Abstract:
A mechanical jack comprising a casing which encloses a reduction unit and a linear actuator device. The jack is characterized by the fact that the driven gear of the reduction unit is directly coupled, i.e. without the interposition of further mechanical elements, with a nut or more nuts of the linear actuator device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    As known, the jack is a mechanical system that transforms a rotary motion, provided, for example, by an electric, hydraulic or pneumatic motor, in a linear motion. 
         [0002]    In general, a mechanical jack comprises two main elements.
   (1) a (worm)/(helical wheel) reduction unit, or a bevel gear reduction unit, and   (2) a linear actuator device, comprising, in turn, a trapezoidal screw, ball screw, planetary roller screw, or hydrostatic screw mating.   
 
         [0005]    It is well known, also, that the main function of a mechanical jack is to generate an axial force able to move or position a given object, with relatively low use of force or torque thanks to the function performed by the reduction unit. 
         [0006]    It is also known that there are different types of jacks, each of which has specific features suitable for various application fields. 
         [0007]    Depending on the combination of the reduction unit and linear actuator device that is chosen, considerable differences of performances rendered by the system can be obtained; this is due to the efficiency of the individual components that constitute the jack itself. 
         [0008]    Some comparative examples are reported below in relation to the efficiency of the different types of jacks:
   considering a jack comprising a (worm)/(helical wheel) reduction unit coupled to a linear actuator device realized with trapezoidal screw a total efficiency of the jack between 10% and 40% is obtained;   whereas, instead, a jack comprising a (worm)/(helical wheel) reduction unit coupled to a linear actuator device realized with recirculating ball screw a total efficiency of the jack between 30% and 70% is obtained.   
 
         [0011]    Therefore, while maintaining the required performance of the two systems (speed and applied load) is possible, by adopting the second solution, to obtain a reduction of the installed power equal to approximately 45-50%. 
         [0012]    Because of this pronounced reduction of required power a mechanical jack has been developed, in accordance with the present invention, which derives from said second solution; this jack of an integrated type comprises a reduction unit and a linear actuator device constituted by a rotating and translating element. 
         [0013]    To better understand the scope of the invention it is felt useful to illustrate in the attached  FIG. 1  a traditional solution, already present in the state of the art where are identified all the characteristic elements common to said known system and to those belonging to the solutions of the present invention (see below). 
         [0014]    In  FIG. 1 , with number  10  is indicated, as a whole, a mechanical jack of traditional type. 
         [0015]    The mechanical jack comprises a casing  11  which encloses a worm)/(helical wheel) reduction unit  12  and a linear actuator device  13 , comprising, in turn, a rotating and translating element. 
         [0016]    The reduction unit  12  comprises, in known manner, a worm screw  14  (of center (C 1 )), symmetrically arranged around an axis (X), which meshes with a crown  15  (of center (C 2 )) symmetrically arranged around an axis (Y). Typically, the worm screw  14  having an involute, grinded profile, is made from hardened and tempered steel and is driven in rotation by an electric motor not shown). In turn, the crown  15  is preferably made of bronze. 
         [0017]    The crown  15  is keyed onto a hub  16  provided with a scraper  17 . 
         [0018]    In the hub  16  is formed a recess  18 , inside which is located a nut  19 . The hub  16  and the nut  19  are rigidly integral to one another. 
         [0019]    The nut  19  is part of the said linear actuator device  13 , which also comprises a rod  20  of diameter (D)) provided with a threaded portion  20 A. 
         [0020]    In a known manner, in the space which is located between the threads of the nut  19  and the threaded portion  20 A is housed a plurality of balls (not shown) to achieve the desired recirculating ball connection between the two mechanical elements. 
         [0021]    From opposite sides with respect to the axis (X) is arranged a pair of bearings  25 ,  26 , in this case cone roller bearings; the bearings  25 ,  26  may also be thrust bearings or angular contact ball bearings. 
         [0022]    In particular, each bearing  25 ,  26  respectively has an inner ring  25 A,  26 A, and an outer ring  25 B,  26 B between which are located the cone rollers. 
         [0023]    While the inner rings  25 A,  26 A are keyed on the outer surface of the hub  16 , the respective outer rings  25 B,  25 B are integral with the casing  11 , or, alternatively, can be housed in the flange or ring nut  30  and  35 . 
         [0024]    The bearing  25  is held against the casing  11  by the flange or ring nut  30  provided with a gasket  31 A. 
         [0025]    Similarly, the bearing  26  is held in place by a corresponding flange or ring nut  35  in turn provided with a respective gasket  37  retained by a cover  36 . Note also the presence in correspondence to the flange  35  of a tube  40  which keeps the nut  19  in place from above. The tube  40  has a central through hole  40 A of axis (Y). 
         [0026]    In special cases only, or if the overall dimensions allow, in the upper part of the tube a greasing radial hole  41  can be made through which a maintenance worker causes (by known means and not illustrated) a suitable lubricating fluid to flow, which, by gravity, will then flow into the free space that there is between the outer surface of the rod  20  and the wall of the through hole  40 A. Obviously the lubricating fluid, always then will flow into the underlying recirculating ball system. 
         [0027]    In most cases the re-lubrication point, consisting of the greasing radial hole, is not present, so it is necessary to perform a rather frequent periodic maintenance. 
         [0028]    By well known mechanical phenomena, a rotation of the crown  15  around the axis (Y) in accordance with one of the two directions indicated by a double-headed arrow (F 1 ) will result in an axial displacement of the rod  20  in accordance with one of the two directions given by a double-headed arrow (F 2 ), thereby completing the transformation of a rotary motion of the crown  15 , induced by the rotation of the worm screw  14 , in a translatory motion of the rod  20 . 
         [0029]    In such a case, having to interface the nut  19  to the crown  15  of the reduction unit  12  through the use of the hub  16 , it is necessary to reduce the diametrical dimensions of the nut  19  itself, thus reducing also the diameter (D) of the rod  20 ; by doing so the under-sizing of the rod  20  itself takes place which constitutes the main supporting element of the system on which acts the load to be moved or lifted. 
         [0030]    Since a standardized axle base (INT) of the reduction unit  12  is always adopted, the current trend is to fix the nut  19  laterally with respect to the crown  15 , just as was shown in  FIG. 1 . 
         [0031]    However, by doing so the angular stiffness of the system is significantly reduced; it is recommended, therefore, to use an additional guide on the rod  20  to reduce this effect of misalignment between the threaded portion  20 A and the nut  19 . 
         [0032]    In other words, by providing a jack with a hub  16  and a relative recess  18 , there is the possibility of creating a “standard” housing that allows to provide the jack with the exclusion of the linear actuator device (ball screw), allowing a subsequent insertion of the desired linear actuator device (also through the use of further reducing bushes), thus making the jack a pure and simple reduction unit. 
       SUMMARY OF THE INVENTION 
       [0033]    The purpose of the present invention is, therefore, to provide a mechanical jack which is free from the drawbacks described above and, at the same time, is of easy and economic implementation. 
         [0034]    Therefore, according to the present invention a mechanical jack is provided, as claimed in claim  1  or in any of claims depending directly or indirectly on claim  1 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    For a better understanding of the present invention, two preferred embodiments are now described, purely by way of non-limiting examples and with reference to the accompanying drawings, wherein: 
           [0036]      FIG. 2  shows a longitudinal section of a first embodiment of a mechanical jack in accordance with the present invention; 
           [0037]      FIG. 3  shows a longitudinal section of a second embodiment of a mechanical jack in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    In  FIG. 2 , with  10 * is indicated, as a whole, a mechanical jack made according to the teachings of the present invention.
   Also worth mentioning is that the elements shown in  FIG. 2 , which are identical, or similar, to the corresponding ones found in  FIG. 1  have been marked with the same numbers with the addition of asterisk.   
 
         [0040]    In  FIG. 2  it is possible to see a first example of how a crown  15 * (of center C 2 *) of a reduction unit  12 * is supported by a hub  16 * and by a nut  19 *. 
         [0041]    The nut  19 * is mechanically fixed directly to the crown  15 * of the reduction unit  12 * through a plurality of screws  38 *, making the nut  19 * and the crown  15 * integral with each other and self-supporting, thereby eliminating all those components, for example the hub  15  of  FIG. 1 , used as an interface in conventional systems (see  FIG. 1 ). 
         [0042]    In the first embodiment of the present invention shown in  FIG. 2  the nut  19 * is directly supported by the cone roller bearing  25 *, which releases stress directly onto the cover  30 * and onto the casing  11 *. 
         [0043]    In the same way the support hub  16 * of the crown  15 * is pushed against the inner ring  26 A* of the bearing  26 *, which, in turn, releases stress onto the cover  36 * and onto the casing  11 *. 
         [0044]    All this confers upon the system a high axial and angular stiffness, also reflecting high performance and high durability of the system itself.
   comparing  FIGS. 1 and 2  it is possible to note that with the same axle base (INT) of the reduction units  12 , respectively,  12 *, the diameter (D*) of the rod  20 * ( FIG. 2 ) appears to be greater than the diameter (D) of the stem  20  ( FIG. 1 ). The rod  20 * is provided with a threaded portion  20 A* coupled to the nut  19 * in a known manner with the usual recirculating ball system (see above).   
 
         [0046]    All this is in favour of the robustness of the system and of its load capacity with the same dimensions of the reduction unit  12 *,  12 , and with the same external dimensions of the jack. 
         [0047]    A solution that envisages the joint use of the hub  16 * and the nut  19 * directly coupled to the crown  15 * allows to create a reserve chamber  16 A*, interposed between the hub  16 * and the rod  20 *, for the lubricant of the same linear actuator  20 A*. 
         [0048]    In addition, the system envisages at least one greasing radial hole  41 * formed on the cover  36 * that ensures the correct amount of lubricant in any angular position the hub  16 * and the nut  19 * may be located. Through the greasing hole  41 * and the radial holes  43 * made on the hub  16 * any operator can enter (by way of known and not illustrated means) the suitable lubricant, which, by gravity, then would reach the reserve chamber  16 A* that is provided between the outer surface of the rod  20 * and the wall of the through hole of the hub. Obviously the lubricating fluid, always by gravity, will pass into the underlying linear actuator element  20 A*. For both the hub  16 *, and the nut  19 *, at the respective ends, sealing scrapers  17 * and  42  are provided, which guarantee the maintenance of the lubricant inside the reserve chamber  16 A*. 
         [0049]    This solution creates a separate area within the jack, dedicated to the exclusive lubrication of the linear actuator, by doing so an area dedicated to the lubrication of the same linear actuator and an area dedicated to the lubrication of the reduction unit are provided, wherein this latter corresponds to the free space between the casing  11 * and the reduction unit  12 *. This solution is not available on all conventional systems because it is not always possible to create or adopt a solution of said type. 
         [0050]    A further embodiment of the present invention is illustrated in  FIG. 3 . 
         [0051]    Also in this case the elements shown in  FIG. 3  that are identical, or similar to the corresponding ones found in FIGS.  1 ,  2  have been designated with the same numbers with the addition of two asterisks. 
         [0052]    Here, the configuration of the jack  10 ** distinguishes itself from the conventional versions, for example that illustrated in  FIG. 1 , for the fact that two nuts  19 A**,  19 B**, are used respectively arranged beneath and above the plane (ψ) (only the trace of the plane (ψ) is shown in  FIG. 3 ) which passes through the axis (C 1 **) of the worm screw  14 ** and is normal to the axis (Y*) of the crown  15 ** of the reduction unit  12 **. 
         [0053]    In this case with the same axle base (INT) the diameter (D**) of the rod  20 ** ( FIG. 3 ) is equal to the diameter (D*) of the rod  20 * shown in  FIG. 2 . 
         [0054]    In  FIG. 3  can be seen how the different components are arranged and how they interact with each other. 
         [0055]    The two nuts  19 A**,  19 B** are mechanically fixed to the crown  15 ** of the reduction unit  12 ** by way ct screws  38 **, that make the three elements integral with each other and self-supporting with respect to conventional systems. All the components used as an interface are also removed, making the structure of the system easier. 
         [0056]    The lubrication system, not shown in  FIG. 3 , is similar to that of the solution shown in  FIG. 2 . 
         [0057]    The free space  70 ** created between the crown  15 ** and the two nuts  19 A** and  19 B**, serves as a reserve chamber for the lubricant of the linear actuator. 
         [0058]    The use of two nuts  19 A**, 19 B** makes the system balanced under the effect of axial and radial loads applied to the rod  20 *; at the same time is significantly increased the load capacity and the angular stiffness of the rod  20 ** since the two nuts  19 A**,  19 B** serve as support to the rod  20 ** itself. 
         [0059]    In the new configuration illustrated in  FIG. 3 , the jack  10 ** has better balance therefore lends itself to be mounted both straight and reversed, without difference in performance with pull and/or thrust load. 
         [0060]    On the contrary, in the conventional configuration shown in  FIG. 1  the specific fitting direction of the nut  19  must be respected with respect to the direction of the applied load, otherwise there will likely be differences in performance, but especially large differences in durability of the entire system. 
         [0061]    Furthermore, in the embodiment shown in  FIG. 3 , since there is a better overall balance of the whole mechanical part, there is a significant optimization of the durability of the following components:
   (screw)/(crown) reduction unit;   bearings; and   screw and nut.   
 
         [0065]    The present invention allows to obtain the following advantages:
   reduction of the number of interface components between the reduction unit and the nut of the rotating and translating component;   increase of the space in which to interpose the nut or nuts;   maximization of the diameter of the rod of the rotating and translating system, and, therefore, increase of the load capacity;   guarantee of a better behavior under load, giving the system better balance under the action of loads acting on the screw, both in compression and in traction;   high rigidity of the system, due to the increase of resistant sections;   increase of the dynamic capabilities of the entire system;   improved balance of the durability of the respective components (linear actuator, bearings and reduction unit);   better behavior under the effect of peak loads;   simplified re-lubrication;   no oil leaking thanks to the gaskets placed on all the rotating components;   periodical maintenance practically canceled; and   significant increase in performance with the same dimensions.