STEERING DEVICE

Abstract: The invention discloses a steering device for a pair of wheels, in which both wheels are turnable more than 180 DEG and where the turning points of the wheels (10) substantially coincide. The invention comprises a two part tie rod (16) with a turnable joint (18), the outer ends of said tie rod (16) each are turnably connected to two arms (20, 28). The first arm (20) is attached to the axis of the wheel (10) by a rigid wheel plate (26), and the second arm (28) is attached to the wheel beam (12). By conveying the joint (18) of the tie rod by assistance of a joint track means (32, 34, 36, 38) along a predetermined track, the wheels (10) are turned according to the principle of coinciding turning points. The attachment to the first and second arms (20, 28) also enables a wheel turning of more than 180 DEG .

Description: STEERING DEVICE The present invention relates to steering devices, particu¬ larly to steering devices for pair of wheels, in which both wheels are turnable more than 180 degrees. The invention is intended for all types of transport devices using turnable, steerable wheels to enable manoeuvring to a requested position. Examples of such devices are industrial trucks, carts, carriages and cars. These devices may have any number of steerable and turnable pair of wheels, but option¬ ally also a plurality of not turnable or following wheels. In many cases where carts or carriages are to be manoeuvred in a limited space it is desirable for the transport device to be turnable around an axis as close as possible to the transport device itself. Three basic methods for steering is known. The first method is using a steerable pair of wheels in which the wheels are located so close together that they in use op¬ erate as one single wheel. A serious limitation of such a method is that the stability against tipping over is low for such a transport device. The small distance between the pair of wheels drastically reduces the range in which the centre of gravity may be located or not overturning the device. Accord¬ ingly, there is a risk for overturning for high loads and/or high velocities. The second principle is based on that only one of the wheels in a pair of wheels is steerable whereas the other one is simply following freely during turning. However, this solution has its limitations when the transport device is supposed to bear heavy load, since the pressure from such load on the free wheel easily may lock it in a direction different from the intended direction of movement. The third method is based on the ability to turn both wheels in a pair of wheels, in which the wheels are separated by a not negligible distance. To achieve a maximum flexibility the steerable wheels should be turnable 180°. To achieve a turning movement giving rise to as small side forces as possible on both the turnable and fixed pairs of wheels, the turning of the wheels should be performed in such a way that they have a common turning point. This means that the two wheels will be turned by different amounts, particularly at large turnings. In prior art, there are a few turning devices of the above mentioned type. For example, there are commercially available solutions based on piston devices. Two separately controlled piston arrangements are used for turning the wheels according to the principle of coinciding turning points. The disadvan¬ tages with such arrangements are that the method is comparably expensive, making it uninteresting for transport devices of simpler types, as well as that the equipment tends to occupy a relatively large volume, causing a large structure height of such wheel devices. It is possible to achieve steering devices according to the third method by means of simple mechanical arrangements. One example can be found in the PCT application No. 92 911 895.8, where turning of more than 180° is provided by introducing one fixed and one movable element between the track rod and the wheel. The steering that provides the common turning point and the restricting that prohibits the movable parts to end up outside intended areas is effected by a number of guide rails and rods. The device does not exactly follow the principle of a common turning point, particularly at large turnings, and the positioning of guide rails and stopping rods resulted in a relatively clumsy design. An object of the present invention is to provide a cheap and simple steering device, which by using simple mechanics is able both to turn the wheels more than 180° and to substan¬ tially follow the principle of wheel turning with common turn- ing points and which easily may be applied on various types of transport devices. This object is achieved by a steering device as defined in the claims. An embodiment of the invention will be further described in the following in conjunction with the accompanying drawings, in which Fig. IA, IB and IC are schematic views from above of an embodiment of the present invention with three different wheel turnings. Fig. 2A, 2B and 2C are schematic views from above of another embodiment of the present invention with three different wheel turnings. Fig. 3A, 3B and 3C are schematic views from above of the embodiment in fig. 1 applied on a wheel frame associated with a transport device with three different wheel turnings. Fig. 4 disclose how the embodiment of the present invention shown in fig. 1 may be applied on two pairs of wheels belong¬ ing to the same transport device. Fig. 5 is a sketch for understanding of the creation of the movement of the junction points around the wheel socket. Figures IA, IB and IC show the same embodiment of the present invention with three different wheel positions. Two wheels 10, turnable around a horizontal axis, are attached through their shafts to opposite ends of a wheel beam 12 by means of one turnable shaft 14 each. The turnable shaft 14 allows a rota¬ tion around a vertical axis. Two tie rod portions 16 are attached to each other by a turnable joint 18, configuring a tie rod. Since the whole embodiment is symmetrical only one side is described below if nothing else is stated. The outer end of the tie rod 16 is attached to a first arm 20 and a second arm 28 by a hinged junction point means 24. The first arm 20 is connected to a wheel plate 26 by a first hinged attachment means 22. The wheel plate 26 is rigidly connected to the axis of the wheel 10. The second arm 28 is connected to the wheel beam 12 by a second hinged attachment means 30. Together, the first and second arms 20, 28 constitute a gap- like construction, the exact look of which is determined by the design and length of the arms and the wheel position. The first and the second arms 20, 28 are arched in this preferred embodiment, but may dependent on the detailed design of the wheel beam 12 and the wheel plate 26 be designed in several different manners, so that for all wheel turnings the turnable shaft 14 is located in front of or within the gap-like con¬ struction formed by these two arms. Here below iε referred to a coordinate system fixed to the wheel beam, as shown in figure 5, and which has an x-axis directed along the connection line between the turnable shaft 14, 14 of the wheels. The second hinged attachment means 30 and the turnable shaft 14 are fixed relative to this coordi¬ nate system on a distance a from each other, and the connec¬ tion line between the points forms an angle α with respect to the x axis, see fig. 5. Since the second arm 28 may turn around the second hinged attachment means 30, the hinged junction point means 24 moves along an arcshaped track 42 with a radius r. The position of the hinged junction point means 24 in the fixed coordinate system is therefore fully character¬ ized by an angle φ defined by the connection line between the second hinged attachment means 30 and the hinged junction point means 24, and the x axis. The connection line between the turnable shaft 14 and the first hinged attachment means 22 forms a determined angle β with respect to the x axis depend¬ ing on the wheel turning. In fig.5 the distance between the turnable shaft 14 and the first hinged attachment means 22 is designated by b and the distance between the first hinged attachment means 22 and the hinged junction point means 24 by d. The angle φ is then fully determined by the angle β by the relation: where c = ~ / a 2 + b 2 - 2 a b cos (7c 2 - β + α ) In the same manner the corresponding hinged attachment means 24 associated with the other wheel will describe a correspond¬ ing inverted arcshaped track. In the above figures an embodiment in which the connection line between the turnable shaft 14 and the first hinged attachment means 22 coincides with the wheel turning is shown. Those skilled in the art easily understand that corresponding relations may be constructed even if these does not coincide. In the above description a symmetrical device is disclosed, where both wheels are equipped with similar, but inverted parts. One may of course equally well use different lengths and angles for the different parts on the two sides. Subse¬ quently, in such a case, the arcshaped tracks may have differ¬ ent radii and different wheel turning dependence. Accordingly, the positions of the two hinged junction point means 24, 24 in a certain embodiment are unambiguously deter¬ mined by the wheel turning. If the wheel turnings are selected to give a common turning point, the positions of the hinged junction point means 24, 24 are unambiguously determined by the position of the turning point. The position of the turn- able joint 18 between the two tie rod portions 16, 16 is determined by the positions of the hinged junction point means 24, 24 and the lengths of the tie rod portions 16, 16. For each pair of positions of the hinged junction point means 24, 24 there are normally two possible positions of the turnable joint 18, if it would be able to move freely. Since the set of positions for the hinged junction point means 24, 24 are determined by the positioning of the turning point, also the position of the turnable joint 18 becomes a function of this position, with two alternative positions for each desirable turning point. Reversely, a certain position of the turnable joint 18 corresponds to a unique set of wheel settings. Although in the above embodiment the two tie rod portions have the same length, those skilled in the art easily realise that a tie rod divided in portions of different lengths would oper¬ ate as well. To control the transport device according to the principle of coinciding turning points, it is now only needed to convey the turnable joint 18 in the plane in such a way that suitable wheel turnings are provided. This is realised by a joint track means. In the embodiment of fig. 1, the joint track means is constituted by a slot 32, in which the turnable joint 18 can move. It is easily understood that instead of a slot one may use an edge, against which the turnable joint is pressed, or similar arrangements. The essential feature with this part is that the turnable joint 18 is conveyed along a predetermined track defined by some mechanical construction. In the embodi¬ ment shown in fig. 1, the requested track forms an arched, almost circular-sector formed structure. Figs. 2A, 2B and 2C illustrate another embodiment of the present invention for three different wheel settings. In this embodiment, the lengths of the first arms 20, 20, the second arms 28, 28, the tie rod portions 16, 16 and the positioning of the first hinged attachment means 22, 22 and the second hinged attachment means 30, 30 have been selected in such a way that the ideal motion of the turnable joint 18 almost follows a circular sector. The joint track means conveying the turnable joint 18 along this ideal track may then be designed in a simple way. An angled lever 34 is attached by a rota¬ tional joint 36 to the wheel beam 12. The angled lever is turnably attached by one of its ends to the turnable joint 18 and by its other end to a steering connecting rod 38 by a turnable steering connecting rod joint 40. The distance between the rotational joint 36 and the turnable joint 18 is adjusted to correspond to the radius of the requested track along which the turnable joint has to move. By moving the steering connecting rod 38 in a forward and backward direction the turnable joint 18 will move along the requested circular sector, which in turn controls the wheel turnings substantial¬ ly according to the principle of coinciding turning points. In both the above described embodiments a turnability of the wheels is achieved by the use of the two arms 20 and 28, which makes it possible to reach around the turnable shaft 14 at very large wheel turnings. Wheel turning of more than 180° can be achieved in this manner. The figures IC and 2C show the two embodiments with the wheels directed straight forward. The turning point is in this situation located at an infinite dis¬ tance. The figures IB and 2B show a situation when the turning point is situated diagonally backwards to the left. The figures IC and 2C show the situation of maximum wheel turning, when the turning point is situated in the central normal to the connecting line of the wheels. The exact value of these wheel turnings is determined by how far behind the connecting line of the wheels the turning point is situated. However, it is obvious that the wheels have to be turned more than 180° to cover all needs. The figures 3A, 3B and 3C show the three above described cases applied on a transport device with one fixed and one movable pair of wheels. In the figures 3A and 3B, the position of the turning point is drawn and the different tracks for the wheels with these wheel turnings are indicated by broken lines. Those skilled in the art realise from these sketches that if one fixed pair of wheels should be used in the present invention in a profitable manner, the turning point should be placed along the connecting line of these fixed wheels. Figure 4 illustrate how the invention may be applied on more than one pair of wheels in the same transport device. In this case, a wheel frame with a pair of steerable wheels in each end and with the turning point placed in-between, is shown. From this sketch, it is easily understood that the invention may be applied to any number of steerable pair of wheels with a common turning point. As closer the pair of wheels is placed to the turning point, as larger wheel turnings are needed.

Claims: CLAIMS 1. A device for steering of a pair of wheels in a trans¬ port device comprising two, around horizontal axes, rotating wheels (10) steerable connected by one turnable vertical shaft (14) each at opposite ends of a wheel beam (12) or similar supporting device, c h a r a c t e r i z e d b y : a tie rod (16) comprising two portions, which by one end each is linked together by a turnable joint (18) ; a wheel socket comprising a first arm (20) attached to the axis of the wheel (10) by a first hinged attachment means (22) and a rigid wheel plate (26), and a second arm (28) attached to the wheel beam (12) by a second hinged attachment meanε (30) , in which wheel socket the first and second arms are connected to each other and the outer end of one of the tie rod portions (10) by a junction point means, and with which wheel socket a movability of the wheels of more than 180° is achieved; and a joint track means conveying the turnable joint (18) of the tie rod along a predetermined track such that the wheel turnings substantially correspond to the principle of coincid¬ ing turning points. 2. A device for steering of a transport device according to claim 1, c h a r a c t e r i z e d in that the joint track means is realised by a track, an edge or similar mechanical template. 3. A device for steering of a transport device according to claim 1, c h a r a c t e r i z e d in that the joint track means is realised by a lever device.

Inventors: VUORENMAA PAULI, VUORENMAA, PAULI
Applicants: VUORENMAA PAULI, VUORENMAA, PAULI
Application year: 1996
Main classification: B62D7
IPC codes: B62D7