http://revach.net/article.php?id=3210

Section: Parshas HaShavua   Category: Quick Vort
Parshas Vayigash: Maharal MiPrague - Why Did Only Yaakov Say Shema And Not Yosef?
Rashi says that the pasuk (46:29) says that only Yosef cried when he met his father.  Yaakov did not cry as he was in middle of Krias Shema.  Why was Yosef not saying Shema at the same time if it was the proper zman?

The Maharal MiPrague (Gur Aryeh) answers that Yosef was also in middle of Krias Shema but Rav Yehuda says in Masechtas Brachos (2:1) that you may stop in middle of Krias Shema to greet someone whom you fear.  Therefore Yosef, fearing his father out of awe, stopped to greet him.  Yaakov however, was halachicly unable to interrupt Shema to greet his son.  The Sifsei Chachomim brings another answer, that Oseik B'Mitzva Patur Min HaMitzva and Yosef was performing Kibbud Av and was therefore patur from Krias Shema at the time.

The Sifsei Chachomim also asks, how do we know Yaakov was saying Shema and not Shemoneh Esrei?  He answers that it is forbidden to walk within four amos of someone davening Shemoneh Esrei.  The mere fact that Yosef approached him, shows that Yaakov was not in middle of Shemoneh Esrei.