DE102012222197A1 - Method for distribution of drive torque to primary axle and secondary axle of motor vehicle, involves limiting maximum adjustable torque of secondary axle to certain maximum value by torque distribution device - Google Patents

Abstract

The method involves determining a current or upcoming parking situation of a motor vehicle and reducing the maximum adjustable axle torque of a secondary axle (2). The maximum adjustable axle torque of the secondary axle is limited to a certain maximum value by a torque distribution device. The axle torque of the secondary axle is reduced or the maximum adjustable axle torque of the secondary axle is reduced by reducing the clutch torque (MK) of a four-wheel drive controllable clutch (3). The clutch torque is increased again in the case of an arising instability of the vehicle. Independent claims are also included for the following: (1) a process for distribution of axle torque to left and right wheels of a common axle of a motor vehicle (2) a motor vehicle with a park assistance system.

Description

The invention relates to a method for torque distribution of a drive torque to a primary axis and a secondary axis of a motor vehicle having an all-wheel drive with a torque split device for dividing the drive torque to the permanently driven primary axis and the secondary axis driven if necessary. Furthermore, the invention relates to a method for torque distribution of an axle torque on a left and a right wheel of a common axle of a motor vehicle having a torque split device for variably dividing an axle torque on the two wheels of this axle, wherein different wheel torques for the left and the right wheel adjustable are. Moreover, the invention relates in each case to a motor vehicle configured for carrying out the respective method.

In switchable four-wheel drives an axle of the motor vehicle is driven permanently; this axis is called the primary axis. A second axis - referred to as the secondary axis - is added on demand by the control electronics. For this purpose, the drive torque of the vehicle drive is divided by means of a torque split device onto the permanently driven primary axle and the secondary axle which can be driven if necessary. Through the torque split device, the torque split ratio between the axle torque of the primary axis and the axle torque of the secondary axle can be changed. By defining a torque split ratio, the traction and drivability of a vehicle can be influenced as needed.

In the simplest case, the torque split device can be switchable between only two states, wherein in the first state the drive torque is completely transferred to the primary axis and in the second state the drive torque is transmitted to the primary axis and the secondary axis in a ratio of 1: 1, for example; but preferably the torque split ratio is continuously variable. The torque split device typically employs a controllable four-wheel clutch that provides torque to the secondary axle when needed; This is also referred to as a clutch-controlled four-wheel drive. In a clutch-controlled four-wheel drive, the four-wheel clutch is preferably controlled electronically. Here, a clutch torque of the four-wheel clutch is set, which at the same time corresponds to the maximum possible torque which can be transmitted from the clutch in the direction of the secondary axis. By varying the clutch torque, the torque ratio between the primary and secondary axles can be varied variably in four-wheel drive, for example from 1: 1 to 2: 1.

In the publication DE 100 54 023 A1 are clutch-controlled four-wheel drive with each front or rear axle described as the primary axis. In this case, depending on the driving dynamics variables such as the steering angle, the rotational or yaw rate and the lateral acceleration, the four-wheel drive is controlled to reduce oversteer or understeer when cornering in a neutral driving behavior.

Furthermore, in the document DE 103 33 654 A1 a clutch-controlled four-wheel drive described in which, depending on the driving speed, a speed-related clutch torque is specified as the maximum permissible limit torque.

In addition, from the document DE 10 2009 031 500 A1 a clutch-controlled four-wheel drive is known in which in the presence of a Einkuppelstoß risk criterion, the four-wheel drive is controlled according to a temporarily reduced clutch torque value.

Furthermore, it is from the document DE 10 2009 032 265 A1 known to set a reduced clutch torque on the four-wheel clutch for the thermal protection of an all-wheel drive.

In analogy to the torque distribution in the longitudinal direction between the two vehicle axles described above, systems are also known with the help of the torque distribution - exclusively or in addition to the above-described longitudinal torque distribution - between axle-facing vehicle wheels, so for example those of the front axle and / or those of the rear axle, can be changed. These systems may be, for example, electronically controllable cross-locks or torque vectoring systems (also referred to as active yaw systems). In contrast to a simple open differential, which divides the axle torque in half on both wheels, the coupling of the wheel speeds can be varied with a controllable transverse lock, so that with increasing coupling of the free speed compensation is hindered; This also has an influence on the distribution of the axle torque between the right and the left wheel. In a torque vectoring system, the axle torque can be distributed variably to the left and right wheels of the common drive axle. By means of this variable transverse division, the traction and driving behavior of a vehicle can be decisively influenced.

An exemplary torque vectoring system is in the article "The Dynamic Performance Control from BMW", ATZ - Automobiltechnische Zeitschrift, 11/2008, pages 984 to 994 described.

In parking assistance systems with transverse guidance, the steering of the vehicle is taken over by the system during the parking process. The driver must accelerate and brake the vehicle during the parking process (longitudinal guidance). In parking assistance systems with transverse and longitudinal guidance, the parking assistance system also performs a longitudinal guidance of the vehicle.

The parking assistance systems described above typically have a parking space measurement, by means of which longitudinal and / or transverse parking spaces are measured during the passage. In addition to the measurement of parking spaces, a trajectory planning and a continuous positioning of the own vehicle in relation to the parking space and the planned trajectory are necessary. The vehicle position is determined by odometry, i. H. based on the observation of the wheels of the vehicle. Based on the number of revolutions of the wheels, the distance covered can be calculated with known wheel circumference; Based on the steering angle of the individual wheels, the direction of the vehicle movement can be determined. For the odometry, a non-driven axle is typically used, as here the slip of the wheels is significantly lower compared to a driven axle.

When the parking assistance system is activated, unwanted functional side effects or effects on the parking assistance system may be caused during active four-wheel drive operation. The reason for this is that in all-wheel drive, in contrast to pure rear or front wheel drive, the wheels of the secondary axle can not roll freely with any wheel speed and therefore the wheel slip compared to a vehicle with pure rear or front wheel drive is greater. The same applies to systems with variable cross-division. When setting a correspondingly large wheel torque difference in a torque vectoring system, unlike a simple open axle differential, the wheel speeds can no longer be set freely, so that increased wheel slip can occur.

With a torque distribution in the longitudinal direction and / or transverse direction, a free rolling of individual vehicle wheels is prevented due to the coupling of the axles or wheels with each other, so that the wheel slip generally increases. This disturbs the odometry; There is a greater error in the determination of the distance, so that the determined position of the vehicle is provided with a larger error. Thus, the automatic measurement of the parking space when driving by, the exact determination of the trajectory for parking and the determination of distance to obstacles (such as other parked vehicles, curbs, etc.) difficult.

It is an object of the invention to reduce the above-described negative influence of a torque distribution in the longitudinal and / or transverse direction on a parking assistance system.

The object is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

A first aspect of the invention relates to a method for torque distribution of a drive torque to a primary axis and a secondary axis of a motor vehicle. For example, the primary axis corresponds to the rear wheel axle and the secondary axle corresponds to the front wheel axle (or vice versa). The vehicle includes an all-wheel drive with a torque split device for dividing the drive torque to the permanently driven primary axis and the driven if necessary secondary axis. Furthermore, a parking assistance system with transverse guide and optional longitudinal guide is provided.

According to the method, a current or imminent parking situation is determined by the vehicle, for example, a parking situation is determined by the vehicle based on the activation of the parking assistance system, which is triggered for example by the driver by pressing an operating element or a reverse gear. To detect a parking situation, for example, an activation bit can be evaluated, which indicates the activation state of the parking assistance system. An upcoming parking situation may alternatively be recognized, for example, by the fact that the vehicle has reached or is about to reach a destination point entered in the navigation system or a specific location (for example, home or workplace).

When determining a current or imminent parking situation, for example, the axle torque of the secondary axle is reduced via the torque distribution device, so that the freewheel of the wheels of the secondary axle increases. Conversely, the axle torque of the primary axle is preferably increased via the torque split device, so that preferably the torque ratio between the axle torque of the primary axle and the axle torque of the secondary axle is increased. For example, the axle torque of the secondary axle are reduced and vice versa, the axle torque of the Secondary axis increased so that the torque ratio between the axis torque of the primary axis and the axle torque of the secondary axis, for example, 50:50 to 80:20 or 100: 0 is increased.

It can also be provided that, when determining a current or imminent parking situation, the maximum torque of the secondary axis which can be set via the torque distribution device is reduced. In this case, it is not absolutely necessary for the currently existing axle torque of the secondary axle to be reduced immediately as well. For example, the adjustable axle torque is reduced by lowering the clutch torque of an all-wheel clutch. When lowering the clutch torque of the four-wheel drive namely the maximum adjustable via the four-wheel clutch on the secondary axle axle torque is reduced, since the clutch torque corresponds to the maximum possible torque, which can be transmitted from the four-wheel drive in the direction of secondary axis.

Alternatively, it can also be provided that, when determining a current or imminent parking situation, the axle torque which can be set via the torque split device is limited upwards (to a specific maximum value for the axle torque), without a limit of the adjustable axle torque being present beforehand.

By reducing the current or the maximum adjustable axle torque of the secondary axle according to the invention or by limiting the adjustable axle torque, the freewheeling of the wheels of the secondary axle tends to be promoted. The above-described disturbance of the odometry, which leads to a larger error in determining the distance covered and the position of the vehicle, is therefore counteracted.

According to a preferred embodiment, the four-wheel drive is a clutch-controlled four-wheel drive, in which the primary axis is permanently driven and the secondary axis can be driven via a controllable with respect to their clutch torque four-wheel clutch. For torque distribution, a controllable four-wheel clutch is used, Here, a clutch torque of the four-wheel clutch is set, which typically corresponds to the maximum possible torque, which can be transmitted at a correspondingly high engine torque from the clutch in the direction of the secondary axis. The current or the maximum adjustable axle torque of the secondary axle is reduced when detecting a current or an imminent parking situation by the clutch torque is reduced. When the axle torque of the secondary axle before lowering the clutch torque is greater than the clutch torque after lowering the clutch torque, not only the maximum axle torque of the secondary axle adjustable via the four-wheel clutch is reduced by lowering the clutch torque, but also the actual axle torque of the secondary axle is reduced.

It is advantageous if with active parking assistance system and occurring instability on a drive wheel or a drive axle (the wheel or the wheels of an axle in this case, for example, an improper traction with respect to the road) the clutch torque is increased again to the stability or traction of the Vehicle to ensure.

For example, in this case, the lowering of the clutch torque can be maintained for this purpose, but superimposed (ie additive) and the four-wheel clutch slip control continues to be effective, which increases the clutch torque in this case substantially wheel slip dependent and temporary. The aim of this is, for example, to ensure sufficient traction performance when parking on roads with unfavorable coefficients of friction (eg ice, snow, loose ground, etc.).

Furthermore, it is advantageous if in the above-described case, the parking assistance system receives information about this, so that the parking assistance system can adjust to a temporarily possible falsification of the odometry (which can lead to a more inaccurate determination of distances to obstacles and a less accurate trajectory determination ).

A second aspect of the invention relates to a method for torque distribution of an axle torque to a left and a right wheel of a common axis, for example the rear axle or the front axle. Thus, in the second aspect of the invention, the longitudinal distribution of torque on two axes as in the first aspect of the invention is transverse distribution of torque between two wheels of a common axis. As in the first aspect of the invention, the vehicle comprises a parking assistance system with transverse guidance and optional longitudinal guidance.

Further, a torque split device for dividing an axle torque is provided on the two wheels of this axis.

About the torque distribution device either different wheel torques for the left and right wheels are adjustable or it the coupling of the wheel speeds for the left and the right wheel is variable.

The torque distribution device is, for example, a so-called torque vectoring system for setting different wheel torques for the two wheels. The torque vectoring system used comprises, for example, a rear axle transmission with a basic transmission, a left superimposition unit and a right superimposition unit. In driving situations without torque transfer, the system behaves like a rear differential with an open differential. Due to the two superposition units, the two wheels of the rear wheel axle can be driven at different high moments. Such a torque vectoring system is in the article "The Dynamic Performance Control from BMW", ATZ - Automobiltechnische Zeitschrift, 11/2008, pages 984 to 994 described; the content of this article is hereby incorporated by reference into the disclosure of the application.

Alternatively, it can also be a controllable transverse lock, via which the coupling of the wheel speeds can be varied.

According to the invention, a current or imminent parking situation is determined by the vehicle, as has already been described in connection with the first aspect of the invention. Upon detection of a current or upcoming parking situation, the difference between the wheel torque of the left wheel and the wheel torque of the right wheel is reduced via the torque split device. Alternatively, it can also be provided that the maximum adjustable difference between the wheel torques via the torque distribution device is reduced. Alternatively, the difference between the wheel torques that can be set via the torque distribution device can also be limited upwards. Alternatively, by a lower coupling of the wheels of an axle with each other, the free speed compensation between these same wheels allows or at least be improved.

By reducing the current or maximum adjustable difference between the wheel torques according to the invention, the freewheeling of the wheels of the secondary axle tends to increase and the slip of the wheels of the secondary axle tends to decrease; the behavior of the torque split device is changed towards the open axle differential. The above-described disturbance of the odometry, which leads to a larger error in determining the distance covered and the position of the vehicle, is therefore counteracted.

It can also be provided that when determining a current or imminent parking situation, both the measures of the inventive method for torque distribution in the longitudinal direction according to the first aspect of the invention and the measures of the method according to the invention are carried out in the transverse direction.

A third aspect of the invention is directed to a motor vehicle which comprises a parking assistance system with transverse guidance and optionally longitudinal guidance and an all-wheel drive. The four-wheel drive includes a torque split device (for example, an all-wheel drive) for dividing the drive torque to a permanently driven primary axis and a driven if necessary secondary axis. The motor vehicle is set up to detect a current or imminent parking situation. When a current or imminent parking situation is detected, the axle torque of the secondary axle, which can be set via the torque split device, is reduced, the axle torque of the secondary axle is reduced via the torque split device, or the axle torque of the secondary axle, which is adjustable via the torque split device, is limited upward.

The above statements on the method according to the invention according to the first aspect of the invention also apply correspondingly to the motor vehicle according to the invention according to the third aspect of the invention. At this point, not explicitly described advantageous embodiments of the vehicle according to the invention according to the third aspect of the invention correspond to the described advantageous embodiments of the inventive method according to the first aspect of the invention.

A fourth aspect of the invention is directed to a motor vehicle, which comprises a parking assistance system with transverse guidance and optionally longitudinal guidance. Further, a torque split device for dividing an axle torque on a left and a right wheel of a common axis (for example, the rear axle) is present. For example, a torque vectoring system is used, in which the axle torque is variably divisible to the two wheels of the axle, wherein different wheel torques for the left and right wheels are adjustable. Alternatively, a controllable transverse lock is used, in which the coupling of the wheel speeds can be varied. The motor vehicle is set up to detect a current or imminent parking situation. When a current or upcoming parking situation is detected, the difference between the wheel torque of the left wheel and the wheel torque becomes of the right wheel is reduced via the torque split device. Alternatively, it can be provided that when determining a current or imminent parking situation, the maximum adjustable difference between the wheel torques via the torque distribution device is reduced in this case. Alternatively, it may be provided that, when determining a current or imminent parking situation, the difference between the wheel torques which can be set via the torque distribution device is limited. Alternatively, for example, in the case of a controllable transverse lock the coupling of the wheel speeds for the left and the right wheel of the common axis can be reduced.

The above statements on the method according to the invention according to the second aspect of the invention also apply correspondingly to the motor vehicle according to the invention according to the fourth aspect of the invention. At this point, not explicitly described advantageous embodiments of the vehicle according to the invention according to the fourth aspect of the invention correspond to the described advantageous embodiments of the method according to the invention according to the second aspect of the invention.

The reduction of the current or maximum adjustable axle torque described in the four aspects of the invention, limiting the adjustable axle torque or decreasing the current or maximum adjustable difference between the wheel torques or limiting the adjustable difference between the wheel torques depends on the determination of a current or upcoming Parking situation, which can be detected for example on the basis of the activation state of the parking assistance system.

• – der Aktivierungszustand (aktiv/passiv) von Regelsystemen des Kraftfahrzeugs (z. B. Antriebsschlupfregelung und/oder stabilisierender Fahrzeugregler und/oder Motorschleppmomentregler und/oder Verzögerungsregler und/oder weitere Fahrwerks- und Antriebsregelsysteme);
• – der Aktivierungszustand von Schutzfunktionen (z. B. Bauteilschutzfunktionen) oder Abgleich-/Lernfunktionen wie z. B. Reifentoleranzabgleich;
• – der Aktivierungszustand von Fahrerwunscheinstellungen (z. B. über Betätigungselemente wie Fahrerlebnisschalter und/oder Sportmodus-Taster);
• – die Geschwindigkeit und/oder ein Geschwindigkeitsgradient des Fahrzeugs und/oder einer Komponente eines Antriebsstrangs; hierbei können insbesondere folgende Geschwindigkeiten berücksichtigt werden: Fahrzeuggeschwindigkeit, Radgeschwindigkeiten, Achsgeschwindigkeiten, Getriebegeschwindigkeit, Differenzialgeschwindigkeit, Kardangeschwindigkeit, Antriebswellengeschwindigkeit, Abtriebswellengeschwindigkeit sowie jeweils die Beschleunigungen dieser Bauteile;
• – das Antriebsmoment und/oder der Antriebsmomentgradient des Kraftfahrzeugs;
• – die Motordrehzahl und/oder der Motordrehzahlgradient;
• – der Lenkwinkel und/oder der Lenkwinkelgradient;
• – die Fahrzeugquerbeschleunigung;
• – die Fahrzeuglängsbeschleunigung;
• – die Fahrzeugdrehrate (Gierrate);
• – der Schwimmwinkel und/oder der Schwimmwinkelgradient;
• – die Erkennung oder Prädiktion einer potentiellen Fahrzeuginstabilität;
• – die Fahrpedalvorgabe, das Fahrervorgabewunschmoment und/oder der Fahrervorgabewunschmomentgradient;
• – die Kraftschlussbedingung oder Reibwertbedingung zwischen Reifen und Fahrbahn aller Räder gemeinsam und/oder einzelner Räder und/oder einzelner Achsen;
• – die Fahrtrichtung und/oder Gangstufe und/oder wirksame Gangübersetzung und/oder Antriebsstranggesamtübersetzung bzw. Antriebstrangverstärkung;
• – die Fahrbahnlängs- und/oder -querneigung; dabei wird vorteilhafterweise die Fahrbahnlängs- und/oder Querneigung über Neigungs- und/oder Längs- und/oder Querbeschleunigungssensoren gemessen;
• – die Masse des Fahrzeugs und/oder die Achslasten bzw. Achsaufstandskräfte und/oder Radlasten bzw. Radaufstandskräfte; dabei wird insbesondere die Fahrzeugbeladung sowie ggf. ein Zustand mit oder ohne Anhänger berücksichtigt;
• – Fahrzeug mit erkanntem Anhänger, z. B. über Sensierung mittels Anhängersteckerbelegung
• – das Maß eines wirksamen Sperrgrades einer Drehmomentverteilungsvorrichtung; oder
• – die Temperatur der Umgebung und/oder der Reifen und/oder der Fahrbahn und/oder einer Komponente des Antriebsstrangs und/oder eines anderen Bauteils des Kraftfahrzeugs.

These measures may optionally additionally depend on one or more of the following condition parameters of the motor vehicle:

• The activation state (active / passive) of control systems of the motor vehicle (eg traction control and / or stabilizing vehicle controller and / or engine drag torque controller and / or deceleration controller and / or other chassis and drive control systems);
• The activation state of protection functions (eg, part protection functions) or matching / learning functions, such as B. tire tolerance adjustment;
• The activation state of driver's warning positions (eg via actuation elements such as driving experience switch and / or sport mode button);
• The speed and / or a speed gradient of the vehicle and / or a component of a drive train; In particular, the following speeds can be taken into account: vehicle speed, wheel speeds, axle speeds, transmission speed, differential speed, cardan speed, drive shaft speed, output shaft speed, and in each case the accelerations of these components;
• The drive torque and / or the drive torque gradient of the motor vehicle;
• The engine speed and / or the engine speed gradient;
• The steering angle and / or the steering angle gradient;
• The vehicle lateral acceleration;
• - the vehicle longitudinal acceleration;
• The vehicle rotation rate (yaw rate);
• The float angle and / or the slip angle gradient;
• The detection or prediction of potential vehicle instability;
• The accelerator pedal command, the driver request torque and / or the driver request desired torque gradient;
• The adhesion condition or friction coefficient condition between tire and roadway of all wheels together and / or individual wheels and / or individual axles;
• The direction of travel and / or gear ratio and / or effective gear ratio and / or powertrain overall transmission or driveline gain;
• - the lane longitudinal and / or bank; In this case, the roadway longitudinal and / or transverse inclination is advantageously measured by means of inclination and / or longitudinal and / or transverse acceleration sensors;
• The mass of the vehicle and / or the axle loads or axle contact forces and / or wheel loads or wheel contact forces; in particular, the vehicle load and possibly a condition with or without trailer is taken into account;
• - Vehicle with recognized trailer, z. B. via sensing by means of trailer pin assignment
• The degree of effective locking degree of a torque distribution device; or
• - The temperature of the environment and / or the tires and / or the road and / or a component of the drive train and / or another component of the motor vehicle.

The value to which the current or maximum adjustable axle torque is reduced or the adjustable axle torque is limited to the upper limit or to which the current or maximum adjustable difference between the wheel torques is reduced or the difference is limited upwards may be one or more of the above Condition parameter dependent. Further, the magnitude of the change may be in reducing the current or maximum adjustable Axis torque or the current or maximum adjustable difference of one or more of the above state parameters dependent. Furthermore, the time course of the reduction (for example, the slope) may also be dependent on one or more of the above state parameters. One or more of the above-described state parameters may also be used to find the optimum time to activate the measures described above.

After completion or termination of a parking process can be carried out as part of the process according to the invention change the torque distribution, z. B. weg- or time-controlled, be reversed again in a suitable manner and so the torque distribution can be adjusted to desired state again.

For example, the method is implemented as software in a suitable control unit for the longitudinal or transverse torque distribution and / or in any other vehicle control system (eg DSC - Dynamic Stability Control or ICM - Integrated Chassis Management). Thus, upon detection of a current or imminent parking situation, the above-described weakness of the odometry can be eliminated or at least reduced in the sense of a precontrol via an at least temporary, partial or complete change in the torque distribution.

The invention will be described below with reference to the accompanying drawings with reference to an embodiment. In these show:

1 schematically a motor vehicle with clutch-controlled four-wheel drive, the rear axle is driven permanently as a primary axis and the front axle is driven as a secondary axis by means of the controllable four-wheel drive;

2 An embodiment of a method for lowering the clutch torque of the four-wheel clutch; and

3 an exemplary time course of the clutch torque of the four-wheel clutch.

1 schematically shows a motor vehicle with clutch-controlled four-wheel drive, the rear axle 1 with the wheels 11 . 12 is permanently driven as the primary axis and the front axle 2 with the wheels 13 . 14 as a secondary axle by means of a controllable four-wheel clutch 3 is drivable. The vehicle is preferably a vehicle with front-engine drive, wherein a propeller shaft between the automatic transmission 5 and the axle drive 15 the rear axle 1 is provided. The method described below can also be applied to a vehicle with the rear axle as the secondary axle and the front axle as the primary axle.

The drive includes a motor 4 and with the engine 4 connected automatic transmission 5 , The transmission output side is the controllable four-wheel clutch 3 , here in the form of a multi-plate clutch.

In the four-wheel clutch, the clutch input is in the direction of the rear axle 1 interconnected, so that the rear axle 1 is permanently driven. Between four-wheel clutch 3 and rear axle 1 are a propeller shaft and a final drive 15 , The front axle 2 as a secondary axis is only when the clutch is closed 3 driven. For this purpose, in the case of a multi-plate clutch, the outside of the basket 6 toothed lamellae 7 and the internal splines on the hub 8th compressed. The friction causes the clutch basket 6 and the clutch hub connected together. The clutch basket 6 is with the secondary side output of the clutch 3 connected, so that in the closed state of the coupling 3 a portion of the transmission output torque through the axle drive 16 to the wheels 13 . 14 the front axle 2 is transmitted.

To close the clutch 3 becomes a certain value for the clutch torque M _{K of} the four-wheel clutch 3 set, which corresponds to the maximum possible torque, which of the clutch 3 can be transmitted in the direction of the front axle, ie which maximum on the four-wheel clutch 3 is adjustable. The calculation of the clutch torque M _{K to be set} is performed by a control unit 9 taken over, for example, from a DSC controller 9 for vehicle stabilization. The clutch torque M _K to be set is from a paged (for example, directly to the all-wheel coupling 3 attached) additional control unit 17 in an electric current to control the adjustment of the four-wheel clutch 3 implemented. Alternatively, this implementation could also be done directly in the controller 9 respectively. An exemplary controller structure for calculating the clutch torque M _{K to be set} is in the article "XDrive - The new all-wheel drive in the BMW X3 and BMW X5", ATZ - Automobiltechnische Zeitschrift, 2/2004, pages 92 to 102 described.

The motor vehicle comprises a semi-automatic parking assistance system with transverse guidance and optionally also longitudinal guidance.

The control unit 9 provides for a reduction of the clutch torque M _K , if an activation of the parking assistance system of the motor vehicle is determined as related to 2 and 3 is explained.

In step 100 of in 2 The method shown, the activation of the parking assistance system is detected. The activation of the parking assistance system is detected, for example, by means of an activation signal of the parking assistance system, which changes from 0 to 1 when the parking assistance system is activated and which changes from 1 to 0 when the parking assistance system is deactivated. The activation signal is applied, for example, to a vehicle bus (for example CAN bus or FlexRay bus) to which the DSC control unit 9 can access. An exemplary time profile of the activation signal and the requested clutch torque M _K is in 3 shown.

At time t _A , the activation signal of the parking assistance system changes from 0 to 1 (see FIG. 3 ). By switching the activation signal from 0 to 1, it is determined that the parking assistance system has been activated and a parking situation exists (see step 100 in 2 ). In addition to the activation of the parking assistance function, the presence of one or more further boundary conditions (state parameters) may optionally be required in order to trigger a reduction in the clutch torque M _K when the parking assistance function is activated, for example a very low lateral acceleration (for example a lateral acceleration smaller or smaller than a low threshold value ), a low roadway pitch (eg, a lane pitch less than or equal to a low threshold), low vehicle speed (eg, in the range of 0 to 40 km / h), no sensing or prediction of vehicle instability.

Upon recognition of the activation of the parking assistance system and fulfillment of the one or more optional boundary conditions, starting from the current desired clutch torque M _K at point A, at which the activation signal changes from 0 to 1, a clutch torque reduction function is activated, via which the clutch torque M _K up to a defined minimum clutch torque M _{K, red} is lowered at point B (see Fig. step 110 in 2 ). The lowering can be done for example as a linear ramp. In extreme cases, the minimum clutch torque M _{K, red can} also be zero, ie it can be a complete interruption of the torque transmission to the secondary axis 2 come. At point C, the activation signal changes from 1 to 0. This deactivates the parking assistance system (see step 120 in 2 ), so that the reduction in the clutch torque is at least partially withdrawn (see step 130 in 3 ) and the clutch torque lowering function is ended. The clutch torque M is in this case, for example, brought to a further calculated in the background clutch desired torque M _K at the operating point D.

The course of the reduction of the clutch torque M between the points A and B (for example, the slope of the clutch torque) and / or the level of the reduced clutch torque M _{K, red} between the points B and C and / or the course of the torque increase between the operating points C and D can be dependent on one or more further state parameters (eg accelerator pedal input, drive torque, road gradient, steering angle) and thus fundamentally variable.

The lowered clutch torque can be temporarily or permanently increased again in the event of instability of the vehicle occurring.

For example, for this purpose, the active clutch torque reduction function under one or more conditions that indicate instability and, for example, result from one or more of the above-mentioned state parameters, temporarily be interrupted or completely aborted. By way of example, it is possible that upon detection of a critical slip situation between the driven wheels of an axle or between the wheels of both axles of a vehicle, the reduced torque level M _{K, red is} left to ensure sufficient driving stability and / or traction. In this case, the clutch torque, starting from the reduced clutch torque M _{K, red} can be adjusted according to a defined function to a required calculated clutch desired torque M _K , which can be both higher and lower than M _{K, red} depending on the situation.

In order to avoid possible toggling of the function after completion or termination of the clutch torque reduction function, a hysteresis for the entry and exit condition can advantageously be provided.

It is also conceivable that upon completion or termination of the clutch torque reduction function, a defined overshoot time delays a subsequent reentry into the clutch torque reduction function to also avoid an unwanted switching back and forth of the clutch torque reduction function.

To increase the clutch torque may alternatively be provided that when occurring instability on a drive wheel or a drive axle (wheel or axle has impermissible traction with respect to the road), the reduction of the clutch torque (ie the clutch torque). Lowering function) is maintained, but superimposed (ie additive) and the four-wheel clutch slip control can continue to be effective, which in this case increases the clutch torque substantially dependent on the slip and temporarily.

If the clutch torque is increased again despite continuing active parking assistance function, the parking assistance system can be informed about this, so that the parking assistance system can adjust to a temporary possible falsification of the wheel speeds.

By the above-described change in the torque transmission ratio by means of the described clutch torque-lowering function, the functional quality of the parking assistance system is increased.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10054023 A1 [0004]
• DE 10333654 A1 [0005]
• DE 102009031500 A1 [0006]
• DE 102009032265 A1 [0007]

Cited non-patent literature

• "The Dynamic Performance Control from BMW", ATZ - Automobiltechnische Zeitschrift, 11/2008, pages 984 to 994 [0009]
• "The Dynamic Performance Control from BMW", ATZ - Automobiltechnische Zeitschrift, 11/2008, pages 984 to 994 [0029]
• "XDrive - The new four-wheel drive in the BMW X3 and BMW X5", ATZ - Automobiltechnische Zeitschrift, 2/2004, pages 92 to 102 [0050]

Claims (11)

Method for torque distribution of a drive torque to a primary axis and a secondary axis of a motor vehicle, which - an all-wheel drive with a torque split device ( 3 ) for dividing the driving torque on the permanently driven primary axis ( 1 ) and the if necessary driven secondary axis ( 2 ) and - a parking assistance system with transverse guidance and optional longitudinal guidance, comprising the steps of: - determining ( 100 ) a current or upcoming parking situation on the part of the vehicle; and - if a current or imminent parking situation is detected, - decrease ( 110 ) of the axle torque of the secondary axle, which can be set at maximum via the torque split device, reducing the axle torque of the secondary axle via the torque split device, or limiting the axle torque of the secondary axle which can be set via the torque split device. The method of claim 1, wherein - the four-wheel drive is a clutch-controlled four-wheel drive, in which the primary axis ( 1 ) is permanently driven and the secondary axis ( 2 ) via a controllable with respect to their clutch torque four-wheel clutch ( 3 ) is drivable, - the torque distribution device the four-wheel clutch ( 3 ), and - the axle torque of the secondary axle ( 2 ) or the maximum adjustable axle torque of the secondary axle ( 2 ) is reduced by the clutch torque (M _K ) of the four-wheel clutch is lowered. The method of claim 2, wherein the clutch torque (M _K ) is increased again in case of occurring instability of the vehicle. Method according to one of the preceding claims, wherein the axle torque of the secondary axis ( 2 ) is reduced to a value or the maximum adjustable axle torque of the secondary axle ( 2 ) is reduced to a value (M _{K, red} ) or the adjustable axle torque of the secondary axle ( 2 ) is limited to an upper value, and the time course of the reduction or the value (M _{K, red} ) is dependent on one or more parameters, in particular an accelerator pedal specification, the driver default torque, the drive torque, a roadway longitudinal gradient, a lateral acceleration and / or the steering angle. A method for torque distribution of an axle torque on a left and a right wheel of a common axle of a motor vehicle, which - A second torque distribution device for dividing an axle torque on the two wheels of this axis, and - A parking assistance system with transverse guide and optional longitudinal guide comprising, with the steps: - determining a current or imminent parking situation by the vehicle; and - when a current or imminent parking situation is detected, Reducing the difference between the wheel torque of the left wheel and the wheel torque of the right wheel via the second torque split device, Reducing the maximum difference between the wheel torques that can be set via the second torque distribution device, Limiting the difference between the wheel torques, which can be set via the second torque distribution device, or - Reduce the coupling of the wheel speeds for the left and the right wheel of the common axis. The method of claim 5, wherein the difference between the wheel torques or the adjustable difference between the wheel torques or the difference of the wheel speeds is reduced to a value or the maximum adjustable difference between the wheel torques is limited to an upper value, and the time course of the reduction or the value depends on one or more parameters, in particular on an accelerator pedal specification, the driver default torque, the drive torque, a lateral acceleration and / or the steering angle. Method according to one of claims 1-4 and according to one of claims 5-6, wherein when determining a current or imminent parking situation, the following steps are performed: - reducing the maximum torque via the torque distribution device adjustable axle torque of the secondary axis ( 2 ), Reducing the axle torque of the secondary axle ( 2 ) via the torque splitting device or limiting the torque of the secondary axle that can be set via the torque splitting device; and - reducing the difference between the wheel torque of the left wheel and the wheel torque of the right wheel via the second torque split device, reducing the maximum adjustable via the second torque split device difference between the wheel torque, limiting the adjustable via the second torque split device difference between the wheel torques up or reducing the coupling of the wheel speeds for the left and right wheels of the common axis. Method according to one of the preceding claims, wherein the parking situation is determined based on the activation of the parking assistance system, in particular based on an activation signal, which signals the activation of the parking assistance system. Method according to one of the preceding claims, wherein the reduction takes place only in the presence of one or more additional conditions, in particular only in the presence of one or more of the following additional conditions: a lateral acceleration less than or equal to a threshold value, a lane gradient less than or equal to equal a threshold, a vehicle speed less than or equal to a threshold, no vehicle instability. Motor vehicle comprising a parking assistance system with transverse guidance and optionally longitudinal guidance and an all-wheel drive, which has a torque distribution device ( 3 ) for dividing the drive torque to a permanently driven primary axis ( 1 ) and an if necessary drivable secondary axis ( 2 ), wherein the motor vehicle is set up to: - detect a current or imminent parking situation; and - upon detection of a current or upcoming parking situation - via the torque split device ( 3 ) maximum adjustable axle torque of the secondary axle ( 2 ), - the axle torque of the secondary axle ( 2 ) via the torque split device ( 3 ) or via the torque distribution device ( 3 ) adjustable axle torque of the secondary axis ( 2 ) to limit upward. Motor vehicle comprising a parking assistance system with transverse guidance and optionally longitudinal guidance and a torque split device for dividing an axle torque on a left and a right wheel of a common axis, wherein the motor vehicle is set up, - determine an actual or imminent parking situation; and - when a current or imminent parking situation is detected To reduce the difference between the wheel torque of the left wheel and the wheel torque of the right wheel via the torque split device, To reduce the maximum adjustable difference between the wheel torques via the torque distribution device, To limit the difference between the wheel torques that can be set via the torque distribution device or - To reduce the coupling of the wheel speeds for the left and the right wheel of the common axis.

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