JP3648980B2 - Torque sensor shaft manufacturing method and manufacturing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a shaft having a specific shape used in a torque sensor and an apparatus suitable for carrying out the method, and in particular, such a shaft having a specific shape can be manufactured at low cost with high accuracy. It is a thing.
[0002]
[Prior art]
As a conventional torque sensor, there is one disclosed in Japanese Patent Application Laid-Open No. 8-207798 previously proposed by the present applicant. Such a conventional torque sensor connects an input shaft and an output shaft via a torsion bar, and a cross-shaped protrusion (cross protrusion) is formed at one end of the input shaft and the output shaft. A plurality of spiral grooves are formed in a predetermined length range of the shaft portion following the cruciform protrusion, and a sensor ring is disposed so as to surround the portion where the plurality of spiral grooves are formed. Two rows of circumferential grooves that are continuous in the circumferential direction are formed on the inner circumferential surface of the sensor ring, and a plurality of balls roll into the gap formed by the circumferential groove and the spiral groove. Contained as possible. Further, the other end of the input shaft and the output shaft is inserted between the one and the sensor ring, and in the slit extending in the axial direction formed at the other end of the input shaft and the output shaft, Some balls are to be accommodated. Therefore, if a relative rotation accompanied by torsion of the torsion bar occurs according to the torque between the input shaft and the output shaft, the sensor ring is guided in the ball and the spiral groove and displaced in the axial direction. By detecting the direction and magnitude, the torque generated on the input shaft and the output shaft can be detected. The cross projection formed on one end of the input shaft and the output shaft is inserted in a cross groove formed on the other side so that a predetermined gap is formed in the rotation direction, thereby The relative rotation between the shaft and the main force shaft is restricted within a predetermined angle range.
[0003]
In such a type of torque sensor, in order to obtain high detection accuracy, the processing accuracy of the rotary shaft on which the cross protrusion and the spiral groove are formed is important. Generally, it was manufactured by a shaving process.
[0004]
Specifically, a cross-shaped projection is formed by milling or the like on the end of a material obtained by cutting a cylindrical round bar into a predetermined length, and a ball end mill is used for the spiral groove based on the cross-shaped projection. It is processed by milling. Thereafter, a heat treatment is performed on a portion requiring hardness.
[0005]
However, in the manufacturing by the above-described machining, the machining time is very long, and an expensive machine such as a machining center must be used as the machining machine, and the cutting tool has a short life, and therefore the machining cost increases. There is a problem.
[0006]
On the other hand, in order to deal with the problems of such machining, recently, it has begun to consider producing a shaft having a specific shape as described above by plastic working. For example, it is conceivable that the cross-shaped protrusion at the end of the shaft is manufactured by extrusion forging, and the spiral groove of the shaft shaft is manufactured by rolling.
[0007]
[Problems to be solved by the invention]
Certainly, the cross projection at the end of the shaft can be formed by extrusion forging, and there is no particular problem in itself. On the other hand, the rolling process of the spiral groove presses a cylindrical tool that has a projection that matches the shape of the spiral groove on the outer periphery against the shaft from both sides to form a recess that becomes a spiral groove on the surface of the shaft. However, in such a processing method, it is difficult to accurately match the phases of the protrusions on the tool pressed on both sides of the shaft, and thus it is difficult to accurately form the spiral groove. This tendency becomes more prominent as the twist angle of the spiral groove increases. Further, in the case of this processing method, in order to avoid interference between the tool for forming the spiral groove and the shaft portion where the spiral groove of the shaft is not formed, the spiral groove forming portion of the shaft portion of the shaft and the portion that is not so It is necessary to form an annular relief groove in advance at the boundary, and there is also a problem that the strength of the shaft is reduced by the amount of this annular relief groove. Moreover, in the case of this processing method, it is technically very difficult to strictly match the phase relationship between the cross-shaped protrusion formed at the tip and the spiral groove formed by rolling.
[0008]
Such a problem cannot be solved even when the spiral groove is first rolled and then the cross projection is formed by extrusion forging. That is, when the cross projections are formed by extrusion forging, the load must be applied so that the material can be deformed in the radial direction, and the shape of the spiral groove is destroyed by the load.
[0009]
Furthermore, it is conceivable to form the cross protrusion and the spiral groove at a time by extrusion forging. With such a manufacturing method, it is possible to precisely match the phase relationship between the cruciform protrusion and the spiral groove if the phase of the cruciform protrusion processing die and the spiral groove processing die is reliably set. However, in this processing method, since a cruciform projection consisting of a projection extending in the axial direction is formed last, a twist occurs between the cruciform projection at the tip and the start position of the spiral groove, The shape will collapse. Also, in this processing method, when the material is taken out from the die after formation, the entire material cannot be rotated until the tip cross projection part is detached from the cross projection forming die. Therefore, it is difficult to remove the molded product from the molding die.
[0010]
The present invention has been made paying attention to various unsolved problems in the conventional technology, and a method for manufacturing a specific-shaped shaft used for a torque sensor with high accuracy at low cost and its The object is to provide an apparatus suitable for carrying out the method.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 has an axial projection extending in the axial direction on the outer peripheral surface of the tip portion, and spirals on the outer peripheral surface of a predetermined length range of the shaft portion following the tip portion. A method for manufacturing a torque sensor shaft having a groove, wherein the axial protrusion is formed on an outer peripheral surface of a tip portion of a round bar-shaped material, and a predetermined length range of a shaft portion following the tip portion of the material is reduced in diameter. A first forging step for performing extrusion forging to cause the second forging step to perform extrusion forging for forming the spiral groove in the shaft portion of the material having the reduced diameter. In the forging process, the position of the material is temporarily fixed using the axial protrusion formed in the first forging process, and the diameter of the material is reduced compared to the shaft portion in the temporarily fixed state. Grab the other end and remove the material Constant and, while maintaining the fixed, said using a die in the apparatus a predetermined positional relationship to perform temporary fixing to carry out the extrusion forging for forming the spiral groove.
[0012]
The invention according to claim 2 is an apparatus for carrying out the second forging step in the method for manufacturing a shaft for a torque sensor according to claim 1, wherein the die is rotatably fixed. And a temporary fixing device that performs the temporary fixing, and the rotational position of the die by the rotating pedestal returns to a predetermined rotational direction position before forming the spiral groove.
[0013]
Here, in the invention according to claim 1, the axial projection formed on the outer peripheral surface of the tip portion of the shaft, and the spiral groove formed in a predetermined length range of the shaft portion following the tip portion of the shaft, Are not formed at the same time. First, in the first forging process, axial protrusions are formed. However, when the axial protrusion is formed, preliminary forging is performed on the area where the spiral groove is formed, and the diameter of the area is reduced. Preliminary forging is mainly performed in order to form a spiral groove with a low load and high accuracy when performing the second forging process.
[0014]
Then, in the second forging step, a spiral groove is formed in the shaft portion where the preliminary forging of the material has been performed. First, the material is temporarily fixed using the already formed axial protrusion. . At this time, since the apparatus for temporarily fixing has a predetermined positional relationship with a die for forming a spiral groove later, the positional relationship between the material and the die is determined by temporary fixing. Temporary fixing uses an axial projection formed on the tip of the material, so as it is, it cannot be inserted into the die from the tip of the material, but in the present invention, in the temporarily fixed state, Since the material is fixed by gripping the other end (the end opposite to the tip formed by the axial projection) of the shaft portion of the material, the material and the die are fixed. The material can be inserted into the die while maintaining the positional relationship. When extrusion forging is performed using a die in this state, a spiral groove having a predetermined phase relationship with the axial projection is formed with high accuracy.
[0015]
Furthermore, in the invention according to claim 2, since the rotational position of the die returns to a predetermined rotational direction position before the spiral groove is formed, the phase between the axial projection and the spiral groove is determined. The relationship can be surely set to a predetermined phase relationship. Therefore, the 2nd forge process of the invention which concerns on the said Claim 1 is implemented suitably.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIGS. 1 to 7 are views showing an embodiment of the present invention. FIG. 1 is a perspective view of a torque sensor shaft 1 in a completed state, and FIG. 2 is a side view of the shaft 1 immediately before completion. FIG. 3 and FIG. 3 are sectional views taken along line AA in FIG.
[0017]
That is, the shaft 1 is a member used in a torque sensor as disclosed in the above-mentioned publication, and is connected coaxially via an input shaft (not shown) coupled to a steering wheel of a steering system and a torsion bar (not shown). It is the shaft which comprises the output shaft made.
[0018]
Then, a cross protrusion 1A including four axial protrusions 1a extending in the axial direction is formed at the tip of the shaft 1, and a predetermined twist angle is included in a predetermined length range of the shaft portion following the cross protrusion 1A. A plurality of (eight in this example) spiral grooves 1 </ b> B are formed. The cylindrical portion 1C is a portion other than the portion where the spiral groove 1B of the shaft portion of the shaft 1 is formed, and the shaft 1 is attached to the end of the cylindrical portion 1C opposite to the spiral groove 1B formation side. A coupling portion 1D for connecting to another member (for example, a pinion shaft of a rack and pinion type steering device) is formed. An opening 1E for spline coupling one end of the torsion bar is formed on the end surface of the shaft 1 on the cross projection 1A side, and the other end of the torsion bar is splined to the input shaft. It has become. The cruciform protrusion 1A is inserted into a cruciform groove formed at the end of the input shaft so that a clearance is formed in the rotational direction, thereby allowing relative rotation between the input shaft and the shaft 1 to be within a predetermined angular range. (For example, about ± 5 °).
[0019]
FIG. 4 is a perspective view showing a manufacturing process of the shaft 1, and the order of (a), (b), and (c) represents the process of progress. That is, first, a round bar-shaped material 2 having a predetermined length is cut out (FIG. 4 (a)), and then a cross projection 1A is formed at the tip, and a spiral groove 1B is formed at the same time as the formation of the cross projection 1A. The shaft portion is drawn (preliminarily molded), and the shaft portion is reduced in diameter to form the reduced diameter portion 3 (FIG. 4B).
[0020]
The cruciform protrusion 1A and the reduced diameter portion 3 are formed by combining a cruciform protrusion forming die and a draw forming die with their centers aligned so that the cruciform protrusion forming die is on the lower side. By doing so, it forms simultaneously by one extrusion forging (1st forge process). At this time, by matching the centers of both dies, the centers of the cross projection 1A and the reduced diameter portion 3 can be reliably matched. Further, at this time, the spiral groove 1B is not formed in the reduced diameter portion 3, so that the shape of the spiral groove 1B cannot be broken when the cross projection 1A is processed. It is also very easy to pull out from the die.
[0021]
Further, the diameter of the reduced diameter portion 3 formed in the first forging step is 3.0 to 3.5% than the diameter of a circle having the same area as the cross-sectional area (see FIG. 3) after forming the spiral groove 1B. Set to increase. If the diameter of the reduced diameter portion 3 is made larger than this, the molding load at the time of processing the spiral groove 1B becomes too large and the shaft 1 is buckled or burrs are generated due to excess material. Becomes difficult. On the other hand, if the diameter of the reduced diameter portion 3 is made smaller than that, the possibility that the spiral groove 1B and the portion in between will be incompletely formed increases.
[0022]
When the first forging process is completed, the spiral groove 1B is formed using the forging device 10 shown in FIG. 5 (second forging process).
That is, the forging device 10 includes a rotating pedestal 11 that is rotatable about a central axis C that faces in the vertical direction, a die 12 that is fixed on the pedestal 11 with its axis aligned, and an opening portion of the die 12 on the die 12. The base plate 13 is installed so as not to block, the temporary fixing device 14 supported by the base plate 13, the two guide posts 15 extending in the vertical direction, and both ends supported by the guide posts 15 to be horizontal. And a fixing device 17 supported on the lower surface side of the base plate 16.
[0023]
As shown in FIG. 6, which is a perspective view of the die 12 in a half-cut state, the die 12 is a substantially cylindrical member, and a through hole 12 </ b> A penetrates between the upper surface and the lower surface coaxially with the central axis. A plurality (eight in this example) of spiral protrusions 12B for forming a spiral groove 1B having an acute angle at the upper end side so as to bite into the reduced diameter portion 3 of the shaft 1 are formed in 12A. Then, the large-diameter portion 12C on the lower surface side is fixed to the rotating pedestal 11, so that the central axis of the through hole 12A and the central axis C of the rotating pedestal 11 coincide. The rotary base 11 is formed with a hole extending in the vertical direction that communicates with the through hole 12A when the die 12 is fixed. Thus, when the spiral groove 1B is processed, the cross projection 1A is formed on the rotary base 11. You can escape to the side.
[0024]
On the other hand, the temporary fixing device 14 includes a pair of cylinders 14A that are disposed at target positions around the central axis C and are driven in synchronization with each other, and a direction and a center approaching the central axis C by each cylinder 14A. The shaft 1 is provided with a pair of fixing claws 14B capable of moving back and forth in a direction away from the axis C, and a fall prevention guide 14C for preventing the fall of the shaft 1 from which the spiral groove 1B is formed. This is a device for temporarily fixing coaxially with C.
[0025]
Specifically, the temporary fixing device 14 manually inserts the cross projection 1A portion of the shaft 1 between the fixing claws 14B from above with the fixing claws 14B retracted, and the cylinder 14A. To move the fixing claw 14B to the central axis C side, and fit the tip of the fixing claw 14B narrowed between the projections 1a of the cross projection 1A from both sides as shown in FIG. The position of the shaft 1 is temporarily fixed.
[0026]
At this time, since the rotational direction position of the cross projection 1A of the shaft 1 is fixed at a predetermined rotational direction position by the fixing claw 14B, if the relative positional relationship between the fixing claw 14B and the die 12 is fixed, The phase relationship between the cross projection 1A and the die 12 is fixed to a predetermined relationship. In other words, the rotational direction position of the die 12 is ultimately determined by the rotating pedestal 11, so that the phase relationship between the rotating pedestal 11 and the die 12 is determined to be a predetermined relationship, and before the processing of the spiral groove 1B, the rotating pedestal is performed. 11 is always returned to a predetermined initial position, the phase relationship between the cross projection 1A and the die 12 before the processing of the spiral groove 1B can be fixed to a predetermined relationship.
[0027]
The fixing claw 14B can be moved back to a position where the entire shaft 1 can pass through the cylinder 14A.
Then, the fixing device 17 is guided by the bearings 17A of four linear guide devices, one on each side fixed to the lower surface side of the base plate 16 so as to be the target position around the central axis C, and these bearings 17A. The rail 17B of the linear guide device capable of moving back and forth in the direction approaching the center axis C and the direction away from the center axis C, and the upper end portion of the columnar portion 1C of the shaft 1 can be gripped from both sides by being fixed to the tip of the rail 17B A pair of gripping claws 17C and a pair of cylinders 17D fixed to the base plate 16 and driven in synchronization with each other to advance and retract the gripping claws 17C.
[0028]
The fixing device 17 holds and fixes the upper end portion of the shaft 1 temporarily fixed by the temporary fixing device 14 as described above while holding the temporarily fixed position. After the fixing is completed, the fixing device 17 is fixed. A space for allowing the shaft 1 to pass therethrough is formed by retreating the claw 14B, and the entire base plate 16 is lowered along the guide post 15 while applying a load from above, thereby allowing the shaft 1 to pass through the through-hole 12A of the die 12. It is used in such a way that it is inserted into.
[0029]
That is, when the fixing device 17 grips the upper end portion of the shaft 1, the phase relationship between the cross projection 1 </ b> A and the die 12 is fixed to a predetermined relationship by the temporary fixing device 14. If the shaft 1 is inserted into the through-hole 12A of the die 12 while applying a load and extrusion forging is performed while holding the upper end portion of the die 12, the reduced-diameter portion 3 has a predetermined shape with each axial projection 1a of the cross projection 1A. The spiral groove 1B having the following phase relationship is formed with high accuracy.
[0030]
More specifically, when the shaft 1 is inserted while applying a load to the through hole 12 </ b> A of the die 12, until the tip of the spiral protrusion 12 </ b> B in the die 12 contacts the outer peripheral surface of the reduced diameter portion 3. Since no external force is applied, the rotational direction position remains at the initial position, but the tip of the spiral projection 12B is in contact with the outer peripheral surface of the reduced diameter portion 3, and the load applied to the shaft 1 causes the spiral projection 12B to When the tip starts to bite into the reduced diameter portion 3, the rotation of the shaft 1 becomes impossible by the fixing device 17, so that the die 12 itself rotates with the rotating base 11 by being guided by the spiral protrusion 12 </ b> B. Then, if the shaft 1 is lowered until the upper end portion of the reduced diameter portion 3 reaches the vicinity of the tip end of the spiral protrusion 12B in the die 12, the material of the outer peripheral surface of the reduced diameter portion 3 becomes the reduced diameter portion 3. As a result, the spiral groove 1B is formed with high accuracy without causing the collapse of the formed spiral groove 1B.
[0031]
When the shaft 1 is lowered to a predetermined position, the base plate 16 is raised along the guide shaft 15. Then, since the cross projection 1A is not in contact with other members, the die 12 can freely rotate together with the rotating base 11 in the direction opposite to that at the time of molding, so that the shaft 1 formed with the spiral groove 1B is It can be easily detached from the die 12, and the shape of the spiral groove 1B does not collapse upon the separation.
[0032]
When the shaft 1 is completely detached from the die 12, the rotational direction position of the rotary pedestal 11 returns to the initial position. Therefore, when the spiral groove 1B is formed on the next shaft 1, the cross protrusion of the shaft 1 is also formed. The phase relationship between 1A and the spiral projection 12B of the die 12 is a predetermined phase relationship. Therefore, even if the second forging step for repeatedly forming the spiral groove 1B on the plurality of shafts 1 is performed, the spiral groove 1B can be formed with high accuracy.
[0033]
When the spiral groove 1B is formed, the coupling portion 1D and the opening portion 1E are appropriately formed, and the torque sensor shaft 1 is completed.
Thus, in the present embodiment, in the first forging process, the cross protrusion 1A and the reduced diameter portion 3 are formed simultaneously, and in the second forging process, the dies 12 are formed using the cross protrusion 1A. Since the spiral groove 1B is formed in the reduced diameter portion 3 after positioning, the phase relationship between the cross projection 1A and the spiral groove 1B can be made with extremely high accuracy. As a result, with such a torque sensor using the shaft 1, the possibility that the torque detection accuracy will deteriorate due to the processing accuracy of the cross projection 1A and the spiral groove 1B is extremely low.
[0034]
Moreover, since the forging is performed in the first forging process to form the reduced diameter portion 3 having a predetermined diameter, when the spiral groove 1B is formed in the second forging process, the load is more reliably reduced. The spiral groove 1B can be formed with high accuracy.
[0035]
And by mass-producing the shaft 1 by the manufacturing process as described above, the manufacturing cost can be remarkably suppressed as compared to forming the shaft 1 by cutting.
[0036]
【The invention's effect】
As described above, according to the first aspect of the present invention, the torque sensor shaft having a specific shape is formed with the axial protrusion on the outer peripheral surface of the tip portion of the round bar-shaped material and at the tip portion of the material. A first forging step for performing extrusion forging to reduce the diameter range of the subsequent shaft portion, and a second forging step for performing extrusion forging to form a spiral groove in the reduced-diameter shaft portion of the material; In the second forging process, the position of the material is temporarily fixed using the axial protrusion formed in the first forging process, and the diameter of the material is reduced in the temporarily fixed state. In order to form a spiral groove by using a die having a predetermined positional relationship with a device that performs temporary fixing while holding the fixed portion by holding the portion on the other end side of the shaft portion and fixing the material. The torque forging A shaft for support, there is an effect that can be produced with high accuracy at low cost.
[0037]
Moreover, if it is the invention which concerns on Claim 2, since the 2nd forge process in the invention which concerns on Claim 1 can be performed more reliably, it is the shaft for torque sensors similarly to the invention which concerns on Claim 1. Can be manufactured with high accuracy at low cost.
[Brief description of the drawings]
FIG. 1 is a perspective view of a shaft according to an embodiment of the present invention.
FIG. 2 is a side view of a shaft immediately before completion.
FIG. 3 is a cross-sectional view taken along line AA in FIG.
FIG. 4 is a perspective view showing a shaft machining process.
FIG. 5 is a front view showing a schematic configuration of an apparatus for executing a second forging process.
FIG. 6 is a perspective view showing a state in which a half of a die is cut off.
FIG. 7 is a diagram showing a state in which a shaft is temporarily fixed.
[Explanation of symbols]
1 Shaft (Shaft for torque sensor)
DESCRIPTION OF SYMBOLS 1a Axial protrusion 1A Cross protrusion 1B Spiral groove 1C Cylindrical part 1D Coupling part 1E Opening part 2 Material 10 Forging apparatus 11 Rotating base 12 Die 13 Base plate 14 Temporary fixing apparatus 15 Guide post 16 Base plate 17 Fixing apparatus

Claims (2)

A method of manufacturing a torque sensor shaft having an axial protrusion extending in the axial direction on the outer peripheral surface of the tip portion and having a spiral groove on the outer peripheral surface of the shaft portion following the tip portion in a predetermined length range,
A first forging step of forming the axial protrusion on the outer peripheral surface of the tip of the round bar-shaped material and performing extrusion forging to reduce the diameter of a predetermined length range of the shaft portion following the tip of the material;
A second forging step of performing extrusion forging for forming the spiral groove in the shaft portion of the material having the reduced diameter, and
In the second forging step, the position of the material is temporarily fixed using the axial protrusion formed in the first forging step, and the diameter of the material is reduced in the temporarily fixed state. In order to form the spiral groove by using a die having a predetermined positional relationship with the temporarily fixing device while holding the fixed portion by holding the portion on the other end side from the portion and fixing the material. A method for producing a torque sensor shaft, comprising performing extrusion forging. An apparatus for performing the second forging step in the method of manufacturing a torque sensor shaft according to claim 1,
A rotating pedestal on which the die is rotatably fixed; and a temporary fixing device that performs the temporary fixing. The rotational position of the die by the rotating pedestal is a predetermined rotational direction position before forming the spiral groove. An apparatus for producing a torque sensor shaft, wherein

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