JP4192700B2 - engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of an engine, particularly an engine configured to introduce exhaust from a preceding cylinder into a subsequent cylinder and burn it again.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a vehicle engine such as an automobile, there has been known a technique for improving fuel efficiency by burning an air-fuel ratio of an air-fuel mixture introduced into each cylinder with a lean air-fuel ratio larger than a theoretical air-fuel ratio. . In such a lean combustion engine, if a three-way catalyst (a catalyst having high purification performance near the theoretical air-fuel ratio with respect to HC, CO, and NOx) is provided as an exhaust purification catalyst, NOx is reduced during lean operation. On the other hand, since a sufficient purification performance cannot be obtained, a lean NOx catalyst that adsorbs NOx in an oxygen-excess atmosphere and desorbs and reduces NOx in an oxygen-concentrated atmosphere may be provided. When such a lean NOx catalyst is used, if the NOx adsorption amount of the lean NOx catalyst increases during the lean operation, the air-fuel ratio of the exhaust gas is enriched and CO is generated, whereby NOx is released and reduced. To promote.
[0003]
However, a lean NOx catalyst requires a relatively large capacity in order to secure a certain amount of NOx adsorption, and is more expensive than a three-way catalyst, which is disadvantageous in terms of cost. Further, in order to maintain the purification performance of the lean NOx catalyst, for example, when the lean operation continues and the NOx adsorption amount increases and becomes saturated, as described above, the additional fuel is removed for the removal and reduction of NOx. Since it is necessary to temporarily enrich the air-fuel ratio by supply or the like, the fuel efficiency improvement effect by lean combustion is reduced.
[0004]
Therefore, there is a demand for a technique that reduces the amount of NOx released to the atmosphere while performing lean operation, thereby eliminating the need for a lean NOx catalyst. For this purpose, for example, the technique disclosed in Patent Document 1 is applied. It is possible to do. That is, in a multi-cylinder engine, a pipe for introducing exhaust from the first cylinder (preceding cylinder) into the second cylinder (subsequent cylinder) is provided, and the air-fuel mixture is burned in two stages in these two cylinders. . In other words, lean combustion is performed in the preceding cylinder, but the lean combustion exhaust gas discharged from the preceding cylinder is introduced into the subsequent cylinder and recombusted, so that the lean exhaust gas is not released into the atmosphere as it is. . This eliminates the need for a lean NOx catalyst. In that case, particularly in the subsequent cylinder, for example, O introduced from the preceding cylinder.₂Combustion at the stoichiometric air-fuel ratio by supplying an amount of fuel corresponding to the concentration, etc., and opening the exhaust of this subsequent cylinder to the atmosphere side, the exhaust gas can be sufficiently purified only with the three-way catalyst (See Japanese Patent Application No. 2002-024548 by the present applicant).
[0005]
[Patent Document 1]
JP-A 61-46421
[0006]
[Problems to be solved by the invention]
By the way, in order to re-combust the exhaust gas generated in the preceding cylinder in the subsequent cylinder, an exhaust introduction passage for introducing the exhaust from the preceding cylinder to the subsequent cylinder is required. In order to fit in the engine room, it is required to make the exhaust introduction passage compact (for example, the degree of protrusion from the engine body is small), and as a result, the exhaust introduction passage tends to be shortened as much as possible. Further, when the preceding cylinder and the succeeding cylinder are adjacent to each other, the exhaust introduction passage is short and bent, for example, in a U shape. As a result, the exhaust introduction passage cannot secure a linear distance from the preceding cylinder to the succeeding cylinder, and cannot ensure a sufficient intake flow in the combustion chamber of the succeeding cylinder. A situation occurs where the lean exhaust generated in the cylinder is discharged as it is.
[0007]
Accordingly, an object of the present invention is to improve the combustibility of the subsequent cylinder in an engine in which the lean exhaust of the preceding cylinder is burned again in the subsequent cylinder in order to eliminate the need for the lean NOx catalyst.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is configured as follows.
[0009]
  In the first aspect of the present invention, the exhaust of the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of cylinders having an even number of cylinders and the exhaust stroke and the intake stroke overlap, is the subsequent cylinder which is the cylinder on the intake stroke side. An engine that is introduced into a cylinder and burned again, wherein the exhaust introduction port is provided in a subsequent cylinder, and the exhaust introduction port is a helical portAt the same time, the intake port that introduces fresh air from the succeeding cylinder is a substantially straight straight port that can generate a tumble flow or a swirl flow, and the exhaust stop for the preceding cylinder that stops exhaust from the preceding cylinder to the atmosphere is stopped. Means, an exhaust introduction stop means for stopping the introduction of exhaust gas from the preceding cylinder to the succeeding cylinder, and a fresh air introduction stopping means for the succeeding cylinder for stopping introduction of fresh air to the succeeding cylinder. Switching means for switching between a normal mode in which only the exhaust introduction stop means is in operation and a recombustion mode in which the exhaust stop means for the preceding cylinder and the fresh air introduction stop means for the subsequent cylinder are in operation, depending on the operating state In the re-combustion mode, the amount of fresh air introduced into the preceding cylinder and the preceding cylinder is burned so that the preceding cylinder burns at a lean air-fuel ratio greater than the stoichiometric air-fuel ratio. Charge supply amount by controlling at least one, in the following cylinders is provided with an air-fuel ratio control means for controlling at least one of the exhaust gas introduction amount and the fuel supply amount to the following cylinder to combust at the stoichiometric air-fuel ratioIt is characterized by that.
[0010]
According to the present invention, since the exhaust introduction port is a helical port, a swirl flow can be formed in the combustion chamber of the subsequent cylinder, and even when a sufficient linear distance cannot be secured in the exhaust introduction passage, Thus, the intake air flow can be formed, and the combustibility in the succeeding cylinder is improved. Therefore, when lean exhaust introduced from the preceding cylinder is subjected to, for example, stoichiometric air-fuel ratio combustion (λ = 1 combustion) or rich combustion in the subsequent cylinder, NOx is biased and increased in a large amount by improving the combustibility in the subsequent cylinder. It is reliably avoided that the lean exhaust gas contained is released into the atmosphere as it is, and the lean NOx catalyst becomes unnecessary.
[0012]
  Also,In the straight port, a sufficient linear distance can be secured for forming the intake air flow in the combustion chamber, so that a tumble flow or a swirl flow can be formed in the combustion chamber and the intake charging efficiency can be ensured. .
[0013]
  Further, according to the present invention, in the normal mode, fresh air is introduced into the subsequent cylinder for combustion, and in the recombustion mode, exhaust from the preceding cylinder is introduced into the subsequent cylinder for combustion. Then, by controlling each of the stop means, it is possible to easily switch to the normal mode in the operation region on the high load and high rotation side, and the recombustion mode in the low load and low rotation region.
[0014]
  In the re-combustion mode, the preceding cylinder performs combustion at a lean air-fuel ratio by controlling at least one of the amount of fresh air introduced into the preceding cylinder and the amount of fuel supplied to increase the thermal efficiency and reduce the pumping loss. The fuel consumption is improved by the reduction, and in the succeeding cylinder, combustion is performed in a state where the theoretical air-fuel ratio is controlled by controlling at least one of the exhaust introduction amount and the fuel supply amount to the succeeding cylinder, and the succeeding cylinder Since only the exhaust of the stoichiometric air-fuel ratio discharged from the cylinder is discharged, the exhaust purification performance of HC, CO, and NOx can be obtained sufficiently efficiently with only the three-way catalyst.
[0017]
  next,Claim 2The invention described inClaim 1In the invention described inExhaust air is exhausted to the atmosphere from the exhaust introduction passage that communicates the first exhaust port of the preceding cylinder and the exhaust introduction port of the succeeding cylinder to the mounting flange to the cylinder head of the exhaust manifold, and the second exhaust port of the preceding cylinder. A preceding cylinder side exhaust passage and a subsequent cylinder side exhaust passage for exhausting the exhaust from the exhaust port of the subsequent cylinder to the atmosphere. The exhaust introduction passage has a substantially constant cross-sectional area, and The cross section of the cylinder side and subsequent cylinder side exhaust passages has a flat opening on the mounting surface side of the cylinder head, and changes to a perfect circle while gradually increasing the cross sectional area toward the downstream side.It is characterized by being.
[0018]
  According to the present invention, since the exhaust introduction passage is formed inside the flange portion of the existing exhaust manifold, it is not necessary to project the passage from the engine body and newly provide it outside, and the compactness is maintained.
[0019]
  In addition, by making the cross-sectional area of the exhaust introduction passage substantially constant, a temperature drop due to expansion of the exhaust discharged from the preceding cylinder is avoided, and the ignitability in the succeeding cylinder is maintained. The combustibility of the subsequent cylinder is improved.
[0020]
  On the other hand, because the leading cylinder side and the trailing cylinder side exhaust passages interfere with the exhaust introduction passage formed in the flange, the space for forming the exhaust passage in the flange is limited. Therefore, according to the present invention, the opening on the mounting surface side of the leading cylinder side and the trailing cylinder side exhaust passage to the cylinder head is formed flat, thereby avoiding interference with the exhaust introduction passage and disconnecting toward the downstream side. Exhaust efficiency can be improved by forming a perfect circle so that the area gradually increases.
[0021]
  next,Claim 3The invention described inClaim 1 or claim 2In the invention described in (1), ignition control means for controlling ignition so that spark ignition is performed in the preceding cylinder and compression self-ignition is performed in the succeeding cylinder is provided.
[0022]
According to the present invention, in the compression self-ignition performed in the succeeding cylinder, since the entire combustion chamber burns at a stretch, the combustion efficiently contributes to work. Further, since the swirl flow formed by the helical port flows until the end of the compression stroke, it is advantageous in improving combustibility when performing spontaneous ignition combustion by compression.
[0023]
  next,Claim 4The invention according to claim 1 is fromClaim 3In any one of the inventions, a three-way catalyst is disposed downstream of the exhaust manifold, and the exhaust manifold has a double-pipe structure.
[0024]
According to the present invention, the exhaust manifold can be introduced into the three-way catalyst disposed downstream without lowering the temperature by improving the exhaust purification performance by adopting a double pipe structure for the exhaust manifold.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
First, the configuration of the engine 1 according to the present embodiment will be described. FIG. 1 shows a schematic configuration of an engine 1 according to an embodiment of the present invention. The engine 1 is a spark ignition direct injection engine, and an engine body 2 including a cylinder block 3 and a cylinder head 4 (see FIG. 2) has four cylinders (first in order from the top in FIG. 1). Cylinder A, No. 2 cylinder B, No. 3 cylinder C, No. 4 cylinder D) are provided. The first cylinder A and the fourth cylinder D, and the second cylinder B and the third cylinder C have similar configurations.
[0026]
As shown in FIG. 2, a combustion chamber 12 defined by a piston 11 is formed in each of the cylinders A, B, C, and D (the illustrated example is the first cylinder A). An ignition plug 13 is installed at the upper center of the combustion chamber 12, and a fuel injection valve 14 is provided so as to face the combustion chamber 12 from the side. Further, intake ports 15... 15 and exhaust ports 16... 16 are provided in the combustion chambers 12... 12 of the respective cylinders A to D (the exhaust ports of the first and fourth cylinders A and D are claimed in the claims). Corresponding to the second exhaust port in the range). Further, the second and third cylinders are provided with an exhaust introduction port 17, and the first and fourth cylinders are provided with an exhaust outlet port 18 (first exhaust port). These ports 15 to 18 are driven by the camshafts 19 and 20 shown in FIG. 2 and the intake valves 21... 21 and the exhaust valves 22. A and D exhaust outlet valves 24 are respectively opened and closed. The spark plug 13 is connected to an ignition circuit 25 that can control the ignition timing by electronic control. In addition, each valve shown with the oblique line in FIG. 1 represents the valve which has the valve stop mechanism 70 mentioned later.
[0027]
The fuel injection valve 14 incorporates a needle valve and a solenoid (not shown). When a pulse signal is input, the fuel injection valve 14 is driven for a time corresponding to the pulse width at the pulse input timing to open the valve. It is comprised so that the quantity of fuel according to may be injected. The fuel injection valve 14 is supplied with fuel by a fuel pump (not shown) via a fuel supply passage or the like, and can apply a fuel pressure higher than the pressure in the combustion chamber 12 during the compression stroke. A fuel supply system is configured.
[0028]
In each cylinder A to D, a pair of intake ports 15... 15 that open to the combustion chambers 12... 15 are connected to the downstream ends of the intake manifolds 31 arranged on the downstream side of the intake pipe 30 that introduces fresh air. Has been. In addition, multiple throttle valves 32... 32 are provided inside each pipe of the intake manifold 31, and the multiple throttle valves 32... 32 are driven by an actuator 33 according to a control signal, thereby adjusting the amount of fresh air introduced. Is done. The intake pipe 30 is provided with an air flow sensor 34 that detects the intake flow rate and sends the flow rate data to an ECU (control unit) described later.
[0029]
Further, the exhaust ports 16... 16 communicate with the exhaust manifold 40 via the atmosphere side exhaust passages 42... 42 provided in the flange portion 41 for attaching the exhaust manifold 40 to the cylinder head 4 (1, 4th cylinder A). , D, the passage 42 corresponds to a "preceding cylinder side exhaust passage", and the passages 42, B, and C correspond to "subsequent cylinder side exhaust passages"). The exhaust manifold 40 collects in one exhaust pipe 43 on the downstream side. Downstream of the exhaust pipe 43 is an O that detects the oxygen concentration in the exhaust.₂A three-way catalyst 45 is disposed further downstream from the sensor 44. The three-way catalyst 45 is a catalyst that exhibits high purification performance for HC, CO, and NOx when the air-fuel ratio of the exhaust is in the vicinity of the stoichiometric air-fuel ratio (excess air ratio λ = 1). On the other hand, the exhaust outlet ports 18 of the first and fourth cylinders A and D communicate with the exhaust inlet ports 17 of the second and third cylinders B and C through exhaust introduction passages 46 and 46 provided in the flange portion 41, respectively. To do. An intermediate portion of the exhaust introduction port 17 has a linear O₂Sensors 47 are provided. This linear O₂The sensors 47 and 47 detect the lean degree of exhaust from the first and fourth cylinders A and D.
[0030]
Next, the structure of the exhaust introduction port 17 will be described with reference to FIG. 3. FIG. 3 is a plan sectional view of the cylinder head 4 showing the ports 15, 15, 16, 17 of the second cylinder B. The port 17 is a helical port 17. The helical port 17 is a port that spirally turns as the port 17 moves toward the downstream side, and forms a lateral vortex flow (swirl flow) in the combustion chamber 12. On the other hand, the shape of each of the intake ports 15 and 15 and the exhaust port 16 is a substantially straight shape that reaches the combustion chamber 12 substantially linearly.
[0031]
The structure of the exhaust manifold 40 will be described with reference to FIGS. The exhaust manifold 40 includes four steel pipe branch pipes 40a, 40b, 40c, and 40d that communicate with the atmosphere-side exhaust passages 42 ... 42 formed in the flange portion 41, respectively. The branch pipes 40 a, 40 b, 40 c, and 40 d are curved and gather at the center lower part of the flange portion 41, and the outer periphery is covered with the inner pipe 50. Furthermore, an outer tube 51 that covers the periphery of the inner tube 50 at a predetermined distance is provided to form a double tube structure. Further, a partition plate 53 made of a heat-resistant metal is provided which divides the exhaust gas introduced from the branch pipes 40a, 40b, 40c, and 40d into two parts and guides it to the downstream side. On the other hand, a spacer 52 made of a stainless wire mesh or the like is interposed in the space between the inner tube 50 and the outer tube 51. A flange 54 for connecting the inner pipe 50 to the exhaust pipe 43 is provided in the vicinity of the downstream end of the exhaust manifold 40, and both are connected by bolts 55, 55 to constitute a so-called 4-2-1 type exhaust system. is doing.
[0032]
FIG. 6 shows a mounting surface of the flange portion 41 to the cylinder head 4. Inside the flange portion 41, four atmosphere side exhaust passages 42 ... 42 and a pair of exhaust introduction passages 46, 46 are formed. The openings 60... 60 on the attachment surface side of the atmosphere side exhaust passages 42... 42 formed in the flange portion 41 to the cylinder head 4 have an elliptical flat shape that is long in the vertical direction. Then, as shown in FIG. 7, the atmosphere side exhaust passages 42... 42 are changed so as to gradually increase the cross-sectional shape in the flange portion 41 toward the downstream side, and the openings 61. It is formed inside the flange portion 41 so as to have a perfect circular shape. In addition, this flange part 41 may perform a lightening for size reduction and weight reduction. On the other hand, the exhaust introduction passages 46 and 46 are folded back into a U shape in the flange portion 41 while keeping the cross-sectional area of the exhaust outlet port 18 provided in the first and fourth cylinders A and D constant, and the second and third cylinders. It reaches the exhaust introduction port 17 provided in B and C. Therefore, the flange portion 41 has a width and a thickness that can ensure at least a cross-sectional area of the exhaust introduction passages 46 and 46.
[0033]
Next, the valve stop mechanism 70 will be described with reference to FIG. 8. The valve stop mechanism 70 includes the exhaust valves 23 of the first and fourth cylinders A and D, the exhaust outlet valves 24 and the intake air of the second and third cylinders B and C. 21 are formed on tappets 71... 71 corresponding to the valves 21... 21 and the exhaust introduction valves 22 (valves represented by hatching in FIG. 1). The tappet 71 is divided into a center tappet 72 for valve operation and a side tappet 73 for valve stop. In addition, a hydraulic lock mechanism 74 for connecting and releasing the center tappet 72 and the side tappet 73 is provided. The center tappet 72 and the side tappet bodies 75, 76 are provided with through holes 80, 81, 82, and bushes 83, 84, 85 are inserted and fixed in the through holes, respectively. The hydraulic plunger 86, the lock pin 87, and the plunger 88 are fitted inside the bushes 83, 84, 85 in a movable state. The bushes 84 and 85 are provided with return springs 89 and 90 for returning the hydraulic plunger 86, the lock pin 87, and the plunger 88 to predetermined positions, respectively.
[0034]
When hydraulic pressure is applied, the hydraulic plunger 86 moves toward the lock pin 87 and pushes the lock pin 87 and the plunger 88 toward the side tappet body 76. At this time, the contact portion between the hydraulic plunger 86 and the lock pin 87 and the contact portion between the lock pin 87 and the plunger 88 are substantially flush with the split portion between the center tappet 72 and the side tappet 73, so that the center tappet 72 is the side tappet. 73 is released and the lock is released. When the hydraulic pressure is released, the return springs 89 and 90 push the lock pin 87 and the plunger 88 back to the side tappet body 75 side, the lock pin 87 is a divided portion of the center tappet 72 and the side tappet body 75, and the plunger 88 is the center. The tappet 72 and the side tappet body 76 are respectively fitted into the divided portions, and they cooperate to couple the center tappet 72 and the side tappet 73 into a locked state.
[0035]
As described above, the lock mechanism 74 can be switched between a locked state and an unlocked state by hydraulic pressure. In the locked state, the center tappet 72 and the side tappet 73 are coupled, and the center tappet 73 and the center driven by the cam 91 are driven. The tappet 72 cooperates to lift the valve. Further, in the unlocked state, the center tappet 72 is detached from the side tappet 73 and freely moves while being pressed against the cam 91 by a lost motion spring (not shown), and the valve-stopping circular cam 92 passes through the side tappet 73. And stop the valve.
[0036]
Then, the effect of the engine 1 which concerns on this Embodiment is demonstrated.
[0037]
Each of the cylinders A to D performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of this engine 1, as shown in FIG. 9, the cycle is provided with a phase difference of 180 ° in each of the cranks in the order of the first cylinder A, the third cylinder C, the fourth cylinder D, and the second cylinder B. Each of the cylinders A to D is injected with fuel by the fuel injection valves 14... 14 in the compression stroke, and then ignited by the spark plugs 13.
[0038]
Between a pair of cylinders where the exhaust stroke and the intake stroke overlap, from the cylinder on the exhaust stroke side (hereinafter referred to as the preceding cylinder) when the exhaust stroke and the intake stroke overlap, to the cylinder on the intake stroke side (hereinafter referred to as the subsequent cylinder) Exhaust gas can be guided through the exhaust gas introduction passages 46 and 46 (see broken line arrows in FIG. 9). Here, the exhaust stroke of the first cylinder A and the intake stroke of the second cylinder B overlap, and the exhaust stroke of the fourth cylinder D and the intake stroke of the third cylinder C overlap, so that the first cylinders A and 4 Number cylinder D is the preceding cylinder, number 2 cylinder B, and number 3 cylinder C are the succeeding cylinders. The succeeding cylinder may be a cylinder having a port through which exhaust is introduced from a port in the exhaust stroke during the intake stroke.
[0039]
FIG. 10 shows a block diagram of the control system of the engine 1. In this figure, an ECU 100 for controlling the engine 1 composed of a microcomputer or the like includes an air flow sensor 34, an O₂Sensor 44 and linear O₂A signal from the sensor 47 is input, and a signal from an engine speed sensor 101 that detects the engine speed and an accelerator opening sensor 102 that detects the amount of depression of the accelerator pedal in order to determine the driving state is also input. Further, control signals are output from the ECU 100 to the first and second control valves 111 and 112, the ignition circuit 25 of each fuel injection valve 14 ... 14, and the actuator 33 of the multiple throttle valves 32 ... 32. Yes. The ECU 100 also includes an operating state determination unit 120, a valve stop mechanism control unit 121, an intake air amount control unit 123, and a fuel injection control unit 124.
[0040]
The operating state discriminating means 120 checks the operating state of the engine 1 at the engine speed and the engine load based on signals from the rotational speed sensor 101 and the accelerator opening sensor 102, and the operating state is low and low as shown in FIG. It is determined whether it is in the operation region X on the rotation side or the operation region Y on the high load side or the high rotation side.
[0041]
The valve stop mechanism control means 121 controls the control valves 111 and 112 according to whether the operation state is in the operation region X on the low load / low rotation side or in the operation region Y on the high load / high rotation side. Then, supply / discharge of hydraulic pressure to / from the valve stop mechanisms 70... 70 is controlled.
[0042]
Specifically, in the operation region X, the first control valve 111 is turned OFF, that is, the exhaust gas introduction valve 23 is not supplied to the valve stop mechanisms 70... 70 corresponding to the exhaust gas introduction valve 23 and the exhaust gas discharge valve 24. The exhaust control valve 112 and the second control valve 112 are turned on, that is, the exhaust valves 23 and 2 and the third and third cylinders B and C provided in the first and fourth cylinders A and D, respectively. The hydraulic pressure is supplied to the valve stop mechanism 70... 70 corresponding to 21 to stop the exhaust valve 23 provided in the first and fourth cylinders A and D and the intake valve 21 provided in the second and third cylinders B and C. (Reburn mode)
[0043]
On the other hand, in the operation region Y, the first control valve 111 is turned on, that is, the control oil pressure is not supplied to the valve stop mechanisms 70. The valve 24 is in an operating state and the second control valve 112 is turned on, that is, the exhaust valve 23 provided in the first and fourth cylinders A and D and the intake valve 21 provided in the second and third cylinders B and C. The hydraulic pressure is supplied to the corresponding valve stop mechanisms 70... 70, and the exhaust valves 23 provided in the first and fourth cylinders A and D and the intake valves 21 provided in the second and third cylinders B and C are stopped. (Normal mode).
[0044]
The intake air amount control means 123 controls the opening degree of the throttle valve by controlling the actuator 33. The intake air amount control means 123 obtains a target intake air amount from a map or the like according to the operating state, and according to the target intake air amount. Control the throttle opening. In this case, in the operation region X on the low load and low rotation side, the intake air from the intake manifold 31 is blocked for the subsequent cylinders B and C, and excess air in the exhaust gas introduced from the preceding cylinders A and D is fuel. Therefore, the throttle opening is adjusted so that air necessary for the combustion of the preceding and succeeding two cylinders is supplied to the preceding cylinder.
[0045]
The fuel injection control means 124 controls the fuel injection amount and the injection timing from the fuel injection valves 14... 14 provided in each of the cylinders A to D according to the operating state of the engine 1. And the control of fuel injection differ in the case of the operation region Y.
[0046]
That is, as shown in FIG. 9, when the operating state is in the operating region X (reburning mode), for the preceding cylinders A and D, the lean air-fuel ratio, preferably the theoretical air-fuel ratio, which is larger than the stoichiometric air-fuel ratio. The fuel injection amount is controlled so as to be approximately twice or more than the air-fuel ratio, and the injection timing is set so that fuel is injected in the compression stroke to cause stratified combustion. On the other hand, for the succeeding cylinders B and C, the fuel injection amount is controlled so that fuel is supplied to the lean air-fuel ratio burned gas introduced from the preceding cylinders A and D so as to obtain the stoichiometric air-fuel ratio. An injection timing is set so that ignition and combustion can be performed under a situation where there is a large amount of fuel gas, and more preferable combustibility can be obtained by injecting fuel in the compression stroke.
[0047]
The control of the fuel injection amount in the re-combustion mode is performed by the air flow sensor 34 and the O₂This is performed by feedback control based on the output from the sensor 44 or the like. Specifically, each of the cylinders A to D according to the intake air amount detected by the air flow sensor 34 so that the preceding cylinders A and D have a predetermined lean air-fuel ratio and the succeeding cylinders B and C have a theoretical air-fuel ratio. Is calculated, and the linear O provided in the exhaust introduction passages 46 and 46 is calculated.₂Based on the output from the sensors 47, 47, the fuel flow injection amount for the preceding cylinders A, D is feedback-corrected, and an O provided in the exhaust pipe 43 is further corrected.₂Based on the output from the sensor 44, the fuel injection amount for the succeeding cylinders B and C is feedback-corrected.
[0048]
On the other hand, as shown in FIG. 12, when the operation state is in the operation region Y (normal mode), the fuel injection amount is controlled so that the air-fuel ratio of each cylinder A to D is the stoichiometric air-fuel ratio or less. The stoichiometric air-fuel ratio is set in the paired region of the operation region Y, and is made richer than the stoichiometric air-fuel ratio in the fully open load and the operation region in the vicinity thereof. And more preferable combustibility can be obtained by setting the injection timing so that uniform combustion is performed by injecting fuel in each cylinder, for example, in the intake stroke.
[0049]
By performing the control as described above, the following effects can be obtained. That is, in the operation region X, fresh air is introduced from the intake manifold 31 in the preceding cylinders A and D, and the linear O₂The fuel is injected in the compression stroke while the fuel injection amount is feedback controlled so that the air-fuel ratio detected by the sensor 47 becomes a predetermined lean air-fuel ratio, and ignition is performed at a predetermined ignition timing to perform stratified combustion at the lean air-fuel ratio Is done.
[0050]
Further, the burned gas discharged from the preceding cylinders A and D is directly introduced into the succeeding cylinders B and C through the exhaust introduction passages 46 and 46, and only the burned gas discharged from the succeeding cylinders B and C is used. Is connected to the exhaust pipe 43 provided with the three-way catalyst 45.
[0051]
Thus, in the preceding cylinders A and D, the stratified combustion is performed at the lean air-fuel ratio, so that the thermal efficiency is increased, the pumping loss is reduced, and the fuel consumption can be improved.
[0052]
Further, since the exhaust introduction port 17 is the helical port 17, a swirl flow can be formed in the combustion chambers 12 and 12 of the succeeding cylinders C and D, and even when the linear distance cannot be secured sufficiently in the exhaust introduction passage 46. An intake air flow can be formed in the combustion chambers 12, 12 of the succeeding cylinders B, C, and the combustibility in the succeeding cylinders B, C is improved. Therefore, when the exhaust air containing a large amount of NOx introduced from the preceding cylinders A and D is subjected to theoretical air-fuel ratio combustion (λ = 1 combustion) or rich combustion in the subsequent cylinders B and C, the combustibility in the subsequent cylinders B and C is increased. By improving, it is reliably avoided that lean exhaust gas that contains a large amount of NOx and is released to the atmosphere as it is, and exhaust from the subsequent cylinders B and C can be sufficiently purified only by the three-way catalyst 45. This eliminates the need for a lean NOx catalyst, thereby reducing costs.
[0053]
On the other hand, in the intake ports 15... 15 of the succeeding cylinders B and C, a sufficient linear distance can be secured for forming the intake air flow in the combustion chambers 12 and 12, so that the combustion chambers of the succeeding cylinders B and C can be secured. 12 and 12 can form a tumble flow or a swirl flow to ensure the intake charging efficiency.
[0054]
Further, the swirl flow formed by the helical port 17 remains until the end of the compression stroke, and the temperature of the exhaust gas introduced into the succeeding cylinders B and C due to combustion in the preceding cylinders A and D is high. , C can be ignited by compression without igniting by the spark plugs 13 and 13 (see FIG. 13). At this time, combustion is performed in the combustion chambers 12 and 12 while the exhaust gas and the fuel are sufficiently agitated. For example, the fuel is injected in the intake stroke, whereby more preferable combustibility is obtained.
[0055]
Further, in order not to lower the temperature of the exhaust gas introduced into the succeeding cylinders B and C, the cross-sectional areas of the exhaust introduction passages 46 and 46 formed in the flange portion 41 of the exhaust manifold 40 are kept constant. Thus, if compression self-ignition is performed, since the whole combustion chambers 12 and 12 will burn at a stretch, combustion will contribute to work efficiently.
[0056]
On the other hand, the exhaust manifold 40 is made of steel pipe branch pipes 40a, 40b, 40c, and 40d, and the downstream side has a double pipe structure of the inner pipe 50 and the outer pipe 51, so that the exhaust temperature can be lowered without lowering the exhaust temperature. Exhaust gas can be introduced into the arranged three-way catalyst 45, and the exhaust purification performance can be improved.
[0057]
Further, by forming the openings 60... 60 on the cylinder head 4 side of the atmosphere side exhaust passages 42... 42 formed in the flange portion 41 of the exhaust manifold 40 in a flat shape, the exhaust introduction passages 46 and 46 in the flange portion 41. As shown in FIG. 6, the cross section of the atmosphere-side exhaust passages 42... 42 can be sufficiently secured, and as a result, the exhaust efficiency can be improved. Can do. Further, exhaust efficiency can be further ensured by forming the atmosphere side exhaust passages 42... 42 so that the cross-sectional area gradually increases toward the downstream side.
[0058]
In the present embodiment, switching between the normal mode and the recombustion mode is performed using a valve stop mechanism 70 provided in the tappet 11. For example, the intake / exhaust manifolds 31, 40, the exhaust introduction passage 46, the ports 15, It is also possible to provide a shutter for conducting / blocking the passage in passages such as 16, 17, 18, etc., and to switch modes by opening and closing the shutter according to the operating state.
[0059]
【The invention's effect】
As described above, according to the present invention, since the exhaust introduction port is a helical port, a swirl flow can be formed in the combustion chamber of the subsequent cylinder, and even when the linear distance cannot be sufficiently secured in the exhaust introduction passage, An intake flow can be formed in the combustion chamber of the subsequent cylinder, and the combustibility in the subsequent cylinder is improved. Therefore, when lean exhaust introduced from the preceding cylinder is subjected to, for example, stoichiometric air-fuel ratio combustion (λ = 1 combustion) or rich combustion in the subsequent cylinder, NOx is biased and increased in a large amount by improving the combustibility in the subsequent cylinder. It is reliably avoided that the lean exhaust gas contained is released into the atmosphere as it is, and the lean NOx catalyst becomes unnecessary.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of an engine according to an embodiment of the present invention.
FIG. 2 is a schematic longitudinal sectional view showing the periphery of a combustion chamber in a first cylinder.
FIG. 3 is a plan sectional view of a cylinder head showing each port provided in the second cylinder.
FIG. 4 is a front view of an exhaust manifold.
5 is a cross-sectional view taken along the line AA in FIG.
FIG. 6 is a front view of a flange portion of an exhaust manifold.
7 is a cross-sectional view taken along the line II in FIG.
FIG. 8 is a cross-sectional view of a main part of the valve stop mechanism.
FIG. 9 is a diagram showing an engine cycle and ignition timing in a reburning mode.
FIG. 10 is a block diagram showing an engine control system.
FIG. 11 is a diagram showing an operation region.
FIG. 12 is a diagram showing ignition timing in a normal mode.
FIG. 13 is a diagram showing ignition timing when performing compression self-ignition combustion.
[Explanation of symbols]
1 engine
4 Cylinder head
15 Intake port
16 Exhaust port (second exhaust port)
17 Exhaust introduction port (helical port)
18 Exhaust outlet port (first exhaust port)
40 Exhaust manifold
41 Flange
42 Atmospheric exhaust passage (preceding cylinder exhaust passage, subsequent cylinder exhaust passage)
45 Three-way catalyst
46 Exhaust introduction passage
60 Flat opening
61 Perfect circle opening
70 Valve stop mechanism (exhaust stop means for preceding cylinders, exhaust introduction stop means, fresh air introduction stop means for subsequent cylinders)
100 ECU (switching means)
123 Fuel injection control means (air-fuel ratio control means, ignition control means)
A, D 1, 4th cylinder (preceding cylinder)
B, C 2, 3rd cylinder (following cylinder)

Claims (4)

An engine that has an even number of cylinders and introduces the exhaust of the preceding cylinder, which is the cylinder on the exhaust stroke side, into the subsequent cylinder, which is the cylinder on the intake stroke side, between a pair of cylinders where the exhaust stroke and the intake stroke overlap. The exhaust introduction port is provided in the subsequent cylinder, the exhaust introduction port is a helical port, and the intake port for introducing fresh air in the subsequent cylinder is an abbreviation that can generate a tumble flow or a swirl flow. An exhaust stop means for the preceding cylinder that stops the exhaust from the preceding cylinder to the atmosphere, an exhaust introduction stop means that stops the introduction of the exhaust from the preceding cylinder to the succeeding cylinder, and the succeeding cylinder And a normal mode in which only the exhaust introduction stop means is in an operating state, and a fresh air introduction stop means for the succeeding cylinder that stops introduction of fresh air into There is provided switching means for switching between the re-combustion mode in which the exhaust stop means for the preceding cylinder and the fresh air introduction / stop means for the subsequent cylinder are operated according to the operating state. Then, at least one of the fresh air introduction amount and the fuel supply amount to the preceding cylinder is controlled so that the air-fuel ratio burns at a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, and the succeeding cylinder is combusted at the stoichiometric air-fuel ratio in the succeeding cylinder. An engine comprising air-fuel ratio control means for controlling at least one of an exhaust gas introduction amount and a fuel supply amount . Exhaust air is exhausted to the atmosphere from the exhaust introduction passage that communicates the first exhaust port of the preceding cylinder and the exhaust introduction port of the succeeding cylinder to the mounting flange to the cylinder head of the exhaust manifold, and the second exhaust port of the preceding cylinder. A preceding cylinder side exhaust passage and a subsequent cylinder side exhaust passage for exhausting the exhaust from the exhaust port of the subsequent cylinder to the atmosphere. The exhaust introduction passage has a substantially constant cross-sectional area, and The cross section of the cylinder side and subsequent cylinder side exhaust passages is characterized in that the opening on the mounting surface side to the cylinder head has a flat shape and changes into a perfect circle shape while gradually increasing the cross sectional area toward the downstream side. The engine according to claim 1 . Performs spark forced ignition in the preceding cylinder engine according to claim 1 or claim 2 in the following cylinders, characterized in that the ignition control means for controlling the ignition so as to perform compression self-ignition is provided. The engine according to any one of claims 1 to 3, wherein a three-way catalyst is disposed downstream of the exhaust manifold, and the exhaust manifold has a double pipe structure.

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