US3234853A - Hydraulic cylinder actuator - Google Patents

Description

Feb. 15, 1966 s A R 3,234,853

HYDRAULIC CYLINDER ACTUATOR Filed 0011. 18, 1963 INVENTOR JOSEPH S. ABER BY 7 4m ATTORNEY United States Patent Ofilice 3,234,853 Patented Feb. 15, 1966 3,234,853 HYDRAULIC CYLINDER ACTUATOR Joseph S. Aber, Philadelphia, Pa. (439 Argyle Road, Drexel Hill, Pa.) Filed Get. 18, 1963, Ser. No. 317,164 1 Claim. (Cl. 914) This invention relates to an actuator for a hydraulic cylinder. More particularly, it relates to actuating means for a hydraulic cylinder in which gas pressure is used in combination with hydraulic fluid.

In certain types of hydraulically actuated cylinders, a reservoir of hydraulic fluid is provided with access to the cylinder on each side of the piston within the cylinder. A differential in the gas pressure applied to the surfaces of the fluid in the cylinders results in an unbalanced force on the opposing faces of the piston, and the cylinder is thus actuated. Accurate positioning of the piston, and carefully controlled movement of it are desirable in certain applications. In many applications, it is important that the position and movement of the piston be held to close tolerances, and that its movement be highly responsive to applied control.

Typically, the hydraulic fluid is oil and the gas is air: the terms oil and air are used throughout this specification as terms of convenience, but it is understood that all gases and hydraulic fluids known or suitable for the use in such hydraulic systems are contemplated within the scope of the invention.

A seemingly straightforward system in practice presents some complications that adversely affect its desirable characteristics. Sudden high pressure bursts of air impinge on the exposed surface of the oil in a reservoir and it has been found that there is a tendency to entrap air bubbles in the oil, in a manner explained below. This condition reduces the sensitivity of the system. It has also been found that when it is desired to hold the piston at a stable position by admitting equal air pressures to each reservoir, there may still be a tendency for the piston to creep because of differentials in the effective pressure on the surface of the oil in the two reservoirs due to differences in the characteristics (such as length) of the lines through which the air is supplied. Expedients have been practiced toward the end of reducing or eliminating these problems, and the present invention is an improvement over other such expedients.

Prior means to prevent the entrapment of air in the oil are shown for example in United States Patents 2,683,- 463 and 3,053,233.

It is an object of this invention to provide a hydraulic cylinder actuator.

It is another object of this invention to provide actuating means for an air oil hydraulic cylinder system.

It is yet another object of this invention to provide an air-oil reservoir system adapted for use with a hydraulic cylinder, in which means are provided to prevent churning of the air and oil, and to reduce unwanted pressure differentials.

It is yet another object of this invention to provide means in a hydraulic cylinder oil reservoir to distribute the flow of incoming gas so as to avoid mixing with the oil.

Other aims and objects of this invention are made apparent in the following specification and claim.

The invention is best understood in connection with the drawing. The drawing is a schematized cross-sectional elevational View of a hydraulic cylinder and its actuating system.

A conventional hydraulic cylinder generally designated 50 is shown. This cylinder 50 is provided with a piston 53 to which is afiixed a piston rod 54. The piston is free to move axially within the cylinder 50 in the ordinary way. Hydraulic fluid, generally oil, 60, is provided inside the cylinder 50 on both sides of piston 53. Oil lines 52 and 51 open into the cylinder on opposite sides of piston 53.

The actuator is generally designated 10. It comprises a base 49 and a top 30. These elements are preferably made of machined metal stock, such as brass, and may typically be rectangular blocks of metal, machined or otherwise fashioned to provide recesses and passages therethrough as indicated in the drawing. It is understood that the actuating means, which constitutes the subject of this invention, is illustrated as much larger thanthe hydraulic cylinder, which is included in the drawing only to show a complete system. In actuality, the scale of the cylinder and actuating means might be reversed.

A pair of reservoir cylinders 34 and 35 are provided between top and base at). As shown, these hollow cylinders may be mounted between the top and the base by being fitted into circular grooves milled or otherwise formed in the facing surfaces of the top and base, re spectively. Thus, a reservoir cylinder together with its closed top and bottom formed by part of the top 30 and base 40, respectively, may be described as a reservoir. It is understood that tight seals are provided at all joints and the shape of the reservoir is not critical to the invention. The exact dimensions of the reservoirs are not critical to the invention, but the typical field of application of this invention normally lies in reservoirs whose reservoir cylinders have diameters of one-inch or more, with the other dimensions of the reservoir typically in somewhat the same proportions shown in the drawing, although not necessarily so. The reservoir cylinders 34 and 35 may be made of metal, or may be made of transparent plastic or glass. There is an advantage in providing the pair of cylinders of transparent material when they are mounted in the close side-by-side relationship on a common base as illustrated in the preferred embodiment shown. The advantage is that the difierential in oil levels between the two cylinders is immediately and easiy visible to the eye of the operator. It is then apparent that this differential is an index to the position of the cylinder. The reservoir cylinders 34 and 35 may be provided with etched, engraved or other markings to provide index marks so that levels may be read quantitatively. Alternatively, linear measuring means may be provided to quantitatively measure the difference between the levels. Such a means includes a simple ruler with provision for raising or lowering it between the two reservoirs. It is also apparent, if the level of the oil 64 in each cylinder is set so as to be the same when the piston 53 is in some central or standard position, that an immediate quantitative or qualitative visual indication is given as to what side of the standard position the piston 53 as at any moment, and how far it is displaced. Thus, in the drawing, the oil 60 in reservoir cylinder 34 stands higher than in cylinder 35, and this corresponds to a displacement of piston 53 toward the left of hydraulic cylinder 50.

The oil lines 51 and 52 communicate respectively to reservoir cylinders 34 and 35 through the respective bores A and 4613 through base 40.

Air lines 25 and 24 communicate through certain connecting means described below respectively to reservoir cylinders 34 and 35. A preferred form of the communicating means is illustrated. Air bores 30A and 3B are provided in top 3% to respectively receive air lines 25 and 24 as shown. These air bores may be horizontal drilled or otherwise formed in the top 30. Air bore 30A opens to J-tube 32 and air bore 30 B opens to I-tube 33. J-tube 32 is a pipe or line curved as shown, and firmly fitted into a bore provided to receive it in top 30, and communicating with the inner end of air bore 30A. The J-tube has a long leg which flts into top 30, and a short leg which terminates below the lower surface of top 30. Preferably a ISO-degree turn is provided in the tube. The end of the tube maybe and preferably is flared outwardly as shown. J-tube 33 is described exactly as is J-tube 32, except that in the preferred embodiment shown, in their mounted positions, tubes 32 and 33 have their handedness reversed. In each J-tube, the center of the open flared end is preferably coaxial with the center line of the corresponding reservoir cylinder.

An air valve of conventional structure is provided to selectively connect air line to air supply line 26 and air line 24 to air supply line 23 in one position, and air line 25 to air supply line 23 and air line to air supply line 26 in a second position. The second position is illustrated by the phantom lines in air valve 20. The air valve 20 comprises a shell 22 having bores 22A, 22B, 22C, and 22D, therein, which respectively receive the lines 25, 26, 24, and 23. A core 21 in valve 20 contains curved channels 21B and 21A which can selectively connect air lines to air supply lines as has been described above when the core 21 is rotated within shell 22. Other means, not shown, may be provided to regulate the pressure available.

The reservoir cylinders 34 and 35 are mounted close together on a single base and underneath a single top to form a single balanced unit. The air valve 20 is provided close to the actuator unit 10 and the lines 24 and 25 are of equal length. The oil lines 51 and 52 are also of equal length, and in general, the structure is such that the total paths to the opposite sides of piston 53 are kept as short and as equal as possible. It has been found that differences in the pressure transmitted to the opposite sides of piston 53 due to differences in frictional line drops can have a significant effect. By thus providing a unitary compact balanced and short line actuator 10, the possibility of imbalance in the pressure ultimately applied against the opposite faces of piston 53 is reduced. This balanced ultimate pressure is desirable where a stable condition is desired. Thus, in addition to the visual check advantages of providing a unitary actuator 10, there is the advantage of a more easiy produced stable condition.

In use, systems of the type herein described, where operating pressures are typically of the order of between and pounds per square inch, there is a sudden burst of air admitted to a reservoir. This sudden burst tends to impinge on the exposed surface of the oil 60 and tends to churn or mix. As has been explained above, this is undesirable when precision control is required. Various expedients have been known to minimize this churning effect. The .T-tube structure herein disclosed has been found to have less tendency to churn or mix than hitherto known expedients.

It is desirable to avoid any direct blast of air from the air lines on the surface of oil 60, and also to have the admitted air act on the exposed oil surface 60 as evenly as possible over the entire surface. A completely even application of impinging air pressure over the entire surface is the ultimate desirable condition in avoiding churning. The herein dsclosed structure is the closest approach yet known to this condition. The direct blast of air coming through the ]-tube strikes the undersurface of top 30, rather than being directed at or near the surface of the oil 60. The passage of the air through the curve in the J-tube is believed to impart a slight swirling motion to the air which helps in the distribution.

The blast of air spreads over the undersurface, and the pressure tends to be uniformly exerted downwardly as if directed from an outlet having the same diameter as the reservoir itself. Any nozzle effect, which is highly undesirable, is here almost completely eliminated. In hitherto known expedients, the effective opening from which the air has come has been smaller in relation to the exposed surface of the oil than is available in the herein disclosed structure, and this smaller effective opening has been found to result in a nozzle effect and consequent blast to at least some degree.

Typically, one air supply line may be connected to a supply of high pressure air, and the other line exhausts to atmosphere. The useful pressure difierential is that between the air supply and atmospheric pressure. Valve 20 may typically have selective positions as follows: air line 24 to pressure, line 25 to exhaust; line 24 to exhaust, line 25 to pressure; lines 24 and 25 both closed; and lines 24- and 25 both to exhaust. The rate of response of the hydraulic cylinder may be regulated by an oil flow control valve in line 51 or 52 (not shown) as is known in the art. When both air lines are closed, there is no creep of the piston even though there is a difference between the effective areas on each side of the piston.

The scope of this invention is to be determined by the appended claim and is not to be limited by the foregoing description and drawing which are intended to be illustrative.

I claim:

An actuation control means for a gas-hydraulic fluid system comprising a single base, a pair of reservoir cylinders mounted close together on said base, a single top covering both of said pair of reservoir cylinders, said reservoir cylinders being made of transparent material, oil lines of equal length and configuration leading from the bottom of each of said reservoir cylinders to opposite ends of said hydraulic cylinder, an air valve, air lines of equal length and configuration leading from said air valve to the top of each of said reservoir cylinders, said air lines communicating to said reservoir cylinders by means of air bores in said top, each of said air bores being connected to a l-tube, each of said J-tubes having a long leg connected to said air bore and extending downwardly into said reservoir cylinder, a curved section connected to said long leg and having a curve of substantially -degrees, a short leg connected to said curved section and having an open flared end pointing upwardly toward and closely spaced from said top, the center of said open end being substantially coincident with the center of said reservoir cylinder.

References Cited by the Examiner UNITED STATES PATENTS 375,761 1/1888 McKim 137-209 666,156 1/1901 Ridgway 91-4 986,143 3/1911 Crawford 137-209 1,147,436 7/1915 Ragonnet 91-4 1,314,153 8/1919 Schneider 91-4 2,151,998 3/1939 Stelzer 91-4 2,638,748 5/1953 Miller 60-546 2,661,847 12/1953 Buettner 60-54.6 2,849,987 9/1958 Shafer 91-4 2.940.518 6/1960 Lawler et al 158-501 3,069,847 12/1962 Vest 60-3966 SAMUEL LEVINE, Primary Examiner.

FRED E. ENGELTHALER, Examiner,

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