HELICAL COMPRESSION SPRING FOR AN ACTUATOR FOR OPENING AND CLOSING A DOOR OR A TAILGATE OF A CAR

Abstract

A helical compression spring has an outer diameter between 15 and 50 mm. The helical compression spring having a helically coiled steel wire. The diameter d of the steel wire is between 2 and 5 mm. The steel wire contains a steel alloy having between 0.8 and 0.95 wt % C; between 0.2 and 0.9 wt % Mn; between 0.1 and 1.4 wt % Si; between 0.15 and 0.4 wt % Cr; optionally between 0.04 and 0.2 wt % V; optionally between 0.0005 and 0.008 wt % B; optionally between 0.02 and 0.06 wt % Al; unavoidable impurities; and the balance being iron. The steel alloy has a carbon equivalent higher than 1. The carbon equivalent is defined as: C wt %+(Mn wt %/6)+(Si wt %/5)+(Cr wt %/5)+(V wt %/5). The microstructure of the steel wire in the helical compression spring is drawn lamellar pearlite.

Claims

1. Helical compression spring, preferably for use in an actuator for opening and closing a door or a tailgate of a car, wherein the helical compression spring has an outer diameter between 15 and 50 mm; wherein the helical compression spring comprises a helically coiled steel wire; wherein the diameter d (in mm) of the steel wire is between 2 and 5 mm; wherein the steel wire comprises a steel alloy; wherein the steel alloy consists out of between 0.8 and 0.95 wt % C; between 0.2 and 0.9 wt % Mn; between 0.1 and 1.4 wt % Si; between 0.15 and 0.4 wt % Cr; optionally between 0.04 and 0.2 wt % V; optionally between 0.0005 and 0.008 wt % B; optionally between 0.02 and 0.06 wt % Al; unavoidable impurities; and the balance being iron; wherein the steel alloy has a carbon equivalent higher than 1, wherein the carbon equivalent is defined as: C wt %+(Mn wt %/6)+(Si wt %/5)+(Cr wt %/5)+(V wt %/5); wherein the microstructure of the steel wire in the helical compression spring is drawn lamellar pearlite.

2. Helical compression spring as in claim 1, wherein the steel wire used for helically coiling the helical compression spring has a tensile strength R.sub.m (in MPa) higher than the value calculated by the formula 2680−390.71*ln(d).

3. Helical compression spring as in claim 1; wherein the steel alloy comprises between 0.2 and 0.6 wt % Mn; or wherein the steel alloy comprises between 0.6 and 0.9 wt % Mn.

4. Helical compression spring as in claim 1, wherein the microstructure of the steel wire in the helical compression spring comprises more than 97% by volume of drawn pearlite.

5. Helical compression spring as in claim 1, wherein the microstructure of the steel wire in the helical compression spring comprises between 0.2 and 2% by volume of bainite.

6. Helical compression spring as in claim 1, wherein the helically coiled steel wire comprises a phosphate coating.

7. Helical compression spring as in claim 1, wherein the helically coiled steel wire comprises a metallic coating layer; wherein the metallic coating layer comprises at least 84% by mass of zinc; and preferably aluminum.

8. Helical compression spring as in claim 7, wherein the metallic coating layer comprises at least 86% by mass of zinc; and between 4 and 14% by mass of aluminum; and optionally magnesium and/or silicon.

9. Helical compression spring as in claim 7, wherein the metallic coating layer consists out of zinc, between 3 and 8 wt % aluminum; optionally between 0.2 and 1 wt % Mg, optionally up to 0.1 wt % rare earth elements; and unavoidable impurities.

10. Helical compression spring as in claim 1, wherein the steel alloy comprises between 0.15 and 0.35 wt % Si, or wherein the steel alloy comprises between 0.6 and 0.8 wt % Si, or wherein the steel alloy comprises between 0.8 and 1.4 wt % Si.

11. Helical compression spring as in claim 1, wherein the steel alloy consists out of between 0.83 and 0.89 wt % C, between 0.55 and 0.7 wt % Mn, between 0.1 and 0.4 wt % Si, between 0.15 and 0.3 wt % Cr, between 0.04 and 0.08 wt % V, optionally between 0.02 and 0.06 wt % Al; unavoidable impurities and the balance being iron.

12. Method for making a helical compression spring as in claim 1; comprising the steps of providing a steel wire rod; patenting the steel wire rod or a steel wire drawn from the steel wire rod, in order to obtain a pearlitic microstructure; drawing, with drawing reduction more than 75%, the patented steel wire rod having a pearlitic microstructure or the patented steel wire having a pearlitic microstructure; thereby obtaining a steel wire with drawn pearlitic microstructure, with diameter d (in mm) between 2 and 5 mm; helically coiling the steel wire into a helical spring; optionally performing a thermal stress relieving on the helical spring; wherein the steel wire rod comprises a steel alloy; wherein the steel alloy consists out of between 0.8 and 0.95 wt % C; between 0.2 and 0.9 wt % Mn; between 0.1 and 1.4 wt % Si; between 0.15 and 0.4 wt % Cr; optionally between 0.04 and 0.2 wt % V; optionally between 0.0005 and 0.008 wt % B; optionally between 0.02 and 0.06 wt % Al; unavoidable impurities; and the balance being iron; wherein the steel alloy has a carbon equivalent higher than 1, wherein the carbon equivalent is defined as: C wt %+(Mn wt %/6)+(Si wt %/5)+(Cr wt %/5)+(V wt %/5).

13. Method as in claim 12; wherein by the drawing operation a steel wire with diameter d (in mm) between 2 and 5 mm having tensile strength R.sub.m (in MPa) higher than the value calculated by the formula: 2680−390.71*ln(d) is obtained.

14. Method as in claim 12; wherein after the patenting operation; and before drawing or between drawing steps a metallic coating is applied on the steel wire via hot dip, wherein the metallic coating comprises at least 84% by mass of zinc; and preferably aluminum.

15. Actuator for opening and closing a door or a tailgate of a car, comprising a helical compression spring as in claim 1, for opening a door or the tailgate of a car when compressive forces of the helical compression spring are released; and a motor, for compressing the helical compression spring in order to close the door or the tailgate of the car.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0066] FIG. 1 shows an SUV comprising an actuator for opening and closing its tailgate.

[0067] FIG. 2 shows an actuator for opening and closing a tailgate of a car.

[0068] FIG. 3 shows a helical compression spring as in the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0069]

TABLE-US-00001 TABLE I Examples of steel alloys that can be used in the invention. C (wt %) Mn (wt %) Si (wt %) Cr (wt %) V (wt %) Al (wt %) Alloy min max min max min max min max min max min max A 0.84 0.88 0.60 0.70 0.15 0.35 0.20 0.30 0.04 0.09 0.02 0.06 B 0.84 0.88 0.60 0.70 0.60 0.80 0.20 0.30 0.04 0.09 0.02 0.06 C 0.80 0.84 0.70 0.85 0.15 0.35 0.20 0.30 0.05 0.08 0.02 0.06 D 0.90 0.95 0.25 0.45 0.15 0.30 0.15 0.30 0.01 E 0.90 0.95 0.25 0.45 1.10 1.30 0.15 0.30 0.01 G 0.90 0.95 0.30 0.60 1.10 1.30 0.20 0.40 H 0.90 0.95 0.30 0.60 1.10 1.30 0.20 0.40 0.04 I 0.88 0.94 0.35 0.55 1.10 1.30 0.20 0.30 J 0.90 0.94 0.35 0.55 1.20 1.40 0.20 0.40 K 0.85 0.90 0.60 0.70 0.15 0.35 0.20 0.30 0.04 0.08 0.02 0.06

[0070] FIG. 1 shows an SUV 12 comprising a tailgate 14 and an actuator 16 for opening and closing the tailgate. The actuator 16 (FIG. 2 shows the actuator 16 for opening and closing the tailgate of a car) comprises a helical compression spring 18 and a motor 20. The actuator comprises two connectors 22, 23, one for connecting the actuator to the door or to the tailgate; and the other one for connecting the actuator to the body of the car. The helical compression spring is provided for opening the tailgate when compressive forces of the helical compression spring are released. The motor is provided for compressing the helical compression spring in order to close the tailgate. An example of a helical compression spring that can be used is shown in FIG. 3, such spring has a length L and a pitch p.

[0071] The helical compression spring comprises a helically coiled steel wire. The diameter d (in mm) of the helically coiled coated steel wire is between 2 and 5 mm.

[0072] Table I provides specific examples of steel alloys (with minimum and maximum wt % of the elements in the steel alloy) that can be used for the steel core in the invention. The microstructure of the steel wire in the helically coiled steel wire is drawn lamellar pearlite.

[0073] A specific example of such helical compression spring has been coiled with a steel wire having a drawn pearlitic microstructure and 3.4 mm diameter. The helical compression spring has a length L 0.8 m in unloaded condition. The spring index of the exemplary helical spring is 6.5. The pitch p of the spring is 15.2 mm. The outer diameter of the helical compression spring is 26.8 mm. However not essential for the invention, the steel wire was provided with a metallic coating layer comprising zinc and aluminum.

[0074] In order to manufacture the steel wire used for coiling the helical compression spring, a steel wire rod of 10 mm diameter was used.

[0075] The steel wire rod was out of a steel alloy consisting out of 0.86 wt % C, 0.63 wt % Mn, 0.2 wt % Si, 0.22 wt % Cr, 0.06 wt % V; 0.04 wt % Al; unavoidable impurities and the balance being iron. This is an alloy of composition “A” of table I. The carbon equivalent is: 0.86+(0.63/6)+(0.2/5)+(0.22/5)+(0.06/5)=1.169.

[0076] The 10 mm diameter steel wire rod has been patented to provide it with a pearlitic microstructure; and—although not essential for the invention—has then been provided with a metallic coating via hot dip. The hot dip process used was a double dip process in which the steel wire was first dipped in a bath of molten zinc; followed by dipping the steel wire in a bath comprising 10% by weight of aluminium and the remainder being zinc. The metallic coating layer of the hot dipped steel wire consisted of 10 wt % aluminum and the balance being zinc.

[0077] The patented—and hot dipped—wire rod of 10 mm diameter has been drawn to a steel wire of 3.4 mm diameter; this means that a drawing reduction of 88.4% has been applied. The resulting steel wire has a drawn pearlitic microstructure. The tensile strength Rm of the steel wire is 2354 MPa; the Rp0.2 value is 1990 MPa, which is 84.5% of the Rm value. The percentage reduction of area Z at break in tensile testing of the steel wire is 44.1%.

[0078] The metallic coating on the drawn wire of 3.4 mm was 45 g/m.sup.2.

[0079] After coiling this coated steel wire into a helical compression spring a thermal stress relieving operation was performed, e.g. by keeping the helical compression spring in unloaded condition at 250° C. during 30 minutes.

[0080] The coated steel wire comprised an intermetallic coating layer between the steel core and the metallic coating layer. The intermetallic coating layer provided 45% of the combined thickness of the intermetallic coating layer and the metallic coating layer. The intermetallic coating layer comprises a Fe.sub.xAl.sub.y phase. It has been observed that the metallic coating layer comprised a globularized aluminum rich phase.

[0081] Samples of the steel wire used for making the helical spring have been subject to a thermal treatment in an oven during 30 minutes at an oven temperature of 250° C. After this thermal treatment, tensile testing has been performed on the steel wire sample: the tensile strength Rm is 2426 MPa; the Rp0.2 value is 2366 MPa, which is 97.5% of the tensile strength Rm; and the percentage reduction of area Z at break was 42%.

[0082] Analysis of the steel wire of the helical compression spring has shown that the steel has a drawn pearlite microstructure, with more than 97% by volume of drawn pearlite and about 1% by volume of bainite.

[0083] The helical compression spring was used in an actuator for a tailgate opening and closing actuator of a car. The metallic coating of the coated steel wire provided the surface of the helical compression spring.