please help me id this perennial vine
The "vine" has a thick large trunk, slightly downy trunk and leaves. The flowers are lavender of a true solid color, are trumpet shaped like a morning glory. The flowers also behave like morning glories in that they open in full sun and close by afternoon. The whole plant can get up to 8 feet tall and just as wide. I saw the plant year after year outside a take-out food place; uncared for, hardly watered, rarely weeded. The store owners do not know what it is. When weather conditions permit, it flowers and looks absolutely gorgeous due to it's impressive size and beautiful flowers. I got a smaller plant dug up from near the parent and am now growing it in a pot. It has flowered but not recently due to a battle with spidermites.
Any ideas? Thanks so much in advance for your help.