EP0757167A2

EP0757167A2 - Air/fuel ratio control method for a lean burn combustion engine

Info

Publication number: EP0757167A2
Application number: EP96112294A
Authority: EP
Inventors: Woo-Jik Lee
Original assignee: Hyundai Motor Co
Current assignee: Hyundai Motor Co
Priority date: 1995-07-31
Filing date: 1996-07-30
Publication date: 1997-02-05
Also published as: KR100187974B1; AU6080896A; EP0757167A3; KR970006824A

Abstract

Disclosed herein is a n air/fuel ratio control method controlling air/fuel ratio for vehicles which have thin combustion engines. The air/fuel ratio control method executes the feedback control the fuel supply of the engines by an ECU(Electric Control Unit) based on the information from the sensors.

During the theoretical air/fuel ratio combustion, the fuel injecting value is set by the amount of multiplying the basic injecting amount by the adaption value set up previously and by detecting the oxygen amount in the waste gas with the λ sensor and the feedback control process is repeated but the aforesaid feedback value will be counted and stored in the ECU's RAM; as the result of this procedure, the next injecting value will be decided; and during the thin fuel/air ratio combustion, after the adaption value stored in the aforesaid RAM is multiplied by the basic injecting amount at the thin fuel/air ratio, the result value decides the fuel injecting amount, and this procedure lets the ratio being closed to the desired fuel/air ratio without the feedback control which is governed by the λ sensor.

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

This present invention relates to an air/fuel ratio control method for thin combustion engine vehicles to increase purification efficiency of waste gas and combustion efficiency.

2. Description of the prior Art

In case of the general engines, to increase the three dimensional catalyst purification ratio, the air/fuel ratio (air : fuel) can be controlled to have the value of between the range of 14.5 ± 0.2 : 1 by the fuel combustion ratio control using the λ-sensor(a sensor for calculating the air excess ratio by measuring the amount of air in the waste gas).
However, the thin air/fuel ratio (22^∼23:1) cannot be measured by a general λ-sensor, and only the relative decision making whether the ratio is thinner or thicker than the theoretical air/fuel ratio(14.5 : 1) is possible.
Accordingly, to practice the feedback control the thin air/fuel ratio, a linear air/fuel sensor having a rectilineal output attitude is needed. However, the lineal air/fuel sensor is more expensive than the ordinary λ-sensor and this fact causes higher vehicle costs. Furthermore, in case of the engine has been used for a long time, air leaking or injector meter change, the feedback costs will be increased.
With particular reference to Fig. 1, there is shown an engine control device generally designated by the reference numeral 1. The engine control device governs an engine 3 and the injector 2 is operated by controlling the injecting amount from the engine control device 1.
In case of general thin combustion engine vehicles, feedback controls are carried out with an air/fuel ratio sensor at both theoretical air/fuel ratio and thin air/fuel ratio driving conditions.
However, in the theoretical air/fuel ratio case, to increase the purification efficiency of the three dimensional catalyst, the feedback control must be fulfilled; on the other hand, in the thin air/fuel ratio case, the precise feedback control of the air/fuel ratio is not necessary because catalyst purification is not nearly influenced.
As described above, at the thin air/fuel ratio driving condition, the feedback control dose not need to be fulfilled, but when a desired air/fuel ratio is not achieved because of the omission of the feedback control, engine operation instability or increasement of NOx discharge amount might be occurred, therefore, it is necessary to amend separately the ratio to approach the desired air/fuel ratio.

SUMMARY OF THE PRESENT INVENTION

It is an object of the invention to provide a control method for a driving operation of the theoretical air/fuel ratio and the thin air/fuel ratio for vehicles having thin combustion engines.
It is a further object of the invention to control the air/fuel ratio to be a precise air/fuel ratio by λ-feedback value.
This present invention gives the solution for the unstability of the engine operation or the increasement of the NOx discharge amount with the desirable air/fuel ratio by applying the preliminary adaption value under the open control condition without the feedback control and because it is possible to use the cheap λ sensor(O₂ sensor) the cost of vehicles will be down.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the objects and advantages of the present invention, reference should be given to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals and wherein;

Fig 1. is a block diagram of a general air/fuel ratio control flow
Fig 2. is a block diagram illustrating an air/fuel control method of this present invention
Fig 3. contains a flow diagram of this present invention

DETAILED DESCRIPTION OF THE PRESENT INVENTION

This present invention relates to an air/fuel ratio control method for thin combustion engine vehicles to increase purification efficiency of waste gas and combustion efficiency.
Therefore, the objects of this present invention are in the theoretical air/fuel ratio combustion, to control the air/fuel ratio to be the precise air/fuel ratio by λ-feedback value after making it be the almost desired air/fuel ratio by adaptive precontol of the fuel amount before the feedback control; and to provide an air/fuel ratio control method in order to get near the desired air/fuel ratio by performing the open loop control with only an adaption value which is obtained by the aforesaid procedure.
To fulfil the above objects this invention performs as follows :
about an air/fuel ratio control method which controls fuel supply of engines by ECU(Electronic Control Unit)s based on the information from the sensors, during the combustion of the theoretical air/fuel ratio, the set-up adaption value is multiplied by the basic injected amount, then after burning the result amount, i. e. fuel injected amount, the amount of oxygen in the waste gas is detected by λ sensor and the feedback control process is repeated; the obtained feedback value will be counted in the adaption value which decides the next injected amount and will constitute the new adaption value by being stored in the ECU's RAM. During the combustion of the thin air/fuel ratio, by deciding the fuel injecting value with the result value from multiplying the upper said adaption value in the RAM by the basic injecting value of the thin air/fuel ratio, an open loop control will be conducted for achieving the desired air/fuel ratio without feedback control by λ-sensor.
Referring the Figures, the detailed description of the invention is following. Fig. 1 represents the flow chart of a general air/fuel ratio control; No. 1 is an ECU which controls an engine; informations regarding absorption air amount, loads, oxygen amount in waste gas, temperature, inhalation temperature and condition of speed from the sensors are transformed as electric signals and transferred to perceive the condition of the engine and by controlling the fuel injecting value through the air absorption amount and the injector 2 based on the signals from the sensors, vehicles can be driven with the optimal air/fuel ratio.
For performing the optimal purification efficiency in the vehicles using three dimensional catalyst, it is always required to set the air/fuel ratio to the theoretical air/fuel ratio under every driving condition, therefore, for controlling the air/fuel ratio, the amount of oxygen in waste gas is measured with a O₂ sensor (λ-sensor) on an exhaust hole expending from the engine 3 and the air excess rate from the aforesaid oxygen amount is calculated; then the air excess rate will be feedback to govern the amount of the air/fuel ratio, therefore, it is possible to control the desired air/fuel ratio.
However, according to existing fuel injecting amount control methods, the feedback control by the O₂ sensor on an exhaust hole has been applied to both theoretical and thin air/fuel ratio. However, because of the engine's aging or the injector's flux change, sometimes the feedback value may not be reached the desired value, but this present invention provides the following features to solve such problems ; as shown in Fig 2, the preliminary adaption value before the feedback control is applied and after making the air/fuel ratio to the somewhat desired value, the precise air/fuel ratio with the λ-feedback value is controlled. If it is under the thin air/fuel ratio condition(it is represented as the switch which is connected to the off terminal), only the fuel injecting value is settled to be near the desired air/fuel ratio by applying the adaption value to the thin air/fuel ratio but the feedback control will not be carried out in the thin air/fuel ratio condition.
The operation of this present invention is expressed in Fig 3, the functional flow chart.
An ECU 1 detects the temperature of cooling water with the WTS(Water Temperature Sensor) which is installed in the engine 3's water-out-let part and evaluates whether the temperature is within the possible feedback control range (step A).
In the ECU 1's RAM, the adaption value needs to pre-settle the air/fuel ratio, for example the initial value is set by the value 1 and to be counted (step B), then the ECU 1 estimates the theoretical air/fuel ratio(14.5:1) which makes supply ratio of the air supplied to the engine 3 and gasoline burned completely (step C); if it is under the theoretical air/fuel ratio condition, the basic injecting amount of the theoretical air/fuel ratio during the combustion input in the ECU 1 is injected through the injector (step D).
The compound air of the theoretical air/fuel ratio is flowed to the engine and burned, and the oxygen amount in the waste gas is measured by the O₂ sensor(step E) through the discharge process . In proportion to the aforesaid oxygen amount, the FBV(Feedback control Value) is decided and is evaluated whether it has the value identical with the initial one(step F).
For example, if the complete combustion is fulfilled, the oxygen amount which is detected from the O₂ sensor will have the value 0, and the FBV will be set with the value 1. In this case, if the value of FBV is not 1, it means the air is short or excessive, therefore, returning to the step B, the initial value should be recounted under consideration of the air excess, the value in the RAM is stored and controlling the theoretical air/fuel ratio is governed by the new adaption value.
If the combustion condition of the engine is under the thin air/fuel ratio rather than the theoretical air/fuel ratio, the density of the compound air will be thickened and the desired air/fuel ratio is attained by injecting the fuel combustion amount value through the value of multiplying the new Adaption value(=Adapt + αadapt) value stored in the RAM to the basic injecting amount which is already decided to be injected during the thin air/fuel ratio input in the ECU 1(step G). The aforesaid adaption value is generally between 0.8∼1.2.

Claims

Referring to an air/fuel ratio control method which performs a feedback control the fuel supply of an engine by an ECU(Electric Control Unit) based on information from the sensors, and
during the theoretical air/fuel ratio combustion, the fuel injecting value is set by the amount of multiplying the basic injecting amount by the adaption value set up previously and by detecting the oxygen amount in the waste gas with the λ sensor and the feedback control process is repeated but the aforesaid feedback value will be counted and stored in the ECU's RAM; as the result of this procedure, the next injecting value will be decided; and
during the thin fuel/air ratio combustion, after the adaption value stored in the aforesaid RAM is multiplied by the basic injecting amount at the thin fuel/air ratio, the result value decides the fuel injecting amount, and this procedure lets the ratio being closed to the desired fuel/air ratio without the feedback control which is governed by the λ sensor.