JP2003278885A - Resin-made worm wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize both stability of dimensional accuracy in tooth parts 4, 4, etc., of the resin-made worm wheel W and reduction of tooth chipping by high toughness, by employing resin materials simultaneously satisfying both low hygroscopicity and high toughness as a rim part 3 (tooth parts 4, 4, etc.), in the resin-made worm wheel having tooth parts 4, 4, etc., in a resin-made outer peripheral rim 3 and a recessed shape in the tooth groove longitudinal direction of a tooth groove bottom part 5 between the tooth parts 4, 4. <P>SOLUTION: The rim 3 comprising tooth parts 4, 4, etc., is made up of thermoplastic polyurethane resin containing 80 wt.% or more of reactant of methylenediphenyldiisocyanate and cyclohexanedimethanol and 3-20 wt.% of acrylic polymer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of resin worm wheels.

[0002]

2. Description of the Related Art Generally, this type of worm wheel is
The outer peripheral portion is formed with a large number of tooth portions that extend spirally (obliquely) with respect to the axial direction. When transmitting between the worm wheel and the worm, the worm wheel is attached to the outer peripheral portion of the worm wheel. Are arranged so that their axes are substantially orthogonal to the axis of the worm wheel, and the rotation of the worm wheel is caused by rotating the worm by engaging the teeth of the worm wheel with the teeth of the worm. It is designed to be transmitted to. Since the tooth groove bottom portion between the tooth portions of the worm wheel meshes with the tooth portion of the worm, the central portion in the tooth groove length direction is usually depressed corresponding to the outer peripheral shape of the tooth portion of the worm. It is formed in a concave shape.

By the way, when manufacturing such a worm wheel with resin, it is common to form a tooth portion by cutting the outer peripheral portion of the blank with a hob, similarly to a metal worm wheel. .

For example, in Japanese Unexamined Patent Publication No. 2000-130564, insert metal fittings which are bosses and arms of a resin gear are arranged and fixed in a mold, and a rim corresponding portion is formed in a cavity around the insert metal fitting. The strength of the resin rim can be increased by injecting resin into the inside, integrally molding the rim made of resin of the rim corresponding part into the insert metal fitting, and performing gear cutting processing on the rim outer peripheral surface of this gear material. Proposed.

However, this method can manufacture a resin worm wheel having high strength and dimensional accuracy, but has a problem that the cost is high because a cutting process is required.

Therefore, the worm wheel may be formed by injection molding the resin in the cavity in the mold by utilizing the moldability of the resin. However, as described above, the bottom of the tooth gap between the outer peripheral teeth is formed. Even if an attempt is made to make a concave shape, the bottom of the tooth groove becomes an undercut, and the worm wheel cannot be released from the mold after molding.

For this reason, as a resin worm wheel manufactured by molding, a helical gear having a tooth groove bottom portion of each tooth portion formed into a flat (linear) shape has been conventionally used.

On the other hand, as disclosed in, for example, Japanese Utility Model Laid-Open No. 4-49254, one half of the bottom of the groove between the teeth of the worm wheel in the lengthwise direction is a concave half. Although it is formed in an arc shape, the other half of the worm wheel is injection-molded with resin in the cavity of the mold by eliminating the undercut part at the bottom of the tooth groove by making it a plane shape parallel to the axis. Something that can be done is proposed.

Further, as disclosed in Japanese Patent Application Laid-Open No. 11-286032, a core die is arranged on both sides of a die having a tooth portion forming portion for forming a tooth portion of a worm wheel formed on an inner peripheral surface thereof. After forming a cavity between these molds and injecting resin into the cavity to form a worm wheel, rotate the worm wheel along the twist angle of the teeth and elastically deform the worm wheel, It has been proposed to use so-called stripping, which uses shrinkage to pull out from a mold.

[0010]

As described above, various injection-moldable thermoplastic resins have been studied as the material of the tooth portion of the resin worm wheel as described above. At present, there are merits and demerits because it is required that the teeth are not damaged and the dimension and shape are stable.

For example, when the material is nylon 66 or nylon 46, it is excellent in toughness and cyclic fatigue,
Since the hygroscopicity is large, the dimensional accuracy is not stable and the meshing accuracy with the worm is reduced.For example, when used in a drive system of an electric power steering device of a vehicle, the steering performance of the vehicle is reduced and noise due to rattling noise is generated. It causes to occur.

On the other hand, since 6T nylon and 9T nylon have low hygroscopicity, the dimensional accuracy is stable and the above-mentioned problems do not occur, but the toughness is inferior to 66 nylon and 46 nylon, and tooth chipping occurs. Easy and unreliable for basic functions.

The present invention has been made in view of the above points, and an object thereof is to specify, as the resin material of the resin worm wheel, a material that can simultaneously satisfy both low hygroscopicity and high toughness. It is intended to achieve both stability of dimensional accuracy of the tooth portion of the resin worm wheel and reduction of tooth chipping due to high toughness.

[0014]

In order to achieve the above object, in the present invention, the material of the resin worm wheel is thermoplastic polyurethane resin.

Specifically, in the invention of claim 1, at least the outer peripheral rim portion is made of resin, the outer peripheral portion of the rim portion has tooth portions, and the tooth groove bottom portion between the tooth portions has a tooth groove. A resin worm wheel having a shape recessed in the length direction, characterized in that an outer peripheral portion including the tooth portion is made of a thermoplastic polyurethane resin.

Further, in the invention of claim 2, the thermoplastic polyurethane resin contains 80 w of a reaction product of methylene diphenyl diisocyanate and cyclohexane dimethanol.
t% or more and 3 to 20 wt% of acrylic polymer (3 w
t% or more and 20 wt% or less).

According to the constitutions of these inventions, the outer peripheral portion of the tooth portion of the resin worm wheel is made of thermoplastic polyurethane resin, and this thermoplastic polyurethane resin is a reaction product of methylenediphenyl diisocyanate and cyclohexanedimethanol of 80 wt%. As described above, the acrylic polymer is contained in an amount of 3 to 20 wt%, so that the hygroscopicity is extremely low, the dimensional accuracy is hard to change due to the hygroscopicity, and the toughness is large. It is possible to obtain a resin-made worm wheel that has low noise such as hammering noise and is unlikely to cause tooth chipping.

The content of the reaction product of methylene diphenyl diisocyanate and cyclohexane dimethanol is
If it is less than 80 wt%, the mechanical strength and heat resistance will decrease, so it is set to 80 wt% or more.

The content of acrylic polymer is 3w.
When it is less than t%, toughness and tensile elongation are lowered, while when it exceeds 20 wt%, mechanical strength and heat resistance are lowered, so 3 to 20 wt% is preferable.

In the invention of claim 3, the average molecular weight of the thermoplastic polyurethane resin is 80,000 or more. This makes it possible to improve and maintain mechanical properties such as strength and wear resistance of the teeth and heat resistance.

According to a fourth aspect of the present invention, the thermoplastic polyurethane resin is used as a matrix, and one kind selected from the group consisting of PTFE (tetrafluoroethylene resin), graphite or silicone oil is used for 100 parts by weight of the matrix resin. It is characterized in that 1 to 30 parts by weight or more of the above substances are combined. As a result, the slidability of the teeth can be improved.

On the other hand, similarly, in the invention of claim 5, a thermoplastic polyurethane resin is used as a matrix, and one kind selected from the group consisting of zinc oxide whiskers, potassium titanate or carbon per 100 parts by weight of this matrix resin. It is characterized in that 1 to 30 parts by weight or more of the above substances are combined. As a result, the strength of the teeth can be increased.

According to a sixth aspect of the invention, the resin worm wheel is used in an electric power steering device. As a result, it is possible to obtain the worm wheel made of resin for the optimum use in which the effects of the present invention are effectively exhibited.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a resin worm wheel W according to an embodiment of the present invention. The resin worm wheel W, which is not shown, constitutes a part of a known gear transmission mechanism in an electric power steering device of an automobile. is doing. That is, the electric power steering device is arranged in a path for transmitting the steering movement of the steering wheel (handle) to the rack and pinion mechanism, and the gear transmission mechanism thereof is a worm wheel drivingly connected to the rack and pinion mechanism and the worm wheel. And a worm meshed with the wheel. The worm wheel is attached to the output shaft of the electric motor, and the electric motor detects the steering direction and steering speed of the steering wheel and is controlled by the ECU (control unit) according to the detected steering direction and steering speed. The resin worm wheel W of this embodiment is used as a worm wheel of the gear transmission mechanism.

The worm wheel W is integrally joined to a cylindrical metal boss portion 1 having a shaft hole 1a through which an output shaft (not shown) of a motor is inserted, and an outer peripheral surface of the metal boss portion 1. The outer peripheral rim portion 3 is formed. The rim portion 3 is made of resin, and extends on the outer periphery of the resin portion spirally (obliquely) with respect to the direction along the axis O of the boss portion 1 (left and right direction in FIG. 1) and meshes with the worm. A large number of tooth portions 4, 4, ... Are formed, and the tooth groove bottom portion 5 between the tooth portions 4, 4 corresponds to the outer peripheral shape of the tooth portion of the worm (not shown).
The center portion in the lengthwise direction of the tooth space has a concave shape that is recessed in an arc shape.

The resin forming the rim portion 3 (outer peripheral portion) of the worm wheel W of this embodiment is made of thermoplastic polyurethane resin. Specifically, this thermoplastic polyurethane resin has a reaction product of methylene diphenyl diisocyanate and cyclohexane dimethanol of 80%.
wt% or more and 3 to 20 wt% (3
wt% or more and 20 wt% or less).

The content of the reaction product of methylenediphenyldiisocyanate and cyclohexanedimethanol is 8
If it is less than 0 wt%, the mechanical strength and heat resistance will decrease, so it is set to 80 wt% or more.

The content of the acrylic polymer is
When it is less than 3 wt%, toughness and tensile elongation are lowered, while when it exceeds 20 wt%, mechanical strength and heat resistance are lowered, so 3 to 20 wt% is preferable.

The average molecular weight of the thermoplastic polyurethane resin is 80,000 or more. This makes it possible to improve and maintain mechanical properties such as strength and wear resistance of the tooth portion 4 and heat resistance. That is, the average molecular weight of the thermoplastic polyurethane resin is usually 90,000 to 110,000, and when it is 50,000 or less, the mechanical properties and heat resistance are about 70% of the usual values. When injection molding is performed in a state where the resin pellet for molding is not sufficiently dried, hydrolysis occurs and the molecular weight decreases. Considering this, by setting the molecular weight to 80,000 or more, such a problem can be avoided.

The thermoplastic polyurethane resin is used as a matrix, and 100 parts by weight of this matrix resin is added to
It is also possible to compound 1 to 30 parts by weight or more of one or more substances selected from the group consisting of PTFE, graphite or silicone oil. These substances have lubricity and can improve the slidability of the tooth portion 4.

Further, using a thermoplastic polyurethane resin as a matrix, 100 parts by weight of this matrix resin is mixed with one or more substances selected from the group consisting of zinc oxide whiskers, potassium titanate or carbon.
˜30 parts by weight or more may be combined. These substances have a reinforcing effect on the resin and can increase the strength of the tooth portion 4.

Therefore, in this embodiment, the rim portion 3 (outer peripheral portion) forming the tooth portions 4, 4, ... Of the resin worm wheel W has a reaction product of methylenediphenyldiisocyanate and cyclohexanedimethanol of 80 wt.
% Or more and 3 to 20 wt% of an acrylic polymer, which is a thermoplastic polyurethane resin. The thermoplastic polyurethane resin is a material that has extremely low hygroscopicity, hardly changes in dimensional accuracy due to moisture absorption, and has high toughness. Therefore, the meshing accuracy of the resin worm wheel W is high, noise such as rattling noise can be reduced, and tooth chipping of the tooth portions 4, 4, ... Is unlikely to occur. Therefore, the resin worm wheel W suitable for use in the electric power steering device can be obtained.

[0033]

EXAMPLES Next, concretely implemented examples will be described.

Example 1 A resin worm wheel (see FIGS. 1 and 2) having the structure of the above-described embodiment was produced. In this Example 1, 80 wt% or more of a reaction product of methylene diphenyl diisocyanate and cyclohexane dimethanol and 3 to 20 w of an acrylic polymer were used as a resin material of an outer peripheral rim portion including a tooth portion in the worm wheel.
Only a thermoplastic polyurethane resin comprising t% was used.

(Example 2) The thermoplastic polyurethane resin having the composition of Example 1 was used as a matrix resin, and 15 parts by weight of zinc oxide whiskers were compounded with 100 parts by weight of the matrix resin.

(Example 3) The thermoplastic polyurethane resin having the composition of Example 1 was used as a matrix resin, and 15 parts by weight of PTFE was compounded with 100 parts by weight of this matrix resin.

Comparative Example 1 MC nylon is used as the resin material of the outer peripheral rim portion including the tooth portion in the resin worm wheel having the structure of the embodiment.

(Comparative Example 2) 9TPA was used as the resin material of the outer peripheral rim portion including the tooth portion in the resin worm wheel having the structure of the embodiment.

Comparative Example 3 PA66 is used as the resin material of the outer peripheral rim portion including the tooth portion in the resin worm wheel of the embodiment.

(Comparative Example 4) PA46 is used as the resin material of the outer peripheral rim portion including the tooth portion in the resin worm wheel of the embodiment.

(Resin Material Characteristic Evaluation Test) Above Example 1
To 3 and Comparative Examples 1 to 4 regarding the resin itself forming the outer peripheral portion, its material properties, specifically, tensile yield strength, tensile elongation at break, bending strength, bending elastic modulus,
80 under the conditions of Izod impact strength, heat distortion temperature at 1.82 MPa which represents heat deformation, 60 ° C. and 90% RH
Table 1 shows the water absorption rate when held for Hr, the linear expansion coefficient at 20 ° C, and the loss coefficient (tan δ) at 23 ° C.

The coefficient of dynamic friction and the amount of wear were evaluated as the slidability of the resin itself. This test is carried out using a Suzuki-type friction and wear tester, and the conditions are: a resin material having a predetermined shape for a mating material made of S45C (carbon steel for machine structure)
It was slid for 2 hours at a constant speed (50 cm / sec) while being pressed at a constant pressure (4.3 MPa) in grease at a temperature of ° C. The results are also shown in Table 1.

[0043]

[Table 1]

(Worm Wheel Performance Evaluation Test for Electric Power Steering) Examples 1 to 3 and Comparative Example 1
4 to 4 are used as worm wheels of an electric power steering device, fracture resistance strength characteristics of teeth,
Impact resistance, dimensional stability, low noise and abrasion resistance were tested. Here, the fracture resistance property of the tooth portion is an index of the fracture energy of the tooth portion based on both strength and elongation. The impact resistance was judged based on the Izod impact strength in the resin material property evaluation test.
Dimensional stability was determined based on both water absorption and linear expansion coefficient. Regarding the low noise property, a resin molded product was hit with a steel rod, and the loudness of the hit sound was subjected to a sensory test. The abrasion resistance was judged based on the amount of resin abrasion by the friction abrasion test. The results are shown in Table 2. still,
In this test item, ⊚ indicates “excellent”, “mark” indicates “good”, Δ indicates “slightly bad”, and “x” indicates “completely bad”. It represents.

[0045]

[Table 2]

Considering the results shown in Table 2, all of Examples 1 to 3 using the thermoplastic polyurethane resin have dimensional stability, impact resistance, abrasion resistance and durability as compared with Comparative Examples 1 to 4. It is found that the effect is excellent and the effect of the present invention is effective.

[0047]

As described above, according to the first aspect of the present invention, the outer peripheral rim portion made of resin has the tooth portions, and the tooth groove bottom portion between the tooth portions has a shape recessed in the tooth groove length direction. With respect to the resin worm wheel, the outer peripheral portion including the above tooth portion was made of thermoplastic polyurethane resin. Further, in the invention of claim 2, the thermoplastic polyurethane resin contains 80 wt% or more of a reaction product of methylene diphenyl diisocyanate and cyclohexane dimethanol and 3 to 20 wt% of an acrylic polymer. Therefore,
According to these inventions, the hygroscopicity of the tooth portion is made extremely low, the dimensional accuracy due to the moisture absorption is unlikely to change, the toughness of the tooth portion can be increased, the meshing accuracy is high, the noise such as the rattling noise is low, and the chipping It is possible to obtain a resin worm wheel that is unlikely to occur.

According to the invention of claim 3, the thermoplastic polyurethane resin has an average molecular weight of 80,000 or more.
It is possible to improve and maintain mechanical properties such as strength and wear resistance of the teeth and heat resistance.

According to the fourth aspect of the present invention, a thermoplastic polyurethane resin is used as a matrix, and 100 parts by weight of this matrix resin is mixed with one or more substances selected from the group consisting of PTFE, graphite or silicone oil. By combining 30 parts by weight or more, the slidability of the teeth can be improved.

According to the invention of claim 5, a thermoplastic polyurethane resin is used as a matrix, and 100 parts by weight of this matrix resin is provided with one or more substances selected from the group consisting of zinc oxide whiskers, potassium titanate or carbon. By combining 1 to 30 parts by weight or more, the strength of the tooth portion can be increased.

According to the invention of claim 6, since the resin worm wheel is used for the electric power steering device, the resin worm wheel for the optimum use can effectively obtain the effect of the present invention. To be

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a resin worm wheel according to an embodiment of the present invention.

FIG. 2 is a front view of a resin worm wheel.

[Explanation of symbols]

W Resin Worm Wheel 3 rim part 4 teeth 5 Tooth groove bottom

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Claims (6)

[Claims] 1. At least an outer peripheral rim portion is made of resin, and a tooth groove is formed on the outer peripheral portion of the rim portion, and a tooth groove bottom portion between the tooth portions is recessed in the tooth groove length direction. A resin worm wheel, wherein the rim portion including the tooth portion is made of a thermoplastic polyurethane resin. 2. The resin worm wheel according to claim 1, wherein the thermoplastic polyurethane resin comprises 80% by weight or more of a reaction product of methylenediphenyldiisocyanate and cyclohexanedimethanol and 3 to 20% of an acrylic polymer.
%, And a resin worm wheel. 3. The resin worm wheel according to claim 1, wherein the thermoplastic polyurethane resin has an average molecular weight of 80,000 or more. 4. The resin worm wheel according to claim 1, wherein a thermoplastic polyurethane resin is used as a matrix, and 100 parts by weight of the matrix resin is selected from the group consisting of PTFE, graphite and silicone oil. A resin worm wheel, characterized in that 1 to 30 parts by weight or more of one or more substances are compounded. 5. The resin worm wheel according to claim 1, wherein the thermoplastic polyurethane resin is used as a matrix, and zinc oxide whiskers, potassium titanate or carbon is added to 100 parts by weight of the matrix resin. A worm wheel made of resin, characterized in that 1 to 30 parts by weight or more of one or more kinds of substances selected by (1) are mixed. 6. The resin worm wheel according to claim 1, which is used in an electric power steering device.