EP0174709B1

EP0174709B1 - Lift truck

Info

Publication number: EP0174709B1
Application number: EP19850302710
Authority: EP
Inventors: Hiroshi Hanaoka
Original assignee: Hanaoka Sharyo Co Ltd
Current assignee: Hanaoka Sharyo Co Ltd
Priority date: 1984-09-11
Filing date: 1985-04-17
Publication date: 1988-11-17
Also published as: EP0174709A1; DE3566244D1; JPS6152559U

Description

The present invention relates to a lifting device and particularly to a lift truck or trolley (hereinafter referred to generally as a "lift truck").
A conventional lifttruck is provided with a frame having front and rear wheels, a pair of elevating link mechanisms, a platform mounted on the top of the pair of elevating link mechanisms, and a hydraulic jack which is actuated by oil supplied from an oil pump so as to expand the link mechanism to raise the platform, and thus facilitate loading and unloading operations.
However, the hydraulic lifting mechanism comprising the hydraulic jack is usually located beneath the platform. Accordingly, the lowermost position of the link mechanism is limited by the hydraulic lifting mechanism, so that the lowest position tends to be rather high, making loading difficult.
GB-A-971031 discloses an arrangement in which a platform (1) has a lift mechanism (13) which is arranged outside the space in which the platform (1) moves up and down, so as not to interfere with the movement, but requires a lifting jack with a long cylinder set vertically behind the platform, in order to provide sufficient vertical travel. Consequently the extendable ram of the jack projects upwardly by a considerable distance, when the platform is raised, constituting a dangerous obstruction when the device is moved around in a factory, for example.
Accordingly the present invention seeks to provide a lift truck which has a compact mechanism, as well as providing a platform which is capable of descending as low as possible.
According to the present invention there is provided a lifting device having a frame (10), a pair of X-links (10a) provided on the frame, a platform (30) provided on the X-links and a lift mechanism comprising a jack (21) having an extendable ram (21 a), the lift mechanism being positioned outside the space in which the platform moves up and down so as not to interfere with the movement, characterised in that the link members of the X-links are pivotally connected to the frame and the platform at their lower and upper ends which are adjacent to the lift mechanism, and slidably engaged with the frame and the platform at their other lower and upper ends, and in that the lift mechanism comprises a link mechanism (22, 23) connected between the top of the ram and the lower portion of each link member which is adjacent the lift mechanism so as to rotate the link member as the ram is extended.
Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a side view of a lift truck of the present invention;
Figure 2 is a plan view of the truck of Figure 1;
Figure 3 is a front view; and
Figure 4 is a perspective view.

The lift truck of the present invention comprises a frame 10, an elevating link mechanism including a pair of X-links 10a, a hydraulic lift mechanism 20, and a platform 30 on the top of the X-links. The frame 10 comprises a pair of side frame members 11 arranged parallel to one another and a rear frame member 12 arranged at right angles to the members 11. Each side frame member 11 is provided with a small front wheel 13 mounted at its front end on a bracket 12a, and with a castor 14 at its rear end mounted on a bracket 17a. The front wheels 13 are at a position below the upper surface of the frame 10. An inverted U-shaped handle 15 is bridged over the rear frame member 12, and each of its lower ends is attached on the castor 14. A channel shaped rail 16 is formed on each of the opposite lateral sides of the frame members 11 for receiving a roller 26b attached to the front/lower end of each X-link as described below.
A hydraulic jack 21 with a foot operated pump is vertically provided on a frame 12a secured to the centre of the rear frame member 12.
An arm 22 comprising a pair of triangular plates is pivotally provided on a supporting stand 17 secured to the frame 10 at the first corner of the arm 22 by a pivot 22b. A roller 22a supported at the second corner of the arm 22 engages the upper end of ram 21 a ofthe hydraulic jack21.Further.the third corner 23a of each triangular plate of the arm 22 is pivotally connected to a rod 23 which in turn is pivotally connected to an X-link driving arm 24 secured to a link member 25.
Each X-link comprises a pair of link members 25 and 26 which are linked by a pivot pin 27 at their intermediate points and are arranged to be rotatable in relation to each other about the pivot pin 27. The lower end of each link member 25 is pivotally fixed to the frame 11 by a pivot 25a. The above mentioned X-link driving arm 24 is connected to the link member 25 at a position nearthe pivot 25a.
The lower end of each link member 26 is provided with a roll 26a which is engaged with the above mentioned rail 16.
The upper end of each link member 26 is pivotally fixed at the rear end of a load supporting platform 30 by a pivot 26a. The platform 30 comprises a flat plate 31 strengthened by a pair of parallel reinforcing members 32 on its undersurface. An inwardly facing channel member 33 is mounted on the innerface of each member32, and a roller 25b provided on the upper end of each link member 25 is engaged in the channel 33. The platform 30 further has a downwardly dependent skirt 35 extending around its front (or leading) and side edges, and a reinforcing member 36 projects upwards from the rear (or trailing) edge. The platform 30 is slightly larger in plan than the frame 11 so that the platform 30 and the skirt 35 closely covertheframe 10 and frontwhesls 13when the X-links are contracted to the lowest position, and the lift mechanism comprising the hydraulic jack 21 and arm 22 is positioned outside the area in which the platform 30 moves up and down.
The operation of the hydraulic jack 21 is as follows. When a pedal 28a of the jack 21 is depressed by the operator's foot repeatedly, oil is supplied to the jack 21 by an oil pump 28 so as to raise the ram 21a vertically. When a lever 29 is operated to actuate a release valve, the ram 21 a retracts.
When the lever 29 is operated to discharge the oil from the jack 21, after the platform 30 has been elevated to its highest position as shown in Figure 1, the ram 21 is retracted, causing rotation of the arm 22 about the pivot 22b in a direction indicated by an arrow M in Figure 1, so that the rod 23 which is connected at its upper end to the other corner of the arm 22 is forced to rotate the link members 25 counterclockwise (Figure 1) through the link driving arm 24. Accordingly, the rollers 25b of the upper ends of the link members 25 roll forward along the rail 33. Consequently, the upper ends of the link members 26 interconnected to the members 25 by the pivot 27 rotate clockwise and the rolls 26b at its lower ends roll forward along the rails 16, so that the X-links contract gradually to their lower flat position on the frame 10. As a result, the platform 30 descends to closely cover the frame 10 and front wheels as shown by chain lines in Figure 1.
On the other hand, when the ram 21a a of the hydraulic jack 21 is extended to move the roller 22a upwards, member 22 is rotated in an opposite direction to the arrow M in Figure 1 so as to raise the corner of the arm 22 that is connected to the rod 23 at its end 23a. The link driving arm 24 is thus pulled up to rotate the link members 25 in the clockwise direction, and the rollers 25b of the link members 25 and the rollers 26b of the link members 26 roll back along the rails 33 and 16, respectively, so that the X-links expand to elevate the platform 30.
It is preferable to provide a slope 31 a on the front end of the platform 30 as shown by chain lines in Figure 1, in order to facilitate loading and unloading of articles having wheels.
From the foregoing, it will be understood that the lift truck of the preferred embodiment of the present invention is provided with a platform designed to have a size and a shape to closely cover the frame, and an operating system including hydraulic jack, oil pump and release valve installed at the rear of the frame so as not to interfere with the up-down movement of the platform. Thus, loading and unloading operations can be easily carried out, since the platform can be positioned at a very low level.

Claims

1. A lifting device having a frame (10), a pair of X-links (10a) provided on the frame, a platform (30) provided on the X-links and a lift mechanism comprising a jack (21) having an extendable ram (21a), the lift mechanism being positioned outside the space in which the platform moves up and down so as not to interfere with the movement, characterised in that the link members of the X-links (10a) are pivotally connected to the frame (10) and the platform (30) at their lower and upper ends which are adjacent to the lift mechanism, and slidably engaged with the frame and the platform at their other lower and upper ends, and in that the lift mechanism comprises a link mechanism (22, 23) connected between the top of the ram (21 a) and the lower portion of each link member which is adjacent the lift mechanism so as to rotate the link member as the ram is extended.

2. A device according to claim 1 wherein the top of the ram (21 a) of the jack (21) is engaged with an end of the link mechanism (22, 23) through a roller (22a).

3. A device according to claim 1 or 2 in which the frame (10) is provided with wheels (13, 14).

4. A device according to claim 3 wherein front wheels (13) of the frame (10) are positioned below the upper surface of the frame, so that the platform (30) can be lowered to a position adjacent the upper surface of the frame.

5. A device according to any preceding claim wherein the platform (30) has a slope (31 a) at the front end thereof.