STEERING SYSTEM FOR A MOBILE WORK MACHINE

Abstract

The disclosure relates to a steering system for a mobile work machine, in particular for a mobile crane, which comprises at least one mechanically steerable front axle, at least one passively-steered rear axle, as well as at least one rear axle that is steerable by means of at least one steering cylinder. The front and rear axles are arranged one behind the other along a longitudinal axis of the steering system and comprise wheels, the axes of rotation of which, virtually extended, in the case of cornering, on the side of the curve center, intersect a common steering pole plane positioned perpendicularly on the longitudinal axis. According to the disclosure, at least one passively-steered rear axle is arranged between a front axle and the steering pole plane. The disclosure furthermore relates to a mobile work machine comprising such a steering system.

Claims

1. Steering system for a mobile work machine, comprising at least one mechanically steerable front axle, at least one passively-steered rear axle, and at least one rear axle which is steerable by means of at least one steering cylinder, wherein the front and rear axles are arranged one behind the other along a longitudinal axis of the steering system, and wherein the front and rear axles comprise wheels, the axes of rotation of which, virtually extended, in the case of cornering, on the side of the curve center, intersect a common steering pole plane positioned perpendicularly on the longitudinal axis, wherein at least one passively-steered rear axle is arranged between a front axle and the steering pole plane (pusher axle).

2. Steering system according to claim 1, comprising a plurality of front axles which are coupled to one another via a mechanical steering device.

3. Steering system according to claim 1, wherein the at least one steering cylinder is a hydraulic cylinder and the steering system comprises a hydraulic circuit for actuating the at least one hydraulic steering cylinder.

4. Steering system according to claim 1, wherein at least one steerable rear axle, comprises an hydraulic centering cylinder, which is configured such that the associated rear axle, in the case of a fault, is blocked with respect to steering and/or is moved into a non-steered position.

5. Steering system according to claim 4, further comprising an acquisition system by means of which a pressure in a hydraulic circuit can be acquired for steering the at least one rear axle, and/or a speed of the mobile work machine and/or a steer angle can be acquired.

6. Steering system according to claim 1, wherein the at least one steerable rear axle comprises two hydraulic steering cylinders.

7. Steering system according to claim 1, wherein at least one passively-steered rear axle is arranged on the side of the steering pole plane opposite the at least one pusher axle (trailing axle), and is configured to follow a steering angle of the at least one front axle in the opposite direction.

8. Steering system according to claim 1, wherein the pusher axle is configured to follow a steering angle of the at least one front axle in the same direction, and/or wherein at least one pusher axle is arranged between a front axle and a steerable rear axle or between two front axles or between two steerable rear axles.

9. Steering system according to claim 1, wherein the at least one front axle, and the at least one steerable rear axle each comprise a steering trapeze comprising a steering link and two steering arms.

10. Steering system according to claim 1, wherein at least one steerable rear axle and/or at least one passively-steered rear axle is arranged on the side of the steering pole plane opposite the at least one pusher axle and comprises a steering trapeze which is mirrored with respect to a steering trapeze of the at least one pusher axle, in relation to the steering pole plane.

11. Steering system according to claim 1, wherein the virtual extensions of the axes of rotation of the wheels of the front and rear axles in the case of cornering meet at a common point (steering pole).

12. Mobile work machine, comprising a steering system according to claim 1, wherein the work machine comprises a mobile undercarriage that comprises the steering system, and an upper structure that is rotatably mounted on the undercarriage.

13. Mobile work machine according to claim 12, comprising at least two rear axles that are steerable via steering cylinders.

14. Mobile work machine according to claim 12, wherein the at least one steerable rear axle comprises at least one hydraulic steering cylinder which can be actuated via a hydraulic circuit of the mobile work machine.

15. Mobile work machine according to claims 12, comprising a control unit, by means of which the at least one steering cylinder of the at least one steerable rear axle can be controlled, wherein the mobile work machine further comprises an acquisition device by means of which a pressure in a hydraulic circuit can be acquired for steering the at least one rear axle, and/or a speed of the mobile work machine and/or a steer angle can be acquired, which is connected to the control unit.

16. Steering system according to claim 1 wherein the work machine is a mobile crane.

17. Steering system according to claim 2, wherein the mechanical steering device includes a steering linkage.

18. Steering system according to claim 4, wherein all steerable rear axles comprise hydraulic centering cylinders.

19. Steering system according to claim 7, wherein the at least one trailing axle is arranged behind the at least one steerable rear axle, proceeding from the at least one front axle.

20. Steering system according to claim 11, wherein the steering pole plane contains the steering pole.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] Further features, details and advantages of the disclosure emerge from the embodiments explained below with reference to the figures, in which:

[0052] FIG. 1: is a side view of the mobile work machine according to the disclosure, according to an embodiment;

[0053] FIG. 2: is a schematic plan view of the steering system according to the disclosure, according to an embodiment;

[0054] FIG. 3: is a schematic plan view of the steered rear axle of the steering system according to the disclosure, according to an embodiment; and

[0055] FIG. 4: is a schematic plan view of a pusher axle of the steering system according to the disclosure, according to an embodiment.

DETAILED DESCRIPTION

[0056] FIG. 1 is a side view of an embodiment of the mobile work machine 10 according to the disclosure, in the form of a mobile crane. Although the following description of the embodiments is made with reference to said mobile crane 10, the steering system according to the disclosure is not limited to such but rather can be used in any mobile work machines.

[0057] The mobile crane 10 according to the embodiment shown comprises a mobile undercarriage 12 comprising a steering system according to the disclosure. The latter comprises a wheel chassis having five axles 13, which each comprise pairs of wheels 15. Here, for example single or double wheels are conceivable on each side, depending on the crane configuration. The undercarriage 12 has an undercarriage cab 17 on the front side, for steering the mobile crane 10 during road travel. Furthermore, the undercarriage 12 comprises a support device having a plurality of support crosspieces which carry support cylinders for lifting the mobile crane 10 from the substrate. In the mobile crane 10 of the embodiment shown, an upper structure 14 is mounted on the undercarriage 12 so as to be rotatable about a vertical axis of rotation, and comprises an upper structure cab 16 for control during crane operation, and a telescopic boom 18 that is mounted so as to be pivotable about a horizontal axis.

[0058] FIG. 2 is a schematic plan view of the steering system of the mobile crane 10 of the embodiment according to FIG. 1. In this case, the dashed line 30 denotes the longitudinal axis of the steering system, which also simultaneously represents the longitudinal axis of the undercarriage 12. In FIG. 2, the front side of the undercarriage 12 is on the right and the undercarriage tail is on the left. The five axles 13 are arranged one behind the other and in parallel with one another along the longitudinal axis 30. Correspondingly, the right-hand axle in FIG. 2 is referred to as the first axle and the numbering increases to the left or to the rear in the direction of the vehicle tail (i.e. the rearmost wheel axle is the fifth axle).

[0059] In the embodiment shown here, the steering system comprises a mechanically steerable front axle 21 (the first axle in FIG. 2), which is steerable in particular by a steering wheel in the undercarriage cab 17 and which can comprise additional hydraulic steering cylinders for assisting the steering force. The remaining four axles 13 follow the wheel steering angle of the front axle 21 in a predetermined manner, such that the virtual extensions 32 of the axes of rotation of the wheels 15 (of which only those of the first and fifth axle are shown) meet at a common point 36, the steering pole 36, on the side of the curve center (cf. FIG. 2). The dot-dashed line 34 shown in FIG. 2 indicates a plane that is positioned perpendicularly on the longitudinal axis 30 and extends through the steering pole 36, which plane is referred to as the steering pole plane 34.

[0060] This is made possible mechanically in that each axle 13 in this embodiment has a steering trapeze 43, which is shown in more detail in FIG. 3. The steering trapezes 43 each comprise a steering link 44 which extends in parallel to the axle in a straight running position and which is pivotably connected to two steering arms 46 which are arranged in the region of the wheels 15 or the wheel suspensions carrying the wheels 15. The steering arms 46 are in turn pivotably connected to the axle, wherein the wheels 15 are deflected, by pivoting the steering arm 46 relative to the axle, by an angle BL on the left-hand side and by an angle BR on the right-hand side. These angles are also referred to as toe angles.

[0061] FIG. 2 shows the individual toe angles of the wheels 15 of the respective axles on the left-hand side (.sub.L1-.sub.L5) and on the right-hand side (.sub.R1-.sub.R5) (warning: for the sake of simplicity, in the schematic FIG. 2 despite the indicated deflection the wheels are shown in the non-steered state, i.e. in the straight running position). It can be seen that the individual toe angles differ in magnitude from axle to axle, and also for each axle, between the right-hand and left-hand wheel 15. Furthermore, the wheels 15 on the right-hand side or in front of the steering pole plane 34 are deflected in the same direction (but by different toe angles) to the left, while the wheels 15 on the left-hand side or behind the steering pole plane 34 are deflected in the opposite direction from the wheels 15 in the region in front of the steering pole plane 34 (and again by different toe angles). Such steering is referred to as Ackerman steering. This can be able to be set for example by selecting a corresponding steering program of the mobile crane 10. In addition, further steering programs can be selectable (e.g. crab steering, in which the wheels of all the actively steered axles 13 are deflected in the same direction and by in particular virtually identical toe angles).

[0062] The steering system comprises actively steerable rear axles 22, which automatically follow the steering angle of the front axle 21 (and specifically such that the Ackerman condition according to FIG. 2 is fulfilled). For this purpose, the steered rear axles 22 optionally each comprise two hydraulic steering cylinders 40, which are in each case arranged on the right-had side and left-hand side on the axles, and in particular connect the steering arms 46 to the axle. An embodiment for a steered rear axle 22 of this kind is shown as a schematic plan view in FIG. 3. Retracting or extending the steering cylinders 40 pivots the steering arms 46 with respect to the axle, and as a result turns or steers the wheels 15 about particular toe angles. In the embodiment shown, in each case two hydraulic steering cylinders 40 are provided, which are supplied or actuated by at least one hydraulic circuit of the work machine 10.

[0063] Depending on the steering program, vehicle speed, and steering angle of the front axle 21, the steering cylinders 40 of the steered rear axles 22 are actuated by a corresponding control unit of the work machine 10.

[0064] The mobile crane 10 can comprise a control unit which is configured, in the event of a faulty or incorrect rear axle steering, to limit an allowable speed range of the mobile crane 10 to a certain maximum speed (e.g. 40 km/h). If the vehicle speed is above 40 km/h when the fault occurs, it can be provided that active braking does not take place, but rather that the speed is maintained and reduced as required. In one embodiment, information or a warning can be output optically and/or acoustically to the driver.

[0065] In the embodiment shown here, the steered rear axles 22 each comprise a hydraulic centering cylinder 42 (cf. FIG. 3), which in the event of a fault (i.e. in the case of faulty rear axle steering) moves the associated rear axle 22 into the neutral position or the straight running position. For this purpose, the centering cylinder 42 is configured such that it can over-press the steering cylinders 40.

[0066] If, in the embodiment of FIG. 2, all four axles which are not mechanically steered front axles 21 (i.e. axles no. 2-5) were actively steerable rear axles comprising centering cylinders 42, then in the event of a fault, if all four rear axles 22 are straight running, the vehicle 10 would push out significantly beyond the front axle 21 in the case of a steering movement by the front axle 21 (the vehicle would oversteer), which would make the steering significantly more difficult. Furthermore, significant tire wear at the front axle 21 would occur.

[0067] In order to improve the steering in the event of a fault, and to achieve a smaller emergency steering radius, according to the disclosure a passively-steered rear axle 23 (=pusher axle) is installed in the region in front of the steering pole 36 or in front of the steering pole plane 34, i.e. in the embodiment of FIG. 2 between the steering pole plane 34 and the front axle 21.

[0068] In contrast to passively-steered rear axles, which, in known steering systems, are located in the tail region and thus significantly behind the steering pole 36 or the steering pole plane 34, and during cornering always steering in the opposite direction from the front axle 21, depending on the steering program, vehicle speed, and steering angle of the front axle(s) 21, according to the disclosure the pusher axle 23 is located in front of the steering pole 36 and must therefore turn in the same direction as the front axle 21, depending on the steering program, vehicle speed and steering angle of the front axle 21.

[0069] For a correct thrust angle at the pusher axle 23 and faultless rolling of the wheels 15 during cornering, the pusher axle 23 in particular comprises a steering trapeze 43 which is arranged rotated or mirrored, in plan view of the steering pole plane 34, with respect to the steered rear axles 22 arranged in the region behind the steering pole plane 34( ) and with respect to the conventional trailing axles) (cf. FIG. 2).

[0070] FIG. 4 is a schematic plan view of an embodiment of the pusher axle 23 according to the disclosure. This can, just like the steered rear axles 22, comprise two steering cylinders 40, via which it is electrohydraulically steered in normal operation (and therefore behaves like the remaining steered rear axles 22). In the event of a fault, the steering cylinders 40 are in particular switched such that the steering cylinders 40 are hydraulically short-circuited and the pusher axle 23, released as a result, can be moved by external forces and functions as a passively-steered axle. The pusher axle 23 in particular does not comprise a centering cylinder 42.

[0071] In the embodiment of FIG. 2, the pusher axle 23 is arranged between a front axle 21 and a steered rear axle 22 (also arranged in the region in front of the steering pole plane 34) which can also be centered in the event of a fault. As a result, the pusher axle 23 is guided by the two surrounding axles 21, 22. Alternatively, the pusher axle 23 could also be arranged between two steered rear axles 22 or between two front axles 21.

[0072] The pusher axle 23 installed according to the disclosure in the front region of the steering system reduces the emergency steering radius of the steering system or of the mobile crane 10 (in the case of some crane types, even halves it). This results in the mobile crane 10 not tending to significant understeering in the case of a fault, and the speed not having to be abruptly significantly reduced by the crane driver in or before tight corners, in order to safely drive around the corner. As a result, the safety in road traffic in the case of steering failure can be increased.

[0073] Alternatively, a plurality of pusher axles 23 can be provided.

[0074] Alternatively, the steering system can comprise one or more trailing axles (i.e. passively-steered rear axles in the region behind the steering pole plane 34). These in particular do not comprise a centering cylinder 42.

[0075] Alternatively, the steering system can comprise a plurality of front axles 21 that are coupled together mechanically.

LIST OF REFERENCE NUMERALS

[0076] 10 mobile work machine (mobile crane) [0077] 12 undercarriage [0078] 13 axle [0079] 14 upper structure [0080] 15 wheel [0081] 16 upper structure cab [0082] 17 undercarriage cab [0083] 18 telescopic boom [0084] 21 front axle [0085] 22 steered rear axle [0086] 23 pusher axle [0087] 30 longitudinal axis [0088] 32 virtual extensions of the wheel axes of rotation [0089] 34 steering pole plane [0090] 36 steering pole [0091] 40 steering cylinder [0092] 42 centering cylinder [0093] 43 steering trapeze [0094] 44 steering link [0095] 46 steering arm