Valve actuator, valve and method for controlling a valve actuator

1. A valve actuator for a valve, having a brushless electric motor which comprises a rotor and a stator, and further having a magnetic detent brake with at least one detent magnet for holding said rotor in a detent position, wherein at least one rotor magnet is arranged on said rotor and wherein the at least one rotor magnet co-operates with said detent brake when holding said rotor in the detent position, wherein the stator comprises coils that generate a rotating electromagnetic field that interacts with the at least one rotor magnet in order to actuate the rotor,

wherein said stator is magnetized by said detent magnet, wherein said detent magnet has a magnetic strength such that said stator achieves saturation magnetization and forms a magnetic circuit which includes the detent magnet and extends through the magnetically saturated stator,

and wherein remaining magnetic field lines, which do not contribute to the saturation of said stator, interact with said at least one rotor magnet in order to hold said rotor in said detent position.

2. The valve actuator of claim 1 wherein said detent brake comprises a permanent magnet.

3. The valve actuator of claim 1 wherein said detent brake includes a permanent magnet and said permanent magnet forms said magnetic circuit.

4. The valve actuator of claim 1 wherein said at least one detent magnet is associated with a side surface of said stator.

5. The valve actuator of claim 1 wherein at least one recess is provided on a side of said stator with which said detent magnet is associated.

6. The valve actuator of claim 5 wherein said recess is an opening extending through the side surface of said stator.

7. The valve actuator of claim 1 wherein said detent brake comprises two of said detent magnets which are arranged on opposite sides of said stator.

8. The valve actuator of claim 1 wherein said detent brake includes at least one flux-conducting element.

9. The valve actuator of claim 8 wherein said flux-conducting element is a pole shoe.

10. A valve having a valve actuator, said valve actuator having a brushless electric motor which comprises a rotor and a stator, and further having a magnetic detent brake with at least one detent magnet for holding said rotor in a detent position, wherein at least one rotor magnet is arranged on said rotor and wherein the at least one rotor magnet co-operates with said detent brake, wherein the stator comprises coils that generate a rotating electromagnetic field that interacts with the at least one rotor magnet in order to actuate the rotor, wherein said valve comprises an input, via which a medium flows into said valve, an output, via which the medium can leave said valve, and a flow path between said input and said output in which a valve element is provided which co-operates with a valve seat in order to influence the flow rate; wherein the detent magnet for holding the rotor of the motor in a detent position forms a magnetic circuit with the stator, the stator being magnetized by the detent magnet, wherein the detent magnet has a magnetic strength such that the stator achieves saturation magnetization so that the stator becomes part of the magnetic circuit which emanates from the detent magnet, and wherein remaining magnetic field lines, which do not contribute to the saturation of the stator, interact with the at least one rotor magnet in order to hold the rotor in said detent position.

11. A method for controlling a valve actuator for a valve comprising a brushless electric motor which comprises a rotor and a stator and a magnetic detent brake with at least one detent magnet for holding said rotor in a detent position, wherein at least one rotor magnet is arranged on said rotor and wherein the at least one rotor magnet co-operates with said detent brake when holding said rotor in the detent position, wherein the stator comprises coils that generate a rotating electromagnetic field that interacts with the at least one rotor magnet in order to actuate the rotor, wherein said stator is magnetized by said detent magnet, wherein said detent magnet has a magnetic strength such that said stator achieves saturation magnetization and forms a magnetic circuit which includes the detent magnet and extends through the magnetically saturated stator, and wherein remaining magnetic field lines, which do not contribute to the saturation of said stator, interact with said at least one rotor magnet in order to hold said rotor in said detent position, the method comprising controlling or regulating said electric motor upon start-up such that said electric motor generates at least one magnetic field which weakens a magnetic field generated by said magnetic detent brake.

12. The method of claim 11 wherein said magnetic field of said detent brake is an additional magnetic field.