Abstract:
The invention relates to an arrangement in a forestry machine ( 1 ), in which there are front and rear units ( 2, 3 ) and bogie wheels ( 14, 15 ) mounted on a set of swing axles ( 12 ), as well as a crawler mat ( 20 ) running around the bogie wheels ( 14, 15 ) and an auxiliary wheel ( 16 ) outside the set of swing axles ( 12 ), and in which the auxiliary wheel ( 16 ) is essentially permanently mounted in bearings in the front and/or rear unit ( 2, 3 ), so that, when the set of swing axles ( 12 ) turns, the tension of the crawler mat ( 20 ) is maintained by means of flexible elements connected to its perimeter, which are principally formed of the flexibility of the auxiliary wheel ( 16 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application of PCT application PCT/FI2008/050531, filed Sep. 24, 2008, and claims the benefit of priority from Finnish Patent Application No. 20075668, filed Sep. 25, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an arrangement in a forestry machine, in which there are front and rear units and bogie wheels mounted on set of swing axles, as well as a crawler mat running around the bogie wheels and an auxiliary wheel outside the set of swing axles, and in which the auxiliary wheel is essentially permanently mounted in bearings in the front and/or rear unit, so that, when the set of swing axles turns, the tension of the crawler mat is maintained by means of flexible elements connected to its perimeter. The invention also relates to a forestry machine using the arrangement. 
         [0004]    2. Description of the Related Art 
         [0005]    In a conventional forestry machine, there are front and rear units pivoted relative to each other. The steering of a machine of this type is usually implemented as so-called articulated steering, in which case steering operating devices, such as hydraulic cylinders, are fitted between the aforementioned units pivoted to each other, in order to provide the power needed as required to set the units at an angle to each other. Which unit is usually referred to as the front unit can vary according to the application, but in this connection it can be agreed that the front unit will be the unit located closest to the cab of the forestry machine, from which is controlled the primary power source located at it, which is used to produce the power required to move and steer the forestry machine and the work devices in it. Such work devices are represented by a loader and a grab attached to it. The forestry machine thus described is particularly an, as such, known loader tractor. The other main type of forestry machine is a harvester, by means of which other kinds of timber harvesting are performed, such a felling, stripping, measuring, and cutting trees. A harvester can be implemented using a chassis structure that largely corresponds to that of a loader tractor, though on the other hand different kinds of construction are also known. However, nearly without exception two units pivoted to each other are to be found in all kinds of forestry machine. In addition, numerous different types of forestry machine, which are not separately described here, are also known. 
         [0006]    As timber must be harvested increasingly from forests on ground with a poor load-bearing capacity, such as bogs and other peat-rich areas, it will be seen that an attempt must be made to minimize the surface pressure imposed by the machine on the ground. Various kinds of implement and devices are known, which can travel on poorly supporting ground, for example, with the aid of wide and long crawler mats. In the case of forestry machines, attempts have been made to increase bearing capacity in light machines with the aid of various kinds of crawler mats. In the case of heavier machines, particularly loader tractors, a low surface pressure has been aimed at mainly by one or more of the machine&#39;s two-wheeled axles being replaced with a set of so-called swing axles, so that a four-wheeled machine, for example, can be converted into a six or eight-wheeled machine. In loader tractors, the set of axles under the load space are typically bogie axles. It is also known to use in connection with the said type of swing-axle crawler tracks, i.e. crawler mats, which are arranged to rotate around the wheels of the bogie axles and thus create a large load-bearing contact surface area against the ground. One such crawler solution is disclosed in patent publication FI822636A. 
         [0007]    However, the relative benefit provided by crawler mats remains small, particularly on ground with a reasonably good bearing capacity, which is the case in the majority of felling sites. Besides, the crawler-mat construction wears easily and is expensive to maintain. Similarly, the effectiveness of the complicated crawler-mat construction may be poor in terms of power use, compared to a simple wheel, or even a swing bogie. The use of a crawler mat and nonskid devices also protects the tyre on stony and difficult ground. 
         [0008]    A crawler track rotating around the bogie wheels fitted in connection with bogie axles will not, however, in all conditions be able to provide a sufficiently low surface pressure. 
         [0009]    Finnish patent 78428 discloses a crawler-mat arrangement for bogie vehicle. Such bogie vehicles can include forestry machines, which are both vehicles, especially harvesters, equipped with a timber-harvester device, such as a harvester head, and vehicles, especially loader tractors, equipped with a load space. Adequate tension in the crawler mat will improve its operation. Complicated tensioning devices are often associated with, as such, known crawler mats. 
         [0010]    In proper tracked vehicles, the crawler mat is typically carried on several wheels, or sets of wheels, but these cannot be considered in this case, instead a search must now be made for a simple conversion arrangement for placing a crawler mat around the bogie wheels of a set of swing axles, with the aid of a suitable additional wheel (or additional wheels). In other words, the intention is to find a solution for equipping an as such known loader tractor with simple additional equipment, so that it can operate effectively on ground with a substantially lower bearing capacity. Publication U.S. Pat. No. 3,744,857 discloses a crawler-mat arrangement built around bogie wheels and an auxiliary sprocket acting as a drive sprocket. Thus, the crawler mat rotates around two freely rotating pneumatic tyres and a special drive sprocket, which sprocket is set clearly higher than the bogie axle. The bogie axles have longitudinal play, which is pressurized, for example, pneumatically. This allows the set of bogie axles to swing, which is its intention. The bogie axles can also be locked, in which case the pneumatic tyres will flex to permit the bogie to turn. However, it is obvious that the pneumatic tyres on the bogie axles of, for example, a heavy forestry vehicle will not be able to flex sufficiently, if the fact that they should also simultaneously carry a considerably large load is also taken into account. The pneumatic tyres dimensioned for a full load require a pressure of at least 4-5 bar in the case of a typical forestry machine tyre, in which case the tyre will not have the flexibility required for the free rotation of a set of bogie axles. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention is intended to create an improved crawler mat arrangement and a forestry machine using it, which is simpler than previously. The characteristic features of the arrangement according to the invention are stated in Claim  1 . Correspondingly, the characteristic features of the forestry machine according to the invention are stated in Claim  14 . According to one embodiment of the invention, the flexibility of the auxiliary wheel is achieved in such a way that it is a pneumatic tyre, in which a lower pressure than in the bogie wheels can now be used. 
         [0012]    According to one embodiment, the auxiliary wheel is essentially the same kind of pneumatic tyre as the bogie wheels, but preferably with a smaller diameter. When examined on a flat base, the auxiliary wheel is preferably only slightly higher than the bogie wheels of the set of bogie axles, thus ensuring the full rotatability of the set of bogie axles and the entire forestry machine in normal conditions, however. In other words, when moving on a flat, hard surface, the length in contact with the ground is essentially equally as great as in the case of a track running around conventional set of bogie axles and the crawler track rotating the bogie wheels of the set of bogie axles. As the size of the auxiliary wheel is about 80-90% of that of a bogie wheel, the upper surfaces of all three wheels lie on essentially the same level when the set of bogie axles is straight. 
         [0013]    In one embodiment, the auxiliary wheel is detachably attached, for example, to a sub-chassis like an additional bunk, i.e. a sliding bunk, the attachment arms of which are pushed into the muff of the rear unit. In this embodiment, the actual additional bunk is not necessarily needed, but can be easily added, if the timber being transported requires it. It should be noted that a muff arrangement of this kind is very common nowadays. 
         [0014]    The auxiliary wheel can also be arranged with transmission, in a manner that is as such known, to increase the traction created by the bogie wheels. In some situations, as the magnitude of the friction of the inner surface of the bogie is limited, this may be necessary, if the force transmitted to the crawler track by the bogie wheels of the bogie axles exceeds the friction and the said wheels begin to slip inside the track. 
         [0015]    In tests made with the aid of a prototype, the crawler mat was able to maintain its load-bearing capacity in bog conditions, in which the ground was so boggy that moving on foot was difficult and a similar machine equipped with conventional bogies could not move forward at all. 
         [0016]    Other embodiments and advantages of the invention are described hereinafter in connection with the description of the examples. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings, in which 
           [0018]      FIG. 1  shows one forestry machine, more specifically a loader tractor, according to the invention, 
           [0019]      FIG. 2  shows the crawler-mat arrangement of the forestry machine of  FIG. 1 , when the vehicle crosses a ditch, 
           [0020]      FIG. 3  shows a top view of a second solution according to the invention in a forestry machine in greater detail, with the rear unit of the forestry machine partly dismantled, 
           [0021]      FIG. 4  shows an angled bottom view of the rear unit of the forestry machine of  FIG. 3 , 
           [0022]      FIG. 5  shows rear view of the rear unit of the forestry machine of  FIG. 3 , 
           [0023]      FIG. 6  shows an exploded view of the rear unit of the forestry machine of  FIG. 3 , 
           [0024]      FIG. 7  shows a direct side view of the rear unit of the forestry machine of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows one basic solution of a forestry machine. In the forestry machine  1  there is a front unit  2  and a rear unit  3 , which are connected to each other by a pivot. On the front unit  2  is the cab  4  of the forestry machine, from which the vehicle is steered and the power source  5  and work devices, in this case a loader  6  and a grab  7  attached to it, are controlled. The load space is defined by bunks  8 , which include an additional bunk  18 . 
         [0026]    In terms of the present invention, it is essential that, in the forestry machine  1  there is a set of swing bogie axles  12 , which can rotate around the upper axle  13  of the bogie axles  12 . The set of swing bogie axles  12 , more simply the bogie axles, is carried by the bogie wheels  14  and  15 , which like conventional ones are powered. The rear part of the chassis  9  of the rear unit  3  includes an additional bunk in its own quick-release sub-chassis, which is pushed into muffs fitted to the sides of the chasses  9  of the rear unit (see also  FIGS. 3-7 ). An auxiliary wheel  16 , which preferably has a slightly smaller diameter than the bogie wheels  14  and  15 , is attached to both sides of the same auxiliary beam  19 . By means of a chassis of this kind, the upper surfaces of both the bogie wheels  14  and  15  and the auxiliary wheel  16  are thus at approximately the same height, so that the crawler mat  20  surrounding them lies essentially horizontally on top of them. 
         [0027]    The chassis  9  of the rear unit  3  typically consists of two main parts  9   a  and  9   b,  which are attached to each other by means of a flange-type bolted joint  9   c.  In addition, under the chassis  9  a set of bogie axles  12 , carrying the rear unit  3 , is attached by means of a bolted joint. In the embodiment shown, the set of bogie axles  12  is thus precisely a set of swing bogie axles, in which the two bogie wheels  14  and  15  of the bogie axles  12  are supported on a bogie frame  12 . 1 . In other words, the bogie frames  12 . 1  are located on both sides of the chassis and are arranged to rotate relative to the upper axle  13  of the set of bogie axles  12 . 
         [0028]    In this example, the pneumatic tyres of the bogie wheels  14  and  15  have a diameter of 1340 mm (pressure, for example, 4,5 bar) and the pneumatic tyre of the auxiliary wheel  16  has a diameter of 1171 mm (pressure, for example, 2 bar). The flexibility of the auxiliary wheel  16  is great enough for the bogie axles  12  to be able to rotate without difficulty from one extreme position to the other. In this case, the variation in the perimeter surrounding the wheel in the height position of the auxiliary wheel is so small, that the flexibility of the pneumatic tyre is sufficient to keep the crawler mat  20  suitably tensioned in all positions of the bogie axles. Thus, the full range of movement of the swing bogie can be exploited. 
         [0029]    Generally, the pressure of the auxiliary wheel is reduced by 30-70%, preferably 40-50% of the pressure of the pneumatic tyres of the bogie wheels. At the same time, the size of the auxiliary wheel is generally 75-95%, preferably 80-90% of the size of a bogie wheel and the auxiliary wheel is installed off the ground by 10-25%, preferably 13-17%, of its diameter. 
         [0030]    Because the front bogie wheel of the powered bogie axles tends to rise due to the torque of the bogie axles when the forestry machine is driven forwards, it is generally advantageous to place the auxiliary wheel behind the powered bogie wheels, so that when the rearmost bogie wheel of the bogie axles drops down, the auxiliary wheel and the additional part of the crawler-mat begin to carry the weight. In addition, the rise of the front bogie wheel of the swing-bogie axles assist the bogie axles to rise up on soft ground. Another reason is often that the load often weighs so heavily on the rear, that the auxiliary wheel at the rear improves load-carrying in precisely the right place. 
         [0031]    As such, the flexible auxiliary wheel can also be in front of the bogie wheels, or both in front of, and behind them. 
         [0032]    The crawler-mat arrangement according to the invention can also be used in connection with the front unit. In other words, for example, a conventional eight-wheeled loader tractor, equipped with two sets of bogie axles, can quite well be equipped with two, or even four crawler-mat arrangements according to the invention, in which case an extremely low surface pressure will naturally be achieved. 
         [0033]    The crawler-mat arrangement according to the invention can naturally also be fitted, using a corresponding principle, to a harvester machine and its set of bogie axles, instead of to a loader tractor. 
         [0034]    Corresponding attachments for installing an auxiliary wheel can be fitted to the front unit of the machine. 
         [0035]    According to  FIG. 2 , a forestry machine  1  equipped with a crawler mat  20  according to the invention can also easily cross various kinds of obstacle, in this case a ditch  30 . The bogie wheels  14  and  15  are in the extreme position of the bogie axles and a long extension is achieved for the crawler mat  20  with the aid of the auxiliary wheel  16 . However, it is obvious that it is not desirable to increase the total width of the forestry machine unnecessarily, because in thinning, for example, the driving track is often narrow and the trees remaining after thinning must not be damaged. This means that additional contact surface area should be sought in the longitudinal direction of the forestry machine. The fact that the additional wheel of the crawler-track arrangement according to the invention is located to the rear of the conventional swing-bogie axles does not substantially, if at all, increase the total length of the machine when loaded. The timber loaded conventionally on the load space of a loader tractor always protrudes to some extent behind the rearmost bunk. 
         [0036]    On the other hand, in an 8-wheeled loader tractor, there may not necessarily be space for an additional wheel in front of the rear set of axles, without restricting the turning circle. 
         [0037]    In addition to the auxiliary wheel&#39;s own flexibility, it is possible to use as such known suspensions or other crawler-mat tensioners in addition. In one embodiment, the air pressure of the auxiliary wheel can also be adjusted while the machine is moving and the wheel rotating. 
         [0038]      FIGS. 3-7  show a second embodiment of the invention. The rear unit is, in a known manner, attached to the front unit through a central pivot  29 . The figures show in detail the rear unit  3  while the same reference numbers as above are used for components with a corresponding function. Some of the wheels are omitted for clarity, so that the other parts can be seen more clearly. The hubs of the bogie wheels  14 ,  15  are marked with the reference numbers  14 . 1  and  15 . 1 .  FIG. 7  shows that the hub  16 . 1  of the auxiliary wheel  16  is on a higher line that those of the bogie wheels  14 ,  15 , as in the version of  FIGS. 1 and 2 . In the version shown, the hub  16 . 1  of the auxiliary wheel  16  is nearly at the level of the upper axle  13  of the set of bogie axles  12 . 
         [0039]    In this version, the sub-chassis  19  carrying the auxiliary wheel  16  is attached to the rear end rearmost main part  9   a  of the chassis  9 , by means of a flange attachment  22 . The opposing flanges  22 . 1  and  22 . 2  can be seen in the exploded view  6 , and are secured to each other, for example, by means of bolts. By means of this solution, it is quite simple to attach and detach the sub-chassis  19  together with the auxiliary wheels. 
         [0040]    In this version, there is a flanged joint  22  between the chassis  9  and the sub-chassis  19 . The pins of the additional bunk  18  are located to slide through the sub-chassis into sleeves in the chassis  9 . 
         [0041]    According to  FIG. 4 , lateral movement means  23  can be fitted to the attachment of the auxiliary wheel  16 , in order to adjust the track width. In this case, for example, three bolts are used to lock the fixed axle to the selected position in the muff of the sub-chassis. Instead of bolts, other attachment means can be used, or even a separate attachment mechanism (not shown). By making the track width adjustable, a single auxiliary-wheel accessory can be used to cover a large number of loader tractors of different sizes and models, thus achieving a greater degree of modularity. 
         [0042]      FIG. 4  shows a tension plate  24  fitted between the attachment flanges  9   c  and  9   d.  Generally, a tension plate, or some other structure transmitting tensile stress is located on the lower surface of the chassis  9 , between the front end of the rear main part  9   a  of the chassis  9  and the front main part  9   b  of the chassis  9 . The tension plate or other structure transmitting tensile stress can be separate, or it can be part of the rearmost main part  9   a  or the frontmost main part  9   b.  The use of such a tension plate or other structure transmitting tensile stress is advantageous and necessary, because a loading of this kind is not normally imposed on the rear unit of a loader tractor and the structure is thus not optimized for a loading in this direction. Depending on ground conditions, the use of an additional axles like that of the present invention may impose even large loadings on the chassis  9  of the rear unit  3 . These stresses will particularly tend to bend the main parts  9   a  and  9   b  of the chassis relative to each other. An attempt can be made to prevent this by placing a tension plate between the attachment flanges  9   c  and  9   d.  In practice, the axle of the auxiliary wheels receives the load and tends to bend the main parts  9   a  and  9   b  of the chassis  9  of the rear unit  3  relative to each other. More specifically, the rearmost main part  9   a  seeks to rotate upwards relative to the frontmost main part  9   b.  With the aid of a tension plate, the chassis of the rear unit can be reinforced to withstand the strains caused by the use of an auxiliary wheel. The application of auxiliary wheels according to the invention in different kinds of loader tractors is possible without extensive alteration work. The thickness of the tension plate is preferably 8-20 mm, so that it is able to withstand a sufficiently large tensile strain, without, however, reducing the ground clearance of the machine unnecessarily.  FIG. 4  also shows an enlarged picture of a detached tension plate  24 . The structure of the rear unit shown in the figures is stiffened simply by means of the tension plate shown. The chassis of the rear unit can also be manufactured in an different way. In that case, according to the invention, the chassis is, however, reinforced in such a way that it will withstand a situation, in which only the auxiliary wheels carry the load. In other words, the chassis is reinforced in such a way that only the auxiliary wheels are load-bearing. In the situation in question, the weights of the rear unit and the load are supported only on the central pivot between the front and rear units and on the auxiliary wheels. This situation can appear, for example, when crossing a ditch, or on steep slopes.