It's a helical gear attached to a standard spur gear. Whether it's standard or not, I'd say it might be just the combination of two standard gears, hard to say. I can't imagine how one would make it as one piece, unless its just molded.
As for how to model it, I have done some spur gears using the standard straight gear involute spline equations and such, but I guess what you can do will depend on why you need a model. If you want a model that is accurate enough to replace the gear in question, I don't know. I'd probably start with an extensive search of online sources for the actual gears, and see what's out there, and if they have any models. Unfortunately, though, the models you tend to get as free downloads from suppliers are often (maybe on purpose) lacking in precision and/or detail. They give you a pretty good idea of the envelope of the part, but not the accurate geometry. I think this might be especially true of gears.
The other troublesome thing to deal with is if that gear is worn, it might be difficult to get a good idea of the dimensions of a "good" gear, or an unworn one. It looks like it's had some trying times in the past. Maybe in a pump?
Good luck, if nothing else, you'll acquire a lot of knowledge about gears.
