NOISE REDUCTION DEVICE FOR HELICAL SPRING.

Abstract

Noise-dampening device for variable-flexibility helical springs consisting of a protective coating formed by a deposit of self-adhesive damping material deposited at room temperature or hot to a thickness of between 2 and 5 mm and located in opposite diametrical planes along three equidistant portions such that each portion of a coil is opposite the portions of the adjacent coil.

Description

NOISE-DAMPENING DEVICE FOR HELICAL SPRING The invention relates to an anti-noise device for a variable-flexibility helical spring, in particular for a motor vehicle suspension spring, part of whose coils may come into mutual contact under the effect of a load. US-A publication 4,753,423 describes a spring whose coils are all coated with a synthetic resin. Applying the coating requires the implementation of a special process designed to increase the adhesion of the coating and to prevent cracking under the effect of impacts between spirals. Publication FR-A 2 350 513 describes a suspension spring sleeve, fitted onto the first coils and sealed at its end to retain a lubricating agent between the spring and the sleeve. Based on this state of the art, the invention aims to simplify previously known construction arrangements by proposing, for example, a deposit of polyurethane or silicone prepolymer deposited at room temperature or hot to a thickness of between 2 mm and 5 mm on the coils located at the end of the spring. According to the invention, the problem is solved in that the coating is formed by a deposit of self-adhesive material with permanent elasticity distributed in opposite diametrical planes of the same turn adjacent to a bare turn. In another embodiment, the self-adhesive material with permanent elasticity is deposited opposite the adjacent spiral. This arrangement offers the advantage of considerably reducing the risk of delamination of the self-adhesive material because, for the same shear stress, the increase in volume results in a reduction of the shear fatigue of said material. Other features of the invention will become apparent upon reading the description of an example embodiment of the spring with reference to the drawing in which: -Figure 1 is a side view of the spring with cross-section partial to show the structure of the spring, -Figures 2 and 3 represent the top views of two coils of the spring coated with the deposit of material self-adhesive, -Figures 4 and 5 are radial sections IV-IV and VV of the spring coils in the areas bearing the coating, -Figure 6 is a side view of the spring with a self-adhesive coating on adjacent spirals, -Figure 7 is a section VI-VI of the spring in the area of ​​adjacent spirals. As shown in Figure 1, reference 10 designates a progressive action spring formed by a spirally wound conical wire. Under these conditions, the wire's cross-section gradually increases from at least one of its supports along a number of turns. When such a spring is subjected to a compressive load, the turns with smaller cross-sections are close together, while the turns with larger cross-sections remain separated. To prevent impacts between the coils during variations in the spring load, the invention provides for the partial coating of the spring with a self-adhesive damping material such as a polyurethane or silicone prepolymer. As shown in the drawing, the damping coating is distributed in two diametrical planes on the upper and lower faces of the same coil 11 or 13 adjacent to a bare coil 12. According to another characteristic of the device, the deposit is located along portions 14a, 14b, 14c of the same spiral. This characteristic is of interest to the coating deposition process due to the programmed passage of the vacuum spring between two nozzles distributing the product at ambient temperature (approximately 20°C). As can be seen in the drawing, the turns 11, 13 carrying the distributed coating come into contact with the bare turn 12 without causing hammering noises as a result of normal variations in load. Under these conditions, the coating which is adhered to the spiral 11 or 13 is also immobilized by its own adhesion to the bare spiral 12, and, if the shear forces are too great to be supported by the elasticity of said coating, it may detach from its attachment spiral 11 or 13. Another embodiment shown in Figures 6 and 7 involves bringing into contact (when the spring is compressed) each strip of coating adhered to a coil in contact with a strip of coating adhered to the adjacent coil. Thus, referring to figure 6, we see that when the spring is compressed, each of the portions 14a, 14b, 14c, of the coils 11 and 13 is opposite an adjacent coil such that: - 14a is opposite 15a and 16a, - 14b is opposite 15b and 16b, - 14c is opposite 10e, 15c, and 16c. In Figure 7, which is a section VI-VI of the spring in a region of adjacent coils, it can be seen that coils 11 and 12 are protected from shock by the contact of the coating strip 14c with the coating strip 15c. This configuration is found three times on each of the coils coming into contact with each other. Without departing from the scope of the invention, the polymerization process can be accelerated by a catalyst such as Betamate E 2400 from GURIT-ESSEX The advantage of the device lies in the fact that the implementation of the device is carried out on springs already protected against corrosion and at ambient temperature.

Claims

DEMANDS 1. Noise-dampening device for helical springs Variable flexibility consisting of a coating protective layer formed by a deposit of damping material self-adhesive like polyurethane prepolymer placed at room temperature or hot on a thickness between 2 and 5 mm and located in opposite diametrical planes along three portions equidistant, characterized in that each of the portions 14a, 14b, 14c, of turns 11 and 13 is in with respect to a portion of an adjacent turn such that: 14a is opposite 15a and 16a 14b is opposite 15b and: 14c is opposite 10e, 15c, and 16c.