JP2013238136A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively avoid a misfire when decelerating, in an internal combustion engine attached with an EGR device.SOLUTION: In a control device for controlling an internal combustion engine attached with an exhaust gas recirculating device, when operating in the direction for reducing opening of an EGR valve in response to reduction in a request load (S2), in a state where the EGR ratio of intake air filled in a cylinder exceeds a misfire limit (S3), a frequency of combustion repeatedly performed in the cylinder is thinned out (S5). Since an intake air quantity filled in an operating cylinder of not resting the combustion and a fuel injection quantity to the cylinder can be increased by thinning out the combustion frequency, the combustion is not unstabilized in the cylinder, and the misfire is avoided.

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 in the cylinder, a EGR device known to reduce the pumping loss. The EGR device connects an exhaust path and an intake path via an EGR passage, and recirculates a part of combustion gas generated in the cylinder to the intake path via the EGR path to be mixed into the intake air.

  In the low pressure loop EGR, the exhaust gas that has passed through the turbine of the exhaust turbocharger and the exhaust gas purifying catalyst is returned to the intake passage. The low pressure loop EGR is advantageous in that a large amount of EGR gas can be returned to the intake passage.

  On the other hand, the low-pressure loop EGR gas is a low-pressure and low-temperature gas close to the atmospheric pressure, and it is difficult to recirculate the EGR gas when the pressure of fresh air in the intake passage is high. In view of this, an intake throttle valve is provided upstream of the outlet of the EGR passage in the intake passage, and the intake throttle valve is throttled to create a negative pressure around the outlet of the EGR passage to promote the recirculation of EGR gas. .

  When the driver requests to decelerate the accelerator pedal or release his or her foot from the accelerator pedal, in other words, when the required load is reduced, not only the intake amount and the fuel injection amount are reduced, but also the EGR rate of the intake air Need to be quickly reduced.

  However, even if the EGR valve is closed, EGR gas remains in the intake passage after the outlet of the EGR passage, and the EGR rate of the intake gas filled in the cylinder does not immediately decrease. If the EGR rate is excessive when the intake air amount and the combustion injection amount are small, the combustion in the cylinder becomes unstable and sometimes misfires.

  This problem becomes significant in the low-pressure loop EGR. In order to recirculate EGR gas close to atmospheric pressure, the outlet of the EGR passage is connected to the upstream side of the compressor of the exhaust turbocharger in the low pressure loop EGR. That is, the EGR gas that has joined from the EGR passage to the intake passage reaches the cylinder through a long route that passes through the compressor, the throttle valve, the surge tank, and the intake manifold. Since a considerable amount of EGR gas remains on the long path, EGR tends to be excessive during deceleration.

  For the purpose of preventing misfire during deceleration, a fresh air bypass passage that communicates the upstream side of the compressor and the downstream side of the throttle valve in the intake passage is provided, and fresh air is sent to the cylinder via the bypass passage during deceleration, Attempts have also been made to reduce the EGR rate of intake air (see, for example, the following patent document). However, there is a tendency that the cost increases due to the provision of the bypass passage.

  Alternatively, it is conceivable to suppress the EGR rate by providing a safety margin in advance in the operation range of medium and high loads, but the original utility of EGR is impaired and fuel consumption is reduced.

JP 2012-007547 A

  An object of the present invention is to effectively avoid misfire during deceleration in an internal combustion engine attached with an EGR device.

  In the present invention, an internal combustion engine attached with an exhaust gas recirculation device in which an EGR valve is provided in an EGR passage communicating the exhaust passage and the intake passage is controlled, and the EGR valve is opened as the required load decreases. When operating in a direction to reduce the degree, the internal combustion engine is characterized in that, in a situation where the EGR rate of the intake air charged in the cylinder exceeds the misfire limit, the number of combustions repeatedly performed in the cylinder is thinned out The engine control device was configured.

  By thinning out the number of times of combustion, it is possible to increase the intake air amount that fills an operating cylinder that does not stop combustion and the fuel injection amount to the cylinder. Then, the combustion does not become unstable in the cylinder, and misfire is avoided.

  ADVANTAGE OF THE INVENTION According to this invention, the misfire at the time of the deceleration in the internal combustion engine attached with the EGR apparatus can be avoided effectively.

The figure which shows the whole structure of the internal combustion engine for vehicles in one Embodiment of this invention. The figure which shows the relationship between a request | requirement load and a request | requirement EGR rate. The flowchart which shows the example of a 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 gasoline 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 ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  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 intake throttle valve 36, a compressor 51 of the exhaust turbocharger 5, an intercooler 35, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream side. Yes.

  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, a drive turbine 52 of the exhaust turbocharger 5, and an exhaust purification 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 n 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.

  An external EGR device 2 is attached to the internal combustion engine of the present embodiment. The external EGR device 2 realizes a so-called low-pressure loop EGR, and an EGR passage 21 that communicates the downstream side of the turbine 52 in the exhaust passage 4 and the upstream side of the compressor 51 in the intake passage 3, and the EGR passage 21. The EGR cooler 22 provided 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 pressure loss of the low-pressure loop EGR passage 21 is as small as several hundred Pa. The inlet of the EGR passage 21 is connected to a predetermined location downstream of the three-way catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined location in the intake passage 3 downstream of the intake throttle valve 36 and upstream of the compressor 51.

  In the low-pressure loop EGR, low-pressure exhaust gas close to atmospheric pressure is recirculated to the intake passage 3 through the EGR passage 2. For this purpose, the pressure around the outlet of the EGR passage 2 is reduced to a negative pressure by restricting the intake throttle valve 36 upstream of the outlet of the EGR passage 2. Incidentally, the pressure on the upstream side of the intake throttle valve 36 in the intake passage 3 becomes substantially atmospheric pressure or somewhat negative pressure due to the operation of the compressor 51.

  An ECU (Electronic Control Unit) 0 that is a control device of 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 (N signal) b output from an engine rotation sensor that detects the rotation angle of the crankshaft and the engine speed, An accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal as a required load, a brake depression amount signal d output from a sensor that detects the amount of depression of the brake pedal, and the intake passage 3 (particularly, the surge tank 33) ) The intake air temperature / intake pressure signal e output from the temperature / pressure sensor for detecting the intake air temperature and the intake pressure, the coolant temperature signal f output from the water temperature sensor for detecting the engine coolant temperature, and the combustion of the fuel Is generated in the combustion chamber of the cylinder 1 and flows between the center electrode of the spark plug 12 and the ground electrode, the intake camshaft or the exhaust gas. A cam angle signal output from cam angle sensor (G signal) h or the like are input by a plurality of cam angle of the cam shaft.

  From the output interface, the ignition signal i for the igniter of the spark plug 12, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the opening operation signal l for the EGR valve 23. The opening operation signal m is output to the intake throttle valve 36, and the opening operation signal n is output to the waste gate valve 44.

  The processor of the ECU 0 that controls the operation of the internal combustion engine interprets and executes a program stored in advance in the memory, calculates an operation parameter, 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, the 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, ignition timing, required EGR rate (or EGR rate) Various operating parameters such as volume). As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, k, l, m, and n corresponding to the operation parameters via the output interface.

  FIG. 2 shows an outline of the relationship between the required load corresponding to the accelerator pedal depression amount and the EGR rate required for the intake air charged in the cylinder 1. Basically, the required EGR rate is the highest in the medium load region and lower in the low load region and the high load region. In the low load region, the required EGR rate decreases as the required load decreases. In the high load region, the required EGR rate decreases as the required load increases. When the driver suddenly loosens the accelerator pedal or releases his or her foot from the accelerator pedal in the driving range of about medium load, the required load becomes low and the required EGR rate also decreases rapidly.

  The low-pressure loop EGR has a weakness that the responsiveness and responsiveness of the control of the intake EGR rate are low. Therefore, in the present embodiment, the number of times the combustion is repeatedly performed in the cylinder 1 is thinned out in the transitional period of deceleration where the required load is reduced, and the opening of the throttle valve 32 is set according to the amount of depression of the accelerator pedal. Therefore, transient control that opens larger than the normal opening is performed to compensate for the delay in EGR control.

  FIG. 3 shows a procedure example of processing executed by the ECU 0 according to the program. When there is a deceleration request for reducing the required load from the operation range of medium load or high load (step S1), the ECU 0 operates in a direction to reduce the opening of the EGR valve 23 according to the required load (step S2). ).

  After that, it is determined whether or not the EGR rate of the intake air charged in the cylinder 1 exceeds the misfire limit (steps S3 and S4). In step S3, the EGR rate at the time of medium load or high load immediately before the deceleration request (according to the medium load or high load) is compared with the misfire limit EGR rate according to the current required load. If the value exceeds the value, it is determined that the EGR rate of the intake air exceeds the misfire limit. In the memory of the ECU 0, map data in which the current required load is associated with the misfire limit EGR rate at the required load is stored in advance. The ECU 0 searches the map using the current required load as a key, and reads and knows the misfire limit EGR rate corresponding to the current required load.

  In step S4, the presence or absence of an event suspected of a combustion failure or misfire in the cylinder 1 is detected. As a method for estimating the combustion state in the combustion chamber of the cylinder 1, it is known to detect and refer to an ionic current flowing through the electrode of the spark plug 12 as the fuel is burned. During poor combustion, the peak of the ionic current is lower than during normal combustion. Moreover, at the time of misfire, an ion current cannot be detected in the first place. It is possible to determine whether or not the combustion in the cylinder 1 is normal by measuring the transition of the ion current and comparing the measured value with a threshold value for determination. If a combustion failure or misfire has occurred, it means that the intake EGR rate is correctly above the misfire limit.

  When it is determined that the intake EGR rate exceeds the misfire limit, the process proceeds to transient control in which the number of combustions is thinned out (step S5). Therefore, the fuel injection to the idle cylinder 1 (the intake air charged therein) that is the object of thinning is stopped, and the ignition in the cylinder 1 is stopped.

  Which cylinder 1 of the plurality of cylinders 1 stops the combustion depends on the thinning rate of the number of combustion times. For example, in order to reduce the number of combustions by 1/3 (33%), the combustion performed sequentially in the plurality of cylinders 1 is performed twice after a pause. In the case of a three-cylinder engine, after the combustion is stopped once in the first cylinder 1, the combustion is performed once in the second cylinder 1 and the third cylinder 1, and then the combustion is stopped once in the first cylinder 1. Control is performed such that combustion is performed once in the second cylinder 1 and the third cylinder 1. In order to decimate the number of combustions by 1/2 (50%), combustion pause and combustion are alternately performed. If the engine is a three-cylinder engine, the combustion is stopped in the first cylinder 1, the combustion is performed in the second cylinder 1, the combustion is stopped in the third cylinder 1, the combustion is performed in the first cylinder 1, and so on. .

  Further, during the transient control period, correction for increasing the opening of the throttle valve 32 is added (step S6). During normal times, the opening degree of the throttle valve 32 is determined according to the depression amount of the accelerator pedal, but in the transient control, the throttle valve 32 is operated to an opening degree larger than the opening degree according to the depression amount of the accelerator pedal. This is because it is necessary to supplement the output of the cylinder 1 that has been deactivated by the combustion of fuel in the cylinder 1 that is not deactivated. In other words, the intake air amount (and the fuel injection amount) that fills the cylinder 1 that operates without stopping is increased. In spite of the deceleration, the amount of intake air to the cylinder 1 that performs combustion increases, and as a result, the misfire limit EGR rate effectively increases for the cylinder 1. Therefore, even if the decrease in the EGR rate of the intake air charged in the cylinder 1 is delayed, there is no possibility of unstable combustion or misfire.

  The opening degree of the throttle valve 32 during the transient control is calculated based on the current required load and the thinning rate of the number of combustions. When the number of combustions is reduced by 1/3, in order to set the output of the internal combustion engine to a magnitude commensurate with the required load, the opening of the throttle valve 32 is compared with the opening of the normal time by 3/2 (1.5 ) Double. That is, the intake air amount that fills the cylinder 1 that operates without stopping is increased to 3/2 times the normal time. When the number of times of combustion is reduced by half, in order to make the output of the internal combustion engine have a magnitude commensurate with the required load, the opening of the throttle valve 32 is doubled compared to the opening of the normal time. That is, the intake air amount that fills the cylinder 1 that operates without stopping is increased to twice the normal time.

  The rate of thinning out the number of times of combustion during transient control should be increased as the difference between the EGR rate at the time of medium load or high load immediately before the deceleration request and the misfire limit EGR rate according to the current required load increases. Is preferred. When a combustion failure or misfire in the cylinder 1 is detected, the rate of decimation of the number of combustions is increased as much as possible to sufficiently increase the amount of intake air charged into the operating cylinder 1 to prevent the successive occurrence of misfires. .

  Thus, the transient control is continued until a sufficient time has elapsed to complete scavenging of the EGR gas remaining on the intake passage 3 from the downstream of the EGR valve 23 to the intake port of the cylinder 1. (Step S7).

  In the present embodiment, an EGR device 2 in which an EGR valve 23 is provided in an EGR passage 21 that communicates the exhaust passage 4 and the intake passage 3 is controlled, and the EGR is reduced as the required load decreases. When the EGR rate of the intake air charged in the cylinder 1 exceeds the misfire limit when operating in the direction of reducing the opening of the valve 23, the number of times of repetitive combustion in the cylinder 1 is thinned out. A control device 0 for an internal combustion engine, which is characterized by the above, is constructed.

  According to the present embodiment, by thinning out the number of times of combustion, the amount of intake air charged into the operating cylinder 1 that does not suspend combustion and the amount of fuel injected into the cylinder 1 in spite of the deceleration period in which the required load decreases is reduced. Can be increased. Therefore, combustion does not become unstable in the cylinder 1, and misfire is avoided.

  Further, for the purpose of preventing misfire during deceleration, it is possible to avoid an increase in cost such as adding a fresh air bypass passage that short-circuits the intake passage. In addition, since it is not necessary to suppress the EGR rate by providing a safety margin in advance in the medium to high load operation region, it is permitted to return a larger amount of EGR gas from the exhaust passage 4 to the intake passage 3. The original utility of EGR is not impaired and contributes to improvement of fuel consumption.

  The present invention is not limited to the embodiment described in detail above. Although the EGR device 2 in the above embodiment realizes the low pressure loop EGR, the internal combustion engine is accompanied by a high pressure loop EGR device that recirculates EGR gas from the upstream side of the turbine in the exhaust passage to the upstream side of the throttle valve in the intake passage. It is naturally possible to use the control device according to the present invention for controlling the engine.

  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 2 ... EGR apparatus 21 ... EGR passage 23 ... EGR valve 3 ... Intake passage 4 ... Exhaust passage

Claims (1)

Controlling an internal combustion engine accompanied by an exhaust gas recirculation device in which an EGR valve is provided in an EGR passage communicating the exhaust passage and the intake passage;
Combustion that is repeatedly performed in the cylinder in a situation where the EGR rate of the intake air charged in the cylinder exceeds the misfire limit when operating in a direction to reduce the opening degree of the EGR valve as the required load decreases. A control device for an internal combustion engine, characterized in that the number of times is reduced.

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