JP4339878B2 - Control device for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a compression ignition internal combustion engine.

  Recently, in an internal combustion engine using gasoline as a fuel, as described in Patent Document 1 below, compression ignition (Homogeneous Charge Compression Ignition) in which an air-fuel mixture supplied to a combustion chamber is subjected to compression ignition combustion in a predetermined operation region. Various so-called compression self-ignition internal combustion engines that perform a spark ignition operation that performs an operation (HCCI operation) and performs spark ignition combustion of an air-fuel mixture via an ignition plug in other operation regions have been proposed. . Such an internal combustion engine can increase the compression ratio more than the spark ignition engine, and can also improve thermal efficiency or fuel efficiency.

In the technique described in Patent Document 1, when the engine coolant temperature detected by the water temperature sensor is lower than a predetermined temperature set according to the intake air temperature detected by the temperature sensor, the compression ignition operation is prohibited. The internal combustion engine is always operated stably.
JP 2000-87749 A

  In the above-described prior art, if the cooling water temperature is equal to or higher than a predetermined temperature set according to the intake air temperature, as long as the cooling water temperature is within the permitted operation region defined by the engine speed and the required torque, the operation is shifted to the compression ignition operation. Be controlled. However, in the above-described prior art, when the cooling water temperature is equal to or higher than a predetermined temperature when in the permitted operation region, there is a disadvantage that the compression ignition operation cannot be fully utilized.

  That is, when the cooling water temperature is low, the wall temperature of the combustion chamber is also low. Therefore, it is necessary to increase the amount of fresh air to increase the temperature, but as a result, the compression ignition operation region moves to the high load side. Therefore, it is conceivable to change the compression ignition operation region in accordance with the cooling water temperature. In this case, knocking occurs when the cooling water temperature rises. However, if the cooling water temperature is low and the wall temperature is low, the compression ignition operation is possible without causing knocking. In that respect, the above-described conventional technique has a disadvantage that the compression ignition operation cannot be fully utilized.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and to allow the switching to the compression ignition operation as long as it is allowable from the operation state of the internal combustion engine including the cooling water temperature and the engine speed, the application range of the compression ignition operation. Is to provide a control device for a compression ignition internal combustion engine.

In order to solve the above-mentioned object, according to claim 1, the combustion chamber is provided with an ignition means, and a compression ignition operation for performing compression ignition combustion of the air-fuel mixture supplied to the combustion chamber in a predetermined operation region is performed. In a control apparatus for a compression ignition internal combustion engine that performs a spark ignition operation in which the air-fuel mixture is spark-ignited and combusted via the ignition means in an operation region other than the predetermined operation region, the required torque of the internal combustion engine is the internal combustion engine Required torque range determining means for determining whether or not the predetermined torque is within a predetermined range set according to the coolant temperature and the engine speed, and when it is determined that the required torque is within the predetermined range, the spark ignition operation wherein together and a switching permitting means for permitting switching to the compression ignition operation, it sets the lower limit value defining the predetermined range so as to decrease as the cooling water temperature decreases from Thus it was constructed as to enlarge the operating region for the compression ignition operation.

  In the control apparatus for the compression ignition internal combustion engine according to claim 2, the predetermined range is further set in accordance with a gear ratio of a transmission connected to the internal combustion engine.

In the control device for the compression ignition internal combustion engine according to claim 1, it is determined whether the required torque of the internal combustion engine is within a predetermined range set according to the cooling water temperature of the internal combustion engine and the engine speed, When it is determined to be within the predetermined range, switching from the spark ignition operation to the compression ignition operation is permitted , and the lower limit value defining the predetermined range is set so as to decrease as the cooling water temperature decreases, so that the compression ignition is performed. Since the operation range for operation is expanded, it is possible to define a region that is optimal in the TDC interval from the engine speed, and that can perform compression ignition operation such as a region where the cooling water temperature is low and the wall temperature is low. Therefore, the utilization range of the compression ignition operation can be expanded.

  In the control apparatus for the compression ignition internal combustion engine according to claim 2, the predetermined range is further set in accordance with the transmission gear ratio of the transmission connected to the internal combustion engine. In addition, when the speed reduction ratio is large (that is, when the speed of change such as the engine speed is large), by setting the predetermined range narrow, deterioration in drivability and emission due to busy switching between spark ignition operation and compression ignition operation When the reduction ratio is small (the speed of change such as the engine speed is small), the fuel consumption can be improved by expanding the predetermined range to the maximum, so that the drivability, emissions, and fuel consumption can be improved. It can be balanced at a high level.

  The best mode for carrying out a control apparatus for a compression ignition internal combustion engine according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram generally showing a control apparatus for a compression ignition internal combustion engine according to a first embodiment of the present invention.

  In FIG. 1, reference numeral 10 denotes a four-cylinder four-cycle internal combustion engine (only one cylinder is shown; hereinafter referred to as “engine”) using gasoline as fuel. In the engine 10, air (intake air) drawn from the air cleaner 12 and passing through the intake pipe 14 is adjusted in flow rate by the throttle valve 16, flows through the intake manifold 20, and two intake valves (only one is shown) 22 are opened. When it is done, it flows into the combustion chamber 24.

  An injector 26 is disposed near the intake port in front of the intake valve 22. Gasoline fuel stored in a fuel tank (not shown) is pumped to the injector 26 via a fuel supply pipe (not shown). The injector 26 is connected to an ECU (Electronic Control Unit) 30 through a drive circuit (not shown).

  The injector 26 opens when a drive signal indicating the valve opening time is supplied from the ECU 30 through the drive circuit, and injects gasoline fuel corresponding to the valve opening time into the intake port. The injected gasoline fuel is mixed with the inflowing air to form an air-fuel mixture (pre-air mixture), and flows into the combustion chamber when the intake valve 22 is opened.

  An ignition plug (ignition means) 32 is disposed in the combustion chamber 24. The spark plug 32 is connected to the ECU 30 via an ignition device (ignition means, not shown) such as an igniter. When an ignition signal is supplied from the ECU 30, a spark discharge is generated between the electrodes facing the combustion chamber. The air-fuel mixture is thereby ignited and burned, driving the piston 34 downward.

  The engine 10 is operated between a compression ignition (Homogeneous Charge Compression Ignition) operation in which an air-fuel mixture is compressed and ignited in a predetermined operation region, and a spark ignition operation in which spark ignition combustion is performed through an ignition plug 32 or the like. It is configured as a compression ignition engine (internal combustion engine) that can be switched.

  Exhaust gas (exhaust gas) generated by combustion flows to the exhaust manifold 40 when two exhaust valves (only one is shown) 36 are opened.

  The exhaust valve 36 and the intake valve 22 are provided with solenoid solenoids 36a and 22a for valve closing, electromagnetic solenoids 36b and 22b for valve opening, springs 36c and 22c, and springs 36d and 22d attached to the stem. The solenoid valve is configured to operate by the electromagnetic force of the solenoids 36a, 22a, 36b, and 22b. Specifically, the exhaust valve 36 and the intake valve 22 are closed by exciting the solenoid solenoids 36a and 22a for closing and demagnetizing the solenoid solenoids 36b and 22b for opening, and the solenoid solenoid for closing the valve. The valves 36a and 22a are demagnetized and the valve opening electromagnetic solenoids 36b and 22b are excited to open the valves. In this way, the exhaust valve 36 and the intake valve 22 are excited and demagnetized by the mounted electromagnetic solenoids 36a, 22a, 36b, 22b, so that the valve is independent of the rotation angle of the crankshaft (not shown). It is configured as a variable valve mechanism 38 that variably adjusts (open / close) timing.

  The exhaust manifold 40 gathers downstream to form an exhaust system gathering portion, to which an exhaust pipe 42 is connected. Exhaust gas flows from the exhaust manifold 40 through the exhaust pipe 42. A catalyst device 44 made of a three-way catalyst is disposed in the exhaust pipe (exhaust system) 42. When the catalyst device 44 is in an active state, the exhaust gas is discharged into the atmosphere outside the engine after removing harmful components such as HC, CO, and NOx.

  The exhaust pipe 42 is connected to the intake pipe 14 via the EGR pipe 46 in the vicinity of the downstream of the position where the throttle valve 16 is disposed. An EGR valve 46 a is inserted in the EGR pipe 46. The EGR valve 46a is electrically connected to the ECU 30 and, when driven, opens the EGR pipe 46 to recirculate a part of the exhaust gas to the intake system (external EGR).

  A turbocharger 50 is provided upstream of the catalyst device 44 in the exhaust pipe 42. As schematically shown in FIG. 1, the turbocharger 50 is disposed in the exhaust pipe 42, and is disposed in the intake pipe 14 while being connected to the turbine 50a and being rotated by the exhaust gas passing therethrough. The compressor 50b is driven by a rotational force and supercharged. A variable nozzle (not shown) is provided in the vicinity of the turbine 50a, and adjusts the flow rate and speed of the exhaust gas flowing through the impeller (not shown) of the turbine 50a.

  A throttle actuator (such as a pulse motor) 52 is connected to the throttle valve 16 disposed in the intake pipe 14 and is opened and closed by the throttle actuator 52. That is, the throttle valve 16 is mechanically disconnected from the accelerator pedal 54 disposed on the driver's seat floor of a vehicle (not shown) on which the engine 10 is mounted, and the throttle valve 16 is operated by the accelerator pedal 54. And a DBW (Drive By Wire) mechanism 56 that opens and closes independently.

  The reciprocating motion of the piston 34 rotates a crankshaft (not shown) through the connecting rod. The engine 10 is connected to an automatic transmission 58 (shown as “A / T” in the figure) composed of five forward speeds and one reverse speed. The rotation of the engine 10 input through the rotation of the crankshaft is shifted by the automatic transmission 58 and transmitted to drive wheels (not shown) to drive the vehicle.

  A crank angle sensor 60 is disposed in the vicinity of the crankshaft of the engine 10 and is obtained by subdividing the cylinder discrimination signal, the TDC signal indicating the TDC (top dead center) of each cylinder or the crank angle in the vicinity thereof, and the TDC signal. A crank angle signal is output. Those outputs are input to the ECU 30.

  The ECU 30 includes a microcomputer, and includes a CPU, ROM, RAM, A / D conversion circuit, input / output circuit, and counter (all not shown). The ECU 30 counts the crank angle signal among the input signals and calculates (detects) the engine speed NE.

  An air flow meter 62 having a temperature detecting element is disposed in the vicinity of the air cleaner 12 and outputs a signal corresponding to a flow rate (indicating engine load) Gair and temperature TA of air (intake air) drawn from the air cleaner 12.

  A MAP sensor 64 is disposed downstream of the throttle valve 16 in the intake pipe 14 and outputs a signal indicating the intake pipe pressure PBA in absolute pressure. A throttle opening sensor 66 is disposed in the throttle valve 16. A signal corresponding to the position (throttle opening) TH is output. A rotary encoder 70 is disposed in the throttle actuator 52 and outputs a signal corresponding to the drive amount (rotation amount) of the throttle actuator 52.

  A water temperature sensor 72 is disposed in a cooling water passage (not shown) of the engine 10 and outputs a signal corresponding to the engine cooling water temperature TW.

  An accelerator opening sensor 74 is provided in the vicinity of the accelerator pedal 54, and outputs a signal corresponding to an accelerator opening (indicating engine load) AP indicating the amount of depression of the accelerator pedal of the driver.

  In the exhaust system, a wide area air-fuel ratio sensor 76 is disposed in the vicinity of the downstream portion of the collection portion of the exhaust manifold 40, and outputs a signal proportional to the oxygen concentration (that is, air-fuel ratio) of the exhaust gas flowing through that portion, and the turbocharger 50. A variable nozzle position sensor 80 is disposed in the vicinity of the variable nozzle disposed in the vicinity of the turbine 50a, and outputs a signal corresponding to the position of the variable nozzle.

  An ATF temperature sensor 82 is disposed at an appropriate position of an oil passage or an oil pan (not shown) for supplying hydraulic oil (Automatic Transmission Fluid) to the automatic transmission 58, and generates an output TATF proportional to the ATF temperature.

  The output of the sensor group described above is also input to the ECU 30. Based on the input value, the ECU 30 functions as a control device that executes control such as switching permission from the spark ignition operation to the compression ignition operation, as will be described later in accordance with a command stored in the ROM.

  Next, the operation of the control device shown in FIG. 1 will be described.

  FIG. 2 is a flowchart showing the operation, specifically, the operation of the ECU 30. The illustrated program is activated by a time interrupt every predetermined time (for example, 10 msec).

  In the following, in S10, it is determined whether or not switching from the spark ignition operation (hereinafter referred to as “SI operation”) to the compression ignition operation (hereinafter referred to as “HCCI operation”) is permitted, and in S12, the HCCI operation is performed according to the determination result in S10. And the operation mode of either SI operation is determined.

  The compression ignition operation requires the temperature inside the combustion chamber 24, that is, the gas temperature of about 1000K. Therefore, the ECU 30 does not close the exhaust valve 36 in the exhaust stroke and discharge part of the exhaust to the exhaust system. The so-called internal EGR that is left in the combustion chamber 24 is performed.

  That is, the ECU 30 controls the valve timings of the intake valve 22 and the exhaust valve 36 as shown by solid lines in FIG. More specifically, as shown in the figure, the closing timing of the exhaust valve 36 is advanced and the opening timing of the intake valve 22 is retarded (at the crank angle). As a result, a predetermined amount of exhaust gas remains in the cylinder to increase the internal temperature of the combustion chamber 24 (in-cylinder gas temperature), thereby enabling the compression ignition operation.

  Further, when the air-fuel mixture is spark-ignited, the ECU 30 controls the valve timing according to the characteristics indicated by the broken line. More specifically, as shown in the figure, both the closing timing of the exhaust valve 36 and the opening timing of the intake valve 22 are changed to near the top dead center of the piston. As a result, the closing of the exhaust valve 36 is retarded and the amount of gas discharged from the combustion chamber is increased, while the opening of the intake valve 22 is advanced and the inflow of intake air is accelerated. It is sent to the exhaust system without remaining in the combustion chamber.

  FIG. 4 is a sub-routine flowchart of the switching permission determination process of S10 in FIG.

  First, a flag F_CIAREAOK (bit thereof) is determined in S100. When this flag bit is set to 1, it means that the HCCI operation is possible, so this determination corresponds to the process of determining whether or not the HCCI operation is possible.

  FIG. 5 is a sub-routine flow chart of the processing.

  In the following, it is determined whether or not the bit of the flag F_CIOK is set to 1 in S200. As will be described later, when this bit is set to 1, this flag means that combustion is possible in HCCI operation. Therefore, the determination here is equivalent to determining whether combustion is possible in HCCI operation. .

  When the result in S200 is affirmative, the program proceeds to S202, in which a map search is performed from the detected engine coolant temperature (engine temperature) TW, engine speed NE, and gear ratio NGEAR to calculate the upper limit value PMC2D of the required torque PMCMD. FIG. 6 is an explanatory diagram showing the map characteristics of the upper limit value of the required torque.

Since the engine 10 according to this embodiment is controlled by the DBW mechanism 56, the required torque PMCMD is calculated as follows.
PMCMD = CONST / PSE / NE
In the above, CONST is a constant. PSE is a required output of the engine 10 obtained by searching a preset map (characteristic not shown) from the accelerator pedal opening AP and the engine speed NE. Specifically, the PSE is set so as to increase as the accelerator opening degree AP increases or as the engine speed NE increases.

  The upper limit value PMC2D of the required torque is obtained by dividing the above-described required torque so as to be searchable for each gear ratio NGEAR from the engine coolant temperature TW and the engine speed NE. As shown in FIG. For example, the engine speed NE and the engine coolant temperature TW are set so as to increase as they increase.

  Returning to the description of FIG. 5, the process then proceeds to S204, where a map search is performed from the similarly detected engine coolant temperature TW, engine speed NE, and gear ratio NGEAR to calculate the lower limit value PMD2C of the required torque. Although illustration of the map characteristic of the lower limit value of the required torque is omitted, it is almost the same as FIG.

  If the result in S200 is NO and it is determined that combustion is not possible in HCCI operation, the process proceeds to S206 and S208, and a map search is similarly performed from the detected engine coolant temperature TW, engine speed NE, and gear ratio NGEAR. A request torque upper limit value PMC2D and a request torque lower limit value PMD2C are calculated. Although illustration of these map characteristics is also omitted, it is almost the same as FIG. The reason why the upper and lower limit values of the required torque are made different depending on whether or not combustion is possible in HCCI operation is to provide hysteresis characteristics and prevent deterioration of drivability due to busy switching between HCCI operation and SI operation.

  Next, in S210, it is determined whether or not the bit of the flag F_THIDLE is set to 1. Since this bit is set to 1 when the engine 10 is not in the idle operation state in another process (not shown), this determination corresponds to determining whether the engine 10 is not in the idle operation state.

  When the result in S210 is affirmative, the process proceeds to S212, where it is determined whether the determined required torque PMCMD is equal to or less than the required torque upper limit value PMC2D calculated in S202 or S206. If the result is affirmative, the process proceeds to S214. It is determined whether the required torque PMCMD is equal to or greater than the required torque lower limit value PMD2C calculated in S204 or S208.

  When the result in S214 is affirmative, the program proceeds to S216, in which the bit of the flag F_CIAREAOK is set to 1. On the other hand, when the result in S210 to S214 is NO, the process proceeds to S218, and the bit of the flag F_CIAREAOK is reset to 0.

  Thus, in the process of FIG. 5, when it is determined that the required torque is within the range of the upper and lower limit values (differently set depending on whether combustion is possible in HCCI operation), the region in which HCCI operation is possible Judge. In other words, HCCI operation is superior to SI operation in terms of NOX reduction and thermal efficiency (fuel consumption performance), but is inferior in terms of output. Therefore, when the engine 10 is in a predetermined operation region such as a middle or low load region, the engine 10 is in HCCI operation. Judge that it is in the possible area. Even in the low load region, the idling operation state is excluded because it is difficult to establish the temperature condition and the combustion tends to be unstable.

  If the above is applied, when the engine speed NE is lower than, for example, 700 rpm, the TDC interval becomes longer and the amount of heat of the internal EGR also moves from the wall surface to the cooling water, causing a temperature drop and making self-ignition difficult. On the other hand, if the engine speed NE exceeds 3500 rpm, for example, the TDC interval becomes too short, and it becomes difficult to obtain the reaction time of the auto-ignition chemical change. Therefore, the engine speed NE that defines the region where the HCCI operation is possible is set to, for example, 700 to 3500 rpm based on the optimum TDC interval.

  Further, when the engine coolant temperature TW is low, the wall temperature of the combustion chamber 24 is also low. Therefore, it is necessary to increase the temperature by increasing the amount of fresh air. As a result, the HCCI operation region moves to the high load side. . Therefore, it is conceivable to change the HCCI operation region in accordance with the engine coolant temperature TW. In this case, knocking occurs when the engine coolant temperature TW rises. However, if the engine coolant temperature TW is low and the wall temperature is low, HCCI operation is possible without causing knocking.

  Therefore, in this embodiment, it is determined whether the required torque PMCMD is within a predetermined range set according to the engine speed NE and the engine coolant temperature TW, and when it is determined that the required torque PMCMD is within the predetermined range, Since the switch from the spark ignition operation to the compression ignition operation is permitted, it is possible to define a region where the HCCI operation is possible such as a region where the engine coolant temperature TW is low and the wall temperature is low. The range can be expanded.

  Further, since the predetermined range is further set in accordance with the gear ratio NGEAR of the automatic transmission 58, the predetermined range is narrowed when the reduction ratio is large (that is, the engine speed NE or the load changing speed is large). By setting it, the deterioration of drivability and emission due to switching busy is prevented, and when the reduction ratio is small (the engine speed NE or the load changing speed is small), the predetermined range is expanded to the maximum. , Fuel efficiency can be improved, and thus drivability, emission, and fuel efficiency can be balanced at a high level.

  Returning to the description of the flow chart of FIG. 4, the process then proceeds to S102 to determine the flag F_TCTCIOK (bit thereof). When this flag bit is set to 1, it means that after the engine 10 is started, the catalytic device 44 is in an active state, so this determination is whether the catalytic device 44 is in an active state or not. This corresponds to the determination process.

  FIG. 7 is a sub-routine flowchart of the processing.

  In the following, it is determined whether or not the flag F_TCTCIOK bit is set to 1 in S300. Since this bit is set to 1 in the processing described below, the determination in S300 is generally denied and the process proceeds to S302 to warm up the catalyst device 44, more specifically, the engine 10 It is determined whether or not the catalyst warm-up operation for rapidly warming up the catalyst device 44 after the start of is completed. This warm-up operation is started when a predetermined time, for example, several seconds elapses after the engine 10 is started.

  When the result in S302 is negative, the program proceeds to S304, sets a predetermined value #TMTC (for example, 2 to 3 sec) in the timer (down counter) TTCT, starts time measurement, proceeds to S306, and resets the bit of the flag F_TCTCIOK to 0 And once exit the program. Also in the program loop after the next time, as long as the process proceeds to S302 and is denied, a predetermined value is reset in S304 and the process proceeds to S306.

  Next, when the result in S302 in the subsequent program loop is affirmative, the process proceeds to S308, where the temperature TCT of the catalyst device 44 is obtained and compared with a predetermined value (threshold value) #TCT. to decide. When the result in S308 is negative, the process proceeds to S304, the timer TTCT is set to a predetermined value and the process proceeds to S306. When the result in S308 is affirmative, the process proceeds to S310, and the timer TTCT value has become zero (set to the predetermined value). Whether the corresponding time has passed) is determined.

  When the result in S310 is negative, the program is terminated via S306. When the result is affirmative, the program proceeds to S312 and the bit of the flag F_TCTCIOK is set to 1 and the program is terminated. Setting this flag bit to 1 means that the catalytic device 44 is determined to be in an active state.

  Accordingly, in the subsequent program loop, the determination in S300 is affirmed and the process proceeds to S314, and the bit of the flag F_TCTCIOK is continuously set to 1. That is, once the bit of this flag is set to 1 in the processing of FIG. 7, the active state determination of the catalyst device 44 is not performed in the trip (travel until the engine 10 is stopped).

  Here, the process for obtaining the temperature TCT of the catalyst device 44 described in S308 will be described. In this embodiment, the temperature of the catalyst device 44 is obtained by estimation by calculation without using a temperature sensor.

  This will be described below. FIG. 8 is a sub-routine flow chart showing the operation. Note that the illustrated program is also activated at predetermined time intervals Δt (that is, 10 msec of the program activation period in FIG. 2).

First, in S400, the specific heat Cp [kcal / ° C · kg], the heat transfer coefficient h [kcal / m ² · ° C · hour], the exhaust system temperature TEX [° C], etc., are operated, and more specifically, the engine speed. Based on NE, load (accelerator opening AP or required torque PMCMD), and target air-fuel ratio KCMD, map search or table search is performed. At the same time, the mass m [kg] and the cross-sectional area A [m ² ] of the catalyst device 44 stored in advance are read out, the process proceeds to S402, and the catalyst temperature TCT (k) is calculated as shown in FIG. Note that (k) means a discrete sample time, specifically, the time of the current program loop.

  The exhaust system temperature TEX needs to be corrected according to the target air-fuel ratio KCMD because the energy generated by the engine differs depending on the air-fuel ratio. However, in the correction, the detected air-fuel ratio detected by the wide-area air-fuel ratio sensor 76 may be used instead of the target air-fuel ratio KCMD.

  Referring to FIG. 9, in this estimation method, the heat transfer of the catalyst device 44 is obtained based on a thermodynamic equation, and the temperature change is approximately estimated. That is, as shown in the upper part of the figure, if the heat quantity of the catalyst device 44 is QCT, the QCT is estimated from the input exhaust system temperature TEX, the mass m [kg] of the catalyst device 44, the specific heat Cp, and the catalyst temperature TCT. can do.

  Assuming that ΔQCT is the amount of heat input to the catalyst device 44 during Δt seconds (the program start cycle shown in the figure), ΔQCT is the current value TCT (k) of the catalyst temperature and the previous value TCT ( It can be approximated by multiplying the difference of k-1) by the product of the mass m of the catalyst device 44 and the specific heat Cp.

This is equivalent to the difference between the input exhaust system temperature TEX and the previous catalyst temperature value TCT (k-1) multiplied by the product of the cross-sectional area A [m ² ] of the catalyst device 44 and the heat transfer coefficient h. . Therefore, rewriting the right side of equation (1) gives equations (2) and (3), and equations (3) to (4) are obtained, and based on this, the current value TCT (k) of the catalyst temperature is obtained. Can do. Note that equation (4) is a recurrence equation and requires an initial value of the previous catalyst temperature value TCT (k-1), but may be set as appropriate according to the engine coolant temperature TW and the like.

  Accordingly, the temperature TCT of the catalyst device 44 can be obtained by calculation or estimation without using a temperature sensor, and the configuration becomes simple. Further, when using a sensor, there is a problem of detection delay, but since the heat balance is calculated, there is no inconvenience.

  Returning to the description of the flow chart of FIG. 4, the process then proceeds to S104 to determine whether or not the bit of the flag F_STMOD is set to 1. Since the flag bit is set to 1 when the engine 10 is in the start mode, this processing corresponds to determining whether or not the engine 10 is in the start mode.

  When the result in S104 is affirmative, the process proceeds to S106, the timer (down counter) TDSST is set to a predetermined value #TMDSST (for example, 2 sec), and time measurement is started. The process proceeds to S108, and the second timer (down counter) TDDC is set. Time measurement is started by setting a predetermined value #TMDC (for example, 1 sec), and the process proceeds to S110, where the bit of the flag F_CIOK is reset to 0, and the process proceeds to S112, where the bit of the flag F_HCCI is reset to 0.

  Resetting the bit of the flag F_HCCI to 0 means that switching from SI operation to HCCI operation is not permitted and setting to 1 is permitted. As in the idle operation state, switching is not permitted because the combustion is not stable when the engine is started.

  On the other hand, when the result in S104 is negative, the program proceeds to S114, in which it is determined whether or not the value of the timer TDSST has reached zero. When the result in S114 is negative, the process proceeds to S108, and when the result is positive, the process proceeds to S116, and it is determined whether or not the bit of the flag F_DSAFCND is set to 1. This flag is set to 1 when the air-fuel ratio detected from the wide-range air-fuel ratio sensor 76 in another process (not shown) matches (completely or almost) the target air-fuel ratio KCMD. This process corresponds to determining whether the detected air-fuel ratio matches the target air-fuel ratio, in other words, whether the air-fuel ratio control is normally performed.

  When the result in S116 is negative, it is determined that the air-fuel ratio is not sufficiently controlled, and thus the process proceeds to S108. When the result is positive, the process proceeds to S118, and it is determined whether or not the bit of the flag F_ICEGRJUD is set to 1. To do. This flag is obtained from the detected opening of the throttle valve 16 and the energization of the throttle actuator 52 (or the output of the rotary encoder 70 attached thereto) in another process (not shown) such that the throttle valve 16 is fixed due to freezing. Since the bit is set to 1 when the error with respect to the target opening is equal to or greater than a predetermined value, this process determines whether the throttle opening control is abnormal, in other words, whether the operation of the DBW mechanism 56 is normal. It corresponds to doing.

  When the result in S118 is affirmative, it is determined that the DBW mechanism 56 is not normal, and thus the process proceeds to S108. When the result is negative, the process proceeds to S120, and it is determined whether or not the bit of the flag F_KEGROK is set to 1. This flag is set to 1 when the deviation between the EGR rate (exhaust gas recirculation rate) KEGR calculated in another process (not shown) and the target EGR rate is less than a predetermined value. The processing corresponds to determining whether or not the operation of the exhaust valve (solenoid valve) 36 that realizes EGR is normal.

As described above, since the HCCI operation requires a gas temperature of about 1000 K in the combustion chamber 24, the exhaust valve 36 is closed during the exhaust stroke so that part of the exhaust is not discharged to the exhaust system. The internal EGR that remains in the combustion chamber 24 is executed. In this embodiment, the EGR rate KEGR is calculated as follows.
KEGR = Gair fresh air / Gair filling In the above, the Gair fresh air means the amount of air sucked from the air cleaner 12 detected from the air flow meter 62.

  Gir filling means the air amount corresponding to the basic fuel injection amount. In other words, since the basic fuel injection amount is calculated from the engine speed NE and the intake pipe absolute pressure PBA, the Gir filling is also calculated from the engine speed NE and the intake pipe absolute pressure PBA. Fill.

  That is, by calculating the air amount corresponding to the basic fuel injection amount required from the current operating state (in other words, required), and calculating the ratio of fresh air to the air amount, the EGR rate is calculated backward. Can do. In the other processing described above, when it is determined that the deviation between the EGR rate KEGR calculated as described above and the target EGR rate is equal to or less than a predetermined value, in other words, the operation of the exhaust valve (solenoid valve) 36 that realizes EGR. Is determined to be normal, the bit is set to 1 in another process.

  When the result in S120 is negative, it is determined that the operation of the exhaust valve 36 that realizes EGR is not normal, and the process proceeds to S108. When the result is affirmative, the process proceeds to S122, and the bit of the flag F_DBWOK is set to 1. Determine whether or not. This flag is similar to the process of S118, but the operation of the throttle actuator 52 is abnormal in another process (not shown). More precisely, the drive amount calculated from the energization command value for the throttle actuator 52 and the rotary encoder 70 are used. Since the bit is set to 1 when it is determined that the difference from the drive amount (rotation amount) of the throttle actuator 52 is less than a certain value, the throttle actuator 52, that is, the DBW mechanism 56 is also normal. This corresponds to determining whether or not.

  When the result in S122 is negative, it is determined that the DBW mechanism 56 is not normal, and the process proceeds to S108. When the result is positive, the process proceeds to S124, and it is determined whether or not the bit of the flag F_VNTOK is set to 1. This flag is determined in another process (not shown) that the difference between the command value to the variable nozzle arranged near the turbine 50a of the turbocharger 50 and the detection value of the variable nozzle position sensor 80 attached thereto is equal to or less than a predetermined value. Since this bit is set to 1, this processing corresponds to determining whether or not the operation of the turbocharger 50, more specifically, the variable nozzle arranged near the turbine 50a is normal. To do.

  When the result in S124 is negative, it is determined that the operation of the variable nozzle disposed in the vicinity of the turbine 50a of the turbocharger 50 is not normal, so that the process proceeds to S108. It is determined whether or not the F_TCTCIOK bit is set to 1. When this flag bit is set to 1, it means that the catalyst device 44 is determined to be in an active state, so the determination here is to determine whether or not the catalyst device 44 is in an active state. Equivalent to.

  When the result in S126 is negative, it is determined that the catalyst device 44 is not in an active state, so that the process proceeds to S108, and when the result is positive, the process proceeds to S128, in which it is determined whether or not the value of the timer TDDC has reached zero. To do.

  When the result in S128 is negative, the process proceeds to S110. When the result is affirmative, the process proceeds to S130, and it is determined whether or not the bit of the flag F_CIAREAOK is set to 1. When this flag bit is set to 1, it means that it is determined that the HCCI operation is possible. Therefore, the determination here corresponds to the determination that the HCCI operation is possible.

  When the result in S130 is negative, the process proceeds to S110. When the result is affirmative, the process proceeds to S132, and the flag F_CISTABLE (bit thereof) is determined.

  FIG. 10 is a sub-routine flow chart showing the processing.

  Explaining below, in S500, a change amount DNEDS of the engine speed NE is calculated. This is calculated by obtaining the difference between the previous value (the value at the previous program loop in FIG. 2) and the current value (the value at the current program loop in FIG. 2) of the engine speed NE. The amount of change is given a positive sign when it is in the increasing (changing) direction, and a negative sign when it is in the decreasing (changing) direction.

  Next, in S502, similarly, the change amount DPMECI of the required torque PMCMD is calculated. This is also calculated by obtaining the difference between the previous value and the current value of the required torque PMCMD. The amount of change in the required torque is also given a positive sign when it is in the increasing (changing) direction and a negative sign when it is in the decreasing (changing) direction.

  Next, the process proceeds to S504, where it is determined whether or not the flag F_CIOK bit is set to 1. When the result is negative, it is determined that combustion is not possible in HCCI operation, so the process proceeds to S506, and the bit of the flag F_CISTABLE is set. Reset to zero.

  Resetting the bit of this flag to 0 means that it is determined that the HCCI operating parameter is not stable, and setting it to 1 means that it is determined to be stable. Specifically, the process of FIG. 10 is an operation for determining whether or not the required torque PMCMD has changed.

  When the result in S504 is affirmative, the program proceeds to S508, in which it is determined whether or not the bit of the flag F_APOPEN is set to 1. This flag is set to 1 when the accelerator opening AP is equal to or greater than a predetermined value (for example, near 0 degrees) in another process (not shown), so this determination is made whether or not the accelerator pedal 54 is depressed. This is equivalent to judging whether or not.

  If the result in S508 is negative, it means that the required torque change does not mean that the process proceeds to S506. If the result is affirmative, the process proceeds to S510, and it is determined whether or not the bit of the flag F_IXRFLRN is set to 1. This bit is set to 1 when the learning value of the required torque during idling is calculated in another process (not shown).

  When the result in S510 is negative, the learning value is not calculated, so the process proceeds to S506. When the result is affirmative, the process proceeds to S512, and when the value calculated in S502 is the change amount DPMECI in the increasing direction of the required torque, The calculated required torque change amount DPMECI is compared with a first predetermined value #DPMECIH (positive value), and it is determined whether or not the calculated required torque change amount DPMECI is equal to or less than the first predetermined value.

  When the result is negative in S512, the process proceeds to S506, and when the result is positive, the process proceeds to S514. The same applies when the change amount DPMECI in the increasing direction of the required torque is not calculated in S502.

  In S514, if the value calculated in S502 is the change amount DPMECI in the decreasing direction of the required torque, the calculated change amount DPMECI of the required torque is compared with the second predetermined value #DPMECI (negative value). It is determined whether or not the required change amount DPMECI of the required torque is greater than or equal to a second predetermined value (whether it is less than the absolute value).

  When the result in S514 is negative, the process proceeds to S506, and when the result is positive, the process proceeds to S516. The same applies when the change amount DPMECI in the decreasing direction of the required torque is not calculated in S502.

  The first predetermined value #DPMECIH (positive value) and the second predetermined value #DPMECIIL (negative value) are set such that #DPMECIH> #DPMECIIL in absolute values, that is, different from each other.

  This is because the change in the required torque PMCMD is the same as the absolute value because the gas temperature in the combustion chamber 24 is slower than the increase (temperature decrease) in the decrease (temperature decrease) direction. However, if the change is in the decreasing direction, it is also possible to follow the gas temperature. Therefore, by changing the predetermined value depending on the change direction of the required torque, it may not be prohibited to switch to the HCCI operation, thereby reducing the NOx by performing the HCCI operation while avoiding premature ignition and misfire. This is because the thermal efficiency or fuel efficiency can be improved.

  As will be described later, when the processing proceeds to S506 and the bit of the flag F_CISTABLE is reset to 0, the HCCI operation is prohibited. In other words, the processing of S512 and S514 is performed by calculating the amount of change in the calculated required torque. When it is determined that exceeds the first or second predetermined value, it means that switching from SI operation to HCCI operation is prohibited.

  Next, the process proceeds to S516, and if the value calculated in S500 is the change amount DNEDS in the increasing direction of the engine speed NE, the calculated change amount DNEDS is compared with the first predetermined value #DNECIH (positive value). It is determined whether the changed amount DNEDS is equal to or less than a first predetermined value.

  When the result in S516 is NO, the process proceeds to S506, and when the result is YES, the process proceeds to S518. The same applies when the amount of change DNEDS in the increasing direction of the engine speed is not calculated in S500.

  In S518, if the value calculated in S500 is the change amount DNEDS in the decreasing direction of the engine speed, the calculated change amount DNEDS is compared with the second predetermined value #DNECIL (negative value). It is determined whether or not the change amount DNEDS is greater than or equal to a second predetermined value (whether it is less than an absolute value).

  When the result in S518 is NO, the process proceeds to S506, and when the result is YES, the process proceeds to S520, and the bit of the flag F_CISTABLE is set to 1. The same applies when the change amount DNEDS in the decreasing direction of the engine speed is not calculated in S500.

  The first predetermined value #DNECIH (positive value) and the second predetermined value #DNECIIL (negative value) are also set so that #DNECIH> #DNECIL, that is, different in absolute value. This is for the same reason as described for the required torque.

  Returning to the description of FIG. 4, the process then proceeds to S134, where it is determined whether or not the flag F_CISTABLE bit is set to 1. If the result is affirmative, the process proceeds to S136, the flag F_CIOK bit is set to 1, and the process proceeds to S138. Then, the bit of the flag F_HCCI is set to 1, and switching from SI operation to HCCI operation is permitted.

  On the other hand, when the result in S134 is NO, the process proceeds to S110, the bit of the flag F_CIOK is reset to 0, and the process proceeds to S112, the bit of the flag F_HCCI is reset to 0, and switching from SI operation to HCCI operation is prohibited.

  In the process of S12 in FIG. 2, when the bit of the flag F_HCCI is reset to 0, the mode is determined as the SI operation mode, and when set to 1, the mode is determined as the HCCI mode (in other words, from the SI operation mode). Switch to HCCI operation). In accordance with the determined operation mode, the ECU 30 controls the valve timings of the intake valve 22 and the exhaust valve 36 according to the characteristics shown in FIG.

In this embodiment, as described above, the combustion chamber 24 is provided with ignition means (such as a spark plug 32), and the compression ignition (HCCI) operation is performed in which the air-fuel mixture supplied to the combustion chamber is subjected to compression ignition combustion in a predetermined operation region. In the control device for a compression ignition internal combustion engine (engine) 10 that performs a spark ignition (SI) operation for performing spark ignition (SI) operation of the air-fuel mixture through spark ignition in an operation region other than the predetermined operation region. Requested torque range determination means (ECU 30, S10, S100, S200 to S214) for determining whether the required torque PMCMD of the engine is within a predetermined range set according to the coolant temperature of the internal combustion engine and the engine speed, And switching to permit the switching from the spark ignition operation to the compression ignition operation when it is determined that the required torque is within the predetermined range. E permission means (ECU30, S12, S100, S216 , S130, S138) and provided with a to set the lower limit PMD2C defining said predetermined range so as to decrease as the cooling water temperature is lower, thus the compression ignition operation Is configured to expand the operating range in which As a result, it is possible to define a region where HCCI operation is possible, such as a region where the engine temperature is optimum in the TDC interval and the cooling water temperature is low, the wall temperature engine cooling water temperature TW is low, and the wall temperature is low. The range of its use can be expanded.

  Further, since the predetermined range is further set according to the speed ratio NGEAR of the (automatic) transmission 58 connected to the internal combustion engine (engine) 10, the reduction ratio is large (that is, the engine speed NE or When the load change rate is high), the predetermined range is set narrow to prevent deterioration in drivability and emission due to busy switching between spark ignition operation and compression ignition operation, and a low reduction ratio (engine speed) When the speed of change of NE and load is small), it is possible to improve the fuel efficiency by expanding the predetermined range to the maximum, and therefore, drivability, emission, and fuel efficiency can be balanced at a high level.

  In the above description, the internal EGR is executed in the HCCI operation. However, an external EGR that recirculates part of the exhaust gas to the intake system via the EGR pipe 46 may be executed together with the internal EGR.

  Further, the valve timing characteristics of the intake valve 22 and the exhaust valve 36 shown in FIG. 3 are merely examples, and the present invention is not limited thereto. Furthermore, although the intake valve 22 and the exhaust valve 36 are composed of electromagnetic valves and the valve timing is variably controlled, they may be variably controlled using other mechanisms.

  Further, although the temperature of the catalyst device 44 is estimated by calculation, a temperature sensor 100 may be provided in the vicinity of the catalyst device 44 as shown by an imaginary line in FIG.

  Although the present invention has been described by taking as an example a configuration in which fuel is injected into the intake port in front of the intake valve 22 using the engine 10 as an example, the present invention is also applicable to a direct injection engine that directly injects fuel into the combustion chamber 24. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an overall control apparatus for a compression ignition internal combustion engine according to a first embodiment of the present invention. It is a flowchart explaining operation | movement of the apparatus shown in FIG. It is a graph which shows the two valve timing characteristics switched by the variable valve mechanism of the apparatus shown in FIG. FIG. 3 is a sub-routine flow chart of switching permission determination processing for HCCI operation in FIG. 2. FIG. 5 is a sub-routine flowchart of the HCCI operable region determination process of FIG. 4. It is explanatory drawing which shows the map characteristic of the upper limit of the request torque used in FIG. FIG. 5 is a sub-routine flowchart of the catalyst device active state determination process of FIG. 4. FIG. FIG. 8 is a sub-routine flow chart of temperature estimation processing of the catalyst device used in FIG. 7. It is explanatory drawing explaining the estimation process of the temperature of the catalyst apparatus of FIG. FIG. 5 is a sub-routine flowchart of a stability determination process for compression ignition operation parameters of FIG. 4. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Compression ignition internal combustion engine (engine), 22 Intake valve, 26 Injector, 30 ECU (electronic control unit), 32 Spark plug (ignition means), 36 Exhaust valve, 38 Variable valve mechanism, 44 Catalytic device, 50 Turbocharger, 56 DBW mechanism, 60 crank angle sensor, 62 air flow meter, 72 water temperature sensor, 74 accelerator opening sensor, 100 temperature sensor

Claims (2)

A combustion chamber is provided with an ignition means, performs a compression ignition operation in which a gas mixture supplied to the combustion chamber is compressed and ignited and combusted in a predetermined operation region, and via an ignition means in an operation region other than the predetermined operation region In a control apparatus for a compression ignition internal combustion engine that performs a spark ignition operation for spark ignition combustion of the air-fuel mixture, a required torque of the internal combustion engine is within a predetermined range set according to a cooling water temperature of the internal combustion engine and an engine speed. Requested torque range determining means for determining whether or not there is, and switching permission means for permitting switching from the spark ignition operation to the compression ignition operation when it is determined that the required torque is within the predetermined range. And a lower limit value that defines the predetermined range is set so as to decrease as the cooling water temperature decreases, thereby expanding the operating range in which the compression ignition operation is performed. Control system for a compression ignition internal combustion engine, characterized in that.   2. The control apparatus for a compression ignition internal combustion engine according to claim 1, wherein the predetermined range is further set in accordance with a transmission gear ratio of a transmission connected to the internal combustion engine.

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