JPH03260329A - Control method of engine provided with supercharger - Google Patents

Abstract

PURPOSE:To control flow rate of exhaust gas accurately by duty-controlling an exhaust changeover valve to open a little at the time of switching single operation of a main turbocharger to double operation of main and sub- turbochargers, and adding a specified integration correction value and a skip value to the duty ratio. CONSTITUTION:Main and sub-turbochargers 7, 8 are operated and stopped according o opening and closing of exhaust and intake changeover valves 17, 18. Before single operation of the main turbocharger 7 is switched to double operation of both the turbochargers 7, 8, the exhaust chargeover valve 17 is duty-controlled to open a little, and then the sub-turbocharger 8 is auxiliarily rotated. An integration constant value for correcting flow rate characteristic of the exhaust changeover valve 17 and a skip value for correcting hysteresis of driving force of the same are added to the duty ratio. The integration constant value is varied in response to the duty ratio.

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. 9, for example. A main turbocharger (T/C-1>92 and a sub-turbocharger (T/C-2>93) are installed in parallel to the engine body 91. The 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 auxiliary turbocharger 93.The rotation of the engine 91 is controlled by a transmission 97. By closing both the intake switching valve 94 and the exhaust switching valve 95, only the main turbocharger 92 is operated for supercharging, and by fully opening both and closing the intake bypass valve 96, the auxiliary turbocharger is The charger 93 can also perform supercharging operation, making it possible to perform two turbocharger operations.

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. 34, 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 approach rotation speed of the auxiliary 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 ratio of energization and non-energization, the average current is variably controlled in an analog manner.

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.

Further, as a prior art related to the present invention, a device in which the exhaust switching valve is a butterfly valve is also known (Japanese Patent Laid-Open No. 104718/1983).

[Problems to be Solved by the Invention] By the way, especially when the exhaust switching valve is a butterfly valve, as shown in Fig. 8, the flow rate change of the exhaust gas becomes large in the region where the opening degree of the valve is small. . therefore,
In an exhaust gas switching valve using normal duty control, the opening/closing speed is constant regardless of the opening amount, so a problem arises that linear flow characteristics cannot be obtained and controllability of supercharging pressure deteriorates. In order to deal with this, it is necessary to change the opening/closing speed of the exhaust switching valve depending on the opening amount of the exhaust switching valve.

In addition, as can be seen from the valve opening pressure characteristics in Figure 8, when operating the exhaust switching valve, the driving force required to start opening and closing the valve is different, so control that takes this into consideration is necessary. It becomes necessary. In other words, since hysteresis exists in the driving force of the exhaust switching valve, if this is not taken into consideration, accurate opening and closing operations will not be possible and desired flow characteristics will not be obtained.

The present invention focuses on the above-mentioned problem, and the present invention accurately controls the flow rate of exhaust gas during small opening duty control even when using an exhaust switching valve in which the flow rate of passing exhaust gas with respect to the opening angle does not have a linear characteristic. The present invention aims to provide a control method that can improve the controllability of boost pressure.

[Means for Solving the Problems] A method for controlling a supercharged engine according to the present invention in accordance with this object includes controlling a main turbocharger, a sub-turbocharger, and an intake/exhaust system of an engine connected to the sub-turbocharger. The main turbocharger has an intake switching valve means and an exhaust switching valve means respectively provided, which cause the auxiliary turbocharger to perform supercharging operation when both are fully open, and stop the supercharging operation of the auxiliary turbocharger when both are fully open. Before switching from supercharging operation of only the charger to supercharging operation of both turbochargers, the exhaust gas switching valve means is slightly opened by duty control to flow part of the exhaust gas to the sub-turbocharger which is not in operation. In a method of controlling a supercharged engine in which a turbocharger is rotated during run-up, the duty ratio during small opening duty control of the exhaust switching valve means is provided with an integral constant value for correcting the flow rate characteristic of the exhaust switching valve means and the exhaust switching valve. A skip value is added to correct the hysteresis of the driving force, and the integral constant value is changed according to the duty ratio.

[Function] 6.
In this system, an integral constant value that corrects the flow rate characteristics of the exhaust switching valve means is added to the duty ratio during small opening duty control of the exhaust switching valve, so the smaller the opening degree of the exhaust switching valve, the faster the opening/closing speed becomes. conversely, the larger the opening degree, the faster the opening/closing speed. As a result, the flow rate characteristics in the specific region of the exhaust switching valve are corrected. Furthermore, since a skip value for correcting the hysteresis of the exhaust switching valve is added to the duty ratio, accurate opening/closing operations are possible.

Therefore, even when using an exhaust switching valve such as a butterfly valve that does not have linear flow characteristics with respect to opening, the flow rate of exhaust gas can be controlled accurately and the controllability of boost pressure can be improved. .

[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 6 show one embodiment of the present invention. Of these, FIG. 4 shows the configuration of an apparatus for carrying out 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 assembled portions are communicated with each other by a communication path 3a. , 7.8 are a main turbocharger and a sub-turbocharger arranged in parallel with each other. Each turbine 7a, 8a of the turbocharger 7.8 is connected to a gathering part of the exhaust manifold 3, and each compressor 7b, 8b is connected to an intercooler 6, a throttle valve 4,
It is connected to the surge tank 2 via.

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.

In order to smoothly switch from one turbocharger to two turbochargers, the intake passage of the auxiliary turbocharger 8 that is stopped in a low speed range is provided with an intake bypass passage 13 that communicates between the upstream and downstream of the compressor 8b. , an intake bypass valve 33 disposed in the middle of the intake bypass passage 13 is provided. 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. This allows air to flow from the upstream side to the downstream side when it becomes large.

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

The intake passage 15 is connected to an air cleaner 23 via an air flow 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, and one actuator 16 can control both small opening and full opening of the exhaust switching valve 17. It is now possible to do so. Note that 9 indicates an actuator that opens and closes the waste gate valve 31. The first, second, third, Fourth
Three-way solenoid valves 25, 26, 27, and 28 are provided. 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
．． The actuator 11.16 is operated to fully open the valve 17, and the actuator 11.16 is operated to close the intake/exhaust switching valve 18.17 when it is OFF. 3
Reference numeral 2 designates a fifth three-way solenoid valve for controlling the small opening of the exhaust switching valve 17. When turned ON, supercharging pressure is introduced into the diaphragm chamber 16b of the actuator 16 to slightly open the exhaust switching valve 17, and when turned OFF, the valve is opened slightly. It is scheduled to be discontinued. Here, 16a,
16b is a diaphragm chamber of actuator 16, 16c
is a small opening adjustment screw, 10a is a diaphragm chamber of actuator 10, lla and llb are actuator 1
1 diaphragm chamber is shown, 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+BX100 (%), 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 vary the operating speed of the actuator 16 and correct the flow rate characteristics of a specific region 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 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 (I/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
In the small opening control of the exhaust switching valve 1 in the duty ratio,
1 and K2 are added to the integral constant value for correcting the flow rate characteristics of 7. The integral constant value is a value that slopes with respect to the duty ratio A extending in the vertical axis direction, and the ratio of this slope can be switched when the duty ratio exceeds 50%. That is, in this embodiment, two types of integral constant values, 1 and K2, are prepared in advance, and when the duty ratio is 50% or less, is added to the integral constant value, and when the duty ratio exceeds 50%, the integral constant value is 2 is added to .

The change pattern of this duty ratio and integral constant value is
It is stored in advance in the ROM of the engine control computer 29.

Next, a method for controlling the duty of the exhaust switching valve in a supercharged engine will be explained based on the flowchart shown in FIG. This control routine is performed, for example, every 8 seconds.

In FIG. 2, a small exhaust opening 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 rotation speed is 4000 rpm or more. Here, the engine speed is 400 rpm
If it 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, 4000 J/min. Here, the intake air amount is 4000A/
If it is greater than min, proceed 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, for example, the intake pipe pressure is +500! It is determined whether or not it is larger than IunH9. Here, the intake pipe pressure is +500mHg
If the value is greater than , proceed to step 107. If it is determined in step 106 that the intake pipe pressure is lower than +500#IHg, the process proceeds to step 118, which will be described later.

In step 107, it is determined whether the skip control is ON. That is, in this step, it is determined whether to select either skip control or integral control. Here, the integral control means correction control of the duty ratio using the above-mentioned integral constant. Skip control is
This control is necessary because there is a difference between the driving force applied to the exhaust switching valve 17 when the valve starts opening and the driving force when the valve ends. That is, there is hysteresis in the driving force of the exhaust gas 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 value.

In step 107, if it is determined that the control is skip control, the process proceeds to step 109, where a skip value S (duty ratio of 5%) is added to the duty ratio. Next, the process proceeds to step 112, where it is determined whether the duty ratio exceeds 30%.

Here, if the duty ratio does not exceed 30%, the process proceeds to step 113, the duty ratio is set to 30%, and the process proceeds to step 114. If it is determined in step 112 that the duty ratio is greater than 30%,
Proceeding to step 114, skip ON is reset.

If it is determined in step 107 that the control is not skip control, the process proceeds to step 108, where it is determined whether the duty control exceeds 50%.

Here, if the duty ratio exceeds 50%, the process proceeds to step 110, where the duty ratio is increased to a large integral constant value.
(For example, a duty ratio of 2%) is added, and the process proceeds to step 115. In step 10B, if the duty ratio does not exceed 50%, the process proceeds to step 111, where a small integral constant value (for example, 1% duty ratio) is added to the duty ratio, and the process proceeds to step 115. In step 115, the skip control is set to OFF, and the process proceeds to step 116.

In step 116, it is determined whether the duty ratio is set to 100% or more. If it is determined that it is 100% or more, the process proceeds to step 117, and the duty ratio is set to 1.
Set (corrected) to 00%. In step 116, if the duty ratio is set to 100% or less, the process proceeds to step 127.

In this way, steps 107 to 117 represent control when the intake pipe pressure or intake air amount exceeds a set value, and in this case, the duty ratio is increased and the exhaust switching valve 1 is
7 in the direction of opening.

Returning to the previous step, the intake air amount is 40001 in step 104.
/min, or if the intake pipe pressure is lower than +500a+Hg in step 106, the process advances to step 118. In this step 118, it is determined whether the skip control is set to OFF. That is, in this step, it is determined whether to select either skip control or integral control. Step 1
If it is determined in step 18 that the control is skip control, the process proceeds to step 120, where the skip value S (duty ratio 5%) is subtracted from the duty ratio. Next, the process proceeds to step 123, where the OFF state of the skip control is reset. If it is determined in step 118 that integral control is being used, the process proceeds to step 119, where the duty ratio is 5.
It is determined whether or not it exceeds 0%. Here, if it is determined that the duty ratio exceeds 50%, the process proceeds to step 121, and the integral constant value is calculated from the duty ratio by 2.
(for example, duty ratio 2%) is subtracted, and step 1
24. In step 119, the duty ratio is 50%
In the following cases, the process proceeds to step 122, where the integral constant value K is determined from the duty ratio.

(for example, duty ratio 2%) is subtracted, and step 1
24. In step 124, the skip control is set to ON, and the process proceeds 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 less than zero, the process proceeds to step 126, where the duty ratio is corrected to zero. Then, the process proceeds to step 126, where the duty ratio is set to zero, and step 12
Proceeding to step 1, duty control of the fifth three-way solenoid valve 32 is performed. From this step 127, the valve control shown in FIG. 3 is started.

As described above, steps 118 to 126 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, the valve control routine is entered in step 2()0, and the intake air amount Q of the engine is read in step 201. The intake air amount is a signal from the air flow meter 24. Next, in step 202, whether it is a high speed range or a low speed range,
In other words, it is determined whether it is in the two-turbocharger operating range or the one-turbocharger operating range.

In the illustrated example, for example, if Q is greater than 5500Q/min, it is determined that the operation should be switched to two turbocharger operation, and if it is less than 5500Q/min, it is determined that the operation is in the one turbocharger operation range. However, as described below, in order to actually switch to two turbocharger operation,
Since there is a time delay, the switching will occur around 6000Q/1l)in.

If it is determined in step 202 that it is necessary to switch to two-turbocharger operation, the process proceeds to step 203. The 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 10a of the actuator 10, and the intake bypass valve 33 is closed. However, at this time, as described later, in the operating range of one turbocharger, the exhaust switching valve 1
7 has already been controlled to open slightly, and the auxiliary turbocharger 8 has been rotated in the run-up.

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 205, and the intake pipe pressure (supercharging pressure) downstream of the compressor is guided to the diaphragm chamber 16a 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 turning on the fourth three-way solenoid valve 28, 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 pressure downstream of the compressor is applied to the diaphragm chamber 118 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-mentioned predetermined time has passed, the intake air amount is approximately 6000 ta/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 close the intake switching valve 18, in step 20B, 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 close 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. For example, the intake pipe pressure PM is +500a7
If it is smaller than IHg, proceed to step 212, and the fifth
The 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 the intake pipe pressure PM is less than -100 sH9, it is determined to be a light load, and if it is -1oo, Hg 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 fully open, the exhaust switching valve 17 is fully open, and the intake bypass 33 is fully open, so one turbocharger is activated when the amount of intake air is small, and boost pressure and torque response are good. Become.

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
, 8b. 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! wIIH
If it is determined that the pressure is greater than or equal to g, 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 +500syH9. 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 +500anH9, but in the parallel turbocharger with variable number of actuations of this embodiment. , waste gate valve 31
Instead of opening the exhaust switching valve 17, a part of the exhaust gas is transferred to the turbine 8 of the auxiliary turbocharger 8 on the stop side.
By introducing 8M, the auxiliary turbocharger 8 is rotated during the run-up. The higher the run-up rotation speed of the auxiliary turbocharger 8, the higher the
The reduction in torque (torque shock) when switching from a single turbocharger to a dual turbocharger is reduced and the switch can be made smoothly.

In this small opening control, the fifth three-way solenoid valve 32 that opens the exhaust switching valve 17 is duty-controlled.

In the duty ratio in the small opening duty control, 1, K2 is added to the integral constant value that corrects the flow rate characteristics of the exhaust switching valve 17, and a skip value S that corrects the hysteresis of the driving force of the exhaust switching valve 11 is added. It has become. By correction based on this integral constant value, the opening/closing speed of the exhaust switching valve 17 by the actuator 16 can be slowed down in a region where the opening degree of the exhaust switching valve 17 is small, and conversely, the opening/closing speed can be accelerated in a region where the opening degree is large. As a result, the exhaust switching valve 17
The passing flow rate characteristic in a specific region is corrected, and the flow rate characteristic is made almost linear.

Therefore, even if the exhaust switching valve is a butterfly valve that does not have a linear flow rate characteristic with respect to the opening degree, the exhaust gas flow rate can be controlled accurately, and the controllability of the supercharging pressure P shown in FIG. improvement is expected.

Furthermore, by adding a skip value S that corrects the hysteresis of the driving force of the exhaust switching valve 17 to the duty ratio, the exhaust switching valve 17 can accurately follow the movement of the actuator 16, and the desired flow characteristics can be achieved. maintained.

In this embodiment, there were two types of integral constant values added to the duty ratio, but as shown in FIG. 7, if this integral constant value Ko is continuously changed with respect to the duty ratio, This enables fine-grained control and further improves controllability. In addition, in this embodiment, the skip control is turned on.
Although the skip value and integral constant value were the same on the side and the OFF side, it is also necessary to change the values on the ON and OFF sides depending on the type of engine.

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. 6, the supercharging characteristics of one turbocharger are superior to the supercharging characteristics of two turbochargers in the low rotation range. By using one turbocharger, the boost pressure and torque rise will be shorter, and the response will be faster.

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 5500ρ/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 the same effect can be obtained even if it is constructed from a swing arm valve.

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 method for controlling a supercharged engine according to the present invention, the flow rate characteristic of the exhaust switching valve means is adjusted to the duty ratio during the small opening duty control of the exhaust switching valve means. By adding an integral constant value to be corrected and a skip value to correct the hysteresis of the driving force of the exhaust switching means, the integral constant value is changed according to the duty ratio, so the difference in flow rate change due to the opening degree of the exhaust switching valve is can be corrected.

Therefore, accurate flow control is possible even with an exhaust switching valve such as a butterfly valve whose passage flow rate characteristic with respect to opening degree does not have a linear characteristic, and controllability of supercharging pressure 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 FIGS. 2 and 3 are control diagrams according to the present invention. FIG. 4 is a system diagram of the apparatus for carrying out the present invention, FIG. 5 is a characteristic diagram showing the relationship between the duty ratio and the opening degree of the exhaust switching valve, and FIG. 6 is the diagram shown in FIG. 4. one turbocharger in the device,
Charging pressure characteristics diagram when using two turbochargers, Figure 7 is the second
Figure 8 is a characteristic diagram showing a modification of the integral constant value, Figure 8 is a characteristic diagram showing the relationship between the flow rate passing through the exhaust switching valve and hysteresis, Figure 9 is a schematic system diagram of a conventional supercharged engine, It 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 actuator 13...
...Intake bypass passage 14...Intake passage (downstream of compressor) 15.
...Intake passage (] Compressor downstream 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 (duty control) 33... Intake bypass valve 1 In Figure 1, K2, KO... Integral constant value S...
・Skip value Fig. 5 (hysterinos) Duty ratio (7 working pressure) Fig. 7 Fig. 8 Fully closed? fW Mine 9 picture activity;, hehehe.

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 the method for controlling a supercharged engine in which a portion of the exhaust gas is supplied to an inactive auxiliary turbocharger and the auxiliary turbocharger is rotated during run-up, the exhaust gas switching valve is set to a duty ratio during small opening duty control of the exhaust switching valve means. A supercharger characterized in that an integral constant value for correcting the flow rate characteristics of the valve means and a skip value for correcting the hysteresis of the driving force of the exhaust switching valve are added, and the integral constant value is changed according to the duty ratio. How to control the attached engine.