I understand what it's like to have a difficult relationship with your mother. It sounds like the removal, or withholding of affection and other emotions is entirely on her side, and even after she's been approached, she will make no effort to contribute to a relationship. I understand how painful this is, because ultimately, we all want our parent's love and approval. Sometimes though, you just have to accept that it's nothing that you have done wrong. You are a good person, worthy of love, and your mother has her own issues to deal with, and you can't fix them...that's up to her. As parents, we believe that our children are the most important things in the world, and should always feel loved and cherished. Not all parents feel like this or, even if they do, are able to show it.
I don't mean to sound callous, because I do understand your pain, but at some point, you have to be an adult and identify yourself as a person independently of your relationship with your mother. You know that she won't change, and while that may always hurt, you can't tear yourself up about it, because think of the impact that will have on your own children, and even your relationship with your husband.
Live your life. If you feel the need to talk to her about it, do so, but then leave it at that, and let her take it from there. Stop making extra efforts to reach out to her. Invite her to be involved, but don't try to push anything, as that will only cause you frustration and pain when you don't get the response you want. Don't bring up the subject to your kids, but if they ask, just explain that some people can show love with big hugs and kisses, and other people can't, but that doesn't mean they don't love you, they just have a tough time showing it....that's why you've always tried so hard to show your kids how to love openly. If being around her hurts you, then don't be around her. Take control.
You can't make the hurt go away completely, but you can stop focusing on it and allowing it to fill your thoughts so completely. Focus on the positive relationships you do have, and go from there, making sure you don't fall into the rut of allowing this to consume you so your kids grow up with their own issues with you. That's really all you can do.
Best of luck....I really do know how tough it is!!