Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Ihis invention rela~es ~o a hydrdulic cylinder-piston
unit provided wi-th a mechanical safety device, particularly
for motor vehicle lifts of the pantograph type.
Mo-tor vehicle lifts of the pantograph type are known.
5 They generally comprises a pair of runways and cylinder-
piston unlts which raise said runways, on which the vehicle
to be lifted has been previously positioned.
Current accident-prevention regulations require the
provision of mechanical safety systerns to ensure that the
10 level attained by the runways is mainteined, even if the
pressure of the hydraulic circuit feeding the cylinder-
pistons units accidentally falls.
Known safety systems generally consist of racks engaged
by pawl assernblies which allow the racks to move Preely
15 relative to them during the raising of the lift, but prevent
their opposite movement, thus ensuring stability of the
attained configuration.
To lower the lift it is necessary firstly to disengage
~ he pawl assemblies frorn the corresponding rack, and then
20 discharge the opera~.ing fluid ~rom the cylinder-piston units.
Known rllechanical safety systems for application to
hydraulic cylinder-piston units, in particular for operating
lifts of the pantograph type, have cer-tain drawbacks, and in
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parti.cular:
- their installation is somewhat complicated because it
involves additional work beyond that required for
installing the cylinder-piston units,
5 - they are somewhat bulky, this being o~ten difficult tO
reconcile with the limited space available,
- they require a self-contained system or circuit for
deactivating them during the lowering of the lift.
An object of the invention is to obviate these drawbacks
10 by providing a hydrauli.c cylinder-piston unit with an
associated mechanical safety device which is without bulk and
requi~es no special additional installation work.
A further object of the invention is to provide a
hydraulic cylinder-piston unit with an associated mechanical
15 safety device which for disengaging this latter uses the
actual hydraulic feed circuit of the cylinder-piston unit.
These and further objects which will be apparent from
the description given hereina~ter are attai,ned according to
the invention by a hydraullc cylinder-piston unit provided
20 with a mechanical safety device, comprising a cylinder in
which there slides a piston provided with a rod emerging from
an endpiece of said cylinder, characterised by comprising
inside the cylinder a portion provided wi-th toothing
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extending along the axis of said cylinder and cooperating
with at least one deactivatable stop member which during the
elongation stage of said cylinder-piston unit moves relative
to said toothed portion by yielding elastically in its
5 passage from one tooth to the next, whereas during the
re~raction staye it engages in the facing notch defined by
two successlve teeth, to thus form the mechanical safety
stop.
Preferably, . the cylinder of the hydraulic cylinder-
10 piston unit according to the invention can be formed with one
endpiece closed and the other endpiece comprising a hole for
the oil-tight passage of the piston rod, this rod being
hollow and housing in its interior a second rod which is
fixed at one end to the closed endpiece of said cylind.er, is
15 mobile axially relative to said hollow rod by means of said
piston, and is provided with a toothed portion cooperating
with a pawl assembly rigid with said hollow rod.
Preferabl.y, acco:cding to the invention, the piston can
comprise radial recesses opening into the passage bore.~for
~Osaid second rod, in order to guide stop blocks which are kept
elastically adhering to t:he lateral surface of said second
rod and are provided with rneans for causing them to retract
into the body of the piston.
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Also according to the present invention, there is
provided a hydraulic cylinder-piston unit provided with a
mechanical safety device, comprising a cylinder having a
closed endpiece and in which there slides a piston provided
wl-th a hollow rod emerging from an opposite enpiece of said
cylinder, said rod housing in its interior a second toothed
rod which is fixed at one end to the closed endpiece of said
cylinder,is movable axially relative to said hollow rod by
means of said piston, and cooperates with a pawl assembly
housed in the piston and comprising at least one stop
member, which during an elongation state of the cylinder
piston unit, moves relative to the toothed rod by yielding
elastically in its passage from one tooth to the next tooth,
whereas during a retraction state said at least are stop
member engages in a facing noth defined by two successive
teeth, to thus form the mechanical safety device, the pawl
assembly comprising for each stop member a plunger
communicating with a rod end chamber of the cylinder and
acting, when in presence of slight pressure in said chamber,
in a sense of withdrawing the respective stop member into
the
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Preferably, according to the invention, the stop pawl
assembly for the toothed rod can be provided with a sensor
which detects its deactivated state.
A preferred embodiment of the present invention is
5 described hereinafter by way of non-limiting example with
reference to the accompanying drawings in which:
Figure 1 is a perspective diagrammatic view of a lift of the
pantograph type provided with hydraulic cylinder-
piston units according to the invention;
0 Figure 2 is an axial section through a cylinder-piston unit
to an enlarged scale;
Figure 3 is a partial longitudinal section through the piston
of the cylinder-piston unit to an enlarged scale;
Figure 4 is a section ,therethrough on the line IV-IV of
Figure 3,
As can be seen from the figures, the hydraulic cylinder-
piston unit according to the invention comprises a cylinder 1
closed lowerly by a sol:id endpiece 2, and closed upperly by
an endpiece 3 comprising a central circular hole for~-the oil-
20 tight passage of a rod ~.
When used in a lift (see Figure 1), the endpiece 2 is
provided with a lug for its connection and hinging to a lower
longitudinal member 6 of the lift, and the outer end of the
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rod 4 is provided Witll a head 5 for its connection and
hinging to an upright 8.
*he rod 4, which is hollow, is connected to a piston 9
slidable in an oil-tight manner inside the cylinder 1. In the
5 interior of the rod 4 there is housed a further rod 10, which
comprises a plurality of equidistant circumferential notches
11 having a profile such as to form a sawtooth pattern, as
can be seen from Figure 2. The rod 10 is mobile axially
relative -to the rod 4, and is fixed at one end to the
10 endpiece 2 of the cylinder 1. The rod 10 also traverses the
piston 9, without any need for sealing.
In the endpiece 2 there is provided an aperture 12 for
the passage of oil into and from the cylinder 1, and an
aperture 13 is provided in the lateral surface of the
15 cylinder 1 in proximity to the endpiece 3.
The piston 9 cons:ists substantially of a pair of annular
~langes indicated overall by 14 and 14', and joined together
by screws.
These flanges have an outer profile whic~ is
20complementary to the profile of a rubber gasket 15 which
seals the piston 9 against the inner lateral surface of the
cylinder 1.
The upper flange 14, which is screwed to the rod 4,
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comprises three radial recesses 16 disposed at 120x apart, in
which stop blocks 17 can slide.
~ lore specifically, each stop block 17 has its front
profile curved to correspond to the facing surface of the
S toothed rod 10, and coMprises two cylindrical cavitles 18 for
housing small helical springs 19 interposed between said
block 17 a,nd the shoulder 20 which delimits the rear of the
corresponding recess 16. It also comprises an inner cavity
having an inclined surface 21 facing upwards in Figure 3. On
said lnclined surface there rests the eccentric stem 22 of a
plunger 23 mobile axially in a sealed manner within a
corresponding cylindrical cavity 24 formed in the upper
flange 14 and communicating with the interior of the cylinder
1.
As there exists a cylindrical cavity 24 for each o~ the
three blocks 17 and as the guide recesses 16 Por these latter
are disposed at 120, apart, the three cylindrical cavities 24
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are also disposed at 120 apar-t.
The operation of the hydraulic cylinder-piGton~ unit
~0 according to the invention is as follows:
when in the rest state (minimum elongation) the piston 9 is
in its lower end-of-stroke position, that cylindrical portion
o~ the rod 10 not provided with toothing faces the three
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blocks 17, the three blocks 17 are urged by the respective
springs 19 to adhere to the cylindrical surface of the rod
10, and the plungers 23 are raised. The piston 9, which is in
its lowered position, divides the inner bore of the cylinder
5 1 into two regions: narnely the lower region connected to the
inlet aperture 12, and comprising the annular cavity defined
by the pis.ton 9,and lower endpiece 2 and also extending into
the space defined by the rods 4 and 10; and the upper region
connected to the outlet aperture 13, and comprising the
10 annular cavity defined vertically by -the piston 9 and the
upper endpiece 3. Under these conditions the two regions are
at the same pressure.
In order to raise the lift, oil is fed under pressure
into the cylinder 1 through the aperture 12. This feed causes
15 the piston 9 to rise, and the cylinder-piston unit to undergo
corresponding elongation.
As the piston 9 wlthdraws Prom the lower endpiece 3, the
rod 10, which is ,Pi~ed to this latter, withdraws from the rod
~ and thus its la~,eral surface slides in front of the'end of
20 the three stop blocks 17, which are urged to adhere
elastically thereto.
As oil feed into the cylinder 1 continues, there is a
progressive withdrawal of the rod 10 from the .rod 4, with
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successive intervention of the stop blocks 17, which because
of the sawtooth profile of ~he circulnferential notches 11
retract into the body of the flange 14 as they pass between
one notch and the next, and elastically emer.ge in a snapwise
5 manner each time a notch appears in front of -them.
It is apparerl-t ~hat when they are in their elnerged state
they constitute a mechanical safety stop which prevents the
rod q from retract:ing i.n~o the cylinder 1, ever if the
pressure o~ the feed circuit should accidentally f~ll.
~ihen this elongaciorl of the cylinder-piston unil is
complete, the feed of oil is suspended and a small arnount o~
this latter is allowed to escape through the aperture 12, in
order to ensure the mechanical engage~nent o~ the blocks 17 in
the corresponding notch 11.
Ln order to lower the lift and thus cause each rod ~ to
retract into the respective cylinder 1, the cylinder-piston
units are firstly rnade to elongate sllghtly by normal methods
in order to disengage the st;op bloclcs 17 frorn the relat:ive
notch 11. Oil ls ~hen fed through the aperture 13. Its
20 pressure acts init:ially on t.he plungers 23, which descend and
press by way of their stern 22 against the inclined surface 21
of the corresponding stop block 17. By virtue of this, the
bloclcs 17 are withdrawn into the piston 9 aloncJ the
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respective recesses 16, so that they no longer interfere with
the toothed rod 10. By continuously ~eeding oil through the
aperture 13 with simultaneouse discharge of other oil through
the aperture 12, the piston 9 is made to descend, with the
5 toothed rod 10, which is no longer hindered by the stop
blocks 17, simultaneously retracting into the rod 4.
The retraction of the stop blocks 17 in-to the piston 9
is opposed by the elastic reaction of the springs 19, and
consequently, when the overpressure in the upper chamber of
10 the cylinder 1 ceases, this reaction prevails and urges the
blocks 17 into their engaged state and, by virtue of the
interaction between each stem 22 and the inclined surface 21
of the relative block 17, causes the release plungers 23 to
rise and to return to their rest configuration.
From the aforegoing it is apparent that the hydraulic
cylinder-piston unit according to the invention has numerous
advan-tages over conventional cylinder-piston units provided
with an external mechanical safety device, in that:
- it involves prac~ically no substantial size increase
deriving frorn the mechanical safety device,
- lt enables the mechanical safety device to be installed
without requiring any work additional to that re~uired for
installing the cylinder-piston uni-t,
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- it requires no independent device or circuit for releasing
the mechanical safety device before the retraction of the
rod into the cylinder is commenced,
- it provides a high guarantee of correct operation and long
life, in that all the moving parts operate immersed in oil.
The cylinder-piston unit according to the invention is
used advan~ageously in pantograph lifts of the type shown
diagrammatically in Figure 1. In this application, if the
lift has no direct transverse connections between the
10 runways, it is preferable tO be able to check that the stop
blocks are effectively in their disengaged state before
lowering the lift, so as to prevent any possible dangerous
consequences deriving from unbalanced loads. For this
purpose, between the rear shoulder 20 of at least one radial
15 recess 16 and ~he corresponding stop block 17 of each
cylinder-piston unit there is provided a member, such as a
microswitch 25, which enables the lift to be lowered onl~ if
activated by the bloclc when in its rear end~of-travel
position.
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