JP4000234B2 - Hardening method and apparatus for rack bar - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rack bar quenching method used in a steering device of an automobile and the like, and a quenching device used in this method, characterized in that variation in tooth pitch due to quenching distortion is extremely small. In addition, a quenching device that can prevent the rack bar from being bent due to quenching strain is also provided.
[0002]
[Prior art]
As shown in FIG. 3, the rack bar 1 has a rack portion 2 in a part of the length of the bar. Recently, a rack bar 1 is made hollow to reduce the weight as shown in FIG. Such a hollow product is manufactured by making a hole after cutting the rack portion in the bar, or by forming the rack portion by special plastic working using a pipe as the material. The rack bar to which the present invention is applied includes both solid and hollow rack bars. The rack bar is usually hardened after processing, but since the cross-sectional shape is asymmetrical, the rack bar is likely to be bent by quenching, and the hollow bar is particularly prone to bend. Therefore, quenching is often performed in a restrained state, and generally, press quenching is performed in which the material is placed in the cooling liquid in a state of being restrained by pressurization after heating.
[0003]
In the case of quenching after high frequency heating, a method of injecting a coolant is also performed. In this case, a jacket for introducing a cooling liquid such as water is provided facing the material to be hardened, and the cooling liquid is sprayed toward the material to be hardened from a plurality of small holes provided in the jacket. When such a quenching method is used in combination with the restraint by the press as described above, for example, an apparatus as disclosed in JP-A-7-216456 is used.
[0004]
FIG. 8 is a cross-sectional view perpendicular to the length direction of the rack bar, showing an example of a conventional constraining quenching apparatus for a rack bar performed while spraying such coolant. In the figure, reference numeral 3 denotes one of the teeth of the rack lined up perpendicular to the paper surface. This device has an upper die 41 and a lower die 42 and is attached to a pressurizing device such as a hydraulic press (not shown). The inner side of the mold usually has a convex portion 43 having a tip position substantially coinciding with the shape of the rack bar. A concave portion 44 is provided between the convex portions, and a coolant jet port 45 is disposed here. Since the convex portions are normally arranged intermittently in the direction perpendicular to the paper surface of FIG. 8, the adjacent concave portions communicate with each other, and the injected cooling liquid is discharged to the outside of the mold through the adjacent concave portions. The In the figure, reference numeral 46 denotes a coolant supply chamber which has the function of the jacket and is connected to a pipe (not shown). The convex portion 44 can be discharged from between the teeth of the rack even if it is continuous in the direction perpendicular to the paper surface with respect to the portion corresponding to the rack portion, and is not necessarily intermittent. However, in any case, the coolant is ejected from a plurality of small holes arranged as appropriate.
[0005]
[Problems to be solved by the invention]
When the rack bar is restrained and hardened by the apparatus shown in FIG. 8 above, the bending distortion of the material to be hardened can be prevented by means such as adjusting the restraining force. The problem was that the pitch was irregular. That is, before quenching, the spacing between adjacent teeth is within a certain error range between teeth, but when quenching, the spacing varies. Such a variation in the spacing between the rack teeth prevents smooth meshing with the pinion, and degrades the performance of the mechanical device using the same. In view of the above problems, an object of the present invention is to provide a rack in which the spacing between adjacent teeth does not change during rack hardening.
[0006]
[Means for Solving the Problems]
The present invention solves the above-described problem, and in quenching of a rack bar in which at least the entire length of the rack portion is heated and quenching is performed by injecting coolant, quenching of the coolant to the rack portion is at least the rack portion. A rack bar quenching method characterized in that it is made into a curtain shape from one or more slits having a length of , and the spray liquid hits the entire length of the rack while crossing all the teeth of the rack. .
[0007]
Further, in a rack bar quenching apparatus for performing quenching by injecting a coolant onto a heated rack bar, a jacket having at least one coolant inlet and having a length of at least a rack portion; provided comprising at least a rack portion one or more coolant injection slits provided to face the perforated rack unit length of the hardenability of the rack bar, characterized in that it comprises an injection device of the cooling liquid relative to the rack section Device.
[0008]
Further, in the rack bar quenching apparatus, two or more convex portions having a length of the rack portion and having a predetermined height are provided on the jacket on both sides of the coolant injection slit, and the convex portions are provided in the rack. By contacting the part, the cooling liquid spraying device for the rack part constitutes one of restraining jigs for preventing the rack bar from being bent by quenching.
[0009]
Furthermore, in the rack bar quenching apparatus, one or more rectifying plates parallel to the cooling liquid injection slit and perpendicular to the cooling liquid injection direction are provided so as to partition the inside of the jacket, and the rectifying plate has an area thereof. And the coolant introduction port is opened in the space farthest from the coolant injection slit among the plurality of spaces in the jacket partitioned by the rectifying plate. It is also characterized by.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors examined the cause of the rack tooth pitch irregularity due to quenching. As a result, it was found that the cooling rate at the time of quenching was uneven in each tooth portion. That is, when cooling is performed from the heating temperature for quenching, contraction corresponding to thermal expansion occurs, but the part that has been cooled earlier contracts earlier than other parts. On the other hand, even if the portion cooled later is to shrink, the restriction by the portion where the strength is increased by cooling first is large, and the shrinkage is limited. As a result, the tooth between the teeth that has been cooled rapidly undergoes large contraction and the tooth pitch is narrow, and the one that has been cooled slowly has a wide tooth pitch. In addition to this, the occurrence of quenching strain is also affected by the martensitic transformation, and the volume expansion due to the martensitic transformation acts so as to cancel the thermal strain. Usually, however, the effect of thermal strain is relatively large, and as a result, irregularities in the spacing between the rack teeth are caused by the deformation as described above.
[0011]
As described above, a conventional rack bar quenching apparatus is used in which a large number of small hole coolant outlets are distributed. This is not because there is a positive reason to do this, but because it is as easy to make as all the shower and watering nozzles you see every day. In this case, the relative positions of the respective injection ports and the rack teeth are not constant because the rack pitch is relatively fine. For this reason, the sprayed coolant flows in all the tooth portions anyway, but the details of the contact of the coolant in each tooth are not constant. In other words, the spray liquid may directly hit any part of the teeth, for example, the peak or valley, or the liquid sprayed around other teeth instead of being directly applied to some teeth. May be cooled by. It is considered that such non-uniformity of how the cooling liquid hits the teeth of the rack causes non-uniformity of cooling at the time of quenching, causing distortion and non-uniform pitch of the teeth.
[0012]
Under these circumstances, the present inventors have studied a method of making the cooling liquid sprayed to the teeth of the rack uniform for each tooth. As a result, it has been found that if the coolant is sprayed onto the rack teeth by means of a slit having the length of the rack, it is possible to prevent irregularities in the rack teeth due to quenching. The jet of coolant from such a slit is in the form of one curtain, and hits the entire length of the rack while intersecting all the teeth of the rack. By doing so, the cooling liquid spray is directly applied to any tooth in the rack, and any tooth is cooled under the same conditions.
[0013]
In this case, if there is only one slit facing the central portion of the tooth width, the sprayed cooling liquid flows on both sides along the tooth surface, so that sufficiently uniform cooling is achieved. Thus, it is not necessary for the coolant to spray directly against the entire width of the teeth, and usually one slit per rack is sufficient. However, the present invention does not prevent two or more slits from being provided in parallel. In addition, the slit length needs to be continuously one in the portion where the rack teeth are present, but the length of the slit is extended from this, and the flat portion on both sides where the rack teeth are not formed, and further It does not matter even if it continues to the cylindrical part that is continuous.
[0014]
As an apparatus for carrying out the rack bar quenching method as described above, a jacket having a length equal to or greater than the length of the rack portion is provided as a cooling device for the rack portion, and at least the length of the rack portion is provided on the side surface thereof. What is necessary is just to provide the 1 or more coolant injection slit which has. Further, one or more coolant inlets are provided in the jacket. The jacket is a coolant supply chamber, and temporarily stores coolant such as water or lowers the flow velocity so that the coolant pressure in each part of the slit is made as uniform as possible. Then, at the time of quenching, the coolant may be sprayed at an appropriate distance, for example, about 10 mm, with the coolant spray slit of the apparatus facing the rack portion of the rack bar. The rack bar is usually hardened by heating not only the rack part but also the entire circumference of the part where the rack bar is formed. In this case, the cooling mechanism of the jacket facing the circumferential portion other than the rack portion is not particularly limited, and a plurality of small hole coolant injection ports similar to the conventional one may be provided. Of course, a jacket that does not participate in cooling of the rack portion, such as a portion that cools the circumferential portion on the opposite side of the rack portion, may be one having a plurality of small hole coolant injection ports as in the prior art.
[0015]
By the way, as described above, the rack bar has an asymmetric cross-sectional shape, so that it is likely to be bent by quenching. In particular, pipe-like hollow rack bars, unlike solid ones, have a tendency to bend because there is no restraining force from the inside of the material against bending force, and quenching should be performed in a state where pressure is restrained by a press. It is common. For this reason, the apparatus of the present invention preferably also has a mechanism for restraining the rack bar during cooling. Accordingly, an example of the rack bar quenching apparatus of the present invention having such restraining means will be described below with reference to the drawings.
[0016]
FIG. 1 is a cross-sectional view perpendicular to the length direction of a rack bar showing an example of the apparatus of the present invention, and FIG. 2 is a cross-sectional view parallel to the length direction of the rack bar. As shown in FIG. 1, in this apparatus, four restraining jigs 11, 12, 13, and 14 are used for pressurization from the vertical direction and the horizontal direction, but in the present invention, several restraining jigs are used. There is no particular limitation. However, in the case of the apparatus using the two restraining jigs of the upper mold 41 and the lower mold 42 shown in FIG. 8, it may be difficult to take out the material because it gets stuck in the mold, but four restraining jigs were used. This device does not have such a problem. At least one of the upper and lower and left and right restraining jigs is pressurized by a pressurizing device such as a hydraulic cylinder (not shown). That is, for example, if the lower restraining jig 11 is fixed at a predetermined position and a hydraulic cylinder is connected to the upper restraining jig 12, pressurization in the vertical direction can be performed.
[0017]
Each of the four restraining jigs 11, 12, 13, and 14 shown in FIG. 1 has coolant supply chambers 15, 16, 17, and 18 inside, and jets the coolant toward the rack bar 1. It has become. That is, all of the restraining jigs in this example also have the jacket function described above as the configuration of the quenching apparatus. Among these four restraining jigs, a particularly characteristic one is the lower restraining jig 11 that contacts the rack portion. As shown in a cross-sectional view parallel to the length direction of the rack bar in FIG. 2, two convex portions 19 having the length of the rack portion and a constant height are provided in parallel. ing. The convex portions come into contact with both sides in the width direction of the rack teeth and restrain the material during quenching. A coolant injection slit 20 is provided between the two convex portions 19 and extends over the entire length of the rack portion in the same manner as the convex portions. In addition, a coolant jet 21 of the coolant jet slit 20 is provided in the recess between the protrusions, and as shown in FIG. ing. However, the shape of this portion is not particularly limited as long as the spread of the injected cooling liquid is not hindered. For example, the periphery of the cooling liquid outlet may be set on a flat surface.
[0018]
On the other hand, the three restraining jigs 12, 13, and 14 other than the lower restraining jig 11 are also shown in the sectional view parallel to the length direction of the rack bar in FIG. As shown, the convex portions 22 are intermittent, and a small hole coolant outlet 24 is provided in the concave portion 23 between the convex portions. These convex portions come into contact with each other at the time of quenching and restrain the rack bar. However, since the convex portions are intermittently arranged, the adjacent concave portions 23 communicate with each other, and the injected coolant is constrained via the adjacent concave portions. It is discharged to the outside of the jigs 12, 13, and 14. However, the restraining jigs 12, 13, 14 other than contacting the rack portion 2 are not particularly limited to such a form in the present invention. In addition, the four code | symbols 25 in FIG. 1 are the jackets for coolant injection, and are the general structures where a plurality of small holes are provided, and the four restraining jigs 11, 12, 13, The coolant is sprayed onto the rack bar 1 at a portion between 14. Thus, in the present invention, it is free to separately add a coolant injection device for cooling other than the rack portion.
[0019]
In the quenching apparatus of FIGS. 1 and 2, the coolant supply chambers 15, 16, 17, and 18 of the respective restraining jigs 11, 12, 13, and 14 have coolant inlets as shown in FIG. 26 is provided to introduce water or the like. In this figure, two coolant inlets 26 are provided in each coolant supply chamber, but this reduces the difference in flow rate as much as possible depending on the position of the coolant injection ports 24 aligned in the rack bar length direction. It is to do. In particular, in the lower restraining jig 11 that cools the rack portion, it is possible to make the cooling liquid injection amount from the cooling liquid injection slit 20 uniform over the entire length of the slit so that the cooling speed is uniform and the teeth are This is necessary to reduce the occurrence of pitch irregularities. For this purpose, in addition to providing two or more cooling liquid inlets as described above, a countermeasure may be considered in which the internal volume of the cooling liquid supply chamber is increased as much as possible to reduce the internal flow rate and to make the pressure distribution uniform. The present invention also provides a particularly effective apparatus configuration for this purpose.
[0020]
That is, as a means for making the spray amount of the coolant uniform over the entire length of the slit, a rectifying plate parallel to the coolant spray slit and perpendicular to the coolant spray direction is provided so as to partition the inside of the jacket. In the example of the apparatus of the present invention shown in FIG. 1 and FIG. 2, the coolant supply chamber 15 corresponds to the inner part of the jacket in the configuration of the present invention. . The coolant introduction port 26 opens in a space on the opposite side of the space in the coolant supply chamber 15 partitioned by the rectifying plate from the coolant injection slit 20. The rectifying plate 27 has holes that occupy a part of its area in the length direction to provide fluid resistance, and by arranging in this way, the coolant entering from the coolant inlet 26 is rectified. A fluid resistance is received when passing through the plate, and the flow velocity can be made uniform over the entire length of the coolant injection slit 20 by this action.
[0021]
The form of the holes provided in the current plate is not particularly limited as long as the holes that occupy a part of the area of the current plate are provided uniformly in the length direction. FIG. 4 is a plan view showing an example of the current plate, but as shown, the small holes 28 may be distributed over the entire surface. In this example, the hole diameter is 3 mm. As another form, one slit may be formed over the entire length of the current plate. Further, not only one but also two or more rectifying plates may be provided in the jacket in parallel, so that the injection amount at each portion of the coolant injection slit can be made even more uniform. In this case, if the coolant introduction port is opened in the space farthest from the coolant injection slit among the plurality of spaces partitioned by the rectifying plate in the jacket, all of the coolant will reach the coolant injection slit. It will pass through the current plate, and the effect of making the flow uniform can be exhibited.
[0022]
The rack bar quenching apparatus of the present invention is not limited to the form shown in FIGS. For example, in this example, only one coolant injection slit 20 is provided at the center of the width of the rack portion, but two or more coolant injection slits 20 may be provided in parallel. In this case, three or more convex portions 19 may be provided so as to be arranged on both sides of two or more coolant injection slits. Furthermore, it is a matter of course that a plurality of protrusions themselves may be provided close together without providing a cooling liquid injection slit therebetween. Further, in the example shown in FIGS. 1 and 2, the convex portion 19 to be in contact with the rack portion is continuous and continuous throughout the entire length of the rack portion. But you can. However, since the sprayed coolant is discharged from between the teeth of the rack at the rack portion, there is no need to be intermittently different from the convex portion 22 that contacts the cylindrical portion.
[0023]
【Example】
The rack bar was quenched by applying the method of the present invention. The rack bar has a hollow shape as shown in FIG. 3, and the dimensions are 23 mm and 19 mm in the outer diameter of the tube where the rack portion is formed and the cross section is cut out. A rack is formed in a portion having a length of 180 mm. The entire circumference of the length portion where the rack was formed was heated to about 950 ° C. by high frequency, and this was quenched by the constrained quenching apparatus shown in FIGS. The coolant was water, and spraying was performed from all four restraining jigs 11, 12, 13, 14 and four jackets 25.
[0024]
As shown in FIG. 5, the rack tooth pitch is measured by placing a rod (pin) 31 so as to fit in the groove between the teeth and measuring the height position h of the side surface of the rod by so-called overpin measurement. I did it. That is, as the distance between the teeth increases, the rod 31 bites deeply into the groove, so that the height position h of the side surface of the rod, that is, the overpin size is reduced. The measurement result of the overpin dimension h for each tooth interval of the rack bar hardened by the apparatus of the present invention is shown in the graph of FIG. Although the measurement results before quenching of the same sample are also shown, it can be seen that there is little variation in dimensions throughout and the spacing between the rack teeth is uniform.
[0025]
On the other hand, in the apparatus shown in FIG. 1 and FIG. 2 as a comparative example, the lower restraining jig 11 is changed to a conventional one in which cooling water is injected from a plurality of small holes, and the others are quenched under the same conditions as described above. I did it. FIG. 7 is a graph showing the measurement result of the overpin dimension h of the comparative example quenched with this conventional apparatus, and it can be seen that there is a considerable variation and the rack tooth spacing is uneven. .
[0026]
【The invention's effect】
According to the quenching method of the rack bar of the present invention, the injection of the cooling liquid to the rack part is changed from the conventional nozzle having a small hole distribution to the slit-like nozzle extending over the entire length of the rack part. The difference in the cooling rate of each was reduced. Thereby, the dispersion | variation in the pitch of the tooth after hardening can be made small. Further, in the quenching apparatus of the present invention, in the restraining jig for restraint quenching, a parallel convex portion that contacts the rack portion is provided, and the slit-shaped cooling liquid injection nozzle is provided therebetween. Restraint quenching can be performed in combination with a restraining jig applied to the other surface of the rack bar. This can also prevent the rack bar from being bent due to quenching.
[Brief description of the drawings]
1 is a cross-sectional view perpendicular to the length direction of a rack bar showing an example of the apparatus of the present invention. FIG. 2 is a cross-sectional view parallel to the length direction of the rack bar of the apparatus of FIG. Fig. 4 is a plan view showing an example of a current plate. Fig. 5 is a diagram for explaining a method for measuring the pitch of rack teeth. Fig. 6 is a pitch of a rack bar quenched by the apparatus of the present invention. FIG. 7 is a graph showing the measurement result of the pitch of the rack bar hardened by the conventional apparatus. FIG. 8 is a longitudinal direction of the rack bar showing an example of the conventional restraint hardening apparatus for the rack bar. Sectional view perpendicular to [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Rack bar 2 Rack part 3 Rack teeth 11, 12, 13, 14 Restraint jigs 15, 16, 17, 18 Coolant supply chamber 19 Convex part 20 Coolant jet slit 21 Coolant jet outlet 22 Convex part 23 Concave part 24 Coolant outlet 25 Jacket 26 Coolant inlet 27 Current plate 28 Small hole 31 Rod 41 Upper die 42 Lower die 43 Convex portion 44 Concavity 45 Coolant outlet 46 Coolant supply chamber

Claims (4)

In quenching a rack bar that heats at least the entire length of the rack portion and performs quenching by spraying a coolant, the coolant is sprayed onto the rack portion in a curtain shape from at least one slit having the length of the rack portion. A rack bar quenching method, characterized in that the spray liquid hits the entire length of the rack while intersecting all the teeth of the rack. In a quenching apparatus for a rack bar that performs quenching by spraying a coolant onto a heated rack bar, a jacket having at least one coolant inlet and having a length of at least a rack portion is provided on the jacket. at least the length of the rack portion possess opposite the rack unit consisting of one or more cooling fluid injection slits provided by, quenching apparatus of the rack bar, characterized in that it comprises an injection device of the cooling liquid relative to the rack portion.   Two or more convex portions having a length of the rack portion and having a certain height are provided on the jacket on both sides of the cooling liquid ejection slit, and the convex portion contacts the rack portion, thereby the rack portion. 3. The rack bar hardening apparatus according to claim 2, wherein the cooling liquid spraying device constitutes one of restraining jigs for preventing bending of the rack bar due to quenching.   One or more rectifying plates parallel to the cooling liquid injection slit and perpendicular to the cooling liquid injection direction are provided so as to partition the inside of the jacket, and the rectifying plate has a hole that occupies a part of its area in the length direction. 3. The cooling liquid introduction port is provided evenly, and the cooling liquid introduction port opens in a space farthest from the cooling liquid injection slit among a plurality of spaces in a jacket partitioned by a rectifying plate. Or the rack bar quenching apparatus according to 3.

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