Friction material for applying friction in liquid medium, and associated device and method

Abstract

A friction material intended to equip a device for applying friction in a liquid medium, including a fiber mat impregnated with a heat-curable resin. The fiber mat consists of fibers whose length is greater than or equal to 12 mm, and is teased, coated and needled. The friction material features a porosity greater than or equal to 30% by volume and less than or equal to 60% by volume. The friction material includes activated charcoal loads whose specific surface is between 500 m2/g and whose mass content in the friction material is greater than or equal to 5% by weight and less than or equal to 15% by weight.

Claims

1. A friction material for friction in liquid medium, the friction material including: a mat of fibers impregnated by a heat-hardening resin; fibers of the mat being carded, lapped and needled during the formation of the mat; the carded, lapped and needled fibers being equal to or in excess of 12 mm in length; and charges of active carbon with specific surface between 500 sq.Math.m.Math./gr and 2500 sq.Math.m.Math./gr and with mass content in the friction material equal to or in excess of 5% in weight and equal to or below 15% in weight; the friction material having porosity equal to or in excess of 30% in volume and equal to or below 60% in volume, wherein one side of the friction material, intended to form a friction surface, comprises between 20 and 70% in volume of active carbon over a thickness between 20 m and 200 m.

2. The friction material according to claim 1, wherein the fibers are selected from the group consisting of glass fibers, cotton fibers, polyacrylonitrile (PAN) fibers, pre-oxidised polyacrylonitrile fibers, ceramic fibers, aramid fibers, peat moss fibers, and their combinations.

3. The friction material according to claim 1, wherein the heat-hardening resin is selected from the group consisting of phenoplast resins, particularly resol or novolac, aminoplast resins, epoxy resins, polyimide resins, silicone resins, and their combinations.

4. The friction material according to claim 3, wherein the resin is a phenoplast resin of resol type modified by cashew nut shell liquid (CNSL), with mass content between 10% and 30% in weight of resin.

5. The friction material according to claim 1, wherein the fibers consist of a mixture of three fibers of different composition.

6. The friction material according claim 5, wherein the volume fraction of each of the fibers of different composition is between 20 and 40% of the mixture of fibers.

7. The friction material according to claim 1, wherein the volume ratio between the resin and the mat of fibers is equal to or in excess of 0.80 and equal to or below 1.20.

8. The friction material according to claim 1, wherein the specific surface of active carbon is equal to or in excess of 800 sq.Math.m.Math./gr and equal to or below 1500 sq.Math.m.Math./gr.

9. The friction material according to claim 1, wherein the mass content of active carbon is equal to or in excess of 8% in weight and/or equal to or below 12% in weight.

10. The friction material according to claim 1, wherein the average grain size of the active carbon is equal to or in excess of 5 m and equal to or below 50 m.

11. A friction part, including a friction material for friction in liquid medium and a friction support upon which the friction material is moulded with a casting; the friction material including: a mat of fibers impregnated by a heat-hardening resin; fibers of the mat being carded, lapped and needled during the formation of the mat; the carded, lapped and needled fibers being equal to or in excess of 12 mm in length; and charges of active carbon with specific surface between 500 sq.Math.m.Math./gr and 2500 sq.Math.m.Math./gr and with mass content in the friction material equal to or in excess of 5% in weight and equal to or below 15% in weight; the friction material having porosity equal to or in excess of 30% in volume and equal to or below 60% in volume, wherein one side of the friction material, intended to form a friction surface, comprising between 20 and 70% in volume of active carbon over a thickness between 20 m and 200 m.

12. A device providing a friction in liquid medium, the device including a friction surface coated with a friction material including: a mat of fibers impregnated by a heat-hardening resin; fibers of the mat being carded, lapped and needled during the formation of the mat; the carded, lapped and needled fibers being equal to or in excess of 12 mm in length; and charges of active carbon with specific surface between 500 sq.Math.m.Math./gr and 2500 sq.Math.m.Math./gr and with mass content in the friction material equal to or in excess of 5% in weight and equal to or below 15% in weight; the friction material having porosity equal to or in excess of 30% in volume and equal to or below 60% in volume, wherein one side of the friction material, intended to form a friction surface, comprises between 20 and 70% in volume of active carbon over a thickness between 20 m and 200 m.

13. The device according to claim 12, wherein the device is a transmission coupling part for motor vehicles.

14. A manufacturing procedure of a friction material, as recited in claim 1, including the following consecutive stages a) to d): a) supplying a mat of fibres carded, glazed and felted, the length of the fibres of which is equal to or in excess of 12 mm; b) impregnating the mat in a heat-hardening resin bath; c) drying the excess resin; d) consolidating under charge the intermediary material obtained after stage c) at a temperature between 120 C. and 250 C. in order to obtain a porosity between 30% and 60% in volume of the final material; and a stage: e) introducing charges of active carbon with specific surface between 500 sq.Math.m.Math./gr and 2500 sq.Math.m.Math./gr at a mass content in the friction material equal to or in excess of 5% in weight and equal to or below 15% in weight during stage b) and/or after stage c) and before stage d).

15. A manufacturing procedure of a friction material according claim 14, wherein stage e) consists of impregnating the mat in a bath including a mixture of resin and active carbon.

16. A procedure according to claim 14, wherein stage e) consists of pulverising a waterborne solution including resin, for example the resin of stage b, and active carbon, then making the water evaporate, for example with the aid of infra-red heating.

17. The friction material according to claim 5, wherein the three fibers are glass fibers, polyacrylonitrile fibers and cotton fibers.

18. The friction material according to claim 5, wherein a volume fraction of each of the fibers of different composition is between 20 and 40% of the mixture of the fibers.

19. The friction material according to claim 7, wherein the volume ratio between the resin and the mat of fibers is equal to or in excess of 0.90 and/or equal to or below 1.10.

20. A friction material for friction in liquid medium, the friction material including: a mat comprising fibers being carded, lapped and needled during the formation of the mat; and charges of active carbon with specific surface between 500 sq.Math.m.Math./gr and 2500 sq.Math.m.Math./gr and with mass content in the friction material equal to or in excess of 5% in weight and equal to or below 15% in weight; the mat of the fibers being impregnated by a heat-hardening resin; the carded, lapped and needled fibers being equal to or in excess of 12 mm in length; the friction material having porosity equal to or in excess of 30% in volume and equal to or below 60% in volume, wherein one side of the friction material, intended to form a friction surface, comprises between 20 and 70% in volume of active carbon over a thickness between 20 m and 200 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the evolution of the reduction of thickness of a material in accordance with the specific pressure applied.

(2) FIG. 2 shows measured results of fatigue strength of materials.

(3) FIG. 3 shows the dynamic values of friction .sub.d in accordance with the dissipated energy.

(4) FIG. 4 shows the ratio .sub.f/.sub.d in accordance with the dissipated energy.

DETAILED DESCRIPTION

(5) FIGS. 1 to 4 attached hereto represent the variation of different parameters measured with examples of material according to the invention and comparative examples.

(6) FIG. 1 shows the evolution of the reduction of thickness of a material (expressed as a %, in y-coordinate) in accordance with the specific pressure applied (expressed in MPa, in x-coordinate). Curves 10 (corresponding to the diamonds) and 12 (corresponding to the squares) were obtained by measuring the variation of thickness of samples of material according to the invention EX1 at temperatures of 80 C. and 120 C. in oil, respectively.

(7) Curves 14 (corresponding to the triangles) and 16 (corresponding to the circles) were obtained by measuring the variation of thickness of samples of material of comparative example EX-C1 at temperatures of 80 C. and 120 C. in oil, respectively.

(8) The measurement is made by applying a given pressure to the example to be measured, arranged between two parallel trays in a vat including oil, with cycles where the pressure is applied for 10 seconds and then released for 10 seconds. One applies 1000 cycles of this type, and then measures the variation of thickness between the initial sample and the sample after these 1000 cycles. The samples tested are rings of the materials in question, with exterior diameter of 50 mm and thickness 1 mm.

(9) One important characteristic of the material corresponds to the specific pressure at which a reduction of thickness of 25% is obtained. From the curves represented in FIG. 1, one deduces the following results, presented in table III.

(10) TABLE-US-00003 TABLE III Specific pressure with T ( C.) reduction of thickness 25% EX1 80 C. 60 MPa 120 C. 43 MPa EX-C1 80 C. 36 MPa 120 C. 30 MPa

(11) One notes that the behaviour of the material according to the invention is particularly advantageous, and that for example, it supports a specific pressure significantly double at 80 C. in comparison with a material where, instead of the charges of active carbon according to the invention, charges of amorphous silica have been introduced.

(12) FIG. 2 shows measured results of fatigue strength of the same materials as the previous ones, and in a similar experimental environment.

(13) For this test, one first of all determines a specific test pressure below 5 MPa at the specific pressure at which a reduction of thickness of 25% was measured according to the previous test. One then determines the number of cycles at the end of which a new sample loses 25% of its initial thickness, for a given temperature. FIG. 2 shows the measured points arranged in accordance with the specific pressure applied (expressed in MPa, in y-coordinate) and the number of cycles determined (expressed in decimal logarithm, in x-coordinate).

(14) Curves 20 and 22 (corresponding to the circles, empty and full respectively) were obtained for samples of materials according to the invention EX1 at temperatures of 80 C. and 120 C. respectively. The curves 24 and 26 (corresponding to the squares, empty and full respectively) were obtained for samples of materials of comparative example EX-C1 at temperatures of 80 C. and 120 C. respectively.

(15) One may also determine that the fatigue resistance of a sample according to the invention is considerably improved in comparison to a sample where, instead of the charges of active carbon according to the invention, charges of amorphous silica have been introduced.

(16) For example, if one considers a point of functioning at 20 MPa, one shows that a material according to EX-C1 may operate for approximately one million cycles at 120 C. before losing 25% of its initial thickness, while a material according to the invention, EX1, may operate in the same conditions for more than one hundred million cycles.

(17) Dynamic friction tests have also been undertaken in order to characterise the materials.

(18) According to a first test technique, one evaluates the evolution of the friction coefficient of a disk over time at a pressure equivalent to that at which a synchronisation ring would be likely to operate. A disk of the material to be studied with external diameter of 130 mm, and internal diameter of 100 mm, 0.8 mm thick, is arranged on a counter-material in steel XC48, in oil at a temperature of 100 C. The test takes place on a dynamometer and develops according to several phases detailed in table IV below.

(19) TABLE-US-00004 TABLE IV Specific Number Inertia Speed Specific Cycle Level energy of cycles (m.sup.2 kg) (rpm) pressure time Measurement Running 50 J/cm.sup.2 500 0.49 1420 1 MPa 10 s Yes in Level 1 50 J/cm.sup.2 100 0.49 1420 1 MPa 15 s Yes Level 2 4800 3 MPa Level 3 100 1 MPa

(20) The friction coefficient and wear are measured. One determines the dynamic friction coefficient .sub.d which makes it possible to express the capacity to develop a friction torque when the gear change speed is not zero. It is measured at different specific pressures.

(21) One also determines the final friction coefficient .sub.f which makes it possible to express the capacity to develop a friction torque when the gear change speed is almost zero.

(22) One also determines the ratio between .sub.d initial at 1 MPa and .sub.f at 1 MPa which makes it possible to quantify the stability of friction over a range of operating pressure.

(23) The tests were carried out with samples of material according to the invention EX1 and samples of comparative material EX-C2. The results are set out in table V below:

(24) TABLE-US-00005 TABLE V EX1 EX-C2 .sub.d at 1 MPa 0.108 0.121 .sub.d at 3 MPa 0.105 0.108 .sub.d at 1 MPa 0.111 0.102 Ratio .sub.d initial/.sub.f at 1 MPa 1.03 0.85 .sub.f/.sub.d at 1 MPa 0.97 1.04 .sub.f/.sub.d at 3 MPa 0.98 1.09 .sub.f/.sub.d at 1 MPa 1.01 1.17

(25) One notes that advantageously, the dynamic friction coefficient .sub.d of a material according to the invention, EX1, is more stable according to the constraint applied than a comparative material EX-C2.

(26) Particularly advantageously, the ratio corresponding to the ratio .sub.d initial on .sub.f is close to 1 for a material according to the invention, EX1, while it is 15% lower for a comparative material EX-C2.

(27) One also notes that the ratio .sub.f/.sub.d at the different constraints applied is stable and close to 1 for a material according to the invention EX1, while it varies by about 15% for a comparative material EX-C2.

(28) This gives a possibility to guarantee greatly improved performances in use.

(29) Another technique of tribological tests has also been commissioned, known as increasing energy.

(30) According to this technique, one studies the tribological behaviour of a material subjected to the stages below, set out in table VI.

(31) TABLE-US-00006 TABLE VI Specific Number Inertia Specific Cycle Level energy of cycles (m.sup.2 kg) Speed (rpm) pressure time Measurement Running 50 J/cm.sup.2 500 0.49 136.6 Sd 1 MPa 10 s Yes in Level 1 50 J/cm.sup.2 500 0.49 136.6 Sd 1 MPa 10 s Yes Level 2 100 J/cm.sup.2 500 0.49 192.9 Sd 1 MPa 12 s Level 3 200 J/cm.sup.2 500 0.49 272.8 Sd 1 MPa 20 s Level 4 300 J/cm.sup.2 500 0.49 334.2 Sd 1 MPa 24 s Level 5 400 J/cm.sup.2 500 0.49 385.8 Sd 1 MPa 28 s Level 6 600 J/cm.sup.2 500 0.49 472.6 Sd 1 MPa 43 s Yes With Sd = 2 S, and S being the surface of the lining in cm.sup.2.

(32) The test is always carried out with rings of material arranged on a counter-material in steel XC48 in oil at 100 C.

(33) One also measures .sub.d/.sub.f, the ratio .sub.f/.sub.d as well as a ratio .sub.d 50 J/cm.sub.2 on .sub.d 200 J/cm.sub.2 which makes it possible to quantify the stability of friction on a range of dissipated energy between 50 J/cm.sup.2 and 200 J/cm.sup.2.

(34) FIGS. 3 and 4 show respectively the dynamic values of friction .sub.d, and of the ratio .sub.f/.sub.d (in y-coordinate) in accordance with the dissipated energy (in x-coordinate).

(35) The tests were carried out with two materials according to the invention, EX1 and EX2, and a comparative material EX-C3, and the results were shown with the respective references 34, 32 and 36 in FIGS. 3 and 44, 42 and 46 in FIG. 4.

(36) One notes in FIG. 3 that the dynamic friction coefficient, .sub.d, is extremely stable in accordance with the dissipated energy when the charges of active carbon are arranged on the surface (EX1, 34) and stable when charges of active carbon are arranged in the volume (EX2, 32) in comparison with the results obtained with a material without charge (EX-C3, 36).

(37) Furthermore, it is advantageous that the dynamic friction coefficient is the highest possible, which make it possible, for example, to use motor units of reduced capacity.

(38) One notes that the dynamic friction coefficient at 200 J/cm.sup.2 of the materials according to the invention, EX1 and EX2, is in the order of 0.1, while it is approximately 20% lower for the material without charges EX-C3.

(39) FIG. 4 shows that the ratio .sub.f/.sub.d is remarkably stable between 1.1 and 1.3 for the materials according to the invention (EX1, 44; EX2, 42) while one notes a very significant variation of this ratio for the comparative material (EX-C3, 46).

(40) The ratio .sub.d 200 J/cm.sub.2 on .sub.d 50 J/cm.sub.2 was calculated for the materials mentioned, as stated in table VII below:

(41) TABLE-US-00007 TABLE VII .sub.d 200 J/cm.sup.2/.sub.d 50 J/cm.sup.2 EX1 0.98 EX2 0.92 EX-C3 0.83

(42) These values also illustrate the remarkable stability of the material according to the invention, EX1, EX2 compared to a comparative example EX-C3, where the material is without charges.

(43) One material according to the invention therefore makes it possible to very advantageously guarantee a torque capacity which is significantly constant according to the level of dissipated energy.

(44) It is therefore possible to considerably simplify the laws of operation of gear box calculators, because whatever the difference of speed to be equalized (corresponding to a dissipated energy), the order of stress given to a motor unit may be linear according to the engine torque to be transmitted.

(45) Generally speaking, the material according to the invention may be formed according to the usual techniques. It may particularly be moulded from a casting on a friction support. The friction support surfaces may be varied, particularly flat, frustoconical, cylindrical, continuous or discontinuous.

(46) It is also possible to create groves in the friction material according to the invention for the operation of moulding from a casting.

(47) By way of example, the material according to the invention is produced in the form of strips in which narrow bands may be cut, which are arranged on a friction support before the moulding stage.

(48) The material according to the invention is particularly well suited for commissioning in automatic or robotised transmission coupling parts, particularly those that operate without opening the drivetrain.

(49) The invention is not limited to the examples of completion, and must be interpreted without limitation, including all means of equivalent completion.