JP4021384B2 - Control method for internal combustion engine - Google Patents

Description

  The present invention relates to a control method mainly used for an internal combustion engine for a vehicle.

  Conventionally, in an internal combustion engine, there has been considered a high expansion ratio engine called an Atkinson cycle engine that performs delayed closing control that sets the closing timing of the intake valve to the timing after the piston passes the bottom dead center, that is, the retarded angle side than usual. Yes. Since the actual compression ratio decreases when the closing timing of the intake valve is retarded from normal, the throttle valve opening is set larger than that of a normal engine that does not perform the delayed closing control in order to obtain a desired torque. There is a need to. Therefore, the intake loss in the throttle valve when obtaining a desired torque can be suppressed, and the fuel efficiency can be improved. FIG. 5 is a graph showing changes in the fuel consumption rate, which is the amount of fuel required per unit output, with respect to torque for an internal combustion engine in which the closing timing of the intake valve is retarded and a normal internal combustion engine. In FIG. 5, the former internal combustion engine is indicated as “retard angle control ON”, and the latter internal combustion engine is indicated as “retard angle control OFF”. As shown in FIG. 5, with the same torque, the internal combustion engine with the intake valve closing timing retarded has a lower fuel consumption rate than that of a normal internal combustion engine, that is, better fuel efficiency.

However, when the closing timing of the intake valve is set to a retarded angle side as usual, the air sucked into the cylinder is blown back, so such control is performed when the opening of the throttle valve is the same. Torque is reduced as compared to the case where the operation is not performed. Such a phenomenon is particularly noticeable in a region where the opening of the throttle valve is low, and affects the running performance such that the acceleration intended by the driver cannot be obtained. Therefore, when such an internal combustion engine is used in a vehicle, in the operating state as described above, the advance timing control of the intake valve closing timing is performed to obtain the necessary torque, and the same timing as that of a normal internal combustion engine is obtained. Thus, it is considered that the amount of fuel supplied to the internal combustion engine is secured by closing the intake valve to eliminate the above-mentioned problems (for example, see Patent Document 1).
JP-A-9-166030

  However, if the advanced angle control is performed after the operation state as described above is eliminated, the intake loss in the throttle valve remains large compared to the case where the delayed closing control is performed. The fuel consumption cannot be improved by the late closing control.

  The present invention solves the above-mentioned problems and reduces the influence on the running performance by performing the retard control of the intake valve closing timing, while increasing the effect of improving the fuel consumption by such retard control. An internal combustion engine control method that can be obtained is provided.

That is, the control method for an internal combustion engine according to the present invention adjusts the intake air amount by the throttle valve and delays the intake valve to control the piston to pass the bottom dead center and reach a predetermined retarded closing position. In an internal combustion engine that can be operated as an Atkinson cycle engine that performs control to close the intake valve in the engine, the control method of the internal combustion engine is configured to advance the intake valve closing timing when the engine is in an operation state that requires torque. When the steady state is determined after the advance angle control is performed, the intake valve closing timing is retarded to operate as an Atkinson cycle, and the intake air amount control means that operates independently of the throttle valve is controlled. It is characterized by controlling to increase.

  By adopting such a control method, when the steady state is determined, the intake valve is delayed and controlled, that is, the intake valve closing timing is delayed and the fuel consumption can be improved. The reduction in the intake amount of the mixed gas due to the retard angle control is offset by the control of the intake air amount control valve so that the output decrease due to the retard angle control while the throttle valve opening is maintained can be suppressed. Become. In other words, since the intake amount of the mixed gas is maintained, the influence on the running performance by performing the retard control of the intake valve closing timing can be reduced, and the effect of improving the fuel consumption by such retard control can be increased. Obtainable.

  As a control method for reducing the uncomfortable feeling given to the driver when returning the intake air amount from the intake air amount control means to the intake air amount before the control described above, during acceleration operation or deceleration operation after the end of the control, Examples include controlling the intake air amount control means to reduce the intake air amount. When the intake air amount control means is controlled to decrease the intake air amount in a steady state, the output decreases due to the decrease in the engine intake air amount without the decrease in the throttle valve opening contrary to the intention of the driver who does not want to change the traveling speed. However, if the intake air amount control means is controlled to reduce the intake air amount during the acceleration operation or the deceleration operation, in such an operation state, the driver has at least the intention to change the traveling speed. It is.

  When the control method for an internal combustion engine according to the present invention is adopted, when the steady state is determined after performing the advance angle control in the operating state where torque is required, the retard control of the intake valve closing timing is performed. However, since the torque can be maintained without changing the opening of the throttle valve, it is possible to reduce the torque drop due to the retard control of the intake valve closing timing and to reduce the uncomfortable feeling given to the driver. More effects of improving the fuel consumption by the retard angle control can be obtained.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The engine schematically shown in FIG. 1 is a three-cylinder engine for automobiles. The engine intake system 1 is mechanically connected to an accelerator pedal 8 and responds to the accelerator pedal 8. The throttle valve 2 that opens and closes is disposed, and a surge tank 3 is provided on the downstream side thereof, and intake air from the surge tank 3 is sucked into the cylinder through an intake valve 37. A fuel injection valve 5 is further provided in the vicinity of the end of the intake manifold 4 of the intake system 1 communicating with the surge tank 3 on the cylinder head side. The fuel injection valve 5 is controlled by the electronic control unit 6. Yes. Further, the exhaust system 20 is provided with an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas discharged from the combustion chamber through the exhaust valve 36 in a pipe line leading to a muffler (not shown). The three-way catalyst 22 is attached at a predetermined position upstream. The engine may be of a single cylinder or two cylinders, or may be of four or more cylinders.

  In addition, this engine includes a continuously variable valve timing mechanism (hereinafter referred to as VVT) 30, and when the piston 9 passes through the bottom dead center and reaches a predetermined retarded closed position, the intake valve 37. It is possible to operate as an Atkinson cycle engine that performs control for closing the engine. The VVT 30 uses a so-called oscillating cylinder mechanism, and a rotor (not shown) fixed to the exhaust camshaft 31, a housing (not shown) fitted on the rotor, and the housing rotated with respect to the rotor. An oil control valve 32 serving as an electromagnetic four-direction switching control valve for this purpose, and a pair of gears 34 and 35 having one fixed to the housing and the other fixed to the intake camshaft 33 so as to mesh with each other.

  Then, the direction and amount of hydraulic oil flowing into and out of the housing is controlled by the oil control valve 32 to change the relative angle of the housing with respect to the rotor, so that an arbitrary rotational position is provided between the exhaust camshaft 31 and the intake camshaft 33. The valve timing is variably controlled by generating a phase difference. That is, the valve timing of the exhaust valve 36 and the valve timing of the intake valve 37 are changed by always changing the valve timing of the intake valve 37 while opening and closing the exhaust valve 36 at a constant timing with respect to the rotation of the crankshaft (not shown). Relative phase difference can be freely changed within a predetermined angle range. A crank sensor 41 that outputs a crank angle signal and an N signal for cylinder discrimination is attached to one end of the exhaust camshaft 31, and 240 ° CA is attached to one end of the intake camshaft 33. A timing sensor 42 that outputs an intake cam signal each time it rotates (crank angle) is attached.

  In this embodiment, the electronic control device 6 causes the intake valve 37 when the piston 9 passes the bottom dead center and reaches a predetermined retarded closed position via the VVT 30 in a steady state such as traveling at a constant speed on a flat ground. Is controlled so as to operate as an Atkinson cycle engine, and in an operating state where torque is required during acceleration or uphill traveling, the same as with a normal four-cycle engine via the VVT 30 When the piston 9 reaches near the bottom dead center, the control for closing the intake valve 37 is performed. Details of these controls will be described later.

  Further, this engine is provided with a bypass passage 70 that bypasses the throttle valve 2. The bypass passage 70 is provided with a bypass valve 7, and the amount of air passing through the bypass passage 70 is adjusted by changing the opening degree of the bypass valve 7. The bypass valve 7 operates independently of the accelerator pedal 8 and the throttle valve 2 during fuel consumption control, and functions as an intake air amount control means. The opening degree control of the bypass valve 7 is performed by the electronic control unit 6, and details thereof will be described later. In the present embodiment, the bypass valve 7 is normally in a fully closed state.

The electronic control device 6 is mainly configured by a microcomputer system including a central processing unit 61, a storage device 62, an input interface 63, and an output interface 64. The input interface 63 outputs the intake pressure signal a output from the intake pressure sensor 13 for detecting the pressure in the surge tank 3 (intake pipe pressure), and the output from the rotation speed sensor 14 for detecting the engine speed NE. The rotation speed signal b, the crank angle signal m output from the crank sensor 41, the intake cam signal n output from the timing sensor 42, and the water temperature signal f output from the water temperature sensor 17 for detecting the cooling water temperature of the engine. The voltage signal h output from the O ₂ sensor 21, the accelerator state signal x output from the accelerator state sensor 81 for detecting the operation amount of the accelerator pedal 8, and the speed sensor for detecting the traveling speed of the vehicle A speed signal v output from 19 is input. On the other hand, from the output interface 64, a drive pulse INJ as a fuel injection signal f for the fuel injection valve 5, an ignition signal g for the spark plug 18, and an opening control signal y for the bypass valve 7 are provided. It is output.

  The electronic control unit 6 controls the delay of the closing timing of the intake valve 37 via the VVT 30 when the steady state is determined, and increases the intake amount of the bypass valve 7 that operates independently of the throttle valve 2. A program for controlling the advance timing of the closing timing of the intake valve 37 via the VVT 30 is incorporated in order to increase the torque when it is determined that it is not in a steady state, such as an operating state where torque is required. .

  Specifically, the steady state is determined by detecting the speed indicated by the speed signal v output from the speed detector 19 every predetermined time, and the absolute value of the difference between the speed detected last time and the speed detected this time is predetermined. It is determined by determining whether or not the change rate of the operation amount of the accelerator pedal 8 indicated by the accelerator state signal x is below a predetermined value. The predetermined value is set in the vicinity of 0.

  The general procedure of this control program will be described with reference to FIG. 2 which is a flowchart and FIG. 3 which is an operation diagram. FIG. 3 shows the travel speed of the vehicle, the amount of operation of the accelerator pedal 8, the advance amount from the time when the piston 9 at the closing timing of the intake valve 37 reaches the retarded close position (hereinafter referred to as VVT advance amount). And the time change of the opening degree of the bypass valve 7 is shown with respect to the same time axis.

  First, in step ST11, it is determined whether or not the vehicle is in a steady state. If it is determined in step ST11 that the vehicle is in a steady state, the process proceeds to step ST12. On the other hand, if not, the process proceeds to step ST15.

  Next, in step ST12, it is determined whether or not the VVT advance amount indicated by the intake cam signal n is greater than or equal to a predetermined value p. If it is determined in step ST12 that the VVT advance amount is equal to or greater than the predetermined value p, the process proceeds to step ST13. On the other hand, if not, the process proceeds to step ST14. The predetermined value p is set near 0.

  In step ST13, a fuel efficiency control routine described later is executed.

  Here, the procedure of the fuel consumption control routine will be described below with reference to FIG. 4 which is a flowchart.

  In step ST21, the bypass valve 7 is opened by referring to a bypass valve opening table (not shown) with the opening of the throttle valve 2 as a parameter in order to maintain the engine torque at an amount before the execution of the fuel consumption control routine. Determine the degree.

  The bypass valve opening table sets the opening of the bypass valve 7 for maintaining the engine torque before and after executing the fuel consumption control routine with the opening of the throttle valve 2 as a parameter. 6 is prepared. In this bypass valve opening table, the opening degree of the bypass valve 7 is set with respect to the opening degree of the typical throttle valve 2, and the opening degree of the bypass valve 7 with respect to the other opening degree of the throttle valve 2 is Calculated by interpolation calculation.

  In step ST22, an opening degree control signal y is output in order to control the opening degree of the bypass valve 7 to the value determined in step ST21.

  In step ST23, the closing timing of the intake valve 37 is retarded so that the VVT advance amount is zero. That is, the engine is operated as an Atkinson cycle engine by closing the intake valve 37 when the piston 9 reaches the retarded closing position.

  In step ST14, control is performed to maintain the closing timing of the intake valve 37 and the opening degree of the bypass valve 7 as they were before the execution of step ST14.

  In step ST15, it is determined whether or not a fuel efficiency control routine is being executed. If it is determined in step ST15 that the fuel efficiency control routine is being executed, the process proceeds to step ST16. On the other hand, if not, the process proceeds to step ST18.

  In step ST16, the opening degree control signal y is output so that the bypass valve 7 is fully closed. Then, the process proceeds to step ST17.

  In step ST17, the closing timing of the intake valve 37 is advanced by setting the VVT advance amount to a value when the fuel efficiency control routine is not performed. That is, the closing timing of the intake valve 37 is moved to the advance side, such as setting the closing timing of the intake valve 37 when the piston 9 reaches the vicinity of the bottom dead center, and the engine is operated in a normal cycle.

  In step ST18, control is performed to maintain the closing timing of the intake valve 37 and the opening degree of the bypass valve 7 as they were before step ST18 was performed.

  By performing the control as described above, the engine operates as an Atkinson cycle engine in a steady state, and operates in a normal cycle in a transient state such as acceleration or deceleration.

  More specifically, when a transition is made from a transient state such as an acceleration state where torque is required to a steady state, each control is performed in the order of steps ST11 → ST12 → ST13, and the closing timing of the intake valve 37 is retarded. The engine is controlled and operated as an Atkinson cycle, and the opening of the bypass valve 7 is increased to maintain the engine torque.

  On the other hand, when the steady state is continued, that is, when the VVT advance amount is already 0, each control is performed in the order of steps ST11 → ST12 → ST14, and the operation as the Atkinson cycle engine is continued. ing.

  Further, when a transition is made from a steady state where the fuel efficiency control routine is performed to a transient state where it is not, for example, an acceleration operation state or a deceleration operation state, each control is performed in the order of steps ST11 → ST15 → ST16 → ST17. In other words, the VVT advance amount is changed from 0 to a value when the fuel consumption control routine is not performed, and the closing timing of the intake valve 37 is advanced to release the state in which the operation as the Atkinson cycle engine is performed. While shifting to the state which is operating in the cycle, the bypass valve 7 is fully closed to secure a room for increasing the opening degree of the bypass valve in the next steady state.

  When a transient state such as an acceleration state is continued, that is, when the fuel consumption control routine has not been performed in the transient state, each control is performed in the order of steps ST11 → ST15 → ST18. The operation as an engine that operates according to the cycle is continued.

  By controlling the internal combustion engine as described above, the following effects can be obtained.

  That is, in the steady state, the closing timing of the intake valve 37 is controlled to be retarded from the case of the engine operating in a normal cycle, and the engine torque is maintained by increasing the opening of the bypass valve 7. Therefore, as the opening of the bypass valve 7 is increased, the intake loss is reduced and the fuel efficiency is improved, and the opening of the throttle valve 2 is kept as it is, that is, the operation amount of the accelerator pedal 8 is kept as it is. Is maintained. Specifically, when only the retard control of the closing timing of the intake valve 37 is performed from the state of the point B in FIG. 5 without changing the opening degree of the throttle valve 2, it moves to the point C in FIG. In this embodiment, the torque of the engine decreases, and in this embodiment, the control is performed to increase the opening of the bypass valve 7 to move to the point A in FIG. It is possible to improve fuel efficiency without causing it. Therefore, the advance angle in a transient state such as an operating state where torque is required in an engine that employs a mechanical throttle in which the throttle valve 2 is mechanically connected to the accelerator pedal 8 and the throttle valve 2 opens and closes in response to the accelerator pedal 8. Since the engine torque can be maintained without changing the operation amount of the accelerator pedal 8 in the steady state after the control is performed, the operation amount of the accelerator pedal 8 when performing the retard control of the closing timing of the intake valve 37. It is possible to suppress the occurrence of a decrease in torque that is not accompanied by a decrease in. Further, it is possible to reduce the torque drop caused by performing the retard control of the intake valve closing timing to reduce the uncomfortable feeling given to the driver, and to obtain more effects of improving the fuel consumption by such retard control. it can.

  In addition, when shifting from the steady state to the transient state, the opening degree of the bypass valve 7 is decreased to return to the fully closed state, that is, the state before performing the control in the steady state as described above. Since the driver originally intended to change the torque even if the intake air amount of the engine is reduced and the torque is reduced by reducing the intake air amount from the intake air amount control means, in the next steady state, It is possible to reduce the uncomfortable feeling given to the driver during the control for securing the room for increasing the opening degree of the bypass valve 7. There is no problem even if the torque decreases during the deceleration operation, and the torque decrease due to the decrease in the opening of the bypass valve 7 due to the increase in the torque due to the increase in the opening of the throttle valve 2 is canceled during the acceleration operation. It is.

  The present invention is not limited to the embodiment described above.

  For example, the bypass passage in the above-described embodiment may be realized by a bypass passage for idling rotational speed control.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is a schematic view of an engine according to an embodiment of the present invention. The flowchart which shows the process which the control apparatus which concerns on the same embodiment performs. The figure which shows the effect | action of control in FIG. The flowchart which shows the process which the control apparatus which concerns on the same embodiment performs. The conceptual diagram which shows the change at the time of retarding the closing timing of an intake valve, and a fuel consumption rate.

Explanation of symbols

2 ... Throttle valve 37 ... Intake valve 6 ... Electronic control device 7 ... Bypass valve (intake amount control means)

Claims (2)

Atkinson cycle engine that controls the intake valve by adjusting the intake air amount with the throttle valve and closing the intake valve when the piston passes the bottom dead center and reaches the predetermined retarded angle closed position by controlling the intake valve slowly An internal combustion engine capable of operating as an internal combustion engine, wherein the control method of the internal combustion engine performs an advance control of the intake valve closing timing when the torque is in an operation state where the torque is required,
When the steady state is determined after performing the advance angle control, the intake valve closing timing is retarded to operate as an Atkinson cycle ,
An internal combustion engine control method comprising: controlling an intake air amount control means that operates independently of a throttle valve so that an intake air amount increases. 2. The control method for an internal combustion engine according to claim 1, wherein the intake air amount control means is controlled to decrease the intake air amount during an acceleration operation or a deceleration operation that is performed after the end of the steady state.

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