JPH03260328A - Control method of engine provided with supercharger - Google Patents

Abstract

PURPOSE:To prevent delay of opening of a valve and deterioration of control characteristics by temporarily increasing a duty ratio for the initial period thereof, duty-controlling the exhaust changeover valve to open a little when performing changeover from single operation of a main turbocharger to double operation of main and sub-turbochargers. CONSTITUTION:In main and sub-turbochargers, turbines 7a, 8a are arranged in exhaust mainfold 3 of an engine 1, and compressors 7b, 8b are connected to a surge tank 2 through an intercooler 6 and a throttle valve 4. The turbochargers 7, 8 are operated and stopped according to opening and closing of exhaust and intake changeover valves 17, 18. The exhaust changeover valve 17 is duty-controlled to open a little by means of a computer 29 and the sub- turbocharger 8 is auxiliary rotated when the single operation of the main turbocharger 7 is changed over to the double operation of both the turbochargers 7, 8. The duty ratio is temporarily decreased at the initial period of a small opening of the exhaust changeover valve 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a turbocharger in which a main turbocharger and a sub-turbocharger are arranged in parallel,
The present invention relates to a method for controlling a supercharged engine in which only the main turbocharger is operated in a low speed range and both turbochargers are operated in a high speed range.

[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. The configuration of this type of supercharged engine is shown in FIG. 11, for example. A main turbocharger (T/C-1>92 and a sub-turbocharger (T/(,-2) 93) are provided in parallel to the engine body 91. Intake and exhaust systems connected to the sub-turbocharger 93 are provided with an intake switching valve 94 and an exhaust switching valve 95, respectively, and an intake bypass valve 96 is provided in an intake bypass passage that bypasses the compressor of the sub-turbocharger 93.The rotation of the engine 91 is controlled by a transmission 97. By fully closing both the intake switching valve 94 and the exhaust switching valve 95, only the main turbocharger 92 is operated for supercharging, and both are fully open, and the intake bypass valve 96 is output.
By also closing the sub-turbocharger 93, the sub-turbocharger 93 can also perform supercharging operation, making it possible to operate two turbochargers.

From 1 turbocharger operation (that is, only the main turbocharger 92 is in supercharging operation) to 2 turbocharger operation (
In other words, in order to more smoothly switch to both turbochargers (92 and 93 supercharging operation),
In the system disclosed in Publication No. 34M, the exhaust switching valve is gradually opened and slightly opened at a boost pressure lower than that at the time of switching the turbocharger, and the run-up rotation speed of the sub-turbocharger is increased before switching.

By the way, an internal combustion engine in which an exhaust switching valve is subjected to duty control is disclosed in Japanese Patent Application Laid-Open No. 63-25319. Duty control is to control the energization time using a duty ratio, and by digitally changing the energization/non-energization ratio, the average current is variably controlled by analog means.

Therefore, the opening degree of the exhaust switching valve is adjusted directly or indirectly depending on the magnitude of the average current depending on the duty ratio.

[Problems to be Solved by the Invention] However, in controlling the exhaust switching valve by duty control, the valve opening torque is small relative to the frictional resistance at the initial stage of opening the valve, so there is a problem that the valve body is difficult to move and a delay in opening the valve occurs. was there. This will be explained with reference to FIGS. 8 and 9. FIG. 8 shows a case where the exhaust gas switching valve is composed of a butterfly valve. As shown in the figure, exhaust gas pressure is applied to the exhaust switching valve 81 from both sides.
Since the exhaust gas pressure P on one side is significantly higher than the gas pressure P2 on the other side, the load acting on the rotating shaft 82 of the exhaust switching valve 81 becomes large, and when the exhaust switching valve 81 is initially opened, the rotating shaft 82
The exhaust switching valve 81 becomes difficult to move due to the frictional resistance between the exhaust switching valve 81 and the member supporting it. As a result, there is a delay in opening the valve,
As shown at P3 in FIG. 9, a problem occurred in that the supercharging pressure overshooted and the supercharging pressure controllability deteriorated.

FIG. 10 shows the change in valve opening torque with respect to the opening degree of the exhaust switching valve. As shown in the figure, the valve opening torque T is large at the beginning of the valve opening, and as the opening degree increases, the valve opening torque temporarily decreases, and then, as the opening degree increases, the valve opening torque T decreases. is also large. therefore,
In a duty-controlled exhaust gas switching valve, in order to eliminate the valve opening delay, it is necessary to drive the exhaust gas switching valve with a large torque at the initial stage of valve opening.

The present invention focuses on the above-mentioned problem, and the present invention provides a control method capable of quickly opening a duty-controlled exhaust switching valve means at the initial stage of valve opening, thereby preventing deterioration in supercharging pressure controllability caused by a delay in opening the valve. The purpose is to provide

[Means for Solving the Problems] The IF control method for a supercharged engine according to the present invention in accordance with this object includes a main turbocharger 17, an auxiliary turbocharger, and an intake and exhaust system of an engine connected to the auxiliary turbocharger. The system includes an intake switching valve means and an exhaust switching valve means, which are respectively provided in the system and cause the auxiliary turbocharger to perform supercharging operation when both are fully open, and to stop the supercharging operation of the auxiliary turbocharger when both are fully closed. , before switching from supercharging operation of only the main turbocharger to supercharging operation of both turbochargers, the exhaust switching valve means is slightly opened by duty control to transfer a part of the exhaust gas to the sub-turbocharger whose operation is stopped. In a method of controlling a supercharged engine in which the auxiliary turbocharger is rotated during run-up, the duty ratio at the beginning of the small opening of the exhaust switching valve means is temporarily set to dog, and then the control of the exhaust switching valve means is controlled normally. It consists of a method of returning to duty control.

[Function] In the method for controlling a supercharged engine configured as described above, the duty ratio is temporarily increased at the beginning of opening of the exhaust switching valve means. That is, the ratio of the energization time to the time of one cycle is increased, and the force for opening the exhaust switching valve means is increased.

Therefore, it is possible to sufficiently overcome the frictional resistance at the initial stage of opening of the exhaust switching valve due to the differential pressure in front of the exhaust switching valve, and the delay in opening of the exhaust switching valve is eliminated.

[Embodiments] Hereinafter, preferred embodiments of the method for controlling a supercharged engine according to the present invention will be described with reference to the drawings.

1 to 5 show one embodiment of the present invention. Of these, FIG. 4 shows the configuration of an apparatus for implementing the present invention, and particularly shows the case where it is applied to a 6-cylinder engine.

In Figure 4, 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 collected parts are communicated with each other by a communication path 38. 7.8 is a main turbocharger and a sub-turbocharger arranged in parallel with each other. The respective turbines 7a and Ba of the turbocharger 7.8 are connected to a collection part of the exhaust manifold 3, and the respective compressors 7b and 8b are connected to the surge tank 2 via the intercooler 6 and the 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 both turbochargers 7.8 to operate and stop, an exhaust switching valve 17 as exhaust switching valve means 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. provided. Here, the exhaust switching valve 17 is composed of a butterfly valve. When both the intake and exhaust switching valves 18.17 are fully open, both turbochargers 7.8 are operated.

The intake passage of the auxiliary turbocharger 8 that is stopped in a low speed range includes an intake bypass passage 13 that communicates between the upstream and downstream of the compressor 8b in order to smoothly switch from a 1 m turbocharger to two turbochargers. 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 a bypass passage that communicates between the upstream and downstream sides of the intake switching valve 18, so that even when the intake switching valve 18 is closed, the pressure at the outlet of the sub-turbocharger 8 is maintained at the main turbocharger 7 side. When it becomes larger, it allows air to flow from the upstream side to the downstream side.

In FIG. 4, 14 indicates an intake passage on the compressor outlet side, and 15 indicates an intake passage on the compressor outlet side.

The intake passage 15 is connected to the air cleaner 23 via an air 70-meter 24. A front pipe 20 forming an exhaust passage is connected to an exhaust muffler 2 via an exhaust gas catalyst 21.
Connected to 2.

The intake switching valve 18 is opened and closed by the actuator 11, and the exhaust switching valve 17 is opened and closed by the two-stage diaphragm actuator 16, so that one actuator 16 can control both small opening and full opening of the exhaust switching valve 17. It looks like this. Note that 9 indicates an actuator that opens and closes the waste gate valve 31. Zero boost or negative pressure to operate actuator 10.11.16
First, second, third, and fourth three-way solenoid valves 25, 26, 27, and 28 are provided for N-OFF (selectively switching between supercharging pressure or negative pressure and atmospheric pressure). There is. Switching of the three-way solenoid valves 25, 26, 27, and 28 is performed according to commands from the engine control computer 29. Three-way solenoid valve 25.28 ON is intake/exhaust switching valve 18.17
The actuator 11.16 is operated so as to fully open the valve, and when it is OFF, the actuator 11.16 is operated so that the intake/exhaust switching valve 18.17 is closed. 32 is a fifth three-way solenoid valve for controlling the small opening of the exhaust switching valve 17;
The boost pressure is increased by N to the diaphragm chamber 16 of the actuator 16.
b, the exhaust switching valve 17 is opened slightly, and the booth is stopped when the exhaust switching valve 17 is turned off. Here, 16a, 16b
16c is a small opening adjustment screw, 10a is a diaphragm chamber of the actuator 10, and 11a and 11b are diaphragm chambers of the actuator 11, respectively.

The actuator 16 that drives the exhaust gas switching valve 17 is duty-controlled by the engine control computer 29. As is well known, duty control is to control the energization time using a duty ratio, and by digitally changing the ratio of energization and non-energization, the average current is variably controlled in an analog manner. Note that the duty ratio is the ratio of the energization time to the time of one cycle, and is expressed as duty ratio=A/A+B×100 (%), where A is the energization time in one cycle and B is the non-energization time.

In this embodiment, by controlling the duty of the fifth three-way solenoid valve 32, the opening amount of this solenoid valve can be varied. By appropriately controlling the fifth three-way solenoid valve, it is possible to improve the responsiveness of the actuator 16 and eliminate the opening delay of the exhaust switching valve 17.

The engine control computer 29 is electrically connected to sensors for detecting various operating conditions of the engine, and receives signals from the various sensors. Engine operating condition detection sensors include an intake pipe pressure sensor 30, a throttle opening sensor 5, and an air flow meter 2 as an intake air amount measurement sensor.
4.02 sensor 19 etc. are included.

The engine control computer 29 includes a central processor unit (CPU) for performing calculations, and a read-only memory (ROM) that is a read-only memory.
, -Random access memory (RAM) for time storage
, input/output interface (1/D interface)
, is equipped with an A/D converter that converts analog signals from various sensors into digital quantities.

FIG. 1 shows the relationship between the opening degree of the exhaust switching valve, the duty ratio, and the boost pressure. As shown in the figure, the exhaust switching valve 17
The duty ratio A at the beginning of the small opening is set to be large. After the exhaust gas switching valve 17 is opened, the duty ratio B is set to -1, and thereafter is set to gradually increase. This duty ratio A,
, B, etc. are stored in the ROM of the engine control computer 29 in advance.

Next, a method for controlling the duty of an exhaust gas switching valve provided in a supercharged engine will be explained based on the flowchart shown in FIG.

In FIG. 2, the exhaust booth duty control routine is entered in step 100, and the engine speed (NE>) is read in step 101. Next, the process proceeds to step 102, where it is determined whether the engine speed is 400 Orpm or more. It is determined that the engine speed is 400 rpm.
If the intake air amount Q is higher than , the process proceeds to step 103, where the intake air amount Q is read. The intake air amount is a signal from the air flow meter 24. When the intake air amount 103 is read in step 103, the process proceeds to step 104, where the intake air amount 103 is read.
is larger than, for example, 40001/min. Here, the amount of intake air is 40001/m
If it is a dog rather than in, the process advances to step 107.

In step 102, the engine speed is 400 Or
If it is lower than pm, the process proceeds to step 105, where the intake pipe pressure (PM) is read. The intake pipe pressure is a signal from the intake pipe pressure sensor 30. When the intake pipe pressure is read in step 105, the process proceeds to step 106, where it is determined whether the intake pipe pressure is greater than +500sy+H9, for example. Here, the intake pipe pressure is +500sxht
If it is larger than g, the process proceeds to step 107. At step 106, the intake pipe pressure is ±500#Kll! If it is determined that it is lower than Hg, then step 117
Proceed to.

In step 107, it is determined whether the duty ratio is set to zero. Here, if the duty ratio is set to zero, the process advances to step 109, where it is determined whether the skip control is ON. Skip control is necessary because there is a difference between the driving force at the time when the exhaust switching valve 17 starts opening and the driving force when it ends closing. That is, there is hysteresis in the driving force of the exhaust switching valve 17, and in order to cope with this, skip control is performed in which the duty ratio is corrected by an integral constant. Step 10
If it is determined in step 9 that the skip control is ON, the process advances to step 110.

If it is determined in step 107 that the duty ratio is not zero, the process proceeds to step 108, where it is determined whether the skip control is set to ON.

If it is determined in step 108 that the skip control is set to ON, the process proceeds to step 111, and if it is not set to ON, the process proceeds to step 112.

In step 110, the duty ratio A is 50, for example.
%, and an integral constant C is added to this duty ratio A1. In step 111, the duty ratio B is set to, for example, 5%, and the integral constant C is added to this duty ratio B1. In step 112, the duty ratio C1 is set to 2%, for example, and the duty ratio C1
An integral constant C is added to . That is, if the duty ratio is set to zero in step 107, it is determined that the exhaust switching valve 17 is closed, and the duty ratio is set to a significantly large value in step 110. Step 11
When 0 is processed, the process proceeds to step 113, where the skip control is reset to ON, and the process further proceeds to step 114, where the skip control is turned OFF.

In step 107, the duty ratio is set to a value other than zero, and in step 108, the skip control is turned ON.
-, it is determined that the exhaust switching valve 17 is slightly open, and the process of step 111 is performed. Then, the duty ratio B is set to 5%,
Proceed to step 113. In step 108, if the skip control is not set to ON, step 1
The process proceeds to step 12, where the duty ratio C1 is set to 2%, and then the process proceeds to step 115.

In step 115, it is determined whether the duty ratio is set to 100% or more. If it is determined that the duty ratio is 100% or more, the process proceeds to step 116, and the duty ratio is set to 1.
Set (corrected) to 00%. In step 115, if the duty ratio is set to 100% or less, the process advances to step 129.

In this way, the processes from steps 107 to 116 represent control when the intake pipe pressure or intake air amount exceeds a set value. In this case, the duty ratio is increased and the direction in which the exhaust switching valve 17 is opened is controlled. Activate it.

Returning to the previous step, the intake air amount is 40001 in step 104.
/min, or if the intake pipe pressure is lower than +500 mHg in step 10&, the process proceeds to step 117. In this step 117, it is determined whether the duty ratio is set to zero, and here,
If the duty ratio is set to zero, step 11
Proceeding to step 9, it is determined whether the skip control is set to OFF.

As described above, the skip control is a control performed because there is hysteresis in the driving force of the exhaust switching valve 17. If it is determined in step 119 that the skip control is OFF, the process proceeds to step 120.

If it is determined in step 117 that the duty ratio is not zero, the process proceeds to step 118, where it is determined whether the skip control is set to OFF. If it is determined in step 118 that the skip control is set to OFF, the process advances to step 121 and the skip control is set to OFF.
If it is not set to F, the process advances to step 122.

In step 120, the duty ratio A is reduced by 50% from the point in FIG. Also, step 121
Then, a duty ratio of 2 to 5% is subtracted from points 1 to 1. Roughly, in step 122, the points will be 3 to 2%.
The duty ratio of is subtracted.

Once steps 120 and 121 have been completed, the process proceeds to step 123, where the OFF state of the skip control is reset. Then, the process further proceeds to step 124, where the skip control is set to ON, and the process proceeds to step 125. Hey, even if the process in step 122 is completed,
Proceed to step 125.

In step 125, it is determined whether the duty ratio is zero or less than zero.

Here, if it is determined that the duty ratio is zero or smaller than zero, the process proceeds to step 126, where the duty ratio is corrected to zero. Then, the process proceeds to step 127, where the duty ratio is set to zero, and step 12
Proceeding to step 9, duty control of the fifth three-way solenoid valve 32 is performed. If the duty ratio is determined to be zero or less than zero in step 125, step 1
After proceeding to step 28 and resetting the duty ratio to zero, the process proceeds to step 129. From this step 129, the valve control shown in FIG. 3 is started.

As described above, steps 117 to 128 indicate control processing when the intake pipe pressure or intake air amount becomes lower than the set value. In this case, the duty ratio is decreased and the exhaust switching valve 17 is closed. Activate.

FIG. 3 is a flowchart showing the procedure of valve control processing in this embodiment, and in the figure, the first to fifth three-way solenoid valves are set to V SV No.

1 to VSV No. 5, the turbocharger is expressed as T/C.

In FIG. 3, a valve control routine is entered at step 200, and an intake air amount Q of the engine is read at step 201. The intake air amount is a signal from the air flow meter 24. Next, in step 202, it is determined whether the vehicle is in a high speed range or a low speed range, that is, a two-turbocharger operating range or a one-turbocharger operating range.

In the illustrated example, for example, if Q is greater than 5500 ρ/min, it is determined that a switch should be made to two turbocharger operation, and if it is less than 5500 C/min, it is determined that the one turbocharger operation is in the range. However, as will be described later, there is a time delay before actually switching to two turbocharger operation, so the switching occurs at around 6000ρ/mn.

If it is determined in step 202 that it is necessary to switch to two-turbocharger operation, the process proceeds to step 203, and the intake switching valve 18 is opened (
(partial loading), the second three-way solenoid valve 26 is turned OFF and the intake switching valve 18 is closed. Next, in step 204, the third three-way solenoid valve 27 is turned on,
The intake pipe pressure (supercharging pressure) downstream of the compressor is introduced to the diaphragm '110a of the actuator 10, and the intake bypass valve 33 is closed. However, at this time, as described below,
1 In the turbocharger operating range, the exhaust switching valve 17
has already been controlled to open slightly, and the auxiliary turbocharger 8 has been rotated in the run-up.

Next, the third three-way solenoid valve 27ON4* causes 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. After the elapse of time, in step 205, the fourth three-way solenoid valve 28 is turned on, and the intake pipe pressure (supercharging pressure) downstream of the compressor is guided to the diaphragm chamber V6a of the actuator 16, and the exhaust switching valve 17 is fully opened. If the compressor pressure of the auxiliary turbocharger 8 becomes larger than the compressor pressure of the main turbocharger 7,
Supercharging air from the sub-turbocharger 8 is supplied to the engine via the check valve 12. Subsequently, after the fourth three-way solenoid valve 280 N, the first three-way solenoid valve 25 is turned on in step 206 after a predetermined period of time, for example, 0.5 seconds, and the intake pipe downstream of the compressor is connected to the diaphragm chamber 11a of the actuator 11. The pressure (supercharging pressure) is guided to fully open the intake switching valve 18. In this state, two turbochargers are operating (note, when switching to two turbochargers after the predetermined time has elapsed, the intake air amount is approximately 600 J/min, which is the target for good turbine efficiency).

The process then proceeds to step 221 and returns.

If it is determined in step 202 that one turbocharger is in the operating range, the process proceeds to step 207, and the first three-way solenoid valve 2
5 is turned OFF to fully open the intake switching valve 18, in step 208 the fourth three-way solenoid valve 28 is turned OFF and the exhaust switching valve 17 is fully opened, and in step 209 the third three-way solenoid valve 27 is turned OFF to fully open the intake bypass valve 33. is fully opened.

Subsequently, in step 210, the intake pipe pressure PM is read. In step 211, it is determined whether the intake pipe pressure is greater or less than a predetermined value. Intake pipe pressure PM is, for example, +500mH
If it is smaller than 9, the process proceeds to step 212, where the fifth three-way solenoid valve 32 is turned off and atmospheric pressure is introduced into the diaphragm chamber 16b of the actuator 16. In this state, the process proceeds to step 213, where it is determined whether the load is light or high. Although the figure shows a case where the intake pipe pressure is used as an example of the load signal, the intake pipe pressure may be replaced by the throttle opening degree or the intake air amount/engine speed. For example, if @tracheal pressure PM is less than -1100a+H9, it is determined to be a light load, and if it is -100 mHg or more, it is determined to be a high load.

If it is determined that the load is high in step 213, step 1
20, the second three-way solenoid valve 26 is turned OFF. That is, the intake switching valve 18 is closed, and the process proceeds to step 221 to return. In this state, the intake switching valve 18 is closed, the exhaust switching valve 17 is closed, and the intake bypass 33 is fully open, so one turbocharger is activated when the amount of intake air is small, and the boost pressure and torque response are reduced. Becomes good.

If it is determined in step 213 that the load is light, the process proceeds to step 214, where the second three-way solenoid valve 26 is turned on, the negative pressure within the surge tank 2 is guided to the diaphragm 11b of the actuator 11, and the intake switching valve 18 is opened. In this state,
Since the exhaust switching valve 17 is closed, the auxiliary turbocharger 8 does not operate, and only the main turbocharger 7 operates. However, since the intake switching valve 18 in the intake passage 14 is open, the intake passages for two turbochargers are open. In other words, compressor 7b of both turbochargers
, Bb. As a result, a large amount of supercharging air can be supplied to the engine 1, and acceleration characteristics from low loads are improved. Subsequently, the process advances to step 121 and returns.

At step 211, the intake pipe pressure PM is +500 am H.
If it is determined to be 1 or more, the fifth three-way solenoid valve 32 is turned on in step 215, and the intake pipe pressure (supercharging pressure) downstream of the compressor of the main turbocharger 7 is introduced into the diaphragm chamber 16b of the actuator 16.

As a result, the exhaust gas switching valve 17 is controlled to be opened slightly.

This small opening control is performed by partially opening the exhaust switching valve 17 so that the intake pipe pressure does not exceed +500 mHg. Normally, the supercharging pressure control of a turbocharger opens the waste gate valve 31 and controls the rotation speed of the main turbocharger 7 when the pressure exceeds the set pressure + 500 mHg, but in the parallel turbocharger with variable number of actuations of this embodiment. Instead of opening the waste gate valve 31, the exhaust switching valve 17 is partially opened to guide a portion of the exhaust gas to the turbine 8a of the auxiliary turbocharger 8 on the stop side, thereby causing the auxiliary turbocharger 8 to perform a run-up rotation. The higher the run-up rotation speed of the auxiliary turbocharger 8, the less the torque drop (torque shock) at the time of switching from one turbocharger to two turbochargers, and the smoother the switching.

In this small opening control, the fifth three-way solenoid valve 32 that opens the exhaust switching valve 17 is duty-controlled;
As shown in Fig. 1, the duty ratio that is opened at the beginning of the small opening is set to 1, so that the boost pressure is increased by the fifth three-way solenoid valve 3.
2 to quickly remove the diaphragm chamber 16 of the actuator 16.
transmitted to b. As a result, the exhaust gas switching valve 17 is rotated quickly and with a large driving force. Therefore, a delay in opening of the exhaust switching valve 17 due to frictional resistance at the initial stage of opening is prevented, and as shown in FIG. 1, controllability of the supercharging pressure P is improved.

In other words, a large current is passed through the fifth three-way solenoid valve 32 at times, so the opening degree of the solenoid valve itself increases, and the amount of air supplied to the actuator 16 that drives the exhaust switching valve 17 increases. However, this eliminates the delay in opening the exhaust gas switching valve 17.

Next, the supercharging characteristics in the case of one turbocharger operation and the case of two turbocharger operation will be explained.

In the high speed range, both the intake switching valve 18 and the exhaust switching valve 17 are opened, and the intake bypass valve 33 is closed. As a result, the two turbochargers 7.8 operate for supercharging, a sufficient amount of supercharging air is obtained, and the output is improved. At this time, the supercharging pressure is controlled by the waste gate valve 31 so as not to exceed, for example, +500 mH9.

In a low speed range and under high load, both the intake switching valve 18 and the exhaust switching valve 17 are closed, and the intake bypass valve 33 is opened. As a result, only one turbocharger 7 is driven. The reason why one turbocharger is used in the low rotation range is that, as shown in FIG. 5, the supercharging characteristics of one turbocharger are superior to the supercharging characteristics of two turbochargers in the low rotation range. By using one turbocharger, boost pressure and torque rise quickly, and response is quick.

In a low speed range and under light load, the intake switching valve 18 is opened while the exhaust switching valve 17 is closed. As a result, the intake passages for two turbochargers are opened while one turbocharger remains driven, and an increase in intake resistance caused by one turbocharger can be eliminated. As a result, the boost pressure rise characteristics and response during the early stages of acceleration from a low load can be greatly improved.

When transitioning from a low speed range to a high speed range, that is, when switching from one turbocharger operation to two turbocharger operation, after the small opening control of the exhaust switching valve 17 is started, the intake air amount Q reaches 55009/min. Sometimes the intake bypass valve 33 is closed, and then with a time delay (
In this embodiment, after one second has elapsed), the exhaust switching valve 17 is fully opened, and then the intake switching valve 18 is fully opened, and the two-turbocharger supercharging operation is started.

In this embodiment, the exhaust switching valve 17 is constructed from a butterfly valve, but similar effects can be obtained by constructing it from a poppet valve 41 shown in FIG. 6 or a swing arm valve 42 shown in FIG. 7.

Further, although this embodiment has been described in detail with respect to the case where two turbochargers are arranged in parallel to the engine body, for example, two large and small turbochargers as disclosed in Japanese Patent Application Laid-Open No. 55-84816. The control method according to the present invention can also be applied to an engine of a so-called two-stage sequential turbo system in which two engines are arranged in series, and the same operations and effects as in the above embodiment can be obtained.

[Effects of the Invention] As explained above, when using the control method for a supercharged engine according to the present invention, the duty ratio is temporarily increased at the beginning of the small opening of the exhaust switching valve means, and then this exhaust Since the control of the switching valve means is returned to the normal duty control, it is possible to eliminate the delay in opening the valve due to the frictional resistance at the initial stage of opening the valve due to the differential pressure across the exhaust switching valve means. Therefore, overshoot of the boost pressure during small opening control is prevented, and boost pressure control characteristics can be improved.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the opening degree of the exhaust switching valve, the duty ratio, and the supercharging pressure in the control method for a supercharged engine according to the present invention, and FIG. 2 and FIG. 3 are according to the present invention. Flowchart showing the flow of control for opening the engine, FIG. 4 is a system diagram of the device for carrying out the present invention, and FIG. 5 is a boost pressure characteristic diagram when the device shown in FIG. 4 has one turbocharger and two turbochargers. , FIGS. 6 and 7 are cross-sectional views showing modified examples of the exhaust switching valve provided in the device shown in FIG. 4, and FIG. Figure 9 is a characteristic diagram showing the change in supercharging pressure when small opening control is performed by the exhaust switching valve in Figure 8, Figure 10 is the opening degree of the exhaust switching valve in Figure 8. FIG. 11 is a schematic diagram of a conventional supercharged engine. 1... Engine 2... Surge tank 3... Exhaust manifold 4... Throttle valve 5... Throttle opening sensor 6... ... Interturf ... Main turbocharger 8 ... Sub-turbocharger 10 ... Intake bypass valve actuator 11
...Intake switching valve actuator 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 70-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 (duty control) 33... Intake bypass valve Application Person Toyota Motor Corporation No. 1 Fig. 8 8 Fig. 9 Fig. 10

Claims (1)

[Claims] 1. A main turbocharger and a sub-turbocharger;
The intake air intake system is installed in the intake and exhaust systems of the engine connected to the auxiliary turbocharger, and when both are fully open, the auxiliary turbocharger performs supercharging operation, and when both are fully closed, the auxiliary turbocharger's supercharging operation is stopped. A switching valve means and an exhaust switching valve means are provided, and before switching from supercharging operation of only the main turbocharger to supercharging operation of both turbochargers, the exhaust switching valve means is slightly opened by duty control to control exhaust gas. In a method for controlling a supercharged engine in which a portion of the exhaust gas is flowed to an inactive auxiliary turbocharger and the auxiliary turbocharger is rotated in a run-up manner, the duty ratio at the beginning of the small opening of the exhaust switching valve means is temporarily increased. . A method for controlling a supercharged engine, the method comprising: thereafter returning control of the exhaust switching valve means to normal duty control.