FORCE-MULTIPLYING HYDRAULIC ACTUATOR

The present invention refers to a force-multiplying hydraulic actuator.

Various types of actuators are known in the art, both of the electro-mechanical and of the hydraulic type. These latter ones have provided a better solution from the point of view of increasing the force with variable multiplying ratios upon their sizing. An example of known actuator allows realising variable multiplying ratios from at least two and up to a maximum of five times the recirculation screw reaction. It is therefore possible to use screws in a construction range of standard sizes and loads and parking and actuating brakes sized even only for 1/5 of the maximum provided force. This type of electro-hydro-mechanical force increasing actuator has the further advantage of appearing in a construction shape which is not different from the shape of an hydraulic cylinder and to be able to replace it without excessive modifications in existing machine structures .

However, the above-described actuator has two main types of problems: first of all, it is equipped with an

actuating spring, which does not provide a constant reaction pressure, but rather a pressure accumulation and therefore does not perform a constant force stroke, and tends to lose its own functionality in time: moreover, its replacement in case of need compels to disassemble the whole actuator, with obvious problems of times and costs. Secondly, such actuator allows realising multiplying ratios which are not greater than five, which are of a rather limited application in the field of existing machines.

The above problems have been solved by the actuator disclosed in EP-A-I 273 805 of the same Applicant of the present invention. Such actuator, however, has the problem of being encumbrant, since it must be equipped with external means for pushing oil, and the problem of being actuated by a solenoid valve, which has a certain response delay and which therefore does not guarantee an optimum operation.

Object of the present invention is solving the above prior art problems, by providing a force-multiplying hydraulic actuator which does not need actuating solenoid valves, thereby avoiding replacement problems of such components and response delays during operation.

A further object of the present invention is providing an actuator of the above described type which is compact and with a reduced encumbrance, providing an oil chamber

actuated by compressed air, which is placed adjacent and parallel to the actuator body.

A further object of the present invention is providing an actuator of the above described type which is further equipped with a lubricating chamber of the actuating nut, which allows a better operation and a more efficient maintainability of this part of the actuator.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained by an hydraulic actuator as claimed in claim 1. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims .

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

- Figure 1 shows a side sectional view of the currently preferred embodiment of the force-multiplying actuator of the present invention in its closing step, with the open valve position detailed in Figure IA;

- Figure 2 is a view similar to Figure 1, with the actuator approaching the pressing operation, with its open valve as detailed in Figure 2A; and

- Figure 3 is a view similar to Figure 1, with the actuator in its pressing step and its valve open, as

detailed in Figure 3A.

As shown in the Figures, the force-multiplying hydraulic actuator 1 of the present invention substantially comprises: an elongated support body 3;

a first anchoring plate 5 and a second anchoring plate

7, each one placed at one end of the elongated support body 3 ; a control reducer 9;

- pushing/pulling means 11, 13 driven by the reducer 9;

a stem 14 pushed and pulled by the pushing/pulling means 11, 13, in which such stem 14 is contained inside a chamber 16 full of oil; and

oil entering/sucking means 18 inside/outside the chamber 16 via a duct 20 through the valve 22.

One of the characteristics of the inventive actuator 1 is that it further comprises valve means 22 placed in the moving liner 46 and communicating with the duct 20 and adapted to be driven for opening and closing by the stem 14 respectively when the stem 14 goes back and advances along the actuator 1 axis. Such valve means 22 are adapted to assume their opening position when the stem 14 goes back to allow oil pushed by the entering/sucking means 18 to penetrate into the chamber 16, and their closing position

when the stem 14 advances for preventing oil from penetrating inside the chamber 16 and for actuating the actuator 1 in a thrust with a force multiplied by the area difference existing between the chamber 16 and outside.

Moreover, the valve means 22 are driven to be opened by an elongated push rod 26 operatively connected to the stem 14 through a connection plate 28, and the valve means 22 are drived to be closed by spring means 30 operatively connected thereto.

Moreover, the inventive actuator 1 comprises an elongated chamber 32 arranged adjacent and with its own axis parallel to the actuator 1 axis, in which such chamber 32 contains oil and is connected to the duct 20, and is closed from its opposite part to the one connected to the duct 20 by a pushing pad 34.

The pushing pad 34 is actuated in its pushing action by compressed air contained in a chamber 36 placed upstream of the pad 34 and compressed by air compressing means (not shown) for facilitating the oil flow.

Moreover, the actuator 1 comprises a lubricating chamber 38 in which the pushing/pulling means 11, 13 are contained for their lubrication: the lubricating chamber 38 is connected to a tank 40 for the lubricating oil made integral with the body 3 of the actuator 1.

In particular, as shown, the pushing/pulling means 11,

13 are composed of a recirculation screw 11 with balls, rollers or planetary rollers and a nut 13.

The inventive actuator 1 further comprises at least one upright 43 adapted to prevent the stem 14 from rotating. The actuator 1 is further equipped with a fixed liner 44 and a moving liner 46, in which the moving liner 46 is operatively connected to the connection plate 28 and the rotation-preventing upright 43.

As regards its operation, the actuator 1 of the invention provides for an advancement step, driven by the reducer 9 which pushes the pushing/pulling means 11, 13 and with them the stem 14 and consequently the second anchoring plate 7 towards the position in which its force has to be exerted. When the second anchoring plate 7 abuts onto such position, it does not advance any more and the further advancement of the stem 14 makes the push rod 26 detach from the check valve 22 which then, being pushed by the spring 30, closes and blocks the oil inflow which reached the chamber 16, preventing oil from being loaded in the chamber 16 itself. In this way, due to the difference between oil volume contained in the chamber 16 and outside, a multiplied thrust is exerted which the actuator 1 must provide.

When such thrust gradually ceases during the return step, the stem 14 is withdrawn through the pushing/pulling

means 11, 13: such withdrawal takes again the push rod 26 in contact with the check valve 22, pushing it to open the duct 20 and allowing oil coming from the chamber 32 and pushed by the pad 34 through the upstream compressed air to be again pushed into the chamber 16, and the cycle starts again till a new actuation of the inventive actuator 1 is performed.

The actuator 1 of the invention finds its most efficient application in the field of pressing, and in particular in the field of forming and cutting materials, without having to use screws and toggles and allowing to perform both workings in a single operation.