A father's rights after divorce in Brazil (São Paulo)

Hi guys, I really need some help and guidance. I am English and my wife is Brazilian. We have a 2 year old son who was born in England but came to São Paulo with us when he was 2 months old (he has duel citizenship).

My relationship with my wife is in trouble. I want to know if I separate from her what rights do I have in terms of my son. I would hope that she would not try to use my son against me and would allow me to continue a 'normal' relationship with him, but her behaviour over the last 6 months has shown me that I can't be sure of anything where she is concerned.

I have heard some terrible stories about fathers having very few rights in Brazil after separation/divorce. I want to know if anyone here has any experience with this or better still actually knows something about the laws around this type of thing.

Thanks in advance,

Matt