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(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: 02.09.2009 Bulletin 2009/36

(21) Application number: 09007860.1

(22) Date of filing: 01.08.2005

(51) Int Cl.:F02D 41/02 (2006.01) F02P 5/15 (2006.01)

F02P 5/152 (2006.01) F02D 41/14 (2006.01)

B60W 30/18 (2006.01) F02D 41/00 (2006.01)

F02D 41/08 (2006.01) F02D 41/16 (2006.01)

(84) Designated Contracting States: DE FR GB IT

(30) Priority: 04.08.2004 JP 2004228103

(62) Document number(s) of the earlier application(s) in accordance with Art. 76 EPC: 05254808.8 / 1 624 173

(71) Applicants: • Toyota Jidosha Kabushiki Kaisha

Toyota-shi, Aichi-ken 471-8571 (JP)• Bosch Corporation

Shibuya-kuTokyo 150-8360 (JP)

(72) Inventors: • Amano, Naoki

Toyota-shiAichi-ken 471-8571 (JP)

• Otsubo, MassakiToyota-shiAichi-ken 471-8571 (JP)

• Yamazaki, AkinoriShibuya-kuTokyo 150-8360 (JP)

• Hatakeyama, TomohiroShibuya-kuTokyo 150-8360 (JP)

(74) Representative: Smith, Samuel LeonardJ.A. Kemp & Co. 14 South Square Gray’s InnLondon WC1R 5JJ (GB)

Remarks: This application was filed on 16-06-2009 as a divisional application to the application mentioned under INID code 62.

(54) Torque calculation method for engine

(57) A torque calculation method for an engine (100)connected to an automatic transmission (300), whereintorque of the engine (100) is controlled based on firstengine torque that is calculated based on a rotationalspeed of the engine (100); and the first engine torque iscorrected so that the rotational speed during idling be-comes equal to a predetermined rotational speed, thetorque calculation method being characterized by com-prising:calculating second engine torque which is used for con-trol of the automatic transmission (300), based on thefirst engine torque; andcorrecting the second engine torque based on a correc-tion amount of the first engine torque.

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Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a torque calculationmethod for an engine, and more particularly to a torquecalculation method for an engine connected to an auto-matic transmission.

2. Description of the Related Art

[0002] Vehicles provided with an engine connected toan automatic transmission have been sold. In such a ve-hicle, control of the automatic transmission needs to beperformed in harmony with an operating state of the en-gine. Therefore, information on engine torque is neces-sary for the control of the automatic transmission.[0003] Japanese Patent Application Publication No.JP (A) 2003-120801 discloses a power transmission ap-paratus which accurately calculates output torque of anengine. The power transmission apparatus disclosed inthe Japanese Patent Application Publication No. JP (A)2003-120801 includes a shifting mechanism which trans-mits rotational driving force of an engine while changinga speed thereof; a parameter setting device which vari-ably sets a control parameter for controlling operation ofthe shifting mechanism; a reference indicated torque cal-culating portion which calculates reference indicatedtorque of the engine in a reference operating state, basedon a rotational speed and a load of the engine; an actualindicated torque calculating portion which calculates ac-tual indicated torque that is generated in an actual oper-ating state, by correcting the reference indicated torquebased on a difference between an operating parameterin the actual operating state of the engine and an oper-ating parameter in the reference operating state of theengine; a friction torque calculating portion which calcu-lates friction torque of the engine based on the rotationalspeed and the load of the engine; and a net torque cal-culating portion which calculates net torque of the engineby subtracting the friction torque calculated by the frictiontorque calculating portion from the actual indicatedtorque calculated by the actual indicated torque calculat-ing portion. The parameter setting device sets the controlparameter according to the net torque calculated by thenet torque calculating portion.[0004] In the power transmission device disclosed inthe publication, the actual indicated torque is calculatedby correcting the reference indicated torque in the refer-ence operating state (i.e., the operating state based onthe reference operating parameter), on the basis of thedifference between the operating parameter in the actualoperating state and the operating parameter in the ref-erence operating state. Thus, no matter what operatingparameter is used (that is, even in the case where theoperating parameter is changed), it is possible to accu-

rately calculate the actual indicated torque that is actuallygenerated by the engine. In this case, only the referenceindicated torque in the reference operating state and acorrection coefficient for the operating parameter arenecessary. Therefore, only a small amount of data is nec-essary for calculating the actual indicated torque. Thus,only small capacity of storage media (i.e., small capacityof ROM) is required. The net torque is calculated by sub-tracting the friction torque of the engine from the actualindicated torque that is calculated in the aforementionedmanner. Thus, no matter what operating parameter isused, it is possible to accurately calculate the net torque.On the basis of the net torque, the parameter setting de-vice sets the control parameter for controlling the oper-ation of the shifting mechanism. Thus, it is possible toaccurately set, for example, engagement capacity of aclutch in the shifting mechanism, which is set using thecontrol parameter.[0005] However, the net torque calculated by the pow-er transmission apparatus disclosed in the aforemen-tioned Japanese Patent Application Publication No. JP(A) 2003-120801 is not necessarily appropriate for thecontrol of the automatic transmission. For example, incontrol of the engine, ignition timing may be changed.When the ignition timing is changed, the indicated torque(i.e., the torque generated by the engine) is suddenlychanged. Since the indicated torque is suddenlychanged, the net torque (the torque transmitted from theengine to the automatic transmission) that is calculatedbased on the indicated torque is suddenly changed.Thus, it is not necessarily appropriate to control the au-tomatic transmission based on such net torque.[0006] Further, since it is difficult to accurately obtainthe friction torque, the friction torque is set to a value thatis the most convenient when used for the control of theengine, among values in a variation range of the frictiontorque. For example, the friction torque is estimated at ahigh value in the variation range when the engine oper-ating state is in a region where an engine stall may occur.When the net torque is calculated by subtracting suchfriction torque from the actual indicated torque, accuracyof the net torque is deteriorated. Thus, it is not necessarilyappropriate to control the automatic transmission basedon such net torque.[0007] Further, in the control of the engine, fuel supplyto the engine is stopped (i.e., fuel cut is performed), forexample, when the engine is idling during running. Evenduring idling, stop of the fuel supply may be prohibitedaccording to request from the automatic transmission. Inthis case, when stop of the fuel supply that has beenprohibited is permitted, the fuel supply is stopped. There-fore, the indicated torque is suddenly changed. As a re-sult, the net torque is suddenly changed. It is not neces-sarily appropriate to control the automatic transmissionbased on such net torque.[0008] Further, in the control of the engine, the torqueof the engine is controlled based on a torque correctionamount that is calculated by idle speed control (herein-

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after, referred to as "ISC") based on a difference betweenan actual rotational speed during idling and a target ro-tational speed during idling. Therefore, the indicatedtorque includes the torque correction amount that is cal-culated by the ISC. Accordingly, the net torque includesthe torque correction amount that is calculated by theISC. It is not necessarily appropriate to control the auto-matic transmission based on such net torque.

SUMMARY OF THE INVENTION

[0009] The invention relates to a torque calculationmethod for an engine, which can calculate torque that isappropriate for control of an automatic transmission.[0010] A first aspect of the invention relates to a torquecalculation method for an engine connected to an auto-matic transmission. Plural cylinders are provided in theengine, and torque in each of the cylinders is controlledby changing ignition timing based on at least one of achange in a rotational speed of the engine and knockingof the engine. The torque calculation method includes astep of calculating first engine torque based on the rota-tional speed of the engine and the ignition timing in eachof the cylinders; and a calculation step of calculating sec-ond engine torque which is used for control of the auto-matic transmission by performing a smoothing processfor the first engine torque based on a change amount ofthe ignition timing in each of the cylinders.[0011] According to the first aspect of the invention,the first engine torque (for example, actual indicated en-gine torque) is calculated based on the rotational speedof the engine. The actual indicated engine torque istorque that is actually generated by the engine. The ac-tual indicated engine torque is changed when the ignitiontiming is changed in order to suppress hunting of theengine rotational speed or to suppress occurrence ofknocking. For example, the actual indicated enginetorque is repeatedly calculated, and the second enginetorque (actual net engine torque) is calculated by per-forming the smoothing process, that is, by adding, to theactual indicated engine torque that was calculated lasttime, an additional value that is calculated based on adifference between the actual indicated engine torquethat was calculated last time, and the actual indicatedengine torque that is calculated this time. The actual netengine torque is torque that is actually transmitted fromthe engine to the automatic transmission. For example,the additional value becomes smaller as the changeamount of the ignition timing becomes larger. Thus, evenin a case where a change amount of the actual indicatedengine torque is large, it is possible to obtain the actualnet engine torque that is smoothly changed, by perform-ing the smoothing process. Accordingly, it is possible tosuppress a sudden change in the actual net enginetorque. As a result, it is possible to provide the torquecalculation method for an engine, which makes it possibleto calculate the torque appropriate for the control of theautomatic transmission.

[0012] According to a second aspect of the invention,in the torque calculation method for an engine accordingto the first aspect of the invention, the first engine torqueis repeatedly calculated. The calculation step includes astep of calculating the second engine-torque by adding,to the first engine torque that was calculated last time,an additional value that is calculated based on a differ-ence between the first engine torque that was calculatedlast time and the first engine torque that is calculated thistime. The torque calculation method further includes astep of calculating the additional value such that the ad-ditional value becomes smaller as the change amount ofthe ignition timing becomes larger.[0013] According to the second aspect of the invention,the actual indicated engine torque is repeatedly calculat-ed. The actual net engine torque is calculated by per-forming the smoothing process, that is, by adding, to theactual indicated engine torque that was calculated lasttime, the additional value that is calculated based on thedifference between the actual indicated engine torquethat was calculated last time and the actual indicatedengine torque that is calculated this time. The additionalvalue becomes smaller as the change amount of the ig-nition timing becomes larger. Thus, even in the casewhere the change amount of the actual indicated enginetorque is large, it is possible to obtain the actual net en-gine torque that is smoothly changed, by performing thesmoothing process. Therefore, it is possible to suppressa sudden change in the actual net engine torque. As aresult, it is possible to calculate the torque appropriatefor the control of the automatic transmission.[0014] A third aspect of the invention relates to a torquecalculation method for an engine connected to an auto-matic transmission. The torque calculation method in-cludes a step of calculating first engine torque based ona rotational speed of the engine; a step of calculatingfriction torque of the engine based on a temperature ofcoolant of the engine; a step of calculating second enginetorque that is used for control of the automatic transmis-sion by subtracting the friction torque from the first enginetorque; and a step of correcting the second engine torqueso that the second engine torque is increased based ona temperature of lubricant of the engine.[0015] According to a third aspect of the invention, thefirst engine torque (for example, the actual indicated en-gine torque) is calculated based on the rotational speedof the engine. The friction torque is calculated based onthe temperature of the coolant of the engine. The secondengine torque (for example, the actual net engine torque)is calculated by subtracting the friction torque from theactual indicated engine torque.The friction torque is used for the control of the engine,as well as in the control of the automatic transmission.Since the friction torque is changed due to a change inthe temperature of the coolant and other various factorssuch as a change in a temperature of oil, a change in anamount of oil, a change in viscosity of oil, and a changeover time, it is difficult to accurately calculate the friction

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torque. Therefore, if the friction torque is calculated at alow value in a variation range, an engine stall may occur.Therefore, for example, the friction torque is estimatedat a high value in the variation range when an engineoperating state is in an operating region where an enginestall or the like may occur. Accordingly, the actual netengine torque is calculated at a value lower than enginenet torque that is actually transmitted from the engine tothe automatic transmission. Therefore, the calculated ac-tual net engine torque is corrected to be increased basedon the temperature of the lubricant of the engine. Thus,it is possible to improve the accuracy of the actual netengine torque. Accordingly, the automatic transmissioncan be controlled using the accurate actual net enginetorque. As a result, it is possible to provide the torquecalculation method which makes it possible to calculatethe torque appropriate for the control of the automatictransmission.[0016] According to a fourth aspect of the invention,the torque calculation method for an engine according tothe third aspect of the invention further include a coolanttemperature detecting step of detecting the temperaturesof the coolant of the engine at plural time points includinga time point at which the engine is started; and a step ofdetecting the temperature of the lubricant of the engine,based on the temperatures of the coolant, which are de-tected at the plural time points including the time point atwhich the engine is started.[0017] According to the fourth aspect of the invention,the temperatures of the coolant of the engine are detect-ed at the plural time points including the time point atwhich the engine is started. The temperature of the lu-bricant varies depending not only the temperature of thecoolant at present but also on the temperature of thecoolant at the time point when the engine is started.Therefore, the temperature of the lubricant of the engineis detected based on the temperatures of the coolant,which are detected at the plural time points including thetime point at which the engine is started. Thus, it is pos-sible to accurately detect the temperature of the lubricant,and to accurately correct the actual net engine torque.[0018] According to a fifth aspect of the invention, inthe torque calculation method for an engine according toany one of the first aspect to the fourth aspect of theinvention, fuel supply to the engine is stopped when apredetermined condition is satisfied; and the second en-gine torque is calculated considering the number of thecylinders for which fuel supply has been stopped.[0019] According to the fifth aspect of the invention, itis possible to calculate the actual net engine torque, forexample, by multiplying the actual indicated enginetorque by (KA - KB) / KA, considering the number of thecylinders for which fuel supply has been stopped. KA isthe number of all the cylinders, and KB is the number ofthe cylinders for which fuel supply has been stopped.Thus, it is possible to improve the accuracy of the actualnet engine torque.[0020] A sixth aspect of the invention relates to a torque

calculation method for an engine connected to an auto-matic transmission. When a predetermined first conditionis satisfied, fuel supply to the engine is stopped. Whena predetermined second condition relating to the auto-matic transmission is satisfied, stop of the fuel supply isprohibited. The torque calculation method include a stepof calculating first engine torque based on a rotationalspeed of the engine; a step of determining whether stopof the fuel supply is being prohibited; and a step of settingthe first engine torque to torque for a case in which thefuel supply is stopped, and calculating second enginetorque which is used for control of the automatic trans-mission, based on the first engine torque, in a case wherestop of the fuel supply is being prohibited.[0021] According to the sixth aspect of the invention,the first engine torque (for example, target indicated en-gine torque) is calculated based on the rotational speedof the engine. The target indicated engine torque is atarget of the torque generated by the engine. For exam-ple, when the fuel supply to the engine is stopped whilethe engine is idling, the target indicated engine torquebecomes equal to the target indicated engine torque forthe case where the fuel supply is stopped (i.e., 0 N·m).Meanwhile, when the engine needs to race in order tosynchronize the engine rotational speed and the rotation-al speed of the input shaft of the transmission, or to syn-chronize the rotational speed of the input shaft of thetransmission and the rotational speed of the output shaftof the transmission during shifting, stop of the fuel supplyis prohibited. In the case where stop of the fuel supply isbeing prohibited, even when the engine is idling, the fuelsupply is not stopped, and the target indicated enginetorque does not become 0 N·m. In this case, when shiftingis completed and stop of the fuel supply that has beenprohibited is permitted, the fuel supply is stopped uponcompletion of shifting, and the target indicated enginetorque becomes 0 N·m. When the target indicated enginetorque is suddenly changed upon completion of shifting,the second engine torque (for example, target net enginetorque) that is calculated based on the target indicatedengine torque is suddenly changed. The target net en-gine torque is a target of the torque that is transmittedfrom the engine to the automatic transmission. A suddenchange in the target net engine torque is undesirable forthe control of the automatic transmission. Therefore, inthe case where the fuel supply is being prohibited, thetarget indicated engine torque is set to the value for thecase where the fuel supply is stopped, and the target netengine torque is calculated based on the target indicatedengine torque. Thus, in the case where the fuel supplyis being prohibited, it is possible to calculate the targetnet engine torque for the case where the fuel supply isstopped. Therefore, when stop of the fuel supply that hasbeen prohibited is permitted, it is possible to suppress asudden change in the target net engine torque. As a re-sult, it is possible to provide the torque calculation methodfor an engine, which makes it possible to calculate thetorque appropriate for the control of the automatic trans-

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mission.[0022] According to a seventh aspect of the invention,in the torque calculation method for an engine accordingto the sixth aspect of the invention, the first condition isa condition that the engine is idling; and the second con-dition is a condition that shifting of the automatic trans-mission is being performed. According to the seventhaspect of the invention, in a case where the engine isidling but stop of the fuel supply is being prohibited sinceshifting is being performed, it is possible to calculate thetarget net engine torque for the case where the fuel sup-ply is stopped. Thus, when stop of the fuel supply thathas been prohibited is permitted upon completion of shift-ing, it is possible to suppress a sudden change in thetarget net engine torque.[0023] An eighth aspect of the invention relates to atorque calculation method for an engine connected to anautomatic transmission. Torque of the engine is control-led so as to be equal to first engine torque that is calcu-lated based on a rotational speed of the engine. The firstengine torque is corrected so that the rotational speedduring idling becomes equal to a predetermined rotation-al speed. The torque calculation method includes a stepof calculating second engine torque which is used forcontrol of the automatic transmission, based on the firstengine torque; and a step of correcting the second enginetorque based on a correction amount of the first enginetorque.[0024] According to the eighth aspect of the invention,the second engine torque (for example, the target netengine torque) is calculated based on the first enginetorque (for example, the target indicated engine torque)which is calculated based on the rotational speed of theengine. The torque of the engine is controlled based onthe target indicated engine torque. The target indicatedengine torque is corrected so that the rotational speedduring idling becomes equal to the predetermined rota-tional speed. Therefore, the target net engine torque ischanged according to the correction amount of the targetindicated engine torque. Since the target net enginetorque is changed based on the rotational speed duringidling, the change in the target net engine torque doesnot reflect driver’s intention. Therefore, the change in thetarget net engine torque is not desirable for the automatictransmission, which needs to be controlled reflecting thedriver’s intention. Accordingly, the target net enginetorque is corrected based on the correction amount ofthe target indicated engine torque, for example, by sub-tracting torque equivalent to the correction amount fromthe target net engine torque. Thus, it is possible to ex-clude the torque equivalent to the correction amount in-cluded in the target net engine torque. Therefore, it ispossible to obtain the target net engine torque reflectingthe driver’s intention. As a result, it is possible to providethe torque calculation method for an engine, whichmakes it possible to calculate the torque appropriate forthe control of the automatic transmission.[0025] According to a ninth aspect of the invention, in

the torque calculation method for an engine according toany one of the first aspect to the eighth aspect of theinvention, the rotational speed of the engine during idlingis controlled so as to be equal to a predetermined rota-tional speed, based on a predetermined torque correctionamount which is set based on the rotational speed; andthe second.engine torque is calculated considering thepredetermined torque correction amount.[0026] According to the ninth aspect of the invention,the rotational speed of the engine during idling is control-led so as to be equal to the predetermined rotationalspeed based on the predetermined torque correctionamount (for example, idling torque deviation learning val-ue) which is set based on the rotational speed. The idlingtorque deviation learning value is an integration term forthe torque correction amount that is calculated based ona deviation between the actual rotational speed duringidling and the target rotational speed during idling. Theidling torque deviation learning value is stored in a com-puter as a torque deviation amount during idling. Thetorque of the engine is controlled so as to be increasedor decreased by the idling torque deviation learning val-ue. The torque correction amount based on the idlingtorque deviation learning value is used for operating theengine itself. Therefore, the torque correction amountbased on the idling torque deviation learning value is notincluded in the net torque transmitted from the engine tothe automatic transmission. Accordingly, the actual netengine torque or the target net engine torque is calculatedconsidering the idling torque deviation learning value.Thus, it is possible to improve accuracy of the actual netengine torque or the target net engine torque.[0027] A torque calculation method for an engine ac-cording to a tenth aspect of the invention is the torquecalculation method for an engine according to any oneof the first aspect to the eighth aspect of the invention,in which the second engine torque is calculated consid-ering pumping loss of the engine.[0028] According to the tenth aspect of the invention,the actual net engine torque or the target net enginetorque is calculated, considering the pumping loss thatis used for operating the engine itself, and that is notincluded in the net torque transmitted from the engine tothe automatic transmission. Thus, it is possible to im-prove accuracy of the actual net engine torque or thetarget net engine torque.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a control block diagram showing a ve-hicle including an ECU which performs computation us-ing a torque calculation method for an engine accordingto a first embodiment of the invention;[0030] FIG. 2 is a control block diagram showing anengine controlled by the ECU which performs computa-tion using the torque calculation method for an engineaccording to the first embodiment of the invention;[0031] FIG. 3 is a diagram showing a clutch;

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[0032] FIG. 4 is a flowchart showing a control structureof a program executed by the ECU which performs com-putation using the torque calculation method for an en-gine according to the first embodiment of the invention;and[0033] FIG. 5 is a flowchart showing a control structureof a program executed by the ECU which performs com-putation using a torque calculation method for an engineaccording to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EM-BODIMENTS

[0034] Hereinafter, embodiments of the invention willbe described with reference to the drawings. In the fol-lowing description, the same components are denotedby the same reference numerals. Names and functionsthereof are the same. Therefore, detailed descriptionthereof will not be repeated.

(First embodiment)

[0035] Referring to FIG. 1, description will be made ofa vehicle including an electronic control unit (hereinafter,referred to as "ECU") 500 which performs computationusing a torque calculation method for an engine accord-ing to an embodiment of the invention. The vehicle runswhen driving force generated by an engine 100 is trans-mitted to a vehicle wheel 404 via a clutch 200, a trans-mission 300, a differential gear 400, and a drive shaft402. The engine 100, the clutch 200, and the transmis-sion 300 are controlled by the ECU 500.[0036] The engine 100 is a four-cylinder gasoline en-gine. The number of the cylinders of the engine 100 maybe a number other than 4. The clutch 200 is connectedto a crankshaft 600 of the engine 100. A clutch outputshaft 202 is connected to an input shaft 302 of the trans-mission 300 via a spline 310.[0037] The transmission 300 includes a constant-mesh gear train. A shift speed of the transmission 300 isselected by sliding a shift fork shaft by an actuator 304.The actuator 304 may be operated by hydraulic pressureor by electric power. The shift speed may be selected byan actuator using a concentric slave cylinder.[0038] The ECU 500 includes an engine ECU 502, atransmission ECU 504, read only memory (hereinafter,referred to as "ROM") 506, and random access memory(hereinafter, referred to as "RAM") 508. The engine ECU502 controls the engine 100. In this embodiment, the en-gine ECU 502 controls torque of the engine 100 basedon target indicated engine torque that is set based on arotational speed of the engine, an accelerator pedal op-eration amount, and the like.[0039] In the engine 100, hunting of the rotationalspeed may occur due to influence of external disturbanceor the like, even if the torque is constant. In such a case,the engine ECU 502 decides a torque correction amount(anti-jerk correction amount) based on a difference be-

tween a theoretical rotational speed (i.e., a rotationalspeed decided based on the target indicated enginetorque) and the actual engine rotational speed, in orderto stabilize the engine rotational speed. The engine ECU502 changes the ignition timing of the engine 100 (i.e.,the engine ECU 502 retards or advances the ignition tim-ing of the engine 100) so as to change the torque by thedecided torque correction amount.[0040] Also, when knocking occurs in the engine 100,the engine ECU 502 repeatedly retards the ignition timingof a cylinder in which knocking occurs by a predeterminedangle until occurrence of knocking is stopped. After oc-currence of knocking is stopped, the engine ECU 502repeatedly advances the retarded ignition timing by a pre-determined angle. Such control is referred to as "knockcontrol".[0041] When the ignition timing is retarded or ad-vanced, the torque of the engine 100 is changed. Thechange in the torque of the engine 100 is noticeable par-ticularly when the ignition timing is changed by the anti-jerk correction.[0042] Also, the engine ECU 502 performs the ISC sothat the engine rotational speed during idle becomesequal to a predetermined target rotational speed. In theISC, the torque of the engine 100 is controlled based onthe torque correction amount that is calculated based onthe difference between the actual rotational speed duringidling and the target rotational speed during idling. Thecalculated torque correction amounts are integrated.That is, the torque of the engine 100 is controlled basedon an integration term for the torque correction amount.When the rotational speed during idling is higher thanthe target rotational speed, the torque of the engine 100is controlled so as to be decreased. When the rotationalspeed during idling is lower than the target rotationalspeed, the torque of the engine 100 is controlled so asto be increased.[0043] When a learning condition is satisfied, the inte-gration term set by the ISC is stored in the RAM 508 asan idling torque deviation learning value. The torque ofthe engine 100 is controlled to so as to be increased ordecreased by the idling torque deviation learning value.[0044] Further, the engine ECU 502 performs fuel cutwhen a predetermined idling time fuel cut performing con-dition is satisfied. The predetermined idling time fuel cutperforming condition includes a condition that the engine100 is idling. As the idling time fuel cut performing con-dition, an ordinary condition is used. Therefore, detaileddescription of the idling time fuel cut performing conditionwill be omitted.[0045] The transmission ECU 504 controls the clutch200 and the transmission 300. In this embodiment, thetransmission ECU 504 controls the transmission 300 ina shifting control mode when shifting of the transmission300 is performed. In the case where the transmissionECU 504 controls the transmission 300 in the shiftingcontrol mode, the transmission ECU 504 controls theclutch 200 so that the clutch 200 is disengaged, for ex-

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ample, when actual net engine torque of the engine 100decreases to approximately 0 N.m. The actual net enginetorque is torque obtained by subtracting the frictiontorque of the engine 100, pumping loss, load torque ofauxiliary machinery, and the idling torque deviation learn-ing value from torque that is actually generated by theengine 100 (i.e., actual indicated engine torque). The ac-tual net engine torque is calculated as the torque that istransmitted from the engine 100 to the transmission 300.[0046] When the clutch 200 is in the disengaged state,the transmission ECU 504 controls the transmission 300so as to change the shift speed. When change in the shiftspeed is completed, the transmission ECU 504 controlsthe clutch 200 so that the clutch 200 is engaged. How-ever, the control of the clutch 200 and the transmission300 in the shifting control mode is not limited to the controldescribed above.[0047] Signals are sent and received between the en-gine ECU 502 and the transmission ECU 504. In thisembodiment, the engine ECU 502 calculates the actualnet engine torque which is used for control of the trans-mission 300, and sends the actual net engine torque tothe transmission ECU 504. The transmission ECU 504controls the transmission 300 using the actual net enginetorque sent from the engine ECU 502.[0048] In this embodiment, when shifting is performed,the transmission ECU 504 starts to disengage the clutch200. When the clutch 200 is in a semi-engaged state, theECU 504 decides engagement torque of the clutch 200based on the actual net engine torque that is sent fromthe engine ECU 502. Also, the transmission ECU 504estimates a time point at which the actual net enginetorque becomes, for example, approximately 0 N·mbased on a rate of change (i.e., inclination of change) inthe actual net engine torque that is sent from the engineECU 502. Then, the transmission ECU 504 controls theclutch 200 so that the clutch 200 is disengaged in ac-cordance with the time point.[0049] The ROM 506 stores programs executed by theECU 500, maps used by the ECU 500, and the like. Inthis embodiment, the transmission ECU 504 determineswhether to control the transmission 300 in the shiftingcontrol mode, based on a shift diagram stored in the ROM506 or shift operation performed by a driver. The RAM508 stores results of computation performed by the ECU500.[0050] The ECU 500 receives signals from a positionsensor 510, an accelerator pedal operation amount sen-sor 512, a brake switch 514, a vehicle speed sensor 516,an input shaft rotational speed sensor 518, an outputshaft rotational speed sensor 520, and a crank positionsensor 524 which is provided so as to be opposed to anouter periphery of a timing rotor 522.[0051] The position sensor 510 detects a shift positionof a shift lever. The accelerator pedal operation amountsensor 512 detects an operation amount of an acceler-ator pedal. The brake switch 514 detects whether a brakepedal has been depressed. The vehicle speed sensor

516 detects a vehicle speed. The input shaft rotationalspeed sensor 518 detects a rotational speed of the inputshaft of the transmission 300. The output shaft rotationalspeed sensor 520 detects a rotational speed of an outputshaft of the transmission 300. The crank position sensor524 detects the engine rotational speed.[0052] The ECU 500 performs computation based onthe signals sent from the sensors, the programs andmaps stored in the ROM 506, and the like. In this em-bodiment, the ECU 500 performs shifting (upshifting anddownshifting) based on the shift operation performed bythe driver. The ECU 500 may perform shifting based onoperation of a switch provided in a steering wheel (notshown), instead of the shift operation.[0053] Referring to FIG. 2, the engine 100 will be fur-ther described. Air taken into the engine 100 is filteredby an air cleaner 102. Then, the air passes through anintake pipe 104 and an intake manifold 106, and is intro-duced into a combustion chamber together with fuel in-jected from an injector 108.[0054] In the combustion chamber, air-fuel mixture isignited by an ignition plug 110, and is burned. When theair-fuel mixture is burned, driving force is generated bythe engine 100. The burned air-fuel mixture, that is, ex-haust gas is guided to an exhaust manifold 112, and pu-rified by a catalyst 144. Then, the exhaust gas is dis-charged to the outside of a vehicle.[0055] The air introduced in the combustion chamberis controlled by a throttle valve 116. The throttle valve116 is an electronically controlled throttle valve that isdriven by a motor. An opening amount of the throttle valve116 is controlled by the ECU 500. A flow rate of air isdetected by an air flow meter 526, and a signal indicativeof the result of detection is sent to the ECU 500.[0056] The engine ECU 502 of the ECU 500 calculatesfilling efficiency of the engine 100 based on the flow rateof air detected by the air flow meter 526, using a theo-retical equation that is stored in the ROM 506 in advance.The filling efficiency may be calculated based on pres-sure of air using a theoretical equation.[0057] The opening amount of the throttle valve 116 isdetected by a throttle opening amount sensor 528, anda signal indicative of the result of detection is sent to theECU 500. A temperature TC of the catalyst 114 is de-tected by a temperature sensor 530, and a signal indic-ative of the result of detection is sent to the ECU 500.The catalyst temperature TC may be estimated basedon the engine rotational speed, the load, a temperatureof coolant, a temperature of intake air, and the like, in-stead of detecting the catalyst temperature TC using thetemperature sensor 530.[0058] Knocking which occurs in the engine 100 is de-tected by a knock sensor 532, and a signal indicative ofthe result of detection is sent to the ECU 500. The tem-perature of the coolant of the engine 100 is detected bya coolant sensor 534, and a signal indicative of the resultof detection is sent to the ECU 500. The engine ECU 502of the ECU 500 detects (estimates) a temperature of lu-

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bricant of the engine 100 based on a temperature of thecoolant that is detected at a time point which the engine100 is started, and a present temperature of the coolant.[0059] Referring to FIG. 3, the clutch 200 will be furtherdescribed. The clutch 200 is a dry type single plate frictionclutch. As shown in FIG. 3, the clutch 200 includes aclutch output shaft 202, a clutch disk 204 provided on theclutch output shaft 202, a clutch housing 206, a pressureplate 208 provided in the clutch housing 206, a diaphragmspring 210, a clutch release cylinder 212, a release fork214, and a release sleeve 216.[0060] When the diaphragm spring 210 applies forceto the pressure plate 208 rightward in FIG. 3, the clutchdisk 204 is pressed to a fly wheel 602 fitted to the crank-shaft 600 of the engine 100, and thus the clutch is en-gaged.[0061] When the clutch release cylinder 212 movesthe release sleeve 216 rightward in FIG. 3 via the releasefork 214, an inner end portion of the diaphragm spring210 is moved rightward in FIG. 3. When the inner endportion of the diaphragm spring 210 is moved rightwardin FIG. 3, the pressure plate 208 is moved leftward inFIG. 3, and the clutch disk 204 is separated from the flywheel 602. Thus, the clutch is disengaged.[0062] The clutch release cylinder 212 is operatedwhen hydraulic pressure of hydraulic oil pumped up bya hydraulic pump 220 from a reservoir 218 is supplied tothe clutch release cylinder 212 via a clutch solenoid valve222. The clutch solenoid valve 222 switches betweensupply of the hydraulic pressure to the clutch releasecylinder 212 and discharge of the hydraulic pressure fromthe clutch release cylinder 212. The clutch solenoid valve222 is controlled by the ECU 500.[0063] When the hydraulic pressure is supplied to theclutch release cylinder 212, a piston of the clutch releasecylinder 212 is moved leftward in FIG. 3, and the releasesleeve 216 is moved rightward in FIG. 3. Thus, the clutchis disengaged. The position of the piston of the clutchrelease cylinder 212 (i.e., clutch stroke) is detected by aclutch stroke sensor 536. A signal indicative of the resultof detection performed by the clutch stroke sensor 536is sent to the ECU 500.[0064] The ECU 500 detects whether the clutch 200is in a disengaged state, in an engaged state, or in asemi-engaged state, based on the signal sent from theclutch stroke sensor 536. The clutch 200 may be oper-ated by electric power.[0065] Referring to FIG. 4, description will be made ofa control structure of a program executed by the ECU500 which performs computation using the torque calcu-lation method for an engine according to the embodimentof the invention.[0066] In step S100, the ECU 500 calculates actualindicated engine torque TZ. The actual indicated enginetorque TZ is calculated using a two-dimensional mapbased on the engine rotational speed and the filling effi-ciency. The engine rotational speed is detected basedon the signal sent from the crank position sensor 524.

The filling efficiency is calculated based on the flow rateof air detected by the air flow meter 526.[0067] In step S102, the ECU 500 calculates the torquecorrection amount in each cylinder, that is, a changeamount A of the ignition timing in each cylinder. Thechange amount A of the ignition timing is an absolutevalue of an angle by which the ignition timing is changedby the anti-jerk correction.[0068] In step S104, the ECU 500 determines whetherthe change amount A of the ignition timing is larger thana predetermined change amount A(0). When the changeamount A of the ignition timing is larger than the prede-termined change amount A(0) ("YES" in step S104), theECU 500 performs step S106. When the change amountA of the ignition timing is equal to or smaller than thepredetermined change amount A(0) ("NO" in step S108),the ECU 500 performs step S108.[0069] In step S106, the ECU 500 sets a time constantT to T(1). The time constant T is used in a smoothingprocess for the actual indicated engine torque TZ that isperformed in step S110 described later. In step S108,the ECU 500 sets the time constant T to T(2) (T(1) isgreater than T(2); T(1) > T(2)).[0070] In this embodiment, the time constant T usedin the smoothing process is set according to a magnitudeof the change amount of the ignition timing based on theanti-jerk correction. However, the time constant T maybe set according to a magnitude of the change amountof the ignition timing set by the knock control. In this case,four time constants may be provided according to com-binations of magnitudes of the change amount of the ig-nition timing based on the anti-jerk correction, and mag-nitudes of the change amount of the ignition timing setby the knock control.[0071] In step S110, the ECU 500 performs thesmoothing process for the actual indicated engine torque,for example, using an equation, TS = TZ (J - 1) + (TZ (J- 1) - TZ(J)) � ES / T. In this equation, TS is an outputvalue that is calculated by the smoothing process; TZ (J- 1) is the actual indicated engine torque TZ that wascalculated last time; TZ(J) is the actual indicated enginetorque TZ that is calculated this time; and ES is a com-putation cycle at which this process is performed; and Tis the time constant.[0072] In step S112, the ECU 500 determines whetherfuel supply is being stopped (i.e., fuel cut is being per-formed). When fuel cut is being performed ("YES" in stepS112), the ECU 500 performs step S114. When fuel cutis not being performed ("NO" in step S112), the ECU 500performs step S116.[0073] In step S114, the ECU 500 performs a subtrac-tion process for the output value TS based on the numberof the cylinders for which fuel cut is being performed. TheECU 500 performs the subtraction process for the outputvalue TS by multiplying the output value TS by (KA - KB)/ KA. KA is the number of all the cylinders, and KB is thenumber of the cylinders for which fuel cut is being per-formed.

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[0074] In step S116, the ECU 500 calculates the fric-tion torque of the engine 100, the pumping loss, and theload torque of the auxiliary machinery. Each of the frictiontorque and the pumping loss is calculated by correctinga value that is calculated using the two-dimensional mapbased on the engine rotational speed and the filling effi-ciency, by the temperature of the coolant and the atmos-pheric pressure. Since it is difficult to accurately calculatethe friction torque, the friction torque is set to a value thatis the most convenient when used for the control of theengine, among values in a variation range of the frictiontorque. For example, the friction torque is set to a valuehigher than a median value in the variation range whenthe engine operating state is in an operating region wherean engine stall may occur. The load torque of the auxiliarymachinery is calculated using a one-dimensional mapbased on the engine rotational speed. Each of the meth-ods of calculating the friction torque, the pumping loss,and the load torque of the auxiliary machinery is not lim-ited to the method described above.[0075] In step S118, the ECU 500 subtracts the frictiontorque of the engine 100, the pumping loss, the loadtorque of the auxiliary machinery, and the idling torquedeviation learning value from the output value TS or theoutput value TS that has been subjected to the subtrac-tion process, whereby the actual net engine torque iscalculated.[0076] In step S120, the ECU 500 detects a tempera-ture TO of the lubricant based on a temperature of thecoolant of the engine 100 at a time point when the engine100 is started and a present temperature of the coolant,using the two-dimensional map stored in the ROM 506.The temperatures of the coolant are detected by the cool-ant sensor 534.[0077] In step S124, the ECU 500 corrects the frictiontorque so that the friction torque is decreased, and cor-rects the actual net engine torque which is calculated bysubtracting the friction torque from the actual indicatedengine torque so that the actual net engine torque is in-creased. The ECU 500 corrects the friction torque thathas been set to a value higher than the median value ina predetermined range so that the friction torque is de-creased to the median value in the predetermined range.[0078] Description will be made of operation of theECU 500 which performs computation using the torquecalculation method for an engine according to the em-bodiment of the invention, based on the aforementionedstructure and the aforementioned flowchart.[0079] While a vehicle system is being started, the ac-tual indicated engine torque TZ is calculated in step S100,and the torque correction amount in each cylinder basedon the anti-jerk correction, that is, the change amount Aof the ignition timing in each cylinder, in step S102.[0080] In the case where the change amount A of theignition timing is larger than the predetermined changeamount A(0) ("YES" in step S104), the difference be-tween the actual indicated engine torque TZ (J - 1) thatwas calculated last time and the actual indicated engine

torque TZ(J) that is calculated this time is large. In thiscase, the time constant T used in the smoothing processfor the indicated torque is set to the time constant T(1)which is larger than the time constant T(2), in step S104.Therefore, the value of (TZ (J - 1) - TZ(J)) � ES / T, whichis the second term of the equation used in the smoothingprocess in step S110, is reduced. Accordingly, a changeamount of the calculated output value TS is reduced.Even when the change amount A of the ignition timing islarge, it is possible to obtain the output value TS that issmoothly changed.[0081] Meanwhile, in the case where the changeamount A of the ignition timing is small, the differencebetween the actual indicated engine torque TZ (J - 1) thatwas calculated last time and the actual indicated enginetorque TZ(J) that is calculated this time is not large. Inthis case, even if the value of (TZ (J - 1) - TZ(J)) � ES /T, which is the second term of the aforementioned equa-tion, is not so reduced as in the case where the changeamount A of the ignition timing is large, it is possible toobtain the output value TS that is smoothly changed. Ac-cordingly, the time constant T is set to the time constantT(2) which is smaller than the time constant T(1). Thus,the output value TS is calculated by the smoothing proc-ess using the time constant T(2) in step S110.[0082] After the smoothing process is performed onthe actual indicated engine torque TZ in step S110, andthe output value TS is calculated, it is determined whetherfuel cut is being performed in step S112. When it is de-termined that fuel cut is being performed ("YES" in stepS112), the actual torque of the engine 100 is decreasedby fuel cut. Therefore, the subtraction process for theoutput value TS is performed in step S114. The followingdescription will be made based on the assumption thatfuel cut is being performed for two cylinders among thefour cylinders. In this case, the output value TS is multi-plied by two-fourths (one-second). When fuel cut is notbeing performed ("NO" in step S112), the subtractionprocess is not performed in step S114.[0083] After the subtraction process for the output val-ue TS is performed in step S114, the friction torque ofthe engine 100, the pumping loss, and the load torqueof the auxiliary machinery are calculated in step S116.The actual net engine torque is calculated by subtractingthe friction torque of the engine 100, the pumping loss,the torque of the auxiliary machinery, and the idlingtorque deviation learning value from the output value TS,in step S118.[0084] The calculated friction torque is used for thecontrol of the engine 100, as well as in the control of thetransmission 300. If the friction torque is estimated at alow value in the variation range, the torque of the engine100 is calculated at a value higher than the actual torqueof the engine 100. In this case, an engine stall may occur.Therefore, for example, when the engine operating stateis in the operating region where an engine stall may oc-cur, the friction torque is set to a value higher than themedian value in the predetermined range, that is, the

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friction torque is estimated at a high value in the variationrange. The deviation between the actual friction torqueand the calculated friction torque becomes larger as thedifference between the temperature of the lubricant ofthe engine 100 and the temperature of the coolant of theengine 100 becomes larger.[0085] When the actual net engine torque that is usedfor the control of the transmission 300 is calculated bysubtracting such friction torque from the actual indicatedengine torque TZ, the actual net engine torque is calcu-lated at a value lower than the torque that is actuallytransmitted to the transmission 300.[0086] In order to correct such actual net enginetorque, the temperature TO of the lubricant of the engine100 is detected using the two-dimensional map basedon the temperature of the coolant of the engine 100 atthe time point at which the engine 100 is started, and thepresent temperature of the coolant, in step S120. Thefriction torque is corrected so as to be decreased accord-ing to the difference between the temperature TO of thelubricant and the temperature of the coolant. Also, asanother method, a friction torque correction amount maybe directly set in this two-dimensional map, without set-ting the temperature of the lubricant in this two-dimen-sional map. Thus, the actual net engine torque, which iscalculated by subtracting the friction torque from the ac-tual indicated engine torque TZ, is corrected so as to beincreased, in step S124. Thus, accuracy of the actual netengine torque can be improved.[0087] As described above, the ECU which performscomputation using the torque calculation method for anengine according to this embodiment performs thesmoothing process for the actual indicated engine torqueTZ using the large time constant T(1), thereby calculatingthe output value TS when the change amount of the ig-nition timing in each cylinder is large. On the basis of theoutput value TS, the actual net engine torque is calculat-ed. Thus, even when the change amount of the actualindicated engine torque TZ is large since the changeamount of the ignition timing is large, it is possible toobtain the actual net engine torque that is smoothlychanged.[0088] Also, after the ECU calculates the actual netengine torque by subtracting the friction torque of theengine from the output value TS, the ECU corrects theactual net engine torque so that the actual net enginetorque is increased, by correcting the friction torque sothat the friction torque is decreased based on the tem-perature of the lubricant of the engine. Thus, it is possibleto improve the accuracy of the friction torque that is es-timated at a high value in the variation range, and to ob-tain the actual net engine torque with high accuracy.

(Second embodiment)

[0089] Referring to FIG. 5, a second embodiment ofthe invention will be described. In the aforementionedfirst embodiment, the ECU calculates the actual net en-

gine torque that is actually transmitted from the engine100 to the transmission 300. In the second embodiment,the ECU calculates target net engine torque that is a tar-get of the net engine torque transmitted from the engine100 to the transmission 300, in addition to the actual netengine torque.[0090] Other portions of the control structure and func-tions thereof are the same as in the aforementioned firstembodiment. Therefore, detailed description thereof willbe omitted.[0091] Referring to FIG. 5, description will be made ofa control structure of a program executed by the ECU500 which performs computation using a torque calcula-tion method for an engine according to the second em-bodiment of the invention. The ECU 500 executes a pro-gram described below, in addition to the program in theaforementioned first embodiment.[0092] In step S200, the ECU 500 calculates the targetindicated engine torque that is used for controlling thethrottle valve 116, based on the accelerator pedal oper-ation amount detected by the accelerator pedal operationamount sensor 512, and the engine rotational speed de-tected by the crank position sensor. The target indicatedengine torque is calculated using the map stored in theROM 506.[0093] In step S202, the ECU 500 determines whetherthere is a request for prohibiting idling time fuel cut in thecase where the idling time fuel cut performing conditionis satisfied. The ECU 500 determines whether there isthe request for prohibiting the idling time fuel cut, basedon the signal that is sent from the transmission ECU 504to the engine ECU 502.[0094] The transmission ECU 504 prohibits the idlingtime fuel cut when the engine needs to race in order tosynchronize the engine rotational speed and the rotation-al speed of the input shaft of the transmission 300, or tosynchronize the rotational speed of the input shaft of thetransmission 300 and the rotational speed of the outputshaft of the transmission 300 for performing shifting.When the idling time fuel cut needs to be prohibited, thetransmission ECU 504 sends a prohibition request signalto the engine ECU 502.[0095] When there is the request for the idling time fuelcut from the transmission ECU 504 ("YES" in step S202),step S204 is performed. When there is no request for theidling time fuel cut ("NO" in step S202), step S206 is per-formed.[0096] In step S204, the ECU 500 sets the target indi-cated engine torque to a value for a case where fuel cutis performed, that is, 0 N·m. The value for the case wherefuel cut is performed may be a value other than 0 N·m.In step S206, the ECU 500 calculates the friction torqueof the engine 100, the pumping loss, and the load torqueof the auxiliary machinery.[0097] In step S208, the ECU 500 calculates the targetnet engine torque by subtracting the friction torque of theengine 100, the pumping loss, the load torque of the aux-iliary machinery, and the idling torque deviation learning

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value from the target indicated engine torque. In stepS210, the ECU 500 corrects the target net engine torqueby subtracting the torque equivalent to the integrationterm set by the ISC, from the calculated target net enginetorque.[0098] Description will be made of operation of theECU 500 which performs computation using the torquecalculation method for an engine according to this em-bodiment of the invention, based on the aforementionedstructure and the aforementioned flowchart.[0099] While the vehicle system is being started, thetarget indicated engine torque that is used for controllingthe throttle valve 116 is calculated in step S200, usingthe map based on the accelerator pedal operationamount and the engine rotational speed.[0100] The target indicated engine torque becomes 0N·m when the idling time fuel cut performing condition issatisfied, and fuel cut is being performed while the engine100 is idling.[0101] Meanwhile, even in the case where the idlingtime fuel cut performing condition is satisfied, when thereis the request for prohibiting the idling time fuel cut fromthe transmission ECU 504 during shifting of the trans-mission 300, fuel cut is not performed. Therefore, thetarget indicated engine torque does not become 0 N.m.[0102] In this situation, that is, in the situation wherethe idling time fuel cut performing condition is satisfied,and there is the request for prohibiting the idling time fuelcut, when shifting of the transmission 300 is completed,the request for prohibiting the idling time fuel cut is can-celed. In this case, fuel cut is performed upon completionof shifting, and the target indicated engine torque be-comes 0 N·m.[0103] The transmission ECU 504 calculates torquewhich the transmission ECU 504 requests the engine100 to generate, based on the target net engine torquecalculated based on the target indicated engine torque.Therefore, if the target indicated engine torque is sud-denly changed upon completion of shifting, a problemmay occur in the control of the transmission 300.[0104] Accordingly, in the case where there is the re-quest for prohibiting the idling time fuel cut from the trans-mission ECU 504 ("YES" in step S202), the target indi-cated engine torque is set in advance to the value for thecase where fuel cut is performed, that is, 0 N.m, in stepS204.[0105] The friction torque of the engine 100, the pump-ing loss, and the load torque of the auxiliary machineryare calculated in step S206. The friction torque of theengine 100, the pumping loss, the load torque of the aux-iliary machinery, and the idling torque deviation learningvalue are subtracted from the target indicated enginetorque. Thus, the target net engine torque is calculatedin step S208.[0106] The target net engine torque is calculatedbased on the target indicated engine torque for control-ling the throttle valve. Since the torque of the engine 100is corrected by the ISC, the integration term for the torque

correction amount is added to the target indicated enginetorque. Accordingly, the target net engine torque includesthe integration term for the torque correction amount setby the ISC.[0107] The integration term is calculated irrespectiveof the driver’s intention. The target net engine torque in-cluding the integration term is not appropriate for the con-trol of the transmission 300, since the transmission 300needs to be controlled reflecting the driver’s intention(that is, the rotational speed of the transmission 300needs to be accelerated or decelerated according to thedriver’s request).[0108] Thus, the torque equivalent to the integrationterm for the torque correction amount set by the ISC issubtracted from the calculated target net engine torque,in step S210. Thus, the target net engine torque can becalculated reflecting the driver’s intention more appropri-ately.[0109] As described above, the ECU which performscomputation using the torque calculation method for anengine according to the second embodiment of the in-vention calculates the target net engine torque used forthe control of the transmission by subtracting the frictiontorque of the engine 100, the pumping loss, the loadtorque of the auxiliary machinery, and the idling torquedeviation learning value from the target indicated enginetorque. In the situation where the idling time fuel cut per-forming condition is satisfied, when there is the requestfor prohibiting fuel cut, the ECU calculates the target netengine torque using the target indicated engine torqueas the torque for the case where fuel cut is performed.Thus, it is possible to calculate in advance the target netengine torque for the case where fuel cut is performedupon completion of shifting.[0110] Also, the ECU corrects the target net enginetorque by subtracting the torque equivalent to the inte-gration term for the torque correction amount that is cal-culated by the ISC, from the calculated target net enginetorque. Thus, it is possible to obtain the target net enginetorque reflecting the driver’s intention more appropriate-ly.[0111] Thus, the embodiments of the invention thathave been disclosed in the specification are to be con-sidered in all respects as illustrative and not restrictive.The technical scope of the invention is defined by claims,and all changes which come within the meaning andrange of equivalency of the claims are therefore intendedto be embraced therein.[0112] There may be provided a calculation methodfor an engine (100) connected to an automatic transmis-sion (300), wherein plural cylinders are provided in theengine (100), and torque in each of the cylinders is con-trolled by changing ignition timing based on at least oneof a change in a rotational speed of the engine (100) andknocking of the engine (100), the torque calculation meth-od being characterized by comprising:

calculating first engine torque based on the rotational

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speed of the engine (100) and the ignition timing ineach of the cylinders; andcalculating second engine torque which is used forcontrol of the automatic transmission (300) by per-forming a smoothing process for the first enginetorque based on a change amount of the ignitiontiming in each of the cylinders.

[0113] In the torque calculation method preferably:

the first engine torque is repeatedly calculated;the calculation step includes a step of calculating thesecond engine torque by adding, to the first enginetorque that was calculated last time, an additionalvalue that is calculated based on a difference be-tween the first engine torque that was calculated lasttime and the first engine torque that is calculated thistime; andthe torque calculation method further includes a stepof calculating the additional value such that the ad-ditional value becomes smaller as the changeamount of the ignition timing becomes larger.

[0114] There may also be provided a torque calculationmethod for an engine (100) connected to an automatictransmission (300), characterized by comprising:

calculating first engine torque based on a rotationalspeed of the engine (100);detecting friction torque of the engine (100) basedon a temperature of coolant of the engine (100);calculating second engine torque that is used forcontrol of the automatic transmission (300) by sub-tracting the friction torque from the first enginetorque; andcorrecting the second engine torque so that the sec-ond engine torque is increased based on a temper-ature of lubricant of the engine (100).

[0115] The torque calculation method preferably fur-ther comprises

detecting the temperatures of the coolant of the en-gine (100) at plural time points including a time pointat which the engine (100) is started; anddetecting the temperature of the lubricant of the en-gine (100), based on the temperatures of the coolant,which are detected at the plural time points includingthe time point at which the engine is started.

[0116] In the torque calculation method preferably:

fuel supply to the engine (100) is stopped when apredetermined condition is satisfied; andthe second engine torque is calculated consideringthe number of the cylinders for which fuel supply hasbeen stopped.

[0117] There may also be provided a torque calculationmethod for an engine (100) connected to an automatictransmission (300), wherein when a predetermined firstcondition is satisfied, fuel supply to the engine (100) isstopped; and when a predetermined second conditionrelating to the automatic transmission (300) is satisfied,stop of the fuel supply is prohibited, the torque calculationmethod being characterized by comprising:

calculating first engine torque based on a rotationalspeed of the engine;determining whether stop of the fuel supply is beingprohibited; andsetting the first engine torque to torque for a case inwhich the fuel supply is stopped, and calculating sec-ond engine torque which is used for control of theautomatic transmission, based on the first enginetorque, in a case where stop of the fuel supply isbeing prohibited.

[0118] In the torque calculation method preferably thefirst condition is a condition that the engine (100) is idling;and the second condition is a condition that shifting ofthe automatic transmission (300) is being performed.

Claims

1. A torque calculation method for an engine (100) con-nected to an automatic transmission (300), whereintorque of the engine (100) is controlled based on firstengine torque that is calculated based on a rotationalspeed of the engine (100); and the first engine torqueis corrected so that the rotational speed during idlingbecomes equal to a predetermined rotational speed,the torque calculation method being characterizedby comprising:

calculating second engine torque which is usedfor control of the automatic transmission (300),based on the first engine torque; andcorrecting the second engine torque based ona correction amount of the first engine torque.

2. The torque calculation method according to claim 1,wherein:

the rotational speed of the engine (100) duringidling is controlled so as to be equal to a prede-termined rotational speed, based on a predeter-mined torque correction amount which is setbased on the rotational speed; andthe second engine torque is calculated consid-ering the predetermined torque correctionamount.

3. The torque calculation method according to claim 1or 2, wherein the second engine torque is calculated

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considering pumping loss of the engine (100).

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the Europeanpatent document. Even though great care has been taken in compiling the references, errors or omissions cannot beexcluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• JP 2003120801 A [0003] [0003] [0005]