Profile tool

Abstract

The profile tool for the cutting of work pieces in the form of spiral and hypoid bevel gears, especially for motor vehicles, has several sections in the form of circles or straight edges. On some of the sections, a profile is optionally radially overlaid which is a nth order polynomial.

Description

[0001] According to the preamble of claim 1, this invention relates to a profile tool for cutting work pieces in the form of spiral and hypoid bevel gears, specially for transmission of motor vehicles.

[0002] An optimization of modern transmissions for motor vehicles regarding power density, transmission precision and noise level reduction implies also an operation-oriented layout of the prevalently hardened and cut toothed gears. The widely known involute toothings are thus being increasingly provided with profile modifications in order to make possible, by desired tip and root relief, shock-free contact ratios within the active flanks. For the root area, a fillet section as transition from the active flank to the bottom of the tooth gap is a required condition for root strength. In the grinding of cutters, the generation of a chamfer on the root is needed when, during the toothed gear hobbing, the cutter also assumes the generation of a head edge fissure. A rounding or chamfer is also often provided as transition from the active flank to the frequently roughly tolerated outer diameter. For special cases, special toothings are used, such as the so-called symmarc toothings, for heavy-load transmissions.

[0003] The multiplicity of profile elements and the operation-oriented layout of the toothings create a tendency to further automation. The flexibility needed for this, for example, of the dressing of this multiplicity of profile elements by means of a CNC dresser for the partial roller grinding, has been described in an article published in Zeitschrift Werkstatt und Betrieb, 124, 1991, No. 8, pages 661 to 663, entitled “Complex Profiles of Double-Coned Grinding Bodies for Numerically Controlled Dressing of Tooth Flanks”.

[0004] The CNC dresser can have here a rotating dressing tool in the form of a diamond molding roller. The perpendicular position of the rotational axis of the diamond molding roller is determined by the working range. The dresser spindle is situated upon a cross slide movable in two CNC axes. The diamond molding roller is guided along the grinding wheel outline, there being taken into account its geometric defining quantities, that is, the profile radius and the diameter. Compared with existing dressing tools, diamond molding rollers have a substantially greater stability of the profile radius so it is possible exactly to also dress grinding wheel outlines having large profile angular area. They are thus suitable both for partial roller grinding and for profile grinding.

[0005] The profile coordinates of grinding wheels, that is, the nominal outline, is calculated here with a special software on the basis of work piece data taking into account the specific conditions of the partial wheel grinding or of the profile grinding.

[0006] The calculated grinding wheel profiles are mathematically describable basic shapes, specifically straight edges for the partial roller grinding and involutes for the profile cutting. The best known CNC controls can directly process only straight edges, arcs or splines. If for the above described reasons, modifications are overlaid on the basic shapes, then these must be described generally by tables of interpretation points in view of the complex calculation.

[0007] For the cutting of spiral and hypoid bevel gears, such as used in bevel gear sets of motor vehicle transmissions, to date there have been used profile tools where the profiles have been defined exclusively by using straight edges and circles and combinations thereof. The profile shape that can be generated in traditional manner diverges considerably from the ideal shape, especially in the processing of bevel gears in the single parts cutting method. The needed corrections on the meshing gear, that is the pinion, are practicable only with limitations. Of this reason, this intrinsically commercial method can be applied only to large ratios.

[0008] The problem of this invention, taking into consideration the increasing demands on the functionality of bevel gear sets, is especially the noise level, the load capacity and the relocation capacity, the same as with regard to an easy assemblage and economic production to propose a profile tool with which the possibilities of design in the development of bevel drives are improved and special profiles are made possible.

[0009] Based on a profile tool of the kind described in detail above, this problem is solved with the features stated in the characteristic part of claim 1; advantageous developments are described in the sub-claims.

[0010] Therefore, the invention provides that the profile of a profile tool for cutting spiral and hypoid bevel gears, which profile is exclusively defined by the use of straight edges and circles and combinations thereof, is modified by overlaying in radial direction a nth order polynomial. The profiles of said sections result then from the radial overlaying of the conventional profile elements, that is, straight edge and/or circle with the new profile element, that is the nth order polynomial.

[0011] The origin of the coordinates can be freely selected for each polynomial used and in the simplest case is in the transition from one section to the other.

[0012] The advantages attained by the inventive radial overlaying of nth order polynomials for defining the tooth profile is that for generating the work piece geometry, via the K1 coefficients, more degree of freedom can be added. This enlarges the possibility of design in the development of bevel drives and makes special profile shapes possible. The profile divergences, for example, on a bevel gear, can thereby be considerably reduced.

[0013] As mentioned above, the generation of the tool profile shape by the machine kinematics is prior art. This can be done on the production machine and also on a special machine for tool production or tool reprocessing. By adequate development and adaptation of the software, the inventive profiles can be generated on the tool.

[0014] The invention is explained in detail herebelow with reference to the drawing that shows an advantageous embodiment of the inventively designed profile tool. In the drawing:

[0015] FIG. 1 shows a radial section through such a tool; and

[0016] FIG. 2 shows an enlarged representation of one part of the tool.

[0017] In FIG. 1 is shown a radial cut through an inventively designed profile tool adequate for cutting spiral and hypoid bevel gears such as for the bevel drive of a motor vehicle. This tool conventionally has a profile with a section 1 in the form of a straight edge on the tool front face and a length of >=0, a second section 2 in the form of a corner radius for generating the work piece fillet section and with a length of >0, a section 3 in the form of a straight edge or of a circular cut for generating a root relief and with a length of >=0, a section 4 in the form of a straight edge or of a circular cut for generating the primary work piece flank and with a length of >0 and a section 5 in the form of a circular cut for generating a tip relief on the work piece and with a length of >=0.

[0018] It is now provided according to the invention that to said known profile sections in the form of straight edges and circles, another profile element be added which is described by a nth order polynomial. Said profile element can optionally be used in the sections 3 to 5, the profile within these individual sections resulting from the radial overlaying of the two profile elements, that is, a straight edge and/or a circle with the nth order polynomial.

[0019] The origin of the coordinates for each polynomial used can be freely selected and in the simplest case lies in the transition from one section to the adjoining section.

[0020] The individual polynomial can here be defined, as shown in FIG. 2, as follows:

&Dgr;—rp=K2*&Dgr;—xp2+K3*&Dgr;—xp3+. . . Ki*&Dgr;—xpi+. . . +Kn*&Dgr;—xpn

[0021] In the enlargement to this polynomial in which the exponents are integral, there also applies the use of non-integral exponents xi in the following form:

&Dgr;—rp=&Sgr;(K1*&Dgr;—xpxi)

[0022] as part of the inventive profile improvement.

[0023] The Ki coefficients are real numbers which, as needed, can be freely selected for each section and in the special case can also assume the value 0.

[0024] It is also possible, according to the invention, to provide profile forms defined by dot sequences or splines when they can be approximated as combination of the above described profile elements (straight edge, circle and polynomial) in the effective area, that is, of the formation of the cutting on the work piece with a maximum radial divergence of 0.003 mm and when the most favorable approximation by straight edge and circle is more inaccurate.

Reference numerals

[0025] 1 profile section

[0026] 2 profile section

[0027] 3 profile section

[0028] 4 profile section

[0029] 5 profile section

Claims

1. Profile tool for cutting work pieces in the form of spiral and hypoid bevel gears, especially for transmissions of motor vehicles, wherein the profile of the tool contacting the work piece has a first section (1) in the form of a straight edge on the tool front face, a second section (2) in the form of a corner radius for generating a fillet section, a third section (3) in the form of a straight edge or of a circular segment for generating a root relief, a fourth section (4) in the form of a straight edge or of a circular segment for generating the primary flank and a fifth section (5) for generating a tip relief, characterized in that for generating the fillet section, for generating the primary flank and for generating the tip relief, on the profile sections (3, 4, 5) is optionally radially overlaid a profile which is a nth order polynomial.

2. Profile tool according to claim 1, characterized in that the origin of coordinates of the nth order polynomial can be freely selected.

3. Profile tool according to claim 1, characterized in that the origin of coordinates of the nth order polynomial is on the transition point between two adjoining sections.

4. Profile tool according to any one of the preceding claims, characterized in that the nth order polynomial has the following form:

&Dgr;—rp=K2*&Dgr;—xp2+K3*&Dgr;—xp3+... Ki*&Dgr;—xpi+... +Kn*&Dgr;—xpn

wherein the ki coefficients are real numbers and the exponents are integral.

5. Profile tool according to any one of the preceding claims, characterized in that the nth order polynomial has the following form:

&Dgr;—rp=&Sgr;(K1*&Dgr;—xpxi)

wherein the Ki coefficients are real number and the exponents xi are not integral.