Steering system for a mobile work machine

Abstract

The invention 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 trailing-steered rear axle, and at least one rear axle 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 whose axes of rotation, which are notionally extended on the side of the curve center when cornering, intersect a common steering pole plane perpendicular to the longitudinal axis. According to the invention, at least one trailing-steered rear axle is arranged between a front axle and the steering pole plane. The invention further relates to a mobile work machine with such a steering system.

Description

The present invention relates to a steering system for a mobile working machine, in particular for a mobile crane, according to the preamble of claim 1.Mobile working machines, such as heavy commercial vehicles, for example, frequently have a greater number of steered wheel axles (also called vehicle axles), which can differ from one another in their arrangement and the type of steering.An example of heavy commercial vehicles of this type are mobile cranes. In a typical embodiment, a mobile crane has a number of N wheel axles, of which one or more (i.e. a number 1 to X, where X<N) together represent front axles mechanically steered via the steering wheel. These can be steered with hydraulic assistance and have corresponding steering cylinders. In the following, the term "front axle" generally denotes a mechanically steerable wheel axle. If a plurality of axles are mechanically connected, then a plurality of front axles are present. This also applies if the front axles are only theoretically mechanically steerable, but without assistance are too difficult to turn the wheels.In addition, the mobile crane can have further electrohydraulically steered wheel axles of the number N-X. Hereinafter, steered wheel axles other than front axles are generally referred to as "rear axles", and electrohydraulically steered rear axles are referred to as "steered rear axles". The steered rear axles are actively steered as a function of the steering program, vehicle speed and steering angle of the front axles, for example via two hydraulic steering cylinders (example: a mobile crane has a total of five wheel axles with two front axles and three steered rear axles).Such mobile cranes are designed such that their emergency steering radius meets legal requirements. The emergency steering circle is the turning circle radius (also called the body turning circle) which the mobile crane describes when the steering system is disturbed. The steering behavior is tested according to the specifications of ECE R79. If the emergency steering circuit is small, the handling behavior of the mobile crane is better in tight turns when the steering system is disturbed. In other words, if the emergency steering circle or emergency steering radius is small, the mobile crane can pass through narrow curves at a higher speed when the steering system is disturbed. If the emergency steering circle is large, the speed must be significantly reduced in order to keep the vehicle on the curve of the roadway.A disturbance on the mechanical front axle steering is excluded in the normative specifications, therefore only the active rear axle steering is focused in the present case. Depending on the number of wheel axles and the ratio of front axles to rear axles, two design variants of the rear axle steering with respect to a disturbance have been produced up to now.1. Embodiment:In certain types of crane, it is possible, due to the ratio of front axles to rear axles with respect to the steering system, to set all axles of the rear axle steering system to "straight running" in the event of a fault (=neutral or unguided position). In the prior art, this is designed in such a way that all the wheel axles involved in the rear axle steering system have a centering cylinder and two steering cylinders, which are in particular hydraulic cylinders. The steering cylinders are installed for the operational steering of the crane (generally a steering cylinder on each right and left). The centering cylinders have the function of setting the associated rear axles to "straight ahead" in the event of a fault (note: in the present text, for the sake of simplicity, frequently a steering or position of a wheel axle is referred to, wherein actually the steering or position of the wheels of the wheel axle is meant). The centering cylinders are therefore typically dimensioned larger than the steering cylinders, so that they can overpress them.Depending on the driving situation and the error situation, the centering cylinder previously performs two tasks because of its interconnection: on the one hand, it centers the associated rear axle (by applying pressure, which is made available, for example, by a wheel-driven pump, it performs a centering movement of the rear axle). On the other hand, the centering cylinder can fulfil a further task by activating a hydraulic circuit. The centering cylinder can ensure that the associated rear axle can only be steered to the center (no longer outward any further in order to drive a tighter turn), which is also referred to as blocking.2. Embodiment:In certain types of crane, it is not possible to meet the legal requirements by positioning all actively steered rear axles straight through centering cylinders. In such cases, it is known to install trailing-jointed rear axles. These may be one to max. N-X of the wheel axles. In the prior art, such trailing-jointed rear axles are installed starting from the last or rearmost wheel axle and are therefore located behind the rear axles which can be centered by centering cylinders. Such a mobile crane is known, for example, from DE 10 245 618 A1.It should be noted at this point that in the present text the details "front" and "rear" relate to the straight-ahead direction of travel of the vehicle or of the working machine. In this case, the front axles are seated in front and the rear axles are seated behind the front axles. The rear region of the steering system corresponds in particular to the rear of the vehicle.In the case of trailing-steered rear axles, the trailing angle is determined by the so-called trailing angle and is achieved by an inclined position of the steering knuckle in the direction of the longitudinal axis of the vehicle with respect to a perpendicular to the roadway. This principle is well known. The oblique position is designed in such a way that the theoretical wheel contact point shifts in front of the center of the axle (the axle is "pulled"). Due to the theoretical distance between the actual wheel contact point and the theoretical wheel contact point (also called the trailing distance), a moment is generated on the trailing-articulated rear axle by the external forces acting on the mobile crane due to the steering of the mechanically steered front axles and due to the centered rear axles (the moment is thus generated due to the steering and not due to the trailing).Until now, the trailing-steered rear axles have been mounted exclusively on the rear of the vehicle, because they have the maximum distance there from the steering pole or from the steering pole plane (the steering pole denotes the imaginary intersection point of the imaginary extensions of the rotational axes of the wheels). The trailing-steered rear axles thus far sit behind the steering pole. In the following, trailing-steered rear axles arranged behind the steering pole, as seen in the longitudinal direction of the vehicle or of the steering system, are referred to as "trailing axles". It has been assumed up to now that this has the greatest effect on the emergency steering radius.In contrast to a centered rear axle, a trailing axle has the advantage that it is freely movable by external forces (cf. shopping trolley) and, in the event of a fault, is thereby steered in by the steering movement of the front axles and thus by the external force acting on the trailing axle. However, the advantage of forward travel is simultaneously a disadvantage of rearward travel. If the trailing axis is moved backward with the trailing axis activated (i.e. unlocked or raised), the trailing axis can be moved by the external force in a direction which is disadvantageous for the backward travel, for example in "travel in serpentine fashion". If necessary, the trailing axis may remain stationary (the return of the trailing axis does not always have to function).If the number of trailing axes is increased (e.g., due to the need to maintain the prescribed emergency steering radius), the described effect for reversing may also occur during forward driving. It is therefore important to ensure that the trailing axis can also be brought back into the straight-ahead position after cornering (forward). If too many trailing axes are provided, it may happen that not all trailing axes can be completely set to straight line again after the end of the cornering.Against this background, the present invention is based on the object of specifying a drivable working machine of the generic type having a low emergency steering radius, in which the disadvantages described above are avoided.According to the invention, this object is achieved by a steering system having the features of claim 1. Advantageous embodiments of the invention are evident from the dependent claims and the following description.Accordingly, a steering system for a mobile working machine, in particular for a mobile crane or mobile crane, is proposed, which comprises at least one mechanically steerable front axle (hereinafter only "front axle"), at least one trailing-steered rear axle and at least one rear axle steerable by means of at least one steering cylinder (hereinafter only "steerable rear axle"). If the term front axle, the steered rear axle or the trailing-steered rear axle (singular) is mentioned below, the at least one front axle, the steered rear axle or the trailing-steered rear axle is always intended to be understood.The front and rear axles are arranged one behind the other along a longitudinal axis of the steering system (which is in particular simultaneously the longitudinal axis of the mobile working machine). The front and rear axles comprise wheels which are rotatably mounted about axes of rotation. The front and rear axles are designed such that, when the mobile working machine is cornering, the axes of rotation of the wheels, which axes of rotation are notionally extended on the side of the center of the curve, intersect a common plane which is perpendicular to the said longitudinal axis. This common plane is referred to below as the steering pole plane, since in the case of a steering knuckle steering system, the imaginary extensions of the rotational axes intersect in a common steering pole which lies in the steering pole plane.According to the invention, at least one trailing-steered rear axle is arranged between a front axle and the mentioned steering pole plane. This trailing-steered rear axle is thus seated "in front of" the steering pole plane and not, as is customary in the prior art, "behind" the steering pole plane and is therefore referred to in the present case as "leading axle".It is to be clarified here that the present front axle is still a rear-drive-linked rear axle (i.e. the theoretical wheel contact point lies in front of the axle center in the straight-ahead direction of travel of the working machine, such that the wheels of the front axle are "pulled"). The distinction between the forward and the rearward axis therefore relates here only to the position with respect to the steering pole plane. It is also conceivable for the forward axis to lie exactly in the steering pole plane.The steering of the mobile working machine is improved by the forward axle in the event of a fault, since the forward axle, due to its position in the front region of the steering system, is seated between two wheel axles with firmly defined steering parameters, e.g. between a front axle and a (in the event of a fault) centered rear axle, between two front axles or between two centered rear axles. As a result, the lead axis is guided, so that the disadvantages that conventional lead axes can show, for example, during reverse travel do not occur.The emergency steering radius of the steering system according to the invention or of the mobile working machine equipped with it is improved, i.e. reduced, by the forward axis (even halved in some types of crane). This has the result that the steering system or the mobile working machine does not tend to be strongly understeered in the event of a fault and the speed of the driver does not have to be abruptly greatly reduced in or before tight curves in order to drive safely through the curve. This can increase the safety in road traffic in the event of failure of the steering system.In addition, the front axle also leads to a cost saving, since in vehicles with a plurality of steered rear axles it can replace one of the steered rear axles in the front region and the centering cylinder is thereby omitted.The at least one forward axle according to the invention can likewise have one or more (in particular two) steering cylinders which, in the event of a fault, are connected or "disconnected" to one another in such a way that the axle is guided in a rearward direction (i.e. follows the steering angle of the front axle(s) in a predefined manner on the basis of the torques acting). In the simplest case, the at least one front axle can have the same structure as the at least one steered rear axle and differ, for example, only in that it does not have a centering cylinder, but instead a rear axle. The front axle can be actively electro-hydraulically steerable via the steering cylinders in normal operation, like the remaining steered rear axles, and can be "released" only in the event of a fault, so that it functions as a rear-steered rear axle. Alternatively, the forward axis can have no steering cylinder and therefore purely passively "run along" at any point in time.The at least one feed axis is preferably designed such that it cannot be blocked and / or cannot be lifted from the ground and thus "deactivated".This results in a simple and cost-effective construction. However, it is alternatively conceivable that the at least one forward movement axis can be blocked for certain situations and / or can be actively lifted from the ground.During steering or cornering, the forward axis strikes in particular in the same direction as the front axis. Conventional trailing axles, which are seated in the rear region, i.e. behind the steering pole plane, engage in contrast in the opposite direction to the front axle.The mechanical steering of one or more front axles can be assisted by hydraulic steering cylinders (power steering principle). For this purpose, one or more front axles can be steerable via in each case one or more (in particular two) hydraulic steering cylinders in addition to the mechanical steering. The hydraulic steering by means of the steering cylinders is effected only in a supporting manner.The steering system preferably comprises exclusively actively steerable wheel axles, i.e. 1 to X mechanically steerable front axles and N-X electrohydraulically steerable rear axles in normal operation, wherein N represents the number of all wheel axles. The at least one feed axle in this case likewise has one or more steering cylinders and is only released in the event of a fault, so that it is steered to the trailing end. The remaining rear axles preferably all have a centering cylinder. In this embodiment, the at least one front axle differs from the remaining rear axles only in that it does not have a centering cylinder, but instead a rear axle and is released as a rear axle in the event of a fault.In one possible embodiment, it is provided that the steering system comprises a plurality of front axles which are coupled to one another via a mechanical steering device, in particular via a steering linkage. The steering device or the steering linkage can be connected via a steering gear to a control element which actuates the steering device or the steering linkage. In particular, the steering linkage ensures synchronous steering of all wheels of the front axles, wherein each wheel is preferably moved with an individual steering angle according to the steering direction and the position of the front axle or the position to the steering center (in particular for realizing a steering knuckle steering).In a further possible embodiment, it is provided that the at least one steering cylinder is a hydraulic cylinder. In particular, the steering cylinder is a double-acting hydraulic cylinder with two pressure chambers each, which, when pressurized, cause a steering angle of the associated wheel in one direction or the other. The steering system comprises at least one hydraulic circuit for actuating the at least one hydraulic steering cylinder. Different hydraulic circuits can be provided for different wheel axles.In a further possible embodiment, it is provided that at least one steerable rear axle, preferably all steerable rear axles, comprises a centering cylinder which is designed such that the associated rear axle is blocked with respect to a steering system in the event of a fault and / or is moved into an unguided 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 the event of a fault, the blocking and / or centering of the steered rear axle(s) takes place in particular automatically. The centering cylinder can be designed as described above with reference to the prior art.The steering system according to the invention can have an active rear axle steering system according to DE 10 245 618 A1, the disclosure of which is explicitly referred to herein. In particular, the at least one steerable rear axle may be configured with centering cylinders according to this disclosure.In a further possible embodiment, it is provided that the steering system comprises a detection system, by means of which a pressure in a hydraulic circuit for steering the at least one steered rear axle and / or a speed of the mobile working machine can be detected. For this purpose, the detection system comprises one or more corresponding sensors. The fault case mentioned above can be detected by the detection system in particular by detecting a pressure drop in the hydraulic circuit and / or by exceeding a defined speed of the working machine and / or by exceeding an implausible steering angle or by exceeding a defined steering angle.The steering system or the mobile working machine having the steering system preferably comprises a control unit which is connected to the detection system or receives the data of the sensor or sensors of the detection system and correspondingly controls one or more wheel axles of the steering system. This can comprise an actuation of the above-mentioned centering cylinder of at least one steered rear axle and / or an actuation of one or more steering cylinders.In a further possible embodiment, it is provided that the at least one steerable rear axle comprises two, in particular hydraulic, steering cylinders. Each of the steering cylinders may be associated with one of the wheels of the associated rear axle ("right" steering cylinder and "left" steering cylinder).In a further possible embodiment, it is provided that, in addition to the at least one forward axle, which is arranged in the "front" region of the steering system (i.e. "in front of" the steering pole plane), at least one rear-steered rear axle is installed on the side of the steering pole plane opposite the at least one forward axle (i.e. "rear"). Such trailing-steered rear axles are referred to herein as "trailing axle.". This at least one trailing axle can be arranged in a manner known per se at the very rear (i.e. starting from the at least one front axle after the at least one steerable rear axle) or else between steered rear axles.The at least one trailing axle is designed, on account of the position behind the steering pole plane, to follow a steering angle of the at least one front axle in the opposite direction.The at least one trailing axle can comprise one or two steering cylinders which, in the event of a fault, are connected or "disconnected" to one another in such a way that the wheel axle is steered to the trailing side (i.e. follows the steering angle of the front axle(s) in a predefined manner on the basis of the torques acting). In the simplest case, the at least one trailing axle can have the same structure as the at least one steered rear axle and differ only in that it does not have a centering cylinder, but rather a trailing axle. Alternatively, the trailing axle may not have a steering cylinder and be trailing-steered at any timeThe at least one front axle and the at least one rear axle can have the same structure and differ only in their position with respect to the steering pole plane (and in particular with respect to their simultaneous or opposite following of the at least one front axle).In a further possible embodiment, it is provided that the forward axle is designed to follow a steering angle of the at least one front axle in the same direction.Alternatively or additionally, at least one forward axle is arranged between a front axle and a steerable rear axle or between two front axles or between two steerable rear axles. As a result, it is well guided even during reversing and cannot remain stationary, as can be the case with conventional trailing axles.In a further 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 axle each comprise a steering wheel which in turn comprises a track rod and two track rod levers. Steering methods of this type are known per se and can form a steering knuckle steering system according to the Ackermann principle, in which the imaginary extensions of the rotational axes of the wheels of the front and rear axles meet in a common steering pole.In a further possible embodiment, it is provided that at least one steerable rear axle and / or at least one trailing-steered rear axle is arranged on the side of the steering pole plane opposite the at least one leading axle and comprises such a steering pitch, wherein the steering pitch of the at least one steered and / or trailing-steered rear axle is arranged on the rear side of the steering pole plane and the steering pitch of the at least one front axle and the at least one leading axle are arranged on the front side of the steering pole plane in a manner mirrored with respect to one another (in plan view of the steering system). This ensures that the wheel on the inside of the curve experiences the greater steering angle. In the case of steering, the wheel axles on the front side of the steering pole plane execute wheel turns in the same direction as the front axle or axles, while the wheel axles on the rear side of the steering pole plane execute wheel turns in the opposite direction thereto.In a further possible embodiment, it is provided that the imaginary extensions of the axes of rotation of the wheels of the front and rear axles meet at a common point (steering pole) when cornering, wherein the steering pole is located in particular in the steering pole plane. The wheel axles of the steering system thus form, in particular, a steering knuckle or Ackermann steering system.The present invention further relates to a mobile working machine, in particular a mobile crane or mobile crane, having a steering system according to the invention. The same properties and advantages as for the steering system according to the invention are clearly obtained here, so that a repeated description is omitted. In particular, the mobile work machine may include a steering system according to any of the previously described embodiments or any combination thereof.The work machine may include a wheeled undercarriage including the steering system and an undercarriage rotatably supported on the undercarriage.In one possible embodiment, it is provided that the working machine comprises at least two, preferably at least three, particularly preferably at least four rear axles steerable via steering cylinders. The working machine can comprise, for example, exactly two, exactly three, exactly four, exactly five, exactly six, etc. rear axles that can be steered via steering cylinders.In a further possible embodiment, it is provided that the at least one steerable rear axle comprises at least one, preferably two, hydraulic steering cylinders which can be actuated via a hydraulic circuit of the mobile working machine.In a further possible embodiment, it is provided that the working machine comprises a control unit (this can be, for example, a crane controller) 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 comprises a detection device described further above, which is connected to the control unit.Further features, details and advantages of the invention are evident from the exemplary embodiments explained below with reference to the figures. The following are shown: FIG. 1 : a side view of the mobile working machine according to the invention according to an exemplary embodiment; FIG. 2 : shows a schematic plan view of the steering system according to the invention according to an exemplary embodiment; FIG. 3 : shows a schematic plan view of a steered rear axle of the steering system according to the invention according to an exemplary embodiment; and FIG. 4 : shows a schematic plan view of a forward axis of the steering system according to the invention according to an exemplary embodiment.FIG. 1 shows an exemplary embodiment of the mobile working machine 10 according to the invention in the form of a mobile crane in a side view. Although the following description of the embodiments will be made with reference to this mobile crane 10, the steering system according to the present invention is not limited to such, but may be applied to any traveling work machine.The mobile crane 10 according to the exemplary embodiment shown comprises a mobile undercarriage 12 with a steering system according to the invention. The latter comprises a wheel chassis having five wheel axles 13 which each have pairs of wheels 15. Here, for example, individual wheels or double wheels are conceivable on each side, depending on the crane design. The undercarriage 12 has an undercarriage driver cabin 17 on the front side for steering the mobile crane 10 during road travel. Furthermore, the undercarriage 12 comprises a support device with a plurality of support beams which carry support cylinders for lifting the mobile crane 10 from the ground. In the mobile crane 10 of the exemplary embodiment shown, an upper carriage 14 is mounted on the lower carriage 12 such that it can rotate about a vertical axis of rotation and comprises an upper carriage driver's cabin 16 for control during crane operation and a telescopic boom 18 mounted such that it can be pivoted about a horizontal axis.FIG. 2 shows a schematic plan view of the steering system of the mobile crane 10 of the exemplary 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 rear on the left. The five wheel axles 13 are arranged one behind the other and parallel to one another along the longitudinal axis 30. Accordingly, the right wheel axle in FIG. 2 is referred to as the first axle and the numbering is performed ascending to the left or to the rear in the direction of the rear of the vehicle (i.e. the rearmost wheel axle is the fifth axle).In the exemplary 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 driver's cabin 17 and can have additional hydraulic steering cylinders for steering power assistance. The remaining four wheel axles 13 follow the wheel angle of the front axle 21 in a predefined manner, so that the imaginary extensions 32 of the axes of rotation of the wheels 15 (of which only those of the first and fifth axles are drawn in) meet on the side of the center point of the curve at a common point 36, the steering pole 36 (cf. FIG. 2 ). The dot-and-dash line 34 shown in FIG. 2 indicates a plane which is perpendicular to the longitudinal axis 30 and runs through the steering pole 36 and is referred to as the steering pole plane 34.This is made mechanically possible in that each wheel axle 13 in this exemplary embodiment has a steering wheel 43 which is designated in more detail in FIG. 3. The steering wheels 43 each comprise a track rod 44 which, in the straight-ahead position, runs parallel to the axis and is pivotably connected to two track rod levers 46 arranged in the region of the wheels 15 or of the wheel suspensions carrying the wheels 15. The track rod levers 46 are in turn pivotably connected to the axle, wherein the wheels 15 are deflected by pivoting the track rod levers 46 with respect to the axle by an angle β L on the left side and by an angle β R on the right side. These angles are also referred to as to track angles.In FIG. 2, the individual toe angles of the wheels 15 of the respective axles are drawn on the left-hand side (β L1- β L5) and on the right-hand side (β R1- β R5) (attention: the wheels are drawn in the schematic FIG. 2 for the sake of simplicity despite the indicated deflection in the non-articulated state, i.e. in the straight-ahead position). It can be seen that the individual toe angles differ from axis to axis and also for each axis between right and left wheels 15 in terms of amount. Furthermore, the wheels 15 on the right 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 side or behind the steering pole plane 34 are deflected in the opposite direction to the wheels 15 in the region in front of the steering pole plane 34 (and again by different toe angles). Such a steering system is referred to as a knuckle steering system or Ackermann steering system. This can be adjustable, 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 actively steered wheel axles 13 are steered in the same direction and by, in particular, almost identical toe angles).The steering system comprises actively steerable rear axles 22, which automatically follow the steering angle of the front axle 21 (namely such that the Ackermann condition according to FIG. 2 is fulfilled). For this purpose, the steered rear axles 22 preferably each have two hydraulic steering cylinders 40, which are arranged on the axles on the right and left, respectively, and connect the track rod levers 46 to the axle, in particular. An exemplary embodiment of such a steered rear axle 22 is illustrated in FIG. 3 as a schematic plan view. By retracting or extending the steering cylinders 40, the track rod levers 46 are pivoted with respect to the axle and the wheels 15 are thereby rotated or steered by specific toe angles. In the exemplary embodiment shown, there are respectively two hydraulic steering cylinders 40, which are supplied or actuated by at least one hydraulic circuit of the working machine 10.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.The mobile crane 10 can comprise a control unit which is configured to limit a permissible speed range of the mobile crane 10 to a specific maximum speed (e.g. 40 km / h) in the event of a disturbed or faulty rear axle steering. If the vehicle speed is above 40 km / h when a fault occurs, it can be provided that the braking is not actively carried out, but that the speed is held and reduced as required. In one exemplary embodiment, an info or warning can be output to the driver visually and / or acoustically.In the exemplary embodiment shown here, the steered rear axles 22 each have a hydraulic centering cylinder 42 (cf. FIG. 3 ), which, in the event of a fault (i.e. in the event of disturbed rear axle steering), moves the associated rear axle 22 into the neutral position or the straight-ahead position. For this purpose, the centering cylinder 42 is designed such that it can overpress the steering cylinders 40.If in the exemplary embodiment of FIG. 2 all four wheel axles which are not mechanically steered front axles 21 (i.e. axles Nos. 2-5) were actively steerable rear axles with centering cylinder 42, then in the event of a fault, if all four rear axles 22 were "straight ahead", the vehicle 10 would push strongly beyond the front axle 21 during a steering movement through the front axle 21 (the vehicle would oversteer), which would make steering considerably more difficult. In addition, a strong tire abrasion would result at the front axle 21.In order to improve the steering in the event of a fault and to achieve a smaller emergency steering radius, a trailing-steered rear axle 23 (=running axle) is installed according to the invention in the region in front of the steering pole 36 or in front of the steering pole plane 34, i.e. in the exemplary embodiment of FIG. 2 between the steering pole plane 34 and the front axle 21.In contrast to rear axles which are steered to the trailing side and which, in known steering systems, are located in the rear region and thus clearly behind the steering pole 36 or the steering pole plane 34 and, during cornering, always steer in the opposite direction of the front axle 21 as a function of the steering program, vehicle speed and steering angle of the front axle(s) 21, according to the invention the front axle 23 is located in front of the steering pole 36 and therefore has to turn in the same direction as the front axle 21 as a function of the steering program, vehicle speed and steering angle of the front axle 21.For a correct angle of difference in toe on the front axle 23 and the correct rolling of the wheels 15 during cornering, the front axle 23 has in particular a steering wheel 43 rotated with respect to the steered rear axles 22 arranged in the region behind the steering pole plane 34 (and with respect to the usual rear axles) or mirrored in plan view on the steering pole plane 34 (cf. FIG. 2 ).FIG. 4 shows a schematic plan view of an exemplary embodiment of the feed axle 23 according to the invention. This steering system, like the steered rear axles 22, can have two steering cylinders 40, via which it is steered electro-hydraulically during normal operation (and therefore behaves like the other steered rear axles 22). In the event of a fault, the steering cylinders 40 are connected in particular such that the steering cylinders 40 are hydraulically short-circuited and the forward axle 23 thus released can be moved by external forces and functions as a post-steered wheel axle. The feed axle 23 has in particular no centering cylinder 42.In the exemplary embodiment of FIG. 2, the forward axle 23 is arranged between a front axle 21 and a steered rear axle 22 (likewise arranged in the region in front of the steering pole plane 34) and which can be centered in the event of a fault. As a result, the forward axle 23 is guided by the two surrounding wheel axles 21, 22. Alternatively, the front axle 23 could also be arranged between two steered rear axles 22 or between two front axles 21.The forward axis 23 installed in the front region of the steering system according to the invention reduces the emergency steering radius of the steering system or of the mobile crane 10 (even halved in some types of crane). This has the result that the mobile crane 10 does not tend to be underdriven strongly in the event of a fault and the speed of the crane driver does not have to be reduced sharply abruptly in or before tight turns in order to drive safely through the turn. This can increase the safety in road traffic in the event of failure of the steering system.Alternatively, a plurality of feed axes 23 may be present.Alternatively, the steering system can comprise one or more trailing axles (i.e. trailing-guided rear axles in the region behind the steering pole plane 34). These do not comprise, in particular, a centering cylinder 42.Alternatively, the steering system may include a plurality of front axles 21 mechanically coupled together.List of reference numbers:10 Mobile working machine (mobile crane) 12 undercarriage 13 wheel axle 14 superstructure 15 wheel 16 superstructure driver cabin 17 undercarriage driver cabin 18 telescopic boom 21 front axle 22 steered rear axle 23 front axle 30 longitudinal axis 32 imaginary extensions of the wheel rotational axes 34 steering pole plane 36 steering pole 40 steering cylinder 42 centering cylinder 43 steering recess 44 tie rod 46 tie rod leverReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 245 618 A1 [0009, 0033]

Claims

Steering system for a mobile working machine (10), in particular for a mobile crane, comprising at least one mechanically steerable front axle (21), at least one trailing-steered rear axle (23) and at least one rear axle (22) steerable 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), which are notionally extended on the side of the center of the curve during cornering, intersecting a common steering pole plane (34) which is perpendicular to the longitudinal axis (30), characterized in that at least one trailing-steered rear axle (23) is arranged between a front axle (21) and the steering pole plane (34) (leading axle).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.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).Steering system according to one of the preceding claims, wherein at least one steerable rear axle (22), preferably all steerable rear axles (22), comprises an in particular hydraulic centring cylinder (42) which is designed in such a way that the associated rear axle (22) is blocked with respect to steering and / or moved into an unguided position in the event of a fault.Steering system according to the preceding claim, comprising a detection system by means of which a pressure in a hydraulic circuit for steering the at least one rear axle (22) and / or a speed of the mobile working machine (10) and / or a steering angle can be detected, wherein the fault case can preferably be detected by detecting a pressure drop in the hydraulic circuit and / or an exceeding of a defined speed and / or an exceeding of a defined steering angle.Steering system according to one of the preceding claims, wherein the at least one steerable rear axle (20) comprises two, in particular hydraulic, steering cylinders (40).Steering system according to one of the preceding claims, wherein at least one trailing-steered rear axle is arranged (trailing axle) on the side of the steering pole plane (34) opposite the at least one leading axle (23) and is designed to follow a steering angle of the at least one front axle (21) in opposite directions, wherein the at least one trailing axle is arranged preferably starting from the at least one front axle (21) downstream of the at least one steerable rear axle (22).Steering system according to one of the preceding claims, wherein the forward axle (23) is designed to follow a steering angle of the at least one front axle (21) in the same direction and / or wherein at least one forward axle (23) is arranged between a front axle (21) and a steerable rear axle (22) or between two front axles (21) or between two steerable rear axles (22).Steering system according to 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 axle (23) each comprise a steering wheel (43) comprising a tie rod (44) and two tie rod levers (46), which preferably form a steering wheel steering system.Steering system according to the preceding claim, wherein at least one steerable rear axle (22) and / or at least one trailing-steered rear axle is arranged on the side of the steering pole plane (34) opposite the at least one leading axle (23) and comprises a steering pitch (43) which is mirrored with respect to the steering pole plane (34) with respect to a steering pitch (43) of the at least one leading axle (23).Steering system according to one of the preceding claims, wherein the imaginary extensions of the axes of rotation (32) of the wheels (15) of the front and rear axles (21, 22, 23) meet at a common point (36) (steering pole) when cornering, wherein the steering pole plane (34) contains in particular the steering pole (36).Mobile working machine (10), in particular mobile crane, having a steering system according to one of the preceding claims, wherein the working machine (10) preferably comprises a mobile undercarriage (12) comprising the steering system and an superstructure (14) rotatably mounted on the undercarriage (12).Mobile working machine (10) according to claim 12, comprising at least two, preferably at least three, particularly preferably at least four rear axles (22) steerable via steering cylinders (40).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).The mobile working machine (10) according to any one of claims 12 to 14, comprising a control unit by means of which the at least one steering cylinder (40) of the at least one steerable rear axle (22) is controllable, wherein the mobile working machine (10) preferably further comprises a detection device according to claim 5, which is connected to the control unit.

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