The Origin of the Four-Stroke Cycle

By Lynwood Bryant

Professor BRYANT of the Massachusetts Institute of Technology has done much research on the origins and development of the internal-combustion engine.

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In an earlier paper¹ on the genesis of a gas engine built by Nicolaus August Otto in 1876, I tried to follow the course of Otto’s thought and to explain the success of his engine. Otto attributed his success to what he called the stratified charge, a special way he devised of mixing the fuel and air in his cylinder. His theory was wrong, but guided by this theory he built a remarkably successful and influential engine, the earliest recognizable ancestor of today’s automobile engine.

I should now like to argue that Otto’s engine of 1876 was the first to use the four-stroke cycle. The four-stroke process, which first made it practical for a gas engine to use compression, was a key idea in the evolution of the internal-combustion engine, and the question of priority in its use was once a matter of critical importance: fortunes were at stake, or at least the owners of the patents involved thought so. Now the patents and the inventors are dead, and all that is at stake is credit for the invention. But the historical literature on early engines still reflects the confusion and disagreement of the old patent litigation, and perhaps it would be a service to review and evaluate the competing claims now that no money is at stake.

Four men are said to have used the four-stroke cycle before 1876. All of these claims arose in the course of patent litigation from ten to forty years after the time of the invention, and they all still appear from time to time in the literature. None is supported by substantial contemporary evidence. In 1862, the French engineer Beau de Rochas expressed the idea of the four-stroke cycle, but there is no evidence that he built an engine of this type or had any influence on anybody who did. The Munich watchmaker Reithmann and the famous Viennese inventor Marcus both were followers and not predecessors of Otto with their four-stroke engines. And the claim that Otto himself used the four-stroke process in an experimental engine in 1862 rests on extremely slight contemporary evidence. I conclude that primary credit for the invention of the four-stroke cycle should go to Otto, and that the invention should be dated 1876.

* * *

The earliest known expression of the idea of the four-stroke cycle is in a queer pamphlet published in 1862 by an obscure French engineer named Alphonse-Eugéne Beau de Rochas (1815-93) as an incidental part of some purely theoretical speculations about the possibility of using gas engines in conjunction with steam engines to improve the performance of railroad locomotives. The idea was clearly and precisely expressed (Fig. 1), but the pamphlet was very obscurely published: it did not enter the stream of public knowledge until it was brought to light in the course of litigation over Otto’s patents in 1884.

Not much is known about Beau de Rochas beyond what may be inferred from a dozen publications of his that have been found.² He was apparently a quixotic inventor familiar with the current literature on thermodynamics and given to enthusiastic attacks on problems in the exciting fields of the telegraph and the railroad. Around the middle of the century, he published proposals for a submarine telegraph, a railroad tunnel under the English Channel, a new kind of drive for canal boats consisting of an endless chain resting on the bottom of the canal (the screw propeller he did not regard as practical except on the high seas), the use of steel for high-pressure boilers, and a way of improving the adhesion of locomotives so that the railroad could conquer the Alps. His proposals impress one as perfectly respectable intellectually, but irresponsible in the sense that he seemed unrestricted by the need to finance or manage the devices he proposed. One suspects that his ideas were too extreme to be influential, too outlandish to enter the normal channels of technical communication. They were sometimes published in pamphlets rather than in technical journals, and occasionally they appeared in peculiar forms.

The booklet that we are concerned with here, for example, is not set in type at all, but is a lithographic reproduction of fifty-three pages of fine handwriting, bearing the title Nouvelles Recherches sur les conditions pratiques de plus grande utilisation de la chaleur et en Général de la force motrice. Avec application au chemin de fer et la navigation. The title page identifies the author as “Ingénieur attaché au Service central des Chemins du Midi.” The book is a collection of suggestions for improving the efficiency of steam engines, a favorite topic in the technical literature of the time. The table of contents outlines these suggestions systematically, but without making any special feature of the gas engine and without mentioning the four-stroke cycle, so that even if the pamphlet happened to fall into the hands of a man working on the gas engine, it might very well not communicate this key idea to him.

Section 6 of the book contains various interesting proposals for combinations of gas and steam engines. The exhaust heat of a gas

engine, for example, could be used to generate steam for a steam engine, Beau de Rochas says. Steam and gas could be used in different cylinders, or on opposite sides of the piston in the same cylinder, with the steam used to get the engine started and up to the speed required by a gas engine. This section includes an interesting statement of the conditions for maximum efficiency of a gas engine: the piston speed should be as high as possible, and the expansion should proceed as far as possible. Cylinder space should have as low a surface-to- volume ratio as possible, so that one large cylinder would be better than several small ones. The initial pressure should be as high as possible, but a practical limit is set by the temperature at which the charge will ignite spontaneously, which will be reached, Beau de Rochas guesses, with a compression ratio of about four to one. (It is interesting to note that Beau de Rochas mentions the possibility of spontaneous ignition of a compressed charge. One could stretch a point and argue that he an- ticipated Diesel as well as Otto, but what is being compressed in his hypothetical engine is a mixture of fuel and air. There is no indication that Beau de Rochas thought of reaching high temperatures by compressing air alone, as Diesel did.)

As an incidental part of this theoretical analysis of the gas engine, Beau de Rochas suggests that a four-stroke cycle will make it possible to achieve the compression within the working cylinder and defines the four strokes as follows (Fig. 1):

1. aspiration pendant une course entiére du piston; (suction during an entire stroke of the piston)

2. compression pendant la course suivante; (compression during the next stroke)

3. inflammation au point mort et détente pendant la troisiéme course; (ignition at neutral and relaxation during the third stroke)

4. refoulement des gas brûlés hors du cylindre au quatriéme et dernier retour. (discharge of burnt gases out of the cylinder at the fourth and final return.)

Actually Beau de Rochas seems rather apologetic about the four-stroke cycle. It is a possible way of compressing the charge, he seems to be saying, not necessarily the best way, but the best he can think of at the moment. He recognizes the obvious objection that it reduces the number of power strokes per revolution, but mentions the compensating advantage of the improved efficiency that will come with compression, and he goes on to suggest that by making the engine double-acting one can achieve at least a half-power engine, so to speak (à demi-effet), by which he means one with half as many power strokes per revolution as an ordinary steam engine.

This clear expression of the four-stroke idea, which seems so remarkable in retrospect, had no influence in the 1860’s and 1870’s. Perhaps nobody read it. I can find no evidence that anybody knew about it before a German manufacturer accused of infringement somehow discovered the pamphlet in 1883 and used it to invalidate Otto’s four-stroke claim in Germany the following year.³ The obscurity of the publication became an issue in 1885 in patent litigation in London. The British court finally refused to admit the booklet as evidence, even though the British Museum had acquired a copy, on the ground that it had not been really published in the sense of being made known and available to people interested in gas engines.⁴ Not even Etienne Lenoir, the best-known gas-engine man of the day, gave any sign of interest in the four-stroke idea. He is supposed to have known Beau de Rochas⁵ (they lived in the same city and had common interests, and Beau de Rochas mentions Lenoir in the book), so the idea should have reached him if it reached anybody, and at the time Lenoir badly needed ideas, for his engine was not working well. He had a double-acting engine like a steam engine that burned illuminating gas without compression, well advertised but not very efficient, which some of his customers were converting to steam because it was so uneconomical and rough running.⁶ Even if the four-stroke idea had reached Lenoir or occurred to him, the proposal to improve the engine by reducing the frequency of power strokes might well have seemed too absurd to try.

And apparently Beau de Rochas himself did not think well enough of the idea to keep his patent alive. He had applied for a patent on his collection of ideas on January 16, 1862, and later filed supplementary applications. The patent was granted, with supplements, but lapsed after a year, probably because the required annual fee was not paid.⁷ It looks as if the author did not place a very high value on the possible commercial application of his ideas.⁸ In fact, Otto himself was slow to recognize the value of the four-stroke cycle. In 1876, he was trying various cycles with and without compression, even the Lenoir process, in the very cylinder used in the first four-stroke engine,⁹ and he never thought of the four-stroke cycle as the essence of his invention.

So it is not a very deep mystery why nobody paid any attention to Beau de Rochas’ four-stroke suggestion in the 1860’s. The author himself apparently did not take it seriously as a practical plan for an engine, and if the idea had reached a man actually working on a gas engine, he might easily regard it as not worth trying. To a man thinking with the analogy of the steam engine, such a drastic reduction in the frequency of power strokes might seem too high a price to pay for the advantages of compression.

It is curious, though, that Beau de Rochas made no claims of priority in the 1880’s when the four-stroke cycle was recognized as the best for gas engines. Otto’s firm, the Gasmotorenfabrik Deutz, had patented the four-stroke mode of operation and was bringing suit against infringers in a half-dozen countries, so that evidence of priority would have had great value. Beau de Rochas was still interested in heat engines in those years and could not have missed all the discussions of the Otto engine and its imitators in the literature. He was not a man indifferent to financial success or insensitive in matters of prestige—at least, he wrote vigorously enough in the 1850’s on the credit due an inventor—but he seems to have made no reference at this time to his own publication of the four-stroke idea back in 1862. With his propensity for peculiar forms of publication, it is possible that he spoke his mind in some obscure article or pamphlet,¹⁰ but so far nothing has turned up.

In his last years, Beau de Rochas was employed by Mignon et Rouart, a firm of engine manufacturers whose product included a four-stroke Lenoir designed to compete with Otto’s engine of 1876, and he was working on a device for measuring the performance of heat engines.¹¹

Recognition came to him in 1891, two years before his death, when the Société d’Encouragement pour I'Industrie Nationale awarded him a prize of three thousand francs for the invention of the four-stroke cycle.¹² Since then, two celebrations, the first on the occasion of the unveiling of a commemorative plaque by the Société des Ingenieurs de I’Automobile in 1938 and the second a centennial ceremony in 1962, have urged the claims of Beau de Rochas and of France to a proper share of the credit for the invention of the automobile engine, and each led to a flurry of papers in the professional journals. Beau de Rochas undoubtedly conceived the idea of the four-stroke cycle, but he did not recognize its significance, and neither did anybody else at the time. If one is concerned about credit for the invention, then the appraisal of the Beau de Rochas claim is a matter of determining what is meant by invention and what sort of credit should be awarded for a pure conception without realization or influence. To a historian tracing the evolution of the internal-combustion engine, this early expression of a key idea is very interesting, but it is not actually a part of that evolution; it is a dead-end idea which had no influence on the development of engines. The idea had to be reconceived by Otto.

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Another claim to priority in the use of the four-stroke cycle that arose in the course of litigation in the 1880’s, and one that still appears in the literature occasionally,¹³ is the claim of Christian Reithmann (1818-1909), a Munich watchmaker who had been using homemade gas engines to drive the light machinery in his shop in the years before 1880.¹⁴ He was discovered in 1882 and used for the defense of an obscure infringer under attack by Otto’s Gasmotorenfabrik Deutz. In 1883, Reithmann testified that he had built an engine that burned hydrogen in 1852, converted it to illuminating gas in 1858, and patented it in Bavaria in 1860 when he heard about Lenoir’s motor. Later in the 1860s, he built another gas engine, a curious one in which the explosion took place between two pistons.¹⁵ From the remains of this engine, he constructed still another one, which was said to have operated in the four-stroke mode at some time between 1870 and 1881. The critical question is “When?” On the whole, testimony was inconsistent and vague, but at one time Reithmann testified clearly that it ran as a four-stroke engine before 1876.

The Gasmotorenfabrik Deutz initiated proceedings against Reithmann at the end of 1883. More important enemies of the Gasmotorenfabrik Deutz interested themselves in the case and retained the distinguished Moritz Schréter to study and evaluate Reithmann’s engine. The drawings that Shréter prepared to show what the engine must have been like according to Reithmann’s recollections represent an engine very much like Otto’s engine of 1876, including flame ignition and also control devices said to make the charge stratified,¹⁶ except that its cylinder was upright. The court allowed Reithmann to reconstruct his old engine to show how it had operated in the early 1870’s, but substantial modifications were necessary before it would run as a compression engine in the four-stroke mode. As it finally ran in the presence of experts in 1884, it had a new electric ignition (Reithmann changed his mind about the type of ignition he had used), new piston rings (there were none in the earlier engine, so that it is questionable whether it could have held any compression at all), and new gearing to control the valves for the four-stroke process. After a year of confusing testimony about this engine, the Bavarian lower court found in Reithmann’s favor.

This decision was a shock to the Gasmotorenfabrik Deutz, with Otto’s new engine at a peak of popularity and six years still to run on the patent. The Deutz people appealed at once but, in the meantime, to protect their interests, they bought Reithmann’s claims and his engine for twenty-five thousand marks plus a new Otto engine, and agreed to publish no statement that would compromise Reithmann.¹⁷ This hasty agreement—unnecessary, as it turned out—could be interpreted by Reithmann’s friends as a recognition by Deutz of Reithmann’s claims.

A short time after the decision, Eugen Langen, head of the firm, had a private interview with Reithmann in Munich, which we know about only through the recollections of Langen’s son, with whom Langen had discussed the interview.¹⁸ In any case, whatever happened in the interview—and one can make damaging inferences either way—in the appeal proceedings that followed, Reithmann was unwilling to fix a time for the conversion of his old engine to the four-stroke mode of operation. The court reviewed the earlier testimony about the operation of the motor in the early 1870’s, found it unconvincing, and decided that Reithmann had not anticipated Otto.

Reithmann owes the persistence of his legend to his friendship with Hugo Giildner, an expert on the internal-combustion engine who wrote an authoritative textbook at the turn of the century. This book, which ran through several editions between 1903 and 1921, has a full and well-illustrated historical section (omitted in the English translation) which has been an important source of information on early engines and which has propagated a number of errors. Giildner tells Reithmann’s story at some length—he got it from Reithmann himself in his old age—and quotes the decision of the lower court with no indication that it was reversed on appeal. He also reproduces Schréter’s drawings as if they represented a real engine.¹⁹

The historian interested in priorities of this kind will do well to follow the higher court and reject Reithmann’s claim. It is not supported by any documents or hardware of the early 1870’s, or by any unequivocal testimony.

* * *

Another man said to have anticipated Otto is Siegfried Marcus (1831-98), an Austrian inventor of the versatile, self-made Edison type. He appears regularly in histories of the automobile as an obscure Viennese mechanic who built automobiles before anybody else did, including one driven by a four-stroke motor, but who strangely had no influence on the development of the automobile because, it is said, he was discouraged when his noisy cars were suppressed by the police, or because he was an eccentric who lost interest in his inventions once they were complete, or simply because he was ahead of his time.²⁰

Actually, Marcus was not at all the unknown tinkerer that Reithmann was: his work was widely reported in the technical press and

exhibited at expositions throughout the latter half of the century, and he was well enough known in the Vienna community to rate a column in an Austrian biographical dictionary as early as 1867.²¹ His experience with the electric telegraph in the 1850’s led him, as it had so many others, to a general interest in electricity. He was said to have installed the first electric bell in the imperial palace and to have served as tutor in science to the young crown prince, Rudolf. In 1864, he won a prize for his work in the direct conversion of heat to electricity. In the 1870's, he turned to electric light and—before Edison, according to the Vienna papers—achieved “subdivision of the electric light,” that is, a parallel circuit in which the lights could be individually controlled.

Two of Marcus’s inventions in the 1860's were of special interest to people working on gas engines, although both were conceived with other applications in mind. They solved the two problems that had to be solved to make the internal-combustion engine usable in places without city gas and to make it applicable to vehicles—the liquid fuel problem and the ignition problem. In the 1850's, Marcus developed a hand-powered magneto-electric device useful for a military field telegraph without batteries. This led him to an electric ignition device for explosive mines, which was adopted by the Austrian, Prussian, and Russian armies, and which apparently brought Marcus enough income to support his other projects. By the 1880's, he had a reliable magnetoelectric ignition system for gas engines that could be driven by the engine itself.

Another of Marcus’s inventions dating from the 1860’s was a large carburetor, or gasifier, for converting liquid petroleum into a flammable gas. This was intended as a portable gas-generating plant to make gas available beyond city gas systems, but its application to gas engines was obvious. To help get his carburetor patented in Prussia, Marcus went to Berlin to see Franz Reuleaux (1829-1905), a distinguished engineer who was a consultant to the patent office, and also an intimate friend of Eugen Langen, Otto’s partner, who at the time was working with Otto on an early gas engine known as the Otto & Langen, which operated on the atmospheric principle like a Newcomen steam engine.²² Reuleaux wrote to Langen promptly in great excite-

Reference

1. “The Silent Otto,” Technology and Culture, VII (Spring 1966), 184-200.
2. Information about Beau de Rochas is concentrated in two groups of articles— one in Bulletin de la Société d’ Encouragement pour VIndustrie Nationale, CXXXVII (1938), 209-39, especially C. Walckenaer, “L’invention de Beau de Rochas,” pp. 212 25; the other in Documents pour l'histoire des techniques, Cahier No. 2 [1962] pp. 3-42, especially Jacques Payen, “Beau de Rochas. Etude biobibliographique,” pp. 3-24, which contains a useful list of the known publications by and about Beau de Rochas.
3. The earliest reference I have seen is in a letter from C. Wigand dated December 14, 1883, published in Zeitschrift des Vereines deutscher Ingenieure, XXVIII (1884), 45-47.
4. In Otto vs. Steel, reported in Engineer, LXI (1886), 9, 35-36, 93.
5. Friedrich Sass, Geschichte des deutschen Verbrennungsmotorenbaues von 1860 bis 1918 (Berlin, 1962), p. 57.
6. “Gasmaschine,” Jabresberichte iiber die Fortschritte der mechanischen Technik und Technologie, II (1864), 164-5.
7. French patent number 52,593, applied for January 16, 1862, delivered March 10, 1862, with an addition applied for June 10, 1862, delivered August 26, 1862 (C. Walckenaer, p. 216). The existence of a French patent at this time does not prove much. It does not prove that anybody had actually tried out the four-stroke cycle, or judged it workable, or intended to exploit it commercially. It was not the four-stroke cycle specifically that was patented, but rather the whole book in which the four-stroke cycle was only one of hundreds of ideas. A French patent was a simple registration of a claim, like a copyright, granted without any investigation to determine the novelty or utility of the invention. The arguments in the British and the German patent litigation seem to refer to the Beau de Rochas book, not the patent, perhaps because the patent was not known at the time. French law required an annual fee of one hundred francs to keep a patent alive and provided for an annual catalogue of new patents by title and for publication, verbatim or by extract, of patents on which the second annual fee had been paid (Thomas Barclay, The Law of France Relating to Industrial Property [London, 1889], p. 50). The title of the Beau de Rochas patent, which was the same as the book title, might not seem significant to a researcher, and the second annual fee was presumably not paid.
8. One account says, without evidence, that Beau de Rochas tried in vain to interest manufacturers in his patent: J. Hirsch, “Rapport fait au nom du Comité des Arts mécaniques . . .,” Bulletin de la Société d’Encouragement pour PIndustrie Nationale, XC (1891), 363.
9. Engineer, LX (1885), 433-34.
10. Jacques Payen makes this suggestion in “Beau de Rochas. Etude biobibliographique,” p. 17. Beau de Rochas was in Africa for some years after 1870—he was a Bonapartist who left France when the Second Empire collapsed—and Gustav Goldbeck suggests, in Gebindigte Kraft: die Geschichte der Erfindung des Otto-motors (Munich, 1965), p. 186, that perhaps he was out of touch with the Parisian technical world and did not hear about Otto’s four-stroke engine.
11. Jacques Payen, p. 20.
12. Bulletin de la Société d’Encouragement pour PIndustrie Nationale, XC (1891), 359-64. E
13. E.g., “A Gas Engine Centenary,” Engineer, CXCIII (1952), 539; Hans Seper, “Christian Reithmann und sein Viertaktmotor. Zu seinem 50. Todestag,” Blätter für Technikgeschichte, XX1 (1959), 15-25.
14. For an account favorable to Reithmann’s claims, see the biographical memoir by Hans Seper just cited, which includes a portrait. For a more critical account, which I am following closely, see Sass, pp. 58-66.
15. Hugo Güldner, Das Entwerfen und Berechnem der Verbremmungsmotoren (2d ed.; Berlin, 1905), pp. 25-26.
16. Otto’s engine of 1876 introduced fuel and air into the cylinder in such a way that he thought he had a rich mixture near the point of ignition to assure reliable ignition, and then layers of decreasing richness toward the piston that were supposed to slow the burning or cushion the shock of the explosions. Schréter’s drawings appeared in Zeitschrift des Vereines deutscher Ingenieure, XXVIII (1884), 46.
17. Arnold Langen, Nicolaus August Otto, Der Schopfer des Verbrennungsmotors (Stuttgart, 1949), pp. 110-13, 214-23. Since the Deutz people scrupulously refrained from comment on Reithmann, the Reithmann legend had time to gather momentum.
18. Ibid., pp. 218-19.
19. Güldner, pp. 39-42.
20. Such stories have appeared recently, e.g., in Allan Nevins, Ford: The Times, the Man, the Company (New York, 1954), pp. 97-98; and in William Greenleaf, Monopoly on Wheels: Henry Ford and the Selden Automobile Patent (Detroit, 1961), pp. 29-30.
21. Constant von Wurzbach, Biographisches Lexikon des Kaiserthums Osterreich (Vienna, 1867), p. 422.
22. In the earliest days of the gas engine, the key problem was how to moderate or cushion the explosive force of the combustion of illuminating gas. In a directacting engine in which the expanding gases drove the output directly through rigid rods and cranks (like an automobile engine), the explosions seemed destructive