On combustion of the fuel mixture in a normal otto cycle engine there is usually an excess of fuel in the mixture to ensure that ignition takes place. Under practical conditions it has proved that the stoichiometric mixing ratio, as also a mixing ratio with excess of air, renders the fuel mixture difficult to ignite.

The thermal efficiency of an internal combustion engine and the power out¬ put obtainable from a given engine for unchanged fuel consumption both increase with the compression ratio of the engine. Higher compression re¬ quires a petrol with higher octane number. But there is also a limit at which knocking phenomena occur.

The compression ratio of an engine is usually chosen so that the knock threshold is not exceeded at full engine load, i.e. when there is maximal quantity of air-fuel mixture. This implies, on the other hand, that when the engine works with a lower load the intake of fuel mixture is considerab¬ ly lower. In such case one could have a higher compression without risk of knocking, at the same time as the fuel economy would be improved.

The object of the present invention is to produce such an engine design and such a combustion process that the engine will not only be more economical in fuel owing to its having variable compression, but it will also be posib- le to work with a greater excess of air in the total gas mixture, which leads to more complete cobustion and thus clean exhaust.

An engine of this kind is described in the Swedish patent application (Swedish patent) 76022179-9• In this engine design a moving piston has been placed in the working cylinder bore for variation of the compression ratio in dependence of the engine load. Since the compression piston has a large area and a small movement there are certain disadvantages, among which the fact that the piston adjustment mechanism is exposed to great forces and that the movement of the piston is small.

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The gas mixture between the pistons will always be homogenous and largel uniform, moreover, one result of which is that the compression volume exhibits no particular portion where the ignition conditions are more favourable.

The invention eliminates the disadvantages attaching both to the latter arrangement and to earlier arrangements with essentially adjustable but, a given load, fixed counteracting pistons. A combustion process is thus achieved which, at partial load, increases the efficiency and reduces th exhaust pollution from an internal combustion engine, preferentially of otto cycle type and comprising working pistons engaging with a crankshaf and moving in working cylinders united with their respective precombusti chambers, in that the volume of the precombustion chamber is changed cyc ly and synchronously with the working cycle of the engine, preferentiall in such a way that the changes of the volume of the precombustion chambe complete a full cycle during two revolutions of the engine crankshaft, whereupon, during each precombustion chamber cycle, fuel is introduced i the known manner and ignited in the precombustion chamber and the ignite fuel-air mixture is transferred to the interacting working cylinder.

Advantages are obtained through the fact that the volume of the precombu ion chamber is so changed that it is a minimum at the commencement of ea intake stroke in the working cylinder and a maximum at the commencement each power stroke in the working cylinder.

Further advantages are attained if the minimum volume of the precombusti chamber is kept constant while its maximum volume is varied in dependenc on the engine load, e.g. according to the negative pressure prevailing i the engine intake system, in such a way that the maximum volume grows wi increasing ^" load and thus increases the engine compression ratio with di ishing load.

A special advantage 'is attained through the' fact that the fuel-air mixtu which is ignited in the precombustion chamber is led to the interacting working cylinder through a channel or passage with a certain constrictio and that the constriction can be kept constant or varied during the engi working cycle in such a way that it is largest at the commencement of th power stroke.

In the present invention the engine compression volume is so arranged that it comprises two separate but mutually associated volumes. The first volume consists, in the ordinary way, of the volume enclosed above the working piston, while the second volume consists of a precombustion chamber with variable volume. The precombustion chamber volume is varied cyclically with a frequency that is synchronous with the engine revolutions, while the amplitude or size of the change of volume is varied in dependence on the engine load.

At the end of the compression stroke and beginning of the power stroke there is great turbulence in the combustion chamber. To ensure ignition with a εtoichiometric ratio of the air-fuel mixture, as also when there is an excess of air, the air-fuel mixture introduced in the precombustion chamber is screened off from the working cylinder by a constriction. In this way an air-fuel mixture which is so rich that no ignition problem a- rises is always obtained in the precombustion chamber.

It- iέ then apparent that the constriction has its chief function in con¬ junction with the ignition of the air-fuel mixture. According to the invent¬ ion a combustion process is also obtained in which the constriction occurs only on the initiation of combustion.

The invention also has as its object to provide an arrangement for imple¬ mentation of the combustion process. An expedient arrangement is attained through the fact that the precombustion chamber consists of a cylinder with a bore and, displacable in it, a compression piston which, by means of transmission devices, is driven from the engine drive shaft so that the compression piston moves cyclically and synchronously with the engine crank¬ shaft, preferentially so that the compression piston completes one full cycle during two revolutions of the engine crankshaft. The transmission de¬ vices can advantageously be designed so as to comprise devices with fixed transminnion ratio in relation to the engine shaft and devices between the latter devices and the compression piston which exhibit a variable trans¬ mission ratio in order to vary the travel of the compression piston, the transmission ratio being varied by means which are actuated in dependence on the engine load. '

One purpose of the invention is so to arrange the transmission and so to

link it to the engine crankshaft that the compression piston is furthest into its bore roughly at the beginning of each intake stroke and furthes out roughly at the beginning of each power stroke, especially so that th innermost dead centre is constant and the outer is displaced inwards wi diminishing load, so increasing the engine compression ratio.

Other objects of the invention are to form an opening as a channel betwe working and compression cylinders by arranging the cylinders parallel to and facing away from one another but with their bores overlapping, so producing a constant constriction between them. A variable conεtrction i achieved by placing on the top of the piston a cam engaging with the ceiling of the working cylinder beside the opening.

The invention will now be described with reference to the attached drawi of which Fig. 1 shows schematically the parts, essential for the inventi of an internal combustion engine of Otto cycle type, viewed in a plane p pendicular to the longitudinal direction of the crankshaft and with cert parst cut away fro greater clarity, Fig. 2 shows the parts ^' in Fig. 1 vie from above, Fig. 3 shows schematically, in the same way as in Fig. 1, th position of the engine parts at the beginning of the intake stroke at lo engine load, Fig. h shows the position of the engine parts at the beginn of the intake stroke at high engine load, Fig. 5 shows the position of t engine parts at the beginning of the power stroke at low engine load, Fi the same parts at the beginning of the power stroke at high engine load, -and Figs. 7 and 8 an alternative arrangement of the parts.

In the figures 1 denotes a working piston and 2 the working cylinder, wh 3 denotes a compression piston in a precompression chamber cylinder h. T .compression piston 3 is hinged through a piston pin 5 to one end of a le 6, the other end of which is hinged through a pin 8 to a piston rod 10, which constitutes a crank mechanism together with an eccentric or crank on the shaft 12. In a portion between the piston pin 5.a d the pin 8 the lever 6 has an oblong coulisse opening or guide-way 20 extending roughly the same direction as the line joining pins 5 and 8. The guide-way has t opposing guide surfaces 20 ^* and 20" on the two sides of and equidistant from a circular midline 20a, all of which are concentric. The radius of curvature of the midline 20a is R2 and its centre is C2 (see Figs. 5 and

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The point C2 thus has a fixed position in relation to the lever 6 and accordingly follows its movements.

In the guide-way a cube 19 is slidably arranged and is revolvingly carried by a shaft 18 arranged on the end of the control arm 16. ^φ he latter is fix¬ ed to a control shaft ~\ which is set by a device of known kind, not shown in the drawings, in an angular position depending on the engine load. With increasing engine load the control shaft Λk is rotated in the direction indicated by the arrow A and with decreasing engine load in the direction indicated by the arrow B. The distance between the centre of shaft 18 and the centre C1 of the control shaft is R1 (see Figs. 5 and 6).

The cube 19 can thus be displaced ϊp the guide-way 20 in the lever 6, the transmission ratio of the lever 6, i.e. the distance between the shaft 88 and the piston pin 5 in relation to the distance between the pin 8 and the shaft 18, being changed in dependence on the load through the rotation of the control shaft 1*f _t When the shaft 18 and the cube 19 are in their left- hand position in the figures, i.e. at high engine load as in Fig. 6, the transmission ratio of the lever 6 is large, so that the travel of the pre- compresεion chamber piston or compression piston is large. At low engine load as in Fig. 5 the shaft 18 and cube 19 are in their right-hand position in the figures, in this case the end position, the transmission ratio is small and the travel of the compression piston 3 small.

The driving shaft 12 for the movement of the .compression piston 3 is given by a transmission (no$ shown) a speed of rotation half that of the engine shaft. This implies that while the working piston 1 performs a movement during an engine revolution from the innermost position in the working cylinder 2, shown in Fig. 1, to the outermost position in the working cylinder and back, the precompression chamber piston 3 performs a movement only in one direction, from the position shown in Fig. 1, where the pre- compression chamber piston is in its innermost position in the precompre.ss- ion chamber cylinder , to the outermost position in the precompression chamber cylinder. At the next full engine revolution the piston 3 will move back in the opposite direction to the innermost position in the cylinder k. This will be described in greater detail below.

Fig. 2 shows the engine parts in Fig. 1 viewed from above, identical pa having the same notations.

It will also be seen from the figures that the compression chamber cons of two εubvolumes, the compression chamber 21 above the working piston and the compression chamber 23 under the compression or precompression chamber piston 3. The two compression chambers communicate with one ano via a channel or passage 22. In the embodiment shown the channel is bou by arcs with radii corresponding to those of the working piston 1 and t piston 3« This opening will be seen more clearly from Fig. 2A, in which portions of the overlying parts are cut away. The channel can be formed smother way without thereby departing from the idea of the invention.

Fig. 3 shows the engine parts at the end of the exhaust stroke or begin of the intake stroke in the case when the engine is working at low load The control shaft h has been rotated counterclockwise in the figure in direction of the arrow B so far as this is possible, so that the cube 1 at the end of the guide-way 20 adjoining piston 3» The eccentric mechan 12 - 13 - 10 - 8 is in the position where the shaft 8 reaches its upper position. This implies in turn that the piston pin 5 and thus the pisto are in their innermost position in the cylinder b.

The midline 20a for the guide-way 20, and thus for the shaft 18, consis of an arc with radius R2 and centre in C2, as described above.

To achieve the properties characteristic of the invention it is arrange that the radii R1 and R2 are equal. It is also arranged that the piston always reaches the same innermost position at distance D from the top o cylinder (see Figs. 3 and k) regardless of the load. This is achieved arranging that centre C2 for the guide-way 20 in lever 6 coincides with centre C1 for the control shaft 1-+ when lever 6 assumes the position sh in Figs. 3 and h. These two figures show a position of lever 6 which is determined by the position of piston pin 5 at the innermost position of piston 3 (distance D) in cylinder ^• *. and the uppermost position of pin 8

Figs. 3 and h show the position of the engine parts at the point in the engine working cycle where the exhaust stroke is completed and the inta stroke is to start (Fig. 3 at lowest engine load and Fig. at highest

engine load). From the description above it is thus apparent that the parts 12 - 13 - 10 - 8 - 6 - 5 - 3 always assume the same position from lowest engine load through all partial loads to highest engine load, i.e. regard¬ less of the engine load and of the position of the parts ik - 16 - 18 - 19 affected by it.

It is apparent from the description that the geometrical form of the engine parts concerned is such that the volume of the compression chambers 21 and 23 is the same at the two extremes of the engine load shown in Figs. 3 and *t, as also at every other load between them, regardless o ^' the load.

From the position shown in Figs. 3 and h the working piston 1 performs a downward intake stroke followed by a compression stroke to the positions shown in Figs. ^" 5 and 6. From there the working piston 1 performs a downward power stroke under combustion of the fuel mixture and then moves upwards under exhaust of the combustion gases, which takes place very effectively owing to the fact that the working piston 1 and the piston 3 move towards one another.

In the position shown in Fig. 3. which thus shows the position of the parts at the beginning of the power stroke at low engine load, the cube 1 is in its right-hand end position, the eccentric 13 and the pin 8 in their lowest positions, so that the piston pin 5 and the piston 3. owing to.rotation of lever 6 round shaft 18, are in their highest position.

Fig. 6 shows the position of the engine parts at the moment of ignition after the working piston 1 at high load has performed during one engine revolution a reciprocal movement in the working cylinder 2 from the position shown in Fig. back to the innermost position. The eccentric mechanism 12 - 13 - 10 has moved the pin 8 to its lowest position. Since the control arm 16, in dependence on the high engine load in Fig. 6, has moved the shaft 18 with cube 19 to the left, the transmission ratio, i.e. the distance between shaft 18 and piston pin 5 in relation to the distance between pin 8 and shaft 18, has increased in comparison with the load condition shown in Fig. 5. This has the result that, at the beginning of the power stroke, the piston 3 is further out in the cylinder k than at the lower load shown in Fig. 5.

When, from the position shown in Fig. 6, the working piston 1 performs a reciprocating movement comprising a power stroke and an exhaust stroke, t piston 3 will move from the position shown in Fig. 6 to that shown in Fig. From the previous description, and on comparison of Figs. 3 and _> with Fi h and 6, it is apparent that the compression volume at the beginning of t intake stroke is the same (see Figs. 3 and *f) both at low and high engine load, whereas the intake volume and the volume at the end of the compress¬ ion stroke are greater at high than at low load (see Figε. 6 and 5 » Thiε has the result, accordingly, that the compression ratio at high load is less than at low, i.e. that change of compression in relation to the engine load has been attained which is desired in order to increase the efficiency of the engine.'

In addition other advantages have been gained in comparison with the earli known design according to Swedish patent . . . (patent application 7602179 Thus the cyclical change of the compression chamber 21 + 23 is achieved by means of a small precompression chamber piston or compression piston 3 pla ed in a precompresεion chamber, which reduces the forces on the operating mechanism 12, 13, 10, 8, 20, 19, 6, 5 for the piston 3* at the same time a the latter has a longer movement in the cylinder , which involves less risk of the compression or precompression chamber piston 3 coking up and ■ seizing, which in turn results in greater reliability of the engine. Like¬ wise an almost complete evacuation of the residual gases is obtained, sinc the working piston and the piston 3 move towards one another.

Another essential advantage of the invention is attained in the design sho in Fig. 6.

A very important advantage of the invention is obtained through the design shown in the figures, with injection of fuel into the precompression chamb or the compression chamber 23. Through the constriction constituted by the channel or passage 22 the fuel-air mixture will be richer in fuel in the compression chamber 23 than in the compression chamber 21 of the working cylinder 2. This ensures good ignition of the fuel-air mixture which, afte passage through the channel 22, enters the working cylinder 2 and is burnt with excess of air. If, accordingly, the sparking plug is placed in or clo to the compression chamber 23, a more reliable and effective ignition is obtained in this way than if ignition were to occur in an entirely homogen ous and leaner fuel-air mixture. ^y C.V

The asymmetry between rich and lean fuel-air mixture can be affected through the form and si__e of the channel 22 between the two cylinders *t and 2, so alwayε enεuring reliable ignition. By suitable design of the channel it is also possible to achieve a stratified combustion with different characters, e.g. by shaping the channel for different flow resistances and constricting effects, varying heat transmission etc. Apart from the almost complete combustion of the hydrocarbons in the fuel owing to the exceεε of air, the combustion time and combustion temperature can also be affected so as to reduce the formation also of nitrogenous oxides.

Figs. 7 and 8 show examples of the form of such a special channel. They show the form of the portion round channel 22, Fig. 7 being a broken-oύt sub- portion corresponding to Figs. 1, 3-6, while Fig. 8 is a view corresponding to Fig. 2A. In the embodiment shown a cam 28 has been placed in an arc on the upper side of the working piston 1, the cam extending up towards the ceiling of the working cylinder 2. Above and at the sides of the cam are formed slots through which the fuel-air mixture flows out from the combust¬ ion chamber 23 to chamber 21 of the working cylinder. Since the cam 28 is in engagement with the working piston 1, it moves with it. There is there¬ fore a slot and constriction, varying with the working cycle of the engine, which are smallest - and therefore cause most constriction - in the top position of the working piston 1.

The embodiment of the invention described is presented for the purpose of exemplification and hot limitation. Several embodiments are possible within the scope of the patent claims. For example the transmission between the engine crankshaft and the compression piston can be arranged in several ways, the position of the cylinders - the working cylinder and the compress¬ ion cylinder - in relation to one another and to the channel uniting them can be varied in many ways, the constriction between working cylinder and precompression chamber cylinder can be varied, etc.