EP2567101B1 - Triggered-stroke actuator comprising sealing means and means for blocking the rod - Google Patents

Description

Background of the invention

This presentation relates to the field of cylinders.

More particularly, the present disclosure relates to a trigger stroke cylinder of the type comprising a body housing a moving assembly comprising a piston and a rod, means, most often a pyrotechnic gas generator, for propelling this assembly in response to a control of tripping, means for locking the rod relative to the body, and sealing means provided between the assembly and the body.

A worm of this type is particularly known from the document DE 10203710 .

Such a cylinder can, for example, be integrated with a security system for protecting a pedestrian in the event of a frontal impact with a motor vehicle. This type of cylinder is designed to suddenly raise the hood of the vehicle by a certain height so as to prevent the pedestrian including his head comes hitting the engine block after deformation of the hood. The lifting of the hood is performed at the rear of the latter, that is to say on the side of the windshield, the hood remaining attached to the front of the motor vehicle.

The cylinders intended to be arranged under the hood of a vehicle must have a good level of sealing with respect to the outside.

In known devices, this seal is generally provided by an O-ring housed at one end of the jack, in a groove formed at the periphery of the rod of the moving assembly, and bearing on the inner face of the cylinder body. During operation of the cylinder, the seal is driven by the rod and slides along the inner face of the cylinder body.

Depending on how the cylinder is assembled on the hood hinge, it may further be required that the rod of the cylinder is held in its initial position to a predetermined force, and released when the force applied to it exceeds this predetermined force, especially in case of activation of the cylinder. This function of maintaining the position of the actuating rod is sometimes ensured by a deformable or breakable ring, usually metal, which is crimped on the cylinder body at one of its axial ends and whose opposite end is housed. in a groove or groove provided for this purpose on the circumference of a portion of the rod projecting from the cylinder body. In known devices, the functions of sealing and holding in position of the rod are therefore provided by two separate devices: an O-ring for sealing and an "elastic" or breakable metal ring for holding the rod in position .

Object and summary of the invention

The object of the present invention is to provide a trigger stroke cylinder performing the dual function of sealing and maintaining position of the rod, but having a configuration simpler and more economical than the cylinders of the prior art.

This objective is achieved by means of a trigger stroke cylinder as defined in claim 1, of the type comprising a body housing a moving assembly comprising a piston and a rod, means for propelling said moving assembly in response to a control of triggering, means for blocking said rod relative to said body, and a seal formed between said movable assembly and said body, and housed in a first annular groove formed at the periphery of said moving assembly, and characterized in that a second annular groove is formed on the inner surface of said body, facing said first groove, so that said seal is partially housed in said first groove and partially in said second groove when the cylinder is in a non-position; triggered, whereby it forms the said locking means, and in that the seal, the first groove and the second groove, are configured s so that beyond a certain force exerted on the piston, the seal is sheared by said grooves, thus releasing the displacement of the moving assembly.

According to the present invention, the seal housed in the respective grooves of the moving assembly and the cylinder body, fulfills both its primary function of sealing, and a function of holding in position of the cylinder rod. A single element therefore ensures these two functions, thus simplifying the assembly of the cylinder and lowering the manufacturing costs. The seal makes it possible to lock the rod relative to the cylinder body as long as an axial force applied to the rod or to the moving assembly does not exceed the shear strength limit. of the seal. When this force becomes greater than the shear threshold of the seal, for example during actuation of the jack, the seal is sheared by said first and second grooves. For this, the edges at the outer edge of the grooves are sharp enough so that the seal is literally cut in half. A portion of the seal then remains in the first groove and moves with the moving assembly, while its complementary portion remains in the second groove, at the inner periphery of the cylinder body.

As the seal is sheared, it does not brake the stroke of the piston, and the movement of the moving assembly is released completely.

According to one aspect of the invention, the first groove is formed in the cylinder rod. In this way, the rod remains fixed as the force applied to the joint does not exceed a predetermined limit value. In this case, the rod and the piston may be indifferently integral or independent of one another.

Alternatively, the first groove may also be formed on the piston when the latter is integral with the rod of the cylinder or formed integrally therewith.

According to another aspect of the invention, the second groove is arranged at the axial end of the body where the rod of the moving assembly protrudes.

According to another aspect of the invention, the body has an extra thickness extending inwardly of the body and forming an internal guide means for the rod, and the second groove is formed in this extra thickness. This arrangement allows to introduce the rod, provided with the seal, inside the cylinder body, without damaging the seal by friction against the inner walls of the cylinder body.

According to an exemplary embodiment, the extra thickness has, on the insertion side of the rod, a decreasing inner diameter section which extends from the axial end of the extra thickness to the entrance of the second groove. In particular, the section is configured so that its smaller internal diameter is smaller than the internal diameter of the second groove. These provisions facilitate the introduction of the seal in the second groove and prevent deterioration. They also avoid that the joint, once positioned, disengages from the first and second grooves.

According to an exemplary embodiment, the body comprises a cylindrical housing and a ring adapted to engage in this housing, forming the extra thickness defined above. These arrangements facilitate the manufacture and assembly of the cylinder.

For example, the ring may include a shoulder at one of its axial ends, which shoulder is adapted to bear against one of the axial end faces of the housing. Thus, the ring can be easily mounted on the housing and held in position, in particular during crimping on the casing of the cylinder or any other securing operation of these two elements. In this case, the decreasing inner diameter section of the ring may extend from its axial end which is opposite to said shoulder, to the entrance of the second groove.

Brief description of the drawings

• La figure 1 montre un vérin selon la présente invention, avant déclenchement,
• La figure 2 montre le vérin de la figure 1 après déclenchement, le joint ayant été cisaillé.

The invention will be better understood and other advantages thereof will appear better in the light of the following description of several embodiments of a cylinder according to its principle, given solely by way of example and made in reference to the accompanying drawings in which:

• The figure 1 shows a jack according to the present invention, before triggering,
• The figure 2 shows the cylinder of the figure 1 after triggering, the seal having been sheared.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

On the figure 1 , there is shown a possible embodiment of a jack 10 according to the invention. Such a cylinder can, for example, be integrated into a safety system for lifting the hood of a vehicle in the event of a frontal impact with a pedestrian to prevent the head of the latter from hitting the engine block.

In the present description, unless otherwise specified, a radial direction is a direction perpendicular to the axis A of the cylinder 10 and intersecting this axis. In addition, an axial direction is a direction parallel to the axis A The axial and radial adjectives are used with reference to the aforementioned axial and radial directions. Similarly, an axial plane is a plane containing the axis A of the jack 10 and a radial plane is a plane perpendicular to this axis.

The jack 10 comprises a body 12, of axis A, consisting of a cylindrical casing 14 open at its two axial ends, and an end guide formed by a ring 16 inserted inside the casing 14. note that according to another embodiment (not shown), the ring 16 can be replaced by an extra thickness made in one piece with the housing 14.

The body of the jack 12 encloses a moving assembly 18 comprising a piston 20 provided with a sliding joint 21 and an actuating rod 22 projecting outside the body of the jack 12. It also contains a pyrotechnic gas generator 24 , here installed in a molded plastic base 26. A combustion chamber 23 is defined in the body of the jack between the pyrotechnic gas generator 24 and the piston 20. In the example, the piston 20 and the piston rod actuation 22 are made in one piece. According to an alternative embodiment, the piston 20 and the rod 22 may also be two independent parts.

As is apparent from the figure 1 , the ring 16 is located at the axial end 14a of the housing where the actuating rod 22 projects outwardly. A part of the ring 16 is inserted inside the casing 14 while a shoulder 32 provided at one of its axial ends 16a abuts against an axial end face 14c of the casing 14. This shoulder 32 allows to ensure accurate positioning of the ring 16 to mounting, and to facilitate its attachment to the housing 14, keeping it in position. In the example shown, the ring 16 has been made integral with the casing 14 by an annular necking (circumferential crimping) materialized on the figure 1 by a deformation line 30.

The ring comprises, on its inner radial face, away from its axial ends 16a, 16b, an annular groove 36 of internal diameter d1. In the example, the groove 36 has a substantially rectangular section in an axial plane.

As illustrated on the figure 1 , the ring 16 has, between the groove 36 and the shoulder 32, a constant internal diameter d2 corresponding substantially to the outer diameter of the actuating rod 22. It thus ensures a guide of the rod 22 when it moves in the axial direction.

The ring 16 further includes a section of decreasing internal diameter 50 with a frustoconical internal surface extending from its axial end 16b opposite to the shoulder 32 (ie directed towards the inside of the casing 14 when the ring 16 is in position climb) to the entrance to the groove 36. In the example of the figure 1 , the largest internal diameter d3 of this section 50 (located at the axial end 16b of the ring 16) is greater than the diameter d2 and substantially equal to the internal diameter d1 of the groove 36. Its smaller internal diameter d4 is it is less than the internal diameter of the groove 36 and substantially equal to the diameter d2, so as to form a recess 51 at the inlet of the groove 36. The section 50 is of particular interest when mounting the cylinder which will be described more in detail in the following.

As shown on the figure 1 an annular groove 34 of substantially rectangular cross section in an axial plane is formed at the periphery of the actuating rod 22.

The relative arrangement of the actuating rod 22 and the ring 16 when the cylinder 10 is in its rest position (before triggering) is such that the groove 34 of the actuating rod 22 is positioned directly in with respect to the groove 36 of the ring 16. In the example, the first and second grooves 34, 36 have a substantially identical axial length.

Together, the groove of the actuating rod 22 (hereinafter first groove) and the groove 36 of the ring 16 (hereinafter second groove) define an annular cavity 38 occupied by an annular seal 40. In the for example, seal 40 is an O-ring. This seal 40 may be made of any suitable elastomeric material. As is apparent from the figure 1 , a first portion 44 of the seal is housed in the first groove 34 of the actuating rod 22 and a second portion 46 of the seal is housed in the second groove 36 of the ring 16. The radial heights and axial lengths of the grooves 34 and 36 allow to adjust the compression ratio of the seal 40. In the example, the sum of the radial heights of the first and the second groove is less than the thickness of the seal 40 (ie to the diameter of the torus in the case of a O-ring as envisioned in the example). Moreover, as is apparent from figure 1 , the first and the second grooves have an identical axial length, greater than the thickness of the seal 40. The seal 40 thus seals by radial deformation.

As is apparent from the figure 1 , the blocking of the seal 40 between the recess 51 on the one hand and the opposite wall 52 of the second groove 36 on the other hand, prevents the displacement of the rod 22 in the axial direction. The seal 40 thus arranged thus ensures both the tightness of the jack 10 and the locking in position of the rod 22 before the operation of the jack 10.

When activation of the jack 10 (by triggering the pyrotechnic gas generator 24), the thrust exerted on the piston 20 reaches a threshold which results in shearing of the seal 40 by sliding of the first groove 34 of the actuating rod 22 in the axial direction.

Advantageously, the lateral edges of the grooves 34 and 36 define, with the adjacent surfaces of the moving assembly 18, and, respectively, of the cylinder body 12, cutting edges. When the mobile assembly 18 is biased outwardly of the cylinder body under the action of the gases generated in the combustion chamber 23, the ridges thus formed on either side of the seal 40 exert on it a force shear such that the seal is literally split into two parts, at these edges.

The rod 22 can then slide freely under the effect of the thrust force exerted by the gases contained in the combustion chamber 23.

The figure 2 shows the end of the cylinder 10 of the figure 1 after operation of the propulsion means of the cylinder, that is to say after triggering the pyrotechnic gas generator 24. As indicated above, the seal 40 is sheared in two parts. The first portion 44, still housed in the first groove 34 of the actuating rod 22, is driven in the movement of the rod 22 while the second portion 46 remains housed in the second groove 36 of the ring 16.

Note that the minimum force causing the shearing of the seal 40 can be adjusted by adjusting one or more of the following parameters: the hardness of the seal 40, the compression ratio of the seal 40 in the first and second grooves 34, 36, the depths of the said throats and the thickness of the seal 40 (ie the diameter of the torus in the case of an O-ring).

The holding force provided by the seal 40 (and therefore the minimum force causing shear) may vary depending on the circumstances in which the cylinder is used. As indicated above, it can for example be integrated into a safety system for lifting the hood of a vehicle in the event of a frontal impact with a pedestrian to prevent the head of the latter from hitting the engine block.

In this case, most of the time, the rod 22 is not connected to the movable part of the hinge of the hood of the vehicle (not shown). The only forces applied to the rod 22 are then those due to the forces of inertia of the mass of the rod 22 or the moving assembly 18 in the case where the rod is integral with the piston (i.e. the forces due to vibration). The holding force provided by the seal 40 can then be very low.

In other cases, where there is a fixed connection between the rod 22 and the hinge of the hood of the vehicle, the seal 40 must make it possible to counteract the vibrations of the assembly comprising the rod 22 (or the moving assembly 18) and the movable part of the hinge. In this case, the holding force provided by the seal 40 must be moderate and the use of an elastomeric seal is perfectly adapted because of its ability to damp the vibrations.

Sometimes, in the case where the jack 10 has an anti-intrusion function in the motor part, it is necessary that the assembly formed by the rod 22 (or the moving assembly 18) and the movable part of the hinge is sufficiently maintained to prevent any displacement due to a tearing force applied to the hood (eg tearing with bare hands). The holding force provided by the seal 40 is, in this case, relatively high.

An example of mounting the cylinder 10 of the figure 1 will now be described in more detail.

In a first step, the ring 16 is inserted inside the casing 14 until its shoulder 32 bears against the axial end face 14c of the casing 14.

The housing 14 and the ring 16 are then secured to one another, for example by an annular necking.

The moving assembly 18 consisting of the piston 20 and the rod 22 provided with the seal 40 previously mounted in the annular cavity 34, is then introduced into the cylinder body 12, through the opening provided at the axial end 14b of the housing 14. opposed to that 14a where the ring 16 is mounted.

The decreasing inner diameter section 50 of the ring 16, provided on the insertion side of the rod, facilitates the assembly and in particular the introduction of the rod 22 provided with the seal 40 through the ring 16. The slope formed by this section 50, which joins the inlet of the second groove 36, makes it possible to gradually compress the seal 40 during the introduction of the rod 22 into the ring 16, until the first groove 34 is finally positioned opposite the second groove 36 and the seal 40, housed in the cavity 38 formed by the two grooves 34, 36. The recess 51 then prevents the seal 40 from disengaging the grooves 34, 36, after assembly.

The propulsion means of the mobile assembly 18 (for example the pyrotechnic gas generator 24) are subsequently reported inside the body of the jack 12.

According to a mounting variant of the jack 10, the rod 22 of the moving assembly 18 is first introduced through the ring 16, out of the housing 14, so as to accommodate the seal 40 in the first and the second groove 34 36. The seal 40 then holds together the ring 16 and the rod 22. As in the previous mounting example, the introduction of the rod 22 inside the ring 16 is facilitated by the decreasing diameter section 50 Then the assembly formed by the ring 16 and the rod 22 is introduced into the casing 14 by its axial end 14a, from which the rod 22 projects outwards. Once the shoulder 32 of the ring 16 bears on the face 14c of axial end 14a of the housing 14, the ring 16 is fixed on the housing 14, for example by an annular necking or crimping. According to this variant embodiment, the propulsion means of the piston 20 (for example the pyrotechnic gas generator 24) can be mounted inside the body of the jack 12 either before or after the assembly of the mobile assembly 18 and the ring 16.

Claims (8)

1. A triggered stroke actuator (10), comprising a body (12) housing a movable assembly (18) comprising a piston (20) and a rod (22);

   · means (24) for propelling said assembly in response to a trigger command;

   · means for blocking said rod (22) relative to said body (12); and

   · a sealing gasket (40) arranged between said assembly (18) and said body (12), and housed in a first annular groove (34) formed in the periphery of said assembly (18), wherein a second annular groove (36) is arranged in the inside surface of said body (12) facing said first groove (34), such that, when the actuator (10) is in a non-triggered position said sealing gasket (40) is housed in part in said first groove (34) and in part in said second groove (36), thereby forming said blocking means;

   the actuator being characterized in that the sealing gasket (40), the first groove (34), and the second groove (36) are configured in such a manner that beyond a certain level of force exerted on the piston (20), the sealing gasket (40) is sheared by said grooves (34, 36) so as to be cut through, a first portion of the sealing gasket remaining housed in the first groove in order to move together with the movable assembly, and a second portion of the sealing gasket remaining housed in the second groove, thereby leaving the movable assembly (18) free to move.
2. A triggered stroke actuator (10) according to claim 1, wherein said first groove (34) is formed in the rod (22) of said movable assembly (18).
3. A triggered stroke actuator (10) according to claim 1 or claim 2, wherein said second groove (36) is arranged at the axial end of the body (12) where said rod (22) projects.
4. A triggered stroke actuator (10) according to any one of claims 1 to 3, wherein said body (12) includes an extra thickness (16) extending towards the inside of the body (12) and forming internal guide means for said rod (22), and said second groove (36) is formed in said extra thickness (16).
5. A triggered stroke actuator (10) according to claim 4, wherein on the side where the rod is introduced, said extra thickness (16) presents a segment (50) of decreasing inside diameter that extends from the axial end (16b) of said extra thickness (16) to the inlet of said second groove (36), said segment (50) being configured so that its smallest inside diameter is less than the inside diameter of said second groove (36).
6. A triggered stroke actuator (10) according to claim 4 or claim 5, wherein said body (12) comprises a cylindrical housing (14) and a ring (16) suitable for engaging in said housing (14), said ring (16) forming said extra thickness.
7. A triggered stroke actuator (10) according to claim 6, wherein said ring (16) includes a shoulder (32) at one of its axial ends (16a), said shoulder (32) being suitable for coming to bear against one of the axial end faces of said housing (14).
8. A triggered stroke actuator (10) according to claims 5 and 7, wherein said segment (50) of decreasing inside diameter extends from the axial end (16b) of said ring (16) that is opposite from said shoulder (32) as far as the inlet of said second groove (36).

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