JP5131396B2 - Fuel type discrimination device and fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel type discrimination device and a fuel injection control device for an internal combustion engine represented by a diesel engine or the like. In particular, the present invention relates to measures for realizing accurate determination of the type of fuel used in an internal combustion engine and fuel injection control using the determination result.

  In recent years, from the viewpoint of oil depletion and global environmental problems, there is an increasing need to use alternative fuels such as biofuels for internal combustion engines. Therefore, the development of internal combustion engines that can handle a wide variety of fuels is being promoted. In order to cope with such a wide variety of fuels, the type of fuel being used is accurately determined, and fuel injection control (fuel injection start timing and fuel injection amount) according to its physical property values (cetane number, etc.) Control). This makes it possible to improve exhaust emission and improve engine performance regardless of the fuel type.

  Specifically, as disclosed in Patent Document 1, for example, in an automobile diesel engine, a very small amount of fuel is put into a cylinder prior to main injection for the purpose of reducing combustion noise and NOx emission. Pilot injection and pre-injection for injecting are performed. Even if the fuel injection start timing and the fuel injection amount are the same, if the physical property value of the fuel injected into the combustion chamber is different, the preheating effect in the combustion chamber will be different, and the preheating in the combustion chamber will be insufficient. If this happens, the ignition timing in the main injection may deviate from the appropriate timing, which may adversely affect exhaust emissions and engine performance. This is mainly due to the difference in cetane number and lower heating value depending on the fuel type.

  In such a case, it is possible to improve the exhaust emission and the engine performance by accurately determining the fuel type and performing the fuel injection control according to the physical property value.

  Note that accurate determination of the fuel type can greatly contribute to not only optimization of preheating in the combustion chamber described above but also optimization of various fuel injection controls (for example, control of main injection).

  Patent Document 2 discloses an apparatus for discriminating a fuel type. In Patent Document 2, the fuel type is determined based on the amount by which the relationship between the engine torque and the accelerator opening deviates from the basic characteristics.

JP 2002-195084 A JP 2009-46081 A

  However, the relationship between the accelerator opening and the fuel injection amount is not necessarily unambiguous, and the actual fuel injection amount may be different even at the same accelerator opening, depending on the cooling water temperature or the outside air temperature. is there. For this reason, in the technique disclosed in Patent Document 2, there is a possibility that the amount of deviation from the basic characteristics does not necessarily reflect the fuel type appropriately, and the fuel type discrimination accuracy is still insufficient. There was a need for further improvement.

  The present invention has been made in view of such points, and an object thereof is to utilize a fuel type discriminating apparatus capable of accurately discriminating the type of fuel used in an internal combustion engine, and a result of the discrimination. An object of the present invention is to provide a fuel injection control device that realizes fuel injection control.

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object is to discriminate the fuel type based on the relationship between the actual fuel injection amount injected into the combustion chamber and the torque generated therewith. . Further, the fuel injection in a form suitable for the determined physical property value of the fuel can improve the exhaust emission and the engine performance.

-Solution-
Specifically, the present invention is premised on a fuel type discriminating device for discriminating the type of fuel injected into a combustion chamber from a fuel injection valve to which fuel is supplied from an accumulator vessel that accumulates and holds high-pressure fuel . This fuel type discriminating device is provided with fuel pressure detecting means, actual injection amount recognizing means, torque recognizing means, and fuel type discriminating means. The fuel pressure detecting means detects the fuel pressure downstream of the fuel outlet of the pressure accumulating vessel. The actual injection amount recognizing means reduces the fuel pressure at the position where the fuel pressure detecting means is disposed after the fuel injection from the fuel injection valve is started with respect to the fuel pressure detected by the fuel pressure detecting means. Fuel injected from the fuel injection valve on the basis of the corrected fuel pressure calculated by multiplying the correction coefficient considering the delay time until the start and the injection period of fuel injection executed at the fuel pressure to estimate the actual injection quantity of. The torque recognition means measures or estimates the output torque of the internal combustion engine generated by the combustion of the fuel injected from the fuel injection valve. Fuel type determining means, based on the output torque of the actual injection quantity and the actual injection quantity estimated fuel by the recognition means, determined by the upper Symbol torque recognition means or estimated engine, the fuel injection The type of fuel injected from the valve into the combustion chamber is determined. The correction coefficient is set larger as the fuel pressure detecting means is closer to the fuel outlet of the pressure accumulating vessel.

  Fuels that can be used in internal combustion engines (for example, diesel oil and various biodiesel fuels in the case of diesel engines) have different physical property values. In particular, even if the amount of fuel injected into the combustion chamber is the same, if the fuel type is different, the magnitude of the torque generated with the fuel injection is significantly different. That is, the magnitude of the output torque with respect to the actual fuel injection amount and the fuel type have a unique relationship. Focusing on this point, the solution means determines the type of fuel currently in use based on the relationship between the actual injection amount obtained by the actual injection amount recognition means and the output torque obtained by the torque recognition means. I try to identify. For this reason, it becomes possible to discriminate the fuel type with high accuracy that could not be obtained by the prior art.

Further, the fuel pressure downstream from the fuel outlet of the pressure accumulating vessel better reflects the pressure fluctuation caused by the fuel injection of the fuel injection valve. In other words, in the case of the conventional configuration for detecting the fuel pressure (rail pressure) in the pressure accumulating vessel, the pressure fluctuation caused by the fuel injection from the fuel injection valve is attenuated until it propagates from the nozzle hole to the pressure accumulating vessel. It is difficult to accurately detect the fuel injection pressure (a value necessary for accurately calculating the actual injection amount). On the other hand, when detecting the fuel pressure downstream of the fuel outlet of the pressure accumulating vessel, it is possible to detect this before the pressure fluctuation caused by fuel injection is attenuated. Accordingly, in the present solution is, the fuel pressure suitable for estimation of the actual injection quantity it becomes possible to detect by the fuel pressure detecting means, it is possible to perform the estimation of the actual injection quantity with high accuracy. As a result, the type of fuel injected from the fuel injection valve into the combustion chamber can be determined with high accuracy.

Moreover, according to this solution, a detection error due to a delay in the detected fuel pressure (detected as a pressure higher than the fuel pressure around the nozzle hole) can be eliminated. For this reason, it is possible to estimate the actual injection amount based on the fuel pressure in accordance with the fuel pressure around the nozzle hole, and it is possible to estimate the actual injection amount with higher accuracy. As a result, the type of fuel injected from the fuel injection valve into the combustion chamber can be determined with high accuracy.

  More preferably, when an execution condition for the fuel injection amount learning operation is satisfied, fuel is injected into the specific cylinder from the fuel injection valve according to the instructed injection period, and the operating state of the internal combustion engine accompanying the fuel injection The fuel injection amount learning operation for acquiring the learning value based on the deviation of the actual fuel injection amount with respect to the target fuel injection amount from the change in the above is executed. And the said torque recognition means measures or estimates the output torque of the internal combustion engine obtained by performing the fuel injection according to the instruction | indication injection period based on the learning value obtained by the said fuel injection amount learning operation | movement It is said.

  When the learned value is updated by executing the fuel injection amount learning operation, the torque recognizing means measures or estimates the output torque of the internal combustion engine for the command injection period. That is, when such a fuel injection amount learning operation is executed, it is difficult to specify the output torque of the internal combustion engine with respect to the actual injection amount. In this case, the actual injection amount of fuel is measured or estimated by the actual injection amount recognition means. As a result, the output torque of the internal combustion engine relative to the actual injection amount can be specified from the relationship between the output torque obtained by the torque recognition unit and the actual injection amount of the fuel obtained by the actual injection amount recognition unit. This makes it possible to determine the type of fuel.

  Examples of the configuration of the device that controls the fuel injection mode according to the fuel type determined as described above include the following. First, the fuel injection operation from the fuel injection valve is premised on a fuel injection control device for a compression auto-ignition internal combustion engine capable of executing at least main injection and sub-injection performed prior to the main injection. The fuel injection control device includes sub-injection control means for adjusting at least one of the injection amount and the injection timing of the sub-injection according to the type of fuel determined by the fuel type determination means in the fuel type determination device. I am letting.

  Thereby, the injection amount and injection timing of the sub-injection suitable for the fuel type can be obtained, and the preheating effect by this sub-injection can be appropriately adjusted regardless of the fuel type. That is, it is possible to avoid a situation in which the preheating due to the sub-injection becomes insufficient or conversely becomes excessive and the ignition timing in the main injection deviates from the appropriate time. As a result, exhaust emission and engine performance can be improved.

  More preferably, the timing at which the heat generation rate due to the combustion of the fuel injected by the sub-injection becomes maximum, the combustion start timing of the fuel injected by the main injection, and the piston that reciprocates in the cylinder are compressed. Fuel injection control means capable of executing a high-efficiency fuel injection control operation for controlling the injection timing and the injection amount of each fuel injection so that the timing of reaching the dead point coincides with each other.

  By setting the injection mode of the sub-injection and the main injection so as to be at such timing, when the combustion of the fuel injected by the main injection is started, the heat generation rate due to the combustion of the fuel injected by the sub-injection is maximized. Thus, the combustion of the fuel injected by the main injection can be started by making the maximum use of the amount of heat generated by the sub-injection. Thereby, the temperature drop due to the endothermic reaction at the start of the main injection is suppressed, and the ignition delay of the fuel injected by the main injection is suppressed. For this reason, it is possible to lead the combustion in the main injection to stable diffusion combustion without ignition delay while suppressing the amount of fuel injected in the sub-injection to the minimum necessary, and to improve the fuel consumption rate. In addition, since the combustion start timing of the fuel injected in the main injection substantially coincides with the compression top dead center of the piston, reverse torque (torque acting in the direction opposite to the rotation direction of the crankshaft) is generated. In addition, since combustion for generating torque is started from a state in which the combustion chamber is substantially minimum, the torque generated by this combustion can be ensured to the maximum.

  More preferably, the fuel injection control means is arranged so that the fuel injected by the main injection does not overlap with the fuel injected by the sub injection and flowing along the swirl flow in the cylinder. The injection execution timing is set.

  Thus, the fuel injected by the sub-injection and the fuel injected by the main injection are not superimposed, so that most of the fuel injected by the sub-injection can contribute to the in-cylinder preheating. For this reason, it becomes possible to start the combustion of the fuel injected by the main injection by making maximum use of the amount of heat generated by the combustion of the fuel injected by the sub injection.

  In the present invention, the fuel type is determined based on the relationship between the actual fuel injection amount injected into the combustion chamber and the torque generated therewith. Further, fuel injection is performed in a form suitable for the determined physical property value of the fuel. For this reason, the fuel type can be discriminated with high accuracy, and as a result, exhaust emission and engine performance can be improved.

FIG. 1 is a schematic configuration diagram of an engine and its control system according to the embodiment. FIG. 2 is a waveform diagram showing a change state of the heat generation rate when main injection is executed. FIG. 3A is a waveform diagram showing a change state of an ideal heat generation rate during execution of pre-injection and main injection, and FIG. 3B is a diagram showing an example of injection patterns of pre-injection and main injection. It is. FIG. 4 is a diagram illustrating an example of a fuel type determination map. FIG. 5 is a diagram showing physical property values of biodiesel fuel, light oil, and rapeseed oil. 6A is a fuel oil fuel injection start timing setting map, FIG. 6B is a biodiesel fuel fuel injection start timing setting map, and FIG. 6C is a rapeseed oil fuel injection start timing setting map. FIG. 7A is a diagram showing a fuel injection amount setting map for light oil, FIG. 7B is a diagram showing a fuel injection amount setting map for biodiesel fuel, and FIG. 7C is a diagram showing a fuel injection amount setting map for rapeseed oil. is there. FIG. 8 is a diagram corresponding to FIG. 3 when light oil, biodiesel fuel, and rapeseed oil are used. FIG. 9 is a view corresponding to FIG. 3 when another alternative fuel and light oil are used. FIG. 10 is a view corresponding to FIG. 3 when another alternative fuel and light oil are used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment demonstrates the case where this invention is applied to the common rail type | mold in-cylinder direct injection type multi-cylinder (for example, 4 cylinders) diesel engine (internal combustion engine) mounted in the motor vehicle.

-Engine configuration description-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its control system according to the present embodiment.

  An intake passage 4 is connected to a combustion chamber 3 formed between the cylinder 1a and the piston 1b in the engine 1 via an intake valve 4a as an intake system. An air cleaner 6 for filtering intake air from the upstream side, an intake air amount sensor (air flow meter) 8 for detecting the intake air amount, and an intake air temperature sensor 10 for detecting the intake air temperature are provided in the intake passage 4. A throttle valve (intake throttle valve) 14 is provided, which is an electronically controlled on-off valve that can adjust the opening degree steplessly.

  The throttle valve 14 is driven to open and close by a drive mechanism 16. The drive mechanism 16 includes a step motor 18 and a gear group that drives and connects the step motor 18 and the throttle valve 14. The step motor 18 is driven and controlled by an electronic control unit (hereinafter referred to as “ECU”) 20 for performing various controls of the engine 1. The drive mechanism 16 is provided with a fully open switch 22 that is turned on when the throttle valve 14 is in the fully open position.

  On the other hand, an exhaust passage 24 is connected to the combustion chamber 3 via an exhaust valve 24a as an exhaust system. An EGR (exhaust gas recirculation) passage 26 branches from the exhaust passage 24. The EGR passage 26 is connected to the downstream side of the throttle valve 14 in the intake passage 4. The EGR passage 26 is provided with an EGR valve 30 that is opened and closed by an actuator 28 controlled by the ECU 20. By adjusting the EGR amount by the EGR valve 30, the ratio of the EGR amount to the intake air amount introduced into the combustion chamber 3 can be freely set. As a result, an appropriate EGR rate can be obtained over the entire operation region of the engine 1.

  The engine 1 is provided with a plurality of cylinders (four cylinders in the present embodiment, but only one cylinder is illustrated) # 1, # 2, # 3, and # 4. Injectors (fuel injection valves) 32 are respectively disposed for the combustion chambers 1 to # 4. The injector 32 includes a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened and injects fuel into the combustion chambers 3 of the cylinders # 1 to # 4. The details of the fuel injection control of the injector 32 will be described later.

  The injector 32 is connected to a common rail 34 as a pressure accumulating container common to each cylinder, and the fuel in the common rail 34 burns from the injector 32 while the injection control electromagnetic valve 32a is open (injector opening period). It is injected into the chamber 3. A relatively high pressure corresponding to the fuel injection pressure is accumulated in the common rail 34. In order to realize this pressure accumulation, the common rail 34 is connected to the discharge port 36 a of the supply pump 36 via the supply pipe 35. A check valve 37 is provided in the middle of the supply pipe 35. Due to the presence of the check valve 37, the supply of fuel from the supply pump 36 to the common rail 34 is allowed, and the backflow of fuel from the common rail 34 to the supply pump 36 is restricted.

  The supply pump 36 is connected to a fuel tank 38 via a suction port 36b, and a filter 39 is provided in the middle thereof. The supply pump 36 sucks fuel from the fuel tank 38 through the filter 39. At the same time, the supply pump 36 receives the rotational driving force from the crankshaft, which is the output shaft of the engine 1, and reciprocates the plunger to increase the fuel pressure to the required pressure, thereby supplying the high-pressure fuel to the common rail 34. To supply.

  Further, a pressure control valve 40 is provided in the vicinity of the discharge port 36 a of the supply pump 36. The pressure control valve 40 is for controlling the fuel pressure (ie, injection pressure) discharged from the discharge port 36a to the common rail 34. By opening the pressure control valve 40, surplus fuel that is not discharged from the discharge port 36a is returned from the return port 36c provided in the supply pump 36 to the fuel tank 38 via the return pipe (return flow path) 41. It is like that.

  As described above, the fuel supply system of the engine 1 is configured with the fuel tank 38, the supply pump 36, the common rail 34, and the injector 32 as main components.

  A glow plug 42 is disposed in the combustion chamber 3 of the engine 1. The glow plug 42 is a start assist device that is heated red when a current is passed through the glow relay 42a immediately before the engine 1 is started, and a part of the fuel spray is blown onto the glow plug 42a to promote ignition and combustion. .

  Note that the crankshaft of the engine 1 is provided with a rotor that rotates in synchronization with the rotation of the crankshaft, and a convex signal formed on the outer peripheral surface of the rotor is detected and a pulse signal corresponding to the rotational speed is generated. A crank position sensor 44 comprising an electromagnetic pickup for output is provided. The output of the crank position sensor 44 is taken into the ECU 20 as a signal that contributes to the calculation of the rotational speed of the engine 1.

  The ECU (Electronic Control Unit) 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup RAM, a timer, a counter, and the like, and an A / D (Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog / Analog An external input circuit including a digital converter and an external output circuit are connected by a bidirectional bus.

  The ECU 20 configured as described above inputs detection signals of various sensors via an external input circuit, and based on these signals, various controls relating to the operating state of the engine 1, such as basic control for fuel injection of the engine 1 and the like. Execute. Specifically, the ECU 20 includes an accelerator opening amount detected by the accelerator opening sensor 46, including the intake air amount information detected by the intake air amount sensor 8 and the intake air temperature information detected by the intake air temperature sensor 10. Degree information (accelerator pedal depression amount information), IG (ignition) switch 48 on / off information, starter switch 50 on / off information, and cooling water temperature detected by a cooling water temperature sensor 52 provided in the water jacket 2a. Information, shift position information detected by a shift position sensor 54 provided in the transmission, vehicle speed information detected by a signal from the vehicle speed sensor 56, and a fuel temperature sensor 58 provided in a return pipe 41 extending from the injector 32. Fuel temperature information, litter above Fuel temperature information detected by a fuel temperature sensor 59 provided near the port 36c, fuel pressure (injection pressure PC) detected by a fuel pressure sensor (fuel pressure detection means) 60 provided near the fuel inlet of the injector 32 ) Information is taken in, and various controls relating to the operating state of the engine 1 are executed based on the information.

  For example, the ECU 20 executes fuel injection control of the injector 32. As fuel injection control of the injector 32, in this embodiment, pilot injection, pre-injection, main injection (main injection), after injection, and post injection, which will be described later, are executed.

  The total fuel injection amount in the main injection is a fuel injection amount necessary for obtaining a required torque that is determined according to operating conditions such as engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and environmental conditions. Is set. For example, the higher the engine speed (the engine speed calculated based on the detection value of the crank position sensor 44), the greater the accelerator operation amount (the accelerator pedal depression amount detected by the accelerator opening sensor 46). The higher the required accelerator torque of the engine 1, the higher the accelerator opening.

  The fuel injection pressure for executing these fuel injections is determined by the fuel pressure supplied from the common rail 34 to the injector 32. The target value of the fuel pressure becomes higher as the engine load (engine load) becomes higher and as the engine speed (engine speed) becomes higher. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large, so that a large amount of fuel must be injected from the injector 32 into the combustion chamber 3. The pressure needs to be high. Also, when the engine speed is high, the injection period is short, so the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 32 must be increased. . Thus, the target fuel pressure is set based on the engine load and the engine speed. This target fuel pressure is set according to a fuel pressure setting map stored in the ROM, for example. That is, in a state in which the fuel pressure is adjusted according to this fuel pressure setting map, the valve opening period (injection rate waveform) of the injector 32 is controlled, thereby making it possible to define the fuel injection amount during the valve opening period. In the present embodiment, the fuel pressure is adjusted between 30 MPa and 200 MPa according to the engine load and the like.

  For example, the ECU 20 makes the fuel pressure detected by the fuel pressure sensor 60 equal to a target fuel pressure (target fuel pressure obtained from the fuel pressure setting map) set based on the engine operating state, that is, fuel injection. The fuel discharge amount of the supply pump 36 is adjusted (feedback control of the fuel discharge amount) so that the pressure matches the target injection pressure.

  Further, the ECU 20 determines the fuel injection amount and the fuel injection form based on the engine operating state. Specifically, the ECU 20 calculates the engine speed (engine speed) based on the detection value of the crank position sensor 44 and also determines the depression amount of the accelerator pedal (accelerator opening) based on the detection value of the accelerator opening sensor 46. The total fuel injection amount (the sum of the injection amount in the pre-injection and the injection amount in the main injection, which will be described later) is determined based on the engine speed, the accelerator opening, and the like as described above.

-Fuel injection mode-
Hereinafter, an outline of each operation of the pilot injection, pre-injection, main injection, after-injection, and post-injection in the present embodiment will be described.

(Pilot injection)
The pilot injection is an injection operation that injects a small amount of fuel in advance prior to the main injection (main injection) from the injector 32. That is, after the pilot injection is performed, the fuel injection is temporarily interrupted, and the compressed gas temperature (in-cylinder temperature) is sufficiently increased until the main injection is started to reach the fuel self-ignition temperature. This ensures good ignitability of the fuel injected in the main injection. That is, the pilot injection function in this embodiment is specialized for preheating in the cylinder. That is, the pilot injection in the present embodiment is an injection operation (preheating fuel supply operation) for preheating the gas in the combustion chamber 3.

Specifically, in this embodiment, in order to optimize spray distribution and local concentration, the injection amount per one pilot injection is set to the minimum limit injection amount (for example, 1.5 mm ³ ) of the injector 32, and the injection is performed. The required total pilot injection amount is secured by setting the number of times. More specifically, the number of pilot injections is determined by the following equation (1).

N = {(Ca · ΔT) · Kc · Kv} / (J · η) (1)
(N: number of pilot injections, Ca: heat capacity of air introduced into the cylinder, ΔT: unsatisfactory temperature with respect to auto-ignition temperature, Kc: heat capacity correction coefficient by EGR rate, Kv: target space for combustion contribution, J: theoretical calorific value of 1.5 mm ³ , η: fuel efficiency)
Here, the unsatisfactory temperature ΔT with respect to the self-ignition temperature refers to the compressed gas temperature at the target ignition timing of the fuel at the time of main injection (for example, the timing when the piston 1b reaches the compression top dead center), and the self-ignition of the fuel. This is a difference from the temperature, and corresponds to the amount of heat necessary to make the compressed gas temperature at the target ignition timing reach the self-ignition temperature of the fuel. By executing the pilot injection with the number of injections obtained by the equation (1), the total pilot injection amount is ensured.

Note that the above formula (1) sets the pilot injection amount per time to a fixed value (for example, 1.5 mm ³ ), and secures the necessary total pilot injection amount by setting the number of injections. . The fixed value of the pilot injection amount per one time is not limited to the above value.

  As a method for setting the total pilot injection amount, a fuel injection amount setting map for pilot injection is stored in advance in the ROM, and the total pilot injection amount is set according to the fuel injection amount setting map. Good.

  Further, the interval of the pilot injection that is divided and injected in this way is determined by the responsiveness of the injector 32 (speed of opening and closing operation). In the present embodiment, it is set to 200 μs, for example. The pilot injection interval is not limited to this value. In addition, the angle said below means the value converted into the rotation angle of the crankshaft.

  Further, the injection start timing of this pilot injection is set by the following equation (2), for example, after crank angle at 80 ° before compression top dead center (BTDC) of the piston 1b.

Pilot injection start angle = Pilot combustion end angle + Pilot injection period working angle + (Crank angle converted value of required combustion time in one pilot injection × N + Crank angle converted value of ignition delay time−Crank angle converted value of overlap time) (2)
Here, the pilot combustion end angle is an angle set in order to complete combustion by pilot injection before the start of pre-injection. The ignition delay time is a time delay from when the pilot injection is executed until the fuel is ignited. Further, the overlap time is the overlap time between the fuel combustion period by the pilot injection executed in advance and the fuel combustion period by the pilot injection executed subsequently (two combustions are performed simultaneously). Time) and the combustion period of the fuel by the final pilot injection and the combustion period of the fuel by the subsequent pre-injection.

  As a method of setting the injection start timing of the pilot injection, a fuel injection start timing setting map for pilot injection is stored in advance in the ROM, and the injection start timing of the pilot injection is set according to the fuel injection start timing setting map. You may make it set.

(Pre-injection)
The pre-injection is an injection operation for injecting a small amount of fuel in advance prior to the main injection from the injector 32. This pre-injection is an injection operation (suppression operation of supplying fuel for torque generation) for suppressing the initial combustion speed by the main injection and leading to stable diffusion combustion, and is also called sub-injection. Further, the pre-injection in the present embodiment has not only a function of suppressing the initial combustion speed by the main injection described above but also a preheating function of increasing the in-cylinder temperature.

  Specifically, in the present embodiment, the total injection amount (the injection amount in the pre-injection and the total injection amount for obtaining the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the coolant temperature, the intake air temperature, etc. For example, the pre-injection amount is set to 10% (for example, when the fuel is light oil) with respect to the sum of the main injection amount). The ratio of the pre-injection amount to the total injection amount is set according to the amount of heat (required pre-heating amount) required when pre-heating the cylinder.

In this case, when the total injection amount is less than 15 mm ³ , the injection amount in the pre-injection is less than the minimum limit injection amount (1.5 mm ³ ) of the injector 32, and therefore the pre-injection is not executed. become. In this case, the fuel injection in the pre-injection may be performed by the minimum limit injection amount (1.5 mm ³ ) of the injector 32. On the other hand, when the total injection amount of the pre-injection is required to be twice or more (for example, 3 mm ³ or more) of the minimum limit injection amount of the injector 32, a plurality of pre-injections are executed, which is necessary for this pre-injection. The total injection amount is secured. Thereby, the ignition delay of the pre-injection can be suppressed, the initial combustion speed by the main injection can be surely suppressed, and the stable diffusion combustion can be led.

  As a pre-injection total amount setting method, a pre-injection fuel injection amount setting map is stored in advance in the ROM, and the pre-injection total injection amount is set according to the fuel injection amount setting map. Also good.

  Further, the injection start angle of this pre-injection is set by the following equation (3).

Pre-injection start angle = Pre-combustion end angle + Pre-injection period working angle + (Crank angle conversion value of combustion required time in pre-injection + Crank angle conversion value of ignition delay time−Crank angle conversion value of overlap time) (3) )
Here, the ignition delay time is a time delay from when the pre-injection is executed until the fuel is ignited. Further, the overlap time is an overlap between the fuel combustion period by the pre-injection executed in advance and the fuel combustion period by the pre-injection executed subsequently in the case where a plurality of pre-injections are performed. Time (time in which two combustions are performed simultaneously), the overlap time of the combustion period of the fuel by the final pre-injection, and the combustion period of the fuel by the subsequent main injection, and the final This is the overlap time between the fuel combustion period by pilot injection and the fuel combustion period by pre-injection.

  In addition to the above formula (3), the crank angle conversion value (ignition delay angle) of the ignition delay time of the pre-injection, and the endothermic reaction at the start of the pre-injection after the ignition delay time has elapsed, The injection start angle of the pre-injection according to the crank angle conversion value (combustion start angle) of the time from when the heat generation amount balance is negative to when this heat generation amount balance becomes positive May be set.

  Further, as a method for setting the injection start angle (injection start timing) of the pre-injection, a fuel injection start timing setting map for pre-injection is stored in advance in the ROM, and the pre-injection is performed according to the fuel injection start timing setting map. The injection start angle may be set.

(Main injection)
The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. Specifically, in the present embodiment, the pre-injection from the total combustion injection amount for obtaining the required torque determined according to the operating state such as the engine speed, the accelerator operation amount, the cooling water temperature, the intake air temperature and the like. It is set as an injection amount obtained by subtracting the injection amount.

  Further, the injection start angle (crank angle position) of the main injection is set by the following equation (4).

Main injection start angle = Main ignition timing + Main injection period working angle + (Crank angle conversion value of combustion required time in main injection + Crank angle conversion value of ignition delay time−Crank angle conversion value of overlap time) (4)
Here, the ignition delay time is a time delay from when the main injection is executed until the fuel is ignited. The overlap time is defined as the overlap time between the fuel combustion period by the pre-injection and the fuel combustion period by the main injection, and the overlap between the fuel combustion period by the main injection and the fuel combustion period by the after injection. Lap time.

  In addition to the above equation (4), the injection start angle of the main injection may be set according to the crank angle conversion value (ignition delay angle) of the ignition delay time of the main injection.

  Further, as a method for setting the injection start angle (injection start timing) of the main injection, a fuel injection start timing setting map for main injection is stored in advance in the ROM, and the main injection is performed according to the fuel injection start timing setting map. The injection start angle may be set.

  The specific injection modes of the pre-injection and the main injection as described above, particularly the details of the relationship with the crank angle position will be described later.

(After spray)
After injection is an injection operation for increasing the exhaust gas temperature. Specifically, in the present embodiment, after-injection is executed at a timing at which most of the combustion energy of the fuel supplied by this after-injection is obtained as exhaust heat energy without being converted into torque of the engine 1. I am doing so. Also in this after injection, as in the case of the pilot injection described above, it is necessary to set the number of injections by setting the injection amount per injection to the minimum limit injection amount (for example, 1.5 mm ³ ) of the injector 32. The total after injection amount is ensured.

(Post injection)
Post injection is an injection operation for directly introducing fuel into an exhaust system to increase the temperature of a catalyst (not shown). For example, when the accumulated amount of PM collected in the DPNR catalyst provided in the exhaust system exceeds a predetermined amount (for example, detected by detecting a differential pressure before and after the catalyst), post injection is performed. It has become.

-Ideal form of combustion-
In the diesel engine 1, it is important to simultaneously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque. In order to satisfy these requirements, it is effective to appropriately control the change state of the heat generation rate in the cylinder during the combustion stroke (change state represented by the heat generation rate waveform).

  FIG. 2 shows an ideal heat generation rate waveform (composition of heat generation rate obtained only by fuel in main injection) with the crank angle on the horizontal axis and the heat generation rate on the vertical axis. Waveform). TDC in the figure indicates the crank angle position corresponding to the compression top dead center of the piston 1b.

  As this heat generation rate waveform, for example, combustion of fuel injected by main injection is started from the compression top dead center (TDC) of the piston 1b, and a predetermined piston position after the compression top dead center (for example, compression top dead center). The heat generation rate reaches a maximum value (peak value) at 10 ° (at the time of ATDC 10 °), and a predetermined piston position after compression top dead center (for example, 25 ° after compression top dead center (ATDC 25 °)). The combustion of the fuel injected in the main injection ends at the time). In order to end the combustion by this time, in the present embodiment, the fuel injection in the main injection is ended by 22 ° (ATDC 22 °) after the compression top dead center. If combustion of the air-fuel mixture is performed in such a state of change in heat generation rate, for example, 50% of the air-fuel mixture in the cylinder burns at 10 ° (ATDC 10 °) after compression top dead center. Completed status. That is, about 50% of the total heat generation amount in the expansion stroke is generated by ATDC 10 °, and the engine 1 can be operated with high thermal efficiency.

  And as a more practical combustion form, the injection timing and the injection quantity for obtaining the ideal combustion form in the case where pre-injection is executed prior to the main injection include the following. That is, as injection forms of the pre-injection and the main injection, the timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection becomes maximum, the combustion start timing of the fuel injected by the main injection, and the reciprocation in the cylinder 1a. The injection timing and the injection amount of the pre-injection and the main injection are controlled so that the timing at which the moving piston 1b reaches the compression top dead center substantially coincides with each other. In other words, the timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection becomes maximum coincides with the combustion start timing of the fuel injected by the main injection, and this timing is compressed by the piston 1b. It almost matches the timing when the top dead center is reached. Hereinafter, the fuel injection control in the pre-injection and main injection modes is referred to as a high-efficiency fuel injection control operation.

  FIG. 3 shows a heat release rate waveform (FIG. 3A) during execution of the high-efficiency fuel injection control operation, and each injection pattern of pre-injection and main injection (FIG. 3B). In addition, this FIG.3 (b) is each injection pattern at the time of using light oil as a fuel.

  As shown in FIG. 3, the pre-injection is executed on the advance side of the compression top dead center (TDC) of the piston 1b (the start timing and end of the pre-injection on the advance side of the compression top dead center of the piston 1b). The timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection is maximized is set to be the timing at which the piston 1b reaches the compression top dead center (FIG. 3 (a)). ) (Refer to the change waveform of the heat generation rate due to the combustion of the fuel injected by the pre-injection indicated by the one-dot chain line).

  Further, the main injection is started slightly on the advance side from the compression top dead center (TDC) of the piston 1b, and the main injection is terminated on the retard side from the compression top dead center of the piston 1b. The combustion start timing of the injected fuel is set to be the timing at which the piston 1b reaches the compression top dead center (heat generation due to the combustion of the fuel injected by the main injection indicated by the broken line in FIG. 3A) See the rate change waveform).

  Thereby, as shown in the heat generation rate waveform shown by the solid line in FIG. 3A, the heat generation rate by the combustion of the fuel injected by the pre-injection and the heat generation rate by the combustion of the fuel injected by the main injection Is a continuous waveform (a waveform forming an envelope).

  When the pre-injection is executed at such timing, the fuel injected by the pre-injection and flowing along the swirl flow in the cylinder does not overlap with the fuel injected by the subsequent main injection.

  Specifically, the flow of air flowing into the cylinder from the intake port during the intake stroke of the engine 1 is a swirl flow with the cylinder center line as the center of rotation, and this swirl flow continues in the compression stroke. Is occurring within.

  For this reason, the fuel injected by the pre-injection flows in the cylinder in the circumferential direction by this swirl flow. That is, with the passage of time in the compression stroke, the fuel (spray lump) injected in the pre-injection is flowed in the circumferential direction along the swirl flow from the position facing the injection hole of the injector 32 (position immediately after injection). It will follow.

  Therefore, at the time when the subsequent main injection is performed after the pre-injection, the fuel that has been injected in the preceding pre-injection is already flowing in the cylinder in the circumferential direction, and the same injection hole The fuels of the two injections injected from (the pre-injection and the main injection) do not overlap (the fuel masses of both injections do not merge).

  In this case, since the pre-injected fuel injected from the upstream nozzle hole in the swirl flow direction flows toward the position facing the downstream nozzle hole in the swirl flow direction, the injection timing of the subsequent main injection In other words, by adjusting the interval between the pre-injection and the main injection, the fuel injected by the pre-injection and the fuel injected by the main injection can be prevented from being combined. .

  More specifically, the case where the swirl flow makes one rotation in the circumferential direction in the cylinder until the piston 1b reaches the top dead center from the bottom dead center (until the crank angle moves 180 °). Think. That is, the swirl ratio is “2”. Further, consider a case where the number of injection holes of the injector 32 is “10”.

  In this case, if the interval between the pre-injection and the main injection is less than 36 ° (crank angle of 18 °) in the circumferential direction in the cylinder, the fuel injected by the pre-injection and the fuel injected by the main injection overlap. It can be made not to match.

  By preventing the fuel injected by the pre-injection from overlapping with the fuel injected by the main injection in this way, most of the fuel injected by the pre-injection can contribute to the in-cylinder preheating. (Pre-injection can be a preheating term). For this reason, it becomes possible to start the combustion of the fuel injected by the main injection by making the maximum use of the amount of heat generated by the combustion of the fuel injected by the pre-injection.

-Fuel injection amount learning control-
Next, fuel injection amount learning control for adjusting the fuel injection amount from the injector 32 will be described.

  Variations in fuel injection amount (individual variation) due to individual differences in the fuel supply system and changes in fuel injection amount over time, that is, individual differences in injectors 32 (injection amount variation) and individual differences in sensors (sensor output Variations) and changes in the characteristics of the injector 32 over time (deterioration of the injector 32) are caused by the target injection amount (for example, the target pre-injection amount) calculated by the ECU 20 and the actual injection amount (for example, the actual pre-injection amount). A deviation from the injection amount). If such a deviation occurs, an appropriate injection amount cannot be obtained.

  For example, in a situation where the actual pre-injection amount deviates significantly from the target pre-injection amount, proper preheating cannot be performed, so that increase in combustion noise and increase in PM (Pattern Matter) emission amount during execution of main injection. This may cause engine misfire and the like. Not only that, but also with this deviation in the fuel injection amount, there is a concern that the drivability deteriorates, white smoke is generated in the exhaust, and the fuel consumption rate deteriorates. For this reason, the fuel injection amount learning operation described below is performed. Hereinafter, the fuel injection amount learning operation for pre-injection will be described as a representative.

  In the pre-injection, the fuel injection at the target pre-injection amount is executed by appropriately setting the valve opening time of the injector 32 according to the fuel injection pressure. Therefore, in the ROM of the ECU 20, the pre-injection amount and the energization time (valve opening time) to the injector 32 for each of a plurality of (eg, four) fuel pressures (eg, 30 MPa, 60 MPa, 90 MPa, and 120 MPa). A pre-injection amount setting map in which the relationship is stored for each cylinder (for each injector) is stored. That is, according to the pre-injection amount setting map, the fuel pressure (the fuel pressure detected by the fuel pressure sensor 60) is applied to the injector 32 according to the pre-injection amount setting map so that the target pre-injection amount determined according to the engine speed or the like is obtained. Energizing time is required. For example, in a 4-cylinder engine in which learning is performed for each of four stages of fuel pressure, 16 learning values (map values) are stored in the pre-injection amount setting map.

  The pre-injection amount learning operation is performed by appropriately correcting the learning value on the pre-injection amount setting map, so that proper pre-injection can be achieved even if individual variations of the fuel injection system or changes in the injection amount occur over time. This is to enable pre-injection in a quantity.

  Specifically, as this learning operation, a very small amount of fuel equivalent to the pre-injection amount is specified when there is no injection when the command injection amount to the injector 32 becomes zero or less (when the execution condition of the fuel injection amount learning operation is satisfied). (Hereinafter, this fuel injection is referred to as “single injection”), the amount of change in the engine speed associated with this single injection, etc. (engine operation) Recognize the amount of state change. Then, the change amount data (target change amount data) of the engine operation state when the single injection of a predetermined amount is accurately executed is compared with the change amount of the engine operation state when the single injection is actually performed, The learning value of the pre-injection amount setting map is corrected according to the deviation amount (deviation of the actual fuel injection amount with respect to the target fuel injection amount). Such an operation is executed for each fuel pressure and each cylinder on the pre-injection amount setting map so that pre-injection can be performed with an appropriate pre-injection amount regardless of the fuel pressure for all cylinders. I have to.

  In this fuel injection amount learning control, the learning value of the pre-injection amount setting map is corrected so that the target change amount (a target increase amount of engine speed, etc.) is achieved. For this reason, if the fuel type is different, the fuel injection amount required to achieve the target change amount is also different. For example, the fuel with which the engine torque with respect to the actual fuel injection amount can be obtained becomes smaller as the fuel injection amount required to achieve the target change amount.

-Fuel type discrimination operation-
Next, an operation for determining the type of fuel currently used by the engine 1 will be described as an operation characteristic of the present embodiment. This determination operation is performed by “torque measurement operation”, “actual injection amount measurement operation”, and “fuel type determination operation”. Hereinafter, each operation will be described. This fuel type determination operation is performed at the time of fuel injection from the injector 32, and may be performed at the time of executing the single injection described above, or during normal operation of the engine 1 (fuel injection is performed with an injection amount corresponding to the load). May be performed during driving).

(Torque measurement operation)
In the torque measurement operation, a predetermined command injection amount signal (command signal for the valve opening period of the injector 32) is given from the ECU 20 to the injector 32, and the torque output from the engine 1 when fuel is injected from the injector 32 accordingly. A measurement or estimation operation. For example, when the torque measurement operation is performed during the execution of the single injection described above, the torque generated with the execution of the single injection is measured or estimated. Specifically, the torque may be measured using a known torque sensor or the like, or the torque may be estimated from the operating state (engine speed, etc.) of the engine 1. Further, when performing a torque measurement operation during normal operation of the engine 1, the required torque is calculated according to the amount of depression of the accelerator pedal, etc., and fuel injection is performed so as to obtain this required torque. This required torque becomes the torque obtained by the torque measurement operation (output torque measurement or estimation operation by the torque recognition means).

  In this torque measurement operation, only the relationship between the command injection amount signal (command signal for the valve opening period of the injector 32) and the torque output from the engine 1 is known. The relationship cannot be identified. This is because the relationship between the command injection amount signal and the actual injection amount is changed (the learning value is corrected) by the fuel injection amount learning control described above. Therefore, it is necessary to measure the actual fuel injection amount (actual injection amount) corresponding to the torque obtained in this torque measurement operation. This makes it possible to specify the relationship between the actual injection amount and the torque. For this purpose, the actual injection amount measuring operation described below is performed.

(Actual injection amount measurement operation)
The actual injection amount measurement operation measures or estimates the fuel injection amount actually injected from the injector 32 when a predetermined command injection amount signal (command signal for the valve opening period of the injector 32) is given from the ECU 20 to the injector 32. It is an operation to do. Specifically, the actual injection is based on the fuel pressure detected by the fuel pressure sensor 60 provided in the vicinity of the fuel inlet of the injector 32 and the valve opening period of the injector 32 indicated by the indicated injection amount signal. A quantity is calculated. That is, based on the fuel pressure information detected by the fuel pressure sensor 60, the fuel injection amount per unit time when the injector 32 is opened is calculated, and the injector 32 instructed by the command injection amount signal is calculated. The actual injection amount is calculated by multiplying the valve opening period (measurement or estimation operation of the actual injection amount by the actual injection amount recognition means).

  Since the fuel pressure sensor 60 is provided in the vicinity of the fuel inlet of the injector 32, there is a slight difference from the fuel pressure in the vicinity of the injection hole of the injector 32. For example, when fuel injection is started, the fuel pressure starts to drop in the vicinity of the injection hole of the injector 32 simultaneously with the start of the fuel injection, whereas the fuel introduction of the injector 32 provided with the fuel pressure sensor 60 is introduced. In the vicinity of the mouth, the fuel pressure begins to drop with a slight delay (delay in the drop in detected fuel pressure). For this reason, taking into account this difference (the delay in the drop in fuel pressure in the vicinity of the fuel inlet of the injector 32), the fuel pressure detected by the fuel pressure sensor 60 is multiplied by a predetermined correction coefficient, An accurate actual injection amount can be calculated.

  Further, when the fuel pressure sensor 60 is disposed in the vicinity of the injection hole of the injector 32, there is almost no delay in the drop of the detected fuel pressure. In this configuration, the fuel pressure is corrected by the correction coefficient. Is no longer needed.

  The fuel pressure sensor 60 is not limited to be disposed in the vicinity of the fuel inlet of the injector 32 or in the vicinity of the injection hole of the injector 32 but may be located downstream of the fuel outlet of the common rail 34. In this case, as the fuel pressure sensor 60 is located closer to the fuel outlet of the common rail 34, the delay in the drop in the detected fuel pressure increases, so the correction coefficient is set larger.

(Fuel type determination operation)
The fuel type determination operation is an operation for determining the type of fuel based on the torque of the engine 1 obtained by the torque measurement operation and the actual fuel injection amount obtained by the actual injection amount measurement operation.

  Specifically, the ROM of the ECU 20 stores in advance a map (hereinafter referred to as a fuel type determination map) regarding the correlation between the actual fuel injection amount, the engine torque, and the fuel type. The fuel type is determined by applying the obtained engine torque and the actual fuel injection amount obtained by the actual injection amount measuring operation to the fuel type determination map (by the fuel type determination means). Fuel type discrimination operation).

  FIG. 4 shows an example of the fuel type determination map. In this fuel type determination map, six types of fuels, fuel A to fuel F, can be determined based on the engine torque and the actual fuel injection amount.

  In this fuel type discrimination map, the fuel type that can obtain a large engine torque even if the actual fuel injection amount is relatively small is defined as fuel A, and the fuel torque increases from the fuel B as the increasing rate of the engine torque with respect to the actual fuel injection amount decreases. F is assigned in order. The broken line α in FIG. 4 shows the relationship between the actual fuel injection amount and the engine torque in the cetane number 58 fuel, and the broken line β shows the relationship between the actual fuel injection amount and the engine torque in the cetane number 45 fuel. (Both are the relationship between the actual fuel injection amount and the engine torque in a low temperature state).

  FIG. 5 shows physical property values of biodiesel fuel (for example, derived from vegetable oil), light oil, and rapeseed oil as examples of diesel fuel. According to FIG. 5, the flash point becomes higher in the order of light oil, biodiesel fuel, and rapeseed oil. The cetane number increases in the order of rapeseed oil, biodiesel fuel, and light oil. These serve as indices indicating the ease of fuel ignition.

  The relationship between the actual fuel injection amount of these diesel fuels and the engine torque on the fuel type discrimination map shown in FIG. 4 is that light oil (cetane number 57) corresponds to fuel B, and biodiesel fuel (cetane number 55.3) It corresponds to fuel C, and rapeseed oil (cetane number 37.6) corresponds to fuel E.

  As specific fuel type determination operation, these are obtained by fitting the torque obtained by the torque measurement operation and the actual fuel injection amount obtained by the actual injection amount measurement operation to the fuel type determination map. It is determined which of the fuel A to fuel F the relationship between the torque and the actual fuel injection amount corresponds to. For example, when the fuel is light oil, the relationship between the torque and the actual fuel injection amount corresponds to the fuel B in FIG. 4, and when the fuel is biodiesel fuel, the torque and the actual fuel are The relationship with the injection amount corresponds to the fuel C in FIG. 4, and when the fuel is rapeseed oil, the relationship between the torque and the actual fuel injection amount corresponds to the fuel E in FIG. .

  In this way, in the fuel type determination operation, the type of fuel currently used by the engine 1 can be determined from the relationship between the actual fuel injection amount and the engine torque.

-Pre-injection operation according to fuel type-
Next, the pre-injection operation corresponding to the fuel type determined by the fuel type determination operation will be described.

  As described above, the ignitability and the magnitude of the engine torque with respect to the actual fuel injection amount differ depending on the fuel type. For example, light oil has higher ignitability than the other two fuels (biodiesel fuel and rapeseed oil), and a large engine torque with respect to the actual fuel injection amount. In contrast, rapeseed oil has lower ignitability than the other two fuels (light oil and biodiesel fuel), and the engine torque relative to the actual fuel injection amount is small.

  Considering this, at the time of executing the pre-injection, the fuel injection start timing and the fuel injection amount (fuel injection period) are changed to those suitable for the fuel type.

  Specifically, the fuel injection start timing is set later for the fuel with higher ignitability (shifted to the retarded angle side), and the fuel injection amount is decreased as the engine torque with respect to the actual fuel injection amount is increased (the fuel injection period). (Short). That is, in the case of the above three types of fuels, when the same preheat amount is obtained by pre-injection, the fuel injection start timing is set to a more retarded side in the order of rapeseed oil, biodiesel fuel, and light oil, and the fuel injection amount is The number is set to be smaller (adjustment operation of the injection amount and injection timing of the sub injection by the sub injection control means).

  FIG. 6 is a fuel injection start timing setting map for setting the fuel injection start timing. FIG. 6A is a fuel injection start timing setting map selected when the fuel being used is light oil. FIG. 6B is a fuel injection start timing setting map selected when the fuel being used is biodiesel fuel. FIG. 6C is a fuel injection start timing setting map that is selected when the fuel being used is rapeseed oil.

  As can be seen from these figures, the fuel injection start timing is set later for the fuel with higher ignitability (shifted to the retard side). Further, the lower the in-cylinder temperature before execution of pre-injection (for example, estimated from the cooling water temperature detected by the cooling water temperature sensor 52), the longer the time from when pre-injection starts until the fuel ignites. Since it takes a long time, even with the same type of fuel, the lower the in-cylinder temperature, the earlier the fuel injection start timing is set (shifted to the advance side).

  FIG. 7 is a fuel injection amount setting map for setting the fuel injection amount from the injector 32. FIG. 7A is a fuel injection amount setting map that is selected when the fuel being used is light oil. FIG. 7B is a fuel injection amount setting map selected when the fuel being used is biodiesel fuel. FIG. 7C is a fuel injection amount setting map selected when the fuel being used is rapeseed oil.

  As can be seen from these figures, the fuel injection amount is set to be smaller as the engine torque is larger than the actual fuel injection amount (the fuel injection period is shortened). Further, the larger the required preheating amount in the pre-injection, the larger the fuel injection amount is set for the same type of fuel.

  The pre-injection operation according to the fuel type described above is not limited to that performed according to the fuel injection start timing setting map or the fuel injection amount setting map for each fuel, but the fuel injection start timing (the above formula (3) is calculated by calculation). When calculating the fuel injection start timing) or when setting the fuel injection amount, change the correction coefficient used for the calculation according to the fuel type and perform pre-injection according to the fuel type Also good.

-Main injection operation according to fuel type-
In the main injection, as in the case of the pre-injection operation described above, the fuel injection start timing is set later for fuel with higher ignitability, and the fuel injection amount is set lower for fuel that can obtain a larger engine torque relative to the actual fuel injection amount. To do. That is, in the case of the above three types of fuel, when obtaining the same amount of torque by main injection, the fuel injection start timing is set to the more retarded side in the order of rapeseed oil, biodiesel fuel, and light oil, and the fuel injection amount is I try to set it less.

  In the main injection operation corresponding to the fuel type, as in the case of the pre-injection operation described above, the main injection is performed according to the fuel injection start timing setting map for main injection and the fuel injection amount setting map for main injection for each fuel type. The fuel injection is set. The fuel injection start timing is not limited to that performed according to the fuel injection start timing setting map or the fuel injection amount setting map for each fuel, but by calculation (when the fuel injection start timing is calculated using the above equation (4)). When the fuel injection amount is set, the correction coefficient used for the calculation may be changed according to the fuel type to perform the main injection according to the fuel type.

  FIG. 8B shows fuel injection patterns of pre-injection and main injection when the above three types of fuel are used. Here, in order to facilitate understanding, description will be made assuming that substantially the entire amount of fuel injected by the pre-injection contributes to preheating in the cylinder.

A one-dot chain line in FIG. 8B is a fuel injection pattern when the fuel is rapeseed oil. A two-dot chain line is a fuel injection pattern when the fuel is biodiesel fuel. The solid line shows the fuel injection pattern when the fuel is light oil (FIG. 8 (b) shows the case where the fuel injection end timings coincide with each other). In this way, the fuel injection start timing is set later for fuel with higher ignitability, and the fuel injection amount is set lower for fuel that provides a larger engine torque with respect to the actual fuel injection amount.

  In this way, by changing the fuel injection pattern of the pre-injection and the main injection according to the fuel type, an ideal combustion mode as shown in FIG. Can be obtained. That is, as described above, the timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection becomes maximum, the combustion start timing of the fuel injected by the main injection, and the piston 1b reciprocating in the cylinder are compressed. It becomes possible to substantially match the timing of reaching the dead point. Further, as the heat generation rate waveform in the main injection, the heat generation rate has a maximum value (peak value) at a predetermined piston position after compression top dead center (for example, at 10 ° after compression top dead center (ATDC 10 °)). (Highly efficient fuel injection control operation by the fuel injection control means).

  By performing fuel injection with such a fuel injection pattern, the fuel injected by the pre-injection is utilized to the maximum extent regardless of the fuel type, generating the necessary and sufficient amount of heat generation, and the cylinder is preheated appropriately. Will be. That is, the combustion of the fuel injected by the main injection can be started by making the maximum use of the amount of heat generated by the combustion of the fuel injected by the pre-injection. For example, the fuel injection timing of the pre-injection is set at a timing of 10 ° before the compression top dead center (BTDC) of the piston 1b in the case of rapeseed oil, and before the compression top dead center of the piston 1b in the case of biodiesel fuel ( (BTDC) is set at a timing of 9 °, and in the case of light oil, it is set at a timing of 8 ° before compression top dead center (BTDC) of the piston 1b. As a result, the timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection is maximized substantially coincides with the timing at which the piston 1b reaches the compression top dead center.

  In order to execute the pre-injection at such timing, the heat generation rate due to the combustion of the fuel injected by the pre-injection using the engine speed, the accelerator opening (engine load), the coolant temperature, etc. as parameters in advance through experiments or the like The execution timing of the pre-injection is mapped so that the timing at which becomes the maximum substantially coincides with the timing at which the piston 1b reaches the compression top dead center, and the above-described fuel injection start timing setting map is stored in the ROM. And when performing pre-injection, the execution timing is set with reference to this map, and pre-injection is executed. Thereby, the timing at which the heat generation rate due to the combustion of the fuel injected by the pre-injection is maximized substantially coincides with the timing at which the piston 1b reaches the compression top dead center. In other words, even if any fuel is used, the in-cylinder preheating amount by the pre-injection can be obtained equally, and as a result, the combustion start timing of the main injection can be set optimally.

  Similarly, the combustion start timing of the fuel injected in the main injection is determined by the piston 1b using the engine speed, the accelerator opening (engine load), the coolant temperature, the fuel injection amount in the pre-injection, and the like as parameters. The execution timing of the main injection that substantially coincides with the timing at which the compression top dead center is reached is mapped, and the above-described fuel injection amount setting map is stored in the ROM. For example, the fuel injection timing of the main injection is set to 4 ° before the compression top dead center (BTDC) of the piston 1b in the case of rapeseed oil, and before the compression top dead center of the piston 1b in the case of biodiesel fuel ( (BTDC) is set to a timing of 3 °, and in the case of light oil, it is set to a timing of 2 ° before the compression top dead center (BTDC) of the piston 1b. And when performing main injection, the execution timing is set with reference to this map, and main injection is performed. Thereby, the combustion start timing of the fuel injected by the main injection substantially coincides with the timing at which the piston 1b reaches the compression top dead center.

  Since the preheating amount in the cylinder can be adjusted by executing the pre-injection according to the fuel type as described above, even if the combustion start timing in the main injection coincides with each fuel (the main injection in any fuel). Even if the combustion start timings in FIG. 8 are matched, it is possible to obtain the same heat release rate waveform as in FIG. 8A by appropriately adjusting the fuel injection mode of the pre-injection according to the fuel type. is there.

  In FIG. 8, the injection end timings of the pre-injections in the respective fuels coincide with each other. Further, the injection end timings of the main injection are also coincident with each other. The present invention is not limited to this, and the injection end timing may be different from each other in order to obtain a necessary fuel injection amount for each fuel.

  For example, when the fuel is less ignitable than light oil and the engine torque obtained with respect to the actual fuel injection amount is significantly smaller than light oil, the pre-injection injection end timing and the main injection Both the injection end timings are set to the retard side with respect to the injection end timing of the pre-injection and the injection end timing of the main injection in the case of light oil. FIG. 9B shows fuel injection patterns of pre-injection and main injection in this case. The solid line in FIG. 9B is a fuel injection pattern when the fuel is light oil, and the alternate long and short dash line is lower in ignitability than light oil and the engine torque obtained for the actual fuel injection amount is significantly larger than that of light oil. This is a fuel injection pattern of a very small fuel (alternative fuel I in the figure).

  In addition, in the case of fuel having low ignitability as compared with light oil, and the engine torque obtained with respect to the actual fuel injection amount is larger than that of light oil, pre-injection injection end timing and main injection end-of-injection Both timings are set to the advance side with respect to the injection end timing of the pre-injection and the injection end timing of the main injection in the case of light oil. FIG. 10B shows fuel injection patterns of pre-injection and main injection in this case. The solid line in FIG. 10B is a fuel injection pattern when the fuel is light oil, and the alternate long and short dash line is lower in ignitability than light oil and the engine torque obtained for the actual fuel injection amount is larger than that in light oil. It is a fuel injection pattern of fuel (alternative fuel II in the figure).

  As described above, according to the present embodiment, based on the relationship between the actual fuel injection amount and the torque, the type of fuel currently used can be determined with high accuracy, and the determined fuel Can be realized. For this reason, it becomes possible to improve exhaust emission and improve engine performance regardless of the type of fuel. It is also possible to reduce combustion noise, improve drivability, prevent the generation of white smoke in the exhaust, and improve the fuel consumption rate.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (4-cylinder) diesel engine has been described. The present invention is not limited to this, and can be applied to a diesel engine having any number of cylinders such as a six-cylinder diesel engine. Further, the present invention is not limited to a diesel engine but can be applied to other internal combustion engines such as a gasoline engine. Furthermore, the engine to which the present invention is applicable is not limited to an automobile engine.

  Moreover, the said embodiment demonstrated the case where the fuel-injection start timing and fuel-injection amount (fuel-injection period) of pre-injection and main injection were changed according to a fuel type. The present invention is not limited to this, and the fuel injection start timing and the fuel injection amount (fuel injection period) may be changed according to the fuel type for the pilot injection, the after injection, and the post injection.

  Further, in the above-described embodiment, the engine 1 to which the piezo injector 32 that changes the fuel injection rate by changing to the fully opened valve state only during the energization period has been described. However, the present invention applies the variable injection rate injector. Application to engines is also possible.

  Further, the fuel pressure sensor 60 may be disposed for all the injectors 32 or only for one injector 32.

  As a means for measuring the actual injection amount of the fuel injected from the injector 32, a flow sensor is provided in the middle of the pipe connecting the common rail 34 and the injector 32, and the fuel flow detected by the flow sensor is measured. You may make it do.

  Further, the means for measuring or estimating the output torque of the engine 1 may be configured to detect the in-cylinder pressure, and the output torque may be estimated from the in-cylinder pressure.

  In the above embodiment, both the fuel injection start timing and the fuel injection amount (fuel injection period) are changed according to the fuel type. However, the present invention is not limited to this, and changing only one of the fuel injection start timing and the fuel injection amount is also within the scope of the technical idea of the present invention.

  The present invention is applicable to accurate determination of the type of fuel used in a common rail in-cylinder direct injection multi-cylinder diesel engine mounted on an automobile, and fuel injection control using the determination result.

1 engine (internal combustion engine)
1a Cylinder 1b Piston 3 Combustion chamber 32 Injector (fuel injection valve)
34 Common rail (accumulation vessel)
60 Fuel pressure sensor (fuel pressure detection means)

Claims (5)

A fuel type discriminating device for discriminating the type of fuel injected into a combustion chamber from a fuel injection valve to which fuel is supplied from a pressure accumulating vessel for accumulating and holding high pressure fuel ,
A fuel pressure detecting means for detecting fuel pressure is disposed downstream of the fuel outlet of the pressure accumulating vessel,
Taking into account the fuel pressure detected by the fuel pressure detecting means, a delay time from when the fuel injection from the fuel injection valve is started until the fuel pressure at the position where the fuel pressure detecting means is disposed starts to drop is taken into consideration. and the fuel pressure after correction is calculated by multiplying the correction coefficient, based on the injection period of fuel injection to be executed by the fuel pressure, to estimate the actual injection quantity of fuel injected from the fuel injection valve An actual injection amount recognition means;
Torque recognition means for measuring or estimating an output torque of the internal combustion engine generated by combustion of fuel injected from the fuel injection valve;
And the actual injection quantity of estimated fuel by the said actual injection quantity recognizing means, based on the output torque of the measured or estimated engine by the upper Symbol torque recognition means, injected into the combustion chamber from the fuel injection valve A fuel type discriminating means for discriminating the type of fuel that has been
The fuel type determination device for an internal combustion engine, wherein the correction coefficient is set to be larger as the fuel pressure detection means is disposed closer to the fuel outlet of the pressure accumulating vessel . The fuel type discrimination device for an internal combustion engine according to claim 1,
When the execution condition for the fuel injection amount learning operation is satisfied, fuel injection is performed in the specified cylinder from the fuel injection valve according to the instructed injection period, and the target fuel injection is performed based on the change in the operating state of the internal combustion engine accompanying the fuel injection. The fuel injection amount learning operation for obtaining a learning value based on the deviation of the actual fuel injection amount with respect to the amount is executed,
The torque recognizing means is configured to measure or estimate an output torque of the internal combustion engine obtained by executing fuel injection corresponding to the command injection period based on a learning value obtained by the fuel injection amount learning operation. A fuel type discrimination device for an internal combustion engine. In a fuel injection control device for a compression ignition type internal combustion engine capable of performing at least main injection and sub-injection performed prior to the main injection as a fuel injection operation from the fuel injection valve,
A sub-injection control means for adjusting at least one of the injection amount and the injection timing of the sub-injection according to the type of fuel determined by the fuel type determination means in the fuel type determination device according to claim 1 is provided. A fuel injection control device for an internal combustion engine. The fuel injection control device for an internal combustion engine according to claim 3,
The timing at which the heat generation rate due to the combustion of the fuel injected by the sub-injection is maximized, the combustion start timing of the fuel injected by the main injection, and the timing at which the piston reciprocating in the cylinder reaches the compression top dead center And a fuel injection control means capable of executing a high-efficiency fuel injection control operation for controlling the injection timing and the injection amount of each of the fuel injections so as to coincide with each other. . In the fuel injection control device for an internal combustion engine according to claim 3 or 4,
The fuel injection control means includes a sub-injection execution timing and a main injection execution timing so that the fuel injected by the main injection does not overlap the fuel injected by the sub-injection and flowing along the swirl flow in the cylinder. And a fuel injection control device for an internal combustion engine.

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