Steering system for mobile working machine

Abstract

The invention relates to a steering system for a mobile working machine, in particular a mobile crane, comprising at least one mechanically steerable front axle, at least one driven steering rear axle and at least one rear axle which can be steered by means of at least one steering cylinder. The invention relates to a steering system comprising a front axle and a rear axle arranged one behind the other along a longitudinal axis of the steering system and comprising wheels, the axes of rotation of the wheels, virtually elongated on one side of the center of the curve, intersecting a common steering polar plane positioned perpendicular to the longitudinal axis in the event of a turn. According to the invention, at least one driven steering rear axle is arranged between the front axle and the steering pole plane. The invention also relates to a mobile working machine comprising such a steering system.

Description

Field of the Invention

[0001] The present invention relates to a steering system for mobile working machines, in particular mobile cranes. Background Art

[0002] Mobile working machines, such as heavy commercial vehicles, typically have multiple steering axles (also called axles), which differ both in their arrangement and in their type of steering.

[0003] Mobile cranes are examples of such heavy commercial vehicles. In a common embodiment, a mobile crane includes N axles, one or more (i.e., a number from 1 to X, where X < N) of which together represent the front axles that are mechanically steered by a steering wheel. These axles can be steered hydraulically assisted and can include corresponding steering cylinders. Hereinafter, the term "front axle" generally refers to the axles that can be mechanically steered. If multiple axles are mechanically connected, there are multiple front axles. This also applies if the front axles are only theoretically mechanically steerable, but without assistance, it is difficult to move the front axles and thus turn the wheels.

[0004] In addition, the mobile crane can also include a number of N - X electrohydraulic steering axles. Hereinafter, the steering axles that are not front axles are generally called "rear axles", and the electrohydraulic steering rear axles are called "steering rear axles". The steering rear axles actively steer according to the steering program, the vehicle speed, and the steering angle of the front axles, for example via two hydraulic steering cylinders (for example: a mobile crane has a total of five axles, including two front axles and three steering rear axles).

[0005] Such mobile cranes are configured such that their emergency steering radius complies with legal regulations. In this case, the emergency steering circle refers to the radius of the steering circle (also called the body steering circle) that the mobile crane travels when the steering system fails. The steering behavior is checked according to the provisions of ECE R79. If the emergency steering circle is smaller, the driving behavior of the mobile crane in a sharp turn is better in the case of a steering system failure. In other words, if the emergency steering circle or radius is smaller, the mobile crane can pass through a sharp turn at a higher speed in the case of a steering system failure. If the emergency steering circle is larger, then in order to keep the vehicle on the curve of the road, the speed must be significantly reduced.

[0006] The failure of the mechanical front axle steering is excluded in the standard specifications. Therefore, in this example, the focus is only on the active rear axle steering. Depending on the number of axles and the ratio of the front axles to the rear axles, two variants of rear axle steering for failure have been produced so far.

[0007] 1. Variant:

[0008] In certain types of cranes, considering the ratio of the front axle to the rear axle, with regard to steering, in the event of a malfunction ( = neutral or non-steering position), all the axles that can be steered at the rear axle can be set to "straight running". This is configured in the prior art such that all relevant axles that can be steered at the rear axle have centering cylinders and two steering cylinders, which are in particular hydraulic cylinders. The steering cylinders are used for the operating steering of the crane (usually including left and right steering, with one steering cylinder for each case). In the event of a malfunction, the function of the centering cylinder is to set the relevant rear axle to "straight ahead" (note: in this document, for simplicity, the steering or position of the axle is often mentioned, where in fact it refers to the steering or position of the wheels of the axle). Therefore, the centering cylinders are usually larger than the steering cylinders, and thus they overpressure the steering cylinders.

[0009] Depending on the driving situation and the malfunction situation, the centering cylinder has so far completed two tasks through its connection: on the one hand, it centers the associated rear axle (by applying pressure, for example the pressure provided by a wheel-driven pump, thus performing the centering movement of the rear axle). On the other hand, the centering cylinder can complete a further task by activating a hydraulic circuit. The centering cylinder can ensure that the relevant rear axle can now only be steered towards the middle (no longer outwards, in order to drive on a narrower curve), which is also referred to as locking.

[0010] 2. Variant:

[0011] In certain types of cranes, it may not be possible to meet the legal specifications by making all the actively steered rear axles run straight via the centering cylinders. In such a case, rear axles that are passively steered are usually installed. These axles can represent one to a maximum of N - X axles. In the prior art, such passively steered rear axles are installed starting from the last or the rearmost axle, and thus they are located behind the rear axles that can be centered by the centering cylinders. This type of mobile crane is known, for example, from DE 10 245 618 A1.

[0012] At this point, it should be noted that the specifications "front" and "rear" in this document relate to the straight-ahead driving direction of the vehicle or the working machine. In this case, the front axle is located in the front, and the rear axles are located behind the front axle. The rear area of the steering system in particular corresponds to the tail of the vehicle.

[0013] In the case of a trailing steering rear axle, the castor is determined by the so-called castor angle and is achieved by the inclination of the steering knuckle relative to the road vertical in the direction of the vehicle longitudinal axis. This principle is well known. In this case, the inclination is configured such that the theoretical wheel contact point is shifted in front of the axle center (the axle is "pulled"). Due to the theoretical distance between the actual wheel contact point and the theoretical wheel contact point (also known as the castor distance), external forces acting on the mobile crane through the steering of the mechanically steered front axle and the centering rear axle generate a torque on the trailing steering rear axle (thus the torque is generated by the steering and not by the castor).

[0014] So far, trailing steering rear axles have only been attached to the rear of the vehicle because they are furthest away from the steering pole or the steering pole plane here (the steering pole refers to the virtual intersection of the virtual extensions of the wheel rotation axes). Therefore, trailing steering rear axles have so far been located behind the steering pole. Hereinafter, when viewed in the longitudinal direction of the vehicle or the steering system, a trailing steering rear axle arranged behind the steering pole is referred to as a "rear trailing axle". So far, it has been considered that this has the greatest impact on the emergency steering radius.

[0015] Compared with the centering rear axle, the advantage of the rear trailing axle is that it can be freely rotated by an external force (see shopping cart), and thus, in case of a fault, it can be rotated by the steering movement of the front axle and thus the external force acting on the rear trailing axle. However, the advantage when driving forward is also a disadvantage when driving backward. In the case of the active (i.e., non-locked or raised) rear trailing axle driving backward, the rear trailing axle may be moved by an external force in a direction that is disadvantageous for backward driving, such as in the case of "snake-like driving". Optionally, the rear trailing axle can remain stationary (the reset of the rear trailing axle does not always work).

[0016] If the number of rear trailing axles increases (e.g., due to the need to maintain a specified emergency steering radius), the above-mentioned effect when driving backward will also occur when driving forward. Therefore, it should be noted that the rear trailing axle can also be restored to the straight-ahead position after a turn (in the forward direction). If too many rear trailing axles are provided, it may not be possible to set all the rear trailing axles completely straight after completing a turn. Summary of the Invention

[0017] In this context, the object of the present invention is to provide a mobile working machine of the above type, which has a small emergency steering radius and in which the above-mentioned disadvantages are avoided.

[0018] According to the present invention, this object is achieved by a steering system according to one aspect of the present invention. Advantageous embodiments of the present invention are described below.

[0019] Thereby, a steering system for a mobile working machine, in particular a mobile crane, is proposed, which steering system comprises at least one mechanically steerable front axle (hereinafter simply referred to as "front axle"), at least one trailing steering rear axle and at least one rear axle, wherein the at least one rear axle is steerable by means of at least one steering cylinder (hereinafter simply referred to as "steerable rear axle"). If the front axle, the steering rear axle or the trailing steering rear axle (singular) is mentioned hereinafter, in each case it means at least one front axle, steering rear axle or trailing steering rear axle.

[0020] The front axle and the rear axle are arranged successively along the longitudinal axis of the steering system (in particular, also the longitudinal axis of the mobile working machine). The front axle and the rear axle comprise wheels rotatably mounted about a rotational axis. The front axle and the rear axle are configured such that, in the case of the mobile working machine turning, the rotational axes of the wheels virtually extended on one side of the center of the curve intersect a common plane perpendicular to the longitudinal axis. Hereinafter, the common plane is referred to as the steering pole plane, since in the case of Ackermann steering, the virtual extensions of the rotational axes intersect at a common steering pole located in the steering pole plane.

[0021] According to the present invention, at least one trailing steering rear axle is arranged between the front axle and the steering pole plane. Thus, the trailing steering rear axle is located "in front of" the steering pole plane, rather than "behind" the steering pole plane as is conventional in the prior art, and is therefore referred to as a "front trailing axle" in this example.

[0022] In this case, it is clear that the current front trailing axle is still a trailing steering rear axle (i.e., the theoretical wheel contact point is located in front of the center of the axle, in the straight-ahead direction of the working machine, such that the wheels of the front trailing axle are "pulled"). Thus, in this case, the difference between the front trailing axle and the rear trailing axle only refers to the position relative to the steering pole plane. It is also conceivable that the front trailing axle is exactly in the steering pole plane.

[0023] Due to the position of the front trailing axle in the front region of the steering system, which is located between two wheel axles with fixedly defined steering parameters, for example between the front axle and the centering rear axle (in case of a fault), between two front axles or between two centering rear axles, the front trailing axle improves the steering of the mobile working machine in case of a fault. Thus, the front trailing axle is guided and thus does not exhibit the disadvantages that a conventional rear trailing axle may exhibit, for example when driving backwards.

[0024] The front trailing axle is improved, i.e., the emergency steering radius of the steering system according to the invention or of a mobile working machine equipped with said steering system is reduced (even halved in the case of some crane types). This results in the steering system or the mobile working machine being less prone to significant understeering in the event of a fault, and the driver does not have to suddenly and substantially reduce the speed during or before a sharp turn in order to safely turn. Thereby, the safety of road traffic can be increased in the event of a steering fault.

[0025] Furthermore, the front trailing axle also results in cost savings, since in the case of a vehicle having multiple steerable rear axles, the front trailing axle can replace one of the steerable rear axles in the front region and thus the centering cylinder is omitted.

[0026] The at least one front trailing axle according to the invention can also include one or more (in particular two) steering cylinders, which are connected to each other or "released" in the event of a fault in such a way that the axle follows the steering passively (i.e., due to the acting torque, follows the steering angle of the front axle in a predetermined manner). In the simplest case, the at least one front trailing axle can have the same design as at least one steerable rear axle and can differ therefrom, for example only in that it does not include any centering cylinder but has a caster. In normal operation, like the remaining steerable rear axles, the front trailing axle can be actively electrohydraulically steered via the steering cylinder and can only be "released" in the event of a fault, such that it acts as a trailing steerable rear axle. Alternatively, the front trailing axle can not include any steering cylinders and can thus only "drift" passively at this point.

[0027] Preferably, the at least one front trailing axle is configured such that it cannot be locked and / or cannot be lifted off the ground and thus "deactivated". This enables a simple and cost-saving configuration. However, alternatively, it is conceivable to lock the at least one front trailing axle and / or to actively lift it off the ground in certain cases.

[0028] In the case of a turn or a bend, the front trailing axle then steers in particular in the same direction as the front axle. In contrast, a typical rear trailing axle located in the rear region (i.e., behind the steering polar plane) steers in the opposite direction to the front axle.

[0029] The mechanical steering of one or more front axles can be assisted by hydraulic steering cylinders (power steering principle). For this purpose, in addition to the mechanical steering, one or more front axles can also be steered via one or more (in particular two) hydraulic steering cylinders respectively. In this case, the hydraulic steering by means of the steering cylinders can only be carried out in an auxiliary manner.

[0030] Preferably, the steering system only includes an active steering axle, namely 1 to X mechanical front steering axles and N - X rear axles that can be electro - hydraulically steered during normal operation, where N represents the total number of axles. In this case, the at least one front follower axle also has one or more steering cylinders and is only released in case of a fault and is thus steered passively. The remaining rear axles preferably all include centering cylinders. In this embodiment, the at least one front follower axle is particularly different from the remaining rear axles only in that it does not include any centering cylinders, but has a caster angle and is released as a passive steering axle in case of a fault.

[0031] In a possible embodiment, it is provided that the steering system includes a plurality of front axles that are interconnected via a mechanical steering device, in particular via a steering linkage. The steering device or the steering linkage can be connected to a control element via a steering mechanism, which actuates the steering device or the steering linkage. In particular, the steering linkage ensures the synchronous steering of all wheels of the front axle, where each wheel preferably moves in a separately rotating manner (in particular to achieve Ackermann steering) according to the steering direction and the position of the front axle or the position relative to the steering center.

[0032] In another possible embodiment, it is provided that at least one steering cylinder is a hydraulic cylinder. The steering cylinder is in particular a double - acting hydraulic cylinder, which in each case has two pressure chambers, and upon application of pressure, causes the associated wheel to generate a steering angle in one or the other direction. In this case, the steering system includes at least one hydraulic circuit for actuating the at least one hydraulic steering cylinder. Different hydraulic circuits can be provided for different axles.

[0033] In yet another possible embodiment, it is provided that at least one steerable rear axle, preferably all steerable rear axles, includes a centering cylinder that is configured such that in case of a fault, it locks the associated rear axle relative to the steering and / or moves it to a non - steering position. The centering cylinder is in particular a hydraulic cylinder, preferably a double - acting hydraulic cylinder. The at least one centering cylinder is controlled by one (or more) hydraulic circuits of the mobile working machine. In case of a fault, the locking and / or centering of the steered rear axles is carried out automatically in particular. The centering cylinder can be configured as described at the beginning of the prior art.

[0034] The steering system according to the invention can include an active rear axle steering according to DE 10 245 618 A1, the disclosure of which is expressly incorporated herein by reference. In particular, the at least one steerable rear axle including a centering cylinder can be configured according to this disclosure.

[0035] In another possible embodiment, it is provided that the steering system includes an acquisition system by which it is possible to acquire the pressure in the hydraulic circuit for steering at least one steered rear axle and / or the speed of the mobile working machine. For this purpose, the acquisition system includes one or more corresponding sensors. The above-described fault situations can be detected by the acquisition system, in particular by acquiring the pressure drop in the hydraulic circuit and / or exceeding the defined speed of the working machine and / or an unrealistic steering angle or exceeding the defined steering angle.

[0036] The steering system or the mobile working machine including the steering system preferably includes a control unit which is connected to the acquisition system or obtains the data of one or more sensors of the acquisition system and correspondingly controls one or more axles of the steering system. This can include the actuation of the above-described centering cylinders of at least one steered rear axle and / or the actuation of one or more steering cylinders.

[0037] In yet another possible embodiment, it is provided that the at least one steerable rear axle includes two, in particular hydraulic, steering cylinders. Each of the steering cylinders can be associated with one of the wheels of the associated rear axle ("right-hand side" steering cylinder and "left-hand side" steering cylinder).

[0038] In another possible embodiment, it is provided that in addition to the at least one front idler axle arranged in the "front" region of the steering system (i.e., "in front" of the steering pole plane), at least one idler steered rear axle is mounted on the side of the steering pole plane opposite to the at least one front idler axle (i.e., the "rear" side). Such an idler steered rear axle is referred to herein as a "rear idler axle". The at least one rear idler axle can be arranged very far to the rear in a manner known per se (i.e., starting from the at least one front axle, behind at least one steered rear axle), or between the steered rear axles.

[0039] Due to its position behind the steering pole plane, the at least one rear idler axle is configured to follow the steering angle of the at least one front axle in the opposite direction.

[0040] The at least one rear idler axle can include one or two steering cylinders which, in the event of a fault, are connected to each other or "released" in such a way that the axle follows the steering in a driven manner (i.e., due to the acting torque, follows the steering angle of the front axle in a predetermined manner). In the simplest case, the at least one rear idler axle can have the same design as the at least one steered rear axle, and the difference from the at least one steered rear axle can only be that it does not include any centering cylinders but has a caster angle. Alternatively, the rear idler axle can not include any steering cylinders and is always steered in a driven manner.

[0041] The at least one front follower axle and the at least one rear follower axle may have the same configuration and differ only in their position relative to the steering pole plane (in particular in terms of whether they follow the at least one front axle in the same or opposite direction).

[0042] In yet another possible embodiment, it is provided that the front follower axle is configured to follow the steering angle of the at least one front axle in the same direction.

[0043] Alternatively or additionally, the at least one front follower axle is arranged between the front axle and the steerable rear axle, or between two front axles, or between two steerable rear axles. Thus, it can also be well guided when traveling backward without getting stuck like a traditional rear follower axle.

[0044] In another possible embodiment, it is provided that the at least one front axle, the at least one steerable rear axle, and in particular the at least one front follower axle each include at least one steering trapezoid, which in turn includes a steering tie rod and two steering tie rod arms. Such a steering trapezoid is known per se and can form an Ackermann steering system according to the Ackermann principle, in which the virtual extensions of the rotational axes of the wheels of the front axle and the rear axle meet at a common steering pole.

[0045] In yet another possible embodiment, it is provided that at least one steerable rear axle and / or at least one follower-steered rear axle is arranged on the side of the steering pole plane opposite to the at least one front follower axle and includes such a steering trapezoid, wherein the steering trapezoid of the at least one steerable and / or follower-steered rear axle is arranged on the rear side of the steering pole plane, and the steering trapezoids of the at least one front axle and the at least one front follower axle are arranged on the front side of the steering pole plane, and these steering trapezoids are mirror images of each other (in a top view of the steering system). This ensures that the wheels on the inner side of the curve can obtain the maximum steering angle in any case. In the case of steering, the steering angle of the wheels of the axles on the front side of the steering pole plane is in the same direction as that of one or more front axles, while the steering angle of the wheels of the axles on the rear side of the steering pole plane is in the opposite direction.

[0046] In another possible embodiment, it is provided that in the case of turning, the virtual extensions of the rotational axes of the wheels of the front axle and the rear axle meet at a common point (steering pole), wherein the steering pole is particularly located in the steering pole plane. Thus, the axles of the steering system particularly form an Ackermann steering system.

[0047] The invention also relates to a mobile working machine, in particular a mobile crane, which includes a steering system according to the invention. Obviously, the same characteristics and advantages arise here for the steering system according to the invention, and thus a repeated description is omitted. In particular, the mobile working machine can include a steering system according to any of the above variants or any combination thereof.

[0048] The working machine may include a mobile chassis and a superstructure, the mobile chassis including a steering system, and the superstructure being rotatably mounted on the chassis.

[0049] In a possible embodiment, it is provided that the working machine includes at least two, preferably at least three, particularly preferably at least four rear axles, which can be steered via steering cylinders. The working machine may for example include exactly two, exactly three, exactly four, exactly five, exactly six, etc. rear axles, which can be steered via steering cylinders.

[0050] In another possible embodiment, it is provided that the at least one steerable rear axle includes at least one, preferably two hydraulic steering cylinders, which can be actuated via the hydraulic circuit of the mobile working machine.

[0051] In yet another possible embodiment, it is provided that the working machine includes a control unit (which can be a crane controller for example), by means of which the at least one steering cylinder of the at least one steerable rear axle can be controlled. The mobile working machine preferably further includes the above-mentioned acquisition device, which is connected to the control unit. Description of the Drawings

[0052] Further features, details and advantages of the present invention emerge from the embodiments explained below with reference to the drawings, wherein:

[0053] Figure 1 is a side view of a mobile working machine according to the present invention according to an embodiment;

[0054] Figure 2 is a schematic plan view of a steering system according to the present invention according to an embodiment;

[0055] Figure 3 is a schematic plan view of a steered rear axle of a steering system according to the present invention according to an embodiment; and

[0056] Figure 4 is a schematic plan view of a front trailing axle of a steering system according to the present invention according to an embodiment. Detailed Description of the Invention

[0057] Figure 1 is a side view of an embodiment of a mobile working machine 10 according to the present invention, in the form of a mobile crane. Although the following description of the embodiment refers to the mobile crane 10, the steering system according to the present invention is not limited thereto, but can be used for any mobile working machine.

[0058] The mobile crane 10 according to the illustrated embodiment includes a mobile undercarriage 12, which includes a steering system according to the present invention. The latter includes a wheel chassis having five axles 13, each axle including a pair of wheels 15. Here, for example, depending on the configuration of the crane, it is conceivable to use single or double wheels on each side. The undercarriage 12 has an undercarriage cab 17 on the front side for steering the mobile crane 10 during road travel. In addition, the undercarriage 12 includes support means having a plurality of support crossbeams, which carry support cylinders for lifting the mobile crane 10 from the base. In the mobile crane 10 of the illustrated embodiment, the superstructure 14 is mounted on the undercarriage 12 so as to be rotatable about a vertical axis of rotation and includes a superstructure cab 16 for control during crane operation, and a telescopic boom 18 mounted so as to be pivotable about a horizontal axis.

[0059] Figure 2 is a schematic plan view of the steering system of the mobile crane 10 according to an Figure 1 embodiment. In this case, the dashed line 30 represents the longitudinal axis of the steering system, which also represents the longitudinal axis of the undercarriage 12. In Figure 2 this, the front side of the undercarriage 12 is on the right side, and the undercarriage tail is on the left side. The five axles 13 are arranged successively along the longitudinal axis 30 and are parallel to each other. Accordingly, Figure 2 the right axle in

[0060] is referred to as the first axle, and the numbering increases to the left or rearward in the direction of the vehicle tail (i.e., the rearmost axle is the fifth axle). Figure 2 In the embodiment shown here, the steering system includes a mechanically steerable front axle 21 ( Figure 2 the first axle in Figure 2 ), which is particularly steerable by a steering wheel in the undercarriage cab 17 and may include an additional hydraulic steering cylinder for assisting the steering force. The remaining four axles 13 follow the steering angle of the wheels of the front axle 21 in a predetermined manner such that the virtual extension lines 32 of the axes of rotation of the wheels 15 (only those of the first and fifth axles are shown therein) intersect at a common point 36 on one side of the center of the curve, i.e., the steering pole 36 (see

[0061] Figure 3 Figure 3is shown in more detail. Each steering trapezoid 43 includes a steering tie rod 44 which extends parallel to the axle in the straight-ahead position and is pivotally connected to two steering tie rod arms 46 which are arranged in the region of the wheels 15 or the wheel suspension carrying the wheels 15. The steering tie rod arms 46 are in turn pivotally connected to the axle, where by pivoting the steering tie rod arms 46 relative to the wheel axle, the wheels 15 are deflected by an angle β on the left-hand side L and by an angle β on the right-hand side R . These angles are also referred to as camber angles.

[0062] Figure 2 On the left-hand side (β L1 -β L5 ) and on the right-hand side (β R1 -β R5 ) the respective camber angles of the wheels 15 of the corresponding axle are shown (warning: for the sake of simplicity, in the schematic Figure 2 , although the deflection is shown, the wheels are shown in the non-steered state, i.e. in the straight-ahead position). It can be seen that the magnitudes of the respective camber angles differ between the individual axles and also between the right-hand side and the left-hand side wheels 15 for each axle. In addition, the wheels 15 in front of the right-hand side or the steering pole plane 34 are deflected in the same direction to the left (but with different camber angles), while the wheels 15 behind the left-hand side or 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 (also with different camber angles). This type of steering is called Ackermann steering. This can be set, for example, by selecting the corresponding steering program of the mobile crane 10. In addition, other steering programs can be selected (such as crab steering, where the wheels of all the actively steerable axles 13 are deflected in the same direction and in particular by almost the same camber angle).

[0063] The steering system includes actively steerable rear axles 22 which automatically follow the steering angle of the front axle 21 (in particular such that the Ackermann condition according to Figure 2 is satisfied). For this purpose, the steerable rear axles 22 preferably each include two hydraulic steering cylinders 40 which are arranged on the right-hand side and the left-hand side of the axle respectively and in particular connect the steering tie rod arms 46 to the axle. An embodiment of such a steerable rear axle 22 is shown in Figure 3 as a schematic plan view. Retracting or extending the steering cylinders 40 pivots the steering tie rod arms 46 relative to the axle and thus turns or steers the wheels 15 through a specific camber angle. 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 working machine 10.

[0064] Depending on the steering program of the front axle 21, the vehicle speed and the steering angle, the steering cylinders 40 of the steerable rear axles 22 are actuated by the corresponding control unit of the working machine 10.

[0065] The mobile crane 10 may include a control unit configured to limit the allowable speed range of the mobile crane 10 to a certain maximum speed (e.g., 40 km / h) in case of a fault or incorrect rear axle steering. If the vehicle speed is higher than 40 km / h when a fault occurs, it may be provided that no active braking is performed, but rather the vehicle speed is maintained and reduced as needed. In one embodiment, information or a warning may be output optically and / or acoustically to the driver.

[0066] In the embodiment shown here, each of the steerable rear axles 22 includes a hydraulic centering cylinder 42 (see Figure 3 ), which moves the associated rear axle 22 to a neutral position or a straight-ahead position in case of a fault (i.e., in case of a fault in the rear axle steering). For this purpose, the centering cylinder 42 is configured such that it can overpressure the steering cylinder 40.

[0067] In Figure 2 's embodiment, if all four axles (the front axle 21 that is not mechanically steered (i.e., axles 2 - 5)) are actively steerable rear axles including centering cylinders 42, then in case of a fault, if all four rear axles 22 are in "straight-ahead", when a steering movement occurs at the front axle 21, the vehicle 10 will significantly protrude beyond the front axle 21 (the vehicle will oversteer), which will make steering significantly more difficult. In addition, significant tire wear will occur at the front axle 21.

[0068] To improve steering in case of a fault and to achieve a smaller emergency steering radius, according to the present invention, a passive steerable rear axle 23 (= front passive axle) is mounted in the region in front of the steering pole 36 or in front of the steering pole plane 34, i.e., in Figure 2 's embodiment, between the steering pole plane 34 and the front axle 21.

[0069] Contrary to the passive steerable rear axle, in known steering systems, the passive steerable rear axle is located in the tail region and thus significantly behind the steering pole 36 or the steering pole plane 34, and always steers in the direction opposite to that of the front axle 21 during a turn according to the steering program of the front axle 21, the vehicle speed, and the steering angle. According to the present invention, the front passive axle 23 is located in front of the steering pole 36 and thus must rotate in the same direction as the front axle 21 according to the steering program, the vehicle speed, and the steering angle of the front axle 21.

[0070] For a correct thrust angle at the front passive axle 23 and a fault-free rolling of the wheels 15 during the turning process, the front passive axle 23 particularly includes a steering trapezoid 43, and in the plan view of the steering pole plane 34, the steering trapezoid is rotationally or mirror arranged relative to the steerable rear axle 22 arranged in the region behind the steering pole plane 34 (and relative to a conventional rear passive axle) (seeFigure 2 )。

[0071] Figure 4 is a schematic plan view of an embodiment of the front trailing axle 23 according to the invention. Just like the steering rear axle 22, this can include two steering cylinders 40 via which, in normal operation, it is steered electrohydraulically (and thus behaves like the remaining steering rear axles 22). In the event of a fault, the steering cylinders 40 are switched in particular such that the steering cylinders 40 are hydraulically short-circuited and, as a result, the released front trailing axle 23 can be moved by an external force and used as a trailing steering axle. The front trailing axle 23 in particular does not include a centering cylinder 42.

[0072] In Figure 2 the embodiment, the front trailing axle 23 is arranged between the front axle 21 and the steering rear axle 22 (also arranged in the region in front of the steering pole plane 34), which steering rear axle can also be centered in the event of a fault. As a result, the front trailing axle 23 is guided by two surrounding axles 21, 22. Alternatively, the front trailing axle 23 can also be arranged between two steering rear axles 22 or between two front axles 21.

[0073] The front trailing axle 23 installed in the front region of the steering system according to the invention reduces the emergency steering radius of the steering system or the mobile crane 10 (in the case of some crane types, even halves it). This results in the mobile crane 10 not tending to exhibit significant understeering in the event of a fault, and the crane driver not having to suddenly reduce the speed significantly during or before a sharp turn in order to turn safely. Thereby, road traffic safety can be improved in the event of a steering fault.

[0074] Alternatively, a plurality of front trailing axles 23 can be provided.

[0075] Alternatively, the steering system can include one or more rear trailing axles (i.e., trailing steering rear axles in the region behind the steering pole plane 34). These in particular do not include a centering cylinder 42.

[0076] Alternatively, the steering system can include a plurality of front axles 21 that are mechanically coupled together.

[0077] List of reference numerals

[0078] 10 Mobile working machine (mobile crane)

[0079] 12 Chassis

[0080] 13 Axle

[0081] 14 Superstructure

[0082] 15 Wheel

[0083] 16 Upper structure cab

[0084] 17 Underframe cab

[0085] 18 Telescopic boom

[0086] 21 Front axle

[0087] 22 Steered rear axle

[0088] 23 Front trailing axle

[0089] 30 Longitudinal axis

[0090] 32 Virtual extension line of wheel rotation axis

[0091] 34 Steering pole plane

[0092] 36 Steering pole

[0093] 40 Steering cylinder

[0094] 42 Centering cylinder

[0095] 43 Steering trapezoid

[0096] 44 Steering tie rod

[0097] 46 Steering link arm.

Claims

1. A steering system for a mobile working machine (10), in particular a mobile crane, comprising: at least one mechanically steerable front axle (21); at least one driven steering rear axle (23); and at least one rear axle (22) which can be steered by means of at least one steering cylinder (40), wherein the front and rear axles (21, 22, 23) are arranged one behind the other along a longitudinal axis (30) of the steering system, and wherein the front and rear axles (21, 22, 23) comprise wheels (15), the axes of rotation (32) of which, in the case of a turn, are virtually extended on one side of the center of the curve and intersect a common steering pole plane (34) which is positioned perpendicular to the longitudinal axis (30), It is characterized in that The at least one driven steering rear axle (23) is arranged between the front axle (21) and the steering pole plane (34) and is referred to as a front driven axle.

2. The steering system according to claim 1, comprising a plurality of front axles (31) which are coupled to one another via a mechanical steering device, in particular via a steering linkage.

3. The steering system according to claim 1 or 2, wherein the at least one steering cylinder (40) is a hydraulic cylinder, and the steering system comprises a hydraulic circuit for actuating the at least one hydraulic steering cylinder (40).

4. A steering system according to any of the preceding claims, wherein at least one steerable rear axle (22), preferably all steerable rear axles (22), in particular comprises a hydraulic centering cylinder (42), which is configured to lock the associated rear axle (22) relative to the steering and / or move the associated rear axle into a non-steering position in the event of a fault.

5. The steering system according to claim 4 comprises a collection system, through which the pressure in the hydraulic circuit used for steering the at least one rear axle (22), and / or the speed of the mobile working machine (10), and / or the steering angle can be collected, wherein errors can preferably be detected by collecting the pressure drop in the hydraulic circuit and / or exceeding a specified speed and / or exceeding a specified steering angle.

6. The steering system according to claim 1, wherein the at least one steerable rear axle (20) comprises two, in particular hydraulic, steering cylinders (40).

7. A steering system according to any one of the preceding claims, wherein at least one driven steered rear axle is arranged on a side of the steering pole plane (34) opposite to the at least one front driven axle (23), and is referred to as a rear driven axle, and is configured to follow the steering angle of the at least one front axle (21) in the opposite direction, wherein the at least one rear driven axle is preferably arranged behind the at least one steerable rear axle (22) starting from the at least one front axle (21).

8. A steering system according to any one of the preceding claims, wherein the front driven axle (23) is configured to follow the steering angle of the at least one front axle (21) in the same direction, and / or wherein at least one front driven axle (23) is arranged between the front axle (21) and the steerable rear axle (22) or between the two front axles (21) or between the two steerable rear axles (22).

9. A steering system according to any one of the preceding claims, wherein the at least one front axle (21), the at least one steerable rear axle (22) and in particular the at least one front driven axle (23) each comprise a steering trapezoid (43), the steering trapezoid comprising a steering tie rod (44) and two steering tie rod arms (46), which preferably form an Ackerman steering system.

10. A steering system according to any one of the preceding claims, wherein at least one steerable rear axle (22) and / or at least one driven steered rear axle is arranged on a side of the steering pole plane (34) opposite to the at least one front driven axle (23), and comprises a steering trapezoid (43) which is mirrored relative to the steering pole plane (34) and the steering trapezoid (43) of the at least one front driven axle (23).

11. A steering system according to any of the preceding claims, wherein in the case of a turn, virtual extensions of the axes of rotation (32) of the wheels (15) of the front and rear axles (21, 22, 23) meet at a steering pole (36) as a common point, wherein the steering pole plane (34) in particular contains the steering pole (36).

12. A mobile working machine (10), in particular a mobile crane, comprising a steering system according to any one of the preceding claims, wherein the working machine (10) preferably comprises a mobile underframe (12) and an upper structure (14), the mobile underframe comprising the steering system, and the upper structure being rotatably mounted on the underframe (12). 13 . The mobile working machine ( 10 ) according to claim 12 , comprising at least two, preferably at least three, particularly preferably at least four rear axles ( 22 ) which are steerable via steering cylinders ( 40 ).

14. The mobile working machine (10) according to claim 12 or 13, wherein the at least one steerable rear axle (22) comprises at least one hydraulic steering cylinder (40) which can be actuated via a hydraulic circuit of the mobile working machine (10).

15. A mobile working machine (10) according to any one of claims 12 to 14, comprising a control unit, by which the at least one steering cylinder (40) of the at least one steerable rear axle (22) can be controlled, wherein the mobile working machine (10) preferably also includes a collection system according to claim 5, which is connected to the control unit.

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