Article by Doug Switzer Moto/ology Publisher
Back in the weird and wonderful; engine department, we thought we’d show off another unusual, alternative configuration. Behold the sleeve valve engine!
We’re familiar with the “poppet valve” engine—a common configuration with multiple round valves that pop up and down to control the intake, exhaust, compression and firing functions, but there’s another type of valve…
Ok, what if instead of having a cylinder head or a block with pistons and valves going up and down, we place the piston inside another cylinder inside the main engine block cylinder—a sleeve if you will?
I know, this immediately begs the question: Why? Well, for several potential advantages, the valve action should be more positive, and we can eliminate valve springs, timing chains and other such mechanisms and the engine should be quieter. As we will see later, these advantages may be delivered, but like most things, there will be suffering in other areas.
By the early 1900’s 4-stroke engine design had pretty well settled on the poppet-valve designs and although noisy and problematic due to metallurgical and cooling issues, strides were being made in the constant improvement of these designs. The improvements, however, were not enough for one Mr. Charles Yale Knight, an American newspaper man and sometime inventor. He felt the clattering noise of these “poppet” valves was entirely insufferable and decided to come up with a better solution.
Knight had been familiar with the rudimentary sliding valves of the early Otto-cycle engines and felt some development of this abandoned technology would provide better service in a more modern engine. It was he who came up with the idea of placing the piston in a vertically moveable, semi-rotating sleeve within the actual cylinder of an engine. With holes strategically placed and shaped in the walls of the sleeve and corresponding holes placed in the cylinder walls of the engine, a mechanism could be developed that served to open and close intake and exhaust ports at the appropriate times, enabling the engine to “breath” efficiently.
After some protracted experimentation and prototyping, Mr. Knight and his backers produced a working double sleeve-valve design (that is, one sleeve moved inside another with both moving within the cylinder) in 1905. In 1906, Knight and his cohorts put a complete car, the “Silent Knight” on display at the Chicago Auto Show.
The car was expensive and met with some ridicule, but Knight pressed on with his development work and patents. After some negotiations, Knight landed a deal with the English Daimler Motor Company to use his engine technology. Within a few more years, Knight had deals with B.S.A., Minerva and Panhard. The Stearns company was partnered with Knight to form the Stearns-Knight company in 1911 and become the first American auto manufacturer to use the “Silent Knight” sleeve-valve system. Later that year a deal with the Willys Company (who would later become famous as the manufacturer of Jeep vehicles for the U.S. military) led to their debut of the Willys-Knight automobile.
Another American automaker, Atlas, also jumped on the bandwagon and began using the Knight double sleeve-valve technology in all their automotive applications. Eventually more than 25 auto manufacturers embraced the technology and for a while, things were going very well indeed for Mr. Knight and his supporters. There was, however, a growing competition from the poppet-valve crowd as metallurgical breakthroughs improved reliability and updated designs gained new popularity.
There was also new competition from within the sleeve valvers themselves. A Scottish automaker, Argyll had developed a single sleeve valve system that was lighter, simpler, more reliable and burned less oil than the double-sleeve Knight system. This design, known as the Burt-McCollum system after its designers, was introduced in the Argyll motorcar with some success. The big advance, however, came when this single-sleeve design was further developed for use in aircraft engines.
Harry Ricardo, a leading engine designer and engineer was contracted by the Shell Oil Company to do research into engine efficiency and the relationship with fuel formulae. While also leading to the concept of octane ratings for the control of fuel detonation, his work showed several big advantages for the sleeve-valve engine designs. They were quieter and provided much better volumetric efficiency than the poppet-valve engines of the day. Better exhaust scavenging and the elimination of a lot of valve driving mechanisms also helped matters although the complex system of gears to drive the sleeves was also seen as a bit of a burden on the sleeve valve designs. However, because of the direct mechanical actuation of the sleeves without the use of springs to facilitate valve closing, there is an elimination of valve float or bounce making the sleeve-valve much better in some high-speed and constant-speed applications.
The Bristol Airplane Company further developed the single sleeve-valve designs in the inter-war years and produced some highly efficient and powerful aircraft engine designs that proved very successful. Starting with the radial nine-cylinder Bristol Perseus in 1932, Bristol went on to develop and produce many successful sleeve-valve aero engines.
The most plentiful was the Bristol Hercules which was a two-row 14-cylinder design by Roy Fadden. These engines found applications in many aircraft from WWII bombers and heavy fighters on to the postwar transport and passenger aircraft of the mid-fifties and beyond. They proved to be adaptable, efficient and reliable and served very well until jet and turboprop engines replaced them. Over 55,000 Hercules engines were produced with the final versions pushing out just over 2000 horsepower. Probably one of the most famous of the Hercules-powered aircraft was the Bristol Beaufighter. It was a heavily armed, twin-engined fighter, fighter-bomber and torpedo bomber that enjoyed great success in anti-shipping, night-fighting and ground-attack roles in many theatres of WWII.
The final iteration of the Bristol sleeve-valve radial aero engines was the mighty Centaurus. This was a massive 18-cylinder, two-row design that pumped out over 3200 horsepower in its final versions and could be found powering some of the last of the piston-engined fighters and several transport and bomber types used by the RAF.
There were also non-radial designs…
The allure of the sleeve-valve design for aircraft engines wasn’t limited only to the folks that liked radial engine designs. The team at Napier fancied using the technology and included sleeve-valves in the humongous liquid-cooled Napier Sabre 24-cylinder H-layout aero engine that powered the initial versions of the Hawker Tempests and Typhoons. These complex engines were indeed powerful but with other factors contributing to reliability and efficiency issues, they were soon replaced by the more proven radial engines and of course, eventually, the gas turbine/jet designs. Another of the stillborn aero engines with sleeve-valves was the astounding Rolls-Royce Crecy, which was tested and experimented with, but never saw production. This was a V12 design displacing 26-litres (similar to the 27-litre Merlin) but offered sleeve-valves, fuel injection, a variable-speed supercharger and most importantly, it was a two-stroke design offering nearly double the output of the regular four-stroke engines of the time. With double the power pulses of its contemporary 4-stroke engines, it is said the Crecy would have literally screamed!
It was bench-tested to 1780 horsepower, and with a supercharger added and the other parasitic losses of the test rig accounted for, the calculated output would have been raised to over 2500 horsepower—considerably more than even the much larger Rolls Royce Griffon. A very interesting calculation for the potential estimated horsepower output of the fully developed Crecy with alternative supercharging placed that figure at possibly more than 5000 horsepower!
Perhaps the ultimate in complex sleeve-valve engine design would be the Rolls-Royce EXE and Pennine 24-cylinder X-design engines. With a similar layout to the troublesome and eventually abandoned Rolls Royce Vulture, the final development of the Pennine boasted a whopping 2,792 cubic inch displacement (45.8 litres) and a projected, reliable output in the region of 3,000 hp. Although built and tested, this engine never saw production and development was halted to divert limited wartime resources to the proven Merlin and Griffon V12 designs. With the advent of the turbojet engine and the development of turbo-prop engines, however, the Crecy, Pennine and most of the other advanced piston-engine designs were abandoned.
So ends the saga of the sleeve-valve engine, however, a few sleeve-valve designs are still being explored in some developmental and prototype engines, most notably in applications for low-cost vehicles in developing markets. With modern metallurgical and lubrication developments, there is renewed interest in the sleeve valve’s potential for high efficiency. These engines are being explored as a cheap alternative solution to bridge the gap while electric vehicles and their infrastructure mature.
For those who are interested, there is a lot of further information on the internet regarding these fascinating engines along with some astounding animations.
Watch for more Manic Motor articles in upcoming issues of Moto/ology!