JP2004137969A - Controller for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a deterioration of a fuel cost due to a continuation of a combustion by assuring a sense of deceleration of a vehicle even if a control for inhibiting fuel cutting is conducted at a decelerating time when an exhaust catalyst temperature is high in order to suppress a deterioration of the catalyst. <P>SOLUTION: A controller for an engine having a plurality of cylinders includes a fuel cutting condition detecting means for detecting that fuel cutting conditions at a vehicle decelerating time are provided, a catalytic temperature detecting means for detecting that the exhaust catalyst temperature is a predetermined temperature or higher, and a control means for pausing at least one of the plurality of the cylinders when it is detected that the fuel cutting conditions are provided and the catalyst temperature is the predetermined temperature or higher. The controller continues the combustion without performing the fuel cutting when the catalyst temperature is higher, and pauses the partial cylinder. Thus, miss firing does not occur even by a small amount of suction air. The deceleration of the vehicle is advanced, and the fuel cost is improved. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an engine having a cylinder deactivation mechanism, and more particularly to prevention of catalyst deterioration due to fuel cut.
[0002]
[Prior art]
In an engine having an electronically controlled combustion injection control device, a fuel cut ("fuel cut", "fuel cut", which stops fuel injection when the vehicle is in a decelerating driving state, etc., for the purpose of reducing emissions and reducing fuel consumption). F / C ”) is performed. However, it has been found that the execution of such a fuel cut causes deterioration of the three-way catalyst for purifying exhaust gas provided in the exhaust system. That is, the execution of the fuel cut causes the exhaust system to have an excessive oxygen state (lean state). Therefore, when the fuel cut is performed in a state where the temperature of the catalyst is high, the periphery of the catalyst becomes a high-temperature lean state, and the deterioration of the catalyst is promoted.
[0003]
The following is known as a reason why the deterioration of the catalyst is promoted when the catalyst is in a lean state at a high temperature. At higher temperatures, atom migration becomes more active. Therefore, in a high temperature state, the small Pt (platinum) in the catalyst is combined with each other by the activated atom transfer to become large Pt, and an oxidation reaction occurs due to excess oxygen to promote the Pt particle growth. Is done. The grain-grown Pt has a small surface area, which means that the area in contact with the exhaust gas is small. As a result, the exhaust gas purifying action is reduced. The above is the reason why the deterioration of the catalyst is promoted at a high temperature and an excess of oxygen.
[0004]
From this point of view, even under conditions where fuel cut should be performed, such as during deceleration, when the exhaust catalyst bed temperature is high, fuel cut execution is prohibited, and combustion is continued to suppress catalyst deterioration. Has been proposed (for example, see Patent Document 1).
[0005]
Also, a method has been proposed in which at least one of an intake valve and an exhaust valve is closed during execution of fuel cut to prevent lean gas from flowing into the catalyst and suppress deterioration of the catalyst (for example, see Patent Document 2).
[0006]
[Patent Document 1]
JP-A-8-144814
[Patent Document 2]
JP 2001-182570A
[0007]
[Problems to be solved by the invention]
As in Patent Document 1, when the exhaust catalyst bed temperature is high and combustion is continued without executing fuel cut even during deceleration, the amount of intake air is reduced to decelerate the vehicle. Need to be done. However, if the intake air amount is reduced indefinitely, there is a possibility that a misfire may occur. Therefore, even if the vehicle is decelerated, the intake air amount cannot be reduced to a certain level when combustion is continued. Note that misfire generally refers to a state in which the amount of air taken into the combustion chamber is small, the compression pressure is insufficient, and combustion cannot be performed. The minimum amount of air that does not cause a misfire is determined by conditions such as the number of revolutions of the engine. However, in order to prevent the occurrence of a misfire, the amount of air per combustion cannot be reduced below a certain level. Nevertheless, engine torque due to combustion is generated, and the deceleration of the vehicle is smaller than that in the case where fuel cut is executed. As a result, even if the driver turns off the accelerator, the driver may not feel a sufficient sense of deceleration, and the driver may feel uncomfortable in terms of drivability.
[0008]
The present invention has been made in view of the above points, and even when performing control to prohibit fuel cut at the time of deceleration when the temperature of the exhaust catalyst is high in order to suppress catalyst deterioration, the sense of deceleration of the vehicle is reduced. An object of the present invention is to provide an engine control device that can secure the fuel consumption and reduce deterioration of fuel efficiency due to continued combustion.
[0009]
[Means for Solving the Problems]
According to one aspect of the present invention, a control device for an engine having a plurality of cylinders includes a fuel cut condition detecting means for detecting that a fuel cut condition at the time of vehicle deceleration is provided, and an exhaust catalyst temperature being equal to or higher than a predetermined temperature. Catalyst temperature detecting means for detecting that the fuel cut condition is satisfied, and when it is detected that the catalyst temperature is equal to or higher than a predetermined temperature, at least one of the plurality of cylinders is deactivated. Control means for causing
[0010]
The engine controlled by the control device has a plurality of cylinders. The control device includes a fuel cut condition detecting unit that detects whether a fuel cut condition is satisfied when the vehicle decelerates. The fuel cut condition can be set, for example, when the accelerator is off (the throttle valve is fully closed) and the engine speed is equal to or higher than a predetermined value, and can be detected by, for example, an ECU according to the output values of various sensors. . Further, the control device includes catalyst temperature detection means for detecting that the exhaust catalyst temperature is equal to or higher than a predetermined temperature. The catalyst temperature detecting means can be constituted by, for example, a temperature sensor provided in a catalytic converter for purifying exhaust gas provided in an exhaust system of a vehicle.
[0011]
The control means constituted by the ECU and the like, when the fuel cut condition is satisfied, and when it is detected that the catalyst temperature is equal to or higher than the predetermined temperature, without executing the fuel cut, the plurality of cylinders At least one cylinder is stopped. Here, stopping the cylinder means that the fuel is not injected into the cylinder and at least one of the intake valve and the exhaust valve of the cylinder is closed. This is because if fuel cut is performed when the catalyst temperature is equal to or higher than the predetermined temperature, unburned air flows to the exhaust-side catalyst, and the catalyst is deteriorated by oxygen. Therefore, the combustion is continued without performing the fuel cut. However, there is a demand for suppressing the generation of the torque by the combustion by suppressing the intake air amount as much as possible during the deceleration. However, if the total intake air amount is reduced while continuing combustion in all cylinders, a misfire may occur. Therefore, by setting a part of the cylinders at rest, misfire is prevented from occurring even with a small intake air amount. As a result, the torque generated by the continuation of the combustion is reduced, so that the deceleration of the vehicle is promoted, and the fuel consumption is reduced with the reduction of the intake air amount, and the fuel efficiency is also improved.
[0012]
In one aspect of the above-described engine control device, the control unit is configured such that, in the deactivated state of the cylinder, both the intake valve and the exhaust valve of the cylinder to be deactivated are closed, and the intake valve is opened. The opening and closing timings of the intake valve and the exhaust valve are controlled so that a combustion process is performed from the time when the exhaust valve opens.
[0013]
According to this aspect, in the deactivated state of the cylinder, since both the intake valve and the exhaust valve of the cylinder to be deactivated are closed, it is possible to reliably prevent unburned air from flowing to the catalyst of the exhaust system. Can be. In addition, when returning from the rest state of the cylinder, the combustion process is always performed between the opening of the intake valve and the opening of the exhaust valve. Flow to the system catalyst can be prevented, and catalyst deterioration can be prevented.
[0014]
Another aspect of the above-described engine control device further includes a unit that detects a need for engine braking, and the control unit is a target to be stopped in a stopped state of the cylinder when the need for engine braking is detected. The intake valve of the cylinder is always closed, and the exhaust valve of the cylinder is controlled to open and close.
[0015]
According to this aspect, when the necessity of engine braking is detected, the intake valve of the cylinder to be stopped is maintained in a closed state to prevent unburned air from flowing to the exhaust system, and the exhaust valve The engine brake is activated by controlling the opening and closing of the valve to generate a pumping loss.
[0016]
Another aspect of the above-described engine control device further includes a unit that detects an engine speed, and a unit that detects a temperature of engine oil, wherein the control unit is configured so that the engine speed is higher than a predetermined speed. And, when the temperature of the engine oil is higher than a predetermined temperature, one of the intake valve and the exhaust valve of the cylinder to be deactivated is always closed in the deactivated state of the cylinder, and the intake valve and the exhaust of the cylinder are deactivated. The other side of the valve is always open.
[0017]
According to this aspect, when the engine speed is higher than the predetermined speed and the temperature of the engine oil is higher than the predetermined temperature, that is, in a situation where the oil rise is likely to occur, the intake valve or the exhaust gas of the cylinder to be stopped is set. When one of the valves is always closed, unburned air is prevented from flowing to the exhaust side, and when the other is always open, the negative pressure generated in the combustion chamber is reduced to prevent oil rising. When the negative pressure in the combustion chamber increases, the engine oil, which is circulated for lubrication of the mechanism located below the piston, passes between the piston and the cylinder and rises into the combustion chamber. A phenomenon that causes
[0018]
Another aspect of the above-described engine control device further includes a unit that detects an engine speed, and a unit that detects a temperature of engine oil, wherein the control unit is configured so that the engine speed is higher than a predetermined speed. And, when the temperature of the engine oil is higher than a predetermined temperature, the intake valve of the cylinder to be deactivated is always closed in the deactivated state of the cylinder, and the intake valve is closed near the next bottom dead center after the exhaust top dead center. Close and maintain the closed state of the exhaust valve of the cylinder.
[0019]
In this aspect, when the engine speed is higher than the predetermined speed and the temperature of the engine oil is higher than the predetermined temperature, that is, in a situation where the oil rises easily, the intake valve of the cylinder to be stopped is always closed. As a state, unburned air is prevented from flowing to the exhaust side. At the same time, the exhaust valve is always closed, but the timing of closing the exhaust valve is set near the bottom dead center next to the exhaust top dead center. As a result, the piston moves to the vicinity of the bottom dead center after the exhaust process, and the exhaust valve is closed in a state where the exhaust gas is introduced to some extent in the combustion chamber, and the combustion chamber when the exhaust valve is closed becomes almost atmospheric pressure. . In this way, the negative pressure generated in the combustion chamber is reduced, and oil rise is prevented.
[0020]
In another aspect of the above-described engine control device, the control unit includes a fuel cut condition for the plurality of cylinders when the fuel cut condition is satisfied and the catalyst temperature is not detected to be equal to or higher than a predetermined temperature. Execute
[0021]
In this aspect, when the catalyst temperature is equal to or lower than the predetermined temperature, the risk of deterioration of the catalyst is low even if unburned air flows to the catalyst in the exhaust system. Therefore, fuel cut is performed to decelerate the vehicle. At the same time, improve fuel efficiency.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0023]
[Engine configuration]
First, an engine provided with a cylinder deactivation mechanism to which the present invention is applied will be described. FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention. Air required for combustion of the engine 50 is filtered by the air cleaner 102, passes through the throttle body 105, and is distributed to the intake pipe 113 of each cylinder by the surge tank (intake manifold) 111. The intake air flow rate is adjusted by a throttle valve 106 provided on a throttle body 105 and measured by an air flow meter 104. The intake air temperature is detected by an intake air temperature sensor 103. Further, the intake pipe pressure is detected by the vacuum sensor 112.
[0024]
The opening of the throttle valve 106 is detected by a throttle opening sensor 109. When the throttle valve 106 is in the fully closed state, the idle switch 110 is turned on, and the output of the throttle fully closed signal is active. An idle speed control valve (ISCV) 108 for adjusting the air flow during idling is provided in the idle adjustment passage 107 that bypasses the throttle valve 106.
[0025]
On the other hand, the fuel stored in the fuel tank 115 is pumped up by the fuel pump 117 and is injected into the intake pipe 113 by the fuel injection valve 121 through the fuel pipe 119. In the intake pipe 113, such air and fuel are mixed, and the air-fuel mixture is sucked into the engine body, that is, the cylinder 1 through the intake valve 123. In the cylinder 1, the air-fuel mixture is compressed by a piston, ignited by an igniter and a spark plug, explodes and burns, and generates power.
[0026]
The ignition distributor 143 has a crank angle sensor 145 whose axis generates a reference position detection pulse every 720 ° CA in terms of, for example, a crank angle (CA), and a reference position detection pulse every 30 ° CA. Is provided. Further, engine 50 is cooled by cooling water guided to cooling water passage 149, and the temperature of the cooling water is detected by water temperature sensor 151.
[0027]
The burned air-fuel mixture is discharged as an exhaust gas through an exhaust valve 124 to an exhaust manifold 127 and then guided to an exhaust pipe 129. The exhaust pipe 129 is provided with an A / F sensor 131 that detects the air-fuel ratio (A / F) of the exhaust gas. Further, a catalytic converter 133 is provided in the exhaust system downstream of the catalytic converter 133. The catalytic converter 133 includes a three-way catalyst that simultaneously promotes the oxidation of unburned components in the exhaust gas and the reduction of nitrogen oxides. Is contained. The exhaust gas thus purified in the catalytic converter 133 is discharged into the atmosphere. The catalytic converter 133 is provided with a catalyst temperature sensor (not shown).
[0028]
The engine 50 is assumed to be an engine equipped with an EGR (exhaust gas recirculation device) for the purpose of reducing NOx (nitrogen oxides), and is provided between an exhaust system and an intake system downstream of the throttle valve 106. Is provided with a passage 125 for circulating exhaust gas. The gas recirculation amount is adjusted by an EGR valve 126 provided in the middle of the passage.
[0029]
The engine electronic control unit (ECU) 60 is a microcomputer system that executes fuel injection control, ignition timing control, idle speed control, and the like. The CPU 61 inputs signals from various sensors via the A / D conversion circuit 64 or the input interface circuit 65 according to a program stored in the ROM 62, executes arithmetic processing based on the input signals, and outputs the arithmetic results. Based on the output interface circuit 66, it outputs various actuator control signals. The RAM 63 is used as a temporary data storage place in the operation / control processing. Each component in the ECU is connected by a system bus (consisting of an address bus, a data bus, and a control bus) 69.
[0030]
In the ignition timing control, the state of the engine is comprehensively determined based on the engine speed and signals from the sensors, the optimal ignition timing is determined, and an ignition signal is sent to the igniter. In the idle speed control, an idle state is detected based on a throttle fully closed signal from the idle switch 10 and the like, and the ISCV 108 is controlled to adjust the amount of air to maintain an optimum idle speed.
[0031]
The fuel injection control is basically performed based on a predetermined amount of intake air per one rotation of the engine calculated from the intake air flow rate measured by the air flow meter 104 and the engine rotation speed obtained from the crank angle sensor 145. In order to achieve the air-fuel ratio, the fuel injection amount, that is, the injection time by the fuel injection valve 121 is calculated, and the fuel is injected when a predetermined crank angle is reached. Note that the intake air flow rate may be estimated based on the intake pipe pressure obtained from the vacuum sensor 112 and the engine speed. Then, at the time of such calculation, correction based on signals from the throttle opening sensor 109, the water temperature sensor 151, the intake air temperature sensor 103, the A / F sensor 131, and the like is added.
[0032]
Further, the fuel injection control executed by the ECU 60 includes fuel cut control. The fuel cut control is executed in various states while the vehicle is running, and for example, a fuel cut at the time of deceleration, a fuel cut at the time of a high rotation, and a fuel cut at the highest speed, which temporarily stop the fuel injection, are performed. The conditions for performing the fuel cut are predetermined. The ECU 60 monitors output signals from various sensors, determines that a fuel cut request has occurred when predetermined fuel cut conditions are satisfied, and gives a fuel cut instruction to the fuel injection valve 121 to stop fuel injection.
[0033]
As various fuel cuts, for example, in the case of a fuel cut at the time of deceleration, when the throttle valve is fully closed and the engine speed is equal to or higher than a predetermined value, it is determined that the fuel supply is in an unnecessary deceleration state. Then, the fuel injection is stopped to improve fuel efficiency, purify exhaust gas, and prevent heating of the catalyst. In the case of high-speed fuel cut, fuel injection is stopped at a predetermined rotation speed (for example, 8000 rpm) or more to prevent the engine from being damaged due to an increase in the engine rotation speed beyond the red zone. It is to suppress. Further, in the case of the highest-speed fuel cut, for example, when the vehicle speed is 180 km or more and the engine rotation speed is 4500 rpm for a predetermined time, the fuel injection is stopped. The present invention can be effectively applied particularly to the case of fuel cut at the time of deceleration.
[0034]
Next, the cylinder deactivation mechanism will be described. As shown in FIG. 2, the engine 50 includes a plurality of cylinders. In the example of FIG. 2, the engine 50 includes four cylinders (# 1 to # 4). The intake air is sent from the surge tank 111 to each cylinder through the intake pipe 113 of each cylinder. On the other hand, the exhaust gas from each cylinder is discharged to the exhaust pipe 129 and sent in the direction of arrow 80. The A / F sensor 131 and the catalytic converter 133 are provided in the exhaust pipe 129 as described above. The exhaust gas that has passed through the catalytic converter 133 is released into the atmosphere through a muffler 174.
[0035]
As described above, the ECU 60 controls the overall operation of the engine 50 based on outputs from various sensors. Further, the ECU 60 supplies the control signal 72 to the variable valve mechanism of each cylinder to control the opening and closing of the intake valve and the exhaust valve of each cylinder.
[0036]
The cylinder is stopped by the ECU 60 closing at least one of the intake valve and the exhaust valve of the target cylinder and stopping the fuel injection to the intake passage of the cylinder. When closing both the intake valve and the exhaust valve, the ECU 60 first controls the variable valve mechanism to close the exhaust valve, then stops fuel injection, and then controls the variable valve mechanism to open the intake valve. close. Thus, the exhaust gas normally remains in the combustion chamber while the cylinder is stopped. On the other hand, when returning from the cylinder deactivated state, the ECU 60 first opens the exhaust valve, then starts fuel injection, and then opens the intake valve.
[0037]
Next, a variable valve operating device that controls opening and closing of an intake valve and an exhaust valve of each cylinder will be described. 3 and 4 show the structure of the variable valve apparatus controlled by the hydraulic circuit. FIG. 3 is a perspective view of the variable valve apparatus, and FIG. 4 is a side sectional view thereof.
[0038]
As shown in FIG. 4, the variable valve device includes a camshaft 10 provided with a cam 11. Below the cam 11, a rocker arm 21 rotatably supported by a rocker shaft 20 is provided. An arm 22 is formed on the tip side of the rocker arm 21 so as to protrude forward. The tip of the arm 22 is in contact with the upper ends of the pair of engine valves 13, and is pressed to the side where the valves 13 are closed by the urging force of the valve spring. The engine valve 13 is driven to open and close based on the pressing of the arm 22 which is swung with the rotation of the rocker arm 21 about the rocker shaft 20.
[0039]
As shown in FIGS. 3 and 4, a movable cam follower 23 corresponding to the cam 11 is provided on the upper surface of the rocker arm 21. The movable cam follower 23 is slidably disposed in a slide hole 35 (FIG. 4) formed along the vertical direction of the rocker arm 21. The movable cam followers 23 are constantly urged toward the cam 11 by the urging force of a coil spring (not shown). Therefore, the movable cam follower 23 receives the pressing while making sliding contact with the cam 11.
[0040]
A cylinder hole 36 is formed below the rocker arm 21 so as to intersect with the slide hole 35 in which the movable cam follower 23 is fitted. In the cylinder hole 36, a lock pin 31 for selectively fastening / unfastening the rocker arm 21 and the movable cam follower 23 is slidably disposed.
[0041]
Next, a cam switching mechanism configured around the lock pin 31 will be described in detail with reference to FIGS. 5 (a) and 5 (b). 5 (a) and 5 (b) are cross-sectional views showing a side cross-sectional structure near the lock pin 31. FIG. 5 (a) shows a state when the fastening is released, and FIG. Are respectively shown.
[0042]
As described above, the movable cam follower 23 is slidably fitted into the sliding hole 35 penetrating the rocker arm 21 vertically. Further, a cylinder hole 36 intersecting with the sliding hole 35 is formed below the rocker arm 21, and the lock pin 31 is slidably fitted in the cylinder hole 36. The lock pin 31 is constantly urged by the coil spring 33 toward the base end side of the rocker arm 21, that is, in the direction away from the movable cam follower 23.
[0043]
A groove 32 is formed in the lock pin 31 from the center to the tip. The lower end of the movable cam follower 23 can be fitted into the groove 32. Further, the bottom of the groove 32 is notched to allow the movable cam follower 23 to slide vertically. On the other hand, the bottom surface of the central portion (base end) of the groove 32 is left so as to be able to contact the lower end of the movable cam follower 23.
[0044]
The space 34 on the base end side of the rocker arm 21 defined by the lock pin 31 in the cylinder hole 36 is a hydraulic chamber into which hydraulic oil for operating the lock pin 31 is introduced. The hydraulic chamber 34 is connected to an oil passage 49 formed in the rocker arm 21. Further, the oil passage 49 is connected to an oil passage 43 formed in the rocker shaft 20, and the hydraulic pressure in the hydraulic chamber 34 is adjusted by the supply and discharge of the working oil through the oil passages 43 and 49. You. Then, the lock pin 31 moves in the cylinder hole 36 in accordance with the balance between the force based on the oil pressure in the hydraulic chamber 34 and the urging force of the coil spring 33, and the position shown in FIG. It slides back and forth between the positions shown in b).
[0045]
When releasing the connection between the rocker arm 21 and the movable cam follower 23, the hydraulic oil is discharged from the hydraulic chamber 34 to lower the hydraulic pressure in the same chamber 34. As a result, the lock pin 31 moves toward the base end side of the rocker arm 21 by the urging force of the coil spring 33, and comes to the position shown in FIG. At this time, since the lower end of the movable cam follower 23 is located at a portion where the bottom surface of the groove 32 of the lock pin 31 is cut out, vertical sliding thereof is allowed.
[0046]
On the other hand, when the rocker arm 21 and the movable cam follower 23 are fastened, hydraulic oil is supplied to the hydraulic chamber 34 to increase the hydraulic pressure in the hydraulic chamber 34. As a result, the lock pin 31 moves toward the distal end of the rocker arm 21 against the urging force of the coil spring 33, and comes to the position shown in FIG. 5B. At this time, the lower end of the movable cam follower 23 is located at a portion where the bottom surface of the groove 32 of the lock pin 31 is left. At this time, when the movable cam follower 23 is pushed down, the lower end surface thereof comes into contact with the bottom surface of the groove 32.
[0047]
The pressing of the cam 11 at this time is directly transmitted to the rocker arm 21 through the contact between the movable cam follower 23 and the lock pin 31. That is, the movable cam follower 23 and the rocker arm 21 at this time are connected to each other, and rotate integrally. In this case, the rocker arm 21 is rotated by the cam 11, and the engine valve 13 is also opened and closed by the cam 11.
[0048]
Therefore, the ECU controls the operation and stop of the engine valve 13 by controlling the supply of hydraulic oil to the hydraulic chamber 34 by controlling an electromagnetic valve or the like provided in the hydraulic circuit of the variable valve operating device. Can be.
[0049]
[Engine control during vehicle deceleration]
Next, engine control during vehicle deceleration according to the present invention will be described.
[0050]
(Basic control)
First, basic control in the present invention will be described. In the present invention, first, when the exhaust catalyst bed temperature of the engine is high, combustion continues without performing fuel cut even in the deceleration state in which the accelerator is off. Thereby, deterioration of the catalyst is suppressed. However, as described above, if the intake air amount is maintained at a certain level in order to prevent a misfire, the feeling of deceleration becomes insufficient. In the present invention, the reduced cylinder operation is performed with some cylinders stopped. Note that, in this specification, "stop a cylinder" means that fuel is not injected into a target cylinder and at least one of an intake valve and an exhaust valve is closed. Stopping a part of all the cylinders of the engine is referred to as “reduced cylinders”.
[0051]
FIG. 6 illustrates changes in the intake air amount at which misfire occurs (hereinafter, referred to as “misfire limit air amount”) in a four-cylinder engine in the case of four-cylinder combustion and the case of two-cylinder combustion. The horizontal axis in FIG. 6 indicates the engine speed, and the vertical axis indicates the total sum of the amount of air taken into all cylinders (four cylinders in this example) as the total intake air amount. As can be seen from the figure, the misfire limit air amount slightly changes according to the engine speed. Also, it can be seen that the misfire limit air amount is smaller in the case of two-cylinder combustion than in the case of four-cylinder combustion. That is, misfire does not occur in the case of two-cylinder combustion even with a smaller intake air amount in the entire engine than in the case of four-cylinder combustion. The reason for this is that, at the time of cylinder reduction, the idle cylinder closes at least one of the intake valve and the exhaust valve. Because it becomes. That is, the total intake air amount is distributed among the four cylinders during four-cylinder combustion, so that each cylinder receives one-fourth of the total intake air amount. Since the amount is distributed among the two cylinders, each cylinder draws in half of the total intake air amount. Therefore, if the total intake air amount is the same, no misfire occurs even with a smaller total intake air amount during the two-cylinder combustion.
[0052]
As described above, in the basic control of the present invention, it is necessary to perform fuel cut at the time of deceleration such as accelerator-off, and when the exhaust catalyst temperature is high, the fuel cut is not performed and the number of cylinders is reduced. As a result, the total intake air amount can be reduced without causing misfire, and accordingly, the fuel injection amount is reduced, and the torque generated by combustion is also reduced, so that a sense of deceleration of the vehicle can be secured. Further, the fuel consumption is also improved by reducing the fuel injection amount.
[0053]
In addition, even when there is a request for fuel cut during deceleration, if the exhaust catalyst temperature is high, fuel cut is not performed and cylinder reduction is performed instead.However, when all cylinders are stopped, mufflers and tail pipes are exhausted from the exhaust pipe. Since exhaust of exhaust gas passing through the exhaust pipe stops, air (oxygen) outside the vehicle flows backward from the tail pipe and enters the exhaust system, and the catalyst may be deteriorated. In this regard, in the present invention, since only a part of the cylinders is stopped, the exhaust gas from the working cylinders is constantly exhausted, and as described above, the air outside the vehicle enters the exhaust system from the tail pipe and the catalyst deteriorates. Can be prevented from being promoted.
[0054]
In the above example, the case where two cylinders are stopped in the four-cylinder engine is described. However, the number of reduced cylinders in the present invention is not limited to this, and all cases where at least one cylinder among a plurality of cylinders is stopped are used. Including. As described above, the combustion is performed by distributing the total intake air amount among the cylinders that are burning. Therefore, if there is at least one idle cylinder, the total intake air amount can be reduced without causing misfiring by that much. Thus, the effect of securing a feeling of deceleration and improving fuel efficiency can be obtained.
[0055]
Next, control of the intake valve and the exhaust valve in the idle cylinder will be described in detail. In the above-described basic control, it is preferable that, in principle, the idle cylinder has both the intake valve and the exhaust valve closed. This is because, by closing both the intake valve and the exhaust valve, there is no movement of air inside and outside the combustion chamber, so that pumping loss is reduced, and as a result, fuel efficiency is improved. However, when the later-described engine brake acceleration control and oil rise prevention control are executed together with the basic control, at least one of the intake valve and the exhaust valve is closed and the other is opened, and the opening and closing are performed. Will be. This will be described in detail later.
[0056]
Further, when both the intake valve and the exhaust valve are closed for the deactivated cylinder, it is necessary to appropriately control the timing to prevent the unburned air (that is, the air containing oxygen) from flowing into the exhaust system. is there. This will be described with reference to FIG. FIG. 7 is a time chart showing an operation cycle of a certain cylinder, and shows an opening / closing state of an intake valve and an exhaust valve during a cycle of intake, compression, combustion, and exhaust. However, parenthesized steps such as intake, compression, and combustion are steps that are not executed because the cylinder is at rest. Periods TP <b> 1 to TP <b> 6 indicated by arrows in the drawing indicate operation periods of the respective steps. In addition, a stop instruction and a return instruction of the cylinder are given from the ECU 60 to the variable valve mechanism of the cylinder at substantially the timing shown in the drawing.
[0057]
In FIG. 7, when a stop instruction is issued in a normal combustion state of the cylinder, the exhaust valve performs an exhaust process in a period TP1, and then stops in a closed state. Thereafter, in a normal operation state, the intake valve is opened and the intake is performed in the period TP2, but in the present embodiment, the intake valve is not opened (in the figure, “×” in the period TP2 indicates that the intake is not performed). Means). Thus, unburned air is not sucked into the combustion chamber. Then, the cylinder enters a cylinder rest state in which both the exhaust valve and the intake valve are closed. Thereafter, when an instruction to return to the operating state is issued, first, the exhaust valve is opened in the period TP3. At this time, assuming that the intake valve is opened in the previous period TP2, unburned air is accumulated in the combustion chamber and is discharged to the exhaust pipe in the exhaust process in the period TP3, so that the catalyst may be deteriorated by oxygen. However, in the present embodiment, as described above, since the intake valve was not opened during the period TP2, there is no unburned air in the combustion chamber, and the unburned air is discharged by the exhaust process during the period TP3. Never. Thus, it is possible to prevent the catalyst from being deteriorated due to the unburned air, that is, the air containing oxygen flowing to the exhaust side.
[0058]
Subsequent to the period TP3, the intake valve is opened in the period TP4 to take in the unburned air into the combustion chamber, and the compression process is performed. In the period TP5, the combustion process is performed. Here, in the present embodiment, after the cylinder is restored, combustion (period TP5) is always performed after the intake valve is first opened (period TP4) and then until the exhaust valve is opened (period TP6). To do. This prevents unburned air from flowing to the exhaust side, and prevents deterioration of the catalyst due to oxygen. After that, each step is executed as usual.
[0059]
As described above, by appropriately controlling the opening and closing of the intake valve and the exhaust valve of the deactivated cylinder, that is, (1) at the time of deactivation, control not to open the intake valve after deactivating the exhaust valve; (2) When returning from rest, control is performed so that combustion is always performed from the opening of the intake valve to the opening of the exhaust valve, so that unburned air flows to the exhaust side, causing deterioration of the catalyst due to oxygen. Can be prevented.
[0060]
(Engine brake acceleration control)
Next, the engine brake acceleration control will be described. This engine brake acceleration control is executed in conjunction with the above-described basic control. That is, when a fuel cut request is generated at the time of deceleration and the catalyst temperature is high, the process is executed when some cylinders are stopped.
[0061]
As described above, in the basic control, the idle cylinder is basically in a state where both the intake valve and the exhaust valve are closed. However, in a state where engine braking is particularly necessary according to the running state of the vehicle, only the intake valve of the deactivated cylinder is always closed, and the exhaust valve is opened and closed according to a normal cycle. In this case, since the exhaust gas flows between the combustion chamber and the exhaust port by opening and closing the exhaust valve, a pumping loss occurs, and as a result, the engine brake torque increases. That is, in this control, by intentionally performing opening and closing of the exhaust valve, a pumping loss is positively generated to promote engine braking. Note that a state in which engine braking is particularly necessary during traveling is, for example, when it is determined that the vehicle is traveling on a downhill at a predetermined vehicle speed or higher, when the return speed of the accelerator pedal is greater than a predetermined value, the brake pedal is depressed. The ECU 60 can determine various states including a case where the ECU 60 is present, and basically determines these based on output signals from various sensors.
[0062]
(Oil rise prevention control)
Next, the oil rise prevention control will be described. This oil rise prevention control is also executed along with the above-described basic control. "Oil rise" means that when the negative pressure in the combustion chamber increases, the engine oil, which is circulated for lubrication of the mechanism originally located below the piston, passes between the piston and cylinder and rises into the combustion chamber. A phenomenon that causes The oil rise is more likely to occur because the negative pressure generated in the combustion chamber increases as the engine speed increases, and more easily as the engine oil temperature increases and the viscosity of the engine oil decreases. If the engine oil enters the combustion chamber due to the rise of oil, there is a problem that the consumption of the engine oil increases. The ECU 60 detects the engine speed and the engine oil temperature, and performs the oil rise prevention control when the engine speed is equal to or higher than a predetermined speed and the engine oil temperature is equal to or higher than a predetermined value.
[0063]
There are two concrete methods for oil rise prevention control, and one of them is selectively executed. First, in the first method, with respect to the deactivated cylinder in the basic control, the intake valve is always closed and the exhaust valve is always opened. By always opening the exhaust valve, the flow of air into and out of the combustion chamber is reduced, and the negative pressure generated in the combustion chamber is reduced. Therefore, in the basic control, in principle, both the intake valve and the exhaust valve are closed, but under the condition where the oil rise easily occurs, only the intake valve of the deactivated cylinder is always closed and the exhaust valve is opened. As a result, oil rise can be suppressed.
[0064]
In the first method described above, the negative pressure is reduced by keeping the intake valve of the deactivated cylinder closed at all times and opening the exhaust valve at all times. The valve may be always closed and the intake valve may be always open. However, in this case, unburned air enters the combustion chamber because the intake valve is open, and it is necessary to prevent the unburned air from flowing directly to the exhaust side to cause deterioration of the catalyst. Therefore, as described with reference to FIG. 7, it is necessary to ensure that combustion is performed before the exhaust valve is opened when returning from the idle cylinder.
[0065]
On the other hand, in the second method, as in principle of the basic control, both the intake valve and the exhaust valve of the deactivated cylinder are always closed. However, the timing of closing the exhaust valve when shifting to the rest state is adjusted. This will be described with reference to FIG. FIG. 8 is a time chart basically similar to that of FIG. 7, and shows each step when the cylinder to be deactivated is deactivated and returned. However, in FIG. 8, the timing of closing the exhaust valve after the stop instruction is delayed unlike FIG. 7, which shows a basic time chart of the basic control. In FIG. 8, while the period TP1 is a period during which the normal exhaust valve is open (similar to FIG. 7), in the second method of oil rise prevention control, the period during which the exhaust valve is opened is defined as a period TP1a. The timing to close the exhaust valve is delayed. Specifically, the exhaust valve is closed near the bottom dead center next to the exhaust top dead center. As a result, since the exhaust valve is open while the piston moves to the vicinity of the bottom dead center after the exhaust process, part of the exhaust gas discharged to the exhaust port side enters the combustion chamber during that time, and the combustion chamber is almost at atmospheric pressure. About. Thereafter, the exhaust valve is closed, so that the combustion chamber can be maintained at substantially the atmospheric pressure for the deactivated cylinder. Oil rise is caused by negative pressure in the combustion chamber. When the exhaust valve is closed according to a normal exhaust cycle, the exhaust valve closes immediately after exhaust gas is discharged, so that the combustion chamber is easily maintained in a negative pressure state. However, this method delays the timing of closing the exhaust valve, and closes the exhaust valve after the piston approaches the next bottom dead center and exhaust gas is taken into the combustion chamber. And negative pressure, which causes oil rise, is unlikely to be generated. Thus, the second method can also prevent the oil from rising.
[0066]
Compared with the first method, the first method opens and closes the exhaust valve of the deactivated cylinder, so that the movement of the exhaust gas flowing between the exhaust port and the combustion chamber may cause some noise in the exhaust system. In the second method, since the exhaust valve is always closed, such noise does not occur. On the other hand, the second method needs to delay the timing of closing the exhaust valve, and thus is suitable for an engine having a high degree of freedom in opening and closing control of the exhaust valve, such as an engine using an electromagnetically driven valve.
[0067]
(Process flowchart)
Next, control during deceleration according to the present invention will be described with reference to the flowchart in FIG. Note that the flowchart shown in FIG. 9 illustrates processing in the case where the engine brake acceleration control and the oil rise prevention control are executed in addition to the above-described basic control. However, in an actual vehicle, only the basic control is executed. It is also possible to execute only one of the engine brake improvement control and the oil rise prevention control in addition to the basic control. The processing shown in FIG. 9 is basically performed by the ECU 60 executing each step while monitoring the outputs of various sensors according to a program prepared in advance.
[0068]
First, the ECU 60 detects the engine speed of the vehicle based on the output of the crank angle sensor 145 and the like, and determines whether or not the engine speed is equal to or higher than a predetermined fuel cut (F / C) execution speed. Step S1). If the rotation speed is not equal to or higher than the fuel cut execution speed (Step S1; No), the fuel cut is not performed, and the combustion is continued in all the cylinders as usual (Step S2).
[0069]
On the other hand, when it is determined that the engine speed is equal to or higher than the predetermined fuel cut execution speed (step S1; Yes), the ECU 60 determines whether the catalyst temperature is equal to or higher than the predetermined temperature (step S3). . The catalyst temperature can be detected by, for example, a catalyst temperature sensor (not shown) that outputs an electric signal corresponding to the exhaust catalyst bed temperature in the catalytic converter 133, but may be detected by other methods. Is also possible. If the catalyst temperature is not equal to or higher than the predetermined temperature (Step S3; No), the ECU 60 executes fuel cut for all cylinders because there is a low possibility of catalyst deterioration due to air (oxygen) (Step S4). On the other hand, when the catalyst temperature is equal to or higher than the predetermined temperature (Step S3; Yes), there is a risk of deterioration of the catalyst due to the inflow of air, so that the fuel cut is not performed according to the above-described basic control.
[0070]
Next, the ECU 60 determines whether or not the engine brake acceleration condition is satisfied (step S5). As described above, the engine brake acceleration condition includes, for example, a case where it is determined that the vehicle is going downhill at a speed equal to or higher than a predetermined vehicle speed, a case where the brake pedal is depressed, and the like. If the engine brake acceleration condition is satisfied (step S5; Yes), the ECU 60 executes the above-described engine brake acceleration control (step S6). That is, first, the ECU 60 suspends a part of the cylinders without performing the fuel cut according to the basic control to perform the reduced cylinder operation, and always closes the intake valve and opens and closes the exhaust valve for the suspended cylinder. By always closing the intake valve, unburned air is prevented from flowing into the exhaust-side catalyst, and by opening and closing the exhaust valve, pumping loss occurs, increasing engine brake torque and accelerating engine braking. You.
[0071]
On the other hand, when the engine brake acceleration condition is not satisfied (Step S6; No), the ECU 60 determines whether or not it is necessary to prevent the oil from rising (Step S7). In this determination, for example, as described above, when the engine speed is equal to or higher than the predetermined engine speed and the engine oil temperature is equal to or higher than the predetermined value, it is determined that it is necessary to prevent oil rising. When it is determined that the prevention of oil rise is necessary (Step S7; Yes), the ECU 60 first performs the reduced-cylinder operation without performing the fuel cut according to the basic control, and further performs the first of the above-described oil rise prevention control. Perform either the method or the second method. That is, when executing the first method, the intake valve is normally closed and the exhaust valve is normally open for the deactivated cylinder. When the second method is executed, the timing of closing the intake valve and closing the exhaust valve of the idle cylinder is adjusted. As a result, the negative pressure in the combustion chamber is reduced, and oil rise is prevented.
[0072]
On the other hand, if it is determined that it is not necessary to prevent the rise of oil (step S7; No), the ECU 60 performs the reduced-cylinder operation without performing the fuel cut according to the basic control, and furthermore, always operates both the intake valve and the exhaust valve. It is closed (step S9). This prevents unburned air from flowing to the exhaust side and deteriorating the catalyst.
[0073]
【The invention's effect】
As described above, according to the present invention, at the time of deceleration such as accelerator-off, when the exhaust catalyst temperature is high, the fuel cut is prohibited, and the unburned air flows to the exhaust side. Prevent deterioration. At this time, in order to prevent the feeling of deceleration from being insufficient for continuing the combustion, the cylinders are partially stopped to perform the reduced cylinder operation. Further, by controlling the opening and closing of the intake valve and the exhaust valve of the stopped cylinder as needed, it is possible to promote the engine brake and prevent the oil from rising.
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of an engine according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a cylinder deactivation mechanism of the engine according to the embodiment of the present invention.
FIG. 3 is a perspective view showing a schematic configuration of a variable valve operating device.
FIG. 4 is a view showing a side sectional structure of the variable valve apparatus shown in FIG. 3;
FIG. 5 is a side sectional view of a cam switching mechanism of the variable valve operating device shown in FIG. 2;
FIG. 6 is a graph showing a misfire limit air amount when all cylinders are operating and when cylinders are reduced.
FIG. 7 is a time chart showing opening / closing control of an intake valve and an exhaust valve in basic control.
FIG. 8 is a time chart showing opening / closing control of an intake valve and an exhaust valve in a second method of oil rise prevention control.
FIG. 9 is a flowchart of control during deceleration according to the present invention.
[Explanation of symbols]
1 cylinder
50 engine
60 ECU
111 surge tank
113 Intake pipe
123 intake valve
124 exhaust valve
129 Exhaust pipe
133 catalytic converter

Claims (6)

An engine control device having a plurality of cylinders,
Fuel cut condition detecting means for detecting that a fuel cut condition at the time of vehicle deceleration is provided,
Catalyst temperature detecting means for detecting that the exhaust catalyst temperature is equal to or higher than a predetermined temperature,
Control means for stopping at least one of the plurality of cylinders when the fuel cut condition is satisfied and the catalyst temperature is detected to be equal to or higher than a predetermined temperature. Engine control device. In the deactivated state of the cylinder, the control unit closes both the intake valve and the exhaust valve of the cylinder to be deactivated, and performs combustion during a period from when the intake valve is opened to when the exhaust valve is opened. The engine control device according to claim 1, wherein opening / closing timings of the intake valve and the exhaust valve are controlled so that a process is performed. Further comprising means for detecting the need for engine braking,
When the necessity of engine braking is detected, the control means always keeps an intake valve of a cylinder to be stopped in a halt state of the cylinder and controls opening and closing of an exhaust valve of the cylinder. The engine control device according to claim 1, wherein: Means for detecting the engine speed;
Means for detecting the temperature of the engine oil,
When the engine rotation speed is higher than a predetermined rotation speed and the temperature of the engine oil is higher than a predetermined temperature, the control unit may be configured to select one of the intake valve and the exhaust valve of the cylinder to be stopped in the stopped state of the cylinder. 2. The engine control device according to claim 1, wherein the control valve is always closed, and the other of the intake valve and the exhaust valve of the cylinder is always open. Means for detecting the engine speed;
Means for detecting the temperature of the engine oil,
The control means, when the engine speed is higher than a predetermined speed, and when the temperature of the engine oil is higher than a predetermined temperature, in the halt state of the cylinder, in the halt state of the cylinder, always keep the intake valve of the cylinder to be deactivated, 2. The engine control device according to claim 1, wherein the exhaust valve of the cylinder is closed and maintained in a closed state near a bottom dead center after the exhaust top dead center. 6. The fuel control system according to claim 1, wherein the control unit executes a fuel cut for the plurality of cylinders when the fuel cut condition is satisfied and the catalyst temperature is not detected to be equal to or higher than a predetermined temperature. An engine control device according to any one of claims 1 to 4.

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