EP0224914B1

EP0224914B1 - Hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for pantograph type motor vehicle lifts

Info

Publication number: EP0224914B1
Application number: EP86116771A
Authority: EP
Inventors: Eride Rossato
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-12-05
Filing date: 1986-12-02
Publication date: 1990-03-07
Anticipated expiration: 2006-12-02
Also published as: EP0224914A1; AU6831387A; GR3000525T3; ES2013593B3; EP0293368B1; ATE53896T1; AU604673B2; IT8584159A0; DE3670888D1; IL80838A; IT1214977B; IL80838A0; EP0293368A1; CA1302206C; WO1987003655A1

Abstract

A hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for motor vehicle lifts of pantograph type and comprising a cylinder (1) in which there slides a piston (9) provided with a rod (4) emerging from an end-piece (3) of said cylinder (1), and comprising inside the cylinder (1) a portion (10) provided with toothing extending along the axis of said cylinder and cooperating with at least one deactivatable stop member (17) which during the elongation stage of said cylinder-piston unit moves relative to said toothed portion (10) by yielding elastically in its passage from one tooth to the next, whereas during the retraction stage it engages in the facing notch (11) defined by two successive teeth, to thus form the mechanical safety stop.

Description

This invention relates to a hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for motor vehicle lifts of the pantograph type.
Motor vehicle lifts of the pantograph type are known. They generally comprises a pair of runways and cylinder-piston units 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 systems to ensure that the level attained by the runways is maintained, 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 assemblies which allow the racks to move freely 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 the pawl assemblies from the corresponding rack, and then discharge the operating fluid from the cylinder-piston units.
Known mechanical safety systems for application to hydraulic cylinder-piston units, in particular for operating lifts of the pantograph type, have certain drawbacks, and in particular :

⁼their installation is somewhat complicated because it involves additional work beyond that required for installing the cyiinder-piston units,
- they are somewhat bulky, this being often 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.

Safety systems have also been proposed (see for example in US-A-4 251 056 ; FR-A-2 376 062 ; US-A-2 998 224 ; GB-A-211 412 ; GB-A-490 886) which foresee to apply or to get the rack in the stem of the piston so as to reduce the workings due to the installation of the cylinder-piston unit, and the whole encumbrance of the system.
Nevertheless these solutions had not allowed to eliminate other considerable drawbacks, and in particular :

- the impossibility to realize double-acting systems, in that the presence of the notches in the stem of the piston does not allow this to have a good seal with respect to the head through which the stem comes out,
- an easy entry of the dust and dirt through the passage opening of the stem which causes unavoidable rifling with the passing of the time, of the inner surface of the cylinder and the quick dateroration of it,
- a laboriousness of the workings for the disengagement of the safety device, which must be disengaged manually or by a separate control circuit.

US-A-2 540 578 discloses a hydraulic internal locking jack comprising a cylinder, a hollow piston operable in the cylinder and emerging from one end closure member of said cylinder, a toothed post fixed to the other end closure member, and a releasable locking means preventing accidential retraction of the piston. The locking means includes a spring actuated pawl assembly associated with the piston and cooperating with the teeth of the post. The pawls are slidingly received in a cage which is fixed to the piston.
A drawback of this hydraulic locking jack consists in that it requires a further device actuable by hand, for releasing the pawl assembly from the teeth of the post. This is particularly disadvantageous when the hydraulic jacks are placed, due to constructive reasons, in positions not well accessible and when they, if more than one, must actuated simultaneously; this happens, in particular, in the case of hydraulic jacks for lifting ramps.
An object of the invention is to obviate these drawbacks by providing a double-acting hydraulic cylinder-piston unit with an associated mechanical safety device which is without bulk and requires no special additional installation work.
A furthere object of the invention is to provide a hydraulic cylinder-piston unit with an associated mechanical safety device which for disengaging this latter uses the actual hydraulic feed circuit of the cylinder-piston unit.
These aims are attained according to the invention by a hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for motor vehicle lifts of pantograph type and comprising a cylinder having a closed endpiece and in which there slides a piston provided with a hollow rod emerging from the opposite endpiece 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 a stop member which during the 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, whereas during the retraction state it engages in the facing notch defined by two successive teeth to thus form the mechanical safety stop, characterised in that the pawl assembly comprises for each stop member a plunger communicating with the rod end chamber of the cylinder and acting, when in the presence of slight pressure in said chamber, in the sense of withdrawing the respective stop member into the piston.
A preferred embodiment of the present invention is 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 ;
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 solid endpiece 2, and closed upperly by and endpiece 3 comprising a central circular hole for the oil-tight passage of a rod 4.
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 rod 4 is provided with a head 5 for its connection and hinging to an upright 8.
The rod 4, which is hollow, is connected to a piston 9 slidable in an oil-tight manner inside the cylinder 1. In the 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 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 cylinder 1 in proximity to the endpiece 3.
The piston 9 consists substantially of a pair of annular flanges indicated overall by 14 and 14', and joined together by screws.
These flanges have an outer profile which is complementary 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, comprises three radial recesses 16 disposed at 120° apart, in which stop blocks 17 can slide.
More specifically, each stop block 17 has its front profile curved to correspond to the facing surface of the toothed rod 10, and comprises two cylindrical cavities 18 for housing small helical springs 19 interposed between said block 17 and 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 inclined 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 of the three blocks 17 and as the guide recesses 16 for these latter `are disposed at 120° apart, the three cylindrical cavities 24 are also disposed at 120° apart.
The operation of the hydrolic cylinder-piston unit 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 of the rod 10 not provided with toothing faces the three 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 1 into two regions : namely the lower region connected to the inlet aperture 12, and comprising the annular cavity defined by the piston 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 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 the piston 9 to rise, and the cylinder-piston unit to undergo corresponding elongation.
As the piston 9 withdraws from the lower endpiece 3, the rod 10, which is fixed to this latter, withdraws from the rod 4 and thus its lateral surface slides in front of the end of 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 successive intervention of the stop blocks 17, which because of the sawtooth profile of the circumferential notches 11 retract into the body of the flange 14 as they pass between one notch and the next, and elastically emerge in a snapwise manner each time a notch appears in front of them.
It is apparent that when they are in their emerged state they constitute a mechanical safety stop which prevents the rod 4 from retracting into the cylinder 1, even if the pressure of the feed circuit should accidentally fall.
When this elongation of the cylinder-piston unit is complete, the feed of oil is suspended and a small amount of this latter is allowed to espace through the aperture 12, in order to ensure the mechanical engagement of the blocks 17 in the corresponding notch 11.
In order to lower the lift and thus cause each rod 4 to retract into the respective cylinder 1, the cylinder-piston units are firstly made to elongate slightly by normal methods in order to disengage _ the stop blocks 17 from the relative notch 11. Oil is then fed through the aperture 13. Its pressure acts initially on the plungers 23, which descend and press by way of their stem 22 against the inclined surface 21 of the corresponding stop block 17. By virtue of this, the blocks 17 are withdrawn into the piston 9 along the respective recesses 16, so that they no longer interfere with the toothed rod 10. By continuously feeding oil through the aperture 13 with simultaneouse discharge of other oil through the aperture 12, the piston 9 is made to descend, with the 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 into the piston 9 is opposed by the elastic reaction of the springs 19, and consequently, when the overpes- sure in the upper chamber of 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 advantages over conventional cylinder-piston units provided with an external mechanical safety device, in that:

- it involves practically no substantial size increase deriving from the mechanical safety device,
- it enables the mechanical safety device to be installed without requiring any work additional to that required for installing the cylinder-piston unit,
- 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 advantageously in pantograph lifts of the type shown diagrammatically in Figure 1. In this application, if the lift has no direct transverse connections between the 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 recess 16 and the 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 only if activated by the block when in its rear end-of-travel position.

Claims

1. A hydraulic cylinder-piston unit provided with a mechanical safety device, particularly for motor vehicle lifts of pantograph type and comprising a cylinder (1) having a closed endpiece (2) and in which- there slides a piston (9) provided with a hollow rod (4) emerging from the opposite endpiece (3) of said cylinder (1), said rod (4) housing in its interior a second toothed rod (10) which is fixed at one end to the closed endpiece (2) of said cylinder (1), is movable axially relativa to said hollow rod (4) by means of said piston (9), and cooperates with a pawl assembly housed in the piston (9) and comprising at least a stop member (17), which during the elongation state _of the cylinder-piston unit moves relative to the toothed rod (10) by yielding elastically in its passage from one tooth to the next, whereas during the retraction state it engages in the facing notch (11) defined by two successive teeth, to thus form the mechanical safety stop, characterised in that the pawl assembly comprises for each stop member a plunger (23) communicating with the rod end chamber of the cylinder (1) and acting, when in the presence of slight pressure in said chamber, in the sense of withdrawing the respective stop member into the piston (9).

2. A hydraulic cylinder-piston unit as claimed in claim 1, characterised in that the plunger (23) is provided with a stem (22) cooperating with an inclined surface (21) provided in the stop member (17) in order, as a result of its axial movement, to cause said stop member (17) to withdraw into the piston (9).

3. A hydraulic cylinder-piston unit as claimed in claim 1, characterised in that each stop member (17) is provided with a sensor (25) which detects its deactivated state.

4. A hydraulic cylinder-piston unit as claimed in claim 3, characterised by comprising a sensor (25) which detects when each stop member (17) has reached its end-of-travel position in a corresponding guide recess (16) foreseen in the piston (9).

5. A hydraulic cylinder-piston unit as claimed in claim 4, characterised in that the sensor (25) consists of a microswitch, which is activated by the relative stop member (17) when this reaches its rear end-of-travel position.