HYDRAULIC ACTUATORS

DESCRIPTION OF THE INVENTION

The object of the present invention is an apparatus for regulating the stroke of double-acting hydraulic actuators for the hydraulic actuation of manoeuvring means of operating machines.

In the prior art, each of these hydraulic actuators, consisting of double-acting hydraulic cylinders, is individually equipped, for safety reasons, with its own shut-off valve, which is fastened to the cylinder itself with the specific task of ensuring, in the event that a hydraulic hose gets broken, the sealing of the cylinder, preventing it from emptying and dropping the operating element and the load applied thereto.

To achieve a certain precision and linearity in the descent of an device such as a hoisting arm of an operating machine driven by a double-acting cylinder, a hydraulic over-center valve is normally provided, through which pressure is given to the stem side of the cylinder and the bottom side is opened in order to lower the arm in safety. With this solution, however, essentially because it uses a hydraulic-mechanical valve, at the time of opening during the descent phase, a more or less abrupt movement occurs, depending on the settings, that is gradually more extended as the loads involved increase. Furthermore, especially for large operating machines using large hoisting arms operated by big cylinders and subjected to their own weight and that of the heavy loads, an actual hopping is caused during lowering due to occurrence of a sudden drop in pressure on the stem side (because the hydraulic liquid supplied to the chamber on the stem side by the distributor is insufficient to fill the volume necessary to keep the chamber under pressure) and this causes the momentary closure of the shut-off valve with consequent stopping of the arm lowering. Lowering, however, resumes immediately after giving rise to a succession of operation steps in rapid succession of the shut-off valve (hopping) until the cylinder on the stem side is restored to operating pressure.

To solve this problem, the use of a hydraulic accumulator is known, which is specifically designed to feed the chamber on the stem side and keep it under pressure throughout the lowering stroke.

However, the known technique has the disadvantage of causing a certain functional and constructive complication in the bottom sides. This is in particular evident when two or more hydraulic actuators work together to hydraulically actuate operating machine parts.

Object of the present invention is to limit the disadvantages and drawbacks of the prior art while maintaining high safety standards, in accordance with what is described, illustrated and claimed below. Another object of the invention is to synchronize the pressures and make them uniform at every point of the circuit of two or more hydraulic actuators that collaborate together coupled to the hydraulic operation of manoeuvring and lifting members mounted onto operating machines. An advantage of the invention is that it has a relatively simple structure in terms of circuitry.

Additional features and advantages will result more evident from the following detailed description of some preferred, but not exclusive, embodiments of the invention, herein illustrated by way of example only in the attached figures, in which: ,

- Figure 1 shows a schematic side view in vertical elevation of a self-propelled operating machine equipped with a manoeuvring device consisting of a telescopic arm for the hydraulic lifting of which a double-acting hydraulic actuator or cylinder is used;

- Figure 2 shows a schematic hydraulic layout of a first embodiment of the invention;

- Figure 3 shows a schematic hydraulic layout of a second embodiment of the invention;

With reference to the above mentioned Figures, numeral 1 indicates as a whole a self-propelled operating machine, made mobile on wheels 2, which is equipped with a manoeuvring member at the top, consisting of a telescopic hoisting arm 3, the movement of which is carried out by means of a double acting hydraulic actuator 4.

The hydraulic actuator 4 is nothing more than a double-acting hydraulic cylinder which is hinged with its bottom side 5 to the frame of the self-propelled operating machine 4 and, with its stem, to the telescopic hoisting arm 3.

The hydraulic actuator or double-acting hydraulic cylinder 4 is fed by a hydraulic control circuit, which is connected to a hydraulic distributor 7, from which a supply line 8 for feeding the bottom side 5 and a supply line 9 for feeding the stem side 6 originate.

A shut-off and regulation valve 10 is provided along the supply line 8 of the bottom side 5, with the function of intercepting and regulating the flow of fluid out coming, the valve being controlled by an electronic regulation valve 11.

This latter is operated by the signal originating from a pressure transducer 12 as a function of a pressure value measured at the stem side 6.

The electronic regulation valve 11 is adjusted to intervene on the shut-off valve 10 in order to control and increase its opening when the pressure of the stem side 6, reported by the pressure transducer 12, reaches a preset minimum value and to open the valve up to reaching a pressure at stem side 6 having a predetermined value.

If the pressure on the stem side falls down, the opening of valve 10, controlled by the electronic control valve 11 , is reduced (when the movement stops it is completely closed), so as to maintain the pressure on the stem side 6 within a pre-established "balancing" pressure range.

The electronic regulation valve 11 is controlled by the value of the pressure on the stem side 6 through interposition of a pressure reducing valve 13.

Of course, starting operation of the electronic control valve 11 is determined by its necessary adjustment, with which the minimum and maximum values that define the range of action of the "balancing" pressure have been set in advance. Therefore, during the lowering step, i.e. the return of the stem, the actual pressure, as reduced by the reducing valve 13, which is detected at the rod side 6 of the double-acting hydraulic cylinder 4, operates the shut-off valve 10.

In other words, the shut-off valve 10 is operated hydraulically through the interposition of the pressure reducing valve 13 and is modulated by the electronic control valve 11 which is a proportional valve.

The combination of the pressure reducing valve 13 and the electronic proportional control valve 1 1 is indicated by the acronym EVP, and hydraulically controls the shut-off valve 10 according to the methods described above.

In this way, all safety measures of the machine and the control of the lowering speed of the hoisting arm remain managed by the hydraulic distributor 7.

The action of the EVP system, including the electronic control valve 11 , thus avoids the inconvenience of possible repeated closing of the shut-off valve 10, which would cause a kind of unwanted "hopping" of the telescopic hoisting arm 3 and the load it supports, thus allowing a continuous and shock-free lowering of the piston stem of the hydraulic actuator consisting of the double acting hydraulic cylinder 4.

This allows the oil pressure on the piston stem side 5 to be maintained within a set interval. This also allows achieving the result of smoothing the abrupt start of the movement, allowing instead gradual start and operation. Operation is simple: when the operator gives the lowering command for the telescopic hoisting arm 3, the hydraulic distributor 7 is used to send oil to the chamber at the stem side 6 of the double acting hydraulic cylinder 4. The electronic control valve 11 operates in such a way that the pressure on the stem side 6 starts to rise, until a certain pre-set value is reached, when the shut-off valve 10 starts to open more and more under control by the electronic regulating valve 11 and hydraulically operated by the pressure on the stem side 6 through the reducing valve 13, so gradually lowering the telescopic hoisting arm 3.

As the opening increases, the lowering speed of the telescopic hoisting arm 3 increases progressively.

As soon as the lowering speed increases above a certain limit, the pressure on the stem side may decrease 6, which would cause the electronic control valve 11 to come into operation, which would command the shut-off valve 10 to reduce its opening, in order to keep the pressure on the stem side 6 within a predetermined minimum and maximum limit.

It will be appreciated that only the hydraulic distributor 7 always controls the lowering speed of the arm.

If, for any reason, the electronic control valve 11 is blocked, even if it is fully open, the telescopic hoisting arm 3 would never fall down, because without pressure on the stem side 6, which occurs only with the opening of the distributor and therefore with the consent of the operator, the shut-off valve 10 does not open mechanically.

This means that all the safety features on the machine are not reduced or dropped. According to a second embodiment of the invention, the movement of the telescopic hoisting arm 3 is carried out by means of two double-acting hydraulic actuators or hydraulic cylinders 4 equal to each other, which work together in conjunction with the hydraulic operation of the telescopic hoisting arm 3, both on lifting and lowering.

Each double acting hydraulic actuator or hydraulic cylinder 4 is served by a hydraulic control circuit, which is connected to the same hydraulic distributor 7 from which, for each of them, a supply line 8 for feeding the bottom side 5 and a supply line 9 for feeding the stem side 6 originate.

On each of the supply lines 8 to the bottom side 5 there is a shut-off valve 10 with the function of intercepting and regulating the flow coming out of the relative bottom side 5.

Each double acting hydraulic actuator or hydraulic cylinder 4 is fed by a hydraulic control circuit, connected to the same hydraulic distributor 7 from which, for each double-acting hydraulic actuator or hydraulic cylinder 4, the supply line 8 for feeding the bottom side 5 and supply line 9 for feeding the stem side 6 originate, as previously mentioned.

An electronic regulation valve 11 is operated by the signal originated by a pressure transducer 12 in accordance with a pressure value detected at the stem side 6 of the double-acting hydraulic actuators or hydraulic cylinders 4.

The electronic regulation valve 11 is adjusted to intervene on the shut-off valves 10 in order to control and increase their openings when the pressure of the stem side 6, reported by the pressure transducer 12, reaches a preset minimum value and to open the valves up to reaching pressures at stem side 6 having a predetermined value.

If the pressure on the stem side falls down, the opening of valve 10, controlled by the electronic control valve 11 , is reduced (when the movement stops it is completely closed), so as to maintain the pressure on the stem side (6) within a pre-established "balancing" pressure range.

The electronic regulation valve 11 is adjusted to intervene on the shut-off valves 10 in order to control and increase their openings when the pressure of the stem side 6, reported by the pressure transducer 12, reaches a pre-set minimum threshold.

If the pressure on the stem side falls down, the openings of valves 10, controlled by the electronic control valve 11 , are reduced (when the movement stops they are completely closed), so as to maintain the pressure on the stem side within a pre-established "balancing" pressure range.

The electronic regulation valve 11 is controlled by the value of the pressure on the stem side 6 through interposition of a pressure reducing valve 13.

In other words, the electronic regulation valve 11 acts on the shutoff valves 10 so as to gradually increase their opening starting when the pressure at the stem side 6 reaches a preset minimum threshold, and to reduce, also gradually, the opening in case the pressure on the stem side is reduced, so as to maintain on the stem side a pre-set so called pressure "balancing" value. Of course, starting operation of the electronic control valve 11 is determined by its necessary adjustment, with which the minimum and maximum values that define the range of action of the "balancing" pressure have been set in advance.

In other words, each shut-off valve 10 is operated by the value of the pressure at the side of the stem 6 through the interposition of a pressure reducing valve 13 and is modulated by the electronic control valve 11.

A connection 16 has been introduced between the chambers at the bottom sides 5 and a similar connection 17 has been inserted between the two chambers at the stem sides 6, which ensures stability and uniformity of pressures within the two chambers.

In particular, the electronic regulation valve 11 operates on both shut-off valves 10 in accordance with the methods previously illustrated, carrying out gradual interventions, without abrupt movements or shocks.

In this way, the two double-acting hydraulic cylinders 4 can be operated synchronously in a simple and effective manner.

Numeral 14 indicates the driving line connecting the second shut-off valve 10, operating on the bottom side 6, to the electronic regulation valve 11 of the second double-acting hydraulic actuator or hydraulic cylinder 4.

A parachute valve 15 is arranged and operates along the bottom side balancing line 16 of the two double-acting hydraulic actuators or hydraulic cylinders 4.

The parachute valves 15 operate in the same way on the bottom sides of the double acting hydraulic actuators or hydraulic cylinders 4, are connected to each other by a connection 16 and have the task of preventing both chambers from emptying in the event of a breakage of a pipe.

This allows the double acting hydraulic actuators or hydraulic cylinders 4 to work in synchronism, especially during the lowering step, guaranteeing the safety standards required by the regulations in force.

The modes of operation are basically those of the first illustrated embodiment characterized by the presence of a single double acting hydraulic actuator or hydraulic cylinder.