JP3320765B2 - Air-fuel ratio control method for sequential turbo engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sequential turbo engine having a plurality of turbochargers and operating in a sequential turbo system as a vehicle engine.
The present invention relates to an air-fuel ratio control method for a sequential turbo engine that performs air-fuel ratio control optimally for each of a single turbo mode and a twin turbo mode.

[0002]

2. Description of the Related Art In recent years, as a supercharged engine for a vehicle, a multi-cylinder exhaust system is equipped with a primary and secondary turbocharger in parallel, and the turbocharger is operated in a sequential turbo type. Something to do is suggested. In this sequential turbo engine, the primary turbocharger is configured to be able to constantly supercharge, and an exhaust control valve, an intake control valve, a supercharging pressure relief valve, and the like are provided on the secondary turbocharger side. For example, only the primary turbocharger is operated in the single turbo mode in the low-speed range, and in the twin turbo mode in the high-speed range, the secondary turbocharger is first preliminarily rotated, and then both the turbochargers are operated to travel. The aim is to obtain the optimum engine output characteristics according to the state.

[0003] In this type of sequential turbo engine, even in the operating state with the same load, the exhaust resistance increases in the single turbo mode due to the inoperative secondary turbocharger. Therefore, the back pressure of the engine increases, the charging efficiency decreases, the combustion slows down, and the exhaust gas temperature rises. For this reason, in general, a fuel correction coefficient (for example, a full increase coefficient) is set to a relatively large value, and the air-fuel ratio is controlled so that the fuel is cooled by the rich mixture to lower the exhaust gas temperature.
On the other hand, in the twin turbo mode, the exhaust resistance is reduced by the operation of both turbochargers, and conversely, the engine back pressure is reduced, the charging efficiency is increased, and the combustion is improved. Therefore, in the twin turbo mode, if the air-fuel ratio is controlled by the same correction coefficient as that of the single turbo mode, the air-fuel ratio becomes over-rich and causes problems such as misfire, poor running performance, and a rise in exhaust gas temperature. This is particularly noticeable when control is performed in a single turbo mode or a twin turbo mode over the entire area by fail-safe operation such as failure diagnosis. Therefore, in the air-fuel ratio control of this type of engine, it is required to set an appropriate correction coefficient for each of the single turbo mode and the twin turbo mode.

Conventionally, as for the above-mentioned sequential turbo engine, there is a prior art disclosed in, for example, Japanese Patent Application Laid-Open No. 3-88917. Here, the exhaust leakage valve is opened, a small amount of exhaust gas is introduced into the secondary turbocharger for pre-rotation, and then the exhaust cut valve is opened to activate the secondary turbocharger. It is shown that the pressure of exhaust gas supplied to the secondary turbocharger is increased by closing the gate valve, and the number of revolutions is increased responsively.

[0005]

In the above prior art, the valve opening / closing control is performed when shifting from the single turbo mode to the twin turbo mode. Therefore, the air / fuel ratio control in each of these modes is performed. I can't deal with it.

The present invention has been made in view of this point, and appropriately sets a correction coefficient for each mode in accordance with exhaust resistance, intake air, combustion characteristics, and the like in a single turbo mode and a twin turbo mode. To control the air-fuel ratio optimally.

[0007]

In order to achieve the above object, the present invention provides a primary turbocharger and a secondary turbocharger arranged in parallel in an intake and exhaust system. Operates only the turbocharger, controls both the primary turbocharger and the secondary turbocharger in the twin turbo mode, and adjusts the fuel injection amount in each mode to the basic injection amount and the full increase coefficient at high load In a sequential turbo engine that calculates and controls the air-fuel ratio, the full boost area is set on the high load side of the single turbo mode and the twin turbo mode, and the full boost coefficient for single in the full boost area of the single turbo mode is set in the twin turbo mode. Full for twin of full increase area
Defined large relative increase coefficient, single turbo mode to the twin for full increase coefficient full up region of the twin turbo mode
It is determined to be smaller than the full increase coefficient for single in the full increase region of the code.

[0008]

According to the above air-fuel ratio control method, the single turbo mode is determined and the primary turbocharger is operated so that only the primary turbocharger is operated in, for example, a low to medium speed range during engine operation. When it comes to twin turbo
Larger than the full increase coefficient for twins in the full increase
The air-fuel ratio is richly controlled by a predetermined single-use full increase coefficient to reduce the exhaust gas temperature. Further, when determining the twin turbo mode at the high speed range, is controlled to operate both turbochargers, single for the full increase engagement of the single turbo mode becomes full increase areas of high load side this time
With the twin full increase coefficient smaller than the number, the air-fuel ratio is controlled to be optimal for the good intake and combustion characteristics in this case.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the overall configuration in the case where a sequential turbocharger is mounted on a horizontally opposed engine will be described. Reference numeral 1 denotes an engine body of a horizontally opposed engine, which is provided in left and right banks 3 and 4 of a crankcase 2.
A combustion chamber 5, an intake port 6, an exhaust port 7, a spark plug 8, a valve mechanism 9, and the like are provided. Due to this engine shortening shape, a primary turbocharger 40 and a secondary turbocharger 50 are respectively provided immediately after the left and right banks 3 and 4. Left and right banks 3, 4 as exhaust system
Are connected to the turbines 40a, 50a of the turbochargers 40, 50, and the turbine 40a,
The exhaust pipe 11 from 50a joins one exhaust pipe 12 and communicates with the catalytic converter 13 and the muffler 14.

As an intake system, intake pipes 16 and 17 branched from the air cleaner 15 into two pipes are connected to blowers 40b and 50b of both turbochargers 40 and 50, respectively, and the intake pipes 18 and 17 from the blowers 40b and 50b are connected. 19 is communicated with the intercooler 20. The air is communicated from the intercooler 20 to a chamber 22 via a throttle body 27 having a throttle valve 21, and is communicated from the chamber 22 to each cylinder of the left and right banks 3 and 4 via an intake manifold 23. In addition, as an idle control system, an idle control valve 25 and a check valve 2 that opens with a negative pressure are provided in a bypass passage 24 directly downstream of the air cleaner 15 and the intake manifold 23.
6 is provided to control the intake air amount during idling or deceleration.

As a fuel system, an injector 30 is provided near a port of the intake manifold 23, and a fuel pump 3
A fuel passage 33 from a fuel tank 32 having a filter 1 and a fuel pressure regulator 35 communicates with the injector 30. The fuel pressure regulator 35 regulates the fuel pressure supplied to the injector 30 at a constant level with respect to the intake pressure, and controls the fuel injection by the pulse width of the injection signal. It is possible to do. The ignition system is connected so that an ignition signal from the igniter 36 is input to the ignition plug 8 as an ignition system.

An operation system of the primary turbocharger 40 will be described. The primary turbocharger 40 uses a blower 40b by the energy of exhaust gas introduced into the turbine 40a.
, And operates so that air is inhaled, pressurized and constantly supercharged. A waste gate valve 41 provided with a diaphragm type actuator 42 is provided on the turbine side. Further, a control pressure passage 44 having a duty solenoid valve 43 is provided in the pressure chamber of the actuator 42 from above and downstream of the blower 40b, and the control pressure is generated by leaking the supercharging pressure by the duty solenoid valve 43. Acting on the actuator 42, the opening degree of the waste gate valve 41 is changed to control the supercharging pressure. Here, for example, when the duty ratio is large, the control pressure is reduced by increasing the leak amount, and the opening degree of the waste gate valve 41 is reduced to increase the supercharging pressure. Conversely, when the duty ratio decreases, the opening degree is increased at a high control pressure, and the supercharging pressure is reduced.

On the other hand, a bypass passage 46 is communicated between the upper and lower portions of the blower 40b in order to prevent a decrease in the rotation of the blower and the occurrence of intake noise when the throttle valve is rapidly closed. An air bypass valve 45 is provided in the bypass passage 46 so as to be opened by the manifold negative pressure when the throttle valve is suddenly closed, so that the pressurized air sealed downstream of the blower leaks quickly.

An operation system of the secondary turbocharger 50 will be described. Similarly, the secondary turbocharger 50 is supercharged by rotating the turbine 50a and the blower 50b by the exhaust gas. A waste gate valve 51 is separately provided on the turbine side, and supercharging pressure is controlled by a control pressure passage 54 having an actuator 52 and a duty solenoid valve 53. On the other hand, an exhaust control valve 55 having a diaphragm actuator 56 is provided in the exhaust pipe 10 upstream of the turbine 50a.
An intake control valve 58 provided with a similar actuator 57 is provided downstream of the blower 50b.
A relief passage 59 having a supercharging pressure relief valve 60 is communicated between the upstream and downstream of Ob.

The pressure operation system of each of these valves will be described. A passage 61 from the intake manifold 23 has a check valve 62 and communicates with a surge tank 63 to store a negative pressure when the throttle valve is fully closed and to generate a pulsating pressure. It is designed to buffer. In one spring chamber of the supercharging pressure relief valve 60, a negative pressure passage 64 from the surge tank 63 and a positive pressure passage 65 by the supercharging pressure downstream of the intake control valve 58 are connected to the switching solenoid valve 70 and the passage 66. And is opened by applying a negative pressure by an electric signal and closed by applying a positive pressure.

The actuator 57 of the intake control valve 58 is
A positive pressure is always applied to one of the chambers by the positive pressure passage 67, and the positive pressure passage 65 and the negative pressure passage 64 are connected to the spring chamber via a switching solenoid valve 71 and a passage 68. Then, a negative pressure is applied to the spring chamber by an electric signal to close the intake control valve 58, and the intake control valve 58 is opened by a spring force when both chambers are set to a positive pressure. The actuator 56 of the exhaust control valve 55 has a second chamber for switching between atmospheric pressure and negative pressure in one chamber.
The switching solenoid valve 74 is communicated via a passage 69, and a first switching solenoid valve 73 for switching between positive pressure and negative pressure is communicated via a passage 75 with the other chamber. The exhaust control valve 55 is closed by applying an atmospheric pressure to one chamber and applying a negative pressure to the other chamber by an electric signal to apply a negative pressure to one chamber and applying a positive pressure to the other chamber to cause the exhaust control valve 55 to operate. Configured to open.

A description will be given of various sensors. A differential pressure sensor 80 is provided to detect a differential pressure between upstream and downstream of the intake control valve 58, and an absolute pressure sensor 81 is controlled by a switching solenoid valve 76 to detect the intake pipe pressure. It is provided to select and detect the atmospheric pressure. Further, a crank angle sensor 82, a knock sensor 83, and a water temperature sensor 84 are provided on the engine body 1, and a cam angle sensor 85 is provided opposite to a cam rotor (not shown) connected to a cam shaft of the valve mechanism 9; 10 is provided with an O2 sensor 86 and the throttle valve 21 is provided.
A throttle opening sensor 87 is provided in the air cleaner 15, and an intake air amount sensor 88 is provided immediately downstream of the air cleaner 15.

Referring to FIG. 2, the overall configuration of the electronic control system will be described. First, a control unit 100 including a microcomputer and the like includes an I / O 101, a CPU 102,
RAM 103, backup RAM 104, ROM 10
5. A constant voltage circuit 106 is provided. When the ignition switch 90 is turned on, the relay 91 is turned on, power is supplied from the battery 92 to the constant voltage circuit 106, various controls of the control unit 100 are executed, the relay 93 is turned on by the drive circuit 107, and the fuel pump 31 is turned on. It is energized and driven. The CPU 102 inputs signals from the various sensors 80 to 88 from the I / O 101 based on an arithmetic program stored in the ROM 105 and converts the signals into data stored in the RAM 103 and fixed data such as a map stored in the ROM 105. Calculation processing is performed based on this. Then, various kinds of switching solenoid valves 70, 71, 73,
The switching signal is supplied to the duty solenoid valve 4
A duty signal is output to 3, 53 to perform sequential turbo control, and an injection signal is output to the injector 30 to perform fuel injection control. Further, it is configured to output an ignition signal to the igniter 36 to control the ignition timing, and output a control signal to the idle control valve 25 to perform the idle control.

Next, the sequential turbo control by the control unit 100 will be described with reference to the flowcharts of FIGS. The main routine of FIG. 3 is executed every predetermined time. First, in step S1, the value of the secondary turbocharger operation determination flag F1 that is set to 1 when the secondary turbocharger is activated is referred to. If F1 = 0 is not operated, the process proceeds to steps S2 to S4, and FIG. The determination is made based on the turbo mode determination map of a).

This turbo mode determination map is based on the basic injection amount Tp as an example indicating the engine load and the set values Tps, Nb and Nc for starting the operation of the secondary turbocharger with respect to the engine speed N. Turbo mode is given. That is, Tp ≦ Tps, N
<Nc low load low medium speed or Tp> Tps, N <Nb
Under the condition of high load and low speed, the single turbo mode is set. In the other conditions of low load and high speed Tp ≦ Tps and N ≧ Nc, or high load medium and high speed of Tp> Tps and N ≧ Nb, the twin turbo mode is set. In order to prevent hunting of operation and stop of the secondary turbocharger, hysteresis is provided for the operation stop set value Na.

Therefore, in S2, the basic injection amount Tp and the set value Tp
If Tp ≦ Tps, the process proceeds to step S3, where the engine speed N is compared with the set value Nc, and N <
In the case of Nc, it is determined that the mode is the single turbo mode, and the process proceeds to step S5. If Tp> Tps in step S2, the process proceeds to step S4, where the engine speed N is compared with a set value Nb, and when N <Nb, the single turbo mode is similarly determined.

In this single turbo control routine, the output signal G1 of the switching solenoid valve 70 is set to 0 in step S5, and the boost pressure relief valve 60 is opened. Step S
In step 6, the output signal G2 of the switching solenoid valve 71 is set to 0 to close the intake control valve 58, and in steps S7 and S8, the output signals G3 and G4 of the switching solenoid valves 73 and 74 are set to 0 to close the exhaust control valve 55. In step S9, the duty ratio Dse of the secondary-side duty solenoid valve 53 is set to FF.
H (100%) to completely close the waste gate valve 51. Thereafter, in step S10, based on the engine speed N and the throttle opening Th, the optimum value in the single turbo mode previously obtained by an experiment or the like is stored.
The target supercharging pressure Pt is set with reference to the single turbo mode target supercharging pressure map stored in the OM 105 with interpolation calculation, and the secondary turbocharger operation determination flag F1 is cleared in step S11. In step S12, the count value C of the delay time is cleared.

Next, in the supercharging pressure control routine of FIGS. 5 and 6, first, in step S13, the target supercharging pressure Pt and the actual supercharging pressure Pt are determined.
is calculated, and if the absolute value | Δp | of the deviation is smaller than the set value Δps in step S14, the actual supercharging pressure Pb converges to the allowable range of the target supercharging pressure Pt. In step S15, the integral control amount Di is set to zero, and in step S16, the proportional control amount Dp is also set to zero. Then, in step S17, the duty ratio D is obtained by adding the control amounts Dp and Di for the integral value and the proportional value to the previous value Do. In this case, the duty ratio D becomes the same as the previous value Do. Then, in step S18, the value of the flag F1 is referred to,
Since it has already become 0, the duty ratio D is output as the duty ratio Dpr of the primary side duty solenoid valve 43 in step S19, and this duty ratio D is stored as the previous value Do in step S20.

In this mode, if the absolute value | Δp | of the difference between the target supercharging pressure Pt and the actual supercharging pressure Pb becomes larger than the set value Δps, the process proceeds from step S14 to step S21, where the target supercharging of the actual supercharging pressure Pb is performed. The magnitude relationship with the supply pressure Pt is checked. Therefore, as shown at t1 in FIG.
Under the condition that b has decreased, the value of the PI control determination flag F2 set to 1 at the time of down correction of the duty ratio D in step S22 is referred to. If F2 = 1 and the increase of the duty ratio D is the first time, the process proceeds to step S22. In S23, the integral control amount Di is set to zero. Then, in step S24, the process proceeds to step S25 with reference to the value of the flag F1, and the proportional increase amount Pup1 corresponding to the deviation Δp is set.

Here, in the single turbo mode, the proportional control amount Dp is a solid line of the proportional correction amount map of FIG. 7C, and the integral control amount Di is a solid line of the integral correction amount map of FIG. 7D. Are set in a step shape with a large control amount as shown in FIG. In the twin turbo mode, the proportional control amount Dp and the integral control amount Di with respect to the difference Δp are set based on the operation distribution of the turbochargers 40 and 50. Therefore, for example, when the operation distribution of the two turbochargers 40 and 50 is set equally, the control amounts Dp and D of the proportional component and the integral component are set.
i only needs to be one type, so that FIG.
One control amount is set as shown by the broken line in (d).

For this reason, in step S25, the proportional increase amount Pup1 corresponding to the deviation Δp is set to a large value according to the map, and in step S26, the proportional increase amount Pup1 is determined as the proportional control amount Dp.
In step S27, the PI control determination flag F2 is cleared, and the process proceeds to step S17 and subsequent steps. Accordingly, the duty ratio Dpr of the primary-side duty solenoid valve 43 increases by the proportional control amount Dp, the opening of the waste gate valve 41 decreases, and the actual supercharging pressure Pb increases relatively greatly as shown in FIG.

After the second time, the process proceeds to step S28 according to the flag F2 in step S22 and refers to the value of the flag F1. In step S29, the integrated amount increase amount Iup1 corresponding to the deviation Δp is searched from the map in FIG. Then, in step S30, this is determined as the integral control amount Di, and in step S31, the proportional control amount Dp is set to zero. FIG.
In the case of the second time or later such as t2, the actual boost pressure Pb is gradually increased by the integral control amount Di, and the actual boost pressure Pb follows the target boost pressure Pt by these corrections. And t
When the deviation Δp becomes smaller than the set value Δps and converges in step 3, the control proceeds from step S14 to step S15 and thereafter to interrupt the control.

On the other hand, when the deviation Δp becomes larger than the set value Δps on the higher side of the actual supercharging pressure Pb as at t5 in FIG. 8, the process proceeds from step S21 to step S32, in which case the flag F2 is set to 0 by the above control. In the case of the first time according to the flag F2, the process proceeds to step S33 and subsequent steps. Therefore, the integral control amount Di is set to 0 in step S33, the process proceeds to step S35 with reference to the value of the flag F1 in step S34, and the proportional map down amount Pdo1 corresponding to the deviation Δp is searched using a similar map. This is determined as the proportional control amount Dp in S36, and PI
The control discrimination flag F2 is set to 1 and the process proceeds to step S17 and subsequent steps. Therefore, the primary side duty solenoid valve 43
Is reduced by the proportional control amount Dp,
As the opening of the waste gate valve 41 increases, the actual supercharging pressure Pb decreases relatively largely as shown in FIG.

After the second time, the process proceeds to step S38 according to the flag F2 in step S32, and refers to the value of the flag F1.
Is searched for the integral down amount Ido1 corresponding to
At 40, this is set as the integral control amount Di, and
At 41, the proportional control amount Dp is set to 0. Therefore, t in FIG.
In the case of the second and subsequent times, such as 6, the actual supercharging pressure Pb is gradually reduced by the integral control amount Di. Thus, in the single turbo mode, the secondary turbocharger 50 does not operate, only the primary turbocharger 40 operates, and the opening degree of the waste gate valve 41 changes according to the PI control amount, so that the comparatively low turbocharger in this case is used. Feedback control is performed so that the actual boost pressure Pb always follows the target boost pressure Pt with good response.

Next, in steps S2 to S4, Tp ≦
Tps, N ≧ Nc, or Tp> Tps, N ≧ Nb
If it is determined that the mode is the twin turbo mode, the preliminary rotation control routine of FIG. 4 is executed.

At the time of this mode switching, three types of valves 55 and 5 provided on the secondary turbocharger side are used.
Focusing on 8, 60, first close the boost pressure relief valve 60,
Next, opening and closing control is performed so that the exhaust control valve 55 is opened and then the intake control valve 58 is opened, so that preliminary rotation control can be performed. Further, by using these valves 55, 58, and 60, the valve characteristics and the like become the same, and it is possible to shift to the twin turbo mode with little torque fluctuation. From this, after the start of the preliminary rotation, the first delay time T1 for closing the boost pressure relief valve 60, the second delay time T2 for opening the exhaust control valve 55, and the third delay time for opening the intake control valve 58.
Are respectively determined as T3 <T2 <
It is set in relation to T3.

Therefore, in step S50, the count value C of the time from the pre-rotation start time ts in FIG. 9 is compared with the first delay time T1, and if C <T1, step S50 is executed.
Proceeding to 51, the count value C is incremented. Then, in step S52, the duty ratio Dpr of the primary side duty solenoid valve 43 is set to FFH, the waste gate valve 41 is fully closed, and the primary turbocharger 40
Is controlled to be slightly higher so that the output does not decrease. In step S53, the secondary side duty solenoid valve 53 is also prepared so that the duty ratio Dse is set to FFH, the waste gate valve 51 is fully closed, and the preliminary rotation can be performed efficiently.

When the count value C reaches the first delay time T1, the process proceeds from step S50 to step S54,
The output state of the switching solenoid valve 70 is checked. If the output signal is an open signal (G1 = 0), the output signal G1 of the switching solenoid valve 70 is set to 1 in step S55, and as shown in FIG. Close. Therefore, thereafter, the process proceeds from step S54 to step S56, where the count value C is compared with the second delay time T2, and if the time has not reached the second delay time T2, the count value C is incremented in the same manner as described above. When the second delay time T2 has been reached, the output state of the switching solenoid valve 73 is checked in step S57, and if the closing signal (G3 = 0), the output signal of the first switching solenoid valve 73 is determined in step S58. By setting G3 to 1, a positive pressure is supplied to one chamber of the actuator 56. In step S59, the output state to the switching solenoid valve 74 is checked, and the close signal (G4 =
0) In step S60, the second switching solenoid valve 7
The output signal G4 of step 4 is set to 1 to supply a negative pressure to the other chamber of the actuator 56. Thus, the exhaust control valve 55 is opened as shown in FIG. Thereby, a part of the exhaust gas is introduced into the turbine 50a of the secondary turbocharger 50 and preliminarily rotated.

Thereafter, in step S61, the count value C is compared with the third delay time T3, and when the time T3 is reached, the output voltage E of the differential pressure sensor 80 is compared with the set value Es in step S62. Then, when the differential pressure becomes substantially zero, the output state to the switching solenoid valve 71 is checked in step S63, and if the closing signal (G2 = 0), the flow proceeds to step S63.
In step 64, the output signal G2 of the switching solenoid valve 71 is set to 1 and the intake control valve 58 is opened as shown in FIG.
In step 5, the secondary turbocharger operation determination flag F1 is set to 1. For this reason, at the time point tg when the intake control valve 58 is opened, the secondary turbocharger 50 ends the preliminary rotation and substantially operates, and automatically shifts to the twin turbo mode with little torque fluctuation. .

In this twin turbo control routine, FIG.
The process proceeds from step S1 to step S70 to check the engine speed N against the set value Na for stopping the operation of the secondary turbocharger. If N ≧ Na, the output signals G1 to G4 for the switching solenoid valves of the respective valves are held in the above-described state in steps S71 to S74. In step S75, based on the engine speed N and the throttle opening Th, the twin turbo mode target supercharging pressure map is referred to with interpolation calculation, and the target supercharging pressure Pt in this mode is calculated as follows.
As shown in FIG. 7 (b), a high level is set, and step S1 is performed.
In S3, S14, S21, the following state of the actual supercharging pressure Pb with respect to the target supercharging pressure Pt is determined. By the way, at the beginning of this mode, the waste gate valves 41, 51 of the primary and secondary turbochargers 40, 50 are both fully closed and are in a full operation state as in the above-described preliminary rotation. Actually, the actual supercharging pressure Pb increases, and t5 in FIG.
The deviation Δp increases on the higher side as shown in FIG.

Therefore, in the supercharging pressure control routine in this case, in the case of the first time, from step S21 to step S32,
The process proceeds to step S76 via S33 and S34, and FIG.
The proportional down amount Pdo2 corresponding to the deviation Δp is searched using the broken line in the map of (c), and the duty ratio D is calculated in step S77 as the proportional control amount Dp. Further, the process proceeds from step S18 to S78 and S79, where the duty ratios Dpr and Dse of the primary and secondary duty solenoid valves 43 and 53 are equal and the duty ratio D
And the actual supercharging pressure Pb is decreased by increasing the opening of both waste gate valves 41 and 51 equally. And 2
After the first time, the process proceeds from step S32 to step S80 via step S38, and the integral down amount Ido2 is searched using the broken line in the map of FIG.
By setting this to the integral control amount Di at 81, the actual supercharging pressure Pb is gradually reduced and approaches the target supercharging pressure Pt.

When the deviation Δp increases on the lower side of the actual supercharging pressure Pb as shown at t1 in FIG. 8, in the case of the first time, the process proceeds from step S21 to steps S82 and S83 via steps S22, S23 and S24. Then, the proportional control amount Dp is determined by the proportional increase amount Pup2 corresponding to the deviation Δp. 2
After the first time, the process proceeds from step S22 to step S84 via steps S28 and S85, and similarly calculates the duty ratio D by determining the integral control amount Di with the integral increase amount Iup2 corresponding to the deviation Δp. Then, the duty ratios Dpr and Dse of the primary and secondary duty solenoid valves 43 and 53 are set equal to the above-mentioned duty ratio D, and the opening degrees of the waste gate valves 41 and 51 are reduced equally, so that the actual supercharging pressure Pb is increased. The actual supercharging pressure Pb follows the target supercharging pressure Pt. Thus, in this twin turbo mode, the primary and secondary turbochargers 40, 50 have their waste gate valves 41,
51, the two turbochargers 4 always operate equally.
The actual supercharging pressure Pb is controlled to an appropriate high level by the co-operation of 0 and 50.

Next, at the time of deceleration, the engine speed N is checked in step S70. If the engine speed N falls below the set value Na for stopping the operation of the secondary turbocharger, the process proceeds from step S70 to step S5 and subsequent steps. Then, the output signals G1 to G4 for the switching solenoid valves are inverted to open the supercharging pressure relief valve 60, close the intake control valve 58 and the exhaust control valve 55, and return to the single turbo mode. FIG. 10 shows the control states and output characteristics of the single turbo mode and the twin turbo mode.

Further, the fuel injection control will be described as the air-fuel ratio control with reference to the flowchart of FIG. This fuel injection control routine is executed at predetermined time intervals. In step S90, the basic injection amount Tp is calculated based on the intake air amount Q, the engine speed N, and the injector characteristic constant K by Tp ← K ·
It is calculated by Q / N. Thereafter, in step S91, a feedback correction coefficient α, an air-fuel ratio learning correction coefficient Kb, various increase correction coefficients COEF, and a voltage correction value Ts are set. In step S92, the engine speed and the basic fuel injection amount Tp as an example of the engine load are set. It is checked whether the engine operation state is in the full increase range D.

Here, the full increase range D is set on the high load side in the single turbo mode and the twin turbo mode according to the relationship between the basic injection amount Tp and the engine speed N as shown in the full increase determination map in FIG. Have been. Therefore, if the condition is not the full increase range D under the low and medium load operation conditions, step S9
Proceeding to 3, the full increase coefficient Kf is set to 1.0. In step S94, the basic injection amount Tp, the feedback correction coefficient α, the air-fuel ratio learning correction coefficient Kb, the various increase correction coefficients COEF, the full increase coefficient Kf, and the voltage correction value T
The fuel injection amount Ti is calculated by the following equation: Ti ← Tp · α · Kb · COEF · Kf + Ts, and the fuel injection amount Ti is set in step S95 to control the fuel injection amount of the injector 30. Therefore, under these operating conditions in which the engine load is relatively small and supercharging is not maximized, the air-fuel ratio is controlled near the optimum stoichiometric air-fuel ratio in any mode.

On the other hand, under the operating conditions on the high load side, the operation proceeds to step S96 from step S92 in the full increase range D, and the secondary turbocharger operation determination flag F1 is checked. Therefore, in the case of the single turbo mode, the process proceeds to step S97, in which a single full increase coefficient K1 is obtained by referring to a map based on the engine speed and set as the full increase coefficient Kf. On the other hand, in the case of the twin turbo mode, the process proceeds to step S98, and similarly, by referring to the map based on the engine speed, the twin full increase coefficient K
Set 2. Here, as shown in FIG. 12 (b), the single full increase coefficient K1 is set with a larger increase function with respect to the engine speed N, and the twin full increase coefficient K2 is a smaller increase function with respect to the engine speed N. Is set.

Therefore, in the high load operation in the single turbo mode, the full fuel increase coefficient K1 for single is set to a large value as the full fuel increase coefficient Kf in step S97. Is done. Therefore, fuel is cooled by the rich mixture in this case, and an increase in exhaust resistance due to an increase in exhaust resistance is suppressed.
In high-load operation in the twin turbo mode, step S
The program proceeds to 98, in which the full increase coefficient K2 for twin is set smaller than that in the single turbo mode as the full increase coefficient Kf. From step S94, the fuel corresponding to the good intake and combustion characteristics due to the reduction of the exhaust resistance in this mode. Is increased to a smaller amount than in the single turbo mode. Therefore, the air-fuel ratio is controlled to the optimum value, thereby preventing over-enrichment.

Although the embodiment of the present invention has been described above, it is needless to say that the present invention can be applied to engines other than the horizontally opposed engine. Further, the present invention can be similarly applied to different sequential turbo control.

[0044]

As described above, according to the present invention,
In the sequential turbo engine, in the full load region on the high load side, the air-fuel ratio is controlled using the respective full increase coefficients in the single turbo mode and the twin turbo mode, so the air-fuel ratio should be optimally controlled for each mode. Can be. The full increase coefficient for single in single turbo mode is the same as the full increase coefficient for twin in twin turbo mode.
On the other hand, since the exhaust gas temperature is set to be large, it is possible to effectively reduce the increase in the exhaust gas temperature due to the increase in the exhaust resistance in this case by the rich air-fuel ratio. In addition , twin turbo mode
The full increase coefficient for twin at the time of single turbo mode
Since it is set to be smaller than the single full increase coefficient, the air-fuel ratio can be controlled to an optimum air-fuel ratio in accordance with the good intake and combustion characteristics in this case, and the over-rich and the accompanying problems are reliably prevented. It becomes possible. The full increase coefficient is appropriately set according to the relationship with the engine speed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment suitable for an air-fuel ratio control method for a sequential turbo engine according to the present invention.

FIG. 2 is an overall circuit diagram of a control system.

FIG. 3 is a flowchart showing a main routine of sequential turbo control.

FIG. 4 is a flowchart showing a preliminary rotation control routine.

FIG. 5 is a flowchart showing a correction of a decrease in a boost pressure control routine and the like.

FIG. 6 is a flowchart illustrating a boost correction and the like in a supercharging pressure control routine.

FIG. 7 is a diagram showing various maps.

FIG. 8 is a time chart showing a state of supercharging pressure control.

FIG. 9 is a time chart showing the opening / closing state of each valve and the state of supercharging pressure in the preliminary rotation mode.

FIG. 10 is a diagram showing control and output characteristics of a single turbo mode and a twin turbo mode.

FIG. 11 is a flowchart illustrating a routine of fuel injection control.

FIG. 12 is a diagram showing various maps of fuel injection control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 10, 11, 12 Exhaust pipe 16, 17, 18, 19 Intake pipe 40 Primary turbocharger 50 Secondary turbocharger 55 Exhaust control valve 58 Intake control valve 60 Supercharging pressure relief valve 100 Control unit

Claims (3)

(57) [Claims] 1. A primary turbocharger and a secondary turbocharger arranged in parallel in an intake and exhaust system, only a primary turbocharger is operated in a single turbo mode, and a primary turbocharger is operated in a twin turbo mode. In a sequential turbo engine that controls both the turbocharger and the secondary turbocharger to operate together, and calculates the fuel injection amount in each mode based on the basic injection amount and the full increase coefficient at high load to control the air-fuel ratio, Set the full increase area on the high load side of the twin turbo mode and the full increase coefficient for single in the single turbo mode
It is set to be larger than the full boost coefficient for the twin in the full boost area, and the full boost coefficient for the twin in the full boost area in the twin turbo mode is single in the full boost area in the single turbo mode.
A method for controlling an air-fuel ratio of a sequential turbo engine, wherein the air-fuel ratio is set to be smaller than a full increase coefficient for use. 2. The method for controlling an air-fuel ratio of a sequential turbo engine according to claim 1, wherein the full increase coefficient for single and the full increase coefficient for twin are set by an increasing function with respect to the engine speed. 3. The engine has a sequential turbo control routine and an air-fuel ratio control routine. The air-fuel ratio control routine includes a procedure for determining a full boost range, a procedure for determining operation of a secondary turbocharger, and a full boost. 2. The method according to claim 1, further comprising: a step of determining a full fuel increase coefficient in a case of a full fuel increase range in a single turbo mode and a twin turbo mode, and a procedure of calculating a fuel injection amount based on the full fuel increase coefficient. An air-fuel ratio control method for a sequential turbo engine as described in the above.