GB2203722A

GB2203722A - Lifting apparatus, particularly for a fork-lift truck

Info

Publication number: GB2203722A
Application number: GB08805360A
Authority: GB
Inventors: Heinz-Jurgen Ostermeyer
Original assignee: MAN Takraf Fordertechnik GmbH
Current assignee: Takraf GmbH
Priority date: 1987-04-23
Filing date: 1988-03-07
Publication date: 1988-10-26
Anticipated expiration: 2008-03-07
Also published as: DE3803844A1; FR2614288A1; GB2203722B; DD260053B5; GB8805360D0; FR2614288B1; DD260053A1

Description

LIFTING APPARATUS, PARTICULARLY FOR A FORK-LIFT TRUCK The invention

relates to a lifting apparatus which produces vertical movement of the load carrier and which is particularly, but not exclusively, suitable for use on fork-lift trucks. The invention also relates to a fork-lift truck provided with such lifting apparatus.

Known from DD-PS 229 387 is a lifting apparatus, particularly for fork-lift trucks, in which the oscillating crank consists of an inner oscillating crank and an outer oscillating crank connected to each other in torsionally rigid fashion via a common lower oscillating crank mounting and a bearing pin, the outer oscillating crank being functionally connected to a compensating cylinder mounted on the vehicle chassis and via a multi-link kinematic transmission to a rack or a pin wheel gear in the region of th"e hydraulic jack. The inclination cylinder which is functionally connected to the thrust rods is disposed in the region of the lower oscillating crank mounting. The compensating cylinder and the multi-link kinematic transmission are functionally connected to the oscillating cranks indirectly via the bearing pin. The inner oscillating crank and the outer oscillating crank are mounted on the front of a box-section member which provides a torsion resistant connection of the two side parts of the vehicle chassis.

The rack or pin wheel transmission consists of an upper thrust rod which is mounted on a hinge pin in the supporting arm jointly with the piston rod of the hydraulic jack, a lower thrust rod which is mounted laterally in the vehicle chassis jointly with the lifting cylinder and on a hinge pin, a movable guide with, mounted on it and engaging both thrust rods, a pinion and a connecting member which is functionally connected via a joint firstly with an oscillating crank mounted in the vehicle chassis and on the other via a link, an angle lever likewise mounted in the vehicle chassis and a further link to the outer oscillating crank or to both oscillating cranks and with the compensating cylinder.

A disadvantage of the known apparatus is the multiplicity of parts required for the control transmission for the vertical movement of the load, particularly the disposition of a rack or pin wheel transmission.

DD -WP B 66 F/289 622 1 discloses a lifting apparatus, particularly for a 2 fork-lift truck, in which the lifting apparatus is mounted vertically in a guide which extends together with the piston rod and which serves at the same time for vertical guidance of a link articulated on the oscillating crank. The hydraulic jack is functionally connected thereto via a thrust member which is guided with a rolling or sliding action in the support arm.

Guidance of the thrust member may be disposed either centrally or also unilaterally or bilaterally on the support arm. The link may be of adjustable length and may consist of a hydraulic jack. When extending the piston rod of the hydraulic jack, the guide which fixes the hydraulic jack in its vertical location is also extended. The thrust member articulated on the piston rod transmits the lifting force to the supporting arm. For this purpose, the thrust member is guided in the support arm or in such a way that it can roll or slide unilaterally or bilaterally thereon. At its rear end, the support arm is articulatedly connected to the oscillating crank mounted on the vehicle chassis. Mounted on the oscillating crank is the link, the other end of which is likewise vertically guided in the hydraulic jack guide. By reason of the link, the oscillating crank is so moved that the fork carrier provided at the front end of the support arm is raised or lowered vertically. The stability of the position of the fork carrier is achieved by the traction or thrust rods disposed parallel with the support arm and with the oscillating crank. A variation in the angle of inclination of the fork carrier occurs by the inclination cylinder, via these traction or thrust rods. By varying the length of the link and thus varying the location of the oscillating crank, it is possible to ensure movement of the fork carrier in the direction of travel.

To guarantee the stability and the prevention of an overload, the associated safety valves are influenced by the relative position of the oscillating crank or a variation in the length of the link.

This proposed solution comprises roller and/or plain bearings for guiding the individual technical media which result in disadvanteous wear and tear phenomena. Furthermore, as a safeguard against overload, a complicated control arrangement is required.

According to the present invention there is provided lifting apparatus comprising a support arm provided at one end with a load carrier, a hydraulic jack for moving said arm, the other end of said arm being articulatedly connected to ar. oscillating crank, said oscillating crank being connected to a compensating cylinder and via a multi-link transmission to 3 the support arm, said multi-link transmission consisting of an upper control rod articulated on th6 support arm between the connection of the hydraulic jack to the support arm and the connection of the oscillating crank to the support arm and extending parallel with the oscillating crank, a control lever disposed parallel with the support arm and connecting the upper control rod to the pivot mounting of the oscillating crank, a lower control rod connecting the control lever to a pivotally mounted angle lever and a coupling rod connected to the oscillating crank and to the angle lever.

The coupling rod can be formed by a double acting adjusting cylinder which varies the distance between the angle lever and the oscillating crank connections. Preferably at half the height of lift, the control lever and the angle lever arm to which the lower control rod is connected are parallel.

The connecting line between the articulation connection of the coupling rod to the oscillating crank in the extreme position of the support arm and the pivot point of the angle lever preferably extends through the point of connection of the angle lever arm and the coupling rod. An exact vertical guidance of the fork carrier and thus of the load is achieved by controlling the oscillating crank movement as a function of the angle of inclination of the support arm. This is achieved by the upper control rod which is articulatedly connected to the support arm between the point of connection of the hydraulic jack and the point of connection of the oscillating crank mounting via the control lever, the lower control rod, the angle lever and the coupling rod connected, to the oscillating crank. The oscillating crank mounting to the support arm which moves about a circular p.ath struck from the pivot point of the oscillating crank, is thus so guided along its circular path that the fork carrier mounted at the front end of the support arm is moved vertically. A variation in the reach of the fork carrier is achieved if the coupling rod is in the form of an adjusting cylinder which permits an adjustment of the oscillating crank regardless of the angle of inclination of the support arm, so that the support arm and thus the fork carrier perform a forward movement.

- An embodiment of the present invention will now be described, by way of an example, with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic side view of the lifting apparatus illustrating the kinematics of the vertical guidance arrangement; 4 Figure 2 is a side view of the complete lifting apparatus with the load carrier in the lowered position; and Figure 3 shows the construction of a coupling rod as an adjusting member for varying the effective range.

Extension of a hydraulic jack 1 produces a change in the angle of inclination of a support arm 2. This movement is transmitted to a control lever 7 via an upper control rod 3 which is connected by an articulation connection 4 to the outside of the support arm 2 between a piston rod mounting 5 of the hydraulic jack 1 and an oscillation crank mounting 6 on the support arm 2. Connected to the mounting 6 is an oscillating crank 9 which oscillates about a pivot point 8. The control rod 3 is parallel with the crank 9. The movement of the control lever 7 is transmitted via a lower control rod 10, an angle lever 11 which is rotatably mounted at 16 in the right-hand side part of the frame of a fork-lift truck to a coupling rod 12 which is articulated at its free end to the oscillating crank 9 by an articulation connection 13. Consequently, the position of the oscillating crank mounting 6 on its circular path which it describes around the pivot point 8 of the oscillating crank 9 and which is associated with a vertical travel of a fork carrier 14 is fixed for every position of lift which is positively linked with a specific angle of inclination of the support arm 2.

The articulation connection 15 between the angle lever 11 and the coupling rod 12, in its midway position, reaches the dead centre position when the distance between the bearing mounting 16 of the angle lever 11 in the frame side part and the articulation connection 13 between the coupling rod 12 and the oscillating crank 9, achieves its maximum value. At this point, the support arm 2 is virtually in its horizontal upper position and the oscillating crank mounting 6 on the support arm 2 is in its extreme rearward position.

Upon reaching the upper extreme position of travel, the angle lever 11 has reached its extreme forward position while the articulation point 13 is again in its starting position as when lifting commenced, in the lower extreme position of lift. The transmission angles of the individual links of this kinematic chain are in every lift position so favourable that there are no excessive loadings on the individual links.

A compensating cylinder 18 is mounted on the vehicle chassis and engages the oscillating crank 9 at an articulation connection 17 which is pivoted by the movement of the oscillating crank 9 and the compensating cylinder 18 counteracts the forces resulting from the hydraulic jack 1 and oscillating crank angle of inclination in the oscillating crank mounting 6 on its circular path, so that the oscillating crank mounting 6 is virtually balanced out by the compensating cylinder 18. The links of the kinematic chain which control the vertical lifting movement only have to transmit minimal differential and friction forces and thus can be of small dimensions.

Extension of the effective range of the fork carrier 14 is achieved in that instead of the coupling rod.12, a differential piston and cylinder device (see Figure 3) can be used as the adjusting cylinder. Thus, the articulation points 13 and 15 of the rigid coupling rod 12 are varied in their spacing from one another. An electrical-hydraulic locking arrangement ensures that the adjusting cylinder 19 can be acted upon within a given range of lifting heights.

Upon retraction of the piston rod 20, the oscillating crank 9 moves and pushes the support arm 2 forwards. When this happens, the hydraulic jack 1 articulated on the support arm 2 also tilts forwardly. The resultant slight variation in the angle of inclination of the support arm 2 is transmitted via the links in the kinematic chain to the adjusting cylinder 19 which takes over this differential movement as an elastic buffer member, compensating for it by displacing or drawing-:in hydraulic fluid. This supply or discharge of fluid takes place through throttle valves which delay the process.

Upon completion of the displacement operation, the feed or discharge of fluid to or from the adjusting cylinder 19 is again blocked, so that once again it acts as a rigid bar. Upon subsequent application of hydraulic fluid to the hydraulic jack 1, the fork carrier 14 again performs a vertical lifting or lowering movement.

The simple configuration of the individual members in the kinematic system guarantees a favourably costed production and assembly, the individual points of articulation requiring only minimal servicing in comparison with the known lifting apparatuses. A further advantage lies in the small amount of space required.

While avoiding complicated transmission and guidance arrangements which are subject to considerable wear and tear, the described embodiment provides a more simple kinematic system than the known apparatuses.

6

Claims

I 1. Lifting apparatus comprising a support arm provided at one end with a load carrier, a hydraulic jack for'moving said arm, the o-ther end of said arm being articulatedly connected to an oscillating crank, said oscillating crank being connected to a compensating cylinder and via a multi-link transmission to the support arm, said multi-link transmission consisting of an upper control rod articulated on the support arm between the connection of the hydraulic jack to the support arm and the connection of the oscillating crank to the support arm and extending parallel with the 7 oscillating crank, a control lever disposed parallel with the support arm and connecting the upper control rod to the pivot mounting of the oscillating crank, a lower control rod connecting the control lever to a pivotally mounted angle lever and a coupling rod connected to the oscillating crank and to the angle lever.
2. Lifting apparatus as claimed in claim 1, in which the coupling rod is formed by a double acting adjusting cylinder which varies the distance between the angle lever and the oscillating crank connections.
3. Lifting apparatus as claimed in claim 1 or claim 2, in which at half the height of lift the control lever and the angle lever arm to which the lower control rod is connected are parallel.
4. Lifting apparatus as claimed in any preceding claim, in which the connecting line between the articulation connection of the coupling rod to the oscillating crank in the extreme positions of the support arm and the pivot point of the angle lever extends through the point of connection of the angle lever arm and the coupling rod.
5. Lifting apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
6. A fork-lift truck provided with lifting apparatus as claimed in any preceding claim.

Publii,hed 1988 at The Patent Office, State House. 6EV71 High Holborn, Iondon WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mai7 Cray, Orpington, Kent BR5 3RD. Printed by Multiplex technicples ltd, St Mary Cray, Kent. Con- 1/87.