WO2008122391A1

WO2008122391A1 - Method for controlling the drive system of a motor vehicle

Info

Publication number: WO2008122391A1
Application number: PCT/EP2008/002607
Authority: WO
Inventors: Michael Back; Harald Braun; Markus Bulling; Norbert Ebner; Ralf KÖRBER; Oliver Vollrath
Original assignee: Daimler Ag
Priority date: 2007-04-05
Filing date: 2008-04-02
Publication date: 2008-10-16
Also published as: DE102007016513A1

Abstract

The invention relates to a method for controlling a drive system (1) for a motor vehicle comprising an internal combustion engine (2) with a crankshaft (4) and at least one electric motor (3) that is or can be coupled to the internal combustion engine (2), in particular the crankshaft (4). According to the invention, when the vehicle is in overrun mode, if the speed near the idling range drops below an idling target speed (nSollLeerv) for the internal combustion engine (2), an anti-stall procedure is activated by means of an actual speed (nIstv) of the internal combustion engine (2), a target torque (MSollE) being applied to the electric motor (3) in the procedure and said torque being less than or equal to the maximum possible current torque (MMaxE) of the electric motor (3).

Description

Method for controlling a drive system for a motor vehicle

The invention relates to a method for controlling a drive system for a motor vehicle with an internal combustion engine comprising a crankshaft and at least one electric motor which can be coupled to the internal combustion engine.

Such a drive system is commonly referred to as a hybrid drive. When developing and optimizing new drive systems for motor vehicles, emissions, fuel consumption, performance and ride comfort are taken into account. Today's internal combustion engines are generally equipped with engine management functions that can set different operating conditions.

For example, to reduce fuel consumption and pollutant emissions as an operating condition, coasting is adjustable when the driver takes his foot off the accelerator pedal while driving. In this case, the internal combustion engine is pushed by the inertia of the motor vehicle in overrun mode, the drive power of the internal combustion engine is no longer needed. By activating a so-called overrun fuel cutoff during coasting, especially above a lower speed limit, which is significantly above the idling speed limit, speed, usually the injection and the ignition of the internal combustion engine is switched off, wherein the motor vehicle is braked by the compression work to be performed by the internal combustion engine. A deactivation of the fuel cut is either at least indirectly by the driver, for example by this gas again, or automatically, for example, when the speed of the engine falls below a certain limit, which is above the idle speed. Then, fuel is supplied again and the ignition is switched on, so that the internal combustion engine again generates a drive torque.

The deactivation of the fuel cut and thus the injection usually takes place in a speed range well above the idle speed in a speed range of about 1500 U / min, while maintaining the fuel cut below this speed range would risk that the idle speed reached o - The falls below and not fast enough torque can be built so that the engine runs out (= so-called "stalling").

The invention is therefore based on the object of specifying an improved method for controlling a drive system of a motor vehicle, in which a stalling is avoided in particular in overrun operation.

The object is achieved by a method having the features of claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims. In the method according to the invention for controlling a drive system for a motor vehicle having an internal combustion engine comprising a crankshaft and at least one electric motor coupled to or coupled to the internal combustion engine, in particular its crankshaft, an anti-swelling protection is activated in the idling speed range when the idling target speed of the internal combustion engine falls short of the current actual rotational speed of the internal combustion engine. in which the electric motor is subjected to a setpoint torque that is less than or equal to a currently possible maximum torque of the electric motor. In this case, the electric motor in the idling speed range is applied to the determined dynamic setpoint torque until an upper speed limit for the internal combustion engine is reached or exceeded. This ensures that, in particular in a speed range below the idling speed of the internal combustion engine, the electric motor is set with the maximum possible and available dynamic torque which may be above a requested setpoint torque and then increases this.

Preferably, the electric motor is set to reach or exceed a predetermined upper speed limit (= a predetermined upper threshold) with the maximum possible torque, which is then applied to the crankshaft. In this case, the setting of the electric motor with the possible maximum torque is active in particular only once per ignition run, unless the predetermined upper speed threshold is reached or exceeded. Thus, it is ver ^¬ avoided that with active Abwürgeschutzfunktion the setting of the maximum torque, for example, more than once active with an empty tank. By setting and applying a torque resulting from the setpoint torque on the electric motor to a maximum available dynamic torque outgoing ("stalling") of the engine is reliably avoided, since the additional rotational torque of the E- lektromotors on the crankshaft, the actual speed of Internal combustion engine is held in the idling speed range. This maintenance of a minimum speed for the internal combustion engine by connecting the electric motor and connecting a torque of the electric motor to the crankshaft thus enables a stall protection function for the internal combustion engine.

Moreover, as a result of the continuous determination of further rotational speed characteristic values of the internal combustion engine, such as the rotational speed difference and / or optionally a rotational speed gradient, the nominal torque can be adapted dynamically to rotational speed fluctuations or critical rotational speed values of the internal combustion engine resulting from these rotational speed characteristics, so that these occurring rotational speed fluctuations correspond to the actual rotational speed of the engine Combustion engine can be compensated by switching on the dynamically set torque of the electric motor and results in a largely uniform and quiet speed curve. In addition, fuel consumption and pollutant emissions are reduced by such an adjustable uniform driving behavior in overrun mode and especially in overrun with overrun fuel cutoff.

The process is preferably in one or more control ^¬ devices, in particular in an existing control device such as an engine control unit, or in a regulator, in particular an existing controller, such as an idle-running regulator ^¬ implemented. Preferably, the currently possible maximum torque of the electric motor depending on the state of charge of a battery, the speed difference, in particular the distance of the actual speed of the idle target speed of the engine, the cooling water temperature, the actual speed of the engine, the temperature of the engine, the temperature of the electric motor and / or the temperature of the battery can be determined. Thus, the electric motor is adjusted only with a currently allowable maximum torque, so that an overload of the electric motor is avoided.

In a further advantageous embodiment, the determined target torque for the electric motor is limited to a predetermined minimum torque of the electric motor, in particular during torque-controlled operation. A torque-guided operation is understood in particular to be a connection and operation of the electric motor in the idling speed range of the internal combustion engine without charging operation. If, according to the method described above, a setpoint torque for the electric motor to achieve stalling protection is determined, which is expediently above the predefined minimum torque of the electric motor, this is preferably switched on, wherein the determined setpoint torque for the electric motor is set at this. The determined setpoint torque is also set when the electric motor is already switched on. In detail, the stall protection function is highly prioritized when the electric motor is switched on, so that the determined target torque is set sufficiently fast.

The permissible minimum torque is preferably dynamic, in particular as a function of the rotational speed difference, in particular the distance of the actual rotational speed from the idling nominal torque. speed of the internal combustion engine, the cooling water temperature and / or determined by the voltage of the electric motor.

In addition, the determined setpoint torque for the electric motor in the loading mode is limited down to a determined mimic load torque. In detail, a variable charging torque is preferably set in the charging operation, which determines depending on the current charging requirement and which is limited to a depending on the distance of the actual speed of the idle target speed of the engine and the cooling water temperature Mimimalladedrehmoment down or to a maximum load torque upwards. As a result, it is ensured that the electric motor is loaded within the permissible limit in the loading mode.

In addition, for the minimum load torque, a lower load torque limit is specified which is limited by a gradient limiter with variable positive gradients and variable negative gradients to avoid a negative charge torque jump in the event of a voltage dip.

Preferably, the difference between idle target speed and instantaneous actual speed of the internal combustion engine (also called engine speed) is determined as the speed difference. As a further speed characteristic for the variable adjustment of the setpoint torque of the electric motor, a torque gradient can be additionally determined, for example. As a torque gradient, the first derivation of the speed changes of the actual rotational speed of the internal combustion engine per predetermined time unit is preferably determined. In this way, for example, a strong reduction of the actual speed can be detected when the overrun fuel cutoff is activated in overrun mode and the actual speed additionally drops sharply due to the deceleration of the motor vehicle due to the compression work to be performed by the internal combustion engine and thus it could quickly lead to falling below the idling speed and to switching off the internal combustion engine in the idling speed range.

Advantageously, the instantaneous actual rotational speed of the internal combustion engine is detected continuously by means of a rotational speed sensor. In addition, for example, from a control unit, in which a Leerlaufregier is implemented, the idling target speed continuously determined.

The electric motor is in particular a rotating electrical machine, which can be operated both as an electric motor and as an electric brake, starter generator and / or generator. In addition, a braking energy obtained in a conventional manner from a set and applied braking torque can be stored, for example in a battery, by the electric motor which can also be operated as a generator.

The electric motor can be coupled or coupled indirectly via an automated manual transmission or an automatic transmission with the internal combustion engine. Alternatively, the electric motor may also be directly coupled or couplable, e.g. when the rotor of the electric motor - similar to a flywheel - is arranged directly on the crankshaft of the internal combustion engine or on a couplable extension of this crankshaft.

Embodiments of the invention are explained in more detail below with reference to drawings. Showing:

Fig. 1 shows schematically a control device for controlling a drive system with an internal combustion engine and a coupled or coupled to this electric motor, and

Fig. 2 is a schematic diagram with different torque curves as a function of time.

Corresponding parts are provided in all figures with the same reference numerals.

FIG. 1 schematically shows a drive system 1 designed as a hybrid drive for a motor vehicle, comprising a combustion engine 2 and an electric motor 3. The electric motor 3 is connected or connectable to and can drive a crankshaft 4 of the internal combustion engine 2, that is. exert positive or negative torques on them. To obtain recuperation energy, the electric motor 3 is connected to a battery 5. Depending on the type and structure of the hybrid drive, e.g. serial hybrid, parallel hybrid or hybrid hybrid, the electric motor 3 is directly or indirectly via a transmission 6, e.g. an automated manual transmission or an automatic transmission, with the crankshaft 4 coupled. In the embodiment of Figure 1, the electric motor 3 can be coupled directly to the crankshaft 4.

For controlling and / or regulating the drive system 1, an electronic control unit 7 is provided. The control unit 7 may be an existing control device such as Bremssteuerge ^¬ advises its engine controller, Leerlaufregier, into which the method described hereinafter is implemented. About that In addition, further control and / or regulation methods, for example for driving stability, recuperation and charging of the battery 5, idling control, engine control and / or brake control, may be implemented in the control unit 7. By means of the control device 7, both the internal combustion engine 2 and the electric motor 3, preferably only the electric motor 3 can be controlled and / or regulated.

In the operation of the motor vehicle, by removing an acceleration request, for example by the driver taking his foot off the accelerator pedal 8 and no longer actuating it, or by requesting an automatic traction drive control, for example a so-called cruise control, not acceleration, but a speed reduction, or a spacer for automatic compliance with a distance requesting a speed reduction, for the motor vehicle as the operating state, a pushing operation are set, in which the motor vehicle is pushed by its inertia and the driving power of the engine 2 is no longer needed.

To control the drive system 1 in such a coasting operation, the control unit 7 is provided with at least the following parameters, a torque request M derived from a set value A of a pedal value transmitter 9 of the accelerator pedal 8, at least one speed n of a speed sensor 10 (eg actual speed n i _st v of the internal combustion engine 2 and actual rotational speed n _est E of the electric motor), temperature _values T _v , T _E and T _B of temperature sensors 11 to 13 of the internal combustion engine 2, the electric motor 3 and the battery 5. Another temperature sensor 14 determines the cooling water temperature T _κ . In addition, the controller 7 further parameters led to ^¬ or determined by this on the basis of other parameters are: an idling nominal speed n _So ii _Lee rv / momentary minimum actual torques M _m i _nV and M _m j _{.nE of} the internal combustion engine 2 and the electric motor 3 of the motor vehicle driving in overrun mode (which are called thrust torques M _m i _n v, MminE) ), Speed limit values n _limit , a request signal S _SAS for activating or deactivating a fuel cut-off SAS and / or a permissible minimum torque Ms _tat minE of the electric motor 3 (= minimum limit value).

In addition, for the consideration of operating and driving parameters for activating or deactivating a fuel cut and / or for activating or deactivating a recuperation or a charging operation of the battery 5 further characteristic values are used: a state of charge value L of a state of charge SOC of the battery 5, an inclination value N of a tilt sensor 15 , a program value P of an automatic program of the transmission 6 selected by means of a switch 16, the vehicle speed v, a longitudinal or lateral acceleration a _L , Q of the motor vehicle.

By means of the control unit 7, a rotational speed gradient dn / dt representing the internal combustion engine 3 for a given time unit and a rotational speed difference Δn are determined directly or indirectly on the basis of the ascertained or acquired characteristic values, parameters and / or physical variables. Both the speed gradient dn / dt and the speed difference Δn are determined continuously.

During operation of the vehicle is in idle speed range depending on the value of the control unit 7 supplied and / or determined by this parameters, in particular depending on the distance of the actual speed n _Ist v of the idling target speed n _So ii _Leer v of the internal combustion engine 2 the Subsequently, with reference to Figure 2 described method for setting a target _torque M _SOIIE for the electric motor 3 executed.

FIG. 2 shows various torque curves V1 to V5 as a function of time t.

Here, the torque curve Vl the course of the target torque Ms _o iiE of the electric motor 3 (= torque specification for electric motor in torque-controlled operation), the torque curve V2 a lower charging torque limit M _Ladeg renz (= lower, dependent on the current load torque request limit), the torque curve V3 charging torque M _charge e

(= virtual charging torque in the torque-controlled operation o- the recalculated charging torque during charging) of the electric motor 3, the torque curve V4 a minimum _load torque M _LademinE (= lower charging torque limit) and the torque curve V5 a permissible minimum torque M _sta tminE

(= lower torque limit) of the electric motor 3 is.

During operation of the vehicle, this is up to the time tl while driving. From the time t1 to the time t2, the vehicle is in overrun with or without fuel cut in which the vehicle is pushed by its inertia alone. At time t2 and t3 is a charging torque request for charging the battery 5, for the operation of electrical loads, eg. As an electric air compressor, and / or to support a vehicle electrical system. At time t4, the driving operation of the vehicle is resumed, for example, the driver again actuates an accelerator pedal. In order to avoid in the overrun mode in the near-idle rotational speed range a so-called engine stall 3, when falling below the desired idling speed _So iiLe _e rv n n by the actual speed V of _the internal combustion engine 2, an exhaust wurgeschutz enabled, through which the electric motor 3 with a setpoint torque M _{SOIIE is} applied, which is less than _or equal to a currently possible maximum torque M _Ma χE, as shown by way of example the variable torque curve Vl for the target torque M _SOIIE from the time t2.

In this case, positive torque _{values are} brought to the crankshaft 4 as a driving torque by means of the set desired torque M _SOIIE . As a result of the additionally applied torque MistE of the electric motor 3 on the crankshaft 4 of the internal combustion engine 2, the actual rotational speed n _{actual of} the internal combustion engine 2 increases and a fall of the actual rotational speed n _actual v of the internal combustion engine 2 is far below the idling rotational speed n _L into a switch-off region for the internal combustion engine 2 safely avoided.

The setpoint _torque M _SOIIE is _limited in particular at Momentenfuh- tion, ie in torque-guided operation down to the predetermined permissible minimum torque Ms _t atmmE and up to the maximum torque M _MaXE . The application of the currently possible maximum torque M _MaxE ensures that in the speed range below the idling speed n _L the electric motor 3 is set with its maximum possible and available dynamic torque M _maX E, which, for example, _exceeds the determined setpoint torque Ms _o ii _{E can} lie. In this case, the electric motor 3 is set to reach or exceed a predetermined upper speed limit n _Gre n _z with the possible maximum torque M _maxE . Depending on the specification, the currently possible maximum torque M _Ma χE is determined as a function of the following parameters: state of charge SOC of the battery 5, instantaneous speed difference Δn, instantaneous actual speed ni _st v of the internal combustion engine 2, instantaneous desired idling speed n _So iiL _e erv of the internal combustion engine 2 , the cooling water temperature T _{K /} the temperature Tv of the internal combustion engine 2, the temperature T _{B of} the battery 5, and / or the temperature T _{E of} the electric motor 3.

The minimum torque Mst _at minE serving as the lower torque limit can also be determined dynamically as a function of at least one of the following parameters: instantaneous speed difference Δn, instantaneous actual speed n _is v of the internal combustion engine 2, instantaneous desired idling speed nsoHLe _e rv of the internal combustion engine 2, the cooling water temperature T _κ , the temperature T _{E of} the electric motor 3 and / or the voltage of the electric motor. 3

If it comes in addition to a charging request and thus to a charging operation (see times t2, t3; Figure 2), then the determined target _torque M _SOIIE down depending on the distance of the actual speed ni _st v of the engine 2 to idle target speed n _So iiL _e erv to a dependent on idle minimum _load torque M _loading minE for the electric motor 3 be ^¬ limits, as shown by way of example on the basis of the torque curve V4.

In addition, a variable charging torque M _Lade E (see torque curve V3) is determined, which depends on a current charging request, for. B. from a battery 5, a vehicle electrical system and / or a load, such as a Klimakompres ^¬ sor, is determined and the up by a maximum load _torque M _LademaxE and down by a Minimalladedreh- torque ML _ade _miEn (see torque curve V4) is limited. In this case, the minimum _{load torque} M _{load is} _determined as a function of the distance of the actual speed n _actual v of the internal combustion engine 2 to the idling nominal speed n _So ii _Leer v of the internal combustion engine 2 and is thus variably predetermined. In order to avoid a negative Ladedrehmomentsprung in the event of a voltage dip, a lower charging torque limit M _Lade grenz (= torque curve V2 = dependent on the current load torque request limit) is variably specified by a Gradientenbegrenzer (= limiting the change of the lower load torque limit M _Lade grenz) with variable positive gradient and variable negative gradient is limited. In particular, high positive gradients, as shown at time t4 on torque curve V2, are permissible.

The total permissible minimum load torque M _e ffLademnE and thus also the desired charging torque M _Ladeso iiE is bounded below by the maximum of the minimum _load torque M _Ladem i _nE (= torque curve V4) and the lower load torque limit M _Lade g _re nz (= torque curve V2). This ensures that the virtual charging torque M _charge E in the torque-guided operation can not be arbitrarily negative.

Further, further, the speed behavior of the motor vehicle influencing parameters can be considered. For this purpose, for example, characteristic curves as a function of the selected automatic program P, of the determined pitch N and / or the temperatures T _v , T _E , T _B , predetermined for a speed-dependent Kenn ^{¬ line} guide the target _torque M _{SOHE of} the electric motor 3. Taking into account these dependencies by a determined characteristic in determining the einzustel ^¬ lumbar desired torque M _{as ļell} serves in particular a ver ^¬ improved ride comfort and / or safety of the vehicle and / or the vehicle stability, whereby in the permissible operating range of the two engines, the stalling protection has priority. For vehicle safety, for example, at a high engine temperature T _{E of} the electric motor 3, the target torque Ms _o ii _{E is} not switched to avoid too high a load of the electric motor 3.

Reference sign list

1 drive system

2 internal combustion engine

3 electric motor

4 crankshaft

5 battery

6 gears

7 control unit

8 accelerator pedal

9 accelerator pedal

10 speed sensor

11 Temperature sensor for internal combustion engine

12 temperature sensor for electric motor

13 temperature sensor for battery

14 Temperature sensor for the cooling water temperature

15 tilt sensor

16 switches for selecting an automatic program

A clamping the accelerator pedal a longitudinal acceleration a _L _Q lateral acceleration

M _maxE maximum torque of the electric motor

M _m i _nE minimum _{torque of} the electric motor

M _La de _E charging torque of the electric motor

M _charging _limit lower charging torque limit of the electric motor

M _L ad _em a _xE Maximum load _{torque of} the electric motor M _Charging i _{nE Minimum load torque of} the electric motor

^ Charge _so IIe charging target torque of the electric motor

Ms _o iiE target torque of the electric motor

N Slope n Speed ni _s tE Actual speed of the electric motor nistv Actual speed of the combustion engine n _L Idling speed nsoiiLeerv idle idle speed

P automatic program

S _SAS request signal for fuel cut

SAS overrun cutoff

SOC State of charge of the battery

Claims

claims

1. A method for controlling a drive system (1) for a motor vehicle with a crankshaft (4) comprising an internal combustion engine (2) and at least one of the internal combustion engine (2), in particular the crankshaft (4) coupled or coupled electric motor (3), wherein when the vehicle is in overrun, in the idling speed range falls below an idle speed (ns _o iiL _ee rv) of the internal combustion engine (2) by an actual speed (ni _st v) of the engine (2) a stall protection is activated, wherein the electric motor ( 3) is acted upon by a setpoint torque (M _So n _E ), which is less than or equal to a currently possible maximum torque (M _MaX E) of the electric motor (3).

2. The method according to claim 1, characterized in that the determined target _torque (M _SOIIE ) for the electric motor (3) as long as the currently possible maximum torque (M _MaxE ) of the electric motor (3) is set until the current actual speed (ni _st v ) of the Verbrennungsmo ^¬ gate (2) is equal to or greater than a predetermined upper threshold value.

3. The method according to claim 1 or 2, characterized in that the currently possible maximum torque (M _MaxE ) of the electric motor (3) in dependence on the state of charge (SOC) of a battery (5), of the speed difference (Δn), of the Kuhlwassertemperatur ( T _κ ), an actual speed (ni _st v) of the internal combustion engine (2), a temperature (T _v ) of the internal combustion engine (2), a temperature (T _E ) of the electric motor (3) and / or of a Temperature (T _B ) of the battery (5) is determined.

4. The method according to any one of claims 1 to 3, characterized in that the target torque determined (M _{as ļell)} ^for (Ms _did MME) the electric motor (3) in momentengefuhrten operation to a predetermined zulassiges minimum torque is limited downwards.

5. The method according to claim 4, characterized in that the permissible minimum torque (Ms _ta TmmE) in dependence on the speed difference (Δn), the Kuhlwassertemperatur (T _K ) and / or of the voltage (U) of the electric motor (3) is determined ,

6. The method according to any one of claims 1 to 5, characterized in that the determined target _torque (M _SOIIE ) for the Elektromo ^¬ tor (3) in the loading mode to a determined Mimimallade- torque (M _Ladem i _nE ) is limited downwards.

7. The method according to any one of claims 1 to 6, characterized in that a variable load torque (M _loading E) is set in the charging mode, which determines in dependence on the current load request and a function of the current rotational speed difference (An) and the cooling water temperature (T _κ) unidentified Mimimalladedrehmo- ment (M _La Demine) is limited at the bottom or the maximum charging torque (M _Lad emaχE) upwards.

8. The method according to claim 7, characterized in that for the minimum _load torque (M _Lade minE) a lower charging torque limit (M _La degrenz) is given, which is limited by a Gradientenbegrenzer with variable positive gradient and variable negative gradient.

9. The method according to any one of claims 1 to 8, characterized in that the speed difference (Δn), the difference between the idle target speed (ns _o iiLeerv) and instantaneous actual speed (n _Ist v) of the internal combustion engine (2) is determined.

10. The method according to any one of claims 1 to 9, characterized in that by means of a speed sensor (10) the instantaneous actual speed (ni _st v) of the internal combustion engine (3) is continuously recorded.

11. The method according to any one of claims 1 to 10, characterized in that the idling target speed (n _So iiLeer) is determined continuously.