JPH09287526A - Exhaust gas recirculation system for compression ignition engine and exhaust gas recirculation control method in the engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and realtimely control a recirculation gas quantity by computing the most suitable rate of a recirculated exhaust gas from absolute pressure in an intake manifold and an exhaust manifold, engine speed, fuel supply speed and air suction temperature for controlling the opening of an exhaust gas recirculation valve. SOLUTION: An exhaust gas recirculation system is equipped with the first and the second pressure sensor 38, 40 for detecting absolute pressure in an intake manifold 22 and an exhaust manifold 24; an engine speed sensor 46; a fuel supply speed sensor 44 and an air suction temperature sensor 48, and their output signals are inputted into a controller 26. The optimum rate of recirculated gas to intake air is computed, and moreover a valve position which enables the recirculated gas having the optimum rate to flow from a conduit 30 to the intake manifold 22 is computed. The exhaust gas reciculation valve 28 is controlled according to the result of computation by a step motor 32. Thus the control ability of exhaust gas recirculation is improved to accomplish the maximum thermal efficiency and the minimum emission of pollution material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD This invention relates to exhaust gas recirculation in internal combustion engines as a method of controlling pollutants, and more particularly to an exhaust gas recirculation system for compression ignition engines.

[0002]

BACKGROUND OF THE INVENTION In the late 1950s, emissions from internal combustion engines were identified as important contributors to photochemical smoke and smog obscuring industrial cities around the world. The damage to human health, animal life or the general environment due to the effects of its emissions has been extensively studied and reported in detail. To reduce smog levels, the government has taken legislative measures to limit pollutant emissions at its sources, including emissions from internal combustion engines.

In the early 1960s, manufacturers of spark ignited (Otto cycle) gasoline fueled engines began to equip the first basic pollutant removal system. Some of them are still in use today. Over the years of the sharp increase in vehicle use, government legislation has become increasingly stringent regarding Otto cycle engine emission levels. To comply with tighter regulations, car manufacturers have installed more complex devices in their engines. While the emissions from Otto cycle engines were tightly regulated, the government was generous with compression ignition engines (diesel engines). This is because the compression ignition engine (diesel engine) has a higher fuel efficiency and a relatively lower emission level than the Otto cycle engine that does not include the pollutant control device. Probably the number of diesel engines
Another factor could be that it was far less than the number of Otto cycle engines used at the same time.

More information has been gained through investigations into the pollution caused by emissions. As a result, the government has enacted legislation that limits such emissions to a greater extent and more strictly. In the early 1980s, any diesel vehicle emissions began to be scrutinized, and diesel engine manufacturers were becoming increasingly complex to comply with government regulations that set acceptable levels of emissions. And they have had to set the precedent for manufacturers of Otto-cycle powered vehicles with a wide variety of equipment applications.

In the mid-1970s, manufacturers of Otto cycle engines burned the recirculated exhaust fraction to control nitrogen oxides (NOx), carbon monoxide (CO) and all hydrocarbons (THC). A method has been developed to recirculate some of the exhaust gas to the intake manifold to meet the conditions. Exhaust gas recirculation (EGR)
Is due to the introduction of gas from the exhaust into the combustion cycle, which causes lower combustion chamber temperatures and, for example, not only promotes the oxidation of some previously burned out hydrocarbons, but also the formation of NOx. Suppress. The control for recirculating the exhaust gas is realized by the EGR valve. This EGR valve is used extensively in Otto cycle engines and in diesel engines to a lesser extent.

Until the early 1990s, EGR valves were operated and controlled pneumatically, and thus were unable to provide accurate observations and quick responses to changes in engine speed and load. Pneumatic actuation and control methods also cause inaccuracies in valve positioning and reaction time delays due to atmospheric pressure changes in the surrounding atmosphere. In the first half of the 1990's, EGR valves controlled by a microprocessor forming the basis of an engine controller using electric actuator motors were introduced for Otto cycle engines.

A system for controlling the amount of recirculated exhaust gas for a diesel engine is described in US Pat. No. 45,751 issued Jan. 7, 1986.
Also known is the one described by Ikeda in 62821. In this system, an electronic controller senses engine speed, intake manifold pressure, fuel supply rate, engine cooling temperature and combustion flame brightness to control exhaust gas recirculation in a diesel engine.

[0008]

However, the system according to the above-mentioned US patent has two main drawbacks.
First, there is a need for an expensive combustion flame brightness detection system. The sensor needs to be specially adapted to the engine and therefore cannot be easily installed on existing engines. Further, the system relies on a vacuum operated EGR valve, which is slow to change the operating conditions of the engine instantaneously, as described above.

Another approach to reducing emissions from diesel engines is to replace some of the diesel fuel normally burned in internal combustion engines with lighter and cleaner combustion gas fuels such as natural gas. There has been the development of dual fuel and systems capable of using more than one fuel. Extensive research has shown that Otto cycle engines and dual / multifuel engines are quite different in terms of EGR compatibility. The optimum EGR in a dual / multifuel engine is 0
% To over 50%, and the manifold pressure differential is extremely low. Thus, it is clear that compression ignition engines in general, and dual / multifuel compression ignition engines in particular, are not suitable for use with EGR systems and methods in Otto cycle engines.

It is an object of the present invention to provide an EGR system for a compression ignition engine which allows precise, real time control of the amount of exhaust gas recirculated to the engine. Another object of the present invention is to provide an EGR system retrofitted to an existing compression ignition engine. Yet another object of the present invention is to provide an EGR system that can be applied as originally installed in a compression ignition engine without redesigning the engine configuration.

[0011]

These objects are achieved in an exhaust gas recirculation system for a compression ignition engine of the following construction. That is, the exhaust gas recirculation system according to the present invention has a first pressure sensor for detecting the absolute pressure in the intake manifold of the engine and a second pressure sensor for detecting the absolute pressure in the exhaust manifold of the engine.
Pressure sensor, an engine speed sensor for detecting the engine rotation speed, a fuel supply speed sensor for detecting the fuel supply speed to the engine, and an air intake for detecting the temperature of intake air in the intake manifold of the engine. A temperature sensor, a conduit providing a fluid passage between the exhaust manifold and the intake manifold, and disposed within the conduit,
An exhaust gas recirculation valve to regulate the flow of exhaust gas from the exhaust manifold to the intake manifold, and an exhaust gas recirculation valve to regulate the flow of exhaust gas from the exhaust manifold through the conduit to the intake manifold. And means for controlling.

In addition, signals from the first and second pressure sensors, the engine speed sensor, the fuel supply speed sensor and the air intake temperature sensor are received, and the recirculated air to the intake air is received based on the received signals. Calculating an optimum ratio of exhaust gas to be exhausted, and further calculating a valve position that allows the optimum ratio of recirculated exhaust gas to the intake air to flow through the conduit to the intake manifold, and It also activates the means for controlling the exhaust gas recirculation valve to position the valve at a calculated valve position that allows an optimal ratio of exhaust gas to intake air flowing through the conduit from the exhaust manifold to the intake manifold. It includes an electronic controller for

The compression ignition engine to which the present invention is applied includes a diesel engine, a dual fuel engine, particularly a dual fuel engine equipped to operate with diesel and natural gas as a fuel, a multiple fuel engine, especially diesel. There is a multi-fuel engine equipped to operate on natural gas and hydrogen. These points are the same in the method of controlling the exhaust gas recirculation in the compression ignition engine described below.

According to another aspect of the present invention, there is provided a method for controlling exhaust gas recirculation in a compression ignition engine, which rather directly controls% EGR, and further the method. Uses the air mass flow rate as a function of engine speed and fuel delivery speed as its basic control variables, which is substantially constant under a given engine speed / engine load combination. Assuming that it should, the EGR acts to maintain the mass flow of the air as intake and exhaust temperatures and pressures change.

In particular, a method is provided for controlling exhaust gas recirculation in a compression ignition engine, the method including the following operations. a) Detecting the fuel supply speed to the engine, b) Detecting the rotation speed of the engine, c) Detecting the absolute pressure of the exhaust manifold of the engine and the absolute pressure of the intake manifold, and between the exhaust manifold and the intake manifold. D) rotating speed and pressure drop as a function and determining the volumetric efficiency of gas flowing through the engine, e) engine rotating speed and fuel supply speed as a function,
%) Determine EGR, f) engine speed and fuel supply speed as a function,
Determining the temperature of the gas in the exhaust manifold, g) determining the intake temperature of the air flowing into the intake manifold, h) the exhaust gas based on the absolute pressure in the exhaust manifold, the molecular weight of the exhaust gas and the temperature of the exhaust gas. Calculate the fluid density of the gas, i) calculate the volumetric flow rate of the exhaust gas through the EGR valve, j) determine the EGR valve based on the volumetric flow rate of the exhaust gas through the EGR valve, the fluid density of the exhaust gas and the pressure drop. Derive variables to bring to required position, k) Move EGR valve to required position.

The present invention thus provides a relatively simple, electronically controlled recirculation system for a compression ignition engine, using standard components on the market, Provide an inexpensive pollution abatement device as a retrofit to an existing compression ignition engine or as a new device in a new engine. The system includes an electronic engine controller, an engine intake manifold absolute pressure sensor, an engine exhaust manifold absolute pressure sensor, a fuel supply speed sensor, an engine speed sensor, and an air intake temperature sensor. Exhaust gas recirculation is controlled by an electronically actuated EGR valve, which is preferably a butterfly valve with a valve position sensor. The position of the valve is preferably controlled by an electronic step motor, so that it will respond to changes in engine load and operating conditions.
Enables accurate and quick reaction.

As described above, the present invention provides a novel method for controlling exhaust gas recirculation in a compression ignition engine, which balances maximum thermal efficiency with minimum pollutants. The optimum% EGR is experimentally derived under a controlled test environment so that

Further, the mass flow rate through the engine is calculated using its limited% EGR and air density compensated for changes in ambient temperature and atmospheric pressure. The mass flow rate is used to calculate the amount of EGR flowing through the EGR valve, with the result that the position of the EGR valve is adjusted to achieve the optimum% EGR. The proper valve position is derived using a function that gives a dimensionless number from the volumetric flow rate of exhaust gas flowing through the EGR valve, the exhaust gas density, and the pressure drop from the exhaust manifold to the intake manifold. The dimensionless number is then used to locate the proper valve position in the two-dimensional table. The method of controlling gas recirculation relies on the following assumptions. 1) In the temperature / pressure range encountered while the engine is operating,
Both air and exhaust gas behave as ideal gases. 2) The change in exhaust gas temperature for a particular engine speed / load condition is negligible with respect to changes in intake air temperature and atmospheric pressure. 3) Volumetric efficiency is only related to engine speed and the pressure difference between the intake and exhaust manifolds. 4) When calculating the characteristics of the exhaust gas, the components of the exhaust gas are properly represented by O ₂ , N ₂ , CO ₂ and H ₂ O, and all other exhaust gas components can be ignored. 5) In a multi-fuel engine, the effect of gaseous fuel on the molecular mass of the mixed air and exhaust gas in the intake manifold is negligible.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus and method according to the present invention can be described in terms of physical layout and hardware components, control logic and calculation procedures. In order to facilitate a complete understanding of the present invention, preferred embodiments are described in detail below.

(Physical Layout and Hardware Components) FIG. 1 shows a schematic diagram of a compression ignition engine 20 equipped in an exhaust gas recirculation system according to the present invention. The compression ignition engine 20 can be a diesel engine or a multi-fuel engine such as a diesel / natural gas engine, as its construction is known in the art,
No explanation is given in this document. Compression ignition engine 20
Includes an intake manifold 22 for supplying compressed air to an engine cylinder (not shown), and a compression ignition engine 20.
Exhaust manifold 2 for exhausting exhaust gas from the cylinder
4 is provided. Exhaust gas recirculation system (hereinafter referred to as EGR
The system) is controlled by an electronic controller 26.

The electronic controller 26 not only controls the EGR system, but can also be an electronic engine controller for controlling other operations in the compression ignition engine 20, and the EGR according to the present invention.
It is also possible to use an electronic controller specialized for the function of controlling the system. The electronic controller 26
It is one of the many processing units on the market configured for engine control systems.

The main function of the electronic engine controller is to position the EGR valve 2 in the exhaust gas recirculation conduit 30 which connects the exhaust manifold 24 and the intake manifold 22 to each other.
8 position. The EGR valve 28 is shown in FIG.
Will be described in more detail in connection with. The EGR valve 28 has a control link mechanism 36. The control link mechanism 36 is connected to the motor link mechanism 34, and further,
Electronic step motor 32 for controlling the turning position of the R valve 28
Is pivotally connected to.

Efficient and optimal control of the EGR valve 28 requires many sensors to monitor the operating condition of the compression ignition engine 20. These sensors include an intake manifold absolute pressure sensor (first pressure sensor) 38 located in the intake manifold 22.
And an absolute pressure sensor 40 (second pressure sensor) for the exhaust manifold arranged in the exhaust manifold 24.

If the compression ignition engine 20 is a multi-fuel engine (such as a diesel / natural gas fuel combination), the fuel mode select switch 4 for switching the engine from diesel only to multi-fuel mode.
2 can be included in the system. The system also includes a fuel delivery rate sensor 44, typically a high resolution potentiometer for monitoring fuel pedal position, or some equivalent such as a throttle position sensor.

The engine includes an engine rotation speed sensor 4 for determining the rotation speed of the engine crankshaft.
6 (hereinafter, referred to as RPM sensor 46). RPM
The sensor 46 is preferably a Hall effect sensor and can be attached to the output end of the diesel fuel injection pump, flywheel or crankshaft of the compression ignition engine 20 as required. The position of the RPM sensor 46 is not critical as long as it can provide a reliable indication of the rotational speed of the engine crankshaft. The system also includes an air intake temperature sensor 48 for measuring the temperature of the compressed air flowing into the intake manifold 22. The exhaust system of compression ignition engine 20 typically also includes a catalytic converter 52, which is ancillary to the exhaust gas recirculation system of the present invention.

FIG. 2 shows a preferred structure of the EGR valve 28 used in the exhaust gas recirculation system according to the present invention.
A partially broken side view is shown. The EGR valve 28 has a central passage 54. The central passage 54 preferably has a diameter equal to the diameter of the exhaust gas recirculation conduit 30 (see FIG. 1), but may have a larger diameter. The central passage 54 can be closed by a butterfly valve 56 positioned to rotate by a valve shaft 58, the valve shaft 58 having its lower end connected to the EGR valve linkage 34 and its upper end in the automotive industry. Is connected to a high resolution potentiometer 60 of the well known type. The high resolution potentiometer 60 is used to determine the pivot position of the butterfly valve 56, as described in detail below. The EGR valve 28 is preferably an electronically controlled butterfly valve so that the response to changing combustion conditions within the compression ignition engine 20 is accurate and rapid control, as will be described in more detail below.

Control Logic FIG. 3 is implemented by the electronic engine controller 26 to control the position of the EGR valve 28, and thereby the amount of exhaust gas recirculation from the exhaust manifold 24 to the intake manifold 22. 3 shows a flow chart of general control logic. The electronic engine controller 26 executes a loop of programs which begins by determining the required fuel delivery rate from the fuel delivery rate sensor 44 to recirculate the intake manifold 22 for optimal exhaust gas recirculation. It ends by orienting the butterfly valve 56 of the EGR valve 28 in the required direction. The control logic will now be described in detail.

As shown in FIG. 3, the process begins at step 62, where the analysis of the input signal from the fuel feed rate sensor 44 determines the fuel feed rate required for the compression ignition engine 20. In step 64, the output signal from the RPM sensor 46, preferably a Hall effect sensor (not shown) attached to the diesel fuel injection pump (not shown) of the engine running at half engine speed for a 4-stroke engine, is output. By analyzing, the electronic engine controller 26 calculates the rotational speed of the engine.

At step 66, the electronic engine controller 26 reads the output signals from the exhaust manifold absolute pressure sensor 40 and the intake manifold absolute pressure sensor 38 and calculates the pressure drop (ΔP) according to the following formula:

In step 68, the results of steps 62-66 are utilized from a table of data experimentally derived from engine tests using a dynamometer monitored compression ignition engine as is well known in the art. Then, the volume efficiency,% EGR and exhaust gas temperature are determined.

FIG. 4 shows engine speed and pressure drop (Δ
P) as a function and the table used to derive the volumetric efficiency of the engine is shown. In that table according to the preferred embodiment, the values of ΔP are arranged for each row and the values of RPM are arranged for each column. Each value arranged in each row and each column in FIG. 4 can be increasing, but need not be expressed as an equal increment. The assigned values depend on the individual engine model with EGR and meet the individual emission standards so that a clearer decision and better control can be made within the individual operating speed range. Can be focused on a particular engine speed.

It should also be understood that the size of the table shown in FIG. 4 is for illustration purposes only, and the actual table size required will depend on the operating characteristics achieved. The data in Figure 4 is derived empirically based on a mathematical definition of engine volumetric efficiency. The volumetric efficiency of the engine is given by Equation 1 below.

[0033]

[Equation 1]

Where η _vol is the volumetric efficiency of the engine, Q
_tot is the total volumetric flow rate through the intake manifold in liters per second, RPM is the engine crankshaft rotation speed, and V _disp is the engine displacement in liters. In a 4-cycle compression ignition engine, there is only one intake stroke per two revolutions of the crankshaft, so the number of intake strokes is divided by two.

Due to this definition and the fact that the temperature of the mixture of air, exhaust gas and gaseous fuel in a multi-fuel engine cannot be measured accurately, it is used to complete the table shown in FIG. The data is preferably obtained from an engine operating only in diesel mode without EGR. If the engine is operated in diesel-only mode on the test bench, Q _tot = Q
is the _air, Q _air is measured by the gas flow meter. RPM
Is measured and the equation is solved for η _vol ,
Volume efficiency is obtained for each cell at.

% EGR is obtained from the table shown in FIG. 5, where% EGR is expressed as a function of engine speed and fuel delivery speed. The data in this table are preferably similarly empirically derived from testing with a dynamometer of the test engine, based on the mathematical definition of% EGR expressed by Equation 2 below.

[0037]

[Equation 2]

Where Q _air is the volumetric flow rate of air flowing into the engine under a predetermined air temperature and intake manifold pressure, and Q _gas is the _gas flowing into the engine if the compression ignition engine 20 is a multi-fuel engine. Is the volumetric flow rate of the _solid fuel, and Q _tot is the total volumetric flow rate through the intake manifold.

With the engine running on the test bench, the EGR valve 28 is positioned so that a maximum thermal efficiency and a minimum pollutant emission are balanced. Q
_gas can be determined from the fuel supply rate in need, Q _tot is also derived known from FIG. 4, and Q _air can be measured using a gas flow meter. The% EGR so calculated completes the data of FIG.

The exhaust gas temperature is derived from the table shown in FIG. 6, where the exhaust gas temperature is expressed as a function of engine speed and fuel supply speed. Temperatures are expressed in degrees Celsius (° C) and are experimentally derived for the test engine from actual temperature measurements after the desired% EGR at a given RPM and fuel delivery rate has been established.
As will be explained below, the temperature derived from the table shown in FIG. 6 is taken to be the Kelvin temperature before being used in the calculations for calculating the exhaust gas flow density and the exhaust gas volumetric flow. Must be converted.

All increment intervals in the tables shown in FIGS. 4-6 and all data in the tables are specific engine models and are derived experimentally through test runs on a dynamometer for each specific model. Furthermore, the electronic controller 26 is programmed to perform a two-dimensional linear interpolation when the sensor values fall between the discrete values listed in the table. This allows
It can respond accurately to the operating environment even when the amount of memory for storing the table is limited.

In step 70 of FIG. 3, the electronic controller 26 uses the air intake temperature sensor 48 to read the air intake temperature. In step 74, based on the absolute pressure in the exhaust manifold, the molecular weight of the exhaust gas, the gas constant, and the exhaust gas temperature obtained from the table shown in FIG. Is calculated.

[0043]

(Equation 3)

Here, ρ _exh represents the fluid density of the exhaust gas, P _exh represents the absolute pressure in the exhaust manifold, MW _exh represents the molecular weight of the exhaust gas, and R is the gas constant (8.3144 kmol / kg · K). ) And T _exh is the exhaust gas temperature derived from the table of FIG.

In step 76, the electronic controller uses the fluid density (ρ _exh ) and the pressure drop (ΔP) to calculate the volumetric flow rate (Q _egr ) of the exhaust gas flowing through the EGR valve 28 according to the following equation (4).

[0046]

(Equation 4)

Where Q _egr represents the volumetric flow rate of the exhaust gas through the EGR valve, m _tot is the total mass flow rate of the gas flowing through the intake manifold, and m _air is the mass of the air flowing through the intake manifold. Is the flow rate, m _gas is the mass flow rate of gaseous fuel flowing through the intake manifold of a multiple fuel engine, R is the gas constant, and T _exh is FIG.
_Is the temperature of the exhaust gas derived from the table shown in, P _exh is the absolute pressure in the exhaust manifold 24, MW _exh
Is g / mol of exhaust gas in the exhaust manifold 24
Is the molecular weight in units. All of the variables on the right side of this equation are known except m _air , m _tot and MW _exh . For a detailed description of m _tot and MW _exh , reference should be made to the calculation procedure section below.

The volumetric flow rate (Q _air ) of _air is expressed by the following equation (5).
Calculated using.

[0049]

(Equation 5)

However, the resulting Q
_air is the air temperature (T _air ) _cal and the intake manifold pressure (P _intake ) _cal when% EGR is specified.
Quoted in. Therefore, the required mass flow rate of air is (MW
It is derived as shown in Equation 6 by multiplying the air density calculated using the gas constant (with _air = 28.97) by the volumetric flow rate of air obtained from this formula.

[0051]

(Equation 6)

Although the mass flow rate of air is calculated in this manner, the mass flow rate does not change due to fluctuations in atmospheric pressure or intake air temperature. Since the mass flow rate of fuel to the engine does not change due to ambient temperature and pressure fluctuations, the optimum amount of air is always provided to completely burn all the injected fuel.

In step 78 of FIG. 3, certain variables for determining the required position of the EGR valve are derived using the following function (Equation 7).

[0054]

(Equation 7)

The volumetric flow rate of the EGR Q _egr is known from the calculations performed as described above, ρ _exh is also known from the calculations performed as described above, and ΔP is also the absolute value of the exhaust manifold as described above. It is calculated by subtracting the absolute pressure of the intake manifold from the pressure. The dimensionless number derived from this function is used to position the valve position (β valve) in FIG.

In step 80, the current position of the EGR valve 28 is set to the number of clocks accumulated by the electronic engine controller in correspondence with the potentiometer signal from the high resolution potentiometer 60 coupled to the valve shaft 58 of the EGR valve 28. It is determined by measuring. The table shown in FIG. 8 shows the relationship between the number of clocks from the fully closed position and the shaft position in degrees for the central passage 54 of the EGR valve 28. After the current position of the EGR valve is determined, the required position of the EGR valve determined in step 78 by referring to the table of FIG. 8 is compared with the current position of the EGR valve, and the correction coefficient is calculated.

In step 84, if the current position is not the same as the required position determined in step 78, electronic controller 26 commands electronic step motor 32 to move EGR valve 28 from its current position to the required position. . The program then returns to step 62 and repeats the above steps. The frequency with which this step is performed depends on a number of factors, including other tasks performed by electronic controller 26. As standard, 4 steps
Repeating every ~ 12 ms ensures that the EGR valve 28 is always in the optimum position, consistent with changes in operating conditions.

(Calculation Procedure) In the calculation, it is necessary to determine the total mass flow rate of the gas flowing through the engine. The molecular weight of the exhaust gas and the specific heat of the exhaust gas component are explained below. The variables used are defined below to aid in understanding the calculations. m _air '= mass flow rate of air flowing through the engine m _egr ' = mass flow rate of exhaust gas flowing through the EGR valve (g / s) m _gas '= mass flow rate of gaseous fuel flowing through the engine m _dsl ' = diesel flowing through the engine Mass flow rate of fuel m _tot '= Total mass flow rate through the intake manifold T _air = Air temperature in the intake manifold just upstream of the mixing point T _exh = Exhaust gas temperature T _gas = _Gaseous state when entering the intake manifold Fuel temperature T _mix = Temperature at which air, exhaust gas and gaseous fuel are mixed P _intake = Absolute pressure of intake manifold P _exh = Absolute pressure of exhaust manifold R = Gas constant 8.33144kmol / kg ・ K Q _air = T Volumetric flow rate of air flowing to the engine with _air and P _intake (l / s) Q _gas = T _Air volumetric flow rate of gaseous fuel flowing to the engine with P _intake (l / s) Q _tot = T _intake with T _air and P _intake Maniho The total volume flow flowing through the de (l / s) V _disp = engine displacement (l / s) MW = Molecular weight (g / mol) h = entropy (kJ / kg · K) Cp = specific heat (kJ / kg · K)

(Calculation of total mass flow rate) The total mass flow rate (m _tot ') is (in the case of a multi-fuel engine) the total volumetric flow rate (Q) at its mixing temperature and intake manifold pressure.
_tot ) multiplied by the density (ρ _intake ) of the mixture of air, exhaust gas and gaseous fuel.
It is obtained as shown in.

[0060]

(Equation 8)

Here, the density ρ _intake can be calculated as in Expression 9 using the gas constant.

[0062]

[Equation 9]

Here, the MW _mix is estimated to be 28.5 kg / kmol. In order to calculate the mixing temperature (T _mix ), the first law of thermodynamics is necessary. The first law of thermodynamics for the mixing process is as shown in Equation 10 below.

[0064]

(Equation 10)

However, with the ideal gas, the following formula 11 is obtained.

[0066]

[Equation 11]

Therefore, this formula 11 becomes like the following formula 12.

[0068]

(Equation 12)

The specific heat of air and gaseous fuel is 1.035 for air.
kJ / kg · K and for gas (eg methane for multi-fuel engines) it is accepted to be constant at 2.2537 kJ / kg · K. However, the specific heat of the exhaust gas depends on the composition and temperature of the exhaust gas.

The calculation of the specific heat and molecular weight of the exhaust gas, which is carried out on the basis of the combustion theory, is explained below. The specific heat of the mixture is a mass average of the specific heats of air, exhaust gas, and natural gas, and is derived from the following Equation 13.

[0071]

(Equation 13)

When the above five formulas are combined and arranged, the following formula 14 is obtained.

[0073]

[Equation 14]

This equation is given by T as shown in the following equation 15.
Expressed as a quadratic equation of _mix .

[0075]

(Equation 15)

By solving the quadratic equation, the following equation 16 is obtained.

[0077]

(Equation 16)

When the temperature T _mix during mixing is known, the density ρ _intake during mixing can be calculated from the following equation 17.

[0079]

[Equation 17]

Further used in Equation 18 below, the total mass flow rate m _tot 'is calculated.

[0081]

(Equation 18)

(Calculation of Molecular Weight and Specific Heat) Necessary for determining the volumetric flow rate Q _egr of exhaust gas passing through the EGR valve,
The optimum ratio of recirculated exhaust gas to intake air, exhaust gas composition, molecular weight, and specific heat depend on diesel fuel.
It is determined by expressing it as H _1.9 . The theoretical combustion of diesel fuel and air in this case is written as CH _1.9 +7.024 (0.21O ₂ + 0.79N ₂ ) → CO ₂ + 0.95H ₂ O + 5.549N _{2 Based on the} mass, this combustion reaction can be written as follows.

1kgCH _1.9 + 3.39kgO ₂ + 11.16kgN ₂ → 3.16kgCO ₂ + 1.23kgH ₂ O + 11.16kgN ₂ Not only diesel but also multi-fuel engine burning natural gas, natural gas is 100% methane. (C
H ₄ ), in which case the theoretical combustion of natural gas in air is written as: CH ₄ +9.524 (0.210O ₂ + 0.79N ₂ ). → CO ₂ + 2H ₂ O + 7.52N _{2 Based on the} mass, this combustion reaction can be written as: 1kgCH ₄ + 3.39kgO ₂ + 13.14kgN ₂ → 2.74kgCO ₂ + 2.25kgH ₂ O + 13.14kgN ₂

Based on the above theory, an appropriate ratio φ of recirculated exhaust gas to intake air is
Given by 9.

[0085]

[Equation 19]

[0086] Each of the x _i and y _i, and the mass of component i and molar fraction. Based on the above theory, the mass fraction of each component in the exhaust gas is given by the following formula 20, formula 21, formula 22, and formula 23.

[0087]

(Equation 20)

[0088]

(Equation 21)

[0089]

(Equation 22)

[0090]

(Equation 23)

The molar fraction of each component is given by the following equation 24.

[0092]

(Equation 24)

The molecular weight of the exhaust gas is given by the following equation 25.

[0094]

(Equation 25)

The specific heat of exhaust gas is given by the following equation 26.

[0096]

(Equation 26)

Here, (C _p ) _i is a constant pressure specific heat in units of kJ / kmol · K for each exhaust component as shown in the following formulas 27, 28, 29 and 30.

[0098]

[Equation 27]

[0099]

[Equation 28]

[0100]

(Equation 29)

[0101]

[Equation 30]

Here, using T _{exh depending} on the Kelvin temperature, θ is expressed by the following formula 31.

[0103]

(Equation 31)

Through these calculation steps, the electronic controller 26 accurately compensates for changes in ambient temperature and atmospheric pressure and maintains an optimum ratio of recirculated exhaust gas to intake air under all operating conditions. It is possible to be done.

(Applicability to industry) EGR according to the present invention
The system uses the major pollutants in compression ignition engines: nitric oxide (NOx) and carbon monoxide (C).
The level of 0) is reduced tremendously. When these oxides combine with water in the atmosphere, various acids are formed which are highly corrosive to organic and inorganic substances. These acids cause acid rain problems, and NOx is also a major factor in the formation of photochemical smog and ozone above ground. The EGR system according to the invention also enhances the combustion of hydrocarbons and thus improves fuel efficiency to a greater extent. At low engine loads, the EGR system helps maintain the air / fuel ratio in a more efficient range without resorting to the forces of throttling the intake throttle of the engine. Similarly, a mixture of hot exhaust gas containing activated chemical groups with air / fuel promotes faster and more complete combustion, and thus total unburned hydrocarbons in the exhaust gas. Lower the level of. Furthermore, the EGR system according to the invention also contributes somewhat to the replacement of the cold intake air with the hot exhaust gas, increasing the exhaust temperature of the engine and consequently the exhaust system of the engine. It realizes earlier activation of the provided precious metal catalyst and more efficient operation. The better performance of the catalyst facilitates more efficient removal of pollutants such as carbon monoxide and total hydrocarbons from the exhaust stream.

Since the EGR valve 28 is operated electronically,
Rather than pneumatic control, the system provides a faster and more accurate response to changes in engine load. The electronic controller 26 also accurately determines the optimum exhaust gas recirculation rate and provides the position of the EGR valve 28 very accurately. Since the system provides the exact changing position of the EGR valve 28, the engine responds at rated power in all operating conditions, which is also a common problem in conventional EGR control systems, but it is exhausted too much. The undesirable effects of black smoke and / or engine stalling that occur when recirculated are eliminated.

Variations and modifications can be made by those skilled in the art to the above-described preferred embodiments without departing from the spirit of the present invention. Accordingly, the scope of the invention is intended to be limited only by the scope of the claims.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a compression ignition engine equipped with an exhaust gas recirculation system according to the present invention.

2 is a partially cutaway side view of a preferred embodiment of an EGR valve used in the exhaust gas recirculation system for the compression ignition engine shown in FIG.

FIG. 3 is a logic diagram of a method of controlling exhaust gas recirculation in a compression ignition engine according to the present invention.

FIG. 4 is an engine speed in a compression ignition engine,
FIG. 6 shows a diagram for determining volumetric efficiency as a function of pressure drop between an exhaust manifold and an intake manifold.

FIG. 5 shows a chart for determining% EGR as a function of engine speed and fuel delivery speed in a compression ignition engine.

FIG. 6 shows a chart for determining exhaust gas temperature as a function of engine speed and fuel delivery speed in a compression ignition engine.

FIG. 7 shows a chart for determining EGR valve position as a function of exhaust gas flow rate, exhaust gas density, and pressure drop between exhaust and intake manifolds in a compression ignition engine.

FIG. 8 shows a diagram for determining the position of the EGR valve as a function of the number of clocks of the electronic engine controller based on the potentiometer output to monitor the position of the EGR valve.

[Explanation of symbols]

20 Compression Ignition Engine 22 Intake Manifold 24 Exhaust Manifold 26 Electronic Controller 28 Exhaust Gas Recirculation Valve (EGR Valve) 30 Conduit (Exhaust Gas Recirculation Conduit) 32 Means for Controlling Exhaust Gas Recirculation Valve (Electronic Step Motor) 34 Motor Link Mechanism 36 Control Link Mechanism 38 First Pressure Sensor (Absolute Pressure Sensor for Intake Manifold) 40 Second Pressure Sensor (Absolute Pressure Sensor for Exhaust Manifold) 42 Fuel Mode Selection Switch 44 Fuel Supply Speed Sensor 46 Engine speed sensor (RPM sensor) 48 Air intake temperature sensor 52 Catalytic converter 54 Central passage 56 Butterfly valve 58 Valve shaft

Claims (13)

[Claims] 1. A first pressure sensor 38 for detecting the absolute pressure in the intake manifold 22 of the engine 20, and a second pressure sensor 40 for detecting the absolute pressure in the exhaust manifold 24 of the engine 20. , An engine speed sensor 46 for detecting the rotation speed of the engine crankshaft, a fuel supply speed sensor 44 for detecting the fuel supply speed to the engine 20, and an intake air temperature in the intake manifold 22 of the engine 20. Of the air intake temperature sensor 48, a conduit 30 providing a fluid passage between the exhaust manifold 24 and the intake manifold 22, and disposed in the conduit 30 for exhaust gas from the exhaust manifold 24 to the intake manifold 22. An exhaust gas recirculation valve 28 for regulating the flow and an intake manifold 24 through the conduit 30 described above. Means 32 for controlling the exhaust gas recirculation valve 28 to regulate the flow of exhaust gas to the manifold 22, first and second pressure sensors 38, 40, engine speed sensor 46, fuel supply speed sensor 44 and A signal from the air intake temperature sensor 48 is received, an optimum ratio of the exhaust gas to be recirculated to the intake air is calculated based on the received signal, and the recirculation is performed to the intake air. Calculates the valve position that allows the exhaust gas to flow through the conduit to the intake manifold at the optimum ratio, and also allows the optimum ratio of exhaust gas to intake air flowing through the conduit from the exhaust manifold to the intake manifold. An electronic for activating the means 32 for controlling the exhaust gas recirculation valve 28 to position the valve at the calculated valve position Includes a controller 26, a,
Exhaust gas recirculation system for compression ignition engines. 2. The exhaust gas recirculation system for a compression ignition engine according to claim 1, wherein the engine speed sensor 46 is a Hall effect sensor mounted on the output shaft of an engine fuel pump. 3. The exhaust gas recirculation system for a compression ignition engine according to claim 1, wherein the fuel supply rate sensor 44 is a high resolution potentiometer that measures pedal position of a fuel pedal of the engine. 4. A mechanically controlled butterfly valve wherein the exhaust gas recirculation valve 28 comprises a mechanical linkage for moving the butterfly valve 56 from a fully closed position to a fully open position. An exhaust gas recirculation system for a compression ignition engine according to claim 1, which is 56. 5. A compression ignition engine as claimed in claim 4, wherein the means 32 for controlling the exhaust gas recirculation valve 28 is an electronic stepper motor operating in connection with a mechanical linkage. Exhaust gas recirculation system. 6. The exhaust gas recirculation system for a compression ignition engine according to claim 5, wherein the butterfly valve 56 comprises a high resolution potentiometer to indicate the current position corresponding to its full closed position. 7. The electronic controller 26 integrates the count number based on the output signal of the high resolution potentiometer, and the count number indicates the current position of the butterfly valve 56 corresponding to the fully closed position. An exhaust gas recirculation system for a compression ignition engine according to claim 6 used for determining. 8. A) detecting a fuel supply speed to the engine 20, b) detecting a rotation speed of the engine 20, c) an absolute pressure of an exhaust manifold 24 of the engine 20, and
The absolute pressure in the intake manifold 22 is sensed and the pressure drop between the exhaust manifold 24 and the intake manifold 22 is calculated, d) the engine speed 2 as a function of the rotational speed and pressure drop.
0) determining the volumetric efficiency of the gas flowing through 0, e) determining the rotational speed of the engine 20 and the fuel supply rate as a function and determining the% EGR, f) the rotational speed of the engine 20 and the fuel supply rate as a function, and the exhaust gas Determine the temperature of the gas in the manifold 24, g) determine the intake temperature of the air flowing into the intake manifold 22, h) based on the absolute pressure in the exhaust manifold 24, the molecular weight of the exhaust gas and the temperature of the exhaust gas. Calculate the fluid density of the exhaust gas, i) calculate the volumetric flow rate of the exhaust gas passing through the EGR valve 28, j) require the EGR valve 28 based on the volumetric flow rate, the fluid density of the exhaust gas and the pressure drop Control variables for exhaust gas recirculation in compression ignition engines, including moving the EGR valve 28 to the required position. Way. 9. The compression ignition engine of claim 8, wherein the volumetric efficiency of the gas flowing through the engine 20 is determined by automatically collating data from a table with experimentally derived data from a compression ignition engine dynamometer test. For controlling exhaust gas recirculation in a vehicle. 10. The exhaust gas recirculation in a compression ignition engine according to claim 8, wherein the% EGR is determined by automatically collating data experimentally derived from compression ignition engine operational tests from a table. How to control. 11. The gas temperature in the exhaust manifold 24 is:
Determined by automatically matching data from a table with experimentally derived data from compression ignition engine operational tests,
A method of controlling exhaust gas recirculation in a compression ignition engine according to claim 8. 12. A method of controlling exhaust gas recirculation in a compression ignition engine as set forth in claim 8 wherein the required EGR valve position is determined by a function of the variable and automatic lookup of the valve position from a table. . 13. A) determining the current position of the EGR valve 28, b) comparing the current position of the EGR valve 28 with a required position of the EGR valve 28, and c) deriving a difference between the current position and the required position. D) further comprising the step of actuating the means 32 for controlling the position of the EGR valve 28 and moving the EGR valve 28 by an amount equivalent to the derived difference between the current position and the demanded position. Item 9. A method for controlling exhaust gas recirculation in a compression ignition engine according to item 8.