WO2024223992A1

WO2024223992A1 - Arm of a tractor hitch device and method for manufacturing an arm of a tractor hitch device

Info

Publication number: WO2024223992A1
Application number: PCT/FI2024/050198
Authority: WO
Inventors: Hannu PAUKAMAINEN; Timo Viikki
Original assignee: Lh Lift Oy
Priority date: 2023-04-27
Filing date: 2024-04-26
Publication date: 2024-10-31

Abstract

The invention relates to an arm (10) of a tractor hitch device, which arm (10) comprises an adjustment tube (80) with a reduction part (85), an inner surface of the reduction part (85) of the adjustment tube (80) having an internal thread (86), and a shaft (71, 72), an outer surface of which has a corresponding external thread, wherein the shaft (71, 72) is at least partially screwed into the adjustment tube (80), and wherein a grease nipple (20) is arranged in the reduction part (85) of the adjustment tube (80) at the internal thread (86). An outer surface of the reduction part (85) of the adjustment tube (80) comprises a raised area (30) where the grease nipple (20) is arranged. The invention also relates to a method for manufacturing an arm (10) of a tractor hitch device.

Description

ARM OF A TRACTOR HITCH DEVICE AND METHOD FOR MANUFACTURING AN ARM OF A TRACTOR HITCH DEVICE

The invention relates to an arm of a tractor hitch device, which comprises an adjustment tube with a reduction part, an inner surface of the reduction part of the adjustment tube having an internal thread, and a shaft, an outer surface of which has a corresponding external thread, wherein the shaft is at least partially screwed into the adjustment tube, and wherein a grease nipple is arranged in the reduction part of the adjustment tube at the internal thread. The invention also relates to a method for manufacturing an arm of a tractor hitch device.

Hitch devices are used in tractors to attach different types of implements to the tractor. Hitch devices comprise a plurality of different arms with the common feature that they comprise a first attachment link and a second attachment link, wherein the length between the attachment links must be adjustable in order to render the arms suitable for use with different tractors and with different implements.

A common hitch device is a three-point hitch device which can be arranged in the rear of the tractor and which includes two drawing arms and one pushing arm, which are generally operated hydraulically. The pushing arm is arranged above the drawing arms and centred between the latter in a horizontal direction. The function of the pushing arm is to control the angle of inclination of the connected implement parallel to the tractor. The drawing arms adjust the height of the connected implement. Lateral stabilizers are also employed between the drawing arms and the tractor by means of which the lateral movement of the implement is limited. By means of the adjustable lifting bar of the drawing arm, it is possible to adjust a height difference between the respective drawing arms and thus an angle of transverse inclination of the connected implement .

It is also possible to use a two-point hitch device, which lacks the pushing arm of the three-point hitch device, to attach implements to a tractor. The drawing arms forming the two points regulate the height of the implement and limit its lateral freedom.

A length adjustment of the arm can be provided by means of a thread or hydraulically according to the prior art. In particular turnbuckle solutions are common. For a length adjustment of the arm between the first attachment link and the second attachment link, a rotatable adjustment tube is frequently used that has two threads in a turnbuckle solution: first threads at a first end of the adjustment screw and second, inverse threads at a second end of the adjustment tube. The adjustment tube is thus freely rotatable relative to the first attachment link and the second attachment link. The adjustment tube can also have a threadless rotary connection at one end and a threaded length adjustment at the other. It is known to reduce an end of the adjustment tube to form the internal thread.

In order to lubricate the threads of the adjustment tube, a lubricant fitting or grease nipple can be arranged at the thread. Normally, a standard grease nipple, e.g. according to DIN 71412, is used. The grease nipple has a first end that is attached to the adjustment tube, typically by means of a threaded coupling, and a second end that is designed to receive a grease gun, from which grease is conducted via the passage running through the grease nipple to the threads of the adjustment tube. The passage between the first end and the second end of the grease nipple contains a check valve, which closes the passage when grease is not being conducted through the grease nipple. The check valve is typically a spring-loaded ball.

A problem with the solutions according to the prior art is that the material of the adjustment tube is typically very thin at the thread, in which case a grease nipple attached to the adjustment tube will strike and jam the thread. In other words, not enough material remains in the adjustment tube at the site of the thread to prevent the grease nipple from striking and jamming the thread. Attempts have been made to resolve the problem of the solutions according to the prior art by, among other things, leaving the grease nipple in a state in which it is not screwed all the way in. However, the reliability of this solution is inadequate and the grease nipple is prone to falling off . In addition, if the end user installs a new grease nipple to replace one that has fallen off, this will likely jam the thread because the end user is likely to screw the grease nipple all the way in. Attempts have also been made to resolve the problem by using a grease nipple with a short thread, but collisions occasionally still occur due to the very small tolerance. The same problem can thus also occur when the end user replaces a used and worn grease nipple with a new one with a longer thread. It is alternatively possible to use a grease nipple with a different thread from the one in the adjustment tube, so that the grease nipple is not screwed all the way in, but problems arise with the grease nipple staying in place and when an end user changes the grease nipple in this case as well.

Instead of a threaded connection, it is also possible to use a drive-type grease nipple, but a drive-type grease nipple will not stay in place as well as a grease nipple with a threaded connection, and a non-threaded grease nipple can cause the same problem when it is driven too deep so that the grease nipple strikes the thread.

It has hitherto been alternatively possible to attach the grease nipple to an unreduced area of the adjustment tube, so that there is no risk of collision, but in this case the effectiveness of the lubrication of the thread is inadequate because the threaded connection is typically located precisely in a reduced area of the adjustment tube.

It is an object of the invention to provide an improved arm of a tractor hitch device, which features an improved attachment of a grease nipple at a thread of an adjustment tube, which enables an improved lubrication of the thread and an improved fixation of the grease nipple to the adjustment tube. The characteristic features of this invention are set out in the attached patent claim 1. A further object of the invention is to provide an improved method for manufacturing an arm of a tractor hitch device, by means of which method an arm is provided that features an improved attachment of a grease nipple at a thread of an adjustment tube, which enables an improved lubrication of the thread and an improved fixation of the grease nipple to the adjustment tube. The characteristic features of this invention are set out in the attached patent claim 11.

An arm of a tractor hitch device according to the invention comprises an adjustment tube with a reduction part, an inner surface of the reduction part of the adjustment tube having an internal thread, and a shaft, an outer surface of which has a corresponding external thread, wherein the shaft is at least partially screwed into the adjustment tube, and wherein a grease nipple is arranged in the reduction part of the adjustment tube at the internal thread. An outer surface of the reduction part of the adjustment tube comprises a raised area where the grease nipple is arranged. More space can thereby be provided between the grease nipple and the thread, so that a sufficient clearance remains between the grease nipple and the thread. There is thus no risk of collision and the grease nipple does not jam the thread.

In other words, there is a hole in the adjustment tube at the raised area to which the grease nipple is attached. Grease can thus be conducted via the grease nipple and the hole into the thread. As the grease nipple is located at the raised area at a distance from the external thread of the shaft, a channel is left between the grease nipple and the external thread .

The arm according to the invention is preferably manufactured by means of a process in which the adjustment tube is reduced in a selected area of the reduction part to a lesser degree than the rest of the reduction part, so that a raised area is formed in the selected area on the outer surface of the reduced part of the adjustment tube, and a grease nipple is attached to the reduction part at the raised area. The reduction is preferably carried out by crimping the selected part of the adjustment tube. The crystal structure of the adjustment tube thus changes smoothly in the area of the reduction part and no discontinuities occur in the structure in the region of the raised area although the crystal structure is condensed due to the reduction.

Preferably, a grease pocket is provided between the adjustment tube and the shaft at the raised area. In other words, the inner surface of the adjustment tube contains a recess at the raised area in which recess the internal thread is slightly less developed over a few turns. This leaves a pocket between the adjustment tube and the shaft for the grease delivered through the grease nipple, whereby the grease spreads into the thread better and thus lubricates the thread better.

In one embodiment, the raised area lies in the selected area of the reduction part in such a manner that the raised area is at a distance from both edges of the reduction part and a length of the raised area in a radial direction is no more than 50% of the circumference of the reduction part. In other words, the raised area does not extend to either edge of the reduction part nor around the reduction part. The length of the raised area in an axial direction can be, for example, up to 80% of the axial length of the reduction part so that at least 10% of the axial length of the reduction part at both edges of the reduction part does not comprise the raised area. This makes the thread structurally strong and reliable, as the raised area for the grease nipple is worked into only a small area in the middle of the reduction part.

In a second embodiment, the raised area extends in an axial direction of the adjustment tube continuously from a first edge of the reduction part to a second edge of the reduction part. In other words, the raised area extends continuously over the entire length of the reduction part. This makes it possible to form a grease pocket over the entire length of the internal thread, so that the thread is well lubricated.

In a third embodiment, the raised area extends in a radial direction of the adjustment tube continuously around the reduction part. The grease can thereby spread well into the thread and the grease nipple can be arranged radially at any point on the reduction part. A material thickness of the reduction part can be 2-10 mm, preferably 4-8 mm, and a height of the raised area measured from the outer surface of the reduction part can be 0.5-5 mm, preferably 1-3 mm. A sufficient amount of space is thereby provided for the grease nipple by means of the raised area, while otherwise the grease nipple jams the thread. The material of the tube is preferably metal, most preferably stainless steel.

Preferably, the grease nipple is arranged in the adjustment tube by means of a thread. The grease nipple can also be arranged without a thread by means of a drive-type grease nipple, but with a threaded connection the grease nipple remains firmly fixed in the adjustment tube and is easily replaceable .

Preferably, the reduction part is at a first end of the adjustment tube or at a second end of the adjustment tube. The attachment of a shaft can thus be carried out in a technically simple manner.

Preferably, both the first end of the adjustment tube and the second end of the adjustment tube have a reduction part and a grease nipple. In an adjustment tube utilizing a turnbuckle solution, this allows the threads at both ends of the adjustment to be lubricated. The reduction part and the grease nipple can also be at only one end of the adjustment tube.

Preferably, the reduction part of the adjustment tube is produced by crimping a selected part of the adjustment tube. The crystal structure of the adjustment tube thus changes smoothly in the area of the reduction part and no discontinuities occur in the structure in the region of the raised area although the crystal structure is condensed due to the reduction.

In a method according to the invention for manufacturing an arm of a tractor hitch device, which arm comprises an adjustment tube with a reduction part, an inner surface of the reduction part of the adjustment tube having an internal thread, and a shaft, an outer surface of which has a corresponding external thread, wherein the shaft is at least partially screwed into the adjustment tube, in which method a selected part of the adjustment tube is reduced in order to form a reduction part, and an internal thread is worked into an inner surface of the adjustment tube in the reduction part, and a grease nipple is attached to the reduction part at the internal thread. The adjustment tube is reduced in a selected area of the reduction part to a lesser degree than the rest of the reduction part in order to form a raised area on an outer surface of the reduction part, and a grease nipple is attached to the reduction part at the raised area. This allows more space to be provided between the grease nipple and the thread, so that a sufficient clearance remains between the grease nipple and the thread. There is thus no risk of collision and the grease nipple does not jam the thread. The crystal structure of the adjustment tube thus changes smoothly in the area of the reduction part and no discontinuities occur in the structure in the region of the raised area although the crystal structure is condensed due to the reduction.

Preferably, the first end and/or the second end of the adjustment tube is reduced in order form a reduction part. This allows a shaft to be attached to the first end and/or to the second end of the adjustment tube. In one embodiment, the selected part of the adjustment tube is crimped by means of a crimping machine in order to form the reduction part, wherein the crimping machine has radially movable jaws, wherein a recess is worked into at least one of the jaws prior to the reduction of the adjustment tube. In other words, the reduction of the adjustment tube preferably occurs by crimping. The raised area on the outer surface of the adjustment tube can thus be readily worked by means of a small, but surprising, modification to an existing crimping machine. The shape of the jaw or jaws can be formed freely, so that it is possible to form a raised area of any shape on the outer surface of the adjustment tube. In this context, working a recess also means that one or more jaws can be entirely lower than the other jaws. Alternatively, one or more jaws can also be removed from the crimping machine.

Preferably, the selected part of the adjustment tube is reduced against a mandrel in order to form the internal thread. In other words, the mandrel will thus have a shape corresponding to the desired internal thread, which forms the internal thread on the inner surface of the reduction part of the adjustment tube when the end of the adjustment tube is reduced against the mandrel. Alternatively, the internal thread can be worked after the reduction by rolling. By reducing the adjustment tube against a mandrel, a total time required for the working of the adjustment tube is shortened while the internal thread produced is neater, so that it is also possible to form a larger grease pocket under the raised area inexpensively, as the internal thread no longer needs to be worked following the reduction of the adjustment tube.

Preferably, the adjustment tube is heated to a temperature of 500-1500 °C, preferably 600-1300 °C, before the reduction.

More specifically, preferably at least the reduction part of the adjustment tube is heated to said temperature before the reduction. As the adjustment tube cools, it thus contracts to its final shape around the mandrel, so that a particularly neat internal thread can be worked into the adjustment tube quickly and easily.

Preferably, the aforementioned heating of the adjustment tube occurs by way of induction heating. This allows the adjustment tube to be heated to a selected temperature very quickly, even in a few seconds.

The described formation of an internal thread in an adjustment tube by reducing the adjustment tube against a mandrel, and preferably by heating the adjustment tube prior to the reduction, can also be applied in the manufacture of adjustment tubes which do not have a grease nipple or a raised area on the outer surface of the reduction part.

The arm of the tractor can thus be manufactured by means of a method for manufacturing an arm of a tractor hitch device, which arm comprises an adjustment tube with a reduction part, an inner surface of the reduction part of the adjustment tube having an internal thread, and a shaft, an outer surface of which has a corresponding external thread, wherein the shaft is at least partially screwed into the adjustment tube, in which method a selected part of the adjustment tube is reduced in order to form a reduction part, and an internal thread is worked into an inner surface of the adjustment tube in the reduction part. The adjustment tube is reduced against a mandrel in order to form the internal thread.

In other words, the mandrel thus comprises a shape corresponding to the desired internal thread, which forms the internal thread on the inner surface of the reduction part of the adjustment tube when the end of the adjustment tube is reduced against the mandrel. By reducing the adjustment tube against a mandrel, a total time required for the working of the adjustment tube is shortened while the internal thread produced is neater. After the reduction, the mandrel can be screwed out of the adjustment tube and a shaft can be screwed at least partially into the adjustment tube. The adjustment tube can be heated to a temperature of 500-1500 °C, preferably 600-1300 °C, before the reduction against the mandrel. As the adjustment tube cools, it thus contracts to its final shape around the mandrel, so that a particularly neat internal thread can be worked into the adjustment tube quickly and easily .

In another embodiment, a selected part of the adjustment tube is reduced by rolling. It is thus possible to form a raised area on an outer surface of the adjustment tube in an alternative manner, wherein the raised area extends in a radial direction of the adjustment tube continuously around the reduction part.

The invention is illustrated in the following in detail with reference to the attached drawings illustrating embodiments of the invention, wherein

Figure 1 illustrates an arm of a tractor hitch device according to the invention,

Figures 2a-2c illustrate an adjustment tube of an arm according to the invention, wherein the adjustment tube comprises a grease nipple.

Figures 3a-3c illustrate steps of a method for manufacturing an adjustment tube of an arm according to the invention, Figures 4a-4c illustrate a jaw of a crimping machine used in the method for manufacturing an adjustment tube of an arm according to the invention,

Figure 5 illustrates a step of a method for manufacturing an adjustment tube of an arm according to the invention as an axonometric projection,

Figure 6 illustrates a second method for manufacturing an adjustment tube of an arm according to the invention,

Figure 7 illustrates a third method for manufacturing an adjustment tube of an arm according to the invention,

Figures 8a-8c illustrate a method for manufacturing an internal thread of an adjustment tube of an arm according to the invention.

Figure 1 illustrates an arm 10 of a tractor hitch device according to the invention, wherein the arm 10 in this case is a pushing arm of a three-point hitch device. The arm 10 according to the invention can also be a lifting bar or a lateral stabilizer or any other length-adjustable arm. The structures illustrated in dashed lines in Figure 1 are internal structures of the arm 10 that are not visible from without .

The arm 10 comprises a first attachment link 61 and a second attachment link 62. A first shaft 71 is attached to the first attachment link 61, and a second shaft 72 is attached to the second attachment link 62. Interposed between the first attachment link 61 and the second attachment link 62 is an adjustment tube 80. The first shaft 71 is attached to a first end 81 of the adjustment tube 80 and the second shaft 72 is attached to a second end 82 of the adjustment tube 80. The adjustment tube 80 is used for adjusting the length of the screw-adjustable arm 10 so that the arm features a length adjustment implemented by means of threads. In order to provide the length adjustment, an outer surface of the first shaft 71 has an external thread 73 and an inner surface at the first end 81 of the adjustment tube 80 has a corresponding internal thread 86 (Fig. 2c) , so that the first shaft 71 is configured to be partially screwable into the adjustment tube 80. In this case, the solution in question is a so- called turnbuckle solution, i.e. an outer surface of the second shaft 72 also has an external thread 74 and an inner surface at the second end 82 of the adjustment tube 80 has a corresponding internal thread, so that the second shaft 72 is also configured to be partially screwable into the adjustment tube 80. This screw-adjustable pushing arm additionally has a quick-release lock 15 with which the second shaft 72 can be locked in any position in the adjustment tube 80 in a continuous manner. The first attachment link 61 here comprises a quick-coupling grapple for coupling an implement to the arm 10 and the second attachment link 62 comprises a hemispherical coupling for coupling the arm 10 to a tractor, although it is also possible to use other types of attachment links in an arm 10 according to the invention.

The first end 81 or the second end 81 of the adjustment tube 80 can also be a non-threaded rotary connection. In other words, it is only essential for the invention that at least one end of the adjustment tube 80 has a threaded connection that is lubricated. In the case of Figure 1, both the first end 81 and the second end 82 of the adjustment tube 80 have a grease nipple 20 at the internal thread 86 for lubrication, although it is accordingly possible for a grease nipple 20 to be at only one end of the adjustment tube 80. The adjustment tube 80 here comprises a reduction part 85 at both the first end 81 and the second end 82. An internal thread 86 is provided in the reduction part 85. The reduction part 85 comprises a raised area 30 according to the invention where a grease nipple 20 is arranged.

An arrangement of a grease nipple 20 in the adjustment tube 80 according to the invention is illustrated in more detail in Figures 2a-2c. Figures 2a and 2b show an outside view of the adjustment tube 80 directly from the side and directly from above. Figure 2c illustrates the adjustment tube 80 in cross section. The adjustment tube 80 according to the invention thus has a raised area 30 in the reduction part 85, at which raised area 30 a grease nipple 20 is arranged. Thanks to the raised area 30, a clearance between the grease nipple 20 and the external thread 73, 74 of the shaft 71, 72 can be augmented, so that there is no risk of the grease nipple 20 striking the external thread 73, 74 and thus blocking a length adjustment of the arm 10. The raised area 30 lies here in a selected area of the reduction part 85 in such a manner that the raised area 30 does not extend to either edge of the reduction part 85 or around the reduction part 85. In the embodiment of Figures 2a-2c, the adjustment tube 80 is symmetrical in a longitudinal direction, but in other embodiments of the invention the adjustment tube 80 can be asymmetrical, and the grease nipple 20 and the raised area 30 can be provided at only one end of the adjustment tube 80.

Figures 3a-3c illustrate a method for manufacturing an adjustment tube 80 of an arm 10 according to the invention in partial cross sections. It is essential for the invention that at least one end 81, 82 or some other selected part of the adjustment tube 80 is reduced in such a manner that a raised area 30 is left in the reduction part 85 for the grease nipple 20. The reduction part 85 can also be provided in some part of the adjustment tube 80 other than an end 81, 82 of the adjustment tube. When a crimping machine with radially movable jaws 95 is used to produce the adjustment tube 80, it is possible to pass the entire adjustment tube 80 through the crimping machine, so that the reduction part 85 can be provided in any part of the adjustment tube 80 in the longitudinal direction. Preferably, the reduction part 85 is at the first end 81 and/or at the second end 82 of the adjustment tube 80.

The reduction part 85 of the adjustment tube 80 can be produced, for example, with a Finn-Power FP120 crimping machine. The crimping machine in question has radially movable jaws 95, whose path of movement can be adjusted extremely precisely, with a precision of up to 0.1 mm. The jaws 95 are individually easy to remove and to replace, so that the individual jaws 95 in this type of machine can be worked into a desired shape, with which it is possible to affect the final shape of the reduced piece. It is evident that the invention can also be replicated by means of other analogous crimping machines. Alternatively, the raised area 30 according to the invention can also be obtained, for example, by rolling.

When a crimping machine with a plurality of radially movable jaws 95 is used to reduce the adjustment tube 80, a recess 96 is worked into one or more jaws 95, which creates the raised area 30 in the reduction part 85 of the adjustment tube 80. It is also possible to use one or more jaws 95 that are lower than the other jaws 95, so that the raised area 30 is created in the adjustment tube 80 over the entire length of the jaw 95.

The adjustment tube 80 in its original state is a straight metal pipe of a constant thickness, preferably made of steel. In Figure 3a, the first end 81 of the adjustment tube 80 has already been reduced. The second end 82 of the adjustment tube 80 is placed between the radially moving jaws 95. One of the jaws 95 contains a recess 96. The structure of this jaw 95 is illustrated in more detail in Figures 4a-4c. In Figure 3b, the second end 82 of the adjustment tube 80 is reduced between the jaws 95, and the recess 96 of the one jaw 95 creates a raised area 30 in the reduction part 85. In Figure 3c, the jaws 95 have been moved back to their original position, leaving the reduced shape of the second end 82 of the adjustment tube 80, i.e. the adjustment tube 80 has undergone plastic deformation.

Following the reduction, a thread is preferably worked at the site of the raised area 30 for the attachment of the grease nipple 20. It is also possible for just a hole to be worked at the site of the raised area 30 for a drive-type grease nipple 20.

Following the reduction, an internal thread 86 is also worked into the reduction part 85 of the adjustment tube 80. The internal thread 86 can be worked, for example, by lathing or tapping. An alternative method for working an internal thread 86 is also illustrated in Figures 8a-8c.

Figures 4a-4c illustrate a design of a jaw 95 that can be used to produce a raised area 30. Figure 4a illustrates a view of the jaw 95 from above. A recess 96 is worked into the jaw 95, while an edge of the jaw 95 additionally has a bevel 97 here by means of which a corresponding bevel is provided in the edge of the reduction part 85 between the reduction part 85 and an unreduced part of the adjustment tube 80. Figure 4b illustrates the section A-A indicated in Figure 4a and Figure 4c illustrates the section B-B indicated in Figure 4b. The recess 96 worked into the jaw 95 here has a depth H of 1.4 mm and a length L of 11.6 mm, which thus determine the height and length of the raised area 30 created in the reduction part 85 of the adjustment tube 80. The raised area 30 formed in the adjustment tube 80 is thus essentially square when viewed from above. The size and shape of the recess 96 of the jaw 95 can also differ from those illustrated in Figures 4a-4c.

Figure 5 illustrates in an axonometric projection the step of the method corresponding to Figure 3b, in which an end of the adjustment tube 80 is reduced between the radially moving jaws 95. The number of jaws 95 can vary depending on the crimping machine used. Eight jaws 95 are provided here. In a practical embodiment, there can be, for example, 5-10 jaws 95 with which an even, radial crimping is achieved at an end of the adjustment tube 80. The range of motion of the jaws 95 is 68 mm here. In a practical application, the range of motion is preferably at least 40 mm. In the method, a first end of the adjustment tube 80 can be reduced, for example, in such a manner that a diameter of an outer edge of the end of the adjustment tube 80 is reduced by 5-15 mm, preferably by 8-10 mm, from the original state.

Figure 6 illustrates a second method for manufacturing an adjustment tube 80 of an arm 10 according to the invention. Here, one of the jaws 95 of the crimping machine is entirely lower than the others, so that a raised area 30 is created which extends in an axial direction of the adjustment tube 80 continuously from the first edge of the reduction part 85 to the second edge of the reduction part. If necessary, the outer surface of the reduction part 85 of the adjustment tube 80 can be worked further after the reduction, for example by decreasing the surface area of the raised area 30 on the outer surface.

Figure 7 illustrates a third method for manufacturing an adjustment tube 80 of an arm 10 according to the invention. Here, a recess is worked into each jaw 95 of the crimping machine, so that a raised area 30 extends in a radial direction of the adjustment tube 80 continuously around the reduction part 85. A raised area 30 that extends in a radial direction of the adjustment tube 80 continuously around the reduction part 85 can also be formed by rolling. Preferably, an empty space which acts as a grease pocket 22 can remain below the raised area 20 between the internal thread 86 and the external thread 73, 74 in this as well as in other embodiments. Thanks to the grease pocket 22, it is possible to improve the lubrication of the thread as the grease spreads better into the thread.

The size and shape of the raised area 30 according to the invention can also differ from the examples illustrated in the foregoing.

Figures 8a-8c illustrate an alternative method for manufacturing an internal thread 86 of an adjustment tube 80 of an arm 10 according to the invention. Alternatively, an internal thread 86 of an adjustment tube 80 can be produced in conjunction with the reduction by placing a mandrel 45 inside the adjustment tube 80 prior to the reduction and reducing the adjustment tube 80 against the mandrel 45. This makes it possible to achieve a strong and neat internal thread 86 as well as a larger grease pocket 22, because it is no longer necessary to work the internal thread 86 after the reduction. In Figure 8a, the mandrel 45 is inserted into an unreduced second end 82 of the adjustment tube 80. In Figure 8b, the second end 82 of the adjustment tube 80 is reduced against the mandrel 45 with a crimping machine, whereby the helical pattern on the outer surface of the mandrel 45 is impressed on the inner surface of the second end 82 of the adjustment tube 80. In Figure 8c, the jaws 95 of the crimping machine have been returned to their initial position and the mandrel 45 has been removed by rotation, after which the internal thread 86 formed by the mandrel 45 remains on the inner surface of the second end 82 of the adjustment tube 80.

Preferably, it is also possible to heat the adjustment tube 80 or, more precisely, the end of the adjustment tube 80 that is to be reduced, for example the second end 82, so as to be red hot, i.e. to a temperature of 500-1500°C, preferably 600- 1300°C, prior to the reduction, i.e. in the step shown in Figure 8a. The red-hot end of the adjustment tube 80 is then crimped against the mandrel 45. As it cools, the end of the adjustment tube 80 contracts further against the mandrel 45, whereby a very neat internal thread 86 forms in the end of the adjustment tube 80.

The method for manufacturing an internal thread 86 illustrated in Figures 8a-8c, i.e. the reduction of an end of an adjustment tube 80 against a mandrel 45, can also be applied to adjustment tubes 80 in which a grease nipple 30 is not used. This makes it possible to accelerate the production of an adjustment tube 80, since a separate step for working the internal thread 86 is no longer required, but rather the internal thread 86 is formed simultaneously with the reduction of the end of the adjustment tube 80.

Claims

1. An arm (10) of a tractor hitch device, which arm comprises

- an adjustment tube (80) with a reduction part (85) , an inner surface of the reduction part (85) of the adjustment tube (80) having an internal thread (86) , and

- a shaft (71, 72) , an outer surface of which has a corresponding external thread (73, 74) , wherein the shaft (71, 72) is at least partially screwed into the adjustment tube (80) , and wherein a grease nipple (20) is arranged in the reduction part (85) of the adjustment tube (80) at the internal thread (86) , characterized in that an outer surface of the reduction part (85) of the adjustment tube (80) comprises a raised area (30) where the grease nipple (20) is arranged.

2. The arm (10) according to claim 1, characterized in that a grease pocket (22) is provided between the adjustment tube (80) and the shaft (71, 72) at the raised area (30) .

3. The arm (10) according to claim 1 or 2, characterized in that the raised area (30) lies in a selected area of the reduction part (85) in such a manner that the raised area (30) is at a distance from both edges of the reduction part (85) and a length of the raised area (85) in a radial direction is no more than 50% of the circumference of the reduction part ( 85 ) .

4. The arm (10) according to claim 1 or 2, characterized in that the raised area (30) extends in an axial direction of the adjustment tube (80) continuously from a first edge of the reduction part (85) to a second edge of the reduction part (85) .

5. The arm (10) according to claim 1 or 2, characterized in that the raised area (30) extends in a radial direction of the adjustment tube (80) continuously around the reduction part (85) .

6. The arm (10) according to any of claims 1-5, characterized in that a material thickness of the reduction part (85) is 2-10 mm, preferably 4-8 mm, and a height of the raised area (30) measured from the outer surface of the reduction part (85) is 0.5-5 mm, preferably 1-3 mm.

7. The arm (10) according to any of claims 1-6, characterized in that the grease nipple (20) is arranged in the adjustment tube (80) by means of a thread.

8. The arm according to any of claims 1-7, characterized in that the reduction part (85) is at a first end (81) of the adjustment tube (80) or at a second end (82) of the adjustment tube (80) .

9. The arm (10) according to any of claims 1-7, characterized in that both the first end (81) of the adjustment tube (80) and the second end (82) of the adjustment tube (80) have a reduction part (85) and a grease nipple (20) .

10. The arm (10) according to any of claims 1-9, characterized in that the reduction part (85) of the adjustment tube (80) is produced by crimping a selected part of the adjustment tube (80) .

11. A method for manufacturing an arm (10) of a tractor hitch device, which arm (10) comprises

- a shaft (71, 72) , an outer surface of which has a corresponding external thread (73, 74) , wherein the shaft (71, 72) is at least partially screwed into the adjustment tube (80) , in which method a selected part of the adjustment tube (80) is reduced in order to form a reduction part (85) , and an internal thread (86) is worked into an inner surface of the adjustment tube (80) in the reduction part (85) , and a grease nipple (20) is attached to the reduction part (85) at the internal thread, characterized in that the adjustment tube (80) is reduced in a selected area of the reduction part (85) to a lesser degree than the rest of reduction part (85) in order to form a raised area (30) on an outer surface of the reduction part (85) , and a grease nipple (20) is attached to the reduction part (85) at the raised area (30) .

12. The method according to claim 11, characterized in that the first end (81) and/or the second end (82) of the adjustment tube (80) is reduced in order to form a reduction part ( 85 ) .

13. The method according to claim 11 or 12, characterized in that the selected part of the adjustment tube (80) is crimped by means of a crimping machine in order to form the reduction part (85) , wherein the crimping machine has radially movable jaws (95) , wherein a recess (96) is worked into at least one of the jaws (95) prior to the reduction of the adjustment tube (80) .

14. The method according to any of claims 11-13, characterized in that the selected part of the adjustment tube (80) is reduced against a mandrel (45) in order to form the internal thread.

15. The method according to any of claims 11-14, characterized in that the adjustment tube (80) is heated to a temperature of 500-1500 °C, preferably 600-1300 °C, before the reduction.

16. The method according to claim 15, characterized in that the heating occurs by way of induction heating.

17. The method according to claim 11 or 12, character- ized in that the selected part of the adjustment tube (80) is reduced by rolling.