Field of the Invention

This invention relates to fluid cylinders. In particu¬ lar, it relates to fluid cylinders having a bypass circuit which permits working fluid to flow back and forth between opposite sides of the piston.

Background of the Prior Art An increasing number of truck manufacturers are designing trucks with suspended cabs which permit relative motion between the cab and the frame. Since the tilt cylinders- are mounted between the cab and the frame, they must accomodate this motion.

Hydraulic cylinders having bypass circuits which per¬ mit hydraulic fluid to flow back and forth between opposite sides of the piston are known in the art. For instance,

United States patent number 3,469,833, issued September 30, 1969, to L.S. Suozzo, and United States patent number 3,827,537, issued August 6, 1974, to H.E. Haller, Jr., et al., both disclose hydraulic shock and sway absorbers having a bypass circuit with valving such that free move-

» ment of hydraulic fluid from one side of the piston to the

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other occurs only when the absorber is not experiencing rapid reciprocating shock movement. United States patent number 1,519,451, issued December 16, 1924, to A.L. Harris; United States patent number 1,527,592, issued February 24, 1925 to H.L. Livezey; United States patent number 2,064,832, issued December 22, 1936, to A.J. Hollander; and United States patent.number 2,618,365, issued November 18, 1952, " ^" to N.G. Seagren all disclose bypass circuits for nonregen- erative hydraulic cylinders in which the bypass circuits have simple on-off valves, and United States patent number 3,502,002/ issued March 24, 1970, to M.E. hiteman, Jr.-, discloses a bypass circuit being a one-way valve in the circuit.

Other hydraulic cylinders are known in which unvalved passageways are provided around the piston. For instance, United States-patent number 3,853,368, issued December 10, 1974, to A.V. Eichelsheim discloses a hydraulic lost motion cylinder in which the bypass is in the form of an external conduit. However, this is a relatively costly way of obtaining a reasonable flowpath, and it also limits the optimum flow-path possibilities of the design. West German offenlegungsschrift number 2,236,311, issued February 7, 1974, to Otto Sauer, discloses a hydraulic lost motion cylinder in which the cylinder is enlarged at one end, so that the piston does not seal against the inner diameter of the cylinder in the enlarged region. This construction gives an optimum flow path, but it requires either the use of a second piston (or guide) or an extremely long front bearing to overcome front end bearing and sealing problems. ^*

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United Kingdom patent number 1,383,884, published on

February 12, 1975, discloses a hydraulic lost motion cylin¬ der in which a groove is provided in the cylinder barrel at the bottom end of the cylinder, providing a connection between the pull chamber and the push chamber. However, the design, shown in this patent requires the use of an auxiliary piston, since otherwise the cab cannot be lifted -due to the shunt flow past the piston.

Object of the Invention It is, therefore, a general object of the invention to provide a fluid lost motion cylinder which obviates or minimizes the disadvanteges of the prior art.

It is a particular object of the invention to provide a lost motion cylinder which is inexpensive to manufacture, which permits transfer of substantial amounts of working fluid back and forth between the two sides of the piston, but which does not require use of a second piston or an unusually long front bearing to overcome front end bearing and sealing problems. Other objectives and advantages of the present inven¬ tion will become apparent from the detailed description of a preferred embodiment thereof given hereafter.

Brief Summary of the Invention The invention is a fluid-operated piston and cylinder device having at least one groove in the inner wall of the cylinder which permits flow of the working fluid back and forth between opposite sides of the piston over at least a portion of the travel of the piston within the cylinder.

Brief Description of the Drawings

Figure 1 is a side view, partly in elevation and partly in cross-section, of the presently preferred embodiment of the invention.

Figure 2 is a view along the line 2-2 in Figure 1.

Figure 3 is a view along the line 3-3 in Figure 2.

Detailed Description of the Presentlv Preferred Embodiment

The drawings illustrate a piston and cylinder device having a cylinder 10 and a piston 12 slidably received in the ^' cylinder 10. A fitting 14 conducts working fluid to and from the push chamber 16, and a fitting 18 and an external conduit 20 conduct working fluid to and from the pull chamber 22. A conventional mounting bore 24 is pro- vided at the "bottom" end of the cylinder 10. A rod 26 is attached to the piston 12, and it is to be understood that another conventional mounting bore (not shown) is provided at the "top" of the rod 26. Packing 28 and a wiping seal 30 are provided at the "top" end of the cylinder 10, with the rod 26 emerging therefrom in conventional fashion. At least one (in the illustrated embodiment, four) groove 32 is provided in the inner suface of the cylinder 10. The groove 32 extends axially along the inner surface for a distance greater than the thickness of the piston 12. Thus, the grooves 32 extend beyond the piston 12 in both axial directions over at least a portion of the travel of the piston 12 within the cylinder 10. In this case, that portion is the "bottom" portion of the cylinder (i.e., the

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extreme portion of the push chamber 16) , but it will be obvious that it could be different portions of the cylinder

(or even the entire length of the cylinder) in the other configurations. Although the grooves 32 could be machined directly into the inner surface of the cylinder 10, in practice it has been found preferable to cold form the wall of the cylinder -radially outwardly. Since the wall of the cylinder is of uniform thickness, the cold forming results in an external fluting 34 shown in elevation in Figure 1 and in cross- section in Figures .2 and 3.

Although a conventional piston 12 may be used with the subject invention, in practice it has been found desirable to replace the usual external seal of the piston 12 with a two-part seal. The outer part 36 is a glass-filled PTFE sleeve, and the inner part 38 is a resilient rubber O-ring which is somewhat compressed by the fit between the outer part 36 and the inner wall of the cylinder 10 between the grooves 32, thereby biasing the outer part 36 outwardly and into close engagement with the inner wall of the cylinder 10.

Caveat While the present invention has been illustrated by a detailed description of a preferred embodiment thereof, it will be obvious to those skilled in the art that various changes in form and detail can be made therein without de¬ parting from the true scope of the invention. For that rea¬ son, the invention must be measured by the claims appended hereto and not by the foregoing preferred embodiment.

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