FRICTION LAYER FOR A BRAKE LINING OF A TRACTOR

The present invention relates to a friction layer of a brake lining for tractor. Such a friction generally comprises at least one type of fibers to transmit torque, in particular mineral fibers such as glass fibers or asbestos fibers, rubber to avoid harmful noises, various fillers and a binder, in practice a phenolic resin to render the whole coherent.

Usually, the brake linings are manufactured in the form of disc, ring with a rectangular cross-section or fragments of such ring.

The friction layer of the brake lining is intended to come into contact with another piece to cause brake torque, slowing down the rotation of said piece. The brake torque in such tractor application may be up to 6500N m and is generally not less than 500 N m.

Brake linings do not consist in fibers more than 15mm in size. Usually, the fibers are chopped strands less than 10mm in size.

Among the problems encountered with the brake lining consisting in chopped strands fibers, the high brake torque leads to a temperature elevation that enhances the pullout of said fibers and embrittles the matrix defined by the rubber, the various fillers and the binder. Each pullout of fibers generates cracks that spread on the side intending to come into contact with the piece that is to be braked or across the volume of the brake lining. These crack issues are particularly relevant near the groove's angles of the brake lining. The cracks cause the loss of rivets disposed for fixing the brake lining to a support disc and this loss leads to brake lining bursts. It appears also an unintended sliding between the brake lining and the piece above-mentioned and the fibers loss leads to a poor and non-uniform friction.

Furthermore, the chopped strands fibers, embedded into the matrix, are randomly oriented and randomly located in said matrix. Some of them could be oriented towards the piece on which the friction layer is intended to come into contact with, some of them may be flush with a friction side defined by the friction layer, notably the cross section of said fibers may be directly in contact with the piece that is to be braked. The chopped strands fibers have low resistance to abrasion especially when they are oriented and disposed as described above and when the torque applied is between 500 N-m and 6500 N m per axle.

The volatile material related to the wear degrades the braking performances and that the brake lining wears out quickly and prematurely. The aim of the present invention is to offer an improved brake lining of a tractor, in term of sustainability and/or in term of friction performance.

This aim is achieved thanks to a friction layer for a brake lining of a tractor comprising at least one continuous impregnated yarn comprising at least one of a glass fiber, a copper wire and an organic fiber, said continuous yarn completing at least one full turn around the axis of the brake lining.

According to the invention, the yarn enables the orientation of the fiber, as the fiber extends substantially in the direction of the yarn. The fiber extends in a direction substantially parallel to a friction side defined by the friction layer and intended to come into contact with another piece that is to be braked. This arrangement provides a good resistance to pullout so that the sliding between the brake lining and said piece is avoided and the friction performance is maintained at a good level. So, brakes lining comprising a friction layer according to the invention have a good sustainability.

The yarn may comprise several fibers or wires that may be meshed together, for example by twisting or by covering. The fibers and/or the wires extend in the same direction which is the yarn direction. The cohesion between the fibers and/or the wires increases the resistance to the pullout.

The friction layer, as the brake lining, is in the shape of a disc defining a rotational axis. It may also be in the shape of a ring surrounding the rotational axis or may consist in annular sector of said ring.

The friction side defined by the friction layer may comprise between six and ten grooves, notably circumferentially distributed around the rotational axis.

The glass fiber or the organic fiber may be constituted of a multitude of filaments being attached to one another. The cross section of these filaments may be comprised between 10 and 25pm.

The texture of the continuous yarn may be comprised between 400 and 5000tex, notably between 650tex and 2500tex, more notably between 800tex and 2200tex. The cross section of the copper wire may be comprised between 100pm and 200pm, notably 150pm.

The continuous yarn may comprise a glass fiber, a copper wire and an organic fiber.

The glass fiber may be, for example, an E-type glass fiber, an S-type glass fiber or an H-type glass fiber.

The organic fiber may be, for example, acrylic fiber, aramid fiber, carbon fiber, cellulose fiber, polyacrylonitrile (PAN) fiber or other organic fiber.

In addition to the copper wire, other metal wires may be provided to constitute the yarn described above, such as brass wires, steel wires, and aluminium wires.

The continuous yarn may be a glass yarn, an organic yarn or a copper yarn. This kind of yarn consists only in one type of fibers or wire.

Preferably, the texture of the glass yarn may be comprised between 650tex and 2500tex.

Several types of yarns may be comprised in the friction layer.

The continuous yarn may define several sublayers those are stacked on top on each other to form said friction layer.

Each sublayer may be defined by several lobes of yarn. The lobes of one sublayer may be advantageously offset from the lobes of another sublayer, at least offset from the lobes of the next and/or of the previous sublayer in the axial direction.

The lobes of one sublayer may be placed between lobes of one or more lobes of other sublayers so that sublayers may interpenetrate each other. In other words, some sublayers may extend in a same plan, perpendicular to the rotational axis. It ensures high mechanical resistance and cohesion of the layer friction.

In one process embodiment, the yarn may be introduced in a device for moulding. The yarn may follow a sinusoidal path around the rotational axis to define the stacked sublayers. The process may comprise a step of pressing, for example a hot molding step, for the interpenetration of the sublayers. The process may be stopped when the desired friction layer is obtained, said friction may be defined by its weight, its height or by the length of the yarn used. According to another embodiment, several types of yarns may be provided. Preferably, the friction layer comprises at least one glass yarn and one copper yarn.

The friction layer may be defined by one or more sub-layers based on different compositions, for example two successive sub-layers may be defined by two yarns based on different constitutions. The interpenetration of the layers permits to have various proportions of yarns and consequently various proportions of their components that vary accordingly to the height of the friction layer.

The friction layer may comprise organic fibers that represent between 0 to 10% of the friction layer in wt%.

The friction layer may comprise thermoset resins that represent between 15 and 25 % of the friction layer in wt%.

These thermoset resins may be chosen alone or in combinations among: phenol formaldehyde resin (Phenol, resol, CNSL...), melamine-formaldehyde resin, epoxy resin, polyamide imide resin and others resins.

The glass fibers may present a sizing with chemistry compatible with the resin in order to reach high adhesion properties after hot molding.

The friction layer may comprise rubbers that represent between 8 and 15% of the friction layer in wt%, for example styrene-butadiene (SBR) latex rubber and/or carboxylated nitrile butadiene latex rubber (XNBR) and/or non- carboxylated nitrile butadiene latex rubber (NBR). In another characteristic, the rubber may be pre-crossl inked or it may be added to the rubber an activating agent may be added to the rubber to crosslink said rubber during the hot molding.

The friction layer may comprise fillers that represent between 10 and 20% of the friction layer in wt%. Fillers may be organic and/or inorganic, for example, sulfates, carbonates or other salts, notably of elements of the first and second main groups of the periodic table. Note that the selected salts do not promote any corrosion effect, so there is no bonding due to the corrosion of said salts. The carbon black and/or barium sulfate and/or calcium sulphate are particularly preferred. It is also possible to use, for example, silicon oxides, coke, carbon black, hollow microbeads, metal powders, such as copper or brass powder or other materials.

The yarn may be impregnated by a matrix comprising the thermoset resins and the rubbers. Fillers may also be added to the matrix.

The invention also relates to a brake lining for a tractor constituted by the friction layer as described above, the brake lining extending between two opposite sides between which the height of the brake lining is defined.

In this embodiment, the continuous yarn may comprise:

- glass fibers that represent between 15 to 30% of the friction layer in wt%.

- copper wires that represent between 15 to 40% of the friction layer in wt%, notably between 20 to 30% of the friction layer in wt%.

The invention also relates to a brake lining for a tractor constituted by:

- the friction layer as described above, and

- a base layer,

the friction layer and the base layer being assembled together so that they extend between two opposite sides between which the height of the brake lining is defined.

It is possible to adapt the composition of these two layers to increase the performance of each layer while keeping production costs of the brake lining down. In particular, the friction layer may contain a high proportion of copper wires to limit the heat-up of the friction layer and so the friction wear at high temperature.

In the base layer, such a proportion of copper wires is not useful as its temperature is significantly lower than the temperature of the friction layer. In the base layer, copper wires may be substituted with glass fibers which provide mechanical strength to the base layer and so to the brake lining.

In such a brake lining with a friction layer and a base layer, the continuous yarn may comprise:

- glass fibers that represent between 25 to 45% of the friction layer and the base layer in wt%.

- copper wires that represent between 5 to 20% of the friction layer and the base layer in wt%. In such a brake lining with a friction layer and a base layer, the height of the base layer may be between 50 to 70% of the height of the brake lining and the height of the friction layer may be between 30 to 50% of the height of the brake lining.

The friction side defined by the friction layer of the brake lining (with or without base layer) is defined between an inner radius and an outer radius of the lining and the ratio between the difference of said radii and the height of the brake lining ranges between 3 and 15, notably between 5 and 1 1 .

The brake lining may comprise at least one groove. The ratio between the width of the groove and the height of the groove may lie between 2.5 and 10, notably between 3 and 5.

The continuous yarn conforms to the shape of the groove's angle of the brake lining and it permits to reinforce the groove.

The invention also refers to a friction layer for a brake lining of a tractor comprising several impregnated yarns, each yarn comprising at least one of a glass fiber, a copper wire and an organic fiber, said yarns being woven.

This woven arrangement of the yarns enhances the cohesion of the yarns one to another. This arrangement further provides a good resistance to fiber and wire pullouts.

As the continuous yarn described above, the length of the yarns is not less than 4cm, notably not less than 30cm.

The woven arrangement of the yarns may be made according to two directions, notably two perpendicular directions, notably again according to the radial direction and to the circumferential direction. Note that in this particular case, the yarns oriented in the circumferential direction may complete at least one full turn around the axis. The woven arrangement may also be made according to several yarns extending according to different directions. The woven arrangement is then defined as pluridirectional.

The woven yarns may define several sublayers those are stacked on top on each other to form said friction layer.

Each sublayer may be defined by a woven fabrics formed by woven yarns. The woven fabrics of each sublayer may be different. The sublayer compositions may be different. From one sublayer to another, the woven fabrics defining the sublayers may have a different orientation so that the sublayers may interpenetrate each other.

In other words some sublayers may extend in a same plan, perpendicular to the rotational axis. It ensures high mechanical resistance and cohesion of the layer friction.

All the characteristics described in respect to the continuous yarn may also apply to the yarns of this woven arrangement (internal composition, components, base and friction layer...)

To explain the subject matter of the invention more clearly, embodiments shown in the accompanying drawings are described next by way of purely illustrative and non-limiting example.

In the drawings:

- figure 1 shows a view of a brake mechanism comprising brake linings according to the invention;

- figure 2 shows a brake lining of a tractor according to the invention;

- figure 3 shows an axial view of the brake lining of figure 2;

- figure 4 shows a schematic section of a brake lining according to prior art; and

- figure 5 shows a schematic section of a brake lining according to the invention.

Figure 1 shows a tractor brake mechanism 1 comprising four brake linings 8 according to the invention to mechanically brake one of the tractor rear wheel axles.

In this embodiment, a cam shaft 2 actuates two different actuators 3. The cam shaft 2 rotation forces the actuators 3 to move linearly along an axis X, parallel to the rotational axis of the cam shaft 2.

The brake mechanism 1 comprises also an axle shaft 4 to transmit the torque from the engine to the wheels of the tractor. This axle shaft 4 may rotate around the axis X and it is locally splined to be rotationally fixed with a hub 5. This hub 5 is also locally splined to be rotationally fixed with two brake discs 6, on each of which are fixed two brake linings 8. So, the brake linings 8 are rotationally fixed to the axle shaft 4. We may note that no progressivity disc or more generally, no progressivity part, is disposed between the brake lining 8 and the brake disc 6.

The axle shaft 4 and the cam shaft 2 may rotate in the opposite direction.

The two brake linings 8, fixed on the two opposite sides of each brake discs 6, are located in the axial direction between a brake housing 10 and one of the two actuators 3. In this embodiment, the brake housing 10 is formed by two different pieces, fixed together.

The brake linings 8 are intended to come into contact with the brake housing 10 and the actuators 3 to cause brake torque slowing down the rotation of the axle shaft 4. This brake torque may lie between 500 N m and 6500 N-m per axle.

These two actuators 3 may move separately and independently along the axis X and they may be controlled by different brake pedals, not shown here. The braking may be actuated by one or both actuators 3 depending, for example, on the application as field application, driving on the road etc...

Figure 2 and 3 show a brake lining 8 suitable for the brake mechanism 1 described in figure 1 .

In this embodiment, the brake lining 8 is in the shape of a ring surrounding a rotational axis coinciding with the axis X. The brake lining 8 defines a friction side between an inner radius and an outer radius and the length L is defined by the difference of said two radii.

The brake lining 8 extends in the axial direction between two opposites sides between which the height H is defined.

In this embodiment, the length L may lie between 23mm and 51 mm, notably between 35mm and 45mm, notably again between 37mm and 39mm, whereas the height H may lie between 4mm and 6mm, notably between 4.4mm and 4.8mm.

The ratio between the length L and the height H of the brake lining 8 may lie between 3 and 15, notably between 5 and 1 1 .

In this embodiment, the brake lining 8 comprises eight grooves 12 circumferentially distributed around the axis X. The grooves 12 extend only radially and an angle a, defined between two successive grooves 12 and measured from the axis X, is 20°. The ratio between the width W of each groove 12 and the height of the groove 12 lies between 2.5 and 10, notably between 3 and 5. The width W of the groove 12 may lies between 2mm and 10mm, the height of the groove 12 may lies between 1 mm and 2mm.

The brake lining 8 is either constituted by a friction layer or is constituted by a friction layer and a base layer. The friction layer defines the friction side intended to come into contact with the actuator or with the brake housing whereas the base layer defines the other side, fixed to the brake disc. The friction layer and the base layer are assembled together so that they extend between the two opposite sides between which the height H of the brake lining 8 is defined.

The height of the base layer may lie between 50 to 70% of the height H of the brake lining 8 and the height of the friction layer may lie between 30 to 50% of the height H of the brake lining 8.

When the brake lining is only constituted by the friction layer, the two opposite sides are defined by the friction layer. In any case, the internal composition of the brake lining 8 does not influence its shape or its height H.

In this embodiment, the brake lining 8 is fixed to the brake disc 10 by means of fixation means for example rivets or screws. The brake lining 8 comprises several holes 13 for the fixation means passage.

As shown in figure 3, the holes 13 are distributed according to two different circles around the axis X. Sixteen holes are provided on the further circle and eight holes 13 on the closer one. The holes 13 are arranged in staggered pattern: circumferentially, two holes 13 of the farthest circle are followed by one hole 13 of the closest circle.

The holes 13 are distributed regularly around the axis X. From this axis X, an angle β defined between

- a straight radial line crossing a hole of the closer circle, and

- a straight radial line crossing a hole of the further circle that is circumferentially the closest one to the hole of the closer circle

lies between 10° and 15°, notably 12°.

The radius R1 of the further circle measures between 215mm and 205mm, notably 209mm whereas the radius R2 of the closer circle lies between 165mm and 175mm, notably 171 mm. Figure 4 shows a schematic section of a brake lining according to the prior art. In particular, this figure shows a brake lining 8 consisting in chopped strands of fibers 15. These fibers 15 are less than 10 mm in size.

The high brake torque applied (more than 500N) leads to a temperature elevation of the friction layer of the brake lining 8 that enhances the pullout of said fibers. Each pullout of fibers 15 generates crack that spreads on the friction side intending to come into contact with the brake housing or with the actuator or across the volume of the brake lining 8. These crack issues are particularly relevant near the groove's angles 12.

In figure 4, the fibers 15 are randomly oriented and randomly located in the friction layer. Some of them are oriented towards the piece on which the friction layer is intended to come into contact with (brake housing or actuator) and some of them may be flush with a friction side.

Also such chopped strands of fibers 15 have low resistance to abrasion especially when they are oriented and disposed as described in the figure 4. The volatile material related to the wear degrades the braking performances and that the brake lining 8 wears out quickly and prematurely.

Figure 5 shows the same schematic section of a brake lining 8 but according to the invention. The friction layer of this brake lining 8 comprises impregnated yarns 17, each completing at least one full turn around the axis X.

The yarns 17 comprise glass fibers, copper wires, organic fibers and eventually other fibers or wires. So, the yarns 17 may comprise different components or only one type of component.

These yarns enable the orientation of the fibers and of the wires, as they extend substantially in the direction of the yarns. The fibers extend in a direction substantially parallel to the friction side.

Compare to the prior art shown in figure 4, this yarn arrangement provides a good resistance to fibers or wires pullout.

The fibers and the wires of each yarn 17 may be meshed together by twisting.

The continuous yarns 17 conform to the shape of the groove's angle, it permits to reinforce the groove 12. The texture of the yarns 17 may lie between 400 and 5000tex, notably between 650tex and 2500tex, more notably between 800tex and 2200tex and the cross section of the glass fibers of the yarns 17 may lie between 10 and 25μηη.

The continuous yarns 17 may define several sublayers those are stacked on top on each other to form said friction layer.

Each sublayer may be defined by several lobes of yarns 17. The lobes of one sublayer may be advantageously offset from the lobes of another sublayer, at least offset from the lobes of the next or of the previous sublayer in the axial direction. The lobes of one sublayer may be placed between lobes of one or more lobes of other sublayers so that sublayers may interpenetrate each other. In other words some sublayers may extend in a same plan, perpendicular to the axis X.

According to one example of brake lining 8, the brake lining components are:

- glass yarns, comprising only glass fibers such as E-type glass fiber or H- type glass fibers. The texture of these yarns may lie between 400tex and 5000tex, notably between 650tex and 2500tex

- copper wires. The cross section of such wires may lie between 100 and 200 pm.

- organic fibers, chosen among acrylic fibers, aramid fibers, carbon fibers, cellulose fibers, polyacrylonitrile (PAN) fibers or other organic fibers.

- thermoset resins, chosen alone or in combination among phenol formaldehyde resins (Phenol, resol, CNSL...), melamine-formaldehyde resins, epoxy resins, polyamide imide resins and others resins.

- rubbers, chosen alone or in combination among styrene-butadiene (SBR) latex rubber and/or carboxylated nitrile butadiene latex rubber (XNBR) and/or non-carboxylated nitrile butadiene latex rubber (NBR).

- fillers that may be organic and/or inorganic. The fillers are chosen alone or in combination among sulfates, carbonates or other salts, notably of elements of the first and second main groups of the periodic table. The carbon black and/or barium sulfate and/or calcium sulphate are particularly preferred. It is also possible to use, for example, silicon oxides, coke, carbon black, hollow microbeads, metal powders, such as copper or brass powder or other materials.

In addition of the glass yarn, yarns comprising glass fibers, copper wires and organic fibbers are provided.

The yarns 17 are impregnated by a matrix comprising the thermoset resins and the rubbers. The fillers may also be added to the matrix.

Proportions of the components mentioned above may vary depending on the presence of a base layer constituting the brake lining 8. Two examples of brake lining 8 compositions are given in the table 1 below.

Table 1

The percentages expressed of the table are percentage compared to the total weight of the brake lining 8. We may note that in the second row, the weight of the brake lining 8 is the weight of the friction layer, and that in the third row, the weight of the brake lining 8 is the weight of the friction layer and the base layer. The presence of the base layer permits to adapt the composition of these two layers.

To illustrate the benefits of the invention, a comparative test has been made with a brake lining of the prior art and a brake lining 8 constituted only by a friction layer. For this test, the brake lining 8 is a specific embodiment of the second row of table 1 , it comprises:

- between 19 and 22% of copper yarn,

- between 21 and 23% of thermoset resins,

- between 1 1 and 13% of rubber,

- between 15 and 16% of fillers,

- between 23 and 24% of glass yarns, and - between 5 and 6% of organic fibers.

This test has been carried out with a brake mechanism 1 comprising brake linings 8 according to this specific embodiment. The test has been carried out on field operations during 500 hours.

The test results show that the wear is around 0,13mm compare to 0,24mm per brake lining of the prior art. There is no crack or burst after 500 hours of test but the brake lining of the prior art cracks on rivet holes at 322 hours. The volatile material is also less important (5 to 10 grams of powder) than in the brake lining of the prior art (150 to 200 grams of powder).