DE112013001807B4 - Determination device for engine fuel properties - Google Patents

Abstract

An engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel, characterized in that the fuel injection is a single injection during a deceleration-time fuel supply interruption, and the time of fuel injection for determining the fuel injection Ignition quality of the fuel according to the exhaust gas recirculation amount during the delay-time fuel supply interruption is varied.

Description

Background of the invention

1. Field of the invention

The invention relates to an engine fuel property estimator that determines the spark quality of fuel based on the engine torque generated by the combustion of the injected fuel.

2. Description of the Related Art

A diesel engine burns injected fuel by igniting it as a result of compression. Diesel engines use light oil as fuel. Commercially available light oils differ in their components and vary in fuel properties such as ignition quality. The ignition quality of fuel greatly affects the occurrence of misfire, the engine output, and so on. Therefore, it is necessary to check the ignition quality of the currently used fuel and to adjust the manners of execution of the engine controls with respect to the time and amount of fuel injection, etc. according to a check result of the ignition quality of the fuel, the output power, the fuel economy performance and the emission performance to improve a diesel engine.

The ignition quality of light oil as fuel of diesel engines is judged by the cetane number. The cetane number of a sample of light oil is expressed in volume percent of the amount of cetane in a mixture of cetane and α-methylnaphthalene having the same ignition quality as the light oil sample.

The JP 2010-024870 A discloses an apparatus that performs a single injection of fuel when the engine speed decreases in a no load and no fuel injection condition and the cetane number of currently used fuel based on the magnitude of the engine torque generated by the combustion of the injected fuel and the injection timing of the single injection certainly.

The principle of the above determination of the cetane number of fuel is as follows. If the in-cylinder pressure or the in-cylinder temperature decreases before the fuel completely burns, a part of the injected fuel does not combust completely and remains unburnt. When the cetane number of fuel is lower, the ignition delay time is longer and the start of combustion of the fuel is later. Thereby, the time from the start of combustion of fuel to a decrease in the in-cylinder pressure or the in-cylinder temperature is shorter when the cetane number of fuel is lower. Therefore, the amount of fuel that is not completely burned and unburned is larger, and the amount of fuel that reaches the combustion is lower, so that the engine torque generated by the combustion of fuel is smaller as the cetane number of fuel is lower , Thereby, by checking the magnitude of the engine torque generated by the combustion of injected fuel, it is possible to determine the cetane number of the fuel, that is, the degree of ignition quality of the fuel.

In addition to the ignition quality of fuel, the gas temperature in the cylinder at the time of combustion also affects the ignition delay time of the fuel. The gas temperature in the cylinder changes depending on the operating situation of the machine. Thereby, the magnitude of the generated engine torque may vary depending on the operating condition of the engine, which precedes the determination of the cetane number of fuel even if the amount of the injected fuel and the cetane number of the injected fuel are fixed. Such variations may possibly deteriorate the determination accuracy of the ignition quality of fuel based on the magnitude of the engine torque generated by the combustion of the injected fuel.

In addition, the reveals EP 1 923 557 B1 a control system for an internal combustion engine having fuel injection means for injecting fuel into combustion chambers of the engine, the control system comprising: fuel property estimation means for estimating a fuel property based on a combustion state of the fuel injected in at least one cylinder of the engine; and a fuel injection control means for controlling the fuel injection means so as to inject into the at least one cylinder a certain amount of fuel and to inject an amount of fuel corresponding to an operating state of the engine into other cylinders not containing the at least one cylinder; wherein the fuel injection control means performs additional fuel injection after the fuel injection of the predetermined amount with respect to the at least one cylinder when at least one of the following conditions a) to c) is satisfied: a) the requested torque of the engine is equal to or greater than a predetermined value; b) a fuel injection amount corresponding to the other cylinders is equal to or greater than a predetermined one Amount; and c) a torque difference parameter indicative of a difference between a torque generated by the at least one cylinder and a torque generated by the other cylinders is equal to or greater than a predetermined threshold.

Summary of the invention

The invention provides an engine fuel characteristics determining apparatus capable of estimating the ignition quality of fuel with increased accuracy.

This object is achieved with the features of claim 1. Advantageous developments of the invention are the subject of the subclaim.

A first aspect of the invention relates to an engine fuel characteristic determining apparatus which determines the ignition quality of fuel based on the magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the exhaust gas recirculation amount. In this aspect, the exhaust gas recirculation amount corresponds to a first amount, the time of fuel injection for determining the ignition quality of the fuel may be set to be compared to when the exhaust gas recirculation amount corresponds to a second amount, which is less than the first amount later.

The ignition delay time of fuel in a cylinder is shorter when the gas temperature in the cylinder is higher. In an engine in which exhaust gas is returned to the intake air, the higher the exhaust gas recirculation amount, the higher the temperature of the intake after mixing the high-temperature exhaust-gas recirculation inlet, and therefore, the higher the gas temperature in the cylinder.

In this regard, in the first aspect, it becomes possible to adjust the fuel injection timing for determining the ignition quality to reduce the influence that the variation of the ignition delay time, which depends on the exhaust gas recirculation amount, has on the results of the ignition quality determination Time of fuel injection for determining the ignition quality of fuel according to the exhaust gas recirculation amount is varied. Specifically, by further retarding the time of fuel injection for the determination, when the amount of exhaust gas recirculation is larger, it is possible to reduce the variation of the engine torque caused by the exhaust gas recirculation and thereby reduce the deterioration of the ignition accuracy determination accuracy. Thereby, according to the above construction, the ignition quality of fuel can be determined with increased accuracy.

A second aspect relates to an engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the vehicle speed. In this aspect, when the vehicle speed corresponds to a first speed, the time of fuel injection for determining the ignition quality of the fuel may be set to be later compared to when the vehicle speed corresponds to a second speed lower than the first speed lies.

The ignition delay time of fuel also varies depending on the amount of heat of the cylinder wall surface. More specifically, the larger the amount of heat of the cylinder wall surface, the shorter the ignition delay is, because the heat of the cylinder wall heats the gas in the cylinder, so that the temperature of the gas in the cylinder increases. If the engine is operated under high load before determining the ignition quality, the heat quantity of the cylinder wall surface at the time of the determination is large. Then, if the vehicle speed is high at the time of determining the ignition quality, it may be determined that the engine has most likely been operated under high load previously.

In this regard, in the second aspect, it becomes possible to adjust the time of fuel injection to determine the ignition quality to reduce the influence that the change in the ignition delay time, which depends on the heat quantity of the cylinder wall surface, has on the results of the determination of the ignition quality, since the ignition timing Time of fuel injection for determining the ignition quality of fuel is varied according to the vehicle speed. More specifically, by further delaying the time of fuel injection for determining when the vehicle speed is higher and therefore determining that the engine load was higher before determining the ignition quality, it is possible to change the engine torque by differences in the heat amount of the cylinder wall surface is caused, and thereby to reduce the deterioration of the determination accuracy of the ignition quality. As a result, according to the above design, the ignition quality of fuel can be determined with increased accuracy.

A third aspect relates to an engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the heat amount of a cylinder wall surface. In this aspect, when the heat quantity of the cylinder wall surface corresponds to a first quantity, the timing of the fuel injection for determining the ignition quality of the fuel may be set to be a second amount compared to when the amount of heat of the cylinder wall surface is whichever is smaller than the first set is later.

As stated above, the ignition delay time of fuel also varies depending on the heat quantity of the cylinder wall surface. Thereby, in the third aspect, it becomes possible to adjust the time of fuel injection for the determination of the ignition quality to reduce the influence that the change of the ignition delay time, which depends on the heat quantity of the cylinder wall surface, has on the results of the determination of the ignition quality the time of the fuel injection for determining the ignition quality is varied according to the heat amount of the cylinder wall surface. More specifically, by further retarding the time of fuel injection for the determination when the amount of heat of the cylinder wall surface is larger, it is possible to reduce the engine torque variation caused by differences in the heat amount of the cylinder wall surface, and thereby reduce the deterioration of the ignition accuracy determination accuracy , Thereby, according to the third aspect, the ignition quality of fuel can be determined with increased accuracy. In this aspect, the amount of heat of the cylinder wall surface can be performed from the load state of the engine which prevails before the determination of the ignition quality.

A fourth aspect relates to an engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the intake air pressure. In this aspect, when the intake air pressure corresponds to a first pressure, the time of fuel injection for determining the ignition quality of the fuel may be set to be higher than the first compared to when the intake air pressure is equal to a second pressure Pressure is earlier.

The ignition delay time of fuel also varies depending on a maximum value of the pressure in a cylinder (peak pressure in the cylinder) of the engine during the compression stroke of the cylinder. More specifically, the lower the peak pressure in the cylinder, the longer the ignition delay of fuel. For example, when the intake air pressure is lower, the peak pressure in the cylinder is lower and thereby the ignition delay is longer. Thereby, by allowing the injection time to be varied for the purpose of determining the ignition quality according to the intake air pressure and by "shifting" the injection time for the purpose of determining the ignition quality the lower the intake air pressure is possible, the influence is possible which the change in the ignition delay time, which depends on the peak pressure in the cylinder, on the results of the determination of the ignition quality, and thereby determine the ignition quality of fuel with improved accuracy.

A fifth aspect relates to an engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the intake temperature. In this aspect, when the intake air temperature corresponds to a first temperature, the timing of the fuel injection for determining the ignition quality of the fuel may be set to be higher than the first compared to when the intake air temperature is a second temperature Temperature is earlier.

The ignition delay time of fuel also varies depending on a maximum value of the temperature of the gas in a cylinder (peak temperature in the cylinder) of the engine during the compression stroke of the cylinder. More specifically, the lower the peak temperature in the cylinder, the longer the ignition delay of fuel. For example, when the temperature of the gas fed into a cylinder (intake gas temperature in the cylinder) is lower, the peak temperature in the cylinder is lower and thereby the ignition delay is longer. In addition, the lower the intake air temperature is, the lower the intake gas temperature in the cylinder is. Thereby, by allowing the injection time to be varied for the purpose of determining the ignition quality according to the intake air temperature, and by further decreasing "Early" shifting the injection time for the purpose of determining the ignition quality, the lower the intake air temperature, it is possible to limit the influence of the change in the ignition delay time, which depends on the inlet gas temperature in the cylinder, on the results of the determination of Ignition quality has, and thereby determine the ignition quality of fuel with improved accuracy.

A sixth aspect relates to an engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel. The time of fuel injection for determining the ignition quality of the fuel is varied according to the engine coolant temperature. In this aspect, when the coolant temperature corresponds to a first temperature, the timing of the fuel injection for determining the ignition quality of the fuel may be set to be higher than the first compared to when the coolant temperature is a second temperature Temperature is earlier.

As stated above, the ignition delay time of fuel also varies depending on the heat quantity of the cylinder wall surface. The temperature of the cylinder wall surface can be determined from the coolant temperature. If the temperature of the cylinder wall surface is lower, the heat quantity of the cylinder wall surface is smaller. Therefore, by allowing the injection time to be varied for the purpose of determining the ignition quality in accordance with the engine coolant temperature, and by shifting the injection timing "early" for the purpose of determining the ignition quality, the influence is increased which the change of the ignition delay time, which depends on the heat quantity of the cylinder wall surface, on the results of the determination of the ignition quality, and thereby determine the ignition quality of fuel with improved accuracy.

Moreover, in the above aspects, the determination of the ignition quality can be performed during a fuel cut of the engine. The determination of the ignition quality of fuel as described above can be performed suitably by performing the determination during the fuel cut of the engine during which a check of the engine torque is easily possible.

Brief description of the illustrations

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

1 Fig. 10 is a general diagram showing an overall construction of a machine control apparatus according to an embodiment of the invention;

2 Fig. 10 is a sectional view showing a structure of a side portion of an injector provided in a diesel engine to which the embodiment is applied;

3 Fig. 10 is a diagram showing an example of a time waveform of a fuel injection rate;

4 Fig. 10 is a flowchart of a cetane number determination routine used in the embodiment;

5 Fig. 10 is a time chart showing a transition of the engine speed and a transition of the speed difference before and after the execution of the fuel injection for detecting the cetane number;

6A Fig. 10 is a diagram showing a transition of the pressure in the cylinder;

6B Fig. 10 is a diagram showing an example of one kind of combustion;

6C Fig. 10 is a diagram showing an example of one kind of combustion when the ignition delay is short; and

6D FIG. 12 is a diagram showing an example of a kind of combustion when the fuel injection time is delayed according to the reduction of the ignition delay. FIG.

Detailed description of embodiments

Below is with reference to the 1 to 6 an embodiment is described in detail, in which a determination device for engine fuel properties is carried out according to the invention. The determination device of this embodiment is applied to a diesel engine to be mounted in a vehicle.

As in 1 shown is a fuel tank 10 a diesel engine to which the determination device of this embodiment is applied with a fuel meter 11 provided, which in the fuel tank 10 measures remaining amount of fuel. In addition, with the fuel tank 10 a fuel supply passage 12 connected, through which fuel to be fed to the machine flows. An intermediate portion of the fuel supply passage 12 is with a high pressure fuel pump 13 provided which fuel from the fuel tank 10 promotes, this pressurizes and pressurized fuel dissipates. A downstream end of the fuel supply passage 12 is with a common rail 14 connected, which receives pressurized fuel.

injectors 16 for the cylinders of the diesel engine are with the common rail 14 connected. Every injector 16 is with a fuel pressure sensor 17 provided, which the fuel pressure in the injector 16 detected. In addition, the injectors 16 with a return passage 18 for returning excess amounts of fuel to the fuel tank 10 connected.

The diesel engine is equipped with an EGR (exhaust gas recirculation) system. The EGR system returns a part of the exhaust gas to the intake air, thereby reducing the oxygen concentration in the gas supplied into the cylinders, so that the combustion temperature decreases, thereby restricting the generation of NOx. The amount of exhaust gas recirculated through the EGR system is provided by an EGR valve 26 adapted to be disposed in an EGR passage connecting an exhaust passage and an intake passage of the diesel engine.

This diesel engine thus constructed is controlled by an electronic control unit 19 controlled. The electronic control unit 19 includes a microcomputer which performs various calculation processes in connection with the machine control. In addition, the electronic control unit 19 provided with an input circuit which receives the input of signals from various sensors which detect operating conditions or conditions of the diesel engine. The fuel meter 11 and the fuel pressure sensors 17 are connected to the input circuit. The other sensors connected to the input circuit include an inlet pressure sensor 20 , a speed sensor 21 , a coolant temperature sensor 22 and an inlet temperature sensor 25 which detect the intake pressure, the rotational speed, the coolant temperature, and the intake air temperature of the diesel engine, respectively, and a vehicle speed sensor 24 , which detects the vehicle speed, an accelerator pedal sensor 23 which detects the amount of depression of an accelerator pedal, etc.

In addition, the electronic control unit 19 provided with drive circuits for actuators, which drive various sections of the diesel engine. These drive circuits contain circuits which the injectors 16 the cylinder drive, and a circuit that the EGR valve 26 drives. The electronic control unit 19 performs EGR control based on an adjustment of the opening degree of the EGR valve 26 as part of the machine control by. It also provides the electronic control unit 19 at the time of the EGR control, the amount of the recirculated exhaust gas contained in the gas inside the cylinder (EGR amount) from the opening degree of the EGR valve 26 (EGR opening degree), engine speed, etc.

Regarding 2 are more details of the structure of each of the injectors 16 , which are provided for the individual cylinders of the diesel engine described. This diesel engine uses injectors of the electrically driven type as the injectors 16 ,

As in 2 shown, each injector possesses 16 a housing 30 which has a hollow, cylindrical shape. Inside the case 30 is a needle valve 31 for reciprocating movements in the up-down directions in 2 arranged. In addition, within a section of the housing 30 which is related to the needle valve 31 in 2 located above, a spring 32 arranged, which the needle valve 31 in 2 always pushes down.

In addition, inside the case 30 two fuel chambers formed by the needle valve 31 are separated from each other, in particular a nozzle chamber 33 , what a 2 with respect to the needle valve 31 is arranged in a downward direction or relatively far below, and a pressure chamber 34 , what a 2 with respect to the needle valve 31 is arranged in a direction upwards or relatively high up.

The nozzle chamber 33 is with injection openings 35 provided, which is a connection between the interior of the nozzle chamber 33 and the exterior of the housing 30 provide. The nozzle chamber 33 is with an introduction passage 36 connected, which within the housing 30 is trained. The introduction passage 36 is with the common rail 14 ( 1 ), allowing fuel through the inlet passage 36 in the nozzle chamber 33 to be led.

On the other hand, the pressure chamber 34 via a connection passage 37 with the nozzle chamber 33 , and via a purge passage 38 with the aforementioned return passage 18 connected. In addition, inside the pressure chamber 34 a valve body 40 provided by an electrical pressure actuator 39 is driven, which is formed by stacking of electrical pressure elements, such as piezoelectric elements. Therefore, such a structure is provided that the pressure chamber 34 by driving the valve body 40 is selectively caused with the connection passage 37 or the purge passage 38 to communicate.

A fuel pressure sensor 17 As described above, with an upper portion of the injector 16 in 2 provided integrally. The fuel pressure sensor 17 is configured to increase the fuel pressure within the introduction passage 36 capture.

Each of the injectors built in this way 16 works as follows. The electric pressure actuator 39 assumes a contracted state in which the total length of the electric pressure actuator 39 is reduced, if this is not supplied with a drive voltage to the valve body 40 to arrange in such a position that the pressure chamber 34 with the connection passage 37 communicates and from the discharge passage 38 cut off or separated. At this time, the nozzle chamber 33 and the pressure chamber 34 in conjunction so that the pressures in the two chambers are substantially equal. Therefore, the needle valve became 31 at this time in 2 by the spring force of the spring 32 arranged below so that the injection openings 35 are closed. Therefore, from the injector 16 No fuel injected at this time.

On the other hand, when the electric pressure actuator decreases 39 energized with a drive voltage, the total length of the same to, to arrange the valve body in such a position that the pressure chamber 34 from the connection passage 37 is disconnected and with the discharge passage 38 communicates. At this time, fuel is from the pressure chamber 34 dissipated and the pressure in the pressure chamber 34 decreases, leaving the pressure in the nozzle chamber 33 greater than the pressure in the pressure chamber 34 , Due to the pressure difference at this time, the needle valve is 31 in 2 arranged above, ie, to move away from the position at which the needle valve 31 the injection openings 35 closes. Therefore injects the injector 16 fuel at this time.

In the embodiment constructed as described above, the electronic control unit performs 19 a fuel injection control of the diesel engine. More specifically, the electronic control unit calculates 19 a target value of the fuel injection amount (target fuel injection amount) from the engine speed, the amount of depression of the accelerator pedal, and an estimated value of the cetane number (control cetane number) of the fuel used. In addition, the electronic control unit calculates 19 Target values of the fuel injection time and the fuel injection duration from the target fuel injection amount and the engine speed. In addition, the electronic control unit brings 19 in accordance with these calculated target values, the drive voltage to the electric pressure actuator 39 each injector 16 on to control the fuel injection.

In addition, the electronic control unit performs 19 In this embodiment, in the context of the fuel injection control described above, control of forming a time waveform of the fuel injection rate of each injector 16 (The amount of injected fuel per unit time) based on the fuel pressure, which by the individual injectors 16 provided fuel pressure sensors 19 is detected. This control is performed as follows.

After the needle valve 31 an injector 16 according to the on the electric pressure actuator 39 Applied drive voltage starts from the injection ports 35 take off, the fuel pressure in the nozzle chamber decreases 33 with the increasing stroke or lift of the needle valve 31 from. Then the application of the drive voltage and the lift of the needle valve ends 31 decreases. With the decreasing lift of the needle valve, the fuel pressure in the nozzle chamber decreases 33 gradually closed. Therefore, it is possible from the fuel pressure sensor 17 of the injector 16 detected fuel pressure, the time at which the needle valve 31 starts to lift off (valve opening drive start time Tos), the time at which the fuel injection rate becomes maximum (acquisition time Toe maximum injection rate), the time at which the fuel injection rate starts to decrease (fuel injection rate decrease). Start time Tcs), and the time at which the lift of the needle valve 31 ends (acquisition time minimum lift tea), specifically to determine. Then, from these determined times, a time waveform of the fuel injection rate, as in 3 shown to be found. From this waveform, the current situation of the fuel injection, that is, the actual fuel injection amount, the actual fuel injection time, etc., can be checked with very high accuracy. In this embodiment, the electronic control unit 19 the rate of change of the Fuel pressure (the time derivative of fuel pressure) within each injector 16 determines and sets the aforementioned times based on the value of the rate of change.

In this embodiment, the electronic control unit determines 19 the cetane number of the currently used fuel, which corresponds to an index value of the ignition quality of the fuel. The determination of the cetane number is determined by the processing of an in 4 shown cetane number determination routine performed. This routine is performed by the electronic control unit 19 during the operation of the diesel engine at each predetermined control cycle time repeatedly performed.

When the processing starts this routine, it is determined at step S100 whether a condition for executing a torque detection cetane number calculation has been satisfied. This execution condition means that all of the following conditions (i) to (iii) are satisfied. (i) The deceleration fuel cut of the diesel engine to be implemented according to the interruption of the accelerator operation (ie, the depression of the accelerator pedal) is executed. (ii) The total amount of fuel injection following the previous refueling (refilling of the tank) is greater than or equal to a predetermined value α. The predetermined value α is set to a value larger than a total amount of fuel that can be received in the fuel passages extending from the fuel tank 10 towards the injectors 16 extend. That is, the satisfaction of the condition (ii) means that the fuel in the aforementioned fuel passages after the preceding refueling by that of the fuel tank 10 supplied new fuel was replaced. (iii) After the previous refueling, the estimated value of the cetane number of the fuel was not determined.

If the above execution condition is not satisfied (NO), the present processing of the routine immediately ends. If the execution condition is satisfied (YES), the process proceeds to step S101. Then, when the operation is advanced to step S101, conditions regarding the rotational speed of the diesel engine are read in, that is, the engine rotational speed NE, the coolant temperature THW, the intake air temperature THA and the intake air pressure are read in at step S101. Subsequently, at step S102, the state in the cylinder of the diesel engine is read; In particular, the EGR opening degree VR, the vehicle speed SPD and the heat quantity Qc of the cylinder wall surface are read. The heat quantity Qc of the cylinder wall surface read at this time was determined by a determination from the state of the engine load before that time.

Subsequently, at step S103, the fuel injection timing for determining the cetane number of fuel (injection time for the purpose of determining the cetane number) is set based on the read condition regarding the rotational speed and the read state in the cylinder. More specifically, the injection time for the purpose of determining the cetane number is set to be earlier, when the engine speed NE is higher, or when the coolant temperature THW is lower or when the intake air pressure PA is lower. Moreover, the injection time for the purpose of determining the cetane number is set to be earlier, when the EGR opening degree VR is smaller, or when the vehicle speed SPD is lower or when the heat quantity Qc of the cylinder wall surface is smaller.

Subsequently, at step S104, a single injection of a predetermined amount of fuel is performed as a fuel injection for the purpose of determining the cetane number at the fuel injection time, which is set as described above. Subsequently, at step S105, the magnitude of the engine torque (generated torque) generated by the combustion of the injected fuel is detected.

The calculation of the generated torque at step S105 is performed as follows. That's how the electronic control unit gets 19 the engine speed every predetermined cycle time, and detects a difference between the obtained engine speed and the engine speed obtained at the previous cycle time (speed difference ΔNE).

An upper section of 5 FIG. 12 shows a transition of the engine speed before and after the execution of the fuel injection for detecting the cetane number, and a lower portion of FIG 5 shows a transition of the speed difference .DELTA.NE at this time. When the engine torque is generated due to the execution of the fuel injection for detecting the cetane number of the fuel, the engine speed increases or the rate of decrease of the engine speed decreases, so that the rotational speed difference ΔNE increases. The time-derived value of the increase in the speed difference ΔNE (which corresponds to the area of a dashed section in FIG 5 corresponds) is larger when the generated torque is larger. Therefore, in this embodiment, the time-derived value of the increase in the rotational speed difference ΔNE is calculated as an amount of change in the rotational speed ΣΔNE, and the Value of the amount is used as an index value of the generated torque.

Subsequently, at step S106, the actual fuel injection time and the actual amount of fuel injection from the time waveform of the fuel injection rate at the fuel injection performed at step S104, and errors of the actual values of the fuel injection time and the amount of fuel injection from their command values (the injection time error and the injection amount error) are calculated. Then, based on the injection timing error and the injection amount error, the amount of change of the rotational speed ΣΔNE is corrected. This correction is performed to reduce the influence that the injection timing error and the injection amount error have on the result of determining the cetane number of the fuel by performing correction of an amount corresponding to the amount of change of generated torque caused by the injection timing error and the injection amount error is caused. More specifically, the generated torque is larger as the injection timing error to the "early" side (the side to which the injection time is advanced further "early") is larger, so that the amount of change of the rotational speed ΣΔNE for the correction is more reduced. Moreover, the generated torque is larger as the injection amount error toward the increased amount side is larger, so that the amount of change of the rotational speed ΣΔNE for the correction is more reduced.

Subsequently, at step S107, an estimated cetane number of the fuel is calculated based on the change amount of the rotational speed ΣΔNE after the correction and the engine rotational speed occurring at the time of execution of the fuel injection. The microcomputer of the electronic control unit 19 empirically preliminarily stores predetermined relationships of the cetane number of fuel to the amount of change of the rotational speed ΣΔNE and the rotational speed. The calculation in step S107 is performed based on the previously stored relationships. After the estimated cetane number is calculated, the present processing of the routine ends.

Hereinafter, an operation of the engine fuel property determiner of the embodiment having the above structure will be described. In this embodiment, the cetane number of fuel is determined based on the torque generated after the fuel injection. The principle of this embodiment is as follows.

As in 6A As shown in FIG. 2, after the piston of the cylinder reaches the top dead center (TDC), the pressure in a cylinder decreases with the piston moving downwards. In addition, as the pressure decreases, the temperature within the cylinder also decreases. Then, the state in the cylinder may reach a combustion limit beyond which no combustion can be realized.

From the injection of fuel to the ignition of the same exists a certain delay time (time difference), as in 6B is shown. The delay time from the injection of fuel to the ignition thereof is shorter when the ignition quality of fuel is higher, that is, when the cetane number of fuel is higher.

As in 6C As shown, if the ignition delay becomes shorter, the time from ignition to the time when the combustion limit is reached, that is, the combustion time becomes longer, so that the amount of fuel which does not completely burn and burn off remains smaller becomes. Therefore, if the ignition delay is shorter, the amount of fuel that burns is larger, and therefore the engine torque generated by the combustion of fuel is larger. Therefore, the ignition quality (cetane number) of fuel can be determined from the magnitude of the engine torque generated after the fuel injection.

In the embodiment, the injection time for the purpose of determining the cetane number is determined based on the conditions of the rotational speed of the diesel engine (the engine speed NE, the coolant temperature THW, the intake air temperature THA, and the intake air pressure PA) and the conditions in the cylinder (the EGR opening degree VR, the vehicle speed SPD and the heat quantity Qc of the cylinder wall surface). This adjustment of the fuel injection time is performed for the following reason.

If the engine speed NE is higher while the injection time remains the same, the combustion time from the ignition to the time when the combustion limit is reached is shorter, and therefore, the generated torque is smaller. Therefore, in the embodiment, by appropriately shifting the time of fuel injection to "early" when the engine speed NE is higher, the time from the injection to the time when the combustion limit is reached is kept constant irrespective of the engine speed NE.

The ignition delay of fuel also varies depending on other quantities as the ignition quality (cetane number) of fuel. For example, also influence a maximum value of the temperature of the gas in a cylinder (peak value of the gas temperature in the cylinder, peak temperature in the cylinder) of the engine during the compression stroke of the cylinder, and a maximum value of the pressure in the cylinder (peak value of the pressure in the cylinder, peak pressure in the cylinder) during the compression stroke, the delay time of the ignition of fuel. More specifically, the retardation of the ignition of fuel is longer when the peak temperature in the cylinder and / or the peak pressure in the cylinder is lower.

If the delay time of the ignition of fuel changes due to a quantity other than the ignition quality of fuel, the time of ignition changes and therefore the combustion time and the generated torque change even if the ignition quality of fuel remains the same. As a result, the determination accuracy of the ignition quality of fuel decreases based on the generated torque.

Even in such a case, if the fuel injection timing is changed by an amount corresponding to the change of the ignition delay of fuel caused by the quantity other than the ignition quality of fuel, the ignition time remains the same and the generated torque remains unchanged, regardless of the change in the ignition quality of fuel, which is caused by the size other than the ignition quality of fuel, provided that the ignition quality of fuel remains the same.

For example, it is assumed that the shortening of the ignition delay, as in 6C shown, due to a different size than the ignition quality of fuel occurs. Also in this case, if the fuel ignition timing is delayed by the amount of the shortening of the ignition delay, as in FIG 6D shown the same ignition timing as in 6B shown can be obtained. Therefore, no change occurs in the combustion time and thus in the generated torque. Therefore, if the fuel injection timing is adjusted according to the change of the time of the ignition delay caused by a quantity other than the ignition quality of fuel, the variation of the generated torque due to the change of the ignition delay caused by the quantity other than the ignition quality of fuel, and the accuracy of determination of the cetane number of fuel can be increased.

Therefore, in the embodiment, the determination accuracy of the cetane number of fuel is determined by detecting the change of the ignition delay caused by a size other than the ignition quality of fuel from the coolant temperature THW, the intake air temperature THA, the intake air pressure PA, the EGR opening degree VR, of the vehicle speed SPD and the amount of heat Qc of the cylinder wall surface, and then variably setting the injection time for the purpose of determining the cetane number according to the amount of change of the ignition delay.

For example, with respect to the intake air pressure PA, the injection time for the purpose of determining the cetane number is variably set in an embodiment described below. When the intake air pressure PA is lower, the peak pressure in the cylinder is lower and the ignition delay is longer. Therefore, in this embodiment, the injection time for the purpose of determining the cetane number is further advanced "early" when the intake air pressure PA is lower.

On the other hand, when the temperature of the gas fed into a cylinder (intake gas temperature in the cylinder) is lower, the peak temperature in the cylinder is lower and the ignition delay is longer. The intake gas temperature in the cylinder is lower when the intake air temperature THA is lower. Therefore, in this embodiment, the injection time for the purpose of determining the cetane number is further advanced "early" when the intake air temperature THA is lower.

In the engine using the EGR system, the intake gas temperature in the cylinder also varies depending on the EGR amount. That is, when the amount of the high-temperature exhaust gas mixed with intake air is larger, the intake gas temperature in the cylinder is higher and therefore the ignition delay is shorter. Therefore, in this embodiment, the injection time for the purpose of the determination is further delayed or "retarded" when the EGR opening degree VR is larger and thus the EGR amount is larger.

In addition, the peak temperature in the cylinder also varies depending on the amount of heat of the cylinder wall surface. That is, if the heat quantity of the cylinder wall surface is large, an increased amount of heat is transmitted to the gas in the cylinder and the temperature of the gas in the cylinder increases. Therefore, in order to keep the ignition timing constant regardless of the heat quantity of the cylinder wall surface, it is necessary to further retard the injection time for the purpose of determining the cetane number when the heat quantity of the cylinder wall surface is larger. Therefore, in the embodiment, the injection time for the purpose of Determination of the cetane number further delayed or postponed to "late", the greater the amount of heat Qc of the cylinder wall surface, which is determined from the load condition of the machine.

In addition, it is likely that the machine was last operated under high load when the vehicle speed SPD is high. In addition, during a high-load operation of the engine during which a large amount of fuel is injected, the amount of heat that receives the cylinder wall surface is large. Thereby, the heat quantity of the cylinder wall surface is estimated to be large when the vehicle speed is high. Therefore, in this embodiment, the injection time for the purpose of determining the cetane number is further delayed or shifted "late" when the vehicle speed SPD is higher.

In addition, the temperature of the cylinder wall surface can be determined from the coolant temperature THW. In addition, the heat quantity of the cylinder wall surface is relatively small if the temperature of the cylinder wall surface is relatively low. Therefore, in this embodiment, the injection time for the purpose of determining the cetane number is further shifted to "early" when the coolant temperature THW is lower.

• (1) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß dem AGR-Betrag (dem AGR-Öffnungsgrad VR) variiert. Daher ist es möglich, den Einfluss zu beschränken, welchen die von dem AGR-Betrag abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt, und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (2) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß der Fahrzeuggeschwindigkeit SPD variiert. Aus der Fahrzeuggeschwindigkeit SPD kann die Wärmemenge der Zylinderwandoberfläche bestimmt werden. Daher ist es möglich, den Einfluss zu beschränken, welchen die von der Wärmemenge der Zylinderwandoberfläche abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (3) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß der Wärmemenge Qc der Zylinderwandoberfläche variiert, welche aus dem Lastzustand der Maschine vor der Bestimmung der Cetanzahl bestimmt wird. Daher ist es möglich, den Einfluss zu beschränken, welchen die von der Wärmemenge der Zylinderwandoberfläche abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (4) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß der Kühlmitteltemperatur THW variiert. Es ist möglich, aus der Kühlmitteltemperatur THW die Temperatur der Zylinderwandoberfläche und daher die Wärmemenge der Zylinderwandoberfläche zu bestimmen. Daher ist es möglich, den Einfluss zu beschränken, welchen die von der Wärmemenge der Zylinderwandoberfläche abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (5) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß der Einlasslufttemperatur THA variiert. Daher ist es möglich, den Einfluss zu beschränken, welchen die von der Einlass-Gas-Temperatur im Zylinder abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (6) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß dem Einlassluftdruck PA variiert. Daher ist es möglich, den Einfluss zu beschränken, welchen die von dem Spitzendruck im Zylinder abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (7) Bei der Ausführungsform wird die Einspritzzeit zum Zwecke der Bestimmung der Cetanzahl gemäß der Maschinendrehzahl NE variiert. Daher ist es möglich, den Einfluss zu beschränken, welchen die von der Maschinendrehzahl NE abhängige Veränderung der Zündverzögerungszeit auf die Ergebnisse der Bestimmung der Zündqualität von Kraftstoff besitzt und die Zündqualität von Kraftstoff mit verbesserter Genauigkeit zu bestimmen.
• (8) Bei der Ausführungsform werden Fehler zwischen den Befehlswerten der Kraftstoff-Einspritzzeit und dem Betrag der Kraftstoffeinspritzung und den tatsächlichen Werten davon (ein Einspritzzeitfehler und ein Einspritzbetragfehler) aus Veränderungen des Kraftstoffdrucks in den Injektoren 16, welcher durch die für die Injektoren 16 vorgesehenen Kraftstoffdrucksensoren 17 erfasst wird, festgestellt. Außerdem wird unter Verwendung dieser Fehler der Veränderungsbetrag der Drehzahl ΣΔNE, welcher einen Indexwert des erzeugten Drehmoments der Maschine darstellt, korrigiert und dadurch wird das Bestimmungsergebnis der Cetanzahl von Kraftstoff korrigiert. Daher ist es möglich, die Verschlechterung der Bestimmungsgenauigkeit der Zündqualität von Kraftstoff, welche durch die Fehler des Kraftstoff-Einspritzbetrages und der Kraftstoff-Einspritzzeit hervorgerufen wird, geeignet zu beschränken.

According to the engine fuel characteristic determining apparatus of the above-described embodiment, the following effects can be achieved.

• (1) In the embodiment, the injection time for the purpose of determining the cetane number is varied according to the EGR amount (the EGR opening degree VR). Therefore, it is possible to restrict the influence which the EGR amount-dependent change in the ignition delay time has on the results of the determination of the ignition quality of fuel, and to determine the ignition quality of fuel with improved accuracy.
• (2) In the embodiment, the injection time is varied for the purpose of determining the cetane number according to the vehicle speed SPD. From the vehicle speed SPD, the amount of heat of the cylinder wall surface can be determined. Therefore, it is possible to limit the influence of the variation of the ignition delay time on the results of the determination of the ignition quality of fuel, which is dependent on the heat quantity of the cylinder wall surface, and to determine the ignition quality of fuel with improved accuracy.
• (3) In the embodiment, the injection time for the purpose of determining the cetane number is varied according to the amount of heat Qc of the cylinder wall surface determined from the load state of the engine before the determination of the cetane number. Therefore, it is possible to limit the influence of the variation of the ignition delay time on the results of the determination of the ignition quality of fuel, which is dependent on the heat quantity of the cylinder wall surface, and to determine the ignition quality of fuel with improved accuracy.
• (4) In the embodiment, the injection time is varied according to the coolant temperature THW for the purpose of determining the cetane number. It is possible to determine from the coolant temperature THW the temperature of the cylinder wall surface and therefore the heat quantity of the cylinder wall surface. Therefore, it is possible to limit the influence of the variation of the ignition delay time on the results of the determination of the ignition quality of fuel, which is dependent on the heat quantity of the cylinder wall surface, and to determine the ignition quality of fuel with improved accuracy.
• (5) In the embodiment, the injection time is varied according to the intake air temperature THA for the purpose of determining the cetane number. Therefore, it is possible to restrict the influence which the ignition-timing-dependent change in the ignition delay time has on the results of determination of the ignition quality of fuel and determine the ignition quality of fuel with improved accuracy.
• (6) In the embodiment, the injection time for the purpose of determining the cetane number is varied according to the intake air pressure PA. Therefore, it is possible to limit the influence which the ignition-delay-time change on the ignition pressure-dependent on the peak pressure in the cylinder has on the results of the determination of the ignition quality of fuel and to determine the ignition quality of fuel with improved accuracy.
• (7) In the embodiment, the injection time is varied for the purpose of determining the cetane number according to the engine speed NE. Therefore, it is possible to restrict the influence that the ignition-delay-time-dependent change in the ignition speed on the results of the determination of the ignition quality of fuel has, and to determine the ignition quality of fuel with improved accuracy.
• (8) In the embodiment, errors between the command values of the fuel injection timing and the amount of fuel injection and the actual values thereof (an injection timing error and an injection amount error) become changes of the fuel pressure in the injectors 16 which by the for the injectors 16 provided fuel pressure sensors 17 detected. In addition, using these errors, the amount of change of the rotational speed becomes ΣΔNE, which represents an index value of the generated torque of the engine, and thereby the determination result of the cetane number of fuel is corrected. Therefore, it is possible to suitably restrict the deterioration of the determination accuracy of the ignition quality of fuel caused by the errors of the fuel injection amount and the fuel injection time.

The above embodiment may also be embodied with the following modifications. In the embodiment, errors between the command values of the fuel injection timing and the amount of fuel injection and the actual values thereof (the injection timing error and the injection amount error) become changes of the fuel pressure in the injectors 16 passing through the fuel pressure sensors 17 detected. In addition, using these errors, the amount of change of the rotational speed ΣΔNE representing an index value of the generated torque of the engine is corrected. Instead of the variation amount of the rotational speed ΣΔNE, an estimated cetane number may also be corrected directly by the injection timing error and the injection amount error. In such a case, it is also possible to suitably restrict the deterioration of the determination accuracy of the ignition quality of fuel caused by the errors in the amount of fuel injection and the fuel injection time.

Although the above embodiment uses the change amount of the rotational speed ΣΔNE as an index value of the generated torque of the engine, the generated torque may also be determined from other parameters such as the amount of increase of the pressure in the cylinder related to the combustion.

Although in the embodiment the cetane number of fuel is determined during the fuel cut of the diesel engine, the determination of the cetane number may be performed in a situation other than the fuel cut, provided that the situation allows an accurate determination of the torque generated after the fuel injection ,

In the case where the engine speed NE is substantially constant at the time of determining the cetane number, the determination of the cetane number may be performed without the need to variably set the injection time for the purpose of determination according to the engine speed NE.

In the case where the coolant temperature THW at the time of determining the cetane number of fuel is substantially constant, or in the case where the influence of the coolant temperature THW on the ignition delay time is negligibly small, the determination of the cetane number may be exact without the need be performed to set the injection time for the purpose of determining the cetane number according to the coolant temperature THW variable.

In the case where the intake air temperature THA is substantially constant at the time of determining the cetane number of fuel, or in the case where the influence of the intake air temperature THA on the ignition delay time is negligibly small, the determination of the cetane number may be exact without the need to set the injection time to be variable for the purpose of determining the cetane number according to the intake air temperature THA.

In the case where the intake air pressure PA is substantially constant at the time of determining the cetane number of fuel, or in the case where the influence of the intake air pressure PA on the ignition delay time is negligibly small, the determination of the cetane number may be exact without the need to set the injection time to be variable for the purpose of determining the cetane number according to the intake air pressure PA.

In the foregoing embodiment, the injection time is set variably for the purpose of determining the cetane number according to the EGR amount (the EGR opening degree VR), the vehicle speed SPD, and the heat quantity Qc of the cylinder wall surface. In the case where the influence of any one or two of the three parameters on the ignition delay can be neglected, it is permissible to ignore the variable setting of the injection time for the purpose of determining the cetane number based on the parameter or parameter whose influence is neglected can do without. More specifically, the following constructions (I) to (VI) are conceivable. (I) A construction in which the variable setting of the injection time for the purpose of determining the cetane number based on the EGR amount (the EGR opening degree VR) is omitted and the injection time for the purpose of determining the vehicle speed SPD and the heat quantity Qc the cylinder wall surface is varied. (II) A construction in which the variable setting injection timing for the purpose of determining the cetane number based on the vehicle speed SPD is omitted and the injection time for the purpose of determination according to the EGR amount (the EGR opening degree VR) and the heat quantity Qc of the Cylinder wall surface is varied. (III) A construction in which the variable setting of the injection time for the purpose of determining the cetane number is omitted based on the heat quantity Qc of the cylinder wall surface and the injection time for the purpose of determination according to the EGR amount (the EGR opening degree VR) and the Vehicle speed SPD is varied. (IV) A construction in which the variable setting of the injection time for the purpose of determining the cetane number based on the EGR amount (the EGR opening degree VR) and the vehicle speed SPD is omitted and the injection time for the purpose of the determination according to the heat quantity Qc the cylinder wall surface is varied. (V) A construction in which the variable setting of the injection time for the purpose of determining the cetane number based on the EGR amount (the EGR opening degree VR) and the heat quantity Qc of the cylinder wall surface is omitted, and the injection time for the purpose of the determination according to Vehicle speed SPD is varied. (VI) A construction in which the variable setting of the injection time for the purpose of determining the cetane number based on the vehicle speed SPD and the amount of heat Qc of the cylinder wall surface is omitted and the injection time for the purpose of determination according to the EGR amount (the EGR opening degree VR) is varied.

In the diesel engine to which the above embodiment is applied, the amount of fuel actually injected becomes changes of the fuel pressure sensors 17 detected fuel pressure within the injectors 16 and the detected actual amount of injected fuel is returned to the drive control of the injectors. The determination of the cetane number of fuel (the ignition quality of fuel) in the above embodiment may also be similarly applied to diesel engines which do not perform such feedback.

The determination logic in the above embodiment may also be applied to a determination of a different index value of the ignition quality of fuel than the cetane number in the same manner or a manner comparable to that employed in the above embodiment. For example, fuels using a lower limit of the cetane number as a dividing line value above which no problem is caused by a misfire, in high cetane number fuels whose cetane numbers are higher than the lower limit and low cetane number fuels whose cetane numbers are lower than the lower limit are divided. With such a construction, substantially the same determination logic as in the previous embodiment may be used to determine which of the two types of fuel corresponds to the fuel currently in use.

Claims (2)

An engine fuel characteristic determining apparatus that determines the ignition quality of fuel based on a magnitude of the engine torque generated by the combustion of the injected fuel, characterized in that the fuel injection is a single injection during a deceleration-time fuel supply interruption, and the time of fuel injection for determining the fuel injection Ignition quality of the fuel according to the exhaust gas recirculation amount during the delay-time fuel supply interruption is varied. The engine fuel property determination apparatus according to claim 1, wherein when the exhaust gas recirculation amount corresponds to a first amount, the time of fuel injection for determining the ignition quality of the fuel is set to be equal to when the exhaust gas recirculation amount corresponds to a second amount less than the first amount is later.

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