Absolutely Continuous Invariant Measures of Piecewise Linear Lorenz Maps

Consider piecewise linear Lorenz maps on $[0, 1]$ of the following form f_{a,b,c}(x)= {ll} ax+1-ac & x \in [0, c) b(x-c) & x \in (c, 1]. We prove that $f_{a,b,c}$ admits an absolutely continuous invariant probability measure (acim) $\mu$ with respect to the Lebesgue measure if and only if $f_{a,b,c}(0) \le f_{a,b,c}(1)$, i.e. $ac+(1-c)b \ge 1$. The acim is unique and ergodic unless $f_{a,b,c}$ is conjugate to a rational rotation. The equivalence between the acim and the Lebesgue measure is also fully investigated via the renormalization theory.