Safety helmet with telescopically adjustable head size

1. A safety helmet comprising:

an arched helmet shell;

a bearing ring attached on an inside to the helmet shell and configured to fully or at least partially encompass a head of a user of the safety helmet and to determine a head size of the safety helmet;

an actuating element accessible from an outside of the helmet shell and rotatably attached to the helmet shell; and

a transmission unit configured to transmit a rotation of the actuating element to the bearing ring such that the head size provided by the bearing ring is changed, wherein the transmission unit comprises:

a helmet shell-side transmission piece non-rotatably connected to the actuating element so as to rotate in unison with the actuating element; and

a bearing ring-side transmission piece, wherein:

the helmet shell-side transmission piece and the bearing ring-side transmission piece together at least partially bridge a distance between the actuating element and the bearing ring and extend along a common longitudinal axis;

the helmet shell-side transmission piece is configured to move, linearly in parallel to the common longitudinal axis, relative to the actuating element in two opposite directions;

the bearing ring-side transmission piece is non-rotatably connected to the helmet shell-side transmission piece so as to be rotatable in unison therewith and is mechanically connected to the bearing ring;

the bearing ring-side transmission piece is configured to move, linearly in parallel to the common longitudinal axis, relative to the helmet shell-side transmission piece in two opposite directions; and

the distance between the actuating element and the bearing ring is changeable both by a linear movement of the helmet shell-side transmission piece relative to the actuating element and by a linear movement of the bearing ring-side transmission piece relative to the helmet shell-side transmission piece.

2. A safety helmet in accordance with claim 1 , further comprising an intermediate piece, wherein:

the intermediate piece is non-rotatably connected to the helmet shell-side transmission piece such that the intermediate piece and the helmet shell-side transmission piece are rotatable in unison;

the intermediate piece is non-rotatably connected to the actuating element such that the intermediate piece and the actuating element are rotatable in unison; and

the helmet shell-side transmission piece is configured to move linearly in parallel to the common longitudinal axis relative to the intermediate piece in two opposite directions.

3. A safety helmet in accordance with claim 2 , wherein:

the intermediate piece comprises at least one intermediate piece-side stop element;

the helmet shell-side transmission piece comprises at least one outer helmet shell-side stop element;

the at least one intermediate piece-side stop element corresponds to the at least one outer helmet shell-side stop element; and

the at least one intermediate piece-side stop element and the at least one outer helmet shell-side stop element together limit a linear movement of the helmet shell-side transmission piece relative to the intermediate piece in parallel to the common longitudinal axis.

4. A safety helmet in accordance with claim 2 , wherein:

the intermediate piece is hollow;

the helmet shell-side transmission piece engages into the intermediate piece; and

the helmet shell-side transmission piece engages into the intermediate piece with different depths depending on a rotary position of the actuating element relative to the helmet shell.

5. A safety helmet in accordance with claim 4 , wherein:

the helmet shell-side transmission piece has an outer profile and

the intermediate piece has an inner profile, which corresponds to the outer profile; and

the connection between the intermediate piece and the helmet shell-side transmission piece, which is a connection enabling a rotation in unison, is established by the two corresponding profiles.

6. A safety helmet in accordance with claim 2 , wherein:

the intermediate piece is rotatably connected to the helmet shell; and

a distance is present between the actuating element and the intermediate piece.

7. A safety helmet in accordance with claim 2 , wherein the actuating element is linearly shiftable relative to the intermediate piece in two opposite directions, which are parallel to the common longitudinal axis.

8. A safety helmet in accordance with claim 2 , wherein the intermediate piece is guided through the actuating element.

9. A safety helmet in accordance with claim 8 , further comprising a plate visible from the outside, wherein:

the plate encloses the intermediate piece; and

the actuating element encloses the plate.

10. A safety helmet in accordance with claim 1 , wherein:

the helmet shell-side transmission piece comprises at least one inner helmet shell-side stop element;

the bearing ring-side transmission piece comprises at least one bearing ring-side stop element;

the at least one inner helmet shell-side stop element corresponds to the at least one bearing ring-side stop element; and

the at least one inner helmet shell-side stop element and the at least one bearing ring-side stop element together limit a linear movement of the bearing ring-side transmission piece in parallel to the common longitudinal axis relative to the helmet shell-side transmission piece.

11. A safety helmet in accordance with claim 1 , wherein:

the helmet shell-side transmission piece is hollow; and

the bearing ring-side transmission piece engages into the hollow helmet shell-side transmission piece with different depths depending on the rotary position of the actuating element relative to the helmet shell.

12. A safety helmet in accordance with claim 11 , wherein:

the bearing ring-side transmission piece has an outer profile;

the helmet shell-side transmission piece has an inner profile, which corresponds to the outer profile; and

the connection between the bearing ring-side transmission piece and the helmet shell-side transmission piece is established by the outer profile and the inner profile.

13. A safety helmet in accordance with claim 1 , wherein the actuating element, the bearing ring-side transmission piece and the helmet shell-side transmission piece are rotatable relative to the helmet shell about the common longitudinal axis.

14. A safety helmet in accordance with claim 1 , wherein:

the transmission unit comprises at least one rotatably mounted transmission element; and

the bearing ring-side transmission piece is permanently connected to the at least one rotatably mounted transmission element.

15. A safety helmet in accordance with claim 1 , wherein:

the bearing ring comprises at least two bearing ring parts movable relative to one another;

the transmission unit transmits a rotation of the actuating element to the bearing ring such that the at least two bearing ring parts move relative to one another;

a movement of the two bearing ring parts relative to one another changes the provided head size of the safety helmet; and

the bearing ring-side transmission piece is mechanically connected to at least one of the at least two bearing ring parts.