Note: Descriptions are shown in the official language in which they were submitted.
1 ~Z~74~
Device for towing loads
The invention relates to a device for towing loads and
especially to a ski tow, that is a device for towing skiers
gliding on their own skis, preferably uphill. However, the
device can also be used in transporting people in chair liEts
or in trolleys running on rails. The device is intended for
installation between a predetermined starting point and a
predetermined end point spaced by a substantial distance of at
least several hundred meters and sometimes more than thousand
meters.
Known devices of this type for transporting people by
towing in open country are based upon the use of a tension
element in the form of a wire, a rope or the like, which
transmits energy to the load towed. To prevent accidents
occuring from a break of the wire a close control and extensive
maintenance of the device are required.
From German printed accepted patent specification
~o. 24 34 817 there is also known a lift which is towed along
two parallel guide pipes containing a sequence of pressure
elements each having at either end an end face contacting the
opposed end face of an adjacent element, thus allowing the
elements to be advanced as a string along the guide pipe~ said
device also comprising a drive means engaging at least one
pressure element of the string at any time and pushing the
string along the guide pipe. Thereby, the difficulties
associated with the inherent risk of a break of a wire, a
chain, a rope or a similar tension element are avoided.
However, the lift according to the German specification
can be used only for relatively short transport stretches,
since the pressure elements will engage the inner walls of the
guide pipe with considerable frictional force, whereby the
propulsion energy imparted to the string of pressure elements
by the drive means will be consumed as frictional energy when
the device is loaded, leaving little or no energy for moving
the payload. For this reason the use of a device according to
the German specification in the towing of loads over long
stretches such as required by ski tows is not possible.
., ~
The object of the invention is to improve the principle of
using a seyuence of pressure elements instcad of a tension
element by reducing the resistance of the string of elements to
movement along a guide means to an extent allowing the use of
this principle for rather long transport stretches, such as
required in ski tows or ski lifts.
The device according to the invention comprises a guide
means extending in a closed path and including a load towing
section, a sequence of pressure elements each having at either
end an end face contacting the opposed end face of an adjacent
element, thus allowing the elements to be advanced as a string
along the guide means, towing means engaging the string and
towing the loads, and drive means engaging at least one
pressure element of the string at any time and pushing the
string along the guide means. The invention is characterized in
that the size and shape of the end faces are such that at any
possible angular position of two adjacent elements due to
tolerances between the guide means and the elements and/or to
curves in the load towing section of the closed path the point
of contact between the contacting end faces lies to the side of
a notional straight line extending through the centres of said
two adjacent elements opposite from the point of intersection
between the longitudinal notional axes of said two adjacent
elements, whereby the string o~ pressure elements when
subjected to a pushing force from the drive means will tend to
form a stable, straight column, still being free to ~old when
required by curves in the guide means.
Preferably, the end faces are substantially plane, whereby
said point of contact will be shifted to the edges of the
contacting end faces as soon as the respective elements
are not in alignment. These edges may be positioned on the
radially outermost contour of the element, whereby a maximum
stabilization of the column is obtained for a given radial
dimension of the elements.
However, the end faces do not need to be exactly plane,
but can be slightly curved provided the radius of curvature is
larger than half the length of the element.
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The preferred configuration of the guide means is the same
as according to the German specification No. 24 34 817, that is
an endless pipe surrounding the pressure elements and having a
longitudinal continuous slot for the towing means. The towing
means may be fastened to one of the pressure elements, thereby
following the continuous string of pressure elements along the
closed path provided by the guide means. However, the towing
means may alternatively be releasably attached to the string, a
solution which provides considerable comfort to the skier, both
when starting and terminating the towing operation.
Due to the fact that the string of pressure elements when
subjected to a longitudinal compressive force will tend to form
a stable, straight column instead of a zigzag line~ the
friction between the string of pressure elements and the guide
pipe will be dramatically reduced. Accordingly, the pressure
energy imparted to the string of pressure elements by the drive
means will in all substantial respects be transferred to the
towing means. This is true even if there are no rollers or the
like guiding the pressure elements on the guide means. The
string of pressure elements may simply slide on the guide
means, and the pressure elements may consequently have a very
simple design, each pressure element preferably consisting of
an axial stem and two flange-like end parts. It will be
understood, however, that there is nothing preventing the
pressure elements from carrying rollers if desired. The
material of the pressure elements may be a metal such as steel
or aluminium or a plastic material,
Further objects, features and advantages of the invention
will be evident to those skilled in the art upon reading of the
following detailed description of a preferred embodiment of the
device according to the invention, reference being had to the
drawings.
Fig. 1 is a diagrammatic plan view of a short ski tow
according to the invention.
Fig. 2 is a longitudinal section through a guide means
in the form of a pipe of circular cross-section, said pipe
containing a string of pressure elements.
~ ig. 3 is a cross-sectional view along the line III-III in
Fig. 2.
Fig. 4 is a longitudinal section corresponding to Fig. 2
showing the relationship between the individual pressure
elements of the string when the guide pipe follows a curve.
Fig. 5 is a highly diagrammatic view illustrating the
principle of a possible drive means.
Fig. 6 is a highly diagrammatic plan view of a closed path
for a ski lift or tow including branch lines for entering and
leaving the lift.
The plan view in Fig. 1 illustrates masts 1, in which a
guide pipe 2 extending in a closed path is suspended. An arrow
3 indicates the towing direction of the device implying that
the left-hand stretch 4 of the guide pipe 2 defines a load
towing section, the other stretch defining a return section 5.
A drive section 6 is indicated in the initial portion of the
load towing section 4 of the closed path.
Figs. 2 and 3 illustrate on a greater scale the guide pipe
2 containing a string of pressure elements 7, each consisting
of an axial stem 8 and ~wo flange-like end parts 9. In order to
allow towing means (not shown) to be connected to the string of
pressure elements 7 in the guide pipe 2 the latter is provided
with a continuous slot 10. Each element 7 has an axial centre
bore 26 allowing the elements to be loosely threaded on a wire,
a rope or a similar element (not shown).
Fig. 4 illustrates the behaviour of the string of pressure
elements 7 when adjacent pressure elements take an angular
position relative to each other due to a curvature in the load
towing section 4 of the guide pipe 2. Also if two adjacent ele-
ments should take up a slightly angular position with respectto each other due to tolerances between the guide pipe 2 and
the element 7, the behaviour of the string of elements 7 will
be the same as illustrated in Fig. 4 and discussed below. For
said discussion reference will be made to the middle element
7a and the right~hand element 7b in Fig. 4. The geometrical
centres of the elements 7a and 7b, are designated as 12a and
12b, respectively. Also the longitudinal notional axes 13a and
13b of the respective elements have been indicated. Finally/
4~
Fig. 4 shows a notional straight line 14 extending thro~lgh the
centres 12a and 12b. The end faces of each elem~nt 7 are
designated by the reference 11. It will be seen from Fig. 4
that the point of contact 15 between the contacting end faces
11 of the elem~nts 7a and 7b, respectively, lies on the side of
the notional straight line 14 opposite from the point of
intersection 16 of the axes 13a and 13b. For this reason the
string of press~re elements 7 will tend to straighten out and
form a stable, straight column when subjected to a longitudinal
compression force such as a pushing force from the drive means
to overcome a towing load. In fact, this tendency will be
stronger the larger the compression force, and if the guide
pipe 2 is straight, the string of pressure elements will in
fact form a stable, straight column. Such a straight, stiff
column will not convey substantial frictional forces to the
walls of the guide pipe 2. Still said column is free to fold as
indicated in Fig. 4 when required by a curvature in the guide
pipe 2. If the curvature i5 slighter than what is shown in Fig.
4, the column may well stay straight for the length of several
elements 7, the column folding as shown in Fig. 4 at intervals
according to the curvature.
Although the string of pressure elements 7 can be pushed
along the guide pipe 2 in various ways, Fig. 5 diagrammaticly
illustrates one possibility of obtaining the desired pushin~
force. At a suitable point of the guide pipe 2 part of the
upper wall thereof has been removed and covered by 3 housing 17
containing a drive chain 18 having carrier dogs 19 and passing
over rollers 20, one of which can be driven by a motor (not
shown) When the chain is driven, the carrier dogs 19 will
engage the rear side of the front end part 9 of at least one
pressure element 7 at any time.
Since the string of pressure elements 7 are advanced by
being pushed against the towing load force transmitted from the
skiers through the towing means ~not shown~ it is hard to
imagine that the load can be damaged by any type of failure in
the string as contrasted with what may happen if a tension
element such as a wire is used for transmitting a towing force
to the towing means.
~2~ 3
The masts 1 may be foundation-~ree rocker frame masts
stayed by two parallel wires (not shown) each following a
catenary between successive masts and carrying the load towing
section 4 and the return section 5, respectively, of the guide
pipe 2. These two sections 4 and 5 are suspended in the
respective wires by vertical rods or wires (not shown) which
are substantially shorter at the points midway between the
masts than directly below the masts, thus providing a much
straighter path of the guide pipe 2 in side view that the
catenary followed by the wires. This structure can be likened
with the way in which an electric pantograph contact wire or a
suspension bridge is suspended. The masts 1 are vertical or
preferably leaning somewhat towards the uphill up which the ski
tow is mounted. Thereby, the greater part of the towing load
force exerted on the ski tow by the skiers and tending to till
the rocker masts in a downhill direction, will be taken up by
the masts and transmitted to the ground. The structure
connecting the masts, i.e. the wires and the guide pipe
sections 4 and 5 suspended therein will resiliently transmit
some of the load to the next masts uphill, whereby also these
masts will transmit parts of load to the ground.
These characteristics of the ski tow according to the
invention are highly advantageous. They are associated not only
with the design of the supporting structure including the
masts, but also with the fact that the towing force is provided
by pressure elements 7 instead of a tension element such as a
wire. A tensioned wire will tend to straighten out, thereby
lifting any mast positioned below a straight line between the
preceding and the following masts, requiring the masts to be
anchored in foundations in the ground.
The ski tow according to the invention needs no anchoring
of the masts in the ground. Only both ends of the wires staying
the masts should be anchored.
Further, in a ski tow having a force transmitting string
of pressure elements the reaction forces from the load towing
force will be dissipated to the ground through one or more of
the nearest masts, whereas in a ski tow using a tension wire
they will be accumulated and transmitted through the return run
7 ~Z~L7~4:~
of the wire all the way down to the drive station, which is
normally located at the bottom of the hill for practical rea-
sons.
The device according to the invention has a very simple
design. Since it can follow the ground and be laterally
deflected to both sides as required, the height above the
ground may be kept at a minimum.
The towing means may be attached to the string of pressure
elements 7 by means of plates (not shown) extending through the
slot 10, each element being permanently attached to an element
7 of the string. E.g. every 15th or 20th element may have a
plate attached thereto. However, a greater flexibility is
obtained if the towing means are not permanently attached to
the elements 7, but are only releasably coupled thereto. Thus,
the towing means may be attached to a trolley or carriage (not
shown) which may run inside the guide pipe 2 between the two
end parts 9 of an element 7. In this case the towing means
including the trolleys may be disconnected from a string of
pressure elements 7 at the end of the load towing section 4 or
the return section 5 and be connected to the string only when
needed, e.g. when a skier wants to be towed to the end of the
towing section 4.
In Fig. 6 some principles of a ski tow employing such
releasable towing means are shown. ~lasts 1 as shown in Fig~ 1
are not illustrated for sake of simplicity. Fig. 6 illustrates
an inner closed path or loop consisting of a towing section 4,
a return section 5 and two bends 22 connecting said sections.
The string of pressure elements 7 is circulated in said loop
by means of one or more driving stations (not shown). At or
ahead of the point 21 where the pressure elements 7 leave the
load towing section 4 and enter the bend 22 leading to the
return section 5 of the guide pipe, the trolleys carrying
towing means are released from the string of elements 7 and
enter a branch line 23. This arrangements allows a much easier
and safer dismounting of the ski tow by a towed skier, since
the speed of the trolley may be zero at one point of the
branch line 23. ~owever, subsequently arriving trolleys will
push the front trolley in the branch line past a summit from
8 3L~ 3
which the trolleys will roll towards a line regulator 24
letting only one trolley pass for each 15 to 20 pressure
elements 7 arriving from the bend 220 A similar arrangement can
be provided at the start of the load towing section 4, whereby
a skier may grasp a towing means when stationary, whereupon the
trolley may be accelerated by an acceleration means 25 to the
same speed as the string of elements 7 and be coupled therewith
by being guided into the space between the two end parts 9 of a
pressure element 7.
Such acceleration means will provide a high degree of
comfort and make it possible to advance the elements 7 along
the load towing section at high speed.
As indicated above more than one driving station may be
used. The driving stations may be standard units provided at
intervals according to the requirements. If placed behind sharp
curves like the bend 22 they will contribute to reducing the
frictional forces.
The device lends itself to self service by skiers. The
parts of the device are very simple, and consequently the
construction costs as well as the operating and maintenance
costs are heavily reduced compared with existing ski tows.
