WO2007054069A1

WO2007054069A1 - Leaf spring consisting of a special fibre-composite material

Info

Publication number: WO2007054069A1
Application number: PCT/DE2006/001940
Authority: WO
Inventors: Clemens Aulich; Rainer Förster; Heiko Kempe
Original assignee: Ifc Composite Gmbh
Priority date: 2005-11-11
Filing date: 2006-11-04
Publication date: 2007-05-18
Also published as: DE112006002663A5; EP1948958A1; DE102005054334A1

Abstract

The invention relates to a leaf spring consisting of a fibre-composite material and having a central longitudinal section and two adjoining axial end sections for a wheel suspension in a vehicle, the end sections of said leaf spring tapering with respect to the leaf spring width. The leaf spring is composed of resin-impregnated fibre layers and axially orientated uncut first fibres of the fibre-composite material extend the full length of the leaf spring to the two axial ends of said spring. Before the finished leaf spring is produced, the axial end sections have an essentially V-shaped geometry or an essentially V-shaped notch and thus form two respective limbs lying transversally to the longitudinal extension of the axis of the untreated leaf spring, said limbs abutting one another in the finished leaf spring. The fibre volume fraction in the cured leaf spring is more than 50 %. According to the invention, said leaf spring is produced from the following fibre-composite material: a) EPR 05322 synthetic resin provided by the company Hexion; b) EPH 778 curing agent provided by Hexion; c) EPC 120 accelerator provided by Hexion; and d) type SE 1500 2400 tex AdvantexT30 fibre glass provided by Owens Corning Fiberglas. In the uncured leaf spring, between 0.012 kg to 0.018 kg curing agent and between 0.003 kg and 0.007 kg accelerator is added to 0.1 kg synthetic resin to form the initially liquid workpiece component.

Description

Leaf spring, consisting of a special fiber composite material

The invention relates to a leaf spring made of a fiber composite material according to the preamble of patent claim 1.

Leaf springs are commonly used for suspensions on a vehicle to cushion it against uneven terrain conditions. Such vehicles may in particular be passenger cars, trucks and other commercial vehicles, but also rail vehicles and the like.

Leaf springs made of steel have been known for a long time. In these individual, narrow steel sheets are superimposed with decreasing lengths to achieve a variable spring constant with increasing load. By clamping and / or screw the plates of the leaf springs are connected to form a package. When mounting a leaf spring in a motor vehicle, for example, this takes place transversely to the direction of travel, wherein the central region thereof is fixed to the vehicle body, while the two axial ends of the leaf spring in the region of the suspension of the right and left vehicle wheel are arranged. Although a metallic leaf spring is comparatively inexpensive to manufacture and reliable in operation, but such is disadvantageously difficult, which contributes to a relatively high vehicle weight and thus ultimately causes increased fuel consumption.

Also known are leaf springs made of fiber composite materials, which are formed, for example, impregnated with synthetic resin glass or carbon fibers and have the same size and comparable spring properties considerably less weight than steel leaf springs. Such composite fiber leaf springs are produced, for example, from individual resin-impregnated fiber layers. These prepregs are manufactured and / or cut to the desired shape and placed one above the other in a mold that corresponds to the dimensions of the leaf spring, and then the green leaf spring in the mold under the influence of Hardened pressure and heat.

From DE 102 21 589 A1, a leaf spring made of a fiber composite material is known, which consists of a central arc section and ends of peripheral sections in one piece. The peripheral portions have at their respective axial end an eyelet with an opening for receiving a bolt for the purpose of securing the leaf spring to the vehicle chassis. The disadvantage here is the introduction of the attachment eye in the leaf spring, which can only be realized by a structurally complex mold or by a severing the fibers punching process.

In other leaf spring structures made of fiber composite materials, the end portions are chamfered. In this case, the respective end section is cut to size after curing of the leaf spring of the bevelled shape. This has the consequence that also the fibers of the material are cut. The interfaces often lead to cracks, which emanate from the interfaces and extend substantially parallel to the longitudinal extent of the fibers at permanent alternating loads of the leaf spring. These cracks in turn can lead to breakage of the leaf spring.

From EP 0 093 707 B1 or the US 4,557,500 B1 parallel thereto, a leaf spring made of a fiber composite material is known, which is narrower and thicker at its axial ends than in a central, rectangular section. The region of the axial ends of the leaf spring can be approximately trapezoidal in plan view. The area of rectangular cross sections of the leaf spring from one spring end to the other spring end may be constant according to another variant. At a Another type of this leaf spring, the composite fibers are uncut from one to the other axial end. The geometry of the leaf spring is produced during its manufacture by compression molding.

Moreover, from DE 102004 010 768 A1 of the applicant a leaf spring made of a fiber composite material having a central longitudinal portion and axial ends for a suspension on a vehicle is known in which the axial ends are formed with respect to the leaf spring width is tapered, and in the axially aligned fibers of the fiber composite material are uncut to the end edge of the leaf spring out. In addition, it is provided in this leaf spring that it is constructed of resin-impregnated fiber layers, which have in the manufacture of the leaf spring at its axial ends in a plan view of a V-shaped geometry or a V-shaped notch and thus two transverse to the longitudinal extent of the leaf spring forming trained thighs. These two legs are placed close together and hardened in the manufacturing process, so that the finished leaf spring is approximately trapezoidal in the region of its ends and has no material thickening in this area.

From this document it is also known that the leaf spring can be reinforced in its central region by geometrically simple, rectangular fiber layers in terms of their component thickness, while being used to form the V-shaped axial ends of the leaf spring appropriately trained and guided over the entire component length fiber layers.

A leaf spring according to DE 10 2004 010 768 A1 has several advantages, since it has substantially constant cross-sectional areas over almost its entire length and a constant thickness with reduced width at the axial end, without having to cut it at its axial ends. Finally, it is known from DE 41 06 658 A1 and DE 44 22 473 C2 that the fiber volume fraction in a fiber composite leaf spring with good technical properties is more than 50%, preferably 60% to 70%.

Against this background, the invention has the object to produce a leaf spring according to DE 10 2004 010 768 A1 from a fiber composite material having such a ratio of fibers and the still liquid workpiece component and such a mixing ratio of the components of the still liquid workpiece component that the Leaf spring technically simple and inexpensive to produce, and, for example, when used in a small commercial vehicle, such as a city delivery vehicle that can withstand during its operation occurring loads on the maximum life.

The solution to this problem results from the features of claim 1. A special selection of the mixing proportions of the still liquid workpiece component is the single subclaim removed.

Accordingly, the invention is based on a leaf spring made of a fiber composite material having a central longitudinal portion and two adjoining axial end portions for a suspension on a vehicle, wherein the end portions are tapered with respect to the leaf spring width, wherein the leaf spring is composed of resin-impregnated fiber layers, said axially aligned fibers of the fiber composite material extend unabridged to the axial ends of the leaf spring, and wherein the axial end portions before completion of the leaf spring have a substantially V-shaped geometry or a substantially V-shaped notch and thus axially two transverse to Form longitudinal extension of the leaf spring formed legs, said legs are close to each other in the finished leaf spring, and wherein the fiber volume fraction in the cured leaf spring is more than 50%. To achieve the object, it is provided that the fiber composite material of said leaf spring consists of: a) the EPR 05322 Hexion, b) the EPH 778 hardener Hexion c) the accelerator EPC 120 Hexion, and d) glass fibers of the type SE 1500 2400 tex AdvantexT30 from Owens Corning Fiberglass, wherein 0.012 kg to 0.018 kg of hardener and 0.003 kg to 0.007 kg of accelerator are mixed in the not yet hardened leaf spring to form the initially liquid workpiece component to a weight of 0.1 kg of synthetic resin.

Preference is given to the not yet cured leaf spring a weight of 0.1 kilograms of resin added 0.015 kg kilogram of hardener and 0.005 kg accelerator.

EPR 05322 resin has also become known as EPIKOTE ™ Resin 05322 or BAKELITE® EPR 05322. It is a water-insoluble, modified epoxy resin with bisphenol A-epichlorohydrin resins MG ≤ 700. The flash point of this synthetic resin is more than 200 ^° C.

The EPH 778 hardener has also become known as EPIKURE ™ Curing Agent 778 or BAKELITE® EPH 778. It is a water-insoluble epoxy hardener with bisphenol A-epichlorohydrin resins MW <700. The flash point of this hardener is more than 200 ⁰ C. The vapor pressure at 20 ° C is less than 0.1 hPa, the density at 20 ° C. is about 1, 2 g / cm ³ . The EPC 120 accelerator has also become known as EPIKURE ™ Catalyst 120 or BAKELITE® EPC 120. This is a water-insoluble epoxy hardener with bisphenol-A-epichloro- hydrinharze molecular weight ≤ 700. The flash point of this accelerator is more than 200 ⁰ C. The ignition temperature is more than 380 ⁰ C. The density at 20 ° C is about 1.2 g / cm ³ .

With the above features of claim 1, a person skilled in the art is told how to use the resin-hardener-accelerator mixture or how the mixing proportions of the liquid component in the not yet cured leaf spring. This is particularly useful because in a continuous Fertig u ngsprozess in a factory in which fiber composite leaf springs are constantly produced, the resin-hardener-accelerator mixture is continuously provided to allow, for example, prepregs, so resin-impregnated fiber layers for To be able to produce a concrete structure of the fiber composite leaf spring. It is known to those skilled in the art that the fiber content should be as high as possible in a cured fiber composite material. In practice, values of 50% to 70% fiber volume fraction are achieved. The remainder is formed by the hardened and formerly liquid material component. Incidentally, a lower fiber content leads at most to a lower quality product. Decisive according to the invention, the composition of the fiber composite leaf spring from the respective specified materials and in particular from the mixing proportions of the initially still liquid material component.

Accordingly, the total weight of the finished mixed still liquid workpiece component based on the mixing proportions in the case of the lower limit of claim 1, for example:

0,1 Kg + 0,012 Kg + 0,003 Kg = 0,115 Kg respectively 100 parts by weight of synthetic resin EPR 05322 + 12 parts by weight of hardener

EPH 778 + 3 parts by weight of accelerator EPC 120, in sum therefore 115 parts by weight, and in the case of the upper mixing limit 0.1 Kg + 0.018 Kg + 0.008 Kg = 0.126 Kg.

According to another way of presentation, these mixing ratios can also be listed as% data. Accordingly:

Lower limit Upper limit

Resin EPR 05322 87.0% 79.4%

+ Hardener EPH 778 10.4% 14.3%

+ Accelerator EPC 120 2.6% 6.3%

= still liquid workpiece component: 100.0% 100.0%

Investigations on leaf springs produced in this way showed that their production is relatively inexpensive and easy to carry out. In addition, such leaf springs hold all static and dynamic loads that typically occur during the life of a motor vehicle, especially a small commercial vehicle, such as in a city delivery vehicle with up to 7,500 kilograms gross vehicle weight.

For the components of the initially liquid workpiece component mentioned above with their current product descriptions, additional material properties are given below:

The first line of this table illustrates that the initially liquid constituents of the leaf spring according to the invention completely cure. A laminate produced according to the invention is characterized by a curing temperature of 85 ^° C. with a minimum curing time of 10 hours.

The glass fibers of type SE 1500 2400 tex AdvantexT30 from Owens Coming Fiberglas have the following material properties:

The glass fibers are provided with an epoxy resin size of EP = 0.55%. The TEX number is 2400 ± 8%, so that a 10 meter long roving unwound from a roll of these glass fibers weighs 2400 grams ± 8%. The maximum tensile strength is 908 MPa and the elongation modulus is 73 GPa ± 1.5 GPa. The filament number 4000 ± 200.

Claims

claims

A leaf spring of a fiber composite material having a central longitudinal portion and two adjoining axial end portions for a suspension on a vehicle, wherein the end portions are tapered with respect to the leaf spring width, wherein the leaf spring is constructed of resin-impregnated fiber fabric layers, wherein axially aligned fibers of the Fiber composite material unabridged extend to the axial ends of the leaf spring, and in which the axial end portions before completion of the leaf spring have a substantially V-shaped geometry or a substantially V-shaped incision and thus axially each two transverse to the longitudinal extent of the leaf spring formed leg form, wherein these legs are close to each other in the finished leaf spring, and wherein the fiber volume fraction in the cured leaf spring is more than 50%, characterized in that the fiber composite material of the leaf spring consists of: a ) the EPR 05322 resin from Hexion, b) the hardener EPH 778 from Hexion, c) the accelerator EPC 120 from Hexion, and d) glass fibers from type SE 1500 2400 Tex AdvantexT30 from Owens Corning Fiberglass, in which uncured leaf spring to form the initially liquid workpiece component is added to a weight of 0.1 kilograms of resin 0.012 kg to 0.018 kilograms of hardener and 0.003 kilograms to 0.007 kilograms of accelerator,

2. Leaf spring according to claim 1, characterized in that in the not yet cured leaf spring a weight of 0.1 kilogram of synthetic resin 0.015 kg kilograms of hardener and 0.005 kg accelerator is added.