JP2000064847A - Exhaust by-pass structure for turbocharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize a passage after bleeding so as to improve turbine efficiency and increase a flow rate by providing a by-pass passage for bleeding exhaust gas from halfway of a turbine impeller, and forming this by-pass passage as a scroll passage gradually increased in cross-sectional area along the rotating direction of the turbine impeller. SOLUTION: When a waste gate valve is closed, exhaust gas of an engine flows into a scroll chamber 2 from an inlet passage 8 and is exhausted from an exhaust outlet chamber to rotate a turbine impeller 3. When boost pressure is heightened to open the waste gate valve 2, exhaust gas is detoured to the exhaust outlet chamber via a by-pass passage 23 so as to suppress the rotation rise of the turbine impeller 3. In this case, the by-pass passage 23 comprises a groove 24 provided at the whole periphery of the internal wall of a turbine storage chamber, a scroll passage 25 provided on the radially outside of the groove 24, and an outlet 26 opened to the exhaust outlet chamber. The flow of bled exhaust gas is therefore optimized to improve turbine efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust bypass structure for a turbocharger mounted on an automobile or the like.

[0002]

2. Description of the Related Art Generally, a turbocharger is designed to drive a turbine by utilizing high temperature and high pressure energy of exhaust gas of an engine, and to drive a compressor coaxial with the turbine for supercharging. On the other hand, the turbocharger has a supercharging pressure control means, of which the exhaust bypass type is typical.

Usually, exhaust gas is extracted on the upstream side of the turbine impeller and bypasses the turbine impeller to be exhausted. As a result, the flow rate of exhaust gas supplied to the turbine is reduced, the increase in rotation thereof is suppressed, and the supercharging pressure is maintained within a fixed value.

However, in this case, the energy of the exhaust gas is simply discarded, and the energy cannot be fully utilized.

Therefore, the applicant of the present invention has proposed a method for extracting exhaust gas from the middle of the turbine impeller in Japanese Patent Application No. 6-200717. According to this, after the exhaust gas energy is used for driving the turbine, it can be discarded, and the energy efficiency can be improved.

[0006]

By the way, in such a bleeding system, the pressure difference between the bleeding section and the exhaust section on the downstream side becomes small, so that the flow path after the bleeding must be properly shaped. The flow path loss increases and the desired effect cannot be expected.

In the above-mentioned prior application, the flow passage is formed by a groove having a constant cross-sectional area provided all around the inner wall of the turbine casing, but this is not sufficient, and it cannot be said to be the optimum flow passage.

[0008]

The exhaust bypass structure for a turbocharger according to the present invention is provided with a bypass passage for extracting exhaust gas from the middle of the turbine impeller, and the bypass passage is sequentially cross-sectional area along the rotational direction of the turbine impeller. Is composed of a scroll passage that increases.

Here, it is preferable that a part of the scroll passage is superposed on the inner side in the radial direction of the scroll chamber for sending the exhaust gas to the turbine impeller.

It is preferable that an upstream bypass passage for extracting the exhaust gas from the upstream side of the turbine impeller is further provided.

Further, it is preferable that outlets of the bypass passage and the upstream bypass passage are adjacent to each other, and these outlets are opened and closed by a common wastegate valve.

[0012]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 2, the turbine casing 1
A scroll chamber (swirl chamber) 2 into which exhaust gas from the engine is introduced, and a turbine housing chamber 4 in which a turbine impeller 3 is rotatably housed are sectioned and formed inside. Here, the configuration of a radial turbine is adopted, and the scroll chamber 2 is located outside the turbine housing chamber 4 in the radial direction. The exhaust gas in the scroll chamber 2 flows into the turbine impeller 3 from the outside in the radial direction, passes through the turbine impeller 3 to work, and then flows out to the axial front end side (the left side in the drawing) to be exhausted from the exhaust outlet chamber 21. It has become. When the turbine impeller 3 is rotationally driven in this manner, the compressor impeller on the right side in the drawing, which is connected to the turbine impeller 3 via the turbine shaft 7, is rotationally driven, and supercharging of intake air is executed.

The turbine impeller 3 is constructed by arranging a plurality of turbine blades 6 on the outer peripheral surface of a disk 10. The inner wall 16 of the turbine housing chamber 4 surrounds the entire turbine impeller 3 from the outside in the radial direction while being slightly separated from the turbine impeller 3.

As shown in FIG. 5, the turbine blade 6 is smoothly bent at its central portion and forms a gas flow path 17 between the turbine blade 6 and the adjacent turbine blade 6. The interval between the gas flow paths 17 is gradually reduced along the gas flow direction, and becomes the smallest at the throat portion 18 serving as an outlet. The axial range in which the throat portion 18 exists is referred to as an outlet area 22.

As shown in FIG. 2, the turbine casing 1
A bypass passage 23 for extracting the exhaust gas from the middle of the turbine impeller 3 is provided in the. Bypass passage 23,
Groove 24 provided all around the inner wall 16 of the turbine housing chamber 4
A scroll passage (spiral passage) 25 provided outside the groove 24 in the radial direction and communicating with the groove 24;
Outlet 2 opening to exhaust outlet chamber 21 from one location in the circumferential direction of 5
6 and 6. By this, the bypass passage 23
However, the gas passage 17 of the turbine impeller 3 and the exhaust outlet chamber 2
It comes to communicate with 1.

Here, the inlet of the groove 24 is opened to the outlet region 22 or the throat portion 18, and the entire inlet is included in the outlet region 22. As a result, the exhaust gas from the throat portion 18 is extracted and bypassed. The scroll passage 25 is a spiral passage as shown in FIG. 1, and substantially surrounds the groove 24, and has a cross-sectional area that increases along the turbine impeller rotation direction R. The outlet 26 is opened at the position of this substantially maximum cross-sectional area. Further, the scroll passage 25 is reversely wound around the scroll chamber 2 for the reason described below, and is partially (upper portion 25a) as shown in FIG.
Are superposed on the inner side of the scroll chamber 2 in the radial direction.

As shown in FIGS. 1 and 2, the upstream bypass passage 19 is provided in the inlet passage 8 on the upstream side of the scroll chamber 2.
Is provided. The outlet 20 of the upstream bypass passage 19 is opened to the exhaust outlet chamber 21, and the outlet 26 of the bypass passage 23 is opened.
Be adjacent to.

As shown in FIG. 3, a waste gate valve 27 is provided in the exhaust outlet chamber 21 so that the outlet 26 of the bypass passage 23 and the outlet 20 of the upstream bypass passage 19 are opened and closed at the same time. That is, wastegate valve 2
7 is common to both outlets 20 and 26. The wastegate valve 27 is specifically a swing type poppet valve. That is, the valve body 2 that substantially opens and closes both outlets 26, 20.
9a and 29b are attached to the support plate 5, and the support plate 5 is fixed to the valve shaft 28. The valve shaft 28 is the turbine casing 1
4 and is projected to the outside, and the operation lever member 9 as shown in FIG. 4 is attached to this projection and is rotated by the actuator 31. Intake pressure or supercharging pressure Pc sent from a compressor (not shown) is introduced into the actuator 31.

According to this, when the supercharging pressure Pc exceeds a predetermined value, the actuator 31 is driven and the valve shaft 28 is rotated via the operating lever member 9, and the valve bodies 29a, 29b are rotated.
Can be separated from the outlets 20 and 26 to open the bypass passage 23 and the upstream bypass passage 19.

Next, the operation of the above embodiment will be described.

With the normal wastegate valve 27 closed, the exhaust gas sent from the engine flows into the scroll chamber 2 through the inlet passage 8 as shown in FIG.
It is supplied to the turbine impeller 3 and rotationally drives the turbine impeller 3. Then, the exhaust outlet chamber 2 is pulled out to the tip in the axial direction.
Emitted from 1.

On the other hand, when the supercharging pressure increases and the waste gate valve 27 is opened, the exhaust gas is bypassed to the exhaust outlet chamber 21 through the bypass passage 23 and the upstream bypass passage 19. As a result, the rotation increase of the turbine impeller 3 is suppressed, and the boost pressure is maintained within a fixed value.

At this time, as the flow of the exhaust gas, a part of the exhaust gas is first bypassed from the upstream bypass passage 19,
The remaining exhaust gas is sent to the scroll chamber 2 and flows into the turbine impeller 3. Since the exhaust gas sequentially escapes from the upstream side in the scroll chamber 2, the cross-sectional area of the scroll chamber 2 is reduced toward the downstream side. In other words, the winding direction is such that the cross-sectional area decreases toward the downstream side.

Next, the exhaust gas flowing into the turbine impeller 3 drives the turbine impeller 3 to rotate and work, and then approaches the throat portion 18. Then, a part of the exhaust gas flows into the groove 24 and is bypassed through the bypass passage 23. At this time, as shown in FIG. 1, the scroll passage 2
Exhaust gas having a swirl component in the same direction as the rotational direction of the turbine impeller 3 flows into the gas turbine 5. Moreover, since the inflowing gas amount increases toward the downstream side in the orbiting direction, the cross-sectional area of the scroll passage 25 also increases toward the downstream side. Then, the exhaust gas flows out from the outlet 26 at the most downstream position of the scroll passage 25 toward the exhaust outlet chamber 21.

Thus, as in the previous application, the exhaust gas can be bypassed after driving the turbine impeller 3, so that the exhaust gas energy can be effectively used.

As shown in FIG. 5, the turbine is generally designed so that the absolute velocity C ₄ of the exhaust gas is oriented in the axial direction at the outlet position of the turbine blade 6. That is, the vector combination of the relative speed W _{4 of} the exhaust gas with respect to the turbine blades 6 and the peripheral speed U ₄ of the turbine blades 6 is the absolute speed C ₄ , and this absolute speed C ₄ is oriented in the axial direction under a certain design flow rate. It has become.

On the upstream side of the outlet position of the turbine blades 6, however, the absolute velocity C ₂ (the vector combination of the relative velocity W ₂ and the peripheral velocity U ₂ ) generally does not face the axial direction, and the rotation direction R of the turbine impeller 3 It has the turning component Cu of.

The present invention pays attention to this swirling component, and by providing the scroll passage 25 whose flow passage is gradually expanded along the swirling direction or the turbine impeller rotation direction, sudden deflection and acceleration / deceleration of the gas flow are prevented. In addition to reducing the path loss, the gas velocity energy is converted into pressure energy in the scroll passage 25 to create a pressure difference with the exhaust outlet chamber 21 to keep the pressure in the groove 24 low, thereby effectively performing exhaust bypass. You can This makes it possible to provide a flow path having an optimum shape, and exhaust gas can be smoothly discharged.

On the other hand, when the engine speed rises and the exhaust gas flow rate reaches a constant value, the throat portion 18 having the minimum passage area is clogged or choked, and the inlet (groove 24) of the bypass passage 23 is provided in this throat portion 18. Since it is opened and bleeds, choking can be prevented and the turbine capacity can be substantially expanded.

In this embodiment, the upstream bypass passage 19 similar to the conventional one is provided to secure the bypass flow rate. However, if the flow rate can be secured only by the bypass passage 23, the upstream bypass passage 19 may be omitted.

In the case of such a combined type, for optimum performance, each of the outlets 20 and 26 is individually opened / closed, that is, the outlet 26 is first opened, and the flow rate cannot be secured only by the bypass passage 23 before the outlet 20 is opened. You should open it. However, when the outlets 20 and 26 of the respective passages are adjacent to each other and opened and closed by the common wastegate valve 27 as in the present embodiment, an increase in the number of parts can be prevented, and simplification and cost reduction can be achieved.

Further, since the scroll passage 25 and the scroll chamber 2 are wound in opposite directions to each other, the large diameter portion and the small diameter portion match each other to improve the layout property, and the radial direction of the scroll chamber 2 as in the present embodiment. If a part of the scroll passage 25 is superposed on the inside, further compactness can be achieved.

In the case of such bleeding on the way, there is a method of exhausting gas in the entire circumferential direction instead of the method of sending gas in the circumferential direction and exhausting it from one place like the bypass passage 23 of the present embodiment. If so, a slide valve that opens and closes in the entire circumferential direction is required, which is not preferable because the structure is complicated and the cost is high.

FIG. 6 is a graph showing the relationship between the exhaust gas flow rate of the turbine and the turbine efficiency. The solid line indicates the air extracted on the upstream side of the conventional turbine impeller, the broken line indicates the air extracted in the middle according to the present embodiment, and the alternate long and short dash line indicates the air extraction position and the bypass passage shape set inappropriately during the air extraction. As can be seen from this, if the bleeding position or the like is set inappropriately, even if the bleeding is performed midway, the efficiency is rather lowered and it may not be preferable. According to this embodiment, both efficiency and flow rate can be improved, and preferable characteristics can be obtained.

Although the bleed air is extracted from the throat portion 18 in this embodiment, the position can be changed at a position other than the throat portion 18 as long as good characteristics are obtained. For example, the groove 24 may be provided so as to partially overlap the throat portion 18, or the groove 24 may be provided upstream from the throat portion 18.

The reasons for increasing the efficiency and increasing the flow rate of this embodiment are also considered as follows. That is, as shown in FIG. 7, when the groove 24 is made to face the throat portion 18 and air is extracted from here, the gas on the pressure surface side of the turbine blade 6 is
The turbine blades 6 can be passed over and fed to the suction surface side through the grooves 24. Therefore, the separation vortex generated on the suction surface side can be eliminated by the gas sent from the pressure surface side, thereby reducing the low energy region that causes loss and substantially expanding the flow passage area. is there.

As described above, various other embodiments of the present invention are possible. For example, a turbine that combines a radial scroll chamber with a mixed-flow turbine impeller (Japanese Patent Application No. 6-19
The present invention is also applicable to (see No. 4469).

[0039]

The present invention exhibits the following excellent effects.

(1) The flow path after extraction can be optimized.

(2) It is possible to improve turbine efficiency and increase flow rate.

[Brief description of drawings]

FIG. 1 is a schematic front view showing a bypass passage and a scroll chamber of the present embodiment.

FIG. 2 is a vertical sectional side view showing a turbine peripheral portion of the turbocharger of the present embodiment.

FIG. 3 is a front view of the turbocharger of the present embodiment viewed from the exhaust outlet side.

FIG. 4 is a side view showing the entire turbocharger of the present embodiment.

FIG. 5 is a diagram showing a turbine impeller.

FIG. 6 is a graph showing the relationship between turbine flow rate and efficiency.

FIG. 7 is a diagram showing a gas flow that wraps around from a pressure surface side to a suction surface side.

[Explanation of symbols]

2 scroll room 3 turbine impeller 19 upstream bypass passage 20 exit 23 Bypass passage 25 scroll passage 26 exit 27 wastegate valve R Turbine impeller rotation direction

Claims (4)

[Claims] 1. A turbocharger, characterized in that a bypass passage for extracting exhaust gas from the middle of the turbine impeller is provided, and the bypass passage is constituted by a scroll passage whose cross-sectional area increases sequentially along the rotational direction of the turbine impeller. Exhaust bypass structure. 2. The exhaust bypass structure for a turbocharger according to claim 1, wherein a part of the scroll passage is superposed on an inner side in a radial direction of a scroll chamber that sends exhaust gas to the turbine impeller. 3. The exhaust bypass structure for a turbocharger according to claim 1, further comprising an upstream bypass passage for extracting exhaust gas from an upstream side of the turbine impeller. 4. The exhaust bypass structure for a turbocharger according to claim 3, wherein outlets of the bypass passage and the upstream bypass passage are adjacent to each other, and these outlets are opened and closed by a common wastegate valve.