This application is based upon and claims the benefit of priority from Japanese patent application No. 2020-119938, filed on Jul. 13, 2020, the disclosure of which is incorporated herein in its entirety by reference.
The present disclosure relates to a method for manufacturing a gear.
Published Japanese Translation of PCT International Publication for Patent Application, No. 2014-519986 (Patent Literature 1) discloses a method for manufacturing a tooth part of a drive spindle for driving a roll of a rolling mill or the like. In the manufacturing method disclosed in Patent Literature 1, a step of processing the tooth root of the arched tooth part so that it is lowered and a step of processing the tooth tip thereof so that it is lowered are performed separately.
In Patent Literature 1, since the processing of a tooth part is divided into a plurality of steps, a precision error is more likely to occur than when the tooth part is processed in just one step. Meanwhile, forming a tooth profile by a quadratic function causes a problem that it is difficult to achieve both reduction of the risk of a collision of tooth tips and quietness.
The present disclosure has been made to solve the above-described problem and an object thereof is to provide a method for manufacturing a gear which is capable of reducing the risk of occurrence of a precision error in a tooth profile and achieving both reduction of the risk of a collision of tooth tips and quietness.
A first exemplary aspect is a method for manufacturing a gear, the method including: setting a function f(x) for forming a predetermined tooth profile in a gear, the function f(x) being defined so that: a surface shape of the tooth profile from a tooth root to a tooth tip has a vertex; a difference between a radius of curvature of the surface shape of the tooth profile at the tooth root and a radius of an arc or a radius of curvature of a parabola at the tooth root is within a predetermined value, the radius of the arc or the radius of curvature of the parabola at the tooth root being in contact with the vertex; a difference between a radius of curvature of the surface shape of the tooth profile at the tooth tip and the radius of the arc or a radius of curvature of the parabola at the tooth tip is equal to or greater than a predetermined value; and the radius of curvature of the surface shape of the tooth profile at the tooth tip becomes smaller than the radius of the arc or the radius of curvature of the parabola at the tooth tip; and forming the tooth root and the tooth tip by using the function f(x).
According to the present disclosure, it is possible to reduce the risk of occurrence of a precision error in a tooth profile and achieve both reduction of the risk of a collision of tooth tips and quietness.
The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure.
An embodiment according to the present disclosure will be described hereinafter with reference to the drawings. The components equivalent to each other are denoted by the same reference sign throughout the drawings, and redundant descriptions will be omitted.
The embodiment relates to a method for manufacturing a gear, the gear having a plurality of teeth and transmitting the rotational motion between two axes by engagement with teeth of a mating gear.
A side surface of the tooth 11 is a tooth flank 12, a part of the tooth 11 on the tip side thereof is a tooth tip 14, and a part of the tooth 11 on the side of a tooth groove formed between the teeth 11 adjacent to each other is a tooth root 15.
When the shape of the tooth flank 12 of the gear 10 is designed, it is classified into the two shapes described below. The first shape is an involute curve, which is an ideal shape that achieves an ideal engagement when the gear is completely rigid and there is no assembly error. The tooth 11 having the tooth flank 12 having an involute curve is formed into a symmetrical standard gear tooth profile 13. The second shape is a corrected shape obtained by taking the quietness and the smoothness of engagement into consideration based on a shape error and an assembling error.
Normally, when the gears 10 and 20 are engaged with each other, the tooth tip and the side surface of a gear causes interference with a mating gear or puts high surface pressure on the mating gear, and thus wear occurs. For example, in a state in which the gears 10 and 20 are rotated at a high torque, when the gears 10 and 20 are engaged with each other, the respective teeth 11 and 21 are deformed by a load and hence a deflection occurs in a direction indicated by an arrow in
Further, when the tooth flanks of the teeth that are to be engaged with each other next are not in the phase in which they are originally engaged, the tooth tip of the gear 20, for example, interferes with the tooth root of the gear 10 or puts a high surface pressure (contact stress) on the tooth root of the gear 10, and local wear of the teeth results. Engagement in which wear has occurred impairs quietness and the lifetime of the tooth tip and, in the worst case, a risk of causing destruction of the tooth tip arises.
As measures for overcoming the above problem, for example, a tooth tip relief shape (a tooth tip relief) obtained by correcting the tooth profile of a standard gear can be used. The actual shape of the tooth profile is a geometric shape formed by combining an ideal shape and a corrected shape, and the corrected shape will be described below.
In each of
As a corrected shape of the tooth shape which takes quietness into careful consideration, a parabolic shape, an arc shape, and the like can be used. In
The surface shape of the tooth profile from the tooth root to the tooth tip has a vertex. A point of contact between the vertex and an ideal shape is defined as O. Further, v is an end of the tooth tip side, and −u(v>u) is an end of the tooth root side. Further, u is located between the vertex and the tooth tip. Further, c is an arbitrary proportional constant. By changing c, it is possible to change the shape of the tooth profile. Further, c shown in
As shown in
In the example shown in
To address the above problem, the inventor of the present disclosure has conceived the following manufacturing method in which the tooth root and the tooth tip are processed in one step. A method for manufacturing a gear according to the embodiment includes: setting a function f(x) for forming a predetermined tooth profile in a gear, the function f(x) being defined so that: a surface shape of the tooth profile from a tooth root to a tooth tip has a vertex; a difference between a radius of curvature of the surface shape of the tooth profile at the tooth root and a radius of an arc or a radius of curvature of a parabola at the tooth root is within a predetermined value, the radius of the arc or the radius of curvature of the parabola at the tooth root being in contact with the vertex; a difference between a radius of curvature of the surface shape of the tooth profile at the tooth tip and the radius of the arc or a radius of curvature of the parabola at the tooth tip is equal to or greater than a predetermined value; and the radius of curvature of the surface shape of the tooth profile at the tooth tip becomes smaller than the radius of the arc or the radius of curvature of the parabola at the tooth tip; and forming the tooth root and the tooth tip by using the function f(x).
As described above, by performing machining by numerical control using the one aforementioned function f(x), it is possible to reduce the risk of occurrence of a precision error in a tooth profile and achieve both reduction of the risk of a collision of tooth tips and quietness. The above function f(x) is one general-purpose expression in which the surface shape of the tooth profile from the tooth root to the tooth tip becomes continuous and smooth. An example of the function f(x) will be described below.
f(x)=−axm−bxn (2)
where a>0, b>0, and m>n, and m and n are positive even numbers.
As shown in
f(v)=−r
f(u)=−c
The following Expressions (3) and (4) are obtained from the above expressions.
av
m
+bv
n
=r (3)
au
m
+bu
n
=c (4)
When H is set to H=vmun−vnum, the following Expression (5) is obtained from Expressions (3) and (4).
where r/c>(v/u)n is required.
In
Further, on the tooth root side, the radius of curvature of the surface shape of the tooth profile and the radius of curvature of the parabola are each within a predetermined value. Further, on the tooth tip side, the radius of curvature of the surface shape of the tooth profile and the radius of curvature of the parabola are each equal to or greater than a predetermined value. Further, on the tooth tip side, the radius of curvature of the surface shape of the tooth profile becomes smaller than the radius of curvature of the parabola. For example, when n=2, it is likely that the shape of from B to A via O is less deviated from the parabolic shape. Further, when m is large, the relief is likely to be closer to the tooth tip.
In this way, it is possible to achieve both reduction of the risk of a collision of tooth tips of a gear and quietness. Further, by performing NC machining using the above function f(x), it is possible to process the tooth root and the tooth tip in one step. Thus, it is possible to reduce a risk of occurrence of a precision error in the tooth profile.
where a is determined from c, r, u, and v, and is equal to or greater than one.
When the point A (u,−c) and the point R (v,−r) are substituted into Expression (6), the following Expressions (7) and (8) are obtained.
Here, τ=(v/u)2 and ρ=r/c, and the convergence calculation shown in
The initial value of a is set to a0 (S1). Then a first derivative by a of g(a) shown in S2 is obtained (S3). Then an error Δg of g(a) with respect to ρ is obtained (S4). If the absolute value of Δg is smaller than a tolerance ε (yes in S5), the calculation ends. On the other hand, if the absolute value of Δg is equal to or greater than the tolerance ε (no in S5), Aa shown in S6 is added to a, to thereby perform approximate correction on a (S7), and the calculation is repeated for the approximate value until the absolute value of the error Δg becomes smaller than the tolerance ϵ.
By using the above function f(x), it is possible to design a tooth profile that can achieve both quietness and durability by one general-purpose expression. Thus, when the surface of the tooth 11 is subjected to NC machining, the tooth flank can be processed so that it becomes continuous and smooth in one step. Since the point A in the tooth profile is smooth, the stress applied to the tooth 11 is further reduced, and thus a gear having resistant to wear can be obtained.
As described above, according to the embodiment, it is possible to set the function f(x) in which the shape of the tooth root becomes a shape similar to the parabolic shape represented by a quadratic function and the shape of the tooth tip becomes a more curved shape than that of the parabolic shape. By performing correction processing of the tooth profile using the above function f(x), it is possible to form the tooth tip that can achieve both reduction of the risk of a collision of the tooth tips and quietness by one function. Thus, it is possible to reduce the number of processing steps, facilitate processing, and prevent errors from occurring.
Note that the present disclosure is not limited to the above-described embodiment and may be modified as appropriate without departing from the spirit of the present disclosure. In the above-described example, although the function f(x) according to the embodiment is compared with a parabola passing through the same vertex, it may instead be compared with an arc passing through the same vertex.
Further, the above-described embodiment provides an example in which in NC machining, operations of a grinding tool, such as a grinding wheel, and a workpiece which is to be a gear are controlled to thereby form a predetermined tooth profile, but the present disclosure is not limited thereto. For example, in a case in which the tooth flank of a workpiece which is to be a gear is grounded with a grinding wheel to thereby finish the predetermined tooth shape, when the grinding wheel is dressed by using a dresser, the grinding wheel can be dressed into a shape corresponding to the predetermined tooth shape by using the function f(x) described above.
Further, when a gear is molded by rolling a workpiece using a rolling die, the rolling die may be formed into a transfer shape corresponding to a predetermined tooth shape by using the function f(x) described above. In a rolling molding, for example, a workpiece is held between a pair of rolling dies rotating in the same direction and the tooth part of the rolling die is transferred as a groove to the outer peripheral surface of the workpiece, whereby it is possible to manufacture a gear having a tooth profile of a predetermined shape.
From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
Number | Date | Country | Kind |
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2020-119938 | Jul 2020 | JP | national |