Method and device for knocking control for internal combustion engine

Abstract

To solve a problem of reduction in torque and degradation in acceleration performance due to ignition timing retard correction by knocking control when a driver requests a full acceleration.SOLUTION: A retard correction of ignition timing is performed at a predefined retard speed when knocking of a knocking determination threshold value or more is detected, and the ignition timing is gradually advanced at a predefined advance angle so as to be closer to an MBT point while the knocking is not detected. When an accelerator opening is equal to or more than an opening equivalent to full opening, and during a retard period (times t1 to t2) until predefined catalyst protection increase amount control starts, the knocking determination threshold value is set higher than normal time, the retard speed is set lower than the normal time, and the advance speed is set higher than the normal time. The ignition timing is relatively closer to the advance side than the trace knock state in the normal time.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a knocking control method and a knocking control device for suppressing knocking in an internal combustion engine by ignition timing feedback control.

Background Art

[0002] As a technique for suppressing knocking in an internal combustion engine, knocking is detected by a knocking sensor (or in-cylinder pressure sensor), and when knocking at a certain level is detected, the ignition timing is corrected by a predetermined amount of retard. Then, if no knocking is detected, the ignition timing is gradually advanced to maintain a trace knock state. This technique is widely known.

[0003] Patent Document 1 discloses a technique in which the knocking determination level is increased when the vehicle speed is high and stronger knocking is allowed than when the vehicle speed is low. This is based on the idea that since the original in-vehicle noise is at a high level at high vehicle speeds, the noise generated by knocking is less likely to give discomfort to the passengers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a situation where the driver fully opens the accelerator pedal, it can be said that the driver is demanding rapid acceleration of the vehicle. However, in such a case, since the ignition timing is corrected to retard based on the detection of knocking so as to enter a trace knock state, the acceleration performance is impaired.

[0006] Patent Document 1 cannot solve the problem during full-throttle acceleration.

Means for Solving the Problem

[0007] This invention is a knocking control method for an internal combustion engine that, when knocking above a knock determination threshold value is detected, corrects the ignition timing by retarding it at a predetermined retard angular velocity, and gradually advances the ignition timing at a predetermined advance angular velocity so as to approach the MBT point while knocking is not detected. The method includes: Performing ignition timing correction targeting a first trace knock state; While the accelerator opening is equal to or greater than a full-open equivalent opening and during a delay period until a predetermined catalyst protection increment control is started, performing ignition timing correction targeting a second trace knock state in which the ignition timing is controlled to be more advanced relative to the first trace knock state.

[0008] That is, when the accelerator opening becomes, for example, full open, in order to protect the catalyst in the exhaust system, after an appropriate delay period, an increase in the fuel injection amount (in other words, enrichment of the air-fuel ratio) is performed. In the present invention, while the accelerator opening is equal to or greater than a predetermined full-open equivalent opening and during the above-described delay period, ignition timing correction is performed targeting a second trace knock state with a relatively high knocking level. Therefore, the ignition timing retard amount for knocking control becomes relatively small.

Advantages of the Invention

[0009] According to this invention, while the accelerator opening is equal to or greater than a full-open equivalent opening and during a delay period until a predetermined catalyst protection increment control is started, a reduction in the torque of the internal combustion engine is reduced, and high acceleration performance in accordance with the driver's intention can be obtained.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] FIG. 1 shows the system configuration of an internal combustion engine 1 for an automobile to which the present invention is applied. The internal combustion engine 1 of this embodiment is, for example, an in-cylinder direct injection type spark ignition internal combustion engine with three cylinders in line, and for each cylinder, it is provided with a fuel injection valve 2 for injecting fuel into the cylinder, and an ignition plug 3 for igniting the generated air-fuel mixture is provided, for example, at the center of the ceiling surface. This ignition plug 3 is connected to an ignition unit 4 provided for each cylinder, and the ignition timing can be controlled for each cylinder by a control signal from the engine controller 12.

[0013] Also, at an appropriate position of the cylinder block of the internal combustion engine 1, a knocking sensor 5 for detecting knocking based on mechanical vibration when knocking occurs in any cylinder is arranged.

[0014] The intake ports opened and closed by the intake valves 6 of each cylinder converge into an intake collector 8, and an electronically controlled throttle valve 9 whose opening degree is controlled by a control signal from the engine controller 12 is arranged at the inlet of this intake collector 8. An exhaust manifold 10 is connected to the exhaust port opened and closed by the exhaust valve 7. A catalytic device 11 for exhaust purification is provided on the outlet side of the exhaust manifold 10.

[0015] The above-mentioned engine controller 12 receives detection signals from sensors such as a crank angle sensor 13 for detecting the engine speed, an air flow meter 14 for detecting the intake air amount corresponding to the load, a water temperature sensor 15 for detecting the cooling water temperature, an accelerator opening sensor 16 for detecting the depression amount of the accelerator pedal operated by the driver, an air-fuel ratio sensor 17 for detecting the exhaust air-fuel ratio, etc., as the operating conditions of the internal combustion engine 1. Based on these detection signals, the engine controller 12 optimally controls the fuel injection amount and injection timing by the fuel injection valve 2, the ignition timing of the spark plug 3 via the ignition unit 4, the opening of the throttle valve 9, etc.

[0016] Here, the fuel injection amount is basically feedback-controlled so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 17 becomes equivalent to the stoichiometric air-fuel ratio. And a catalyst protection enrichment region is set in the high-load operation region close to full load. When the operating conditions determined from the load and the rotational speed are within this catalyst protection enrichment region, after an appropriate delay time, based on the catalyst temperature, etc., fuel enrichment, that is, catalyst protection enrichment, is executed to enrich the air-fuel ratio. By enriching the air-fuel ratio, the exhaust temperature decreases, and deterioration of the catalyst due to excessive high temperature is avoided.

[0017] Next, the knocking control executed by the above-mentioned engine controller 12 will be described. FIG. 2 is a functional block diagram of the knocking control according to an embodiment. The knocking determination unit 21 extracts a knock signal 22 for each cylinder from the detection signal of the knocking sensor 5, and compares this with a knock determination threshold value in the comparison unit 23 to detect knocking for each cylinder. For example, a signal within a predetermined crank angle range is extracted for each cylinder from the output signal of the knocking sensor 5, and it is determined whether or not a knocking vibration component equal to or greater than the knock determination threshold value is included therein. If there is a knocking vibration equal to or greater than the knock determination threshold value, it is determined that knocking has occurred.

[0018] The knock determination threshold values are stored in advance in a first threshold table 24 and a second threshold table 25 with the engine rotational speed as a parameter, and the value of either table selected by a switching unit 26 is output to a comparison unit 23.

[0019] The first threshold table 24 assigns the normal knock determination threshold value, whereby the knocking intensity in a normal trace knock state (referred to as the first trace knock state) is generally determined.

[0020] The second threshold table 25 has a knock determination threshold value that is relatively higher than the value of the first threshold table 24. That is, the knock determination threshold value for the same engine rotational speed is relatively higher so that knocking vibrations with relatively high intensity are allowed. Thereby, the knocking intensity in a trace knock state (referred to as the second trace knock state) during a delay period until the catalyst protection increment control described above is started when the accelerator opening is equal to or greater than the full-open equivalent opening is generally determined.

[0021] Input to the switching unit 26 are a delay period flag 27 indicating that it is during the delay period until the start of the catalyst protection increment control, a full-open flag 28 indicating that the accelerator opening is equal to or greater than the full-open equivalent opening, and a permission setting flag 29 indicating the availability of control for the second trace knock state. The switching unit 26 selects the second threshold table 25 when all three of these signals are ON, and selects the first threshold table 24 when any one of them is OFF. Note that the permission setting flag 29 is a software switch and can be set to OFF by the user's initial settings or the like.

[0022] Therefore, in the knocking determination unit 21, knocking determination is performed using a relatively high knocking determination threshold value according to the second threshold value table 25 only when the accelerator opening degree is equal to or greater than the full-throttle equivalent opening degree and during the delay period until the start of the catalyst protection increment control. Otherwise, knocking determination is performed using the normal knocking determination threshold value according to the first threshold value table 24. Therefore, if the same knocking vibration is output from the knocking sensor 5, the former has a lower probability of being determined to have knocking occur. That is, it is less likely that ignition timing retard correction associated with knocking detection will occur in the former case.

[0023] The above-mentioned "full-throttle equivalent opening degree" strictly means an accelerator opening degree that is not exactly full throttle but can be regarded as full throttle, and is preset for each engine rotation speed, for example. At an accelerator opening degree equal to or greater than this full-throttle equivalent opening degree, usually, the operating conditions (load and rotation speed) of the internal combustion engine 1 are included in the catalyst protection increment region described above. Also, in order to avoid control hunting, an appropriate hysteresis is given to the "full-throttle equivalent opening degree". Strictly speaking, it includes a first full-throttle equivalent opening degree used in the opening degree increase direction and a relatively small second full-throttle equivalent opening degree used in the opening degree decrease direction. However, hereinafter, the "full-throttle equivalent opening degree" will be described without particularly distinguishing between the two.

[0024] When the knocking determination unit 21 detects knocking, the ignition timing correction unit 31 corrects the ignition timing by a predetermined retard angular velocity, and gradually advances the ignition timing by a predetermined advance angular velocity so as to approach the MBT point while knocking is not detected. The ignition timing correction unit 31 of the embodiment includes a feedback correction amount calculation unit 32 for the MBT control region and a feedback correction amount calculation unit 33 for the trace control region. That is, the operating region determined from the load and rotation speed of the internal combustion engine 1 is roughly divided into a trace control region where knocking is likely to occur and an MBT control region where knocking is less likely to occur, and feedback control of the ignition timing suitable for each is performed. The vicinity of the full-throttle equivalent opening degree targeted by the present invention is included in the trace control region.

[0025] In the MBT control region, the MBT feedback correction amount calculation unit 32 calculates the MBT feedback correction amount for each cylinder based on knocking detection. Specifically, the MBT feedback correction amount increases relatively largely when knocking is determined to have occurred in the target cylinder, and is calculated by decreasing it by a predetermined minute amount when knocking is not detected. That is, in this example, an increase in the feedback correction amount corresponds to a change toward the retard side of the ignition timing. The MBT feedback correction amount is held as it is without being updated while the operating conditions are in the trace control region. In the MBT control region, the corrected ignition timing for the MBT control region is determined by subtracting the above MBT feedback correction amount from the MBT reference ignition timing output by the MBT reference ignition timing output unit 34.

[0026] Similarly, in the trace control region, the trace feedback correction amount calculation unit 33 for the trace control region calculates the trace feedback correction amount for each cylinder based on knocking detection. Specifically, the trace feedback correction amount increases relatively largely when knocking is determined to have occurred in the target cylinder, and is calculated by decreasing it by a predetermined minute amount when knocking is not detected. The trace feedback correction amount is held as it is without being updated while the operating conditions are in the MBT control region. In the trace control region, the corrected ignition timing for the trace control region is determined by subtracting this trace feedback correction amount from the trace reference ignition timing output by the trace reference ignition timing output unit 35.

[0027] Finally, in the comparison unit 36, the corrected ignition timing for the MBT control region and the corrected ignition timing for the trace control region are compared, and the one on the relatively retard side (the one with a smaller advance angle amount) is output as the ignition timing of the corresponding cylinder.

[0028] As described above, in this embodiment, ignition timing correction based on knocking detection and final ignition timing setting are performed for each cylinder. However, in the present invention, such cylinder-by-cylinder ignition timing control is not essential. That is, the present invention can also be applied to a form in which the ignition timings of all cylinders are simultaneously feedback-controlled.

[0029] The acceleration rate of increase of the trace feedback correction amount at the time of knocking detection (i.e., the ignition timing retard angular velocity) and the deceleration rate of decrease of the trace feedback correction amount at the time of non-detection of knocking (i.e., the ignition timing advance angular velocity) in the trace feedback correction amount calculation unit 33 are either the values (retard angular velocity and advance angular velocity) set as constants in the retard / advance angular velocity constant unit 38 or the values (retard angular velocity and advance angular velocity) read from the retard / advance angular velocity table 39. That is, either the retard / advance angular velocity constant unit 38 or the retard / advance angular velocity table 39 is selected by the switching unit 40, and the selected retard angular velocity and advance angular velocity are given to the trace feedback correction amount calculation unit 33.

[0030] The switching unit 40 receives a delay period flag 27 indicating that it is during the delay period until the start of catalyst protection increment control, a full open flag 28 indicating that the accelerator opening is equal to or greater than the full open equivalent opening, and a permission setting flag 29 indicating the availability of control for the second trace knock state. The switching unit 40 selects the retard / advance angular velocity table 39 when all of these three signals are ON, and selects the retard / advance angular velocity constant unit 38 when any one of them is OFF.

[0031] The retard / advance angular velocity constant unit 38 has, as constants, the ignition timing retard angular velocity at the time of knocking detection and the ignition timing advance angular velocity at the time of non-detection of knocking, respectively.

[0032] In the retard angle / advance angular velocity table 39, values of the increasing speed of the trace feedback correction amount at the time of knocking detection corresponding to the retard angular velocity and the decreasing speed of the trace feedback correction amount at the time of non-knocking detection corresponding to the advance angular velocity are stored using the engine rotational speed as a parameter. Note that since these values of the increasing speed and the decreasing speed are given as speeds corresponding to real time in the retard angle / advance angular velocity table 39, by reading the corresponding value using the engine rotational speed output from the engine rotational speed calculation unit 41 as a parameter, it becomes a speed substantially corresponding to the crank angle.

[0033] The retard angular velocity at the time of knocking detection in the retard angle / advance angular velocity table 39 is relatively low compared to the retard angular velocity in the retard angle / advance angular velocity constant unit 38. Also, the advance angular velocity at the time of non-knocking detection in the retard angle / advance angular velocity table 39 is relatively high compared to the advance angular velocity in the retard angle / advance angular velocity constant unit 38. Therefore, assuming that knocking is detected at the same frequency, according to the retard angle / advance angular velocity in the retard angle / advance angular velocity table 39, the final ignition timing is kept relatively more advanced than the control by the retard angle / advance angular velocity of the retard angle / advance angular velocity constant unit 38.

[0034] As described above, in the above embodiment, during the delay period until the accelerator opening is equal to or greater than the full-open equivalent opening and the predetermined catalyst protection increment control is started, compared to the normal time when these conditions are not satisfied, the knock determination threshold value is set relatively high, and the ignition timing retard angular velocity at the time of knocking detection becomes relatively low while the ignition timing advance angular velocity at the time of non-knocking detection becomes relatively high. As a result, the ignition timing in the trace knock state obtained by the ignition timing feedback control becomes relatively more advanced. In other words, the ignition timing retard angle amount from the MBT point in the trace knock state becomes smaller, and the torque reduction becomes smaller.

[0035] FIG. 3 is a time chart showing the operation in knocking control according to an embodiment. In order from the top of the figure, (a) vehicle speed, (b) engine rotational speed, (c) catalyst carrier temperature, (d) knock score which is a sensory value indicating the quality of knocking noise, (e) ignition timing advance amount (the upper side of the figure is the advance side), (f) output torque of the internal combustion engine 1, (g) equivalence ratio indicating fuel dilution, and (h) accelerator opening are shown. Note that this time chart is simplified for explanation purposes and does not show exact characteristics. From the start to time t1 of the illustrated time chart, it is normal driving, so-called road load (R / L) driving. In this example, during the period up to time t1, it is also in a trace knock state (the first trace knock state), and the knock score is maintained at a relatively good high value.

[0036] At time t1, the driver shifts to full-throttle acceleration with the accelerator opening fully open. For example, based on the subsequent increase in the catalyst temperature (column (c)), the catalyst protection increment starts at time t2, which is delayed from the accelerator opening change.

[0037] From time t1 to time t2, it is the delay period until the start of the catalyst protection increment control. The equivalence ratio shown in column (g) maintains "1" corresponding to the stoichiometric air-fuel ratio, the same as during the period up to time t1. During this time, the ignition timing is retarded for knocking control, resulting in a trace knock state (the second trace knock state). However, due to the change in the knock determination threshold value and the retard / advance angular velocity as described above, the ignition timing advances relatively compared to the previous first trace knock state. Therefore, the knock score in column (d) indicating knocking noise deteriorates, that is, decreases. However, since the ignition timing advances relatively and approaches the MBT point, the torque of the internal combustion engine 1 shown in column (f) increases, and the acceleration performance of the vehicle improves as shown in column (a). Note that the characteristics indicated by the dashed lines between times t1 and t2 are all characteristics of a comparative example without changing the knock determination threshold value and the retard / advance angular velocity based on the fact that the accelerator opening is equal to or greater than the fully open equivalent opening and it is the delay period until a predetermined catalyst protection increment control starts.

[0038] At time t2, the catalyst protection fuel increment starts, and the equivalence ratio increases as shown in column (g). Also, since the knock determination threshold value and the retard / advance angular velocity return to the values for normal ignition timing feedback control, a first trace knock state occurs. However, since knocking is less likely to occur due to the fuel increment, i.e., the enrichment of the air-fuel ratio, the ignition timing in the first trace knock state becomes a relatively advanced ignition timing as shown in column (e).

[0039] After time t3, since the catalyst temperature shown in column (c) decreases, the catalyst protection fuel increment ends, and normal high-load operation is achieved. When the catalyst protection fuel increment ends, the equivalence ratio becomes equivalent to the stoichiometric air-fuel ratio, and the ignition timing in the first trace knock state changes toward the retard side.

[0040] As described above, one embodiment of the present invention has been explained. However, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, a straight-three cylinder internal combustion engine has been described as an example. However, the present invention can be applied to any multi-cylinder internal combustion engine, and it may be a port injection type internal combustion engine. Also, an in-cylinder pressure sensor that detects the in-cylinder pressure of each cylinder may be used as the knocking detection sensor. Further, the control roughly classified into the MBT control region and the trace control region as in the above embodiment is not essential to the present invention.

[0041] Furthermore, in the above embodiment, both the change of the knock determination threshold value and the change of the retard / advance angular velocity are performed so that the second trace knock state is controlled relatively more on the advance side than the first trace knock state. However, the ignition timing may be controlled relatively more on the advance side by only one of them.

Explanation of Reference Numerals

[0042] 1... Internal combustion engine 3... Spark plug 5... Knocking sensor 12... Engine controller 16... Accelerator opening sensor 21... Knocking determination unit 25... Second threshold table 31…Ignition timing correction section 33…Trace feedback correction amount calculation section 39…Retard / advance angular velocity table

Claims

1. A knocking control method for an internal combustion engine, which corrects the ignition timing by retarding it at a predetermined retard angular velocity when knocking above a knocking determination threshold is detected, and gradually advances the ignition timing at a predetermined advance angular velocity so as to approach the MBT point while knocking is not detected. The method includes: Performing ignition timing correction aiming at a first trace knock state; During a delay period until the accelerator opening is equal to or greater than the full-open equivalent opening and a predetermined catalyst protection increment control is started, performing ignition timing correction aiming at a second trace knock state in which the ignition timing is controlled to be more advanced relative to the first trace knock state; A knocking control method for an internal combustion engine.

2. During a delay period until the accelerator opening is equal to or greater than the full-open equivalent opening, relatively increasing the knocking determination threshold; The knocking control method for an internal combustion engine according to Claim 1.

3. During a delay period until the accelerator opening is equal to or greater than the full-open equivalent opening, relatively decreasing the retard angular velocity and relatively increasing the advance angular velocity; The knocking control method for an internal combustion engine according to Claim 1.

4. During a delay period until the accelerator opening is equal to or greater than the full-open equivalent opening, relatively increasing the knocking determination threshold, relatively decreasing the retard angular velocity, and relatively increasing the advance angular velocity; The knocking control method for an internal combustion engine according to Claim 1.

5. The full-open equivalent opening is preset for each engine rotational speed; The knocking control method for an internal combustion engine according to Claim 1.

6. The full-open equivalent opening includes a first full-open equivalent opening used in the opening increase direction and a second full-open equivalent opening with a relatively small opening used in the opening decrease direction so as to obtain hysteresis; The knocking control method for an internal combustion engine according to Claim 1.

7. A knocking detection sensor provided in the internal combustion engine; A knocking determination unit that compares a signal from the knocking detection sensor with a knocking determination threshold to perform a knocking determination; An ignition timing correction unit that corrects the ignition timing by retarding it at a predetermined retard angular velocity when knocking above the knocking determination threshold is detected by the knocking determination unit, and gradually advances the ignition timing at a predetermined advance angular velocity so as to approach the MBT point while knocking is not detected; Comprising The ignition timing correction unit performs ignition timing correction targeting the first trace knocking state, and performs ignition timing correction targeting a second trace knocking state in which the ignition timing is controlled to be more advanced relative to the first trace knocking state during a delay period until the accelerator opening is equal to or greater than the full opening equivalent opening and a predetermined catalyst protection increment control is started. Knocking control device for an internal combustion engine.

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