GB2258712A

GB2258712A - Steering shaft and manufacturing method therefor

Info

Publication number: GB2258712A
Application number: GB9117676A
Authority: GB
Inventors: Takeru Tanaka
Original assignee: MITSUBOSHI SEISAKUSHO CO Ltd
Current assignee: MITSUBOSHI SEISAKUSHO CO Ltd
Priority date: 1991-08-16
Filing date: 1991-08-16
Publication date: 1993-02-17
Anticipated expiration: 2011-08-16
Also published as: GB2258712B; DE4130557A1; GB9117676D0

Description

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TITLE OF THE INVENTION

Steering Shaft and Manufacturing Method Therefor is SUM4ARY OF THE INVENTION This invention relates to a shock absorbing type steering shaft for steering front wheels of a vehicle by converting rotation of a steering wheel to reciprocation of a tie rod, and to a method of manufacturing the steering shaft.

The steering shaft has energy absorbers formed by filling a synthetic resin between the shaft and an def o-m, abl outer sleeve. This steering shaft comprises a plasticaiiy/ metal pipe including, in a region remote from the steering wheel, a flat portion for torque transmission to the outer sleeve, and a plurality of annular grooves to be filled with the synthetic resin. In a region adjacent the steering wheel, the plastic metal pipe includes an upper bearing mount, a screw for engaging a bearing retaining nut, a serrated shaft for engaging the steering wheel, and a screw for engaging a retainer 1 nut, all defined as integral parts of the plastic metal pipe and arranged in the stated order toward an extreme end of the pipe. This steering shaft is lightweight, and may be manufactured in a reduced shaping time and at low cost.

BACKGROUND OF THE INVENTION

Conventional steering shafts include the following shock absorbing type steering shaft.

A steering shaft having a shock absorbing struc- ture is formed of a solid round bar, and has a steering wheel connected to an upper end, and an outer sleeve connected to a lower end thereof. An energy absorber is formed between the solid bar steering shaft and outer sleeve by filling a synthetic resin into annular grooves defined on the shaft. The engagement structure consisting of the resin between the shaft and.outer sleeve is broken upon collision of the vehicle. In this way, the collision energy is absorbed to prevent the steering shaft from moving backward to the chest of 20 the driver. The known steering shaft having the above structure defines a flat portion for torque transmission to the outer sleeve. The flat portion is formed by cutting a region of the solid round bar remote from the steering wheel. Similarly, two resin filling annular grooves, for example, are cut in the solid bar. In a region adjacent the steering wheel, the solid round bar includes an upper bearing mount, a bearing retaining nut receiving portion, a steering wheel mount, and a retainer nut receiving portion, all cut and arranged in the stated order toward an extreme end of the bar. The steering shaft is manufactured by the further steps of cutting screws in the nut receiving portions, and serrating the steering wheel mount. It is difficult for this steering shaft to be formed lightweight. Moreover, this steering shaft has the disadvantages of requiring a long cutting time, being ill suited for mass production, and involving a high manufacturing cost.

OBJECTS OF THE INVENTION A primary object of this invention is to provide a steering shaft formed of a plastic metal pipe, which realizes lightweight, a reduced shaping time and low manufacturing cost.

Another object of this invention is to provide a method of manufacturing a steering shaft from a plastic metal pipe, which realizes lightweight, a reduced shaping time and low manufacturing cost.

Other objects of this invention will be apparent from the following description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side view partly in section of a steering shaft according to the present invention.

Fig. 2 is a side view of a plastic metal pipe prior to shaping.

Fig. 3 is an explanatory view of a first manufac turing step.

Fig. 4 is a sectional view showing a first movable die and a fixed die in a separated state.

Fig. 5 is an explanatory view of a second manufac- turing step.

is Fig. 6 is an enlarged sectional view of the first movable die.

Fig. 7 is an explanatory view of a two-stage shaft portion resulting from the second manufacturing step.

Fig. 8 is a sectional view of a second movable die.

Fig. 9 is an explanatory view of a three-stage shaft portion resulting from a third manufacturIng step and having preforming dimensions.

Fig. 10 is a sectional view of a third movable die.

Fig. 11 is an explanatory view of a three-stage shaft portion resulting from a fourth manufacturing step and having intermediate forming dimensions.

Fig. 12 is a sectional view of a fourth movable die.

Fig. 13 is an explanatory view of a four-stage shaft portion resulting from a fifth manufacturing step and having dimensions close to final dimensions.

Fig. 14 is a sectional view of a fifth movable die.

Fig. 15 is an explanatory view of a four-stage shaft portion resulting from a sixth manufacturing step and having final dimensions.

Fig. 16 is an explanatory fragmentary view of the steering shaft resulting from a seventh manufacturing step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of this invention will be described in detail hereinafter with reference to the drawings.

The drawings show a steering shaft and a manufac- turing method therefor. In Fig. 1, the steering shaft (dEforrr,able) 1 comprises a plastic/metal pipe 2 defining, in a region thereof remote from a steering wheel (right side in Fig. 1), a flat portion 4 for torque transmission to an outer sleeve 3, and two annular grooves 5 to be filled with a synthetic resin. In a region adjacent the steering wheel (left side in Fig. 1), the plastic metal pipe 2 includes a curved portion 6, an upper bearing mount 7, a taper 8, a screw 9 for engaging a bearing retaining nut, a taper 10, a shank 11, a taper 12, a serrated shaft 13 for engaging the steering wheel, a taper 14, and a screw 15 for engaging a retainer nut, which are defined as integral parts thereof and arranged in the stated order toward an extreme end of the pipe 2.

The outer sleeve 3 defines resin injection openings 16 for injecting a synthetic resin 17 to fill spaces defined between the annular grooves 5 and outer sleeve 3. The synthetic resin hardened therein forms energy absorbers 18 and 19 between the steering shaft 1 and outer sleeve 3.

The method of manufacturing the above steering shaft 1 and a die structure used in the manufacture will be described next with reference to Figs. 2 through 16.

Fig. 2 shows a plastic metal pipe 2 which is an unshaped blank having a predetermined length. This pipe 2 has a wall thickness of 2 to 3mm and an outside diameter D1 of about 22mm, for example.

As shown in Fig. 3, the annular grooves 5 having an outside diameter of 18 to 19mm are formed in positions of the above plastic metal pipe 2 corresponding to the energy absorbers 18 and 19. This shaping 7 is process is carried out by means of roller pressed plastic deformation (first manufacturing step).

As a result of the above roller shaping processF uniform annular gaps of 1.5 to 2mm are formed through the entire circumference between the outside diameter of pipe 2 and the outside diameter of annular grooves 5.

Fig. 4 shows the die structure in which a fixed die 20 includes a first fixed die 21 and a second fixed die 22 rigidly connected together. The first fixed die 21 defines a recess 24 for guiding a first movable die 23 and other movable dies 37, 51, 65 and 83 to be described later, and a bore 25 for maintaining the outside diameter of the blank pipe 2. The second fixed die 22 defines a form surface 26 at least on one side, preferably on both sides, of a pipe receiving bare 27 for shaping the flat portion 4 in the region of the pipe 2 remote from the steering wheel to be connected to the outer sleeve 3. The pipe receiving bore 27 communicates at one end thereof with the bore 25 of the first fixed die 21, the other end of the pipe receiving bore 27 being a bottomed end.

As shown in Fig. 6, the first movable die 23 defines, from a forward end (right end in Fig. 6) inwardly (leftward in Fig. 6), a tapered surface 28 having a predetermined angle el, a cylindrical surface 29 for squeezing the region of the pipe 1 adjacent the steering wheel, a tapered surface 30 having a predetermined angle 92, and a cylindrical surface 31 for squeezing the region of the pipe 1 adjacent the steering wheel. The various sections shown in Fig. 6 have 10 the following dimensions and angles, for example: D1 = D2 = D3 = is 22mmo 2 0. lmm(p 18.2mmo el = 15 degrees e2 = 15 degrees Ll = 2lmm Thus, the dimensions are set to establish the relational expression D3<W<D1.

The pipe 2 resulting from the first manufacturing step as shown in Fig. 3 is placed in the fixed die 20 and subjected to press working by the fixed die 20 and first movable die 23. As a result, as shown in Figs. 5 9 and 7, the pipe is squeezed at the region thereof remote from the steering wheel to form the flat portion 4, and at the end region adjacent the steering wheel to form a two-stage shaft portion 32 having smaller diameters than the outside diameter of the pipe 2 (second manufacturing step).

The two-stage shaft portion 32 includes a taper 33 having the angle el, a cylindrical portion 34 having the outside diameter D2, a taper 35 having the angle 82, and a cylindrical portion 36 having the outside diameter D3. These sections are arranged in the stated order toward the extreme end to correspond to the form surface structure of the first movable die 23.

Fig. 8 shows a second movable die 37 for shaping the two-stage shaft portion 32 (Fig. 7) into a threestage shaft portion 44 having preforming dimensions (Fig. 9). As shown in Fig. 8, the second movaIle die 37 defines, from a forward end inwardly, a tapered surface 38 having a predetermined angle e3, a cylindri- cal surface 39, a tapered surface 40 having a predetermined angle 04, a cylindrical surface 41, a tapered surface 42 having a predetermined angle eS, and a - 10 cylindrical surface 43 for squeezing the region of the pipe 1 adjacent the steering wheel. The various sections shown in Fig. 8 have the following dimensions and angles, for example:

D1 = 22mmo D2 = D3 = D4 = L1 = L2 = G3 = e4 = 95 = Thus, the dimensions and angles are set to estab- lish the relational expressions D4<M<D2<D1, e3>G1 and e4>62. The pipe 2 resulting from the second manufacturing step as shown in Fig. 7 is placed in the fixed die 20 (Fig. 4) and subjected to press working by the fixed die 20 and second movable die 37. As a result, the pipe 2 is squeezed to have the three-stage shaft portion 44 having the preforming dimensions shown in 2 0. lmmo 18. 2mmo 15. lmm 2lmm 2 Omm 30 degrees 25 degrees 13 degrees - 1 1 - Fig. 9 (third manufacturing step).

The three-stage shaft portion 44 includes a taper 45 having the angle e3, a cylindrical portion 46 having the outside diameter D2, a taper 47 having the angle 94, a cylindrical portion 48 having the outside diameter D3, a taper 49 having the angle 95, and a cylindrical portion 50 having the outside diameter D4. These sections are arranged in the stated order toward the extreme end to correspond to the form surface structure of the second movable die 37.

Fig. 10 shows a third movable die 51 for shaping the three-stage shaft portion 44 having the preforming dimensions (Fig. 9) into a three-stage shaft portion 58 having intermediate forming dimensions (Fig. 11). The third movable die 51 defines, from a forward end inwardly, a curved surface 52, a cylindrical surface 53, a tapered surface 54 having the predetermined angle e4, a cylindrical surface 55, a tapered surface 56 having a predetermined angle e6, and a cylindrical surface 57 for squeezing the region of the pipe 1 adjacent the steering wheel. The various sections shown in Fig. 10 have the following dimensions and for example: = 22mmo = 20.1mmo = 18.2mmg = 14.97mmg 2 Omm 25 degrees 7 degrees angles, D1 D2 D3 D5 L1 L2 94 e 6 R1 = lmm Thus, the dimensions and angles are set to establish the relational expressions D5<M<D2<D1 and e6>95.

The pipe 2 resulting from the third manufacturing step as shown in Fig. 9 is placed in the fixed die 20 and subjected to press working by the fixed die 20 and third movable die 51. As a result, the pipe 2 is squeezed to have the three-stage shaft 58 having the intermediate forming dimensions shown in Fig. 11 (fourth manufacturing step).

The three-stage shaft portion 58 having the intermediate forming dimensions includes a curved portion 59, a cylindrical portion 60 having the outsid 13 diameter D2, a taper 61 having the angle 94, a cylindrical portion 62 having the outside diameter D3, a taper 63 having the angle 06, and a cylindrical portion 64 having the outside diameter D5. These sections are arranged in the stated order toward the extreme end to correspond to the form surface structure of the third movable die 51.

Fig. 12 shows a fourth movable die 65 for shaping the three-stage shaft portion 58 having the intermedi- ate forming dimensions (Fig. 11) into a four-stage shaft portion 74 having dimensions close to final dimensions (Fig. 13). The fourth movable die 65 defines, from a forward end inwardly, a curved surface 66, a cylindrical surface 67, a tapered surface 68 having a predetermined angle e7, a cylindrical surface 69 for squeezing the region of the pipe 1 adjacent the steering wheel, a tapered surface 70 having a.predetermined angle H, a cylindrical surface 71, a tapered surface 72 having a predetermined angle G9, and a cylindrical surface 73 for squeezing the region of the pipe 1 adjacent the steering wheel. The various sections shown in Fig. 12 have the following dimensions 14 - for example:

and angles, D1 = 22mm 2 0. lmmcA 19.23mmo 14.97mMP 12.9mm 8mm 33mm 14mm lmm 15 degrees 5.7 degrees 15 degrees D2 = D6 = D5 = D7 = L3 = L4 = L5 = Rl = 97 = H e9 Thus, the dimensions and angles are set to establish the relational expressions D7<M<D6<D2<D1, 97<G4 and e8>e6.

The pipe 2 resulting from the fourth manufacturing step as shown in Fig. 11 is placed in the fixed die 20 and subjected to press working by the fixed die 20 and fourth movable die 65. As a result, the pipe 2 is squeezed to have the four-stage shaft portion 74 having the dimensions close to final dimensions as shown in - is Fig. 13 (fifth manufacturing step).

The four-stage shaft portion 74 includes a curved portion 75, a cylindrical portion 76 having the outside diameter D2, a taper 77 having the angle 07, a cylin- drical portion 78 having the outside diameter D6, a taper 79 having the angle H, a cylindrical portion 80 having the outside diameter DS, a taper 81 having the angle e9, and a cylindrical portion 82 having the outside diameter D7. These sections are arranged in the stated order toward the extreme end to correspond to the form surface structure of the fourth movable die 65.

Fig. 14 shows a fifth movable die 83 for shaping the four-stage shaft portion 74 having the dimensions close to final dimensions (Fig. 13) into a four-stage shaft portion 94 having the final dimensions (Fig. 15).

The fifth movable die 83 defines, from a forward end inwardly, a curved surface 84, a cylindrical surface 85, a tapered surface 86 having the predetermined angle e7, a cylindrical surface 87, a tapered surface 88 having a predetermined angle C10, a cylindrical surface 89, a tapered surface 90 having the predetermined angle is lish R2<R1 88, a cylindrical surface 91, a tapered surface 92 having a predetermined angle 911, and a cylindrical surface 93. The various sections shown in Fig. 14 have the following dimensions and angles, for example: D1 = 22mmo D8 D6 D5 D7 L3 L6 L7 L8 R2 e7 eio e8 ell 25 degrees Thus, the dimensions and angles are set to estab- the relational expressions D7<D5<D6<D8, D8<D2 and 2 Omm 19.23mm 14.97mm 12. 9mmp 8mm 12mm 19.65mm 13. 3 Smm 0. 2mm 15 degrees 25 degrees 5.7 degrees The pipe 2 resulting from the fifth manufacturing is step as shown in Fig. 13 is placed in the fixed die 20 and subjected to press working by the fixed die 20 and fifth movable die 83. As a result, the pipe 2 is squeezed to have the four-stage shaft 94 having the final dimensions shown in Fig. 15 (sixth manufacturing step).

The four-stage shaft portion 94 includes the curved portion 6, the upper bearing mount 7 having the outside dimameter D8, the taper 8 having the angle e7, a bearing retainer nut receiving portion 95 having the outside diameter D6, the taper 10 having the angle e10, the shank 11, the taper 12 having the angle H, a steering wheel mount 96 having the outside diameter DS, the taper 14 having the angle 911, and a retainer nut mount 97 having the the outside diameter D7. The above sections are arranged in the stated order toward the extreme end to correspond to the form surface structure of the fifth movable die 83.

Next, the pipe 2 shown in Fig. 15 is withdrawn from the fixed die 20 and fifth movable die 83. An outer end is cut off by a predetermined dimension of about 3mm at the retainer nut mount 97 as shown in a phantom line in Fig. 16. Thereafter, the bearing retainer nut mount 95 is threaded to form the screw 9 for engaging a bearing retainer nut. Similarly, the retainer nut mount 97 is threaded to form the screw 15 5 for engaging a retainer nut. The steering wheel mount 96 is serrated to form the serrated shaft 13. Consequently, the steering shaft 1 is completed as shown in solid lines in Fig. 16 and Fig. 1 (seventh manufacturing step).

The steering shaft 1 manufactured as above includes the flat portion 4 for connection, annular grooves 5, upper bearing mount 7, screw 9 for engaging a bearing retaining nut, serrated shaft 13 for engaging the steering wheel, and a screw 15 for engaging a retainer nut, which are formed mainly by press working as integral parts of the steering shaft 1. Compared with a conventional steering shaft formed of a solid round bar, the steering shaft 1 according to this invention has the advantages of being lightweight and manufactured in a reduced shaping time and at low cost.

In the described manufacturing method, the steering shaft 1 is manufactured by successively squeezing 19 the plastic metal pipe 2. Compared with a conventional steering shaft formed of a solid bar, the steering shaft 1 manufactured by the method of this invention is lightweight. As distinct from the conventional manufacturing method mainly comprising cutting processes, the manufacturing method according to this invention mainly comprises press working which provides the advantages of a substantial reduction in the shaping time and low manufacturing cost.

Furthermore, since the steering shaft 1 has a hollow structure, vibrations transmitted from a vehicle body may be absorbed by the hollow and microvibrations of the steering shaft 1 may also be prevented. Being a press worked product, the steering shaft 1 has smooth surfaces and high dimensional precision, and does not require a special finishing treatment after shaping.

1 - 20

Claims

1. A steering shaft having energy absorbers formed by filling a synthetic resin between the shaft and an outer sleeve, said steering shaft or de formable comprising a plastic/metal pipe including, in a region remote from a steering wheel, a flat portion for connection to said outer sleeve, and a plurali- ty of annular grooves to be filled with said 1 -Location of the synthetic resin, and, in a region adjacent the/steering wheel, an upper bearing mount a screw for engaging a bearing retaining nut, a serrated shaft for engaging the steering wheel, and a screw for engaging a retainer nut, all defined as integral parts of said plastic metal pipe and arranged in the stated order toward an extreme end of said pipe

2. A method of manufacturing a steering shaft having energy absorbers formed by filling a synthetic resin between the shaft and an outer sleeve comprising:

21 - a first step of forming, by roller pressing, annular grooves in positions corresponding to the or deformable energy absorbers of a plastic/metal pipe having a predetermined length, a second step of subjecting said pipe to press working by a fixed die having a form surface for forming a flat portion in a region of the pipe thelocaticn of remote from/a steering wheel for connection to said outer sleeve and a first movable die having form surfaces for forming a two-stage shaft portion in a region of the pipe adjacent the steering wheel, thereby to squeeze said pipe to form the flat portion in the region of the pipe remote from the steering wheel and to form the twa stage shaft portion in the region of the pipe adjacent the steering wheel, said two-stage shaft portion having smaller diameters than an.outside diameter of said pipe 01 a third step of subjecting said pipe to press working by said fixed die and a second movable die for forming a three-stage shaft portion having preforming dimensions, thereby to squeeze the - 22 region of said pipe adjacent the steering wheel to shape said two-stage shaft portion into said three-stage shaft portion having the preforming dimensions, a fourth step of subjecting said pipe to press working by said fixed die, and a third movable die for shaping the three-stage shaft portion having the preforming dimensions into a three-stage shaft portion having intermediate forming dimen sions, thereby to squeeze the region of said pipe adjacent the steering wheel to shape said three-stage shaft portion having the preforming dimensions into said three-stage shaft portion hav4Lng the intermediate forming dimensions, a fifth step of subjecting said pipe to press working by said fixed die, and a fourth movable die for shaping the three-stage shaft portion having the intermediate forming dimensions into a four-stage shaft portion having dimensions close to final dimensions of a bearing mount, a nut a steering wheel receiving therebv receiving portion portion and a nut receiving portion to squeeze the region of said pipe adjacent the steering wheel to shape said three-stage shaft portion having the intermediate forming dimensions into said four-stage shaft portion having the dimen sions close to the final dimensions, a sixth step of subjecting said pipe to press working by said fixed die, and a fifth movable die for shaping the four-stage shaft portion having the dimensions close to the final dimensions to have the final dimensions of the bearing mount, the nut receiving portion, the steering wheel receiv- ing portion and the nut receiving portion JP thereby to squeeze the region of said pipe adjacent the steering wheel to shape said four-stage shaft portion having the dimensions close to the final dimensions into a four-stage shaft portion having the final dimensions, and a seventh step of cutting off an outer end having a predetermined dimension of said nut receiving portion., thereafter threading said nut receiving portions.

and serrating said steering wheel receiving portion.

24

3. Steering shafts substantially as hereinbefore described with reference to the accompanying drawings.

4. The methods of manufacturing steering shafts substantially as hereinbefore described with reference to the accompanying drawings.