US 3182959 A
Description (OCR text may contain errors)
May 1l, 1965 G. T. HVEMMETER 3,182,959
GONTROLLED NEUMATIC JACK Filed April 29. 1963 4free/vir.;
United States Patent sgisassa CUNTRGLLED PNEUMATIC JACK George T. Hemmeter, 10791 Magdalena Ave., Los Altos, Calif. Files Apr. 29, 1963, ser. No. 276,290 5 Claims. (Cl. 254-93) My invention relates to jack mechanisms, particularly cylinder and piston arrangements, which are driven o r operated by compressed air in order to extend the overall length of the jack and to permit it to contract when the air is released. Devices of this `sort are often used for lifting heavy weights, particularly in the automotive field and especially in shops where shop air under pressure is readily available. The operation of these devices is generally satisfactory for the purpose except that the operating air, being elastic, permits variations in the expected operation of thejack. Sometimes the piston is suddenly expelled (often due to loss of load) instead of moving gradually as expected, and sometimes the air pressure falls abruptly and the jack drops the load. Also, jacks operating on a pneumatic supply often move in a jerky or erratic manner instead of in a relatively |smooth and controlled manner due to variations in stick friction and other factors.
It is therefore an object of my invention to provide a controlled pneumatic jack in which the motion of its piston or piston rod is under careful and well regulated control and erratic and spasmodic operation does not occur.
Another object of my invention is to provide a controlled pneumatic jack which will Ynot descend suddenly in theY event of sudden cessation'of actuating air pressure or loss of load.
Another object of the invention is to provide a controlled pneumatic jack in which there is provided means for absorbing surplus energy in order to regulate the motion of the jack.
A still further object of the invention is to provide a controlled pneumatic jack in which the temperature of the controlling element is maintained within a satisfactory range.
A still further object of the invention is to provide an improved and controlled pneumatic jack.
Other objects together with the foregoing are attained in the embodiment of the invention described in the accompanying description and illustrated in the accompanying drawings, in which:
FIGURE 1 is a cross section on a vertical plane showing the controlled pneumatic jack of the invention in its retracted position; and j FIGURE 2 is a cross section comparable to FIGURE 1, but showing the controlled pneumatic jack in a partially extended position, a portion of the ligure being broken away to reduce its size. l
While the controlled pneumatic jack can be embodied in a number of different forms and hasnumerws different iields of application, it has successfully been embodied as shown herein particularly for use in connection with an automotive hoist of the sort shown in my copending ap'- plication entitled Safety Lift, Serial No. 276,231, filed April 29, 1963.
In this or the other customary environments, the jack is preferably inclusive of a jack cylinder 6. This conveniently is a metallic tube provided with a circular-cylindrical, inside fini-shed surface 7 symmetrical about a central axis 8. The jack cylinder 6 at its lower end is joined, as by'welding 9, to a transversely extending base head 11 having supporting feet 12 or other mounting mechanisms. The jack cylinder 6 is similarly spanned at its other end by a guide head 14. This conveniently is a separate body having a central disc 16 with a flange 17 ICS overlying one end of the cylinder 6 and having an inturned collar 18 fitting Within the cylinder 6 and held in position by a set screw 19. The guide head in its central portion'has a collar 2li upstanding from the plane of the disc 16.
Designed to reciprocate smoothly' within the cylinder 6 is an air piston 21. This is a composite member and includes an air piston hub 22 with a flange 23Yextending radially therefrom. The hub 22 has a central boss 24 extending a predetermined distance toward the base head 11 and carries a plurality of cap screws 26 passing through the flange 23 to engage a similar liange 25. An air piston packing 27 has a central disc with a peripheral flange 2S downturned toward the base head 11. The axial extent of the flange 28 is less than that of the boss 24, so that at no time can the packing flange 28 come into'direct abutment with the base head 11. The packing 27 is sup-v ported by a reinforcing or stilfening disc 29 which is interposed between the flange 23 and the flange 25, so that when the cap screws 26 are tightened, the air piston assembly is held in rigid relationship.
Fastened to and extending upwardly from the flange is a tube 31. At its lower end the tube has a reduced portion 32 to serve as a pilot boss for the flange 25 and the disc 29 and also to serve as a centering device for the packing 27. In it-s unreduced portion the tube 31 is secured by welding 33 to the flange 25. The tube 31 ex-V tends upwardly through the jack cylinder and slidingly engages and passes through the hub Z2 to project beyond the jack cylinder 6. The tube 31Y at its upper end is ini ternally threaded and receives a closure plug 34 similarly threaded and carrying a sealing ring 36 so that there is no leakage along the threads between the plug and the tube 31. A fastener 37 engages the plug 34 and secures a work member 38 in position. The work member repre sents any mechanism that is to be moved relative to the body of the jackt relative to the supports 12.
The tube 31 is provided with a nished inside surface 39 andan oil piston 41 islocated concentrically with the axis 8 within the tube 31. The piston 41 has a predetermined length to rest against a shoulder 42 near the upper end of a piston rod 43; The lower end of the piston rod passes through a bore` 44 in the air piston hub 22 and is protected against leakage by a pair of packing rings 46 and 47. The piston rod 43 adjacent its lower end'is provided with a similar shoulder 51 to butt against the upper surface of the basehead 11. The piston rod passes through an opening S2 in the base head and is secured in place and against leakage by a washer 53 and a securing nut S4. The air piston hub also contains a sealing ring 56 fOr precluding any leakage between it and the tube 31;
The piston rod 43 not only'carries the piston 41, but likewise receives a pair of reversed cup-like packings 61 and 62, each of which is ang'ed. The flange"63 of the vpacking 62 extends downwardly toward the base head,
but to a lesser extent than does the piston 41 itself. In this way, the piston'41 not only serves to support in part the packings 61 and 62, but serves also as a stop to prevent accidental collision between the flange 63 and adjacent parts. The packings 61-and 62 are held in location against the piston 41 by a washer 64 and a nut 66 threaded to engage the similarly threaded upper end of the piston rod 43 and extending higher than the packing 61 to avoid injury thereto.
Extending from one side to the other of the oil piston assembly formed by the packings 61 and 62, the piston 41 and the washer 64 is a restricted passage 67. This is constituted by a central bore 68 leading inwardly from the upper end of the piston rod 43 as well as by a cross bore 69 intersecting the bore 68 and opening to the opposite sides of the piston rod 43 below the piston 41.
adsense As a matter of convenience, air from any suitable source of pressure air is led to a controlling valve 71 mounted on the guide head 14. The mount is accomplished by ixing the valve 71 at the upper end of a conductor pipe 72 passing through an 4opening 73 in the guide head 14 and secured in place by a set screw 74. The pipe 72 not only communicates with the source of air under pressure through the valve 71, but also at its lower end is connected through a tting 76 to a passageway 77 leading into the cylinder 6 beneath the air piston in its lowermost position.
Prior to the operation of this structure, the plug 34 is removed and a suitable oil, preferably one of fairly light viscosity and of a viscosity that does not vary a great deal with the temperatures normally encountered, is introduced into the inside of the tube 31. This can easily be done with the tube projected from the cylinder 6, although that is not a necessary position. The oil introduced into the tube 31 Hows through the passage 67 including the bore 68 and the bore 69 and eventually occupies all of the space below the oil piston 41 and some, but not all, of the space above the oil piston. As the oil is introduced into the interior of the tube 31, the air previously therein is automatically expelled. When the tube 31 is suiciently charged with oil, the plug 34 is restored to seal the oil in place and the mechanism is then connected to its load 38.
When the valve 71 is actuated to admit air under pressure, air flows through the pipe 72 and through the passage 77 into the cylinder 6 beneath the air piston. The air piston is thus urged upwardly and if the force urging it in that direction is moderate with respect to the load imposed, then the ascent of the piston and of the tube 31 is at a rate so that the oil beneath the oil piston 41 can readily transfer through the restricted passage 67 to lie above the oil piston. Considered dilerently, the piston 41 moves relative to the oil. Should the air pressure become excessive and the resulting acceleration tend to be too great, there is an opposing, limiting resistance since the restricted passageway 67 precludes extra-rapid ow of oil. The oil acts as a resistor to upward movement of the piston at too great a rate, the extra energy being transformed into heat in the oil.
As the tube 31 projects farther and farther from the cylinder 6, the level of the oil within the tube 31 tends to drop relative to the plug 34 (or the plug rises above the oil level) since the volume within the tube 31 above the oil piston is greater than that below the oil piston by the amount of the volume of the piston rod 43. Thus a vacuum may be drawn in the interior of the tube 31 just beneath the plug 34. That is to say, the pressure beneath the plug 34 falls as the tube 31 rises. It is possible for the tube 31 to rise so much that the air piston hub 22 comes into abutment with the piston 41. While this is an effective stop, it might also serve to cut off flow through the transverse bore 69. For that reason, the air piston hub 22 is provided with a cross slot 81, as shown particularly in FIGURE 2, so that despite the abutment of the parts, there is always free oil flow through the cross channel 69.
When air is released from beneath the air piston, either on purpose by manipulation of the valve 71, or perhaps 4 accidentally by breakage, the load 38 does not descend disastrously since despite the absence of supporting force beneath the air piston the oil cannot transfer from one side to the other of the oil piston except as restricted or throttled by the passage 67. This controls the maximum rate of descent of the load.
Under some circumstances, it is desired to have the load 38 descend at a greater rate. Then the upper packing 61 is omitted. This is shown in my above-identitied application. In this case, when the tube 31 descends, oil ows through the restricted passage 67, as before, but also there can be more or less oil leakage by the remaining downturned packing 62, thus allowing a faster descent than before. Since the packing 62 does not leak appreciably when under pressure from below, there is no substantial change in the rate of upward movement when the packing 61 is omitted.
What is claimed is:
1. A controlled pneumatic jack comprising a jack cylinder, a base head closing one end of said cylinder, an air piston hub having a central bore therein, a rst flange on said air piston hub surrounding said bore, a tube, a second flange on said tube adjacent one end thereof, means engaging said first ange and said second flange for securing said tube against said first flange and around said air piston hub, an oil piston engaging the inner wall of said tube, a piston rod passing through said oil piston and through said central bore, means for detachably fastening said oil piston on said piston rod, means for detachably fastening said piston rod to said base head, and means forming a passage of determined ow area in said piston rod from one side of the other of said oil piston.
2. A controlled pneumatic jack as in claim l in which an air piston packing is clamped between said rst ange and said second flange.
3. A controlled pneumatic jack as in claim l in which an air piston packing and a stiiening disc are clamped between said rst flange and said second flange.
4. A controlled pneumatic jack yas in claim l in which an oil piston packing has a marginal ange extending a predetermined distance toward said air piston hub and said oil piston forms a stop extending more than said predetermined distance toward said air piston hub.
5. A controlled pneumatic jack as in claim 1 in which said oil piston includes only a single packing having a flange extending toward said air piston.
References Cited by the Examiner UNITED STATES PATENTS 2,624,318 1/ 53 Walder4 92-9 X 2,664,859 1/54 Green 92-12 3,002,581 10/61 Deibel 92-10 X 3,042,006 7/62 Butorac 92-9 3,106,257 10/63 Helm 92-12 X wrLLrAM FELDMAN, Primary Examine.
MILTON S. MEHR, M. HENSON WOOD, JR.,