Hydraulic pump having impeller pump and trochoid pump

A hydraulic pump, comprising:

• a casing,
• an impellor pump comprising a rotor that is rotationally mobile with respect to the casing about a first axis, the rotor comprising several blades in helix form,
• a transition piece defining a transition zone within the casing and said transition piece having, on a side of the impellor pump, a ramp in helix form developing in a same direction as the helix form of the blades,
• a trochoid pump comprising a rotor with outer toothing secured to the rotor of the impellor pump, and a rotor with internal toothing that is rotationally mobile with respect to the casing about a second axis parallel to and offset from the first axis, the trochoid pump being fed by the impellor pump through the transition zone running along the ramp.