Height adjustable frame for automotive vehicle seats with two side parts

The invention relates to a height-adjustable underframe of a motor vehicle seat with a left and a right rail pair (20, 22) of a longitudinal adjustment device and with a left and a right side part (24, 26), which are each articulately connected via a rear and a front pivot arm (28, 30) to the associated seat rail of the rail pair (20). Furthermore, a locking arm (36) is provided, which is articulated with a lower end region at the pivot point (34) of a rear pivot arm (28) to the associated seat rail and which is releasably fixed in the vicinity of its upper end in a locking device (38) which is attached to the associated side part (24).