Self-tapping fixing screw

Abstract

Self-tapping fixing screw. The fixing screw has a screw head (4), a threaded shank (8) with at least one thread (28), and a pilot tip (10) that is frustoconical and smooth. Figure for abbreviation: Figure 1

Description

Title of the invention: Self-tapping fixing screw

[0001] The present invention relates to the field of fixing screws, and in particular a self-tapping fixing screw, in particular a self-tapping fixing screw adapted for screwing into a hole made in a body made of plastic material.

[0002] There are strong cost constraints in the field of vehicles, and in particular motor vehicles, as well as constraints of mechanical performance, size and ease of assembly.

[0003] One of the aims of the invention is to provide a self-tapping fixing screw that can be easily positioned in a hole, the screw ensuring an effective and reliable fixing, while having a limited length.

[0004] To this end, the invention proposes a self-tapping fixing screw comprising a screw head, a threaded rod provided with at least one thread and a smooth frustoconical pilot end.

[0005] In particular embodiments, the screw comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0006] - the pilot tip has a minimum diameter between 1 mm and 2 mm;

[0007] - the pilot tip has an axial length between 0.3 mm and 0.8 mm;

[0008] - the threaded rod includes a distal section joined to the pilot end, on which the thread presents a gradually decreasing height;

[0009] - the height of the net decreases until it becomes zero;

[0010] - the height of the net decreases over a fraction of a loop of the net;

[0011] - the net ends at a non-zero axial distance from the pilot end;

[0012] - the axial distance between the terminal end of the thread and the pilot end is included between 0.3 mm and 0.5 mm;

[0013] - the threaded rod has a proximal section on which the thread has a height constant over several turns;

[0014] - the screw includes a collar, preferably smooth, located axially between the screw head and the threaded rod;

[0015] - the axial length of the collar is between 0 mm and 1 mm;

[0016] - the axial distance between the free end of the pilot end and the screw head is included between 10 mm and 14 mm;

[0017] - the axial length of the screw head is between 2 mm and 3 mm;

[0018] - the net has an angle at the top between 25° and 30°;

[0019] - in which the threaded rod has at least one V-profiled thread root;

[0020] - each net bottom 36 is delimited by two lateral walls 38,

[0021] - each lateral wall 38 joins a side 34 of a net 28 at a non-zero angle with side 34;

[0022] - the bottom fillet angle formed between the two side walls 38, is preferably between 110° and 130°, preferably approximately equal to 120°.

[0023] The invention and its advantages will be better understood upon reading the following description, given solely by way of example, and made with reference to the accompanying drawings, in which:

[0024] - [Fig. 1] [Fig. 1] is a side view of a screw and the entrance of a receiving hole of the screw;

[0025] - [Fig.2] [Fig.2] is a partial axial cross-sectional view of a threaded rod of the screw the [Fig. 1]; and

[0026] - [Fig.3] [Fig.3] is a top view of the screw illustrating the screw head.

[0027] Screw 2 in Figures 1 to 3 is a self-tapping fastening screw. Screw 2 extends along a longitudinal axis A, and comprises, successively along the longitudinal axis A, a screw head 4, optionally a collar 6, a threaded rod 8 and a pilot end 10.

[0028] The screw 2 is intended for fixing parts together. The screw 2 is intended to be screwed into a hole 12 provided in a body 14, for example a body 14 made of plastic.

[0029] The screw 2, which is self-tapping, is intended to form a thread in the initially smooth hole 12 when the screw 2 is first screwed into the hole 12.

[0030] The screw head 4 has a lower surface 16 by which the screw head 4 is intended to bear against a part fixed by means of the screw 2.

[0031] The lower surface 16 is oriented axially towards the threaded rod 8. The lower surface 16 is for example a radial surface, i.e. planar and perpendicular to the longitudinal axis A of the screw 2.

[0032] The screw head 4 has at least one relief suitable for cooperating with a tool for driving the screw 2 in rotation around its longitudinal axis A.

[0033] The screw head 4 has a top surface 18 oriented opposite to the threaded rod 8.

[0034] The upper surface 18 is for example provided with a recessed imprint configured for the rotational drive of the screw 2, preferably using a tool.

[0035] As illustrated, the upper surface 18 has, for example, a multilobed imprint 20 with six lobes.

[0036] Other imprints are conceivable.

[0037] For example, alternatively, the upper surface 18 is provided with a slot (slotted head), a cruciform indentation, a hexagonal indentation, a square indentation or an indentation with two spaced holes.

[0038] Alternatively or as an option, the screw head 4 is externally driven, the screw head 4 presenting an outline that allows it to cooperate with a complementary training tool.

[0039] The screw head 4 is for example hexagonal, square or external lobed.

[0040] The screw head 4 has, for example, a central domed part 22, extended ra- diamentally outwards by a peripheral radial part 24 in the shape of a collar surrounding the central part 22.

[0041] The central part 22 has for example a truncated vertex having a radial planar face 22A.

[0042] In this case, if an imprint 20 is provided, it is for example formed in the flat face 22A.

[0043] The collar 6 is optional. Alternatively, the screw 2 is without a collar 6, the screw head 4 and the threaded rod 8 being joined.

[0044] When the screw 2 has the collar 6, the latter is located axially between the screw head 4 and the threaded rod 8. The collar 6 connects the screw head 4 to the threaded rod.

[0045] The collar 6 preferably has a smooth external surface 6A.

[0046] The threaded rod 8 has a central core 26 and a thread 28 extending helix around the longitudinal axis A.

[0047] The threaded rod 8 comprises, for example, a single thread 28. Alternatively, the threaded rod 8 comprises several similar threads 28.

[0048] The net 28 comprises a base 30, a top 32 and two lateral sides 34 joining at the top 32 of the net 28

[0049] The angle at the apex a, which is the angle formed between the sides 34 of the net 28 meeting at the apex 32, is preferably between 25° and 35°.

[0050] The threaded rod 8 has at least one thread root 36, each thread root 36 being located between the turns of the same thread 28 or between two adjacent threads 28).

[0051] Each fillet bottom 36 is preferably V-profiled.

[0052] Each net bottom 36 is delimited by two lateral walls 38. Each wall lateral 38 joins a flank 34 of a thread, in particular a respective flank of the thread 28 (when the screw 2 has a single thread 28) or of two adjacent threads 28 (when the screw 2 has at least two threads 28), making a non-zero angle with the flank 34.

[0053] The bottom fillet angle [3, formed between the two side walls 38 of each bottom fillet 28, is preferably between 110° and 130°, preferably about equal to 120°.

[0054] The height H of the net 28 is taken radially between the lowest point 40 of the bottom of the net 36 (closest to the longitudinal axis A) and the top 32 of the net 28.

[0055] The thread 28 is of the self-tapping type and is suitable for screwing into a hole in a plastic body. The shallow apex angle allows the thread 28 to form a thread inside the hole 12 during the initial tightening of the screw 2. The root of the thread 36 profile allows the creep of the plastic material pushed back due to the formation of the tapping during the first screwing.

[0056] The threaded rod 8 has a proximal section 42, adjacent to the screw head 4, and a distal section 44, distant from the screw head 4 and abutting the pilot end 10. The thread 28 extends continuously over the proximal section 42 and the distal section 44

[0057] On the proximal section 42, preferably, the thread 28 has several turns and a constant profile. In particular, the thread 28 has a constant height on the proximal section 42.

[0058] On the distal section 44, the thread 28 advantageously has a variable profile. In particular, the thread 28 has a progressively decreasing height on the distal section 44 until it becomes zero before the pilot end 10, here at a non-zero distance from the pilot end 10.

[0059] The thread 28 advantageously has a decreasing height over a fraction of a turn or over more than one turn, preferably over a fraction of a turn.

[0060] The net 28 has a terminal end 28C at which its height is zero, and which is spaced at a non-zero axial distance from the pilot end 10.

[0061] Due to the decrease and the stopping of the thread 28, the distal section 44 has a guiding portion 46 without a thread, which is smooth and extends over at least a fraction of the circumference of the threaded rod 8.

[0062] The optional guide portion 46 extends axially between the junction of the threaded rod 8 with the pilot end 10 and the first turn of the thread 8.

[0063] The guiding portion 46 is at least a cylindrical surface portion, preferably with a diameter equal to the diameter of the core 26 of the rod, i.e. to the diameter of the threaded rod 8 taken at the lowest point 40 of the thread root 36.

[0064] As illustrated in [Fig. 1], the guide portion 46 extends axially, for example, beyond the terminal end 28A of the thread 28, presenting a smooth cylindrical surface on this extension. The length of this extension is small here and could be increased.

[0065] The pilot tip 10 is a terminal part of the screw 2.

[0066] The pilot end 10 axially extends the threaded rod 8, more precisely here the section distal 44 of the threaded rod 8, converging opposite the threaded rod 8.

[0067] The pilot end is preferably frustoconical and smooth.

[0068] The pilot end 10 has a smooth frustoconical lateral surface 10A.

[0069] The pilot end 10 has, for example, a flat and radial terminal face 10B, i.e. perpendicular to the longitudinal axis A. The terminal face 10B is preferably circular.

[0070] The pilot end 10 has, for example, a maximum diameter equal to that of the core 26 and a minimum diameter corresponding to that of its terminal face 10B.

[0071] The screw 2 advantageously has the following dimensions:

[0072] - the overall axial length L1 of the screw 2 is, for example, between 13 mm and 16 mm;

[0073] - the axial length L2 of the screw head 4, taken between the lower surface 16 and the flat face 24A, for example, is between 2 mm and 3 mm;

[0074] - the axial length L3 of the collar 6 is between 0 mm and 1 mm;

[0075] - the axial length L4 of the threaded rod 8 is, for example, between 10mm and 12 mm;

[0076] - the axial length L5 of the pilot end 10 is between 0.3 mm and 0.8 mm;

[0077] - the axial length L6 under the head of the screw 2, taken between the head of the screw 4 and the end free from the pilot end 10, is for example between 10 mm and 14 mm;

[0078] - the minimum diameter of the pilot end 10 (here the diameter of the terminal face 10B) is between 1 mm and 2 mm;

[0079] - the axial distance between the terminal end 28C of the thread 28 and the pilot end 10 is between 0.3 mm and 0.5 mm;

[0080] - the threaded rod 8 has a thread root diameter DI between 2 mm and 2.5 mm; and / or

[0081] - the threaded rod 8 has a thread crest diameter D2 between 4 mm and 4.5 mm.

[0082] During the first screwing of the screw 2 into the hole 12, the pilot end 10 allows the screw 2 to be guided and centered with respect to the hole 12 reliably, before initiating the screwing, without it being necessary to provide a counterbore at the entrance of the hole 12.

[0083] The pilot end 10 and the guide part 46, advantageously smooth, facilitate the mounting of the screw 2 for an operator.

[0084] The pilot end 10 and the guide part 46 of the threaded rod 8 ensure good satisfactory centering over a short axial length.

[0085] The thread 28 has a constant maximum height over a relatively large axial length compared to the overall axial length of the screw 2.

[0086] The absence of counterboring in the hole 14 allows the most adjacent portion of the thread 28 to be in contact with the internal surface of the hole 14, and thus to increase the useful length of the thread 28 on the side of the screw head 4.

[0087] This ensures good fixing using screw 2, while maintaining a limited axial screw length compatible with the use of screw 2 for applications where available space is restricted.

[0088] The screw 2 is also easy to manufacture and package, in particular because of the absence of a point.

Claims

Claims

1. Self-tapping fixing screw comprising a screw head (4), a threaded rod (8) provided with at least one thread (28) and a smooth frustoconical pilot end (10).

2. A screw according to claim 1, wherein the pilot tip (10) has a minimum diameter of between 1 mm and 2 mm.

3. A screw according to claim 1 or 2, wherein the pilot tip (10) has an axial length of between 0.3 mm and 0.8 mm.

4. Screw according to any one of the preceding claims, in which the threaded rod (8) comprises a distal section (44) adjoining the pilot end (10), on which the thread (28) has a progressively decreasing height.

5. A screw according to claim 4, wherein the height of the thread (28) decreases until it is zero.

6. A screw according to claim 4 or 5, wherein the height of the thread (28) decreases over a fraction of a turn of the thread (28).

7. A screw according to any preceding claim, wherein the thread (28) terminates at a non-zero axial distance from the pilot tip (10).

8. A screw according to claim 8, wherein the axial distance between the terminal end (28C) of the thread (28) and the pilot tip (10) is between 0.3 mm and 0.5 mm.

9. A screw according to any preceding claim, wherein the threaded rod (8) has a proximal section (42) on which the thread (28) has a constant height over several turns.

10. Screw according to any one of the preceding claims, comprising a collar (6), preferably smooth, located axially between the screw head (4) and the threaded rod (8).

11. Screw according to claim 10, wherein the axial length of the collar (6) is between 0 mm and 1 mm.

12. A screw according to any preceding claim, wherein the axial distance between the free end of the pilot tip (10) and the screw head (4) is between 10 mm and 14 mm.

13. A screw according to any preceding claim, wherein the axial length of the screw head (4) is between 2 mm and 3 mm.

14. A screw according to any preceding claim, in which the thread (28) has an apex angle of between 25° and 30°.

15. Screw according to any one of the preceding claims, in which the threaded rod (8) has at least one V-shaped thread root (36).

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