This patent covers SunTour's sealed parallelogram design.
The patent covers two designs in detail. The first used a wire element as one leg of the parallelogram. This is the design that SunTour actually used in the SunTour Superbe Tech range.
The other design uses cog wheels to keep the pulley cage aligned to the chainline. SunTour never used this system on a production model - but 30 years later it was replicated in surprising detail in the FSA K-Force WE.