JP2000234558A - Ignition timing detecting device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate reference pressure (compression pressure of inner-cylinder air exept for the pressure rise due to combustion) according to operation conditions during engine operation, and accurately detect an ignition timing based on the reference pressure and detected value of inner-cylinder pressure. SOLUTION: This device detects waveform of inner-cylinder pressure (motoring pressure) Pm of one cycle at the time of cutting fuel and stores it in a memory. A ratio between a reference pressure Pb (compression pressure of inner-cylinder air except for the pressure rise due to combustion) under the present engine operation condition and the motoring pressure Pm is obtained during engine operation, by comparing pressure Pk detected by the inner cylinder pressure sensor at a crank angle θ0 before ignition to the motoring pressure Pm. At the crank angle after the angle θ0, the motoring pressure Pm read from the memory is multiplied by the pressure ratio, so as to calculate the reference pressure Pb. When the difference between the detected pressure Pk and the reference pressure Pb exceeds the ignition determination value, the ignition timing θf is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition timing detecting device for an internal combustion engine which detects an in-cylinder pressure of an internal combustion engine (engine) and detects an ignition timing from the detected pressure.

[0002]

2. Description of the Related Art The ignition timing of an engine depends on the engine output,
It is a control parameter that directly affects fuel economy and emissions. In general, the ignition timing varies depending on engine operating conditions, environmental conditions, changes over time in the fuel injection system, and the like. In particular, in a diesel engine, the air-fuel mixture is highly compressed and self-ignitions. is there.
Therefore, it is necessary to control the ignition timing in order to improve the engine output, fuel efficiency and emission.

Therefore, in a diesel engine, as shown in Japanese Patent Application Laid-Open No. 9-68081, an in-cylinder pressure sensor detects the in-cylinder pressure and detects a pressure rise due to combustion (ignition) based on the in-cylinder pressure. Therefore, a technology for detecting an actual ignition timing and performing feedback control of the fuel injection timing so as to match the ignition timing with a target ignition timing has been studied.

However, since a diesel engine has a large compression ratio and draws a large amount of air into a cylinder, the compression pressure of the cylinder air (hereinafter referred to as "reference pressure") is relatively higher than the pressure increase due to combustion. growing. For this reason, unless the reference pressure is removed from the detected value of the in-cylinder pressure, the pressure rise due to combustion cannot be accurately detected.

In the above publication, the reference pressure at each crank angle is calculated in advance and stored in a map or the like, and the reference pressure is subtracted from the detected in-cylinder pressure to eliminate the influence of the reference pressure. Combustion pressure (pressure rise due to combustion)
When the combustion pressure exceeds the ignition determination value, the ignition timing is determined.

[0006]

Incidentally, the reference pressure is not constant but changes depending on the engine operating conditions and the like. In particular, the change tends to be large in an engine with a supercharger. Therefore, in the technique disclosed in the above publication, it is necessary to subtract a reference pressure according to the engine operating condition at that time from the detected in-cylinder pressure in order to obtain an accurate combustion pressure. Therefore, it is necessary to calculate the reference pressure at each crank angle in advance for each engine operating condition and store the reference pressure in a map or the like. However, it is practically difficult to calculate and store in advance all the reference pressures for all the engine operating conditions that change every moment. Moreover, it is necessary to store a huge amount of data relating to the reference pressures of all the engine operating conditions, so that a large-capacity memory is required and the cost is increased.

The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to operate an engine without having to calculate a reference pressure for each engine operation condition in advance and store the reference pressure in a map or the like. Provided is an ignition timing detection device for an internal combustion engine that can easily obtain a reference pressure according to engine operating conditions during the operation and accurately detect an ignition timing from a detected value of the in-cylinder pressure using the reference pressure. Is to do.

[0008]

In order to achieve the above object, an ignition timing detecting apparatus for an internal combustion engine according to the first aspect of the present invention comprises: Based on the pressure (hereinafter, referred to as “motoring pressure”), a current pressure of the in-cylinder air (hereinafter, referred to as “reference pressure”) excluding a pressure increase due to combustion is calculated by reference pressure calculation means, and the in-cylinder pressure detection means is calculated. The ignition timing is detected by the ignition timing detection means by comparing the current in-cylinder pressure (hereinafter, referred to as “detected pressure”) detected in the above with the reference pressure.

In this case, the motoring pressure is the in-cylinder pressure during non-combustion under a certain engine operating condition, that is, the compression pressure of in-cylinder air excluding a pressure increase due to combustion. Therefore, since the motoring pressure is equivalent to the reference pressure under the engine operating conditions when the motoring pressure is detected, the motoring pressure is based on the relationship between the engine operating conditions at the time of detecting the motoring pressure and the current engine operating conditions. The reference pressure under the current engine operating conditions can be calculated as data. For this reason, in the present invention, it is possible to easily calculate the reference pressure according to the engine operating condition at the time during the engine operation, without having to previously calculate the reference pressure for each engine operating condition and store it in a map or the like. The ignition timing can be accurately detected from the comparison between the reference pressure and the detected pressure. In addition, since there is no need to store a huge amount of data relating to the reference pressure for each engine operating condition, a large-capacity memory is not required.
Cost can be reduced. Further, since the motoring pressure serving as base data for calculating the reference pressure is detected by the in-cylinder pressure detecting means during the operation of the engine, it is possible to cope with differences in motoring pressure characteristics due to individual differences between the engines.

Here, the fuel injection cut performed at the time of deceleration of the vehicle, at the time of high rotation, or the like is performed because the inside of the cylinder is in a non-combustion state.
It is preferable that the in-cylinder pressure detecting means detects the in-cylinder pressure at the time of fuel injection cut as the motoring pressure. In this way, it is not necessary to create a non-combustion state for detecting the motoring pressure during the operation of the engine, and the motoring pressure can be reduced by using the fuel injection cut at the time of deceleration of the vehicle without impairing the drivability. Can be detected.

It is preferable that the reference pressure is calculated by multiplying the motoring pressure by a coefficient obtained from the pressure ratio between the detected pressure and the motoring pressure.
In other words, the motoring pressure is the detected pressure under the engine operating conditions at the time of detecting the motoring pressure (= the reference pressure at the time of detecting the motoring pressure). The pressure ratio with the reference pressure at the time of detecting the pressure is a powerful parameter for estimating the pressure ratio between the reference pressure under the current engine operating conditions and the reference pressure at the time of detecting the motoring pressure. Therefore, by multiplying the motoring pressure (= the reference pressure at the time of detecting the motoring pressure) by the coefficient obtained from the pressure ratio, the reference pressure under the current engine operating conditions can be easily calculated.

In this case, it is preferable that the pressure ratio between the detected pressure and the motoring pressure is calculated at at least one crank angle before the fuel is ignited.
As shown in FIG. 2, before the fuel ignition, the in-cylinder pressure does not increase due to the combustion, so that the detected pressure and the reference pressure substantially match. Therefore, if the pressure ratio is calculated before the fuel is ignited, it is possible to calculate the pressure ratio which is not affected by the pressure increase due to the combustion, and to accurately calculate the reference pressure even at the crank angle after the fuel is ignited.

By the way, an in-cylinder pressure sensor used as an in-cylinder pressure detecting means sometimes has an offset error in output characteristics depending on operating conditions such as temperature, and this causes a reduction in ignition timing detection accuracy.

As a countermeasure, an offset error of the output characteristic of the in-cylinder pressure detecting means is calculated based on a plurality of detected pressures detected at a plurality of crank angles by the in-cylinder pressure detecting means. The output characteristic of the in-cylinder pressure detecting means may be corrected by the offset error.
With this configuration, even if an offset error occurs in the output characteristics of the in-cylinder pressure detecting means, the ignition timing is accurately detected using the correction value excluding the offset error from the output of the in-cylinder pressure detecting means. be able to.

Further, it is preferable that the motoring pressure is detected by the in-cylinder pressure detecting means under a predetermined condition every time fuel injection is cut, and the stored value of the motoring pressure is updated. In this way, even if the characteristics of the internal combustion engine and the output characteristics of the in-cylinder pressure detecting means change over time, the reference pressure can be accurately calculated based on the latest motoring pressure updated according to the change over time. Therefore, it is possible to prevent a decrease in the detection accuracy of the ignition timing due to a change over time.

In the output characteristics of the in-cylinder pressure detecting means, a gain (output sensitivity) with respect to a pressure change may change due to a use condition, a temporal change, or the like. As a countermeasure, the gain error of the output characteristic of the in-cylinder pressure detecting means is obtained by comparing the motoring pressure detected at at least one crank angle by the in-cylinder pressure detecting means with its standard value. The output of the in-cylinder pressure detecting means may be corrected by the gain error. With this configuration, even if a gain error occurs in the output characteristics of the in-cylinder pressure detecting means, it is possible to accurately detect the ignition timing using the correction value obtained by eliminating the gain error from the output of the in-cylinder pressure detecting means. it can.

The ignition timing may be detected, for example, when the ratio between the detected pressure and the reference pressure exceeds an ignition determination value, the ignition timing is determined. When the pressure difference between the pressure and the reference pressure exceeds the ignition determination value, the ignition timing may be determined. Since the pressure difference between the detected pressure and the reference pressure corresponds to the pressure increase due to combustion, the ignition timing can be accurately detected from the pressure difference.

Here, in a system for calculating the differential pressure between the detected pressure and the reference pressure at every predetermined sampling interval Δθ,
As shown in FIG. 6A, for example, when ignition occurs immediately after calculating the differential pressure ΔP (θf−1) at the sampling timing angle θf−1, the next sampling timing angle θf
The differential pressure ΔP (θf) calculated by (= θf-1 + Δθ) exceeds the ignition determination value F for the first time. In this case, if the sampling timing angle θf is determined to be the ignition timing, a deviation occurs between the detected value of the ignition timing and the actual ignition timing.
For this reason, when the sampling interval Δθ is increased, the detection error of the ignition timing increases, and when the sampling interval Δθ is reduced, the CPU load increases.

As a countermeasure, when the differential pressure between the detected pressure and the reference pressure is calculated every predetermined period,
A characteristic line connecting at least two consecutive pressure differences exceeding the ignition determination value may be obtained, and the time when an extension of this characteristic line exceeds the ignition determination value may be determined as the ignition timing. FIG.
As shown in (b), for example, the differential pressure ΔP is equal to the ignition determination value F
ＰP (θf) and ΔP (θf +
Δθ), and if the crank angle θff at which the extension of the straight line intersects the ignition determination value F is determined as the ignition timing, even if the sampling interval Δθ is increased, the actual ignition timing and the ignition The deviation from the detected value of the timing can be reduced, and the ignition timing can be accurately detected. In addition, since the sampling interval Δθ can be increased, the CPU load can be reduced.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment (1)] An embodiment (1) in which the present invention is applied to a four-cylinder diesel engine will be described below with reference to FIGS.

First, the configuration of the entire engine control system will be described with reference to FIG. An electromagnetic valve type fuel injection valve 12 is attached to each cylinder of the diesel engine 11 which is an internal combustion engine. Each of the fuel injection valves 12 is provided with a common rail fuel that is stored at a high pressure from a high pressure pump (not shown). 13
Distributed through The common rail 13 has a fuel pressure (common rail fuel pressure) distributed to the fuel injection valves 12.
Is installed. Further, one representative cylinder of the diesel engine 11 is provided with an in-cylinder pressure sensor 15 (in-cylinder pressure detecting means) for detecting an in-cylinder pressure.

Further, a crank angle sensor 16 for outputting a pulse signal at predetermined crank angles is provided near the crankshaft 20 of the engine 11, and a cylinder discriminating sensor 17 is provided near the camshaft (not shown). Is installed. Also,
A load sensor 18 such as an accelerator sensor is provided on an accelerator pedal (not shown).

The output signals of the various sensors described above are input to an engine electronic control circuit (hereinafter referred to as “ECU”) 19. The ECU 19 is mainly composed of a microcomputer, and calculates a fuel injection amount and a fuel injection timing based on an engine operating state detected by various sensors.
The fuel injection valve 12 is controlled based on the calculation result.

Further, the ECU 19 calculates the non-combustion in-cylinder pressure (motoring pressure) Pm detected by the in-cylinder pressure sensor 15 under predetermined conditions at the time of fuel injection cut.
In addition to functioning as a reference pressure calculating means for calculating the current in-cylinder air compression pressure (reference pressure) Pb excluding the pressure increase due to combustion, the in-cylinder pressure (detected pressure) Pk detected by the in-cylinder pressure sensor 15 and the reference It functions as ignition timing detection means for detecting the ignition timing based on the pressure difference from the pressure Pb (pressure rise due to combustion). Then, the ECU 19 performs feedback control of the injection timing of the fuel injection valve 12 so that the detected ignition timing matches the target ignition timing.

Here, a method of detecting the ignition timing by the ECU 19 will be described. Motoring pressure P shown in FIG.
The waveform of m (θ) indicates the output of the in-cylinder pressure sensor 15 for one cycle (720 when the predetermined operating condition is satisfied during the fuel injection cut (for example, when the engine speed reaches the predetermined speed N)). ° C) and stored in a non-volatile memory (not shown) such as a backup RAM in the ECU 19. This waveform of the motoring pressure Pm (θ) is newly detected every time a predetermined running time T1 (for example, 100 hours) elapses and a predetermined operating condition is satisfied during the fuel injection cut, and the stored value is updated.

The detected pressure Pk (θ) is detected by the in-cylinder pressure sensor 15 at a predetermined sampling interval Δθ (for example, 1 ° C.). On the other hand, the reference pressure Pb (θ) is
It is calculated as follows from the motoring pressure Pm (θ) and the detected pressure Pk (θ).

Detected pressure Pk (θ) before fuel ignition
Does not include the pressure rise due to combustion, so the reference pressure Pb
(Θ) substantially coincides with (θ). Therefore, the detected pressure Pk (θ at the calculated crank angle θ0 set in the compression stroke before ignition
By calculating the pressure ratio H between 0) and the motoring pressure Pm (θ0) according to the following equation, it is possible to calculate the pressure ratio H that is not affected by the pressure rise due to combustion at all. H = Pk (θ0) / Pm (θ0) Here, the calculated crank angle θ0 is preferably immediately before ignition as much as possible in order to increase the calculation accuracy of the pressure ratio H. For example, BTDC 10 ° C. (before compression top dead center) 10 ° C)
It is good to set to. Also, the crank angle θ at one point before ignition
Although the pressure ratio H may be calculated using only 0, the pressure ratio H may be calculated at a plurality of crank angles before ignition, and an average value of the plurality of pressure ratios H may be used.

By multiplying the motoring pressure Pm (θ) by the pressure ratio H for each crank angle θ after the calculated crank angle θ0, the reference pressure P at each crank angle θ is obtained.
b (θ) is calculated. Pb (θ) = H × Pm (θ) Accordingly, the reference pressure Pb (θ) can be easily calculated.

As shown in FIG. 4, at a crank angle θ after the calculated crank angle θ 0 at which the pressure ratio H is calculated, the detected pressure Pk (θ) and the calculated reference pressure Pb (θ) are obtained at predetermined sampling intervals Δθ. Is calculated by the following equation. ΔP (θ) = Pk (θ) -Pb (θ) Since this differential pressure ΔP (θ) corresponds to the pressure increase due to combustion, this differential pressure ΔP (θ) is compared with an ignition determination value F, The crank angle θf at which the pressure difference ΔP (θ) exceeds the ignition determination value F is determined as the ignition timing. As a result, the ignition timing can be accurately detected by extracting only the pressure increase due to combustion from the detected pressure Pk (θ). The ignition determination value F is
For example, the pressure may be set to 100 kPa in consideration of the detection error.

The detection of the ignition timing by the ECU 19 described above is executed by the ignition timing detection program shown in FIG. This program is executed every predetermined time or every predetermined crank angle, and the ignition timing of the representative cylinder provided with the in-cylinder pressure sensor 15 is detected. When the present program is started, first, in step 101, it is determined whether or not the accumulated traveling time since the previous update of the waveform of the motoring pressure Pm (θ) has exceeded a predetermined time T1 (for example, 100 hours). I do. If the accumulated traveling time has not reached the predetermined time T1, the process proceeds to step 105 without updating the waveform of the motoring pressure Pm (θ).

On the other hand, if the integrated running time exceeds the predetermined time T1, the routine proceeds to step 102, where the predetermined operating condition is satisfied during the fuel injection cut (for example, when the engine speed reaches the predetermined speed N). ), The output of the in-cylinder pressure sensor 15 is read as the motoring pressure Pm (θ) for one cycle, and the data of the motoring pressure Pm (θ) stored in the nonvolatile memory of the ECU 19 is updated.
Thereafter, in step 103, it is determined whether or not the updated peak pressure Pmax of the motoring pressure Pm (θ) is higher than a predetermined value Ps. If the peak pressure Pmax is equal to or less than the predetermined value Ps, it is determined that the in-cylinder pressure is abnormally reduced.
Proceeding to step 104, an abnormal display is made by lighting a warning lamp (not shown) or the like to notify the driver of the abnormal decrease in the in-cylinder pressure, and the program ends.

On the other hand, if it is determined in step 103 that the peak pressure Pmax is higher than the predetermined value Ps,
It is determined that the in-cylinder pressure is normal, and the routine proceeds to step 105. In this step 105, the waveform of the motoring pressure Pm (θ) stored in the nonvolatile memory of the ECU 19 is read, and in the next step 106, the current crank angle θ
Is compared with the calculated crank angle θ0 (for example, BTDC 10 ° C.).
Wait at 6. Thereafter, when the calculated crank angle θ0 is reached, the routine proceeds to step 107, where the detected pressure Pk (θ0) and the motoring pressure Pm (θ
0) is calculated by the following equation, and step 106
Return to H = Pk (θ0) / Pm (θ0)

Thereafter, the crank angle θ is calculated as the calculated crank angle θ.
When it exceeds 0, the process proceeds from step 106 to step 108, and for each crank angle θ after the calculated crank angle θ0,
By multiplying the motoring pressure Pm (θ) by the pressure ratio H, the reference pressure Pb (θ) at each crank angle θ is calculated by the following equation. Pb (θ) = H × Pm (θ) The data of the reference pressure Pb (θ) is temporarily stored in a memory such as a RAM in the ECU 19 until this program ends.

After calculating the reference pressure Pb (θ), step 1
09, the crank angle θ after the calculated crank angle θ0
The differential pressure ΔP (θx) in the following (hereinafter referred to as θx) is calculated by the following equation. ΔP (θx) = Pk (θx) -Pb (θx)

Thereafter, the routine proceeds to step 110, where the differential pressure ΔP
It is determined whether or not (θx) exceeds the ignition determination value F. If the differential pressure ΔP (θx) is equal to or less than the ignition determination value F, step 1 is executed.
In step 11, it is determined whether the current crank angle θx has exceeded the ignition detection end crank angle θk. The ignition detection end crank angle θk is set to a crank angle near the end of the expansion stroke. Therefore, if ignition is performed normally, the differential pressure ΔP (θx) exceeds the ignition determination value F by the ignition detection end crank angle θk.

Until it is determined in step 111 that the crank angle θx exceeds the ignition detection end crank angle θk,
The above-described processing of steps 106 → 108 → 109 → 110 is repeated, and the processing of comparing the differential pressure ΔP (θx) with the ignition determination value F is repeated. In step 110, the differential pressure ΔP (θ
x) is determined to be greater than the ignition determination value F,
Proceeding to step 112, the ignition is determined, the crank angle θf at that time is stored as the ignition timing, and the program is terminated.

On the other hand, at step 110, the differential pressure ΔP (θx
If it is determined in step 111 that the crank angle θx has exceeded the ignition detection end crank angle θk without determining that the ignition determination value F has exceeded the ignition determination value F, it is determined that a misfire has occurred and the process proceeds to step 113 to display a misfire. To inform the driver of the misfire and terminate the program.

By the way, as in the conventional example shown by a broken line in FIG. 3, for example, when a reference pressure corresponding to a low engine load is calculated and stored in advance and this reference pressure is applied to all engine operating conditions, the engine At the time of high load, the reference pressure greatly differs from the actual reference pressure, and the ignition timing may be erroneously detected. As a countermeasure, if the reference pressure is calculated in advance for each engine operating condition and stored in a map or the like, and the reference pressure corresponding to the engine operating condition is obtained from the map or the like, the ignition timing detection accuracy can be improved. However, it is practically difficult to calculate and store all the reference pressures in advance for all the ever-changing engine operating conditions. In addition, it is necessary to store a large amount of data relating to the reference pressure for each engine operating condition, and there is a disadvantage that a large-capacity memory is required and the cost is increased.

On the other hand, in this embodiment (1), FIG.
Focusing on the point where the detected pressure Pk (θ0) at the calculated crank angle θ0 before the fuel ignition and the reference pressure Pb (θ0) at the calculated crank angle θ0 of the engine operating conditions at that time substantially match as shown in FIG. By calculating the pressure ratio H between the detected pressure Pk (θ0) and the motoring pressure Pm (θ0) at the calculated crank angle θ0 before ignition, the pressure between the reference pressure Pb and the motoring pressure Pm under the current engine operating conditions is calculated. The ratio H is calculated, and the motoring pressure Pm (θx
) Is multiplied by the pressure ratio H to obtain each crank angle θx
, The reference pressure Pb (θx) is calculated. As a result, the pressure ratio H is completely unaffected by the pressure rise due to combustion.
, The reference pressure Pb of the crank angle after fuel ignition (θ
x) can be accurately calculated, and the reference pressure Pb
(Θx) and the pressure difference ΔP (θx) between the detected pressure Pk (θx)
Thus, the ignition timing can be detected with high accuracy. Moreover, since it is not necessary to previously calculate the reference pressure for each engine operating condition and store the reference pressure in a map or the like unlike the related art, a large-capacity memory is not required, and the cost can be reduced accordingly.

In the above-described embodiment (1), the in-cylinder pressure sensor 1 is used at the time of fuel injection cut which is performed when the vehicle is decelerated.
Since the motoring pressure Pm is detected in step 5, differences in motoring pressure characteristics due to individual differences between individual engines can be dealt with, and variations in ignition timing detection accuracy due to individual differences between engines can be reduced. . Moreover, since the motoring pressure Pm is updated every time the predetermined time T1 has elapsed, even if the engine characteristics and the output characteristics of the in-cylinder pressure sensor 15 change over time, the motoring pressure Pm is updated based on the updated motoring pressure Pm. The reference pressure Pb can be calculated with high accuracy, and it is possible to prevent a decrease in the detection accuracy of the ignition timing due to a temporal change.

In the above embodiment (1), the motoring pressure Pm is updated every elapse of the predetermined time T1, but may be updated every elapse of the predetermined travel distance.
The in-cylinder pressure sensor 15 may be of a type that is integrated with the fuel injection valve 12 and a glow plug (not shown).

Further, in the above embodiment (1), the ignition timing is detected for the representative cylinder provided with the in-cylinder pressure sensor 15, but the in-cylinder pressure sensor 15 is provided for all cylinders, The ignition timing detection program of FIG. 5 may be executed for each cylinder to detect the ignition timing for each cylinder.

Further, the ignition timing detection method according to the above-mentioned embodiment (1) includes the detection of the ignition timing of pilot injection performed prior to the main injection for generating the engine output, and the compression in a so-called "uniform premixed combustion system". It may be applied to the detection of the ignition timing of the fuel injection in the first half of the stroke.

[Embodiment (2)] As shown in FIG. 6A, when ignition occurs immediately after the sampling timing angle θf-1, the next sampling timing angle θf (= θf−
It is determined that the differential pressure ΔP (θf) has exceeded the ignition determination value F for the first time when it has reached 1 + Δθ). In this case, if the sampling timing angle θf is determined to be the ignition timing, a deviation occurs between the detected value of the ignition timing and the actual ignition timing. For this reason, if the sampling interval Δθ is increased, the detection error of the ignition timing increases, and if the sampling interval Δθ is reduced, the CPU load of the ECU 19 increases. The deviation from the actual ignition timing becomes large.

In consideration of such circumstances, in the embodiment (2) of the present invention, as shown in FIG. 6B, in the region where the differential pressure ΔP exceeds the ignition determination value F, the sampling timing angle θf At the next sampling timing angle θf + Δθ and the differential pressure ΔP (θf + Δ
θ), and the crank angle θff at the intersection of the extension line of the differential pressure rise straight line A and the ignition determination value F is determined as the ignition timing. Thus, even if
Even if the sampling interval Δθ is increased, the deviation width between the actual ignition timing and the detected value of the ignition timing can be reduced, and the ignition timing can be detected with high accuracy. Moreover, since the sampling interval Δθ can be increased, the ECU
Nineteen CPU loads can also be reduced.

The ignition timing correction as described above is executed by an ignition timing correction program shown in FIG. When this program is started, first, in step 201, the differential pressure Δ
It is determined whether or not P exceeds the ignition determination value F. When the pressure difference ΔP exceeds the ignition determination value F, the process proceeds to the next step 202, where the pressure difference ΔP (θ at the sampling timing angle θf is determined.
f) and the differential pressure ΔP (θf + Δθ) at the next sampling timing angle θf + Δθ is calculated.

Thereafter, the routine proceeds to step 203, where the differential pressure ΔP
(Θf) and the differential pressure ΔP (θf + Δθ) are determined, the crank angle θff at the intersection of the differential pressure rise straight line A and the ignition determination value F is determined, and the crank angle θff is determined as the ignition timing. Is determined (step 204).

In the above embodiment (2), the differential pressure rise straight line A is obtained from the differential pressure ΔP at two consecutive crank angles exceeding the ignition determination value F. A differential pressure rise straight line (or a differential pressure rise curve) may be obtained from the differential pressure ΔP at the above crank angle.

[Embodiment (3)] Next, an embodiment (3) of the present invention will be described with reference to FIGS. The in-cylinder pressure sensor 15 may have an offset error in its output characteristics depending on operating conditions such as temperature (see FIG. 8A), which causes a reduction in ignition timing detection accuracy. This offset error can be obtained as follows.

Here, the offset error is b, the detected pressures at the crank angles θ1 and θ2 (where θ1 <θ2 <θ0) before ignition are Ps (θ1) and Ps (θ2), respectively, and the true in-cylinder pressure is Assuming that Pt (θ1) and Pt (θ2), they can be expressed as follows. Ps (θ1) = Pt (θ1) + b (1) Ps (θ2) = Pt (θ2) + b (2)

Further, assuming that the state change of the in-cylinder air from the crank angle θ1 to the crank angle θ2 is an adiabatic change, the following equation can be obtained. Pt (θ1) × ｛V (θ1)｝ γ = Pt (θ2) × {V (θ2)} γ Pt (θ2) / Pt (θ1) = {V (θ1) / V (θ2)} γ = K (3) where V (θ) is the cylinder volume, γ is the specific heat ratio, and K is V
(Θ) and γ.

By solving the above equations (1) to (3), the offset error b can be calculated by the following equation. b = 1 / (K−1) × {K × Ps (θ1) −Ps (θ2)} (4) If this offset error b is subtracted from the output of the in-cylinder pressure sensor 15, the in-cylinder pressure sensor 15 Can be corrected.

The output characteristics of the in-cylinder pressure sensor 15 are as follows:
The gain (output sensitivity) with respect to the pressure change may change due to use conditions, aging, and the like (see FIG. 9), which also reduces the ignition timing detection accuracy. This gain error can be obtained as follows.

Here, the gain error is a, and the standard value of the motoring pressure at the calculated crank angle θ0 is Pmt (θ0
), Assuming that the detected value of the motoring pressure is Pms (θ0), the following expression can be obtained. The standard value Pmt (θ0) of the motoring pressure is calculated from the calculated crank angle θ0.
Is the standard motoring pressure in, set in advance based on design data, or in the initial state (before deterioration)
The motoring pressure detected by the in-cylinder pressure sensor 15 may be used. Pms (θ0) = a × Pmt (θ0)

Therefore, the gain error a can be calculated by the following equation. a = Pms (θ0) / Pmt (θ0) (5) By dividing the output of the in-cylinder pressure sensor 15 by the gain error a, the gain error of the output of the in-cylinder pressure sensor 15 can be corrected. . Since the detected value Pms (θ0) of the motoring pressure changes depending on the engine operating conditions such as the engine speed, a standard value Pmt (θ0) is set for each engine operating condition, and the standard value Pmt (θ0) is set according to the engine operating condition at that time. It is preferable to select the standard value Pmt (θ0).

In the present embodiment (3), the ECU 19 executes the ignition timing detection program shown in FIGS. 10 and 11 to obtain the output of the in-cylinder pressure sensor 15 using the above equations (4) and (5). In addition to functioning as offset error correction means and gain error correction means for correcting the offset error and gain error of the characteristic, the ignition timing is detected using the differential pressure in which the offset error and gain error have been corrected.

The ignition timing detection program shown in FIGS. 10 and 11 is executed every predetermined time or every predetermined crank angle.
When this program is started, first, at step 301
Then, the waveform of the motoring pressure Pm (θ) is updated. As a result, the motoring pressure Pm (θ) is updated in accordance with the temporal change in the output characteristics of the in-cylinder pressure sensor 15.
It should be noted that the motoring pressure Pm (θ) is updated by one cycle when the predetermined operating condition is satisfied during the fuel injection cut, as in the embodiment (1).
And updates the data of the motoring pressure Pm (θ) stored in the nonvolatile memory of the ECU 19.

Thereafter, at step 302, the motoring pressure Pm (θ
1), Pm (θ2) is read out and the motoring pressure Pm
The offset error bm of (θ) is calculated by the following equation. bm = 1 / (K-1) × ｛K × Pm (θ1) −Pm (θ
2)｝

In the next step 303, the offset error of the motoring pressure Pm (θ) is corrected by using the offset error bm according to the following equation. Pm ′ (θ) = Pm (θ) −bm The motoring pressure Pm ′ (θ) after the offset error correction obtained in this way is temporarily stored in a memory such as a RAM of the ECU 19 until this program ends. Remember.

Thereafter, when the crank angle θ becomes the crank angle θ1, the detected pressure Pk (θ1) is detected.
When the crank angle θ becomes the crank angle θ2, the detected pressure Pk (θ2) is detected, and the offset error bk of the detected pressure Pk (θ) is calculated by the following equation (steps 304 to 3).
08). bk = 1 / (K−1) × ｛K × Pk (θ1) −Pk (θ
2)｝

After that, the crank angle θ is calculated.
When it becomes 0, the process proceeds from step 309 to step 310, in which the motoring pressure Pm '(θ0) after the offset error correction at the calculated crank angle θ0 and the standard value Pmt (θ0) of the motoring pressure at the calculated crank angle θ0.
) Is read from the nonvolatile memory of the ECU 19, and the gain error a is calculated by the following equation. a = Pm '(. theta.0) / Pmt (.theta.0) At this time, the standard value Pmt (.theta.0) of the motoring pressure should preferably be selectable according to the engine operating conditions.

In the next step 311, the offset error b
Using k, the offset error of the detected pressure Pk (θ0) is corrected by the following equation. Pk '(θ0) = Pk (θ0) -bk

Thereafter, at step 312, the pressure ratio H 'between the detected pressure Pk' (. Theta.0) after the offset error correction and the motoring pressure Pm '(. Theta.0) after the offset error correction.
Is calculated by the following equation. H '= Pk' (θ0) / Pm '(θ0)

Thereafter, the crank angle θ is calculated by the calculated crank angle θ.
When it exceeds 0, the process proceeds from step 309 to step 313, where the detected pressure Pk (θ) is calculated using the offset error bk.
Is corrected by the following equation. Pk ′ (θ) = Pk (θ) −bk

In the next step 314, the reference pressure Pb '(θ) after the offset error correction is calculated by the following equation. Pb ′ (θ) = H ′ × Pm ′ (θ)

In the next step 315, the gain error of the differential pressure ΔP ′ (θ) between the detected pressure Pk ′ (θ) after the offset error correction and the reference pressure Pb ′ (θ) is calculated using the gain error a. Correct by the formula. ΔP ′ (θ) = 1 / a × {Pk ′ (θ) −Pb ′
(Θ)｝ The differential pressure ΔP ′ (θ) calculated in this manner is a value in which both the offset error and the gain error have been corrected.

Thereafter, at step 316, the differential pressure ΔP '
It is determined whether or not (θ) exceeds the ignition determination value F ′. If the differential pressure ΔP ′ (θ) is equal to or less than the ignition determination value F, the above-described processing of steps 309 → 313 → 314 → 315 → 316 is performed. The process of repeatedly comparing the differential pressure ΔP ′ (θ) with the ignition determination value F is repeatedly executed.

Thereafter, at step 316, the differential pressure ΔP '
When it is determined that (θ) exceeds the ignition determination value F ′,
Proceeding to step 317, ignition is determined, the crank angle θ'f at that time is stored as the ignition timing, and the program ends.

In the embodiment (3) described above, even if an offset error or a gain error occurs in the output of the in-cylinder pressure sensor 15 due to a use condition or a change over time, the offset error or the gain error is obtained and the detected pressure is detected. Since the motoring pressure and the differential pressure are corrected, the ignition timing can be detected using the data from which the offset error and the gain error of the output of the in-cylinder pressure sensor 15 have been removed, and the ignition timing can be detected with higher accuracy. It is possible.

In the embodiment (3), the standard value Pmt of the motoring pressure at one crank angle θ0 is set.
(Θ0) is stored, and the gain error a is obtained at one crank angle θ0, but the standard value Pmt of the motoring pressure is obtained.
The waveform of (θ) may be stored, a gain error may be obtained at two or more crank angles, and the average value thereof may be used as the gain error.

In the above embodiment (3), after the offset errors of both the detected pressure and the motoring pressure are corrected, the gain error of the differential pressure between the detected pressure after the offset error correction and the reference pressure is corrected. However, conversely, the offset error may be corrected after the gain error is corrected, and both the offset error and the gain error are read at the stage of reading the output of the in-cylinder pressure sensor 15. May be corrected. In short, the offset error and the gain error may be corrected before the differential pressure is compared with the ignition determination value. Alternatively, only one of the offset error and the gain error may be corrected.

[Embodiment (4)] Next, an embodiment (4) of the present invention will be described with reference to FIGS. In the present embodiment (4), as shown in FIG. 12, a NOx catalyst 22 is provided in the exhaust pipe 21 of the engine 11 in addition to the system configuration described in FIG. This NOx catalyst 22 is a catalyst component (for example, Cu-zeolite or Pt-) that can reduce and purify NOx (nitrogen oxide) in the presence of a reducing agent (HC) even in an oxygen-excess atmosphere on the surface of a carrier such as ceramic or metal. (Zeolite).

The fuel injection valve 12 is, as shown in FIG.
A main injection for generating the engine output is performed near the compression top dead center, and a pilot injection is performed prior to the main injection. Further, the expansion stroke after the main injection (for example, AT
DC 90-180 ° C.), post-injection to inject a small amount of fuel (eg, 1-5% of main injection)
Fuel (HC) as a reducing agent is supplied to the NOx catalyst 22.

Normally, the post-injection is performed at a time when the temperature in the cylinder is lower than the combustion temperature of the fuel. Therefore, the post-injected fuel does not burn, and is appropriately decomposed (reformed) by the heat of combustion in the cylinder. ) To change to low boiling point HC having high reactivity (small molecular weight). This gives N
The amount of reaction in the Ox catalyst 22 is increased to increase the NOx purification rate.

However, when the engine output is large,
Since the temperature in the cylinder increases, the post-injected fuel burns in the cylinder, is not supplied to the NOx catalyst 22, and the NOx purification rate decreases.

To prevent this, it is only necessary to retard the post-injection timing, but if it is too retarded, the temperature in the cylinder becomes too low, and the post-injected fuel is not sufficiently thermally decomposed. Low boiling (high molecular weight) high boiling point HC
Increases, and the NOx purification rate decreases.

Therefore, in this embodiment (4), when the post-injection fuel is ignited (combusted), as shown in FIG.
Focusing on the point where the differential pressure ΔP between the detected pressure Pk and the reference pressure Pb increases, the post-injection timing correction program shown in FIG. 16 is executed, whereby the post pressure is determined based on the differential pressure ΔP between the detected pressure Pk and the reference pressure Pb. Determine the presence or absence of ignition of the injected fuel,
The post-injection timing is corrected accordingly.

The post-injection timing correction program shown in FIG.
It is determined whether or not ignition has occurred only when the temperature is .theta.B (for example, ATDC 90 to 180.degree. A). That is, it is determined whether or not the ignition timing is within the range of θA to θB.

When the program is started, first, in step 401, it is determined whether or not the crank angle θ is equal to or larger than the crank angle θA. When the crank angle θ is equal to or larger than the crank angle θA, the process proceeds to step 402. In the same way as 1),
The differential pressure ΔP (θ) between the detected pressure Pk and the reference pressure Pb is calculated, and in the next step 403, the differential pressure ΔP calculated this time is calculated.
It is determined whether the difference between (θ) and the previously calculated differential pressure ΔP (θ-1) is greater than the ignition determination value ΔP1.

If .DELTA.P (.theta.)-. DELTA.P (.theta.-1) is equal to or smaller than the ignition determination value .DELTA.P1, the routine proceeds to step 404, where it is determined whether or not the crank angle .theta.
Each time it is determined that θB, steps 402 and 40 described above are performed.
Step 3 is repeated. If it is determined in step 403 that ΔP (θ) −ΔP (θ−1) is larger than the ignition determination value ΔP1 before θ ≧ θB, the process proceeds to step 405, where the post-injection fuel is ignited ( (Combustion). In this case, since HC is no longer supplied to the NOx catalyst 22, the process proceeds to step 406, and the post injection timing is retarded. As a result, the temperature in the cylinder during the post-injection decreases, so that the combustion of the post-injection fuel is suppressed.

On the other hand, in step 403, ΔP (θ) -Δ
If it is not determined that P (θ-1) is greater than the ignition determination value ΔP1 and θ ≧ θB, step 404 is reached.
Then, the process proceeds to step 407, where it is determined that the post-injection fuel is not ignited (burned). However, if the post-injection timing is too late, the temperature in the cylinder is too low and the post-injection fuel is not sufficiently thermally decomposed, so that a high NOx purification rate cannot be obtained. Therefore, if the post-injection fuel is not ignited (burned), the post-injection timing is advanced in step 408. Thereby, the temperature in the cylinder at the time of post-injection increases, so that thermal decomposition of the post-injection fuel is promoted, and the NOx purification rate is increased.

In the above manner, the post-injection timing is corrected to a time immediately before the post-injection fuel starts to ignite, and the post-injection fuel is thermally decomposed most efficiently with almost no combustion. HC can be supplied to the NOx catalyst 22, and the NOx purification rate can be improved.

In each of the embodiments (1) to (4),
Although the present invention is applied to a four-cylinder diesel engine having a common-race type injection system, the present invention may be applied to a diesel engine having an injection system other than the common rail type or a diesel engine other than the four-cylinder type.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an entire system according to an embodiment (1) of the present invention.

FIG. 2 is a diagram showing waveforms of a detected pressure, a reference pressure, and a motoring pressure.

3A and 3B are diagrams illustrating characteristics of a detected pressure and a reference pressure in the embodiment (1) and a conventional method, wherein FIG. 3A is a diagram when the engine is under a low load, and FIG. .

FIG. 4 is a diagram for explaining a method of detecting an ignition timing.

FIG. 5 is a flowchart showing a flow of processing of an ignition timing detection program according to the embodiment (1).

FIGS. 6A and 6B are diagrams for explaining a method of correcting ignition timing detection in the embodiment (2).

FIG. 7 is a flowchart showing a processing flow of an ignition timing detection correction program according to the embodiment (2).

8A is a diagram illustrating output characteristics of an in-cylinder pressure sensor before offset error correction, and FIG. 8B is a diagram illustrating output characteristics of an in-cylinder pressure sensor after offset error correction.

FIG. 9 is a diagram for explaining a gain error of an output characteristic of the in-cylinder pressure sensor.

FIG. 10 is a flowchart (part 1) illustrating a processing flow of an ignition timing detection program according to the embodiment (3).

FIG. 11 is a flowchart (part 2) illustrating a processing flow of an ignition timing detection program according to the embodiment (3).

FIG. 12 is a diagram illustrating a schematic configuration of an entire system according to an embodiment (4).

FIG. 13 is a time chart showing timings of pilot injection, main injection, and post injection.

FIG. 14 is a diagram showing a change characteristic of a temperature in a cylinder.

FIG. 15 is a diagram for explaining a method for detecting the ignition timing of post-injection fuel.

FIG. 16 is a flowchart illustrating a flow of a post injection timing correction program process according to the embodiment (4).

[Explanation of symbols]

11: diesel engine (internal combustion engine), 12: fuel injection valve, 15: in-cylinder pressure sensor (in-cylinder pressure detecting means), 1
6 ... Crank angle sensor, 19 ... ECU (reference pressure calculation means, ignition timing detection means, offset error correction means, gain error correction means), 22 ... NOx catalyst.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301H 301J 301Z (72) Inventor Kazuo Kobayashi 1-chome, Showa-cho, Kariya-shi, Aichi Prefecture No. 1 In Denso Co., Ltd. (72) Inventor Kanehito Nakamura 1-chome, Showa-cho, Kariya-shi, Aichi F-term (reference) 3G084 BA13 BA15 BA17 BA33 CA00 DA04 DA27 EA05 EA11 EB06 EB12 EB25 EC04 FA19 FA21 FA38 3G301 HA02 JA01 JA15 JA21 KA16 KA26 MA11 MA18 MA23 MA26 NA08 NB03 NC01 ND01 PB08Z PC00A PC00Z PC01Z PE03Z PE05Z PF03Z

Claims (9)

[Claims] 1. An ignition timing detection device for an internal combustion engine which detects in-cylinder pressure of an internal combustion engine by an in-cylinder pressure detection means and detects an ignition timing based on the detected value. Based on the detected in-cylinder pressure during non-combustion (hereinafter referred to as "motoring pressure"), a reference pressure for calculating the current in-cylinder air pressure (hereinafter referred to as "reference pressure") excluding a pressure increase due to combustion Calculation means; and ignition timing detection means for detecting the ignition timing by comparing the current in-cylinder pressure (hereinafter referred to as “detected pressure”) detected by the in-cylinder pressure detection means with the reference pressure. An ignition timing detection device for an internal combustion engine, characterized in that: 2. The ignition timing detecting device for an internal combustion engine according to claim 1, wherein the in-cylinder pressure detecting means detects an in-cylinder pressure when fuel injection is cut off as the motoring pressure. 3. The reference pressure calculating means calculates the reference pressure by multiplying the motoring pressure by a coefficient obtained from a pressure ratio between the detected pressure and the motoring pressure. 3. The ignition timing detection device for an internal combustion engine according to claim 1. 4. The ignition timing detecting device for an internal combustion engine according to claim 3, wherein said reference pressure calculating means calculates the pressure ratio based on at least one crank angle before fuel ignition. 5. An offset error of an output characteristic of said in-cylinder pressure detecting means is calculated based on a plurality of detected pressures detected at a plurality of crank angles by said in-cylinder pressure detecting means. 5. The ignition timing detection device for an internal combustion engine according to claim 1, further comprising an offset error correction unit that corrects an output characteristic of the internal pressure detection unit. 6. A motoring pressure updating means for detecting the motoring pressure by the in-cylinder pressure detecting means under a predetermined condition for each fuel injection cut and updating a stored value of the motoring pressure. The ignition timing detecting device for an internal combustion engine according to any one of claims 1 to 5, wherein 7. A gain error of an output characteristic of the in-cylinder pressure detecting means is obtained by comparing the motoring pressure detected at at least one crank angle by the in-cylinder pressure detecting means with a standard value thereof. 7. The ignition timing detection device for an internal combustion engine according to claim 1, further comprising a gain error correction unit that corrects an output characteristic of the in-cylinder pressure detection unit by an amount corresponding to the error. 8. The ignition timing detecting means according to claim 1, wherein said ignition timing detecting means determines an ignition timing when a pressure difference between said detected pressure and said reference pressure exceeds an ignition determination value. An ignition timing detection device for an internal combustion engine according to claim 1. 9. The ignition timing detecting means calculates a differential pressure between the detected pressure and the reference pressure every predetermined period, and connects the differential pressures of at least two consecutive points exceeding the ignition determination value. 9. The ignition timing detection device for an internal combustion engine according to claim 8, wherein a line is obtained, and when the extension of the characteristic line exceeds the ignition determination value, the ignition timing is determined.