HELICAL COMPRESSION SPRING WITH NON-ROUND CROSSSECTION FOR AN ACTUATOR FOR OPENING AND CLOSING A DOOR OR A TAILGATE OF A CAR

Abstract

Helical compression spring for use in an actuator for opening and closing a door or a tailgate of a car has an outer diameter between 15 and 50 mm and comprises a helically coiled steel wire. The steel wire has a non-circular cross-section with an equivalent diameter d (in mm) of the steel wire is between 1 mm and 12 mm. The cross-section may have at least two opposing parallel sides. The cross-section further has rounded edges, wherein the rounded edges have a radius of curvature ranging from 0.10 mm to 5.0 mm. The microstructure of the steel wire in the helical compression spring is cold deformed pearlite. In comparison with helical compression springs with round cross-sections, the non-round helical compression springs may occupy less space or reach higher breaking loads within the same space.

Claims

1. A helical compression spring 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 steel wire has a non-circular cross-section, wherein the equivalent diameter d (in mm) of the steel wire is between 1 mm and 12 mm, wherein said cross-section has at least two opposing parallel sides, wherein said cross-section further has rounded edges, wherein said rounded edges have a radius of curvature ranging from 0.10 mm to 5.0 mm, and wherein the microstructure of the steel wire in the helical compression spring is cold deformed pearlite.

2. The helical compression spring according to claim 1, wherein said rounded edges have a radius of curvature ranging from 0.15 mm to 1.0 mm.

3. The helical compression spring according to claim 1, wherein said cross-section has the form of a trapezium.

4. The helical compression spring according to claim 3, wherein said trapezium has two acute angles and two obtuse angles, said acute angles having radii of curvature differing from the radii of curvature of the obtuse angles.

5. The helical compression spring according to claim 3, said helically coiled steel wire making bends to obtain a helix form, the longest side of said trapezium being located at the inner side of the bends.

6. The helical compression spring according to claim 1, said cross-section further comprising two additional opposing parallel sides.

7. The helical compression spring according to claim 1, wherein said cross-section comprises only two opposing parallel sides that are connected with rounded edges.

8. Helical A helical compression spring, 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 steel wire has a non-circular cross-section, wherein the equivalent diameter d (in mm) of the steel wire is between 1 mm and 12 mm, wherein said cross-section is oval or elliptical, wherein the microstructure of the steel wire in the helical compression spring is cold deformed pearlite.

9. The helical compression spring according to claim 1, wherein said equivalent diameter d (in mm) of the steel wire is between 2.8 mm and 5.6 mm.

10. The helical compression spring according to claim 1, wherein said steel wire has a phosphate coating.

11. The helical compression spring according to claim 1, wherein said steel wire has zinc aluminium coating, the amount of aluminium ranging from 3% to 17% in said coating, the remainder being zinc.

12. The helical compression spring according to claim 11, said zinc aluminium coating having a weight ranging from 10 g/m.sup.2 to 250 g/m.sup.2.

13. The helical compression spring according to claim 11, said zinc aluminium coating having a weight ranging from 25 g/m.sup.2 to 150 g/m.sup.2.

14. The helical compression spring according to claim 4, said helically coiled steel wire making bends to obtain a helix form, the longest side of said trapezium being located at the inner side of the bends.

15. The helical compression spring according to claim 8, wherein said equivalent diameter d (in mm) of the steel wire is between 2.8 mm and 5.6 mm.

16. The helical compression spring according to claim 8, wherein said steel wire has a phosphate coating.

17. The helical compression spring according to claim 8, wherein said steel wire has zinc aluminium coating, the amount of aluminium ranging from 3% to 17% in said coating, the remainder being zinc.

18. The helical compression spring according to claim 17, said zinc aluminium coating having a weight ranging from 10 g/m.sup.2 to 250 g/m.sup.2.

19. The helical compression spring according to claim 17, said zinc aluminium coating having a weight ranging from 25 g/m.sup.2 to 150 g/m.sup.2.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0082] FIG. 1 shows an SUV comprising an actuator for opening and closing its tailgate.

[0083] FIG. 2 shows an actuator for opening and closing a tailgate of a car.

[0084] FIG. 3 shows a helical compression spring as in the invention.

[0085] FIG. 4 shows a square cross-section of a steel wire.

[0086] FIG. 5 shows an elliptical cross-section of a steel wire.

MODE(S) FOR CARRYING OUT THE INVENTION

[0087]

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

[0088] 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.

[0089] The helical compression spring comprises a helically coiled steel wire. The equivalent diameter d (in mm) of the helically coiled coated steel wire is between 1 and 12 mm.

[0090] 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 cold deformed lamellar pearlite.

[0091] A specific example of such helical compression spring has been coiled with a steel wire having a cold deformed 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.

[0092] In order to manufacture the steel wire used for coiling the helical compression spring, a steel wire rod of 10 mm diameter was used.

[0093] 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.

[0094] 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.

[0095] The patented—and hot dipped—wire rod of 10 mm diameter has been cold deformed to a steel wire of 3.4 mm equivalent diameter; this means that a deformation reduction of 88.4% has been applied. The resulting steel wire has a deformed pearlitic microstructure. The tensile strength R.sub.m of the steel wire is 2354 MPa; the Rp0.2 value is 1990 MPa, which is 84.5% of the R.sub.m value. The percentage reduction of area Z at break in tensile testing of the steel wire is 44.1%.

[0096] The metallic coating on the cold deformed wire of 3.4 mm was 45 g/m.sup.2.

[0097] 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.

[0098] 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.

[0099] 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 R.sub.m is 2426 MPa; the Rp0.2 value is 2366 MPa, which is 97.5% of the tensile strength R.sub.m; and the percentage reduction of area Z at break was 42%.

[0100] Analysis of the steel wire of the helical compression spring has shown that the steel has a cold deformed pearlite microstructure, with more than 97% by volume of cold deformed pearlite and about 1% by volume of bainite.

[0101] 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.

Example for Using the Same Available Space, but Achieve Higher Total Strength

[0102] A patented and cold drawn round steel wire provided with a zinc alloy coating for a helical compression spring with a diameter of 3.50 mm has a minimum tensile strength of 2190 MPa or a minimum breaking load of 21075 Newton.

[0103] Using the same confined space, a 3.50 mm×3.50 mm square patented and cold deformed steel wire with radii of curvature of 0.35 mm has an equivalent diameter of 3.93 mm and the cross sectional area of this profile is 12.14 mm.sup.2. Using the same formula as above (but with diameter replaced by equivalent diameter), the minimum tensile strength is 2145 MPa or a minimum breaking load of 26043 Newton, or 23% higher than in case of the round embodiment.

Example for Using Same Total Strength, but Making the Wire Smaller

[0104] In order to achieve a tensile strength of 1970 MPa or a breaking load of 18953 Newton, a round patented and drawn steel wire must have a diameter of 3.30 mm.

[0105] To achieve the same total strength of 18953 Newton with patented and cold deformed square steel wire, the dimensions must be 2.94×2.94 mm with radii of curvature of of 0.35 mm. S.sub.o a reduction of more than 10% in linear dimension is achieved.