Thanks for the additional info. ianal but I think you are screwed as far as trying to challenge their right to the invention. They surely had you assign all IP created in the course of your work to them. They can proceed with a filing even without your consent or help (although they are going to much prefer to do so with your assistance and good will).

btw as an aside : how can someone work in this industry and _not_ know this? I'm not questioning your sincerity but I mean why isn't everyone handed a short pamphlet to read when they get into this business that explains this stuff?

Anyway, back to your situation : based on what you have said I'd suggest going to your management and asking if they would be interested in commercializing your invention as some sort of joint venture or spin-off company. They would provide your company with a license in exchange for, say, equity. In return they would get to enjoy your full and enthusiastic participation in the patent filing and defense process. Worth a try.