The object of the invention is a friction protector for a rubber drive wheel, which includes slip-stops set on the surface of the circumference, circumference supports providing radial support on either side of the drive wheel, the slip-stops and circum¬ ference supports being connected by attachment chains.

Rubber drive wheels are in general use in the transfer of long objects such as logs and similar, for example in the felling grab of timber-harvesters. Several species of trees have, during their growth, a stage when the bark is easily detached, the so- called bast time. It is then difficult for harvesters to handle timber, as the drive wheels tend to slip during operations. In many cases rubber drive wheels have good properties when com¬ pared to metal drive wheels, but in some special types of forest very hard, dry branches form on the trees, which cause great wear on rubber drive wheels.

Due to the occasional slipperiness and great wear, it is sen¬ sible to protect the drive wheels and reduce slipping, when these special circumstances occur.

The use of friction chains made from steel chain is a usual way of reducing slipping. The grip of traditional chains on top of drive wheels manufactured as traditional smooth solid rubber wheels is not very great, because the chain tends to rotate on the contact surface between the tree trunk and the drive wheel.

This causes slipping, which in turn causes an increase in the power required and makes longitudinal measurement difficult, as well as causing the log to be moved backwards and forwards while searching for the cutting point. In stone quarries and similar so-called protector chains are used in excavators and similar.

On account of their massiveness, complexity, and constructional solutions, they are difficult to adapt as drive wheel protector chains.

By means of a rubber drive wheel friction protector in accor¬ dance with this invention, these difficulties can be overcome in a simple manner. By means of the invention it is possible to manufacture a friction protector that protects a rubber drive wheel, increases the gripping surface as the pressure increases, prevents slipping, and is easily installed. The characteristic features of the invention are described in the accompanying Patent Claims. When, in accordance with the invention, the chain that was previously used as a slip-stop is replaced at each place with plates equipped with gripping spikes, the under surface of which is equipped with members that prevent slipping against a rubber surface, a friction protector is created that does not rotate and has a good grip.

In what follows, the invention is illustrated with reference to the accompanying figures, which present various friction protec¬ tors in accordance with the invention.

Figure 1 shows the use of a rubber drive wheel friction protec- tor in connection with the opposing drive wheels of a timber harvester. Figure 2 shows a partial enlargement of Figure 1. Figure 3 shows a form of application of another friction protector. Figure 4 shows a form of application of a third friction protector. Figure 5 shows a slip-stop from the friction protector in

Figure 4.

In Figure 1, the drive wheels are shown as they would appear seen from beneath the harvester, when log 6 is moved as the drive wheels 1 rotate. The pressure of the wheels 1 against the log 6 can be adjusted, which at the same time adjusts their gripping power in relation to the log. On top of each drive wheel 1 there are friction protectors, which consist of slip- stops 2 covering the entire circumference and are formed from separate plates. Gripping spikes 3 are welded onto them. The plate-like slip-stops are connected to one another by means of

triangular connector pieces 4, the length of which can be adjusted by turning them to different positions. On the other hand, here they form auxiliary slip-stops, which prevent the plate-like slip-stops from moving along the circumferential surface of the rubber drive wheel 1. This auxiliary slip-stop can also be arranged in other ways on these plate-like slip- stops 2. The plate-like slip-stops 2 are connected to the circumference support 7 by means of the connector pieces 4 and chains 5.

The triangular connector pieces 4 help during the installation of the friction protector in that by means of them the circum¬ ference of friction protector can be made larger than that of the drive wheel, when it is easy to set the protector on top of the circumference of the drive wheel 1. After this, a sufficient number of the connector pieces are turned to a position that reduces the circumference, when the friction protector tightens round the drive wheel. After this, the connector pieces 4 with

'their slip-stops 2 are locked in place by tightening the chains 5 running from the connector pieces 4 to the attachment points of the circumference supports 7, or in a traditional way by threading them through a circular tensioning chain, which is tightened in a suitable manner. Either the rim of the rubber drive wheel directly, or another corresponding piece, can be used as a circumferential support.

Figure 2 shows schematically the operation of a friction protec¬ tor as it presses against the surface of a tree 6 being moved. In this figure the situation is such that there is great pres- sure from the drive wheels. Depending on the pressure the friction protector can be made to grip the surface of the timber in different ways. When the pressure is small, the outer grip¬ ping spikes 3 of the plate-like slip-stops 2 press very flexibly onto the surface of the timber. When an extremely effective grip is required, pressure is increased, when, due to the flexibility of the rubber drive wheel 1, one or two friction plates are pressed in their entirety against the trunk 6. This friction protector is made to work in such a way that as pressure in-

creases it automatically increases the number of gripping spikes 3 on the surface of the tree being moved, when the area in contact increases. As the plate-like slip-stops 2 cover most of the surface of the drive wheel 1, they provides it with the best possible protection.

Figure 3 shows another form of application of a friction protec¬ tor in accordance with the invention. For operationally similar components, the same reference numbers are used as above. In this version, the abovementioned triangular connector pieces are not used, instead each plate-like slip-stop 2 is attached to the circumferential support 7 by means of its own attachment chain 5. Here the edges of the slip-stops 2 on the side of the chains 5 are shaped as auxiliary slip-stops 8, which correspond to the aforementioned connector pieces 4 in that they prevent the slip- stops 2 from slipping along the circumference of the rubber drive wheel.

The friction protector in Figure 4 is similar to that shown in Figure 3. Here too the same reference numbers as above are used for operationally similar components. As in Figure 3, the circumference of drive wheel 1 is covered with slip-stops 2, which are secured by means of chains 5 to the circumference support 7. In this version, the circumferential support 7 consists of U-loops 9 tightened by nuts 10. In this manner it is easy to tighten the slip-stops 2 to the desired pressure.

Each slip-stop 2 is advantageously in accordance with Figure 5. It is manufactured from flat sheet metal, which, it is true, bends somewhat when the gripping spikes 3 are welded in place. At the ends, strips 11 are formed upwards from the edges, which support the attachment loops 10 from the side. Thus the loop 10 can be securely welded to the base plate. The under parts of the attachment loops 10 are formed by the aforementioned auxiliary slip-stops 8, which press against the rubber drive wheel.