KR20130050115A - Method of checking fuel/air ratio difference of each engine cylinder - Google Patents

Abstract

The present invention relates to a method for checking the air-fuel ratio deviation for each engine cylinder in consideration of a response delay until the detection of the oxygen concentration measurement value by the oxygen sensor, the specific exhaust exhausted from a specific cylinder among the engine cylinders An oxygen concentration measuring step of measuring the oxygen concentration of the gas with an oxygen sensor; An air-fuel ratio deviation determining step of determining whether an air-fuel ratio is in a lean or rich state using a value measured in the oxygen concentration measuring step in an engine control unit (ECU); When the air-fuel ratio is determined to be lean or rich in the air / fuel ratio deviation determination step, the specific cylinder is identified using a detection time required until the detection of the oxygen concentration measurement value for each engine cylinder in advance. Includes an air-fuel ratio deviation occurrence cylinder identification step.

Description

How to check the deviation of air-fuel ratio by engine cylinder {METHOD OF CHECKING FUEL / AIR RATIO DIFFERENCE OF EACH ENGINE CYLINDER}

The present invention relates to a method for checking the air-fuel ratio deviation for each engine cylinder, and more specifically to checking the air-fuel ratio deviation for each engine cylinder to check a specific cylinder in which the air-fuel ratio deviation occurred in consideration of the response delay until the detection of the oxygen concentration measurement value by the oxygen sensor It is about a method.

In general, a gasoline engine is provided with an oxygen sensor in the exhaust pipe, and the air-fuel ratio feedback correction for increasing or decreasing the fuel injection amount is performed by the output signal. By maintaining the exhaust air-fuel ratio near the theoretical performance ratio, the purification rate of the three-way catalyst is increased and the exhaust purification is achieved.

In a multi-cylinder engine, if there is a deviation in the exhaust air-fuel ratio of each cylinder, even if the average exhaust air-fuel ratio of the entire cylinder is maintained at the theoretical performance ratio, each cylinder burns in a rich or lean state. Exhaust gas is emitted.

When the exhaust gas is rich, HC and CO pass through the three-way catalyst in large quantities, while in the lean state, NOx passes through the three-way catalyst in large quantities, so that problems cannot be effectively purified.

Therefore, in order to avoid such a problem, a technique for estimating the fuel injection amount by estimating the deviation of the exhaust air-fuel ratio of each cylinder from the measured value of the oxygen sensor provided before the three-way catalyst has been proposed.

For example, Patent No. 10-0373009 "Aerodynamic Ratio Deviation Compensation Method for Each Cylinder of the Engine".

The above-described patent, the process of grouping the cylinders for each load region according to the position of the oxygen sensor mounted on the exhaust manifold, setting the fuel amount learning reference value for the load region for each condition, and feedback conditions compensated for warming up after engine start Calculating the theoretical air-fuel ratio according to the oxygen concentration in the exhaust gas, engine speed, load and water temperature, extracting the average value of the calculated theoretical air-fuel ratio, and determining whether the load region is a high speed high load or a low speed low load A process of performing fuel quantity learning for each of the determined load regions, a process of determining a group set according to a position of an oxygen sensor mounted on a corresponding exhaust pipe, and when the group is determined, the amount of fuel of a load and a theoretical air-fuel ratio And a process of performing fuel amount correction for each cylinder in consideration of the fuel amount learning value for each load region.

Conventional air-fuel ratio deviation correction methods, including the above-described patent, set the reference value by grouping the cylinders as shown in the registered patent shown in Figure 1, or the air-fuel ratio deviation checking means for judging the exhaust air-fuel ratio itself of each cylinder separately It is provided so that the fluctuation | variation of the exhaust air fuel ratio between each cylinder is eliminated, and exhaust purification is aimed at.

In the prior art, the crank angle of each cylinder is obtained by experiment or calculation in advance, and the degree of enrichment or lean is independently detected for each cylinder according to the crank angle, and the feedback is then fed back to the deviation between the detected value and the theoretical performance ratio. In this way, the respective absolute values of the respective cylinders are evaluated to correct the deviation of the exhaust air-fuel ratio.

However, the above-described prior art does not consider the response delay from the exhaust valve of each cylinder to the oxygen sensor, and in particular, when the exhaust pipes are of the same length, the response delay is different for each cylinder to determine the corresponding crank angle. There is a problem that requires very complex programming or previous experiments.

The present invention has been made to solve the problems of the prior art, to propose a method for checking the air-fuel ratio deviation for each engine cylinder by a simple method for identifying a particular cylinder burned and exhausted in the lean or rich state of the air-fuel ratio of the engine cylinder.

In order to solve the above problems, the air-fuel ratio deviation checking method for each engine cylinder according to the present invention includes an oxygen concentration measuring step of measuring an oxygen concentration of a specific exhaust gas exhausted from a specific cylinder among engine cylinders; An air-fuel ratio deviation determining step of determining whether an air-fuel ratio is in a lean or rich state using a value measured in the oxygen concentration measuring step in an engine control unit (ECU); When the air-fuel ratio is determined to be lean or rich in the air / fuel ratio deviation determination step, the specific cylinder is identified using a detection time required until the detection of the oxygen concentration measurement value for each engine cylinder in advance. Includes an air-fuel ratio deviation occurrence cylinder identification step.

In this case, the detection time is a time from when the exhaust valve is opened to when the oxygen concentration measurement value is detected by the oxygen sensor, the air-fuel ratio deviation occurrence cylinder confirmation step, the detection time for each engine cylinder By each retrospective point, the cylinder in which the exhaust valve was opened may be regarded as the specific cylinder.

In addition, the air-fuel ratio deviation occurrence cylinder identification step may be configured to identify a cylinder regarded as the specific cylinder by using a value detected from a cam position sensor.

On the other hand, the air-fuel ratio deviation determination step, by comparing the measured value of the oxygen concentration with a predetermined reference value may be made to determine that the air-fuel ratio is lean or rich state.

At this time, in the air-fuel ratio deviation determination step, if it is determined that the air-fuel ratio is lean or rich state, the fuel injection amount correction step of correcting the fuel injection amount by using the difference value between the measured value of the oxygen concentration and the reference value in the engine control unit May be further included.

According to the present invention, there is an advantage that it is possible to easily and accurately identify the specific cylinder in which the air-fuel ratio deviation occurs in the engine cylinder by using the detection time.

Due to these advantages, the ECU can easily control the air-fuel ratio correction of a particular cylinder, so that the vehicle to which the present invention is applied can have an exhaust capability that complies with environmental regulations such as, for example, on board diignosis (OBD) regulation. Can be.

1 is a group-by-cylinder grouping diagram of an exhaust manifold used in a conventional air-fuel ratio deviation compensation method per engine cylinder,
2 is a flowchart illustrating a method for checking air-fuel ratio deviation for each engine cylinder according to an embodiment of the present invention.
3 is a schematic diagram illustrating an exhaust manifold;
4 is a graph showing a change in voltage value for each time zone detected from an oxygen sensor.

With reference to the accompanying drawings, a method for checking the air-fuel ratio deviation for each engine cylinder according to a preferred embodiment of the present invention will be described in detail.

As shown in FIG. 2, the method for checking air-fuel ratio deviation for each engine cylinder according to an exemplary embodiment of the present invention includes an oxygen concentration measuring step S10, an air-fuel ratio deviation determining step S20, and an air-fuel ratio deviation generating cylinder checking step. (S30) is included.

Oxygen concentration measurement step (S10) is a step of measuring the oxygen concentration of the exhaust gas exhausted through the exhaust manifold using an oxygen sensor.

As the oxygen sensor, various oxygen sensors capable of measuring the oxygen concentration of the exhaust gas, such as a binary oxygen sensor or a linear oxygen sensor, may be used. As shown in FIG. 3, the oxygen sensor is provided at an exhaust manifold 200 at a portion of the conduit pipe 220 in which exhaust pipes 210 individually connected to each cylinder 100 are collected into one. The oxygen concentration of the exhaust gas exhausted through is measured.

The oxygen sensor 300 measures the oxygen concentration of the exhaust gas and detects it as a voltage value, and the measured value detected as the voltage value is collected by an engine control unit (hereinafter referred to as an ECU).

In the air-fuel ratio deviation determination step (S20), the ECU collecting the oxygen concentration measurement value determines whether the air-fuel ratio is in a lean or rich state or a steady state by using the measured value. It is a step of determining whether there is an air-fuel ratio deviation using the measured value.

More specifically, the ECU compares the oxygen concentration measurement value with the reference value to determine whether the air-fuel ratio is lean or rich. The reference value is a value preset in the ECU and may be a value for realizing the theoretical air-fuel ratio, or may be an air-fuel ratio target value determined through information such as engine speed and engine load collected and confirmed from various sensors. The ECU compares the reference value and the oxygen concentration measurement with each other to determine whether the air-fuel ratio is lean or rich.

Since the method of checking whether the air-fuel ratio is lean or rich is already known, a detailed description thereof will be omitted. In addition, the method of determining the lean or rich state of the air-fuel ratio by measuring the oxygen concentration of the exhaust gas may be selected as the most appropriate method considering the various conditions given in the type of the oxygen sensor or the various environments in which the engine is located. In addition to the above-described known methods presented as methods, various determination methods may be provided.

In the air-fuel ratio deviation determination step (S20), when it is determined that the air-fuel ratio is in a lean or rich state by determining whether the air fuel ratio is lean or rich, the ECU does not control to correct the fuel injection amount (S21). However, if it is determined that the lean or rich state is subjected to the air-fuel ratio deviation occurs cylinder (S30) to be described later.

In the air-fuel ratio deviation generating cylinder confirmation step (S30), when it is confirmed that there is an air-fuel ratio deviation in the air-fuel ratio deviation determination step (S20) described above, that is, comparing the oxygen concentration measurement value and the reference value of the exhaust gas, the air-fuel ratio is lean or rich. When it is confirmed that the state, the cylinder which discharged the exhaust gas of the lean or rich state among the engine cylinders, ie, the cylinder in which the air-fuel ratio deviation occurred is a certain cylinder.

Exhaust gas is discharged from the engine cylinder through the exhaust valve, and the exhaust gas passes through the exhaust manifold, and a predetermined time elapses until the oxygen concentration is measured by the oxygen sensor. Therefore, the above-mentioned constant exhaust gas, which is the exhaust gas that has been the oxygen concentration measurement target by the oxygen sensor and the air-fuel ratio deviation is confirmed in the step of determining whether there is an air-fuel ratio deviation, is exhausted from which cylinder among the engine cylinders. This may be possible by considering the time.

The method for checking the air-fuel ratio deviation for each engine cylinder according to the present embodiment is to provide a method for identifying a specific cylinder exhausting a specific exhaust gas that is confirmed to have an air-fuel ratio deviation. We present a method of using the detection time that elapses until the concentration is measured.

The detection time can be regarded as a time obtained by adding a delay time to a time constant. This can be described in detail with reference to FIG. 4, and FIG. 4 is a graph showing a change in voltage value for each time period until the oxygen sensor detects an oxygen concentration measurement value. In this case, the delay time is calculated up to a time (b) when the specific exhaust gas reaches the oxygen sensor, that is, the time when the oxygen sensor starts to behave, and the start time is, for example, a fuel injection time, or a fuel It may be the start time or the end time of any one of the engine strokes performed after the injection. The start point or end point of each stroke performed in the cylinder can be confirmed by a cam position sensor and a crank position sensor. Alternatively, the delay time may be calculated based on a time point a at which the exhaust gas is exhausted through the exhaust valve. Hereinafter, a method of identifying an air-fuel ratio deviation occurrence cylinder by specifying an example of calculating a delay time using the exhaust point a as a start point will be described in more detail.

The time constant, i.e., the oxygen sensor, is determined at a delay time calculated from the start of the exhaust point a, and the time at which the exhaust gas reaches the oxygen sensor, i.e., the start point of the oxygen sensor's behavior. When the time taken up to the time point c at which the concentration measurement value is detected is added, the detection time is calculated.

This detection time varies from cylinder to cylinder. The reason is that the distance from each cylinder to the part of the exhaust manifold where the oxygen sensor is located may vary from cylinder to cylinder, and even from the internal shape of the exhaust manifold, which may be affected in the process of exhaust gas moving through the exhaust manifold, the cylinder varies. Because there may be. The detection time is based on any one of the cylinders, and the difference in the detection time is caused by the change in the engine speed and the engine load.

Therefore, the ECU calculates and sets the detection time that changes according to the change in engine speed and engine load in advance for each cylinder, and when the air-fuel ratio deviation is confirmed in the air-fuel ratio deviation checking step (S20), the engine rotates. By the detection time required for each cylinder corresponding to the number and engine load, the time point retrospective from the detection of the oxygen concentration measurement value is checked.

The retrospective time point is confirmed for each cylinder, and in the case of a four-cylinder engine, the retrospective time point for each of the four cylinders is confirmed. Then, at the retrospective point of time, it is confirmed that the cylinder that the exhaust valve was opened is, and the cylinder that is confirmed that the exhaust valve is opened is the specific cylinder in which the air-fuel ratio deviation occurred. The deviation is regarded as a specific cylinder and the fuel injection amount increase and decrease control for this specific cylinder is performed.

Checking whether the exhaust valve is open may be possible using a cam position sensor and a crank position sensor. By checking the position information of the exhaust cam shaft and the crank shaft detected by the cam position sensor and the crank position sensor, it is possible to confirm whether the exhaust valve is opened according to the exhaust stroke. Therefore, the ECU collects and records the positional information of the exhaust camshaft and the crankshaft by time, and performs the step (S31) of checking the positional information of the camshaft and the crankshaft at a time point retroactively by the detection time, and then exhausting the exhaust. The air-fuel ratio deviation occurrence cylinder identification step S30 is completed by performing the step S32 of identifying the cylinder in which the valve is in the open state and considering it as a specific cylinder.

On the other hand, when confirming the cylinder in which the air-fuel ratio deviation occurs through the above-described process, the ECU can control the increase or decrease of the fuel injection amount for the identified cylinder (S40).

To this end, the method for checking the air-fuel ratio deviation for each engine cylinder according to the present embodiment may further include a fuel injection amount correction step. In the fuel injection amount correction step, when it is confirmed that there is an air-fuel ratio deviation in the air-fuel ratio deviation determination step, the ECU calculates the increase / decrease degree of the fuel injection amount, that is, the fuel injection amount correction value, based on the difference between the oxygen concentration measurement value and the reference value. Step S22. The ECU controls the injection time of the injector by reflecting the correction value thus calculated, that is, the fuel injection amount corrected for the specific cylinder in which the air-fuel ratio deviation occurs by performing the step S40 of increasing or decreasing the fuel injection amount for a specific cylinder. The injection control, and such feedback control allows the air-fuel ratio in all cylinders to approach the theoretical air-fuel ratio or the air-fuel ratio target value.

As described above, according to the method for checking the air-fuel ratio deviation for each engine cylinder according to the present embodiment, it is possible to easily check the air-fuel ratio deviation generating cylinder using the detection time. Therefore, the vehicle to which the present embodiment is applied can have accurate fuel injection amount increase / decrease control for the air-fuel ratio deviation generating cylinder, and thus can have an exhaust capability that complies with environmental regulations.

As the present invention can be variously modified by those skilled in the art without departing from the scope of the claims claimed in the claims, the protection scope of the present invention is limited to the specific preferred embodiments described above It doesn't work.

S10; Oxygen concentration measurement step S20; Determination stage of air fuel cost deviation
S30; Checking cylinder for air-fuel ratio deviation
S40; Control of fuel injection volume increase and decrease of a specific cylinder

Claims (5)

An oxygen concentration measuring step of measuring an oxygen concentration of a specific exhaust gas exhausted from the specific cylinder among the engine cylinders with an oxygen sensor;
An air-fuel ratio deviation determining step of determining whether an air-fuel ratio is in a lean or rich state using a value measured in the oxygen concentration measuring step in an engine control unit (ECU);
When the air-fuel ratio is determined to be lean or rich in the air / fuel ratio deviation determination step, the specific cylinder is identified using a detection time required until the detection of the oxygen concentration measurement value for each engine cylinder in advance. Air-fuel ratio deviation generating cylinder identification step;
The method according to claim 1,
The detection time is a time from when the exhaust valve is opened to when the oxygen concentration measurement value is detected by the oxygen sensor,
In the air-fuel ratio deviation generating cylinder identification step, the air-fuel ratio deviation checking method for each engine cylinder, characterized in that the cylinder that the exhaust valve was opened at each time point retrospectively by the detection time for each engine cylinder as the specific cylinder.
The method according to claim 2,
The air-fuel ratio deviation occurrence cylinder identification step, by the engine cylinder, characterized in that for identifying the cylinder that is considered as the specific cylinder by using the position information of the exhaust cam shaft and the crank shaft detected from the cam position sensor and the crank position sensor How to check the air-fuel ratio deviation.
The method according to any one of claims 1 to 3,
The air-fuel ratio deviation determining step, by comparing the measured value of the oxygen concentration with a predetermined reference value to determine the air-fuel ratio deviation for each engine cylinder, characterized in that the air-fuel ratio is lean or rich.
The method of claim 4,
In the air-fuel ratio deviation determination step, if it is determined that the air-fuel ratio is lean or rich,
And a fuel injection amount correcting step of correcting a fuel injection amount by using the difference value between the measured value of the oxygen concentration and the reference value in the engine control unit.

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