Flow control and check valve for a hydraulic control circuit of a lifting installation

Abstract

 Flow control valve (101) for a hydraulic control circuit of a lifting installation, comprising a slider (102) slidably movable inside a valve body (103) between a fully open valve position and a fully closed valve position, so as to regulate the flow which passes through the flow control valve (10), further comprising an electric stepper motor acting on said slider (102) by means of a reversible pair (105, 106), preferably a pinion (105) on the motor side meshing with a rack (106) integral with said slider (102), and resilient means (107) also acting on said slider (102) and designed to move it into and/or keep it in the fully closed valve position in the absence of the power supply to the electric stepper motor (104).

Description

Field of application

[0001] The present invention relates to a hydraulic circuit designed to control the flow to the hydraulic actuating cylinder of a lift, platform, hoist or similar lifting system.

[0002] The invention also relates to a flow control valve and to a flow control unit specifically designed to be used inside said hydraulic circuit.

Prior Art

[0003] Lifting installations of the hydraulic type, where a loading platform or cabin is raised by one or more hydraulic cylinders, are commonly used in a plurality of applications where the vertical travel movements are sufficiently small to suggest use thereof.

[0004] The operation of these lifting installations is performed by an oil-hydraulic circuit, in which one or more valves for controlling the flow to the hydraulic cylinders allow adjustment of the speed during the start and stop transients, both during raising and during lowering of the load.

[0005] These control valves may consist in particular of electrovalves which are directly driven by the control electronics, allowing proportional adjustment of the oil flow to and from the hydraulic cylinders of the installation.

[0006] Attempts to achieve precise control performed by low-cost components have resulted in the adoption of electrovalves provided with a stepper motor which is connected to the slider via a screw transmission system. Thus, the linear position of the slider and the consequent oil flow are specifically determined by the angular position of the motor and it is possible to reproduce in a faithful manner a desired speed profile during the various load displacement operations.

[0007] On the other hand, in order to ensure the safety of the installation, in particular where the latter is designed to raise persons, stop valves which prevent uncontrolled emptying of the hydraulic cylinder in the event of a malfunction or power failure must be provided. In the specific case of lifting installations for persons, at least two normally closed valves must be provided in order to prevent the uncontrolled return of the circuit oil into the storage tank.

[0008] The aforementioned opposing requirements of safety and precise control result in the need for a multiplicity of components and ultimately result in a high complexity and consequent increase in the costs of the hydraulic plant.

[0009] The technical problem forming the basis of the present invention is therefore that of devising a flow control valve and a corresponding hydraulic circuit for a lifting installation such as to ensure the desired characteristics of safety and precision, achieved, however, with a number of components and a structural simplicity not encountered in the prior art.

Summary of the invention

[0010] The aforementioned technical problem is solved by a flow control valve for a hydraulic control circuit of a lifting installation, comprising a valve body, a flow path extending between an inlet opening and an outlet opening, a slider slidably movable inside a seat formed in the valve body along said flow path between a fully open valve position and a fully closed valve position, further comprising an electric stepper motor acting on said slider so as to regulate the flow which passes along said flow path, a reversible kinematic pair between the stepper motor and the slider and resilient means acting on the slider so as to urge it constantly towards the fully closed valve position.

[0011] A person skilled in the art will appreciate how the aforementioned valve is able to perform in an excellent manner flow control with optimum precision owing to the use of the stepper motor and how moreover the use of a reversible pair allows the resilient means - preferably consisting of a simple spring - to exert their action on the slider in the absence of a power supply to the electric motor, this preventing untimely and potentially damaging emptying of the hydraulic control circuit of the lifting system.

[0012] The said slider allows preferably throttling of the flow which passes between an inlet opening and an outlet opening of the flow control valve, namely a proportional action of the flow control valve.

[0013] The aforementioned reversible pair comprises preferably a pinion on the motor side meshing with a rack integral with said slider.

[0014] The flow control valve may also comprise at least one magnetic sensor for detecting at least one position from among the fully open position and fully closed position of the flow control valve. This sensor allows the position of the stepper motor to be calibrated with respect to the actual position of the slider so as to avoid positioning errors in the long run.

[0015] In one embodiment of the present invention, the slider may be arranged so as to open out inside a pressure chamber supplied by a pilot duct. Said pressure chamber is, at least in certain configurations of the slider, hydraulically separate from the inner chambers which lead to the inlet and outlet openings.

[0016] In one embodiment of the invention, the flow control valve is formed so that the fluid pressure inside the pressure chamber acts on said slider in the same sense as the resilient means.

[0017] In other words, if the slider in the fully closed valve position separates an inlet chamber which communicates with the inlet opening and an outlet chamber which communicates with the outlet opening, said inlet chamber is arranged between the pressure chamber and the outlet chamber.

[0018] In this embodiment, the pressure in the pressure chamber helps keep the slider in the fully closed valve position.

[0019] The pressure chamber is preferably pressurized by a three-way pilot electrovalve which, when not activated, places the pressure chamber in fluid communication with the inlet opening of the flow control valve and, when activated, places the pressure chamber in communication with the outlet opening.

[0020] Thus, it is necessary to activate the pilot electrovalve in order to open the flow control valve.

[0021] In another embodiment of the invention, the flow control valve is formed so that a fluid pressure inside the pressure chamber acts on said slider in the opposite sense to the resilient means.

[0022] In other words, if the slider in the fully closed valve position separates an inlet chamber which communicates with the inlet opening and an outlet chamber which communicates with the outlet opening, said outlet chamber is arranged between the pressure chamber and the inlet chamber.

[0023] In this embodiment, the cross-section of the surface of the slider facing the pressure chamber is greater than the cross-section of the opposite surface of the slider, facing a chamber in direct communication with the inlet opening.

[0024] Thus, if the pressure chamber is placed in communication with the inlet opening, the resultant of the forces facilitates the opening action of the valve by the stepper motor.

[0025] This embodiment thus allows the use of low-power stepper motors, also in the case of high operating flowrates.

[0026] In this case also, the pressure chamber is preferably pressurized by a three-way pilot electrovalve. When activated, the electrovalve places the pressure chamber in fluid communication with the inlet opening of the flow control valve and, when not activated, places the pressure chamber in fluid communication with the outlet opening.

[0027] A flow control unit comprising a flow control valve and a pilot electrovalve associated therewith in the ways described above also forms part of the present invention.

[0028] The aforementioned problem is also solved by a hydraulic circuit for controlling the flow to and from a hydraulic actuating cylinder of a lifting installation, comprising: a delivery branch, along which a pump which connects a supply tank to said hydraulic actuating cylinder operates; and a return branch, which departs from said delivery branch after a first section of the latter and returns to the supply tank; said hydraulic circuit comprising at least one flow control valve of the type previously described, said flow control valve being arranged so as to intercept the flow along said return branch.

[0029] Thus connected, the flow control valve performs the dual function of indirect regulation of the flow sent to the actuating cylinder and safety check valve.

[0030] In the hydraulic circuit, the first section of the delivery branch may advantageously connect the supply tank to a one-way pump check valve, said return branch departing from said delivery branch downstream of said pump check valve.

[0031] A second check valve, operated by a pilot electrovalve, may be advantageously arranged on the delivery branch upstream of said one-way pump check valve.

[0032] The hydraulic circuit may also comprise an electronic control unit designed to control operation of the stepper motor of the flow control valve, said electronic control unit receiving at its input the signal of at least one flow transducer, which may be advantageously incorporated in the second check valve.

[0033] Further characteristic features and advantages of the flow control valve, flow control unit associated therewith and corresponding hydraulic circuit will emerge from the description hereinbelow, of a number of examples of embodiment, provided by way of a non-limiting example, with reference to the accompanying drawings

Brief description of the drawings

[0034] 

Figure 1 shows a cross-sectional view of a first embodiment of a flow control valve according to the present invention;

Figure 1a shows a cross-sectional view of a variant of the flow control valve in accordance with the first embodiment of Figure 1;

Figure 2 shows a cross-sectional view of the two components of a flow control unit in accordance with the present invention, more particularly a flow control valve in accordance with a second embodiment of the present invention and a pilot electrovalve associated therewith;

Figure 3 shows a cross-sectional view of the two components of a flow control unit in accordance with the present invention, more particularly a flow control valve in accordance with a third embodiment of the present invention and a pilot electrovalve associated therewith;

Figure 4 shows a cross-sectional view of the various components of a hydraulic circuit in accordance with the present invention for controlling a lifting installation, comprising the flow control unit of Figure 2;

Figure 5 shows the hydraulic diagram of an oil-hydraulic control circuit in accordance with the present invention, comprising the flow control unit of Figure 2;

Figure 5a shows a variant of the hydraulic diagram shown in Figure 5.

Detailed description

[0035] With reference to the accompanying Figures 1 and 1a, 1 denotes in general a first embodiment of the flow control valve according to the present invention.

[0036] Said flow control valve 1, as will be described more fully below, is intended to be used in a hydraulic circuit for controlling the flow to and from a hydraulic actuating cylinder of a lifting installation, be it a lift, platform, hoist or similar device.

[0037] In particular, as described more fully below, this flow control valve 1 is preferably positioned on a branch for conveying back to the control unit the oil which supplies the hydraulic cylinder and performs the dual function of regulating the flow of discharged oil - and therefore, indirectly, the oil conveyed to the cylinder - and stopping the flow when there is an interruption in the electric power supply.

[0038] The flow control valve 1 comprises a valve body 3, which defines internally a flow path between an inlet opening 10, which receives the oil from the delivery of the pump supplying the hydraulic circuit, and an outlet opening 11, which is connected to the storage tank of the control unit of the installation.

[0039] The inlet opening 10 and the outlet opening 11 consist of externally communicating openings of an inlet chamber, or duct, and of an outlet chamber 23, or duct, respectively. The ducts are parallel and staggered with respect to each other and define the two aligned and concentric chambers which are connected together by a first portion of a transverse channel 14. The transverse channel 14, from the outlet chamber 24, extends perpendicularly and encounters the inlet chamber 22 and then continues with a second portion.

[0040] The first portion of the transverse channel 14 is formed by a first sleeve 20 which is sealingly inserted between two valve body portions 3 which contain respectively the two aforementioned chambers 22, 23, while the second portion is defined by a simple bore in the valve body 3 closed at the end by a second sleeve 21, inserted between the valve body portion 3 which contains the inlet chamber 22 and a further portion which defines a tubular extension of the body.

[0041] The valve body 3 comprises a slider 2 which is slidably movable inside it and in particular inside the aforementioned transverse channel 14. The slider 2 has an elongated form and comprises a regulating head 16 and an actuating end-piece 17 which are connected together by a connecting screw 19 which passes through an intermediate tubular section 26 of the said slider 2.

[0042] The actuating end-piece 17 has a cup-shaped form; the end surface has a projection for connection of the cup externally, inside which the connecting screw-bolt 19 is screwed. In the opposite direction, a guide stem 18 is screwed onto the other side of the end surface and is inserted at the other end inside the second sleeve 21.

[0043] The guide stem 18 is surrounded by resilient means namely by a helical spring 7, which is compressed between the actuating end-piece 17 and the second sleeve 21, bearing against the aforementioned end surface of the actuating end-piece 17 and around a guide hole of the second sleeve 21 inside which the free end of the guide stem 18 slides.

[0044] The regulating head 16 has a front opening, which leads into the outlet chamber 23, and a plurality of lateral apertures 15 communicating with the front opening. The lateral apertures 15, depending on the linear position of the slider 2 inside the transverse channel 14, may be fully closed by the surrounding surface of the transverse channel 14; or they may open out - partially or totally - inside the inlet chamber 22. Only in this latter case does the flow control valve 1 allow the oil to flow along the fluid path which connects the inlet opening 10 to the outlet opening 11.

[0045] It should be noted in particular that the slider 2 is movable between two end positions: a fully closed valve position (shown in Figures 1 and 1a), in which the lateral apertures 15 are fully closed and the oil flow through the valve is interrupted; and a fully open valve position (not shown in the attached figures), opposite to the first position, in which the lateral apertures 15 are fully open. The intermediate positions of the slider 2 allow a proportional control of the valve, namely greater or lesser throttling of the flow depending on the amount of area of the lateral apertures 15 which is kept covered.

[0046] It should be noted that the valve body 3 has, screwed inside it, a regulating screw 24, the free end of which makes contact against the regulating head 16 of the slider 2, defining the end-of-travel position of the latter, namely the fully closed valve position.

[0047] The aforementioned helical spring 7, which acts against the actuating end-piece 17 pushing the entire slider 2 away from the second sleeve 21, tends to keep the slider in the fully closed valve position.

[0048] Operation of the slider 2, which allows the position between the fully closed valve position and the fully open valve position to be varied in a controlled manner, is performed by means a stepper motor, which is not shown in Figures 1 and 1a. The electric motor rotationally drives a pinion 5 which is housed inside a niche which at the bottom opens out along the second portion of the transverse channel 14. The pinion 5 is rotatable about an axis of rotation perpendicular to the sliding axis of the slider 2, namely the longitudinal extension of the transverse channel 14, and meshes at the top with a rack 6 formed on the bottom outer portion of the cup-shaped body of the actuating end-piece 17.

[0049] The kinematic pair defined by the pinion 5 and the rack 6 allows variation of the position of the slider 2, and consequent throttling of the flow, by means of operation of the electric stepper motor. Moreover, since the kinematic pair is reversible, when the power supply is interrupted and the torque provided by the stepper motor is no longer present, the helical spring 7 is able to exert its action and push the slider 2 into - or keep it in - the fully closed valve position, so as to form a check valve which constitutes an additional safety features for the lifting installation.

[0050] It should be noted finally that magnetic sensor means 25 intended to allow detection of the position of the slider 2 are provided. These magnetic sensor means are arranged at the free end of the guide stem 18 and the tubular extension of the valve body 3 inside which said free end extends.

[0051] The variant shown in Figure 1a differs from the embodiment described above only in that it comprises two elastomer seals arranged at the ends of the tubular intermediate section 26 of the slider 2 and intended to improve the seal of the flow control valve 1, namely on the one hand ensure the impermeability of the inlet chamber 22 with respect to the second portion of the transverse channel 14 and on the other hand prevent leakages into the outlet chamber 23 out of the lateral apertures 15.

[0052] With reference to the attached Figure 2, 101 denotes in general a second embodiment of the flow control valve according to the present invention.

[0053] The flow control valve 101 has, in a manner similar to that of the first embodiment, a valve body 103 inside which an inlet chamber or duct 122 and an outlet chamber or duct 123 are formed. The ducts, which are staggered and parallel, lead into an inlet opening 110 and an outlet opening 111, respectively, and define aligned and concentric chambers.

[0054] The two chambers 122, 123 are in this case also connected by a transverse channel 114 which is perpendicular with respect to said chambers and houses in a slidable manner a slider 102 operated by an electric stepper motor 104 (shown in Figures 5 and 5a).

[0055] In this case, however, differently from the previous embodiment, the transverse channel 114 extends beyond the two chambers and is sealingly closed at a first end by an end cover of the valve body 103 and at the other end by a tubular appendage of said valve body. The direction of the flow path from the inlet chamber 122 to the outlet chamber 123 is from the first end towards the second end.

[0056] The transverse channel 114, which in a downstream portion (towards the second end) is formed by a simple bore in the valve body 103, comprises instead a first upstream portion defined by a first sleeve 120 and by a second sleeve 121 housed in sequence inside said valve body 3 and kept in position by the aforementioned end cover.

[0057] The first sleeve 120, which is arranged upstream, has a first smaller-diameter portion and a second larger-diameter portion having, formed therein, a number of holes communicating with the inlet chamber 122. The second sleeve 121, which is arranged downstream, also has a smaller-diameter portion which, arranged next to the larger-diameter portion of the first sleeve 120, defines a shoulder inside the transverse channel 114. This portion also widens in this case along a second section having, formed therein, holes communicating with the outlet duct 123.

[0058] The slider 102 has an elongated form and comprises, from upstream to downstream, a guiding end-piece 117 followed by a regulating member 116 and an actuating stem 118. The three parts are held together by a connecting screw 119 which, being screwed into one end of the actuating stem 118, tightens a locking disk which clamps in position the guiding end-piece 117 and the regulating member 116.

[0059] The guiding end-piece 117, which has a tubular shape, is introduced sealingly inside the smaller-diameter portion of the first sleeve 120 so as to define, between itself and the end cover of the valve body 103, a sealing chamber 109 which communicates with the outside by means of a pilot duct 108, the function of which will become clearer from the continuation of the description.

[0060] The opposite end of the guiding end-piece 117 has instead an enlarged portion which is arranged over the adjacent regulating member 116, forming a bearing surface which cooperates in an end-of-travel position with the shoulder defined by the second sleeve 121. A resilient seal is inserted between the regulating member 116 and the said enlarged portion and ensures a sealed closure of the transverse channel when the bearing surface rests against the shoulder.

[0061] It should be noted that the guiding end-piece 117 has a hole for communication with the sealing chamber 109, which opens out on the portion of the first sleeve 120 communicating with the inlet chamber 122 only when the slider 102 is in the end-of-travel position with the guiding end-piece 117 bearing against the shoulder.

[0062] The guiding end-piece 117 houses resilient means or a helical spring 107, which is compressed between the end cover of the valve body 103 and the stop disk which retains the said guiding end-piece 117, such as to keep the aforementioned bearing surface against the shoulder.

[0063] The regulating member 116 has a cup-shaped form and is inserted snugly inside the smaller-diameter portion of the second sleeve 121. The side surface of said regulating member is provided with a plurality of lateral apertures 115 which establish fluid communication between inlet chamber 122 and outlet chamber 123 when the slider 102 is slid towards the end cover and the said lateral apertures 115 open out beyond the shoulder inside the first sleeve 120.

[0064] The actuating stem 118 moves away from the end surface of the cup-shaped regulating member 116 until it fits snugly inside a hole formed in the opposite wall of the tubular appendage of the valve body 103.

[0065] A larger-diameter central portion of the actuating stem 118 has a rack 106 on a bottom surface. As in the case of the first embodiment described above, the rack 106 meshes with a pinion 105 connected to the electric stepper motor 104.

[0066] As in the first embodiment, the reversible kinematic pair defined by the pinion 105 and the rack allows transmission of the movement to the slider 102 which is slidable between two end-of-travel positions: a fully closed valve position (shown in Figure 2), in which the end of the guiding end-piece bears against the shoulder and the oil flow through the valve is interrupted; and a fully open valve position (not shown in the attached figures), situated opposite to the first position, in which the lateral apertures 115 are fully open. The intermediate positions of the slider 102 allow, in this case also, proportional control of the valve.

[0067] In this case also, when the power supply of the motor is interrupted, the helical spring 107 pushes the slider 102 into the fully closed valve position so as to form a check valve.

[0068] It should also be noted that the aforementioned valve is designed to be associated with a three-way pilot electrovalve 130 with which it forms a flow control unit 150.

[0069] The three paths of the pilot electrovalve 130 are associated with the pilot duct 108, the inlet chamber 122 and the outlet chamber 123, so as to be able to place selectively the pilot duct 108 in communication with the inlet chamber 122 (electrovalve not activated) or the outlet chamber 123 (electrovalve activated).

[0070] When the pilot electrovalve 130 is not activated, the pressure inside the pressure chamber 109 helps push, together with the helical spring 107, against the upstream end of the slider 102 so as to move the latter into or keep it in the fully closed position.

[0071] In order to open the flow control valve 101, it is therefore necessary to activate the pilot electrovalve 130 so as to balance firstly the pressure on both the opposite sides of the slider 102.

[0072] It should be noted finally that in this case, as in the first embodiment, magnetic sensor means 125 are provided at the free end of the actuating stem 118 and the tubular extension of the valve body 103 inside which said free end extends.

[0073] With reference to the attached Figure 3, 201 denotes finally a third embodiment of the flow control valve according to the present invention.

[0074] The flow control valve 201 has, as in the two preceding embodiments, a valve body 203 inside which an inlet chamber or duct 222 and an outlet chamber or duct 223 are formed. The ducts, which are staggered and parallel, lead into an inlet opening 210 and an outlet opening 211, respectively, and define aligned and concentric chambers.

[0075] The two chambers 222, 223 are in this case also connected by a transverse channel 214 which is perpendicular with respect to said chambers and houses in a slidable manner a slider 202 operated by an electric stepper motor (not shown in the Figures).

[0076] The transverse channel 214 extends from a first end which merges with the inlet chamber 222, reaches the outlet chamber 223 and then continues as far as a second end where it is closed by a first tubular appendage 203a of the valve body 203. The direction of the flow path from the inlet chamber 222 to the outlet chamber 223 is therefore from the first end towards the second end.

[0077] The transverse channel 214, which is formed by a simple bore in the valve body 203, comprises a first portion inside which the inlet chamber 222 emerges, an intermediate portion inside which the outlet chamber 223 emerges and a third portion with a diameter smaller than the preceding portion. The first portion and the second portion are separated by a short cylindrical section with a smaller diameter.

[0078] The slider 202 has an elongated form and comprises, from upstream to downstream, a closing end-piece 217 followed by a regulating member 216 and an actuating stem 218.

[0079] The closing end-piece 217, which has a cylindrical portion and an end shoe, is housed inside the first portion of the transverse channel 214. The regulating body 216, associated with the closing end-piece by means of a screw-bolt, extends beyond the shoe.

[0080] The shoe defines a bearing surface designed to bear against the shoulder defined by the reduction in diameter at the outlet of the first portion of the transverse channel. The cylindrical portion instead has the function of supporting resilient means, namely a helical spring 207, which is compressed between the upstream end of the transverse channel and the shoe of the closing end-piece 217, so as to keep the aforementioned bearing surface against the shoulder.

[0081] A resilient seal is inserted between the shoe and the regulating body 216 and ensures a sealed closure of the transverse channel 214 when the bearing surface rests against the shoulder.

[0082] The regulating body 216 has a cylindrical form and fits snugly inside the cylindrical section which separates the first portion and the intermediate portion of the transverse channel, extending then inside said intermediate portion and the following third portion.

[0083] At the end remote from the closing end-piece 217, the regulating body has an enlarged portion which defines a disk 228 which slides sealingly along the cylindrical bore of the third portion, defining, between itself and the first tubular appendage 203a, a sealing chamber 209 which communicates with the outside by means of a pilot duct 208 and in certain conditions with the outlet chamber 223.

[0084] The side surface of the regulating body 216 is provided with a plurality of lateral apertures 215 defined by concave zones on the cylindrical surface which allow fluid communication between the inlet chamber 222 and the outlet chamber 223 when the regulating body 216 opens out inside the first portion of the transverse channel 214.

[0085] The actuating stem 218 is inserted slidably inside a longitudinal hole 227 which is formed in the regulating body 216 and opens out on the free side of the disk 228. This longitudinal hole 227 is placed in communication with the outlet chamber 223 via a transverse passage.

[0086] The actuating stem 218 extends, from said longitudinal hole 227, passing firstly through a form-fitting hole provided in the first tubular appendage 203a of the valve body 203 and then a form-fitting hole provided on a second tubular appendage 203b which closes the preceding appendage.

[0087] An enlarged central portion of the actuating 218, enclosed within the first tubular appendage 203a, is provided with a rack 206 on a bottom surface. As in the case of the embodiments described above, the rack 206 meshes with a pinion 205 connected to the electric stepper motor.

[0088] The end portion of the actuating stem 218 which is inserted inside the longitudinal hole 227 of the regulating body 216 is provided laterally with through-flow apertures 229. In certain configurations of the actuating stem 218, the through-flow apertures 229 allow flow communication between the sealing chamber 209 and the inside of the longitudinal hole 227 and from here, via the aforementioned transverse passage, with the outlet chamber 223.

[0089] It should also be noted that the aforementioned valve is designed to be associated with a three-way pilot electrovalve 230 with which it forms a flow control unit 250.

[0090] The three paths of the pilot electrovalve 230 are associated with the pilot duct 208, the inlet chamber 222 and the outlet chamber 223, so as to be able to place selectively the pilot duct 208 in communication with the outlet chamber 223 (electrovalve not activated) or the inlet chamber 222 (electrovalve activated).

[0091] As in the preceding embodiments, the reversible kinematic pair defined by the pinion 205 and the rack allows transmission of the movement to the actuating stem 218 which is slidable inside the regulating body 216 of the slider 202.

[0092] When the pilot electrovalve 230 is not activated, the pressure inside the first portion of the transverse channel 214, not being counterbalanced by a corresponding pressure inside the pressure chamber 209, helps push, together with the helical spring 207, against the shoe of the closing end-piece 217 so that the slider 202 is moved into or kept in the fully closed valve position and the oil flow through the valve is interrupted.

[0093] When the pilot electrovalve 230 is activated, the pressure inside the chamber 209, acting on the surface of the disk 208, which is higher than the opposing pressure area of the regulating body 216, produces a thrust on the slider 202 only if the through-flow apertures 229 formed in the actuating stem 218 are kept sufficiently closed with respect to the longitudinal duct 227 of the regulating body 216.

[0094] It is clear that the movement of the actuating stem 218 by means of the stepper motor, by opening or closing the through-flow apertures 229 depending on the direction of movement of the stem itself, disables or enables the action of the electrovalve 230.

[0095] In fact, when the apertures are open, the chamber 209 is placed in communication with the outlet chamber 223, eliminating the thrust of the pressure on the slider 202 which, under the thrust of the spring 207 and the pressure acting on the regulating body 216, tends to move into the closed position.

[0096] Vice versa, when the apertures are closed, the pressure inside the chamber 209, acting on a diameter greater than that of the regulating chamber 216, will tend to displace the closing member into the open position.

[0097] Therefore, the slider 202 will move together with the actuating stem 218, assuming the position and the displacement speed transmitted by the stepper motor via the rack and pinion mechanism.

[0098] It is thus possible to operate the flow control valve using a motor with a relatively low power even when there are high flowrates of the oil in the valve.

[0099] In this case also, when the power supply of the motor is interrupted, the helical spring 207 pushes the slider 202 into the fully closed valve position, so as to form a check valve.

[0100] It should be noted finally that in this case also, as in the preceding embodiments, magnetic sensor means 225 are provided at the free end of the actuating stem 218 and the second tubular extension 203b of the valve body 203 inside which said free end extends.

[0101] With reference to Figures 4, 5 and 5a, we shall now describe a hydraulic circuit 300 for controlling the flow to and from a hydraulic actuating cylinder of a lifting installation, comprising internally a flow control valve and/or a flow control unit according to one of the embodiments described above.

[0102] It should be noted that, with regard to the attached figures and the following description, they refer in particular to use of a control unit 150 provided with a flow control valve 101 in accordance with the second of the embodiments described above, such reference being understood as being made by way of a non-limiting example. In other words, the hydraulic circuit described below may comprise any of the control valves according to the present invention.

[0103] The hydraulic circuit comprises a delivery branch consisting of a first section 302 and a second section 307 and has, circulating inside it, the liquid sent by a pump 301 which draws from inside an oil tank 310 of the lifting installation.

[0104] The first section of the delivery branch 302 therefore reaches a check valve for stopping return to the pump 303, from which the return branch to the tank 304 departs, along which branch the control unit 150 described above is mounted.

[0105] The fluid which is not conveyed back along said return branch to the tank 304 continues its path via a second check valve 305 which must be enabled by a corresponding pilot electrovalve 306.

[0106] After passing through the second check valve, the fluid continues further along the second section 307 of the delivery branch, which finally leads to the actuating cylinder (not shown).

[0107] The action of the flow control unit 150 allows regulation of the oil flow in the return branch 304, and therefore, indirectly, of the flow conveyed in the second section 307 of the delivery branch and from here to the actuating cylinder. Moreover, the flow control unit 150, in the ways described above, is able to carry out an additional fluid stopping function, preventing the undesirable return of the fluid into the tank 310 in the absence of the electric power supply.

[0108] In a main variant of the circuit diagram, shown in Figure 5, an electronic control unit 320 receives at its input the signal of two pressure transducers 308 which are arranged, respectively, upstream and downstream of the second check valve 305, a flow transducer associated with a flow measurement valve 309 arranged upstream of the second check valve 305, and a temperature transducer 311 associated with the tank 310.

[0109] On the basis of this data, the electronic control unit 320 controls the stepper motor 104 so as to follow the desired speed profiles.

[0110] In an alternative variant of the circuit diagram, shown in Figure 5a, the flow transducer is incorporated in the second check valve 305.

[0111] Obviously, a person skilled in the art, in order to satisfy any specific requirements which arise, may make numerous modifications and variations to the devices described above, all of which being moreover contained within the scope of protection of the invention, as defined by the following claims.

Claims

1. Flow control valve (1; 101; 201) for a hydraulic control circuit (300) of a lifting installation, comprising a valve body (3; 103; 203), a flow path extending between an inlet opening (10; 110; 210) and an outlet opening (11; 111; 211), a slider (2; 102; 202) slidably movable inside a seat formed in the valve body (3; 103; 203) along said flow path between a fully open valve position and a fully closed valve position, characterized in that it comprises an electric stepper motor (104) acting on said slider (2; 102; 202) so as to regulate the flow which passes along said flow path, a reversible kinematic pair (5, 6; 105, 106; 205; 206) between the stepper motor (104) and the slider (2; 102; 202) and resilient means (7; 107; 207) acting on the slider (2; 102; 202) so as to urge it constantly towards the fully closed valve position.

2. Flow control valve (1; 101; 201) according to Claim 1, wherein said slider (2; 102; 202) allows throttling of the flow which passes between the inlet opening (10; 110; 210) and the outlet opening (11; 111; 211) of the flow control valve (1; 101; 201).

3. Flow control valve (1; 101; 201) according to Claim 2, wherein said reversible pair (5, 6; 105, 106; 205, 206) comprises a pinion (5; 105; 205) on the motor side meshing with a rack (6; 106; 206) integral with said slider (1).

4. Flow control valve (1; 101; 201) according to one of Claims 2 or 3, further comprising at least one magnetic sensor (12; 112; 212) designed to detect at least one position from among the fully open position and fully closed position of the flow control valve (1; 101; 201).

5. Flow control valve (101; 201) according to one of Claims 2 to 4, wherein said slider (102; 202) opens out inside a pressure chamber (109; 209) supplied by a pilot duct (108; 208).

6. Flow control valve (101) according to Claim 5, where a fluid pressure inside the pressure chamber (109) acts on said slider (102) in the same sense as the resilient means (107).

7. Flow control valve (201) according to Claim 5, where a fluid pressure inside the pressure chamber (209) acts on said slider (202) in the opposite sense to the resilient means (207).

8. Flow control valve (201) according to Claim 7, wherein the cross-section of the surface of the slider (202) facing the pressure chamber (209) is greater than the cross-section of the opposite surface of the slider (202), facing a chamber in direct communication with the inlet opening (210).

9. Flow control unit (150; 250) comprising a flow control valve (101; 201) according to one of Claims 5 to 8 and a pilot electrovalve (130; 230) designed to pressurize said pressure chamber (109; 209).

10. Flow control unit (150) according to Claim 9, wherein said pilot electrovalve (130) is a three-way electrovalve designed to place the pressure chamber (109) in fluid communication with the inlet mouth (110) of the flow control valve (101) when not activated and with the outlet mouth (111) of the flow control valve (101) when activated.

11. Flow control unit (250) according to Claim 9, wherein said pilot electrovalve (230) is a three-way electrovalve designed to place the pressure chamber (209) in fluid communication with the inlet opening (210) of the flow control valve (201) when activated and with the outlet opening (211) of the flow control valve (201) when not activated.

12. Hydraulic circuit (300) for controlling the flow to and from a hydraulic actuating cylinder of a lifting installation, comprising: a delivery branch (302, 307), along which a pump (301) connecting a supply tank (310) to said hydraulic actuating cylinder operates; and a return branch (304) which departs from said delivery branch (302, 307) after a first section (302) thereof and returns to the supply tank (310); said hydraulic circuit (300) comprising at least one flow control valve (1; 101; 201) according to one of Claims 1 to 7, said flow control valve (1; 101; 201) being arranged so as to intercept the flow along said return branch (304).

13. Hydraulic circuit (300) according to Claim 10, wherein said first section (302) of the delivery branch (302, 307) connects the supply tank (310) to a one-way check valve stopping return to the pump (303), said return branch (304) departing from said delivery branch (302, 307) downstream of said check valve stopping return to the pump (303).

14. Hydraulic circuit (300) according to Claim 11, further comprising a second check valve (305) operated by a pilot electrovalve (306) arranged on the delivery branch (302, 307) upstream of said one-way check valve stopping return to the pump (303).

15. Hydraulic circuit (300) according to Claim 12, comprising an electronic control unit (320) designed to control the stepper motor (104) of the flow control valve (1; 101; 201), said electronic control unit (320) receiving at its input the signal of at least one flow transducer incorporated in the second check valve (305).

Amended claims

Amended claims in accordance with Rule 137(2) EPC.

1. Flow control valve (1; 101; 201) for a hydraulic control circuit (300) of a lifting installation, comprising a valve body (3; 103; 203), a flow path extending between an inlet opening (10; 110; 210) and an outlet opening (11; 111; 211), a slider (2; 102; 202) slidably movable inside a seat formed in the valve body (3; 103; 203) along said flow path between a fully open valve position and a fully closed valve position, further comprising an electric stepper motor (104) acting on said slider (2; 102; 202) so as to regulate the flow which passes along said flow path, and resilient means (7; 107; 207) acting on the slider (2; 102; 202) so as to urge it constantly towards the fully closed valve position; characterized in that it comprises a reversible kinematic pair (5, 6; 105, 106; 205; 206) between the stepper motor (104) and the slider (2; 102; 202).

2. Flow control valve (1; 101; 201) according to Claim 1, wherein said slider (2; 102; 202) allows throttling of the flow which passes between the inlet opening (10; 110; 210) and the outlet opening (11; 111; 211) of the flow control valve (1; 101; 201).

3. Flow control valve (1; 101; 201) according to Claim 2, wherein said reversible pair (5, 6; 105, 106; 205, 206) comprises a pinion (5; 105; 205) on the motor side meshing with a rack (6; 106; 206) integral with said slider (1).

4. Flow control valve (1; 101; 201) according to one of Claims 2 or 3, further comprising at least one magnetic sensor (12; 112; 212) designed to detect at least one position from among the fully open position and fully closed position of the flow control valve (1; 101; 201).

5. Flow control valve (101; 201) according to one of Claims 2 to 4, wherein said slider (102; 202) opens out inside a pressure chamber (109; 209) supplied by a pilot duct (108; 208).

6. Flow control valve (101) according to Claim 5, where a fluid pressure inside the pressure chamber (109) acts on said slider (102) in the same sense as the resilient means (107).

7. Flow control valve (201) according to Claim 5, where a fluid pressure inside the pressure chamber (209) acts on said slider (202) in the opposite sense to the resilient means (207).

8. Flow control valve (201) according to Claim 7, wherein the cross-section of the surface of the slider (202) facing the pressure chamber (209) is greater than the cross-section of the opposite surface of the slider (202), facing a chamber in direct communication with the inlet opening (210).

9. Flow control unit (150; 250) comprising a flow control valve (101; 201) according to one of Claims 5 to 8 and a pilot electrovalve (130; 230) designed to pressurize said pressure chamber (109; 209).

10. Flow control unit (150) according to Claim 9, wherein said pilot electrovalve (130) is a three-way electrovalve designed to place the pressure chamber (109) in fluid communication with the inlet mouth (110) of the flow control valve (101) when not activated and with the outlet mouth (111) of the flow control valve (101) when activated.

11. Flow control unit (250) according to Claim 9, wherein said pilot electrovalve (230) is a three-way electrovalve designed to place the pressure chamber (209) in fluid communication with the inlet opening (210) of the flow control valve (201) when activated and with the outlet opening (211) of the flow control valve (201) when not activated.

12. Hydraulic circuit (300) for controlling the flow to and from a hydraulic actuating cylinder of a lifting installation, comprising: a delivery branch (302, 307), along which a pump (301) connecting a supply tank (310) to said hydraulic actuating cylinder operates; and a return branch (304) which departs from said delivery branch (302, 307) after a first section (302) thereof and returns to the supply tank (310); said hydraulic circuit (300) comprising at least one flow control valve (1; 101; 201) according to one of Claims 1 to 7, said flow control valve (1; 101; 201) being arranged so as to intercept the flow along said return branch (304).

13. Hydraulic circuit (300) according to Claim 12, wherein said first section (302) of the delivery branch (302, 307) connects the supply tank (310) to a one-way check valve stopping return to the pump (303), said return branch (304) departing from said delivery branch (302, 307) downstream of said check valve stopping return to the pump (303).

14. Hydraulic circuit (300) according to Claim 13, further comprising a second check valve (305) operated by a pilot electrovalve (306) arranged on the delivery branch (302, 307) upstream of said one-way check valve stopping return to the pump (303).

15. Hydraulic circuit (300) according to Claim 14, comprising an electronic control unit (320) designed to control the stepper motor (104) of the flow control valve (1; 101; 201), said electronic control unit (320) receiving at its input the signal of at least one flow transducer incorporated in the second check valve (305).

Drawing