This invention relates to chain idler of guide bar on chain sawing device, and particularly a chain idler which has a construction as simple as possible, and on which the lubri¬ cation is ensured in all circumstances.

Guide bars, around which an endless cutting saw chain is rotating with a speed of 45 - 70 m/s, are used on chain saws, such as power saws and cutting device of multi-function machines. The chain idler is installed on the nose of the guide bar, with the purpose to help the saw chain to turn 180° around the nose of the guide bar and to bear all the great loadings which rests on the nose of the guide bar.

The chain idlers on guide bars are traditionally and almost in all available solutions insufficiently lubricated and very difficult to be installed or changed. Lubrication is naturally extremely important, while the speed of rotation of the idler may be 2000 - 6000 rpm. and the loads on it are huge, especially when the nose of the guide bar get squeezed in a way or another.

One well-known construction of the chain idler is such, where a needle bearing, consisting of 32 needles, has been put around the hub which is riveted with four rivets in a score on the nose of the guide bar and the inner surface of the outer cage of the idler functions as the exterior ring of the bearing. Besides damageing the inner slide surface by riveting, usually forming bulbs on it, this solution has even some other disadvantages.

It is obvious that, if for example a driver of a multi¬ function machine has to change the idler on the guide bar in the forest in cold weather, it is an impossible task to carry out in acceptable time and reliably, when trying to edge a bearing, with 32 needles between two very narrow surfaces, through the score on the nose of the guide bar.

It also has to be mentioned that the lubrication of the chain idler in question is as insufficient as the lubrication of all other similair solutions. Also the bearing surface provided by a needle is very small.

The purpose of this invention is to solve the disadvantages on the technical level and to produce a chain idler which gets a sufficient and an abundant lubrication in all cir¬ cumstances, and which is changeable in an easy and simple way. In accordance to the invention, also the problem which has troubled the guide bar and the chain idler when urea has been used to be sprayed on the sawn surface of the stump, i.e. the corrosive effect of the urea on the construction.

In addition, in accordance to one form of performance of this invention, the meaning is to produce a simplified and an improved construction, regarding the bearing.

The advantages of this invention will be achieved as it is presented to be characteristic in the attached patent claims.

The invention will now be described more detailed with reference to the attached drawings, in which

Figure 1 presents the side view of the construction of chain idler in accordance to the invention and

Figure 2 presents another embodiment in accordance to the solution of the invention.

Figure 1 presents in accordance to the invention, as mentioned, the side view of the chain idler 1 which consists of an immoveable hub 2, surrounded by a rotating cage 3. The hub 2 is fixed to the steel guide bar in any desired way, but especially so that is it possible to remove the hub and again to fix it rapaidly. The fixing may be done by using a bushing-like part provided with an female thread and a corresponding peglike part provided with a compatible

male thread. Figure 1 shows the head 4 of the peglike part of this fixing system. In the middle of this head is a suitable hollow or hole 5, for example for an alien key. With the help of this key, the fixing parts can be screwed into each other and fix the hub into the score of the bar nose at the same time.

As can be seen on figures 1 and 2, the chain idler construc¬ tion does not include any needle bearing. Consequently, when handling a chain idler one has to deal only with two parts, namely the hub 2 and the cage 3 (Fig. 2) . A change of the bearing to a slide bearing or, as it is presented in figure 1, to a ball bearing 8 is possible due to the surprising and exceptional design of the chain idler in accordance to the invention.

As it is known, a cutting chain which rotates around the guide bar in an endless loop, as well as around the idler, leaning against the groove, is lubricated by feeding a desired amount of oil through a channel at the root of the guide bar to the groove of the bar, where from it is transported to the idler. In accordance to the invention, a part of this oil will be catched with the help of grooves or hollows 6, which have been made on the rotating idler, and will be transported further towards the hub. On the slide bearing (Fig. 2) , between the hub and the outer cage, is an overpressure oil bed formed, which lubricates the bearing in an effective way.

On the other hand, while the grooves or hollows 6 are on the outer surface of the idler and the cage 3 is loose to a certain degree in the score of the bar nose, the oil will spread effectively even on the surface of the idler as well as on the inner surface of the score. This ensures effective lubrication even if the chain idler is exposed to extreme pressure.

In figure 2 there is a diagrammatic presentation that the

grooves or hollows 6 on the surface of the idler have been positioned on the both sides of the outer cage, and the direction of the grooves is essentially the same on both sides. This is the solution when the guid bar is not turned around every now and then. This means that the idler rotates allways to the same direction. In this case, grooves on both sides, becomes the oil pressure towards the hub more effective. A guide bar, which is not turned, is used especially when urea is sprayed during the cutting on the sawn surface of the tree, especially on the surface of the stump. Urea is though a very corrosive substance which causes more problems on the durability of guide bar/chain idler consturction. Even these problems are solved in accordance to a solution of the invention.

In regular guide bar constructions, it is usual to turn the bar every now and then, so that the side which earlier was upwards comes downwards and is set for stronger wear. In that case does the direction of rotation of the idler naturally change and the grooves or hollows on the surface of the outer cage have to be able to transport sufficient lubrication to the bearing even in this direction. In practice this has been simply solved so that the direction of the grooves or hollows on the surface are essentially contrary, like presented in figure 1, so that when the bar is turned will the grooves on one side of the idler still be in a

"catching" position, regarding the direction of rotation.

It is obvious that the grooves of the chain idler on the other side will always bring oil out from the hub, in this embodiment.

According the invention the oil is catched at the root of a cog on the outer cage, and the oil is pressed towards the hub forming an oil bed on which the bearing moves well lubri- cated. But in the case of a turnable guide bar, as it was mentioned above, a part of the oil from the bearing gets out through the channels on the opposite side, causing oil circulation by this, which again ensures the lubrication.

The exit of oil is naturally less forced than the hurl towards the bearing, while the starting point locates on a con¬ siderable smaller circle.

If using a guide bar which is not turnable, a so called urea bar, the lubrication is surprisingly good despite the fact that even urea/water is transported with the chain. The solution according the invention does actually catch oil more effective than water/urea, so that expressly the oil gets towards the bearing and urea/water stays on the outer cage.

In accordance to one form of performance, which has found to be good, the hub is provided with oil pockets 7, as is shown in figure 2. Their purpose is to maintain oil supply in the hub. These pockets 7 supply oil for lubrication, for example when the temperature of the bar nose rises due to pressure or bending. In this way the lubrication is ensured even in severe circumstances. The number of oil pockets 7 is not critical, a few pockets 7 is enough.

As mentioned above, Figure 1 presents an embodiment for assembling the hub 2 and the outer cage 3 together, in which the needle bearing of the prior art has been replaced with ball bearing, which in the presented form has several advantages compared to the needle bearing.

Figure 1 presents a solution, according which there is a concave groove, known as such, on the outer surface of the hub, and a corresponding concave groove on the inner surface of the cage, so that if a suitable ball is put between the hub and cage, the above mentioned concave surfaces forms bearing surfaces for the balls 8. The bearing balls 8 then again are put on their place according the invention so that on the hub 2 and cage 3 is bored a side boring which in figure 1 is illustrated with reference number 9. The diameter of the boring is essentially the same as the diameter of the bearing balls, but especially a bit larger. The boring is

made when the hub 2 and the cage 3 are in their presumable final positions with the bearing on its place. The boring is made from the side, exactlly in the middle of the gap between the hub and cage, so that the boring covers as much on both parts in the direction of the radius, and to the middle of the bearing surface in the depth.

The assembling of the bearing goes in this case as follows. The borings 9 on the hub 2 and the cage 3 are placed so that they match. The bearing balls 8 are pressed through the boring 9, one by one, between the concave surfaces where from they easily roll _. to fill the room between the bearing surfaces, for example when the bearing is held the boring upwards. When the last bearing ball is on its place, the hub and cage are rotated to opposite directions, and the balls can not drop out from their places any more, while the halves of the boring 9 and the bearing balls do not easily match, if not matched by purpose. On the other hand, due to the dimensioning, half of the balls can be collected on the inner side of the cage before the hub is assembled on its place, and the rest of the bearing balls can be put on their place in the above mentioned way.

A complete product, which is coherent without any measures, has been thus achieved. The ball bearing, which consists of several bearing balls 8, keeps the hub 2 and the cage 3 together. In this case, handling and changing of such a compact assembly is very simple, and it is not necessary to worry about bearing needles any more.

Usually the hub 2 is a bit thicker than the cage 3 because by this the cage is given free space to rotate in the score of the guide bar nose. The dimensioning of the bearing can be done so that the diameter of a bearing ball is close to the dimension of the cage, but the dimension of the bearing is rather chosen to get a maximum bearing surface for the bearing.

A considerably larger bearing surface is reached with a ball bearing arrangement in accordance to the invention, compared to the needle bearing according the prior art. It can be said that the improvment on the bearing surface is roughly at least 30 %. -And instead of the linelike contacting surface of the needle bearing it is now achieved a better form on the contacting surface. The total solution in accordance to the invention does not cause any risk of the lubrication not to be ensured in all circumstances.

It is obvious that the solution according the invention can be modified in many different ways. Therefore the inclination of the grooves or hollows 6 is, with respect to the direction of the radius, chosen on the base of tests in working conditions. It is thought that the inclination is at its best at 5 - 15° . It is also obvious that the grooves or hollows can be formed so that maximum benefits are achieved. The grooves can be equal in width or they can be, for example, wider or deeper at the outer end. The depth is chosen so that it does not cause any faults in the durability but it is adequate for the purpose. Also the number of grooves or hollows can be chosen as needed.