JP4736403B2 - Flow rate calculation device for internal combustion engine - Google Patents

Description

  The present invention relates to a flow rate calculation device for an internal combustion engine.

Since the natural world is a continuous system with Δt = 0, hunting does not occur. However, when the calculation is performed by discrete system modeling such as calculation of the intake air amount of the internal combustion engine, the calculation result may be hunted. In order to make hunting difficult in the convergence calculation, the calculation interval (Δt) may be made extremely small. On the other hand, the calculation load increases.
In Patent Document 1, in an intake air amount calculation device for an engine, an intake air amount passing through a throttle valve is calculated from a throttle valve opening area and a flow coefficient based on a valve front-rear pressure ratio (downstream pressure / upstream pressure of the throttle valve). It is described to do. When the intake air amount is discretely calculated when the pressure ratio is near 1.0, the upper limit of the pressure ratio is limited to a constant value such as 0.98, thereby suppressing an intake air amount calculation error caused by hunting.
JP 2003-254148 A

However, since the upper limit of the pressure ratio is limited to a constant value in Patent Document 1, the intake air amount is calculated when the pressure ratio is near 1.0, such as when the engine is started, that is, when the intake air amount (flow velocity) passing through the throttle valve is small. There was a problem that accuracy deteriorated.
The present invention has been made in view of the above problems, and an object of the present invention is to improve the calculation accuracy of the intake air amount while suppressing hunting in a state where the pressure ratio is near 1.0.

Therefore, in the present invention, an apparatus for calculating the volumetric flow rate of the gas passing through the throttle valve from the throttle valve opening area and the flow coefficient based on the throttle valve front-rear pressure ratio,
Limit the throttle valve front-rear pressure ratio to the maximum pressure ratio that can be theoretically taken,
The maximum pressure ratio is an equilibrium value of the pressure ratio when the throttle valve opening is substantially fully open, and is obtained by a flow rate when the throttle valve opening is substantially fully open and a function of the flow rate and the pressure ratio. I made it.

  According to the present invention, the valve front-rear pressure ratio is limited to the maximum pressure ratio, so that hunting can be suppressed and the calculation accuracy of the intake air amount can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system configuration diagram of a flow rate calculation device of the engine 1.
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.

Further, the ECU 30 receives signals from the throttle valve opening sensor 23, the pressure sensor 24, the boost sensor (pressure sensor) 25, the temperature sensor 26, and the crank angle sensor 27.
The throttle valve opening sensor 23 outputs a signal corresponding to the opening degree of the electric throttle valve 13.

The pressure sensor 24 is provided in the intake passage 9 upstream of the electric throttle valve 13 and outputs a signal corresponding to the pressure (upstream pressure).
The boost sensor 25 is provided in the collector 11 downstream of the electric throttle valve 13 and outputs a signal corresponding to the pressure in the collector 11 (downstream pressure).
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, and the like are performed.

FIG. 2 shows the relationship between the pressure ratio (downstream pressure / upstream pressure of the electric throttle valve 13) and the flow coefficient (a value proportional to the flow rate or flow velocity).
When the front / rear pressure ratio of the electric throttle valve 13 is 1.0, that is, when the intake air is not flowing, the flow coefficient (value relating to the pressure ratio) is 0, and the flow velocity is 0. 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. When the pressure ratio decreases until it becomes critical, the flow coefficient converges to a predetermined value (flow velocity = sound velocity).

The flow rate (volume flow rate) of the air passing through the electrically controlled throttle valve 13 is calculated by multiplying the opening area of the electrically controlled throttle valve 13 and the flow coefficient by the following equation.
However, as shown in FIG. 2, when the pressure ratio is in the vicinity of 1.0, the change in the flow coefficient (flow velocity) becomes large, which may cause an error in the flow rate. This is because the pressure change in the collector 11 due to the change in the flow velocity becomes too large with respect to the calculation interval Δt (here, Δt = 10 ms). If the calculation interval Δt is not calculated with a sufficiently fine discrete system, the flow coefficient changes too much and hunting occurs as shown in FIG.

3A shows the elapsed time and the pressure (downstream pressure) P ₂ in the collector 11, and FIG. 3B shows the elapsed time and the flow coefficient (flow velocity). In FIG. 3, the front-rear pressure ratio is not limited at all, and hunting occurs because the calculation interval Δt is not calculated with a sufficiently fine discrete system.
Here, the downstream pressure (collector pressure [kPa]) P ₂ of the electric throttle valve 13 is expressed by the following equation by modifying the equation of state of the ideal gas.

P ₂ · V _C = n ・ R ・ T
ΔP ₂ = Δn · R · T ₂ / V _C
P ₂ −P _{2 (n−1)} = (n _in −n _out ) R · T ₂ / V _C
P ₂ = P _{2 (n−1)} + (n _in −n _out ) Δt · R · T ₂ / V _C
This expression indicates that the current collector pressure P ₂ is obtained by adding a change amount with respect to the calculation time Δt to the previous value P _{2 (n−1)} . T ₂ is the temperature in the collector 11 (downstream temperature [K]), R is the gas constant, V _C is the volume [m ³ ] of the collector 11, Δt is the calculation interval [sec], and n _in is entering the collector 11. The mass [kg / s] of air and n _out are the mass [kg / s] of air exiting from the collector 11.

Since this equation obtains the state quantity of each part (pressure P ₂ in the collector 11) by convergence calculation, as shown in FIG. 2, the pressure ratio is near 1.0, that is, when the valve opening is near full open, Hunting becomes easier as the calculation interval Δt is larger.
Further, as in Patent Document 1, when the upper limit value of the pressure ratio is set to 0.98, hunting is suppressed as shown in FIG. 4 (b), but 0.98 even when the pressure ratio is 0.98 or more. In order to limit to the flow coefficient (a constant value) in FIG. 8, the actual value is discarded as shown in FIG. 8 (B), which will be described later, resulting in a large flow rate error in the pressure ratio range of 0.98 to 1.00. turn into.

Therefore, in the present invention, even in the range of 0.98 to 1.00, by restricting the front / rear pressure ratio of the electric throttle valve 13 to the maximum pressure ratio that can be theoretically taken, the flow rate is prevented while preventing hunting. The accuracy of calculation is to be ensured.
FIG. 5 is a flowchart showing the processing of the present invention. This process is performed when the flow rate passing through the electric throttle valve 13 is small (when the flow velocity is low).

In Step 1 (shown as “S1” in the figure, the same applies hereinafter), the engine speed Ne, the upstream pressure P ₁ and the downstream pressure P ₂ of the electric throttle valve 13 are calculated. The upstream pressure P ₁ is calculated based on the output signal of the pressure sensor 24. The upstream pressure may be a constant value corresponding to atmospheric pressure. Further, the downstream pressure P ₂ is calculated based on the output signal of the boost sensor 25.
In step 2, the maximum opening area of the electric throttle valve 13 is obtained. The maximum opening area uses a value when the throttle valve opening is 80 deg with reference to a table showing the relationship between the throttle valve opening and the opening area. Thereby, the opening area in the vicinity of the pressure ratio of 1.0 is calculated.

In step 3, the volumetric efficiency η is obtained. As shown in FIG. 6, the volumetric efficiency η is obtained with reference to a table showing the relationship between the rotational speed Ne and the efficiency η. In this table, the efficiency η increases as the rotational speed Ne increases to a predetermined value, and the efficiency η tends to decrease when the rotational speed Ne increases.
In step 4, as shown in the following equation, the volume efficiency η, the displacement V [m ³ ], the engine speed Ne [rpm], and the maximum opening area Ath [m ² ] of the electric throttle valve 13 are maximized. Calculate the temporary flow velocity [m / s].

Maximum temporary flow velocity = η x V x Ne / (Ath x 120)
In step 5, the maximum pressure ratio (equilibrium value) Rmax of the electric throttle valve 13 is obtained based on the maximum temporary flow velocity calculated in step 4. As shown in FIG. 7, the maximum pressure ratio Rmax is obtained by referring to a table of flow velocity (maximum temporary flow velocity) and pressure ratio. This table is a function of the flow rate and the pressure ratio. When the flow rate is high, the pressure ratio is low, and when the flow rate is low, the pressure ratio tends to be high.

The maximum pressure ratio Rmax calculated by this table is an equilibrium value in a state where the opening degree of the electric throttle valve 13 is substantially fully opened and the flow velocity is low. Thereby, the maximum pressure ratio Rmax that can be theoretically taken by the front-rear pressure ratio (downstream pressure / upstream pressure) of the electric throttle valve 13 is calculated.
In step 6, the upstream pressure P ₁ calculated by the pressure sensor 24 is divided from the downstream pressure P ₂ calculated by the boost sensor 25 to calculate a pressure ratio (P ₂ / P ₁ ) based on the sensor output.

In step 7, whether or not the pressure ratio (P ₂ / P ₁ ) based on the sensor output calculated in step 6 is less than the maximum pressure ratio Rmax (P ₂ / P ₁ <Rmax) based on the flow velocity calculated in step 5. Determine whether. If it is determined that P ₂ / P ₁ <Rmax, the routine proceeds to step 8 where the pressure ratio is set to P ₂ / P ₁ .
On the other hand, if it is determined in step 7 that P ₂ / P ₁ ≧ Rmax, the process proceeds to step 9 and the pressure ratio is set to Rmax. As a result, the front / rear pressure ratio of the electric throttle valve 13 is limited to the maximum pressure ratio Rmax that can be theoretically taken.

In step 10, the flow coefficient is calculated by assigning the pressure ratio calculated in step 8 or 9 to the flow coefficient calculation table shown in FIG.
In step 11, the flow rate of the gas passing through the electric throttle valve 13 is calculated by the above formula (flow rate = opening area × flow rate coefficient).
FIG. 8 is a view showing a state in which the front-rear pressure ratio is limited when the electric throttle valve 13 is substantially fully open. In (A), the horizontal axis indicates the elapsed time (ms), and the vertical axis indicates the pressure (downstream pressure) P ₂ in the collector 11. (B) shows the elapsed time (ms) on the horizontal axis and the flow coefficient on the vertical axis.

Here, the upper limit value of the pressure P ₂ in the collector 11 is set to the equilibrium value Rmax of the pressure ratio when the electric throttle valve 13 is substantially fully open (80 deg), so that the same calculation interval Δt as in the case of FIG. Hunting can be prevented even at (10 ms). In the present invention, the actual flow coefficient is calculated without hunting even at a pressure ratio of 0.98 or more.
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 an opening (effective opening area) of the electric throttle valve 13, an upstream pressure (atmospheric pressure) P _{1 of} the electric throttle valve 13, and a downstream pressure (pressure in the collector 11) of the electric throttle valve 13. P ₂ is input. The front-rear pressure ratio (P ₂ / P ₁ ) of the electric throttle valve 13 is calculated and compared with the above-mentioned maximum pressure ratio Rmax (P ₂ / P ₁ <Rmax). The flow coefficient is calculated based on (P ₂ / P ₁ or Rmax). Then, the flow rate of the gas 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) (see FIG. 5).

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 Ne.
The collector model 33 calculates a collector pressure (density) P ₂ based on the throttle-passing gas flow rate, the upstream pressure P ₁ , the intake air temperature, the engine speed Ne, and the volume intake air amount. The throttle valve downstream pressure P ₂ is calculated from the throttle valve upstream pressure P ₁ and the maximum pressure ratio Rmax (P ₂ = P ₁ × Rmax), and the pressure P ₂ in the collector 11 that changes over time is sequentially applied. You may make it update. In this case, the pressure (downstream pressure) P ₂ in the collector 11 is limited to the convergence value.

The cylinder model 34 calculates the cylinder intake amount based on the collector density and the volume intake amount.
Incidentally, in this intake system model, the collector model 33 be calculated based downstream pressure P ₂ of the electronic throttle valve 13 throttle-passing gas flow, at atmospheric pressure, intake air temperature, engine speed Ne, and volume intake air amount However, the downstream pressure P ₂ calculated by the boost sensor 25 described above may be used. In this case, the throttle model 31 calculates the pressure ratio, and calculates the flow rate of the gas passing through the electric throttle valve 13 according to the above formula (flow rate = opening area × flow rate coefficient).

Even when a turbocharger (turbo) is used, the volumetric flow rate of the gas passing through the valve can be calculated with high accuracy while preventing hunting by setting the upstream pressure to the supercharged pressure. May be.
Note that the present invention can be similarly applied to an in-cylinder direct injection internal combustion engine.
According to the present embodiment, the apparatus calculates the volume flow rate of the gas passing through the valve 13 from the throttle valve opening area and the flow coefficient based on the valve front-rear pressure ratio, and is the maximum that can theoretically take the valve front-rear pressure ratio. The pressure ratio is limited to Rmax. For this reason, hunting can be suppressed, and the calculation accuracy of the flow rate of the gas passing through the electric throttle valve 13 can be improved even when the intake air amount is low.

Further, according to the present embodiment, the maximum pressure ratio Rmax is an equilibrium value of the pressure ratio when the throttle valve opening is substantially fully open (for example, the opening of the electric throttle valve 13 is 80 deg) (step 5). For this reason, the conditions when the maximum pressure ratio Rmax takes the upper limit value can be set appropriately.
Further, according to the present embodiment, the maximum pressure ratio Rmax is obtained from a flow rate when the throttle valve opening is substantially fully open and a function of the flow rate and the pressure ratio (step 5). For this reason, the maximum pressure ratio Rmax can be obtained in consideration of the flow velocity and the pressure ratio.

Further, according to the present embodiment, the flow velocity is calculated based on the throttle valve opening area and the engine speed (steps 2 to 4). For this reason, the flow velocity of the gas passing through the electric throttle valve 13 can be calculated with high accuracy.
Further, according to this embodiment, the valve front-rear pressure ratio is obtained by dividing the downstream pressure P ₂ of the throttle valve 13 by the upstream pressure P ₁ (downstream pressure P ₂ / upstream pressure P ₁ ). For this reason, the upstream and downstream pressures of the throttle valve 13 due to the intake action of the engine 1 can be considered. The front-rear pressure ratio (P ₂ / P ₁ ) is calculated from the outputs of the pressure sensors 24 and 25 as described above, or the pressure P ₂ in the collector 11 is calculated by the collector model 33, and this pressure P ₂ is calculated. Input into the throttle model 31 to calculate.

Further, according to the present embodiment, the upstream pressure P ₁ of the throttle valve 13 uses an atmospheric pressure equivalent value (steps 1 and 8). For this reason, the maximum pressure ratio can be simply calculated.
According to the present embodiment, the upstream pressure of the throttle valve 13 is a supercharged pressure. For this reason, it becomes applicable also to a diesel engine.
Further, according to the present embodiment, the downstream pressure P ₂ of the throttle valve 13 is calculated by the collector model 33. For this reason, even when the boost sensor 25 is not used, the downstream pressure P ₂ can be calculated. Further, even when other piping (for example, EGR piping, purge piping, etc.) is provided in the collector 11, these influences can be taken into consideration.

Further, according to the present embodiment, the downstream pressure P ₂ of the throttle valve is calculated from the throttle valve upstream pressure P ₁ and the maximum pressure ratio Rmax (collector model 33 in FIG. 9). For this reason, the pressure P ₂ in the collector 11 that changes with the passage of time can be sequentially updated.
Further, according to the present embodiment, the throttle model 31, the pump model 32, and the collector model 33 constitute a model for calculating the state quantities (the intake air amount that passes through the electric throttle valve 13, the collector pressure, and the volume intake air amount). Then, the intake air amount sucked into the cylinder 2 is calculated based on these calculated values. Therefore, the cylinder intake air amount can be calculated from the model.

System configuration diagram of flow rate calculation device Flow coefficient calculation table Diagram showing hunting state The figure which shows the case where the upper limit of the pressure ratio is 0.98 Flow chart showing processing of the present invention Volumetric efficiency calculation table Pressure ratio calculation table The figure which shows the case where the pressure ratio restriction | limiting of this invention is performed Block diagram showing the intake system model

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 23 Throttle valve opening sensor 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 (8)

An apparatus for calculating a volumetric flow rate of gas passing through a throttle valve from a throttle valve opening area and a flow coefficient based on a throttle valve front-rear pressure ratio,
Limit the throttle valve front-rear pressure ratio to the maximum pressure ratio that can be theoretically taken,
The maximum pressure ratio is an equilibrium value of the pressure ratio when the throttle valve opening is substantially fully open, and is obtained by a flow rate when the throttle valve opening is substantially fully open and a function of the flow rate and the pressure ratio. A flow rate calculation device for an internal combustion engine characterized by the above. The flow rate, the flow rate calculation apparatus for an internal combustion engine according to claim 1, characterized in that calculated on the basis of said throttle valve opening area and the engine speed. 3. The flow rate calculation device for an internal combustion engine according to claim 1, wherein the throttle valve front-rear pressure ratio is obtained by dividing the downstream pressure of the throttle valve by the upstream pressure. 4. The internal combustion engine flow rate calculation apparatus according to claim 3 , wherein the upstream pressure of the throttle valve uses an atmospheric pressure equivalent value. 4. The internal combustion engine flow rate calculation apparatus according to claim 3, wherein the upstream pressure of the throttle valve is a supercharged pressure. The flow rate calculation device for an internal combustion engine according to any one of claims 3 to 5 , wherein the downstream pressure of the throttle valve is calculated by a collector model. The flow rate calculation device for an internal combustion engine according to any one of claims 3 to 5 , wherein the downstream pressure of the throttle valve is calculated from the upstream pressure of the throttle valve and the maximum pressure ratio. The throttle model, the pump model, and the collector model constitute a model for calculating the state quantity of each part, and the intake air amount sucked into the cylinder is calculated based on these calculated values. 8. The flow rate calculation device for an internal combustion engine according to any one of 7 above.

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