This invention relates to an improvement of two stroke engine in which a sleeve piston is employed to move up and down in the cylinder and to control alternatively the opening and closing of the intake guide and exhaust guide and to prevent the lubricant from exuding out of the crank case in an effort to ensure an environmental-friendly clean exhaust. In other aspects the invention relates to the use of these compounds in a method for therapy and to pharmaceutical compositions comprising the compounds of the invention. The motor phase current commutation causes eddy current losses in the rotor magnets and core which are insignificant due to the low phase currents and relatively low rotor speed.