Electrical, telescopic jack

Abstract

 A hoisting device is disclosed, in particular for use in test fields of aircrafts such as helicopters and small airplanes, comprising an extensible, electrically operated assembly provided with coaxial sleeves (8,9,10) slidable by being screwed to one another, and a telescopic rod (11) integral with the base (2) of the jack and located at the centre of the sleeve assembly, the last extensible arm of said rod (11) being rotatably connected to the innermost sleeve (10) along which said arm can axially slide. The outermost sleeve (8) is rotated by a threaded bush (7), which is itself rotated by a worm screw/crown gear mechanism (4,5), and is unscrewed by reaction from the threaded bush (7) as all of the remaining sleeves engaged with one another are prevented from rotating by the telescopic rod (11). This is also the case in the following steps for the remaining sleeves without the need of retaining the jack.

Description

[0001] The present invention relates to a hoisting device, in particular for large vehicles, vessels, aircrafts, helicopters, a.s.o., which is extremely precise and safe.

[0002] The hoisting of vehicles of considerable dimensions, in particular aircrafts and helicopters, is a very usual operation during maintenance, weighing and levelling but has hitherto been carried out by using devices not specifically designed to that purpose. A number of commercial, manually operated jacks have always been used. They have involved a number of problems bound to the short safety for the workers, the lack of precision in reaching and keeping the predetermined height, the wearisomeness of the preparation steps.
The hydraulic jacks of the prior art need the aircraft be secured by steel supports formed of sectional modules which are manually arranged. This allows the aircraft to be hoisted only at prefixed heights corresponding to multiples of the heights of the available modules, besides involving a lot of work.

[0003] The present invention seeks to overcome the problems mentioned above by providing electrically operated telescopic jacks which are particularly suitable for the test fields of helicopters and small airplanes and able to assure the maximum precision of the hoisting displacement, thus allowing a full-safe work without the use of any support scaffolding or external fastening bond of any type, thereby facilitating the weighing and levelling steps.

[0004] According to the invention each jack is formed by an extensible, adjustable assembly comprising a number of coaxial sleeves slidable by being screwed to one another, and an axial member which is resistant to torsion, integral with the base of the jack, and formed of a telescopic rod placed at the centre of the sleeve assembly, the last extensible arm of which is connected to the base of the innermost jack in a groove where it can only axially slide but not rotate, thus making the sleeve rotatably integral with the base of the jack. Each sleeve is externally threaded along its length and is provided at the upper side with an inner threading to which the next coaxial sleeve of right lesser diameter is screwed. This inner threading is formed in a section having lower diameter and forming a shoulder serving as abuting stop for an annular edge projecting from the base of each sleeve, thus avoiding the latter to be completely drawn.
The outermost sleeve at the base of the jack is driven by a threaded bush which is rotated by an worm screw/crown gear mechanism.
With this arrangement, as the bush is rotated, the outer sleeve will begin to rotate in the reverse direction, thus being unscrewed by reaction from the same bush as all of the remaining sleeves engaged with one another are prevented from rotating by the telescopic rod engaged with the latter sleeve.
As the unscrewing controlled by the above-mentioned stop is completed, the outer sleeve becomes integral with the adjoining sleeve and imparts to the same its movement, thus causing it to unscrew and the jack to extend. This is also the case in the following steps for the other sleeves until the maximum (or the desired) extension of the jack is reached without the need for outer constraints which would be necessary for the operation if the above-described devices were not provided.

[0005] Further features and advantages of the invention will be more readily apparent from the following description with reference to the accompanying drawings which show by way of a non-limitative example a preferred embodiment of the invention. In the drawings:

Fig. 1 is a elevation section view of a jack according to the invention in its maximum extension;

Fig. 2 is a plan view of the same jack;

Fig. 3 shows the jack in retracted position.

[0006] With reference to the drawings the described jack includes an annular base 1 preferably of cast iron supporting a base plate 2 by which a threaded bush 7 preferably of bronze is rotatably carried with the interposition of thrust bearings 3, said bush being connected through a key 6 to a crown gear 4. Crown gear 4 is driven by a worm screw 5 operated through an intermediate reduction gear (not shown) by an electric motor 20.
Threaded bush 7 engages with the threading of sleeve 8 which is the outermost sleeve of a set of three coaxial sleeves 8, 9 and 10 forming telescopically extensible assembly. A suitable selection of materials, for example steel for sleeve 8 and bronze for sleeve 9, allows a self-lubrication. It is evident that the number of the illustrated sleeves is only indicative as it can be changed according to the size of the jack.
Sleeves 8, 9 and 10 are screwed to one another through thread 22 formed at their upper side in an inner shoulder 24 acting as abuting stop for the annular edge 26 projecting from the lower base of the same sleeves. Rigidly connected to the plate 2 is the lower end of a telescopic rod 11 formed by a plurality of extensible sections which are axially guided by means of appropriate grooves and sliding seats 13 and 15, the former being carried by the first section, the latter being connected to base 28 of sleeve 10. Such rod 11 is an ideal axial fulcrum for the rotating sleeve assembly as its upper end can only slide in seat 15 but non rotate relative to sleeve 10, thus avoiding any further rotation thereof.

[0007] From the foregoing the operation is self-evident: when crown gear 4 rotates threaded bush 7, the latter causes by reaction sleeve 8 to unscrew in the reverse direction as all of the remaining sleeves 9 and 10 screwed to each other are prevented from rotating by telescopic rod 11. The unscrewing of sleeve 8 is stopped as its annular edge 26 abuts against shoulder 27 of threaded bush 7; sleeve 8 causes sleeve 9 to rotate and then to unscrew until its annular edge 26 abuts against shoulder 24 of sleeve 8. This is also the case in the following steps until the desired length is reached.

[0008] The advantages of this invention are evident: the jacks are strong and quite safe as they self-lock in the reached position and cannot be moved by chance even in the presence of mechanical troubles or power failure. The screwing extension system allows even millimetric movement to be controlled with very high precision. The jack of the present invention is capable to operate as a common hydraulic jack but makes the supporting of the aircraft useless and does not involve the use of further outer constraints.

[0009] The present invention has been described with reference to a preferred embodiment thereof but it should be understood that a number of construction modification can be made by those skilled in the art without departing from the scope of the present industrial invention.

Claims

1. A telescopic jack wherein it comprises an extensible, adjustable assembly including a plurality of coaxial sleeves slidable by being screwed to one another, and a telescopic rod integral with the base of the jack and located axially relative to said sleeve assembly, the last extensible arm of said rod being rotatably connected to the innermost sleeve so as to be rotatably connected to and be able to slide relative to the latter in order to allow the jack to be operated between the bearing plane of the base and the load to be lifted without the need for outer constraints.

2. The telescopic jack of claim 1, characterized in that each of the sleeves is threaded at the outer side and is provided at the upper side with a corresponding inner thread to which the next coaxial sleeve of right lesser diameter is screwed.

3. The telescopic jack of the preceding claims characterized in that the inner thread is formed in a section of lower diameter forming a shoulder acting as abuting stop for an annular edge projecting from the base of each sleeve, thus avoiding the latter to be completely drawn.

4. The telescopic jack of the preceding claims characterized in that the outermost sleeve is driven at the base of the jack by a threaded bush which is rotated by an electric motor through a worm screw/crown gear mechanism.

5. The telescopic jack of the preceding claims characterized in that the telescopic rod is formed by a plurality of tubular grooved sections inserted in one another which are axially guided into proper sliding seats.

6. The telescopic jack of the preceding claims characterized in that said telescopic rod is an ideal axial fulcrum for the assembly of sleeves screwed to one another as the upper end thereof prevents the innermost sleeve from rotating.

7. The telescopic jack of the preceding claims characterized in that the sleeves are provided at the lower end with annular edges which abut against corresponding shoulders formed in both the threaded bush at the base of the jack and the upper end of each sleeve.

Drawing