Method for forming a captive spacer housed in a mounting base of an accelerometer sensor and sensor equipped with such a mounting base

1. A method for forming a spacer ( 3 ) extending at least partially within the length of a central bore ( 4 ) passing from one side to the other of a barrel ( 2 a ) of a mounting base ( 2 ) of an accelerometer sensor ( 1 ), the central bore ( 4 ) being designed to receive a fastening element ( 5 ) for fixing the mounting base ( 2 ) onto a support element, the fastening element ( 5 ) being centered by the spacer ( 3 ) in the central bore ( 4 ), the mounting base ( 2 ) being at least partially surrounded by an encapsulation ( 7 ) of overmolded plastic material, wherein, when the plastic material is overmolded around the mounting base ( 2 ) to form the encapsulation ( 7 ), part of the plastic material passes through the barrel ( 2 a ) to form the spacer ( 3 ) while fixing it to the encapsulation ( 7 ).

2. The method as claimed in claim 1 , wherein, before the overmolding of the encapsulation ( 7 ) and the fixed spacer ( 3 ), a core ( 6 c ) having a shape similar to that of the fastening element ( 5 ) is positioned in the central bore ( 4 ) of the barrel ( 2 a ) of the mounting base ( 2 ), the core ( 6 c ) having at least one shoulder ( 22 ) contacting the wall of the central bore ( 4 ) and forming, during the overmolding, a stop for a longitudinal end ( 4 a ) of the fixed spacer ( 3 ).

3. A mounting base ( 2 ) for an accelerometer sensor ( 1 ) for the application of the method as claimed in claim 2 , wherein the barrel ( 2 a ) of the mounting base ( 2 ) is pierced by at least one channel ( 8 ) having, on the one hand, an inlet end ( 8 a ) opening outside the barrel ( 2 a ) on a portion of the barrel ( 2 a ) to be surrounded by the encapsulation ( 7 ), and, on the other hand, an outlet end ( 8 b ) opening into the central bore ( 4 ) of the barrel ( 2 a ).

4. The mounting base ( 2 ) as claimed in claim 3 , wherein said at least one channel ( 8 ) opens into the central bore ( 4 ) near a first longitudinal end ( 4 a ) of the central bore ( 4 ) opposite a second longitudinal end ( 4 b ) which is to be fixed onto the support element.

5. The mounting base ( 2 ) as claimed in claim 3 , wherein said at least one channel ( 8 ) opens into the central bore ( 4 ) near a first longitudinal end ( 4 a ) of the central bore ( 4 ) opposite a second longitudinal end ( 4 b ) which is to be fixed onto the support element.

6. A mounting base ( 2 ) for an accelerometer sensor ( 1 ) for the application of the method as claimed in claim 1 , wherein the barrel ( 2 a ) of the mounting base ( 2 ) is pierced by at least one channel ( 8 ) having, on the one hand, an inlet end ( 8 a ) opening outside the barrel ( 2 a ) on a portion of the barrel ( 2 a ) to be surrounded by the encapsulation ( 7 ), and, on the other hand, an outlet end ( 8 b ) opening into the central bore ( 4 ) of the barrel ( 2 a ).

7. The mounting base ( 2 ) as claimed in claim 6 , wherein the barrel ( 2 a ) of the mounting base ( 2 ) comprises a plurality of channels ( 8 ) whose outlet ends ( 8 b ) are distributed regularly around the whole of the central bore ( 4 ).

8. The mounting base ( 2 ) as claimed in claim 6 , wherein said at least one channel ( 8 ) opens into the central bore ( 4 ) near a first longitudinal end ( 4 a ) of the central bore ( 4 ) opposite a second longitudinal end ( 4 b ) which is to be fixed onto the support element.

9. The mounting base ( 2 ) as claimed in claim 8 , wherein the barrel ( 2 a ) of the mounting base ( 2 ) comprises a plurality of channels ( 8 ) whose outlet ends ( 8 b ) are distributed regularly around the whole of the central bore ( 4 ).

10. The mounting base ( 2 ) as claimed in claim 6 , wherein said at least one channel ( 8 ) extends substantially perpendicularly to the central bore ( 4 ).

11. The mounting base ( 2 ) as claimed in claim 10 , wherein the barrel ( 2 a ) of the mounting base ( 2 ) comprises a plurality of channels ( 8 ) whose outlet ends ( 8 b ) are distributed regularly around the whole of the central bore ( 4 ).

12. The mounting base ( 2 ) as claimed in claim 10 , wherein said at least one channel ( 8 ) opens into the central bore ( 4 ) near a first longitudinal end ( 4 a ) of the central bore ( 4 ) opposite a second longitudinal end ( 4 b ) which is to be fixed onto the support element.

13. The mounting base ( 2 ) as claimed in claim 12 , wherein said at least one channel ( 8 ) opens into the central bore ( 4 ) near a first longitudinal end ( 4 a ) of the central bore ( 4 ) opposite a second longitudinal end ( 4 b ) which is to be fixed onto the support element.

14. An accelerometer sensor ( 1 ) comprising a mounting base ( 7 ) with a barrel ( 2 a ) having a central bore ( 4 ) which receives a fastening element ( 5 ) designed to fix the accelerometer sensor ( 1 ) onto a support element, the central bore ( 4 ) comprising a spacer ( 3 ) extending at least partially along the length of the central bore ( 4 ) and gripping the fastening element ( 5 ) so as to center it in the central bore ( 4 ), an encapsulation ( 7 ) of plastic material being overmolded around an outer wall of the mounting base ( 2 ), wherein the mounting base ( 2 ) is as described in claim 6 , with at least one channel ( 8 ) pierced in the barrel ( 2 a ), said at least one channel ( 8 ) being filled with the plastic material and the spacer ( 3 ) being formed of the plastic material of the encapsulation ( 7 ) that has passed through said at least one channel ( 8 ), the spacer ( 3 ) being thus fixed to the encapsulation ( 7 ).

15. A crankcase of an internal combustion engine of a motor vehicle, wherein the crankcase is the support element of an accelerometer sensor ( 1 ) as claimed in claim 14 , the accelerometer sensor ( 1 ) being a knock sensor of the internal combustion engine, the crankcase having a bore for receiving an end portion ( 5 b ) of the fastening element ( 5 ) which projects from the central bore ( 4 ) of the barrel ( 2 a ) of the mounting base ( 2 ) of the sensor ( 1 ) toward the crankcase for fixing the knock sensor ( 1 ) to the crankcase.

16. The accelerometer sensor ( 1 ) as claimed in claim 14 , wherein a part of the fastening element ( 5 ) inside the central bore ( 4 ) carries on its periphery a retaining ring ( 11 ) to keep it bearing against an end of the fixed spacer ( 3 ), and to prevent the fastening element ( 5 ) from being withdrawn from the accelerometer sensor ( 1 ) before the fastening element ( 5 ) is fixed to the support element.

17. A crankcase of an internal combustion engine of a motor vehicle, wherein the crankcase is the support element of an accelerometer sensor ( 1 ) as claimed in claim 16 , the accelerometer sensor ( 1 ) being a knock sensor of the internal combustion engine, the crankcase having a bore for receiving an end portion ( 5 b ) of the fastening element ( 5 ) which projects from the central bore ( 4 ) of the barrel ( 2 a ) of the mounting base ( 2 ) of the sensor ( 1 ) toward the crankcase for fixing the knock sensor ( 1 ) to the crankcase.

18. The accelerometer sensor ( 1 ) as claimed in claim 14 , wherein the fastening element ( 5 ), at a first longitudinal end ( 4 a ) of the central bore ( 4 ), has a head ( 9 ) bearing externally on the barrel ( 2 a ), while at a second longitudinal end of the central bore ( 4 ) it has a threaded part ( 5 b ) projecting from the sensor ( 1 ) when the head ( 9 ) of the fastening element ( 5 ) bears externally on the barrel ( 2 a ), the threaded part ( 5 b ) being designed to fix the sensor ( 1 ) onto a support element.

19. The accelerometer sensor ( 1 ) as claimed in claim 18 , wherein a part of the fastening element ( 5 ) inside the central bore ( 4 ) carries on its periphery a retaining ring ( 11 ) to keep it bearing against an end of the fixed spacer ( 3 ), and to prevent the fastening element ( 5 ) from being withdrawn from the accelerometer sensor ( 1 ) before the fastening element ( 5 ) is fixed to the support element.

20. A crankcase of an internal combustion engine of a motor vehicle, wherein the crankcase is the support element of an accelerometer sensor ( 1 ) as claimed in claim 18 , the accelerometer sensor ( 1 ) being a knock sensor of the internal combustion engine, the crankcase having a bore for receiving an end portion ( 5 b ) of the fastening element ( 5 ) which projects from the central bore ( 4 ) of the barrel ( 2 a ) of the mounting base ( 2 ) of the sensor ( 1 ) toward the crankcase for fixing the knock sensor ( 1 ) to the crankcase.