After the execution of an on_change method the returned values are displayed in the view. But how can I get them for further processing?

def onchange_date(self, cr, uid, ids, date, context=None):
    vals={'field1': 123};
    .
    .
   return {'value': vals};

In particular I need the values to be available in a button method.

def save_action(self, cr, uid, ids, context):
    a = context.get('val1', False);
    .
    .
    return True;

I've tried passing them over using a context in the xml view.

<button name="save_action" string="Save" type="object"
        context="{'val1': field1, 'val2': 6, 'val3': 'abc'}"></button>

But only the default values are passed. Not the return values of the onchange method.