Shock absorber arrangement for a vehicle suspension and use of a lubricant for same

Abstract

The invention relates to a shock absorber arrangement (1) for a vehicle suspension, comprising a shock absorber (3) having a damper cap (7) and a piston rod (5) and a supplementary spring (9) which is arranged on the piston rod (5) opposite the shock absorber (3) and has an outer surface (13) facing the damper cap (7) and an inner surface (21) facing the piston rod (5) and is configured for damping the movement of the shock absorber (3) in the direction of the piston rod (5) on contact with the damper cap (7), wherein the outer surface (13) and / or the inner surface (21) is at least partially coated with a lubricant (17). According to the invention, said lubricant (17) comprises modified or unmodified polyether polyol. The invention further relates to a supplementary spring, a method and a corresponding use.

Description

[0001] Shock absorber arrangement for a vehicle suspension and use of a lubricant for same

[0002] The present invention relates to a shock absorber arrangement for a vehicle suspension, comprising a shock absorber having a damper cap, a piston rod and a supplementary spring which is arranged on the piston rod opposite the shock absorber and has an outer surface facing the damper cap and an inner surface facing the piston rod and is configured for damping the movement of the shock absorber in the direction of the piston rod on contact with the damper cap, wherein the outer surface and / or the inner surface is at least partially coated with a lubricant.

[0003] Shock absorber arrangements of the type indicated above are generally known. In the operation of a vehicle, a spring-in movement of the wheel suspension of the vehicle usually results in the shock absorber with its damper cap moving in the direction of the piston rod. In order to avoid damage to the shock absorber and possibly other components of the suspension on bottoming of the suspension of the vehicle, shock absorber arrangements frequently have a supplementary spring which after a particular degree of compression of the suspension and corresponding degree of movement of the shock absorber comes into contact with the damper cap and dampens further compressive movement. Volume- compressible materials which bring about material damping by means of their geometry and / or volume compression are advantageously used for this purpose.

[0004] It has been observed that squeaking noises occur during operation of the abovementioned shock absorber arrangements, and although these do not impair the function of the shock absorber arrangement as such, they are perceived as annoying. To manufacture shaped bodies forming the supplemental spring, the surface of the mold is frequently, even usually, pretreated with a mold release agent. Mold release agents based on oils, waxes, silicones and / or solid inorganic or organic additives, for example Teflon powder, or further products which reduce adhesion of the polyurethane to the mold surface are known to a person skilled in the art. It is known that particular mold release agents themselves can reduce or even prevent emissions of noise, especially some types of silicone-containing mold release agents. However, for reasons of protecting health and the environment, these variants are not preferred.

[0005] A residue of the mold release agent almost always remains on the surface of the molding in production of the shaped bodies. The type of residue can be influenced by the choice of the mold release agent, but the amount of residue depends on numerous factors during manufacture. These residues in places modify the emission of noise. Since the mold release agent is frequently an indispensable constituent of the manufacturing process, when reference is made in the following in connection with the invention to the shaped body composed of microcellular polyurethane this always refers both to the pure polyurethane shaped body and also the shaped body to the surface of which residues of a mold release agent still adhere. If reference is made in the following to a “dry” shaped body, this is intended to refer both to shaped bodies which are free of mold release agent and also to shaped bodies to which residues of mold release agents adhere.

[0006] To combat the above-described emissions of noise, attempts have been made in the past to use silicone-containing mold release agents in the manufacturing process. Owing to hazards to health which can arise from some silicon-containing compounds, this solution is however undesirable. From WO 2016 52 47 A1 it is known to utilize a lubricant for coating the outer surface and / or the inner surface of a spring of a shock absorber at least partially. However, it has been found that the lubricants proposed therein may cause hydrolysis in polyurethane components, which is highly unwanted and reduces the service life of such polyurethane components.

[0007] It was therefore an object of the invention to provide an alternative solution for decreasing noises in the operation of shock absorber arrangements. In particular it was also an object of the invention to provide such a solution which does not negatively affect the service life of the coated component.

[0008] The invention achieves the object of the invention in a shock absorber arrangement of the above-mentioned type in that said lubricant comprises modified or unmodified polyether polyol. It has been found that polyether polyol not only decreases noise in the operation of shock absorber arrangements but also provides high compatibility with polyurethane supplementary springs regularly utilized in such shock absorber arrangements.

[0009] The use of polyether polyol has been identified as particularly suitable, because the percentage of primary hydroxy groups within the terminal hydroxy groups is rather low. This has been found to be beneficial with regard to compatibility with polyurethane components, such as polyurethane supplementary springs, because primary hydroxy groups have been found to trigger hydrolysis. A high content of primary hydroxy groups may decompose polyurethane, which is highly unwanted. The polyether polyol may either be unmodified or modified with respect to terminal hydroxyl groups.

[0010] The modified polyether polyol comprises terminal hydroxy groups that are at least partially reacted such that the hydrogen is replaced by an organic substituent such as alkylic, aromatic or acylic. Such modification has not been conducted for the unmodified polyether polyol. Thus, an OH value of the modified polyether polyol may be lower than an OH value of the unmodified polyether polyol.

[0011] Suitable polyether polyols have a number average molecular weight of from 62 to 30,000 g / mol. They are based on propylene oxide, ethylene oxide, butylene oxide, or propylene oxide and ethylene oxide or other combinations of alkylene oxides. Suitable polyether polyols are prepared from a starter molecule comprising from 1 to 6 reactive hydrogen atoms in bound form by polymerization of ethylene oxide and / or propylene oxide by known methods. The polymerization can be carried out as an anionic polymerization using alkali metal hydroxides or alkali metal alkoxides as catalysts or as a cationic polymerization using Lewis acids such as antimony pentachloride or boron fluoride etherate. Furthermore, multimetal cyanide compounds, known as DMC catalysts, can also be used as catalysts. It is also possible to use tertiary amines, e.g. triethylamine, tributylamines, trimethylamines, dimethylethanolamine or dimethylcyclohexylamine, as catalyst. Ethylene oxide, butylene oxide, and propylene oxide can be polymerized in pure form, alternately in succession or as mixtures. Suitable starter molecules having from 1 to 6 reactive hydrogen atoms are, for example, water and dihydric or trihydric alcohols such as acetic acid, methanol, ethanol, fatty alcohols, ethylene glycol, 1 ,2- and 1 ,3-propanediol, diethylene glycol, dipropylene glycol, 1 ,4-butanediol, glycerol, trimethylolpropane, also pentaerythritol, sorbitol and sucrose. Further suitable starter molecules are amine starters such as triethanolamines, diethanolamines, ethylenediamines and toluenediamines. The polyether polyols preferably have an OH number in the range from 1 to 1 ,825 mg KOH / g. Particularly preferred polyether polyols are prepared from monohydric, dihydric or trihydric alcohols, in particular methanol, ethanol, fatty alcohol, ethylene glycol, trimethylolpropane or glycerol, and are ethylene oxide homopolymers, propylene oxide homopolymers or ethylene oxidepropylene oxide copolymers. A further class of preferred polyether polyols are alpha-hydro- omega-hydroxypoly (oxy-1 ,4-butanediyls), which are also known as PTHF. These particularly preferred polyether polyols have a molecular weight of from 62 to 10,000 g / mol and an OH number of from 5 to 1 ,825 mg KOH / g, preferably from 5 to 500 mg KOH / g, more preferably from 5 to 100 mg KOH / g.

[0012] In one embodiment, the polyether polyol comprises polypropylene glycol. Polypropylene glycol has been found to be beneficial, since the share of primary hydroxy groups is low, in particular about 4 % - 6 % of the terminal hydroxy groups. The polypropylene glycol is preferably based on propylene oxide.

[0013] In one embodiment, the polyether polyol comprises terminal hydroxy groups comprising hydrogen, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that the hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic. Preferably, the OH value of the modified polyether polyol is lower the OH value of the unmodified polyether polyol. The OH value is defined as milligrams of potassium hydroxide (KOH) required to neutralize the acetic acid taken up on acetylation of one gram of a chemical substance that contains free hydroxyl groups. OH value gives information about the average molecular weight of a molecule per OH group. It is measured according to DIN 53240. By modifying the polyether polyol, the share of hydroxy groups, in particular primary hydroxy groups, can be reduced.

[0014] In one embodiment, the supplementary spring comprises or consists of polyurethane. In a preferred embodiment, the polyurethane comprises or consists of a microcellular polyurethane. Microcellular polyurethane is a volume-compressible material. Said volume- compressible material has the particular advantage that in comparison with other materials such as rubber, they have extremely high capability for elastic change of shape together with high durability.

[0015] In one embodiment, the polyether polyol comprises terminal hydroxy groups and wherein less than 50 % of the terminal hydroxy groups are primary hydroxy groups. In a preferred embodiment, less than 25 % of the terminal hydroxy groups are primary hydroxy groups, preferably wherein in particular less than 10 % of the terminal hydroxy groups are primary hydroxy groups. The low share of primary hydroxy groups is beneficial for avoiding hydrolysis of polyurethane components. Methods for determining the content of primary or secondary hydroxy groups, also referred to as OH-groups, are known to those skilled in the art, e.g., from any of the following references:

[0016] Goodlett, V. W. 1965. 'Use of In Situ Reactions for Characterization of Alcohols and Glycols by Nuclear Magnetic Resonance', Analytical Chemistry, 37: 431-32. Hirama, Masahiro, and Tohru Oishi. 'Trichloroacetyl Isocyanate.' in, Encyclopedia of Reagents for Organic Synthesis. (Trichloroacetyl Isocyanate - Hirama - Major Refer-ence Works - Wiley Online Library). Meyer zur Heyde, Manfred. 1979. 'Neuere Anwendungen von Trichloracetylisocyanat in der 1 H-NMR-Spektroskopie', Fresenius' Zeitschrift fiir analytische Chemie, 295: 125-42. Bose, A. K., and P. R. Srinivasan. 1975. 'NMR spectral studies — XII: Trichloroacetyl isocyanate as an in situ derivatizing reagent for 13C NMR spectroscopy of alcohols, phenols and amines', Tetrahedron, 31 : 3025-29.

[0017] Low shares of primary hydroxy groups can be found in polymerizates where propylene oxide is polymerized on starters as described above. These products are called polypropylene ether polyol or polypropylene glycol.

[0018] In a preferred embodiment, the OH functions of the modified polyether polyol are at least partially reacted so that the OH value of the product is below that one of the original polyether polyol. In a more preferred embodiment, the modified polyether polyol is reacted with acetic anhydride, with acetyl chloride or oxalic dichloride so that an acetic or oxalic ester is formed. The reaction by-products (acetic acid or HCI, resp.) are removed from the product.

[0019] In another preferred embodiment, the polyether polyol is at least partially reacted with other products that can react with alcoholic OH functions, i.e. dimethyl sulfate, methyl iodide, or phenyl isocyanate, so that the OH value is below that one of the original polyether polyol.

[0020] In a preferred embodiment, the lubricant coating comprises an area density of more than 0.8 mg / cm2, preferably between 1 .5 mg / cm2and 50 mg / cm2, more preferably between 1 .5 mg / cm2and 10 mg / cm2, very preferably between 3 mg / cm2- 4 mg / cm2. Said area density of the lubricant has been found to be beneficial to provide sufficient damping properties while the total amount of lubricant to be applied to the component is kept to a suitable minimum. The invention has, in a first aspect, been described in relation to the shock absorber arrangement of the invention. In a further aspect, the invention also relates to a supplementary spring having an outer surface, facing a damper cap of a shock absorber and an inner surface configured to accommodate a piston rod of a shock absorber, wherein the outer surface and / or the inner surface is at least partially coated with a lubricant.

[0021] The invention achieves its underlying object in a supplementary spring in that said lubricant comprises or consists of modified or unmodified polyether polyol. The supplementary spring according to the invention utilizes the same advantages as the shock absorber arrangement of the invention. Preferred embodiments of the shock absorber arrangement are thus at the same time a preferred embodiment of the supplementary spring of the invention, and vice versa.

[0022] In one embodiment, the polyether polyol comprises or consist of polypropylene glycol. In one embodiment, the polyether polyol comprises terminal hydroxy groups comprising hydrogen, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that the hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic. Preferably, the OH value of the modified polyether polyol is lowerthan that of the conventional polyether polyol.

[0023] In a preferred embodiment, the supplementary spring comprises or consists of polyurethane. Preferably, the polyurethane is a microcellular polyurethane. In a preferred embodiment, the lubricant coating comprises an area density of more than 0.8 mg / cm2, preferably between 1 .5 mg / cm2and 50 mg / cm2, more preferably between 1 .5 mg / cm2and 10 mg / cm2, very preferably between 3 mg / cm2- 4 mg / cm2.

[0024] In a further aspect, the invention relates to a method for manufacturing a supplementary spring, the supplementary spring having an outer surface facing a damper cap of a shock absorber and an inner surface facing a piston rod of a shock absorber. The method achieves its underlying object in the step: coating the outer surface and / or the inner surface at least partially with a lubricant, wherein said lubricant comprises or consists of modified or unmodified polyether polyol.

[0025] In a further aspect, the invention relates to a method for manufacturing a supplementary spring, the method comprising the steps: Providing a mold for foaming the supplementary spring therein, applying a release agent to the mold, foaming the supplementary spring in the mold, applying a lubricant, wherein said lubricant comprises modified or unmodified polyether polyol, and wherein said lubricant is applied to the mold along with the release agent and / or after the application of the release agent, and / or as part of the release agent formulation.

[0026] The methods according to the invention utilize the same advantages and preferred embodiments as the shock absorber arrangement and the supplementary spring of the invention. Preferred embodiments of the shock absorber arrangement and the supplementary spring are thus at the same time preferred embodiments of the methods of the invention, and vice versa.

[0027] In a further aspect, the invention also relates to the use of a lubricant for reducing noise of a shock absorber arrangement comprises a shock absorber having a damper cap, a piston rod and a supplementary spring which is arrangement opposite of the shock absorber and has an outer surface facing the damper cap and an inner surface facing the piston rod and is configured for damping the movement of the shock absorber in the direction of the piston rod on contact with the damper cap, wherein the outer surface and / or the inner surface is at least partially coated with the lubricant. The invention achieves its underlying object in the use of a lubricant in that said lubricant comprises or consists of modified or unmodified polyether polyol.

[0028] In one embodiment, the polyether polyol comprises or consist of polypropylene glycol. In one embodiment, the polyether polyol comprises terminal hydroxy groups comprising hydrogen, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that the hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic. Preferably, the OH value of the modified polyether polyol is lower than that of the unmodified polyether polyol. In a preferred embodiment, the supplementary spring comprises or consists of polyurethane. Preferably, the polyurethane is a microcellular polyurethane.

[0029] In yet another embodiment, the polyether polyol comprises terminal hydroxy groups and wherein less than 50 % of the terminal hydroxy groups are primary hydroxy groups. In a preferred embodiment, less than 25 % of the terminal hydroxy groups are primary hydroxy groups, preferably wherein in particular less than 10 % of the terminal hydroxy groups are primary hydroxy groups.

[0030] Particular preference is given to microcellular polyurethane elastomers which, in a preferred embodiment, have a density in accordance with DIN 53420 of from 200 kg / m3to 1 ,100 kg / m3, preferably from 300 kg / m3to 800 kg / m3. Such microcellular polyurethane elastomers are also referred to as volume-compressible material (also: volume- compressible material of construction). Volume-compressible materials such as the abovementioned have the particular advantage that in comparison with other materials such as rubber they have extremely high capability for elastic change of shape together with high durability.

[0031] The production process usually takes place via reaction of isocyanates with compounds reactive toward isocyanates. Microcellular polyurethane is usually produced in a mold in which the reactive starting components are reacted with one another. Molds that can be used here are generally conventional molds, for example metal molds, which by virtue of their shape ensure that the spring element has the inventive three-dimensional shape. In one embodiment, a foaming mold is used to produce the contour elements. In another embodiment, they are incorporated subsequently into the concentric main element. Another conceivable method uses parts manufactured from semifinished products. The manufacturing process can by way of example use water-jet cutting.

[0032] Microcellular polyurethane products can be produced by well-known processes, for example by using the following starting materials in a single- or two-stage process:

[0033] (a) isocyanate,

[0034] (b) compounds reactive toward isocyanates,

[0035] (c) water and optionally

[0036] (d) catalysts,

[0037] (e) blowing agents and / or

[0038] (f) auxiliaries and / or additives, for example polysiloxanes and / or fatty acid sulfonates.

[0039] The surface temperature of the inner wall of the mold is usually from 30 °C to 110 °C, preferably from 50 °C to 100 °C. Production of the moldings is advantageously carried out at an NCO / OH ratio of from 0.85 to 1 .20, by mixing the heated starting components and introducing an amount thereof corresponding to the desired density of the molding into a heated mold which preferably closes tightly. The moldings have cured and can therefore be removed from the mold after from 1 minute to 60 minutes. The amount of reaction mixture introduced into the mold is usually calculated so that the shaped bodies obtained have the density indicated above. The starting components are usually introduced with a temperature of from 15 °C to 120 °C, preferably from 30 °C to 110 °C, into the mold. The degrees of compaction for producing the shaped bodies are in the range from 1.1 to 8, preferably from 2 to 6. Microcellular polyurethane products are advantageously produced by the "one shot" process with the aid of high-pressure technology, low-pressure technology, or in particular reaction injection molding technology (RIM), in open or preferably closed molds. Alternatively, a prepolymer process is used. The reaction is in particular carried out with compaction in a closed mold. Reaction injection molding technology is described by way of example by H. Piechota and H. Rohr in "Integralschaumstoffe" [Integral foams], Carl Hanser- Verlag, Munich, Vienna 1975; D.J. Prepelka and J.L. Wharton in Journal of Cellular Plastics, March / April 1975, pages 87-98 and U. Knipp in Journal of Cellular Plastics, March / April 1973, pages 76-84.

[0040] It has been recognized according to the invention that no or at least not very annoying emissions of noise occur in the case of a “dry” shock absorber arrangement and simultaneous use of a volume-compressible material such as microcellular polyurethane foam (see above). It has also been recognized that emissions of noise occur, for example, when damper fluid exits from the shock absorber and becomes distributed over the damper cap and / or the piston rod, even though the damper fluid, frequently a mineral oil, frequently intrinsically has usually friction-reducing properties. Proceeding therefrom, it has surprisingly been found that the undesirable noises can be significantly reduced by addition of a further lubricant which is different from the damper fluid and preferably likewise has a friction-reducing effect. The purported contradiction of the exit of the damper fluid itself having resulted in the annoying noises could be resolved in this way. Water, or combinations of water and damper fluid, can have the same effect.

[0041] There are two approaches to apply the lubricant onto the surface of the supplementary spring: (1) During the foaming process or (2) afterwards.

[0042] (1) During the manufacture of the supplementary spring, in many cases the surface of a mold is pretreated with a mold release agent. In other cases, the surface of the mold is modified to provide a permanent or semi-permanent surface that is so unpolar that polyurethane does not stick to it. The lubricant can be applied along with the release agent (a) before the application of the release agent, and / or (b) after the application of the release agent, and / or (c) as part of the release agent formulation. It can likewise be applied on a modified mold surface. In other words, in one embodiment, the lubricant is applied along with a release agent applied to a surface of a mold during the manufacture of the supplementary spring, before the application of the release agent, and / or after the application of the release agent, and / or as part of the release agent formulation.

[0043] (2) The lubricant can alternatively be applied onto the surface of the supplementary spring after the foaming process. In the method or use according to the invention, the lubricant can be, for example, sprayed and / or brushed or painted onto the supplementary spring, or as an alternative or in addition be applied by dipping. The lubricant can also be applied a plurality of times in this way, if necessary, or can be renewed after predetermined periods of time.

[0044] The invention will be illustrated below with reference to the accompanying figures with the aid of a preferred working example. The figures show:

[0045] Fig. 1 a, b a shock absorber arrangement according to a preferred working example in different operating states,

[0046] Fig. 2 a detailed depiction of the shock absorber arrangement of Fig. 1 a, b, and

[0047] Fig. 3a - c further detailed depictions of the shock absorber arrangement according to Fig. 1 a, b and 2 in different operating states.

[0048] Fig. 1 shows a shock absorber arrangement 1. The shock absorber arrangement 1 comprises a shock absorber 3 having a damper cap 7 and a piston rod 5 which extends through the damper cap 7.

[0049] Opposite the damper cap 7, a supplementary spring 9 is arranged along the piston rod 5. The supplementary spring 9 is accommodated by a base 11 .

[0050] The supplementary spring 9 has an outer surface 13 which faces an outer surface 15 of the damper cap 7.

[0051] During operation of the shock absorber arrangement 1 , a state as shown in Fig. 1 B can arise as a result of the movement of the damper. In this state, the outer surface 13 of the supplementary spring 9 is in contact with the end face 15 of the damper cap. If the shock absorber 3 continues to move, the supplementary spring 9 performs an evasive movement, as a result of which a relative movement of the outer surface 13 along the end face 15 occurs. The working principle according to the invention, which then comes to bear, is explained in more detail in Fig. 2 and 3a - c.

[0052] In Fig. 2, the supplementary spring 9 is firstly depicted in the partially sectioned state. The supplementary spring 9 is not compressed in the state shown in Fig. 2.

[0053] On the outer surface 13, the supplementary spring 9 is at least partially coated with a lubricant 17, wherein said lubricant 17 comprises or consists of polyether polyol. The lubricant 17 is, in the working example shown, additionally applied by way of example at least partially along an inner surface 21 of the supplementary spring 9, with the inner surface 21 facing the piston rod 5. A gap 19 is present between the inner surface 21 and the piston rod 5.

[0054] When compression of the supplementary spring occurs as indicated by way of example in Fig. 1 b, the supplementary spring 9 expands in the radial direction, i.e. transverse to the piston rod 5, in an outward direction and an inward direction. The inner surface 21 then comes into contact with the piston rod 5. Here too, the lubricant 17 brings about the advantages according to the invention. Although the noise-reducing effect is not as pronounced as in the case of application of the lubricant 17 to the outer surface 13, it is nevertheless present and advantageous according to the invention.

[0055] The working example of Fig. 2 should be considered to be illustrative in so far as the exclusive coating of the inner surface 21 (at least partially) and also the exclusive coating of only the outer surface 13 (at least partially) are to be considered as separately encompassed preferred embodiments.

[0056] Fig. 3a - c show the behavior of the lubricant 17 in different operating states. In the interests of a simple depiction, only the coating on the outer surface 13 is shown here. The concept could, however, be carried over analogously to the behavior of a coated inner surface 21 relative to the piston rod 5 (cf. Fig. 2).

[0057] In Fig. 3a, a state in which the supplementary spring 9 has been coated with lubricant 17 on the outer surface 13 but has not yet come into contact with the damper cap 7 is firstly shown. Damper fluid 23 has collected on the end face 15 of the damper cap 7 as a result of operation of the shock absorber. If, proceeding from Fig. 3a, the supplementary spring 9 is brought into contact with the damper cap 7, the outer surface 13 takes up some of the damper fluid 23. Both damper fluid 23 and lubricant 17 are then present on the outer surface 13.

[0058] Due to the additional presence of the lubricant 17, an undesirable stick-slip effect is reliably decreased during continued operation.

[0059] Fig. 3c shows the state after prolonged operation or the state in the case of only very sparing wetting of the outer surface 13 with lubricant 17. The amount of damper fluid 23 and of lubricant 17 on the outer surface 13 is overall very much smaller than in the state shown in Fig. 3b. A significant noise reduction is nevertheless still achieved in the case of such an arrangement relative to a state in which damper fluid 23 but no additional lubricant 17 of a different nature than the damper fluid 23 is present on the outer surface 13.

[0060] It is a particular advantage of the invention that it can also be implemented retrospectively with little expense in existing damper systems. Since a partial and / or very thin coating of the supplementary spring 9 with the lubricant 17 suffices for reliable noise reduction, any envisaged maintenance intervals for renewing the coating can be made correspondingly long.

[0061] In the embodiment, the supplementary spring 9 comprises or consists of microcellular polyurethane.

[0062] The polyether polyol comprises terminal hydroxy groups and wherein less than 50 % of the terminal hydroxy groups are primary hydroxy groups. In a preferred embodiment, less than 25 % of the terminal hydroxy groups are primary hydroxy groups, preferably wherein in particular less than 10 % of the terminal hydroxy groups are primary hydroxy groups.

[0063] The lubricant coating may comprise an area density of more than 0.8 mg / cm2, preferably between 1 .5 mg / cm2and 50 mg / cm2, more preferably between 1 .5 mg / cm2and 10 mg / cm2, very preferably between 3 mg / cm2- 4 mg / cm2.

[0064] Subsequently, the invention will be further described by means of the following examples.

[0065] To identify suitable lubricants that prevent microcellular polyurethane supplementary springs from generating noise when rubbing against a solid surface (e.g. plastic or metal), a specific type of supplementary spring was sprayed or coated with the additive at the upper bending lip. Here, 0.04 g to 0.06 g additive was used. Hard PVC or ABS was used as the surface. Screening tests showed that the type of plastic used has hardly any influence on the noise development. PC, POM and different PA types were tested.

[0066] Initially, a drop of shock absorber oil was applied to the end face 15 (Fig. 1 a).

[0067] The supplementary spring 9 was then repeatedly pressed to the end face 15 and rotated around the piston rod 5 so that there is a transversal movement along the piston rod 5 and a rotational movement on the end face 15 of the damper cap 7. This produced creaking noises on the untreated auxiliary spring. For comparison, a supplementary spring treated with the additive on the outer surface 13 was then tested in the same way.

[0068] For repeated measurements, a drop of shock absorber oil is applied to a fresh end face 15 of a damper cap 7 each time and the same supplementary spring is tested again until noise is observed.

[0069] Unsuitable additives already showed noise development during the first or second measurement and were excluded directly, while effective additives failed only after 10 or more measurements.

[0070] As a suitable additive, a polypropylene glycol with a molecular weight between 7,200 and 9,000 g / mol was identified (“polypropylene glycol 8,000”). In the above set-up, the number of measurements until the first noise was 21 .

[0071] Thereafter, compatibility of the additive with regard to microcellular polyurethane was tested by means of a comparison of tensile strength and elongation of treated and untreated material according to DIN EN ISO 1798. It was the object of the test to determine possible damage to a substrate caused by the action of products on the substrate. The substrate here was microcellular polyurethane (Cellasto®).

[0072] In a first step, at least eight test specimens PK1 were produced from one batch of the substrate. The tensile testing of one part (min. four) of the test specimens was conducted within ten days after production ("original tensile strength"). The other part (min. four) of the test specimens was stored in test medium for 3 days at 100 °C.

[0073] Thereafter, the test specimens were removed from the test medium. They were drained and blotted. After a cooling for 30 to 60 min, a tensile test on stored test specimens (stored material) was conducted and the tensile strengths or elongations at break were compared. In particular, the results were compared with the initial value of the untreated test specimens.

[0074] A decrease in tensile strength of more than 10 % indicates incompatibility or accelerated material degradation, while an almost constant value can be taken as a sign of compatibility. As a reference, a tensile strength of 4.6 (standard deviation 0.3) N / mm2was determined. For the lubricant polypropylene glycol 8,000 a tensile strength of 5.2 (standard deviation 0.5) N / mm2was determined. There has been no decrease in tensile strength when applying polypropylene glycol 8,000 to the test material.

Claims

Claims1 . A shock absorber arrangement (1) for a vehicle suspension, comprising a shock absorber (3) having a damper cap (7), a piston rod (5) and a supplementary spring (9) which is arranged on the piston rod (5) opposite the shock absorber (3) and has an outer surface (13) facing the damper cap (7) and an inner surface (21) facing the piston rod (5) and is configured for damping the movement of the shock absorber (3) in the direction of the piston rod (5) on contact with the damper cap (7), wherein the outer surface (13) and / or the inner surface (21) is at least partially coated with a lubricant (17), characterized in that said lubricant (17) comprises modified or unmodified polyether polyol.

2. The shock absorber arrangement (1) according to claim 1 , wherein the polyether polyol comprises polypropylene glycol.

3. The shock absorber arrangement (1) according to claim 1 or 2, wherein the polyether polyol comprises terminal hydroxy groups, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic.

4. The shock absorber arrangement (1) according to any of the preceding claims, wherein the polyether polyol comprises terminal hydroxy groups, and wherein less than 50 % of the terminal hydroxy groups are primary hydroxy groups, preferably wherein less than 25 % of the terminal hydroxy groups are primary hydroxy groups, in particular wherein less than 10 % of the terminal hydroxy groups are primary hydroxy groups.

5. The shock absorber arrangement (1) according to any of the preceding claims, wherein the supplementary spring (9) comprises polyurethane, in particular microcellular polyurethane.

6. The shock absorber arrangement (1) according to any of the preceding claims, wherein the lubricant coating comprises an area density of more than 0.8 mg / cm2, preferably between 1 .5 mg / cm2and 50 mg / cm2, more preferably between 1 .5 mg / cm2and 10 mg / cm2, very preferably between 3 mg / cm2- 4 mg / cm2.

7. Supplementary spring (9) having an outer surface (13) facing a damper cap (7) of a shock absorber (3) and an inner surface configured to accommodate a piston rod of a shock absorber (3), wherein the outer surface (13) and / or the inner surface (21) is at least partially coated with a lubricant (17), characterized in that said lubricant (17) comprises modified or unmodified polyether polyol.

8. The supplementary spring (9) according to claim 7, wherein the polyether polyol comprises terminal hydroxy groups, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic.

9. The supplementary spring (9) according to claim 8, wherein the supplementary spring (9) comprises polyurethane, in particular microcellular polyurethane.

10. The supplementary spring (9) according to any of claims 7-9, wherein the polyether polyol comprises terminal hydroxy groups, and wherein less than 50 % of the terminal hydroxy groups are primary hydroxy groups, preferably wherein less than 25 % of the terminal hydroxy groups are primary hydroxy groups, in particular wherein less than 10 % of the terminal hydroxy groups are primary hydroxy groups.11 . Method for manufacturing a supplementary spring (9), the supplementary spring (9) having an outer surface (13) facing a damper cap (7) of a shock absorber (3) and an inner surface (21) facing a piston rod (5) of a shock absorber (3), the method comprising the step: coating the outer surface (13) and / or the inner surface (21) at least partially with a lubricant (17), wherein said lubricant (17) comprises modified or unmodified polyether polyol.

12. Method for manufacturing a supplementary spring (9), the method comprising the steps: providing a mold for foaming the supplementary spring (9) therein, applying a release agent to the mold, foaming the supplementary spring (9) in the mold, applying a lubricant (17), wherein said lubricant (17) comprises modified or unmodified polyether polyol, and wherein said lubricant is applied to the mold along withthe release agent and / or after the application of the release agent, and / or as part of the release agent formulation.

13. The use of a lubricant (17) for reducing noise of a shock absorber arrangement (1) comprising a shock absorber (3) having a damper cap (7) and a piston rod (5) and a supplementary spring which is arranged opposite the shock absorber (3) and has an outer surface (13) facing the damper cap (7) and an inner surface (21) facing the piston rod (5) and is configured for damping the movement of the shock absorber (3) in the direction of the piston rod (5) on contact with the damper cap (7), wherein the outer surface (13) and / or the inner surface (21) is at least partially coated with the lubricant (17), characterized in that said lubricant (17) comprises modified or unmodified polyether polyol.

14. The use according to claim 13, wherein the polyether polyol comprises terminal hydroxy groups comprising hydrogen, and wherein for the modified polyether polyol, the terminal hydroxy groups are at least partially reacted so that the hydrogen is replaced by an organic substituent, in particular wherein the organic substituent is alkylic, aromatic or acylic.

15. The use according to claim 13 or 14, wherein the supplementary spring comprises polyurethane, in particular a microcellular polyurethane.

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