JP2015169164A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation of emission and deterioration of drivability caused by fuel cut control of an internal combustion engine.SOLUTION: In a control device of an internal combustion engine for controlling the internal combustion engine provided with an exhaust gas recirculation device capable of recirculating a part of an exhaust gas flowing in an exhaust passage, to an intake passage to be mixed with intake air, an opening of an intake air throttle valve on the intake passage and an opening of an EGR valve on an EGR passage, are controlled so that a pressure of the intake air flowing to a cylinder is converged to a target intake air pressure during execution of fuel cut which temporarily interrupts fuel supply into the cylinder, and an EGR ratio as a ratio of an EGR gas in the intake air flowing into the cylinder, is increased in accordance with decrease of a temperature of the exhaust passage or a temperature of a catalyst for purifying the exhaust gas.

Description

  The present invention relates to a control device that controls an internal combustion engine that is accompanied by an exhaust gas recirculation (Exhaust Gas Recirculation) device.

While reducing the emissions of the combustion temperature is lowered by NO _x of the air-fuel mixture in the cylinder, a EGR device known to reduce the pumping loss (e.g., see Patent Document 1). The EGR device connects an exhaust path and an intake path via an external EGR passage, and recirculates a part of combustion gas generated in the cylinder to the intake path via the EGR passage to mix with the intake air.

  In addition, it is known that an internal combustion engine mounted on a vehicle performs a fuel cut that temporarily stops fuel injection in accordance with its operating condition (for example, see Patent Document 2 below). Normally, when the accelerator pedal depression amount is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed, the fuel cut is started assuming that the fuel cut condition is satisfied. Then, when any fuel cut end condition is satisfied, such as when the accelerator pedal depression amount exceeds the threshold value, or the engine speed decreases to the fuel cut return speed, the fuel cut ends and the fuel injection resumes. .

JP2012-167601A Japanese Patent Laid-Open No. 10-030477

  During the fuel cut, fuel does not burn in the cylinder, and low-temperature air that does not contain combustion gas flows into the exhaust purification three-way catalyst through the exhaust passage. As a result, the catalyst is filled with a large amount of oxygen, and the temperature of the catalyst is also lowered. Therefore, there is a concern that the purification efficiency of harmful substances by the catalyst is reduced and the emission is deteriorated after the fuel injection is restarted.

  Further, as the secular change of the internal combustion engine, deposits adhere to and accumulate on an intake throttle valve (such as a throttle valve or an ISC (Idle Speed Control) valve) on the intake passage, and the intake flow rate relative to the opening of the intake throttle valve decreases. . Due to such a secular change, the magnitude of the opening of the intake throttle valve required to keep the strength of the engine braking action during fuel cut to a certain degree changes. Nevertheless, in the past, the intake valve was operated at a certain opening during fuel cut. For this reason, the deceleration of the internal combustion engine and the vehicle during the fuel cut changes, which may lead to a decrease in drivability.

  An object of the present invention is to suppress deterioration in emissions and drivability due to fuel cut control of an internal combustion engine.

  The present invention controls an internal combustion engine with an EGR device that can recirculate a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas and mix it with the intake air, and temporarily supplies fuel to the cylinder. During execution of the fuel cut to be interrupted, the opening of the intake throttle valve on the intake passage and the opening of the EGR valve on the EGR passage are manipulated so that the pressure of the intake air flowing into the cylinder converges to the target intake pressure. A control device for an internal combustion engine is configured in which the EGR rate, which is the proportion of EGR gas in the intake air flowing into the cylinder, is increased as the temperature of the passage or the temperature of the exhaust purification catalyst is lower.

  That is, EGR is performed by opening the EGR valve as necessary during fuel cut, and the temperature of the intake air is increased while lowering the oxygen concentration of the intake air flowing into the cylinder. Note that when EGR is performed, the pumping loss of the internal combustion engine is reduced and the deceleration of the internal combustion engine and the vehicle is reduced. However, in the present invention, the target intake pressure is set in advance, and the intake air flowing into the cylinder is reduced. By making the pressure follow the target intake pressure, fluctuations in pumping loss are suppressed, and consequently fluctuations in deceleration are suppressed.

  In addition, during fuel cut, it is preferable to lower the target intake pressure as the EGR rate is higher. Then, the deceleration of the internal combustion engine and the vehicle can be adjusted to a suitable magnitude regardless of the EGR rate, that is, the temperature of the exhaust passage, and drivability can be kept high.

  ADVANTAGE OF THE INVENTION According to this invention, the deterioration of the emission resulting from the fuel cut control of an internal combustion engine and the fall of drivability can be suppressed.

The figure which shows the structure of the internal combustion engine and control apparatus in one Embodiment of this invention. The flowchart which shows the example of the procedure of the process which the control apparatus of the embodiment performs.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type four-stroke engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32 as an intake throttle valve, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The EGR device 21 communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3, and the EGR passage 21. The EGR cooler 22 provided in the EGR passage and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  An ECU (Electronic Control Unit) 0 serving as a control device for an internal combustion engine according to the present embodiment is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. Accelerator opening signal c output from a sensor that detects the amount as an accelerator opening (engine output required by the driver, so-called required load), and output from a sensor (shift position switch) to know the range of the shift lever The shift range signal d, the intake air temperature / intake pressure signal e output from the temperature / pressure sensor for detecting the intake air temperature and the intake pressure in the intake passage 3 (particularly, the surge tank 33), and the cooling indicating the temperature of the internal combustion engine. The coolant temperature signal f output from the water temperature sensor for detecting the water temperature, the intake camshaft or the exhaust camshaft A cam angle signal g output from the cam angle sensor at a cam angle of the outside air temperature signal h or the like to be output from the temperature sensor for detecting the outside air temperature is input.

  From the output interface, an ignition signal i for the igniter 13 of the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, and an opening operation signal for the EGR valve 23. l etc. are output.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Based on the engine speed and intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, required EGR rate (or EGR amount), Various operating parameters such as ignition timing are determined. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  In principle, the EGR rate required for the intake air charged in the cylinder 1 is the highest in the medium load operation region where the accelerator opening is medium, and decreases as the accelerator opening decreases from that. Decreases with expansion. In the full load operation region where the accelerator opening is fully open or close to full open, the required EGR rate becomes 0 and the EGR valve 23 is fully closed.

  Moreover, ECU0 performs the fuel cut which stops fuel injection from the injector 11 temporarily according to a driving | running condition. The ECU 0 determines that the fuel cut condition is satisfied at least on the condition that the accelerator opening is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed.

  Incidentally, even if the combustion cut condition is satisfied, the fuel injection to the cylinder 1 is not immediately stopped. The ECU 0 stops the fuel injection (and ignition) only when the situation where the fuel injection can be stopped is ready while maintaining the operation of injecting and burning the fuel into the cylinder 1 even after the fuel cut condition is satisfied. . The situation where the fuel injection may be stopped is a situation where the engine torque is sufficiently low and does not cause a large torque shock even if the fuel injection is stopped. In the delay time from when the fuel cut condition is satisfied to when the fuel cut is started, the ignition timing is retarded and the engine torque is actively reduced.

  If the fuel cut end condition is satisfied after the fuel cut condition is satisfied, the fuel cut is ended and fuel injection (and ignition) is restarted. The ECU 0 establishes the fuel cut end condition when either the accelerator pedal is depressed by the driver and the accelerator opening exceeds the threshold, or the engine speed is reduced to the fuel cut return speed. Judge that.

  Therefore, the ECU 0 according to the present embodiment is configured to perform the inertial driving (on the downhill road) under a deceleration request in which the accelerator opening is 0 or less than a threshold value close to 0 and the engine speed exceeds the predetermined idle speed. Feedback control for converging the pressure of the intake air flowing into the cylinder 1 to the target intake pressure is performed.

  In FIG. 2, the example of a procedure of the process which ECU0 of this embodiment performs is shown. The ECU 0 determines whether or not the fuel cut is being executed in a situation where the accelerator opening is 0 or less than a threshold value close to 0 and the engine speed is greater than or equal to a predetermined speed (step S1). And subsequent processes are selected (step S2).

  If the fuel cut is not currently executed, that is, in the low load operation region in which the fuel is injected from the injector 11 and burned, the required EGR rate is set to 0, the EGR valve 23 is fully closed, and then the sensor is connected. Feedback control is performed to manipulate the opening of the throttle valve 32 so as to reduce the deviation between the actually measured intake pressure in the surge tank 33 and the target intake pressure (step S3).

  The feedback control of the intake pressure in the surge tank 33, in other words, the intake negative pressure downstream of the throttle valve 32, to the target intake pressure serves to suppress fluctuations in the pumping loss of the internal combustion engine. This feedback control absorbs aging of the internal combustion engine, for example, a decrease in the flow rate of intake air caused by deposits and deposits on the throttle valve 32, and keeps the strength of the engine brake, that is, the deceleration of the internal combustion engine and the vehicle constant. To contribute.

  The target intake pressure is set based on the engine speed. The target intake pressure is determined so that the deceleration of the internal combustion engine and the vehicle speed becomes a suitable magnitude, and the lubricant is removed from the cylinder 1 to the intake passage 3 by the intake negative pressure as much as possible. Of course, during the operation of injecting and burning the fuel, it is necessary to secure a minimum intake pressure and therefore an oxygen amount so as not to cause a combustion failure. In the memory of the ECU 0, map data that defines the relationship between the engine speed and the target intake pressure is stored in advance. The ECU 0 searches the map using the current engine speed as a key, and obtains the target intake pressure to be set.

  On the other hand, if the fuel cut is currently being executed, the subsequent process is selected according to the current temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 (step S4).

  When a sensor for detecting the temperature in the exhaust passage 4 or a sensor for detecting the temperature of the catalyst 41 is mounted on the internal combustion engine, the temperature in the exhaust passage 4 or the temperature of the catalyst 41 can be measured. If such a sensor does not exist, the temperature in the exhaust passage 4 or the temperature of the catalyst 41 is estimated in the ECU 0. For example, the temperature of the exhaust gas flowing through the exhaust passage 4 during fuel cut is estimated from the outside air temperature, the cooling water temperature of the internal combustion engine, the engine speed, the intake pressure in the surge tank 33 (that is, the intake amount charged into the cylinder 1), and the like. Is possible.

  The temperature of the catalyst 41 can be estimated based on the integration (time integration) of the amount of heat received and the amount of heat released per unit time of the catalyst 41. The amount of heat received per unit time is estimated from the engine speed, the intake pressure in the surge tank 33, the fuel injection amount (increase correction or decrease correction), ignition timing, etc. during the operation in which fuel is injected and burned. Is done. The amount of heat released per unit time is estimated from the vehicle speed indicating the flow rate of the driving wind blowing into the engine room and the outside air temperature indicating the temperature of the driving wind during operation in which fuel is injected and burned. The If the fuel is being cut, in addition to the vehicle speed and the outside air temperature, the temperature is estimated from the temperature of the exhaust gas flowing through the exhaust passage 4, the engine speed, the intake pressure in the surge tank 33 (that is, the exhaust gas flow rate), and the like.

  In addition, when the temperature of the exhaust passage 4 is equal to or higher than the predetermined value and / or the temperature of the catalyst 41 is the predetermined value, as in step S3, the required EGR rate is set to 0, the EGR valve 23 is fully closed, and the sensor is turned on. The opening of the throttle valve 32 is manipulated so as to reduce the deviation between the intake pressure in the surge tank 33 and the target intake pressure that are actually measured (step S5). This is because the current temperature drop of the catalyst 41 is small, or immediately after the start of fuel cut, the amount of oxygen occluded in the catalyst 41 is not excessive, and the problem of deterioration in the purification performance of harmful substances is not considered to be obvious. It depends. Further, when the fuel cut end condition is satisfied and the fuel injection is resumed, the internal combustion engine has a high probability of being in the idle operation or low load operation region, and the required EGR rate in the operation region is 0 or minimal. There is also the implication that the EGR valve 23 is closed in preparation for the completion of the cut end condition.

  Conversely, when the temperature of the exhaust passage 4 is less than the predetermined value and / or the temperature of the catalyst 41 is less than the predetermined value, unlike step S5, the EGR valve 23 is opened and the surge measured through the sensor is measured. The opening of the throttle valve 32 and the opening of the EGR valve 23 are operated so as to reduce the deviation between the intake pressure in the tank 33 and the target intake pressure (step S6). The EGR valve 23 is opened to perform the EGR because the temperature of the gas discharged from the cylinder 1 and flowing into the catalyst 41 via the exhaust passage 4 is increased to suppress the temperature drop of the catalyst 41 and the gas flowing into the catalyst 41 is reduced. The intention is to reduce the amount of oxygen stored in the catalyst 41 by reducing the oxygen concentration as much as possible.

  In order to keep the temperature of the catalyst 41 more accurately, it is preferable to set the required EGR rate in step S6 higher as the temperature of the exhaust passage 4 is lower and / or higher as the temperature of the catalyst 41 is lower. As a result of increasing the required EGR rate, the opening degree of the EGR valve 23 is relatively increased and the opening degree of the throttle valve 32 is relatively reduced. In the memory of the ECU 0, map data defining the relationship between the temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 and the required EGR rate is stored in advance. The ECU 0 searches the map using the current temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 as a key to know the required EGR rate to be set.

  The target intake pressure in step S6 is set based on the engine speed, the temperature of the exhaust passage 4, and / or the temperature of the catalyst 41. More specifically, the target intake pressure is decreased as the required EGR rate increases, thereby avoiding excessive expansion of the opening of the EGR valve 23, that is, excessive decrease in pumping loss, and deceleration of the internal combustion engine and the vehicle. To ensure a certain level. In the memory of the ECU 0, map data defining the relationship between the engine speed, the temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 (or the required EGR rate) and the target intake pressure is stored. The ECU 0 searches the map using the current engine speed, the temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 as keys, and knows the target intake pressure to be set.

  When the EGR valve 23 is opened during the fuel cut and the feedback control of the intake pressure in the surge tank 33 is performed, if the fuel cut end condition is satisfied, the EGR valve 23 is set before the fuel injection is restarted. It is ideal to fully close. In particular, when the fuel cut is completed by the driver's intention, that is, when the accelerator opening exceeds the threshold, an operation of closing the EGR23 valve is executed, and the fuel injection is resumed after the opening becomes 0 or minimal. It is desirable. On the other hand, when the fuel cut ends without the intention of the driver, for example, when the engine speed decreases to the fuel cut return speed, there is a risk of engine stall. Regardless, restart fuel injection as soon as possible.

  In the feedback control of step S3, S5 or S6, the throttle valve 32 opening (the feedback correction amount) in a state where the absolute value of the deviation between the actually measured intake pressure in the surge tank 33 and the target intake pressure has converged below a predetermined value. And / or learning control in which the opening degree of the EGR valve 23 (the feedback correction amount thereof) is used as a learning value and associated with the engine speed at that time and stored in the memory of the ECU 0 may be executed. When step S3, S5 or S6 is to be performed again later, the learned value of the throttle valve 32 opening and / or the EGR valve 23 opening previously stored in the memory using the current engine speed as a key. The learning value is retrieved and read, and the throttle valve 32 and / or the EGR valve 23 are operated at the opening degree of the learning value.

  In this embodiment, a part of the exhaust gas flowing through the exhaust passage 4 is recirculated to the intake passage 3 as EGR gas and the internal combustion engine attached with the exhaust gas recirculation device 2 that can be mixed with the intake air is controlled. During the fuel cut for temporarily interrupting the fuel supply to the cylinder 1, the opening of the intake throttle valve 32 on the intake passage 3 and the EGR passage 21 so that the pressure of the intake air flowing into the cylinder 1 converges to the target intake pressure. The EGR valve 23 is opened, and the EGR rate, which is the ratio of EGR gas in the intake air flowing into the cylinder 1, increases as the temperature of the exhaust passage 4 and / or the temperature of the exhaust purification catalyst 41 decreases. The control device 0 for the internal combustion engine is configured.

  According to the present embodiment, the fluctuation of the pumping loss of the internal combustion engine is suppressed, the deceleration of the internal combustion engine and the vehicle is kept as constant as possible, the oxygen concentration of the intake air flowing into the cylinder 1 is lowered, the intake air temperature is increased, and the catalyst It is possible to prevent the amount of stored oxygen from becoming excessive while keeping 41 warm. Therefore, it is possible to suppress or avoid the deterioration of the emission and the decrease in drivability caused by the fuel cut control of the internal combustion engine.

  In addition, due to aging of the internal combustion engine, the opening of the intake throttle valve 32 required to avoid the engine speed increase and the engine stall during the combustion operation when the accelerator opening is 0 or a deceleration request close to 0 is required. The degree of opening of the intake throttle valve 32 required to keep the strength of the engine braking action during fuel cut constant. Since the control device 0 of the present embodiment absorbs the influence of such aging through feedback control of the intake pressure, the engine speed during the combustion operation under a deceleration request is maintained at a suitable speed over the medium to long term. In addition, the strength of the engine brake during fuel cut can be kept constant.

  The present invention is not limited to the embodiment described in detail above. For example, in the above embodiment, the opening degree of the EGR valve 23 in the feedback control in step S6 is variable, but the opening degree of the EGR valve 23 in the feedback control in step S6 may be set to a certain size. In this aspect, the EGR valve 23 is closed in step S5, and the EGR valve 23 is opened in step S6. The two-stage switching according to the temperature of the exhaust passage 4 and / or the temperature of the catalyst 41 during fuel cut. It becomes.

  In the above embodiment, the opening degree of the electronic throttle valve 32 is operated for feedback control of the intake pressure in the surge tank 33. However, in an internal combustion engine in which an ISC valve is mounted as an intake throttle valve, (EGR The intake pressure may be feedback controlled by manipulating the opening of the ISC valve (along with the opening of the valve 23). As is well known, the ISC valve is a flow control valve that opens and closes a bypass communicating the upstream side and the downstream side of the throttle valve 32 in the intake passage 3.

  In addition, the specific configuration of each unit, the processing procedure, and the like can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle.

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 11 ... Injector 2 ... Exhaust-gas recirculation (EGR) apparatus 23 ... EGR valve 3 ... Intake passage 32 ... Intake throttle valve (throttle valve)
4 ... Exhaust passage

Claims (2)

A part of the exhaust gas flowing through the exhaust passage is recirculated to the intake passage as EGR gas to control the internal combustion engine attached with the exhaust gas recirculation device capable of intermingling with the intake air;
During the fuel cut to temporarily interrupt the fuel supply to the cylinder, the opening of the intake throttle valve on the intake passage and the opening of the EGR valve on the EGR passage are made to converge the pressure of the intake air flowing into the cylinder to the target intake pressure. A control device for an internal combustion engine that increases the EGR rate, which is the proportion of EGR gas in the intake air flowing into the cylinder, as the temperature of the exhaust passage or the temperature of the exhaust purification catalyst decreases. The control apparatus for an internal combustion engine according to claim 1, wherein the target intake pressure is lowered as the EGR rate is higher.

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