US3850080A

US3850080A - Seal for non-bottoming piston cylinder assembly

Info

Publication number: US3850080A
Application number: US00345825A
Authority: US
Inventors: G Ekstrom
Original assignee: Eaton Corp
Current assignee: Yale Materials Handling Corp
Priority date: 1973-03-28
Filing date: 1973-03-28
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26
Also published as: GB1406023A; DE2414787A1; JPS5025984A; JPS5647405B2

Abstract

A non-bottoming piston cylinder assembly. The push rod and one cylinder head define therebetween an annular passage communicating with the cavity within the cylinder and the exterior of the cylinder. The annular passage is used for the introduction and removal of fluid into the cylinder during actuation of the piston. An annular resilient seal is generally located within an opening within the piston and encircles the push rod. One end of the seal projects beyond the face of the piston. An annular, radially inwardly extending foot of the seal is located within an annular groove on the exterior of the push rod. When the piston reaches a position adjacent the annular passage, the end of the seal encompasses the passage and thereby entraps a quantity of fluid between the face of the piston and the cylinder head. The entrapped fluid prevents contact between the piston and the cylinder head.

Description

United States Patent Ekstrom NOV. 26, 1974 SEAL FOR NON-BOTTOMING PISTON CYLINDER ASSEMBLY George A. Ekstrom, Churchville, Pa.

Assignee: Eaton Corporation, Cleveland, Ohio Filed: Mar. 28, 1973 Appl. No.: 345,825

[75] Inventor:

U.S. Cl 91/395, 91/409, 92/85 Int. Cl. Fl5b 15/22 Field of Search 92/85; 91/394, 395, 396,

Referenirs Cited UNITED STATES PATENTS 5/l943 Krout 91/395 6/1951 Loewe 91/395 6/1953 Stevens ..9l/395 7/1967 Klaus 92/85 Primary Examiner-Paul E. Maslousky Attorney, Agent, or Firm-Teagno & Toddy [5 7 ABSTRACT A non-bottoming piston cylinder assembly. The push rod and one cylinder head define therebetween an annular passage communicating with the cavity within foot of the seal is located within an annular groove on the exterior of the push rod. When the piston reaches a position adjacent the annular passage, the end of the seal encompasses the passage and thereby entraps a quantity of fluid between the face of the piston and the cylinder head. The entrapped fluid prevents contact between the piston and the cylinder head.

2 Claims, 1 Drawing Figure SEAL FOR NON-BOTTOMING PISTON CYLINDER ASSEMBLY BACKGROUND OF THE DISCLOSURE 1. Field of the Invention The invention relates generally to a piston cylinder assembly and, more particularly, to a seal to prevent bottoming of the piston against one of the cylinder heads.

2. Description of the Prior Art An apparatus to prevent overturning of lift trucks is disclosed in US. Letters Pat. No. 3,007,593 (Hancock). In that apparatus, the pressures of the fluids on opposite sides of the piston in the piston cylinder assembly used to tilt the mast of the truck is fed to a valve. The valve operates to prevent further tilting of the mast and raising of the forks when the pressure on one side of the piston exceeds the pressure on the other side of the piston by a predetermined value. The difference in pressures on opposite sides of the piston is directly related to the force exerted on the push rod. This force is in turn directly related to the moment tending to overturn the truck. If the piston bottoms, i.e., makes contact with a cylinder head, the force exerted on the push rod is transmitted directly to the cylinder head and not to the fluid. When the piston is bottomed against the cylinder head the force on the push rod is no longer related to the difference in pressures. Such bottoming, therefore, makes the valve ineffective.

Piston cylinder assemblies of known design do not operate in a manner that is satisfactory for use with a Hancock type apparatus. As previously described, a standard piston cylinder assembly will bottom. Cushioning piston cylinder assemblies are designed for uniform deceleration and gradual stopping of the piston with minimum impact between the piston and the cylinder head at the end of the stroke. Such impact is, nevertheless, bottoming, which is detrimental to reliable operation ofthe valve. Piston cylinder assemblies with external stops do prevent contact between the piston and the cylinder head. The force on the push rod, however, is transmitted through the external stop to the cylinder and not through the fluid again making the valve ineffective during certainconditions of operation.

Two piston cylinder assemblies which solve the bottoming and loss of pressure problem have been conceived. These assemblies are set out in US. Pat. application Ser. No. 312,087 (Young) and US. Pat. application Ser. No. 345,826 (Neuman), both assigned to the assignee of the present invention. These assemblies use a seal to close a passage and thereby prevent fluid from flowing out of the cylinder when the piston approaches the cylinder head thus entrapping a quantity of fluid be tween the piston and cylinder head. The pressure of the entrapped fluid is related to the force exerted on the push rod. While these assemblies have been found to be generally satisfactory for their intended usages, it is contemplated that they may develop sealing problems under conditions of special or severe usage.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a non-bottoming piston cylinder assembly having an improved seal which will effectively prevent fluid from leaving the cylinder through a given opening tant to dislodging during movement of the piston or as a result of pressure differentials existing within the cylinder.

According to a feature of the invention an annular resilient member encircles the push rod of the piston cylinder assembly and has an annular radially inwardly extending foot located within an annular external groove in the rod and an end which encompasses and seals an annular passage defined by the push rod and the cylinder head.

According to another feature of the invention a cupshaped opening is defined in the piston and the annular resilient member is generally located within the opening with the end extending beyond the face of the piston toward the annular passage. I

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawings comprises a side elevational view, in longitudinal section, of a nonbottoming piston cylinder assembly according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS A piston cylinder assembly 10 is illustrated in the drawing. The assembly includes a cylinder 12 made up of an annular body portion 14 defining a cylindrical cavity 16. Body portion 14 is enclosed by first and second cylinder heads 18 and 20 in a known manner. A piston 22 is in sliding engagement with the cavity defining surface of body portion 14 and divides cavity 16 into first and second chambers 24 and 26. Annular resilient seals 28, of a known design, are engaged with piston 22 and prevent fluid from flowing between chambers 24 and 26. A generally cylindrical push rod 30, axially aligned with body portion 14, projects out of cylinder 12 through head 18. Push rod 30 includes a shoulder 32 in abutting'engagement with a washer 33 which contacts piston 22. A nut 34 is in threaded engagement with push rod 30 and secures the rod and piston together in a known manner. A number of annular resilient seals 36, of a known design, are mounted in head 18 in encircling relationship to push rod 30. Seals 36 prevent fluid from flowing out of chamber 24 around push rod 30. A rod wiper 37 is used to wipe off dirt during retraction of rod 30. An annular plate 38 is secured to head 18 by a number of screws 40, only one shown, that are circumferentially spaced around push rod 30. An annular opening 42 in plate 38 defines an annular passage between push rod 30 and plate 38 that communicates with chamber 24 and an annular cavity 44 in head 18. Passage 46 is used for the introduction and removal of fluid from chamber 24. Annular resilient seals 48 are located between plate 38 and head 18 to prevent fluid from flowing therebetween. A sensing passage 50 is located in head 18 and communicates with chamber 24 and the exterior of cylinder 12. Passage 50 is located so that it is always in communication with chamber 24. Feed passage 52 and sensing passage 54 are located in head 20 and communicate with the exterior of cylinder 12 and chamber 26. Passage 52 is used for the introduction and removal of fluid into and out of second chamber 26. Passage 54 is located so that it is always in communication with chamber 26.

In a typical application, such as illustrated in US. Letters Pat. No. 3,007,593 (Hancock), FIG. 3, sensing passages 50 and 54 of the disclosure would be respectively connected to feed lines and 4. Similarly, feed passages 46 and 52 of the disclosure would be respectively connected to feed lines 17 and 4.

Piston 22 includes an annular cavity 56 defined by the outer surface of a frustum of a cone. Annular cavity 56 is concentric with push rod 30 and diverges in crosssectional area from left to right in the drawing. At the left-hand end of cavity 56 there is located a cylindrical surface 58 defined by piston 22. Juxtaposition surface 58 is located an annular groove 60 defined by push'rod 30. Groove 60 is spaced radially inwardly toward the axis of push rod 30 away from surface 58. The diameter of the inner surface of groove 60 is less than the outer diameter of the push rod. A resilient seal 62 has an inner end 64 defining an annular radially inwardly extending foot that is located within groove 60. The outer end 66 of seal 62 projects outwardly into chamber 24 away from the face 68 ofthe piston. The outer diameter of outer end 66 of seal 62 is greater than the outer diameter of annular opening 42 to allow seal 62 to encompass annular opening 42.

In operation, if piston 22 is to be moved from right to left in the drawing, fluid would be introduced into passage 46 and removed from passage 52. If the movement of piston 22 is to be from left to right the fluid flow would be reversed, i.e., fluid would be introduced into passage 52 and removed from passage 46. For all practical purposes, fluid flow through passages 50 and 54 may be considered to be zero. As referenced in the previously referred to Hancock patent, the passages 50 and 54 are primarily used to transmit, to a pressure sensitive device, the pressures of the fluids existing, respectively, in chambers 24 and 26. When the piston moves to the right in the drawing it will reach a position at which outer end 66 makes contact with surface 70 of plate 38. Such contact will result in the sealing of annular opening 42. When opening 42 is sealed, fluid is no longer permitted to flow out of first chamber 24 and further movement of piston 22 to the right will result in an increase in the pressure of the fluid in chamber 24. Seal 62 is free to yield to any movement of piston 22 to the right and will eventually compress to conform in part to cavity 56. Due to the mass of material of seal 62 extending beyond face 68 of the piston toward head 18, at no time will face 68 contact surface 70 of plate 38. After seal 62 conforms in part to cavity 56 the remainder of seal 62 extending beyond face 68 will compress a slight amount between face 68 and surface 70.

During the sealing of opening 42, the force of the fluid in first chamber 24 will be acting against the outer surface of seal 62 to urge seal 62 radially inwardly toward the axis of the push rod results in the forcing of the foot on the inner end 64 of seal 62 into groove 60. This inward movement of the foot on end 64 results in a tighter gripping of push rod 30 by seal 62 and correspondingly a more secure placement of seal 62 relative to the push rod and the piston.

What is claimed is:

1. In a piston cylinder assembly having a housing with a body portion intermediate first and second heads, the body and heads defining together a cavity, a piston within the cavity in sliding engagement with the body portion, and a rod connected to the piston and extending out of the cavity'through the first'head, the rod and the first head defining therebetween an annular opening communicating the cavity with the exterior of the housing; the improvement wherein:

the rod defines a stepped down portion; and

an annular resilient member encircles the rod and includes a. an annular foot extending radially inwardly toward the stepped down portion, and

b. an axially extending body member having an annular end face, intermediate the piston and the first head, which abuts the first head, and seals the annular opening upon movement of the resilient member toward the first head and entraps a quantity of fluid between the piston and the first head, thereby preventing contact between the piston and first head and causing the entrapped fluid to press radially against the resilient member toward the axis of the rod and thereby urge the foot of the resilient member toward the stepped down portion.

2. A piston cylinder assembly according to claim 1 wherein:

the piston defines a cup-shaped opening generally concentric with the annular resilient member and having a generally axially extending portion;

the stepped down portion of the rod is defined adjacent the closed end of the cup-shaped opening; and

the resilient member is generally located within the cup-shaped opening.

Claims

1. In a piston cylinder assembly having a housing with a body portion intermediate first and second heads, the body and heads defining together a cavity, a piston within the cavity in sliding engagement with the body portion, and a rod connected to the piston and extending out of the cavity through the first head, the rod and the first head defining therebetween an annular opening communicating the cavity with the exterior of the housing; the improvement wherein: the rod defines a stepped down portion; and an annular resilient member encircles the rod and includes a. an annular foot extending radially inwardly toward the stepped down portion, and b. an axially extending body member having an annular end face, intermediate the piston and the first head, whIch abuts the first head, and seals the annular opening upon movement of the resilient member toward the first head and entraps a quantity of fluid between the piston and the first head, thereby preventing contact between the piston and first head and causing the entrapped fluid to press radially against the resilient member toward the axis of the rod and thereby urge the foot of the resilient member toward the stepped down portion.

2. A piston cylinder assembly according to claim 1 wherein: the piston defines a cup-shaped opening generally concentric with the annular resilient member and having a generally axially extending portion; the stepped down portion of the rod is defined adjacent the closed end of the cup-shaped opening; and the resilient member is generally located within the cup-shaped opening.