A hydraulic pump includes a casing, and an impeller pump having a rotor that is rotationally mobile with respect to the casing about a first axis. The rotor includes several blades in helix form, a transition zone belonging to the casing and having, on the side of the impeller pump, a ramp in helix form developing in the same direction as the helix form of the blades. A trochoid pump includes a rotor with outer toothing secured to the rotor of the impeller pump. A rotor with internal toothing is rotationally mobile with respect to the casing about a second axis parallel to and offset from the first axis. The trochoid pump is fed by the impeller pump through the transition zone running along the ramp.