JP2011174404A - Two-stage supercharging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To safely reduce the diameter of a high-pressure stage turbocharger without using a waste gate pipe. <P>SOLUTION: A bypass flow path 17 is attached to an engine intake flow path which feeds intake air A from a high-pressure stage compressor 4 to an engine 1, a turbine generator 18 is mounted in the bypass flow path 17, and a three-way valve 19 (a flow path change-over means) is provided in the inlet of the bypass flow path 17 for changing over the intake air A flowing from the high-pressure stage compressor 4 to the engine 1 to flow properly to the side of the bypass flow path 17. In a high-speed and high-load region (an operation region shown in the graph of Fig.6 with a cross-hatching) of the engine 1 where exhaust gas G conventionally split-flows into the waste gate pipe 7 (refer to Fig.5), the three-way valve 19 changes over the intake air A flowing from the high-pressure stage compressor 4 to flow to the side of the bypass flow path 17, to guide it to the engine 1 via the turbine generator 18. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a two-stage supercharging system.

  In recent years, a two-stage turbocharging system that uses a small-diameter high-pressure turbocharger has been studied in order to improve fuel efficiency, increase torque, and achieve a high EGR rate in the low-speed and light-load range. In the system, as shown in FIG. 5, the high-pressure turbine 3 is operated by the exhaust G sent from the exhaust manifold 2 of the engine 1 and the intake air A compressed by the high-pressure compressor 4 is supplied to the intake manifold 5 of the engine 1. The high-pressure stage turbocharger 6 and the exhaust A sent from the high-pressure stage turbine 3 of the high-pressure stage turbocharger 6 actuates the low-pressure stage turbine 8 and is compressed by the low-pressure stage compressor 9 into the high-pressure stage compressor 4. A low-pressure turbocharger 10 for feeding is provided.

  Further, an intercooler 12 is interposed in the engine intake passage between the discharge side of the low-pressure stage compressor 9 of the low-pressure stage turbocharger 10 and the suction side of the high-pressure stage compressor 4 of the high-pressure stage turbocharger 6. An aftercooler 13 is interposed in the engine intake passage between the discharge side of the high-pressure compressor 4 and the intake manifold 5 of the engine 1.

  Further, the EGR pipe 14 extends from the upstream side (specifically, the exhaust manifold 2) of the engine exhaust passage to the downstream side (specifically, the intake manifold 5) of the aftercooler 13 of the engine intake passage. The EGR pipe 14 is provided with an EGR cooler 15 that cools the exhaust gas G that has been diverted from the engine exhaust flow path, and an EGR valve 16 that adjusts the flow rate of the exhaust G to be recirculated to the engine intake flow path. ing.

  Thus, in such a two-stage supercharging system, when the engine 1 is in operation, the exhaust G sent from the exhaust manifold 2 flows into the high-pressure turbine 3 and drives the high-pressure compressor 4. The intake air A that flows into the low-pressure turbine 8 and drives the low-pressure compressor 9 and flows into the low-pressure compressor 9 and is compressed is supplied to the high-pressure compressor 4 through the intercooler 12, and the high-pressure compressor 4 is compressed again and supplied to the intake manifold 5 via the aftercooler 13. Therefore, if the amount of intake A supplied to the cylinder is increased and the fuel injection amount per cycle is increased, the output of the engine 1 is increased. Can be increased.

  Further, a part of the exhaust G flows from the exhaust manifold 2 into the EGR pipe 14, and the exhaust G cooled by the EGR cooler 15 and adjusted in flow rate by the EGR valve 16 is combined with the intake air A with the intake manifold 5. Thus, the combustion temperature in the cylinder is lowered, and the generation of NOx is reduced.

  For example, Patent Documents 1 and 2 listed below already exist as the general technical level related to the two-stage turbocharging system as described above.

JP 2005-147030 A JP-A-5-180089

  However, in the two-stage turbocharging system that achieves high output with the small-diameter high-pressure turbocharger 6 as described above, a high-speed and high-load region where the flow rate of the exhaust G is large (shown with cross-hatching in the graph of FIG. 6). In the operation region), the high-pressure turbocharger 6 having a small diameter rotates excessively and the supercharging pressure is increased more than necessary, and the maximum in-cylinder pressure of each cylinder of the engine 1 exceeds the limit value, so that the operation becomes impossible. A waste gate pipe 7 that bypasses the stage turbine 3 is provided, a waste gate valve 11 that opens and closes the flow path is provided in the middle of the waste gate pipe 7, and the waste gate valve 11 is opened in a high-speed and high-load region to obtain an appropriate flow rate. Only the exhaust gas G is allowed to flow to the high-pressure stage turbine 3, and the rest is bypassed to the high-pressure stage turbine 3 and led to the low-pressure stage turbine 8. If the waste gate pipe 7 is increased, peripheral devices such as electronic boards that are vulnerable to heat cannot be placed nearby, so there are significant restrictions in terms of layout, and the waste gate valve 11 must have sufficient heat resistance. There was a problem that the equipment cost would rise due to the failure.

  On the other hand, it is possible to increase the capacity by increasing the diameter of the high-pressure turbocharger 6 so that it can accommodate the total exhaust gas amount without excessive rotation even in the high speed and high load range. This will cause problems such as deterioration of fuel economy and inability to obtain the EGR amount necessary for NOx reduction, and impairs the significance of achieving high output with the small-diameter high-pressure turbocharger 6. End up.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a two-stage turbocharging system that can realize a reduction in the diameter of a high-pressure turbocharger without any trouble without using a wastegate pipe.

  The present invention relates to a high-pressure stage turbocharger that operates a high-pressure stage turbine by exhaust gas delivered from an engine and supplies intake air compressed by a high-pressure stage compressor to the engine, and the high-pressure stage turbine of the high-pressure stage turbocharger. In a two-stage supercharging system that operates a low-pressure turbine by exhaust gas and supplies intake air compressed by a low-pressure compressor to the high-pressure compressor, the intake air is supplied from the high-pressure compressor to the engine. A bypass flow path attached to the engine intake flow path, a turbine generator equipped in the bypass flow path, and flow path switching means for appropriately switching the flow of intake air from the high pressure compressor toward the engine to the bypass flow path side. Equipped with the flow path switching means in the high speed and high load region of the engine. Is characterized in that it has configured to obtain guidance on the engine were allowed to through the turbine generator the flow of intake air from the intermediate pressure stage compressor is switched to the bypass flow.

  Thus, in this case, when the flow of the intake air from the high-pressure compressor is switched to the bypass flow path side by the flow path switching means in the high speed and high load region of the engine and guided to the engine through the turbine generator, While the turbine generator is driven by the flow of the intake air to generate electricity, the supercharging pressure is lowered by working with the turbine generator, and the intake air amount (fresh air amount) supplied to the engine is reduced accordingly. As a result, the exhaust gas discharged from the engine is reduced, and even a small-diameter high-pressure turbocharger can cope with the total exhaust gas amount without excessive rotation.

  Furthermore, since the power generated by the turbine generator is reduced, the burden on the existing alternator is reduced, and it is possible to cover the power with an alternator having a smaller capacity than before, so the burden on the engine side required to drive the alternator is reduced. The fuel consumption will be greatly improved.

  In the present invention, it is preferable to dispose the bypass flow path and the turbine generator upstream of the aftercooler provided between the high-pressure compressor and the intake manifold. In this way, before the heat is recovered by the aftercooler. The power can be efficiently recovered from the intake air having a high temperature energy, and the intake air temperature is lowered by reducing the supercharging pressure through the turbine generator first, and the cooling load in the aftercooler is reduced.

  According to the two-stage supercharging system of the present invention, various excellent effects as described below can be obtained.

  (I) According to the invention of claim 1 of the present invention, the flow of intake air from the high-pressure stage compressor by the flow path switching means in the high-speed and high-load region of the engine without using the wastegate piping that requires countermeasures against heat. Is switched to the bypass flow path side and passed through the turbine generator to perform the work of driving the turbine generator to lower the supercharging pressure, thereby reducing the intake air amount (fresh air amount) supplied to the engine. Since the exhaust exhausted from the engine can be reduced, even a small-diameter high-pressure turbocharger can cope with the total exhaust gas amount without excessive rotation, and the high-pressure turbocharger can be reduced in diameter without any trouble. It is possible to greatly relax the layout restrictions on the layout of peripheral devices that are vulnerable to heat, such as electronic boards, and it has high heat resistance. The wastegate valve may be reduced in significant equipment cost by eliminating the need such.

  (II) According to the invention according to claim 1 of the present invention, the load on the alternator can be reduced by generating power with the turbine generator, and the capacity of the alternator can be made smaller than before. The fuel consumption can be greatly improved by reducing the load on the engine side required for driving the vehicle.

  (III) According to the invention of claim 2 of the present invention, power can be efficiently recovered from intake air having high temperature energy before heat recovery by the aftercooler, while excessive power can be recovered by first passing through the turbine generator. Since the intake air temperature can be lowered by reducing the supply pressure, the cooling load in the aftercooler can be greatly reduced, the capacity of the aftercooler can be reduced to reduce the equipment cost, and the cooling capacity of the aftercooler can be maintained as it is. The NOx reduction effect can be enhanced by lowering the intake air temperature than before.

It is the schematic which shows an example of the form which implements this invention. It is the schematic which shows the state which switched the flow path with the three-way valve of FIG. It is a graph which shows the effect of the supercharging pressure fall by a turbine generator. It is a graph which shows that the driving | operation within the limit value of the maximum in-cylinder pressure is attained. It is the schematic which shows an example of the conventional two-stage supercharging system. It is a graph which shows the operation area | region which utilized the conventional wastegate piping.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1 and 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 5 represent the same items.

  As shown in FIG. 1, the basic configuration of the two-stage turbocharging system of this embodiment is the same as that of the conventional two-stage turbocharging system described above with reference to FIG. The engine intake passage for supplying the intake air A from the high-pressure compressor 4 to the engine 1 while eliminating the waste gate pipe 7 (see FIG. 5) and the waste gate valve 11 (see FIG. 5) used in the supercharging system. A bypass flow path 17 is provided upstream of the aftercooler 13 in the engine, and a turbine generator 18 is provided in the bypass flow path 17, and the flow of intake air A from the high-pressure compressor 4 toward the engine 1 at the inlet of the bypass flow path 17. Is provided with a three-way valve 19 (flow path switching means) for switching to the bypass flow path 17 side as appropriate, and the exhaust G is divided into the wastegate pipe 7 (see FIG. 5) in the past. The three-way valve 19 switches the flow of intake air A from the high-pressure compressor 4 to the bypass passage 17 side in the high-speed and high-load region of the engine 1 (the operation region indicated by cross-hatching in the graph of FIG. 6). Thus, the engine 1 can be guided through the turbine generator 18.

  In the example shown here, the three-way valve 19 is controlled by a control signal 20a from a control device 20 constituting an engine control computer (ECU: Electronic Control Unit). Is incorporated with a two-dimensional control map of the fuel injection amount and the rotational speed of the engine 1, and when the intake air A is led directly from the high-pressure compressor 4 to the engine 1, the high-pressure turbine 3 rotates excessively. In a high-speed and high-load region where the maximum in-cylinder pressure of the cylinder is assumed to exceed the limit value, a control signal 20a for switching the flow path from the state of FIG. 1 to the state of FIG. It is supposed to be.

  Thus, in this case, after the flow of the intake air A from the high-pressure compressor 4 is switched to the bypass flow path 17 side by the three-way valve 19 in the high-speed and high-load region of the engine 1 and passed through the turbine generator 18. When guided to the engine 1, the turbine generator 18 is driven by the flow of the intake air A to generate electric power. On the other hand, when the turbine generator 18 performs work, a differential pressure as shown in the graph of FIG. As the pressure (supercharging pressure) of the manifold 5 decreases, the intake air amount (new air amount: see the graph of FIG. 4) supplied to the engine 1 is reduced, and the exhaust G discharged from the engine 1 also decreases. Therefore, even the small-diameter high-pressure turbocharger 6 can cope with the total exhaust gas amount without excessive rotation.

  That is, as shown in the graph of FIG. 4, if the expansion ratio of the turbine generator 18 is appropriately adjusted, a required differential pressure is generated before and after the turbine generator 18, so that the maximum in-cylinder pressure Pmax in each cylinder of the engine 1 is increased. The maximum in-cylinder pressure Pmax of each cylinder of the engine 1 exceeds the limit value (allowable Pmax) as in the case of using the conventional wastegate pipe 7 (see FIG. 5). It becomes possible to avoid the situation where driving becomes impossible.

  In addition, since power is generated by the turbine generator 18, the burden on the existing alternator is reduced, and it is possible to cover the power with an alternator having a smaller capacity than the conventional one. Therefore, the engine 1 side required for driving the alternator The burden will be reduced and fuel efficiency will be greatly improved.

  The electric power generated at this time may be stored in a battery or the like. However, an electric assist mechanism is attached to the engine 1 to positively utilize the electric power as auxiliary power for the engine 1. Thus, it is possible to significantly improve fuel consumption.

  Further, particularly in the case of this embodiment, since the bypass flow path 17 and the turbine generator 18 are arranged upstream of the aftercooler 13, the power is efficiently recovered from the intake air A having a high temperature energy before being recovered by the aftercooler 13. In addition, since the supercharging pressure is lowered through the turbine generator 18 first, the intake air temperature is also lowered, and the cooling load on the aftercooler 13 is reduced.

  Therefore, according to the above-described embodiment, the intake air A from the high-pressure compressor 4 can be obtained by the flow path switching means in the high-speed and high-load region of the engine 1 without using the wastegate pipe 7 (see FIG. 5) that requires heat countermeasures. Is switched to the bypass flow path 17 side and passed through the turbine generator 18 to perform the work of driving the turbine generator 18 to reduce the supercharging pressure, whereby the intake air amount (fresh air) supplied to the engine 1 is reduced. The amount of exhaust discharged from the engine 1 can be reduced, so that even a small-diameter high-pressure turbocharger 6 can correspond to the total exhaust gas amount without excessive rotation, and the high-pressure turbocharger 6 Can be achieved without hindrance, and layout restrictions on the placement of heat-sensitive peripheral devices such as electronic boards can be greatly relaxed. Moreover, it is also possible to by a costly waste gate valve 11 (see FIG. 5) required significant reduction of equipment costs having heat resistance.

  Furthermore, by generating power with the turbine generator 18, the load on the alternator can be reduced, and the capacity of the alternator can be reduced as compared with the prior art. Therefore, the load on the engine 1 side required for driving the alternator can be reduced. Significant improvement in fuel consumption can be achieved.

  Particularly in the present embodiment, power can be efficiently recovered from the intake air A having a high temperature energy before being recovered by the aftercooler 13, while the supercharging pressure is reduced by passing the turbine generator 18 first. Therefore, the cooling load on the aftercooler 13 can be greatly reduced, the capacity of the aftercooler 13 can be reduced to reduce the equipment cost, or the cooling capacity of the aftercooler 13 can be maintained as it is and the intake air can be reduced. The NOx reduction effect can be enhanced by lowering the temperature than before.

  The two-stage turbocharging system of the present invention is not limited to the above-described embodiment. The control of the intake throttle means is not necessarily based on the two-dimensional control map of the fuel injection amount and the engine speed. Of course, various modifications can be added without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Engine 3 High pressure stage turbine 4 High pressure stage compressor 6 High pressure stage turbocharger 8 Low pressure stage turbine 9 Low pressure stage compressor 10 Low pressure stage turbocharger 13 After cooler 17 Bypass flow path 18 Turbine generator 19 Three-way valve (flow path switching means)
A Intake G Exhaust

Claims (2)

  A high-pressure stage turbocharger that operates a high-pressure stage turbine by exhaust gas sent from the engine and supplies intake air compressed by a high-pressure stage compressor to the engine, and a low-pressure stage by exhaust gas sent from the high-pressure stage turbine of the high-pressure stage turbocharger Engine intake flow for supplying intake air from a high-pressure stage compressor to an engine in a two-stage supercharging system comprising a low-pressure stage turbocharger that operates a turbine and compresses intake air compressed by a low-pressure stage compressor to the high-pressure stage compressor A bypass flow path attached to the road, a turbine generator equipped in the bypass flow path, and flow path switching means for appropriately switching the flow of intake air from the high-pressure compressor toward the engine to the bypass flow path side. In the high-speed and high-load region, the flow path switching means Two-stage supercharging system, characterized in that the flow of air is switched to the bypass flow and configured to obtain guidance on the engine were allowed to via the turbine generator from suppressor.   The two-stage turbocharging system according to claim 1, wherein a bypass flow path and a turbine generator are arranged upstream of an aftercooler provided between the high-pressure compressor and the intake manifold.

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