WO2013043089A1

WO2013043089A1 - A safety device

Info

Publication number: WO2013043089A1
Application number: PCT/SE2011/051129
Authority: WO
Inventors: Stefan Kuntzsch
Original assignee: Autoliv Development Ab
Priority date: 2011-09-21
Filing date: 2011-09-21
Publication date: 2013-03-28

Abstract

A hood-lifting safety device (1)for a motor vehicle is disclosed. The device comprises a cylinder (2) having a longitudinal axis (3), a piston (6) provided at least partially within the cylinder for movement along said longitudinal axis, and an actuator (15) operable to drive the piston (6) from an initial position to an actuated position in order to lift part of the hood of the motor vehicle. The device is characterised in that the piston (6) comprises first and second discrete piston parts (7, 8), each arranged for movement between a respective first position corresponding to the initial position of the piston (6) and a respective second position corresponding to the actuated position of the piston (6). The piston parts (7, 8) are arranged for movement together from their respective first positions to their respective second positions under the action of said actuator (15) during movement of said piston (6) from said initial position to said actuated position to lift the hood, and are configured to thereafter separate from one another for independent movement.

Description

A SAFETY DEVICE

The present invention relates to a safety device, and more particularly relates to a hood- lifting safety device for a motor vehicle.

When a motor vehicle such as a motor car is involved in an accident in which the front part of the vehicle strikes a pedestrian, it is not uncommon for the head of the pedestrian to be brought forcibly into contact with the hood or bonnet (hereinafter referred to as "hood") of the vehicle. This may cause the hood to deform, but in many cases that deformation is arrested as the hood engages part of the engine block, or other component within the engine compartment, immediately beneath the hood. As a consequence, the movement of the pedestrian's head is suddenly stopped, and the pedestrian's head is thus subjected to a very severe deceleration, which is undesirable.

It has therefore been proposed to provide one or more lifting devices located beneath a rear part of the hood, between the hood and the structure of the motor vehicle, and which are adapted to be actuated in an accident situation of the type described, so that the rear edge of the hood is lifted, thus spacing the hood from the underlying engine block or other similar components within the engine compartment. A safety arrangement of this type thus enables the head of a pedestrian, if it strikes the hood or bonnet in an accident, to be decelerated more gradually, as the hood or bonnet deforms, with reduced risk of the hood or bonnet impinging on the underlying engine. Previously proposed mechanical lifting devices generally comprise a moveable piston mounted in a cylinder and which is arranged to be driven rapidly upwardly upon deployment of the device in order to lift the rear part of the hood. However, a problem with many such devices is that they do not provide a sufficient force damping effect upon actuation. The actuating force applied to the piston must be very large in order to overcome inertia and to drive the hood upwardly with sufficient speed in an accident situation. With insufficient damping of this force in the lifting direction, the hood and/or hinge arrangement can become damaged as the piston reaches the upper limit of its stroke. Also, in the event that the hood reaches its uppermost position at the upper limit of the piston's stroke as, or shortly after, it connects with the torso or head of a downwardly moving pedestrian then the pedestrian may be injured. Another issue with such prior art lifting devices concerns the provision of a damping affect in the reverse direction, in order to absorb energy arising from the impact of a pedestrian on top of the hood. As will be appreciated, the weight of a pedestrian impacting on the top of a raised hood applies a very significant downward force on the hood and the lifting device beneath it. It is advantageous to configure the lifting device to permit a degree of downwards yield, to thereby absorb some of this impact energy dampening the downwards movement of the hood during deformation in order to prevent significant injury to the pedestrian.

Previously proposed hood lifting devices have been unable to combine the above-mentioned force damping function in both the opposing lifting and impact directions in a simple and convenient mechanism.

It is an object of the present invention to provide an improved hood-lifting safety device for a motor vehicle.

According to the present invention, there is provided a hood-lifting safety device for a motor vehicle, the device comprising: a housing having a longitudinal axis, a piston provided at least partially within the housing for movement along said longitudinal axis, and an actuator operable to drive the piston from an initial position to an actuated position in order to lift part of the hood of the motor vehicle, the device being characterised in that said piston comprises first and second discrete piston parts, each arranged for movement between a respective first position corresponding to the initial position of the piston and a respective second position corresponding to the actuated position of the piston, the piston parts being arranged for movement together from their respective first positions to their respective second positions under the action of said actuator during movement of said piston from said initial position to said actuated position to lift the hood, and to thereafter separate from one another for independent movement. Preferably, the first and second piston parts are initially coupled for movement together from their respective first positions to their respective second positions, and are arranged to thereafter decouple in order to separate from one another.

Advantageously, the device further comprises a damper arrangement configured to dampen movement of the piston from its initial position to its actuated position during lifting of the hood, and also to dampen subsequent relative movement of the two piston parts towards one another after separation Conveniently, said damper arrangement is configured to urge the first piston part from its second position towards its first position to thereby separate the two piston parts after actuation of the device.

Preferably, said damper arrangement comprises a resilient biasing element arranged to bias the first piston part towards its second position, the biasing element being deformed during movement of said first piston part from its first position to its second position.

Advantageously, said resilient biasing element is a compression spring arranged for compression during movement of said first piston part from its first position to its second position. Conveniently, the safety device further comprises a locking mechanism operable to engage said second piston part when the second piston part adopts its second position

corresponding to the actuated position of the piston, but to permit substantially free movement of the second piston part from its first position to its second position.

Preferably, said locking mechanism is effective to retain said second piston part substantially in its second position under the weight of the hood lifted by the piston after actuation of the device.

Advantageously, said locking mechanism is provided within the housing for movement along the longitudinal axis of the housing, and the damping arrangement is configured to urge the locking mechanism in a direction opposite to the direction in which it urges the first piston part.

Conveniently, the damping arrangement is configured to operate the locking mechanism so as to engage the second piston part in response to movement of the first piston part towards its second position.

Preferably, the locking mechanism comprises a plurality of pawls arranged radially about the second piston part and moveable between respective release positions in which they do not engage the second piston part, and respective locking positions in which they grip against the surface of the second piston part.

Advantageously, said biasing element is arranged to urge the locking mechanism and the first piston part away from one another. Conveniently, said compression spring is arranged between said locking mechanism and the first piston part for compression during movement of the first piston part from its first position towards its second position.

Preferably, said biasing element is arranged to apply a force to the locking mechanism which is effective to operate the locking mechanism as the first piston part approaches or reaches its second position.

Advantageously, said biasing element and the locking mechanism are configured such that said force is effective to urge said pawls from their release positions to their locking positions.

Conveniently, the second piston part is arranged for movement from its second position towards its first position under a generally downwards force applied to the lifted hood of the vehicle, the locking mechanism being arranged for movement with the second piston part, said movement of the locking mechanism being against the biasing action of the damping arrangement.

Preferably, said movement of the locking mechanism, with the second piston part, is effective to compress said compression spring

Advantageously, the safety device is provided on a motor vehicle having a hood mounted to the structure of the vehicle via at least one hinge, the hinge being configured for movement during actuation of the safety device to lift the hood and defining a limit to the movement of the piston from its initial position to its actuated position, and thus defining the respective second positions of the first and second piston parts.

So that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is vertical cross-sectional view through a safety device in accordance with an embodiment of the present invention, showing the device in an initial configuration prior to actuation;

Figure 2 is a schematic view of the safety device as viewed from above with part removed;

Figure 3 is a view corresponding generally to that of figure 1 , showing the device upon deployment to lift part of the hood of a motor vehicle; Figure 4 shows the device in fully deployed configuration effective to support the hood in its lifted position;

Figure 5 shows the device in a energy-absorbing configuration in which dampens

subsequent downward movement of the hood, for example under the weight and force of an impacting pedestrian;

Figure 6 shows the device repositioned into its deployed configuration ready to absorb a subsequent impact on the hood;

Figure 7 shows the device being manually released ready to be lowered after deployment of the device; and

Figure 8 shows the device fully lowered and re-latched after deployment.

A hood-lifting safety device 1 is illustrated in figures 1 and 2, and which comprises an elongate housing 2, which preferably takes the form of a cylinder having a longitudinal axis 3. The device is shown orientated such that its longitudinal axis 3 is substantially vertical, as would be the case in a typical vehicle installation. As will be appreciated, the housing 2 will be mounted to the structure of the vehicle (not shown), beneath the rear part of the vehicle's hood (also not shown in figures 1 and 2).

The housing 2 is closed at its upper end by an end wall 4, but the end wall has a central aperture 5 formed therein which is centred on the axis 3.

A piston 6 is provided within the housing 2 for axial movement within the housing. The piston 6 comprises two discrete parts; namely a first lower part 7 and a second upper part 8. The lower part 7 of the piston 6 takes the form of a hollow cylinder whose outer diameter is very slightly less than the inner diameter of the housing 2. The lower part 7 is thus provided as a close-sliding fit within the housing 2. The lower part 7 of the piston is closed at its upper end by an end wall 9 having a central aperture 10 which is centred on the axis 3. The central aperture 10 in the lower part 8 of the piston and the aperture 5 at the upper end of the housing are co-aligned.

The upper piston part 8 is generally elongate in form and has a relatively narrow lower section 1 1 and a relatively wide upper section 12, the two sections being separated by a peripheral step or shoulder 13. The upper end region of the upper section 12 is received as a close sliding fit within the aperture 5 provided at the end of the housing 2, and the lower end region of the lower section 1 1 is received within the aperture 10 provided in the top of the lower piston part 7. In the preferred arrangement illustrated, the lowermost end of the lower section 1 1 is formed into a point and thus defines an outwardly directed conical surface, the purpose of which will be described below. The upper piston part 8 thus extends along the axis 3 of the housing, between the lower piston part 7 and the upper end of the housing 2. More particularly, it will be noted that in the initial position of the piston illustrated in figure 1 , the uppermost end of the upper piston part 8 projects slightly above the end wall 4 of the housing 2, for connection or engagement with a hinge mechanism of the vehicle's hood (not shown).

A locating flange 14 is provided on the upper piston part 8. The flange 14 extends outwardly from the narrow lower section 1 1 , and is spaced a short distance above the lowermost end of the lower section. Figure 1 illustrates the two piston parts 7, 8 in respective first positions prior to deployment of the lifting device 1 , and in this position the lowermost annular surface of the flange sits on the upper surface of the end wall 9 of the lower piston part 7. The flange 14 thus defines the extent to which the lower end of the upper piston part 8 is received in the aperture 10 of the lower piston part. In the initial position illustrated in figure 1 , the lower end of the upper piston part 8 effectively plugs the aperture 10 of the lower piston part. The two piston parts 7, 8 are thus coupled. An actuator arrangement 15 is provided at the lower end of the housing 2, the actuator being located within the space defined inside the hollow lower piston part 7 when the lower piston part is located in its initial position illustrated in figure 1 . The actuator can take several optional forms, but is preferably electrically triggered and comprises a pyrotechnic charge 16 located generally below the upper wall 9 of the lower piston part 7. The actuator is operably connected to a sensor arrangement in the motor vehicle and is thus configured to trigger upon receipt of a signal from the sensor arrangement indicating the occurrence or likely occurrence of an accident requiring the vehicle's hood to be lifted (for example a likely impact with a pedestrian), in a manner known per se.

At the upper end of the housing 2, immediately below the upper wall 4, there is provided a locking mechanism 17. The locking mechanism 17 is configured for sliding movement along the longitudinal axis 3 of the housing and comprises an annular support member 18 which is sized and configured to be close-sliding fit inside the housing 2, and which extends around the upper section 12 of the upper piston part 8 in spaced relation thereto. The support member 18 carries a plurality of locking members in the form of pawls 19 which are arranged radially about the upper piston part 8 as illustrated most clearly in figure 2. The locking pawls 19 are each pivotally mounted to the support member 18 at their outer ends via generally 5 tangential pivot axes 20 and extend radially inwardly towards the upper piston part 8, where they terminate and carry a plurality of gripping formations 21 . The gripping formations 21 are preferably provided in the form of upwardly directed serrations having a so-called "shark- tooth" configuration for selective gripping engagement with the outer surface of the upper section 12 of the upper piston part 8, as will be described in more detail below. o The locking mechanism 17 is supported in its initial position at the upper end of the housing 2 by a damper arrangement 22 comprising a resilient biasing element 23, which in the favoured embodiment illustrated takes the form of a helically wound compression spring. As illustrated in figure 1 , the compression spring 23 is provided inside the housing, between the locking mechanism and the lower piston part 7. More particularly, it can be seen that the5 lower end of the spring 23 is supported on an annular support member 24 which is provided as a close sliding fit inside the housing 2 and which sits on top of the first piston part 7.

In the initial configuration of the device 1 illustrated in figure 1 , the spring 23 is placed under light compression and so serves to urge the locking mechanism 17 upwardly against the upper end wall 4 of the housing 2. The pawls 19 are thus urged into light contact with the o outer surface of the upper section 12 of the upper piston part 8.

As already indicated above, figure 1 shows the various components of the lifting device 1 in their initial positions prior to actuation of the device. In particular, it is to be noted that in this configuration the lower and upper piston parts 7, 8 are each positioned in a respective first position corresponding to the first position of the piston 6 as a whole. 5 Upon receipt of an appropriate firing signal from a sensor, the actuator 15 is triggered and the pyrotechnic charge 16 is fired. This serves to drive the piston 6 upwardly in the housing 2, away from its initial position, as illustrated in figure 3. Furthermore, it is to be noted that because the lower end of the upper piston part 8 initially plugs the aperture 10 in the lower piston part 7, and because the flange 14 engages the upper surface of the end wall 9 of the0 lower piston part 7, both piston parts 7, 8 are effectively coupled and are thus driven

upwardly together towards respective second positions which, as illustrated in figure 3, correspond to a raised actuated position of the piston 6. As illustrated in figure 2, in the actuated position of the piston, the upper section 12 of the upper piston part 8 has been driven upwardly out of the end wall of the housing 2, and so because of its connection or engagement with the hinge mechanism of the hood, is effective to lift the rear part of the hood of the vehicle. It is to be noted at this juncture that the hinge mechanism is preferably configured to comprise a mechanical stop to define a limit to the upward movement of the piston 6, and more particularly the upper piston part 12. The piston is thus prevented from being driven upwardly beyond the actuated position illustrated in figure 3 in which the shoulder 13 between the lower and upper sections 1 1 , 12 of the upper piston part 8 is stopped immediately before entering the gap between the locking pawls 19. As will be appreciated, as the lower piston part 7 is driven upwardly as described above from its first position illustrated in figure 1 to its second position illustrated in figure 3, the biasing spring 23 becomes forcibly compressed and thus urges the locking mechanism 17 more forcefully against the upper end wall 4 of the housing 2. The effect of this is to urge the locking pawls more tightly against the outer surface of the upper section 12 of the upper piston part 8. However, because of the upwardly directed shark-teeth configuration of the gripping formations, the upper section 12 is still permitted to slide upwardly through the pawls to achieve its second position illustrated in figure 3.

It is to be noted that during compression of the spring 23 as described above, the spring 23 serves to dampen the movement of the piston in the upwards direction from its initial position to its actuated position.

Because the locking pawls 19 of the locking mechanism 17 are urged more firmly against the upper section 12 of the upper piston part 8 in the actuated position of the piston, and also because of the upwardly directed shark-tooth configuration of their gripping formations, the locking mechanism 17 is thus effective to prevent subsequent downward movement of the upper piston part 8 through its locking pawls 19. In a preferred arrangement, the locking mechanism is configured to have sufficient locking strength in this configuration to support the weight of the lifted hood of the vehicle and thus to prevent downward movement of the hood under its own weight.

As will be appreciated, in the highly compressed condition of the biasing spring 23 in the actuated position of the piston 6 illustrated in figure 3, the spring acts to bias the lower piston part 8 downwardly from its second position illustrated in figure 3 back towards its first position at the lower end of the housing. As the driving force produced by the actuator 15 decays, this biasing force from the spring becomes free to urge the lower piston part 7 back down towards its first position as illustrated in figure 4, thus decoupling and separating the first and second piston parts 7, 8 from one another for independent movement.

In the separated configuration illustrated in figure 4, the biasing spring 23 is returned from the heavily compressed condition illustrated in figure 3 during actuation, to a lightly compressed condition in which it lightly urges the locking mechanism 17 and the first piston part 7 apart from one another in the post-actuated configuration.

Because the locking mechanism 17 has been operated by the upwards movement of the lower piston part 7 during actuation of the device, it is now firmly locked against the upper piston part 8. This means that should any subsequent downwards force be applied to the lifted hood of the vehicle, for example as a result of impact with a pedestrian, the upper piston part 8 and the locking mechanism 17 will move downwardly together as illustrated in figure 5, with the spring 23 thus compressing to dampen the movement and absorb some of the impact energy, thereby reducing the risk of injury to the pedestrian. It is thus important to note the spring 23 serves not only to dampen upward lifting movement of the piston 6 during actuation of the lifting device, but also to dampen subsequent downward movement of the upper piston part 8 arising from impact with a pedestrian.

The limit of the downwards movement of the upper piston part 8 towards the lower piston part 7 will be defined by re-engagement of the lower end of the upper piston part in the aperture 10 of the lower piston part 7. The pointed lower end of the upper piston part serves to ensure that the lower end properly re-engages in the aperture 10 in the event that the upper piston part 8 has become tilted out of alignment with the axis 3 during the accident. However, it is to be appreciated that for most impact situations with pedestrians, this limit of downwards movement will not be reached; the spring 23 instead accommodating the entire range of movement.

Following compression of the spring 23 during downwards movement of the hood and the upper piston part 8, the spring will then tend to expand again, thereby urging the upper piston part 8 and the hood upwardly, back towards their raised positions as illustrated in figure 6, in readiness for any supplementary impacts. After an accident involving actuation of the hood-lifting device 1 , it is considered

advantageous to be able to lower the hood of the vehicle back to (or least closer to) its initial position to permit unimpeded driving of the motor vehicle (for example to a repair shop for repair). The preferred embodiment of the lifting device 1 illustrated is configured to permit such re-lowering of the hood.

In order to lower the hood manually following operation of the safety device, it is possible for a person to forcibly pull the upper section 12 of the upper piston 8 upwardly from its second position illustrated in figure 6 in which it will sit after an accident. It is envisaged that this may require disconnection of the upper piston part 8 from the hinge mechanism of the hood in order to overcome the limit to upwards movement defined by the hinge.

Figure 7 illustrates such upwards pulling of the upper section 12. As will be appreciated, because the shark-tooth gripping formations 21 are directed upwardly, the locking mechanism does not offer significant resistance to an upward pull on the upper piston part 8 in this manner. With the stop mechanism in the hinge disabled or overcome, the upper piston part 8 can be pulled above the normal limit of its movement, such that the shoulder 13 moves past the locking pawls 19. The relatively narrow lower section 1 1 of the upper piston part 8 is thus moved into position between the locking pawls 19. However, the locking pawls 19 are not sufficiently long to engage the relatively narrow section 1 1 , and so the upward biasing force of the spring 23 pressing the locking mechanism 17 against the upper end wall 4 of the housing 2 serves to turn the locking pawls 19 downwardly and slightly outwardly at their inner ends, the inner ends of the locking pawls thus swinging slightly away from the relatively wide upper section 12 now located above them.

The upper piston part 8 can thus then be pressed downwardly to return it towards its first position in coupling engagement with the power piston part 7, as denoted by arrow D in figure 8, without the locking pawls gripping it. However, with the locking pawls pointed downwardly at their inner ends as illustrated in figure 8, they now serve to engage the upper section 12 of the upper piston 8 in its re-set first position as illustrated in figure 8 and resist subsequent upwards movement of the upper piston part 8. The lifting device has thus been manually re-latched to hold the rear part of the vehicle's hood down. The device can then either be repaired and re-set back to its initial armed configuration illustrated in figure 1 , or more likely replaced before the vehicle is recommissioned. The above-described lifting device has a simple construction, yet permits the damping of forces in both directions along its longitudinal axis 3. During actuation of the device to lift the hood of a vehicle, the two parts 7, 8 of the piston move together as a coupled unit, and their movement is damped by compression of the spring 23. Subsequent downwards movement of the hood, under the force of an impacted pedestrian is then permitted by separation of the two piston parts, and the subsequent recompression of the spring 23 serves to damp such impact forces in the opposite direction.

5 When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or integers.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for i o performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those 15 skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

A hood-lifting safety device (1 ) for a motor vehicle, the device comprising: a housing (2) having a longitudinal axis (3), a piston (6) provided at least partially within the housing (2) for movement along said longitudinal axis (3), and an actuator (15) operable to drive the piston (6) from an initial position to an actuated position in order to lift part of the hood of the motor vehicle, the device (1 ) being characterised in that said piston (6) comprises first and second discrete piston parts (7,8), each arranged for movement between a respective first position corresponding to the initial position of the piston (6) and a respective second position corresponding to the actuated position of the piston (6), the piston parts (7,8) being arranged for movement together from their respective first positions to their respective second positions under the action of said actuator (15) during movement of said piston (6) from said initial position to said actuated position to lift the hood, and to thereafter separate from one another for independent movement.

A hood-lifting safety device according to claim 1 , further comprising a damper arrangement (22) configured to dampen movement of the piston (6) from its initial position to its actuated position during lifting of the hood, and also to dampen subsequent relative movement of the two piston parts (7,8) towards one another after separation

A hood-lifting safety device according to claim 2, wherein said damper arrangement (22) is configured to urge the first piston part (7) from its second position towards its first position to thereby separate the two piston parts (7,8) after actuation of the device.

A hood-lifting safety device according to claim 3, wherein said damper arrangement (22) comprises a resilient biasing element (23) arranged to bias the first piston part (7) towards its second position, the biasing element (23) being deformed during movement of said first piston part (7) from its first position to its second position.

5. A hood-lifting safety device according to claim 4, wherein said resilient biasing element is a compression spring (23) arranged for compression during movement of said first piston part (7) from its first position to its second position.

6. A hood-lifting safety device according to any preceding claim, further comprising a locking mechanism (17) operable to engage said second piston part (8) when the second piston part (8) adopts its second position corresponding to the actuated position of the piston (6), but to permit substantially free movement of the second piston part (8) from its first position to its second position.

7. A hood-lifting safety device according to claim 6, wherein said locking mechanism (17) is effective to retain said second piston part (8) substantially in its second position under the weight of the hood lifted by the piston (6) after actuation of the device.

8. A hood-lifting safety device according to claim 6 or claim 7 as dependant upon any one of claims 3 to 6, wherein said locking mechanism (17) is provided within the housing (2) for movement along the longitudinal axis (3) of the housing, and the damping arrangement (22) is configured to urge the locking mechanism (17) in a direction opposite to the direction in which it urges the first piston part (7).

9. A hood-lifting safety device according to claim 8, wherein the damping

arrangement (22) is configured to operate the locking mechanism (17) so as to engage the second piston part (8) in response to movement of the first piston part (7) towards its second position.

10. A hood-lifting safety device according to any one of claims 6 to 9, wherein the locking mechanism (17) comprises a plurality of pawls (19) arranged radially about the second piston part (8) and moveable between respective release positions in which they do not grip the second piston part (8), and respective locking positions in which they grip against the surface of the second piston part.

1 1 . A hood-lifting safety device according to any one of claims 8 to 10, as dependant upon claim 4 or claim 5, wherein said biasing element (23) is arranged to urge the locking mechanism (17) and the first piston part (7) away from one another.

12. A hood-lifting safety device according to claim 1 1 as dependant upon claim 5, wherein said compression spring (23) is arranged between said locking mechanism (17) and the first piston part (7) for compression during movement of the first piston part (7) from its first position towards its second position.

13. A hood-lifting safety device according to claim 1 1 or claim 12, wherein said

biasing element (23) is arranged to apply a force to the locking mechanism (17) which is effective to operate the locking mechanism as the first piston part (7) approaches or reaches its second position.

14. A hood-lifting safety device according to any one of claims 8 to 13, wherein the second piston part (8) is arranged for movement from its second position towards its first position under a generally downwards force applied to the lifted hood of the vehicle, the locking mechanism (17) being arranged for said movement with the second piston part (8), said movement of the locking mechanism (17) being against the biasing action of the damping arrangement (22).

15. A hood-lifting safety device according to claim 14 as dependant upon claim 12, wherein said movement of the locking mechanism (23), with the second piston part (8), is effective to compress said compression spring (23).