United States Patent
`
`5,713,317
`[11] Patent Number:
`Feb. 3, 1998
`[45] Date of Patent:
`Yoshioka
`
`
`[:9]
`
`U50057l3317A
`
`[54] METHOD OF AND APPARATUS FOR
`CONTINUOUSLY AND VARIABLY
`CONTROLLING VALVE TIMING OF
`INTERNAL COMBUSTION ENGINE
`
`[75]
`
`Inventor. Mamaru Yoshloka, Susono. Japan
`
`[73] Asstgnec: Toyota Mocha Kabnahiki Keisha.
`Aiclu'. Japan
`
`[21] Appl. No; 684.592
`
`[22] Filed:
`
`Jul. 15, 1996
`
`[30]
`
`Foreign Application Priority Data
`
`1111.26.1995
`
`[1?]
`
`Japanc 1-190524
`
`Int. Cl.6 ............................... F02!) 13/02; FOIL 1184
`{51]
`
`[52] US. Cl. _..............
`................... 12390.15; 12390.17
`[58] Field of Search .............................. 123390.15. 90.16.
`123190.17. 90.18. 90.31
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`FOREIGN Pm DOCUMENTS
`
`331991
`342345
`3.99344 1011991
`4—1—5430
`91992
`
`Japan.
`Japan.
`Japan.
`
`Primyy WMr—Weflun Lo
`Attorney Agent, or Finn—Kenyon & Kenyon
`
`[57]
`
`ABSTRACT
`
`A method or an apparatus controls a continuously variable
`valve timing mechanism of an internal combustion engine to
`continuously and variably control the timing of an intake
`valve according to atmospheric pressure. The method or
`apparatus reads an engine revolution speed NE. an engine
`load GN. and an atmospheric pressure PA. refers to a map
`according to the atmospheric pressure PA. to find an acne-
`spheric pressure correction coefficient Kpa. which is 1.0 at
`low altitudes with PA=760 mran and decreases as the
`allimde increases.
`i.e.. as the atmospheric pressure PA
`den-eases. calculates a corredcd engine load GNpa as
`GNpai—GNKpa. and refers to a map according to the
`corrected engine load GNpa and engine revolution speed
`NE. to find a target displacement to be imposed on the
`openlclose timing of the intake valve.
`
`.......................... 123190.17
`5,2?1360 1211993 Kanoeta].
`5,494,008
`211996 Ohkawa etal.
`.......
`12390.15
`
`6Claims. 15 Draw-hag Sheets
`
`51
`
`50 BL
`
`53
`
`5?
`
`“null;
`
`--IIII
`
`
`
`
`
`53
`
`£6
`
`VEHICLE SPEED SENSOR
`
`ATMOSPHER1 C PRESSURE
`SENSCR
`
`VW EX1005
`
`US. Patent No. 6,557,540
`
`VW EX1005
`U.S. Patent No. 6,557,540
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 1 of 15
`
`5,713,317
`
` .\“"“ ‘\\‘
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 2 of15
`
`5,713,317
`
`(NI
`(.0
`
`mmp_zw_
`
`we>umH
`
`weQ_J:¢mo>1
`
`mmnmmwma
`
`
`
`
`
`mowzmmmqwzqxz<mu
`
`Iuk_gmmJD_
`
`
`
`
`
`momzmmommamwguwxm>
`
`
`
`memzmmQ.Hmzw¢2me_m
`
`
`
`m>4<>JomHzoum0w2mmo_Hmzqu9200mm
`
`
`
`
`
`
`
`
`
`ommohumfiz_4mm;mOmmezo_p_w0¢mQmemmmm
`
`
`
`
`
`
`
`
`
`momzwmoz_2m¢omJHHomIH
`
`
`
`
`
`memzwmmmzwqmmazmpqupz_
`
`mq
`
`ma
`
`qq
`
`
`
`
`
`momzwmwaqummafimpmmpqz
`
`
`
` momzmwz::u<:we2a4_qmmbm0mmoq
`
`mOmZMwNo
`
`
`
`
`
`momzmmwmsmmmmau.mmImm0§Hq
`
`mu
`
`mu
`
`om
`
`cm
`
`mm
`
`mm
`
`gm
`
`
`
`
`
`
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 3 of 15
`
`5,713,317
`
`F i g . 3
`
`TOP DEAD CENTER
`
`
`
`IVO(VARIABLE)
`
`(REFERENCE)
`IVOr
`EVC (FIXED)
`
`r [
`
`r
`
`INTAKE VALVE
`OPEN
`
`
`
`
`
`
`
`EXHAUST VALVE
`OPEN
`
`/
`IVCr
`(REFERENCE)
`
`IVC
`(VARIABLE)
`
`EVO
`(FIXED)
`
`BOTTOM DEAD CENTER
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 4 of 15
`
`5,713,317
`
`Fig.4
`
`ENGINE REVOLUTION SPEED NE [rpm]
`
`
`Elm-
`
`
`lfllzllfiifiiiiiifijiiiitjiiiitjiilllllllllfllllllflll_________——_——_‘‘
`
`mm—
`Enl------
`Imm—
`
`
`
`
`
`
`
` ENGINELOADGN[E/rev.]
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 5 of 15
`
`5,713,317
`
`Fig.5
`
`NE = 2000 [rpm]
`
`C1
`
`0.2 0.4
`
`0.6
`
`0.8
`
`1.0
`
`1.2
`
`1.4
`
`1.6
`
`1.8
`
`2.0
`
`GN [g/revJ
`
`
`
`IVTD['CA]
`
`60
`
`50
`
`1+0
`
`30
`
`20
`
`10
`
`0
`
`0
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 6 of 15
`
`5,713,317
`
`60
`
`50
`
`40
`
`
`
`IVTD['CA]
`
`10
`
`3O
`
`20
`
`0
`
`0.2 0.1.
`
`0.6 0.3
`
`1.0
`
`1.2
`
`1.4
`
`1.6
`
`1.8
`
`2.0
`
`GN[g/rev.]
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 7 of 15
`
`5,713,317
`
`Fig.7
`
`WT CONTROL ROUT | NE
`
`READ NE
`
`READ PA
`
`102
`
`10"
`
`105
`
`FIND Kpa FROM PA
`
`GNpa-c—GN/Kpa
`
`103
`
`110
`
`FIND [VTDDa FROM GNpa AND NE
`
`‘12
`
`IVTDx-e———IVTDpa
`
`11‘
`
`FEEDBACK—CONTROL T0 IvTD:
`
`116
`
`RETURN
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 8 of 15
`
`5,713,317
`
`
`
`PA
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 9 of 15
`
`5,713,317
`
`
`
`
`
`
`
`FIND IVTDo FROM GN AND NE
`
`'
`Ivmx é—-—IVTDOXLpa
`
`FEEDBACK—CONTROL TO IVTDt
`
`
`
`
`
`RETURN
`
`2’10
`
`212
`
`
`
`
`
`21L
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 10 of 15
`
`5,713,317
`
`
`
`760mmHg
`
`PA
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 11 of 15
`
`5,713,317
`
`Fig.11
`
`NE = 2000 [rpm]
`
`0'! CD
`
`01 O
`
`Jr- C)
`
`LI.) D
`
`h.) C)
`
`10
`
`
`
`IVTD['CA]
`
`
`
`0
`
`0.2 0.4 0.6 0.8 1.0
`
`1.2 1.4
`
`1.5
`
`1.0 2.0
`
`GN [g/rev.]
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 12 of 15
`
`5,713,317
`
`Fig.12
`
`302
`
`301.
`
`306
`
`316
`
`308
`
`m
`
`312
`
`N (H | GH LOAD)
`
`
`
`IVTDpa > IVTDo
`
`
`
`Y (LOW/MED | UM LOAD)
`IVTDtih—IVTDO
`315 IVTDii——IVTDpa
`
`
`
`320
`
`FEEDBACK—CONTROL TO IVTDt
`
`322
`
`RETURN
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 13 of 15
`
`5,713,317
`
`Fig.13
`
`LIM¥TS DUE TO ALLOWABLE
`iNTERNAL’FGR QUANTITY
`
`,’/ REQUIRED
`
`OUTPUT
`
`
` IVTDo
`HIGH
`LOW
`ALTITUDES ALTITUDES
`
`IVTD
`
`GN
`
`

`

`US. Patent
`
`Feb. 3, 1998
`
`Sheet 14 of 15
`
`5,713,317
`
`Fig.14
`
`NE =2000 [rpm]
`
`60
`
`50
`
`40
`
`3D
`
`’20
`
`10
`
`
`
`IVTD[‘CA]
`
` 0
`
`0.6 0.8 1.0
`
`0.2 0.4
`
`1.2 1.4 1.6 1.8
`
`2.0
`
`GN [g/rev.]
`
`

`

`US. Patent
`
`Feb. 3, 1993
`
`Sheet 15 of 15
`
`5,713,317
`
`Fig.15
`
`402
`
`m
`
`[.05
`
`408
`
`“0
`
`1.16
`
`N (HIGH LOAD)
`
`IVTDpa >IVTDo
`
`
`Y (LOW/MED | UM LOAD)
`(IVTDpa-IVTDo)Xa+IVTDo
`
`
`
`IVTDI4—
`
`«520
`
`IVTDI 4t—IVTDpa
`
`FEEDBACK—CONTROL T0 IVTDt
`
`£22
`
`RETURN
`
`

`

`1
`METHOD OF AND APPARATUS FOR
`CONTINUOUSLY AND VARIABLY
`CONTROLLING VALVE TIMING OF
`INTERNAL COMBUSTION ENGINE
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a. method of and an
`apparatus for controlling a continuously variable valve tim-
`ing mechanism of an intmal combustion engine. to con-
`tinuously and variably control the openlclcse timing of an
`intake or exhaust valve of the engine according to a target
`timing.
`2. Desaiption of the Related Art
`There are many variable mechanism that optimize the
`openlclose timing of a valve of an automobile engine
`according to driving conditions. One of them is an ONIOFF
`mechanism. which changes the timing of an intake valve of
`the engine from normal timing to early timing when an
`engine load exceeds a switching tineshold. Japanese Unex-
`amined Utility Model Publication No. 3-99844 decreases the
`switching threshold or increases a detected engine load in
`response to a decrease in ammsphcric pressure. to optimize
`the valve timing.
`To provide high-performance engines. continuously vari-
`able valve timing mechanisms for optimizing valve timing at
`all times have been developed in place of the ONIOFF
`mechanism. as disclosed in Japanese Unexamined Patent
`Publication No. 4—175430 (cotrmponding to us. Pat. No.
`5.2?1360). This mechanism continuously changes the cpen!
`close timing of a valve. and therefore. never employs the
`idea of changing the switching threshold in response to a
`change in atmospheric pressure. There is a requirement.
`therefore. to provide a method of properly controlling the
`continuously variable valve timing mechanism.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention is to provide a method
`of and an apparatus for optimizing valve timing according to
`atmospheric pressure for a continuously variable valve tim-
`ing mechanism of an internal combustion engine.
`The present invention intends to improve the output of an
`engine at high altitudes under high load. as well as reducing
`fuel consumption and improving exhaust purifying perfor-
`mance at high altitudes under lowlmedium load. In order to
`accomplish the objects. the present invention provides the
`following technical arrangements:
`A first aspect of the present invention provides a method
`of controlling a continuously variable valve timing mecha-
`nism of an internal combustion engine. to continuously and
`variably control the openiclose timing of at least one of the
`intake and the exhaust valves of the engine. including the
`steps of (a) detecting an engine load. (b) detecting an
`atmospheric pressure. (c) caressing the detected engine load
`such that the lower the detected atmospheric pressure the
`more the engine load is increased. and (d) setting a target
`valve timing for the valve timing mechanism according to
`the wrrected engine load.
`The first aspect also provides an apparatus for controlling
`valve timing of an internal combustion engine. having a
`valve timing mechanism for continuously and variably con~
`trolling the opentclose timing of at least one of the intake
`and the exhaust valves of the engine. a load detector ft:
`detecting an engine load. a pressure detector for detecting an
`atmospheric pressure. a load corrector for czar-acting the
`
`5,713,317
`
`2
`
`detected engine load such that the lower the detected anno-
`spheric pressure the more the engine load is increased. and
`a timing setter for setting target a valve timing for the valve
`timing mechaniSmacoordingtomecorrectedengineload.
`A second aspect of the present invention provides a
`method of controlling a continuously variable valve timing
`mechanism of an internal combustion engine. to continu-
`ously and variably control the openlclose timing of at least
`one of intake and exhaust valves of the engine. including the
`steps of (a) detecting an engine load. (b) detecting an
`atmospheric pressure. (c) setting. accouling to the detected
`engine load. a displacement from a reference timing as a
`target valve timing for the valve timing mechanism. and (d)
`correcting the set displacement such that the lower the
`deteaed ahnospheric pressure the more the displacement is
`reduced.
`
`The second aspect also provides an apparatus for control-
`ling valve timing of an internal combustion engine. having
`a valve timing mchanism for continuously and variably
`controlling the openlclose timing of at least one of intake
`and exhaust valves of the engine. a load detector for detect-
`ing an engine load. a pressure detector for detecting an
`annospheric Inessme. a displacement setter for setting.
`according to the detected engine load. a displacement from
`a reference timing as target valve timing for the valve timing
`mechanism. and a displacement oorrector for correcting the
`set displacement such that the lower the detected atmo~
`spheric pressure the more the set displacement is reduced
`When driving at high altitudes. an engine receives a
`smaller quantity of intake air due to the low concentration of
`air. The first and second aspects of the present invention are
`capable of optimizing valve timing to maintain the output of
`the engine at high altitudes.
`A third aspect of the present invention provides a method
`including the step of. in addition to the steps of the first
`aspect. (e) prohibiting the correction in step (c) if the
`detected engine load is in a lowfmedium range.
`'I‘hethirdaspectalsoprovidesanapparahrshaving.in
`addition to the components d the first :15pr a prohibition
`unit for prohibiting the correction carried out by the load
`corrector if the detected engine load is in a lowhneditun
`range.
`The first aspect corrects an engine load in any range
`awn-ding to atmospheric pressure to maintain the output of
`the engine when driving at high altitudes. If such a correc-
`tion is can-led out under a lowimedinm engine load the
`quantity of internally recirculated exhaust gas of an internal
`exhaust gas recirculation (EGR) systemwill increase exces-
`sively to cause incomplete combustion. The internal EGR
`system is employed to improve exhaust gas purifying per-
`formance and reduce pimping loss and fuel consumption.
`Accordingly,
`the third aspect prohibits the engine load
`correction under a lcwfmodium engine load. thaeby pre-
`venting an excessive amount of exhaust gas being recircu~
`lated.
`
`invention provides a
`A fourth aspect of the peanut
`methodincludingthestep ctinndditiontothestepsofthe
`first aspect. (e) correcting the target valve timing set in step
`(d) to an intermediate value between the target valve timing
`and valve timing determined according to the detected
`engine load. if the detected engine load is in a lowfmedium
`range.
`The fourth aspect also provides an apparatus having. in
`addition to the components of the first aspect. a timing
`connector for curecfing the target valve timing Set by the
`timing setter to an intermediate value bettveen the target
`
`10
`
`15
`
`20
`
`35
`
`45
`
`SS
`
`65
`
`

`

`5,713,317
`
`3
`valve timing and valve timing determined awarding to the
`engine load detected by the load detectu. if the detected
`engine load is in a lowlmedium range.
`The third aspect simply prohibits the engine load correc-
`tion according to atmospheric present if the engine load is
`in a lowl‘medium range. When driving at high altitudes. the
`negative pressure of an intake duct of the engine decreases
`to reduce the quantity of internally recirctrlated exhaust gas.
`Accordingly. we {ctn‘th aspect corrects the engine load
`according to atmospheric pressure. to optimize the quantity
`of recirwlated internal exhaust gas at high altitudes undo"
`the lowlrrtedium engine load.
`
`BRIEF DESCRH’I'ION OF THE DRAWINGS
`
`5
`
`10
`
`15
`
`Further features and advantages of the present invention
`will be apparent from the following description with refer~
`ence to the accompanying drawings. in which:
`FIG. 1 is a general view showing an elemonimlly con-
`trolled internal combustion engine having an apparatus for
`continuously and variably controlling valve timing accord-
`ing to an embodiment of the present invention;
`FIG. 2 is a block diagram showing an electronic engine
`control unit according to the embodiment;
`FIG. 3 is a timing chart showing crank angles representing
`the openlclose timing of intake and exhaust valves;
`FIG. 4 is a map used to determine a displacement to be
`imposed on the openlclcse timing of an intake valve accord—
`ing to the revolution speed and load of an engine (the load
`being represented by the mass of intake air per revolution);
`FIG. 5 is a graph showing the relationship between an
`engine load and a target displacement to be imposed on the
`openlclose timing of an intake valve at an engine greed (NE)
`of 2000 rpm;
`FIG. 61's agrapbexplaining acmecticnofan enginelcad
`according to atmospheric pressure according to a first
`embodiment of the present invention;
`FIG. 7 is a flowchart showing a routine of variably
`controlling the openfclose timing or“ a valve according to the
`first embodiment;
`
`FIG. 8 is a map used to determine an atmospheric pressure
`correction coeficient Kpa according to an engine load GN:
`FIG. 9 is a flowchart showing a routine of variably
`controlling the openiclose timing of a valve according to a
`second embodiment of the present invention:
`FIG. 10isamapuscdtodeterrnineanahnosphtric
`[rename correction coeflicient Lpa according to a displace-
`ment to be imposed on the openl'close timing of an intake
`valve;
`FIG. 11isagraphexp1ainingaeoarectionofanengine
`load according to stratospheric pressure according to a third
`embodiment of the present invention;
`FIG. 12 is a flowchart showing a routine of variably
`connolling the openlclose timing of a valve according to the
`third embodiment;
`
`FIG. 13 is a graph showing the relationship between an
`engine load and a displacement to be imposed on the
`openiclose timing of an intake valve at
`low altitudes
`(IVTDG) and high altitudes (IVTDpn);
`FIG. 14 is a graph explaining a correction of an engine
`load according to annosphtx‘ic pressure according to a {cloth
`embodiment of the present invention; and
`FIG. 15 is a flowuhart showing a routine of variably
`controlling the open/close timing of a valve according to the
`fotn'th embodiment.
`
`35
`
`45
`
`55
`
`4
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`invention will be
`The embodiments of the present
`explained with reference to the drawings.
`FIG. 1 is a general view showing an electronically con-
`trolled internal combustion engine having an apparatus for
`continuously and variably controlling the qrenlclose timing
`of a valve according to an embodiment of the potent
`invention. An air cleaner 2 filters air necessary for
`combustion. a throttle body 4 passes the air. and a surge tank
`(intakemanitoldlfidisnibutesdteahtcanintalteduct'lof
`each cylinder. A throttle valve 5 arranged in the throttle body
`4 adjusts the quantity of intake air. An airflow meter 40
`measures the mass flow rate of intake air. A temperature
`sensor 43 detects the teammture of intake air. A vacuum
`sensor 41 deteas the treasure of the intake duct 7. An
`atmospheric presstn'e sensor 46 is arranged so that it is not
`influenced by wind pressure during driving
`Athrottlesensor42detectstheopening ofthe dtrottle
`valve 5. When the throttle valve 5 is completely closed. an
`idle switch 52 is turned on to generate a throttle closed
`signal. An idling adjusting path 8 bypasses the throttle valve
`5 and has an idling speed control valve (ISCV) 66 for
`adjusting an airflow rate dining an idling period.
`Fuelinafireltankltispumpedupbyafuelpump 11. is
`passed through a fuel pipe 12. and is injected by a fuel
`injector 60.
`The intake duct 7 mixes fuel with air. and the air-fuel
`mixture is drawn into a combustion chamber 21 of a cylindu'
`20 through an intake valve 24. The air-fuel mixun'e is
`compressed by a piston 23. ignited. exploded. and corn-
`busted to produce power. Namely. an ignite: 62 generates an
`ignition signal to control a [rimary current of an ignition coil
`63. A secondary current of the ignition coil 63 is supplied to
`a spark plug 65 through an ignition distributor 64. to thereby
`ignite the air-fuel mixture in the combustion chamber 21.
`The ignition distributor 64 has a reference position sensor
`50 and a crank angle sensor 51. The reference position
`sensor 50 generates a rderence position pulse for every 720
`degrees ofcrank angle. The u-ank angle sensor 51 generatw
`a position pulse for every 30 degrees of crank angle. A
`vehicle speed sensor 53 generates a pulse representing an
`actual running speed. A cooling water path 2 guides cooling
`water to cool the engine 20. A water temperann'e sensor 44
`deterxs the temperature of the cooling warm
`An exhaust valve 26 discharges an exhaust gas of the
`combusted air-fuel mixttn‘e into an exhaust manifold 30
`connectedtoanexhaustpipefidflhe exhaustpipe34hasan
`0, sensor 45 to detect the concentration of oxygen in the
`exhaust gas. A catalytic converter 38 is arranged in the
`exhaust pipe 34 downstream from the sensor 45. The cata-
`lytic converter 38 contains a three-way catalyst for promot-
`ing the oxidization of unburned components such as HC and
`CD as well as the reduction of nitrogen oxides (NO). The
`purified exhaust gas from the catalytic converter 38 is
`discharged outside.
`Amechanisrn for opening and closing the intake valve 24
`and exhaust valve 26 will be explained. The piston 23 is
`connected to a u'ankshaft 81 thrmgh a connecting rod 80.
`Anendofthecrankshaftslhasatimingpulleysd.'l'he
`intake valvezdis (hivenbyacamflattadredtoacamahaft
`85. The exhaust valve 26 is driven by a earn 88 attached to
`acamshaft86.AnendofthecamshaftBShasatiming
`pulley89.Anendofthecamshaftfléhasatimingpulleyfl.
`The timing pulleys 89 and 90 are connected to the timing
`
`

`

`5
`
`6
`
`5,713,317
`
`pulleylldlhrough atimingbelt9l.Asaresnlt.thecranksbaft
`81 drives the cam shafts 85 and 86 to open and close the
`intake valve 24 and exhaust valve 26 at predetermined mnk
`angles. The crank shaft 81 has a buried magnet 82. so that
`a first magnetic sensor 54 arranged close to the mnkshaft 81
`may generate a refine-nee pulse. The cam shaft 85 of the
`intakevalve 24hasa buriedmagnet93. sothata second
`magnetic sensor 55 arranged close to the cam shaft 85 may
`generate a reference pulse.
`A continuously variable medianism 92 having a known
`shuaure to determine the openiclose timing of the intake
`valve 24 is arranged between thecam mess and the liming
`pulley89.1hemed1anism92ntrusthecamshaft85and
`timing pulley 89 relative to each other. More precisely. the
`mechanism92usesthccamshaft85andtimingpulleyfl9as
`external gears and connects them to each other through an
`intermediate helical gear. The helical gear is axially moved
`by hydraulic pressure. to drive the cam shaft 85 and timing
`pulley 89 relative to each other. The hydraulic pressure is
`controlled by a control valve 68.
`An electronic engine control unit (ECU) 70 is a micro-
`conrputa to control fuel injection. ignition timing. idling
`speed. and in addition. the openlclose timing of a valve
`according to the present invention. FIG. 2 is a block diagram
`showing the hardware of the control unit 70. A read-only
`memory (ROM) 73 stores programs and maps. A central
`processing unit (CPU) 71 receives signals from the sensors
`and switches through an AD converter 75 and an interface
`76. processes the signals. and provides actuator control
`signals through drive control circuits 77a to 77.4. A random-
`access memory (RAM) 74 temporarily stores data during the
`operation of the CPU ‘71. These elements are connected to
`one another through a system bus 72 containing address.
`data. and control buses.
`
`An engine control process carried out by the control unit
`70 will be explained
`Fuel injection control refers to the mass of intake air pa
`engine revolution. calculates the fuel injection quantity. i.e..
`injection period of the fuel injector 60 to achieve a target
`air-fuel ratio. and instructs the drive control cirorit 77a to
`inject fuel from the fuel injector 60 at a given crank angle.
`The mass of intake air per engine revolution is calwlated
`acocrdingtomemassflowrateofintakeairmeasuredbythe
`airflow meter 40 and an engine revolution speed detected by
`the crank angle sensor 51. Alternatively.
`it is estimated
`according to the pressure of the intake tluct‘ll detected by the
`vacuum senstr 41 and the engine revolution speed The fuel
`injection quantity is subjectedto corrections such as a basic
`correction according to signals from the ductile senses 42.
`intake temperature sensor 43. water temperature sensor 44.
`etc. an air-fuel ratio feedback correction acctl'ding to a
`signal from the 02 sensor 45. and an air-fuel ratio learning
`correction to equalize a central feedback median value
`with a theoretical air-fuel ratio.
`
`Ignition timing control collectively checks engine condi-
`tions according to an engine revolution speed detected by
`the crank angle sensor 51 and signals from other sensors,
`calculates optimum ignition timing. and govides an ignition
`signal to the igniter 62 through the drive control circuit 77b.
`Idlingspeedcontroldetectsanidling stateaccordingtoa
`throttle closed signal from the idle switch 52 and a vehicle
`speed signal from the vehicle speed Sense: 53. calculates a
`target revolution speed according to the temperature of
`cooling water measured by the water temperature sensor 44.
`compares the target speed with an actual revolution speed.
`determines a control quantity to attain the target revolution
`
`speed according to the difa'ence between the target and
`neural revolution speeds. and controls the idling speed
`control valve 66 though the drive control ciratit 770. to
`thueby adjust the quantity of air and optimize the idling
`speed.
`Valve timing control sets the target openlclose timing of
`the intalm valve 24 amrding to cperating conditions and
`controls the continuously variable mechanism 92. More
`precisely.
`the hydraulic pressure control valve 68 is
`feedback-controlled awarding to signals from the first and
`second magnetic sensors 54 and 55 so that the cam shaft 85
`of the intake valve 24 maintains a required rotational phase
`with respect to the o'anlrshai’t 81. The valve timing control
`according to the present invention will be explained. in
`detail.
`
`10
`
`15
`
`FIG. 3 is a timing chart showing crank angles correspond-
`ing to the openlclose timing of the intake and exhaust valves
`21 and 26. The exhaust valve 26 is opened at fixed valve
`open timing EVO. for example. 50 degrees before a bottom
`exhaust dead center and is closed at fixed valve close timing
`BVC. for exanrple. 3 degrees after a top exhaust dead center.
`On the other hand. the intake valve 2:! involves a fixed open
`period and variable valve opening timing IVO and valve
`close timing NC. The most delayed timing “(Or and NC:-
`of the intake valve 24 serve as reference positions. The
`open/close timing of the intake valve 24 is optionally set at
`positions ahead of the reference positions. A valve timing
`displacement IVTD serves as a control target quantity. The
`reference valve open timing “Dr is. for example. 3 degrees
`sits the top exhaust dead center. and the reference valve
`close tithing NC: is. for example. 65 degrees after a bottom
`intake dead center If the displacement IVTD is equal to a
`crank angle of 30 degrees. the valve open timing NO is 27
`degrees before the top exhaust dead center. and the valve
`close timing NC is 35 degrees after the bottom intake dead
`center.
`
`FIG. 4 is a mapusedtodetermine adisplacement IVTD
`for optimizing the openfclose timing of the intake valve 24.
`The displacement NT!) is determined according to an
`engine revolution speed NE and an engine load GN. Le.. the
`mass of intake air pa- engine revolution.
`FIG. 5 is a graph showing the relationship behveen an
`engine load GN and a displacement IVTD with NE=2000
`rpm. In a lowhnedium range (GER—1.2 gfrev). a valve
`overlapping pa'iod in which the intake and exhaust valves
`arebcthopenisintreasedtoincreasethequantityof
`internally recirculated exhaust gas.
`to thereby improve
`exhaust gas ptnifying performance and deucase a pimping
`loss to reduce fuel consumption. To achieve this. the dis-
`placementNl‘Disgraduallyincreasedlnahighrange
`(GNé—lj ghev). the displacement IVTD is adjusted to
`improve the output of the engine. When GN=2.0 girev
`corresponding to a full tln'ottle condition. the displacement
`WTDissettoamnkangleoffldegrees.
`Values of FIGS. 4 and 5 are for low altitudes. At high
`altitudes. air concentration is low to reduce the quantity of
`intake air. When driving at lost.r altitudes with NE=2000rprn
`and if the tla'otde valve 5 is fully opened. the quantity of
`intake air is 2.0 gj‘rev as shown in FIG. 5. Namely. if GN=2.0
`ghev, it is determined that the throttle valve Sis fully opened
`and that high culprit is required. To meet the requirement.
`the displacementNI‘D is set tc40degrees in a-aukangle.
`Athighaltimdes.flrequanfitycfintakeairis.forexample.
`1.6 gfrev even if the throttle valve 5 is fully opened. If the
`displacement IVTD is calculated normally under this
`situation. it will be 50 degrees in crank angle as showu in
`
`35
`
`45
`
`50
`
`55
`
`

`

`7
`
`5,713,317
`
`8
`
`[G
`
`15
`
`35
`
`45
`
`Step 212 curects the displacement M130 and provides
`a target displacement IVTDt as follows:
`
`Hans—mun
`
`To bring the actual displacement of the intake valve 24 to the
`target displacement film. the hydraulic control valve 68 is
`feedback-contented.
`'I‘hcthirdembodiroeutaoccrdingtothethirdaspectcfthe
`present invention will he explained The first embodiment
`corrects an engine load in any range according to atmo-
`spheric pressrne. If this correction is made when the engine
`load is in a lowimediurn range. a valve overlapping paiod
`increases to excessively increase the quantity of internally
`recirculated exhaust gas.
`to deteriorate combustion.
`Accordingly. the third unbodiment prohibits the engine load
`correction based on atmospheric pressure if the engine load
`is in the lowlmedirnn range. As indicated with a ctuve C3 of
`FIG. 11. the third embodiment largely corrects an engine
`load when the engine load is in a high range with armo-
`spheric pressure being low. However.
`it carries out no
`couect'ton if the engine load is in the lowfmedium range.
`Curves C1 and C2 of FIG. 11 correspond to the curves C1
`and C2 of FIG. 6.
`FIG. 12 is a flowchart showing a variable valve timing
`(WT) control routine acctrding to the third embodiment.
`Stepsil.2to312arethe sameassteps 102m 112ofthefirst
`embodiment of FIG. 7. Step 314 refers to the map of FIG.
`4 according to the engine load GN and engine revolution
`speedNE. andfinds adisplaccmcntNTDtltobcimposedon
`the openfclose timing of the intake valve 24.
`Step 316 compares the displacement IVTDpa of step 312
`with the displacement. IVTDO of step 314 and determines
`whether the engine load is in a lowlmcdiurn range or in a
`high range. The reason why this comparison can determine
`a load range will be explained. As a displacement to be
`imposed on the openlclose timing ofthe intake valve 24
`inn-eases. the quantity of internally redrculated exhaust gas
`increases. and an allowable quantity of internally recircu-
`lated exhaust gas incream as the engine load increases.
`Acctrdingly. a maximumvalve timing displacement is in the
`high load range in principle However. if the maximum
`valve timing displacement is kept until the throttle valve 5
`is frilly opened. combustion will deteriorate to lower the
`output of the engine. Accordingly. the valve timing displace-
`ment is adjusted to realize a required engine output in the
`'gh load range. As a result the displacement map has a
`maximum in the middle load range. This is the reason why
`the displacement IVTDpa corrected for high altitudes is
`compared with the displacement IVTDO without correction.
`as shown in FIG. 13. Then. it is determined as follows:
`
`if IV'I‘Dpa>IV'1"D0 then engine load is in lowfmedium
`range
`
`FIG. 5. This displacement will never provide high output. It
`ispreferableto setIVI‘D=4-0degreesin crankangleathigh
`altitudes if the throttle valve 5 is fully cpened. l-Iigh-altimde
`corrections of atmospheric pressure and air concentration
`will be explained accreding to four embodiments of the
`present invention.
`The first embodiment accta'dr‘ng to the first aspect of the
`present invention will he explaincd. The first embodiment
`increases an engine load as a detected annnspha'ic pressure
`becomes lower. to maintain the output of the engine at high
`altitudes unda' a high load. A curve C1 of FIG. 6. which is
`equal to the curve C] of FIG. 5. is proper when driving at
`low altixudes. Atmospheric pressure is low at high altitudes.
`and therefore. the present invention employs a curve C2 of
`FIG. 6 to correct an engine load GN.
`FIG. 7 is a flowchart showing a variable valve timing
`(VVT) control routine according to the first embodiment.
`This routine is carried out regularly. Step 102 reads an
`engine revolution speed NE. calculach according to the
`output of the crank angle sensor 51. Step 104 reads an engine
`load (the mass of intake air pu- engine revolution) calculated
`acoordingto dremassfiowrateofintakeairdetcctedbythe
`airflow meter 4. and the engine revolution speed provided
`by the crank angle sensor 51. Step 106 reads an ahnosphn-ic
`pressure PA detected by the atmospheric pressure sensor 46.
`SteplflireferstoamapofFIG.8acctrdiugtcthe
`atmospheric pressure PA and finds an atmospheric pressure
`(air concentration) eta-rection coeflicient Kpa. The coeffi-
`cient Kpa is 1.0 at low altitudw with PA==760 mmflg and
`decreases as the altitude increases. Le.. as the stratospheric
`presstne PA decreases. The map of FIG. 8 is stored in the
`ROM 73 in advance. Step 110 calculates an engine loarl
`GNpa after the atmospheric pressure correction as follows:
`GNpat—flhb'xpa
`
`Step 112 refers to the map of FIG. 4 according to the
`engine load GNpa and engine revolution speed NE. to find
`a displacement IVTDpa to be imposed on the openlclose
`timingoftheintakevalvezll.'1‘hemapofFIG.-Iisalso
`stored in the ROM 73 in advance.
`Step 114 sets the displacement mm as a target dis-
`placement IVTDt. To bring an actual displacement to the
`target displacement mm. signals from the first and second
`magnetic sensors 54 and 55 are monitored to feedback-
`control the hydraulic pressure control valve 68.
`The second embodiment according to the second aspect of
`the present invention will be explained. The second embodi—
`ment sets a target displacement to be imposed on the
`openlclose timing of the intake valve 11 according to a
`detected engine load and decreases the target displacement
`as an atmospheric measure becomes lower. to maintain the
`output of the engine at high altitudes under high load. similar
`to the first embodiment. FIG. 9 is a flowchart showing a
`variable valve timing (WT) control routine according to the
`secondembcdimenLStepthoMarethesameasstqas
`102 to 106 of the first embodiment of FIG. 7.
`Stein 208 refers to a map of FIG. 10 according to the
`atmospheric pressure PA and finds a correction coefliciem
`Lpa for correcting a displacement to be imposed on the
`opem’close timing of the intake valve 24. The ccrrection
`coefl‘icient Lpa is 1.0 at. low altitudes with PA=760 mmHg
`and decreases as the altitude increases. i.e.. as the anno-
`spheric pressure PA derreases. The map of FIG. 10 is stored
`in the ROM ’13 in advance. Step 210 refers to the map of
`FIG. 4 according to the engine load GN and engine revo-
`lution speed NE and finds a displacement IVTDO to be
`imposed on the openlclcse timing of the intake valve 24.
`
`55
`
`65
`
`if MDpas—IVTDO then engine load is in high range
`If it is determined that it is in the lowlmedium range. step
`318 sets the displacement IV‘TDtl as a target displacement
`IV'I‘Dtlfitis determinedthatitisinthehighrange. step320
`sets the displacement IVTDpa as the target displacement
`IVTDt. Step 32 feedback-controls the hydraulic pressure
`control val