We've known him to work all night to meet a deadline. = He's been known to work all night to meet a deadline.我们知道他为赶上最后期限通宵工作。

I've never known her to be wrong. [=I do not know of any time when she has been wrong]我就没见她出过错。

He's been known to do this kind of thing before.大家知道他以前干过这种事。