JPH0192564A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To improve the exhaust gas purifying performance and driveability by starting air fuel ratio feed-back control when engine temperature exceeds a predetermined starting temperature, while setting the starting temperature according to the flow speed of exhaust gas. CONSTITUTION:When the running condition of an engine is judged to be within a predetermined feed-back range, an air fuel ratio regulating means C is controllably fed back by an air fuel ratio control means A so that the air fuel ratio of exhaust gas detected by an air fuel ratio detecting means B provides a predetermined desired air fuel ratio. Then, a temperature detecting means D for detecting engine temperature and a flow detecting means E for detecting the flow speed of exhaust gas are provided. When the engine temperature exceeds a predetermined starting temperature, the air fuel ratio feed-back control is allowed to be executed by an air fuel ratio control starting means F, and the staring temperature in the slow flow speed of exhaust gas is set by a starting temperature changing means G, higher than that in the fast flow speed of exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine.

(Prior Art and its Problems) In recent engines, there are an increasing number of engines that perform feedback control of the air-fuel ratio mainly as a measure to purify exhaust gas. That is, based on the output from the air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas, feed pump control is performed to control the air-fuel ratio of the mixture supplied to the engine so that the air-fuel ratio of exhaust gas becomes a predetermined target air-fuel ratio. (See, for example, Japanese Unexamined Patent Publication No. 57-44752).

Such feedback control of the air-fuel ratio is generally performed only when the engine operating state is within a predetermined feedback region, and this feedback region is set when the engine speed is below a predetermined value. and the engine load is often set to be within a predetermined value or higher.

On the other hand, in boat fishing, the feedback control described above is started when the engine temperature reaches a predetermined starting temperature or higher. This starting temperature is determined taking into consideration both engine operability and exhaust gas purification, and conventionally has been set to a uniform temperature such as 30°C. More specifically, from the perspective of exhaust gas purification, it is desirable that the starting temperature be as low as possible, but if the starting temperature is too low, drivability will deteriorate due to feedback control. The starting temperature was set as high as possible within an allowable range.

(Objective of the Invention) The present invention performs feedback control of the air-fuel ratio when the engine temperature reaches a predetermined starting temperature, and satisfies both exhaust gas purification and drivability at a higher level. An object of the present invention is to provide an air-fuel ratio control device for an engine that can control the air-fuel ratio of an engine. .

(Structure and operation of the invention) As a result of various studies on the deterioration of drivability when performing feedback control, the present invention has found that this deterioration of drivability is caused by a response delay due to feedback control, and that this response delay is greatly affected by the exhaust gas flow velocity. This was done with a focus on the fact that In other words, when the exhaust gas flow rate is high and the responsiveness of the feedback control is good, the starting temperature when starting this feedback control is set low, but when the exhaust gas flow rate is slow and the responsiveness of the feedback control is deteriorated. When this feedpa
The starting temperature when starting link control is set high.

Specifically, as shown in FIG. 5, the system includes: an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the air-fuel mixture supplied to the engine; an air-fuel ratio detecting means for detecting the air-fuel ratio of exhaust gas from the engine; air-fuel ratio control means for feedback-controlling the air-fuel ratio adjustment means so that the air-fuel ratio of exhaust gas detected by the air-fuel ratio detection means becomes a predetermined target air-fuel ratio when the state is in a predetermined feedback region; , a temperature detection means for detecting the temperature of the engine; a flow velocity detection means for detecting the flow velocity of exhaust gas; , an air-fuel ratio control start means for allowing the air-fuel ratio control means to perform feedback control, and a start temperature change means for setting the start temperature higher when the exhaust gas flow rate is slow than when it is fast. This is the configuration.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

In FIG. 1, reference numeral l denotes a four-cycle reciprocating type engine body of the oscillator type, and as is known, this engine body J includes a cylinder block 2, a cylinder head 3, and a cylinder 2a of the cylinder block 2. A combustion chamber 5 is defined by a piston 4 fitted therein. A spark plug 6 is disposed in the combustion chamber 5, and an intake boat 7 and an exhaust boat 8 are opened.
are opened and closed by the intake valve 9 or the exhaust valve 10 at known timings in synchronization with the engine output shaft.

In the intake passage 21 connected to the intake boat 7, the -L
Sequentially from the upstream side to the downstream side, an air cleaner 22, an air flow meter 24 that detects the amount of intake air, a throttle valve 25,
A surge tank 26 and a fuel injection valve 27 are provided.

Further, in the exhaust passage 28 connected to the exhaust boat 8, an air-fuel ratio sensor 29 and a three-way catalyst 3o as an exhaust gas purification device are arranged in order from the flow side to the downstream side. In the embodiment, the air-fuel ratio sensor 29 uses an 02 sensor whose output voltage changes greatly between ON and OFF with the stoichiometric air-fuel ratio (14, 7) as the boundary (see FIG. 4).

In FIG. 1, 31 is a control unit constituted by a microcomputer, and the control units 1 to 31 include M
iIn addition to each signal from each sensor 24 and 29, sensor 3
The signal from 3.34 is input. ”
The first sensor 33 is for detecting the engine cooling water temperature, and the sensor 34 is attached to the destroyer 36 and is for detecting the crank angle, that is, the engine rotation speed. Further, the control unit 31 outputs a predetermined signal corresponding to the amount of fuel to be injected to the fuel injection valve 27.

Note that the control unit 31 basically includes a CPU and a ROM.
, 1 (ΔM, Cl-7OCK, Δ/I), D/Δ converter, and input/output interface, but these are known configurations when used as a micro combi coater. I will omit the detailed explanation.
3 The control unit 31 adjusts the air-fuel ratio based on the output from the air-fuel ratio sensor 29 so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio (target air-fuel ratio) when the exhaust gas is in a predetermined feedback region. The amount of fuel injected from the fuel injection valve 27 as an adjusting means is feedback-controlled. In the embodiment, as shown in FIG. 3, the region in which this feedback control is performed is when the engine speed N is below N2,
It is also set as when the fuel injection amount (engine load) TP is less than or equal to TP2.

The feedback area is further divided into area A and area B as shown in FIG.

Region B is defined as when the engine speed N is smaller than Nl and the fuel injection amount TP is smaller than TPI. The regions A and B correspond to regions where the flow velocity of exhaust gas is fast and slow. That is, in region B, the engine speed is low and the fuel injection amount (engine load) is also small, so the exhaust gas flow velocity is slow.
is considered to be a region where the exhaust gas flow velocity is high. Then, the starting temperature W of feedback control when the exhaust gas flow rate is slow
-B is set as high as, for example, 40°C, and the feedback control start temperature W-A when the exhaust gas flow rate is high is set as low as, for example, O'C. 1 Now, next, regarding the control contents by the control unit 31,
This will be explained in detail with reference to the flowchart shown in FIG. In addition, in the following explanation, P does not indicate sudetsubu.

First, at Pl, engine speed N, intake air amount Q
, the cooling water temperature W is read in 52, then in P2, N
Based on and Q. Basic fuel injection iTP as known
is calculated.

At P3, it is determined whether or not the current is in the feedback area (determination as to whether N is less than N2 and TP is less than 1゛P2). If this judgment is YES, P
4, it is determined whether N<N I, and this P
If the determination in step 4 is YES, it is determined in P5 whether TP<TPI.

If the determination in P5 of section 1 is YES, the current operating state of the engine is in region B, that is, in a region where the exhaust gas flow velocity is slow. At this time, in P6, the starting temperature of the feedback control is set to 1 as a high temperature W-B, and then it is determined whether the current cooling water temperature W is W-8 or higher. When the determination of Pl is YES, the process moves to P8 and feedback control is executed, and when the determination of Pl is NO, the process moves to P9 and the execution of feedback control is prohibited.

When the determination in P4 or P5 is No, it is in region A, that is, when the flow rate of exhaust gas is high. At this time, the transition is made to PIO, and the low temperature W.8 is set as the starting temperature for feedback control.
] 11, it is determined whether the current cooling water temperature W is greater than or equal to W·Δ. When the pH determination is YES, the process moves to P8 and feedback control is executed, and when the pH determination is NO, the process moves to P9 and the feedback control is prohibited.

If the determination in P3 is No, it is not the feedback area, so the process moves to P9, where execution of feedback control is prohibited.

Although the embodiments have been described above, the present invention is not limited thereto, and includes, for example, the following cases.

(2) Feedback control may be such that an air-fuel ratio other than the stoichiometric air-fuel ratio is set as the target air-fuel ratio. In this case, the air-fuel ratio sensor 29 may be a so-called lean sensor whose output changes continuously and variably according to the air-fuel ratio of the exhaust gas (one that does not operate ON or OFF).

■A sensor for directly detecting the flow velocity of exhaust gas may be used separately. In this case, since the flow rate of exhaust gas essentially corresponds to the flow rate of intake air (mixture), the flow rate of this intake air can also be detected. However, it is more advantageous in terms of cost and the like to theoretically determine the magnitude of the flow velocity using the outputs of other sensors as in the embodiment.

(2) The flow rate may be divided into three or more stages (including stepless) and a different starting temperature may be set for each stage.

(Effects of the Invention) As is clear from what has been described below, the present invention can satisfy both exhaust gas purification and drivability at a higher level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall system diagram showing one embodiment of the present invention. FIG. 2 is a flow chart showing a control example of the present invention. FIG. 3 is a graph showing an example of setting the region where feedback control is performed, together with a region where the flow velocity is high and a region where the flow velocity is slow. FIG. 4 is a graph showing the relationship between the output of the air-fuel ratio sensor and the air-fuel ratio. FIG. 5 is an overall configuration diagram of the present invention. 5: Combustion chamber 21: Intake passage 24: Air flow meter 27: Fuel injection valve (L stage air-fuel ratio adjustment) 28: Exhaust passage 29: Air-fuel ratio sensor 30: Exhaust gas purification catalyst 31: Control unit 33: Cooling water temperature sensor 34: Engine speed sensor

Claims (1)

[Claims] (1) An air-fuel ratio adjusting means for adjusting the air-fuel ratio of the air-fuel mixture supplied to the engine, an air-fuel ratio detecting means for detecting the air-fuel ratio of exhaust gas from the engine, and the operating state of the engine is within a predetermined feedback range. an air-fuel ratio control device for an engine, comprising: air-fuel ratio control means for feedback-controlling the air-fuel ratio adjustment means so that the air-fuel ratio of exhaust gas detected by the air-fuel ratio detection means becomes a predetermined target air-fuel ratio; A temperature detection means for detecting the temperature of the engine; a flow velocity detection means for detecting the flow velocity of exhaust gas; Air-fuel ratio control for an engine, comprising: an air-fuel ratio control start means that allows the air-fuel ratio control; and a start temperature change means that sets the start temperature higher when the exhaust gas flow rate is slow than when it is fast. Device.