Description:
My present invention relates to a fluid-operated hoist for raising and lowering a load, e.g. an automotive vehicle, under manual control with the aid of an electric switching circuit.
Conventional semi-automatic hoisting systems of this type are equipped with several actuators e.g. levers) for starting and stopping the fluid pump, for controlling the ascent and descent of the load, and for mechanically arresting the load at a selected level of elevation. The proper co-ordination of these multiple controls requires the constant attention of the operator and is a potential source of human error.
It is, therefore, the general object of my present invention to provide an improved and virtually foolproof electrohydraulic (or possibly electro-pneumatic) control system for the purpose set forth, particularly for a heavy-duty hoist requiring mechanical arresting by suitable backstops at one or more predetermined levels. A more specific object is to provide a control system of this type utilizing but a single manual actuator for the different operations of starting, stopping and locking as well as for determining the sense of motion (up or down).
These objects are realized, pursuant to the present invention, by the provision of two cascaded valves in the output line of a source of high-pressure fluid, the first of these valves controlling the admission of fluid to the elevating means of the hoist (such as a hydraulic cylinder with a plunger supporting the load) and to the fluid-controlled detent means for backstopping the load; the second valve serves for the selective blocking and unblocking of the fluid flow to the first valve. Thus, upon a setting of the first valve (referred to hereinafter as a distributor) to any of its various operating positions such as "up," "down" or "lock," the system will remain inoperative until a command lever or equivalent actuator has been shifted from an "off" position to an "on" position with concurrent displacement of the second valve (referred to hereinafter as a controller). An exception, in the specific embodiment described below, is the "up" position of the distributor which does not require a shifting of the controller but involves operation of an electric switch closed in an intermediate position of the command lever between "off" and "on," this switch completing an energizing circuit for the motor of a pump delivering the hydraulic fluid. In this case, a lost-motion coupling between the command lever and the controller enables the latter to remain in its blocking position as the lever is moved into its intermediate position; this motion is advantageously limited by indexing means such as an indented stop plate with a relatively shallow notch engaged by the lever in the "up" position and two relatively deep notches engaged by the lever in the two other positions of the distributor, these deeper notches permitting a shifting of the controller as the lever is moved fully into its "on" position. In addition, or alternatively, any untimely shifting of the controller may be prevented by a hydraulic holding circuit responsive to operation of the pump motor.
The two degrees of freedom of the command lever, serving for the independent displacement of the distributor and the controller, advantageously allow a swinging of the lever about an axis and a translation thereof parallel to that axis, the two valves being then provided with a rotatable and slidable valve body, respectively, entrainable by the lever. In the preferred embodiment described hereinafter, the rotary valve body forms part of the three-position distributor whereas the slidable valve body is included in the two-position controller. With the output line of the hydraulic pump split into two branches at a junction ahead of the two valves, one of these branches leading directly to the hoisting cylinder while the other branch passes through these valves in series, the energization of the pump motor causes a raising of the load in the absence of a discharge path for the fluid which comes into existence only in the open position of the controller and with the distributor simultaneously in its "down" position. Thus, both the raising and the lowering of the load requires a positive displacement of the command lever from its normal "off" position toward or into its "on" position.
The notched stop plate, aside from determining the extent of the lever shift in the various operating positions of the distributor, also prevents a swinging of the lever in its intermediate and "on" positions so that the setting of the distributor cannot be changed until this lever is restored to normal and hydraulic pressure is positively cut off. Even if the lever is held in its shallow notch, the motor circuit is automatically interrupted by a limit switch as soon as the load reaches its top position. Other switches in that circuit, described in detail hereinbelow, serve to raise the load a small distance above its selected level of elevation preparatorily to a release of the previously engaged detent means; one of these latter switches, therefore, may be tripped by the command lever upon rotation of the distributor into or from its "lock" position.
These and further features of my invention will be described in greater detail hereinafter with reference to the accompanying drawing in which:
FIG. 1 is an overall view of a hoisting system embodying my invention, with an elevator shaft shown in sectional elevation and with the associated electro-hydraulic control means illustrated somewhat diagrammatically;
FIG. 2 is a diagram of the hydraulic circuit of the system of FIG. 1; and
FIG. 3 is a diagram of the associated electric circuit.
The system shown in FIG. 1 comprises a frame 100 forming an elevator shaft for a platform 101 to be used, for example, in the raising and lowering of automotive vehicles between different levels (e.g. floors of a parking garage). Platform 101 is suspended from a plunger 102 whose head is received in a vertical cylinder 1 at the top of frame 100. The interior of cylinder 1 is divided by the plunger head into an upper compartment 1', communicating with a conduit 9', and a lower compartment 1", communicating with a conduit 9".
The frame 100 includes several uprights 3 (only one shown) with recesses or slots 3" separated by solid portions 3'. Each of these uprights 3 co-operates with a respective detent member 4 designed to form a mechanical backstop for the load 101 at any selected level. Member 4 is a generally triangular latch pivoted at 4' on an extension of platform 101 and urged by a spring 4" in a sense (here counterclockwise) tending to maintain the latch disengaged from the recessed upright 3. A hydraulic cylinder 5, also carried on platform 101, has a piston rod 5a bearing from below upon the latch 4 so as to tend to swing the latter in the opposite sense (clockwise), i.e. into engagement with an aligned slot 3", upon a raising of the piston by hydraulic fluid admitted to that cylinder. If desired, the piston rod 5a could also be linked with the latch 4 in order to withdraw it from the slot when the detent is to be released, thus supplementing or replacing the spring 4".
A switch 28, preferably of the microsensitive type, is also mounted on platform 101 so as to co-operate with the solid portions 3' and slots 3" of upright 3, this switch being closed when the latch 4 is in its locking position (full lines) but being open when the latch is withdrawn and confronts one of the slots 3" in a position ready for engagement (dot-dash lines). Thus, the position of the camming roller of switch 28 is so chosen that this roller steps off the upper edge of a slot 3" when the descending latch 4, swung inwardly by the piston rod 5", approaches the lower edge of that slot; switch 28 remains closed whenever the latch 4 adjoins a solid portion 3', opening as soon as the latch clears that solid portion to an extent sufficient to enable its locking engagement with the upright 3.
Platform 101 further carries a limit switch 24 which coacts with a bevel 24' near the top of another upright 24" rigid with frame 100. Limit switch 24, which is normally closed, thus opens whenever the load 101 reaches its uppermost position illustrated in dot-dash lines.
A bevel 101' at the underside of platform 101 coacts with the end 18' of a horizontally shiftable rod 18, forming part of a slide valve 13, whenever the platform descends to its bottom position. The opposite end of rod 18 forms a lost-motion coupling with a sleeve 17' at the lower end of a command lever 17 topped by a knob 20. Lever 17 is shiftable in axial direction of rod 18 (arrow A) and swingable about the rod axis (arrow B), sleeve 17' being also coupled with a splined shaft 19 of a rotary valve 16. Lever 17 fits into any of three notches 41, 42, 43 of a curved stop plate 40 defining three distinct operating positions I (DOWN), II (UP) and III (LOCK) for the rotary valve 16 which acts as a fluid distributor as more fully described hereinafter with reference to FIG. 2. Shaft 19, whose rotation within the limited range of positions I - III has been indicated by an arrow b, is axially fixed.
The three notches 41-43 of plate 40 are of unequal length, notch 42 being shallower than the other two so that a shifting of lever 17 into that notch will not displace the nonrotatable but axially slidable rod 18 in view of the play afforded by its lost-motion coupling with sleeve 17'. Such shifting of the lever and sleeve from one limiting position to another, i.e. from an OFF position (left) toward an ON position (right), closes a normally open microsensitive switch 25 by the action of a cam 21 on sleeve 17'. If lever 17 is aligned with either of the two other notches 41, 43, such a rightward shift does not operate the switch 25 but, in view of the greater depth of these notches, allows the rod 18 to be axially entrained (arrow a) so that its tip 18' projects into the path of bevel 101' of platform 101. Since the platform can descend only in the DOWN position (I) of the distributor 16, for reasons that will presently become apparent, the arrival of the platform at the bottom of its travel will automatically restore the rod 18 to normal and will also force the lever 17 back toward the left if it had been inadvertently held in its ON position by the operator. In position III (LOCK), lever 17 is indexable in an undercut of notch 43, as shown.
A further switch 29 has a pair of normally open contacts which are momentarily closed by a projection 22 on lever 17 whenever that lever is swung from distributor position II to position III or vice versa. Switch 29 controls, in a manner to be explained, the raising of platform 101 preparatorily to a release of latch 4 from its locking position.
FIG. 2 shows details of the structure of the two valves 13, 16 and of the associated hydraulic circuit. Valve 13, acting as a hydraulic controller, has a slidable body 13' rigid with rod 18 and a spring 13" urging that body and rod toward the left, i.e. into the retracted position of FIG. 1 in which the connection between two ports M', M" in the valve housing is interrupted. Port M' is linked via a conduit 15' with a port M in the housing of the rotary valve 16, serving as a hydraulic distributor, in which a valve body 16' is movable between three positions designated I, II and III in conformity with the corresponding designations on the stop plate 40 of FIG. 1. From a companion port C a conduit 5' extends to a set of four latching cylinders 5 in parallel, each of these cylinders being associated with a respective detent 4 (FIG. 1) positioned, for example, at the four corners of platform 101. The piston rods 5a emerging from these cylinders have heads 5b under downward pressure from respective loading springs 5c, these springs opposing the hydraulic pressure generated in conduit 5' when the two ports M and C are interconnected in distributor position III. The hydraulic fluid (oil) is drawn from a reservoir or sump 9, via a filter 8, by a pump 7 whose output line 15 includes a CHECK valve 10 and terminates at port M", a branch 14 of this line from a junction 14' upstream of valves 13, 16 leading to the lower port of cylinder 1 (FIG. 1) by way of pipe 9" with interposition of a check valve 2 in parallel with a throttle valve 21. The effect of the valve combination 2, 2' is to allow free influx of oil into cylinder 1 but to retard the discharge of the oil from that cylinder, thereby slowing the descent of the load 101.
The combination of filter 8, pump 7 and check valve 10 (which prevents a return flow to the pump) is bridged by a bypass 11' leading through an overflow valve 11 normally pressure would closed by a spring 11" but adapted to be forced open by excessive fluid pressure in the output of pump 7. Another bypass 12 extends from output line 15 to the right-hand end of the valve housing of controller 13 in order to place the valve body 13' thereof under a hydraulic holding pressure, preventing a shifting to its open position whenever the pump 7 is operated by an associated drive motor 6. Since this motor goes into action whenever the switch 25 (FIG. 1) is closed upon entry of lever 17 into notch 42, this holding pressure would prevent a full shifting of the lever to its ON position even if the notch 42 had the same depth as notches 41 and 43. The upper compartment 1' of cylinder 1 (FIG. 1) communicates via pipe 9' with reservoir 9.
In the illustrated distributor position I, oil entering the conduit 15' upon the opening of controller 13 is allowed to pass to an outlet port R M leading to the sump 9 through a drain pipe 15". Conduit 5' then also communicates with the sump via an outlet port R C and a drain pipe 5". In distributor position II, port M is cut off while port C still communicates with outlet R C . In distributor position III, port M is connected not only to port C leading to cylinders 5 but also to a supplemental outlet port R S from which a drain pipe 23' extends to reservoir 9 through a preferably adjustable throttle valve 23.
The energizing circuit of motor 6, shown in FIG. 3, includes a source 31 of alternating current which may be a threephase network but, for simplicity, has been shown as comprising only one grounded and one ungrounded bus bar, the latter carrying a high voltage of, say, 220V (RMS) sufficient to operate the heavy-duty pump motor. The live bus bar of network 31 is connected to a field winding of that motor, which may be of the squirrel-cage type, by way of a front contact and armature 26' of a relay 26 in series with the winding of an overload relay 27 having a back contact and armature 27' in the operating circuit of motor relay 26. This operating circuit includes the contacts of the two aforedescribed switches 24 and 25 in series with the secondary winding of a transformer 32 whose primary winding is connected across the power supply 31, in series with a fuse 33, and which serves to step down the voltage of that power supply to a relatively low level of, say, 48V. It will be understood that the system may also include a master switch, not shown, for removing power from both the motor 6 and the transformer 32.
An alternate energizing circuit for motor relay 26 includes an armature 30" of an ancillary relay 30 bridging the two switches 24 and 25, relay 30 also having a holding armature 30' in series with the contacts of switches 24 and 28. Switch 29, when closed momentarily upon rotation of the distributor 16 (FIGS. 1 and 2) into or out of its locking position III, connects the winding of relay 30 across the secondary of transformer 32 by way of switches 24 and 28, both these switches being closed in the load position shown in full lines in FIG. 1.
I shall now describe the several modes of operation of this electro-hydraulic system under the control of command lever 17.
RAISING OF LOAD FROM UNLATCHED POSITION
At the lower end of its travel, platform 101 may rest directly on the foundation, with controller 13 positively closed by the bevel 101' bearing upon rod 18 (though this is not absolutely essential). Lever 17 can be effectively manipulated only in the UP position, i.e. by being introduced into notch 42, this operation resulting in the closure of switch 25 while the distributor 16 occupies its position II. Relay 26 operates and energizes the motor 6 which drives the pump 7 so that high pressure in conduits 14, 9" is applied to the head of plunger 102 in cylinder 1. With valve body 13' immobilized in its closed position by the fluid pressure in conduit 12, the full force of the pump is brought to bear upon the load. Since cylinders 5 are drained via the fluid path established between ports C and R C , their pistons 5b are retracted by the springs 5c so that all the detents 4 are disengaged from the associated uprights 3.
The rise of load 101 and plunger 102 continues until the operator withdraws the lever 17 from notch 42 into its OFF position, thereby reopening the switch 25, or until the limit switch 24 opens on encountering the camming face 24'. With pump 7 now at standstill, and with the discharge of conduits 9", 14 blocked by the check valve 10 and the valve body 13', the load 101 remains in the position it has reached, subject to a possible slow descent due to unavoidable oil leakage. Such leakage, incidentally, is minimized by the fact that the return flow from conduit 15 by way of its extensions 15' and 15" to the sump 9 is interrupted not only by the valve body 13' but also by the valve body 16' in series therewith.
The procedure is basically the same with the load starting from either its bottom position or some intermediate level.
LOWERING OF LOAD FROM UNLATCHED POSITION
This operation can occur only with the distributor 16 in either position I or position II. In the latter case, lever 17' is swung into alignment with notch 41 so that distributor 16 assumes its position I and establishes the aforedescribed drainage path for cylinder 1 through conduit 9", throttle 2' and conduits 14, 15, 15' as soon as the lever has been thrust into the notch to a sufficient extent to open the controller 13. As the oil is slowly discharged from cylinder compartment 1", platform 101 descends until valve body 13' is restored to its closed position by a leftward movement of lever 17 or by the action of bevel 101' upon rod 18; if the mechanical shutoff 101', 18' were not present, the descent would be eventually halted by the platform coming to rest on the foundation.
It should be observed that, under the conditions here described, the four latching cylinders 5 are already drained at the beginning of the descent and the detents 4 are held by the springs 4" in their inoperative positions.
With the distributor 16 left in position I, only the valve body 13' prevents a further descent of the unlatched platform by blocking the discharge of oil from conduit 14.
MECHANICAL LATCHING
The restoration of lever 17 to its OFF position, i.e. its shifting to the left as viewed in FIG. 1, may occur with the load 101 at its selected level or in an off-level position; in the latter case, latch 4 confronts a solid portion 3' rather than a slot 3" of upright 3, switch 28 being closed as its roller extends partly into one of the slots 3". If, now, lever 17 is swung into alignment with notch 43 to lock the load in place, microsensitive switch 29 is briefly closed by the projection 22 whereby ancillary relay 30 is energized if switch 28 is closed as well as limit switch 24, i.e. if the load has not risen to the top of its stroke. Relay 30 thereupon locks over its holding armature 30', independently of switch 29 but in series with switches 24 and 28, thereby completing the energizing circuit of motor relay 26 via its armature 30". Motor 6 now operates as before and drives the pump 7, thereby immobilizing the valve body 30' in its blocking position so that lever 17 cannot be fully inserted into notch 43 while the motor is running. As soon as the latch 4 is properly aligned with the slot 3" entered by the roller of switch 28, this roller is cammed outwardly to open the switch whereby relays 30 and 26 release, thus stopping the motor.
The operator can now complete the shifting of lever 17 into its ON position in notch 43 in which it may be indexed so as to maintain that position even if the lever is biased toward its OFF position by a restoring spring not shown. (The depth of the undercut of the notch 43 is, of course, so slight that the resulting rotation of the lever will not materially alter the operating position of the distributor 16; alternatively, a spring-biased knob or the like on lever 17 may drop into the undercut so that the lever itself does not swing on being thus indexed.) Controller 13 then opens the path between ports M" and M' whereby the oil in line 15, which is under high pressure from the loaded plunger 102 in cylinder 1, is channeled from port M on the one hand to conduit 5' via port C and on the other hand to conduit 23' via port R S . With a portion of the oil returning to sump 9 through throttle valve 23, another portion acts upon the pistons 5b of latching cylinders 5 (which advantageously are of identical construction) so as to pivot the associated detents 4 into aligned slots 3" of the associated uprights 3. With suitable adjustment of throttle valve 23, the oil pressure in cylinders 5 drops relatively quickly so that the springs 5c retract the piston rods 5a from latches 4 almost as soon as these latches have seated on the lower edges of their slots 3" with consequent cessation of fluid flow from cylinder compartment 1" into conduit 15'. Thus, the system is ready for instant unlatching by the operation about to be described.
UNLATCHING
If it is desired to raise or to lower the load latched in the aforedescribed manner, the operator withdraws the lever 17 from the notch 43 and aligns it with either the notch 42 or the notch 41, briefly reclosing in either case the switch 29 so as to re-establish the aforedescribed energizing circuit of ancillary relay 30 inasmuch as switch 28 is closed at this time. If the load is to be lifted, the operator may immediately insert the lever 17 into the notch 42 since such movement is not prevented by the holding pressure in conduit 12, owing to the lost-motion coupling 17', 18; in that case the closure of the microsensitive switch 25 maintains the motor relay energized even after the opening of switch 28 releases the ancillary relay 30. If, however, the load is to be lowered, the operator must await the stopping of pump 7 by the de-energization of relay 30 through the opening of switch 28 (or possibly 24) as platform 101 rises sufficiently to allow the springs 4" to retract the latches 4 from the engaged slots 3". Thereafter, the lever can be shifted into its ON position to initiate a controlled descent of the load as described above.
The one-way throttle 2,2' should be disposed as close as possible to the lower port of cylinder 1 so as to minimize the risk of a break in pipe 9" which could rapidly drain the lower compartment 1".
Although, for the sake of simplicity, I have shown the detent 4 of FIG. 1 and the associated switch 28 as co-operating with the same upright 3, it will be understood that this need not be the case. In any event, however, it will be necessary to coordinate the operation of these elements in such a manner that the switch 28 stops the platform 101 always at one of the levels determined by the locations of the vertically superposed slots or recesses 3", with sufficient tolerances to allow for the effects of inertia, dimensional changes under stress or temperature variations, and so forth. Obviously, switch 28 could also be of the type which opens when confronting a recess and closes when in contact with a solid portion or tooth of a rack-like structure similar to upright 3, with a shaping of the rack generally complementary to that of this upright. If desired, separate limit switches individually associated with the several detents 4 and their uprights 3 may be serially interconnected to assure a more accurate positioning of the platform. The limit switch 24 also need not be tripped by a cam 24' on the elevator shaft (or, if stationary, by a similar cam on the platform 101) but could be actuated by any mobile element mechanically coupled with the load, again with proper allowance for possible elongation of cables and the like used in the transmission of motion.
The latches 4 are merely representative of a variety of detent members (e.g. wedges) hydraulically controllable with the aid of valves 13 and 16. The cascaded or tandem operation of these valves, with the former controlling the fluid supply to the latter, could be brought about also by series and/or parallel combinations of fluid passages other than the arrangement specifically illustrated.