关于know sb to be/to do sth 我觉得有三点需要说明。

第一，这个结构通常用于被动结构（但不是说不能用于主动结构）。词典例句也基本都是被动结构。

第二，这个结构主要用来表示一个人（know的宾语）的声誉，即多数人认为宾语是一种什么样的人。因此，主语或被动语态省略的施事者通常是泛指的人们（people或most people). 第三，不定式通常为静态意义，即要么是静态动词表示状语，或动态动词表示习惯意义（静态概念）。此时不定式用一般体to be或to do形式，状态或习惯与谓语动词具有时间上的同时性。如果不定式为动态动词表示事件意义，则与谓语动词同时的事件要用不定式的进行体to be doing；先于谓语动词时间的事件要用不定式的完成体to have done.通常不用不定式表示将来的事件。

以下为词典对know sb to be/to do sth解释和例句

《麦克米伦词典》

[TRANSITIVE] [OFTEN PASSIVE] used about things that most people think or believe are true

The ancient city is known to have existed in the region.

know someone/something to be something: 

The pilots were experienced and known to be very competent.

know someone/something to do something: 

Some drugs are known to cause damage to unborn children.

《牛津词典》

reputation

[transitive, usually passive] to think that somebody/something is a particular type of person or thing or has particular characteristics

know somebody/something as something 

It's known as the most dangerous part of the city.

know somebody/something for something 

She is best known for her work on the human brain.

know somebody/something to be/do something 

He's known to be an outstanding physicist.

更多的例句：

He is known to be an honest man. 被动语态。to be为静态动词表示状态。与谓语时间同时的状态。

He is known to help his classmates whenever it is necessary. 被动语态。to help为习惯意义（静态），与谓语时间同时的习惯。

He is known to have written a new book. 被动语态。不定式为事件意义，先于谓语时间。

He is known to be writing a new book. 被动语态。不定式为事件意义，与谓语时间同时。

He is known to write a new book.  被动语态。不定式为事件意义，to write为形式错误。

I know him to be an honest man. 主动语态。主语为单数的I，不符合该句型表示宾语的声誉或多数人的看法这种词典释义，故为不大妥当的句子。