Patent ID: 7121798

Claim:
A radial fan wheel for supplying cooling air for an electrical machine, comprising: a number of fan blades ( 16 ) attached along the circumference of the fan wheel ( 10 ) that have arc-shaped blade ends ( 18 ), which, at their radially inner edge, enclose a first angle (β 1 ) with a tangent ( 22 ) to the inner circumference ( 20 ) of the fan wheel ( 10 ) and at their radially outer edge, enclose a second angle (β 2 ) with a tangent ( 26 ) to the outer circumference ( 24 ) of the fan wheel ( 10 ), wherein the second angle (β 2 ) is selected to be more than 75% greater than the first angle (β 1 ) in order to minimize the turbulence noise in the vicinity of the fan blades ( 16 ) during operation of the fan wheel ( 10 ), wherein the fan blades ( 16 ) are divided into exactly three blade sectors, wherein the angular distances between adjacent fan blades ( 16 ) in a first blade sector have the maximal distance (tmax), wherein the angular distances between adjacent fan blades ( 16 ) in a second blade sector have the minimal distance (tmin), wherein the angular distances between adjacent fan blades ( 16 ) in a third blade sector have an average distance (tavg) that corresponds to half the sum of the maximal distance (tmax) and the minimal distance (tmin), wherein the numbers of fan blades ( 16 ) in the first and second blade sectors are equal, and wherein the values for the maximal distance (tmax) and the minimal distance (tmin) are selected so that the degree of irregularity u =2*( tmax−tmin )/( tmax+tmin ) is between 0.35 and 0.55.