head restraint          
noun [ C ] uk/ˈhed rɪˌstreɪnt/ us/ˈhed rɪˌstreɪnt/
 (尤指汽车座椅的)头枕,头部保护装置
a part attached to a chair, especially a seat in a car, that supports the head and stops it from moving too far back
  In the 1980s many cars had no rear seat belts, no airbags, and no head restraints.  在1980年代,许多汽车没有后座安全带,没有安全气囊,也没有头枕。 
 Synonym: headrest
  (赛车手戴在头盔上的)头部保护装置
a device or strap attached to a helmet worn by a racing driver, that stops the head from moving too far forward if there is an accident
  Neither racer was wearing a head restraint. 两位参赛者都没有戴头部保护装置。 
 - More examples
 - Millions of motorists and their passengers are risking neck injuries because of badly positioned head restraints.
 - The rear seats can easily be folded, without having to remove the head restraints.
 - A lack of head restraint was the culprit in many racing injuries.
 - Gordon credited his head restraint with saving his life in a crash.
 - He pleaded with NASCAR drivers to wear head restraints.