Hello guys, i have develped a custom module for a car managment, where i'm using a lot of extra fields, float, char, selection and in this case i'm working with a many2one field.. 
Something like this

two models...

car.brands                  car.model

                                   ---- M3

BMW --------------  ---- M4

                                   ----Z4

All is working fine in backend, but the things become difficult in the website/shop

i'm trying to make a filter for this fields... i need a filter for every field by separate

i've been stuying the website.sale controller, and some examples like the price filter and the tag filter, but all of these, work in a different way from eachother, i tried to replay the attributes filter and i got something  "working" but not really working well... so is not what i want....

what i think i need is very simple in words... understand how to indicate  the controler to 
1- render the values inside the field. (done)
2- set the url with the values(ids) of the fields example bmw(1) nissan(2) etc..  (done)
3- capture de value of the url and filter the products in the sop (not working)

So my problem is that don't know how to make the controller capture those ids and filter...

if someone knows how to do this please help me. 

Thank you.