Patent Application
20080125231
The present invention relates to a telescopic shaft adapted to be incorporated in a steering shaft or the like of a vehicle.
In a conventional steering mechanism of an automobile, in order to absorb a displacement in the axial direction generated in the running state of the automobile and not to transmit such displacement or vibrations to the steering wheel, a telescopic shaft, formed by a spline coupling of a male shaft and a female shaft, is employed in a part of the steering mechanism. In such telescopic shaft, it is required to reduce a sliding resistance in a sliding motion of the spline part in the axial direction.
Because of such situation, the sliding resistance has been lowered by coating a nylon film on the spline part of the male shaft of the telescopic shaft and by coating a grease on the sliding part. Also there is known a telescopic shaft for vehicle steering in which, in groove portions provided on an external periphery portion of an inner shaft and on an internal periphery portion of an outer shaft, a ball is disposed with an elastic member which is disposed between the groove portion of the inner shaft and the ball, wherein the ball is rotated at a displacing movement in the axial direction thereby reducing the sliding resistance of the male shaft and the female shaft, while the ball is constricted at a rotating movement thereby transmitting a torque (cf. Patent Reference 1). In such telescopic shaft for vehicle steering, in order to enable a torque transmission even in case of the breakage in the ball, a male groove and a female groove of combined cross sections having a certain play are provided on the inner shaft and the outer shaft.
Patent Reference 1: JP-A-2001-50293
However, even in the telescopic shaft having such spline coupling, a sticking or a torque variation occurs in the sliding portion in a telescoping motion in the axial direction and is transmitted as a vibration to the steering wheel, thereby detrimentally affecting the feeling of steering. The present invention is made in consideration of such situation, and an object of the present invention is to provide a telescopic shaft capable of torque transmission without detrimentally affecting the feeling of steering.
In order to accomplish the aforementioned object, according to the present invention, there is provided a telescopic shaft including:
a male shaft and a female shaft which are so fitted as to be capable of a sliding motion but incapable of a rotation, an external periphery of the male shaft and an internal periphery of the female shaft being in contact with each other to transmit a torque in case of rotation, wherein
a grease, containing a base oil having a dynamic viscosity of from 10 to 210 mm2/s at 25° C. and an extreme pressure additive, is sealed in a gap between the external periphery of the male shaft and the internal periphery of the female shaft.
The telescopic shaft of the present invention, in which the sealed grease contains a base oil of a specified dynamic viscosity and an extreme pressure additive, enables to reduce a difference between static friction and dynamic friction in case of a sliding motion of the telescopic shaft, thereby to suppress a sticking or a torque variation and to prevent deterioration in the feeling of steering.
In the following, the present invention will be described in detail, with reference to the accompanying drawings.
The lower steering shaft part 107 and the upper steering shaft part 120 each includes a telescopic shaft. The telescopic shaft includes, as illustrated in
The telescopic shaft may also be constructed as illustrated in
In such telescopic shaft, after the female shaft 42 is spline fitted with the male shaft 41, the penetrating holes 44 and 45 are aligned in the radial direction and the adjusting screw 47 is tightened radially inwards through the penetrating holes 44 and 45, whereby the screw part 48 and the receiver part 49 of the diameter-expanding member 46 spread in the distance in the radial direction to pressurize the male shaft 41 radially outwards to the female shaft 42. Thus, an adjustment of the tightening force of the adjusting screw 47 allows to regulate the pressure of the male shaft 41 in the radial direction on the female shaft 42, whereby the sliding resistance of the shafts 41, 42 can be easily regulated and the looseness between the shafts 41, 42 can be securely prevented. Also the work efficiency can be improved since the sliding resistance can be easily regulated even after the shafts 41, 42 are assembled. In a portion indicated by 51 in the screw part 48 of the diameter-expanding member 46, a caulking is formed in advance, in order to prevent the adjusting screw 47 from being loosened.
The telescopic shaft can also be constructed as illustrated in
Between the axial groove 63 of the male shaft 61 and the spherical members 67, a plate spring 69 is provided for contacting and pressurizing the spherical members 67. The plate spring 69 includes, as illustrated in
As illustrated in
Also as illustrated in
In such telescopic shaft, the spherical members 67 are disposed between the male shaft 61 and the female shaft 62 while the plate spring 69 pressurizes the spherical members 67 to the female shaft 62 in such a level as not to cause a slackness, whereby the slackness between the male shaft 61 and the female shaft 62 can be securely prevented when the torque is not transmitted, and the male shaft 61 and the female shaft 62, in a relative displacement in the axial direction, can slide under a stable sliding load without a slackness. In a state of torque transmission, the plate spring 69 causes an elastic deformation to constrict the spherical members 67 in the circumferential direction, and the cylindrical members 68 disposed in three rows between the male shaft 61 and the female shaft 62 principally perform the function of torque transmission. For example when a torque is entered from the male shaft 41, in an initial stage, no slackness is present by the pressurization with the plate spring 69, and the torque is transmitted under a repulsive force to the torque generated the plate spring 69. In such state, the overall torque transmission is executed in a state where the torques transmitted among the male shaft 61, the plate spring 69, the spherical members 67 and the female shaft 62 are balanced with the input torque. When the torque increases further, the gap between the male shaft 61 and the female shaft 62 across the cylindrical members 68 in the rotational direction is removed, and the subsequent increasing portion of the torque is transmitted by the cylindrical members 68 through the male shaft 61 and the female shaft 62. It is therefore possible to securely prevent the slackness between the male shaft 61 and the female shaft 62 in the rotational direction, and to transmit the torque in a highly rigid state.
In each telescopic shaft of the aforementioned constructions, a following grease is sealed in the gap between the external periphery of the male shaft and the internal periphery of the female shaft.
In the grease, a base oil is not restricted in the type thereof so far as it has a dynamic viscosity at 25° C. of from 10 to 210 mm2/s, but a mineral oil-based lubricating oil and a synthetic lubricating oil can be employed advantageously. A base oil having a dynamic viscosity at 25° C. exceeding 210 mm2/is difficult to penetrate into the sliding contact part, and is difficult to suppress a sticking or a torque variation in the sliding portion, where the external periphery of the male shaft and the internal periphery of the female shaft contact with each other. A base oil having a dynamic viscosity at 25° C. of 110 mm2/s or less is more effective. The dynamic viscosity is more preferably 100 mm2/s or less (25° C.) and most preferably 80 mm2/s or less (25° C.). On the other hand, a lower limit of the dynamic viscosity is 10 mm2/s (25° C.), and an even lower dynamic viscosity is undesirable because of a lowered oil film forming ability. The dynamic viscosity is preferably 20 mm2/s or more (25° C.) and more preferably 40 mm2/s or more (25° C.).
The mineral oil-based lubricating oil is not particularly restricted, but a paraffin-based mineral oil, a naphthene-based mineral oil or a mixture thereof may be used, and preferred is an oil purified by suitably combining vacuum distillation, solvent deasphalting, solvent extraction, hydrogenolysis, solvent dewaxing, sulfuric acid treating, clay refining and hydrogenation refining. Also the synthetic lubricating oil is not restricted, but for example a synthetic hydrocarbon oil, an ether oil, an ester oil or a fluorinated oil may be used. Specific examples of the synthetic hydrocarbon oil include a poly-α-olefin oil; those of the ether oil include a dialkyl diphenyl ether oil, an alkyl triphenyl ether oil and an alkyl tetraphenyl ether oil; those of the ester oil include a diester oil, a neopentyl-type polyol ester oil, a complex ester oil thereof, and an aromatic ester oil. Such lubricating oils may be employed singly or in a suitable combination of plural kinds, and are regulated to the dynamic viscosity described above. Among these, an ester oil such as a diester oil, a polyol ester oil or an aromatic ester oil is advantageous, and a polyol ester oil is particularly preferable as a principal component of the base oil.
As the thickener, a substance that can be dispersed in colloidal state in the base oil and that can form the base oil into a semi-solid or solid state may be employed Examples of such thickener include metal soaps such as a lithium soap type, a calcium soap type, a sodium soap type, an aluminum soap type, a lithium complex soap type, a calcium complex soap type, a sodium complex soap type, a barium complex soap type and an aluminum complex soap type, inorganic compounds such as a bentonite type and a clay type, and organic compounds such as a monourea type, a triurea type, a tetraurea type, an urethane type and a sodium terephthalamate type. Such thickeners may be employed singly or in a mixture of two or more kinds.
A content of the thickener is from 5 to 30% by mass of the entire amount of the grease. An amount less than 5% by mass is difficult to maintain a greasy state, while an amount exceeding 30% by mass results in an excessively thick state and cannot obtain a sufficient lubricating state. The amount is preferably from 13 to 23% by mass, more preferably from 14 to 22% by mass and most preferably from 15 to 21% by mass, with respect to the entire amount of grease.
Also an urea compound employed as a thickener allows to form a protective film on a metal surface at a sliding motion thereof, thereby providing more satisfactory friction characteristics. Further, an amount of the thickener from 15 to 21% by mass enables a firmer protective film formation, thereby suppressing a sticking and a torque variation.
Among the urea compounds, a diurea compound is a thickener advantageously applicable to the telescopic shaft for vehicles, as it has a heat resistance and an excellent oil holding property and is inexpensive. In particular, preferred is a diurea compound represented by a following general formula [I].
In the formula, R2 represents an aromatic hydrocarbon group having 6 to 15 carbon atoms; R1 and R3 may be same or different each other and each represents a hydrocarbon group or a condensed-ring hydrocarbon group, wherein, in R1 and R3, the hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and the condensed-ring hydrocarbon group preferably has 9 to 19 carbon atoms.
The diurea compound represented by the general formula [I] can be obtained by reacting, in the base oil, a diisocyanate having R2 in the skeleton thereof in a proportion of 1 mole and a monoamine having R1 or R3 in the skeleton thereof in a proportion of 2 moles in total.
As the diisocyanate having R2 in the skeleton thereof, diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, dimethyldiphenylene diisocyanate or an alkyl-substituted compound thereof can be employed advantageously.
As the monoamine having a hydrocarbon group as R1 or R3 in the skeleton, employable advantageously is aniline, cyclohexylamine, octylamine, toluidine, dodecylaniline, octadecylamine, hexylamine, heptylamine, nonylamine, ethylhexylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, pentadecylamine, nonadecylamine, eicodecylamine, oleylamine, linoleylamine, linolenylamine, methylcyclohexylamine, ethylcyclohexylamine, dimethylcyclohexylamine, diethylcyclohexylamine, butylcyclohexylamine, propylcyclohexylamine, amylcyclohexylamine, cyclooctylamine, benzylamine, benzhydrylamine, phenethylamine, methylbenzylamine, biphenylamine, phenylisopropylamine or phenylhexylamine.
Also as the monoamine having a condensed-ring hydrocarbon group as R1 or R3 in the skeleton, employable advantageously is an indene-type amine compound such as aminoindene, aminoindane or amino-1-methyleneindene; a naphthalene-type amino compound such as aminonaphthalene(naphthylamine), aminomethylnaphthalene, aminoethylnaphthalene, aminodimethylnaphthalene, aminocadalene, aminovinylnaphthalene, aminophenylnaphthalene, aminobenzylnaphthalene, aminodinaphthylamine, aminobinaphthyl, amino-1,2-dihydronaphthalene, amino-1,4-dihydronaphthalene, aminotetrahydronaphthalene, or aminooctaline; a condensed bicyclic amine compound such as aminopentalene, aminoazulene or aminoheptalene; an aminofluorene-type amine compound such as aminofluorene, or amino-9-phenylfluorene; an anthracene-type amine compound such as aminoanthracene, aminomethylanthracene, aminodimethylanthracene, aminophenylanthracene, or amino-9,10-dihydroanthracene; a phenanthrene-type compound such as aminophenanthrene, amino-1,7-dimethylphenanthrene, or aminoretene; a condensed tricyclic amine compound such as aminobiphenylene, amino-s-indacene, amino-as-indacene, aminoacenaphthylene, aminoacenaphthene, or aminophenalene; a condensed tetracyclic compound such as aminonaphthacene, aminochrysene, aminopyrene, aminotriphenylene, aminobenzoanthracene, aminoaceanthrylene, aminoaceanthrene, aminoacephenanthrylene, amincacephenanthrene, aminofluoranthene, or aminopleiadene; a condensed pentacyclic compound such as aminopentacene, aminopentaphene, aminopicene, aminoperylene, aminodibenzoanthracene, aminobenzopyrene, or aminocholanthrene; or a condensed polycyclic (six or more rings) amine compound such as aminocoronene, aminopyranthrene, aminoviolanthrene, amincisoviolanthrene, or aminoovalene.
The particularly preferable urea compound is a diurea in which, in the general formula [I], R1 and R3 each is an alicyclic hydrocarbon group having 6 to 19 carbon atoms or an aromatic hydrocarbon group having 6 to 12 carbon atoms, and R2 is 4,4′-methyelenediphenyl isocyanate or tolylene diisocyanate. As the grease composition of the present invention contains an extreme pressure additive, it is preferable to employ a thickener, such as the above-described alicyclic/aromatic diurea, that shows little influence such as softening or thickening of grease, by the extreme pressure additive.
In the grease, an extreme pressure additive is added as an essential additive. An amount of addition thereof is preferably from 0.1 to 10% by mass with respect to the entire amount of grease. An amount less than 0.1% by mass is unable to provide a sufficient effect by the addition, while an amount exceeding 10% by mass shows a saturation of the effect. The amount of addition is more preferably from 0.5 to 7% by mass, and most preferably from 0.5 to 5% by mass, with respect to the entire amount of grease.
As the extreme pressure additive, a solid lubricant such as molybdenum disulfide may be employed. The solid lubricant has a laminar lattice structure and is easily cleaved into a thin layer by a sliding movement, thereby avoiding a metal contact.
Also an organic molybdenum compound is adsorbed on a metal surface constituting a rolling surface to form a film rich in reactivity (reactive film layer) to improve a sticking resistance, a load resistance and an abrasion resistance even under a high load and at a low speed. As the organic molybdenum compound, preferred are molybdenum dithiocarbamate, an amine complex of molybdenum and the like, among which molybdenum dithiophosphate (Mo-DTP) is excellent in these properties and is therefore preferable.
Also examples of the organometallic compound capable of similarly forming a reactive film layer include metal dihydrocarbyl dithiophosphates, metal dihydrocarbyl dithiocarbamates and naphthenic acid salts, which may also be used in combination, if necessary. The metal dihydrocarbyl dithiophosphate is preferably a metal dihydrocarbyl dithiophosphate in which each hydrocarbyl group has 4 to 20 carbon atoms, such as zinc dimethyl dithiophosphate, zinc butylisooctyl dithiophosphate, zinc di(4-methyl-2-pentyl)dithiophosphate, zinc di(tetrapropenylphenyl)dithiophosphate, zinc (2-ethyl-1-hexyl) dithiophosphate, zinc (octyl)dithiophosphate, zinc(ethylphenyl)dithiophosphate, zinc(amyl)dithiophosphate, or zinc di(hexyl)dithiophosphate, or foregoing compounds containing lead, cadmium or antimony as a metal instead of zinc.
The metal dihydrocarbyl dithiocarbamate is preferably a metal dihydrocarbyl dithiocarbamate in which each hydrocarbyl group has 4 to 20 carbon atoms, such as zinc dimethyl dithiocarbamate, zinc butylisooctyl dithiocarbamate, zinc di(4-methyl-2-pentyl)dithiocarbamate, zinc di(tetrapropenylphenyl)dithiocarbamate, zinc (2-ethyl-1-hexyl)dithiocarbamate, zinc(isooctyl)dithiocarbamate, zinc(ethylphenyl)dithiocarbamate, zinc(amyl)dithiocarbamate, or zinc di(hexyl)dithiocarbamate, or foregoing compounds containing lead, cadmium, antimony, nickel or iron as a metal instead of zinc.
Also polytetrafluoroethylene (PTFE) may be used as the extreme pressure additive. Polytetrafluoroethylene has a cohesion energy smaller than in other polymer compounds, and has a very low critical surface tension, so that the polytetrafluoroethylene particles present in a sliding part become small thin pieces by a shear stress under sliding motion, and easily extends over a counterpart material of the sliding part, thereby providing the sliding part with an excellent lubricating property. In particularly polytetrafluoroethylene having a molecular weight from several thousand to several hundred thousand is preferred.
The grease may contain additives ordinarily added to the grease, such as a load resistance additive, an antioxidant, an antirusting agent and an anticorrosion agent. Amounts of addition thereof are preferably 10% by mass or less in total, with respect to the entire amount of the grease.
Also the grease preferably has a worked penetration of from 220 to 340, in order to secure an appropriate fluidity. The worked penetration is more preferably from 250 to 310 and most preferably from 260 to 290.
Test greases are prepared with the formulations shown in Table 1. Diurea employed as the thickener is a diurea compound represented by the general formula [I], and the addition amount of the extreme pressure additive is selected as 3% by mass of the entire amount of grease. In Examples 2 and 3 and Comparative Example 2, these are added in equal amounts by 3% by mass in total. Then each test grease is sealed in a gap between the external periphery of the male shaft and the internal periphery of the female shaft of a steering mechanism having the construction illustrated in
Table 1 summarizes the presence/absence of sticking and torque variation, based on the results of measurement.
Test greases are prepared with the formulations shown in Table 2, and each test grease is sealed in a gap between the external periphery of the male shaft and the internal periphery of the female shaft of a steering mechanism having the construction illustrated in
Test greases are prepared by employing a polyol ester oil as the base oil, blending a diurea in which, in the general formula [I], R1 and R3 each is an alicyclic hydrocarbon group and R2 is 4,4′-methylenediphenyl isocyanate, in different amounts and by adding MoDTP in a constant amount. The worked penetration is selected as 250 to 310. Each test grease is sealed in a gap between the external periphery of the male shaft and the internal periphery of the female shaft of the steering mechanism having the construction illustrated in
Test greases are prepared by employing a polyol ester oil as the base oil, blending a diurea in which, in the general formula [I], R1 and R3 each is an alicyclic hydrocarbon group and R2 is 4,4′-methylenediphenyl isocyanate, in a constant amount and by adding MoDTP in different amounts. The worked penetration is selected as 270 in any grease. Test greases are evaluated in a similar manner as in Example 11. Results are illustrated as a graph in
Test greases are prepared by employing polyol ester oils of different dynamic viscosities as the base oil, blending a diurea in which, in the general formula [I], R1 and R3 each is an alicyclic hydrocarbon group and R2 is 4,4′-methylenediphenyl isocyanate, and MoDTP respectively in a constant amount. The worked penetration is selected as 270 in any grease. Test greases are evaluated in a similar manner as in Example 11. Results are illustrated as a graph in FIG. 10.
Based on Examples and Comparative Examples, it is identified, by sealing a grease containing a base oil of a dynamic viscosity at 25° C. of 210 mm2/s or less and an extreme pressure additive according to the present invention, to suppress generation of sticking or torque variation, and to reduce the difference between static friction and dynamic friction at the sliding motion of the telescopic shaft, thereby suppressing a change in the frictional force and preventing deterioration in the feeling of steering.
While the present invention is described in detail with reference to specified embodiments, it will be apparent to those skilled in the art that various alterations and modification are possible without departing from the scope and spirit of the present invention. The present application claims the benefit of Japanese Patent Application No. 2004-381077 filed Dec. 28, 2004 and Japanese Patent Application No. 2005-13187 filed Jan. 20, 2005, which are hereby incorporated by reference in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-381077 | Dec 2004 | JP | national |
| 2005-013187 | Jan 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/24146 | 12/28/2005 | WO | 00 | 6/28/2007 |
