THE FOUR LITRE ENGINE RICARDO PATENTS
FOUR LITRE ENGINE-THE RICARDO PATENTS
By Alan C Smith
Some time ago David Smethurst kindly sent me a copy of a patent
No. 280,544 taken out by Ricardo & co in 1928, which is the basis for the 4 litre cylinder head design.
The “High Power Head” as Ricardo called it, was based on his previous invention, the “Turbulent Head” which was patented in 1920, so the story of the 4 litre head must begin there.
Trying to find details of this patent on the net provided some surprising results. Typing in “patent 148046” into the search engine, for some reason, trawled in a plethora of rather insalubrious web sites that would certainly make your granny blush.
After several phone calls to Government establishments I was able to find out that patents of that age are contained in the web site: Patent.gov.uk where I was able to download the Ricardo patent in p.d.f. format free of charge.
Both patents seem to be written in a special form of labour intensive English which could be difficult for the layman to comprehend.
The explanation or “specification “ as it`s called is made up of three parts. The first part sets out the limitations of the existing technology and how the invention will improve that technology. The second part is an explanation of the new invention this time with reference to the reference points on the drawing. The third and final part is yet another version of the invention explanation worded slightly differently.
What I will attempt to do is to cut through the mass of words and bring to the reader the bare bones of the subject. Readers that want to see the original text can access this in the website above.
PATENT SPECIFICATION 148,046.
Application Date: July 22, 1919. No. 18,235 / 19
Complete accepted: July 29, 1920
- The drawing shows a cross section through the cylinder block and head of a typical side valve engine in which the valves lie side by side in the Cylinder block.
- The plan view shows the combustion chamber relative to the cylinder bore, please note the small gap between the combustion chamber and the cylinder bore as this is the basis for the invention.
- In the opening paragraphs of Ricardo`s specification he describes all the problems which plague this type of side valve engine, the main one being the lack of turbulence in the head.
- Another problem he outlines is “that increase of the compression beyond a certain and fairly low figure merely results in a greatly increased tendency to detonation without affecting any appreciable improvement in either the power output or economy”.
- The text then goes on to explain that “all things being equal” an overhead valve engine with a symmetrical cylinder head will give 10% to 20% improvement in power output over the side valve arrangement.
- Having set down the disadvantages of the side valve layout, Ricardo then goes on to outline the basis of his invention.
- The cylinder head would be flat with a minimum clearance between it and the piston, the combustion chamber would be formed over the valves and connected to the cylinder by a small passage created by overlapping the combustion chamber with the cylinder bore, the passage having the same area as the inlet valve port
- Ricardo argues that this layout will create turbulence in the combustion chamber and with the sparking plug placed centrally in the combustion chamber will give conditions for greater power and economy and will permit a much higher compression ratio to be used without a tendency to detonation. In Ricardo`s books he points out that major car manufacturers such as Austin and Ford rather cheekily used his invention without paying him any royalties, he even successfully sued Ford for damages.
- Anyone who has seen an Austin Seven cylinder head 1936 onwards will have seen a Ricardo “Turbulent Head”.
- Now we come to the patent that is engraved on the patent plate fixed to the 4 litre rocker cover.
Convention Date ( France ) : nov. 9, 1926.
Application Date ( In the United Kingdom ): Nov. 8, 1927
No. 29,904 / 27.
Complete Accepted: April 26, 1928.
Improvements in or Relating to the Cylinders of Internal Combustion Engines
This
drawing shows a cross section of the cylinder head and block of the improved
layout Ricardo calls the “High Power Head”
The main difference between this configuration and the previous one is the placement of the inlet valve in the cylinder head.
In the first paragraph of the specification it is made clear that it is a joint application from Ricardo & co and Société Industrielle Et Commerciale De Gennevilliers. ( SIC. )
SIC were the agents in Europe for Ricardo`s patents and was a subsidiary of Chenard Et Walker the automobile manufacturers.
Chenard had previously manufactured several types so called “F Head” engines with overhead inlet valve and side exhaust. The difference here was that they used Ricardo`s “turbulent head” as a basis This company was situated in Gennevilliers a Suberb North of Paris.Today Gennevilliers is a collection point for all the garbage of Paris sent by barge down the river Seine.
The specification continues with a brief description of Patent No. 148,046 stating that the present application is based on it.
Ricardo continues with a description of the different types of turbulence.
“(1) “ General ” Turbulence in which particles are moving in all directions.
(2) “ Organised ” Turbulence in which substantially the whole body of the charge is involved in a unidirectional state of motion.
(3) “ Eddying ” Turbulence in which a portion or several portions of the charge are in a state of independent unidirectional motion.
"Experiment has shown that of these three forms of turbulence, that described as “General”, is of the greatest practical use for engines operating on the constant volume cycle.”
The specification then starts to describe the limitations of the “Turbulent Head” arguing that the restriction imposed by the passage can limit the amount of air drawn in during the suction stroke.
Ricardo then explaining his invention, proposes that by placing the inlet valve above the piston, and flush with the cylinder head, the air can be drawn into the cylinder without passing through the restriction, thereby improving breathing.
That is the nub of it really but in the patent specification as before, the principle is explained three times over.
Author`s note:
To Use Ricardo`s phrase “all things being equal” there will probably be little difference in performance whether the inlet valve is in the head or the block, if the constriction area is the same as the inlet valve area.
In the text explaining the improvement, Ricardo refers obliquely to “One or more valve controlled inlet ports are disposed as part of the cylinder head”.
Although he doesn`t directly say this, he obviously means that the advantage with the overhead inlet valve is, that a larger valve, or valves, can be utilised to improve volumetric efficiency, as one of the limiting factors with a side valve layout is the size of the valves.
So the essence of this new improvement is that a larger inlet valve or valves can be used to draw in air more efficiently than with the side valve arrangement. Also the constriction can be designed without consideration of the inlet valve.
Then this larger volume of air can be compressed into the combustion chamber through the restriction to create the desired turbulence and ignited by the spark plug, which Ricardo placed directly over the exhaust valve.
The downside is that the new head is more expensive as the casting is more complex and valve rocker gear is required.
In this patent the only difference from the previous one was to move the inlet valve from the block to the cylinder head. There is no doubt this arrangement was successful having been used by Rolls Royce Rover and the Bentley 4 litre where the engine gave a better output per litre than any of the other Bentley engines except the Blower.
At the end of the day, I think any Engineer has to ask himself, if it`s a big step cost wise to change to the F head from a side valve configuration, but not so big to change from the F head to the full overhead valve layout. So why not just go for the full overhead valve layout in the first place, with all the advantages it offers.
To put things into perspective, in 1927, when Ricardo submitted his patent application, most car engines had sidevalves, so his invention was probably aimed at conservative board members who baulked at the cost of overhead valves, but might be swayed by a semi overhead valve layout giving greatly improved performance. In the event Ricardo`s hopes were not fully realised.
For the designers of our modern car engines there is no such dilemma, the F head has long been consigned to the scrapheap, and it`s only us backward looking petrolheads that are concerned with it now.
Or perhaps in some secret location technicians are preparing a new generation of F head to relaunch onto the market, only time will tell
THIS ARTICLE WAS FIRST PUBLISHED IN THE BDC REVIEW
The main difference between this configuration and the previous one is the placement of the inlet valve in the cylinder head.
In the first paragraph of the specification it is made clear that it is a joint application from Ricardo & co and Société Industrielle Et Commerciale De Gennevilliers. ( SIC. )
SIC were the agents in Europe for Ricardo`s patents and was a subsidiary of Chenard Et Walker the automobile manufacturers.
Chenard had previously manufactured several types so called “F Head” engines with overhead inlet valve and side exhaust. The difference here was that they used Ricardo`s “turbulent head” as a basis This company was situated in Gennevilliers a Suberb North of Paris.Today Gennevilliers is a collection point for all the garbage of Paris sent by barge down the river Seine.
The specification continues with a brief description of Patent No. 148,046 stating that the present application is based on it.
Ricardo continues with a description of the different types of turbulence.
“(1) “ General ” Turbulence in which particles are moving in all directions.
(2) “ Organised ” Turbulence in which substantially the whole body of the charge is involved in a unidirectional state of motion.
(3) “ Eddying ” Turbulence in which a portion or several portions of the charge are in a state of independent unidirectional motion.
"Experiment has shown that of these three forms of turbulence, that described as “General”, is of the greatest practical use for engines operating on the constant volume cycle.”
The specification then starts to describe the limitations of the “Turbulent Head” arguing that the restriction imposed by the passage can limit the amount of air drawn in during the suction stroke.
Ricardo then explaining his invention, proposes that by placing the inlet valve above the piston, and flush with the cylinder head, the air can be drawn into the cylinder without passing through the restriction, thereby improving breathing.
That is the nub of it really but in the patent specification as before, the principle is explained three times over.
Author`s note:
To Use Ricardo`s phrase “all things being equal” there will probably be little difference in performance whether the inlet valve is in the head or the block, if the constriction area is the same as the inlet valve area.
In the text explaining the improvement, Ricardo refers obliquely to “One or more valve controlled inlet ports are disposed as part of the cylinder head”.
Although he doesn`t directly say this, he obviously means that the advantage with the overhead inlet valve is, that a larger valve, or valves, can be utilised to improve volumetric efficiency, as one of the limiting factors with a side valve layout is the size of the valves.
So the essence of this new improvement is that a larger inlet valve or valves can be used to draw in air more efficiently than with the side valve arrangement. Also the constriction can be designed without consideration of the inlet valve.
Then this larger volume of air can be compressed into the combustion chamber through the restriction to create the desired turbulence and ignited by the spark plug, which Ricardo placed directly over the exhaust valve.
The downside is that the new head is more expensive as the casting is more complex and valve rocker gear is required.
In this patent the only difference from the previous one was to move the inlet valve from the block to the cylinder head. There is no doubt this arrangement was successful having been used by Rolls Royce Rover and the Bentley 4 litre where the engine gave a better output per litre than any of the other Bentley engines except the Blower.
At the end of the day, I think any Engineer has to ask himself, if it`s a big step cost wise to change to the F head from a side valve configuration, but not so big to change from the F head to the full overhead valve layout. So why not just go for the full overhead valve layout in the first place, with all the advantages it offers.
To put things into perspective, in 1927, when Ricardo submitted his patent application, most car engines had sidevalves, so his invention was probably aimed at conservative board members who baulked at the cost of overhead valves, but might be swayed by a semi overhead valve layout giving greatly improved performance. In the event Ricardo`s hopes were not fully realised.
For the designers of our modern car engines there is no such dilemma, the F head has long been consigned to the scrapheap, and it`s only us backward looking petrolheads that are concerned with it now.
Or perhaps in some secret location technicians are preparing a new generation of F head to relaunch onto the market, only time will tell
THIS ARTICLE WAS FIRST PUBLISHED IN THE BDC REVIEW