Odoo v8

I have wizard with two fields:

class Roll_wizard(models.TransientModel):
    _name = 'roll.wizard'
    calc_model = fields.Many2one("techdoc", "Car Model")
    calc_year = fields.Many2one("techdoc.year", "Car Year")

I need to display in field calc_model a model of the car, instead of field name, so i decided to override name_get()

The model "techdoc" has fields: 

class Car(models.Model):
    _name = 'techdoc'
    name = fields.Char(string="Brand", size=30, required=True)
    car_model = fields.Char(string="Model", size=30, required=True)
    car_year = fields.Integer(string="Year", size=30, required=True)
    car_engine = fields.Float(string="Engine size", digits=(3, 1), required=True)
    car_transmission = fields.Char(string="Transmission type", size=30, required=True)
    car_modify = fields.Char(string="Model Modification", size=30)
            
    def name_get(self,cr,uid,ids,context=None):
        model = []
        result = self.browse(cr,uid,ids,context=context)
        for record in result:
            tup=(record.car_model, record.car_model.title())
            model.append(tup)
        model = list(set(model))
        return sorted(model)

But after this in field calc_year i need to display car manufactures years.

I've created a new model, inherit "techdoc" model and overrides name_get() agan to display years

class Car_year(models.Model):
    _name = 'techdoc.year'
    _inherit= 'techdoc'

    def name_get(self,cr,uid,ids,context=None):
        model = []
        result = self.env['techdoc'].browse(cr,uid,ids,context=context)
        for record in result:
            tup=(record.car_year, record.car_year)
            model.append(tup)
        model = list(set(model))
        return sorted(model)

And I have an error:

AttributeError: 'techdoc.year' object has no attribute 'env'

I want to use instances from "techdoc" model.