AT525556B1 - Method for operating a motor vehicle with an electric drive - Google Patents

Abstract

In a method for operating a motor vehicle with an electric drive, the wheels (11) of the axle assembly (2) having at least one steerable wheel are steered only by means of drive and/or braking forces acting around the respective wheel axle (13). If a corresponding driving situation is present, an electronic control system issues commands in a plurality of first time windows, by means of which the wheels (11) of this axle assembly (2) are determined in their angular positions and the right and left wheels (11) have different positions Driving and / or braking forces are applied to transmit different longitudinal forces on the ground. In a plurality of second time windows, commands are issued by the control system, through which the pivoting of the wheels (11) is released by the holding device (31, 38) and the angular positions of the wheels (11) about the respective pivot axis (14) by means of drive and /or braking forces are changed.

Description

Description

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, wherein the wheels of 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 drive mechanisms 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 electric drive, the two steerable wheels of a front axle assembly forming a front axle are 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. There is neither a part acting mechanically on the rod parts nor a separate steering actuator for steering the wheels. Rather, the motor vehicle is steered in that the individual wheel drives of the wheels arranged on the steerable axle are used to transmit drive and/or braking torques 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 that an individual wheel drive fails, there is a holding device which interacts with the rod parts connecting the wheel carriers in order to brake or block them.

A similar device also emerges from 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 bearing 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.

[0005] 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 being carried out by means of the remaining drive units. 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 greatly 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 about the vertical axis of the vehicle, which leads to

uncontrolled turning of the vehicle around the vertical axis. In practice, the wheels with the stronger traction are only braked so hard 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 a respective wheel carrier about the pivot axis. These steering actuators are available in addition to the electric individual wheel drives. The electric motors are arranged 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, a device for adjusting the toe difference angle of the non-steered rear wheels is described in DE 10 2006 055 294 A1. For this purpose, a distance in the transverse direction of the vehicle between the pivot point of the wheel control arm and the wheel carrier is adjusted by means of an actuator. DE 10 2018 201 670 B4 discloses toe adjustment of a rear wheel by means of an actuator which acts on a control arm in the longitudinal direction of the vehicle.

The object of the invention is to provide a method of the type mentioned, by which in an electrically operated motor vehicle in which the steering of the wheels takes place only by means of the respective wheel axle acting drive and / or braking forces, the driving dynamics in certain situations can be improved.

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 there is a driving situation 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 such a driving situation is detected by the control system, the control system issues commands in a plurality of first time windows, by means of 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 on the right and left wheels of this Axle assembly different driving and / or braking forces are applied to transmit the different longitudinal forces on the ground. 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 axle Assembly to be changed to the respective pivot axis by means of driving and / or braking forces.

The fact that the wheels are determined in the first time window by means of the holding device in their respective angular positions, the different longitudinal forces for the right and left wheel can be transferred 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 window can take place due to a change in a predetermined 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. It is also possible, however, for the angular positions of the wheels to be changed in the second time windows without there being a change in the predefined trajectory, specifically in order 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, which results in oversteering or understeering of the motor vehicle . Commands can then be issued by the control system in the first time windows, by 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) in the second time window can also be taken into account.

Another example of a driving situation in which different longitudinal forces are to be transmitted to the ground from the right and left wheel of an axle assembly that has steerable wheels is braking or accelerating the motor vehicle on a ground that is different Has friction ratios for the right and the left wheel. If the control system determines that the motor vehicle is oversteering or understeering, the commands issued by the control system can be used to brake the wheels in the first time window, preferably with the maximum possible braking values, and in the second time window commands issued by the control system can be used to change the swivel positions of the wheels around the respective swivel axis in such a way that oversteering or understeering is counteracted. A “u-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, being contiguous or separated by intervals 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 steered. 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 from 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 computer to carry out the method according to the invention.

Further advantages and details of the invention are explained below with reference to the accompanying drawing. In this show:

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

Figure 2 is a side view;

Figure 3 is a bottom view;

[0023] FIG. 4 shows 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);

[0024] FIG. 5 shows an oblique view (without the parts arranged on both wheel carriers);

Figure 6 is a plan view; Figure 7 is a front view; 8 shows an exemplary embodiment of a holding device for determining the win

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; Figure 10 is an oblique view analogous to Figure 9, but with one of the jaws removed; Fig. 11 is an oblique view of a trailing arm with a wheel carrier and a

lockable pivot bearing for forming a second embodiment of a holding device for determining 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; [0033] Fig. 143)-c) highly schematized representations of a motor vehicle in a short

Procedure for explaining 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 predefined trajectory for the motor vehicle take place;

15a) and b) schematic representations 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 through selective braking of wheels and through countersteering of the rear wheels;

163)-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 road surface that has different coefficients of friction in the areas of the left and right wheels, both different braking forces are to be transferred to the ground, and countersteering of both the front and rear wheels is to be carried out to prevent oversteering;

[0036] FIG. 17 shows a simplified flowchart for further explanation of the method according to the invention described with reference to FIGS. 14a)-c);

Figure 18 is a representation of the first and second time windows.

An 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. The platform has a chassis 1 on which a front axle assembly 2 and a rear axle assembly 3 are carried. In the figures, the chassis 1 is only shown schematically as a contoured plate. In practice the chassis will have different parts, for example interconnected beams and/or plate parts. Preferably, accumulators for the electric drive are also attached to the chassis, which are not shown in the figures.

The wheels 11 at the front 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 embodiment. The rear axle assembly 3 includes the rear wheels 7 together with their wheel suspension and forms the rear

teraxle off.

In a further advantageous embodiment, the rear axle assembly 3 could 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. two rear axle assemblies in addition to a front axle assembly.

Such a platform can also be referred to as a skateboard platform.

The rear axle assembly 3 is formed with a rigid axle 4 in the embodiment. 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, which are 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 provided. 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 slow down the rotation of the respective wheel about its wheel axle 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 base unit 10 is used to connect to the chassis 1. The front axle assembly 2 is preferably connected to the chassis 1 by a screw connection.

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 13 are pivotably mounted about pivot axes 14 .

The wheels 11 of the front axle assembly 2 are individually driven about the respective wheel axle 13 by a respective electric motor 15 . 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 context, a brake disc 16 and a brake caliper 17 are shown in FIG.

It would also be conceivable and possible to have a design without a mechanical braking device which brakes the rotation of the respective wheel about its wheel axle. 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 suspended on the base unit 10 and thus on the chassis 1 via a trailing arm wheel suspension. There is a trailing arm 20 for both the right wheel and the left wheel 11 , which is connected to the base unit 10 so that it can pivot about a respective transverse axis 21 . The transverse axes 21 are perpendicular to the longitudinal direction of the platform and are 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 so as to be pivotable 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 torsion bar spring 22 for the respective trailing arm 20 . Each torsion bar spring 22 extends coaxially to the respective transverse axis 21. So that the torsion bar springs 22 can be 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, related in the exemplary embodiment to the longitudinal direction of the platform, i.e. one of the two transverse axes 21 is further forward and the other of the two transverse axes 21 further back. The offset of the transverse axes 21 could also take place in height instead or in addition.

In the exemplary embodiment, the trailing arms 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). A holding part 23 is used for this purpose, which is in a non-rotatable connection with the respective torsion bar spring 22 . In order to enable the spring force to be adjusted, a respective 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 . In order to move the respective holding part 23 in the transverse direction, an electrically operated control part 24 (ie an actuator) is preferably provided in each case. 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. Its rotational position relative to the holding part 23 can be adjusted and fixed, as a result of which a preload 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, rotary dampers are provided as dampers 26, via which the longitudinal links 20 are mounted on a downwardly projecting leg 10a of the base unit 10 such that they can pivot about the lower transverse axes 21. 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 in order to steer the wheels 11, are connected to one another via a connecting rod 28, 29, 30, as a result of which the pivoting of the right and left wheel carriers 12 about the respective pivot axis 14 is coupled is. 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 by the base unit 6 in the transverse direction. 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. 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 therefore no steering mechanism by which the rotation of a steering wheel is mechanically transmitted to the angular position of the wheels. There are also no additional steering actuators which 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 further comprises 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 make possible.

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 linings 33 are arranged, which interact with the rod part 30 . To actuate the clamping jaws 32 are used electrically operated actuators 34, which 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 jaws 32 are slidably guided by guide pins 36 on which springs 37 are arranged, which move the jaws 32 to an open position in which the clamping pads are lifted from the central rod part 30 when the actuators 34 are not actuated. When the 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 the latter 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 embodiment is shown schematically in FIGS. 11 to 13. FIG. 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 pivot bearings form the holding device 38 here. For the lockability of 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 indicated schematically in FIG. 14a). The control system 40 comprises 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 are output to the electric motors, braking devices and holding devices 31, 38 become. The control system 40 can convert steering commands from a driver into the corresponding angular positions of the wheels 11.

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. 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 to counteract oversteer or understeer.

An exemplary embodiment of the method according to the invention is first explained with reference to FIGS. 14 a) to c), a driving situation being present in which when the motor vehicle is cornering (through a left-hand bend in the exemplary embodiment) in the same or overlapping period of time both an ESP - Intervention and a steering intervention is to be carried out.

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 specified 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 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 now to be changed in the same period (for example 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 is required in addition to the ESP intervention. Assemble 2 to perform.

[0075] In order to carry out the ESP intervention and the steering intervention in the same period, first and second time windows which alternate with one another are specified in this period. 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 by the control unit 41 of the control system 40 in the second time windows, so that the pivoting of the wheels 11 about the pivot axes 14 is 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.

Thus, in the first and second time windows, the respective selective braking forces 43, 44 shown in Fig. 14 a) and b) are exerted on the front wheels 11, which thus alternate with one another, with the holding device 31, 38 is activated and determine the angular positions of the wheels 11 about the pivot axis 14 and are open in the second time window and the angular positions of the wheels 11 about the pivot axis 14 release. This is repeated until the specified trajectory of the motor vehicle is reached. 14

c) 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 previously described procedure. As a result of this procedure, the control system 40 provides a vehicle dynamics control system for cornering. If no intervention by this vehicle dynamics control system is required, the motor vehicle is steered on the basis of the trajectory specified by the driver or by the autonomous or semi-autonomous driving system without intervention by this vehicle 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 Step 48 determines data which is used to determine whether the actual values of the angular positions of the front wheels 11 correspond to the desired target values The specified trajectory can also be changed by an autonomous or semi-autonomous driving system Instead or in addition, 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 a change in the angular positions of the front wheels 11 is to be carried out (step 49) is negative, then in step 50 an ESP intervention for the front wheels 11 is initiated by one of the front wheels selectively is braked continuously, i.e. without a division into first and second time windows. The holding device 31, 38 is thereby activated, i.e. closed.

If it is determined that the angular positions of the front wheels 11 need to be changed (branch "Y" after step 49), a steering intervention must also be carried out. In step 51, an ESP intervention of the front wheels 11 carried out, i.e. one of the front wheels 11 is braked selectively, 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 changed by means of drive and/or braking forces The sequence then begins again in step 45. Steps 51, 52 are therefore repeated as long as both the ESP intervention and the steering intervention are to be carried out on the front wheels It could also be provided that steps 51, 52 are carried out several times before the sequence is started again at step 45. In any case, since the first and second time windows are each only of short duration and the duration for a complete ESP intervention is much longer, just like for a steering intervention, 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 window 53, 54 alternate. In the exemplary embodiment shown, the second time windows 54 immediately follow the first time windows, while there is a short interval x between the second time windows and the first time windows, in which the other commands of the sequence shown in FIG. 17 are carried out. There could instead or additionally be short gaps between the first and second time windows. The intervals between successive time windows 53, 54 or 54, 53 are expediently shorter than the time windows 53, 54.

As can be seen schematically from FIG. 18, 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 in each case Range of 5 milliseconds to 300 milliseconds, with the range of 10 milliseconds to 50 milliseconds being preferred and the range of 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 is shown as an example in FIGS. 15 a) and b). Again, this is an ESP intervention when cornering to counteract understeer.

First, the front and rear wheels on the inside of the curve are selectively braked, as shown in FIG. 14 a). Since the rear wheels 7 can now also be steered, the rear axle assembly also has a holding device in order to determine the instantaneous angular positions of the rear wheels, analogously to 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 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. 15a), 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 first and second time windows until the state 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, both 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 window for the front Axle assembly and for the rear axle assembly here may be the same or different from each other.

If oversteering occurs when cornering, the ESP intervention takes place in an analogous manner, with the wheels on the outside of the curve now being braked selectively.

An exemplary embodiment of the method according to the invention is explained with reference to FIGS. 16 a) to c) 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-hand wheels than with the left-hand wheels, as is indicated in FIG. 16a) 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. By braking the right and left wheels at different levels, a torque is generated about the vertical axis of the vehicle, 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 that are exerted on the wheels in the second time window are indicated by arrows in FIG. 16 b). The holding devices for determining the angular positions of the front and rear wheels are deactivated in this case. For the front wheels, braking force is applied only to the left wheel. As a result, the front wheels 11 pivot slightly in the counterclockwise direction in each of the second time windows. 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 window results in a 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) the angular positions of the front and rear wheels are shown when the counter-steering against U-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. It can thus be used with different traction of the right and left wheels 11, 7, the maximum traction of each wheel.

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 are steerable, 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 acceleration of the motor vehicle can be carried out in an analogous manner when the right and left wheels have different traction.

The procedure can also be analogous if, in the same or an overlapping period of time, the ground 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, e.g On the one hand, braking or acceleration is to be carried out, especially when 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 being deactivated is

The invention has been described by way of example for various driving situations. The procedures described can have various modifications without departing from the scope of the invention as defined in the claims.

LEGEND TO THE NOTES:

1 chassis 30 _rod part

2 Front Axle Assembly 31 Holding Device

3 rear axle assembly 32 jaws

4 rigid axle 33 clamping lining

5 leaf spring package 34 actuator

6 base unit 35 mounting part

7 wheel 36 guide pin

8 wheel axle 37 spring

10 base unit 38 holding device 10a leg 39 magnetorheological fluid 10b support leg 40 electronic control system 11 wheel 41 _control unit 12 wheel carrier 42 arrow

13 wheel axle 43 arrow

14 pivot axis 44 arrow

15 electric motor 45 step

16 brake disc 46 step

17 caliper 47 step

18 pivot bearing 48 step

20 _Trailing arm 49 step

21 transverse axis 50 step

22 torsion bar spring 51 step

23 holding part 52 step

24 control part 53 first time window 25 connecting piece 54 second time window 26 damper 55 arrow

27 circle line 28 rod part 29 rod part

Claims (12)

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 different longitudinal forces are present from the right and left wheel (11) of an axle assembly (2) which has steerable wheels (11). 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, commands are issued by the control system (40) in a plurality of first time windows (53), through which the wheels (11) of this axle assembly (2) are changed in their angular positions by means of a holding device (31, 38). the respective pivot axis (14) are fixed and different driving and/or braking forces are exerted on the right and the left wheel (11) of this axle assembly (2) for the transmission of different longitudinal forces to the ground, and the control system (40) in a plurality of second time windows (54), which lie in time periods between two respective first time windows (53), commands are issued, through which the pivoting of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) of the Holding device (31, 38) is released and the angular positions of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) can be changed by means of drive and/or braking forces. 2. 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 change by the driver or by an autonomous or semi-autonomous driving system follows a predetermined trajectory for the motor vehicle. 3. The 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 Uoversteering or understeering is detected by Control system (40) in the first time windows (53) to counteract U oversteer or understeer, commands are issued, by which the left or the right wheel (11) of this axle assembly (2) is braked and the other of these wheels (11 ) is not braked or braked less. 4. The 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 that if oversteering or understeering is detected by the Control system (40) in the second time window (54) commands are issued, through which the angular positions of the wheels (11) of this axle assembly (2) about the respective pivot axis (14) counteracting oversteer or understeer are changed. 5. The method according to any one of claims 1 to 4, characterized in that if the control system (40) when braking or accelerating the motor vehicle oversteering or understeering of the motor vehicle is detected, the control system (40) in the first time window ( 53) commands are issued through which the wheels (11) of this axle assembly (2) are braked, and commands are issued by the control system (40) in the second time window (54) through which the angular positions of the wheels (11) to the respective Pivot axis (14) can be changed counteracting oversteer or understeer. 6. The method according to claim 5, characterized in that when braking or accelerating the motor vehicle with different traction of the right and left wheel (7, 11) of this axle assembly (2), the maximum traction of the respective wheel (7, 11) is utilized . 7. The method according to any 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). 8. The method according to any one of claims 1 to 7, characterized in that the first and second time windows (53, 54) alternate, being immediately following one another or being separated by intervals shorter than the first and second time windows (53, 54 ) are. 9. The method according to any 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) are steerable about respective pivot axes and individually by a respective electric motor are driven around a respective wheel axle (8, 13), the steering of the steerable front and rear wheels (7, 11) taking place only by means of drive 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. 10. The method according to claim 9, characterized in that in a driving situation in which the right and the left wheel (7, 11) of both the front and the rear axle assembly (2, 3) to transmit different longitudinal forces to the ground are and also a steering operation of both the wheels (7, 11) of the front 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) as well as 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) by means of the respective holding device in their respective angular positions around the respective pivot axes are determined and different driving and/or braking forces are exerted on the right and the left wheel (7, 11) of the respective axle assembly (2, 3) 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), commands are issued by the control system (40) through which the pivoting of the wheels (7, 11) of the respective axle assembly ( 2, 3) about the respective pivot axis (14) by the holding device (31, 38) and the angular positions of the wheels (7, 11) of the respective axle assembly (2, 3) about the respective pivot axis (14) by means of a drive - and/or braking forces are changed. 11. The 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 (3rd ) differentiate. 12. A computer program comprising instructions which, when the program is executed by a computer, cause the latter to execute the method according to any one of claims 1 to 11. 6 sheets of drawings