The invention relates to a combustion engine combination having a plurality of power units, each of which is made up of its independent crankshaft and one or more actuating cylinders driving it, as well as of mechanisms for combining these power units to rotate the power output shaft or shafts.

Constructions comprising a combustion engine combination made up of a plurality of power units are known per se. The purpose has been either to increase the power obtained, as in ships which have a plurality of engines to drive their own propellers and in trains in which a plurality of engines are, when neces¬ sary, connected to pull the train, or to save fuel, in which case, depending on the power requirement, some of the engine cylinders are disconnected in one way or another. The last- mentioned saving of fuel is based on the fact that a combustion engine uses the least fuel in proportion to the power it yields when it is operating at that speed of rotation which is within the range of the peak torque of the engine, since at that time the thermal efficiency is at its best.

Combustion engine combinations of this type, in which the en¬ gine is typically divided into two parts, one part being oper¬ ated at low speeds of rotation when the power requirement is also rather low, and both units are operated at rather high speeds of rotation when the power requirement is higher, have been disclosed in, for example publications SE-440 386, SE- 447 007, SE-450 718, and DE-31 33 892. All of these publica¬ tions are based substantially on the same above-mentioned prin¬ ciple and include, as compared with each other, primarily dif¬ ferent structural solutions for disconnecting the different parts of the engine and, when necessary, for connecting them to drive the power output shaft. The essential feature of these reference publications is, however, that in them it is possible

to connect to the power output at any given time different numbers of mutually similar actuating cylinders of the combus¬ tion engine. The disadvantage of all of these systems is that they do not change the combustion engine feature that the poin of maximum power output of the engine is at crucially higher speeds of rotation of the crankshaft than is the point of the maximum torque yielded by it. In other words, the peak torque and the peak power always remain at the same speeds of rotatio even if the number of cylinders is changed; only their values change in proportion to the number of cylinders used. Further¬ more, all of these constructions are very complicated, because in them different numbers of cylinders have to be connected in a different order, or together, to the drive shaft, as can be noted from, for example, publication SE-440 386. This also increases the price of the engine construction.

The object of the invention is thus to provide a combustion engine combination by means of which more torque is obtained at high speeds of rotation, and more power at low speeds of rota¬ tion, than is obtained with a conventional combustion engine or with prior-art combustion engine combinations. It is another .object of the invention to provide a combustion engine combina¬ tion of this type, which makes a simple construction possible without expensive special arrangements and auxiliary devices. It is a further object of the invention to provide a combustion engine combination of the type described above, in which the fuel consumption is low or which can be used in a manner re¬ sulting in very low consumption. A further object of the inven¬ tion is to implement a combustion engine combination which is especially suitable for a road vehicle while providing an ad¬ vantageous power distribution and achieving the other objects described above.

In order to achieve the objects defined above and to solve the problems described above, the combustion engine combination according to the invention is characterized in what is stated

in the characterization clause of Claim 1.

The most essential advantage of the invention is that by means of it, by using a very simple construction resembling a conven tional single-part combustion engine, the torque output can be raised at high speeds of rotation, while the power can be raised at small speeds of rotation. It is another advantage of the invention that, by a modification of the construction ac¬ cording to the invention, power and torque distributions more advantageous in terms of driving than conventional four-wheel drive are obtained for the front and rear wheels of the vehi¬ cle. It is a further advantage of the invention that, with one of its modifications, torque and power are obtained from the power output shaft in a manner in which the speed of rotation of the required drive corresponds well to a thermodynamically advantageous speed of rotation of the engine, whereby a very advantageous fuel economy is achieved.

The invention is described below with reference to the accom¬ panying drawings.

Figure 1 depicts the torque and power curves of one power unit of a combustion engine combination according to the invention. Figure 2 depicts the torque and power curves of a second power unit of the combustion engine combination according to the invention.

Figure 3 depicts the combustion engine combination according t the invention in its theoretically most simple form. Figure 4 depicts diagrammatically another embodiment of the combustion engine combination according to the invention. Figure 5 depicts a third embodiment of the combustion engine combination according to the invention, depicted diagrammati¬ cally in a vehicle.

Figure 6 depicts diagrammatically a fourth embodiment of the combustion engine combination according to the invention. Figure 7 depicts the torque and power curves of the combustion

engine combination according to Figure 3, as well as the fuel consumption curves accomplished with the different embodiment depicted so as to illustrate the principle.

Figure 3 shows the combustion engine combination 3 according t the invention in its most simple embodiment. Therein the com¬ bustion engine combination is made up of a continuous cylinder block 14 in which there are formed two power units 1 and 2, their length proportions in the cylinder block 14 being indi¬ cated by reference numerals LI and L2, respectively. In the first power unit 1 the diameter Dl of the cylinders SI is sub¬ stantially greater than in the second power unit 2, in which the diameter D2 of the cylinders S2 is thus smaller than in th said first power unit. In the embodiment of Figure 3, the num¬ ber n2 of cylinders S2 in the second power unit is double the number nl of cylinders SI in the first power unit, the numbers thus being n2 = 4 and nl = 2. Especially if the cylinder diame ters Dl and D2 have been selected so as to be equal within the first power unit 1 and, respectively, within the second power unit 2 and, respectively, the stroke lengths in both power units have been selected so as to be, for example, equal, in such a manner that the total stroke volumes of the power units 1 and 2 are approximately equal, the torque and power curves according to Figure 1 are arrived at for the first power unit and the torque and power curves according to Figure 2 for the second power unit 2. Thus, in this case the peak Tl of the torque curve of power unit 1 is of the same order of magnitude as the peak T2 of the torque curve of power unit 2 , but with respect to power unit 1 the peak Tl appears at considerably lower speeds of rotation, i.e. at approx. 2000 r/min as com¬ pared to the location of the peak T2 of the torque curve yield ed by power unit 2, which appears at almost 4000 r/min. Respec tively, the peak PI of the power curve of power unit 1 appears at approx. 4000 r/min, whereas the peak P2 of the power curve of power unit 2 appears at approx. 6000 r min, but the values of these powers are of the same order of magnitude. When these

two power units 1 and 2 are closely interconnected by their crankshafts, for example by having a common crankshaft the power of which is taken from shaft 10, the torque curve T and power curve P of the combustion engine combination 3, shown in Figure 7, are arrived at. It can be seen that, in comparison with the torque and power curves of either power unit 1, 2, shown in Figures 1 and 2, relatively more torque is obtained for high speeds of rotation, while power is obtained for lower speeds of rotation, i.e. both the torque and power curves are relatively even within a considerably wide range of speeds of rotation. Torque T is substantially even within a rotation speed range of approx. 1800-6000 r/min, and power is substan¬ tially even within a rotation speed range of approx. 2300- 7000 r/min. It is clear that in aiming at this result it is also possible to use more than two power units and to propor¬ tion in them the cylinder diameters, numbers, stroke lengths and total stroke volumes in various ways to achieve the optimu result. The ratio of the diameters Dl and D2 of the different power units must be at least one and a half, preferably at least two or more.

Figure 4 shows a slightly modified solution, which continues t be made up of two power units 1 and 2 of the described type an in which combustion engine combination 3 power is taken from one power output shaft 10. Therein the crankshafts of power units 1 and 2 are separated either by a lockingly engageable coupling or, alternatively, by a clutch 4 which makes possible a rotation speed difference of varying magnitude between the power units. In this case the combustion engine combination 3 can be driven so that at low speeds of rotation of the shaft 10 only the first power unit 1 is used, and at high speeds of rotation the second power unit 2 is additionally connected, whereupon the units operate in conjunction with each other. In this case it may be advantageous to design the power units so as to have different total stroke volumes, _# for example so that the second power unit 2 has a higher total stroke volume, by

using in it a considerably high number of cylinders and/or a stroke length of a considerable magnitude. The units of the combustion engine combination may be interconnected not only b such a clutch 4, which is preferably a magnetic or viscose clutch, but also by means of a variator, torque converter, differential gear, or the like, in order to obtain the desired torque and power distributions for different rotation speed ranges.

Figure 6 shows a third embodiment according to the invention, wherein power unit 1 is connected via a clutch 14a and a shaft 11 to a gear system 13, and power unit 2 is connected via a clutch 14b and a shaft 12 to the said gear system 13, from which power is taken from a power output shaft 10. In a con¬ struction of this type, the power units can be used, for ex¬ ample, so that, at low speeds of rotation, power unit 1 is connected and power unit 2 disconnected; within the medium rotation speed range, power unit 2 is connected and power unit 1 disconnected; and at high speeds of rotation, both power units 1 and 2 are connected. By a construction of this type, a very effective saving of fuel can also be achieved, as is de¬ scribed below. Depending on the thermodynamic design of the power units 1 and 2 , the gear system 13 can also be construed so that the same speed of rotation of shafts 11 and 12 is cor¬ responded to by different speeds of rotation of the power out¬ put shaft 10. For example, it is conceivable that, if the transmission ratio between shafts 11-10 is 1:1 and the trans¬ mission ratio between shafts 12-10 is 2:1, and with respect to stroke length, number of cylinders and the combustion chamber the power units 1 and 2 are designed in a manner different from that in the solutions described above, a most preferred operat¬ ing method is achieved, in which at low speeds of rotation the second power unit 2 is used, and at medium speeds of rotation the first power unit 1 is used, and at high speeds of rotation both power units are used. It is clear that the transmission ratios in the gear system 13 may vary considerably depending on

the targeted use, as may the number of power units and the rest of the construction. The clutches 14a and 14b may also vary in their type considerably, as described above with respect to clutch 4.

Figure 5 depicts the principle of one specific application of the combustion engine combination according to the invention, wherein the power units 1 and 2 of the combustion engine com¬ bination 3 both have separate power output shafts 6 and 7. The first power unit 1 has been arranged to drive with its power output shaft set 7 the rear wheels 9 of the vehicle, and the second power unit 2 has been arranged to drive with its power output shaft set 6 the front wheels 8 of the vehicle. Thus there is achieved, for example, an automobile four-wheel drive in which, during acceleration, torque is obtained at the most efficient point, i.e. in the rear wheels 9, and, during con¬ stant drive, at the most expedient point, i.e. in the front wheels 8. The power units 1 and 2 may be almost independent of each other, in which case they are maintained in synchroniza¬ tion by measuring, for example, the speeds of rotation of their crankshafts and by regulating the feeding in of fuel in a man¬ ner known per se. However, the power units can also be inter¬ connected by an intermediate shaft 5, which may be connected directly or via some non-depicted gear system or via a locking- ly engageable coupling or via a clutch which permits a rotation speed difference of variable magnitude or via a corresponding structure to either power unit 1 or 2, as described above in connection with Figures 4 and 6.

Figure 7 shows diagrammatically the fuel consumption of combus¬ tion engine combinations according to the invention when the targeted use is a vehicle, curve K in the figure depicting the driving speed of the vehicle and thereby the torque used as a function of the speed of rotation. If the transmission ratio of the gear system in Figure 6 is in the order of 1:1:1 with re¬ spect to shafts 11-10-12, and the power units 1 and 2 are ap-

proximately of the type depicted in Figures 1-3, the followin characteristics are arrived at. In the curve sets, the consum tion of fuel increases in the order A1-A2-A3-A4, B1-B2-B3, Cl C2-C3-C4-C5, the values being not absolute but theoretical an proportional. When in the construction of Figure 6 the first power unit 1 is used at low speeds of rotation, its peak torq is reached at even a relatively low velocity, which at the sa time means a low consumption of fuel within the range Al. Whe the second power unit 2 is used within the medium rotation speed range, its peak torque range is reached, which means a relatively low consumption of fuel within the range Bl. When thereafter both power units are used at high speeds of rota¬ tion, the range of the peak torque of the combined structure, where there would be the lowest fuel consumption Cl, is indeed not reached, but nevertheless a moderate fuel consumption rang C3, in which case the total consumption will remain very low i varying conditions of use.

Here it can also be noted that the set of fuel consumption curves C1-C5 corresponds to the fuel consumption of the fixed combustion engine combination of Figure 3, the torque curve of _the combination being also shown in Figure 7 and its peak T3 thus corresponding to the fuel consumption minimum Cl. In this set of curves, the ranges (C1-C5) always corresponding to the same consumption are, starting from the minimum consumption Cl considerably wider, corresponding to a gently sloping torque curve T, than the situation would be in an engine equipped wit cylinders of only one size. Even a fixed combustion engine combination will thus result in lower than conventional fuel consumption under varying conditions of use. In other words, a combustion engine combination according to the invention will always lead to lower consumption of fuel, regardless of whethe it is used as a fixed entity (consumption curves C) or one power unit at a time (consumption curves A, B, C) than do con¬ ventional combustion engines. It is clear that, depending on the conditions of use, the cylinder diameters, numbers of cyl-

inders, stroke lengths, total stroke volumes in the different power units, as well as the order of use, can be designed to suit different conditions of use within the scope of the inven¬ tion.