JP6345303B1 - Control device and control method for internal combustion engine - Google Patents

Abstract

A control device for an internal combustion engine capable of retarding the ignition timing for each cylinder in order to suppress the occurrence of knocking while limiting the torque difference between the cylinders within a desirable range even if the retard amount of the ignition timing changes. And a control method.
Among the ignition timings of the cylinders retarded by the cylinder-by-cylinder knock retardation control, the most retarded ignition timing θrmax is determined, and a torque ignition timing characteristic is used to allow the inter-cylinder tolerance at the most retarded ignition timing θrmax. The torque allowable ignition timing difference Δθmax corresponding to the torque difference ΔTmax is calculated, and the ignition timing of each cylinder is set to the most retarded ignition timing θrmax, which is advanced by the torque allowable ignition timing difference Δθmax from the most retarded ignition timing θrmax. A control device and a control method for an internal combustion engine that calculate an ignition timing that is limited within a range of an advance side upper limit ignition timing as a final ignition timing of each cylinder.
[Selection] Figure 8

Description

  The present invention relates to a control device and a control method for an internal combustion engine for controlling knock generated in the internal combustion engine.

  2. Description of the Related Art Conventionally, a control device that detects a knock phenomenon (knock phenomenon) generated in an internal combustion engine by a vibration sensor (hereinafter referred to as a knock sensor) directly attached to a cylinder block of the internal combustion engine is known. If a knock occurs during operation of the internal combustion engine, vibration in a specific frequency band is generated according to the bore diameter of the internal combustion engine and the vibration mode of the knock. Therefore, the control device measures the vibration intensity at this natural frequency. Detect knocks.

  Further, as a characteristic of the internal combustion engine, when the ignition timing is advanced, the output torque of the internal combustion engine increases, but knocking is likely to occur. Therefore, the control device suppresses the knock by correcting the ignition timing to the retard side when the knock is detected, and returns the ignition timing to the advance side when the knock is not detected, thereby outputting the output of the internal combustion engine. Knock control is performed to suppress torque reduction. By the knock control, the ignition timing is controlled to the knock limit ignition timing that is the most advanced ignition timing immediately before the occurrence of the knock.

  As a technique for performing such knock control, for example, techniques described in Patent Document 1 and Patent Document 2 below are already known. In the technique of Patent Document 1, when knocking occurs in the first cylinder, the ignition timing of the first cylinder is retarded, and then when knocking occurs in the second cylinder, The ignition timing is retarded, and the ignition timing is retarded for each cylinder. In the technique of Patent Document 1, in order to suppress an increase in torque fluctuation between cylinders due to a decrease in torque of a retarded cylinder, the sum of the retard amount of the first cylinder and the retard amount of the second cylinder is suppressed. The retardation amount of the second cylinder is limited so that the value is equal to or less than a preset limit value.

  The technique of Patent Document 2 is configured to detect knock for each cylinder and retard the ignition timing for each cylinder. According to the technique of Patent Document 2, the allowable ignition timing difference from the most retarded ignition timing is set for each cylinder according to the knock detectability of each cylinder, which differs depending on the knock sensor mounting position, and the ignition timing of each cylinder is limited. Is configured to do.

JP 2009-281251 A Japanese Patent No. 4213693

  Incidentally, the relationship between the torque generated by each cylinder and the ignition timing is as shown in FIG. 4, and as the ignition timing moves to the retard side, the amount of torque decrease with respect to the retard amount of the ignition timing increases. . That is, the torque fluctuation sensitivity increases as the ignition timing retardation amount increases.

However, in the techniques of Patent Document 1 and Patent Document 2, it is not considered that the fluctuation sensitivity of the torque with respect to the change in the ignition timing varies depending on the retard amount of the ignition timing, and depending on the retard amount of the ignition timing. The limit value or allowable ignition timing difference is too large, the torque difference between cylinders becomes too large, the limit value or allowable ignition timing difference is too small, the torque difference between cylinders is too small, and ignition An appropriate limit value or allowable ignition timing difference could not be set according to the amount of retarded timing.

  Further, in the technique of Patent Document 1, since the retardation amount of the second cylinder is limited, there is a possibility that the occurrence of knocking in the second cylinder cannot be prevented, and the ignition timing of other cylinders is not changed. There is a limit to reducing the torque difference between cylinders.

  Therefore, even if the retard amount of the ignition timing changes, an internal combustion engine control device capable of retarding the ignition timing for each cylinder in order to suppress the occurrence of knocking while limiting the torque difference between the cylinders within a desired range, and A control method is required.

  An internal combustion engine control apparatus according to the present invention includes a knock detection unit that detects, for each cylinder, a knock generated in an internal combustion engine having a plurality of cylinders, and retards the ignition timing of the cylinder in which the knock is detected for each cylinder. An ignition timing calculation unit that calculates the ignition timing for each cylinder by performing cylinder-by-cylinder knock retardation control, and ignition that ignites the air-fuel mixture in each cylinder at the ignition timing calculated by the ignition timing calculation unit A control unit, wherein the ignition timing calculation unit determines the most retarded ignition timing that is the most retarded ignition timing among the ignition timings of each cylinder retarded by the cylinder-by-cylinder knock retardation control. Calculating the allowable torque difference between the cylinders, which is the maximum torque difference allowed between the cylinders, and using the torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is set in advance, the most retarded ignition timing In the above-mentioned, permissible cylinder The torque allowable ignition timing difference, which is the ignition timing difference corresponding to the torque difference, is calculated, and the ignition timing of each cylinder is set to the most retarded ignition timing and the torque allowable ignition timing difference from the most retarded ignition timing. The ignition timing limited within the range of the advance side upper limit ignition timing which is the advance side ignition timing is calculated as the final ignition timing of each cylinder.

  The internal combustion engine control method according to the present invention includes a knock detection step for detecting, for each cylinder, a knock generated in an internal combustion engine provided with a plurality of cylinders, and an ignition timing of the cylinder in which the knock is detected for each cylinder. The ignition timing calculating step for calculating the ignition timing for each cylinder by performing the retarding control for each cylinder to be retarded, and igniting the mixture of each cylinder at the ignition timing of each cylinder calculated in the ignition timing calculating step The ignition timing calculating step, and in the ignition timing calculating step, the most retarded ignition timing which is the most retarded ignition timing among the ignition timings of each cylinder retarded by the cylinder-by-cylinder knock retardation control. And calculating the allowable torque difference between the cylinders, which is the maximum torque difference allowed between the cylinders, and using a torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is preset, In the most retarded ignition timing, a torque allowable ignition timing difference, which is a difference in ignition timing corresponding to the cylinder allowable torque difference, is calculated, and the ignition timing of each cylinder is determined as the most retarded ignition timing and the most retarded ignition timing. The final ignition timing of each cylinder is calculated by limiting the ignition timing within the range of the advance-side upper limit ignition timing, which is the ignition timing on the advance side, by the torque allowable ignition timing difference from the angular ignition timing. .

  According to the control device and the control method for an internal combustion engine according to the present invention, the torque allowable ignition timing difference corresponding to the cylinder allowable torque difference is calculated at the most retarded ignition timing using the torque ignition timing characteristics. As the most retarded ignition timing during this period changes from the maximum torque ignition timing to the retarded angle side, the torque allowable ignition timing difference corresponding to the inter-cylinder allowable torque difference can be reduced. In addition, since the ignition timing of each cylinder is limited within the range of the torque allowable ignition timing difference, even if the retard amount of the ignition timing changes, the torque difference between the cylinders is reliably within the range of the allowable torque difference between the cylinders. Can be limited to. Further, since the ignition timing of each cylinder excluding the most retarded ignition timing is changed to the retard side, the occurrence of knocking in each cylinder can be suppressed.

1 is a schematic configuration diagram of an internal combustion engine according to a first embodiment of the present invention. It is a block diagram of the control apparatus which concerns on Embodiment 1 of this invention. It is a hardware block diagram of the control apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the torque ignition timing characteristic which concerns on Embodiment 1 of this invention. It is a figure explaining the ignition timing difference and torque difference for demonstrating a subject. It is a figure explaining calculation of the torque permissible ignition timing difference corresponding to the permissible cylinder torque difference according to the first embodiment of the present invention. It is a figure for demonstrating the ignition timing of each cylinder before and behind the restriction | limiting process which concerns on Embodiment 1 of this invention. It is a figure explaining the reduction | decrease of the torque permissible ignition timing difference according to the increase in the amount of retardation which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the restriction | limiting process by the small allowable ignition timing difference which is the smaller one of the torque allowable ignition timing difference which concerns on Embodiment 1 of this invention, and a comparison allowable ignition timing difference. It is a flowchart which shows the process of the control apparatus which concerns on Embodiment 1 of this invention.

Embodiment 1 FIG.
A control device 50 (hereinafter simply referred to as a control device 50) of the internal combustion engine 1 according to the first embodiment will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an internal combustion engine 1 according to the present embodiment. Although the internal combustion engine 1 according to the present embodiment includes a plurality of cylinders 25 and pistons 5, only one cylinder 25 and piston 5 are shown in FIG. 1 for convenience. The internal combustion engine 1 and the control device 50 are mounted on a vehicle, and the internal combustion engine 1 serves as a driving force source for the vehicle (wheel).

1. Configuration of Internal Combustion Engine 1 First, the configuration of the internal combustion engine 1 will be described. The internal combustion engine 1 has a plurality of cylinders 25 (four cylinders in this example) that combust an air-fuel mixture. The internal combustion engine 1 includes an intake passage 23 that supplies air to each cylinder 25 and an exhaust passage 17 that discharges exhaust gas burned in each cylinder 25. The internal combustion engine 1 includes a throttle valve 6 that opens and closes an intake passage 23. The throttle valve 6 is an electronically controlled throttle valve that is driven to open and close by an electric motor controlled by the control device 50. The throttle valve 6 is provided with a throttle opening sensor 7 that outputs an electrical signal corresponding to the opening of the throttle valve 6.

  An air cleaner 24 that purifies the air sucked into the intake passage 23 is provided at the most upstream portion of the intake passage 23. An air flow sensor 3 that outputs an electrical signal corresponding to the flow rate of the intake air drawn into the intake passage 23 is provided in the intake passage 23 upstream of the throttle valve 6. A portion of the intake passage 23 on the downstream side of the throttle valve 6 is an intake manifold 11 and is connected to a plurality of cylinders 25. The upstream portion of the intake manifold 11 is a surge tank that suppresses intake pulsation.

  The intake manifold 11 is provided with a manifold pressure sensor 8 that outputs an electrical signal corresponding to the manifold pressure that is the pressure of the gas in the intake manifold 11. Only one of the air flow sensor 3 and the manifold pressure sensor 8 may be provided. An injector 13 for injecting fuel is provided at an intake port which is a downstream portion of the intake manifold 11. The injector 13 may be provided so as to inject fuel directly into the cylinder 25.

At the top of each cylinder 25, an ignition plug 18 that ignites an air-fuel mixture and an ignition coil 16 that supplies ignition energy to the ignition plug 18 are provided. Each cylinder 2
5 is an intake valve 14 for adjusting the amount of intake air taken into the cylinder 25 from the intake passage 23 and an exhaust valve 15 for adjusting the amount of exhaust gas discharged from the cylinder to the exhaust passage 17. Is provided. The intake valve 14 is provided with an intake variable valve timing mechanism that makes the valve opening / closing timing variable. The intake variable valve timing mechanism 14 has an electric actuator that changes the opening / closing timing of the intake valve.

  The crankshaft of the internal combustion engine 1 is provided with a signal plate provided with a plurality of teeth on the outer periphery at predetermined angular intervals. The crank angle sensor 9 is fixed to the cylinder block so as to face the teeth of the signal plate of the crankshaft, and outputs a pulse signal synchronized with the passage of the teeth. Although not shown, the camshaft of the internal combustion engine 1 is provided with a signal plate having a plurality of teeth provided at predetermined angular intervals on the outer periphery. The cam angle sensor 10 is fixed to face the teeth of the signal plate of the camshaft, and outputs a pulse signal synchronized with the passage of the teeth.

  The control device 50 detects the crank angle based on the top dead center of each piston 5 and determines the stroke of each cylinder 25 based on the two types of output signals of the crank angle sensor 9 and the cam angle sensor 10. .

  A knock sensor 12 is fixed to the cylinder block. The knock sensor 12 outputs a signal (vibration waveform signal) corresponding to the vibration of the internal combustion engine 1. Knock sensor 12 includes a piezoelectric element or the like.

2. Next, the control device 50 will be described.
The control device 50 is a control device that controls the internal combustion engine 1. As shown in the block diagram of FIG. 2, the control device 50 includes control units such as a knock detection unit 51, an ignition timing calculation unit 52, and an ignition control unit 53. The control units 51 to 53 and the like of the control device 50 are realized by a processing circuit provided in the control device 50. Specifically, as shown in FIG. 3, the control device 50 includes, as a processing circuit, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), and a storage device 91 that exchanges data with the arithmetic processing device 90. , An input circuit 92 for inputting an external signal to the arithmetic processing unit 90, an output circuit 93 for outputting a signal from the arithmetic processing unit 90 to the outside, and the like.

As the arithmetic processing unit 90, an ASIC (Application Specific Integrated Circuit),
An IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, various signal processing circuits, and the like may be provided. Moreover, as the arithmetic processing unit 90, a plurality of the same type or different types may be provided, and each process may be shared and executed. As the storage device 91, a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing device 90, a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing device 90, and the like. Is provided. The input circuit 92 is connected to various sensors and switches, and includes an A / D converter or the like that inputs output signals of these sensors and switches to the arithmetic processing unit 90. The output circuit 93 is connected to electric loads, and includes a drive circuit that outputs a control signal from the arithmetic processing unit 90 to these electric loads.

  The arithmetic processing device 90 executes software (programs) stored in the storage device 91 such as a ROM, and the storage device 91 and the input circuit 92 serve as the functions of the control units 51 to 53 provided in the control device 50. , And in cooperation with other hardware of the control device 50 such as the output circuit 93. Note that setting data such as torque ignition timing characteristics, maps, and judgment values used by the control units 51 to 53 are stored in a storage device 91 such as a ROM as part of software (program).

  In the present embodiment, the input circuit 92 is connected to the air flow sensor 3, the throttle opening sensor 7, the manifold pressure sensor 8, the crank angle sensor 9, the cam angle sensor 10, the knock sensor 12, the accelerator position sensor 26, and the like. ing. The output circuit 93 is connected to the throttle valve 6 (electric motor), the injector 13, the intake variable valve timing mechanism 14, and a plurality of ignition coils 16 (four in this example) for each cylinder. The control device 50 is connected to various sensors, switches, actuators and the like not shown.

  The control device 50 detects the intake air amount based on the output signal or the like of the air flow sensor 3 or the manifold pressure sensor 8, detects the throttle opening based on the output signal of the throttle opening sensor 7, and controls the accelerator position sensor 26. The accelerator opening is detected based on the output signal. The control device 50 detects the angle and rotational speed of the crankshaft and the opening / closing timing of the intake valve 14 based on the output signals of the crank angle sensor 9 and the cam angle sensor 10.

  As a basic control, the control device 50 calculates the fuel injection amount, the ignition timing, and the like based on the input output signals of various sensors, and drives and controls the injector 13, the ignition coil 16, and the like. The control device 50 calculates the output torque of the internal combustion engine 1 requested by the driver based on the accelerator opening, etc., and controls the throttle valve 6 and the like so as to obtain the intake air amount that realizes the requested output torque. Control. Specifically, the control device 50 calculates the target throttle opening, and drives and controls the electric motor of the throttle valve 6 so that the throttle opening approaches the target throttle opening. The control device 50 calculates the target opening / closing timing of the intake valve 14 based on the rotational speed of the crankshaft (internal combustion engine 1), the intake air amount, and the like so that the opening / closing timing of the intake valve 14 approaches the target opening / closing timing. The electric actuator of the intake variable valve timing mechanism 14 is driven and controlled.

2-1. Knock detection unit 51
The knock detection unit 51 performs a knock detection process for detecting, for each cylinder 25, a knock generated in the internal combustion engine 1 provided with a plurality of cylinders 25. Knock detection unit 51 performs a knock frequency component extraction process on the output signal of knock sensor 12. Knock frequency component extraction processing is performed by bandpass filter processing, Fourier transform processing, or the like. The knock detection unit 51 calculates the peak value of the extracted value of the knock frequency component in the knock detection period of each cylinder as the knock detection value VP (m) of each cylinder. The knock detection period of each cylinder is set to, for example, a crank angle interval from the top dead center of each piston to 50 ° CA after top dead center).

  Here, “m” is a cylinder number, and when the number of cylinders is 4, VP (1) is a knock detection value of the first cylinder, and VP (2) is a knock detection value of the second cylinder. VP (3) is a knock detection value of the first cylinder, and VP (4) is a knock detection value of the fourth cylinder.

  The knock detection unit 51 performs a statistical process such as an averaging process for each cylinder on the knock detection value VP (m) of each cylinder to calculate a knock determination value TH (m) for each cylinder. For example, a statistical process is performed on the knock detection value VP (1) of the first cylinder to calculate the knock determination value TH (1) of the first cylinder. This process is performed for each cylinder.

The knock detection unit 51 compares the knock detection value VP (m) of each cylinder with the knock determination value TH (m) of each cylinder to determine the occurrence of knocking in each cylinder. For example, as shown in the following equation, the knock detection unit 51 knocks the first cylinder when the knock detection value VP (1) of the first cylinder is larger than the knock determination value TH (1) of the first cylinder. When the knock detection value VP (1) of the first cylinder is equal to or less than the knock determination value TH (1) of the first cylinder, it is determined that no knock has occurred in the first cylinder. . This knock determination process is performed for each cylinder.
m = 1, 2, 3, 4
1) When VP (m)> TH (m)
Knock occurs in the m-th cylinder (1)
2) When VP (m) ≤ TH (m)
No knock in cylinder m

2-2. Ignition timing calculation unit 52
The ignition timing calculation unit 52 performs an ignition timing calculation process for calculating the ignition timing θrf (m) for each cylinder by performing cylinder-by-cylinder knock retardation control for retarding the ignition timing of the cylinder in which the knock is detected for each cylinder. Run. The ignition timing θrf (m) of each cylinder calculated by the ignition timing calculation unit 52 is a crank angle based on the top dead center of each cylinder.

<Cylinder-specific knock retard control section 52a>
The ignition timing calculation unit 52 includes a cylinder-specific knock retardation control unit 52a that calculates a knock retardation amount Δθr (m) of the ignition timing of each cylinder. The cylinder specific knock retard control unit 52a increases the knock retard amount Δθr (m) of the cylinder in which the knock is detected. For example, as shown in the following equation, when the knock detection unit 51 determines that knocking has occurred in the first cylinder by the knock detection unit 51, the knock retardation amount Δθr (1 ) Is increased by a preset retardation increase amount Kin. On the other hand, when the knock detection unit 51 determines that no knock has occurred in the first cylinder, the cylinder specific knock retardation control unit 52a sets the knock retardation amount Δθr (1) of the first cylinder in advance. The retarded return amount Kdc is decreased. The retard return amount Kdc is set to a value smaller than the retard increase amount Kin. The retardation increase amount Kin may be changed according to the deviation between the knock detection value VP (m) and the knock determination value TH of each cylinder. The cylinder specific knock retardation control unit 52a limits the upper and lower limits of the knock retardation amount Δθr (m) of each cylinder between 0 and the retardation amount upper limit value Δθrmax.
m = 1, 2, 3, 4
1) When knock occurs in the m-th cylinder
Δθr (m) = Δθr (m) + Kin
2) When knock does not occur in the m-th cylinder (2)
Δθr (m) = Δθr (m) −Kdc
Kdc <Kin
0 ≦ Δθr (m) ≦ Δθrmax

<Basic ignition timing calculation unit 52b>
The ignition timing calculation unit 52 includes a basic ignition timing calculation unit 52 b that calculates a basic ignition timing θb based on the operating state of the internal combustion engine 1. The basic ignition timing calculation unit 52b refers to a basic ignition timing map in which the relationship between the operating state such as the rotation speed and charging efficiency of the internal combustion engine 1 and the basic ignition timing θb is set in advance, and the current rotation speed and charging efficiency. The basic ignition timing θb corresponding to the operating state is calculated.

As shown in the following equation, the ignition timing calculation unit 52 retards the basic ignition timing θb by the knock retardation amount Δθr (m) of each cylinder, and the ignition timing θr (m) after the knock retardation of each cylinder. Is calculated.
m = 1, 2, 3, 4
θr (m) = θb−Δθr (m) (3)

<Challenges of knock retard control by cylinder>
However, if the ignition timing is varied for each cylinder by the cylinder-specific knock retard angle control, the torque generated by each cylinder varies. If the torque difference between the cylinders becomes too large, vibration of the internal combustion engine 1 becomes large and torque fluctuations are transmitted to the wheels, which is not desirable. Therefore, in order to keep the torque fluctuation between the cylinders within a desired range, it is conceivable to limit the difference in ignition timing (variation width) between the cylinders.

FIG. 4 shows torque ignition timing characteristics indicating the relationship between the torque generated by each cylinder and the ignition timing. As shown in the following equation, the torque T can be approximated by a quadratic function with the ignition timing θ as a variable. When the ignition timing θ is the maximum torque ignition timing B (θ = B), the torque T becomes the maximum value C.
T = −A × (θ−B) ² + C (4)

  The basic ignition timing θb is basically set near the maximum torque ignition timing B in order to improve fuel consumption. As the ignition timing θ is retarded from the basic ignition timing θb, the torque T decreases. However, as the ignition timing θ moves to the retard side, the decrease amount of the torque T with respect to the retard amount of the ignition timing θ increases. That is, as the retard amount of the ignition timing θ increases, the fluctuation sensitivity of the torque T increases.

  Therefore, as shown in FIG. 5, even if the ignition timing difference Δθm between the cylinders is the same, the most retarded ignition timing θrmax between the cylinders is retarded from the maximum torque ignition timing B by θ1, θ2, θ3. The torque difference ΔTm between the cylinders increases with the change to.

  Therefore, if the ignition timing difference Δθm between the cylinders is limited only to a predetermined width, the torque difference ΔTm between the cylinders may increase or decrease depending on the retard amount of the ignition timing, and cannot be managed. For this reason, it is desired that the ignition timing can be retarded for each cylinder while the torque difference ΔTm between the cylinders is limited within a desirable range even if the retard amount of the ignition timing is changed.

<Ignition timing difference limiting unit 52c>
Therefore, the ignition timing calculation unit 52 includes an ignition timing difference limiting unit 52c that limits the difference in ignition timing between the cylinders. The ignition timing difference limiting unit 52c determines the most retarded ignition timing θrmax which is the most retarded ignition timing among the ignition timings θr (m) of the respective cylinders retarded by the cylinder specific knock retarding control. In addition, the ignition timing difference limiting unit 52c calculates an inter-cylinder allowable torque difference ΔTmax that is a maximum torque difference allowed between the cylinders.

  The ignition timing difference limiting unit 52c uses a torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is set in advance, and the ignition corresponding to the inter-cylinder allowable torque difference ΔTmax at the most retarded ignition timing θrmax. A torque allowable ignition timing difference Δθmax, which is a timing difference, is calculated. Specifically, as shown in FIG. 6, the ignition timing difference limiting unit 52c includes a maximum retard torque Trmax that is a torque corresponding to the most retarded ignition timing θrmax and an allowable torque difference between cylinders to the most retarded torque Trmax. A torque allowable ignition timing difference Δθmax, which is a difference in ignition timing corresponding to a torque difference from the torque obtained by adding ΔTmax, is calculated using torque ignition timing characteristics.

  The ignition timing calculation unit 52 sets the ignition timing θr (m) of each cylinder to the most retarded ignition timing θrmax and the ignition timing on the advance side by a torque allowable ignition timing difference Δθmax from the most retarded ignition timing θrmax. The ignition timing limited within a certain advance angle upper limit ignition timing θamax is calculated as the final ignition timing θrf (m) of each cylinder. For example, as shown in FIG. 7, the ignition timing θr (1) of the first cylinder is the most retarded ignition timing θrmax, the ignition timing θr (2) of the second cylinder, and the ignition timing θr (3) of the third cylinder. The fourth cylinder ignition timing θr (4) is set to the advance side, and the third and fourth cylinder ignition timings θr (3) and θr (4) are the most retarded ignition timing θrmax. Is outside the range of the advance-side upper limit ignition timing θamax (= θrmax + Δθmax), the advance-side upper limit ignition timing θamax becomes the final ignition timing θrf ( 3) and θrf (4) are set.

According to the above configuration, the torque allowable ignition timing difference Δθmax corresponding to the cylinder allowable torque difference ΔTmax is calculated at the most retarded ignition timing θrmax using the torque ignition timing characteristics. Therefore, as shown in FIG. As the most retarded ignition timing θrmax between the cylinders changes from the maximum torque ignition timing B toward the retarded side with θ1, θ2, θ3, the torque allowable ignition timing difference Δθmax corresponding to the inter-cylinder allowable torque difference ΔTmax is decreased. Is able to. Since the ignition timing θr (m) of each cylinder is limited within the range of the torque allowable ignition timing difference Δθmax, even if the retard amount of the ignition timing changes, the inter-cylinder torque difference ΔTm is determined as the allowable cylinder-to-cylinder torque. It can be surely limited within the range of the difference ΔTmax. Further, since the ignition timing θr (m) of each cylinder excluding the most retarded ignition timing θrmax is changed, it is possible to suppress the occurrence of knocking in the cylinder having the most retarded ignition timing θrmax. Therefore, the torque difference between the cylinders can be prevented from becoming too large, the vibration of the internal combustion engine 1 can be suppressed from increasing, and torque fluctuations can be suppressed from being transmitted to the wheels.

  In the present embodiment, the ignition timing difference limiting unit 52c uses, as the torque ignition timing characteristic, a characteristic represented by a quadratic function with the torque T as a variable as shown in the equation (4). The coefficients A, B, and C of the quadratic function are set based on the operating state of the internal combustion engine. For example, the ignition timing difference limiting unit 52c refers to a coefficient setting map in which the relationship between the operating state of the internal combustion engine such as the rotational speed and the charging efficiency and the coefficients A, B, and C is set in advance, and the current internal combustion engine The respective coefficients A, B, and C corresponding to the driving state are calculated.

The ignition timing difference limiting unit 52c calculates the most retarded angle torque Trmax, which is a torque corresponding to the most retarded ignition timing θrmax, using the equation (4), as shown in the following equation.
Trmax = −A × (θrmax−B) ² + C (5)

The ignition timing difference limiting unit 52c uses the following equation obtained by arranging the equation (4) with respect to the ignition timing θ, and uses the following equation to calculate the ignition timing corresponding to the torque obtained by adding the inter-cylinder allowable torque difference ΔTmax to the most retarded torque Trmax. The upper limit ignition timing θamax is calculated.
θamax = √ {(Trmax + ΔTmax−C) / (− A)} + B
... (6)

Then, the ignition timing difference limiting unit 52c calculates the torque allowable ignition timing difference Δθmax by subtracting the most retarded ignition timing θrmax from the advance side upper limit ignition timing θamax. Since the advance side upper limit ignition timing θamax is calculated, the torque allowable ignition timing difference Δθmax may not be calculated.
Δθmax = θamax−θrmax (7)

Alternatively, as a simple method, the ignition timing difference limiting unit 52c calculates the gradient dT / dθ of the torque T at the most retarded ignition timing θrmax using the equation (8) obtained by differentiating the equation (4) with respect to the ignition timing θ. As shown in the equation (9), the allowable torque difference ΔTmax between the cylinders may be divided by the gradient dT / dθ of the torque T to calculate the allowable torque difference Δθmax.
dT / dθ = −2 × A × (θrmax−B) (8)
Δθmax = ΔTmax / (dT / dθ) (9)

<Comparison allowable ignition timing difference>
As shown in FIG. 9, the torque allowable ignition timing difference Δθmax increases when the most retarded ignition timing θrmax is in the vicinity of the maximum torque ignition timing B only by the limitation by the torque allowable ignition timing difference Δθmax. Therefore, the ignition timing difference limiting unit 52c uses the smaller allowable ignition timing difference Δθmaxs, which is the smaller of the torque allowable ignition timing difference Δθmax and the preset comparative allowable ignition timing difference Δθcmax, to determine the ignition timing θr (m ) Is configured to restrict. According to this configuration, even when the most retarded ignition timing θrmax is near the maximum torque ignition timing B, it is possible to prevent the ignition timing difference between the cylinders from becoming too large.

  In the present embodiment, the ignition timing difference limiting unit 52c uses the per-cylinder permissible ignition timing difference Δθcmax (m), which is the permissible ignition timing difference set for each cylinder, as the comparative permissible ignition timing difference. A small allowable ignition timing difference Δθmaxs (m), which is a smaller one of the per-cylinder allowable ignition timing difference Δθcmax (m) and the torque allowable ignition timing difference Δθmax, is determined, and the most retarded ignition timing θrmax is determined for each cylinder. With respect to the cylinder specific advance side upper limit ignition timing θacmax (m) (= θrmax + Δθmaxs (m)), which is the ignition timing on the advance side by a small allowable ignition timing difference Δθmaxs (m) of each cylinder from the most retarded ignition timing θrmax. The ignition timing θr (m) of each cylinder is limited within the range.

The cylinder-by-cylinder allowable ignition timing difference Δθcmax (m) is set in advance based on the knock detectability of each cylinder, which varies depending on the distance between the knock sensor 12 and each cylinder. For example, the cylinder-by-cylinder allowable ignition timing difference Δθcmax (m) of each cylinder is set as follows.
Δθcmax (1) = 1, Δθcmax (2) = 3
Δθcmax (3) = 3, Δθcmax (4) = 1 (10)

  When the torque allowable ignition timing difference Δθmax is set to 2, the small allowable ignition timing differences Δθmaxs (1), (4) between the first cylinder and the fourth cylinder are Δθcmax (1), (4) (= 1) ) And Δθmax (= 2), which is the smaller one, the small allowable ignition timing differences Δθmaxs (2) and (3) between the second and third cylinders are Δθcmax (2), (3) ( = 3) and Δθmax (= 2), whichever is smaller, is set to 2.

  The ignition timing θr (1) of the first cylinder is advanced by the most retarded ignition timing θrmax and a smaller allowable ignition timing difference Δθmaxs (1) (= 1) of the first cylinder than the most retarded ignition timing θrmax. The cylinder-side advance angle upper limit ignition timing θacmax (1) (= θrmax + Δθmaxs (1)) of the first cylinder on the side is limited. The ignition timing θr (2) of the second cylinder is advanced by the most retarded ignition timing θrmax and a small allowable ignition timing difference Δθmaxs (2) (= 2) of the second cylinder from the most retarded ignition timing θrmax. The cylinder-specific advance side upper limit ignition timing θacmax (2) (= θrmax + Δθmaxs (2)) of the second cylinder is limited. The ignition timing θr (3) of the third cylinder is advanced by the most retarded ignition timing θrmax and a small allowable ignition timing difference Δθmaxs (3) (= 2) of the third cylinder from the most retarded ignition timing θrmax. The third cylinder advance angle side upper limit ignition timing θacmax (3) (= θrmax + Δθmaxs (3)) is limited. The ignition timing θr (4) of the fourth cylinder is advanced by the most retarded ignition timing θrmax and a small allowable ignition timing difference Δθmaxs (4) (= 1) of the fourth cylinder from the most retarded ignition timing θrmax. The cylinder-by-cylinder advance side upper limit ignition timing θacmax (4) (= θrmax + Δθmaxs (4)) is limited.

2-3. Ignition control unit 53
The ignition control unit 53 performs an ignition control process for igniting the air-fuel mixture of each cylinder at the ignition timing θrf (m) of each cylinder calculated by the ignition timing calculation unit 52. The ignition control unit 53 energizes the ignition coil 16 of each cylinder during the energization period, and then shuts off the energization to the ignition coil 16 of each cylinder at the ignition timing θrf (m) of each cylinder, and the ignition plug of each cylinder 18 causes a spark discharge. For example, the ignition control unit 53 cuts off the energization to the ignition coil 16 of the first cylinder at the ignition timing θrf (1) of the first cylinder, and causes a spark discharge in the ignition plug 18 of the first cylinder.

2-4. Flowchart A schematic processing procedure (control method of the internal combustion engine 1) of the control device 50 according to the present embodiment will be described based on the flowchart shown in FIG. The processing of the flowchart of FIG. 10 is repeatedly executed at predetermined calculation cycles when the arithmetic processing device 90 executes software (program) stored in the storage device 91.

  In step S01, the knock detection unit 51 executes a knock detection process (knock detection step) for detecting, for each cylinder, a knock generated in the internal combustion engine 1 provided with the plurality of cylinders 25 as described above.

  Next, in step S02, the ignition timing calculation unit 52 performs the cylinder-specific knock retard control for retarding the ignition timing of the cylinder in which knocking has been detected for each cylinder as described above, so that the ignition timing is determined for each cylinder. An ignition timing calculation process (ignition timing calculation step) for calculating θrf (m) is executed. The ignition timing calculation unit 52 determines the most retarded ignition timing θrmax that is the most retarded ignition timing among the ignition timings θr (m) of each cylinder retarded by the cylinder-by-cylinder knock retardation control, An inter-cylinder allowable torque difference ΔTmax, which is a maximum torque difference allowed in The ignition timing calculation unit 52 uses a torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is set in advance, and corresponds to the allowable torque difference ΔTmax between the cylinders at the most retarded ignition timing θrmax. A torque allowable ignition timing difference Δθmax that is a difference in ignition timing is calculated. The ignition timing calculation unit 52 sets the ignition timing θr (m) of each cylinder to the most retarded ignition timing θrmax, which is an ignition timing that is advanced from the most retarded ignition timing θrmax by a torque allowable ignition timing difference Δθmax. The ignition timing limited within the range of the angle side upper limit ignition timing θamax is calculated as the final ignition timing θrf (m) of each cylinder.

  In step S03, the ignition control unit 53 executes an ignition control process (ignition control step) for igniting the air-fuel mixture of each cylinder at the ignition timing θrf (m) of each cylinder calculated by the ignition timing calculating unit 52. To do.

  In the present invention, the embodiments can be appropriately modified or omitted within the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine, 12 knock sensor, 50 Control apparatus of internal combustion engine, 51 Knock detection part, 52 Ignition timing calculation part, 53 Ignition control part, θ ignition timing, θamax advance angle side upper limit ignition timing, θacmax Advance angle side upper limit for each cylinder Ignition timing, θrf (m) Ignition timing of each cylinder, θrmax Most retarded ignition timing, Δθr Knock retardation amount, Δθm Ignition timing difference, Δθmax Torque allowable ignition timing difference, Δθcmax Permissible ignition timing difference for each cylinder, Δθmaxs Small allowable ignition Time difference, T torque, Trmax most retarded torque, ΔTmax Allowable torque difference between cylinders

Claims (6)

A knock detection unit for detecting, for each cylinder, a knock generated in an internal combustion engine provided with a plurality of cylinders;
An ignition timing calculation unit for performing cylinder-by-cylinder knock retardation control for retarding the ignition timing of the cylinder in which knocking is detected for each cylinder, and calculating the ignition timing for each cylinder;
An ignition control unit for igniting an air-fuel mixture of each cylinder at the ignition timing of each cylinder calculated by the ignition timing calculation unit,
The ignition timing calculation unit
Determining the most retarded ignition timing which is the most retarded ignition timing among the ignition timings of each cylinder retarded by the cylinder-specific knock retard control,
Calculate the allowable torque difference between cylinders, which is the maximum torque difference allowed between cylinders,
Torque allowable ignition is a difference in ignition timing corresponding to the allowable torque difference between the cylinders at the most retarded ignition timing using a torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is set in advance. Calculate the time difference,
The ignition timing of each cylinder is limited within the range of the most retarded ignition timing and the advance-side upper limit ignition timing that is the advance timing ignition timing difference by the torque allowable ignition timing from the most retarded ignition timing. A control device for an internal combustion engine that calculates the ignition timing as the final ignition timing of each cylinder.   The ignition timing calculation unit includes an ignition timing corresponding to a torque difference between a most retarded torque that is a torque corresponding to the most retarded ignition timing and a torque obtained by adding the inter-cylinder allowable torque difference to the most retarded torque. The control device for an internal combustion engine according to claim 1, wherein the torque allowable ignition timing difference, which is a difference between the two, is calculated using the torque ignition timing characteristic.   The ignition timing calculation unit uses, as the torque ignition timing characteristic, a characteristic in which torque is represented by a quadratic function with the ignition timing as a variable, and each coefficient of the quadratic function is determined based on an operating state of the internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2, wherein the control device is set.   The ignition timing calculation unit limits the ignition timing of each cylinder by a small allowable ignition timing difference which is a smaller one of the torque allowable ignition timing difference and a preset comparative allowable ignition timing difference. The control apparatus for an internal combustion engine according to any one of the above.   The ignition timing calculation unit uses a per-cylinder permissible ignition timing difference, which is a permissible ignition timing difference set for each cylinder, as the comparative permissible ignition timing difference, and for each cylinder, A small allowable ignition timing difference which is a smaller one of the torque allowable ignition timing difference is determined, and for each cylinder, the most retarded ignition timing and the small allowable ignition timing difference of each cylinder from the most retarded ignition timing. The control apparatus for an internal combustion engine according to claim 4, wherein the ignition timing of each cylinder is limited within a range of a cylinder-by-cylinder advance side upper limit ignition timing that is an advance side ignition timing. A knock detection step of detecting, for each cylinder, a knock generated in an internal combustion engine provided with a plurality of cylinders;
Ignition timing calculation step of performing cylinder-specific knock retard control for retarding the ignition timing of the cylinder in which knock is detected for each cylinder, and calculating the ignition timing for each cylinder;
An ignition control step of igniting an air-fuel mixture in each cylinder at the ignition timing calculated in the ignition timing calculation step,
In the ignition timing calculation step,
Determining the most retarded ignition timing which is the most retarded ignition timing among the ignition timings of each cylinder retarded by the cylinder-specific knock retard control,
Calculate the allowable torque difference between cylinders, which is the maximum torque difference allowed between cylinders,
Torque allowable ignition is a difference in ignition timing corresponding to the allowable torque difference between the cylinders at the most retarded ignition timing using a torque ignition timing characteristic in which the relationship between the torque generated by each cylinder and the ignition timing is set in advance. Calculate the time difference,
The ignition timing of each cylinder is limited within the range of the most retarded ignition timing and the advance-side upper limit ignition timing that is the advance timing ignition timing difference by the torque allowable ignition timing from the most retarded ignition timing. A control method for an internal combustion engine that calculates the ignition timing as the final ignition timing of each cylinder.

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