JPS6355326A - Exhauster for engine - Google Patents

Abstract

PURPOSE:To improve the durability and efficiency of an engine, by advancing the open time of a second exhaust port with respect to the open time of a first exhaust port and disabling a stop means under high rotation and heavy load. CONSTITUTION:Under high rotation and heavy load operation of an engine E, the pulsating high pressure exhaust gas being produced during blowdown bypasses a turbine 12c and then discharged through a second exhaust port 4, second branch exhaust path 15 and second exhaust path 17. In order to prevent increase of the exhaust pressure and to smooth the fluctuation of exhaust pressure caused by blowdown gas, a second exhaust valve 3 is arranged to function. The open-valve timing of the second exhaust valve 3 is set to the quicker than that of a first exhaust valve 1.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an engine exhaust system.

[Prior art] In order to improve the output of the ennon by utilizing the energy contained in the exhaust gas of the engine, a turbine is inserted in the exhaust passage of the ennon, and this turbine is driven by the exhaust gas. 2. Description of the Related Art Exhaust turbo superchargers are well known in which a blower driven by a turbine is disposed in an intake passage, and each cylinder is filled with intake air pressurized by the blower.

Incidentally, in an engine that has a wide operating range from low speed to high speed, such as an automobile engine, the amount of exhaust gas also fluctuates over a wide range. First, in an engine equipped with an exhaust turbo supercharger as described above, when the amount of exhaust gas increases as the rotation speed increases and the load increases, the turbine acts as an exhaust resistance, causing the exhaust pressure to rise excessively. As the exhaust pressure increases, there are problems such as an increase in residual gas in the combustion chamber and a decrease in the charging amount, so generally a wastegate passage is provided in the exhaust passage to bypass the turbine.
A method is adopted in which when the exhaust pressure rises to a set value, the wastegate passage is opened and the turbine is bypassed.

However, even in this wastegate method, in order to increase turbine efficiency, it is necessary to narrow down the area of the exhaust passage leading to the turbine to some extent, so there is a problem that the exhaust resistance cannot be made as low as necessary.

For this reason, the first. A first exhaust port and a second exhaust port are provided which are opened and closed by a second exhaust valve, and the exhaust gas discharged from the first exhaust port is connected to a turbine interposed in a first exhaust passage communicating with the first exhaust port. The turbine drives a blower installed in the intake passage to perform supercharging, while a second exhaust passage is provided that communicates with the second exhaust port and bypasses the turbine. An engine exhaust system has been proposed in which an increase in exhaust pressure is suppressed by discharging the exhaust gas directly from the second exhaust port to the second exhaust passage (for example, Japanese Patent Application Laid-Open No. 1983-1999)
(See Publication No. 146021).

By the way, during the engine's exhaust stroke, especially during high-speed, high-speed operation, when the exhaust valve is opened, the high-pressure combustion gas trapped in the combustion chamber is released as high-temperature, high-pressure exhaust gas called blowdown gas. It is discharged all at once into the exhaust passage in a pulsed manner.

In conventional exhaust systems that are provided with a second exhaust passage that bypasses the turbocharger turbine, as described above, the increase in exhaust pressure at high speeds and high loads is suppressed overall, but the exhaust valve is not opened. When this occurs, the above-mentioned blowdown gas acts directly on the turbine, which causes the turbine to undergo rapid pressure fluctuations and excessively rise in temperature, resulting in a reduction in the durability and efficiency of the turbine.

[Object of the Invention] The present invention effectively suppresses the increase in exhaust pressure when the engine rotates at high speeds and under high load, smoothes pressure fluctuations in the exhaust gas due to blowdown gas flowing into the turbine, and lowers the turbine temperature. An object of the present invention is to provide an exhaust system for an engine equipped with an exhaust turbo supercharger, which prevents excessive rise and improves the durability and efficiency of a turbine.

[Structure of the Invention] In order to achieve the above object, the present invention includes a first exhaust port and a second exhaust port, and exhaust gas discharged through the first exhaust port is interposed in a first exhaust passage. The turbine drives a blower installed in the intake passage to perform supercharging, while the exhaust gas discharged through the second exhaust port is guided to a second turbine installed bypassing the turbine. In an engine exhaust system configured to exhaust gas through two exhaust passages, means for opening the second exhaust port earlier than the opening time of the first exhaust port and stopping the flow of exhaust gas from the second exhaust port during operation. An exhaust system for an engine is provided, characterized in that the stopping means is inoperative at least at high rotation and high load.

[Effects of the Invention] According to the present invention, when the engine is running at high speed and under high load, the stopping means is deactivated so that high-temperature, high-pressure pulsed blowdown gas is released from the second exhaust port whose opening timing is set early. The second bypassing the exhaust turbocharger turbine
Since the exhaust gas is discharged into the exhaust passage, pulse-like high-pressure waves do not directly act on the turbine, preventing an excessive temperature rise in the turbine, and smoothing the pressure of the exhaust gas flowing into the turbine. This increases the durability and efficiency of the turbine. Furthermore, the increase in exhaust pressure is suppressed and fuel efficiency is improved.

Furthermore, at low engine speeds, the stop means is activated to shut off the second exhaust passage, allowing all exhaust gas to be introduced into the turbine, allowing effective dynamic pressure supercharging to increase engine output.

[Example] " Embodiments of the present invention will be described in detail below.

As shown in FIG. 1, each cylinder #1 to #4 constituting a four-cylinder reciprocating engine E has a first exhaust port 2 that is opened and closed by a first exhaust valve 1, and a second exhaust port 2 that is opened and closed by a second exhaust valve 3. A second exhaust port 4 is provided which opens and closes slightly earlier than the first exhaust port 2 (see FIG. 4). Although not specifically shown, the first and second exhaust valves are driven to open and close at predetermined timings synchronized with the rotation of the engine by a well-known valve mechanism. is disconnected from the valve operating mechanism in a predetermined operating state in response to a stop signal from a control circuit 5 composed of a microcomputer, and the valve opening operation is stopped.

The control circuit 5 receives input information such as engine rotation speed detected by a rotation speed sensor (not shown), boost pressure detected by a pressure sensor (not shown), etc.
The exhaust valve 3 is controlled to operate and stop.

Each of the first exhaust ports 2 is connected to a first branch exhaust passage 6 formed to have a relatively small diameter in order to ensure the dynamic pressure of the exhaust. These first branch exhaust passages 6 are gathered into a single first exhaust passage 8 at a first gathering portion 7 . The first exhaust passage 8 includes a blower 12 of an exhaust turbo supercharger 12, which is interposed in the intake passage 11 downstream of the air flow meter 9.
Turbine 1 for driving a via shaft +2b
2c is interposed. Note that the first exhaust passage 8 is narrowed just before the turbine 12c in order to increase the flow velocity of exhaust gas and ensure dynamic pressure. And the first exhaust passage 8
A bypass passage 13 that bypasses the turbine 12c is provided between a position downstream of the first collecting portion 7 and upstream of the turbine +2c and a position slightly downstream of the turbine 12C. A waste gate valve 1 is installed to open and close the bypass passage 13 in order to adjust the amount of exhaust gas flowing into the turbine 12c and to control the boost pressure in the intake passage li to below the maximum boost pressure. There is.

On the other hand, each of the second exhaust ports 4 has a second exhaust port formed with a relatively large diameter in order to suppress an increase in exhaust pressure of the engine E.
It is connected to the branch exhaust passage 15. These second branch exhaust passages 15 are combined into a single second exhaust passage 17 at a second gathering part 16, and this second exhaust passage 17 is further connected to the first exhaust passage 8 at a merging part 18. and are connected to a common exhaust passage 19.

Next, a method for controlling the second exhaust valve 3 by the control circuit 5 will be described in detail with reference to the control flowchart shown in FIG.

When the control is started, first in step S1, the microcomputer checks the engine rotation ff1N detected by a rotation speed sensor (not shown) and the supercharging pressure P in the intake passage ll detected by a pressure sensor (not shown). The data is read into the configured control circuit 5 (see FIG. 1).

Subsequently, the control proceeds to step S2, in which it is determined whether the engine speed N is in a low speed range where the operation of the second exhaust valve 3 should be stopped (kept closed). Next, the engine speed N is compared with a predetermined set speed Nm1n. The set rotational speed Nm1n is a constant indicating a limit at which the operation of the second exhaust valve 3 is stopped when the engine rotational speed is lower than this, regardless of the magnitude of the engine load, and is stored in the control circuit 5 in advance.

As a result of the above comparison, when the operating state of engine E is in the low rotation range, that is, when N<Nm1n, the increase in exhaust pressure is small, so the entire exhaust gas is introduced into the turbine +2c, and the flow velocity of the exhaust gas is reduced. In order to effectively perform high dynamic pressure supercharging and thereby improve the engine output, the control is branched to step S6, and the operation of the second exhaust valve 3 is stopped in step S6.

However, if the operation of the second exhaust valve 3 has been stopped in the previous control scan, the stopped state continues.

When the operation of the second exhaust valve 3 is stopped (remains closed), the exhaust system of this embodiment is different from the conventional exhaust system in which a turbine of an exhaust turbo supercharger is interposed in a single exhaust passage. produces exactly the same effect. Next, step S7
It is determined whether the ignition switch is on or not, and if it is on, the engine E continues to operate, so the control returns to step St and continues. On the other hand, if the ignition switch is off, the engine operation is stopped and the control ends.

On the other hand, in step S2, if the operating state of the engine E is in a high rotation range, that is, N≧Nm1n, the second exhaust valve 3
The control proceeds to step S3 to determine whether or not the operation is necessary.

In step S3, in order to operate or stop the second exhaust valve 3 depending on the magnitude of the load on the engine E, a set pressure Ps of the supercharging pressure in the intake passage 11 at which the second exhaust valve 3 should be operated is calculated. do. The set pressure Ps is expressed, for example, as a linear function Ps(N) of the engine speed N, and this function Ps(N) is stored in the control circuit 5 in advance. Therefore, in step S3, the set pressure Ps(N) corresponding to the engine speed N at every moment is calculated.

Next, control proceeds to step S4, where the state of the engine load is determined. In step S4, the intake passage read in step Sl! ! boost pressure P in step S3
The set pressure P s (N) calculated in is compared.

As a result of the above comparison, when the operating condition of engine E is in the low load range, that is, when P≦Ps(N), the increase in exhaust pressure is small, as in the case of low rotation speed, so the entire amount of exhaust gas is In order to increase the flow velocity of exhaust gas by introducing it into the turbine +2c and effectively perform dynamic pressure supercharging, thereby improving the output of the engine, control is branched to step S6, and branched to the YES side in step S2. In exactly the same way as before, the operation of the second exhaust valve 3 is stopped in step S6, and then in step S7, depending on whether the ignition switch is turned on or off,
Control is continued or stopped, respectively.

On the other hand, in step S4, if the operating state of the engine E is in the high load range, that is, P>P9(N), the control proceeds to step S5. In step S5, the exhaust gas that becomes high-pressure in a pulsed manner during blowdown is made to bypass the turbine 12c, and is passed from the second exhaust port 4 to the second branch exhaust passage 15 and the second exhaust passage! The second exhaust valve 3 is operated to prevent exhaust pressure from increasing and to smooth exhaust pressure fluctuations due to blowdown gas. This will be explained below.

As shown in FIG. 4, the opening/closing timing of the first exhaust valve 1 is similar to the opening/closing timing of the exhaust valve of a conventional engine; It is set to close immediately after dead center TDC. On the other hand, the opening timing of the second exhaust valve 3 is set earlier than the opening timing of the first exhaust valve l (for example, the opening timing of the second exhaust valve 3 is set earlier than the opening timing of the second exhaust valve 3 in terms of crank angle). °, the opening timing of the first exhaust valve 1 is 3406), while the closing timing of the second exhaust valve 3 is a timing slightly later than the bottom dead center BDC of the exhaust stroke (for example, at a crank angle from the bottom dead center BDC). 400). The opening/closing timing of the second exhaust valve 3 is as follows:
Substantially, high-temperature, high-pressure exhaust gas during blowdown bypasses the turbine 12c and flows into the second branch exhaust passage 15 and the second
is discharged through the exhaust passage 17, and then the first exhaust valve 1
When the combustion chamber is opened, other exhaust gases in the combustion chamber pass through the first branch exhaust passage 6 and the first exhaust passage 8 to the turbine 12c.
It is set up to be guided by.

Therefore, as shown in Fig. 5, in the conventional system, the exhaust pressure characteristic has a shape as shown by the curve C1 with respect to the crank angle, and during blowdown, the pressure increases in a pulse-like manner, resulting in a highly fluctuating characteristic. In the system according to this embodiment, the second exhaust valve 3 is opened before the first exhaust valve 1, and the high pressure in the combustion chamber is initially released from the second exhaust port 4. The upstream exhaust pressure characteristic is curve C with respect to crank angle! The exhaust pressure acting on the turbine 12c is substantially smoothed. In addition, as the ignition timing is changed according to the operating state, the opening/closing timing of the second exhaust valve 3 set by the control circuit 5 can be shifted forward or backward in time according to the operating state of the engine E. hand,
By ensuring that the pulsed blowdown gas bypasses the turbine 12c, more appropriate exhaust pressure control can be achieved.

As mentioned above, the second! By operating the air valve 3, the turbine 12c is protected from overheating and pressure fluctuations, improving the durability of the turbine and improving the turbine efficiency. In addition, since the increase in exhaust pressure is suppressed,
Fuel efficiency will improve.

Subsequently, in step S7, it is determined whether or not the ignition switch is on. If it is on, the control returns to step Sl and continues, and if it is off, the control ends.

As a result of controlling the second exhaust valve 3 as described above,
An example of how the opening degree of the second exhaust valve 3, the opening degree of the waste gate valve 14, the supercharging pressure in the intake passage ll, and the average effective pressure Pe of the engine E change with respect to the engine speed will be described below. It is shown in Figure 6.

As shown in Fig. 6, as the engine speed N gradually increases, the boost pressure P increases linearly at first, but when the boost pressure reaches the maximum boost pressure PA, the engine speed N =N,
From the point in time, the waste gate valve 14 starts to open, and the waste gate valve 14 controls the boost pressure to be constant at the maximum boost pressure PA. When the engine speed N further increases, the wastegate valve 14 gradually increases its opening and maintains the boost pressure at the maximum boost pressure PA, but the engine speed N reaches the minimum speed Nm1n. At that point, the second exhaust valve 3 starts operating. In this example, the supercharging pressure P=PA at the time N=Nmin is greater than the set pressure Ps(N), so PA>PS(N), and the control flowchart (step According to S4), the second exhaust valve 3 starts operating.

For this reason, the exhaust pressure decreases, so the boost pressure is reduced to the maximum boost pressure PA.
The waste gate valve is controlled to be constant. The opening degree of 4 decreases in a stepwise manner. When the engine speed N increases further, the wastegate valve 1
4 controls the boost pressure to be constant at the maximum boost pressure PA while increasing the opening degree.

At this time, when the second exhaust valve 3 is kept fully closed, the average effective pressure Pe of the engine E initially increases as the engine speed N increases, as shown by the curve G1, but reaches a maximum point. After reaching M, it gradually decreases. On the other hand, when the second exhaust valve 3 is driven to open and close at the engine speed Nm1n or more, the average effective pressure Pe is
As shown in , the time point N= when the second exhaust valve 3 operates
In a region where the engine speed N is higher than Nmin, the blowdown gas is passed through bypassing the turbine 12c, so Pe rapidly decreases. Therefore, when the second exhaust valve 3 is operated, the average effective pressure Pe of the engine E decreases by the difference between the curve GI and the curve G (as shown in region (B)),
The corresponding wasteful piston work is reduced, improving fuel efficiency.

Moreover, FIG. 7 shows the opening degree of the second exhaust valve 3 and the opening degree of the wastegate valve 14 as a function of the average effective pressure Pe when the engine speed N is kept constant at Nmln or higher and the engine load is increased. Indicates a state of change.

As shown in FIG. 7, when the engine speed N is constant at Nmln or more, the supercharging pressure P in the intake passage II also increases linearly as the average effective pressure Pe increases, and the supercharging pressure P but,
The second exhaust valve 3 is activated when the average effective pressure Pe=Pe1 reaches the set pressure Pg (N) corresponding to the engine speed N.

Next, another preferred embodiment of the present invention is shown in FIG. However, members having the same configuration and function as those of the embodiment shown in FIG. 1 are given the same numbers, and their explanations will be omitted to avoid duplication.

In the embodiment shown in FIG. 2, a positive pressure wave generated by exhaust gas blowing out at the beginning of the exhaust stroke of a certain cylinder propagates to the exhaust port of another cylinder at the end of the exhaust stroke, increasing the residual gas pressure. In order to prevent so-called exhaust interference, which reduces the volumetric efficiency, the second exhaust passage is separated into two systems. That is, the firing order is not consecutive.
The second branch exhaust passages 15a115d of each of the four cylinders (hereinafter referred to as the first cylinder nP) are the second P exhaust passages 2! The second P exhaust passage 2I is connected to the second P exhaust passage 2I, and a first waste gate valve 22 for controlling the supercharging pressure in the intake passage 11 is interposed.

On the other hand, the second branch intake passages 15 of the #2 and #3 cylinders (hereinafter referred to as second cylinder group S) whose ignition order is not consecutive
b115c is connected to the 28th exhaust passage 23, and this second
A second waste gate valve 24 for controlling the supercharging pressure in the intake passage It is provided in the 8 exhaust passage 23.

In this embodiment, supercharging pressure control is performed only by the first waste gate valve 22 and the second waste gate valve 24, so there is no need to provide a bypass passage and a waste gate valve in the first exhaust passage 8. . Further, the flow of exhaust gas from the second exhaust port 4 is carried out between the first waste gate valve 22 and the second waste gate valve 24.
Since the second exhaust valve 3 can be stopped at , there is no need to provide a stopping means for the second exhaust valve 3. Therefore, the number of parts can be reduced, the system can be simplified, and costs can be reduced.

The second P exhaust passage 21 through which the exhaust gas from the first cylinder group P passes and the second S exhaust passage 23 through which the exhaust gas from the second cylinder nS passes are each assembled downstream of the first exhaust passage 8 and the turbine 12c to form one common exhaust passage. It is connected to 19.

By the way, the common exhaust passage 19 downstream of the confluence of the first exhaust passage 8 and the second P exhaust passage 21 has a sufficient volume in order to enhance the effect of blowing out the residual gas in the cylinder using pressure waves. A volume portion 25 is provided.

Hereinafter, the action of the volume portion 25 will be described as a representative example for the #l cylinder, but the same applies to the #2 to #4 cylinders.

A positive pressure wave generated in the vicinity of the second exhaust port 4 by the blowdown gas at the beginning of the exhaust stroke of the #1 cylinder gradually moves downstream at approximately sonic speed to the two-branch exhaust passage +5a, the second
P exhaust passage 21. It propagates through the common exhaust passage 19 and is reflected as a negative pressure wave at the open end volume 25, and again,
The gas propagates upstream at approximately the speed of sound through the common exhaust passage 19, the second P exhaust passage 21, and the second branch exhaust passage +5a, reaches the second exhaust port 4 at the latter stage of the exhaust stroke, and removes the residual gas in the #1 cylinder. It is supposed to be sucked out. Needless to say, the position of the volume portion 25 is set so that the time required for the pressure wave to propagate back and forth within the series of exhaust passages matches the opening/closing timing of the second exhaust valve 3. . As a result, the effect of blowing out residual gas can be improved, and fuel efficiency can be improved.

As described above, according to the embodiment shown in FIG. 2, the fuel efficiency is improved by suppressing the increase in exhaust pressure, and the efficiency of the turbine +2c is increased by smoothing the exhaust pressure. Furthermore, the exhaust system can be simplified and cost reduced, and the exhaust efficiency can be improved by utilizing pressure waves.

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram of a four-cylinder reciprocating engine equipped with an exhaust turbo supercharger showing an embodiment of the present invention. FIG. 2 is a system configuration diagram of a four-cylinder reciprocating engine equipped with an exhaust turbo supercharger showing another preferred embodiment of the present invention. FIG. 3 is a flowchart showing a method of controlling the operation and stop of the second exhaust valve. Figure 4 is ! It is a figure which shows the opening and closing timing of an exhaust valve and a 2nd exhaust valve. FIG. 5 is a diagram showing the exhaust pressure characteristics of the conventional system and this embodiment. FIG. 6 is a diagram showing the operating state of the exhaust system in this embodiment with respect to the engine rotation speed. FIG. 7 is a diagram showing the operating state of the exhaust system in this embodiment with respect to the average a-dynamic pressure. l...first exhaust valve, 2...first exhaust port, 3...
...Second exhaust valve, 4...Second exhaust port, 8...
First exhaust passage, 12... Exhaust turbo supercharger, 12a.
...Blower, 12C...Turbine, 17...Second exhaust passage.

Claims (1)

[Claims] (1) A first exhaust port and a second exhaust port are provided.
Exhaust gas discharged through the exhaust port is guided to a turbine disposed in the first exhaust passage, and the turbine drives a blower disposed in the intake passage to perform supercharging, while the second exhaust port In an engine exhaust system, the exhaust gas discharged through the turbine is discharged through a second exhaust passage provided to bypass the turbine, and the opening timing of the second exhaust port is set to the opening timing of the first exhaust port. An exhaust system for an engine, characterized in that a means is provided to stop the flow of exhaust gas from the second exhaust port when activated, and the stopping means is inactivated at least at high speeds and high loads. .