设$\stackrel{\rightharpoonup }{e_1}$、$\stackrel{\rightharpoonup }{e_2}$为单位向量，非零向量$\stackrel{\rightharpoonup }{b}=x\stackrel{\rightharpoonup }{e_1}+y\stackrel{\rightharpoonup }{e_2}$，$x$、$y\in R$．若$\stackrel{\rightharpoonup }{e_1}$、$\stackrel{\rightharpoonup }{e_2}$的夹角为${30}^{°}$，则$\frac{\left|x\right|}{\left|\stackrel{\rightharpoonup }{b}\right|}$的最大值等于．