阅读说明：本技术 一种发动机燃气控制方法、发动机燃气控制系统及发动机 (Engine gas control method, engine gas control system and engine ) 是由 韩雨 周凯 李维龙 于 2021-09-16 设计创作，主要内容包括：本发明属于车辆技术领域,公开了一种发动机燃气控制方法、发动机燃气控制系统及发动机。该发动机燃气控制方法包括以下步骤：获取发动机燃气参数,其中发动机燃气参数包括喷射阀的进口和出口之间的实际压力差、和/或喷射阀的实际开度、和/或喷射阀的占空比、和/或发动机的实际燃气压力；根据喷射阀的进口和出口之间的实际压力差,和/或喷射阀的实际开度,和/或喷射阀的实际占空比,和/或发动机的实际燃气压力,限制发动机的输出扭矩。该发动机燃气控制方法,动态控制发动机扭矩输出限制,避免因燃气压力不足,导致燃气量供给不足,影响发动机空燃比控制。(The invention belongs to the technical field of vehicles and discloses an engine gas control method, an engine gas control system and an engine. The engine gas control method comprises the following steps: acquiring engine gas parameters, wherein the engine gas parameters comprise an actual pressure difference between an inlet and an outlet of an injection valve, and/or an actual opening degree of the injection valve, and/or a duty ratio of the injection valve, and/or an actual gas pressure of the engine; the output torque of the engine is limited based on the actual pressure difference between the inlet and the outlet of the injection valve, and/or the actual opening of the injection valve, and/or the actual duty cycle of the injection valve, and/or the actual gas pressure of the engine. The engine gas control method dynamically controls the torque output limit of the engine, and avoids the influence on the air-fuel ratio control of the engine due to insufficient gas quantity supply caused by insufficient gas pressure.)

1. An engine gas control method is characterized by comprising the following steps:

acquiring engine gas parameters, wherein the engine gas parameters comprise an actual pressure difference between an inlet and an outlet of an injection valve, and/or an actual opening degree of the injection valve, and/or a duty ratio of the injection valve, and/or an actual gas pressure of the engine;

the output torque of the engine is limited based on the actual pressure difference between the inlet and the outlet of the injection valve, and/or the actual opening of the injection valve, and/or the actual duty cycle of the injection valve, and/or the actual gas pressure of the engine.

2. The engine gas control method of claim 1, wherein limiting the output torque of the engine based on the actual pressure difference between the inlet and the outlet of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual pressure difference between the inlet and the outlet of the injection valve is less than a preset pressure difference;

if the actual pressure difference between the inlet and the outlet of the injection valve is greater than or equal to the preset pressure difference, the output torque of the engine is not limited.

3. The engine gas control method according to claim 1, wherein the limiting the output torque of the engine according to the actual opening degree of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual opening of the injection valve is greater than the preset opening;

if the actual opening degree of the injection valve is less than or equal to the preset opening degree, the output torque of the engine is not limited.

4. The engine gas control method according to claim 1, wherein the limiting the output torque of the engine according to the actual duty ratio of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual duty cycle of the injection valve is greater than the preset duty cycle;

and if the actual duty ratio of the injection valve is less than or equal to the preset duty ratio, the output torque of the engine is not limited.

5. The engine gas control method according to claim 1, wherein the limiting the output torque of the engine according to the actual gas pressure of the engine comprises the steps of:

if the actual gas pressure of the engine is smaller than the preset pressure, limiting the output torque of the engine;

and if the actual gas pressure of the engine is greater than or equal to the preset pressure, the output torque of the engine is not limited.

6. The engine gas control method according to claim 1, characterized by further comprising, before said obtaining the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening degree of the injection valve, the duty ratio of the injection valve, and the actual gas pressure of the engine, the steps of:

acquiring the working state of an engine;

and if the working state of the engine is the running state, starting the protection function of the gas system.

7. The engine gas control method of claim 1, wherein said obtaining an actual pressure differential between an inlet and an outlet of an injection valve comprises the steps of:

acquiring an inlet gas pressure P1 of the injection valve and an outlet gas pressure P2 of the injection valve;

calculating an actual pressure difference Δ P between the inlet and the outlet of the injection valve, wherein Δ P ═ P1-P2 |.

8. The engine gas control method according to claim 7, characterized in that the inlet gas pressure of the injection valve is detected by an inlet sensor provided at an inlet of the injection valve, and the outlet gas pressure of the injection valve is detected by an outlet sensor provided at an outlet of the injection valve.

9. An engine gas control system characterized by being controlled by the engine gas control method according to any one of claims 1 to 8.

10. An engine comprising the engine gas control system of claim 9.

Technical Field

The invention relates to the technical field of vehicles, in particular to an engine gas control method, an engine gas control system and an engine.

Background

At present, the engine generally adopts a mode of single-point injection of natural gas, an oxygen sensor is utilized to detect the oxygen content in air, the air quantity is calculated according to the oxygen content, and the injection of an injection valve is controlled, so that the aim of accurately controlling the gas quantity of the engine is fulfilled.

When the pressure of the whole gas cylinder is low, the pressure of gas is also low under the influence of the design characteristics of a gas system, and the air-fuel ratio of an engine is influenced by simply adjusting parameters such as power-up time of a gas supply system, so that the gas supply requirement cannot be met. However, the existing engine exhaust gas treatment device includes EGR and a three-way catalyst, and the EGR can reduce the temperature of exhaust gas, maintain the three-way catalyst within a range of an optimum operating temperature, and improve conversion efficiency. Among them, the conversion efficiency of the three-way catalyst is greatly affected by the air-fuel ratio.

Therefore, when the pressure of the gas system is insufficient, it may cause an abnormality in the air-fuel ratio control, affect the conversion efficiency of the three-way catalyst, affect the emission control, and even further may accelerate the aging of the three-way catalyst, affecting the service life of the three-way catalyst.

Disclosure of Invention

The invention aims to provide an engine gas control method, an engine gas control system and an engine, which can ensure the stability of an air-fuel ratio and improve the reliability of a three-way catalytic converter.

In order to achieve the purpose, the invention adopts the following technical scheme:

an engine gas control method comprises the following steps:

acquiring engine gas parameters, wherein the engine gas parameters comprise an actual pressure difference between an inlet and an outlet of an injection valve, and/or an actual opening degree of the injection valve, and/or a duty ratio of the injection valve, and/or an actual gas pressure of the engine;

the output torque of the engine is limited based on the actual pressure difference between the inlet and the outlet of the injection valve, and/or the actual opening of the injection valve, and/or the actual duty cycle of the injection valve, and/or the actual gas pressure of the engine.

Preferably, said limiting the output torque of the engine based on the actual pressure difference between the inlet and the outlet of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual pressure difference between the inlet and the outlet of the injection valve is less than a preset pressure difference;

if the actual pressure difference between the inlet and the outlet of the injection valve is greater than or equal to the preset pressure difference, the output torque of the engine is not limited.

Preferably, said limiting the output torque of the engine based on the actual pressure difference between the inlet and the outlet of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual pressure difference between the inlet and the outlet of the injection valve is less than a preset pressure difference;

if the actual pressure difference between the inlet and the outlet of the injection valve is greater than or equal to the preset pressure difference, the output torque of the engine is not limited.

Preferably, the limiting the output torque of the engine according to the actual opening degree of the injection valve includes:

limiting the output torque of the engine if the actual opening of the injection valve is greater than the preset opening;

if the actual opening degree of the injection valve is less than or equal to the preset opening degree, the output torque of the engine is not limited.

Preferably, the limiting the output torque of the engine according to the actual duty ratio of the injection valve includes:

limiting the output torque of the engine if the actual duty cycle of the injection valve is greater than the preset duty cycle;

and if the actual duty ratio of the injection valve is less than or equal to the preset duty ratio, the output torque of the engine is not limited.

Preferably, the limiting the output torque of the engine based on the actual gas pressure of the engine includes the steps of:

if the actual gas pressure of the engine is smaller than the preset pressure, limiting the output torque of the engine;

and if the actual gas pressure of the engine is greater than or equal to the preset pressure, the output torque of the engine is not limited.

Preferably, the method further comprises the following steps before the obtaining of the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening degree of the injection valve, the duty ratio of the injection valve and the actual gas pressure of the engine:

acquiring the working state of an engine;

and if the working state of the engine is the running state, starting a gas system protection function, and then acquiring the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening of the injection valve, the duty ratio of the injection valve and the actual gas pressure of the engine.

Preferably, the step of obtaining the actual pressure difference between the inlet and the outlet of the injection valve comprises the steps of:

acquiring an inlet gas pressure P1 of the injection valve and an outlet gas pressure P2 of the injection valve;

calculating an actual pressure difference Δ P between the inlet and the outlet of the injection valve, wherein Δ P ═ P1-P2 |.

Preferably, the inlet gas pressure of the injection valve is detected by an inlet sensor provided at an inlet of the injection valve, and the outlet gas pressure of the injection valve is detected by an outlet sensor provided at an outlet of the injection valve.

In order to achieve the purpose, the invention also provides an engine fuel gas control system which is controlled by adopting the engine fuel gas control method.

In order to achieve the purpose, the invention further provides an engine which comprises the engine gas control system.

The invention has the beneficial effects that:

the engine gas control method provided by the invention can influence parameters such as the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening of the injection valve, the duty ratio of the injection valve and the actual gas pressure of the engine based on the gas pressure change, dynamically control the torque output limit of the engine, and dynamically control the gas system to inject by limiting the output torque of the engine, thereby avoiding the insufficient gas quantity supply and the influence on the air-fuel ratio control of the engine due to the insufficient gas pressure.

The engine gas control system provided by the invention is controlled by adopting the engine gas control method based on the influence of the gas pressure change on the supply characteristic of the injection valve, so that the air-fuel ratio of the engine can be kept in a required control range under different gas pressures, the stability of the air-fuel ratio of the engine is ensured, the conversion efficiency and the reliability of the three-way catalyst are ensured, and the service life is prolonged.

The engine provided by the invention comprises the engine gas control system, so that the problem of abnormal air-fuel ratio control caused by insufficient gas pressure and other reasons is solved, the driving feeling is prevented from being influenced only by a fault torque limit mode and the like, and the use feeling of a user is improved.

Drawings

FIG. 1 is a flow chart of an engine gas control method of the present invention.

Detailed Description

In order to make the technical problems solved, technical solutions adopted and technical effects achieved by the present invention clearer, the technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, removably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The air-fuel ratio of the engine is the mass ratio between air and fuel in a mixed gas, if the gas pressure is insufficient, the control of the air-fuel ratio is influenced, and when the air-fuel ratio is abnormal, the aging of the three-way catalyst can be accelerated while the conversion efficiency of the three-way catalyst is influenced, so that the service life and the reliability of the three-way catalyst are influenced.

In order to solve this problem, the present embodiment provides an engine gas control method including the steps of:

acquiring engine gas parameters, wherein the engine gas parameters comprise an actual pressure difference between an inlet and an outlet of an injection valve, and/or an actual opening degree of the injection valve, and/or a duty ratio of the injection valve, and/or an actual gas pressure of the engine;

the output torque of the engine is limited based on the actual pressure difference between the inlet and the outlet of the injection valve, and/or the actual opening of the injection valve, and/or the actual duty cycle of the injection valve, and/or the actual gas pressure of the engine.

The engine gas control method provided by the embodiment can influence parameters such as the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening of the injection valve, the duty ratio of the injection valve and the actual gas pressure of the engine based on the gas pressure change, dynamically control the torque output limit of the engine, and dynamically control the gas system to inject by limiting the output torque of the engine, so that the problem that the gas quantity supply is insufficient due to insufficient gas pressure and the air-fuel ratio control of the engine is influenced is avoided.

It can be understood that the engine gas control method provided by the embodiment may select at least one of the parameters of the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening degree of the injection valve, the duty ratio of the injection valve, and the actual gas pressure of the engine, that is, any one of them, or any two or all of them, may be selected within the protection scope of the embodiment, and the embodiment preferably selects all of the parameters to ensure the comprehensiveness and accuracy of the control.

If the pressure of the whole vehicle gas cylinder is relatively low correspondingly, the pressure is influenced by the design characteristics of a gas system, the gas pressure is low, the gas supply requirement cannot be met by adjusting parameters such as the power-on time of a gas supply system, and the transient control of the air-fuel ratio of the engine is influenced. To solve this problem, limiting the output torque of the engine according to the actual gas pressure of the engine includes the steps of:

if the actual gas pressure of the engine is smaller than the preset pressure, limiting the output torque of the engine;

and if the actual gas pressure of the engine is greater than or equal to the preset pressure, the output torque of the engine is not limited.

If the actual gas pressure of engine is less than preset pressure, it is less to mean the actual gas pressure of engine this moment is less, and gas pressure is not enough, and engine activation moment of torsion limit function this moment, developments limit torsion, through the output torque who limits the engine, makes the required gas volume of engine reduce, means to control from the source of engine gas volume, improves the condition that gas pressure is not enough. If the actual gas pressure of the engine is larger than or equal to the preset pressure, the actual gas pressure of the engine is larger at the moment, the gas pressure is sufficient, the engine can be guaranteed to have a better air-fuel ratio, and the torque of the engine is not limited.

For the actual gas pressure of the parameter engine, if direct measurement may have certain difficulty, the actual gas pressure can be characterized by other parameters convenient for measurement. The existing engine injects natural gas through the injection valve to achieve the purpose of accurately controlling the gas quantity of the engine, so that the actual gas pressure of the engine can be represented according to various indexes of the injection valve.

It can be understood that the process of injecting the fuel gas by the injection valve is similar to the water outlet process of the water faucet, and if the water pressure is higher, the water outlet requirement can be realized only by the water faucet with a smaller valve opening degree on the assumption that the water outlet quantity of the water faucet required in daily life is a fixed value; if the water pressure is relatively low, the water tap is required to have a larger valve opening to meet the requirement of water yield; if the water pressure is normal, the valve opening of the water faucet does not need to be too large.

Based on this principle, limiting the output torque of the engine according to the actual opening degree of the injection valve in the present embodiment includes the steps of:

limiting the output torque of the engine if the actual opening of the injection valve is greater than the preset opening;

if the actual opening degree of the injection valve is less than or equal to the preset opening degree, the output torque of the engine is not limited.

If the actual opening degree of the injection valve is larger than the preset opening degree, the actual opening degree of the injection valve is larger, the pressure of the fuel gas in the injection valve is smaller, the fuel gas in the injection valve is insufficient, and the requirement of the fuel gas injection amount can be met only by maintaining the actual opening degree of the injection valve in a larger range, so that the fuel gas amount required by the engine is reduced by limiting the output torque of the engine at the moment, and the problem of insufficient fuel gas in the injection valve is solved. If the actual opening of the injection valve is smaller than or equal to the preset opening, the actual opening of the injection valve is smaller, the pressure of the fuel gas in the injection valve is larger at the moment, the fuel gas in the injection valve is sufficient, the actual opening of the injection valve is maintained in a smaller range, the requirement of the fuel gas injection quantity can be met, and the injection state is considered to be a better injection state at the moment, and the output torque of the engine is not limited.

The actual opening of the injection valve is actually characterized by the remaining capacity of the injection valve, wherein the duty cycle of the injection valve specifically refers to the proportion of the energization time to the total time in one pulse cycle, and therefore the remaining capacity of the injection valve can be characterized by the actual duty cycle of the injection valve in addition to the actual opening of the injection valve.

For this purpose, limiting the output torque of the engine according to the actual duty cycle of the injection valve comprises the steps of:

limiting the output torque of the engine if the actual duty cycle of the injection valve is greater than the preset duty cycle;

and if the actual duty ratio of the injection valve is less than or equal to the preset duty ratio, the output torque of the engine is not limited.

If the actual duty ratio of the injection valve is larger than the preset duty ratio, the actual duty ratio of the injection valve is larger, the pressure of the internal gas of the injection valve is smaller, the internal gas of the injection valve is insufficient, and the requirement of the gas injection amount can be met only by maintaining the actual duty ratio of the injection valve in a larger range, so that the gas amount required by the engine is reduced by limiting the output torque of the engine at the moment, and the problem of insufficient gas in the injection valve is solved. If the actual duty ratio of the injection valve is smaller than or equal to the preset duty ratio, the actual duty ratio of the injection valve is smaller, the internal gas pressure of the injection valve is larger at the moment, the internal gas of the injection valve is sufficient, the actual duty ratio of the injection valve is maintained in a smaller range, the requirement of the gas injection quantity can be met, the injection state is considered to be a better injection state, and the output torque of an engine is not limited.

The method is characterized in that the actual opening degree and the actual duty ratio of the injection valve are used for representing the allowance of the injection valve, further representing the change of gas pressure, and being used for adapting to the change of different working conditions of an engine, activating a torque limiting function of the engine, limiting the torque of the engine, dynamically adjusting the injection quantity requirement, and maintaining the duty ratio or the opening degree of the injection valve within a certain range through PID (proportion integration differentiation) adjustment so as to ensure that the air-fuel ratio of the engine is maintained within a required range, thereby ensuring the stability of the air-fuel ratio control of the engine.

When the pressure difference between the inlet pressure of the injection valve and the outlet gas pressure of the injection valve does not meet the requirement, the flow calculation precision of the injection valve is low, and the accurate control of the air-fuel ratio cannot be met. To solve this problem, the present embodiment provides an engine gas control method in which limiting an output torque of an engine according to an actual pressure difference between an inlet and an outlet of an injection valve includes the steps of:

limiting the output torque of the engine if the actual pressure difference between the inlet and the outlet of the injection valve is less than a preset pressure difference;

if the actual pressure difference between the inlet and the outlet of the injection valve is greater than or equal to the preset pressure difference, the output torque of the engine is not limited.

If the actual pressure difference between the inlet and the outlet of the injection valve is smaller than the preset pressure difference, the actual pressure difference is smaller, the internal gas pressure of the injection valve is smaller at the moment, and the gas in the injection valve is insufficient, the gas quantity required by the engine is reduced by limiting the output torque of the engine at the moment, and the problem that the gas in the injection valve is insufficient is solved. Based on the actual pressure difference between the inlet and the outlet of the injection valve, different engine output torques are selected, the pressure difference of the injection valve is maintained within a certain range by activating the dynamic torque limiting function and utilizing PID (proportion integration differentiation) regulation, and the control stability of the air-fuel ratio of the engine is ensured. If the actual pressure difference between the inlet and the outlet of the injection valve is larger than or equal to the preset pressure difference, the fact that the actual pressure difference is larger means that the pressure in the injection valve is larger, the air in the injection valve is sufficient, and the injection state is considered to be the better injection state at this moment, and the output torque of the engine is not limited.

Further, obtaining an actual pressure differential between the inlet and the outlet of the injection valve comprises the steps of:

acquiring an inlet gas pressure P1 of the injection valve and an outlet gas pressure P2 of the injection valve;

calculating an actual pressure difference Δ P between the inlet and the outlet of the injection valve, wherein Δ P ═ P1-P2 |.

After the inlet gas pressure P1 of the injection valve and the outlet gas pressure P2 of the injection valve are obtained, the inlet gas pressure P1 and the outlet gas pressure P2 are subjected to difference to obtain the actual pressure difference delta P of the injection valve.

In order to obtain the inlet gas pressure P1 and the outlet gas pressure P2, an inlet sensor is provided at the inlet of the injection valve for detecting the inlet gas pressure of the injection valve, and an outlet sensor is provided at the outlet of the injection valve for detecting the outlet gas pressure of the injection valve.

Therefore, the import gas pressure of injection valve detects and obtains through the import sensor that sets up in the injection valve import, and the export gas pressure of injection valve detects and obtains through the export sensor that sets up in the injection valve export, adopts this kind of mode, and convenient operation reduces and detects the degree of difficulty, measures the accuracy height.

Further, the following steps are included before acquiring the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening degree of the injection valve, the duty ratio of the injection valve, and the actual gas pressure of the engine:

acquiring the working state of an engine;

and if the working state of the engine is the running state, starting a gas system protection function, and then acquiring the actual pressure difference between the inlet and the outlet of the injection valve, the actual opening of the injection valve, the duty ratio of the injection valve and the actual gas pressure of the engine.

And if the working state of the engine is not the running state, the protection function of the gas system is not started.

By adopting the mode, the protection function of the gas system can be started only when the working state of the engine is the running state, unnecessary waste is reduced, and the effects of energy conservation and emission reduction are achieved.

As shown in fig. 1, the steps of the engine gas control method provided by the embodiment are as follows:

s1, acquiring the working state of the engine;

s2, judging whether the working state of the engine is the running state, if so, executing S3, otherwise, returning to S1;

s3, starting a protection function of the gas system;

s4, acquiring the actual gas pressure of the engine;

s41, judging whether the actual gas pressure of the engine is smaller than the preset pressure, if so, executing S100, and if not, executing S200;

s100, limiting the output torque of the engine, and returning to S1;

s200, the output torque of the engine is not limited, and the operation returns to S1;

s5, acquiring the actual opening of the injection valve;

s51, judging whether the actual opening of the injection valve is larger than a preset opening, if so, executing S100, and if not, executing S200;

s6, acquiring the duty ratio of the injection valve;

s61, judging whether the actual duty ratio of the injection valve is larger than the preset duty ratio, if so, executing S100, and if not, executing S200;

s7, acquiring inlet gas pressure P1 of the injection valve and outlet gas pressure P2 of the injection valve;

s71, calculating an actual pressure difference Δ P between the inlet and the outlet of the injection valve, wherein Δ P ═ P1-P2 |;

and S72, judging whether the actual pressure difference between the inlet and the outlet of the injection valve is smaller than the preset pressure difference, if so, executing S100, and otherwise, executing S200.

The prior art aims at insufficient gas pressure, carries out torque limitation after fault reporting, and has relatively poor adaptability. In order to solve the problem, the embodiment further provides an engine gas control system, which is controlled by the engine gas control method based on the influence of the gas pressure change on the supply characteristic of the injection valve, so that the air-fuel ratio of the engine can be kept within a required control range under different gas pressures, the stability of the air-fuel ratio of the engine is ensured, the conversion efficiency and the reliability of the three-way catalyst are ensured, and the service life is prolonged.

The embodiment also provides an engine, which comprises the engine gas control system, so that the problem of abnormal air-fuel ratio control caused by insufficient gas pressure and other reasons is solved, the driving feeling is prevented from being influenced only by the modes of fault torque limitation and the like, and the use feeling of a user is improved.

In the description herein, it is to be understood that the terms "upper", "lower", "right", and the like are based on the orientations and positional relationships shown in the drawings and are used for convenience in description and simplicity in operation, but do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be constructed in a particular operation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used merely for descriptive purposes and are not intended to have any special meaning.

In the description herein, references to the description of "an embodiment," "an example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example.

In addition, the foregoing is only the preferred embodiment of the present invention and the technical principles applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.