fig1 shows part of the chassis 10 of a forage harvester on which there is mounted an engine driving a pulley 12 , a cutter driven by a pulley 14 and a blower driven by a pulley 16 . the engine , cutter and blower are not shown in the drawing but reference may be made to gb 2 414 373 for a fuller description of the harvester . the blower and the cutter are driven by a belt 18 which also passes over an idler roller 20 and a tensioning roller 22 . because the blower pulley 16 can move between two different positions ( for the reasons explained previously ), a tensioning system 24 is required that is capable of maintaining the belt 18 correctly tensioned in both positions of the pulley 16 and when the blower and pulley 16 are moving between these two positions . the tensioning system of the invention is shown in greater detail in fig2 to 6 . the roller 22 is mounted on the end of a spring biased tensioning rod 34 . the rod 34 carries a first abutment 36 for a spring 40 which surrounds the rod 34 . the other end of the spring 40 acts against a second abutment 42 which is connected to the chassis 10 of the forage harvester . conventionally , the second abutment cannot move relative to the chassis and installation involves fitting the spring over the rod , adjusting the position of the rod in the second abutment and the position of the abutment on the rod until the desired tension is achieved . this is a very tiring and time consuming procedure and requires space for the tools needed to achieve the correct tensioning . in the illustrated embodiment of the invention , the second abutment is formed by a collar 42 mounted on an arm 26 which is pivoted about a pin 28 relative to the chassis 10 . the collar 42 lies on one side of the arm 26 and its other side is secured by a tie bar 30 of adjustable length to a pin 32 mounted on the pivot frame carrying the blower . the tie bar 30 is formed by two parts in threaded engagement with one another , so that its length can be adjusted by turning a nut 31 . the abutment 36 is defined by a flange at the end of a tube 38 which surrounds the tensioning rod 34 . the tube 38 has inserts at each of its two ends , the abutment 36 may be formed by a flange of one of these two inserts , which is in threaded engagement with the tensioning rod 34 . the insert 44 at the opposite end of the tube 38 , as more clearly shown in fig6 , has a head 44 a which is hexagonal to enable it to be gripped by means of a spanner . beyond the hexagonal head 44 a there is a sleeve 44 b which is threaded both internally and externally . a locknut 48 serves to prevent rotation of the sleeve 44 b and with it the tube 38 relative to the rod 34 once the spring tension has been correctly set . a second nut and washer 46 screwed onto the external thread of the sleeve 44 b serve as an end stop to allow the spring 40 to be retained and tensioned about the tube 38 prior to its installation over the rod 34 . this allows the spring 40 and tube 38 to be fitted as a sub - assembly over the rod 34 , thus saving time and effort during the installation . the collar 42 that acts as the second abutment for the spring 40 , is constructed as swivel that is free to pivot about pins 42 a ( see fig5 ) between two plates 60 and 62 mounted on rods 64 and 65 that project laterally from the pivotable arm 26 . the plate 60 is removable to allow the collar 42 to be secured to and separated from the pivotable arm 26 . the tie bar 30 is held in a similar manner in a swivel on the opposite side of the pivotable arm 26 and is connected through the pivotable arm 26 to the collar 42 by means of rod 64 . fig5 also shows that when installed in a forage harvester , a panel 68 of the harvester separates the arm 26 from the tensioning rod 34 , the two rods 64 and 65 passing through arcuate slots in the panel 68 . at the commencement of assembly , the tie bar 30 , while connected to the pivot frame of the blower , is extended to its maximum length so that the arm 26 is rotated clockwise in fig2 . a pre - assembly comprising the tube 38 , the collar 42 , the first abutment 36 , the insert 44 , the nut with washer 46 and the spring 40 , is next placed over the end of the tensioning rod 34 remote from the roller 22 . the pre - assembly unit is screwed onto the tensioning rod 34 and secured by locknut 48 . the length of the rod 34 projecting from the tube 38 is set so that the collar 42 aligns with the hole in the plate 62 . the plate 60 is then bolted to the rods 64 and 65 to secure the collar 42 to the arm 26 and tie bar 30 . next , the nut 31 is rotated to shorten the tie bar 30 and cause the arm 26 to pivot about the pin 28 , in a counter clockwise direction as viewed in fig2 thus moving the tensioning arm with collar 42 towards the belt 18 . as the arm 26 pivots , the collar 42 slides over the outer surface of the tube 38 and compresses the spring 40 between itself and the first abutment 36 defined by the flange of the insert at the opposite end of the tube 38 . the length of the tie bar 30 is chosen so that when the two parts of the tie bar are turned in completely and thus the tie bar is at its minimum length , the hexagonal head 44 a of the insert 44 becomes accessible . fully tensioning the belt 18 by the tensioning roller 22 is achieved by rotating the tube 38 relative to the tensioning rod 34 . when the locknut 48 is loosened , the tube 38 may be turned by gripping the hexagonal head 44 a thus moving the tensioning rod 34 with the tensioning roller towards the belt 18 while the tube 38 is being turned inside the threaded first abutment 36 . after the correct setting has been achieved , the locknut 48 is tightened again to retain the setting . because the tie bar 30 is anchored to the pivot frame of the blower , the point 32 will move when the blower is repositioned and by suitable selection of the geometry of the tie bar 30 and the pivoting arm 26 it is possible to ensure that the belt tension will remain correctly set in both positions of the blower . removing the tensioning roller 22 from the belt 18 for any reason , can be done by only loosening nut 31 and varying the length of the tie bar 30 . when the nut 31 is turned , the arm 26 will move clockwise around pin 28 thus moving the collar 42 because of their connections through rods 64 and 65 . however , this turning of the nut 31 needs to be against the tension of the spring 40 and this entails a large effort . to simplify the task , a u - shaped spacer 80 ( see fig4 and 6 ) can be slipped over the tube 38 to bridge a large part of the gap between the collar 42 and the stop but 46 before the nut 31 is undone . only a limited distance over which the nut 31 needs to be turned against the force of the spring 40 remains . once the spacer is firmly wedged between the stop nut 46 and the collar 42 , undoing the nut is no longer against the force of the spring . when further undoing the nut 31 , the complete tensioning system 24 will move away from the belt by rotating about pin 28 without changing the relative distance between the first abutment 36 and the collar 42 . re - assembly then merely requires repositioning the tensioning roller 22 by turning the nut 31 and shortening the length of the tie bar 30 . the complete tensioning system 24 will then move towards the belt . only the last distance over which the tie bar 30 needs to be shortened will be against the force of the spring . once the u - shaped spacer 80 is no longer wedged between the collar 42 and washer of the nut 46 , the collar 42 will be moved towards the first abutment 36 together with the shortening tie bar 30 . once the tie bar 30 is again in its shortest position , the tensioning of the belt is complete . in this way , the tensioning system can be removed and replaced quickly and as long as the tie bar 30 is shortened to its original length , the tension setting will not be affected and will not require adjustment . when not in use , the u - shaped spaced 80 can be secured to the arm 26 in a storage position , as shown in fig3 and 5 . if the tensioning system 24 needs to be dismantled for any reason , it would be possible to reverse the above steps and to remove the pre - assembly unit from between the plates 60 and 62 . the complete installation and tensioning the belt by the tensioning system needs to be done by using the variable tie bar 30 and the hexagon 44 a .
a tensioning system for a drive belt of a blower of a forage harvester includes a tensioning roller , a rod for moving the tensioning roller towards and away from the belt , a spring surrounding the rod and acting between a first abutment mounted on the rod and a second abutment connected to the chassis of the harvester to urge the roller towards the belt . the chassis connected abutment is carried by an arm that is movable relative to the chassis and anchored by a tie bar .