Torque transmission shaft having universal joint yoke and method of manufacturing the same

Abstract

A rod-shaped element having an outer diameter, which is the same as an outer diameter of a completed rod part, has one axial end portion and the other axial end portion to which a base end portion of a bifurcated yoke is fixed. The one axial end portion is subject to plastic working for diametrically deforming an outer periphery of the one axial end portion. Thereby, the outer periphery of the one axial end portion is formed with a male spline part having a groove bottom diameter smaller than an outer diameter of a rod part and having a tooth tip diameter larger than the outer diameter of the rod part.

Claims

1. A torque transmission shaft having a universal joint yoke, the torque transmission shaft comprising: a rod part which has a round rod shape and includes a male spline part provided on an outer periphery of a first axial end portion thereof; and a yoke which is fixed to a second, opposite, axial end portion of the rod part and includes a pair of arm parts configured to pivotally support end portions of a cross shaft configuring a cross shaft type universal joint, wherein a groove bottom diameter of the male spline part is smaller than an outer diameter of a part of the rod part axially distant from the male spline part, wherein a surface of the male spline part is provided with a coating layer made of a low friction material, wherein in the coating layer, a groove bottom layer formed on each of all groove bottoms of the male spline part has a diametrical thickness larger than a diametrical thickness of a tooth tip layer formed on each of all tooth tip portions of the male spline part.

2. The torque transmission shaft having the universal joint yoke according to claim 1, wherein a sectional shape of a spline groove of the male spline part is a partial arc shape.

3. A telescopic shaft comprising: the torque transmission shaft having the universal joint yoke according to claim 1, and another torque transmission shaft which has a round tube shape at least at one axial end portion and includes a female spline part formed on an inner periphery of said one axial end portion and configured to be spline-engaged with the male spline part, wherein a part of the rod part axially distant from the male spline part has an outer diameter smaller than an inscribed circle diameter of the female spline part of the other torque transmission shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a torque transmission shaft having a universal joint yoke according to a first embodiment of the present invention.

(2) FIG. 2A is an end view illustrating a torque transmission shaft having the universal joint yoke, as seen from a left side of FIG. 1, and FIG. 2B is a sectional view illustrating a state where the torque transmission shaft having the universal joint yoke and another torque transmission shaft having a round tube shape are combined.

(3) FIGS. 3A and 3B are partial side views illustrating a process of providing one axial end portion of a rod part with a male spline part so as to make the torque transmission shaft having the universal joint yoke, and FIG. 3C is a partial sectional view illustrating a state where the male spline part is combined with a female spline part of the other torque transmission shaft.

(4) FIGS. 4A and 4B are side views illustrating the entire torque transmission shaft having the universal joint yoke at the same states as FIGS. 3A and 3B.

(5) FIGS. 5A and 5B are enlarged sectional views taken along a V-V line of FIG. 1, which illustrate two examples of a structure where a coating layer made of a low friction material is provided for the male spline part.

(6) FIG. 6 is an enlarged sectional view corresponding to a VI part of FIG. 2B, which illustrates a relation between spline teeth configuring both male and female spline parts and a pitch circle diameter of spline engaging portions.

(7) FIG. 7 is the same view as FIG. 6, which illustrates another shape of the spline teeth configuring the male spline part.

(8) FIG. 8 is the same view as FIG. 2B, which illustrates a second embodiment of the present invention.

(9) FIG. 9 is the same view as FIG. 6, which illustrates the second embodiment of the present invention.

(10) FIG. 10 is a view corresponding to the enlarged V-V sectional view of FIG. 1, which illustrates a sectional shape of a male serration, which is a type of the male spline part.

(11) FIG. 11 is a partially cut side view illustrating one example of an automobile steering apparatus, in which an intermediate shaft including a torque transmission shaft having a universal joint yoke which is a subject of the present invention is incorporated.

(12) FIG. 12 is a cut side view illustrating the intermediate shaft.

(13) FIG. 13A is an end view illustrating a torque transmission shaft having a round rod shape, as seen from a left side of FIG. 12, and FIG. 13B is a sectional view illustrating a state where the torque transmission shaft is combined with another torque transmission shaft having a round tube shape.

(14) FIGS. 14A to 14C are side views illustrating processes of manufacturing a conventional torque transmission shaft having a universal joint yoke.

DETAILED DESCRIPTION OF EMBODIMENTS

(15) [First Embodiment]

(16) A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 illustrates a completed torque transmission shaft 17a having a universal joint yoke according to this embodiment. The torque transmission shaft 17a having the universal joint yoke is provided on an outer periphery of one axial end portion (a left end portion in FIG. 1) of a rod part 19 having a circular section with a male spline part 11a, and a base end portion of a yoke 9 having a pair of arm parts 20, 20 for pivotally supporting two end portions, which are diametrically opposite to each other, of four end portions of the cross shaft 10 (refer to FIG. 12) configuring the cross shaft-type universal joint 4a is fixed to the other axial end portion (a right end portion in FIG. 1) of the rod part 19. In particular, in the case of the torque transmission shaft 17a having the universal joint yoke of this embodiment, a groove bottom diameter d.sub.11 of the male spline part 11a is made to be smaller than an outer diameter D.sub.19 of the other axial end side part (a part of the rod part 19 axially distant from the male spline part 11a) of the rod part 19 (d.sub.11<D.sub.19). As shown in FIGS. 2B and 3C, the male spline part 11a of the torque transmission shaft 17a having the universal joint yoke is spline-engaged with a female spline part 18 provided on an inner periphery of the other torque transmission shaft 8b having a round tube shape. Thereby, the torque can be transmitted between the torque transmission shaft having the universal joint yoke and the other torque transmission shaft 8b, and the intermediate shaft (refer to FIGS. 11 to 13) of which axial size can be expanded and contracted is configured.

(17) As shown in FIGS. 3A, 3B, 4A and 4B, the torque transmission shaft 17a having the universal joint yoke as described above is made by performing only plastic working for a hollow or solid rod-shaped metal material, in principle. That is, even though cutting processing and grinding processing may be performed for finishing, the cutting processing and grinding processing causing a shape and a size to be changed are not performed in principle, except for a chamfering of an end portion, for example. In this embodiment, in order to make the torque transmission shaft 17a having the universal joint yoke as described above, a rod-shaped element 21 as shown in FIGS. 3A and 4A is first made by performing the plastic working such as press working and forge processing for a metal material such as carbon steel and stainless steel. The base end portion of the yoke 9 is fixed to the other axial end portion of the rod-shaped element 21 and an outer diameter D.sub.21 of one axial half part (a part except for the other axial end portion) thereof is made to be the same as an outer diameter D.sub.19 of the completed rod part 19 (D.sub.21=D.sub.19). The plastic working for making the rod-shaped element 21 is the same as the plastic working for making the first intermediate material 12, except that the outer diameter D.sub.21 of the rod-shaped element 21 is made to be smaller than the outer diameter D.sub.13 of the first base rod part 13 of the conventional first intermediate material 12 shown in FIG. 14A and to be substantially the same as the outer diameter D.sub.8a of the intermediate part of the completed torque transmission shaft 8a shown in FIG. 14C (D.sub.13>D.sub.21D.sub.8a). Also, since the well-known method can be applied to a method of implementing the plastic working for making the rod-shaped element 21, the specific illustration and description thereof will be omitted.

(18) After the rod-shaped element 21 as described above is made, the plastic working for diametrically deforming an outer periphery of one axial end portion of the rod-shaped element 21 is performed for the outer periphery of one axial end portion, as shown in FIGS. 3A and 3B, so that the male spline part 11 a is formed on the outer periphery of one axial end portion. As described above, the male spline part 11a is formed to have the groove bottom diameter d.sub.11 smaller than the outer diameter D.sub.19 of the rod part 19 (d.sub.11<D.sub.19) and to have a tooth tip diameter D.sub.11 larger than the outer diameter D.sub.19 of the rod part 19 (d.sub.11<D.sub.19<D.sub.11). Also, the groove bottom diameter and the outer diameter D.sub.19 of the rod part 19 are smaller than a tooth tip circle diameter (an inscribed circle diameter) D.sub.18 of the female spline part 18 formed on the inner periphery of the other torque transmission shaft 8b having the round tube shape (d.sub.11<D.sub.19<D.sub.18). Therefore, as described later, there is no interference between tooth tips of respective spline teeth 22a, 22a configuring the rod part 19 and the groove bottoms of the male spline part 11a or outer periphery of the rod part 19 at a state where the male spline part 11a and the female spline part 18 are spline-engaged.

(19) Incidentally, during the plastic working for forming the male spline part 11a, the outer periphery of one axial end portion of the rod-shaped element 21 is crushed diametrically inwards at a plurality of circumferential places, so that a plurality of spline groove portions 23, 23, each of which extends axially, are formed. At the same time, extra thicknesses (metal material) extruded from the respective spline groove portions 23, 23 are moved towards between the respective circumferentially adjacent spline groove portions 23, 23 and respective portions therebetween are thus projected (bulged) diametrically outwards, so that a plurality of spline teeth 22, 22, each of which has an axially long bank shape, are formed. For this reason, any plastic working capable of denting circumferential portions diametrically inwards to form the spline groove portions 23, 23, each of which is axially long, and projecting the portions between the respective circumferentially adjacent spline groove portions 23, 23 diametrically outwards to form the spline teeth 22, 22, each of which is axially long, can be applied. For example, the press working, the forge processing, the rolling processing and the like can be adopted.

(20) Regarding the plastic working, the forge processing, particularly, the cold forge processing is most preferable because it is possible to obtain the high size precision and shape precision and the male spline part 11a of high strength. When forming the male spline part 11a on the outer periphery of one axial end portion of the rod-shaped element 21 by the forge processing, one axial end portion of the rod-shaped element 21 is strongly axially pressed in a die, which is a type of a mold and has an inner surface shape conforming to (a concavo-convex shape is reverse to and the other basic shape coincides with) an outer surface shape of the male spline part 11a, the outer periphery of one axial end portion of the rod-shaped element 21 is pressed diametrically inwards over the axial direction at a plurality of circumferential places (actually, the diametrically outward bulging is suppressed) to form the respective spline groove portions 23, 23 and the portions between the respective circumferentially adjacent spline groove portions 23, 23 are projected (bulged) diametrically outwards to have a bank shape, so that the outer surface shape of one axial end portion is made to coincide with the inner surface shape of the die.

(21) The torque transmission shaft 17a having the universal joint yoke, in which the male spline part 11a is integrally provided on the outer periphery of one axial end portion and the yoke 9 is integrally provided at the other axial end portion as described above, is spline-engaged at the male spline part 11a with the female spline part 18 formed on the inner periphery of the other torque transmission shaft 8b having the round tube shape, as shown in FIGS. 3C and 2B, so that the torque can be transmitted between the torque transmission shaft 17a and the other torque transmission shaft 8b and the intermediate shaft 5 of which axial size can be expanded and contracted is configured, as shown in FIGS. 11 and 12. At this state, the tooth tips of the respective spline teeth 22, 22 configuring the male spline part 11a are positioned at a diametrical outer side of a pitch circle P and the tooth tips of the respective spline teeth 22a, 22a configuring the female spline part 18 are positioned at a diametrical inner side of the pitch circle P, as shown in FIG. 6. For example, the respective spline teeth 22, 22a are located with the pitch circle P being interposed therebetween from both diametrical sides. Therefore, the stiffness of the engaged portions (spline engaging portions) between both spline parts 11a, 18 is increased, so that it is possible to transmit the high torque easily and stably by the intermediate shaft 5. Incidentally, when a sectional shape of the spline groove portions 23, 23 between the respective spline teeth 22, 22 configuring the male spline part 11a is formed to have a partial arc shape, as shown in FIG. 7, the stiffness of the spline teeth 22, 22 provided between the respective spline groove portions 23, 23 can be increased. As a result, it is possible to transmit the high torque more easily and stably by the intermediate shaft 5.

(22) Incidentally, the spline engaging state (axial engaging strength) between the male spline part 11a and the female spline part 18 is appropriately adjusted by performance required for the intermediate shaft 5. In order to enable the spline parts to be axially displaced with small force so that the intermediate shaft 5 can smoothly adjust a position of a steering wheel in a front-rear direction, for example, a surface of the male spline part 11a may be provided with a coating layer 24a, 24b made of a low friction material for reducing an axial frictional resistance of the spline engaging portions with the female spline part 18, as shown in FIGS. 5A and 5B. As the low friction material for configuring the coating layer 24a, 24b, a variety of materials having required heat resistance and wear resistance can be used. However, for example, a solid lubricant such as molybdenum disulfide may also be used, in addition to a synthetic resin such as polyamide resin (PA), polyphenylenesulfide resin (PPS) and polyacetal resin (POM).

(23) The coating layer 24a shown in FIG. 5A of the coating layers 24a, 24b is thickened at parts corresponding to bottoms of the respective spline groove portions 23, 23. Therefore, the female spline part 18 and the coating layer 24a are contacted or closely face each other over an entire surface at a state where the male spline part 11a and the female spline part 18 are spline-engaged. In contrast, the coating layer 24b shown in FIG. 5B is formed to be entirely thin, including parts corresponding to the bottoms of the respective spline groove portions 23, 23. Therefore, at the state where the male spline part 11a and the female spline part 18 are spline-engaged, there is a gap between the tooth tip portions of the female spline part 18 and the coating layer 24b.

(24) In the gap, grease for lubricating the spline engaging portions between the male spline part 11a and the female spline part 18 may be collected, so that the lubricating state of the spline engaging portions by the grease can be favorably maintained for a long time.

(25) According to the torque transmission shaft 17a having the universal joint yoke having the above configuration and manufactured as described above, it is possible to save the manufacturing cost of the torque transmission shaft 17a having the universal joint yoke and to easily reduce a weight of the torque transmission shaft 17a having the universal joint yoke.

(26) That is, according to the manufacturing method of this embodiment, in order to form the male spline part 11a on the outer periphery of one axial end portion of the rod-shaped element 21, the outer periphery of one axial end portion is crushed diametrically inwards at the plurality of circumferential places, so that the plurality of spline groove portions 23, 23, each of which extends axially, are formed. At the same time, the extra thicknesses extruded from the respective spline groove portions 23, 23 are bulged diametrically outwards between the circumferentially adjacent spline groove portions 23, 23, so that the plurality of spline teeth 22, 22, each of which extends axially, are formed. Therefore, it is not necessary to perform the cutting processing such as turning machining for the intermediate part or base end portion of the rod-shaped element 21, which is a base rod part becoming the rod part 19, so as to prevent the interference between the tip portions of the spline teeth 22a, 22a configuring the female spline part 18 formed on the inner periphery of the other torque transmission shaft 8b having the round tube shape and the outer periphery of the rod part 19 of the torque transmission shaft 17a having a universal joint yoke. For this reason, it is possible to save the manufacturing cost of the torque transmission shaft 17a having the universal joint yoke.

(27) Also, since the male spline part 11a is made by the plastic working, the hardness and toughness of the respective spline teeth 22, 22 configuring the male spline part 11a are not particularly lowered but are sufficiently increased by densification and work hardening of the metal material resulting from the plastic working. Therefore, even when the tooth tip circle diameter of the male spline part 11a is not made to be particularly large (even when the height of the respective spline teeth 22, 22 configuring the male spline part 11a is made to be lower to some extent), it is possible to secure the sufficient strength of the spline engaging between the male spline part 11a and the female spline part 18 formed on the inner periphery of the other torque transmission shaft 8b, and to secure a capacity of the torque which can be transmitted by the intermediate shaft 5 including the torque transmission shaft 17a having the universal joint yoke. For this reason, it is not necessary to enlarge the pitch circle diameter of the spline engaging portions of the male and female spline parts 11a, 18 and the outer diameter (the groove bottom diameter d.sub.11 and the tooth tip circle diameter D.sub.11) of the part, for which the spline engaging portions are provided, of the torque transmission shaft 17a having a universal joint yoke, beyond necessity, so that it is easy to reduce weights of the torque transmission shaft 17a having the universal joint yoke and the intermediate shaft 5 including the torque transmission shaft 17a having the universal joint yoke.

(28) [Second Embodiment]

(29) A second embodiment of the present invention is described with reference to FIGS. 8 and 9. FIG. 8 illustrates the intermediate shaft 5 configured by combining a torque transmission shaft 17b having a universal joint yoke of this embodiment and the torque transmission shaft 8b. Incidentally, the torque transmission shaft 17b having the universal joint yoke of this embodiment is characterized in a structure of a coating layer 24c made of a low friction material and provided on the surface of the male spline part 11a. Since the other structures and manufacturing method are the same as those of the torque transmission shaft 17a having the universal joint yoke of the first embodiment, the structure of the coating layer 24c is focused in the below descriptions.

(30) In this embodiment, the coating layer 24c is formed over the entire length and entire circumference of the male spline part 11a. A thickness size W.sub.25 of groove bottom layers 25, 25 of the coating layer 24c, which are formed on the groove bottom of the male spline part 11a, in the diametrical direction (a direction orthogonal to a groove bottom surface) is larger than a thickness size W.sub.26 of tooth tip layers 26, 26 in the diametrical direction (a direction orthogonal to the tooth tip) formed on the tooth tip portions of the male spline part 11a (W.sub.25>W.sub.26). Specifically, the thickness size W.sub.25 of each groove bottom layer 25, 25 is set to be twice to three times as large as the thickness size W.sub.26 of each tooth tip layer 26, 26 (W.sub.25=(2 to 3)W.sub.26). Incidentally, a thickness size W.sub.27 of a side surface layer 27 of the coating layer 24c, which is formed on a circumferential side surface of each spline tooth of the male spline part 11a, in a direction orthogonal to the circumferential side surface is the same as the thickness size W.sub.26 of each tooth tip layer 26, 26 (W.sub.27=W.sub.26).

(31) Also, an outer diameter size D.sub.25 of each groove bottom layer 25, 25 is larger than an outer diameter size D.sub.19 of the rod part 19 (D.sub.25>D.sub.19). Also, as shown in FIGS. 8 and 9, at the state where the intermediate shaft 5 is configured, a gap for collecting grease is formed between the outer periphery of each groove bottom layer 25, 25 and a tooth tip surface of the female spline tooth of the female spline part 18 configuring the torque transmission shaft 8b and between the outer periphery of each tooth tip layer 26, 26 and the groove bottom surface of the female spline part 18. That is, the outer diameter size D.sub.25 of each groove bottom layer 25, 25 is smaller than a tooth tip circle (an inscribed circle) diameter D.sub.18a of the female spline part 18 (D.sub.25<D.sub.18a). Also, an outer diameter size D.sub.26 of each tooth tip layer 26, 26 is smaller than a groove bottom circle diameter D.sub.18b of the female spline part 18 (D.sub.26<D.sub.18b).

(32) A part of the torque transmission shaft 17b having the universal joint yoke of this embodiment except for the coating layer 24c is made by the same manufacturing method as the first embodiment. According to the torque transmission shaft 17b having the universal joint yoke made by the manufacturing method of the present invention, the groove bottom diameter d.sub.11 of the male spline part 11a is smaller than the outer diameter D.sub.19 of the rod part 19 (d.sub.11<D.sub.19), and the tooth tip diameter D.sub.11 is larger than the outer diameter D.sub.19 of the rod part 19 (d.sub.11<D.sub.19<D.sub.11) due to the distinguishing manufacturing process. Therefore, at a state where the coating layer 24c is not provided, a space (gap) between the groove bottom surface of the male spline part 11a and the tooth tip surface of the female spline part 18 is increased, as shown in FIG. 2, for example. The space preferably has a certain level of size so as to collect the grease therein. However, if the space is excessively large, a vibration suppression effect (damping effect) by the grease present in the space is deteriorated, so that the vibrations occurring at the axial expansion and contraction of the intermediate shaft 5 are transmitted to the steering wheel and the driver may feel uncomfortable.

(33) However, in this embodiment, the thickness relation between the respective groove bottom layers 25, 25 of the coating layer 24c and the respective tooth tip layers 26, 26 is adjusted as described above. For this reason, it is possible to make the space small and to adjust the same to an appropriate size by the respective groove bottom layers 25, 25. As a result, it is possible to improve the vibration suppression effect (damping effect) by the grease filled in the space. The other structures, operations and effects are the same as the first embodiment.

(34) In the meantime, the present invention is not limited to the above embodiments and can be appropriately modified and/or improved.

(35) For example, regarding the plastic working for forming the male spline part of the present invention, any plastic working capable of denting circumferential portions of one axial end portion of a rod-shaped element diametrically inwards to form spline groove portions, each of which extends axially, and projecting (bulging) portions between the circumferentially adjacent spline groove portions diametrically outwards to form spline teeth, each of which extends axially, can be applied. For example, the press working, the forge processing, the rolling processing and the like can be adopted. According to the press working, one axial end portion of the rod-shaped element is compressed diametrically between a plurality of molds configured to be diametrically displaced (perspective movement). Thereby, a concavo-convex shape formed on an inner periphery, which is a processing surface of each mold, is transferred to an outer periphery of one axial end portion of the rod-shaped element, so that the male spline part is formed.

(36) Also, according to the forge processing, one axial end portion of the rod-shaped element is strongly axially pressed in a die, which is a type of a mold and has an inner surface shape conforming to (a concavo-convex shape is reverse to and the other basic shape coincides with) an outer surface shape of the male spline part. Thereby, one axial end portion of the rod-shaped element is bulged diametrically outwards to make the outer surface shape of one axial end portion coincide with the inner surface shape of the die.

(37) Also, according to the rolling processing, one axial end portion of the rod-shaped element is strongly sandwiched between a pair of rack-shaped press dies each of which is a mold and is formed on each of side surfaces thereof facing each other with teeth conforming to the outer surface shape of the male spline part. At this state, both press dies are reciprocally displaced in a direction along which the respective teeth are arranged. Thereby, the shape of the teeth formed on both the press dies is transferred to the outer periphery of one axial end portion of the rod-shaped element, so that the male spline part is formed.

(38) The present application is based on Japanese Patent Application No. 2013-157518 filed on Jul. 30, 2013 and Japanese Patent Application No. 2014-050230 filed on Mar. 13, 2014, the contents of which are here incorporated by reference.

INDUSTRIAL APPLICABILITY

(39) In the above descriptions, the present invention is applied to the intermediate shaft which configures the automobile steering apparatus and is configured to transmit the rotation of the steering shaft to the input shaft of a steering gear unit. However, the present invention can also be applied to a variety of torque transmission shafts in which a cross shaft type universal joint is provided at an end portion and spline engaging portions are provided at an intermediate part. Also, when the torque to be transmitted is not so high, the engaging portions of the torque transmission shaft having the round rod shape and the torque transmission shaft having the round tube shape may also be made by serrations having a fine pitch, as shown in FIG. 10.

DESCRIPTION OF REFERENCE NUMERALS

(40) 1: steering wheel

(41) 2: steering gear unit

(42) 3: steering shaft

(43) 4a, 4b: universal joint

(44) 5: intermediate shaft

(45) 6: input shaft

(46) 7: tie rod

(47) 8a, 8b: torque transmission shaft

(48) 9, 9a, 9b: yoke

(49) 10: cross shaft

(50) 11, 11a: mail spline part

(51) 12: first intermediate material

(52) 13: first base rod part

(53) 14: second intermediate material

(54) 15: second base rod part

(55) 16: large diameter part

(56) 17a, 17b: torque transmission shaft having a universal joint yoke

(57) 18: female spline part

(58) 19: rod part

(59) 20: arm part

(60) 21: rod-shaped element

(61) 22, 22a: spline tooth

(62) 23, 23a: spline groove portion

(63) 24a, 24b: coating layer

(64) 25: groove bottom layer

(65) 26: tooth tip layer

(66) 27: side surface layer