Diagnostic device for supercharged V-type engines

Abstract

To perform imbalance diagnosis which is adapted to a V-type engine with a supercharger.SOLUTION: An analysis device of a V-type engine with a supercharger is employed with a V-type engine with a supercharger having: a first wastegate valve for opening and closing a first bypass passage which bypasses a first turbine of a first supercharger arranged in a first exhaust passage of a first bank; a second wastegate valve for opening and closing a second bypass passage which bypasses a second turbine of a second supercharger arranged in a second exhaust passage of a second bank; a first air-fuel ratio sensor arranged at a downstream side of the first exhaust passage; and a second air-fuel ratio sensor arranged at a downstream side of the second exhaust passage. The analysis device performs imbalance diagnosis for analyzing a variation in air-fuel ratio between first cylinders by the first air-fuel ratio sensor, and in air-fuel ratio between second cylinders by the second air-fuel ratio sensor, and when both the first and second banks satisfy a prerequisite for the execution of the imbalance diagnosis, the analysis device performs the imbalance diagnosis by fixing openings of both the first and second wastegate valves to prescribed values.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a diagnostic device for a V-type engine with a turbocharger.

Background Art

[0002] An imbalance diagnosis for diagnosing the variation in the air-fuel ratio between cylinders of a turbocharged engine is known. The imbalance diagnosis is executed in a state where the opening degree of the waste gate valve is fixed to a predetermined value when a predetermined precondition is satisfied (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of a V-type engine with a turbocharger, the preconditions for executing the imbalance diagnosis may be satisfied for each bank. Therefore, it is conceivable to execute the imbalance diagnosis for each bank. For example, when the preconditions are satisfied only for one bank, it is conceivable to fix the opening degree of the waste gate valve on one bank side and execute the imbalance diagnosis only for one bank without fixing the opening degree of the waste gate valve on the other bank side. However, in this case, the boost pressure is different between the two banks, and there is a possibility that the engine rotational fluctuation increases.

[0005] Therefore, it is conceivable to perform an imbalance diagnosis on only one bank while the opening degree of the wastegate valves on both banks is fixed at a predetermined value. In this case, the opening degree of the wastegate valve on the other bank is fixed even though the imbalance diagnosis is not performed on that bank. Even if the preconditions are met only for the other bank, the imbalance diagnosis of the other bank is performed while the opening degree of the wastegate valve on the one bank is fixed. As a result, the period during which the opening degree of the wastegate valve is fixed may be prolonged until the imbalance diagnosis for both banks is completed, which may lead to various problems.

[0006] Therefore, the present invention aims to provide a diagnostic device for a supercharged V-type engine that can perform an imbalance diagnosis suitable for a supercharged V-type engine. [Means for solving the problem]

[0007] The above objective is to provide a first bank having a plurality of first cylinders, a second bank having a plurality of second cylinders, a first wastegate valve for opening and closing a first bypass passage that bypasses the first turbine of a first supercharger located in a first exhaust passage connected to the first bank, a second wastegate valve for opening and closing a second bypass passage that bypasses the second turbine of a second supercharger located in a second exhaust passage connected to the second bank, a first air-fuel ratio sensor located downstream of the downstream end of the first bypass passage in the first exhaust passage, and a second air-fuel ratio sensor located downstream of the downstream end of the second bypass passage in the second exhaust passage. This diagnostic device for a supercharged V-type engine is applied to a supercharged V-type engine and performs an imbalance diagnosis in which the first air-fuel ratio sensor diagnoses variations in the air-fuel ratio between the first cylinders and the second air-fuel ratio sensor diagnoses variations in the air-fuel ratio between the second cylinders, and the diagnostic device for a supercharged V-type engine is provided, and comprises a determination unit that determines whether both the first and second banks meet the preconditions for performing the imbalance diagnosis, and an execution unit that, if the determination unit makes an affirmative determination, fixes the opening of both the first and second wastegate valves to a predetermined value and performs the imbalance diagnosis. [Effects of the Invention]

[0008] According to the present invention, a diagnostic device for a supercharged V-type engine that can perform an imbalance diagnosis suitable for a supercharged V-type engine can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the engine's configuration. [Figure 2] This flowchart illustrates the imbalance diagnostic control performed by the ECU. [Figure 3] This timing chart illustrates the imbalance diagnosis between this embodiment and the comparative example. [Modes for carrying out the invention]

[0010] [Engine Overview] Figure 1 is a schematic diagram of engine 1. Engine 1 has a pair of banks 2L and 2R arranged around the crankshaft at an appropriate bank angle relative to each other. Bank 2L has cylinders #1, #3, and #5. Bank 2R has cylinders #2, #4, and #6. In other words, engine 1 is a V-type 6-cylinder engine, but the number of cylinders is not limited to this. Also, engine 1 is a gasoline engine, but it may also be a diesel engine. Banks 2L and 2R correspond to the first and second banks, respectively. Cylinders #1, #3, and #5 correspond to the first cylinder. Cylinders #2, #4, and #6 correspond to the second cylinder. Furthermore, as will be described later, engine 1 is equipped with a supercharger. In other words, engine 1 is a supercharged V-type engine.

[0011] Engine 1 comprises an intake passage 4M and intake branch passages 4L and 4R. The intake branch passages 4L and 4R branch off from each other downstream of intake passage 4M and are connected to banks 2L and 2R, respectively. The intake passage 4M is equipped with an air cleaner 2, an air flow meter 2S, and a throttle valve 2V, in that order from upstream. The air cleaner 2 filters dust and other particles from the intake air. The air flow meter 2S detects the amount of intake air. The throttle valve 2V adjusts the amount of intake air. A single throttle valve 2V is provided in the intake passage 4M where the intake branch passages 4L and 4R merge, but this is not limited to that. For example, separate intake passages may be connected to banks 2L and 2R, and each intake passage may be equipped with its own throttle valve and air flow meter.

[0012] The intake branch passage 4L has branch sections that branch downstream and connect to the intake ports of cylinders #1, #3, and #5 of bank 2L, respectively. Similarly, the intake branch passage 4R has branch sections that branch downstream and connect to the intake ports of cylinders #2, #4, and #6 of bank 2R, respectively. Each branch section of the intake branch passage 4L is provided with a port injection valve PL that injects fuel into the intake ports of cylinders #1, #3, and #5, respectively. Similarly, the intake branch passage 4R is provided with a port injection valve PR that injects fuel into the intake ports of cylinders #2, #4, and #6, respectively. In addition to the port injection valves PL and PR, or in addition to the port injection valves PL and PR, an in-cylinder injection valve may be provided.

[0013] In bank 2L, cylinders #1, #3, and #5 are each equipped with spark plugs IL for igniting the fuel-air mixture. Similarly, in bank 2R, cylinders #2, #4, and #6 are each equipped with spark plugs IR. Engine 1 also includes exhaust passages 5L and 5R connected to banks 2L and 2R, respectively.

[0014] The exhaust passage 5L has branching sections upstream, connected to the exhaust ports of cylinders #1, #3, and #5, respectively. These branching sections merge downstream. Downstream of the merged section, in order from upstream, are the turbine 6L, the air-fuel ratio sensor SL, and the catalyst 7L.

[0015] Turbine 6L is located in the supercharger and rotates together with the compressor that supercharges the intake pressure. The compressor, although not shown in the diagram, is located upstream of the air cleaner 2 in the intake passage 4M. The air-fuel ratio sensor SL detects the air-fuel ratio of the exhaust gas. The catalyst 7L purifies the exhaust gas. Similarly, the branching section of the exhaust passage 5R merges downstream, and downstream of the merger, from upstream to downstream, are the turbine 6R, air-fuel ratio sensor SR, and catalyst 7R. Turbines 6L and 6R are examples of the first and second turbines. Air-fuel ratio sensors SL and SR are examples of the first and second air-fuel ratio sensors.

[0016] Bypass passages 8L and 8R are connected to exhaust passages 5L and 5R, respectively. Bypass passages 8L and 8R bypass turbines 6L and 6R, respectively. Wastegate valves 9L and 9R are provided in bypass passages 8L and 8R, respectively. Air-fuel ratio sensors SL and SR are installed in exhaust passages 5L and 5R, downstream of the downstream ends of bypass passages 8L and 8R, respectively.

[0017] The ECU (Electronic Control Unit) 10 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The ECU 10 is electrically connected to the air flow meter 2S, throttle valve 2V, port injection valves PL and PR, spark plugs IL and IR, air-fuel ratio sensors SL and SR, and wastegate valves 9L and 9R. The ECU 10 acquires the detected values ​​from the air flow meter 2S and air-fuel ratio sensors SL and SR, and controls the throttle valve 2V, port injection valves PL and PR, spark plugs IL and IR, and wastegate valves 9L and 9R based on these values ​​to control the entire engine 1. The ECU 10 also performs the imbalance diagnosis described below. The ECU 10 is an example of a diagnostic device for a supercharged V-type engine.

[0018] [Imbalance Diagnosis] When certain conditions are met, the ECU10 performs an imbalance diagnosis for banks 2L and 2R. In the imbalance diagnosis for bank 2L, the ECU10 acquires time-series data of the air-fuel ratio for a predetermined number of combustion cycles based on the air-fuel ratio sensor SL. The time-series data of the air-fuel ratio detected by the air-fuel ratio sensor SL for one combustion cycle shows the air-fuel ratios for cylinders #1, #3, and #5 sequentially at time intervals of 120° in crank angle. A large amplitude in this time-series data indicates a large variation in the air-fuel ratio between cylinders #1, #3, and #5. Therefore, the ECU10 performs an imbalance diagnosis based on the magnitude of the difference between the upper and lower peak values ​​of the air-fuel ratio in the time-series data. The ECU10 performs an imbalance diagnosis for bank 2R using a similar method.

[0019] Figure 2 is a flowchart exemplifying the imbalance diagnosis control executed by the ECU 10. The ECU 10 determines whether the imbalance diagnosis has been completed in the current trip (step S1). If the answer in step S1 is No, that is, if the imbalance diagnosis has been completed in the current trip, this control ends. If the answer in step S1 is Yes, the ECU 10 determines whether the preconditions for the imbalance diagnosis are satisfied for both banks 2L and 2R (step S2).

[0020] The preconditions for the imbalance diagnosis include, for example, (1) the temperature of the cooling water of the engine 1 being equal to or higher than a predetermined value, (2) the atmospheric pressure being equal to or higher than a predetermined value, (3) the rotational speed and load of the engine 1 being within a predetermined range, (4) the main feedback control of the air-fuel ratio being in execution, (5) the rich control after fuel cut not being in execution, (6) the vapor concentration learning value per unit purge rate being equal to or higher than a predetermined value, and (7) the number of updates of the purge concentration learning value being equal to or higher than a predetermined value. The main feedback control in (4) is to control the respective fuel injection amounts at the port injection valves PL and PR so that the respective detection values of the air-fuel ratio sensors SL and SR become the respective target values. The rich control after fuel cut in (5) is to control the target air-fuel ratio to a rich air-fuel ratio smaller than stoichiometry for a predetermined time when returning from fuel cut. The unit purge rate in (6) is the ratio of the evaporated fuel gas to the intake air amount. The vapor concentration learning value in (6) is a coefficient reflecting the concentration of the vapor component in the purge gas. The conditions (1) to (7) are merely an example of the preconditions for the imbalance diagnosis and are not limited thereto.

[0021] Each of the above conditions (1) to (3) can hold in common for banks 2L and 2R. That is, for each of conditions (1) to (3), if one of banks 2L and 2R holds, the other also holds, and if one does not hold, the other does not hold either. On the other hand, for each of the above conditions (4) to (7), it can hold for each of banks 2L and 2R. That is, for each of conditions (4) to (7), one of banks 2L and 2R may hold while the other may not hold. Therefore, for example, if one of banks 2L and 2R satisfies all of the conditions (1) to (7), and the other satisfies the conditions (1) to (3) but does not satisfy any of the conditions (4) to (7), then a No determination is made in step S2. When a No occurs in step S2, this control ends. Step S2 is an example of the processing executed by the determination unit.

[0022] When both banks 2L and 2R satisfy all of the above conditions (1) to (7), a Yes determination is made in step S2. When a Yes occurs in step S2, ECU 10 requests to fix the opening degrees of both waste gate valves 9L and 9R to a predetermined value (step S3). Specifically, ECU 10 requests the opening degrees of waste gate valves 9L and 9R to be fully open or fully closed. The reason for setting to fully open or fully closed is to make the way the exhaust hits the air-fuel ratio sensors SL and SR constant and to ensure the accuracy of the imbalance diagnosis. ...

[0023] ECU 10 determines whether to permit the request for fixing the opening degree (step S4). When a No occurs in step S4, this control ends. When a Yes occurs in step S4, ECU 10 fixes the opening degrees of both waste gate valves 9L and 9R to fully open or fully closed in accordance with the request for fixing the opening degree and executes an imbalance diagnosis (step S5). Incidentally, during the execution of the imbalance diagnosis, ECU 10 switches the diagnosis flag from off to on.

[0024] The ECU10 determines whether the number of combustion cycles during the imbalance diagnosis exceeds a predetermined value (step S6). If the answer in step S6 is No, step S6 is executed again. If the answer in step S6 is Yes, the ECU10 completes the imbalance diagnosis (step S7). When the imbalance diagnosis is complete, the ECU10 switches the diagnosis completion flag from off to on.

[0025] Figure 3 is a timing chart illustrating the imbalance diagnosis for this embodiment and the comparative example. Figure 3 shows the success or failure of the preconditions for each bank 2L and 2R, whether or not there is a request for opening degree fixing, the status of the "diagnosis in progress" flag, and the status of the "diagnosis complete" flag. This embodiment is shown with solid lines, and the comparative example is shown with dotted lines. Therefore, the parts where the line segments of this embodiment and the line segments of the comparative example overlap are shown with solid lines.

[0026] First, the comparative example will be explained. In the comparative example, if at least one of banks 2L and 2R satisfies the above-mentioned preconditions, an imbalance diagnosis is performed for that bank. If only bank 2L satisfies the preconditions (times t1-t2), the openings of both wastegate valves 9L and 9R are fixed, and an imbalance diagnosis is performed only for bank 2L. If both banks 2L and 2R satisfy the preconditions (times t3-t4), the openings of both wastegate valves 9L and 9R are fixed, and an imbalance diagnosis is performed for both banks 2L and 2R. At this point, the imbalance diagnosis for bank 2L is completed (time t4). Next, if only bank 2R satisfies the preconditions (times t5-t6), the openings of both wastegate valves 9L and 9R are again fixed, and an imbalance diagnosis is performed only for bank 2R. At this point, the imbalance diagnosis for bank 2R is completed (time t6).

[0027] In this way, the opening positions of both wastegate valves 9L and 9R are fixed until the imbalance diagnosis for both banks 2L and 2R is completed. As a result, the period during which the opening positions of both wastegate valves 9L and 9R are fixed is prolonged. For example, if the period during which the opening positions of both wastegate valves 9L and 9R are fixed to fully open is prolonged, acceleration response may decrease, potentially reducing drivability. If the period during which the opening positions of both wastegate valves 9L and 9R are fixed to fully closed is prolonged, fuel efficiency may worsen.

[0028] In this embodiment, if only bank 2L satisfies the preconditions (times t1-t2), the openings of wastegate valves 9L and 9R are not fixed, and the imbalance diagnosis is not performed. Only when the preconditions for both banks 2L and 2R are satisfied (times t3-t4, t5-t6), the openings of both wastegate valves 9L and 9R are fixed, and the imbalance diagnosis is performed for both banks 2L and 2R. Therefore, unlike the comparative example, it is possible to suppress the prolonged period during which the openings of both wastegate valves 9L and 9R are fixed. This makes it possible to suppress a decrease in drivability or a deterioration in fuel efficiency. Thus, in this embodiment, an imbalance diagnosis suitable for a supercharged V-type engine 1 can be performed.

[0029] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0030] 1. Engine (supercharged V-type engine) 2L Bank (Bank 1) 2R Bank (Second Bank) Cylinders #1, #3, and #5 (First Cylinder) Cylinders #2, #4, and #6 (second cylinder) 5L exhaust passage (first exhaust passage) 5R Exhaust passage (2nd exhaust passage) 6L Turbine (First Turbine) 6R Turbine (2nd Turbine) 8L Bypass Passage (First Bypass Passage) 8R Bypass Passage (Second Bypass Passage) 9L Wastegate Valve (First Wastegate Valve) 9R Wastegate Valve (Second Wastegate Valve) SL Air-Fuel Ratio Sensor (First Air-Fuel Ratio Sensor) SR Air-Fuel Ratio Sensor (Second Air-Fuel Ratio Sensor) 10. ECU (Diagnostic device for supercharged V-type engines)

Claims

[Claim 1] This invention is applied to a supercharged V-type engine comprising: a first bank having a plurality of first cylinders; a second bank having a plurality of second cylinders; a first wastegate valve for opening and closing a first bypass passage that bypasses the first turbine of a first supercharger located in a first exhaust passage connected to the first bank; a second wastegate valve for opening and closing a second bypass passage that bypasses the second turbine of a second supercharger located in a second exhaust passage connected to the second bank; a first air-fuel ratio sensor located downstream of the downstream end of the first bypass passage in the first exhaust passage; and a second air-fuel ratio sensor located downstream of the downstream end of the second bypass passage in the second exhaust passage. A diagnostic device for a supercharged V-type engine that performs an imbalance diagnosis by diagnosing variations in the air-fuel ratio between the first cylinders using the first air-fuel ratio sensor and diagnosing variations in the air-fuel ratio between the second cylinders using the second air-fuel ratio sensor, A determination unit that determines whether both the first and second banks have met the prerequisites for performing the imbalance diagnosis, The system includes an execution unit that, when the determination unit makes a positive determination, fixes the opening of both the first and second wastegate valves to fully closed and performs the imbalance diagnosis, In the imbalance diagnosis, the variation in the air-fuel ratio between the first cylinders is diagnosed based on the magnitude of the difference between the upper peak value and the lower peak value of the time-series data of the air-fuel ratio detected by the first air-fuel ratio sensor, and the variation in the air-fuel ratio between the second cylinders is diagnosed based on the magnitude of the difference between the upper peak value and the lower peak value of the time-series data of the air-fuel ratio detected by the second air-fuel ratio sensor. The aforementioned preconditions include conditions that can be met in common for the first and second banks, and conditions that can be met for each of the first and second banks. The conditions that can be commonly met in the first and second banks include that the temperature of the coolant in the supercharged V-type engine is above a predetermined value, that the atmospheric pressure is above a predetermined value, and that the rotational speed and load of the supercharged V-type engine are within a predetermined range. The conditions that can be met for each of the first and second banks include: that the main feedback control of the air-fuel ratio is being performed; that rich control after fuel cut is not being performed; that the vapor concentration learning value per unit purge rate is equal to or greater than a predetermined value; and that the number of updates of the purge concentration learning value is equal to or greater than a predetermined value. The diagnostic device for a supercharged V-type engine comprises a determination unit which makes a negative determination if at least one of the conditions that can be commonly held in the first and second banks and the conditions that can be held individually for the first and second banks is not met, and makes an positive determination if all of the conditions that can be commonly held in the first and second banks and the conditions that can be held individually for the first and second banks are met.

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