The invention is not however restricted to this particular application and may have a more general application.

In some countries a motor vehicle bonnet is known as a hood, but hereinafter, the term bonnet will be used.

There are increasing demands for motor vehicle design to take account of pedestrian safety and, so far as possible, to design vehicles so that in an impact between a pedestrian and a vehicle, the pedestrian has a reasonable chance of avoiding serious injury or death.

In the case of a frontal impact between a moving vehicle and a pedestrian, the pedestrian is usually thrown onto the vehicle bonnet. If there was an empty space beneath the bonnet, the deformable nature of the sheet metal itself would afford some protection because the energy of the impact could be absorbed to some extent by deformation of the bonnet. However modern vehicle design also calls for no wasted space in the engine compartment and so there is usually a very limited amount of possible deformation of the bonnet before the impact of the pedestrian on the vehicle is transmitted to (unyielding) engine components.

In order to avoid this problem it is known from, for example, DE 197 12 961 to provide a mechanism which lifts the rear edge of the bonnet in the event of an impact so

that the energy of the pedestrian falling into the vehicle can be absorbed by deformation of the bonnet.

It is one object of the invention to provide a mechanism which will allow the rear edge of the bonnet to be rapidly lifted in the event of a pedestrian collision.

According to the invention, there is provided a hinge mechanism for providing a hinged connection between two components, the hinge mechanism comprising: a first hinge leaf to be fixedly attached to a first component; a second hinge leaf to be fixedly attached to a second component; and a linkage mechanism between the first and second hinge leaves, wherein a part of the linkage mechanism moves with and is normally fixedly connected to one of the leaves by a normally fixed releasable connection such that under normal conditions the first and second leaves are able to pivot relative to one another about a single pivot axis and wherein the normally fixed connection can be released when sufficient force is applied thereto, such that the linkage mechanism then allows the first and second leaves to move apart from each other and towards each other by pivoting about more than one pivot axis.

The hinge mechanism can be used to make a hinged connection between the bonnet of a motor vehicle and the vehicle body by fixing the first and second leaves to the bonnet and the vehicle body respectively, so that in normal use the bonnet opens by pivoting on a normally fixed pivot point between the first leaf and the second leaf. In the event that the vehicle should collide with a pedestrian, an air bag or similar lifting device located beneath the bonnet will be deployed, thereby providing a sufficient force to break the or each releasable

connection in order to push the first and second leaves apart and raise the bonnet away from the vehicle engine.

The bonnet will then have room to deform and absorb some of the energy of the collision.

It will be understood that the first leaf could be fixed to the vehicle body and that the second leaf could be fixed to the bonnet, but for simplicity the first leaf will refer to the leaf fixed to the bonnet and the second leaf will refer to the leaf fixed to the vehicle body.

Since the hinge mechanism allows the subsequent movement of the leaves towards one another (assuming they are not damaged), the hinge mechanism will allow the bonnet to move in a downward direction during a collision, further reducing the risk of injury to a pedestrian, particularly in the event that the pedestrian should fall on the bonnet close to a hinge mechanism.

The linkage mechanism which connects the first and second leaves may comprise a third hinge leaf pivotally attached at spaced apart respective pivot points to the first and second leaves, wherein the third leaf is fixedly connected to the first leaf under normal operating conditions so that a pivot axis is provided at the pivot point between the second hinge leaf and the third hinge leaf.

However, the linkage mechanism will preferably comprise a third leaf and a fourth leaf, wherein the third leaf is pivotally attached at spaced apart respective pivot points to the first leaf and to the fourth leaf, and the fourth leaf is pivotally attached at spaced apart respective pivot points to the third leaf and to the second leaf,

wherein the third leaf is fixed to the first leaf by a first releasable connection and the fourth leaf is fixed to the second leaf by a second releasable connection under normal operating conditions so that a pivot axis is provided at the pivot point between the third and fourth leaves. The use of two leaves in the linkage mechanism will allow the for a greater freedom in the movement of the hinge mechanism. This may be important if the hinge mechanism is used to allow the rear end of a bonnet to rise whilst the front end pivots on the bonnet latch.

To reduce the width of the hinge mechanism in the axial direction, the leaves will preferably have elongate portions arranged to move parallel to one another along a displaced set of parallel planes, the pivot axes corresponding to the respective pivot points being normal to these planes. A hinge mechanism can then be situated on each side of the bonnet to pivotally attach the rear end of the bonnet to the vehicle body.

Each releasable connection will preferably be formed by the co-operation of a lip, tab or ridge or other protrusion in one leaf, with a depression, notch, groove or other corresponding recess in the other leaf. When the protrusion of one leaf is received by the corresponding recess in the other leaf, the two leaves will be unable to pivot with respect to one another, and will be therefore fixedly connected.

In one embodiment, each releasable connection is formed by the co-operation of a tab in one leaf with a depression in the other leaf.

Alternatively each releasable connection between a pair of pivotally connected leaves may be formed by the co- operation of a ridge on the surface of one leaf with a groove in the oppositely facing surface of the other leaf, the ridge and groove being aligned in a radial direction along each leaf with respect to the axis of pivotal movement between the leaves.

As a further alternative, the releasable connections may be formed by shear pins.

The leaves will be sufficiently rigid to prevent the ridge and groove from becoming separated under the forces experienced during normal use. However, if sufficient force is used to pivot the two leaves with respect to one another, the leaves will preferably reversibly deform in order to allow the ridge and groove to separate. A releasable connection formed in such a way can thus be released without damaging the leaves.

If the leaves have not been damaged by releasing the releasable connection, the releasable connection can be re-formed preferably by pushing the leaves together so that the leaves deflect slightly in an axial direction to allow the ridge on the surface of one leaf to be received in the groove in the surface of the other leaf, in the manner of a snap-fit arrangement.

Hence if the air bag is deployed and the bonnet is raised inadvertently, the hinge mechanism used to attach the bonnet to the vehicle body can be returned to the normal operating position once the air bag has deflated by pushing down on the bonnet so that the releasable connections snap fit.

The grooves and ridges will preferably be rounded in a direction transverse to their length to reduce the force needed to undo and re-do the or each releasable connection. However, to deter vandals or other unauthorized persons from lifting the bonnet when secured by the hinge mechanism, the or each releasable connections will be sufficiently strong to limit the ease with which it can be undone by a person.

The grooves and ridges will preferably extend along a substantial length of the leaves in order to increase the load that the leaves are able to bear.

For ease of manufacture and assembly, the leaves will preferably be formed from a pressed metal blank and the releasable connections between the leaves will be formed integrally with the leaves.

The maximum separation and relative lateral displacement in one direction of the first and second leaves when they move apart will preferably be limited by a maximum angle through which the third leaf is able to pivot with respect to the fourth leaf. The hinge mechanism when used with a bonnet as described above will then be more likely to prevent the bonnet from rising too far and obscuring the view through the vehicle windscreen and/or moving too far in a rearward direction and coming into contact with the windscreen.

The maximum angle through which the third leaf is able to pivot with respect to the fourth leaf will preferably be limited by a tag extending from the third leaf close to the axis of pivot between the leaves, the tag being

adapted to engage with a with a stop on the fourth leaf when the third leaf reaches a pre-set angular position, so as to inhibit any further movement of the third leaf.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of the front part of a motor vehicle with a hinge mechanism according to the invention, where the hinge mechanism is in a normal position; Figure 2 is a view according to Figure 1 but where the hinge mechanism is in an extended position; Figure 3 is an expanded view of the hinge mechanism in Figure 1; Figure 4 is an expanded view of the hinge mechanism in Figure 2; and, Figure 5 is a side view of hinge mechanism in an extended position according to an alternative embodiment of the invention; Figure 6 is a side view of the hinge mechanism of Figure 5 in a normal position; Figure 7 is a cross sectional view through the dashed line A-A in Figure 6, and

Figure 8 is a side view of a hinge mechanism in the extended position according to another embodiment of the invention.

In Figure 1, a motor vehicle 10 is shown with a bonnet 12 in the closed position. The front end of the bonnet is retained by a catch 16 mounted on the vehicle body 13 and the rear end of the bonnet 12 is pivotally attached to the vehicle body 13 at each side by a hinge mechanism 14, shown here in a normal operating position. When the catch 16 is released, the front end of the bonnet 12 can be raised so that the bonnet 12 opens in the normal way by pivoting about a first axis 18 provided by the hinge mechanism 14.

However, if a collision sensor (not shown) senses a collision of the type that might involve a pedestrian, an air bag 20 located beneath the rear end of the bonnet 12 is deployed, thereby producing an upward force on the bonnet 12. The upward force causes the rear end of the bonnet to rise whilst the front end pivots on the latch mechanism 16, so that the bonnet adopts an emergency position that is raised and inclined with respect to the closed position as shown in Figure 2. This emergency bonnet position is likely to reduce the risk of serious injury to a pedestrian falling upon the bonnet since the bonnet can now deform to a greater depth before coming into contact with the engine components beneath, and the inclination of the bonnet will help to deflect a pedestrian away from the vehicle wind screen wipers (not shown).

In order to allow the rear end the bonnet to be lifted as shown in Figure 2, the hinge mechanism 14 shown in more detail in Figures 3 and 4 comprises three leaves: an upper leaf 22 fixedly attached to the bonnet. 12, a lower leaf 24 fixedly attached to the vehicle body 13, and a middle leaf 26 pivotally attached to the lower and upper leaves 24, 22 about a first pivot axis 18 and a second pivot axis 28 respectively. The pivot axes are situated at opposite ends of the middle leaf 26 such that at each end, the middle leaf 26 forms an elbow joint with the upper and lower leaves 22, 24 respectively.

Here, the leaves have elongate and substantially planar portions arranged to move parallel to one another along a displaced set of parallel planes, the pivot axes 18, 28 being normal to these planes. However, the leaves could alternatively be arranged such that the pivot axes 18, 28 are parallel the planes of the leaves.

During normal operation of the hinge mechanism, the end of the upper leaf 22 remote from the second pivot axis 28 is releasably attached to the middle leaf 26 by a clip mechanism 30 as shown in Figure 3. The clip mechanism 30 (which here is a pair of punched tabs) is strong enough so that under normal forces, the upper leaf 22 is prevented from pivoting with respect to the middle leaf 26 about the second axis 28, and the hinge mechanism 14 behaves as an ordinary hinge with a single pivot axis, here the first pivot axis 18.

When the air bag 20 begins to deploy, the upward force exerted by the air bag 20 on the bonnet 12 is sufficient to open the clip mechanism 30 and release the upper leaf 22 from the middle leaf 26 so that the upper and middle

leaves 22, 26 are free to pivot with respect to one another about the second pivot axis 28. The hinge mechanism can then open out into an extended position in the form of an inverted Z as the rear end of the bonnet is lifted by the deployment of the air bag.

To reduce the risk of the bonnet lifting too far and/or moving too far in a rearward lateral direction and into the vehicle windscreen, the maximum possible angle through which the middle leaf 26 can pivot with respect to the lower leaf 24 is limited by a set of tags 32, 34 on the elbow joint between the lower and middle leaves 24, 26. One tag 32 extends from the lower leaf 24 in a generally radial direction with respect to the first pivot axis 18 and is bent out of the plane of the lower leaf 24 towards the plane in which the middle leaf 26 resides. The other tag 34 extends from the middle leaf in a similar fashion but is bent towards the plane of the lower leaf 24, so that when the middle leaf 26 is pivoted beyond a maximum angle, the two tags come into contact and thereby prevent any further angular movement of the middle leaf 26 with respect to the lower leaf 24.

Once the air bag 20 has deflated and if the bonnet has not been deformed, then the hinge mechanism 14 can collapse back into the original position that the hinge assumes during normal use. This will allow the bonnet to close again so that the vehicle can be driven after the air bag 20 has been deployed accidentally, for example if the collision sensor senses a minor collision which does not result in a pedestrian falling on the bonnet.

The ability of the hinge mechanism 14 to collapse back into the normal position also helps to reduce the risk of the hinge mechanism injuring a pedestrian falling upon it.

Since in normal use the inclination of the upper leaf 22 and hence the bonnet 12 is determined by the angle of the middle leaf 26, the maximum possible angle through which the middle leaf 26 can pivot will be sufficient to allow the bonnet to be opened during normal use.

In another embodiment of the hinge mechanism 14 shown in Figure 8, the hinge mechanism is inverted so that the upper leaf becomes the lower leaf and vice versa. As in the previous embodiment, the hinge mechanism has three leaves pivotally connected end to end about a first pivot axis 18 between the lower and middle leaves, and a second pivot axis 28 between the upper and middle leaves.

However, in this embodiment the lower leaf 24 (fixedly attached to the vehicle body, not shown) is releasably connected to the middle leaf 26 by tabs 30 so that during normal operation the upper leaf 22 (fixedly attached to the bonnet 12) is free to pivot about the second axis 28.

In the extended position, the hinge mechanism assumes the form of a Z and rearward movement of the bonnet is constrained by the pivot axis 18 which is fixed relative the vehicle body.

An alternative embodiment of the hinge mechanism 14 is shown in Figure 5 in the extended position, after an air bar (not shown) beneath the bonnet 12 has deployed. Parts corresponding to those in the previous embodiment have been given the same reference numerals.

The hinge mechanism 14 in Figures 5 and 6 comprises four leaves: an upper leaf 22, upper-middle leaf 26, lower- middle leaf 25 and a lower leaf 24; the upper leaf 22 and bottom leaf 24 being affixed to the bonnet 12 and vehicle body 13 respectively (for convenience the bonnet 12 and vehicle body 13 are not shown in Figure 5). The upper- middle and lower-middle leaves 25, 26 are each respectively pivotally connected to the upper and lower leaves 22, 24 at upper and lower pivot axes 28, 38, and the upper-middle and lower-middle leaves 25, 26 are pivotally connected at a middle pivot axis 18.

The leaves 22, 24, 25, 26 have elongate portions arranged to move parallel to one another along a displaced set of parallel planes, the pivot axes 18, 28, 38 being normal to these planes.

A tag 50 extending from the lower middle leaf 26 close to the middle pivot axis 18 is adapted to interact with a stop 52 when the upper middle leaf 26 reaches as pre-set angular position, so as to prevent any further movement of the upper middle leaf 26. Limiting the angular movement of the upper middle leaf 26 in this way limits the lateral displacement of the bonnet in the rearward direction, and reduces the risk that the bonnet 12 will collide with the vehicle windscreen when the hinge mechanism 14 is in the extended position, particularly if the latch mechanism 16 retaining the front end of the bonnet has been damaged.

Limiting the angular movement of the upper middle leaf 26 also limits the upward movement of the hinge mechanism when it extends under the force of the air bag 20, so that the view of a vehicle driver is not excessively obstructed by the bonnet 12 when a collision is sensed. Typically,

the hinge mechanism 14 will allow the rear end of the bonnet to rise by 10 cm.

When the hinge mechanism 14 is in a normal operating position as shown in Figure 6 (when the bonnet is closed), a rounded groove 40 on the side of the lower leaf 24 is received in a rounded ridge 42 on the side of the lower- middle leaf, the co-operation between the ridge 42 and the groove 40 preventing angular movement of the lower-middle leaf 25 with respect to the lower leaf 24. In a similar fashion, the upper leaf 22 is prevented from moving with respect to the upper middle leaf 26 during normal operation of the hinge 14 by the co-operation between a rounded groove 48 and a corresponding ridge 44 on the oppositely facing sides of the upper leaf 22 and upper- middle leaf 26 respectively.

The leaves 22, 24, 25, 26 are sufficiently stiff such that under normal forces, due to the co-operation between the grooves 40, 48 and the ridges 42, 44, substantial angular movement between the leaves can only occur at the middle axis 18; the upper and upper middle leaves 22, 26 behave as a single leaf, and similarly the lower and lower middle leaves 24, 25 also act together as a single leaf. Hence when the hinge mechanism 14 is in the normal operating position, the bonnet 12 opens and closes by pivoting about the middle axis 18. Since the maximum angular movement of the upper middle leaf 26 is limited by the tag 52 when it reaches the stop 52, the maximum inclination of the bonnet 12 when it opens is also limited.

When the air bag 20 below the bonnet expands, the upward force exerted on the hinge mechanism 14 is sufficient to release the ridges 42 and 44 from the respective grooves

40,44 and the hinge is then free to assume the extended position shown in Figure 5.

As the air bag 20 deflates, the rear end of the bonnet 12 will drop under its own weight, since the rear end of the bonnet is only supported by the air bag 20. Therefore, if the air bag 20 deploys but a pedestrian does not collide with the bonnet 12, or if the air bag 20 is deployed accidentally, the vehicle driver can push the bonnet 12 down back into the normal position, and the bonnet 12 will remain secure so that the vehicle driver can continue his journey.