Hydraulic rotary oscillator comprising a hydraulic rotary actuator that is driven by a hydraulic fluid flow and comprises a solid cylindrical rotary actuator inner part and at least one hollow cylindrical rotary actuator outer part, which parts are arranged so as to be mutually concentric and radially spaced, radially define at least two work chambers (5, 5') in the shape of ring segments, and are rotatable relative to one another, in a limited manner, in two directions of rotation, the work chambers (5, 5') being separated from one another by means of a co-rotating, radially extending rotary actuator wall, being adjustable in size, and being connected to a hydraulic rotary pump (2, 2') via hydraulic connecting lines (4, 4'), and said oscillator comprising at least one control means that guides the hydraulic fluid flow alternately to the at least two work chambers (5, 5'), the rotary actuator outer part being rotatable and the rotary actuator inner part being rotationally fixed, characterised in that the hydraulic rotary actuator comprises the rotary actuator inner part and three mutually adjacent rotary actuator outer parts (7, 7', 7"), the central rotary actuator outer part always moving in the opposite direction from the two outer rotary actuator outer parts (7, 7"), an outer part extension being formed on each of the rotary actuator outer parts (7, 7', 7") and a fin being fastened to or moulded on each of the outer part extensions, and the hydraulic fluid flow that drives the hydraulic rotary actuator oscillates constantly and is generated by means of two hydraulic rotary pumps (2, 2') that are continuously driven, via a common drive unit comprising a drive motor, the two hydraulic rotary pumps (2, 2') being fluidically connected in parallel with one another and with the hydraulic rotary actuator, and each hydraulic rotary pump (2, 2') comprising a cavity that is in the shape of a spherical segment, is filled with a hydraulic fluid and has a circular cavity base plate, a rotatably driven spherical segment arranged in the cavity and having a planar spherical segment base and a globular spherical segment top, a spherical wedge-shaped space between the cavity base plate and the spherical segment base, and comprising a drive axle of the spherical segment that extends, as an axis of rotation, perpendicularly to the cavity base plate and so as to be inclined relative to the central axis of the spherical segment and is aligned with the centre of the cavity base plate, comprising a swinging plate that is introduced centrally and at right-angles into the cavity base plate and the contact edge of which swinging plate touches the spherical segment base, which swinging plate is pivotable about a virtual fulcrum of the swinging plate in the centre of the contact edge, and comprising passage channels (31, 31') for the hydraulic fluid on either side of the swinging plate, in the cavity base plate, in order to transport the hydraulic fluid out of and into the space between the cavity base plate and the spherical segment base, and the oscillation frequency of the hydraulic fluid flow being variable by means of the freely adjustable rotational speed of the two hydraulic rotary pumps (2, 2'), and the quantity and pressure of the oscillating hydraulic fluid flow that drives the hydraulic rotary actuator is variably adjustable, using a phase adjustment device, by means of the phase position of the rotating spherical segments of the two hydraulic rotary pumps (2, 2'), the phase position of the rotating spherical segments of the two hydraulic rotary pumps (2, 2') being mutually variable, preferably between 0° and 180°, and the pivot angle of the at least three rotary actuator outer parts (7, 7', 7") relative to the rotary actuator inner part, which angle is dependent on the phase position, being able to be variably set between zero degrees and the degree value specified by the rotary stops.