This invention discloses a hydraulic steering device and an all-
terrain vehicle hydraulic
steering system. The steering gear 6 of the hydraulic steering device adjusts its displacement via a
variable displacement control cylinder 9, which is controlled by an electro-proportional two-position three-way
directional valve 11. The opening of the oil circuit within the electro-proportional two-position three-way
directional valve 11 is controlled by an electrical
signal converted from vehicle speed. When the vehicle speed increases, the displacement of the steering gear 6 decreases; when the vehicle speed decreases, the displacement of the steering gear 6 increases. The outlet of the
variable displacement pump 1 is connected to a steering oil
circuit switching valve 7 via a one-way valve 4. The steering oil
circuit switching valve 7 connects the steering gear 6 and the steering cylinder 3. This invention addresses the problem of easy
rollover and fishtailing in hydraulically driven all-
terrain vehicles at high speeds by providing a hydraulic
steering control system that links vehicle speed and
steering wheel angle control, adjusting the control ratio of
steering wheel angle and overall vehicle angle according to vehicle speed.