JP2005153821A - Rack/pinion type steering device and manufacturing method for pinion shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rack/pinion type steering device not requiring for applying machining treatment to a pinion shaft after the pinion shaft is cured by heat treatment in a manufacturing step and a manufacturing method for a pinion shaft of the rack/pinion type steering device. <P>SOLUTION: The rack/pinion type steering device is provided with the pinion shaft 2; and a rack shaft 3 engaged with the pinion shaft 2. The pinion shaft 2 has a constitution wherein a plasma nitriding cured layer is formed on a tooth surface (4) engaged with at least the rack shaft 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rack and pinion steering device that is widely used as a steering device for a vehicle, and a method for manufacturing a pinion shaft of the rack and pinion steering device.

  The rack and pinion type steering device is connected to a steering member such as a steering wheel, and has a pinion shaft having pinion teeth provided on a peripheral surface thereof, and extends in the left-right direction of the vehicle body. And a rack shaft in which rack teeth are arranged side by side. The rotation of the pinion shaft according to the operation of the steering member by the driver is converted into the movement in the axial direction of the rack shaft, and the steering wheels connected to the left and right ends of the rack shaft via separate tie rods ( In general, the left and right front wheels are actuated.

In such a rack and pinion type steering device, the pinion teeth provided on the pinion shaft and the rack teeth provided on the rack shaft are cut using a machine tool such as a gear cutter or a broaching machine in order to obtain high meshing accuracy. It is generally formed by processing, and in many cases, tooth surfaces are heat treated to increase surface hardness and improve durability (see, for example, Patent Document 2).
JP-A-8-113149 Japanese Patent Publication No.8-25462

  When manufacturing the pinion shaft of the rack and pinion type steering device described above, conventionally, after rough cutting, heat treatment including induction hardening and tempering is performed, distortion generated by the heat treatment is removed, and the outer diameter is reduced. Grinding, and finally finishing the teeth, there is a large distortion such as shaft bending and tooth surface deformation caused by heat treatment, so it is necessary to remove the distortion, further processing after hardening by heat treatment There was a problem that had to be given.

  The present invention has been made in view of the above-described circumstances. In the first invention, after the pinion shaft is cured by heat treatment in the manufacturing process, the rack and pinion need not be processed on the pinion shaft. It aims at providing a type steering device. It is an object of the second invention to provide a method of manufacturing a pinion shaft that does not need to be processed after being cured by heat treatment.

  A rack and pinion type steering device according to a first aspect of the present invention is a rack and pinion type steering device comprising a pinion shaft and a rack shaft that meshes with the pinion shaft, wherein the pinion shaft has at least teeth that mesh with the rack shaft. A plasma nitriding hardened layer is formed on the surface.

  The pinion shaft manufacturing method according to the second invention is a pinion shaft manufacturing method for manufacturing a pinion shaft of a rack and pinion type steering device, wherein after rough cutting, outer diameter grinding is performed to finish the teeth. Thereafter, heat treatment is performed by plasma nitriding.

  According to the rack and pinion type steering device according to the first aspect of the present invention, in the manufacturing process, after the pinion shaft is hardened by heat treatment, the rack and pinion type steering device that does not need to be processed on the pinion shaft is realized. I can do it.

  According to the method for manufacturing a pinion shaft according to the second aspect of the present invention, it is possible to realize a method for manufacturing a pinion shaft that does not need to be processed after being cured by heat treatment.

  Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof. FIG. 1 is a schematic diagram showing a configuration of an embodiment of a rack and pinion type steering apparatus according to the present invention. In this rack and pinion type steering device, a rack shaft 1 supported so as to be movable in the axial length direction is extended in the left-right direction of a vehicle body (not shown) inside a cylindrical rack housing 10. Both ends of the rack shaft 1 projecting on both sides of the rack housing 10 are connected to the knuckle arms 12 and 12 of the left and right front wheels 11 and 11 which are steering wheels via respective tie rods 13 and 13. .

  Further, a pinion housing 20 is provided in the vicinity of one end of the rack housing 10 so as to cross the shaft center thereof, and the pinion shaft 2 is rotatably provided around the shaft inside the pinion housing 20. Is supported. A part of the pinion shaft 2 protrudes above the pinion housing 20 by an appropriate length, and this protruding end is connected to a steering wheel 22 that is a steering member via a column shaft 21.

  The lower half portion of the pinion shaft 2 extending inside the pinion housing 20 is increased in diameter over an appropriate length, and pinion teeth 4 are formed on the outer peripheral surface of the large diameter portion. In addition, rack teeth 3 are formed on the outer surface of the rack shaft 1 supported inside the rack housing 10 over an appropriate length including a portion facing the pinion shaft 2. The pinion teeth 4 provided on the peripheral surface of the pinion shaft 2 are engaged with each other.

  With the above configuration, when the steering wheel 22 is rotated for steering, the pinion shaft 2 connected to the steering wheel 22 via the column shaft 21 rotates, and this rotation is caused by the pinion teeth 4 and the rack teeth. 3 is converted into movement in the axial direction of the rack shaft 1, and the rack shaft 1 moves in both left and right directions.

  The movement of the rack shaft 1 thus generated is transmitted to the left and right knuckle arms 12 and 12 via the tie rods 13 and 13 connected to both ends of the rack shaft 1, and the knuckle arms 12 and 12 are pushed and pulled. The left and right front wheels 11 and 11 are steered in the operation direction of the steering wheel 22 until an angle corresponding to the operation amount is reached.

  The rack and pinion type steering device shown in FIG. 1 is configured as an electric power steering device including a motor 5 that assists the steering performed as described above. The steering assist motor 5 is attached to the outer periphery near the lower end of a cylindrical column housing 23 that supports the column shaft 21 so as to be substantially orthogonal to the internal column shaft 21. The rotation of the motor 5 is configured to be transmitted to the column shaft 21 via a worm gear speed reducer (not shown) configured inside the column housing 23. Further, in the column housing 23, a torque detection device 24 that detects rotational torque (steering torque) applied to the column shaft 21 is arranged above the mounting portion of the motor 5. The detected steering torque is used for drive control of the steering assist motor 5.

  With the above configuration, when the steering wheel 22 is rotated, the steering torque applied to the column shaft 21 along with this is detected by the torque detection device 24. The rotational force of the steering assisting motor 5 that is driven and controlled based on the detected torque is applied to the column shaft 21 and transmitted from the column shaft 21 to the pinion shaft 2, so that a moving force in the axial direction is added to the rack shaft 1. This movement assists the steering performed as described above.

  FIG. 2 is an outline view showing an example of the pinion shaft 2 of the rack and pinion type steering apparatus according to the present invention. One end of the pinion shaft 2 is a connecting portion 41 for connecting to the column shaft 21. A shaft portion 42 is formed from the connecting portion 41 to the intermediate portion, and from the intermediate portion to the other end portion. The pinion teeth 4 are formed, and a fitting portion 44 for fitting to a bearing (not shown) provided in the pinion housing 20 is formed at the other end portion. A plasma nitriding hardened layer is formed on the pinion shaft 2 on at least the tooth surface (4) meshing with the rack shaft 1.

  In order to manufacture such a pinion shaft 2, first, rough cutting is performed on a steel bar which is a material, and the pinion teeth 4 are roughly processed. Next, after grinding the outer diameters of the connecting portion 41, the shaft portion 42, the pinion teeth 4 and the fitting portion 44, the pinion teeth 4 are finished. Finally, as an alternative to the conventional hardening process such as quenching, a heat treatment by a plasma nitriding method is performed.

In the heat treatment by the plasma nitriding method, as shown in FIG. 3, the pinion shaft 2 is accommodated in a vacuum chamber 30 whose pressure is reduced, the pinion shaft 2 is used as a cathode (−), and the vacuum chamber 30 is used as an anode (+). When the inside of the vacuum chamber 30 is in a reduced pressure atmosphere (1 to 10 Torr (133 to 1333 Pa)) of nitrogen (N ₂ ) + hydrogen (H ₂ ) and a voltage of several hundred volts is applied to the DC power source 31, the cathode side (pinion shaft 2 Glow discharge occurs on the side. During the glow discharge, a large amount of atmospheric gas ions (N ⁺ and H ⁺ ) exist and collide with the pinion shaft 2, which is the cathode, with high energy. Therefore, the temperature of the pinion shaft 2 is increased by ion bombardment, and at the same time, nitrogen reacts with iron to generate iron nitride on the surface layer of the pinion shaft 2 and further diffuses toward the inside and nitriding proceeds. The thickness (depth) of the hardened layer made of iron nitride is 0.2 to 0.3 mm.

  In the heat treatment by the plasma nitriding method, the high temperature stops only in the vicinity of the surface of the pinion shaft 2, so that the deformation is minute. Therefore, outer diameter grinding can be performed before the heat treatment, and a distortion removing step is not necessary. Further, finishing teeth can be processed before heat treatment, and finishing teeth after heat treatment are not necessary.

  In the above embodiment, a steering assist motor is provided between the steering member and the pinion shaft, and the rotational force of this motor is transmitted to the pinion shaft to perform steering in response to the rotation of the pinion shaft. The auxiliary electric power steering apparatus, that is, the rack and pinion type steering apparatus configured as a so-called column assist type electric power steering apparatus has been described. You may apply to a type steering device. Further, a rack and pinion type steering device configured as a manual type steering device that performs steering only by a steering torque applied to the steering wheel 22 by a driver, and further generation of a hydraulic cylinder provided in the middle of the rack housing 10 Needless to say, the present invention can also be applied to a rack and pinion type steering device configured as a hydraulic power steering device that applies steering force to the rack shaft 1 to assist steering.

It is a mimetic diagram showing composition of an embodiment of a rack and pinion type steering device concerning the present invention. It is an outline drawing which shows the example of the pinion shaft of the rack and pinion type steering apparatus according to the present invention. It is explanatory drawing which shows typically the heat processing by a plasma nitriding method.

Explanation of symbols

1 Rack shaft 2 Pinion shaft 3 Rack teeth 4 Pinion teeth 22 Steering wheel (steering member)
30 vacuum chamber

Claims (2)

In a rack and pinion type steering apparatus comprising a pinion shaft and a rack shaft meshing with the pinion shaft,
A rack and pinion type steering apparatus, wherein the pinion shaft has a plasma nitriding hardened layer formed on at least a tooth surface meshing with the rack shaft. In the manufacturing method of the pinion shaft for manufacturing the pinion shaft of the rack and pinion type steering device,
A method for manufacturing a pinion shaft, comprising: roughing teeth, grinding the outer diameter, finishing the teeth, and then performing a heat treatment by plasma nitriding.

Images