I tried to create a tool that would mach all requirements without
making a sophisticated design. My motto was to "keep it simple".
The base of my design consists of two pivotally mounted levers. The levers may be easilly locked in 2 positions ( one for mounting and second for removing the tire). The second key element is the system of two centrally mounted arms. Arms are used to operate the levers along the circumference of the wheel. To protect the rim from scratches, the arms have pieces of felt underneath ( in the connection area).
Device was ment to be simple and easy to maintenance. It consists of less than 20 parts. It can be completely disassembled and stored while not needed.