This paper presents a novel adaptive gain tuning Second Order Generalized Integrator (SOGI) – Higher Order Sliding Mode (HOSM) observer for robust speed estimation for an induction motor's entire speed range. This paper introduces a hyperbolic tangent function and a varying gain exponent that ensures accurate speed estimation under noisy conditions and significantly reduces chattering observed in conventional Sliding Mode Observers. The robustness of the proposed speed estimation method is verified through simulations conducted on MATLAB/Simulink R2024a, demonstrating its capability to effectively track the motor's actual speed even under varying load torque conditions, parameter variations and additional sensor noise. The proposed approach's superiority and robustness were compared with the conventional SOGI-Frequency Locked Loop (FLL) and Super Twisting Algorithm (STA) Sliding Mode Observer.