WO2014146163A1

WO2014146163A1 - A straddle carrier

Info

Publication number: WO2014146163A1
Application number: PCT/AU2014/000229
Authority: WO
Inventors: Tommy Schults
Original assignee: Tommy Schults
Priority date: 2013-03-20
Filing date: 2014-03-10
Publication date: 2014-09-25
Also published as: AU2014234950A1

Abstract

A straddle carrier which is operable to lift a shipping container and move so as to convey the lifted shipping container is disclosed. The straddle carrier has at least four weight-bearing portions which bear the weight of the shipping container when it is lifted by the straddle carrier. At least four weight-bearing portions of the straddle carrier are directly or indirectly connected and fixed in position relative to one another in at least the direction of the straddle carrier's forward movement. Also, at least four weight- bearing portions each have two or more separated wheels which support the respective weight-bearing portion on the ground. At least one of the wheels supporting each weight-bearing portion is able to move in a vertical direction relative to the weight- bearing portion.

Description

A STRADDLE CARRIER

TECHNICAL FIELD

[0001] The present invention relates to straddle carriers, and particularly small or "mini" straddle carriers.

BACKGROUND

[0002] In general, straddle carriers are a kind of equipment/vehicle used for lifting and conveying shipping containers, normally over relatively short distances. Straddle carriers may be said to fall into two general categories; namely "large" straddle carriers on the one hand, and small or "mini" straddle carriers on the other. The distinction between the two categories is discussed below.

[0003] Large straddle carriers are used mainly at major cargo shipping ports, to move shipping containers into position to be loaded onto ships, to transport shipping containers away from the cranes etc after they are unloaded from ships, etc. Due to the nature of major shipping port facilities where huge volumes of cargo (i.e. huge numbers of containers) must be loaded and unloaded on a time-critical basis, large straddle carriers used at such major port facilities are necessarily very large and heavy pieces of equipment, often capable of lifting multiple full shipping containers at once (which may weigh in excess 60 tonnes in total, not including the weight of the large straddle carrier itself). Also, to enable cargo to be loaded/unloaded as quickly as possible at major ports, large straddle carriers are often capable of moving (including whilst carrying one or more shipping containers) at relatively high-speeds, often up to 30 km/h (or even faster). Large straddle carriers are also typically designed to be able to lift or carry shipping containers high in the air. This can be important or necessary at major shipping ports where containers are often stacked high one on top of another (in multiple layers), while they are being stored and waiting to be loaded onto ships, etc. Hence, the frame/support/lifting structures of large straddle carriers typically extend high above the ground into the air.

[0004] Large straddle carriers are unsuitable for use in smaller non-shipping-port type applications/facilities such as, for example, distribution centres or temporary storage yards where smaller numbers/volumes of containers are taken (and perhaps temporarily stored) before individual containers are loaded onto trucks for separate delivery/distribution to their ultimate destination. Distribution centres for supermarkets or retail store chains, military storage/maintenance yards, etc, are possible examples of such facilities. Those skilled in the art will appreciate that numerous other examples of such or similar facilities may also exist. There are several reasons why large straddle carriers are generally unsuitable for use in such facilities. For one thing, large straddle carriers are often too large, and in particular too high, to fit inside storage warehouses or other buildings or sheds inside which shipping containers are often kept at such facilities. However, perhaps even more significantly, the weight of large straddle carriers is typically so great that it would damage (and ultimately destroy) the concrete or other sealed surface of the yard, roads, etc, on which the straddle carriers operate (i.e. the open areas in which the straddle carriers move around) at such facilities.

[0005] For this reason, small or "mini" straddle carriers are typically employed for lifting and transporting shipping containers at these kinds of smaller, non-port facilities. Compared to large straddle carriers, mini straddle carriers are much smaller and lower (e.g. they normally have a frame/structure that is only high enough to lift a single shipping container onto a truck, and they can often fit inside, and through the doors of warehouses, storage sheds, etc). Mini straddle carriers are also generally much lighter than large straddle carriers. For instance, many mini straddle carriers may have a maximum carrying capacity of approximately 30 tonnes (this being the rough maximum weight of a single, fully loaded 40-50 ft shipping container),

[0006] Whilst mini straddle carriers are generally considerably smaller and lighter than large straddle carriers, nevertheless the weight of existing mini straddle carriers, and the potential for damage to the concrete or other sealed surface of the yards, roads, etc, on which the mini straddle carriers operate, remains a significant issue. In particular, the concentration of pressure/stress on the ground surface beneath the wheels of existing mini straddle carriers can still be sufficiently high to cause damage to the concrete or other sealed surface, especially over time. It may therefore be desirable if this problem could be overcome or at least reduced.

[0007] It is to be clearly understood that mere reference herein to previous or existing apparatus, products, systems, methods, practices, publications or any other information, or to any associated problems or issues, does not constitute an acknowledgement or admission that any of those things individually or in any combination formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.

SUMMARY OF THE INVENTION

[0008] In one broad form, the invention relates to a straddle carrier which is operable to convey a shipping container, the straddle carrier having at least four weight- bearing portions which bear the weight of the shipping container, wherein:

at least four weight-bearing portions are directly or indirectly connected to one another, and fixed in position relative to one another at least in the direction of the straddle carrier's forward movement,

at least four weight-bearing portions each have two or more separated wheels which support the weight-bearing portion on the ground, and

at least one of the wheels supporting each weight-bearing portion is able to move in a generally vertical direction relative to the weight-bearing portion.

[0009] As mentioned above, the invention relates particularly to small or "mini" straddle carriers. Therefore, hereafter, references to a/the straddle carrier in explanations should generally be understood as referring to mini straddle carriers, unless the context dictates otherwise.

[0010] Embodiments of the invention will generally have at least four weight-bearing portions which bear the weight of the shipping container, for example, when the shipping container is lifted and/or conveyed by the straddle carrier. Thus, the weight of the shipping container (plus the weight of the straddle carrier itself) will be supported, on at least four distinct regions of the ground, by multiple wheels on the ground in each region, and the weight-bearing portions are the parts or portions of the straddle carrier which perform the weight-bearing function and which connect or extend to the wheels (or at least to the wheels' supporting structures) in each region.

[001 1] It is of course possible that some embodiments may have more than four weight-bearing portions (e.g. six or eight or more, or even an odd number). In any event, those skilled in the art will appreciate that four weight-bearing portions will ordinarily be the minimum number of weight-bearing portions required to stably support a shipping container as it is conveyed by the straddle carrier, bearing in mind that if the straddle carrier were to have only three or fewer weight-bearing portions there may be a risk that the straddle carrier could tip or topple over, which could present a potentially life-threatening hazard.

[0012] It is to be clearly understood that the form and configuration of the weight- bearing portions is not critical to the invention. Indeed, the weight-bearing portions could take any suitable form. Some examples might include simple vertical (or near vertical) uprights (e.g. resembling pillars or posts), or multiple structural members which together form one single weight-bearing portion (these could perhaps distribute the load between them in a similar manner to a truss or space frame structure), or curved structural members or structural members of other shapes, etc. It is envisaged that, in some embodiments, at least four of the weight-bearing portions may be, or include, substantially vertical uprights. However, as has been said, no particular limitation is to be implied in this regard.

[0013] As mentioned above, in embodiments of the present invention, at least four weight-bearing portions will generally be fixed in position relative to one another in (at least) the direction of the straddle carrier's forward movement. It should therefore be understood that, for at least four weight-bearing portions, the position of one said weight-bearing portion relative to another said weight-bearing portion in a direction (or along an axis) parallel to the straddle carrier's direction of forward movement cannot change. Often, the direction of forward movement of the straddle carrier may correspond to the straddle carrier's "long" or "lengthwise" dimension. Where this is so, and where the straddle carrier has a total of four weight-bearing portions, the distance between those weight-bearing portions will remain fixed in the straddle carrier's lengthwise direction. It may be possible, however, that weight-bearing portions of the straddle carrier could be movable relative to one another in other directions. For example, it may be possible for the weight-bearing portions (or some of them) to move closer together or further apart in the straddle carrier's "widthwise" direction (i.e. sideways "in and out", perpendicular to the straddle carrier's direction of forward movement). This may allow the widthwise distance between weight-bearing portions (e.g. on respective sides of the straddle carrier) to be increased or decreased, perhaps to accommodate larger or smaller shipping containers, or to assist in positioning and connecting the straddle carrier relative to a shipping container, etc. The weight-bearing portions of the straddle carrier (or some of them) could also be extendable/retractable in a generally vertical direction (e.g. telescopically or in some other way) to alter/adjust the vertical length/height of the said weight-bearing portion(s) or of the straddle carrier as a whole.

[0014] It will generally be the case that at least four weight-bearing portions will each have two or more separated (or spaced apart) wheels which support the weight- bearing portion on the ground. In other words, on each one of four or more weight- bearing portions, there will be two or more separated wheels supporting that weight- bearing portion on the ground. In this regard, by "separated" it is meant that two or more wheels of a given weight-bearing portion are spaced apart relative to one another and not positioned immediately beside or side-by-side each other (this might otherwise cause the two or more wheels to operate, in effect, as a single wheel in terms of the way pressure caused by the weight of the straddle carrier and its load is applied to the ground). In embodiments of the present invention, the wheels of the straddle carrier may each be separated by a distance which is, at least, the same as the wheel radius. Often, the separation between wheels will be greater than a wheel radius.

[0015] It will generally also be the case that at least one of the wheels supporting each weight-bearing portion will be able to move in a generally vertical direction relative to the weight-bearing portion. The reason for this is to allow the straddle carrier to travel over bumps or traverse uneven ground, and to help ensure that weight still remains distributed over (i.e. is still borne by) the wheels (rather than becoming borne by individual or particular wheels) when doing so. This will be discussed further below.

[0016] In embodiments such as some referred to briefly above, where at least four of the weight-bearing portions are (or include) substantially vertical uprights, the uprights may be substantially rigid and directly or indirectly connected to one another. They may be connected by substantially rigid connecting members, and if so, the uprights and connecting members together may form a substantially rigid frame of the straddle carrier. In certain particular embodiments, the straddle carrier frame may have a total of four uprights. The connecting members may be inextensible, and if so, this may prevent, for example, uprights of the straddle carrier being movable relative to one another in the widthwise direction.

[0017] It is discussed above that each one of four or more weight-bearing portions of the straddle carrier will generally have two or more separated wheels supporting that weight-bearing portion on the ground. In some embodiments, the wheels supporting each individual weight-bearing portion may be separated from each other, one in front of another in the direction of the straddle carrier's forward movement. In particular, the wheels supporting each individual weight-bearing portion may be arranged (relative to one another) substantially in a line in the direction of the straddle carrier's forward movement. Positioning respective wheels of a given weight-bearing portion relative to each other in this way may be advantageous, not only in that pressure applied to the ground by the wheels is applied at spaced apart locations beneath each said wheel, but also because orienting the wheels in a line in the direction of the straddle carrier's forward movement (rather than, say, in the straddle carrier's widthwise direction) means that the wheels may not be positioned underneath or otherwise in the way of the shipping container (which typically have an elongate shape). In other words, positioning the wheels in this way may at least help to minimize the extent to which the wheels get in the way of the shipping container, and/or improve the ease with which the straddle carrier can be positioned or moved around relative to the shipping container, etc. Also, it may help to minimize the problem that, if wheels supporting a given weight- bearing portion were to be spaced from each other in the straddle carrier's widthwise direction, some wheels may then be positioned further away from the shipping container than others potentially causing some wheels to support more of the weight whilst others support little or no weight. By positioning respective wheels in a line in the direction of the straddle carrier's forward movement, it may be possible (or easier) to ensure that the weight is at least somewhat more evenly borne/shared by the different wheels.

[0018] For the avoidance of doubt, it should be clearly understood that the wheels which support each weight-bearing portion on the ground may attach to the weight- bearing portion in any suitable way. Therefore, the way in which the wheels attach is not critical to the invention. In some embodiments, for each individual weight-bearing portion, or for some of the individual weight-bearing portions, the wheels supporting the given weight-bearing portion may be connected to the weight-bearing portion by a bogie. In these embodiments, for each individual weight-bearing portion that has an associated bogie, the bogie may be pivotable relative to the weight-bearing portion to allow at least one wheel to move in a vertical direction relative to the weight-bearing portion. For each individual weight-bearing portion that has an associated bogie, the wheels may be mounted to the bogie so as to be arranged substantially in a line in the direction of the straddle carrier's forward movement. The reason why this may be advantageous is explained above. Often, for each individual weight-bearing portion that has an associated bogie, the associated bogie will be pivotally connected to a part of the weight-bearing portion which is close to the ground. In certain particular embodiments, for each individual weight-bearing portion that has an associated bogie, there may be two wheels per bogie, one wheel connected towards the front of the bogie and the other connected towards the back of a bogie, and a part of the weight-bearing portion which is close to the ground may connect to the bogie in between and approximately equidistant the respective wheels.

[0019] Straddle carriers in accordance with embodiments of the present invention may include means for lifting the shipping container. Importantly, the particular form or configuration of the said lifting means is not critical to the invention. Therefore, any form, kind or configuration of lifting means suitable for lifting a shipping container may be used. In some embodiments, the means for lifting the shipping container may include one or more flexible members operable to attach to one or more points on the shipping container, and means for retracting the flexible member(s) towards a part of the straddle carrier which is above the shipping container while the flexible member(s) are attached to the shipping container such that the container is lifted. The one or more flexible members may comprise, for example, one or more metal cables or chains, although the invention is by no means limited to this and other forms of flexible members may be used. The means for retracting the flexible member(s) may comprise one or more hydraulic cylinders each containing a piston to which one or more of the flexible member(s) are directly or indirectly connected, and for each hydraulic cylinder, pressurizing the hydraulic cylinder may cause the piston to move whereupon the flexible member(s) may be caused to retract towards the said part of the straddle carrier which is above the shipping container.

[0020] In straddle carriers according to embodiments of the present invention, at least some wheels of the straddle carrier may be driven, and rotation of said driven wheels may cause the straddle carrier to move. Also, at least some wheels of the straddle carrier may turn (i.e. pivot) about an axis which is approximately vertical, and said turning of said wheels while the straddle carrier is moving may be used to steer the straddle carrier. In relation to wheels which can turn to steer the straddle carrier, the amount that each such wheel turns in a given direction relative to the amount that others of said wheels turn in said direction may be controlled by a steering linkage so that all said wheels turn the correct amount, given that said wheels which are located at different positions relative to the straddle carrier must trace out paths of different instantaneous radii as the straddle carrier is steered.

[0021] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[0023] Figure 1 is a perspective illustration of a straddle carrier in accordance with one possible embodiment of the invention carrying a shipping container.

[0024] Figure 2 is a side on view of the straddle carrier and shipping container in Figure 1.

[0025] Figure 3 is an end-on view of the straddle carrier and shipping container in Figure 1 (from the rear).

[0026] Figure 4 is a plan (i.e. top-down) view of the straddle carrier and shipping container in Figure 1.

DETAILED DESCRIPTION [0027] Before discussing the particular embodiment of the invention shown in the drawings, it is useful to refer again to the problem outlined above; namely that, even for existing small or "mini" straddle carriers, the concentration of pressure/stress beneath the wheels of the straddle carrier can be sufficiently high to cause damage to the concrete or other sealed surface on which the straddle carrier operates, especially over time.

[0028] This is a particular problem because many existing and previously-proposed mini straddle carriers designs have a frame that includes a number of (typically four) vertical legs which together bear the weight of the shipping container (plus the weight of the straddle carrier itself), and wherein there is only a single wheel located at the base of (or immediately beneath) each leg (or occasionally two wheels mounted coaxially immediately side-by-side each other at the base of or beneath each leg). By providing only one wheel at the base of each leg (or two immediately side-by-side wheels, which amounts to much the same thing practically), the weight of the shipping container together with the weight of the straddle carrier itself is concentrated solely in the four locations immediately below each leg where the single wheels of each of the legs contact the ground.

[0029] At this point, it might be assumed that this problem could be addressed or adequately minimised simply by increasing the size of the wheels (or the tyres thereof) so that the surface area of the wheel(s) (hereafter reference to wheel(s) includes the tyre(s) thereof) which is in contact with the ground at the base of each leg is increased. This, it might be thought, would effectively spread the weight over a greater surface area, thereby reducing the pressure on the concrete surface. However, it has been found that, whilst this might seem to make intuitive sense, on the contrary simply increasing the size of the wheels does not necessarily reduce or prevent damage from being caused to the concrete or other sealed surface, particularly over time.

[0030] A possible explanation for this may lie in the fact that, even though increasing the size of the wheel increases the surface area which is in direct contact with the ground (spreading the immediately transferred mass over a larger area), nevertheless the actual mass which is supported at the base of each leg is unchanged by increasing wheel/tyre size. This is important when the structure of the concrete or other ground surface is considered. Typically, the hard surface which the wheels are in direct contact with (normally made from concrete, bitumen, etc) is only a comparatively thin layer (often 6 inches thick or less) which rests immediately on top of a sublayer typically comprising sand or gravel (or a mixture thereof). This layer of sand/gravel itself then typically sits on top of a further base layer of ground soil. As a result, even though the top concrete/bitumen layer forms a hard surface the material structure of which holds itself together as (essentially) a solid, the underlying layer of sand/gravel immediately therebeneath is often much looser and not held together as a solid (this sand/gravel layer generally has no inherent material structure holding it together). Therefore, this sand/gravel layer has a much greater propensity to move or shift when subjected to large pressures/stresses (i.e. pressures/stresses applied to it by/through the solid concrete/bitumen layer above). This is particularly so given that the sand/gravel layer sits upon a ground soil layer which also has a propensity to shift/move. Consequently, even if the size of the straddle carrier wheels are increased so as to increase the surface area over which the borne mass is directly applied to the upper concrete/bitumen layer, nevertheless the same total mass will still be applied in the localised area immediately beneath each leg of the straddle carrier, meaning that the amount of pressure/stress applied to the underlying sand/gravel in that region is not necessarily lessened. Consequently, the possibility of this giving rise to movement/shifting/subsidence in the sand/gravel layer and/or the ground soil layer, which can in turn lead to cracking or failure of the top concrete/bitumen layer (especially over time) is not necessarily lessened.

[0031] This is one of the reasons why, in straddle carriers according to embodiments of the present invention, at least four weight-bearing portions each have two or more separated wheels (i.e. wheels which are spaced apart from each other) which support the weight-bearing portion on the ground. In this way, the overall mass of the straddle carrier plus its load truly is more spread out and distributed; i.e. the load is shared between or spread over a greater number of spaced apart contact points, such that each individual contact point (and the various concrete/sand -gravel/soil layers beneath it) truly does bear less of the overall load, thus reducing the propensity for damage for the reasons described above.

[0032] The drawings show a straddle carrier in accordance with one possible embodiment of the invention carrying a shipping container. The general way in which the straddle carrier transports the shipping container can be easily appreciated from the drawings.

[0033] From Figure 1 , it can be seen that the frame of the straddle carrier includes four main uprights 10a-10d. Uprights 10a and 10b are the straddle carrier's front uprights, and uprights 10c and 10d are the straddle carrier's rear uprights (upright 10d is visible only in Figure 3; it is hidden from view in the other Figures). The uprights 10a- 10d, together with the diagonal bracing members 12 associated with each respective upright, function as weight-bearing portions (for bearing at least the vertical components of the load, plus the vertical load created by the straddle carrier's self-weight). The respective uprights are supported above the ground by the straddle carrier's wheels etc as discussed below. [0034] The uprights 10a-1 Od are connected to one another by other frame members (i.e. other parts of the straddle carrier's frame). These other frame members include the elongate top bearers 141 and 14r, the transverse connecting members 16f and 16r and the longitudinal connecting members 181 and 18r (longitudinal connecting member 18r is hidden from view in the Figures but it essentially mirrors longitudinal connecting member 181). There is also a bogie pivotally connected to the base of each of the uprights. The bogie connected to the base of upright 10a is labelled as bogie 20a, the bogie connected to the base of upright 10b is labelled as bogie 20b, etc.

[0035] The straddle carrier has a driver's cabin 22. The controls for operating the straddle carrier are located inside the cabin 22, such that a driver can sit inside the cabin 22 to drive the straddle carrier and operate the straddle carrier's other functions (e.g. the lifting mechanism - see below). The driver's cabin 22 is mounted to or otherwise supported (directly or indirectly) by the longitudinal connecting member 181. The driver's cabin 22 is therefore located partially beneath the longitudinal connecting member 181. Also mounted to or supported (directly or indirectly) by the longitudinal connecting member 81 is the straddle carrier's engine. The engine itself is not shown in the Figures, but the engine cover 24 is clearly visible immediately behind the driver's cab and 22. The engine and associated equipment are housed inside the engine cover 24. A fuel tank 26 is also supported underneath the engine cover 24.

[0036] Pump(s) (engine driven), valves, etc, which operate the straddle carrier's hydraulic systems (based on driver controls) are located near the engine, many just behind and/or above the engine cover 24. Hydraulic lines (not individually labelled in the drawings) which convey fluid to different parts of the straddle carrier can also be seen. For example, there are hydraulic lines extending from the engine area:

directly to the rear wheels attached to bogie 20c, up upright 10c, along the forward-facing side of connecting member 16r and down upright 10d to the rear wheels attached to bogie 20d,

along the outside of the longitudinal connecting members 181 and 18r and down the front uprights 10a and 10b towards the straddle carrier's front wheels,

etc.

[0037] Parts of the straddle carrier which are operated by the fluid delivered by these hydraulic lines include:

hydraulic motors located inside the straddle carrier's four rear wheels, namely the wheels attached to bogie 20c and bogie 20d (the hydraulic motors in these rear wheels drive rotation of the said wheels in order to impart motion to the straddle carrier),

the straddle carrier's steering mechanism (discussed below),

the straddle carrier's lifting mechanism (discussed below),

etc.

[0038] As just mentioned, the straddle carrier has a hydraulically driven steering mechanism. In this embodiment, the four front wheels can turn to steer the straddle carrier. That is to say, the two wheels attached to front bogie 20a, and the two wheels attached to front bogie 20b, can turn in order to steer that straddle carrier. Note that in Figure 1 , only the two wheels attached to front bogie 20a are shown in a "turned" orientation. The other two front wheels (the two wheels attached to front bogie 20b) appear to be facing straight ahead. This would not occur in practice. In practice, all four of the front wheels would turn at the same time in order to steer the straddle carrier smoothly. Whilst all four front wheels turn at the same time in a given direction, the amount that each one turns in said direction relative to the amount that the others turn in said direction is controlled by a steering linkage. This is so that the four respective front wheels each turn the correct amount (and the amount that each individual wheel turns may be different to the others). The reason why each of the four front wheels will often turn by a different amount is because the four front wheels are located at different positions and must therefore trace out curved paths of different instantaneous radii as the straddle carrier is steered.

[0039] A part of the steering linkage 28 which connects the two wheels of bogie 20a, and which helps to ensure those two wheels turn the correct amount relative to one another, is visible in Figure 1. A similar steering linkage is present on bogie 20b, although this is hidden from view in the Figures. The straddle carrier can be steered using controls housed in the driver's cabin 22. In other words, controls in the driver's cabin 22 can be used to operate steering linkages to turn the front wheels, and naturally if this is done (i.e. if the front wheels are turned) while the rear wheels are being driven to impart motion to the straddle carrier, the straddle carrier will "corner" (i.e. it will traverse a curved path according to the instantaneous orientation of the front wheels).

[0040] The straddle carrier is also able to lift a shipping container. More specifically, the straddle carrier is able to lift the shipping container off the ground so that the shipping container can be transported, and it can lower the shipping container back to the ground afterwards. To this end, the straddle carrier has four flexible members which, in this embodiment, comprise metal chains/cables. There is one cable/chain for attachment to each of the four base comers of the shipping container. The chains/cables are labelled 30a, 30b, 30c and 30d in the drawings. There is also a hydraulic lifting cylinder 32a, 32b, 32c and 32d associated with each of the respective chains/cables. The hydraulic cylinders are generally elongate in shape. Cylinders 32a and 32c are positioned and extend along the top of the left hand top bearer 141 while cylinders 32b and 32d are positioned and extend along the top of the right hand top bearer 14r. Cylinders 32a and 32b are oriented such that their respective chains/cables (30a and 30b) extend along and over the front ends of the top bearers (so that these two cable/chains can extend down to attach to the forward two base comers of the shipping container), whereas cylinders 32c and 32d are oriented such that their respective chains/cables (30c and 30d) extend along and over the rear ends of the top bearers (so that these two cables/chains can extend down to attach to the rearward two base corners of the shipping container). A pulley is provided on either end of both of top bearers 141 and 14r. The pulleys operate as a guide for the respective cables/chains, and help to prevent damage to the cables/chains and the top bearers as the cables/chains move.

[0041] Each of the hydraulic lifting cylinders contains a piston, with the piston being linked to the cable/chain associated with that particular cylinder. Pressurizing a cylinder causes the piston inside the cylinder to move in a direction that causes the associated chain/cable to retract away from the ground (i.e. upwards). It will therefore be appreciated that, if all four chains/cables are first attached to respective base corners of the shipping container and the hydraulic cylinders are then pressurised simultaneously, the four chains/cables will be withdrawn away from the ground thus causing the shipping container to be lifted off the ground and into the air (i.e. to become suspended by the straddle carrier as shown). Controls may be provided to ensure that (or at least help enable) all of the pistons (to) move (and therefore all of the cables to retract) at the same speed such that the shipping container is lifted in a controlled, level manner (i.e. so that the shipping container does not tip or roll whilst being lifted). The shipping container can be lowered to the ground by reversing the lifting process.

[0042] It should be noted that the wheels of the straddle carrier, and even wheels which are connected to the same bogie, are separated from each other by an appreciable distance. This distance (i.e. the separation between wheels) is at least equal to the radius of the wheels, and generally more. In the illustrated embodiment, the distance between pairs of front wheels which are attached to a common front bogie is also greater than the distance between pairs of rear wheels which are attached to a common rear bogie. The reason for the separation (i.e. distance) between individual wheels, as has previously been explained, is to distribute the straddle carrier load over a greater number of separated (i.e. spaced apart) contact points, such that each individual contact point (and the various concrete/sand-gravel/soil layers beneath each contact point) bears less of the overall load, thus reducing the propensity for damage to the concrete surface for the reasons described above.

[0043] As also mentioned above, the respective bogies are pivotally attached to their respective uprights. That is, bogie 20a is pivotally attached at the base of upright 10a, bogie 20b is pivotally attached at the base of upright 10b, etc. On each bogie, the location where the bogie is connected to the upright is at the centre of the bogie, equidistant between each of the bogie's wheels. The pivotal connection between each bogie and its upright means that the bogies are able to pivot relative to the uprights. This is illustrated in Figure 2, where the rear bogie 20c is shown in a slightly pivoted orientation compared to the front bogie 20a.

[0044] In Figure 2, it may be envisaged that the front wheels (those attached to bogie 20a) are resting on or moving over level/horizontal ground, however the rear wheels (those attached to bogie 20c) are resting on or moving over slightly uneven ground which slopes slightly upwards in the straddle carrier's direction of forward movement. In this situation, despite the slightly angled inclination of the ground beneath the rear wheels, nevertheless both wheels attached to bogie 20c remain in contact with the ground and therefore both wheels continue to support the straddle carrier.

[0045] By way of further explanation consider the following hypothetical example: in Figure 2, if bogie 20c were instead rigidly (non-pivotably) fixed on the end of upright 10c (and therefore bogie 20c could not pivot relative to upright 10c, and if the wheels could not otherwise move vertically relative to the upright), then in this hypothetical situation when the forward wheel of bogie 20c reached the sloped section of ground, that forward wheel would begin to move up the slope. However, as the forward wheel of bogie 20c began to move up the slope, this would cause the rearward wheel of bogie 20c to be un-weighted or it might even lift into the air (recall that the bogie 20c cannot pivot in this hypothetical situation). This would mean that the entire proportion of the weight borne by upright 10c would then be transferred to the ground by a single wheel (the forward wheel of bogie 20c) and therefore would not be shared between the two spaced apart wheels of bogie 20c. This could potentially cause or lead to damage to the concrete surface, etc. The pivotal connection of the bogies in the illustrated embodiment (and more generally, the way one or more wheels supporting each weight- bearing portion can move in a vertical direction relative to the weight-bearing portion in other embodiments of the invention) therefore helps to address this problem.

[0046] In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0047] Reference throughout this specification to One embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0048] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

A straddle carrier which is operable to convey a shipping container, the straddle carrier having at least four weight-bearing portions which bear the weight of the shipping container, wherein:

at least four weight-bearing portions are directly or indirectly connected and fixed in position relative to one another in at least the direction of the straddle carrier's forward movement,

A straddle carrier as claimed in claim 1 wherein at least four of the weight- bearing portions are, or include, substantially vertical uprights.

A straddle carrier as claimed in claim 2 wherein the uprights are substantially rigid and directly or indirectly connected to one another by substantially rigid connecting members such that the uprights and connecting members together form a substantially rigid frame of the straddle carrier.

A straddle carrier as claimed in claim 3 wherein the straddle carrier frame has a total of four uprights.

A straddle carrier as claimed in any one of the preceding claims, wherein the wheels supporting each individual weight-bearing portion are separated from each other, one in front of another in the direction of the straddle carrier's forward movement.

A straddle carrier as claimed in claim 5, wherein the wheels supporting each individual weight-bearing portion are arranged substantially in a line in the direction of the straddle carrier's forward movement.

7. A straddle carrier as claimed in any one of the preceding claims wherein, for each individual weight-bearing portion, or for some of the individual weight- bearing portions, the wheels supporting that weight-bearing portion are connected to the weight-bearing portion by a bogie.

8. A straddle carrier as claimed in claim 7 wherein, for each individual weight- bearing portion that has an associated bogie, the bogie is pivotable relative to the weight-bearing portion to allow at least one wheel to move in a generally vertical direction relative to the weight-bearing portion.

9. A straddle carrier as claimed in claim 7 or 8 wherein, for each individual weight- bearing portion that has an associated bogie, the wheels are mounted to the bogie so as to be arranged substantially in a line in the direction of the straddle carrier's forward movement.

10. A straddle carrier as claimed in claim 7, 8 or 9 wherein, for each individual weight-bearing portion that has an associated bogie, the associated bogie is pivotally connected to a part of the weight-bearing portion which is close to the ground.

11. A straddle carrier as claimed in any one of claims 7 - 10 wherein, for each individual weight-bearing portion that has an associated bogie, there are two wheels per bogie, one wheel connected towards the front of the bogie and the other connected towards the back, and a part of the weight-bearing portion which is close to the ground connects to the bogie in between and approximately equidistant the respective wheels.

12. A straddle carrier as claimed in any one of the preceding claims wherein the wheels of the straddle carrier are each separated by a distance which is, at least, the same as the wheel radius.

13. A straddle carrier as claimed in any one of the preceding claims including means for lifting the shipping container.

14. A straddle carrier as claimed in claim 13, wherein the means for lifting the shipping container includes one or more flexible members operable to attach to one or more points on the shipping container, and means for retracting the flexible member(s) towards a part of the straddle carrier which is above the shipping container while the flexible member(s) are attached to the shipping container.

15. A straddle carrier as claimed in claim 14, wherein the one or more flexible members comprise one or more metal cables or chains.

16. A straddle carrier as claimed in claim 14 or 15, wherein the means for retracting the flexible member(s) comprises one or more hydraulic cylinders each containing a piston to which one or more of the flexible member(s) are directly or indirectly connected, and wherein for each hydraulic cylinder, pressurizing the hydraulic cylinder causes the piston to move whereupon the flexible member(s) are caused to retract towards the said part of the straddle carrier which is above the shipping container.

17. A straddle carrier as claimed in any one of the preceding claims wherein at least some wheels are driven, and rotation of said driven wheels causes the straddle carrier to move.

18. A straddle carrier as claimed in any one of the preceding claims wherein at least some wheels can turn about an axis which is approximately vertical, and said turning of said wheels while the straddle carrier is moving can be used to steer the straddle carrier.

A straddle carrier as claimed in claim 18 wherein, in relation to wheels which can turn to steer the straddle carrier, the amount that each such wheel turns in a given direction relative to the amount that others of said wheels turn in said direction is controlled by a steering linkage so that all said wheels turn the correct amount, given that said wheels which are located at different positions must trace out circles of different radii as the straddle carrier is steered.