Mercedes Benz

OFFICIAL PRESS RELEASE

Stuttgart, Germany, Mar 06, 2009

- Sleeve-valve engine based on the principle established by Charles J. Knight

- Extraordinary smoothness and refinement

- A good 5500 units of the four-litre model were built within 14 years

In April 1909 Daimler-Motoren-Gesellschaft decided to build test vehicles using the sleeve-valve engine invented by the American Charles J. Knight, which dispensed with the usual poppet valves. The first of six units of a test series was completed on 23 June 1909. Testing was successful, and so in March 1910 Daimler-Motoren-Gesellschaft (DMG) purchased licences to manufacture the Knight engines for an initial period of ten years. In mid-1910 the first production model with a Knight engine, a 16/40 hp Mercedes with four-litre four-cylinder power plant, debuted at the Paris Motor Show. Series production of the model commenced in early 1911, and it remained in the production range until 1924. Two other four-cylinder models, the 10/30 hp and the 25/65 hp, went into production in 1913 and were built until 1915.


In mid-1913 the 16/40 hp was renamed, as were all other models of the DMG sales range, getting the new model designation 16/45 hp. In spring 1924 the model designation was changed to reflect the actual engine output and from then on was called the 16/50 hp. Starting in summer 1924 the16/50 hp was fitted with four-wheel drum brakes, making it the second DMG model after the 28/95 hp to be offered with brakes on the front wheels too.

The Mercedes-Knight occupied a special position among the many car models manufactured by DMG prior to the First World War. Advantages and drawbacks of the Knight design were a subject of controversial debate among automobilists and engineers at the time. Undisputed advantages of the system were its smoothness, quietness and refinement, which were quite remarkable for the period and set the Mercedes-Knight apart. In addition, in the 500 to 1500 rpm range Knight engines developed a higher output than conventional power plants of equal size. These and other reasons brought Paul Daimler to have the test series produced. He had taken over the management of the design office in April 1907 as successor to Wilhelm Maybach.

But the Knight principle of operation had not only advantages. For example, the sleeve-valve engines necessitated much effort and expense for design and manufacture and called for an extremely sensitive hand in operation. A particularly critical point which cost the company a great deal of money because of the many vehicles described as fault-prone was the proper lubrication of the cylinder and sleeve contact faces. It often could not be guaranteed with the lubricants available at the time, especially if maintenance was neglected. This aspect caused increasing problems at engine speeds of more than 1600 rpm – a speed at which, moreover, the sleeve-valve engine ceased to be superior in terms of specific output. The maximum attainable engine speed was about 1750 rpm, which translates to a maximum vehicle speed of about 80 km/h. As a result, the development potential and practical usability of the Knight engine were limited, at least in the long term.

Nevertheless, there were dyed-in-the-wool Knight advocates among the customers of Daimler-Motoren-Gesellschaft – more than 5500 units of the four-litre model, no small number, were built within its 14-year production run.

Despite the technical limitations of the operating principle, there were even racing cars featuring Knight engines. Though only a peripheral phenomenon, they have notable successes to show for themselves. The most remarkable achievement was the showing of the Belgian Mercedes agent Theodor Pilette in the Indianapolis 500 on 30 May 1913. His 16/45 hp Mercedes-Knight had the smallest displacement of any car entered in the field and barely managed to qualify. And yet Pilette finished the race in fifth place after seven hours and 19 minutes, without making a pit stop. The petrol consumption of the sleeve-valve engine was astonishingly low too: 11.8 litres for 100 kilometres or about 20 mpg. In the years 1912 and 1913, in Mercedes-Knight cars Pilette's countryman Léon Elskamp won a number of races and placed well in others.