I've made a personal module:

import datetime
import time
from openerp.osv import fields, osv
import logging

_logger = logging.getLogger("WORK2MEETING")
class project_task_work(osv.osv):
    _name = "project.task.work"
    _inherit="project.task.work"
    _columns = {
        'meeting_id': fields.many2one('crm.meeting', 'Meeting')
    }

    def create(self, cr, uid, vals, *args, **kwargs):
        _logger.debug('Create a %s with vals %s', self._name, vals)
        meeting_obj = self.pool.get('crm.meeting')
        varDeadline= datetime.date.today()#TODO deadline=date+hours
        meeting_vals = {
            'name': vals['name'],
            #'categ_ids': ,#TODO récup l'id du tag "avancement de projet"
            'duration': vals['hours'],
            'description':task_id.project_id.name+'->'+task_id.name+'->'+name,
            'user_id': vals['user_id'].id,
            'date': vals['date'],
            'end_date': varDeadline,
            'date_deadline': varDeadline,
            'state': 'open',# to block that meeting date in the calendar
        }
        meeting_id = meeting_obj.create(cr, uid, meeting_vals)
        vals['meeting_id'] = meeting_id
        return super(project_task_work,self).create(cr, uid, vals, *args, **kwargs)

When I check fields with dev mode I can see my personal field "meeting_id". But when I create a new task.work, I've no new meeting and there are no message on log file. Did I make a mistake?