JP2011099332A - Two-stage supercharging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-stage supercharging system capable of reducing the diameter of a high pressure stage turbocharger with no hindrance without using waste gate piping. <P>SOLUTION: The waste gate piping and a waste gate valve used for a conventional two-stage supercharging system are eliminated, and an intake throttle valve 17 (an intake throttle means) for throttling an intake amount (flow rate of intake air A) supplied to an engine 1 from a high pressure stage compressor 4 is provided between an after-cooler 13 and an intake manifold 5 to throttle the intake amount by the intake throttle valve 17 in a high-speed high-load region of the engine 1 where exhaust G has been diverted to the waste gate piping in a conventional system. <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. In addition to simply complicating the piping configuration, adding additional wastegate piping 7 has a great restriction on the layout because peripheral devices such as electronic boards that are vulnerable to heat cannot be placed nearby, There is also a problem that the equipment cost increases due to the waste gate valve 11 having to have sufficient heat resistance.

  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 having a low-pressure stage turbocharger that operates a low-pressure stage turbine by exhaust gas and supplies intake air compressed by a low-pressure stage compressor to the high-pressure stage compressor, the intake air is supplied from the high-pressure stage compressor to the engine Intake throttle means for reducing the intake air amount is provided, and the intake air amount is restricted by the intake air throttle means in a high-speed and high-load region of the engine.

  Thus, in this case, if the intake amount is narrowed by the intake throttle means in the high speed and high load region of the engine, the pressure difference between the front and rear of the intake throttle means increases as the intake throttle means is reduced. As the pressure decreases, the amount of intake air (fresh air) supplied to the engine is reduced and the exhaust discharged from the engine is also reduced. Even with a small-diameter high-pressure turbocharger, the entire exhaust gas does not rotate excessively. It becomes possible to cope with the amount of gas.

  In general, in the case of single-stage supercharging, the supercharging pressure in the high-speed and high-load region of the engine is high and the turbine speed is high. The compressor peripheral speed limit is imposed, and intake throttling cannot be performed in the high speed and high load region.

However, in the case of two-stage supercharging, the supercharging pressure in the high-pressure turbocharger in the high-speed and high-load region is lower and the turbine speed is lower than in the case of single-stage supercharging. Even if it is narrowed down, it can be operated in a region where a sufficient margin to the compressor peripheral speed limit can be secured, and there is no concern that the compressor peripheral speed limit will be imposed.
In addition, as the intake air amount is reduced by the intake air throttle means, the operating region moves to the high efficiency region side of the high pressure stage compressor, so the compressor efficiency improves (single stage turbocharging reduces efficiency) and fuel consumption deteriorates. It will be very slight.

  According to the two-stage turbocharging system of the present invention, it is possible to reduce the diameter of the high-pressure turbocharger without hindrance by using the intake throttle means without using the wastegate pipe, so that the pipe can be reduced without any trouble. The configuration can be simplified and the layout constraints on the placement of heat-sensitive peripheral devices such as electronic boards can be greatly relaxed, and there is no need for expensive heat-resistant wastegate valves. As a result, it is possible to achieve an excellent effect that the facility cost can be greatly reduced.

It is the schematic which shows an example of the form which implements this invention. It is a graph which shows the effect of an intake throttle. It is a graph which shows that the driving | operation within the limit value of the maximum in-cylinder pressure is attained. It is an operation diagram of the high-pressure stage turbocharger when the intake throttle is applied. 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 to 4 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. While eliminating the wastegate piping 7 (see FIG. 5) and the wastegate valve 11 (see FIG. 5) used in the supercharging system, the intake air that narrows the intake air amount supplied from the high-pressure compressor 4 to the engine 1 is reduced. A throttle valve 17 (intake throttle means) is provided between the aftercooler 13 and the intake manifold 5, and a high-speed and high-load region of the engine 1 that conventionally shunts the exhaust G to the wastegate pipe 7 (see FIG. 5) ( The intake air amount is narrowed down by the intake throttle valve 17 in the operation region indicated by cross-hatching in the graph of FIG.

  In the example shown here, the intake throttle valve 17 is controlled by a control signal 18a from a control device 18 constituting an engine control computer (ECU: Electronic Control Unit). If a two-dimensional control map of the fuel injection amount and the rotational speed of the engine 1 is incorporated in 18 and the intake throttle valve 17 remains open, the high-pressure turbine 3 rotates excessively and the maximum in-cylinder pressure of each cylinder is limited. A control signal 18a for narrowing the intake throttle valve 17 according to the opening degree read from the two-dimensional control map may be output from the control device 18 in a high-speed and high-load region where the value is expected to be exceeded. .

  Thus, in such a case, if the intake A amount is narrowed by the intake throttle valve 17 in the high speed and high load region of the engine 1, the differential pressure before and after the intake throttle valve 17 is reduced as the intake throttle valve 17 is narrowed. This greatly occurs and the pressure (supercharging pressure) of the intake manifold 5 decreases (see the graph of FIG. 2), and the intake A amount (fresh air amount) supplied to the engine 1 is reduced accordingly (FIG. 3). The exhaust G discharged from the engine 1 is also reduced, and the small-diameter high-pressure turbocharger 6 can cope with the total exhaust gas amount without excessive rotation.

  At this time, if the intake A amount is appropriately throttled by the intake throttle valve 17, the maximum in-cylinder pressure Pmax in each cylinder of the engine 1 can be suppressed to a limit value (allowable Pmax) or less. As in the case of using (see FIG. 5), it is possible to avoid the situation where the maximum in-cylinder pressure Pmax of each cylinder of the engine 1 exceeds the limit value (allowable Pmax) and the operation becomes impossible.

  In general, in the case of single-stage supercharging, the supercharging pressure in the high-speed and high-load region of the engine 1 is high and the turbine speed is high. Due to the increase, the compressor peripheral speed is limited, and the intake A throttling cannot be performed in the high speed and high load region.

  However, in the case of two-stage supercharging, the supercharging pressure in the high-pressure turbocharger 6 in the high-speed and high-load region is lower and the turbine speed is lower than in the case of single-stage supercharging. As described above, even if the intake air A is throttled in the high speed and high load region, it can be operated in a region (a point indicated by a triangle in FIG. 4) that can secure a sufficient margin until the peripheral speed of the high-pressure compressor 4 is limited. There is no worry of it taking.

  Further, as the intake A amount is reduced by the intake throttle valve 17, the operating region moves in the direction indicated by the arrow X in the graph of FIG. 4, which moves to the high efficiency region side of the high-pressure stage compressor 4. Therefore, the compressor efficiency is improved (the efficiency is reduced in the single-stage supercharging), and the deterioration of the fuel consumption is extremely suppressed.

  Therefore, according to the above embodiment, the diameter of the high-pressure turbocharger 6 can be reduced without any trouble by reducing the intake A amount by the intake throttle valve 17 without using the wastegate pipe 7 (see FIG. 5). As a result, the piping configuration can be simplified, the restrictions on the layout related to the arrangement of peripheral devices that are vulnerable to heat, such as an electronic board, can be greatly relaxed, and the cost is high with heat resistance. Since the waste gate valve 11 (see FIG. 5) is also unnecessary, the equipment cost can be greatly reduced.

  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 17 Intake throttle valve (intake throttle means)
18 Control device 18a Control signal A Intake G Exhaust

Claims (1)

  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 In a two-stage turbocharging system that includes 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, the amount of intake air supplied from the high-pressure stage compressor to the engine is narrowed down. A two-stage turbocharging system comprising an intake throttle means, wherein the intake air quantity is reduced by the intake throttle means in a high speed and high load region of an engine.

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