I have an ulterior motive in offering to help you.

我主动提出要帮助你是有私心的。

《牛津词典》

Sheila had an ulterior motive for trying to help Stan.

希拉设法帮助斯坦是别有用心。

《柯林斯英汉双解大词典》

But I had an ulterior motive.

但我还有一个私底下的目的。

youdao

But some will inevitably suspect an ulterior motive, at least in the timing of the attack.

ECONOMIST: Showdown in Jericho | The

Maybe Clint Eastwood has an ulterior motive for speaking at the Republican National Convention two weeks ago.

FORBES: Wacky RNC Speech Was Good Marketing For Clint Eastwood's New Movie

Google has actually been using reCAPTCHA with an ulterior motive: crowdsourcing the digitization of old newspapers and books.

FORBES: Artificial Intelligence Will Defeat CAPTCHA -- How Will We Prove We're Human Then?