JP2005083240A - Intake air amount estimation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately estimate an intake air amount even immediately even after starting an engine more accurately than conventional devices in an intake air amount estimation device for an internal combustion engine that calculates the intake air amount by using a linear function where an intake pressure at a downstream of a throttle valve is a variable. <P>SOLUTION: In the intake air amount estimation device for the internal combustion engine that specifies a linear function for calculating the intake air amount where the intake pressure at the downstream of the throttle valve 6 is a variable based on the operation state of the engine and calculates the intake air amount using the specified linear function, the liner function is specified in view of intake air heating temperature based on the engine temperature as well. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an intake air amount estimation device for an internal combustion engine.

  In order to realize accurate air-fuel ratio control, it is necessary to accurately grasp the intake air amount. In order to detect the intake air amount, it is common to install an air flow meter in the engine intake system. However, since the air flow meter has a response delay, a relatively accurate intake air amount can be detected when the engine is stationary. However, only an incorrect intake air amount can be detected during engine transition.

  In order to grasp a relatively accurate intake air amount even during engine transition, it has been proposed to model the engine intake system and sequentially calculate the intake air amount (see, for example, Patent Document 1). In this intake air amount estimation device, the intake air amount is calculated by a linear function based on the intake pressure downstream of the throttle valve. The linear function used to calculate the intake air amount changes with each engine operating state, and the coefficient and constant for specifying the linear function are mapped and adapted for each engine speed and each valve overlap period. ing.

  At the time of mapping, since the coefficients and constants are set for the internal combustion engine at the specific engine temperature after warm-up, even if a linear function specified based on the current engine operating state is used immediately after engine startup, An accurate intake air amount may not be calculated.

JP 2001-41095 A JP 2002-332884 A

  Accordingly, an object of the present invention is to provide an intake air amount estimation device for an internal combustion engine that calculates an intake air amount using a linear expression with the intake pressure downstream of the throttle valve as a variable, as compared with the conventional system even immediately after engine startup. It is possible to accurately calculate the intake air amount.

  According to a first aspect of the present invention, there is provided an internal combustion engine intake air amount estimation device that identifies and specifies a linear function for calculating an intake air amount based on an intake air pressure downstream of a throttle valve as a variable. In the intake air amount estimation apparatus for an internal combustion engine that calculates the intake air amount using a linear function, the linear function is specified in consideration of the intake heating temperature based on the engine temperature.

  According to a second aspect of the present invention, there is provided an internal combustion engine intake air amount estimation device that specifies and identifies a linear function for calculating an intake air amount based on an intake air pressure downstream of a throttle valve as a variable. In the intake air amount estimation device for an internal combustion engine that calculates the intake air amount using a linear function, the calculated intake air amount is corrected based on an intake heating temperature based on the engine temperature.

  An intake air amount estimation device for an internal combustion engine according to claim 3 according to the present invention is the intake air amount estimation device for an internal combustion engine according to claim 1 or 2, wherein the engine temperature is based on a cooling water temperature or a lubricating oil temperature. It is determined.

  An intake air amount estimation device for an internal combustion engine according to a fourth aspect of the present invention is the intake air amount estimation device for an internal combustion engine according to any one of the first to third aspects, wherein the intake heating temperature is the engine temperature. It is determined based on temperature and atmospheric temperature.

  According to the intake air amount estimation apparatus for an internal combustion engine according to claim 1, the linear function for calculating the intake air amount is specified in consideration of not only the engine operating state but also the intake heating temperature based on the engine temperature. Therefore, the intake air amount can be accurately calculated even when the engine temperature is low immediately after the engine is started and the intake air is not excessively expanded.

  According to the intake air amount estimating apparatus for an internal combustion engine according to claim 2, the intake air amount calculated using the linear function specified based on the engine operating state is the intake air heating temperature based on the engine temperature. Therefore, the intake air amount can be accurately calculated even when the engine temperature is low and the intake air is not thermally expanded immediately after the engine is started.

  FIG. 1 is a schematic diagram showing an internal combustion engine to which a control device according to the present invention is attached. In the figure, 1 is an engine body, and 2 is a surge tank common to each cylinder. An intake branch pipe 3 communicates the surge tank 2 with each cylinder, and 4 is an intake passage upstream of the surge tank 2. A fuel injection valve 5 is disposed in each intake branch pipe 3, and a throttle valve 6 is disposed immediately upstream of the surge tank 2 in the intake passage 4. Here, the throttle valve 6 is not linked to the accelerator pedal, but can be freely set by a driving device such as a step motor. However, the throttle valve 6 may be linked to the accelerator pedal. A throttle valve opening sensor for measuring the throttle valve opening is attached to the throttle valve 6. In the engine body 1, 8 is an intake valve, 9 is an exhaust valve, and 10 is a piston.

  In order to set the combustion air-fuel ratio in the internal combustion engine 1 to a desired air-fuel ratio such as, for example, the theoretical air-fuel ratio, it is necessary to accurately estimate the amount of intake air flowing into the cylinder including when the engine is in transition. . In this embodiment, the engine intake system is modeled and the intake air amount is estimated by calculation.

First, by modeling the throttle valve 6, using the energy conservation law, the momentum conservation law, and the state equation when intake air passes through the throttle valve 6, the current throttle valve passage air amount mt _(i) (G / sec) can be expressed by the following equation (1). Including the following expression, the subscript (i) of the variable such as the throttle valve passing air amount indicates the current time, and (i-1) indicates the previous time.

Here, μ _(i) is a flow coefficient, and A _(i) is an opening area (m ² ) of the throttle valve 6. Of course, when an idle speed control valve (ISC valve) is provided in the engine intake system, the opening area of the ISC valve is added to A _(i) . Each of the flow coefficient and the opening area of the throttle valve is a function of the throttle valve opening TA _(i) (degree), and FIGS. 2 and 3 show maps for the respective throttle valve openings TA. Yes. R is a gas constant. Ta is an intake air temperature (K) on the upstream side of the throttle valve, and may be measured on the upstream side of the throttle valve in the intake passage 4, but may be an atmospheric temperature. Pac is an intake passage pressure (kPa) upstream of the throttle valve (hereinafter referred to as upstream pressure), and Pm _(i) is an intake pipe pressure (kPa) downstream of the throttle valve (hereinafter referred to as downstream pressure). Called). The function Φ (Pm _(i) / Pac) is expressed by the following equation (2) using the specific heat ratio κ, and FIG. 4 shows a map for Pm / Pac.

  Although the upstream pressure Pac may be atmospheric pressure, an air cleaner is provided at the most upstream part of the engine intake system, and strictly speaking, it is preferable to calculate by subtracting the pressure loss of the air cleaner from atmospheric pressure. The pressure loss of the air cleaner can be calculated by Bernoulli's theorem based on the flow rate of air passing through the air cleaner. This air flow rate can be the output value when an air flow meter is provided immediately downstream of the air cleaner, or may be the previous throttle valve passing air amount calculated by the equation (1). .

Next, the intake valve is modeled. Since the intake air amount mc _(i) (g / sec) supplied into the cylinder changes substantially linearly based on the downstream pressure Pm _(i) , the linear expression shown in the following equation (3) Can be represented.

Here, Tm _(i) is the intake air temperature (K) on the downstream side of the throttle valve, and the coefficient a and the constant b for specifying the equation (3) are adapted values set to suit each internal combustion engine. is there. Here, b is a value corresponding to the amount of residual burned gas in the cylinder, and increases as the valve overlap period is longer because a larger amount of burned gas flows back to the intake pipe. Accordingly, in order to calculate an accurate intake air amount mc, it is preferable that the coefficient a and the constant b are set for each engine state. That is, not only for each engine speed, but also when the internal combustion engine has a variable valve tamming mechanism, there are control devices that affect the valve overlap amount, the maximum lift amount of the intake valve, and other intake air amounts. If provided, it is preferable to map the values of the coefficient a and the constant b that specify the primary expression for calculating the intake air amount mc for each control amount.

Next, the intake pipe is modeled. Using the intake mass conservation law, the energy conservation law, and the equation of state existing in the intake pipe, the rate of time change in the ratio between the downstream pressure Pm and the intake air temperature Tm downstream of the throttle valve is expressed by the following equation (4): The time change rate of the downstream pressure Pm is expressed by the following equation (5). Here, V is the volume (m ³ ) of the intake pipe on the downstream side of the throttle valve 6 in the engine intake system. Specifically, the downstream side of the throttle valve 6 in the intake passage 4, the surge tank 2, and the intake branch pipe 3. And the total volume.

Equations (4) and (5) are discretized to obtain the following equations (6) and (7), respectively, and if the current downstream pressure Pm _(i) is obtained by equation (7), 6) to obtain the current intake air temperature Tm _(i) in the intake pipe, and based on the current throttle valve opening area A _(i) and the current flow coefficient μ _{(i) according} to equation (1). The throttle valve passage air amount mt _(i) can be obtained. Further, the current intake air amount mc _(i) can be obtained based on the current intake temperature Tm _(i) and the current downstream pressure Pm _(i ) by the expression (3). At the next calculation time, the downstream pressure Pm _(i) of this time is calculated by the equation (7), with the downstream pressure, the intake air temperature, the throttle valve passing air amount, and the intake air amount as previous values. By repeating this, the intake air amount mc is sequentially calculated. In the equations (6) and (7), the discrete time Δt is a time interval for calculating the intake air amount mc, for example, 8 ms. In addition, the throttle valve opening area A _(i) and the flow coefficient μ _(i) used for calculating the throttle valve passing air amount mt _{( i)} are determined based on the current depression amount of the accelerator pedal. It is estimated in consideration of the response delay of the device (step motor).

  By the way, the intake air temperature Tm in the intake pipe calculated in the equation (6) is a value calculated as a result of adiabatic compression in the intake pipe, and no transfer of heat to and from the intake pipe is considered. In the equation (3) for calculating the intake air amount mc, the coefficient a and the constant b for specifying this linear equation are generally set for each engine operating state at a specific engine temperature after warm-up. That is, it is assumed that the intake air receives heat from the intake branch pipe 5 (particularly, the intake passage in the cylinder head) that is at a specific engine temperature after warming up and thermally expands. . Thereby, if the current engine temperature is the specific engine temperature after warming up when the coefficient a and the constant b are set (for example, the cooling water temperature is 90 ° C.), there is no problem, but immediately after the engine is started. If it is before warm-up, the intake air in the intake branch pipe does not expand much, and the primary equation specified by the coefficient a and the constant b based on the current engine operating state is used to specify the Even if the intake air amount mc is calculated on the premise of thermal expansion with respect to the engine temperature, the intake air amount is smaller than the actual amount.

  In order to solve this problem, in this embodiment, a coefficient a and a constant b for specifying a primary expression for calculating the intake air amount not only for each engine operating state but also for each engine temperature are mapped, The linear expression (3) is specified using the coefficient a and the constant b selected based on the current engine operating state and the current engine temperature. By such mapping, it is considered that the lower the engine temperature, the smaller the degree of thermal expansion of the intake air, and the primary expression is specified so that the calculated intake air amount increases in accordance with the actual amount. become.

Further, as shown in the following equation (8), the intake air amount may be calculated by multiplying and correcting the equation (3) specified by the current engine operating state by the correction coefficient K. The correction coefficient K is increased as the engine temperature is lower, and is 1 if the specific engine temperature after warm-up when the coefficient a and the constant b are set.

  The engine temperature described above can be represented by the coolant temperature detected by the coolant temperature sensor or the lubricating oil temperature detected by the oil temperature sensor. FIG. 5 is a map of the correction coefficient K when the coolant temperature THW is used as the engine temperature. In FIG. 5, the correction coefficient K is 1 when the coolant temperature (for example, 90 ° C.) corresponds to the specific engine temperature when the coefficient a and the constant b are set, and the correction coefficient when the coolant temperature is higher than that. However, strictly speaking, since the intake air further expands at this time, the correction coefficient K may be set to a value smaller than 1 as indicated by a dotted line.

  Thus, the lower the engine temperature is the intake air heating temperature, the smaller the degree of thermal expansion of the intake air due to the heat received from the intake branch pipe, and the more the intake air amount increases, the more accurate it is compared to the prior art. The amount of intake air can be calculated. However, strictly speaking, the degree of thermal expansion of the intake air is based on the difference between the engine temperature and the atmospheric temperature. That is, if the atmospheric temperature is high and the difference is small with respect to the same engine temperature, the degree of thermal expansion of the intake air is small. Thereby, the intake air heating temperature is preferably set to a difference between the engine temperature and the atmospheric temperature.

  FIG. 6 is a map of the correction coefficient K ′ similar to the above when the intake air heating temperature is the difference TD between the engine temperature and the atmospheric temperature. Of course, instead of multiplying and correcting the equation (3) by the correction coefficient K ′, the coefficient a and the constant b for specifying the primary expression for calculating the intake air amount are set for each engine operating state and the difference TD. You may make it map every time. Further, the difference TD may be calculated as the intake air temperature Tm in the intake pipe calculated by the equation (6) based on the atmospheric temperature Ta instead of the atmospheric temperature. In the present embodiment, the downstream pressure Pm for calculating the intake air amount mc is calculated based on the throttle valve passing air amount mt or the like. Of course, the downstream pressure Pm is actually measured by a pressure sensor, This may be used to calculate the intake air amount mc. Even in this case, by applying the above-described concept, the intake air amount can be accurately calculated immediately after the engine is started.

By the way, in order to accurately control the combustion air-fuel ratio, it is necessary to estimate the correct intake air amount into the cylinder and determine the fuel injection amount before starting the fuel injection. However, in order to estimate the accurate intake air amount, strictly speaking, the intake air flow rate when the intake valve is closed must be calculated. That is, when determining the fuel injection amount, the intake air amount mc _{(i + n)} when the intake valve is closed must be calculated instead of the current intake air amount mc _(i) . This applies not only to the internal combustion engine that injects fuel into the intake branch pipe 3 as shown in FIG. 1 but also to the internal combustion engine that directly injects fuel into the cylinder during the intake stroke.

To this end, not only the current throttle valve opening area A _(i) (or opening) but also the throttle valve opening area A _{(i + 1)} , every time Δt until the intake valve closes, Based on A _{(i + 2)} ,... A _{(i + n)} , it is necessary to calculate the throttle valve passage air amount mt at each time by changing the steady downstream pressure Pmta in the equation (11). .

  The opening area A (or opening TA) of the throttle valve at each time is based on the change in depression of the accelerator pedal with respect to the current time, and it is assumed that the change in depression lasts until the intake valve closes. It is conceivable that the amount of depression of the throttle valve is estimated and the estimated amount of depression is determined in consideration of the response delay of the throttle valve actuator. This method can also be applied when the throttle valve is mechanically connected to the accelerator pedal.

However, the estimated opening area A _{(i + n)} of the throttle valve when the intake valve is closed as described above is merely a prediction, and there is no guarantee that it matches the actual situation. In order to make the opening area A _{(i + n)} of the throttle valve coincide with the actual value when the intake valve is closed, the throttle valve may be controlled to be delayed. When the amount of depression of the accelerator pedal changes, the throttle valve opening varies with delay due to the response delay of the actuator. This delay control intentionally increases the response delay of the throttle valve.

For example, during an engine transition, the actual response delay (dead time) so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal when determining the fuel injection amount is realized when the intake valve is closed. If the throttle valve actuator is controlled in consideration of the above, the throttle valve opening areas A _(i) , A _{(i + 1)} ,... A _{(i + n )} Can be grasped accurately. More specifically, when the amount of depression of the accelerator pedal changes, an operation signal is not immediately sent to the actuator, but the dead time is subtracted from the time from when the fuel injection amount is determined to when the intake valve is closed. An operation signal to the actuator is issued when the time has elapsed. Of course, the throttle valve delay control may be performed so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal is realized after the intake valve is closed.

1 is a schematic view of an internal combustion engine to which an intake air amount estimation device according to the present invention is attached. It is a map which shows the relationship between throttle-valve opening degree TA and the flow coefficient (micro | micron | mu). It is a map which shows the relationship between the throttle valve opening degree TA and the opening area A of a throttle valve. It is a map which shows the relationship between the ratio of the intake pipe pressure Pm and the upstream pressure Pac, and the function Φ. It is a map which shows the relationship between engine temperature and a correction coefficient. It is a map which shows the relationship between the difference of engine temperature and atmospheric temperature, and a correction coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine body 2 ... Surge tank 3 ... Intake branch pipe 4 ... Intake passage 6 ... Throttle valve

Claims (4)

  In an intake air amount estimation device for an internal combustion engine that specifies a linear function for calculating an intake air amount based on an engine operating state using an intake pressure downstream of a throttle valve as a variable, and calculates the intake air amount by the specified linear function The linear function is specified in consideration of an intake air heating temperature based on the engine temperature.   In an intake air amount estimation device for an internal combustion engine that specifies a linear function for calculating an intake air amount based on an engine operating state using an intake pressure downstream of a throttle valve as a variable, and calculates the intake air amount by the specified linear function The calculated intake air amount is corrected based on an intake air heating temperature based on the engine temperature.   The intake air amount estimation device for an internal combustion engine according to claim 1 or 2, wherein the engine temperature is determined based on a cooling water temperature or a lubricating oil temperature.   The intake air amount estimation device for an internal combustion engine according to any one of claims 1 to 3, wherein the intake air heating temperature is determined based on the engine temperature and the atmospheric temperature.

Images