JPH07293262A - Sequential supercharger for diesel engine - Google Patents

Abstract

PURPOSE:To obtain a sequential supercharger of a diesel engine which carries out the smooth selection from a small turbo to a large turbo and prevents the generation of smoke in the selection. CONSTITUTION:A sequential supercharger is constituted so that a small turbo 2 and a large turbo 3 are arranged in parallel in the exhaust pipe 4 of a diesel engine 1, and the small turbo 2 is used when the exhaust gas quantity is small, and the switching to the large turbo 3 is performed as the exhaust gas quantity increases, anf an auxiliary turning pipe 28 for introducing a portion of exhaust to the turbine 3t of the large turbo 3 is installed in the turbine inflow pipe 5 of the small turbo 2, and an auxiliary turning valve 29 which is opened in precedence to the switching from the small turbo 2 to the large turbo 3 is installed in the auxiliary turning pipe 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sequential supercharging device for a diesel engine which can smoothly switch from a small turbo to a large turbo.

[0002]

2. Description of the Related Art A small turbo and a large turbo are installed side by side in an exhaust pipe of a diesel engine, the small turbo is used when the exhaust gas amount is small, and the large turbo is switched to the large turbo as the exhaust gas amount increases. Feeders are known. The outline is shown in FIG. As shown,
The exhaust manifold b of the diesel engine a is provided with an exhaust pipe d for the small turbo c and an exhaust pipe f for the large turbo e in parallel, and these exhaust pipes d, f each have a turbine of the small turbo c. g and the turbine h of the large turbo e are connected. The compressors i and j of the turbos c and e are connected to the intake chamber m of the engine a via intercoolers k and l, respectively.

When the rotational speed of the engine a is low and the amount of exhaust gas is small, the valve o provided in the small turbo exhaust pipe d is opened and the valve p provided in the large turbo exhaust pipe f is closed to reduce the exhaust gas. Only the turbo c is driven. At this time, the valve R is closed and the valve Q is open. After that, when the engine speed increases and the exhaust gas amount increases, the valve o provided in the small turbo exhaust pipe d is closed and the valve p provided in the large turbo exhaust pipe f is opened, and only the large turbo e is opened. Drive it. At this time, the valve Q is closed and the valve R is open.

By such sequential control, it is possible to match the amount of exhaust gas that changes according to the rotation speed of the engine a with the capacities of the turbines g and h of the turbos c and e, so that the engine exhaust gas amount is low and the engine speed is low. Therefore, turbocharging can be efficiently performed over a high engine speed region where the amount of exhaust gas is large.

[0005]

However, in the above-mentioned device, when the supercharger is switched from the small turbo c to the large turbo e, the valve p provided in the exhaust pipe f for the large turbo until just before switching. Is closed, the large turbo e is stopped. Therefore, the turbine h of the large turbo e is started up from zero rotation, and it takes a certain time until the boost pressure (boost pressure) is started up. Especially, since the large turbo e has a large moment of inertia,
There is a large delay in the rise of rotation.

That is, as shown in FIG. 5, a small turbo c
From the big turbo e which was stopped
Immediately after that, since the boost pressure is not supercharged at all, the boost pressure drops once, and thereafter, the boost pressure gradually rises as the large turbo e accelerates. Therefore, turbo c,
After switching e, the engine output decreases until the boost pressure of the switched large turbo e matches the boost pressure of the small turbo c before switching, and the driver viability deteriorates. Further, since the intake air amount is drastically reduced at the time of switching, the injected fuel becomes relatively rich and smoke is generated.

As shown in FIG. 6, the large turbo e
It is also known that a medium turbo is used instead of, and it switches from (small turbo) → (medium turbo) → (small turbo + medium turbo) as the engine speed increases, but this is not an essential solution. .

The object of the present invention, which was devised in view of the above circumstances, is to enable a smooth switching from a small turbo to a large turbo, and to prevent smoke from being generated during the switching. To provide a supercharger.

[0009]

In order to achieve the above object, the present invention provides a diesel engine in which an exhaust pipe is provided with a small turbo and a large turbo in parallel, and when the exhaust gas amount is small, the small turbo is used. In a sequential supercharging device that switches to a large turbo as the amount increases, a pre-rotation pipe that guides a part of exhaust gas to the large turbo turbine is provided in the turbine inflow pipe of the small turbo, and the pre-rotation pipe is , A pre-rotation valve that is opened prior to switching from the small turbo to the large turbo. Further, an exhaust pressure release pipe that reduces a boost pressure by opening a part of exhaust pressure to the turbine downstream pipe side of the small turbo is provided in the small turbo turbine inflow pipe, and the small exhaust pressure release pipe is provided with a small exhaust pressure release pipe. An exhaust pressure release valve may be provided that is opened and closed to match the boost pressure of the small turbo with the pre-rotated big turbo boost pressure when switching from the turbo to the large turbo. Further, EGR for returning EGR by returning a part of exhaust gas to the intake pipe side of the engine to the exhaust pipe on the upstream side of each turbo.
A pipe may be provided, and the EGR pipe may be provided with an EGR valve that is appropriately opened when exhaust pressure> intake pressure by supercharging pressure control by the exhaust pressure release valve. Further, when the boost pressure due to the large turbo becomes excessive, the pre-rotation valve is opened to bypass a part of the exhaust gas toward the large turbo to the small turbo side, and the bypassed exhaust gas is exhausted to the exhaust gas. The pressure release valve may be opened and closed as appropriate to thereby perform supercharging pressure control of the large turbo. ‥‥‥

[0010]

According to the configuration of (1), the pre-rotation valve provided in the pre-rotation pipe is opened before switching from the small turbo to the large turbo, and a part of the exhaust gas going to the small turbo passes through the pre-rotation pipe. Guided to the big turbo, the big turbo is pre-rotated. This allows
It is possible to prevent a drop in boost pressure when switching from a small turbo to a large turbo, and to achieve smooth switching with small engine output fluctuations. Moreover, since the intake air amount of the engine does not drop at the time of switching the turbo, the generation of smoke at the time of switching is prevented.

According to the above construction, during the pre-rotation of the large turbo, the exhaust pressure release valve provided in the exhaust pressure release pipe of the small turbo is appropriately opened and closed to control the supercharging pressure of the small turbo. The supply pressure and the pre-rotated large turbocharging pressure are matched. Therefore, when the small turbo is switched to the large turbo after that, there is no difference in supercharging pressure before and after the switching, and smoother switching can be achieved.

According to the construction of (1), it is possible to easily establish the condition of exhaust pressure> intake pressure by opening the exhaust pressure release valve to reduce the supercharging pressure, and at this time, the exhaust pipe communicates with the intake pipe.
If the EGR valve of the GR pipe is opened, EGR can be easily applied due to the pressure difference. As a result, the combustion temperature is lowered and NOx is reduced.

According to the above construction, when the supercharging pressure due to the large turbo becomes excessive, the pre-rotation valve is opened to bypass a part of the exhaust gas toward the large turbo to the small turbo side, and the bypassed exhaust gas is exhausted. The gas is relieved by opening the exhaust pressure relief valve. This makes it possible to control the supercharging pressure of the large turbo. That is, the exhaust pressure release valve performs not only the supercharging pressure control for the small turbo but also the supercharging pressure control for the large turbo.

[0014]

An embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a diesel engine 1
The small turbo 2 and the large turbo 3 are arranged in parallel in the exhaust pipe of the vehicle. When the amount of exhaust gas is small, the small turbo 2 is used, and as the amount of exhaust gas increases, the large turbo 3 can be switched to. .

More specifically, in the exhaust manifold 4 of the diesel engine 1, an inflow pipe 5 connected to the turbine 2t of the small turbo 2 and an inflow pipe 6 connected to the turbine 3t of the large turbo 3 are installed in parallel. There is. The inflow pipes 5 and 6 are provided with open / close valves 7 and 8 for opening and closing the respective pipelines. In addition, the outflow pipes 9 and 10 of the turbines 2t and 3t, respectively.
Are joined and connected to a muffler side exhaust pipe (not shown). Further, the turbine outflow pipe 9 of the small turbo 2 is provided with an on-off valve 11 that opens and closes the pipeline.

On the other hand, the compressor 2 of each turbo 2 and 3
The outflow pipes 12 and 13 of c and 3c are connected to the intake chamber 16 of the engine 1 via intercoolers 14 and 15, respectively. Intercoolers 14 and 15 are
The intake air temperature is cooled to increase the air density and improve the filling efficiency. On / off valves 19 and 20 for opening and closing the pipelines are provided in the connecting pipes 17 and 18 that connect the intercoolers 14 and 15 to the intake chamber 16, respectively. In addition, the inflow pipe 2 of each compressor 2c, 3c
1, 22 are connected to an intake pipe on the air cleaner side (not shown).

The exhaust manifold 4 and the intake pipe (connection pipe 18) of the engine 1 are connected via an EGR pipe 23. The EGR pipe 23 returns a part of the exhaust gas to the intake side of the engine 1. As a result, the combustion temperature is lowered and NOx is reduced. The EGR pipe 23 is provided with an EGR valve 24 that opens and closes the pipeline.

The turbine inflow pipe 5 of the small turbo 2 and the turbine outflow pipe 9 of the small turbo 2 are communicated with each other via an exhaust pressure release pipe 25. The exhaust pressure release pipe 25 bypasses the exhaust gas toward the turbine 2t of the small turbo 2 and relieves it to the downstream side of the turbine, lowers the rotation of the compressor 2c and lowers the supercharging pressure. The exhaust pressure release pipe 25 is provided with an exhaust pressure release valve 26 (so-called waste gate) that opens and closes the pipeline. The exhaust pressure release valve 26 is opened and closed by an actuator 27.

The turbine inlet pipe 5 of the small turbo 2 and the turbine inlet pipe 6 of the large turbo 3 are connected by a pre-rotation pipe 28. The pre-rotation pipe 28 guides a part of the exhaust gas toward the turbine 2t of the small turbo 2 to the turbine 3t of the large turbo 3 to pre-rotate the large turbo 3 before switching from the small turbo 2 to the large turbo 3. Is. Pre-rotating tube 2
8 is provided with a pre-rotation valve 29 that opens and closes the pipeline.

The pre-rotation valve 29, the actuator 27 that drives the exhaust pressure release valve 26, the EGR valve 24, and the on-off valves 7, 8, 11, 19, 20 are connected to a controller (not shown), and are controlled by this controller. The opening / closing control is performed as shown in FIG.

The operation of this embodiment having the above configuration will be described.

2 and 3 in the low engine speed range.
As shown in FIG. 5, the open / close valves 7, 19, 11 on the small turbo 2 side are opened, and the open / close valves 8, 20 on the large turbo 3 side are closed.
As a result, the engine 1 is supercharged only by the small turbo 2.

Since the small turbo 2 has a small inertia moment, the small turbo 2 quickly starts to rotate even if the exhaust gas amount is small in the low engine speed region, and the so-called turbo lag is reduced. Further, since the capacity of the turbine 2t is tuned according to the small exhaust gas amount, the small turbo 2 can be efficiently rotated even by a small amount of exhaust gas in the low engine speed region. At this time, the large turbo 3 is not rotating at all. (A) After that, as the engine 1 accelerates and the exhaust gas amount increases, the boost pressure Pp of the small turbo 2 increases. Boost pressure P
When p reaches a preset value P1, the pre-rotating tube 28
The pre-rotation valve 29 is opened. As a result, a part of the exhaust gas flowing toward the turbine 2t of the small turbo 2 through the small turbo inflow pipe 5 is guided to the turbine 3t of the large turbo 3 through the pre-rotation pipe 28, and the large turbo 3 pre-rotates. To be done. At this time, the pre-rotated compressor 3c of the large turbo 3 does not supercharge the engine 1 because the open / close valve 20 of the outflow pipe 18 is closed.

In this way, the compressor 3 of the large turbo 3
In the case of c, since it is in a clogged state with a dung, the passing flow rate decreases and the work amount (load) decreases. Therefore, the rotation of the large turbo 3 rapidly increases even with a small amount of exhaust gas diverted from the small turbo 2 side. When the rotation speed of the compressor 3c of the large turbo 3 becomes excessive and a surge state is reached, the on-off valve 29 is closed to reduce the rotation of the turbine 3t for surge control. (B) After that, the engine 1 further accelerates and the amount of exhaust gas increases, and the supercharging pressure of the small turbo 2 has a preset value P2 of Pp.
At this time, the exhaust pressure release valve 26 provided in the exhaust pressure release pipe 25 of the small turbo 2 is appropriately opened and closed by the actuator 27, and the supercharging pressure Pp of the small turbo 2 is controlled to P2.
Then, when the supercharging pressure Ps (substantially surge-controlled pressure) of the pre-rotated large turbo 3 matches P2, the supercharger can be switched from the small turbo 2 to the large turbo 3. (C) That is, the open / close valves 7, 19, 11 on the small turbo 2 side are closed, the open / close valves 8, 20 on the large turbo 3 side are opened, and the exhaust pressure release valve 26 is closed. As a result, the engine 1 is supercharged only by the large turbo 3. Since the capacity of the turbine 3t of the large turbo 3 is tuned according to the large amount of exhaust gas, the large turbo 3 can be efficiently rotated by a large amount of exhaust gas in the middle-high rotation range of the engine. (D) Here, when switching from the small turbo 2 to the large turbo 3, both the supercharging pressure of the small turbo 2 and the supercharging pressure of the large turbo 3 are P2. Therefore, it is seen from the engine 1 before and after the switching. There is no difference in boost pressure. Therefore, the drop of the supercharging pressure when switching from the small turbo 2 to the large turbo 3 is prevented, and smooth switching with a small output fluctuation of the engine 1 can be achieved. Further, since the intake air amount of the engine 1 does not drop when the turbos 2 and 3 are switched, the occurrence of smoke at the time of switching is prevented.

By the way, when the exhaust pressure release valve 26 provided in the exhaust pressure release pipe 25 is appropriately opened / closed to reduce the supercharging pressure of the small turbo 2 (region C in FIG. 2), the exhaust pressure> intake pressure is easily increased. Therefore, if the EGR valve 24 of the EGR pipe 23 that connects the exhaust manifold 4 and the intake pipe (connection pipe 18) is opened at this time, the EG can be easily adjusted due to the pressure difference.
R is applied. As a result, the combustion temperature decreases and NO
x is reduced.

After switching to the large turbo 3 in this way, when the engine 1 is further accelerated and the supercharging pressure Ps of the large turbo 3 reaches a preset P3, the exhaust pressure release pipe 25 The pressure release valve 26 is appropriately opened and closed by the actuator, and the supercharging pressure of the large turbo 3 is controlled to P3.
Of course, at this time, the pre-rotation valve 29 is opened. Further, the on-off valve 11 is closed, which allows
The compressor 2c of the small turbo 2 (the on-off valve 19 of the outflow pipe 17 thereof is closed) is prevented from idling in the surge region. (E) Further, when the supercharging pressure of the large turbo 3 is reduced in this way (region E in FIG. 2), it is possible to easily establish a state of exhaust pressure> intake pressure. If the EGR valve 24 of the EGR pipe 23 that communicates with the intake pipe (connection pipe 18) is opened, EGR can be easily applied due to the pressure difference. As a result, the combustion temperature is lowered and NOx is reduced. That is, the exhaust pressure release valve 26 and the actuator 27 perform supercharging pressure control of the small turbo 2 and supercharging pressure control of the large turbo 3, and also function as EGR generating means.

By controlling the duty ratio of the actuator 27 that opens and closes the exhaust pressure release valve 26, the boost pressures P1 and P2 can be set arbitrarily. As a result, it is not necessary to raise unnecessary supercharging pressure during acceleration. In addition, when the EGR is performed in the C and E regions in FIG. 2, the engine is most frequently used during driving on a highway, for example, in the middle rotation region (for example, 1200 to 1600).
rpm) should be avoided. This is because the output decreases if EGR is performed, and the accelerator is apt to be depressed, resulting in deterioration of running fuel consumption and smoke.

[0029]

As described above, according to the present invention, the following excellent effects can be exhibited.

(1) According to the sequential supercharging device of the first aspect, it is possible to prevent the boost pressure from dropping when the small turbo is switched to the large turbo, so that there is no smooth switching with a small output fluctuation of the engine. obtain. Moreover, since the intake air amount of the engine does not drop when the turbo is switched, it is possible to prevent smoke from being generated when the turbo is switched.

(2) According to the sequential supercharging device of claim 2, since the supercharging pressure of the small turbo and the pre-rotated large turbo supercharging pressure can be matched, the small turbo is changed to the large turbo. When switching is performed, there is no difference in supercharging pressure before and after switching, and smoother switching can be achieved.

(3) According to the sequential supercharging device of the third aspect, it is possible to easily establish a state of exhaust pressure> intake pressure. Therefore, at this time, the EG connecting the exhaust pipe and the intake pipe
EGR can be easily applied by opening the EGR valve of the R pipe.
As a result, NOx can be reduced.

(4) According to the sequential supercharging device of claim 4, the supercharging pressure control of the small turbo and the supercharging pressure control of the large turbo can be performed by one exhaust pressure release valve, so that the cost can be reduced. Can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a sequential supercharging device for a diesel engine showing an embodiment of the present invention.

FIG. 2 is a diagram showing a supercharging pressure of the sequential supercharging device and a chart of each switching valve for producing the supercharging pressure.

FIG. 3 is a diagram showing an opening / closing procedure of each of the switching valves at the time of engine acceleration.

FIG. 4 is a schematic view of a sequential supercharging device for a diesel engine showing a conventional example.

FIG. 5 is a diagram showing supercharging pressure and smoke of the sequential supercharging device.

FIG. 6 is a diagram showing supercharging pressure and smoke of another conventional sequential supercharging device.

[Explanation of symbols]

 1 diesel engine 2 small turbo 2t small turbine 2c small compressor 3 large turbo 3t large turbine 3c large compressor 4 exhaust manifold as exhaust pipe 5 small turbo turbine inflow pipe 6 large turbo turbine inflow pipe 23 EGR pipe 24 EGR valve 25 exhaust Pressure release pipe 26 Exhaust pressure release valve 28 Pre-rotation pipe 29 Pre-rotation valve

Claims (4)

[Claims] 1. A sequential engine in which a small turbo and a large turbo are installed in parallel in an exhaust pipe of a diesel engine, the small turbo is used when the exhaust gas amount is small, and the large turbo is switched to as the exhaust gas amount increases. In the feeder, a pre-rotation pipe for guiding a part of exhaust gas to the turbine of the large turbo is provided in the turbine inflow pipe of the small turbo, and the pre-rotation pipe is opened before switching from the small turbo to the large turbo. Sequential supercharger for diesel engine, which is equipped with a pre-rotation valve. 2. An exhaust pressure releasing pipe for reducing a supercharging pressure by opening a part of exhaust pressure to a turbine downstream pipe side of the small turbo, is provided in the turbine inflow pipe of the small turbo, and the exhaust pressure releasing pipe is provided with: The exhaust pressure release valve which is opened and closed so as to match the supercharging pressure of the small turbo with the pre-rotated large turbocharging pressure when switching from the small turbo to the large turbo. Sequential supercharger for engine. 3. An EGR pipe for returning a part of exhaust gas to the intake pipe side of an engine to perform EGR is provided in an exhaust pipe on the upstream side of each turbo, and the EGR pipe is provided with the exhaust pressure release valve. 3. The sequential supercharging device for a diesel engine according to claim 2, further comprising an EGR valve that is appropriately opened when exhaust pressure> intake pressure is satisfied by supercharging pressure control. 4. When the supercharging pressure due to the large turbo becomes excessive, the pre-rotation valve is opened to bypass a part of the exhaust gas directed to the large turbo to the small turbo side, and the bypassed exhaust gas is used as the above. 3. The sequential supercharging device for a diesel engine according to claim 2, wherein the exhaust pressure release valve is opened and closed appropriately to thereby perform supercharging pressure control of the large turbo.