  The bipolar collimated outflows of the Hb4 Planetary Nebula (PN) exhibit an
evident decrease in their expansion velocity with respect to the distance from
the central star. So far, similar velocity law has also been found in
Herbig-Haro objects. The interpretation of this peculiar velocity law and the
classification of the outflows is the main focal point of this paper. High
dispersion long-slit echelle spectra along with high resolution images from
Hubble Space Telescope (HST) are applied in the astronomical code SHAPE in
order to reproduce a three-dimensional morpho-kinematical model for the core
and the bipolar outflows. Its central part shows a number of low-ionization
filamentary structures (knots and jets) indicative of common-envelope PNe
evolution and it is reconstructed assuming a toroidal structure. The
high-resolution HST [N II] image of Hb4 unveils the fragmented structure of
outflows. The northern and southern outflows are composed by four and three
knots, respectively, and each knot moves outwards with its own expansion
velocity. They are reconstructed as string of knots rather than jets.This
string of knots is formed by ejection events repeated every 200- 250 years. Hb4
displays several indirect evidence for a binary central system with a [WR]
companion evolved through the common envelopes channel.The observed
deceleration of the knots is likely associated with shock collisions between
the knots and the interstellar medium or nebular material.
