spring pad, suspension element and motor vehicle

Abstract

Spring support (14) for a suspension element of a motor vehicle (2), wherein the spring support (14) - an electroactive polymer and - has a piezoactive element (22).

Description

[0001] The invention relates to a spring support for a suspension element of a motor vehicle, a suspension element and a motor vehicle.

[0002] To achieve desired driving characteristics and a comfortable ride, the axles of a motor vehicle absolutely require the installation of springs and dampers to stabilize the vehicle body against road vibrations. Accordingly, suspension elements for motor vehicles, which are generally combined with a damping system, have been known for a long time. In practice, the spring element is usually a coiled steel wire spring mounted at the top and bottom on an elastic element, which can be called a spring pad or spring support. These elements are generally made of a natural rubber-based elastomer and are manufactured as molded rubber parts. The purpose of these elements is, on the one hand, to provide support for the spring and, on the other hand, to act as insulation for acoustic decoupling.Nevertheless, in the high frequency spectrum (>100 Hz) and at small amplitudes (<0.5 mm), short-term resonant vibrations can occur during transient processes, which can manifest, for example, as a so-called "noise-ping" when a car door is slammed. Technically, these vibrations are irrelevant, but they can lead to an acoustically inferior impression because they occur in the high-frequency range.

[0003] WO 2014 / 106607 A1 describes a chassis device with at least one wheel suspension, which includes at least one shock absorber and at least one wheel suspension longitudinal extension aligned at least substantially parallel to a longitudinal direction of the shock absorber. Furthermore, the chassis device includes at least one chassis element designed to change the wheel suspension longitudinal extension in at least one operating state. It is proposed that the chassis element incorporate at least one smart material. The document refers to a wheel suspension and its integration into a shock absorber or strut. The core of the teaching is a "change in the wheel suspension longitudinal extension during operation," which, in certain embodiments, but not exclusively, is caused by an electroactive material or an elastomer as a result of a stimulus, for example, by applying an electric field.

[0004] From EP 2 172 352 A1, a motor vehicle suspension spring is known which is equipped at its ends with an active spring pad. The spring pad consists of a lower part, an upper part, and a piezo actuator arranged between them. To increase the frequency range of a dampable spectrum, the piezo actuator can be appropriately controlled, for example with a phase shift, by means of an electrical voltage.

[0005] WO 2012 / 120 009 A1 describes a layered composite comprising at least one piezoelectric layer and one dielectric elastomer layer sandwiched between electrically conductive layers. This hybrid layered composite combines sensor, actuator, and energy harvesting functions in a compact unit, with the piezoelectric layers converting mechanical energy into electrical energy and the dielectric elastomer layers being used for actuator applications. Cascading multiple layers maximizes energy yield, while the multifunctional structure enables broad applicability.

[0006] The known spring pads according to the prior art are either limited with regard to the possible frequency spectrum or require complex active control, in which an electrical voltage or electric field must be applied to achieve a desired effect. This also requires sensors connected to the control system to determine state variables to which a short-term reaction is then required.

[0007] It is therefore the object of the present invention to provide a simple way to avoid unwanted frequencies, in particular so-called “noise pings”, during the operation of a motor vehicle.

[0008] The problem is solved by a spring pad of the type mentioned above, wherein the spring pad comprises an electroactive polymer and a piezoactive element. The problem is further solved by a suspension element with such a spring pad, and by a motor vehicle with at least one such spring pad or with such a suspension element.

[0009] This makes it possible to create a self-regulating system that automatically reacts to a stimulus in the form of a mechanical vibration and thereby changes the stiffness of the spring pad. According to the invention, the spring pad is constructed such that it consists wholly or partially, for example in segments, of an electroactive element, such as a dielectric elastomer, and incorporates a piezoactive element, in particular a piezoelectric sensor element. A piezoactive element, or piezoelectric element, is understood to be, in particular, a component or element that utilizes the piezoelectric effect to produce an electrical voltage when a mechanical force is applied.

[0010] The vibration of the spring exerts mechanical pressure on the spring pad. Due to the integration of the piezoelectric element into the spring pad, this mechanical pressure also acts on the piezoelectric element itself. Consequently, an electrical voltage generated by the piezoelectric element corresponds to the mechanical pressure. When this voltage is coupled to the dielectric elastomer, it leads to a change in the dielectric elastomer's stiffness. This change depends on the magnitude of the electrical voltage. By adjusting the stiffness properties and their changes to the voltage generated by the piezoelectric element and the operating frequency, a variable stiffness of the spring pad can be achieved, which counteracts any resonant frequency that may occur.

[0011] The portion of the spring pad containing the electroactive polymer and the piezoelectric element are electrically connected. A voltage generated by a mechanical force acting on the piezoelectric element is then applied to the electroactive polymer and can thus influence its mechanical properties.

[0012] It is advantageous for the electroactive polymer to be a dielectric elastomer. Dielectric elastomers belong to the group of electroactive polymers (EAPs). They are sheet-like elastomer composites consisting of an electrically non-conductive, highly stretchable elastomer film made of silicone, acrylic, polyurethane, or natural rubber, which is covered on both sides by conductive and stretchable electrode layers. Electrically speaking, this is a flexible, stretchable capacitor. The dielectric between the electrodes can consist of various elastomers. The electrode layers, for example, consist of carbon or metal particles in an elastomer matrix. Applying an electrical voltage causes the elastomeric material to stretch. This stretching is proportional to the electrical voltage.

[0013] According to one embodiment, the piezoactive element is arranged adjacent to the electroactive polymer along a load direction of the spring support. The load direction can, for example, correspond to the central axis of an associated spring of a suspension element. In this way, it can be ensured that when the spring support is loaded in the spring direction or in the load direction, a voltage is generated by the piezoactive element, since the force acting on the spring support or on the electroactive polymer also acts, at least partially, on the piezoactive element.

[0014] The spring support can advantageously be designed such that a load applied to the spring support along a specific direction causes a change in its overall stiffness. In this way, the frequency range that can be damped by the spring support can be varied. When a high-frequency vibration acts on the spring support, its stiffness is modulated at the same frequency, thus suppressing resonance phenomena.

[0015] The spring pad can have a round circumference, in particular a circular circumference. The spring pad can be disc-shaped, plate-shaped, or ring-shaped. Any other shape commonly used for a spring pad is also possible.

[0016] It is possible for the electroactive polymer to have an elastomeric film with electrodes arranged on opposite sides of the film. The elastomeric film then forms a dielectric, bounded on both sides by the electrodes. Together, these elements form a capacitor. The electrodes can be designed as stretchable electrode layers. This creates a flexible, deformable component with long-lasting durability and reliability.

[0017] It is advantageous for the electrodes to have carbon particles and / or metal particles arranged in an elastomer matrix. This makes the electrodes stretchable and flexible, allowing them to adapt to changes in the shape of the dielectric.

[0018] The piezoactive element can be designed as a thin piezoactive film, a printed piezoelectric material, or piezoelectric particles. The piezoactive element can be made so thin that it has minimal impact on the damping function of the spring pad. For example, the piezoactive element can consist of polyvinylidene fluoride or polyvinylidene fluoride trifluoroethylene, or at least contain one of these elements. Elements made of these materials can be produced very thinly using printing processes, for example, on cost-effective, flexible polymer substrates.

[0019] Accordingly, it is advantageous if the piezoactive element has a thickness of less than 1 mm, preferably less than 0.5 mm, and particularly preferably less than 0.3 mm, along a load direction of the suspension element.

[0020] The spring pad can have a layered structure. Each layer can extend over parts of the spring pad's cross-section or over the entire cross-section. A central layer can be formed by the dielectric, for example, the electroactive elastomer. An upper electrode layer can be applied to the top side of the dielectric. A lower electrode layer can be applied to the underside of the dielectric. An upper protective layer can be attached to the upper electrode layer, and a lower protective layer can be enclosed within the lower electrode layer. Such an exemplary structure has five layers. Accordingly, the spring pad can have a first protective layer, a first electrode layer, a polymer layer, a second electrode layer, and a second protective layer along a load direction.In addition, the spring base naturally includes the piezoelectric element, which can, for example, be attached to the lower protective layer. The protective layer can be made of polyethylene or PTFE. The electrical contacts can be formed using a printing process with flexible polymer substrates. Electrical contact between the polymer and the piezoelectric element can be established via appropriate printed or vapor-deposited conductive traces.

[0021] It is possible that the spring pad contains a non-electroactive polymer in addition to the electroactive polymer. The non-electroactive polymer then simply performs the classic functions of a spring pad, namely facilitating contact between the spring and the adjacent vehicle components, as well as providing damping. This allows for the production of a particularly cost-effective spring pad.

[0022] One possible embodiment, in which the spring pad comprises both an electroactive polymer and a non-electroactive polymer, provides that alternating sections of the electroactive polymer and the non-electroactive polymer are arranged along one circumference of the spring pad. The alternating sections can be in the form of circular or ring segments. If the spring pad has a layered structure, the alternating sections can be arranged within the elastomer layer. In other words, the elastomer layer can consist of sections of electroactive and non-electroactive polymer, with the electroactive and non-electroactive sections arranged alternately along a circumferential direction.

[0023] Advantageously, the piezoelectric element can be arranged on a side of the spring pad opposite the side intended for connection to a spring element. In this way, the piezoelectric element is subjected to relatively little stress from the spring movement, resulting in beneficial effects on the durability of the spring pad.

[0024] The thickness of the spring support can, for example, be less than 50%, preferably less than 30%, and particularly preferably less than 20% of the spring support's diameter. Such a relatively flat spring support allows for relatively direct contact between the spring and the adjacent vehicle components. Accordingly, the spring support can be designed to have a disc-shaped or annular base.

[0025] Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. The drawings show: Fig. 1: a schematic representation of a motor vehicle axle with two spring-damper elements, Fig. 2: a first embodiment of a spring support according to the invention in the context of a spring, Fig. 3: a schematic cross-section through a second embodiment of a spring support according to the invention, Fig. 4: an enlarged section from Fig. 3 and a schematic detailed representation of the elastomer unit, Fig. 5: a schematic representation of a top view of a third embodiment of a spring support according to the invention, Fig. 6: a fourth embodiment of a spring support according to the invention with an associated spring in different load states, and Fig. 7: a schematic representation of the stress and capacity ratios during a load and subsequent unloading of a spring support according to the invention.

[0026] Fig. Figure 1 shows a schematic representation of an axle 4 of a motor vehicle 2 with two spring-damper elements 10, each of which can contain a spring pad according to the invention. The axle 4 carries two wheels 6 and is connected via the spring-damper elements 10 to the superstructure 8, which essentially corresponds to the body of the motor vehicle 2 as well as other assemblies and components of the motor vehicle 2. The spring pads according to the invention can be arranged either between a lower end of the respective spring of the spring-damper element 10 and the axle 4 or between an upper end of the respective spring of the spring-damper element 10 and the superstructure 8. Naturally, it is also possible for the spring pads according to the invention to be arranged at both the upper and lower ends of the respective spring of the spring-damper element 10.A spring element according to the invention can therefore have one spring support according to the invention or two spring supports according to the invention.

[0027] Fig. Figure 2 shows a first embodiment of a spring support 14 according to the invention in the context of a spring 12, such as is used, for example, in a spring-damper element as in Fig. The individual components are shown in an exploded view. A first spring support 14.1 has a first base body 16.1 and a first central opening 18.1. In its installed state, the first spring support 14.1 rests with the underside of the first base body 16.1 on an upper coil of the spring 12. The second spring support 14.2 accordingly has a second base body 16.2 and a second central opening 18.2. The second spring support 14.2 is designed so that, in its installed state, the upper side of the second base body 16.2 rests against the underside of a lower coil of the spring 12. The two base bodies 16.1, 16.2 of the two spring supports 14.1, 14.2 have an annular shape. The central opening 18.1, 18.2 also has a circular circumference, so that the spring supports 14.1, 14.2 have a roughly plate-shaped basic form. The central openings 18.1, 18.2 are bounded by a short protrusion in the form of a collar pointing towards the spring 12. A fastening clip is shown between the second spring support 14.2 and the spring 12, which is used to clip the spring support into the control arm of the rear axle. This is optional and not essential to the present invention.

[0028] Fig. Figure 3 shows a schematic cross-section through a second embodiment of a spring pad 14 according to the invention. It can be seen that the spring pad 14 again has a base body 16 and a central opening 18. The structure of the base body 16 is shown in more detail. A portion of the spring pad 14 located near the spring consists of an elastomer unit 20. The elastomer unit 20, in turn, has several layers. Essentially, the elastomer unit 20 has two types of layers: electrode layers and dielectric layers. These types of layers are arranged alternately. In the simplest case, the elastomer unit 20 consists of two electrode layers with a dielectric layer between them. Typically, the elastomer unit 20 is composed of n dielectric layers and n + 1 electrode layers.

[0029] The portion of the spring support 14 furthest from the spring has a piezoactive element 22. In the illustrated embodiment, the piezoactive element 22 is also ring-shaped. The piezoactive element 22 is electrically conductively connected to at least one of the electrode layers. In the illustrated embodiment, the piezoactive element 22 has a smaller diameter than the elastomer unit 20. However, it is also possible for the piezoactive element 22 to have the same or a larger diameter than the elastomer unit 20. For example, the piezoactive element 22 can be congruent with the elastomer unit 20. In other words, the piezoactive element 22 can have the same cross-section as the elastomer unit 20.

[0030] Fig. Figure 4 shows an enlarged section from Fig. 3 and a schematic detailed representation of the elastomer unit 20. As in Fig. The spring base 14 is composed of the elastomer unit 20 and the piezoactive element 22. The elastomer unit 20, in turn, consists of a total of five individual layers. These are, in detail, the upper protective layer 24, the upper electrode layer 26, the polymer layer 28 in the form of a dielectric layer, the lower electrode layer 30, and the lower protective layer 32. Each individual layer is designed to be flexible or stretchable. The polymer layer 28 can consist of an electroactive polymer, and the two electrode layers 26 and 30 can, for example, consist of conductive particles embedded in a polymer matrix. The protective layers 24 and 32 are flexible or elastic and can be made of polyethylene or PTFE. A thin film of "normal," i.e., electrically inactive, natural rubber is also conceivable. However, practical experience shows that such a protective layer cannot be made arbitrarily thin.

[0031] Fig. Figure 5 shows a schematic top view of a third embodiment of a spring base 14 according to the invention. The figure shows a surface of the elastomer unit, which in the illustrated embodiment is segmented. The elastomer unit consists of the electroactive sections 34.1, 34.2, and 34.3, as well as the non-electroactive sections 36.1, 36.2, and 36.3. The different sections are arranged alternately, such that each of the electroactive sections 34.1, 34.2, and 34.3 borders two of the non-electroactive sections 36.1, 36.2, and 36.3. Similarly, each of the non-electroactive sections 36.1, 36.2, and 36.3 borders two of the electroactive sections 34.1, 34.2, and 34.3. The electroactive sections 34 and the non-electroactive sections 36 are each designed in a ring segment shape.In the illustrated embodiment, the electroactive sections 34 each have a larger extent than the non-electroactive sections 36. However, it is also possible for the electroactive sections 34 to have a smaller extent than the non-electroactive sections 36. In other words, the proportion of the electroactive sections 34 to the total surface area of ​​the elastomeric unit can be greater or less than the proportion of the non-electroactive sections 36 to the total surface area of ​​the elastomeric unit. In a special case, both proportions can also be equal. The electroactive sections 34 can have a structure similar to the elastomeric units described above. In particular, a layered structure of the electroactive sections 34 can include one or more dielectric layers, several electrode layers, and optionally one or more protective layers.The electroactive sections are preferably in electrical connection with in the . Fig. 5 piezoelectric elements not shown.

[0032] Fig. Figure 6 shows on the left a spring support 14 with an associated spring 12 in a neutral state, and on the right the same spring support 14 with the spring 12 in a state where the spring support 14 is under greater load. The different load states are symbolized by the two arrows representing the forces F1 and F2. In the neutral state, a downward force exerted by the mass of the assembly acts on the spring 12 and thus also on the spring support 14. If the force acting on the spring 12 and thus on the spring support 14 increases due to a load, the spring 12 is compressed, as shown on the right side of the figure. Fig. Figure 6 illustrates this. Simultaneously, the force acting on the piezoactive element 22 is also increased, which then generates an electrical voltage or increases the voltage it generates. Since the piezoactive element 22 is connected to at least one of the electrodes 38, the voltage is also applied to the capacitor formed by the electrodes 38 and the dielectric in the form of the polymer layer 28, which then increases its capacitance. The changing electrical voltage or the changing capacitance of the capacitor causes a change in the stiffness of the elastomer unit 20, which dynamically changes the resonance frequency of the system and prevents oscillation of the system.

[0033] Fig.Figure 7 schematically describes the voltage and capacitance relationships during loading and subsequent unloading of the spring pad according to the invention. The dielectric elastomer in the form of the elastomer unit 20 and the piezoelectric element (not shown in the figure) are conductively connected. Even the static pressure exerts a mechanical preload, which is converted into an electrical voltage by the piezoelectric element and acts on the dielectric elastomer. This results in a basic stiffness. In the diagram shown in the lower part of the figure, where the electric field strength is plotted against the strain, this corresponds to the point marked 1. The change in the spring force, i.e., its increase in the illustrated example, initially leads to a strain of the dielectric.This state corresponds to the right-hand image in the upper part of the figure and to the point marked 2 in the cycle. Due to the higher pressure acting upon it, the piezoelectric element generates a higher voltage, resulting in a correspondingly higher field strength, which in turn leads to a change in the stiffness of the elastomer. In the upper part of the figure, this state corresponds to the lower image, and in the cycle, to the point marked 3. When the spring support, and thus also the elastomer unit 20, is subsequently relieved of pressure, it relaxes again, so that the strain decreases to its initial value. In the upper part of the figure, this corresponds to the left-hand image, and in the cycle, to the point marked 4. Subsequently, the voltage generated by the piezoelectric element also decreases again, and the cycle closes when the point marked 1 is reached again.

[0034] The basic operating principle is described in the cycle. The dielectric elastomer can react quickly to changes in voltage and thus respond immediately to transient processes, avoiding the resonance range by changing its stiffness. Near its natural frequency, the substrate, due to its variable stiffness, acts as a damper, as it is designed to react in the opposite direction. An increase in pressure raises the voltage generated by the piezoelectric element, leading to a change in the elastomer's stiffness. Reference symbol list 2 motor vehicles 4-axis 6 wheels 8. Body dimensions 10 Spring-damper unit 12 springs 14 Spring pad 16 basic shapes 18 central opening 20 elastomer units 22 piezoactive element 24 upper protective layer 26 upper electrode layer 28 Dielectric 30 lower electrode layer 32 lower protective layer 34 electroactive section 36 non-electroactive section 38 electrode

Claims

Spring support (14) for a suspension element of a motor vehicle (2), wherein the spring support (14) comprises an electroactive polymer and a piezoactive element (22). Spring pad (14) according to one of the preceding claims, wherein the electroactive polymer is a dielectric elastomer. Spring support (14) according to one of the preceding claims, wherein the piezoactive element (22) is arranged adjacent to the electroactive polymer along a load direction of the spring support (14). Spring support (14) according to one of the preceding claims, wherein the spring support (14) is designed such that a load on the spring support (14) along a load direction causes a change in the overall stiffness of the spring support (14). Spring support (14) according to one of the preceding claims, wherein the electroactive polymer comprises an elastomer film, and wherein electrodes (30, 32) are arranged on opposite sides of the elastomer film. Spring support (14) according to one of the preceding claims, wherein the spring support (14) has a layered structure. Spring support (14) according to claim 6, wherein the spring support (14) has a first protective layer, (24) a first electrode layer (26), a polymer layer (28), a second electrode layer (30) and a second protective layer (32) along a load direction. Spring pad (14) according to one of the preceding claims, wherein the spring pad (14) comprises a non-electroactive polymer in addition to the electroactive polymer. Suspension element with at least one spring support (14) according to one of claims 1 to 8 . Motor vehicle (2) with a spring support (14) according to one of claims 1 to 8 or with a suspension element according to claim 9 .

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