JP2010084530A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve torque in a wide rotation area of an engine by efficiently discharging exhaust gas using exhaust pulsation and appropriately setting the valve opening timing of an exhaust valve. <P>SOLUTION: This exhaust emission control device for the engine performs control so that during the valve opening overlap period of an intake valve 4 with the exhaust valve 5 in the same cylinder, a negative pressure wave of the exhaust pulsation is made to reach an exhaust port 3 opened/closed with the exhaust valve 5. The exhaust emission control device includes a valve opening timing changing means 13 changing the valve opening timing of the exhaust valve 5, and an engine speed detection means S1 detecting engine speed. A controller U controls the valve opening timing changing means 13 so that the negative pressure wave is made to reach the exhaust port 3 during the valve opening overlap period according to engine rotation, and also so controls that the valve opening timing of the exhaust valve 5 is advanced in the high-rotation area of the engine in comparison with the low-rotation area thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine exhaust control device.

In an engine, in order to improve exhaust efficiency and volume efficiency, that is, torque, it is common to set a valve opening overlap period in which both the intake valve and the exhaust valve are opened. On the other hand, exhaust pulsation acts on the exhaust port opened and closed by the exhaust valve, but exhaust efficiency is improved at the timing when the negative pressure wave of the exhaust pulsation reaches the overlap period. In Patent Document 1, this overlap period is increased at the timing when the negative pressure wave of the exhaust pulsation reaches the exhaust port during the overlap period, and conversely, the timing when the positive pressure wave reaches the exhaust port during the overlap period. Discloses that the overlap period is reduced. Patent Document 2 discloses that the phase of the overlap period can be changed, and the timing at which the negative pressure wave reaches the exhaust port during the overlap period is disclosed. Patent Document 3 discloses variable valve means for changing the lift amount and valve opening angle of an intake valve.
JP-A-11-022499 Japanese Patent No. 3678861 JP 2006-348774 A

  By the way, recent engines, particularly automobile engines, are strongly required to secure torque while improving fuel efficiency. From such a viewpoint, it is desired to increase the expansion ratio. In order to increase the expansion ratio, it is desired to delay (retard) the opening timing of the exhaust valve. On the other hand, in the high engine speed range, in order to sufficiently discharge a large amount of exhaust gas, it is desired to open the exhaust valve earlier.

  The present invention has been made in view of the above circumstances, and its purpose is to provide a wide range of engines by efficiently exhaust gas exhaust using exhaust pulsation and appropriately setting the opening timing of the exhaust valve. An object of the present invention is to provide an engine exhaust control device that can improve torque in a rotation range.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1 in the claims,
An exhaust control device for an engine for controlling a negative pressure wave due to exhaust pulsation to reach an exhaust port where the exhaust valve opens and closes during a valve opening overlap period of the intake valve and the exhaust valve in the same cylinder,
A valve opening timing changing means for changing the valve opening timing of the exhaust valve;
A rotational speed detecting means for detecting the engine rotational speed;
The valve opening timing changing means is controlled so that the negative pressure wave reaches the exhaust port during the overlap period in accordance with the engine rotation detected by the rotation speed detecting means, and is low in the high engine speed range. Control means for controlling the valve opening timing of the exhaust valve to be advanced relative to the rotation range;
It is supposed to be equipped with.

  According to the above solution, the exhaust valve pulsation phase itself is changed by changing the exhaust valve opening timing, that is, the timing (phase) at which the negative pressure wave reaches the exhaust port can be changed. Become. In the low engine speed range where it is desired to increase the expansion ratio, the opening timing of the exhaust valve is retarded relative to the engine high engine speed range, while the intake valve and exhaust valve When the negative pressure wave reaches the access point during the valve opening overlap period, torque can be improved in the low engine speed range. Further, in the high engine speed range where a large amount of exhaust gas is required to be exhausted sufficiently, the overlap period is set while the exhaust valve opening timing is relatively advanced as compared to the engine low engine speed range. When the negative pressure wave reaches the exhaust port, the torque can be improved even in the high engine speed range. In this way, an improvement in torque can be obtained over a wide rotational range of the engine.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
The control means is configured to advance the opening timing of the exhaust valve as the engine speed increases in an extremely low engine speed range (corresponding to claim 2). In this case, in the extremely low engine speed range, it is assumed that the exhaust valve opening timing is sufficiently retarded and the expansion ratio is ensured to be large, while the exhaust valve opening timing is advanced as the engine speed increases. By making the angle, the exhaust gas can be efficiently discharged using the negative pressure wave.

  In the engine speed range in which the timing for causing the negative pressure wave to reach the exhaust port during the overlap period is not obtained, the overlap period is reduced (corresponding to claim 3). In this case, it is possible to prevent or suppress a situation where exhaust gas exhaust efficiency deteriorates due to a positive pressure wave of exhaust pulsation.

The exhaust passage has a plurality of collective exhaust passages formed by temporarily gathering the exhaust passages of cylinders that are not adjacent to each other in the exhaust order, and has a collecting portion in which the downstream ends of the collective exhaust passages are gathered together. Composed of
A switching valve that communicates and blocks the plurality of collective exhaust passages on the upstream side of the collective portion is provided,
The control means controls the switching valve according to the engine speed so that the negative pressure wave reaches the exhaust port during the overlap period in the entire engine speed range.
(Corresponding to claim 4). In this case, the position where the positive pressure wave generated when the exhaust valve is opened and the negative pressure wave is generated by switching the switching valve is adjusted (the part of the plurality of collective exhaust passages or the part of the collective part). Thus, the timing (phase) at which the negative pressure wave of the exhaust pulsation reaches the exhaust port can be changed, and the overlap period can be changed over the entire engine rotation range together with the change in the opening timing of the exhaust valve. It is possible to cause a negative pressure wave to reach. Further, the negative pressure wave that reaches the overlap period is preferably as a negative pressure wave of the smallest order, that is, a negative pressure wave having a maximum amplitude reaches the overlap period, which is preferable for further improving the torque. Become.

  The valve opening timing changing means is set to change the valve opening timing of the exhaust valve while keeping the valve closing timing of the exhaust valve unchanged or substantially unchanged (corresponding to claim 5). In this case, it is preferable to secure the overlap period to a predetermined size.

  According to the present invention, torque can be improved over a wide rotation range of the engine.

  In FIG. 1, an engine E is an in-line four-cylinder spark ignition engine for automobiles in the embodiment. Each cylinder 1 </ b> A to 1 </ b> D of the engine E has two intake ports 2 and two exhaust ports 3. As shown in FIG. 2, the intake port 2 is opened and closed by an intake valve 4, and the exhaust port 3 is opened and closed by an exhaust valve 5. Each cylinder 1A to 1D is provided with a fuel injection valve 6 and a spark plug 7. The fuel injection valve 6 is a direct injection type that directly injects fuel into the combustion chamber, but may be a port injection type that injects fuel into the intake port 2.

  In FIG. 2, 8 is a cylinder block, 9 is a cylinder head, 10 is a piston, 11 is an intake valve camshaft that drives the intake valve 4 to open and close, and 12 is an exhaust valve camshaft that drives the exhaust valve 5 to open and close. The exhaust valve camshaft 12 is provided with a variable valve mechanism 13 as means for changing the opening timing of the exhaust valve 5. Of course, each of the camshafts 11 and 12 is interlocked with a crankshaft (not shown) connected to the piston 10.

  Each intake port 2 is connected to a surge tank 22 via a branch intake passage 21. A common intake passage 23 is connected to the surge tank 22, and an air cleaner 24 and a throttle valve 25 are disposed in the common intake passage 23 sequentially from the upstream side to the downstream side.

  Each exhaust port 3 is connected to a branch exhaust passage 31. The branch exhaust passages 31 for the respective cylinders are gathered at the gathering portion 32 and are finally connected to one common exhaust passage 33. The common exhaust passage 33 is provided with a three-way catalyst 34 as an exhaust gas purification catalyst.

  Here, the collecting portion 32 becomes an inverting portion where the pressure wave (positive pressure wave) of the exhaust gas discharged from each exhaust port 3 is reversed, and the exhaust passage length from the collecting portion 32 to each exhaust port 3 is Equivalent exhaust pipe length for exhaust pulsation. That is, the pressure wave (negative pressure wave, positive pressure wave) of the exhaust pulsation reciprocates between each exhaust port 3 and the collecting portion 32 at the speed of sound.

  FIG. 3 shows the valve opening timing of the intake valve 4 and the valve opening timing of the exhaust valve 5. The valve opening timing of the intake valve 4 is fixed, and is opened to the front side (advanced side) from the intake top dead center, and is closed to the rear side (retarded side) from the intake bottom dead center. On the other hand, the valve closing timing of the exhaust valve 5 is fixed by the variable valve mechanism 13 (in the embodiment, it is slightly later than the intake top dead center as in the general setting). Is variable. That is, the valve opening timing shown by the solid line in FIG. 3 is the basis, and the valve opening timing can be continuously changed from the basic valve opening timing to the advance side and the retard side. Such a change in the opening / closing timing of the exhaust valve 5 can be performed using a variable valve mechanism as described in Patent Document 3.

  As shown in FIG. 2, the variable valve mechanism 13 is controlled as described below by a controller (control unit) U configured using a microcomputer. Further, the controller U receives a signal from the rotation speed sensor S1 that detects the engine rotation speed.

  The broken line in FIG. 4 shows how the engine torque changes while the opening / closing timing of the exhaust valve 5 is set to the basic mode shown by the solid line in FIG. As shown by the broken line in FIG. 4, the engine torque drops significantly at around 2000 rpm (indicated by α6) and around 3000 rpm (indicated by α4), and slightly decreases at around 5000 rpm (indicated by α2). . On the other hand, the torque increases near 2200 rpm (indicated by α5) and near 3600 rpm (indicated by α3). The torque increases in the rotational range indicated by α3 and α5 because the negative pressure wave of the exhaust pulsation is generated in the exhaust port 3 during the overlap period (hereinafter referred to as the overlap period) in which both the intake valve 4 and the exhaust valve 5 are opened. This is due to the arrival timing of. On the other hand, the torque decreases in the rotation range indicated by α2, α4, α6 because the exhaust pressure exhaust efficiency deteriorates at the timing when the positive pressure wave of the exhaust pulsation reaches the exhaust port 3 during the overlap period. It is.

  Here, as shown in FIG. 3, the exhaust pulsation rises immediately after the exhaust valve 5 is opened, and a positive pressure wave and a negative pressure wave are repeatedly generated. A negative pressure wave (primary negative pressure wave), a second negative pressure wave (secondary negative pressure wave), and a third negative pressure wave (third negative pressure wave) are repeatedly generated. The negative pressure wave of the first time is indicated by α, the negative pressure wave of the first time, α2, the negative pressure wave of the third time of α3,... . Note that the negative pressure wave has a smaller amplitude as the order becomes larger.

  The transmission speed of the exhaust pulsation is a constant speed called sound speed, while the timing at which the overlap period occurs is changed according to the engine speed. Therefore, FIG. 3 shows the timing at which the secondary negative pressure wave α2 arrives in the overlap period. However, when the engine speed is changed, the overlap period is shifted in phase from the secondary negative pressure wave α2. .

  In the present invention, the valve opening timing of the exhaust valve 5 is changed according to the engine speed so that the negative pressure wave reaches the exhaust port 3 during the overlap period. That is, in the present invention, the timing at which exhaust pulsation occurs is changed by changing the valve opening timing of the exhaust valve so that the negative pressure wave reaches the exhaust port 3 during the overlap period, and the overlap period In addition, the order of the negative pressure wave reaching the exhaust port 3 is also changed. More specifically, in order to set the timing at which the negative pressure wave reaches the exhaust port 3 during the overlap period, the opening timing of the exhaust valve 5 is retarded from the basic opening timing in the low engine speed range. In the high engine speed range, the opening timing of the exhaust valve 5 is advanced from the basic opening timing. FIG. 5 shows a specific change mode of the valve opening timing of the exhaust valve 5. In FIG. 5, EO is the opening timing of the exhaust valve 5, EC is the closing timing (fixed timing) of the exhaust valve 5, and IO is the opening timing (fixed timing) of the intake valve 4. The orders of the negative pressure waves that reach the exhaust port 3 during the overlap period are distinguished by α2 to α6.

  As is clear from FIG. 5, in the extremely low engine speed range (around 2000 rpm in the embodiment) in the engine low engine speed range, the exhaust valve 5 so that the sixth-order negative pressure wave α6 reaches the exhaust port 3 during the overlap period. The valve opening timing of the exhaust valve 5 is gradually retarded, and thereafter, the valve opening timing of the exhaust valve 5 is gradually advanced as the engine speed increases to be the basic valve opening timing. At this basic valve opening timing, the fifth negative pressure wave α5 reaches the exhaust port 3 during the overlap period. The order of the negative pressure wave that reaches the exhaust port 3 during the overlap period is as shown in FIG. 5, but the opening timing of the exhaust valve 5 is changed according to the engine speed at which the engine torque drops as shown in FIG. The order of the negative pressure wave that reaches the exhaust port 3 during the overlap period is changed. That is, when the engine speed is such that the fifth negative pressure wave does not act on the exhaust port 3 during the overlap period (in the embodiment, around 2600 rpm), the opening timing of the exhaust valve 5 is retarded (opening around 2000 rpm). The order of the negative pressure wave is changed to the lower order so that the fourth-order negative pressure wave α4 reaches the exhaust port 3 in the overlap period. Thereafter, as the engine speed increases, the opening timing of the exhaust valve 5 is gradually advanced to the basic opening timing. At the time when this basic valve opening timing is reached (in the embodiment, around 3300 rpm), the third-order negative pressure wave α3 reaches the exhaust port 3 during the overlap period. Further, when the engine speed (the vicinity of 4000 rpm in the embodiment) is such that the tertiary negative pressure wave α3 does not act on the exhaust port 3 during the overlap period, the opening timing of the exhaust valve is retarded again (opening around 2000 rpm). The order of the negative pressure wave is changed to a lower order so that the secondary negative pressure wave α2 reaches the exhaust port 3 during the overlap period. Thereafter, as the engine speed increases, the opening timing of the exhaust valve 54 is gradually advanced, and further advanced from the basic opening timing, so that the opening timing of the exhaust valve 5 is advanced. The corners will remain unchanged. Thus, the valve opening timing of the exhaust valve 5 is further advanced in the high engine speed range than in the engine low engine speed range.

  As is clear from FIG. 5, the opening timing of the exhaust valve 5 is higher in the engine high speed range than in the engine low speed range typically represented by α6 and α4, as typically represented by α2. , Relatively advanced. That is, in the low engine speed region, the opening timing of the exhaust valve 5 is retarded, so that a large expansion ratio is ensured, and in addition, the use of the negative pressure wave greatly improves the torque. . On the other hand, in the high engine speed region, the opening timing of the exhaust valve 5 is advanced, so that a large amount of exhaust gas can be sufficiently discharged, and the torque can be improved by utilizing the negative pressure wave. become. The torque obtained by the present invention is as shown by the solid line in FIG. 4, and the torque is improved over a wide range of the engine speed, and the torque variation is small (flat torque). ), Which is extremely preferable for practical use. The opening timing of the exhaust valve 5 as shown in FIG. 5 is stored in the controller U in advance in association with the engine speed.

  FIG. 6 shows a second embodiment of the present invention. In the present embodiment, the exhaust gas discharge order (that is, the ignition order) is, for example, the first cylinder 1A, the third cylinder 1C, the fourth cylinder 1D, and the second cylinder 1B. The exhaust gas discharge order (that is, the ignition order) is configured as a collective exhaust passage 41 in which the first cylinder 1A and the fourth cylinder 1D, which are cylinders that are not adjacent to each other, are configured, and the second cylinder 1B and the third cylinder A collective exhaust passage 42 once assembled with the cylinder 3C is configured. The collective exhaust passages 41 and 42 are gathered at the gathering portion 43, and the downstream side of the gathering portion 43 is configured as one common exhaust passage 44.

  The collective exhaust passages 41 and 42 communicate with each other on the upstream side of the collective portion 43 through a communication port 45, and the communication port 45 is opened and closed by a switching valve 46. Thereby, when the switching valve 46 is closed (when the communication port 45 is shut off), the exhaust pulsation is reversed by the collecting portion 43 and returned to the exhaust port 3. On the other hand, when the switching valve 46 is opened, the communication port 45 becomes an inversion portion of the exhaust pulsation, and the equivalent exhaust pipe length in which the exhaust pulsation is reciprocated is substantially short. Thus, the equivalent exhaust pipe length is changed according to the opening and closing of the switching valve 46, and the timing at which the negative pressure wave reaches the exhaust port 3 during the overlap period can be changed. Note that the position of the communication port 4 is selected so that the timing at which the negative pressure wave of the exhaust pulsation is generated at the exhaust port 3 does not coincide between when the switching valve 46 is opened and when the switching valve 46 is closed.

  In the present embodiment, even when the opening timing of the exhaust valve 5 is changed at a specific engine speed, even when the timing for the negative pressure wave to reach the exhaust port 3 cannot be obtained during the overlap period, Using the opening and closing, it is possible to reliably reach the negative pressure wave during the overlap period. Even if the negative pressure wave can reach the exhaust port 3 during the overlap period only by changing the opening timing of the exhaust valve 5 in the entire engine speed range, the switching valve 46 can be opened and closed. It is also possible to cause a negative pressure wave having a larger amplitude (smaller order) to reach the exhaust port 3 during the overlap period. Of course, the opening / closing control of the switching valve 46 is performed by the controller U.

  FIG. 7 shows a third embodiment of the present invention, in which a variable phase mechanism is used as the variable valve mechanism 13. That is, the valve opening period of the exhaust valve 5 is entirely offset (phase change). In the present embodiment, the exhaust valve 5 can be advanced until the overlap period becomes zero. In this embodiment, if the timing at which the negative pressure wave reaches the exhaust port 3 cannot be obtained in the overlap period even if the valve opening timing of the exhaust valve 5 is changed at a specific engine speed, the overlap period is reduced. (Including 0) makes it possible to prevent or suppress a situation where exhaust gas exhaust efficiency is deteriorated by a positive pressure wave of exhaust pulsation.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The engine E may be another multi-cylinder engine such as 3 cylinders or 6 cylinders. Moreover, it is not limited to a spark ignition engine represented by a gasoline engine, but may be a compression ignition engine represented by a diesel engine. An engine having a variable valve mechanism for an intake valve that makes the valve opening timing of the intake valve 3 variable may be used. As the variable valve mechanism for the exhaust valve or the intake valve, an appropriate one can be selected. For example, the exhaust valve 5 (the same applies to the intake valve 3) is driven directly or indirectly by an actuator, This can be performed by controlling the actuator (the actuator constitutes a variable valve mechanism). Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

The simplified top view which shows one Embodiment of this invention and shows the whole system | strain of an engine. The simplified side sectional view of the engine shown in FIG. The figure which shows the example of a relationship between the valve opening overlap period of an intake valve and an exhaust valve, and exhaust pulsation. The characteristic view which shows an example which obtains torque improvement by a negative pressure wave. The characteristic view which shows the example of a change of the valve opening time of an exhaust valve. The principal part simple plane sectional view which shows the 2nd Embodiment of this invention. The figure which shows the 3rd Embodiment of this invention, and respond | corresponds to FIG.

Explanation of symbols

U: Controller S1: Speed sensor E: Engines 1A to 1D: Cylinder 2: Intake port 3: Exhaust port 4: Intake valve 5: Exhaust valve 13: Variable valve mechanism 32: Collecting portion 41, 42: Collecting exhaust passage 43: Meeting part 45: Communication port 46: Switching valve

Claims (5)

An exhaust control device for an engine for controlling a negative pressure wave due to exhaust pulsation to reach an exhaust port where the exhaust valve opens and closes during a valve opening overlap period of the intake valve and the exhaust valve in the same cylinder,
A valve opening timing changing means for changing the valve opening timing of the exhaust valve;
A rotational speed detecting means for detecting the engine rotational speed;
The valve opening timing changing means is controlled so that the negative pressure wave reaches the exhaust port during the overlap period in accordance with the engine rotation detected by the rotation speed detecting means, and is low in the high engine speed range. Control means for controlling the valve opening timing of the exhaust valve to be advanced relative to the rotation range;
An exhaust control device for an engine, comprising: In claim 1,
The engine exhaust control device characterized in that the control means advances the opening timing of the exhaust valve as the engine speed increases in an extremely low engine speed range. In claim 1 or claim 2,
An engine exhaust control apparatus according to claim 1, wherein the overlap period is reduced in an engine speed range in which the timing for causing the negative pressure wave to reach the exhaust port during the overlap period cannot be obtained. In any one of Claims 1 thru | or 3,
The exhaust passage has a plurality of collective exhaust passages formed by temporarily gathering the exhaust passages of cylinders that are not adjacent to each other in the exhaust order, and has a collecting portion in which the downstream ends of the collective exhaust passages are gathered together. Composed of
A switching valve that communicates and blocks the plurality of collective exhaust passages on the upstream side of the collective portion is provided,
The control means controls the switching valve according to the engine speed so that the negative pressure wave reaches the exhaust port during the overlap period in the entire engine speed range.
An exhaust control device for an engine. In any one of Claims 1 thru | or 4,
The engine exhaust control device according to claim 1, wherein the valve opening timing changing means is set to change the valve opening timing of the exhaust valve while keeping the valve closing timing of the exhaust valve unchanged or substantially unchanged.

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