JP4367472B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine provided with an EGR device that recirculates a part of exhaust gas as EGR gas in the engine.

In order to reduce the combustion temperature of the engine and reduce harmful emissions such as NO _x, a technique for recirculating a part of the engine exhaust gas to the engine combustion chamber as EGR gas is known. Further, it is known that even in a diesel engine that normally performs lean air-fuel ratio operation, harmful emissions in exhaust gas can be reduced by supplying a relatively large amount of EGR gas to the combustion chamber.

However, EGR gas has a large effect on combustion. Particularly in a diesel engine, after the start of fuel injection, the ignition delay time until the injected fuel starts combustion has a large effect. For this reason, if EGR gas is excessively supplied to the combustion chamber, the combustion state of the engine deteriorates, resulting in deterioration of engine performance and deterioration of exhaust gas properties.
On the other hand, when the amount of EGR gas is small, the harmful emission suppressing effect is lowered. For this reason, it is necessary to control the amount of EGR gas to an appropriate amount according to the operating state of the engine.

  However, precise control of the EGR gas amount has not been performed in the past. In particular, in a diesel engine, the opening degree of the EGR valve that controls the EGR gas flow rate is determined by the engine speed and the accelerator opening degree (depressing amount of the accelerator pedal). Normally, open loop control was performed to a value determined from

  However, in recent years, there has been a need to precisely control the EGR gas flow rate to an optimum value due to the requirement for exhaust gas regulations and noise reduction. When precise EGR control is performed as described above, sufficient accuracy cannot be obtained by open loop control based on the engine speed and the accelerator opening as in the prior art. In a gasoline engine, for example, an air-fuel ratio sensor can be arranged in the engine exhaust passage, and the EGR gas amount can be controlled based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor. In an engine that may be operated in a state in which the air-fuel ratio is extremely lean, the detection accuracy of the air-fuel ratio sensor is low, so that controlling the EGR gas amount based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor causes a large error. There is a problem.

  On the other hand, the combustion chamber pressure of the engine is detected, a characteristic value representing the combustion state of the engine is calculated based on the detected combustion pressure, and the EGR gas flow rate is optimized using this characteristic value. There has been proposed a control device that performs feedback control of the signal.

An example of such a control device for an internal combustion engine is disclosed in Patent Document 1.
The device of Patent Document 1 is not related to a diesel engine, but is related to a gasoline engine. However, the heat generation rate in the combustion chamber is used as a combustion parameter representing the combustion state of the engine so that the heat generation rate becomes a predetermined pattern. In addition, it controls the EGR gas flow rate, fuel injection timing, fuel injection amount, ignition timing, and the like.

  That is, in the apparatus of Patent Document 1, an in-cylinder pressure sensor that detects an engine combustion chamber pressure is arranged in a cylinder, and heat generation at each crank angle is performed based on the detected actual combustion chamber pressure (combustion pressure) and the crank angle. Calculating the rate, and feedback-controlling the EGR gas amount, ignition timing, fuel injection timing, etc. so that the change pattern of the heat release rate with respect to the crank angle matches the ideal change pattern determined in advance according to the operating conditions Thus, optimum combustion is obtained.

JP 2000-54889 A JP-A-11-148410 JP-A-3-233162

  In the apparatus of Patent Document 1, focusing on the heat generation rate as a parameter related to combustion, a heat generation rate pattern in an actual operation state is calculated, and the calculated heat generation rate pattern is a predetermined ideal change pattern. The ignition timing, fuel injection amount, etc. are feedback controlled so that The apparatus of Patent Document 1 relates to a gasoline engine. For example, in a diesel engine as well, by providing an in-cylinder pressure sensor, a heat generation rate pattern is calculated based on the output of the in-cylinder pressure sensor, and the calculated heat generation is calculated. It is also conceivable to perform feedback control of the fuel injection timing and the fuel injection amount so that the rate pattern becomes a predetermined heat generation rate pattern.

  However, in the apparatus of Patent Document 1, feedback control of the combustion state is performed using only the heat generation rate in the combustion chamber as a parameter representing the combustion state of the engine. In the apparatus of Patent Document 1, a gasoline engine is used. In the gasoline engine, premixed gas is normally formed by port injection, and the combustion pattern such as ignition and combustion does not change greatly. For this reason, even if only the heat generation rate is used as a parameter representing the combustion state, no large error occurs.

  However, in a diesel engine, for example, the combustion pattern may change greatly depending on the EGR gas amount, fuel injection timing, etc., and it is not always appropriate to perform feedback control such as the EGR gas amount and fuel injection only by the heat generation rate. Absent.

In addition, in order to perform control based on the heat generation rate pattern as in the apparatus of Patent Document 1, for example,
dQ / dθ = (κ · P · (dV / dθ) + V (dP / dθ)) / (κ−1)
The heat generation rate dQ / dθ is expressed as a function of θ in the form of (P is the actually detected pressure in the combustion chamber, V is the actual cylinder volume determined from the crank angle, and κ is the specific heat ratio). It is necessary to perform complicated calculations such as For this reason, the problem that the calculation load of a control circuit increases arises.

  In general, since the detection of the crank angle is not very accurate, there is a problem that an error is likely to occur when the crank angle is frequently used as in the above formula for calculating the heat generation rate. For this reason, if the EGR gas amount, the fuel injection amount, the timing, and the like are controlled based on the heat generation rate calculated using the above calculation formula, the combustion state may be deteriorated due to a control error.

  In view of the above problems, the present invention provides an engine in which the EGR flow rate, fuel injection amount, fuel injection timing, and the like of an internal combustion engine are feedback controlled according to the combustion state of the engine to improve engine performance and exhaust properties. It is an object of the present invention to provide a control device for an internal combustion engine that can perform accurate control while suppressing an increase in calculation load of a control circuit without requiring calculation of the heat generation rate of the control circuit.

  According to the first aspect of the present invention, a fuel injection valve that injects fuel into the engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and a pressure in the engine combustion chamber are detected. A control apparatus for an internal combustion engine comprising an in-cylinder pressure sensor that performs combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period based on a pressure in the combustion chamber detected by the in-cylinder pressure sensor A combustion timing calculating means for calculating a pressure characteristic value, and the EGR gas amount so that a combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means by controlling the EGR device becomes a predetermined target value. The combustion timing calculation means includes a combustion chamber volume V determined from a combustion chamber pressure P detected by the in-cylinder pressure sensor and a crank angle θ. Based on the product PV value, a time ΔT until the PV value reaches the maximum value PVmax after the start of fuel injection from the fuel injection valve is calculated as a combustion pressure characteristic value corresponding to the combustion timing, and the control The means adjusts the amount of EGR gas so that the ΔT becomes a predetermined target value, the target value is determined according to the engine speed and the accelerator opening, and the internal combustion engine is a compression ignition engine The control means further causes the engine to perform fuel injection at a later stage of the compression stroke to perform combustion with a large excess air ratio, advance the fuel injection timing from the normal combustion mode, and set the EGR gas amount. The engine is operated by switching to the increased low-temperature combustion mode, and the EGR gas amount control based on the value of ΔT is performed during the low-temperature combustion mode operation of the engine. When switching to the low-temperature combustion mode, the fuel injection timing is continuously changed from the injection timing in the normal combustion mode to the target fuel injection timing in the low-temperature combustion mode over a predetermined transition time. There is provided a control device for an internal combustion engine that performs the EGR gas amount control based on the value of ΔT calculated using the target fuel injection timing in the low-temperature combustion mode after switching instead of the fuel injection timing.

That is, in the first aspect of the invention, the combustion pressure characteristic value corresponding to the combustion timing is calculated based on the pressure in the combustion chamber detected by the in-cylinder pressure sensor. Here, the combustion timing includes one or both of an ignition delay time and a combustion period.
Further, the combustion pressure characteristic value referred to here is a value corresponding to one or both of the ignition delay period and the combustion period calculated based on the pressure in the combustion chamber, for example, a value such as ΔT, Δtc, Δtd described later. is there.

  The ignition delay period and the combustion period show a close correspondence with the EGR rate (the ratio of EGR gas in the amount of gas sucked into the cylinder, that is, (EGR gas amount / (new air amount + EGR gas amount))). It is known. That is, as the EGR rate increases, combustion is less likely to occur, so the ignition delay time becomes longer, and the combustion speed of the air-fuel mixture decreases, so the combustion period (that is, the period from the start to the end of combustion) Becomes longer.

  The present invention focuses on the above, and the amount of EGR gas (EGR rate) so that the actual ignition delay period and / or the combustion period (for example, the sum of the ignition delay period and the combustion period) matches the optimum value obtained in advance. ) Is feedback controlled. As a result, the EGR gas amount can be accurately controlled to the optimum amount.

  In addition, it is difficult to directly measure the ignition delay period, the combustion period, and the like during actual engine operation. Therefore, in the present invention, based on the pressure in the combustion chamber, a value (combustion pressure characteristic value) that can be calculated by simple calculation corresponding to the ignition delay period and the combustion period is calculated. The amount of EGR gas is controlled to be a value.

  As a result, the EGR gas amount is controlled to an optimal value easily and accurately without increasing the calculation load of the control circuit.

  In the present invention, based on the time ΔT from the start of fuel injection until the value of the product PV of the combustion chamber pressure P detected by the in-cylinder pressure sensor and the combustion chamber volume V determined from the crank angle θ takes the maximum value PVmax. Feedback control of the EGR gas amount.

  Although there are various parameters related to the combustion state calculated from the combustion pressure (in-cylinder pressure), the timing at which the maximum value PVmax of the product PV of the pressure P in the combustion chamber and the cylinder volume occurs is the combustion stroke of the cylinder. Corresponds to the time when combustion is completed. For this reason, the time ΔT from the start of fuel injection to the occurrence of PVmax is the time until the fuel injected by the engine starts combustion and the time from the start of combustion to completion, ie, the ignition delay period and the combustion period (Hereinafter referred to as “combustion completion time”).

  As described above, the ignition delay time and the combustion period show a close correspondence with the EGR rate of the engine (the ratio of EGR gas in the amount of gas sucked into the cylinder), and therefore, the combustion pressure corresponding to the combustion timing described above. Combustion completion time ΔT is calculated as a characteristic value, and the EGR gas amount (EGR rate) is feedback-controlled so that ΔT matches an optimal value obtained in advance. Thus, the EGR gas amount is accurately controlled to an optimal value without increasing the calculation load of the control circuit.

  The combustion completion time ΔT may be expressed as time (milliseconds) or may be expressed as a crank rotation angle (CA).

  Furthermore, in the present invention, the target values of the combustion pressure characteristic values such as ΔT, ΔPVmax, and θmax described above are the accelerator opening (the operation amount of the accelerator pedal, that is, the depression amount of the accelerator pedal by the driver is referred to as “accelerator opening”). ) And the engine speed.

  In general, the accelerator opening and the engine speed are used as values representing the operating state of the engine. By setting the target value of each combustion pressure characteristic value according to the accelerator opening and the engine speed, the EGR gas amount, fuel injection amount, and fuel injection timing that give the optimal combustion state for each engine operating state can be simplified. Can be set to

  In the present invention, a compression ignition engine is used as the internal combustion engine. By applying the above-described control to the compression ignition engine, it is possible to accurately control the EGR gas amount in the compression ignition engine.

  Furthermore, in the present invention, an engine that operates by switching between the normal combustion mode and the low temperature combustion mode is used, and EGR gas amount control using the combustion pressure characteristic value ΔT is performed during the low temperature combustion mode operation.

In the low-temperature combustion mode, the fuel injection timing is greatly advanced to form a premixed gas in the cylinder, and the EGR gas amount is greatly increased to perform combustion with a low air-fuel ratio, thereby lowering the combustion temperature. is significantly combustion mode to reduce both soot and NO _X in the exhaust Te.

  However, since a large amount of EGR gas is supplied to the combustion chamber in the low-temperature combustion mode, even a slight change in the EGR gas amount (EGR rate) may cause the combustion state to deteriorate abruptly. Sensitivity of changes in combustion state is increased.

  As described above, the EGR gas amount can be controlled to the optimum value very accurately by performing the feedback control of the EGR gas amount using the combustion pressure characteristic value ΔT. For this reason, in the present invention, by performing EGR gas amount control using ΔT, it is possible to easily achieve an appropriate combustion state even in a low-temperature combustion mode that is highly sensitive to changes in the EGR gas amount.

  Further, in the present invention, EGR gas amount control using the combustion pressure characteristic value ΔT is also performed at the time of switching from the normal combustion mode to the low temperature combustion mode.

  However, at the time of switching to the low-temperature combustion mode, so-called smoothing control at the time of transition is performed in which the fuel injection timing is continuously changed over a period of time in order to avoid a shock due to a sudden change in the fuel injection timing.

  In this case, if ΔT is calculated using the actual fuel injection timing (while changing to the target value injection timing) from the start of the transition period, the value of ΔT becomes significantly smaller than the target value, and this is corrected. For this reason, the amount of EGR gas is greatly increased, which causes a problem that combustion at the time of transition becomes unstable.

  Therefore, in the present invention, during the transition period, ΔT is calculated using the fuel injection timing after the transition to the low temperature combustion mode is completed instead of the actual fuel injection timing (that is, the target value of the fuel injection timing in the low temperature combustion mode). I am trying to calculate.

  As a result, the value of ΔT during the transition to the low-temperature combustion mode is calculated as a relatively large value, the EGR gas amount can be appropriately feedback controlled during the transition period, and combustion is not caused by an excessive increase in the EGR gas amount. Stability is prevented from occurring.

  According to the second aspect of the present invention, the combustion timing calculation means further calculates a combustion chamber pressure determined by a compression of the piston and a combustion chamber volume determined from a crank angle when it is assumed that no combustion has occurred in the combustion chamber. The product PVbase is calculated, and the difference ΔPVmax between PVmax and PVbase is calculated using the value of PVbase at the crank angle θmax at which the PV becomes the maximum value PVmax. The control means further calculates the value of ΔPVmax and θmax. The control apparatus for an internal combustion engine according to claim 1, wherein the control unit controls the fuel injection amount from the fuel injection valve and the fuel injection timing so that each of the predetermined target values is obtained.

  That is, in the invention of claim 2, in addition to the EGR control based on ΔT, the fuel injection amount and the fuel injection timing are feedback controlled based on the values of ΔPVmax and θmax.

  The product PV of the pressure P in the combustion chamber and the volume V of the combustion chamber is a value corresponding to the sum of the energy generated by combustion and the energy by piston compression. Therefore, the PV value (PVbase) by only piston compression is subtracted from the maximum value PVmax. The value ΔPVmax is a value corresponding to the amount of fuel supplied to the combustion chamber, that is, the fuel injection amount.

  Further, θmax is a value corresponding to the point in time when the combustion in the combustion chamber ends, and therefore changes according to the fuel injection timing if other conditions (for example, EGR) are constant.

  For this reason, for example, by performing feedback control of the fuel injection amount so that ΔPVmax becomes a predetermined target value and the fuel injection timing so that θmax becomes a predetermined target value, it is added to the EGR gas amount. Thus, the fuel injection amount and the fuel injection timing can be accurately controlled without increasing the calculation load of the control circuit.

According to the third aspect of the invention, a fuel injection valve that injects fuel into the engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and a pressure in the engine combustion chamber are detected. A control apparatus for an internal combustion engine comprising an in-cylinder pressure sensor that performs combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period based on a pressure in the combustion chamber detected by the in-cylinder pressure sensor A combustion timing calculating means for calculating a pressure characteristic value, and the EGR gas amount so that a combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means by controlling the EGR device becomes a predetermined target value. The combustion timing calculation means includes a combustion chamber volume V determined from a combustion chamber pressure P detected by the in-cylinder pressure sensor and a crank angle θ. , Based on the value of the PV ^kappa calculated from the specific heat ratio kappa combustion gas, the combustion pressure time Δtd values of the PV ^kappa after starting fuel injection from the fuel injection valve until the minimum value PV ^kappa min There is provided a control device for an internal combustion engine, which is calculated as a characteristic value, and wherein the control means adjusts the EGR gas amount so that the Δtd becomes a predetermined target value.

That is, the combustion pressure characteristic value corresponding to the combustion timing in the invention of claim 3, the value of the fuel injection after the start PV ^kappa from the fuel injection valve is calculated time Δtd until the minimum value PV ^kappa min, this Δtd The EGR gas amount (EGR rate) is adjusted so that becomes a predetermined target value.

As will be described later, PV ^{κ assumes} a constant value if there is no heat in and out of the air-fuel mixture in the cylinder from the gas equation of state. However, since there is actually heat dissipation through the piston and cylinder wall, the value of PV ^κ decreases before combustion starts in the compression stroke. When combustion starts, the value of PV ^κ increases due to the generation of heat.

That the value of this for PV ^kappa starts to increase from the reduced, i.e. when the value of PV ^kappa becomes the minimum value PV ^kappa min is the period when the combustion is started. Therefore, the time Δtd value of the fuel injection after the start PV ^kappa until a minimum value PV ^kappa min, the time to actually burn the fuel injection is started is started, i.e. in correspondence with the ignition delay time Yes.

  As described above, the ignition delay time has a close correlation with the EGR gas amount (EGR rate). Therefore, the time Δtd representing the ignition delay time is calculated as the combustion pressure characteristic value, and the EGR gas amount (EGR rate) is feedback-controlled so that this Δtd matches the optimum value obtained in advance, thereby controlling the control circuit. It is possible to accurately control the EGR gas amount to the optimum value without increasing the calculation load.

  Note that the ignition delay time Δtd may be expressed in time (milliseconds) or in crank rotation angle (CA).

According to the fourth aspect of the present invention, a fuel injection valve that injects fuel into the engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and a pressure in the engine combustion chamber are detected. A control apparatus for an internal combustion engine comprising an in-cylinder pressure sensor that performs combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period based on a pressure in the combustion chamber detected by the in-cylinder pressure sensor A combustion timing calculating means for calculating a pressure characteristic value, and the EGR gas amount so that a combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means by controlling the EGR device becomes a predetermined target value. The combustion timing calculation means includes a combustion chamber volume V determined from a combustion chamber pressure P detected by the in-cylinder pressure sensor and a crank angle θ. , Based on the value of the PV ^kappa calculated from the specific heat ratio kappa combustion gas, the maximum value PV ^kappa max value of the PV ^kappa after starting fuel injection from the fuel injection valve from taking the minimum value PV ^kappa min A control device for an internal combustion engine is provided in which a time Δtc to be taken is calculated as the combustion pressure characteristic value, and the control means adjusts the EGR gas amount so that the Δtc becomes a predetermined target value.

That is, the combustion pressure characteristic value corresponding to the combustion timing in the invention of claim 4, calculates the time Δtc from the value of PV ^kappa is taking the minimum value PV ^kappa min until a maximum value PV ^kappa max, this Δtc The EGR gas amount (EGR rate) is adjusted so that becomes a predetermined target value.

As described above, the value of PV ^κ decreases unless combustion occurs. For this reason, the point at which PV ^κ changes from increase to decrease, that is, the point at which PV ^κ reaches the maximum value is the point at which combustion is completed. Therefore, time Δtc from the value of PV ^kappa becomes the minimum value PV ^kappa min to the maximum value PV ^kappa max time to the end from the start combustion, i.e. corresponding to the combustion period.

  As described above, the combustion period has a close correlation with the EGR gas amount (EGR rate). Therefore, using the combustion period Δtc as the combustion pressure characteristic value, and performing feedback control of the EGR gas amount (EGR rate) so that this Δtc matches the optimal value obtained in advance, the calculation load of the control circuit is increased. In addition, the EGR gas amount can be accurately controlled to the optimum value without performing the above process.

  The combustion period Δtc may be expressed in time (milliseconds) or may be expressed in crank rotation angle (CA).

According to the fifth aspect of the present invention, the fuel injection valve performs pilot injection for injecting a small amount of fuel into the combustion chamber prior to main fuel injection, and the combustion timing calculation means is configured to calculate the value of PV ^κ min. The control apparatus for an internal combustion engine according to claim 3 or 4, wherein the detection of the engine is started after the main fuel injection is started.

That is, in the engine the pilot injection is carried out in the invention of claim 5, the detection of the minimum value PV ^kappa min of PV ^kappa is initiated after the start the main fuel injection.

When pilot injection is performed, combustion of fuel injected by pilot injection occurs prior to main fuel injection. Therefore, it is necessary to distinguish the combustion start timing of main fuel injected fuel from the combustion start timing of pilot fuel injected fuel. EGR control cannot be performed. Usually, the combustion of the pilot-injected fuel is terminated before the start of the main fuel injection. Therefore, the determination of whether the value of PV ^κ is the minimum value, that is, the detection of the value of PV ^κ min is started after the start of the main fuel injection. This makes it possible to accurately detect the ignition timing of main fuel injection.

  According to the invention described in each claim, when the EGR flow rate of the internal combustion engine is feedback controlled in accordance with the combustion state of the engine, the ignition delay period and the combustion period, or the combustion pressure characteristic value closely correlated with these are obtained. By controlling the amount of EGR gas so that these combustion pressure characteristic values become a predetermined target value, it is possible to control the control circuit easily and accurately while suppressing an increase in the calculation load of the control circuit. There is a common effect.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the fuel injection device of the present invention is applied to an automobile diesel engine.

  In FIG. 1, 1 is an internal combustion engine (in this embodiment, a four-cylinder four-cycle diesel engine having four cylinders # 1 to # 4 is used), 10a to 10d are # 1 to # 4 of the engine 1 A fuel injection valve that directly injects fuel into each cylinder combustion chamber is shown. The fuel injection valves 10a to 10d are each connected to a common pressure accumulation chamber (common rail) 3 via a fuel passage (high pressure fuel pipe). The common rail 3 has a function of storing the pressurized fuel supplied from the high-pressure fuel injection pump 5 and distributing the stored high-pressure fuel to the fuel injection valves 10a to 10d via the high-pressure fuel pipe.

  In the present embodiment, an EGR device that recirculates part of the exhaust gas of the engine to each cylinder combustion chamber of the engine is provided. The EGR device includes an EGR passage 33 that connects an engine exhaust passage and an intake passage of the engine or an intake port of each cylinder, and an exhaust gas (EGR gas) flow rate that is disposed in the EGR passage and recirculates from the exhaust passage to the intake passage. And an EGR valve 35 having a function as a flow control valve for controlling. The EGR valve 35 includes an actuator 35a of an appropriate type such as a stepper motor, and the EGR valve opening degree is controlled according to a control signal from the ECU 20 described later.

  1 is an electronic control unit (ECU) that controls the engine. The ECU 20 is configured as a known microcomputer in which a read only memory (ROM), a random access memory (RAM), a microprocessor (CPU), and an input / output port are connected by a bidirectional bus. In this embodiment, the ECU 20 performs fuel pressure control for controlling the discharge amount of the fuel pump 5 to control the common rail 3 pressure to a target value determined according to the engine operating conditions, and in addition to the fuel pressure according to the engine operating state. Fuel injection that controls the injection timing and injection amount of the injection, and feedback-controls fuel injection parameters such as EGR flow rate, fuel injection amount, and injection timing using a combustion pressure characteristic value obtained based on an in-cylinder pressure sensor output to be described later Performs basic control of the engine such as control.

  In order to perform these controls, in this embodiment, the common rail 3 is provided with a fuel pressure sensor 27 for detecting the fuel pressure in the common rail, and the accelerator pedal position (not shown) in the vicinity of the accelerator pedal of the engine 1 is provided. An accelerator opening sensor 21 that detects (a driver's accelerator pedal depression amount) is provided.

  In FIG. 1, reference numeral 23 denotes a cam angle sensor for detecting the rotational phase of the cam shaft of the engine 1, and reference numeral 25 denotes a crank angle sensor for detecting the rotational phase of the crank shaft. The cam angle sensor 23 is disposed near the cam shaft of the engine 1 and outputs a reference pulse every 720 degrees in terms of a crank rotation angle. The crank angle sensor 25 is disposed in the vicinity of the crankshaft of the engine 1 and generates a crank angle pulse at every predetermined crank rotation angle (for example, every 15 degrees).

  Pulse signals from the cam angle sensor 23 and the crank angle sensor 25 are supplied to the ECU 20 and used for calculating the crankshaft rotation phase angle and the engine speed.

  Further, in FIG. 1, 29a to 29d are known in-cylinder pressure sensors which are arranged in the cylinders 10a to 10d and detect the pressure in the cylinder combustion chamber. Each combustion chamber pressure detected by the in-cylinder pressure sensors 29 a to 29 d is supplied to the ECU 20 via the AD converter 30.

  The ECU 20 calculates a combustion pressure characteristic value, which will be described later, based on the cylinder combustion chamber pressure detected by the cylinder pressure sensors 29a to 29d, and based on the combustion pressure characteristic value, calculates an EGR gas amount, a fuel injection amount, a fuel injection timing, and the like. Feedback control.

  Hereinafter, details of feedback control of the EGR gas amount, the fuel injection amount, and the fuel injection timing based on the combustion pressure characteristic value in the present embodiment will be described.

  In the present embodiment, PVGR, θmax, ΔPVmax, and ΔT are used as combustion pressure characteristic values calculated based on the pressure in the combustion chamber detected by the cylinder pressure sensors 29a to 29d, and the EGR gas amount, fuel injection amount, and fuel injection timing are calculated. Perform feedback control.

  FIG. 2 shows the combustion pressure characteristic values PVmax, θmax, ΔPVmax and ΔT used in this embodiment.

  The horizontal axis in FIG. 2 represents the crank angle (CA) from the compression stroke to the expansion stroke of the cylinder, and the vertical axis represents the PV value described later. The horizontal axis indicates the compression top dead center indicated by TDC.

  The PV value in the present embodiment is the product of the combustion chamber pressure at each crank angle detected by the in-cylinder pressure sensors 29a to 29d and the combustion chamber volume (given as a function of the crank angle) V at that crank angle (PV = P XV).

  The solid line in FIG. 2 shows the change in the PV value during actual combustion. As shown in FIG. 2, the PV value increases rapidly with the start of combustion, and decreases rapidly after reaching the maximum value PVmax.

  Since the PV value is the product of pressure and volume, the equation of state of gas PV = MRT (M: number of moles of gas, R: general gas constant (J / mol · K), T: temperature (° K)) ), The value corresponds to the in-cylinder temperature. Further, from the experiment, the timing at which PV reaches the maximum value PVmax (FIG. 2, θmax) corresponds to the time when combustion of the fuel injected in the cylinder ends (strictly, when 90% of the fuel burns). It has been confirmed. Therefore, θmax can be used as an index representing the end of combustion in the cylinder.

  In FIG. 2, θinj indicates the fuel injection start timing from the fuel injection valves (10a to 10d, hereinafter collectively referred to by reference numeral 10). Also, ΔT in FIG. 2 is the combustion completion time defined by the time (crank angle) from the start of fuel injection (θinj) to the end of combustion (θmax). The fuel injected from the fuel injection valve 10 starts to burn after a certain ignition delay time, and the combustion ends after the combustion time determined by various conditions. For this reason, the combustion completion time ΔT (= θmax−θinj) corresponds to the sum of the fuel ignition delay time and the combustion time.

  Also, the dotted line in FIG. 2 represents the change in PV value (PVbase) when no combustion occurs in the cylinder. PVbase represents a compression and expansion of the gas in the cylinder only due to the vertical movement of the piston, and therefore is a symmetrical curve with respect to the top dead center.

  In this embodiment, the difference between the above-described maximum PVmax PV value and the PVbase value at θmax is defined as ΔPVmax.

  The value of PVbase at θmax can be easily calculated from the in-cylinder pressure at the end of the intake stroke and the in-cylinder volume at θmax. However, as described above, the PVbase curve is symmetric with respect to the compression top dead center. For this reason, in the present embodiment, after detecting θmax, ΔPVmax is calculated using the value of PVbase at the compression stroke point (indicated by θmax ′ in FIG. 2) that is symmetric with respect to the top dead center. In the compression stroke before combustion occurs, the PV value and the PVbase value are the same. For this reason, in the present embodiment, the value of ΔPVmax is simply calculated by actually using the PV value at θmax ′ as the PVbase value at θmax.

  Next, the meaning of the combustion pressure characteristic values ΔT, PVmax, θmax, and ΔPVmax will be described.

  As described above, the combustion completion time ΔT, which is the period from the start of fuel injection to θmax, corresponds to the sum of the ignition delay time and the combustion time of the injected fuel. On the other hand, both the ignition delay time and the combustion time are greatly influenced by the EGR rate (the ratio of the amount of EGR gas to the gas sucked into the cylinder), and ΔT increases as the EGR rate increases. Therefore, the combustion completion time ΔT has a close correlation with the in-cylinder EGR rate, and can be used as an index representing the EGR rate.

  Further, the timing θmax at which PVmax occurs correlates with the end timing of combustion, and is greatly related to the combustion state in the cylinder. If the other conditions are the same, the combustion end timing changes according to the fuel injection timing.

  Furthermore, since the value of ΔPVmax is a difference (temperature difference) between the PV value when combustion is not occurring and when combustion is not generated, it is correlated with the amount of fuel combusted in the combustion chamber, that is, the fuel injection amount.

  In the present embodiment, paying attention to the above, the EGR gas amount, the fuel injection timing, and the fuel injection amount are feedback-controlled to the optimum values using ΔT, θmax, and ΔPVmax.

  That is, in the present embodiment, the fuel injection amount that allows the engine to operate in advance by changing the engine operating state (combination of the accelerator opening and the rotational speed) to obtain the optimum combustion state in terms of fuel consumption, exhaust gas properties, etc. Search the fuel injection timing and EGR rate (EGR valve opening), and use these values as the reference values for the fuel injection amount, fuel injection timing, and EGR valve opening in each operating state, and use the accelerator opening and the rotational speed. The two-dimensional numerical map (hereinafter referred to as “reference injection condition map” for convenience) is stored in the ROM of the ECU 20.

  Further, in the present embodiment, the values of the combustion pressure characteristic values ΔT, θmax and ΔPVmax when the optimum combustion state is obtained in each of the above operating states are calculated, and a two-dimensional numerical map using the accelerator opening and the rotational speed is calculated. (Hereinafter referred to as “target characteristic value map” for convenience) and stored in the ROM of the ECU 20.

  In actual operation, the ECU 20 first obtains the fuel injection amount, the fuel injection timing, and the EGR valve opening from the engine speed and the accelerator opening using the reference injection condition map, and calculates the fuel injection amount, the fuel injection timing, the EGR valve. The opening is controlled to the reference injection condition map value.

  In this state, the combustion pressure characteristic values of ΔT, θmax, and ΔPVmax of each cylinder are calculated based on the pressures of the cylinder pressure sensors 29a to 29d. Then, the target values ΔT, θmax, ΔPVmax of the combustion pressure characteristic values in the optimum combustion state are obtained from the aforementioned target characteristic value map using the current accelerator opening and the rotational speed, and the actual combustion pressure characteristic values are obtained from these values. The fuel injection amount, the fuel injection timing, the EGR valve opening degree, and the like determined from the reference injection condition map are adjusted so as to match the target value.

  Specifically, the ECU 20 adjusts the opening degree of the EGR valve 35 and performs feedback control so that the actual combustion pressure characteristic value ΔT becomes a target value, and θmax and ΔPVmax coincide with each target value. The fuel injection timing and the fuel injection amount are feedback controlled.

  Thereby, EGR and fuel injection are controlled so that the actual combustion state becomes an optimum state.

  3 and 4 are flowcharts specifically illustrating a control operation based on the combustion pressure characteristic (combustion pressure characteristic value control operation). 3 and 4 are each performed as a routine executed by the ECU 20 at regular intervals.

  FIG. 3 shows basic control operations of fuel injection and EGR. In the operation of FIG. 3, the ECU 20 sets the fuel injection amount, the fuel injection timing, and the EGR valve 35 opening to the reference value determined from the engine speed NE and the accelerator opening ACCP, and from the operation of FIG. It is set as the sum of the correction amount determined based on this.

In FIG. 3, at step 301, the accelerator opening ACCP and the engine speed NE are read. At step 303, the above-mentioned reference stored in the ROM of the ECU 20 in the form of a two-dimensional numerical map using ACCP and NE, respectively. From the injection condition map, the reference fuel injection amount FI ₀ , the reference fuel injection timing θI ₀ , and the reference EGR valve opening EGV ₀ are read using the values of ACCP and NE read in step 301.

  The reference fuel injection amount, the reference fuel injection timing, and the reference EGR valve opening are the fuel injection amount, the fuel injection timing, and the EGR valve opening that are obtained in advance by actually operating the engine to obtain an optimal combustion state.

  The above reference values are the fuel injection amount, timing, and EGR valve opening at which the optimum combustion state can be obtained in the environment at the time of the experiment. In actual operation, the difference in fuel and the engine operating environment (temperature, large Therefore, an optimal combustion state cannot always be obtained even if the operation is performed using the reference value.

Therefore, in the present embodiment, values obtained by adding correction amounts α, β, γ to the reference values FI ₀ , θI ₀ , EGV ₀ obtained as described above to obtain the actual fuel injection amount, fuel injection timing, EGR valve opening degree. Set as. That is, in step 305, the actual fuel injection amount FI, the fuel injection timing θI, and the EGR valve opening EGV are set as FI = FI ₀ + α, θI = θI ₀ + β, and EGV = EGV ₀ + γ. In step 307, Fuel injection and EGR valve opening degree control are performed with the values set in step 305.

  Here, α, β, and γ are feedback correction amounts set based on the combustion pressure characteristic value by the operation of FIG.

The operation of FIG. 4 will be described. First, at step 401, the accelerator opening ACCP and the engine speed NE are read. In step 403, target values θmax ₀ , ΔPVmax ₀ , ΔT _{0 of} θmax, ΔPVmax, ΔT are read from a two-dimensional map using ACCP and NE stored in advance in the ROM of the ECU 20. The target values θmax ₀ , ΔPVmax ₀ , ΔT ₀ are values of θmax, ΔPVmax, ΔT when optimum combustion is obtained at the respective accelerator opening and rotation speed.

  In step 405, the combustion pressure characteristic values of θmax, ΔPVmax, and ΔT of each cylinder are calculated based on the outputs of the in-cylinder pressure sensors 29a to 29d.

  In steps 407 to 411, the correction amounts α, β, and γ are feedback controlled so that the actual combustion pressure characteristic value calculated in step 405 matches the target value obtained from the map in step 403.

That is, in step 407, first, the fuel injection amount correction amount α is feedback-controlled so that the actual ΔPVmax value matches the target value ΔPVmax _{0. In} step 409, the actual θmax value matches the target value θmax ₀ . Thus, the correction amount β of the fuel injection timing is feedback-controlled, and in step 411, the correction amount γ of the EGR valve opening is feedback-controlled so that the actual value of ΔT coincides with the target value ΔT ₀ . The feedback control in steps 407 to 411 is, for example, PID control based on a deviation of an actual value from each target value.

For example, the PID control in the present embodiment will be specifically described by taking the correction amount β of the fuel injection timing as an example. If the deviation between the actual value of θmax and the target value θmax ₀ is δ, the correction amount β is expressed by the following equation: Is calculated using

β = K ₁ × δ + K ₂ × Σδ + K ₃ × (δ−δ _i−1 )
Here, the first term K ₁ × δ on the right side is a proportional term, the second term K ₂ × Σδ is an integral term, and Σδ represents an integrated value (integrated value) of the deviation δ. The third term K ₃ × (δ−δ _i−1 ) is a differential term, and (δ−δ _i−1 ) represents the amount of change (differential value) of the deviation δ from the previous time (δ _{i -1} is the previous value of δ). K ₁ , K ₂ and K ₃ are constants.

  As described above, by repeating the operations in FIGS. 3 and 4, the actual fuel injection amount, the fuel injection timing, and the EGR valve opening (EGR rate) are set so that the combustion pressure characteristic value matches the target value. Be controlled.

  In this way, by performing feedback control of the fuel injection amount, the fuel injection timing, and the EGR rate so that the combustion pressure characteristic value in the actual operation matches the target value, for example, a difference in engine operating environment or a change in equipment characteristics The optimum combustion state can be easily obtained without taking into consideration individual differences, variations, fuel differences, and the like.

  3 and 4, the fuel injection amount, timing, etc. are first controlled to the reference value, and the correction amount for this reference value is feedback-controlled using the combustion pressure characteristic value so that the fuel injection amount, etc. It converges in a short time to a value that gives the optimum combustion state. However, it is also possible to feedback control the fuel injection amount, the timing, and the EGR rate itself without using a reference value such as the fuel injection amount in advance.

By the way, when the fuel injection timing θI is controlled based on the deviation δ between θmax and θmax ₀ as shown in FIGS. 3 and 4, the target of the fuel injection timing particularly when operating in the low-temperature combustion mode to be described later. If the value itself is significantly advanced, control can diverge.

For example, when the actual value of θmax is delayed from the target value θmax ₀ , the fuel injection timing θI is advanced to advance θmax. However, if the fuel injection timing has already been set to a large advance, such as during low-temperature combustion, if the fuel injection timing is excessively advanced, combustion becomes unstable and misfire tends to occur. On the other hand, if the fuel injection timing is advanced, θmax may occur later.

  In such a case, if the fuel injection timing is controlled using θmax, the fuel injection timing is further advanced, and not only the control is diverged, but also, for example, due to excessive fuel injection advance, The fuel is injected at a position where the piston is not sufficiently raised, and the injected fuel overflows from the inside of the recess (bowl) formed on the piston, or the injected fuel directly hits the cylinder wall. (Bore flushing) occurs, and liquid fuel adheres to the cylinder wall, which causes problems such as dilution of the lubricating oil, deterioration of fuel consumption and exhaust properties.

  In particular, when the EGR gas amount is controlled using ΔT at the same time as in step 411 in FIG. 4, if the fuel injection timing is excessively advanced, the value of ΔT also becomes excessive and the EGR gas amount becomes Since the fuel consumption is greatly reduced, the change in the fuel injection timing and the increase / decrease in the EGR gas amount may affect each other and control may not be stable.

  Therefore, in this embodiment, an advance angle guard value θImax is provided for the fuel injection timing θI calculated in step 305 in FIG. 3 so that the fuel injection timing does not advance more than θImax.

Specifically, when the fuel injection timing θI is calculated as θI = θI ₀ + β in step 305 in FIG. 3, the ECU 30 compares the calculated θI with the advance angle guard value θImax, and θI is equal to or greater than θImax. If the advance angle is set (θI ≧ θImax), fuel injection control is executed in step 307 using θImax instead of the calculated θI. That is, the value of θI calculated in step 305 is used in step 307 only when it is on the retard side (θI ≦ θImax) with respect to the advance guard value θImax.

  This prevents excessive advance in the fuel injection timing feedback control using the combustion pressure characteristic value θmax, thereby preventing dilution of the lubricating oil, fuel consumption, and deterioration of exhaust properties due to bore flushing, as well as excessive progress. Divergence of fuel injection timing control by the angle and interference with EGR gas amount feedback control using ΔT are prevented, and the fuel injection timing and EGR gas amount converge to the target values in a short time.

  The advance angle guard value θImax of the fuel injection timing is a time when the fuel injected from the fuel injection valve does not overflow from the inside of the piston bowl or adhere to the wall surface. The value is determined by the injection conditions such as the injection pressure. Since this value varies depending on various conditions such as piston shape, fuel injection valve arrangement, engine speed, and injection pressure, it is a numerical value for each speed (fuel injection pressure) based on experiments using an actual engine. It is preferable to create it as a map.

Next, another embodiment of the present invention will be described.
In the present embodiment, the engine 1 performs fuel injection at the end of the normal diesel combustion mode, that is, the end of the compression stroke, and performs the combustion mode in which diffusion combustion with a high air-fuel ratio is performed, and the low-temperature combustion mode, that is, fuel injection timing is greatly advanced. Then, the premixed gas is formed in the cylinder, and the operation is performed by switching between two combustion modes, that is, a combustion mode in which the EGR gas amount is greatly increased and combustion with a low air-fuel ratio is performed. In the low temperature combustion, significantly inhibited the generation of harmful substances such as NO _X by feeding to the combustion chamber a large amount of EGR gas while a relatively low combustion air, the premixed combustion while being further diesel engine By doing so, the amount of soot generated can be greatly reduced.

  However, in the operation in the low-temperature combustion mode, the change in the combustion state is extremely sensitive to the change in the EGR rate, and there may be a case where the combustion state is greatly deteriorated by a slight change in the EGR rate.

  Therefore, in the present embodiment, when the engine is operated in the low temperature combustion mode, the EGR rate (EGR valve opening) is feedback controlled based on the combustion pressure characteristic value.

  FIG. 5 is a flowchart for explaining the EGR rate control operation based on the combustion pressure characteristic value of the present embodiment. This operation is performed as a routine executed by the ECU 20 at regular intervals.

  In the operation of FIG. 5, it is first determined in step 501 whether or not the engine is currently operating in the low temperature combustion mode. If the engine is not operating in the low temperature combustion mode, this operation is immediately terminated without executing step 503 and the subsequent steps. . In this case, for example, the EGR rate is controlled by open loop control based on the accelerator opening and the engine speed similar to the conventional one.

If the engine is currently operating in the low-temperature combustion mode in step 501, then the process proceeds to step 503, where the current accelerator opening ACCP and engine speed NE are read from the corresponding sensors, and in step 505 in advance. The target value ΔT ₀ of ΔT at the current ACCP and NE is read from the target value map of the combustion completion time ΔT stored in the ROM of the ECU 20 in the form of a two-dimensional numerical map of ACCP and NE.

Here, ΔT ₀ is the combustion completion time when EGR gas is supplied at an EGR rate at which an optimal combustion state is obtained in the low temperature combustion mode.

Next, at step 507, the current actual combustion completion time ΔT is calculated based on the outputs of the in-cylinder pressure sensors 29a to 29d. In step 509, the EGR valve opening is feedback-controlled so that the actual combustion completion time ΔT matches the target value ΔT ₀ . This feedback control is, for example, PID control based on the deviation between the target value ΔT ₀ and the actual value ΔT, as in the case of FIG.

  In the present embodiment, the fuel injection amount and the fuel injection timing are set in advance to optimum values for operation in the low-temperature combustion mode by a routine separately executed by the ECU 20.

  As shown in FIG. 5, by controlling the EGR rate of the engine based on the combustion pressure characteristic value ΔT during operation in a low-temperature combustion mode that is particularly sensitive to changes in the EGR rate, an optimal combustion state that is stable even during low-temperature combustion is achieved. Can be obtained.

  By the way, after shifting to the low-temperature combustion mode as described above, an optimal EGR rate can be obtained by control based on ΔT. However, when shifting from the normal combustion mode to the low-temperature combustion mode, feedback control based on ΔT is performed. If the amount of EGR gas is adjusted, the EGR rate at the time of transition to the low temperature combustion mode may change excessively and combustion may become unstable.

  As described above, the fuel injection timing is greatly advanced in the low-temperature combustion mode compared to the normal combustion mode. However, if the fuel injection timing is advanced all at once during the transition to the low-temperature combustion mode, the engine output torque fluctuates due to a sudden change in the combustion state, which causes a so-called torque shock. For this reason, a fixed transition period is provided when shifting from the normal combustion mode to the low temperature combustion mode, and within this transition period (time), the fuel injection timing is relatively set from the value in the normal combustion mode to the target value in the low temperature combustion mode. A transition process (annealing process) is performed that gradually and continuously changes.

  Accordingly, during the transition process, the fuel injection timing used for calculating ΔT (FIG. 2, θinj) gradually changes (advance), and the timing at which PVmax occurs (FIG. 2, θmax) also changes gradually (advance). Therefore, at the start of switching, the value of ΔT does not change much from the value before switching, and becomes a relatively small value.

On the other hand, in order to quickly converge the EGR rate to the target value after shifting to the low temperature combustion mode, it is attempted to perform feedback control of the EGR valve opening degree and the injection timing using ΔT and θmax even during the transition period to the low temperature combustion mode. Since the value of ΔT calculated based on the actual fuel injection timing is considerably smaller than the target value ΔT ₀ at the beginning of the transition period, control is performed in the direction of increasing ΔT, and a fresh air amount is required. The combustion may become unstable due to the above reduction.

  Therefore, in the present embodiment, during the transition period, the actual fuel injection timing is not used when calculating ΔT, but the target fuel injection timing after completion of the transition to the low temperature combustion is used. As a result, at the start of the transition period, the value of ΔT becomes larger and the deviation from the target value ΔT becomes smaller than when the actual fuel injection timing is used. In this embodiment, since the EGR valve opening is feedback controlled based on the deviation between ΔT and the ΔT target value, this prevents the EGR rate from being increased excessively, and during the transition to the low-temperature combustion mode. It becomes possible to maintain the EGR rate appropriately.

  FIG. 6 is a diagram for explaining a change in ΔT in a transition period of switching from the normal combustion mode to the low temperature combustion mode in the present embodiment.

  In FIG. 6, a curve θinj represents a change in fuel injection timing, and a curve θmax represents a change in timing at which PVmax occurs, and the actual ΔT (actual ΔT) is equal to the distance between the two curves (FIG. 6). 6).

  In FIG. 6, when the transition period for switching from the normal combustion mode is started, the fuel injection timing θinj is continuously advanced, and becomes the target fuel injection timing in the low-temperature combustion mode at the end of the transition period.

In this case, as shown in FIG. 6, θinj does not change greatly even at the start of the transition, so ΔT (actual ΔT) using the actual fuel injection timing becomes a relatively small value at the start of the transition period, and becomes the target value ΔT ₀ . The difference between the two becomes relatively large, and the control proceeds in the direction of greatly increasing the EGR gas amount at the beginning of the transition period, resulting in a problem that the EGR rate becomes excessive. For this reason, if the amount of EGR gas is controlled based on ΔT during the transition to the low temperature combustion mode, combustion may become unstable and misfire may occur in extreme cases.

  On the other hand, ΔT calculated using the fuel injection timing target value after switching to the low-temperature combustion mode instead of the actual fuel injection timing is larger than the actual ΔT as shown in FIG. The difference from the target value becomes smaller. Therefore, in the present embodiment, the EGR rate is prevented from increasing rapidly, and the EGR rate gradually increases according to the advance angle of the injection timing.

  As a result, in this embodiment, it is possible to converge the EGR rate to the target value after switching in a short time while preventing instability of combustion or misfiring when switching from the normal combustion mode to the low temperature combustion mode. Become.

  Next, the control at the time of switching from the low-temperature combustion mode to the normal combustion mode opposite to the above will be described using FIG.

  For example, consider a case where control of the fuel injection amount, fuel injection timing, EGR rate, etc. using the combustion pressure characteristic value is performed only during the low temperature combustion mode operation, and the conventional open loop control is performed in the normal combustion mode.

  In this case, during low-temperature combustion mode operation, the fuel injection amount, fuel injection timing, EGR gas amount, etc. are feedback controlled based on the combustion pressure characteristic values (ΔT, θmax, ΔPVmax, etc.), and the actual fuel injection amount, fuel injection The timing, EGR gas amount, etc. include feedback correction amounts.

For example, taking fuel injection timing as an example, as described in step 305 in FIG. 3, the actual fuel injection timing during low-temperature combustion is an amount obtained by adding the feedback correction amount β to the target value θI ₀ .

  Normally, as shown in FIG. 7, a transition period similar to that described in FIG. 6 is provided when switching from the low temperature combustion mode to the normal combustion mode, and the target value of the fuel injection timing is that in the low temperature combustion mode. To the target value in the normal combustion mode is continuously changed within the transition period.

  However, as described above, the actual fuel injection timing in the low-temperature combustion mode includes the feedback correction amount β, and the fuel injection timing in the normal combustion mode does not include the feedback correction amount β. Loop control). For this reason, it becomes a problem at which point feedback control is stopped and the feedback correction amount β is set to zero. For example, if the feedback control is stopped immediately with the start of the transition period, the fuel injection timing changes abruptly by the feedback correction amount β simultaneously with the start of the transition period, and torque fluctuation may occur due to a sudden change in the fuel injection timing. The same applies to the case where the feedback control is continued during the transition period and the feedback control is stopped upon completion of the transition.

  Therefore, in the present embodiment, as shown in FIG. 7, the feedback control is stopped simultaneously with the start of the transition period, but the feedback correction amount β at the start of the transition period is not immediately set to 0, but becomes 0 at the end of the transition period. The feedback correction is gradually reduced continuously.

In FIG. 7, the dotted line indicates the target value θI ₀ of the fuel injection timing, and the solid line indicates the actual fuel injection timing θI. As shown in the figure, in the low-temperature combustion mode operation, feedback control based on the combustion characteristic value θmax is performed, and there is a difference by a feedback correction amount β between the target value θI ₀ and the actual fuel injection timing θI. ing.

  When the transition period is started, the feedback control is immediately stopped in the present embodiment, but at the start of the transition, the actual fuel injection timing θI is maintained at a value including the feedback correction amount β at the start of the transition period. For this reason, in this embodiment, a sudden change in the fuel injection timing due to the feedback control stop at the start of the transition period is prevented.

Then, as shown in FIG. 7, during the transition period, the value of β is continuously reduced so as to become 0 at the end of the transition period (for example, the value of β is decreased in proportion to the passage of time after the start of the transition period. ) Accordingly, the actual fuel injection timing θI gradually approaches the target fuel injection timing θI ₀ during the transition period, and coincides with θI ₀ at the end of the transition period. Thereby, in this embodiment, it is possible to shift from the feedback control of the fuel injection timing in the low temperature combustion mode to the open loop control in the normal combustion mode without causing torque fluctuation.

  Although FIG. 7 has been described by taking the fuel injection timing as an example, it goes without saying that the same transition control can be performed for the fuel injection amount or the EGR gas amount.

  Next, another application example of EGR control using the above combustion pressure characteristic value will be described. In each of the above embodiments, the EGR rate is accurately controlled using the combustion pressure characteristic value ΔT, and it is possible to obtain an optimal EGR rate for combustion even during low-temperature combustion.

For example, absorbs NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage of a lean, when the occluded by adsorption, or both, the air-fuel ratio of the exhaust gas flowing becomes rich, in the exhaust gas the example, when provided with a known of the NO _X occluding and reducing catalyst for reducing and purifying the occluded NO _X with reducing components and HC and the like such as CO performing exhaust gas purification, the _the NO _X storage reduction catalyst occluded the NO _X At the time of reduction purification, it is necessary to accurately control the exhaust air-fuel ratio (engine air-fuel ratio). However, although the above control can obtain an optimal EGR rate with good responsiveness, it cannot always accurately control the combustion air-fuel ratio (exhaust air-fuel ratio) of the engine.

  For example, if the injection characteristic of the fuel injection valve changes due to wear of the internal mechanism, or if the injection characteristic varies from product to product, the target air-fuel ratio does not necessarily change even if the combustion pressure characteristic value is controlled to the target value. It is not necessarily obtained.

  On the other hand, in order to control the exhaust air-fuel ratio to the target air-fuel ratio, an EGR control valve is arranged so that the exhaust air-fuel ratio becomes the target value by arranging an air-fuel ratio sensor in the exhaust passage and directly measuring the exhaust air-fuel ratio. It is also possible to perform feedback control.

  However, EGR control using an air-fuel ratio sensor has a delay in the engine operating conditions such as during transient operation due to a delay in gas transportation to the sensor mounting position of exhaust gas and a response delay in the sensor itself. It is not always possible to accurately control the amount of EGR gas.

  Therefore, in this embodiment, by combining EGR feedback control using the combustion pressure characteristic value with feedback learning control based on the air-fuel ratio sensor output, the EGR gas amount is controlled with good responsiveness including transient operation, and exhaust gas The air-fuel ratio can be controlled with high accuracy.

That is, in the present embodiment, for example, a predetermined learning control condition (for example, the engine is operated in a steady state) in a state where ΔT is controlled so as to coincide with the target value ΔT ₀ by the feedback control of FIG. And so on), the exhaust air-fuel ratio detected by the air-fuel ratio sensor arranged in the exhaust passage matches the target air-fuel ratio determined from the accelerator opening ACCP and the engine speed NE, and the target value for the combustion completion period The value of ΔT ₀ is changed little by little.

For example, when the actual exhaust air-fuel ratio is richer than the target air-fuel ratio, the target value ΔT ₀ is decreased by a predetermined amount GT, and when the actual exhaust air-fuel ratio is leaner than the target air-fuel ratio, the target value ΔT ₀ is set. Increase by quantitative GT.

Then, using the target value ΔT ₀ after the increase / decrease, the EGR gas amount control based on ΔT is performed again, and the EGR gas amount is adjusted so that the actual ΔT matches the target value ΔT ₀ after the increase / decrease. If the corrected target value ΔT ₀ matches, it is determined again whether the exhaust air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio. If they do not match, the target value ΔT ₀ is set again. Increase or decrease by the predetermined value GT and repeat the above operation.

Then, an operation is performed to store the target value ΔT ₀ when both the exhaust air-fuel ratio and ΔT coincide with the target value as a new target value (learning value) in the accelerator opening ACCP and the engine speed NE. Thus, by performing learning correction of the combustion pressure characteristic value ΔT ₀ based on the actual air-fuel ratio sensor output, it is possible to accurately control the exhaust air-fuel ratio while controlling the EGR rate with good responsiveness. Become.

Next, another embodiment of the present invention will be described.
In the above-described embodiments, the PV value is calculated, and the EGR gas amount is controlled using ΔT obtained based on PVmax as the combustion pressure characteristic value. However, the combustion pressure characteristic value suitable for the control of the EGR gas amount should be similarly used as long as it has a close correlation with one or both of the ignition delay period and the combustion period in addition to PVmax or ΔT. Can do.

For example, a time Δtd until the value of PV ^kappa takes the minimum value PV ^kappa min as a combustion pressure characteristic value with a close correlation to the combustion period and the ignition delay period in the present embodiment, the minimum value of PV ^kappa value PV The time Δtc from when ^κ min is taken until the maximum value PV ^κ max is obtained is used.

Here, PV ^κ is the product of the internal combustion pressure P at each crank angle and the value obtained by raising the combustion chamber volume V at that crank angle to the κ power. Κ is the specific heat ratio of the air-fuel mixture.

Here, PV ^κ = constant in the adiabatic change from the gas equation of state, but in the actual cylinder compression stroke, there is heat radiation from the air-fuel mixture through the cylinder wall and piston, so in the cylinder compression stroke, PV ^κ Gradually decreases from the start of compression.

On the other hand, since combustion heat is generated when the air-fuel mixture is ignited and combustion is started, the value of PV ^κ starts to increase. For this reason, the point at which the value of PV ^κ changes from decreasing to increasing, that is, the point at which PV ^κ becomes the minimum value PV ^κ min is the starting point of combustion. Further, during combustion similarly but continues to increase the value of PV ^kappa, the value of the heat is not generated by the combustion is completed PV ^kappa begins to decrease again. Therefore, the point at which the value of PV ^κ changes from increasing to decreasing, that is, the point at which PV ^κ reaches the maximum value PV ^κ max is the end point of combustion.

Assuming that the fuel injection start timing is θinj and the crank angle at which PV ^κ is the minimum value PV ^κ min is θstart, Δtd = θstart−θinj is a period from the start of fuel injection to the start of combustion, and thus becomes equal to the ignition delay period. .

If the crank angle at which PV ^κ reaches the maximum value PV ^κ max is θend, Δtc = θend−θstart is equal to the period from the start to the end of combustion, that is, the combustion period.

  As described above, both the ignition delay period and the combustion period have a close correlation with the EGR rate. When the EGR rate increases, both the ignition delay period and the combustion period increase, and when the EGR rate decreases, both decrease. To do.

  Therefore, in the present embodiment, the EGR rate is controlled in the same manner as in the case of using the above-described ΔT using either the ignition delay period Δtd or the combustion period Δtc.

In other words, in the present embodiment, the value of the ignition delay period (or combustion period) in the combustion state in which the optimal EGR rate has been obtained in advance is set as the target value Δtd ₀ (or Δtc ₀ ), and each accelerator opening ACCP and engine speed NE. It is set to. In actual operation, the value of PV ^κ is calculated from the pressure in the combustion chamber and the crank angle for each stroke cycle, and the crank angle at which the value of PV ^κ becomes the minimum value (or minimum value and maximum value) is detected. Then, Δtd (or Δtc) in the actual operation is calculated.

Then, the EGR control valve opening is feedback-controlled based on the deviation between Δtd (or Δtc) and the target value Δtd ₀ (or Δtc ₀ ) in the current operating state (ACCP, NE).

The specific heat ratio κ can be approximately set to a constant value, and the combustion chamber volume V can be calculated in advance as a function of the crank angle. Therefore, when calculating PV ^κ , the value of V ^κ for each crank angle is calculated in advance and stored in the ROM of the ECU 30 in the form of a numerical table, so that the value of PV ^κ can be easily calculated. it can.

  As a result, as in the case of feedback control using ΔT, the EGR rate can be controlled accurately and with good responsiveness without increasing the calculation load of the control circuit.

In addition, in the case of performing pilot injection that prepares a favorable temperature pressure condition for combustion of the main fuel injection fuel by injecting a small amount of fuel prior to main fuel injection and burning it in the combustion chamber, the calculated PV ^κ If the determination of whether or not the value is the minimum value PV ^κ min is started after the start of the main fuel injection, it is possible to prevent erroneous detection of the combustion start time of the pilot fuel injected fuel as the injection start point of the main fuel injected fuel Is done.

It is a figure which shows schematic structure of embodiment which applied this invention to the diesel engine for motor vehicles. It is a figure explaining the definition of the combustion pressure characteristic value used by this embodiment. It is a flowchart explaining basic control, such as fuel injection, in this embodiment. It is a flowchart explaining control operation, such as fuel injection using a combustion pressure characteristic value in this embodiment. It is a flowchart explaining another embodiment of EGR rate control using a combustion pressure characteristic value. FIG. 6 is a timing diagram illustrating switching control from a normal combustion mode to a low temperature combustion mode. FIG. 6 is a timing diagram illustrating switching control at the time of returning from the low-temperature combustion mode to the normal combustion mode.

Explanation of symbols

1 Diesel engine 10a-10d In-cylinder fuel injection valve 20 Electronic control unit (ECU)
21 Accelerator opening sensor 25 Crank angle sensor 29a to 29d In-cylinder pressure sensor 35 EGR valve

Claims (5)

An internal combustion engine comprising a fuel injection valve that injects fuel into an engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and an in-cylinder pressure sensor that detects pressure in the engine combustion chamber A control device,
Further, based on the pressure in the combustion chamber detected by the in-cylinder pressure sensor, combustion timing calculation means for calculating a combustion pressure characteristic value corresponding to a combustion timing including at least one of an ignition delay period and a combustion period, and the EGR device are controlled. Control means for adjusting the EGR gas amount so that the combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means becomes a predetermined target value,
The combustion timing calculation means is configured to calculate the PV after the start of fuel injection from the fuel injection valve based on the product PV of the combustion chamber pressure P detected by the cylinder pressure sensor and the combustion chamber volume V determined from the crank angle θ. Is calculated as a combustion pressure characteristic value corresponding to the combustion timing, and the control means sets the EGR gas amount so that the ΔT becomes a predetermined target value. Adjust
The target value is determined according to the engine speed and the accelerator opening,
The internal combustion engine is a compression ignition engine;
The control means further includes a normal combustion mode in which fuel is injected at a later stage of the compression stroke to perform combustion with a large excess air ratio, and a low temperature in which the fuel injection timing is advanced from the normal combustion mode and the EGR gas amount is increased. The operation is performed by switching the combustion mode, and the EGR gas amount control based on the value of ΔT is performed during the operation of the low temperature combustion mode of the engine.
Further, the control means continuously changes the fuel injection timing from the injection timing in the normal combustion mode to the target fuel injection timing in the low temperature combustion mode over a predetermined transition time when switching from the normal combustion mode to the low temperature combustion mode. In addition, during the transition period, the EGR gas amount control is performed based on the value of ΔT calculated using the target fuel injection timing in the low-temperature combustion mode after switching instead of the actual fuel injection timing. Control device.   The combustion timing calculation means further calculates a product PVbase of the pressure in the combustion chamber generated only by piston compression and the combustion chamber volume determined from the crank angle when it is assumed that no combustion has occurred in the combustion chamber, and the PV is a maximum value. A difference ΔPVmax between PVmax and PVbase is calculated using the value of PVbase at a crank angle θmax that becomes PVmax, and the control means is further configured so that the values of ΔPVmax and θmax become predetermined target values, respectively. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the control unit controls a fuel injection amount from the fuel injection valve and a fuel injection timing. An internal combustion engine comprising a fuel injection valve that injects fuel into an engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and an in-cylinder pressure sensor that detects pressure in the engine combustion chamber A control device,
Further, based on the pressure in the combustion chamber detected by the in-cylinder pressure sensor, combustion timing calculation means for calculating a combustion pressure characteristic value corresponding to a combustion timing including at least one of an ignition delay period and a combustion period, and the EGR device are controlled. Control means for adjusting the EGR gas amount so that the combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means becomes a predetermined target value,
The combustion timing calculation means is based on the value of PV ^κ calculated from the combustion chamber pressure P detected by the cylinder pressure sensor, the combustion chamber volume V determined from the crank angle θ, and the specific heat ratio κ of the combustion gas. the time Δtd value of the fuel injection starting after the PV ^kappa from the fuel injection valve to a minimum value PV ^kappa min was calculated as the combustion pressure characteristic value, said control means, a target value which the Δtd is predetermined A control apparatus for an internal combustion engine, which adjusts the EGR gas amount so as to become. An internal combustion engine comprising a fuel injection valve that injects fuel into an engine combustion chamber, an EGR device that recirculates part of the engine exhaust as EGR gas to the engine combustion chamber, and an in-cylinder pressure sensor that detects pressure in the engine combustion chamber A control device,
Further, based on the pressure in the combustion chamber detected by the in-cylinder pressure sensor, combustion timing calculation means for calculating a combustion pressure characteristic value corresponding to a combustion timing including at least one of an ignition delay period and a combustion period, and the EGR device are controlled. Control means for adjusting the EGR gas amount so that the combustion pressure characteristic value corresponding to the combustion timing calculated by the combustion timing calculating means becomes a predetermined target value,
The combustion timing calculation means is based on the value of PV ^κ calculated from the combustion chamber pressure P detected by the cylinder pressure sensor, the combustion chamber volume V determined from the crank angle θ, and the specific heat ratio κ of the combustion gas. calculating a time Δtc value of the fuel injection starting after the PV ^kappa from the fuel injection valve from taking the minimum value PV ^kappa min until a maximum value PV ^kappa max as the combustion pressure characteristic value, said control means, A control device for an internal combustion engine, which adjusts the EGR gas amount so that the Δtc becomes a predetermined target value. The fuel injection valve performs pilot injection for injecting a small amount of fuel into the combustion chamber prior to main fuel injection, and the combustion timing calculation means starts detection of the value of PV ^κ min after the start of main fuel injection, The control device for an internal combustion engine according to claim 3 or 4.

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