JP2008280861A - Two stage turbo system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two stage turbo system capable of improving the supercharging responsiveness during transition of the engine load increasing. <P>SOLUTION: The two stage turbo system 1 is provided with an intake change-over valve 8 capable of being changed over between an OFF mode of allowing a low pressure compressor 19 to communicate with a high pressure compressor 17 and an engine 2, respectively, and an ON mode of allowing the low pressure compressor 19 to communicate with only the high pressure compressor 17; control means 12 for controlling the intake change-over valve 8 to be changed over to the OFF mode at the time of engine heavy load; and recirculation detecting means 45 for detecting the supercharged intake air recirculating during which a part of the supercharged intake air discharged from an outlet of the high pressure stage compressor 17 passes through the intake change-over valve 8 changed over to the OFF mode and then is sucked into an inlet of the high pressure stage compressor 17. The control means 12 controls the intake change-over valve 8 to be changed over to the ON mode when the recirculation detecting means 45 detects the supercharged intake air recirculating in a case where the intake change-over valve 8 is changed over to the OFF mode in response to increase of the engine load at the time of acceleration of a vehicle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a two-stage turbo system capable of switching between a single-stage supercharging and a two-stage supercharging.

  2. Description of the Related Art Conventionally, there is known a two-stage turbo system in which two turbochargers (turbo) are provided in series to perform two-stage supercharging on an engine such as a vehicle (see, for example, Patent Document 1).

  An example of such a two-stage turbo system will be described with reference to FIGS.

  First, from the exhaust side (turbine side), in the two-stage turbo system 61 of FIG. 9, the high-pressure stage turbine 65 of the high-pressure stage turbocharger 64 is connected to the exhaust manifold 63 of the engine 62. An exhaust gas switching valve (valve) 66 is provided downstream of the high-pressure turbine 65, and the exhaust gas switching valve 66 is also connected to the exhaust manifold 63. A low-pressure stage turbine 68 of a low-pressure stage turbocharger 67 is connected downstream of the exhaust gas switching valve 66. The upstream and downstream of the high-pressure stage turbine 65 are connected by a high-pressure stage turbine bypass pipe 69 for bypassing the high-pressure stage turbine 65, and the exhaust amount passing through the high-pressure stage turbine bypass pipe 69 through the high-pressure stage turbine bypass pipe 69. There is provided a high-pressure stage exhaust regulating valve 70 for regulating the above.

  The movement of the high-pressure turbine 65 and the low-pressure turbine 68 will be described.

  When the high-pressure stage exhaust adjustment valve 70 is fully closed while the exhaust gas switching valve 66 is closed, the entire amount of exhaust gas (exhaust gas) passes through the high-pressure stage turbine 65. The exhaust gas works in the high pressure stage turbine 65, then passes through the low pressure stage turbine 68, and further works in the low pressure stage turbine 68.

  When the high-pressure stage exhaust adjustment valve 70 starts to open, a part of the exhaust gas passing through the high-pressure stage turbine 65 bypasses the high-pressure stage turbine 65 and flows directly into the low-pressure stage turbine 68. Therefore, the work of the high-pressure stage turbine 65 is reduced, and the work of the low-pressure stage turbine 68 is increased. Furthermore, when the exhaust gas switching valve 66 starts to open, the work distribution in the low pressure stage increases.

  When the exhaust gas switching valve 66 is fully opened, the entire amount of exhaust gas bypasses the high-pressure stage turbine 65 and flows to the low-pressure stage turbine 68. Therefore, the high-pressure stage turbine 65 does not work, and only the low-pressure stage turbine 68 does work. Become.

  In this way, the work distribution between the high-pressure turbine 65 and the low-pressure turbine 68 is controlled by adjusting the opening degrees of the high-pressure exhaust gas adjustment valve 70 and the exhaust gas switching valve 66.

  Next, the intake side (compressor side) will be described.

  The high-pressure stage compressor 71 of the high-pressure stage turbocharger 64 and the low-pressure stage compressor 72 of the low-pressure stage turbocharger 67 are arranged with the high-pressure stage compressor 71 on the downstream side and the low-pressure stage compressor 72 on the upstream side, respectively.

  A branch pipe 73 exiting from the outlet of the low-pressure compressor 72 is bifurcated in front of the high-pressure compressor 71, one connected to the inlet of the high-pressure compressor 71, and the other via the high-pressure compressor outlet pipe 74. Connected to the outlet of the high pressure compressor 71.

  An intake switching valve 75 is provided at the junction of the high-pressure compressor outlet pipe 74 on the outlet side of the high-pressure compressor 71 and the branch pipe 73.

  By switching the flow of intake air by the intake air switching valve 75, (a) a path from the low pressure stage compressor 72 through the high pressure stage compressor 71 to the engine 62 (hereinafter referred to as a high pressure stage intake path), and (b) a low pressure stage compressor A path (hereinafter referred to as a low pressure stage intake path) from 72 to the engine 62 without passing through the high pressure stage compressor 71 is formed (see FIG. 10).

  Hereinafter, the state (A) is referred to as “ON” of the intake air switching valve 75, and the state (B) is referred to as “OFF” of the air intake switching valve 75.

  As shown in FIG. 10, the intake air switching valve 75 has a valve body 76 that is pivotally supported at a connection portion between the high-pressure compressor outlet pipe 74 and the branch pipe 73, and the valve body 76 is an air cylinder (not shown) or the like. Driven.

The valve body 76 closes the branch pipe 73 (low pressure stage intake path) when the intake air switching valve 75 is ON. As a result, the intake path becomes the high-pressure stage intake path of (a). On the other hand, when the intake switching valve 75 is OFF, the valve body 76 is positioned at an intermediate position between the low-pressure stage and the high-pressure stage, and the high-pressure stage compressor outlet pipe 74. And both the branch pipes 73 are opened.

  When the intake air switching valve 75 is OFF, both the branch pipe 73 and the high-pressure stage compressor outlet pipe 74 are fully opened, but the high-pressure stage compressor 71 does not perform supercharging work because the high-pressure stage turbine 65 is not working. The intake path thus made becomes the low pressure stage intake path (b).

  The ON / OFF switching timing of the intake switching valve 75 will be described.

  When the high-pressure stage exhaust adjustment valve 70 and the exhaust switching valve 66 are fully closed, the intake side switching valve 75 is turned on on the compressor side to take the high-pressure stage intake path of (a), and the low-pressure stage compressor 72 to the high-pressure stage. Two-stage supercharging through the compressor 71 is performed.

  This is because if the high-pressure stage exhaust adjustment valve 70 and the exhaust switch valve 66 are fully closed, the high-pressure stage turbine 65 rotates if the intake switch valve 75 is turned OFF and the low pressure stage intake path is set to (b). Nevertheless, since there is a path (circuit) in which the amount of air introduced into the high-pressure compressor 71 is small, air passing through the high-pressure compressor 71 does not flow, and the high-pressure turbine 65 may overspeed and be destroyed. It is.

  When the high-pressure stage exhaust adjustment valve 70 is opened at a certain opening and the exhaust switching valve 66 is also less than a certain opening (predetermined opening), the intake side switching valve 75 is turned on on the compressor side and the above (a) Take the high-pressure stage intake route. In this case, a two-stage excess is performed by changing the work distribution ratio between the high-pressure stage turbocharger 64 and the low-pressure stage turbocharger 67, compared to when the high-pressure stage exhaust adjustment valve 70 and the exhaust gas switching valve 66 are fully closed. Pay is done.

  The high-pressure stage intake path is also taken at this time if the high-pressure stage exhaust adjustment valve 70 is opened at a certain opening degree and the exhaust gas switching valve 66 is also less than a certain opening degree. This is because there is no path through which the air supercharged by the high-pressure compressor 71 passes, so that the high-pressure turbine 65 over-rotates or does a wasteful work just to stir the trapped air. .

  When the exhaust switching valve 66 is fully opened from a certain opening degree or more, basically, only the low-pressure stage turbine 68 performs work, and therefore the compressor side is connected to the low pressure stage intake path (the intake switching valve 75) of (b). Is turned off), only the low-pressure stage turbocharger 67 is supercharged.

  This is because if (i) the high-pressure stage intake path (intake switching valve 75 is ON), the supercharged intake air pumped by the low-pressure stage compressor 72 passes through the high-pressure stage compressor 71 toward the engine 62 side. However, since the work of the high-pressure stage turbine 65 is 0, the high-pressure stage turbine 65 is rotated by the high-pressure stage compressor 71, so that the supercharging pressure to the engine 62 (supercharging pressure at the high-pressure stage side outlet) is greatly reduced. It is because it ends up.

  The above control of the high-pressure stage exhaust regulating valve 70, the exhaust switching valve 66, and the intake switching valve 75 indicates each valve opening determined by the rotational speed of the engine 62 and the amount of fuel supplied, or the valve ON / OFF. It is controlled using a computer by MAP. FIG. 4 shows an example of the operating range of each valve 66, 70, 75.

JP-A-4-164125

  When the control of the high pressure exhaust control valve 70, the exhaust switching valve 66, and the intake switching valve 75 is performed by the MAP control method as shown in FIG. 4, the opening / closing timing (ON / OFF timing) of the intake switching valve 75 is also the rotation of the engine 62. It is uniquely determined by the speed and amount of fuel.

  In this MAP control, when the engine load increases from a low load to a high load during acceleration of the vehicle, any of the following phenomena (1) to (3) occurs when the intake switching valve 75 is switched. .

  (1) When the engine load increases gently, MAP control can sufficiently cope with changes in the intake system and the exhaust system.

  (2) When the engine load increases rapidly, it passes through the switching transition region (IV) of the intake switching valve 75 in FIG. 4 in an instant, so that the problem does not appear remarkably and there is no problem with the MAP control.

  (3) When performing rapid acceleration in the middle of (1) and (2), even if the exhaust gas switching valve 66 is set to a constant opening degree (an opening degree at which the intake air switching valve 75 changes from ON to OFF) according to the MAP instruction, The rise of the supercharging pressure of the low-pressure compressor 72 is delayed by the response delay of the low-pressure turbocharger 67 and the inertia of the exhaust.

  If the intake path is switched from the high-pressure stage intake path to the low-pressure stage intake path before the boost pressure of the low-pressure stage compressor 72 rises, the intake air supercharged by the high-pressure stage compressor 71 passes through the intake air switching valve 75 and the high-pressure stage compressor 71. Will be sucked into the entrance again.

  Therefore, until the supercharging pressure of the low-pressure stage compressor 72 increases to a constant pressure or until the rotation of the high-pressure stage turbine 65 sufficiently decreases, the outlet of the high-pressure stage compressor 71 passes through the intake air switching valve 75 to the inlet of the high-pressure stage compressor 71. And some supercharged intake air circulates. This circulating intake air is only heated by the work of the high-pressure compressor 71 and does not contribute to the supercharging work of the engine 62. This phenomenon becomes remarkable in the intake air switching transition region (IV) in FIG.

  When the phenomenon (3) described above occurs, there is a problem that the rise of the supercharging pressure of the low-pressure turbocharger 67 is further delayed, the air becomes insufficient, and soot is generated from the engine 62.

  In addition, when EGR is performed, a sufficient amount of EGR cannot be applied, and there is a problem that NOx emissions also increase at the same time.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a two-stage turbo system that solves the above-described problems and improves the supercharging response at the time of transient when the engine load increases.

  To achieve the above object, the present invention provides a high-pressure stage turbocharger having a high-pressure stage turbine provided in an exhaust passage of an engine and a high-pressure stage compressor provided in an intake passage of the engine, and more than the high-pressure stage turbine. A low-pressure stage turbocharger having a low-pressure stage turbine provided in a downstream exhaust passage and a low-pressure stage compressor provided in an intake passage upstream of the high-pressure compressor; and provided in an intake passage downstream of the high-pressure compressor. Are connected to an intake passage between the high-pressure stage compressor and the low-pressure stage compressor, and communicates an outlet of the low-pressure stage compressor to an inlet of the high-pressure stage compressor and an intake inlet of the engine, and the low-pressure stage Compressor outlet to the above high-pressure stage compressor inlet An intake switching valve that can be switched to ON only for communication, and a control means for controlling the intake switching valve, and the control means turns on the intake switching valve when the engine is under a low load. A two-stage system in which the intake air supercharged by a stage compressor is further supercharged by the high-pressure stage compressor, and when the engine is heavily loaded, the intake air switching valve is turned off and the intake air is supercharged only by the low-pressure stage compressor. In a turbo system, recirculation of supercharged intake air that is re-intaken into the inlet of the high-pressure stage compressor through an intake switching valve in which a part of the supercharged intake air discharged from the high-pressure stage outlet is turned off is detected. A recirculation detecting means for controlling the intake switching valve in response to an increase in engine load during acceleration of the vehicle. Upon detection of a re-circulation of the turbocharged by serial recirculating detecting means, in which switching to ON the intake switching valve.

  Preferably, the exhaust passage is provided in an exhaust passage between the low-pressure turbine and the high-pressure turbine and is connected to an exhaust outlet of the engine. When fully closed, only the exhaust from the outlet of the high-pressure turbine is supplied to the low-pressure turbine. As the valve opening increases, the exhaust flowing from the high-pressure turbine outlet to the low-pressure turbine inlet is reduced, and the exhaust flowing from the engine exhaust outlet to the low-pressure turbine inlet is increased and fully opened. An exhaust switching valve that sometimes flows only the exhaust from the exhaust outlet of the engine to the inlet of the low-pressure turbine, and an exhaust passage upstream of the high-pressure turbine to bypass the high-pressure turbine and the exhaust switching to the high-pressure turbine High-pressure turbine bypass passage connected to the exhaust passage between the valve and the high-pressure turbine bypass passage provided in the fully closed state A high-pressure stage exhaust regulating valve for closing the high-pressure stage turbine bypass passage, and the control means fully closes the exhaust switching valve and the high-pressure stage exhaust regulating valve when the engine is under a low load, and the engine load increases. Increase the valve opening of the high-pressure exhaust adjustment valve, open the exhaust switching valve when the high-pressure exhaust adjustment valve reaches full open, and increase the valve opening as the engine load increases. The intake switching valve is turned OFF when the valve opening degree reaches a predetermined opening degree.

  Preferably, the intake passage has an upstream end connected to the outlet of the low-pressure stage compressor and a downstream side branched into a bifurcated shape at a branching portion, and one of the branched downstream ends is connected to the inlet of the high-pressure stage compressor. A branch passage connected to the intake inlet of the engine at the other downstream end, and a high-pressure compressor outlet passage connecting the outlet of the high-pressure compressor to the branch passage branched to the engine side. A valve is provided at a connection portion between the branch passage branched to the engine side and the high-pressure compressor outlet passage.

  Preferably, the recirculation detection means detects low temperature compressor outlet temperature detection means for detecting the temperature of intake air discharged from the low pressure compressor, and detects the temperature of intake air sucked into the high pressure compressor. The high-pressure stage compressor inlet temperature detecting means.

  Preferably, the control means has a predetermined temperature difference obtained by subtracting the low-pressure stage compressor outlet temperature detected by the low-pressure stage compressor outlet temperature detection means from the high-pressure stage compressor inlet temperature detected by the high-pressure stage compressor inlet temperature detection means. When the temperature difference is exceeded, it is determined that recirculation of the supercharged intake air has occurred in the high pressure compressor.

  Preferably, the low-pressure stage compressor outlet temperature detecting means is provided in a branch passage between the outlet of the low-pressure stage compressor and the branch portion, and the high-pressure stage compressor inlet temperature detecting means is connected to the inlet of the high-pressure stage compressor. It is provided in the branch passage between the branch portions.

  Preferably, the recirculation detection means detects the pressure of the intake air discharged from the high pressure compressor and the high pressure compressor inlet pressure detection means for detecting the pressure of the intake air sucked into the high pressure compressor. And a high-pressure compressor outlet pressure detecting means.

  Preferably, the control means has a predetermined pressure difference obtained by subtracting the high-pressure stage compressor inlet pressure detected by the high-pressure stage compressor inlet pressure detection means from the high-pressure stage compressor outlet pressure detected by the high-pressure stage compressor outlet pressure detecting means. When the pressure difference is exceeded, it is determined that recirculation of the supercharged intake air has occurred in the high pressure compressor.

  Preferably, the high-pressure stage compressor inlet pressure detecting means is provided in a branch passage between the high-pressure stage compressor inlet and the branch portion, and the high-pressure stage compressor outlet pressure detecting means is provided in the high-pressure stage compressor outlet passage. It is provided.

  Preferably, an engine rotation speed detection means for detecting the rotation speed of the engine and a supply fuel amount detection means for detecting the amount of fuel supplied to the engine are provided, and the control means includes the supply fuel When the engine load is obtained based on the supplied fuel amount detected by the amount detection means, and the intake switching valve is turned OFF in accordance with the increase in the engine load, the engine rotation speed detected by the engine rotation speed detection means is When the vehicle is in the middle speed range, the recirculation detection means performs control to switch the intake switching valve to ON based on detection of recirculation of the supercharged intake air.

  The control means turns off the intake air switching valve when the recirculation detection means detects recirculation of the supercharged intake air when the intake air switching valve is turned off in response to an increase in engine load during vehicle acceleration. When the valve opening of the exhaust gas switching valve is equal to or greater than the predetermined valve opening after a predetermined period of time has elapsed, the intake air switching valve may be turned off again.

  According to the present invention, it is possible to improve the supercharging response at the time of transition in which the engine load increases.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The two-stage turbo system of the present embodiment is applied to, for example, a diesel engine (hereinafter referred to as an engine) mounted on a large vehicle such as a truck.

  First, a schematic structure of the two-stage turbo system of the present embodiment will be described based on FIGS.

  The two-stage turbo system 1 of the present embodiment includes an intake passage 3 for supplying intake air to the engine 2, an exhaust passage 4 for discharging exhaust of the engine 2, and intake air (air) supercharged to the engine 2. The high-pressure stage turbocharger 5 and the low-pressure stage turbocharger 6 for supplying gas, the exhaust gas switching valve 7 for switching the exhaust path for driving the low-pressure stage turbocharger 6, and the low-pressure stage turbocharger 6 were supercharged. An intake switching valve 8 for switching the intake path, a high-pressure exhaust adjusting valve 9 for adjusting the exhaust amount passing through the high-pressure turbocharger 5, and an engine rotational speed detecting means for detecting the rotational speed of the engine 2 10, supply fuel amount detection means 11 for detecting the amount of fuel supplied to the engine 2, engine rotation speed detection means 10 and Based on the detection value of the fuel quantity detecting means 11 includes an intake switching valve 8 exhaust switching valve 7 and a control means for respectively controlling the high-pressure stage exhaust control valve 9 (hereinafter, referred to as a computer) 12.

  The engine 2 is provided with an EGR device (not shown). The EGR device returns a part of the exhaust gas in the exhaust passage to the intake passage through the EGR pipe to reduce NOx, and an EGR valve provided in the EGR pipe. The EGR rate is controlled.

  The high-pressure stage turbocharger 5 and the low-pressure stage turbocharger 6 are arranged in series with the high-pressure stage turbocharger 5 facing the engine 2.

  More specifically, the high-pressure stage turbocharger 5 includes a high-pressure stage turbine 16 provided in the exhaust passage 4 and a high-pressure stage compressor 17 provided in the intake passage 3, and the low-pressure stage turbocharger 6 includes a high-pressure stage turbocharger 6. A low-pressure turbine 18 provided in the exhaust passage 4 downstream of the turbine 16 and a low-pressure compressor 19 provided in the intake passage 3 upstream of the high-pressure compressor 17 are provided.

  The exhaust passage 4 has an exhaust manifold 21 connected to each cylinder of the engine 2, a high-pressure turbine inlet pipe 22 that connects the exhaust manifold 21 to the inlet of the high-pressure turbine 16, and a low-pressure outlet of the high-pressure turbine 16. A turbine connection pipe 23 connected to the inlet of the stage turbine 18 and provided with the exhaust switching valve 7, an exhaust introduction pipe 24 connecting the exhaust switching valve 7 to the exhaust manifold 21, and a high pressure stage to bypass the high pressure stage turbine 16. A high pressure turbine bypass pipe (high pressure) for connecting the turbine inlet pipe 22 (the exhaust passage 4 upstream of the high pressure turbine 16) to the turbine connection pipe 23 (the exhaust passage 4 between the high pressure turbine 16 and the exhaust switching valve 7). Stage turbine bypass passage) 25.

  The exhaust switching valve 7 is provided in a turbine connection pipe 23 that forms an exhaust passage 4 between the low-pressure stage turbine 18 and the high-pressure stage turbine 16, and is connected to an exhaust manifold 21 that forms an exhaust outlet of the engine 2 via an exhaust introduction pipe 24. Connected.

  The exhaust gas switching valve 7 has a valve body (not shown) that freely opens and closes between the exhaust manifold 21 and the turbine connection pipe 23 at a specified opening degree.

  Specifically, the exhaust switching valve 7 allows only the exhaust from the outlet of the high-pressure turbine 16 to flow into the inlet of the low-pressure turbine 18 when fully closed, and the low-pressure from the outlet of the high-pressure turbine 16 increases as the valve opening increases. The exhaust gas flowing to the inlet of the stage turbine 18 is reduced, the exhaust gas flowing from the exhaust manifold 21 to the inlet of the low pressure turbine 18 is increased, and only the exhaust gas from the exhaust manifold 21 flows to the inlet of the low pressure turbine 18 when fully opened. The

  The exhaust gas switching valve 7 is connected to a computer 12, and the valve opening degree is continuously controlled based on an opening degree signal (designated opening degree) input from the computer 12.

  The high-pressure stage exhaust adjustment valve 9 is provided in the high-pressure stage turbine bypass pipe 25 and adjusts the amount of exhaust gas flowing through the high-pressure stage turbine bypass pipe 25. The high-pressure stage exhaust regulating valve 9 has a valve body (not shown) that freely opens and closes at a specified opening.

  The high-pressure stage exhaust adjustment valve 9 is configured to close the high-pressure stage turbine bypass pipe 25 when fully closed, and to increase the exhaust gas passing through the high-pressure stage turbine bypass pipe 25 as the valve opening increases.

  The high-pressure stage exhaust regulating valve 9 is connected to a computer 12, and the valve opening is continuously controlled based on an opening signal (designated opening) input from the computer 12.

  The intake passage 3 includes a low-pressure compressor inlet pipe 31 for introducing intake air (air, fresh air) to the inlet of the low-pressure compressor 19, an outlet of the low-pressure compressor 19, an inlet of the high-pressure compressor 17, and an intake inlet of the engine 2. Are connected to the outlet of the low-pressure stage compressor 19, and the downstream side is bifurcated at the branching portion 32, and one of the branched downstream ends is connected to the inlet of the high-pressure stage compressor 17. A branch pipe (branch passage) 33 whose other downstream end is connected to the intake inlet of the engine 2 and a high-pressure compressor outlet pipe (the outlet pipe of the high-pressure compressor 17 connected to the branch pipe 33 branched to the engine 2 side) High-pressure compressor outlet passage) 34.

  The branch pipe 33 includes a low pressure stage compressor outlet pipe 36 that connects the outlet of the low pressure stage compressor 19 to the branch section 32, a high pressure stage compressor inlet pipe 37 that connects the branch section 32 to the inlet of the high pressure stage compressor 17, and the branch section 32. Is connected to the intake switching valve 8 and an engine inlet pipe 39 that connects the intake switching valve 8 to an intake manifold (not shown) that forms the intake inlet of the engine 2.

  In the following description, in order from the outlet of the low-pressure stage compressor 19, the low-pressure stage compressor outlet pipe 36, the branch portion 32, the high-pressure stage compressor inlet pipe 37, the high-pressure stage compressor 17, the high-pressure stage compressor outlet pipe 34, the intake air switching valve 8, and the engine A path that passes through the inlet pipe 39 and reaches the intake manifold is referred to as a high-pressure stage intake path (see the white arrow in FIG. 2). A path from the outlet of the low-pressure compressor 19 to the intake manifold through the low-pressure compressor outlet pipe 36, the intake bypass pipe 38, the intake air switching valve 8 and the engine inlet pipe 39 in this order is called a low-pressure stage intake path (white in FIG. 3). See the drop arrow).

  The intake air switching valve 8 is provided at a connection portion between the high-pressure stage compressor outlet pipe 34 and the intake bypass pipe 38 (the branch pipe 33 branched to the engine 2 side). The intake air switching valve 8 is connected to the outlet of the high pressure compressor 17 via the high pressure compressor outlet pipe 34, and is connected to the outlet of the low pressure compressor 19 via the intake bypass pipe 38 and the branch portion 32.

  As shown in FIG. 2 and FIG. 3, the intake air switching valve 8 is disposed at the junction of the high-pressure compressor outlet pipe 34 and the intake bypass pipe 38 and can be switched ON / OFF and the valve main body 41. Valve drive means (for example, an air cylinder) (not shown) for switching and driving.

  More specifically, a downstream portion of the high-pressure compressor outlet pipe 34, a downstream portion of the intake bypass pipe 38, and an upstream portion of the engine inlet pipe 39 are connected in a Y shape, and a proximal end portion of the valve body 41 is connected to the crotch portion thereof. Is pivotally supported.

  As shown in FIG. 2, when the intake air switching valve 8 is ON, the valve body 41 is located at a closed position where the downstream end of the intake bypass pipe 38 is closed, and the outlet of the low pressure compressor 19 is connected to the high pressure compressor 17. Communicate only to the entrance. When the intake air switching valve 8 is ON, the above-described high-pressure stage intake path is formed.

  On the other hand, as shown in FIG. 3, when the intake air switching valve 8 is OFF, the valve body 41 is positioned at an intermediate position where both the downstream end of the intake bypass pipe 38 and the downstream end of the high-pressure compressor outlet pipe 34 are opened. Then, the outlet of the low pressure compressor 19 is communicated with the inlet of the high pressure compressor 17 and the intake inlet of the engine 2. As the intermediate position, for example, a position where the opening areas of the intake bypass pipe 38 and the high-pressure compressor outlet pipe 34 are equal can be considered.

  When the intake air switching valve 8 is OFF, the above-described low pressure stage intake path is formed when the high pressure stage compressor is inactive.

  The intake air switching valve 8 is connected to a computer 12 and controlled based on an ON / OFF signal input from the computer 12.

  As the engine speed detecting means 10, for example, a crank angle sensor of the engine 2 can be considered. The supply fuel amount detection means 11 may be, for example, an engine ECU that determines the supply fuel amount (fuel injection amount) based on the operating state of the engine 2 (accelerator opening, engine speed, etc.).

  The engine rotation speed detection means 10 and the supply fuel amount detection means 11 are connected to a computer 12 and input detection signals (engine rotation speed, supply fuel amount) to the computer 12. The computer 12 is connected to an air amount detecting means (for example, MAF sensor) 42 and receives an engine air amount (see FIG. 1).

  The computer 12 basically controls the intake switching valve 8 to be turned on / off based on the input engine speed, the amount of supplied fuel, etc., and opens the exhaust switching valve 7 and the high-pressure stage exhaust adjustment valve 9. Control the degree.

  For example, the computer 12 obtains the engine load based on the supplied fuel amount detected by the supplied fuel amount detecting means 11 and switches the intake air switching valve 8 according to the increase in the engine load.

  Basically, when the engine is under a low load (and / or when the engine is running at a low speed), the computer 12 turns on the intake air switching valve 8 and further supercharges the intake air supercharged by the low pressure compressor 19 with the high pressure compressor 17. To pay. On the other hand, at the time of high engine load (and / or at high engine speed), the intake air switching valve 8 is turned OFF, and the intake air is supercharged only by the low pressure compressor 19.

  More specifically, the computer 12 closes the exhaust switching valve 7 and the high-pressure stage exhaust adjustment valve 9 and turns on the intake switching valve 8 when the engine is under a low load, and the engine load increases as the vehicle accelerates. The valve opening of the high-pressure stage exhaust control valve 9 is increased. When the high-pressure stage exhaust control valve 9 reaches full open, the exhaust switching valve 7 is opened and the valve opening is increased as the engine load increases. When the valve opening of the switching valve 7 reaches a predetermined opening, the intake switching valve 8 is turned OFF.

  When the intake switching valve 8 is switched from ON to OFF, for example, when the vehicle is accelerating, the intake air passing through the intake switching valve 8 flows back to the high-pressure compressor 17 through the intake bypass pipe 38 and is recirculated. There is a risk that the supply response will be reduced.

  Therefore, in this embodiment, in order to suppress the recirculation of the supercharged intake air, the recirculation is detected, and the intake air switching valve 8 that is switched off at the time of the recirculation is turned back on again.

  That is, in the two-stage turbo system 1 of the present embodiment, a part of the supercharged intake air discharged from the outlet of the high-pressure stage compressor 17 passes through the intake switching valve 8 turned off and is again sucked into the inlet of the high-pressure stage compressor 17. Recirculation detection means 45 for detecting recirculation of the supercharged intake air.

  The recirculation detection means 45 is connected to the computer 12, and the computer 12 detects the recirculation when the intake switching valve 8 is turned off in response to an increase in engine load (and / or engine speed) during vehicle acceleration. When the recirculation of the supercharged air is detected by the means 45, the intake switching valve 8 is switched to ON.

  The recirculation detection means 45 of the present embodiment includes a low pressure stage compressor outlet temperature detection means (hereinafter referred to as a low pressure stage compressor outlet thermometer) 46 for detecting the temperature of the intake air discharged from the low pressure stage compressor 19, and a high pressure stage. A high pressure compressor inlet temperature detecting means (hereinafter referred to as a high pressure compressor inlet thermometer) 47 for detecting the temperature of the intake air sucked into the compressor 17 is constituted.

  The low-pressure stage compressor outlet thermometer 46 is close to the low-pressure stage compressor 19 upstream of the branch portion 32 of the branch pipe 33 that branches to the high-pressure stage compressor 17 side and the intake air switching valve 8 side downstream of the low-pressure stage compressor 19. Placed in position. That is, the low-pressure stage compressor outlet thermometer 46 is disposed in the low-pressure stage compressor outlet pipe 36, and is preferably disposed close to the outlet of the low-pressure stage compressor 19.

  The high-pressure stage compressor inlet thermometer 47 is disposed at a position near the inlet of the high-pressure stage compressor 17 downstream of the branch portion 32 of the branch pipe 33. That is, the high-pressure stage compressor inlet thermometer 47 is disposed in the high-pressure stage compressor inlet pipe 37, and is preferably disposed close to the inlet of the high-pressure stage compressor 17.

  The low-pressure stage compressor outlet thermometer 46 and the high-pressure stage compressor inlet thermometer 47 are respectively connected to the computer 12 and input detection signals (low-pressure stage compressor outlet temperature Tout and high-pressure stage compressor inlet temperature Tin) to the computer 12.

  The computer 12 subtracts the low-pressure stage compressor outlet temperature Tout detected by the low-pressure stage compressor outlet thermometer 46 from the high-pressure stage compressor inlet temperature Tin detected by the high-pressure stage compressor inlet thermometer 47 to obtain a temperature difference ΔT = Tin−Tout. When the temperature difference ΔT exceeds the predetermined temperature difference Tr, it is determined that the recirculation of the supercharged intake air in the high pressure compressor 17 has occurred.

  Further, when the computer 12 detects the recirculation of the supercharged intake air by the low-pressure stage compressor outlet thermometer 46 and the high-pressure stage compressor inlet thermometer 47 when the intake air switching valve 8 is turned off, the computer 12 When the valve opening degree of the exhaust gas switching valve 7 is equal to or larger than the predetermined opening degree after the lapse of a predetermined period, the intake air switching valve 8 is returned to OFF again.

  Further, the two-stage turbo system 1 of this embodiment includes a transmission means 49 for transmitting (transmitting) detection signals of the low-pressure stage compressor outlet thermometer 46 and the high-pressure stage compressor inlet thermometer 47 to the computer 12. The transmission means 49 may be an electric cable, for example.

  Next, the operation of the two-turbo system of this embodiment will be described using the control flowcharts of FIGS. 4, 5, and 6.

  FIG. 4 is an example of the MAP of the valve opening (instructed opening) of the exhaust gas switching valve 7, the high-pressure stage exhaust adjustment valve 9, and the intake air switching valve 8 determined based on the supplied fuel amount and the engine speed. This MAP is stored in the memory of the computer 12, for example, and the computer 12 MAP-controls the exhaust gas switching valve 7, the high-pressure stage exhaust adjustment valve 9, and the intake air switching valve 8 based on the MAP.

  In FIG. 4, a line LQ is a line indicating the full load fuel amount. A region divided by the line LQ, the vertical axis (supply fuel amount Q), and the horizontal axis (engine rotation speed rpm) is divided into regions (I)-(V), and each region (I)-(V) is divided. Further, the opening degrees of the exhaust gas switching valve 7, the high pressure exhaust gas adjusting valve 9, and the intake air switching valve 8 are set.

  Region (I) is a region where the exhaust gas switching valve 7 is fully closed, the high-pressure stage exhaust regulating valve 9 is fully closed, and the intake air switching valve 8 is set to ON.

  Region (II) is a region where the exhaust gas switching valve 7 is fully closed, the high-pressure stage exhaust regulating valve 9 is opened, and the intake air switching valve 8 is set to ON. In this region (II), the valve opening of the high-pressure stage exhaust regulating valve 9 is fully closed in the line L1, and is set larger as the engine speed is higher and the amount of fuel supplied is larger, and is fully opened in the line L2. Reach.

  Region (III) is a region where the exhaust gas switching valve 7 is in an open state with a predetermined opening or less, the high-pressure stage exhaust adjustment valve 9 is fully opened, and the intake air switching valve 8 is set to ON. In this region (III), the valve opening degree of the exhaust gas switching valve 7 is fully closed in the line L2, and is set to be larger as the engine speed is higher and the amount of fuel supplied is larger. Reach.

  In the above region (I) to region (III), basically, both the high-pressure stage turbocharger 5 and the low-pressure stage turbocharger 6 operate.

  Region (IV) is a region in which the transition is made when the exhaust switching valve 7 is in an open state exceeding a predetermined opening, the high-pressure stage exhaust regulating valve 9 is fully opened, and the intake switching valve 8 is set to OFF. In this region (IV), the opening degree of the exhaust gas switching valve 7 is a predetermined opening degree in the line L3, and is set to be larger as the engine rotational speed is higher and the supplied fuel amount is larger, and reaches the full opening in the line L4. .

  The region (V) is a region where the exhaust gas switching valve 7 is fully opened, the high-pressure stage exhaust regulating valve 9 is fully opened, and the intake air switching valve 8 is set to OFF.

  In the above region (IV) and region (V), basically, only the low-pressure stage turbocharger 6 operates.

  When the one-stage supercharging by the low-pressure stage turbocharger 6 is switched from the two-stage supercharging by the high-pressure stage turbocharger 5 and the low-pressure stage turbocharger 6, the supercharged intake of the high-pressure stage compressor 17 in the region (IV) is changed. There is a risk of recirculation.

  That is, region (III) and region (IV) in the figure are regions from when the high-pressure stage exhaust regulating valve 9 is fully opened and until the exhaust gas switching valve 7 is opened until it is fully opened. In the region (III), the intake air switching valve 8 is ON, and when the exhaust gas switching valve 7 is opened to a predetermined opening in this region (III), the air intake switching valve 8 enters the region (IV) and is turned OFF.

  Here, when the engine load gradually increases from a low load to a high load, there is no problem because the supercharging system follows even if all the valves are opened and closed at the opening set by MAP. Further, when the engine load increases instantaneously from a low load to a high load, it passes through the transition region (IV) of the intake switching valve 8 instantaneously, so even if there is a response delay of the supercharging system, there is little actual harm.

  However, if the engine load increases at an intermediate speed between the two cases, the high-pressure stage exhaust adjustment valve 9 is fully opened and the exhaust gas passing through the high-pressure stage turbine 16 is inertial even if the exhaust gas switching valve 7 is opened to a predetermined opening. The high-pressure compressor 17 does not instantaneously reduce the rotational speed.

  Therefore, the high-pressure compressor 17 still works and the pressure at the outlet (discharge pressure) remains high to some extent. On the other hand, the start-up response of the low-pressure compressor 19 is delayed, and the discharge pressure of the low-pressure compressor 19 does not increase immediately.

  At this time, if the intake air switching valve 8 is immediately turned OFF based on the MAP control in FIG. 4, a part of the supercharged intake air discharged from the outlet of the high pressure compressor 17 passes through the intake air switching valve 8 to the high pressure compressor 17. The supercharged intake air is sucked from the inlet and recirculates through the high-pressure compressor 17 (see FIG. 5).

  Therefore, in order to suppress this recirculation, in this embodiment, the inlet intake temperature (inlet air temperature) Tin of the high-pressure compressor 17 is higher than the outlet intake temperature (outlet air temperature) Tout of the low-pressure compressor 19 by a specified value ( When the temperature exceeds a predetermined temperature difference Tr), it is determined that recirculation has occurred, and on the MAP, the intake switching valve 8 is turned on for a predetermined period even if the intake switching valve 8 is OFF (described later). The flow chart of FIG. 6 will be described by taking 1 second as an example). That is, by closing the downstream end of the intake bypass pipe 38 with the intake switching valve 8, the supercharged air discharged from the high-pressure compressor 17 is prevented from flowing back through the intake bypass pipe 38.

  More specifically, since the temperature of the intake air discharged from the low-pressure compressor 19 rises further when it is supercharged by the high-pressure compressor 17, the intake air temperature at the outlet of the high-pressure compressor 17 is excessive by the low-pressure compressor 19. It is higher than the temperature Tout of the supplied intake air.

  When the high-temperature air discharged from the high-pressure compressor 17 is recirculated to the inlet of the high-pressure compressor 17 via the intake air switching valve 8, the high-pressure compressor inlet intake temperature Tin rises higher than the low-pressure compressor outlet intake temperature Tout. .

  In this embodiment, this phenomenon is detected and the intake air switching valve 8 is controlled to prevent recirculation of the intake air sucked back from the outlet of the high pressure compressor 17 to the inlet of the high pressure compressor 17, thereby allowing the engine 2 It is possible to suppress deterioration of the supply of supercharged intake air (air) to the intake air switching transition region (IV).

  Thus, there may be a case where the suction side sucks back the pressurized discharge air depending on the state of the supercharger system such as steady operation or a transient state, so it is extremely difficult to determine whether the intake switching valve 8 can be switched ON / OFF. It becomes important, and whether it is possible or not is not uniquely determined by the engine speed, fuel load, or the like.

  In the present embodiment, as shown in FIG. 4, switching from the two-stage supercharging to the first-stage supercharging (the switching from the ON to the OFF of the intake air switching valve 8) is performed in the medium speed range of the engine 2. Yes. Therefore, when the engine speed detected by the engine speed detecting means 10 is in the middle speed range, the computer 12 turns on the intake air switching valve 8 based on the detection of the recirculation of supercharged air by the recirculation detecting means 45. Switching control is performed.

  Next, an example of the operation of the two-stage turbo system 1 of the present embodiment will be described in detail based on the flowchart of FIG. The flowchart of FIG. 6 is executed by the computer 12.

  In step S1, the key switch is turned on and the operation is started.

  After step S1, the computer 12 controls the exhaust switching valve 7, the intake switching valve 8, and the high-pressure stage exhaust adjustment valve 9 by MAP based on the MAP shown in FIG. During the MAP control, when the engine speed and the amount of fuel supplied enter the region (IV) in FIG. 4, the computer 12 switches the intake air switching valve 8 to OFF and proceeds to step S2.

In step S2, the engine speed detecting means 10 measures the engine speed Nrpm, the supplied fuel quantity detecting means 11 measures the supplied fuel quantity Qmm ³ / st charged into the engine 2, and these measured values are stored in the computer 12. Is input.

  In step S3, the computer 12 opens the valve opening of the high-pressure stage exhaust regulating valve 9 and the valve opening of the exhaust gas switching valve 7 from MAP in FIG. 4 based on the conditions (engine speed, fuel supply amount) measured in step S2. And the ON / OFF of the intake air switching valve 8 is read.

  In step S4, the computer 12 controls the high pressure stage exhaust regulating valve 9 and the exhaust switching valve 7 to values read by the MAP.

  In step S5, the computer 12 determines that the opening degree of the exhaust gas switching valve 7 read in step S3 is an intermediate opening degree (in this example, an opening degree exceeding 0% (fully closed) and less than 100% (fully opened)). The process proceeds to step S6.

  In step S <b> 6, the computer 12 reads the low-pressure stage compressor outlet temperature Tout from the low-pressure stage compressor outlet thermometer 46 and reads the high-pressure stage compressor inlet temperature Tin from the high-pressure stage compressor inlet thermometer 47.

  In step S7, the computer 12 calculates the temperature difference ΔT = subtracting the low-pressure compressor outlet temperature Tout from the high-pressure compressor inlet temperature Tin based on the low-pressure compressor outlet temperature Tout and the high-pressure compressor inlet temperature Tin read in step S6. Calculate Tin-Tout.

  In step S8, the computer 12 determines whether or not the temperature difference ΔT exceeds a predetermined temperature (also referred to as a prescribed value, 5 ° C. in the illustrated example) Tr. If the temperature difference ΔT exceeds the predetermined temperature Tr, the high-pressure stage turbocharger 5 is still operating, so the high-pressure stage air path is opened regardless of the MAP instruction in step S9. That is, in step S9, the computer 12 sets the intake air switching valve 8 to ON.

  On the other hand, if there is almost no temperature difference ΔT in step S8, the high-pressure stage turbocharger 5 has not been operated, so the low-pressure stage intake path is opened in step S10. That is, when the temperature difference ΔT is equal to or lower than the predetermined temperature Tr in step S8, the computer 12 sets the intake air switching valve 8 to OFF in step S10.

  In step S11 and step S13, the intake air switching valve 8 is fixed to ON or OFF for a predetermined period (in this example, 1 second). This predetermined period is actually determined by experiment.

  Specifically, the computer 12 determines whether or not the timer T0 is 0 seconds (whether or not it exceeds 0 seconds) in step S11. If the timer is 0 seconds, it means that the engine has entered the intake switching transition region (IV) for the first time. Therefore, the timer T0 is operated in step S12, the process returns to step S2, and the measurement of the engine speed and the amount of supplied fuel is started again. To do.

  On the other hand, when the timer T0 exceeds 0 seconds, the process proceeds to step S13.

  In step S13, the computer 12 determines whether or not the timer T0 is less than 1 second. If the timer T0 is operating for 1 second or longer, the timer T0 is stopped and reset in step S14, and the intake switching valve 8 is set to ON or OFF instructed by MAP in step S15 and controlled. Then, it returns to step S2 and starts measurement again.

  If the timer T0 is less than 1 second in step S13, the computer 12 fixes the state of the intake air switching valve 8 to ON or OFF, returns to step S2 again, and starts measurement.

  If the exhaust gas switching valve 7 is not at the intermediate opening degree in step S5, the computer 12 proceeds to step S16 and determines whether or not the timer is operating. If the timer T0 is in operation for less than 1 second in step S16, it is a period during which the intake switching valve 8 is fixed to ON or OFF, so the process returns to step S2 and the high-pressure stage exhaust adjustment valve 9 and the exhaust switching valve 7 are returned. Control only.

  As a result, the intake air switching valve 8 is fixed during a transition in which the engine load increases as the vehicle accelerates.

  For example, during a transition during acceleration of the vehicle, first, in the first control cycle, it is determined in step S5 that the exhaust switching valve 7 is at the intermediate opening (region III or region IV), and in step S9, the intake switching valve 8 is turned on. It can be switched on. In the next control cycle, it is determined in step S5 that the exhaust gas switching valve 7 is fully open (region V), and the process returns to step S2 via step S16. Steps S2 to S16 are repeated until the timer T0 becomes 1 second or longer (until a predetermined period elapses), and the intake switching valve 8 is fixed to ON for the predetermined period.

  On the other hand, if the timer T0 is 1 second or longer in step S16, the timer T0 is stopped and reset in step S14, and then the process proceeds to step S15 to control the intake switching valve 8 to ON or OFF indicated by MAP. .

  As described above, in the two-stage turbo system of the present embodiment, a part of the supercharged intake air (air) is recirculated along the path from the outlet of the high-pressure compressor 17 through the intake air switching valve 8 to the inlet of the high-pressure compressor 17. In this case, the intake switching valve 8 is not turned OFF even in the transition region (IV) of the intake switching valve 8, and the abnormal response delay of the supercharging pressure is avoided by utilizing the high-pressure stage intake path for a predetermined time. Can be suppressed.

  That is, at the time of a transient when the engine load increases, the supercharging response can be improved in accordance with the transient state, and soot can be suppressed. Moreover, when operating EGR, NOx can be suppressed.

  In addition, by stopping the recirculation of the supercharged air in the high-pressure compressor 17 at an early stage, it is possible to reliably secure the supercharged intake by suppressing the decrease in the supercharged intake of the engine 2.

  Further, by determining whether or not a part of the supercharged air is recirculated, by comparing the intake air temperature at the inlet of the high pressure compressor 17 and the intake air temperature at the outlet of the low pressure compressor 19, Recirculation can be reliably detected.

[Other Embodiments]
Next, a two-stage turbo system according to another embodiment will be described with reference to FIGS.

  The present embodiment is substantially the same as the above-described embodiment of FIG. 1 except for the configuration of the recirculation detection means. Accordingly, the same elements as those in the above-described embodiment are given the same reference numerals in the drawings, and detailed description thereof is omitted.

  As shown in FIG. 7, in the two-stage turbo system 51 of the present embodiment, it is determined whether or not the high-pressure stage compressor 17 is operating based on the pressure difference between the inlet side and the outlet side of the high-pressure stage compressor 17. Determine recharging of supercharged intake air.

  That is, the recirculation detection means 52 includes a high pressure compressor inlet pressure detection means (hereinafter referred to as a high pressure compressor inlet pressure gauge) 53 for detecting the pressure of the intake air sucked into the high pressure compressor 17, and the high pressure compressor 17. High pressure compressor outlet pressure detection means (hereinafter referred to as a high pressure compressor outlet pressure gauge) 54 for detecting the pressure of the intake air discharged from the engine.

  The high pressure stage compressor inlet pressure gauge 53 is close to the high pressure stage compressor 17 downstream of the branch portion 32 of the branch pipe 33 that branches to the high pressure stage compressor 17 side and the intake air switching valve 8 side downstream of the low pressure stage compressor 19. Placed in position. In other words, the high-pressure stage compressor inlet pressure gauge 53 is arranged in the high-pressure stage compressor inlet pipe 37, and is preferably arranged close to the inlet of the high-pressure stage compressor 17.

  The high pressure compressor outlet pressure gauge 54 is disposed downstream of the high pressure compressor 17 and upstream of the intake air switching valve 8. That is, it is disposed at the high-pressure stage compressor outlet pipe 34, and is preferably disposed close to the outlet of the high-pressure stage compressor 17.

  The high-pressure stage compressor inlet pressure gauge 53 and the high-pressure stage compressor outlet pressure gauge 54 are connected to the computer 12 via a transmission means 49 such as an electric cable, and the computer 12 detects detection signals (high-pressure stage compressor inlet pressure Pin, high-pressure stage compressor). Each of the outlet pressures Pout) is input.

  The computer 12 subtracts the high-pressure stage compressor inlet pressure Pin detected by the high-pressure stage compressor inlet pressure gauge 53 from the high-pressure stage compressor outlet pressure Pout detected by the high-pressure stage compressor outlet pressure gauge 54 to obtain a pressure difference ΔP = Pout−Pin. When the pressure difference ΔP exceeds the predetermined pressure difference Pr, it is determined that the recirculation of the supercharged intake air in the high pressure compressor 17 has occurred. The predetermined pressure difference Pr is less than the suction negative pressure of the high-pressure compressor 17 and is at most about several kPa.

  Furthermore, when the high-pressure compressor outlet pressure Pout is higher than the inlet pressure Pin by a predetermined pressure difference Pr (specified value) when the intake air switching valve 8 is switched to OFF, the computer 12 (see FIG. 8 described later). In this flowchart, the explanation will be made by taking 1 second as an example.) The intake switching valve 8 is turned ON to make use of the high-pressure stage intake path.

  As a result, the recirculation of the intake air returning from the outlet of the high pressure compressor 17 to the inlet is prevented, and the supply of the intake air to the engine 2 can be prevented from deteriorating in the intake air switching transition region (IV).

  Thus, since there may occur a state in which the suction side sucks back the pressurized discharged intake air (air) depending on the state of the turbocharger system such as steady operation or a transient state, whether or not the intake switching valve 8 can be switched on / off. Judgment is extremely important, and the decision as to whether or not it is possible is not uniquely determined by engine speed, fuel load, or the like.

  Next, an example of the operation of the two-stage turbo system 51 of the present embodiment will be described in detail based on the flowchart of FIG.

  The flowchart of FIG. 8 differs from the flowchart of FIG. 6 described above in steps S106 to S108. Therefore, only step S106 to step S108 will be described.

  In step S106, the computer 12 reads the high-pressure stage compressor inlet pressure Pin from the high-pressure stage compressor inlet pressure gauge 53 and also reads the high-pressure stage compressor outlet pressure Pout from the high-pressure stage compressor outlet pressure gauge 54.

  In step S107, the computer 12 determines a pressure difference ΔP = subtracting the high-pressure compressor inlet pressure Pin from the high-pressure compressor outlet pressure Pout based on the high-pressure compressor inlet pressure Pin and the high-pressure compressor outlet pressure Pout read in step S106. Pout-Pin is calculated.

  In step S108, the computer 12 determines whether or not the obtained pressure difference ΔP exceeds a predetermined pressure (also referred to as a prescribed value, 2 kPa in the illustrated example) Pr. When the pressure difference ΔP exceeds the predetermined pressure Pr, the high-pressure stage turbocharger 5 is still operating, so the high-pressure stage air path is opened regardless of the MAP instruction in step S9. That is, in step S9, the computer 12 sets the intake air switching valve 8 to ON.

  On the other hand, when there is almost no pressure difference ΔP in step S108, the high-pressure stage turbocharger 5 has not been operated, so the low-pressure stage intake path is opened in step S10. That is, when the pressure difference ΔP is equal to or smaller than the predetermined pressure Pr in step S108, the computer 12 sets the intake air switching valve 8 to OFF in step S10.

  In this embodiment, the same effect as that of the above-described embodiment of FIG. 1 can be obtained.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, in the embodiment of FIG. 1, whether or not the high pressure compressor 17 is in operation due to the temperature of the recirculated intake air that flows backward from the intake air switching valve 8 to the inlet of the high pressure compressor 17 (whether recirculation has occurred). I was judged. Therefore, it is conceivable to provide a thermometer in the intake bypass pipe 38 instead of the high-pressure stage compressor inlet thermometer 47 provided in the high-pressure stage compressor inlet pipe 37.

  In the embodiment of FIG. 7, it is determined whether or not the high pressure compressor 17 is operating (whether recirculation has occurred) based on the pressure difference between the inlet pressure and the outlet pressure of the high pressure compressor 17. However, the present invention is not limited to this, and the occurrence of recirculation may be determined based on the pressure difference between the outlet pressure of the low-pressure compressor 19 and the inlet pressure of the high-pressure compressor 17. For example, instead of the high-pressure stage compressor inlet pressure gauge 53 provided in the high-pressure stage compressor inlet pipe 37, a pressure gauge may be provided in the low-pressure stage compressor outlet pipe 36.

FIG. 1 is a schematic configuration diagram of a two-stage turbo system according to an embodiment of the present invention. FIG. 2 is a view for explaining the operation of the intake air switching valve of the present embodiment, and shows the time when the intake air switching valve is ON. FIG. 3 is a view for explaining the operation of the intake air switching valve of the present embodiment, and shows the time when the intake air switching valve is OFF. FIG. 4 is a diagram for explaining an example of the control MAP of the exhaust gas switching valve, the high-pressure stage exhaust adjustment valve, and the intake air switching valve according to the present embodiment. FIG. 5 is a view for explaining recirculation of intake air. FIG. 6 is an example of a flowchart of the two-stage turbo system of the present embodiment. FIG. 7 is a schematic configuration diagram of a two-stage turbo system according to another embodiment. FIG. 8 is an example of a flowchart of a two-stage turbo system according to another embodiment. FIG. 9 is a schematic configuration diagram of a conventional two-stage turbo system. FIG. 10 is a diagram for explaining the operation of a conventional intake switching valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 51 Two-stage turbo system 2 Engine 3 Intake passage 4 Exhaust passage 5 High-pressure stage turbocharger 6 Low-pressure stage turbocharger 7 Exhaust switching valve 8 Intake switching valve 9 High-pressure stage exhaust adjustment valve 12 Control means 16 High-pressure stage turbine 17 High-pressure stage compressor 18 Low-pressure turbine 19 Low-pressure compressor 25 High-pressure turbine bypass passage 45, 52 Recirculation detection means

Claims (11)

A high-pressure stage turbocharger having a high-pressure stage turbine provided in the exhaust passage of the engine and a high-pressure stage compressor provided in the intake passage of the engine;
A low-pressure stage turbocharger having a low-pressure stage turbine provided in an exhaust passage downstream of the high-pressure stage turbine and a low-pressure stage compressor provided in an intake passage upstream of the high-pressure stage compressor;
It is provided in an intake passage downstream of the high pressure compressor and is connected to an intake passage between the high pressure compressor and the low pressure compressor, and an outlet of the low pressure compressor is connected to an inlet of the high pressure compressor and an intake air of the engine. An intake switching valve that can be switched between an OFF communicating with each of the inlets and an ON communicating the outlet of the low-pressure compressor only with the inlet of the high-pressure compressor;
Control means for controlling the intake air switching valve,
When the engine is under a low load, the control means turns on the intake air switching valve and further supercharges the intake air supercharged by the low pressure stage compressor with the high pressure stage compressor. In a two-stage turbo system where the intake air is supercharged with only the low-pressure compressor turned off,
Recirculation for detecting recirculation of supercharged intake air that is re-intaken into the inlet of the high pressure compressor through an intake switching valve in which part of the supercharged intake air discharged from the outlet of the high pressure compressor is turned off A detection means,
The control means turns off the intake air switching valve when the recirculation detection means detects recirculation of the supercharged intake air when the intake air switching valve is turned off in response to an increase in engine load during vehicle acceleration. 2-stage turbo system characterized by switching to ON. It is provided in an exhaust passage between the low-pressure turbine and the high-pressure turbine and is connected to the exhaust outlet of the engine. When fully closed, only the exhaust from the outlet of the high-pressure turbine flows to the inlet of the low-pressure turbine. As the valve opening increases, the exhaust flowing from the outlet of the high pressure turbine to the inlet of the low pressure turbine is reduced, the exhaust flowing from the exhaust outlet of the engine to the inlet of the low pressure turbine is increased, and the engine is fully opened. An exhaust switching valve for flowing only the exhaust from the exhaust outlet of the low-pressure turbine to the inlet of the low-pressure turbine,
A high-pressure turbine bypass passage that connects an exhaust passage upstream of the high-pressure stage turbine to an exhaust passage between the high-pressure turbine and the exhaust switching valve to bypass the high-pressure turbine; A high-pressure stage exhaust regulating valve that is provided and closes the high-pressure stage turbine bypass passage when fully closed,
When the engine is under low load, the control means fully closes the exhaust gas switching valve and the high-pressure stage exhaust regulating valve, and increases the opening of the high-pressure stage exhaust regulating valve as the engine load increases. When the adjustment valve reaches full open, the exhaust switching valve is opened and the valve opening is increased as the engine load increases, and the intake switching valve is opened when the exhaust switching valve reaches a predetermined opening. The two-stage turbo system according to claim 1, wherein is turned off. The intake passage has an upstream end connected to the outlet of the low-pressure stage compressor, and a downstream side branched into a bifurcated shape at a branch portion, and one of the branched downstream ends is connected to the inlet of the high-pressure stage compressor. A downstream end of which is connected to the intake inlet of the engine, and a high pressure compressor outlet passage that connects the outlet of the high pressure compressor to the branch passage branched to the engine side,
3. The two-stage turbo system according to claim 1, wherein the intake air switching valve is provided at a connection portion between a branch passage branched to the engine side and the high-pressure compressor outlet passage.   The recirculation detection means includes a low pressure stage compressor outlet temperature detection means for detecting the temperature of the intake air discharged from the low pressure stage compressor, and a high pressure stage for detecting the temperature of the intake air sucked into the high pressure stage compressor. The two-stage turbo system according to any one of claims 1 to 3, further comprising a compressor inlet temperature detecting means.   The control means is configured such that a temperature difference obtained by subtracting the low-pressure stage compressor outlet temperature detected by the low-pressure stage compressor outlet temperature detection means from the high-pressure stage compressor inlet temperature detected by the high-pressure stage compressor inlet temperature detection means has a predetermined temperature difference. 5. The two-stage turbo system according to claim 4, wherein when it exceeds, the recirculation of the supercharged intake air in the high-pressure stage compressor is determined to occur.   The low-pressure stage compressor outlet temperature detecting means is provided in a branch passage between the outlet of the low-pressure stage compressor and the branch part, and the high-pressure stage compressor inlet temperature detecting means is provided at the inlet of the high-pressure stage compressor and the branch part. The two-stage turbo system according to claim 4 or 5, provided in a branch passage between   The recirculation detecting means includes a high pressure compressor inlet pressure detecting means for detecting the pressure of the intake air sucked into the high pressure compressor, and a high pressure stage for detecting the pressure of the intake air discharged from the high pressure compressor. The two-stage turbo system according to any one of claims 1 to 3, further comprising a compressor outlet pressure detecting means.   The control means is configured such that a pressure difference obtained by subtracting a high-pressure stage compressor inlet pressure detected by the high-pressure stage compressor inlet pressure detection means from a high-pressure stage compressor outlet pressure detected by the high-pressure stage compressor outlet pressure detecting means has a predetermined pressure difference. The two-stage turbo system according to claim 7, wherein when it exceeds, it is determined that recirculation of the supercharged intake air has occurred in the high-pressure stage compressor.   The high-pressure stage compressor inlet pressure detecting means is provided in a branch passage between the inlet of the high-pressure stage compressor and the branch portion, and the high-pressure stage compressor outlet pressure detecting means is provided in the high-pressure stage compressor outlet passage. The two-stage turbo system according to claim 7 or 8. Engine rotation speed detection means for detecting the rotation speed of the engine, and supply fuel amount detection means for detecting the amount of fuel supplied to the engine,
The control means obtains the engine load based on the supplied fuel amount detected by the supplied fuel quantity detection means, and detects the engine rotation speed when the intake switching valve is turned OFF in response to the increase in the engine load. 10. The switching control to turn on the intake switching valve based on detection of recirculation of the supercharged intake air by the recirculation detection means when the engine rotation speed detected by the means is in a medium speed range. The two-stage turbo system described in 1.   The control means turns off the intake air switching valve when the recirculation detection means detects recirculation of the supercharged intake air when the intake air switching valve is turned off in response to an increase in engine load during vehicle acceleration. 3. The two-stage turbo system according to claim 2, wherein when the valve opening degree of the exhaust gas switching valve is equal to or greater than the predetermined opening degree after the predetermined period has elapsed, the intake air switching valve is turned off again.

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