It's natural to ask: "Of all R&D expenditures, what percentage came from each year?"
On a side note, time series is not a great phrase for the original data set ("time sequence" would have made more sense, since the numbers shown are not cumulative)
Also note that 'time series' is a well-defined and widely-used term that exactly describes the dataset presented here (http://en.wikipedia.org/wiki/Time_series).
Pie charts are by far one of the worst forms of graphs ever devised and should be killed off as a concept for good, as in, please remove this from Excel.