Oil-bath air cleaners used to be a benchmark in the automotive industry. However, today they are hardly to be found at all in the car segment as they were successively replaced by paper air filters after the 1970s. This changeover took place simply because the new paper inserts enabled a substantial increase in separation efficiency. The paper variant is characterized by a lower flow resistance which is beneficial for engine performance and at the same time is a cheaper solution.
At that time MANN+HUMMEL naturally also started to develop the first air cleaner with a paper filter element and a plastic housing. I was lucky enough to be involved in the tests for the first paper air filters for the VW Beetle, whereby at the time I was not sure about being so lucky as the first tests were back-breaking work. It’s worth remembering that the oil-bath air cleaners at that time were manufactured from sheet steel and were also used in the VW Beetle. But Volkswagen planned to change over to a system with a paper filter in a plastic housing. There were plans to produce more than 3000 pieces per day in series. This was potentially a big order for us and so there were many specifications to meet. Numerous questions required answers and solutions had to be found for potential problems.
A challenge seldom comes alone
An area we were very concerned about was the filtration performance itself. Some questions we asked ourselves were: Would the separation efficiency be sufficient? Would the dust holding capacity of the filter be enough for a car with a rear engine? Where was the best position for the duct for the crankcase ventilation? And would it be necessary to preheat the intake air? Then there were also questions concerning the design characteristics, such as: Which plastic should we use for the housing? How are the shock-absorbing properties of plastic? What about durability? These were the many questions which the development team at MANN+HUMMEL considered over a number of months.
One of five
VW then decided, for the first time ever, to carry out large-scale dust tests in the Sahara desert in Africa. The location was southern Algeria where in those days there were hardly any tourists. We started our trip in September 1971 without any idea of what we could expect. Six VW employees and five Beetles made the journey via France, Spain and Morocco to Oran in Algeria. I, as the only representative from MANN+HUMMEL, was lucky enough to fly in directly. Together we then traveled to the South and finally arrived at El Golea, our final destination.
We stayed at the former French Hotel Grand Erg, a simple establishment. There was no telephone or fax and the telex only worked every now and then so we were practically cut off from the world. The food consisted of goat’s milk and baguettes for breakfast which were two days old and mutton and goat bones with a little bit of meat on the bone for the evening meal. But we were all young, dynamic and resilient so that we were able to take on these difficult conditions as a real challenge.
We then concentrated on our tests which consisted of many dust drives on different surfaces using oil-bath cleaners and paper air filters respectively with and without warm air regulation and also with or without crankcase ventilation, etc.. But the tests were also a challenge in other respects. Those who have driven in the desert and have had to dismantle and reassemble their suspension struts and Bowden cables in the sand without a great deal of technical help will understand the problems we had to face.
This is because we had no access to a garage with a lifting platform. But our team worked well and was able to overcome all challenges. We quickly established how easy it is to change a paper element and how awful in comparison it is to remove the accumulated dirt in the lower part of the oil-bath cleaner with a screwdriver and hammer.
We were there for a total of 32 days. When we finally returned, we were tanned from the sun and wind and had a few kilos less on our bodies (the record was twelve) with many experiences to look back on. But the most important result was that we had shown that the use of a paper air filter in a plastic housing was not only theoretical but feasible in practice. Accordingly, in 1972 the first Beetle with a paper air filter in a plastic housing from MANN+HUMMEL came off the production line.