WO2023151896A1

WO2023151896A1 - Method for operating a motor vehicle with an electric drive

Info

Publication number: WO2023151896A1
Application number: PCT/EP2023/050815
Authority: WO
Inventors: Giacomo Danisi; Marco Fainello
Original assignee: e-more AG
Priority date: 2022-02-14
Filing date: 2023-01-16
Publication date: 2023-08-17
Also published as: AT525556A4; AT525556B1

Abstract

In a method for operating a motor vehicle with an electric drive, steering of the wheels (11) of the at least one axle assembly (2) having steerable wheels takes place only by means of drive and/or braking forces which act around the respective wheel axle (13). In the case of the presence of a corresponding driving situation, commands are output in a plurality of first time windows by an electronic control system, using which commands the wheels (11) of this axle assembly (2) are fixed in their angular positions and different drive and/or braking forces are exerted on the right-hand and the left-hand wheel (11), in order to transmit different longitudinal forces to the underlying surface. In a plurality of second time windows, commands are output by the control system, using which commands the swivelling of the wheels (11) is released by the holding device (31, 38) and the angular positions of the wheels (11) are modified about the respective swivelling axis (14) by means of drive and/or braking forces.

Description

Method for operating a motor vehicle with an electric drive

The invention relates to a method for operating a motor vehicle with an electric drive, which has at least one front axle assembly with a right and a left wheel and at least one rear axle assembly with a right and a left wheel, the wheels at least one of the axle assemblies can be steered about a respective pivot axis and are driven individually by a respective electric motor about a respective wheel axle, the wheels of the axle assembly having at least one steerable wheels being steered only by means of a drive acting about the respective wheel axle and/or braking forces, which are controlled by an electronic control system of the motor vehicle.

In four-wheel motor vehicles with an electric drive, the two steerable wheels of a front axle assembly forming a front axle being driven individually by means of wheel hub motors, it is already known to steer the wheels only by means of drive and/or braking forces. This emerges, for example, from DE 10 2019 104 391 A1 or WO 2020/169134 A1. The wheel carriers belonging to the front axle, which can be pivoted about pivot axes in order to steer the wheels, are connected to one another via a connecting rod, which has rod parts connected to one another in an articulated manner. To steer the Wheels there is neither a part acting mechanically on the rod parts nor a separate steering actuator. Rather, the motor vehicle is steered in that, with the individual wheel drives of the wheels arranged on the steerable axle, drive and/or braking torques are transmitted to these wheels, which steer the wheels in a predetermined direction. Braking torques for steering the wheels can be exerted instead or additionally by means of a mechanical braking device for the respective wheel. In the event of an individual wheel drive failing, there is a holding device which interacts with the rod parts connecting the wheel carriers in order to brake or immobilize them. To block .

A similar device is also disclosed in US Pat. No. 10,562,400 B2. The holding device, in order to be able to fix one of the steerable wheels in a given angular position, interacts here directly with the pivot mounting of the wheel carrier about the pivot axis.

These are concepts that are intended in particular for use in self-propelled motor vehicles in which the maximum achievable speed is limited to relatively low values. Vehicle dynamics control systems are therefore not mentioned in the previously known documents.

US 2017/0120753 A1 also discloses a self-propelled motor vehicle in which each of the wheels has a drive unit with a drive motor, the vehicle being driven and steered by means of the drive units. Various error states are described, in which at least one drive unit has failed, the drive unit being put out of operation and the steering and the drive by means of the remaining drive units is carried out. No vehicle dynamics control system is mentioned in this document either.

Driving dynamics control systems are common in today's motor vehicles and are used to control the dynamic driving behavior of motor vehicles in different driving situations. With the ESP (Electronic Stability Program), also known as ESC (Electronic Stability Control), it is checked when the motor vehicle is cornering whether the motor vehicle is oversteering or understeering. If such oversteering or understeering is detected, individual wheels of the motor vehicle are selectively braked in order to counteract the oversteering or understeering. Another driving situation relates to the case in which the motor vehicle is braked on a surface that has very different friction conditions for the left and right wheels, for example because there is snow on one side of the road. If the wheels on both sides are braked to the maximum possible deceleration values, there is a torque around the vertical axis of the vehicle, which can lead to an uncontrolled turning of the vehicle around the vertical axis. In practice, the wheels with the stronger traction are only braked to such an extent that the vehicle remains largely stable. However, this increases the braking distance.

Another type of steering without a mechanical connection to a steering wheel is known from US Pat. No. 9,221,495 B2. The wheels are steered here by means of steering actuators, which actively adjust the angular position of each wheel carrier about the pivot axis. These steering actuators are in addition to the electric individual wheel drives. The electric motors are arranged here outside of the respective wheel and are connected to it via a drive shaft. It is also known that the occurrence of vehicle instability under load changes or when braking on a roadway with different coefficients of friction for the left and right wheels can be counteracted by bringing the rear wheels into toe-in when driving straight ahead or cornering. For this purpose, DE 10 2006 055 294 A1 describes a device for adjusting the track difference angle of the non-steered rear wheels. For this purpose, a distance in the transverse direction of the vehicle between the point of articulation of the wheel control arm and the wheel carrier is adjusted by means of an actuator. DE 10 2018 201 670 B4 discloses a toe adjustment of a rear wheel by means of an actuator which acts on a wheel control arm in the longitudinal direction of the vehicle.

The object of the invention is to provide a method of the type mentioned at the outset by which the driving dynamics in an electrically operated motor vehicle, in which the wheels are steered only by means of drive and/or braking forces acting around the respective wheel axle, is improved in certain situations can be . According to the invention, this is achieved by a method having the features of claim 1 .

In the method according to the invention, the control system of the motor vehicle checks whether a driving situation is present in which different longitudinal forces are to be transmitted to the ground from the right and left wheel of an axle assembly which has steerable wheels and also - in the same or in an overlapping Period - a steering operation of the wheels of this axle assembly is to be carried out. If the control system detects such a driving situation, the control system in a plurality of first time windows, commands are issued through which the wheels of this axle assembly are fixed in their respective angular positions about the pivot axes by means of a holding device and different drive and/or braking forces are exerted on the right and left wheels of this axle assembly , in order to transfer the different longitudinal forces to the subsoil . In a plurality of second time windows, which lie in periods between two respective first time windows, commands are issued by the control system, through which the pivoting of the wheels of this axle assembly about the respective pivot axis is released by the holding device and the angular positions of the wheels of this Axis assembly to be changed to the j eweilige pivot axis by means of driving and / or braking forces.

Because the wheels are fixed in their respective angular positions in the first time windows by means of the holding device, the different longitudinal forces for the right and left wheel can be transmitted to the ground without affecting the steering of the wheels. In the second time window, on the other hand, the angular positions of the wheels about the pivot axes are changed.

In particular, the change in the angular positions of the wheels about the pivot axes in the second time windows can take place on the basis of a change in a predefined trajectory for the motor vehicle. This change in the predefined trajectory can be carried out by a driver or by an autonomous or semi-autonomous driving system for the motor vehicle. However, it is also possible for the angular positions of the wheels to be changed in the second time windows without there being a change in the predefined trajectory, namely by to stabilize the vehicle. This is explained in more detail below.

An example of a driving situation in which different longitudinal forces are to be transmitted to the ground from the right and left wheels of an axle assembly that has steerable wheels is cornering, in which oversteering or understeering of the motor vehicle occurs. Commands can then be issued by the control system in the first time windows, through which the left or the right wheel of this axle assembly is braked and the other of these wheels is not braked or is braked less, in order to counteract the oversteering or understeering. In the second time window, the angular positions of the wheels of this axle assembly can then be changed about the respective pivot axis. Changing the angular positions of the wheels on this axle assembly can act to counteract oversteer or understeer. A change in the trajectory specified for the motor vehicle (by the driver or the autonomous or semi-autonomous driving system) can also be taken into account in the second time windows.

Another example of a driving situation in which different longitudinal forces are to be transmitted to the ground from the right and left wheels of an axle assembly that has steerable wheels is braking or accelerating the motor vehicle on a ground that has different friction conditions for the has the right and the left wheel. If the control system determines that the motor vehicle is oversteering or understeering, the wheels can be braked in the first time windows by the commands issued by the control system, preferably in each case the maximum possible braking values, and in the second time windows, the swivel positions of the wheels about the respective swivel axis can be changed by commands issued by the control system in such a way that oversteering or understeering is counteracted. A "p-split braking" can thus be carried out in an advantageous manner.

The durations of the first and the second time window can differ from one another. The first time window, in which the different longitudinal forces are transmitted to the ground, can advantageously be longer than the second time window.

Preferably, the first and second time windows alternate, either immediately following one another or being separated by intervals that are shorter than the first and second time windows.

In one possible embodiment of the invention, only the wheels of one of the axle assemblies, preferably the front axle assembly, can be steerable. In a further possible embodiment of the invention, both the wheels of the front axle assembly and the wheels of the rear axle assembly can be steerable and steered only by means of driving and/or braking forces.

The control system of the motor vehicle thus also forms a computer, by which the method according to the invention is carried out. A computer program according to the invention thus comprises instructions which, when the program is executed by the computer formed by the control system, cause the latter to carry out the method according to the invention. Further advantages and details of the invention are explained below with reference to the attached drawing. In this show:

1 shows an oblique view of an exemplary embodiment of a platform for a motor vehicle, which is operated according to the method according to the invention;

Figure 2 is a side view;

Figure 3 is a bottom view;

Fig. 4 is an exploded view of a front axle

Assembly (without the parts arranged on the wheel carrier on the left in relation to the direction of travel);

5 shows an oblique view (without the parts arranged on the two wheel carriers);

Figure 6 is a plan view;

Fig. 7 is a front view;

Fig. 8 shows an embodiment of a holding device for

determining the angular positions of the wheels of the front axle assembly in a view in the axial direction of the rod part of the connecting rod with which the holding device cooperates;

9 shows an oblique view of the holding device;

FIG. 10 is an oblique view similar to FIG. 9, but with one of the jaws removed;

11 shows an oblique view of a trailing arm with a wheel carrier and a lockable swivel bearing to form a second embodiment of a holding device for locking the angular position of the wheels of the front axle assembly;

Figure 12 is an exploded view of the parts of Figure 11;

13 shows a vertical section through the pivot axis;

Fig. 14a) -c) highly schematic representations of a motor vehicle cornering to Explanation of an exemplary embodiment of the method according to the invention in a driving situation in which both an ESP intervention against understeering and a change in the specified trajectory for the motor vehicle take place;

Fig. 15a) and b) schematic illustrations to explain a further exemplary embodiment of the method according to the invention in a driving situation in which an ESP intervention against understeer takes place both by selective braking of wheels and by countersteering of the rear wheels;

Fig. 16a)-c) schematic representations to explain a further exemplary embodiment of the method according to the invention in a driving situation in which, due to braking on a roadway which has different coefficients of friction in the areas of the left and right wheels, both different braking forces on the ground are to be transferred, and countersteering of both the front and rear wheels is to be carried out to prevent oversteering;

Fig. 17 shows a simplified flow chart for further explanation of the process shown in FIG. 14a)-c) described method according to the invention;

Fig. 18 shows a representation of the first and second time windows.

From an exemplary embodiment of a platform for a motor vehicle, which is operated according to the method according to the invention, is shown in FIGS. 1-10 shown . The platform has a chassis 1, of which a front axle Assembly 2 and a rear axle assembly 3 are worn. In the figures, the chassis 1 is only shown schematically as a contoured plate. In practice, the chassis will have different parts, e.g. B. interconnected carrier and / or plate parts. Accumulators for the electric drive, which are not shown in the figures, are preferably also attached to the chassis.

The front wheels 11 in relation to the direction of travel can be steered. The motor vehicle therefore has a steered front axle. The front axle assembly 2 includes the front wheels 11 together with their wheel suspension and forms the steered front axle, as described in more detail below.

The rear wheels 7 are not steerable in the exemplary embodiment. The rear axle assembly 3 includes the rear wheels 7 together with their wheel suspension and forms the rear axle.

In a further advantageous embodiment, the rear axle assembly 3 could also have steerable wheels. In particular, the rear axle assembly could be designed analogously to the front axle assembly.

A platform for carrying out the method according to the invention could also have more than two axle assemblies, e.g. B. in addition to a front axle assembly, two rear axle assemblies.

Such a platform can also be called a skateboard platform. In the exemplary embodiment, the rear axle assembly 3 is designed with a rigid axle 4 . This is suspended from a base unit 6 of the rear axle assembly 3 by means of leaf spring assemblies 5 . The inherently rigid base unit 6 is fastened to the chassis 1 by means of a screw connection.

The wheels 7 rotatably mounted by the rigid axle 4 about the respective wheel axle 8 can be driven individually or together by means of at least one electric motor, for example by means of wheel hub motors. An additional mechanical braking device for each wheel, as is known, can be present. However, an embodiment without an additional mechanical braking device, which brakes the rotation of the respective wheel about its wheel axis, is also conceivable and possible. In this case, braking forces that brake the rotation of the respective wheel about its wheel axis could only be exerted by at least one drive motor for the wheels 7 .

A drive for the wheels of the rear axle assembly could also be omitted.

In the exemplary embodiment, the front axle assembly 2 has an inherently rigid base unit 10 which carries the wheel suspension. The connection to the chassis 1 takes place via the base unit 10 . The front axle assembly 2 is preferably connected to the chassis 1 by a screw.

The right and left wheels 11 of the front axle assembly 2 are rotatably mounted on a respective wheel carrier 12 about a respective wheel axle 13 . The wheels 11 are steerable. To this end, the right and left wheel carriers are 13 µm

Pivot axes 14 pivotably mounted.

The wheels 11 of the front axle assembly 2 are driven individually by a respective electric motor 15 about the respective wheel axle 13 . In the exemplary embodiment shown, the electric motors are designed in the form of wheel hub motors. It would also be conceivable and possible for electric motors attached to the base unit 10 to be present, which are connected to the respective wheel 11 via a respective drive shaft.

In the exemplary embodiment, there is also a mechanical braking device for each wheel 11 . In this connection, in FIG. 4 shows a brake disc 16 and a brake caliper 17 .

Also conceivable and possible would be an embodiment without a mechanical braking device, which brakes the rotation of the respective wheel about its wheel axis. In this case, braking forces that brake the rotation of the respective wheel about its wheel axle could only be exerted by the electric motors 15 .

In the exemplary embodiment, the wheels 11 of the front axle assembly 2 are hung on the base unit 10 and thus on the chassis 1 via a trailing arm wheel suspension. There is one trailing arm 20 each for the right wheel and for the left wheel 11 , which is pivotably connected to the base unit 10 about a respective transverse axis 21 . The transverse axes 21 are perpendicular to the longitudinal direction of the platform and preferably horizontal. The longitudinal direction of the platform is parallel to the direction of straight travel.

The wheel carriers 12 are mounted on the respective trailing arm 20 by means of a respective pivot bearing 18 such that they can pivot about a respective pivot axis 14 in order to enable the respective wheel 11 to be steered.

The pivoting of the trailing arms 20 about the transverse axes 21 are spring-loaded. For this purpose, there is a respective torsion bar spring 22 for the respective trailing arm 20 . This respective torsion bar spring 22 extends coaxially to the respective transverse axis 21 . So that the torsion bars 22 can be made as long as possible, i.e. can have a length greater than half the track width, the transverse axes 21 for the right and left trailing arm 20 are offset from one another, in the exemplary embodiment from the longitudinal direction of the platform, d. H . one of the two transverse axes 21 is further to the front and the other of the two transverse axes 21 is further to the rear. The offset of the transverse axes 21 could also take place in height instead or in addition.

In the exemplary embodiment, the longitudinal links 20 on the right and left sides are of different lengths, corresponding to the offset of the transverse axes 21 , so that the wheel axles 13 of the right and left wheels 11 coincide. The wheel axles 13 of the right and left wheels 11 could also be offset from one another in relation to the longitudinal direction of the platform.

In a region spaced apart from the connection to the respective trailing arm 20, the respective torsion bar spring 22 is non-rotatably connected to the base unit 10 (and via the base unit 10 to the chassis 1). serves this purpose in each case a holding part 23 which is in a torsionally fixed connection with the respective torsion bar spring 22 . In order to enable the spring force to be adjusted, each holding part 23 is connected to the respective torsion bar spring 22 so that it can be displaced in relation to the transverse direction parallel to the transverse axes 21 and is mounted on the base unit 10 so that it can be displaced in the transverse direction. A respective holding part 23 can thus also be displaced in the transverse direction with respect to the chassis 1 . An electrically operated adjustment part 24 (ie an actuator) is preferably provided in each case for displacing the respective holding part 23 in the transverse direction. The suspension can thus be adjusted by means of an electrical control device (not shown in the figures), even when the vehicle is in operation.

The respective holding part 23 is non-rotatably connected to the respective torsion bar spring 22 via a respective connecting piece 25 . Whose rotational position relative to the holding part 23 is adjustable and fixable, whereby a bias of the respective torsion bar spring 22 can be adjusted.

The pivoting of the respective trailing arm 20 is damped by a respective damper 26 . In the exemplary embodiment, 26 rotary dampers are provided as dampers, via which the trailing arms 20 are mounted pivotably about the lower transverse axes 21 on a downwardly projecting leg 10a of the base unit 10 . The connections between the dampers 26 and the trailing arms 20 on the one hand and the legs 10a on the other hand can be made by screw connections (not shown in the figures). The wheel carriers 12 of the right and left wheel 11, which can be pivoted about the pivot axes 14 to steer the wheels 11, are connected to one another via a connecting rod 28, 29, 30, whereby the pivoting of the right and left wheel carriers 12 about the respective pivot axis 14 is coupled. A respective lateral rod part 28 , 29 is articulated (= articulated) on the respective wheel carrier 12 . The lateral rod parts 28, 29 are connected to one another via a central rod part 30, with which they are each connected in an articulated manner. In the exemplary embodiment, the articulated connections are designed as ball joints. The articulated connections could also be made in other ways, for example via cardan joints.

The middle rod part 30 is slidably guided in the transverse direction by the base unit 6 . For this purpose, the base unit 6 has support legs 10b which have openings through which the middle rod part 30 passes.

In principle, the wheel carriers 12 can also be coupled in their angular positions in a manner other than by a connecting rod which has rod parts 28, 29, 30, e.g. B. via a hydraulic device.

The wheels 11 are steered, ie the angular position of the wheels 11 about the pivot axes 14 is adjusted, as already mentioned, only by means of drive and/or braking forces which act about the wheel axes 13 . There is thus no steering mechanism available, by means of which the rotation of a steering wheel is mechanically transmitted to the angular position of the wheels. There are also no additional steering actuators that are not used to drive the wheels about the wheel axles 13 but only to actively adjust the angular position of the wheels about the pivot axles 14 . The front axle assembly 2 also has a holding device 31 by means of which the middle rod part 30 can be held in place in order to block the displacement of the middle rod part 30 in the transverse direction. As a result, the wheels 11 of the front axle assembly 2 are fixed in their current angular positions about the respective pivot axis 14 . The holding force exerted by the holding device 31 can be limited to such a value that even if the holding device malfunctions, its holding force can still be overcome by means of drive and/or braking forces acting around the wheel axles 13 in order to still be able to steer to allow .

In the exemplary embodiment, the holding device 31 has two opposing clamping jaws 32 which act on the rod part 30 from opposite sides. For this purpose, the clamping jaws 32 have semicircular recesses in which clamping pads 33 are arranged, which interact with the rod part 30 . Electrically actuated actuators 34 are used to actuate the clamping jaws 32 , which actuators can be designed in particular in the form of electromagnets. As shown, the actuators 34 can be supported on the sides facing away from the clamping jaws 32 on the side legs of a U-shaped assembly part 35 which is firmly connected to the base unit 10, in the exemplary embodiment to one of the support legs 10b.

The clamping jaws 32 are slidably guided by guide pins 36, on which springs 37 are arranged, which move the clamping jaws 32 into an open position in which the clamping linings are lifted off the central rod part 30 when the actuators 34 are not actuated. Will the When actuators 34 are actuated, they compress the jaws 32, overcoming the force of the springs 37, and the clamping pads against the central rod member 30, thus restraining it against displacement in the transverse direction.

A holding device to determine the angular positions of the wheels 11 about the pivot axes 14 could also be designed in a different way. For example, such a determination could also take place directly at the pivot axes 14 . Such an example is shown schematically in FIGS. 11 to 13 . The wheel carriers 12 of the wheels 11 of the front axle assembly are mounted here relative to the trailing arms by means of pivot bearings so as to be rotatable about the pivot axes 14, which can be locked. These lockable swivel bearings form the holding device 38 here. In order to be able to fix the respective pivot bearing, it can have, for example, a magnetorheological fluid 39 in a joint gap, which can be activated by means of an electromagnet (not shown in the figures). When activated, the magnetorheological fluid blocks relative rotation between the two parts of the pivot between which it is located.

The driving and/or braking forces acting on the wheels 11, 7 about the respective wheel axle 13, 8 are controlled by an electronic control system 40, which is only shown in FIG. 14 a ) is indicated schematically . The control system 40 includes a control unit 41, various sensors, by means of which, for example, the angular positions of the wheels 11 about the pivot axes 14 are detected and fed to the control unit 41, as well as control lines, by means of which, for example, commands the electric motors, braking devices and holding devices 31, 38 are output. The control system 40 can convert steering commands from a driver into the corresponding angular positions of the wheels 11 in order to move the motor vehicle on a trajectory specified by the driver. An autonomous driving system can also be implemented by the control system, with the motor vehicle being guided on a trajectory specified by the autonomous driving system. The autonomous driving system can be operated with different degrees of automation.

The control system thus includes both hardware, which also forms a computer, and software, ie a computer program running on the computer formed by the control system.

A driving dynamics control system is also implemented by the control system 40, which can carry out driving interventions in various situations in order to influence the dynamic driving behavior of the motor vehicle. In this way, ESP can be provided when cornering to counteract oversteer or understeer. It is characteristic of an ESP driving intervention that an individual wheel or individual wheels is/are selectively braked in order to counteract oversteering or understeering. Additionally or alternatively, automated countersteering can be carried out in order to counteract oversteering or understeering.

Based on the Fig. 14 a) to c) an exemplary embodiment of the method according to the invention is first explained, with a driving situation present in which when the motor vehicle is cornering (in the exemplary embodiment through a left-hand bend) in an identical or overlapping Period both an ESP intervention and a steering intervention is to be carried out ff.

Fig. 14 a) shows a highly schematic view of the motor vehicle which is cornering, with understeer being detected by the control system. In order to counteract this understeer, the front and rear wheels 7 , 11 on the inside of the curve are selectively braked by the control unit 41 of the control system 40 . The braking forces are indicated by arrows 42 , 43 . This is intended to keep the motor vehicle on the predetermined trajectory as far as possible.

Different longitudinal forces are thus transmitted to the ground from the right and left wheel of the front axle assembly as well as from the right and left wheel of the rear axle assembly. So that the angular positions of the front wheels 11 about the pivot axes 14 do not change in the case of the steerable wheels of the front axle assembly, the angular positions of the front wheels 11 are determined by means of the holding device 31 , 38 .

If the angular positions of the front wheels 11 are to be changed in the same period (e.g. because the specified trajectory is changed by the driver or by the autonomous or semi-autonomous driving system), a steering operation of the wheels 11 of the front axle assembly is required in addition to the ESP intervention 2 to perform .

In order to carry out the ESP intervention and the steering intervention in the same period of time, first and second time windows which alternate with one another are specified in this period of time. The ESP intervention described above is carried out in the first time window. The steering intervention is carried out in the second time window. For this purpose the holding device 31, 38 is opened in the second time window by the control unit 41 of the control system 40, so that the pivoting of the wheels 11 about the pivot axes 14 are released. For example, in order to reduce the radius of the curve traveled through compared to the angular position of the wheels 11 shown in FIG. In a respective second time window, the angular position of the wheels 11 thus changes by a certain amount in the direction of straight-ahead travel.

In the first and second time windows, the respective selective braking forces 43, 44 shown in FIGS. 14 a) and b) are exerted on the front wheels 11, which thus alternate with one another, with the holding device 31, 38 being activated in the first time windows and determine the angular positions of the wheels 11 about the pivot axes 14 and are open in the second time window and release the angular positions of the wheels 11 about the pivot axis 14 . This is repeated until the specified trajectory of the motor vehicle is reached. 14c) shows the angular positions of the wheels 11 after the steering intervention carried out in the second time window. When the steering intervention to be carried out has ended and an ESP intervention is still to be carried out, which is shown in FIG. 14 c) by the braking forces indicated by the arrows 42, 43, this ESP intervention can now take place permanently for as long as necessary .

17 shows a simplified flow chart for carrying out the procedure described above

Cornering Provided. If no intervention by this Driving dynamics control system is required, the steering of the motor vehicle is carried out based on the trajectory specified by the driver or by the autonomous or semi-autonomous driving system without intervention of this driving dynamics control system.

In step 45, vehicle stability data is determined by the control system. As long as the query in step 46 shows that there is no oversteer or understeer, the vehicle stability is determined in step 45 (branch “N” after step 46).

If oversteer or understeer is detected (branch "Y"), the control system performs an ESP intervention for the rear wheels 7 in step 47, i.e. one of the rear wheels 7 is selectively braked determined by which it is determined whether the actual values of the angular positions of the front wheels 11 correspond to the desired target values.The actual values deviate from the target values, for example, if the driver changes the specified trajectory. The specified trajectory can also be changed by an autonomous or semi-autonomous driving system Instead or additionally, a change in the angular positions of the wheels 11 can be expedient due to oversteering or understeering and can be specified by the vehicle dynamics control system in order to follow the specified trajectory.

If the result of the query as to whether the angular positions of the front wheels 11 are to be changed (step 49) is negative, an ESP intervention for the front wheels 11 is initiated in step 50 by selectively braking one of the front wheels. namely continuous, ie without a division into first and second Time window. The holding device 31, 38 is thereby activated, ie closed.

If it is determined that the angular positions of the front wheels 11 are to be changed (branch "Y" after step 49), then a steering intervention is also to be carried out. one of the front wheels 11 is selectively braked, with the holding device 31, 38 being activated.In the subsequent step 52, a steering intervention is carried out in a second time window, i.e. the holding device 31, 38 is deactivated (opened) and the angular positions of the wheels 11 are Drive and/or braking forces changed.The sequence then begins again in step 45. As long as both the ESP intervention and the steering intervention in the front wheels are to be carried out, steps 51, 52 are carried out repeatedly could also be provided to carry out steps 51, 52 several times before the sequence is started again at step 45. In any case, since the first and second time window are each only of short duration and the duration for a complete ESP intervention as well as for a steering intervention is much longer, repeats the first and second time window with the aforementioned actions several times until the ESP intervention or the steering intervention is completed.

This is indicated schematically in FIG. The commands for the ESP intervention take place in the first time window 53 . The commands for the steering intervention take place in the second time window 54 . The first and second time windows 53, 54 alternate. In the exemplary embodiment shown, the second time windows 54 immediately follow the first time windows, while between the second time windows and there is a short interval x in the first time windows, in which the other commands of the system shown in FIG. 17 shown process are carried out. There could instead or additionally be short gaps between the first and second time windows. The intervals between consecutive time windows 53, 54 and . 54, 53 are expediently shorter than the time windows 53, 54.

As from Fig. 18 can be seen schematically, the first and second time windows 53, 54 can have different durations, for example the first time windows 53 can be longer than the second time windows 54. The durations of the first and second time windows are preferably each in the range from 5 milliseconds to 300 milliseconds, with the range from 10 milliseconds to 50 milliseconds being preferred and the range from 15 milliseconds to 30 milliseconds being particularly preferred.

If the wheels 7 of the rear axle assembly are designed to be steerable, a steering intervention can also be carried out on these wheels 7 in order to follow a change in a trajectory specified by the driver or by an autonomous driving system or to stabilize the vehicle. for example, to counteract oversteer or understeer when cornering.

Such a steering intervention f f is shown in FIG. 15 a ) and b ) shown as an example . Again, this is an ESP intervention when cornering to counteract understeer.

First, the inside front and rear wheels are selectively braked, as shown in FIG. 14 a ) is shown . Here, since the rear wheels 7 are now also steerable, the rear axle assembly also has a

Holding device on to the current angular positions of the Lock the rear wheels in the same way as the front axle assembly. This holding device is activated during this selective braking of the rear wheel on the inside of the curve.

The commands for selectively braking one of the rear wheels are issued in the first time windows. The steering intervention is carried out in second time windows, with the holding device of the rear axle assembly being deactivated and the angular positions of the rear wheels being changed by means of drive and/or braking forces. In Fig. 15 a ), the braking force exerted on the rear wheel 7 on the outside of the curve for this purpose is indicated by the arrow 55 . The angular positions of the rear wheels gradually change over several cycles of the first and second time windows until the position shown in FIG. 15 b ) is reached . If the ESP intervention is not yet complete, the rear wheel on the inside of the curve can now be permanently braked with the holding device activated until the ESP intervention is complete.

If, in the same period or in an overlapping period, both for the front and for the rear wheels, different longitudinal forces are to be transmitted from both wheels to the ground and a steering intervention is to be carried out, the first and second time windows for the front axle Assembly and for the rear axle assembly may be the same or differ from each other.

If oversteer occurs when cornering, ESP intervenes in the same way, with the wheels on the outside of the corner being selectively braked. Based on the Fig. 16 a) to c) an exemplary embodiment of the method according to the invention is explained when braking is performed on a surface on which the traction of the left wheels is less than that of the right wheels. Greater longitudinal forces can thus be transmitted to the ground with the right wheels than with the left wheels, as can be seen in FIG. 16 a) is indicated by the arrows of different lengths. In this exemplary embodiment, both the rear wheels 7 and the front wheels 11 are designed to be steerable, it also being possible for only one of the axle assemblies to have steerable wheels. When the different longitudinal forces are transmitted to the ground, the holding devices for determining the angular positions of the front and rear wheels 11 , 7 are activated. It is assumed here that the vehicle is initially driving straight ahead. The different degrees of braking of the right and left wheels generate a torque about the vehicle's vertical axis, which would cause the vehicle to rotate about the vertical axis, ie in the exemplary embodiment to oversteer clockwise. In order to counteract this, the control system carries out a steering intervention in the exemplary embodiment of both the front and the rear wheels 11 , 7 . Specifically, the steering intervention is carried out in second time windows, which alternate with the first time windows, in which the different transmission of the longitudinal forces to the ground takes place.

The braking forces applied to the wheels in the second time windows are shown in FIG. 16 b ) indicated by arrows . The holding devices for determining the angular positions of the front and rear wheels are deactivated in this case. For the front wheels, braking is applied only to the left wheel. It comes through in the second Time windows to a respective small pivoting of the front wheels 11 counterclockwise. In the case of the rear wheels, the same braking forces can be exerted in the second time window as in the first time window. The deactivation of the holding device for the angular positions of the rear wheels in the second time windows results in a respective small pivoting of the wheels 7 in the clockwise direction due to the greater braking force exerted on the right rear wheel.

In Fig. 16 c ) shows the angular positions of the front and rear wheels when countersteering against oversteer is complete . If the braking of the vehicle has not yet been completed, the appropriate braking forces can now be applied permanently to the wheels 11, 7, with the holding devices for the front and rear wheels being activated. With different traction of the right and left wheels 11 , 7 , the maximum traction of the respective wheel can thus be utilized.

In an analogous manner, braking occurs when the left wheels have more traction than the right wheels.

Instead of a steering intervention of both the front wheels and the rear wheels, a steering intervention of only the front wheels or only the rear wheels could also take place in the second time window in order to stabilize the motor vehicle.

Even if only the front wheels or only the rear wheels can be steered, a steering intervention of these steerable wheels could be carried out in an analogous manner in the second time window in order to stabilize the motor vehicle. The motor vehicle can be accelerated in an analogous manner if the right and left wheels have different traction.

The procedure can also be analogous if, in the same or overlapping period of time, on a surface that has different friction values for the right and left wheel of an axle group whose wheels can be steered by means of drive and/or braking forces, on the one hand braking or acceleration is to be carried out, in particular if the braking or acceleration is to be relatively strong, and on the other hand the angular positions of the wheels are to be changed due to a change in the trajectory of the motor vehicle made by the driver or by the autonomous or semi-autonomous driving system. In turn, different longitudinal forces can be transmitted to the ground in the first time windows, with the holding device being activated to determine the angular positions of the wheels about the pivot axes, and in the second time windows, the steering intervention can be carried out by means of drive and/or braking forces, with the holding device is deactivated

The invention has been described as an example for various driving situations. The processes described can have various modifications without departing from the scope of the invention as defined in the claims. Key to the reference numbers:

Chassis 30 Rod part front axle assembly 31 Retaining device rear axle assembly 32 Jaws

Rigid axle 33 clamping lining

Leaf spring package 34 actuator

Base unit 35 mounting part

wheel 36 guide pin ft

Wheel axle 37 spring

Base unit 38 holding devicea leg 39 magnetorheologicalb support leg liquid

Wheel 40 electronic

Wheel carrier control system

Wheel axle 41 control unit

Pivot axis 42 arrow

Electric motor 43 arrow

Brake disc 44 arrow

Caliper 45 step

Swivel bearing 46 step

Trailing arm 47 step

Transverse axis 48 step

Pivot spring 49 step

holding part 50 step

Actuator 51 step

Connector 52 step

Damper 53 first time window

Circle line 54 second time slot

Rod part 55 arrow

rod part

Claims

32330/33/ss 20221219 29 patent claims

1. A method for operating a motor vehicle with an electric drive, which has at least one front axle assembly (2) with a right and a left wheel (11) and at least one rear axle assembly (3) with a right and a left wheel ( 7), wherein the wheels (11) of at least one of the axle assemblies (2, 3) can be steered about a respective pivot axis (14) and are driven individually by a respective electric motor (15) about a respective wheel axle (8, 13). , wherein the steering of the wheels (11) of the at least one steerable axle assembly (2) takes place only by means of drive and/or braking forces acting around the respective wheel axle (8, 13), which are controlled by an electronic control system (40) of the Motor vehicle are controlled, characterized in that the control system (40) checks whether a driving situation is present in which the right and left wheel (11) of an axle assembly (2) having steerable wheels (11), different longitudinal forces are to be transferred to the ground and also a steering operation of the wheels (11) of this axle assembly (2) to change the angular positions of the wheels (11) about the respective pivot axis (14) is to be carried out, and that, if the control system (40) such a driving situation is detected by the control system (40) in a plurality of first time windows (53) Commands are issued by which the wheels (11) of this axle assembly (2) are fixed in their angular positions about the respective pivot axis (14) by means of a holding device (31, 38) and on the right and left wheels (11) of this Axle assembly (2) different driving and / or braking forces are applied to transmit different longitudinal forces on the ground, and from the control system (40) in a plurality of second time windows (54) in periods between two respective first time windows ( 53), commands are issued by which the pivoting of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) is released by the holding device (31, 38) and the angular positions of the wheels (11) of this Axle assembly (2) are changed to the respective pivot axis (14) by means of driving and / or braking forces. The method according to claim 1, characterized in that the change in the angular positions of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) in the second time window (54) due to a

A trajectory specified by the driver or by an autonomous or semi-autonomous driving system is changed for the motor vehicle. Method according to Claim 1 or 2, characterized in that when the motor vehicle is cornering, the control system (40) checks whether the motor vehicle is oversteering or understeering, and that if oversteering or understeering is detected by the control system ( 40) commands are issued in the first time windows (53), by which the left or right wheel (11) of this axle assembly (2) is braked and the other of these wheels (11) is not braked or is braked to a lesser extent in order to counteract oversteer or understeer. Method according to Claim 2 or 3, characterized in that when the motor vehicle is cornering, the control system (40) checks whether the motor vehicle is oversteering or understeering, and in that if oversteering or understeering is detected by the control system ( 40) commands are issued in the second time windows (54) through which the angular positions of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) are changed in such a way that oversteering or understeering is counteracted. Method according to one of Claims 1 to 4, characterized in that if the control system (40) detects oversteering or understeering of the motor vehicle when braking or accelerating the motor vehicle, the control system (40) issues commands in the first time windows (53). by which the wheels (11) of this axle assembly (2) are braked, and commands are issued by the control system (40) in the second time windows (54) through which the angular positions of the wheels (11) about the respective pivot axis ( 14) can be modified to counteract oversteer or understeer. Method according to claim 5, characterized in that when braking or accelerating the motor vehicle with different traction of the right and left wheels (7, 11) of this axle assembly (2) the maximum traction of the respective wheel (7, 11) is utilized. Method according to one of Claims 1 to 6, characterized in that the duration of the first time window (53) differs from the duration of the second time window (54). Method according to any one of Claims 1 to 7, characterized in that the first and second time slots (53, 54) alternate, being contiguous or separated by intervals shorter than the first and second time slots (53, 54). . Method according to one of Claims 1 to 8, characterized in that both the wheels (11) of the front and the wheels (7) of the rear axle assembly (2, 3) can be steered about respective pivot axes and are turned individually by a respective electric motor a respective wheel axle (8, 13) are driven, wherein the steering of the steerable front and rear wheels (7, 11) takes place only by means of driving and/or braking forces acting around the respective wheel axle (8, 13), which are controlled by the electronic control system ( 40) of the motor vehicle are checked. Method according to Claim 9, characterized in that in a driving situation in which different longitudinal forces are to be transmitted to the ground from the right and from the left wheel (7, 11) of both the front and the rear axle assembly (2, 3) and in addition, a steering operation of both the wheels (7, 11) of the front axle and the wheels (7, 11) of the rear axle Assembly (2, 3) is to be carried out by the control system (40) for both the front axle assembly (2) and for the rear axle assembly (3) in a plurality of first time windows (53) commands are issued, through which the wheels (7, 11) of the respective axle assembly (2, 3) are fixed in their respective angular positions about the respective pivot axes by means of the respective holding device and the right and left wheels (7, 11) of the respective axle assembly ( 2, 3) different driving and/or braking forces are exerted in order to transmit different longitudinal forces to the ground, and in a plurality of second time windows (54), which lie in periods of time between two respective first time windows (53), from the control system ( 40) commands are issued, by means of which the pivoting of the wheels (7, 11) of the respective axle assembly (2, 3) about the respective pivot axis (14) is released by the holding device (31, 38) and the angular positions of the wheels ( 7, 11) of the respective axle assembly (2, 3) can be changed about the respective pivot axis (14) by means of drive and/or braking forces. Method according to Claim 10, characterized in that the first and second time windows (53, 54) for the front axle assembly (2) differ from the first and second time windows (53, 54) for the rear axle assembly (3). . Computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to one of Claims 1 to 11.