JPH01163436A - Air-fuel ratio control device for lean combustion internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent disturbance of an air-fuel ratio during switching, by a method wherein a suction control valve, a first map means to control a fuel feed means, and a second map means are provided, and during switching between the first and the second map means, switching is gradually effected. CONSTITUTION:A first map means 1 to set an amount of fuel fed from a fuel feed means 26 according to a state in which a suction control valve is closed and a second map means 2 to set an amount of fuel fed from the fuel feed means 26 according to a state in which the suction control valve 32 is opened are provided. In which case, when the suction control valve 32 is switched between a closed state and an opening state, transient switching is detected by a switching state detecting means 3, and switching of a map is gradually effected between the first and second map means 1 and 2 by means of a means 4 to perform switching of a maps.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for an internal combustion engine that includes an intake control valve and controls the air-fuel ratio over a wide range from ultra-lean to rich.

[Prior Art] An internal combustion engine that uses an intake control valve is known as an internal combustion engine that enables combustion with an air-fuel mixture whose air-fuel ratio is extremely leaner than the stoichiometric air-fuel ratio. For example, see Japanese Unexamined Patent Publication No. 196931.

That is, the intake boat is provided with two intake ports, a straight intake port and a helical intake port, and an intake control valve is installed on the straight intake boat. The opening and closing of the intake control valve is controlled by the negative pressure of the engine. When the engine is fully loaded, the intake control valve is opened, so air is introduced from both intake ports. At this time, the air-fuel ratio is set to a value richer than the stoichiometric air-fuel ratio (for example, 12.5). When the engine is under partial load and the engine speed is less than a predetermined value, the intake control valve is closed and air is introduced only through the helical intake port, creating a swirl in the cylinder bore. Therefore, a stratification effect is achieved, and stable combustion with an ultra-lean mixture (air-fuel ratio = 21 to 22) is achieved. When the engine speed changes from low to high under partial load, the intake control valve is switched from the closed state to the open state. In the high rotation range under this partial load, the intake control valve is kept open, and unlike at low rotation speeds, the intake control valve is not opened or closed according to the load.

However, in the full load range, the air-fuel ratio is set to a rich value in order to obtain output, and in the partial load range, it is set to a value on the rich side (for example, 16 to 18) to improve fuel consumption efficiency. .

[Problems to be solved by the invention] In general, electronically controlled fuel injection P! In the engine, the basic fuel injection amount is calculated based on the engine load and rotation speed. Here, the basic fuel injection amount is set to the fuel injection amount that makes the air-fuel ratio the stoichiometric air-fuel ratio at that specific load and rotation speed. Therefore, in a fuel injection system (so-called DJ type fuel injection system) in which load is detected by intake pipe pressure, the basic fuel injection map is constructed as a two-dimensional map of load and rotational speed.

However, when an intake control valve is provided, the air flow rate is not the same even if the intake pipe pressure is the same when the intake control valve is opened or closed. That is, when the intake control valve is closed, the flow rate decreases, while when the intake control valve is open, the flow rate increases. Therefore, it is difficult to obtain a basic fuel injection amount that is suitable for both opening and closing of the intake control valve using only one map.

Therefore, it has been proposed to switch between two maps in order to obtain the optimum basic fuel injection amount for both opening and closing of the intake control valve. However, considering the transient state in which the intake control valve is switched between open and closed states, the operation of the intake control valve is inevitably accompanied by a mechanical delay. On the other hand, the delay in switching the air-fuel ratio is small.

In particular, when switching the intake control valve from closed to open, a means such as an orifice is provided to delay the transmission of the driving pressure of the intake control valve, and even though the air-fuel ratio immediately shifts to the rich side, the intake control This results in the valve remaining closed for some time. Therefore, there has been a problem in that a spike-like rich state occurs in a transient switching state of the intake control valve from closed to open.

The object of the present invention is to prevent the air-fuel ratio from becoming rough during the switching process between opening and closing of an intake control valve.

[Means for solving problems]

The air-fuel ratio control device for a lean-burn internal combustion engine of the present invention has a first
As shown in the figure, an intake control valve 32 that changes the size of the flow path system of the intake pipe, a fuel supply means 26 that supplies the required amount of fuel to the internal combustion engine, and a fuel supply amount from the fuel supply means 26 that controls the intake air flow. a first map means 1 for setting the amount of fuel supplied from the fuel supply means 26 in accordance with the closed state of the control valve 32; a second map means 2 for setting the amount of fuel supplied from the fuel supply means 26 in accordance with the open state of the intake control valve 32; switching state detection means 3 for detecting a transient switching state between the closed state and the open state of the control valve 32; and means 4 for gradually switching maps between map means 2 and map means 2.

〔Example〕

In FIG. 2, 10 is a cylinder block, and 12 is a cylinder bore. 12a and 12b are intake boats, 14a
, 14b are exhaust ports, and each boat has a so-called four-valve configuration in which intake valves 16a, 16b and exhaust valves 18a, 18b are provided. The first intake boat 12a is of a so-called helical type, and is configured to have a shape convenient for forming an intake swirl. The second intake boat 12b is of a straight type. The intake boats 12a and 12b are the intake pipes 20
, are connected to the throttle body 23 via the surge tank 22. Throttle valve 24 inside throttle body 23
will be installed. A fuel injector 26 is arranged in the intake pipe 20 adjacent to the intake boats 12a and 12b of each cylinder. The exhaust bows L4a and 14b are connected to the exhaust manifold 28. Note that 30 is a distributor.

An intake control valve 32 as a butterfly valve is provided on the straight intake boat 12b. When the intake control valve 32 is closed, intake air is introduced only from the helical intake boat l2a, a swirl S is formed in the cylinder bore 12, and combustion of an ultra-lean mixture is achieved. Intake control valve 32
When the intake control valves 12a and 12b are opened, air is guided from both intake control valves 12a and 12b, and the swirl is weakened. A lever 34 is attached to the valve shaft of the intake control valve 32 of each cylinder, and is connected to a negative pressure actuator 38 via a rod 36.

The negative pressure actuator 38 is composed of a diaphragm 40 and a spring 41. When no negative pressure is applied to the diaphragm 40, the diaphragm 40 is pushed downward in the figure by the action of the spring 41, and the intake control valve 32 is placed in the open position. When negative pressure is applied to the diaphragm 40, the diaphragm 40 is pulled against the spring 41, and the intake control valve 32 assumes a position that closes the intake boat 12b.

The diaphragm 40 includes a negative pressure delay valve 42 and an electromagnetic three-way valve 44.
, and the surge tank 2 via the negative pressure maintenance check valve 46.
It is connected to No. 2 negative pressure extraction boat 22a. Negative pressure delay valve 4
2 is configured by arranging an orifice 42a and a check valve 42b in parallel, and the rate at which atmospheric pressure is introduced into the diaphragm 40,
That is, the opening speed of the intake control valve 32 is controlled to an appropriate value. On the other hand, the check valve 46 maintains the negative pressure applied to the diaphragm 40. Solenoid valve 44
is equipped with three boats 44a, 44b, and 44c, and when electricity is removed, the boats 44a and 44b are communicated, and the diaphragm 40 is communicated with the negative pressure boat 22a, and when electricity is applied, the boats 44a and 44c are communicated, Diaphragm 40 is in communication with the atmosphere (filter 48). The solenoid valve 44 is driven by the control circuit 50 and controls the operation of the intake control valve 32.

The control circuit 50 is configured as a microcomputer system, for example, and controls the injector 26 and the solenoid valve 44 according to the present invention. The intake pipe pressure sensor 52 is installed in the surge tank 22 and measures the intake pipe pressure PM.
Generates a signal according to the Crank angle sensor 54,5
6 is provided in the distributor 30, the first crank angle sensor 54 is for detecting the reference position and generates a signal every 720 degrees of the engine crankshaft, and the second crank angle sensor 56 is for detecting the crank angle. For example, it generates a signal every 30 degrees and is useful for knowing the engine speed NE. Further, an air-fuel ratio sensor 58 such as a so-called lean sensor is provided in the exhaust manifold 28, and a signal corresponding to the air-fuel ratio OX is obtained. 59 is a throttle valve wide opening switch (VL switch), which is turned ON when the throttle valve 24 is depressed to an opening corresponding to the full load, and is normally OFF.

The control circuit 50 executes necessary arithmetic processing based on the signals from these sensors, and controls the driving of the injector and the solenoid valve.

The operation of the control circuit 50 will be explained below using a flowchart. FIG. 3 shows a routine for driving the intake control valve (SCV) 32. This routine runs for a certain period of time (
For example, it is executed every 32 msec). In step 70, the counter C3CVDLY is incremented.

C5CVDLY has the role of measuring the elapsed time from the start of the transition from closing to opening of the intake control valve 32.

In step 71, it is determined whether the intake control valve 32 is open or closed.

The intake control valve 32 is closed in a low rotation range under partial load, and is opened in other regions.

When the intake control valve 32 is closed, the air-fuel ratio is controlled to the lean side, and when the intake control valve 32 is open, the air-fuel ratio is controlled to the rich side. The details of determining whether the intake control valve 32 is open or closed are not directly related to the present invention, so a description thereof will be omitted. In step 72, it is determined based on the determination result in step 70 whether or not the intake control valve 32 is in a closed region. If the intake control valve 32 is in the closed region, the process advances to step 74 and the counter C3CVDLY is
is cleared, and then the process proceeds to step 75, where the flag yscv is set. This flag is the intake control valve 32
This indicates whether an open signal is output (0) or whether a close signal is output (1). Next, proceed to step 76 and turn the solenoid valve 44 to O.
A signal to be used as an FF is output. Therefore, the solenoid valve 44
takes the black boat position, and the negative pressure of the negative pressure boat 22a of the surge tank 22 is at the check valve 46. Negative pressure delay valve 42
The air pressure is applied to the diaphragm 40 through the check valve 42b, the diaphragm 40 is attracted against the spring 42, and the intake control valve 32 is closed. In addition, the intake control valve 3
Once the negative pressure that closes check valve 4 is generated, check valve 4 closes.
6 maintains this negative pressure, and even if the negative pressure in the boat 22a is insufficient to close the valve, the intake control valve 32 can be kept closed.

If the region in which the intake control valve 32 should be closed is Step 72.
The process then proceeds to step 78, where yscv=o is reset, and in step 80, a signal to turn on the solenoid valve 44 is output. Therefore, the solenoid valve 44 takes the white boat position, and atmospheric pressure is applied from the air filter 48 to the diaphragm 40 through the orifice 42a of the negative pressure delay valve.
The diaphragm 40 is lowered by a spring 42;
The intake control valve 32 is opened. The orifice 42a appropriately regulates the opening speed of the intake control valve 32.

FIG. 4 shows a fuel injection routine, and this routine is started when the crank angle sensors 54 and 56 detect the crank angle slightly before the fuel injection timing. In step 90, an interpolation calculation of the basic fuel injection amount is performed from the first map TPS which determines the basic fuel injection amount when the intake control valve 32 is closed. As is well known, the basic fuel injection amount is determined based on the engine load (P
M) and the engine speed (NE). In step 94, it is determined whether yscv=o, that is, whether a signal to open the intake control valve 32 is being output. When YSCV=1, that is, when the closing signal of the intake control valve 32 is output, the process advances to step 96, and T
PS is put into TP.

When yscv=o, that is, when a signal to open the intake control valve 32 is issued, the process proceeds from step 94 to step 98.
Then, interpolation calculation of the basic fuel injection amount is executed from the second map TPO which determines the basic fuel injection amount when the intake control valve 32 is opened. Similarly, this map is a value determined by the engine load (PM) and the engine speed (NE) so that the air-fuel ratio is the stoichiometric air-fuel ratio when the intake control valve is opened. Next, proceed to step 100 and check the counter C3CVDLY<1
It is determined whether 500 msec has elapsed, that is, whether 1500 msec has elapsed since the signal to switch the intake control valve from closed to open was first issued. If it has not yet elapsed, the process proceeds to step 102, where an interpolation calculation of the correction coefficient KTPSCV for the basic fuel injection amount during the transient period is executed. KTPSCV is C3CVDLY
The intake control valve 32 takes a value from O to 1 depending on the value of
The optimum basic fuel injection amount value between TPS and TPO is determined in advance so that an optimum basic fuel injection amount value between TPS and TPO can be obtained in a transient state from the start of output of the opening signal until the intake control valve 32 is actually fully opened. The memory of the control circuit 50 is C3CVD.
A two-dimensional map of LY and KTPSCV is stored, and an interpolation calculation of the value of KTPSCV with respect to the current value of C5CVDLY will be executed. Next step 1
04, the basic fuel injection amount TP at the time of transition is calculated by TP=TPS+KTPSCVX (TPO-TPS). Using this equation, it is possible to obtain a basic fuel injection amount suitable for the actual open state of the intake control valve 32 after the opening signal for the intake control valve 32 is output.

When 1.5 seconds have elapsed since the start of outputting the open signal of the intake control valve 32, that is, when the intake control valve 32 has actually been opened, the process flows from step 100 to step 106, and TPO is put into TP.

In step 108, the final injection amount TAU is determined as TAU=TP
Calculated by Xα+β. Here, α and β generally indicate correction coefficients and correction amounts whose explanations are omitted because they are not directly related to the present invention. Of course, this includes a correction coefficient that corrects the air-fuel ratio to the lean side when the intake control valve 32 is closed, an increase correction during acceleration, a correction that feeds back the air-fuel ratio to the set air-fuel ratio, etc.

In step 110, a fuel injection signal is sent to the injector 2 so that the fuel injection amount calculated in step 108 is injected.
6.

FIG. 5 is a timing diagram illustrating the present invention in detail. Assuming that YSCV=1 is switched from 0 to 0 at point (2) due to the transition from the closed to open condition of the intake control valve 32, the orifice of the negative pressure delay valve 42 Since the atmospheric pressure is gradually introduced into the diaphragm 40 via 42a, the actual opening degree of the intake control valve 32 changes slowly as shown by the dashed line, and the air amount also changes gradually as shown in (b). The basic fuel injection ITP in the closed state of the intake control valve 32 is determined by the first map TPS, and in the open state the basic fuel injection ITP is determined by the second map TPO. In the transition state from closing to opening, the equation in step 104 is used to determine an intermediate point between the first map and the second map depending on the time after switching (ie, the value of C5CVDLY). Therefore,
Basic fuel injection amount T adapted to changes in air amount in transient conditions
P is obtained (c). Therefore, the air-fuel ratio is adapted to the target air-fuel ratio even transiently, as shown by the solid line in (d). If the map is switched at the same time as the intake control valve switching signal from closed to open, the basic fuel injection amount will change suddenly as shown in the broken line in (c), and the air-fuel ratio will also shift to the rich side as shown in the broken line in (d). There is a problem with shifting.

〔effect〕

According to the present invention, in accordance with the transient state of switching between the closed region and the open region of the intake control valve, the map is gradually switched according to the elapsed time from the output of the switching signal, so that the optimum basics in the transient state can be achieved. It is possible to obtain the value of the fuel injection amount, and it is possible to prevent transient fluctuations in the air-fuel ratio. Therefore, drivability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is an overall schematic diagram of an embodiment of the invention. FIGS. 3 and 4 are flowcharts illustrating the operation of the control circuit of the present invention. FIG. 5 is a timing diagram illustrating the operation of the device of the present invention. 12a, 12b...Intake port 22...Surge tank 26...Fuel injector 32...Intake control valve 38...Negative pressure actuator 44...3-way solenoid valve 46...For maintaining negative pressure Check valve 50...Control circuit 52...Intake pipe pressure sensor 54.56...Crank angle sensor 59...Throttle valve wide opening switch Fig. 3

Claims (1)

[Claims] An intake control valve that makes the flow path system of the intake pipe variable in size, a fuel supply means for supplying a necessary amount of fuel to an internal combustion engine, and a fuel supply amount from the fuel supply means adapted to the closed state of the intake control valve. a first map means for setting, and a second map means for setting the amount of fuel supplied from the fuel supply means in accordance with the open state of the intake control valve.
map means; switching state detection means for detecting a transient switching state between a closed state and an open state of the intake control valve; An air-fuel ratio control device for a lean-burn internal combustion engine, comprising means for gradually switching between two maps.