Patent ID: 12234787

DESCRIPTION OF EMBODIMENTS

Hereinafter, an electronic control device according to an embodiment (hereinafter, referred to as the “present example”) of the present invention will be described with reference to the accompanying drawings.

[Configuration of Internal Combustion Engine]

FIG.1illustrates a configuration of an internal combustion engine99controlled by an electronic control device of the present example.

The internal combustion engine99includes an air flow sensor1that measures an amount of intake air, a compressor2that supercharges the intake air, an intercooler3that cools the supercharged intake air, and a throttle valve4that adjusts the amount of air sucked into a cylinder5. A throttle sensor19for detecting the opening degree of the throttle valve4is provided in the vicinity of the throttle valve4.

In addition, the internal combustion engine99includes an ignition plug6that supplies ignition energy to the cylinder5of each cylinder, a fuel injection device9that injects fuel into the cylinder5of each cylinder, and a piston10that compresses an air-fuel mixture of fuel and gas flowing into the cylinder5. In addition, the internal combustion engine99includes an intake valve7that adjusts the air-fuel mixture flowing into the cylinder5and an exhaust valve8that discharges the exhaust gas after combustion. Note that although only one cylinder is illustrated for the cylinder5inFIG.1to simplify the description, the cylinder5actually includes a plurality of cylinders.

In addition, the internal combustion engine99includes a crank angle sensor11that detects a signal of a signal rotor attached to a crankshaft, and a water temperature sensor12that measures a temperature of cooling water. In addition, the internal combustion engine99includes a turbine13that transmits kinetic energy of the exhaust gas to the compressor2via a shaft, and a three-way catalyst14that purifies harmful substances in the exhaust gas. Then, an A/F sensor15that detects the concentration of oxygen contained in the exhaust gas is attached in the vicinity of the three-way catalyst14.

In addition, the internal combustion engine99includes an EGR passage pipe16that recirculates an exhaust gas (EGR gas) from the downstream of the three-way catalyst14to the upstream of the compressor2, an EGR cooler17that cools the EGR gas, and an EGR valve18that adjusts the flow rate of the EGR gas passing through the EGR passage pipe16. Then, a differential pressure sensor21that detects a differential pressure before and after the EGR valve18is attached in the vicinity of the EGR valve18. Here, the differential pressure before and after the EGR valve18is a difference between the pressure on the upstream side of the EGR valve18and the pressure on the downstream side in the EGR passage pipe16.

In the internal combustion engine99having such a configuration, the fuel injection device9injects fuel into the air sucked into the cylinder5through the intake valve7to generate an air-fuel mixture. The generated air-fuel mixture explodes due to a spark generated from the ignition plug6at a predetermined ignition period, and pushes down the piston10by the combustion pressure to generate a driving force. The exhaust gas after the explosion is sent to the three-way catalyst14through an exhaust pipe, and harmful substances are purified by the three-way catalyst14.

A part of the exhaust gas purified by the three-way catalyst14flows into the EGR passage pipe16without being discharged to the outside, and is used as the EGR gas. After passing through the EGR cooler17and the EGR valve18, the EGR gas joins the intake air upstream of the compressor2. Thereafter, the air-fuel mixture of the EGR gas and the intake air flows into the cylinder5after passing through the intercooler3and the throttle valve4.

The internal combustion engine99controls an amount of intake air, an EGR amount, and a fuel injection amount to form an air-fuel mixture, and burns the air-fuel mixture by ignition to generate thermal energy. The thermal energy moves the piston and rotates the crankshaft through a link mechanism. The rotation of the crankshaft becomes a propulsive force of a vehicle body through a mission.

[Requirements for Improving Combustion Stability of Internal Combustion Engine]

In the internal combustion engine99, when the EGR amount is increased, a pumping loss is reduced, so that efficiency is improved. On the other hand, in the internal combustion engine99, when the EGR amount is increased, a combustion speed decreases, and the combustion becomes unstable eventually.

FIG.2illustrates an example of a change in heat generation due to a change in the EGR rate of the internal combustion engine.

The upper part ofFIG.2compares the heat generation in three cases (a), (b), and (c) of the EGR amount. In the upper part ofFIG.2, a vertical axis represents the amount of heat generated by combustion, and a horizontal axis represents time.

In addition, the middle part ofFIG.2illustrates the combustion torques (vertical axis) in three cases (a), (b), and (c), and the lower part ofFIG.2illustrates the crankshaft rotation speeds (vertical axis) in three cases (a), (b), and (c), and each horizontal axis represents time.

In three cases illustrated in the upper part ofFIG.2, (a)<(b)<(c) is satisfied in the ascending order of EGR. As illustrated in the upper part ofFIG.2, when the EGR increases, the speed at which heat is generated decreases. Then, as illustrated in the middle part ofFIG.2, when the heat generation is delayed, the peak of the combustion torque is also delayed in conjunction therewith. Furthermore, as illustrated in the lower part ofFIG.2, when the peak of the combustion torque is delayed, the rotation of the crankshaft is also delayed.

Such a change in the heat generation speed (the heat generation speed is obtained by time-differentiating the heat generation amount in the upper part ofFIG.2) due to the change in the EGR rate can be detected, for example, by observing a pressure change in the cylinder by using an in-cylinder pressure sensor. By detecting the heat generation speed by using the in-cylinder pressure sensor and increasing the EGR rate when the heat generation speed becomes lower than a certain threshold, it is possible to ensure the stability of combustion. However, there is a problem that the in-cylinder pressure sensor is expensive. In this regard, in the case of the present example, the combustion speed is detected on the basis of the internal combustion engine rotation speed measured by the crank angle sensor.

An in-cylinder pressure P, a combustion torque τcomb, and a rotation speed ω of the internal combustion engine have relationships represented by the following [Expression 1] and [Expression 2].

τc⁢o⁢m⁢b=Pcomb⁢Ac⁢y⁢l⁢R⁢sin⁡(α+β)cos⁢α[Expression⁢1]J⁢ω.=τc⁢o⁢m⁢b+τfric+τiner+τl⁢o⁢a⁢d[Expression⁢2]

Angles α and β and a length R in [Expression 1] are as illustrated in the drawing of the internal combustion engine ofFIG.3. That is, as illustrated inFIG.3, the angle α indicates an angle between a connecting rod32and a central axis o, and the angle β indicates an angle between a crank arm31and the central axis o. The length R is the length of the crank arm31, the in-cylinder pressure is indicated by Pcomb, and the cylinder cross-sectional area is indicated by Acyl.

When the generation of heat by combustion is accelerated, the peak of the in-cylinder pressure Pcombis accelerated, and the peak of the combustion torque is also accelerated as illustrated in the middle part ofFIG.2. Since the combustion torque is the derivative of the rotation speed, that is, the rotational acceleration multiplied by the inertia of the rotational system, the peak of the heat generation can be estimated by searching for the peak of the derivative of the rotation speed ω.

Incidentally, in a case where the rotation speed ω is obtained by the crank angle sensor, the measurement accuracy of the rotation speed ω is determined by the resolution of the crank angle sensor. For example, in a case where the crank angle sensor is a sensor that outputs a pulse every rotation of 10°, the resolution is insufficient as compared with 1° of the resolution expected at the time of controlling the combustion phase. In addition, even when the rotation speed ω obtained discretely is differentiated, the torque cannot be smoothly obtained.

Therefore, in the present example, processing is performed in which the rotation speed ω is approximated by a trigonometric function, and the approximated function is differentiated, so that the rotation speed ω at a pitch of 10° is differentiated to obtain the combustion torque at a pitch of 1°.

Here, it is considered to realize differential operation by a filter.

First, as shown in the following [Expression 3], a filter that differentiates w is denoted by g(t).

ω.⁢(t)=∫g⁡(τ)⁢ω⁡(t-τ)⁢dt[Expression⁢3]

Fourier transform is performed on both sides of [Expression 3] to obtain the following [Expression 4]. In [Expression 4], j is an imaginary unit, f is a frequency, Ω is the Fourier transform of ω, and G is the Fourier transform of a filter g.

j⁢2⁢π⁢f⁢Ω=G⁢Ω[Expression⁢4]

From this, it can be seen that the Fourier transform G of the filter g having the differential characteristic may be expressed by [Expression 5].

G=j⁢2⁢π⁢f[Expression⁢5]

Therefore, in the frequency-gain characteristic of the Fourier transform G of the filter g having the differential characteristic, the frequency f and a gain |G| are proportional to each other as illustrated inFIG.4A. InFIGS.4A,4B, and4C, a vertical axis represents the gain |G|, and a horizontal axis represents the frequency f. As described above, the frequency f and the gain |G| are proportional to each other, but since there is noise in an actual signal, it is necessary to cut the noise.

Therefore, in the case of the present example, as illustrated inFIG.4B, a filter that attenuates the gain is used at a frequency larger than a predetermined frequency f0. Here, the predetermined frequency at which the gain is attenuated is set by experimentally examining the combustion torque or the rotation speed.

FIG.5illustrates a result of Fourier transform of the rotation speed. InFIG.5, a horizontal axis represents a frequency, and a vertical axis represents a frequency intensity on a linear scale. As illustrated inFIG.5, the frequency component of the rotation speed is such that combustion frequency > two times combustion frequency > three times combustion frequency > four times combustion frequency, and the frequency component attenuates as the frequency increases. Furthermore, it is illustrated that the component of five times the combustion frequency is almost the same as the level of noise. Therefore, when the frequency f0 at which the gain is attenuated is set to four times or less the combustion frequency, it is sufficient to reproduce the combustion torque. Even when the frequency is set to be higher than this, only noise is picked up, and thus the accuracy can be improved by setting the frequency to be four times or less.

FIG.6illustrates rotation speeds S11, S12, S13, and S14(solid lines) and combustion torques P11, P12, P13, and P14(broken lines) when the frequency f0 for attenuating the gain is set to the combustion frequency (uppermost part), two times (second part), three times (third part), and four times (lowermost part) thereof. In each drawing, a horizontal axis represents the crank angle, a vertical axis represents the rotation speed, and a position Px of the combustion peak of the combustion torque P11, P12, P13, P14is illustrated in the drawing. In addition, in the four drawings, a line Pa for comparing the position Px of the combustion peak is illustrated at the same position.

As illustrated in the uppermost part ofFIG.6, it can be seen that when the frequency f0 at which the gain is attenuated is the combustion frequency, the combustion torque P11is not appropriately reproduced, and in particular, the position Px of the peak is not sufficiently reproduced. On the other hand, as illustrated in the second part, the third part, and the lowermost part ofFIG.6, it can be seen that the combustion torques P12, P13, and P14are appropriately reproduced when the combustion frequency is set to two times, three times, and four times, respectively, and in particular, the position Px of the peak is reproduced to coincide with the line Pa. In addition, there is almost no difference in the peak position Px between two times and four times.

Therefore, as illustrated inFIG.4C, the frequency at which the gain is attenuated is preferably set within a frequency range of about two times to four times the combustion frequency fcomb. Note that the combustion frequency fcomb, is a reciprocal of the combustion cycle θcomb, and the combustion cycle θcomb, is an interval at which combustion occurs and is 720°/number of cylinders. By setting the frequency f0 for attenuating the gain in this manner, it is possible to achieve both the accuracy of reproduction of the combustion torque and the robustness against noise.

Therefore, as illustrated inFIG.4B, it is sufficient to prepare a filter in which the gain is proportional to the frequency f up to a predetermined frequency f0 and the gain attenuates at a frequency larger than the predetermined frequency f0.

Such a filter can be designed by inverse Fourier transform, a window function method, or the like. With the filter g designed in this manner, the differentiation of ω can be calculated by [Expression 6] and [Expression 7]. Here, N is a ratio between an interval θsenof the crank angle sensor and a combustion torque resolution θestto be obtained, ωNis the rotation angular velocity of the resolution θsenobtained by the crank angle sensor, ω is the rotation angular velocity of the combustion torque resolution θest, and L is the length of the filter, that is, a ratio between the combustion cycle θcomband the combustion torque resolution θest.

ω.⁢(Nn+m)=∑i=0Lg⁡(l)⁢ω⁡(N⁢n+m-l)[Expression⁢6]ω⁢(Nn+m)={ωN(n)m=00m≠0[Expression⁢7]

Note that the relationship among θsen, θest, θcomb, N, and L is summarized inFIG.7.

As illustrated inFIG.7, crank angle sensor signals CS1, CS2, CS3, CS4, and so on are obtained at the intervals θsen, and the ratio (θsen/θest) between the interval θsenand the combustion torque resolution θestto be obtained is denoted by N. In addition, the ratio (θcomb/θest) of the combustion cycle θcomb/combustion torque resolution θestis denoted by L.

Since combustion occurs at constant intervals, the combustion torque and the crank rotation speed have periodicity. The cycle is a combustion cycle θcomb=720°/number of cylinders.

InFIG.4B, it has been described that the attenuation frequency f0 of the filter for smoothing the rotation speed is desirably two times to four times the combustion frequency. The combustion frequency fcombis a reciprocal of the combustion cycle θcomb, and in the example illustrated inFIG.4C, the combustion frequency fcombis set between two times the combustion frequency fcomb(fcomb×2) and four times the combustion frequency fcomb(fcomb×4).

The upper part ofFIG.8illustrates a change S21in the crank rotation speed, and the lower part ofFIG.8illustrates a change S22in the combustion torque. The vertical axis represents the values of the crank rotation speed and the combustion torque, and the horizontal axis represents time.

As illustrated inFIG.8, the combustion torque S22and the crank rotation speed S21have periodicity that changes for each combustion cycle co.

As shown in [Expression 8], when the length L of the filter is determined in accordance with the combustion cycle θcomb, noise on the crank angle sensor signal can be efficiently removed. This is because the signal is repeated in the combustion cycle.

L=θcombθe⁢s⁢t[Expression⁢8]
[Configuration of Combustion State Detection Device]

Next, a configuration of a combustion state detection system that obtains the combustion torque by filtering the rotation speed obtained from the crank angle sensor and detects the combustion peak in the processing described above will be described.

FIG.9illustrates a configuration of a combustion state detection device100to which the combustion state detection system of the present example is applied.

The combustion state detection device100includes a crank angle synchronization processing unit110and a time synchronization processing unit120.

In the detection of the combustion state of the internal combustion engine, when all the processing is performed in a concentrated manner by one processing unit in synchronization with the input of the crank angle sensor detection signal, the load is concentrated, which is not desirable. Therefore, it is preferable that the functions are shared and processed by the crank angle synchronization processing unit110and the time synchronization processing unit120as illustrated inFIG.9.

The crank angle synchronization processing unit110performs processing of calculating the rotation speed from the acquisition of the crank angle sensor detection signal. Then, the crank angle synchronization processing unit110passes the information of the rotation speed for at least two combustion cycles to the time synchronization processing unit120to be activated at constant time intervals (for example, every 10 ms).

The time synchronization processing unit120performs processing of estimating the combustion torque from the received rotation speed for two combustion cycles and detecting the peak of the combustion torque as the combustion phase.

Hereinafter, when the configuration illustrated inFIG.9is described, the detection signal of the crank angle sensor11is a signal that repeats on and off in synchronization with the unevenness of the tooth attached to the crankshaft, and is a pulse signal that falls every time the crankshaft rotates by a certain angle, for example, 10°.

A falling detection unit111of the crank angle synchronization processing unit110detects the falling timing of the detection signal of the crank angle sensor11.

A rotation speed calculation unit112calculates the time from the falling timing detected by the falling detection unit111to the next falling timing, and calculates the crank rotation speed by taking the reciprocal of the calculated time or dividing the interval between the teeth attached to the crankshaft by the calculated time.

The time synchronization processing unit120is activated at constant time intervals such as 10 ms, and when detecting the switching of the combustion cylinder from a cylinder determination signal, receives the rotation speed for the past two combustion cycles from the crank angle synchronization processing unit110.

An upsampling unit121upsamples the signal of the angular resolution of the pitch θsen(for example, 10°) of the crank angle sensor11to improve a sampling rate to the detection resolution θest(for example, 1°).

FIGS.10A and10Billustrate processing in the upsampling unit121. Here, the received rotation speed is denoted by ωN(the vertical axis inFIG.10A), and the rotation speed after the resolution improvement is denoted by w (the vertical axis inFIG.10B). As shown in the following [Expression 9], by using the data S32obtained by performing the processing of inserting “0” into the data S31illustrated inFIG.10Aat timing other than the falling timing (m≠0) as illustrated inFIG.10B, the angular resolution of the rotation speed can be improved.

ω⁢(Nn+m)={ωN(n)m=00m≠0[Expression⁢9]

As illustrated inFIG.4B, a filtering processing unit122calculates the combustion torque by filtering the upsampled rotation speed ω with a characteristic that the gain is proportional to the frequency up to the predetermined frequency f0, and the gain attenuates when the frequency exceeds the predetermined frequency f0.

By performing the processing in this manner, it is possible to estimate the smooth combustion torque with high resolution as illustrated in the lower part ofFIG.8from the rotation speed with rough resolution as illustrated in the upper part ofFIG.8.

The upsampled w has a conspicuous component of the cycle θsenas illustrated inFIG.10B. That is, as illustrated inFIG.10A, compared to the data S31obtained by sampling rotation speed ωNas it is, in ω of data S32obtained by upsampling to the combustion torque resolution θest, only a component synchronized with cycle θsenof the sensor signal is conspicuous as illustrated inFIG.10B.

FIG.11illustrates a characteristic S41obtained by correcting the characteristic of the filter ofFIG.4Cby focusing on the reciprocal θcomb, of the combustion frequency fcombon the horizontal axis. InFIG.11, a vertical axis represents the gain, and a horizontal axis represents the frequency. Assuming an interval of 10° between teeth attached to a normal crankshaft and a four-cylinder internal combustion engine, the sampling cycle θsenof the rotation speed ω is as shown in the following [Expression 10].

θ⁢sen=10∘[Expression⁢10]θ⁢comb=720°/4=1⁢8⁢0°θ⁢sen=θ⁢comb/18

Since the sampling cycle θsenof the rotation speed belongs to the region where the gain of the filter is attenuated, as described inFIGS.10A and10B, the components of the conspicuous sampling cycle are smoothed by upsampling, and the combustion torque synchronized with the combustion cycle is smoothly obtained.

That is, processing in which the received information of the rotation speed or the rotation time is interpolated with the sensor signal itself with respect to the timing at which the sensor signal is received and with zero with respect to the timing at which the sensor signal is not received is performed as the upsampling. Then, with respect to the upsampling result, the combustion torque is calculated by performing filtering processing in which the gain is proportional to the frequency up to a predetermined frequency and the gain attenuates at the predetermined frequency or more, and the peak of the calculated combustion torque is searched for to calculate the combustion phase of the internal combustion engine, whereby the combustion torque synchronized with the combustion cycle is smoothly obtained.

Since the combustion torque output from the filtering processing unit122is repeated for each combustion cycle, a peak search unit123searches for a peak in each combustion cycle. Then, the peak search unit123sets a peak angle as the combustion phase. The information on the combustion phase searched by the peak search unit123is sent to an EGR control unit of the electronic control device. Note that the configuration of the EGR control will be described later with reference toFIG.13.

As illustrated in the lower part ofFIG.8, since the combustion torque is repeated for each combustion cycle θcomb, it is desirable to search for the combustion peak from the combustion torque of the length of the combustion cycle. In addition, when the combustion torque is calculated, it is desirable to perform filtering utilizing the periodicity of the combustion torque or the crankshaft rotation speed. Since the cycle of the combustion torque or the crankshaft rotation speed is the combustion cycle θcomb, it is desirable to set the length of the filter when obtaining the combustion torque to the combustion cycle θcomb.

As described above, the combustion peak is searched for from the combustion torque for one combustion cycle, and each sample value of the combustion torque is calculated from the crankshaft rotation speed for one combustion cycle. On the basis of this, the combustion peak of each combustion cycle is calculated from the crankshaft rotation speed for two combustion cycles.

Therefore, assuming that the information given from the crank angle synchronization processing unit110that calculates the rotation speed or the rotation time to the time synchronization processing unit120that calculates the combustion torque and searches for the peak is the crankshaft rotation speed for two combustion cycles or the crankshaft rotation time for two combustion cycles, the combustion peak can be searched for with excellent visibility.

In addition, a case where the time synchronization processing unit is activated at intervals of 10 ms will be considered. When the four-cylinder internal combustion engine is operated at 3000 rpm, the time during which the internal combustion engine makes one rotation is 20 ms, and the time corresponding to the combustion cycle of 180° is 10 ms. Therefore, by estimating the torque and calculating the combustion peak in all the time synchronization processing activated every 10 ms, the combustion peaks corresponding to all the combustion cycles are obtained.

When the engine speed of the internal combustion engine is less than 3000 rpm, the time corresponding to the combustion cycle is longer than 10 ms, so that it is not necessary to perform combustion torque estimation and combustion peak search in all the time synchronization processing activated every 10 ms. In this regard, if it is determined that the combustion torque estimation and the combustion peak search are performed in the time synchronization processing immediately after the combustion cylinder is switched, it is possible to prevent the combustion peak search from being performed redundantly.

In addition, when the engine speed of the internal combustion engine exceeds 3000 rpm, the time corresponding to the combustion cycle becomes shorter than 10 ms, and thus the time synchronization processing also needs to be activated at a time interval shorter than 10 ms. When the number of cylinders of the internal combustion engine is denoted by C and the engine speed of the internal combustion engine is denoted by Neng [rpm], an activation interval Tjob of the time synchronization processing is given by [Expression 11].

Tjob=120⁢1000C⁢Neng[ms][Expression⁢11]

The combustion state detection device100having such a configuration enables estimation of the combustion torque with high resolution and high accuracy, and enables combustion phase detection with high accuracy on the basis of the estimation.

[Example of Calculation Using Rotation Time]

Even when the rotation speed calculation unit112illustrated inFIG.9performs required rotation time calculation processing, a change in positive/negative sign of the amplitude of the combustion torque is obtained, and the position of the combustion movement does not change.

That is, the relationship between a time T required for the crankshaft to rotate θsenand the angular velocity is as shown in [Expression 12] when T is considered to be divided into an average value T0and an AC component Tdev=T−T0.

ω=θsenT0+Td⁢e⁢v≈θsenT0⁢(1-Td⁢e⁢vT0)[Expression⁢12]

Therefore, when the rotation speed ω is considered to be divided into an average value wo and an AC component ωdev=ω−ω0, [Expression 13] is obtained.

ωd⁢e⁢v=-θsenT02⁢Td⁢e⁢v[Expression⁢13]

Since the filter g is a filter that extracts the AC component, in the example ofFIG.9, whether the filtering processing unit122filters the rotation speed or filters the required rotation time, only a proportionality factor is changed, and the positions of the peaks of the filtering result are the same.

Therefore, even when the rotation speed calculation unit112inFIG.9is replaced with a rotation time calculation unit (required rotation time calculation unit), a change in positive/negative sign of the amplitude of the combustion torque is obtained, and the position of the combustion peak does not change.

[Configuration for Controlling EGR Rate]

Next, the configuration of the electronic control device that controls the EGR rate on the basis of the combustion phase obtained by the combustion state detection device of the present example will be described.

FIG.12illustrates a relationship between the EGR rate, the combustion phase, and the fuel consumption. The upper part ofFIG.12illustrates the relationship between the EGR rate (horizontal axis) and the combustion phase (vertical axis), and the lower part ofFIG.12illustrates the relationship between the EGR rate (horizontal axis) and the fuel consumption (vertical axis). Two lines illustrated in the upper part ofFIG.12indicate an upper limit characteristic S51(upper line) and a lower limit characteristic S52(lower line) of the combustion phase.

As illustrated in the lower part ofFIG.12, when the EGR rate is increased, a fuel consumption characteristic S53is improved by reducing the pumping loss. On the other hand, as illustrated in the upper part ofFIG.12, a difference between the upper limit characteristic S51and the lower limit characteristic S52of the fuel phase also increases as the combustion phase is delayed. That is,FIG.12illustrates that the combustion becomes unstable when the EGR rate is increased.

In this regard, in order to avoid the operation in such an unstable region, the detected combustion phase is compared with a preset limit combustion phase as shown in [Expression 14].

[Combustion⁢Phase⁢Detection⁢Value]>[Expression⁢14][Limit⁢Combustion⁢Phase]

When the relationship of [Expression 14] is satisfied, the electronic control device preferably performs control to reduce the EGR rate.

Alternatively, a variation in the combustion phase is calculated, and it is determined whether the relationship shown in [Expression 15] is satisfied.

[Variation⁢in⁢⁢Combustion⁢Phase]>[Expression⁢15][Allowable⁢Value⁢of⁢Combustion⁢Phase⁢Variation]

When the relationship of [Expression 15] is satisfied, the electronic control device performs control to reduce the EGR rate, thereby increasing the EGR rate to the utmost and reducing the margin of the EGR rate control.

The electronic control device illustrated inFIG.13performs such processing.

That is, an electronic control device200includes the combustion state detection device100(FIG.9), and calculates the combustion phase on the basis of the detection signal of the crank angle sensor11. As described above, the combustion state detection device100here may include a required rotation time calculation unit instead of the rotation speed calculation unit112.

The information on the combustion phase calculated by the combustion state detection device100is supplied to a combustion phase determination unit201.

The combustion phase determination unit201compares the calculated combustion phase with the limit combustion phase as described in [Expression 14]. In addition, the combustion phase determination unit201calculates the variation in the combustion phase and compares the calculated variation with the allowable value of the combustion phase variation as described in [Expression 15] to determine whether the combustion state is stable or unstable.

The EGR control unit202calculates the set value of the opening degree of the EGR valve18so as to increase the EGR rate when the determination result of the combustion phase determination unit201is “stable” and to reduce the EGR rate when the determination result is “unstable”. This result is output to the EGR valve18.

By feedback-controlling the EGR rate in this manner, it is possible to reduce a margin obtained by taking into account the individual difference or deterioration of the internal combustion engine or the accuracy of the differential pressure sensor21of the EGR valve18, increase the EGR rate to the limit, and reduce the fuel consumption.

[Modification]

Note that the present invention is not limited to the above-described embodiments, and includes various modifications.

For example, the combustion phase detected by the combustion state detection device100can be reflected not only in the EGR rate but also in air-fuel ratio control, ignition timing control, and the like.

That is, even when the horizontal axes of the upper part and the lower part ofFIG.12represent the air-fuel ratio instead of the EGR rate, the characteristic diagram having the same tendency is obtained.

In a case where the air-fuel ratio control is performed, the threshold of the combustion phase determination unit201may be set to correspond to the air-fuel ratio, the EGR control unit202may be replaced with an air-fuel ratio control unit, and the fuel injection device9may be controlled instead of the EGR valve18. In this case, the internal combustion engine can be operated at the air-fuel ratio immediately before the combustion becomes unstable, and it is possible to reduce the margin obtained by taking into account the individual difference or deterioration of the internal combustion engine or the accuracy of the differential pressure sensor21of the EGR valve18.

Then, the fuel consumption can be reduced by increasing the air-fuel ratio to the limit. In addition, the reduction effect of NOx emission can also be expected by increasing the air-fuel ratio to the limit in a lean region. The reduction in NOx emission leads to a reduction in the capacity of the exhaust catalyst, so that there is also an effect of cost reduction.

Furthermore, it is also conceivable to control the ignition timing in addition to the EGR rate and the air-fuel ratio.

In ignition, the efficiency is generally increased when the ignition is advanced, so the ignition is advanced until a knock sensor detects knock. Advancing the ignition means advancing the ignition period by a predetermined angle with respect to the top dead center of the crank angle. Here, when the ignition timing is delayed so as to intentionally lower the efficiency of the internal combustion engine for early warming of the air-fuel ratio sensor and the catalyst at the time of starting the internal combustion engine, control is also performed to increase the amount of heat discharged to the exhaust gas accordingly.

FIG.14illustrates a relationship between the ignition timing, the combustion phase, and the exhaust heat amount at this time. In the upper part ofFIG.14, a vertical axis represents the combustion phase, and a horizontal axis represents the ignition timing, and in the lower part ofFIG.14, a vertical axis represents the exhaust heat amount, and a horizontal axis represents the ignition timing. Two lines in the upper part ofFIG.14indicate an upper limit characteristic S61and a lower limit characteristic S62of the combustion phase.

As indicated by a characteristic S63in the lower part ofFIG.14, the exhaust heat amount increases as the ignition timing is delayed, but with this, the combustion phase is delayed and the variation in the combustion phase also increases as shown in the upper part ofFIG.14.

Therefore, similarly to the case of controlling the EGR rate, by determining the stability of the combustion from the combustion phase or the variation thereof, and performing control to delay the ignition timing when the combustion is stable and advance the ignition timing when the combustion is unstable, the ignition timing can be controlled such that the warm-up is accelerated.

Note that on the basis of the combustion phase, the electronic control device200may simultaneously control any one of the EGR valve opening degree, the throttle opening degree, the fuel injection amount, or the ignition timing of the internal combustion engine described above. Alternatively, a plurality of the EGR valve opening degree, the throttle opening degree, the fuel injection amount, and the ignition timing of the internal combustion engine may be simultaneously controlled on the basis of the combustion phase.

In addition, the above-described embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to those having all the described configurations. For example, although the electronic control device200illustrated inFIG.13is configured to incorporate the combustion state detection device100illustrated inFIG.9, the combustion state detection device (combustion state detection system)100may be configured as a device separate from the electronic control device200.

In addition, the configuration of the device illustrated inFIGS.9and13may be configured by dedicated hardware for executing each processing, but may be configured by a program (software), in which a processor realizes each function, so that a computer is caused to execute the program.

The Information such as a program for realizing each function in this case can be stored in a recording medium such as a memory, an IC card, an SD card, or an optical disk in addition to a nonvolatile storage such as an HDD or an SSD.

In addition, in a case where a part or all of the devices illustrated inFIGS.9and13are configured by hardware, the devices may be realized by hardware such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC).

In addition, in the block diagrams illustrated inFIGS.9and13, only the control lines and the information lines considered to be necessary for the description are illustrated, and not all the control lines and the information lines on the product are necessarily illustrated. It may be considered that almost all the components are connected to each other in actual. In addition, the configuration of the internal combustion engine illustrated inFIG.1is also an example, and the internal combustion engine to which the present invention is applied is not limited to the configuration ofFIG.1.

REFERENCE SIGNS LIST

1air flow sensor2compressor3intercooler4throttle valve5cylinder6ignition plug7intake valve8exhaust valve9fuel injection valve10piston11crank angle sensor12water temperature sensor13turbine14three-way catalyst15air-fuel ratio sensor16EGR passage pipe17EGR cooler18EGR valve19throttle sensor21differential pressure sensor31crank arm32connecting rod100combustion state detection device101crank angle sensor110crank angle synchronization processing unit111falling detection unit112rotation speed calculation unit120time synchronization processing unit121upsampling unit122filtering processing unit123peak search unit200electronic control device201combustion phase determination unit202EGR control unit