JP5494204B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to a control device for an internal combustion engine provided with an evaporated fuel processing device.

  2. Description of the Related Art There is known an evaporative fuel processing device for preventing evaporative fuel generated in a fuel tank of an internal combustion engine for a vehicle from being released into the atmosphere. This evaporative fuel processing apparatus has a canister filled with activated carbon inside, and temporarily adsorbs and collects evaporative fuel on the activated carbon. Here, the fuel adsorbed and collected by the canister is desorbed by a purge process using the negative pressure of the intake air at a predetermined timing during operation of the internal combustion engine, and introduced into the combustion chamber of the internal combustion engine together with fresh air. It is burned.

  In this purge process, the amount of fuel contained in the purge gas (gas containing evaporated fuel) introduced into the internal combustion engine is not constant and varies depending on the amount of fuel adsorbed and held in the canister. Therefore, from the viewpoint of improving the air-fuel ratio control accuracy, it is desired to accurately grasp the fuel amount in the purge gas introduced in the purge process and correct the fuel injection amount accordingly.

  For example, Patent Document 1 discloses a technique for detecting fluctuations in surge torque during purge processing and estimating the evaporated fuel concentration (vapor concentration) in the purge gas in accordance with the torque fluctuation.

Japanese Patent Laid-Open No. 08-28369 JP 2005-76613 A

  In the case of the method of Patent Document 1 in which the torque fluctuation during the purge process is detected and the vapor concentration is thereby detected, a large amount of evaporated fuel may be purged during the purge process. As a result, the air-fuel ratio is disturbed. May occur.

  An object of the present invention is to solve the above-described problems, and to provide an improved control device for an internal combustion engine that can estimate a vapor concentration while suppressing disturbance of an air-fuel ratio.

In order to achieve the above object, the first invention allows the evaporated fuel in the fuel tank to be adsorbed and collected by the canister, and the evaporated fuel adsorbed by the canister to the intake system of the internal combustion engine via the vapor passage. A control device for an internal combustion engine that performs a purge process for desorption from the canister by supplying,
First in-cylinder pressure detecting means for detecting a first in-cylinder pressure that is an in-cylinder pressure when the purge process is stopped and the air-fuel ratio of the internal combustion engine is controlled to a predetermined air-fuel ratio;
First heat generation amount detecting means for detecting a first heat generation amount that is a heat generation amount in the cylinder according to the first in-cylinder pressure;
A purge rate setting means for setting a small purge rate that does not change the air-fuel ratio control of the internal combustion engine;
Second in-cylinder pressure detecting means for detecting a second in-cylinder pressure that is an in-cylinder pressure during purge processing at the purge rate and controlling the internal combustion engine to the predetermined air-fuel ratio;
Second heat generation amount detecting means for detecting a second heat generation amount that is a heat generation amount in the cylinder according to the second in-cylinder pressure;
An evaporative fuel amount calculating means for calculating the amount of evaporative fuel supplied to the internal combustion engine via the purge passage according to the difference between the first calorific value and the second calorific value;
Is provided.

  A second invention is characterized in that, in the first invention, the predetermined air-fuel ratio is a stoichiometric air-fuel ratio.

  According to the present invention, the amount of evaporated fuel can be obtained according to the difference between the first heat generation amount and the second heat generation amount, which are the heat generation amounts before and after the purge process. At this time, the air-fuel ratio is set to a predetermined air-fuel ratio, and the purge rate is set to a small value that does not affect the air-fuel ratio control. Therefore, even when the amount of evaporated fuel is obtained during the purge process, it is possible to suppress the occurrence of a large disturbance in the air-fuel ratio.

It is a schematic diagram for demonstrating the structure of the internal combustion engine and its peripheral device of embodiment of this invention. It is a timing chart for demonstrating the control in embodiment of this invention. In embodiment of this invention, it is a figure for demonstrating the relationship between the air quantity of an internal combustion engine, and the emitted-heat amount. It is a figure for demonstrating the routine of control which a control apparatus performs in embodiment of this invention. It is a figure for demonstrating the change of the emitted-heat amount ratio with respect to an excess air ratio in the other example of embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment.
FIG. 1 is a schematic diagram for explaining the overall configuration of a system including an internal combustion engine and peripheral devices thereof according to an embodiment of the present invention. The system of FIG. 1 has an internal combustion engine 2. The internal combustion engine 2 includes a plurality of cylinders (not shown). Each cylinder is provided with a spark plug 4, a fuel injection valve 6, and an in-cylinder pressure sensor 8.

  An intake passage 10 and an exhaust passage 12 communicate with the combustion chamber of each cylinder. In the intake passage 10, an air cleaner 14 is installed on the upstream side of the intake passage 10, and an air flow meter 16 is installed immediately downstream of the air cleaner 14. A throttle valve 18 is installed downstream of the air flow meter 16, and a surge tank 20 is installed downstream thereof.

  Fuel is supplied to the fuel injection valve 6 from the fuel tank 22 through a fuel supply passage (not shown). One end of a vapor passage 24 is connected to the fuel tank 22. The other end of the vapor passage 24 is connected to a canister 26. The canister 26 is filled with activated carbon. The evaporated fuel (vapor) generated in the fuel tank 22 reaches the canister 26 through the vapor passage 24 and is adsorbed and collected by the activated carbon in the canister 26.

  One end of a vapor passage 28 is connected to the canister 26. The other end of the vapor passage 28 joins the intake passage 10 downstream of the throttle valve 18 and upstream of the surge tank 20. The vapor passage 28 is provided with a purge VSV (Vacuum Switching Valve) 30 that opens and closes the vapor passage 28.

  This system has a control device 32. The control device 32 is electrically connected to, for example, the in-cylinder pressure sensor 8, the air flow meter 16, the crank angle sensor, and the like, and receives these outputs to detect information related to the operating state of the internal combustion engine 2. The control device 32 is electrically connected to each actuator (not shown) that drives the spark plug 4, the fuel injection valve 6, the throttle valve 18, the purge VSV 30, and the like, for example, and generates these signals by issuing control signals. Control.

  As described above, the evaporated fuel (vapor) from the fuel tank 22 is adsorbed to the canister 26. The system in FIG. 1 performs a purge process for desorbing the adsorbed evaporated fuel. Specifically, when the purge process is executed, the purge VSV 30 is opened. As a result, the evaporated fuel adsorbed by the canister 26 is introduced into the intake passage 10 as purge gas through the vapor passage 28 by the intake negative pressure, and the purge gas is introduced into the internal combustion engine 2 together with fresh air. The evaporated fuel adsorbed and collected in the canister 26 by the purge process as described above is desorbed from the canister 26.

  Here, the concentration of the evaporated fuel contained in the purge gas in the purge process (hereinafter referred to as “vapor concentration”) depends on the amount of evaporated fuel adsorbed by the canister 26 and is not constant. Therefore, the system of the present embodiment estimates the vapor concentration of the purge gas during the purge process by the following process.

  FIG. 2 is a timing chart for explaining the control executed by the system for estimating the vapor concentration in the embodiment of the present invention. As shown in FIG. 2, it is assumed that the air-fuel ratio A / F is controlled to be substantially constant in the vicinity of the theoretical air-fuel ratio (hereinafter “stoichiometric”) during this control. The purge rate is set to such an extent that it does not significantly affect the control of the air-fuel ratio A / F, that is, a very small amount that does not significantly change the intake air amount of each cylinder. The purge rate is controlled by duty-controlling the purge VSV 30.

  In the example shown in FIG. 2, the purge VSV 30 is fully closed at time t1, and the purge process is stopped. From this state, at time t2, the purge VSV 30 is duty-controlled, and the purge process is started at the determined purge rate. During the vapor concentration estimation, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio A / F_st before and after the purge process is started, and the fuel injection amount is also controlled to be constant.

  Here, even if the fuel injection amount is controlled to be constant, after the purge process starts (after time t2), the evaporated fuel contained in the purge gas is supplied to each cylinder together with fresh air. Therefore, the amount of supplied fuel is increased as compared to before the start of the purge process. Accordingly, the amount of heat generated in the cylinder is greater after the purge process is started (after time t2) than when the purge process is stopped.

Next, a vapor concentration detection method will be described. FIG. 3 is a diagram for explaining the relationship between the air amount and the calorific value when the air-fuel ratio A / F is the stoichiometric air-fuel ratio. In FIG. 3, the horizontal axis represents the amount of air, and the vertical axis represents the amount of heat generated. As shown in FIG. 3, the air amount and the heat generation amount have a certain correlation regardless of the engine speed, and the relationship of the following equation (1) is established.
Calorific value Q = α x Air quantity KL (1)
Here, α is a coefficient and is a value when the air-fuel ratio is stoichiometric. According to the above equation (1), the calorific value (hereinafter referred to as “stoichiometric calorific value”) Qst when the air-fuel ratio is stoichiometric can be calculated as a value corresponding to the air amount KL (detected value) at that time. it can.

Under the same air amount KL, the stoichiometric heat generation amount Qst and the actual heat generation amount (hereinafter referred to as actual heat generation amount) Q corresponding to the actual air-fuel ratio have the relationship of the following equation (2).
Air-fuel ratio A / F = Air-fuel ratio A / F_st (Stoichiometric calorific value Qst / actual calorific value Q) (2)
In the above equation (2), the air-fuel ratio A / F_st is a stoichiometric air-fuel ratio. In this embodiment, gasoline is used as the fuel, and A / F_st = 14.6. If both calorific values Q_st and Q are known from the following equation (2), the actual air-fuel ratio is calculated.

On the other hand, the relationship of the following equation (3) is established between the fuel amount tau, the actual air-fuel ratio A / F, and the air amount KL.
Fuel amount tau = Air amount KL / Air-fuel ratio A / F (3)

From the above equations (1), (2), and (3), it can be seen that the relationship of the following equation (4) is established.
Fuel amount tau = Actual calorific value Q / (α · A / F_st) (4)

  In this embodiment, the actual calorific values Q1 and Q2 are calculated from the output of the in-cylinder pressure sensor 8 before the purge process is started and after the purge process is started (time t1). Since the calculation of the heat generation amount based on the in-cylinder pressure is known in various ways, the description here is omitted.

  If the actual heat generation amounts Q1 and Q2 are obtained, the fuel amounts tau1 and tau2 before and after the purge process can be calculated according to the equation (4). As described above, in the vapor concentration detection, the fuel injection amount is constant before and after the purge process. Therefore, the fuel amount difference tau2-tau1 generated before and after the purge process can be considered as the vapor amount tau_prg contained in the purge gas.

The vapor amount tau_prg, the purge rate prg, and the vapor concentration Density_prg have the relationship of the following equation (5).
Vapor concentration Density_prg = vapor amount tau_prg / purge rate prg (5)

  As described above, in this embodiment, the vapor concentration Density_prg can be detected by calculating the actual calorific values Q1 and Q2 from the in-cylinder pressure detection values before and after the purge.

  FIG. 4 is a flowchart for illustrating a control routine executed by the control device in the embodiment of the present invention. In the routine of FIG. 4, it is detected whether there is a purge processing execution instruction (S102). If the purge process execution instruction is not accepted, the current process ends.

  On the other hand, when the purge processing execution instruction is accepted in step S102, the purge VSV 30 is first controlled to be fully closed (S104), the fuel injection amount is set to a predetermined amount (S106), and the air-fuel ratio A / F is It is controlled to become stoichiometric (S108).

  Next, in-cylinder pressure is detected in this state (S110). The in-cylinder pressure is detected according to the output of the in-cylinder pressure sensor 8. Next, the actual calorific value Q1 is calculated based on the in-cylinder pressure (S112). Here, the control device 32 calculates the actual calorific value Q1 corresponding to the in-cylinder pressure based on a calculation method stored in advance.

  Next, the fuel amount tau1 is calculated (S114). The equation (4), the coefficient α, and the stoichiometric air-fuel ratio A / F_st (= 14.6) are stored in the control device 32 in advance. The fuel amount tau1 is calculated as a value corresponding to the actual calorific value Q1 according to the above equation (4).

  Next, the purge rate Prg is set (S116). When the air-fuel ratio A / F is controlled to be stoichiometric, the purge rate Prg is very small in a range that does not affect the control during the purge process. Such a range that does not affect the air-fuel ratio control is obtained by experiments or the like, and the purge rate setting method is stored in advance in the control device 32 so that the purge rate is set within this range.

  Next, the purge process control is started, and the purge VSV 30 is duty-controlled based on the purge rate Prg (S118). As a result, the purge gas flows into each cylinder of the internal combustion engine 2 together with fresh air and is processed.

  Next, the in-cylinder pressure is detected (S120). The in-cylinder pressure is detected by the control device 32 using the output of the in-cylinder pressure sensor 8 as input information. Next, the actual calorific value Q2 corresponding to the in-cylinder pressure is calculated (S122). Next, the fuel amount tau2 is calculated (S124). The fuel amount tau2 is calculated according to the equation (4) according to the actual calorific value Q2.

  Next, the vapor amount tau_prg is calculated (S126). The vapor amount tau_prg is an amount increased after the start of the purge process with respect to the fuel amount tau1 before the start of the purge process. More specifically, the vapor amount tau_prg is calculated as a value obtained by subtracting the fuel amount tau1 from the fuel amount tau2.

  Next, the vapor concentration Density_prg is calculated (S128). Here, since the vapor amount tau_prg and the purge rate prg are known, the vapor concentration Density_prg is calculated according to the equation (5) accordingly. Thereafter, the current process is terminated.

  As described above, according to the system of this embodiment, the vapor concentration can be detected while the air-fuel ratio A / F is controlled in the vicinity of the stoichiometric range. That is, since the vapor concentration can be detected with the purge rate set to a very small value, it is possible to suppress the occurrence of large disturbance in the air-fuel ratio during the vapor concentration detection.

  In the system of this embodiment, the vapor concentration can be detected according to the output of the in-cylinder pressure sensor without installing a special sensor. Therefore, the vapor concentration can be calculated with a simpler system. In addition, since the vapor concentration can be detected according to the output of the in-cylinder pressure sensor, the vapor concentration can be detected earlier than when the vapor concentration is calculated using an air-fuel ratio sensor or the like.

  In this embodiment, the case where the air-fuel ratio is controlled in the vicinity of stoichiometry has been described. However, the present invention is not limited to this, and any other air-fuel ratio may be controlled as long as the air-fuel ratio is controlled to a preset constant air-fuel ratio.

  FIG. 5 is a diagram for explaining the relationship between the air-fuel ratio and the calorific value ratio. In FIG. 5, the horizontal axis represents the excess air ratio λ (value obtained by dividing the air-fuel ratio by the theoretical air-fuel ratio), and the vertical axis represents the heat generation ratio (value obtained by dividing the heat generation amount at the air-fuel ratio by the stoichiometric heat generation amount). Yes.

The air-fuel ratio (or λ) and the calorific value ratio have a correlation as shown in FIG. From such a relationship, even when the air-fuel ratio is not stoichiometric, the above equation (4) for calculating the fuel amount from the actual calorific value is used as the following equation (6), so that the stoichiometric air-fuel ratio A / F_st Even when the air-fuel ratio is controlled to other than the above, the vapor concentration calculation of this embodiment can be applied.
β x calorific value Q = α x air quantity KL (6)

  In equation (6), β is a coefficient of the calorific value according to the excess air ratio λ (or air-fuel ratio A / F), and is appropriately set as a value according to the air-fuel ratio based on the relationship shown in FIG. Is done. Therefore, the vapor concentration estimation method according to the present embodiment can be effectively applied not only to the case where the control is performed in the vicinity of the stoichiometric but also to the case of lean combustion, for example.

  In the embodiment of the present invention, the case where the purge rate is not changed has been described. However, the vapor concentration changes as the purge gas flows. Therefore, it is necessary to learn the vapor concentration at any time. Such a case can be dealt with by controlling the purge VSV 30 so that the air-fuel ratio A / F does not disturb the target air-fuel ratio.

  Specifically, during the purge process, when the purge rate is switched in the process of controlling the air-fuel ratio A / F to be constant, a calorific value change amount dQ before and after the switching is calculated. A fuel amount change amount dtau corresponding to the actual calorific value in equation (4) is calculated. In addition, the vapor concentration can be calculated using the fuel amount change amount dtau and the purge rate change amount dprg as the vapor amount tau_prg and the purge rate prg in the equation (5), respectively.

  In the present embodiment, the fuel injection amount and the air-fuel ratio are controlled to be constant during the vapor concentration calculation process. However, the present invention is not limited to this. During the normal operation of the internal combustion engine 2, the current operation state is that the air-fuel ratio is the stoichiometric air-fuel ratio, and the fuel injection amount is the injection amount for calculating the vapor concentration. If it is determined whether or not the condition is satisfied, the in-cylinder pressure can be detected to estimate the vapor concentration.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., the reference is made unless otherwise specified or the number is clearly specified in principle. The invention is not limited to the numbers. Further, the structure, method, and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

2 Internal combustion engine 6 Fuel injection valve 8 In-cylinder pressure sensor 16 Air flow meter 20 Surge tank 22 Fuel tank 24 Vapor passage 26 Canister 28 Vapor passage 30 Purge VSV
32 Controller

Claims (2)

A purge process is performed in which the evaporated fuel in the fuel tank is adsorbed and collected by the canister, and the evaporated fuel adsorbed by the canister is supplied to the intake system of the internal combustion engine through the vapor passage so as to be desorbed from the canister. A control device for an internal combustion engine to perform,
First in-cylinder pressure detecting means for detecting a first in-cylinder pressure that is an in-cylinder pressure when the purge process is stopped and the air-fuel ratio of the internal combustion engine is controlled to a predetermined air-fuel ratio;
First heat generation amount detecting means for detecting a first heat generation amount that is a heat generation amount in the cylinder according to the first in-cylinder pressure;
A purge rate setting means for setting a small purge rate that does not change the air-fuel ratio control of the internal combustion engine;
Second in-cylinder pressure detecting means for detecting a second in-cylinder pressure that is an in-cylinder pressure during purge processing at the purge rate and controlling the internal combustion engine to the predetermined air-fuel ratio;
Second heat generation amount detecting means for detecting a second heat generation amount that is a heat generation amount in the cylinder according to the second in-cylinder pressure;
An evaporative fuel amount calculating means for calculating the amount of evaporative fuel supplied to the internal combustion engine via the purge passage according to the difference between the first calorific value and the second calorific value;
A control device for an internal combustion engine, comprising:   The control apparatus for an internal combustion engine according to claim 1, wherein the predetermined air-fuel ratio is a stoichiometric air-fuel ratio.

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