Hydraulic control unit

A hydraulic control unit, comprising:

• a valve comprised of a piston integrated with a valve element, a cylinder holding the piston while allowing to reciprocate axially, a positive pressure chamber which is formed on one side of the piston and to which hydraulic pressure to open the valve is applied, a back pressure chamber which is formed on the other side of the piston and to which the hydraulic pressure to close the valve is applied, and a connection passage having a function to differentiate hydraulic pressures in the positive pressure chamber and the back pressure chamber;
• a pilot valve that selectively connects the back pressure chamber with a site where the pressure is lower than that of the back pressure chamber;
• a low pressure section to which the hydraulic pressure lower than that applied to positive pressure chamber is applied;
• and
• a controller configured to deliver hydraulic fluid from the low pressure section to the back pressure chamber if an opening motion of the valve is slower than a predetermined reference value, by opening the pilot valve to connect the back pressure chamber with the low pressure section.