Description

APPARATUS FORFORMING RACK OF RACKBAR

Technical Field

[1] The present invention relates to an apparatus for forming a rack of a rack bar, and more particularly, to a rack forming apparatus for a rack bar which heightens tooth form precision of a rack gear and lengthens lifetime of a tool by a progressive forming work.

Background Art

[2] A rack bar is generally used to go in gear with a pinion and change the rotational motion of the pinion into the linear motion of the rack bar.

[3] The rack bar is also applied to a steering apparatus of a vehicle. The steering apparatus includes a steering shaft which is provided in the lower side of a steering handle at a driver's seat, a rotary valve connected to the steering shaft, and a rack bar which is extended to the left and right sides of a steering wheel and connected to the steering wheel in order to directly operate the steering wheel according to operation of the rotary valve.

[4] FlG. 1 is a cross-sectional view showing essential elements of a steering apparatus in which a rack bar is employed. FlG. 2 is a cross-sectional view showing a rack bar.

[5] In FlG. 1, a rotary valve 1 connected with hydraulic oil pipes Ia is provided to control oil supplied through a hydraulic pump (not shown). An input shaft Ib which is connected to a steering shaft (not shown) to thus receive a rotational force generated in a steering handle (not shown) is provided in the inside of the rotary valve 1.

[6] A pinion (not shown) which is rotated by a rotational force delivered through the input shaft Ib is prepared in the inner-bottom of the rotary valve 1, and a rack housing 2 which is integrally formed with the rotary valve 1 and extended in either side of the rotary valve 1 is prepared in the outer-lower portion of the rotary valve 1.

[7] The rack housing 2 is formed of a hollow pipe in which a space is formed so that the oil supplied through the rotary valve 1 flows. An oil seal 7 and a bellows 4 are installed at the inlet side of the rack housing 2.

[8] Referring to FIGS. 1 and 2, a rack bar 3 is formed in the rack housing 2. A rack gear 3c going in gear with a pinion prepared in the rotary valve 1 is formed in the rack bar 3.

[9] The rack bar 3 is prepared to axially move in the rack housing 2. The rack gear 3c going in gear with the pinion prepared in the rotary valve 1 is formed in the middle of the rack bar 3. Tie-rod ends 5 directly connected to the steering wheel are movably prepared in the left and right sides of the rack bar 3, respectively.

[10] A piston 3a is prepared in one side of the rack bar 3, in which the piston 3a closely contacts the inner surface of the rack housing 2 and slided in the rack housing 2. The piston 3a is installed between in the two hydraulic oil pipes Ia connected to the rotary valve 1 and the piston 3a operates with the hydraulic oil pressure of the oil supplied through the rotary valve 1.

[11] In this way, the rack bar 3 employed in the steering apparatus is formed of a hollow shape so as to resist a torsional force.

[12] The rack gear 3c in the hollow rack bar 3 is press-molded. However, since a tool is pressed perpendicularly with the rack bar to mold a tooth form in the press-molding work, a large force is applied to the tool. As a result, there is a problem that the lifetime of the tool including tool breakage is shortened.

[13] Moreover, in order to prevent deformation of the hollow rack bar at the time of pressurizing the tool, a supporting tool including a mandrel is inserted in the inner portion of the hollow rack bar. As described above, in the case that the tool is pressurized to mold a tooth form, there is a problem that since the thickness of the bottom of the tooth becomes thinner, a rigidity is lowered. Disclosure of Invention Technical Problem

[14] To solve the above problems, it is an object of the present invention to provide a rack forming apparatus for a rack bar which lengthens lifetime of a tool for forming a tooth form by a progressive forming work.

[15] It is another object of the present invention to provide a rack forming apparatus for a rack bar which enhances a rigidity of a rack gear and heightens tooth form precision of the rack gear.

[16] It is still another object of the present invention to provide a rack forming apparatus for a rack bar which minimizes deformation of a rack bar when a rack gear is formed in the rack bar. Technical Solution

[17] To accomplish the above object of the present invention, according to an aspect of the present invention, there is provided a rack forming apparatus for a rack bar in which a rack gear is formed on the outer circumference of the rack bar, the rack forming apparatus comprising: a forming roller on the outer circumference of which a forming rib corresponding to the rack gear is formed in which the forming roller can be horizontally moved and rotated; and a transfer unit which makes the forming roller and the rack bar move relatively to each other and which pressurizes the forming rib and the rack bar progressively.

[18] Moreover, the rack forming apparatus according to the present invention is char-

acterized in that the transfer unit comprises: a fixed block on which an inclined surface is formed; a moving block which is provided to slidably move along the inclined surface of the fixed block, in which a seating groove for seating the rack bar is formed; and a hydraulic or air cylinder which makes the moving block move, to thereby make the rack bar move toward the forming roller so as to pressurize the forming roller.

[19] Moreover, the rack forming apparatus according to the present invention is characterized in that the rack bar is fixed at a position, and the transfer unit comprises a horizontal cylinder and a vertical cylinder which make the forming roller horizontally and vertically with respect to the rack bar, respectively.

[20] Moreover, the rack forming apparatus according to the present invention is characterized in that the forming roller is positioned and the transfer unit comprises: a fixed block on which an inclined surface is formed and which can be moved horizontally; a moving block which is provided to slidably move along the inclined surface of the fixed block, in which a seating groove for seating a rack bar is formed; and any one selected from the group including a pressure cylinder, a threaded screw or a gear which makes the moving block move horizontally and vertically, to thereby make the rack bar move toward the forming roller so as to pressurize the forming roller.

[21] Moreover, the rack forming apparatus according to the present invention is characterized in that the forming roller is horizontally reciprocated by a vertical cylinder, and the transfer unit comprises: a fixed block with which part of the rack bar is fixedly coupled; and a horizontal cylinder which makes the fixed block horizontally reciprocated, in which the rack bar and the forming roller are moved mutually horizontally and vertically, to thereby contact and pressurize each other.

[22] Moreover, the rack forming apparatus according to the present invention is characterized by further comprising a guide groove through which the forming rib is guided to the moving block contacting the seating groove.

[23] Moreover, the rack forming apparatus according to the present invention is characterized in that the rack bar is formed of a hollow shape, and comprises a support rod which is inserted into a hollow portion at a location corresponding to the rack gear formed on the outer circumference of the hollow rack bar.

[24] Moreover, the rack forming apparatus according to the present invention is characterized in that the moving block is divided into a first moving block and a second moving block in which a coupling aperture is respectively formed, and comprises fastening bolts coupled with the coupling apertures to thus clamp the rack bar.

[25] Moreover, the rack forming apparatus according to the present invention is characterized in that the hollow rack bar is of an annular section and is filled with a core whose hardness is relatively lower than the rack bar, at a location corresponding to a direct-under portion of the rack gear to be formed.

[26] According to the features of the present invention, the rack forming apparatus forms a rack gear while pressurizing the forming roller and the rack bar progressively, to thus extend the lifetime of the forming roller, and does not require any support tool like the conventional art to thereby heighten the strength of the bottom of the tooth, and improve a tooth form precision by increasing the number of the rack forming times by a progressive forming work.

Advantageous Effects

[27] As described above, the rack forming apparatus according to the present invention provides the following advantage. [28] Firstly, since a rack gear is formed on a rack bar while a forming roller and the rack bar are pressurized mutually progressively, the lifetime of the forming roller can be extended. [29] Secondly, since the rack forming apparatus according to the present invention does not require any support tool, the rigidity of the bottom portion of a tooth can be enhanced in comparison with that of the conventional art. [30] Thirdly, a tooth form precision can be enhanced by increasing the number of the rack forming times by a progressive forming work. [31] Fourthly, a support rod is inserted into the hollow rack bar, to thus make a rack gear formed while supporting the rack bar when the rack gear is formed on the outer ci rcumference of the rack bar. Accordingly, deformation of the rack bar can be minimized. In addition, a flat portion is provided in the support rod, to thereby make the root portion of the tooth of the rack gear to be formed have a plane structure. Accordingly, an operational feature of a driving unit employing the support rod having the flat portion can be enhanced.

Brief Description of the Drawings [32] The above and/or other objects and/or advantages of the present invention will become more apparent by describing the preferred embodiments thereof in detail with reference to the accompanying drawings in which: [33] FIG. 1 is a cross-sectional view showing essential elements of a steering apparatus in which a rack bar is employed;

[34] FIG. 2 is a cross-sectional view showing a rack bar;

[35] FIG. 3 is a perspective view schematically showing a rack forming apparatus according to an embodiment of the present invention; [36] FIGS. 4 and 5 are cross-sectional views explaining schematic operations of the rack forming apparatus of FIG. 3, respectively; [37] FIGS. 6 to 8 are cross-sectional views explaining schematic operations of the rack forming apparatus according to another preferred embodiment of the present invention,

respectively;

[38] FlG. 9 is a cross-sectional view showing a hollow bar in which a tie bar is inserted at the time of the rack gear formation;

[39] FlG. 10 is a cross-sectional view of FlG. 9;

[40] FlG. 11 is a perspective view showing a rack forming apparatus according to still another preferred embodiment of the present invention; and

[41] FlG. 12 is a cross-sectional view showing a rack bar according to still another preferred embodiment of the present invention. Best Mode for Carrying Out the Invention

[42] Hereinbelow, a rack forming apparatus for a rack bar according to preferred embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numerals and symbols denote like elements through the following embodiments.

[43] As shown in FlG. 2, a rack bar 3 applied in a rack forming apparatus according to an embodiment of the present invention includes a rack gear 3c which is formed on a portion of the outer circumference of the rack bar 3. Since the rack bar is applied in a steering apparatus of a vehicle like the description of the conventional technique, the detailed description of the use of the rack bar will be omitted.

[44] Referring to FIGS. 3 to 5 showing a rack forming apparatus according to an embodiment of the present invention in which a rack gear 3c is formed on the outer circumference of the rack bar 3, the rack forming apparatus includes a forming roller 30 on the outer circumference of which a forming rib 31 corresponding to the rack gear 3c of FlG. 2 is formed in which the forming roller 30 can be rotated, and a transfer unit which makes the forming roller 30 and the rack bar 3 move relatively to each other and which pressurizes the forming rib 31 and the rack bar 3 progressively.

[45] The transfer unit includes a fixed block 10 on which an inclined surface is formed, a moving block 20 which is provided to slidably move along the inclined surface of the fixed block 10, in which a seating groove 23 for seating the rack bar is formed, and a hydraulic or air cylinder (not shown) which makes the moving block 20 move, to thereby make the rack bar 3 move toward the forming roller 30 so as to pressurize the forming roller 30.

[46] The reference numerals 11 and 21 are guide grooves and guide rails which are formed in the fixed block 10 and the moving block 20, respectively. Here, the guide grooves and guide rails play a role of guiding the moving block 20 stably.

[47] In the meantime, a guide groove 22 through which the forming rib 31 is guided is formed in the moving block 20 contacting with the seating groove 23.

[48] FlG. 9 is a cross-sectional view showing a hollow bar in which a tie bar is inserted

at the time of the rack gear formation, and FlG. 10 is a cross-sectional view of FlG. 9.

[49] Referring to FIGS. 9 and 10, the rack bar 3 is formed of a hollow shape, and the rack forming apparatus according to another embodiment of the present invention further includes a support rod 40 which is inserted into a hollow portion at a location corresponding to the rack gear 3c formed on the outer circumference of the hollow rack bar 3. The hollow rack bar 3 is of an annular section. A support rod 40 having a flat surface 41 at a location corresponding to a direct-under portion of the rack gear 3c to be formed is inserted into the hollow rack bar 3.

[50] The rack forming apparatus having the above-described structure according to the present invention will operate as follows.

[51] Firstly, a hollow rack bar 3 is safely seated into the seating groove 23 of the moving block 20. Here, the rack bar 3 is firmly fixed by a vice (not shown) so that the rack bar 3 does not move in the seating groove 23.

[52] Subsequently, the moving block 20 is ascended along the inclined surface of the fixed block 10 by a pneumatic or air cylinder. Otherwise, the forming roller 30 is descended to thus make the forming rib 31 and the hollow rack bar 3 mutually contact and pressurize each other. As shown in FlG. 5, the forming roller 30 is horizontally reciprocated to thus make part of the forming rib 31 molded on the outer circumference of the rack bar 3. The forming roller 30 is rotated using a driving motor or a hydraulic motor (not shown).

[53] Then, the moving block 20 is progressively ascended and the forming roller 30 is reciprocated, to thus form the rack gear 3c progressively. Here, the forming roller 30 is horizontally reciprocated and contacts the outer circumference of the rack bar 3 to then pressurize the rack bar 3. The forming roller 30 is rolled by a friction due to a contact to the rack bar.

[54] As described above, since the rack gear 3c is formed while the forming roller 30 and the rack bar 3 are accessed closely progressively, a large amount of force is not required in the forming roller 30. The lifetime of the forming roller 30 can be lengthened.

[55] Moreover, the rigidity of the bottom of the tooth in the rack gear 3c can be enhanced in comparison with that of the conventional art, since the rack gear 3c is formed according to a progressive access method.

[56] Here, once a plurality of forming rollers 30 are provided in the rack forming apparatus according to the present invention, a plurality of rack bars can be molded.

[57] In the above-described embodiment, the forming roller 30 is rotatably driven by a drive motor or a hydraulic motor (not shown). Moreover, the forming roller 30 can move horizontally or elevatedly ascended and descended. The horizontal movement and the vertical movement of the forming roller 30 can be implemented by a general

transfer unit. For example, the forming roller 30 can move horizontally or elevatedly by a pneumatic cylinder and a hydraulic cylinder.

[58] In the meantime, as shown in FIG. 6, the rack bar 3 is fixed at a random position and the transfer unit is configured as follows. The transfer unit includes a horizontal cylinder (not shown) and a vertical cylinder (not shown) which make the forming roller 30 horizontally and vertically with respect to the rack bar 3, respectively.

[59] As described above, the rack forming apparatus according to the present invention can form a rack gear while the forming roller 30 is moved horizontally or vertically with respect to the rack bar 3 whose position is fixed.

[60] Moreover, referring to FIG. 7 showing a rack forming apparatus according to another preferred embodiment of the present invention, the transfer unit includes a fixed block 10 on which an inclined surface is formed and which can be moved horizontally, a moving block 20 which is provided to slidably move along the inclined surface of the fixed block 10, in which a seating groove 23 for seating a rack bar 3 is formed, and any one selected from the group including a pressure cylinder, a threaded screw or a gear which makes the moving block 20 move.

[61] As described above, the rack forming apparatus according to the present invention can form a rack gear while the rack bar 3 is moved horizontally and vertically to then pressurize the forming roller 30 whose position is fixed.

[62] Moreover, as shown in FIG. 8, he forming roller 30 is horizontally reciprocated by a vertical cylinder (not shown), and the transfer unit includes a fixed block 10 with which part of the rack bar 3 is fixedly coupled, and a horizontal cylinder (not shown) which makes the fixed block 10 horizontally reciprocated, in which the rack bar 3 and the forming roller 30 are moved mutually horizontally and vertically, to thereby contact and pressurize each other, and to thus form a rack gear 3c.

[63] Moreover, the rack gear 3c can be formed while the forming roller 30 and the rack bar 3 are moved horizontally or vertically together.

[64] In the meantime, as shown in FIGS. 9 and 10, in order to form the rack gear 3c in the hollow rack bar 3, a support rod 40 is inserted into the hollow rack bar 3. Then, the forming roller 30 is rotated on the outer circumference of the rack bar 3. Accordingly, the rack bar 3 is pressurized to thus form the rack gear 3c. Once the rack gear 3c has been formed on the outer circumference of the rack bar 3 by the forming roller 30, the outer circumference of the rack bar 3 is pressed down by the forming roller 30, and thus the rack bar 3 is deformed. At the initial time of deformation, the inner surface of the rack bar 3 is supported by the support rod 40, to thus prevent deformation of the rack bar 3.

[65] Moreover, as shown in FIG. 10, the hollow rack bar 3 is of an annular section and uses a support rod 40 having a flat surface 41 at a location corresponding to a direct-

under portion of the rack gear 3c to be formed. Accordingly, since the root portion of the tooth of the rack gear 3c has a plane structure, an accurate engagement between the forming roller 30 and the rack gear 3c in the rack bar 3 is accomplished to thus enhance an operational performance characteristic.

[66] In the meantime, with reference to FlG. 11 showing a rack forming apparatus according to still another preferred embodiment of the present invention, an idling of a rack bar 3 is prevented at the time of forming a rack gear 3c on the surface of the rack bar 3 to thereby enable a smooth molding operation. As the configuration of FlG. 11 is similar to the embodiment of FlG. 3, and like reference numerals and symbols denote like elements, the detailed description of the like elements will be omitted.

[67] According to the characteristic portion of the embodiment, the moving block 20 is partitioned into a first moving block 20a and a second moving block 20b, in which the first moving block 20a and the second moving block 20b can be coupled through coupling apertures 25 by fastening bolts (not shown). That is, after the rack bar 3 is positioned between the first and second moving blocks 20a and 20b, and then the first and second moving blocks 20a 20b are mutually tightened to thus clamp the rack bar 3. Then, the forming roller 30 is pressurized to thus form the rack gear 3c.

[68] In this case, the idle of the rack bar 3 is prevented and thus a precise tooth form is molded. Particularly, the clamping state of the rack bar 3 is released, and then the rack gear 3c is formed while the rack bar 3 is rotated in order to be put a portion where the rack gear 3c is not formed in the rack bar 3 on a location facing the forming roller 30.

[69] In the meantime, with reference to FlG. 12 showing a rack forming apparatus according to still another preferred embodiment of the present invention, the hollow rack bar 3 is of an annular section and is filled with a core 100 of a material including copper, lead, rubber, synthetic resin etc., whose hardness is relatively lower than the rack bar 3, at a location corresponding to a direct-under portion of the rack gear 3c to be formed, in the hollow rack bar 3. In this manner, the rack gear 3c is formed. After the rack gear 3c has been molded, the core 100 is removed. This embodiment of FlG. 12 can be applied and performed in the similar method of the FlG. 9 embodiment. Mode for the Invention

[70] As described above, the present invention has been described with respect to particularly preferred embodiments. However, the present invention is not limited to the above embodiments, and it is possible for one who has an ordinary skill in the art to make various modifications and variations, without departing off the spirit of the present invention. Thus, the protective scope of the present invention is not defined within the detailed description thereof but is defined by the claims to be described later and the technical spirit of the present invention.

Industrial Applicability

[71] As described above, the present invention relates to a rack forming apparatus for a rack bar in which the rack forming apparatus can be used in a steering apparatus for a vehicle.