JP2019098790A - Steering knuckle - Google Patents

Abstract

To provide a steering knuckle which can improve the rigidity of a bent portion of a lower arm part connected to a lower arm.SOLUTION: A steering knuckle 1 comprises a main body part 10 for supporting wheels, and a lower arm part 11 extending downward from the main body part 10, and connected to a lower arm 4. The lower arm part 11 has a lower arm attachment part 13 which is bent toward the inside in a vehicle width direction at its tip, and connected with the lower arm 4 at its tip. The bent portion 12 of the lower arm part 11 has an inclined tissue in which a perlite rate of an outside region 12o located outside in the vehicle width direction is higher than a perlite rate of an inside region 12i located inside in the vehicle width direction, and the perlite rates are increased toward the outside from the inside in the vehicle width direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a steering knuckle including a lower arm portion coupled to a lower arm.

  A vehicle such as a car is provided with a steering knuckle that supports wheels. In general, a steering knuckle includes a main body supporting a wheel, and a lower arm extending downward from the main body and coupled to a lower arm. Patent Document 1 discloses a steering knuckle provided with a lower arm mounting portion in which a lower arm portion is bent inward in the vehicle width direction and a lower arm is coupled to the front end. The lower arm is coupled to the lower arm attachment portion by a ball joint, and the lower arm portion and the lower arm are coupled via the ball joint.

  The steering knuckle is generally formed of cast iron (eg, spheroidal graphite cast iron). Patent Document 2 discloses a technology for improving strength and toughness by forming a steering knuckle of cast steel of a predetermined composition.

JP, 2013-173494, A Unexamined-Japanese-Patent No. 2017-31451

  A load is mainly input from the lower arm toward the outside in the vehicle width direction, for example, at the time of a collision (contact) with a curb while the vehicle is traveling, for example, at the lower arm attachment portion of the lower arm portion of the steering knuckle. At that time, stress concentration is likely to occur at the bent portion of the lower arm portion, which tends to be a weak point in strength. Therefore, it is desirable to improve the strength against the load to the outer side in the vehicle width direction input to the lower arm attachment portion at the bent portion of the lower arm portion.

  One of the objects of the present invention is to provide a steering knuckle that can improve the strength at the bending portion of the lower arm portion connected to the lower arm.

  The inventors of the present invention obtained the following findings as a result of intensive studies on the lower arm portion of the steering knuckle connected to the lower arm. As shown in FIG. 2, when a load (indicated by an arrow F in the drawing) to the outer side in the vehicle width direction is input to the lower arm attachment portion 13, the bending portion 12 of the lower arm portion 11 is positioned inside in the vehicle width direction. Stress in the tensile direction is applied to the inner portion 12i, and stress in the compressive direction is applied to the outer portion 12o located on the outer side in the vehicle width direction. That is, stress in different directions is received between the inside and the outside of the bending portion 12 in the vehicle width direction. Then, since the inner portion 12i of the bent portion 12 is subjected to stress in the tensile direction, a crack serving as a fracture starting point is easily generated, so it is preferable that the elongation be large. On the other hand, the outer portion 12o of the bent portion 12 receives a stress in the compression direction, so that a crack is not easily generated, but from the viewpoint of suppressing the deformation of the bent portion 12, it is desirable that the elongation be small and the yield point be large.

  The inventor has found that the strength of the bent portion can be improved by changing the tissue between the inside and the outside in the vehicle width direction at the bent portion of the lower arm portion. Specifically, the inclined tissue is formed so that the pearlite rate in the inner part is low and the pearlite rate in the outer part is high (see FIG. 3 described later). Generally, in cast iron, a structure with a low pearlite rate has a small yield point and a large elongation, whereas a structure with a high pearlite rate has a large yield point and a small elongation. As described above, since the tensile stress is applied to the inside portion of the bent portion, it is possible to suppress the generation of the crack which is the starting point of the fracture by reducing the pearlite rate and increasing the elongation. On the other hand, since a compressive stress is applied to the outer side portion of the bent portion, deformation of the bent portion can be suppressed by increasing the pearlite rate to increase the yield point. Thus, breakage or deformation of the bent portion of the lower arm portion can be suppressed with respect to the load to the outer side in the vehicle width direction input to the lower arm attachment portion, and the strength of the bent portion is improved.

  By the way, a steering knuckle is manufactured by pouring molten iron of cast iron into a mold, and cooling and casting in the mold. In the conventional casting method, the entire mold is generally uniformly cooled, and it is cooled from the surface side of the steering knuckle in contact with the inner surface of the mold, the surface side has a faster cooling rate, and the center side has a slower cooling rate. . Therefore, due to the difference in the cooling rate, the pearlite rate is low in the surface portion, and the structure is high in the pearlite rate toward the central portion. FIG. 5 schematically shows the structure of a cross section (A-A cross section in FIG. 2) in a bending portion of a lower arm portion provided in a conventional steering knuckle. In FIG. 5, it is indicated that the pearlite rate is high in the order of a part indicated by hatching of lower left hatching, a part of hatching of horizontal line, a part of hatching of lower right hatching and a part of hatching with vertical line. In the case of the conventional steering knuckle, as shown in FIG. 5, in the bent portion of the lower arm portion, substantially the same tissue is formed on the inner side and the outer side in the vehicle width direction, and in the inner and outer portions, pearlite is compared to the central portion. The rate is low.

  The present invention has been made based on the above findings. Hereinafter, the present invention will be described.

(1) A steering knuckle according to one aspect of the present invention is
A body supporting the wheels,
A lower arm portion extending downward from the main body portion and coupled to a lower arm,
The lower arm portion has a lower arm attachment portion in which a tip end portion is bent inward in the vehicle width direction and the lower arm is coupled to the tip portion.
In the bent portion of the lower arm portion, the pearlite rate at the outer side located outside in the vehicle width direction is higher than the pearlite rate at the inner side located inside in the vehicle width direction, and the pearlite rate increases from the inside to the outside in the vehicle width direction Has a graded tissue.

  The steering knuckle has an inclined structure in which the pearlite rate at the outer side portion is higher than the pearlite rate at the inner side portion in the bent portion of the lower arm portion, and the pearlite rate increases from the inside to the outside in the vehicle width direction. According to the steering knuckle, since the pearlite rate at the inside portion of the bent portion is low and the elongation is large, it is possible to suppress the generation of the crack due to the tensile stress. Moreover, since the pearlite rate of the outer side part of a bending part is high and a yield point is large, the deformation | transformation by compressive stress can be suppressed. Therefore, the steering knuckle can suppress breakage or deformation of the bent portion of the lower arm portion with respect to the load to the outer side in the vehicle width direction input to the lower arm attachment portion. Therefore, the strength at the bent portion of the lower arm portion connected to the lower arm can be improved.

1 is a schematic front view showing a state in which a steering knuckle according to Embodiment 1 is attached to a vehicle. 1 is a schematic front view of a steering knuckle according to a first embodiment as viewed from the front side. FIG. 7 is an image view schematically showing a cross-sectional structure of a bent portion of a lower arm portion provided in the steering knuckle according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a mold used for manufacturing the steering knuckle according to Embodiment 1. It is an image figure which shows typically the cross-sectional structure | tissue of the bending part of the lower arm part with which the conventional steering knuckle is equipped.

  A steering knuckle according to an embodiment of the present invention will be described with reference to the drawings. The same reference numerals in the drawings indicate the same names. In the following description, “front”, “rear”, “upper”, “lower”, “left”, and “right” mean that the front of the vehicle is “front” and a direction based on this is a reference. Do. In the figure, the arrow FR indicates the front side in the longitudinal direction of the vehicle, the arrow UP indicates the upper side in the vertical direction of the vehicle, the arrow IN indicates the inner side (center side) in the vehicle width direction, and the arrow OUT indicates the outer side.

Embodiment 1
[Steering knuckle]
A steering knuckle 1 according to a first embodiment will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the steering knuckle 1 includes a main body 10 that supports the wheel 2 and a lower arm 11 that extends downward from the main body 10 and is connected to the lower arm 4. The lower arm portion 11 has a lower arm attachment portion 13 in which the lower arm 4 is bent at the tip end thereof inward in the vehicle width direction and the lower arm 4 is coupled to the tip end (see also FIG. 2). In addition, the steering knuckle 1 is provided with a knuckle arm 21 and an upper arm portion 31. The steering knuckle 1 is a cast product made of cast iron, specifically, spheroidal graphite cast iron, and the main body 10, the lower arm 11, the knuckle arm 21 and the upper arm 31 are integrally formed. One of the features of the steering knuckle 1 is, as shown in FIGS. 2 and 3, in the bending portion 12 of the lower arm portion 11, the pearlite rate of the outside portion 12o located outside in the vehicle width direction is located inside in the vehicle width direction. It has a graded texture which is higher than the pearlite rate of the inside portion 12i and increases in pearlite rate from the inside to the outside in the vehicle width direction. FIG. 1 shows a steering knuckle 1 supporting a left front wheel as viewed from the front of the vehicle. Hereinafter, each part of the steering knuckle 1 will be mainly described with reference to FIG. 1, and thereafter, the structure of the bending portion 12 of the lower arm portion 11 will be described in detail with reference to FIGS.

(Body part)
The main body portion 10 has a support hole penetrating in the vehicle width direction, and the axle 3 is inserted into the support hole via a bearing (not shown), and the wheel 2 fixed to the axle 3 is rotatable. To support. The tire 2 t is assembled to the wheel 2.

(Lower arm part)
The lower arm portion 11 extends downward from the main body portion 10 and is connected to the lower arm 4. A lower end portion (lower end portion) of the lower arm portion 11 is formed with a bent portion 12 which is bent inward in the vehicle width direction, and a lower arm attachment portion 13 to which the lower arm 4 is coupled is provided at the front end portion. The lower arm 4 is connected to the lower arm attachment portion 13 by a ball joint 15, and the lower arm portion 11 and the lower arm 4 are connected via the ball joint 15. The area of the cross section (a cross section orthogonal to the longitudinal direction of the lower arm portion 11) of the lower arm portion 11 (including the bent portion 12) is, for example, 400 mm ² or more and 700 mm ² or less.

  The lower arm mounting portion 13 of the lower arm portion 11 is loaded from the lower arm 4 toward the outside in the vehicle width direction, as shown in FIG. 2, for example, at the time of a collision (contact) with a curb while traveling (Indicated by F) is input. At that time, in the bending portion 12, a tensile stress is generated at the inside portion 12i located inside in the vehicle width direction, and a compression stress is generated at the outside portion 12o located outside on the vehicle width direction.

(Knuckle arm)
The knuckle arm 21 extends forward from the main body 10 and is connected to the tie rod 5. A tie rod attachment portion 23 to which the tie rod 5 is coupled is provided at the tip (front end) of the knuckle arm 21, and the tie rod 5 is coupled by a ball joint 25.

(Upper arm)
The upper arm portion 31 extends upward from the main body portion 10 and is connected to the shock absorber 6 a of the strut type suspension 6. A strut mounting portion 33 to which the shock absorber 6a is coupled is provided at a tip end portion (upper end portion) of the upper arm portion 31, and the shock absorber 6a is coupled by a bolt 35.

(Tissue of the bending part of the lower arm)
The tissue of the bent portion 12 of the lower arm portion 11 will be described with reference to FIG. FIG. 3 schematically shows the structure of an AA cross section (a cross section orthogonal to the longitudinal direction of the lower arm portion 11) of the bent portion 12 shown in FIG. In FIG. 3, it is indicated that the pearlite ratio is high in the order of a part shown by left hatching, a part shown by hatching, a part shown by hatching right and a part shown by hatching. In the present embodiment, in the bent portion 12 of the lower arm portion 11, as shown in FIG. 3, the tissues are different between the inside and the outside in the vehicle width direction. Specifically, the pearlite rate changes so that the outer side is higher than the inner side in the vehicle width direction, and has an inclined structure in which the pearlite rate increases from the inner side to the outer side in the vehicle width direction. That is, the pearlite rate of the outer side portion 12 o shown in FIG. 2 is higher than the pearlite rate of the inner side portion 12 i. Therefore, while the extension is large at the inside portion 12i of the bent portion 12, the yield point is large at the outer portion 12o. The outer region 12 o pearlite rate is, for example, 1.5 or more times, and further 2 or more times the pearlite rate of the inner region 12 i, depending on the composition, casting conditions and the like.

  The "pearlite ratio" refers to the area ratio of pearlite structure per unit area in the cross section. The pearlite rate is the area ratio of the pearlite structure occupied by 100% of the area of the structure excluding the graphite by measuring the area of the pearlite structure in the observation field of view by observing the structure of the cross section with a metallurgical microscope etc. It can be measured by calculating In this example, the cross section along the radial direction of bending of the bent portion is taken, and a plurality of points (for example, 4 or more points) on a straight line along the radial direction passing through the center (center of gravity) of the cross section of the bent portion The pearlite rate is determined from the inside to the outside in the vehicle width direction by measuring the pearlite rate of. As the measurement conditions, for example, the magnification: 50 times or more, the visual field size: 500 μm × 500 μm or more can be mentioned. As a structure other than pearlite, a ferrite structure is mainly mentioned.

  The composition of the steering knuckle 1 can adopt the composition of a well-known cast iron (for example, spheroidal graphite cast iron) and contains C, Si, Mn, P, S, and the rest is Fe and unavoidable impurities. Be Besides, for example, an element such as Mg, Cu, or Cr may be added.

  The steering knuckle 1 is manufactured by pouring molten iron of cast iron into a mold, and cooling and casting in the mold. The cross-sectional structure of the bent portion 12 of the lower arm portion 11 shown in FIG. 3 has a cooling rate of the outer portion 12 o (see FIG. 2) located outside in the vehicle width direction at the bent portion 12 of the lower arm portion 11 during casting. It is obtained by making it slower than the cooling rate of the inner part 12i (refer FIG. 2) located in the width direction inner side. By making the cooling rate of the outer side portion 12o slower than that of the inner side portion 12i, the pearlite rate of the outer side portion 12o can be made higher than that of the inner side portion 12i. This is because pearlite is less likely to be produced when the cooling rate is fast, and pearlite is produced as the cooling rate is slower.

  As a method of making the cooling rate of the outer site 12o slower than the cooling rate of the inner site 12i, temperature control of the mold may be mentioned. For example, at least one of a cooling mechanism for quenching the inside portion 12i side and a heating mechanism for gradually cooling the outside portion 12o side may be provided at a position corresponding to the bent portion 12 of the lower arm portion 11 in the mold. As an example of a structure of a casting_mold | template, as shown to FIG. 4 (A), in the casting_mold | template 40, the cooling water piping 41 is used as a cooling mechanism in the inner site | part 12i side among the parts corresponding to the bending part 12 of the lower arm part 11. It is possible to arrange. Alternatively, a heater (not shown) may be embedded as a heating mechanism on the outer portion 12 o side. As a cooling mechanism, a radiation fin (not shown) may be provided on the outer peripheral surface of the mold 40 on the inner side 12i side, and wind may be applied to the radiation fin to increase the cooling rate on the inner side 12i. A cooling water pipe may be provided on the outer side 12o side, in which case the number of cooling water pipes on the outer side 12o side and the cross sectional area of the flow path are smaller than those on the inner side 12i side, or the cooling water on the outer side 12o side The temperature of the cooling water flowing into the pipe may be higher than that of the inner portion 12i.

  Further, as another example, as shown in FIG. 4B, a pusher 42 may be provided on the side of the outer portion 12o, and the cooling rate of the outer portion 12o may be reduced by the pusher 42.

<Function effect>
The steering knuckle 1 of the first embodiment described above has the following effects.
In the bent portion 12 of the lower arm portion 11 connected to the lower arm 4, the pearlite rate of the outer side portion 12o is higher than the pearlite rate of the inner side portion 12i, and has an inclined tissue in which the pearlite rate increases from the inside to the outside of the vehicle width direction. Therefore, while the pearlite rate of the inside part 12i of the bending part 12 is low and elongation is large, the pearlite rate of the outer side part 12o is high, and the yield point is large. Therefore, when the load from the lower arm 4 to the lower arm attachment portion 13 is input to the outer side in the vehicle width direction, the inner portion 12i receiving the tensile stress has a large elongation, so that the generation of a crack due to the tensile stress can be suppressed. On the other hand, since the yield point is large at the outer portion 12 o which receives the compressive stress, the deformation due to the compressive stress can be suppressed. Accordingly, breakage or deformation of the bent portion 12 of the lower arm portion 11 can be suppressed with respect to the load to the outer side in the vehicle width direction input to the lower arm attachment portion 13, and the strength of the bent portion 12 can be improved.

  Further, the following appendices will be disclosed in connection with the embodiment of the present invention described above.

[Supplementary Note 1]
A manufacturing method of a steering knuckle in which a cast iron molten metal is poured into a mold, and cooled and cast in the mold,
The steering knuckle is
And a lower arm portion extending downward from the main body portion and connected to the lower arm.
A tip of the lower arm is bent inward in the vehicle width direction, and a tip of the lower arm has a lower arm attachment portion to which the lower arm is coupled.
The manufacturing method of a steering knuckle comprising the step of casting at a bending portion of the lower arm portion a cooling speed of an outer part located outside in the vehicle width direction slower than a cooling speed of an inner part located inside in the vehicle width direction.

  According to the manufacturing method of the steering knuckle of appendix 1, by setting the cooling rate of the outer side portion slower than the cooling rate of the inner side portion at the bending portion of the lower arm portion, the pearlite rate of the outer side portion is greater than the pearlite rate of the inner side portion It is possible to form a sloped structure in which the pearlite rate increases from the inside to the outside in the vehicle width direction. By reducing the pearlite rate at the inner portion of the bent portion to increase the elongation, it is possible to suppress the generation of a crack due to a tensile stress. Moreover, the deformation | transformation by compressive stress can be suppressed by making the pearlite rate of the outer side part of a bending part high, and enlarging a yield point. Therefore, it is possible to suppress breakage or deformation of the bent portion of the lower arm portion with respect to the load to the outer side in the vehicle width direction input to the lower arm attachment portion. Therefore, the method of manufacturing the steering knuckle can improve the strength at the bent portion of the lower arm portion connected to the lower arm.

  The present invention is not limited to the embodiments described above, is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

  The steering knuckle of the present invention is applicable to automobiles such as passenger cars and freight cars.

DESCRIPTION OF SYMBOLS 1 steering knuckle 2 wheel 2t tire 3 axle 4 lower arm 5 tie rod 6 suspension 6a shock absorber 10 main body 11 lower arm 12 bent portion 12i inner portion 12o outer portion 13 lower arm attachment portion 15 ball joint 21 knuckle arm 23 tie rod attachment portion 25 ball Joint 31 upper arm 33 strut mounting part 35 bolt 40 mold 41 cooling water piping 42 pouring water

Claims (1)

A body supporting the wheels,
A lower arm portion extending downward from the main body portion and coupled to a lower arm,
The lower arm portion has a lower arm attachment portion in which a tip end portion is bent inward in the vehicle width direction and the lower arm is coupled to the tip portion.
In the bent portion of the lower arm portion, the pearlite rate at the outer side located outside in the vehicle width direction is higher than the pearlite rate at the inner side located inside in the vehicle width direction, and the pearlite rate decreases from the outer side to the inside in the vehicle width direction Steering knuckles with inclined tissue.

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