Drop foot jack

Details Drop foot jack Drop foot jack

2000-02-10

2001-07-31

Watson, Robert C. (Department: 3723)

Implements or apparatus for applying pushing or pulling force

Vehicle attached jack

Semi-trailer landing gear

Reexamination Certificate

active

06267357

ABSTRACT:

FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to apparata such as jacks for lifting and suspending vehicles, trailers, and other large objects, and more specifically to drop foot jacks (also known as landing gear jacks or vehicle landing gear).
BACKGROUND OF THE INVENTION
Drop foot jacks (also known as vehicle landing gear or landing gear jacks) are commonly used to lift and suspend vehicles, trailers, and other large bodies into elevated positions, with examples of such jacks being illustrated in U.S. Pat. No. 5,904,342 to Laarman and U.S. Pat. No. 5,423,518 to Baxter et al. Brief descriptions of these jacks will now be described so that the reader may better understand the structure and function of drop foot jacks.
U.S. Pat. No. 5,904,342 to Laarman illustrates a drop foot jack wherein an elongated drop foot is telescopically borne within an elongated sleeve, and a crank mechanism is interposed between the drop foot and sleeve so that winding a crank will cause the drop foot to extend from or retract within the sleeve. As a result, when the sleeve engages a trailer (or other object to be lifted) with the drop foot engaging the ground, rotating the crank allows the drop foot to raise or lower the trailer.
U.S. Pat. No. 5,423,518 to Baxter et al. illustrates a drop foot jack similar to that of Laarman, but wherein a potentially greater range of extension is allowed. As in Laarman, an elongated drop foot is telescopically borne within an elongated sleeve, but this sleeve is provided as an inner sleeve which is itself telescopically situated within an outer sleeve. A crank-driven screw engages the inner and outer sleeves so that they may be extended and retracted with respect to each other. Further, the drop foot may be extended or retracted within the inner sleeve, and apertures on the inner sleeve and drop foot may be aligned to allow pins to be inserted to engage the inner sleeve and drop foot together. Thus, a user may extend the drop foot with respect to the inner sleeve to some desired length and then engage them together, and may then crank the inner sleeve with respect to the outer sleeve to attain further height adjustment.
Several problems are perceived as being common in prior drop foot jacks. One significant problem is that in multi-stage drop foot jacks (i.e., those having multiple extending sections, as in Baxter), the mechanisms provided for locking the drop foot to the inner sleeve can provide less than optimal results. These mechanisms must often be compact owing to the telescoping arrangement of the drop foot jack and the need for easy engagement and disengagement, but a compact design tends to cause weakness insofar as pins (or other structure) bridging the inner sleeve and drop foot are subject to shear failure. As a result, the locking mechanism tends to impose the primary limitation on the jack's load capacity. Another significant problem is that drop foot jacks generally operate in harsh environments—they are exposed to road conditions, and therefore experience wide temperature variations and exposure to road grime, snow, salt, etc.—and they can therefore experience early failure. In large part, this arises owing to difficulties in keeping the moving parts of the jacks properly lubricated.
SUMMARY OF THE INVENTION
The invention, which is defined by the claims set out at the end of this disclosure, is directed to a drop foot jack which addresses the aforementioned problems (among others), and which provides numerous advantages which are not known to be present in prior drop foot jacks. While the drop foot jack can take any form defined by the claims, particularly preferred versions of the drop foot jack include at least one of the following features:
First, in versions wherein the drop foot is telescopically borne within an inner sleeve, locking of the drop foot with respect to the inner sleeve is performed by providing an inner sleeve aperture on the inner sleeve which may be aligned with one of several drop foot apertures spaced along the length of the drop foot, and then providing a latch plate having a generally planar configuration which can be selectively moved into aligned apertures in the inner sleeve and the drop foot. The plane of the latch plate is situated generally perpendicular to the lengthwise axes of the inner sleeve and drop foot, thereby increasing the contact area between the latch plate and the drop foot (as well as the latch plate and the inner sleeve). This provides the latch plate with higher resistance to shearing when the inner sleeve and drop foot are loaded, thereby greatly enhancing the load capacity of the drop foot jack.
Second, in versions wherein the drop foot is telescopically borne within an inner sleeve, the drop foot (and also preferably the inner sleeve) has a circumference with well-defined discrete sides, e.g., a polygonal circumference. For example, the drop foot may have a square or rectangular cross-section whereby it has four discrete sides. An inner sleeve aperture on the inner sleeve may be aligned with one of several drop foot apertures on the drop foot so that a latch may be selectively inserted within aligned apertures in the drop foot and the inner sleeve, thereby restraining them from relative movement. The drop foot apertures preferably extend across two or more adjacent sides of the drop foot so that when the latch is inserted in the inner sleeve and drop foot, it engages two or more adjacent sides of the drop foot. Since the latch extending between the inner sleeve and drop foot bears against the drop foot on multiple sides (i.e., in multiple planes), the drop foot is highly resistant to canting with respect to the inner sleeve; in other words, the drop foot and inner sleeve will remain locked together in their respective positions, and will not tip or rock about the latch with respect to each other. This increases the stability of the drop foot jack, as well as decreasing its shear susceptibility (and it thereby increases its loading capacity).
Third, the inner sleeve is preferably telescopically received within an outer sleeve. A rotatable screw extends within at least a portion of the interior of the outer sleeve, which includes a lubrication passage extending between its exterior and its interior. The inner sleeve has a top surface wherein the screw is rotatably received, whereby rotation of the screw will move the outer sleeve and inner sleeve with respect to each other. Additionally, the top surface of the inner sleeve has a depression adjacent the screw. The lubrication passage allows lubricant injected from the exterior of the outer sleeve to access the depression, whereby lubricant may pool in the depression to maintain the screw in a lubricated state. Most preferably, the lubrication passage is provided within an insert member which is inserted from the exterior of the outer sleeve to extend within its interior.


REFERENCES:
patent: 2687268 (1954-08-01), Hawes
patent: 2867409 (1959-01-01), Southerwick
patent: 2974490 (1961-03-01), Hott
patent: 3489395 (1970-01-01), Glassmeyer
patent: 3647183 (1972-03-01), Rishovd
patent: 4066243 (1978-01-01), Johnson
patent: 4176824 (1979-12-01), Linton et al.
patent: 4624447 (1986-11-01), Richmeier
patent: 5174550 (1992-12-01), Pittman
patent: 5423518 (1995-06-01), Baxter et al.
patent: 5664796 (1997-09-01), Huzyers
patent: 5904342 (1999-05-01), Laarman

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