US2637302A - Low oil control - Google Patents

Description

May 5, 1953 J. B. HARRISON ErAL 2,637,302

Low OIL CONTROL Filed Nov. 12. 1949 2 SHEETS-SHEET 1 May 5, 1953 .1.5. HARRISON ETAL 2,637,302

Low oIL CONTROL Filed Nov. 12. 1949 2 SHEETS-SHEET 2 Patented May 5, 1953 Tenn.,

assignors to Rotary Lift Company,

Memphis, Tenn., acorporationof Delaware Application November 12, l94=9Seria1N0,.125,858,

(Cl. LZ1-469i- 3A Claims.

OurA invei i more specific y a c ntrol for a hydraulic lift or elevator Wnich responds to an undesirably low level of hydraulic fluid to check the upward movement of the lift.

Almost all modern hydraulic lifts, and particularly those used for automobile servicing have oneV characteristic in common; each system contalus tivo connected' reservoirs for hydraulic liquid,r and the raising of the lift is accomplished by adinittrlg air under pressure to the fluid surface in one of the reservoirs resulting in the expelling or the liquid into the other reservoir. Thus, for example, in one common type oi motor vehicle serviciiugA li't the liquidusually oilis expelled, by compressed air., from an external tank to the cylinder of the lift ram *to elevate the plunger and returns from the cylinder to the external reservoir as the plunger descends; andl in another type the plunger, which is hollow, takes the place of the external tank from and back to which the liquid ilows as the lift ascends and descends. The liquid flow through the connection is restricted as by a small orifice, elongated tubing, or any device Which serves to` provide resistance to iiow. This struc-ture or mode of operation has as one maior advantage the avoidance ci' the jerkiness and uncontrollability of' direct unrestrained pneumatic operation resulting from static friction, inertia, variations in moving friction, etc. The restricted liquidlow smooth.; the pneumatic drive in rriuchy the saine fashion as a dashpot operates. lt will be noted, however, that if the level ci oil is W, as it is expelled from the irst reservoir, the contents ci, this reservoir willv be exhausted and air will blow directly' into the second reservoir, so converting the drive to the direct and unrestrained pneumatic opera-tion with all its disadvantages, amplified by the fact that the system is designedaround the viscosity characteristics of the oil and uct thoseoi a gas.

The type of lift to 'which our control is intended primarily to be applied, although it is suitable for use with any of. the forms of this pn'eumatir cally iinpelled hydraulic lift, is that known as the solf-contained lift wherein the movable plunger forms the storage reservoir from which oil. flows to thev cylinder and returns from theA cylinder through oriiice in the bottom thereof. Hydoulic fluid lille completely the outer casing or cilinder and in large part' also the interior or the plunger when the lift is in its lower position.

To, raise the lift, air under pressure is admitted" into the top of the plunger against the surface o a low oil control or' of*y the. oil containedv therein and an even movement of the plunger is insured by restricting the` orifice out ofV which the oil in the plunger must pass to the casing in order to permit the plungerto rise.

It Will be evident that'ify air escapes from this orifice, the lift vvill be Without the oil restraint and so be subjcctto the jerking discussed above. i secondary effect oflthis escape of air-Will be to introduce an air bubble into the annular space between the outer casing andthe; plunger, so providing` a resilient cushion not'. subject to the restraint of the orifice whichV will permit a jerking startlfor allV subsequent elevations until the bubble is ventedl oli". One way, and one of frequent occurrence in the absencel of any control, by which air may escape from the plunger is that, in the event of' an insuicient oil supply Within the casing; the plungeivfill lift above the surface of the oiLTso permitting-air to blow out through the orifice into the casing reservoir.

One object or" our invention is to haltthe raising ofv a hydraulic lift when the oil'level is too low.

Anotherobject is. to indicateV to the operator a too low `oil level in a hydraulic'lift byV this premature cessati-on of movement.

Another object of ourinvention is to provide a novel control fora self-containedlift preventing the plunger'f-rom rising tosuch an extent as might permit the emissionA of air from the lower orifice-thereof.

Another object of our invention is to provide a novel control which responds to an undesirably lovv` level of hydraulic iluid in a lift during a raising operation to checkthe'movement of the lift to prevent the total' exhaustion of oil inthe reservoirto which` pneumatic pressure is being applied;

Still another obj ect of' our invention is-to provide a novelvv control for a hydraulicV lift which is responsive to a tooV lovvv hydraulic uid level in the course of a liftingoperation and which shuts on" the flow of air raising the lift ata point in the course of the liftprior-to` that point which would per-init airto escape-from theplunger.

Still another object ofourV invention is toprovide a novel low oil control? for a hydraulic lift of the self-contained type which is substantially morepractical andlongerlasting than any hitherto known.

Another object of our invention is the provision of a low oil control for a hydraulic lift which is simple and inexpensive in `construction and sure in operation.

`Other objects and advantages of our invention 3 will be apparent from the following description and drawings, in which:

Fig. l is a section through a self-contained type hydraulic lift in its lowered position, illustrating an embodiment of our invention in plan;

Fig. 2 is a vertical section through the valve portion of our invention;

Fig. 3 is a section similar to Fig. l through a self-contained hydraulic lift showing, however, the lift in elevated position and with an insulcient oil supply; and

Fig. 4 is a fragmentary plan of a modified form or our control, broken away in part to show a section through the valve.

A hydraulic lift of the self-contained type consists generally of a cylindrical casing I closed at its lower end by a wall l2 and provided with bearing rings I4 which receive and guide a cylindrical plunger I6. Packing I'! furnishes a liquidand air-tight joint between the top of the casing and the wall of the plunger. The plunger is closed at its lower end by a plunger head I8 having a central opening 2li in which a thimble 22 is loosely inserted. An air pipe 24 connected at its upper end 2B to a valve and a source of air under pressure (not shown) enters the casing It axially through the bottom wall I2 thereof to admit or relieve the operating air under pressure. The thimble 22 possesses a central opening 28 and the air pipe extends upwardly from its point of entry into the bottom Wall i2 of the casing through the hole 28 in the thimble 22 into the plunger and to a point above the normal oil level Si). The casing is usually sunk in a floor 29 so that the top edge is flush therewith, and an air vent passage 3i is provided to bleed off any air which may be entrapped between the plunger and casing. The passage is closed by a plug 33. It will be evident that as air is admitted into the space 3ft above the normal level 3i) of the oil, the plunger will be raised and the rate of this raising will be controlled not only by the pressure admitted to the space 34 but also by the velocity of ow of the oil from within the plunger I6 through the opening 2i?, particularly as this iow is restricted by the thimble 22.

A primary source of the jerky or bumpy operation of the lift arises from the fact that in moving the plunger from a stopped position there is a static frictional engagement between the plunger I6 and the packing l1 and it requires substantially greater air pressure to break this engagement than it does to maintain in movement the already moving plunger. Thus, were it not for the restricted outflow of the oil from the plunger, when the pressure reached a point sufIicient to break this engagement the plunger would jerk suddenly upward, but the thimble, by restricting the outow of oil, serves as a dashpot to control and steady the rate of elevation regardless of relatively great variances in pressure in the space 34.

Attempts have been made to provide low oil controls for this type of liit. They have usually taken the form of a buoyant valve situated adjacent the plunger head i8, so as to permit or cut oi the iiow of oil therethrough. It is apparent from the very nature of a low oil control which operates by preventing the exit of oil from the plunger that the valve controlled opening can be the only opening through the bottom plunger head. Otherwise there would not be the desired termination of movement. In such case a sliding seal must be effected between the pipe and the plunger head. Assuming the use of packing to obtain this seal as the most logical expedient, and any seal forming means would be subject to the same disability, there would be substantial Wear between the pipe and the packing, such that constant tig tening or replacement would be required to maintain the necessary seal or, in other words, prevent the formation of a econd` opening. Furthermore, such packing would be only doubtfully, and then diicultly, accessible to the normally equipped garage or filling station. The packing would have to be in tight engagement with the exteriol` of the pipe over a travel of about 6 to 8 feet per elevation and the same distance per lowering. No packing could stand up under the length of travel represented in several hundred elevations and under the pressures involved and maintain the necessary tight seal without frequent adjustment,

Furthermore, the control is intended to handle an emergency situation. A failure of the packing would not appear until the low oil control was called on to perform its function, and there would be consequently no signal that the seal was in need of adjustment.

Oui' invention accomplishes the halting of the upward travel ci the plunger not by checking the iiow of oil from the plunger but rather by checking the admission of air into the plunger and avoids the above difficulties attributable to wear by effecting the necessary closure with a minimum of relative travel between the parts and by no relative movement at all ii the oil level is properly maintained.

In the illustrated embodiment of our invention a generally cylindrical valve body di! having a longitudinal bore 4l therethrough and a threaded portion cl3 is attached by the threaded portion to the upper end of the pipe 24. The upper portion 42 oi the body is somewhat reduced in diameter tc aiord a shoulder i5 and has a ground or otherwise smoothly finished outer surface 44. This upper portion is perforated by a plurality of radial perforations 46 which constitute the ports for admitting and relieving the air in the space 34. A valve ring 48 is slidably mounted on this upper portion l2 and a snap ring 5U is situated at the upper end thereof so as to limit the travel of the valve ring. The relation between the snap ring 5) and the ports 46 is such that when the valve ring is at its uppermost point of travel against the snap ring 5t, the ports are uncovered, whereas at the lowermost point of travel of the slide ring 48 against the shoulder 45 of the body, the ports are closed. The upper end of the valve body likewise communicates with the interior space 34 of the plunger through the open end 52 of the bore fil and a valve seat 54 is provided in the bore upon which a ball valve 55 may seat to close the end 52. The ball valve is retained in a position close to the valve seat by pin 58,

The valve ring 48 has press -ltted thereinto downwardly extending arms B of a yoke 62 which is fixed at its lower end by a bracket 64 to a float 6G. The ioat 66 is annular in section, having formed longitudinally therethrough a hole 88 slightly larger than the pipe 24 to permit the oat to be mounted thereon and be guided thereby.

An alternative construction of our control is illustrated in Fig. 4, the principal difference between the two modifications lying in the means of connection between the ring valve and the float. In the second form, one end of a thin Walled pipe section l!) of larger inside diameter than the outside diameter of the air pipe 24 is welded as lat l2 to the tubular float Eid coaxially with the hole @il so that the float and pipe section are slidable on the air pipe 24. At the opposite end of the pipe, metal is removed to denne opstanding arms 'l/i. The upper ends of these m be secured to the ring valve i8 manner such as providing ms which lit over studs alve fill tubular riviecs nit-tei ove the stud "J8 which prethe arm from slipping o the stud 78. foins may be offset outwardly as at 82 r to 'afford proper clearance betvveen the lll and the valve body ili. rom the foregoing description the operation of our may be readily understood. As the plunger raised the amount of plunger Wall displacing the hydraulic fluid becomes continually less and therefore the oil level gradually drops. The float is so positioned with respect to the ports it that when the oil reaches a low level approaching the point of air escape through the opening 2d in the plunger head it it no longer buoys up the float and thereby permits it to drop, carrying the valve ring lil with it to cover the ports d5. When the oil is at its proper normal level the lowering of the oil level by removing the vvalls of the plunger from t reservoir will not cause sufoient lowering oil to produce a dropping of the oat. will, be continued to he buoyed up, so maint ming the valve ring in its upper positi. n to permit the desired degree of lift of the piling iovvever, should the oil supply be initially insuiilcient as from lealrage, etc., the oil level will lower 'to the point of iioat nonsupport, whereat the valve ring ydescends to cover the ports it so preventing more air from enten ing the space 3d.

Were the ports :l5 the only openings in the body lil a diiliculty would appear. Assuming that the ports (le are closed because the lift has reached the maximum allowable travel under the circumstances of lovv oil level, it will be seen that there is no Way of subsequently exhausting the air from the plunger in order to lower it, and to answer this problem the open end 52 of the body 42 and ball valve Fili have been provided. The ball valve 5S and its associated seat lill are so ladjusted that appreoiably higher pressure inside the valve body than outside Will serve to close the valve. Thus as pressure is loe-- ing admitted into the plunger the valve Will normally be held against its seat so as to close this port lill and this situation will pertain even more when the ports @lli have been closed, under which `cirfmrnstance there will be maximum pressure drop across the port 52. In this fashion the ring valve operates to control the air supply substantially as if the outlet ports lli were the only ports in the valve body. However, when the pressure is shut off or relieved in the line 2i so las to create reverse or no pressure drop across the port 52, the ball 5E Will fall away from its seat so permitting an outflow of the air from the plunger.

Having thus described one embodiment of our invention, what We claim as new and useful and desire to secure by Letters Patent is:

l. Low oil control for use With a lift including a reservoir having a supply of oil therein land an open ended pipe through which air under pressure may be delivered to the surface of the oil supply to expel `a portion of the oil from the reservoir, comprising in combination la cylindrical valve housing attachable to the open end of on the rin the pipe and having a valve port in the cylindrical Wall thereof and a relief port. a ring valve member slidable on the exterior wall of said housing and adapted to control the ilovv of air through said Valve port, means on said housing to limit the movement of said ring valve member, a float secured to said ring valve member and responsive to changes in the oil supply level to control the position of said ring valve member so that when the oil in 'the reservoir falls below a predetermined level said float will move said ring valve member to port closing position, and a second valve member adapted to close said relief port when air under pressure is admitted to said housing from the pipe and to open said relief port when the pressure in the pipe is relieved.

2. Low oil control for use with a lift including a reservoir having a supply ol' oil therein and an open ended pipe through which air under pressure may be delivered to the surface of the oil supply to expel a portion of the oil from the reservoir, comprising in combniation a cylindrical valve housing attachable the open end of the pipe and having a valve port in 'the cylindrieal wall thereof and a relief port, a ring valve member slidable on the exterior Wall of saol housing and adapted to control the flow of through said valve port, means on said housing to limit the movement of said ring valve member. a float secured to said ring valve member and respcn""ve to changes in the oil supply level to control the position of said ring valve member' so that when oil in the reservoir falls below a predatori-dined level said float will move said ring valve member to port closing position, and a valve member gravitationally movable to open position adapted to close said relief port when air under pressure is admitted to said housing from the pipe and to open relief' port 'when the pressure in the pipe is relieved.

3. Low oil control for use vfi"i a lift including a reservoir having a supply of oil 'therein and an open ended pipe through air under presk sure may be delivered to the surface of the oil supply to expel a portion of the oil from the reservoir, comprising in combination a valve housing having a smooth surfaced longitudinally' extending exterior Wall and being attacliable to the open end oi the pipe and having a valve port in said wall thereof and a relief port, a ringlike valve member longitudinally slidable on said exterior vvall of said housing and adapted to control the ow of air through said valve port, means on said housing to limit the longitudinal movement of said ring-like valve member, a float secured to said ring-like valve member and responsive to changes in the oil supply level to control the position of said ring-like valve niember so that when the oil in the reservoir falls below a predetermined level said float will move said ring-like valve member to port closing position, and a second valve member adapted to close said relief port when air under pressure is aclmitted to said housing from the pipe and to open said relief port when the pressure in the pipe is relieved.

JOHN B. HARRXSON. GILBERT 'l'. ADAMS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,800,020 Holmes Apr. 7, 1931 2,550,882 Sturm et a1. May 1, 1951

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