JP2007092557A - Turbocharger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement a high EGR ratio without combustion failure in a cylinder caused by insufficient intake air amount and thereby to implement good NO<SB>x</SB>reduction effect. <P>SOLUTION: A turbocharger 2 is mounted on an engine provided with an EGR pipe which takes part of exhaust gas out of an exhaust manifold and recirculates the part of the exhaust gas in an intake side (intake pipe). A lot of nozzle vanes 16 whose angles can be adjusted are circularly disposed to a nozzle part 15 on a turbine 2b side. A characteristic value acquired by dividing an opening area of whole circumference by a turbine outlet area (an opening area of the turbine outlet 24) at a position where the nozzle vanes 16 are arranged is within a range of 0.50 to 0.75. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a turbocharger.

  2. Description of the Related Art Conventionally, in an automobile engine or the like, a part of exhaust gas is extracted from the exhaust side and returned to the intake side, and combustion of fuel in the engine is suppressed by the exhaust gas returned to the intake side so that the combustion temperature is increased. So-called exhaust gas recirculation (EGR) is performed in which the generation of NOx is reduced by lowering.

  In general, when this type of exhaust gas recirculation is performed, an EGR pipe is used between an appropriate position of the exhaust passage extending from the exhaust manifold to the exhaust pipe and an appropriate position of the intake passage extending from the intake pipe to the intake manifold. The exhaust gas is recirculated through the EGR pipe.

  In addition, if the exhaust gas recirculated to the engine is cooled in the middle of the EGR pipe, the temperature of the exhaust gas is reduced and the volume thereof is reduced, so that the combustion temperature is effectively reduced without significantly reducing the output of the engine. Since the generation of nitrogen oxides can be reduced, a water-cooled EGR cooler is provided in the middle of an EGR pipe for recirculating exhaust gas to the engine.

  FIG. 6 shows an example of the EGR device for performing the exhaust gas recirculation described above. In FIG. 6, reference numeral 1 denotes an engine that is a diesel engine, and the engine 1 includes a turbocharger 2. The intake air 3 guided from the air cleaner is sent to the compressor 2a of the turbocharger 2 through the intake pipe 4, and the intake air 3 pressurized by the compressor 2a is sent to the intercooler 5 to be cooled. The intake air 3 is guided to 6 and distributed to each cylinder 7 of the engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 6).

  The exhaust gas 8 discharged from each cylinder 7 of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 9, and the exhaust gas 8 driving the turbine 2b is discharged out of the vehicle through the exhaust pipe 10. I have to do it.

  An end portion of the exhaust manifold 9 in the arrangement direction of the cylinders 7 and one end portion of the intake pipe 4 connected to the intake manifold 6 are connected by an EGR pipe 11. A part of 8 can be extracted and guided to the intake pipe 4.

  Here, the EGR pipe 11 is equipped with an EGR valve 12 for opening and closing the EGR pipe 11 as appropriate, and an EGR cooler 13 for cooling the recirculated exhaust gas 8, and the EGR cooler 13 Then, the temperature of the exhaust gas 8 can be lowered by exchanging heat between the cooling water (not shown) and the exhaust gas 8.

  However, in the engine 1 with the turbocharger 2 as described above, since the intake side is supercharged, the pressure difference from the exhaust side is reduced, and it is difficult to achieve a high EGR rate. As the turbocharger 2, a multi-vane variable geometry turbocharger that is provided with a ring-shaped nozzle vane that can adjust the angle at the nozzle part on the turbine 2b side and that can change the nozzle opening arbitrarily is adopted. In particular, in the low speed region where the gas flow rate is small, the nozzle opening on the turbine 2b side is narrowed to a value smaller than the intermediate opening (50% opening between fully closed and fully open), and the passage resistance of the exhaust gas 8 at the nozzle on the turbine 2b side is reduced. It is proposed to increase the pressure of the exhaust manifold 9 and thereby secure a pressure difference between the intake side and the exhaust side. .

  On the other hand, when this type of variable geometry turbocharger is used as the turbocharger 2, in a high speed region where the gas flow rate is large, the nozzle opening on the turbine 2b side is opened larger than the intermediate opening, and the nozzle on the turbine 2b side is opened. The passage resistance of the exhaust gas 8 in the part is reduced as much as possible.

  That is, in the variable geometry turbocharger, the gas flow rate limiting portion on the turbine 2b side is on the nozzle portion side while the nozzle opening on the turbine 2b side is small, whereas the nozzle opening on the turbine 2b side is large. Since it will shift to the turbine outlet side, if excessive passage resistance is given at the nozzle part in the middle of the turbine outlet in the high speed region where the gas flow rate is large, the gas flow rate determined on the turbine outlet side will be further reduced. This is because it results.

As prior art document information disclosing an example in which a part of the exhaust gas 8 extracted from the exhaust manifold 9 is recirculated to the intake pipe 4, there is the following Patent Document 1.
JP 2001-123889 A

  However, as shown in the graph of FIG. 7, the volumetric efficiency of the intake air (fresh air) with respect to the nozzle opening on the turbine 2b side is the nozzle in both the low speed range (curve A) and the high speed range (curve B). It has been found as a result that the maximum opening is obtained when the opening is used in the vicinity of an intermediate opening (50% opening between the fully closed and fully open position), whereas in the low speed range indicated by curve A, In order to increase the pressure of the exhaust manifold 9 for exhaust gas recirculation, the nozzle opening on the turbine 2b side is used with a nozzle opening α that is narrowed more than the intermediate opening. In order to suppress the pressure loss of the turbine 2b, the actual condition is that the nozzle opening on the turbine 2b side is used with the nozzle opening β that is larger than the intermediate opening, and the pressure of the exhaust manifold 9 in the low speed range. Make it higher When trying to suppress the pressure loss of the turbine 2b in the high speed range, the efficiency of the turbocharger 2 is reduced, so that the intake air amount (fresh air amount) is drastically reduced, resulting in poor combustion in the cylinder. There was a fear.

  Here, the volumetric efficiency of the intake air (fresh air) with respect to the nozzle opening on the turbine 2b side is maximized when the nozzle opening is used in the vicinity of the intermediate opening. It is considered that the combined effect of the flow velocity and the inflow angle to the turbine wheel is maximized. More specifically, if the nozzle opening is excessively narrowed in the low speed region, the flow velocity of the exhaust gas 8 increases. The angle of inflow of the exhaust gas 8 into the turbine wheel becomes worse and it becomes difficult to maintain the rotational speed of the turbine wheel. If the nozzle opening is opened too much in the high speed region, the flow velocity of the exhaust gas 8 will drop too much and the turbine wheel This is thought to be because it is difficult to maintain the number of rotations.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to achieve a high EGR rate and obtain a good NOx reduction effect without causing a combustion failure in a cylinder due to a shortage of intake air amount. It is said.

  The present invention is a turbocharger to be mounted on an engine equipped with an EGR pipe that extracts a part of exhaust gas from an exhaust manifold and recirculates it to the intake side, and is capable of adjusting the angle of a nozzle portion on the turbine side. The nozzle vane is provided in a ring shape, and the characteristic value obtained by dividing the opening area of the entire circumference of the nozzle portion at the position where each nozzle vane is arranged by the turbine outlet area is in the range of 0.50 to 0.75. Is.

  In this way, with regard to the turbocharger in which each nozzle vane in the nozzle portion of the turbine scroll can be angle-adjusted and the nozzle opening can be arbitrarily changed, there are only those having a similar characteristic value exceeding 0.75. Compared with the existing one that is not present, a turbocharger is obtained in which the opening area of the entire circumference of the nozzle portion at the arrangement position of each nozzle vane on the turbine side is relatively small and the turbine outlet area is relatively large.

  And, according to the turbocharger adopting such a characteristic value, the nozzle opening on the turbine side is narrowed to be smaller than the intermediate opening in the low speed region where the gas flow rate is small, and the passage resistance of the exhaust gas in the nozzle part on the turbine side is increased. As a result, when increasing the pressure of the exhaust manifold and increasing the exhaust gas recirculation amount, it is possible to narrow down the nozzle opening (channel cross-sectional area) to the same extent without tilting the nozzle vanes in the closing direction as in the past. It is possible to increase the pressure of the exhaust manifold by bringing the nozzle opening on the turbine side close to the intermediate opening that maximizes the combined effect of the exhaust gas flow velocity and the inflow angle to the turbine wheel, and the efficiency of the turbocharger is maximized. A sufficient pressure difference between the intake side and the exhaust side is ensured without dropping, achieving a higher EGR rate than before, and the intake air amount at that time is conventional Ri becomes possible to more secure.

  On the other hand, in the high-speed region where the gas flow rate is high, the nozzle opening on the turbine side is opened larger than the intermediate opening to reduce the exhaust gas passage resistance at the nozzle part on the turbine side as much as possible, and thus the pressure when the exhaust gas passes through the turbine. In order to suppress the loss, the area of the turbine outlet that forms the rate-limiting part of the gas flow rate when the nozzle opening is large becomes relatively large, so that it is not necessary to tilt each nozzle vane in the opening direction as in the conventional case. Since pressure loss can be suppressed to the same extent, the nozzle opening on the turbine side is brought close to the intermediate opening that maximizes the combined effect of the exhaust gas flow velocity and the inflow angle to the turbine wheel. The pressure loss on the turbine side can be suppressed without reducing the efficiency of the turbocharger as much as possible, and the suction air at that time can be reduced. The amount of it is possible to ensure more than before.

  According to the above-described turbocharger of the present invention, the middle nozzle opening on the turbine side can be maximized in the combined effect of the exhaust gas flow velocity and the inflow angle to the turbine wheel in either the low speed range or the high speed range. Since it can be used close to the opening, it achieves a high EGR rate without reducing the efficiency of the turbocharger as much as possible, and can ensure more reduction of the intake air amount at that time than in the past, combustion in the cylinder An excellent effect that a good NOx reduction effect can be obtained while avoiding defects can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 to 5 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 6 represent the same items.

  The feature of this embodiment is that the engine 1 described above with reference to FIG. 6, that is, the engine 1 equipped with the EGR pipe 11 that extracts a part of the exhaust gas 8 from the exhaust manifold 9 and recirculates it to the intake pipe 4. The turbocharger 2 for mounting on the engine 1 (see FIG. 6 for the structure on the engine 1 side) is a multi-vane variable geometry turbocharger as follows.

  That is, in the turbocharger 2 of FIGS. 1 to 4, the nozzle portion 15 in the turbine scroll 14 is provided with a large number of nozzle vanes 16 that can be angle-adjusted, and FIG. 3 schematically shows an example of the angle adjustment mechanism. As shown, each nozzle vane 16 disposed so as to surround the turbine wheel 17 is attached to a nozzle ring plate 18 via a pin 19 so as to be tiltable, and the angle of each nozzle vane 16 is a link plate with respect to the nozzle ring plate 18. The link plate 20 is rotated through the link 23 by the tilting operation of the lever 22 by the actuator 21. .

  Moreover, in the turbocharger 2 shown here, the characteristic value (Sn / St value) obtained by dividing the opening area Sn of the entire circumference of the nozzle portion 15 at the position where each nozzle vane 16 is arranged by the turbine outlet area St is 0.50. It is formed to be in the range of ~ 0.75.

  Here, the opening area Sn of the entire circumference of the nozzle portion 15 at the position where each nozzle vane 16 is disposed is the width w of the nozzle portion 15 on the circumference of the pitch circle C where the pin 19 forming the tilting central axis of each nozzle vane 16 is disposed. (Refer to FIG. 1) refers to the area of the cylindrical region calculated by multiplication, and the turbine outlet area St is the opening of the turbine outlet 24 that opens laterally at the center of the turbine scroll 14. It refers to the area.

  In FIG. 1, reference numeral 25 denotes a compressor wheel, 26 denotes a compressor scroll, 27 denotes a compressor inlet, and 28 denotes a shaft integrally connecting the turbine wheel 17 and the compressor wheel 25.

  Thus, when the turbocharger 2 configured in this way is used in the engine 1 with the EGR pipe 11 (see FIG. 6), the existing one in which only the same characteristic value exceeds 0.75 exists. As a result, the turbocharger 2 having a relatively small opening area of the entire circumference of the nozzle portion 15 at the arrangement position of the nozzle vanes 16 on the turbine 2b side and a relatively large turbine outlet area can be obtained.

  According to the turbocharger 2 employing such characteristic values, the nozzle opening on the turbine 2b side is narrowed to be smaller than the intermediate opening in the low speed region where the gas flow rate is small, and the exhaust gas 8 in the nozzle section 15 on the turbine 2b side is reduced. In order to increase the passage resistance and thereby increase the pressure of the exhaust manifold 9 to increase the exhaust gas recirculation amount, the nozzle opening degree (flow passage cross-sectional area) is kept to the same level without tilting the nozzle vanes 16 in the closing direction as in the prior art. Since the nozzle opening on the turbine 2b side is brought close to an intermediate opening at which the combined effect of the flow velocity of the exhaust gas 8 and the inflow angle into the turbine wheel 17 is maximized, the pressure of the exhaust manifold 9 is increased. It is possible to secure a sufficient pressure difference between the intake side and the exhaust side without reducing the efficiency of the turbocharger 2 as much as possible. Realized by and the intake air amount when the it is possible to secure more than before.

  On the other hand, the nozzle opening on the turbine 2b side is opened larger than the intermediate opening in the high speed region where the gas flow rate is large, thereby reducing the passage resistance of the exhaust gas 8 in the nozzle portion 15 on the turbine 2b side as much as possible. In order to suppress the pressure loss when passing through the nozzle, the area of the turbine outlet 24 that forms the rate-limiting part of the gas flow rate when the nozzle opening is large is relatively large, so that each nozzle vane 16 is opened in the opening direction as in the past. Since the pressure loss on the turbine 2b side can be suppressed to the same level without tilting, the combined effect of the flow rate of the exhaust gas 8 and the inflow angle to the turbine wheel 17 is maximized. It is possible to suppress the pressure loss on the turbine 2b side by approaching the intermediate opening obtained in the above, and without reducing the efficiency of the turbocharger 2 as much as possible. Suppressing pressure loss in the turbine 2b side and it is possible to the intake air amount at that time to ensure more than before.

  According to the verification experiment by the present inventor, as shown in the graph of FIG. 5, the light impermeability of the exhaust gas with respect to the characteristic value (Sn / St value) described above (contamination of the exhaust gas due to smoke caused by poor combustion) Exhaust gas recirculation performed at different EGR rates (10% is represented by curve X, 20% is represented by curve Y, and 30% is represented by curve Z). As a result of the survey, the optimum point for each EGR rate (the survey point where the light opacity is the lowest among the survey points forming each curve X, Y, Z: the survey point that is plotted large in FIG. 5) 5 is confirmed to shift from the right side to the left side in FIG. 5 as the EGR rate increases, and the tendency that each curve X, Y, Z becomes U-shaped increases as the EGR rate increases. confirmed.

  In order to comply with stricter exhaust gas regulations in the future, it is considered necessary to increase the EGR rate to about 20% to 40% and recirculate the exhaust gas 8, but the EGR rate is 20%. Considering that the optimum point is determined to be a characteristic value slightly smaller than the characteristic value 0.75 on the curve Y, and that the optimum point shifts to a lower characteristic value side as the EGR rate increases, the future high value When trying to realize the EGR rate, it is considered that the existing variable geometry turbocharger that only has a characteristic value exceeding 0.75 cannot suppress the generation of smoke well. It is considered necessary to adopt a variable geometry turbocharger that has been reduced to 0.75 or less, which has never been proposed before.

  On the other hand, as shown particularly prominently in the curve Z with an EGR rate of 30%, the light opacity tends to deteriorate abruptly when the characteristic value falls below 0.50, and this tendency further increases the EGR rate. It is thought that it appears more prominently.

  This is because there is no data yet to establish combustion by raising the EGR rate from 30%, but if the EGR rate exceeds 30%, the characteristic value is around 0.60 on the curve Z This is because it is considered that the optimum point determined in (1) shifts to a lower characteristic value side, and the tendency to form a U-shape is stronger than the curve Z.

  Therefore, even if the characteristic value is lowered to 0.75 or less, which has never been proposed before, the lower limit is considered to be automatically determined to be 0.50 or more. In fact, in each of the curves Y and Z, In addition, it can be confirmed that the lower region of the light opacity is almost covered in the range of the characteristic value of 0.50 to 0.75.

  Therefore, according to the above-described embodiment, the combined effect of the flow rate of the exhaust gas 8 and the flow angle of the exhaust gas 8 can be maximized in the nozzle opening on the turbine 2b side in either the low speed range or the high speed range. Since it can be used close to the intermediate opening, it is possible to achieve a high EGR rate without reducing the efficiency of the turbocharger 2 as much as possible, and to ensure more reduction in the intake air amount at that time than in the conventional cylinder. A good NOx reduction effect can be obtained while avoiding poor combustion.

  The turbocharger according to the present invention is not limited to the above-described embodiment. A part of the exhaust gas extracted from the exhaust manifold may be recirculated to the intake manifold, and the nozzle vane Of course, the configuration of the angle adjusting mechanism is not limited to the illustrated example, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing which shows an example of the form which implements this invention. It is sectional drawing of the II-II arrow of FIG. It is explanatory drawing which shows roughly an example of the angle adjustment mechanism of each nozzle vane. It is an arrow view of the IV-IV direction of FIG. It is a graph which shows the light opacity of the exhaust gas with respect to a characteristic value according to EGR rate. It is the schematic of the engine for demonstrating a prior art. It is a graph which shows the volumetric efficiency of the intake air (fresh air) with respect to a nozzle opening degree.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Turbocharger 2a Compressor 2b Turbine 3 Intake 4 Intake pipe 8 Exhaust gas 9 Exhaust manifold 10 Exhaust pipe 11 EGR pipe 14 Turbine scroll 15 Nozzle part 16 Nozzle vane 17 Turbine wheel 24 Turbine exit

Claims (1)

  A turbocharger to be mounted on an engine equipped with an EGR pipe that extracts a part of the exhaust gas from the exhaust manifold and recirculates it to the intake side. And a turbocharger formed so that a characteristic value obtained by dividing the opening area of the entire circumference of the nozzle portion at the nozzle vane arrangement position by the turbine outlet area is in a range of 0.50 to 0.75.

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