Dry clutch friction disc

Abstract

The invention relates to a dry clutch friction disc (1) comprising a web (2) and at least one two-layer friction lining (3) fixed to the web (2) by means of rivets (4), said friction lining (3) comprising: a friction layer (5) having an excitation factor less than 0 Nms over a temperature range between 50 and 300°C, an inner layer (6) disposed between the web (2) and the friction layer (5) and having an excitation factor greater than 0 Nms over a temperature range between 150 and 300°C, and a transition zone (7) disposed between the friction layer (5) and the inner layer (6), said transition zone (7) being formed by partial interpenetration of the materials of the friction layer (5) and the inner layer (6) and having a gradient of the excitation factor increasing from the friction layer (5) to the inner layer (6), said transition zone (7) extends above the rivets (4) in a direction of insertion of said rivets (4).

Description

Title of the invention: Dry clutch friction disc

[0001] The present invention relates to a dry clutch friction disc comprising a two-layer friction lining, particularly for use in clutch devices for motor vehicles. The friction disc according to the invention can thus be used, in particular, in dry transmissions such as a dual dry clutch, a clutch for a manual transmission, or an automated manual transmission (AMT).

[0002] A dry-operating motor vehicle clutch generally comprises a friction disc carrying friction linings on each of its faces, which are riveted to a support or possibly a common disc. The support is fixed to a splined hub that meshes with an input shaft of a gearbox.

[0003] The friction disc is, in service, placed between, on the one hand, a reaction plate connected directly or indirectly to the crankshaft of the vehicle's engine and, on the other hand, a pressure plate of a clutch mechanism comprising a cover connected to the reaction plate and an annular diaphragm, axially stressing the pressure plate which is rotationally connected to the cover while being able to move axially relative to it in a limited way.

[0004] In the engaged position, the friction disc linings are clamped between the reaction plate and the pressure plate, so that the rotational torque of the internal combustion engine is transmitted to the gearbox input shaft.

[0005] A friction lining must transmit torque from the engine to the gearbox and vice versa. To achieve this, the lining must have good mechanical strength under various stresses—radial, axial, circumferential—with or without shear stresses under load, and with or without thermal stresses, as well as good thermal resistance, meaning it must withstand mechanical stresses after thermal damage and not lose its friction capacity (no slippage) at high temperatures. Furthermore, a friction lining must exhibit a relatively high and uniform coefficient of friction across its surface to transmit engine torque to the gearbox.

[0006] Friction linings are wear parts that wear down over time due to constant friction between the lining and other clutch components (such as the flywheel or pressure plate). This friction, which is essential for transmitting torque, inevitably leads to lining degradation as particles of the friction material detach and are removed, gradually reducing the lining thickness.

[0007] When the friction lining of a clutch wears to the point of reaching the heads of the rivets that secure it to the backing plate, several serious problems can occur. For example, there may be a loss of friction because the contact area between the clutch disc and the flywheel (or input disc) will become partly metallic (rivets) rather than friction material. The coefficient of friction between the metal rivets and the flywheel is much lower than that of the lining, which reduces the clutch's effectiveness. Furthermore, since the clutch disc can no longer properly engage with the flywheel, this results in slippage. The engine runs, but the transmission is not properly driven, leading to a loss of power in the system.Other problems such as damage to the flywheel and pressure plate, overheating and deformation of components, or complete clutch failure are likely to occur.

[0008] It is known in the prior art to use high-strength materials that last longer and delay the wear process through abrasion and thermal degradation. However, these materials are relatively expensive. It is also possible to add visual wear indicators or to perform regular clutch checks, but this implies frequent visits to a mechanic or specialist workshop, resulting in additional inspection costs, even if no repairs are necessary.

[0009] The invention aims to provide a dry clutch friction disc that solves the aforementioned problems.

[0010] To this end, the invention relates to a dry clutch friction disc comprising a web and at least one two-layer friction lining fixed to the web by means of rivets, said friction lining comprising: - a friction layer exhibiting an excitation factor of less than 0 Nms over a temperature range between 50 and 300°C, - an inner layer positioned between the veil and the friction layer and exhibiting an excitation factor greater than 0 Nms over a temperature range of 150 to 300°C, and - a transition zone disposed between the friction layer and the inner layer, said transition zone being formed by partial interpenetration of the materials of the friction layer and the inner layer and exhibiting a gradient of the excitation factor increasing from the friction layer to the inner layer,

[0011] in which the transition zone extends above the rivets in a direction of insertion of said rivets.

[0012] The invention also relates to a dry clutch friction disc comprising a web and at least one two-layer friction lining fixed to the web by means of rivets, said friction lining comprising: - a friction layer exhibiting an excitation factor of less than 0 Nms over a temperature range of 50 to 300°C and - an inner layer positioned between the veil and the friction layer and exhibiting an excitation factor greater than 0 Nms over a temperature range between 150 and 300°C,

[0013] in which the inner layer extends above the rivets in a direction of insertion of said rivets.

[0014] In summary, the invention relates to a dry clutch friction disc comprising a web and at least one two-layer friction lining fixed to the web by means of rivets, said friction lining comprising: - a friction layer exhibiting an excitation factor of less than 0 Nms over a temperature range between 50 and 300°C, - an inner layer positioned between the veil and the friction layer and exhibiting an excitation factor greater than 0 Nms over a temperature range of 150 to 300°C, and - optionally, a transition zone disposed between the friction layer and the inner layer, said transition zone being formed by partial interpenetration of the materials of the friction layer and the inner layer and exhibiting a gradient of the excitation factor increasing from the friction layer to the inner layer,

[0015] in which the inner layer or the transition zone when the friction disc includes one, extends above the rivets in a direction of insertion of said rivets.

[0016] The friction disc according to the invention thus allows, thanks to the internal layer or the transition zone, to warn the driver that one is approaching the maximum wear of the friction lining and this before reaching the head of the rivets.

[0017] Indeed, the excitation factor in the context of a clutch represents the measure of the variations in transmission torque during the engagement or disengagement phase of the clutch, as a function of time. This factor is crucial for evaluating the dynamic behavior of the clutch, in particular its response to temperature changes, which can cause variations in friction, slippage, and therefore vibrations known as "judder." A clutch friction lining with good judder behavior is one that minimizes the vibrations and jolts felt during clutch engagement. This lining will have a factor negative excitation means that torque variations are smoother. A friction layer with an excitation factor below 0 Nms across a temperature range of 50 to 300°C therefore exhibits good chatter behavior even at high temperatures.

[0018] On the contrary, a layer exhibiting a positive excitation factor, namely greater than 0 Nms over the entire temperature range between 150 and 300°C, is a layer exhibiting poor chattering behavior under heavy usage conditions since the latter amplifies vibrations.

[0019] Thus, within the framework of the present invention, the friction layer is defined by its excitation factor being less than 0 Nms over the entire temperature range between 50 and 300°C, the inner layer is defined by its excitation factor being greater than 0 Nms over the entire temperature range between 150 and 300°C, and the transition zone by a gradient of the excitation factor increasing from the friction layer to the inner layer.

[0020] The gradient of the excitation factor of the transition zone is therefore increasing between the value of the excitation factor of the friction layer and that of the inner layer.

[0021] The sudden or gradual appearance of chattering when passing respectively from the friction layer directly to the inner layer or via the transition zone thus allows the driver to be warned that the maximum wear of the friction lining is approaching, and this before reaching the rivet heads.

[0022] The present invention also relates to a clutch device for a motor vehicle comprising a dry clutch friction disc according to the present invention.

[0023] The invention and its advantages will be readily understood in the light of the description and embodiment examples that follow.

[0024] [Fig-1] represents a schematic cross-sectional view of a friction disk according to a first embodiment of the invention.

[0025] [Fig.2] represents a schematic cross-sectional view of a friction disk according to a second embodiment of the invention.

[0026] [Fig.3] represents the evolution of the excitation factor as a function of temperature of the friction layer and the inner layer of a friction lining according to the invention.

[0027] For clarity, the dimensions of the various elements shown in these figures are not in proportion to their actual dimensions. In all figures, identical reference numerals correspond to identical elements.

[0028] Figure 1 shows a schematic view of a friction disc 1 according to the invention. Within the scope of the invention, the terms "axial" and "radial" are defined in relation to the axis of rotation of the friction disc. The friction disc 1 includes a web 2 which extends radially and a hub (not shown) capable of being joined to a driven shaft and at least one two-layer friction lining 3 fixed to the web 2 by means of rivets 4.

[0029] The fitting 3 includes countersunk holes with a portion 32 sufficiently wide to receive the head of the rivet 4 and a narrower portion 33 to allow movement of the rivet body without permitting the passage of the rivet head. At the bottom of the wider portion 32 is a counterbore face 31 against which the rivet head 4 can bear. The portion of the web 2 intended to be in contact with the area of ​​the hole 33 in the fitting 3 also includes a hole 21 of the same diameter. A rivet 4 is set to secure the friction lining 3 and the web 2 without gluing or any other pre-assembly step by placing one head of this rivet on one side in contact with the counterbore face 31 and placing the other head of this rivet on the web 2, the body of the rivet passing through the holes 21, 33. Only one rivet 4 is shown in [Fig.1], but it is clear that several rivets 4 are necessary to fix the friction lining(s) 4 to the web 2.

[0030] The friction lining according to the present invention is a two-layer lining, that is to say, it has a friction layer 5 and an inner layer 6.

[0031] The friction layer 5 is the layer that comes into contact with the surface of the flywheel or clutch disc. Its role is to generate sufficient friction to allow efficient power transmission between the engine and the transmission, while preventing excessive slippage.

[0032] The friction layer 5 is composed of wear- and heat-resistant materials such as a fibrous base material comprising glass fibers, organic fibers, and / or metallic fibers, as well as resin that binds the components together. Preferably, the resin content is 30 to 60% by weight relative to the total weight of the friction layer. The friction layer must maintain a stable coefficient of friction at different temperatures, resist thermal and mechanical variations (chattering), and prevent premature wear.

[0033] The inner layer 6 is positioned between the web 2 and the friction layer 5 and is not intended to come into direct contact with the clutch surfaces, as it serves as structural support for the friction layer. It helps transmit the mechanical forces generated during clutch engagement and disengagement. The inner layer 6 is often made of materials that are more rigid and less expensive than the friction layer 5, such as metal or composite fibers, with a low resin content (generally less than 20%). This material must be robust enough to withstand mechanical stresses without excessive deformation.

[0034] In the example considered, the friction layer 5 and the inner layer 6 are joined together by hot pressing. This hot pressing is carried out in a mold. A pressure force of between 5 and 50 MPa is applied, and the mold is then gradually heated to a temperature between 50 and 300°C (depending on the type of resin, particularly the thermosetting resin used) to activate the resin and initiate the polymerization process. The holding time at this temperature varies between 10 minutes and 1 hour, depending on the thickness of the friction lining and the properties of the materials used. After the heating and pressing cycle, the mold is generally cooled gradually and in a controlled manner to avoid excessive thermal stress in the material. Finally, if necessary, the lining undergoes finishing operations, such as grinding or machining the edges to obtain precise dimensions and drilling to install rivets or screws for mounting the lining to its final support.

[0035] During this assembly process, a transition zone 7, located between the friction layer 5 and the internal layer 6, is formed by partial interpenetration of the materials of the friction layer 5 and the internal layer 6.

[0036] In the context of the present invention, the friction layer 5 has an excitation factor of less than 0 Nms over a temperature range of 50 to 300°C, and the inner layer 6 has an excitation factor of more than 0 Nms over a temperature range of 150 to 300°C. The transition zone 7 exhibits a gradient of increasing excitation factor from the friction layer 5 to the inner layer 6. The method used to measure the excitation factor will be described in more detail later in the description.

[0037] In the present invention, the transition zone 7 extends above the rivets 4 in the direction of insertion of said rivets 4. In other words, the transition zone 7 extends above the rivets in an ortho-radial direction. As can be seen in [Fig. 1], the transition zone 7 extends from the inner layer 6 towards the friction layer 5 and further towards the friction layer than the rivet 4 extends towards the friction layer. Having this transition zone formed from the inner layer 6 and the friction layer 5 with their defined excitation factors allows for a gradient of the excitation factor increasing from the friction layer 5 to the inner layer 6. Thus, the excitation factor will gradually increase as one moves from the friction layer towards the inner layer.This gradual growth will allow for a progressive chattering sound to alert the driver that they are approaching the rivet heads.

[0038] Advantageously, the transition zone 7 extending above the rivets 4 has a thickness of at least 2 mm. The thickness of a friction lining refers to the distance between the two main surfaces of the lining: the surface in contact with the moving element (such as the flywheel or clutch disc) and the opposite surface fixed to the veil 2. The thickness is therefore measured along the orthoradial direction.

[0039] Advantageously, the transition zone 7 has a thickness between 15 and 45% of the total thickness of the friction lining 3. Advantageously, the transition zone 7 extends in the orthoradial direction over the entire thickness of the rivet head.

[0040] In the example considered in [Fig.1], the inner layer 6 does not extend above the rivets 4 in a direction of insertion of said rivets 4.

[0041] Figure 2 shows a schematic cross-sectional view of a friction disc according to a second embodiment of the invention. The only difference compared to the first embodiment is that there is no transition zone 7. Indeed, the friction layer 5 and the inner layer 6 are bonded together. It is therefore the inner layer 6 that extends over the rivets 4 in the direction of insertion of said rivets.

[0042] The remainder of the description relates to the two embodiments shown in figures 1 and 2.

[0043] Advantageously, the friction layer 5 has a thickness between 30 and 60% of the total thickness of the friction lining 3.

[0044] Advantageously, the inner layer 6 has a thickness between 20 and 60% of the total thickness of the friction lining 3.

[0045] Advantageously, at least one friction lining 3 consists of a circular lining or of several segments forming together a circular lining.

[0046] Preferably, the friction layer 5 has an excitation factor of less than -0.1 Nms over the whole of a temperature range between 50 and 200°C.

[0047] Preferably, the inner layer 6 has an excitation factor greater than 0.1 Nms over the whole of a temperature range between 200 and 300°C.

[0048] Examples of a friction layer 5 exhibiting an excitation factor less than 0 Nms over a temperature range of 50 to 300°C and of an inner layer 6 exhibiting an excitation factor greater than 0 Nms over a temperature range of 150 to 300°C are given below. In what follows, the compositions of the layers are expressed as percentages by weight, with the percentages given as a percentage of the total weight of the layer.

[0049] Example 1: Example of a friction layer 5 having an excitation factor less than 0 Nms over a temperature range between 50 and 300°C

[0050] The friction layer 5 comprises: • 45 to 55% of a reactive material comprising: • 27 to 42% of a mixture of phenolic resin and melamine / formaldehyde and NBR type rubber • 3 to 10% lubricating fillers, • there, 10% vulcanization catalyst and other fillers, • 5 to 10% copper fibers, • 30 to 45% glass fibers • 3 to 8% polyacrolynitrile fibers.

[0051] Advantageously, the lubricating fillers consist of mineral and / or organic fillers. Advantageously, the mineral lubricating fillers consist of metal sulfides preferably selected from the group consisting of iron sulfide, copper sulfide, zinc sulfide, molybdenum disulfide, tin sulfide, tin disulfide and mixtures thereof.

[0052] Advantageously, the organic lubricating fillers consist of graphite, for example synthetic or natural graphite.

[0053] Typically, the vulcanization catalyst is sulfur or zinc oxide. Other fillers are advantageously chosen from among so-called "friction" fillers. For example, such fillers may be chosen from carbon black, barium sulfate, activated carbon, kaolin, hollow microspheres (especially glass) or calcium carbonate.

[0054] Glass fibers can be of the roving and / or textured type. Fibers are said to be of the roving type when they are grouped together in the form of a strand by sizing. Textured or bulked fibers are derived from roving fibers by opening a portion of their volume by injecting air.

[0055] Example 2: Example of an inner layer 6 exhibiting an excitation factor greater than 0 Nms over a temperature range between 150 and 300°C

[0056] The inner layer 6 comprises: • 40 to 45% of a reactive material comprising: • 16 to 20% of a mixture of phenolic resin and melamine, • 10 to 12% SBR type rubber, • 10 to 15% vulcanization catalyst and other fillers, • 30 to 35% copper fibers, • 15 to 20% glass fibers, • 6 to 10% acrylic fibers.

[0057] Method used to measure the excitation factor:

[0058] The excitation factor (also called the gain factor or vibration amplification factor) in the context of chatter tests is measured through a combination of dynamic testing and vibration analysis on friction systems (such as clutches). 1. Basic principle

[0059] The excitation factor is calculated by analyzing the vibrations generated by the friction system when subjected to different operating conditions (temperature, pressure, speed). Essentially, it measures how the system reacts to small disturbances (natural vibrations). If these vibrations are amplified with each cycle, a positive excitation factor is obtained. If the vibrations are damped (gradually reduced), a negative excitation factor is obtained. 1. Testing Procedure

[0060] The excitation factor test takes place in a controlled environment, either on a test bench (in the present case), or in a vehicle. a. Device preparation: the clutch device including the friction discs with a diameter of 240mm and the pressure plate is installed on the test bench. b. Usage simulation: i. A first measurement of the chatter level is taken at room temperature, ii. We then perform 1000 wear cycles at 120°C, during which 15kJ of energy is applied to the material in continuous sliding mode for each cycle. iii. A second measurement of the chatter level is performed at room temperature, iv. A first phase of 100 cycles is carried out during which an energy of 35 kJ is supplied to the continuously sliding material every 20 seconds, allowing a temperature rise from 40 to 350°C. The chatter is measured during this temperature rise. v. A second recovery phase is then carried out with 100 cycles of 15 KJ at a temperature between 80 and 120°C. vi. The two phases are repeated 6 times. vii. The result is presented in such a way as to show, for each temperature, the maximum chatter of the 6 series of tests. c. Vibration analysis: The system's vibrations are measured at each cycle using accelerometers. The vibrations are measured in terms of angular and linear accelerations. The data are recorded and compared from one cycle to the next to detect whether the vibrations are increasing or decreasing. d. Calculation of the excitation factor: The excitation factor is calculated by measuring the rate of amplification or reduction of vibrations from one cycle to the next. The excitation factor R is calculated according to the following formula: R = 2J.F.lnA. J being the overall inertia (bench + clutch disc) in kg.m2, F the average frequency in s (P) and A the logarithmic decrement

[0061] A positive factor means that the amplitude of the vibrations increases from one cycle to the next, indicating chatter. A negative factor means that the vibrations gradually dissipate, indicating a more stable device. a. Data processing: The captured data (vibrations, temperature) are then analyzed to plot a graph of vibration amplification as a function of temperature.

[0062] Figure 3 represents the evolution of the excitation factor as a function of temperature (°C) for a friction layer and an internal layer according to the invention.

[0063] The excitation factors were measured according to the procedure defined above with 36 tests for the friction layer 5 according to example 1 (exl) and 6 tests for the inner layer 6 according to example 2 (ex2).

[0064] As can be seen in [Fig. 3], the friction layer 5 exhibits an excitation factor of less than 0 Nms over a temperature range of 50 to 300°C and even less than -0.1 Nms over a temperature range of 50 to 200°C. This friction layer 5 therefore provides good comfort during gear changes in the gearbox.

[0065] On the other hand, the inner layer 6 exhibits an excitation factor greater than 0 Nms over the entire temperature range of 150 to 300°C and even greater than 0.1 Nms over the entire temperature range of 200 to 300°C. This inner layer 6 is therefore a source of vibrations from 150°C and even more so at 200°C.

[0066] Of course, the preceding description has been given by way of example only and does not limit the scope of the invention, which would not be exceeded by replacing the various elements with any other equivalents.

[0067] Furthermore, the different features, variants, and / or embodiments of the present invention can be combined with each other in various ways, provided that they are not incompatible or mutually exclusive.

Claims

Demands

1. A dry clutch friction disc (1) comprising a web (2) and at least one two-layer friction lining (3) fixed to the web (2) by means of rivets (4), said friction lining (3) comprising: • a friction layer (5) having an excitation factor less than 0 Nms over a temperature range of 50 to 300°C, • an inner layer (6) disposed between the web (2) and the friction layer (5) and having an excitation factor greater than 0 Nmover a temperature range of 150 to 300°C, and • a transition zone (7) disposed between the friction layer (5) and the inner layer (6), said transition zone (7) being formed by partial interpenetration of the materials of the friction layer (5) and the inner layer (6) and having a gradient of the excitation factor increasing from the friction layer (5) to the inner layer (6), characterized in that the transition zone (7) extends above the rivets (4) in a direction of insertion of said rivets (4).

2. Dry clutch friction disc (1) according to claim 1 characterized in that the inner layer (6) does not extend over the rivets (4) in a direction of insertion of said rivets (4).

3. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the transition zone (7) has a thickness between 15 and 45% of the total thickness of the friction lining (3).

4. Dry clutch friction disc (1) comprising a web (2) and at least one two-layer friction lining (3) fixed to the web (2) by means of rivets (4), said friction lining (3) comprising: • a friction layer (5) having an excitation factor less than 0 Nms over a temperature range of 50 to 300°C, and • an inner layer (6) disposed between the web (2) and the friction layer (5) and having an excitation factor greater than 0 Nms over a temperature range of 150 to 300°C, and characterized in that the inner layer (6) extends above the rivets (4) in a direction of insertion of said rivets (4).

5. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the friction layer (5) has a thickness between 30 and 60% of the total thickness of the friction lining (3).

6. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the inner layer (6) has a thickness between 20 and 60% of the total thickness of the friction lining (3).

7. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that at least one friction lining (3) consists of a circular lining.

8. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the friction layer (5) has an excitation factor of less than -0.1 Nms over the whole of a temperature range between 50 and 200°C.

9. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the inner layer (6) has an excitation factor greater than 0.1 Nms over the whole of a temperature range between 200 and 300°C.

10. Dry clutch friction disc (1) according to any one of the preceding claims, characterized in that the friction layer (5) and the inner layer (6) are joined together by bonding or hot pressing.

11. Clutch device for motor vehicle characterized in that it comprises at least one dry clutch friction disc (1) according to any one of the preceding claims.

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