Commercial lifting device-two-position lift bridge

A two part jack system includes a power unit having a generally rectangular frame with a forward end, a rearward end, a pair of longitudinal side flanges that extend upward therefrom, and a rear cover that extends from the side flanges at the rearward end of the frame. A lifting mechanism mounted on the frame includes a pair of parallel lift arms having forward ends thereon each having a leveling pad pivotally attached to the outer side thereof. A two-position lift bridge includes a rectangular plate having a forward end, a rearward end, an upper surface, a bottom surface and a pair of sides. The bridge is for being positioned laterally and horizontally on the leveling pads at the forward ends of the lift arms, whereby the power unit is operable for use as a load lifting jack. The bridge is alternatively for being positioned on the rear cover of the power unit, whereby the power unit is operable for use with a jack stand. The cover at the rearward end of the power unit further includes apertures therein for receiving the bottom of the bridge.

CROSS REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

The invention relates to a commercial system for lifting and supporting an object i.e. a corner of an automobile; particularly to a two part jacking system including an improved robust power unit that can be used to place and elevate an improved robust jack stand. The inventor of the present invention is a pioneer of the two part jacking system and holds numerous patents for two part jacking systems, some of which are described below.

Briefly, the commercial two part jacking system consists of a mobile power unit and a set of separate mechanical jack stands. Examples of the two part jacking system and mobile power unit are described in detail in Re. 32,715; U.S. Pat. Nos. 4,589,630 and 6,986,503. Some examples of the jack stands are described in detail in U.S. Pat. Nos. 4,553,727; 5,110,089; 5,183,235 and 5,379,974. The stands are capable of being vertically extended and retracted from the garage floor or road surface and, when extended, can be locked in place at a desired position by a ratchet and pawl assembly. The power unit has a wheeled mobile chassis adapted to carry a plurality of the jack stands, and has a pair of lift arms adapted to mate with the outermost jack stand for placement and removal.

In use, the commercial mobile power unit is operated from its handle. It is maneuvered under a vehicle to place a jack stand in a desired location for lifting and supporting the vehicle. The power unit is activated from the handle, and the jack stand is then extended vertically to the desired height, thus lifting the vehicle on the stand. By operating the controls at the end of the handle, the operator can cause the power unit to disengage from the stand, and the stand will remain locked in its extended supporting position under the vehicle.

After the stand is raised and locked in place supporting the vehicle, or other load, in an elevated position, the power unit lift arms are lowered and the power unit is disengaged from the stand and pulled away, leaving the stand in position supporting the load. Another jack stand, carried within the chassis, is automatically transferred to the forward end the chassis for placement at another desired location of the vehicle or for use in lifting and supporting another vehicle.

To lower the vehicle and remove the stand, the power unit is maneuvered to re-engage with the stand. The engagement causes any existing jack stands carried within the chassis to be automatically transferred rearward within the chassis. By manually operating a control at the end of the handle, the operator can cause the power unit to re-engage with the stand, and to disengage the ratchet locking mechanism of the stand, and to lower the stand to its original position. The power unit remains engaged with the stand and can be pulled away from the vehicle with the stand carried within the chassis.

The original commercial power units were adapted to carry up to four jack stands within the chassis. Additional jack stands could be acquired to reload the power unit, so that a single power unit could be utilized to efficiently place and actuate numerous jack stands. It was found that many commercial users would utilize all of their available jack stands, and the power unit was thereafter useless until another jack stand was available to be extracted and reused. The present inventor developed a slide forward bridge that adapted the power unit to function as a load-lifting jack to more fully utilize the power unit. This invention is illustrated in U.S. Pat. No. 6,779,780 entitled Lift Bridge For Use With a Power Unit and a Load Lifting Jack, along with several other patents related to additional features of the lifting system.

In the development of these lifting devices, several design challenges were presented that led to improved, innovative components and assembles of the present invention.

One such design challenge of the jack stand related to a lifting plate raised by the ends of a pair of lift arms on the power unit would sometime shift during lifting, and required redesign of these mating components so they would be self-aligning.

Another design challenge of the jack stand related to a locking mechanism that retained the second frame during elevation of the control frame was not reliable and had a short life, and required redesign with specific new cam angles, materials and heat treating specifications.

Another design challenge of the power unit related to the original hydraulic ram operating on the middle of the lift arms and required excessive and pivotal travel. A new design pushing directly on the rear of the lift arms, and retained within rugged retaining channels was developed.

Another design challenge was to improve the control features of the handle during use, and to improve the handle for movement of the power unit and for compact storage of the handle on the power unit for shipping and when the power unit was not in use.

Another design challenge was that a manual lift bridge should be provided for the basic power unit, stored at a first position on the power unit; and readily available to be placed at a second position on the forward ends of the lift arms, so that the basic power unit could also function as a load lifting jack.

Another design challenge related to the lift arms of the power unit having an extruded recessed channel in the upper surface for retaining a compression spring for advancing the automatic-slide-forward-bridge. The lift arms were difficult to manufacture, had a high scrap rate and were thus not robust to produce. Also, the slide-forward bridge was difficult to produce, was difficult to assemble, and was not as smooth in operation as desired. A new slide-forward bridge for the mobile commercial power unit needed to be developed.

Another design challenge resulted from the redesign of the retaining channels for the rearward ends of the lift arms. This led to the design of a new safety mechanism to lock the rear ends in position when the power unit was functioning as a load lifting jack.

In view of the foregoing design challenges, it is an object of the present invention to provide an improved commercial power unit having components that are robust to manufacture and assemble.

It is another object to provide an improved jack stand that has a self aligning lift plate.

It is another object to provide an improved jack stand with a reliable locking mechanism between the extendable frames.

It is another object to provide a power unit with improved controls for the jack stand.

It is another object to provide an improved handle for the power unit for control of the jack stand; and for positioning the handle for movement, shipment and storage of the power unit.

It is another object to provide a manual two-position bridge component that can be reliable and durable in use and can be stored on the power unit.

It is another object to provide and an automatic-slide-forward-bridge assembly having components that are robust to produce and assemble, and that are reliable and durable in use.

It is another object to provide an improved durable safety mechanism for a hydraulic jack and for the power unit when it is used with the bridge directly as a load lifting device.

SUMMARY OF THE INVENTION

The foregoing object of a power unit having a manual two-position lift bridge that can be stored on the unit is accomplished by the power unit of the present invention.

The power unit includes a generally rectangular frame having a forward end and a rearward end. The frame has a pair of longitudinal side flanges that extend upward therefrom, with the rearward end having a hydraulic cylinder attached along the longitudinal center thereof. A rear cover extends from the side flanges at the rearward end of the frame and over the cylinder. A lifting mechanism mounted on the frame includes a pair of parallel lift arms having forward ends thereon each having a leveling pad pivotally attached to the outer side thereof. The forward ends of the lift arms are extendable by the hydraulic cylinder.

A key feature of the present invention is the lift bridge. The lift bridge includes a rectangular plate having a forward end, a rearward end, an upper surface, a bottom surface and a pair of sides. The bridge is for being positioned laterally and horizontally on the leveling pads at the forward ends of the lift arms, whereby the power unit is operable for use as a load lifting jack. The bridge is alternatively for being positioned on the rear cover of the power unit, whereby the power unit is operable for use with a jack stand.

Each leveling pad includes a vertical generally rectangular portion that is attached to the outer side of the lift arm and having a horizontal upper edge, with a flange extending outward therefrom and having a vertical aperture therein. The bottom surface of the sides of the bridge further include a pair of pins extending downward therefrom for engaging the apertures in the leveling pads.

The lift bridge plate preferably has an aperture through the center thereof having screw threads formed therein, and further for use with a double-screw-out saddle. The double-screw-out saddle has a first threaded shaft extending downward therefrom and a second tubular shaft having internal threads for receiving the screw threads of the first shaft and having external threads for engaging the threaded aperture in the plate.

The cover at the rearward end of the power unit further includes a large aperture therein for receiving the double-shaft extending from the bottom of the bridge, and further includes a pair of apertures therein for receiving the pins extending from the bottom of the bridge.

The lift bridge further preferably includes at least one of the forward end or the rearward end of the plate further includes a flange extending downwardly therefrom for strengthening the bridge.

The side flanges of the frame of the power unit are arcuate, and the rear cover is similarly arcuate to conform to the shape of the side flanges. At least on of the forward and rearward flanges of the lift bridge has a bottom edge that is generally concave conforming to the arcuate contour of the cover.

DETAILED DESCRIPTION OF THE INVENTION

The figures and the following specification may describe and define several distinctive inventions that are interrelated within a lifting and supporting system, and may be included in patents (or pending applications) having distinctive sets of claims directed to the respective invention. Also, the improved power unit and jack stands are discussed and described in terms of an automotive jack system, but it should be understood that the system is not limited to automotive uses and can be utilized for lifting and supporting any type of load.

The components are fabricated from strong, rugged steel materials that are precisely retained in fixtures during any punching and welding processes to retain the designed configuration for a very high-yield and robust fabrication. The present Jack Stand and Power Unit function similarly to those described in U.S. Pat. Nos. 5,183,235 and 5,110,089 which are incorporated herein by reference; however, the present Jack Stands and Power Unit are fabricated from much heavier and upgraded materials; and further include specific improved features as herein described. The improved design and features result in robust manufacturability, and reliability and durability of the jacking system for the commercial user. The system is initially introduced in a 3-ton capacity model, and a 2-ton capacity model, both having a lifting range from about 7 inches to a maximum of about 19 inches for the jack stands and for the power unit.

Robust Commercial Lifting System

Referring first toFIG. 1there is illustrated a first embodiment of a mobile power unit10of the present invention for conventional use with one or more jack stands12and12′ of the present invention for lifting and supporting a load. The power unit is also readily convertible for use directly as a load lifting jack by a manual two-position lift bridge14. The lift bridge as shown inFIG. 1is placed on the power unit in its first (stored) position, and can be manually placed into its second (operative) position (seeFIG. 29) on the forward end of the power unit to convert the power unit for use directly as a load-lifting jack. The two-position lift bridge will be discussed later in detail. The jack stands are designed to have a very low initial height, and the power unit is designed to be very sleek, having a smooth, arcuate, low-profile for maneuvering into low lifting applications and having a unique functional and industrial appearance. The system will be discussed in terms of its structure including significant improved features by the use of descriptive sub-headings.

Robust Commercial Lifting Device—Jack Stand

Referring also toFIGS. 2-11, the overall arrangement of the extendible jack stand12includes a horizontal base assembly26, a vertical tubular first frame21which is fixedly attached to the base assembly, a vertical tubular second frame22which is telescopically received within the first frame21, and a vertical tubular third frame23which is telescopically received within the second frame22. There is an optional vertical fourth frame24(a screw-out saddle) threaded into the upper end of third frame23. The third frame23has an improved unique lifting plate25on the upper end thereof and will be discussed later in detail. The base assembly is provided for aligning and locking the jack stand within the power unit10, and a ratchet mechanism is provided for establishing a precise extension position of the jack stand.

The base assembly26includes a bottom plate27, an upper plate28supported on side walls, a pair of spring-loaded latch fingers29occupying respective ends of the space between plates27and28, and a pair of lateral ramps30(each having a lateral aligning hole31therein) is secured to the respective side walls forming side rails thereon. The latch fingers29function to secure two or more jack stands12,12′, etc., in a series relationship within the frame of the power unit10. The lateral ramps30initially provide side rails (that are above and parallel with the bottom plate27) that are engagable by the separated forward extension ends of the frame of the power unit10that straddle the base assembly26for loading the jack stands into the power unit, as shown inFIG. 1. The lateral ramps and aligning holes31are further utilized for aligning and locking the jack stand into the frame of the power unit, and will be further described later along with the related components of the power unit.

The tubular first frame21has a lower end that extends downward through the upper plate28of base26and is welded to bottom plate27. The tubular second frame22is telescopically received within first frame21. The second frame has vertical rows of ratchet teeth32formed on two opposite sides of its outer wall surface. In order to maintain the rotational orientation of the ratchet teeth32relative to base assembly26, there is a vertical groove33formed at one point on the circumference of the outer wall surface of second frame22and which extends throughout most of the length of the second frame. A short pin34, secured through an opening in the wall of first frame21, extends into the groove33and thus secures the second frame22against rotation (seeFIG. 3).

The first frame21has a pair of ratchet arm housings35secured to opposite sides of its exterior surface and aligned with the ratchet teeth of the second frame22. Within each such housing there is a vertically extending ratchet arm36having a tooth or pawl37formed on its upper end. Each ratchet arm is supported near its longitudinal center by a pivot pin38which is in turn secured within the corresponding housing. A tapered compression spring39forces the lower end of each ratchet arm outward so that the pawl37on its upper end will reliably engage the ratchet teeth of second frame22(or third frame23). The lowermost end40of each ratchet arm36is exposed beneath the corresponding housing where a horizontal force may be applied for releasing the engagement of its pawl37with the ratchet teeth.

The tubular third frame23likewise has vertical rows of ratchet teeth42formed on two opposite sides of its outer wall surface, similarly as the second frame22. In order to maintain the rotational orientation of the ratchet teeth42relative to the base assembly26there is a vertical groove43formed at one point on the circumference of the outer wall surface of third frame23and which extends throughout most of the length of the third frame. A short pin44secured through an opening in the wall of second frame22extends into the groove43and thus secures third frame23against rotation.

Commercial Jack Stand—Improved Frame Locking Mechanism

Referring particularly toFIGS. 3-9, as the power unit10elevates the lift plate25of the jack stand12, the third tubular frame23is extended upward and the ratchet teeth thereon are engaged by the ratchet arm pawls37to secure the third frame in position. However, there is typically internal friction between the telescopic tubular frames, and the second tubular frame22(unless secured within first frame21) tends to be prematurely extended upward along with the third frame. Upon the premature elevation of the second frame, the ratchet teeth thereon are then engaged by the pawls, but the ratchet teeth on the third frame are otherwise not engaged or locked. The third frame is lifted by the power unit, but is not locked or supported; and when the lifting by the power unit is released, the third frame drops from the force of the load.

This problem was “conceptually” solved with a dual locking mechanism for automatically locking the second frame in fixed relation to the first frame while the third frame is being raised, and for locking the third frame in fully extended relation to the second frame while the second frame is being raised (seeFIG. 3), as generally described in U.S. Pat. No. 5,110,089. However, the components of the locking mechanism had a relatively short life and required frequent repair.

The basic dual locking mechanism includes a pair of upwardly extending fingers46fixedly secured on opposite sides to the upper end of the first frame21; a guide member47secured to the upper end of the second frame22and extending horizontally outward therefrom, and having a pair of opposed recessed channels48therein with slotted openings49therein for receiving upper ends62of the respective fingers; and a pair of latch members50each horizontally slidable in the recessed channels of the guide member and having a slotted opening51therein for receiving the upper end of one of the fingers. The mechanism includes a set of suitable compression springs52for urging the latch members inwardly along the guide member at the upper end of the second frame. The third frame23has a horizontal groove45in its outer surface near the lower end thereof for receiving the latch members when the third frame is fully extended (seeFIGS. 4-6).

Each latch member50has a horizontally curved inner end53(conforming to the diameter of the tubular frame23) having a rounded nose thereon, and the slotted opening therein has an inward edge54and an outward edge55thereof for cooperating with the upper end of the respective finger46. The latch member has an outer end56having suitable notches57for abutting one end of the springs52that are nested within the outer ends of the guide member47. The latch members and the springs are slideably retained and enclosed within the guide member by a pair of covers58each having a dome59thereon providing clearance for the upper end of the fingers, and having side and outer end flanges60for fastening the cover to the upper surface of the guide member.

Each finger46has the upper end62extendable into the slotted openings51of the latch members50. The upper end62has an angled outward surface63thereon that acts as a cam for engaging the outward edge56of the slotted opening in the latch member, and has an inward surface64that act as an angled notch for engaging with the inward edge54of the slotted opening of the latch member.

The fingers46, the guide member47and the latch members48are in frictional engagement and are locked and unlocked every time the jack stand is raised and lowered. After extensive analysis and development of the interaction of these components, specific materials, levels of heat treating, and specific angles of the upper end of the fingers have been determined, resulting in robust manufacturing, reliable commercial use, and extended life of the jack stands. These unique refinements are described below in detail.

More particularly, each finger has the upper end62with the outward surface63thereof extending outwardly and downwardly suitably inclined at an angle “α” ranging from about 28° to about 38°, and preferably at about 32°. This cam angle of about 32° provides smooth engagement with the outward edge55of the slotted opening in the latch member50for sliding the latch member outwardly along the recessed channels48of guide member47.

The upper end62has the inward surface64thereon suitably extending outwardly and downwardly at an angle “β” ranging from about 40° to about 50° and preferably at about 45° for a vertical distance of about the thickness of the latch member50, and then having a generally vertical portion65extending downwardly a distance of about the thickness of the latch member. The vertical portion65of the inward surface acts as a recessed notch with the upper end62extending inwardly over the inward edge54in the slotted opening of the latch member50and thereby captures the second frame22against any premature upward movement. The angle of 45° (even at low range 40°) insures that there is no binding of the inward edge54with the finger during the engagement of the outward edge55by the angled outer surface63acting at 32° (even at high range 38°), and further provides a smooth gradual unlatching of the finger over this surface when the latch member slides into the groove45of the third frame23when the third frame is fully extended (seeFIG. 6).

The inward surface62of the finger continues further with a clearance portion66that extends outwardly and downwardly inclined at a suitable angle “γ” ranging from about 18° to about 28° and preferably at an angle of about 23° a vertical distance of about the thickness of the latch member. This portion66of the upper end provides some tolerance and clearance for welding the finger to the first frame21and insures clearance with the latch member during use.

The fingers46, guide member47, and latch members50components were initially formed by conventional stamping processes, but this method was not successful for providing the desired working surfaces needed for reliable performance with a long commercial life. The preferred method for forming these components is by the well known “lost wax” casting process, and this process results in very satisfactory performance.

In the “lost wax” casting process, a series of impressions of the components are first molded in wax. These wax moldings are then dipped, sprayed or otherwise coated in a “plaster-of-paris” type material; and are allowed to harden; they are then heated and the wax is melted out, and the hardened materials are used as molds, to cast the components in the desired steel material. The process is repeated in production to produce each of the components.

The fingers46, guide member47, and latch members48are suitably cast out of 4130-4140 carbon steel. It has further been determined that these components should be of about the same hardness, and preferably are heat treated to a hardness of about 40-45 Rockwell C. Extended life tests of the jack stands have shown that heat treatment of the components to a hardness of less than 40 Rockwell C results in excess wear; and hardness above 50 Rockwell C result in components than are too brittle that tend to break.

The above described components cast from 4130-4140 steel, heat treated to 40-45 Rockwell C, and having the contoured fingers and latch members as defined, provide reliable locking of the respective frames when the jack stand is raised; and provides reliable unlocking of the respective frames when the jack stand is lowered, over an extended long commercial use of the jack stand.

Commercial Lifting Device—Self Aligning Jack Stand

Referring now also toFIGS. 9-11, the commercial jack stand12has been further improved so that the lifting pad25tends to be self-centering during lifting by the commercial mobile power unit10, and tends to be self-aligning to compensate for small movements of the load.

The power unit will be discussed later in more detail, but for purposes of the improvement of the jack stand, the power unit includes an improved feature related to a pair of parallel lift arms68having forward ends69thereof for engaging the lifting plate25of the jack stand. The inner sides of the forward ends of each lift arm includes a frusta-conical disc70rotatably attached to a lateral axel thereon. The greater diameter of the disc extends inwardly so that the upper surface thereof inclines upwardly at an acute angle ranging from about 15° to about 30°, and preferably at about 20°.

The lifting plate25comprises a rectangular plate attached to the upper end of the third frame23, having parallel side flanges71extending downwardly therefrom. The side flanges each have a lower end72with an inner surface extending outwardly and downwardly at an acute angle for engaging the upper surface of the frusta-conical discs of the power unit. The acute angle should correspond with the angle of the frusta-conical disc, ranging from about 15° to about 30° and is preferably at an angle of about 20°. As shown, particularly inFIG. 11, the angular engagement of the bottom surfaces of the lifting plate and the upper surfaces of the discs, the lifting plate tends to seek a neutral balance laterally between the lift arms. The rotatable discs also provide for the lifting plate to translate along the upper ends of the lift arms, with small longitudinal shifts of the load relative to the jack stand (without tending to tip the jack stand).

As shown inFIG. 10, in a most preferable configuration of the lifting plate, the side flanges71have flat corner portions73extending downwardly therefrom. The corner portions create the lower end72to now be within central recessed portions74between the corner portions. The angled lower end72is provided only in the recessed central portions. The angled inner surface of the lower end72can readily engage the upper surface of the frusta-conical disc70to laterally center the lifting plate and longitudinally translate along the bottom of the lifting plate with any longitudinal shift of the load, as described above. And further, any longitudinal translation is limited to the recessed central portion74thereof, so that the lifting plate will not translate completely off of the discs in the event of a more sever shift of the load.

As discussed above, the bottom inner surface72of the recessed portion74of the lifting plate25extends outwardly and downwardly at an angle ranging from about 15° to about 30° and preferably at an angle of about 20° (corresponding to the upper surface of the disc70).

Referring again particularly toFIG. 10, the lifting plate25has a lower surface75thereof further improved by a pair of recesses76therein for nesting the lifting plate over the pawls37of the ratchet arms; and a pair of recesses77for nesting the lifting plate over the domed covers58of the dual locking mechanism. The rugged robust design of the components of the commercial jack stand tends to increase the overall height of the jack stand, and the pairs of recesses76and77help to minimize the height of the commercial jack stand (to about 6 inches).

Robust Commercial Power Unit—Frame and Lifting Assembly

Referring now toFIGS. 1,9,14and15, the mobile commercial power unit10is shown for use with the jack stands12, and for use with the lift bridge14.

The power unit10has a generally rectangular frame80having a central longitudinal axis, a forward end81for loading and unloading the jack stands, a middle portion82for securing the lifting mechanism, a rearward end83for controlling the power unit, and a bottom84thereof. The bottom84(seeFIG. 14) has a rectangular slotted opening85therein extending longitudinal from the forward end through the middle portion thereof. The opening is a little wider than the width of the base assembly26of the jack stand12. The forward end has a pair of flat separated extensions86with laterally rounded noses87thereon extending from the edge of the slot to the respective side of the bottom of the frame, for straddling the jack stands. The separated extensions are used to ride up over the bottom plate27of the jack stand, to straddle the base assembly26thereof and to engage the lower surface of the side rails and ramps30thereof, to retain and transport one or more jack stands in the frame of the power unit.

The prior art power units utilized a frame with separated forward ends (as shown in phantom lines inFIG. 12) typically with a slotted openings therein that extended only to a distance corresponding to the end of the latch finger29of a jack stand that had been previously loaded into the power unit. The initial jack stand12could be readily straddled and loaded, but the loading of any additional jack stands12′ etc., required precise pre-staging to line-up squarely with the end of the bottom plate27and with the latch finger29of the additional jack stand. The separated extensions86of the frame of the present invention are extended about 1.50 inches beyond the latch finger and have rounded noses thereon. The improved extensions86of the power unit can readily straddle the base assembly26of the additional jack stand and self-align this jack stand squarely for loading and latching it into the power unit. This is a significant improvement in the efficient commercial use of the lifting system.

The bottom84of the frame further has the forward end81thereof substantially flat (for about 12 inches) for providing a solid lifting platform, and has the middle portion and rearward end thereof angled longitudinally upwardly (at about 5°) for facilitating mobility of the power unit by a pair of wheels88located near the rearward end83of the frame.

A hydraulic cylinder89having an extendable ram90at the forward end thereof, and having a rotatable control valve91at the rearward end thereof, is attached along the longitudinal center near the rearward end83of the bottom84of the frame. The hydraulic cylinder preferably utilizes dual piston type actuators92having a first piston actuator for rapidly extending the ram with only a few strokes, until a load exceeding about 150 pounds is encountered; the second piston actuator then takes over to extend the ram (i.e. to lift the load) in the conventional manner. This is another commercially efficient feature of the power unit10.

The frame has a pair of longitudinal side flanges93extending upward from the bottom84thereof; and has the pair of wheels88attached to the outer sides of the flanges on lateral axels near the rearward end83thereof. Each side flange has an upper edge94with a rounded vertical nose95at the forward end81thereof and a smooth generally vertical blunted tail96at the rearward end thereof, and has a smooth arcuate contour extending upwardly from the rounded nose to about the height of the wheels and then downwardly mating with the blunted tail, providing an attractive appearance for the frame of the power unit. Each flange further includes a “U” shaped longitudinal retaining channel97facing inwardly and attached horizontally along the inner sides of the middle portion thereof.

The rearward end83of the frame includes a generally rectangular cover plate98that extends over and along the upper edges94of the side flanges93and covers the hydraulic cylinder89and some of the control mechanism. The cover plate is contoured to match the upper edge of the side flanges, and provides some protection for some of the components and a clean appearance for the rear of the power unit10

The power unit includes the pair of lift arms68that act in parallel and have forward ends69, middle portions100and rearward ends101. The lift arms are interconnected at the rearward ends thereof by a lateral push bar102, with the respective ends of the push bar slidably retained (in suitable pivotal bushings) within the respective retaining channel97of the flanges; and the forward ends of the lift arms extend toward the forward end81of the frame.

A pair of connecting arms104act in parallel and have forward ends106and rearward ends108, have the respective forward end pivotally connected (at106) near the forward end of the respective flange (and within reinforcing flange107) of the frame80. The respective rearward end is pivotally connected (at108) on the middle portion100of the respective lift arm68.

The hydraulic cylinder89has the ram90at the forward end thereof attached to the center of the lateral push bar102. When the ram is extended, the push bar and the rearward ends101of the lift arms68are translated forward along the retaining channels97in the flanges of the frame, and the forward ends69of the lift arms are thereby raised (in scissor-like fashion with connecting arms104).

As previously discussed in reference to the jack stand12, the lift arms68have a pair of frusta-conical discs70pivotally attached (through suitable bushings and axels) on the inner sides of the forward ends69thereof. The discs provide for lateral self-centering and longitudinal self-aligning engagement with the angled inner surfaces72of the lower ends of the side flanges of the lifting plate25of the jack stand.

The forward ends69of the lift arm68have also a pair of leveling pads110acting in parallel and are pivotally attached to the outer sides thereof (through suitable bushings and fasteners co-axel with the discs70), for providing a level platform thereon for supporting the lift bridge14. Each leveling pad includes a vertical rectangular plate having a first lever arm112extending downward and forwardly at an angle from the plate, and with the plate having an upper flange114extending horizontally therefrom, providing a level platform thereon. The horizontal flange has a vertical aperture115therein for retaining the lift bridge. The platform has another flange extending vertically downward and forwardly therefrom forming a second parallel lever arm116thereon. The first and second lever arms having mating lateral apertures117in the forward ends thereof.

The leveling pads110utilize a pair of leveling links118that have a forward end120connected to the apertures117at the forward ends of the lever arms, and have a rearward end122connected to a point (at122) on the connecting arm104; so that as the forward ends of lift arms68are raised and lowered, the platforms formed by the upper flanges114of the leveling pads are maintained in a substantially horizontal orientation. The leveling pads, with the double lever arms and leveling links, provide a strong, rugged level platform for use with the lift bridge14to be discussed later in detail.

Robust Commercial Power Unit—Controls for Aligning and Operating the Jack Stands

Referring also toFIGS. 14 and 15, a tubular operating handle124is shown that typically extends rearwardly and upwardly from the rearward end83of the frame of the power unit10. The operating handle is used in conventional fashion for maneuvering the power unit about on its wheels, to be pumped up and down for providing energy to actuate the hydraulic cylinder89; and also for controlling the inter-engagement and the cooperative action of the power unit and the jack stand12.

The rearward end83of the frame further includes a reinforcing rear bracket125that further supports the hydraulic cylinder89, control valve91, the actuator pistons92and includes a pair of handle flanges127. The handle flanges are inboard about an inch from the side flanges93of the frame and extend upward from the bottom of the frame to above the pivot point of the tubular handle. The bracket supports the tubular handle and all of the mechanism for controlling the angle and position of the tubular handle.

The tubular handle124has a yoke126at the distal end thereof with lateral axels128thereon pivotally attached to the sides of the handle flanges127with suitable bushings and fasteners. The tubular handle has a “T-bar” hand grip130transversely attached to the proximal end thereof; and further has a rotatable control knob132extending through the hand grip for controlling the locking and releasing of the control valve91on the hydraulic cylinder89. The control knob is fixedly attached to a rotatable control shaft134that extends through the tubular handle with the distal end thereof connected to a universal joint136so that the center of the u-joint is precisely between the lateral axels128; and the other end of the u-joint is interconnected through a suitable coupling shaft138to the rotatable control valve91on the hydraulic cylinder (see alsoFIG. 24).

The u-joint136connected precisely between the lateral axels128allows the control shaft to freely pivot up and down, and to be folded over through a 180° arc, about the axels with the pivotal movement of the handle. The control knob is rotatable for locking the control valve of the hydraulic cylinder (with clockwise rotation) when needed, and for releasing hydraulic pressure inside the cylinder (with counter-clockwise rotation) when the pressure is no longer needed.

Referring also toFIGS. 24 and 28, the yoke126at the distal end of the handle124further includes a pair of flanges140extending rearward therefrom and supporting an axel142having a pair of cylindrical cams144thereon. The cams are positioned to contact the upper ends146of the dual piston actuators92, and to pump the actuators with each downward stroke of the handle to extend the ram90of the cylinder. As previously discussed, both piston actuators are engaged by the cams; however one has a larger diameter for quickly advancing the ram with only a few strokes of the handle, but this piston can exert very little force; then, when the load is encountered, the other piston takes over to lift the load in the conventional manner. This allows the power unit to efficiently take up any initial space between the lift arms and the load.

Referring particularly toFIGS. 14-23, the tubular handle124has a control lever148extending through an opening149on the right side thereof and into an attachment member152that is slidably disposed within the tubular handle. The control lever is readily within the grasp of an operator having his right hand on the T bar hand grip130. The control lever controls the engagement; inter-engagement and disengagement of the jack stand12carried within the frame of the power unit10.

A control rod150has its proximal end secured to the attachment member152and extends (along the right side, adjacent to and parallel with the control shaft134) from the control lever148to the distal end of the tubular handle. The control rod also includes a second universal joint153at the distal end thereof and between the lateral axels128, so that the control rod can pivot with any pivotal movement of the handle, even 180° to fold the handle over the power unit.

Near the distal end of the handle124, and within the rearward end83of the frame of the power unit10, a transversely extending actuator or torsion tube154serves to transmit the action of the control lever148to the forward end of the power unit10. Specifically, the torsion tube is supported on a transverse rod155whose ends are fixedly secured in the corresponding side flanges93of the rearward end of the frame. An actuator arm156acts as a lever, having one end rigidly attached to the torsion tube at the horizontal center thereof; while its otherwise free end is connected, through a coupling rod157, to the other end of the second u-joint153at the distal end of the control rod150.

Also, rigidly attached to the torsion tube154, but near its lateral ends, is a pair of pull arms158which also act as levers. Each of the pull arms has one end fixedly attached to the torsion tube, and the outer end attached to the rearward end of an operating rod160. Each operating rod has its rearward end (bent at a right angle) pivotally attached to an eye or opening in the lower end of the associated pull arm158. On the inner part of the rearward end of each operating rod, a tension spring162is attached, and each spring is secured (by a suitable hook thereon) to the bottom of the frame. The springs tend to pull the control rod150downward, away from the hand grip130.

The operating rods160control the inter-engagement of the associated control mechanisms with the corresponding side of the jack stand12. Because of the springs162, each operating rod is normally urged toward the forward end of the power unit10, i.e. toward the forward end of the corresponding frame extension86.

A portion of the control mechanism has been described as part of the jack stand12. Thus, the lower ends40of the ratchet arms36stands ready to release the corresponding upper pawl37from the particular ratchet teeth with which it may then be engaged (when also there is insufficient vertical stress of the jack stand12to keep the pawl engaged). Also, the alignment holes31, located in the longitudinal center of the ramps30of the jack stands, are available to assist in providing a locking action whenever a position of alignment has been reached within the power unit10.

In the power unit10, each forward extension86of the frame has a generally inner horizontal part, and an outer vertical part provided by the side flanges93. An alignment pin block164is attached to the horizontal portion of each forward extension. An alignment pin166is supported within each corresponding pin block, extending horizontally in a direction transverse to the longitudinal axis of the frame of the power unit10. A pin tab168is attached to the outermost end of each pin (near, but spaced away from the vertical side flange), and a (compression) pin spring170housed inside the pin block urges each alignment pin in the forward direction, i.e. toward the lateral center of the frame. The movement of the alignment pins166in the direction towards or away from the lateral center of the frame, is controlled by the action of the control lever148, acting through the control rod150, and the operating rods160and a pair of generally rectangular shaped flippers172.

Each of the pair of flippers172is pivotally mounted at its inward rearward corner upon a fixed vertical post174that extends upward from the horizontal frame extensions86. Each flipper is also pivotally coupled, at its outward rearward corner175, directly to the associated operating rod160, and the flipper acts as a lever arm (seeFIG. 21). The movement of the operating rods controls the movements of the flippers, and the movement of the flippers in turn controls the movement of both the associated alignment pins166and the associated ratchet release arms lower ends40.

More specifically, each flipper172has an arcuate inner edge176which is selectively engageable with the associated ratchet arm lower end40. On its outer edge, the flipper has a downwardly extending tab178at the center thereof which fits inside the pin tab168of the associated alignment pin166. When the flipper is moved horizontally to its extreme inward position (seeFIG. 22) it pushes ratchet release end40inward, and at the same time alignment pin166is free to be urged into its innermost position by its spring170. When the flipper is moved horizontally towards its extreme outward position (seeFIG. 23), it first disengages from the ratchet arm lower end40, and subsequently forces the pin tab168toward the outer wall of the associated frame extension86thereby withdrawing the alignment pin166away from any engagement with the aligning hole31of the jack stand12.

Referring particularly toFIGS. 16-20, The control lever148extends through the opening149in the right side of handle124, the opening being somewhat P-shaped in that it has a lower notch180, another separate intermediate notch181, and has an upper end edge182.

If lever148is positioned by the operator to drop into the lower notch180(seeFIGS. 17 and 22), then operating rods160assume their most forward positions, and the downward tabs178of the flippers172position the alignment pins166inward; and the inner edge176of the flippers press the lower arms40of the ratchet release arms36inward. In this position, the pawls37cannot engage the ratchet teeth32,42of the second or third frames of the jack stands12. This is the typical position of the control lever when the power unit10is used to load a jack stand12into the frame thereof.

When control lever148is pulled back toward hand grip130by the operator and then positioned to rest in the intermediate notch181of opening149(seeFIGS. 18 and 21) the locking pins166lock the power unit10to the jack stand12, but the inner edges176of the flippers172do not press the lower ends40of the ratchet release arms36inward, and thus the pawls37of the ratchet arms are engagable with the respective teeth32,42of the frames22,23of the jack stand. This is the typical position of the control lever to raise the jack stand to lift the load, and will be discussed later in more detail.

The third position of the control lever148is used to release the power unit10from the jack stand12. The operator pulls the control lever to its uppermost position182in the opening149(seeFIGS. 19 and 23). The alignment pins166are withdrawn from the alignment holes31of the jack stand, and the inner edges176flippers do not press the lower ends40of the ratchet release arms36inward. This is the typical position of the control lever so that the power unit10can be pulled in the longitudinal direction for disengaging it from the jack stand12.

To lift a load with the jack stand12, the power unit10will first have been used to pick up the jack stand from a previous location, align and lock it within the frame of the power unit, and transport it with the hand grip130of the handle124to the location where it is to be used.

When the jack stand is in the proper location with the bottom plate27securely resting upon the floor or other supporting surface, the operator rotates the control knob132(in the clockwise direction) to lock the pressure valve of the hydraulic cylinder89. The operator positions the control lever148in the intermediate notch181of opening149of the handle124. The operator then pumps the handle up and down to energize the hydraulic cylinder to raise the forward ends of the lift arms68under the lifting plate27of the jack stand, to lift the load. The pawls37of the ratchet arms36engage successive ratchet teeth32,42of the tubular frames23,33as the jack stand is raised to the desired elevation.

When the load has been raised to the desired elevation, the pumping of the handle is naturally discontinued. The control knob132on the handle129is rotated (in the counter-clockwise direction) to release the pressure in the hydraulic cylinder, and the lift arms68will drop down into the frame, leaving the load supported solely by the extended tubular frames of the jack stand, locked in position by the pawls37of the ratchet arms36. The control lever148is then pulled upward to the edge182of the opening149in the handle, for releasing the aligning pins166of the power unit from the jack stand, and the power unit can then be disengaged from the jack stand, leaving the load mechanically supported solely by the jack stand.

When the load is to be lowered, the control lever148is placed in the lower notch180, and the power unit10is aligned with and locked to base assembly26of the elevated jack stand12. The control knob132is locked and the operator pumps the handle to raise the lift arms upward and under the lifting plate of the jack stand. The operator then positions the control lever to rest in the intermediate notch,181. At this time the lateral edges176of flippers172are pressing inward against the respective lower ends40the release arms36. However, the pawls37do not then release, because the configuration of the ratchet teeth and the weight of the vertical load on the respective frame combine to wedge the pawls into the ratchet teeth, and prevent the disengagement of the pawls.

The next step to lower the load is to utilize the handle124to extend the lift arms68to raise the lifting plate27at least a slight amount. This action relieves the vertical load on the ratchet teeth so that the flippers can then press the lower ends40of the ratchet arms36inward, thereby permitting the pawls37to disengage from the ratchet teeth. The operator then slowly rotates the control knob (counter-clockwise) to release the hydraulic pressure and thus the lift arms68, and the extended tubular frames of the jack stand12descend and telescope into each other, allowing the load to be lowered.

The simple T bar hand grip130with the central control knob132and the right side control lever148are very straight forward for the operator to quickly understand, and are very simple to operate. An operator can load a jack stand12into the power unit10, position the jack stand, raise the jack stand, and finally lower the jack stand, all with only the need to use one hand to control the hand grip, position the control knob and position the control lever.

Referring also toFIGS. 12 and 13, as described in detail in earlier patents by the present inventor, when two or more of the jack stands12,12′ etc., are placed adjacent to each other in a longitudinal series, the latch fingers29on the front end of one jack stand becomes hooked with the similar latch finger on the rearward end of the other jack stand. However, pivotal inward movement of a release arms186, by a tripper188will automatically cause the two latch fingers to become disengaged, thus permitting the two jack stands to be separated. This feature is also utilized in the present invention.

Briefly, when a first jack stand is picked up by the power unit, the frame extensions86of the power unit are simply moved past the opposing sides of the base assembly26of the jack stand, above bottom plate27but below ramps30, until alignment pins166of the power unit lock into the respective alignment holes31in the ramps of the jack stand. If a second jack stand is to be picked up for transport, the operator then moves the control lever148into its full disengagement position at upper edge182of opening149(seeFIGS. 19 and 23) to release the aligning pins. Using the handle124, the operator then pushes the power unit further forward so that the frame extensions pick up the next jack stand; again, by entering the vertical space between bottom plate27and side ramps30. The power unit is pushed forward until alignment pins166lock with the holes31in the second jack stand, and the latch fingers29are automatically hooked together.

When two or more jack stands are thus being transported by the power unit, the forward jack stand is necessarily the one that will be positioned first for lifting a load. As previously discussed, after the jack stand is elevated, the power unit is lowered and pulled away. Since the first jack stand is hooked to the second jack stand, as the power unit is pulled away, the hooked latch fingers29pulls the second jack stand toward the front of the power unit. It is at this time that the latch release arm186on the jack stand cooperates with the tripper188on the power unit for unlatching the two stands. The tripping action occurs somewhat in advance of the location where the power unit becomes locked to the second jack stand. Thereafter, further rearward movement of the power unit relative to the second jack stand, results in it being aligned with and locked to the second jack stand.

The tripper188is located on frame extension86of the power unit slightly forwardly of the associated flipper172. Its position is fixed relative to the frame extension, and it accomplishes its function not by its own movement, but by the longitudinal movement of the power unit relative to the jack stand. The tripper188is supported at an elevation above the horizontal frame extension86, somewhat below the horizontal plane occupied by the flipper172, and also at a slightly lower elevation than the top of the alignment pin block164.

Commercial Power Unit—Controls for Positioning the Handle

Referring again toFIGS. 24 and 28, the handle124at the rearward end83of the frame of the power unit10is shown in its operative position to pump the actuator pistons91to extend the hydraulic cylinder89. However, it is often desirable to lock the handle in a fixed position for maneuvering the power unit around the shop, and into confined spaces for the placement or retrieval of the jack stands12, or for compactly shipping or storing the power unit. The control of the position of the handle is discussed in terms of the power unit10, but such controls are also applicable for any conventional hydraulic floor jack.

The controls for positioning the handle124include a pair of generally cylindrical discs190that are oriented vertically and fixedly attached to the lateral ends of the yoke126of the handle, and are coaxial with the axels128. Each of the discs has a diameter of about one inch and a thickness of about 0.25 inches and has a matching set of radial notches formed (at pre-determined angles, generally as shown) in the periphery thereof, specifically, a first notch192, a second notch193and a third notch194. The notches are about 0.13 inches deep with angled sides to an inner length of about 0.25 inches.

A pair of lever arms196acting in parallel each have one end197thereof pivotally attached to the handle flange frame80, just below and adjacent to the notched disc190; and extends generally tangentially to the notched disc190. The lever arm has a lug198thereon projecting upwardly toward the periphery of the disc. The lever arm has a lever handle199extending beyond the rearward end83of the frame for readily pivoting the lever arm, preferably by the toe of the operator. The lever arm is pivoted upward so that the lug is engagable with a respective notch in the disc, to fix the position of the handle124; or is pivoted downward to disengage the lug from any notch in the disc, so the handle124can pivot freely on the axels128of the power unit10.

The pair of lever arms196is preferably in the form of a U-shaped bar of steel about 0.38 inches thick. The ends197are typically in the form of vertical eyelets attached to the frame with suitable bushings and fasteners. The lugs198are somewhat tapered and have a flat upper tip about 0.25 inches by 0.25 inches to readily fit within a respective notch of the disc190. The base of the U-shaped bar provides a rugged lever handle199to synchronize the lugs within the disc and is readily operable by the toe of the operator. (The handle controls can function with only one notched disc190and only one lever arm196, but it is preferable to have the balanced engagement provided with two discs and the U-shaped pair of lever arms.)

The handle controls further includes at least one lever arm retaining clip200that is attached to the side of the frame adjacent to of the lever arms196. The retaining clip is typically made of spring steel having a first detent position201for retaining the lever arm into the upward engageable position, and a second detent position for retaining the lever arm in the downward disengaged position

Referring now toFIG. 25, the handle124is shown fixed in the normal upward angle (of about 60°) with the lug198of the lever arm196engaged in the first notch192of the notched disc190. The lever arm is retained in this upward position by the retaining clip200. In this fixed position, the handle can be readily pushed downward thereby raising the front end of the power unit about the rear wheels, for maneuvering and positioning the power unit into a desired location.

Referring again toFIG. 28, the handle124is shown released in the normal upwardly angled position with the lug198of the lever arm196in the downward position and disengaged with the notched disc190. The lever arm is retained in this downward position by the retaining clip200. In this position, the handle can be readily pumped up and down to actuate the actuators92of the hydraulic cylinder89to raise the lift arms of the power unit10. The handle can also be folded over the power unit, as further discussed later.

The handle controls further includes a pawl202that is pivotally attached to the frame, slightly above and adjacent to at least one of the notched discs190so that the pawl is biased into light contact with the periphery of the notched disc. The pawl normally just rides smoothly on the disc as the handle124is pivoted and pumped, but it is provided to prevent the handle from falling forward over the power unit at an undesirable time (possibly into an auto or just forward requiring it to be retrieved). When the handle reaches the vertical position of about 90°, the third notch194is positioned so that the pawl engages the notch and prevents any further forward pivoting by the handle. The handle is free to be pulled backward, whereby the pawl is automatically released from the notch, and the handle remains free to pivot and pump within the 0° to 90° range.

Referring now toFIG. 27, the handle124is shown released and folded over (about 180°) onto the power unit with the lug198of the lever arm196disengaged from the notched disc190. The lever arm is retained in this downward position by the retaining clip200. To get to this folded over position, the handle is naturally pivoted forward; however, the pawl202will normally engage the third notch193at about 90° and prevent any further forward pivotal movement by the handle. It is necessary to manually lift the pawl from the notch (either flip it over, or just raise it while the handle is pivoted passed the third notch). In this folded over position, the power unit can be compactly shipped or stored (efficiently without the need for reassembly).

In the power unit10, the folded over position of the handle124is facilitated by the u-joint connections of the control shaft134and the control rod150at the axel128of the handle, that permit these components to be folded over along with the handle.

Robust Commercial Power Unit—Two Position Bridge

Referring now toFIGS. 29-31, the two-position lift bridge14is described in more detail. The lift bridge is utilized to “bridge” the otherwise open span between the forward ends69of the lift arms68of the power unit, so that the power unit can function as a conventional floor jack for directly lifting a load. The two position bridge refers to the lift bridge being stored in one position on the rear cover of the power unit, as shown in phantom inFIG. 29(see alsoFIG. 1), and being moved to a second position, as shown inFIG. 29, secured on the pair of leveling pads110at the forward ends of the lift arms. As previously described, each leveling pad has a vertical aperture115therein for retaining the bridge.

The lift bridge14comprises a generally rectangular plate204having a forward end205, a rearward end206, an upper surface207, a bottom surface208and a pair of sides209. The bottom surface has a pair of large cylindrical pins210extending downward from the center of each side (seeFIG. 30). The pins are engageable with the apertures115in the leveling pads for retaining the lift bridge on the lift arms. (The leveling pads can further include optional cylindrical tubes or cups extending from the underside of the apertures, for further supporting and retaining the pins.)

The forward end of the plate has a forward flange212extending downward therefrom and the flange has a bottom edge213preferably shaped (concaved) to match with the contour of the rear cover98of the power unit. The rearward end of the plate has a rearward flange214extending downward therefrom and the flange has a bottom edge215also preferable shaped (concaved) to match with the contour of the rear cover of the power unit. The plate can further include optional side flanges (not shown) extending downward over the flange114of the leveling pads. The flanges provide substantial strength and rigidity to the plate of the bridge.

The bottom side of the plate further includes a central cylindrical boss216having a threaded aperture therein for receiving the threads of a screw-out saddle. For extended range, the bridge, preferably utilizes a unique double-screw-out-saddle218having a first threaded shaft220extending downward therefrom, and a second tubular shaft222having internal threads for receiving the screw threads of the first shaft220and having external threads for engaging the threaded aperture216in the boss at the center of the bridge. The double-screw-out-saddle in shown in its lowered position inFIGS. 29 and 30; and is shown in its fully extended position inFIG. 31.

The rectangular plate204of the bridge14, including the pins210, the flanges213,214, the central boss216, and any additional flanges and ribs thereon can be fabricated by a welding process, but is preferably produced by an integral casting thereof.

The rear cover98, at the rearward end of the power unit, and longitudinally along one side thereof further includes a large aperture224therein for receiving the threaded shaft222extending from the bottom of the bridge (inserted therein, not threaded); and further includes a pair of apertures226for receiving the pins210extending from the bottom of the bridge. The apertures224,226, along with the contoured flanges213,214allow the bridge to be compactly and securely stored in its position on the cover. Due to the low profile of the power unit and the space occupied by the hydraulic cylinder (see alsoFIG. 24) the bridge can only be conveniently nested longitudinally along either side of the rear cover. It is shown preferably stored along the right side thereof for convenience for operators that are operating the handle controls with their right hand.

Commercial Power Unit—Automatic-Slide-Forward-Bridge

Referring now toFIGS. 32-34, a second embodiment of the two-part lifting system is shown wherein a power unit230incorporates an improved automatic-slide-forward-bridge assembly240. Briefly, the slide forward bridge is slidably retained on the upper surfaces of the lift arms and is always biased toward the forward ends thereof. When the power unit has jack stands loaded in the frame thereof, the jack stands automatically push the bridge rearward along the lift arms, and the power unit is operable for use with the jack stands. When there are no jack stands in the frame of the power unit, and the lift arms are lowered to their lowest position in the frame, the bridge is automatically biased onto the forward ends of the lift arms, and the power unit is operable for use directly as a load lifting jack.

The power unit230features the same components and inter-engagement of the components as previously discussed in reference to power unit10, except the power unit230does not incorporate the two-position bridge14, does not require the apertures115in the leveling pads114, does not require the apertures in the cover98, and includes a new pair of lift arms232(that are slightly different from the lift arms68of power unit10).

The present lift arms232have a generally flat upper surface234and have forward ends236that are somewhat extended in length (about 0.25 inches more) beyond the pivot connection238at the forward ends thereof, and are otherwise interconnected as previously discussed.

The slide-forward-bridge is fabricated from a steel casting comprising a generally rectangular (horizontally oriented) plate242having a generally flat upper surface244, a bottom surface246, a forward end248, a rearward end250and a pair of sides252. Each side252of the plate includes a longitudinal inner channel254in the bottom thereof for engaging the outward flange114of each leveling pad110; and includes a finger256extending rearward from the upper surface having a downward end flange257for abutting the rearward edge of each leveling pad. The plate further includes a cylindrical boss258, extending downward from the center of the plate having a central vertical threaded aperture259therein for receiving the threaded shaft of a screw-out saddle260.

The plate12further includes an inner securing plate262soldered along the lower outer edge of each channel providing an inward flange for engaging (the underside of) the outward flange114of the respective leveling pad. The bottom surface of the plate includes a pair of recesses264for receiving the extended forward ends236of the lift arms (when the lift are rotated upward as shown inFIG. 33). The recesses having the forward ends of the lift arms engaged therein, lock the bridge to the leveling pads, and prevent the bridge from slipping rearward therefrom. When the lift arms are lowered, the extended forward ends rotate out of engagement with the recesses, and the bridge can slide along the lift arms biased forward in the usual manner.

See particularlyFIG. 34, the plate further includes a pair of centered flanges266extending downward from the bottom near the rearward end thereof. The flanges are machined with apertures to receive a lateral pivot pin268. The lateral pivot pin supports a set of telescoping tubular sleeves270,272, as part of the automatic-slide-forward-bridge assembly.

The first pair of sleeves270, suitably formed from tubular galvanized steel, are each connected at one end thereof in parallel to the lateral pivot pin268. A pair of compression springs274are inserted within the first pair of sleeves. The springs and the free ends of the first pair of sleeves are telescopically inserted into the second pair of tubular sleeves272. The second pair of sleeves are connected at the free ends thereof in parallel to a lateral support axel276. This collection of components comprises the slide-forward-bridge-assembly240.

The lateral support axel276is fixedly secured between the lift arms at104(the connection of the connecting arms) The automatic slide forward bridge assembly is biased toward the forward ends of the lift arms, but can only be positioned on the leveling pads when the lift arms in their lowest position and aligned with the flanges of the leveling pads, whereby the bridge automatically snaps into the forward position by the compression springs of the assembly.

It is concluded that the foregoing designs and materials of the commercial power units and the commercial jack stands describe features, components and assemblies that are robust to manufacture and that provide reliable and durable commercial use. The improved jack stand describes a self-centering and self-aligning lift plate; and a robust durable dual locking mechanism for controlling the frames. The improved power unit describes a frame for efficiently loading the jack stands and maneuvering the power unit; and a handle with improved controls for operating the jack stands, and for easily locking the angle of the handle in a fixed position for efficient movement, shipment and storage of the power unit.

An improved two-position bridge component is described that can be stored in one position on the cover of the power unit, and manually positioned on the lift arms for converting the power unit directly into a load lifting device. An improved automatic-slide-forward-bridge is also described having components that are robust to produce and assemble, and that are reliable and durable in commercial use.

While specific embodiments and examples of the present invention have been illustrated and described herein, it is realized that modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as may fall within the spirit and scope of the invention.