Pedestrian protection device for a motor vehicle

1. A pedestrian protection device for a motor vehicle, comprising:

a bumper crossmember;

a deformation element, which is arrangeable on the bumper crossmember and which has a first element and a second element which, in an event of a collision of the motor vehicle, are displaceable relative to each other; and

a mechanical locking mechanism which has a moveable locking element that interacts with a contact surface and which is pretensionable or is pretensioned with a spring device, the movable locking element being arranged on the first element or the second element and being latchable in a form fitting manner with a depression or step to the other of the first element and the second element, wherein

at a high displacement speed which is greater than or equal to a predetermined second displacement speed, the locking mechanism prevents a displacement of the first element relative to the second element by self locking of the locking element,

at an average displacement speed which is less than the predetermined second displacement speed and greater than a predetermined first displacement speed, the locking mechanism permits a displacement of the first element and the second element relative to each other, and

at a low displacement speed which is less than or equal to the predetermined first displacement speed, the locking mechanism prevents a displacement of the first element and the second element relative to each other at least partially by a form-fitting latching of the locking element with the depression or step.

2. The pedestrian protection device as claimed in claim 1 , wherein

the locking element and the spring device are configured to interact such that, with a displacement of the first element and the second element relative to each other, the locking element is pretensionable by the spring device, and

the spring device is substantially relaxed in a starting position.

3. The pedestrian protection device as claimed in claim 2 , wherein

the contact surface is arranged and configured such that, upon a relative movement of the first element and the second element with respect to each other, the locking element is moveable along the contact surface in contact with the contact surface counter to the spring force of the spring device and is therefore pretensionable before the locking element reaches the form fit with the depression or the step, and

the spring device, the locking element and the contact surface interact in such a manner that:

at the high displacement speed, when the locking element is in engagement with the contact surface, a movement of the locking element along the contact surface and therefore a displacement of the first element and the second element relative to each other is prevented by the self locking of the locking element,

at the average displacement speed, when the locking element is in engagement with the contact surface, a movement of the locking element along the contact surface is permitted, and, owing to a mass inertia of the locking element, the locking element, on leaving the contact surface, springs over the depression or step, and therefore does not latch into place in a form fitting manner, and a further displacement of the first element and the second element with respect to each other is permitted, and wherein,

at the slow displacement speed, when the locking element is in engagement with the contact surface, a movement of the locking element along the contact surface is permitted, and the locking element latches into place in a form fitting manner with the depression or step at the slow displacement speed.

4. The pedestrian protection device as claimed in claim 3 , wherein

the contact surface is formed obliquely with respect to a displacement direction of the first element and the second element relative to each other, and has a slope in the direction of the contact surface in the displacement direction of the locking element.

5. The pedestrian protection device as claimed in claim 1 , wherein

the deformation element is adapted in order, in a state of the locking mechanism, in which a displacement of the first element relative to the second element has been/is at least partially prevented by self locking or latching, to absorb collision energy by plastic deformation and/or brittle failure of the deformation element over a predetermined deformation distance.

6. The pedestrian protection device as claimed in claim 5 , wherein

the predetermined deformation distance is within a range of 60 mm to 110 mm.

7. The pedestrian protection device as claimed in claim 5 , wherein

in the event of the average displacement speed, at which the locking mechanism is neither self locked nor latched, an energy absorption of the deformation element is lower than an energy absorption of the deformation element in the event of the low and high displacement speed.

8. The pedestrian protection device as claimed in claim 1 , wherein

at the average displacement speed, the first element and the second element are moveable relative to each other over a distance of 60 to 110 mm.

9. The pedestrian protection device as claimed in claim 1 , wherein

the first element is a cylindrical element which is displaceable in a corresponding guide of the second element, and

the locking element is mounted moveably on the first element or the second element.

10. The pedestrian protection device as claimed in claim 1 , wherein

a deformation region of the deformation element is formed between a bumper cladding and the bumper crossmember.

11. The pedestrian protection device as claimed in claim 1 , wherein

the second element is secured on the bumper crossmember or is an integral component of the bumper crossmember.

12. The pedestrian protection device as claimed in claim 10 , wherein

the first element is displaceable into an opening of the bumper crossmember.