TECHNICAL FIELD

The present disclosure generally relates to the field of frequency-tuned vibration dampers for motor vehicles. A damper unit for use in a vibration-reducing assembly for a steering wheel is disclosed. A frequency-tuned vibration damper assembly including one or more such damper units is also disclosed, as well as methods of making a damper unit and a frequency-tuned vibration damper assembly.

BACKGROUND

The function of frequency-tuned vibration dampers, also termed tuned mass dampers, dynamic dampers or vibration absorbers, is based on a dampened spring-mass system which counteracts and reduces vibrations in a structure or surface to which the damper is connected by using one or more elastic damper elements for transferring vibrations from a vibrating structure to at least one mass which is caused to vibrate out of phase such as to dampen the vibrations. WO 01/92752 A1, WO 2013/167524 A1, and WO 2008/127157 A1 disclose examples of frequency-tuned vibration dampers.

In the automotive industry, some steering wheels are provided with frequency-tuned vibration dampers for reducing steering wheel vibrations caused by vibrations from the road and engine being transferred to the steering wheel. In such damper structures, the weight of an airbag module may be used as part of the weight of the mass in the spring-mass system. Also, steering wheels are generally provided with a horn activation mechanism by which a driver may activate a horn of the vehicle. Horn activation mechanisms of mechanical type typically comprise one or more metal spiral springs, referred to as horn springs, for returning the horn activation mechanism to its normal state after a horn activation. Electronic horn activation mechanisms without horn springs are also available.

EP 2 085 290 discloses an example of a prior-art vibration-reducing damper structure for a steering wheel, including an elastic damper element arranged on a slider which is slidably mounted on a bolt shaft. Vibrations in the steering wheel are transferred by the elastic damper element to the airbag assembly for dampening purposes. During horn activation, the slider may slide along the bolt shaft. A conventional spiral spring is placed on the bolt shaft and is compressed upon horn activation for bringing the slider back to its normal position when the horn activation is terminated. One drawback of this prior art is that is that the assembly of the overall structure is complicated and time consuming, increasing manufacturing time and cost.

U.S. Pat. No. 8,985,623 B2 discloses an alternative damper structure fora steering wheel. The overall operation is similar to the one in disclosed in EP 2 085 290 mentioned above, but the elastic element is encapsulated in a rigid multi-part protector structure. The protector is slidably arranged on a shaft and is biased by a horn spring towards the non-activated position of the horn activation mechanism. This prior-art solution has essentially the same drawbacks, and actually requires additional cost and time of manufacturing the protector.

Other drawbacks in the prior art include difficulties in frequency-tuning, frequency range limitations, in difficulties in maintaining a frequency tuning, and difficulties in obtaining desired spring characteristics upon horn activation.

SUMMARY OF INVENTION

In the light of the above, it is an object of the present inventive concept to address one or more of the above-mentioned disadvantages of the prior art and, to this end, provide (i) a damper unit for use in a vibration-reducing damper assembly for a steering wheel, (ii) a vibration damper assembly for dampening vibrations in a steering wheel, (iii) a method of manufacturing a damper unit, and (iv) a method of making a frequency-tuned vibration damper assembly.

According to a first aspect, there is provided a damper unit for use in a frequency-tuned vibration damper assembly for a steering wheel, said damper unit having an insertion end and an opposite rear end, and being configured to be inserted with its insertion end through a mounting opening provided in a horn plate of said assembly,

said damper unit comprising:a sleeve having a central bore extending along an axis, andan elastomeric damper element which molded on a radial outer side of the sleeve such that the sleeve and the damper element together form a unitary structure,

wherein:the elastomeric damper element presents an elastomeric insertion part configured to be inserted into the mounting opening of the horn plate, and an elastomeric support part configured to define a final mounting position of the damper unit;the elastomeric insertion part presents a plurality of elastomeric ribs which extend at least partially along said axis and are mutually spaced in a circumferential direction in relation to said axis, said ribs together forming a radially outer engagement surface configured to be brought into direct engagement with an inner surface of said mounting opening;the radially outer engagement surface has a first radial dimension, and the elastomeric support part has a second radial dimension, larger than said first radial dimension;at least some of the elastomeric ribs present a radially outward extending snap-lock protrusion configured to be inserted through the mounting opening to snap-lock the damper unit in its final mounting position; and

said elastomeric support part presents a plurality of elastomeric support studs, which are mutually spaced in the circumferential direction, extend at least partially in the direction of said axis, and each presents a distal end surface facing the insertion end of the damper unit, said elastomeric support studs being flexible in all directions transverse to said axis, wherein said distal end surfaces of the support studs are configured, during assembly of the damper unit in the mounting opening of the horn plate, to be brought into contact with a rear side of the horn plate in the final mounting position.

During the dampening operation, the elastomeric material of the damper element is compressed in the direction of the vibrations. An advantage obtained by the ribbed configuration is that the elastomeric material during the dampening operation may expand out in spaces between the ribs. Thereby, the spring constant of the damper element will present a more linear characteristic compared to “compact” prior-art non-ribbed damper elements having no spaces into which the compressed elastomeric may expand. Using damper units according to the inventive concept thus makes it possible to configure a dynamic spring-mass system which will stay better tuned to aimed at target frequency or frequencies, resulting in a more efficient and reliable dampening operation.

A further advantage obtained by the ribbed configuration is an increased flexibility in the frequency tuning during design and manufacturing. The dampening frequency of the damper assembly may be frequency tuned by varying the number of ribs, varying the circumferential, radial, and/or axial dimensions of the ribs and/or varying the spaces between the ribs. Thus, one may use thicker or thinner ribs in the circumferential direction; longer or shorter ribs in the axial direction; longer or shorter ribs in the radial direction, etc.

Also, the frequency interval within which the damper element is tunable may also be expanded and or moved by using a ribbed configuration compared to prior-art elastomeric damper elements. It may also be easier to design damper units having different damping frequencies in different direction by varying the rib design in different directions.

At least some, preferably all, of the elastomeric ribs present a radially outward extending snap-lock protrusion. The snap-lock protrusions are configured to be inserted into and passed through the mounting opening to snap-lock the damper unit in its final mounting position. During the insertion procedure, the snap-lock protrusions may be temporarily compressed and/or moved inwards in the radial direction as they pass through the mounting opening. When the damper unit has been inserted to its final mounting position, the elastomeric snap-lock protrusions will automatically move and/or expand radially outwards in order to engage a distal side of the horn plate or a sleeve fixed at the mounting opening.

The support part of the elastomeric damper element has a larger radial dimension than the engagement surface of the insertion part. The dimensions of the support part may be selected sufficiently large to prevent the support part from passing through the mounting opening during assembly. Thereby, the support part of the elastomeric damper element may act as an insertion stop during the assembly, defining the final mounting position of the damper element relative to the horn plate. In the final assembly, the elastomeric support part will typically be in direct contact with a rear side of the horn plate or the rear side of a sleeve arranged in the mounting opening. In the final assembly, the support part and the snap-lock protrusions will thus be arranged on opposite sides of the horn plate and together keep the damper unit in a fixed position in relation to the horn plate.

The support part of the elastomeric damper element presents a plurality of elastomeric support studs the ends of which are facing the insertion or distal end of the damper unit. The support studs are mutually spaced in the circumferential direction and preferably distributed in 360 degrees around the axis. They extend at least partially in the direction of said axis. In preferred embodiments, the extend in parallel with the axis. The elastomeric support studs are flexible in all directions transverse to said axis, i.e. including radial directions, circumferential directions and combinations thereof. During assembly, the distal end surfaces of the support studs facing the insertion end of the damper unit will be brought into contact with the rear side of the horn plate in the final mounting position. This contact between the support studs and the horn plate will remain during all operations of the assembly, both during vibration damping and during horn activation. Due to frictional forces between the support studs and the rear side of the horn plate, the support studs will move in the transverse direction in response to the vibration damping operation. A specific advantage of this design using individual and transversely flexible support studs on the rear side of the horn plate is that the vibration damping effect (which occurs substantially on the opposite side of the horn plate only) will be substantially less affected by the interface or contact on the rear side between the horn plate and the elastomeric damper element. If for instance the steering wheel is vibrating back and forth horizontally in a clock direction 3 o'clock↔9 o'clock, then support studs located at or near positions 3 o'clock and 9 o'clock may flex horizontally, which would be in the radial direction in relation to the center of the steering wheel, in order not to substantially affect the vibration damping function. Support studs located at positions 12 o'clock and 6 o'clock may also flex horizontally, which however would be in the circumferential direction, in order not to substantially affect the vibration damping function. Other support studs would flex in directions being partly radial, partly circumferential.

In some embodiments, especially embodiments in which the damper unit is used in a vibration damper assembly for a steering wheel having a mechanical horn activation mechanism relying on an axial movement of the horn plate, said plurality of support studs form a first set of a first support studs each having a distal end facing axially towards the insertion end of the damper unit, and said elastomeric support part further presents one or more second elastomeric support studs, each second support stud having a distal end facing axially towards the insertion end of the damper unit and extending at least partially in the direction of said axis, wherein the distal ends of the first support studs are located axially closer to the insertion end of the damper unit than the distal ends of the second support studs. In preferred embodiments, there are a plurality of such second support studs. In some embodiments, the first and the second support studs may have different height.

An advantage obtained by this design is that two desirable, but seemingly incompatible properties may be obtained by one and the same damper unit, one property relating to vibration damping and the other property relating to horn activation. With regard to vibration damping, a flexible interface is preferred between the elastomeric material and the rear side of the horn plate as discussed above in order to reduce the influence on the vibration damping operation. On the other hand, with regard to horn activation a stiff interface is preferred in order to initiate the horn spring compression as soon as possible when the driver presses the horn pad. Since the horn plate is supported by an elastomeric and thus compressible material on its rear side, there is a risk that the horn spring is not compressed until later during the horn activation since the elastomeric material will first be compressed in the axial direction upon horn activation before the force may be transferred to the horn spring. This will give an undesired varying spring constant when the horn pad is pressed, where the horn spring is not compressed during the initial movement of the horn plate. This “dilemma” may be solved by the design having first and second support studs, creating a “dynamic” support interface which changes its properties during the movement of the horn plate.

Before horn activation, the first support studs are in contact with the rear side of the horn plate, but the second support studs are axially spaced form the rear side of the horn plate by an axial gap. The size Δ of this axial gap may be in the order of one or few millimeters as an example. Other sizes are possible. When the driver has just initiated the horn activation by pressing a horn activation pad, the horn plate will move, and the first support studs will be compressed. It is preferred that the first support studs have relatively total limited cross-sectional dimension or stiffness in order for this compression to occur. The total “spring constant” of the whole set of the first support studs is preferably selected to be less than the spring constant of the horn spring. Therefore, the compression of the horn spring has not yet started. When the first support studs have been axially compressed by an amount Δ to a degree where their distal end surfaces are flush with the distal end surfaces of the second set of support studs, the rear side of the horn spring will have contact with both the first support studs and now also the second support studs. The gap Δ is now eliminated. Accordingly, selecting small dimensions for the first set of support studs has the advantage of both ensuring a flexible interface and ensuring a fast axial compression during the initial phase of the horn activation. When the axial gaps Δ between the second support studs and the horn plate have been eliminated, the total axial stiffness or total spring constant of all the first and second support studs in combination is preferably selected sufficiently large for the horn spring to be compressed when the driver presses the horn activation pad.

In preferred embodiments, if the total axial spring constant of the first and the second set of support studs is k1and k2, respectively, and the spring constant of the horn spring is k3, then the support studs should preferably be designed such that k1+k2>k3in in order to ensure that the horn spring is compressed when the gaps Δ have been eliminated and the combined force from the support studs becomes larger than the pre-compression horn spring force given by k3.

In preferred embodiments, k1<k2or k1<<k2in order to keep the interface as flexible as possible when no horn activation is present. However, other relations between k1and k2are also possible. The stiffness or compressibility of the support studs may be varied in different ways. For instance, the second support studs may have a larger cross-section transverse to the axis of the damper than the first support studs.

In some embodiments, said one or more second support studs form a second set of a plurality of second support studs which are mutually spaced in the circumferential direction and which are circumferentially interlaced with the first supports studs and spaced therefrom. In other embodiments, there may be only one single second support stud, for example in the shape of a continuous ring extending circumferentially around the axis of the damper unit

In some embodiments, the horn spring is pre-compressed before horn activation.

In some embodiments, the sleeve of the damper unit is a slider being configured, upon horn activation on the steering wheel, to slide in the direction of said axis along a guide shaft received in said central bore of the slider. In such embodiments, the elastomeric vibration damper element may be molded on a first part of the slider, wherein the damper unit may further comprise an elastomeric horn spring element having a horn spring part and an attachment part molded in one piece with each other. The attachment part of the horn spring element may be molded on a second part of the slider. The horn spring part may be configured to exert a force on the slider in the direction of the axis before and upon horn activation on the steering wheel.

Embodiments including an elastomeric horn spring integrally formed with the damper unit present at least the following advantages:The number of components to manufacture, manage and assemble is reduced. During assembly, the damper unit is already provided with the molded horn spring element. Thereby, no separate horn spring has to be handled during assembly since the horn spring is already in place as an integral component of the damper unit. The mechanical horn spring mechanism is directly and automatically obtained upon mounting the slider on the guide shaft.The horn plate can be quickly and easily connected to the base structure by one or more damper units, wherein each damper unit automatically provides—as a direct result of mounting the unit—both a vibration dampening function and a horn spring function without any need of handling or assembling a separate damping element or a separate horn spring.It is possible to manufacture a multi-function unitary damper unit by molding the damper element and the horn spring element in one piece with each other on the slider in one single molding step. The unitary damper unit—including a slider plus an elastomeric damper element plus a horn spring element—will present a slider function, a vibration damping function and a horn spring function, respectively.By molding the elastomeric horn spring element on the slider, it is possible to both manufacture the horn spring and to bond the horn spring to the slider in one single molding operation.By molding the horn spring element on the slider, the quality of the final product may be increased since no separate alignment and mounting of the horn spring is needed.

The damper unit may also be used with a separate horn spring, such as a conventional metallic spiral spring. In other embodiments, where the damper units are used in a damper assembly for a steering wheel having an electronic horn activation instead of a mechanical horn activation, the damper units may be used without any horn springs, just for connecting the horn plate to the base structure via the elastomeric elements in order to achieve the dynamic vibration damping effect.

Other preferred embodiments of the damper unit are set out in the dependent claims.

According to a second aspect, there is provided frequency-tuned damper assembly for dampening vibrations in a steering wheel, said assembly comprising:a base structure which is fixed to a steering wheel and presents vibrations to be dampened;a horn plate;one or more damper units according to claim1, each damper unit being arranged in an associated mounting opening in the horn plate with its radially outer engagement surface in direct contact with the horn plate for transferring said vibrations, and with the distal end surfaces of the support studs in contact with a rear side of the horn plate;one or more guide shafts, each guide shaft being fixed to the base structure and being received in the central bore of the sleeve of the associated damper unit; anda mass which is supported by the base structure via the damper elements of the damper units for allowing movement of the mass transverse to said axis;

wherein the damper element and the mass are configured to operate as a frequency-tuned spring-mass system forming a frequency-tuned dynamic damper for dampening said vibrations.

In some embodiments of the damper assembly with a mechanical horn activation, a distal part of the elastomeric damper assembly of each damper unit may protrude axially beyond the mounting opening in the horn place. Upon horn activation, when a driver presses a horn pad of the steering wheel, the horn plate is moved against the spring force of one or more horn springs. When the driver subsequently releases the horn pad, the horn plate is moved back to its normal position by the horn springs. An advantage obtainable by this design is that the elastomeric distal part of the damper element, which protrudes axially beyond the mounting opening in the horn plate, may operate as an elastomeric stop element during the return movement of the horn plate. Upon horn activation, the distal part of the damper element may move away from the bolt head. When the horn pad is released, the horn springs will push the horn plate back towards its normal position. During the return movement, the elastomeric distal part of the damper element will engage the bolt head defining a “soft” dampened stop position for the return movement. Thus, the elastomeric damper elements of damper unites used in a damper assembly for a steering wheel may have multiple functions, including but not limited to transferring radially directed vibrations in the frequency-tuned dampening operation, and dampening an axially directed horn mechanism return movement.

As known as such in the prior art, the weight of an airbag assembly in the steering wheel may be preferably be used as part of the mass for the dynamic damping function of the dynamic spring-mass system in order to use a separate dead weight for this purpose. The weight of the horn plate and of further components supported by the horn plate will also contribute to the total weight of the vibrating mass.

In preferred embodiments, the part of the elastomeric damper element involved in the vibration dampening operation is pre-compressed as a result of the damper unit being inserted and mounted in the horn plate.

As a result of the insertion and mounting of the damper unit, the outer engagement surface of the damper unit is brought into direct engagement with an inner engagement surface of a mounting opening of the horn plate for transferring the vibrations. The inner engagement surface may be formed by the horn plate as such (made of metal for instance) or by a sleeve fixedly connected or molded to the horn plate and extending axially from the horn plate for providing an axially extended engagement interface. Such a sleeve may be a sleeve molded on the horn plate, for instance by a relatively rigid plastic material.

The vibration-reducing damper assembly comprises at least one, but preferably a plurality of damper units according to the invention. Optionally the damper units may be configured to dampen vibrations in different directions. This may be achieved by using one or more damper units for one vibration direction, and one or more other damper units for a second vibration direction. It may also be possible to design each damper unit such that it may dampen different vibrations in different directions.

Preferred embodiments of the damper assembly may comprise one or more damper units according to any of the dependent claims2to8. Preferred embodiments of the assembly are set out in the dependent claims.

According to a third aspect, there is provided a method of manufacturing a damper unit, comprising:molding, on a radially outer first part of a sleeve, an elastomeric vibration damper element having an elastomeric insertion part configured to be inserted into a mounting opening of the horn plate, and an elastomeric support part configured to define a final insertion position of the damper unit; wherein:the elastomeric insertion part presents a plurality of elastomeric ribs which extend at least partially along said axis and are mutually spaced in a circumferential direction in relation to said axis, said ribs together forming a radially outer engagement surface configured to be brought into direct engagement with an inner surface of a mounting opening;the radially outer engagement surface has a first radial dimension, and the elastomeric support part has a second radial dimension, larger than said first radial dimension; andsaid elastomeric support part presents a plurality of elastomeric support studs, which are mutually spaced in the circumferential direction, extend at least partially in the direction of said axis, and each presents a distal end surface facing the insertion end of the damper unit, said elastomeric support studs being flexible in all directions transverse to said axis, wherein said distal end surfaces of the support studs are configured, during assembly of the damper unit in the mounting opening of the horn plate, to be brought into contact with a rear side of the horn plate in the final mounting position.

There is also disclosed a method for use in making a frequency-tuned vibration damper assembly for dampening vibrations in a steering wheel, said method comprising:

using one or more damper units, each damper unit comprising a sleeve having a central bore which extends along an axis, and an elastomeric vibration damper element which is molded on a radial outer side of the sleeve such that the sleeve and the damper element together form a unitary structure, said elastomeric vibration damper element having:an elastomeric insertion part presenting one or more radially outward extending snap-lock protrusions at an insertion end, and a radially outer engagement surface axially spaced from the snap-lock protrusions, said radially outer engagement surface having a first radial dimension, andan elastomeric support part which has a second radial dimension, larger than said first radial dimension;andinserting each damper unit, in an insertion direction, into an associated mounting opening in a horn plate along an axis of the damper unit, wherein the damper unit is inserted into the mounting opening until a final insertion position is reached in which:the radially outer engagement surface of the elastomeric insertion portion is in direct contact with an inner surface of the mounting opening,the snap-lock protrusions have been inserted through the mounting opening to form a snap-lock of the damper unit in relation to the horn plate, andthe elastomeric support part has been brought into axial contact with a rear side of the horn plate.

Specific features of the disclosed method of making a frequency-tuned damper assembly include that the elastomeric damper element and the slider/sleeve are inserted together into the mounting opening of the horn plate from one side of the horn plate only during the assembly, and that the elastomeric damper element is inserted in the insertion direction to such an extent that the elastomeric engagement surface is brought into engagement with the inner engagement surface of the mounting opening, and a distal part of the elastomeric damper element including the snap-lock protrusions projects axially beyond the inner engagement surface of the mounting opening.

A first advantage of the method of making a frequency-tuned damper assembly is that the assembly of the components may be performed in a shorter time since the elastomeric damper element and the slider are inserted into the mounting opening of the horn plate together and from one side of the horn plate only during the assembly. The elastomeric damper element and the slider form a unitary structure to be assembled from said one side of the horn plate.

A second advantage of the method of making a frequency-tuned damper assembly is that the damper unit may easily be snap-locked to the mounting plate. The damper unit is inserted to an extent that the one or more radially outward extending snap-lock protrusions of the elastomeric damper element project over a distal axial edge of the mounting opening. Thereby, the inserted elastomeric damper element may be held in its correct position in relation to the horn plate by the snap-lock protrusions. Since said one or more snap-lock protrusions are integrally formed with the elastomeric element and, accordingly, are made of an elastomeric material, they may be temporarily radially compressed and/or bent during the insertion step in order to pass through the mounting opening. Thereby, no separate locking element has to be assembled from the opposite side of the horn plate, reducing assembly time and manufacturing costs.

The method of making a damper assembly may include the use of any of the embodiments of damper units as described above or as defined in the claims. Thus, the damper units may comprise ribs, support studs, integrated elastomeric horn springs. However, other designs are also possible, such as designs having no ribs but instead a continuous radially outer engagement surface.

Terminology

In the present disclosure, when an elastomeric element is stated to be “molded” on the sleeve or slider is should be interpreted as the relevant element is first of all a molded detail being manufactured by molding. Second, the expression “molded” is to be interpreted as the relevant element is created/molded directly on the sleeve or slider, in contrast to prior-art solutions where the relevant element is made as a separate part, such as in the form of a conventional spiral-shaped metal spring made separately and mounted in the assembly as a separate part. In preferred embodiments, the elastomeric material includes silicone rubber.

In the present disclosure, the term “slider” may refer to an element which is arranged to slide along a guide shaft during horn activation. This is the case when a mechanical horn activation mechanism is used. However, the term “slider” may also refer to a sleeve which is arranged to be mounted on but not to slide along a guide shaft. This is the case when an electronic horn activation is used where the horn plate is not configured to move axially relative to the guide shaft during horn activation.

In the present disclosure, the expression “in contact with the rear side of the horn plate” is to be interpreted as covering both direct contact with the horn plate as well as direct contact with a sleeve fixed to the horn plate around the mounting opening for the damper unit.

In the present disclosure, the terms “bonding” or “bonded” are to be interpreted as a connection or attachment between the relevant element and the sleeve or slider preventing the element from falling off from or being easily removed from the sleeve or slider. The term “bonding” is thus to be interpreted as an attachment or connection ensuring that the relevant element, as an integral part of the damper unit from an assembly perspective, is being held by the bond in its intended position on the slider. In embodiments where an element can easily be removed from the slider or easily fall of from the slider, such as a cylindrical damper element having a central bore in which a guide shaft is received without any mechanical bonding or adhesion acting in the axial direction, the element is not considered to be “bonded” to, the slider although radial movement relative to the slider may be restricted.

In the present disclosure, “mechanically bonded” or “mechanical bonding” is to be interpreted as an alternative to “chemical bonding”. Mechanically bonding should be interpreted as a non-chemical attachment of the relevant element to the slider, ensuring that the relevant element is mechanically maintained in its intended position on the slider.

In the present disclosure, expressions as “chemically bonded”, “chemical bonding”, “adhesion” binding or “adhesion” and the like should be interpreted as an alternative to mechanical bonding. Chemical bonding is considered a bonding between molecules. In some embodiments, mechanical and chemical bonding may be used in combination. A preferred chemical bonding may be adhesion bonding rather than glue. Chemical bonding may be provided during molding. In some embodiments, chemical bonding may be obtained by using an overmolding technique with adhesion bonding between similar or related polymers.

In the present disclosure, the term “snap-locking” and the like should be interpreted as a locking mechanism which results in a locking function as a result of the damper unit being inserted into its final mounting opening. Especially, the term should be interpreted to cover also embodiments where there is not necessarily a distinct “snap” occurring during the insertion but rather a gradual expansion/movement of the snap-lock protrusion.

