United States Patent [19]
`B011
`
`USO05327992A
`[11] Patent Number:
`
`-
`
`[45] Date of Patent:
`
`5,327,992
`Jul. 12, 1994
`
`[54] METHOD FOR CONTROLLING A HYBRID
`DRIVE WHICH DRIVES A VEHICLE
`
`[75] Inventor: Wolf Boll, Weinstadt, Fed. Rep. of
`Germany
`
`[73] Assignee: Mercedes-Benz AG, Fed. Rep. of
`Germany
`
`[211 App]. NO.: 53,262
`
`'
`
`Apr. 28, 1993 4
`
`[22] Filed:
`[30]
`Foreign Application Priority Data
`May 28, 1992 [DE] Fed. Rep. of Germany ..... .. 4217668
`
`[51] Int. 01.5 .............................................. ..B60K 6/04
`[52] u.s.c1. ......................... ..180/65.2;180/65.4;
`290/45; 290/50
`[58] Field Of Search .................. .. 180/652, 65.3, 65.4,
`180/656, 65.7, 65.8; 290/45, 50
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,791,473 2/1974 Rosen ............................... .. 180/652
`4,021,677 5/1977 Rosen et al. ......... ..
`ISO/65.2
`4,305,254 12/1981 Kawakatsu et a1.
`180/652
`4,335,429 6/1982 Kawakatsu .................... .. 364/424
`4,407,132 10/1983 Kawakatsu et a1. ............ .. 60/716
`
`5,081,365 1/1992 Field et a1. . . . . . . . . .
`. . . . . .. 290/45
`5,117,931 6/1992 Nishida ............................ .. ISO/65.2
`
`24
`
`11
`
`10
`
`FOREIGN PATENT DOCUMENTS
`2501386 7/1976 Fed. Rep. of Germany .
`2465884 3/1981 France .
`WO91/08919 6/1991 World Int. Prop. 0. .
`Primary Examiner—Margaret A. Focarino
`Assistant Examiner-Peter English
`[57]
`ABSTRACT
`A method for controlling a hybrid drive consisting of an
`internal combustion engine and at least one electric
`motor which can be driven via an electrical energy
`source, in which the electric motor can be operated as a
`generator when required. In order to reduce the fuel
`consumption and the emission of noxious substances of
`the internal combustion engine in those operating
`ranges in which the torque to be output by the internal
`combustion engine to overcome the instantaneous trac
`tive resistances lies below a torque corresponding to
`ideal operation of the internal combustion engine with
`respect to efficiency and/or exhaust gas behavior, the
`internal combustion engine is operated essentially with
`the torque corresponding to ideal operation. The differ
`ential torque between the torque corresponding to ideal
`operation and the torque to be output by the internal
`combustion engine to overcome the instantaneous trac
`tive resistances is used to drive the electric motor which
`is switched as a generator.
`
`16 Claims, 2 Drawing Sheets
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`13 14
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`22
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`23
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`US. Patent
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`July 12, 1994
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`Sheet 1 of 2
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`5,327,992
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`Fig. 1
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`Page 2 of 7
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`US. Patent
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`July 12, 1994
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`Sheet 2 of 2
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`5,327,992
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`Fig. 2
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`Page 3 of 7
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`1
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`METHOD FOR CONTROLLING A HYBRID DRIVE
`WHICH DRIVES A VEHICLE
`
`5
`
`25
`
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`The present invention relates to a method for control
`ling a hybrid drive which includes an internal combus
`tion engine and at least one electric motor which can be
`driven via an electrical energy source, and drives a
`vehicle and in which the electric motor is switched over
`to generator mode when a preset requirement to gener
`ate electricity is present.
`German Patent Document DE-OS 25 01 386 dis
`closes a method of the above-described type, in which
`the electric motor which is provided to drive the vehi
`cle operates when required as a generator driven by the
`internal combustion engine in order to produce current,
`for example for charging up the battery feeding the
`electric motor.
`An object of the present invention is to provide a
`method of the initially described type in which the fuel
`consumption of the internal combustion engine and its
`emission of noxious‘ substances are further reduced.
`This and other objects are achieved by the present
`invention which provides a method for controlling a
`hybrid drive that drives a vehicle, the hybrid drive
`including an internal combustion engine and at least one
`electric motor which can be driven via an electrical
`energy source. The method comprises the steps of
`switching the electric motor over to a generator mode
`when a preset requirement to generate electric energy is
`present, and operating the internal combustion engine
`substantially at a torque corresponding to ideal opera
`tion of the internal combustion engine with respect to at
`least one of ef?ciency and exhaust gas behavior when
`the internal combustion engine is in operating ranges in
`which an amount of torque to be output by the internal
`combustion engine for overcoming instantaneous trac
`tive resistances lies below a torque corresponding to the
`ideal operation of the internal combustion engine. A
`differential torque between the torque corresponding to
`the ideal operation and the torque to be output by the
`internal combustion engine for overcoming the instanta
`neous tractive resistances is used to drive the electric
`motor operated as a generator.
`'
`Using the method according to the invention, it is
`achieved that whenever the vehicle is being driven via
`the internal combustion engine and there is a need to
`generate electric energy, for example to charge up a
`battery which is supplying energy for the electric motor
`or for other electrical loads, the internal combustion
`engine can be operated over wide ranges always in an
`operating range which is most favorable with respect to
`the speci?c fuel consumption and/ or with respect to the
`emission of noxious substances. The taking up of the
`torque of the electric motor running in generator mode
`is controlled in this process in such a way that the pre
`60
`cise difference between the torque output by the inter
`nal combustion engine in these load ranges and the
`torque required to overcome the instantaneous tractive
`resistances, provided this difference is greater than zero,
`is taken up by the generator to generate electric energy.
`Both the storage of the electric energy required to oper
`ate the electric motor and the drive of the vehicle via
`the internal combustion engine can thus be achieved in
`
`5,327,992
`2
`these operating ranges with optimum efficiency and/ or
`with minimum emission of noxious substances.
`In certain embodiments of the present invention, the
`control of the hybrid drive takes place according to a
`characteristic diagram. This has the advantage that the
`most varied parameters can be taken into account for
`the control of the internal combustion engine and of the
`generator so that changes in individual operating pa
`rameters and ambient parameters can be reacted to as
`quickly as possible.
`In certain embodiments of the invention, a battery is
`coupled to the electric motor and is an energy source to
`drive the electric motor. The take-up of the torque of
`the electric motor operating in the generator mode is
`controlled to a set value which is greater than the
`torque corresponding to ideal operation, whenever the
`battery is discharged to a severe degree. With these
`embodiments, it remains ensured that in the event of the
`generation of a high electric energy being required
`briefly, for example when the battery is discharged to a
`severe extent and a plurality of electrical loads are
`switched on at the same time, this required electric
`energy can be provided as quickly as possible.
`Other objects, advantages and novel features of the
`present invention will become apparent from the fol
`lowing detailed description of the invention when con
`sidered in conjunction with the accompanying draw
`mgs.
`
`20
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`30
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows a basic illustration of a device for carry
`ing out the method according to the invention;
`FIG. 2 shows a ?rst exemplary embodiment of the
`method according to the invention in a diagram
`M=f(n); and
`FIG. 3 shows a further exemplary embodiment of the
`method according to the invention in a diagram
`M=f(n).
`DETAILED DESCRIPTION OF THE
`DRAWINGS
`FIG. 1 shows a hybrid drive for a motor vehicle. This
`drive comprises a diesel engine i and an electric motor
`2. A hydraulically actuable disconnect-type clutch 3 is
`arranged in the power train between the diesel engine 1
`and the electric motor 2. In the engaged state of the
`clutch 3, the crankshaft 6 of the diesel engine i is non
`rotatably connected to the input shaft 7 of the electric
`motor 2. The power take-off of the electric motor 2 is
`non-rotatably connected to the input shaft of a conven
`tional multispeed gearbox 8 of the vehicle. The power
`take-off of the gearbox 8 acts via a differential gear (not
`illustrated in the drawing for the sake of clarity) on the
`drive axle or on the drive wheels 9 of the vehicle.
`The diesel engine i has an intake line 10 and an ex
`haust gas line 11, with a soot particle ?lter 12 being
`arranged in the exhaust gas line 11 in order to reduce
`the emission of soot particles. Fuel is injected via a
`known fuel injection pump 13 whose actuation element
`(control rod 14), which determines the amount of fuel
`injected, can also be actuated by the electronic control
`unit 4 via the control line 15.
`In addition, an electrical energy source in the form of
`a battery 16 is provided which, when the electric motor
`2 is intended to drive the vehicle alone or together with
`the diesel engine 1, provides the electric energy neces
`sary for this driving. The electric motor 2 can also be
`operated as a generator which is driven in this operating
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`mode (the “generating mode”) with the clutch 3 en
`gaged by the diesel engine 1. In the generating mode,
`the electric motor 2 produces current which is fed via
`the lines 17 and a device (not illustrated in the drawing)
`for controlling charge current into the battery 16. The
`size of the torque which is taken up by the generator 2
`in this operating mode is determined via a controller 19
`which is also actuated by the electronic control unit 4
`via the control line 18. The electronic control unit 4 is
`fed: 1) a signal which corresponds to the current speed
`n of the diesel engine 1 via a sensor 20 and a measured
`value line 21; 2) a signal which corresponds to the cur
`rent load setting a (de?ection a of the accelerator pedal
`28) via a sensor 22 and a measured value line 23; 3) a
`signal corresponding to the current temperature T of
`the soot ?lter body 12 via the sensor 24 and a measured
`value line 25; and 4) a signal corresponding to the cur
`rent charge state of the battery 16 via a sensor 26 and a
`measured value line 27.
`The hybrid drive can be operated in the following
`four basic modes (a)—(d).
`In mode (a), the vehicle is driven exclusively by the
`diesel engine 1. In this mode, the disconnect-type cou
`pling 3 is engaged, but the electric motor 2 is inactive.
`This means that no additional driving torque is supplied
`by the electric motor 2. The electric motor 2 is actuated
`via the controller 19 in such a way that no driving
`torque whatsoever is tapped off from the diesel engine
`1 to generate electric energy.
`In mode (b), the vehicle is driven exclusively by the
`electric motor 2. In this mode, the disconnect-type cou
`pling 3 is open, i.e. the diesel engine 1 is separated from
`the electric motor 2. The electric motor 2 draws from
`the battery 16 via the accelerator pedal 28 (accelerator
`pedal position a) the appropriate energy required by the
`driver for driving the vehicle. With an opened discon
`nect-type coupling 3, the diesel engine 1 is generally
`switched off.
`'
`In mode (c), the vehicle is driven by the diesel engine
`1 and the electric motor 2. In this mode, the clutch 3 is
`also engaged (closed). Depending on the instantaneous
`gear ratio and load setting, the driving torque to be
`produced to drive the vehicle is provided partially by
`the diesel engine 1 and partially by the electric motor 2.
`This mode of operation is selected predominantly on
`45
`accelerating and, furthermore, is necessary to obtain
`free charge capacity in the battery for the subsequently
`described operating mode ((1).
`In mode (d), the vehicle is driven by the diesel engine
`1 and the electric motor 2 operates in generator mode,
`i.e. a portion of the driving torque produced by the
`diesel engine 1 is taken up, with the clutch 3 engaged,
`by the electric motor 2 which is now operating in gener
`ator mode in order to generate a torque of load for the
`diesel engine 1. The electric motor 2 is con?gured in
`55
`such a way that it is able to take up in generator mode
`approximately up to half the torque output by the diesel
`engine 1.
`All four operating modes (a)—(d) have in common
`that the electric motor 2 can act as a generator in a
`thrust mode of the vehicle.
`The electric motor 1 is operated as a generator (oper
`ating mode (d)) if the electronic control unit 4 is sig
`nalled via the sensor 26 that the battery 16 is discharged
`beyond a speci?c degree, in other words, if there is a
`need to generate electric energy via the electric motor
`and to feed this energy into the battery 16. The diagram
`in FIG. 2 shows the interrelation between the torque M
`
`4
`(ordinate) output by the diesel engine 1 and the respec
`tive engine speed it (abscissa). The magnitude of the
`torque M here is a direct measure of the quantity of fuel
`injected.
`The line 30 characterizes the variation of the torque
`under full load, that is to say when the amount of fuel
`injected is at a maximum. At 31', 31", 31”’ and 31"",
`curves of constant speci?c fuel consumption or constant
`ef?ciency are illustrated. Of these, the curve 31' is the
`curve with the greatest ef?ciency and 31"” is the curve
`with the smallest efficiency.
`The curve 32 represents that variation of the torque
`along which the maximum ef?ciency, with respect to
`the respective engine speed it, is always given. It can be
`seen that this curve 32 extends in relatively high load
`ranges.
`By contrast 33 constitutes that curve which, in the
`event that the vehicle is driven exclusively via the diesel
`engine 1, represents the torque which has to be pro
`duced by the diesel engine 1 in order to overcome the
`instantaneous tractive resistances in a speci?c gear. It
`can be seen that below the engine speed n; the torque to
`be provided by the diesel engine 1 to overcome the
`tractive resistances (curve 33) is smaller than the torque
`which is output by the diesel engine 1 whenever the
`engine is operated in the range of maximum efficiency
`(curve 32). According to the present invention, there is
`provision to allow the electric motor 2 to operate in
`generator mode and to operate the diesel engine 1 along
`the curve 32 in the engine speed range below the engine
`speed n2 whenever the electronic control unit 4 is sig
`nalled via sensor 26 that the charge state of the battery
`16 is below a predetermined limit value. The diesel
`engine 1 produces a higher torque up to the engine
`speed n2 than is required to overcome the tractive resis-‘
`tances. The electric motor 2 is actuated via the control
`ler 19 in such a way that precisely the differential torque
`AM (illustrated in FIG. 2 at a speed n1) between the
`torque Mnmax corresponding to the ideal operation and
`the torque MFW to be output by the diesel engine 1 in
`order to overcome the instantaneous tractive resis
`tances is always taken up by the electric motor 2, run
`ning in generator mode, for the purpose of producing
`current or for charging the battery 16. In this way, the
`operation of the diesel engine 1, and thus also the gener
`ation of current for charging the battery 16 always can
`take place at optimum efficiency in this phase. More
`over, by virtue of the fact that the diesel engine 1 is
`always operated in a relatively high load range during
`this phase, an exhaust gas temperature predominately
`exists which lies above the limit temperature required
`for automatic regeneration of the soot ?lter 12. The soot
`?lter 12 is thus prevented from clogging up.
`If the battery 16 is discharged to a very severe de
`gree, the control provides for the diesel engine 1 to be
`operated brie?y above the curve 32.
`Should the battery 16 be completely charged, that is
`to say should generation of current not be required, no
`further torque is taken up by the electric motor 2. The
`vehicle can then be driven again by means of one of the
`three drive modes (a), (b) or (c), as required. In this
`case, the electronic control unit 4 can for example en
`sure that, in the interim, current is consumed by the
`operating mode (b) or (0) so that the soot ?lter 12 is
`regularly burnt free by the mode (cl).
`-
`The soot particle ?lter 12 can also be prevented from
`clogging during the phase in which the electric motor 2
`is operating in generator mode if the diesel engine 1 and
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`the electric motor 2 are controlled in accordance with
`the characteristic line according to FIG. 3. Like FIG. 2,
`the diagram in FIG. 3 shows the interrelation between
`the torque M (ordinate) output by the diesel engine 1
`and its speed 11 (abscissa). The curve 35 in turn repre
`sents the full-load characteristic line. The lines 36’-36""
`describe curves of constant speci?c fuel consumption or
`constant ef?ciency, analogously with FIG. 2, 36' repre
`senting here the curve with the greater ef?ciency and
`36"" representing the curve with the smaller ef?ciency.
`In this diagram, curve 37 also designates the tractive
`resistances to be overcome by the diesel engine 1 in a
`speci?c gear. However, curve 38 characterizes a limit
`line above which an automatic regeneration (automati
`cally occurring burning off) of the soot ?lter 12 is possi
`ble. Therefore, if the internal combustion engine is al
`ways operated at an operating point above the limit line
`38, the ?lter 12 is prevented from clogging. In contrast,
`when the diesel engine 1 is operated below this limit line
`38, the exhaust gas temperature is so low that automatic
`regeneration of the ?lter 12 cannot occur and the ?lter
`consequently clogs up. Below the limit speed n2, the
`torque (curve 37) to be supplied by the diesel engine 1
`to overcome the instantaneous tractive resistances lies
`below that torque (curve 38) starting from which a
`suf?ciently high exhaust gas temperature for automatic
`regeneration of the ?lter 12 is ensured. Accordingly, the
`present invention actuates the electric motor 2 via the
`electronic control unit 4 and the controller 19 in such a
`way that precisely the differential torque AM (illus
`trated in FIG. 3 at a random speed n1, n1<n2) between
`the torque MTg (curve 38) corresponding to the ideal
`operation and the torque MFW (curve 37) to be output
`by the diesel engine 1 to overcome the instantaneous
`tractive resistances is always taken up by the electric
`motor 2 operating in generator mode in order to gener
`ate current or to charge up the battery 16.
`In addition, the curve 32 which has already been
`explained in greater detail with respect to FIG. 2 and
`shows the variation of the torque at which the diesel
`engine i is operated at the maximum degree of ef?ciency
`is illustrated in FIG. 3. It can be seen that the curve 38
`is at a higher position than the curve 32 between the
`idling speed nLL and the speed n3. This means that in
`this region, when the diesel engine 1 is only operated
`along the optimum efficiency curve 32, the exhaust gas
`temperature is not suf?ciently high to be able to ensure
`the automatic regeneration of the ?lter 12. Therefore, in
`a further embodiment of the invention, the diesel engine
`1 is operated along the characteristic line 38 or above it
`as far as the speed n; so that the exhaust gas temperature
`required for automatic regeneration of the ?lter 12 is
`also given here. Above this speed n3 up to the speed n4,
`starting from which the curve 37 is located above the
`curve 32, the diesel engine i is then operated along the
`55
`characteristic line 32 provided this is possible in view of
`the charge capacity of the battery. Thus, it is not only
`ensured above this speed n3 that the diesel engine 1 is
`operated at maximum ef?ciency but also that the ex
`haust gas temperature is always so high that the ?lter 12
`can regenerate itself. The differential torque between
`the torque (curve 37) required to overcome the tractive
`resistances and the torque corresponding to ideal opera
`tion, here the curve 38 between nLL and n3 and the
`curve 32 above n3, is also taken up here according to the
`invention by the electric motor 2 operating in the gener
`ator mode in order to generate current to charge up the
`battery 16.
`
`6
`The electronic control unit 4 can monitor and control
`the burning-off process in such a way that operating
`states may brie?y occur in which a burning-off temper
`ature is not present in the soot ?lter 12, in particular in
`the region between an and n; with a view to saving
`fuel. Likewise, the electronic control unit can pursue
`other control priorities (optimization of consumption) if
`a relatively long soot ?lter regeneration process has
`taken place immediately prior to this. The electronic
`control unit 4 is a conventional control unit which is
`readily programmed by one of ordinary skill in the art
`to control the arrangement as described above.
`.
`It is the case for all the embodiments that the battery
`16 can also be charged up via a connection to an exter
`nal power supply (alternating current mains, solar cur
`rent, etc.).
`In a further development of the invention, it is also
`conceivable to provide an additional electric motor
`which can be operated as a generator and can be driven
`for example by .the crankshaft or by an exhaust gas
`turbine arranged in the exhaust gas line of the diesel
`engine. In the generator mode, this electric motor can
`also be load-controlled in accordance with the method
`according to the invention. The current generated can
`serve both for charging the battery and also for supply
`ing the other electric motor.
`The embodiment with two electric machines in the
`power train permits both machines to operate as a gen
`erator, one machine to operate as a generator and the
`other to operate as a driving electric motor, both or one
`of the two to operate as a motor in order to support the
`driving performance of the internal combustion engine,
`or permits an electric motor to serve as the only travel
`drive.
`The electric motor (electric motor 2 in FIG. 1) lo
`cated on the gear shaft makes it more difficult to syn
`chronize the gear input shaft when changing gears due
`to its inertia. This can be remedied by means of electro
`motive forces during synchronization and/or a clutch
`can be provided between the gear shaft and the electric
`motor.
`~
`The electric machines can be arranged both concen
`trically with respect to the crankshaft or gear shaft or
`else offset laterally with respect thereto, in which case
`the electric machines are connected to the power train
`by a lateral drive.
`In all of the embodiments of the present invention, it
`is not absolutely necessary to provide a diesel engine as
`internal combustion engine, as an internal combustion
`engine with compression of the mixture can also be
`used.
`In vehicles with automatic gears, the selection of the
`gear can be included in the characteristic diagram con
`trol, a high gear being selected when the battery is fully
`charged and a lower gear being selected when the bat
`tery is discharged so that the additional load of the
`generator can be taken up.
`Although the invention has been described and illus
`trated in detail, it is to be clearly understood that the
`same is by way of illustration and example, and is not to
`be taken by way of limitation. The spirit and scopeof
`' the present invention are to be limited only by the terms
`of the appended claims.
`What is claimed:
`1. Method for controlling a hybrid drive that drives a
`vehicle, the hybrid drive including an internal combus
`tion engine and at least one electric motor which can be
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`driven via an electrical energy source, the method com
`prising the steps:
`switching the electric motor over to a generator
`mode when a present requirement to generate elec
`tric energy is present;
`'
`operating the internal combustion engine substan
`tially at a torque corresponding to ideal operation
`of the internal combustion engine with respect to at
`least one of ef?ciency and exhaust gas behavior
`when the internal combustion engine is in operat
`ing ranges in which an amount of torque to be
`output by the internal combustion engine for over
`coming instantaneous tractive resistances lies
`below a torque corresponding to the ideal opera
`tion of the internal combustion engine; and
`using a differential torque between the torque corre
`sponding to the ideal operation and the torque to be
`output by the internal combustion engine for over
`coming the instantaneous tractive resistances to
`drive the electric motor operated as a generator;
`wherein the internal combustion engine is a diesel
`engine which is coupled to a soot ?lter via an ex
`haust gas line, and further comprising the step of
`controlling the amount of torque taken up by the
`electric motor operating in the generator mode
`25
`such that, as a function of operating parameters,
`exhaust gas temperatures are reached which causes
`automatic burning off of the soot ?lter.
`2. Method according to claim 1, further comprising
`controlling the amount of torque taken up by the elec
`tric motor operating in generator mode to a set value
`corresponding to the differential torque.
`3. Method according to claim 2, wherein a battery is
`coupled to the electric motor and is an energy source to
`drive the electric motor, further comprising the step of
`35
`operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`4. Method according to claim 1, further comprising
`controlling the hybrid drive according to a characteris
`tic diagram.
`5. Method according to claim 4, wherein a battery is
`coupled to the electric motor and is an energy source to
`drive the electric motor, further comprising the step of
`45
`operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`6. Method according to claim 1, wherein a battery is
`coupled to the electric motor and is an energy source to
`drive the electric motor, further comprising the step of
`operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`7. Method according to claim 1, wherein an auto
`matic transmission is coupled to at least one of the inter
`nal combustion engine and the electric motor, and fur
`ther comprising the step of controlling the transmission
`such that, with a discharged battery, a low gear is se
`lected.
`8. Method according to claim 1, further comprising
`controlling the amount of torque taken up by the elec
`tric motor operating in generator mode to a set value
`corresponding to the differential torque.
`9. Method for controlling a hybrid drive that drives a
`vehicle, the hybrid drive including an internal combus
`
`8
`tion engine and at least one electric motor which can be
`driven via an electrical energy source, the method com
`prising the steps:
`switching the electric motor over to a generator
`mode when a preset requirement to generate elec
`tric energy is present;
`operating the internal combustion engine substan
`tially at a torque corresponding to ideal operation
`of the internal combustion engine with respect to at
`least one of efficiency and exhaust gas behavior
`when the internal combustion engine is in operat
`ing ranges in which an amount of torque to be
`output by the internal combustion engine for over
`coming instantaneous tractive resistances lies
`below a torque corresponding to the ideal opera
`tion of the internal combustion engine; and
`using a differential torque between the torque corre
`sponding to the ideal operation and the torque to be
`output by the internal combustion engine for over
`coming the instantaneous tractive resistances to
`drive the electric motor operated as a generator;
`wherein the internal combustion engine is a diesel
`engine which is coupled to a soot ?lter via an ex
`haust gas line, and further comprising the step of
`controlling the amount of torque taken up by the
`electric motor operating in the generator mode
`such that exhaust gas temperatures are constantly
`reached which causes automatic burning off of the
`soot ?lter.
`10. Method according to claim 9, further comprising
`controlling the amount of torque taken up by the elec
`tric motor operating in generator mode to a set value
`corresponding to the differential torque.
`11. Method according to claim 10, wherein a battery
`is coupled to the electric motor and is an energy source
`to drive the electric motor, further comprising the step
`of operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`12. Method according to claim 9, further comprising
`controlling the hybrid drive according to a characteris
`tic diagram.
`13. Method according to claim 12, wherein a battery
`is coupled to the electric motor and is an energy source
`to drive the electric motor, further comprising the step
`of operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`14. Method according to claim 9, wherein a battery is
`coupled to the electric motor and is an energy source to
`drive the electric motor, further comprising the step of
`operating the internal combustion engine at a torque
`equal to a set value which is greater than the torque
`corresponding to ideal operation, whenever the battery
`is discharged to a severe degree.
`15. Method according to claim 9, wherein an auto
`matic transmission is coupled to at least one of the inter
`nal combustion engine and the electric motor, and fur
`ther comprising the step of controlling the transmission
`such that, with a discharged battery, a low gear is se
`lected.
`16. Method according to claim 9, further comprising
`controlling the amount of torque taken up by the elec
`tric motor operating in generator mode to a set value
`corresponding to the differential torque.
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