Additive property of pseudo Drazin inverse of elements in a Banach algebra

We study properties of pseudo Drazin inverse in a Banach algebra with unity 1. If $ab=ba$ and $a,b$ are pseudo Drazin invertible, we prove that $a+b$ is pseudo Drazin invertible if and only if $1+a^\ddag b$ is pseudo Drazin invertible. Moreover, the formula of $(a+b)^\ddag$ is presented . When the commutative condition is weaken to $ab=\lambda ba ~(\lambda \neq 0)$, we also show that $a-b$ is pseudo Drazin invertible if and only if $aa^\ddag(a-b)bb^\ddag$ is pseudo Drazin invertible.