Engine control unit

Abstract

The objective is to provide an engine control device that suppresses the deterioration of exhaust emissions. [Solution] An engine control device comprising: a learning unit that learns the steady-state deviation of the air-fuel ratio deviation in air-fuel ratio feedback control based on the air-fuel ratio deviation of the engine's target air-fuel ratio as an air-fuel ratio learning value; an acquisition unit that acquires the amount of dilution fuel, which is the amount of fuel used to dilute the engine oil; and a determination unit that determines whether the amount of dilution fuel before the engine oil was changed is below a threshold when the engine oil is changed, wherein the learning unit resets the air-fuel ratio learning value to an initial value when the determination unit makes a positive determination, and retains the air-fuel ratio learning value when the determination unit makes a negative determination, and the threshold is set to an upper limit of the amount of dilution fuel such that retaining the air-fuel ratio learning value rather than resetting the air-fuel ratio learning value to an initial value shortens the time required for the air-fuel ratio learning value to converge after the engine oil is changed.

Description

Technical Field

[0001] The present invention relates to an engine control device.

Background Art

[0002] With the continued use of engine oil, the amount of diluted fuel, which is the amount of fuel diluting the engine oil, gradually increases. The fuel vaporized from the engine oil is burned in the combustion chamber of the engine as blow-by gas. Therefore, the fuel dilution amount is reflected in the air-fuel ratio learning value learned by the air-fuel ratio feedback control. Therefore, when the engine oil is replaced, the fuel dilution amount becomes zero, and the air-fuel ratio learning value is reset to the initial value (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the air-fuel ratio learning value is reset to the initial value, the learning of the air-fuel ratio is performed again from the initial value. For example, even if the amount of diluted fuel before the replacement of the engine oil is small, if the above reset is performed, it takes time for the air-fuel ratio learning value to converge in the subsequent learning, and there is a risk that the exhaust emission deteriorates during that time.

[0005] Therefore, an object of the present invention is to provide an engine control device that suppresses deterioration of exhaust emissions.

Means for Solving the Problems

[0006] The above objective can be achieved by an engine control device comprising: a learning unit that learns the steady-state deviation of the air-fuel ratio deviation in air-fuel ratio feedback control based on the air-fuel ratio deviation of the engine's target air-fuel ratio as an air-fuel ratio learning value; an acquisition unit that acquires the amount of dilution fuel, which is the amount of fuel used to dilute the engine oil; and a determination unit that determines whether the amount of dilution fuel before the engine oil was changed is below a threshold when the engine oil is changed, wherein the learning unit resets the air-fuel ratio learning value to an initial value if the determination unit makes a positive determination, and retains the air-fuel ratio learning value if the determination unit makes a negative determination, and the threshold is set to an upper limit of the amount of dilution fuel such that retaining the air-fuel ratio learning value shortens the time required for the air-fuel ratio learning value to converge after the engine oil is changed compared to resetting the air-fuel ratio learning value to an initial value.

[0007] The air-fuel ratio learning value includes a first learning value learned in the first load region of the engine and a second learning value learned in a second load region where the engine load is different from that of the first load region, wherein the first learning value is more significantly affected by the amount of diluted fuel than the second learning value, and the learning unit may reset the first learning value to its initial value and retain the second learning value if the determination unit makes a positive determination, and retain the first and second learning values ​​if the determination unit makes a negative determination. [Effects of the Invention]

[0008] According to the present invention, an engine control device that suppresses deterioration of exhaust emissions can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of a vehicle equipped with an engine. [Figure 2] This flowchart illustrates the learning control performed by the ECU. [Modes for carrying out the invention]

[0010] [Vehicle Outline] Figure 1 is a schematic diagram of a vehicle 1 equipped with an engine 10. Vehicle 1 comprises an engine 10, an ECU (Electronic Control Unit) 30, and drive wheels 40. The engine 10 is the power source for driving vehicle 1 and is a gasoline engine, but may also be a diesel engine. Vehicle 1 may also be a hybrid vehicle equipped with an electric motor in addition to the engine 10 as a power source for driving. The engine 10 is, for example, an inline cylinder engine with four cylinders, but is not limited to this.

[0011] The engine 10 has a cylinder head 10a, a cylinder block 10b, and a crankcase 10c. Air is drawn into the combustion chamber 11 formed in the cylinder head 10a through an intake passage 12, and fuel is supplied from an in-cylinder injector 13. The in-cylinder injector 13 provided in the cylinder head 10a is a fuel injector that directly injects fuel into the combustion chamber 11. A port injector that injects fuel into the intake port may be provided instead of or in addition to the in-cylinder injector 13. When the mixture of intake air and injected fuel is ignited by the spark plug 14, the mixture burns, causing the piston 15 to reciprocate within the cylinder block 10b, and the crankshaft 16 of the engine 10 to rotate. The rotational power of the crankshaft 16 is transmitted to the drive wheels 40 via a transmission (not shown). The mixture after combustion is sent out as exhaust from the combustion chamber 11 of the engine 10 to the exhaust passage 17. The exhaust passage 17 is provided with a catalyst 17a for purifying the exhaust gas.

[0012] Engine oil is stored in the crankcase 10c and transported to each lubrication part by an oil pump (not shown). The engine oil used for lubrication is then recovered back into the crankcase 10c. One end of the blow-by gas passage 10d is connected to the crankcase 10c, and the other end of the blow-by gas passage 10d is connected to the intake passage 12 downstream of the throttle valve 19. A PCV (Positive Crankcase Ventilation) valve 18 is provided in the blow-by gas passage 10d. The PCV valve 18 opens when the intake negative pressure downstream of the throttle valve 19 in the intake passage 12 exceeds a specified value. As a result, the blow-by gas generated in the crankcase 10c is released into the combustion chamber 11 via the blow-by gas passage 10d and the intake passage 12 for combustion.

[0013] The ECU 50 performs various controls for the operation of vehicle 1. This ECU 50 includes a central processing unit that performs various calculations related to the various controls, a non-volatile memory that stores programs and data necessary for those calculations, a volatile memory that temporarily stores the calculation results of the central processing unit, and input and output ports for inputting and outputting signals to and from the outside.

[0014] Various sensors are connected to the ECU50. These sensors include a throttle position sensor 32, an air flow meter 34, a crank angle sensor 35, and an air-fuel ratio sensor 36. The throttle position sensor 32 detects the opening of the throttle valve 19. The air flow meter 34 detects the amount of intake air passing through the intake passage 12. The crank angle sensor 35 detects the rotational speed of the crankshaft 16, i.e., the rotational speed of the engine 10. The air-fuel ratio sensor 36 detects the air-fuel ratio of the exhaust before it flows into the catalyst 17a.

[0015] The ECU 50 understands the operating conditions of the engine 10, such as rotational speed and load, based on output signals from various sensors. The ECU 50 controls the opening degree of the throttle valve 19, the amount of fuel injected from the in-cylinder injection valve 13, and the ignition timing of the fuel-air mixture by the spark plug 14, according to the understood operating conditions. The ECU 50 functionally implements a learning unit, an acquisition unit, and a judgment unit, as will be described in more detail later. The ECU 50 is an example of an engine control device.

[0016] A portion of the fuel injected from the in-cylinder injection valve 13 adheres to the inner wall surface of the cylinder block 10b, drips into the crankcase 10c, and mixes with the engine oil. In this way, the engine oil is diluted by the fuel. The amount of fuel used to dilute the engine oil is called the dilution fuel amount. Consequently, the blow-by gas released into the combustion chamber 11 via the blow-by gas passage 10d and the intake passage 12 also contains this fuel. The greater the dilution fuel amount, the greater the amount of fuel contained in the blow-by gas. Since the blow-by gas is released into the combustion chamber 11, a large dilution fuel amount tends to cause the air-fuel ratio of the engine 10 to shift towards the rich side relative to the target value.

[0017] The ECU 50 performs learning control, which learns the steady-state deviation of the air-fuel ratio deviation in the air-fuel ratio feedback control, based on the air-fuel ratio deviation of the actual air-fuel ratio relative to the target air-fuel ratio of the engine 10, as the air-fuel ratio learning value. The target air-fuel ratio is determined according to the operating state of the engine 10. The actual air-fuel ratio is the air-fuel ratio detected by the air-fuel ratio sensor 36. In the feedback control, the fuel injection amount of the engine 10 is controlled so that the air-fuel ratio deviation is eliminated, based on the air-fuel ratio deviation of the actual air-fuel ratio relative to the target air-fuel ratio. In addition, a steady-state deviation that occurs steadily is calculated from the trend of the air-fuel ratio deviation, and this steady-state deviation is learned as the air-fuel ratio learning value. The above learning control is an example of the control performed by the learning unit. As described above, the amount of diluted fuel is reflected in the air-fuel ratio of the engine 10 and is also reflected in the air-fuel ratio learning value. The learning control will be explained in detail below.

[0018] [Learning control] Figure 2 is a flowchart illustrating the learning control performed by the ECU 50. This control is repeatedly performed while the ignition is on. The ECU 50 acquires the amount of diluted fuel (step S1). The amount of diluted fuel is calculated based on, for example, the coolant temperature at the start of the engine 10 and the cumulative amount of intake air until the coolant temperature reaches 40°C after starting. The amount of diluted fuel increases, for example, if the engine 10 is frequently stopped before warm-up is complete. The amount of diluted fuel may be an estimated value, a calculated value, or a detected value. Furthermore, the calculation method, estimation method, and detection method may be any method, and may be a known method. Step S1 is an example of the processing performed by the acquisition unit.

[0019] Next, the ECU50 determines whether or not the engine oil has been changed (step S2). For example, if the dealer has switched on the oil change, step S2 will be determined to be Yes. Also, if the user has made an input to the oil mileage system, step S2 will be determined to be Yes. The oil mileage system is a system that notifies the user to change the oil when the mileage since the last oil change reaches a predetermined distance, and the user inputs that the oil has been changed in response to this notification. In addition, the determination of whether or not the engine oil has been changed may be achieved by other known methods. For example, the determination of whether or not the engine oil has been changed may be made when the opening of the engine oil drain bolt or an increase in the amount of engine oil is detected. If step S2 is No, this control terminates. Step S2 is an example of the processing performed by the determination unit.

[0020] If the answer in step S2 is Yes, it is determined whether the amount of diluted fuel immediately before the engine oil is changed is less than or equal to the threshold value (step S3). If the answer in step S3 is No, the ECU 50 resets the air-fuel ratio learning value to the initial value (step S4). Therefore, after the air-fuel ratio learning value is reset, the learning of the air-fuel ratio is executed again from the initial value. If the answer in step S3 is Yes, the ECU 50 holds the air-fuel ratio learning value (step S5). In this case, the air-fuel ratio learning value before the engine oil is changed is held and the learning of the air-fuel ratio is continued, and the above-described feedback control is executed based on this air-fuel ratio learning value. Incidentally, if the answer in step S2 is Yes, the amount of diluted fuel is reset to zero. Step S3 is an example of the process executed by the determination unit. Steps S4 and S5 are examples of the processes executed by the learning unit.

[0021] When the answer in step S3 is Yes, it indicates that the difference in the amount of diluted fuel before and after the engine oil is changed is small. Since the engine oil after the change is new, the amount of diluted fuel after the change is zero. That is, when the answer in step S3 is Yes, it is considered that the difference in the amount of diluted fuel before and after the engine oil is changed is small, and the difference in the convergence values of the air-fuel ratio learning values before and after the change is also small. When the difference in the convergence values of the air-fuel ratio learning values before and after the change is small in this way, it is considered that the time required for the air-fuel ratio learning value to converge after the change is shorter by holding the air-fuel ratio learning value and continuing the air-fuel ratio learning than by resetting the air-fuel ratio learning value to the initial value.

[0022] In the case of "No" in step S3, it is considered that the difference in diluted fuel amount before and after the engine oil replacement is large, and the difference in the convergence values of the air-fuel ratio learning values before and after the replacement is also large. When the difference in the convergence values of the air-fuel ratio learning values before and after the replacement is large like this, rather than holding the air-fuel ratio learning value, it is considered that resetting the air-fuel ratio learning value to the initial value and continuing the air-fuel ratio learning will take less time until the air-fuel ratio learning value converges after the replacement. Based on the above, the threshold value in step S3 is set to the upper limit value of the diluted fuel amount such that holding the air-fuel ratio learning value takes less time until the air-fuel ratio learning value converges after the engine oil replacement than resetting the air-fuel ratio learning value to the initial value. The threshold value is determined in advance by experiments, analysis, etc.

[0023] As described above, when it is "No" in step S3, the air-fuel ratio learning value is reset to the initial value, and when it is "Yes" in step S3, the air-fuel ratio learning value is held. As a result, the time until the air-fuel ratio learning value converges after the engine oil replacement is shortened, and the deterioration of exhaust emissions is suppressed. Also, one of the conditions for purging the evaporated fuel adsorbed on a charcoal canister (not shown) into the intake passage 12 is that the air-fuel ratio learning value has converged. Since the time until the air-fuel ratio learning value converges after the engine oil replacement is shortened, the purge of the evaporated fuel can also be executed earlier.

[0024] Here, the learning of the air-fuel ratio is performed for each load region of the engine 10. That is, the air-fuel ratio learning value is calculated for each load region of the engine 10. For example, the air-fuel ratio learning value in the low load region is different from the air-fuel ratio learning value in the high load region. The air-fuel ratio learning value reset to the initial value in step S4 is the air-fuel ratio learning value in the load region where the influence of the diluted fuel amount on the air-fuel ratio learning value is large. The load region where the influence of the diluted fuel amount on the air-fuel ratio learning value is large is the load region where the air-fuel ratio learning value increases significantly in response to an increase or decrease in the diluted fuel amount. Generally, the influence of the diluted fuel amount on the air-fuel ratio learning value is larger in the low load region than in the high load region. This is because the intake air amount and fuel injection amount are relatively small in the low load region, and the influence of the diluted fuel amount on the air-fuel ratio is large.

[0025] Therefore, in step S4, for example, the air-fuel ratio learning value in the low-load region is reset to its initial value, while the air-fuel ratio learning value in the high-load region is retained. In this way, the air-fuel ratio learning value in load regions where the influence of the dilution fuel amount on the air-fuel ratio learning value is small is retained. This suppresses the deterioration of exhaust emissions during the period from when such air-fuel ratio learning values ​​are reset until they converge again. In step S5, both the air-fuel ratio learning values ​​in the low-load region and the high-load region are retained. The low-load region and the high-load region are examples of the first and second load regions, respectively. The air-fuel ratio learning value in the low-load region is an example of the first learning value. The air-fuel ratio learning value in the high-load region is an example of the second learning value.

[0026] Furthermore, the load range in which the amount of diluted fuel has a significant impact on the air-fuel ratio learning value differs from engine to engine. Therefore, such a load range is not necessarily limited to the low-load range. Also, air-fuel ratio learning may be performed for three or more load ranges. In this case, for example, the air-fuel ratio learning value in the load range in which the amount of diluted fuel has the greatest impact on the air-fuel ratio learning value may be reset to its initial value. Alternatively, the air-fuel ratio learning value in the load range in which the amount of diluted fuel has the greatest impact on the air-fuel ratio learning value, and the air-fuel ratio learning value in the load range with the next greatest impact, may be reset to their initial values.

[0027] 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]

[0028] 1 vehicle 10 Engines 50 ECU (Engine Control Unit, Learning Unit, Acquisition Unit, Judgment Unit)

Claims

1. A learning unit learns the steady-state deviation of the air-fuel ratio deviation in air-fuel ratio feedback control based on the air-fuel ratio deviation relative to the engine's target air-fuel ratio as an air-fuel ratio learning value, An acquisition unit that acquires the amount of dilution fuel, which is the amount of fuel used to dilute the engine oil, The system includes a determination unit that determines whether the amount of diluted fuel before the engine oil was changed is below a threshold when the engine oil is changed, The learning unit resets the air-fuel ratio learning value to its initial value if the determination unit makes a positive determination, and retains the air-fuel ratio learning value if the determination unit makes a negative determination. An engine control device wherein the threshold is set to the upper limit of the amount of diluted fuel such that retaining the air-fuel ratio learning value rather than resetting the air-fuel ratio learning value to the initial value shortens the time required for the air-fuel ratio learning value to converge after the engine oil is changed.

2. The air-fuel ratio learning value includes a first learning value learned in the first load region of the engine, and a second learning value learned in a second load region where the engine load is different from that of the first load region. The first learned value is more influenced by the amount of diluted fuel than the second learned value. The engine control device according to claim 1, wherein the learning unit resets the first learning value to its initial value and holds the second learning value when the determination unit makes an affirmative determination, and holds the first and second learning values ​​when the determination unit makes a negative determination.

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