JP2006132499A - Flow rate calculation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an accurate intake air flow passing a valve when a pressure ratio across the valve is equal to or lower than a prescribed value. <P>SOLUTION: A valve opening area is calculated by using a map of the valve opening and the valve opening area according to the opening (duty ratio) of an electrically controlled throttle valve. A coefficient of flow rate after correction when the pressure ratio across the valve is 0.2 or below is calculated by using a map of the pressure ratio (downstream side pressure/upstream side pressure) of the electrically controlled throttle valve and the coefficient of flow rate. Then, a volumetric flow rate is calculated by multiplying the opening area by the coefficient of flow rate after correction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flow rate calculation device.

  In an apparatus in which a valve (throttle valve, electric throttle valve) is provided in an intake system of an internal combustion engine, as shown in Patent Document 1, the valve opening area and the valve front-rear pressure ratio (valve downstream pressure / valve upstream pressure) It is described that the flow rate (volume flow rate) of the gas passing through the valve is calculated from the flow rate coefficient based on it. FIG. 7 of Patent Document 1 and FIG. 4 and FIG. 4 of Patent Document 3 show the relationship between the valve front-rear pressure ratio and the flow coefficient, but are always constant in a choke region (region where the flow rate is constant) where the pressure ratio is a predetermined value or less. It was value.

FIG. 7 of Patent Document 4 and FIG. 9 of Patent Document 5 show the correlation between the pressure ratio and the flow velocity, and state that the flow velocity converges to the sound velocity.
JP 2002-130039 A JP 59-162341 A JP 2002-180877 A JP-A-62-78443 JP-A-1-121529

However, when the valve front-rear pressure ratio becomes a predetermined value or less, a phenomenon occurs in which the flow rate or valve opening area increases in inverse proportion to the pressure ratio. That is, in spite of the choked state (the flow rate is constant), the flow rate increases when the pressure ratio is reduced.
As in Patent Documents 1 to 5, since this phenomenon has not been dealt with conventionally, there has been a problem that the estimation accuracy of the intake flow rate is lowered when the pressure ratio becomes small, such as during idling or deceleration.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an accurate intake flow rate when the valve front-rear pressure ratio is a predetermined value or less.

  Therefore, the present invention is an apparatus for calculating the volumetric flow rate of the gas passing through the valve from the valve opening area and the flow coefficient based on the valve front-rear pressure ratio, and when the valve front-rear pressure ratio is less than a predetermined value, The volume flow rate is calculated so as to be smaller.

  According to the present invention, it is possible to improve the estimation accuracy of the volume flow rate (intake flow rate) when the valve front-rear pressure ratio is equal to or less than a predetermined value (for example, when idling or decelerating in an internal combustion engine).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system configuration diagram of an engine control apparatus according to the first embodiment.
The combustion chamber 4 defined by the cylinder 2 and the piston 3 of each cylinder of the engine 1 is provided with an intake valve 6 and an exhaust valve 7 so as to surround the spark plug 5. 8 is an exhaust passage, and 9 is an intake passage.

An air cleaner 12 and an electric throttle valve (butterfly valve) 13 are disposed in the intake passage 9 from the upstream side, and air is introduced into the combustion chamber 4 in accordance with the valve opening area of the electric throttle valve 13. The electric throttle valve 13 has a valve opening area determined based on an opening degree command (duty ratio) of an engine control unit (ECU) 30.
A fuel injection valve 10 is disposed in the manifold branch portion of the intake passage 9 downstream of the collector 11.

The collector 11 includes a purge pipe 15 that guides evaporated fuel from the fuel tank adsorbed to the canister to the intake side when the engine is stopped, an EGR pipe 16 that recirculates a part of the exhaust to the intake side from the exhaust passage 8, and a brake booster. A brake negative pressure pipe 17 for guiding negative pressure to the pipe is connected.
The purge pipe 15 and the EGR pipe 16 are provided with a purge valve 19 and an EGR valve 20 that control the opening degree (flow rate) of the pipes 15 and 16. The brake negative pressure pipe 17 is provided with a check valve 21 as a check valve.

Further, the ECU 30 receives signals from the pressure sensor 24, the boost sensor (pressure sensor) 25, the temperature sensor 26, and the crank angle sensor 27.
The pressure sensor 24 is provided in the intake passage 9 upstream from the electric throttle valve 13 and outputs a signal corresponding to the pressure.
The boost sensor 25 is provided in the collector 11 downstream from the electric throttle valve 13 and outputs a signal corresponding to the pressure in the collector 11.

The temperature sensor 26 is provided in the collector 11 and outputs a signal corresponding to the intake air temperature.
The crank angle sensor 27 is provided in the engine 1 and outputs a signal corresponding to the crank angle of the engine 1. The engine speed can be detected from the signal of the crank angle sensor 27.
The ECU 30 performs various controls. For example, opening control of the electric throttle valve 13 by duty control, control of fuel injection timing and injection amount, ignition timing control, opening control of the purge valve 19, and opening control of the EGR valve 20 are performed.

Next, the flow of air passing through the electric throttle valve 13 will be described with reference to FIG.
FIG. 2 (a) is a diagram showing the flow around the electric throttle valve 13, and (b) is the front / rear pressure ratio of the throttle valve 13 (the pressure on the downstream side of the valve 13 / the pressure on the upstream side) exceeds a predetermined value. FIG. 6C is a diagram showing a state where the pressure ratio is equal to or less than a predetermined value. The predetermined value of the pressure ratio before and after the electric throttle valve is a value in the range of 0.2 to 0.3. Hereinafter, the predetermined value will be 0.2.

As shown in FIG. 2A, when the electric throttle valve 13 is controlled to be closed, the pressure ratio exceeds 0.2 (pressure ratio> 0.2), and the pressure ratio is 0.2 or less (pressure ratio). In the state of ≦ 0.2), the intake passage 9 at a predetermined position on the downstream side of the electric throttle valve 13 (A-A line shown in FIG. 2 (B), BB line shown in FIG. 2 (C)). The flow near the wall will be different.
That is, in FIG. 2B, the intake air becomes a laminar flow (steady flow) at the position of line AA. On the other hand, in FIG. 2C, the flow (turbulent flow) is a state where the intake air is separated from the intake passage 9 at the position of the line BB. This is because the flow around the electric throttle valve 13 is accompanied by a vortex flow and is not an isentropic flow, and the valve opening area is not always constant.

FIG. 3 shows the relationship between the pressure ratio and the flow coefficient (a value proportional to the flow rate or flow velocity, and physically the sound speed ratio) in the state of FIG.
FIG. 3 shows that the flow rate coefficient is 0 and the flow rate is 0 when the front-rear pressure ratio of the electric throttle valve 13 is 1.0, that is, when no intake air is flowing. On the other hand, when the engine 1 sucks air, the pressure on the downstream side of the electric throttle valve 13 decreases with respect to the pressure on the upstream side, so the pressure ratio decreases.

Here, when the pressure ratio decreases to a critical value (for example, about 0.4 or less), the flow coefficient converges to a predetermined value (flow velocity = sound velocity). Even when the pressure ratio is 0.2 or less, the convergence value (the value of the flow coefficient indicated by the dotted line) that is the pressure ratio of the one-dimensional flow is used.
However, since the actual flow rate (volumetric flow rate) increases when the pressure ratio is 0.2 or less as shown by the solid line, an error occurs between the value calculated by the following formula and the actual value. End up.

Therefore, in the present invention, in order to calculate the flow rate accurately even when the front / rear pressure ratio of the electric throttle valve 13 is 0.2 or less, the valve opening area or flow coefficient is calculated using the pressure ratio. (Value obtained as a function of pressure ratio) is corrected.
Next, a process for calculating the volume flow rate by correcting the flow coefficient with the pressure ratio will be described with reference to FIG. This process is performed in the ECU 30.

The opening of the electric throttle valve 13 (duty ratio from the ECU 30) is assigned to a table of throttle valve opening and effective opening area, and the effective opening area corresponding to the throttle valve opening is calculated.
The front-rear pressure ratio (downstream pressure / upstream pressure) of the electric throttle valve 13 is assigned to the pressure ratio and flow coefficient table, and the corrected flow coefficient is calculated. In the table of the pressure ratio and the flow coefficient, the pressure ratio and the flow coefficient are inversely proportional when the pressure ratio is 0.2 or less. That is, the flow coefficient increases as the pressure ratio decreases.

Then, the volumetric flow rate is calculated by substituting the opening area and the corrected flow rate coefficient into the above formula for calculating the flow rate (flow rate = opening area × flow rate coefficient). As a result, when the front-rear pressure ratio of the electric throttle valve 13 is 0.2 or less, the flow rate is calculated with high accuracy by increasing the flow coefficient.
Next, the intake system model of the present invention will be described with reference to FIG.

The intake system model is roughly divided into a throttle model 31, a pump (engine) model 32, a collector model 33, and a cylinder model 34.
The throttle model 31 has the opening degree (opening area) of the electric throttle valve 13, the pressure upstream of the electric throttle valve 13 (atmospheric pressure), and the pressure downstream of the electric throttle valve 13 (pressure in the collector 11). Entered. The front-rear pressure ratio of the electric throttle valve 13 is calculated, and the flow coefficient is calculated based on this. Then, the amount of intake air (volumetric flow rate) passing through the electric throttle valve 13 is calculated by the above formula for calculating the flow rate (flow rate = opening area × flow rate coefficient).

The pump model 32 considers the intake air of the engine 1 as a pump action, and calculates the volume intake air amount based on the engine speed.
The collector model 33 calculates the collector pressure (density) based on the throttle passage intake air amount, the atmospheric pressure, the intake air temperature, the engine speed, and the volume intake air amount.
The cylinder model 34 calculates the cylinder intake amount based on the collector density and the volume intake amount.

FIG. 6 shows a case where the virtual flow velocity (flow coefficient) is corrected from the front-rear pressure ratio in order to calculate the volume flow rate passing through the electric throttle valve 13.
The virtual flow velocity is calculated based on the total stroke volume [m ³ ], the volume efficiency when the throttle valve 13 is fully opened, the engine speed [rpm], and the throttle valve opening area [m ² ] as shown in the following equation. To do.

Virtual flow velocity = total stroke volume × efficiency × number of revolutions / (opening area × 120)
The calculated virtual flow velocity is assigned to the flow velocity / pressure ratio table to calculate the equilibrium value of the flow velocity. Here, the table of flow velocity and pressure ratio is a log-log display, and the flow coefficient (flow velocity) is corrected by multiplying by the inverse of the pressure ratio. For example, when the pressure ratio is 0.2, the flow coefficient (flow velocity) is corrected to be 5 times, and when the pressure ratio is small, the flow rate is calculated accordingly (flow rate = opening area × By substituting in (flow rate coefficient), the corrected flow rate is calculated.

Note that the above-described virtual flow velocity is calculated, assigned to the flow velocity and pressure ratio table (FIG. 6), the pressure ratio is obtained, the flow coefficient is calculated based on this pressure ratio, and the aforementioned flow rate is calculated. The corrected flow rate may be calculated by substituting into the equation (flow rate = opening area × flow rate coefficient).
Further, since the mass flow rate or mass flow rate is calculated using state quantities such as pressure, temperature, density, etc., the mass flow rate or the mass flow rate may be obtained by multiplying the volume flow rate by the mass density or molar density. Thus, if the pressure and temperature are known, the volume flow rate can be obtained, and if the type of gas is known, a physical flow rate such as mass flow rate or molar flow rate can be obtained.

  Heretofore, the amount of air passing through the electric throttle valve 13 has been described as the amount of air passing through the valve, but the present invention is not limited to this. That is, the same applies to the purge gas flow rate passing through the purge valve 19, the EGR gas flow rate passing through the EGR valve 20, or the gas flow rate passing through the check valve 21. In these cases, the collector pressure (density) of the collector model 33 described above may be calculated in consideration of the pressure change due to the purge gas flow rate, the EGR gas flow rate, or the gas flow rate passing through the check valve 21.

Then, by taking into account the purge gas flow rate, the EGR gas flow rate, and the gas flow rate of the check valve 21 portion, the intake air amount sucked into the engine 1 is more accurately calculated, and the correction amount in the fuel injection amount control or the like based on this calculated value To be reflected.
According to the present embodiment, the device calculates the volume flow rate of gas passing through the valve from the valve opening area and the flow coefficient based on the valve front-rear pressure ratio (downstream pressure / upstream pressure), and the valve front-rear pressure ratio is predetermined. When the value is less than or equal to the value, the volumetric flow rate is calculated to increase as the pressure ratio decreases. Therefore, it is possible to improve the estimation accuracy of the volume flow rate (intake flow rate) when the valve front-rear pressure ratio is equal to or less than a predetermined value (for example, when idling or decelerating in an internal combustion engine). In particular, if the fuel injection amount or the like is controlled based on the above estimation, the air-fuel ratio accuracy, idling stability, and torque control accuracy can be improved.

Further, according to the present embodiment, the valve is provided in the intake system (intake passage 9) of the internal combustion engine 1 and the opening area is variable. For this reason, even when the valve front-rear pressure ratio changes according to the opening area of the valve, the volume flow rate can be calculated with high accuracy.
According to the present embodiment, the valve is the throttle valve 13. For this reason, the volume flow rate can be accurately calculated according to the front-rear pressure ratio of the throttle valve 13 in the intake passage 9.

  Further, according to the present embodiment, the valve is a purge valve 19 that controls the opening degree of the purge pipe 15 that guides the evaporated fuel from the fuel tank to the intake side, and an EGR pipe that recirculates part of the exhaust from the exhaust passage 8 to the intake side. 16 is an EGR valve 20 that controls the opening of 16 or a check valve 21 that guides negative pressure to the brake booster. For this reason, the volume flow rate can be calculated with high accuracy for these valves 19 to 21.

Further, according to the present embodiment, the volume flow rate is calculated by correcting the flow rate coefficient so as to be inversely proportional to the pressure ratio when the pressure ratio is a predetermined value or less. For this reason, the characteristics of the pressure ratio and the flow coefficient are a one-to-one function of the pressure ratio and the flow rate, and the flow coefficient correction according to the pressure ratio can be included. The volumetric fluid can be corrected without increasing.
Further, according to the present embodiment, the volume flow rate is calculated by correcting the flow coefficient by multiplying the flow coefficient by the reciprocal of the pressure ratio. For this reason, the flow coefficient can be accurately corrected, and the estimation accuracy of the volume flow rate can be improved.

In this embodiment, the volume flow rate is multiplied by the mass density or the molar density to obtain a mass flow rate or a substance flow rate. Therefore, the mass flow rate or the mass flow rate can be calculated using state quantities such as pressure, temperature, and density.
In the present embodiment, the predetermined value of the valve front-rear pressure ratio is a value in the range of 0.2 to 0.3. For this reason, the error of the flow rate due to the decrease in the pressure ratio can be appropriately suppressed.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram illustrating a process of calculating the volume flow rate by correcting the opening area with the pressure ratio.
The opening of the electric throttle valve 13 is assigned to a table of throttle valve opening and effective opening area, and the opening area corresponding to the throttle valve opening is calculated.
A ratio of correcting the opening area is calculated by assigning the front / rear pressure ratio (downstream pressure / upstream pressure) of the electric throttle valve 13 to a table of the pressure ratio and the opening area correction coefficient. In the opening area correction coefficient calculation table, when the pressure ratio is 0.2 or less, the pressure ratio and the opening area correction coefficient are inversely proportional. That is, the opening area correction coefficient increases as the pressure ratio decreases.

The corrected opening area is calculated by multiplying the opening area by the opening area correction coefficient.
The flow ratio is calculated by assigning the pressure ratio to the table of pressure ratio and flow coefficient.
Then, the volumetric flow rate is calculated by substituting the corrected opening area and the flow rate coefficient into the above-described equation for calculating the flow rate (flow rate = opening area × flow rate coefficient). As a result, even when the front-rear pressure ratio of the electric throttle valve 13 is 0.2 or less, a highly accurate flow rate is calculated by correcting the opening area.

  According to the present embodiment, the volume flow rate is calculated by correcting the valve opening area so as to be inversely proportional to the pressure ratio when the pressure ratio is equal to or less than a predetermined value. For this reason, since it can set so that an opening area may be faithfully increased along with a physical phenomenon, it can correct a flow volume reliably and accurately. The characteristics of the flow rate can be obtained by experiments and used, and can be applied even when theoretical calculation is difficult.

  Heretofore, the flow rate passing through the electric throttle valve 13, the purge valve 19, the EGR valve 20, and the check valve 21 has been described as the volume flow rate, but the present invention is not limited to this. That is, instead of the electric throttle valve 13, a valve (for example, an orifice) fixed so that the intake passage 9 has a constant opening area is used, and the pressure ratio before and after this valve (pressure downstream of the valve / upstream pressure). The amount of air passing through the valve may be calculated by

Then, the intake air amount sucked into the engine 1 is calculated from the purge flow rate, the EGR flow rate, and the flow rate flowing out from the check valve 21, and based on this calculated value, it is reflected in the correction amount in the fuel injection amount control or the like.
Note that the present invention can be similarly applied to an in-cylinder direct injection internal combustion engine.

Configuration diagram showing the flow rate calculation device Diagram showing the flow around the electric throttle valve Table showing pressure ratio and flow coefficient Block diagram for correcting volumetric flow with a corrected flow coefficient based on pressure ratio Block diagram showing the intake system model Block diagram to calculate pressure ratio based on virtual flow velocity Block diagram for correcting the volume flow rate by the correction coefficient of the opening area based on the pressure ratio

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder 5 Spark plug 9 Intake passage 10 Fuel injection valve 11 Collector 13 Electric throttle valve 19 Purge valve 20 EGR valve 21 Check valve 24 Pressure sensor 25 Boost sensor 26 Temperature sensor 27 Crank angle sensor 30 ECU
31 Throttle model 32 Pump model 33 Collector model 34 Cylinder model

Claims (13)

An apparatus for calculating a volumetric flow rate of gas passing through a valve from a valve opening area and a flow coefficient based on a valve front-rear pressure ratio,
When the valve front-rear pressure ratio is less than or equal to a predetermined value, the flow rate calculation device calculates the volumetric flow rate to increase as the pressure ratio decreases.   2. The flow rate calculating device according to claim 1, wherein the valve is provided in an intake system of an internal combustion engine and the opening area is variable.   The flow rate calculation device according to claim 2, wherein the valve is a throttle valve.   3. The flow rate calculation device according to claim 2, wherein the valve is a purge valve that controls an opening degree of a purge pipe that guides the evaporated fuel from the fuel tank to the intake side.   The flow rate calculation device according to claim 2, wherein the valve is an EGR valve that controls an opening degree of an EGR pipe that recirculates a part of the exhaust gas from the exhaust passage to the intake side.   The flow rate calculating device according to claim 2, wherein the valve is a check valve that guides a negative pressure to a brake booster.   2. The flow rate calculating device according to claim 1, wherein the valve is a fixed valve provided in an intake system of an internal combustion engine and having a constant valve opening area.   8. The volume flow rate is calculated by correcting a flow rate coefficient so as to be inversely proportional to the pressure ratio when the pressure ratio is equal to or less than the predetermined value. The flow rate calculation device described in 1.   The volume flow rate is calculated by correcting a valve opening area so as to be inversely proportional to the pressure ratio when the pressure ratio is equal to or less than the predetermined value. The flow volume calculation apparatus as described in one.   8. The flow rate calculation according to claim 1, wherein the volume flow rate is calculated by multiplying the flow rate coefficient by a reciprocal of the pressure ratio to correct the flow rate coefficient. apparatus.   The flow rate calculation device according to claim 1, wherein a mass flow rate is obtained by multiplying the volume flow rate by a mass density.   The flow rate calculation device according to any one of claims 1 to 10, wherein the volume flow rate is multiplied by a molar density to obtain a substance flow rate.   The flow rate calculation device according to any one of claims 1 to 12, wherein the predetermined value of the valve front-rear pressure ratio is a value in a range of 0.2 to 0.3.

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