JP2008190465A - Multi-fuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure desired engine performance even if any fuel is used in a multi-fuel engine. <P>SOLUTION: Fuel injection quantity Q<SB>base</SB>is calculated based on demand torque on the assumption that used fuel is base fuel. Control of an actuator (for example, EGR valve) 6 operating an engine 2 with cooperating with a fuel injection valve 4 is executed based on the fuel injection quantity Q<SB>base</SB>. On the other hand, control of the fuel injection valve 4 is executed based on fuel injection quantity corrected based on density and calorific value of fuel actually used. In a concrete example, values of operation period τ are renewed to values corresponding to fuel injection quantity corrected based on density and calorific value of fuel actually used in a τ-Q map 20 for correlating fuel injection quantity Q<SB>base</SB>with operation period τ of the fuel injection valve 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multi-fuel engine capable of using a plurality of types of fuel.

  Multi-fuel engines that can use multiple types of fuel are known. The diesel engine can also be used as a multi-fuel engine, and GTL (Gas To Liquid) fuel can be used in addition to light oil. GTL fuel is a fuel mainly composed of saturated hydrocarbons, and has characteristics such as high cetane number, aroma free, and sulfur free. In the diesel engine, biofuel such as BTL (Biomass To Liquid) fuel can also be used.

Naturally, different fuel types have different properties, but the fuel properties affect engine output performance and exhaust gas performance. For this reason, in the multi-fuel engine, it is necessary to determine the fuel property and correct the control content of the engine according to the fuel property. The patent documents listed below disclose a technique for determining fuel properties and a technique for correcting the fuel injection amount in response to a change in fuel properties.
JP 2004-324509 A Japanese Patent Laid-Open No. 2005-6401 JP 2005-48703 A JP 2005-239229 A Japanese Patent Laid-Open No. 5-240853

  By the way, an engine normally operates by cooperation of a plurality of actuators including a fuel injection valve. In a diesel engine, these actuators are controlled based on the fuel injection amount. That is, when the fuel injection amount is determined from the required torque, the control amount of the actuator is determined according to a predetermined rule. In the fuel injection valve, the injection period is determined based on the fuel injection amount, and in the EGR valve, the EGR opening is determined based on the fuel injection amount. The rules for determining the control amount of each actuator from the fuel injection amount in a diesel engine are determined by conformance testing in the engine development stage. In this conformance test, the engine is operated using a predetermined basic fuel (generally light oil), and the conformity value of the control amount of each actuator is determined so that the desired output performance and exhaust gas performance can be obtained. Yes.

  When a diesel engine is used as a multi-fuel engine, the difference in fuel properties between the basic fuel and the actual fuel used becomes a problem. For example, when the actual fuel used has the same density as the basic fuel but has a low calorific value, the amount of fuel injection required for the required torque is greater for the actual fuel used. In that case, if the correction for simply increasing the fuel injection amount is performed, the control amount of another actuator controlled based on the fuel injection amount will deviate from a value suitable for the required torque. Therefore, when a fuel other than the basic fuel is used, the original potential of the fuel cannot be exhibited.

  The above-mentioned problem is due to the fact that the rule for determining the control amount of each actuator from the fuel injection amount corresponds only to the basic fuel. Therefore, if the rule for determining the control amount is prepared for each fuel type and the rule can be changed according to the fuel to be used, it is considered that the above problem can be solved. However, it is difficult to predict all of the fuels that can be used in a multi-fuel engine, and it is not practical from a cost standpoint to conduct a compliance test on all of them.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a multi-fuel engine capable of ensuring desired engine performance regardless of the type of fuel used. .

In order to achieve the above object, a first aspect of the present invention is a multi-fuel engine capable of using a plurality of types of fuel including a predetermined basic fuel.
A fuel injection valve for injecting fuel;
An actuator for operating the engine in cooperation with the fuel injection valve;
Fuel injection amount calculating means for calculating a fuel injection amount based on a required torque under the assumption that the fuel to be used is the basic fuel;
Actuator control means for controlling the actuator based on the fuel injection amount calculated by the fuel injection amount calculation means;
Information acquisition means for determining the fuel to be actually used and acquiring its calorific value and density;
Fuel injection amount correction means for correcting the fuel injection amount based on the calorific value and density of the fuel used so that a torque equivalent to that when using the basic fuel is obtained;
Fuel injection valve control means for controlling the fuel injection valve based on the fuel injection amount corrected by the fuel injection amount correction means;
It is characterized by having.

According to a second invention, in the first invention,
The fuel injection valve control means includes a rule for making the fuel injection amount calculated by the fuel injection amount calculation means correspond to the operation period of the fuel injection valve, and the value of the operation period in the rule is the fuel injection amount correction. And a rule updating means for updating to a value corresponding to the fuel injection amount corrected by the means.

According to a third invention, in the first or second invention,
The basic fuel is light oil, and the plurality of types of fuel include GTL fuel.

  According to the first invention, the fuel injection amount is corrected according to the heat generation amount and density of the fuel used, so that even if the actual fuel used is different from the basic fuel, the fuel used is further separated. Even when the fuel is replaced, it is possible to obtain the same torque as when the basic fuel is used. Further, since the fuel injection amount for controlling the operation of the actuator is a fuel injection amount calculated based on the required torque on the assumption that the fuel to be used is the basic fuel, the actual fuel used is the basic fuel. Even if it is different from the above, or even if the fuel used is changed to another fuel, the actuator can be controlled with an optimal operation according to the required torque. Therefore, according to the present invention, the desired engine performance can be ensured regardless of the fuel used, and the original potential of the fuel used can be exhibited.

  According to the second invention, when the fuel injection amount is calculated based on the required torque on the assumption that the fuel to be used is the basic fuel, the operation period of the fuel injection valve corresponding to the fuel injection amount Is determined according to a predetermined rule. If the actual fuel used is different from the basic fuel, or if the fuel used is replaced with another fuel, the value of the operation period in this rule is updated to a value corresponding to the fuel injection amount required for the actual fuel used. Therefore, by controlling the fuel injection valve in the operation period determined in accordance with the rules, it is possible to obtain the same torque as when the basic fuel is used regardless of which fuel is used. Therefore, according to the second invention, it is not necessary to prepare a rule for determining the fuel injection amount from the required torque for each fuel used.

  According to the third invention, in a diesel engine whose main fuel is light oil, GTL fuel having characteristics such as high cetane number, aroma-free, and sulfur-free can be used, and the original potential of GTL fuel is exhibited. Can be used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a system of a multi-fuel engine as an embodiment of the present invention. This system includes an engine 2 and an ECU (Electronic Control Unit) 10 that controls the engine 2. The engine 2 according to the present embodiment is a diesel engine, and it is possible to use a fuel having a fuel property (for example, a density, a calorific value, a cetane number, and the like) that is significantly different from that of a light oil as well as a light oil such as GTL fuel and biofuel. ing.

  The engine 2 operates by cooperation of a plurality of actuators including the fuel injection valve 4. Here, for simplicity of explanation, the actuator other than the fuel injection valve 4 is limited to the EGR valve 6 for explanation. However, the “actuator that operates the engine in cooperation with the fuel injection valve” according to the present invention is not limited to the EGR valve 6. The fuel injection valve 4 and the EGR valve 6 are controlled by the ECU 10.

The function of the ECU 10 includes a function as the fuel injection amount calculation unit 12. The fuel injection amount calculation unit 12 calculates a fuel injection amount Q _base corresponding to the required torque in accordance with a predetermined rule such as a map or a function. A map using the engine speed and the accelerator opening as variables is used to calculate the required torque.

  The fuel that presupposes the above rules is the basic fuel that was used for conformance testing in the engine development stage. In the present embodiment, it is assumed that light oil is used as the basic fuel. However, not all diesel oils correspond to basic fuels, but those with specific fuel properties among diesel oils are used as basic fuels. Therefore, some diesel oils that are actually used do not fall under basic fuel. Although light oil is used as the basic fuel here, fuel other than light oil can be used as the basic fuel.

The ECU 10 has a function as a fuel injection valve control unit 14 that controls the fuel injection valve 4. The fuel injection valve control unit 14 determines the fuel injection period with reference to the τ-Q map 20 stored in the ECU 10. The τ-Q map 20 is a rule for making the fuel injection period Q correspond to the fuel injection amount Q _base . The τ-Q map 20 is an updatable map, and the map data updating unit 18 can update the map data. The initial data of the τ-Q map 20 is determined by a conformance test using basic fuel. The map data update unit 18 updates the map data according to the fuel properties of the fuel actually used in the engine 2.

If the fuel to be used is different from the basic fuel, there is a difference between the fuel injection amount necessary for realizing the required torque and the fuel injection amount Q _base calculated by the fuel injection amount calculation unit 12. If the actual fuel used has the same density as the basic fuel but the heat generation amount is low, the fuel injection amount required for the required torque is greater than the fuel injection amount _Qbase . Therefore, the map data updating unit 18 updates the value of the fuel injection period τ with respect to the fuel injection amount Q _base in accordance with the fuel properties of the fuel used so that a torque equivalent to that when using basic fuel is obtained. ing.

That is, in the present embodiment, a rule for determining the fuel injection amount Q _base from the required torque is not prepared for each fuel used, but the relationship between the fuel injection amount Q _base and the fuel injection period τ is used for the fuel used. We will make corrections accordingly. According to this, it is not necessary to predict all the fuels that may be used and to perform a conformance test for determining the fuel injection amount Q _base for all of them. The procedure for correcting the actual fuel injection amount in accordance with the change in the fuel used will be described in detail later using a flowchart.

Further, the ECU 10 has a function as an EGR valve control unit 16 that controls the EGR valve 6. The EGR valve control unit 16 is not the actual fuel injection amount injected from the fuel injection valve 4, but the control amount of the EGR valve 6 based on the fuel injection amount Q _base calculated by the fuel injection amount calculation unit 12, that is, Determine the EGR opening. The rule for determining the EGR opening degree from the fuel injection amount Q _base is determined by a conformance test in the engine development stage. As described above, the conformity test is performed using the basic fuel, and the conformity value of the EGR opening degree with respect to the fuel injection amount _Qbase is determined so that desired output performance and exhaust gas performance can be obtained. Therefore, according to the control of the EGR valve 6 by the EGR valve control unit 16, even when the actual fuel used is different from the basic fuel, or when the fuel used is replaced with another fuel. The EGR valve 6 can be controlled with an optimum operation according to the required torque.

Thus, the fuel injection amount Q _base is calculated based on the required torque on the assumption that the fuel used is the basic fuel, and the control amount of each actuator including the EGR valve 6 is determined based on the calculated fuel injection amount Q _base. For example, the rule (map or function) for determining the control amount of each actuator is only a rule corresponding to the basic fuel. On the other hand, the difference between the required fuel injection amount and the fuel injection amount Q _base caused by the change in the fuel used can be compensated by correcting the correspondence between the fuel injection amount Q _base and the fuel injection period τ.

  Hereinafter, the procedure for correcting the actual fuel injection amount in accordance with the change in the fuel used will be described with reference to the flowcharts of FIGS.

  The flowchart of FIG. 2 shows a routine for discriminating changes in the fuel used. In the first step S10 of the routine shown in FIG. 2, the fuel change flag is initialized. The fuel change flag is a flag indicating that the fuel used has changed to another fuel. The initial state of the fuel change flag is OFF, and the fuel change flag is turned ON when a change in the fuel used is recognized.

In the next step S12, new information relating to the fuel properties of the used fuel is acquired. The acquired information includes density, calorific value (low calorific value), and cetane number. Such information is acquired by a fuel property sensor. There is no limitation on the configuration of the fuel property sensor and its measurement method. Hereinafter, newly acquired values of density, calorific value, and cetane number are denoted as ρ _new , H _new , CN _new, and values of density, calorific value, and cetane number stored in the memory of the ECU 10 are denoted by ρ, Indicated as H and CN.

In the next step S14, the values ρ _new , H _new , CN _{new of} the density, calorific value and cetane number newly acquired in step S12 and their stored values ρ, H, CN are stored. If there is no change in density, calorific value, or cetane number as a result of comparison, it can be determined that there is no change in the fuel used. In this case, this routine ends.

On the other hand, if any of the density, the calorific value, and the cetane number is changed as a result of the comparison in step S14, it can be determined that the used fuel has changed. In this case, in step S16, the stored values ρ, H, and CN of the density, the calorific value, and the cetane number are replaced with the newly acquired values ρ _new , H _new , and CN _new . Then, in the next step S18, the fuel change flag is turned ON, and this routine ends.

  The determination result of the change in the used fuel is reflected in the control of the fuel injection amount by the ECU 10. The flowchart of FIG. 3 shows a routine for controlling the fuel injection amount. In the first step S20 of the routine shown in FIG. 3, it is determined whether or not the fuel change flag is ON.

  If the fuel change flag is ON, that is, if there is a change in the fuel used, the process of step S22 is performed. In step S22, the fuel injection period is updated in accordance with the change in fuel used, that is, the τ-Q map 20 is updated. Specific contents of the process of step S22 will be described later. In the next step S24, the fuel injection period τ is calculated using the updated τ-Q map 20, and fuel injection by the fuel injection valve 4 is performed.

  On the other hand, when the fuel change flag is OFF, there is no change in the used fuel. In this case, the τ-Q map 20 is not updated, and in the next step S24, the fuel injection period τ is calculated using the current τ-Q map 20, and the fuel injection by the fuel injection valve 4 is performed.

  In the next step S26, it is determined whether or not the engine has stopped. This routine is repeated until the engine stops.

  The flowchart of FIG. 4 shows a specific process of step S22, that is, a routine for updating the τ-Q map 20. In the present embodiment, the “fuel injection amount correcting means” according to the first invention and the “rule updating means” according to the second invention are realized by the ECU 10 executing the routine shown in FIG. In the first step S30 of the routine shown in FIG. 4, the calorific value H and density ρ of the fuel used are read from the memory.

In the next step S32, the following equation (1) is used to calculate the injection amount correction rate β from the calorific value H and the density ρ read in step S30. In the equation (1), ρ _base is the density of the basic fuel, and H _base is the calorific value of the basic fuel. The density ρ _base and the calorific value H _base of the basic fuel are acquired in advance at the stage of the conformance test using the basic fuel.
β = (ρ _base / ρ) ^3/2 (H _base / H) (1)

The above formula (1) will be described. This formula is derived from an energy balance formula and a conditional formula for generating the torque. First, when the fuel injection amount Q of the actual fuel used and the fuel injection amount Q _base when the basic fuel is used are expressed using energy balance equations, respectively, the following equations (2) and (3) are obtained. Become. In the equations (2) and (3), ΔP is the pressure difference between the inside and outside of the fuel injection valve 4, α is the flow coefficient (product of the viscosity coefficient and the contraction coefficient), and A is the cross-sectional area of the nozzle of the fuel injection valve 4. is there.
Q = αA (2ΔP / ρ) ^1/2 (2)
Q _base = αA (2ΔP / ρ _base ) ^1/2 (3)

According to the above equations (2) and (3), the relationship between the fuel injection amount and the density between the basic fuel and the used fuel can be expressed by the following equation (4).
Q / Q _base = (ρ _base / ρ) ^1/2 (4)

On the other hand, the conditions for obtaining the same torque as when using the basic fuel can be expressed by the following equation (5) when the injection amount correction factor β is used.
ρ _bas Q _base H _base = βρQH (5)

The above equation (1) can be obtained by removing the fuel injection amounts Q and Q _base of each fuel using the equations (5) to (4).

When the injection amount correction factor β is used, the fuel injection amount Q necessary for obtaining the same torque as the basic fuel with the actually used fuel can be expressed by the following equation (6).
Q = βQ _base (6)

In the next step S34, a fuel injection period τ for realizing the corrected fuel injection amount βQ _base is calculated. For the calculation of the fuel injection period τ, a map that defines the relationship between the fuel injection period, the fuel injection amount, and the injection pressure is used. The data of this map is determined by conformity tests using basic fuel. By referring to this map, the fuel injection period τ corresponding to the corrected fuel injection amount βQ _base can be obtained.

In the next step S36, the value of the fuel injection period τ in the τ-Q map 20 is updated. Specifically, the value of the fuel injection period τ corresponding to the fuel injection amount Q _base is updated to the fuel injection period τ calculated in step S34, that is, the value of the fuel injection period τ corresponding to the fuel injection amount βQ _base. To do. Thereby, by controlling the fuel injection valve 4 according to the fuel injection period τ obtained with reference to the τ-Q map 20, the actual fuel injection amount from the fuel injection valve 4 is obtained when the basic fuel is used. Instead of the fuel injection amount Q _base , the fuel injection amount βQ _base corrected according to the actual fuel used can be used.

  As described above, according to the multi-fuel engine of the present embodiment, even when a fuel having a fuel property different from that of light oil, which is a basic fuel, for example, GTL fuel is used, the actual heat generation of the used fuel is generated. By correcting the fuel injection amount according to the amount H and the density ρ, it is possible to obtain a torque equivalent to that when using the basic fuel. On the other hand, the fuel injection amount for controlling the operation of other actuators including the EGR valve 6 is a fuel injection amount calculated based on the required torque on the assumption that the fuel to be used is the basic fuel. Even if the actual fuel used is different from the basic fuel, each actuator can be controlled by an optimum operation according to the required torque. Therefore, according to the multi-fuel engine of the present embodiment, it is possible to ensure desired engine performance regardless of the fuel used, and to exhibit the original potential of the fuel used. .

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications can be made without departing from the spirit of the present invention.

It is the schematic of the system of the multi-fuel engine as embodiment of this invention. It is a flowchart which shows the routine for discriminating the change of the use fuel performed in embodiment of this invention. It is a flowchart which shows the routine for controlling the fuel injection quantity performed in embodiment of this invention. It is a flowchart which shows the routine for correct | amending the (tau) -Q map performed in embodiment of this invention.

Explanation of symbols

2 Engine 4 Fuel injection valve 6 EGR valve 10 ECU
12 Fuel injection amount calculation unit 14 Fuel injection valve control unit 16 EGR valve control unit 18 Map data correction unit 20 τ-Q map

Claims (3)

In a multi-fuel engine capable of using a plurality of types of fuel including a predetermined basic fuel,
A fuel injection valve for injecting fuel;
An actuator for operating the engine in cooperation with the fuel injection valve;
Fuel injection amount calculating means for calculating a fuel injection amount based on a required torque under the assumption that the fuel to be used is the basic fuel;
Actuator control means for controlling the actuator based on the fuel injection amount calculated by the fuel injection amount calculation means;
Information acquisition means for determining the fuel to be actually used and acquiring its calorific value and density;
Fuel injection amount correction means for correcting the fuel injection amount based on the calorific value and density of the fuel used so that a torque equivalent to that when using the basic fuel is obtained;
Fuel injection valve control means for controlling the fuel injection valve based on the fuel injection amount corrected by the fuel injection amount correction means;
A multi-fuel engine characterized by comprising:   The fuel injection valve control means includes a rule for making the fuel injection amount calculated by the fuel injection amount calculation means correspond to the operation period of the fuel injection valve, and the value of the operation period in the rule is the fuel injection amount correction. 2. A multi-fuel engine according to claim 1, further comprising a rule updating means for updating to a value corresponding to the fuel injection amount corrected by the means.   The multi-fuel engine according to claim 1 or 2, wherein the basic fuel is light oil, and the plurality of types of fuel include GTL fuel.

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