JPH0235864B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention includes a secondary air passage that guides a part of air pressurized by a supercharger to an exhaust passage, and also provides fuel injection in accordance with the amount of intake air. The present invention relates to a supercharged engine that controls the amount of fuel injected from the device.

(Prior art) Conventionally, a turbocharger has been used to improve engine output, and a portion of the air pressurized by the turbocharger has been used as secondary air for exhaust purification. A supercharged engine provided with a secondary air passage is known. In particular, this type of engine is equipped with an electronically controlled fuel injection device, for example, as shown in Japanese Patent Publication No. 59-5781, a supercharging passage equipped with a supercharger is branched from the main intake passage.
A first air amount detection device is provided upstream thereof, and a second air amount detection device is provided in a secondary air passage whose one end is connected to the supercharging passage and the other end is connected to the exhaust passage. There is a system in which the fuel injection amount is controlled by the output obtained by subtracting the output of the second air amount detection device from the output of the device, that is, the amount of intake air supplied to the combustion chamber that is obtained by subtracting the amount of secondary air from the total intake amount. .

Incidentally, in this type of engine, a flow control valve is generally provided in the secondary air passage to control the flow rate of the secondary air depending on the operating state. Further, the supercharger provided in the supercharging passage usually uses a positive displacement air pump driven by the engine. When controlling the fuel injection amount as described above in such a structure, when the flow rate of the secondary air is relatively large, the secondary air amount can be detected with high accuracy by the second air amount detection device. However, when the amount of secondary air is small, the value detected by the second air amount detection device is likely to be affected by the pulsation of the discharge pressure of the supercharger and cause an error, so the fuel injection amount in such a case is It has been desired to develop a means that can perform control with higher precision.

(Objective of the Invention) In view of these circumstances, the present invention provides a system for adjusting the amount of fuel injection in accordance with the amount of intake air into the combustion chamber, which is obtained by subtracting the amount of secondary air supplied to the exhaust system from the total amount of intake air introduced into the intake passage. To provide a supercharged engine that can control the fuel injection amount with high precision even when the flow rate of secondary air is small.

(Structure of the Invention) The present invention has one end connected to an intake passage downstream of a supercharger and the other end connected to an exhaust passage of an engine, so that a part of the air pressurized by the supercharger is transferred to the exhaust passage. a first air amount detection device provided in the intake passage upstream of the supercharger and outputting a signal corresponding to the amount of air flowing through the passage; A second air amount detection device outputs a signal corresponding to the amount of air flowing through the passage, and receives the outputs of the first and second air amount detection devices and calculates a second signal from the air amount detected by the first air amount detection device. In a supercharged engine equipped with an electronically controlled fuel injection device that determines and supplies a fuel injection amount corresponding to the air amount obtained by subtracting the air amount detected by the air amount detection device, the secondary air passage is sent to the exhaust passage. a flow rate data setting means for providing a flow rate control valve for controlling the amount of air introduced and outputting a signal corresponding to a secondary air flow rate preset in accordance with the engine speed and intake air amount or load; When the amount of secondary air controlled by the flow control valve is small, the output of the second air amount detection device used for determining the fuel injection amount of the electronically controlled fuel injection device is set as the output of the flow rate data setting means. A switching means for switching is provided. In other words, the amount of secondary air that needs to be detected to control the fuel injection amount according to the amount of intake air supplied to the combustion chamber is detected by the second air amount detection device when the flow rate of the secondary air flow is large. However, when the flow rate in the secondary air passage is low, it is determined from preset flow rate data.

(Embodiment) Fig. 1 shows an embodiment of the device of the present invention. In this embodiment, a supercharger is provided in an intake passage (supercharging passage) branching from a main intake passage, and a downstream part of the supercharger is provided. The present invention is applied to a structure in which a secondary air passage is connected between a supercharging passage and an exhaust passage. In this figure, 1 is a cylinder of an engine, 2 is a piston, and 3 is a combustion chamber formed above the piston 2 in the cylinder 1. A main intake port 4, a supercharging port 5, and an exhaust port 6 are opened in this combustion chamber 3, and a main intake valve 7,
A supercharging intake valve 8 and an exhaust valve 9 are provided.

10 is an air cleaner, 11 is an air cleaner 10
This is the intake passage connected to the The intake passage 11 is
Consisting of a main intake passage 12 and a supercharging passage 13 branched from the main intake passage 12, the downstream end of the main intake passage 12 is connected to the main intake port 4, and the downstream end of the supercharging passage 13 is connected to the supercharging passage 13. Connected to port 5. A first air amount detection device 14 including an air flow meter or the like is provided in the intake passage 11 upstream of the branch point between the main intake passage 12 and the supercharging passage 13. Further, a first throttle valve 15 is provided in the main intake passage 12 and is opened and closed in accordance with the operation of an accelerator pedal, and a fuel injection device 16 is provided downstream of the first throttle valve 15 .

On the other hand, the supercharging passage 13 is provided with a supercharger 17 consisting of a vane type air pump driven by the engine. An intercooler 18 is provided downstream of the supercharger 17 to cool the supercharged air supplied from the supercharger 17 in order to increase its density.
A surge tank 19 is formed downstream thereof.
Further, a second throttle valve 20 is provided in the supercharging passage 13 downstream of the surge tank 19, and this second throttle valve 20 is opened to an opening degree corresponding to the load when the load is higher than a predetermined load. When the throttle valve 15 is opened to a predetermined opening degree or more, it is opened in conjunction with this. Further, from the surge tank 19 of the supercharging passage 13, there is a secondary air passage 21 that sends a part of the supercharging air to the exhaust system as secondary air for exhaust gas purification, and a relief valve that relieves excess supercharging air. The passage 22 is branched.

The secondary air passage 21 is connected to the exhaust system, and in the embodiment shown in the figure, the secondary air passage 21 has a large flow passage 21a having a relatively large passage area and a large flow passage 21a having a small passage area at its downstream portion. The large flow passage 21 a opens into an exhaust passage 24 upstream of the catalytic converter 23 , and the small flow passage 21 b opens into an intermediate portion of the catalytic converter 23 . The reason why the secondary air passage 21 is configured in this way is to supply a relatively large amount of secondary air to the upstream side of the catalytic converter 23 during idling when operating with a rich air-fuel mixture. , acts as an oxidation catalyst to reduce CO, and when operating at approximately the stoichiometric air-fuel ratio, a small amount of secondary air is supplied to the rear half of the catalytic converter 23 to reduce NOx.
This is because it functions as a three-way catalyst for reducing HC and CO.

This secondary air passage 21 is provided with a second air amount detection device 25 that detects the flow rate of the secondary air, and in the figure, detects the pressure difference between the upstream side and the downstream side of the throttle 25a in the secondary air passage 21. The differential pressure sensor 25b is used to detect the amount of secondary air in a control unit 40, which will be described later, based on its output, thereby forming a second air amount detection device 25. Furthermore, in the secondary air passage 21, as a flow control valve,
An on-off valve 26 opens and closes the secondary air passage 21 downstream of the secondary air amount detection device 25, and at a branch point between the large flow passage 21a and the small flow passage 21b, one of the passages 21a and 21b is connected. A switching valve 27 that opens is provided. The above on-off valve 26
is composed of a valve body 26a and a diaphragm type actuator 26b, and opens the secondary air passage 21 when negative pressure is introduced into the actuator 26b, and closes the secondary air passage 21 when the atmosphere is introduced. There is. The switching valve 27 is also composed of a valve body 27a and a diaphragm type actuator 27b, and when negative pressure is introduced into the actuator 27b, the large flow passage 21a is opened, and when the atmosphere is introduced, the small flow passage 21b is opened. That's what I do. The actuator 27b of the on-off valve 27 is
The actuator 27b of the switching valve 27 is connected to a negative pressure passage 28 whose one end is connected to the main intake passage 12 downstream of the first throttle valve 15 via a passage 29 and a first three-way solenoid valve 30. It is connected to the negative pressure passage 28 via a passage 31 and a second three-way solenoid valve 32. The three-way solenoid valves 30 and 32 selectively connect the actuators 26b and 27b to the negative pressure passage 28 or the openings 30a and 32a to the atmosphere, respectively.

Further, the relief passage 22 is arranged so as to recirculate surplus supercharging air to the main intake passage 12 or the supercharging passage 13 upstream of the supercharger 17. It is connected to the intake passage 12. This relief passage 22 includes a boost pressure control valve 33 that mainly controls the maximum boost pressure during high loads, and a boost pressure control valve 33 that opens the relief passage 22 when the on-off valve 26 of the secondary air passage 21 is opened, and A relief control valve 34 for preventing excessive supply of secondary air is arranged in parallel with the air conditioner. The supercharging pressure control valve 33 has a valve body 33a disposed at an opening 35 of the relief passage 22 with respect to the surge tank 19.
and the diaphragm 3 connected to this valve body 33a.
3b and a pressure control chamber 33c formed on one side thereof.
and a spring 33d that biases the valve body 33a in the valve closing direction, and when the supercharging pressure applied to the valve body 33a becomes excessively high, the valve body 33a opens to relieve supercharging air. This controls the maximum boost pressure. By connecting the pressure control chamber 33c to the negative pressure passage 28, the maximum boost pressure can be suppressed to a certain level during low loads where the intake negative pressure is large, and the maximum boost pressure can be suppressed to a certain level during high loads where the intake negative pressure is small. I'm trying to improve it.

The relief control valve 34 includes a valve body 34a disposed in a communication hole 36 between the relief passage 22 and the surge tank 19, and a diaphragm type actuator 34b. It is connected to the negative pressure passage 28 via one three-way solenoid valve 30 . Therefore, this relief control valve 34 is connected to the secondary air passage 2.
It is designed to be opened and closed in response to the opening and closing valve 26 of No. 1.

The fuel injection device 16 and the three-way solenoid valves 30, 32 are controlled by a control unit 40 using a microcomputer or the like, and the control unit 40 includes a control unit 40 including the first air amount detection device 14 and the differential pressure sensor 25b. In addition to each detection signal from the second air amount detection device, the engine rotation speed detection signal from the rotation speed sensor 41 and the load from the throttle opening sensor 42 that detects the opening degree of the first throttle valve 15 are detected. A throttle opening detection signal is input.

In order to control the secondary air supply according to the operating state, the control unit 40 preliminarily sets the operating region where the engine speed and the load are below predetermined values as the secondary air supply region, as shown in FIG. The rest of the area is set as the air cut area (area where the supply of secondary air is stopped), and of the secondary air supply area, the low rotation area and low load area are set as the secondary air large area, and the other areas are set as the secondary air cut area. It is set as a small amount area. When the operating state detected from the engine speed and the throttle opening (load) is in a high secondary air volume region, the large flow passage 21a is opened, and when the operating state is in a low secondary air volume region, the high flow passage 21a is opened. The on-off valve 26 and the switching valve 27 are controlled via the three-way solenoid valves 30 and 32 so that the small flow passage 21b is opened and the secondary air passage 21 is closed when in the air cut region.

Furthermore, this control unit 40 for the fuel injection device 16 basically controls the fuel injection amount using the output obtained by subtracting the output of the second air amount detection device 25 from the output of the first air amount detection device 14. In addition to this, there is also a flow rate data setting means that outputs a signal corresponding to a preset secondary air flow rate corresponding to the engine speed and intake air amount or load, and a secondary air flow rate controlled by a flow rate control valve. It includes switching means for switching the output of the two-air detection device 25 used for determining the fuel injection amount to the output of the flow rate data setting means when the air supply amount is small. In other words, the control unit 40 controls the amount of fuel supplied to the combustion chamber 3, which is calculated by subtracting the secondary air amount from the intake air amount detected by the first air amount detection device 14, as will be described in detail later. In this case, the secondary air amount is detected by the second air amount detection device 25 when the injection amount is in the secondary air amount region, and the secondary air amount is detected by the second air amount detection device 25 when the secondary air amount is in the secondary air amount region. The amount of air is determined from the flow rate data. This flow rate data is obtained by experimentally determining the flow rate of secondary air supplied to the exhaust system through the small flow passage 21b under various engine speeds and load conditions, and then correlating this with the engine speed and load. This map is stored in the memory within the control unit 40 as a flow rate map.

In addition, in a specific example of control described later, in order to more accurately determine the flow rate of secondary air sent to the exhaust system through the small flow passage 21b, the value read from the flow rate map is further corrected according to variations in discharge pressure. I try to do that. In other words, as shown in FIG. 3, the discharge pressure of the supercharger 17 acting on the secondary air passage 21 increases to a certain extent as the engine speed increases, and is maintained at the upper limit pressure in the high speed range. However, the characteristics of the discharge pressure change depending on the engine speed may vary due to variations in the performance of the supercharger 17 and the like. For example, if the flow rate map is set with values that have been investigated in advance under conditions where the discharge pressure change has the characteristics shown by the solid line in this figure, the characteristics of the discharge pressure change will be shown by the broken line in this figure. If the flow rate fluctuates in this way, there will be some deviation between the value determined from the flow rate map and the actual flow rate. Therefore, as will be described later, a correction coefficient (K ₁ below) for the low rotational speed range below the critical rotational speed R ₀ (approximately 2000 rpm) at which the discharge pressure reaches the upper limit value, and a correction coefficient for the high rotational speed range higher than the critical rotational speed R ₀ mentioned above. Correction coefficient for (see below)
K ₂ ) and the specific rotation speed R ₁ within each rotation range,
At _R2 , the reference pressure (pressures previously investigated under the discharge pressure characteristics shown by the solid line) _P1 , _P2 is found by comparing with the actual pressure, and this correction coefficient is used to find the value from the flow rate map. I am trying to correct it.

A specific example of the control of the fuel injection amount by the control unit 40 will be explained below using a flowchart.

In this flowchart, we will first
In _{step S1} , the engine rotation speed R detected by the rotation speed sensor 41 and the throttle opening detected by the throttle opening sensor 42 are read, and further in step _S2 , the first air amount detection device 14 is read. Read the intake air amount Qa detected by . Next, in step _S3 , it is determined whether the operating state detected from the engine speed and throttle opening (load) is in the secondary air supply region. If the determination result in step _S3 is NO, the actual operating state is in the air cut region, and therefore the on-off valve 26
As a result, the secondary air passage 21 is in a closed state. At this time, the secondary air amount Qb is set to zero (step S ₄ ). Also, the judgment result in step _S3 is YES.
If so, it is determined in step _S5 whether or not the secondary air amount is in a small amount region.

If the determination result in step _S5 is NO, the actual operating state is in the secondary air large amount region, and therefore the opening/closing valve 26 and the switching valve 27 control the high flow rate passage of the secondary air passage 21. 21a is in an open state. At this time, in step _S6 , the differential pressure sensor 2 is
5b is read, and the flow rate Qb ₂ detected based on the output of the differential pressure sensor 25b in steps S ₁₃ and S ₁₄ is set as the secondary air amount Qb. Also, when the secondary air is in the large amount region, step _S6 and step _S13 are performed.
Through steps S ₇ to S ₁₂ between , correction coefficients K ₁ and K ₂ are calculated for correcting the expected flow rate Qb ₁ in the secondary air small amount region, which will be described later. In other words, in the calculation process of this correction coefficient, when the engine rotation speed R is at a specific rotation speed _R1 lower than the critical rotation speed _R0 , the pressure P detected by the differential pressure sensor 25b and the pressure P detected in advance are calculated. This specific rotation speed
The ratio of R ₁ to the reference pressure P ₁ is set as a correction coefficient K ₁ for the low rotation range (steps S ₇ and S ₈ ). Further, when the engine speed R is at a specific speed _R2 higher than the critical speed _R0 , the exhaust pressure Pex is calculated from the intake air amount, and the pressure P detected by the differential pressure sensor 25b is calculated.
Find the pressure P′ by adding the pressure Pex and the exhaust pressure Pex, and calculate this pressure
The ratio of P′ and reference pressure P ₂ is the correction coefficient for high rotation range.
_K2 (steps _S9 to _S12 ).

If the determination result in step _S5 is YES, the small flow passage 21b of the secondary air passage 21 is opened by the on-off valve 26 and the switching valve 27. At this time, from the flow rate map, an assumed value Qb ₁ of the flow rate of the secondary air passage 21 according to the engine speed and load is determined (step 1).
_S15 ). Furthermore, if the engine rotation speed R is below the critical rotation speed R ₀ , the secondary air amount is calculated by multiplying the above assumed value Qb ₁ by a correction coefficient K ₁ for the low rotation range.
Find Qb, and if the rotation is higher than the critical rotation speed R ₀ ,
The secondary air amount Qb is determined by multiplying the above assumed value Qb ₁ by a correction coefficient K ₂ for the high rotation range.

After obtaining the secondary air amount Qb in any of steps S ₄ , S ₁₄ , S ₁₇ , and S ₁₈ in this way, the intake air amount
The intake air supply amount Q to the combustion chamber 3 is determined by subtracting the secondary air supply amount Qb from Qa (step
S ₁₉ ), and the fuel injection amount is controlled according to this intake air supply amount Q (step S ₂₀ ).

By controlling according to this flowchart, when a relatively large amount of secondary air is being supplied to the exhaust system through the large flow passage 21a of the secondary air passage 21, the second air The secondary air amount is detected by the amount detection device 25, and the amount of intake air supplied to the combustion chamber 3 is determined based on the detected value of the intake air amount by the first air amount detection device 14 and the detected value of the secondary air amount. The calculation and the fuel injection amount are controlled accordingly. Furthermore, when a small amount of secondary air is supplied to the exhaust system through the small flow passage 21b, instead of using the detected value of the secondary air amount by the second air amount detection device 25, the The amount of secondary air is detected based on the value determined from the flow rate map. By doing this, when the amount of secondary air is small, the second air amount detection device 2, which is prone to errors due to the influence of pulsations in the discharge pressure of the supercharger, etc.
The secondary air amount can be determined more accurately than the detected value in step 5.
Calculation of the amount of intake air supplied to the combustion chamber 3 and control of the fuel injection amount accordingly are performed with high precision.

Note that the structure of the secondary air passage 21 and the flow rate control valve provided in this passage is not limited to the above-mentioned embodiment, and any structure can be used as long as the flow rate of the secondary air passage 21 can be changed depending on the operating state. good. Furthermore, the flow rate map (flow rate data) for determining the amount of secondary air when the flow rate of the secondary air passage 21 is reduced by the flow rate control valve is mapped in advance to the engine speed and the amount of intake air. In this case, the flow rate may be determined from the flow rate map according to the engine speed and the intake air amount detected by the first air amount detection device 14.

(Effects of the Invention) As described above, the supercharged engine of the present invention adjusts the fuel injection amount according to the value obtained by subtracting the secondary air amount from the total intake air amount detected by the first air amount detection device. When controlling, when a relatively large amount of secondary air is supplied to the exhaust system, the secondary air amount is detected by the second air amount detection device, but when the flow rate of secondary air is small, By switching the output of the second air amount detection device to read out the flow rate data set in advance depending on the engine speed and intake air amount or load, the secondary air amount can be determined from the flow rate data checked in advance. That's what I do. Therefore, the flow rate of the secondary air is small and the second air amount detection device detects the
Even when errors are likely to occur in the detected value of the secondary air amount, the secondary air amount can be determined accurately and the fuel injection amount can be controlled with high precision.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the operating range in which a large amount of secondary air is supplied to the exhaust system, a small amount is supplied, and the supply is stopped. FIG. 4 is a flowchart for controlling the fuel injection amount. 12... Main intake passage, 13... Supercharging passage, 14
...First air amount detection device, 16...Fuel injection device, 21...Secondary air passage, 25...Second air amount detection device, 26...Opening/closing valve, 27...Switching valve, 4
0...Control unit.

Claims (1)

[Claims] 1 One end is connected to the intake passage downstream of the supercharger, and the other end is connected to the exhaust passage of the engine,
A secondary air passage that guides a portion of the air pressurized by the turbocharger to the exhaust passage, and a primary air passage that is provided in the intake passage upstream of the turbocharger and outputs a signal corresponding to the amount of air flowing through the passage. an amount detection device, a second air amount detection device provided in the secondary air passage and outputting a signal corresponding to the amount of air flowing through the passage, and receiving outputs from the first and second air amount detection devices, an electronically controlled fuel injection device that determines and supplies a fuel injection amount corresponding to the air amount obtained by subtracting the air amount detected by the second air amount detection device from the air amount detected by the first air amount detection device; In a supercharged engine, 2
A flow control valve is provided in the secondary air passage to control the amount of air introduced into the exhaust passage, and a signal corresponding to the secondary air flow rate that is preset according to the engine speed and intake air amount or load is output. When the amount of secondary air controlled by the flow rate data setting means and the flow control valve is small, the output of the second air amount detection device used for determining the fuel injection amount of the electronically controlled fuel injection device is set as described above. 1. A supercharged engine characterized by comprising: switching means for switching to the output of the flow rate data setting means.