Hypercentral automorphisms of nil-triangular subalgebras in Chevalley algebras

Let $N\Phi(K)$ be the nil-triangular subalgebra of the Chevalley algebra over an associative commutative ring $K$ with the identity associated with a root system $\Phi$. (All elements $e_r \in \Phi^+$ of Chevalley basis give its basis.) We study automorphisms of the Lie ring $N\Phi(K)$; this problem is closely related to the modeltheoretic study of Lie rings $N\Phi(K)$. Our main theorem shows that the largest height of hypercentral automorphisms of $N\Phi(K)$ is bounded by a constant, except orthogonal cases $B_n$ and $D_n$, when $2K\neq K$.