DE102024111328A1 - Motor vehicle and method for mounting a heat shield - Google Patents

Abstract

The invention relates to a motor vehicle (1) with an exhaust system (2) which becomes hot during operation of the motor vehicle (1), and with a supporting structure (7) which is formed from a first material with a first thermal expansion behavior and to which a heat shielding plate (5) made from a second material with a second thermal expansion behavior which differs greatly from the first thermal expansion behavior is attached, wherein the heat shielding plate (5) is fastened to the supporting structure (7) at fastening points (8-12) by means of screw-nut connections (13-15).
In order to reliably prevent undesired damage to the heat shielding plate (5) under very high thermal loads, the screw-nut connection (15) is designed to be force-decoupled at at least one of the fastening points (8-12) in a temperature-critical proximity to the exhaust system (2) in such a way that the heat shielding plate (5) can expand mechanically without force at this fastening point (12) in relation to the screw-nut connection (15).

Description

The invention relates to a motor vehicle with an exhaust system that becomes hot during operation of the motor vehicle, and with a supporting structure formed from a first material with a first thermal expansion behavior, to which a heat shielding plate made of a second material with a second thermal expansion behavior that differs significantly from the first thermal expansion behavior is attached. The heat shielding plate is attached to the supporting structure at fastening points by means of screw-nut connections. The invention further relates to a method for mounting a heat shielding plate on such a motor vehicle.

From the German utility model DE 20 2013 007 579 U1, a motor vehicle body is known with a substructure and a cladding element, which have different thermal expansion coefficients, and with at least one connecting assembly passing through openings in a plate of the substructure and a plate of the cladding element, wherein one of the plates is held in a groove of the connecting assembly with play in the direction of its surface normal, and the connecting assembly further comprises a bushing having two parts movable relative to one another in the direction of the surface normal, between which the other plate is held, wherein one plate is made of metal and the other of plastic. The Japanese publication JP H09166123 A discloses a screw connection between a synthetic resin layer and a metal layer, wherein the screw connection is intended to prevent breakage of the resin layer. A sleeve is inserted into a through-hole of the resin layer, which is slightly longer than the thickness of the resin layer. A screw is inserted into the sleeve and screwed into a corresponding mating thread in the metal layer, so that the force of the screw is not transmitted through the sleeve and is not conducted through the resin layer. The Japanese publication JP H0514950 Y2 discloses the attachment of resin components to a car body, with elongated holes combined with spacers to compensate for thermal expansion. The German patent specification DE 197 14 700 C2 discloses an exhaust system arrangement with two components, an exhaust system element which is subject to heat stress and a heat shielding plate which is arranged beneath the exhaust system element and is connected thereto via a connecting device in such a way that a relative displaceability of the exhaust system element and the heat shielding plate to one another is possible due to different thermal expansion behavior, wherein the connecting device has sliding tongues with sliding surfaces for the slidable reception of a first component, which receive the first component with a predetermined spring force in a substantially horizontal direction, wherein the connecting device is rigidly connected to the second component, and clamping means are provided which fix the second component on the connecting device and clamp the connecting device to the first component.

The object of the invention is to reliably prevent undesirable damage to a heat shielding plate on a motor vehicle with an exhaust system, even under very high thermal loads.

The problem is solved in a motor vehicle with an exhaust system that becomes hot during operation of the motor vehicle, and with a support structure that is made of a first material with a first thermal expansion behavior and to which a heat shielding plate made of a second material with a second thermal expansion behavior that differs greatly from the first thermal expansion behavior is attached, wherein the heat shielding plate is attached to the support structure at attachment points by means of screw-nut connections, in that the screw-nut connection at at least one of the attachment points in a temperature-critical proximity to the exhaust system is designed to be force-decoupled in such a way that the heat shielding plate can expand mechanically force-free at this attachment point, relative to the screw-nut connection. Critical proximity to the exhaust system in this context means that the attachment point is arranged so close to a heating exhaust pipe of the exhaust system that an undesirable but unavoidably high thermal load occurs on the heat shielding plate. In tests and investigations conducted within the scope of the present invention, this has led, among other things, to a heat shielding plate that was optimized for weight and tool cost failing at the fastening point. The heat shielding plate is, in particular, a very thin-walled sheet made of an aluminum material. Such a heat shielding plate is produced, for example, from a two-layer semi-finished product, using very thin-walled aluminum foils with material thicknesses between two-tenths of a millimeter and five-tenths of a millimeter. Such a heat shielding plate is manufactured in a special manufacturing process. The semi-finished product is first contour-trimmed, with the resulting edge trim being flanged and then formed and perforated. The aluminum material from which the heat shielding plate is preferably formed has a thermal expansion The thermal expansion coefficient is almost twice as large as the thermal expansion coefficient of the steel material from which the bolt-nut connection is made. The force decoupling at the fastening point provides the advantage that the heat shielding plate can move relative to the bolt-nut connection and the supporting structure. This reliably prevents unwanted failure of the heat shielding plate at this fastening point. The heat shielding plate is held more or less loosely to the supporting structure at the critical fastening point.

A preferred embodiment of the motor vehicle is characterized in that the screw-nut connection is designed to be force-decoupled at at least one of the fastening points in a temperature-critical proximity to the exhaust system, such that the heat shielding plate at this fastening point, relative to the screw-nut connection, can expand mechanically force-free in an axial direction. The term "in an axial direction" refers to a longitudinal axis of the force-decoupled screw-nut connection. Axial means in the direction of or parallel to this longitudinal axis. During its manufacture, the heat shielding plate is preferably formed, for example, deep-drawn. Due to the manufacturing process, the heat shielding plate is not 100% smooth or flat in the area of the screw-nut connection. In the area of the screw-nut connection, the heat shielding plate is, for example, slightly curved. This means that after assembly, the heat shielding plate feels firmly in place in the area of the screw-nut connection, despite a deliberately specified amount of play in the axial direction. This means that the heat shielding plate in the area of the screw-nut connection is held rattle-free despite the force-decoupled design of the screw-nut connection. Thermal expansion and relative movement are intentionally permitted by the force-decoupled design of the screw-nut connection. The heat shielding plate can work its way free when installed under the influence of heat. The slight clamping of the heat shielding plate in the area of the screw-nut connection can be described as a haptic fit. Under higher loads during driving, thermal expansion and compensatory movements of the heat shielding plate are intentionally permitted at the respective fastening point.

A further preferred embodiment of the motor vehicle is characterized in that the screw-nut connection is designed to be force-decoupled at at least one of the fastening points in a temperature-critical proximity to the exhaust system, such that the heat shielding plate at this fastening point, relative to the screw-nut connection, can expand mechanically force-free in a radial direction, with play in the radial direction being at least ten times as large as play in the axial direction. The term in a radial direction also refers to the longitudinal axis of the force-decoupled screw-nut connection. Radial means perpendicular to this longitudinal axis. The significantly greater radial play ensures that the heat shielding plate can deform almost unlimitedly in the radial direction. This prevents the heat shielding plate from undesired deformation due to clamping in the radial direction at the respective fastening point when high temperatures occur there.

A further preferred embodiment of the motor vehicle is characterized in that the force-decoupled screw-nut connection with a supporting structure part and a decoupling body is designed as a hard screw joint, wherein the decoupling body with the supporting structure part is arranged between a screw head of a screw and a nut of the force-decoupled screw-nut connection. The hard screw joint is standardized. According to a special standard with the abbreviation ISO 5393, a hard screw joint is defined as one in which a specified tightening torque is achieved within a tightening angle of up to 30 degrees. The screw, the nut, and the decoupling body of the screw-nut connection in question are advantageously made of a steel material. The hard screw joint with the decoupling body reliably prevents unwanted loosening of the screw-nut connection, even under high dynamic loads. Nevertheless, the special design of the screw-nut connection enables the previously described, deliberately permitted relative movement of the heat shielding plate under extremely high temperature loads.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling body is arranged in a decoupling space which is arranged in the axial direction between the supporting structure part and the nut of the force-decoupled screw-nut connection. The term in the axial direction refers to the longitudinal axis of the force-decoupled screw-nut connection. Axial means in the direction of or parallel to this longitudinal axis. The decoupling body in combination with the screw-nut connection ensures that the decoupling space maintains its size in the axial direction. In a first embodiment, the decoupling space is delimited in the axial direction by the supporting structure part and a positioning collar of the nut, which in the radial direction is arranged overlapping the heat shielding plate. In a second embodiment, the decoupling space is delimited in the axial direction by a retaining collar, which is provided on the decoupling body and is arranged radially overlapping the shielding plate.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling space is designed as an annular space that surrounds a screw shaft of the screw of the force-decoupled screw-nut connection with the decoupling body. The decoupling space, designed as an annular space, is bounded radially inward by the decoupling body and radially outward by the heat shielding plate. The decoupling space is advantageously designed to be large enough to allow for the expected expansion of the heat shielding plate without the heat shielding plate coming into contact with the decoupling body.

A further preferred embodiment of the motor vehicle is characterized in that the screw shaft of the screw extends from the screw head through a first through-hole in the structural part and through a second through-hole in the decoupling body. This ensures that the decoupling body is held captively in the decoupling space in a simple manner during assembly.

A further preferred embodiment of the motor vehicle is characterized in that the heat shielding plate comprises a third through-hole that surrounds the decoupling body in the decoupling space without any play. This lack of play ensures, in a simple manner, that the heat shielding plate can expand unhindered in the decoupling space under extreme thermal loads.

A further preferred embodiment of the motor vehicle is characterized in that the third through-hole is designed significantly larger than the decoupling body. The third through-hole advantageously has a diameter that is significantly larger than an outer diameter of the decoupling body, which is designed, for example, as a circular disk. The through-hole can also be designed as an elongated hole.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling body has a retaining collar with a peripheral edge that overlaps the third through-hole in the heat shielding plate. In this context, "overlap" means that an intentional overlap is provided between the retaining collar and the heat shielding plate. This overlap is, for example, somewhat larger than one millimeter. The retaining collar provides, among other advantages, that a conventional nut can be used to form the screw-nut connection. Without the retaining collar, it may be necessary to use a special nut with an enlarged positioning collar that performs the function of the retaining collar.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling body with the retaining collar has a T-shaped annular cross-section. The retaining collar is preferably arranged centrally in the axial direction on the preferably circular disc-shaped decoupling body. This prevents assembly errors. The retaining collar is preferably connected to the decoupling body in one piece.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling body has the shape of a circular disk, which is clamped with the supporting structure part between the screw head of the screw and the nut of the force-decoupled screw-nut connection. This allows the hard screw connection to be realized using means that are easily realized in terms of manufacturing technology. However, the design of the decoupling body without a retaining collar requires a special nut with an enlarged positioning collar that overlaps the third through hole in the heat shielding plate.

A further preferred embodiment of the motor vehicle is characterized in that the decoupling body has a greater thickness than the heat-shielding plate in the decoupling space. In combination with the hard screw connection, this ensures that the heat-shielding plate can expand thermally. The difference in thickness between the decoupling body and the heat-shielding plate is preferably in the millimeter range. The difference in thickness is preferably more than one-tenth of a millimeter and less than ten-tenths of a millimeter. In a particularly preferred embodiment, the decoupling body has a thickness that is approximately two-tenths of a millimeter greater than the corresponding dimension of the heat-shielding plate in the decoupling space.

In a method for mounting a heat shielding plate on a previously described motor vehicle, the above-mentioned object is achieved alternatively or additionally in that the force-decoupled screw-nut connection is tightened with a predetermined tightening torque until the decoupling body between The supporting structure and the nut are in a tight fit, while maintaining radial and axial clearance on the heat shielding plate in the decoupling space. This makes it easy to ensure the desired expansion of the heat shielding plate under extreme thermal loads during assembly.

The invention further relates to a heat shield, a decoupling body, a screw, a nut, and/or a supporting structure part for a motor vehicle as described above. These parts are sold separately.

• 1 eine perspektivische Darstellung eines Kraftfahrzeugs mit einer Abgasanlage und einem Wärmeabschirmblech, das an einer Tragstruktur montiert ist, von innen;
• 2 einen Längsschnitt durch eine Schrauben-Mutter-Verbindung an einer Befestigungsstelle in einer temperaturkritischen Nähe zu der Abgasanlage des Kraftfahrzeugs aus 1 gemäß einem ersten Ausführungsbeispiel; und
• 3 eine ähnliche Darstellung wie in 2 gemäß einem zweiten Ausführungsbeispiel.

Further advantages, features, and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawings. They show:

• 1 a perspective view of a motor vehicle with an exhaust system and a heat shield mounted on a supporting structure, from the inside;
• 2 a longitudinal section through a screw-nut connection at a fastening point in a temperature-critical proximity to the exhaust system of the motor vehicle 1 according to a first embodiment; and
• 3 a similar representation as in 2 according to a second embodiment.

In 1 A motor vehicle 1 with an exhaust system 2 is shown in an interior perspective. The exhaust system 2 comprises two exhaust pipes combined with tailpipe trims 3 and 4 fixed to the rear section.

Between the two tailpipe trims 3 and 4 of the exhaust system 2, a heat shielding plate 5 is fastened to a supporting structure part 6 of a supporting structure 7 of the motor vehicle 1. The heat shielding plate 5 and a rear panel 34 are fastened to the supporting structure 7. The heat shielding plate 5 is fastened to the supporting structure part 6 of the supporting structure 7 at various fastening points 8 to 12 using screw-nut connections 13 to 16 at the top and bottom.

In 2 The screw-nut connection 15 is shown at the fastening point 12 in a longitudinal section. 1 It can be seen that the fastening point 12 with the screw-nut connection 15 is arranged in a temperature-critical proximity to the tailpipe trim 4 of the exhaust system 2 of the motor vehicle 1. This leads to the heat shielding plate 5 deforming significantly depending on the temperature when the nearby exhaust pipe of the exhaust system 2 becomes very hot during operation of the motor vehicle 1.

In 2 It can be seen that the screw-nut connection 15 comprises a screw 23 with a longitudinal axis 18 and a nut 24. The screw 23 comprises a screw head 21 from which a screw shaft 22 extends. The screw shaft 22 is provided with an external thread onto which the nut 24 with an internal thread is screwed.

The nut 24 has a positioning collar 25 that extends radially outward from the nut 24. The positioning collar 25 has a larger outer diameter than the screw head 21 of the screw 23.

The screw shaft 22 of the screw 23 extends through a first through-hole 31 in the supporting structure part 6. Furthermore, the screw shaft 22 of the screw 23 extends through a second through-hole 32 of a decoupling body 20.

The decoupling body 20 has the shape of a circular disk with a rectangular cross-section. The decoupling body 20 is clamped axially between the supporting structure part 6 and the positioning collar 25 of the nut 24.

The supporting structure part 6, in turn, is clamped in the axial direction between the screw head 21 and the decoupling body 20. The decoupling body 20 and the supporting structure part 6 are clamped together between the screw head 21 of the screw 23 and the nut 24.

The heat shielding plate 5 comprises a third through-hole 33, which radially surrounds the decoupling body 20. The heat shielding plate 5 has, as shown in 2 is shown enlarged, has a smaller thickness than the decoupling body 20. Thickness refers to a dimension in the axial direction, i.e., in the direction of the longitudinal axis 18 of the screw-nut connection 15.

The screw 23, the nut 24, and the decoupling body 20 are made of a steel material, for example. When tightening the screw-nut connection 15, a hard screw joint is created. This hard screw joint prevents unwanted loosening of the screw-nut connection 15 under high dynamic loads.

The relatively large positioning collar 25 of the nut 24 of the screw-nut connection 15 defines a decoupling space 26 in the axial direction, which is delimited in the radial direction by the decoupling body 20. In a second axial direction, the decoupling space 26 is delimited by the structural part 6.

The decoupling chamber 26 is delimited radially inward by the decoupling body 20. The decoupling chamber 26 is delimited radially outward by the third through-hole 33 of the heat shielding plate 5. In the axial direction, the decoupling body 20 is two-tenths of a millimeter thicker than the heat shielding plate 5 in the decoupling chamber 26.

In 3 is a second embodiment in a similar representation as in 2 To identify identical or similar parts, 3 the same reference numerals as in 2 used to describe the 3 identical or similar parts, please refer to the preceding description of the 2 The following mainly focuses on the differences between the two examples.

In the 3 In the illustrated embodiment, the decoupling body 20 is combined with a retaining collar 35. The retaining collar 35 protrudes radially outward from the circular disc-shaped decoupling body 20. In the axial direction, the retaining collar 35 is arranged centrally on the decoupling body 20.

The decoupling body 20 is in 3 , in a similar way as in 2 , together with the supporting structure part 6 of the supporting structure 7, is clamped tightly between the screw head 21 of the screw 23 and the nut 24. The retaining collar 35 is spaced apart in the axial direction from both the supporting structure part 6 of the supporting structure 7 and the nut 24, in particular from a collar 37 of the nut 24. However, the collar 37 is significantly smaller in the radial direction than the positioning collar 25 of the nut 24 in 2 .

In the 3 In the embodiment shown, the nut 24 has a collar 37 which is significantly smaller in the radial direction than the positioning collar 25 in 2 . Thus, a conventional nut 24 can be used advantageously in the screw-nut connection 15 at the fastening point 12. The function of the positioning collar is taken over in the embodiment of the 3 the retaining collar 35, which extends radially outwards from the decoupling body 20 and overlaps the heat shielding plate 5 with a peripheral edge 36.

In 3 It can be seen that the retaining collar 35 with its peripheral edge 36 and the heat shielding plate 5 radially overlap in the area of the third through-hole 33. The retaining collar 35 is arranged in a decoupling space 38, which corresponds to the decoupling space 26 in 2 corresponds.

Double arrows indicate 3 a diameter 41 of the first through-hole 31, a diameter 42 of the second and third through-holes 32 and 33 are designated. An outer diameter 44 of the decoupling body 20 is designated by another double arrow. An outer diameter 45 of the retaining collar 35 is designated by another double arrow. A difference between the diameter 41 of 31 and the outer diameter 44 of 20 is designated by a double arrow 46.

In an overlap area 47, the heat shielding plate 5 and the retaining collar 35, which extends from the decoupling body 20, overlap. In the overlap area 47, the heat shielding plate 5 has a thickness 48 subject to tolerance and provided with axial play. The retaining collar 35 has a thickness 49 in the region of its peripheral edge 36.

For example, diameter 41 is eighteen millimeters. Diameter 42 is 6.2 millimeters. Outer diameter 44 is twelve millimeters, for example. Outer diameter 45 is twenty-four millimeters, for example. The difference 46 is three millimeters, for example.

The heat shielding plate 5 has a thickness of 1.4 millimeters in the overlap area 47, for example. The distance or thickness 48 is, for example, 1.6 millimeters. The thickness 49 is, for example, one millimeter.

Reference symbol

1

motor vehicle

2

exhaust system

3

tailpipe trim

4

tailpipe trim

5

Heat shield plate

6

supporting structure part

7

supporting structure

8

Attachment point

9

Attachment point

10

Attachment point

10

Attachment point

11

Attachment point

12

Attachment point

13

screw-nut connection

14

screw-nut connection

15

screw-nut connection

16

screw-nut connection

18

Longitudinal axis

20

Decoupling body

21

screw head

22

screw shaft

23

screw

24

Mother

25

Positioning collar

26

Decoupling room

31

first through hole

32

second through hole

33

third through hole

34

Rear panel

35

Retaining collar

36

peripheral edge

37

Federal Government

38

Decoupling room

41

Diameter of 31

42

Diameter of 32, 33

44

Outer diameter of 20

45

Outer diameter of 35

46

Difference between 41 and 44

47

Overlap area

48

thickness

49

thickness

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP H09166123 A [0002]
• JP H0514950 [0002]
• DE 197 14 700 C2 [0002]

Claims (15)

Motor vehicle (1) with an exhaust system (2) which becomes hot during operation of the motor vehicle (1), and with a supporting structure (7) which is formed from a first material with a first thermal expansion behavior and to which a heat-shielding plate (5) made from a second material with a second thermal expansion behavior that differs greatly from the first thermal expansion behavior is attached, wherein the heat-shielding plate (5) is fastened to the supporting structure (7) at fastening points (8-12) by means of screw-nut connections (13-15), characterized in that the screw-nut connection (15) is designed to be force-decoupled at at least one of the fastening points (8-12) in a temperature-critical proximity to the exhaust system (2) in such a way that the heat-shielding plate (5) can expand mechanically force-free at this fastening point (12) with respect to the screw-nut connection (15). Motor vehicle (1) according to Claim 1 , characterized in that the screw-nut connection (15) is designed to be force-decoupled at at least one of the fastening points (8-12) in a temperature-critical proximity to the exhaust system (2) in such a way that the heat shielding plate (5) at this fastening point (12), relative to the screw-nut connection (15), can expand mechanically force-free in an axial direction. Motor vehicle (1) according to one of the preceding claims, characterized in that the screw-nut connection (15) is designed to be force-decoupled at at least one of the fastening points (8-12) in a temperature-critical proximity to the exhaust system (2) in such a way that the heat shielding plate (5) at this fastening point (12), relative to the screw-nut connection (15), can expand mechanically force-free in a radial direction, wherein a play in the radial direction is at least ten times as large as a play in the axial direction. Motor vehicle (1) according to one of the preceding claims, characterized in that the force-decoupled screw-nut connection (15) with a supporting structure part (6) and a decoupling body (20) is designed as a hard screw case, wherein the decoupling body (20) with the supporting structure part (6) is arranged between a screw head (21) of a screw (23) and a nut (24) of the force-decoupled screw-nut connection (15). Motor vehicle (1) according to Claim 4 , characterized in that the decoupling body (20) is arranged in a decoupling space (26; 38) which is arranged in an axial direction between the supporting structure part (6) and the nut (24) of the force-decoupled screw-nut connection (15). Motor vehicle (1) according to Claim 5 , characterized in that the decoupling space (26; 38) is designed as an annular space which surrounds a screw shaft (22) of the screw (23) of the force-decoupled screw-nut connection (15) with the decoupling body (20). Motor vehicle (1) according to Claim 6 , characterized in that the screw shaft (22) of the screw (23), starting from the screw head (21), extends through a first through-hole (31) in the structural part (6) and through a second through-hole (32) in the decoupling body (20). Motor vehicle (1) according to Claim 7 , characterized in that the heat shielding plate (5) comprises a third through-hole (33) which surrounds the decoupling body (20) in the decoupling space (26; 38) without play. Motor vehicle (1) according to Claim 8 , characterized in that the third through hole (33) is designed to be significantly larger than the decoupling body (20). Motor vehicle (1) according to Claim 8 or 9 , characterized in that the decoupling body (20) has a retaining collar (35) with a peripheral edge (36) which engages over the third through-hole (33) in the heat shielding plate (5). Motor vehicle (1) according to Claim 10 , characterized in that the decoupling body (20) with the retaining collar (35) has a T-shaped ring cross-section. Motor vehicle (1) according to one of the Claims 2 until 11 , characterized in that the decoupling body (20) has the shape of a circular ring disc which is clamped with the supporting structure part (6) between the screw head (21) of the screw (23) and the nut (24) of the force-decoupled screw-nut connection (15). Motor vehicle (1) according to one of the Claims 7 until 12 , characterized in that the decoupling body (20) has a greater thickness than the heat shielding plate (5) in the decoupling space (26; 38). Method for mounting a heat shielding plate (5) on a motor vehicle (1) according to one of the preceding claims, characterized characterized in that the force-decoupled screw-nut connection (15) is tightened with a predetermined tightening torque until the decoupling body (20) lies on a block between the supporting structure part (6) and the nut (24), wherein a radial and an axial play is maintained on the heat shielding plate (5) in the decoupling space (26). Heat shielding plate (5), decoupling body (20), screw (23), nut (24) and/or supporting structure part (6) for a motor vehicle (1) according to one of the Claims 1 until 13 .