JP2010168953A - Internal combustion engine injecting fuel in proportion to lift quantity of variable intake valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve control accuracy of fuel injection quantity by calculating valve lift quantity according to operation characteristics of an actual variable valve system. <P>SOLUTION: This engine includes an electronic control device for program control, a means detecting crank angle, a means detecting actual lift quantity of an intake valve, and a mechanism varying lift quantity of the intake valve. The electronic control device determines an estimation value of the lift quantity per each crank angle corresponding to next control cycle per each prescribed crank angle, determines a component value of valve lift per the prescribed crank angle in the next control cycle from an estimation value of lift quantity per the prescribed crank angle, determines an estimation value of total lift quantity of the next control cycle by integrating the component value, and calculates injection quantity of fuel in the next control cycle based on the estimation value of the total lift quantity in the next control cycle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an internal combustion engine controlled to inject fuel according to a lift amount of a variable intake valve.

  In recent internal combustion engines, it has been proposed to mount a mechanism capable of changing the lift amount of the intake valve and control the intake air amount to the internal combustion engine using the mechanism. In Patent Document 1, in an internal combustion engine equipped with such a mechanism, when a change in lift curve exceeding the response capability of the mechanism is required, the target intake air amount corresponding to the accelerator opening is set as the target lift curve. The method based on the final target intake air amount obtained by subjecting the target intake air amount to the smoothing process is described. An estimated intake air amount is calculated from a time average value of the final target intake air amount during the lift period, and a fuel injection amount is calculated based on the estimated intake air amount.

  Patent Document 2 describes that in an internal combustion engine capable of variably controlling the lift amount of the intake valve, the fuel injection amount is controlled with reference to control history data of the lift amount with respect to the crank angle.

  In Japanese Patent Application No. 2008-046351 by the applicant of the present application, the inventor, in an internal combustion engine having a variable valve mechanism that can change the lift amount of the intake valve, sets the actual lift amount (ALIFT) of the intake valve to a predetermined time constant. Feedback control is performed so that the target lift amount (ALCMD) converges at (τp), and a value obtained by multiplying the difference between the target lift amount and the actual lift amount by a predetermined gain (C) is added to the actual lift amount. It has been proposed to calculate the predicted value (HALIFT) of the lift amount in the control cycle and to calculate the fuel injection amount to be injected in the next control cycle based on the predicted value of the lift amount.

  According to this proposal, the lift amount of the next control cycle is predicted, and the fuel injection amount is calculated based on the predicted value. Therefore, proper fuel injection can be performed even in a transition period in which the valve lift amount is changed. .

JP 2006-250042 A JP 2004-108259 A

  Since the lift amount of the intake valve is changed by driving the mechanical structure, it takes time to reach the target value. In this transitional period, there is a discrepancy between the correlation between the valve lift amount and the intake air amount and the actual intake air amount, which may reduce the control accuracy of the fuel injection amount. Further, in the method described in Patent Document 2, since the control history is calculated based only on the valve opening timing and the valve closing timing, the accuracy of the estimated control history is increased when the actual operating characteristics of the variable valve system change. The fuel injection amount control accuracy decreases. As a result, the air-fuel ratio deviates from the target value, which may cause a decrease in acceleration performance and a decrease in emissions.

  Therefore, there is a need for a technique that can calculate the valve lift amount according to the actual operating characteristics of the variable valve system and improve the control accuracy of the fuel injection amount.

  The internal combustion engine of the present invention includes a program-controlled electronic control unit, means for detecting a crank angle, means for detecting the actual lift amount of the intake valve, and a mechanism for making the lift amount of the intake valve variable. The electronic control unit obtains a predicted value of the lift amount for each crank angle corresponding to the next control cycle for each predetermined crank angle, and calculates the predicted value for the lift amount for each predetermined crank angle from the predicted value for the next control cycle. A component value of the valve lift for each predetermined crank angle is obtained, and the component value is integrated to obtain a predicted value of the total lift amount (total lift amount) in the next control cycle, and the total lift amount in the next control cycle. The fuel injection amount in the next control cycle is calculated based on the predicted value.

  According to this invention, the component value of the valve lift at the corresponding crank angle in the next control cycle is obtained from the predicted lift amount for each predetermined crank angle, and this component value is integrated to calculate the predicted value of the total lift amount. Therefore, since the lift amount corresponding to the operating characteristics of the variable valve system is obtained, the fuel injection amount in the next control cycle is calculated based on this lift amount, so that the control accuracy of the fuel injection amount can be improved. it can.

  In one embodiment of the present invention, the electronic control unit converges the detected actual lift amount to the target lift amount with a predetermined time constant, so that the actual lift amount obtained from the means for detecting the actual lift amount for each predetermined crank angle is obtained. A value obtained by multiplying a difference between a lift amount and a target lift amount determined based on an operating state of the internal combustion engine by a predetermined gain is added to the actual lift amount, whereby the predetermined crank in the next control cycle is added. Obtain the predicted lift value for each corner. The gain is determined according to the predetermined time constant.

In a more specific embodiment of the present invention, the target lift amount is calculated in synchronization with the top dead center of the piston. Further, the gain is obtained by multiplying the rotation period, which is the reciprocal of the rotation speed of the internal combustion engine, by the value obtained by multiplying the crank angle CA _i at the time of calculation (i) by 360 degrees (Stime _i ) and the predetermined value. It is a function of time constant.

  In another embodiment of the present invention, when the predicted value of the lift amount is obtained for each predetermined crank angle, the crank angle interval is configured to be variable according to the rotational speed of the internal combustion engine.

  In yet another embodiment, the electronic control unit obtains the intake air amount of the internal combustion engine using the correlation between the predicted value of the total lift amount in the next control cycle and the intake air amount of the internal combustion engine, The fuel injection amount is determined based on the air amount.

1 schematically shows an internal combustion engine and a control device therefor according to one embodiment of the present invention. FIG. The figure which shows schematically the structure of the valve action characteristic variable apparatus according to one Example of this invention. The figure which shows schematically the structure of the 1st mechanism according to one Example of this invention. The figure which shows the outline of a structure of the apparatus which controls the lift amount according to one Example of this invention. The figure for demonstrating the principle of the predicted value calculation according to this invention. The functional block diagram of the control apparatus which controls the fuel injection quantity according to one Example of this invention. The flowchart of the process which calculates the fuel injection quantity according to one Example of this invention. The map for calculating | requiring the intake air amount and fuel injection amount in prior invention. The figure which shows the waveform of a valve lift on the horizontal axis of a crank angle. The figure which shows the main routine of the process which calculates the fuel injection quantity according to one Example of this invention. The figure which shows the flow of the process which thins out a crank angle. The figure which shows the flow of time area calculation in one Example of this invention. The map for calculating | requiring the time area, intake air amount, and fuel injection amount in one Example of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as an engine) and its control device according to an embodiment of the present invention.

  An electronic control unit (hereinafter referred to as “ECU”) 1 is a computer including a central processing unit (CPU) and a memory. The memory can store a computer program for realizing various controls of the vehicle and data (including a map) necessary for executing the program. The ECU 1 receives a signal from each part of the vehicle and performs an operation according to data and a program stored in the memory to generate a control signal for controlling each part of the vehicle.

  The engine 2 is an engine having, for example, four cylinders. An intake pipe 3 and an exhaust pipe 4 are connected to the engine 2. The intake pipe 4 is provided with a throttle valve 5. The opening degree of the throttle valve 5 is controlled in accordance with a control signal from the ECU 1. By controlling the opening degree of the throttle valve 5, the amount of air taken into the engine 2 can be controlled. A throttle valve opening (θTH) sensor 6 for detecting the opening of the throttle valve is connected to the throttle valve 5, and this detected value is sent to the ECU 1.

  A fuel injection valve 7 is provided for each cylinder between the engine 2 and the throttle valve 5 and slightly upstream of the intake valve (not shown) of the engine 2. The fuel injection valve 7 is connected to a fuel pump (not shown). The fuel injection timing and the fuel injection amount of the fuel injection valve 7 are changed according to a control signal from the ECU 1. Alternatively, the fuel injection valve may be attached so as to face the cylinder of the engine 2.

  An air flow meter (AFM) 8 that detects the amount of air flowing through the intake pipe 3 is provided upstream of the throttle valve 5.

  An intake pipe absolute pressure (PBA) sensor 10 is provided downstream of the throttle valve 5 to detect the pressure in the intake pipe. An intake air temperature (TA) sensor 11 is provided downstream of the intake pipe absolute pressure sensor 10 to detect the temperature in the intake pipe. These detected values are sent to the ECU 1. The engine 2 is provided with an engine water temperature sensor 12 for detecting the engine water temperature TW, and the detected value of the sensor is sent to the ECU 1.

  The engine 2 is based on the first mechanism 21 capable of continuously changing the lift amount and opening angle (opening period) of the intake valve and the exhaust valve, and the crankshaft of the cam that drives the intake valve. A valve operating characteristic variable device 20 having a second mechanism 22 for continuously changing the phase is provided. The phase of the cam that drives the intake valve is changed by the second mechanism 22, and thus the phase of the intake valve is changed.

  The ECU 1 is connected with a crank angle sensor 13 that detects the rotation angle of the crankshaft of the engine 1 and a cam angle sensor 14 that detects the rotation angle of the camshaft to which the cam that drives the intake valve of the engine 1 is coupled. The detection values of these sensors are supplied to the ECU 1. The crank angle sensor 13 generates one pulse (CRK signal) every predetermined crank angle (for example, 30 degrees), and can specify the rotational angle position of the crankshaft by the pulse. The cam angle sensor 14 generates a pulse (CYL signal) at a predetermined crank angle position of a specific cylinder of the engine 2 and a pulse (TDC signal) at the top dead center (TDC) at the start of the intake stroke of each cylinder. . These pulses are used for detection of various control timings such as fuel injection timing and ignition timing, and engine speed NE. The actual phase of the cam shaft of the intake valve is detected from the relative relationship between the TDC signal output from the cam angle sensor 14 and the CRK signal output from the crank angle sensor 13.

  The valve operating characteristic variable device 20 is provided with a control shaft rotation angle sensor (CSA) sensor 15 for detecting the rotation angle position of the control shaft for controlling the lift amount of the intake valve.

  The ECU 1 detects the operating state of the engine 2 in accordance with programs and data (including a map) stored in the memory in accordance with input signals from the various sensors, and controls the throttle valve 5, the fuel injection valve 7, and the valve operation. A control signal for controlling the characteristic variable device 20 is generated.

  FIG. 2 shows a more specific configuration diagram of the valve operation characteristic variable device 20. As shown in the figure, the variable valve operating characteristic device 20 includes a first mechanism 21 that can continuously change the lift amount and opening angle (hereinafter simply referred to as lift amount) of the intake valve, A second mechanism 22 capable of continuously changing the phase, an actuator 24 including a motor 23 for continuously changing the lift amount of the intake valve via the first mechanism 21, and the second In order to continuously change the phase of the intake valve via the mechanism 22, an actuator 26 having an electromagnetic valve 25 whose opening degree can be changed continuously is provided.

  As a parameter indicating the phase of the intake valve, the cam axis phase CAIN of the intake valve is used. Lubricating oil in the oil pan 28 is pressurized and supplied to the solenoid valve 25 by the oil pump 27. The motor 23 and the electromagnetic valve 25 operate according to a control signal from the ECU 1. A more specific configuration of the second mechanism 22 is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-227013.

  The first mechanism 21 will be described with reference to FIG. As shown to (a), the cam shaft 31 provided with the cam 32, the control arm 35 supported by the cylinder head so that rocking is possible centering on the shaft 35a, and the control cam 37 which rocks the control arm 35 are provided. The control shaft 36 provided and the control arm 35 are supported so as to be swingable via a support shaft 33b. The sub cam 33 swings when the cam 32 is driven. The sub cam 33 is driven and the intake valve 40 is moved. And a rocker arm 34 to be driven. The rocker arm 34 is swingably supported in the control arm 35.

  The sub cam 33 has a roller 33 a that contacts the cam 32, and swings about the shaft 33 b as the cam shaft 31 rotates. The rocker arm 34 has a roller 34a that contacts the sub cam 33, and the movement of the sub cam 33 is transmitted to the rocker arm 34 via the roller 34a.

  The control arm 35 includes a roller 35b that contacts the control cam 37, and swings about the shaft 35a by the rotation of the control shaft 36. In the state shown in (a), since the movement of the sub cam 33 is hardly transmitted to the rocker arm 34, the intake valve 40 is maintained in a substantially fully closed state. In the state shown in (b), the movement of the sub cam 33 is transmitted to the intake valve 40 via the rocker arm 34, and the intake valve 40 opens to the maximum lift amount LFTMAX (for example, 12 mm).

  Therefore, the control shaft 36 is connected to the output shaft of the motor 23 (FIG. 2) of the actuator 24 through a gear, and the control shaft 36 is rotated by the motor 23, thereby continuously increasing the lift amount of the intake valve 40. Can be changed. In this embodiment, the first mechanism 21 is provided with a CSA sensor 15 (FIG. 1) for detecting the rotation angle position of the control shaft 36, and the detected rotation angle position CSA is a parameter indicating the lift amount. Used as. A more detailed configuration of the first mechanism 21 is shown in a patent application (Japanese Patent Application No. 2006-197254) filed by the present applicant.

  It should be noted that the present invention is not limited to the first mechanism 21 as shown in the figure, and a mechanism capable of variably controlling the lift amount of the intake valve can be realized by any appropriate means. I want. In the above example, the first mechanism 21 changes not only the lift amount but also the opening angle. However, the present invention can be applied to a mechanism configured to change only the lift amount.

  FIG. 4 is a block diagram of a control device for controlling the lift amount of the intake valve according to an embodiment of the present invention. The lift controller 51 is realized in the ECU 1. The plant 52 here includes the first mechanism 21 and the actuator 24 of FIG. The lift controller 51 calculates an operation amount for converging the actual lift amount of the intake valve to the target lift amount according to a control method described later. The motor 23 of the actuator 24 operates the first mechanism 21 according to the operation amount, and changes the lift amount of the intake valve. The changed lift amount is detected by the CSA sensor 15 (FIG. 1) as an actual lift amount and fed back to the lift controller 51.

FIG. 5 is a diagram for explaining the principle of predictive value calculation according to Japanese Patent Application No. 2008-046351 by the applicant of the present application cited above. First, after citing this content, the principle of the present invention will be described. The control of the lift amount and the fuel injection amount is executed according to a predetermined cycle, and in each cycle, the target lift amount is determined according to the engine operating state (for example, the opening degree of the accelerator pedal, etc.). The figure shows the behavior of a target lift amount, an actual lift amount (detected by the CSA sensor 15), and a predicted lift amount over three cycles n to (n + 2) for a certain cylinder. The length of one cycle is represented by Stime. The control period may be a fixed time such as 10 milliseconds, for example, and may be determined based on the engine speed in synchronization with the TDC signal. For example, when the TDC signal is output at the top dead center of the intake stroke and the detected engine speed is NE (rpm), the length of the cycle n is calculated as follows. When the rotational speed NE is converted into a speed per second, NE / 60 is obtained. If this is multiplied by 360 degrees and converted to angular velocity, and the reciprocal thereof is taken, a period of 60 / NE x 1/360 is obtained. This is multiplied by the crank angle (CA) from the TDC of the intake stroke to obtain Stime. That is, Stime corresponds to the cycle of the suction stroke.

  In each cycle, the lift controller 51 controls the intake valve so that the actual lift amount becomes the target lift amount. Referring to the cycle n, the target lift amount is X (mm), and the actual lift amount detected in the cycle n is Z (mm). The predicted lift amount calculated based on the target lift amount and the actual lift amount is Y (mm). In the cycle n, the fuel injection amount to be injected in the next cycle (n + 1) is determined based on the predicted lift amount. In the cycle (n + 1), the actual lift amount almost reaches the value Y of the predicted lift amount calculated in the cycle n. Therefore, an amount of fuel injection suitable for the actual lift amount realized in the cycle (n + 1) is injected. Will be.

  Thus, the fuel injection amount is calculated one cycle before the injection timing. If the fuel injection amount is calculated with the actual lift amount detected in the cycle n, there is a possibility that an amount of fuel suitable for the actual lift amount in the control cycle (n + 1) in which actual injection is performed may not be injected. This may cause a deviation of the air-fuel ratio. According to the present invention, since the lift amount after one cycle is predicted and the fuel injection amount is calculated based on the predicted lift amount, an amount of fuel suitable for the actual lift amount when actual injection is performed is supplied. can do.

The predicted lift amount is calculated according to the following formula.
HALIFT (n)
= C (ALCMD (n) -ALIFT (n)) + ALIFT (n) (2)
Here, C = Stime / (τp + Stime)

  ALIFT (n) indicates the actual lift amount detected in the cycle n. ALCMD (n) indicates the target lift amount in period n. C is a gain, which is calculated based on the period length Stime and the time constant τp of lift amount control by the lift controller 51. HALIFT (n) indicates the predicted lift amount for the next period calculated in the period n. The predicted lift amount is calculated by adding a value obtained by multiplying the deviation between the target lift amount and the actual lift amount by a gain to the actual lift amount.

  According to the above equation (2), the predicted value HALIFT (n) is calculated in the cycle n, and the fuel injection amount to be supplied in the next cycle (n + 1) is determined according to the predicted value. In order to change the lift amount, as described with reference to FIG. 3, it is necessary to move the mechanical structure, so that a certain time is required. On the other hand, since the fuel injection amount is changed by changing the time for opening the injector's injection valve, it can be changed in a short time. By performing the control as described above, it is possible to perform fuel injection based on the intake air amount corresponding to the transient lift amount of the intake valve in the transition period that is changed toward the target lift amount. The basis of the above formula (1) is explained in detail in the specification of the prior application referred to above.

  FIG. 6 is a functional block diagram of an apparatus for controlling the fuel injection amount in the prior invention. In one embodiment of the present invention, the same configuration can be used. The function by each functional block can be realized in the ECU 1.

  The target lift decimation unit 91 obtains a value p by dividing the invalid time of the intake valve by the period Stime. The past value of the target lift amount (the target lift amount calculated in the previous cycle) is stored in the memory of the ECU 1. The decimation unit 91 outputs the target lift amount calculated in the cycle (n−p) before p times.

  In the variable lift mechanism (first mechanism 21), an invalid time is generated for the intake valve to transition from the stationary state to the operating state. That is, the lift controller 51 outputs an operation amount for controlling the lift amount of the intake valve in accordance with the target lift amount to the actuator 24 in FIG. 2, but until the intake valve actually starts moving according to the operation amount, There is a delay for the invalid time. Therefore, the decimation process as described above is performed in order to more accurately associate the actual lift amount with the target lift amount.

  For example, if the invalid time is 30 ms and the calculation cycle is 10 ms, the decimation unit 91 outputs the target lift amount determined three cycles before (n-3). In this case, the start of operation of the intake valve in the current calculation cycle is based on the target lift amount determined three cycles ago. The invalid time can be calculated in advance by simulation or the like and stored in the memory of the ECU 1 depending on the variable lift mechanism.

  The operation determination unit 92 determines whether or not the intake valve has transitioned from the stationary state to the operating state in the current cycle n. More specifically, the operation determination unit 92 calculates the difference between the actual lift amount detected in the current cycle n and the actual lift amount detected in the previous cycle (n−1) via the CSA sensor 15. Then, the difference is divided by the period Stime. The value obtained by the division represents the operating speed of the intake valve. If the operating speed is equal to or higher than a predetermined value, it is determined that the intake valve is in operation, and an operation flag of value 1 is output. If the operating speed is lower than the predetermined value, it is determined that the intake valve is stationary in the previous cycle, and the intake valve has started operating in the current cycle, and a zero-valued operation flag is output.

  The switching unit 93 checks the value of the operation flag, and if the value of the operation flag is 1, employs the value of the target lift amount given in the current cycle n as the target lift amount ALCMD (n). As described above, the target lift amount can be determined by any known method according to the operating state of the engine. If the value of the operation flag is zero, the value of the target lift amount before p times passed from the decimation unit 91 is adopted as the target lift amount ALCMD (n). Thus, when the intake valve is not in operation but transitions from a stationary state to an operating state, it indicates that an invalid time has occurred, so the target lift amount before p times is used. This is to reflect the mechanical state of the valve operating characteristic variable device 20 (FIG. 3).

  Thus, it can be considered that the invalid time does not substantially occur when the intake valve is in operation. Alternatively, when the intake valve is in operation, there may be a slight dead time in the stricter sense. For example, since the operation amount calculated by the lift controller 51 reaches the actuator 24 via the communication line, such an invalid time may occur. Therefore, the dead time may be taken into account even when the intake valve is in operation. In that case, the invalid time is measured in advance through simulation or the like and stored in the memory of the ECU 1, and the decimation unit 91 calculates a value p ′ obtained by dividing the invalid time by the length of the cycle, and p 'Output the target lift amount determined in the previous cycle. The switching unit 93 selects, as the target lift amount ALCMD (n) of the current cycle, the target lift amount of the cycle before p ′ times or the target lift amount of the cycle before p times according to the value of the operation flag.

  The gain calculation unit 94 calculates the gain C according to the above-described equation (2) based on the period Stime and the time constant τp. As described above, the time constant τp can be set to a desired value, and can be stored in advance in the memory of the ECU 1.

  The predicted lift calculation unit 95 is selected in the above formula (2) by the gain C, the actual lift amount ALIFT (n) detected by the CSA sensor 15 in the current control cycle n, and the switching unit 93 in the current cycle n. The target lift amount ALCMD (n) is substituted to calculate the predicted lift amount HALIFT (n).

  The fuel injection amount calculation unit 96 calculates the fuel injection amount based on the predicted value HALIFT (n) in the current cycle n. The fuel injection amount is passed to a fuel controller (not shown) realized by the ECU 1, and the fuel injection valve is driven by the controller so that the fuel injection amount is injected in the next cycle (n + 1). .

  In addition, it supplements about the case where the period length Stime is not constant like the case where control is performed according to a TDC signal. First, regarding the calculation of the value of p, in this case, the past value of the time length of the cycle is stored in the memory of the ECU 1. The decimation unit 91 determines how many periods the invalid time corresponds to. For example, when the invalid time is 30 ms, the length of the period (n-1) is 9 ms, the length of (n-2) is 11 ms, and the length of (n-3) is 12 ms, the invalid time Since a place 30 ms back corresponds to the period (n-3) (30-9-11-12 becomes zero or less), p = 3 can be obtained. Instead of storing the past value of the cycle length, the past value of the engine speed may be stored. As described above, the length of the cycle n can be obtained from the engine speed detected at the cycle n.

  Further, since the previous actual lift amount is detected according to the previous TDC signal, and the current actual lift amount is detected according to the current TDC signal, the operation determination unit 92 calculates the operation speed. It is preferable to use the length of the previous cycle n-1. The gain C is a value for predicting how much the actual lift amount detected according to the current TDC signal changes until the lift amount detection according to the next TDC signal is detected. The unit 94 preferably calculates the gain C using the length Stime of the current cycle n.

  FIG. 7 is a flowchart of a process for calculating the fuel injection amount. The process is executed by the ECU 1 in accordance with the control cycle described above, and more specifically, is realized by a functional block shown in FIG.

  In step S11, as described above with reference to FIG. 6, the target lift amount p times before is obtained based on the invalid time. If it is determined in step S12 that the intake valve has moved from the stationary state to the operating state in the current cycle by calculating the operating speed of the intake valve, the operation flag is set to zero, and the intake valve is set over the current cycle. If it is determined that is operating, the operation flag is set to 1.

  In step S13, if the operation flag is a value 1 indicating that the intake valve is operating, the target lift amount determined in the current cycle is set to the target lift amount ALCMD (n) (S14). If the operation flag is zero indicating that the intake valve has transitioned from the stationary state to the operating state, the target lift amount determined in the previous p cycles is set to the target lift amount ALCMD (n) (S15). ).

  In step S16, the gain C is calculated according to the above-described equation (2) based on the period length Stime and the time constant τp. In step S17, using the gain C, the actual lift amount ALIFT (n) and the target lift amount ALCMD (n) detected by the CSA sensor 15, the predicted lift amount HALIFT (n) is calculated according to the above equation (2). . In step S18, an intake air amount is obtained by referring to a predetermined map based on the engine speed detected in the current cycle and the predicted lift amount HALIFT (n) obtained in step S17. The map is a three-dimensional map of lift amount, engine speed, and intake air amount.

  An example of the map is shown in FIG. 8 (a). The intake air amount increases as the engine speed increases and the lift amount increases. A map corresponding to the predicted lift amount HALIFT is selected, and the map is referred to based on the detected engine speed to obtain the corresponding intake air amount.

  In step S19, the fuel injection amount is obtained by referring to a predetermined map based on the intake air amount obtained in step S18. An example of the map is shown in FIG. As the intake air amount increases, the fuel injection amount increases. The maps shown in FIGS. 8A and 8B are stored in the memory of the ECU 1.

  The contents of Japanese Patent Application No. 2008-046351, which is the basis of the present invention, are cited above. The invention of the present application is a modification of the invention of the prior application and realizes fuel injection amount control with higher accuracy. An embodiment of the present invention will be described with reference to FIGS.

  FIG. 9 is a waveform showing changes in the lift amount with the crank angle (CA) as the time axis (horizontal axis) when the lift amount of the intake valve is L1, L2, and L3. The amount of intake air is proportional to the area defined by this waveform and the time axis. In one embodiment of the present invention, an area AKAREA (i) of a minute rectangle formed by a valve lift value and a minute width of a time axis corresponding to a crank angle of 10 degrees at every predetermined crank angle, for example, every 10 degrees of crank angle. Ask for. This area is called a time area (time area). The time area is integrated from the time when the intake valve opens to the time when it closes, and the total time area created by the waveform representing the change in lift amount and the time axis is obtained. Based on the total time area thus obtained, the fuel injection amount in the next intake stroke is obtained.

  According to this method, since the valve lift amount is sampled at every minute crank angle, even if the valve operating characteristic variable device 20 (FIG. 3) is operating so as to change the lift amount, the lift amount change waveform can be accurately obtained. Therefore, the fuel injection amount in the next intake stroke can be obtained with high accuracy.

  FIG. 10 shows a main routine of a process for calculating the fuel injection amount according to the present invention. This process is executed in synchronization with the top dead center (TDC) of the piston at the start of the intake stroke. When a top dead center of a new intake stroke is detected based on the TDC signal from the cam angle sensor 14 (FIG. 1) (S101), a sampling crank angle (CA) thinning number is calculated (S102). When sampling is performed at a constant crank angle, the sampling frequency on the time axis increases at a high engine speed, and the calculation load becomes excessive. Therefore, sampling is thinned out according to the engine speed.

  FIG. 11 shows a flow of a process for calculating the thinning number. If the engine speed is less than a predetermined value NE_CA (S111), a predetermined value m_CA is set as m. The value of m_CA is 18, for example, and the time area is calculated at a cycle of a crank angle of 10 degrees obtained by 180 / m = 10. If the engine speed is greater than or equal to NE_CA, m is set to 1/2 of m_CA. In this case, m = 9, and the time area calculation is performed with a cycle of a crank angle of 20 degrees obtained by 180/9 = 20.

When the calculation cycle is thus determined, the routine enters time area calculation routine S103. Referring to FIG. 12, this routine forms a loop that starts from i = 1 and circulates until i = m (S121). The crank angle CA _i used for the calculation is obtained by the equation shown in the block of step S123. If m = 18, the first crank angle CA _i is 10 degrees, and 20 degrees, 30 degrees,..., 180 degrees in the subsequent loop.

In the embodiment of the present invention, the expression (1) representing the control cycle length Stime used in the prior application cited above is modified to the form shown in step S125. That is,
Stime _i ← 60 / NE × CA _i / 360 (3)

Divide the engine speed NE (rpm) by 60 to convert it to NE / 60 per second, multiply this by 360 degrees and convert it to angular speed NE / 60 x 360. The cycle of this angular velocity is 60 / NE x 1/360. Stime _i is a value obtained by multiplying the crank angle CA _i as an object in the loop operation in this period. That is, Stime _i is a value obtained by converting CA _i into time within the rotation period of the engine. Stime in the prior invention is subdivided into Stime _i (i = 1,..., M) in the present invention.

Then, in step S127, obtains the gain K _i in the calculation loop.
K _i ← Stime _i / (τp + Stime _i ) (4)
The gain K _i corresponds to the gain C in the prior invention cited above, but the definition of Stime _i is different, so the notation is changed and expressed as K _i . Step S121 as evidenced by S127, the gain K _i, the value for each loop is updated.

Next, in step S129, the predicted lift amount ALIFT (n + 1) _i in the calculation loop is obtained by the following equation. Since the predicted lift amount is for calculating the fuel injection amount in the next cycle, the notation of ALIFT (n + 1) is used in the embodiment of the present invention.
ALIFT (n + 1) _i ← K _i (ALCMD (n) −ALIFT (n) _i ) + ALIFT (n) _i (5)

In this equation, ALCMD (n) is the target lift amount at the time of the current intake stroke. This value does not change for each calculation loop. ALIFT (n) _i is the actual lift amount in the calculation loop, and is a value detected by the CSA sensor 15 (FIG. 1). The actual lift amount does not necessarily need to be updated for each calculation loop, and may be updated once, for example, in two calculation loops in order to reduce the calculation load.

Based on the predicted lift amount ALIFT (n + 1) _i and CA _i thus obtained, the time area ALAREA (i) for each calculation loop is obtained with reference to the three-dimensional map of FIG. 13A (S131). A plurality of curves shown in this map represent values of the predicted lift amount ALIFT (n + 1) _i corresponding to i = 1,..., M. The larger the ALIFT at the same crank angle, the larger the time area. This map is created in advance and stored in the memory of the ECU 1.

Returning to the main routine of FIG. 10, using the time area ALAREA (i) obtained for each calculation loop, time area integration is performed to calculate the total time area ALAREAF in the control cycle n (S105). ALAREAF is an area defined by the valve lift curve described with reference to FIG. 9 and the time axis. This integral can be expressed as:

  Subsequently, in step S105, the intake air amount is obtained based on the engine speed NE and the total time area ALAREAF in the control cycle n with reference to the three-dimensional map of FIG. 13 (b). Each of the curves in FIG. 13 (b) shows the value of one total time area ALAREAF. The larger the ALAREAF at the same engine speed, the larger the intake air amount. This map is also created in advance and stored in the memory of the ECU 1.

  Next, the process proceeds to a fuel injection amount calculation step S106, and a fuel injection amount corresponding to the intake air amount obtained in step S105 is obtained with reference to the map of FIG.

  As mentioned above, although this invention was demonstrated about the specific Example, this invention is not limited to such an Example.

Claims (7)

An internal combustion engine comprising an electronic control unit for program control, a means for detecting a crank angle, a means for detecting an actual lift amount of an intake valve, and a mechanism for making the lift amount of an intake valve variable,
The electronic control unit obtains a predicted lift amount for each crank angle corresponding to the next control cycle for each predetermined crank angle, and calculates the predicted lift amount for each predetermined crank angle in the next control cycle. A valve lift component value for each predetermined crank angle is obtained, and the component value is integrated to obtain an overall predicted value of the lift amount in the next control cycle. The internal combustion engine is configured to calculate a fuel injection amount in the next control cycle based on the control period.   The electronic control unit converges the detected actual lift amount to a target lift amount with a predetermined time constant, and the actual lift amount obtained from the means for detecting the actual lift amount for each predetermined crank angle, By adding to the actual lift amount a value obtained by multiplying the difference from the target lift amount determined based on the operating state of the internal combustion engine by a predetermined gain, the lift for each predetermined crank angle in the next control cycle. The internal combustion engine of claim 1, wherein the internal combustion engine is configured to determine a predicted value of the quantity.   The internal combustion engine according to claim 2, wherein the gain is determined according to the predetermined time constant.   The internal combustion engine according to claim 2, wherein the target lift amount is calculated in synchronization with a top dead center of the piston.   4. The internal combustion engine according to claim 3, wherein the gain is a function of a time (Stime) obtained by multiplying a rotation cycle that is the reciprocal of the rotation speed of the internal combustion engine by a crank angle at the time of calculation and the predetermined time constant. .   The internal combustion engine according to claim 2, wherein when the predicted lift amount is determined for each predetermined crank angle, the interval between the crank angles is configured to be variable according to the rotational speed of the internal combustion engine.   The electronic control unit obtains the intake air amount of the internal combustion engine using a correlation between the overall predicted value of the lift amount in the next control cycle and the intake air amount of the internal combustion engine, and based on the intake air amount The internal combustion engine according to claim 2, wherein the internal combustion engine is configured to determine a fuel injection amount.

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