  We investigate the quantum dynamics of the 1D spinless Fermi-Hubbard model
with a linear-tilted potential. Surprisingly in a strong resonance regime, we
show that the model can be described by the kinetically constrained effective
Hamiltonian, and it can be spontaneously divided into two commuting parts
dubbed Hamiltonian dimerization, which consist of a sum of constrained two-site
hopping terms acting on odd or even bonds. Specifically it is showed that each
part can be independently mapped onto the well-known PXP model, therefore the
dimerized Hamiltonian is equivalent to a two-fold PXP model. As a consequence,
we numerically demonstrate this system can host the so-called quantum many-body
scars, which present persistent dynamical revivals and ergodicity-breaking
behaviors. However in sharp contrast with traditional quantum many-body scars,
here the scarring states in our model driven by different parts of Hamiltonian
will oscillate in different periods, and those of double parts can display a
biperiodic oscillation pattern, both originating from the Hamiltonian
dimerization. Besides, the condition of off-resonance is also discussed and we
show the crossover from quantum many-body scar to ergodicity breaking utilizing
level statistics. Our model provides a platform for understanding the interplay
of Hilbert space fragmentation and the constrained quantum systems
