Control method of internal combustion engine and control device

Abstract

To avoid discomfort caused by continuous driving of an internal combustion engine 2 at low vehicle speed with little background noise while enabling it to complete secondary diagnostic executed by active method early.SOLUTION: An internal combustion engine of a hybrid vehicle of which combustion operation is stopped during operation of the vehicle is provided with self diagnostic function. Stop of the internal combustion engine until diagnostic is completed is inhibited after setting fuel cut inhibition flag if vehicle speed is diagnostic permission vehicle speed VSPH or more (t1) when the secondary diagnostic being subject to condition that the internal combustion engine is in operation is required. The diagnostic is stopped and at the same time stop of the internal combustion engine is permitted after resetting the fuel cut inhibition flag if the vehicle speed is below diagnostic stop vehicle speed VSPL (t2).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to the control of an internal combustion engine with a self-diagnosis function, and in particular to the control of an internal combustion engine of a hybrid vehicle in which the combustion operation is stopped on demand while the vehicle is in operation. [Background technology]

[0002] Among the many diagnostics performed by the internal combustion engine's self-diagnostics function may be diagnostics that are performed while the internal combustion engine is operating.

[0003] Patent document 1 discloses that in a plug-in hybrid vehicle, when the internal combustion engine starts operating in accordance with engine operation start conditions such as vehicle required output while the vehicle is operating in a charge consumption mode in which battery power is actively consumed, the internal combustion engine continues to operate in order to complete a diagnosis even after the engine operation start condition is no longer satisfied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-140698 A Summary of the Invention [Problem to be solved by the invention]

[0005] If the self-diagnosis function as described above prevents the internal combustion engine from stopping its combustion operation, the internal combustion engine will continue to operate under conditions in which it is not necessary to do so, which can cause passengers to feel uncomfortable when the vehicle is traveling at low speeds or when the vehicle is stopped, where there is little background noise from sources other than the internal combustion engine. [Means for solving the problem]

[0006] The present invention relates to a method for controlling an internal combustion engine, which comprises the steps of: setting a fuel cut prohibition flag when one or more specific diagnoses that require the internal combustion engine to be in operation are started, thereby prohibiting the internal combustion engine from being stopped until the diagnosis is completed; If the vehicle speed falls below the diagnosis stop speed before the diagnosis is completed, the diagnosis is stopped and the fuel cut prohibition flag is reset to permit the internal combustion engine to be stopped. Effect of the Invention

[0007] According to this invention, if the vehicle speed is equal to or higher than the diagnosis stop speed, the internal combustion engine is prohibited from being stopped until the diagnosis is completed, increasing the probability of completing the diagnosis. If the vehicle speed falls below the diagnosis stop speed, the internal combustion engine is permitted to be stopped, improving the quietness of the vehicle and preventing the occupants from feeling uncomfortable due to the combustion operation of the internal combustion engine while the vehicle is stopped. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a series hybrid vehicle. [Diagram 2] 6 is a flowchart showing a flow of processes such as stopping combustion operation when a secondary diagnosis is requested. [Diagram 3] FIG. 4 is a functional block diagram of a main part of an engine controller related to a fuel cut prohibition flag. [Figure 4] 6 is a time chart showing an example of an operation when a secondary diagnosis is requested. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment in which the present invention is applied to an internal combustion engine for generating electricity in a series hybrid vehicle will be described. FIG. 1 shows a schematic configuration of a series hybrid vehicle. The series hybrid vehicle is configured to include a power generating motor generator 1 that mainly operates as a generator, an internal combustion engine 2 used as a power generating internal combustion engine that drives the power generating motor generator 1 in response to an electric power request, a traveling motor generator 4 that mainly operates as a motor to drive driving wheels 3, and a battery 5 that temporarily stores the generated electric power. The electric power obtained by the internal combustion engine 2 driving the power generating motor generator 1 is stored in the battery 5 via an inverter device (not shown). The traveling motor generator 4 is driven and controlled using the electric power of the battery 5. The electric power generated by the traveling motor generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown). In the illustrated example, the motor generator 1 and the internal combustion engine 2 are linked via a gear train, but they may be directly connected to each other.

[0010] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of a plurality of controllers connected to each other so as to be able to communicate with each other, such as a motor controller 7 for controlling the motor generators 1 and 4, an engine controller 8 for controlling the internal combustion engine 2, and a battery controller 9 for managing the battery 5. Information such as the accelerator pedal opening degree and the vehicle speed (not shown) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. When the required driving force of the vehicle is large, the internal combustion engine 2 similarly generates electricity and supplies the electricity to the traveling motor generator 4. The driving modes of such a series hybrid vehicle include an EV mode in which the vehicle runs on the power of the battery 5 without the combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity by the combustion operation of the internal combustion engine 2.

[0011] In other words, the internal combustion engine 2 is not constantly operated for combustion while the vehicle is in operation with the main switch of the vehicle turned on, but is automatically stopped and automatically restarted repeatedly in response to a request for power generation.

[0012] The internal combustion engine 2 of the embodiment is a spark ignition type internal combustion engine, a so-called gasoline engine, and is controlled by an engine controller 8. The engine controller 8 receives detection signals of the accelerator pedal opening and vehicle speed, as well as detection signals of a number of sensors that are equipped in a general internal combustion engine, such as a crank angle sensor for detecting the engine speed, an air-fuel ratio sensor provided in the exhaust passage, a coolant temperature sensor, an intake air temperature sensor, a knocking sensor, and the like. The engine controller 8 executes output control, air-fuel ratio control, ignition timing control, and the like of the internal combustion engine 2 based on these detection signals. In this embodiment, the air-fuel ratio sensor includes an upstream air-fuel ratio sensor (generally a wide-range air-fuel ratio sensor) located upstream of the catalyst in the exhaust passage, as well as a downstream air-fuel ratio sensor located downstream of the catalyst. The downstream air-fuel ratio sensor is, for example, an oxygen sensor (a so-called O2 sensor) that can only distinguish between rich and lean.

[0013] After the vehicle starts a trip, the engine controller 8 executes several fault diagnoses by its self-diagnosis function. The fault diagnoses include one or more specific fault diagnoses that are performed under the condition that the internal combustion engine 2 is in a combustion operation. One example is the fault diagnosis of the downstream air-fuel ratio sensor (rear O2 sensor). The fault diagnosis of the rear O2 sensor is performed in two stages, a primary diagnosis and a secondary diagnosis, in order to eliminate erroneous detections and improve diagnostic accuracy. The primary diagnosis is a so-called passive method, and for example, under air-fuel ratio control during normal operation, a voltage difference between the lean side voltage and the rich side voltage is obtained, and if this voltage difference is an abnormal value, it is diagnosed as abnormal. The secondary diagnosis is a so-called active method that is performed when an abnormality is diagnosed in the primary diagnosis, and for example, the air-fuel ratio is periodically changed from rich to lean, and the response of the rear O2 sensor to this periodic change is detected to diagnose whether it is abnormal. In this embodiment, the latter secondary diagnosis corresponds to the specific fault diagnosis.

[0014] Further, examples of fault diagnosis include diagnosis of a catalyst in an exhaust passage and diagnosis of an evaporated fuel processing system using a canister. These are similarly performed in two stages: a primary diagnosis in a passive manner and a secondary diagnosis in an active manner, with the secondary diagnosis corresponding to a specific fault diagnosis. For example, the primary diagnosis of a catalyst is performed by comparing the output of an upstream air-fuel ratio sensor upstream of the catalyst with the output of a downstream air-fuel ratio sensor downstream of the catalyst during normal operation in which air-fuel ratio control is performed, and when an abnormality is diagnosed in this primary diagnosis, a secondary diagnosis is performed to diagnose the oxygen storage capacity, which indicates deterioration of the catalyst, by actively reversing the air-fuel ratio to rich-lean. Furthermore, the primary diagnosis of a fault of an evaporated fuel processing system is performed by comparing the line pressure when the purge valve is open during normal operation with the line pressure when the purge valve is closed. When an abnormality is diagnosed in the primary diagnosis, the vent valve of the canister is temporarily closed with the purge valve open to a predetermined opening for diagnosis, and the change in line pressure is monitored, to perform a secondary diagnosis.

[0015] In this manner, in any of the above diagnoses, since the secondary diagnosis is performed by an active method in which some parameter is intentionally changed, it is desirable to complete the diagnosis in as short a time as possible.

[0016] For this reason, in this embodiment, when the secondary diagnosis using the above-mentioned active method is started, a fuel cut prohibition flag is set and stopping of the internal combustion engine 2 (stopping of combustion operation) is prohibited until the diagnosis is completed. On the other hand, in order to avoid an uncomfortable feeling caused by the internal combustion engine 2 continuing to be driven at low vehicle speeds with little background noise or while the vehicle is stopped, the diagnosis is started (permitted) when the vehicle speed is equal to or higher than the diagnosis permission vehicle speed VSPH, and if the vehicle speed falls below the diagnosis stop vehicle speed VSPL before the diagnosis is completed, the diagnosis is stopped and the fuel cut prohibition flag is reset to permit stopping of the internal combustion engine 2. The diagnosis stop vehicle speed VSPL is a vehicle speed lower than the diagnosis permission vehicle speed VSPH, and a relatively large hysteresis is provided between the two.

[0017] FIG. 2 is a flowchart showing the flow of processing such as stopping combustion operation when a secondary diagnosis of the rear O2 sensor is requested as an example. The routine shown in this flowchart is repeatedly executed when an abnormality is diagnosed in the primary diagnosis and a secondary diagnosis is requested. In the first step 1, it is determined whether the vehicle speed condition for the secondary diagnosis of the rear O2 sensor is established. The vehicle speed condition is that the vehicle speed VSP is equal to or higher than the diagnosis stop vehicle speed VSPL after being equal to or higher than the diagnosis permission vehicle speed VSPH. If the answer is NO here, the process proceeds to step 2 and the fuel cut prohibition flag is reset.

[0018] If the vehicle speed condition in step 1 is met, the process proceeds to step 3, where the fuel cut prohibition flag is set (or kept set). This prohibits the internal combustion engine 2 from being stopped. In the next step 4, it is determined whether or not a diagnosis permission condition other than the vehicle speed (e.g., cooling water temperature) is met. If the answer is NO here, the process proceeds to step 5, where no diagnosis is performed while stopping of the internal combustion engine 2 is prohibited. If the answer is YES in step 4, the process proceeds to step 6, where a diagnosis (secondary diagnosis) is performed while stopping of the internal combustion engine 2 is prohibited.

[0019] After the diagnosis starts, if the vehicle speed condition in step 1 is no longer satisfied, the fuel cut prohibition flag is reset in step 2 and the diagnosis is interrupted.

[0020] If the diagnosis is resumed in step 6 after the diagnosis is interrupted, the secondary diagnosis of the rear O2 sensor will discard all previous diagnostic data and start a new secondary diagnosis from the initial stage. The same applies to the secondary diagnosis of the fuel vapor treatment system. The secondary diagnosis of the catalyst will resume from the stage before the diagnosis was interrupted.

[0021] 3 is a functional block diagram of the main parts of the engine controller 8 related to the fuel cut prohibition flag. A request for prohibiting fuel cut during the above-mentioned secondary diagnosis (fuel cut prohibition flag) is output from an AND circuit 11. One of the inputs to the AND circuit 11 is the output of a flag set circuit 12. An input A indicating that the air-fuel ratio has experienced a rich-lean reversal is input to the flag set circuit 12 as a Set signal, and an input B indicating that the secondary diagnosis has ended is input to the flag set circuit 12 as a Clear signal. Therefore, the flag set circuit 12 outputs 1 from the end of the primary diagnosis until the end of the secondary diagnosis.

[0022] Another input to the AND circuit 11 is the output of the OR circuit 13. The OR circuit 13 receives an input C indicating that an external diagnostic terminal is connected to the engine controller 8 and various tests are being performed, an input D indicating that the above-mentioned vehicle speed condition (the vehicle speed is equal to or higher than the diagnosis stop vehicle speed VSPL after reaching or exceeding the diagnosis permission vehicle speed VSPH) is satisfied, and an input E indicating whether or not to use the vehicle speed condition.

[0023] Therefore, if the vehicle speed condition is satisfied between the end of the primary diagnosis and the end of the secondary diagnosis, the AND circuit 11 outputs a fuel cut prohibition flag as 1. If the vehicle speed condition is not satisfied, the fuel cut prohibition flag becomes 0.

[0024] The above-mentioned AND circuit 11 and OR circuit 13 constitute a fuel cut prohibition section and a fuel cut prohibition release section.

[0025] Next, FIG. 4 is a time chart showing an example of an operation when a secondary diagnosis (for example, a secondary diagnosis of a rear O2 sensor) is requested. Here, the primary diagnosis has already been completed. From the top of the figure, (a) vehicle speed VSP (also showing diagnosis permission vehicle speed VSPH and diagnosis stop vehicle speed VSPL), (b) engine speed Ne, (c) fuel cut prohibition flag, (d) secondary diagnosis permission flag, (e) vehicle speed condition flag, and (f) secondary diagnosis end flag are shown. The (e) vehicle speed condition flag is set to 1 when the above-mentioned vehicle speed condition (the vehicle speed is equal to or higher than diagnosis stop vehicle speed VSPL after becoming equal to or higher than diagnosis permission vehicle speed VSPH) is satisfied. The (d) secondary diagnosis permission flag is set to 1 when other diagnosis permission conditions are satisfied in addition to the vehicle speed condition, and the secondary diagnosis permission flag being 1 indicates that the secondary diagnosis is being performed. The (f) secondary diagnosis end flag indicates that the secondary diagnosis has been completed. Also, the period during which the (b) engine speed Ne is 0 indicates that the internal combustion engine 2 is stopped.

[0026] In the illustrated example, at time t1, the vehicle speed VSP becomes equal to or higher than the diagnosis permission vehicle speed VSPH, and the vehicle speed condition flag becomes 1. Accordingly, the fuel cut prohibition flag becomes 1, and the internal combustion engine 2, which was in a stopped state, is started for the secondary diagnosis. This enables the secondary diagnosis, but in the illustrated example, the secondary diagnosis permission flag becomes 1 later than time t1 due to restrictions of other diagnosis permission conditions, and the secondary diagnosis is started at this point. Thereafter, at time t2 before the secondary diagnosis is completed, the vehicle speed VSP falls below the diagnosis stop vehicle speed VSPL, and the vehicle speed condition flag becomes 0. Therefore, the fuel cut prohibition flag becomes 0, the internal combustion engine 2 is stopped, and the secondary diagnosis permission flag becomes 0. As a result, the secondary diagnosis is interrupted.

[0027] After that, at time t3, the vehicle speed VSP again becomes equal to or greater than the diagnosis permission vehicle speed VSPH, and the vehicle speed condition flag becomes 1. Accordingly, the fuel cut prohibition flag becomes 1, and the internal combustion engine 2, which was stopped, is started for the secondary diagnosis. This enables the secondary diagnosis, but in the illustrated example, the secondary diagnosis permission flag becomes 1 later than time t3 due to restrictions of other diagnosis permission conditions, and the secondary diagnosis is resumed at this point. After that, at time t4, the secondary diagnosis is completed, and the secondary diagnosis end flag becomes 1. Accordingly, the fuel cut prohibition flag is reset to 0. Therefore, thereafter, the internal combustion engine 2 is repeatedly stopped and restarted in accordance with requests from the vehicle side.

[0028] Note that in a preferred embodiment, secondary diagnostics are only permitted once per trip.

[0029] As described above, according to the embodiment, when the secondary diagnosis using the active method is started, the fuel cut prohibition flag is set and the internal combustion engine 2 is prohibited from being stopped (stopping combustion operation) until the diagnosis is completed, so that the probability of completing the diagnosis quickly increases. On the other hand, when the vehicle speed is low and background noise is low, stopping of the internal combustion engine 2 is permitted in preference to continuing the diagnosis, so that the discomfort caused by the internal combustion engine 2 continuing to be driven can be avoided.

[0030] The above describes the secondary diagnosis of the rear O2 sensor, but the same applies to the secondary diagnosis of the fuel vapor processing system and the secondary diagnosis of the catalyst. In addition, the present invention is not limited to these diagnoses, and can be widely applied to other diagnoses performed by the active method. The diagnosis permission vehicle speed VSPH and the diagnosis stop vehicle speed VSPL may be the same vehicle speed for each of the multiple types of diagnoses, or may be different vehicle speeds that are more optimal for each type of diagnosis.

[0031] In addition, in the above embodiment, an example of application to a series hybrid vehicle has been described, but the present invention is not limited to the power generating internal combustion engine of a series hybrid vehicle, and can also be applied to the internal combustion engine of other types of hybrid vehicles that can run on the motor while the internal combustion engine is stopped. [Explanation of symbols]

[0032] 1,4...Motor generator 2. Internal combustion engine 5. Battery 6…Controller 8. Engine controller

Claims

1. An internal combustion engine of a hybrid vehicle in which combustion operation is stopped upon request while the vehicle is in operation, the internal combustion engine having a self-diagnosis function, setting a fuel cut prohibition flag when one or more specific diagnoses that are based on the condition that the internal combustion engine is operating are started, thereby prohibiting the internal combustion engine from being stopped until the diagnosis is completed; If the vehicle speed falls below the diagnosis stop speed before the diagnosis is completed, the diagnosis is stopped and the fuel cut prohibition flag is reset to permit the internal combustion engine to be stopped. A method for controlling an internal combustion engine.

2. After the diagnosis is stopped, when the vehicle speed becomes equal to or exceeds the diagnosis permission speed, the diagnosis is resumed from the stage before the diagnosis was stopped, and a fuel cut prohibition flag is set.

2. A method for controlling an internal combustion engine according to claim 1.

3. After the diagnosis is stopped, when the vehicle speed becomes equal to or exceeds the diagnosis permission speed, the diagnosis is restarted from the initial stage and a fuel cut prohibition flag is set.

2. A method for controlling an internal combustion engine according to claim 1.

4. The above diagnosis stop vehicle speed is set according to the type of diagnosis.

2. A method for controlling an internal combustion engine according to claim 1.

5. A control device for an internal combustion engine of a hybrid vehicle in which a combustion operation is stopped upon request while the vehicle is being driven, A self-diagnosis unit that diagnoses each part of the internal combustion engine; a fuel cut prohibition unit that sets a fuel cut prohibition flag when one or more specific diagnoses that are performed while the internal combustion engine is in operation are started, and prohibits the internal combustion engine from being stopped until the diagnosis is completed; a fuel cut prohibition release unit that, when the vehicle speed falls below a diagnosis stop speed before the diagnosis is completed, stops the diagnosis and resets the fuel cut prohibition flag to permit the internal combustion engine to be stopped; A control device for an internal combustion engine comprising:

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