WO1996005980A1

WO1996005980A1 - A lifting device

Info

Publication number: WO1996005980A1
Application number: PCT/SE1995/000944
Authority: WO
Inventors: Olle BERGSTRÖM; Lars Jonasson
Original assignee: Halna Direktförsäljning Ab
Priority date: 1994-08-19
Filing date: 1995-08-18
Publication date: 1996-02-29
Also published as: SE502972C2; NO970746D0; NO970746L; SE9402772L; AU3269395A; EP0776277A1; SE9402772D0

Abstract

The invention concerns a lifting device (1) attached to a vehicle (2), and designed to facilitate loading and unloading of the vehicle by raising and lowering a loading ramp (3). The lifting device comprises at least one upper lifting arm (4) and one lower lifiting arm (5), which arms (4, 5) are hingedly connected at one of the ends to a lifting frame (6) by means of one upper pivot point (7) in the frame and one lower pivot point (8) in the frame. At their opposite ends they are hingedly connected to the loading ramp (3) by means of pivot points (9, 10). Either one of said lifting arms (4, 5) are provided adjacent its point (7, 8) of pivotal connection with the frame, with a lifting lug (11), containing a point of pivotal connection (12) for lifting movements, and an actuating means (13) is disposed between the lifting pivot point (12) and a pivotal connection in the lifting frame.

Description

A lifting device

Technical Field

The subject invention relates to a lifting device attached to a carrier structure, preferably a vehicle, and designed to facilitate loading and unloading operations by raising and lowering a loading ramp essentially in parallel with the ground, which loading ramp is part of the lifting device and is positioned adjacent a storage space or other similar load-receiving space, said lifting device comprising at least one pair of lifting arms, one upper and one lower, which arms are hingedly connected at one of their ends to a lifting frame by means of one upper pivot point in the frame and one lower pivot point in the frame and at their opposite ends to the loading ramp by means of one upper pivot point in the ramp and one lower pivot point in the ramp, said lifting frame in turn attached to the vehicle, and one of said lifting arms be provided adjacent its point of pivotal connection with the frame, with a lifting lug, i.e. a lug or a projection containing a pivot point for lifting movement, and an actuating means, such as a hydraulically, pneumatically or electrically operated piston-and- cylinder unit disposed between the lifting pivot point and a pivotal connection in the lifting frame, or directly in the vehicle.

Background of the Invention

Lifting devices for vehicles often are of a type arranged to lift a loading ramp from ground level up to a higher level for loading into the associated vehicle or its load-receiving platform. In this case, the load usually is provided with wheels, such as for instance in the care of pallet loaders and, goods transport carriages but also wheel chairs, for example. As a rule, the lifting device is placed at the rear of the vehicle and when the lifting device assumes its upright position the loading ramp may serve as the means closing the rear of the loading space of a lorry, in which case it is oftened referred to as a tail gate lift. Some-times, a lifting device of this nature could also be placed laterally of the vehicle, adjacent a loading space or a load-receiving platform. As a rule, these lifting devices are constructed in such a manner that the loading ramp is suspended from an upper lifting arm and from a lower lifting arm, forming a mechanism known as a tilting cylinder. A lifting piston-and-cylinder unit of considerable lengthwise extension is mounted in the vehicle or the lifting frame to actuate the upper lifting arm in or closely adjacent the outer attachment thereof. The tilting cylinder is used to tilt the loading ramp, allowing a load to the rolled on the ramp. When the load subsequently is to be lifted the operator must first actuate the tilting cylinder to ensure that the loading ramp is essentially horizontal. He thereafter actuates the lifting cylinder which, however, often starts moving in a jerk-like fashion. Consequently, in connection with the tilting, some consider¬ able skill is always involved in making the loading ramp assume a horizontal position, i.e. as a rule in parallel with the ground. Also the folding upwards of the loading ramp is effected by actuating the tilting cylinder and also this operation requires skill. In all, these require¬ ments lead to a complicated, sensitive, heavy, and comparatively expensive lifting device. In smaller vehicles, such as minibuses and pick-ups, the weight is a considerable problem because the permitted safe load of the vehicle is largely reduced. A lifting device having a capacity of 750 k often weighs almost 200 k, and the loading capacity of the vehicle thus is reduced to 550 k. A further problem found in this kind of lifting device is that different applications, i.e. involving lifting arms of different lengths, require tilting and lifting cylinders of different lengths.

Purpose of the Invention

The purpose of the subject invention is to considerably reduce the above problem by providing a lifting device which in a simple manner provides an automatic tilting function while at the same time the lifting device may be of a more simple and lighter construction.

Summary of the Invention

The above purpose is achieved in that the lifting device in accordance with the invention possesses the characteristics appearing from the appended claims. Thus, the lifting device in accordance with the invention is essentially characterized in that either the upper or the lower of the pivot points in the frame is displaceable essentially in the direction away from or towards the lifting frame, said displaceability of either one of said pivot points in the frame arranged essentially in the longitudinal direction of the actuating means, and in that the loading ramp is formed with one or several support faces positioned closely adjacent the inner ramp side facing the vehicle, whereby upon lowering move-ments said support faces are the first to reach the ground and upon subsequent reduction of the force of either one of the lifting arms will be dis-placed in a direction away from or towards the lifting frame, with consequential lowering of the outer side of the loading ramp towards the ground. Owing to this construction the length of the actuating means is not directly dependent on the length of the lifting arms, allowing a more convenient adjustment of their lengths to various applications.

In accordance of a further development of the invention either the upper or the lower of the pivot points in the frame is displaceable essentially in a direction away from or towards the lifting frame and in that the loading ramp is formed with one or several support faces positioned closely adjacent the inner ramp side facing the vehicle, whereby upon lowering movements said support faces are the first to reach the ground and upon subsequent reduction of the force either one of the lifting arms will be displaced in a direction away from or towards the lifting frame, with consequential lower of the outer side of the loading ramp towards the ground. Owing to this construction an automatic tilting function is achieved without the need for a separate tilting cylinder. By displacement of either one of the pivot points in the frame the actuating means, or the lifting cylinder, is able also to perform the tilting function. The result is a construction that is less complicated, less expensive and lighter. A further advantages is the smooth and even operation of the loading ramp lifting movements.

Further characterstics and advantages of the invention will appear from the following detailed description of various embodie- ments with reference to the accompanying drawings. Such advantages and characterstics will be more easily understood with the support of the drawings. Brief Description of the Drawings

Fig. 1 is a perspective view of a lifting device according to the invention. It is intended to be attached to a vehicle to facilitate loading and unloading of the vehicle. This is effected in that a loading ramp is lifted and lowered essentially in parallel with the ground.

Fig. 2 is a perspective view of a lifting frame incorporated in the lifting device. This lifting frame also is incorporated in the embodi¬ ment of the invention according to Figs. 6-9.

Fig. 3 is a lateral view of the lifting frame according to Fig. 2. Fig. 4 illustrates a particularly simple embodiment of the inven¬ tion in a position wherein the lowermost point of the loading ramp is located immediately above ground.

Fig. 5 illustrates a lifting device according to Fig. 4 when its loading ramp has been lowered so as to assume a position wherein it is supported on the ground and its lifting device has been consider¬ ably relieved.

Fig. 6 illustrates in an enlarged view a part of a second embodi¬ ment of the lifting device which is particularly compact in structure. The lifting device is illustrated with the loading ramp assuming the same position as in Fig. 4, i.e. immediately above the ground.

Fig. 7 is an enlarged view of the same part of the lifting device as in Fig. 6 but illustrates the situation when the loading ramp assumes the position corresponding to Fig. 5.

Fig. 8 illustrates a lifting device with the loading ramp raised to a maximum elevated position.

Fig. 9 illustrates the loading ramp having been turned to an essentially vertical position by prolongation of the lower lifting arm.

Description of Preferred Embodiments In Fig. 1, numeral reference 1 designates one embodiment of the lifting device in accordance with the invention. The lifting device essentially comprises lifting frame 6 which is attached to the vehicle, and two lifting arms 4, 5 and a loading ramp 3 and at least one power or actuating means 13. For the sake of clarity no lifting arms 4, 5 are shown at the left-hand side of the lifting frame. Thus, the manner in which a first pivoting arm 14 which in this case is configured as a fork, is attached to a rotary shaft 15 becomes more clearly apparent. The rotary shaft in turn is attached to the lifting frame 6 or to the vehicle. A second pivoting arm 16 is also non-rotationally secured to the rotational shaft 15. The second arm 16 in turn affects a traction or pressure rod 17 which in this case is two-part component. The left- hand and the right-hand part of the lifting frame including the lifting arms are entirely identical. It is also possible, particularly in the case of lifts of lesser magnitude, to use only one pair of lifting arms 4, 5. In this case these lifting arms must be designed to absorb oblique loads from the loading ramp in exactly the same excellent way as the shown lifting device comprising two pairs of lifting arms. In this case prefer¬ ably at least one of the lifting arms may be designed to absorb such bending forces. This means that it is designed with larger width and strength and that its points of mounting also are widened compared to that shown in the case of one of the pairs of lifting arms in Fig. 1. Fig. 2 illustrates the lifting frame 6 in a perspective view as seen from the opposite direction from that in Fig. 1 , i.e. as seen from the loading ramp 3. The lifting frame has an upper face 18 which normally is attached to the vehicle frame or the like. The vehicle could be a larger lorry or a pick-up or perhaps a van. The lifting frame is formed with a front 19 in which various attachment lugs 22-24 are secured. It should be noted that the attachment lugs are arranged symmetrically with respect to the lifting frame centre. The outermost attachment lugs 22 on each side thus are identical just as are the intermediate ones 23 and the innermost ones 24. Apertures 25, arranged in alignment, are made in the outermost and the inter¬ mediate attachment lugs. Through these apertures and through the lower lifting arm 5 positioned intermediate these lugs a pivot pin is introduced. Thus, the latter will form the lower pivot point 8 in the frame, as appears from Figs. 6-9. The intermediate lug 23 also have an upper attachment aperture 26. The inner attachment lug 24 has a corresponding attachment aperture 26 in alignment with aperture 26 in the intermediate attachment lug. It should be noted that the aper¬ tures 26 are oblong in shape. Consequently, the pivot pin positioned so as to extend through these two apertures and support the upper lifting arm 4 becomes displaceable essentially inwards and outwards with respect to the lifting frame 6. This arrangment is of importance for the function of the lifting device and will be explained in detail in connection with subsequent drawing figures. Thus, the attachment lugs 22-24 always are positioned so as to enclose each lifting arm 4, 5 in a fork-like fashion. Obviously, each lifting arm 4, 5 could be formed with a fork-like end attachment, in which case a lesser number of attachment lugs would be needed in the lifting frame 6. The front 19 is formed with two openings 27, 28 in each part. The opening 27 serves as a passage-through for the piston rod of the actuating means 13 that actuates the lower lifting arm 5. The opening 28 is intended for the link arms 17 affecting the upper pivot point 7 in the frame. The upper face 18 and the front 19 of the lifting frame 6 are interconnect¬ ed by a number of staying sheet metal plates 20, 21 , in the illustrated case for such plates. Each side of the lifting frame is formed with an outer staying plate 20 and an internal staying plate 21. Alignment apertures 29 are formed in neighbouring staying plates. These holes are used to mount the rotary shaft 15, as illustrated in Fig. 1. Fig. 3 illustrates the lifting frame 6 as seen straight from the side.

Fig. 4 illustrates a particularly simple embodiment of the invention. In this case a lifting device assumes a position, wherein the loading ramp 3 is located immediately above the ground 30. In this case the lifting device 1 is positioned in such a way that its lifting frame is disposed underneath the platform 31 of the vehicle, behind the rear wheel 32 thereof as appears from Fig. 5. In Figs. 4-9 the outermost staying plate 20 has been removed in order to show the actuating means 13 etc more clearly. The lifting frame 6 illustrated in Fig. 4 differs somewhat from the one illustrated in Fig. 2. The most important difference is that the holes 25 associated with the lower pivot point 8 in the frame, in this case are oblong, in order to allow displaceability of the lower pivot point 8 in the frame. This displace- ability of the displaceable pivot point 8 in the frame is arranged to be effected essentially in the longitudinal direction of the actuating means 13. This is true in all embodiments of the invention. The oval holes 25 or 26 preferably, in accordance with different embodiments, have a longitudinal axis forming an angle between 0 and -45° to the horizontal plane. The holes 26, on the other hand, associated with the upper pivot point 7 in the frame are round, thus making this pivot point a fixed one. The embodiment in accordance with Figs. 4 and 5 is somewhat simplified compared with the embodiment appearing from the rest of the drawing figures. For this reason an explanation of the function of the automatical tilting feature thus can be made more conveniently with reference to Figs. 4 and 5. By means of one of its ends an upper lifting arm 4 is pivo tally mounted in the lifting frame 6 by means of an upper pivot point in the frame. The opposite end of the upper lifting arm 4 is pivotally mounted in the loading ramp 3 in an upper pivot point 9 in the ramp. By means of one of its ends a lower lifting arm 5 is pivotally mounted in the lifting frame 6 in a lower pivot point 8 in the frame and by means of its opposite ends it is articulated to the loading ramp by means of a lower pivot pin 10 in the ramp. If a line were to be drawn between pivot point 7 and pivot point 8 and between pivot point 9 and pivot point 10 respectively, these two lines would be parallel during lifting operations. This is the principle of the parallel arms suspension, the result of which is that the loading ramp 3 will be lifted and lowered essentially in parallel with the ground 30. One of the lifting arms, in this case the lower lifting arm 5, is provided close to its pivot point 7, 8 in the frame with a lifting lug 1 1 , i.e. a lug or a projection 1 1 in which a lifting pivot point 12 is formed. A power or actuating means 13, for instance a hydraulically, pneumatically or electrically operated piston and cylinder unit 13 is mounted between the pivot point 12 and an articulated connection in the lifting frame 6 or directly in the vehicle. By an electrically operated piston and cylinder unit is intended in this case a type of electrically operated jack designed in such a manner that a rotary nut advances a threaded rod inwards or outwards. The actuating means may be of pull or thrust type. In this case a thrust type of cylinder is shown, acting on a lug 1 1 positioned on the bottom face of the lower lifting arm 5. A thrust type of cylinder could also act on a lug positioned on the lower face of the upper lifting arm 4. Simi- larly, a traction or pulling type of cylinder could act on a lug position¬ ed on the upper face of the upper lifting arm 4 or on the upper face of the lower lifting arm 5. The functional principle involved, i.e. that a lifting lug 11 is positioned close to the pivot points 7, 8 of lifting arms 4, 5 in the frame and is affected by an actuating means 13, involves a number of advantages. For instance, it means that the length of the actuating means 13 is not directly affected by the length of a lifting arm, contrary to the case in conventional lifting devices. For in prior art lifting devices the actuating means for both lifting and tilting operations normally is positioned intermediate the frame and the pivot points in the ramp. In the present case, on the other hand, the length of the lifting arms may be altered in a simple manner in order to adapt to various applications. For the purpose of further facilitating this option versatility feature telescopic tubes of square configuration have been chosen for both lifting arms. This facilitates the adaptation of the length of the pivoting arms for various applications. The upper lifting arm is of predeter-mined length, its inner and outer tube being welded together at the joint therebetween but obviously other joining methods could be used, such as through-screws or rivets. The lower lifting arm is of variable length but has a minimum length adapted to the application in question. For, during lifting operations, it will be compressed to its maximum during the entire operation. By severing its inner tube and possibly also the outer tube it is easy to adapt the arms for various applications. In addition, the outer lifting arm 4 and the lower lifting arm 5 are positioned side by side, spaced a certain distance apart laterally. This is necessary because they partly overlap, as appears from Figs. 4-9. For space-economy reasons the lifting arms 4 and 5 have been given a curved configuration adjacent their outer ends, near the loading ramp 3, as appears from the drawing figures. Owing to the particular position of the actuating means 13 the latter does not either negatively affect the lifting of the loading ramp 3 but its position attributes to a maximum lifting capacity of the lifting device.

Fig. 4 thus illustrates a position, wherein the loading ramp 3 is located immediately above the ground. In this position the actuating means 13, which may be e.g. a hydraulically operated cylinder, then has pushed the lifting lug 1 1 and thus the lower lifting arm 5 to the maximum forward position, i.e. until the pivot pin in the pivot point 8 in the frame reaches the bottom of the outermost end of the oval aperture 26. The pivot pin thus is securely joined to the lower lifting arm 5. During all lifting operations the lower pivot point 8 in the frame will assume this position, because the force needed to push the lower pivotable arm 5 outwards is less than the force required to turn it upwards. The reasons therefor are purely geometrical. The distance between the pivot points 9 and 10 in the ramp and between the lower pivot point 8 in the frame and the lifting pivot point 12 quite simply has been chosen to obtain this configuration. When, on the other hand, the loading ramp 3 is lowered so as to be supported on the ground, conditions starts to change. For one or several support faces 14 on the loading ramp 3 are positioned close to the inner face of the loading ramp 3, i.e. the face that is turned towards the vehicle, for which reason these support surfaces will be the first ones to reach the ground upon lowering operations. The support faces 14 just like the pivot points 9 and 10 in the frame are in this case positioned in a lifting profile member 31 of conical shape, which is designed to absorb loads from the loading ramp 3. The latter could be of light-weight type. The support faces 14 could also be in the form of small rubber wheels or the like. Owing to the position of the support faces 14 close to the inner face of the loading ramp the loading ramp will tilt down- wards at its outer end, as illustrated in Fig. 5. This happens when the power of the cylinder 13 is no longer sufficient to counter-act the pressure in the lower lifting arm 5. Upon relief of the actuating means 13 the loading ramp 3 thus will be automatically tilted downwards at an angle α, usually amounting to approximately 10°. In the position assumed by the loading ramp in Fig. 5, a transportation carriage or a wheel-chair may be driven onto the loading ramp. When the actuating means 13 is thereafter charged at first tilting upwards occurs to the horizontal position in Fig. 4 and only then will the load be lifted in parallel with the ground. The tilting upwards will take place first, because of the smaller power need required for this function. One consequence is a particularly even operation of the lifting device be¬ cause the same actuating means performs the tilting as well as the lifting functions. This is an advantage since conventional lifting means have a tendency to jerk when the lifting movement starts. However, in the present case, the actuating means has already started to move and has accumulated considerable power during the tilting, at the time the lifting movement proper starts. For the risks for jerks are at its maximum precisely when e.g. hydraulic aggregates start their operation. Also the high friction at rest in the cylinder seals attributes to this effect. The automatic tilting thus is achieved because either the upper pivot point 7 or the lower pivot point 8 in the frame is displace¬ able essentially in a direction outwards, away from or inwards towards the lifting frame 6, and because the loading ramp is formed with one or several support surfaces 14 positioned closely adjacent the inner face of the loading ramp that is turned towards the vehicle, with the result that during lowering operations the support faces are the first to reach the ground. The displacement of either one of the pivot points in the frame is made possible by means of oblong holes 26 or channels 26 in the attachment lugs 23, 24. However, it would be equally possible to position the pivot point in the frame in a pivotable bracket which turns about a pivot point in both directions between stop means. Possibly this version is a more wear- resistant one.

The embodiment in accordance with Figs. 4 and 5 is one of several possible solutions. Another simple solution is the position the lifting lug 11 on the upper lifting arm 4 and facing upwards. A pull or traction-type of actuating means 13 is in this case connected to the lifting pivot point 12. The upper pivot point 7 in the frame is dis¬ placeable for instance with the aid of the oblong apertures 26, as illustrated in Fig. 2. The function is identical to that of the embodi¬ ment according to Figs. 4 and 5 but contrary thereto a traction-type of actuating means 13 is used, e.g. a hydraulically operated pulling cylinder. The advantage of this arrangement is that the piston rod of the hydraulically operated cylinder will be completely retracted in the oil during the position of transportation of the lifting device illustrated in Fig. 9. A traction-type of cylinder may also give a smoother opera- tion of the lifting device. Both embodiments described are simple but involve a comparatively large building height of the lifting device. By building height should be undestood the distance from the upper face 18 of the lifting frame 6 down to the lowermost point of the device when the latter assumes its position of transportation according to Fig. 9. From an installation point of view normally no adjacent part of the lifting arm must project above the upper face 18 of the lifting frame. In the version including the traction-type of cylinder the lifting arms 4 and 5 therefore reasonably should have had to be moved downwards in order for lifting lug 1 1 not to project above the top surface 18.

Figs. 6 and 7 illustrate an embodiment according to which the building height is fewer than that in accordance with the two previ- ously described embodiments. In this case the lifting lug 11 has been placed on the top surface of the lower lifting arm 5 and the actuating means 13 affects the pivoting point 12 in the lug 1 1. Owing to this position the lifting lug 11 thus will not add to the building height of the lifting device. However, it means that the automatic tilting func¬ tion must be solved in a similar but slightly different way. The oppo¬ site end of the actuating means 13 is attached so as to be displace¬ able. This is effected by attaching it to a first pivoting arm 14 which is attached to a rotary shaft 15 which is rotationally mounted in the lifting frame 6 or possibly in the vehicle, compare Fig. 1. The rotary shaft 15 is provided with a second pivoting arm 16 which affects a link of pull or thrust type, in this case a pull type of link which in turn affects either one of pivot points 7, 8 in the frame, in this case the upper pivot point 7. Fig. 7 illustrates a position wherein the actuating means 13 is relieved and the loading ramp assumes a position illustrated in Fig. 5. When the pull type of actuating means 13 is activated it will both exert a pulling action on the lifting pivot point 12 and on the first pivoting arm 14, whereby the latter will tend to rotate the rotational shaft 15 and the second pivoting arm 16 will pull the traction link 17 rearwards. The opposite end of the traction link 17 is rotatably mounted on the pivot pin associated with the upper lifting arm 4. Consequently, when the force in the actuating means 13 reaches a sufficiently high value the traction link 17 will pull the upper pivot point 7 in the frame from the position illustrated in Fig. 7 to the position illustrated in Fig. 6. Consequently, the loading frame 3 is tilted upwards to the position illustrated in Fig. 4. The support faces 14 are still in contact with the ground, however. As mentioned before, the automatic tilting takes place as a result of the distances mentioned having been chosen in a particular way. In this case the possibilities of variation are even more numerous because of a step-up gear arrangement between the actuating means 13 and the traction link 17, giving the latter a larger pull than the actuating means 13. The reason therefor is that the pivoting arm 16 in this case has smaller moment arm than the pivoting arm 14. Also the longi- tudinal direction between the actuating means 13 and the traction link 17 is slightly different. As a result, this embodiment is more compact than those described previously and its construction lends itself more easily to variations.

A very similar embodiment to the one just described but with a thrust-type of actuating means is possible. In this case the lifting lug 11 is positioned on the upper lifting arm 4 and faces downwards. The thrust- type of actuating means 13 has its one end mounted in the lift¬ ing pivot point 12 whereas its opposite end is connected to an essential similar arrangement of pivoting arms and rotational shaft as in the previous embodiment. In this case, the second pivoting arm 16 is secured to a thrust link 17, the opposite end of which is mounted in the lower pivot point 8 in the frame. Pivot point 8 is arranged in the same way as in accordance with the embodiments in Figs. 4 and 5. Upon relief of the actuating means 13 the lower pivot point in the frame thus will assume an inner position just like in Fig. 5. When the actuating means 13 is thereafter activated the pivot point 8 in the frame will first be displaced outwards to the position in Fig. 4, where¬ after the lifting of the loading ramp 3 will commence.

Fig. 8 illustrates the loading ramp 3 in its maximum elevated position. As a rule the maximum elevated position coincides with the loading position but this is not necessary. Sometimes it may be desirable to position the loading ramp 3 level with e.g. a loading quay. In the maximum elevated position the loading ramp 3 as a rule will be positioned closest to the vehicle because the latter as a rule has an essentially vertical rear. In Figs. 8 and 9, the actuating means thus assumes an end position. The difference is that in Fig. 9 the loading ramp 3 has been tilted upwards to a position of transportation or storage position in which it assumes a vertical position behind the rear of the vehicle. In conjunction with a truck it may then completely or partly close the lorry loading space. The tilting upwards has been effected by extension of the lower lifting arm 5. In this case, it is telescopically extensible. The extension may be effected manually or mechanically. Lifting of the loading ramp 3 results in the latter being pivoted about the upper pivot point 9 in the ramp while at the same time the lower lifting arm 5 is extended. This need not be a particu- larly work-consuming task since preferably a very light-weight loading ramp 3 is used, such as for instance a loading ramp of a composite structure including aluminium side members which are glued to a core of honeycomb construction. The extension of the lower lifting arm may also be considerably facilitated but providing it with a gas- operated spring or similar recsilient means. It would also be possible to make the lower lifting arm 5 of fixed length and arranged for the upper lifting arm 4 to be shortened. In that case the lifting arm 4 should be designed in such a manner that its maximum length is an adapted length from which it may be shortened to smaller longitudi¬ nal extensions. In addition, the alterations of the longitudinal exten¬ sion of either the upper lifting arm or the lower lifting arm 5 could be effected by a motor drive, for instance by providing the lifting arm proper 4, 5 with an internal actuating means, for instance a hydrauli¬ cally, pneumatically or electrically operated piston and cylinder unit which changes the arm length. The drive motor proper then preferably is positioned on the external face of the lifting arm. In some cases it may also be possible to make the cylinder unit form the lifting 4, 5 proper in a more traditional manner. However, this solution is made difficult on account of the curved configuration of each lifting arm, which causes biased loads on the cylinder piston rod. In principle, it is also possible to tilt the loading ramp 3 upwards without changing the length of anyone of the lifting arms 4, 5. However, a condition for this solution is the existence of some kind of releasable "turn-table" positioned in the loading ramp and on which the pivot points in the ramp are mounted. Obviously this "turn-table" may also be rotatable mechanically about its pivot point which typically is situated approxi- mately half way between the pivot point 9, 10 in the ramp.

The typical application of the lifting device is in connection with vehicles. However, it is likewise possible to use the device to lift loads between two different levels, e.g. between a loading ramp and ground level. The automatic tilting function means that a load on wheels can be rolled onto the loading ramp in a simple manner without recesses in the ground or floor being necessary to accommodate the loading ramp lifting arms and the like.

Claims

1. A lifting device (1) attached to a carrier structure, preferably a vehicle (2), and designed to facilitate loading and unloading operations by raising and lowering a loading ramp (3) essentially in parallel with the ground, which loading ramp is part of the lifting device and positioned adjacent a storage space or other similar load-receiving space, said lifting device comprising at least one pair of lifting arms (4, 5), one upper (4) and one lower (5), which arms (4, 5) are hingedly connected at one of the ends to a lifting frame (6) by means of one upper pivot point (7) in the frame one lower pivot point (8) in the frame, and at their opposite ends to the loading ramp (3) by means of one upper pivot point (9) in the ramp and one lower pivot point (10) in the ramp, said lifting frame in turn attached to the vehicle, and either one of said lifting arms (4, 5) being provided adjacent its point (7, 8) of pivotal connection with the frame, with a lifting lug ( 11), i.e. a lug or a projection (11) containing a point of pivotal connection (12) for lifting movements, and an actuating means (13), such as a hydraulically, pneumatically or electrically operated piston-and-cylinder unit (13) is disposed between the lifting pivot point (12) and a pivotal connection in the lifting frame (6) or directly in the vehicle, c h a r a c t e r i z e d in that either the upper (7) or the lower (8) of the pivot points in the frame is displaceable essentially in a direction away from or towards the lifting frame (6), said displaceability of either one of said pivot points (7, 8) in the frame arranged essentially in the longitudinal direction of the actuating means (13), and in that the loading ramp (3) is formed with one or several support faces (14) positioned closely adjacent the inner ramp side facing the vehicle, whereby upon lowering movements said support faces are the first to reach the ground and upon subsequent reduction of the force either one of the lifting arms (4, 5) is displaced in a direction away from or towards the lifting frame (6) with consequential lowering of the outer side of the loading ramp (3) towards the ground.

2. A lifting device (1) as claimed 1, c h a r a c t e r i z e d in that the actuating means (13) is arranged in such a manner that its longi¬ tudinal extension during the lifting movement essentially coincides with the direction of the levers.

3. A lifting device (1) as claimed in claim 1 or 2, charac¬ terized in that the upper pivot point (7) in the frame is displace¬ able essentially in the direction away from or towards the lifting frame (6) and in that the upper lifting arm (4) is provided with a lifting lug (11) positioned on the upper face of the carrier arm and in that an actuating means (13) of traction or pull type is connected to the lifting pivot point (12) of the lug.

4. A lifting device (1) according to claim 1 or 2, charac¬ terized in that the lower pivot point (8) in the frame is displace- able essentially in a direction outwards away from or inwards towards the lifting frame (6) and in that the lower lifting arm (5) is provided with a lifting lug (11) positioned on the lower face of the support arm and a thrust type of actuating means (13) is connected to the lifting pivot point (12) of the lug.

5. A lifting device (1) as claimed in claim 1 or 2, charac¬ ter i z e d in that the actuating means (13) is connected to a first pivoting arm (14) which is attached to a rotational shaft (15) attached to the lifting frame (6) or to the vehicle, and in that the rotational shaft (15) is provided with a second pivoting arm (16) which actuates a link (17) of traction or thrust type which in turn actuates either one of the pivot points (7, 8) in the frame.

6. A lifting device (1) as claimed in claim 5,character- i z e d in that the lower lifting arm (5) is provided on its upper face with a lifting lug (11) to which a traction type of actuating means (13) is connected and in that the traction link (17) is mounted in the upper pivot point (7) in the frame, said pivot point being displaceable where¬ by said pivot point (7) in the frame, at an increase of the pull in the actuating means (13), is pulled inwards, towards the lifting frame.

7. A lifting device as claimed in any one of the preceding claims, characterized in that either the upper lifting arm (4) or the lower lifting arm (5) has a variable length, for instance by telescopic- ally extension or shorteing, and in that a tilting upwards of the load¬ ing ramp may be performed to an essentially vertical position of said ramp, the latter thus assuming a suitable storage position and e.g. closing a loading space in a lorry.

8. A lifting device as claimed in claim 6 and 7, charac- t e r i z e d in that the lower lifting arm (5) is telescopically separable.

9. A lifting device as claimed in claims 7or8,characte r i z e d in that a change of the length of the lifting arm is effected by some kind of motor drive e.g. by providing the lifting arm proper (4, 5) with an internal power means, for instance a hydraulically, pneuma¬ tically or electrically operating piston-and-cylinder unit which changes its length or by the cylinder itself serving as a lifting arm (4, 5)*