HYDRAULIC ACTUATOR, PARTICULARLY FOR A MOTOR VEHICLE LIFT

Abstract: A hydraulic actuator particularly for a motor vehicle lift, characterised by comprising at least one cylinder (22, 22') and a piston (58, 58') slidable within said cylinder and provided with a rod (34, 34') comprising annular toothing cooperating with retention members (36) applied to the cylinder (22, 22').

Description: HYDRAULIC ACTUATOR, PARTICULARLY FOR A MOTOR VEHICLE LIFT This invention relates to a hydraulic actuator, particularly for motor vehicle lifts. Motor vehicle lifts are known; they comprise a pair of base longitudinal members resting on the ground, a pair of vehicle mounting runways and pairs of arms pivoted to each longitudinal member and to the corresponding runway in order to raise said runway by means of hydraulic cylinder-piston units fed by an external control centre. If the articulated arms are parallel to each other, the lift is of so-called "parallelogram type". If they are crossed and pivoted to each other at their centre the lift is of so-called "pantograph type". If, in the case of a vehicle lift of pantograph type, the connection between the runways and longitudinal members instead of being made by only one series of pairs of pivoted arms is made by two series, in which the arms are pivoted together at one end and are pivoted at their other end to the runways and longitudinal members respectively, the lift is of so called "multiple pantograph type". Independently of the type of lift, it is generally provided with safety devices, the purpose of which is to prevent accidental fall of the lift should the hydraulic system feeding the cylinder-piston raising units develop a fault. Known mechanical safety devices generally comprise a rack and a pawl which cooperates with it and can slide unidirectionally along the rack during the raising of the lift. To enable the lift to descend, the safety device must be previously deactivated, ie the pawl must be disengaged from the rack. The drawback of this known arrangement is that generally the safety devices are separate from the hydraulic cylinder- piston units, resulting in non-uniformity of thrust of the components on the lift, given the difference between the direction of thrust of the cylinder-piston units and the direction of reaction of the safety device. A further drawback is the fact that the need to separately mount these components on the lift results in considerable constructional complexity, accentuated by the need to feed both the cylinder-piston units and the safety devices with the necessary operating fluid. Moreover, independently of the type of lift, in general when it is lowered, the cylinder-piston raising units are positioned with their axis substantially horizontal between the runways and the corresponding longitudinal members. As a result, the axes on which each cylinder-piston unit is pivoted to the two structural elements to which it is applied are virtually coplanar with the axis on which said structural elements are pivoted together, so that high power is required to commence the raising travel, by obtaining a vertical thrust component from a substantially horizontal force. This high power is obtained by cylinder-piston units of large diameter, resulting in two problems of different type. A first problem derives from the large vertical bulk of the lift when lowered, and which cannot therefore be used with vehicles having a very low body. A second problem derives from the high power required to raise the lift and the consequent need for an adequately dimensioned hydraulic control centre. Consequently in known vehicle lifts of pantograph type a small overall size when in its lowered state and low power for its raising represent conflicting requirements to which a satisfactory overall solution has not been found up the present time. An object of the invention is to eliminate all the drawbacks which jointly and disjointly are present in known motor vehicle lifts. According to the invention this object and further ones are attained according to the invention through a hydraulic actuator as described in claim 1. The present invention is clarified hereinafter with reference to the accompanying drawings, in which: Figure 1 is a side view of a vehicle lift of pantograph type according to the invention in its raised state; Figure 2 shows it in its lowered state; Figure 3 is a partial front view thereof on the line III-III of Figure 1; Figure 4 is a schematic view of the pair of actuators for raising the lift of Figure 2 and their connections to the hydraulic feed circuit; Figure 5 is a side view of a vehicle lift of multiple pantograph type in its raised state; and Figure 6 is a partial view thereof to a reduced scale in the same view as Figure 1, but with the runways elongated. As can be seen from the figures, the vehicle lift which uses the hydraulic cylinder-piston unit of the invention comprises a pair of base longitudinal members 2 by which the lift rests on or is fixed to the ground, a pair of runways 4 on which the vehicle to be raised is mounted, and pairs of crossed arms 6,6' which are pivoted upperly to the runways 4, pivoted lowerly to the longitudinal members 2, and pivoted together at their centre. Specifically, as in the case of all vehicle lifts of pantograph type, the lower end of the corresponding arms 6 is pivoted to the longitudinal members 2 about a horizontal axis 8, which is fixed relative to the longitudinal members, whereas their upper end, provided with bearings 10, is pivoted to the runways 4 about a horizontal axis 12 which is movable parallel to the runways. Likewise the lower end of the corresponding arms 6' , ie the other arms of the pairs, is pivoted to the longitudinal members 2 about a horizontal axis 14 which is movable parallel to the longitudinal members and for this purpose is provided with a bearing 16, whereas the upper end of said arms 6' is pivoted to the runways 4 about a horizontal axis 18 which is fixed relative to the runways. These latter are also provided with traditional sliding elements 5 which can be withdrawn outwards to elongate the runways. To the vehicle lift two hydraulic cylinder-piston lifting units 20,20' are applied interposed between each longitudinal member 2 and the respective arms 6'. Specifically, each cylinder-piston unit 20,20' comprises a cylinder 22 pivoted via a pin 24 to a pair of metal link- plates 26, themselves pivoted via a pin 28 to the respective arms 6'. These link-plates have the approximate shape of an obtuse angled scalene triangle, with the obtuse angle situated in correspondence with the pin 28 which is positioned in proximity to the upper edge of the arms 6'. That side of each link-plate 26 adjacent to the obtuse angle is disposed in such a manner as to be able to adhere to a plate 30 applied to the upper edge of the arms 6', to the vertex opposite this side there being applied a bearing 32 arranged, as will be seen hereinafter, to oppose through rolling a plate 40 applied to the corresponding arms 6. The rod 34 of the cylinder-piston unit 20,20' externally comprises a sort of annular toothing, making the rod similar to a rack. It is associated with a pair of retention members 36 applied to the cylinder 22, and acting in the sense of engaging the annular toothing of the rod 34 to prevent the return axial movement of the rod 34 in the cylinder 22, but to allow the opposite withdrawal axial movement. The retention members 36 are made to open (disengage) and close by a transverse pneumatic cylinder 38 applied to the cylinder 22. The two cylinder-piston units 20,20', although externally of identical dimensions, are in reality different to ensure that when they are connected in series they undergo to the same elongation. For this purpose, as in apparent from Figure 4, their rod 34,34' is provided at the end within the cylinder 22,22' with an axially fixed piston 58,58' for the passage of a hollow stem 60,60' which at one end (the left end for the observer) is fixed to a closure cap 62,62' for the cylinder 22,22' and at the opposite end is provided with a further piston 64,64' slidable within the toothed rod 34,34' . The axial cavity of the stem 60,60' communicates at one end with the exterior of the cylinder 20,20' and at the other end, via openings 68,68', with that cavity portion 66,66' of the toothed rod 34,34' lying between the pistons 58,58' and 64,64' . As stated, the external dimensions of the two cylinder- piston units 20,20' are identical, whereas their internal dimensions are different, and in particular the area of the annular section through the cavity portion 66' bounded by the two pistons 58' and 64' of the cylinder-piston unit 20' is equal to the area of the circular section through the other cavity part 66 of the cylinder-piston unit 20, ie that part situated on the opposite side of the piston 64. In the hydraulic feed circuit (see Figure 4) the delivery side P of the feed pump, not shown on the drawings, ie connected to the inlet of the cylinder-piston unit 20', ie to the opening 70' situated in proximity to its head 62', the return S to the feed pump being connected to the outlet of the cylinder-piston unit 20, ie to the external opening of the axial cavity of its stem 60. In addition, the outlet of the cylinder piston unit 20', ie the external opening of the axial cavity of its stem 60', is connected via a pipe 72 to the inlet of the cylinder-piston unit 20, ie to the opening 74 situated in proximity to the outer end of the rod 34. The operation of the vehicle lift is as follows: with the lift in its lowered state (see Figure 2) the runways 4 substantially rest on the respective longitudinal members 2, the longitudinal compartment defined by these latter housing the folded arms 6,6' and the cylinder-piston units 20,20' in their minimum elongation state. Under these conditions the bearings 32 provided on the link-plates 26 rest on the plate 40 of the arms 6 with the link-plates occupying the position in which they are rotated to a maximum extent in the anti¬ clockwise direction (observing the drawings) , with their minor side separated from the relatve plate 30. In addition the retention members 36 embrace the respective rods 34 in the manner of a clamp. To raise the lift, on the runways 4 of which there may have been mounted a vehicle, the operator by operating the hydraulic feed control centre for the cylinder-piston units 20,20' feeds oil through the opening 70' of the cylinder- piston unit 20'. The oil which enters into the cylinder 22' acts on the piston 58' causing the rod 34' to extend, with consequent axial reduction in the chamber bounded by the two pistons 58' and 64'. This axial reduction results in the oil contained in this chamber being urged through the opening 68', the axial cavity of the stem 60', the pipe 72 and the opening 74 in the cylinder-piston unit 20, to enter the chamber 66 and cause the rod 34 of said cylinder-piston unit 20 to extend. Because of the fact that the area of the sections through that annular cavity 66' of the rod 34' bounded by the two pistons 58' and 64' and through the cylindrical cavity 66 of the rod 34 are equal, identical elongation of the two cylinder-piston units 20 and 20' is ensured. This allows synchronized operation of the retention members 36 which act on the two toothed rods 34 and 34' and which, although allowing said elongation, mechanically oppose the opposite movement. Because of the fact that the axis of the pins 28, the axis of the pins 24 and the axis on which the cylinder-piston units 20,20' are pivoted to the respective arms 6' are not coplanar, the initial stage of elongation of the cylinder- piston units 20 causes the link-plates 26 to rotate relative to the arms. Hence during this rotation the bearings 32, provided at the end of the link-plates 26, slide on the respective plates 40, to cause raising of the arms 6' by mechanical effect, and hence of the arms 6 and of the runways 4, which are constrained to the upper end of these latter arms. This rotation of the link-plates 26 and hence the raising of the runways 4 by mechanical effect continues until the minor side of the link-plates 26, ie the side opposite the bearings 32, rests on the counteracting plates 30 provided on the arms 6'. From this point onwards, the link- plates 26 and the arms 6' constitute for the cylinder-piston units 20 a rigid counteracting assembly so that the subsequent elongation of the cylinder-piston units 20 causes the lift to rise hydraulically by the direct effect of the cylinder-piston units 20, this raising taking place at a higher speed that its initial part because there is no longer the reduction effect due to the movement of the link-plates. To cause the lift to descend it is necessary for the operator merely to feed the appropriate commands to the control centre, which firstly deactivates the mechanical safety devices, by feeding the pistons 38 to cause the retention members 36 to withdraw from each other and disengage the annular grooves in the rod 34,34' and then allows the oil forced out of the cylinder-piston units 20,20' by the effect of the weight of the lift and the vehicle lying thereon to flow towards the control centre. To accelerate the descent of the lift, the oil can be fed into the cylinder- piston units 20,20' in the opposite direction to that which caused the lift to rise. To prevent the longitudinal member falling due to a sudden fault in the hydraulic system during the descent of the lift in which the mechanical safety devices are deactivated, it is advantageous to provide a traditional safety valve (parachute valve) in the feed conduit of each cylinder-piston unit 20. The cylinder-piston units 20,20' according to the invention can also be applied to vehicle lifts of different type from that described heretofore, and in any event because of their particular configuration comprising a toothed rod 34,34' and retention members 36 applied to the cylinder 22,22' and cooperating with the toothed rod, they ensure correct and balanced operation, while at the same time being of easy and reliable operation. Because of the fact that the two cylinder-piston units are fed in series and that their elongation is rigorously constant, absolute synchronism is achieved between the times of action of the retention members 36 on the respective toothed rod 34,34' and the maintaining of a balanced orientation of the vehicle lift under any condition, in particular during the operation of the safety devices. Moreover, when the cylinder-piston units are applied to the lift via the link-plates 26, the upward travel of the lift takes place in two different ways: the initial part, which is the more difficult because of the substantial coplanarity between the various pivotal axes and the axis of the cylinder-piston unit 20, is entrusted to the interaction between the link-plates 26, moved directly by the cylinder- piston units 20,20' and the plates 40 on which the bearings 32 with which the link-plates 26 are provided can slide. Subsequently, after the initial part of the upward travel has been completed, and the further raising can hence be achieved without excessive force on the part of the cylinder-piston units 20,20' these latter exert a direct hydraulic effect on the upper arms 6' of the lift, to complete its upward travel. This splitting of the manner of action of the cylinder- piston units 20,20' results in the further following advantages: - the ability to use cylinder-piston units of smaller dimensions, so enabling the overall height of the lift when in its lowered state to be reduced and requiring a control centre of only low power; - the ability to vary the initial part of the upward travel of the lift because of the possibility of adequately shaping the plates 40 on which the bearings 32 roll; - very simple installation, it being sufficient to provide a single connection to the lower inlet of each rod 34 to feed the corresponding cylinder-piston unit 20. In the embodiment shown in Figure 6 the lift is of multiple pantograph type, ie with two series 6,6' and 56,56' of crossed arms instead of a single series 6,6'. In this case the link-plates 26 are preferably pivoted to the arms 56 and have their minor side acting against a plate 54 applied to the arms 56.

Claims: C L A I M S 1. A hydraulic actuator particulary for a motor vehicle lift, characterised by comprising at least one cylinder (22,22') and a piston (58,58') slidable within said cylinder and provided with a rod (34,34') comprising annular toothing cooperating with retention members (36) applied to the cylinder (22,22') . 2. An actuator as claimed in claim 1, characterised by comprising two jaw-shaped retention members (36) embracing the rod (34,34') and pivoted to the cylinder (22,22') , to be operated in opposite directions by an actuator (38) also applied to the cylinder (22,22'), so that they pass from a position in which they engage said rod to a position in which they are disengaged. 3. An actuator as claimed in claim 1, characterised in that the toothed rod (34,34') comprises an axial cavity (66,66') along which there slides a piston (64,64') mounted on an axially holed stem sealedly traversing an axial cavity provided in the piston (58,58') and fixed at its other end to a closure head (62,62') for the cylinder (22,22') and communicating with the outside, that part of the annular cavity (66,66') bounded by the two pistons (58,58' and 64,64') communicating with the axial cavity of the stem (60,60') via at least one opening (68,68'). 4. An actuator as claimed in claim 1, characterised by comprising a pair of cylinder-piston units (20,20'), a conduit connecting the exit opening of the axial cavity of the stem (60') of the first cylinder-piston unit (20') to the cylinder cavity of the toothed rod (34) of the second cylinder-piston unit (20) , a conduit connecting the delivery of a feed pump to the the cavity of the cylinder (22') of the first cylinder-piston unit (20') in correspondence with its closure head (62'), and a conduit connecting the pump return to the exit opening of the axial cavity of the stem (60) of the second cylinder-piston unit (20) , the area of the section through that annular cavity portion (66') of the rod (34') of the first cylinder-piston unit (20') lying between the two pistons (58',64') being equal to the area of the section through that cylindrical cavity portion (66) of the rod (34) of the second cylinder-piston unit (20) between the outer end of said rod and the piston (64) . 5. A motor vehicle lift using a hydraulic actuator in accordance with one or more of claims 1 to 4, its structural elements consisting of pair of base longitudinal members (2) , a pair of runways (4) and at least one series of pairs of arms (6, 6' ,56,56') pivoted to said longitudinal members (2), pivoted to said runways (4) and pivoted together, and with hydraulic actuators (20,20') pivoted to parts of different structural elements, the distance apart of which varies as the extent of raising of the lift varies, characterised in that each actuator (20,20') is directly pivoted to a first structural element (6) and is pivoted to a second structural element (6',56') via an intermediate member (26) which is itself pivoted to said second structural element in such a manner as to be able to undergo angular excursions, the upward travel of the lift comprising an initial part during which said intermediate member (26) rotates and one of its portions (32) interferes with a corresponding portion (40) of a structural element (6) , and a subsequent part during which the rotation of said intermediate member (26) relative to said second structural element (6',56') is blocked. 6. A vehicle lift as claimed in claim 5, characterised in that the runways (4) are of extendable type. 7. A vehicle lift as claimed in claim 5, characterised in that the intermediate member (26) consists of metal link- plates pivoted to the arms (6',56') in correspondence with plates (30,54) against which said link-plates rest on termination of the initial part of the upward travel of the lift. 8. A vehicle lift as claimed in claim 7, characterised in that to the link-plates (26) there is applied a bearing (32) acting against a plate (40) applied to the arms other than those to which said link-plates (26) are pivoted. 9. A vehicle as claimed in claim 5, characterised by comprising one pair of series of articulated arms (6,6'). 10. A vehicle lift as claimed in claim 5, characterised by comprising two pairs of series of articulated arms (6,6' ,56,56') .

Inventors: ROSSATO ERIDE, ROSSATO, ERIDE
Applicants: ROSSATO ERIDE, ROSSATO, ERIDE
Application year: 1996
Main classification: B66F7
IPC codes: B66F7, F15B15