EP0067152A1

EP0067152A1 - Lift mast with offset tilt cylinder mountings

Info

Publication number: EP0067152A1
Application number: EP81901400A
Authority: EP
Inventors: Daniel L. Ervin
Original assignee: Towmotor Corp
Current assignee: Caterpillar Industrial Inc
Priority date: 1980-12-19
Filing date: 1980-12-19
Publication date: 1982-12-22
Also published as: EP0067152A4; JPS57501959A; WO1982002188A1; NO813127L

Abstract

Un mat de levage (16) avec des cylindres d'inclinaison decales possede des poutres verticales (20) jointes en une position superieure (23) par une entretoise (22). Un organe de projection s'etend vers l'exterieur depuis chaque poutre (20) et possede un cylindre d'inclinaison (32) fixe sur cet organe de projection de telle sorte que chaque cylindre d'inclinaison (32) soit lie a une certaine distance d'espacement la poutre correspondante (20). Chaque cylindre d'inclinaison (32) est egalement fixe a un vehicule de travail (14) et peut s'etendre de maniere controlee pour incliner le mat de levage (16). Le positionnement vers l'exterieur des cylindres d'inclinaison (32) sert a augmenter la resistance du mat de levage (16) aux couples de charge d'inertie.A lifting mast (16) with offset tilt cylinders has vertical beams (20) joined in an upper position (23) by a spacer (22). A projection member extends outwardly from each beam (20) and has a tilt cylinder (32) fixed to this projection member so that each tilt cylinder (32) is connected to a certain distance between the corresponding beam (20). Each tilt cylinder (32) is also fixed to a work vehicle (14) and can extend in a controlled manner to tilt the lifting mast (16). The outward positioning of the tilt cylinders (32) serves to increase the resistance of the lifting mast (16) to the inertia load torques.

Description

Lift Mast With Offset Tilt Cylinder Mountings

Technical Field

This invention relates generally to controllably tiltable load lifting mast assemblies and more particularly to mounting arrangements for the tilt cylinders on the mast assemblies of lift trucks.

Background Art

Lift trucks are commonly provided with tilt cylinders for permitting controlled fore and aft tipping of a lift mast on the lift truck. Generally the tilt cylinders are connected directly to vertical beams which constitute a part of a support frame for the lift mast. The tilt cylinders also serve to strengthen the support frame against twisting or "wrack" of the vertical beams caused by unbalanced loadings.

In the operation of a lift truck substantial forces imposed by steady state and transient unbalanced loads on the lift mast tend to force the vertical beams out of parallel relationship. This can result in some plastic deformation of certain elements of the lift mast resulting in misalignment and increased wear and friction between moving members of the mast. Were the tilt cylinders better able to counter the forces imposed by these unbalanced loads the beams would be retained in better alignment. This would reduce or eliminate the possibility of plastic deformation of any portion of the lift mast.

Many currently available lift trucks with tiltable masts have tilt cylinders positioned substantially above the operator. This is disadvantageous in that it unduly obstructs the operator's vision. This tilt cylinder placement can also permit oil to leak onto the operator or onto a windscreen of the lift truck. The present invention is di rected to overcoming one or more of the problems set forth above.

Disclosure of the Invention

A load lifting device is disclosed which has a supportive structure and a suppo rt frame pivotally attached thereto. The support frame includes two substantially vertical beams connected one to the other by a crossmember. At least one beam has a projection member which projects outboard therefrom. An extens ible means having a first and a second end is connected by its second end to the projection member at a point a spaced distance from said one beam. The first end of the extensible means is connected to the supportive structure.

Brief Description of the Drawings

Fig. 1 is a diagrammatic isometric view of a lift truck incorporating an embod iment of the present invention; and Fig. 2 is a diagrammatic top plan view of the lift mast of the lift truck of Fig. 1 detailing the connection of the tilt cylinders to the lift mast.

Best Mode for Carrying Out the Invention Referring more particularly to the drawings, a lift mast, embodying the principles of the present invention, is generally indicated by the reference numeral 10. The lift mast is utilized on a work vehicle 14 such as a lift truck. As best shown in Fig. 1, a support frame 16 for the lift mast 10 is pivotally mounted at pivot points 18 on the work vehicle 14 so as to be pivotable fore and aft with respect thereto. The support frame 16 supports a load engaging carriage 19. The support frame 16 includes two upwa rdl y extending beams 20, each having an outboard edge 21, which serves as a guide and supports for the carriage 19. These beams 20 are parallel to a central axis 42 therebetween. These beams 20 are connected by a c rossmember 22 for aiding in maintaining them in relatively rigid spaced apart relationship. Preferably the crossmember 22 is connected between upper end portions 23 of the beams 20. As best shown in Fig. 2, this crossmember 22 has first and second end portions 24,26 each extending outboard from the corresponding beam 20. Each end portion 24,26 has a connecting plate 28 rigidly attached thereto at a connecting surface 30 which is an outboardmost reg i on of each end po rti on 24,26. A tilt cylinder 32 having a first end portion 34 and a second end portion 36 is pivotally connected by its second end portion 36 to each connecting plate 28. As shown in Fig. 1 the first end portion 34 of each tilt cylinder 32 is pivotally connected to the work vehicle 14. Preferably the tilt cylinders 32 are so positioned so as to be parallel one to the other. The tilt cylinders 32 extend sufficiently far that the first end portions 34 thereof are located aft of an operator's station 38 which itself is af t of the lift mast 10. Alternatively, the first and second end portions 24,26 may be located on discrete pro j ect i on members (not shown) each rigidly connected to and projecting outboardly from a respective one of said beams 20. This would obviate the need for d i r ectl y connecting the tilt cylinders 32 to the crossmember 22. Functionally, this embodiment would be essentially the same as that previously described, having the tilt cylinders 32 mounted on projections provided by the crossmember itself.

Industrial Applicability

By rigidly connecting each of the tilt cylinders 32 to the support frame 16 at a position substantially outboard from the corresponding beam 20 a number of advantageous results are obtained.

In the operation of a lift truck unbalanced and often substantial fore and aft loadings are often imposed upon the beams 20, as for example when the lift truck changes translational speed or turns a sharp corner while transporting a load. These examples of transient loadings are termed "inertial loadings" in the art and can either cause both beams 20 of the support frame 16 to move identically and synchronously as in the former example or cause torque of the joined beams 20 about the central axis 42 parallel and intermediate the beams 20 as in the latter example.

For a typical lift truck elastic deformation of the support frame 16 owing to these loadings is countered by the rigidity of the support frame 16 itself and also by the resistance of the tilt cylinders 32 to compression and extension. By positioning the tilt cylinders 32 an increased distance from the central axis 42 lying intermediate the beams 20 the elastic deformation owing to inertial loading torques, or "wrack", is lessened.

It is well known that the force required to displace through compression or extension of a hydraulically locked cylinder is d i rectly related to the magnitude of the displacement. It is also well known that a torque may be viewed as the product of a force and a moment arm. By placing each tilt cylinder 32 outboard from its corresponding beam 20 the moment arm countering an inertial loading torque (that is, the distance from the central axis 42 to the point at which the tilt cylinder 32 is connected) is increased. Consequently, a smaller force exerted by the tilt cylinders 32 is required to counter a given inertial loading. This smaller force can be provided by a decreased displacement of said cylinder resulting in a substantially reduced degree of "wrack".

Assume, for example, that the connecting surface 30 is half again as far outboard from each beam 20 as the center-to-center distance between the beams 20. This is the case in the preferred embodiment detailed in Figs. 1 and 2. As the torque acts about the central axis 42 this outward repositioning of the connecting surface 30 would double the moment arm requiring, then, half as great a force to be applied by each tilt cylinder 32 to counter the inertial loading torque. This smaller force to be applied by each tilt cylinder 32 is achieved with a decreased compression or expansion of the tilt cylinder 32 resulting in a smaller fore or aft displacement of each connecting point 30 from its normal position than would have been the case in the absence of offset tilt cylinders. The angle of "wrack" for this case then is less than half that of the case for non-offset tilt cylinders 32. For tilt cylinders 32 whose resistance to displacement is, for small displacements, a linear function of the magnitude of displacement locating the connection points 30 each half again as far outboard from the corresponding beam 20 as the center-to-center distance between the beams would cause the angle of "wrack" for a given inertial loading to be decreased by a factor of nearly 4. Such a drastic improvement would allow a decrease in needed beam 20 crossbracing, beam 20 rigidity, and other advantages as would be recognized by one skilled in the art. Even were the offset distance only 10 percent as great as the distance between the beams 20, a decrease in "wrack" of between 20 and 40 percent is obtained. Such a significant benefit could be obtained v/ith an offset distance of less than 20 cm for a typical lift mast.

Another of the substantial advantages yielded by the tilt mast 10 with the offset tilt cylinders 32 is that the tilt cylinders need not be as powerful as would be necessary were there no offset. This is due to the fact that offset tilt cylinders will be countering decreased forces. Additionally, outward placement of the tilt cylinders 32 increases upward visibility for the operator. Also, this outward placement makes it less likely that hydraulic fluid leaks from the tilt cylinders 32 will contact the operator or a windshield on the lift truck. Other aspect, objects and advantages of the present invention of this invention can be obtained from a study of the drawings, claims and the disclosure.

Claims

Cl a ims

1. A load lifting device comprising:, a supportive structure ( 14); a support frame (16) pivotally connected to said suppo rt ive structure (14), said support frame (16) having two substantially vertical beams (20); a crossmember (22) rigidly interconnecting said beams (20) and providing first and second end portions (24,26) with at least one end portion (24) extending from the beam to which it is adjacent in a direction away from the other of said beams (20); controllably extensible means (32) having a first end portion (34) connected to said supportive structure (14) and a second end portion (36); and a connection surface (30) mounted on said one end portion (24) of said crossmember (22) providing a connection for said second end portion (36) of said controllably extensible means (32) outboard of said beams (20).

2. The load lifting device of claim 1 wherein said crossmember (22) is a beam-like member.

3. The load lifting device of claim 1 or claim 2 wherein said connection surface (30) is separated more than 20 cm from both of said beams (20).

4. The load lifting device of claim 1 wherein the center to center distance of said connection surfaces (30) is in the range of about 1.20 to 2.00 times as great as the center to center distance of said beams (20).

5. The load lifting device of claim 4 wherein the distance from an outboard edge (21) of said beam (20) to said connection surface (30) is in the range of about 10 to 1.00 times the center-to-center distance of said beams (20).

6. The load lifting device of claim 5 wherein said means (32) for controllably pivoting said support f rame ( 16) includes a contro llably extens ible f luid jack.

7. A load lifting device comprising: a supportive structure (14); a support frame (16) pivotally connected to said supportive structure (14), said support frame (16) having two substantially verticaly beams (20) rigidly connected one to the other; a projection member projecting outboardly from one of said beams (20); and means (32) for controllably pivoting said support frame (16) said means (32) having first and second end portions (34,36), said means (32) being connected to said supportive structure (14) by the first end portion (34) and connected by the second end portion (36) to said projection member (40) at a connection surface (30) thereon.

8. The load lifting device of claim 7 wherein each of said beams (20) has a projection member (40) outboardly projecting therefrom.

9. The load lifting device of claim 8 wherein the center to center distance of said connection surfaces (30) is in the range of about 1.20 to 2.00 times as great as the center to center distance of said beams ( 20).

10. The load lifting device of claim 7 wherein the distance from an outboard edge (21) of said beam (20) to said connection surface (30) is in the range of about .10 to 1.00 times the center-to-center distance of said beams (20).

11. The load lifting device of claim 7 wherein said crossmember (22) and at least one of said projection members are integrally connected one to the other.

12. The load lifting device of claim 7 wherein said means (32) for controllably pivoting said support frame (16) includes a controllably extensible fluid jack.