BMW, the German maker of luxury cars, said Monday that the head of its prestigious Rolls-Royce unit, Karl-Heinz Kalbfell, had quit after only five months on the job. Kalbfell, 54, "has asked BMW to relieve of his duties", BMW said in a statement. The manager was quitting to "pursue other duties outside the group", the statement said. His responsibilities would be assumed in the interim by BMW's chief financial officer Stefan Krause. Kalbfell's resignation comes at a time of disappointing sales for BMW's prestigious Rolls-Royce brand. The British car maker sold only 485 cars in the first nine months of this year, meaning the annual target for unit sales of around 1,000 is looking increasingly difficult to attain.