JP2007100526A - Egr control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR control device of an internal combustion engine capable of excellently maintaining an exhaust gas characteristic and drivability by securing stable combustion by compressed self-ignition even when the combustion temperature varies by a change in an operation state and an environmental condition of the internal combustion engine. <P>SOLUTION: This EGR control device has a means for calculating an unburnt gas quantity GCYL filled in a cylinder 3a in response to the target unburnt gas temperature by setting the target unburnt gas temperature TempCYL in response to the operation state of the internal combustion engine 3, a means for detecting the temperature TA of fresh air sucked in the cylinder 3a, a means for acquiring the temperature TEXGAS of burnt gas for every combustion, a means for calculating a target EGR quantity (a target inside EGR quantity nEGR) in response to the target unburnt gas temperature TempCYL, the target unburnt gas quantity GCYL, the burnt gas temperature TEXGAS and the fresh air temperature TA, and a means for controlling a variable EGR mechanism 72 capable of changing an EGR quantity based on the target EGR quantity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an EGR for an internal combustion engine that controls an EGR amount in which a part of burned gas generated by combustion remains in a cylinder in an internal combustion engine capable of compression ignition combustion operation for compressing and igniting unburned gas in a cylinder. The present invention relates to a control device.

  As a conventional control device for an internal combustion engine, for example, one disclosed in Patent Document 1 is known. The internal combustion engine is a gasoline engine (hereinafter simply referred to as “engine”), and is configured to operate by switching between spark ignition by a spark plug and self-ignition by compression. Moreover, it has a variable valve mechanism for changing the opening / closing timings of the intake valve and the exhaust valve. The intake pipe is provided with an intake air temperature sensor for detecting the intake air temperature, and the exhaust pipe is provided with an exhaust gas temperature sensor for detecting the exhaust gas temperature.

  In this control device, it is determined whether the engine is in the spark ignition combustion region or the self-ignition combustion region in accordance with the engine speed and the required load. When the engine is in the spark ignition combustion region, the opening / closing timing of the intake / exhaust valves is controlled to a normal timing by the variable valve mechanism. On the other hand, when the engine is in the self-ignition combustion region, the exhaust valve is controlled to close early during the exhaust stroke, and the intake valve opens late during the intake stroke, thereby It remains in the cylinder as EGR gas. Thereby, in the next combustion cycle, the internal EGR gas is added to the intake fresh air, and the temperature of the cylinder internal gas is increased, so that the cylinder internal gas is easily ignited by compression.

  Further, the amount of internal EGR gas at this time is controlled as follows. That is, the required temperature of the in-cylinder gas at the start of compression is calculated according to the engine speed and the required load. This required temperature is set so that the self-ignition timing of the in-cylinder gas becomes an appropriate timing. Next, a required EGR amount that is a required amount of internal EGR gas is calculated according to the intake air temperature and the exhaust gas temperature. The required EGR amount is calculated so that the in-cylinder gas has the calculated required temperature when the internal EGR gas is added to the intake fresh air. The intake / exhaust valve opening / closing timing is calculated based on the calculated required EGR amount.

  As described above, in order to self-ignite the in-cylinder gas at an appropriate timing by compression, it is necessary to adjust the temperature of the in-cylinder gas to an appropriate temperature using the internal EGR gas. However, in the control device of Patent Document 1, as described above, the required EGR amount is calculated according to the exhaust gas temperature, and therefore, the temperature of the gas in the cylinder cannot be adjusted to an appropriate temperature for the following reason. There is a possibility that the gas cannot be ignited at an appropriate timing.

  Since the exhaust temperature is detected by an exhaust temperature sensor provided in the exhaust pipe, after the cylinder gas in the cylinder burns, it is discharged to the exhaust pipe, reaches the exhaust temperature sensor, and there is a delay until it is detected. Accompany. For this reason, the operating state and environmental conditions change when the operating state and environmental conditions of the internal combustion engine are changing, for example, immediately after the engine operating state is switched from spark ignition to self-ignition or during operation by self-ignition. As a result, when the combustion temperature fluctuates, the detected temperature is deviated from the gas temperature after combustion in the cylinder due to the detection delay of the exhaust temperature sensor. For this reason, if the required EGR amount is calculated using the detected exhaust gas temperature, the temperature of the in-cylinder gas cannot be controlled to an appropriate temperature, and the ignition timing is deviated from the appropriate timing. As a result, the combustion becomes unstable, the output of the engine is not stabilized, torque shock occurs, and further, misfire and knocking thereby occur, which may deteriorate exhaust gas characteristics and drivability.

  The present invention has been made to solve the above problems, and can ensure stable combustion by compression ignition even when the combustion temperature fluctuates due to changes in the operating state and environmental conditions of the internal combustion engine. Thus, an object of the present invention is to provide an EGR control device for an internal combustion engine that can maintain good exhaust gas characteristics and drivability.

JP 2001-289092 A

  In order to achieve the above object, the invention according to claim 1 is an internal combustion engine capable of performing compression ignition combustion operation for compressing and igniting unburned gas in the cylinder 3a (an engine in the embodiment (hereinafter the same in this section)). 3, an EGR control device 1 for an internal combustion engine that controls an EGR amount that causes a part of burned gas generated by combustion to remain in the cylinder 3 a, and is a variable EGR that can change the EGR amount remaining in the cylinder 3 a. The engine (exhaust valve holding mechanism 72) and the operation state detection means (crank angle) for detecting the operation state (engine speed NE, engine water temperature TW, required torque PMCMD, exhaust temperature TEX, compression ignition combustion flag F_HCCI) of the internal combustion engine 3 Sensor 20, water temperature sensor 21, accelerator opening sensor 24, exhaust temperature sensor 25, ECU 2, step 17) of FIG. 7, and detected operating conditions of the internal combustion engine And a target unburned gas temperature setting means (ECU2, step 2 in FIG. 5) for setting a target unburned gas temperature TempCYL that is a target value of the temperature in the vicinity of the top dead center of the unburned gas compression stroke. Unburned gas amount calculating means (ECU 2, step 3 in FIG. 5) for calculating the amount of unburned gas charged into the cylinder 3a (unburned gas amount GCYL) according to the target unburned gas temperature TempCYL. The fresh air temperature detecting means (intake air temperature sensor 22) for detecting the temperature of fresh air sucked into the cylinder 3a (intake air temperature sensor 22), and the burnt gas temperature (burnt gas temperature TEXGAS) Burned gas temperature acquisition means (ECU 2, step 6 of FIG. 5) acquired for each combustion, set target unburned gas temperature TempCYL, calculated unburned gas amount GCYL, acquired burned gas temperature TEXGAS, Oh And a target EGR amount calculating means for calculating a target EGR amount (target internal EGR amount nEGR), which is a target value of the EGR amount, and a variable based on the calculated target EGR amount according to the detected fresh air temperature. And EGR control means (ECU 2, step 5 in FIG. 5) for controlling the EGR mechanism.

  According to the EGR control device for an internal combustion engine, the unburned gas to be generated in the cylinder for the next combustion according to the operating state of the internal combustion engine, near the top dead center of the compression stroke, for example, after the top dead center The target unburned gas temperature, which is the target value of the temperature in the vicinity of the crank angle of 0 ° to 10 °, is set, and the amount of unburned gas is calculated according to the target unburned gas temperature. Further, the temperature of the burned gas in the cylinder caused by the combustion of the unburned gas is acquired for each burn of the unburned gas by the burned gas temperature acquisition means. Further, a target EGR amount that is a target value of the EGR amount is calculated in accordance with the target unburned gas temperature, the unburned gas amount, the burned gas temperature, and the temperature of fresh air sucked into the cylinder. The variable EGR mechanism is controlled by the EGR control means based on the target EGR amount, so that the burned gas of the target EGR amount remains in the cylinder as the internal EGR gas and is not used for the next combustion. The temperature of the fuel gas is controlled to the target unburned gas temperature.

  As described above, the temperature of the burned gas in the cylinder is acquired for each combustion, and the target is determined according to the burned gas temperature, the target unburned gas temperature, the unburned gas amount, and the fresh air temperature acquired as such. The amount of EGR is calculated. Therefore, even when the temperature of burned gas, that is, the temperature of EGR gas fluctuates for each combustion due to changes in the operating state and environmental conditions of the internal combustion engine, by setting the target EGR amount appropriately, The temperature of the fuel gas can be accurately controlled to the target unburned gas temperature. As a result, it is possible to control the ignition timing to an appropriate timing, thereby ensuring stable combustion by compression ignition of the internal combustion engine and stabilizing the output of the internal combustion engine. Therefore, generation | occurrence | production of a torque shock and also generation | occurrence | production of misfire and knocking can be prevented, and exhaust gas characteristics and drivability can be maintained favorable.

  Hereinafter, an EGR control device for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 2, the control device 1 includes an ECU 2. As will be described later, the ECU 2 performs an EGR control process or the like according to an operating state of an internal combustion engine (hereinafter referred to as “engine”) 3 or the like. Various control processes are executed.

  As shown in FIGS. 1 and 3, the engine 3 is, for example, an in-line four-cylinder gasoline engine having four cylinders 3a (only one is shown), and is mounted on a vehicle (not shown), and the piston of each cylinder 3a. A combustion chamber 3g is formed between 3b and the cylinder head 3c.

  The engine 3 includes a pair of intake valves 4, 4 (only one is shown) and a pair of exhaust valves 7, 7 (only one is shown) provided for each cylinder 3 a, and an intake side movement that opens and closes the intake valve 4. A valve mechanism 40, an exhaust side valve mechanism 60 that opens and closes the exhaust valve 7, a fuel injection valve 10 (see FIG. 2), a spark plug 11 (see FIG. 2), and the like are provided.

  The stem 7a of the exhaust valve 7 is slidably fitted to a guide 7b, and this guide 7b is fixed to the cylinder head 3c. Further, the exhaust valve 7 is urged toward the valve closing side by a valve spring 7e provided between the upper and lower spring seats 7c, 7d. Further, the configuration of the intake valve 4 and the vicinity thereof is the same as that of the exhaust valve 7 side.

  Since the intake side valve mechanism 40 and the exhaust side valve mechanism 60 have substantially the same configuration, the exhaust side valve mechanism 60 will be described below as a representative of them. The exhaust side valve mechanism 60 includes an exhaust camshaft 8 having an exhaust cam 9, an exhaust cam 9, a rocker arm 63, and an exhaust valve holding mechanism 72 described later. The exhaust camshaft 8 is rotatably attached to the cylinder head 3c via a holder 3f fixed to the upper surface of the cylinder head 3c, and extends along the arrangement direction of the cylinders 3a. An exhaust sprocket (not shown) is coaxially provided at one end of the exhaust camshaft 8. The exhaust sprocket is connected to the crankshaft 3d via a timing chain (not shown), and the exhaust camshaft 8 rotates once every time the crankshaft 3d rotates twice.

  Further, the exhaust cam 9 is provided for each exhaust valve 7 integrally with the exhaust camshaft 8 (only one is shown), and is in contact with the central portion of the rocker arm 63 from above. The rocker arm 63 is disposed below the exhaust camshaft 8, is rotatably supported by the rocker arm shaft 62 at one end, and is in contact with the exhaust valve 7 from above at the other end. The rocker arm shaft 62 is supported by the holder 3 f and extends in parallel with the exhaust camshaft 8. With the above configuration, each exhaust valve 7 is moved along the guide 7b by rotating the rocker arm 63 around the rocker arm shaft 62 with the exhaust cam 9 by the rotation of the exhaust camshaft 8 accompanying the rotation of the crankshaft 3d. It is opened and closed in the vertical direction.

  The fuel injection valve 10 is provided for each cylinder 3a, and is attached to the cylinder head 3c so as to inject fuel directly into the cylinder 3a. That is, the engine 3 is configured as a direct injection engine. Further, the valve opening time and valve opening timing of the fuel injection valve 10 are controlled by the ECU 2, thereby controlling the fuel injection time and the fuel injection timing.

  A spark plug 11 is also provided for each cylinder 3a and attached to the cylinder head 3c. The discharge of the spark plug 11 is controlled by the ECU 2 according to the ignition timing, whereby the unburned gas in the combustion chamber 3g is spark-ignited and burned.

  The intake pipe 12 of the engine 3 is provided with a throttle valve mechanism 13. The throttle valve mechanism 13 includes a throttle valve 13a and a TH actuator 13b that opens and closes the throttle valve 13a. The throttle valve 13a is rotatably provided in the intake pipe 12. The throttle valve 13a is rotated by being driven by the TH actuator 13b, and the amount of air sucked into the cylinder 13a is determined according to the opening degree. Change.

  The engine 3 is provided with a crank angle sensor 20 and a water temperature sensor 21. The water temperature sensor 21 detects the engine water temperature TW, which is the temperature of the cooling water circulating in the cylinder block 3e of the engine 3, and outputs a detection signal representing it to the ECU 2. The crank angle sensor 20 includes a magnet rotor and an MRE pickup, and outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft 3d rotates.

  The CRK signal is output every predetermined crank angle (for example, 10 °), and the ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3b of each cylinder 3a is at a predetermined crank angle position slightly ahead of the TDC position of the intake stroke, and in this example, which is a four-cylinder engine, 180 °. Is output every time.

  In addition, an intake air temperature sensor 22 and an intake pipe internal pressure sensor 23 (both of which are shown in FIG. 2) are provided downstream of the throttle valve mechanism 13 of the intake pipe 12. The intake air temperature sensor 22 detects the temperature (hereinafter referred to as “intake air temperature”) TA of air (fresh air) drawn into the cylinder 3a, and outputs a detection signal indicating the detected temperature to the ECU 2. The intake pipe internal pressure sensor 23 detects the pressure in the intake pipe 12 (hereinafter referred to as “intake pipe internal pressure”) PBA as an absolute pressure, and outputs a detection signal representing the detected pressure to the ECU 2.

  The exhaust valve holding mechanism 72 is provided for each exhaust valve 7 and constitutes a variable EGR mechanism in the present embodiment. By changing the closing timing of the exhaust valve 7, the cylinder 3a is burned by combustion of unburned gas. Internal EGR is performed in which part of the burned gas generated in the cylinder 3a remains in the cylinder 3a. The exhaust valve holding mechanism 72 is configured in the same manner as already proposed in Japanese Patent Application Laid-Open No. 2004-52580, and the schematic configuration thereof will be described below.

  The exhaust valve holding mechanism 72 is fixed to the holder 3 f above the corresponding exhaust valve 7, and has an electromagnetic actuator 73, a hydraulic damper mechanism 80, and an armature locking mechanism 90. The electromagnetic actuator 73 has a pair of yokes 74 and 74 each having a large number of laminated plates, and a coil 75 wound around a bobbin is fitted in a coil housing groove 74 a of each yoke 74. An armature 76 is provided above the yokes 74 and 74, and a holding rod 77 extending in the vertical direction is integrally provided at the center thereof. The holding rod 77 extends from the armature 76 between the yokes 74 and 74 and abuts against the rocker arm 63 of the exhaust valve 7. The coil 75 is connected to the ECU 2, and is energized and excited by the ECU 2 to attract the armature 76.

  The hydraulic damper mechanism 80 is provided above the electromagnetic actuator 73, and includes a casing 81, a cylinder 81a formed in the casing 81, first and second oil passages 81b and 81c communicating with the cylinder 81a, A piston 82 is slidably fitted into the cylinder 81a, and a return spring 83 is provided between the piston 82 and the casing 91. Further, the piston 82 is in contact with the upper surface of the armature 76. The first and second oil passages 81b and 81c are respectively connected to a hydraulic pump (not shown), and the hydraulic pump is driven by the ECU 2 so as to pass through the first and second oil passages 81b and 81c. Hydraulic pressure is supplied to the cylinder 81a.

  The armature locking mechanism 90 includes a lower casing 91 and an upper casing 92. An armature locking member 93 is provided in a guide hole 91a formed in the lower casing 91, a piston 94 is provided in a cylinder 92a of the upper casing 92, Each is slidably fitted. The armature locking member 93 is urged upward by a return spring 95 provided in the guide hole 91a, thereby abutting against the end of the lower surface of the armature 76 and the lower surface of the piston 94, and pressing them. Yes. The cylinder 92a is supplied with hydraulic pressure from the hydraulic pump.

  Next, the operation of the exhaust valve holding mechanism 72 described above will be described with reference to FIG. In the exhaust stroke, the exhaust valve 7 is driven by the exhaust cam 9, and the coil 75 of the electromagnetic actuator 73 is excited in accordance with the timing when the lift amount becomes maximum. As a result, the armature 76 is attracted to the coils 75, 75 against the urging force of the return spring 95, whereby the holding rod 77 is lowered and presses the rocker arm 63. As a result, as shown by the broken line (a) in the figure, the exhaust valve 7 is held in the open state with the maximum lift amount.

  Thereafter, for example, when the coil 75 is de-excited at the closing angle d 1, the attractive force to the armature 76 disappears, and the armature 76 and the holding rod 77 are pushed upward by the urging force of the return spring 95. As a result, the armature 76 leaves the upper surface of the yokes 74 and 74 and collides with the upper piston 82. The impact at this time is alleviated by the return spring 83 of the hydraulic damper mechanism 80 and the hydraulic pressure. Further, the exhaust valve 7 immediately returns to the closed state by the urging force of the valve spring 7e when the pressing force of the holding rod 77 acting via the rocker arm 63 disappears.

  As described above, since the exhaust valve 7 is kept open while the coil 75 is excited, the valve closing timing of the exhaust valve 7 is changed by changing the closing angle d1 at which the coil 75 is de-energized. It can be controlled steplessly. Thus, the amount of burned gas discharged to the exhaust pipe 14, that is, the amount of burned gas remaining in the cylinder 3a (internal EGR amount) can be freely controlled. Specifically, when the closing angle d1 is changed to the retarding side, the valve closing timing is delayed, thereby reducing the internal EGR amount. On the other hand, when the closing angle d1 is changed to the advance side, the valve closing timing is advanced, so that the internal EGR amount increases.

  The intake valve holding mechanism 71 on the intake valve 4 side is configured in the same manner as the exhaust valve holding mechanism 72 and excites the coil in accordance with the timing at which the lift amount of the intake valve 4 becomes maximum in the intake stroke. By controlling the de-excitation timing (closing angle d2), it is possible to control the closing timing of the intake valve 4 steplessly (broken line (b)).

  Further, an accelerator opening sensor 24 and an exhaust temperature sensor 25 are connected to the ECU 2. The accelerator opening sensor 24 detects an accelerator opening AP, which is an operation amount of an accelerator pedal (not shown), and outputs a detection signal representing it to the ECU 2. Further, the exhaust temperature sensor 25 detects the temperature (hereinafter referred to as “exhaust temperature”) TEX of the exhaust gas flowing in the exhaust pipe 14 and outputs a detection signal indicating it to the ECU 2.

  The ECU 2 is composed of a microcomputer (all not shown) including an I / O interface, CPU, RAM, ROM and the like. The detection signals from the various sensors 20 to 25 described above are each input to the CPU after A / D conversion and shaping by the I / O interface.

  In accordance with these input signals, the CPU discriminates the operating state of the engine 3 according to a control program stored in the ROM, etc., and sets the operating mode of the engine 3 with the spark plug 11 according to the discriminated operating state. Either a spark ignition combustion mode in which unburned gas is burned by spark ignition or a compression ignition combustion mode in which unburned gas is burned by compression ignition without spark ignition is set. In the present embodiment, the ECU 2 constitutes a target unburned gas temperature setting means, an unburned gas amount calculation means, a burned gas temperature acquisition means, a target EGR amount calculation means, and an EGR control means.

  Hereinafter, the EGR control process executed by the ECU 2 will be described with reference to FIG. This EGR control process controls the internal EGR amount by controlling the closing timing of the exhaust valve 7 by the exhaust valve holding mechanism 72 in accordance with the set operation mode of the engine 3. This process is executed in synchronization with the input of the TDC signal.

  First, in step 1 (illustrated as “S1”, hereinafter the same), the required torque PMCMD is calculated by searching the map shown in FIG. 6 according to the engine speed NE and the accelerator pedal opening AP. In this map, the required torque PMCMD is set as the indicated mean effective pressure, and is set to a larger value as the engine speed NE is higher and the accelerator pedal opening AP is larger. This is because the higher the engine speed NE and the greater the accelerator pedal opening AP, the greater the load on the engine 3, which is to be dealt with.

  Next, the target unburned gas temperature TempCYL is set (step 2). This target unburned gas temperature TempCYL is a target value of the temperature of the unburned gas that is to be charged into the cylinder 3a for the next combustion and is a combination of fresh air and internal EGR gas.

  FIG. 7 shows a process for setting the target unburned gas temperature TempCYL. First, in steps 11 to 13, are the engine water temperature TW, the intake air temperature TA, and the exhaust gas temperature TEX higher than the respective predetermined temperatures TWHCCI (for example, 80 ° C.), TAHCCI (for example, 0 ° C.), and TEXHCCI (for example, 250 ° C.)? Whether or not is determined.

  If both of these answers are YES, TW> TWHCCI, TA> TAHCCI, and TEX> TEXHCCI, the process proceeds to step 14 to determine whether or not the engine 3 is in an operation region where compression ignition is possible. This determination is performed by searching the map shown in FIG. 8 according to the required torque PMCMD and the engine speed NE. In this map, an operation region where the engine speed NE and the required torque PMCMD are both medium is set as an HCCI operation region where compression ignition combustion is to be performed, and another operation region is an SI operation region where spark ignition combustion is to be performed. Is set as

  If the answer to step 14 is YES and the engine 3 is in the HCCI operation region, the compression ignition combustion flag F_HCCI is set to “1” to indicate that the execution condition of the compression ignition combustion operation is satisfied. (Step 15). As a result, the engine 3 is operated in the compression ignition combustion mode. On the other hand, when the answer to any of the above steps 11 to 14 is NO, the compression ignition combustion flag F_HCCI is set to “0” in step 16 because the execution condition of the compression ignition combustion operation is not satisfied. As a result, the engine 3 is operated in the spark ignition combustion mode.

  In step 17 following step 15 or step 16, it is determined whether or not the compression ignition combustion flag F_HCCI is “1”. When the answer is YES and the engine 3 is operating in the compression ignition combustion mode, a target unburned gas for the compression ignition combustion mode is searched by searching a map (not shown) according to the engine speed NE and the required torque PMCMD. The temperature TempCYL is calculated (step 21). In this map, the target unburned gas temperature TempCYL is prioritized to obtain good exhaust gas characteristics, and is set to a smaller value as the required torque PMCMD is larger, and is larger as the engine speed NE is larger. Is set to a value. Further, the target unburned gas temperature TempCYL for the compression ignition combustion mode is set to a value generally higher than a target unburned gas temperature TempCYL for a spark ignition combustion mode described later. This is because it is effective to increase the temperature of the unburned gas in order to perform the compression ignition of the unburned gas satisfactorily, whereas there is no such necessity for the spark ignition. .

  On the other hand, if the answer to step 17 is NO and the engine 3 is operating in the spark ignition combustion mode, it is determined whether or not the required torque PMCMD is equal to or greater than a predetermined torque PMCMD1 (step 18). When the answer is NO, a target unburned gas temperature TempCYL for the spark ignition combustion mode is calculated by searching a map (not shown) according to the engine speed NE and the required torque PMCMD (step 20). In this map, the target unburned gas temperature TempCYL is set with the same tendency as the target unburned gas temperature TempCYL for the compression ignition combustion mode, giving priority to obtaining good exhaust gas characteristics.

  On the other hand, if the answer to step 18 is YES and the required torque PMCMD is equal to or greater than the predetermined torque PMCMD1, the target unburned gas temperature TempCYL is set to the predetermined temperature TempCYL1 (for example, 40 ° C.), giving priority to the output of the engine 3. (Step 19).

Returning to FIG. 5, in step 3, in the cylinder 3 a according to the following equation (1) according to the intake pipe internal pressure PBA detected by the intake pipe internal pressure sensor 23 and the target unburned gas temperature TempCYL set in step 2. An unburned gas amount GCYL charged in the gas is calculated.
GCYL = K · PBA / TempCYLA (1)
This equation (1) is based on the gas equation of state, TempCYLA is a value obtained by converting the target unburned gas temperature TempCYL into an absolute temperature, and K is determined according to the volume of the cylinder 3a, the gas constant, and the like. It is a constant.

  Next, in step 4, a target internal EGR amount nEGR is calculated. The target internal EGR amount nEGR is the amount of internal EGR gas that should remain in the cylinder 3a for the next combustion among the burned gases generated by the combustion of the unburned gas.

FIG. 9 shows processing for calculating the target internal EGR amount nEGR. First, in step 31, the internal EGR temperature TEGR is calculated by the following equation (2). The internal EGR temperature TEGR is a temperature when the burned gas is used as the internal EGR gas in the next combustion.
TEGR = α × TEXGAS (n−1) + β × TempB (n−1)
(2)
TEXGAS (n-1) is the previous value of the burned gas temperature TEXGAS obtained by the TEXGAS calculation process described later. TempB (n-1) is the temperature of a component that affects the temperature change of the burned gas until the burned gas is used as the internal EGR gas in the next combustion, represented by the wall portion of the cylinder 3a. (Hereinafter referred to as “ambient temperature”). In addition, α and β are weighting factors having a sum of 1.0 and values of 0 and 1.0, respectively.

  A part of the burned gas generated by the combustion remains in the cylinder 3a until it is used as the internal EGR gas in the next combustion, and is therefore affected by the cylinder wall temperature, which is the wall temperature of the cylinder 3a. . Therefore, as shown in the above equation (2), the burned gas temperature TEXGAS, which is the temperature of the burned gas immediately after combustion, and the ambient temperature TempB are weighted and averaged using the weighting factors α and β, thereby generating the internal EGR. The temperature TEGR can be estimated with high accuracy.

Next, the ambient temperature TempB is calculated by the following equation (3) (step 32).
TempBn = (1-α) × TEXGAS (n−1)
+ (1-β) × TempB (n−1) (3)

Next, using the target unburned gas temperature TempCYL and unburned gas amount GCYL calculated in steps 2 and 3 above, the internal EGR temperature TEGR calculated in step 31 above, and the intake air temperature TA, An EGR amount nEGR is calculated (step 32).
nEGR = GCYL
× (TempCYL-TA) / (TEGR-TA) (4)

This equation (4) is derived from the following relationship. That is, when the intake air amount sucked into the cylinder 3a is QA, the following equation (5) is established.
TempCYL = (nEGR × TEGR + QA × TA) / (nEGR + QA)
...... (5)
Moreover, Formula (7) is materialized from the relationship of the following Formula (6).
nEGR + QA = GCYL (6)
QA = GCYL-nEGR (7)
Then, when this equation (7) is substituted into equation (5) and nEGR is solved, equation (4) is obtained. Therefore, the target internal EGR amount nEGR can be appropriately calculated by this equation (4).

  Returning to FIG. 5, in step 5, the closing angle d1 of the exhaust valve 7 is calculated. FIG. 10 shows the closing angle calculation process. First, in step 41, a closing angle d1 of the exhaust valve 7 is calculated by searching a map (not shown) according to the engine speed NE, the required torque PMCMD, and the target internal EGR amount nEGR calculated in step 4. .

  Next, a drive signal based on the calculated closing angle d1 of the exhaust valve 7 is output to the electromagnetic actuator 73 of the exhaust valve holding mechanism 72 (step 42). Thereby, the internal EGR amount is controlled to the calculated target internal EGR amount nEGR, and as a result, the temperature of the unburned gas is controlled to the set target unburned gas temperature TempCYL.

  Returning to FIG. 5, in step 6, the burned gas temperature TEXGAS is calculated, and the present process is terminated. The burned gas temperature TEXGAS is a temperature immediately after combustion of the burned gas generated by burning the unburned gas generated when the closing angle d1 of the exhaust valve 7 is controlled by the execution of step 5 described above.

  FIG. 11 shows a calculation process of the burned gas temperature TEXGAS. First, in step 51, the burnt gas temperature TEXGAS calculated in the previous loop is shifted to the previous value TEXGASZ.

  Next, it is determined whether or not the fuel cut flag F_FC is “1” (step 52). The fuel cut flag F_FC is set to “1” when the fuel cut operation is being executed. If the answer is YES and the fuel cut operation is being executed, the cylinder wall temperature TCYLWAL of the cylinder 3a is set as the currently calculated value TEXGAST of the burned gas temperature (step 53). This is because combustion is not performed during the fuel cut operation, and thus the temperature of the gas remaining in the cylinder 3a substantially matches the cylinder wall temperature TCYLWAL.

  On the other hand, if the answer to step 52 is NO and the fuel cut operation is not being executed, it is determined whether or not a compression ignition combustion flag F_HCCI is “1” (step 55). When this answer is NO and the engine 3 is operated in the spark ignition combustion mode, the map for the spark ignition combustion mode shown in FIG. 12 is retrieved according to the intake air temperature TA and the required torque PMCMD, so that the burned A map value TEXGASM of the gas temperature is calculated (step 56). In this map, the map value TEXGASM is set to a larger value as the intake air temperature TA is higher and the required torque PMCMD is larger, assuming that the engine rotational speed NE is a predetermined rotational speed (for example, 6000 rpm). ing.

  During the spark ignition combustion mode, the internal EGR amount is controlled to a small amount in accordance with the target unburned gas temperature TempCYL being set to a low value. For this reason, the influence of the temperature of the internal EGR gas on the temperature of the burned gas is small, and the influence of the intake air temperature TA is rather large. Therefore, in the spark ignition combustion mode, the burned gas temperature map value TEXGASM is calculated using the intake air temperature TA.

  On the other hand, when the answer to step 55 is YES and the engine 3 is operated in the compression ignition combustion mode, the amount of internal EGR is large and the temperature of the unburned gas is high. Therefore, the target unburned gas temperature TempCYL and the required torque PMCMD Accordingly, a map value TEXGASM for the burned gas temperature is calculated by searching a map for the compression ignition combustion mode (not shown) (step 57). As with the spark ignition combustion mode, this map value TEXGASM assumes that the engine speed NE is a predetermined speed (for example, 6000 rpm), and the required unburned gas temperature TempCYL increases and the required torque PMCMD increases. A larger value is set to a larger value.

In step 58 following step 56 or 57, the current calculated value TEXGAST of the burned gas temperature is obtained by the following equation (8) according to the burned gas temperature map value TEXGASM.
TEXGAST = TEXGASM
X (1-KTEXGME x (TDCME-5))
+ TCYLWAL × KTEXGME × (TDCME-5)
...... (8)

  As is apparent from this equation (8), the currently calculated value TEXGAST of the burnt gas temperature is the difference between the burned gas temperature map value TEXGASM and the cylinder wall temperature TCYLWAL using KTEXGME × (TDMEE-5) as a weighting factor. Calculated by weighted average. As the temperature difference between the combustion temperature and the cylinder wall temperature is larger, the combustion temperature is more easily affected and is more easily cooled. Therefore, by using the cylinder wall temperature TCYLWAL as one of the weighted averages, the currently calculated value TEXGAST of the burned gas temperature can be appropriately obtained while reflecting the influence of the cylinder wall temperature. As the cylinder wall temperature TCYLWAL, a predetermined value (for example, 80 ° C.) may be used, or an estimated value of the exhaust gas temperature calculated by inputting the burned gas temperature TEXGAS into the exhaust system delay model, and You may use what was corrected one by one by deviation with exhaust temperature TEX detected by exhaust temperature sensor 25.

  Of the weighting factors KTEXGME × (TDMEE-5), KTEXGME is a basic value of a weighting factor between values 0 and 1.0, and TDME-5 is a correction factor thereof. Of these, TDME is the TDC signal generation interval (msec), and the value 5 of the subtraction term is when the engine speed NE = 6000 rpm, which is the reference speed when the burned gas temperature map value TEXGASM is set. The time interval (msec) of the TDC signal.

  With the above setting, the weight coefficient KTEXGME × (TDMEE-5) becomes 0 when the engine speed NE is the reference speed, the weight of the cylinder wall temperature TCYLWAL becomes 0, and the lower the engine speed NE, Since the TDC signal generation interval TDME is increased and the weighting coefficient KTEXGME × (TDMEE-5) is increased, the influence of the cylinder wall temperature is increased. Also, the lower the engine speed NE, the longer the time interval between combustions, and the greater the influence of the cylinder wall temperature on the combustion temperature. Therefore, the current value TEXGAST of the burnt gas temperature can be appropriately obtained while reflecting the influence of the engine speed NE by using the weight coefficient KTEXGME × (TDMEE-5) as described above.

In step 54 following step 53 or step 58, the burned gas temperature TEXGAS is calculated by the following equation (9).
TEXGAS = γTEXGAST + (1-γ) TEXGASZ (9)
Here, γ is a predetermined weighting factor between the values 0 and 1.0. As is clear from this equation (9), the burned gas temperature TEXGAS is calculated as a weighted average value of the current calculated value TEXGAST of the burned gas temperature and the previous value TEXGASZ of the burned gas temperature TEXGAS.

  FIG. 13 is a timing chart showing an operation example by the EGR control process of FIG. In this example, the required torque PMCMD is constant, and the operation mode of the engine 3 is switched from the spark ignition combustion mode to the compression ignition combustion mode at time t1 in accordance with a change in the engine speed NE.

  First, in the spark ignition combustion mode before time t1, the compression ignition combustion flag F_HCCI is “0”, and the execution of step 20 causes the target unburned gas temperature TempCYL to be a relatively low value for the spark ignition combustion mode ( For example, the required torque PMCMD is constant, and is therefore maintained at a constant value. Further, at step 56 and step 31, the burned gas temperature TEXGAS and the internal EGR temperature TEGR are calculated to be relatively high values (for example, 400 ° C.). As described above, in accordance with the setting of the target unburned gas temperature TempCYL and the internal EGR temperature TEGR, the target internal EGR amount nEGR is set to a low value (for example, 10%) according to the equation (4). The closing angle d1 of the exhaust valve 7 is set to the retard side (for example, 300 °). As a result, the actual unburned gas temperature is controlled to substantially the same value as the target unburned gas temperature TempCYL.

  When the operation mode of the engine 3 is switched to the compression ignition combustion mode from this state, the target unburned gas temperature TempCYL is higher than the spark ignition combustion mode in step 21 in the first loop (t1) immediately after that. It is set to a value for the compression ignition combustion mode (for example, 200 ° C.), and thereafter maintained at that value.

  Further, the internal EGR temperature TEGR is the same as that before the switching because the value in the spark ignition combustion mode immediately before switching is used as the previous value of the burned gas temperature TEXGAS and the previous value of the ambient temperature TempB in the equation (2). Maintained at the value. From the above setting, the target internal EGR amount nEGR is set to a larger value than in the spark ignition combustion mode according to the equation (4), and accordingly, the closing angle d1 of the exhaust valve 7 is set to be larger than that in the spark ignition combustion mode. Set to the advance side. In addition, the burned gas temperature TEXGAS is calculated to be smaller than that in the spark ignition combustion mode in step 57, and is calculated so as to decrease stepwise according to the equation (9).

  In the second and third loops (t2 and t3) after switching to the compression ignition combustion mode, the previous value of the burnt gas temperature TEXGAS is used in equation (2), so that the internal EGR temperature TEGR is And finally set to 300 ° C., for example. Accordingly, the target internal EGR amount nEGR increases stepwise and is finally set to 50%, for example, and the closing angle d1 of the exhaust valve 7 is also set to the advance side stepwise. Is set to 100 °. After switching to the compression ignition combustion mode, the target internal EGR amount nEGR and the closing angle d1 of the exhaust valve 7 are controlled as described above. As a result, the actual unburned gas temperature is as shown at the bottom of the timing chart. It is controlled with high accuracy so as to coincide with the target unburned gas temperature TempCYL.

  As described above, according to the present embodiment, the burned gas temperature TEXGAS, which is an estimated value of the burned gas generated in the cylinder 3a, is calculated for each combustion (step 6). Then, the target unburned gas amount nEGR is calculated according to the calculated burned gas temperature TEXGAS, the target unburned gas temperature TempCYL, the unburned gas amount GCYL, and the burned gas temperature TEXGAS (step 33). Even when the combustion temperature and thus the temperature of the internal EGR gas fluctuate for each combustion due to changes in the operating conditions and environmental conditions, the actual temperature of the unburned gas can be accurately controlled to the target unburned gas temperature TempCYL. The ignition timing can be controlled to an appropriate timing.

  Further, when calculating the current value TEXGAST of the burned gas temperature, the map value TEXGASM of the burned gas temperature calculated according to the target unburned gas temperature TempCYL and the required torque PMCMD is used as the TDC signal generation interval TDMEE and the cylinder wall temperature. Since the correction is performed according to TCYLWAL, the burned gas temperature TEXGAS can be calculated with high accuracy while reflecting the influence of the TDC signal generation interval TDCME and the cylinder wall temperature TCYLWAL on the combustion temperature. Further, since the internal EGR temperature TEGR is calculated according to the ambient temperature TempB using the burned gas temperature TEXGAS calculated as described above (step 31), the temperature change until the burned gas is used as the internal EGR gas. The internal EGR temperature TEGR can be accurately calculated while reflecting the above.

  Since the target internal EGR amount nEGR is calculated using the internal EGR temperature TEGR calculated with high accuracy as described above, the target internal EGR amount nEGR can be appropriately set for each combustion cycle. Thereby, the actual temperature of the unburned gas can be accurately controlled by the unburned gas temperature TempCYL. As a result, the ignition timing of the unburned gas can be controlled more appropriately, thereby ensuring stable combustion by compression ignition of the engine 3 and stabilizing the output of the engine 3. Therefore, at the time of switching the operation mode of the engine 3, it is possible to prevent the occurrence of torque shock, and further the occurrence of misfire and knocking, and it is possible to maintain good exhaust gas characteristics and drivability.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the internal EGR amount is controlled by controlling the closing angle d1 of the exhaust valve 7 by the exhaust valve holding mechanism 72, but in addition to this, the closing angle d2 of the intake valve 4 is set by the intake valve holding mechanism 71. The amount of internal EGR gas may be controlled more finely by changing and controlling the valve closing timing of the intake valve 4. In the embodiment, the exhaust valve holding mechanism 72 is used as a variable EGR mechanism for changing the internal EGR amount. Instead, other variable mechanisms, for example, the phases and lifts of the exhaust cam 9 and the intake cam are used. The internal EGR amount may be changed using a changeable mechanism.

  Further, the embodiment is an example in which the present invention is applied to a gasoline engine. However, the present invention is not limited to this, and various engines other than a gasoline engine, such as a diesel engine or an outboard motor in which a crankshaft is arranged in a vertical direction, are used. It can also be applied to a marine vessel propulsion engine. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 is a schematic diagram illustrating a schematic configuration of an internal combustion engine to which an EGR control device according to an embodiment of the present invention is applied. It is a block diagram which shows schematic structure of an EGR control apparatus. It is sectional drawing which shows schematic structure of the exhaust side valve operating mechanism of an internal combustion engine including an exhaust valve opening degree holding mechanism. It is a figure which shows the lift curve of an exhaust valve and the intake valve when performing compression ignition combustion. It is a flowchart which shows an EGR control process. It is a figure which shows an example of the map used for calculation of request | requirement torque PMCMD. It is a flowchart which shows a target unburned gas temperature setting process. It is a figure which shows an example of the map used for the driving | running | working area | region determination of an internal combustion engine. It is a flowchart which shows a target internal EGR amount calculation process. It is a flowchart which shows the closing angle calculation process of an exhaust valve. It is a flowchart which shows a burnt gas temperature calculation process. It is a figure which shows an example of the map used for the setting of the map value of burnt gas temperature. It is a timing chart at the time of the operating state of an internal combustion engine switching from spark ignition combustion mode to compression ignition combustion mode by EGR control processing.

Explanation of symbols

1 EGR control device 2 ECU (operating state detection means, target unburned gas temperature setting means,
Unburned gas amount calculating means, burned gas temperature obtaining means,
(Target EGR amount calculation means, EGR control means)
3 Internal combustion engine 3a Cylinder 20 Crank angle sensor (operating state detection means)
21 Water temperature sensor (operating state detection means)
22 Intake air temperature sensor (fresh air temperature detection means)
24 Accelerator opening sensor (operating state detection means)
25 Exhaust temperature sensor (operating state detection means)
72 Exhaust valve holding mechanism (variable EGR mechanism)
NE engine speed (operating condition)
TW engine water temperature (operating condition)
PMCMD required torque (operating condition)
TEX Exhaust temperature (operating condition)
TA Intake temperature (fresh air temperature)
TempCYL Target unburned gas temperature GCYL Unburned gas amount nEGR Target internal EGR amount (target EGR amount)
TEXGAS Burnt gas temperature (burnt gas temperature)
F_HCCI Compression ignition combustion flag (operational state)

Claims (1)

In an internal combustion engine capable of compression ignition combustion operation for compressing and igniting unburned gas in a cylinder, an EGR control device for an internal combustion engine for controlling an EGR amount in which a part of burned gas generated by combustion remains in the cylinder There,
A variable EGR mechanism capable of changing the amount of EGR remaining in the cylinder;
An operating state detecting means for detecting an operating state of the internal combustion engine;
In accordance with the detected operating state of the internal combustion engine, target unburned gas temperature setting means for setting a target unburned gas temperature that is a target value of the temperature near the top dead center of the compression stroke of the unburned gas,
Unburned gas amount calculating means for calculating the amount of unburned gas charged in the cylinder according to the set target unburned gas temperature;
Fresh air temperature detecting means for detecting the temperature of fresh air sucked into the cylinder;
A burned gas temperature obtaining means for obtaining a temperature of the burned gas for each combustion of the unburned gas;
A target EGR that is a target value of the EGR amount according to the set target unburned gas temperature, the calculated unburned gas amount, the acquired burned gas temperature, and the detected fresh air temperature. A target EGR amount calculating means for calculating the amount;
EGR control means for controlling the variable EGR mechanism based on the calculated target EGR amount;
An EGR control device for an internal combustion engine, comprising:

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