1.  Field of the Invention
The invention relates to a seat in a means of transportation, such as in a motor vehicle. 
2.  Description of the Related Art
A seat for a means of transportation comprises a lower part for supporting the posterior and thighs of an occupant and a rear part for supporting the posterior, back and head of the occupant.  Each of the lower and rear parts has a rigid seat cushion structure covered by padding.  The lower end of the seat back structure is mounted in the seat cushion structure.  The seat back structure has two side parts and upper and lower crosspieces.  The upper crosspiece is rigid and connects upper ends of the two side parts to each other.  The lower crosspiece connects the two side parts at a position below the lower crosspiece. 
DE 695 15 604 T2 discloses a seat of type described above.  The lower crosspiece of the seat disclosed in DE 695 15 604 T2 is arranged at a small distance from the lower ends of the side parts of the seat back structure and therefore at a small distance from the connecting region of the seat back structure and seat cushion structure.  The lower cross part typically is made of metal, but may be plastically deformed by the occupant in the event of a rear-end crash of the means of transportation.  The cross part, however, is sufficiently strong to avoid breaking. 
This configuration of the seat in the region of the lower cross part of the seat back structure should be considered in view of the possibility of a rear-end crash of the means of transportation.  More particularly, the occupant in the seat is moved rearward toward the seat back structure in the event of a rear-end crash due to inertia forces that occur.  The posterior of the occupant is supported on the lower crosspiece, and the forces that are introduced into the crosspiece via the occupant in the event of a rear end crash are of such a magnitude that the crosspiece is deformed plastically.  The positioning of the lower cross part in the vicinity of the lower end of the seat back structure is not suitable for ensuring a positioning of the vehicle occupant in the seat in the event of a rear-end crash. 
There is a great risk of the occupant being subject to a whiplash injury in the event of a rear-end crash.  The impact on the means of transportation in the event of a rear-end crash leads to the movement being transmitted to the occupant.  This takes place after a short delay time when the means of transportation is a motor vehicle.  More particularly, the crumple zone of the vehicle is deformed first and the vehicle itself that has been hit then is set into motion in a manner corresponding to the momentum of the impact.  The acceleration is transmitted via the seat to the occupant.  The occupant is moved rearward in the seat as a result of the inertia forces.  The crosspiece of the seat back structure that is arranged quite far down has the effect here that the occupant who is moving rearward is subjected to a moment that rotates the upper body of the occupant rearward and up about the lower crosspiece.  This inertia of the occupant causes the upper body, following contact with the lower crosspiece, to move up in addition to the rearwardly directed movement.  This upward movement should be prevented to minimize the whiplash effect.  In particular, the upper body of the occupant should not move up in the event of a rear-end crash to an extent that the occupant's head is moved beyond the region of the head restraint and then can move rearward. 
An object of the invention is to develop seat for a means of transportation that reduces risk of injury to an occupant due to whiplash in the event of a rear-end crash.