WO2015106990A1

WO2015106990A1 - Composite steering knuckle

Info

Publication number: WO2015106990A1
Application number: PCT/EP2015/050112
Authority: WO
Inventors: Richard Schaake
Original assignee: Aktiebolaget Skf
Priority date: 2014-01-16
Filing date: 2015-01-06
Publication date: 2015-07-23
Also published as: GB201400708D0

Abstract

The invention resides in a composite part comprising a bearing connection interface (110) for connecting a bearing (200) to the composite part and comprising a further connection interface (120) for connecting the composite part to a further component. The composite part further comprises a curved beam (130), which interconnects the bearing connection interface and the further connection interface. The curved beam is partly made from a first composite material comprising unidirectional fibers (140) in a matrix material. The unidirectional fibers extend between the bearing connection interface and the further connection interface in a radial direction, with an axial offset, and have a positive curvature. According to the invention, the first composite material comprising the unidirectional fibers is arranged at one side of a neutral axis (135) of the curved beam, which side experiences tensile stresses when a compressive load acts on the curved beam in a longitudinal direction.

Description

COMPOSITE STEERING KNUCKLE

FIELD OF THE INVENTION

The present invention relates to a composite part, comprising a fibre-reinforced material, which serves as an interface between a bearing and a further component.

BACKGROUND TO THE INVENTION

In the interests of fuel economy, there is an increasing drive within the automotive industry towards weight reduction of the component parts of vehicles. A vehicle wheel bearing is one example of an automotive component where weight reduction is desirable, also in view of the fact that the wheel bearings belong to the unsprung weight of a vehicle. Raceways of the bearings need to be made from a material of sufficient hardness in order to withstand the stresses of rolling contact. Titanium and certain ceramics are materials that possess the necessary mechanical properties and are also low in weight. They are also expensive and, consequently, bearing steel is more commonly used. Bearing steel has excellent hardenability but cannot be viewed as a lightweight material. Thus, one solution for reducing the weight of a wheel bearing comprising bearing steel is to form the bearing rings from bearing steel and to form further structural elements of the wheel bearing from a fibre-reinforced polymer.

An example of such a wheel bearing is disclosed in JP201 1 178314. The wheel bearing has a flanged inner ring, for connecting a vehicle wheel and brake disc to the bearing, and has a flanged outer ring for connecting the bearing to e.g. a steering knuckle. Each bearing flange is made of a laminated body of a carbon- fibre prepreg, formed by e.g. braiding the fibres and binding them in resin around a cylindrical surface of the bearing inner ring or outer ring. A steering knuckle is another example of an interface component for a bearing that may be reduced in weight by manufacturing the component from a fibre-reinforced polymer. An example of such a steering knuckle is disclosed in DE102007053120 A1 . The steering knuckle is formed from a laminar textile comprising fibres bound in a matrix. These examples of composite parts that form an interface between a bearing and a further component achieve a weight reduction. In use, however, a bearing can experience high forces, which are transmitted through the composite part. This part must therefore possess sufficient strength and stiffness to withstand the application loads.

There is still room for improvement.

SUMMARY OF THE INVENTION

The present invention resides in a composite part as specified in claim 1 , whereby the dependent claims describe advantageous embodiments and further developments of the invention.

Specifically the invention resides in a composite part comprising a bearing connection interface for connecting a bearing to the composite part and comprising a further connection interface for connecting the composite part to a further component. The composite part further comprises a curved beam, which interconnects the bearing connection interface and the further connection interface. The curved beam is partly made from a first composite material comprising unidirectional fibers in a matrix material, such as a polymer matrix. The unidirectional fibers extend between the bearing connection interface and the further connection interface in a radial direction, with an axial offset, and have a positive curvature. According to the invention, the first composite material comprising the unidirectional fibers is arranged at one side of a neutral axis of the curved beam, which side experiences tensile stresses when a compressive load acts on the curved beam in a longitudinal direction.

The forces acting on the composite part are introduced via the connection interfaces. In bearing applications, e.g. wheel bearing applications, the forces concerned can be substantial. A force acting on one connection interface results in a reaction force on the other connection interface. The resulting load path runs between the connection interfaces, and therefore runs through the curved beam in a composite part according to the invention. The beam is shaped such that a compressive load acting between the bearing connection interface and the further connection interface results in bending of the beam, rather than purely compressive deformation. Unidirectional fibers possess excellent tensile strength, but poor compressive strength. By arranging the first composite material at the tensile side of the curved beam, with the UD fibers oriented as described above, the composite part thus makes optimal use of the strength of the UD fibers, even when the curved beam is subjected to compressive loading in longitudinal direction.

Suitably, the curved beam is further made from a second material, which possesses good compressive strength, whereby the second material is arranged at the side of the neutral axis which is subject to compressive stresses when the curved beam experiences a compressive load. The second material may be a lightweight metal, a polymer, or a fibre-reinforced polymer such as a short-fiber or long-fiber moulding compound.

The curved beam may comprise a larger proportion of the second material than of the first composite material. Suitably, the first composite material comprising the unidirectional fibers is arranged at the tensile side of the curved beam, as far as possible from the neutral axis.

The unidirectional fibers of the first material, and the fibers of the second material (when applicable) may be made from glass, carbon, aramid, PBO (polybenzoxazole) or HDPE (high-density polyethelene). Suitable matrix materials include expoxy resin, phenolic resin, bismaleimide resin and polyimide resin.

In one example, a composite part according to the invention is manufactured in a two-stage moulding process. First, a pre-form of the composite part is moulded from the second material. The pre-form comprises at least part of the bearing connection interface, part of the curved beam and at least part of the further connection interface. The further connection interface may comprise a hole that is machined into the pre-form or may be a hole that is moulded into the pre-form. In some examples, a threaded insert or a bracket is glued into the hole, for enabling the composite part to be connected to the further component. Suitably, the moulded pre-form is then used as a cast for the unidirectional fibers, which are draped over the pre-form and then ovemoulded with matrix material in a second moulding stage. When the pre-form comprises a hole for the further connection interface, the unidirectional fibers are preferably draped around the hole with a quasi-isotropic layup.

In an alternative example, the composite part of the invention is manufactured according to a method in which a first step of the method comprises pre-shaping the unidirectional fibers of the curved beam, to form a UD fiber structure. In a second step, further portions of the curved beam, the bearing connection interface and the further connection interface are formed by overmoulding the UD fiber structure with the second material.

Suitably, the UD fibers have a curvature that is adapted to the direction of the expected application loads. Assuming that the composite part experiences loads which act at angle β relative to the radial direction, the UD fibers preferably have an angle of curvature relative to the radial direction which changes monotonically from a first angle αι to a second angle a₂ as a function of the radial height (y) and the axial offset (x).

Preferably, the first angle αι is greater than the largest expected angle max (β) of the compressive load and the second angle a₂ is greater than the smallest expected angle min (β) of the compressive load. More preferably, αι≥ φ + max (β) and α₂≥ φ + min (β), where φ is an angle which describes fiber misalignment. Typically, the angle of fiber misalignment is around 2 degrees.

In one embodiment, the composite part is a steering knuckle. The bearing connection interface may be formed as an annular part with a bore for receiving an outer ring of a wheel bearing unit. Alternatively, the bearing connection interface may be overmoulded to the bearing outer ring or to a metal sleeve for receiving the bearing outer ring. The steering knuckle comprises a number of further connection interfaces. An upper and a lower connection interface are provided for connecting the steering knuckle to the vehicle suspension via an upper and a lower control arm. Further connection interfaces are provided for a steering arm and for mounting a brake calliper device to the knuckle. Preferably, each further connection interface is connected to the bearing connection interface by a curved beam with curving unidirectional fibers at the tensile side of the beam. More preferably, two curved beams are used, which may themselves be interconnected with one or more further beams to provide the knuckle with additional strength and stiffness. In a second embodiment of the invention, the composite part is flanged bearing ring. A wheel bearing unit is an example of a bearing with at least one flanged bearing ring. For example, the inner ring of the wheel bearing unit may have a wheel mounting flange for mounting a wheel rim and a brake disc to the bearing. The outer ring may also comprise a flange for attaching the bearing to e.g. a steering knuckle.

The flange is suitably formed by a number of flange parts, which extend from the bearing connection interface in a radial direction and are arranged at evenly spaced circumferential intervals. Each flange part has a bolt hole and between the bolt hole and the bearing connection interface, the flange part is curved and acts as the curved beam of the invention, whereby unidirectional fibers are arranged at the tensile side of the curved beam.

A composite part according to the invention may thus be used in several applications where a bearing is connected to a further part and there is a need for a strong and lightweight part that can transmit compressive loads. Other advantages of the present invention will become apparent from the following detailed description and accompanying figures. DRAWINGS

The invention will now be described further, with reference to the following Figures, in which: is a perspective view of an example of a composite part according to the invention, embodied as a steering knuckle, comprising a bearing connection interface and a number of further connection interfaces which are joined to the bearing connection interface via curved beams;

is a side view of a section of the composite part, showing a portion of the bearing connection interface joined to a further connection interface via a curved beam that comprises unidirectional fibers, is a schematic cross-sectional view showing the path of one unidirectional fiber that extends between the further connection interface and the bearing connection interface;

is a side view of a further example of a composite part according to the invention, embodied as a flanged bearing ring of a wheel bearing unit; and

is a cross-sectional view of the flanged bearing ring of Fig. 4a.

DETAILED DESCRIPTION

In an embodiment of the invention, as shown in Fig. 1 , the composite part is a steering knuckle 1 00 comprising an annular part 1 10 with a bore for receiving a wheel bearing unit. An outer ring 200 (refer Fig. 2) of the wheel bearing unit is mounted to the annular part 1 10, which is defined as a bearing connection interface. The knuckle 100 comprises a number of further connection interfaces. In use, the knuckle is mounted to a vehicle suspension via an upper control arm, a lower control arm and a steering arm. The knuckle 1 00 comprises a corresponding upper connection interface 120A and a lower connection interface 1 20B. The steering arm is connected to the knuckle 100 at an intermediate connection interface 120C. At an opposite side from the intermediate connection interface 120C, the knuckle further comprises first and second connection interfaces 120D, 120E for attaching a brake caliper device to the knuckle. In the depicted embodiment, the further connection interfaces are joined to the bearing connection interface via two curved beams 130. The curved beams are partly made from a fiber-reinforced polymer material comprising unidirectional fibers. To provide added strength and stiffness, adjacent further connection interfaces may be joined by stiffening beams 125.

In use, a variety of forces act on the knuckle. The largest forces are the wheel forces, which are transmitted to the knuckle 100 through the bearing unit. These forces are transmitted to the vehicle suspension mainly through the upper and lower connection interfaces 120A, 120B of the knuckle and are thus transmitted through the curved beams 130 that connect the annular part 1 10 to these connection interfaces. Predominantly, the wheel forces generate compressive loads in the knuckle. As mentioned, the curved beams are partly made from a fiber-reinforced polymer material comprising unidirectional fibers. Such materials have excellent strength in tension, but have significantly lower strength in compression. The curved beams 130 of the steering knuckle 100 must therefore also be capable of withstanding high compressive stresses.

According to the invention, this is achieved in that the curved beams 130 are designed so that a compressive load on the beam in longitudinal direction is transformed into a bending moment, which exerts a tensile force on the unidirectional fibers.

A side view of an example of a curved beam 130 in a composite part according to the invention is shown in Figure 2. The curved beam extends between the bearing connection interface 1 1 0 and the further connection interface 120 in a radial direction, with an axial direction component. In this example, the further connection interface is a bolt hole. When a compressive force F acts on the bolt hole 1 20, a bending moment is created in the curved beam 130, about a neutral axis 1 35 of zero bending. At a first side 131 of the neutral axis 135, the curved beam 130 is in tension; at a second side 132 of the neutral axis, the curved beam is in compression. In the depicted example, the beam curves outwardly and an outer side of the beam is the first side 131 or tensile side. It is also possible for the beam to curve inwardly, in which case the inward side of the beam is the tensile side. According to the invention, the tensile side 1 31 of the curved beam 130 is made from the composite material comprising the unidirectional fibers. In Figure 2, only one unidirectional fiber 140 is shown, so as not to obscure the drawing. The unidirectional fiber 140 also follows a curved path between the further connection interface 120 to the annular part 1 10 and experiences tensile forces when a compressive load is applied on the beam 130. In the depicted example, the fiber 140 extends into the annular part 1 10.

At the second side 132 of the neutral axis (compression side), the beam is made from a second material with a high compressive strength. The second material may also be a fiber-composite material, like a short-fiber or long-fiber moulding compound. Thus, the dual material curved beam 130 is optimized for transmitting the application loads on the bearing 200 to the vehicle suspension. The actual curvature of the curved beam 130 and of the unidirectional fibers 140 is optimized depending on the angular direction of the expected loads. This will be explained with reference to Fig. 3, which shows a single fiber 340 that extends between a bearing connection interface 310 and a further connection interface 320. The single fiber is again part of a curved beam in a knuckle according to the invention, whereby the further connection interface is an upper connection interface for connecting the knuckle to the upper control arm of a vehicle suspension.

During use of the knuckle, compressive loads with an axial component are expected. The loads have a range of angles β relative to a purely radial load acting in a radial direction perpendicular to a rotation axis of the bearing. The unidirectional fiber 340 extends between the connection interfaces 310, 320 with a radial height y and an axial offset x. At the upper connection interface 320, the fiber 340 has an angle αι relative to the radial direction. At the bearing connection interface 310, the fiber 340 has an angle a₂ relative to the radial direction. Suitably, the angle of the unidirectional fiber 340 relative to the radial direction changes monotonically from αι to a₂ as a function of x and y. Preferably, αι ≥ φ + max (β) and α₂≥ φ + min (β), whereby φ is an angle which describes fiber misalignment. Typically, fiber misalignment is approximately 2 degrees. In a further embodiment of the invention, the composite part for connecting a bearing to a further part is flanged ring for receiving a wheel bearing unit.

An example of such a flanged ring is shown in figures 4a and 4b. The flanged ring 400 comprises a sleeve 410 with a bore for receiving an outer ring of the wheel bearing unit. The sleeve 410 forms part of the bearing connection interface. The flanged ring comprises four flange parts 430A, 430B, 430C, 430D, each of which comprises a corresponding bolt hole 420A, 420B, 420C, 420D. In the depicted example, the bolt holes are formed by threaded inserts which are overmoulded with a preform made of short-fiber moulding compound. The preform is also overmoulded on the sleeve 410 and comprises a portion of the material that forms the final flange parts. The flange parts are curved, as best seen in Figure 4b, and act as curved beams which transform a compressive load on each beam into bending. Continuous fibers are arranged at the tensile side of each beam. Suitably, the continuous fibers are draped over the preform and then overmoulded with polymer matrix material, to produce the final flanged ring 400.

As best seen in Figure 4b, the flange parts 430A and 430B comprise first and second curved beam portions, whereby a centre of curvature of the first curved beam portion (431 ) lies at an opposite axial side from a centre of curvature of the second curved beam portion (432). In effect, the flange parts 430A, 430B comprise two curved beams with separate neutral axes. Correspondingly, the flange parts 430A, 430B comprise a first set of unidirectional fibers 440A, which are arranged at a first side of the flange part, where the curved beam portion (431 ) is curved such that the first side is the side which experiences tension under a compressive load. The flange parts further comprise a second set of unidirectional fibers 440B, which are arranged at a second side of the flange part, where the curved beam portion (432) is curved such that the second side is the side which experiences tension under a compressive load on the flange part. A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. Moreover the invention is not restricted to the described embodiments, but may be varied within the scope of the accompanying patent claims.

Claims

1 . Composite part (1 00, 400) comprising a bearing connection interface (1 10, 310, 410) for connecting a bearing (200) to the composite part and comprising a further connection interface (120, 120A, 120B, 120C, 120D,

120E, 320, 420A, 420B, 420C, 420D) for connecting the composite part to a further component, wherein:

^■ the further connection interface is joined to the bearing connection interface by a curved beam (130, 430A, 430B);

- the curved beam is partly made of a first composite material which comprises unidirectional fibers (140, 340, 440A, 440B) in a matrix material;

^■ the unidirectional fibers extend at least partly between the bearing connection interface and the further connection interface with a radial height (y) and an axial offset (x), and have a positive curvature; and

^■ the unidirectional fibers (140, 340, 440A, 440B) are arranged at a tensile side (131 ) of the curved beam, which lies at one side of a neutral axis (135) of the curved beam and which experiences tensile stresses when a compressive load acts on the curved beam (130, 430A, 430B) in a longitudinal direction.

2. Composite part according to claim 1 , wherein the curved beam (130) is further made from a second material arranged at a compression side (132) of the curved beam (130), which lies at an opposite side of the neutral axis (1 35) and which experiences compressive stresses when the compressive load acts on the curved beam in longitudinal direction.

3. Composite part according to claim 1 or 2, wherein the unidirectional fibers (140, 340, 440A, 440B) have an angle curvature relative to the radial direction which changes monotonically from a first angle (ai) to a second angle (a₂) as a function of the radial height (y) and the axial offset (x).

4. Composite part according to claim 3, wherein the first angle ai is greater than a maximum value, max (β), of an angular direction (β) of the compressive load relative to the radial direction and the second angle a₂ is greater than a minimum value, min (β), of the angular direction (β).

5. Composite part according to claim 4, wherein αι≥ φ + max (β) and α₂≥ φ + min (β), where φ is an angle which describes fiber misalignment.

6. Composite part according to any preceding claim, wherein the second material is moulded into a preform which comprises part of the curved beam (1 30, 430A, 430B), part of the bearing connection interface (1 10, 31 0, 410) and part of the further connection interface (120, 120A, 120B, 1 20C, 120D,

120E, 320, 420A, 420B, 420C, 420D) and wherein the unidirectional fibers (140, 340, 440A, 440B) are draped over the preform and then overmoulded with matrix material.

7. Composite part according to claim 6, wherein the further connection interface comprises a hole (120) that is moulded or machined into the preform of the composite part (1 00, 400).

8. Composite part according to claim 7, wherein the unidirectional fibers are draped around the hole with a quasi-isotropic layup.

9. Composite part according to any of claims 6 to 8, wherein the preform is overmoulded on a bearing ring (200).

10. Composite part according to any preceding claim, the composite part being a steering knuckle (100), wherein the further connection interface is formed by one or more of:

- an upper connection point (120A) or a lower connection point (120B) for connecting the knuckle to an upper or a lower control arm of a vehicle suspension;

- an intermediate connection point (120C) for connecting the knuckle to a steering arm;

- a connection point (120D, 1 20E) for mounting a brake calliper device to the knuckle. Composite part according to any of claims 1 to 9, the composite part being a flanged ring (400), wherein the curved beam is formed by a flange part (430A, 340B) of the flanged ring.

Composite part according to claim 1 1 , wherein the flanged ring is an inner ring or an outer ring of a wheel bearing unit.

Composite part according to any preceding claim, wherein the curved beam comprises a first curved portion (431 ) and a second curved portion (432) having a centre of curvature lying at opposite axial sides of the beam (430A, 430B) and wherein a first set of unidirectional direction al (340A) is provided at the tensile side of the first curved portion and a second set of unidirectional fibers (340B) is provided at the tensile side of the second curved portion.