Control method and control device for an internal combustion engine

Abstract

The internal combustion engine (1) includes: an exhaust gas recirculation device having an exhaust gas recirculation control valve (9); a crankshaft angle sensor (11) for detecting the graphical mean effective pressure variation rate (cPi), which is an indicator of the combustion stability of the internal combustion engine (1); and a controller (10) for correcting the EGR rate of the exhaust gas recirculation device based on the combustion stability. If the graphical mean effective pressure variation rate (cPi) is less than a threshold for a specified number of cycles, the controller (10) increases the EGR rate by a specified amount. If the graphical mean effective pressure variation rate (cPi) is greater than or equal to the threshold, the EGR rate is immediately decreased.

Description

Technical Field

[0001] This invention relates to a control method and control device for an internal combustion engine that corrects the exhaust gas recirculation rate based on combustion stability. Background Technology

[0002] Regarding exhaust recirculation devices that redirect a portion of the exhaust gas discharged from the exhaust system of an internal combustion engine back to the intake system, increasing the exhaust recirculation rate is beneficial for improving fuel efficiency, while conversely, combustion stability decreases. In other words, the exhaust recirculation rate is limited by combustion stability.

[0003] Patent document 1 discloses a technique that detects torque variation related to fluctuations in the illustrated average effective pressure, compares the torque variation with a threshold at predetermined intervals, specifically every 16 intervals, and increases the exhaust return rate by a predetermined amount if the torque variation is less than or equal to the threshold, and decreases the exhaust return rate by a predetermined amount if the torque variation exceeds the threshold.

[0004] However, this current control method is not a preferred approach because the unstable combustion state persists for a specified number of cycles until the combustion is unstable.

[0005] Patent Document 1: Japanese Patent Application Publication No. 60-104754 Summary of the Invention

[0006] In this invention, an index representing the combustion stability of an internal combustion engine is determined, and the exhaust gas recirculation rate is corrected based on this combustion stability. When the combustion stability meets a specified level, the exhaust gas recirculation rate is increased by a specified amount every specified number of cycles. When the combustion stability is detected to be worse than the specified level, the exhaust gas recirculation rate is immediately decreased.

[0007] In this way, when increasing the exhaust recirculation rate, the increase is performed by a specified amount every specified number of cycles. This avoids the delayed and rapid deterioration of combustion that occurs after increasing the exhaust recirculation rate and allows the exhaust recirculation rate to be increased to its limit. As a result, fuel consumption can be improved.

[0008] On the other hand, when combustion deterioration is detected, the exhaust recirculation rate is immediately corrected to a lower value without waiting for the specified number of cycles to pass, thus minimizing the continued deterioration of combustion. Attached Figure Description

[0009] Figure 1 This is a structural illustration of an internal combustion engine applying an embodiment of the present invention.

[0010] Figure 2 This is a flowchart illustrating the correction control of the exhaust recirculation rate in one embodiment.

[0011] Figure 3 This is a timing diagram illustrating the actions of one embodiment. Detailed Implementation

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0013] Figure 1 This is a structural illustration of an internal combustion engine 1 for a vehicle, according to an embodiment of the present invention. The internal combustion engine 1 is, for example, a spark-ignition internal combustion engine that uses gasoline as fuel, and includes a turbocharger 2 as a supercharger. Specifically, a turbine 2A of the turbocharger 2 is installed in the exhaust passage 3 of the internal combustion engine 1, and a compressor 2B, driven by the turbine 2A, is installed in the intake passage 4 of the internal combustion engine 1 on the same shaft. The turbine 2A is located upstream of the catalytic converter 5 in the exhaust passage 3. Furthermore, an electronically controlled throttle valve 6 is located downstream of the compressor 2B in the intake passage 4. An air filter (not shown) is installed at the inlet side of the intake passage 4, and an air flow meter 7, which detects the amount of intake air, is installed downstream of the air filter.

[0014] Furthermore, as an exhaust recirculation device that recirculates a portion of the exhaust gas back to the intake system, it includes an exhaust recirculation path 8 from the exhaust passage 3 to the intake passage 4, and an exhaust recirculation control valve 9 disposed in the exhaust recirculation path 8. In one embodiment, the exhaust recirculation path 8 branches off from the exhaust passage 3 downstream of the catalytic converter 5. Additionally, the front end of the exhaust recirculation path 8 merges with the intake passage 4 at a position further downstream of the air flow meter 7 and further upstream of the compressor 2B. That is, the exhaust recirculation device illustrated in the figure is configured as a so-called low-pressure EGR form, where exhaust gas recirculates from the downstream side of the turbine 2A to the upstream side of the compressor 2B, where the pressure is lower, even in the turbocharged region of the internal combustion engine 1. An EGR gas cooler 12 for cooling the exhaust gas is disposed upstream of the exhaust recirculation control valve 9 in the exhaust recirculation path 8.

[0015] The opening degree of the exhaust recirculation control valve 9 is controlled by the engine controller 10. Furthermore, the exhaust recirculation control valve 9 can be of any form. The opening degree of the exhaust recirculation control valve 9 is controlled based on the intake air volume detected by the airflow meter 7, etc., to achieve the target EGR rate.

[0016] Various sensors typically required for the control of the internal combustion engine 2 are connected to the engine controller 10. Additionally, signals are transmitted and received between the engine controller 10 and other controllers (not shown) within the vehicle. Based on the aforementioned input signals, the engine controller 10 performs controls such as throttle valve 6 opening, fuel injection quantity and timing based on a fuel injection valve (not shown), ignition timing based on spark plugs (not shown), and exhaust recirculation control via exhaust recirculation control valve 9.

[0017] Here, the internal combustion engine 1 illustrated in the figure has a crankshaft angle sensor 11 that outputs a pulse signal for each unit crankshaft rotation angle as the crankshaft rotates. The engine controller 10 calculates the illustrated average effective pressure variation rate cPi as an indicator of the combustion stability of the internal combustion engine 1 based on the angular velocity change obtained by processing the output signal of the crankshaft angle sensor 11. Furthermore, as described later, the target EGR rate is corrected based on the illustrated average effective pressure variation rate cPi. In addition, the illustrated average effective pressure variation rate cPi is an indicator known from Japanese Patent Application Publication No. Hei 9-14028, Japanese Patent Application Publication No. 2014-177911, etc., and a larger value indicates more unstable combustion. The illustrated average effective pressure variation rate cPi is calculated for each period as a moving average (or weighted average) of data using an appropriate number of periods (e.g., 100 periods). Furthermore, the method of using an in-cylinder pressure sensor is also known as a method for calculating combustion stability. In this invention, an indicator of combustion stability can be obtained using an in-cylinder pressure sensor.

[0018] In one embodiment, the internal combustion engine 1 is used in a series hybrid vehicle. Unless otherwise illustrated, the series hybrid vehicle is primarily composed of the following components: a generator-generator that primarily functions as a generator; the internal combustion engine 1 that drives the generator-generator upon power demand; a driving generator-generator that primarily functions as a motor to drive the drive wheels; a battery that temporarily stores the generated electricity; and an inverter that performs power conversion between the battery and each generator-generator. The electricity obtained by the internal combustion engine 1 driving the generator-generator is stored in the battery via the inverter. The battery power is used to drive and control the driving generator-generator via the inverter. The electricity generated by the driving generator during regeneration is also stored in the battery via the inverter.

[0019] In this series hybrid vehicle, the internal combustion engine 1, which drives an electric generator for power generation, operates intermittently based on power requests, including the battery's state of charge (SOC). That is, if the engine controller 10 receives a power request from the vehicle-side controller based on the vehicle's accelerator pedal opening, vehicle speed, and SOC, it starts the internal combustion engine 1 to generate electricity. If the SOC reaches a predetermined level, the internal combustion engine 1 stops. Therefore, the internal combustion engine 1 operates in a manner of repeated starting and stopping during vehicle operation. The load and rotational speed of the internal combustion engine 1 are typically controlled to operate within a specific operating range near the optimal fuel consumption point. In other words, compared to the case where the vehicle is mechanically driven by the output of the internal combustion engine, the frequency of change in the operating point (rotational speed and load) is relatively small in the internal combustion engine 1 used in a series hybrid vehicle.

[0020] Furthermore, this invention is not limited to internal combustion engines used in series hybrid vehicles, but can be widely applied to internal combustion engines that drive vehicles mechanically.

[0021] Figure 2 This is a flowchart illustrating the processing flow for exhaust gas recirculation rate control in one embodiment. In the engine controller 10, the process shown in this flowchart is repeatedly executed during each combustion cycle of the internal combustion engine 1. In other words, assuming the internal combustion engine 1 is a 3-cylinder internal combustion engine, the process is executed every 240°CA. Figure 2 The process.

[0022] In the initial step 1, it is determined whether the changes in the rotational speed and load of the internal combustion engine 1 are less than a threshold. In other words, it is determined whether the operating point of the internal combustion engine 1 has changed or whether it is operating stably. If the operating point has changed, proceed to step 2, and reset the target EGR rate reduction empirical flag to zero (set to 0). As will be described later, the target EGR rate reduction empirical flag is a flag indicating whether a reduction correction based on the deterioration of combustion stability has occurred for the target EGR rate, and it is 0 immediately after the operating point changes.

[0023] If the result in step 1 is YES, proceed to step 3 to determine whether the change in the target EGR rate is less than the threshold. That is, determine whether a change in the target EGR rate greater than the threshold has just occurred. The change in the target EGR rate here includes both increases and decreases. If the result in step 3 is NO, meaning a change in the target EGR rate has occurred, the process ends directly. Furthermore, step 3 is used to exclude the transitional state immediately following a change in the target EGR rate from the combustion stability assessment. Therefore, as shown in the timing diagram described later, after a stepwise change in the target EGR rate, a NO result is determined within a short period (an appropriate number of cycles or time).

[0024] If the result in step 3 is YES, proceed to step 4 to read the value of the graphical average effective pressure variation rate cPi, which represents the combustion stability, and the count value n, which represents the number of cycles. The graphical average effective pressure variation rate cPi is calculated as a moving average for each cycle through different processes.

[0025] Next, in step 5, the average effective pressure variation rate (cPi) shown in the diagram is compared with a specified threshold to determine if it is less than the threshold. If the average effective pressure variation rate (cPi) shown in the diagram is less than the threshold, it indicates that the combustion stability meets the specified level. In this case, proceed to step 6 to determine if the target EGR rate reduction empirical indicator is 1. If the target EGR rate reduction empirical indicator is 1, the process ends.

[0026] The empirical indicator for the reduction in the target EGR rate is 0 immediately after the change in the operating point. In this case, proceed from step 6 to step 7 to determine whether the count value n, representing the number of cycles, has reached the specified number of cycles (e.g., 100 cycles). If it is NO, proceed to step 8, increment the count value n, and end the process. Alternatively, if the count value n has reached the specified number of cycles, reset the count value n in step 9 and proceed to step 10 to increase the target EGR rate by a small specified amount. Furthermore, a baseline target EGR rate is preset for each operating point, and in step 10, the correction amount for the baseline target EGR rate is increased by a specified amount.

[0027] Thus, if the illustrated mean effective pressure variation rate cPi remains below a specified threshold, and the number of combustion cycles entering steps 5, 6, and 7 reaches a specified number of cycles, then at that moment, the target EGR rate is increased by a specified amount as a correction. Furthermore, the count value n is reset when the specified number of cycles is reached. Therefore, if the illustrated mean effective pressure variation rate cPi remains below the threshold for an extended period, the correction is increased by a specified amount each time a specified number of cycles are elapsed.

[0028] On the other hand, if the illustrated average effective pressure variation rate cPi is greater than or equal to the threshold in step 5, it indicates that the combustion stability is worse than the specified level. The process then proceeds from step 5 to step 11, where it is determined whether the target EGR rate reduction experience indicator is 1. If the target EGR rate reduction experience indicator is 0 immediately after the change in operating point, the process proceeds from step 11 to step 12, where the count value n is reset, and then proceeds to step 13, where the target EGR rate reduction experience indicator is set to 1. Furthermore, the process proceeds from step 13 to step 17, where the target EGR rate is reduced by a specified amount. That is, if the illustrated average effective pressure variation rate cPi is greater than or equal to the threshold within a certain combustion cycle, the target EGR rate is immediately reduced without waiting for a specified number of cycles.

[0029] If step 13 causes the target EGR rate reduction empirical flag to become 1, then in the next process, if step 5 determines that the illustrated mean effective pressure change rate cPi is greater than or equal to the threshold, the determination result of the target EGR rate reduction empirical flag in step 11 becomes YES. Therefore, from step 11, proceed to step 14 to determine whether the count value n, representing the number of cycles, has reached the specified number of cycles (e.g., 100 cycles). If it is NO, proceed to step 15, increment the count value n, and end the process. Alternatively, if the count value n has reached the specified number of cycles, then in step 16, the count value n is reset, and proceed to step 17 to reduce the target EGR rate by a small specified amount.

[0030] That is, if the initial illustrated mean effective pressure variation rate cPi is greater than or equal to the threshold and the target EGR rate is reduced in step 17, then the empirical flag for reducing the target EGR rate is set to 1 in step 13. Therefore, even if the illustrated mean effective pressure variation rate cPi is greater than or equal to the threshold in a certain combustion cycle, the target EGR rate reduction correction will not be performed thereafter. When the illustrated mean effective pressure variation rate cPi is greater than or equal to the threshold for a predetermined number of cycles, the target EGR rate reduction correction will be performed again. Alternatively, if the illustrated mean effective pressure variation rate cPi is greater than or equal to the threshold for a long period, the target EGR rate reduction correction will be performed every predetermined number of cycles.

[0031] Figure 3 This is a timing diagram illustrating the corrective control action for the aforementioned target EGR rate. In this diagram, from top to bottom, it shows (a) the stability determination state, (b) the illustrated mean effective pressure variation rate cPi, (c) the EGR rate correction amount, and (d) the empirical indicator of the target EGR rate reduction. The pulse waveform for (a) the stability determination state indicates whether the internal combustion engine speed, load, and target EGR rate are in a stable state, based on the determinations in steps 1 and 2. The timing of the rising edge of the waveform in (a) is... Figure 2 The flowchart shows the timing for steps after step 3 enters step 4.

[0032] In this example, during the period up to time t5, the average effective pressure change rate cPi is less than a specified threshold, becomes greater than or equal to the threshold for a short period after time t5, and then becomes less than the threshold again.

[0033] Therefore, in this example, it is executed repeatedly starting from time t1. Figure 2 Steps 5, 6, 7, and 8, after the state has lasted for a specified number of cycles t2, as shown in (c), involve increasing the target EGR rate by a specified amount. With this increase in correction, Figure 2The result of step 3 is NO. After a slight delay, the process is repeated at time t3. Figure 2 Steps 5, 6, 7, and 8, after the state has persisted for a specified number of cycles (t4), as shown in (c), further increase the target EGR rate by a specified amount. That is, if the state of the illustrated mean effective pressure variation rate cPi being less than the threshold persists, the target EGR rate is increased in small, stepwise increments after each specified number of cycles. There is a lag until the change in the target EGR rate is reflected in the illustrated mean effective pressure variation rate cPi, therefore, the subsequent increase correction is performed after a specified number of cycles. This avoids combustion deterioration caused by a sharp increase in the EGR rate and keeps the EGR rate close to its limit. In particular, if the illustrated mean effective pressure variation rate cPi is calculated as a moving average, the influence of the combustion state from a recent cycle (a cycle where the EGR rate is still low) remains, thus making it impossible to accurately obtain the combustion stability at the EGR rate after the increase correction. Waiting for a specified number of cycles before performing the subsequent increase correction avoids sharp combustion deterioration.

[0034] This increase in EGR rate leads to a decrease in combustion stability, and therefore, shortly thereafter, the average effective pressure variation rate cPi shown in the figure becomes greater than or equal to the threshold. In the example shown in the figure, the average effective pressure variation rate cPi becomes greater than or equal to the threshold at time t5. At this point, through the aforementioned... Figure 2 The processing steps 5, 11, 12, 13, and 17 immediately reduce the target EGR rate. Simultaneously, step 13 sets the empirical indicator for reducing the target EGR rate to 1. In other words, when the empirical indicator for reducing the target EGR rate is 0, if the average effective pressure variation rate cPi is greater than or equal to the threshold, the target EGR rate immediately decreases without waiting for the number of cycles to elapse. Thus, the long-term persistence of combustion degradation is suppressed.

[0035] If the target EGR rate is reduced at time t5, then after a slight lag that is determined to be a transitional state, at time t6, from Figure 2The process proceeds from step 3 to step 4. The illustrated mean effective pressure change rate cPi is greater than or equal to the threshold at time t6, but the empirical indicator for the target EGR rate reduction is 1 at this time. Therefore, the process proceeds from step 11 to step 14. Thus, at time t6, no reduction correction is applied to the target EGR rate. If the state of mean effective pressure change rate cPi being greater than or equal to the threshold continues for a specified number of periods, the target EGR rate is reduced again at time t7. This process of waiting for the specified number of periods to pass before the second reduction correction is performed minimizes the target EGR rate. In other words, the influence of periods before time t5 where the EGR rate was still high can be eliminated.

[0036] In the illustrated example, combustion stability is improved through two reductions in the target EGR rate. For instance, the illustrated mean effective pressure variation rate (cPi) is less than the threshold at time t8 and at time t9, respectively, after a specified number of cycles. However, the empirical indicator for the reduction in the target EGR rate is 1 at this point, therefore further increases in the target EGR rate are prohibited. That is, via... Figure 2 The process ends at step 6, thus avoiding correction of the target EGR rate. This is because increasing the EGR rate at the same operating point (internal combustion engine speed and load) actually causes combustion degradation, thus preventing combustion degradation from occurring due to a further increase in the EGR rate.

[0037] As mentioned earlier, if the operating point changes, the empirical indicator for the reduction in the target EGR rate becomes 0. Therefore, as long as the operating point remains the same, combustion degradation caused by an increase in the useless EGR rate is avoided.

[0038] Furthermore, in the illustrated example, for the sake of simplicity, the correction amount for increasing the EGR rate is shown to be equal to the correction amount for decreasing the EGR rate, but the correction amounts can also be different. Additionally, the correction amount for the initial decrease correction can be set to a different value than the correction amounts for subsequent decrease corrections; for example, the initial decrease correction amount can be increased.

[0039] Furthermore, the specified number of periods for increasing the target EGR and the specified number of periods for decreasing the target EGR may not be the same. Similarly, the aforementioned number of periods may be different from the number of periods used to calculate the moving average of the graphical mean effective pressure change rate cPi. In one embodiment, the specified number of periods for increasing the correction and the number of periods for decreasing the correction are equal to each other, and this is substantially equal to the number of periods used to calculate the moving average of the graphical mean effective pressure change rate cPi.

Claims

1. A control method of an internal combustion engine, which calculates an index indicating combustion stability of the internal combustion engine, and corrects an exhaust gas recirculation rate based on the combustion stability, wherein, in a case where the combustion stability satisfies a prescribed level, an increase correction of the exhaust gas recirculation rate is made by a prescribed amount each time a prescribed period elapses, in a case where it is detected that the combustion stability is worse than the prescribed level, an immediate decrease correction of the exhaust gas recirculation rate is made, in a case where the decrease correction of the exhaust gas recirculation rate based on the combustion stability is made during a period in which the internal combustion engine stays at a constant operating point, an increase correction of the exhaust gas recirculation rate based on the combustion stability after that is prohibited based on the operating point, and after the decrease correction of the exhaust gas recirculation rate by the prescribed amount, if a state in which the combustion stability is worse than the prescribed level continues for a prescribed period, a further decrease correction of the exhaust gas recirculation rate by the prescribed amount is made.

2. The control method of an internal combustion engine according to claim 1, wherein, whether the combustion stability satisfies the prescribed level is judged for each period, if periods in which the combustion stability satisfies the prescribed level continue for a prescribed period, an increase correction of the exhaust gas recirculation rate is made by a prescribed amount, in a case where the combustion stability does not satisfy the prescribed level at a certain period, an immediate decrease correction of the exhaust gas recirculation rate by a prescribed amount is made, and after the decrease correction, if periods in which the combustion stability does not satisfy the prescribed level continue for a prescribed period, a further decrease correction of the exhaust gas recirculation rate by a prescribed amount is made.

3. A control device of an internal combustion engine, wherein the control device of the internal combustion engine has an exhaust gas recirculation device having an exhaust gas recirculation control valve, at least one sensor which detects a rotational variation or an in-cylinder pressure associated with combustion stability of the internal combustion engine, and a controller which corrects an exhaust gas recirculation rate of the exhaust gas recirculation device based on the combustion stability, in a case where the combustion stability satisfies a prescribed level, the controller makes an increase correction of the exhaust gas recirculation rate by a prescribed amount each time a prescribed period elapses, in a case where it is detected that the combustion stability is worse than the prescribed level, the controller makes an immediate decrease correction of the exhaust gas recirculation rate, in a case where the decrease correction of the exhaust gas recirculation rate based on the combustion stability is made during a period in which the internal combustion engine stays at a constant operating point, an increase correction of the exhaust gas recirculation rate based on the combustion stability after that is prohibited based on the operating point, and after the decrease correction of the exhaust gas recirculation rate by the prescribed amount, if a state in which the combustion stability is worse than the prescribed level continues for a prescribed period, a further decrease correction of the exhaust gas recirculation rate by the prescribed amount is made.

4. The control device of an internal combustion engine according to claim 3, wherein, whether the combustion stability satisfies the prescribed level is judged for each period, if periods in which the combustion stability satisfies the prescribed level continue for a prescribed period, an increase correction of the exhaust gas recirculation rate is made by a prescribed amount, in a case where the combustion stability does not satisfy the prescribed level at a certain period, an immediate decrease correction of the exhaust gas recirculation rate by a prescribed amount is made, and after the decrease correction, if periods in which the combustion stability does not satisfy the prescribed level continue for a prescribed period, a further decrease correction of the exhaust gas recirculation rate by a prescribed amount is made. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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