DE102017118089B4 - Process for producing a leaf spring from fiber composite material and a leaf spring for motor vehicles - Google Patents

Abstract

Method for producing a leaf spring (1) from fiber composite material for a motor vehicle, wherein a fiber composite material is formed in a mold (14) and at least partially cured, characterized in that at least one metallic bearing shoe (4) arranged on the end of the leaf spring (1) or during the closing of the mold (14) is inserted into the mold (14) in such a way that the matrix resin nestles against an inner lateral surface (6) of a receiving opening (5) of the bearing shoe (4), the receiving opening (5) being the end (2) overlaps the leaf spring (1) in its longitudinal direction (22), the outer lateral surface (8) of the end (2) of the leaf spring (1) and the inner lateral surface (6) of the receiving opening (5) being materially connected by means of the matrix resin of the fiber composite material will.

Description

The present invention relates to a method for producing a leaf spring made of fiber composite material for a motor vehicle according to the features in the preamble of claim 1.

The present invention further relates to a motor vehicle leaf spring made of fiber composite material according to the features in the preamble of patent claim 9.

It is known from the prior art to use springs in the area of the chassis in motor vehicles, so that the respective wheel or the axle can spring in and out in relation to a motor vehicle body. On the one hand, helical compression springs are used.

However, it is also known that leaf springs are used. These leaf springs can be arranged, for example, as a transverse leaf spring or as a longitudinal leaf spring in the motor vehicle.

Such leaf springs are made of metallic materials. However, it is also known that the leaf springs are made of fiber composite material. For this purpose, fiber material is mixed with matrix resin and brought into shape or post-compacted and at least partially, preferably completely, cured in a mold. The leaf spring made of fiber composite material produced in this way is then reworked and, for example, reworked at its end with a bearing eye. To fasten such a leaf spring in a motor vehicle, receptacles are provided at the ends, in particular bearing eyes, in which, for example, a bonded rubber bearing is in turn arranged. However, clamp mounts or other mounts can also be provided at the ends of the leaf spring. Such recordings are usually referred to as bearing shoes.

Such an arrangement is, for example, from DE 10 2016 100 743 A1 famous.

For this purpose, the leaf spring made of fiber composite material is first produced and then, in a subsequent processing step, the bearing shoe is coupled to the end of the leaf spring. For this purpose, in particular, the leaf spring is pushed into a receiving opening of the bearing shoe and fastened in a non-positive manner or clamped.

Due to manufacturing tolerances and/or production contamination, the coupling of the end of the leaf spring and the bearing shoe is sometimes suboptimal. In particular, there may be an increased preload force, which sometimes affects the longevity of the connection made between the bearing shoe and the end of the leaf spring.

For example, from the U.S. 3,900,357 , the EP 0 106 249 A1 , the GB 2 236 160A or the DE 10 2013 217 769 A1 each disclosed a mechanical coupling or a coupling by means of frictional engagement.

In the DE 40 33 438 C1 a leaf spring is produced in which an inner eye is integrated by compressing the leaf spring.

Also is from the EP 0 106 249 A1 a manufacturing process for a leaf spring is known. After completion of the manufacturing process, a bracket is mechanically coupled to one end of a leaf spring by means of screw bolts and cohesively by means of gluing.

The object of the present invention is therefore to show a possibility of coupling an end of a leaf spring made of fiber composite material to a bearing shoe, which is easier to produce than in the prior art, while at the same time improving the quality of the connection.

The aforementioned object is achieved according to the invention with a method for producing a leaf spring made of fiber composite material with the features in claim 1.

A specific part of the task is solved with a motor vehicle leaf spring made of fiber composite material with the features in claim 9.

Advantageous design variants of the present invention are the subject matter of the dependent claims.

The method for producing a leaf spring made of fiber composite material for a motor vehicle provides that a fiber composite material is formed in a mold and is at least partially cured. It is characterized according to the invention in that at least one metal bearing shoe arranged at the end of the leaf spring is inserted into the mold itself before or during the closing of the mold or before or during the insertion of the fiber composite material. This means that during the molding of the leaf spring from the fiber composite material itself, the matrix resin nestles against an inner lateral surface of a receiving opening of the bearing shoe that is particularly U-shaped in cross section, with the U-shaped receiving opening overlapping the end of the leaf spring. The receiving opening can also have an omega-shaped or dovetail-shaped cross section. It will thus a material connection is made between the leaf spring made of fiber composite material and the receiving opening of the bearing shoe by means of the matrix resin.

The bearing shoe itself is designed to accommodate the leaf spring in cross-section with an upper leg and a lower leg and a valley area lying between them. The upper and lower legs can be of the same length, but they can also be of different lengths. The valley area is preferably rounded in cross section, but can also be angular. The receiving opening can be closed on its transverse sides, so that the end of the leaf spring is completely encompassed on the peripheral side. However, the receiving opening can also be open on its transverse sides, so that only an upper leg and a lower leg of the end rest on the upper side and the lower side of the leaf spring.

Various manufacturing processes known from the prior art for leaf springs made of fiber composite material can be combined with the process according to the invention.

For example, an RTM process (Resin Transfer Molding) can be carried out. In the RTM process, the dry fibers are provided in the form of several textile layers and are stacked on top of each other or pre-fixed by applying a binder. The dry semi-finished product, which already has a leaf spring contour, is then placed in an RTM tool. The bearing shoe is also inserted at the same time or beforehand according to the invention. Matrix resin is then injected into the cavity of the mold and the matrix resin penetrates through the fibers. The leaf spring dries out under temperature. When carrying out the method according to the invention, the bearing shoe is preferably already attached to the leaf spring semi-finished product made of dry fiber composite material and placed in the RTM tool together with the leaf spring semi-finished product.

A prepreg process can also be carried out. To build up the leaf spring, several layers of fibers saturated or impregnated with matrix resin are placed one on top of the other. The semi-finished product produced in this way is placed in a compression molding press and the leaf spring geometry is produced by compression molding. Here, too, the bearing shoe can be slipped onto the prepreg semi-finished product and inserted into the molding press together with the prepreg semi-finished product. The leaf spring with bearing shoe formed in this way hardens at least partially in the molding press. However, a complete curing process can also take place, for example, in a downstream oven device. The curing process can also take place in the molding press itself or in a downstream molding press.

A towpreg process can also be carried out. Here, a semi-finished leaf spring is produced in a winding process. A bearing shoe is placed on the leaf spring semi-finished product produced in this way by winding and transported into a compression molding press, where it is formed into a leaf spring. A curing process can then in turn take place, for example, in a downstream oven device. The curing process can also take place in the molding press itself or in a downstream molding press.

It is also possible to initially only insert the bearing shoe into the mold and then to subsequently introduce the appropriate fiber composite material.

According to the invention, complete contact can be made in the area of the contact surface between the inner lateral surface of the receiving opening and the outer lateral surface of the end of the leaf spring. Any prestressing or stress deformations of two components that are initially produced differently during the subsequent coupling process are avoided according to the invention.

Another advantage is that the matrix resin also fits snugly in a valley area of the receiving opening and thus complete contact between the inner lateral surface of the receiving opening and the outer lateral surface of the leaf spring is established up to the end face of the end of the leaf spring.

According to the invention, one bearing shoe is particularly preferably arranged at both ends of the leaf spring. The bearing shoe itself can in particular also have a bearing eye, for example to accommodate a bonded rubber bearing. The bearing shoe itself is also preferably designed as a one-piece component made of the same material. The bearing shoe is made of metallic material. For example, made of light metal or a steel alloy.

The effect according to the invention is now that the matrix resin rests against the inner lateral surface of the receiving opening in the resulting contact area during the molding process and thus a complete connection, in particular complete contact in the contact surfaces, is ensured. At the same time, the matrix resin forms a material bond with the inner lateral surface of the receiving opening.

The quality of the connection produced, in particular with regard to stresses occurring during operation, is significantly improved compared to the coupling methods known from the prior art. Any gaps that could arise between the inner lateral surface of the receiving opening and the outer lateral surface of the end of the leaf spring are avoided according to the invention. If there are minor production contaminations, these are enclosed by the matrix resin and therefore do not affect the quality of the connection produced. During the process, the leaf spring and bearing shoe have a large surface area that is always in contact with one another and is not critical to tolerances.

For this purpose, the mold can particularly preferably be a press tool. The proportion of matrix resin is measured in the end area of the leaf spring in such a way that at least in the end area there is an excess of matrix resin, so that when the mold is closed the inner surface of the receiving opening is covered or wetted with emerging matrix resin. Alternatively or additionally, the molding tool can recompact the fiber composite material during the molding process in such a way that matrix resin emerging in the area of the end of the leaf spring nestles against the inner lateral surface of the receiving opening. In particular, a valley area of the U-shaped cross section of the receiving opening is therefore also wetted with matrix resin.

In a preferred embodiment variant, the bearing shoe and in particular the receiving opening of the bearing shoe already has its desired geometry before the method according to the invention is carried out.

Alternatively, however, it is also possible for the receiving opening to have a loose fit at the beginning of the molding process, based on the thickness of the end of the leaf spring. This loose fit is compressed to a transition fit or a press fit by the forming process itself. The advantage is that, in particular, the receiving opening can be slipped onto a semi-finished product of the fiber material or the fiber composite material if it has a loose fit. As a result of the forming process itself, not only does the matrix resin and possibly the fiber material have to adapt to the inner lateral surface of the receiving opening, but the receiving opening is also adapted to the end of the leaf spring to be produced. In particular, the receiving opening is compressed or squeezed here.

To improve the substance-to-substance connection that is produced, a primer is also particularly preferably applied to the inner lateral surface of the receiving opening.

Furthermore, particularly advantageously, the bearing shoe can be coupled to the end of the leaf spring via form-fitting means, with the end of the leaf spring preferably being penetrated by the means itself. These are in particular bolts or screws. For this purpose, in order to carry out the method according to the invention, holes can be introduced that penetrate the bearing shoe and the end of the leaf spring and then screws or bolts or else rivets can be introduced into these holes. The screw also serves as a frictional connection. In particular, the contact surfaces between the matrix/resin and the legs of the receiving opening are pressed on the one hand by the screw pretensioning forces and on the other hand shrinkage stresses or even possible detachment gaps are closed again. A rivet or bolt can be pushed in accordingly.

During the thermal hardening process in particular, the leaf spring itself shrinks more when it cools down compared to a bearing shoe made of metallic material. The screws or bolts or rivets are inserted with a pressing force for calibration. Due to the fact that the fiber composite material shrinks more than a comparable metal material, a self-calibration process occurs. Screw bolts and/or rivets used are thus kept fixed in the metallic bearing shoe. Due to the greater/further shrinkage of the fiber composite material, a self-calibration process takes place for the fiber composite material, so that it is held accordingly in the receiving opening of the bearing shoe. It is also conceivable to apply another pressing force with an external tool in order to insert or press in the screws or bolts and/or rivets further.

Furthermore, the receiving opening has a width that is equal to or smaller than the width of the leaf spring itself. The receiving opening thus protrudes laterally beyond the leaf spring. A better sealing effect can thus be achieved during production in the mold.

The present invention further relates to a motor vehicle leaf spring made of fiber composite material with at least one bearing shoe made of metallic material arranged at the end, with a receiving opening of the bearing shoe having a U-shaped cross section overlapping the end of the leaf spring. According to the invention, the motor vehicle leaf spring is characterized in that an inner surface of the receiving opening of the bearing shoe with a Outer lateral surface of the leaf spring rests completely against the contact surfaces or the contact areas. For this purpose, the inner lateral surface of the receiving opening is cohesively coupled to areas of the outer lateral surface of the end of the leaf spring by means of the matrix resin of the fiber composite material of the leaf spring.

• 1 eine Blattfeder in perspektivischer Ansicht aus dem Stand der Technik,
• 2 das Ende einer Blattfeder in Seitenansicht, bekannt aus dem Stand der Technik,
• 3 das Ende in Seitenansicht, hergestellt mit der vorliegenden Erfindung,
• 4 eine Blattfeder in Seitenansicht, hergestellt mit der vorliegenden Erfindung,
• 5 einen Teilausschnitt eines Werkzeuges zur Durchführung des erfindungsgemäßen Verfahrens,
• 6 eine Schnittlinie durch ein Ende der Blattfeder gemäß Schnittlinie A-A aus 4,
• 7 eine alternative Ausgestaltungsvariante zu 6,
• 8 eine perspektivische Ansicht des Endes einer Blattfeder mit Lagerschuh, und
• 9 ein Ende einer erfindungsgemäßen Blattfeder.

Further advantages, features, properties and aspects of the present invention are the subject of the following description. Preferred design variants are shown in schematic figures. These serve to make the invention easier to understand. Show it:

• 1 a leaf spring in a perspective view from the prior art,
• 2 the end of a leaf spring in side view, known from the prior art,
• 3 the end in side view made with the present invention,
• 4 a leaf spring in side view made with the present invention,
• 5 a partial section of a tool for carrying out the method according to the invention,
• 6 a section line through one end of the leaf spring according to section line AA 4 ,
• 7 an alternative design variant 6 ,
• 8th a perspective view of the end of a leaf spring with bearing shoe, and
• 9 an end of a leaf spring according to the invention.

In the figures, the same reference numbers are used for the same or similar components, even if a repeated description is omitted for reasons of simplification.

1 shows a leaf spring 1 known from the prior art for arrangement on a motor vehicle, not shown in detail. The leaf spring 1 is designed as an elongate body and has a length L, a height H and a width B. Shown here, the leaf spring 1 is constant in its dimensions over the entire length L, width B and height H. However, the width B and height H can also vary over the length L. The leaf spring 1 is made of fiber composite material.

One end 2 of the leaf spring 1 is arranged on opposite sides. There is also a face 3 at the respective end 2.

2 now shows a coupling option at one end 2 of a leaf spring 1 in side view according to the prior art. Here, a bearing shoe 4 is placed on the end 2 of the leaf spring 1. The bearing shoe 4 can be pushed on from one side, ie in the direction of the width B, or pushed on in the longitudinal direction, ie over the end face 3 . The bearing shoe 4 itself has a receiving opening 5 with an inner lateral surface 6 . It can be seen on the lower image plane that a gap 7 remains between the inner lateral surface 6 in the lower image plane area and the outer lateral surface 8 also in the lower image plane area of the end 2 of the leaf spring 1 .

Now, if a bolt or a screw the bearing shoe 4 and the end 2 of the leaf spring 1 arranged by reaching, occurs here on a strain. In addition, 3 recesses 9 remain in corner areas on the front side. In the variant shown here, the bearing shoe 4 also has a bearing eye 10 for receiving a rubber-metal bearing 11. The leaf spring 1 can have individual layers, which is indicated schematically.

3 now shows a leaf spring 1, produced with the method according to the invention. Here, too, a bearing shoe 4 is placed on the end 2 of the leaf spring 1, but in the contact areas between the inner lateral surface 6 and the outer lateral surface 8 a complete system contact is made in each case. There are therefore no gaps or recesses. During the manufacturing process, the matrix material of the leaf spring 1 has thus completely applied to the inner lateral surface 6 in the resulting contact areas, in particular also in a valley area 21 of the receiving opening 5. The receiving opening 5 overlaps the end 2 of the leaf spring 1 in its longitudinal direction 22.

Furthermore, rounded edges 13 are preferably arranged in the inlet areas 12 of the receiving opening 5 . This is advantageous for assembly during the production process. At the same time, however, there is also an advantage during operation, since voltage peaks in this area are avoided.

4 shows a side view of a leaf spring 1 produced according to the invention. At each end 2 a bearing shoe 4 is arranged over the end 2 here. The bearing shoe 4 has a bearing eye 10 in each case, but this is not mandatory.

5 shows a schematic cross-sectional view through a molding tool 14 according to the invention. An upper tool 15 and a lower unit Tool 16 can be moved relative to one another and, when the mold 14 is closed, have a mold cavity 17 in between. In 5 however, the mold 14 is shown open. According to the invention, it is now provided that the bearing shoe 4 is already inserted into the mold 14 . This can be done in terms of time with a semi-finished product of a fiber composite material that is not shown in detail. However, the bearing shoe 4 can also be inserted into the mold 14 before the semi-finished product of the fiber composite material is inserted.

6 Fig. 12 shows a cross-sectional view according to section line AA 4 . It is shown here that the end 2 of the leaf spring 1 is overlapped by an upper leg 18 and a lower leg 19 of the receiving opening 5 of the bearing shoe 4 . The width B18 is smaller than the width of the end 2 of the leaf spring 1.

7 shows an alternative embodiment. It can be seen here that the receiving opening 5 completely surrounds the end 2 of the leaf spring 1 on the outside, consequently also on the left and right side in relation to the plane of the image.

8th shows a perspective view of an end 2 of the leaf spring 1 according to the invention. Openings 20 which pass through the bearing shoe 4 and the leaf spring 1 can be seen. A screw or bolt (not shown) or else a rivet can be introduced here in order to enable an additional form-fitting coupling. It can also be seen that the bearing shoe 4 protrudes laterally beyond the leaf spring.

9 shows an end 2 of a leaf spring 1 according to the invention. Here, in the vertical direction Z of the motor vehicle, the lower leg 19 in relation to the plane of the drawing is longer in the longitudinal direction 22 of the leaf spring 1 than the upper leg 18 in relation to the plane of the figure and located above it in the vertical direction Z of the motor vehicle. The valley area 21 is formed here essentially angular. This configuration is also in the 4 , 5 and 8th shown.

Alternatively, it is also possible for the upper leg 18, referred to the motor vehicle vertical direction Z, to be longer than the lower leg 19. The legs 18, 19 can also be of different lengths at one end 2 and the legs are at the opposite end 2 18, 19 are essentially the same length. By lengthening the leg on the bottom 19 or top 18, it would be possible to influence the deflection behavior of the leaf spring 1. Furthermore, in particular the durability of the connection produced can be positively influenced, especially in the case of alternating bending stress, due to a correspondingly arranged longer leg.

reference list

1

leaf spring

2

end to 1

3

Front side to 2

4

bearing shoe

5

intake opening

6

Inner lateral surface to 5

7

gap

8th

Outer jacket surface to 2

9

recess

10

bearing eye

11

bonded rubber bush

12

inlet area

13

rounded edge

14

molding tool

15

upper tool

16

lower tool

17

mold cavity

18

upper thigh

19

lower thigh

20

openings

21

valley area

22

Longitudinal to 1

L

length

H

height

B

broad

Z

motor vehicle vertical direction

Claims (11)

Method for producing a leaf spring (1) from fiber composite material for a motor vehicle, wherein a fiber composite material is formed in a mold (14) and at least partially cured, characterized in that at least one metallic bearing shoe (4) arranged on the end of the leaf spring (1) is provided or during the closing of the mold (14) is inserted into the mold (14) in such a way that the matrix resin nestles against an inner lateral surface (6) of a receiving opening (5) of the bearing shoe (4), the receiving opening (5) being the end (2) the leaf spring (1) in its longitudinal direction (22) overlaps, the outer lateral surface (8) of the end (2) of the leaf spring (1) and the inner lateral surface (6) of the receiving opening (5) being materially connected by means of the matrix resin of the fiber composite material. procedure after claim 1 , characterized in that the molding tool (14) is a press tool, the proportion of matrix resin being dimensioned in such a way that at least in the end area of the leaf spring (1) there is an excess, so that when the molding tool (14) is closed, the inner lateral surface (6) of the receiving opening (5) is covered with matrix resin and/or that the molding tool (14) post-compacts the fiber composite material in such a way that matrix resin escaping in the area of the end (2) of the leaf spring (1) nestles against the inner lateral surface (6) of the receiving opening (5). , especially in a valley area of the U-shaped cross section. procedure after claim 1 or 2 , characterized in that the bearing shoe (4) is a one-piece component made of the same material and/or that the bearing shoe (4) has a bearing eye (10) for receiving a rubber-metal bearing (11). Procedure according to one of Claims 1 until 3 , characterized in that the bearing shoe (4) is made of light metal or steel. Procedure according to one of Claims 1 until 4 , characterized in that the receiving opening (5) at the beginning of the molding process has a loose fit, based on the height (H) of the end (2) of the leaf spring (1) and is compressed by the forming process to a transition fit or press fit. Procedure according to one of Claims 1 until 5 , characterized in that a primer is applied to the inner lateral surface (6) of the receiving opening (5). Procedure according to one of Claims 1 until 6 , characterized in that the bearing shoe (4) is coupled to the end (2) of the leaf spring (1) via form-fitting means, the end (2) of the leaf spring (1) being penetrated by the means. Procedure according to one of Claims 1 until 7 , characterized in that the receiving opening (5) has a width (B18) which is less than or equal to the width (B) of the leaf spring (1). Motor vehicle leaf spring (1) made of fiber composite material with at least one bearing shoe (4) made of metallic material arranged at the end, with a receiving opening (5) overlapping the end (2) of the leaf spring (1) in its longitudinal direction (22), characterized in that a The inner lateral surface (6) of the receiving opening (5) of the bearing shoe (4) rests completely on the contact surface with an outer lateral surface (8) of the leaf spring (1), the inner lateral surface (6) being cohesively coupled to the outer lateral surface (8) by means of the matrix resin of the fiber composite material is. Motor vehicle leaf spring (1). claim 9 , characterized in that the receiving opening (5) is configured in a U-shaped cross-section and/or that the receiving opening (5) has an upper leg (18) and a lower leg (19) and a valley region (21) lying therebetween. Motor vehicle leaf spring (1). claim 10 , characterized in that the legs (18, 19) have different lengths, in particular the lower leg (19) in the vertical direction Z of the motor vehicle in the installation situation is longer than the upper leg (18), or the upper leg (18) is longer than the lower leg (19).

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