  Background: The $^{44}$Ti nucleus has been known to have a $^{40}$Ca+$\alpha$
cluster structure, and inversion doublet structure has been observed; however,
$\alpha$ cluster structure tends to be washed out when the breaking of the
$\alpha$ cluster is allowed due to the spin-orbit interaction. Nevertheless,
$\alpha$ clustering in medium-heavy nuclei is quite a hot subject recently.
  Purpose: The tensor interaction has been known to play an essential role in
the strong binding of the $^4$He nucleus, which induces the
two-particle-two-hole (2p2h) excitation. Since this excitation is blocked when
another nucleus approaches, it is worthwhile to show whether the tensor effect
works to keep the distance between $^4$He and $^{40}$Ca and becomes the
salvation of the clustering in $^{44}$Ti.
  Methods: The spin-orbit effect is included in the cluster model by using the
antisymmetrized quasi cluster model (AQCM) developed by the authors. We have
also developed an improved version of the simplified method to include the
tensor contribution ($i$SMT), which allows us to estimate the tensor effect
within the cluster model. The competition of these two is investigated in the
medium-heavy mass region for the first time.
  Results: According to AQCM, the spin-orbit interaction completely breaks the
$\alpha$ cluster and restores the symmetry of $jj$-coupling shell model when
the $\alpha$ cluster approaches the $^{40}$Ca core. On the other hand, $i$SMT
gives a large distance between $\alpha$ and $^{40}$Ca due to the tensor effect.
  Conclusions: In $^{44}$Ti, because of the strong spin-orbit and tensor
contributions, two completely different configurations ($jj$-coupling shell
model and cluster states) almost degenerate, and their mixing becomes
important.
