1. A hybrid navigation device for a vehicle, comprising: at least one auxiliary sensor (DET 1 ) adapted to deliver at least one auxiliary signal representative of an auxiliary navigation parameter of the vehicle, and a plurality of hybrid navigation systems (INH 1 , INH 2 ), each hybrid navigation system comprising at least one inertial navigation system comprising at least one inertial measuring unit (IMU- 1 , IMU- 2 ) including three gyroscopes and three accelerometers and, said inertial measuring unit (IMU- 1 , IMU- 2 ) being adapted to deliver corresponding instantaneous rotation and acceleration signals representative of inertial measurements respectively made by the three gyroscopes and the three accelerometers, and each hybrid navigation system comprising at least one calculator (CALC-H 1 , CALC-H 2 ) configured in such a manner to hybridize at least one of said signals representative of inertial measurements with said at least one auxiliary signal, to form a hybrid signal at the output of each hybrid navigation system (DATA 1 , DATA 2 ), characterized in that: said hybrid navigation device comprises a module (MOD) for the weighting of said hybrid navigation systems (INH 1 , INH 2 ), said module (MOD) being configured in such a manner to receive, said at least one auxiliary signal and said hybrid signals (DATA 1 , DATA 2 ) at the output of each hybrid navigation system (INH 1 , INH 2 ), respectively, to calculate, for each hybrid navigation system, a likelihood of a residue between said hybrid signal output from the concerned hybrid navigation system and said auxiliary signal using a variance estimate of said hybrid signal and a variance estimate of the auxiliary signal, and to deduce therefrom a weighting coefficient for each hybrid navigation system (INH 1 , INH 2 ), said weighting coefficient being respectively calculated as a function of the likelihood of the residue between said hybrid signal (DATA 1 , DATA 2 ) and said auxiliary signal, and said module (MOD) being configured in such a manner to calculate a weighted hybrid signal (DATAOPT) as a function of said hybrid signals (DATA 1 , DATA 2 ) and of the weighting coefficients of each hybrid navigation system, respectively.