WO2012144940A1

WO2012144940A1 - Hood lifting arrangement and method for producing an actuator

Info

Publication number: WO2012144940A1
Application number: PCT/SE2011/050466
Authority: WO
Inventors: Stefan Kuntzsch
Original assignee: Autoliv Development Ab
Priority date: 2011-04-18
Filing date: 2011-04-18
Publication date: 2012-10-26
Also published as: CN103476641A; EP2699456A1; EP2699456A4

Abstract

The invention relates to an actuator (1) for a hood lifting arrangement in a vehicle safety system in order to provide protection for a pedestrian hit by the vehicle and a vehicle comprising such a system including the actuator (1). The actuator (1) comprises a housing (2) having a first end (3) and a second end (4) and a piston (5) having a first end (6) and a second end (7) adapted to fit in the housing (2). The first end (3) of the housing (2) is adapted to comprise or be connected to a power source and the second end (4) of the housing (2) is provided with an opening (10) through which said piston (5) will extend when the actuator (1) is activated. The piston(5) comprises a non-metallic material, e.g. a plastic polymer. The piston (5) may be made completely by one or several non-metallic materials or compositions. The piston (5) may be in the form of a central stem (12) provided with bars (11) stretching along the length of the stem (12 )and attached to the stem (12) by a first longitudinal edge of the bar (11). The bars (11) a restretching radially outwards from the stem (12). Optionally may the distallongitudinal ends of the bars (11) be connected to each other by ring shaped elements (13).The invention further relates to a manufacturing method for an actuator (1) comprising a housing (2), a piston (5) and a pyrotechnic device (9).

Description

Hood lifting arrangement and method for producing an actuator

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 .

It has been observed that if a motor vehicle hit a

pedestrian will the bumper of the vehicle often strike the legs or lower torso of the pedestrian. Hence, the legs of the pedestrian will normally be pushed in the direction of travel 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 of the pedestrian caused from such an impact as described above, 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. 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 in the case when a vehicle hit 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 for a person being hit by a vehicle.

In order to lift the hood, there are several different suggestions of how the hood lifter shall be designed. One suggestion is to use some kind of piston and housing which when actuated will push the piston 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

invention aims in particular to provide an actuator which in a cost efficient way make it possible to produce a hood lifter which functions even after several years of use of the vehicle without the actuator being activated and avoid deterioration of the actuator due to environmental

influence. The invention is in particular directed to a piston comprised in a housing forming part of said actuator for lifting of the hood. The piston of the present invention comprises a non- metallic material. The material is for example 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 in an amount of 15 - 50 per cent. Another working example could be to use 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. In general, for the sake of

lowering production costs and weight of the actuator, is it desired to manufacture the piston without the inclusion of a metallic material. In order to facilitate the production of the piston, it is desired to be able to produce the piston from a single material or material blend, e.g. to mould or extrude a plastic or polymeric blend from one single material batch to form the piston. However, there may sometimes be advantageous to use a metallic material for reinforcement of the piston even though there may be alternative non-metallic material such as a rod made of carbon fibres or the like material which also may be used for a reinforcing, load bearing structure. The use of non-metallic materials for the piston will provide an improvement concerning problems with for example oxidation which may lead to corrosion of the piston. If a piston corrodes it may be stuck in the housing and not work satisfactorily when the actuator is activated. Hence, the actuator may be constructed in a less complicated way than ordinary actuators provided with metallic pistons which demand a more efficient sealing and/or specific surface treatments of the piston in order to avoid oxidation or corrosion of the piston. As described above, the piston may be made from only non- metallic material or may be a combination of metallic and non-metallic material. Even if a metallic material is included in the piston, the piston comprises preferably at least 50 percent by volume of non-metallic materials, e.g when a metallic structure is used as a reinforcing, central rod. In some cases it may be desirable to include small parts, 10 per cent by volume or less, of reinforcing metal structures, e.g. to use a metallic disc or the like at the base of the piston to reinforce parts of the piston which are subjected to particularly strong forces during

activation . A suitable non-metallic material for producing a piston according to the invention is for example a plastic

material referred to as PA6 (Polyamide (Nylon) 6) . In case there is no other reinforcing or load bearing rigid

structure included, metallic or non-metallic, the plastic material is preferably reinforced by being blended with another material, e.g. glass fibres, such that the piston better may withstand the strong forces acting on the piston when actuated. A suitable material for a piston made from a single material blend is for example PA6 with 30% by weight of glass fibres. Even though PA6 is exemplified as a suitable plastic polymer, there are numerous of other suitable plastic polymers known to the skilled person in the art which are suitable to be used for manufacturing the piston . The piston may be a solid rod having a circular cross sectional area or made as a hollow pipe section. If it is made as a hollow pipe section, a rod (hollow or solid) of a metallic or non-metallic strong, load bearing material may be inserted in the hollow shell. The reinforcing rod, extending or stretching along the longitudinal length of the piston, should in general have a length which

corresponds to at least half the length of the piston, in most cases is the reinforcing rod extending at least along 80 % of the length of the piston. If a metallic reinforcing rod is used and it is stretching essentially throughout the complete length of the piston, the respective ends of the piston could be provided with a protection, e.g. a non- metallic sealing, in order to avoid direct contact between the metallic rod and the environment. The piston is

preferably made such that no metallic material forms part of the surface of the piston in order to avoid direct contact between metal and ambient air.

The size of a (circular) piston is typically within the range of having a diameter of its cross sectional area of 14 to 20 millimeters and having a length of 60 to 100 millimeters . The piston rod may of course have other dimensions and shapes. The piston may for example comprise a rod or central stem provided with elongated bars or flanges attached by one of their longitudinal edges to the central stem along the length of the stem. The radial cross

sectional area of the piston will thus have an appearance corresponding to a central hub having a number of spokes or bars extending radially outwards therefrom. The stem and its attached flanges or bars will stretch essentially along the complete length of the piston from its first end to its second end so as to form the piston. The piston may be designed such that its base has a cross sectional area corresponding to the size and geometry of the inner walls of the casing while its middle portion has a size and geometry adapted to fit in the opening through which the piston will extend when the actuator is activated. In the case of a piston comprising a central stem and thereto attached flanges or bars could the piston be constructed such that the part of the bars located in the base portion stretches in the radial direction all the way from the stem to the inner side of the housing and above the base portion has a gradually decreasing radial extension until the radial length of the bars defines a cross sectional area corresponding to or somewhat smaller than the opening area of the housing through which the piston will extend when activated. Hence, the major portion of the length of the piston is normally sized to form a main body being able to extend through the opening while a minor part of the longitudinal extension of the piston forms the enlarged base portion of the piston which normally functions as a stop for the piston when it has reached its extended position in its activated state. The distal ends of the flanges or bars, i.e. the ends of the flanges facing away from the central stem, may be disposed equidistant from each other and the stem. Hence, the flanges are preferably shaped equally and symmetrically located around the stem. The specific number of flanges to be used is not critical but there should be at least three flanges attached to the stem in order to stabilize the piston in a housing, the number of flanges are normally from 3 to 8 even though more could be used.

The bars or flanges may be connected to each other at its distal, free ends by circumferential rings located at desired distances from each other along the length of the piston. Such a design provides a strong structure suitable for making a piston of plastic material while at the same time using less material so as to lower the material costs and weight of the piston. By designing the piston in an appropriate way, it may be possible to include features such as a tight sealing at the opening, through which the piston will be pushed when the actuator is activated, before the piston is activated.

Optionally, the cylinder may be provided with an elastic 0- ring at the opening for the piston in order to provide a tight seal. It will also be easy to provide a tight fit of the piston against the inner side of the wall of the housing in the other end such that the piston will be efficiently pushed when activated. Hence, the use of for example a plastic or the like material for the piston will provide benefits in getting a tight fit between the piston and the housing where desired due to the material

properties of a suitable non-metallic material as compared to metallic material. It may thus be possible to form tight sealings at the front end as well as a gas tight, close fit of the piston base and the housing at its other end.

The actuator described above is particularly designed to be used in a hood lifting arrangement forming part of a pedestrian safety system in which the actuator may serve as a hood lifter. Such a hood lifter have a particular need for environmental resistance since it is located in a position where it may suffer from moist and dirt from the environment as well as relatively strong temperature variations due to heat from the engine compartment.

Hence, there are several benefits associated with a piston made completely or partly of a plastic or similar material such as weight, costs and resistance to oxidation or corrosion. These advantages are in particular present if the piston rod is manufactured completely in a plastic material. However, it may be difficult to find a single material which is suitable for the complete piston. The piston may thus be made using two or more different non- metallic materials or compositions for different structures of the piston, e.g. a stronger and stiffer material for building up the load bearing structure and a softer

material for forming sealings and providing a close fit between the piston and the housing where desired.

A further advantage which may be achieved by using a non- metallic material for the piston compared to using a piston made completely by metal is that a deformable or

collapsible structure may be formed easier. The piston may be designed to use the deformation to slow down the motion of the piston to provide for a smooth stop of the movement of the piston in order to avoid or decrease oscillations of a hood lifted by the piston caused by an instant stopping of the piston. In addition, the piston may be designed such that the deformation also will contribute to an improved sealing at the opening through which the piston extend after activation in order to prolong the stay up time of the piston. In order to manage with the manufacturing of a piston suitable to serve in an actuator for lifting of a hood, the non-metallic material (e.g. a plastic polymer composition) or materials to be used must be selected to withstand the forces when the piston is actuated. According to one embodiment of the invention is also the cylinder made of, or comprising, a nonmetallic material, e.g a housing made of composition comprising carbon fibres. However, since the housing must withstand rather large pressures when the actuator is activated, it may also include metallic reinforcing elements. By providing a housing and a piston of non-metallic materials it will be possible to eliminate the risk of corrosions of these parts of the actuator.

The invention is also directed to a vehicle comprising a hood lifting arrangement comprising an actuator as

disclosed herein. The hood lifter described herein could for example be used in the system described in US 6,530,449 and replace the actuator described therein.

An actuator comprising a piston made of a plastic material may be manufactured according to the following procedure. A plastic piston is introduced in a housing, e.g. a pipe which may be a cold forged metallic cylinder. The piston may be made to cooperate with the housing such that a tight sealing is provided at the top of the pipe, i.e. the end of the pipe through which the piston will extend when

activated. Optionally, the part of the piston forming the seal is made of another material, preferably softer, than the main portion of the actuator since other properties may be desired for the sealing than for the load bearing main portion of the piston. Likewise, the lower part of the piston, or at least the part of the piston which is

intended to seal against the inner surface of the housing, may also comprise a softer material in order to provide for a tight fit between the lower part and the inside of the housing to assure an efficient activation and lifting of the piston when the actuator is activated. The softer material could be a softer kind of plastics, rubber or other suitable material.

Once the piston has been inserted to its resting position in the housing, the second end of the housing (through which the piston is inserted and will extend when actuated) may be manipulated. This end portion is modified such that the cross sectional area is decreased to such an extent that a main body portion of the piston may pass through while an enlarged base portion of the piston is prevented from passing through. The pipe may be manipulated by crimping. The opening will then provide a stop for the piston when its base reaches the narrowing section after the actuator has been activated. The opening may also include a braking portion, e.g. a slightly narrowing cross sectional area of the housing close to the final stop, whereby the piston will slow down in a smooth manner before it is completely stopped. The piston is also preferably designed such that when the pipe is crimped at the end, there will be a tight seal formed between the piston and the opening in the housing. In case the actuator is provided with a pyrotechnic charge, the pyrotechnic device may be inserted into the pipe at its first, lower end. Also in this case is the pipe manipulated such that the cross sectional area is decreased and the pyrotechnical device is prevented from being able to escape out of the pipe. The reduction of the cross sectional area of the pipe around the pyrotechnic device and/or at the very end of the pipe may be achieved by crimping.

The method may be performed by first introducing a piston and manipulating the end of the housing thereafter to form a stop for the piston followed by the introduction of the pyrotechnic device into the pipe through the other end followed by manipulation of the other end in order to secure the pyrotechnic device in the pipe thereafter.

Alternatively, the pyrotechnic device is introduced first through the first end which thereafter is manipulated followed by the introduction of the piston into the other end followed by manipulation of the second end of the pipe. Still another way of assembling the actuator is to insert the piston and the pyrotechnic device firstly and

thereafter manipulating both the first and second end of the housing. The above described method discloses an efficient way of producing the actuator. Its however obvious that the actuator could be manufactured in other ways and the stopping and braking portions could be made by forming protrusions on the inside of the housing and the

pyrotechnic device could be fixed by using a plug or threaded lid screwed onto a threaded portion of the

housing .

The invention will be further explained by the embodiments described in association with the following figures. FIGURES 1 a-d disclose an actuator and its main parts according to an embodiment of the invention.

FIGURES 2 a-g disclose cross sectional views of different embodiments of a piston according to the invention.

FIGURES 3 a-d disclose activation stages of an actuator according to an embodiment of the present invention.

FIGURES 4 a-e disclose manufacturing of an actuator

according to an embodiment of the present invention.

Figure la discloses an actuator 1 comprising a housing 2, a piston 5 and a pyrotechnic device 9. The figure shows a schematic view of the piston 5 and the pyrotechnic device 9 in the housing 2 which has been cut in halves along its longitudinal extension. The housing 2 is in the form of a hollow cylinder or pipe section having a first, lower end 3 and a second, upper end 4 and a piston 5 at least partly made of a non-metallic material, e.g. a plastic polymer, having a piston base 14 at its lower, first end 6. The piston 5 comprises a number of longitudinally stretching flanges or bars 11 extending along the length of the piston 5. The bars 11 are attached at a first, longitudinal side to a central stem 12 (see figure lb) wherefrom the bars are directed radially outwards. The bars 11 are connected to each other by a number of circumferential rings 13 at its other, distal end such that a cross sectional view reminds of wheel having a central hub provided with spokes. The housing 2 is provided with inwardly protruding flanges 8 which serve as a partition of the cylinder and support for the piston 2 and the pyrotechnic device 9 intended to be used as a power source when activating the actuator. The pyrotechnic device 9 is located at the first end 3 of the housing 2 and is connected to a cable 17 which is intended to be connected to a control unit for triggering activation of the actuator. In the second end 4 of the housing 2 is located an opening 10 through which the piston 5 will extend when the actuator 1 is activated. In the upper part of the housing 1 close to its second end 4 is the housing narrowing such that the part of the housing 2 adjacent to the opening 10 will form a stopping segment 15 for the enlarged piston base 14 in order to finally stop the piston 5 when the actuator 1 is activated. The section of the housing 2 right below the stopping portion 15 is only slightly narrower than the main portion of the housing 2 and forms a braking portion 16 such that an enlarged piston base 14 will be squeezed and slow down its motion before it finally reaches the stopping portion 15. In the embodiment shown is the braking portion 16 formed by slightly

narrowing the cross sectional area of the housing 2 towards its second end 4 while the stopping portion 15 is more aggressively narrowing and preferably adapted to cooperate with the conically shaped portion of the piston base 14 connecting it to the piston main portion 18 in order to finally stop the movement of the piston. Figure lb shows a radial cross sectional view of the actuator 1. In this view is it clearly shown the structure of the piston 5 comprising a central rod or stem 12 having flanges or bars 11 extending radially outwards therefrom such that this view reminds of a wheel having a central hub provided with spokes. In this view is it also obvious that the portions of the flanges or bars 12 which forms the piston base 14 (se fig. la) and shown as non-visible dotted lines not will pass through the narrowing portions at the opening forming the stopping portion 15 of the housing 2. Figure lc discloses a side view of the piston 5 having a piston base 14 at its lower, first end 6, a middle piston main portion 18 and an anchoring portion 19 at its second, upper end 7. The piston comprises longitudinally stretching flanges or bars 11 extending along the length of the piston 5 and attached at a first, longitudinal side to a central stem 12 (se figure lb) . At its other distal end are the flanges 11 attached at selected distances along the

longitudinal length of the piston 5 to circumferential rings 13 in order to stabilize the structure. At its first end 6 is the cross sectional area of the piston 5 enlarged to form the base 14. The base 14 is adapted to fit closely with the inner sides of the housing such that the piston may be effectively activated by the elevated pressure from a power source, e.g. a pyrotechnic charge. The part of the base 14 which is intended to be in contact with the inner side of the housing may comprise a material which is softer than the non-metallic material used in the main portion of the piston 5, e.g. for the load bearing structure formed of the bars and the central stem, in order to provide for a gas tight seal between the base 14 and a housing. Likewise, the upper part of the main portion 18 of the piston 5, close to the anchoring portion 19, which is intended to be in contact with the edges of an opening of a housing may also comprise a softer material in order to provide an efficient sealing of the actuator preventing dirt or moist to enter into an actuator. Even though the piston 5 is shown with an anchoring portion provided a loop, the pistons upper part could also be an ordinary flat surface or have any desired shape.

In figure Id is shown a housing 2 which is divided in two parts by support flanges 8 on the inner side of the housing 2. The part of the housing comprising the first end 3 is adapted to receive a pyrotechnic charge and the other part comprising the second end 4 is adapted to receive a piston and the support flanges 8 is adapted to support the piston and the pyrotechnic device when inserted into the housing 2. The flanges 8 shall preferably be designed such that there is a rather large opening between the two

compartments of the housing 2 in order to allow the

expanding gas from the power source, e.g a pyrotechnic device, to efficiently push a piston. The housing 2

according to this embodiment is preferably manufactured such that it is finally finished when a piston has been located in the housing and the wedge shaped stopping portions 15 and braking portions 16 narrowing the inner side of the housing 2 close to the opening 10 in the second, upper end 4 is made after a piston has been

introduced into the housing 2. The narrowing sections may for example be made by crimping of a cold forged pipe or be prefabricated protrusions on the inside.

The piston described above is primarily intended to be manufactured completely by using one or several non- metallic material, e.g. PA6 which may be reinforced with glass fibres, optionally together with further materials or reinforcing structures. However, it may also comprise a load bearing structure of a metallic material and a central stem could for example comprise a metallic rod. In figures 2a - 2g are suggested different shapes of a piston suitable for an actuator according to the present invention and these figures shows the radial cross

sectional views of these different embodiments.

In figure 2a is disclosed a shape of a piston which is similar to the shape disclosed in figure 1 but there are only six "spokes" (actually bars or flanges) instead of eight. Also in this case could there optionally be included a central stem made of metal or a reinforcing non-metallic material . In figure 2b is disclosed a piston which is solid and has a circular radial cross sectional shape. The piston is made from a non-metallic material.

In figure 2c is disclosed a piston formed as hollow

cylinder or pipe from a plastic material. In figures 2d and 2e is the plastic pipe reinforced in its central portion by a load bearing rod respectively a load bearing pipe of another material than the material used for the outer pipe. The material of the reinforcing structure may be metallic or non-metallic. In figure 2 f-g are disclosed different shapes of solid pistons made from a single material or compound. In figure 2 f is disclosed a piston having a cross shaped cross sectional area, in figure 2g is the cross sectional shape of the piston circular provided with four symmetrically located semicircular cut-outs at its edges and in figure 2h is the shape octagonic. If desired, also these suggested pistons may be provided with a reinforcing structure, e.g. a load bearing central rod. It may be advantageous to have a piston which not is shaped to have a close fit with the inner side of the housing, e.g to have a cross sectional shape of a piston as disclosed in figures 2 f - g which not are circular if the housing is circular. By designing the piston and the housing in this way, the frictional forces between the piston and the housing may be lowered and there is a lower risk the piston may get stuck to the inside of the housing.

Figures 3a - 3d disclose different stages of an actuator during activation. In figure 3a is the actuator 1 shown when it is at rest before it has been activated.

In figure 3b has the actuator been activated by triggering the pyrotechnic device 9 and the piston 5 has started to move further out of the opening 10 in the cylinder 2.

In figure 3c has the enlarged piston base 14 reached the location where the housing is getting narrower and the braking portion 16 on the inside of the cylinder 2 starts. When the piston 5 moves to be further extended through the opening 10, its base 14 will start to deform somewhat while the movement of the piston will be braked or slowed down at the same time. In figure 3d has the piston 5 reached its end position in which the piston 5 is pushed by the pressure in the cylinder 2 such that the frustoconical part of the piston base 14 rests on the wedge shaped stopping portion 15 of the cylinder 2.

To be noted, the inclusion of the braking portion 16 and wedge shaped stopping portion 15 of the housing 2 adapted to the conical shape of the base 14 of the piston 2 shown in association with figure 3 involves beneficial features which are particularly suitable for a plastic or non- metallic piston. However, the plastic piston may of course have other shapes and could also be an ordinary solid rod provided with an enlarged base plate, e.g a piston having an ordinary T-shaped longitudinal cross sectional profile and having a stop at the upper part of the housing adapted to a changed shape of the base portion of the piston, e.g. an ordinary edge being orthogonal to the inner wall of the cylinder .

In figures 4a - 4e is disclosed an example of how an actuator 1 according to the invention may be assembled and produced from a housing 2 in the form of a hollow cylinder or pipe and a piston 5.

In figure 4a is shown a housing 2 which has been provided with protrusions on the inside of the pipe forming

supporting flanges 8 in order to define resting positions for a piston and a pyrotechnic device. The housing 2 may for example be a cold forged pipe made of metal.

In figure 4b is shown how the piston 5 has been introduced into the housing 2. The piston has been introduced through the opening 10 at the second end 4 of the pipe. The piston 5 may be made such that the part of the piston forming the seal is made of a softer material than its load bearing structure .

In figure 4c is shown that when the piston 5 has been located in the housing 2, the pipe is crimped close to its second end 4 in order to provide a narrowing section forming a stopping portion 15 and a braking portion 16 and to provide a close fit between the piston 5 and the pipe at its second end so as to form a tight seal. The decreased cross sectional area of the housing 2 will thus provide for an efficient sealing of the actuator before it is activated as well as forming a stopping restriction for an enlarged base 14 of the piston 5 when the actuator is activated.

In figure 4d has a pyrotechnic device 9 been introduced into the housing 2 at its first end 3. In figure 4e has the housing 2 been crimped at the very end of its first end 3 of the pipe 2 in order to keep the pyrotechnic device 9 in its desired position, clamping it between the crimped end portion 3 and the supporting flanges 8, and preventing it from escaping out of the housing 2.

When assembling the actuator, the assembling may be made in the order of appearance of the figures as described above. However, it may also be possible to introduce the

pyrotechnic device and crimp the pipe at the end close to the pyrotechnic device before the piston is introduced into the pipe through the other end and thereafter crimping the other end of the pipe. Still an alternative is to introduce both the piston and the pyrotechnic device before the pipe is crimped at or close to the respective ends. When

producing the actuator as described above, the essential feature is to perform the crimping at the ends after the devices, i.e. the piston and the pyrotechnic device, has been introduced into the housing at the respective ends.

Claims

An actuator (1) for a hood lifting arrangement in a vehicle safety system in order to provide protection for a pedestrian hit by the vehicle, said actuator (1) comprising a housing (2) having a first end (3) and a second end (4) and a piston (5) having a first end (6) and a second end (7) adapted to fit in the housing (2), said first end (3) of the housing (2) adapted to comprise or be connected to a power source and said second end (4) of the housing (2) provided with an opening (10) through which said piston (5) will extend when the actuator (1) is activated, characterised in that said piston (5) comprises a non-metallic material.

2. An actuator (1) according to claim 1 characterised in that said piston (5) comprises at least 50 % by volume of non-metallic material.

An actuator (1) according to claim 1 characterised in that said piston (5) comprises at least 90 % by volume of non-metallic material.

An actuator (1) according to any previous claims characterised in that the outer surfaces of said piston (5) is covered by non-metallic material.

An actuator (1) according to any previous claims characterised in that said piston (5) comprises a reinforcing metallic rod stretching along the longitudinal length of the piston having a length corresponding to at least 50 % of the length of the piston .

An actuator (1) according to claim 5 characterised in that said metallic rod stretches along the longitudinal length of the piston having a length corresponding to at least 90 % of the length of the piston .

An actuator (1) according to claim 1 characterised in that said piston (5) consists of only non- metallic materials.

An actuator (1) according to any previous claim characterised in that said non-metallic material used in said piston (5) includes a plastic polymer.

An actuator (1) according to any previous claims characterised in that said piston (5) is built up by a central stem (12) stretching essentially from the first end (6) to the second end (7) of the piston, said stem being provided with at least three bars (11) stretching along the length of the stem (12), said bars (11) attached to the stem (12) by a first edge of the bar (11) and the bar (11) is stretching radially outwards from the stem (12) unto its second distal end.

An actuator (1) according to claim 9 characterised in that said distal edges of the bars (11) are disposed equidistant from each other and the central stem ( 12 ) . An actuator (1) according to claim 9 or 10

characterised in that said distal edges of the flanges (11) are connected with each other by several ring shaped elements disposed at desired distances along the length of the piston (5) .

An actuator (1) according to any previous claims characterised in that said actuator (1) comprises a housing (2) made completely or partly by a non- metallic material.

A vehicle comprising a hood lifting arrangement characterised in that said hood lifting arrangement comprises an actuator (1) according to anyone of claims 1 to 12.

A method for producing an actuator (1) , said method comprising the steps of:

a) Introducing a pyrotechnic device (9) into a

housing (2) from a first end (3)

b) Introducing a piston to the housing (2) from a second end (4)

c) Manipulating said housing (2) at its first end

(3) such that the cross sectional area of the housing is decreased to such an extent that said pyrotechnic device (9) is prevented from being able to pass through said first end (3)

d) Manipulating said housing at said second end such that the cross sectional area of the housing is decreased to such an extent that a main body portion of the piston (5) may pass through the opening (10) in the second end while the base portion of the piston is prevented from passing through .

A method according to claim 14 characterised in that said decrease of the cross sectional area of the housing (2) is made by crimping.