Steering procedure for operating a forklift truck, forklift truck

Abstract

Steering method for operating a forklift truck (1), wherein the forklift truck (1) has at least two front wheels (2.1, 2.2) and at least one rear wheel (3.1, 3.2), wherein a steering angle sensor (5) is actuated to initiate a turn around a steering pole (P) and both the at least two front wheels (2.1, 2.2) and the at least one rear wheel (3, 3.1, 3.2) are steerable, wherein the forklift truck (1) has a longitudinal axis (X) and a transverse axis (Y) which intersect at a vehicle center (M), characterized in that when the forklift truck (1) is steered, a longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) is controlled depending on a transverse distance (Q) of the steering pole (P) to the longitudinal axis (X).

Description

[0001] The present invention relates to a steering method for operating a forklift truck and to a forklift truck for carrying out such a steering method.

[0002] Such steering methods are known in the art in a variety of different configurations. In particular, single-axle steering methods, in which the wheels of only one axle are steered, multi-axle steering methods, in which the wheels of more than one axle are steered, and all-wheel steering methods, in which all wheels can be steered, especially each wheel individually, are known.

[0003] To initiate a turn with a forklift, a turning radius is typically set using a steering angle sensor, such as a steering wheel or joystick. Subsequently, one or more steerable wheels of the forklift rotate or steer around an axis parallel to the forklift's vertical axis, so that the steered wheels are no longer parallel to the forklift's longitudinal or transverse direction. A distinction can be made between actively steerable wheels, i.e., wheels that have a steering gear or drive for rotating or steering the respective wheel or wheel suspension, and passively steerable wheels, i.e., those that are not motor-driven for steering but are, for example, designed as trailing wheels. Due to the angled position of the steered wheels relative to the forklift's longitudinal or transverse direction, the forklift executes a turn around a steering axis.

[0004] The steering center is the point where straight lines perpendicular to the wheels of the industrial truck, each coinciding with its respective axis of rotation, can intersect. Advantageously, the lines of all steered wheels meet at a common steering center, thus essentially preventing slippage or rubbing.

[0005] Typically, the steering pole is shifted along a steering line when initiating a turn. For example, when driving straight ahead, all wheels of the industrial truck are typically parallel to each other. In this case, the steering pole is at infinity. Such a steering process is known, for example, from DE 10 2019 109 995 A1. If a turn is initiated by actuating a steering angle sensor, the steering pole moves along the steering line from infinity towards the industrial truck. If one or more wheels of the industrial truck do not steer when initiating the turn, i.e., if one or more wheels of the industrial truck do not rotate about an axis parallel to the vertical axis when initiating the turn, the steering line becomes a straight line that intersects the center point of the unsteered wheel.

[0006] It should be clear that the vertical axis, also called the z-axis, a longitudinal axis, also called the front-back axis or x-axis, and a transverse axis of the industrial truck, also called the y-axis, are orthogonal to each other and typically intersect in the center of the vehicle.

[0007] From publication EP 2 956 350 B1, a three-wheeled industrial truck and a steering method applicable to it are known, in which, during longitudinal driving operation, also called front-loading operation, two front wheels of the industrial truck are arranged non-steered or permanently parallel to the longitudinal axis to initiate a turn, and the vehicle is steered exclusively by turning a rear wheel of the industrial truck. In particular, the rear wheel can be aligned obliquely to the longitudinal axis so that the industrial truck performs a turn about a steering pole, which is arranged on a steering line that extends as a straight line through the two front wheels. The steering line thus lies on a front axle, also called the front wheel axle, of the industrial truck.In a lateral driving mode, also known as side-loader operation, according to EP 2 956 350 B1, the rear wheel remains permanently aligned parallel to a transverse axis of the vehicle, while the vehicle is steered exclusively via the two steerable front wheels. The steering line runs, in particular, through a rotation axis of the rear wheel, which, if the rear wheel is centrally located, can correspond to the longitudinal axis of the vehicle.

[0008] In addition to the aforementioned straight rigid steering line, curved rigid steering lines are also known, in which the steering pole can be displaced along a constant, predefined circular path. Such a steering method is known, for example, from DE 10 2009 021 693 A1. Here, the steering pole can be displaced along a circular path arranged around the vehicle.

[0009] It has been shown that steering methods known from the prior art have disadvantages. In particular, the inflexible guidance of the steering line makes maneuvering the industrial truck difficult in narrow aisles. If the industrial truck is equipped with forks for picking up a load, such as pallets or the like, the operator must always take into account unintended movement of the forks when steering and approaching the load. Furthermore, as implemented in EP 2 956 350 B1, it is sometimes necessary, especially when the steering pole moving along the steering line passes through the vertical axis of a wheel and the direction of rotation of this wheel must be reversed due to physical limitations.

[0010] It is therefore the object of the present invention to provide a steering method for operating a forklift truck and a forklift truck which do not have the disadvantages of the prior art and in particular make it significantly easier to maneuver safely under difficult space conditions.

[0011] This problem is solved by a steering method having the features of claim 1 and by a forklift truck having the features of claim 15.

[0012] According to the invention, the steering method is particularly suitable for industrial trucks which, viewed in the direction of longitudinal travel, have at least two front wheels and at least one rear wheel. It is conceivable that the industrial truck has more than two front wheels and one rear wheel, for example, two front wheels and two rear wheels. It is also conceivable that the industrial truck has three or more front and / or rear wheels and / or one, two, or more wheels on additional axles, which, with respect to the longitudinal axis of the industrial truck, are arranged in front of the front wheels, between the front and rear wheels, and / or behind the rear wheels. The industrial truck in question can, in particular, be designed as a forklift truck.

[0013] At least one of these wheels can be driven to propel the industrial truck, particularly in the circumferential direction. Preferably, at least one front wheel and at least one rear wheel are driven by a motor. The drive systems for the wheels can be independent of each other; for example, each driven wheel can have its own drive motor, which can be controlled independently of the other drive systems. The drive system can, for example, be an electric motor. Furthermore, each drive system can be individually controlled depending on the steering angle of the respective wheel and / or the industrial truck.

[0014] Furthermore, it is stipulated that all wheels of the industrial truck are steerable. It is conceivable that the industrial truck has actively steerable wheels (i.e., steerable wheels driven for steering) and passively steerable wheels (i.e., wheels not driven for steering), such as a trailing roller. The steerable wheels driven for steering can have a steering gear or each have its own steering drive, such as a steering drive motor, to rotate the respective wheel around its vertical axis, which is parallel to the vertical axis of the industrial truck. The steering drives can, in particular, be controlled independently of one another, so that each steerable wheel equipped with a steering drive can be steered individually. For the sake of clarity, only the "wheel" is referred to here as the steerable component.Of course, it can also be provided that an entire wheel suspension with one or more individual wheels is rotated or steered around a vertical axis of the wheel suspension by means of a steering gear or steering drive.

[0015] To initiate a turn around the steering axis, the steering angle sensor is activated. The steering angle sensor can be, for example, a steering wheel, a joystick, a slider, a rotary knob, or a pedal assembly. It is also conceivable that the steering angle sensor is a sensor for automatically initiating a turn, for example, along a predetermined path, or a computer configured to initiate a pre-programmed or situation-dependent turn. Upon activation of the steering angle sensor, both the at least two front wheels and the at least one rear wheel are steered; that is, the at least two front wheels and the at least one rear wheel are each rotated about an axis parallel to the vertical axis of the industrial truck.

[0016] When initiating a turn - especially from a straight-ahead journey - the steering pole is moved along a steering curve from infinity towards the industrial truck.

[0017] According to the invention, the longitudinal distance of the steering pole to a transverse axis of the industrial truck is regulated depending on the transverse distance of the steering pole to a longitudinal axis of the industrial truck. This results in a steering line, which, when considering the overall path of the steering pole, does not necessarily have to be a straight line. Rather, the steering line can have different gradients in sections with respect to the longitudinal and / or transverse axis of the industrial truck. In particular, the steering line is not necessarily a straight line parallel to the front axle or to a rear axle (also called the rear wheel axle) of the industrial truck. This allows the industrial truck to be maneuvered particularly safely and easily in every respect.

[0018] Advantageous embodiments and further developments of the invention can be found in the dependent claims, the description and the drawings.

[0019] Preferably, the steering axis of the industrial truck is guided along a steering line when steering, wherein the steering line is formed at least partially at an angle to the transverse axis and / or at an angle to the longitudinal axis. In particular, it can be provided that the steering line is not parallel to the transverse axis and / or the longitudinal axis of the industrial truck, at least in part. This can result, for example, in front-loading forklift operation, in a steering line which, viewed over its entire length, and especially in sections, has different distances to the transverse axis of the industrial truck. Consequently, depending on the set steering angle, the point around which the industrial truck is steered, in particular the steering axis, can be positioned at different distances not only to the longitudinal axis but also to the center of the vehicle.

[0020] According to a preferred embodiment, when steering the industrial truck, the steering pole is guided along a steering line, wherein the steering line is at least partially straight and / or partially curved. Curved, in the sense of the present invention, is a non-straight line, for example, a parabola. The steering line can therefore be designed as a curve function, particularly in certain driving situations. Overall, the steering line can thus have both a straight section and a curved section. This allows the industrial truck to be steered in such a way that, depending on the steering angle, it can navigate particularly small turning radii and curves, making it exceptionally maneuverable overall.

[0021] According to a particularly preferred embodiment, when steering the industrial truck, the steering pole is guided along a steering line. This steering line has a gradient angle with respect to the longitudinal and / or transverse axis, which changes depending on the longitudinal and / or transverse distance of the steering pole. The steering line can, for example, have two straight sections with different gradients with respect to the longitudinal or transverse axis. This results in a steering line with two straight sections and a kink connecting them. The connection between the two straight sections is preferably curved, so that when the steering pole is turned and shifted across the connection between the two straight sections, the wheel is not turned or steered too quickly.

[0022] It is particularly preferred that, when steering the industrial truck, the steering pivot is guided along a steering line, with the steering line always being spaced apart from the vertical axis of both the front and rear wheels. In other words, with this design, the steering pivot is never located in the center of a wheel or intersecting it. This eliminates the need to stop or even reverse the rotation of a wheel, especially the inside wheel, during sharp turns. Instead, each wheel rotates in only one direction—the direction of travel—and contributes to the steering, at least above a predefined steering angle.

[0023] It is possible for the steering line to be mirrored across the longitudinal axis of the industrial truck. Mirroring the steering line across the longitudinal axis results in a symmetrical steering procedure for both left and right turns. It is conceivable that the steering line has a discontinuity at its intersection with the longitudinal axis, particularly a liftable discontinuity. If the steering line is mirrored across the longitudinal axis of the industrial truck and curved on both sides of the longitudinal axis, this leads to very intuitive handling of the industrial truck when cornering. However, it is also conceivable that the steering line—as previously explained—has straight sections on both sides of the longitudinal axis. These straight sections can, for example, be arranged non-parallel to the transverse axis. Furthermore, it is conceivable that the steering line is mirrored across the transverse axis of the industrial truck.Reflecting the steering line on the transverse axis can enable a symmetrical steering method, especially during lateral movements.

[0024] According to a further preferred embodiment of the present invention, a steering ratio is set depending on a steering angle to initiate cornering. The steering angle, as defined in the present invention, can be inversely proportional to the lateral distance of the steering pivot to the longitudinal axis of the industrial truck. At small steering angles, i.e., at large lateral distances, large turning radii are achieved. The industrial truck steers only slightly. At large steering angles, i.e., at small lateral distances, small turning radii are achieved. The industrial truck steers sharply. The steering ratio, as defined in the present invention, determines the proportionality between the degree of actuation of the steering angle sensor and the resulting turning radius. In other words, with a small steering ratio, the industrial truck steers less sharply when the steering wheel is turned than with a large steering ratio.If, as in this preferred embodiment, the steering ratio depends on the steering angle, then smaller movements of the steering angle sensor have less of an effect on the forklift's movement, for example, when driving straight ahead, than when turning sharply. This makes the forklift easier for the operator to handle, especially when maneuvering in confined spaces. It is conceivable that the relationship between the steering ratio and the steering angle is linear. However, it is also conceivable that the relationship between the steering ratio and the steering angle is non-linear. It is also conceivable that the relationship between the steering ratio and the steering angle can be individually adjusted by the operator. This advantageously allows the forklift's behavior to be adapted to the operator's personal preferences.

[0025] According to a further preferred embodiment of the present invention, the longitudinal distance of the steering pole to the transverse axis is increased as the transverse distance of the steering pole to the longitudinal axis decreases. In other words, the steering pole can be moved forward, for example, when turning with small radii. It is conceivable, for instance, that the steering pole is arranged on a fork tine or between the fork tines of the industrial truck, i.e., in the area of ​​the transported load, when turning with small radii. This has the advantage that, especially in confined spaces, rotation occurs around a point close to the load of the industrial truck. For example, the pivot point can be located at a corner of the load or at the center of gravity of the load. This enables the vehicle to rotate around the load or around a corner of the load. This is particularly advantageous when pivoting the vehicle into a narrow aisle or load unloading area located to the side of the vehicle.

[0026] Furthermore, it can also be provided that the longitudinal distance of the steering pole to the transverse axis decreases as the lateral distance of the steering pole to the longitudinal axis decreases. This pulls the steering pole towards the operator of the industrial truck when cornering with small radii. This, in particular, enables the vehicle to rotate on its own axis. This is especially advantageous when reversing. It should be noted that the steering line can, in principle, also run in opposite directions in certain sections, so that the two aforementioned features of increasing or decreasing the longitudinal distance of the steering pole to the transverse axis with decreasing lateral distance are not necessarily mutually exclusive.Rather, the steering line can be designed in a first section such that the longitudinal distance of the steering pole to the transverse axis is increased as the transverse distance of the steering pole to the longitudinal axis decreases, and in a second section such that the longitudinal distance of the steering pole to the transverse axis is decreased as the transverse distance of the steering pole to the longitudinal axis decreases.

[0027] According to a further preferred embodiment of the present invention, the maximum longitudinal distance of the steering pole to the transverse axis corresponds to half the vehicle length. If the industrial truck is designed as a forklift with forks, it is particularly preferred that the maximum longitudinal distance of the steering pole to the transverse axis corresponds to the distance of the front end of the fork to the transverse axis. In particular, it can be provided that the steering pole is then arranged at the level of the front end of the fork when the steering pole is located on the longitudinal axis of the industrial truck. In other words, it is particularly provided that the industrial truck can perform a carousel movement, with the center of the carousel movement lying between the ends of the forks. This advantageously makes it possible to approach a load easily and precisely, even in very confined spaces.

[0028] It is particularly preferred that, with at least two front wheels arranged parallel to the longitudinal axis of the industrial truck, a front axle is defined that intersects the at least two front wheels centrally and is arranged orthogonally to the longitudinal axis of the industrial truck, and that, at least in longitudinal driving mode, a steering line, along which the steering pole is guided when steering the industrial truck, coincides at least partially with the front wheel axle and is designed such that, when cornering in longitudinal driving mode, the steering pole is initially moved towards the inside front wheel, in particular lying on the front wheel axle, and the steering pole is deflected and spaced from the front wheel axle at a predefined distance to a vertical axis of the inside front wheel, in particular when the steering angle of the rear wheel with respect to the longitudinal axis of the industrial truck is equal to or greater than 40°, preferably greater than 45°.Particularly preferably more than 60°. Or, put another way: If, in front-loading forklift operation, the steering line coincides with the front wheel axle, at least partially, the steering pole is deflected from the front wheel axle from a predefined steering angle of the rear wheel relative to the longitudinal axis of the forklift, particularly from 40° or more, and consequently, according to this design, when cornering in longitudinal driving mode, the steering pole lies outside the front axle; in particular, the steering pole does not cross the vertical axis of the inside wheel when turning. This means that when turning in front-loading forklift operation, the forklift is initially steered only by the rear wheel until it reaches or exceeds the predefined steering angle. From this moment on, the at least two front wheels also steer. Therefore,The fact that, when cornering, the steering center point is no longer located on the front axle from a predefined steering angle of at least one rear wheel results in advantageous driving dynamics characteristics for the industrial truck. In particular, when cornering in longitudinal driving mode, the steering center point does not run through the vertical axis of the inside wheel, but is always positioned at a distance from it.

[0029] A front axle within the meaning of the present invention is defined as a straight line that intersects the at least two front wheels centrally when these are arranged parallel to the longitudinal axis of the industrial truck and is orthogonal to the longitudinal axis of the industrial truck. A rear axle within the meaning of the present invention is defined as follows: in longitudinal travel mode, the rear axle is a straight line that intersects the at least one rear wheel centrally when this wheel is arranged parallel to the longitudinal axis of the industrial truck and is orthogonal to the longitudinal axis of the industrial truck; and in transverse travel mode, it intersects the at least one rear wheel centrally when this wheel is arranged parallel to the transverse axis of the industrial truck and is orthogonal to the transverse axis of the industrial truck. Thus, front and rear axles within the meaning of the present invention are not mechanical components, but rather geometric positional designations.

[0030] A longitudinal driving mode within the meaning of the present invention, also called front forklift operation, is a driving mode in which the industrial truck travels straight ahead along its longitudinal axis. A transverse driving mode within the meaning of the present invention, also called side forklift operation, is a driving mode in which the industrial truck travels straight ahead along its transverse axis.

[0031] The steering pattern described above can also be applied accordingly in lateral driving mode. It is preferably provided that, with at least one rear wheel arranged orthogonally to the longitudinal axis of the industrial truck, a rear axle is defined that intersects the rear wheel centrally and is arranged parallel to the longitudinal axis of the industrial truck. At least in lateral driving mode, a steering line, along which the steering pole is guided when steering the industrial truck, coincides at least partially with the rear wheel axle and is designed such that, when cornering in lateral driving mode, the steering pole is initially moved towards the inner rear wheel, in particular lying on the rear wheel axle. The steering pole is then deflected and spaced from the rear wheel axle at a predefined distance to the vertical axis of the inner rear wheel (if multiple rear wheels are present).In particular, when the steering angle of at least one front wheel relative to the transverse axis of the industrial truck is equal to or greater than 40°, preferably greater than 45°, and especially greater than 60°. In other words, if the steering line coincides with the rear axle at least partially during side-loading operation, the steering pole of at least one of the front wheels relative to the transverse axis of the industrial truck, for example, of equal to or greater than 40°, is deflected from the rear axle. Consequently, according to this design, when cornering in a transverse driving mode of the industrial truck, the steering pole lies outside the rear axle; in particular, the steering pole does not cross the vertical axis of the rear wheel when turning. This means that when turning in a front-loading operation, the industrial truck is initially steered only by the front wheels.until one of these reaches or exceeds the predefined steering angle. From this moment on, at least one rear wheel also steers. Because the steering axis no longer falls on the rear axle when cornering beyond a predefined angle, the industrial truck exhibits advantageous driving dynamics. In particular, when cornering in lateral driving mode, the steering axis does not run through the vertical axis of one of the at least one rear wheel, but is always positioned at a distance from it.

[0032] Consequently, it may be provided that the steering pole is not located on the front axle when cornering in longitudinal driving mode of the industrial truck from a predefined steering angle, and that the steering pole is not located on the rear axle when cornering in transverse driving mode of the industrial truck from a predefined steering angle.

[0033] According to a particularly preferred embodiment of the present invention, both the longitudinal distance of the steering pole to the transverse axis and the lateral distance of the steering pole to the longitudinal axis are controlled by a single input to the steering angle sensor. In other words, for example, turning a steering wheel is sufficient to control both the lateral and longitudinal distances of the steering pole. "Only one input" in the context of the present invention means that only a single input is necessary. This input could, for example, be a movement of the steering angle sensor by the operator of the industrial truck.

[0034] According to a further preferred embodiment of the present invention, at least one predefined steering pole can be selected independently of the steering angle sensor. For example, such a steering pole can be selected directly by the operator using a button or touchpad. Such a predefined steering pole can, for example, be a steering pole at the free end of a fork tine. After the steering pole has been selected, the vehicle rotates accordingly around this steering pole when the steering sensor is turned.

[0035] Another object for solving the problem stated at the outset is a forklift truck which has a steering device configured to carry out the steering method according to the invention by controlling the position of the steering pole. The steering device of the forklift truck according to the invention controls the longitudinal distance of the steering pole to the transverse axis depending on the transverse distance of the steering pole to the longitudinal axis. The steering device can include the steering angle sensor, electrical components, hydraulic components and / or a microcomputer.

[0036] All advantages, features and details of the steering method according to the invention mentioned in the description text also refer to the industrial truck according to the invention.

[0037] Further details, features, and advantages of the invention will become apparent from the drawings and from the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the inventive concept.

[0038] They show: Fig. 1: A schematic view of a forklift truck according to an exemplary embodiment of the present invention in straight-ahead driving in longitudinal mode, Fig. 2: a schematic view of the in Fig. 1. Forklift truck shown in a curve, Fig. 3: another schematic view of the in Fig. 1. Forklift truck shown in a curve, Fig. 4: A schematic view of a forklift truck according to a further exemplary embodiment of the present invention in a curve, Fig. 5: a schematic view of a forklift truck according to a further exemplary embodiment of the present invention in a curve, Fig. 6: a schematic view of the in Fig. 1. The forklift truck shown is traveling straight ahead in lateral operation, and Fig. 7: a schematic view of a forklift truck according to a further exemplary embodiment of the present invention in a curve.

[0039] The Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 shows a forklift truck 1 according to an exemplary embodiment of the present invention. The forklift trucks 1 shown have a left front wheel 2.1 and a right front wheel 2.2 as well as a rear wheel 3 ( Fig. 1 to 3 and 5 to 7) or a left rear wheel 3.1 and a right rear wheel 3.2 ( Fig. 4). Furthermore, a steering angle sensor 5, here in the form of a steering wheel, is shown. The industrial trucks 1 also have steering and control devices (not shown) configured to carry out the steering method according to the invention.

[0040] Fig. Figure 1 shows the industrial truck 1 in longitudinal driving mode, traveling straight ahead. Longitudinal driving mode, also called front forklift operation, means that the industrial truck 1 primarily moves towards or away from the loading forks 4 attached to the industrial truck 1. In the Fig. In Figure 1, the straight-ahead journey in longitudinal driving mode is shown, with the front wheels 2.1, 2.2 and the rear wheel 3 aligned parallel to a longitudinal axis X of the industrial truck 1. Fig. Figure 6 shows the industrial truck 1 in a lateral driving mode while traveling straight ahead. Lateral driving mode, also called side-loader driving mode, means that the industrial truck 1 moves in a main direction of travel, which essentially corresponds to a direction perpendicular to the arrangement of the loading forks 4 on the industrial truck 1. In the Fig. In the straight-ahead driving in lateral operation shown in Figure 6, the front wheels 2.1, 2.2 and the rear wheel 3 are aligned parallel to a transverse axis Y of the industrial truck 1. Fig. 2, Fig. 3, Fig. 4 to Fig. Figures 5 and 7 show the industrial truck 1, for example, with steered wheels 2.1, 2.2, 3, 3.1, 3.2 for performing a steering or turning movement of the industrial truck 1.

[0041] The longitudinal axis X is orthogonal to the transverse axis Y of the industrial truck 1. The longitudinal axis X intersects the transverse axis Y at the vehicle's center M. A third axis can be formed by a vertical axis of the industrial truck 1 (not shown), which is orthogonal to both the longitudinal axis X and the transverse axis Y. Also shown is a vehicle length T, extending from the rear end of the industrial truck 1 to the front end of the forks 4 of the industrial truck 1.

[0042] A front axle V is arranged parallel to the transverse axis Y and intersects the two front wheels 2.1 and 2.2 at their midpoints. If the front wheels 2.1 and 2.2 of the industrial truck 1 – as for example in Fig. As shown in Figure 1, if the wheels are aligned for straight-ahead driving in longitudinal mode, then both wheel axles of the front wheels 2.1 and 2.2 lie on the front axle V. The front axle V, as defined in the present invention, is not a mechanical component, but a geometric position designation.

[0043] A rear axle H intersects the rear wheel 3 in the middle and forms its wheel axle. If the rear wheel 3 of the industrial truck 1 - as for example in Fig. 1 shown - if it is oriented for straight-ahead travel in longitudinal operation, then the rear axle H is arranged parallel to the transverse axis Y. If the rear wheel 3 of the industrial truck 1 - as for example in Fig. As shown in Figure 6 – when oriented for straight-ahead driving in lateral operation – the rear axle H lies on or parallel to the longitudinal axis X. Within the scope of the invention, the rear axle H merely describes a geometric position and not a mechanical component.

[0044] In the Fig. Figures 2 to 5 and 7 do not show the rear axle H, the front axle V, or the vehicle length T for clarity. These figures depict industrial trucks 1 driving around curves. The turns are executed around a steering center point P. The steering center point P is the intersection of straight lines perpendicular to the centers of all wheels 2.1, 2.2, 3, 3.1, 3.2 of the respective industrial truck 1. The curve radius is the distance between the steering center point P and the vehicle's center. When driving straight ahead, the steering center point P is at infinity. When the steering angle sensor 5 is activated, initiating a turn, the steering center point P moves from infinity along a steering line S in the direction of the industrial truck 1.

[0045] The following discussion focuses solely on longitudinal driving. The observations and accompanying descriptions can be applied, mutatis mutandis, to lateral driving. In particular, the same steering lines and driving characteristics may result.

[0046] The closer the steering point P is moved along the steering line S towards the longitudinal axis X, the tighter the curve to be negotiated and the smaller the curve radius. A lateral distance Q of the steering point P to the longitudinal axis X is controlled by the steering angle sensor 5. Here, a steering angle is set on the steering angle sensor 5, and the position of the steering point P on the steering line S relative to the longitudinal axis X is adjusted using a steering ratio. The steering ratio is preferably dependent on the steering angle. The larger the steering angle selected on the steering angle sensor 5, the larger the steering ratio is set. This means that, for example, when driving straight ahead, a lower steering ratio results in a smaller change in the lateral distance Q of the steering point P from the longitudinal axis X.However, if, for example, the steering wheel is already turned and the industrial truck 1 is going around a curve, then entering a steering angle by means of a higher steering ratio causes a greater change in the lateral distance Q of the steering pole P from the longitudinal axis X.

[0047] According to the invention, the longitudinal distance L of the steering pole P to the transverse axis Y is controlled depending on the transverse distance Q of the steering pole P to the longitudinal axis X. In other words, the steering pole P moves forward or backward when steering.

[0048] In the Fig. 2, Fig. 3 to Fig. Figure 4 shows industrial trucks 1 in which the longitudinal distance L of the steering pole P from the transverse axis Y decreases as the transverse distance Q of the steering pole P from the longitudinal axis X decreases. In the embodiments shown in these figures, the maximum longitudinal distance L of the steering pole P from the transverse axis Y corresponds to half the vehicle length T and is reached when the transverse distance Q of the steering pole P from the longitudinal axis X is 0. In other words, the steering line S is designed here such that the industrial truck 1 can perform a carousel movement around a point midway between the ends of the forks 4 of the industrial truck 1. Of course, the Fig. 1, Fig. 2, Fig. 3 to Fig. The steering line S shown in each case can also have any other technically possible curve shape.

[0049] In the Fig. Figure 5 shows a preferred embodiment of the industrial truck 1 according to the present invention, in which the longitudinal distance L of the steering pole P is reduced as the lateral distance Q of the steering pole P from the longitudinal axis X decreases. Here, the steering pole P moves towards the vehicle center M as the steering angles increase.

[0050] The in the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. The steering lines S shown in Figure 5 are depicted as curves for clarity and are at least partially not parallel to the front axle V or the rear axle H. The steering line S can, of course, have other shapes. Furthermore, the steering line S – especially with otherwise identical design – can also be shifted along the longitudinal axis X and / or the transverse axis Y or arranged at an angle.

[0051] In the Fig.Figure 7 shows a particularly preferred embodiment of the industrial truck 1 according to the present invention. In longitudinal driving mode, the steering line S with a substantially straight section lies within the front wheel axis V. As a result, when turning from straight-ahead driving, the industrial truck 1 is initially steered exclusively via the rear wheel 3. The front wheels 2.1, 2.2 initially remain unsteered, in particular aligned parallel to the longitudinal axis X. From a predefined steering angle of the rear wheel 3 with respect to the longitudinal axis X, preferably 40°, the steering pole P is deflected or displaced laterally next to the front wheel axis V by the curve of the steering line S, so that the steering pole P does not pass through the center of one of the front wheels 2.1, 2.2 during further steering. Accordingly, it is provided according to the invention that the front wheels 2.1, 2.22. Steering only begins at a predefined steering angle, particularly of the rear wheel 3. The front wheels 2.1, 2.2 maintain their rotational movement in the same direction, controlled by drive motors (not shown) for the rotational turning of the wheels.

[0052] In particular, it can be provided that the steering line S never crosses the center of a front wheel 2.1, 2.2 or a rear wheel 3, 3.1, 3.2, but always runs laterally past them, so that the rotational direction of either of the front wheels 2.1, 2.2 or the rear wheel 3, 3.1, 3.2 is never reversed. This allows for advantages in driving dynamics. Reference symbol list: 1 forklift truck 2.1 left front wheel 2.2 right front wheel 3 rear wheel 3.1 left rear wheel 3.2 right rear wheel 4 Forks 5 Steering angle sensors H Rear axle L Longitudinal distance M vehicle center P Steering pole Q Lateral spacing S steering line Vehicle length V front axle X Longitudinal axis Y transverse axis

Claims

Steering method for operating a forklift truck (1), wherein the forklift truck (1) has at least two front wheels (2.1, 2.2) and at least one rear wheel (3.1, 3.2), wherein a steering angle sensor (5) is actuated to initiate a turn around a steering pole (P) and both the at least two front wheels (2.1, 2.2) and the at least one rear wheel (3, 3.1, 3.2) are steerable, wherein the forklift truck (1) has a longitudinal axis (X) and a transverse axis (Y) which intersect at a vehicle center (M), characterized in that when the forklift truck (1) is steered, a longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) is controlled depending on a transverse distance (Q) of the steering pole (P) to the longitudinal axis (X). Steering method according to claim 1, characterized in that when steering the industrial truck (1) the steering pole (P) is guided on a steering line (S), wherein the steering line (S) is formed at least sectionally at an angle to the transverse axis (Y) and / or at an angle to the longitudinal axis (X). Steering method according to one of claims 1 or 2, characterized in that when steering the industrial truck (1) the steering pole (P) is guided on a steering line (S), wherein the steering line (S) is designed at least section by section as a straight line and / or section by section as a curve. Steering method according to one of the preceding claims, characterized in that when steering the industrial truck (1) the steering pole (P) is guided on a steering line (S), wherein the steering line (S) has an angle of inclination with respect to the longitudinal axis (X) and / or the transverse axis (Y), which changes depending on the longitudinal distance (L) and / or transverse distance (Q) of the steering pole (P). Steering method according to one of the preceding claims, characterized in that when steering the industrial truck (1) the steering pole (P) is guided on a steering line (S), wherein the steering line (S) always runs at a distance from a respective vertical axis of the front wheels (2.1, 2.2) and / or a vertical axis of the rear wheel (3, 3.1, 3.2). Steering method according to one of claims 2 to 5, characterized in that the steering line (S) is mirrored on the longitudinal axis (X) of the industrial truck (1). Steering method according to one of the preceding claims, characterized in that a steering ratio is set depending on a steering angle to initiate the cornering maneuver. Steering method according to one of the preceding claims, characterized in that the longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) is increased with decreasing transverse distance (Q) of the steering pole (P) to the longitudinal axis (X). Steering method according to one of the preceding claims, characterized in that the longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) is reduced with decreasing transverse distance (Q) of the steering pole (P) to the longitudinal axis (X). Steering method according to one of the preceding claims, characterized in that the industrial truck (1) preferably has a fork (4) and the maximum longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) corresponds to the distance of the front end of the fork (4) to the transverse axis (Q), wherein the steering pole (P) is arranged at the level of the front end of the fork (4) in particular when the steering pole (P) is arranged on the longitudinal axis (X) of the industrial truck (1). Steering method according to one of the preceding claims, characterized in that, in the case of at least two front wheels (2.1, 2.2) arranged parallel to the longitudinal axis (X) of the industrial truck (1), a front axle (V) is defined which intersects the at least two front wheels (2.1, 2.2) centrally and is arranged orthogonally to the longitudinal axis (X) of the industrial truck (1), and, at least in longitudinal driving mode of the industrial truck (1), a steering line (S) on which the steering pole (P) is guided when steering the industrial truck (1) coincides at least section by section with the front wheel axle (V) and is designed such that, when cornering in longitudinal driving mode, the steering pole (P) is initially moved towards the inside front wheel (2.1, 2.2), in particular on the front axle (V), and at a predefined distance to a vertical axis of the inside front wheel (2.1, 2.2).2) is deflected and spaced away from the front axle (V), in particular when the steering angle of at least one rear wheel (3, 3.1, 3.2) with respect to the longitudinal axis (X) is equal to or greater than 40°. Steering method according to one of the preceding claims, characterized in that, in the case of at least one rear wheel (3, 3.1, 3.2) arranged orthogonally to the longitudinal axis (X) of the industrial truck (1), a rear axle (H) is defined which intersects the rear wheel (3, 3.1, 3.2) centrally and is arranged parallel to the longitudinal axis (X) of the industrial truck (1), and, at least in a transverse driving mode of the industrial truck (1), a steering line (S) on which the steering pole (P) is guided when steering the industrial truck (1) coincides at least sectionally with the rear axle (H) and is designed such that, when cornering in the transverse driving mode, the steering pole (P) is initially moved towards the inner rear wheel (3, 3.1, 3.2), in particular on the rear axle (H), and at a predefined distance to a vertical axis of the inner rear wheel (3, 3.1, 3.2).2) is deflected and spaced away from the rear axle (H), in particular at least at a steering angle of at least one of the front wheels (2.1, 2.2) with respect to the transverse axis (Y) of 40° or more. Steering method according to one of the preceding claims, characterized in that both the longitudinal distance (L) of the steering pole (P) to the transverse axis (Y) and the transverse distance (Q) of the steering pole (P) to the longitudinal axis (X) are controlled by exclusively one input at the steering angle sensor (5). Steering method according to one of claims 1 to 12, characterized in that at least one predefined steering pole (P) can be selected, in particular independently of the steering angle sensor (5). Industrial truck (1), characterized in that the industrial truck (1) has a steering device which is configured by controlling the position of the steering pole (P) to perform a steering procedure according to one of the preceding claims.

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