Hydraulic pumping cylinder and method of pumping hydraulic fluid

A hydraulic jack includes a frame and a pump connected to the frame. The pump is connected to the frame. The pump includes a rod, a housing, and a piston, with hydraulic fluid being in the housing. The rod has a cross-sectional area and has a longitudinal axis. The housing has an end through which the rod slides. The housing has an interior open cross-sectional area in a direction normal to the longitudinal axis, and the housing has an interior wall. The piston is coupled to the rod. The piston establishes a rod side chamber and a piston side chamber within the housing. The piston has a cross-sectional area, which is smaller than the cross-sectional area of the housing thereby allowing a portion of the hydraulic fluid to flow between said piston and said interior wall to and from the rod side chamber and the piston side chamber when the piston is moved in the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydraulic pumping cylinder, and, more particularly, to a low-load rapid fluid movement pumping cylinder.

2. Description of the Related Art

Hydraulic cylinders are common devices used in industry and for the jacking of loads using a jacking mechanism having a input cylinder and an output cylinder. The output cylinder is used to lift the load to a predetermined height with a considerably small force utilized on the mechanical portion that moves the input cylinder. The working principal of the hydraulic jack system provides for an applied small force that moves the input piston of a small cross-sectional area and pushes the hydraulic fluid or oil into an output cylinder, which then forces an output piston of large cross-sectional area to jack up a load.

The path of the input piston is often far longer than that of the output piston. The input piston must be repeatedly pumped to jack a load to a predetermined position. During the jacking process, each stroke of the input piston moves the output piston based upon the fluid transfer from the input cylinder to the output cylinder. Typically the same number of pumping strokes is needed to move the jack to a predetermined height regardless of whether there is a load on the output cylinder or not. Under the no-load condition the rate at which the ram of the output cylinder extends, directly or by way of a lifting arm, is not noticeably changed from the rate at which it travels under a loaded condition.

A disadvantage of the systems presently in use is that time and energy are wasted in moving the output piston/ram to the desired location or to encounter a load which is to be moved and/or lifted. Solutions utilized prior to the present invention typically utilize many hydraulic components, which are complex and expensive to manufacture, and due to the additional number of parts, are often unreliable.

What is needed in the art is an easy to operate and inexpensive to manufacture pumping cylinder system that moves a large quantity of hydraulic fluid under low pressure yet delivering high pressure when a load is encountered.

SUMMARY OF THE INVENTION

The present invention provides a hydraulic pumping cylinder.

The invention in one form is directed to a hydraulic jack including a frame and a pump connected to the frame. The pump is connected to the frame. The pump includes a rod, a housing and a piston, with hydraulic fluid being in the housing. The rod has a cross-sectional area and has a longitudinal axis. The housing has an end through which the rod slides. The housing has an interior open cross-sectional area in a direction normal to the longitudinal axis, and the housing has an interior wall. The piston is coupled to the rod. The piston establishes a rod side chamber and a piston side chamber within the housing. The piston has a cross-sectional area, which is smaller than the cross-sectional area of the housing thereby allowing a portion of the hydraulic fluid to flow between said piston and said interior wall to and from the rod side chamber and the piston side chamber when the piston is moved in the housing.

An advantage of the present invention is that under a no-load or near no-load condition the pumping piston moves a large volume of hydraulic fluid as compared to when the fluid is under a high pressure resistance.

Another advantage of the present invention is that an output cylinder is rapidly moved under a no-load condition to thereby allow the output cylinder to rapidly engage a load to undertake the necessary work.

Yet another advantage of the present invention is that the apparatus is inexpensive to manufacture and can be readily adapted into systems currently using prior art designs.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is shown a hydraulic jack10having a frame12, a handle14and a hydraulic pump16. Hydraulic jack10is similar on the exterior to numerous jack systems currently in use. Jack10is rolled under a device, such as a vehicle, and it is positioned so that the lifting arm will engage a portion of the underside of the car. Handle14is pumped up and down to actuate hydraulic pump16, which is hydraulically linked to an output cylinder, not shown, that extends the lifting arm for the purpose of jacking the load, such as the vehicle. Hydraulic jack10may utilize any one of the embodiments to be described hereinafter as a hydraulic pump16.

Now, additionally referring toFIG. 2there is shown a hydraulic pump16that includes connections to a reservoir18, a valve20, check valves22,24and26, a shaft28, a housing30, and a piston38, that operates within housing30having chambers40and42defined by the relative position of piston38. Chamber40is herein referred to as a rod side or shaft side of the assembly and chamber42is herein referred to as a piston side of the assembly. Reservoir18holds hydraulic fluid that is pumped by way of hydraulic pump16to a working cylinder, not shown. Reservoir18may be vented to the air and allows a fluid flow into and out of reservoir18as directed by actions carried out by the positioning of valve20and pumping on handle14. Valve20may be manually operated or under the control of an automatic control system. Valve20is opened to allow fluid flow from the work cylinder back into reservoir18. Typically the fluid in the work cylinder, when it is under a load, is under pressure that has been built up by the operation of hydraulic pump16.

Housing30has an interior wall32and a diameter34. Although, for the sake of understanding of the present invention the interior of housing30is illustrated and discussed as being cylindrical and piston38as round, other shapes are contemplate as well. A longitudinal axis36is shown with it extending through rod28and housing30. Piston38has a diameter44and a side46, with hydraulic fluid being able to pass between interior wall32and side46. Piston38may be centered around axis36and not come into contact with interior wall32, but it is also contemplated to have bearings48or bearing surfaces48, which may contact wall32to assist in keeping piston38centered in housing30. The hydraulic fluid is free to flow between side46and wall32substantially around the entire circumference of piston38.

Check valves22,24and26allow for fluid to enter into housing30at appropriate times and to exit in a pressurized manner through check valve26to the work cylinder. Check valves22,24and26may be spring biased to allow fluid flow through only in one direction.

Shaft28, also known as a rod28, is connected either directly to handle14or by way of a leveraging method utilized by those familiar with the art. Shaft28is hydraulically sealed where it enters into housing30and shaft28is slidingly engaged with housing30allowing shaft28to enter and exit in a longitudinal direction of shaft28. Hydraulic lines are shown schematically entering through portions of housing30and may be appropriately positioned along end portions of housing30or along the sides thereof. The actual positioning of the hydraulic lines is not limited by the positions shown in the figure and their positions are merely for the ease of illustration and explanation of the present invention.

Piston38is slidable substantially parallel to the interior walls of housing30. The shape of piston38may correspond to the interior shape of housing30, which is typically a cylindrical shape, although other shapes are also possible. In a similar fashion shaft28is typically of a cylindrical nature although other shapes are also contemplated.

In the operation of pumping pump16, shaft28is withdrawn to the left toward the inner housing wall of housing30. In this position chamber40is much smaller than chamber42. Force is applied to shaft28pushing it further into housing30causing piston38to advance with shaft28. As shaft28continues to move into housing30, chamber40increases in size causing fluid to travel from reservoir18through check valve22into chamber40. Fluid in chamber42is forced through the hydraulic line and through check valve26and is sent to the work cylinder. This cycle can be repeated with shaft28being moved longitudinally into and out of housing30causing large transfers of fluid to the work cylinder. When shaft28is moved out of housing30, check valve26is closed and check valves24and22are open to allow for transfer of fluid into chamber42. When shaft28is being moved out from housing30hydraulic fluid is transferred from chamber40to chamber42. The hydraulic fluid is introduced through check valve22since the overall displacement within housing30is being reduced since shaft28is being removed through the wall of housing30.

When the work cylinder encounters a load, pressure in the line increases and as shaft28is further inserted into housing30the pressure in chamber42is such that a significant amount of the hydraulic fluid flows past piston38in housing30. As shaft28continues to enter into housing30, shaft28displaces an amount of fluid that corresponds to the volume of shaft28that is moved into housing30to thereby providing for two different pumping volumes. The volume of fluid moved in this high pressure mode is based on the relative cross-sectional area of shaft28rather than on the cross-sectional area of piston38.

The non-sealed nature of piston38with housing30allows for some fluid to move from chamber42to chamber40, when operating under low pressure conditions, but with most of the flow going through check valve26. Although the schematic illustration show a gap extending around all sides of piston38, other configurations are also contemplated, such as contact along one side of housing30, or a groove in housing30with piston38being otherwise substantially sealed with housing30. During high pressure operation a substantial amount of fluid will flow between chamber42and40due to the “leaky” nature of the fit of piston38with housing30. It is during this high pressure operation that the high pressure output of pump16is due to the movement of shaft28into housing30.

The ratio between the surface area of piston38and the area of the leak around piston38is selected so that the switch between the low pressure mode to the high pressure mode takes place at a desirable pressure. The viscosity of the fluid may coact with this ratio to determine the pressure at which pump16transitions from low-to-high and high-to-low pressure. It is also contemplated that a temperature compensation device, which can be in the form of a temperature sensitive valve might be used to counter any change in the fluid flow relative to temperature changes of the fluid. Further, piston38and/or housing30can be fabricated from a material having a coefficient of expansion that, in combination, compensates for a change of viscosity of the fluid. For example, the piston can be fabricated from a material with a higher coefficient of expansion than housing30to compensate for a change in viscosity of the fluid. A specific example is a piston38made of Nylon 6/6 and housing30made of steel. Alternately, a fluid with a near constant viscosity over an extended temperature range, such as Chevron Rando® HD can be used.

It was determined that a gap between side46and wall of32of at least 0.005 inches is preferred and that a gap of at least 0.0075 is more preferred. In one embodiment of the present invention a housing diameter34of 2.000 inches was selected, with a piston diameter44of 1.985 inches and a rod diameter50of 0.625 inches was used. The fluid used was Chevron Rando® HD oil with a viscosity index of 200. The ratio of the cross sectional area of piston38to the cross sectional area of chambers40and42for this one embodiment are related, in this example, to be the ratio of the square of the two radii, or 0.985. This ratio may be thought of one which is not to be exceeded, or a value in a range of between approximately 0.99 and 0.95. The ratio between the cross sectional area of piston38to the cross sectional area of rod28is 10.09, or approximately 10. This means as pump16transitions to it's high pressure mode that it has 10 times the pressure generating capacity than when it is in the low pressure mode. The advantage also exists in the low pressure mode that pump16moves 10 times as much fluid, allowing the working cylinder to advance to an encountered load much faster than the prior art.

It is also contemplated to select the aforementioned ratios to correspond with desired pump capacities. For example, the selection of ratios for a 1 ton jack would vary from the selection for a 10 ton jack so that the input forces on handle14might be comparable and yet they may also have similar low pressure ram extension capabilities. It is also contemplated to select the hydraulic fluid and the ratios so that the properties of the fluid and the gap between piston side46and wall32are optimized.