METHOD FOR MANUFACTURING A FLYWHEEL

Description

[0001] The present invention relates to a method for manufacturing a flywheel in which a damping sheet metal part is produced by joining at least one first metallic sheet metal element provided for the flywheel with at least one second parallel sheet metal layer on top of each other by a joining process to form a disk-shaped structural unit.

[0002] Flywheels within the meaning of the present invention are in particular flywheels for vehicles such as cars and trucks, namely both so-called automatic flywheels and manual flywheels (dual-mass flywheels), such as those used, for example, in the start / stop automatic system of motor vehicles, but also flywheels used in vehicles without start / stop automatic systems, i.e. standard flywheels or flywheels for any other transmission variants.

[0003] A disadvantage of the known flywheels is the disturbing noise they make during driving.

[0004] DE 602 19 270 T2 describes a sound-dampening starter flywheel in which an element made of a viscoelastic material is arranged between the radial surface located at the outer circumferential end section of a carrier and the radial counter-surface located at the inner circumferential end section of a toothed ring. This element is subjected to compressive stress in both the radial and axial directions. This element is a ring seal that is pressed into a groove in the carrier and thereby placed under tension.

[0005] DE 600 08 991 T2 describes a flywheel for an internal combustion engine with a ring gear. To reduce the noise level during starting, a ring made of a deformable elastomeric material is bonded between a circumferential surface of a flywheel carrier and a complementary circumferential surface of a ring gear mounted on the flywheel. Additionally, a lining made of elastomer or plastomer can be attached to a radial surface between the carrier and the ring gear, which runs approximately perpendicular to the circumferential surface, in order to allow sliding contact between the carrier and the ring gear. The noise reduction is thus achieved by allowing deformation of the ring gear radially to the flywheel shaft.

[0006] German patent DE 10 2011 001 881 A1 describes a method for manufacturing a flywheel with the characteristics of the aforementioned type, in which a damping plate component made of a composite material comprising a layer of sheet steel and a viscoelastic damping layer is permanently bonded to a metallic base element intended as a flywheel in a joining process under pressure and partial forming, forming a sandwich component. Alternatively, a damping layer and / or an adhesive with similar material properties can be used. Here, the flywheel component is constructed from several layers in a sandwich design, at least one of which, preferably an inner layer, is a viscoelastic damping layer. In this known method, the damping plate component made of the steel / damping layer composite must be manufactured separately.Experience with this established process has shown that the material of the viscoelastic insulating layer can cause detrimental adhesion of the tools. In such cases, the forming and joining tools must be cleaned, resulting in additional effort and delays in the manufacturing process.

[0007] Furthermore, tests with the sandwich components known from DE 10 2011 001 881 A1 have shown that no forces are transmitted via the damping sheet component with the viscoelastic insulating layer. In addition, the stiffness of the sandwich component was increased in a detrimental way.

[0008] In DE 10 2014 111 581 A1 a method for manufacturing a flywheel with the characteristics of the aforementioned type is described, in which the first sheet metal element is joined to at least one second parallel sheet metal layer lying on top of each other without an intermediate viscoelastic layer by a joining process to form a disk-shaped structural unit.

[0009] DE 85 01 367 U1, on which the preamble of claim 1 is based, describes a flywheel for manual transmissions with a flywheel disc made in one piece from cold-formed sheet metal with external teeth, wherein, for noise reduction, a ring surrounding the mounting hub of the flywheel is connected to the flywheel disc on one side.

[0010] DE 10 2012 100 278 A1 discloses a rotationally symmetrical component made of sheet steel, which is produced by forming, wherein the sheet steel is formed from two inseparably connected layers of steel, wherein the two layers of steel have different strengths.

[0011] US 2013 / 193 802 A1 discloses a pressure machining method for machining cylindrical parts comprising the steps of joining at least two sheets of metal plates by bringing together the sheet surfaces of the metal plates; rotating the metal plates using a rotating shaft arranged perpendicular to the sheet surfaces of the metal plates; applying a separating and deformation force at a coupling position to a circumference of the at least two sheets of metal plates to separate and deform the metal plates while the at least two sheets of metal plates are rotating; and applying a cylinder-forming force to at least one of the metal plates to form a cylinder along the rotating shaft.

[0012] EP 0 251 243 A1 describes a one-piece flywheel with a toothed ring arranged at an angle on the outer circumference and formed without machining, wherein a thin disc is applied to a side surface of the wheel compared to the wheel cross-section, which adapts to the outer circumference of the angled shape and bears against the tooth flanks leading into the root circle of the toothing.

[0013] JP S61 56743 A discloses the manufacture of a lightweight, robust and precise V-pulley by press forming flange parts on a circumferential wall and rolling a poly-V groove on a circumferential wall of two pressed-together metal discs.

[0014] Based on the aforementioned prior art, the object of the present invention is to provide an alternative method for manufacturing a flywheel which results in a flywheel with vibration-damping and noise-reducing properties and avoids the aforementioned disadvantages. A further object of the present invention is to provide a flywheel with even further improved properties.

[0015] The solution to this problem provides a method for manufacturing a flywheel of the aforementioned type with the characterizing features of the main claim or a flywheel with the features of claim 13.

[0016] According to the invention, it is provided that at least two layers of sheet metal made of different materials and different material thicknesses are joined together.

[0017] According to the invention, the first sheet metal layer has a greater sheet thickness, enabling it to absorb the greater proportion of the torque load during engine start-up and ferry operation. The second sheet metal layer serves to supplement the torque absorption and is constructed with a thinner sheet thickness.

[0018] The thinner second sheet layer has the effect of dampening the noise and creating greater flexibility in the flywheel during operation. Therefore, when two sheet layers are used according to the invention, the first sheet layer has a greater thickness than the second sheet layer.

[0019] Furthermore, according to the invention, in the case of two sheet metal layers, the first sheet metal layer consists of a softer steel material than the second sheet metal layer. For example, when using two sheet metal layers with different material thicknesses according to the invention, the first sheet metal layer can have a sheet thickness of more than 1 mm, preferably more than 1.5 mm, and the second sheet metal layer can have a sheet thickness of less than 1 mm.

[0020] It has already been mentioned that the first sheet is made of a softer steel material than the second sheet. For example, the first sheet layer can consist of a thermomechanically rolled, low-carbon, high-strength steel material suitable for cold forming with a minimum yield strength of 355 N / mm², while the second sheet layer consists of a thermomechanically rolled, low-carbon, high-strength steel material suitable for cold forming with a minimum yield strength of 700 N / mm².

[0021] In the present process, more than two sheet metal layers can be joined together. For example, in this case, a plurality of sheet metal layers, each comprising pairs of sheet metal layers with different material thicknesses and / or different steel materials, can be joined together.

[0022] In the process according to the invention, at least two sheet metal layers with different forming contours, at least in the initial state before the joining process, are joined together.

[0023] The concept of the present invention allows for a wide variety of flywheel designs. For example, this concept makes it possible to produce a flywheel with a multitude of stacked sheets, depending on the load and required flexibility. By using different sheet thickness pairings and different material grades, flywheels can be designed for both high and low loads.

[0024] The exceptionally high flexibility of the flywheels according to this concept allows for low axial pressure on the engine mounts while simultaneously ensuring high torque transmission from the drivetrain. An additional advantage is the low noise level mentioned above.

[0025] Flywheels manufactured according to the inventive method have a number of advantages. They exhibit high flexibility for compensating for tolerances and movement with each engine revolution. They have a low weight, particularly since individual sheets with different (sometimes smaller) outer diameters can be used.

[0026] The manufacturing process step in flywheels in which the joining of two or more sheet metal layers is provided can be carried out in an automatic transfer operation.

[0027] This enables the production of flywheels with maximized torque transmission through the more variable use of sheet thicknesses and material grades. This allows for precise, customized flywheel design according to a defined set of requirements.

[0028] The flywheels according to the invention have very high sound attenuation. They exhibit lower axial stiffness compared to flywheels made from a single sheet.

[0029] According to the present invention, the disc-shaped sandwich component of the drive plate of a flywheel is assembled from two or more sheet metal layers without the interposition of a viscoelastic material; that is, a double sheet or multiple sheet is produced. This double-sheet principle means that the power transmission from the crankshaft to the converter is now transmitted not by just one, as before, but by two or more superimposed sheet metal layers with different materials and / or different material thicknesses.

[0030] Manufacturing such drive plates using the double-sheet principle offers advantages in the area of ​​acoustics. Due to the reduced stress on adjacent components, disruptive resonance noises are minimized. Furthermore, the two- or multi-layered construction provides excellent sound damping. Noises generated by the engaging starter pinion in a flywheel are significantly reduced and are only perceptible as a muffled sound. This is particularly advantageous for a flywheel used in a modern start-stop system.

[0031] Further economic advantages arise in the manufacture of the flywheel. The previously required sound-damping plate with a viscoelastic layer is no longer needed. In the previously mentioned known method, such a sound-damping plate had to be manufactured in a separate operation and joined to the sheet metal part of the drive disc. The method according to the invention reduces the number of necessary operations and is therefore more cost-effective.

[0032] Furthermore, it is advantageous that the solution according to the invention reduces the load on other engine components. The double-sheet principle achieves greater axial and radial flexibility with the same power transmission. This significantly lower stiffness results in reduced stress on the bearings in the gearbox and engine. Eliminating the previously used sound-dampening sheet with a viscoelastic layer also reduces the overall weight of the drive plate. The resulting lower moment of inertia relieves the adjacent components, which in turn can be made smaller.

[0033] According to the invention, unlike previous solutions, damping no longer occurs between the support and the toothed ring of the flywheel, but rather within the support component (now corresponding to the sandwich-like damping sheet metal part) of the flywheel itself, and across its entire surface, so that the support component is essentially vibration- and noise-damping over its entire surface area. During the joining process, two or more essentially round sheet metal elements with a disc-shaped base are joined along their axis in such a way that they subsequently form a multi-layered composite, bonding to each other at their facing surfaces. The sheet metal layers to be joined each have a similar disc-shaped basic geometric outline, but may differ in details. They may also additionally exhibit corresponding or different deformations perpendicular to the plane of the disc shape.

[0034] Preferably, the sandwich component, comprising the first sheet metal element, the second sheet metal layer, and any further sheet metal layers, is deformed at least partially out of the main plane of the disc-shaped sandwich component according to the shape of the flywheel, and holes or cutouts are optionally made in it. The two sheet metal layers can be joined under pressure to form a single component. During this joining process, the entire assembly is typically pressed together so that the initial layers are permanently and firmly bonded.

[0035] The joining process of the sheet metal layers can also include, for example, additional mutual fixing of the sheet metal layers in a radial direction by clipping them together.

[0036] In one possible variant of the invention, it may be provided that, for example, only one sheet layer of the disc-shaped sandwich component receives a raised edge or bend in a radially outer edge region, which the second or further sheet layers do not have.

[0037] According to a preferred embodiment of the invention, the overlapping sheet metal layers of the disk-shaped sandwich component do not have any mutual fixation to one another, so that relative positional changes of the sheet metal layers relative to each other are possible in the radial direction and / or in the axial direction in the micro range.

[0038] The basic shape of the flywheel or the flywheel drive disc can, for example, be determined by a first sheet layer of the sandwich component, and during the joining process, the second or further sheet layers fit snugly against this basic shape, so that a flywheel in the desired shape with a structure of at least two layers is obtained afterwards.

[0039] It can also be advantageous if the joining process of the sheet metal layers includes additional fixing of both components by means of retaining tabs.

[0040] Within the scope of the present invention, a wide variety of material pairings are generally possible. Preferably, the sheet metal layers of the sandwich component consist of an unalloyed, cold-formable steel sheet.

[0041] The joining of the sheet metal layers is preferably carried out under a press, whereby the pressure to be exerted during the joining process naturally depends on the material pairing, as well as on the material thickness of the sheet metal layers used. The contact pressure applied to the sheet metal layers to be joined can therefore vary over a wide range and, for example, be in the range of one or more bar, or even be considerably higher.

[0042] Following the joining process, further operations typically take place, such as forming and trimming, although these processes can also occur before joining. Generally, an outer ring gear is attached to the flywheel after joining. Other flywheel components can be riveted, welded, or bolted on.

[0043] The present invention further relates to a flywheel intended for a motor vehicle starter, which is manufactured according to a method as previously described. Such a flywheel can be used in a motor vehicle, for example, in the area of ​​a start / stop system. The noise damping according to the invention advantageously reduces the disturbing noises generated during starting, which is particularly beneficial in motor vehicles with these systems, since starting processes occur considerably more frequently in these vehicles than in conventional vehicles. However, the use of the flywheels according to the invention is also advantageous in motor vehicles with conventional starters.

[0044] The features described in the dependent claims relate to preferred embodiments of the solution to the problem according to the invention. Further advantages of the present invention will become apparent from the following detailed description.

[0045] The present invention will now be explained in more detail with reference to exemplary embodiments and the accompanying drawings. These drawings show: Figure 1 a view of a disc-shaped starting sheet, from which the manufacture of the flywheel is based; Figure 2 a view of an exemplary double sheet according to the invention for a flywheel; Figure 3 a schematically simplified sectional view through the double sheet according to the invention along the section line AA in Figure 2 ; Figure 4 an enlarged detail view of a section B from the double sheet according to the illustration of Figure 3 .

[0046] Figure 1shows a disc-shaped sheet metal blank for a flywheel according to the invention before deformation and further processing.

[0047] The following refers to the Figure 2 Reference is made to Figure 10. This figure shows, in perspective, a double sheet metal component, designated by reference numeral 10, for a flywheel, which was manufactured according to the inventive method. In principle, such a double sheet metal component 10 has the form of a disc-shaped base body made of sheet metal, which is also referred to herein as a drive disc. A toothed ring (not shown here) is subsequently attached, for example, by welding, around the outer circumference of this disc-shaped base body.

[0048] The disc-shaped base body 10 has perforations in various areas, usually distributed around its circumference. For example, such perforations with smaller holes 18 can be present in the area of ​​an outer annular flat flange 11 of the drive disc, each spaced apart from the others around the circumference of the drive disc 10. In addition to these smaller holes 18, holes 19 can also be present at other locations, for example in a radially inner area 17 of the drive disc. The hole pattern, shape, and number of the various holes 18, 19 are not important within the scope of the present invention, since the focus is primarily on the method of manufacture and the construction of the flywheel according to the invention.

[0049] The aforementioned central area 17 of the flywheel is, as can be seen from Figure 3The disc-shaped base body 10 is deformed by a forming process, such that this central area 17 is raised above the radially outwardly extending areas. This central area has a central hole 16, with a ring of holes containing several smaller holes 19 that concentrically surround the central hole 16. However, these design details concerning the construction of the flywheel are not crucial for the present invention, since the focus here is rather on the method of manufacturing the disc-shaped base body 10, which, as can be seen from the Figures 3 and 4 It can be seen that it is a sandwich-like component made of at least two layers of sheet metal.

[0050] This sandwich-like structure of the disc-shaped base body is described below with reference to the sectional views according to the Figures 3 and 4explained in more detail. As can be clearly seen there, the disc-shaped base body 10 consists of a double sheet, i.e., there are two sheet layers 13, 14 that run parallel to each other in most areas, one above the other, and essentially abut each other. As can be seen from the Figure 4 As can be seen, the first sheet layer, located at the bottom, is made of a greater material thickness of more than one millimeter, for example, 1.8 mm. In comparison, the sheet thickness of the second sheet layer 14, which forms the upper sheet layer, is less and is, for example, less than 1 mm; for instance, the sheet thickness of the second sheet layer 14 is approximately 0.8 mm, which is less than half the sheet thickness of the first sheet layer 13.

[0051] Furthermore, the two sheet layers 13, 14 in this example consist of different steel materials, whereby the first lower sheet layer 13 in the example consists of a softer steel material, for example the material S355MC, while the second upper sheet layer 14 consists of a harder steel material, for example the material S700MC, which has a higher minimum yield strength of 700 N / mm2 compared to the first steel material, while the first softer steel material only has a minimum yield strength of 355 N / mm2.

[0052] In a joining process under pressure, these two superimposed sheet metal layers 13, 14 are permanently bonded together to form a sandwich component. Tests regarding the noise-dampening properties of such a flywheel during operation during a starting process have shown that such a sandwich-like double sheet reacts more softly under the influence of forces than a single sheet. The flywheel is connected to the transmission via the outer ring gear during operation. For example, a pinion (not shown here) engages with the ring gear when the flywheel is used in a starter starter's start / stop device. In the central area 17, the flywheel's drive plate is connected to the engine's crankshaft (these engine / transmission elements, which are known per se, are not shown in the present application).

[0053] When a flywheel according to the invention deforms by, for example, 1 mm in the axial direction, only a force of approximately 1080 N needs to be applied, whereas this force is about twice as high for a conventional flywheel according to the prior art. This results in significantly less wear in important components such as the bearings, and the load on the crankshaft is considerably lower.

[0054] By eliminating a viscoelastic layer, weight is saved compared to conventional solutions, resulting in a lighter flywheel with a lower moment of inertia. The noise-dampening effect of the double sheet metal remains excellent. Instead of two stacked layers, three or more layers can be used if the specific application requires it.

[0055] The connection of the double sheet metal, consisting of the two sheet layers 13 and 14, to the toothed ring of a flywheel at its outer circumference can be achieved, for example, by means of a weld. The two sheet layers 13 and 14 can each have different shapes in their respective outer edge regions.

[0056] The two sheet metal layers 13, 14 can also be further deformed, for example by clinching, to achieve better mutual fixation. This type of connection facilitates, for example, the transport of the components until assembly by welding.

[0057] According to a preferred method, the production of a damping plate part according to the invention and of a flywheel can be carried out, for example, with the following sequence of process steps: The first sheet layer 13 and the second sheet layer 14 are placed together in a press and are formed together in one or more steps according to the desired shape of the drive disc to be manufactured; if one of the sheet layers receives a raised edge or bend in its radially outer area - which is not absolutely necessary - this has the advantage that it leads to a stiffening and a smoothing of the sheet layer in the plane of the drive disc; the two sheet layers are fixed to each other by clinching, this step is optional and not absolutely necessary.The two sheet metal layers are then punched together, according to the required hole pattern for the drive plate to be manufactured; the two sheet metal layers are then preferably welded together in their radially outer area, as well as to a toothed ring that radially surrounds the sheet metal layers on the outside; in the radially inner area, the drive plate with toothed ring thus obtained, which therefore forms a flywheel, is connected to a crankshaft by a bolted connection. Reference symbol list

[0058] 10 disc-shaped base body, drive disc 11 outer annular area 13 first (lower) sheet layer 14 second (upper) sheet layer 16 central hole 17 raised central area 18 smaller holes on the outside 19 holes all around central hole

Claims

1. Method for producing a flywheel, in which a damping sheet metal part is produced, in that at least one first sheet metal element (13) provided for the flywheel is connected to at least one second parallel sheet metal layer (14), one lying on top of the other, by means of a joining process so as to form a disc-shaped structural unit, wherein at least two sheet metal layers (13, 14) having different material thicknesses are connected to one another, wherein the first sheet metal layer (13) has a greater sheet metal thickness than the second sheet metal layer (14) and wherein at least two sheet metal layers (13, 14) having different forming contours at least in the initial state prior to the joining process are connected to one another, characterised in that the at least two sheet metal layers (13, 14) consist of different materials and the first sheet metal layer (13) consists of a softer steel material than the second sheet metal layer (14).

2. Method according to claim 1, characterised in that the first sheet metal layer (13) has a sheet metal thickness of more than 1 mm, preferably a sheet metal thickness of more than 1.5 mm.

3. Method according to any of claims 1 and 2, characterised in that the second sheet metal layer (14) has a sheet metal thickness of less than 1 mm.

4. Method according to any of claims 1 to 3, characterised in that the first sheet metal layer (13) consists of a thermomechanically rolled, low-carbon, high-strength steel material that is suitable for cold forming and has a minimum yield strength of 355 N / mm2.

5. Method according to any of claims 1 to 4, characterised in that the second sheet metal layer (14) consists of a thermomechanically rolled, low-carbon, high-strength steel material that is suitable for cold forming and has a minimum yield strength of 700 N / mm2.

6. Method according to any of claims 1 to 5, characterised in that a plurality of sheet metal layers (13, 14) each comprising sheet metal layer pairings each consisting of two sheet metal layers (13, 14) having a different material thickness and / or each having different steel materials are joined to one another.

7. Method according to any of claims 1 to 6, characterised in that at least two sheet metal layers (13, 14) having different cutting contours at least in the initial state prior to the joining process are connected to one another.

8. Method according to any of claims 1 to 7, characterised in that at least two sheet metal layers (13, 14) that have been heat-treated differently prior to the joining process are connected to one another.

9. Method according to any of claims 1 to 8, characterised in that the sandwich component comprising the first sheet metal element (13), the second sheet metal layer (14) and, if applicable, further sheet metal layers is deformed at least partially out of the main plane of the disc-shaped sandwich component in accordance with the shape of the flywheel (10) and in that, if applicable, perforations (18, 19) or punched holes are made therein.

10. Method according to any of claims 1 to 9, characterised in that only one sheet metal layer (13) of the disc-shaped sandwich component is folded up or bent in a radially outer edge region, which is not featured by the second or further sheet metal layers (14).

11. Method according to any of claims 1 to 10, characterised in that the joining process for the sheet metal layers (13, 14) additionally comprises mutually securing the sheet metal layers in the radial direction by clipping them in.

12. Method according to any of claims 1 to 11, characterised in that the sheet metal layers (13, 14) of the disc-shaped sandwich component lying one on top of the other are not mutually secured to one another and position changes of the sheet metal layers relative to one another are possible in the radial direction and / or in the axial direction in the micro range.

13. Flywheel provided for a starter motor of a motor vehicle, in particular for a motor vehicle having an automatic start / stop system, characterised in that said flywheel is produced according to a method according to any of claims 1 to 12.