JP5854830B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device that controls an internal combustion engine.

  In an internal combustion engine mounted on a vehicle or the like, it is known to perform a fuel cut that temporarily stops fuel injection in accordance with its operating condition (see, for example, the following patent document).

  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. .

  Torque shock in which the output torque of the engine (and hence the engine speed and the vehicle speed) drops stepwise if the throttle valve is wide open, that is, when the fuel supply is suddenly cut off when the output of the internal combustion engine is relatively large Occurs and makes the driver or passenger feel a shock.

  Conventionally, in order to avoid such a torque shock, even if the fuel cut condition is satisfied, the fuel injection is not stopped immediately, but the opening torque of the throttle valve and the fuel injection amount are reduced to gradually decrease the engine output torque. Transient control is executed, and then fuel injection is stopped.

  In the period from when the fuel cut condition is satisfied to when fuel injection is actually stopped, fuel injection and combustion continue. Therefore, if this period is long, the effective fuel consumption may be deteriorated, and the intake air amount and fuel injection amount charged into the cylinder may be insufficient, causing misfire, and gas containing unburned fuel may be discharged. There was also.

JP 2006-183536 A

  An object of the present invention is to shorten a period from establishment of a fuel cut condition to stop of fuel injection while avoiding a torque shock.

In the present invention, when a predetermined fuel cut condition is satisfied, a fuel cut is performed to temporarily stop fuel supply to the cylinder, and the combustion pressure in each cylinder reaches a peak as the fuel cut condition is satisfied. The timing is detected and correction control is performed to advance the ignition timing at each combustion opportunity so that the combustion pressure peak gradually approaches the target crank angle before the compression top dead center. A control device for an internal combustion engine characterized in that fuel supply to the cylinder is stopped.

  In other words, as the fuel cut condition is established, the ignition timing is extremely advanced to cause the fuel to explode and burn during the compression stroke, and to generate pressure in the combustion chamber that pushes back the piston toward the compression top dead center. Thus, the output torque of the internal combustion engine is quickly reduced.

  According to the present invention, it is possible to shorten the period from the establishment of the fuel cut condition to the stop of fuel injection while avoiding the torque shock.

The figure which shows the whole structure of the internal combustion engine in one Embodiment of this invention. The circuit diagram of the spark ignition device in the embodiment. The figure which illustrates each transition of the combustion pressure and ion current of each cylinder of an internal combustion engine. The figure which illustrates each transition of the combustion pressure and the ionic current of each cylinder of an internal combustion engine after execution of fuel cut conditions and before execution of fuel cut. The figure which illustrates transition of the output torque of an engine at the time of performing correction control by the control device of the embodiment.

  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. This spark ignition type internal combustion engine is of a direct injection type, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1) and an injector 10 for injecting fuel into each cylinder 1. An intake passage 3 for supplying intake air to each cylinder 1, an exhaust passage 4 for discharging exhaust from each cylinder 1, and an exhaust turbocharger 5 for supercharging intake air flowing through the intake passage 3; And an external EGR device 2 that recirculates EGR (Exhaust Gas Recirculation) gas from the exhaust passage 4 toward the intake passage 3.

  A spark plug 13 is attached to the ceiling of the combustion chamber of the cylinder 1. FIG. 2 shows an electric circuit for spark ignition. The spark plug 13 receives spark voltage generated by the ignition coil 12 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 12 is integrally incorporated in a coil case together with an igniter 11 that is a semiconductor switching element.

  When the igniter 11 receives an ignition signal i from an ECU (Electronic Control Unit) 0 that is a control device for the internal combustion engine, the igniter 11 is first ignited and a current flows to the primary side of the ignition coil 12, and at the ignition timing immediately thereafter. The igniter 11 is extinguished to interrupt this current. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 13, and spark discharge occurs between the center electrode and the ground electrode.

  The ECU 0 detects an ionic current generated in the combustion chamber of the cylinder 1 during the explosive combustion of the fuel, and refers to this ionic current to determine the combustion pressure in the combustion chamber during the period from the latter stage of the compression stroke to the latter stage of the expansion stroke. In other words, the in-cylinder pressure is estimated.

  As shown in FIG. 2, the electrical circuit for spark ignition has a bias power supply unit 14 for effectively detecting the ionic current, and an amplification that amplifies and outputs a detection voltage corresponding to the amount of the ionic current. The part 15 is attached. The bias power supply unit 14 includes a capacitor 141 that stores a bias voltage, a Zener diode 142 for increasing the voltage of the capacitor 141 to a predetermined voltage, current blocking diodes 143 and 144, and a load that outputs a voltage corresponding to the ion current. A resistor 145. The amplifying unit 15 includes a voltage amplifier 151 typified by an operational amplifier.

  During arc discharge between the center electrode and the ground electrode of the spark plug 13, the capacitor 141 is charged, and then an ion current flows through the load resistor 145 by the bias voltage charged in the capacitor 141. The voltage between both ends of the resistor 145 generated due to the flow of the ionic current is amplified by the amplifying unit 15 and received by the ECU 0 as the ionic current signal d.

  The intake passage 3 takes in air from the outside and guides it to the intake port of the cylinder 1. On the intake passage 3, an air cleaner 31, a compressor 51 of the supercharger 5, an intercooler 32, an electronic throttle valve 33, a surge tank 34, and an intake manifold 35 are arranged in this order from the upstream side.

  The exhaust passage 4 guides exhaust generated as a result of burning fuel in the cylinder 1 from the exhaust port of the cylinder 1 to the outside. An exhaust manifold 42, a drive turbine 52 for the supercharger 5, and a three-way catalyst 41 are disposed on the exhaust passage 4. In addition, an exhaust bypass passage 43 that bypasses the turbine 52 and a waste gate valve 44 that is a bypass valve that opens and closes the inlet of the bypass passage 43 are provided. The waste gate valve 44 is an electric waste gate valve that can be opened and closed by inputting a control signal l to the actuator, and a DC servo motor is used as the actuator.

  The exhaust turbocharger 5 is configured such that the drive turbine 52 and the compressor 51 are connected and linked in a coaxial manner. Then, the driving turbine 52 is rotationally driven by using the energy of the exhaust gas, and the compressor 51 is pumped by using the rotational force, whereby the intake air is pressurized and compressed (supercharged) and sent to the cylinder 1.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The inlet of the external EGR passage is connected to a predetermined location upstream of the turbine 52 in the exhaust passage 4. The outlet of the external EGR passage is connected to a predetermined location downstream of the throttle valve 33 in the intake passage 3, specifically to a surge tank 34. An EGR cooler 21 and an EGR valve 22 are also provided on the external EGR passage.

  The ECU 0 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, an engine rotation 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. The accelerator opening signal c output from an accelerator opening sensor that detects the amount or the opening of the throttle valve 33 as an accelerator opening (so-called required load), generation of plasma in the combustion chamber, and combustion of the air-fuel mixture Ion current signal d output from a circuit that detects the generated ion current, and output from a temperature / pressure sensor that detects intake air temperature and intake pressure (or supercharging pressure) in intake passage 3 (especially surge tank 34). The intake air temperature / intake pressure signal e, the coolant temperature signal f output from the water temperature sensor for detecting the coolant temperature of the internal combustion engine, and the like are input. That.

  From the output interface, an ignition signal i for the ignition plug igniter 11, an opening operation signal j for the EGR valve 22, an opening operation signal k for the throttle valve 33, and an opening for the waste gate valve 44. The operation signal l, the fuel injection signal m and the like are output to the injector 10.

  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, and f necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and estimates the amount of intake air charged in the cylinder 1 To do. Based on the engine speed and intake air amount, the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, ignition timing, EGR amount (or EGR rate) Various operating parameters are determined. As the operation parameter determination method itself, a known method can be adopted. Thus, various control signals i, j, k, l, and m corresponding to the operation parameters are applied through the output interface.

  The ECU 0 of the present embodiment starts a fuel cut that stops fuel injection from the injector 10 (and ignition by the spark plug 13) when a predetermined fuel cut condition is satisfied. The fuel cut condition is, for example, that the accelerator pedal depression amount is 0 or less than a threshold value close to 0, and that the engine speed is equal to or higher than the fuel cut permission speed.

  Then, when a predetermined fuel cut end condition is satisfied during the fuel cut, the fuel injection (and ignition) from the injector 10 is resumed. The fuel cut end condition is, for example, that the accelerator pedal depression amount exceeds a threshold value, or that the engine speed has decreased to the fuel cut return speed.

In addition, in this embodiment, the fuel injection into the cylinder 1 is not stopped immediately when the fuel cut condition is satisfied, but the ignition timing in the cylinder 1 is set to the combustion pressure in the cylinder 1 at the compression top dead center. Correction control for advancing to a peak in the vicinity or before compression top dead center is performed, and then fuel injection into the cylinder 1 is stopped.

  In general, the ignition timing is a so-called MBT (Minimum Advance for Best Torque) point or a timing delayed from that point. In FIG. 3 (FIGS. 3 and 4, the combustion pressure is drawn by a broken line, and the measured value of the ionic current is obtained. Is drawn with a solid line), the combustion pressure of the cylinder 1 reaches its peak after compression top dead center.

  On the other hand, in the transition period from the establishment of the fuel cut condition to the cutoff of the fuel supply, the ignition timing is gradually advanced, and finally the extreme over-advanced angle is set. As a result, as shown in FIG. 4, the combustion pressure of the cylinder 1 reaches a peak before the compression top dead center, and tries to push the piston toward the compression top dead center toward the bottom dead center during the compression stroke. . That is, a torque that reversely rotates the crankshaft is generated, producing an engine braking action.

  Incidentally, while the vehicle is decelerating such that the fuel cut condition is satisfied, the required load on the internal combustion engine is smaller than before, so there is no possibility of causing knocking even if the ignition timing is advanced.

  In the ignition timing advance correction control described above, the ECU 0 according to the present embodiment refers to the ion current signal d, detects the timing at which the combustion pressure in each cylinder 1 peaks, and the peak is before the compression top dead center. In order to gradually approach the vicinity of the target crank angle, feedback control is performed to manipulate the ignition timing at each combustion opportunity of each cylinder 1. The reason why the ignition timing is not immediately brought close to the target crank angle but is gradually advanced toward the target crank angle is to prevent a large torque shock from being generated.

  FIG. 3 and FIG. 4 exemplify transitions of the ion current (shown by a solid line in the figure) and the combustion pressure in the cylinder 1 (shown by a broken line in the figure). In the case of normal combustion, the ionic current cannot be detected during the discharge for ignition. In the case of normal combustion, the ionic current decreases by a chemical reaction before the compression top dead center after the end of spark ignition, and then increases again by thermal dissociation. In addition, the ionic current reaches a maximum almost simultaneously with the peak of the combustion pressure. Therefore, by measuring the maximum value of the ionic current, it is possible to detect the timing at which the combustion pressure reaches a peak.

  The ECU 0 calculates a deviation between the combustion pressure peak timing for each cylinder 1 detected based on the ionic current and the target crank angle, and feedback correction (advance correction or delay correction) to reduce the deviation. ) The amount is added to the ignition timing of the cylinder 1 to obtain the ignition timing at the next combustion in each cylinder 1. Depending on the ignition timing control for each cylinder 1, the ignition timing in each cylinder 1 may be different from each other, but the peak of the combustion pressure in each cylinder 1 is gradually advanced toward the vicinity of the target crank angle, and finally Will be aligned near the target crank angle.

  The final target crank angle can be set according to the amount of output torque of the engine when the fuel cut condition is satisfied or just before the fuel cut condition is satisfied. In this case, the target crank angle is set to a more advanced side as the output torque at the time when the fuel cut condition is satisfied or just before the fuel cut condition is larger.

  The ECU 0 receives the injector 10 after the peak of the combustion pressure in the cylinder 1 has reached the vicinity of the target crank angle, or after the output torque of the engine that is constantly being repeatedly calculated by the ECU 0 has decreased to a predetermined level. The fuel injection from is completely stopped.

In the present embodiment, when a predetermined fuel cut condition is satisfied, a fuel cut is performed in which the fuel supply to the cylinder 1 is temporarily stopped. As the fuel cut condition is satisfied , the combustion pressure in each cylinder 1 is increased. Detects the timing of the peak, and performs correction control to advance the ignition timing at each combustion opportunity of each cylinder 1 so that the peak of the combustion pressure gradually approaches the target crank angle before the compression top dead center Then, the control device 0 for the internal combustion engine is configured to stop the fuel supply to the cylinder 1 after that.

  According to the present embodiment, while avoiding a torque shock, FIG. 5 (in FIG. 5, the transition of the output torque of the engine according to the present embodiment is drawn by a solid line, and the transition of the output torque of the engine by the conventional control method is indicated by a broken line. The engine output torque can be reduced more rapidly after the fuel cut condition is established, as compared to the conventional control method. Since the period from when the fuel cut condition is satisfied to when the fuel supply is actually cut off is shortened, it contributes to the improvement of the effective fuel consumption and can also prevent the occurrence of misfire due to excessive reduction of the intake air amount and the fuel injection amount. .

  The present invention is not limited to the embodiment described in detail above. In the above embodiment, the ignition timing is advanced so that the combustion pressure of the cylinder 1 reaches a peak before the compression top dead center with the establishment of the fuel cut condition. The ignition timing may be advanced so as to reach a peak in the vicinity of the compression top dead center after the point. In short, the energy that pushes the piston so that the in-cylinder pressure reversely rotates the crankshaft in the compression stroke is larger than the energy that pushes the piston so that the in-cylinder pressure rotates the crankshaft in the combustion stroke. The ignition timing may be advanced until the timing at which negative rotational kinetic energy is given from the cylinder 1 to the crankshaft as a sum total.

  In the above embodiment, the ECU 0 senses the peak of the combustion pressure in the combustion chamber of the cylinder 1 by referring to the ionic current. However, when the cylinder pressure sensor is incorporated in the cylinder 1, the ECU 0 uses the cylinder pressure sensor. By directly measuring the combustion pressure, the peak can be detected.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

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

0 ... Control unit (ECU)
1 ... Cylinder 13 ... Spark plug

Claims (1)

A fuel cut for temporarily stopping fuel supply to the cylinder when a predetermined fuel cut condition is satisfied,
Combustion opportunities in each cylinder are detected so that the timing at which the combustion pressure in each cylinder reaches its peak is detected as the fuel cut condition is established, and the combustion pressure peak gradually approaches the target crank angle before compression top dead center. A control apparatus for an internal combustion engine, wherein correction control for advancing the ignition timing every time is performed, and thereafter fuel supply to the cylinder is stopped.

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