"I don't know" means you don't have the knowledge at this time, but "I didn't know" indicates that you DO know now, but did NOT know at some previous time.

I DONT KNOW .. in present tense which the action happens in the present " i dont know now " I DIDNT KNOW .. in the past tense which the action happend in the past " i didnt know yestersay .."

They have the same meaning. We use i dont know in present time, and i didnt know to show past time.

i do not know - i don't know i did not know - i didn't know or *i did not knew* I sware, I sware, I didn't knew what happend. I sware, I sware, I don't know what is happening. sorry I didn't thrust you sorry I don't thrust you hope you se the differance.

Thank you for every one answer my question.