US20010020459A1 - Valve timing control system for internal combustion engine - Google Patents

Valve timing control system for internal combustion engine Download PDF

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US20010020459A1
US20010020459A1 US09/796,550 US79655001A US2001020459A1 US 20010020459 A1 US20010020459 A1 US 20010020459A1 US 79655001 A US79655001 A US 79655001A US 2001020459 A1 US2001020459 A1 US 2001020459A1
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amount
control
current
cam phase
cam
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US6367437B2 (en
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Mitsuhiro Nakamura
Yoshiharu Sudani
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Honda Motor Co Ltd
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Honda Motor Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D35/00—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
    • F02D35/0007—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for using electrical feedback
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
    • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
    • F01L1/34—Valve-gear or valve arrangements, e.g. lift-valve gear characterised by the provision of means for changing the timing of the valves without changing the duration of opening and without affecting the magnitude of the valve lift
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0203—Variable control of intake and exhaust valves
    • F02D13/0215—Variable control of intake and exhaust valves changing the valve timing only
    • F02D13/0219—Variable control of intake and exhaust valves changing the valve timing only by shifting the phase, i.e. the opening periods of the valves are constant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/20—Output circuits, e.g. for controlling currents in command coils
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F02D2041/001—Controlling intake air for engines with variable valve actuation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/20—Output circuits, e.g. for controlling currents in command coils
    • F02D2041/202—Output circuits, e.g. for controlling currents in command coils characterised by the control of the circuit
    • F02D2041/2024—Output circuits, e.g. for controlling currents in command coils characterised by the control of the circuit the control switching a load after time-on and time-off pulses
    • F02D2041/2027—Control of the current by pulse width modulation or duty cycle control
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • This invention relates to a valve timing control system for an internal combustion engine, which varies the cam phase of at least one of an intake cam and an exhaust cam, relative to a crankshaft of the engine, to thereby control valve timing.
  • a valve timing control system of the above-mentioned kind was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 9-217609.
  • a cam phase change mechanism supplied with hydraulic pressure controlled by an hydraulic pressure control valve changes the cam phase by changing the angle of a camshaft relative to a cam pulley.
  • the hydraulic pressure control valve formed by a linear solenoid valve includes a coil and a spool driven by a force generated by the coil.
  • the output duty factor of current supplied to the coil is controlled to drive the spool to a position corresponding to the output duty factor, i.e.
  • the output duty factor is controlled to a hold duty factor value approximately in the center of a control range thereof, the spool is controlled to a neutral position for simultaneously closing the advance chamber and the retard chamber, thereby cutting off supply of the hydraulic pressure to both of the chambers. This holds the cam phase.
  • the output duty factor is feedback-controlled such that an actual cam phase detected becomes equal to a desired cam phase set in dependence on operating conditions of the engine.
  • the control system suffers from a problem that the cam phase cannot be controlled with accuracy when the temperature condition of the hydraulic pressure control valve is changed. More specifically, in the linear solenoid valve which is used in the control system as a hydraulic pressure control valve, the resistance of the coil varies with its temperature, so that the amount of current actually flowing through the coil varies even if the output duty factor remains the same. For instance, under a low temperature condition of the coil, the resistance of the coil is small, so that even if the output duty factor remains the same, the amount of current actually flowing through the coil increases.
  • This increase in the current amount reduces the hold duty factor value, thereby causing the whole control range of the output duty factor to shift in the direction of a lower output duty factor, and at the same time increases a change in hydraulic pressure per unit change in the output duty factor (i.e. increases sensitivity of the hydraulic pressure control valve), resulting in an inevitable decrease in the controllable range of the output duty factor.
  • the resistance of the coil increases, so that the amount of current flowing through the coil increases even if the output duty factor remains the same.
  • This increases the hold duty factor value, thereby causing the whole control range of the output duty factor to shift in the direction of a higher output duty factor, and at the same time reduces a change in hydraulic pressure per unit change in the output duty factor (i.e. decreases sensitivity of the hydraulic pressure control valve), resulting in an increased controllable range of the output duty factor and enhanced control accuracy.
  • the actual temperature of the coil is detected to correct the output duty factor based on a result of the detection.
  • a temperature sensor for detecting the coil temperature is additionally required.
  • temperatures are slow in change, and the temperature of the coil largely depends on environments surrounding the coil, such as the temperature within an engine room of an automotive vehicle on which the control system is installed, wind generated by running of the vehicle, and heat generated in the coil by current flowing therethrough. This makes it difficult to accurately estimate the amount of current which is actually flowing through the coil at the time of detection of the coil temperature, based on the detected coil temperature or compensate for variation therein. As a result, the cam phase cannot be controlled with accuracy.
  • the present invention provides a valve timing control system for an internal combustion engine, which includes a crankshaft, an intake valve, an exhaust valve, an intake cam, and an exhaust cam, and controls valve timing of at least one of the intake valve and the exhaust valve, by changing a cam phase which is a phase of at least one of the intake cam and the exhaust cam, relative to the crankshaft.
  • valve timing control system is characterized by comprising:
  • a control valve having a coil, for driving the cam phase change mechanism according to an amount of current flowing through the coil
  • desired cam phase-setting means for setting a desired cam phase depending on operating conditions of the engine
  • cam phase feedback control means for feedback-controlling a control value for control of the amount of current such that the actual cam phase becomes equal to the desired cam phase
  • desired current amount-setting means for setting a desired amount of current based on the control value controlled by the cam phase feedback control means
  • actual current amount-detecting means for detecting an actual amount of current actually flowing through the coil of the control valve
  • current feedback control means for feedback-controlling an output control value for control of the amount of current supplied to the control valve such that the actual amount of current becomes equal to the desired amount of current.
  • a control value used for controlling the amount of current flowing through the coil is feedback-controlled such that the actual cam phase becomes equal to the desired cam phase. Further, a desired amount of current is set based on the control value controlled by the feedback control, while an actual amount of current flowing through the coil of the control valve is detected. An output control value for control of the amount of current supplied to the control valve is feedback-controlled such that the actual amount of current becomes equal to the desired amount of current. This causes current to be supplied to the control value in an amount corresponding to the calculated output control value, whereby the amount of current flowing through the coil is properly controlled.
  • the valve timing control system carries out not only cam phase feedback control in which the control value for control of the amount of current supplied to the control valve is feedback-controlled such that the actual cam phase becomes equal to the desired cam phase, but also current feedback control in which the output control value for finally controlling the amount of current supplied to the control valve is feedback-controlled such that the actual amount of current flowing through the coil of the control valve becomes equal to an optimum desired amount of current set based on the control value calculated by the cam phase feedback control.
  • the actual amount of current flowing through the coil is directly detected, and the output control value is feedback-controlled such that the actual amount of current becomes equal to the optimum desired amount of current.
  • control value and the output control value are values of an identical kind of control amount, and a range of values of the identical kind of control amount within which the output control value can be set is wider than a range of values of the identical kind of control amount within which the control value can be set.
  • the identical kind of control amount is a duty factor of output of the current supplied to the coil.
  • the desired current amount-setting means includes a conversion table for converting the control amount to the desired amount of current.
  • the conversion table represents an optimum relationship between the control value and the desired amount of current obtained by the control value, under a normal temperature condition of the coil.
  • FIG. 1 is a block diagram schematically showing the arrangement of an internal combustion engine incorporating a valve timing control system according to an embodiment of the invention
  • FIG. 2 is a flowchart showing a main routine of a VTC control process carried out by the FIG. 1 valve timing control system;
  • FIG. 3 is a flowchart showing a subroutine for carrying out a cam phase feedback control process in FIG. 2;
  • FIG. 4 is a continuation of the FIG. 3 flowchart
  • FIG. 5 is a flowchart showing a subroutine for carrying out a current F/B control process in FIG. 2;
  • FIG. 6 is a flowchart showing a subroutine for carrying out a PID feedback control process which is executed in FIG. 5 for calculating an output duty factor;
  • FIG. 7 shows an example of a table for converting a provisional duty factor to a desired current amount
  • FIG. 8 is a flowchart of a program for detecting a failure of a coil system of a hydraulic pressure control valve
  • FIG. 9 is a flowchart of a program for executing alignment checking
  • FIG. 10 is a flowchart of a program for detecting a failure of a cam angle sensor
  • FIG. 11 is a flowchart of a program for causing a cam pulse counter to carry out counting operation.
  • FIG. 1 there is schematically shown the arrangement of an internal combustion engine incorporating a valve timing control system (hereinafter simply referred to as “the control system”) according to an embodiment of the invention.
  • the control system 1 includes an ECU 2 .
  • the ECU 2 forms or implements actual cam phase-detecting means, desired cam phase-setting means, cam phase feedback control means, desired current amount-setting means, and current feedback control means, and carries out control processes, described hereinbelow, in dependence on operating conditions of the internal combustion engine (hereinafter simply referred to as “the engine”) 3 .
  • the engine 3 is a four-stroke cycle DOHC (double overhead camshaft) gasoline engine, for instance, which includes an intake camshaft 6 and an exhaust camshaft 7 .
  • DOHC double overhead camshaft
  • the intake and exhaust camshafts 6 , 7 are connected to a crankshaft 9 by their respective driven sprockets 6 b, 7 b, and a timing chain, not shown, for rotating through 360 degrees as the crankshaft 9 rotates through 720 degrees.
  • the intake camshaft 6 is integrally formed with a plurality of intake cams 6 a (only one of them is shown) for opening and closing respective intake valves 4 (only one of them is shown), and the exhaust camshaft 7 is integrally formed with a plurality of exhaust cams 7 a (only one of them is shown) for opening and closing respective exhaust valves 5 (only one of them is shown).
  • the intake camshaft 6 is rotatably connected to the driven sprocket 6 b thereof such that the intake camshaft 6 can be rotated or turned within a range of a predetermined angle.
  • the phase angle (hereinafter simply referred to as “the cam phase”) CAIN of each intake cam 6 a relative to the crankshaft 9 is changed to advance or retard the opening/closing timing (valve timing) of the intake valve 4 .
  • a cam phase change mechanism hereinafter referred to as “the VTC” 8 for controlling the cam phase CAIN
  • an hydraulic pressure control valve 10 control valve
  • the VTC 8 includes an advance chamber, not shown, and a retard chamber, not shown, which are defined on opposite sides of a vane, not shown, integrally formed with the intake camshaft 6 , and is configured such that hydraulic pressure from an oil pump driven by the engine 3 is selectively supplied to the advance chamber or the retard chamber under control of a hydraulic pressure control valve 10 to thereby turn the intake camshaft 6 in an advancing direction or a retarding direction relative to the driven sprocket 6 b.
  • the hydraulic pressure control valve 10 is formed by a linear solenoid valve which includes a coil 100 , and a spool, not shown, driven by a force generated by the coil 100 .
  • the hydraulic pressure control valve 10 is constructed such that the position of the spool thereof is continuously changed according to an output duty factor DDOUT (control value), controlled by the ECU 2 , of current (pulse current) supplied to the coil 100 .
  • DDOUT control value
  • the advance chamber or retard chamber of the VTC 8 is opened and closed depending on the position of the spool.
  • the output duty factor DDOUT output control value
  • a hold duty factor value e.g. 50%
  • the spool is moved from its neutral position toward the other side for opening the retard chamber, whereby the hydraulic pressure is supplied to the retard chamber to place the VTC 8 in a state retarding the cam phase CAIN.
  • the intake cam 6 a can be moved through 60 degrees crank angle with its full retard position being 25 degrees crank angle BTDC and its full advance position being 85 degrees crank angle BTDC.
  • the cam phase CAIN is 0 degrees crank angle when it is in the full retard position, whereas when the cam phase CAIN is in the full advance position, it is 60 degrees crank angle.
  • the hydraulic pressure control valve 10 is placed in a cam phase-holding state in which the spool thereof is located in the neutral position for simultaneously closing the advance chamber and the retard chamber. In this state, supply of the hydraulic pressure to the advance chamber and the retard chamber is cut off, and the intake camshaft 6 and the driven sprocket 6 b are fixedly connected to each other, whereby the cam phase CAIN is held at a value to which it has been controlled by the VTC 8 .
  • a cam angle sensor 28 (actual cam phase-detecting means) is arranged at the other end of the intake camshaft 6 , opposite to the one end at which the VTC 8 is arranged.
  • the cam angle sensor 28 is comprised e.g. of a magnet rotor and an MRE (magnetic resistance element) pickup, and delivers a cam pulse CAM to the ECU 2 whenever the camshaft 6 rotates through a predetermined angle (e.g. 180 degrees).
  • the sensor 28 detects a cam angle CASVIN of the intake cam 6 a measured with respect to a TDC (top dead center) position, and delivers a signal indicative of the sensed cam angle CASVIN to the ECU 2 .
  • the crankshaft 9 has a crank angle position sensor 29 (actual cam phase-detecting means) arranged therefor.
  • the crank angle position sensor 29 is constructed similarly to the above cam angle sensor 28 , and delivers a crank pulse CRK to the ECU 2 whenever the crankshaft 9 rotates through a predetermined angle (e.g. 30 degrees).
  • the crank angle position sensor 29 is formed with a tooth, not shown, indicating a reference position of the crankshaft 9 . The tooth causes a reference pulse to be output whenever the crankshaft 9 rotates through 360 degrees.
  • the ECU 2 calculates (detects) an actual cam phase CAIN based on the crank pulse CRK and the signal indicative of the cam angle CASVIN output from the cam angle sensor 28 . Further, the ECU 2 determines an engine rotational speed NE based on the crank pulse CRK.
  • the engine 3 has an intake pipe 30 in which is arranged a throttle valve 31 having a throttle valve opening sensor 37 attached thereto. Further, injectors 32 (only one of them is shown), an intake air temperature sensor 33 , and an intake air pressure sensor 34 are inserted into the intake pipe 30 at respective locations downstream of the throttle valve 31 . Each injector 32 has its fuel injection time period (fuel injection amount) TOUT controlled by a drive signal delivered from the ECU 2 .
  • the intake air temperature sensor 33 senses a temperature (intake air temperature TA) of intake air within the intake pipe 30 and supplies a signal indicative of the sensed intake air temperature TA to the ECU 2 .
  • the intake air pressure sensor 34 senses an absolute pressure PBA within the intake pipe 30 and supplies a signal indicative of the sensed absolute pressure PBA to the ECU 2 .
  • the throttle valve opening sensor 37 senses an opening degree ⁇ TH of the throttle valve 31 (hereinafter referred to as “the throttle valve opening ⁇ TH) and supplies a signal indicative of the sensed throttle valve opening ⁇ TH to the ECU 2 .
  • an engine coolant temperature sensor 35 is mounted in the cylinder block of the engine 3 .
  • the engine coolant temperature sensor 35 senses a temperature (engine coolant temperature TW) of an engine coolant circulating within the cylinder block of the engine 3 and supplies a signal indicative of the sensed engine coolant temperature TW to the ECU 2 .
  • the ECU 2 is formed by a microcomputer including an I/O interface, a CPU, a RAM, and a ROM, none of which are shown.
  • the signals from the above sensors are each input to the CPU after A/D conversion and waveform shaping by the I/O interface.
  • the ECU 2 includes a current-detecting circuit 2 a (actual current amount-detecting means) which detects an actual amount VTCIACT of current actually flowing through the coil 100 of the hydraulic pressure control valve 10 .
  • the CPU 2 determines an operating condition of the engine 3 based on these signals, and in dependence on the determined operating condition, carries out control of the VTC 8 (hereinafter referred to as “the VTC control”) in the manner described hereinafter, according to a control program and data read from the ROM, and data read from the RAM.
  • FIG. 2 is a flowchart showing a main routine of an overall control process for the above VTC control. This control process is executed at predetermined time intervals (e.g. every 10 ms).
  • a cam phase feedback (F/B) control process is carried out in which a provisional duty factor DOUTVT is calculated by feedback control based on a desired cam phase CAINCMD set in dependence on operating conditions of the engine 3 , and the actual cam phase CAIN detected by the cam angle sensor 28 .
  • a current feedback (F/B) control process is carried out in which the output duty factor DDOUT for finally controlling the amount of current supplied to the hydraulic pressure control valve 10 is calculated by feedback control based on a desired current amount VTCIOBJ set based on the provisional duty factor DOUTVT calculated at the step S 1 , and the actual current amount VTCIACT detected by the current-detecting circuit 2 a.
  • FIGS. 3 and 4 are diagrams showing a subroutine for carrying out a cam phase F/B control process. It should be noted that in the following description, a symbol # is added to each of heads of fixed values stored as data and table values beforehand in the ROM to thereby distinguish the fixed values from other variables which are updated.
  • a cam phase difference DCAINCMD (desired cam phase CAINCMD—actual cam phase CAIN) calculated on the immediately preceding occasion is stored as an immediately preceding value DCAINCMDX of the cam phase difference.
  • a VTC operation enable flag F_VTC assumes “1”.
  • the VTC operation enable flag F_VTC is set to “1” by a subroutine, not shown, when conditions for execution of the VTC control are satisfied. If the answer to the question of the step S 12 is negative (No), i.e.
  • the program proceeds to steps S 13 to S 18 .
  • the cam phase difference DCAINCMD is set to a value “0”
  • an I term (integral term) DVIIN of a PID feedback control referred to hereinafter, is set to a learned hold duty factor value DVTHLD.
  • the learned hold duty factor value DVTHLD is obtained by learning the provisional duty factor DOUTVT determined when the hydraulic pressure control valve 10 is in the cam phase-holding state, through carrying out a subroutine, not shown, for correcting an error in the hold duty factor, caused by variations in hardware of the VTC 8 and the hydraulic pressure control valve 10 .
  • the learned hold duty factor value DVTHLD is set to be used as an initial value of the I term DVIIN at the start of the cam phase F/B control.
  • a calculation duty value DVIN referred to hereinafter, is set to “0”.
  • a perturbation timer TDVIN referred to hereinafter, is reset to “0”, and at a step S 17 , a perturbation flag F_DVINPB is set to “0”.
  • the provisional duty factor DOUTVT is set to “0”, followed by terminating the program.
  • a step S 20 it is determined at a step S 20 whether or not the calculated cam phase difference DCAINCMD is larger than “0”. If the answer to the question of the step S 20 is affirmative (Yes), i.e.
  • the P-term gain KVP, I-term gain KVI, and D-term gain KVD of the control are set to advancing gains #KVPA, #KVIA, and #KVDA, respectively, which are fixed values identical to each other.
  • the P-term gain KVP, the I-term gain KVI, and the D-term gain KVD are set to retarding gains #KVPR, #KVIR, and #KVDR, respectively, which are fixed values identical to each other, and at the same time identical to the above advancing gains.
  • the six gains are all set to the same value, it is also possible to set the retarding gains to values larger or smaller than the advancing gains.
  • the P-term gain KVP, the I-term gain KVI, and the D-term gain KVD calculated at the step S 21 or S 22 are used to calculate a P term DVPIN, the I term DVIIN, and a D term DVDIN, respectively, by the following equations:
  • step S 25 limit checking of the I term DVIIN calculated at the step S 23 is carried out. More specifically, it is determined at the step S 25 whether or not the I term DVIIN is larger than an upper limit value #DVLMTIH (e.g. 65%). If DVIIN>#DVLMTIH holds, at a step S 26 , the I term DVIIN is set to the upper limit value #DVLMTIH. If the answer to the question of the step S 25 is negative (No), it is determined at a step S 27 whether or not the I term DVIIN is smaller than a lower limit value #DVLMTIL (e.g. 45%).
  • #DVLMTIH e.g. 65%
  • the I term DVIIN is set to the lower limit value #DVLMTIL. If the answer to the question of the step S 27 is negative (No), i.e. if #DVLMTIL ⁇ DVIIN ⁇ #DVLMTIH holds, the I term DVIIN is maintained. After the above limit checking of the I term DVIIN, at a step S 29 , the P term DVPIN, the I term DVIIN, and the D term DVDIN are added to calculate the calculation duty value DVIN.
  • a perturbation process is carried out at steps S 30 to S 39 .
  • the perturbation process is executed in order to prevent decrease of a cam phase-holding force which is caused by reduction of hydraulic pressure in the advance chamber and retard chamber of the VTC 8 due to leakage of hydraulic fluid in the cam phase-holding state of the hydraulic pressure control valve 10 .
  • hydraulic pressure is supplied to the advance chamber and retard chamber of the VTC 8 by reciprocating (forcibly vibrating) the hydraulic pressure control valve 10 alternately in the advancing and retarding directions with respect to the neutral position.
  • step S 30 it is determined at the step S 30 whether or not the engine coolant temperature TW is higher than an upper limit value #TWDVPB (e.g. 100° C.). If TW ⁇ #TWDVPB holds, the perturbation process is not carried out since it is determined that the temperature of the hydraulic fluid is not so high, which means that there is no fear of reduction of hydraulic pressure due to an increased oil temperature. Therefore, the program proceeds to a step S 40 , wherein the provisional duty factor DOUTVT is set to the calculation duty value DVIN calculated at the step S 29 . If the answer to the question of the step S 30 is affirmative (Yes), i.e.
  • step S 31 it is determined at a step S 31 whether or not the calculation duty value DVIN is equal to or larger than a lower limit value #DVIPBL (e.g. 45%), and at the same time equal to or lower than an upper limit value #DVIPBH (e.g. 60%) thereof.
  • This determination is carried out to determine whether or not the calculation duty value DVIN is a value for placing the hydraulic pressure control valve 10 in the cam phase-holding state. Therefore, if the answer to the question of the step S 31 is negative (No), it is determined that conditions for carrying out the perturbation process are not satisfied, and the program proceeds to the step S 40 .
  • step S 31 determines whether or not the count of the perturbation timer TDVIN is equal to “0”.
  • the perturbation timer TDVIN is reset to “0”at the step S 16 when the conditions for carrying out the VTC control are not satisfied, and hence the first answer to the question of the step S 32 is affirmative (Yes), so that the program proceeds to a step S 33 , wherein the perturbation timer TDVIN is set to a predetermined time period #TMDVPB (0.1 second, for instance).
  • TMDVPB 0.1 second, for instance
  • the perturbation flag F_DVINPB is also set to “0” at the step S 17 , and the first answer to the question of the step S 34 is negative (No), so that the program proceeds to a step S 35 , wherein the perturbation flag F_DVINPB is set to “1”. If the answer to the question of the step S 34 is affirmative (Yes), the perturbation flag F_DVINPB is set to “0” at a step S 36 . In short, the perturbation flag F_DVINPB is inverted between “1” and “0” every predetermined time period #TMDVPB.
  • #DVINPBP e.g. 5%
  • the additional amount #DVINPBP and the subtractive amount #DVINPBM are set to the same value, this is not limitative, but it is also possible to set the additional amount #DVINPBP to a larger value than the subtractive amount #DVINPBM so as to compensate for tendency of the intake cam 6 a to return in the retarding direction due to the reaction force thereof.
  • a cleaning enable flag F_VTCCLN assumes “1”.
  • the cleaning enable flag F_VTCCLN is set to “1” by a subroutine, not shown, in order to prevent the VTC 8 and the hydraulic pressure control valve 10 from being undesirably fixed, when conditions for carrying out “cleaning” in which the VTC 8 is forcibly moved from the full retard position to the full advance position are satisfied. If the answer to the question of the step S 41 is affirmative (Yes), i.e. if the conditions for carrying out the cleaning are satisfied, at a step S 42 , the provisional duty factor DOUTVT is set to an upper limit value #DVLMTH (90%, for instance) for carrying out the cleaning, followed by terminating the program.
  • step S 41 limit checking of the provisional duty factor DOUTVT is carried out. More specifically, it is determined at a step S 43 whether or not the provisional duty factor DOUTVT is larger than the upper limit value #DVLMTH. If DOUTVT>#DVLMTH holds, the program proceeds to the above step S 42 , wherein the provisional duty factor DOUTVT is set to the upper limit value #DVLMTH. If the answer to the question of the step S 43 is negative (No), it is determined at a step S 44 whether or not the provisional duty factor DOUTVT is smaller than a lower limit value #DVLMTL (e.g. 10%).
  • a lower limit value #DVLMTL e.g. 10%
  • the provisional duty factor DOUTVT is set to the lower limit value #DVLMTL at a step S 45 . If the answer to the question of the step S 44 is negative (No), i.e. if #DVLMTL ⁇ DOUTVT ⁇ #DVLMTH holds, the provisional duty factor DOUTVT is maintained, followed by terminating the program. As described above, the cam phase F/B control is executed based on the desired cam phase CAINCMD and the actual cam phase CAIN, whereby the provisional duty factor DOUTVT is calculated.
  • FIG. 5 shows a subroutine for carrying out the current F/B control process executed at the step S 2 in FIG. 2.
  • the current F/B control process is carried out to set the desired current amount VTCIOBJ based on the provisional duty factor DOUTVT calculated as above, and calculate the output duty factor DDOUT for finally controlling the amount of current supplied to the hydraulic pressure control valve 10 , by the feedback control, based on the desired current amount VTCIOBJ and the actual current amount VTCIACT detected by the current-detecting circuit 2 a.
  • step S 51 it is determined at a step S 51 whether or not the VTC operation enable flag F_VTC assumes “1”. If the answer to the question of the step S 51 is negative (No), i.e. if the conditions for carrying out the VTC control are not satisfied, the output duty factor DDOUT is set to a lower limit value #DVTLMTL (5%, for instance) which is smaller than the above-mentioned lower limit value #DVLMTL of the provisional duty factor DOUTVT, at a step S 52 . On the other hand, if the answer to the question of the step S 51 is affirmative (Yes), i.e.
  • the output duty factor DDOUT is calculated by the current F/B control at a step S 53 .
  • This calculation is performed by a subroutine, shown in FIG. 6, for calculating the output duty factor DDOUT. This subroutine will be described in detail hereinafter.
  • limit checking of the calculated output duty factor DDOUT is carried out at steps S 54 to S 56 .
  • step S 54 it is determined at the step S 54 whether or not the output duty factor DDOUT is larger than an upper limit value #DVTLMTH (95%, for instance) which is larger than the upper limit value #DVLMTH of the provisional duty factor DOUTVT, described above. If DDOUT>#DVTLMTH holds, the output duty factor DDOUT is set to the upper limit value #DVTLMTH at the step S 55 . If the answer to the question of the step S 54 is negative (No), it is determined at a step S 56 whether or not the output duty factor DDOUT is smaller than the above lower limit value #DVTLMTL.
  • step S 52 the output duty factor DDOUT is set to the lower limit value #DVTLMTL. If the answer to the question of the step S 56 is negative (No), i.e. if #DVTLMTL ⁇ DDOUT ⁇ #DVTLMTH holds, the output duty factor DDOUT is maintained.
  • FIG. 6 shows a subroutine executed at the step S 53 in FIG. 5 for calculating the output duty factor DDOUT by the current F/B control.
  • the actual current amount VTCIACT is read in which is an amount of current actually flowing through the coil 100 of the hydraulic pressure control valve 10 and detected by the current- detecting circuit 2 a.
  • the provisional duty factor DOUTVT calculated by the cam phase F/B control is converted to a desired current amount VTCIOBJ by using a VTCIOBJ conversion table stored in the ROM.
  • FIG. 7 shows an example of the VTCIOBJ conversion table.
  • This table shows an optimum (standard) relationship between the provisional duty factor DOUTVT and the amount of current to be supplied to the coil 100 of the hydraulic pressure control valve 10 , which is obtained by the provisional duty factor DOUTVT, under a normal temperature condition of the coil 100 .
  • This table enables the desired current amount VTCIOBJ to be set according to the provisional duty factor DOUTVT in an unconditional and optimum manner. More specifically, the desired current amount VTCIOBJ is linearly set such that the same is increased as the provisional duty factor DOUTVT becomes larger.
  • the desired current amount VTCIOBJ is 0.6 A
  • the desired current amount VTCIOBJ is 0.2 A
  • the desired current amount VTCIOBJ is 0.8 A.
  • a region wherein the value of DOUTVT is equal to or smaller than the lower limit value #DVLMTL, and a region wherein the value of DOUTVT is equal to or larger than the upper limit value #DVLMTH are saturated regions wherein the operating condition of the hydraulic pressure control valve 10 is not changed even if the amount of current flowing through the coil 100 is made smaller than the lower limit value #DVLMTL or larger than the upper limit value #DVLMTH. Therefore, values within the above two regions are subjected to limit checking when the provisional duty factor DOUTVT is calculated, as described hereinbefore, and omitted from the table.
  • step S 65 it is determined at a step S 65 whether or not the immediately preceding value flag F_BUVTC associated with the VTC operation enable flag F_VTC stored at the step S 57 in FIG. 5 assumes “0”. If the answer to the question of the step S 65 is affirmative (Yes), i.e. if the present loop is a loop executed immediately after the conditions for carrying out the VTC control have been satisfied, an I term IFBI is set to an initial value #KIFIRST (e.g. 0%) at a step S 66 , followed by the program proceeding to a next step S 67 . Further, if the answer to the question of the step S 65 is negative (No), i.e. if the present loop is a second or any other subsequent loop after satisfaction of the conditions for carrying out the VTC control, the step S 66 is skipped, followed by the program proceeding to the step S 67 .
  • #KIFIRST e.g. 0%
  • a P term IFBP is calculated by multiplying the current amount difference ERR calculated at the step S 63 by a P-term gain #NKP (e.g. 0.5). Then, at a step S 68 , the present value IFBIN of the I term is calculated by multiplying the current amount difference ERR by an I-term gain #NKI (e.g. 0.05), and at a step S 69 , the present value IFBIN of the I term is added to the immediately preceding value IFBI of the I term to thereby calculate the I term IFBI.
  • P-term gain #NKP e.g. 0.5
  • step S 70 limit checking of the I term IFBI calculated at the step S 69 is carried out. More specifically, it is determined at the step S 70 whether or not the I term IFBI is larger than an upper limit value #KILMTH (95%, for instance). If IFBI>#KILMTH holds, the I term IFBI is set to the upper limit value #KILMTH at a step S 71 . If the answer to the question of the step S 70 is negative (No), it is determined at a step S 72 whether or not the I term IFBI is smaller than a lower limit value #KILMTL (e.g. 5%).
  • #KILMTH e.g. 5%
  • the I term IFBI is set to the lower limit value #KILMTL at the step S 73 . If the answer to the question of the step S 72 is negative (No), i.e. if #KILMTL ⁇ IFBI ⁇ #KILMTH holds, the I term IFBI is maintained.
  • a D term IFBD is calculated by multiplying the actual current amount difference DERR calculated at the step S 64 by a D-term gain#NKD (e.g. 0.01).
  • a D-term gain#NKD e.g. 0.01.
  • the P term IFBP, I term IFBI, and D term IFBD calculated at the preceding steps are added to each other, thereby calculating the output duty factor DDOUT, followed by terminating the program.
  • the provisional duty factor DOUTVT is feedback-controlled such that the actual cam phase CAIN becomes equal to the desired cam phase CAINCMD, and at the same time, after converting the provisional duty factor DOUTVT obtained as above to the optimum desired current amount VTCIOBJ by using the VTCIOBJ conversion table, the final output duty factor DDOUT is also feedback-controlled such that the actual current amount VTCIACT flowing through the coil 100 of the hydraulic pressure control valve 10 becomes equal to the desired current amount VTCIOBJ.
  • the actual current amount VTCIACT or the amount of current flowing through the coil 100 is directly detected, and at the same time the output duty factor DDOUT is feedback-controlled such that the detected actual current amount VTCIACT becomes equal to the optimum desired current amount VTCIOBJ.
  • This makes it possible to cope with all the temperature conditions of the coil 100 , so as to suitably compensate for variations in the behavior of the hydraulic pressure control valve 10 , caused by changes in the temperature of the coil 100 . Therefore, it is possible to carry out optimum control of the operations of the hydraulic pressure control valve 10 and the VTC 8 irrespective of the temperature conditions of the coil 100 , thereby enhancing accuracy of the cam phase feedback control.
  • the upper limit value #DVTLMTH of the output duty factor DDOUT is set to a value larger than the upper limit value #DVLMTH of the provisional duty factor DOUTVT
  • the lower limit value #DVTLMTL of the output duty factor DDOUT is set to a value smaller than the lower limit value #DVLMTL of the provisional duty factor DOUTVT, so that the range of values which can be assumed by the output duty factor DDOUT is expanded.
  • This makes it possible to suitably control the output duty factor DDOUT in a manner coping with a shift of a controllable range of values of the output duty factor DDOUT, due to the above changes in the temperature of the coil 100 .
  • FIG. 8 shows a flowchart of a program for detecting a failure of the coil system of the hydraulic pressure control valve 10 , due to a wire breaking, a short-circuit, or the like.
  • the program is executed after the actual current amount VTCIACT is read in, and the output duty factor DDOUT is calculated.
  • a VTC failure flag F_FSA assumes “1”.
  • the VTGC failure flag F_FSA is set to “1” when a failure of the VTC 8 is detected. Therefore, if the answer to the question of the step S 81 is affirmative (Yes), determination of a failure of the coil system of the hydraulic pressure control valve 10 is not carried out, and the program is immediately terminated.
  • step S 82 determines whether or not the output duty factor DDOUT is larger than a determination threshold #DDVTFSLM (40%, for instance), and at a step S 83 whether or not the actual current amount VTCIACT is larger than a determination threshold #IACTFSLM (e.g. 200 mA). If the answer to the question of the step S 82 is negative (No) (DDOUT ⁇ #DDVTFSLM), it is determined that the output duty factor DDOUT is not very large and the conditions for carrying out the determination of a failure are not satisfied, followed by the program proceeding to a step S 84 .
  • a determination threshold #DDVTFSLM 40%, for instance
  • #IACTFSLM e.g. 200 mA
  • an abnormality detection timer TFSA formed by a downcount timer is set to a predetermined time period #TMFSA (e.g. 0.5 seconds), followed by terminating the program. Further, if the answer to the question of the step S 83 is negative (No), i.e. if VTCIACT ⁇ #IACTFSLM holds, it is determined that a sufficient current is flowing through the coil 100 of the hydraulic pressure control valve 10 for normal operation thereof, and hence the step S 84 is executed.
  • TMFSA e.g. 0.5 seconds
  • step S 85 it is determined at a step S 85 whether or not the count of the abnormality detection timer TFSA is equal to “0”. If the answer to the question of the step S 85 is negative (No), the program is immediately terminated, whereas if TFSA 0 holds, it is determined that a failure has occurred in the coil system of the hydraulic pressure control valve 10 , and to indicate this failure, a coil system failure flag F_FSDA is set to “1” at a step S 86 , followed by terminating the program.
  • FIG. 9 shows a flowchart of a program for executing alignment checking, that is, for detecting an abnormal cam phase shift relative to the crank angle.
  • the abnormal cam phase shift is detected depending on whether or not the cam angle CASVIN from the cam angle sensor 28 is output normally relative to the crank pulse CRK delivered from the crank angle position sensor 29 when the VTC 8 is stopped and placed in the full retard position.
  • the present program first, it is determined at a step S 91 whether or not the designated failure has already been detected and the detection of the failure is finally determined or finalized.
  • step S 92 If the answer to the question of the step S 91 is affirmative (Yes), the program is immediately terminated, whereas if the answer to the question of the step S 91 is negative (No), it is determined at a step S 92 whether or not the VTC operation enable flag F_VTC assumes “0”. If the answer to the question of the step S 92 is negative (No), i.e. if the VTC 8 is in operation, a full retard position shift wait timer TCAMZP is set to a predetermined time period #TMCAMZP (10 ms, for instance) at a step S 93 . The full retard position shift wait timer TCAMZP is used for waiting for the VTC 8 to reliably shift to the full retard position after being stopped.
  • TCAMZP a predetermined time period #TMCAMZP (10 ms, for instance
  • an abnormality detection timer TFSC, and a normality detection timer TOKC are set to a predetermined time period #TMFSC (100 ms, for instance) respectively, followed by terminating the program.
  • #TMFSC 100 ms, for instance
  • step S 96 determines whether or not an alignment determination pass flag F_FIRST assumes “1”.
  • the alignment determination pass flag F_FIRST is reset to “0” when the ignition is turned on, and set to “1” at a step S 105 once the alignment checking is carried out by using the cam angle CASVIN detected by the cam angle sensor 28 , as described hereinbelow. If the answer to the question of the step S 96 is affirmative (Yes), i.e.
  • step S 97 it is determined at a step S 97 whether or not the count of the full retard position shift wait timer TCAMZP is equal to “0”, i.e. whether or not the predetermined time period #TMCAMZP has elapsed after the stop of the VTC 8 . If the answer to the question of the step S 97 is negative (No), the above steps S 94 and S 95 are executed, followed by terminating the program.
  • step S 98 it is determined whether or not the engine rotational speed NE is equal to or higher than a lower limit value #NEPHASEL (e.g. 500 rpm).
  • step S 100 it is determined at a step S 100 whether or not an absolute value
  • the predetermined value #CAINZPS which indicates a reference value in the case of the VTC 8 being in the full retard position is set e.g. to 20 degrees BTDC.
  • the determination threshold #FSWC is set to 10 degrees which corresponds to two teeth of the driven sprocket 6 b.
  • step S 100 If the answer to the question of the step S 100 is affirmative (Yes), i.e. if
  • step S 103 it is determined at a step S 103 whether or not the count of the normality detection timer TOKC is equal to “0”, i.e. whether or not the predetermined time period #TMFSC has elapsed after the alignment was determined to be normal at the step S 100 . If the answer to the question of the step S 103 is negative (No), the program proceeds to the above-mentioned step S 105 , wherein the alignment determination pass flag F_FIRST is set to “1”, whereas if the answer to the question of the step S 103 is affirmative (Yes), it is finally determined that the alignment is normal, and to indicate the fact, an alignment normality flag F_OKC is set to “1” at a step S 104 . Then, the step S 105 is carried out, followed by terminating the program.
  • the alignment determination pass flag F_FIRST 0 holds (No to S 96 ), it is determined that the ignition has just turned on, and that the VTC 8 is in the full retard position, so that the step S 97 is skipped, whereby it is possible to execute the alignment checking at the step S 100 promptly without waiting for the predetermined time period #TMCAMZP to elapse in order to wait for the VTC 8 to shift to the full retard position. Further, after the alignment is determined to be normal by the alignment checking, the initial alignment flag F_ENVTC is immediately set to “1” at the step S 102 without waiting for the predetermined time period #TMFSC to elapse.
  • the alignment check control described above when the engine 3 is restarted e.g. immediately after the ignition is turned off, the alignment checking at the step S 100 can be executed in the course of shift of the VTC 8 to the full retard position. Even in such a case, wrong determination is prevented since the alignment is not finally determined to be normal until the normality detection timer TOKC has timed out.
  • step S 100 If the answer to the question of the step S 100 is negative (No), i.e. if
  • step S 105 the alignment determination pass flag F_FIRST is set to “1”, whereas if the answer to the question of the step S 107 is affirmative (Yes), it is finally determined that the alignment is abnormal, and to indicate the fact, the alignment normality flag F_OKC is set to “0” at a step S 109 , and an alignment abnormality flag F_FSDC is set to “1” at a step S 109 . Then, the step S 105 is carried out, followed by terminating the program.
  • FIGS. 10 and 11 are flowcharts of a program for detecting a failure of the cam angle sensor 28 due to a wire breaking, a short-circuit, noise, a missing tooth or the like.
  • the failure detection is carried out based on whether or not the cam pulse CAM from the cam angle sensor 28 is output normally with respect to the crank pulse CRK delivered from the crank angle position sensor 29 .
  • it is determined at a step S 111 whether or not the designated failure has already been detected and the detection of the failure is finally determined.
  • step S 112 If the answer to the question of the step S 111 is affirmative (Yes), the program is immediately terminated, whereas if the answer to the question of the step S 111 is negative (No), it is determined at a step S 112 whether or not the engine rotational speed NE is equal to or larger than a lower limit value #FSNEPH (500 rpm, for instance). If NE ⁇ #FSNEPH holds, the program is terminated.
  • #FSNEPH 500 rpm, for instance
  • step S 112 If the answer to the question of the step S 112 is affirmative (Yes), i.e. if NE ⁇ #FSNEPH holds, it is determined at a step S 113 whether or not the count of a wire breaking detection counter CFS 04 A arranged in the crank angle position sensor 29 is smaller than a predetermined count #CHKCNDA (e.g. 10), and it is determined at a step S 114 whether or not the count of a noise detection counter CFS 04 B arranged in the crank angle position sensor 29 is smaller than a predetermined count #CHKCNDB (e.g. 10). If either of the answers to the questions of the steps S 113 and S 114 is affirmative (Yes), i.e.
  • step S 116 If the answer to the question of the step S 115 is affirmative (Yes), it is determined at a step S 116 whether or not the count of a cam pulse counter CCAMPLS is equal to “0” or “2”.
  • the cam pulse counter CCAMPLS is incremented at a step S 132 in the FIG. 11 subroutine which is carried out by an interrupt handling routine responsive to each input of the cam pulse.
  • the cam pulse counter CCAMPLS is reset to “0” at a step S 120 , referred to hereinafter.
  • the count of the cam pulse counter CCAMPLS at the step S 116 indicates the number of times of detecting the cam pulse CAM between the immediately preceding stage “0” and present stage “0” of the crank angle.
  • the cam angle sensor 28 is designed such that it outputs a cam pulse CAM whenever the camshaft 6 rotates through 180 degrees, so that if the cam angle sensor 28 operates normally, the count of the cam pulse counter CCAMPLS is equal to “2”.
  • step S 116 Therefore, if the answer to the question of the step S 116 is negative (No), i.e. if the count of the cam pulse counter CCAMPLS is neither “0” nor “2” but an odd number, it is determined that there has occurred an abnormal condition due to noise or a missing tooth, and the noise detection counter CFSB is decremented at a step S 117 . It should be noted that the noise detection counter CFSB is reset to an initial value #FSNB (e.g. 50) when the ignition is turned on. Then, it is determined at a step S 118 whether or not the count of the noise detection counter CFSB is equal to “0”.
  • #FSNB e.g. 50
  • step S 118 If the answer to the question of the step S 118 is negative (No), the program proceeds to the step S 120 , wherein the cam pulse counter CCAMPLS is reset to “0”. On the other hand, if the answer to the question of the step S 118 is affirmative (Yes), i.e.
  • a noise/missing tooth failure flag F_FSDB is set to “1” at a step S 119 , followed by the program proceeding to the step S 120 .
  • step S 116 if the answer to the question of the step S 116 is affirmative (Yes), i.e. if the count of the cam pulse counter CCAMPLS is equal to “0” or “2”, especially if the count of CCAMPLS is equal to “0”, this means that there has occurred an abnormal condition in which a wire breaking or a short-circuit prevents detection of the cam pulse CAM, and hence determination as to the abnormal condition is carried out at a step S 121 following the step S 120 , et seq. That is, the wire breaking detection counter CFSA is decremented at the step S 121 , and it is determined at a step S 122 whether or not the count of CCAMPLS is equal to “0”.
  • the wire breaking detection counter CFSA is reset to an initial value #FSNA (50, for instance) at a step S 131 in the FIG. 11 subroutine, i.e. whenever the cam pulse CAM is input. Therefore, so long as the cam pulse CAM is normally input, the wire breaking detection counter CFSA is reset to the initial value #FSNA and thereby prevented from assuming “0” even when it is decremented at the step S 121 . Hence, if the answer to the question of the step S 122 is negative (No), it is determined that the cam angle sensor 28 is in normal operation. In this case, the program is immediately terminated.
  • #FSNA 50, for instance
  • the wire breaking detection counter CFSA continues to be decremented at the step S 121 without being reset to the initial value #FSNA.
  • the answer to the question of the step S 122 becomes affirmative (Yes), so that it is determined that a failure due to a wire breaking or a short-circuit has occurred in the cam angle sensor 28 , and to indicate the fact, a wire breaking/short-circuit failure flag F_FSDAA is set to “1” at a step S 123 , followed by terminating the program.
  • the above-mentioned method makes it possible to appropriately detect a failure of the cam angle sensor 28 , while discriminating between two groups of failures, i.e. noise and a missing tooth, and a wire breaking and a short-circuit, and further set flags indicative of the respective causes independently of each other.
  • the invention is not necessarily limited to the above embodiments, but it can be put into practice in various forms.
  • the relationship in size between the desired current amount VTCIOBJ and the actual current amount VTCIACT may be determined to thereby set a gain in the case of the desired current amount VTCIOBJ being larger than the actual current amount VTCIACT to a value larger than a gain in the case of VTCIOBJ being smaller than VTCIACT.
  • This makes it possible to control the output duty factor DDOUT more suitably in a manner coping with a change in sensitivity of the hydraulic pressure control valve 10 , due to a change in temperature of the coil 100 , described hereinbefore.
  • the invention is applied to the valve timing control system with a variable intake cam phase (variable phase angle of the intake cam relative to the crankshaft), by way of example, this is not limitative, but of course the invention can be applied to a valve timing control system with a variable exhaust cam phase (variable phase angle of the exhaust cam relative to the crankshaft).
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