A STEERING DEVICE

Abstract: A wheel-pair steering arrangement in which each of the wheels can be pivoted or swung so as to follow a respective circular line which has a common centre on the same circular line (22), includes a generally vertical pivot axle (3, 4) for respective wheels, a tie bar (8) which connects the wheels through the intermediary of an intermediate pivot member (12, 15) mounted on respective pivot axles (3, 4), and a rigid arm (7) pivotally mounted on a pivot axle. The rigid arm is connected to the tie bar (8) by means of a pivot (9). Respective intermediate pivot members are comprised of a member (12) which is rigidly mounted on respective pivot axles (3, 4) and an intermediate arm (15) which is pivotally mounted to the tie bar (8) and also to the aforesaid member. Stop means (13, 14, 18) are provided for restricting pivotal movement of the intermediate arm (15), between an angled position in which it forms an acute angle in relation to the tie bar (8) and a position in which it lies in a straight line with the tie bar (8).

Description: A STEERING DEVICE The present invention relates to steering devices and more specifically, but not exclusively, to a steering device for coaction with a wheel pair in which both wheels can be swung through 180°. The invention is intended for application with pallet trucks or fork-lift trucks of the kind which include a pair of prongs for insertion beneath the pallet or the like to be lifted and moved, and which trucks are sup¬ ported at the free end thereof by wheels or rollers which are not steerable and are supported at the other end or operating end by a pair of steerable wheels. In order to obtain the degree of adjustability of the pivotal wheels that is required in order for these wheels to permit the truck to be swung and moved at one and the same time it is normally the practice either to place the wheels of each wheel pair so close together that, in practice, the wheels will function as one single wheel, or either to provide steering for only one of the wheels of said wheel pair and to allow the other to pivot freely. The arrangement in which two steered wheels are placed close to one another cannot be used with narrow pallet trucks, since the truck will then become unstable, i.e. the truck is liable to topple when swung. The wheel arrangement in which only one wheel is pivotal or steer¬ able will readily result in locking problems, particu¬ larly when the truck carries a heavy load and the free¬ ly-swinging wheel points in a direction which differs from the direction in which the truck is to be moved. Attempts have been made to solve this problem with the aid of different chain and sprocket wheel arrangements, and also with the aid of purely gear transmissions. Although these solutions function in the manner desired, they are relatively expensive and complicated and conse- quently have not been used to any great extent, particu¬ larly with simpler and cheaper types of pallet trucks. An object of the present invention is to solve the aforesaid problem. This object is achieved with a steering arrangement of the kind defined in the Claims, said Claims also setting forth the special characteris¬ tic features of the invention. The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 is a schematic top view of an inventive steer¬ ing arrangement and shows the wheels position¬ ed for movement of the truck straight ahead; and Figure 2 is a top view corresponding to Figure 1, but showing the wheels swung to a maximum posi¬ tion, i.e. through an angle greater than 180°. The steering arrangement 1 shown in Figures l and 2 includes three points at which the arrangement 1 is connected to the pallet truck or the like (not shown), namely the rotational axle 2 and the pivot axles 3, 4. A block 5 is journalled for rotation around the rota¬ tional axle 2, which is thus firmly mounted on the pallet truck and extends generally vertical. A steering and pulling rod 6 is attached to the block 5 in a known manner, such that when the rod 6 is swung up and down in a vertical plane, a hydraulic pump is activated so as to lift the fork prongs, and when the rod 6 is swung side- ways, the block 5 is rotated. The hydraulic system has no significance with respect to the present invention and will not therefore be described here. Extending generally horizontally from the block 5 is a rigid arm 7 which swings around the rotational axle 2 when the rod 6 is swung. The free, outer end of the arm 7 is attached by means of a pivot joint 9 to a parallel brace or tie 8 which extends between the two wheel assemblies. The two wheel assemblies are mutually identical , but mirror images of one another, and conse¬ quently a description of just one of the wheel assemb¬ lies will suffice to provide an understanding of the present invention. The pivot axle 3 is attached to the actual truck itself in a generally vertical position with the aid of a journal means (not shown) which enables the axle 3 to rotate. The bottom end of the axle 3 is attached to a fork 10, in which a wheel 11 is journalled for rotation. Firmly mounted on the top of the axle 3 is an essential¬ ly rectangular plate 12, said axle 3 being located in the proximity of one short end of the plate 12. A stop 13 and a steering pin 14 are firmly welded onto the upper surface of the plate. Mounted between the end of the tie rod or tie bar 8 and the plate 12 is an interme¬ diate arm 15 whose one end is pivotally mounted to the tie bar 8 by means of a pivot pin 16 and whose other end is pivotally mounted to the plate 12 by means of a pivot pin 17. The intermediate arm 15 is able to swing around the pivot pin 17 between a position in which one end- part of the arm is in abutment with the stop 13 and another position in which said intermediate part lies in abutment with the steering pin 14, both the stop 13 and the steering pin 14 being located on one and the same side of the intermediate arm 15. The intermediate arm 15 also has a upstanding stop 18 located adjacent the pin 16. In the starting position illustrated in Figure 1, in which both wheels are parallel with one another, the generally rectangular plates 12 slope outwardly from one another, i.e. they are angled slightly outwards. As previously mentioned, the axle 3 forms a swinging or swivel centre for the plate 12. The stop 13 is offset slightly to the outer long side of the plate 12, whereas the steering pin 14 is placed in the vicinity of the inner long side of the plate 12 and adjacent the short side opposite to the short side where the axle 3 is mounted. An arcuate member 19 whose centre of arc lies in the pin 16 extends out from the tie bar 8 and abuts the steering pin 14 in the position shown in Figure 1. This arcuate member 19 has its primary function when the wheels are turned to a maximum, as illustrated by the left-hand wheel assembly in Figure 2. As before mentioned, the intention is to enable the wheels to be rotated such that the truck is able to swing around the wheels (not shown) at the free or forward ends of the forks. This is achieved in the following manner: When the steering rod 6 is swung around the rotational axle 2 in the direction of the arrow 20, the tie bar 8 will be moved in the direction of the arrow 21. In the right-hand wheel assembly (according to the Figures), there will then occur in the intermediate arm 15 a pulling force which functions to swing the right-hand wheel outwards while the intermediate arm 15 in the left-hand wheel assembly will be pressed obliquely upwards and outwards at the same time as the tie bar is moved towards the axles 3. This forces the left-hand wheel to swing inwards, i.e. both wheels swing in gener¬ ally the same direction. In the terminal position, shown in Figure 2, the steering pin 14 is enclosed between the arcuate member 19, the intermediate arm 15 and the tie bar 8, thereby securely holding the left- hand wheel in its terminal position. Since in the right-hand wheel assembly in Figure 2, the pin 16 is placed on the outwardly facing side of the plate 12 and the plate 12 is also angled outwards in relation to the rolling line of the wheel, the tie bar 8 and the inter¬ mediate arm 15 will lie in a straight line, wherein the intermediate arm 15 is held in position by the stops 13 and 18 and functions to hold the wheel assembly stable in the illustrated terminal position. The curved chain line 22 in Figure 2 shows the circular line about which the truck is swung on the wheels at the front ends of the forks, and it can be seen from Figure 2 that the wheels will follow this circular line. It will be seen from the aforegoing that the object of the invention has been realized in a simple and inexpen¬ sive, but nevertheless positive fashion.

Claims: CLAIMS 1. A steering arrangement for steering a wheel pair in which respective wheels are pivotal and each follow a respective circular line having a common centre on the same circular line (22), said arrangement including a generally vertical pivot axle (3, 4) for respective wheels, a tie bar (8) which connects said wheels through the intermediary of an intermediate pivot member (12, 15) adjacent respective pivot axles (3, 4), and further comprises a rigid arm (7) which is pivotal about a rotational axle and which is connected to the tie bar (8) by means of a pivot member (9), c h a r a c t e r i z e d in that respective intermediate pivot members are comprised of a member (12) which is attached rigidly to a respective pivot axle (3, 4); in that an intermediate arm (15) is pivotally mounted to said tie bar (8) and to said member (12); and in that stop means (13, 14, 18) are provided for limiting the extent of pivotal movement of the intermediate arm (15) between an angled position in which it defines an acute angle in relation to the tie bar (8) and a position in which it is in a straight line with said tie bar (8). 2. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that the pin (16) by means of which the intermediate arm (15) is attached to the member (12) mounted on respective pivot axles (3, 4) is located outside the centre of the rolling path of respective wheels. 3. An arrangement according to Claim 1 or 2, c h a r ¬ a c t e r i z e d in that arcuate members (19) are provided at the ends of the tie bar (8), said arcuate member (19) functioning, in coaction with the tie bar (8) and the intermediate arm (15), to lock a steering pin (14) in one of the terminal positions of the wheels, said steering pin being located in the proximity of the member (12) mounted on respective pivot axles (3, 4).

Inventors: VUORENMAA PAUL, VUORENMAA, PAUL
Applicants: VUORENMAA PAUL, VUORENMAA, PAUL
Application year: 1992
Main classification: B62D7
IPC codes: B62D7