SE1550007A1 - Industrial truck with caster wheel assembly - Google Patents

Abstract

The invention relates to an industrial truck (600) that comprises at least one pair of caster wheel assemblies (608). Each caster wheel assembly (608) comprises a yoke frame (603), a caster wheel (602) and mounting means (606) for connecting the caster wheel assembly (608) to the industrial truck (600). The yoke frame (603) is arranged to rotatably support the caster wheel (602) for rotation around a wheel axle (605) during motion of the industrial truck (600) and is further rotatably connected to the mounting means (606) to swivel about a swivel axis. (609) to align the caster wheel (602) with a direction of motion. The swivel axis (609) projects in an orthogonal direction relative to the wheel axle (605). The caster wheel assemblies (608) of the at least one pair of caster wheel assemblies (608) are positioned symmetrically on each side of a centreline (604) of the industrial truck (600). When the industrial truck (600) is arranged horizontally, an offset is provided between the direction of the respective swivel axes (609) and a vertical direction so that symmetry lines of the respective swivel axes (609) intersect each other at a point (P) above the at least one pair of caster wheel assemblies (608).(Figure 6)

Description

1 INDUSTRIAL TRUCK WITH CASTER WHEEL ASSEMBLY TECHNICAL FIELD The disclosure relates to an industrial truck adapted for improved manoeuvrability. The present disclosure also relates to a method for adapting an industrial truck to improve manoeuvrability.

BACKGROUND ART Industrial trucks often have to operate in defined spaces, such as in the isle of a warehouse, where safe and flexible operation is of utmost importance, while at the same time the space to manoeuvre is limited. Both the industrial truck and the load carried by the truck are typically very heavy and require that the industrial truck can manoeuvre smoothly to provide safe operation. An industrial truck comprises one or more drive wheels and a plurality of support wheels for providing stability to the truck. Such support wheels typically include at least one pair of caster wheels flanking the drive wheel.

Stability is important for all types of industrial trucks that carry heavy loads. It is particularly important for industrial trucks performing high lifting operations, such as stackers.

DE102014102470A1 discloses an industrial truck in the area of alignment perturbations. The disclosed truck replaces the traditional caster wheels by wheel arrangements that comprise essentially spherical wheels. DE102014102470A1 is not applicable to an industrial truck comprising caster wheels.

Thus, there is a need to improve the prior art.

SUMMARY OF THE INVENTION Caster wheels in general are not applicable to industrial truck technology. Industrial trucks carry loads in the order of 500-2000 kg. Thus any caster wheel in general is not applicable. And further, the industrial truck in itself carries in general a large battery that often is a considerable weight. Thus a skilled person would not apply caster wheel technology in general due to risks of failure of the caster wheel. 2 The industrial truck is provided with caster wheels to enable it to steer at a sharp angle. When the industrial truck changes direction, the caster wheels rotate about their swivel axis to align themselves in the new direction. There is a slight delay before the caster wheels have fully aligned themselves in the new direction. During the alignment, the industrial truck exhibits a small jerk, which in turn gives rise to a slight sway, in the following described as an alignment perturbation, of the industrial truck.

As an industrial truck comprising a pair of load lifters, e.g. a forklift truck, backs out from a pallet space in a racking, the resulting alignment perturbation may move the load lifters or a load on the load lifters sideways and collide with adjacent loads or racking. The alignment perturbation also reduces the smoothness of operating the industrial truck. In particular, industrial trucks operated by a tiller arm without servo assistance may exhibit a jerk of the tiller arm, when the industrial truck changes direction.

The alignment perturbation does not impact the safety of operating the truck, since the maximum working load for the industrial truck is set based on knowledge of the trucks behaviour during manoeuvring, but an operator of the truck may find the alignment perturbation discomforting. Thus, there is a need to provide a solution that solves the problem of alignment perturbations for an industrial truck comprising caster wheels.

An object of the present invention is to adapt an existing industrial truck to reduce the caster wheel alignment perturbation during turning or change of direction of the industrial truck.

The object is solved by an industrial truck according to the present disclosure; comprising at least one pair of caster wheel assemblies. The at least one pair of caster wheel assemblies are arranged mirror symmetrically on each side of a centreline of the industrial truck. Each caster wheel assembly comprises a yoke frame, a caster wheel and mounting means for connecting the caster wheel assembly to the industrial truck. The yoke frame is arranged to rotatably support the caster wheel for rotation around a wheel axle during motion of the industrial truck and is further rotatably connected to the mounting means to swivel about a swivel axis to align the caster wheel with a direction of motion. The swivel axis projects in an orthogonal direction relative to the wheel axle. When the industrial truck is arranged horizontally, an offset is provided between the direction of the respective swivel axes and a vertical direction 3 so that symmetry lines of the respective swivel axes intersect each other at a point above the at least one pair of caster wheel assemblies.

During swivelling of the caster wheel about the swivel axis for alignment with the direction of motion, the incline of the wheel axle with respect to the underlying surface varies. The variation of the incline of the wheel axle during the alignment provides for a more even distribution of the pressure under the caster wheel, resulting in smoother turns and reduced alignment perturbation when changing of the direction of the industrial truck.

An advantage is that the industrial truck will have a wider base, compared to if the swivel axis were arranged in a vertical direction, the wider base providing more stable turning characteristics of the industrial truck. A further advantage is that the alignment perturbation of the industrial truck can be significantly reduced or even eliminated. In cases where the industrial truck is operated using a tiller arm without servo assistance, the alignment perturbation in the tiller arm can be significantly reduced. A wider base is important for all types of industrial trucks that carry heavy loads, for increased stability. It is particularly important for industrial trucks performing high lifting operations, such as stackers.

According to an aspect of the invention, the offset of the direction of the swivel axis and the vertical direction forms an angle falling in a range of 1.00 to 5.0°. According to a further aspect of the invention, the offset of the direction of the swivel axis and the vertical direction forms an angle falling in a range of 1.5° to 3.0°.

By keeping the angle of the offset in the ranges above, the benefits of the technical effects associated with a varying incline of the wheel axle during alignment of the caster wheel with the direction of motion can be achieved without having to subject the caster wheel assembly to undue stress associated with greater angles of the offset. A further advantage is that wear and tear on the caster wheel is reduced compared to embodiments where the angle of the offset is higher than the maximum for said ranges of the offset. By keeping the angle of the offset in the narrower of said ranges, shear forces in the caster wheel assembly due to a particular load of the industrial truck on the caster wheel assembly is reduced, compared to shear forces associated with a corresponding load of the industrial truck on the caster wheel assembly at greater angles of the offset. 4 According to an aspect of the invention, at least one shim is arranged, at least in part, between the mounting means of the respective caster wheel assembly of the at least one pair caster wheel assemblies and the industrial truck.

Arranging at least one shim, at least in part, between the mounting means of the respective caster wheel assembly of the at least one pair caster wheel assemblies and the industrial truck enables an easy and flexible way of arranging the angle with respect to a vertical axis and the orientation of the swivel axis. An additional advantage is that the shims may be replaced, should other angles and/or orientations of the swivel axis be desired. A further advantage is that shimming requires few and inexpensive components. Another advantage is that shimming enables the use of existing caster wheel assemblies, i.e. it enables so-called retrofitting.

An additional object of the present invention is to provide a caster wheel assembly for operational use under an industrial truck, where the caster wheel assembly is arranged to reduce the caster wheel alignment perturbation during turning or change of direction of the industrial truck.

The object is solved by a caster wheel assembly according to the present disclosure; the caster wheel assembly comprises a yoke frame, a caster wheel and mounting means for connecting the caster wheel assembly to the industrial truck. The yoke frame is arranged to rotatably support the caster wheel for rotation around a wheel axle during motion of the industrial truck and is further rotatably connected to the mounting means to swivel about a swivel axis to align the caster wheel with a direction of motion. The swivel axis projects in an orthogonal direction relative to the wheel axle. When the industrial truck is arranged horizontally, the caster wheel assembly is arranged to provide an offset between the direction of the swivel axis and a vertical direction.

A further object of the present invention is to provide a method for arranging a pair of caster wheel assemblies under an industrial truck in order to reduce the caster wheel alignment perturbation during turning or change of direction of the industrial truck.

The object is solved by a method for arranging a pair of caster wheel assemblies under an industrial truck. The caster wheel assemblies are arranged for operational use under an industrial truck. The caster wheel assemblies are positioned symmetrically on each side of a centreline of the industrial truck. Each caster wheel assembly comprises a yoke frame, a caster wheel and mounting means for connecting the caster wheel assembly to the industrial truck. The yoke frame is arranged to rotatably support the caster wheel for rotation around a wheel axle during motion of the industrial truck and is further rotatably connected to the mounting means to swivel about a swivel axis to align the caster with a direction of motion. The swivel axis projects in an orthogonal direction relative to the wheel axle. When the industrial truck is arranged horizontally, an offset is provided between the direction of the respective swivel axes and a vertical direction so that symmetry lines of the respective swivel axes intersect each other at a point above the at least one pair of caster wheel assemblies.

The disclosed caster wheel assembly and method for arranging a caster wheel assembly under an industrial truck provide the advantages discussed above in relation to the disclosed industrial truck.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a bottom view of an industrial truck according to embodiments of the invention; Figure 2a shows a side view of an industrial truck according to embodiments of the invention; Figure 2b shows a side view of an industrial truck according to embodiments of the invention.

Figure 3a shows a side view of a caster wheel assembly mounted to an industrial truck according to embodiments of the invention; Figure 3b shows a side view of a caster wheel assembly mounted to an industrial truck according to embodiments of the invention; Figure 4 shows a side view of a caster wheel assembly according to embodiments of the invention; Figure 5 shows a side view of a pair of caster wheel assemblies mounted to an industrial truck according to embodiments of the invention; Figure 6 shows a rear view of an industrial truck according to embodiments of the invention. DETAILED DESCRIPTION 6 Figure 1 shows a bottom view of an industrial truck 100, according to of the invention. The industrial truck 100 has a five-point chassis, comprising a wheel base with a wheel 101, 102, 103 at each of the five points, for providing stability during operation of the industrial truck 100. The industrial truck 100 comprises a pair of load carriers in the form of forks arranged at the front of the industrial truck. The wheel base comprises a drive wheel 101 and four support wheels 102, 103 arranged mirror-symmetrically with respect to a centreline 104 in a longitudinal direction of the industrial truck 100. The drive wheel 101 is arranged underneath the industrial truck 100, adjacent a rear side of the industrial truck 100 and on the centreline 104 of the industrial truck 100. The four support wheels 102, 103 comprise a pair load rollers 103 and a pair of caster wheel assemblies 108. The industrial truck 100 comprises steering means to change the orientation of the drive wheel 101. For the disclosed embodiments, a change of orientation of the drive wheel 101 may be carried out by turning a steering wheel, by redirecting a tiller arm, by remote signalling or by auto pilot. The industrial truck of Figure 1 represents any type of industrial truck where caster wheels are applicable. In general the industrial truck 100 is a support wheel truck, but according to aspects of the disclosure, the industrial truck 100 is a low lifter industrial truck, a stacker truck, a combi truck, a very narrow isle truck, a reach truck or any type of order picker truck. The industrial truck 100 is not a counter balance truck that only can act in counter balance configuration. It must be understood that Figure 1 discloses a support wheel truck that have load lifters in the form of forks, that can be lowered down on to the support legs, comprising the support wheels 103.

For the discussed different industrial trucks, some of them do not have this configuration. This means that the support legs are positioned at a larger distance laterally such that the forks can descend between these. In general the industrial truck of Figure 1 is powered by an electric drive motor. The electric drive motor is powered by an on board battery.

Figure 2a discloses embodiments of an industrial truck 200a having a five-point chassis as shown in Figure 1 and discussed above. The shown industrial truck 200a discloses a forklift truck where the operator is standing on a pivotal platform and changes the orientation of the drive wheel 201a by operating a tiller arm. The industrial truck of figure 2a is disclosed as a stacker.

Figure 2b discloses embodiments of an industrial truck 200b having a five-point chassis as discussed above. The shown industrial truck 200b discloses a forklift truck where the operator 7 is seated and operates the controls in seated position to change the orientation of the drive wheel. Figure 2b discloses a stacker in the form of a reach truck. The principles discussed for the five-point chassis shown in Figure 1 is applicable also to these embodiments of an industrial truck 200b. There is full compatibility between the embodiments of figures 1, 2a, and 2b with regard to all features.

Turning back to Figure 1, the pair of caster wheel assemblies 108 flanks the drive wheel 101 mirror-symmetrically about the centreline 104. Each caster wheel assembly 108 comprises a yoke frame, a caster wheel 102 and mounting means 106 for connecting the caster wheel assembly 108 to the industrial truck 100. The yoke frame is arranged to rotatably support the caster wheel 102 for rotation around a wheel axle 105 during motion of the industrial truck 100 and is further rotatably connected to the mounting means 106 to swivel about a swivel axis to align the caster wheel 102 with a direction of motion. The swivel axis projects in an orthogonal direction relative to the wheel axle. When the industrial truck 100 arranged horizontally, an offset is provided between the direction of the swivel axis and a vertical direction so that symmetry lines of the respective swivel axes intersect each other at a point above the at least one pair of caster wheel assemblies 108. According to an aspect, the offset of the direction of the swivel axis and the vertical direction forms an angle falling in a range of 1.00 to 5.0°, preferably in the range of 1.5° to 3.0°. The narrow range is a good alternative as it further enhances the effects already described.

When the caster wheel 102 swivels around the non-vertical swivel axis, the effect is a varying incline of the wheel axle 105 with respect to the underlying surface during varying rotational positions of the caster wheel 102. When the truck is standing still or moving slowly, e.g. turning slowly, and the wheel axle 105 of the caster wheels 102 is arranged non-horizontally, the area of contact between the caster wheels 102 and an underlying surface is smaller than a corresponding area of contact with the caster wheels 102 in a vertical position. As the area of contact between the caster wheels 102 and the underlying surface decreases, the pressure over said area increases, both on the caster wheels 102 and on the underlying surface. An advantage of keeping the angle of the offset in the ranges above is that the pressure on the caster wheels 102 for a given load is kept within a preferred range or tolerance level. A further advantage is that wear and tear on the caster wheels 102 is reduced compared to embodiments where the angle of the offset is higher than the maximum for said ranges of the 8 offset. An additional advantage is that the maximum local pressure on the underlying surface for a given load of the industrial truck 100 is kept within a preferred range or tolerance level.

Figures 3a and 3b show side views of caster wheel assemblies 308a, 308b, including a caster wheel 302a, 302b arranged under a chassis of an industrial truck, e.g. an industrial truck as illustrated in Figures 1, 2a or 2b. For illustrative purposes, each caster wheel 302a, 302b is disclosed rotated 900 with respect to a centreline 304a, 304b in a longitudinal direction of the industrial truck, so that the caster wheel 302a, 302b of Figures 3a and 3b are disclosed in a position rotated away from the centreline 304a, 304b.

The caster wheel assembly 308a, 308b comprises a yoke frame 303a, 303b, a caster wheel 302a, 302b and mounting means 306a, 306b. The mounting means 306a, 306b is/are arranged for connecting the caster wheel assembly 308a, 308b to the industrial truck. The yoke frame 303a, 303b is arranged to rotatably support the caster wheel 302a, 302b for rotation around a wheel axle 305a, 305b during motion of the industrial truck and is further rotatably connected to the mounting means 306a, 306b to swivel about a swivel axis 309a, 309b to align the caster wheel 302a, 302b with a direction of motion. The swivel axis 309a, 309b projects in an orthogonal direction relative to the wheel axle 305a, 305b. When the industrial truck is arranged horizontally, the caster wheel assembly 308a, 308b is arranged to provide an offset between the direction of the swivel axis 309a, 309b and a vertical direction.

A chassis of an industrial truck 300a, 300b comprising a centreline 304a, 304b in the longitudinal direction of the industrial truck together with the caster wheel assemblies 308a, 308b and the at least one shim 313a, 313b represent part of an aspect of the disclosed industrial truck, e.g. the industrial truck disclosed in Figure 1. The shown caster wheel assemblies 308a, 308b in Figures 3a and 3b are to be understood as one caster wheel assembly 308a, 308b of a pair of caster wheel assemblies.

The caster wheel assemblies 308a, 308b of Figures 3a and 3b are connected to a chassis 300a, 300b of an industrial truck so that the offset of the swivel axis 309a, 309b is such that the wheel base is wider in a direction perpendicular to the centreline 304a, 304b than a wheel base were the caster wheel assemblies 308a, 308b are mounted at the corresponding places, but without an offset of the swivel axes 309a, 309b, i.e. the swivel axes 309a, 309b being 9 vertical. The wider wheel base will provide additional stability during sharp turns of the industrial truck.

Swivelling of the caster wheel 302a, 302b about the swivel axis 309a, 309b, e.g. during the alignment to the direction of the drive wheel, also causes a change of the incline of the wheel axle 305a, 305b with respect to the underlying surface 312a, 312b. During sharp turns, the drive wheel of the industrial truck is directed nearly perpendicular to the longitudinal direction 304a, 304b of the truck. When the wheel axle 305a, 305b of the caster wheels 302a, 302b is arranged non-horizontally, as will happen during the alignment of the caster wheels 302a, 302b with the direction of the drive wheel, the pressure profile on the caster wheels 302a, 302b from the underlying surface changes 312a, 312b. When providing a slight tilt of the caster wheel 302a, 302b with the angle al, a2 disclosed above, the inertia experienced for a sharply turning industrial truck towards the edges of the caster wheels 302a, 302b that are farthest away from the centre of rotation is reduced. The tilt of the caster wheels 302a, 302b due to swivelling about a non-vertical swivel axis 309a, 309b tilts the top of the caster wheel 302a, 302b towards the centre of rotation and provides a more even distribution of the pressure on the caster wheels 302a, 302b from the underlying surface 312a, 312b.

An additional technical effect is that when the industrial truck is turning, with the drive wheel orthogonal to the centre of rotation and the caster wheels 302a, 302b aligned with the direction of motion, i.e. aligned with the drive wheel and orthogonal to the centre of rotation, the industrial truck will lean in a direction opposite the direction of motion. The reason for the leaning is that, as the caster wheels 302a, 302b align themselves with the direction of motion, the offset of the swivel axis 309a, 309b will bring one caster wheel 302a, 302b closer to the chassis of the industrial truck and the other caster wheel 302a, 302b farther away from the chassis of the industrial truck. Since the caster wheels 302a, 302b maintain contact with the underlying surface 312a, 312b, the two sides of the industrial truck about the centreline 304a, 304b must vary in distance to the underlying surface 312a, 312b. With the swivel axes 309a, 309b of the caster wheel assemblies 308a, 308b facing away from each other, the caster wheel 302a, 302b on the side of the industrial truck leading into the direction of motion will be rotated around the swivel axis 309a, 309b so that its distance to the chassis of the industrial truck increases, and vice versa for the opposite caster wheel 302a, 302b. This situation is further described in relation to Figure 5.

In accordance with the present invention, the offset of the direction of the swivel axis 309a, 309b and the vertical direction forms an angle al, a2 falling in a range of 1.00 to 5.0°, preferably in the range of 1.5° to 3.0°.

By keeping the angle al, a2 of the offset in the ranges above, the benefits of the technical effects associated with a varying incline of the wheel axle during alignment of the caster wheel 302a, 302b with the direction of motion can be achieved without having to subject the caster wheel assembly 308a, 308b to undue stress associated with greater angles of the offset. A further advantage is that wear and tear on the caster wheel 302a, 302b is reduced compared to embodiments where the angle of the offset is higher than the maximum for said ranges of the offset. By keeping the angle of the offset in the narrower of said ranges, shear forces in the caster wheel assembly 308a, 308b due to a particular load of the industrial truck on the caster wheel assembly is reduced, compared to shear forces associated with a corresponding load of the industrial truck on the caster wheel assembly 308a, 308b at greater angles of the offset.

According to an aspect of the disclosure, at least one shim 313a, 313b is arranged, at least in part, between the mounting means 306a, 306b and the industrial truck.

By using shims 313a, 313b as a means for arranging the swivel axis 309a, 309b, conventional caster wheel assemblies 308a, 308b can be used, i.e. the invention enables retrofitting. According to an aspect, the at least one shim 313a, 313b comprises a shim in the form of a spacer shim. Figure 3a shows an aspect, where the at least one shim 313a is in the form of a spacer shim 313a. According to an aspect, the at least one shim 313a, 313b comprises a shim in the form of a wedge or a tapered plate. Figure 3b shows an aspect of the disclosure, where the at least one shim 313b comprises a tapered plate 313b. According to another aspect of the disclosure, the angle of the swivel axis 309a, 309b is obtained by using a caster wheel assembly 308a, 308b being predesigned to arrange the swivel axis 309a, 309b non-vertically, e.g. by having a mounting means 306a, 306b that tapers off in one direction with respect to a designated essentially horizontal mounting surface of the industrial truck and thereby arranging the swivel axis 309a, 309b non-vertically. According to yet another aspect of the disclosure, the angle al, a2 of the swivel axis 309a, 309b is obtained by using a combination of a caster wheel 302a, 302b that is predesigned to arrange the swivel axis 309a, 309b non- 11 vertically and arranging at least one shim 313a, 313b between the mounting means 306a, 306b of the caster wheel 302a, 302b and the industrial truck.

According to a yet further aspect of the disclosure, each point on the swivel axis 309a, 309b projects vertically over a line orthogonal to the centreline 304a, 304b of the industrial truck.

This aspect provides the widest wheelbase in a direction orthogonal to the centreline 304a, 304b, with respect to having the caster wheel assembly 308a, 308b mounted so that the swivel axis 309a, 309b is oriented in a vertical direction.

According to an aspect, the mounting means 306a, 306b of the caster wheel assemblies 308a, 308b tapers in one direction and by mounting the caster wheel assemblies 308a, 308b under the chassis the industrial truck, the taper arranges the caster wheel assemblies 308a, 308b and thus the swivel axis 309a, 309b at an angle al, a2. In variations of this aspect, the mounting means 306a, 306b of the caster wheel assemblies 308a, 308b can be manufactured such that the caster wheel assemblies 308a, 308b are already adopted for certain models of industrial trucks and no further adjustments are necessary to arrange the swivel axis 309a, 309b at the angle al, az.

Figure 4 shows a side view of a caster wheel assembly 408 arranged under a chassis of an industrial truck, e.g. an industrial truck according to Figure 1, Figure 2a or 2b. The caster wheel assembly 408 is disclosed rotated 900 with respect to a centreline 404 in a longitudinal direction of the industrial truck, so that the caster wheel assembly 408 of Figure 4 is disclosed in a position rotated away from the centreline 404. The caster wheel assembly 480 is adapted for operational use under a chassis 401 of an industrial truck. The caster wheel assembly 408 comprises a yoke frame 403, a caster wheel 402 and mounting means 406. The mounting means 406 is/are arranged for connecting the caster wheel assembly 408 to the industrial truck. The yoke frame 403 is arranged to rotatably support the caster wheel 402 for rotation around a wheel axle 405 during motion of the industrial truck and is further rotatably connected to the mounting means 406 to swivel about a swivel axis 409 to align the caster wheel 402 with a direction of motion. The swivel axis 409 projects in an orthogonal direction relative to the wheel axle 405. When the industrial truck is arranged horizontally, the caster wheel assembly 408 is arranged to provide an offset between the direction of the swivel axis 409 and a vertical direction. 12 The caster wheel 402 comprises offsetting means 413. The offsetting means 413 is/are arranged to offset the swivel axis 409 from the vertical direction. The swivel axis 409 is offset from the vertical direction by the offsetting means 413. According to an aspect, the offsetting means is arranged to offset the swivel axis from a vertical direction with an angle a3 falling in a range of 1.00 to 5.0°. According to an aspect, the mounting means 406 comprises the offsetting means 413. An adjustable means of the offsetting means 413, e.g. a screw, is used to adjust a part of the mounting means 406 in which the swivel axis 409 rotates, so that the swivel axis is offset at said angle a3. The offsetting means 413 provides an easy and flexible means for adjusting different angles a3 of the swivel axis 409.

According to an aspect, the mounting means 406 of the caster wheel assembly 408 tapers in one direction and by mounting the caster wheel assemblies 408 under the chassis the industrial truck, the advantages of tapered mounting means 406 as discussed in relation to Figures 3a and 3b can be obtained.

Figure 5 shows a side view of a pair of caster wheel assemblies mounted to an industrial truck according to embodiments of the invention. A pair of caster wheel assemblies 508, e.g. a pair of the caster wheel assembly 308a as shown in Figure 3a, is arranged mirror-symmetrically about a centreline 504 of the industrial truck. The pair of caster wheels 502 is disclosed rotated perpendicular with respect to a centreline 504 in a longitudinal direction of the industrial truck. One caster wheel 502 on a first side of the centreline 504 of Figure 5 is disclosed in a position rotated away from the centreline 504. The other caster wheel 502 on a second side of the centreline 504 of Figure 5 is disclosed in a position rotated towards the centreline 504. Each caster wheel assembly 508 comprises a yoke frame 503, a caster wheel 502 and mounting means 506. The mounting means 506 is/are arranged for connecting the caster wheel assembly 508 to the industrial truck. The yoke frame 503 is arranged to rotatably support the caster wheel 502 for rotation around a wheel axle 505 during motion of the industrial truck and is further rotatably connected to the mounting means 506 to swivel about a swivel axis 509 to align the caster wheel 502 with a direction of motion. The swivel axis 509 projects in an orthogonal direction relative to the wheel axle 505. The caster wheel assemblies 508 are positioned symmetrically on each side of a centreline 504 of the industrial truck.

When the industrial truck is arranged horizontally, an offset is provided between the direction of the respective swivel axes 509 and a vertical direction so that symmetry lines of the 13 respective swivel axes 509 intersect each other at a point above the at least one pair of caster wheel assemblies 508. According to an aspect, for each caster wheel assembly 508, the offset of the direction of the swivel axis 509 and the vertical direction forms an angle a4, a falling in a range of 1.00 to 5.0°, preferably in the range of 1.5° to 3.0°. The offset of the swivel axis 509 means that the distance of a centre point of the wheel axle 505 of the respective caster wheel assembly 508 to a plane 510 common to the mounting means 506 of the pair of caster wheel assemblies 508, the distance being measured orthogonal to said plane 510, varies as the caster wheels 502 are rotated around their respective swivel axis 509. As one of the caster wheels 502 is rotated towards the centreline 504, the situation as disclosed in Figure 5 arises.

The increased distance between the centre point of the wheel axle 505 of the caster wheel assembly 508 and the plane 510 common to the mounting means 506 of the pair of caster wheel assemblies 508 due to rotating the caster wheel 502 towards the centreline 504 results in a minute leaning of the industrial truck. As the industrial truck finishes a sharp turn, the minute leaning will counter the effect of inertia by providing the industrial truck with a counterbalancing effect. The minute leaning is exaggerated in Figure 5 for illustrative purposes.

Figure 6 shows a rear view of an industrial truck 600 according to embodiments of the invention. The industrial truck 600 is a support leg truck having at least a five point chassis. A pair of caster wheel assemblies 608 is positioned symmetrically on each side of a centreline 604 of the industrial truck 600. The industrial truck 600 further comprises a centrally positioned drive wheel 601. The caster wheel assemblies 608 are positioned laterally offset of the centrally positioned drive wheel 601. The caster wheel assemblies 608 are disclosed rotated 90° with respect to a centreline 604 in a longitudinal direction of the industrial truck 600, so that the caster wheel assemblies 608 of Figure 6 are disclosed in a position rotated away from the centreline 604. Each caster wheel assembly 608 comprises a yoke frame 603, a caster wheel 602 and mounting means 606. The mounting means 606 is/are arranged for connecting the caster wheel assembly 608 to the industrial truck. The yoke frame 603 is arranged to rotatably support the caster wheel 602 for rotation around a wheel axle 605 during motion of the industrial truck and is further rotatably connected to the mounting means 606 to swivel about a swivel axis 609 to align the caster wheel 602 with a direction of motion. The swivel axis 609 projects in an orthogonal direction relative to the wheel axle 605. 14 When the industrial truck 600 is arranged horizontally, an offset is provided between the direction of the respective swivel axes 609 and a vertical direction so that symmetry lines of the respective swivel axes 609 intersect each other at a point P above the at least one pair of caster wheel assemblies 608.

The potential energy of the industrial truck 600 is lower the closer to the underlying surface 612 it is. Due to the orientation of the swivel axis 609 of the respective caster wheel assemblies 608, as well as the mirror symmetrical arrangement of the caster wheel assemblies 609 with respect to the centreline 604, it is energetically favourable for the caster wheels to face away from the centreline 604 during rotation of the caster wheels 602 about the swivel axis 609. This makes changes of direction in the longitudinal direction 604 of the industrial truck 600 smoother. The improved coordination of the rotation of the caster wheels 602 about the swivel axis 609 also reduces sideway perturbations.

The invention also relates to a method for arranging a pair of caster wheel assemblies under an industrial truck. The pair of caster wheel assemblies is positioned symmetrically on each side of a centreline of the industrial truck. Each caster wheel assembly comprises a yoke frame, a caster wheel and mounting means. The mounting means is/are arranged for connecting the caster wheel assembly to the industrial truck. The yoke frame is arranged to rotatably support the caster wheel for rotation around a wheel axle during motion of the industrial truck and is further rotatably connected to the mounting means to swivel about a swivel axis to align the caster wheel with a direction of motion. The swivel axis projects in an orthogonal direction relative to the wheel axle. When the industrial truck is arranged horizontally, an offset is provided between the direction of the respective swivel axes and a vertical direction so that symmetry lines of the respective swivel axes intersect each other at a point above the at least one pair of caster wheel assemblies.

During a sharp turn of the industrial truck, the pressure on the caster wheel would usually shift towards the edge of the caster wheel that is the farthest from the centre of rotation, due to the inertia associated with the moving truck. By arranging the swivel axis at an angle, as described above, the pressure is distributed more evenly over a slightly larger area of contact between the caster wheels and the underlying surface, during sharp turns.

According to an aspect of the method, the offset of the direction of the swivel axis and the vertical direction forms an angle falling in a range of 1.00 to 5.0° and preferably in a range of 1.5° to 3.0°.

According to an aspect, the method comprises a step of arranging at least one shim so that a first mounting area of the mounting means bears against the at least one shim and a second mounting area of the mounting means bears against the industrial truck.

The technical effects and advantages of said aspects have been discussed above relating to the disclosed industrial truck and the disclosed caster wheel assembly.

Claims (10)

1. An industrial truck (100; 200a; 200b; 600) comprising at least one pair of caster wheel assemblies (108; 308a; 308b; 408; 508; 608) that are arranged mirror symmetrically on each side of a centreline (104; 304a; 304b; 404; 504; 604) of the industrial truck (100; 200a; 200b; 600), each caster wheel assembly (108; 308a; 308b; 408; 508; 608) comprising a yoke frame (303a; 303b; 403; 503; 603), a caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) and mounting means (106; 306a; 306b; 406; 506; 606) for connecting the caster wheel assembly (108; 308a; 308b; 408; 508; 608) to the industrial truck (100; 200a; 200b; 600), wherein the yoke frame (303a; 303b; 403; 503; 603) is arranged to rotatably support the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) for rotation around a wheel axle (105; 305a; 305b; 405; 505; 605) during motion of the industrial truck (100; 200a; 200b; 600) and is further rotatably connected to the mounting means (106; 306a; 306b; 406; 506; 606) to swivel about a swivel axis (309a; 309b; 409; 509; 609) to align the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) with a direction of motion, the swivel axis (309a; 309b; 409; 509; 609) projecting in an orthogonal direction relative to the wheel axle (105; 305a; 305b; 405; 505; 605), characterized in that, when the industrial truck (100; 200a; 200b; 600) is arranged horizontally, an offset is provided between the direction of the respective swivel axes (309a; 309b; 409; 509; 609) and a vertical direction so that symmetry lines of the respective swivel axes (309a; 309b; 409; 509; 609) intersect each other at a point (P) above the at least one pair of caster wheel assemblies (108; 308a; 308b; 408; 508; 608).

2. An industrial truck (100; 200a; 200b; 600) according to claim 1, wherein the offset of the direction of the swivel axis (309a; 309b; 409; 509; 609) and the vertical direction forms an angle (al; az; a3; al, as) falling in a range of 1.00 to 5.00 .

3. An industrial truck (100; 200a; 200b; 600) according to claim 2, wherein the angle (a1; az; a3; azI, a5) falls in the range of 1.0 to 3.0°. 17

4. An industrial truck (100; 200a; 200b; 600) according to any claims 1 to 3, wherein at least one shim (313a; 313b; 413; 513; 613) is arranged, at least in part, between the mounting means (106; 306a; 306b; 406; 506; 606) of the respective caster wheel assembly (108; 308a; 308b; 408; 508; 608) of the at least one pair caster wheel assemblies (108; 308a; 308b; 408; 508; 608) and the industrial truck (100; 200a; 200b; 600).

5. A caster wheel assembly (108; 308a; 308b; 408; 508; 608) for operational use under an industrial truck (100; 200a; 200b; 600), the caster wheel assembly (108; 308a; 308b; 408; 508; 608) comprising a yoke frame (303a; 303b; 403; 503; 604), a caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) and mounting means (106; 306a; 306b; 406; 506; 606) for connecting the caster wheel assembly (108; 308a; 308b; 408; 508; 608) to the industrial truck (100; 200a; 200b; 600), wherein the yoke frame (303a; 303b; 403; 503; 603) is arranged to rotatably support the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) for rotation around a wheel axle (105; 305a; 305b; 405; 504; 604) during motion of the industrial truck (100; 200a; 200b; 600) and is further rotatably connected to the mounting means (106; 306a; 306b; 406; 506; 606) to swivel about a swivel axis (309a; 309b; 409; 509; 609) to align the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) with a direction of motion, the swivel axis (309a; 309b; 409; 509; 609) projecting in an orthogonal direction relative to the wheel axle (105; 305a; 305b; 405; 505; 605), characterized in that, when the industrial truck (100; 200a; 200b; 600) is arranged horizontally, the caster wheel assembly (108; 308a; 309b; 408; 508; 608) is arranged to provide an offset between the direction of the swivel axis (309a; 309b; 409; 509; 609) and a vertical direction.

6. A caster wheel assembly (108; 308a; 308b; 408; 508; 608) according to claim 5, wherein the offset of the direction of the swivel axis (309a; 309b; 409; 509; 609) and the vertical direction forms an angle (a1; a2; a3; a4, a5) falling in a range of 1.00 to 5.00 and preferably in a range of 1.0 to 3.0°.

7. A caster wheel assembly (108; 308a; 308b; 408; 508; 608) according to claim 5 or 6, wherein the caster wheel assembly (108; 308a; 308b; 408; 508; 608) comprises offsetting means (313a; 18 313b; 413; 513; 613), the offsetting means (313a; 313b; 413; 513; 613) being arranged to offset the swivel axis (309a; 309b; 409; 509; 609) from the vertical direction.

8. A method for arranging a pair of caster wheel assemblies (108; 308a; 308b; 408; 508; 608) under an industrial truck (100; 200a; 200b; 600), positioned symmetrically on each side of a centreline (104; 304a; 304b; 404; 504; 604) of the industrial truck (100; 200a; 200b; 600), each caster wheel assembly (108; 308a; 308b; 408; 508; 608) being arranged for operational use under an industrial truck (100; 200a; 200b; 600), each caster wheel assembly (108; 308a; 308b; 408; 508; 608) comprising a yoke frame (303a; 303b; 403; 503; 603), a caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) and mounting means (106; 306a; 306b; 406; 506; 606) for connecting the caster wheel assembly (108; 308a; 308b; 408; 508; 608) to the industrial truck (100; 200a; 200b; 600), wherein the yoke frame (303a; 303b; 403; 503; 603) is arranged to rotatably support the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) for rotation around a wheel axle (105; 305a; 305b; 405; 505; 605) during motion of the industrial truck (100; 200a; 200b; 600) and is further rotatably connected to the mounting means (106; 306a; 306b; 406; 506; 606) to swivel about a swivel axis (309a; 309b; 409; 509; 609) to align the caster wheel (102; 202a; 202b; 302a; 302b; 402; 502; 602) with a direction of motion, the swivel axis (309a; 309b; 409; 509; 609) projecting in an orthogonal direction relative to the wheel axle (105; 305a; 305b; 405; 505; 605), characterized in that, when the industrial truck (100; 200a; 200b; 600) is arranged horizontally, an offset is provided between the direction of the respective swivel axes (309a; 309b; 409; 509; 609) and a vertical direction so that symmetry lines of the respective swivel axes (309a; 309b; 409; 509; 609) intersect each other at a point (P) above the at least one pair of caster wheel assemblies (108; 308a; 308b; 408; 508; 608).

9. A method according to claim 8, wherein the offset of the direction of the respective swivel axis (309a; 309b; 409; 509; 609) and the vertical direction forms an angle (a1; a2; a3; a4, a) falling in a range of 1.00 to 5.0° and preferably in a range of 1.5° to 3.0°. 19

10. A method according to claim 8 or 9, wherein the method further comprises a step of arranging at least one shim (313a; 313b; 413; 513; 613), at least in part, between the respective mounting means (106; 306a; 306b; 406; 506; 606) and the industrial truck (100; 200a; 200b; 600).