JP2005125972A - Rack and pinion type steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent abrasion or the like by enhancing abrasion-resistance property by enhancing tooth surface hardness by outstandingly enhancing hardness of a pinion, a rack tooth surface and a rack back surface. <P>SOLUTION: In the rack and pinion type steering device provided with an electric power steering device, a first curing layer 3 is formed on the surfaces of the pinion 1 and the rack 2 and a second curing layer 4 is formed on an outer surface of the first curing layer 3. The first curing layer 3 is, for example, a usual hardening curing layer or the like. The second curing layer 4 is a martensite hardening curing layer in which a ratio of increase of the hardness at a shot treatment part relative to a surface hardness of the first curing layer by a usual hardening treatment is 20% or more by shotpeening of at least one of the tooth surface of the rack 2 and the back surface of the rack 2, remained austenite is less than 0-10% and curing depth is 9 μm or more. Further, in the shotpeening, a steel ball of shot particle diameter of 40-200 μm is used and injection speed is 100 m/sec or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rack and pinion type steering apparatus including an electric power steering apparatus that urges a tearing shaft with a rotational force of an electric motor.

  A rack and pinion type steering device is widely used to convert the rotation of the steering shaft into the axial motion of the connecting shaft of the left and right steered wheels.

  In manual steering without power bias, the rotational force of the driver's steering wheel is converted into rack axial force by the rack and pinion type steering device, so the transmission force in the rack and pinion type steering device is generated by humans. Since it is only the torque to do, it becomes a small thing.

  In order to reduce steering work, a hydraulic power steering device is also widely used. However, the urging force by the hydraulic pressure is not provided through the rack and pinion type steering device, but is provided integrally with the rack shaft. Since it is given to the piston of the cylinder, the steady force acting on the rack and pinion type steering device is only the torque that twists the torsion bar of the hydraulic control valve, and is very small. Also in the rack assist type EPS in which the rotational force of the motor is thrust on the rack shaft by a ball screw or the like, the force acting on the rack and pinion type steering device is the same as that of the hydraulic power steering.

  In the column assist type EPS and pinion assist type EPS that urge the power to the steering shaft, the torque obtained by combining the rotational force of the steering wheel of the driver and the power urging force from the electric motor passes through the rack and pinion type steering device. , Converted into rack axial force.

  Usually, the pinion teeth and the rack teeth and the back surface of the rack teeth are hardened and hardened to a surface hardness of about HRC55 to 63 by carburizing quenching, induction quenching, etc. in order to improve wear prevention strength. The former center part is supposed to be 10 to 20 points lower in hardness.

  The torque that is constantly transmitted by the rack and pinion type steering device is more than 10 times larger than that of manual steering, hydraulic power steering, etc., which is very severe in terms of stress and wear on the tooth surface.

  The rack shaft is supported by pressing the back side of the rack teeth with a rack guide toward the pinion shaft with an elastic force. The rack guide is pressed with a relatively small pressing force of about 200 N in order to achieve a smooth engagement with a small stroke so as to allow a variation in the distance between both shafts due to gear accuracy.

  The rack guide is pushed back to the full stroke when power is transmitted by the separation force that is mainly a component of meshing caused by the pressure angle of the gear (maximum 10000N, which depends on the gear specifications, but is at most about the same as the rack thrust). fall back. Since the transmission tooth surface is switched when the rotational force is reversed, the separation force once becomes zero, and the rack teeth that have been separated strike the pinion teeth vigorously and generate a striking sound (rattle sound).

  The rack-and-pinion device generates a rattle sound because the separation force fluctuates even by input excitation from the wheel side such as road surface irregularities and shimmies. In this case, the load is usually only the inertia of the steering wheel in manual steering or the like, but in the electric power steering device (EPS) that biases the assist force to the steering shaft, the reduction gear and the motor are used as inertia on the steering shaft. Since it works, the inertia is more than doubled, and there is a characteristic that rattle noise is likely to occur.

  Further, when the tooth surface wears, the retraction amount of the rack guide increases and the impact speed of the tooth surface increases. As shown in Table 1, the impact sound suddenly increases and the steering feeling deteriorates. there were.

磨耗抑制の為に、歯面の面圧を緩和する手段として、歯幅を増やす方法があるが、ラック軸を太くせざるを得ず、重量が増加するという問題が起こってしまう。

In order to reduce wear, there is a method of increasing the tooth width as a means for reducing the tooth surface pressure. However, the rack shaft has to be thickened, which causes a problem that the weight increases.

  For this reason, there is a demand for improving the tooth surface hardness and improving the wear resistance in increasing the output of the rack and pinion type steering device provided with the electric power steering device.

  Further, EPS Patent Document 1 relating to shot peening discloses a configuration in which a concave portion is provided on the surface by shot peening to reduce sliding resistance as shot peening of a gear tooth surface. A configuration adapted to be applied to a rack bearing sliding portion is disclosed.

  Furthermore, Patent Document 2 discloses a configuration in which shot peening is performed for the same purpose for all mechanical sliding parts.

Further, Patent Document 3 discloses a power transmission component made of carburized steel and having a surface hardness of HRC 63 to 68 and a surface retained austenite amount of 13 to 30%. Further, a hardening method by shot peening of a gear tooth surface is disclosed. It is disclosed.
Japanese Patent Laid-Open No. 2001-278074 JP-A-5-84662 Japanese Patent Laid-Open No. 7-54049

  However, even in the shot and peening disclosed in the various patent documents mentioned above, in the rack and pinion type steering device provided with the electric power steering device, the pinion, the rack tooth surface, and the rack back surface do not necessarily have sufficient hardness. May not be obtained, and problems such as rattle noise may occur accompanying wear and the like.

  The present invention was made in view of the circumstances as described above, and the hardness of the pinion, the rack tooth surface and the rack back surface is remarkably improved, the tooth surface hardness is improved and the wear resistance is improved. An object of the present invention is to provide a rack and pinion type steering device capable of improving wear and the like.

In order to achieve the above object, a rack and pinion type steering device according to claim 1 of the present invention is a rack and pinion type steering device provided with an electric power steering device for energizing a steering shaft with the rotational force of an electric motor. In the device
The surface of the 1st hardening layer by a normal hardening process by shot peening at least one of the 1st hardening layer by which the pinion, the rack, and the rack back were hardened by carburizing or induction hardening, and at least one of the pinion, the rack tooth surface, and the rack back It is characterized in that a second hardened layer having a hardness increase rate of 20% or more, a retained austenite of 0 to less than 10%, and a hardening depth of 9 μm or more with respect to the hardness is provided. To do.

  The rack and pinion type steering apparatus according to claim 2 of the present invention is characterized in that the pressure angle between the pinion and the rack is 20 degrees or more.

  The rack and pinion type steering apparatus according to claim 3 of the present invention is characterized in that the shot peening is performed with a shot particle size of 40 to 200 μm and an injection speed of 100 m / sec or more.

  As described above, according to the present invention, the upper limit of the hardness of the first hardened layer obtained by normal heat treatment (carburization quenching, induction quenching) is about HRC68 (= HV940), but the pinion, the rack tooth surface, and the rack At least one of the back surfaces is 20% or more of the increase in hardness in the shot treatment portion with respect to the surface hardness of the first hardened layer by the normal quenching treatment by shot peening, and 0 to less than 10% of retained austenite, Since the second hardened layer with a hardened depth of 9 μm or more is provided, the hardness of the pinion, the rack tooth surface and the back of the rack is remarkably improved without impairing the toughness, and the wear resistance is improved. Can be improved.

  Hereinafter, a rack and pinion type steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a rack-and-pinion type steering apparatus according to an embodiment of the present invention in a meshed state of a pinion and a rack.

  FIG. 2 is a graph showing the relationship between the overpin height correction amount and the rack tooth gap position.

  As shown in FIG. 1, in this embodiment, in a rack and pinion type steering apparatus including an electric power steering apparatus that urges a steering shaft with the rotational force of an electric motor, surfaces of a pinion 1 and a rack 2 are provided. In addition, a first cured layer 3 is formed, and a second cured layer 4 is formed on the outer surface of the first cured layer 3.

  This 1st hardening layer 3 is a normal hardening hardening layer etc., for example, and others may be sufficient as it.

  The second hardened layer 4 is a hardened layer in which at least one of the pinion 1, the tooth surface of the rack 2 and the back surface of the rack 2 is subjected to shot peening to have a surface hardness of 940 Hv or more, residual austenite of 0 to less than 10%, and a hardening depth of 9 μm or more. It is. At this time, the pressure angle between the pinion 1 and the rack 2 is set to 20 deg or more. Shot peening is performed with a steel ball having a shot particle size of 40 to 200 μm and an injection speed of 100 m / sec or more. Thereby, the hardness of the pinion 1, the tooth surface of the rack 2, and the back surface of the rack 2 can be remarkably improved, the tooth surface hardness can be improved, the wear resistance can be improved, and the wear and the like can be improved.

  By the way, in the relationship between the amount of backward movement of the rack guide and the rattle noise, it rapidly deteriorates when it exceeds 0.1 mm.

  Also, if the steering force near the center of the steering wheel is too light, the running wheel will be steered even with a slight steering force, and the straight running stability will be impaired. Therefore, as shown in FIG. The nearby teeth are raised and both sides are lowered to increase the pressing force near the center.

  The assembly distance between the pinion 1 and the rack 2 is wide at the center and close on both sides. The rack guide requires a minimum set value of 0.05 mm so as to allow this amount of retraction and to absorb some variation in the center-to-core distance due to gear accuracy.

  Therefore, it is necessary to increase the amount of backward movement of the rack guide to 0.05 mm or less.

  If the total wear amount of both tooth surfaces is δ and the retraction amount of the rack guide is 1, δ = 1 × Sinα, and the influence of the wear on the retraction amount of the rack guide is more remarkable as the pressure angle α is smaller. Therefore, if α = 20 ° and l = 0.05 mm, then δ = 0.017 mm.

  Therefore, the wear limit of one tooth surface is 0.0076 mm. At least in this range, it is necessary to increase the surface hardness and suppress wear.

  On the other hand, as disclosed in Patent Document 4, it is known that retained austenite undergoes martensitic transformation during the process of use, expands, and the surface roughness deteriorates.

  For this reason, in order to prevent the deterioration of the surface condition due to local expansion during the process of use, the surface is superheated and quenched in advance to the A3 transformation point or higher by the collision energy of the shot grains, and martensite is precipitated to increase the surface hardness. It is effective to make it up.

  Further, in normal shot peening, residual compressive stress can be applied, but residual austenite does not decrease.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

It is sectional drawing in the meshing state of the pinion and rack of the rack and pinion type steering device concerning an embodiment of the invention. It is a graph which shows the relationship between an overpin height correction amount and a rack tooth space position.

Explanation of symbols

1 pinion 2 rack 3 first cured layer 4 second cured layer

Claims (3)

In a rack and pinion type steering device used in an electric power steering device that powers a steering shaft or a pinion shaft with the rotational force of an electric motor,
The first hardened layer obtained by hardening the pinion and the back surface of the rack by heat treatment, and at least one of the pinion, the rack tooth surface, and the back surface of the rack are shot against the surface hardness of the first hardened layer by a normal quenching process by shot peening. A rack-and-pinion steering device characterized in that the second hardened layer has a hardness increase rate of 20% or more in the treated portion, a retained austenite of 0 to less than 10%, and a hardened depth of 9 μm or more.   The rack and pinion type steering apparatus according to claim 1, wherein a pressure angle between the pinion and the rack is set to 20 deg or more.   The rack-and-pinion steering device according to claim 1 or 2, wherein the shot peening is performed with a steel ball having a shot particle diameter of 40 to 200 µm and an injection speed of 100 m / sec or more.

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