JP2013108609A - Worm reducer and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a worm reducer that can reduce tooth-hitting noise, can reduce vibration, and can be improved in durability.SOLUTION: In the worm reducer 30, a worm 32 is engaged with a worm wheel 31. The worm 32 is formed by aluminum die casting, and at least gear tooth of the worm is subjected to hard alumite treatment.

Description

  The present invention relates to a worm reducer and an electric power steering apparatus including a worm and a worm wheel.

  In an electric power steering device for a vehicle, a relatively high rotation and low torque motor is used as an electric motor for steering assist output. Therefore, a gear reduction mechanism is incorporated between the electric motor and the steering shaft. As a gear reduction mechanism, a gear reduction mechanism using a spur gear or other gear is also known, but it is generally composed of a worm and a worm wheel for reasons such as obtaining a large reduction ratio with one set. Well-known worm reducers are used.

  In such a worm speed reducer, if both the worm and the worm wheel are made of metal, there is an inconvenience that unpleasant noise such as rattling noise and vibration noise is generated when the handle is operated (hereinafter referred to as a first problem). ). In addition, it is necessary to create a complex-shaped worm from a steel bar by a combination of multi-stage cutting and casting, and there is a problem that the number of processing is large and a cost image is formed (hereinafter referred to as a second problem).

Regarding the first problem, since the worm speed reducer is often arranged near the driver who operates the steering wheel, in order to suppress the generation of unpleasant noise such as rattling noise and vibration noise, , The worm is made of iron-based metal, and the worm wheel meshing with the worm is formed by integrally molding gear teeth made of synthetic resin on the outer periphery of a metal core bar, to take measures against sound and vibration.
However, even if the gear teeth are made of synthetic resin, the specific gravity of the ferrous metal used in the worm and worm wheel core is heavy, so the inertia force of the worm wheel is large. Depending on the height, rattling noise and vibration noise are generated.
As a countermeasure for this, for example, Patent Document 1 describes a method of reducing the mass and improving the rattling noise by using a worm wheel core metal as an aluminum wrought material.

JP 2005-201332 A

However, there was room for improvement with respect to the worm only by improving the worm wheel. In addition, with respect to the second problem, there has been no effective means from the past, and there has been a demand for countermeasures by drastic changes in worm production.
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and can reduce the rattling noise, improve the durability, and reduce the manufacturing cost. An object of the present invention is to provide a worm speed reducer and an electric power steering device.

In order to achieve the above object, a worm speed reducer according to claim 1 of the present invention is a worm speed reducer in which a worm and a worm wheel mesh with each other, wherein the worm is made of aluminum die casting, At least the gear teeth are hard anodized.
According to the present invention, since the worm is made of aluminum die casting having a small mass, the inertial force is small, and the rattling noise is reduced and the vibration is also reduced as compared with the steel worm. Also, since at least the gear teeth of the worm are hard anodized, the wear amount of the gear teeth is reduced and the durability is improved. Furthermore, the manufacturing cost of the aluminum die-cast worm can be reduced.

The worm reducer according to claim 2 of the present invention is a worm reducer formed by meshing a worm and a worm wheel, wherein the worm is made of an aluminum die casting manufactured by a non-porous die casting method, T6 heat treatment is performed.
According to the present invention, since the worm is made of aluminum die casting having a small mass, the inertial force is small, and the rattling noise is reduced and the vibration is also reduced as compared with the steel worm. In addition, since the worm is manufactured by a non-porous die casting method, it is possible to obtain a dense die casting with few pores. And since T6 heat processing is performed, the abrasion loss of a gear tooth reduces and durability improves. Furthermore, the manufacturing cost of the aluminum die-cast worm can be reduced.

The worm reducer according to claim 3 according to the present invention is a worm reducer formed by meshing a worm and a worm wheel, wherein the worm is made of an aluminum die casting manufactured by a non-porous die casting method, A T6 heat treatment is performed, and at least the gear teeth of the worm are subjected to a hard anodizing treatment.
According to the present invention, since the worm is made of aluminum die casting having a small mass, the inertial force is small, and the rattling noise is reduced and the vibration is also reduced as compared with the steel worm. In addition, since the T6 heat treatment is performed and at least the gear teeth of the worm are subjected to the hard alumite treatment, the durability is further improved. Furthermore, the manufacturing cost of the aluminum die-cast worm can be reduced.

According to a fourth aspect of the present invention, there is provided an electric power steering apparatus that detects a steering torque transmitted from a steering wheel, an electric motor generates an auxiliary steering torque corresponding to the detected steering torque, and the auxiliary steering. Torque is decelerated by the worm reducer according to any one of claims 1 to 3 and transmitted to the output shaft of the steering mechanism.
According to the present invention, it is possible to obtain an electric power steering apparatus with reduced rattling noise, reduced vibration, and improved durability.

  According to the worm speed reducer and the electric power steering apparatus according to the present invention, it is possible to reduce rattling noise, reduce vibration, improve durability, and reduce manufacturing costs.

It is a figure which shows the structure of the electric power steering apparatus of this embodiment. It is a fragmentary sectional view which shows the structure of the worm reduction gear of this embodiment. It is a perspective view which shows the structure of the worm wheel of this embodiment, and a worm.

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
FIG. 1 is a view showing a column type electric power steering apparatus 10 suitable for implementing the present invention.
The electric power steering apparatus 10 includes a steering wheel shaft (steering shaft) 11, a steering wheel shaft housing 12, an electric motor 13, and a worm reducer 30.

The steering wheel shaft 11 has a steering wheel (not shown) fixed to one end thereof, and is supported rotatably around the axis of the steering wheel shaft housing 12 so as to rotate according to the steering of the steering hole. It has become.
An electric motor 13 is connected to an intermediate portion in the axial direction of the steering wheel shaft 11 via a worm speed reducer 30, and a steering assist force that assists the rotational force of the steering wheel shaft 11 is supplied from the electric motor 13. ing.

  A rack shaft 21 is connected to the other end of the steering wheel shaft 11 via a rack and pinion type motion conversion mechanism 20, and the steering torque increased by the supply of the steering assist force is transmitted to the rack shaft 21. The rack and pinion type motion conversion mechanism 20 is a mechanism for converting the rotational motion of the steering wheel shaft 11 into a reciprocating linear motion in the axial direction of the rack shaft 21, so that the axial direction becomes parallel to the width direction of the vehicle. The rack shaft 21 arranged in the straight line moves linearly according to the steering torque of the rudder wheel shaft 11, and the wheels are steered.

  The steering wheel shaft 11 is composed of an upper steering wheel shaft 11a and a lower steering wheel shaft 11b. The upper steering wheel shaft 11a and the lower steering wheel shaft 11b are coupled by a torsion bar (not shown), and the steering wheel is connected to the upper steering wheel. The steering torque transmitted to the lower steering wheel shaft 11b via the shaft 11a is detected by a torsion bar, and the output of the electric motor 13 is controlled based on the detected steering torque.

2 is a partial cross-sectional view showing the configuration of the worm speed reducer 30 of the electric power steering apparatus 10, and FIG. 3 is a perspective view showing the configuration of the worm wheel and the worm in detail.
The worm speed reducer 30 of the electric power steering apparatus 10 according to the present embodiment includes a worm wheel 31 and a worm 32 that meshes with the worm wheel 31, which are housed in a gear case 33 and attached to the electric motor 13. It has been.

At the attachment port of the gear case 33 to the electric motor 13, the worm shaft 32 a rotatably supported at both ends by ball bearings 34 a installed inside the gear case 33 and the drive shaft 13 a of the electric motor are coaxial. These are spline-coupled or serrated-coupled to rotate according to the drive of the electric motor 13.
The worm 32 is a cylindrical member integrally formed with the worm shaft 32a at an axially intermediate portion of the worm shaft 32a, and screw-like gear teeth are formed on the outer peripheral surface thereof.

The worm wheel 31 is a substantially cylindrical gear having a diameter larger than that of the worm 32, the outer peripheral surface thereof is in contact with the outer peripheral surface of the worm 32, and the axial direction thereof is substantially perpendicular to the axial direction of the worm shaft 32 a. Thus, the rotational force of the electric motor 13 transmitted through the worm 32 is transmitted to the lower steering wheel shaft 11b fitted to the substantially circular center.
The worm wheel 31 includes a substantially cylindrical core metal 42 having a through hole into which the lower rudder wheel shaft 11b is fitted at a substantially circular center, and a substantially cylindrical resin integrally formed on the outer periphery of the core metal 42. And a gear tooth 44 that is formed on the outer peripheral surface of the resin portion 43 and meshes with the gear teeth of the worm 32. Here, the core metal 42 of the worm wheel 31 is made of steel, and the gear teeth 44 are made of resin.

The worm 32 is made of die-casting made of JIS H 5302 Al—Si—Cu-based aluminum alloy ADC12.
Next, Table 1 shows manufacturing processes of various worms 32. In Table 1, the worms 32 of Examples 1 to 3 and Comparative Examples 2 and 3 are made of die casting, and the worm 32 of Comparative Example 1 is made of steel.

In Table 1, die casting (PF method) (Pore Free) is a non-porous die casting method. This non-porous die casting method is a special die casting method in which spaces such as cavities, runners, and sleeves are replaced with active gas (mainly oxygen) before the molten aluminum alloy is injected. Since the active gas becomes a fine aluminum oxide solid by a chemical reaction with the aluminum alloy, a dense die-cast with few pores can be obtained. If there are pores, they expand due to heat treatment and become casting defects such as blisters, but the non-porous die casting method with few pores enables heat treatment. In Table 1, die casting (ordinary) is an ordinary die casting method, which is a casting method in which molten aluminum alloy is injected into a mold at a high speed.
Next, Table 2 shows the heat treatment, surface treatment, and performance evaluation results of the worm 32 of Examples 1 to 3 and Comparative Examples 1 to 3.

In Table 2, T6 of heat treatment indicates T6 heat treatment described in JIS H0001. The surface-treated hard anodized film is an industrial hard anodized film specified by JIS H 8603, having a thickness of about 70 μm and a hardness of 400 HV or more.
The worm 32 of Examples 1 to 3 and Comparative Examples 1 to 3 is combined with the worm wheel 31 in which resin gear teeth 44 are integrally formed on a steel core 42, and Examples 1 to 3 are combined. Processing was performed so that a gap was formed between the worm 32 of Example 3 and Comparative Examples 1 to 3 and the gear teeth 44 of the worm wheel 31. Then, the worm 32 and the worm wheel 31 are combined and attached to the test apparatus, the worm wheel 31 is fixed, the worm 32 is vibrated at a predetermined amplitude of 50 Hz, and the noise at that time is measured, whereby the rattling sound measurement test. I do. The test result of the rattling sound measurement test is shown as a relative value when the noise level of Comparative Example 1 is 10.

  Further, the worms of Examples 1 to 3 and Comparative Examples 1 to 3 are combined with the worm wheel 31 in which resin gear teeth 44 are integrally formed on a steel core 42 to combine the electric power of an actual automobile. A steering test was conducted by incorporating it into a power steering device. This steering test repeats a reciprocating steering operation in which the steering wheel is steered from the left end position to the right end position and then returned to the left end position. This reciprocating steering operation was performed in an environment of 30 degrees, 50% RH and 100,000 reciprocations, and if there was no rattling or discomfort when the steering operation was further performed after 100,000 reciprocations, there was no abnormality.

After the steering test, the amount of wear of the gear teeth (screw-like gear teeth formed on the outer peripheral surface) of the worm 32 and the worm shaft of the worm 32 splined to the drive shaft 13a of the electric motor 13 are disassembled. The wear amount of the spline 32a is measured, and the durability test is performed.
According to Table 2, the worm 32 of Examples 1 to 3 has a small inertia force because it is made of an aluminum alloy having a small mass, and the rattling noise is reduced compared to Comparative Example 1 in which the worm 32 is made of steel. Vibration is also reduced.

In Example 2, the surface of the worm 32 is hard anodized, and in Embodiment 3, the worm 32 has an artificial aging effect by the T6 heat treatment. Is reduced and durability is improved.
In particular, in the first embodiment in which the surface of the worm 32 is subjected to the hard alumite treatment and the T6 heat treatment is performed, the wear amount of the gear teeth and splines of the worm 32 is further reduced, and the durability is further improved.

On the other hand, Comparative Example 2 which is manufactured by a normal die casting method and does not perform heat treatment and surface treatment, and Comparative Example 3 which is manufactured by a non-porous die casting method and which does not perform heat treatment and surface treatment are the gear teeth and splines of the worm 32. Since the amount of wear increases, there are problems in terms of rattling noise and durability.
Furthermore, as shown in Table 1, the die-cast worm 32 of Examples 1 to 3 is manufactured in comparison with the steel worm 32 that requires the cutting process and the forging process shown in Comparative Example 1. Therefore, the manufacturing cost can be reduced.

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 11 ... Steering wheel shaft, 11a ... Upper steering wheel shaft, 11b ... Lower steering wheel shaft, 12 ... Steering wheel shaft housing, 13 ... Electric motor, 13a ... Drive shaft, 20 ... Rack and pinion type motion conversion mechanism, DESCRIPTION OF SYMBOLS 21 ... Rack shaft, 30 ... Worm speed reducer, 31 ... Worm wheel, 32 ... Worm, 32a ... Worm shaft, 33 ... Gear case, 34a ... Ball bearing, 42 ... Core metal, 43 ... Resin part, 44 ... Gear tooth

Claims (4)

In a worm speed reducer in which a worm and a worm wheel mesh,
The worm is made of aluminum die-casting, and at least the gear teeth of the worm are subjected to hard anodizing treatment. In a worm speed reducer in which a worm and a worm wheel mesh,
The worm is made of an aluminum die cast manufactured by a non-porous die casting method, and is subjected to T6 heat treatment. In a worm speed reducer in which a worm and a worm wheel mesh,
The worm is made of an aluminum die cast manufactured by a non-porous die casting method, is subjected to T6 heat treatment, and at least a gear tooth of the worm is subjected to a hard alumite treatment. Machine.   4. The worm according to claim 1, wherein a steering torque transmitted from the steering wheel is detected, and an electric motor generates an auxiliary steering torque corresponding to the detected steering torque. An electric power steering device, wherein the electric power steering device is decelerated by a reduction gear and transmitted to an output shaft of a steering mechanism.

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