Directional control valve in a full hydraulic type steering control system

A full hydraulic type steering control system in which there are provided:

• a steering control valve for outputting a flow of a pressurized discharge fluid of a hydraulic pump in a proportion to an amount of steering at a steering wheel, and
• a directional control valve being switched for delivering the pressurized discharge fluid of the hydraulic pump into a steering control cylinder with the output flow of pressurized fluid of the steering control valve as a pilot fluid pressure, and
• in which said directional control valve comprises a spool adapted to be slidably inserted in a spool bore of a valve body, said spool having a neutral position and being adapted to be displaceable from said neutral position towards a first position for delivering the pressurized discharge fluid of said hydraulic pump into a first fluid chamber of said steering control cylinder while permitting a pressurized fluid in a second fluid chamber thereof to flow out into a reservoir and towards a second position for delivering the pressurized discharge fluid of said hydraulic pump into said second fluid chamber of said steering control cylinder while permitting a pressurized fluid in said first fluid chamber thereof to flow out into the reservoir,
• wherein said spool is formed with a small diameter portion and a notched groove portion for allowing a fluid to flow out of said steering control cylinder into the reservoir, said notched groove portion being configured to have an aperture whose area is adapted to be increased as said spool is displaced from said neutral position towards said first or said second position up to an intermediate position towards said position and thereafter towards the latter to be decreased.