Driver for torque and rotation transfer from a rotational chuck to a drill steel

A driver (3) for the transfer of torque and rotation from a rotation chuck (5) to a drill steel (2), whereby the cross-section of the driver (3) is limited outwards by curves, in particular by arcs, united to form a closed FIG. 6 that can be approximately described as a polygon, and limited inwards by splines (4). The FIG. 6 comprises four sides (7) and four corners (8). The splines (4) comprise a number of spline teeth (10), the number of which is divisible by four.

BACKGROUND OF THE INVENTION

The invention concerns a driver for the transfer of torque and rotation to the drill steel in a rock drilling machine. The driver is an exchangeable part subject to wear, and has been designed for mounting in the gear housing of the rock drilling machine, where its task is to transfer torque and rotation from a rotation chuck to the drill steel. The drill steel can be displaced axially in the driver during the transfer. The driver is for this purpose externally provided with a polygonal profile and internally provided with splines. The polygonal profile and the splines are in the present invention arranged in an innovative manner that increases the lifetime of the driver and reduces the risk of fatigue failure. The invention concerns also a rock drilling machine that comprises at least one such driver.

FIG. 1shows a reduced section of a prior art gear housing1of a rock drilling machine. The upper part, known as the shank adapter, of a drill steel2can be seen in the centre of the gear housing1. The shank adapter is externally provided with splines. The shank adapter is inserted into a known driver3that is provided with internal splines4that correspond to the splines of the shank adapter. The driver3is provided with an external polygonal profile and is mounted into a rotation chuck5that has an internal polygonal profile that corresponds to the polygonal profile of the driver3. The rotation chuck5is arranged on bearings in the gear housing1and is rotated by the rotational motor of the rock drilling machine through a gear (not shown in the drawing). The torque that is transferred may amount to 1000 Nm or more.

The cross-section of the driver3is limited outwards by curves, united to form a closedFIG. 6that is approximately described by a polygon with three sides7and three corners8. This type of united figure is normally known as a “polygon profile”. TheFIG. 6is transversed by three imaginary lines9of symmetry, drawn from the centre of the driver3and passing through the corners8of theFIG. 6such that these are symmetrically distributed around the lines9of symmetry.

The cross-section of the driver3is limited inwards by the splines4with eight spline teeth10and eight spline spaces11. The drawing makes it clear that it is possible to arrange only one of the eight spline spaces11symmetrically around any one of the three lines9of symmetry. When one of the spline spaces11is arranged symmetrically around the uppermost of the lines9of symmetry, two of the spline teeth10acquire an asymmetric distribution around the two lower lines9of symmetry. Similar results would have been obtained if one of the spline teeth10had been initially taken. The asymmetry leads to certain parts being subject to considerably higher load than other parts of the driver3.

FIG. 2shows an enlarged cross-section of one of the spline spaces11of the prior art driver3, the shank adapter of the drill steel2and the rotation chuck5fromFIG. 1. The direction of rotation of the rotation chuck5is shown by an arrow at the bottom. The driver3is arranged such that the ratio between the diameter d2of the bottom circle of the spline4and the diameter d1of the top circle is 1.38. The diameter D2of the top circle of the spline teeth of the shank adapter is adapted such that it constitutes approximately 98% of the diameter d2of the bottom circle of the splines4of the driver3. The arrangement and the contact pressure between the spline teeth10of the shank adapter and the driver3lead to small amounts of the material of the driver3being pressed down to the root radii12of the spline spaces11during the transfer of torque. The material that is pressed down constitutes fracture notches or burrs13along the radii12and impairs in this way its function of protecting from fatigue failure. The drawing shows how these burrs13initiate the formation of cracks in the root radii12.

SUMMARY OF THE INVENTION

The aim of the present invention is to obtain, according to the claims, a driver and a rock drilling machine in which the previously described disadvantages are overcome. The polygonal profile and the splines are arranged in the present invention in an innovative manner that reduces the loads and distributes them symmetrically in the driver. The splines of the driver are so designed that a burr that arises as a consequence of wear is separated from the bottom of the radius. An additional advantage of the invention is that it can be introduced without significant increase in the outer dimensions of the gear housing.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows a cross-section of a driver3a. The driver has essentially the same cross-section along its complete length. The length of the driver3ais adapted such that an acceptable contact pressure is obtained during the transfer of torque. The driver3ais made from bronze, but may be made from cast iron or other material with similar frictional properties.

The cross-section of the driver3ais limited outwards by curves, or to be more precise arcs, united to form a closedFIG. 6. The closedFIG. 6in the present invention comprises four sides7and four corners8and can be approximately described by a convex polygon. A polygon is defined as a plane figure that is limited by straight lines, i.e. by straight curves. If straight lines are drawn between the intersection points of the imaginary extensions of the sides7of the closedFIG. 6, a polygon is formed. (The extensions and the polygon are shown in the drawing by dashed lines.) This fact defines the significance of the concept of “approximately” in this context.

Each side7comprises an arc of a circle and all of the arcs of the circles for all sides7have the same radius and length. The corners8are arranged in a similar manner. Each corner8comprises an arc of a circle and all of the arcs of the circles for all corners8have the same radius and length. It is also possible to allow the sides7or the corners8to comprise other types of arcs and/or curves, than arcs of a circle. The connections between the arcs are arranged at points at which the tangents to the connected arcs coincide. The result of this is that high concentrations of tension do not arise in the driver3a.

The cross-section of the driver3ais limited inwards by splines4that comprise a number of spline teeth, the number of which is divisible by 4, for example, one spline set4with eight spline teeth10and eight spline spaces11. It is also possible to arrange the splines4to have twelve or sixteen spline teeth10. The splines4are arranged such that four of the spline teeth10acquire a symmetrical distribution around imaginary lines9of symmetry that extend from the centre of the driver3athrough the closedFIG. 6. The lines9of symmetry have been drawn such that theFIG. 6is symmetrically distributed around the lines9of symmetry. It is optimal if the splines4are arranged with eight or twelve spline teeth10and such that four of the spline teeth10acquire a symmetrical distribution around imaginary lines9of symmetry that extend from the centre of the driver3athrough the corners8of the closedFIG. 6. The arrangement ensures that loads are minimal and symmetrically distributed within the driver3a. These positive properties are independent of the direction of rotation of the driver3a, and thus the risk of erroneous assembly is small. It is possible also to distribute four of the spline spaces11of the splines4symmetrically around the lines9of symmetry through the corners8. The loads in the driver3awill in this case be somewhat greater, but they will still be lower than in the previously described prior art driver3.

The spline teeth10and spline spaces11of the splines4can be arranged also asymmetrically around the lines9of symmetry through the corners8, as illustrated byFIG. 8. While it is true that the loads will acquire a displaced symmetrical distribution in the driver3aduring the transfer of torque, this distribution may even so be advantageous for the transfer in a specified direction of rotation. The driver3aaccording to the latter design must be assembled such that it acquires the specified direction of rotation.

The relationship between the diameter d2of the bottom circle of the splines4and the diameter d1of the top circle is arranged to be greater than in the prior art driver. (Both d1and d2are shown with dashed circles in the figure.) This brings advantages that will be described in more detail in association withFIG. 4. Good results can be achieved at a ratio of 1.39 or higher, for example a ratio of 1.48±0.02. It is, however, best to arrange the splines4such that the ratio d2/d1is 1.48. Greater ratios that 1.48 can require significant increases in the outer dimensions of the gear housing.

FIG. 4shows how the new ratio d2/d1=1.48 (as shown inFIG. 3) contributes to creating chambers14between the top of the spline teeth of the shank adapter (the drill steel2) and the bottom of the spline spaces11of the driver3a. The shank adapter of the drill steel2will therefore be controlled radially by the tops and the flanks of the spline teeth10of the splines4. The drawing shows also how the diameter D2of the top circle of the spline teeth of the shank adapter constitutes approximately 95% of the diameter d2of the bottom circle of the splines4of the driver3a. A burr13forms as a consequence of wear, in accordance with the same process as has been previously described in association withFIG. 2. However, due to the chambers14, these burrs13are never pressed so deeply down into the bottoms of the spline spaces11such that they reach the root radii12at the transition to the spline teeth10. The burrs13can therefore be said to be separated from the root radii12, and the new driver3ais in this respect better protected against fatigue failure than the prior art drivers3shown inFIGS. 1-2.

It is preferable that the driver3abe arranged such that the chambers14are created between the top of all of the spline teeth of the shank adapter (the drill steel2) and the bottom of all spline spaces11of the driver3ain order to eliminate fracture notches or burrs13also in the radii that experience the least load. It should, however, be noted that the driver3acan be arranged such that only one or a few of the spline teeth of the shank adapter (the drill steel2) make contact with the bottom in only one or a few of the spline spaces11of the driver3a, as is shown inFIG. 7. It is namely the case inFIG. 7that the ratio between the diameter d2(not shown in the drawing) of the bottom circle of the splines4and the diameter dl (not shown in the drawing) of the top circle is not the same for all spline spaces11of the driver3d.

The bottoms of the spline spaces11in the splines4are arranged inFIGS. 3-4as arcs of a circle with a diameter of the bottom circle equal to d2.FIG. 5andFIG. 6show alternative arrangements of the spline spaces11of the splines4of drivers3band3c, respectively. The bottoms inFIG. 5comprise an arc of a circle with a diameter that is considerably smaller than the diameter d2of the bottom circle. The bottoms inFIG. 6comprise a straight line and semicircular arcs at the transition to the spline teeth10. The tops of the spline teeth10of the splines4are arranged as arcs of a circle with a diameter of the top circle equal to d1It is, however, possible to arrange the tops with other diameters or other curves, or other diameters and other curves, than arcs of a circle. The diameter d2of the bottom circle and the diameter d1of the top circle are defined in the arrangements described above, and in similar designs, as the diameters of the imaginary circles (shown with dashed lines in the drawings) that can be narrowly placed with their curves in the region between the circles.

The new arrangement of the splines4of the drivers3a,3b,3c, and3dhave been introduced in the description above such that it includes all spline teeth10and spline spaces11of the splines4. It is, however, possible under certain circumstances to arrange some of the spline teeth10and spline spaces11of the splines4according to the design of the present invention and the remainder of the spline teeth and spline spaces according to the design of the splines in prior art drivers. Such a “combined” driver is to be considered to lie within the scope of the claims of the present application.