JP2002097996A - Device for detecting combustion state of internal combustion engine - Google Patents

Abstract

(57) Abstract: Provided is a combustion state detection device capable of obtaining a combustion state parameter accurately indicating a combustion state of an engine from a smaller detected value of a combustion chamber pressure. A first combustion chamber pressure P2 at, for example, 60 degrees before top dead center in a compression stroke of the engine, and a second combustion chamber pressure P at, for example, 60 degrees after top dead center during an expansion stroke.
3 and the pressure ratio P3 / P2 is calculated. The combustion state parameter PRX is defined as PRX = P3 / P2-1, thereby detecting the combustion state of the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a combustion state of an internal combustion engine, and more particularly to an apparatus for detecting a combustion state using an in-cylinder pressure sensor for detecting a pressure in a combustion chamber of an internal combustion engine.

[0002]

2. Description of the Related Art A method of detecting a pressure in a combustion chamber of an internal combustion engine using a pressure sensor and obtaining a combustion state parameter indicating a combustion state of the internal combustion engine from the detected pressure value is disclosed in Japanese Patent Laid-Open Publication No. Hei 6-1994.
No. 2,490,491.

According to the technique disclosed in this publication, the pressure in the combustion chamber P (120B) at a crank angle position of 120 ° before the top dead center during the compression stroke of the internal combustion engine and the pressure before the top dead center during the compression stroke are also determined. A combustion chamber pressure P (60B) at a crank angle position of 60 degrees and a combustion chamber pressure P (60A) at a crank angle position of 60 degrees after the top dead center during the expansion stroke are detected, and the combustion state parameter Cio is calculated by the following equation. Is calculated. Cio = (P (60A) -P (60B)) / (P (60B) -P
(120B))

[0004]

The sampling of the pressure in the combustion chamber, which is detected by using the in-cylinder pressure sensor, is performed at as many crank angle positions as possible during the compression stroke and the expansion stroke of the engine, so that the combustion state can be described in more detail. However, if the data amount is too large, there is a problem that the required memory capacity increases and the amount of calculation after pressure detection increases.

In the technique disclosed in Japanese Patent Application Laid-Open No. 6-249049, a combustion state parameter can be obtained from three detected pressure values. However, a combustion state parameter that accurately indicates the combustion state of the engine can be obtained with a smaller detected pressure value. It is desirable to be able to obtain. The present invention has been made in view of this point, and it is an object of the present invention to provide a combustion state detection device that can obtain a combustion state parameter that accurately indicates a combustion state of an engine from a smaller detected value of a combustion chamber pressure. And

[0006]

According to one aspect of the present invention, there is provided a pressure detecting means for detecting a pressure in a combustion chamber of an internal combustion engine, and an angle detecting means for detecting a crankshaft rotation angle of the engine. Pressure ratio calculating means for calculating a pressure ratio between a first combustion chamber pressure during a compression stroke of the engine and a second combustion chamber pressure during an expansion stroke of the engine. And combustion state detecting means for detecting a combustion state of the engine based on the pressure ratio.

According to this configuration, the pressure ratio between the pressure in the first combustion chamber during the compression stroke of the engine and the pressure in the second combustion chamber during the expansion stroke is calculated, and the combustion state of the engine is calculated based on the pressure ratio. Since it is detected, a combustion state parameter indicating the combustion state can be obtained based on a smaller detected pressure value than in the related art. The second for the first combustion chamber pressure
The parameter (pressure ratio -1) obtained by subtracting "1" from the combustion chamber pressure ratio (the second combustion chamber pressure / the first combustion chamber pressure) is the calorific value per unit weight due to combustion. It is a parameter that is approximately proportional and can be used as a parameter that accurately indicates the combustion state.

According to a second aspect of the present invention, in the combustion state detecting device for an internal combustion engine according to the first aspect, the combustion state detecting means calculates the amount of heat generated by the combustion using the pressure ratio. It is characterized by having a calculating means. According to this configuration, since the amount of heat generated by the combustion is calculated using the pressure ratio, the combustion state of the engine can be grasped in detail.

According to a third aspect of the present invention, in the combustion state detecting device for an internal combustion engine according to the first aspect, the combustion state detecting means compares the pressure ratio with a predetermined pressure ratio. And a misfire detecting means for detecting misfire of the engine. According to this configuration, the misfire of the engine is detected by comparing the pressure ratio with a predetermined pressure ratio. Since this detection is based on the amount of heat generated by the combustion, it is hardly affected by a change in the operating state or a change in the environmental condition, and accurate misfire detection can be performed.

The combustion state detecting means subtracts "1" from the ratio of the pressure in the second combustion chamber to the pressure in the first combustion chamber (the pressure in the second combustion chamber / the pressure in the first combustion chamber). It is desirable to use the obtained parameter as a parameter indicating the combustion state.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an internal combustion engine (hereinafter simply referred to as “engine”) and a control device thereof according to an embodiment of the present invention. For example, a four-cylinder engine 1
In the middle of the intake pipe 2, a throttle valve 3 is arranged.
A throttle valve opening (THA) sensor 4 is connected to the throttle valve 3 and outputs an electric signal corresponding to the opening of the throttle valve 3 to output an electronic control unit for engine control (hereinafter referred to as “ECU”) 5. To supply.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of the fuel injection valve 6 based on a signal from the ECU 5.

On the other hand, immediately downstream of the throttle valve 3, an intake pipe absolute pressure (PBA) sensor 7 for detecting the pressure in the intake pipe is provided. Is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 8 is mounted downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.

The engine water temperature (TW) sensor 9 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5. The ECU 5 includes the engine 1
A crank angle position sensor 10 as angle detecting means for detecting a rotation angle of a crankshaft (not shown) is connected, and a signal corresponding to the rotation angle of the crankshaft is output from the ECU 5.
Supplied to The crank angle position sensor 10 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. )
A TDC sensor that outputs a TDC signal pulse at a crank angle position earlier than a predetermined crank angle (every 180 degrees of a crank angle in a four-cylinder engine) and one pulse at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse ( CRK that generates a “CRK signal pulse”)
A CYL signal pulse, a TDC signal pulse and a CRK signal pulse are supplied to the ECU 5. These signal pulses correspond to the sample timing of the pressure in the combustion chamber of the engine 1 (hereinafter referred to as “in-cylinder pressure”), the fuel injection timing,
It is used to control various timings such as ignition timing and to detect the engine speed (engine speed) NE.

In the exhaust pipe 12, NOx, HC,
A three-way catalyst 16 for purifying CO is provided.
An oxygen concentration sensor 14 as an air-fuel ratio sensor is mounted at an upstream position of the sensor 6. The O2 sensor 14 outputs an electric signal corresponding to the oxygen concentration (air-fuel ratio) in the exhaust gas,
Supply to U5.

An exhaust gas recirculation passage 21 is provided between the intake pipe 2 downstream of the throttle valve 3 and the exhaust pipe 12 upstream of the three-way catalyst 16. An exhaust gas recirculation valve that controls the amount of exhaust gas recirculation (hereinafter referred to as an “EGR valve”)
22) are provided. The EGR valve 22 is an electromagnetic valve having a solenoid, and its valve opening is controlled by the ECU 5. The EGR valve 22 is provided with a lift sensor 23 for detecting the valve opening (valve lift amount) LACT, and the detection signal is supplied to the ECU 5. The exhaust gas recirculation passage 21 and the EGR valve 22 constitute an exhaust gas recirculation mechanism.

The ECU 5 has an input circuit having a function of shaping input signal waveforms from various sensors, correcting a voltage level to a predetermined level, and converting an analog signal value to a digital signal value, and a central processing unit (hereinafter referred to as a central processing unit). A CPU that stores various arithmetic programs executed by the CPU, arithmetic results, and the like, an output circuit that supplies a drive signal to the fuel injection valve 6 and the like.

The ECU 5 determines an engine operating state based on various engine parameter signals, and sets EG which is set according to the engine speed NE and the intake pipe absolute pressure PBA.
The valve opening command value LCMD of the R valve 22 and the lift sensor 23
The control signal is supplied to the solenoid of the EGR valve 22 so as to make the deviation from the actual valve opening LACT detected by the control routine to zero. Further, the ECU 5 calculates the fuel injection time TOUT as the valve opening time of the fuel injection valve 6 according to the engine operating state, and controls the fuel supply amount so as to obtain an optimum air-fuel ratio according to the engine operating state.

As shown in FIG. 2, each cylinder (#
Cylinders 1 to 4) are provided with in-cylinder pressure sensors 31 to 34 as pressure detecting means for detecting the pressure in the combustion chamber, respectively, and output signals of these sensors are output to a multiplexer 35 via a charge amplifier (not shown). Is supplied to the A / D converter 36 via the. Multiplexer 35
Switches the output signals of the in-cylinder pressure sensors 31 to 34 every 180 degrees of the crank angle, and supplies the signals indicating the in-cylinder pressure in the compression stroke and the expansion stroke of each cylinder to the A / D converter 36. The A / D converter 36 samples the input signal at a predetermined timing, converts the sampled value into a digital signal, and supplies the digital signal to the ECU 5.

FIG. 3 is a graph showing the transition of the in-cylinder pressure PCYL. The solid line L1 shows the characteristic during normal combustion, and the broken line L2 shows the characteristic during misfire. In the present embodiment, the in-cylinder pressure PCYL is sampled at a crank angle position of 60 degrees before the top dead center and at a crank angle position of 60 degrees after the top dead center, and the detected pressures are P2 and P3. Then, a parameter obtained by subtracting "1" from the pressure ratio PR = P3 / P2 of the detected pressure P3 to the detected pressure P2 is adopted as a combustion state parameter PRX (= PR-1) indicating the combustion state of the engine 1. .

The reason will be described below. The heat value Q due to the combustion of the engine 1 is given by the following equation (1). Here, ηh is the combustion efficiency, B is the supplied fuel amount, Hu is the low calorific value of the fuel, G is the operating gas weight, λ is the excess air ratio, Ga
th is the theoretical air weight.

The constant volume specific heat is Cv, and the pressure and temperature before and after combustion at the top dead center in an ideal cycle are P2 'and P2, respectively.
Assuming 3 ′, T2 ′ and T3 ′, the calorific value Q is given by the following equation (2). Q = G × Cv × (T3′−T2 ′) (2) Equation (2) can be modified as follows. Q = G × Cv × T2 ′ × (T3 ′ / T2′−1) = G × Cv × T2 ′ × (P3 ′ / P2′−1) = P2 ′ × V2 ′ × (P3 ′ / P2′−1) ) / (Κ-1) (3) where V2 ′ is the combustion chamber volume at the top dead center, and κ is the specific heat ratio of the air-fuel mixture. The specific heat ratio κ is defined as constant pressure specific heat Cp / constant volume specific heat Cv, and it has been experimentally confirmed that in an actual engine, κ is approximately constant at κ = 1.3.

From the equations (1) and (3), the calorific value q per unit weight is given by the following equation (4). q = ηh × Hu / (1 + λ × Gath) = (P2 ′ / G) × V2 ′ × (P3 ′ / P2′−1) / (κ−1) = R × T2 ′ × (P3 ′ / P2′− 1) / (κ−1) = R × T1 × ε ^(κ−1) × (P3 ′ / P2′−1) / (κ−1) Here, P3 ′ / P2 ′ is substantially equal to P3 / P2. Therefore, q ≒ R × T1 × ε ^(κ-1) × (P3 / P2-1) / (κ-1) (4) where R is the gas constant, ε is the compression ratio, and T1 is the start of the compression stroke. , And (P3 / P2-1) is a combustion state parameter PRX. As described above, the combustion state parameter PRX is an index corresponding to the calorific value q per unit weight (proportional to the calorific value q if the temperature T1 is constant), and is a parameter that accurately indicates the combustion state. I understand.

As described above, in the present embodiment, the pressure ratio PR (= P3) between the in-cylinder pressure P2 at 60 degrees before the top dead center in the compression stroke and the in-cylinder pressure P3 at 60 degrees after the top dead center in the expansion stroke.
/ P2) Combustion state parameter RPX obtained using
Since the combustion state of the engine 1 is detected by (= PR-1), the combustion state can be accurately grasped with a small detected pressure value.

The compression stroke start in-cylinder temperature T1 is obtained by changing the intake air temperature TA, the engine speed NE, and the exhaust gas recirculation amount (EGR amount).
And by correcting according to the engine coolant temperature TW. More specifically, 1) a KNE table shown in FIG. 4A is searched according to the engine speed NE to calculate a correction coefficient KNE, and 2) an EGR amount (a lift amount of the EGR valve 22). The KEGR table shown in FIG. 3B is searched to calculate the correction coefficient KEGR. 3) The KTW table shown in FIG. 3C is searched according to the engine coolant temperature TW to calculate the correction coefficient KTW. Applying the correction coefficient to the following equation (5), the compression stroke starting cylinder temperature T1
Is calculated. T1 = TA × KNE × KEGR × KTW (5) The temperature T1 and the in-cylinder pressure detection value P thus calculated
By applying P2 and P3 to the above equation (4), the heat value q due to combustion of the engine 1 can be calculated.

FIG. 5 shows the average of the measured values of the combustion state parameter PRX when the engine speed NE is changed. The dashed-dotted line L3 in the figure shows the characteristics during normal combustion, and the broken line L4 shows the characteristics during misfire. As is apparent from this figure, if the threshold value PRXTH is set to, for example, around 1, PRX <PRXTH over the entire range of the engine speed.
When it is determined that misfire has occurred. That is, by using the combustion state parameter PRX,
Accurate misfire determination can be performed over a wide range of the engine speed NE.

In this embodiment, the ECU 5 constitutes a pressure ratio calculating means, a combustion state detecting means, a calorific value calculating means and a misfire detecting means. Further, the in-cylinder pressure P2 during the compression stroke is the first pressure.
, The in-cylinder pressure P3 during the expansion stroke
Corresponds to the pressure in the second combustion chamber.

The present invention is not limited to the embodiment described above, and various modifications are possible. For example, in the above-described embodiment, the combustion state parameter PRX obtained by subtracting “1” from the pressure ratio PR = P3 / P2 is used.
The pressure ratio PR itself may be used as the combustion state parameter. In this case, the predetermined pressure ratio for misfire determination may be, for example, “2”.

The sampling of the in-cylinder pressure is performed at two timings centered on the top dead center, namely, SA before the top dead center during the compression stroke and SA after the top dead center during the expansion stroke (0 <SA <
(90 degrees), but it is also possible to use a detection pressure sampled at another timing. That is, assuming that the pressure value sampled at the timing of the SB degree before top dead center is P2B, the pressure value P2B can be converted into the pressure value P2 of the SA degree before top dead center by the following equation (6). P2 = P2B × (V2B / V2) ⁿ (6)

Here, V2 is the volume of the combustion chamber at SA degree before top dead center, V2B is the volume of the combustion chamber at SB degree before top dead center, and n is the polytropic index (about 1.3 to 1.4). Incidentally, it is possible in terms according to equation (6), the sample timing (SB degree) in the range of polytropic change, i.e. it is necessary to be within a range where the P × V ⁿ becomes substantially constant.

In the above-described embodiment, the compression stroke start cylinder temperature T1 is obtained by the equation (5). However, a correction coefficient corresponding to the engine load (intake pipe absolute pressure PBA) is further calculated, and this is corrected by the above correction. Coefficients KNE, KEGR and KTW
At the same time, it may be obtained by multiplying the intake air temperature TA.

[0032]

As described in detail above, according to the first aspect of the present invention, the ratio of the pressure of the first combustion chamber during the compression stroke of the engine to the pressure of the second combustion chamber during the expansion stroke is determined. The combustion state of the engine is calculated based on the calculated pressure ratio. Since the pressure ratio is an index indicating the amount of heat generated by combustion, a combustion state parameter indicating a combustion state can be obtained based on a smaller detected pressure value than in the related art.

According to the second aspect of the present invention, the amount of heat generated by combustion is calculated using the pressure ratio.
The combustion state of the engine can be grasped in detail. According to the third aspect of the present invention, the misfire of the engine is detected by comparing the pressure ratio with a predetermined pressure ratio.
Since this detection is based on the amount of heat generated by the combustion, it is hardly affected by a change in the operating state or a change in the environmental condition, and accurate misfire detection can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an arrangement of an in-cylinder pressure sensor and an output signal processing circuit thereof.

FIG. 3 is a graph showing a change characteristic of an in-cylinder pressure with respect to a rotation angle of a crankshaft.

FIG. 4 is a diagram showing a table used for calculating an in-cylinder temperature (T1) at the start of a compression stroke.

FIG. 5 is a diagram showing a change characteristic of a combustion state parameter (PRX) with respect to an engine speed.

[Explanation of symbols]

Reference Signs List 1 internal combustion engine 5 electronic control unit (pressure ratio calculating means, calorific value calculating means, misfire detecting means) 31, 32, 33, 34 in-cylinder pressure sensor (pressure detecting means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G019 CD09 DC06 GA16 3G084 BA15 BA17 BA20 BA23 DA13 FA00 FA01 FA10 FA11 FA20 FA21 FA24 FA29 FA33 FA38

Claims (3)

[Claims] 1. A combustion state detecting device for an internal combustion engine, comprising: pressure detecting means for detecting a pressure in a combustion chamber of the internal combustion engine; and angle detecting means for detecting a crankshaft rotation angle of the engine. A first pressure in the first combustion chamber,
A pressure ratio calculating means for calculating a pressure ratio with the pressure in the second combustion chamber during an expansion stroke; and a combustion state detecting means for detecting a combustion state of the engine based on the pressure ratio. Combustion state detector. 2. The combustion state detecting device for an internal combustion engine according to claim 1, wherein said combustion state detecting means includes a calorific value calculating means for calculating the amount of heat generated by combustion using said pressure ratio. 3. The apparatus according to claim 1, wherein the combustion state detecting means includes misfire detecting means for detecting misfire of the engine by comparing the pressure ratio with a predetermined pressure ratio. A combustion state detection device for an internal combustion engine.