GB2125007A - Scissor type jack - Google Patents

Abstract

A scissor type jack in which the head (1) is raised or lowered relative to the base (3) by linkage (2) comprising mutually inclinable pairs of pivotally connected links (20, 21), has the linkage (2) operated by a linear actuator such as a hydraulic ram (4) pivotally connected between the links such as the lower links (20) by pivotal connections (42, 432). The latter are offset from the respective plane through the end pivotal connections (22, 32) of the links (20) in order to provide leverage to assist operation of the jack especially from the fully retracted condition. A ramp (30) on the base (3) supports the ram (4) during pump operation of the latter as it rises with the linkage (2). The upper links (21) are preferably of greater upward inclination than the lower links (20) and of longer effective length. The linear actuator may be of other suitable form such as a screw. <IMAGE>

Description

SPECIFICATION Scissor type jack This invention relates to jacks of the kind known as scissor type jacks primarily for vehicle use, i.e. in which a head for supporting contact with an axle or jacking point of a vehicle is connected by upper and lower opposed pairs of mutually inclinable pivotally jointed links from a base which in use rests on the ground or floor, appropriate operation of the linkage causing raising or lowering of the head relative to the base.

Hitherto in such jacks the linkage has been hand operated by screw mechanism connected between the pivot joints of the links for either drawing opposite pairs of links towards one another in raising the head or for moving them apart, or permitting their movement apart, in lowering the head. However, such jacks are often difficult to operate especially from the fully retracted condition.

The object of this invention is to provide a scissor type jack having an improved means of operation of the linkage of which practical advantages as regards ease of operation and compact arrangement will be apparent from the following disclosure. According to this invention a scissor type jack is provided with a linear actuator connected between opposed links of the pivotally connected pairs thereof at pivotal connections which are respectively offset from the planes through end pivotal connections of the links (i.e. to one another and to the base or head of the jack) in order to provide leverage in effecting relative movement of the links in raising the jack head.

Further in accordance with the invention further opposed links of the pivotally connected pairs thereof are such as to assume a greater extent of mutual inclination, e.g. from the horizontal than any such inclination of the opposed links to which the linear actuator is pivotally connected, particularly when the jack is in the substantially retracted condition.

Practical examples of the jack are shown in the accompanying drawings in which: Figure 1 is a side elevation of a hydraulically operated form of the jack in the lowered condition, Figure 2 is a sectional side elevation of the jack also in the lowered condition, Figure 3 is a sectional plan view taken on the line Ill-Ill of Fig. 2, Figure 4 is an end view in the direction of the arrow IV of Fig. 2, Figure 5 is a sectional side elevation of the jack in the partially raised condition and in which the ram cylinder has been broken away to reveal construction, Figure 6 is a detail internal perspective view of one of the links, Figures 7 8 8 are a side elevation and part sectional plan view showing modifications.

Figure 9 is a graph showing the reduction of mechanical disadvantage obtained, Figures 10 8 11 are diagrams indicating the action obtained together with basic mathematical treatment, and Figures 12 to 14 are a part sectional plan view, side elevation and end view respectively of a screw operated form of the jack.

Like parts are referred to by the same or similar reference numerals throughout the drawings.

In the usual manner of a scissor type vehicle jack the head 1 is connected by linkage 2 comprising opposed pairs of mutually inclined links 20, 21 to a base 3, the links 20, 21 being pivotally inter-connected or jointed at 22. Also in the usual manner the links 20, 21 are respectively pivotally connected to the head 1 and base 3 at separate adjacent points 12, 32 whilst for balanced operation of the links 20, 21 to obtain firm and level support of a jacked vehicle, adjacent ends of the links at the pivot points 32, 1 2 have a meshing toothed engagement at 200 and 210 respectively.

In the example shown and for adequate strength the pivot points 12, 32 are interconnected by reinforcing links 1 20 and 1 32 respectively to maintain the meshing engagement at 200 and 210. In some cases the pivot points 1 2 may coincide and likewise the pivot points 32 as later referred to.

For the purpose of this invention the linkage 2 is operated by a linear actuation which advantageously may consist of a hydraulic ram 4 or screw mechanism (as later described) or linear ratchet or similar mechanism (e.g. having a friction irretractile action) and which is connected between opposed pairs of links 20, 21 (preferably the lower links 20) in an offset manner to provide leverage to assist the operation of the jack as described below.

In order to provide a compact arrangement of hydraulic ram operation of the linkage 2 (Figs. 1 to 6) the ram 4 is horizontally located within the jack, i.e. between the links 20, 21 at each side and the piston rod 41 and cylinder 40 of the ram 4 are connected to preferably intermediate points of respective lower links 20 at 42, 432. Thus the cylinder 40 is shown pivotally connected at its forward end by radial studs 42 to one pair of lower links 20 and the piston rod 41 acts on the other pair of lower links 20 by a yoke 43 having rearwardly extending arms 430 pivotally connected by studs or rivets 432 to said other pair of lower links 20. The arms 430 are longitudinally slotted at 434 for passage of the studs 42 therethrough and to permit their relative sliding movement whilst the piston rod 41 is provided with a channelled head 41 3 engaging the yoke 43.

The pivotal connections 42, 432 of the ram 4 to the links 20 are offset from and interme diate the pivot joints 22 and the pivotal connections 32 to the base 3, i.e. offset from the planes, through said pivotal connections 22, 32. This results in the pivotal connections 42, 432 being in a raised position relative to the connections 22, 32 when the jack is fully retracted as will be seen in Figs. 1 to 3. This provides leverage about the pivots 32 in assisting initial operation of the links 20, 21 from the retracted position and avoids resistance due to end compressive loading being applied to the links 20 which can otherwise occur when the links 20, 21 are actuated at the pivot joints 22 in the previously known manner. Connection of the ram 4 to the links 20 is also facilitated having regard to its diameter.

The linkage mechanism of a scissor type jack inherently operates with a mechanical disadvantage especially when commencing extension from the retracted condition as indicated by the curve J of the graph shown in Fig. 9. However, due to the leverage afforded by the offset pivotal connections 42, 432, the mechanical disadvantage is considerably reduced as indicated by the curve H. The low position of the pivot joints 22 when the jack is retracted enables an effective upward offset of the pivotal connections 42, 432 to be obtained. The resulting leverage is further assisted by the upward inclination of the upper links 21 as later described.

The action of the jack is also indicated in the diagram shown in Fig. 10 together with basic mathmatical treatment whilst comparison is made with the action of the well known conventional screw jack indicated in Fig. 11.

A plunger type pump 45 to the ram cylinder 40 is carried by an under part 440 of the cylinder base 44 and is pivotally linked at 46 to a lever 47 pivotally mounted at 447 to the underpart 440 and provided with a socket 470 which receives a removable operating lever 7.

In addition to the above mentioned leverage, the mechanical advantage obtained by pumping operation of the ram 4 is such that the linkage 2 can be easily actuated for raising the head 1, the pairs of links 20 being drawn towards one another as the ram is extended (see Fig. 5). Appropriate operation of the release valve 48 enables lowering operation of the jack head 1 to take place in a controlled manner under the weight of the vehicle. The release valve 48 can be conveniently operated by a suitable formed end of the lever 7 such as a flattened end or cross piece (not shown) thereat, after withdrawal of the lever from the socket 470.

As indicated in Fig. 5 a considerable extent of lifting movement of the jack head 1 can be obtained by only a short stroke or travel of the piston and piston rod 41 of the ram 4 as will be evident from the position apart of the pivot points at 42 and 432. Thus by way of practical example a ram 4 having a short pistion travel of 75 mm. (3 inches) can provide a vertical lift of the head 1 of 275 mm. (11 inches) of a typical arrangement of scissor jack. However, the extent and relationship of such movements may be varied according to requirements.

As will be evident from Fig. 1, the upper links 21 have a greater inclination to the horizontal than any inclination of the lower links 20 in the lowered condition of the jack.

This is due to the low position of the pivot joints 22 in such condition of the jack and has the effect of reducing the compressive forces in the upper links 21 and bringing the line of action close to the pivotal connection 32 (i.e.

reducing the perpendicular distance E in Fig.

10) thereby further assisting the operation of the jack from the fully retracted condition.

For this purpose and as also shown in Fig.

1 the upper links 21 are usually of greater effective length (i.e. between the end pivotal connections 12, 22) than that of the lower links 20 (i.e. between the pivotal connections 22, 32). However, this is dependent upon the relative sizes of the pitch circle diameters of the meshing engagements at 200, 210.

If desired the upper links 21 may have a common upper pivotal connection and/or similarly the lower links 20 may have a common lower pivotal connection replacing the corresponding meshing engagement. Particularly, where upper and lower common pivotal corrections are provided lateral stability of the jack is required by suitable external means which may include provision for positive locating engagement with a vehicle jacking point.

When the jack is in the fully lowered position the lower end of the lever 47 rests on the base 3 but as pumping is effected to raise the jack head 1, the lower end of the lever 47 rides up a curved or other suitable incline or ramp 30 (see Fig. 5) of the base 3 in order to maintain support of the base end of the cylinder 40 as it rises with the links 20 during pumping. The rocking action of the lever 47 facilitates its travel up the ramp 30. The head 1, links 20, 21 and base 3 may be inexpensively produced as sheet metal pressings, adjacent links 20, 21 being united by webs 202 and 212 for adequate strength. Assembly of the ram 4 within the structure of the jack is facilitated by engaging reduced portions 421, 431 of the studs 42, 432 with open ended slots 204 in the lower links 20 when the slots 204 are in the substantially horizontal position shown in Fig. 5. On such engagement tongues 205 pressed out of the links 20 are bent into the respective slots 204 to retain the studs 42 and 432 in pivotal engagement with the slots 204.

As will be seen in Fig. 6 each tongue 205 is pressed out of a cranked wall portion of each link 20 in relation to the associated slot 204 and in such a manner that the reduced part 421 or 431 of a stud 42 or 432 can be initially slid into engagement with the slot 204.

To ensure that the socket 470 remains in a position for insertion of the lever 7 therein when the jack is fully lowered, the socket 470 is provided with an upstanding projection or rib 472 (Fig. 2) which abuts the lunderside of the web 202 of adjacent lower links 20 to limit upward inclination of the socket 470.

In addition to ease of operation and a compact arrangement a simple form of hydraulic ram having a short stroke can be employed in conjunction with the low cost construction of a scissor type jack for providing a considerable extent of lifting movement.

Referring to Figs. 7 and 8 basically the same construction and arrangement of jack is shown, but incorporating various modifications especially to increase its strength for heavy duty usage. (The ram 4 and pump mechanism have been omitted from Fig. 7 for clarity).

Thus the pivotal connection 432 of the yoke arms 430 to the corresponding lower links 20 is reinforced in each case by a plate 49 parallel with the associated link 20, each plate 49 being connected about the respective lower pivotal connection 32 of the link 20 to the base 3 and located by a projection 490 at its upper end in a slot 209 in the web 202 which unites the relevant pair of links 20.

The pivotal connection of the plate 49 at 32 facilitates assembly of the ram 4 within the jack structure and which, as before, is effected by sliding the studs 42, 432 into slots 204 in the links 20, the slots 204 being covered and strengthened by channel pieces 207 which carry the tongues 205 and which are pressed under the heads of the studs 42, 432 to retain them in position fully home in the slots 204.

Prior to sliding each stud 432 into its associated slot 204 it is engaged with a hole in a corresponding yoke arm 430 and also in a plate 49 pivotal movement of the latter enabling the stud 432 to be slid into the slot 204. Each stud 432 is flanged at 435 for retention against axial movement and also provide spacing.

Pivotal connection at 42 is provided by a flanged bush 425 for the same purpose and has a push fit on a corresponding radial trunnion 422 extending from a ring or collar 420 about the cylinder 40 and abutting a cap 436 at the adjacent end of the latter. Each trunnion 422 is slidable in a slot 434 of the corresponding yoke arm 430.

On full engagement of the studs 432 in the slots 204, the projections 490 of each plate 49 engages the slot 209 in the web 202 and is retained therein by a lug 208 which is pressed down into the slot 209, e.g. by the connecting web 212 of the upper links 21 on initial full closing of the jack.

Again for increased strength the upper links 21 are reinforced with upturned lateral flanges 217 especially to provide extra location at the pivotal connections 22 and the lower links 20 are flanged at 203. The head 1 is also strengthened by deeper end flanges 11 accommodated by slots 211 in the webs 212.

Alternatively, or additionally the pivotal connections 22 may be strengthened by bosses welded on to the links 20 and/or 21. Similarly, the pivotal connections 432 may be reinforced by bosses welded to the links 20.

In order to improve the action of the jack the base 3 is provided with an underface 34 inclined to the main underface 33. This enables the jack to rock onto the underface 34 as lifting of a vehicle proceeds and to allow for relative movement of the jacking point of the vehicle over the jack. Conversely as the vehicle is lowered, the jack rocks back onto the main underface 33.

Whereas the above described form and arrangement of ram 4 is preferred in practice for simplicity and effective operation, if desired the arrangement may be such that contraction of the ram draws the links 20 towards one another for raising the jack head 1 and vice versa in which case direct pivotal connection to the links 20 can be employed without the need for a yoke 43 and arms 430. Since the ram would then be extended when the jack is fully retracted for stowage, bellows or other suitable protection of the piston rod 41 would be necessary to protect it from rust and dirt.

Referring to Figs. 1 2 to 14 a scissor type jack basically similar to that already described is shown in which the linear actuator consists of a screw 400 connected in accordance with this invention between the lower links 20 i.e.

to pivotal connections 442 which are offset from the pivot joints 22 and pivotal connections 32 i.e. from the plane through said pivotal connections 22, 32 in each case.

The offset pivotal connections 442 are shown in the vicinity of the pivot joints 22 but they may be located intermediate the pivotal connections 22, 32 or beyond (i.e. outwardly) of the pivot joints 22, in order to provide suitable leverage.

The screw 400 is threaded at 403 through a cross pin 443 at one pivotal connection 442 and a plain portion 404 of the screw rod 400 is rotatable through a cross pin 444 at the other pivotal connection 442 and is constrained against axial movement relative to the cross pin 444 mainly by a thrust bearing 445 and also by a washer 446 located by projections 405 on the plain rod portion 404. A turning eye is provided at 406.

The above arrangement of screw operation is preferred to minimise friction, but if desired the screw 400 may have threaded end portions of opposite hard engaging corresponding threaded bores through the cross pins 443, 444.

Here again the pivot joints 22 are able to assume a low position and the upper links 21 are preferably longer in effective length than the lower links 20 in order to obtain their upward mutual inclination. The webs 212 of the upper links 21 are formed to provide a protective cover or tunnel for the screw 400 e.g. in the event of the vehicle jacking point slipping off the head 1.

The reduced mechanical disadvantage obtained is indicated by the curve S in the graph of Fig. 9 from which it will be appreciated that an inexpensive screw operated scissor jack can be provided having a considerable advantage as regards ease of use.

As in the case of the ram operation, the reduction of the mechanical disadvantage effected by the leverage obtained and also by the inclined arrangement of the upper links 21 detracts to a less extent from the mechanical advantage of the screw so that an improved overall mechanical advantage of the jack is obtained especially from the retracted condition when it is often necessary to effect lifting where only low clearance is available between an axle or jacking point and the ground.

If desired the ram 4 or screw 400 may act between the upper links 21 in the same manner with appropriate arrangement of the lower links 20, i.e. though the jack shown in the drawings were operated in an inverted positions.

Although primarily intended for vehicle use, a jack according to this invention is capable of a wide variety of practical applications, e.g.

where lifting, lateral displacement or pressure application is required and with appropriate adaption.

Claims (14)

1. A scissor type jack in which there is provided a linear actuator connected between opposed links of the pivotally connected pairs thereof at pivotal connections which are respectively offset from the plane through end pivotal connections of the links (i.e. to one another and to the base or head of the jack) in order to provide leverage in effecting relative movement of the links in raising the jack head.

2. A scissor type jack according to Claim 1 wherein the offset pivotal connections of the linear actuator to opposed links are position intermediate the end pivotal connections of said links or adjacent or beyond the pivotal jointing of the links to one another.

3. A scissor type jack according to Claim 1 or 2 wherein the linear actuator is connected between lower links of the pivotally connected pairs thereof.

4. A scissor type jack according to Claim 1, 2 or 3 wherein further opposed links of the pivotally connected pairs thereof are such as to assume a greater extent of mutual inclination, e.g. from the horizontal than any such inclination of the opposed links to which the linear actuator is pivotally connected, particularly when the jack is in the substantially reatracted condition.

5. A scissor type jack according to any of the preceding claims wherein pivotal connection between pairs of the links is arranged to assume a low position when the jack is in the substantially retracted condition.

6. A scissor type jack according to any of the preceding claims wherein further opposed links of the pivotally connected pairs thereof are of longer effective length than that of the opposed links to which the linear actuator is pivotally connected.

7. A scissor type vehicle jack according to any of the preceding claims, wherein the linear actuator consists of a fluid pressure operated (e.g. hydraulic) ram.

8. A scissor type jack according to any of Claims 1 to 6 wherein the linear actuator consists of screw mechanism or linear ratchet or like mechanism.

9. A scissor type jack according to Claim 7 wherein the ram is substantially horizontally disposed within the linkage of the jack when the latter is in position of use.

10. A scissor type jack according to Claims 7 or 9 wherein the connection of the ram to the links directly operated thereby is such that extension of the ram effects movement of said links towards one another and likewise of the other links of the linkage in effecting raising of the jack head and vice versa.

11 .A scissor type jack according to Claim 10 wherein pivotal connection of the ram to the links directly operated thereby includes connection by means of at least one member or yoke for obtaining movement of the links towards one another on extension of the ram for raising the jack head and vice versa.

1 2. A scissor type jack according to Claim 10 wherein the connection of the ram to the links operated thereby is such that contraction of the ram effects movement of the links towards one another and likewise of the other links in effecting raising of the jack head and vice versa.

1 3. A scissor type jack according to any of Claims 7 and 9 to 12 wherein a base of the jack from which the mutually inclinable links are pivotally mounted is provided with a ramp for supporting the ram during pumping of the latter and as the ram rises with upward extension of the links.

14. A scissor type jack according to any of the preceding claims wherein pivotal connections of the linear actuator to opposed links have a sliding and retentive engagement with respective links for assembly purposes.

1 5. A scissor type jack substantially as herein described with reference to Figs. 1 to 6 or 7 and 8 or 12 to 14 of the accompnying drawings.