JPH0441957A - Air-fuel ratio control device for supercharge lean-burn gasoline internal combustion engine - Google Patents

Abstract

PURPOSE:To control an air-fuel ratio to a lean side without deteriorating operability in a device wherein a lean combustion is performed under a supercharge condition by changing the shifting speed to a lean air-fuel ratio according to an acceleration degree in an intermediate range from a theoretical air-fuel ratio to the lean air-fuel ratio. CONSTITUTION:A supercharge condition detecting means B detects a condition where supercharging is substantially carried out by a supercharger A. When a non-supercharge condition is judged by the supercharge condition detecting means B, a rich air-fuel ratio is set by a rich air-fuel ratio setting means D. Under the supercharge condition, a target lean air-fuel ratio is set by a lean air-fuel ratio setting means D through an intermediate air-fuel ratio which is inclined to the lean side a little compared to the rich air-fuel ratio. When an acceleration condition of an engine is detected by an acceleration detecting means E, the changing speed of the air-fuel ratio is adjusted so as to accelerate the shifting to the target lean air-fuel ratio by means of an air-fuel ratio changing speed adjusting means G.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for a gasoline internal combustion engine that performs lean combustion during supercharging.

[Prior art]

Patent Application No. 1-156685 is an internal combustion engine that uses gasoline as fuel and is equipped with a supercharger. engine (hereinafter referred to as a high-density supercharged lean-burn internal combustion engine). Strong supercharging increases the density of the air-fuel mixture, and even on the lean side of the air-fuel ratio, the amount of fuel per unit volume of the air-fuel mixture increases. This aims to achieve stable lean combustion even under high loads.

In conventional systems, when a supercharging effect cannot be obtained (that is, when the boost is below θ (negative pressure)), the air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and after a supercharging effect is obtained, the air-fuel ratio is adjusted to a lean air-fuel ratio. is switching to. Ideally, the air-fuel ratio is switched from the stoichiometric air-fuel ratio (:14.5) to a lean air-fuel ratio (for example, 19.0) in steps. This is No. at intermediate air-fuel ratios.
This is because the amount of x component discharged increases. However, when switching the air-fuel ratio in steps, if the throttle valve is slightly operated near the switching line, there is a risk that an unnatural phenomenon may occur where the fuel injection amount decreases even though the throttle valve is open. There is. Therefore, an intermediate air-fuel ratio (for example, 16.0) is used between the stoichiometric air-fuel ratio range and the lean air-fuel ratio range.
It has an area.

[Problem that the invention seeks to solve]

In the prior art, the value of the air-fuel ratio is determined in the intermediate region between the stoichiometric air-fuel ratio and the lean air-fuel ratio according to the engine load and rotation speed. The size of the intermediate region is set so that an appropriate change in air-fuel ratio can be obtained in response to a change in rotational speed during normal acceleration. However, with this setting, the transition of the air-fuel ratio is delayed during sudden acceleration. Although the air-fuel ratio can be changed rapidly during rapid acceleration, the air-fuel ratio actually changes only slowly, resulting in a longer period of operation at an intermediate air-fuel ratio, which has the disadvantage of increasing the amount of nitrogen oxide component emissions.

[Means to solve the problem]

According to this invention, in FIG. 1, in an internal combustion engine that uses gasoline as fuel and is equipped with a supercharger, supercharging state detection means B for detecting a state in which supercharging is substantially performed by supercharger A; , a means C for setting a non-lean air-fuel ratio when a non-supercharged state is determined, and a means for setting a target lean air-fuel ratio via an intermediate air-fuel ratio that is somewhat leaner than the non-lean air-fuel ratio in a supercharged state. It also includes means E for detecting the acceleration state of the engine, and means G for adjusting the air-fuel ratio change speed so as to hasten the transition to the target lean air-fuel ratio in the acceleration state.

[Effect]

The supercharging state detection means B detects a state in which supercharging is substantially performed by the supercharger A.

The non-lean air-fuel ratio setting means C sets a non-lean air-fuel ratio when it is determined that the non-supercharging state is present.

The lean air-fuel ratio setting means sets the original target lean air-fuel ratio via an intermediate air-fuel ratio that is somewhat leaner than the non-lean air-fuel ratio in the supercharging state.

The acceleration detection means E detects the acceleration state, and the air-fuel ratio change rate adjusting means G adjusts the air-fuel ratio change speed so as to hasten the transition to the target lean air-fuel ratio in the acceleration state.

〔Example〕

FIG. 2 shows an embodiment of the present invention, in which 10 is an engine body, to which an intake pipe 12 and an exhaust pipe 14 are connected. The intake pipe 12 has a fuel injector 15 and a throttle valve 16. A large turbocharger 17 and a small turbocharger 18 are arranged in series. The large turbocharger 17 includes a compressor 2Q, a turbine 22, and a rotating shaft 24. small turbocharger 18
is composed of a compressor 26, a turbine 28, and a rotating shaft 25. In the intake pipe 12, in the flow direction of intake air, a compressor 20 of a large turbocharger 17,
The compressor 26 of the small turbocharger 18 is arranged in this order, the intercooler 29 is arranged downstream of the compressor 26, and the throttle valve 16 is arranged downstream of the intercooler 29.

In the exhaust pipe 14, the turbine 28 of the small turbocharger 18 and the turbine 22 of the large turbocharger 17 are arranged in this order in the flow direction of exhaust gas.

A first exhaust bypass passage 30 is connected to the exhaust pipe, bypassing the turbine of the large turbocharger 17, and a wastegate valve 32, which is a swing door type valve, is arranged in the first exhaust bypass passage 30.

The waste gate valve 32 is connected to a diaphragm actuator 34, and its diaphragm 34a is connected to the uniform gate valve 32. Waste gate valve 32
Normally biased to close by spring 34b, the positive pressure applied to diaphragm 342 causes wastegate valve 32 to open against spring 34b.

A second exhaust bypass passage 36 is provided to bypass the turbine 28 of the small turbocharger 18, and an exhaust switching valve 38 as a butterfly valve is provided in the second bypass passage 36. The exhaust switching valve 38 is connected to its actuator 40, and the actuator 40 is configured as a two-stage diaphragm mechanism.

As will be described later, this actuator 40 closes the exhaust switching valve 38 until the large turbocharger 17 exerts its full supercharging capacity, and switches the exhaust switching valve 38 when the large turbocharger 17 reaches its full supercharging capacity. It has the property of causing the valve 38 to open rapidly. The actuator 40 is a diaphragm 40a.

40b, and springs 40c and 40d, one diaphragm 40a is connected to the rod 4. The other diaphragm 40b is connected to a rod 40f. The rod 40f is on the left side of the figure (
It moves in conjunction with the rod 40e (in the direction in which the exhaust gas switching valve 38 is opened), but it can move independently of the rod 40e to the right in the figure. The step-like opening characteristic of the exhaust gas switching valve 38 can be obtained by applying supercharging pressure to the diaphragm 40a or by applying supercharging pressure to the diaphragm 40b. That is, when supercharging pressure is applied to the diaphragm 40b, the exhaust switching valve 38 is opened against the force of the spring 40c and the combined force of the spring 40d, so that the valve is opened slowly. When supercharging pressure acts on the diaphragm 40a, the exhaust switching valve 38 is opened against only the force of the spring 40c, so that the valve opening operation is quick.

An intake bypass passage 44 that bypasses the compressor 26 of the small turbocharger 18 is provided, and an intake bypass valve 46 is disposed in the intake bypass passage 44. The intake bypass valve 46 is connected to a diaphragm actuator 48, and the operation of the intake bypass valve 46 is controlled by the pressure applied to the diaphragm 48a. This intake bypass valve 46 closes the intake bypass passage 44 in the operating range of the small turbocharger 18 before the startup of the large turbocharger 17 is completed, but after the startup is completed, supercharging pressure acts on the diaphragm 48a from below, Intake bypass valve 46
The valve is opened.

In this embodiment, the internal combustion engine is provided with an exhaust gas recirculation (EGR) device, the EGR device comprising an exhaust gas recirculation passage (EGR).
R passage) 50, and an exhaust gas recirculation control valve (EGR valve) 52 on the EGR passage 50.The EGR valve 52 is provided with a diaphragm 52a, and opens and closes depending on the pressure applied to the diaphragm 52λ. controlled.

A three-way solenoid valve (VSVI) 54 is provided for pressure control to the actuator 34 of the wastegate valve 32;
This solenoid valve 54 is located at a position where atmospheric pressure is introduced into the diaphragm 34a and at the compressor 2 of the small turbocharger 18.
6 downstream of the intercooler 29 and a position 56 upstream of the intercooler 29 where the supercharging pressure is introduced. When atmospheric pressure is introduced, the wastegate valve 32 is driven to close by the spring 34b, and when the supercharging pressure is introduced, the wastegate valve 32 is opened against the spring 34b.

A three-way solenoid valve (VSV2) 58 is provided to control the pressure on the diaphragm 40a of the actuator 40 of the exhaust switching valve 38, and this solenoid valve 58 is located at a position where atmospheric pressure is introduced into the diaphragm 40a, and at the compressor of the small turbocharger 18. It changes depending on the position of the outlet 60 where the supercharging pressure is introduced. Moreover, the pressure of the compressor outlet 60 of the small turbocharger 18 is constantly introduced into the diaphragm 40b.

Two three-way solenoid valves 64,66 are provided for pressure control to the actuator 48 of the intake bypass valve 46. A three-way solenoid valve (VSV3) 64 is provided above the diaphragm 48a of the actuator 48 of the intake bypass valve 46 for pressure control;
The position is switched between a position where atmospheric pressure is introduced to the upper side of the compressor and a position where supercharging pressure from the compressor outlet 60 of the small turbocharger 18 is introduced. In addition, 3-way solenoid valve (VSV4) 66
is provided to control the pressure below the diaphragm 48a of the actuator 48 of the intake bypass valve 4e, and this solenoid valve 66 is provided below the diaphragm 48a of the throttle valve 1.
The position is switched between the position where the negative pressure of the negative pressure boat 68 downstream of 6 is introduced and the position where the compressor outlet pressure P of the large turbocharger is introduced. If the negative pressure is insufficient, instead of introducing the negative pressure from the negative pressure boat 68, negative pressure from a negative pressure pump driven by the engine may be introduced.

Three-way solenoid valve (VSV5) 70 is provided to control the operation of the EGR valve 52, and this solenoid valve 70 is connected to the diaphragm 5.
The position is switched between the position where atmospheric pressure is introduced into 2a and the position where negative pressure from the negative pressure boat 68 is introduced.

A control circuit 72 is provided for supercharging control in this invention, and each solenoid valve 54 (VSVI), 58 (VSV
2), 64 (VSV3), 66 (VSV4), drive the fuel injector 15. Further, the ignition plug is also controlled via the EGR solenoid valve 70 (VSV5), the igniter 74, and the distributor 76, but since these controls are not directly related to the present invention, detailed explanation will be omitted. The control circuit 72 is connected to various sensors in order to execute control according to the present invention. First, a first pressure sensor 78 is provided to detect the outlet pressure P1 of the compressor 20 of the large turbocharger 17, and a second pressure sensor 80 is provided to detect the outlet pressure P of the compressor 26 of the small turbocharger 18. is provided. An air-fuel ratio sensor 82 is provided downstream of the turbine 22 of the large turbocharger 17. In addition, an air flow meter (not shown) is provided to measure the intake air amount Q, and the crank angle is 30° and 720° for timing control.
A pulse signal for each degree is input.

The operation of the control circuit 72 will be explained below with reference to the flowcharts shown in FIGS. 3-5. FIG. 3 shows a routine for controlling boost pressure. In step 100, it is determined whether compressor outlet pressure Pt of small turbocharger 18>compressor outlet pressure P1 of large turbocharger 17 holds.

FIG. 6 shows changes in the compressor outlet pressure P2 of the small turbocharger 18 and changes in the compressor outlet pressure P of the large turbocharger 17 when the throttle valve 16 is fully open (full load operation). The rise of the small turbocharger outlet pressure P2 is the large turbocharger outlet pressure P.
, which is faster than the rise of . Therefore, in a state where the engine speed has not yet increased, p,>P holds true, and the solenoid valve 54 (VSVI) is turned off in step 102.
FF sags, atmospheric pressure is introduced into the diaphragm 34a,
The spring 34b closes the Uniis gate valve 32. In step 104, the solenoid valve 58 (VSV2) that controls the exhaust switching valve 38 is turned off. Therefore, atmospheric pressure acts on the diaphragm 40a of the actuator 40. On the other hand, since the compressor outlet pressure of the small turbocharger 18 is always introduced into the diaphragm 40b, the exhaust switching valve 38 is controlled by the compressor outlet pressure of the small turbocharger 18, which opposes the spring force corresponding to the resultant force of the springs 40c and 40d. Actuation is controlled. That is, until the rotation speed at which the supercharging pressure P2 reaches the predetermined value PSET (NE in FIG. 6), the biasing force of the spring is dominant, so the exhaust switching valve 38 remains fully closed, and P,=
When the predetermined value pseT is reached (point A), the exhaust switching valve 3
The valve 8 gradually starts to open against the closing biasing force which is the resultant force of the springs 40c and 40d.

Regarding the operation of the intake bypass valve 46 at low rotation speeds,
In step 106, the solenoid valve 64 (VSV3) is turned on and the compressor outlet pressure P2 of the turbocharger 18 acts on the upper side of the diaphragm 48a, so the intake bypass valve 4
6 is closed. Further, in step 108, the solenoid valve 66
(VSV4) is turned off, the intake pipe negative pressure downstream of the throttle valve 16 acts on the lower side of the diaphragm 48a, so the diaphragm 48a is pulled downward, increasing the closing force of the intake bypass valve 46 and ensuring its Ensures proper valve closure.

In the acceleration state, the engine rotation speed NE is NE.

When the compressor outlet pressure P+ of the large turbocharger 17 rises to
catches up with the compressor outlet pressure P2, and P 2 =
When P + is reached, the process proceeds from step 100 to step 110, the solenoid valve 54 (VSVI) is turned on, supercharging pressure from position 56 is introduced into the diaphragm 34a, and the wastegate valve 32 is moved in the opening direction against the spring 34d. Forced. In step 112, the operating solenoid valve 58 (VSV2) of the exhaust switching valve 38 is turned on. Therefore, since the supercharging pressure acts on the diaphragm 40a, the spring 40d does not participate in the force to close the exhaust switching valve 38 that opposes the supercharging pressure, and only the weak biasing force of the spring 40c participates in the closing force. Therefore, the actuator 40 opens the exhaust switching valve 38 all at once.

To explain the operation of the intake bypass in the region where the exhaust switching valve 38 is fully open, in step 114, the solenoid valve 64 (VS
V3) is turned off, atmospheric pressure is applied to the diaphragm 48a.
In step 116, the solenoid valve 66 (VSV
4) is turned on and supercharging pressure acts on the lower side of the diaphragm 48b, so the diaphragm 48a is pressed upward and the intake bypass valve 46 is opened all at once.

In FIG. 7, the characteristics of the supercharging pressure when the throttle valve is fully open shown in FIG. 6 are shown by a broken line X with respect to load and rotation speed. The line y extending from point A of the NEI rotation speed at which the exhaust switching valve 38 starts opening when the throttle valve is fully opened is the line where the exhaust switching valve starts opening when the throttle valve is not fully opened (P2=P,E>
P), and the smaller the throttle valve opening, the more the valve opening start point shifts to the higher rotation side. NE2 where the exhaust switching valve 38 starts to fully open when the throttle valve is fully opened
Line 2 extending from point B at the rotation speed is the fully open line of the exhaust switching valve when the throttle valve is not fully open (P2・P5.!work=
P, ), and the smaller the throttle valve opening, the more the full opening point shifts to the higher rotation side.

FIG. 4 shows the air-fuel ratio control routine. This routine is executed at the calculation timing of fuel injection for each cylinder (occurs every 180° CA in a four-cylinder internal combustion engine). This timing can be known from the 30° CA signal and 720° CA signal. In step 122, the basic fuel injection amount TP is calculated by TP = K X (Q/NE). Here, K is a constant, and the basic fuel injection amount TP corresponds to the fuel injection amount to obtain the stoichiometric air-fuel ratio at the rotation speed and load.

In step 124, it is determined whether or not the feedback control state is present. In Fig. 7, line a is the upper limit line controlled by the stoichiometric air-fuel ratio.
/NE) and the rotating shaft rotation speed NE. Line a shows the intake air amount-engine rotation speed ratio and rotation speed at which supercharging is substantially started by the supercharger. The air-fuel ratio is controlled to the stoichiometric air-fuel ratio in the region (2) below this line a, and the air-fuel ratio is controlled to the lean air-fuel ratio in the upper regions (2) and (3). In step 124, it is determined whether or not the intake air amount--engine rotational speed ratio and the rotational speed at that time are below line a. If it is determined that it is below line a, that is, that it is in a feedback state, the process proceeds to step 126, where the fuel injection amount TAU is calculated by TAU=Tp x FAF. FAF is an air-fuel ratio feedback correction coefficient, and the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio.

If it is determined that the feedback control state is not in effect, that is, the intake air amount-engine speed ratio and engine speed are above line a, the process proceeds to step 128, and the set air-fuel ratio is determined to be between the stoichiometric air-fuel ratio and the target lean air-fuel ratio. It is determined whether or not it is in the intermediate region between. Here, the intermediate lean air-fuel ratio refers to a lean air-fuel ratio intermediate between the stoichiometric air-fuel ratio and the target lean air-fuel ratio, and specifically ranges from 16 to 18. In FIG. 6, line b is the line at which control is started to achieve the target lean air-fuel ratio, and the intermediate lean air-fuel ratio region (2) is indicated by diagonal lines between a and b. When the air-fuel ratio is in the region (3) above line b, that is, when the air-fuel ratio is to be controlled to the set lean air-fuel ratio, the process proceeds from step 128 to step 132, where the lean correction coefficient KLEAN is calculated from the map. KLEAN is a coefficient for reducing the fuel injection amount with respect to the stoichiometric air-fuel ratio obtained by TP and obtaining the target lean air-fuel ratio. The value of KLEAN is set such that an air-fuel ratio of, for example, 19.0 to 20.0 can be obtained depending on the ratio and engine speed. Intake air amount - engine speed ratio Q/NE and engine speed NE
It is constructed as a map of Q/NE and N at that time.
KLEAN is calculated by interpolation from E. In step 134, the fuel injection amount TALI is calculated by TAU4p x KLEAN.

When it is determined in step 128 that the air-fuel ratio is in the intermediate air-fuel ratio control region, the process proceeds to step 140, where it is determined whether Q/NE-Q/NEo≧C. Q/NEo was last time (180 in crank angle)
' Before CA) This is the value of Q/NE when this routine is executed. Q/NE is a load factor of the engine, and the determination in step 140 allows it to be known whether the engine is accelerating or not. If not accelerated, step 132
Branches below.

When it is determined that Q/NE-Q/NEO≧C1, that is, acceleration is in progress, the process proceeds to step 142, and Q/NE+A
/NE, and in step 144, KLEAN is interpolated. That is, during acceleration, the lean correction coefficient is 1, and the value of Q/NH for calculating EAN is corrected to be larger than its original value. Therefore, lean control to the set lean air-fuel ratio is performed early during acceleration. The values of A and C can be determined appropriately. Step 146 indicates calculation of the fuel injection amount, and is similar to step 134. In step 150, TAU>T
It is determined whether AU o holds true. TAU is the value of the fuel injection amount TAU obtained in step 146 when this routine was executed last time, and is used to determine whether or not the fuel injection amount is increasing. If it is increasing, proceed directly to step 154, but if it is not increasing, proceed to step 1.
Proceeding to step 52, the TAU is placed in the TAU. Step 154 is when Q/NE is put into Q/NEO and step 1
At 56, the TAU is placed in TAUo. This is to be used as a step in the next fuel injection process (ie, after 180° CA).

In step 158, steps 126.134.146.
A fuel injection signal is generated to the injector 15 for injecting the amount of fuel TAU calculated at 152 .

FIG. 5 schematically shows the air-fuel ratio feedback control routine. In step 160, it is determined whether or not feedback control is being performed, and in the case of non-feedback control, step 161 is performed.
Then, FAF=1.0. When performing air-fuel ratio feedback, the process proceeds from step 160 to re-step 162, where the signal from the air-fuel ratio sensor 82 is input, and step 164
Then, it is determined whether the air-fuel ratio is leaner than the stoichiometric air-fuel ratio based on the signal from the air-fuel ratio sensor, and if it is determined to be lean, the process proceeds to step 166, where the feedback correction coefficient FAF is increased, and if it is determined to be rich. is step 168
Then, the feedback correction coefficient is decreased.

FIG. 8 schematically shows changes in the air-fuel ratio and fuel injection amount with respect to the intake air amount--engine speed ratio when the engine speed is fixed. ■ is the stoichiometric air-fuel ratio control region, ■ is the intermediate air-fuel ratio region, and ■ is the lean air-fuel ratio region. In the intermediate air-fuel ratio region (■), the air-fuel ratio is gradually increased from the stoichiometric air-fuel ratio to the lean air-fuel ratio.

During the acceleration time m shown by the broken line, the air-fuel ratio changes more rapidly than during the normal time l.

Therefore, the transition to the lean air-fuel ratio region can be made earlier than in the steady state.

〔effect〕

In this invention, in a high-density supercharged lean-burn internal combustion engine, in the intermediate range where the stoichiometric air-fuel ratio is controlled to the lean air-fuel ratio, the speed at which the air-fuel ratio changes to the lean air-fuel ratio is changed according to the degree of acceleration, so that the drivability is not deteriorated. The air-fuel ratio can be quickly controlled to a lean air-fuel ratio.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the functional configuration of the present invention. FIG. 2 is a diagram showing the configuration of an embodiment of the invention. 3 to 5 are flowcharts illustrating the operation of the control circuit shown in FIG. 2. FIG. 6 is a characteristic diagram of supercharging pressure versus rotational speed by the supercharging device of the present invention. FIG. 7 is a diagram schematically showing the operation timing. FIG. 8 is a timing diagram illustrating the invention in detail. IO...Engine body, 12...Intake pipe, 14...
・Exhaust pipe, 17...Large turbocharger, ■8...
・Small turbocharger, 30...first exhaust bypass passage, 32...-wastegate valve, 36...second exhaust bypass passage,

Claims (1)

[Claims] In an internal combustion engine that uses gasoline as fuel and is equipped with a supercharger, a supercharging state detection means detects a state in which supercharging is substantially performed by the supercharger, and a supercharging state detection means detects a state in which supercharging is substantially performed by the supercharger, and a supercharging state detection means detects a state in which supercharging is performed by the supercharger, means for setting a fuel ratio; means for setting a target lean air-fuel ratio via an intermediate air-fuel ratio that is somewhat leaner than the non-lean air-fuel ratio in a supercharging state; means for detecting an acceleration state of the engine; an air-fuel ratio control device for a supercharged lean-burn gasoline internal combustion engine, comprising means for adjusting an air-fuel ratio change speed so as to hasten the transition to the target lean air-fuel ratio.