JP3888054B2 - Fuel control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel control device for an internal combustion engine intended to reduce deterioration of a catalyst that purifies exhaust gas without deteriorating drivability.
[0002]
[Prior art]
An internal combustion engine of an automobile is provided with a catalyst in an exhaust pipe in order to perform exhaust gas purification processing. In order to improve fuel efficiency and maintain a feeling of deceleration during deceleration, a fuel cut is performed to stop the supply of fuel to the internal combustion engine when a predetermined fuel supply stop condition is met when the vehicle decelerates. It has come to be. Since the catalyst provided in the exhaust pipe is exposed to the high heat of the exhaust gas, the catalyst may become high temperature during high load traveling (for example, during high speed traveling). If the fuel cut is executed in this state, there is a risk that high concentration of oxygen will flow into the high-temperature catalyst, causing the catalyst to become an oxidizing atmosphere and causing deterioration (reduction of the purification rate).
[0003]
Therefore, conventionally, for example, as shown in JP-A-8-312421 and JP-A-9-217642, when the catalyst temperature is high, an internal combustion engine that prohibits fuel cut even during deceleration. A control apparatus has been proposed. In a conventional control device for an internal combustion engine, fuel cut is prohibited when the catalyst temperature is high, thereby preventing the catalyst from deteriorating and protecting the catalyst.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional control device for an internal combustion engine, when the catalyst temperature is high, fuel cut is prohibited even at the time of deceleration. Therefore, although the catalyst can be protected at high temperature, torque is generated and the engine is generated. There was a problem that the braking force was reduced. For this reason, depending on the catalyst temperature, engine braking force may or may not be obtained during deceleration, and drivability has deteriorated. Incidentally, Japanese Patent Laid- Open No. 11-257131 discloses a technique for intermittently supplying fuel in order to prevent the amount of oxygen accumulated in the catalyst from being saturated when the fuel is cut in the deceleration operation state. There is no idea of protecting the catalyst at high temperatures.
[0005]
The present invention has been made in view of the above situation, and an object of the present invention is to provide a fuel control device for an internal combustion engine that can achieve both proper engine braking force retention during deceleration and catalyst protection at high temperatures. .
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, when the vehicle is in a decelerating state, the fuel control means stops the fuel supply to secure the engine braking force, and the catalyst temperature deriving means ensures that the catalyst temperature is equal to or higher than a predetermined temperature. In this case, the fuel is intermittently supplied to prevent the catalyst from becoming an oxidizing atmosphere to prevent deterioration, and to maintain appropriate engine braking force at the time of deceleration and to protect the catalyst at high temperature.
[0007]
The higher the temperature of the catalyst derived by the catalyst temperature deriving means, the longer the fuel stop period, so that a larger amount of fuel is supplied and the engine braking force is maintained, and the catalyst protection at high temperatures can be performed reliably. Further, by reducing the ratio of the fuel stop time to the fuel supply time as the catalyst temperature is higher, the catalyst can be reliably protected at a high temperature while supplying more fuel and maintaining the engine braking force.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. The illustrated embodiment is an example of a spark ignition type multi-cylinder in-cylinder injection internal combustion engine in which the air-fuel ratio of the air-fuel mixture is controlled to be leaner than the stoichiometric air-fuel ratio and fuel is directly injected into the combustion chamber. It is listed in the description. FIG. 1 is a schematic configuration of an internal combustion engine including a control device according to an embodiment of the present invention, FIG. 2 is a flowchart of a fuel cut operation, FIG. 3 is a state of drive pulses of the fuel cut operation, and FIG. Indicates a graph showing the deterioration of the catalyst.
[0009]
As the multi-cylinder in-cylinder internal combustion engine, for example, an in-cylinder in-line four-cylinder gasoline engine (in-cylinder injection engine) 1 that directly injects fuel into a combustion chamber is applied. For example, the in-cylinder injection engine 1 can perform fuel injection in the intake stroke (intake stroke injection mode) or fuel injection in the compression stroke (compression stroke injection mode) by switching the combustion mode (operation mode). ing. The in-cylinder injection engine 1 can be operated at a lean air-fuel ratio (lean air-fuel ratio operation) in addition to an operation at a stoichiometric air-fuel ratio (stoichiometric) or an operation at a rich air-fuel ratio (rich air-fuel ratio operation). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio that has a larger air-fuel ratio than a lean air-fuel ratio operation in the intake stroke.
[0010]
As shown in FIG. 1, a spark plug 3 is attached to each cylinder of the cylinder head 2 of the direct injection engine 1, and an electromagnetic fuel injection valve 4 is attached to each cylinder. An injection port of the fuel injection valve 4 is opened in the combustion chamber 5 so that the fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. A piston 7 is supported on the cylinder 6 of the direct injection engine 1 so as to be slidable in the vertical direction, and a hemispherical cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a clockwise reverse tumble flow in FIG.
[0011]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 9 is connected so as to communicate with each intake port. A drive-by-wire (DBW) electric throttle valve (ETV) 21 is connected to the other end of the intake manifold 9, and a throttle position sensor 22 for detecting a throttle opening θth is provided in the ETV 21. The in-cylinder injection engine 1 is provided with a crank angle sensor 23 that detects the crank angle, and the crank angle sensor 23 can detect the engine rotational speed Ne.
[0012]
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 10 is connected so as to communicate with each exhaust port. The exhaust manifold 10 is provided with an EGR device (not shown). On the other hand, an exhaust pipe 11 is connected to the exhaust manifold 10, and a muffler (not shown) is connected to the exhaust pipe 11 via a catalyst 13. The catalyst 13 is provided with a temperature sensor 15 as catalyst temperature deriving means, and the temperature sensor 15 detects (derived) the temperature of the catalyst 13.
[0013]
The vehicle is provided with an electronic control unit (ECU) 31, and this ECU 31 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, a timer, and counters. The ECU 31 performs comprehensive control of the internal combustion engine of the present embodiment including the in-cylinder injection engine 1. Detection information of various sensors is input to the ECU 31. The ECU 31 determines the ignition timing and the like including the fuel injection mode and the fuel injection amount based on the detection information of the various sensors, and the fuel injection valve 4, the ignition plug 3, etc. Is controlled.
[0014]
In the in-cylinder injection engine 1, the intake air flow that flows into the combustion chamber 5 from the intake manifold 9 forms a reverse tumble flow, and fuel is injected after the middle of the compression stroke to use the reverse tumble flow and the top of the combustion chamber 5. A small amount of fuel is collected only in the vicinity of the spark plug 3 disposed at the center, and an extremely lean air-fuel ratio is obtained at a portion separated from the spark plug 3. By making only the vicinity of the spark plug 3 a stoichiometric or rich air-fuel ratio, fuel consumption is suppressed while realizing stable stratified combustion (stratified super lean combustion).
[0015]
When high output is obtained from the direct injection engine 1, the fuel from the fuel injection valve 4 is injected into the intake stroke to be homogenized throughout the combustion chamber 5. The inside of the combustion chamber 5 has a stoichiometric or lean air-fuel ratio. Premixed combustion is performed in a mixed gas state. Of course, the stoichiometric or rich air-fuel ratio can provide a higher output than the lean air-fuel ratio. In this case as well, fuel injection is performed at such a timing that the atomization and vaporization of the fuel is sufficiently performed. I try to get the output.
[0016]
In the ECU 31, a target in-cylinder pressure corresponding to the engine load, that is, a target average effective pressure Pe, is obtained based on the throttle opening degree θth from the throttle position sensor 22 and the engine rotational speed Ne from the crank angle sensor 23. A fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotational speed Ne. For example, when the target average effective pressure Pe and the engine speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe is increased, or When the engine speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke. Then, a target air-fuel ratio (target A / F) that is a control target in each fuel injection mode is set from the target average effective pressure Pe and the engine rotational speed Ne, and an appropriate amount of fuel injection amount is set to this target A / F. To be determined.
[0017]
Further, the ECU 31 is based on the throttle opening θth detected by the throttle position sensor 22 (or the accelerator opening detected by an accelerator opening sensor (not shown)) and the engine rotational speed Ne detected by the crank angle sensor 23. The deceleration operation is determined. For example, the conditions for the deceleration operation are that the engine speed Ne is 900 rpm or more and the throttle opening θth is a predetermined opening or less (accelerator opening fully closed). When the conditions for the deceleration operation are satisfied, the fuel cut operation for stopping the fuel supply is executed (fuel control means). Thereby, the engine braking force at the time of deceleration is ensured.
[0018]
Further, the ECU 31 has a function of supplying fuel intermittently even in the deceleration operation state when the temperature of the catalyst 13 detected by the temperature sensor 15 is equal to or higher than a predetermined value. Thereby, it is suppressed that fuel is intermittently supplied during the deceleration operation when the temperature of the catalyst 13 is high and the catalyst 13 becomes an oxidizing atmosphere, and thermal deterioration is prevented.
[0019]
Accordingly, it is possible to achieve both maintenance of an appropriate engine braking force at the time of deceleration and protection of the catalyst 13 at a high temperature.
[0020]
The catalyst temperature deriving means is not limited to the temperature sensor 15, but the exhaust temperature, throttle opening, manifold pressure, engine speed, net average effective pressure, indicated average effective pressure, A / N, intake air amount, exhaust flow rate. It is also possible to estimate (derived) the catalyst temperature based on these information using at least one of the exhaust gas flow velocity and the exhaust A / F.
[0021]
In order to secure the engine braking force, it is not always necessary to stop the fuel in all cylinders. Further, the catalyst 13 is not subject to thermal degradation immediately when the temperature becomes high. This is because, even when the temperature of the catalyst 13 exceeds 1000 ° C., for example, the stoichiometric feedback operation, that is, the overall total air-fuel ratio is stoichiometric, but the air-fuel ratio repeats rich and lean in a cycle of about 1 second. It can be judged from the fact that the thermal degradation rate is extremely slow in the operation that is in the oxidized state for about 0.3 seconds.
[0022]
For this reason, in the fuel cut operation at the time of deceleration while the catalyst 13 is at a high temperature, the fuel is not cut continuously for a long period of time, but the fuel is injected for a short period of time, that is, intermittently even in the deceleration operation state. By supplying the fuel in an appropriate manner, the period in which the catalyst 13 is in an oxidizing atmosphere at a high temperature is shortened to prevent thermal deterioration and to ensure engine braking force.
[0023]
Incidentally, the deterioration of the catalyst 13 due to high temperature oxidation increases as the amount of oxygen flowing into the catalyst increases. Therefore, the fuel cut operation is performed between the inflowing oxygen amount during the fuel cut operation and the inflowing oxygen amount during the feedback operation. The amount of inflow oxygen is larger at the time. For this reason, it is necessary to make the period of the oxidation state, that is, the fuel cut period shorter than the lean period during the feedback operation.
[0024]
The state of control for intermittently supplying fuel even in the above-described deceleration operation state will be described with reference to FIG.
[0025]
In step S1, the counter value is subtracted under the condition of a positive value (counter-1), and in step S2, the detected value of the temperature sensor 15 (temperature of the catalyst 13) Tcat is greater than or equal to a predetermined value T1 (for example, 800 ° C.). It is determined whether or not there is. If it is determined in step S2 that the temperature Tcat of the catalyst 13 is equal to or higher than the predetermined value T1, it is determined in step S3 whether or not the vehicle is decelerating. If it is determined in step S3 that the vehicle is decelerating, it is determined in step S4 whether the counter is not zero. If it is determined in step S4 that the counter is not 0, fuel injection is executed in step S5, and the process returns. If it is determined in step S4 that the counter is 0, fuel cut is executed in step S6. That is, when the temperature Tcat of the catalyst 13 is equal to or higher than the predetermined value T1 and the vehicle is decelerating, fuel injection is performed until the counter reaches 0, and when the counter reaches 0, fuel cut is performed and fuel is intermittently consumed. Supplied.
[0026]
After the fuel cut is executed, whether or not the detected value (temperature of the catalyst 13) Tcat of the temperature sensor 15 is less than a second predetermined value T2 (for example, 850 ° C.), that is, the temperature of the catalyst 13 is increased in step S7. It is determined whether or not. When it is determined that the temperature Tcat of the catalyst 13 is lower than the second predetermined value T2, the counter is set to the predetermined number S in step S8, and the process returns. That is, if the temperature of the catalyst 13 is equal to or higher than the predetermined value T1 and is not high during deceleration, the fuel cut operation in which the fuel cut is performed one time (in the S cycle) out of the number S of the fuel injection pulses rising. Is executed. For example, when the number of times S is set to 4 times, as shown in FIG. 3A, the fuel is cut intermittently by performing fuel cut once every 4 cycles without driving one of the four pulses. Supplied.
[0027]
On the other hand, if it is determined in step S7 that the detected value (temperature of the catalyst 13) Tcat of the temperature sensor 15 is equal to or higher than the second predetermined value T2 (for example, 850 ° C.), the counter is set to α a predetermined number of times S in step S9. Set to the value added with and return. In other words, if the temperature of the catalyst 13 is equal to or higher than the predetermined value T1 and is high during deceleration, the number S of fuel injection pulses rises by α, and one of S + α (in the S + α cycle) is fueled. A fuel cut operation for cutting is performed. That is, the higher the temperature of the catalyst 13, the longer the fuel stop cycle. For example, if the number of times S is 4 and α is 1, as shown in FIG. 3 (b), the fuel is cut once every 5 cycles without driving one of the 5 pulses, and intermittently The fuel is supplied.
[0028]
When the fuel cut operation indicated by a dotted line in FIG. 4 in which the THC purification rate is reduced when the fuel cut operation is not performed and the fuel cut operation is performed once in the number of times S (in the S cycle) is performed, FIG. As shown by the thick solid line, the decrease in the THC purification rate is less than when the fuel cut operation is not performed. When the fuel cut operation is performed in which the fuel cut is one out of the number of times S + α (in the S + α cycle), as shown by the thin solid line in FIG.
[0029]
As described above, fuel is intermittently supplied during the deceleration operation in which the temperature of the catalyst 13 is Tcat equal to or higher than the predetermined value T1, and the catalyst 13 is prevented from being in an oxidizing atmosphere, thereby preventing thermal degradation. In addition, as the temperature of the catalyst 13 becomes higher as the Tcat becomes equal to or higher than the second predetermined value T2, the fuel cut cycle becomes longer, so that more fuel is supplied and the engine braking force is maintained and the catalyst protection at high temperatures is ensured. Yes.
[0030]
The frequency of the fuel cut is a fixed cycle of S cycle or S + α cycle in the above-described embodiment, but other high frequencies (for example, 5 continuous fuel cuts in 20 cycles) may be used. It may be a regular frequency. Further, the fuel cut frequency is not limited to the fixed frequency as in the embodiment, and the fuel cut frequency can be made variable depending on the operation state and the state of the catalyst 13. Further, as shown in FIG. 3 (a), the width of the fuel cut pulse width m is made smaller than the fuel supply pulse width M, and the number of fuel cut cycles is set to the number of fuel supply cycles during the unit period. It is also possible to make it smaller.
[0031]
In the above-described embodiment, in order to secure the engine braking force when the fuel supply is intermittently performed, the ignition timing may be retarded to the extent that the combustion does not become unstable to reduce the generated torque. . In this case, the engine braking force is ensured, and at the same time, the deceleration feeling such as a sudden feeling at the time of fuel cut entry / exit can be improved.
[0032]
In the above embodiment, the spark ignition type engine in which the fuel is directly injected into the combustion chamber is described as an example of the internal combustion engine. However, the fuel mixture is injected into the diesel engine or the intake pipe. It is also possible to apply to a spark ignition type engine introduced into the combustion chamber.
[0033]
【The invention's effect】
The control apparatus for an internal combustion engine according to the present invention stops fuel supply by the fuel control means when the vehicle is in a decelerating state, and is intermittent when the catalyst temperature deriving means derives that the catalyst temperature is equal to or higher than a predetermined temperature. Therefore, the engine braking force can be secured, and the deterioration of the catalyst due to the oxidizing atmosphere can be suppressed. As a result, it is possible to achieve both maintenance of appropriate engine braking force during deceleration and catalyst protection at high temperatures.
[0034]
Also, the higher the temperature of the catalyst derived by the catalyst temperature deriving means, the longer the fuel stop period, so that when the catalyst is hot, more fuel is supplied and the engine braking force is maintained while maintaining the engine braking force. The catalyst can be reliably protected. In addition, the higher the catalyst temperature, the smaller the ratio of the fuel stop time to the fuel supply time, so when the catalyst is hot, more fuel is supplied to protect the catalyst at high temperatures while maintaining engine braking force. Can be done reliably.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine including a control device according to an embodiment of the present invention.
FIG. 2 is a flowchart of a fuel cut operation.
FIG. 3 is a time chart showing the state of drive pulses in a fuel cut operation.
FIG. 4 is a graph showing a deterioration state of a catalyst.
[Explanation of symbols]
1 In-cylinder injection engine 4 Fuel injection valve 13 Catalyst 15 Temperature sensor 31 Electronic control unit (ECU)

Claims (2)

In an internal combustion engine provided with a catalyst for purifying exhaust gas, it has a fuel control means for detecting a deceleration state of the vehicle and stopping fuel supply, and a catalyst temperature deriving means for deriving the temperature of the catalyst,
When the temperature of the catalyst derived by the catalyst temperature deriving unit is equal to or higher than a predetermined value, fuel is intermittently supplied to the fuel control unit even in the deceleration operation state, and the catalyst temperature derived by the catalyst temperature deriving unit is supplied. A fuel control device for an internal combustion engine, characterized by having a function of extending a fuel stop cycle as the temperature increases. In an internal combustion engine provided with a catalyst for purifying exhaust gas, it has a fuel control means for detecting a deceleration state of the vehicle and stopping fuel supply, and a catalyst temperature deriving means for deriving the temperature of the catalyst,
When the temperature of the catalyst derived by the catalyst temperature deriving unit is equal to or higher than a predetermined value, fuel is intermittently supplied to the fuel control unit even in the deceleration operation state, and the catalyst temperature derived by the catalyst temperature deriving unit is supplied. A fuel control device for an internal combustion engine, which has a function of reducing the ratio of the fuel stop time to the fuel supply time as the temperature increases.

Images