AT524936B1 - Platform for at least four-wheel motor vehicles with electric drive - Google Patents

Abstract

A platform for at least four-wheel motor vehicles with an electric drive comprises at least one front and at least one rear axle group, which are spaced apart from one another in a longitudinal direction of the platform and of which at least the front axle group has wheels (11) which can be steered about a respective pivot axis (14) and which are attached to Wheel carriers (12) are rotatably mounted about wheel axles (13) and are driven individually by electric motors, the wheel carriers (12) pivotable about the pivot axes (14) being connected to one another via a connecting rod (31). The wheels (11) are steered only by means of drive and/or braking forces. The platform has a modular structure and has a chassis module (1) and a front axle module (2) forming the front axle group, which can be connected as a whole to the chassis module (1) and can be removed from the chassis module (1).

Description

description

The invention relates to a platform for at least four-wheel motor vehicles with an electric drive, comprising at least one front and at least one rear axle group, which are spaced apart from one another in a longitudinal direction of the platform and of which at least the front axle group has wheels that can be steered about a respective pivot axis which are rotatably mounted on wheel carriers about wheel axles and are driven individually by electric motors, the wheel carriers pivotable about the pivot axes being connected to one another via a connecting rod and the wheels being steered only by means of drive and/or braking forces.

Platforms for four-wheel motor vehicles with electric drives are known in different embodiments.

Among other things, with regard to autonomous driving, with some areas of application with limited maximum speeds, for example in the range of up to 80 or 90 km/h, there are new requirements and possibilities, which have already led to new starting points.

So specially adapted for such applications platforms have been developed, which can be easily equipped with different structures to allow different purposes, such as passenger transport or load transport. Such platforms are also referred to as skateboard platforms.

In four-wheel motor vehicles with electric drive, the two steerable wheels of a front axle group 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 an axle, which can be pivoted about pivot axes in order to steer the wheels, are connected by means of a connecting rod. There is neither a part mechanically acting on the connecting rod 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 connecting rod in order to brake or block it.

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.

In contrast, in the steering device known from US Pat. No. 9,221,495 B2, the wheels are steered 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.

[0008] In addition, a modular design of a platform has already become known in that there is a separate wheel module for each of the wheels. In addition to the wheel and its suspension, this includes an electric wheel hub motor for driving, a brake and an electric steering actuator for actively steering the wheel. The wheels are therefore steered by means of separate steering actuators. The wheel modules are mounted on a chassis module. In addition, FR 2721559 shows a motor vehicle with an electric drive, which has a platform with a chassis module and axle modules mounted thereon, which form a front and a rear axle group.

The object of the invention is to provide an advantageous platform of the type mentioned, which has a high degree of flexibility for adaptation to different applications with a simple design. According to the invention, this is achieved by a platform with the features of claim 1.

The platform according to the invention has a modular structure which comprises a chassis module and a front axle module forming the front axle group. This front axle module, which has steerable right and left wheels, the wheels being steered only by means of drive and/or braking forces, can be connected to the chassis module as a whole and can be removed from the chassis module. The front axle module has a rigid base unit, via which the connection to the chassis module takes place when the front axle module is connected to the chassis module and to which the wheel suspension is attached.

Because the invention provides a front axle module, preferably also a rear axle module, which can be connected as a whole to the chassis module and can be removed from the chassis module, a modular design of a platform is made possible which steers the steerable wheels only by means of driving and/or braking forces, it being necessary to connect the steerable right and left wheels of a relevant axle group via a connecting rod.

The front and/or rear axle module is advantageously connected to the chassis module by means of a screw connection, with the rear axle module advantageously also having a rigid base unit via which the connection to the chassis module takes place and to which the wheel suspension is attached.

If in the platform according to the invention, the rear axle group is also designed as a modular axle module, which is preferred, the wheels can not be steerable or also steerable in this rear axle module. If the wheels of the rear axle module are steerable, they are preferably driven individually by means of electric motors and the steering takes place only by means of drive and/or braking forces.

In an advantageous embodiment of the invention, the wheels of the front axle module and/or rear axle module are suspended via a trailing arm wheel suspension, which has at least one left and at least one right trailing arm, each of which is pivotably connected to the base unit about a transverse axis. The pivoting of the trailing arm relative to the base unit is expediently spring-loaded and damped. With this configuration, advantages in terms of the required installation space are achieved, particularly when it is an axle with wheels that are driven individually by electric motors and steered only by means of drive and/or braking forces. This also advantageously enables the modular design of the axle group.

Appropriately, it is provided here that an upper and a lower trailing arm are provided for both the left wheel and for the right wheel, which store the wheel carrier, which is assigned to the respective wheel, pivotable in the manner of a parallelogram. The upper and lower trailing arms on the respective side of the front and/or rear axle module are thus connected at different heights to the wheel carrier, which is assigned to the respective wheel, so that they can pivot about a respective transverse axis and are at different heights on the base unit of the axle module respective transverse axis pivoted. It can be achieved that there is no change in the angular position of the pivot axes of the wheel carriers (ie no change in the caster angle) when the trailing arms are pivoted relative to the base unit about the transverse axes. This leads to significant advantages when the wheels are steered only by means of drive and/or braking forces when there are different pivot positions of the trailing arms about the respective transverse axis, which result during compression.

The suspension of the trailing arm is preferably via torsion bar springs. These are expediently arranged coaxially to the respective transverse axis about which the respective trailing arm to which the respective torsion bar spring is connected can be pivoted. This cross

The axes are advantageously offset relative to one another in relation to the longitudinal direction of the platform and/or in terms of height. As a result, torsion bar springs arranged coaxially to the transverse axes can extend over more than half of the track width. In addition, an advantageous adjustment of the spring force of the torsion bar springs is made possible by this design, in which purely rotational movements of the torsion bar springs occur. For this purpose, in a region spaced apart from the connection of the torsion bar spring with the trailing arm, a holding part is connected to the respective torsion bar spring in a rotationally fixed (= non-rotatable) manner but displaceable in relation to the transverse direction parallel to the transverse axis, with the holding part being mounted on the base unit of the axle module so that it can be adjusted in the transverse direction is. The spring force of the respective torsion bar spring can thus be influenced by the displacement of the holding part relative to the base unit. In this case, an actuator for displacing the holding part in the transverse direction with respect to the base unit is preferably present.

In an advantageous embodiment of the invention, a holding device is provided, by means of which the present angular position of each of the steerable wheels of the front axle module and/or rear axle module about the respective pivot axis can be determined with a holding force. Such a holding device is advantageous if one of the electric motors of the wheels of a steerable axle fails. A desired angular position of the wheels can then still be set with the remaining electric motor and/or a mechanical braking device for the respective wheel and the wheels can be fixed in the set angular position with the holding device. In one possible embodiment, the holding force with which the fixing takes place can only be selected to be so large that it can still be overcome by means of the drive and/or braking forces that can be applied. The steerable wheels can thus still be steered by means of the drive and/or braking forces even if the holding device malfunctions.

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

Figure 1 is an oblique view of an embodiment of a platform according to the invention;

Figure 2 is a side view; [0021] FIG. 3 shows a bottom view, [0022] FIG. 4 shows an oblique view analogous to FIG. 1 but with the axle modules removed;

[0023] FIG. 5 shows an exploded view of a front axle module (without the parts arranged on the left-hand wheel carrier in relation to the direction of travel);

6 shows an oblique view (without the parts arranged on both wheel carriers); Figure 7 is a plan view;

Figure 8 is a front view;

Figure 9 is a side view;

Figure 10 is a section along line A-A of Figure 8;

Figure 11 is an exploded view of a second embodiment of a front axle module (without the parts arranged on the left wheel carrier);

Figure 12 is an oblique view; Figure 13 is a front view; Figure 14 is a side view;

Fig. 15 is an exploded view of a front axle module according to a third embodiment of the invention (without the parts arranged on the left knuckle);

Figure 16 is an oblique view; 17 is a front view.

For the sake of clarity, these are simplified, partially schematic representations.

A first embodiment of the invention is explained below with reference to FIGS. 1 to 10. The modular platform has a chassis module 1, a front axle module 2 and a rear axle module 3. A rigid supporting platform base 1a of the platform is formed from the chassis module 1 . In the figures, the chassis module 1 is only shown schematically as a contoured plate. In practice, the chassis module will have different parts, e.g. Preferably, accumulators for the electric drive are also attached to the platform base 1a of the chassis module (not shown in the figures).

The front right and left wheels relative to the direction of travel are steerable. The motor vehicle therefore has a steered front axle. A front axle group has the front wheels together with their wheel suspension and forms the steered front axle. The front axle group is formed by the front axle module, which is described in more detail below.

The rear wheels are not steerable in the embodiment. A rear axle group includes the rear wheels together with their wheel suspension and forms the rear axle. In the exemplary embodiment, the rear axle group is formed by the rear axle module 3 . A rear axle module could also be used, which also has steerable wheels. This could be designed analogously to the front axle module.

A platform according to the invention could also have more than one front and/or more than one rear axle module.

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

The rear axle module 3 is designed with a rigid axle 4 in the exemplary embodiment. This is suspended from a base unit 6 of the rear axle module 3 by means of leaf spring assemblies 5 . The inherently rigid base unit is attached to the chassis module 1 by means of a screw connection. For this purpose, screws 7 that pass through openings in the base unit 6 are screwed into screw threads of the chassis module 1 . The connection between the chassis module 1 and the rear axle module 3 can be rigid or, as indicated, can comprise springing and/or damping elements 9, such as rubber bushings or hydraulic bushings, in order to reduce the transmission of vibrations and/or noise.

The wheels 8 rotatably mounted by the rigid axle 4 can be driven by electric motors, for example by means of wheel hub motors. An additional mechanical braking device for each wheel, as is known, is expediently present.

The front axle module 2 has an inherently rigid base unit 10 which carries the wheel suspension. The base unit 10 is used to connect to the chassis module 1. This is preferably designed as a screw connection. Screws 18 pass through openings in the base unit 10 and are screwed into screw threads of the chassis module 1. The connection can be rigid or, as indicated, suspension and/or damping elements 19 can be interposed, for example in the form of rubber bushes or hydraulic bushes, in order to reduce the transmission of vibrations and/or noise.

The right and left wheels 11 of the front axle module 2 are rotatably mounted on wheel carriers 12 about wheel axles 13 . The wheels 11 are steerable. For this purpose, the right and left wheel carriers 13 are pivotably mounted about pivot axes 14 .

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

A mechanical braking device is provided for each wheel 11 . In this

A brake disc 16 and a brake caliper 17 are shown in connection.

It would also be conceivable and possible for the braking to be carried out solely by the electric motors.

The wheels 11 of the front axle module 2 are suspended from the base unit 10 via a trailing arm wheel suspension. There is a lower trailing arm 21 and an upper trailing arm 20 for both the left wheel and the right wheel 11 . The respective lower trailing arm 21 is connected to the base unit 10 such that it can pivot about a respective lower transverse axis 22 and is connected to the respective wheel carrier 12 such that it can pivot about a respective lower transverse axis 23 . The respective upper trailing arm 20 is connected to the base unit 10 such that it can pivot about a respective upper transverse axis 24 and is connected to the respective wheel carrier 12 such that it can pivot about a respective upper transverse axis 25 . The transverse axes 22-25 are perpendicular to the longitudinal direction of the platform. The longitudinal direction of the platform is parallel to the direction of straight travel.

The upper transverse axes 24 are higher than the lower transverse axes 22 and the upper transverse axes 25 are higher than the lower transverse axes 23. A parallelogram guide for the respective wheel carrier 12 is formed. When the trailing arms 20, 21 are pivoted about the transverse axes 24, 22 relative to the base unit 10, the angular positions of the wheel carriers 12 do not change.

The connections of the trailing arms 20, 21 with the wheel carriers 12 are in the form of ball joints. The wheel carriers 12 can thus also be pivoted about the respective pivot axis 14 relative to the trailing arms 20, 21 in order to steer the wheels 11.

The inclination of the pivot axes 14 at the top backwards or forwards represents the caster angle. As can be seen from FIG. A platform according to the invention is preferably designed with the caster angle equal to 0° or a (slightly) negative caster angle for the steered wheels (less than 5°).

The angle of inclination of a respective pivot axis 14 upwards inwards is referred to as spread. As can be seen from Fig. 7, the respective pivot axis 14 in the exemplary embodiment is oriented vertically when viewed from the front, i.e. the spread is 0°. In a platform according to the invention for the steered wheels, the spread is preferably formed with the value 0° or a (slightly) negative value (less than 5°).

[0054] The torque differences between the right and left wheels, in order to adjust the position of the wheels about the pivot axes 14, can be kept low by the design of the caster angle and the spread mentioned. It can be achieved low drive or braking torques required to steer the wheels.

The pivoting of the trailing arms 21 about the transverse axes 22 is spring-loaded. For this purpose, a respective torsion bar spring 26 is present for the respective lower trailing arm 21 . This respective torsion bar spring 26 extends coaxially to the respective lower transverse axis 22 about which the respective lower trailing arm 21 is pivotable. So that the torsion bar springs 26 can be as long as possible, i.e. can have a length greater than half the track width, the lower transverse axes 22 for the right and left lower trailing arm 21 are offset from one another, in the exemplary embodiment in relation to the longitudinal direction of the platform, i.e. one of the two Transverse axes 22 is further forward and the other of the two transverse axes 22 further back. Correspondingly, the upper transverse axes 24 of the right and left upper trailing arms 20 are offset from one another in relation to the longitudinal direction of the platform.

The offset of the lower and upper transverse axes 22, 24 could also take place in height instead or in addition.

In the exemplary embodiment, the trailing arms 20, 21 on the right and left sides are of different lengths corresponding to the offset of the transverse axes 22, 24, 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 related to one another in relation to the longitudinal direction of the platform.

puts his

In a region spaced apart from the connection to the respective trailing arm 21, the respective torsion bar spring 26 is non-rotatably connected to the base unit 10. A holding part 27 is used for this purpose, which is in a non-rotatable connection with the respective torsion bar spring 26 . In order to enable the spring force to be adjusted, a respective holding part 27 is connected to the respective torsion bar spring 26 so that it can be displaced in relation to the transverse direction parallel to the transverse axes 22-25 and is mounted on the base unit 10 so that it can be displaced in the transverse direction. An electric actuator 28 is preferably provided in each case for displacing the respective holding part 27 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 non-rotatable connection of the respective holding part 27 with the respective torsion bar spring 26 takes place via a respective connecting piece 29. Its rotational position relative to the holding part 29 can be adjusted and fixed, whereby a pretension of the respective torsion bar spring 26 can be adjusted.

The pivoting of the respective lower trailing arm 21 is damped by a respective damper 30 . In the exemplary embodiment, rotary dampers are provided as dampers 30, via which the lower trailing arms 21 are mounted on a downwardly projecting leg 10a of the base unit 10 such that they can pivot about the lower transverse axes 22.

The right and left wheel carriers 12, which can be pivoted about the pivot axes 14, are connected to one another via a connecting rod 31, which synchronizes the pivoting of the right and left wheel carriers 12 about the pivot axes 14. The connecting rod 31 has a center piece 31a, which is mounted on the base unit 10 so that it can be displaced in the transverse direction by means of bearing legs 10b of the base unit 10. A right and a left side piece 31b, 31c are articulated to the center piece 31a, the side pieces 31b, 31c being articulated to the wheel carriers 12.

A more than three-part or two-part design of the connecting rod (where the two side pieces 31b, 31c are extended and are directly connected to each other) is also conceivable and possible.

The displaceability of the center piece 31a in the transverse direction can be fixed by means of a holding device 32 up to a holding force exerted by the holding device 32 in the activated state. The holding device has at least one electrical actuator 32a, by means of which the holding device is adjusted between its passive state (open state), in which the displacement of the center piece 31a is released, and its activated state (closed state), in which a holding force is exerted on the center piece will. The holding device 32 is in this case attached to one of the bearing legs 10b.

A momentary angular position of the wheels 11 can thus be determined with a holding force by means of the holding device 32 . This can be advantageous if one of the electric motors 15 fails. The holding force can only be chosen so large that even when the holding device 32 is in the closed state, an adjustment of the instantaneous angular position of the wheels 11 can still be achieved by means of sufficiently high driving and/or braking forces.

The steering of the wheels 11, ie the setting of the angular position of the wheels 11 about the pivot axes 14, takes place, as already mentioned several times, only by means of drive and/or braking forces. 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 .

A steering of the wheels only by means of driving and braking forces is already known in principle and does not have to be explained in detail in this document. A serving electrical control device is not shown, and this is generally

not part of the platform. Apart from the electric motors for the individual wheel drives and the additional actuators 28, 32a described, other parts of the electrical equipment, such as electrical lines and sensors, for example sensors for detecting the angular position of the wheel carriers 12 about the pivot axes 14, are not shown.

A second exemplary embodiment of the invention is explained below with reference to FIGS. 11 to 14. The differences from the first exemplary embodiment are essentially described below. Unless otherwise described, the design corresponds to that of the first exemplary embodiment and the description of the first exemplary embodiment and possible modifications thereof can be used accordingly.

In this second embodiment, in contrast to the first embodiment, only a single left and a single right trailing arm 121 is present. Analogous to the lower trailing arms 21, these trailing arms 121 are mounted on the base unit 10 so as to be pivotable about transverse axes 22, their pivoting being sprung by torsion bar springs 26 in the same manner as in the first exemplary embodiment. To dampen the pivoting, telescopic dampers are provided as dampers 130 , which act between the respective trailing arm 121 and the base unit 10 . Instead, rotary dampers could also be provided again.

The wheel carriers 12 are mounted here on the respective individual trailing arm 121 such that they can be pivoted about the respective pivot axis 14 .

A holding device 132, which interacts directly with the respective wheel carrier 12, is used here to determine the current angular position of the wheels 11 about the respective pivot axis 14. The holding device has a brake part 132b which fixes the pivot position of the respective wheel carrier 12 about the respective pivot axis 4 and is actuated by a respective actuator 132a.

The holding device could, however, again interact with the connecting rod 31 analogously to the first exemplary embodiment.

A third embodiment of the invention is shown in FIGS. 15 to 17. FIG. The difference compared to the second embodiment is the type of damping of the pivoting of the respective trailing arm 121. The up and down movement of the trailing arm 121 is converted here by means of toggle levers 33 into a horizontal movement in the transverse direction, with this movement of the toggle lever 33 by means of linear dampers 230, which are arranged in the transverse direction and act between the upwardly directed leg of the respective toggle lever 33 and the base unit 10. Such an arrangement has advantages in terms of the space required.

Various further modifications of the shown exemplary embodiments of the invention are conceivable and possible without departing from the scope of the invention as defined in the claims. For example, the wheel suspension for the steerable wheels could be designed in different ways. Instead of a trailing arm wheel suspension, another type of wheel suspension could also be used, for example a McPherson wheel suspension, a double wishbone wheel suspension or a wheel suspension by means of a rigid axle.

Instead of the rear axle module 3 shown with non-steerable wheels, a rear axle module with steerable wheels could also be used, with these wheels also being steered only by means of drive and/or braking forces. For example, the rear axle module could be designed in a manner analogous to the front axle module.

There could also be more than one front axle module with steerable wheels and/or there could be more than one rear axle module with non-steerable wheels or steerable wheels.

LEGEND TO THE NOTES:

1 chassis module 25 upper transverse axis

1a platform base 26 torsion bar spring

2 front axle module 27 retaining part

3 rear axle module 28 actuator

4 live axle 29 connector

5 leaf spring package 30, 130, 230 damper

6 base unit 31 connecting rod

7 Screw 31a center piece

8 wheel 31b side piece

9 spring and/or side piece 31c damping element 32, 132 holding device

10 base unit 32a, 132a actuator

10a leg 132b braking part

10b bearing leg 33 toggle lever

11 wheel

12 wheel carriers

13 wheel axle

14 pivot axis

15 electric motor

16 brake disc

17 caliper

18 screw

19 suspension and/or damping element

20 trailing arms

21, 121 trailing arms

22 lower transverse axis

23 lower transverse axis

24 upper transverse axis

Claims (14)

patent claims 1. Platform for at least four-wheel motor vehicles with an electric drive, comprising at least one front and at least one rear axle group, which are spaced apart from one another in a longitudinal direction of the platform and of which at least the front axle group has wheels (11) that can be steered about a respective pivot axis (14), which are mounted on wheel carriers (12) so that they can rotate about wheel axles (13) and are driven individually by electric motors (15), the wheel carriers (12) which can be pivoted about the pivot axes (14) being connected to one another via a connecting rod (31) and the steering of the wheels (11) takes place only by means of drive and/or braking forces, characterized in that the platform is of modular design and has a chassis module (1) and a front axle module (2) forming the front axle group, which as a whole is connected to the chassis module ( 1) can be connected and removed from the chassis module (1), the front axle module (2) having a rigid base unit (10), üb he which is connected to the chassis module (1) connected state of the front axle module (2) with the chassis module (1) and to which the wheel suspension is attached. 2. Platform according to claim 1, characterized in that the front axle module (2) is connected to the chassis module (1) by means of a screw connection. 3. Platform according to claim 1 or 2, characterized in that the wheels (11) of the front axle module (2) are suspended via a trailing arm wheel suspension which has at least one left and at least one right trailing arm (20, 21, 121), which are each pivotably connected to the base unit (10) about a transverse axis (24, 22), the wheel carriers (12) being pivotably connected to the trailing arms (20, 21, 121) about the respective pivot axis (14). 4. Platform according to claim 3, characterized in that an upper and a lower trailing arm (20, 21) are provided both for the left wheel (11) and for the right wheel (11), which the respective wheel (11) associated wheel carrier (12) pivotably store in the manner of a parallelogram. 5. Platform according to Claim 3 or 4, characterized in that at least one torsion bar spring (26) assigned to the at least one left trailing arm (21, 121) and at least one torsion bar spring (26) assigned to the at least one right trailing arm (21, 121) for suspension pivoting of the respective trailing arm (20, 121) about the respective transverse axis (22) relative to the base unit (10). 6. Platform according to claim 5, characterized in that the torsion bar springs (26) are arranged coaxially to the respective transverse axis (22) about which the respective trailing link (21, 121) to which the respective torsion bar spring (26) is connected can be pivoted , these transverse axes (22) being offset relative to one another in relation to the longitudinal direction of the platform. 7. Platform according to Claim 6, characterized in that the respective torsion bar spring (26) is held in a rotationally fixed manner by a holding part (27) in a region spaced from the connection to the respective trailing arm (21, 121), which in relation to the parallel to the transverse axis (22) lying in the transverse direction is displaceably connected to the torsion bar spring (26) and which is mounted on the base unit (10) of the axle module (2) so that it can be adjusted in the transverse direction. 8. Platform according to claim 7, characterized in that the holding part (27) can be displaced in the transverse direction relative to the base unit (10) by means of an actuator (28). 9. Platform according to one of Claims 1 to 8, characterized in that the respective angular position of each of the steerable wheels (11) of the front axle module (2) about the respective pivot axis (14) can be determined by means of a holding device (32, 132) with a holding force is. 10. Platform according to claim 9, characterized in that to determine the angular position of the respective steerable wheel (11) with the holding force, the holding device (32, 132) interacts with the connecting rod (31) or with the respective wheel carrier (12). 11. Platform according to one of Claims 1 to 10, characterized in that the connecting rod (31) has a center piece (31a) which is mounted on the base unit (10) of the axle module (2) so that it can be displaced in the transverse direction and side pieces (31b, 31c ) which are articulated to the center piece (31a) and to the respective wheel carrier (12). 12. Platform according to one of Claims 1 to 11, characterized in that the platform also has a rear axle module (3) forming the rear axle group. 13. Platform according to one of claims 1 to 12, characterized in that the caster angle is 0 ° or is negative. 14. Platform according to one of claims 1 to 13, characterized in that the spread is 0° or negative. 6 sheets of drawings