ANTI-SKID DEVICE

Abstract: Anti-skid device of the type including an arm (21), carrying in its outer end a chain provided pulley that is brought in contact with a vehicle wheel so that the chains are thrown in under the vehicle wheel. The arm is in its inner end journaled in a U-shaped or fork-shaped bracket (26) via a short axle (22) that in its ends rests in bowl shaped semisspherical (24) bearings (25) that are threaded in the legs of the bracket (26), the bearing bowls (25) are pretensioned against the axle (23). At the apex of the shaft's spherical ends recesses are made that take up lub­ rication grease and in this way a point-like contact bet­ ween the bearing shells and the axle is eliminated.

Description: This invention concerns so called auto-matic anti-skid devices of the kind that for instance is described in US-A-4 299 310. Anti-skid devices of this kind includes a pulley on which has been arranged a number of chains. At use the pulley is brought in contact with the side of a vehicle wheel causing the pulley to rotate with the wheel and the chain pieces are thrown in under the wheel thereby improving the traction of the vehicle wheel. The chain provided pulley is journaled in the outer end of an arm actuated by for instance a pressurized air-cylinder so that the pulley can be moved from its working position in contact with the side of the vehicle wheel and a parking position out of the way. Essentially this construction has turned out very well in praxis even if other and new constructions have been added to the market. In order to secure that the chain provided pulley always is brought in contact with the vehicle wheel at the correct position the amount of play that is acceptable in the journaling of the arm at its inner pivot point is limited. Furthermore the arm must be very easily pivotable in order not to increase size and cost of the pressurized air-cylinder. On the other hand the journaling of the pivot-point may not became to expensive. Due to the limited amount of space at many vehicles today the journaling of the the arm may furthermore not be bulky. In order to handle the very great loads that the arm is subjected to this has been journaled in ball bearings (see EP-A-0 195 973). This works very well to start with. However the ball bearings wear out prematurely. The exchange frequency has turned out to be essentially independent of the quality of the bearings. An increased play in the bearings result in a poorer funktion and possible damages to other parts of the anti-skid device. The journaling of the arm has thus turned out to be a weak point and a better bearing is needed. The above problem is in accordance with the invention solved by journaling the arm by a stub shaft that in its outer ends are journaled in bearings that in a bowl like way enclose the shaft axially as well as radially. Preferably the bearings are spherical bowl shaped shells with correspondingly spherically shaped stub shaft ends. Seals can be applied to prevent dirt from entering into the bearings and the bearing shells are in preferably arranged in a fork like construction gripping over the end of the arm. In this way can, in particular if the bearing shells are threaded in the supporting structure, a certain axial pretension be given for the bearing which in turn contribute to a play free bearing with a great life span. Since the angle of the chain provided pulley in its working position is very important in order to secure an absolut correct "throw in" or path for the chains so that these optimally are placed below the vehicle wheel. To solve this problem it is necessary or at least practical to have an adjustment for the pulley in the outer end of the arm. Such adjustment devices are shown in EP-A-0 151 098 and the German patent application DE-A-3 509 062. A problem is however that this adjustment must be so stiff or tough that it can sustain the really great loads on the chains and the chain provided pulley as the chains pass under the vehicle wheel. No adjustment devices has yet been developed that can sustain these very great loads without beeing bulky, thus increasing the weight of the device and the load on the arm and its bearing. Therefor another object of the invention is to solve this problem. This is done by providing an adjustable ball device at the very center of the chain provided pulley or centrally in the virtual plane of the forces imparted to the chains and the pulley. This will also reduce the stress on the pulley itself. An embodiment according to the present invention is below described in greater detail with reference to the accompaning drawings in which fig 1 is a perspective view from below of a partially cut of truck axle with two tires and a device according to the known is technique mounted below the spring assembly for the drive axle, fig 2 in a larger scale the inner end of the swing arm according to the invention is shown and fig 3 depicts the outer end of the same swing arm. In fig 1 a device of the type Onspot 01 (US patent 4299310) is shown. A chain provided pulley 8 is rotatably mounted on an arm 6, which in turn is pivotably journaled on a bracket situated on the bottom of the spring assembly of a vehicle. Arm and pulley are shown in active position with the pulley in contact with the wheel. The arm is actuated by means of a remotely controlled air cylinder 10. The arm is the weak point of this device as of many others and therefor the improvements shown in fig 2 and 3 are a great step forward. In fig 2 is shown how in accordance with the invention the inner end of the swing arm is journaled. The swing arm 21 is arranged on a stub shaft 22. This can be done in different manners but in the shown case the stub shaft 22 is of stainless steel and the arm is made of common steel. The stub shaft is preferably a press fit in the end of the arm and in order further to improve the grip they are welded to each other. Of course also other fastening methods are possible. The stub shaft 22 is in its end provided with essentially spherical surfaces 24 fitting in opposed bowl shaped bearing shells 25. These bearing shells are circumferentially provided with a thread and they are threaded in two legs of a U-shaped arm bracket 26. Each bearing shell is provided with key grips 27 and on the inner side or the side that is turned against the stub shaft 22 the bearing shells are provided with seals or scrapers 28 in order to prevent dirt from entering the bearing surfaces and also to retain the bearing grease in the the bearing. At the very center of ends of the stub shaft the spherical surfaces are slightly machined or recessed 29 in order to provide a small space for bearing grease and also to secure that contact will not take place in a point but along a spherical segment which in turn will increase the life spann of the bearing. The arm bracket 26 is preferably dimensioned in such way that its resilience or elasticity does not push away the grease in the bearings but allow a certain wear before any play will occur. In the shown embodiment the bracket is expanded about a half millimeter and consequently a wear of the same size can be taken befor any play appears. Since the bearing surfaces are spherical a possible missalignement between the two bearings 25 is without importance. This possible misalignement can be the result of the pretensioning on mounting, machining tolerances or even the forces on the arm. In other words witout any tendency towards binding the journaling of the arm is in itself resilient which reduce the stress on practically all parts in the device. When the bearing shells has been tightened with the desired torque in order to achieve this relationship they are secured by means of a suitable thread locking glue or by means of a punch mark. The probable reason why ball bearings are so unsatisfactory is presumably not the large forces on use of the device but instead the comparatively moderate forces that are excerted on the arm bearing when the device is in rest. These forces are well below the forces that a ball bearing should be able to take without being damaged even if the load is for a long time. The circumstances are however made more difficult by the fact that the arm only executes a forth and back movement that in each actuation cycle goes from exactly the same starting position to a working position and back to the same starting position. This means that when the device is well mounted on the car the balls of the ball bearing will in the resting or parking position of the swing arm always be in exactly the same position and with the vibration load that it is then subjected to the grease is in the end pushed aside and wear starts. This would explain why ball or roller bearings are improper for arm bearings. It must however be pointed out that this is not self-evident in any way and that it has taken considerable time and research to understand all these circumstances. In fig 3 is shown the outer end of the swing arm 31. In this end the chain provided pulley 32 is mounted. The pulley is journaled on a bearing 37 which in turn is mounted on a hub portion 34. The hub portion 14 is on its outside provided with a cylindrical surface with a flange in one end and a groove in the other end in order to between the flange and a lock ring grip the inner race of the bearing 27. On its inside the hub part 34 is provided with a spherical surface, the center which is located essentially in the middle of the length of the hub part 34. Inside the hub part 34 a ball 33 is arranged. The ball 33 has a spherical outer surface corresponding to that of the inner surface of the hub part 34. Furthermore the ball 33 is provided with a central hole through which a bolt 35 extends. The bolt 35 is threaded in the outer end of the swing arm and between the ball 33 and the swing arm is arranged a distance piece or washer 38. The hole in the ball 13 on the side turned away from the swing arm is provided with a conical chamfering with a conical washer 36 on the bolt. When the device is mounted the swing arm is brought to the position in which the chain provided pulley is in contact with the vehicle wheel and the angles lengthwise and transversally relative the vehicle wheel are adjusted to provide a correct path for the chains when these are thrown in under the vehicle wheel. The bolt 15 is then tightened and the conical washer 36 will expand the ball 33 so that the position between the hub portion 34 and the ball 33 is locked. Since the bolt can excert very great forces on the ball a very secure grip is obtained. The ball 33 is axially slotted over a major part of its length into four segments faciliating mounting as well as the expansion thereof. Preferably stainless steel is used as material for the ball since this will prevent corrosion and allow for future adjustment if this becomes neccesary due to wear, change of tyres or damages to arm or supporting structure. This possibility has not existed with the known devices,because it has been neccesary to secure the joints by welding or similiar nonretacable methods in order to prevent loosening. Within the scope of the invention the inner race of the ball bearing and the hub portion 34 can be integrated. Since the ball joint is placed in the force center of the chain provided pulley the forces excerted on the ball joint will be unable to alter its position despite the very compact dimensions. By means of the ball joint it will also be possible to adapt the device for left hand and right hand devices reducing the number of parts. Finally it should be noted that the measurements according to the invention at the inner end and the outer end of th arm respectively can be used or carried out independently of each other. It should also be noted that the invention is not restricted to the shown embodiments but that these are only given by way of example.

Claims: An anti-skid device of the kind that includes a rotateable pulley provided with a plurality of chains that are thrown in between a vehicle wheel and the gound by the rotation of the pulley when this is brought in contact with the vehicle wheel and which pulley is carried by a swing arm (21) transporting the pulley between its working position against the vehicle wheel and the parking position characterized in that the arm (21) in its inner end is fastened to a short axle or shaft that in both ends is journaled in bowl shaped bearings (25) enclosing the ends of the shaft axially as well as radially. An anti-skid device according to claim 1, characterized in that the bowl shaped bearings (25) are plain slide bearings. Device according to claim 1 characterized in that the bearings (25) and the shaft ends constitute half spheres (24). Device according to claim 3 characterized in that the apex of the half spheres (24) are machined away. Device according to claim 1 characterized in that the bowl shaped bearings (25) on the outside are provided with a thread and threaded into corresponding threads in the legs of a U-shaped bracket (26). Device according to claim 5 characterized in that the bracket (26) for the arm is resilient between its two bearings (2.5) so that these can be pretensioned against the axle (22). Device according to claim 2 characterized in that the shaft (22) is of stainless steel while the bowl shaped bearings (25) are of bearing bronze. Anti-skid device of the kind that includes a chain provided pulley (32) that is journaled in the end of a swing arm (31) so that it can be brought from a parking position to a working position in contact with a vehicle wheel where the pulley (32) is rotated by the contact with a wheel throwing pieces of chains arranged on the pulley under the wheel, characterized in that a ball joint (33, 34) is situated with its center coinciding with the point in which the forces excerted on the pulley cross each other. Device according to claim 8, characterized in that the ball bearing is constituted by a ball (33) that is mounted by means of a bolt (15) extending through a hole in the ball and into the arm (31) where the bolt is threaded and that the bolt and ball are provided with a conical cooperating surfaces (36) expanding the ball when the bolt is tightened thereby also locking the fit between ball (33) and the surrounding concave hub part (34). Device according to claim 8, characterized in that the concave part (34) of the ball joint is an integral part with the inner race of a bearing for the chain provided pulley (32).

Inventors: KARLSSON, LENNART
Applicants: VBG PRODUKTER AB
Application year: 1989
Main classification: B60B39
IPC codes: B60B39