Telescopic boom

The present invention relates to a telescopic boom with at least one outer structure and at least one inner structure, each of which is designed as a hollow section with upper flange and lower flange, the upper flange having a half-basket profile with two rounded edges to which the lower flange is joined with a liner of an essentially U-shaped profile, and each structure being mounted on the adjoining structure with a front and a back bearing. To achieve a stable bearing of the structures and a great usable extension length with this boom under high force level, the invention proposes that the front bearing has a slide element in the area between the lower flanges only in the region of the curvature, and the back bearing has a separate plain bearing half liner in the area between the upper flanges only in the region of each rounded edge.

TECHNICAL FIELD 
The present invention relates to a telescopic boom comprising at least one 
outer structure and at least one inner structure, each of which is 
designed as a hollow section with an upper flange connected to a lower 
flange. The upper flange has a half-basket profile with a web portion 
extending between two rounded edge portions (also referred to herein as 
rounded corner portions) and opposing side portions connected to and 
extending away from the edge portions. The lower flange has an essentially 
U-shaped profile and is connected to the side portions of the upper 
flange. Each outer and inner structure is mounted on an adjoining outer or 
inner structure with a front and rear bearing assembly. 
BACKGROUND OF THE INVENTION 
Booms of this type are known from practice, for instance from mobile 
cranes. A load is hung on the front end of an extended inner structure so 
that the inner structure with its lower flange exerts a load on the front 
end section of the lower flange of the outer structure. At the same time, 
the rear end of the inner structure exerts a load on the upper flange of 
the outer structure with its upper flange. Within the scope of this 
invention, "front" designates the direction towards the load-receiving 
free end of the boom, and "rear" designates the direction towards the end 
opposite to the free boom end. 
On account of the great forces to be transmitted, special attention has to 
be paid to the design of the front and rear bearings connected to the 
inner and outer structures. Apart from a reliable support, these bearings 
are also designed to counteract undesired deformations of the profile 
cross-sections of the inner and outer structures. Normally, full support 
of slide elements of the front and rear bearings is therefore sought to be 
achieved. The slide elements are each fixed on one side to a laterally 
bordered plane bearing block on one of the inner or outer structures and 
the slide elements are each supported on the adjoining outer or inner 
structure at the opposite side of the respective slide element. 
Reinforcing support means in the form of collars are required for 
receiving the forces acting on the slide elements and the bearing blocks. 
As a rule, the collars on the inner structures for the rear bearings are 
made continuous over the cross-sectional shape of the inner structure and 
jointly form an enclosure for the slide elements, whilst the collars of 
the front bearings are normally mounted externally on the outer structure 
and consist of solid material with a dimension of 150 to 300 mm in the 
longitudinal direction of the boom. The collars thereby reduce the usable 
extension length of the structure in question. As shown in FIG. 6 (prior 
art), the inner structures cannot be fully telescoped into one another, as 
they are hindered from doing so by the inner collars. The same happens 
analogously in the region of the front bearing with the outer collars. 
DE-OS 1531174 suggests a roller bearing for telescopic booms with a 
polygonal cross-section. To receive the edge stresses occurring upon load, 
each edge of the lower flange has assigned thereto an outer roll, and each 
edge of the upper flange an inner roll. The outer and inner rolls present 
obstacles to one another in a disadvantageous manner, whenever the 
structures are slid into one another, so that the usable extension length 
of the structures is reduced at least by the sum of the diameter of the 
rolls arranged side by side. Moreover, the inner rolls occupy a lot of 
space in the hollow profile cross-section of the inner structure, so that 
there is only little space for the telescopic cylinder unit arranged 
therein for extending the boom. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide a telescopic boom of 
the type outlined at the outset, which boom is able to receive a high 
force level and which is distinguished by a stable bearing of the 
structures and a great usable extension length. 
This object is achieved according to the invention in that the front 
bearing assembly has a slide member, also referred to as a slide element, 
in the area between the lower flanges only in a region of curvature of the 
lower flanges, and a rear bearing assembly has a separate slide member, 
referred to as a "plain bearing half liner" in an area between the upper 
flanges only in a region of each rounded edge or corner portion of the 
upper flanges. 
On account of such a support provided by the present invention, the forces 
between two adjacent outer and inner structures are only transmitted via 
rounded portions of the outer and inner structures that are substantially 
stiffer than the straight surface of the bearings. This prevents bulging 
of the surfaces and deformation of the profile cross-section of the outer 
and inner structures. The function of the collar can substantially be 
limited to the measure of preventing the structure from expanding at its 
end. Since the collar need no longer receive the support forces to the 
full extent, it can be made substantially shorter in the longitudinal 
direction of the structures. In practice, the collar can be reduced to a 
length of about 50 mm. This means that the individual structures, as shown 
in FIG. 5, can be moved into one another to a substantially greater 
degree, so that a larger usable extension length of the telescopic boom is 
available. 
On the other hand, the slide element and the plain bearing half liners of 
the front and rear bearing assemblies, respectively, may be made 
considerably thinner. Whilst in the prior art thicknesses of 40 to 50 mm 
are still required, the thickness in the inventive solution can be reduced 
to less than 20 mm. This means that in an outer structure there is more 
space for additional inner structures which increase the usable extension 
length. With the support provided by the present invention, it is possible 
to slide seven structures into one another without any problem, and the 
cross-section of the outermost structure does not exceed the outer 
cross-section of conventional telescopic booms. With the supports 
according to the prior art, it has so far only been possible to slide a 
maximum of five structures into one another. 
Moreover, the tolerances of the slide element and the plain bearing half 
liners of the front and rear bearing assemblies, respectively, can quite 
accurately be adapted to the rounded corner portions in the upper flange 
and the region of curvature of the lower flange. The front and rear 
bearing assemblies permit slight deformations of the straight side 
portions of the structures' cross-sections whilst the rounded corner 
portions and the regions of curvature in the upper and lower flanges, 
respectively, provide support of the structures within one another. As a 
result, additional tolerance compensating elements as have normally been 
required in the prior art can be dispensed with. 
The slide element and the plain bearing half liners of the front and rear 
bearing assemblies, respectively, are advantageously self-centered at the 
rounded corner portions of the upper flanges and at the regions of 
curvature of the lower flanges. As a consequence, the slide elements and 
the plain bearing half liners need not be fixed in the circumferential 
direction of their respective cross section. 
In an especially advantageous embodiment, the rear bearing in the area 
between the lower flanges comprises at least one liner-shaped slide 
element which extends at least partially along each of the regions of 
curvature, also referred to herein as curved sides of the lower flanges. 
This arrangement of the slide elements between adjacent lower flanges is 
especially advantageous for receiving lateral forces which are for 
instance created when a mobile crane having a telescopic boom of the 
present invention is turned. The liner-shaped slide elements prevent 
torsion of the boom cross-section. 
The liner-shaped slide element of the rear bearing assembly comprises two 
separate sliding block elements in the area between the lower flanges, 
with a respective one of the sliding block elements being arranged along 
each of the curved sides of the lower flanges which adjoin the upper 
flanges. Hence, the liner-shaped slide element is divided into the two 
separate sliding block elements of which each receives the torsional 
forces. Accordingly, a supporting bearing in the lower U-shaped portion of 
the lower flange is unnecessary and is not a component of the telescopic 
boom of the present invention. This facilitates production of the profile 
cross-section in this area, since exact tolerances need not be indicated. 
In an alternate embodiment of the invention, the front bearing assembly, 
which is also referred to herein as a front bearing, comprises a separate 
slide member or "plain bearing half liner" in the area between the upper 
flanges only in the region of each rounded corner portion of the upper 
flanges. These additional plain bearing half liners between the upper 
flanges also prevent torsion of the inner and outer structures at the 
rounded corner portions. 
Preferably, the sliding block element and the plain bearing half liners of 
the rear bearing assembly are fixed to the inner structure. 
The slide element(s) and the plain bearing half liners of the front bearing 
assembly can specifically be fixed to the outer structure. 
In a preferred embodiment, the radial distance between inner and outer 
structures is greater in the area between the rounded corner portions than 
in the area between the straight portions of the upper flange. As a 
result, the plain bearing half liners can be made slightly thicker in the 
area of the rounded corner portions so that they are capable of 
transmitting greater forces. The remaining space in the straight portions 
is minimized in a space-saving manner. 
Possibly, the center point of the outer rounded corner portion of the outer 
structure's upper flange and the center point of the inner rounded corner 
portion of the inner structure's upper flange are arranged in spaced-apart 
fashion, with the center point of the outer rounded corner portion being 
arranged closer to the outer rounded corner portion than the center point 
of the inner rounded corner portion. This increases the space for the 
plain bearing half liners in the space between the inner and outer rounded 
corner portions, whereby the distance can be kept small in the adjoining 
straight portions. 
Preferably, the plain bearing half liners between the rounded corner 
portions and/or the slide elements between the lower flanges extend beyond 
the curved portions into the straight side portions of the upper flanges, 
with the plain bearing half liners and the slide elements resting, as the 
side of the structure moved relative, thereto, only in the curved area on 
said structure. This limits the support of the plain bearing half liners 
and the slide elements on the relatively moved structure to the, 
structure's stable curved portions (e.g., the rounded corner portions in 
the upper flanges and the regions of curvature in the lower flanges). This 
prevents jamming of the structures, since the end of the 
force-introducing-zone (curvature) does not coincide with the end edge of 
the plain bearing half liner. On the structure to which the slide element 
is, for instance, fixed, the slide element extends into the straight 
portions adjacent to the region of curvature, so that the slide element is 
positioned at the transition of curved and straight portions of the lower 
flange independently in the circumferential direction of the slide 
element's profile cross-section. 
Advantageously, the plain bearing half liners are fixedly attached to one 
of the inner and outer structures and the plain bearing half liners have 
inclined surfaces facing toward the adjacent other one of inner and outer 
structures to which the plain bearing half liner is not fixedly attached. 
The inclined surfaces extend away from the rounded corner portion of the 
upper flange and into the straight side or web portions of the upper 
flanges. The inclined surfaces are spaced apart from the straight side or 
web portions of the upper flanges which the respective inclined surface 
faces and defines an angle .alpha. relative to the straight side 
therebetween, so as to define an inclined starting zone. Similarly, each 
of the slide element is fixedly attached to the lower flange of one of the 
inner and outer structures, and the slide element has inclined surfaces 
facing toward the adjacent other one of the inner and outer structures to 
which the slide element is not fixedly attached. The inclined surface 
extends away from the region of curvature of the lower flange to which the 
slide element is not fixedly attached. The inclined surfaces are spaced 
apart from the lower flange which the inclined surfaces faces to define an 
angle .alpha. therebetween, so as to define an inclined starting zone. The 
inclined starting zones prevent the inner and outer structures from 
getting jammed. 
In one embodiment, the outer structure in the area of the front bearing 
includes a front collar and the inner structure in the area of the rear 
bearing has a rear collar which serve as an axial abutment of the slide 
element and plain bearing half liners, respectively. The collars reinforce 
the structure's profile and prevent an expansion or compression of the 
structures at their ends, with the slide bodies (e.g., the plain bearing 
half liners and slide elements) being simultaneously positioned on the 
collars. 
It is suggested that the sheet thickness of the front and rear collars is 
1.2 to 2.5 times the sheet thickness of the respective boom profile. 
In a variant of the invention, the sheet thickness of the upper flange 
differs from the sheet thickness of the lower flange. 
In one embodiment, the U-shaped cross-section of the lower flange comprises 
two spaced-apart curved portion's which are interconnected with a straight 
web arranged thereinbetween. This special profile cross-section of the 
U-shaped form has turned out to be especially suited, because the 
structure exhibits a great moment of resistance to bending. According to 
the invention the transverse forces are also introduced into the curved 
portions of the profile so that the whole profile is very resistant to 
bulging due to the effect of the curved portions. The membrane effect is 
thereby exploited. 
Preferably, the length of the straight web in the U-shaped lower flange to 
the profile width corresponds approximately to a ratio of 1:3. The 
distance of the straight sides between upper flange and lower flange of a 
structure must here be regarded as the profile width. 
The front bearing assembly should comprise a separate slide element in the 
area between the lower flanges in the area of each curved portion. The 
forces are solely transmitted via the curved portions also in the lower 
flange region of the front bearing. Tolerances in the width of the 
individual structures can be suitably compensated by the separate divided 
arrangement of the slide elements. Furthermore, there are no moments in 
the transition area to the straight side of the upper flange or to the 
straight web, respectively, since the circumferential tensions are 
introduced tangentially. 
Advantageously, the radial distance between inner and outer structures in 
the area of the round liners! curved portions of the U-shaped lower flange 
can be greater than the distance between the straight portions of the 
lower flange. 
In a preferred embodiment, the center point of the outer and the center 
point of the inner curved portion of the inner structure's lower flange 
are spaced apart from each other, with the center point of the outer 
center portion being arranged closer to the outer curved portion than the 
center point of the inner curved portion. 
The ratio of profile width to profile height is about 1:1.15 to 1:1.4. 
The ratio of the length of the straight side between a rounded edge! corner 
portion of the upper flange and the subsequent curved portion of the lower 
flange to the profile height may specifically be 1:1.6 to 1:2.

DETAILED DESCRIPTION OF THE INVENTION 
An outer structure 14 and an inner structure 16 are shown in each of FIGS. 
1 to 3. The inner structure 16 is positioned in the interior of a front 
section of the outer structure 14 over part of the inner structure's 
length. Each of the outer and inner structures 14 and 16 consists of two 
bent sheet-metal portions or half liners which are interconnected by 
longitudinal welds. The outer and inner structures 14 and 16 each include 
an upper flange 1 having a U-shaped cross-section with rounded corner 
portions R in the form of quarter circles. In FIGS. 2 and 3, the two 
rounded corner portions R of the inner structure 16 are designated by Ri, 
and the two rounded corner portions of the outer structure 14 are 
designated by Ra. The rounded corner portions extend over 60.degree. to 
90.degree.. 
The outer and inner structures 14 and 16 each also have a lower flange 2 
connected to the respective upper flange 1. Each lower flange 2 has a 
semicircular shape with a radius equal to half the width (b) of the 
associated upper flange 1. The radius of the lower flange 2 of the inner 
structure 16 is correspondingly smaller than the radius of the lower 
flange of the outer structure 16. Upper and lower flanges 1 and 2 may have 
different sheet thicknesses. 
The upper and lower flanges 1 and 2, which are welded together, have a 
front collar 7 at their respective front ends at the longitudinal side and 
a rear collar 8 at their respective rear ends in the form of sheets welded 
thereonto. These collars are made corrosion-proof and serve as bearings. 
Each lower flange 2 has assigned thereto a lower slide member, referred to 
as a slide element 10, of a front bearing assembly 3, and each upper 
flange 1 has assigned thereto upper slide members, referred to as "rear 
plain bearing half liners" 12 of a rear bearing assembly 4. 
The two collars 7 and 8 simultaneously form a stop for the slide element 10 
and rear plain bearing half liners 12 each of which is made of a plastic 
material, and which are provided at least in the area of the bearings 
between inner structure 16 and outer structure 14. A slide element 10 made 
of a plastic material, preferably polyamide, has a shape that corresponds 
to the semicircular interspace between the lower flange 2 of the inner 
structure 16 and the lower flange of the outer structure 14, and the slide 
element is provided in the area of each front bearing assembly 3 assigned 
to the lower flange 2. Furthermore, in the area of each rear bearing 
assembly 4 attached to the upper flange 1, supporting rear plain bearing 
half liners 12 are provided at least in the two interspaces between the 
inner structure's upper flange and outer structure's upper flange 1 in the 
area of the two rounded corner portions Ri and Ra, as illustrated in FIG. 
3. The semicircular slide element 10 advantageously extends upwards up to 
the horizontal line designated by C in FIGS. 2 and 3. 
The rear plain bearing half liners 12 are each fixed to the outer structure 
14 and the slide element 10 is fixed to the inner structure 16. 
Cooperation of the two bearings 3 and 4 permits a transmission of 
transverse forces and bending moments from an inner structure 16 to the 
adjoining outer structure 14. 
If, as illustrated in FIG. 1, a force F acts on the inner structure 16, the 
force causes a moment M which, in turn, creates transverse forces Qv and 
Qh. The transverse force Qv deforms the lower flange 2 of the inner 
structure 16 into an oval form. The transverse force Qv is introduced via 
slide element 10 into the outer structure 14, whereupon the cross section 
thereof is equally deformed into an oval form. In particular, the cross 
section becomes longer in the vertical direction and shorter in the 
horizontal direction. It is this shortening in the transverse direction 
that effects an advantageous stabilization of bearing 3 by way of a 
Fassdauge effect as a consequence of the pressure exerted on the inner 
structure 16. Furthermore, bulging is prevented by the large-surface 
contact imparted by the slide element 10. Furthermore, undesirable bulging 
is prevented by the transverse force Qv acting on the lower flange 2 of 
semicircular shape, so that the membrane effect of a portion can be 
exploited. As a consequence, the sheet thickness of the lower flange may 
be small, which reduces the dead weight of the structure. 
The rear bearing force Qh stresses the inner surface of the outer structure 
14 in the area of the rear bearing 4. As shown in FIG. 3, the two inner 
rounded corner portions Ri of the inner structure 16 are connected in the 
area of the rear bearing 4 with the aid of the two rear plain bearing half 
liners 12 to the two outer rounded corner portions Ra of the outer 
structure. As for this rear bearing assembly 4, it should be noted that 
the rear plain bearing half liners 12 are not supported on a separate 
collar, as in the prior art, but are supported by the arched sheet of the 
inner structure 16. At the same time, the disc effect of the upper flange 
1 is exploited upon introduction of a load. This, in turn, has the effect 
that in the telescopic boom of the invention the width of the rear plain 
bearing half liners 12 and of the slide element 10 (i.e., its dimension in 
the longitudinal direction of the boom) depends on the width of the 
associated collar 8. As already mentioned, such a construction leads again 
to an increase in the usable boom length. 
The sheet thickness of the front collar 7 and the sheet thickness of the 
rear collar 8 are preferably 1.2 to 2.5 times the sheet thickness of the 
sheet used for the respective boom profile (e.g., the upper and lower 
flanges 1 and 2). 
The front bearing assembly 3 also has upper slide members referred to as 
"front plain bearing half liners" 18. The front plain bearing half liners 
18 are made of plastic material, as shown in FIG. 2. The front plain 
bearing half liners 18 are assigned to the front collar 7 in the 
interspaces between the outer rounded corner portions Ra and the inner 
rounded corner portions Ri. Instead of the two front plain bearing half 
liners 18 shown in FIG. 2, in an alternate embodiment there may only be 
provided a single slide member. The front plain bearing half liners 18 
must be designed and arranged such that the inner structure 16 is 
prevented from tilting inside the outer structure 14. 
The front plain bearing half liner 18 is not permanently acted upon with 
forces. 
As illustrated in FIG. 3, the rear bearing assembly 4 also has lower slide 
members referred to as sliding block elements 15. The sliding block 
elements 15 are made of plastic material and may be provided in the area 
of the rear collar 8, namely in the area of the lower flange 2 thereof. 
These sliding block elements 15 are arranged between the semicircular 
lower flange 2 of the inner structure 16 and the semicircular lower flange 
of the outer structure 14. The sliding block elements 15 advantageously 
extend with their upper ends up to the horizontal line C. Instead of the 
bipartite configuration of the sliding block elements 15 as shown in FIG. 
3, the sliding block elements 15 in an alternate embodiment may be of a 
one-part configuration. As a rule, sliding block elements 15 must be 
designed and arranged such that the inner structure 16 does not tilt into 
the interior of the outer structure 14, since the sliding block elements 
are specifically stressed upon the action of a lateral force or a 
transverse force component on the inner structure. 
The above-discussed front plain bearing half liners 18 (FIG. 2) connected 
to the outer structure 14 at the forward end are only loaded in the 
maximally extended state, i.e., only at a minimum clamping length of the 
inner structure 16 to support the inner structure against lateral escape 
(tilting). 
FIG. 4 illustrates a front plain bearing half liner 12 between two rounded 
corner portions Ri, Ra of the upper flanges 1 at the rear end of the inner 
structure 16. In the area of the rounded corner portions Ri, Ra, the 
distance between the two upper flanges 1 of the inner and outer structures 
16 and 14 is greater than in the straight web and side portions of the 
upper flanges. The rounded corner portions Ri, Ra have center points Ma, 
Mi which are spaced apart, with the center point Ma of the rounded edge Ra 
being arranged closer to the plain bearing half liner 12 and the rounded 
edges Ri, Ra, respectively. In the figure, the center point Ma is 
represented by two drawn radii ra each, and center point Mi is represented 
by two radii ri in analogy therewith. 
The front plain bearing half liner 12 is fixed to the inner structure 16, 
so that it performs a relative movement relative to the rounded corner 
portion Ra of the outer structure 14. The front plain bearing half liner 
12 extends partially into the straight portions adjoining the rounded 
corner portions Ri, Ra, and engages the inner structure 16 in the straight 
portion. With respect to the outer structure 14, the front plain bearing 
half liner 12 recedes, starting from the transitions to the straight 
portions, at an angle .alpha. from the outer structure 14. Hence, the 
front plain bearing half liner 12 only engages the outer structure 14 in 
the area of the rounded corner portion Ra. By analogy with FIG. 4, the 
front plain bearing half liners 18 at the front end of the outer structure 
14 are similarly formed and fixed to the outer structure. The front plain 
bearing half liners 18 also rest in the straight portions adjoining the 
rounded corner portions Ri, Ra on the outer structure 14 and recede in the 
straight portions of the inner structure 16 at an angle .alpha. from the 
upper flange 1 thereof. 
FIG. 5 illustrates a telescoped boom with three structures. In vertical 
section, a sectional view of the rear plain bearing half liners 12 is 
shown. The rear plain bearing half liners 12 rest with one side on the 
small rear collar 8 and are bordered at the other side by an edge 20. The 
edge 20 is circumferentially limited to the portion of the rear plain 
bearing half liners 12. In the illustrated telescoped state, the rear 
plain bearing half liners 12 of the adjoining structures partly overlap 
and can thus be slid into one another to a very great extent. 
FIG. 6 illustrates three structures in the retracted state according to a 
bearing arrangement of the prior art. The structures are here supported 
within one another by a round surrounding, with the bearing elements 30 
being each received in a half-basket bearing block 31 which is offset 
relative to the associated structure towards the inside. The border of the 
bearing block 31 is respectively formed by two collars 32 which are 
continuous across the cross-section of the structure. 
As shown in FIG. 6, which shows the prior art, the continuous collars 32 
which are required for stability reasons prevent further insertion of the 
inner structures 16, so that the rear ends of the structures 16 must be 
arranged side by side. Moreover, as shown in the drawing, the bearing 
elements 30 are substantially thicker in the radial direction than the 
slide elements 12 according to the invention (FIG. 5). 
In FIG. 7, a telescopic boom according to the invention is shown with eight 
structures in which the U-shaped portion of each lower flange 2 is formed 
from two spaced-apart round portion 33 shaped as quarter circles. A 
straight web portion 34 which extends in parallel with the straight 
portion of the upper flange 1 between the rounded corner portions Ri, Ra 
is arranged between the rounded portions 33. 
A slide element 10 which is substantially shaped as a quarter circle is 
respectively arranged between the round portion 33 of two adjacent 
structures. The slide element 10 is adapted to the respective shape of the 
round portion 33. The slide elements 10 are each fixed to their outer 
structure 14 and extend at this side portionwise into the straight web 
portion 34 and into the straight side 35, respectively, between lower 
flange 2 and upper flange 1. At the side of the inner structure 16, the 
slide elements 10 rest only in the curved portion of the round portion 33. 
In the straight portion, the slide elements 10 are formed by analogy with 
the ends of the plain bearing half liners 12 illustrated in FIG. 4. 
Starting from the rounded portion 33, the slide elements 10 recede at the 
side of the inner structure 16 in an oblique taper zone at an angle 
.alpha. from the inner structure. 
Of course, the rear bearing assembly 4 may also be formed in the lower 
flange portion 2, as illustrated in FIG. 7. In this case, the sliding 
block elements 15 are formed at the round portions 33. 
In the cross-section illustrated in FIG. 7, in the upper flange portion 1, 
the same arrangement of the front plain bearing half liners 18 can be 
chosen in the area of the rounded corner portions ri, ra as in the 
embodiments illustrated in the remaining figures.