JPH09317507A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the noise and the vibration of an engine by providing output changing means for changing the output of at least one of two cylinder groups such that the outputs of two cylinder groups are made equal in an internal combustion engine whose two cylinder groups are different in distance to the reflection position of exhaust pressure wave. SOLUTION: A V-type engine has two cylinder groups referred to as banks 1a, 1b and the exhaust pipes 2a, 2b of each cylinder group are merged at an exhaust collecting part 3 and are open to atmosphere via a catalytic converter 4. The cylinder groups are provided with variable valve timing mechanisms 5a, 5b for changing an intake valve opening timing. Since the exhaust pipes 2a, 2b are different in length because they are mounted on a vehicle, when the exhaust gas of the cylinder groups is reflected at the collecting part 3, the different pulsations of exhaust gas are generated in the exhaust pipes 2a, 2b. Therefore, in order to compensate the different pulsations of exhaust gas, the outputs of the cylinder groups are changed such that they are equal to thereby reduce the noise and the vibration of an engine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine having a plurality of cylinder groups.

[0002]

2. Description of the Related Art Like a general V-type engine, it has two cylinder groups, and the exhaust pipes of each cylinder group are collected at an exhaust collecting portion and communicated to the atmosphere through a single catalytic converter. Internal combustion engines are known. In such an internal combustion engine, the exhaust collecting portion is arranged so as to avoid interference with the transmission located at the center of the vehicle, so that the length of one exhaust pipe is considerably longer than that of the other exhaust pipe. As a result, the exhaust gas passing through the long exhaust pipe is considerably cooled by the time it reaches the catalytic converter via the exhaust collecting portion, and in particular, in the engine operating state where the exhaust gas amount is small, the temperature becomes considerably low, The exhaust emission was deteriorated because the catalytic converter could not be maintained at the activation temperature.

[0003] In order to solve this problem
Japanese Patent No. 145806 uses a variable valve timing mechanism provided for each cylinder group, and particularly in an engine operating state with a small amount of exhaust gas, an exhaust valve for a cylinder group on the exhaust pipe side having a long length. By advancing the valve opening timing of and exhausting high-temperature exhaust gas from each cylinder of this cylinder group, the exhaust gas temperature is maintained at a relatively high temperature even if it is considerably cooled by the time it reaches the catalytic converter. It has been proposed to prevent the converter from falling below the activation temperature.

[0004]

The above-mentioned prior art certainly solves the problem of the catalytic converter being below the activation temperature. However, if the length of each exhaust pipe is different for each of the plurality of cylinder groups, not only such a problem but also
In each exhaust pipe, the distance to the reflection position of the exhaust pressure wave discharged from each cylinder group is different, and different exhaust pulsation occurs in each exhaust pipe.Therefore, the output of each cylinder group may vary depending on the engine operating condition. It becomes uniform and generates large noise and vibration.

Therefore, an object of the present invention is to reduce noise and vibration in an internal combustion engine having a plurality of cylinder groups and having different distances to the reflection position of the exhaust pressure wave in at least two cylinder groups. .

[0006]

An internal combustion engine according to the present invention according to claim 1 has a plurality of cylinder groups, and the distances to the reflection position of the exhaust pressure wave in at least two of the cylinder groups are different from each other. In the engine, in consideration of the difference in the exhaust pulsation of the two cylinder groups, an output changing means for changing the output of at least one of the two cylinder groups is provided so that the outputs of the two cylinder groups become substantially equal. It is characterized by doing.

An internal combustion engine according to a second aspect of the present invention is the internal combustion engine according to the first aspect, wherein the output changing means reduces the output of one of the two cylinder groups.

According to a third aspect of the present invention, in the internal combustion engine according to the first aspect, the output changing means increases the output of one of the two cylinder groups.

An internal combustion engine according to a fourth aspect of the present invention is the internal combustion engine according to the first aspect, wherein the output changing means decreases the output of one of the two cylinder groups and increases the output of the other. It is characterized by

[0010]

1 is a schematic view showing an embodiment of an internal combustion engine according to the present invention. As shown in the figure, the internal combustion engine of the present embodiment is a general V-type engine, has two cylinder groups called a first bank 1a and a second bank 1b, and an exhaust pipe for each cylinder group. 2a and 2b are connected. The two exhaust pipes 2 a and 2 b join together at the exhaust collecting portion 3 and communicate with the atmosphere via a single catalytic converter 4. The two exhaust pipes 2a and 2a are mounted on the vehicle for reasons of mounting.
The lengths of b are different.

In the internal combustion engine of this embodiment, for each cylinder group,
Variable valve timing mechanisms 5a and 5b are provided for changing the valve overlap by changing the valve opening timing of the intake valve using a helical gear or the like. The engine intake system has surge tanks 6a and 6b for each cylinder group, and throttle valves 7a and 7b are arranged upstream of the surge tanks 6a and 6b, respectively. These throttle valves 7a and 7b are not interlocked with the accelerator pedal, and their degrees of opening are freely adjusted by a step motor or the like so that the intake amount can be controlled for each cylinder group.

Exhaust gas discharged from each cylinder group is a pressure wave, and in the exhaust system configured as described above, the exhaust merging portion 3
In order to be reflected at the distance L1 from the cylinder group in the two exhaust pipes 2a, 2b to the reflection position of the exhaust pressure wave.
L2 is different from each other, and different exhaust pulsations occur in the two exhaust pipes 2a and 2b.

Exhaust pulsation generated in the exhaust pipe changes depending on the engine speed, and a pressure different for each engine speed is provided in the vicinity of the exhaust valve immediately before the exhaust valve of the corresponding cylinder group is closed. FIG. 2 is a graph showing changes in the pressure provided to the vicinity of the exhaust valve with respect to the engine speed immediately before the exhaust valve is closed in each cylinder group due to different exhaust pulsations generated in the exhaust pipes 2a and 2b. . The upper graph shows the first bank 1a in which the length of the exhaust pipe 2a is long, that is, the distance L1 from the cylinder group to the reflection position of the exhaust pressure wave is long, and the lower graph shows the length of the exhaust pipe 2b. Is short, that is, the second bank 1b has a short distance L2 from the cylinder group to the reflection position of the exhaust pressure wave.

FIG. 3 shows the variable valve timing mechanism 5 of the first bank 1a and the second bank 1b under a specific engine load.
It is a 1st map which shows valve overlap control with respect to the engine speed using a and 5b. In this map, the dotted line shows the control of valve overlap that does not consider the exhaust pulsation.In both banks, the lower the engine speed, the earlier the intake valve opening timing, that is, the larger the valve overlap. Has been done. Although the valve overlap control maps for other engine loads are not shown, they have the same tendency. As a result, when the engine speed is low and high output is not required, a large amount of exhaust gas flows back into the intake system during the exhaust stroke and is supplied again to the cylinder during the intake stroke, that is, a large amount of exhaust gas is internally generated. Be recycled. Therefore, the combustion temperature is lowered by the inert gas which is the main component of the exhaust gas, the amount of NOx generated can be considerably reduced, and the fuel supplied to the engine intake system is sufficiently vaporized. , The combustion can be improved. As described above, it is preferable to increase the valve overlap, but since exhaust gas recirculation involves a slight decrease in engine output, the valve overlap is reduced as the engine speed increases and the engine output is required. It has become.

However, even if the valve overlap is simply changed as shown by the dotted line for the purpose of controlling the amount of recirculated exhaust gas, as described above, the exhaust pulsation in each exhaust pipe causes each cylinder to change. Since positive pressure or negative pressure acts near the exhaust valves of the group, the amount of recirculated exhaust gas cannot be controlled as intended. When a positive pressure acts, the exhaust gas in the cylinder becomes difficult to flow out to the exhaust pipe side, and the reverse flow rate to the intake system increases correspondingly, and the recirculated exhaust gas amount increases as compared with the normal time, and The fresh air quantity tends to decrease. On the contrary, when negative pressure acts, the exhaust gas in the cylinder easily flows out to the exhaust pipe, and the amount of recirculated exhaust gas tends to decrease considerably and the charging efficiency of fresh air tends to increase as compared with the normal time. . Therefore, in the two cylinder groups, since the engine speed at which the positive pressure or the negative pressure acts is different, a large difference occurs not only in the recirculated exhaust gas amount but also in the fresh air amount depending on the engine speed. The engine output in one cylinder group becomes non-uniform, and large engine vibration and noise occur.

In the internal combustion engine of the present embodiment, as shown by the solid line in FIG. 3, with respect to the first bank 1a, a relatively large positive coefficient is taken into consideration in consideration of the pressure change in the vicinity of the exhaust valve in the first bank 1a of FIG. In the engine rotation region where pressure changes occur, the valve overlap is controlled to decrease according to the magnitude of positive pressure, and in the engine rotation region where relatively large negative pressure changes occur The valve overlap is controlled to be reduced according to the magnitude of pressure.

Also, as shown by the solid line in FIG. 3, with respect to the second bank 1b as well, in consideration of the pressure change in the vicinity of the exhaust valve in the second bank 1b shown in FIG. In the engine rotation area where the pressure is generated, the valve overlap is controlled so as to be reduced according to the magnitude of the positive pressure. Accordingly, the valve overlap is controlled so as to be reduced.

By controlling such valve overlap in each cylinder group, even if different exhaust pulsations occur in the two cylinder groups, the fresh air amounts for each engine speed in the two cylinder groups are made equal to each other. The output can be made uniform, and large vibration and noise are prevented. Further, in particular, when a positive pressure acts, the amount of recirculated exhaust gas can be reduced to an appropriate value, so that deterioration of exhaust emission at this time can be prevented.

Further, for example, when a positive pressure acts on one cylinder group and neither a positive pressure nor a negative pressure acts on the other cylinder group, a positive pressure that causes valve overlap in one cylinder group. The engine output is increased to some extent by reducing the engine output to some extent, and the valve overlap in the other cylinder group is increased to some extent to increase the recirculated exhaust gas amount to reduce the engine output to some extent. It is also possible to equalize the engine output in both cylinder groups. On the contrary, when the negative pressure acts on one cylinder group and neither the positive pressure nor the negative pressure acts on the other cylinder group, the valve overlap in the one cylinder group is reduced to some extent. It is also possible to reduce the output to some extent, reduce the valve overlap in the other cylinder group to some extent, reduce the amount of recirculated exhaust gas, increase the engine output to some extent, and even out the engine output in both cylinder groups. Is.

Further, when a positive pressure acts on both cylinder groups, the valve overlap in the cylinder group where a large positive pressure acts is reduced to some extent to increase the engine output to some extent, and the reduced engine output in the other cylinder group. It is also possible to make it uniform. Conversely, when negative pressure acts on both cylinder groups, the valve output in the cylinder groups where a large negative pressure acts is reduced to some extent to reduce the engine output to some extent, and the engine output in both cylinder groups is made uniform. It is also possible to convert.

FIG. 4 shows the change in the output difference between the first bank 1a and the second bank 1b with respect to the engine speed due to the difference in exhaust pulsation when the linear valve overlap control is performed for both cylinder groups. It is a graph shown. It is also possible to control the throttle valves 7a and 7b provided for each cylinder group so as to eliminate such an engine output difference.
That is, the intake air amount in the cylinder group with a large engine output is
If the corresponding throttle valves are used to reduce the difference according to the engine output, the engine output can be made uniform in both cylinder groups, and large vibration and noise can be prevented.

Further, the engine output can be reduced by retarding the ignition timing. If the ignition timing in the cylinder group having a large engine output is retarded according to the difference in the engine output, both cylinders can be retarded. The engine output in the group is made uniform, and large vibration and noise can be prevented. Of course, such intake amount and ignition timing control can be applied to an internal combustion engine that does not have a variable valve timing mechanism and has a fixed valve overlap.

Of course, even in an internal combustion engine that does not have a variable valve timing mechanism and has a fixed valve overlap, an engine output difference occurs between the two cylinder groups due to the difference in exhaust pulsation. The output can be made uniform by controlling the intake air amount or the ignition timing.

The control of the valve overlap described above is
The purpose is to equalize the engine output of the two cylinder groups, but for example, at the time of high engine load, high output may be required even at the expense of vibration and noise. As shown in FIG. 5, in the rotation region where negative pressure acts on each cylinder group due to exhaust pulsation, the valve overlap of each cylinder group is increased to further improve the fresh air charging efficiency and It is also possible to increase the engine output.

The above-mentioned control of the valve overlap is
Although it was explained that the opening timing of the intake valve is changed,
Of course, the opening timing of the exhaust valve may be changed, or the opening timing of the intake valve and the exhaust valve may be changed.

In the internal combustion engine shown in FIG. 6, sub-catalyst converters 8a and 8b for warming up early and purifying exhaust gas when the engine is started are arranged near the engine body of the exhaust pipes 2a and 2b. is there. Each sub catalytic converter 8a,
Although an energization heat generation type catalytic converter or the like can be used as 8b, in any case, in order to avoid various parts protruding from the engine body, the exhaust pipe length from each cylinder group to each sub catalytic converter 8a, 8b L1 'and L2' are different. In such a configuration, the exhaust pressure wave is generated by the sub-catalyst converters 8a,
It reflects at 8b and causes different exhaust pulsations in each exhaust pipe 2a, 2b.

As described above, the valve overlap control, the intake air amount control, and the ignition timing control described above effectively function in the internal combustion engine in which the distances to the reflection position of the exhaust pressure wave in the two cylinder groups are different from each other. Further, when the number of cylinder groups is two or more, by performing the above-mentioned control for at least two cylinder groups having different distances to the reflection position of the exhaust pressure wave in the cylinder groups, these two The engine output in the cylinder group can be made uniform, and vibration and noise can be reduced accordingly.

[0028]

As described above, according to the internal combustion engine of the present invention, in an internal combustion engine having a plurality of cylinder groups and different distances to the reflection position of the exhaust pressure wave in at least two of the cylinder groups, The changing means changes the output of at least one of the two cylinder groups so as to make the outputs of the two cylinder groups substantially equal in consideration of the difference in the exhaust pulsation of the two cylinder groups. It is possible to realize uniform output and to prevent the accompanying large noise and vibration.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an internal combustion engine according to the present invention.

FIG. 2 is a graph showing changes in pressure acting on the vicinity of an exhaust valve of two cylinder groups with respect to engine speed.

FIG. 3 is a map showing valve overlap control of two cylinder groups.

FIG. 4 is a graph showing changes in engine output difference between two cylinder groups with respect to engine speed.

FIG. 5 is a map showing valve overlap control of two cylinder groups.

FIG. 6 is a schematic view showing another embodiment of the internal combustion engine according to the present invention.

[Explanation of symbols]

 1a ... 1st bank 1b ... 2nd bank 2a, 2b ... Exhaust pipe 3 ... Exhaust merging part 4 ... Catalytic converter 5a, 5b ... Variable valve timing mechanism 6a, 6b ... Surge tank 7a, 7b ... Throttle valve 8a, 8b ... Sub Catalytic converter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 45/00 364 F02D 45/00 364D

Claims (4)

[Claims] 1. In an internal combustion engine having a plurality of cylinder groups and having different distances to reflection positions of exhaust pressure waves in at least two of the cylinder groups, the difference in exhaust pulsation between the two cylinder groups is taken into consideration. An internal combustion engine comprising output changing means for changing the output of at least one of the two cylinder groups so that the outputs of the two cylinder groups become substantially equal to each other. 2. The internal combustion engine according to claim 1, wherein the output changing means reduces the output of one of the two cylinder groups. 3. The internal combustion engine according to claim 1, wherein the output changing means increases the output of one of the two cylinder groups. 4. The internal combustion engine according to claim 1, wherein the output changing means decreases the output of one of the two cylinder groups and increases the output of the other of the two cylinder groups.