Some ideas that might help:
Go for very short rides, 5 - 10 minutes, around your block and slowly increase the drive time. This will help him get used to the motion of the car.
If that is still too much, just try sitting in the car with your dog and not drive. The anxiety they feel in the car could be adding to the problem.
If these don't work, check with your vet. There might be some medication that they can give you for the longer trips that are necessary for your dog to go on.