Isobaric piston internal combustion engine

Abstract

FIELD: engines.SUBSTANCE: invention can be used in the design of engines for small aircraft, as well as for land and water vehicles and mobile power plants. An isobaric piston internal combustion engine comprises a cylinder (1), in the upper cover (2) of which a bypass valve is located and a glow plug placed in a pipe connecting the bypass valve with the cavity of the cylinder (1). The engine comprises a lower cylinder cover and a piston with a rod (10) extended through the lower cover seal to a crosshead mechanism connected to a mechanism for converting the reciprocating movements of the rod into continuous rotation of the power take-off shaft (8). The lower cylinder cover (1) comprises an automatic inlet valve, as well as an automatic discharge valve connected to the receiver, which, in turn, is connected to the bypass valve. The engine comprises eight cylinders (1), the sub-piston spaces of which communicate with a common receiver. The common receiver, in turn, is connected to all working cylinders (1). Eight cylinders (1) are arranged in a star-shaped manner around a common flat cam mechanism for converting the reciprocating movements of the rods (10) into the rotational movement of the power take-off shaft (8). The cam profile (21) is made single-period.EFFECT: reducing the specific weight of the engine.2 cl, 4 dwg

Description

[0001] The invention relates to the design of piston internal combustion engines (ICE) and can be used in small aircraft, in particular in unmanned aircraft, as well as in power plants of land and floating vehicles, in particular in hybrid power plants of cars.

[0002] REVIEW OF THE LEVEL OF TECHNOLOGY

[0003] Piston internal combustion engines remain relevant in the power range of less than a few hundred kilowatts, where gas turbine engines face the problem of excessively small flow path cross-sections, which, in addition to their non-compact, slot-like shape, are subject to boundary effects in the gas environment. Internal combustion engine design is determined by the choice of thermodynamic cycle, as well as the type of mechanisms implementing individual cycle operations, and the optimal structural design.

[0004] The main components of a piston engine are the expansion mechanism, combustion chamber, and piston motion conversion mechanism. The most common piston engines feature an expansion mechanism in the form of a round cylinder with a piston performing a rectilinear reciprocating motion. The piston motion conversion mechanism converts the piston's reciprocating motion into continuous rotary motion of the power take-off shaft. The wide variety of piston engine mechanisms available is achieved by combining various cylinder arrangements and their combinations with various types of motion conversion mechanisms.

[0005] A comparative analysis of the efficiency of various operating processes in heat engines from a thermodynamic perspective has been well studied and described. Of particular interest for lightweight power plants is, for example, the isochoric cycle, i.e., a cycle with combustion of a gaseous combustible mixture at a constant volume. Depending on the difference between the ambient atmospheric pressure and the pressure at the moment of ignition, the isochoric cycle can be implemented either with preliminary compression (Otto cycle) or without preliminary compression (Lenoir cycle) (see, for example, the book: A. Morawski and M. Fain, "Fire in Harness." Moscow, "Znanie," 1990). The Diesel cycle differs from the Otto cycle in that air is mixed with fuel after compression and autoignition occurs. Isochoric cycles in most cases are produced with ignition of the combustible mixture concentrated in a small part of the combustion chamber volume, followed by spontaneous propagation of the combustion front throughout the entire combustion chamber.

[0006] The fundamental drawback of this process is the excitation of rapid gas-dynamic oscillations within the chamber, caused by the rapid additional adiabatic compression of the combustible mixture in parts of the combustion chamber volume remote from the ignition point. As a result of this additional compression of the combustible mixture in areas remote from the spark plug, their temperature rises to a limit at which further combustion occurs due to the propagation of an acoustic wave at the speed of sound. The resulting transient pressure field in the combustion chamber emits powerful acoustic oscillations that are repeatedly reflected off the combustion chamber walls and excite elastic oscillations in them, audible as a ringing or knocking sound. These are known as detonation oscillations. This increases the intensity of heat transfer to the combustion chamber walls, and the overall gas heating process becomes highly dissipative.

[0007] A more advanced method is heating the compressed combustible mixture at constant pressure, also known as isobaric heating. This occurs in open (flow-through) combustion chambers, such as gas turbine engines, where detonation combustion does not occur, making it possible to use cheaper fuels.

[0008] A method for implementing an isobaric combustion process in piston engines is proposed in Russian Patent No. 2746820, priority dated November 19, 2018 (author and patent holder A.A. Gorshkov). This method involves compressing air or a combustible mixture in a separate compressor and storing it in a receiver. Ignition occurs during the intake of the combustible mixture into the cylinder using a glow plug installed in the intake manifold of the working cylinder.

[0009] The ignition principle is explained with the help of Fig. 4 of the present application, which is not used in the main part of the description, therefore the designations in Fig. 4 are made with the index 0. Fig. 4 shows the inlet pipe 1.0 with the glow plug 2.0. The pipe continuously passes on the left into the compressor cylinder with the piston 3.0, and on the right into the expansion cylinder (expander) with the piston 4.0. The pistons are rigidly connected to each other in terms of movement. The compressor cylinder communicates with the receiver 5.0 serving to stabilize the pressure during the movements of the said pistons. Moreover, the compressor and receiver are separated from the glow plug 2.0 by a controlled bypass valve 6.0. During the movement of the pistons to the right. The combustible mixture, supplied by the compressor piston 3.0 and accumulated in the receiver 5.0, shifts to the right and passes at a small distance from the heated glow plug 2.0.As a result, fully burnt combustion products with a flame temperature of approximately 2,500 degrees Kelvin or higher emerge from the glow plug area on the right side. This means that the glow plug transforms the flow of the combustible mixture into a flow of hot combustion products without changing the flow direction. Only the flow velocity changes abruptly. The intake process resembles the operation of a gas burner. The pressure increases very slowly, as it is stabilized by a large-volume receiver 5.0. (The temperature of the combustible mixture to the left of the glow plug (500 degrees Kelvin) is acquired during the preliminary adiabatic compression of the combustible mixture (or atmospheric air) in the compressor.) Thus, combustion does not occur in the working (expander) cylinder. Backpropagation of the flame is prevented by the high flow velocity in the glow plug area or bypass valve 6, which will not allow combustion due to the high velocity of the combustible mixture in its gap.In the starting mode, when the pressure of the combustible mixture is not yet high, flame penetration into the receiver can be prevented using a 7.0 copper flame barrier mesh.

[0010] The advantages of the isobaric cycle of a piston internal combustion engine over isochoric cycles are:

[0011] a) - absence of the above-mentioned detonation during combustion;

[0012] b) - ensuring the possibility of using low-octane fuels;

[0013] c) - the possibility of using fuels with low volatility, since the combustible mixture is prepared outside the cylinder, and it is not necessary to use very fine atomization, since the adiabatic compression temperature in the compressor is high enough to ensure the evaporation of fuels such as kerosene.;

[0014] g) - a reduction in the specific mass of the engine structure, which is due to the absence in this cycle of a sharp peak in pressure on the piston, which also occurs when the piston is in the TDC position and therefore does not increase useful work;

[0015] d) - the exhaust pressure of combustion products is reduced (similar to the gas turbine cycle), which reduces exhaust noise and, in many cases, eliminates the need for a muffler;

[0016] e) - due to the reduction of the peak temperature, the toxicity of the exhaust is reduced, in particular, the content of nitrogen oxides in the combustion products is reduced, as well as the content of thermal dissociation products of the combustible mixture, which enter the exhaust as a result of the so-called hardening of thermal dissociation products caused by the rapid expansion of gases in the cylinder;

[0017] g) - restrictions on increasing the engine speed are removed under the condition of ensuring complete combustion (The latter is due to the fact that the ignition of the combustible mixture occurs during the process of its intake into the cylinder, in which the expansion of the already prepared combustion products occurs and, thus, the process of propagation of the combustion front in the cylinder cavity is eliminated.

[0018] i) - ignition is carried out by a glow plug, which eliminates the need for a magneto or coil, which have a rather large mass, unacceptable for low-power power plants, such as for personal mobility vehicles or small unmanned aerial vehicles.

[0019] Due to the above-mentioned advantages of the isobaric working process of the internal combustion engine compared to the isochoric one, the following review of the designs of mechanisms used to implement thermodynamic cycles will be carried out from the point of view of the optimality of their use for implementing the above-mentioned isobaric cycle of operation of a piston internal combustion engine.

[0020] The primary mechanism for executing the internal combustion engine's working cycle is the so-called expansion mechanism. In Otto cycle engines, it also serves to compress the working fluid. However, implementing an isobaric cycle requires separating the compression and expansion processes. Therefore, engines with an isobaric cycle are classified as having a so-called split cycle (see, for example, Russian patent No. 2425992, which describes an engine operating on a split cycle. In this case, compression and expansion occur in separate cylinders, although thermodynamically, patent No. 2425992 implements a conventional isochoric Otto cycle).

[0021] The most common expansion mechanism in piston-driven internal combustion engines is a cylinder-piston expansion mechanism. However, the mechanical work performed in it is performed in the form of reciprocating motion, while the consumer most often requires rotary motion at the output. Therefore, the use of a cylinder-piston expansion mechanism requires a mechanism to convert the piston's reciprocating motion into continuous rotary motion of the power take-off shaft.

[0022] Numerous attempts have been made to create expansion mechanisms that produce a direct rotary motion at the output. Such engines are called rotary piston engines. The most well-known engine of this type is the Wankel rotary piston engine. However, in all the numerous known variants of the rotary piston engine, the rotary motion at the output is achieved at the expense of a significant reduction in the functional and consumer qualities of the expansion mechanism (seal quality, wear, heat transfer to the walls, poor design, etc.). Therefore, the classic cylinder with a piston remains the preferred choice in internal combustion engines, including for creating an efficient isobaric ICE design. Next, we will examine existing mechanisms for converting the reciprocating motion of the piston into continuous rotation of the power take-off shaft.

[0023] The crank mechanism for converting piston motion (hereinafter referred to as the CRM) is the most widely used mechanism in piston engine construction. The successful adoption of piston engines in industry and transportation is largely due to the use of the CRM. The CRM is simple, compact, reliable, and allows for acceptable balancing in practice. The main complaints arise from the lateral pressure of the trunk (crosshead) piston on the cylinder bore, resulting in friction and wear due to the inability to ensure adequate lubrication of the cylinder and piston.

[0024] However, a crosshead mechanism, while eliminating this drawback, significantly increases the mechanism's dimensions per unit of piston stroke. In a trunk-type (crossheadless) engine, compactness is achieved by allowing a significant portion of the connecting rod length to enter the cylinder cavity. However, this eliminates the possibility of using the sub-piston space. For example, the sub-piston space could be used to create a double-acting cylinder, which would double the power. A second possible use for the sub-piston space is to implement preliminary compression, as is done in split-cycle engines, and in particular in an isobaric engine. Other options for using the sub-piston space include: - as a scavenging compressor or for supercharging. A crosshead crank mechanism is particularly poorly suited for a radial cylinder arrangement.

[0025] Another disadvantage of the crank mechanism, which causes many problems in the development and operation of the internal combustion engine, is the presence of a heavily loaded bearing on the crank, in particular the problem of ensuring reliable lubrication of this bearing.

[0026] To build a split-cycle engine, particularly an isobaric one, it is also advisable to use the sub-piston space of the working cylinder so as not to double the number of required cylinders.

[0027] There are various options for connecting rod-less and crankless mechanisms that serve as an alternative to the crank mechanism.

[0028] A well-known and striking example of a connecting rod-less engine is the Balandin engine (see, for example, the book: S.S. Balandin "Connecting Rodless Internal Combustion Engines" Moscow, Mashinostroenie, 1972). The operating principle of the Balandin mechanism can be most simply explained as follows.

[0029] If two piston rods are mounted in guides for translational motion, perpendicular to each other (crossing each other) and connected to each other by a rod hinged to the piston rods, the resulting system will have a single degree of freedom: the piston rods can only perform coordinated, straight-line movements within their guides, within a range limited by the length of the rod. Moreover, the midpoint of this rod will move precisely in a circle. This occurs because this rod sums the sinusoidal movements of the two mutually perpendicular piston rods with an equal coefficient. If a power take-off crank, also moving in a circle, is attached to this midpoint, we obtain a mechanism that converts the shaft rotation into sinusoidal movements of these piston rods, with a 90-degree phase shift.By using this mechanism in reverse mode, we obtain a mechanism for converting sinusoidal two-phase movements of the pistons into continuous rotation of the shaft at a constant speed.

[0030] Strictly speaking, the Balandin mechanism cannot be called connecting rodless, as the connecting rod (which in real designs resembles a crankshaft) essentially functions as a generalization of the connecting rods of two pairs of pistons into a single connecting rod. This would be achieved by shortening the connecting rods of a conventional star-shaped internal combustion engine as much as possible. Thus, in the Balandin mechanism, one generalized connecting rod can serve four pistons, connecting them to a common crank. However, it would be more correct to call this mechanism a linkage mechanism, as the piston rods, mounted in guides for translational movement, are analogous to the sliders of a linkage mechanism.

[0031] However, virtually all mechanisms contain errors due to manufacturing inaccuracies or thermal deformations. The practical operability of mechanisms in most cases is largely ensured by their ability to adapt to these inaccuracies and deformations through the presence of kinematic degrees of freedom. A mechanism lacking the kinematic freedom to adapt to dimensional inaccuracies in its components is called a mechanism with redundant constraints, or (in calculations of the acting forces) statically indeterminate. An example is a mechanism in the form of a rigid beam supported on three collinear support points. The Balandin engine mechanism has several redundant kinematic constraints, necessitated by the need to rigidly connect three mechanisms, each of which individually represents a mechanism with a single degree of freedom.Such mechanisms include two piston rods located in guides for linear motion, as well as a crank, which also has a single degree of freedom—circular motion. Rigidly connecting them, even through one degree of freedom, is tantamount to introducing redundant coupling, creating static uncertainty of forces or blocking the mechanism's mobility. Thus, if the crank attachment point is offset even slightly from the center of the rod connecting the piston rods, the summation coefficients of the two sines of the piston stroke will be unequal, resulting in an ellipse. The same result occurs if the relative angle of the piston rod axes is slightly off 90 degrees.

[0032] There are attempts to eliminate the aforementioned shortcomings of the Balandin engine mechanism. For example, in the Vul connecting rod engine (see, for example: "The Vul connecting rod engine. An alternative history."<dzen.ru / a / XEYJ4vCTgQCt_z47> January 21, 2019), where the pistons are located at only one end of the piston rods. However, the redundancy of the connections has not been completely eliminated, so manufacturing precision remains highly critical.

[0033] The redundancy of kinematic connections is absent in connecting rod-less mechanisms for converting the reciprocating motion of the piston into continuous rotational motion of the power take-off shaft, made in the form of cam mechanisms used in reverse mode, i.e. when the oscillatory motion of the pusher interacting with the cam profile is converted into unidirectional rotation of the shaft, the cam, performing the function of the power take-off shaft. Such connecting rod-less mechanisms, which are also crankless, are described, for example, in Russian patents No. 2089733, 2296871, 2476700, 2480648, 2528486. The listed patents propose cam mechanisms characterized by the fact that the piston rod, usually having a roller at the end, moves parallel to the axis of rotation of the power take-off shaft, on which a cam is rigidly fixed, having a periodic, in particular sinusoidal, profile.The cam profile span and the number of periods contained within its circumference determine the shaft speed reduction ratio relative to the piston's double stroke frequency. Several working cylinders with mutually parallel axes can be positioned circumferentially around the shaft. Kinematic locking of the mechanism is achieved by the presence of a pair of rollers on each piston rod, rolling on opposite sides of the cam with mutually negative profiles. Opposite cylinder arrangements are also possible, achieving self-balancing of the translational masses.

[0034] The fundamental disadvantages of such a mechanism for converting piston movements into shaft rotation in an internal combustion engine are:

[0035] a) - the impossibility of eliminating roller slippage along the cam due to the roller axis moving in a straight line, while the points on the cam's working surface, along which the piston roller rolls, are located on a sphere. To reduce roller slippage along the raceway, it is necessary to limit the piston stroke or increase the cam's circumference, which increases the dimensions and weight of the mechanism and the entire engine;

[0036] b) - the long power take-off shaft is required when using an opposed cylinder arrangement. If the engine is balanced by positioning all cylinders on the same side of the camshaft rotation plane, two negative-positive camshaft profile pairs are required, which complicates the design and increases the dimensions and weight;

[0037] c) - the large mass of the axial action cam structure, due to its cantilever bending load;

[0038] г) - the complexity of the shape of a non-flat cam with the need, at the same time, to maintain high accuracy of matching the positive profile with the negative one.

[0039] The most suitable design for the proposed isobaric engine is a flat cam mechanism, in which the piston rods are aligned with the camshaft in a star-shaped pattern. The piston rods track the camshaft profile via power rollers located at their ends. The cam is secured to the power take-off shaft, and the ends of the power roller axes are equipped with guide rollers capable of rolling along radially oriented, rectilinear guides that form a crosshead mechanism (see, for example, the publication:<dzen.ru / a / Y110gjIlrBZYjfle> Binimot, October 21, 2022. "Connecting Rod Engines. Past and Future." Fig.: Schematic diagram of a connecting rod mechanism. Image: Youtube.com. This publication shows a variant of the mechanism with a cam profile consisting of three periods arranged circumferentially.

[0040] The advantages of a flat cam mechanism for converting piston motion, compared to the above examples of engines with spatial cam mechanisms for converting motion, are:

[0041] a) - absence of roller slippage when it rolls along the cam profile at any profile swing, which allows increasing the piston stroke to a value close to half the overall diameter of the crankcase;

[0042] b) - reduction of the length of the power take-off shaft regardless of the configuration of the placement of multiple cylinders around a common cam;

[0043] c) - increasing the strength of the mechanism per unit of material consumption due to the absence of cam bending.

[0044] Thus, the well-known flat cam mechanism is free from the above-mentioned disadvantages inherent in the crank mechanism, as well as Balandin crankless mechanisms and spatial cam mechanisms.

[0045] The only known design of an isobaric piston internal combustion engine is the one described in the aforementioned Russian Federation Patent No. 2746820 for the method. Therefore, it should be considered a prototype for an engine design operating on an isobaric cycle. A key necessary feature of this known design is the use of a sub-piston space for compressing the working fluid, as well as the resulting requirement for a crosshead mechanism, the use of which, according to current practice, is considered incompatible with the design of lightweight internal combustion engines for transport applications.

[0046] A disadvantage of the single-cylinder isobaric engine design described in patent No. 2746820, when considered as a prototype, is the increased specific gravity of the engine structure, which is due to the presence of a receiver for pre-compressed combustible mixture, the volume of which must be many times greater than the volume of the combustible mixture inlet into the cylinder (the so-called intake cutoff volume). In addition, the engine necessarily uses a crosshead crank mechanism. Therefore, the dimensions and specific gravity of the design increase due to the fact that the crank mechanism connecting rod, which is a long component, often exceeding the height of the cylinder, cannot be retracted into the cylinder cavity, as is done in engines with a trunk-type crank mechanism design, since the sub-piston cavity in the isobaric ICE under consideration is closed by a cover and is used for preliminary compression. Another disadvantage of the prototype is the unresolved problem of lubrication of the cylinder bore, sincethe inner surface of the cylinder is closed on all sides, and the supply of oil by injection into the cylinder cavity will cause oil consumption due to its entrainment by air passing through the sub-piston cavity.

[0047] SUMMARY OF THE INVENTION

[0048] The purpose of the proposed invention is to improve the weight and size characteristics of the design of an isobaric piston internal combustion engine and to solve the problem of providing economical lubrication in the presence of a lower cylinder cover.

[0049] The proposed isobaric piston internal combustion engine comprises a cylinder with a bypass valve located in the top cover and a glow plug located in a pipe connecting the bypass valve to the cylinder cavity. It also has a lower cylinder cover and a piston with a piston rod extending through the lower cover seal to a crosshead mechanism connected to a mechanism converting the reciprocating motion of the piston rod into continuous rotation of the power take-off shaft. The lower cylinder cover contains an automatic inlet valve vented to the atmosphere, as well as an automatic discharge valve connected to a receiver, which in turn is connected to the aforementioned bypass valve.

[0050] The objective of the invention is achieved by the engine comprising the eight aforementioned cylinders, the sub-piston spaces of which communicate with a common receiver, which, in turn, is connected to all working cylinders. Moreover, these eight cylinders are arranged in a star-shaped pattern around a common flat cam mechanism that converts the reciprocating motion of the piston rods into rotary motion of the power take-off shaft. The cam profile is single-period.

[0051] The specific mass of the engine structure is reduced primarily due to the fact that the mass of the cam mechanism structure is distributed across multiple cylinders, whose volumes, which determine power, are summed, and therefore the power is summed. Meanwhile, the mass of the cam mechanism, due to the fact that the star cylinders load it alternately, remains virtually unchanged. It should also be noted that the total mass of the cylinders is virtually independent of the distribution of the total volume among individual cylinders. In other words, increasing the number of cylinders in a star configuration, while maintaining their total volume, leads to a reduction in piston area and, consequently, a reduction in the force load on the cam mechanism, which leads to a proportional reduction in the relative mass of the cam mechanism structure within the engine.

[0052] Secondly, due to the distribution of the total cylinder volume across many small-volume cylinders, the required volume of the receiver is reduced, and consequently the intake cutoff volume, which also reduces the weight of the receiver as part of the engine design.

[0053] The specified number of cylinders, equal to eight, additionally minimizes the specific weight of the engine design in comparison with engine variants with a different number of cylinders, since, if we maintain complete filling of the available outer circumference of the crankcase with cylinders (which, in turn, is also required by the condition of minimizing the specific weight of the engine), then with a number of cylinders less than eight, namely six or four (for the kinematic closure of the cam mechanism, only an even number of cylinders is suitable), the cylinders will be obtained with a small, non-optimal ratio of diameter to height, since with a decrease in the number of cylinders, the maximum possible value of the piston stroke, set by the cam mechanism, which can be placed in a too tight crankcase, fitting in a hexagonal or quadrangular space under the cylinders, decreases.If we take the nearest even number of cylinders, equal to ten, then, in addition to increasing the design complexity, we obtain a smaller total volume of the cylinders located on the circumference of the same crankcase, since the total crankcase volume is determined by the product of the total crankcase circumference, the cylinder height, and the thickness of the annular space occupied by the cylinders in the star. And the thickness of the annular space occupied by the cylinders, equal to the cylinder diameter, is less for ten cylinders than for eight.

[0054] The need for a single-period cam is driven, firstly, by the fact that with an increase in the number of periods, the maximum possible piston stroke is proportionally reduced, limited by the increasing profile steepness. Secondly, it complicates the engine's balancing mechanism, which, in the case of a single-period cam, is solved by using a rotating counterweight, which is the simplest solution. Moreover, in low-power gearless aircraft engines, approximately half the mass of the rotating counterweight can be replaced by a significantly smaller balancing mass mounted at the tip of the propeller blade.

[0055] In a particular embodiment of the proposed engine, lubrication of the cylinder bore and piston rings is accomplished by a plurality of elastic, oil-impregnated printing elements arranged in a circle on the inner surface of the lower cylinder cover so that the printing elements touch the underside of the piston when it is at bottom dead center. The oil contained within them is transferred to the piston surface similar to the printing process, i.e., without the formation of droplets or being carried away by air currents passing through the sub-piston cavity. The oil then spreads across the piston surface through wetting forces, particularly reaching the lower piston ring, thereby lubricating the cylinder.Moreover, due to the absence of lateral piston pressure on the cylinder in this engine design, as well as due to the gas pressure on the rings being many times lower than in isochoric engines, and also due to the absence of piston repositioning, a small influx of oil is sufficient to replenish the capillary layer on the surface of the lubricated parts of the piston and cylinder.

[0056] In a specific embodiment, oil is replenished in the printing elements from a common reservoir for all cylinder elements through check valves, as well as through small orifices—throttles that regulate the oil flow. This ensures equal oil flow across all printing elements, regardless of the engine's orientation. Oil is pumped into the printing element during the vacuum phase in the sub-piston cavity, i.e., when air is drawn into the cylinder from the atmosphere. Therefore, a low oil supply pressure is sufficient. An oil reservoir with pressurization from the engine's fuel system receiver can serve as the oil source. Periodic or, even more so, episodic (i.e., with long breaks) oil supply to the printing elements from a point is also possible using a pulse electric pump.

[0057] The invention is explained by the following detailed description of examples of implementation and three figures.

[0058] DETAILED DESCRIPTION

[0059] Fig. 1 schematically depicts the general appearance of the proposed isobaric engine. The crankcase is shown with the side wall removed. R denotes the radius of the circle that forms, in this embodiment, the cam profile over a 180-degree section from point "a" to point "b." The line with two dots is an extension of this circle, allowing one to see the difference in the cam profile on the other half of the profile, which is the closing half. The profile on the second half of the circle must ensure precise, play-free and stick-free, so-called kinematic closure of the cam mechanism without the use of springs (similar to springless valve timing mechanisms, also called desmodromic). The axes of the opposing power rollers are rigidly connected to each other by strips with a window serving to pass the power take-off shaft. Only one of the four strips located on the visible side is shown in full. The remaining strips are shown cropped.

[0060] Fig. 2 shows (enlarged) a section of the proposed engine by a plane passing through the axis of the power take-off shaft and through the axis of one of the opposite pairs of cylinders.

[0061] Fig. 3 shows the PV diagram of the working cycle of the proposed piston internal combustion engine. The vertical axis represents the pressure in absolute atmospheres [ata], and the horizontal axis represents the volume of the air portion or its combustion products, which is of little importance in the approximate consideration. This volume is expressed in cubic centimeters [cm 3 ]. Moreover, the portion of gas at point A has a pressure of 1 atm and a volume of 1 cm 3 , which means that the cycle shown in Fig. 3 is performed over a portion of air of 1 cm 3 , taken initially from the atmosphere above sea level, i.e. at a pressure of 1 atmosphere.

[0062] The proposed engine contains eight cylinders 1 arranged in a star-shaped manner. All cylinders have the same design. In the upper cover 2 of each cylinder, there is a bypass valve 3 driven by a conical cam 4. A glow plug 5 is installed in the pipe under the valve 3. There is also an exhaust valve 6 driven by a cam 7. Cams 4 and 7 are fixed on a power take-off shaft 8. A piston 9 is located in the cylinder, which has a lens-shaped shape and is fixed on a piston rod 10. Heat is removed from the piston by means of a liquid or low-melting metal located in the piston cavity, transferring heat to the periphery of the piston to a ring 11, through which the heat is transferred to a thin-walled cylinder liner 12 equipped with a liquid cooling jacket 13, which also extends to the upper cover 2 of the cylinder.The sleeve shells 12 and liner 13 are welded and form a single piece with the cylinder top cover, which is made from stamped parts. The parts are joined by flanging, contact welding, or brazing. The lower edge of the cylinder is equipped with a flange (not shown), which is used to secure the lower cover 14 to the cylinder with screws and a gasket, and the cylinder itself is secured to the crankcase.

[0063] Piston 10 passes through a sealed hole in the lower cylinder cover 14. At the end of the rod, there is a fork 15 with an axis 16, on which a power roller 17 is mounted for rotation. In this particular case, the power roller may be made of textolite and rotate on a plain bearing lubricated by oil mist in the crankcase. Crosshead rollers 18 are mounted at the ends of axis 16, interacting with rectilinear guides 19 of the crosshead mechanism, secured to the side walls 20 of the crankcase.

[0064] Power rollers 17 interact with the profile of the power cam 21. Moreover, the axes of all oppositely located rods are rigidly connected to each other by strips 22, equipped with a window 23, which serves to pass the shaft 8.

[0065] The profile of the power cam 21 is single-period. In a particular embodiment, the profile has the shape of an eccentric circle of radius R, extending 180 degrees from the maximum point "a" to the minimum point "b" of the cam profile (see Fig. 1). Smooth closure of the profile along the other half of the cam must satisfy the condition of continuous contact of both opposite rollers with the cam profile. This condition can be called the condition of equidiametrical cam profile. It corresponds to the possibility of free rotation of the power take-off shaft 8 without the occurrence of a gap with the cam profile of both rollers of the opposite pair, and also without jamming. This is ensured by constructing a closing profile as a curve having the form of a tangent to the family of positions of the circles of one power roller, obtained by rolling the opposite power roller along the original profile from point “a” to point “b” (in a particular case, along the eccentric circle of radix R).This construction method can be understood using Fig. 1, where five power rollers, located to the left of the vertical axis, are tangent to the initial eccentric circle of radius R, while the rollers opposite them are located at equal distances from their pair, defined by bars 22. All bars 22 have the same length, determined by the distance between the axes of the power rollers when they are located at points "a" and "b." In Fig. 1, we thus obtain only three positions of the opposite roller, from which it is impossible to uniquely determine the tangent curve. By repeating a similar construction for a larger set of intermediate positions of the opposite roller, for the intermediate positions of the initial rollers, we can obtain a sufficiently dense family of roller circumference positions, defining the tangent curve with sufficient unambiguity for practice.

[0066] A technological solution to this problem is to mill the cam profile on a CNC machine using a program based on the algorithm described above. Another option is milling using the original profile (specifically, a round eccentric) as a jig. In this case, the milling cutter must have a diameter equal to the diameter of the power roller.

[0067] The profile of the initial half-circle of the power cam can be non-circular. However, it must ensure the minimum possible piston acceleration range, which determines the maximum permissible shaft speed of 8 revolutions per second.

[0068] The lower cover of cylinder 14 has automatic valves: suction valve 24, which communicates with the atmosphere, and discharge valve 25, which communicates with receiver 26, which is common to all cylinders and has the shape of an annular (toroidal) manifold. Pipes 27 connect receiver 26 to bypass valves 3 of each cylinder.

[0069] The engine is balanced using two counterweights 28, fixed on the power take-off shaft 8 and sweeping the free space under the cylinders within the crankcase diameter and within the cylinder diameter.

[0070] The combustible mixture can be prepared by pumping fuel (gasoline, kerosene, propane, etc.) into receiver 26 using a controlled pump (not shown). Fine atomization is not required, as the temperature in the receiver, at a compression ratio of 5, approaches 200 degrees Celsius. The volume of receiver 26 should be several times greater than the intake cutoff volume, so that the pressure drop during intake is minimal (e.g., no more than 20%). However, if the volume is too large, volatile fuels cannot be used, as they will partially oxidize in the receiver.

[0071] The bearings of the 17 power rollers can be lubricated by spraying oil into the crankcase using a special nozzle with a pump that draws oil from the drain system at the lowest points in the crankcase. The uniformity of lubricant distribution across the sprocket cylinders will be significantly improved by positioning the PTO shaft vertically. This is especially useful in vehicles with hybrid powertrains, where a horizontally positioned, virtually flat sprocket can be located under the hood or trunk floor.

[0072] Cylinder lubrication is more problematic because the sub-piston cavity does not directly communicate with the crankcase, which in conventional engines serves as the source of oil for the cylinder surface. In the proposed engine, cylinder lubrication can be achieved using elastic porous printing elements 29, into which oil is continuously or periodically supplied at a specified frequency from oil sources 30. These can be pieces of open-pore rubber made of a heat-resistant elastomer. Printing elements 29 are uniformly distributed around the circumference of the inner surface of the lower cylinder cover 14 and come into contact with the lower surface of the piston when it is at the bottom dead center. The points of contact are shown by lines "k" with arrows in Fig. 2. Printing element 29 operates similarly to printed type - on the principle of contact transfer of liquid using wetting forces and without the formation of droplets.Upon reaching the lower surface of the piston, the oil, having high wettability of the metal surface, spreads, in particular, toward the piston ring, from which the oil is transferred to the cylinder bore. This prevents oil from being carried away by air currents in the sub-piston cavity. Printing lubricating elements 29 are supplied with oil from a centralized low-pressure source 30 through ball check valves (not shown). The oil is metered by a nozzle with a small orifice incorporated into the design of each printing element 29. This ensures uniform distribution of the oil flow across the entire piston circumference, regardless of the engine's orientation relative to gravity. The oil source can be a common oil tank for all engine cylinders, connected to receiver 26, the pressure of which is used for boost. However, a dedicated oil pump, such as a pulse electric pump with a low pulse rate, can also be used.

[0073] ENGINE FUNCTIONING

[0074] When the power take-off shaft 8 rotates, each of the pistons 9, which, via a pair of power rollers 17, has a two-way interaction with the rotating power cam 21, performs reciprocating movements according to a law determined by the cam profile. The cam profile is selected based on the condition of minimizing piston acceleration for a given value of the working stroke. Strictly speaking, such a law is uniformly accelerated motion alternating with uniformly decelerated motion. However, this will cause impacts on the derivative of acceleration, leading to abrupt changes in the sign of the stresses in the piston rod and pistons, so it is better to choose a harmonic, close to sinusoidal, law of piston motion, in which the acceleration will differ from the variant with uniformly accelerated motion by only π / (2×2 1 / 2)=1.1, i.e., insignificantly. The cam profile illustrated in Fig. 1, designed in the form of an eccentric circle, is close to sinusoidal. The law of piston motion during the return stroke differs from the power stroke, as is evident from the divergence of the closing part of the cam profile relative to the eccentric circle, shown in Fig. 1 by a dashed line with two dots. However, the difference is insignificant.

[0075] At its highest position, piston 9 approaches the upper cover 2 as close as possible. At this point, bypass valve 3 opens, through which, as the piston moves downward, the combustible mixture enters from receiver 26. Passing by the glow plug located in the pipe beneath valve 3, the combustible mixture flow is transformed into a stream of hot combustion products, which fill the space above the piston. At a certain stage of piston 9's descent, determined by the shape of conical cam 4, bypass valve 3 closes with the assistance of the engine's thrust control system. This is called intake shutoff, as in a steam engine. From this point on, the combustion products begin to expand. Simultaneously, the air entering the sub-piston space through automatic suction valve 24 is compressed.As piston 9 approaches lower cover 14, when the air compression pressure exceeds the pressure in receiver 26, automatic delivery valve 25 opens. This replaces the air lost during the aforementioned bypass into the above-piston space. The average pressure in receiver 26 is determined by achieving a balance in the air flow through the receiver. Since the upper and lower volumes swept by the piston are equal, while the volume of air consumed from the receiver expands many times during combustion, equality of air flow is achieved by increasing the pressure in the receiver. Due to the slight shortfall between piston 9 and lower cover 1, i.e., the presence of the so-called "dead" space, the volume of air pumped into the receiver decreases as the pressure increases. Thus, at a certain pressure, no air will be forced into the receiver at all. All of it will remain in the dead space beneath the piston.Thus, by designing the volume of the dead space under the piston, one can set the steady-state operating pressure in the receiver corresponding to the optimal thermodynamic cycle at rated power. By adjusting the dead space using an attached controlled volume chamber (not shown), one can control the maximum operating cycle pressure.

[0076] When the piston moves upward, the exhaust valve 6 opens and the process of releasing combustion products occurs while simultaneously sucking air into the sub-piston space from the atmosphere.

[0077] The calculated PV diagram of the working cycle (see Fig. 3) was obtained for a polytropic index of 1.33…, which is due to the simplicity of calculating the temperature rise coefficient as the third root of the compression ratio. The compression ratio is assumed to be 5. In Fig. 3, the solid line "φ" on the graph corresponds to an intake cutoff of 40% of the piston stroke, which corresponds to the forced (takeoff) mode. The expansion process is completed before full expansion is achieved, which corresponds to an optimized ratio between fuel efficiency and specific gravity of the structure, acceptable for medium-range aircraft.

[0078] Figure 3 also shows three other intake cutoff values. The dashed line "n" with one dot corresponds to the rated (cruising) power, which is a compromise between power and efficiency. It corresponds approximately to half the intake cutoff value compared to the boost mode. The dashed line "e" with two dots corresponds to the fuel-efficient mode with full expansion. This mode is useful for achieving a quiet exhaust without a muffler.

[0079] Let's estimate the engine power. The work of the cycle per unit volume of air consumed from the atmosphere at sea level can be determined by measuring the area of ​​the PV diagram shown in Fig. 3, which represents the work of 1 cm 3The initial combustible mixture is pressurized to one atmosphere. The work is determined by dividing the area covered by the graph into small elements and multiplying the height of each element, expressed in atmospheres, by the width, expressed in cubic centimeters. The work done by a pressure of 1 atmosphere over a distance of one square centimeter is equal to a force of 1 kgf = 10 newtons acting on 1 cm. 2 , multiplied by the displacement under the action of this force of 1 cm. That is, it is equal to 10 N * 1 / 100 m = 0.1 J. This is the work of 1 cm 3 combustible mixture, which was used to calculate the given graph. The area covered by the closed curve "ABVGDA" of the working cycle shown in Fig. 3, presented in units of [atmosphere-centimeter], can be estimated by cutting off the tail of the PV diagram along the contour "AVGDA" and filling it with the area of ​​the contour "109BA1", considering these figures to be of equal area. Then the area of ​​the PV diagram can be calculated as the area of ​​the rectangle "09B10. It is equal to nine atmospheres multiplied by 1 cm 3, which is equal to the work of 90N * 1 / 100 m = 0.9 J. This is an approximate estimate of the useful work of the proposed engine per 1 cm 3 of atmospheric air consumed at sea level. The corresponding engine power per liter at 100 PTO shaft revolutions per second will be 0.9 J / cm 3 * 1000 cm 3 / liter * 100 cycles / sec = 90 kW / liter. This is the specific power per liter of the engine in boost mode, corresponding to an intake cutoff of 40% of the full piston stroke.

[0080] In the nominal "n" mode, the area described by the diagram, and therefore the power per liter, will be approximately half as large. However, the expansion coefficient will be higher, and therefore the efficiency will be higher. According to rough estimates, the specific work of 1 cm 3 The air efficiency in the nominal mode will be about 1 J. In the economic mode "e" the efficiency is even higher.

[0081] We will calculate specific power values ​​for an eight-cylinder engine with a piston diameter of 80 mm, a piston stroke of 40 mm, an overall sprocket diameter of 350 mm and an axial dimension of 100 mm.

[0082] The total cylinder volume of this engine is 1.6 liters. The volume of air consumed per revolution of the shaft, corresponding to operation along the ABCDEA circuit (see Fig. 3), is 0.8 liters.

[0083] Assuming the permissible nominal rotation speed for such an engine to be 100 revolutions per second, we obtain for the specific useful work estimated above 0.9 J / cm 3 air capacity 800 cm 3 * 0.9 J / cm 3 * 100 rpm = 72 kW. This is the boost mode, corresponding to an intake manifold cutoff of 40%.

[0084] For the nominal power mode (graph “n”), we obtain, taking into account the higher specific work of 1 J / cm 3 , 800 / 2 * 1 * 100 = 40 kW.

[0085] For the full expansion economy mode (graph "e"), the engine power rating is estimated to be around 34 kW.

[0086] In the above modes, useful work can also be estimated using heat balance. Mechanical work consists of two components. The first is the work of isobaric expansion, which can be estimated from the difference between the isobaric and isochoric heat capacities of air, which is approximately 0.3 J / g. The other component is generated during adiabatic expansion and is determined by the temperature change coefficient during adiabatic expansion. The negative work expended during the preliminary compression process should also be taken into account. However, all of this is necessary only for calculating specific fuel consumption. The calculations performed are too cumbersome to describe in detail. However, they show fuel consumption in the three modes listed above, varying in the range of 320-210 g / hp / hour, which differs little from the values ​​for gasoline internal combustion engines operating on the Otto cycle.

[0087] It is more interesting to determine the specific gravity of the design of the proposed engine, since it is the reduction of the specific gravity of the design that is the goal of the proposed invention.

[0088] ESTIMATION OF ENGINE SPECIFIC GRAVITY

[0089] We will estimate the specific mass of the proposed engine as follows. The structural components, which comprise the bulk of the mass, are represented as consisting of eight single-cylinder blocks, each containing two covers, a piston, a piston rod, a textolite roller at the end of the rod, as well as one connecting bar with the opposite roller and two textolite crosshead guides attached to the crankcase side walls. The second structural component is the power take-off shaft with a textolite power cam and two main bearings, as well as two octagonal crankcase side walls.

[0090] We will estimate the cylinder liner wall thickness, based on the strength condition for a peak cylinder pressure not exceeding 10 atmospheres, as follows. Since the linear tensile force of the shell is defined as the force acting on a shell segment with a length equal to its radius of curvature, then with a liner curvature radius of 4 cm, the force per linear centimeter of the shell will be 40 kg, which, with a permissible steel load limit of 20 kg / mm 2 , will require a cross-section of 2 mm 2 / running cm. The corresponding liner wall thickness will be 0.2 mm. For manufacturability and abnormal loads, we will adopt a liner thickness of 0.4 mm, which ensures operation with possible loading inhomogeneities. The cylinder is assumed to be welded. This is acceptable due to the significant reduction in peak pressure in an isobaric engine compared to engines operating on an isochoric cycle (Otto cycle), and also due to the absence of lateral piston load, due to the crosshead mechanism.

[0091] The mass of a 0.4 mm thick cylinder liner of the above dimensions with two caps will be approximately 100 g. Adding here the mass of the cooling jacket, as well as the mass of all other parts related to one cylinder, including the mass of a thin-walled lens-shaped piston of a hollow design, the mass of a rod with textolite rollers on plain bearings, etc., we obtain an estimate of the mass of the structure of the entire block of one cylinder of 300 g. The mass of eight blocks will be 2.4 kg.

[0092] Adding to the cylinders the shaft mass of 0.3 kg, the textolite cam mass of 0.1 kg, the crankcase walls made of 1 mm thick sheet metal, which is 1 kg, and the main ball bearing mass of 0.2 kg, we obtain a rough estimate of the engine structure mass of 4 kg.

[0093] Then the specific gravity of the engine structure will be:

[0094] Based on the nominal mode - 4 kg / 40 kW = 0.1 kg / kW.

[0095] Based on the forced mode 4 kg / 72 kW = 56 g / kW,

[0096] Based on the economy mode, 4 kg / 34 kW=0.12 kg / kW.

[0097] It should be noted that there is another mode—supercharged, corresponding to a 100% intake cutoff. In this case, the work of the cycle is estimated by the area of ​​the ABVEDA contour (see Fig. 3). In this case, work is performed solely due to the isobaric intake process and in the absence of adiabatic expansion. The area of ​​this contour is approximately 1.5 times greater than the area of ​​the supercharged mode discussed above. Consequently, the power will be 72 kW * 1.5 = 107 kW, and the specific mass in the supercharged mode will be 4 kg / 107 kW = 38 grams per kilowatt. However, fuel consumption will increase by approximately 2.5 times compared to the first supercharged mode, which follows from the corresponding increase in line BE compared to line BV of isobaric heating in Fig. 3.

[0098] It should be noted that 100 rpm for an engine with a piston stroke of 40 m will result in an average piston speed of 8 m / s, which is similar to that found in automotive engines. Piston speed is limited by the overload from its acceleration. However, it should be noted that there is no lateral piston pressure on the liner. Also, the peak cycle pressure is reduced several times (4-5 times), meaning less gas pressure on the rings against the cylinder wall. There is also no so-called ring repositioning when passing dead centers. This allows a rotation speed of 100 rpm to be extended to larger engines, for example, engines with twice the linear dimensions. Thus, by doubling the linear dimensions of an engine with a 350 mm diameter sprocket, we obtain an engine with a 700 mm diameter sprocket. The engine's displacement and power will increase by a factor of 8, i.e. up to 320 kW in nominal mode and up to 570 kW in forced mode.Moreover, the mass of the structure, determined by the cross-sections of the force flows, varying quadratically with the size multiplied by the length of the force flows, determined by the linear size, will also increase to the third power. Thus, the specific mass of the structure is virtually independent of scaling. (Although, more precisely, scaling down slightly increases the specific mass of the structure due to technological limitations on thinning, for example, cylinder liner walls, which are difficult to make thinner than 0.3 mm for engines with a power output of several kilowatts.)

[0099] CONCLUSION

[0100] The above rough estimates of the specific gravity of the proposed isobaric piston ICE may be somewhat inaccurate. However, they nevertheless demonstrate that, contrary to conventional wisdom, the piston ICE's mass could not only approach the specific gravity of aircraft gas turbine engines, which is approximately 0.15 kg / kW, but even be lower. This will significantly impact applications where gas turbines are ineffective, namely, the power range from 30 kW to 1000 kW per unit. These include small aircraft, ground vehicles, and medium-tonnage vessels. Moreover, the relevance of piston ICEs is particularly increasing with the transition to hybrid power plants, in which the engine will operate in a stationary and highly fuel-efficient mode with an efficiency no lower than that of central power plants. This will significantly reduce the weight of batteries installed onboard electric vehicles.Moreover, this will ensure all-fuel efficiency, reduce toxicity and exhaust noise, making vehicles more environmentally friendly. Carbon emissions will also be reduced on average, which is currently being addressed through the use of batteries, without taking into account that the entire cycle of electricity generation and battery production and disposal increases carbon emissions.

[0101] In addition to the above, the radical reduction in the specific mass of piston internal combustion engines estimated above will open up the possibility of radical improvements in vehicles, similar to those that occurred in large-scale aviation in connection with the advent of gas turbine engines.

Claims

1. An isobaric piston internal combustion engine comprising a cylinder, in the upper cover of which is located a bypass valve and a glow plug placed in a branch pipe connecting the bypass valve with the cylinder cavity, and also comprising a lower cylinder cover and a piston with a rod brought out through the seal of the lower cover to a crosshead mechanism connected to a mechanism for converting the reciprocating movements of the rod into continuous rotation of the power take-off shaft, wherein the lower cylinder cover contains an inlet automatic valve, as well as a discharge automatic valve connected to a receiver, which, in turn, is connected to the above-mentioned bypass valve, characterized in that the engine contains eight of the above-mentioned cylinders, the sub-piston spaces of which communicate with a common receiver, which, in turn, is connected to all the working cylinders,wherein the said eight cylinders are arranged in a star-shaped manner around a common flat cam mechanism for converting the reciprocating movements of the piston rods into the rotary movements of the power take-off shaft, and the cam profile is made single-period.

2. An engine according to paragraph 1, characterized in that, for lubricating the cylinder, elastic printing lubricating elements are located on the lower cover of the cylinder, equipped with a system for supplying them with oil and evenly distributed around the circumference of the lower cover so that they touch the lower surface of the piston when it is in its extreme lower position.

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