JP2007120389A - Internal combustion engine and control method thereof - Google Patents

Abstract

Provided is a control means that can be applied to a wide range of torque-down control while avoiding excessive temperature rise of a catalyst.
An engine (1) includes a throttle valve (42) for controlling the amount of air supplied to a combustion chamber (26), a fuel injection valve (20) for controlling the amount of fuel supplied to the combustion chamber (26), a throttle valve (42), and a fuel injection valve (20). ECU8 which controls these. When the ECU 8 limits the rotational speed of the engine 1 during fuel increase, this is done by reducing the amount of air supplied, limiting the rotational speed of the engine 1 in the normal mode, that is, when the load is relatively small. This is done by stopping the fuel supply.
[Selection] Figure 2

Description

  The present invention relates to an internal combustion engine and a control method thereof.

  In an internal combustion engine, in particular, a gasoline engine of a vehicle that uses a three-way catalyst in an exhaust system, the ratio of air to fuel (air-fuel ratio) is generally set by controlling the supply of air and fuel introduced into the engine. Control is performed to keep the stoichiometric air-fuel ratio. The stoichiometric air-fuel ratio refers to an air-fuel ratio in which neither fuel nor oxygen in the air remains when the fuel is completely burned.

Even in such an engine, exceptionally, when the engine load is high (high load), the purpose is to secure output, or unburned gasoline is generated to reach the exhaust system catalyst, thereby cooling the catalyst. For this purpose, control is performed to increase the fuel injection amount from the stoichiometric air-fuel ratio equivalent amount. In this case, since the fuel is larger than the stoichiometric air-fuel ratio, almost no oxygen in the air remains in the exhaust gas, the reaction between oxygen and fuel on the catalyst is slow, and the catalyst does not overheat.
On the other hand, for the purpose of protecting the engine from damage by preventing over-rotation of the engine, and for the purpose of decelerating when the vehicle speed is exceeded, there is a known control for torque reduction by fuel cut. Was proposed. For example, if the fuel is cut when the vehicle is overspeed, the exhaust gas containing the fuel component flows to the catalyst before the fuel cut, the fuel component adheres to the catalyst, and a large amount of oxygen is supplied to the catalyst after the fuel cut. . For this reason, thermal deterioration occurs in the catalyst due to excessive temperature rise due to the reaction. In order to avoid this problem, it has been proposed to use both fuel cut and intake air amount reduction control.
An example of such an internal combustion engine and its control method is disclosed in Patent Document 1.

JP 2001-152942 A

  The control device for an internal combustion engine disclosed in Patent Document 1 measures the temperature of the exhaust purification catalyst with a sensor and uses it for control. When preventing overspeed or overspeed, if the catalyst temperature is low, the fuel is cut, and if the catalyst temperature is high, the intake air amount is controlled to decrease. As described above, when the engine is torque-down, the fuel temperature is cut or the air is reduced depending on the catalyst temperature.

Engine torque-down control has been used for purposes other than preventing engine overspeed and vehicle overspeed. An example is fuel cut control based on a driver's accelerator pedal off operation. However, since the air-fuel ratio suddenly changes with respect to the control based on the pedal-off operation described above, there is a concern that the same problem as in Patent Document 1, that is, thermal deterioration and melting damage of the catalyst.
Here, it is considered effective to selectively use and reduce the intake air amount reduction control and the fuel cut control. However, if the control disclosed in Patent Document 1 is used, a misfire may newly occur. When misfire occurs, the fuel / air mixture introduced into the combustion chamber of the engine does not react (combust), and the mixture flows to the exhaust system catalyst and reacts on the catalyst. This heat of reaction may cause the catalyst to deteriorate or melt.

  The case where the aforementioned misfire occurs will be described in detail. A case where the vehicle is approaching a downhill when the catalyst temperature is high while continuing high speed traveling or uphill traveling is applicable. When the speed of the vehicle starts to increase after entering the downhill, the driver normally releases the accelerator pedal, and the accelerator pedal is largely returned, so that torque reduction control is executed for so-called engine braking. When the technique of Patent Document 1 is applied to the above-described situation, since the catalyst temperature is high, control for reducing the amount of air is selected. In this case, since the load is light, the amount of fuel and intake air is small. However, if the control for further reducing the amount of air is performed here, the amount of air-fuel mixture becomes extremely small, and misfires are likely to occur. In this state, the amount of the air-fuel mixture is small as being supplied to the combustion chamber, but is usually larger than the amount of HC contained in the exhaust gas discharged from the combustion chamber after combustion, and if it reacts on the catalyst. Causes overheating.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a control means that can be applied to a wide range of torque-down controls while avoiding excessive temperature rise of the catalyst.

In order to solve the above-described problems, an internal combustion engine according to the present invention is an internal combustion engine that obtains an output by mixing and burning fuel with air, supplying fuel, and a supply amount being variable. A fuel supply means; and air supply means for supplying air, the supply amount being variable, and a control means for controlling the fuel supply means and the air supply means. In an internal combustion engine that selectively executes control in other cases and performs control to limit the rotational speed of the internal combustion engine in accordance with a predetermined input, control for limiting the rotational speed when the load is high Is to control the air supply means so that the amount of air supply is reduced, and the control for limiting the rotation speed is to control the fuel supply means so as to stop the fuel supply when the load is not high. It is characterized by To.
The control means performs this by reducing the amount of air supply when limiting the rotational speed of the internal combustion engine at high loads, and otherwise restricts the fuel when limiting the rotational speed of the internal combustion engine. Do this by stopping the supply.

The internal combustion engine is an internal combustion engine for a vehicle, and the predetermined input includes the rotational speed of the internal combustion engine and the speed of the vehicle, and the control for limiting the rotational speed is performed when the rotational speed is greater than the predetermined rotational speed, or This may be performed when the speed is higher than a predetermined speed.
The control at the time of high load is to control at least one of the fuel supply means and the air supply means so that the ratio of the air supply amount to the fuel supply amount is smaller than a predetermined ratio. The control in may be characterized in that at least one of the fuel supply means and the air supply means is controlled so that the ratio of the air supply amount to the fuel supply amount maintains a predetermined ratio.

The control method for an internal combustion engine according to the present invention is a control method for an internal combustion engine that obtains an output by mixing and burning fuel with air, the supply amount of fuel and air being variable, Control of the normal mode in which at least one of the supply amount of fuel and air is controlled so that the ratio of the supply amount to the fuel supply amount maintains a predetermined ratio, and the ratio of the air supply amount to the fuel supply amount is predetermined. Control that selectively controls at least one of the supply amount of fuel and air so as to be smaller than the ratio, and control of the fuel increase mode, and that controls the rotational speed of the internal combustion engine according to a predetermined condition In the control method of the internal combustion engine that performs the control, the control for limiting the rotational speed is to stop the fuel supply when in the normal mode, and the rotational speed is to be stopped in the fuel increase mode. Control limit to is characterized in that it is intended to reduce the amount of air supply.
In this control method for an internal combustion engine, when the number of revolutions of the internal combustion engine is limited during fuel increase, this is done by reducing the amount of air supplied, and when the number of revolutions of the internal combustion engine is limited during normal times. Do this by stopping the fuel supply.

  The internal combustion engine is an internal combustion engine for a vehicle, and the predetermined condition is that at least one of the rotational speed of the internal combustion engine being greater than the predetermined rotational speed and the vehicle speed being greater than the predetermined speed is satisfied. It may be characterized by being.

  According to the present invention, when the rotational speed of the internal combustion engine is limited during normal times, that is, when the load is not high, this is done by stopping the supply of fuel, so that the mixture of fuel and air is burned by misfire. The situation of being discharged from the chamber can be avoided.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 shows an engine 1 according to the first embodiment. The engine 1 is an internal combustion engine for a vehicle and is a gasoline engine. The engine 1 controls the engine body 2, an intake device 4 that is air supply means for supplying air to the engine body 2, an exhaust device 6 that exhausts gas discharged from the engine body 2 to the outside, and the engine 1. ECU (electronic control unit) 8 which is a control means is provided.

The intake device 4 includes an air cleaner 40 that removes foreign matters contained in the intake air, and a throttle valve 42 that controls the amount of air supplied to the engine body 2. An air flow meter 44 that detects the amount of air supplied to the engine body 2 is attached to the intake device 4.
The exhaust device 6 includes a catalytic converter 60, and a catalyst 62 is installed inside the catalytic converter 60. The catalyst 62 reduces carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) contained in the exhaust gas from the engine body 2, and a three-way catalyst is used. Note that the three-way catalyst in the present embodiment has an oxygen storage function. That is, when the proportion of oxygen contained in the exhaust gas is large (exhaust lean state), some oxygen is occluded in the three-way catalyst, and the proportion of oxygen contained in the exhaust gas is small (exhaust rich state). The three way catalyst releases oxygen stored in itself. The three-way catalyst functions most efficiently with respect to the exhaust gas when the air-fuel mixture has the stoichiometric air-fuel ratio. Purifying performance is maintained by storing and releasing oxygen. In addition, an air-fuel ratio sensor 64 that detects the composition of the exhaust gas is attached to the exhaust device 6. The air-fuel ratio sensor 64 is, for example, an O ₂ sensor that detects an oxygen concentration.

The engine body 2 has the same configuration as, for example, a well-known vehicle gasoline engine. In the example of FIG. 1, a combustion chamber 26 that causes fuel and air to react and burn, and one or more fuel injection valves 20 that are fuel supply means for supplying fuel into the intake air are provided. The fuel injection valve 20 controls the amount of fuel supplied. Further, the engine body 2 includes one or more spark plugs 22 that ignite an air-fuel mixture of air supplied from the intake device 4 and fuel supplied from the fuel injection valve 20.
Further, the engine body 2 is provided with a rotation speed detector 24 that is an engine rotation sensor for measuring the engine rotation speed.

The ECU 8 is connected to the air flow meter 44, the rotation speed detector 24, and the air-fuel ratio sensor 64, and receives these outputs as inputs. The ECU 8 is also connected to an accelerator sensor 80 provided outside the engine 1 for detecting the accelerator opening (step angle) and a speed sensor 82 for detecting the speed of the vehicle, and outputs from these sensors. Receive as input.
The ECU 8 is connected to the throttle valve 42 and controls its opening. Thus, the intake device 4 including the throttle valve 42 can vary the amount of air supplied to the engine body 2. Further, the ECU 8 is connected to the fuel injection valve 20 and controls the injection amount. Thereby, the fuel injection valve 20 makes the supply amount of the fuel supplied to the engine body 2 variable.

Next, the operation of the engine 1 according to the first embodiment will be described.
The air supplied from the intake device 4 and the fuel supplied from the fuel injection valve 20 are introduced into the combustion chamber 26, ignited by the spark plug 22, and combusted / expanded to generate power. This power becomes the output of the engine body 2 and the engine 1. The exhaust gas after combustion is guided to the exhaust device 6, purified by the catalyst 62, and then discharged to the outside.

Next, control of the engine 1 according to the first embodiment will be described.
The ECU 8 controls the opening degree of the throttle valve based on the engine operating state detected by the engine speed detected by the rotational speed detector 24 and the accelerator depression angle determined from the output of the accelerator sensor 80. . Further, the fuel supply amount is controlled based on the intake air amount detected by the air flow meter 44 and the set air-fuel ratio. Here, the air-fuel ratio is the ratio of the mass of air supplied to the mass of fuel supplied (air-fuel ratio, A / F). The stoichiometric air-fuel ratio is the amount of exhaust gas in the exhaust gas when the fuel is completely burned. The air-fuel ratio when no fuel or oxygen remains. The theoretical air-fuel ratio is 14.6, for example.

The ECU 8 selectively switches between (A) normal mode control and (B) fuel increase mode control.
(A) Normal mode control.
The normal mode control is control when the load is relatively small, and is control for maintaining the air-fuel ratio at the stoichiometric air-fuel ratio. The ECU 8 receives the air supply amount detected by the air flow meter 44, calculates the corresponding fuel supply amount from this and the theoretical air-fuel ratio, and controls the fuel injection valve 20 according to the calculated supply amount. This control is performed, for example, by changing the injection time of the fuel injection valve 20 and is also made according to the rotational speed detected by the rotational speed detector 24. Further, feedback is performed to control the fuel injection valve 20 in accordance with the composition of the exhaust gas detected by the air-fuel ratio sensor 64. For example, if the oxygen concentration in the exhaust gas is higher than a predetermined value, the fuel supply amount is increased. Otherwise, the fuel supply amount is decreased.

(B) Control of fuel increase mode.
The fuel increase mode control is control when the load is large (high load), and is control for supplying a larger amount of fuel than the stoichiometric air-fuel ratio. Specifically, since a high output is required at a high load, in order to ensure the output, control is performed so as to approach the air-fuel ratio at which the output becomes larger. This is control that makes the air-fuel ratio rich, that is, control that makes the air-fuel ratio smaller than the stoichiometric air-fuel ratio. Theoretically, when the entire amount of fuel and air having the stoichiometric air-fuel ratio burns completely, there is no more oxygen, so even if the fuel is increased, it does not contribute to combustion and a large output cannot be obtained. However, in actuality, the fuel and air (oxygen) cannot be entirely burned, so increasing the amount of fuel increases the utilization rate of air (oxygen) and provides a large output. The target air-fuel ratio is, for example, the air-fuel ratio at which the output is maximized, which is 12.5, for example. At this time, feedback control based on the output of the air-fuel ratio sensor 64 is not performed.
The determination as to whether the load is high is performed by the ECU 8 based on the output of the accelerator sensor 80, for example. When the accelerator is depressed more than a predetermined amount, it is determined that the load is high.
In the case of the above operation state, the control in the fuel increase mode is selected, but in the other case, the control in the normal mode is selected.

The ECU 8 performs control to reduce (torque down) the output of the engine 1 in accordance with a predetermined input, that is, control to limit the rotational speed, regardless of whether in the normal mode or the fuel increase mode.
FIG. 2 shows a flowchart of control for limiting the rotation speed.
First, the ECU 8 reads detection values relating to the operating state such as the engine speed N, the accelerator pedal angle r, and the vehicle speed V from the speed detector 24, the accelerator sensor 80, and the speed sensor 82 (step S1).
Next, the rotation speed N obtained as an output from the rotation speed detector 24 is compared with a reference rotation speed N0 that is a reference for overspeed (step S2).
When N ≦ N0 in step S2, that is, when there is no overspeed, the ECU 8 compares the vehicle speed V obtained as an output from the speed sensor 82 with a reference speed V0 that is a reference for overspeed (step S3). ). Here, V0 is a function of the accelerator depression angle r detected by the accelerator sensor 80, and this function is determined in advance.
In step S3, if V ≦ V0, it is determined whether or not the conditions for executing the torque reduction control during normal operation are satisfied (step S4). In this embodiment, the condition for executing the torque reduction control during normal operation is a state in which the driver releases the accelerator pedal in anticipation of deceleration by the engine brake, and there is no fear of engine stall (stop). Specifically, the vehicle speed (V0 ≧) V ≧ V1 and the accelerator depression angle r = 0.

If N> N0 in step S2, V> V0 in step S3, or if the conditions for executing the normal operation torque down control are satisfied in step S4, the ECU 8 determines the control mode. (Step S5).
If the normal mode is set in step S5, the ECU 8 controls the fuel injection valve 20, thereby stopping the fuel supply (step S6). In this case, since no fuel is supplied to the combustion chamber 26, combustion does not occur and the rotational speed of the engine 1 is suppressed.
When the fuel increase mode is set in step S5, the ECU 8 controls the throttle valve 42 in the closing direction, thereby reducing the air supply amount (step S7). In this case, when a decrease in the intake air amount is detected by the air flow meter 44, the fuel supply amount is decreased so as to maintain the air-fuel ratio based on the fuel increase mode. Thereby, the air-fuel mixture supplied to the combustion chamber is suppressed.

As described above, in the engine 1 according to the first embodiment, the ECU 8 restricts the rotation speed of the engine 1 during the fuel increase mode corresponding to a high load by performing a throttle valve throttle. This is done by stopping the supply of fuel when the engine 1 is limited in the normal mode corresponding to a case other than the load, that is, in the light load state to the medium load state. Therefore, the control of further reducing the throttle valve is not performed in a state where the air-fuel mixture supplied to the combustion chamber is small due to the light load.
For this reason, the engine 1 according to Embodiment 1 can avoid a situation in which a mixture of fuel and air is discharged from the combustion chamber 26 due to misfire. As a result, for example, deterioration and melting loss of the catalyst 62 can be prevented.
Further, since such control is performed even when torque down control during normal operation is being performed, it is possible to avoid excessive temperature rise of the catalyst in a wide range of torque down control.

  In step S6, when the supply of fuel is stopped, combustion does not occur in the combustion chamber, and oxygen contained in the intake air reaches the catalyst 62, but no reaction occurs because there is no fuel. When applying to the driving state of the vehicle, step S6 is applied when the engine performs overspeed prevention when the engine is lightly loaded due to a downhill, or based on an operation in which the driver releases the accelerator pedal. This applies when braking. In these operating states, the control of the air-fuel ratio immediately before is in the normal mode, so that a large amount of fuel does not adhere to the catalyst. Further, in a state where air is directly supplied to the catalyst 62 after the fuel supply is stopped, a part of oxygen is stored in the catalyst by the oxygen storage function of the three-way catalyst. However, even if the fuel supply is resumed due to the change in the conditions in steps S2, S3, and S4, and the operation is immediately performed in the fuel increase mode, the catalyst does not overheat. Unlike the fuel adhering to the catalyst, the oxygen stored in the catalyst is released and reacted gradually, and the catalyst is cooled by the state in which only the immediately preceding air is supplied. Therefore, the catalyst 62 is not deteriorated or melted.

  In step S5, when the amount of air supplied decreases, the fuel that remains unburned in the combustion chamber 26 reaches the catalyst 62. However, since all the oxygen is consumed in the combustion chamber 26, the reaction on the catalyst 62 does not occur. Absent. Even when the supply of air increases again due to a change in the conditions in steps S1 and S2, the air supplied from the intake device 4 is appropriate for the fuel (an amount corresponding to or close to the theoretical air-fuel ratio). Most of the oxygen is consumed in the combustion chamber 26, and a large amount of oxygen does not reach the catalyst 62. Therefore, the catalyst 62 is not deteriorated or melted.

  That is, the engine 1 according to the first embodiment repeats the fuel supply stop (a part of oxygen reaches the catalyst 62) and the air supply amount decrease (a part of fuel reaches the catalyst 62). A situation in which both fuel and oxygen are simultaneously present on the catalyst 62 can be avoided.

  In the above-described first embodiment, the normal mode and the fuel increase mode are switched according to the accelerator opening detected by the accelerator sensor 80, but this may be switched according to other criteria. For example, a sensor for detecting the opening degree of the throttle valve 42 may be provided and the output thereof may be taken into consideration.

  In the first embodiment, the air-fuel ratio is adjusted by controlling the fuel injection valve 20 based on the amount of air detected by the air flow meter 44. However, the present invention is not particularly limited to this embodiment. Absent. For example, the fuel supply amount is first determined based on the engine load or the depression angle of the accelerator pedal, and the throttle air is supplied so that the intake air amount having the set air-fuel ratio is supplied to the determined fuel supply amount. The valve 42 may be adjusted.

  In the first embodiment, a specific air-fuel ratio is assumed such that the air-fuel ratio in the fuel increase mode is 12.5, for example. However, the air-fuel ratio in the fuel increase mode is limited to one. is not. For example, a plurality of air-fuel ratios in the fuel increase mode are determined between the air-fuel ratio in the normal mode and the air-fuel ratio at which the output is maximized, and control is performed to switch the air-fuel ratio according to the engine load in the operating range at high load May be. In this case, it is not always necessary to change the torque down control between the normal mode and the fuel increase mode, and the fuel cut control is executed in the normal mode region with a predetermined air-fuel ratio as a threshold value. May be. If there is a small amount of fuel adhering to the catalyst immediately before the fuel cut, even if air is directly supplied to the catalyst by the fuel cut, the temperature rise of the catalyst due to the reaction of the adhering fuel is small and the catalyst stands out. It does not lead to deterioration or erosion.

It is a figure which shows the structure containing the engine 1 which concerns on Embodiment 1 of this invention. It is a flowchart which shows the flow of control which restrict | limits the rotation speed of the engine 1 which concerns on Embodiment 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine (engine), 4 Air supply means (intake device), 8 Control means (ECU), 20 Fuel supply means (fuel injection valve).

Claims (5)

An internal combustion engine that obtains output by mixing fuel with air and combusting,
Fuel supply means for supplying the fuel, the supply amount being variable;
Air supply means for supplying the air, the supply amount being variable;
Control means for controlling the fuel supply means and the air supply means,
In the internal combustion engine, the control means selectively executes control at high load and control in other cases, and performs control for limiting the rotation speed of the internal combustion engine according to a predetermined input.
In the case of the high load, the control for limiting the rotation speed is to control the air supply means so that the supply amount of the air is reduced.
An internal combustion engine characterized by controlling the fuel supply means so as to stop the supply of the fuel in the control other than the time of the high load. The internal combustion engine is an internal combustion engine for a vehicle,
The predetermined input includes the rotational speed of the internal combustion engine and the speed of the vehicle,
The internal combustion engine according to claim 1, wherein the control for limiting the rotational speed is performed when the rotational speed is greater than a predetermined rotational speed or when the speed is greater than a predetermined speed. The control at the time of the high load is to control at least one of the fuel supply unit and the air supply unit such that a ratio of the air supply amount to the fuel supply amount is smaller than the predetermined ratio.
The control in the case other than the time of the high load is to control at least one of the fuel supply means and the air supply means so that the ratio of the air supply amount to the fuel supply amount maintains a predetermined ratio. The internal combustion engine according to claim 1, wherein the internal combustion engine is provided. A method for controlling an internal combustion engine, wherein an output is obtained by mixing fuel with air and burning it,
The supply amount of the fuel and the air is variable,
A control in a normal mode for controlling a supply amount of at least one of the fuel and the air so that a ratio of the supply amount of the air to the supply amount of the fuel maintains a predetermined ratio;
And selectively performing a fuel increase mode control for controlling at least one of the fuel and the air so that a ratio of the air supply to the fuel supply is smaller than the predetermined ratio. With
In a control method of an internal combustion engine that performs control for limiting the rotational speed of the internal combustion engine according to a predetermined condition,
In the normal mode, the control for limiting the rotational speed is to stop the fuel supply,
In the fuel increase mode, the control for limiting the rotational speed is to reduce the supply amount of the air. The internal combustion engine is an internal combustion engine for a vehicle,
The predetermined condition is that at least one of a rotational speed of the internal combustion engine larger than a predetermined rotational speed and a speed of the vehicle larger than a predetermined speed is satisfied. 5. A method for controlling an internal combustion engine according to 4.

Images