JPH03275940A - Control for engine equipped with supercharger - Google Patents

Abstract

PURPOSE:To prevent the overrunning of a main turbocharger and protect a turbocharger by compulsorily opening an exhaust bypass valve in a no-loaded state. CONSTITUTION:It is detection-judged if an engine 1 is substantially in no-load state or not, from the gear position signal of a transmission, clutch signal, etc., and when the substantially no-load state is judged, an exhaust bypass valve 41 is always compulsorily opened. In a loaded state, the compulsory valve opening of the exhaust bypass valve 41 is not executed. Accordingly, before the no-load racing, the exhaust bypass valve 41 is in the compulsorily opened state, and even if racing is executed in this state, a portion of the exhaust gas is allowed to flow into a subturbocharger 8 side, and the quantity of the exhaust gas supplied to a main turbocharger 7 side is reduced by that portion, and the overrunning of the main turbocharger 7 is properly prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a supercharged engine in which a main turbocharger and a subturbocharger are arranged in parallel.

[Prior art] Two turbochargers, a main turbocharger and a sub-turbocharger, are arranged in parallel to the engine body, and in the low speed range, only the main turbocharger is operated to form a single turbocharger, and in the high speed range, both turbochargers are operated. A supercharged engine employing a so-called two-stage turbo system is known (for example, Japanese Patent Application Laid-Open Nos. 112734-1982 and 259722-1980). The configuration of this type of supercharged engine is shown in FIG. 6, for example. The main turbocharger (T
/C-1>92 and sub-turbocharger (T/C-2>9
3 are provided in parallel. The intake and exhaust systems connected to the sub-turbocharger 93 each include an intake switching valve 94,
An exhaust switching valve 95 is provided, and in low series, an intake switching valve 94 is provided.
, by closing the exhaust switching valve 95 at both ε, only the charger 92 is operated for supercharging, and the high speed range (
Both are fully open. For each 6-6, the auxiliary turbocharger i.93 also performs supercharging operation, and the two turbochargers
- The camera can be activated.

In such a two-stage turbocharger I8 engine, the exhaust switching valve 95 must be slightly opened or the exhaust switching An exhaust bypass passage 16 bypassing the valve 95 is provided (), and an exhaust bypass valve (not shown) is installed therein. By opening the exhaust bypass valve ε, a part of the exhaust gas is allowed to flow to the sub-turbocharge meter 93. Sub-turbocharger 9
It is possible to increase the run-up rotation speed of 3.1. Therefore, it is important to obtain a smooth transition between 17 and 8 o'clock in the turbo charge.

[Problem to be solved by the invention J] In the above-mentioned two-stage turbo system,
In particular, when the first engine is in a no-load state, that is, when the vehicle is stopped, and when the transmission is in the 21-toral position or in the idle state with the clutch disconnected, the following J.-There is a risk of causing problems.

First 1. L iii: When racing with no load and six colors,
Inversion number 1-stomach, 11゛゛G:ul <,-shunout)
1. Switch to 1 turbo engine, 2 turbos from 7N7 to 7H, and change the timing of IJ and exhaust valve cutter H as shown in Figure 7. Etc. (,: The nearness of the cut-off H control principle 15, Ak-T1 daughter for the exhaust cut-off valve (for example, Dai A? Noram type i7 Sy-
:h,',,1m-Y) to f-IU + father has a positive pressure transmission delay'S-[Thus, 2 turbochargers), 2 is not switched and 1 turbocharger is operated up to 4 or higher high speed range. If this happens, the normally active main turbo engine V-SHI will be 1-' over the allowable value (13"E).

Further, in a supercharged engine as shown in FIG. 6, a butterfly valve is often used for the exhaust switching valve 95 (as shown in FIG. 8). This J, eel butterfly valve 9
When using 5, the difference in thermal expansion should be taken into account since it will be installed in the high temperature part of the exhaust system (7)
In other words, the shaft 96, which is in direct contact with the exhaust gas, becomes warmer than the bearing 97, so the difference in thermal expansion between them is c, must be 13.

However, if such a lance 98 is installed, when the exhaust switching valve 95 is closed, the butterfly valve 95 will flutter downward as shown in Figure 8 due to the pulsation of the exhaust gas. Therefore, chattering noise may occur. This fluttering is caused by an increase in the amount of intake air and an increase in static exhaust pressure11.
When this happens, the shaft 96 of the butterfly valve 9:) is pressed downward in the figure, so it no longer occurs. When the engine is at 7-idle with no load, the amount of intake air is extremely small, so the flutter described above is likely to occur. Furthermore, during idling, the temperature of the exhaust gas is low, so the clearance 98 between the shaft 96 and the bearing 97 increases, making the occurrence of flapping even more disadvantageous.

The present invention addresses the above-mentioned problems in four ways, and particularly provides a 2-sy-1 system equipped with an exhaust bypass passage a3 that bypasses the exhaust switching valve and an exhaust bypass valve that opens and closes the exhaust bypass passage.
When the turbo system is in the 4 engine position, the T engine rotation speed suddenly changes from s'I to 4 during no-load racing.
．． The purpose is to prevent the noise of the turbo f-v-sha, and to prevent the banging and chatter noise of the exhaust switching valve at idle when there is low intake air mVi-Z.

[Step 1 for solving the problem The method for controlling the supercharged engine of the present invention in accordance with this purpose is that the turbocharger is provided in parallel with the engine body] The intake and exhaust switching valves provided in the intake and exhaust systems of the engine connected to the turbo chassis It is equipped with an exhaust bypass valve that opens and closes the exhaust bypass passage, and by opening and closing the intake switching valve a3 and the exhaust switching valve, the number of activated turbochargers τ is switched (1).
Before switching from single turbocharger to dual turbocharger operation, open the exhaust bypass valve to remove exhaust scum.
In a supercharged engine in which the auxiliary turbocharger is rotated by running up to the auxiliary turbocharger, as shown in Fig. 1, the engine is virtually unloaded due to the gear position value of the transmission and the clutch signal. If the exhaust bypass valve is in a substantially no-load state (step 83), the method of forcibly opening the exhaust bypass valve is avoided (step 83).

If the exhaust bypass valve is not in a no-load state, the forced opening of the exhaust bypass valve is not executed (step 84).

[Function] In such a control method, the exhaust bypass valve is already forcibly opened before no-load racing, and even if racing is carried out in that state, a portion of the exhaust gas will flow to the sub-turbo. Since the amount of exhaust gas flowing to the charger side is reduced and the amount of exhaust gas flowing to the regenerating turbocharger side is reduced, overrun of the main turbocharger is appropriately prevented.

Additionally, since the exhaust bypass valve is forcibly opened during idling, the front and back of the closed exhaust switching valve are communicated via the exhaust bypass passage, eliminating the pressure difference before and after the exhaust switching valve. . As a result, the force that causes the exhaust switching valve to flap no longer acts on the exhaust switching valve, thereby preventing the occurrence of flapping and chattering noise.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 and FIG. 3 show a supercharged engine according to an embodiment of the present invention, and show the case of a six-cylinder engine.

In Figure 2, 1 is the engine, 2 is the surge tank, and 3 is the engine.
indicates the exhaust manifold. The exhaust manifold 3 is assembled into two groups, a #1 to #3 cylinder group and a #4 to #6 cylinder group, which do not cause exhaust interference, and the assembled portions are communicated with each other by a communication path 3a. 7.8 is a main turbocharger and a sub-turbocharger arranged in parallel with each other. Each of the turbines 7a and 3a of the turbocharger 7.8 is connected to a collection part of the exhaust manifold 3, and each of the compressors 7b and 8b is connected to the surge tank 2 via an intercooler 6 and a throttle valve 4.

The main turbocharger 7 is operated from a low engine speed range to a high engine speed range, and the auxiliary turbocharger 8 is stopped in a low engine speed range.

In order to enable operation and stop of both turbochargers 7.8, an exhaust switching valve 17 is provided downstream of the turbine 8a of the auxiliary turbocharger 8, and an intake switching valve 18 is provided downstream of the compressor 8b. Suction/exhaust switching valve 18.17
When both turbochargers are fully open, both turbochargers 7.
8 is activated.

The exhaust passage of the exhaust switching valve 17 section is provided with an exhaust bypass passage 40 that bypasses the exhaust switching valve 17, and the exhaust bypass passage 40 is provided with an exhaust bypass valve 41 that opens and closes the exhaust bypass passage 40. It is being

The exhaust bypass valve 41 is opened and closed by a diaphragm actuator 42. By introducing negative pressure from the reserve tank 43 that stores the negative pressure of the surge tank 2 into the diaphragm chamber 42a of the actuator 42, the exhaust bypass valve 41 is opened. It is now possible to do so. The exhaust bypass valve 41 is configured as a swing arm type valve, and the direction in which exhaust pressure is applied is the valve opening direction. Note that in this embodiment, the exhaust bypass passage 40 is connected to the exhaust switching valve 17.
Although the upstream part of the exhaust flow and the downstream part of the exhaust flow of the main turbocharger 7 are connected, the upstream and downstream parts of the exhaust flow of the exhaust switching valve 17 may be connected.

In order to smoothly switch from one turbocharger to two turbochargers P, an intake bypass passage 13 is provided in the intake passage of the auxiliary turbocharger 8 that is stopped in a low speed range, which communicates the upstream and downstream of the compressor 8b. An intake bypass valve 33 is provided in the middle of the intake bypass passage 13. The intake bypass valve 33 is opened and closed by the actuator 10.

Note that the air flow downstream side of the intake bypass passage may be communicated with the intake passage upstream of the compressor of the main turbocharger 7. In addition, a check valve 12 is provided in the bypass passage that communicates the upstream and downstream sides of the intake switching valve 18, so that even when the intake switching valve 18 is closed, the compressor outlet pressure on the auxiliary turbocharger 8 side is lower than that on the main turbocharger 7 side. When it becomes large, it allows air to flow from the upstream side to the downstream side. 7. In FIG. 2, 14 indicates the intake passage on the LJ side from which the engine comes out, and 15 indicates the intake passage on the LJ side of the engine.

The intake passage 15 is connected to a near cleaner 23 via an enoflow meter 24. A front pipe 20 forming an exhaust passage is connected to an exhaust manor 22 via an exhaust gas catalyst 21.

The intake switching valve 18 is opened and closed by an actuator 11, and the exhaust switching valve 17 is opened and closed by a diaphragm type actuator 16.
It can be opened and closed by In addition, 7 cutuators for opening and closing the 9 machined stop gate valves 31 are shown. The first and second 2, 3rd, 4th three-way solenoid valve 25.26.27.
28 are provided. 3y) Solenoid valve 25.26.27
．． Switching of 28 is carried out according to the command from the engine control 1-le computer 29.
! ,! I cut it so that the intake switching valve 18 is fully open.
When the switch 11 is activated, the actuator 11 is set so that the intake switching valve 18 is fully closed. - Activate the motor 11.

When the third three-way solenoid valve 28 is turned on, the exhaust cutoff H valve 17 is fully opened, the actuator 16 is activated, and the exhaust cutoff H valve 17 is fully opened.
- is the actuator 1 that fully closes the exhaust switching valve 17.
6 is activated. 3rd σ-masu - Three-way "Solenoid valve 27 ON"
1-7 operates the 1-7 compressor 10 to fully close the intake bypass valve 33, and closes the intake bypass valve 33 by
Operate the 7th gear and 10th row so that it is fully open.

5th 3j) Turn ON the solenoid valve 32 to open the exhaust valve and pass valve 41 (actuate the acquisition valve 42, and turn OFF the exhaust valve 42 to close the exhaust bypass valve 41). 16a is the diamondorum chamber of the actuator 16, and 10a is the)
-The diamondorum room of evening 10, lla, llb are akubu:-x], -,, -The diamondorum room of evening 11,
are shown respectively.

] Carrot 1 and D-) Ren 1 and Bi 1 and 29 are electrically connected to various operating condition detection sensors of the engine, and the signals from the various sensors are input manually. 1 Engine operating condition detection sensor 1, intake pipe pressure sensor 30, slot opening 5, air nozzle as intake air amount measuring sensor
It includes a J-meter 24.0zt-lean 19, a gear position sensor 36 that detects the gear position of the transmission 35, and a clutch switch 738 that detects whether or not the clutch pedal 37 is depressed. It will be done.

The engine Nikon D~Rulombi coater 29 has a central processing unit (CPtJ) for calculation;
Read-on lift (RO) is a read-only memory.
M>, -Random access memory (RAM) for time storage
), a human output interface (1/D interface), and an A/D converter that converts afD signals from various sensors into digital quantities. Figure 4 shows the interface for opening and closing each switching valve. O-gram, stored in ROM,
Block 1- is read out by the CPU and executes valve opening/closing calculations.
” grams.

First, let us introduce the control in this embodiment to the control number 7 in Fig. 4.
This will also be explained with reference to FIG.

In addition, in FIG. 4, the first to fifth three-h solenoid valves are respectively represented by VSV No. 1 to VSVN 0.5. In addition, in FIGS. 4 and 55, turbo boat keys are expressed as T, . . . 'C.

First, in the 41st step 1, the hull 1 control routine is entered in step 100, and in step 101-(- engine intake air star 0 is read. The intake air black is airf [1 meter 2
This is the signal from 4. Tsuki'(, Is this j-tsuzo 102 one high speed series or low speed range?
・Determine whether it is in the operating range or in the Turbotage P operating range. In the illustrated example, for example, if S is greater than O or 550 ON/m1rl, it is determined that two turbochargers should be activated. There is 1,
However, as will be explained later, there is a time delay before the actual switching to two-turbocharger operation, so the 6000u
It will switch around the /m group. 3 subj-tsubu 10
If it is determined in step 2 that it is necessary to switch the intake switching valve 1 to 1, the process advances to step 103, and the intake switching valve 1
8 is open (partially open), the second three-way solenoid valve 26 is turned OFF and the intake switching valve 18 is closed. Subsequently, in step 104, the third three-way solenoid valve 27 is turned on, and the diaphragm chamber 10a of the actuator 10 is opened.
The intake pipe pressure (supercharging pressure) downstream of the compressor is guided to close the intake bypass valve 33.

Next, after the third three-way solenoid valve 270N, a predetermined time delay, for example, 1 second, necessary to increase the run-up rotation speed of the turbocharger on the inactive side, that is, the auxiliary turbocharger 8, is provided. After seconds have elapsed, the fourth three-way solenoid valve 28 is turned on in step 105, the boost pressure downstream of the compressor is introduced into the diaphragm chamber 16a of the actuator 16, and the exhaust switching valve 17 is fully opened. If the compressor pressure of the sub-turbocharger 8 becomes higher than the compressor pressure of the main turbocharger 7, the supercharged air of the sub-turbocharger 8 is supplied to the engine via the check valve 12. Subsequently, after turning on the fourth three-way solenoid valve 28, the first three-way solenoid valve 25 is turned on in step 106 after a predetermined period of time, for example, 0.5 seconds, and the intake pipe pressure downstream of the compressor is applied to the diaphragm chamber 11a of the actuator 11. (supercharging pressure) and fully open the intake switching valve 18. In this state, two turbochargers operate (note that when switching to two turbochargers after the above predetermined time has elapsed, the intake air amount is approximately 6000.j/mn, which is the target for good turbine efficiency. ). Next step 1
Proceed to step 22 and return.

If it is determined in step 102 that one turbocharger is in the operating range, the process proceeds to step 107, where the gear position sensor 36
Read the gear position signal from. In step 108, it is determined whether the gear position is neutral, and if it is not neutral, the process proceeds to step 109, where the clutch switch 3
8 is ON or OFF. clutch switch 38
If it is OFF, it is determined that it is not neutral, and the process proceeds to step 110, where the fifth three-way solenoid valve 32 is turned OFF and the exhaust bypass valve 41 is fully opened. In this case, since it is neither a no-load state nor a racing state, one turbocharger is used with the exhaust bypass valve 41 closed.

If the gear position is determined to be neutral in step 108, or if it is determined in step 108 that the gear position is not neutral, it is determined that the clutch switch is ON in step 109, and even if the gear position is not neutral, the engine is activated by the clutch. If it is determined that the no-load state is the same as neutral because the transmission is disconnected from the The bypass 41 is forcibly opened. When racing is carried out in this no-load state, the exhaust bypass 41 is forcibly opened even if one turbocharger is in the operating region, and the exhaust gas is transferred to the auxiliary turbocharger 8 on the non-operating side.
It also flows through the turbine 8a. Therefore, the amount of exhaust gas flowing to the main turbocharger 7 side is reduced, and overrun of the main turbocharger 7 is prevented.

Further, the exhaust bypass valve 41 can be operated with a smaller actuator 42 than the exhaust switching valve 17 and the like, and can perform the above-mentioned predetermined operation with a small pressure.

Further, if the exhaust bypass valve 41 is configured as a swing arm type valve, the swing arm type exhaust bypass valve 41 can be opened in the direction in which exhaust pressure is applied, and can be operated with a lower pressure.

Step 110 or Step 111 to Step 112
In step 113, the fourth three-way solenoid valve 28 is turned off and the exhaust switching valve 17 is fully opened. The solenoid valve 27 is turned off and the intake bypass valve 33 is fully opened. Even when the sub-turbocharger 8 rotates, the air sent out by the compressor 8b is returned to the compressor inlet side of the sub-turbocharger 8 or the main turbocharger 7 through the intake bypass passage 13. Subsequently, in step 115, the intake pipe pressure PM is read.

In step 116, it is determined whether the intake pipe pressure is greater or less than a predetermined value. For example, if the intake pipe pressure PM is +500m
If it is smaller than Hg, the process proceeds to step 117, where the fifth three-way solenoid valve 32 is turned OFF, the power is introduced into the inlet 42a of the actuator 42, and the exhaust bypass valve 42 is closed. In this state, proceed to Slurtub 118,
Determine whether the load is light or high. Figure 1 shows the case where the intake pipe pressure is taken as an example of the load reduction, but instead of the intake pipe pressure, the intake pipe opening, intake air amount, /I engine rotation speed (-""7ff4:) J, yes. Example λ
If the intake pipe pressure PM is less than 1100 mm t-19, it is considered a light load, and if it is less than 100 mm t-19, it is judged as a high load.

Step 118? ``If it is determined that the load is high, proceed to step 121 and turn off the second three-way solenoid valve 26.
In this state, the intake switching valve 18 is fully closed, the intake switching valve 18 is fully closed, the exhaust switching valve 17 is fully closed, and the intake bypass valve 33 is fully open, so the intake air is completely closed. In a state where the amount is small (in this case, one turbo charge A is activated, and the supercharging force and torque response are good. During no-load racing [this is the case, as mentioned above, the exhaust valve, Ibus 41 or the valve is forcibly opened) The main turbo ↑・−
Overrun of the shaft 7 is prevented.

If it is determined that the load is light in step 118, proceed to step 119 and turn on the second three-way solenoid valve 26.
・, Funokubuyu-dou-Yu 11 Diamond Nome 11bt, Q
Nisashi 7. (Intake f1 in Tsuk2 is guided to intake switching valve 1.
In this state, since the exhaust switching valve 11 is closed, only the auxiliary turbob (7-jar 8) operates.
4, the intake switching valve 18 is open, so the intake passages for two small chargers are open. ')ball,
Both turbochargers ω=1 umbretsusa 7b, 8b
Air is inhaled through. As a result, a large amount of supercharging air is supplied to the J' engine 1, and the self-speed characteristics are improved even at low loads. Subsequently, the process advances to step 122 and returns. In the case of no-load racing (J is the same as above,
By opening the strong valve 11 of the exhaust bypass 41, overrun of the main turbocharger 7 is prevented.

Sue 1-tube 116 and intake pipe 11-force I) M or +500
If it is determined that mm t-4'; Next, the process proceeds to step 121. Like this ((, 1 turbo to 2 turbo
The supercharging pressure is set before switching to the arsenal operation.
For example, when the temperature reaches 500 mH9), the exhaust bypass valve 41 is first opened to increase the run-up rotation speed of the auxiliary turbocharger 8, and the turbocharge V switching connection becomes smooth.

Incidentally, the supercharging pressure characteristics in the case of one turbocharger operation and the case of two turbocharger operation, which are applicable to the above control, are as shown in FIG. In Fig. 5 below, the characteristics during no-load racing do not appear.

415Figure 1. In the high speed range, the intake switching valve 18 and the exhaust switching valve 1? It opens at the corner and closes when the intake bypass valve ↑33. Therefore, the two turbos "F Yasha 7.8" operate to supercharge, obtain a sufficient amount of supercharging air, and improve the output. At this time, the supercharging pressure is → -500°■9
The wastegate pulse 131 is controlled so as not to exceed the threshold value.

When the speed is low and the load is high (at this time, both the intake valve 18 and the exhaust switching valve 17 are closed, and the intake bypass valve 33 is opened. This causes only one turbocharger 7 to be driven. Reason for choosing one turbocharger A in the rotation range [31. As shown in Figure 5, the low rotation range has either one turbocharger supercharging characteristics or two turbochargers.
This is because the supercharging characteristics are superior to those of the conventional engine. By using one turbocharger (this makes it possible to increase the boost pressure and I to Rw faster), resulting in a faster response.

In a low speed range and under eave load, the intake switching valve 18 is opened while the exhaust switching valve 17 is closed. As a result, while one turbocharger remains driven, two intake passages are opened, thereby eliminating the increase in intake resistance caused by one turbocharger at 5V. This (, 2, therefore, force I from low load) speed first!
, the response can be further improved.

When transitioning from low speed range to high speed range, that is, one tar ij
- When switching from the charger to two-turbocharging operation, if the exhaust switching valve 17 is closed, the exhaust bypass valve 41 is opened at 8' to increase the run-up rotation speed of the auxiliary turbo booster 8. It becomes possible to perform the switching more smoothly (with less shock at the time of switching).

[Effects of the Invention] As explained above, when using the supercharged engine control method of the present invention, the exhaust bypass valve is forcibly opened when there is no load. Under these conditions, exhaust gas can always flow to the auxiliary turbocharger side, preventing overrun of the main turbocharger and properly protecting the turbocharger.

Furthermore, since the exhaust bypass valve is opened during idling, there is no pressure difference before and after the exhaust switching valve, and it is possible to prevent the exhaust switching valve from flapping or chattering noise due to exhaust pulsation.

Furthermore, the exhaust bypass valve can be operated with a smaller actuator than an exhaust switching valve or the like, and can perform a predetermined operation with a small pressure.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the control steps of a method for controlling a supercharged engine according to the present invention, FIG. 2 is a system diagram of a supercharged engine according to an embodiment of the present invention, and FIG. Fig. 2 is a more specific system diagram, Fig. 4 is a control flow diagram of the device shown in Fig. 2, Fig. 5 is an operational characteristic diagram when switching the turbocharger according to the control flow shown in Fig. 4, and Fig. 6 is a diagram of the conventional system. A schematic system diagram of a supercharged engine; Fig. 7 is a characteristic diagram of a conventional supercharged engine at the time of racing; Fig. 8 is an enlarged cross-section near the exhaust switching valve of the device shown in Fig. 6. Figure, is. 1... Engine 2... Surge tank 3... Exhaust manifold 4... Throttle valve 5... Throttle opening sensor 6... ... Intercooler 7 ... Main turbocharger 8 ... Sub-turbocharger 10 ... Intake bypass valve actuator ~ 11
...Intake switching valve 7 unit 13...
...Intake bypass passage 14...Intake passage (downstream of compressor) 15.
...Intake passage (upstream of compressor) 16...
...Exhaust switching valve actuator 17...-Exhaust switching valve 18...Intake switching valve 24...Air flow meter 25...First three-way solenoid valve 26 ...Second three-way solenoid valve 27...Third three-way solenoid valve 28...Fourth three-way solenoid valve 29...Engine control computer 30. ... Intake pipe pressure sensor 31 ... Waste gate valve 32 ...
- Fifth three-way solenoid valve 33...Intake bypass valve 40...Exhaust bypass passage 41...Exhaust bypass valve 42...Exhaust bypass valve actuator 43
······Reserve tank

Claims (1)

[Claims] 1. A main turbocharger and a sub-turbocharger provided in parallel to the engine body, an intake switching valve and an exhaust switching valve provided respectively in the intake and exhaust systems of the engine connected to the sub-turbocharger, and the exhaust switching valve. It is equipped with an exhaust bypass passage that bypasses the valve and an exhaust bypass valve that opens and closes the exhaust bypass passage, and by opening and closing the intake switching valve and the exhaust switching valve, the number of operating turbochargers can be switched, and the number of turbochargers can be changed from one to two. In a supercharged engine in which the exhaust bypass valve is opened before switching to turbocharger operation, part of the exhaust gas flows to the auxiliary turbocharger, and the auxiliary turbocharger rotates during run-up, the engine is in a substantially no-load state. 1. A method for controlling a supercharged engine, comprising: detecting and determining whether or not the exhaust bypass valve is in a substantially no-load state, and forcibly opening the exhaust bypass valve at all times when the exhaust bypass valve is in a substantially no-load state.