrations (J) and (K) detected by the pair of NOx sensors (3) and (4) including the replaced NOx sensor are transmitted to the engine diagnostic tool (2) (S305). Based on the transmitted data, the engine diagnostic tool (2) performs a function recovery check diagnosis (S309) of the engine for the NOx purification function after the NOx sensor replacement, as shown in FIG. 6(A).

[0041] As shown in FIG. 6A, in the engine diagnostic tool (2), if the absolute value of the difference between the theoretical NOx purification rate (E) of the SCR (7) calculated based on the detection data of the pair of NOx concentrations (J) and (K) and the actual NOx purification rate (F) is equal to or less than a predetermined judgment threshold value (G), a functional recovery confirmation judgment (S310) is made for the engine with respect to the NOx purification function, and if the absolute value of the difference exceeds the judgment threshold value (G), a functional recovery confirmation judgment (S312) is made for the engine with respect to the NOx purification function.

[0042] As shown in FIG. 6A, in the engine diagnostic tool (2), in response to the engine function recovery confirmation determination (S311) or the engine function recovery unconfirmed determination (S313), the tool display unit (2a) of the engine diagnostic tool (2) displays the engine function recovery confirmation determination (S311) or the engine function recovery unconfirmed determination (S313) after the NOx sensor replacement.

[0043] As shown in FIG. 6A, when the display (S313) indicates that the engine's NOx purification function has not yet been restored, a display recommending inspection of parts other than the pair of NOx sensors (3) and (4) is also displayed. A service technician who sees this display will inspect other parts, such as the SCR inlet exhaust temperature sensor (7c) and the urea water injector (9).

[0044] As shown in FIG. 1 , the engine diagnostic tool 2 is a portable information terminal device with electronic control functions, such as a laptop computer or tablet. It includes a tool display 2a, a fault diagnosis command switch 2b, a function recovery check diagnosis command switch 2c, and a transceiver 2d for transmitting and receiving data and signals via wired or wireless communication between the tool display 2a and the transceiver 8a of the electronic control unit 8 of the engine 1. The tool display 2a can be a liquid crystal display (LCD), an organic electroluminescence (EL) display, or the like, similar to the display device 1b of the engine 1. In this case, the tool display 2a can display text information such as the NOx sensor failure determination indicators (S110) and (S210) and the pair of NOx sensor normality determination indicators (S112) and (S212) shown in FIGS. 4A and 5A. The tool display 2a can also be an indicator lamp or an LED. LED is an abbreviation for light-emitting diode. In this case, the display on the tool display section (2a) can be displayed in a distinguishable manner by lighting, blinking, turning off, etc.

[0045] This engine diagnostic method will be described with reference to the flowcharts shown in Figures 3 to 6. Figure 3 is a flowchart of engine fault diagnosis during normal operation. This fault diagnosis is performed under the control of the electronic control unit (8). In step (S1), the NOx concentration (J) upstream of the SCR, the NOx concentration (K) downstream of the SCR, and other data are input to the input section of the electronic control unit (8). The other data refers to data necessary for calculating the theoretical NOx purification rate (E), calculating the actual NOx purification rate (F), and setting the judgment threshold (G), which will be described later. Specifically, this refers to the SCR inlet exhaust gas temperature used to estimate the catalyst temperature of the SCR (7), the intake air flow rate used to estimate the flow rate of the exhaust gas (15), and the injection amount of urea water (9a) from the urea water injector (9) used to estimate the ammonia adsorption amount of the SCR (7).

[0046] In step (S2), the calculation unit of the electronic control unit 8 calculates the theoretical NOx purification rate E and the actual NOx purification rate F, and in step (S3), a judgment threshold value G is set. The judgment threshold value G is a positive number. When a judgment condition for a malfunction of the engine 1 is met in step (S4), a diagnosis unit of the electronic control unit 8 judges a malfunction of the engine 1 in step (S5). The judgment condition for a malfunction of the engine 1 in step (S4) is that the absolute value of the difference between the theoretical NOx purification rate E and the actual NOx purification rate F exceeds the judgment threshold value G. In step (S6), a display instruction unit of the electronic control unit 8 causes the display device 1b of the engine 1 to display a malfunction judgment display (S6) for the engine 1 and also to display a recommendation for NOx sensor diagnosis.

[0047] 4 shows the flow of the NOx sensor failure diagnosis (first time). This NOx sensor failure diagnosis (first time) is performed by a service technician who, upon confirmation of the NOx sensor diagnosis recommendation displayed on the display device 1b of the engine 1 in step S6 shown in FIG. 3, requests the user to have the NOx sensor failure diagnosis performed by the service technician using the engine diagnostic tool 2.

[0048] In step S101 shown in FIG. 4A, a NOx sensor fault diagnosis command signal is transmitted from the diagnosis command unit of the engine diagnostic tool 2 based on the service technician's operation of the fault diagnosis command switch 2b of the engine diagnostic tool 2 shown in FIG. 1. In step S102 shown in FIG. 4B, when the reception determination unit of the electronic control unit 8 of the engine 1 determines that the NOx sensor fault diagnosis command signal has been received, in step S103, the operation control unit of the electronic control unit 8 controls the NOx sensor fault diagnosis operation. The NOx sensor fault diagnosis operation involves DPF regeneration processing, EGR stop, and urea water injection stop. The DPF regeneration processing, EGR stop, and urea water injection stop are automatically performed by the electronic control unit 8 of the engine 1 based on the NOx sensor fault diagnosis command signal. In step (S104), a pair of detection data of the NOx concentration (J) upstream of the SCR and the NOx concentration (K) downstream of the SCR is acquired by the data acquisition unit of the electronic control unit (8) of the engine (1), and in step (S105), the pair of detection data is transmitted from the transmitting / receiving unit (8a) of the electronic control unit (8) shown in FIG. 1 to the transmitting / receiving unit (2d) of the engine diagnostic tool (2).

[0049] In step S106 shown in FIG. 4A, when the reception determination unit of the engine diagnostic tool 2 determines that the pair of detection data has been received, in step S107, a determination threshold value setting unit of the engine diagnostic tool 2 sets a determination threshold value L. The determination threshold value L is a positive number. In step S108, a diagnosis unit of the engine diagnostic tool 2 performs a NOx sensor failure diagnosis. The condition for determining whether a NOx sensor has failed in the NOx sensor failure diagnosis in step (S108) is that the absolute value of the difference between the pair of detection data for the NOx concentration upstream of the SCR (J) and the NOx concentration downstream of the SCR (K) exceeds a determination threshold value (L). If this condition is met, in step (S109), the failure determination unit of the engine diagnostic tool (2) determines that the NOx sensor has failed, and in step (S110), the display instruction unit of the engine diagnostic tool (2) causes the tool display unit (2a) to display a failure determination of the NOx sensor, as well as a recommendation to replace one of the NOx sensors and a recommendation to diagnose the NOx sensor after the replacement of the other NOx sensor.

[0050] The NOx sensor failure diagnosis in step S108 shown in FIG. 4A cannot determine which of the pair of NOx sensors 3 and 4 is faulty. Therefore, the replacement recommendation display for one of the NOx sensors in step S110 does not specify which of the pair of NOx sensors 3 and 4 is faulty. In this case, the service technician arbitrarily selects one of the pair of NOx sensors 3 and 4 and replaces that one with a NOx sensor that has already been confirmed to be normal. Note that if it is predicted that one of the pair of NOx sensors is highly likely to be faulty due to differences in the thermal loads that the pair of NOx sensors 3 and 4 receive, the replacement recommendation display for one of the pair of NOx sensors in step S110 may specify the NOx sensor with the highest probability of failure. In this case, the service technician can follow the recommendation and replace the specified NOx sensor of the pair of NOx sensors 3 and 4 with a NOx sensor that has already been confirmed to be normal. The NOx sensor designated in the display of the replacement recommendation for one of the NOx sensors in step (S110) may be either of the pair of NOx sensors (3) and (4).

[0051] As shown in FIG. 4A, if the NOx sensor failure diagnosis in step S108 does not satisfy the conditions for determining a NOx sensor failure, i.e., if the absolute value of the difference between the pair of detection data for the NOx concentration upstream of the SCR (J) and the NOx concentration downstream of the SCR (K) is equal to or less than the determination threshold value L, then in step S111 the failure determination unit of the engine diagnostic tool 2 determines that the pair of NOx sensors 3, 4 are normal, and in step S112 the display instruction unit of the engine diagnostic tool 2 causes the tool display unit 2a to display a normal determination of the pair of NOx sensors 3, 4 and also to display an inspection recommendation for parts other than the pair of NOx sensors 3, 4, and recommends that a service technician inspect sensors such as the SCR inlet exhaust gas temperature sensor 7c and actuators such as the urea water injector 9.

[0052] 5A and 5B show the flow of the second NOx sensor failure diagnosis. This second NOx sensor failure diagnosis is performed by a service technician using the engine diagnostic tool 2 after the technician has confirmed on the tool display unit 2a of the engine diagnostic tool 2 that the replacement recommendation for one of the NOx sensors is displayed in step S110 shown in FIG. 4A and has replaced the other NOx sensor with a NOx sensor that has already been confirmed to be normal.

[0053] The NOx sensor failure diagnosis (second time) shown in Fig. 5 is performed in the same procedure as the NOx sensor failure diagnosis (first time) shown in Fig. 4 after one of the pair of NOx sensors is replaced in the NOx sensor failure diagnosis (first time) shown in Fig. 4, and the processing of steps (S201) to (S212) shown in Fig. 5, except for the advisory displays of steps (S210) and (S212), is the same as the processing of steps (S101) to (S112) having the same last two digits in the NOx sensor failure diagnosis (first time) shown in Fig. 4. The displays of steps (S210) and (S212) shown in Fig. 5 differ from the displays of steps (S110) and (S112) shown in Fig. 4(A) in the following respects. That is, the display in step (S110) is a display indicating that the NOx sensors have failed, a display recommending the replacement of one of the NOx sensors, and a display recommending that the NOx sensors be diagnosed for failure after the replacement of the other NOx sensor, whereas the display in step (S210) is a display indicating that the NOx sensors have failed, and a display recommending that the engine should be diagnosed for functional recovery after the NOx sensors have been replaced. Also, the display in step (S112) is a display indicating that the pair of NOx sensors are normal, and a display recommending the inspection of components other than the pair of NOx sensors, whereas the display in step (S212) is a display indicating that the pair of NOx sensors are normal, and a display recommending that the engine should be diagnosed for functional recovery after the NOx sensors have been replaced.

[0054] The reason why a replacement recommendation for the other (unreplaced) NOx sensor is displayed in step S210 is because one of the NOx sensors has been replaced with one previously confirmed to be normal, and therefore the NOx sensor failure determination in step S209 is presumed to be due to a failure of the other (unreplaced) NOx sensor. The reason why a diagnosis recommendation for confirming engine recovery after NOx replacement is displayed in step S210 is because the other (unreplaced) NOx sensor has also been replaced with a NOx sensor previously confirmed to be normal, and both NOx sensors 3 and 4 are now normal, and it is expected that the engine's NOx purification function will be restored after the NOx sensor replacement. The reason why a diagnosis recommendation for confirming engine recovery after NOx replacement is displayed in step S212 is because the normality determination of the pair of NOx sensors in step S211 confirms that both NOx sensors 3 and 4 are normal, and it is expected that the engine's NOx purification function will be restored after the NOx sensor replacement.

[0055] 6 shows a flow chart of a diagnosis for confirming the recovery of the engine's NOx purification function after replacement of the NOx sensor. This diagnosis for confirming the recovery of the engine's function after replacement of the NOx sensor is typically performed by a service technician using the engine diagnostic tool 2 after checking the display device 1b of the engine 1 for a recommendation to diagnose the recovery of the engine's NOx purification function after replacement of the NOx sensor in step S110 shown in FIG. 4A or steps S210 and S212 shown in FIG. 5A.

[0056] In step S301 shown in FIG. 6A, a diagnostic command unit of the engine diagnostic tool 2 transmits a diagnostic command signal for verifying engine recovery based on a command operation of the engine diagnostic tool 2 by a service technician. In step S302 shown in FIG. 6B, if the reception determination unit of the electronic control unit 8 of the engine 1 determines that the diagnostic command signal for verifying engine recovery is received, in step S303, the operation control unit of the electronic control unit 8 controls the engine to perform a diagnostic operation for verifying engine recovery. The NOx sensor failure diagnosis operation involves DPF regeneration, EGR shutdown, and urea water injection. The DPF regeneration, EGR shutdown, and urea water injection shutdown are automatically performed by the electronic control unit 8 of the engine 1 based on the diagnostic command signal for verifying engine recovery. In step (S304), the data acquisition unit of the electronic control unit (8) of the engine (1) acquires a pair of NOx concentrations (J) upstream of the SCR and NOx concentrations (K) downstream of the SCR, as well as other detected data, and in step (S305), the transmission / reception unit (8a) of the electronic control unit (8) transmits the detected data to the transmission / reception unit (2d) of the engine diagnostic tool (2).

[0057] In step S306 shown in FIG. 6A, when the reception determination unit of the engine diagnostic tool 2 determines that the detection data has been received, in step S307, the calculation unit of the engine diagnostic tool 2 calculates the theoretical NOx purification rate E and the actual NOx purification rate F, and in step S308, the threshold setting unit of the engine diagnostic tool 2 sets a judgment threshold G. The judgment threshold G is a positive number. In step S309, the diagnostic unit of the engine diagnostic tool 2 performs a functional check diagnosis of the engine. The condition for determining whether engine function recovery has not been confirmed in the engine function check diagnosis in step (S309) is that the absolute value of the difference between the theoretical NOx purification rate (E) and the actual NOx purification rate (F) is equal to or less than a determination threshold value (G), and if this condition is met, in step (S310), the function check determination unit of the engine diagnostic tool 2 determines whether engine function recovery has been confirmed, and in step (S311), the display instruction unit of the engine diagnostic tool 2 causes the tool display unit 2a to display the engine function recovery confirmation determination. If the function check determination unit of the engine diagnostic tool 2 determines whether engine function recovery has been confirmed in step (S310), the electronic control unit 8 of the engine 1 releases the output limit of the engine 1.

[0058] As shown in FIG. 6A, if the engine function recovery confirmation conditions are not met in the engine function recovery confirmation diagnosis of step (S309), i.e., if the absolute value of the difference between the theoretical NOx purification rate (E) and the actual NOx purification rate (F) exceeds the judgment threshold value (G), then in step (S312), the failure determination unit of the engine diagnostic tool (2) determines that engine function recovery has not been confirmed, and in step (S313), the display instruction unit of the engine diagnostic tool (2) causes the tool display unit (2a) to determine that engine function recovery has not been confirmed and to display an inspection recommendation for parts other than the pair of NOx sensors (3) and (4).

[0059] If the user has access to the engine diagnostic tool 2, the user can diagnose the pair of NOx sensors 3 and 4 and check the recovery of the engine's NOx purification function after replacing the NOx sensors.

[0060] (1) Engine, (2) Engine diagnostic tool, (2a) Tool display, (3) NOx sensor upstream of exhaust gas, (4) NOx sensor downstream of exhaust gas, (5) EGR device, (6) DPF, (7) SCR, (8) Electronic control unit, (9) Urea water injector, (E) Theoretical purification rate, (F) Actual purification rate, (G) Judgment threshold, (J) NOx concentration upstream of SCR, (K) Downstream of SCR Downstream NOx concentration, (L)...determination threshold, (S103)...NOx sensor failure diagnosis operation, (S105)...detection data transmitted to engine diagnosis tool, (S108)...NOx sensor failure diagnosis, (S109)...NOx sensor failure determination, (S110)...NOx sensor failure determination display, (S111)...pair of NOx sensors normal determination, (S112)...pair of NOx sensors normal determination display, (S203 )...NOx sensor failure diagnosis operation after NOx sensor replacement, (S205)...detection data sent to engine diagnostic tool, (S208)...NOx sensor failure diagnosis after NOx sensor replacement, (S209)...failure determination of unreplaced NOx sensor, (S210)...failure determination display of unreplaced NOx sensor, (S211)...normality determination of pair of replaced and unreplaced NOx sensors, (S212)...normality determination display of pair of replaced and unreplaced NOx sensors, (S303)...engine function recovery confirmation operation after NOx sensor replacement, (S305)...transmission, (S309)...engine function recovery confirmation diagnosis, (S310)...engine function recovery confirmation determination, (S311)...engine function recovery not confirmed determination display, (S312)...engine function recovery not confirmed determination, (S313)...engine function recovery not confirmed determination display.

Claims

1. An engine comprising a DPF, an SCR, a pair of NOx sensors on the upstream and downstream sides of the exhaust of the SCR, an electronic control unit, an EGR device, and an aqueous urea injector, configured to perform a NOx sensor failure diagnosis operation involving DPF regeneration processing, EGR stop, and aqueous urea injection stop under the control of the electronic control unit, and transmit detection data of a pair of NOx concentrations detected by the pair of NOx sensors in this NOx sensor failure diagnosis operation to an engine diagnosis tool outside the engine for performing a failure diagnosis of the pair of NOx sensors based on this detection data.

2. The engine according to claim 1, configured to perform an engine function recovery confirmation operation for the NOx purification function after NOx sensor replacement involving DPF regeneration processing, EGR stop, and aqueous urea injection under the control of the electronic control unit, and transmit detection data of a pair of NOx concentrations detected by the pair of NOx sensors in this function recovery confirmation operation to the engine diagnosis tool for performing an engine function recovery confirmation diagnosis for the NOx purification function after NOx sensor replacement based on this detection data.

3. An engine diagnosis method, wherein under the control of the electronic control unit, the engine is caused to perform a NOx sensor failure diagnosis operation involving DPF regeneration processing, EGR stop, and aqueous urea injection stop, and detection data of a pair of NOx concentrations detected by a pair of NOx sensors on the upstream and downstream sides of the exhaust of the SCR in this NOx sensor failure diagnosis operation is transmitted to the engine diagnosis tool, and the engine diagnosis tool performs a failure diagnosis of the NOx sensors based on the above detection data.

4. The engine diagnosis method according to claim 3, wherein in the engine diagnosis tool, when the absolute value of the difference between the pair of NOx concentrations exceeds a predetermined determination threshold, a failure determination of the NOx sensors is made, and when the absolute value of the difference is equal to or less than the predetermined determination threshold, a normal determination of the pair of NOx sensors is made.

5. The engine diagnosis method according to claim 4, wherein in the engine diagnosis tool, a failure determination display of the NOx sensors or a normal determination display of the pair of NOx sensors is made on the tool display part of the engine diagnosis tool corresponding to the failure determination of the NOx sensors or the normal determination of the pair of NOx sensors.

6. In the engine diagnostic method according to claim 4, in response to the failure determination of the NOx sensor, after the NOx sensor is replaced, under the control of the electronic control unit, a NOx sensor failure diagnostic operation after NOx sensor replacement is performed, which involves DPF regeneration processing, EGR stop, and urea water injection stop. In this NOx sensor failure diagnostic operation, detection data of a pair of NOx concentrations detected by the pair of NOx sensors including the replaced NOx sensor is transmitted to the engine diagnostic tool, and based on the above detection data, the engine diagnostic tool performs a failure diagnosis of the NOx sensor after NOx sensor replacement. This is a characteristic of the engine diagnostic method.

7. In the engine diagnostic method according to claim 6, in the engine diagnostic tool, when the absolute value of the difference between the pair of NOx concentrations exceeds a predetermined determination threshold value, a failure determination of the non-replaced NOx sensor is performed. When the absolute value of the difference is equal to or less than the predetermined determination threshold value, a normal determination of the pair of replaced and non-replaced NOx sensors is performed. This is a characteristic of the engine diagnostic method.

8. In the engine diagnostic method according to claim 7, in the engine diagnostic tool, corresponding to the failure determination of the non-replaced NOx sensor or the normal determination of the pair of replaced and non-replaced NOx sensors, a failure determination display of the non-replaced NOx sensor or a normal determination display of the pair of replaced and non-replaced NOx sensors is performed on the tool display unit of the engine diagnostic tool. This is a characteristic of the engine diagnostic method.

9. In the engine diagnostic method according to claim 4 or claim 7, in response to the failure determination of the NOx sensor or the failure determination of the non-replaced NOx sensor, after the NOx sensor is replaced, under the control of the electronic control unit, a function recovery confirmation operation of the engine for the NOx purification function after NOx sensor replacement is performed, which involves DPF regeneration processing, EGR stop, and urea water injection for the engine. In this function recovery confirmation operation of the engine, detection data of a pair of NOx concentrations detected by the pair of NOx sensors including the replaced NOx sensor is transmitted to the engine diagnostic tool, and based on the transmitted data, the engine diagnostic tool performs a function recovery confirmation diagnosis of the engine for the NOx purification function after NOx sensor replacement. This is a characteristic of the engine diagnostic method.

10. In the engine diagnostic method according to claim 9, in the engine diagnostic tool, when the absolute value of the difference between the theoretical NOx purification rate and the actual NOx purification rate of the SCR calculated based on the detection data of the pair of NOx concentrations is equal to or less than a predetermined determination threshold value, the engine diagnostic tool is made to perform a function recovery confirmation determination of the engine with respect to the NOx purification function, and when the absolute value of the difference exceeds the determination threshold value, the engine diagnostic tool is made to perform a function recovery non-confirmation determination of the engine with respect to the NOx purification function. A method for diagnosing an engine, characterized by this.

11. In the engine diagnostic method according to claim 10, in the engine diagnostic tool, corresponding to the function recovery confirmation determination or the function recovery non-confirmation determination of the engine, a function recovery confirmation determination display or a function recovery non-confirmation determination display of the engine after NOx sensor replacement is performed on the tool display unit of the engine diagnostic tool. A method for diagnosing an engine, characterized by this.

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