已知函数$f\left(x\right)=\left\{\begin{array}{l}\left|x^2+5x+4\right|,x\le 0\\ 2\left|x-2\right|,x>0\end{array}\right.$若函数$y=f\left(x\right)-a\left|x\right|$恰有4个零点，则实数$a$的取值范围为.