Description of invention

The invention relates to an actuator for the lifting of a hood or bonnet of a vehicle in a vehicle safety system in order to provide protection for a pedestrian hit by the vehicle. The actuator comprises a housing and a piston, the piston having a first end and a second end. The piston is adapted to at least partly be positioned in the housing. The actuator further comprises a pyrotechnic charge arranged to exert a displacing force on the piston when the actuator is activated such that the piston is displaced via an opening in the housing, the first end facing the direction of the piston's displacement.

It has been observed that if a motor vehicle hits a pedestrian, the bumper of the vehicle often hits the legs or lower torso of the pedestrian. Hence, the legs of the pedestrian will normally be pushed in the travel direction of the vehicle, and the head and upper torso will normally be tilted towards the hood and windscreen of the vehicle. This tilting movement often causes the head or upper torso of the pedestrian to first make contact with the hood and thereafter, if the impact force from the hit is strong enough and the vehicle continues forward, also reach the windscreen .

In order to minimize the damages afflicted to the pedestrian in the event of such an impact, it has been proposed to use some kind of hood lifting arrangements. These arrangements are generally constructed such that the rear part of the hood, i.e. the part closest to the windscreen, is lifted in the event of a collision with a pedestrian. Such arrangements are for example disclosed in WO 2007/067 121 and EP 2 256 007.

The hood will in general provide an efficient, flexible impact energy absorbing structure when a vehicle hits a pedestrian. However, if the hood is not lifted, there is a higher risk that the hood will be deformed to such an extent that hard, non-flexible parts beneath the hood, e.g. an engine block, make contact with the hood and an undesired, stiff impact may be the result from the collision between the pedestrian and the vehicle. In addition, the raising of the rear part of the hood will make the surface of the hood further inclined and contribute to a reduced speed of a body moving towards the windshield. Furthermore, a less acute angle between the windshield and the hood will also contribute to a less severe condition for a person being hit by a vehicle.

Hence, the use of an active safety arrangement for lifting the hood contributes significantly to reduce the risk of damages/injuries for a pedestrian that is hit by a vehicle. In order to lift the hood, there are several different suggestions of how a hood lifting arrangement shall be designed. One suggestion is to use a piston and a housing where, in the event of actuation, the piston will be pushed to extend out of the housing and thereby cause a lifting action of the hood or bonnet. Such lifting devices are for example disclosed in JP 2008-075739 and US 6,530,449. Even though the above described prior art provides working examples of actuators serving as hood lifters, there is still a desire for improvements of hood lifters with respect to their functionality and reliability. The object of the present invention is to provide an actuator which in a cost efficient way makes it possible to produce a hood lifter with a reliable functionality, consisting of a minimum of parts.

Said object is obtained by means of an actuator which comprises a housing and a piston, the piston having a first end and a second end. The piston is adapted to at least partly be positioned in the housing. The actuator further comprises a pyrotechnic charge arranged to exert a displacing force on the piston when the actuator is activated such that the piston is displaced via an opening in the housing, the first end facing the direction of the piston's displacement. The pyrotechnic device is arranged at the second end of the piston, for example in a cavity inside the piston.

According to an example, the initial main direction of propelling gases that are released by the pyrotechnic device when ignited is opposite the direction of the piston's displacement.

According to another example, the pyrotechnic device may be arranged to be displaced together with the piston in the direction of the piston' s displacement when the actuator has been activated.

According to another example, the housing comprises a first end and a second end, where the opening is located at the first end and the second end is constituted by an end wall. Advantageously, an end cap may be mounted to cover the opening before the actuator is activated. Other examples are disclosed in the dependent claims.

A number of advantages are provided by means of the present invention. Mainly a hood lifter with a reliable functionality, consisting of a minimum of parts, is acquired .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail with reference to the appended drawings, where:

Figure 1 shows a vehicle before activation of a hood lifting actuator;

Figure 2 shows a vehicle after activation of a hood lifting actuator;

Figure 3 shows a cut-open side view of a part of a vehicle hood, windscreen and a hood lifting actuator, before activation, according to a first example;

Figure 4 shows a cut-open side view of a part of a vehicle hood, windscreen and a hood lifting actuator, after activation, according to a first example;

Figure 5 shows a side view of a hood lifting actuator according to a second example;

Figure 6 shows a cut-open side view of a hood lifting actuator according to a second example; Figure 7 shows a cut-open side view of a part of a vehicle hood, windscreen and a mounted hood lifting actuator, before activation, according to a second example;

Figure 8 shows a cut-open side view of a part of a vehicle hood, windscreen and a mounted hood lifting actuator, at activation, according to a second example; and

Figure 9 shows a cut-open side view of a part of a vehicle hood, windscreen and a mounted hood lifting actuator, after activation, according to a second example .

DETAILED DESCRIPTION

Figure 1 shows a vehicle 1 with a hood 2 and a windscreen 3 in a normal condition. The vehicle 1 has a forward direction of movement that is indicated with an arrow D. In the event of a collision with a pedestrian (not shown) , the rear part of the hood 2, i.e. the part closest to the windscreen, is raised as shown in Figure 2.

Figure 3 shows a schematic cut-open view of the rear part of the hood 2, a part of the windscreen 3 and a plenum part 4. The plenum part 4 is positioned between the windscreen 3 and the hood 2. Figure 3 also shows an actuator 5 positioned at a main side of the hood 3 facing towards an engine (not shown) of the vehicle 1. The actuator 5 comprises a housing 6 with an opening 6a facing the hood 2, a piston 7 and a pyrotechnic device 8. The piston 7 is attached to the hood 2 via a link arm 9, via the opening 6a in the housing 6. The piston 7 has a first end 7a and a second end 7b, where the first end is connected to the link arm 9 and here is shown to partly extend out from the housing 6 via the opening 6a. Figure 4 shows the same view as Figure 3, but here the actuator has been activated, the pyrotechnic device 8 having been ignited such the piston 7 is displaced in a direction indicated by a piston arrow P, out from the housing 6 via the opening 6a. The first end 7a faces the direction P of the piston's displacement.

According to the present invention, the pyrotechnic device 8 is arranged at the second end 7b of the piston, preferably in a cavity 10 inside the piston.

This arrangement preferably results in that the initial main direction of propelling gases that are released by the pyrotechnic device 8 when ignited, indicted with a gas direction arrow G, is opposite the direction P of the piston's displacement.

The displacement of the piston results in a raised hood 2 as shown in Figure 2. An example of an alternative hood lifting actuator will now be described, first with reference to Figure 5. The actuator 11 comprises a housing 12 with an end cap 13 that covers an opening 15 in the housing 12. The housing is arranged to be mounted a hinge that is fastened to a hood which will be discussed later. Figure 6 shows a schematic view of the housing 12 and a piston 17 where they have been cut in halves along their longitudinal extension L. The housing 12 is in the form of a hollow cylinder or pipe section having a first end 12a and a second end 12b, where the opening 15 is located at the first end 12a. The second end 12b is constituted by an end wall. The piston 17 comprises a wedge part 17a and a cavity part 17b, where the wedge part 17a faces the first end 12a and the cavity part 17b faces the second end 12b. The wedge part narrows towards an edge 14 which is adjacent an inner side of the end cap 13 and runs perpendicular to the longitudinal extension L.

The cavity part 17b comprises a cavity 18 which in turn comprises a pyrotechnic device 19. The pyrotechnic device 19 is connected to an actuating device (not shown) by means of electrical wires 20a, 20b that run in a slot 21 in the piston 17 and are connected to the pyrotechnic device 19 by means of a connector 28. The pyrotechnic device 19 is shown as one unit, filling a part of the cavity 18, but may be comprised by several parts such as an ignition device part and a fuel part. The pyrotechnic device 19 may furthermore more or less fill the cavity 18.

This means that when the piston 17 is mounted in the housing 12, the pyrotechnic device 19 and its wires 20a, 20b are already in place in the piston 17, the wires 20a, 20b extending from the cavity part 17b towards the wedge part 17a in the slot 21. The piston 17 is inserted into the housing 12 through the opening 15, first the cavity part 17b such that the cavity part 17b faces the second end 12b when the piston 17 is mounted. The wires 20a, 20b emerge through the opening, and are squeezed into a rigid position when the end cap 13 is mounted to cover the opening 15.

The piston comprises an opening 29 in the piston through which gases escape when the pyrotechnic device 19 is activated 17, the opening 29 facing the second end 12b.

In Figure 7, Figure 8 and Figure 9, a side view of the actuator 11 is shown, where the housing 12 and the piston 17 have been cut in halves along their longitudinal extension L as in Figure 6. The actuator is mounted to a hinge 22 which in turn is mounted to a hood (not shown) . The actuator 11 is here shown in three different states; in Figure 7 before actuation, in Figure 8 at actuation, and in Figure 9 after actuation. For increased clarity, the wires, the slot 21 and the connector 28 are not shown in the Figures 7-9 although they are to be regarded as present. The hinge 22 has a first hinge end 22a and a second hinge end 22b, the second hinge end 22b being arranged to be positioned closest to a windscreen (not shown) of the hinge ends 22a, 22b.

As shown in Figure 7, actuator 11 is mounted to the hinge 22 in any suitable way, for example by means of screws, rivets, welding or other attachment means. The hinge comprises a pivoting axis 24 at the first hinge end 22a, around which pivoting axis 24 the hinge 22 turns during activation of the actuator 11, as will be described below. Adjacent an outer side of the end cap 13 a rod 25 runs parallel to the edge 14. The rod 25 is firmly mounted to the chassis of the vehicle, independent of the actuator 12 and the hinge 22. In Figure 8, the pyrotechnic device 19 is ignited, indicated by an explosion symbol 26, such that the piston 17 is displaced in a direction indicated by a piston arrow P towards the second hinge end 22a, out from the housing 12 via the opening 15. The direction of propelling gases that are released by the pyrotechnic device 19 when ignited, indicted with a gas direction arrow G, is opposite the direction P of the piston's displacement and escape through the opening 29. The end cap 13 is shown as falling off as it is removed from the opening 15 by the displaced edge 14 of the piston's wedge part 17a. Practically, the end cap 13 probably brakes into several parts or is at least deformed at this stage, although this is not shown in Figure 8.

It is to be noted that the wires 20a, 20b run in the same direction from the pyrotechnic device 19 as the direction P of the piston's displacement.

During the displacement of the piston 17, the edge 14 of the wedge part 17b enters between the rod 25 and the hinge 22. Since the rod is mounted to the chassis of the vehicle, independent of the actuator 12 and the hinge 22, the wedge part 17a increases the distance between the rod and the hinge 22 during the piston's displacement towards the first hinge end 22a.

As shown in Figure 9, this results in a pivoting movement of the hinge 22 around the pivoting axis 24 such the second hinge end 22b is raised. Since a hood is attached to the hinge 22, the hood is also raised, resulting in a raised hood 2 as shown in Figure 2.

The present invention is not limited to the above, but may vary freely within the scope of the appended claims. For example, the piston 7, 17 of the present invention may comprise a non-metallic material. The piston 7, 17 may be made from only non-metallic material or may be a combination of metallic and non-metallic material.

The piston 7, 17 may for example be made in a plastic polymer such as polyamide (PA) or polybutylene terephthalate (PBT) which may be reinforced by different materials, e.g. by mixing with glass fibres or carbon fibres. It may also be possible to use a metallic core or stem which is covered by a non-metallic material, e.g. a plastic polymer.

The invention is in particular directed to a piston comprised in a housing forming part of said actuator for lifting of the hood, where a pyrotechnic device 8, 19 is arranged at the second end 7b, 17b of the piston 7, 17, preferably in a cavity 10, 18 inside the piston 7, 17, although types of mounting at the second end 7b, 17b of the piston 7, 17 are conceivable.

As shown in the examples discussed, the direction G of propelling gases that are released by a pyrotechnic device 8, 19 when ignited is opposite the direction P of the piston's displacement.

In the examples, the pyrotechnic device 8, 19 is displaced together with the piston 7, 17 in the direction P of the piston's displacement as the pyrotechnic device 8, 19 is more or less consumed during its development of propellant gases, but the pyrotechnic device 8, 19 may alternatively be liberated from the piston 7, 17 during its path.

As an example of typical time spans between the occurrences shown in Figure 7, Figure 8 and Figure 9, if Figure 7 occurs at the time t = 0s, Figure 8 occurs at the time t = 2ms and Figure 9 occurs at the time t = 30ms.

When the piston 17 is displaced, the wedge part 17a may slide against a sliding guide part 27 comprised in the hinge 22. Terms like opposite, perpendicular and parallel should be regarded as indications of directions within what is practically obtainable, and not as mathematically exact directions . Where the pyrotechnic device 19 is filling a part of the cavity 18, as shown in Figure 6 - Figure 8, is it to be understood that the pyrotechnic device 19 can be placed anywhere in the cavity, even at the opening 29 in the piston, i.e. at the other end of the cavity than shown in these Figures. Such a placement of the pyrotechnic device is illustrated in Figure 3 and Figure 4. The opening 29 may have any suitable size.