EP0224446B1 - A hydraulic load limiting device for hydraulic cranes - Google Patents
A hydraulic load limiting device for hydraulic cranes Download PDFInfo
- Publication number
- EP0224446B1 EP0224446B1 EP19860830202 EP86830202A EP0224446B1 EP 0224446 B1 EP0224446 B1 EP 0224446B1 EP 19860830202 EP19860830202 EP 19860830202 EP 86830202 A EP86830202 A EP 86830202A EP 0224446 B1 EP0224446 B1 EP 0224446B1
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- Prior art keywords
- valve
- pressure
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- cylinder
- valves
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- 230000000670 limiting effect Effects 0.000 title claims description 19
- 239000012530 fluid Substances 0.000 claims description 17
- 238000011144 upstream manufacturing Methods 0.000 claims description 4
- 241001052209 Cylinder Species 0.000 claims 1
- 230000004044 response Effects 0.000 description 11
- 230000008901 benefit Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000010276 construction Methods 0.000 description 2
- 230000002401 inhibitory effect Effects 0.000 description 2
- 230000001960 triggered effect Effects 0.000 description 2
- 230000001143 conditioned effect Effects 0.000 description 1
- 229940084430 four-way Drugs 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B66—HOISTING; LIFTING; HAULING
- B66C—CRANES; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS, WINCHES, OR TACKLES
- B66C23/00—Cranes comprising essentially a beam, boom, or triangular structure acting as a cantilever and mounted for translatory of swinging movements in vertical or horizontal planes or a combination of such movements, e.g. jib-cranes, derricks, tower cranes
- B66C23/88—Safety gear
- B66C23/90—Devices for indicating or limiting lifting moment
Definitions
- the invention described herein relates to a hydraulic load limiting device for hydraulic cranes.
- a device as disclosed is intended for application to cranes of the general type consisting of a column to which a boom with one or more folding and/or telescopic stage or stages is attached, the single stage being operated by a relative hydraulic cylinder.
- One of the requirements of safety regulations existing in numerous countries the world over, is that any movement in the boom liable to overload the crane by exceeding its maximum rated lift capacity, must be inhibited.
- any subsequent movement in the boom that would lead to an increase in the load-related moment of force must be disallowed; more exactly, any movement whereby a telescopic boom is further extended, and any rotational movement of the boom stages such as distances the load from the crane's slewing axis, must be prevented from taking place.
- an increase in moment of force generated by the load is converted, in substantially linear manner, into a build-up of pressure in the rear end of the hydraulic cylinder which operates the hinged boom stage, or supports the hinged boom assembly; accordingly, control and subsequent limiting of the moment of force generated by the load is effected by monitoring pressure of the fluid that impinges on the rear end of the cylinder in question, and limiting it in relation to a given preset level.
- the prior art embraces devices in which use is made of an electrical signal, relayed from a pressure switfh triggered by pressure in the rear end of the cylinder, to energize the solenoids of valves that prevent further ingress of hydraulic fluid to the cylinders such as might lead to an increase in the moment of force generated by the load.
- Prior art devices also offer a level-sensing system by means of which to produce an electrical signal, triggered by the angle of the boom above of below horizontal, such as will operate means whereby movement of the boom is enabled insofar at the load-related moment of force will diminish, and inhibited where bound to increase -i.e., when the load matches the maximum rated lift capacity of the crane.
- a further drawback of prior art devices is that the wiring required for their operation can deteriorate and fail with the passage of time, and with use of the crane.
- boom level-sensing systems involves considerable complication of the hydraulic load limiting circuit.
- the prior art embraces load-limiting devices which are hydraulic but which all the same need boom level-sensing systems to indicate the crane boom angle.
- One such device is illustrated in DE 3414183.
- Other devices of this type are illustrated in figs 1-5 of the present application, and are described in detail also in the present application.
- the devices equipped with boom level-sensing systems as in figs 1-5 are illustrated and described simply as examples of possible embodiments of load-limiting devices with crane boom angle indicators, but they do not form part of the claims for the present invention.
- Hydraulic laod-limiting devices with boom levelsensing systems do not present problems of an electrical nature, but present however the above-mentioned drawbacks due to the presence of said load-limiting device.
- One object of the invention described herein is that of overcoming the drawbacks mentioned above, providing a device that can respond to all such safety requirements as are envisaged under law, whilst making no use whatever of electrical circuits, whether for relaying control signals or for actuating the valves which shut off flow of hydraulic fluid to the boom cylinders.
- a further object of the invention is that of providing a device that will not be sensitive to any accidental surge in the moment of force generated by the load, and which will cut in at the precise overload setting selected, whatever the operating conditions.
- Another object of the invention is that of providing a device which, at maximum rated lift capacity, will inhibit any movement in the crane liable to produce overload conditions, regardless of the configuration of the crane at that instant, and do so without any need for indication of the angle at which the boom stages happen to be disposed.
- a clear advantage of the device disclosed is that it is all-hydraulic, and uses the same source of energy for its operation (pressurized fluid) as that used by the crane as a whole; such a feature is especially advantageous in terms of circuit design and cost.
- a device according to the invention employs hydraulic on-off and/or switching valves which respond to a pressure signal from one of the boom cylinders, and produce a hydraulic control signal, used without the need of employing a level-sensing system to pilot hydraulic valves installed on the lines connecting with the boom cylinders, to the end of shutting off pressure flow to the cylinders whenever further extension or retraction would cause the boom to assume a configuration whereby maximum rated lift capacity is exceeded.
- the crane illustrated in the drawings consists of a column 1, a first boom stage 2 which is hinged to the top of the column 1 and rotated about its pivot by a hydraulic cylinder 4, and a second boom stage 3 which is both hinged and telescopic, rotated about its pivot by one hydraulic cylinder 5, and extended. and retracted telescopically by a further hydraulic cylinder 6.
- the hydraulic cylinders are connected to a directional control valve assembly denoted 15, each single section of which, when operated, provides a relative cylinder with fluid supplied under pressure from a pump 14.
- 4a, 5a and 6a denote lines connecting each section of the control valve with the rear end of the relative cylinder
- 4b, 5b and 6b denote similar lines connecting with the rod end of each cylinder
- the ′a′ and ′b′ lines of each circuit thus alternate between pressure and return functions, according to the position of the control valve.
- 4c, 5c and 6c denote respective holding valves installed one in each of the cylinder circuits to the end of preventing jerky descent of the load.
- the device as embodied in figs 1, 4, 10, 11 and 12 comprises two-way two-position hydraulic valves, denoted 7a, 7b, 8a, 8b and 9, which are installed in the circuits operating the two hinged cylinders 4 and 5, and in the line connecting with the rear end of the telescoping cylinder 6, respectively.
- each such valve blocks pressure flow through the relative line while allowing return flow through the same line; in the second position, flow is permitted in either direction.
- Each valve is held in the second position by pressure of the fluid through the line upstream of the valve itself, and biased toward the first position by a respective spring 17a, 17b, 18a, 18b and 19, as well as being piloted into the first position by a hydraulic control signal described in detail below.
- the device as embodied in figs 1 & 4 comprises load-sensing means incorporating a two-way two-position hydraulic response valve 10, first position open, second position closed.
- the first port of the valve 10 connects with the pump 14, and the second port with a first send line 11 that carries the hydraulic control signal utilized for direct or indirect operation of the shut-off valves 7a, 7b, 8a, 8b and 9.
- the response valve 10 is biased into normally closed position by a spring 10a, and piloted to open in direct fashion by a pressure signal generated in the rear end of the first stage cylinder 4 and carried to the valve 10 by a relative line 22; the valve 10 is thus operated directly by pressure impinging on the rear end of the cylinder 4 which, it will be remembered, is proportional to the moment of force generated by the load.
- the device as embodied in figs 1 & 4 also comprises level sensing means in the form of a three-way hydraulic valve 25 with a ball 26 that is free to float within the valve chamber.
- the first port of such a valve is located in the side wall of the chamber and remains permanently open, whereas the second and the third port are located at either end of the chamber, which also offer relative seats in which the ball 26 may register.
- the valve 25 is made fast to the third stage 3 of the boom, and thus serves to indicate the position of boom as regards the angle assumed above or below horizontal; more exactly, indication of the position A or B of the boom (see fig 1) is made possible by the fact that the ball 26 will shift toward one or other end of the valve chamber, according to the angle assumed by the boom.
- the first port of the level sensing valve 25 is connected to the first send line 11, whereas the second and the third ports are connected to a second and a third send line 12 and 13, respectively.
- the hydraulic signal utilized for operation of the valve denoted 9 is taken off the first send line 11.
- the valves 7a and 8a installed on the lines connecting with the rear ends of the two respective hinged cylinders 4 and 5 are operated by a hydraulic signal supplied through the second send line 12
- the valves 7b and 8b on the lines connecting with the rod ends of the same cylinders are operated by a signal supplied through the third send line 13.
- the mechanical structure of a given crane may be such that no linear relationship can exist between pressure in the rear end of the cylinder 4 and the moment of force generated by the load; the result is that certain movements of the boom may overload the crane beyond rated lift capacity without rear end pressure in the cylinder 4 actually registering at the maximum setting envisaged.
- Fig 2 illustrates how the second valve 10′ would be incorporated, where appropriate.
- the element of the response valve 10 is piloted to close by a pressure signal taken off the rod end line 4b, and the area of the valve element on which this signal impinges differs from the area invested by the signal from the rear end line 4a to an extent commensurate with the difference in piston area between the rod end and rear end of the cylinder 4.
- Fig 3 illustrates how the response valve 10 may be embodied so as to remain unaffected by pilot pressure through the rod end line 4b of the cylinder circuit.
- the embodiment of fig 1 also comprises a manually operated hydraulic unloading valve 20 installed in normally closed configuration between the sensing line 22 and the return line, the purpose of which is described in detail below.
- each send line is provided with a respective restriction connecting to tank.
- one has a third two-way two-position hydraulic response valve 10 ⁇ , first position open, second position closed, biased into its normally closed position by a spring 10a ⁇ , and piloted to open in direct fashion by, pressure signal supplied through the sensing line 22.
- the first port of the valve 10" connects with the pump 14, and the second port with a fourth send line 51.
- the first response valve 10 will be piloted to open whenever pressure impinging on the rear end of the cylinder 4 and relayed through the sensing line 22 reflects maximum rated lift capacity of the crane, whereas the third shut-off valve 10" is caused to open by a pressure level marginally in excess of this setting.
- This second embodiment of the device also incorporates a three-way two-position switching valve 52, a first port of which is connected to the first send line 11, the second and third ports being connected respectively to a fifth and a sixth send line 53 and 54 which supply the control signal for opera(ion of two of the shut-off valves 7b and 7a, respectively; signals for operation of the valves denoted 8a and 8b continue to be supplied by the second and third send lines 12 and 13.
- the switching valve 52 is biased by a spring 55 into first position, whereby first and second ports are connected, and piloted into the second position, in which the first and third ports connect, by a signal supplied through the fourth send line 51.
- sensing means comprise a three-way two-position valve 41 which is biased by a spring 45 into its first position, whereby first and third ports are connected; the valve 41 is piloted into its second position, in which second and third ports are connected, by a pressure signal taken off from the rear end of the first cylinder 4 and routed to the valve by way of a branched leg 22a of the sensing line 22. Shift of the valve from first to second position occurs whenever the signal reaches a preset pressure level marginally below that which reflects maximum rated lift capacity of the crane.
- the sensing means in figs 10 and 11 further comprise a four-way two-position valve 42 biased by a spring 46 into its first position, in which the first port connects with the third and the second port connects with the fourth; the valve 42 is piloted into its second position, in which the first port connects with the fourth, and the second port with the third, by the same pressure signal as aforementioned, which is routed to the valve by way of the remaining leg 22b of the branched sensing line 22. Shift of the valve from first to second position occurs whenever the signal reaches a pressure level reflecting the maximum rated lift capacity of the crane.
- the first port of both valves 41 and 42 is connected to tank; the second and third ports of the valve denoted 41 are connected to the pump 14, and to the second port of the valve denoted 42, respectively.
- the third port of the four-way valve 42 connects via a send line 47 with the pilot circuits of two of the shut-off valves 7b and 8b; the fourth port of the valve connects via a further send line 48 with the pilot circuits of the shut-off valves denoted 7a and 8a.
- the pilot circuit of the remaining shut-off valve 9 connects via an additional send line 49 with the third port of the three-way valve 41.
- the third port of the four-way valve 42 connects by way of the first send line 47 with the pilot circuits of valves 7a and 8a; the fourth port of the valve connects via the second send line 48 with the pilot circuits of valves 7b and 8b.
- the pilot circuit of the remaining shut-off valve 9 connects via an additional send line 49 with the third port of the three-way valve 41, as in the previous embodiment.
- the leg denoted 22b which branches from the sensing line 22 incorporates a check valve 44a allowing flow of hydraulic fluid, hence of the pressure signal, toward the four-way valve 42.
- valve 44 denotes a pressure balancing valve that connects the one leg 22a of the branched sensing line 22 with a point on the remaining leg 22b between the check valve 44a and the four-way valve 42. Biased into the normally closed position by a spring, the valve 44 is obliged to close by pressure through the one leg 22a, and piloted to open by pressure through the remaining leg 22b.
- the pressure balancing valve 44 is set in such a way as to connect the two legs 22a and 22b of the sensing line 22 with one another whenever the difference in pressure between the two is marginally greater than the difference between the respective pressure levels that produce shift of the four-way load sensing valve 42 and the three-way load sensing valve 41 from first to second position.
- the purpose of the valve 44 in question is to restore normal conditions in the limiting device once both sensing valves 41 and 42 have been piloted into second position, and will become clear in due course. Return of the fourway valve 42 to the first position is enabled only after the three-way valve 41 has been returned to first position.
- the embodiment of fig 10 comprises a normally closed manual unloading valve 43 which connects the sensing line 22 to tank, and performs the identical function to that denoted 20 aforedescribed.
- Sensing means in the embodiment of fig 12 are the same as those illustrated in fig 10, with the exception that the manual unloading valve 43 is dispensed with; valves and connections serving the second and third cylinder circuits 5a-5b and 6a-6b likewise remain the same.
- the line denoted 4b is connected directly to the rod end of the first cylinder 4, and exhausted to tank by a relief valve 60 whenever pressure through the line itself rises beyond the relative setting; the relief valve 60 is set to operate independently of the limiting device.
- Shut-off valves 7a and 7b are connected to the rear end line 4a in series, and a further relief valve 61 downstream of the second valve 7b will exhaust the rear end to tank whenever pressure through the line 4a rises above the valve setting; in this instance, the valve 61 is set to a pressure marginally in excess of that reflecting maximum rated lift capacity of the crane.
- the pressure signal that pilots the valves denoted 7a and 8a is supplied through the second send line 48, whilst that piloting the valves denoted 7b and 7b is supplied through the first send line 47.
- the signal which pilots the remaining shut-off valve 9 continues to be supplied via the third send line 49.
- 63 denotes a second three-way two-position valve maintained normally in the first position, in which first and third ports are connected; the valve is piloted into its second position by pressure flow from the pump 14, thereby connecting the second and third ports, whenever there is a rise beyond the maximum pressure envisaged during retraction of the cylinder rods, hence descent of the boom.
- Retract pressure is easily quantifiable, corresponding as it does to descent of the boom with no load, and in any event will be considerably lower than the pressure level reflecting maximum rated lift capacity of the crane.
- the three ports of the valve 63 are connected thus: first port to tank; second port direct to the pump 14; and third port to a pilot line 64. Pressure registering through the pilot line 64 will be transmitted to the four-way sensing valve 42, on which it impinges in the same direction as the force exerted by the spring 46 and thus assists in biasing the valve 42 into first position.
- valves 10 and 10′ in the embodiments of figs 1 and 2 will be normally closed. Supposing that maximum rated capacity is reached in the configuration denoted A in fig 1, then the pressure signal deriving from the rear end of the first cylinder 4 will open the valve denoted 10, connecting the pump 14 to the first send line 11, in which a hydraulic control signal is duly set up.
- control signal will be set up by whichever valve opens first.
- the control signal acts directly on the telescoping shut-off valve 9, preventing it from opening even though the relative control valve spool may be moved into the position whereby fluid is directed through the respective line 6a; clearly, any further extension of the telescoping cylinder 6 would increase the load, regardless of the angle A or B. No load limiting components whatever are incorporated into the rod end line 6b of the cylinder 6 in question, since normal retraction reduces the load automatically.
- the control signal is fed through the first send line 11 and into the level-sensing valve 25, the ball 26 of which blocks the second send line 12 and opens up the third send line 13, given the position of the boom.
- the third send line 13 being open, the control signal impinges on the shut-off valves 7b and 8b installed on the rod end lines to the first and second cylinders 4 and 5; pressure reaching the rod end of either cylinder at this point would turn the relative boom stage toward the ground and increase the load beyond the permissible limit.
- valves 7a and 8a controlling the lines to the rear end of the two cylinders 4 and 5 are in receipt of no such load limiting signal, and shift of the relative control valve spools will direct fluid to the service as normal; ingress of fluid into the rear end will in fact raise the boom, reducing the load.
- valve denoted 10 will once again be opened by the signal originating from the rear end of the first cylinder 4; as far as the telescoping cylinder 6 is concerned, the same situation obtains as described above.
- the two-way sensing valve 10 closes, and pressure in the send lines is exhausted via the restrictions in readiness for further operation of the entire set of load limiting valves.
- a spring-loaded check valve 30 is installed upstream of the manual facility; this will close whenever the difference in pressure between inlet and outlet ports of the valve is of an order greater than the bias spring setting.
- the control signal will be relayed to one or other of the two second stage shut-off valves 8a or 8b, depending on the angle of the second boom stage 3 and the corresponding state of the level-sensing valve 25.
- the signal will be transmitted through the third send line 13 to the rod end valve 8b, thereby disallowing downward rotation of the boom stage 3 and preventing resultant increase of the load; no such signal will impinge on the rear end valve 8a, since upward rotation of the same stage 3 will automatically reduce the load and is thus permissible.
- the load limiting device prevents overload on the crane at the moment that its maximum rated lift capacity is either matched or exceeded. It will be obvious to a person skilled in the art, however, that a load in excess of maximum rated capacity can be avoided altogether simply by setting the one load sensing valve 10" at a pressure to match the maximum load, and setting the other 10 at a level marginally below this same pressure.
- the sensing valves 10 ⁇ and 10 will reassume closed position, and control signal pressure through the send line 11 and the various passages leading to the shut-off valves 7a, 7b, 8a, 8b and 9 will exhaust via their relative restrictions, returning the device to its original configuration in which all movements are enabled.
- the switching valve 52 memorizes second position until otherwise instructed by a return to normal operating conditions.
- arrival at maximum rated lift capacity causes the signal set up by the load sensing valve 10 to be transmitted direct to the valves denoted 7b and 9, and neither downward rotation of the first stage 2 nor telescoping of the second stage 3 are allowed, whatever their position; downward rotation of the second stage 3 will be inhibited only where the boom is angled above horizontal as in fig 9.
- the level-sensed control signal will be relayed via the send line 13 to the valve denoted 8b, which blocks pressure flow to the rod end of the relative cylinder 5.
- the relative valve 8b will be in receipt of no control signal by reason of the fact that the level-sensing valve 25 blocks the send line 13, and downward rotation is therefore permitted.
- upward rotation of the stage 3 will be disallowed only where the movement is such as to produce an increase in load, reflected by a build-up of rear end pressure in the relative cylinder 5 and consequent operation of the relief valve 58.
- a further reduction in load produces a further drop in pressure through the leg of the branched sensing line denoted 22a, and once the difference in pressure between the two branches 22b and 22a reaches a preset level, which at all events will be higher than the difference between the respective pressure levels causing shift of the three-way and four-way sensing valves 41 and 42 from first to second position, then the pressure balancing valve 44 will open so as to exhaust pressure from the leg denoted 22b and enable the four-way sensing valve to return to first position.
- Flow to and from the service through the rear end line 4a is controlled by the valves denoted 7a and 7b, respectively; accordingly, shift of the threeway and the four-way load sensing valves 41 and 42 to second position disallows flow to the service and from the service, respectively, any excess pressure through the line 4a being exhausted by the relief valve 61.
- the second advantage is that the unloading valve 43 of fig 10 becomes unnecessary. With arrival of the cylinder 4 at its stroke limit, excess pressure becoming trapped in the stretch of line 4a connecting the cylinder with the holding valve 4c (pressure which is exploited for operation of the load sensing valves 41 and 42) can be relieved by connecting the free rod end line 4b with pressure; the load holding valve 4c can thus be piloted to open, and the excess pressure relieved.
- valve denoted 63 provides a further significant advantage. In the event that circuit pressure should rise beyond the maximum pump rating calculated to occur during retraction (the situation in question can arise only during extension, clearly enough), the valve 63 will be shifted into second position, thereby relaying a signal to the four-way load sensing valve 42 that prevents its moving from first to second position under any circumstance.
- valve 63 remains inoperative as long as the cylinders are retracting, whereas on the extending stroke, the moment that maximum rated lift capacity is reached, pressure through the two lines denoted 4a and 5a will be disallowed regardless of other conditions.
- This will prevent a particularly skilled operator from juggling the control valves 15 in such a way as to produce pressure surges capable of shifting the four-way load sensing valve 42, and thus managing to supply additional pressure through either line 4a or 5a, the result of which would be to overload the crane beyond maximum rated capacity.
- Embodiments of the device as illustrated in figs 10, 11 and 12 provide the considerable advantage of requiring no boom level-sensing system for their correct operation. This represents a particularly welcome feature in crane hydraulics when one considers that the installation of level-sensing facilities, which must of course be applied direct to the boom, involves major complication of the system.
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Description
- The invention described herein relates to a hydraulic load limiting device for hydraulic cranes. A device as disclosed is intended for application to cranes of the general type consisting of a column to which a boom with one or more folding and/or telescopic stage or stages is attached, the single stage being operated by a relative hydraulic cylinder. One of the requirements of safety regulations existing in numerous countries the world over, is that any movement in the boom liable to overload the crane by exceeding its maximum rated lift capacity, must be inhibited. Thus, whenever the crane lifts a load such as sets up a moment of force equal to its maximum rated capacity, any subsequent movement in the boom that would lead to an increase in the load-related moment of force must be disallowed; more exactly, any movement whereby a telescopic boom is further extended, and any rotational movement of the boom stages such as distances the load from the crane's slewing axis, must be prevented from taking place.
- In cranes of the type in question, an increase in moment of force generated by the load is converted, in substantially linear manner, into a build-up of pressure in the rear end of the hydraulic cylinder which operates the hinged boom stage, or supports the hinged boom assembly; accordingly, control and subsequent limiting of the moment of force generated by the load is effected by monitoring pressure of the fluid that impinges on the rear end of the cylinder in question, and limiting it in relation to a given preset level.
- The prior art embraces devices in which use is made of an electrical signal, relayed from a pressure switfh triggered by pressure in the rear end of the cylinder, to energize the solenoids of valves that prevent further ingress of hydraulic fluid to the cylinders such as might lead to an increase in the moment of force generated by the load.
- Prior art devices also offer a level-sensing system by means of which to produce an electrical signal, triggered by the angle of the boom above of below horizontal, such as will operate means whereby movement of the boom is enabled insofar at the load-related moment of force will diminish, and inhibited where bound to increase -i.e., when the load matches the maximum rated lift capacity of the crane.
- Such devices are simple enough from the design and construction standpoints, but are beset by significant drawbacks as a result of being electric. Cranes are generally utilized and parked outdoors, and faultless operation of the above devices is very often jeopardized by weather conditions.
- A further drawback of prior art devices is that the wiring required for their operation can deteriorate and fail with the passage of time, and with use of the crane.
- Another drawback with the circuits of prior art load limiting circuits is that the solenoid valves employed reguire heavy coils, which are cumbersome and consume power. Electrical systems of the type are also notably expensive.
- Lastly, the inclusion of boom level-sensing systems involves considerable complication of the hydraulic load limiting circuit.
- The prior art embraces load-limiting devices which are hydraulic but which all the same need boom level-sensing systems to indicate the crane boom angle. One such device is illustrated in DE 3414183. Other devices of this type are illustrated in figs 1-5 of the present application, and are described in detail also in the present application. The devices equipped with boom level-sensing systems as in figs 1-5 are illustrated and described simply as examples of possible embodiments of load-limiting devices with crane boom angle indicators, but they do not form part of the claims for the present invention.
- Hydraulic laod-limiting devices with boom levelsensing systems do not present problems of an electrical nature, but present however the above-mentioned drawbacks due to the presence of said load-limiting device.
- One object of the invention described herein is that of overcoming the drawbacks mentioned above, providing a device that can respond to all such safety requirements as are envisaged under law, whilst making no use whatever of electrical circuits, whether for relaying control signals or for actuating the valves which shut off flow of hydraulic fluid to the boom cylinders.
- A further object of the invention is that of providing a device that will not be sensitive to any accidental surge in the moment of force generated by the load, and which will cut in at the precise overload setting selected, whatever the operating conditions. Another object of the invention is that of providing a device which, at maximum rated lift capacity, will inhibit any movement in the crane liable to produce overload conditions, regardless of the configuration of the crane at that instant, and do so without any need for indication of the angle at which the boom stages happen to be disposed.
- A clear advantage of the device disclosed is that it is all-hydraulic, and uses the same source of energy for its operation (pressurized fluid) as that used by the crane as a whole; such a feature is especially advantageous in terms of circuit design and cost. The stated objects and advantages, and others, are fully realized with a device as described herein and as characterized in the appended claims; a device according to the invention employs hydraulic on-off and/or switching valves which respond to a pressure signal from one of the boom cylinders, and produce a hydraulic control signal, used without the need of employing a level-sensing system to pilot hydraulic valves installed on the lines connecting with the boom cylinders, to the end of shutting off pressure flow to the cylinders whenever further extension or retraction would cause the boom to assume a configuration whereby maximum rated lift capacity is exceeded. The invention will now be described in detail by way of example, with the aid of the accompanying drawings, in which:
- fig 1 illustrates the hydraulic circuit in a first embodiment of the device using a hydraulic level-sensing system
- fig 2 illustrates the embodiment of certain of the components making up the device in fig 1;
- fig 3 shows an alternative embodiment of a part of the device in fig 2, seen on larger scale;
- fig 4 illustrates the hydraulic circuit in a second embodiment of the device using a hydraulic level-sensing system
- fig 5 illustrates the device using a hydraulic level-sensing system
- figs 6, 7, 8 and 9 are schematic diagrams illustrating certain possible configurations of the boom;
- fig 10 illustrates the hydraulic circuit in fourth embodiment of the device which does not employ a hydraulic level-sensing system.
- fig 11 illustrates the hydraulic circuit in a fifth embodiment of the device which does not employ a hydraulic level-sensing system.
- fig 12 illustrates the hydraulic circuit in a sixth embodiment of the device which does not employ a hydraulic level-sensing system.
- The crane illustrated in the drawings consists of a
column 1, afirst boom stage 2 which is hinged to the top of thecolumn 1 and rotated about its pivot by ahydraulic cylinder 4, and asecond boom stage 3 which is both hinged and telescopic, rotated about its pivot by onehydraulic cylinder 5, and extended. and retracted telescopically by a furtherhydraulic cylinder 6. - The hydraulic cylinders are connected to a directional control valve assembly denoted 15, each single section of which, when operated, provides a relative cylinder with fluid supplied under pressure from a
pump 14. - 4a, 5a and 6a denote lines connecting each section of the control valve with the rear end of the relative cylinder, whereas 4b, 5b and 6b denote similar lines connecting with the rod end of each cylinder; the ′a′ and ′b′ lines of each circuit thus alternate between pressure and return functions, according to the position of the control valve.
- 4c, 5c and 6c denote respective holding valves installed one in each of the cylinder circuits to the end of preventing jerky descent of the load.
- All of the components described thus far are of a conventional type widely used in hydraulic cranage. The device as embodied in figs 1, 4, 10, 11 and 12 comprises two-way two-position hydraulic valves, denoted 7a, 7b, 8a, 8b and 9, which are installed in the circuits operating the two hinged
cylinders telescoping cylinder 6, respectively. When in the first position, each such valve blocks pressure flow through the relative line while allowing return flow through the same line; in the second position, flow is permitted in either direction. Each valve is held in the second position by pressure of the fluid through the line upstream of the valve itself, and biased toward the first position by arespective spring - As long as there is no pressure through the relative branch of the circuit, the valve will remain springbiased toward the closed position, whereas pressure will cause the valve to open and allow passage of the fluid through that branch; in the event of there being a load on the hook that matches the crane's maximum rated lift capacity, the valves in question act as a shut-off facility disallowing passage of fluid under pressure to the cylinder. The manner in which shut-off occurs is described in detail below. The device as embodied in figs 1 & 4 comprises load-sensing means incorporating a two-way two-position
hydraulic response valve 10, first position open, second position closed. The first port of thevalve 10 connects with thepump 14, and the second port with afirst send line 11 that carries the hydraulic control signal utilized for direct or indirect operation of the shut-offvalves response valve 10 is biased into normally closed position by a spring 10a, and piloted to open in direct fashion by a pressure signal generated in the rear end of thefirst stage cylinder 4 and carried to thevalve 10 by arelative line 22; thevalve 10 is thus operated directly by pressure impinging on the rear end of thecylinder 4 which, it will be remembered, is proportional to the moment of force generated by the load. - 23 denotes a set of restrictions located upstream of the
response valve 10 on theload sensing line 22, the purpose of which is to avoid unwarranted operation of thevalve 10 caused by accidental pressure surge occurring in thecylinder 4. - The device as embodied in figs 1 & 4 also comprises level sensing means in the form of a three-way
hydraulic valve 25 with aball 26 that is free to float within the valve chamber. The first port of such a valve is located in the side wall of the chamber and remains permanently open, whereas the second and the third port are located at either end of the chamber, which also offer relative seats in which theball 26 may register. Thevalve 25 is made fast to thethird stage 3 of the boom, and thus serves to indicate the position of boom as regards the angle assumed above or below horizontal; more exactly, indication of the position A or B of the boom (see fig 1) is made possible by the fact that theball 26 will shift toward one or other end of the valve chamber, according to the angle assumed by the boom. - The first port of the
level sensing valve 25 is connected to thefirst send line 11, whereas the second and the third ports are connected to a second and athird send line - For reasons which will become clear in the course of the description, the hydraulic signal utilized for operation of the valve denoted 9 is taken off the
first send line 11. In the embodiment of fig 1, thevalves cylinders second send line 12, whereas thevalves third send line 13. - The mechanical structure of a given crane may be such that no linear relationship can exist between pressure in the rear end of the
cylinder 4 and the moment of force generated by the load; the result is that certain movements of the boom may overload the crane beyond rated lift capacity without rear end pressure in thecylinder 4 actually registering at the maximum setting envisaged. - This is a drawback which can be overcome by inclusion of a second
hydraulic response valve 10′ identical to and connected in parallel with the firstsuch response valve 10; both valves will be integrated into the system in exactly the same fashion, except for the fact that the pressure signal which pilots thesecond valve 10′ to open is taken off the rear end of thesecond cylinder 5, or at all events, a cylinder other than thefirst cylinder 4, and carried by arelative sensing line 22′. - Fig 2 illustrates how the
second valve 10′ would be incorporated, where appropriate. - Pressure through the
rod end line 4b of the circuit controlling thefirst cylinder 4, which pilots theholding valve 4c to open, impinges on the rear end of the cylinder in a measure commensurate with the difference in piston area between the rear and rod ends; such pressure can therefore affect the control signal supplied to theresponse valve 10 and cause the valve to operate even though rear end pressure in thecylinder 4 may not correspond to the maximum rated lift capacity of the crane. In order to overcome such a drawback, the element of theresponse valve 10 is piloted to close by a pressure signal taken off therod end line 4b, and the area of the valve element on which this signal impinges differs from the area invested by the signal from therear end line 4a to an extent commensurate with the difference in piston area between the rod end and rear end of thecylinder 4. - Fig 3 illustrates how the
response valve 10 may be embodied so as to remain unaffected by pilot pressure through therod end line 4b of the cylinder circuit. - The embodiment of fig 1 also comprises a manually operated
hydraulic unloading valve 20 installed in normally closed configuration between thesensing line 22 and the return line, the purpose of which is described in detail below. - Finally, each send line is provided with a respective restriction connecting to tank.
- In the embodiment of fig 4 one has a third two-way two-position
hydraulic response valve 10˝, first position open, second position closed, biased into its normally closed position by a spring 10a˝, and piloted to open in direct fashion by, pressure signal supplied through thesensing line 22. The first port of thevalve 10" connects with thepump 14, and the second port with a fourth send line 51. - The
first response valve 10 will be piloted to open whenever pressure impinging on the rear end of thecylinder 4 and relayed through thesensing line 22 reflects maximum rated lift capacity of the crane, whereas the third shut-offvalve 10" is caused to open by a pressure level marginally in excess of this setting. - This second embodiment of the device also incorporates a three-way two-
position switching valve 52, a first port of which is connected to thefirst send line 11, the second and third ports being connected respectively to a fifth and asixth send line valves third send lines - The switching
valve 52 is biased by a spring 55 into first position, whereby first and second ports are connected, and piloted into the second position, in which the first and third ports connect, by a signal supplied through the fourth send line 51. - In the third embodiment of the device illustrated in fig 5, two of the shut-off
valves valve 8b is operated by a signal supplied via the send line denoted 13. In this embodiment, the second port of the level-sensing valve 25 and thesecond send line 12 are both eliminated. The rear end lines of the circuits operating the two hingedboom cylinders second relief valves - In the embodiments of figs 10 and 11, sensing means are provided that comprise a three-way two-
position valve 41 which is biased by aspring 45 into its first position, whereby first and third ports are connected; thevalve 41 is piloted into its second position, in which second and third ports are connected, by a pressure signal taken off from the rear end of thefirst cylinder 4 and routed to the valve by way of abranched leg 22a of thesensing line 22. Shift of the valve from first to second position occurs whenever the signal reaches a preset pressure level marginally below that which reflects maximum rated lift capacity of the crane. - The sensing means in figs 10 and 11 further comprise a four-way two-
position valve 42 biased by aspring 46 into its first position, in which the first port connects with the third and the second port connects with the fourth; thevalve 42 is piloted into its second position, in which the first port connects with the fourth, and the second port with the third, by the same pressure signal as aforementioned, which is routed to the valve by way of the remainingleg 22b of the branched sensingline 22. Shift of the valve from first to second position occurs whenever the signal reaches a pressure level reflecting the maximum rated lift capacity of the crane. - The first port of both
valves pump 14, and to the second port of the valve denoted 42, respectively. - In the embodiment of fig 10, the third port of the four-
way valve 42 connects via asend line 47 with the pilot circuits of two of the shut-offvalves further send line 48 with the pilot circuits of the shut-off valves denoted 7a and 8a. The pilot circuit of the remaining shut-offvalve 9 connects via anadditional send line 49 with the third port of the three-way valve 41. - In the embodiment of fig 11, the third port of the four-
way valve 42 connects by way of thefirst send line 47 with the pilot circuits ofvalves second send line 48 with the pilot circuits ofvalves valve 9 connects via anadditional send line 49 with the third port of the three-way valve 41, as in the previous embodiment. - The leg denoted 22b which branches from the
sensing line 22 incorporates acheck valve 44a allowing flow of hydraulic fluid, hence of the pressure signal, toward the four-way valve 42. - 44 denotes a pressure balancing valve that connects the one
leg 22a of the branched sensingline 22 with a point on the remainingleg 22b between thecheck valve 44a and the four-way valve 42. Biased into the normally closed position by a spring, thevalve 44 is obliged to close by pressure through the oneleg 22a, and piloted to open by pressure through the remainingleg 22b. - The
pressure balancing valve 44 is set in such a way as to connect the twolegs sensing line 22 with one another whenever the difference in pressure between the two is marginally greater than the difference between the respective pressure levels that produce shift of the four-wayload sensing valve 42 and the three-wayload sensing valve 41 from first to second position. The purpose of thevalve 44 in question is to restore normal conditions in the limiting device once both sensingvalves fourway valve 42 to the first position is enabled only after the three-way valve 41 has been returned to first position. - 22c denotes restrictions on the
sensing line 22 that perform the identical function to those denoted 23 in fig 1. - The embodiment of fig 10 comprises a normally closed
manual unloading valve 43 which connects thesensing line 22 to tank, and performs the identical function to that denoted 20 aforedescribed. - Sensing means in the embodiment of fig 12 are the same as those illustrated in fig 10, with the exception that the
manual unloading valve 43 is dispensed with; valves and connections serving the second andthird cylinder circuits 5a-5b and 6a-6b likewise remain the same. - The line denoted 4b is connected directly to the rod end of the
first cylinder 4, and exhausted to tank by arelief valve 60 whenever pressure through the line itself rises beyond the relative setting; therelief valve 60 is set to operate independently of the limiting device. Shut-offvalves rear end line 4a in series, and afurther relief valve 61 downstream of thesecond valve 7b will exhaust the rear end to tank whenever pressure through theline 4a rises above the valve setting; in this instance, thevalve 61 is set to a pressure marginally in excess of that reflecting maximum rated lift capacity of the crane. - In this embodiment, the pressure signal that pilots the valves denoted 7a and 8a is supplied through the
second send line 48, whilst that piloting the valves denoted 7b and 7b is supplied through thefirst send line 47. The signal which pilots the remaining shut-offvalve 9 continues to be supplied via thethird send line 49. - Finally, 63 denotes a second three-way two-position valve maintained normally in the first position, in which first and third ports are connected; the valve is piloted into its second position by pressure flow from the
pump 14, thereby connecting the second and third ports, whenever there is a rise beyond the maximum pressure envisaged during retraction of the cylinder rods, hence descent of the boom. Retract pressure is easily quantifiable, corresponding as it does to descent of the boom with no load, and in any event will be considerably lower than the pressure level reflecting maximum rated lift capacity of the crane. The three ports of thevalve 63 are connected thus: first port to tank; second port direct to thepump 14; and third port to a pilot line 64. Pressure registering through the pilot line 64 will be transmitted to the four-way sensing valve 42, on which it impinges in the same direction as the force exerted by thespring 46 and thus assists in biasing thevalve 42 into first position. - Operation of the load limiting device in its various embodiments will now be described.
- As long as a load on the hook remains within maximum rated lift capacity, all circuits operate in entirely straightforward fashion, inasmuch as by shifting any one of the control valve spools 15, the corresponding rear and rod end circuit shut-off
valves - In such conditions, the
valves first cylinder 4 will open the valve denoted 10, connecting thepump 14 to thefirst send line 11, in which a hydraulic control signal is duly set up. - Needless to say, in the event of there being two
load sensing valves 10 and 10', the control signal will be set up by whichever valve opens first. - The control signal acts directly on the telescoping shut-off
valve 9, preventing it from opening even though the relative control valve spool may be moved into the position whereby fluid is directed through therespective line 6a; clearly, any further extension of thetelescoping cylinder 6 would increase the load, regardless of the angle A or B. No load limiting components whatever are incorporated into therod end line 6b of thecylinder 6 in question, since normal retraction reduces the load automatically. - The control signal is fed through the
first send line 11 and into the level-sensing valve 25, theball 26 of which blocks thesecond send line 12 and opens up thethird send line 13, given the position of the boom. Thethird send line 13 being open, the control signal impinges on the shut-offvalves second cylinders - The
valves cylinders - Assuming the boom to be in the B position of fig 1, illustrated in broken line, and lifting to maximum rated capacity, the valve denoted 10 will once again be opened by the signal originating from the rear end of the
first cylinder 4; as far as thetelescoping cylinder 6 is concerned, the same situation obtains as described above. - In the case of the hinged
cylinders second send line 13, since with the boom positioned at B, thethird send line 13 will be blocked by theball 26 of thelevel sensing valve 25. Pressure is thus prevented from reaching the rear end of eithercylinder cylinders - Once the load condition returns below maximum rated lift capacity, the two-
way sensing valve 10 closes, and pressure in the send lines is exhausted via the restrictions in readiness for further operation of the entire set of load limiting valves. - Should the piston of the
first cylinder 4 happen to reach stroke limit, one has an appreciable rise in pressure on the rear end without maximum rated lift capacity being registered, causing theload sensing valve 10 to open and trigger operation of certain of the shut-offvalves - To prevent such a situation from arising, one has incorporation of the
manual unloading valve 20 which connects thesensing line 22 to tank for as long as is necessary to reduce pressure through the line and allow theload sensing valve 10 to close. - In order to avoid difficulties that could arise from accidental jamming of the unloading
valve 20 in open position, a spring-loadedcheck valve 30 is installed upstream of the manual facility; this will close whenever the difference in pressure between inlet and outlet ports of the valve is of an order greater than the bias spring setting. - In the case of the embodiment of figs 4 & 5, arrival at maximum rated lift capacity will once again cause the
load sensing valve 10 to open, setting up a control signal through thefirst send line 11. The effects remain the same as before as far as regards thetelescoping cylinder 6 and relative shut-offvalve 9. - In the embodiment of fig 4, the control signal will be relayed to one or other of the two second stage shut-off
valves second boom stage 3 and the corresponding state of the level-sensing valve 25. In the position shown in the drawing, which corresponds to the diagram of fig 9, the signal will be transmitted through thethird send line 13 to therod end valve 8b, thereby disallowing downward rotation of theboom stage 3 and preventing resultant increase of the load; no such signal will impinge on therear end valve 8a, since upward rotation of thesame stage 3 will automatically reduce the load and is thus permissible. - Where the first hinged
stage 2 of the boom is concerned, it will be observed that the position shown in fig 4, which corresponds to the diagrams of figs 8 and 9, is such that downward rotation of the stage would produce an increase in the load; accordingly, the movement in question is inhibited by the switchingvalve 52, the first and second ports of which are connected and thus relay the control signal to the rod end shut-offvalve 7b, disallowing descent. Supposing, on the other hand, that the boom is in either of the configurations illustrated in figs 6 and 7, it will be seen that on arrival at maximum load, the control signal set up by theload sensing valve 10 will be relayed via the switchingvalve 52 to therod end valve 7b, whereas therear end valve 7a remains in the enabling condition. With pressure flow thus directed through therear end line 4a, thefirst stage 2 lifts, producing an increase in load beyond the permissible limit; in response to such a situation, pressure impinging on the rear end of thecylinder 4 rises beyond the load limit setting and shifts the valve denoted 10˝ into second position. The result is that a signal is set up through the fourth send line 51, and the switchingvalve 52 is piloted into the position in which its first and third ports are connected; the control signal from thefirst sensing valve 10 is now directed to the rear end shut-offvalve 7a, inhibiting further upward movement of the boom while allowing the descent which will automatically mitigate load conditions. - In short, whatever the configuration of the column and boom, the load limiting device prevents overload on the crane at the moment that its maximum rated lift capacity is either matched or exceeded. It will be obvious to a person skilled in the art, however, that a load in excess of maximum rated capacity can be avoided altogether simply by setting the one
load sensing valve 10" at a pressure to match the maximum load, and setting the other 10 at a level marginally below this same pressure. - Once a return within the maximum rated capacity of the crane has been effected using such movements as are enabled by the load limiting device (retraction of the
telescopic stage 3, for instance) thesensing valves 10˝ and 10 will reassume closed position, and control signal pressure through thesend line 11 and the various passages leading to the shut-offvalves - It will be observed that the switching
valve 52 returns to first position only when the valve denoted 10 has likewise been returned to closed position, since this is the only situation in which pressure can be exhausted from thesend line 11. - In short, the switching
valve 52 memorizes second position until otherwise instructed by a return to normal operating conditions. - In the third embodiment of the device illustrated in fig 5, arrival at maximum rated lift capacity causes the signal set up by the
load sensing valve 10 to be transmitted direct to the valves denoted 7b and 9, and neither downward rotation of thefirst stage 2 nor telescoping of thesecond stage 3 are allowed, whatever their position; downward rotation of thesecond stage 3 will be inhibited only where the boom is angled above horizontal as in fig 9. In the configuration of fig 9, in fact, the level-sensed control signal will be relayed via thesend line 13 to the valve denoted 8b, which blocks pressure flow to the rod end of therelative cylinder 5. - In configurations where the
second boom stage 3 is angled below horizontal, as in figs 6, 7 and 8 for instance, therelative valve 8b will be in receipt of no control signal by reason of the fact that the level-sensing valve 25 blocks thesend line 13, and downward rotation is therefore permitted. In the case in point, upward rotation of thestage 3 will be disallowed only where the movement is such as to produce an increase in load, reflected by a build-up of rear end pressure in therelative cylinder 5 and consequent operation of therelief valve 58. - The same principle applies where upward rotation of the
first stage 2 is concerned. Any situation where such movement produces an increase in load (as in figs 6 and 7, for instance) will give rise to an excessive build-up of pressure in the rear end of therelative cylinder 4, hence through theline 4a, with the result that therespective relief valve 57 will operate and prevent further pressurization of the cylinder - Likewise in this instance, a return to within the maximum rated lift capacity causes the load
sensitive valves - Referring to the embodiment illustrated in fig 10, when one has a load on the hook slightly less than the maximum permitted, then pressure building up in the rear end of the
first cylinder 4 will reach the preset level which causes the three-wayload sensing valve 41 to shift from first to second position; it will be remembered that rear end pressure is proportional to the load in substantially linear fashion. The third port of thevalve 41 in question, which is connected via thethird send line 49 to the pilot circuit of the telescoping shut-offvalve 9, and via thesecond send line 48 to the pilot circuits of the first and second cylinder rear end shut-offvalves pump 14; pilot pressure is thus relayed to thesevalves cylinders - In the event that the configuration assumed by the crane is such that retraction of the
cylinders telescoping stage cylinder 6 has the effect of reducing the load in any given configuration of the boom. - In the event, on the other hand, of the boom configuration being such that retraction of the two hinged
cylinders cylinder 4, resulting in the set-up of a signal which is relayed to the four-wayload sensing valve 42; with pressure ultimately at the level which matches maximum rated lift capacity, thevalve 42 shifts from first to second position. In this situation, the pilot circuit's of the first and second cylinder rear end line shut-offvalves end line valves - With a reduction in load, pressure in the rear end of the
cylinder 4 will drop, and the three-wayload sensing valve 41 is returned to first position. The four-way valve 42 will remain in second position by reason of the fact that thecheck valve 44a prevents pressure exhausting from therelative leg 22b of the branched sensingline 22; regular movement of the boom is in no way impeded, however, since with the three-way valve 41 once more in first position, all ports of the four-way valve 42 can exhaust to tank. A further reduction in load produces a further drop in pressure through the leg of the branched sensing line denoted 22a, and once the difference in pressure between the twobranches way sensing valves pressure balancing valve 44 will open so as to exhaust pressure from the leg denoted 22b and enable the four-way sensing valve to return to first position. - The expression, adopted throughout the description, that the crane is returned to "normal operating conditions", signifies the condition in which a load on the hook remains within maximum rated lift capacity of the crane, and thus implies the return of the load limiting device to its initial, non-operative configuration.
- Operation of the embodiment illustrated in fig 11 is identical to that of the embodiment in fig 10, with the sole difference that a shift in position of the three-way
load sensing valve 41 inhibits retraction of the hingedcylinders way valve 42 will inhibit extension. In the case of thetelescoping cylinder 6, clearly enough, retraction will be enabled and extension inhibited whenever the load limiting device is operative. - In contrast to the device as illustrated in fig 10, there is no requirement in the device of fig 11 for an unloading valve 43 -viz, should it happen that the
cylinder 4 reach stroke limit and thus trigger operation of theload sensing valves - In the sixth embodiment of the device illustrated in fig 12, operation remains identical to the embodiment of fig 10 as far as regards the second and
third cylinder circuits 5a-5b, 6a-6b and relative shut-offvalves rod end line 4b of the first cylinder, any excess pressure being exhausted via therelief valve 60. - Flow to and from the service through the
rear end line 4a is controlled by the valves denoted 7a and 7b, respectively; accordingly, shift of the threeway and the four-wayload sensing valves line 4a being exhausted by therelief valve 61. - With such a circuit, it becomes possible to inhibit extension and retraction of the
cylinder 4 according to requirements, with pressure remaining available to the service through therod end line 4b. - This is a feature bringing two marked advantages. First, in the instance of pressure being supplied through the
rod end line 4b and maximum load being reached, limiting action is achieved by disallowing therear end line 4a to exhaust, thereby avoiding a sudden pressure drop through therod end line 4b and preventing any instability occasioned by sudden loss of the rear end pressure required for piloted operation of theload holding valve 4c; this pressure, it will be remembered, is conditioned by dimensional factors deriving from construction of the cylinder. Clearly enough, if pressure is cut off from therod end line 4b by shifting the relativecontrol valve spool 15, the holdingvalve 4c closes and the system will lock up until the load returns within maximum rated lift capacity, and the limiting device can thus be released. - The second advantage is that the unloading
valve 43 of fig 10 becomes unnecessary. With arrival of thecylinder 4 at its stroke limit, excess pressure becoming trapped in the stretch ofline 4a connecting the cylinder with the holdingvalve 4c (pressure which is exploited for operation of theload sensing valves 41 and 42) can be relieved by connecting the freerod end line 4b with pressure; theload holding valve 4c can thus be piloted to open, and the excess pressure relieved. - Inclusion of the valve denoted 63 provides a further significant advantage. In the event that circuit pressure should rise beyond the maximum pump rating calculated to occur during retraction (the situation in question can arise only during extension, clearly enough), the
valve 63 will be shifted into second position, thereby relaying a signal to the four-wayload sensing valve 42 that prevents its moving from first to second position under any circumstance. - More exactly, the
valve 63 remains inoperative as long as the cylinders are retracting, whereas on the extending stroke, the moment that maximum rated lift capacity is reached, pressure through the two lines denoted 4a and 5a will be disallowed regardless of other conditions. This will prevent a particularly skilled operator from juggling thecontrol valves 15 in such a way as to produce pressure surges capable of shifting the four-wayload sensing valve 42, and thus managing to supply additional pressure through eitherline
Claims (8)
and in that the ports of the three-way valve (41) are connected: first, to tank; second, to a pump (14); and third, to the second port of the four-way valve (42), and the ports of the four-way valve (42) are connected: first, to tank; second, to the third port of the three-way valve (41); third and fourth, to respective send lines (47, 48); and the pilot circuit of the third stage shut-off valve (9) connects via a further send line (49) with the third port of the three-way valve (41).
Applications Claiming Priority (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IT40128/85A IT1187219B (en) | 1985-11-27 | 1985-11-27 | Hydraulic load limiting device for hydraulic crane |
IT4012885 | 1985-11-27 | ||
IT4013585 | 1985-12-20 | ||
IT40135/85A IT1202291B (en) | 1985-12-20 | 1985-12-20 | Hydraulic load limiting device for hydraulic crane |
IT40016/86A IT1189792B (en) | 1986-02-28 | 1986-02-28 | Hydraulic load limiting device for hydraulic crane |
IT4001686 | 1986-02-28 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0224446A2 EP0224446A2 (en) | 1987-06-03 |
EP0224446A3 EP0224446A3 (en) | 1988-07-13 |
EP0224446B1 true EP0224446B1 (en) | 1991-04-24 |
Family
ID=27273594
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19860830202 Expired EP0224446B1 (en) | 1985-11-27 | 1986-07-15 | A hydraulic load limiting device for hydraulic cranes |
Country Status (2)
Country | Link |
---|---|
EP (1) | EP0224446B1 (en) |
DE (1) | DE3678905D1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2015193394A1 (en) * | 2014-06-18 | 2015-12-23 | Cnh Industrial Italia S.P.A. | A safety hydraulic circuit |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5058752A (en) * | 1990-03-20 | 1991-10-22 | Simon-R.O. Corporation | Boom overload warning and control system |
US5597080A (en) * | 1994-08-02 | 1997-01-28 | Kranco Crane Services, Inc. | Snag load protection system for a crane |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3371800A (en) * | 1966-07-21 | 1968-03-05 | Grove Mfg Co | Safe load control device for cranes |
DE2164628C3 (en) * | 1971-12-24 | 1978-03-16 | Siegfried Dipl.-Ing. Dr.-Ing. 4930 Detmold Gross | Overload cut-off device for hydraulic lifting and lifting devices coupled in series. Adjustment mechanisms |
SE422315B (en) * | 1980-06-04 | 1982-03-01 | Hiab Foco Ab | OVERLOAD PROTECTION FOR HYDRAULIC DRIVE CRANES |
DE3414183A1 (en) * | 1984-04-14 | 1985-10-24 | Robert Bosch Gmbh, 7000 Stuttgart | HYDRAULIC OVERLOAD PROTECTION DEVICE FOR A LOADING CRANE |
-
1986
- 1986-07-15 EP EP19860830202 patent/EP0224446B1/en not_active Expired
- 1986-07-15 DE DE8686830202T patent/DE3678905D1/en not_active Expired - Lifetime
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2015193394A1 (en) * | 2014-06-18 | 2015-12-23 | Cnh Industrial Italia S.P.A. | A safety hydraulic circuit |
CN106536944A (en) * | 2014-06-18 | 2017-03-22 | 凯斯纽荷兰(中国)管理有限公司 | A safety hydraulic circuit |
CN106536944B (en) * | 2014-06-18 | 2019-04-16 | 凯斯纽荷兰(中国)管理有限公司 | Safe hydraulic pressure circuit |
Also Published As
Publication number | Publication date |
---|---|
DE3678905D1 (en) | 1991-05-29 |
EP0224446A3 (en) | 1988-07-13 |
EP0224446A2 (en) | 1987-06-03 |
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