Magnetic exhalation valve with compensation for temperature and patient airway pressure induced changes to the magnetic field

An exhalation valve for a patient ventilator having a patient airway for breathing gas, comprising:

• a valve housing adapted to be connected to the patient ventilator, said valve housing having an exhalation line inlet port for receiving breathing gas from the patient airway, a valve seat on said inlet port, and an exhalation outlet port;
• a valve poppet disposed in said valve housing adjacent to said valve seat, said valve poppet having a longitudinal shaft and a face perpendicular to the shaft with a surface defining an annular groove, and said valve seat having an annular shoulder corresponding to and adapted to interfit with said valve poppet annular groove;
• a magnetic body disposed in said valve housing having a generally cylindrical longitudinal bore, said valve poppet shaft being disposed in said generally cylindrical longitudinal bore in said magnetic body, said valve poppet shaft being suspended in said generally cylindrical longitudinal bore in said magnetic body by a plurality of annular low friction bearings;
• an annular permanent magnet disposed around said magnetic body for producing a magnetic field of predetermined flux density;
• an annular magnetic ring disposed around said magnetic body adjacent to said annular permanent magnet for providing a flux path, said annular permanent magnet and said annular magnetic ring being spaced apart from said magnetic body so as to define an air gap therebetween;
• an armature disposed adjacent to said magnetic body having a central plate portion extending into said air gap, said armature including an electromagnetic coil disposed on said armature central plate portion in said air gap between said magnetic ring and said magnetic body, said valve poppet shaft having a generally cylindrical longitudinal bore, said armature including a cylindrical longitudinal shaft having an upper portion extending within said central bore of said valve poppet shaft, and a lower portion;
• a control mechanism for supplying current to said electromagnetic coil for causing an axial force for axial movement of said poppet with respect to said valve seat;
• and
• means for positioning said magnetic body relative to said valve housing.