Note: Descriptions are shown in the official language in which they were submitted.
1~5~794 1 ¦
Background of the ~nvention .
lo Field of the Invention - .
The present invention concerns a flexible hose of
-reinforced elastomer suitable for brakin5 sys~ems of motor
vehicles.
2. Description of the Prior Art
Conventional hydraulic brake hoses ~e~erall~ ~ave
internal diameters of between 3 and 3.5 mm~ externa~ ~lam~ter~
o~ between 8 and 12 mm7 a length of between 15 an~ 90 cm, and
~ 10 such hoses.are constructed ~o a~ to re.~ist internal pxessure.s up
: to 150 kg./cm2 when in service.
i Generally, these flexible hose.s for braking s~stem~ have
.1 a well ~efined structure in that they are fo~me~ fxom th~ insi~e.
L towards the outside by a first la~er of elastomeric mat~r~ a
. 15 fixst reinforcing sheath formed with bxaided threads, a second
layer of elastomer.ic material, a second reinfo~cing sheath formed
with braided threads, and a third cove~ing layer of elastomeric
material. .
: The expression "layer o~ elastomeric material" ~s here;n
intended to mean a composition ~ased on elas~omer;c materîal
containing the usual in~redient5j vulcanizing a~entsr etc~ ai~
. composition being in a vulcani~ed ~tate.
Hoses of the type cited above, usual.~ present certai~
dxawbac~s. In fact, the two reinforoil-y sheaths, ~eing formed
. out:of thickly braided threads fox their entire length~ form
~suraces with scarcely any interstices pre~sent on one side and
~ p~ssing through to:the other side. As a conse~uencet the thread~
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of the xein~orcin~ sheaths are insuf:Eicient~y embedded inside the ¦
elastomeric layers, and hence, the hose does not ~end ~o be compact
enough, ana. there is very little co-operati~n between the
elastomeric layers and the reinforcin~ sheaths promising small
possibility o~ an adequate resistance to the stresses occurring
when in service. . . .
. In general, and as ~ar as it was possi~le; technicians .
have tried to improve the surface adhesion between the elastomeric .
l.ayers and the reinforcing sheaths, resortin~ to ~he use of specia~
compositions, or by chemicall~ preparin~ the layers ~o suit a
particular purpose. .
As a consequence of the above, satis~actory results were
o~tained. But in o~ercomin~ the technical ~rawback, another .
dis~dvantage - an economic one - ollowea.
This economic disa~vantage was due to the hose now 1~
nvolving higher cost, ~ecause o~ the special ingreaients used ~ .
for the com~osition, and/or the gxeatex accurac~ ana attention ¦
required, ~uring the manufacturing steps~ for ~rvmoting good a~-
hesion between the layexs an~l the shea~hs.
Another defect which is encountere~ is caused by the fac~
that each of the rein~orcing sheath threads, passing alternately
over and urlder other intersecting threads fox the entirP length of ~ .
the sheath, corresponds, at the points of intersection, to a
reciprocal block created practically by the point of intersection, ~
Because of this configuration, hig~ stresses have been verified .
.(at the above mentioned points ~f intersections) ~uriny the
flexions to which the ho5e is sub~ittPd when in ~ervice. ~oreover~
it is even possible for localiz~ ruptur~ to occur in the rein-
forcing stxucture.
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In order to overcome the a~ove cited drawbacks, someone
ought to have considered the idea of employing other reinforc-
ing structures completely different from the type usually
employed in making hoses for braking systems of motor vehicles.
Reinforcing structures7 for example, known as "spiralled" are
presently being employed in various other applied fields.
Structures, such as these "spiralled" reinforcing
structures, form part of hoses used for oleodynamic high
pressure control systems with internal diameters, for example,
of 20 mm.
These structures substantially comprise a first
reinforcing sheath, formed by thread which is helically wound
around an elastomeric underneath layer, and a second reinforcing
sheath formed by a thread helically wound in a direction
opposite to that of the first sheath, the latter thread being
placed above an intermediate elastomeric layer. This '9spiralled"
' structure, due to the presence of an intermediate layer placed
between the threads (of the two reinforcing sheaths)~ can be
expected to prevent the points o~ intersection batween the
threads from being in direct contact with each other and hence,
could overcome the drawback of excessive localized stresses
occurring, as in structures with braided thread reinforcing
sheaths.
Moreover, the "spiralled" structure, because of the
`l interstices present between the thread coils of the sheath, and
consequently, because there would exist a good embedding
facility in the elastomeric material between the coils, should
definitely overcome the above citqd drawbacks o~ the insuffi-
,
cient compactness existing between the elastomeric layers and
reinforcing sheaths as in the hoses with braided thread
(reinforcing sheath) structures.
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However, even in view of the above, the "spiralled"
structures have certain defects which have made them, to date,
unacceptable for ~eing employed in hydraullc brake hoses.
As a matter of fact, it has been verified, that threads,
wound thus in spiral fashion, are subject in the winding process
to ''twisting around themselves" in the same sense of the winding.
This "twisting" has a negative effect since it tends to
modify the selected posi~ion imposed on the threads -,ns~ide the
hose for better resist~ng the various stresses.
~t has also been verified that, because of the different
diameters on to which the reinforcing sheaths have been placed,
there is generally hardly any contribution between the threads of
the different reinforcing sheaths in resisting the stresses to
which the hose will be subjected.
This negative characteristic is probably due to the
fact that a hose expansion, caused by fluid pressure, would
initially involve just the first reinforcing sheath threads,
and could sometimes deform them excessively before any part of
the load could become absorbed by the threads of the external
sheath as well.
-~ The above are the main reasons why, to date, braided
threads have been preferred in the reinforcing sheath structures
of hoses for braking systems.
Summary of the Invention
' The aim of the present invention is to provide a flex-
ible hose for braking systems of motor vehicles, composed of a
reinforced "spira:Lled" structure capable of overcoming the afore-
said draw~acks, without however involving a rise in cost as com-
pared to the price of conventional .hoses now employed.
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The object of the present invention is to provide a
hydraulic brake hose of reinforced elastomeric material, suit-
able for braking systems of motor vehicles, of the type formed
from the inside towards the outside by a first layer of elasto-
meric material a first reinforcing sheath formed by a plurality
of parallel wires helically wound around said first layer, a
second intermediate layer of substantially elastomeric material,
a second reinforcing sheath formed by a plurality of parallel
wires helically wound, around said interme~iate layer, at equal
angles to and with the winding direction opposite to that of
the plurality of wires in the first sheath, a third covering
layer of elastomeric material, characterized in that said inter-
mediate layer comprises elastomeric material having a hardness
of between 72 and 76 Shore-A and a thickness of less than
0.25 mm, and wherein each of the wires of the reinforcing sheaths
is an elementary filament having a diameter of between 0.12 and
0.25 mm.
The hose according to the invention will provee~to be
particularly acceptable for braking systems of motor vehicles,
-~ 20 as will be better understood further on, from the description of
the tests carried out, and from the advantages attained with
respect to the characteristics of the other known hoses. This
j aim has been obtained by combining the aforesaid characteristics
{ of the intermediate layer and of the reinforcing wires. The
reasons are not quite clear as to why the combination of these
characteristics of the invention allow for the spiralled
structure to be feasibly employed in braking hoses for motor
vehicles.
Hereunder, (rom among the various possible explanations)
Applicants have formulated the following non-limiting hypothesis.
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The presence of an intermediate elastomeric layer,
having a hardness of ~etween 72 and 76 Shore-A, allows for
high penetration between the elastomer and the wires of the
reinforcing sheath. Hence, it can be held that the intermediate
layer and the re~nforcing wires forming a single compact cylin~
drical body act together efficiently in sustaining the stresses
to which the hose is subjected.
The other characteristics of the intermediate elasto-
meric layer, relating to the thickness, should allow for the
formation of a structure with "balanced" sheaths. As a matter
of fact, it can be supposed that each un-twisting action of the
wires of the first sheath will be transmitted to the intermediate
layer and, due to the extremely reduced thickness of this layer,
it will immediately be balanced by a contrary action on the
part of the wires of the second sheath which are forced to
tighten because of the effect produced by ~he movement of the
covering layer.
Therefore, by thus combining the two cited character-
` istics of the intermediate layer, the wires on the hose walls
ought to effectively maintain their pre-established position,
so as to better withstand the stresses occurring in service. In
particular, the very close vicinity of the two reinfor~ing sheaths
could bring about another advantage in that the stresses, re-
sulting from the expansion caused by fluid pressure, would be
transmitted almost contemporane~sly, to the wires o~ the rein-
forcing sheaths. Because of this consideration, the risk of
one of the sheath wires becoming excessively deformed before
another sheath wire could also take o~er part of the load,
thus should be averted.
Apart ~ ~ the a~ove~ the characteristic o the
elementary filaments having diameti~rs of between 0.12 mm and
0.25 mm (hence, with a non-high rigidity) together with the
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limited thickness of the intermediate layer, should contribute
toward complete hose flexibility, which should very satisfactorily
serve to reslst the repeated fle~ing stresses which the hose
will have to undergo when employed.
Preferably, between the first layer of elastomeric
material and the first sheath, a suitable fabric will be inter-
posed ~to allow the metallic filaments of the first sheath to be
helically wound with the desired winding tension. In such a way,
the potential risk of these wires penetrating into the first
layer, and thus dangeroulsy reducing the thickness of the hose,
will be propitiously prevented.
The aforesaid fabric may be of either a woven, or a
non-woven fabric. It has to be placed around the first layer
with the edges parallel to the hose axis, and with the ends
overlapped.
It is more preferable if the fabric is of large-woven
synthetic fibers.
It is preferable also that the two reinforcing sheath~
each be compr~sed of the same number of wires as the other.
The aforesaid characteristics result in two valid
advantages. The first advantage is the fact that the hose of the
invention can be constructed with a simplified spiralling machine,
since the two single spiral units, used for winding the wires of
' the sheaths, both contain the same number of bobbins. The second
advantage is derived from the fact that the same number of wires
is distributed in the sheath with the bigger diameter as well as
in the sheath with the smaller diameter. In this way, in ea~h
of the transversal sections of the hose, the distance between the
two adjacent wires, when measured along the circumference, is
greater in the second sheath (the~outermost one) than in the first
sheath. More brie1y stated/ the second sheath has a lesser
density than the first sheath.
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This di~erence in the density of wires~ w1th regard to
the two reinforcing sheaths, is contrary t~ what is used normally
for braided spiralled hoses (which are alreaay well-known in
other applied ~ields) with, ~Eor example, diameters oE 20 mm.
As a ma~ter of fact in the braided hoses a5 well as in
the spixalled hoses mentioned above, the out~most reinforcing
sheath usually has a greater number o* threads than the i~nermo9t ¦
sheath. Consequently, the hose of the inven~lon when compaxed
.with braidad and/or spiralled hoses tused in other applied fiel~s),~
with an equal number of threads on the inner~st or fixs~
. reinforcing sheaths~ presents a secondr moxe *lexible sheath~ an~
f~r this reason, the hose o the in~ention has the advant~e of
. having better endurance against flexing fati~ue, which is the
gravest problem encounterea in brakin~ s~stems o~ motor vehicle~
In particular~ the hose of the i.nventlon has a ~nsity Qf
wire~ between 40% and 95~ the distance between two elementar
adjacent ~ilaments, mea~ured i~ the direction parallel to ~he axi.s
of the hose, being between 0.15 and 0.7~ mm.
: Pref~rably, al7 of the filaments h~ve ~irculax sect~o~s
of equal diameter.
¦ ~rief Des~ription of the Drawing
The present inven~ion will.be bettex under5tood xo~ ~he
following detailed description, referrin~ by way of non-limiting
example ta the accompanying drawin~ of Figure 1, illus~trating a
2~ pexspective ~iew vf a hose for brakin~ s~stems of motor vehicles;
¦ Description of the Preferred Embodiment
~s illustrated in Pig. 1, a hose 1 for braking s~s~ems o
motor vehicIes is formed, from the ins;de towaras the outs.ideby: a
first layer 2 of elastomeric material, a ~abric 3 made fxom
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~L~S~794
.large-woven fibers, a first reinforcing sheath 4 formed b~
elementa~y parallel threads wound helically around the ~abric 3,
~a second layer 5 made substantially o elastomeric material having !
. a Shore-A hardness o 72, and a thickness of 0.23 mm; a second
reinforcing sheath 6 of elementar~ paxallel ~hreads wound
helically around the layer 5 with the angle of win~i~g o~ egual .
value to and with the direckion o~ winding conkxary to tllat oP the
.threads o~ the first sheath; a third covexi~g layer 7 o elasto-
meric material.
The unctions of the elastomerl~ laye~s5 of the ~ric,
and of the reinforcing sheaths, are as ~ollows: -
. the layers 2 and 7, as or the brai~ed hoses, serve
respectively for containing the fluid, and ~or protectin~ ~he hose~
from any mechanical or corrosive action from the ~u~side;
. 15 the la~er 5 separates the reinoxcin~ sheaths ~ and 6~ I'
. : preventing any local ~amage which could xesul~ from the thread~ !
rubbing against each other;
the abric 3, as already explail~ed, prevents any pene-
tration on the part o~ the sheath thr~ad5 4 ln~o the elastomeri~
. 20 layer 2 and als~ preva~ts any eventual formation o~ corrugatlonS
,on the internal surface o~ the elastomexic la~er 2.
Consequently, the fabric 3 besides eli.mina~ an~ risk o
:; .
reducing the thickness of the first lay~x, also excludes any
possible loss of pressure which could otherwise occur i~ ~uid
was forced to flow through c~rrugations~
The a~oresaid first and sec~nd æhea~hs serve to re.~nforc~
. khe layer ~f elastomeric material i~l withs~an~ing the stxesse~
which the hose will undergo when employed~
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In particular, the said first ana secon~ sheaths are each !
composed of a spiral structure where ~he helix is of the 60 s~art j
type consisting of elemen~ary filaments of zinc-plated or brass-
coated metal, having diameters of 0..15 mm app~ied arouna the
;respective elastomeric layers at an angle ~f 54 44~ with respect
~'to the axis of the hose.
: . In the firs~ sheaths the pitch of the helicoid formea by
an elementary f ilament is 12. 8 mm, with ~he ~istance between ~he
two a~jacent turns of ~ifferen~ filaments measurea paral~el to
~-the hose axis egual to 0.21 mm (not shown in the Figure).
j In the second sheath, the pitch o* the helicoid is 14.1
.mm, and the aistance betw.een the ~wo adjacent ~urns is equal to
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: j The hose described above was subject~a to the most binaing,
~tests for hydraulic brake hoses ~or motor ~ehicles. The results
~at~ained were compared to the xequirement set ~own by the ST~NDARD l~:
SAE J 1401, an~ were also compared with the resul~s obtaine~ on
; conventional braided hydraulic hoses employed ~or the s~me type
of motor vehicles.
The conventional hose substan~ially comprises a layer of
elastomexic material with an internal diameter e~ual to that of
$he hose ofthe invention, a ~irst reinforcin~ sheath formed by a
braid of 1 x 12 threads, and a second xei~forcing sheath ~orme~
by a braia of 3 x :L2 threads.
The threads used ~or making the bxaia are of ra~n~ ~e
type sold under the txade mark "R~YON SAU by SICRE~
Bc)th the hose oiE the inventio~ as well as the convention
al hose were put to the following iaentical l~ests, namely:
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a) BURST PRESSUR13 TEST
. Il b~ FATIGUE TEST
t' c) HOS:E l~:XPANSION TEST~
~ ~) BURST PRESSURE TEST
,'~ This test was c~rried out by using hose p~eces having
lengths of 400 mm. ~ach hose piece was i~rodu~ed i~to a
l~hydraulic machine filled with water at a pressu~e of 280 kg.jcm~.,
'and was le~t at that pressurç for a period ~f two minutes~ -
. ,' Then~ the pressure was increased at a speed of 105 kg.~m.
, 10 ¦pex minute unti.l a break occurred.
! The average test results obtained ~ere as follows:
.~HOSE ACCO~DING TO THE INVENTION B~E~ 2
I~ ~ONVENTIONAL HOSE ~50 k~ Cm2
~.PRESSU:RE VALUES TO BE EXCEEDED BEFORE BREARIMG POINT~350 kg./cm~
'' (set down by the STANDARD SPE J 1401)
. 'I b) ~ATIGUE TEST
~, This test was carried out accordin~ t~ the regulations
., se~ down by the STA~DARD U. S .A. FMVSS No. 106 .
! For this test,pie~es of hose were used (taken ~rom bo~h
20 ~- ~ ,..the conventional hose as well as the hose of the ln~ent.ion~ e~c~
.having a length of ~00 ~m. Each hos~ len~th was intr~auced i~t~
,the machine (according to the cited STAND~RD~, comprisin~ .
ubstan~ial.ly~
!l
. ',. means for ~ecuxin~ one end of hose in a fixed po~ition,
- ~, a disc, rotating around its own axis, corresponding to
:the periphery of which the other end o~ the hose.length i~ con-
1.. . . .
nected;
i a h~dxaulic circuit for intxoducing and for maintainins
the hose inside the mac~ine at a pressure of 16~55 kg~cm2.
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The disc ~as rotated at a speed of 800 r.p.m. and the
time at ~hich break occur;red was duly measured.
The average test results obtained were as follows:
BREAK
HOSE ACCORDING TO T~E INVENTION >124 hours
CONVENTIONAL HOSE 58 hours
NUMBER OF HOURS REQUIRED TO sE EXCEEDED BEFORE
BREAK POINT (set down by the STANDARD SAE J 1401) >35 hours
c) HOSE EXPANSION TEST
This test was carried out by arranging a piece of hose
of length 400 mm inside the circuit of a hydraulic machine
adapted for filling the hose length with water and for main-
taining a water pressure inside the hose and then meausring the
volume variations inside the hoae length at pressures of 70 and
106 kg/cm .
The average tests results obtained from the experiments
conducted on pieces of conventional hose, and on pieces of hose
according to the invention were as follows:
70~g./cm2106 kg/cm2
HOSE ACCORDING TO T~E INVENTION 0.51 cm3 0.58 cm3/m
CONVENTIONAL HOSE 0.56 cm3O.~ cm3~m
VALUES OF VOLUMETRIC EXPANSION1.08 cm31.38 cm /m
i (admissible by the STANDARD SAE J 1401)
Thus, the analyses of the test prove that the hose of
the invention in all stress conditions more than satisfies the
requisites demanded by the STAN~RD SAE J 1401, and that, con-
sequently, the use to which it will be applied, i.e., good
- ~orking of the hraking system, is completely guaranteed.
Moreover, the hose of the invent~on ha~ anothe~ ad-
vantage, namely that it has a high~r resistance to stresses whencompared to
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the oonventional hose having a hraidea structure. This fact is
rather surprising when the fact, tha~ a certain amoun~ of
~ prejud.ice still exists (for various xeasons) against adoptin~
.. 'reinfoxcing spiralle~ structures~ is also taken into account.
S , Actuall~, it was held that in ~draulic brake hoses~
~since each eleme~tary filament o~ the spiral was also ~ubje~t-
: ~(in exercise) to pressure stresses, it would behave as a~ element
.subjected to buokling load, and it would, in ~ase o~ par~i~ular
.maximum compression values, bend to form a cusp shape thus
,reducing the expansion resistance of the hose to break~
. ~' It was also believed that the thread of the spiralle~ -
. ''reinforcing structure, being a rigid element~ would co~tribu~e
considerably towards forming an excessively rigid structure
. resulting in a hose which would not be able ~o provid~ ade~uate 1~ resistance to flexion stxesses.
. However, the volume~ric expansion test and the atigue
. test ha~e made it quite clear that not onl~ does the hose of the
inventi.on ~vercome the above-cited prejudic`es and ampl~ sa~isfy
the requirements of the STANDARD SAE, but $hat the hose o~ the
i~vention evidentl~ expands to a lessex de~ree, and resists
,fatigue to a greater extent than aOes the hose with the braided
structure. ..
Applican~s also wish to point out ~hat ~he notable
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improvement~ attained b~ the.hose o the invention~ as demonstr~d ¦
by the test results, were obtained on structures comprised o-~ ju.s~
. ,
two reinforcing sheaths, each composed of elemen~ar~ ilaments only
so that the invention offers a furth~r important economic advan.~g~
. What is also evident is that~ b~ usi~g elementar~ ~ila-
~ents and by employiny two shéaths o~, this fact ~ontribu-tes
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favorably towards holding up the mass o~ the hose; and, taking
into account the cyclic vibrations in the motor ~ehicle when
xunning, there is less risk of damaging the ends of the hose
. . ~which are anchored down to parts of the vehicle structure).S '. It is urther observed that khe hose ~f the in~ention
.also produces bet-ter results, when ~ompared with an~ other ~ose
! ` .
employed in braking systems where reinforcing sheaths of pol~meric
;yarns are used, instead of metallic ~ilamen~s.
As a ~atter of fact, it can be vexi~ied that metallic
.filaments are quite capable of resls~ing the hi~her tem~erature~ ;
arising when the braking system is bein~ opera~ed; whereas poly~
;meric yarns, with time and temperature, reduce ~heir resis~ant
characteristic, giving the entire hose a shorter life~span.
With respect to hoses braided with ~arns, the hose of
the invention has a further advantage ove~ them in that the hose
the invention ensures greater security in braking even whPn the
externalcovexing-layeriswornout
: In such circumstances, in act, whereas the hose with the
metailic spiralled structur~ ~oes resist the ~ssaults of iceJ mud,
or various acciden~al shocks and jerks, the tex-~lle yarns ~f the
braided hose are subjected to the influence o these ab~e-
mention~d outside influences and sooner or later d~terioration
. .
sets in, to the extent of causing breakin~ in the hose~
Generally speakin~, it has also been ~exlfied ~hat braided
hoses made o~ textile yarns, for instance xayon, appear to have a
oonsid~rable tendency for absorbing moisture~ The contrar~ is true .
in the case of hoses with metallic spixals. This is als~ an
important adwantage in the case of the hos_ o~ the invention, since
the absence o~ water excludes/an~ dangerous risk o~ bubbles forming
30. inside the ~raking circuit when the temperature exc.eeds 100C,
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Xt should be understood that the present invention i~ not
, limited to what is indica~ed above, but includes an~ othex alter-
¦ E,
,native embodiment deriying from the above indicated inven~ive
~,principle.
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