Vehicle bonnets

A vehicle bonnet assembly has a bonnet hinged to the vehicle body by means of a hinge assembly including a first link pivoted intermediate of its extremities to the vehicle body and second and third links pivoted at one end, each to a different end of the first link, and at their other ends to the bonnet, the links being arranged such that when the bonnet is closed, the bonnet will move rearwardly upon an impact above a predetermined magnitude being applied to the leading edge of the bonnet, the links pivoting to lift the trailing edge of the bonnet, the bonnet pivoting between an open and closed position about the pivotal connection of the first link to the vehicle body.

BACKGROUND TO THE INVENTION 
The present invention relates to vehicle bonnets and in particular to 
bonnets for motor cars. 
In modern motor car design, for visibility, aerodynamic and styling 
reasons, it is desirable that the bonnet line is kept as low as possible. 
As a result, there is generally very little clearance between the bonnet 
and the engine bay contents of the motor vehicle. Consequently the bonnet 
will provide very little cushioning effect when impacted by a pedestrian 
during an accident. 
EP-A-0,509,690 discloses a vehicle bonnet which is hinged at its leading 
edge. The hinge mechanism by which the bonnet is attached to the vehicle, 
is arranged to cause the trailing edge of the bonnet to lift when the 
forward edge of the bonnet is impacted by a pedestrian during an accident. 
With the hinge mechanism disclosed in the above patent specification, the 
leading edge of the bonnet moves downwardly, requiring a clearance beneath 
the bonnet forward of the hinge assembly. This requirement will impose 
restrictions on the height of the bonnet at its leading edge and/or the 
positioning of components, for example the radiator beneath the bonnet 
adjacent its leading edge. 
The present invention provides a hinge mechanism for a forwardly hinged 
bonnet, which will enable the trailing edge of the bonnet to be raised 
whilst minimising the lowering of the leading edge. 
SUMMARY OF THE INVENTION 
In accordance with the present invention a vehicle bonnet assembly includes 
a bonnet, said bonnet being hinged to the vehicle body adjacent a first 
edge transverse to the longitudinal axis of the vehicle and having 
releasable latch means adjacent a second edge transverse to the 
longitudinal axis of the vehicle, the bonnet being hinged to the vehicle 
body by means of a hinge assembly comprising a first link pivoted 
intermediate of its extremities to either the vehicle body or bonnet and 
second and third links pivoted at one end, each to a different end of the 
first link, and at their other ends to the other of said bonnet or vehicle 
body, the links being arranged such that when the bonnet is closed, upon 
rearward movement of the bonnet in response to an impact above a 
predetermined magnitude being applied to the leading edge of the bonnet, 
the links will pivot to lift the bonnet, the bonnet being pivoted between 
an open and closed positions about the pivotal connection of the first 
link to the vehicle body or bonnet. 
Preferably, the links are arranged such that an impact to the leading edge 
of the bonnet will cause the bonnet to lift along its full length. Lifting 
of the bonnet in this manner may be controlled by pivoting of the second 
and third links or pivoting of all three links. When the bonnet is moved 
between its open and its closed positions, in addition to pivoting of the 
first link about its pivotal connection to the vehicle body or bonnet, the 
second and third links may also pivot, in order to increase the degree to 
which the bonnet will open. 
The hinge assembly may be tuned to provide the required movement of the 
bonnet in the various modes of movement of the bonnet, by appropriate 
selection of the lengths of the links and the torsional stiffness of the 
pivots. Alternatively or in addition, one or more of the links may be 
resiliently biased by spring means. 
Preferably, in addition to the hinge mechanism, means is provided for 
controlling movement of the trailing edge of the bonnet.

DESCRIPTION OF A PREFERRED EMBODIMENT 
As illustrated in FIGS. 1 to 3, a vehicle bonnet assembly 10 comprises a 
bonnet 11 which is secured adjacent its leading edge 12 to the vehicle 
body 13 by means of a pair of hinge assemblies 14, one hinge assembly 14 
being located adjacent each of the longitudinal edges of the bonnet 11. 
Towards the trailing edge 15 of the bonnet 11, a pair of latch assemblies 
16 are located adjacent each longitudinal edge of the bonnet 11. 
As illustrated in greater detail in FIGS. 2 and 3, the hinge assemblies 14 
comprise a first link 20 which is mounted intermediate of its ends to a 
bracket 21 which is secured to the vehicle body 13, by means of a pivot 
22, so that the link 20 is free to pivot in a plane parallel to the 
longitudinal axis of the vehicle. A second link 25 is pivotally secured at 
one end to one end of the link 20 by means of pivot 26 and at the other 
end to a bracket 27 that is secured to the bonnet 11, by means of pivot 
28. A third link 30 is pivotally secured at one end to the other end of 
link 20 by means of pivot 31 and at the other end to bracket 27 at a 
position spaced rearwardly longitudinally of the pivot 28, by pivot 32. 
Latch assemblies 16 each comprise a latch arm 40 which is pivotally 
attached to a bracket 41 mounted on the bonnet 11, for movement in the 
plane parallel to the longitudinal axis of the bonnet 11, by means of a 
pivot 42. The other end of the latch arm 40 has a pin 43 adapted to engage 
a latch mechanism 44 when the bonnet 11 is closed, engagement of the pin 
43 by the latch mechanism 44 clamping the bonnet 11 in its closed 
position. A shear pin 45 is located between the arm 40 and bracket 41 to 
locate the arm 40 with respect to the bonnet 11, during normal operation 
of the bonnet 11 as illustrated in full line in FIG. 2. 
If a load above a predetermined limit is applied to the leading edge 12 of 
the bonnet 11, for example as a result of a collision with a pedestrian, 
the bonnet 11 will move rearwardly shearing pin 45 and permitting the 
latch arm 40 to pivot upwardly about pin 43, thereby raising the trailing 
edge of the bonnet 15. The rearward movement of the bonnet 11 causes links 
25 and 30 to pivot rearwardly also raising the leading edge 12 of the 
bonnet 11, as illustrated in broken line on FIG. 2. Raising of the bonnet 
11 in this manner will increase the clearance beneath the bonnet 11, so 
that the bonnet 11 may deform to absorb the impact of a pedestrian 
therewith. For normal operation of the bonnet 11, the latch mechanism 44 
is disengaged to release pin 43 so that the bonnet 11 may be pivoted 
upwardly from the trailing edge 15, about the pivot 22. The links 25 and 
30 may be biased by means of springs (not shown) to pivot clockwise and 
increase the degree of opening of the bonnet 11 for a given rotational 
movement of the link 20 as illustrated in broken line in FIG. 3. 
Various modifications may be made without departing from the invention. For 
example, the lengths of links 20, 25 and 30, the position of pivot 22 
relative to pivots 26 and 31 and the length of latch arm 40 may be varied 
to provide the desired amount of lift of the bonnet at the forward and 
trailing ends 12 and 15. Furthermore, in addition to or as an alternative 
to the shear pin 45, shear pins may be provided between links 25 or 30 and 
the bracket 27 or between links 25 or 30 and the link 20. Alternatively, 
one or more of the pivots 22, 26, 28, 31, 32 or 42 may be torque loaded to 
appropriately control movement of the bonnet in its various modes of 
movement. The various links of the hinge and latch mechanisms may also be 
resiliently biased or balanced by spring means. 
In the embodiment illustrated in FIG. 4 the latch arm 40 of latch assembly 
16 is replaced by a pair of links 46, 47; link 46 having the latch pin 43 
adjacent one end and link 47 being pivotally attached to bracket 41 by 
pivot 42; the links 46, 47 being pivotally interconnected by pivot 48. 
In normal operation the links 46 and 47 are rigidly fixed together and to 
the bracket 41, in a closed position, by means of shear pin 45. The latch 
pin 43 will consequently be held in fixed relationship to the bonnet 11 
and will function in conventional manner to permit release or latching of 
the bonnet 11. 
When the leading edge 12 of the bonnet 11 strikes a pedestrian, rearward 
movement of the bonnet 11 as described above, will cause pin 45 to shear, 
permitting links 46 and 47 to pivot with respect to the bracket 41 and 
each other to an open position, allowing the trailing edge 15 of the 
bonnet 11 to move upwardly. Opening of the links 46 and 47 may be assisted 
by pretensioned spring means (not shown). Such spring means may also serve 
to retain the bonnet 11 in its raised position when struck by the 
pedestrian. Alternatively or in addition, the links 46, 47 may be arranged 
to toggle over centre and thereby lock the links 46, 47 in the raised 
position. Suitable abutment means may be provided to prevent over rotation 
of the links 46 and 47. 
In the above embodiments, abutment means may also be provided to prevent 
anticlockwise rotation of latch arm 40 about pivot 42 or links 46 and 47 
about pivot 42, when the latch assembly 16 is in its normal condition, 
thereby avoiding stressing of the shear pin 45 when the latch pin 43 
engages the latch mechanism 44 as the bonnet 11 is closed. 
In the embodiment illustrated in FIG. 5, the latch assembly 16 is replaced 
by a pair of arcuate tracks 50. The tracks 50 are mounted on the vehicle 
body 13 adjacent each side of the bonnet 11. Brackets 52 mounted on the 
bonnet 11 towards the trailing edge 15 thereof, have pins 53 which engage 
in and slide along the tracks 50 as the bonnet 11 is pivoted between its 
opened and closed positions. Latching mechanisms 54 are provided at lower 
ends of the tracks 50 for engagement of the pins 53, when the bonnet is in 
its closed position. 
With this modified arrangement, to open the bonnet 11, the latching 
mechanisms 54 are released and the trailing edge 15 of the bonnet 11 
pivoted upwardly on the hinge assemblies 14 in simmilar manner to that 
described above. When a load is applied to the leading edge 12 of the 
bonnet 11, rearward movement of the bonnet will cause the latching 
mechanisms 54 to disengage permitting the pins 53 to ride up tracks 50 and 
raise the trailing edge 15 of the bonnet 11. The leading edge 12 of the 
bonnet 11 is raised by the hinge assemblies 14 as described above. 
FIG. 6 illustrates an alternative assembly, in which the first link 20 is 
pivoted to the bonnet 11 and the second and third links 25 and 30 are 
pivotally connected between the first link 20 and the vehicle body 12.