Controller of internal combustion engine

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 including an EGR device that recirculates a part of exhaust gas as EGR gas to the engine.

NO by lowering the combustion temperature of the engine_XIn order to reduce harmful emissions such as, a technique is known in which a part of the engine exhaust gas is returned to the engine combustion chamber as EGR gas. It is also known that even in a diesel engine that normally operates in a lean air-fuel ratio, it is possible to reduce harmful emissions in the exhaust gas by supplying a relatively large amount of EGR gas to the combustion chamber.

However, EGR gas has a large effect on combustion, and especially in a diesel engine, it has a large effect on the ignition delay time from the start of fuel injection to the start of combustion of the injected fuel. Therefore, if an excessive amount of EGR gas is supplied to the combustion chamber, the combustion state of the engine deteriorates, resulting in deterioration of engine performance and exhaust gas properties. On the other hand, if the amount of EGR gas is small, the effect of suppressing harmful emissions decreases. Therefore, it is necessary to control the amount of EGR gas to an appropriate amount according to the operating condition of the engine.

However, the amount of EGR gas has not been precisely controlled in the past, and especially in diesel engines, the opening degree of the EGR valve that controls the EGR gas flow rate is the engine speed and the accelerator opening (the amount of depression of the accelerator pedal). It was usual to perform open-loop control to a value determined from.

However, in recent years, due to the tightening of exhaust gas regulations and the demand for noise reduction, it has become necessary to precisely control the EGR gas flow rate to the optimum value. When performing such precise EGR control, sufficient accuracy cannot be obtained by open-loop control based on the engine speed and the accelerator opening as in the conventional case. Further, for example, in a gasoline engine, it is possible to arrange an air-fuel ratio sensor in the engine exhaust passage and control the amount of EGR gas based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor. In an engine that may be operated in a state where the air-fuel ratio is extremely lean, the detection accuracy by the air-fuel ratio sensor is low, so if the EGR gas amount is controlled based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor, an error will be large. There is a problem.

On the other hand, the pressure in the combustion chamber 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 used to optimize the combustion state. A control device for feedback control has been proposed.

As an example of such a control device for an internal combustion engine, there is one described in Patent Document 1. The device of Patent Document 1 is not related to a diesel engine but to a gasoline engine, but the heat generation rate in the combustion chamber is used as a combustion parameter indicating the combustion state of the engine so that the heat generation rate becomes a predetermined pattern. It also controls the EGR gas flow rate, fuel injection timing, fuel injection amount, ignition timing, etc.

That is, in the device of Patent Document 1, an in-cylinder pressure sensor for detecting the engine combustion chamber pressure is arranged in the cylinder, and heat is generated at each crank angle based on the detected actual combustion chamber pressure (combustion pressure) and the crank angle. The rate is calculated, and the EGR gas amount, ignition timing, fuel injection timing, etc. are feedback-controlled so that the change pattern of the heat generation rate with respect to the crank angle matches the ideal change pattern predetermined according to the operating conditions. Therefore, the optimum combustion is obtained.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2000-54889</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 11-148410</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 3-233162</text></patcit>

<p> In the device of Patent Document 1, the heat generation rate is focused on as a parameter related to combustion, the heat generation rate pattern in the actual operating state is calculated, and the calculated heat generation rate pattern is a predetermined ideal change pattern. Ignition timing, fuel injection amount, etc. are feedback-controlled so as to match. The device 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 pattern of heat generation rate is calculated based on the output of the in-cylinder pressure sensor, and the calculated heat generation is calculated. It is also conceivable to feedback-control the fuel injection timing and the fuel injection amount so that the rate pattern becomes a predetermined heat generation rate pattern.</p><p> However, in the apparatus of Patent Document 1, feedback control of the combustion state is performed by using only the heat generation rate in the combustion chamber as a parameter indicating the combustion state of the engine. In the apparatus of Patent Document 1, a gasoline engine is used, and in the gasoline engine, a premixture is usually formed by port injection, and the combustion pattern such as ignition and combustion does not change significantly. Therefore, even if only the heat generation rate is used as a parameter representing the combustion state, a large error does not occur.</p><p> However, in a diesel engine, for example, the combustion pattern may change significantly depending on the amount of EGR gas and the fuel injection timing, so it is not always appropriate to perform feedback control of the amount of EGR gas and fuel injection based only on the heat generation rate. Absent.</p><p> Further, in order to perform control based on the pattern of the heat generation rate 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 combustion chamber pressure, V is the actual cylinder internal volume determined from the crank angle, and κ is the specific heat ratio). It is necessary to perform complicated calculations such as. Therefore, there arises a problem that the calculation load of the control circuit increases.</p><p> Further, since the detection of the crank angle is generally 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-mentioned calculation formula of the heat generation rate. Therefore, if the EGR gas amount, fuel injection amount, timing, etc. are controlled based on the heat generation rate calculated using the above formula, the combustion state may deteriorate due to a control error.</p><p> In view of the above problems, the present invention is to improve the performance and exhaust properties of an internal combustion engine by feedback-controlling the EGR flow rate, fuel injection amount, fuel injection timing, etc. of the internal combustion engine according to the combustion state of the engine. It is an object of the present invention to provide a control device for an internal combustion engine capable of performing accurate control while suppressing an increase in a calculation load of a control circuit without requiring calculation of the heat generation rate of the above.</p>

<p> According to the invention of claim 1, a fuel injection valve that injects fuel into the engine combustion chamber, an EGR device that recirculates a part of the engine exhaust as EGR gas to the engine combustion chamber, and a pressure in the engine combustion chamber are detected. It is a control device of an internal combustion engine provided with an in-cylinder pressure sensor, and further, based on the combustion chamber pressure detected by the in-cylinder pressure sensor, combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period. The amount of EGR gas so that the combustion timing characteristic value corresponding to the combustion timing calculated by the combustion timing calculation means by controlling the EGR device and the combustion timing calculation means for calculating the pressure characteristic value becomes a predetermined target value. The combustion timing calculation means is provided with a control means for adjusting the fuel injection based on 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. The time ΔT from the start of fuel injection from the valve until the value of the PV reaches the maximum value PVmax is calculated as the described combustion pressure characteristic value corresponding to the combustion timing, and the control means has a target value predetermined by the ΔT. The EGR gas amount is adjusted so as to be, the target value is determined according to the engine rotation speed and the accelerator opening, the internal combustion engine is a compression ignition engine, and the control means further controls the engine. , Operate by switching between the normal combustion mode in which fuel is injected in the latter half of the compression stroke and combustion with a large excess air ratio is performed, and the low temperature combustion mode in which the fuel injection timing is advanced from the normal combustion mode and the amount of EGR gas is increased. At the same time, 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, and the control means further sets the fuel injection timing to the normal combustion mode when switching from the normal combustion mode to the low temperature combustion mode. The target fuel injection timing in the low temperature combustion mode is continuously changed from the injection timing over a predetermined transition time, and during the transition period, the target fuel injection in the low temperature combustion mode after switching is performed instead of the actual fuel injection timing. A control device for an internal combustion engine that controls the amount of EGR gas based on a value of ΔT calculated using a period is provided.</p><p> That is, in the invention of claim 1, the combustion pressure characteristic value corresponding to the combustion timing is calculated based on the combustion chamber pressure detected by the in-cylinder pressure sensor. Here, the combustion timing includes one or both of the ignition delay time and the combustion period. Further, the combustion pressure characteristic value referred to here is a value corresponding to one or both of the above ignition delay period and the combustion period calculated based on the combustion chamber pressure, and is a value such as ΔT, Δtc, Δtd described later, for example. is there.</p><p> The ignition delay period and the combustion period are closely related to the EGR rate of the engine (the ratio of EGR gas to the amount of gas sucked into the cylinder, that is, (EGR gas amount / (fresh air amount + EGR gas amount))). It is known to show. That is, as the EGR rate increases, combustion becomes less likely to occur, so that the ignition delay time becomes longer, and the combustion rate of the air-fuel mixture decreases, so that the combustion period (that is, the period from the start to the end of combustion). Becomes longer.</p><p> Focusing on the above, 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. This makes it possible to accurately control the amount of EGR gas to the optimum amount.</p><p> In addition, it is difficult to directly measure the ignition delay period, combustion period, etc. during actual engine operation. Therefore, in the present invention, a value (combustion pressure characteristic value) that can be calculated by a simple calculation corresponding to the ignition delay period and the combustion period is calculated based on the combustion chamber pressure, and this combustion pressure characteristic value is a predetermined optimum value. The amount of EGR gas is controlled so that it becomes a value.</p><p> As a result, the amount of EGR gas can be easily and accurately controlled to the optimum value without increasing the calculation load of the control circuit.</p><p> Further, in the present invention, it is 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 reaches the maximum value PVmax. EGR gas amount is feedback controlled.</p><p> There are various parameters related to the combustion state calculated from the combustion pressure (in-cylinder pressure), but the timing at which the maximum value PVmax of the product PV of the combustion chamber pressure P and the cylinder volume occurs is the combustion stroke of the cylinder. Corresponds to the time when combustion is completed in. Therefore, the time ΔT from the start of fuel injection to the occurrence of PVmax is the time from the start of combustion to the completion of combustion of the injected fuel of the engine, that is, the ignition delay period and the combustion period. Corresponds to the total (hereinafter referred to as "combustion completion time").</p><p> As mentioned above, since the ignition delay time and the combustion period closely correspond to the EGR rate of the engine (the ratio of the EGR gas to the amount of gas sucked into the cylinder), the combustion pressure corresponding to the above-mentioned combustion timing. The combustion completion time ΔT is calculated as a characteristic value, and the EGR gas amount (EGR rate) is feedback-controlled so that this ΔT matches the optimum value obtained in advance. As a result, the amount of EGR gas is accurately controlled to the optimum value without increasing the calculation load of the control circuit.</p><p> The combustion completion time ΔT may be expressed in time (milliseconds) or crank rotation angle (CA).</p><p> Further, in the present invention, the target values of the combustion pressure characteristic values such as ΔT, ΔPVmax, and θmax described above are referred to as the accelerator opening degree (the amount of operation of the accelerator pedal, that is, the amount of depression of the accelerator pedal by the driver is referred to as accelerator opening degree. ) And the engine speed.</p><p> Generally, 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 optimum combustion state for each engine operating state are simplified. Can be set to.</p><p> Further, in the present invention, a compression ignition engine is used as an internal combustion engine. By applying the above control to the compression ignition engine, it is possible to accurately control the amount of EGR gas in the compression ignition engine.</p><p> Further, in the present invention, an engine that operates by switching between the normal combustion mode and the low temperature combustion mode is used, and the EGR gas amount control using the combustion pressure characteristic value ΔT is performed during the operation in the low temperature combustion mode.</p><p> In the low-temperature combustion mode, the combustion temperature is lowered by significantly advancing the fuel injection timing to form a premixture in the cylinder, and by significantly increasing the amount of EGR gas to perform combustion with a low air-fuel ratio. Soot and NO in the exhaust_XIt is a combustion mode that significantly reduces both.</p><p> However, in the low-temperature combustion mode, a large amount of EGR gas is supplied to the combustion chamber, so even a slight change in the amount of EGR gas (EGR rate) may cause the combustion state to deteriorate sharply. The sensitivity of changes in combustion state increases.</p><p> As described above, the EGR gas amount can be controlled to the optimum value extremely accurately by performing feedback control of the EGR gas amount using the combustion pressure characteristic value ΔT. Therefore, in the present invention, by controlling the amount of EGR gas using ΔT, it is possible to easily achieve an appropriate combustion state even in the low temperature combustion mode in which the sensitivity to the change in the amount of EGR gas is high.</p><p> Further, in the present invention, the EGR gas amount control using the combustion pressure characteristic value ΔT is also performed when switching from the normal combustion mode to the low temperature combustion mode.</p><p> However, when 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 certain period of time in order to avoid a shock due to a sudden change in the fuel injection timing.</p><p> In this case, if ΔT is calculated using the actual fuel injection timing (during the change to the target value injection timing) from the start of the transition period, the value of ΔT will be significantly smaller than the target value, and this will be corrected. Therefore, the amount of EGR gas is significantly increased, which causes a problem that combustion becomes unstable at the time of transition.</p><p> Therefore, in the present invention, ΔT is set by using the fuel injection timing (that is, the target value of the fuel injection timing in the low temperature combustion mode) after the transition to the low temperature combustion mode is completed instead of the actual fuel injection timing during the transition period. I try to calculate it.</p><p> As a result, the value of ΔT during the transition period to the low-temperature combustion mode is calculated as a relatively large value, and the amount of EGR gas can be appropriately feedback- controlled during the transition period. Stability is prevented.</p><p> According to the invention of claim 2, the combustion timing calculating means further includes a combustion chamber pressure generated only by compression of a piston and a combustion chamber volume determined from a crank angle when it is assumed that combustion does not occur in the combustion chamber. The product PVbase is calculated, and the difference ΔPVmax between PVmax and PVbase is calculated by using the value of PVbase at the crank angle θmax at which the PV is the maximum value PVmax. The control device for an internal combustion engine according to claim 1, which controls the fuel injection amount and the fuel injection timing from the fuel injection valve so as to reach predetermined target values, respectively, is provided.</p><p> 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.</p><p> The product PV of the combustion chamber pressure P and the combustion chamber volume V is the value corresponding to the sum of the energy generated by combustion and the energy generated by piston compression, and therefore the PV value (PVbase) due to piston compression alone is subtracted from the maximum value PVmax. The value ΔPVmax is the amount of fuel supplied to the combustion chamber, that is, the value corresponding to the fuel injection amount.</p><p> Further, since θmax is a value corresponding to the time when combustion in the combustion chamber is completed, it changes according to the fuel injection timing if other conditions (for example, EGR) are constant.</p><p> Therefore, for example, by feedback-controlling 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, the fuel injection amount is added to the EGR gas amount. Therefore, it is possible to accurately control the fuel injection amount and the fuel injection timing without increasing the calculation load of the control circuit.</p><p> According to the invention of claim 3, the fuel injection valve that injects fuel into the engine combustion chamber, the EGR device that recirculates a part of the engine exhaust as EGR gas to the engine combustion chamber, and the pressure in the engine combustion chamber are detected. It is a control device of an internal combustion engine provided with an in-cylinder pressure sensor, and further, based on the combustion chamber pressure detected by the in-cylinder pressure sensor, combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period. The amount of EGR gas so that the combustion timing characteristic value corresponding to the combustion timing calculated by the combustion timing calculation means by controlling the combustion timing calculation means and the combustion timing calculation means for calculating the pressure characteristic value becomes a predetermined target value. The combustion timing calculation means is calculated from the combustion chamber pressure P detected by the in-cylinder pressure sensor, the combustion chamber volume V determined from the crank angle θ, and the specific heat ratio κ of the combustion gas. PV^κBased on the value of, the PV after the start of fuel injection from the fuel injection valve^κValue is the minimum value PV^κA control device for an internal combustion engine is provided, which calculates the time Δtd until min is taken as the combustion pressure characteristic value, and adjusts the EGR gas amount so that the Δtd becomes a predetermined target value. To.</p><p> That is, in the invention of claim 3, PV after the start of fuel injection from the fuel injection valve is set as the combustion pressure characteristic value corresponding to the combustion timing.^κValue is the minimum value PV^κCalculate the time Δtd until min is taken, and adjust the EGR gas amount (EGR rate) so that this Δtd becomes a predetermined target value.</p><p> As will be described later, PV if there is no heat in and out of the air-fuel mixture in the cylinder from the equation of state of gas.^κIs a constant value. However, since heat is actually dissipated through the piston and cylinder walls, PV is used before combustion starts in the compression stroke.^κThe value of is decreasing. Then, when combustion starts, PV is generated due to heat generation.^κThe value of will increase.</p><p> Therefore PV^κThe point at which the value of is changing from decreasing to increasing, that is, PV^κValue is the minimum value PV^κWhen it reaches min, it is the time when combustion started. Therefore, PV after the start of fuel injection^κValue is the minimum value PV^κThe time Δtd until min is taken corresponds to the time from the start of fuel injection to the actual start of combustion, that is, the ignition delay time.</p><p> As mentioned above, the ignition delay time is closely correlated with the amount of EGR gas (EGR rate). Therefore, the time Δtd, which represents 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. It is possible to accurately control the amount of EGR gas to the optimum value without increasing the calculation load.</p><p> The ignition delay time Δtd may be expressed in time (milliseconds) or crank rotation angle (CA).</p><p> According to the invention of claim 4, the fuel injection valve that injects fuel into the engine combustion chamber, the EGR device that recirculates a part of the engine exhaust as EGR gas to the engine combustion chamber, and the pressure in the engine combustion chamber are detected. It is a control device of an internal combustion engine provided with an in-cylinder pressure sensor, and further, based on the combustion chamber pressure detected by the in-cylinder pressure sensor, combustion corresponding to a combustion timing including at least one of an ignition delay period and a combustion period. The amount of EGR gas so that the combustion timing characteristic value corresponding to the combustion timing calculated by the combustion timing calculation means by controlling the combustion timing calculation means and the combustion timing calculation means for calculating the pressure characteristic value becomes a predetermined target value. The combustion timing calculation means is calculated from the combustion chamber pressure P detected by the in-cylinder pressure sensor, the combustion chamber volume V determined from the crank angle θ, and the specific heat ratio κ of the combustion gas. PV^κBased on the value of, the PV after the start of fuel injection from the fuel injection valve^κValue is the minimum value PV^κMaximum value PV after taking min^κA control device for an internal combustion engine is provided, which calculates the time Δtc until max is taken as the combustion pressure characteristic value, and adjusts the EGR gas amount so that the Δtc becomes a predetermined target value. To.</p><p> That is, in the invention of claim 4, PV is used as the combustion pressure characteristic value corresponding to the combustion timing.^κValue is the minimum value PV^κMaximum value PV after taking min^κThe time Δtc until max is taken is calculated, and the amount of EGR gas (EGR rate) is adjusted so that this Δtc becomes a predetermined target value.</p><p> As mentioned above, PV^κThe value of decreases if there is no combustion. Therefore, PV^κTurns from increasing to decreasing, that is, PV^κIs the maximum value when combustion is completed. Therefore, PV^κValue is the minimum value PV^κMaximum value PV after becoming min^κThe time Δtc until reaching max corresponds to the time from the start to the end of combustion, that is, the combustion period.</p><p> As mentioned above, the combustion period is closely correlated with the amount of EGR gas (EGR rate). Therefore, the calculation load of the control circuit is increased by using the combustion period Δtc as the combustion pressure characteristic value and feedback-controlling the EGR gas amount (EGR rate) so that this Δtc matches the optimum value obtained in advance. It is possible to accurately control the amount of EGR gas to the optimum value without doing so.</p><p> The combustion period Δtc may be expressed in time (milliseconds) or crank rotation angle (CA).</p><p> According to the invention of claim 5, 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 the PV.^κThe control device for an internal combustion engine according to claim 3 or 4, wherein the detection of a value of min is started after the start of main fuel injection.</p><p> That is, in the invention of claim 5, PV is used in an engine in which pilot injection is performed.^κMinimum value PV^κThe detection of min is started after the start of main fuel injection.</p><p> When pilot injection is performed, the combustion of the fuel injected by pilot injection occurs before the main fuel injection, so it is accurate to distinguish the combustion start time of the main fuel injection fuel from the combustion start time of the pilot fuel injection fuel. EGR control cannot be performed. Normally, the combustion of pilot injection fuel ends before the start of main fuel injection, so PV^κJudgment whether the value of is the minimum value, that is, PV^κBy starting the detection of the min value after the start of the main fuel injection, it is possible to accurately detect the ignition timing of the main fuel injection.</p>

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

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 4-cylinder 4-cycle diesel engine having four cylinders # 1 to # 4 is used), and 10a to 10d are engines # 1 to # 4. A fuel injection valve that injects fuel directly into each cylinder combustion chamber is shown. The fuel injection valves 10a to 10d are each connected to a common pressure accumulator 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 from the fuel injection valves 10a to 10d via the high-pressure fuel pipe.

In this embodiment, an EGR device is provided to recirculate a part of the exhaust gas of the engine to each cylinder combustion chamber of the engine. The EGR device is arranged in the EGR passage 33 that connects the exhaust passage of the engine and the intake passage of the engine or the intake port of each cylinder, and the exhaust gas (EGR gas) flow rate that is arranged in this EGR passage and returns from the exhaust passage to the intake passage. It is equipped with an EGR valve 35 that functions as a flow control valve that controls the air flow. 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.

Figure 1 shows 20 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 the present embodiment, the ECU 20 controls the discharge amount of the fuel pump 5 to control the pressure of the common rail 3 to a target value determined according to the engine operating conditions, and also performs fuel pressure control according to the engine operating state. Fuel injection that controls the injection timing and injection amount of the injection and feedback-controls the fuel injection parameters such as the EGR flow rate, fuel injection amount, and injection timing using the combustion pressure characteristic values obtained based on the in-cylinder pressure sensor output described later. Performs basic control of the engine such as control.

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

In FIG. 1, 23 is a cam angle sensor that detects the rotation phase of the camshaft of the engine 1, and 25 is a crank angle sensor that detects the rotation phase of the crankshaft. The cam angle sensor 23 is arranged near the cam shaft of the engine 1 and outputs a reference pulse every 720 degrees in terms of the crank rotation angle. Further, the crank angle sensor 25 is arranged near the crankshaft of the engine 1 and generates a crank angle pulse for each predetermined crank rotation angle (for example, every 15 degrees).

The pulse signals of the cam angle sensor 23 and the crank angle sensor 25 are supplied to the ECU 20 and used to calculate the crankshaft rotation phase angle and the engine speed.

Further, what is shown by 29a to 29d in FIG. 1 is a known type of in-cylinder pressure sensor which is arranged in each cylinder 10a to 10d and detects the pressure in the cylinder combustion chamber. Each combustion chamber pressure detected by the in-cylinder pressure sensors 29a to 29d is supplied to the ECU 20 via the AD converter 30.

The ECU 20 calculates the combustion pressure characteristic value described later based on the cylinder combustion chamber pressure detected by the in-cylinder pressure sensor 29a to 29d, and calculates the EGR gas amount, fuel injection amount, fuel injection timing, etc. based on this combustion pressure characteristic value. Feedback control.

Hereinafter, the details of the 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 this embodiment, PVmax, θmax, ΔPVmax and ΔT are used as combustion pressure characteristic values calculated based on the combustion chamber pressure detected by the in-cylinder pressure sensors 29a to 29d, and the EGR gas amount, fuel injection amount, and fuel injection timing are determined. Perform feedback control.

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

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

The PV value in this embodiment is the product (PV = P) 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. Defined as × V).

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

Since the PV value is the product of pressure and volume, the relationship of gas state equation 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. Also, from the experiment, the timing when PV reaches the maximum value PVmax (Fig. 2, θmax) corresponds to the time when the combustion of the fuel injected in the cylinder ends (strictly speaking, the time when 90% of the fuel burns). It has been confirmed. Therefore, θmax can be used as an index indicating the end of combustion in the cylinder.

In FIG. 2, θinj indicates the fuel injection start timing from the fuel injection valve (10a to 10d, hereinafter collectively referred to by reference numeral 10). Further, what is indicated by 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 combustion after a certain ignition delay time elapses, and ends combustion after a combustion time determined by various conditions elapses. Therefore, the combustion completion time ΔT (= θmax-θinj) corresponds to the sum of the fuel ignition delay time and the combustion time.

In addition, the dotted line in FIG. 2 represents the change in PV value (PV base) when combustion does not occur in the cylinder. Since PVbase represents the compression and expansion of the gas in the cylinder only by the vertical movement of the piston, it has a curve symmetrical with respect to the top dead center.

In this embodiment, the difference between the maximum value PVmax of the above-mentioned 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 mentioned above, the PVbase curve is symmetric with respect to compression top dead center. Therefore, in the present embodiment, after θmax is detected, ΔPVmax is calculated using the value of PVbase at the point of the compression stroke (indicated by θmax in FIG. 2) that is symmetrical with respect to the top dead center. In the compression stroke before combustion occurs, the PV value and PVbase value are the same. Therefore, 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 meanings 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 affected by the EGR rate (the ratio of the amount of EGR gas to the gas sucked into the cylinder), and ΔT also 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 showing the EGR rate.

In addition, the time when PVmax occurs θmax has a correlation with the end time of combustion, and is greatly related to the combustion state in the cylinder. Further, if other conditions are the same, the end time of combustion changes according to the fuel injection time.

Further, since the value of ΔPVmax is the difference (temperature difference) between the PV values during combustion and when combustion does not occur, there is a correlation with the amount of fuel burned 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 by using ΔT, θmax, and ΔPVmax.

That is, in the present embodiment, the fuel injection amount that can obtain the optimum combustion state in terms of fuel efficiency, exhaust gas properties, etc. by operating the engine by changing the operating state of the engine (combination of accelerator opening and rotation speed) in advance. Find 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 rotation speed. It is stored in the ROM of the ECU 20 in the form of a two-dimensional numerical map (hereinafter referred to as "reference injection condition map" for convenience).

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 rotation speed is used. It is stored in the ROM of ECU20 in the form of (hereinafter referred to as "target characteristic value map" for convenience).

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

Then, in this state, the combustion pressure characteristic values of ΔT, θmax, and ΔPVmax of each cylinder are calculated based on the pressures of the in-cylinder pressure sensors 29a to 29d. Then, the target values ΔT, θmax, and ΔPVmax of the combustion pressure characteristic values in the optimum combustion state are obtained from the above-mentioned target characteristic value map using the current accelerator opening and the number of rotations, and the actual combustion pressure characteristic values are these. Adjust the fuel injection amount, fuel injection timing, EGR valve opening, etc. determined from the reference injection condition map so that they match the target values.

Specifically, the ECU 20 adjusts the opening degree of the EGR valve 35 to perform feedback control so that the actual combustion pressure characteristic value ΔT becomes the target value, and so that θmax and ΔPVmax match the respective target values. Feedback control is performed between the fuel injection timing and the fuel injection amount.

As a result, the EGR and fuel injection are controlled so that the actual combustion state becomes the optimum state.

3 and 4 are flowcharts for specifically explaining the control operation (combustion pressure characteristic value control operation) based on the combustion pressure characteristic. The operations shown in FIGS. 3 and 4 are performed as routines executed by the ECU 20 at regular intervals.

Figure 3 shows the basic control operation of fuel injection and EGR. In the operation shown in Fig. 3, the ECU 20 sets the fuel injection amount, fuel injection timing, and EGR valve 35 opening to the reference value determined by the engine speed NE and the accelerator opening ACCP, respectively, and the combustion pressure characteristic value from the operation shown in Fig. 4. Set as the sum of the correction amount determined based on.

In FIG. 3, in step 301, the accelerator opening ACCP and the engine speed NE are read, and in step 303, the above-mentioned reference is stored in advance 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, using the values of ACCP and NE read in step 301, the reference fuel injection amount FI₀, Reference fuel injection timing θI₀, Reference EGR valve opening EGV₀Is read out.

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 the optimum combustion state.

The above reference values are the fuel injection amount, timing, and EGR valve opening that can obtain the optimum combustion state in the environment at the time of the experiment, but in actual operation, the difference in fuel and the engine operating environment (temperature, large) Due to differences in (pressure, etc.), variations in equipment, changes in characteristics, etc., it is not always possible to obtain the optimum combustion state even when operating using the above reference values.

Therefore, in the present embodiment, the reference value FI obtained as described above₀, ΘI₀, EGV₀The corrected values are set as the actual fuel injection amount, fuel injection timing, and EGR valve opening. That is, in step 305, the actual fuel injection amount FI, fuel injection timing θI, and EGR valve opening EGV are FI = FI.₀+ α, θI = θI₀+ β, EGV = EGV₀It is set as + γ, and in step 307, fuel injection and EGR valve opening control are performed at the value set in step 305.

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

Explaining the operation of FIG. 4, first, in step 401, the accelerator opening ACCP and the engine speed NE are read. Then, in step 403, the target values θmax of θmax, ΔPVmax, and ΔT are obtained from the two-dimensional map using ACCP and NE stored in the ROM of the ECU 20 in advance.₀, ΔPVmax₀, ΔT₀Is read out. Target value θmax₀, ΔPVmax₀, ΔT₀Is the value of θmax, ΔPVmax, and ΔT when optimum combustion is obtained at each accelerator opening and rotation speed.

Then, 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.

Then, 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 actual value of ΔPVmax is the target value ΔPVmax.₀The correction amount α of the fuel injection amount is feedback-controlled so as to match, and in step 409, the actual value of θmax is the target value θmax.₀The fuel injection timing correction amount β is feedback-controlled so as to match, and in step 411, the actual value of ΔT is the target value ΔT.₀The correction amount γ of the EGR valve opening is feedback-controlled so as to match. The feedback control in steps 407 to 411 is, for example, PID control based on the deviation of the actual value from each target value.

For example, when the PID control in the present embodiment is specifically described by taking the correction amount β of the fuel injection timing as an example, the actual value of θmax and the target value θmax₀Assuming that the deviation from and is δ, the correction amount β is calculated using the following formula.

β = K₁× δ + K₂× Σδ + K₃× (δ-δ_i-1) Here, the first term K on the right side₁× δ is the proportional term, the second term K₂× Σδ is an integral term, and Σδ represents the integrated value (integrated value) of the deviation δ. In addition, item 3 K₃× (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-1Is the previous value of δ). Also, K₁, K₂, K₃Is a constant.

By repeating the operations of FIGS. 3 and 4 as described above, the actual fuel injection amount, fuel injection timing, and EGR valve opening (EGR rate) are adjusted so that the combustion pressure characteristic values match the target values. Be controlled.

In this way, by feedback-controlling the fuel injection amount, fuel injection timing, and EGR rate so that the combustion pressure characteristic values in actual operation match the target values, for example, differences in the operating environment of the engine and changes in the characteristics of the equipment The optimum combustion state can be easily obtained without individually considering the difference in combustion, the difference in fuel, and the like.

In the operations shown in FIGS. 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 to reduce the fuel injection amount, etc. It is designed to converge in a short time to the value that gives the optimum combustion state. However, it is also possible to feedback control the fuel injection amount, timing, and EGR rate itself using the combustion pressure characteristic value without setting a reference value such as the fuel injection amount in advance.

By the way, as shown in FIGS. 3 and 4, the fuel injection timing θI is set to θmax and θmax.₀When controlling based on the deviation δ from, the control diverges, especially when the target value of the fuel injection timing itself is significantly advanced, such as when operating in the low temperature combustion mode described later. there's a possibility that.

For example, the actual value of θmax is the target value θmax.₀In the case of a further delay, the fuel injection timing θI is advanced in order to accelerate θmax. However, when the fuel injection timing has already been set significantly, such as during low-temperature combustion, if the fuel injection timing is advanced excessively, combustion becomes unstable and misfires are likely to occur. When the fuel injection timing is advanced, θmax may be delayed.

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 diverges, but also, for example, due to an excessive fuel injection advance angle, the inside of the cylinder Fuel injection is performed 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. In such a case (bore flushing), there is a problem that liquid fuel adheres to the cylinder wall, which causes dilution of lubricating oil and deterioration of fuel efficiency and exhaust properties.

In particular, when the EGR gas amount is controlled by using ΔT at the same time as shown in step 411 of FIG. 4, if the fuel injection timing is excessively advanced, the ΔT value becomes excessive and the EGR gas amount becomes excessive. Since it is significantly reduced, the change in fuel injection timing and the increase / decrease in the amount of EGR gas may affect each other and the control may become unstable.

Therefore, in the present embodiment, the advance angle guard value θImax is provided for the fuel injection timing θI calculated in FIG. 3 and step 305 so that the fuel injection timing does not advance beyond θImax.

Specifically, in step 305 of FIG. 3, the fuel injection timing θI is θI = θI.₀When calculated as + β, the ECU 30 compares the calculated θI with the advance guard value θImax, and when θI is set to advance above θImax (θI θImax), the calculated θI Instead, θImax is used to perform fuel injection control in step 307. 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) of the advance guard value θImax.

As a result, excessive advancement is prevented in the feedback control of the fuel injection timing using the combustion pressure characteristic value θmax, so that dilution of the lubricating oil due to bore flushing and deterioration of fuel efficiency and exhaust properties are prevented, and overadvancement is prevented. The divergence of the fuel injection timing control by the angle and the interference with the feedback control of the EGR gas amount using ΔT are prevented, and the fuel injection timing and the EGR gas amount converge to the target value in a short time.

The advance guard value θImax of the fuel injection timing is the period during which the fuel injected from the fuel injection valve does not overflow from the inside of the piston bowl or adhere to the wall surface, and the engine speed and fuel. The value is determined by the injection conditions such as injection pressure. This value varies depending on various conditions such as the shape of the piston, the arrangement of the fuel injection valve, the engine speed, and the injection pressure. Therefore, based on an experiment using an actual engine, this value is a numerical value for each rotation speed (fuel injection pressure). 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 significantly advances the normal diesel combustion mode, that is, the combustion mode in which fuel injection is performed at the end of the compression stroke and diffusion combustion with a high air-fuel ratio, and the low temperature combustion mode, that is, the fuel injection timing. Along with forming a pre-mixture in the cylinder, the operation is performed by switching between two combustion modes, a combustion mode in which the amount of EGR gas is significantly increased and combustion with a low air-fuel ratio is performed. In low-temperature combustion, NO by supplying a large amount of EGR gas to the combustion chamber while the combustion has a relatively low air-fuel ratio._XThe amount of soot generated can be significantly reduced by significantly suppressing the production of harmful substances such as, and by performing premixed combustion even though it is a diesel engine.

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 even a slight change in the EGR rate may cause the combustion state to deteriorate significantly.

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

FIG. 5 is a flowchart illustrating an 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, first, in step 501, it is determined whether or not the engine is currently operated in the low temperature combustion mode, and when the engine is not operated in the low temperature combustion mode, this operation is immediately terminated without executing step 503 or lower. .. In this case, for example, the EGR rate is controlled by open-loop control based on the accelerator opening and the engine speed as in the conventional case.

If the engine is currently operating in the low temperature combustion mode in step 501, the next step is to proceed to step 503, read the current accelerator opening ACCP and the engine rotation speed NE from the corresponding sensors, and in step 505 in advance. From the target value map of combustion completion time ΔT stored in the ROM of ECU20 in the form of a two-dimensional numerical map of ACCP and NE, the target value ΔT of ΔT in the current ACCP and NE₀Is read.

Where ΔT₀Is the combustion completion time when the EGR gas is supplied at the EGR rate at which the optimum combustion state can be obtained in the low temperature combustion mode.

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

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

As shown in Fig. 5, when operating in the low-temperature combustion mode, which is particularly sensitive to changes in the EGR rate, the EGR rate of the engine is controlled based on the combustion pressure characteristic value ΔT, so that the optimum combustion state is stable even during low-temperature combustion. Can be obtained.

By the way, as described above, the optimum EGR rate can be obtained by the control based on ΔT after the transition to the low temperature combustion mode, but when the transition from the normal combustion mode to the low temperature combustion mode is performed, the feedback control based on ΔT is used. 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, in the low temperature combustion mode, the fuel injection timing is significantly advanced as compared with the normal combustion mode. However, if the fuel injection timing is advanced all at once when shifting to the low temperature combustion mode, the engine output torque fluctuates due to a sudden change in the combustion state, and there is a problem that a so-called torque shock occurs. Therefore, a certain transition period is provided when shifting from the normal combustion mode to the low temperature combustion mode, and 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 within this transition period (time). A transition process (smoothing process) is performed that changes slowly and continuously.

Therefore, during the transition process, the fuel injection timing (Fig. 2, θinj) used for ΔT calculation gradually changes (advance angle), and the time when PVmax occurs (Fig. 2, θmax) also gradually changes (advance angle). 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 the transition to the low temperature combustion mode, feedback control of the EGR valve opening and injection timing is performed using ΔT and θmax even during the transition period to the low temperature combustion mode. At the beginning of the transition period, the value of ΔT calculated based on the actual fuel injection timing is the target value ΔT.₀Since it is considerably smaller than the above, control is performed in the direction of increasing ΔT, and the amount of fresh air may be reduced more than necessary, resulting in unstable combustion.

Therefore, in the present embodiment, the actual fuel injection timing is not used when calculating ΔT during the transition period, but the target fuel injection timing after the transition to low temperature combustion is completed 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 the present 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 excessively increased, and during the transition period to the low temperature combustion mode. It is also possible to maintain the EGR rate properly.

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

In FIG. 6, the curve θinj represents the change in the fuel injection time, the curve θmax represents the change in the time when PVmax occurs, and the actual ΔT (actual ΔT) is equal to the distance between these two curves (Fig. 6). 6).

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

In this case, as shown in Fig. 6, θinj does not change significantly 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 the target value ΔT.₀At the beginning of the transition period, the difference between the above and the above becomes relatively large, and the control proceeds in the direction of significantly increasing the amount of EGR gas, causing a problem that the EGR rate becomes excessive. Therefore, if the amount of EGR gas is controlled based on ΔT during the transition period to the low temperature combustion mode, combustion becomes unstable and misfire may occur in an extreme case.

On the other hand, ΔT calculated by using the fuel injection timing target value after switching the low temperature combustion mode instead of the actual fuel injection timing is larger than the actual ΔT as shown in FIG. 6, and ΔT. The difference from the target value of is small. Therefore, in the present embodiment, it is prevented that the EGR rate is suddenly increased, and the EGR rate is gradually increased according to the advance angle of the injection timing.

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

Next, control at the time of switching from the low temperature combustion mode to the normal combustion mode, which is the opposite of the above, will be described with reference to FIG. 7.

For example, consider a case where the fuel injection amount, fuel injection timing, EGR rate, etc. are controlled using the combustion pressure characteristic value only during the operation in the low temperature combustion mode, 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 and fuel injection. The timing, EGR gas amount, etc. include the feedback correction amount.

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

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. It is designed to continuously change from to the target value in the normal combustion mode 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 (open). Loop control). Therefore, at what point the feedback control is stopped and the feedback correction amount β is set to 0 becomes a problem. For example, if the feedback control is stopped immediately at the start of the transition period, the fuel injection timing will change abruptly by the feedback correction amount β at the same time as the transition period starts, and there is a possibility that torque fluctuation will occur due to a sudden change in the fuel injection timing. This also applies when the feedback control is continued during the transition period and the feedback control is stopped when the transition is completed.

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

In FIG. 7, the dotted line is the target value θI of the fuel injection timing.₀The solid line shows the actual fuel injection timing θI. As shown in the figure, in the low temperature combustion mode operation, feedback control is performed based on the combustion characteristic value θmax, and the target value θI₀There is a difference by the feedback correction amount β between the actual fuel injection timing θI and the actual fuel injection timing θI.

When the transition period is started, the feedback control is stopped immediately 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. Therefore, in the present embodiment, a sudden change in the fuel injection timing due to the suspension of feedback control at the start of the transition period is prevented.

Then, as shown in FIG. 7, the value of β during the transition period is continuously reduced to 0 at the end of the transition period (for example, the value of β decreases in proportion to the passage of time after the start of the transition period. Let). As a result, the actual fuel injection timing θI gradually becomes the target fuel injection timing θI during the transition period.₀At the end of the transition period, θI₀Will match. As a result, in the present 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 by using the combustion pressure characteristic value ΔT, and it is possible to obtain the optimum EGR rate for combustion even during low-temperature combustion.

For example, NO during exhaust when the air-fuel ratio of the exhaust flowing into the engine exhaust passage is lean._XWas occluded by absorption, adsorption, or both, and when the air-fuel ratio of the inflowing exhaust became rich, NO was occluded using reducing components such as CO in the exhaust and HC._XKnown NO to reduce and purify_XWhen purifying exhaust gas by installing a storage reduction catalyst, the above NO_XNO stored in the occlusion reduction catalyst_XIt is necessary to accurately control the exhaust air-fuel ratio (engine air-fuel ratio) at the time of reduction purification. However, although the optimum EGR rate can be obtained with good responsiveness by the above control, it is not always possible to accurately control the combustion air-fuel ratio (exhaust air-fuel ratio) of the engine.

For example, if the injection characteristics of the fuel injection valve change due to wear of the internal mechanism, or if the injection characteristics vary from product to product, the target air-fuel ratio will not necessarily be the target air-fuel ratio even if the combustion pressure characteristic value is controlled to the target value. Not always obtained.

On the other hand, in order to control the exhaust air-fuel ratio to the target air-fuel ratio, an air-fuel ratio sensor is placed in the exhaust passage and the exhaust air-fuel ratio is directly measured so that the exhaust air-fuel ratio becomes the target value. It is also possible to control the feedback.

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

Therefore, in the present embodiment, by combining the EGR feedback control using the combustion pressure characteristic value with the feedback learning control based on the air-fuel ratio sensor output, the EGR gas amount is controlled with good responsiveness including during transient operation, and the exhaust gas is exhausted. It is possible to control the air-fuel ratio with high accuracy.

That is, in the present embodiment, for example, ΔT is the target value ΔT by the feedback control of FIG.₀When a predetermined learning control condition (for example, the engine is operating in a steady state) is satisfied while being controlled to match the above, the air-fuel ratio sensor placed in the exhaust passage detects it. Combustion completion period target value ΔT so that the exhaust air-fuel ratio matches the target air-fuel ratio determined by the accelerator opening ACCP and the engine speed NE.₀Change the value of.

For example, if the actual exhaust air-fuel ratio is on the rich side of the target air-fuel ratio, the target value ΔT₀Is reduced by a predetermined amount GT, and if it is leaner than the target air-fuel ratio, the target value ΔT₀Is increased by a predetermined amount GT.

And the target value ΔT after increase / decrease₀EGR gas amount control based on ΔT is performed again using, and the target value ΔT after the actual ΔT increases or decreases.₀Adjust the amount of EGR gas so that it matches the actual ΔT and the corrected target value ΔT.₀If they match, it is determined again whether the exhaust air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio match, and if they do not match, the target value ΔT is again determined.₀Is increased or decreased by a predetermined value GT, and the above operation is repeated.

Then, the target value ΔT when both the exhaust air-fuel ratio and ΔT match the target value.₀Is stored as a new target value (learning value) in the accelerator opening ACCP and the engine speed NE. In this way, the combustion pressure characteristic value ΔT is based on the actual air-fuel ratio sensor output.₀By performing the learning correction of, it is possible to accurately control the exhaust air-fuel ratio while controlling the EGR rate with good responsiveness.

Next, another embodiment of the present invention will be described. In each of the above-described embodiments, the PV value is calculated, and the EGR gas amount is controlled by using ΔT obtained based on PVmax as the combustion pressure characteristic value. However, as a combustion pressure characteristic value suitable for controlling the amount of EGR gas, a value other than PVmax or ΔT that has a close correlation with one or both of the ignition delay period and the combustion period should be used in the same manner. Can be done.

For example, in the present embodiment, PV is used as a combustion pressure characteristic value having a close correlation between the ignition delay period and the combustion period.^κValue is the minimum value PV^κTime to take min Δtd and PV^κValue is the minimum value PV^κMaximum value PV after taking min^κThe time to take max is used with Δtc.

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

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

On the other hand, when the air-fuel mixture is ignited and combustion is started, combustion heat is generated, so PV^κThe value of begins to increase. Therefore, PV^κThe point at which the value of is changing from decreasing to increasing, that is, PV^κIs the minimum value PV^κThe point that becomes min is the starting point of combustion. Similarly, PV during combustion^κThe value of PV continues to increase, but when combustion is completed and heat is no longer generated, PV^κThe value of begins to decrease again. Therefore PV^κThe point at which the value of is changing from increasing to decreasing, that is, PV^κIs the maximum value PV^κThe point of max is the end point of combustion.

Now, the fuel injection start time is θinj, PV^κIs the minimum value PV^κAssuming that the crank angle of min is θstart, Δtd = θstart-θinj is the period from the start of fuel injection to the start of combustion, and is therefore equal to the ignition delay period.

Also, PV^κIs the maximum value PV^κAssuming that the crank angle at 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 mentioned 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 by using either the ignition delay period Δtd or the combustion period Δtc in the same manner as when ΔT is used.

That is, in the present embodiment, the value of the ignition delay period (or combustion period) in the combustion state in which the optimum EGR rate is obtained in advance is set as the target value Δtd.₀(Or Δtc₀) Is set for each accelerator opening ACCP and engine speed NE. Then, in actual operation, PV is calculated from the combustion chamber pressure and crank angle for each stroke cycle.^κWhile calculating the value of, this PV^κThe crank angle at which the value of is the minimum value (or the minimum value and the maximum value) is detected, and Δtd (or Δtc) in actual operation is calculated.

Then, Δtd (or Δtc) and its target value Δtd in the current operating state (ACCP, NE).₀(Or Δtc₀), The EGR control valve opening is feedback-controlled.

The specific heat ratio κ can be approximately constant, and the combustion chamber volume V is a function of the crank angle and can be calculated in advance. Therefore, PV^κWhen calculating, V for each crank angle in advance^κBy calculating the value of and storing it in the ROM of ECU30 in the form of a numerical table, PV can be easily obtained.^κThe value of can be calculated.

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

The calculated PV is used when pilot injection is performed to prepare favorable temperature and pressure conditions for combustion of the main fuel injection fuel by injecting a small amount of fuel and burning it in the combustion chamber prior to the main fuel injection.^κValue is the minimum value PV^κIf the determination as to whether or not it is min is started after the start of main fuel injection, it is possible to prevent erroneous detection of the time when the combustion of the pilot fuel injection fuel starts as the injection start point of the main fuel injection fuel.

<figref num="1">It is a figure which shows the schematic structure of the embodiment which applied this invention to the diesel engine for automobiles.</figref><figref num="2">It is a figure explaining the definition of the combustion pressure characteristic value used in this embodiment.</figref><figref num="3">It is a flowchart explaining the basic control such as fuel injection in this embodiment.</figref><figref num="4">It is a flowchart explaining the control operation such as fuel injection using a combustion pressure characteristic value in this embodiment.</figref><figref num="5">It is a flowchart explaining another embodiment of EGR rate control using a combustion pressure characteristic value.</figref><figref num="6">It is a timing diagram explaining the switching control from a normal combustion mode to a low temperature combustion mode.</figref><figref num="7">It is a timing diagram explaining the switching control at the time of returning from a low temperature combustion mode to a normal combustion mode.</figref>

Code description

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