JP4665835B2 - Residual gas amount calculation device for internal combustion engine - Google Patents

Description

  The present invention relates to a residual gas amount calculation device for an internal combustion engine that calculates a gas amount remaining in a cylinder of the internal combustion engine.

  2. Description of the Related Art Conventionally, a technique for obtaining the amount of intake air newly flowing into each cylinder of an internal combustion engine or the amount of gas remaining in each cylinder is known. For example, Patent Document 1 discloses the in-cylinder residual gas ratio (ratio between the amount of gas remaining in the cylinder and the amount of intake air flowing into fresh air) based on the polytropic index from the measured value of the in-cylinder pressure during the compression stroke. The technique to calculate is described. In this technique, the in-cylinder residual gas rate is obtained on the assumption that the polytropic index and the in-cylinder residual gas rate have a negative correlation.

JP-A-11-166447

  However, in the technique described in Patent Document 1 described above, the relationship between the polytropic index and the in-cylinder residual gas rate changes due to changes in the in-cylinder gas temperature and the in-cylinder gas composition, and the in-cylinder residual In some cases, the gas rate could not be determined with high accuracy. Such a change in the in-cylinder gas temperature and the gas composition in the cylinder may be caused by a difference in exhaust gas temperature or operation history.

  The present invention has been made to solve the above-described problems, and provides a residual gas amount calculation device for an internal combustion engine capable of accurately calculating the amount of gas remaining in a cylinder of the internal combustion engine. For the purpose.

In one aspect of the present invention, a residual gas amount calculation device for an internal combustion engine includes: an in-cylinder pressure acquisition unit that acquires an in-cylinder pressure in a cylinder of the internal combustion engine; In-cylinder gas temperature calculating means for calculating an in-cylinder gas temperature of the cylinder, and a residual gas for calculating a residual gas amount remaining in the cylinder based on the in-cylinder pressure, the in-cylinder volume, and the in-cylinder gas temperature. An in- cylinder gas temperature calculating unit that calculates a ratio of the in-cylinder gas temperature at two predetermined crank angles, the in-cylinder gas temperature ratio, and the in-cylinder wall temperature. Based on the above, the in-cylinder gas temperature is calculated .

The above-described residual gas amount calculation device for an internal combustion engine is a device that calculates the amount of gas remaining in a cylinder in the internal combustion engine. The in-cylinder pressure acquisition unit acquires the in-cylinder pressure, the in-cylinder volume acquisition unit acquires the in-cylinder volume, and the in-cylinder gas temperature calculation unit calculates the in-cylinder gas temperature. Then, the residual gas amount calculation means calculates the residual gas amount from the in-cylinder pressure, the in-cylinder volume, and the in-cylinder gas temperature using a gas state equation or the like. By calculating the residual gas amount as described above, the residual gas amount can be accurately obtained even when the polytropic index or the like changes due to changes in the in-cylinder gas temperature or the in-cylinder gas composition. it can. That is, according to the residual gas amount calculation apparatus for an internal combustion engine, the residual gas amount can be accurately obtained without being affected by the change in the polytropic index. Further, according to the above-described residual gas amount calculation device for an internal combustion engine, the residual gas amount can be calculated with a simple device configuration without providing an intake air temperature sensor or an exhaust gas temperature sensor.
In this case, the cylinder gas temperature calculation means calculates the cylinder gas temperature based on the wall temperature in the cylinder. This is because the in-cylinder gas temperature changes due to the in-cylinder wall temperature, so that the in-cylinder gas temperature can be uniquely calculated from the in-cylinder wall temperature. More specifically, the in-cylinder gas temperature calculating means calculates a ratio of the in-cylinder gas temperature at two predetermined crank angles, and based on the ratio of the in-cylinder gas temperature and the wall temperature in the cylinder. In-cylinder gas temperature is calculated. For example, the predetermined two crank angles can be set to two points such that there is no inflow / outflow of gas in the cylinder and fuel ignition is not performed while the crank angle changes. By setting the two crank angles in this way, the change in the in-cylinder gas temperature when the crank angle changes is uniquely determined by the in-cylinder wall temperature. Therefore, the in-cylinder gas temperature can be accurately calculated based on the relationship between the in-cylinder gas temperature ratio and the in-cylinder wall temperature.

  Preferably, the wall temperature in the cylinder is calculated based on the cooling water temperature. In this case, the in-cylinder wall temperature corresponding to the detected cooling water temperature is obtained based on the relationship established between the in-cylinder wall temperature and the cooling water temperature.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[overall structure]
First, the configuration of the internal combustion engine according to the embodiment of the present invention will be described.

  FIG. 1 is a schematic diagram illustrating a configuration of an internal combustion engine 1 to which a residual gas amount calculation device for an internal combustion engine according to the present embodiment is applied. In FIG. 1, solid arrows indicate gas flows, and broken arrows indicate input / output of signals.

  The internal combustion engine 1 mainly includes an air flow meter 2, an intake passage 3, a throttle valve 4, a fuel injection valve 5, a cylinder (cylinder) 6 a, an intake valve 7, an exhaust valve 8, and an exhaust passage 9. The spark plug 10, the in-cylinder pressure sensor 11, the crank angle sensor 12, and the coolant temperature sensor 13 are included. The internal combustion engine 1 is configured as, for example, a gasoline engine or a diesel engine. In FIG. 1, only one cylinder 6a is shown for convenience of explanation, but the internal combustion engine 1 actually has a plurality of cylinders 6a.

  Air (fresh air) introduced from the outside passes through the intake passage 3, and the throttle valve 4 adjusts the flow rate of air passing through the intake passage 3. The air that has passed through the intake passage 3 is supplied to the combustion chamber 6b of the cylinder 6a. The fuel injected by the fuel injection valve 5 is supplied to the combustion chamber 6b. In the combustion chamber 6b, the mixture of the supplied air and fuel is combusted by being ignited by ignition of the spark plug 10. In this case, the piston 6c reciprocates by combustion, and this reciprocating motion is transmitted to the crankshaft (not shown) via the connecting rod 6d, and the crankshaft rotates. An exhaust passage 9 is connected to the internal combustion engine 1, and exhaust gas generated by combustion is discharged from the exhaust passage 9.

  Furthermore, an intake valve 7 and an exhaust valve 8 are provided in the combustion chamber 6 b of the internal combustion engine 1. The intake valve 7 controls conduction / interruption between the intake passage 3 and the combustion chamber 6b by opening and closing. Further, the exhaust valve 8 controls opening / closing of the exhaust passage 9 and the combustion chamber 6b by opening and closing.

  The air flow meter 2 is a sensor that detects the amount of fresh air that passes through the intake passage 3. The in-cylinder pressure sensor 11 is a sensor that detects the pressure in the cylinder 6a (in-cylinder pressure). For example, the in-cylinder pressure sensor 11 is composed of a ring-shaped piezoelectric element that is mounted as a washer for the spark plug 10, and detects the in-cylinder pressure as a relative pressure with respect to the tightening load of the spark plug 10. The in-cylinder pressure sensor 11 is provided for each of the plurality of cylinders 6a and detects the in-cylinder pressure of each cylinder 6a.

  The crank angle sensor 12 is provided in each cylinder 6a and detects a crank angle in each cylinder 6a. Specifically, the crank angle sensor 12 outputs an angle signal and a reference angle signal for each predetermined piston position in addition to each unit crank angle. The cooling water temperature sensor 13 detects the temperature of the cooling water (cooling water temperature) of the internal combustion engine 1.

  The arithmetic processing unit 20 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). The arithmetic processing unit 20 acquires detection signals from the various sensors described above, and performs arithmetic processing based on the detection signals. The arithmetic processing unit 20 can be incorporated into, for example, an ECU (Engine Control Unit).

  In the present embodiment, the arithmetic processing unit 20 calculates the amount of gas remaining in the cylinder 6a (residual gas amount) based on the detection signals acquired from the various sensors described above. Specifically, the arithmetic processing unit 20 has an in-cylinder pressure acquired from the in-cylinder pressure sensor 11, an amount of fresh air acquired from the air flow meter 2 (hereinafter, also referred to as “fresh air gas amount”), and cooling water. Based on the cooling water temperature acquired from the temperature sensor 13, the residual gas amount is calculated. Thus, the arithmetic processing unit 20 functions as a residual gas amount calculation device for an internal combustion engine according to the present invention. Specifically, the arithmetic processing unit 20 operates as in-cylinder pressure acquisition means, in-cylinder volume acquisition means, in-cylinder gas temperature calculation means, and residual gas amount calculation means.

[Residual gas amount calculation method]
Next, the basic concept of the residual gas amount calculation method according to this embodiment will be described.

  In the present embodiment, the cylinder pressure in the cylinder 6a, the volume in the cylinder 6a (hereinafter referred to as “cylinder volume”), and the temperature of the gas in the cylinder 6a (hereinafter referred to as “cylinder gas temperature”). Based on the above, the amount of residual gas remaining in the cylinder is calculated. Specifically, by substituting the in-cylinder pressure, the in-cylinder volume, and the in-cylinder gas temperature into the gas state equation, the total gas amount in the cylinder (hereinafter also referred to as “in-cylinder gas amount”) is obtained. The residual gas amount is obtained by subtracting the fresh gas amount acquired from the air flow meter 2 from the in-cylinder gas amount.

  More specifically, since it is difficult to directly detect the in-cylinder gas temperature, the in-cylinder gas temperature is calculated based on the wall temperature of the cylinder 6a (hereinafter referred to as “in-cylinder wall temperature”). In this case, the wall temperature in the cylinder is calculated based on the cooling water temperature. The in-cylinder gas temperature is calculated based on the ratio of the in-cylinder gas temperature at two predetermined crank angles and the above-described in-cylinder wall temperature. Specifically, the predetermined two crank angles are set to two points such that there is no gas inflow / outflow in the cylinder 6a and fuel ignition is not performed while the crank angle changes. . That is, two points of the crank angle during the compression stroke are selected. By setting the two crank angles in this way, the change in the in-cylinder gas temperature when the crank angle changes is uniquely determined by the in-cylinder wall temperature. Therefore, the in-cylinder gas temperature can be accurately obtained based on the relationship between the in-cylinder gas temperature ratio and the in-cylinder wall temperature. The ratio of the in-cylinder gas temperature is obtained from Boyle-Charles' law using the in-cylinder pressure and the in-cylinder volume at two predetermined crank angles.

  By calculating the residual gas amount as described above, even if the relationship between the polytropic index and the in-cylinder residual gas ratio changes due to changes in the in-cylinder gas temperature or the in-cylinder gas composition, The amount of gas can be determined with high accuracy. That is, according to the residual gas amount calculation method according to the present embodiment, the residual gas amount can be accurately obtained without being affected by the change in the polytropic index. Further, according to the present embodiment, the residual gas amount can be calculated with a simple device configuration without providing an intake air temperature sensor, an exhaust gas temperature sensor, or the like.

[Processing in the arithmetic processing unit]
Next, specific processing in the arithmetic processing unit 20 will be described. Hereinafter, an example in which the mass of the residual gas in the cylinder is calculated as the residual gas amount will be described.

  FIG. 2 is a block diagram illustrating a schematic configuration of the arithmetic processing unit 20 according to the present embodiment. As shown in the figure, the calculation processing unit 20 includes an in-cylinder volume calculation unit 21, a temperature ratio calculation unit 22, a cylinder inner wall temperature calculation unit 23, an in-cylinder gas temperature calculation unit 24, and an in-cylinder gas mass calculation unit 25. And a residual gas mass calculation unit 26.

  The in-cylinder volume calculation unit 21 calculates in-cylinder volumes V1 and V2 corresponding to the crank angles C1 and C2, respectively. In this case, the in-cylinder volume calculation unit 21 acquires the crank angles C1 and C2 from the crank angle sensor 12, and calculates the in-cylinder volumes V1 and V2 corresponding to the crank angles C1 and C2. Specifically, the in-cylinder volume calculation unit 21 calculates the in-cylinder volume corresponding to the crank angle based on a design value, a map, or the like. The crank angles C1 and C2 are crank angles located between when the intake valve 7 is closed and when it is ignited, and are determined in advance.

  The temperature ratio calculation unit 22 calculates a ratio (T2 / T1) between the in-cylinder gas temperature T1 at the crank angle C1 and the in-cylinder gas temperature T2 at the crank angle C2. Specifically, the temperature ratio calculation unit 22 acquires the in-cylinder pressures P1 and P2 corresponding to the crank angles C1 and C2 from the in-cylinder pressure sensor 11, and the in-cylinder volume calculation unit 21 calculates the crank angles C1 and C2. The in-cylinder volumes V1 and V2 corresponding to each are acquired. The temperature ratio calculation unit 22 calculates the temperature ratio (T2 / T1) by substituting the in-cylinder pressures P1 and P2 and the in-cylinder volumes V1 and V2 into the equation (1) based on Boyle-Charles' law. To do.

T2 / T1 = (P2 / V2) / (P1 / V1) Formula (1)
The cylinder inner wall temperature calculation unit 23 calculates the cylinder inner wall temperature Tw using the cooling water temperature Tclnt supplied from the cooling water temperature sensor 13. Specifically, the cylinder inner wall temperature calculation unit 23 calculates the cylinder inner wall temperature Tw from the cooling water temperature Tclnt with reference to a map or a relational expression showing the relationship between the cooling water temperature and the cylinder inner wall temperature obtained in advance. . For example, the cylinder inner wall temperature Tw is obtained from the following equation (2) using a function f _Tw indicating the relationship between the coolant temperature and the cylinder inner wall temperature.

Tw = f _Tw (Tclnt) Formula (2)
The in-cylinder gas temperature calculation unit 24 is based on the ratio (T2 / T1) of the in-cylinder gas temperature supplied from the temperature ratio calculation unit 22 and the in-cylinder wall temperature Tw supplied from the in-cylinder wall temperature calculation unit 23. An in-cylinder gas temperature T1 at the crank angle C1 is calculated. Specifically, the in-cylinder gas temperature calculation unit 24 refers to a map or a relational expression that is obtained in advance and indicates a relationship between the in-cylinder gas temperature ratio, the in-cylinder wall temperature, and the in-cylinder gas temperature. A gas temperature T1 is calculated. This is because the in-cylinder gas temperature can be uniquely determined based on the relationship between the in-cylinder gas temperature ratio and the in-cylinder wall temperature. That is, the change from the in-cylinder gas temperature T1 when the intake valve is closed to the in-cylinder gas temperature T2 near the time of ignition (corresponding to the ratio (T2 / T1) of the in-cylinder gas temperature) is caused by the combustion of the fuel. Since the cylinder wall temperature Tw is not transmitted, the cylinder gas temperature T1 is uniquely determined based on the relationship between the cylinder gas temperature ratio (T2 / T1) and the cylinder wall temperature Tw. Can be sought.

  FIG. 3 shows an example of the relationship between the in-cylinder gas temperature ratio (T2 / T1) and the in-cylinder gas temperature T1, and the relationship between the in-cylinder wall temperature Tw and the in-cylinder gas temperature ratio (T2 / T1). FIG. 3A shows the relationship between the in-cylinder gas temperature ratio (T2 / T1) and the in-cylinder gas temperature T1 when the in-cylinder wall temperature Tw is constant. From this, it can be seen that the in-cylinder gas temperature T1 decreases as the ratio (T2 / T1) of the in-cylinder gas temperature increases. In other words, the cylinder gas temperature ratio (T2 / T1) decreases as the cylinder gas temperature T1 increases. FIG. 3B shows the relationship between the cylinder wall temperature Tw and the ratio of the cylinder gas temperature (T2 / T1). From this, it can be seen that the higher the in-cylinder wall temperature Tw, the larger the in-cylinder gas temperature ratio (T2 / T1).

  Returning to FIG. 2, another processing unit in the arithmetic processing unit 20 will be described.

  The in-cylinder gas mass calculation unit 25 is supplied from the in-cylinder volume V1 supplied from the in-cylinder volume calculation unit 21, the in-cylinder gas temperature T1 supplied from the in-cylinder gas temperature calculation unit 24, and the in-cylinder pressure sensor 11. Based on the in-cylinder pressure P1, the mass M of all gases in the cylinder (hereinafter simply referred to as “in-cylinder gas mass”) is calculated. Specifically, as shown in Expression (3), the cylinder gas mass M is calculated by substituting the cylinder volume V1, the cylinder gas temperature T1, and the cylinder pressure P1 into the gas state equation. In addition, "R" in Formula (3) has shown the gas constant.

M = (P1 · V1) / (R · T1) Formula (3)
The residual gas mass calculation unit 26 includes an in-cylinder gas mass M supplied from the in-cylinder gas mass calculation unit 25 and a mass Mn corresponding to the amount of fresh gas supplied from the air flow meter 2 (hereinafter referred to as “fresh gas mass”). Based on the above, the residual gas mass Me is calculated. Specifically, the residual gas mass Me is obtained by subtracting the fresh gas mass Mn from the in-cylinder gas mass M (see equation (4)).

Me = M-Mn Formula (4)
[Residual gas mass calculation processing]
Next, the residual gas mass calculation process according to the present embodiment will be described.

  FIG. 4 is a flowchart showing a residual gas mass calculation process. This process is a process for calculating the mass of the gas remaining in the cylinder, and is repeatedly executed by the arithmetic processing unit 20 described above.

  First, in step S101, the arithmetic processing unit 20 determines predetermined two crank angles C1 and C2. Specifically, the arithmetic processing unit 20 determines two crank angles at the time of the compression stroke. Then, the process proceeds to steps S102 and S103.

  In step S <b> 102, the temperature ratio calculation unit 22 in the arithmetic processing unit 20 acquires in-cylinder pressures P <b> 1 and P <b> 2 corresponding to the crank angles C <b> 1 and C <b> 2 from the in-cylinder pressure sensor 11. Then, the process proceeds to step S104. In step S103, the in-cylinder volume calculation unit 21 in the arithmetic processing unit 20 calculates in-cylinder volumes V1 and V2 corresponding to the crank angles C1 and C2, respectively. In this case, the in-cylinder volume calculation unit 21 calculates the in-cylinder volumes V1 and V2 corresponding to the crank angles C1 and C2 based on the design value and the map. Then, the process proceeds to step S104.

  In step S104, the temperature ratio calculation unit 22 in the arithmetic processing unit 20 calculates a ratio (T2 / T1) between the in-cylinder gas temperature T1 at the crank angle C1 and the in-cylinder gas temperature T2 at the crank angle C2. Specifically, the temperature ratio calculation unit 22 described above in-cylinder pressures P1 and P2 acquired in step S102 and in-cylinder volumes V1 and V2 acquired in step S103 based on Boyle-Charles' law. The temperature ratio (T2 / T1) is calculated by substituting into the equation (1). Then, the process proceeds to step S107.

  On the other hand, in step S <b> 105, the cylinder inner wall temperature calculation unit 23 in the arithmetic processing unit 20 acquires the cooling water temperature Tclnt from the cooling water temperature sensor 13. Then, the process proceeds to step S106. In step S106, the in-cylinder wall temperature calculating unit 23 in the arithmetic processing unit 20 calculates the in-cylinder wall temperature Tw using the cooling water temperature Tclnt acquired in step S105. Specifically, the cylinder inner wall temperature calculation unit 23 calculates the cylinder inner wall temperature Tw from the cooling water temperature Tclnt with reference to a map or a relational expression showing the relationship between the cooling water temperature and the cylinder inner wall temperature obtained in advance. . For example, the in-cylinder wall temperature Tw is calculated using the relational expression (2) described above. Then, the process proceeds to step S107.

  In step S107, the in-cylinder gas temperature calculation unit 24 in the arithmetic processing unit 10 calculates the ratio (T2 / T1) of the in-cylinder gas temperature calculated in step S104 and the in-cylinder wall temperature Tw calculated in step S106. Based on this, the in-cylinder gas temperature T1 at the crank angle C1 is calculated. Specifically, the in-cylinder gas temperature calculation unit 24 calculates the in-cylinder gas temperature T1 with reference to a map or a relational expression showing the relationship between the in-cylinder gas temperature ratio, the in-cylinder wall temperature, and the in-cylinder gas temperature. To do. Then, the process proceeds to step S108.

  In step S108, the in-cylinder gas mass calculation unit 25 in the arithmetic processing unit 20 acquires the in-cylinder volume V1 calculated in step S103, the in-cylinder gas temperature T1 calculated in step S107, and the step S102. The in-cylinder gas mass M is calculated based on the in-cylinder pressure P1. Specifically, the in-cylinder gas mass M is calculated by substituting the in-cylinder volume V1, the in-cylinder gas temperature T1, and the in-cylinder pressure P1 into the gas state equation, as shown in the above-described equation (3). . Then, the process proceeds to step S110.

  On the other hand, in step S <b> 109, the residual gas mass calculation unit 26 in the arithmetic processing unit 20 acquires the fresh gas mass Mn from the air flow meter 2. Then, the process proceeds to step S110.

  In step S110, the residual gas mass calculation unit 26 in the arithmetic processing unit 20 determines the residual gas mass based on the in-cylinder gas mass M calculated in step S108 and the fresh gas mass Mn acquired in step S109. Me is calculated. Specifically, the residual gas mass Me is obtained by subtracting the fresh gas mass Mn from the in-cylinder gas mass M (see equation (4)). When the above process ends, the process exits the flow.

  As described above, in the residual gas mass calculation process according to the present embodiment, the residual gas mass is calculated based on the in-cylinder pressure, the in-cylinder volume, and the in-cylinder gas temperature. Thereby, even when the relationship between the polytropic index and the in-cylinder residual gas ratio changes due to the change in the in-cylinder gas temperature or the in-cylinder gas composition, the residual gas amount can be obtained with high accuracy. Further, according to the residual gas mass calculation process according to the present embodiment, the residual gas mass can be calculated by a simple process without using the intake air temperature or the exhaust gas temperature.

It is the schematic which shows the structure of the internal combustion engine to which the residual gas amount calculation apparatus which concerns on this embodiment of this invention was applied. It is a block diagram which shows schematic structure of the arithmetic processing part which concerns on this embodiment. It is a figure which shows an example of the relationship between cylinder gas temperature ratio, cylinder gas temperature T1, and cylinder wall temperature. It is a flowchart which shows a residual gas mass calculation process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Air flow meter 3 Intake passage 4 Throttle valve 6a Cylinder 7 Intake valve 8 Exhaust valve 9 Exhaust passage 11 In-cylinder pressure sensor 12 Crank angle sensor 13 Coolant temperature sensor 20 Arithmetic processing part

Claims (2)

In-cylinder pressure acquisition means for acquiring in-cylinder pressure in a cylinder of the internal combustion engine;
In-cylinder volume acquisition means for acquiring the in-cylinder volume of the cylinder;
In-cylinder gas temperature calculating means for calculating an in-cylinder gas temperature of the cylinder;
A residual gas amount calculating means for calculating a residual gas amount remaining in the cylinder based on the in-cylinder pressure, the in-cylinder volume, and the in-cylinder gas temperature ;
The in-cylinder gas temperature calculation means calculates a ratio of the in-cylinder gas temperature at two predetermined crank angles, and the in-cylinder gas temperature is calculated based on the ratio of the in-cylinder gas temperature and the wall temperature in the cylinder. the residual gas quantity calculating apparatus for an internal combustion engine and calculates a. The residual gas amount calculation device for an internal combustion engine according to claim 1 , wherein the wall temperature in the cylinder is calculated based on a coolant temperature.

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