Reinforced hose

A brake hose has an inner rubber layer, an outer rubber layer, and at least two reinforcing layers provided between the inner rubber layer and the outer rubber layer. The reinforcing layers include an upper yarn layer, and a lower yarn layer. Polyester yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±1.0% at 2.7 g load per unit dtex is used as lower yarn in the lower yarn layer. The braid angle of the lower yarn layer with respect to the axial direction of the hose is set at 59±2°.

This application is based on Japanese Patent Application No. 2003-352509, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reinforced hose having an inner rubber layer, an outer rubber layer, and at least two reinforcing layers including an upper yarn layer and a lower yarn layer.

2. Description of the Related Art

Of this type reinforced hoses, a hose shown inFIG. 7is heretofore known as a brake hose used in a vehicle.FIG. 7is a sectional view showing important part of the brake hose100according to the related art. The brake hose100is formed in such a manner that a plurality of rubber and fiber yarn layers are laminated because the brake hose100needs to have high pressure resistance to brake oil pressure. That is, the brake hose100is formed as a laminate which has: an inner rubber layer102for forming a flow path101in which brake oil flows; a lower yarn layer104; an intermediate rubber layer106; an upper yarn layer108; and an outer rubber layer110,

In the brake hose100, fluid pressure is transmitted from the inner rubber layer102to the lower yarn layer104, the intermediate rubber layer106and the upper yarn layer108successively and transmitted to the outer rubber layer110finally. Constraint force which suppresses expansion against the pressure of pressure fluid is generated in the respective layers. On this occasion, large part of the constraint force depends on the lower yarn layer104and the upper yarn layer108because the respective rubber layers, that is, the inner rubber layer102, the intermediate rubber layer106and the outer rubber layer110are so highly elastic that only small part of the constraint force is generated in the respective rubber layers. Therefore, to increase constraint force generated on the basis of reaction force caused by expansion of the lower yarn layer104and the upper yarn layer108is to improve expansion resistance of the brake hose100, that is, to reduce the amount of volumetric expansion. To improve durability of the lower yarn layer104and the upper yarn layer108against repeated contraction and expansion is to improve durability of the brake hose100per se. However, fiber yarn having a high stretchability is excellent in durability but inferior in expansion resistance whereas fiber yarn having a low stretchability is excellent in expansion resistance but inferior in durability. That is, durability and expansion resistance are contrary to each other.

A technique using high-modulus polyester yarn (high-modulus PET yarn) in the lower yarn layer104to keep durability high and using inextensional vinylon yarn in the upper yarn layer108to reduce the amount of volumetric expansion is known as a technique for successfully combining durability and expansion resistance with each other (see Japanese Patent No. 2,692,480). A technique in which lower yarn constituted by fine fiber yarn is braided to form a thin and dense reinforcing layer to thereby attain improvement in durability and expansion resistance is also known (see Japanese Patent No. 3,003,769).

The demand for higher pressure resistance and higher expansion resistance, however, has increased recently with the advance of increase in pressure of a hydraulic device of a vehicle. sufficient characteristic has never been obtained by the aforementioned change in kind of yarn in the lower yarn layer104and the upper yarn layer108.

SUMMARY OF THE INVENTION

Upon such circumstances, an object of the invention is to provide a brake hose in which both durability and expansion resistance (the amount of volumetric expansion) can be improved on the basis of examination of the braid angle of reinforcing yarn in each reinforcing layer.

To solve the aforementioned problem, the brake hose according to the invention is a reinforced hose having an inner rubber layer, an outer rubber layer, and at least two reinforcing layers provided between the inner rubber layer and the jacket layer, including a lower yarn layer formed on the inner rubber layer and an upper yarn layer formed outside of the lower yarn layer, wherein the lower yarn layer is braided from a reinforcing yarn at a braid angle 59±2° with respect to an axial direction of the hose, and the reinforcing yarn is made of polyester yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±1.0% at 2.7 g load per unit dtex.

In the reinforced hose according to the invention, fluid pressure is transmitted from the inner rubber layer to the reinforcing layers and further transmitted to the outer rubber layer. On this occasion, the reinforcing layers operate so that volumetric expansion is suppressed by resistance force which is generated when the reinforcing yarn is stretched in accordance with the change of the fluid pressure.

The polyester yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±1.0% at 2.7 g load per unit dtex can be used as the reinforcing yarn. The polyester yarn may comprise a high-modulus PET yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±1.0% at 2.7 g load per unit dtex. Thus, high durability and low volumetric expansion against repeated load can be combined successfully with each other. That is, because the high-modulus PET yarn is lower in expansion per predetermined load than ordinary PET yarn which has a tensile strength of not lower than 6.6 g per unit dtex and has a stretchability of 4.0±1.0% at 2.7 g load per unit dtex, the amount of volumetric expansion can be reduced. In addition, because polyester yarn is used in place of vinylon yarn in the lower yarn layer (or the upper yarn layer), the reinforcing layers are also excellent in fatigue resistance. The term “unit dtex” used herein means the number of grams per 10,000 m of filament yarn.

As described above, the high-modulus PET yarn is higher in the function of suppressing the amount of volumetric expansion than the ordinary PET yarn. When the braid angle of the reinforcing yarn is set at 59±2°, the amount of volumetric expansion can be suppressed more greatly. The reason why the amount of volumetric expansion can be reduced when the braid angle is set to be in the aforementioned range will be described. The reinforcing layers are formed in such a manner that the outer circumference of the inner rubber layer is wound with two kinds of reinforcing yarn rotating in clockwise and counterclockwise directions opposite to each other. The term “braid angle of reinforcing yarn” means an angle of inclination with respect to the axial direction of the hose. When the fluid pressure in the reinforced hose increases, force acts on the reinforcing yarn to stretch the reinforcing yarn. This force operates to expand the hose in the radial direction and stretch the hose in the axial direction. It is conceived that the amount of volumetric expansion of the reinforced hose will be minimized when the braid angle is equal to an angle of repose, that is, an angle of 54.44° because these parts of force reach a state of equilibrium. Accordingly, in the related-art reinforced hose, fiber is braided at an angle equal or close to the aforementioned repose angle.

The present inventor, however, has found that the amount of volumetric expansion of a reinforced hose having reinforcing layers made of high-modulus PET yarn and embedded between the inner rubber layer and the outer rubber layer can be reduced when the braid angle is set at 59±2°, especially preferably at 59±1° which is larger than the repose angle. That is, the braid angle at which the amount of volumetric expansion can be minimized is equal to the repose angle (54.44°) when examined geometrically, but is equal to 59±2° which is larger than the repose angle when actually applied to the reinforced hose. In consideration of this fact, the braid angle is set to be in the aforementioned range.

For example, the reinforcing layers are produced as follows. While an inner rubber layer is extrusion-molded from an inner-tube extrudate, reinforcing layers of reinforcing yarn are braided on the inner rubber layer by a braider. Further, an outer rubber layer is extrusion-molded on the reinforcing layers. The braid angle of each reinforcing layer can be set on the basis of the ratio of the speed of extruding the inner rubber layer to the rotational speed of the braider.

In a preferred embodiment, the thickness of the inner rubber layer is preferably set at 0.6±0.2 mm, especially preferably set at 0.6±0.1 mm. When the thickness of the inner rubber layer is set at a small value, the outer diameter of the inner rubber layer can beset at a small value. Accordingly, the reinforcing layers can be braided on the inner rubber layer densely and firmly though the amount of reinforcing yarn is small As a result, the slack or gap between pieces of reinforcing yarn can be reduced, so that the amount of volumetric expansion can be reduced. Although the function of reducing the amount of volumetric expansion becomes more intensive as the thickness of the inner rubber layer becomes smaller, the inner rubber layer can be hardly extrusion-molded or the pressure fluid may penetrate into the inner rubber layer if the thickness of the inner rubber layer is smaller than 0.4 mm. It is therefore preferable that the thickness of the inner rubber layer is not smaller than 0.4 mm.

In a preferred embodiment, the reinforcing yarn has a size of 1,100±100 dtex. In this case, each reinforcing layer with a small outer diameter can be formed so densely that the amount of volumetric expansion can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the invention will be described below to make the aforementioned configuration and operation of the invention clearer.

(1) schematic structure of Brake Hose10

FIG. 1is a partly cutaway perspective view showing an embodiment in which are inforced hose according to the invention is applied to a brake hose10.FIG. 2is a half-sectional view of the brake hose10. InFIGS. 1 and 2, the brake hose10is used so that a master cylinder used in a vehicle oil pressure brake not shown can be connected to a tire side hydraulic device by the brake hose10. The brake hose10is formed as a laminate of five layers so that the brake hose10can bear the pressure of brake fluid. That is, the brake hose10has: an inner rubber layer12including a flow path11; a lower yarn layer14; an intermediate rubber layer16; an upper yarn layer18; and an outer rubber layer20; wherein a mouse piece22is tightened to an end portion of the brake hose by caulking.

(2) Layer Configuration of Brake Hose10

The materials, thicknesses, braid angles, etc. of the respective layers are decided so that the brake hose10can have characteristic such as pressure resistance, durability and expansion resistance to withstand maximum brake fluid pressure of 50 MPa.

The inner rubber layer12is extrusion-molded from rubber such as etylene-propylene-diene terpolymer rubber (EPDM), isobutylene-isoprene copolymer rubber (IIR) or styrene-butadiene copolymer rubber (SBR) mainly to obtain oil resistance. When either EPDM or IIR or a blend of EPDM and IIR is used in this case, permeability to moisture can be improved on the basis of the solid-state properties of the inner rubber layer12. The inner diameter of the inner rubber layer12is selected to be in a range of from 3.0 mm to 3.4 mm. The thickness of the inner rubber layer12is selected to be in a range of from 0.4 mm to 0.8 mm. When the inner rubber layer is thin, the inner rubber layer is effective in reducing the amount of volumetric expansion, If the inner rubber layer is thinner than 0.4 mm, there is however a possibility that the inner rubber layer will be hardly extrusion-molded or will be made permeable to pressure fluid. It is therefore preferable that the thickness of the inner rubber layer is not smaller than 0.4 mm.

The lower yarn layer14is formed on the inner rubber layer12so as to be braided from 20 or 24 carriers of lower yarn15each made of two- or three-strand high-modulus PET yarn. Polyester yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±1.0% at 2.7 g load per unit dtex is used as the high-modulus PET yarn. More preferably, polyester yarn having a tensile strength of not lower than 6.9 g per unit dtex and having a stretchability of 2.6±0.5% at 2.7 g load per unit dtex is used as the high-modulus PET yarn. The lower yarn15is formed as a bundle of 200 to 400 pieces of filament yarn. After the pieces of filament yarn are bundled, a primer coat layer is applied on the bundle. Then, an RFL process is carried out. In this manner, the lower yarn layer14is formed. The term “RFL process” used herein means a process in which an adhesive thin film serving as an adhesive agent and containing resorcin-formaldehyde-latex resin and rubber latex as main components is applied on a surface of yarn, Incidentally, the thickness of the lower yarn layer14is selected to be in a range of from 0.55 mm to 0.95 mm, preferably in a range of from 0.65 mm to 0.85 mm.

The braid angle of the lower yarn layer14is set at 59±2°, preferably 59±1° to reduce the amount of volumetric expansion.FIG. 3is an explanatory view for explaining the braid angle of the lower yarn layer14. As shown inFIG. 3, the lower yarn layer14is formed on the inner rubber layer12so as to be helically braided from the lower yarn15at a braid angle θ. The term “braid angle θ” used herein means an angle of the lower yarn15with respect to the axial direction of the hose. When, for example, the lower yarn layer14is braided on the inner rubber layer by a braider while the inner rubber layer is extrusion-molded, the braid angle θ can be changed on the basis of the ratio of the speed of extruding the inner rubber layer to the rotational speed of the braider.

The intermediate rubber layer16is a layer for preventing the lower yarn layer14and the upper yarn layer18from being displaced. The intermediate rubber layer16is formed by a method such as a method of extruding a rubber material onto the lower yarn layer14, a method of winding a sheet material16A on the lower yarn layer14or a method of applying rubber paste on the lower yarn layer14. EPDM, isobutylene-isoprene copolymer rubber (IIR) or natural rubber (NR) can be used as the rubber material. When either EPDM or ITR or a blend of EPDM and IIR is used as the rubber material in this case, heat resistance and moisture permeability can be improved on the basis of the solid-state properties of the rubber material. The thickness of the intermediate rubber layer16is preferably selected to be in a range of from 0.1 mm to 0.35 mm. The reason is as follows. If the intermediate rubber layer16is thinner than 0.1 mm, the intermediate rubber layer16is too thin to be formed on the lower yarn layer14. On the other hand, if the intermediate rubber layer16is thicker than 0.35 mm, the function of suppressing the displacement of the lower yarn layer14is reduced because the thick intermediate rubber layer16serves as an elastic layer allowing the displacement of the lower yarn layer14.

The upper yarn layer18is formed in the same manner as the lower yarn layer15. That is, 200 to 400 pieces of filament yarn are bundled to form high-modulus PET yarn. After an REL process, two or three pieces of high-modulus PET yarn are plied into upper yarn19. 20 or 24 carriers of the upper yarn19are braided on the intermediate rubber layer16. In this manner, the upper yarn layer18is formed. Like the braid angle of the lower yarn layer14, the braid angle of the upper yarn layer18is preferably set at 59±2°, especially preferably at 59±1° which is larger than the repose angle, to reduce the amount of volumetric expansion.

The outer rubber layer20is made of a material such as EPDM or a blend of EPDM and CR mainly to obtain ozone resistance. The thickness of the outer rubber layer20is selected to be in a range of from 0.8 mm to 1.3 mm.

(3) Method for Producing Brake Hose10

A method for producing the brake hose10will be described below. The brake hose10can be produced by a commonly known method, that is, by a rubber extruding step, a fiber yarn braiding step and a vulcanizing step.

FIG. 4is an explanatory view for explaining a hose producing apparatus30. InFIG. 4, the hose producing apparatus30has a first extruder31, a first braider32, an intermediate sheet former34, a second braider35, and a second extruder37. The first extruder31is a device for extruding the rubber material to form the inner rubber layer12. The first braider32is a device which has a bobbin carrier mounted in a drum32aand which is provided for braiding the lower yarn15on the inner-tube extrudate12A while feeding the lower yarn15out of the bobbin carrier to thereby form the lower yarn layer14. The intermediate sheet former34is a device for feeding the sheet material16A out of a roller to thereby form the intermediate rubber layer16on the lower yarn layer14braided by the first braider32. The second braider35substantially has the same configuration as that of the first braider32. That is, the second braider35is a device which has a bobbin carrier mounted in a drum35aand which is provided for braiding the upper yarn19on the intermediate rubber layer16while feeding the upper yarn19out of the bobbin carrier to thereby form the upper yarn layer18. The second extruder37is a device for extruding the rubber material to form the outer rubber layer20.

(3)-2 Steps for Producing Brake Hose10

A series of steps for producing the brake hose10by the hose producing apparatus30will be described below with reference toFIG. 3. First, the rubber material is extruded by the first extruder31to thereby form the inner rubber layer12. On this occasion, a mandrel (not shown) is inserted in the inner rubber layer12. Then, pieces of lower yarn15are fed out of bobbins onto the extruded inner rubber layer12while the drum32aof the first braider32rotates, so that the lower yarn layer14is braided from the pieces of lower yarn15on the inner rubber layer12. When, for example, the lower yarn layer14needs to be braided from 20 carriers of lower yarn15in this case, the 20 carriers of lower yarn15are fed out of twenty bobbins in twenty locations in total while the twenty bobbins rotate in reverse directions alternately. The braid angle θ of the lower yarn layer14can be set at 59±2° on the basis of the ratio of the speed of extruding the inner rubber layer12to the rotational speed of the drum32a. Then, the intermediate sheet former34supplies the sheet material16A onto the lower yarn layer14to thereby form the intermediate rubber layer16. Further, while the drum35aof the second braider35rotates, pieces of upper yarn19are fed out of bobbins onto the intermediate rubber layer16so that the upper yarn layer18is braided from the pieces of upper yarn19on the intermediate rubber layer16. Then, the rubber material is extruded onto the upper yarn layer18by the second extruder37to thereby form the outer rubber layer20.

Then, the vulcanizing step is carried out. A temperature of 120° C. to 170° C. and a time of 15 minutes to 60 minutes are set as a condition for the vulcanizing step. The upper yarn layer18and the lower yarn layer14subjected to the RFL process by heat generated in the vulcanizing step are bonded to the inner rubber layer12, the intermediate rubber layer16and the outer rubber layer20. In this manner, the brake hose10is formed integrally.

(4) Operation and Effect of Brake Hose

(4)-1 Test of Brake Hose

Next, durability and expansion resistance (the amount of volumetric expansion) of the brake hose produced according to the aforementioned embodiment were examined.FIG. 5shows the configuration and performance of a brake hose sample produced in each of Examples 1 and 2 and Comparative Examples 1 and 2. Each brake hose sample was produced to have an inner diameter of 3.1 mm to 3.2 mm and an outer diameter of 10.2 mm to 10.5 mm.

In each of Examples 1 and 2, the braid angle θ of the lower yarn layer was set at 59° while high-modulus PET yarn was used both in the upper yarn layer and in the lower yarn layer. The high-modulus PET yarn used in Example 1 has a size of 1670 dtex and has a tensile strength of not lower than 11.5 Kg for 1670 dtex and a stretchability of 2.6±1.0% at 4.5 Kg load for 1670 dtex. The high-modulus PET yarn used in Example 2 has a size of 1100 dtex smaller than the size of fiber yarn in Example 1 and has a tensile strength of not lower than 7.6 Kg for 1100 dtex and a stretchability of 2.6±1.0% at 3.0 Kg load for 1100 dtex. On the other hand, in each of Comparative Examples 1 and 2, the braid angle θ of the lower yarn layer was not larger than 56°. In Comparative Example 1, PET yarn was used both in the upper yarn layer and in the lower yarn layer. In Comparative Example 2, high-modulus PET yarn was used in the lower yarn layer while polyvinyl alcohol (PVA) yarn was used in the upper yarn layer. That is, Comparative Example 2 shows an example described in Japanese Patent No. 2692480.

(4)-1-1 Durability Test

The durability test was carried out as a repeated pressure test in which brake pressure oil was actually applied to the brake hose. That is, repeated pressurizing due to brake fluid pressure was combined with bumping and steering motion to imitate motion of tires in the condition that the brake hose was disposed in the same course as actually disposed in a vehicle. The brake fluid pressure was applied so that a pressure of 0 MPa and a pressure of 9.8 MPa were repeated alternately at 0.7 Hz. The bumping motion was repeated at 2.5 Hz. The bumping motion was repeated at 0.28 Hz. In this condition, the number of times of steering motion up to the breaking of the brake hose was examined. As a result, it was found that durability was not changed even in Examples in which high-modulus PET yarn was used both in the upper yarn layer and in the lower yarn layer while the braid angle was set to be larger than that in Comparative Examples.

(4)-1-2 Volumetric Expansion Test

The volumetric expansion test was carried out in such a manner that the amount of change in internal volume of the brake hose having a free length of 305 mm (1 foot) was measured under an oil pressure of 10.3 MPa in accordance with JIS-2601. It was found that the amount of volumetric expansion in each of Examples 1 and 2 was reduced compared with that in each of Comparative Examples 1 and 2.

(4)-2 Relation between Braid Angle θ and Volumetric Expansion

The relation between the braid angle θ and the amount of volumetric expansion was further examined.FIG. 6is a graph showing the relation between the braid angle and the amount of volumetric expansion. The brake hose was produced to have an outer diameter of 10.2 mm while the braid angle θ of the upper yarn layer18was set at 59°. The braid angle θ was changed variously to prepare samples S1to S6. The amount of volumetric expansion of each sample was measured. As a result, it was found that the amount of volumetric expansion decreased when the braid angle θ exceeded 57° as represented by the samples53to S6. It was also found that the amount of volumetric expansion increased when the braid angle θ exceeded 61°.

Incidentally, the invention is not limited to the aforementioned embodiment and various modifications may be made without departing from the gist of the invention. For example, the invention may be modified as follows.

Although the embodiment has shown the case where a brake hose is formed as the reinforced hose, the invention is not limited thereto but may be applied to a power steering hose of a vehicle or a hydraulic hose for building equipment as long as the hose is a high-pressure hose.