Two-stroke internal combustion engine piston-cylinder system

Abstract

A two-stroke internal combustion engine piston-cylinder system, comprising a first small-diameter cylinder (13) closed at one end and a second large-diameter cylinder (16) closed at both ends. A first piston (11) is provided in the first cylinder (13) to form a first gas chamber (10) for fuel combustion. A second piston (15) is provided in the second cylinder (16), and divides the second cylinder (16) into a second gas chamber (5) with a gas intake valve (4) and a third gas chamber (6) with an exhaust valve. The first piston (11) and the second piston (15) are rigidly connected to each other, and perform linear reciprocating motion together, and the effective area of the first piston (11) is smaller than the effective area of the part of the second piston (15) within the second gas chamber (5). The system further comprises two controllable gas passages: one brings the first gas chamber (10) into communication with the third gas chamber (6), and the other brings the first gas chamber (10) into communication with the second gas chamber (5). The efficiency of an internal combustion engine is improved, and an impact force generated at the moment of combustion can be reduced.

Description

Two-stroke internal combustion engine piston cylinder system Technical Field

[0001] This application relates to the field of internal combustion engines, and particularly to piston and cylinder technology for two-stroke internal combustion engines. Background Technology

[0002] This section is intended to provide background or context for understanding the implementation of this application and is for reference only. It should not be construed as an admission by the applicant that this section pertains to prior art that was disclosed before the filing date of this application.

[0003] Internal combustion engines are widely used as power sources in various fields. However, as people's requirements for energy conservation and environmental protection continue to increase, the demands for the efficiency of internal combustion engines are also rising.

[0004] For internal combustion engines, an effective way to improve energy efficiency is to increase the compression ratio. However, with the continuous increase in compression ratio, some problems have also emerged: first, the combustion chamber becomes too flat, causing uneven and incomplete combustion; second, there is a risk of knocking. Increasing the compression ratio by increasing the piston stroke will lead to an increase in crank radius, resulting in a decrease in engine speed, as well as an increase in the size and weight of the engine.

[0005] On the other hand, cylinder cooling results in a loss of over 20% of energy. With the development of high-temperature resistant materials such as ceramics, researchers are attempting to develop insulated engines that eliminate cylinder heat dissipation to improve energy efficiency. However, because high-temperature resistant materials are often brittle and cannot withstand excessive mechanical and thermal shocks, the harsh high-temperature, high-pressure, and high-impact operating environment of engines, especially the pressure shock at the moment of fuel ignition and the thermal shock of cold air on the high-temperature resistant surfaces of the intake chamber, causes premature damage to the high-temperature resistant materials that construct the cylinder and piston. This has delayed the practical application of insulated engines.

[0006] In addition, traditional internal combustion engines generate a huge impact force at the moment of fuel ignition, which not only increases engine wear but also affects the smooth operation of the engine.

[0007] Therefore, how to improve the efficiency of internal combustion engines while reducing the impact force at the moment of fuel ignition has become a technical problem that urgently needs to be solved by those skilled in the art.

[0008] Summary of the Invention

[0009] The purpose of this application is to provide a piston-cylinder system for a two-stroke internal combustion engine that can improve the efficiency of the internal combustion engine and reduce the impact force during combustion.

[0010] This application discloses a piston-cylinder system for a two-stroke internal combustion engine, comprising:

[0011] A first cylinder with one end closed and a second cylinder with both ends closed, wherein the inner diameter of the first cylinder is smaller than that of the second cylinder;

[0012] A first piston is disposed in the first cylinder to form a first chamber; the fuel of the internal combustion engine is burned in the first chamber.

[0013] A second piston is disposed in the second cylinder, dividing the second cylinder into a second chamber and a third chamber; the second chamber is provided with a first valve for air intake; the third chamber is provided with a second valve for air exhaust.

[0014] The first piston and the second piston are rigidly connected and together perform linear reciprocating motion;

[0015] The effective piston area of ​​the first piston in the first gas chamber is smaller than the effective piston area of ​​the second piston in the second gas chamber;

[0016] A first air passage is provided between the first air chamber and the third air chamber, and a third valve for opening or closing the first air passage is provided in the first air passage;

[0017] A second air passage is provided between the first air chamber and the second air chamber, and a fourth valve for opening or closing the second air passage is provided in the second air passage.

[0018] In a preferred embodiment, the operation of the system includes a first stroke and a second stroke, wherein,

[0019] At the start of the first stroke, fuel burns and expands in the first chamber, pushing the first piston and the second piston away from the closed end of the first cylinder, thus increasing the volume of the first chamber. As the pistons move, the volume of the second chamber increases, at which point the first valve opens, allowing fresh air to enter the second chamber. Simultaneously, the volume of the third chamber decreases, the second valve opens, and exhaust gas is discharged from the third chamber.

[0020] When the first piston reaches the position furthest from the closed end of the first cylinder, the second valve closes and the third valve opens, allowing the combustion products in the first chamber to enter the third chamber through the first air passage to begin secondary expansion.

[0021] Subsequently, the first valve closes, and the first piston and the second piston begin to move toward the closed end of the first cylinder, entering the second stroke;

[0022] As the piston continues to move, the volume of the first chamber decreases, continuously pushing combustion products into the third chamber; at the same time, the volume of the third chamber increases, receiving combustion products from the first chamber and achieving secondary expansion; simultaneously, the volume of the second chamber begins to decrease, compressing the air within it; when the pressure in the second chamber exceeds the pressure in the first chamber, the fourth valve opens, allowing compressed air to enter the first chamber from the second chamber through the second air passage;

[0023] Once the combustion products have fully entered the third chamber, the third valve is closed; when the second stroke is about to end, the fourth valve is closed.

[0024] When the first piston is closest to the closed end of the first cylinder, it enters the first stroke again.

[0025] In a preferred embodiment, it also includes:

[0026] A piston rod is rigidly connected to a piston assembly, which includes the first piston and the second piston.

[0027] Guide bearing; the piston rod passes through the guide bearing and is constrained by the guide bearing to reciprocate linearly in a direction parallel to the central axis of the first cylinder;

[0028] An oil seal is provided between the guide bearing and the piston assembly, and the piston rod passes through the oil seal to prevent lubricating oil from the guide bearing side from entering the piston assembly side;

[0029] A linear reciprocating motion assembly is connected to the piston rod.

[0030] In a preferred embodiment, the linear reciprocating motion component includes:

[0031] Two motors of identical specifications, wherein the stator windings of the two motors are connected in series.

[0032] A symmetrical double-crank connecting rod mechanism includes a transverse connecting rod rigidly connected to the second end of the piston rod, two connecting rods symmetrically distributed along an axis, and two cranks; one end of each of the two connecting rods is hinged to both ends of the transverse connecting rod, and the other end is hinged to the ends of the two cranks; the rotor shafts of the two motors are respectively connected to the crank shafts of the two cranks.

[0033] Two flywheels are rigidly connected to the crankshafts of the two cranks, respectively.

[0034] In a preferred embodiment, a crankcase is also included, wherein the symmetrical double crank connecting rod mechanism is disposed within the crankcase, and the crank shafts of the two cranks extend outside the crankcase as dual-path drive shafts.

[0035] In a preferred embodiment, the expansion ratio of the system is greater than the compression ratio, wherein the compression ratio is the sum of the maximum volume of the second chamber and the minimum volume of the first chamber divided by the minimum volume of the first chamber, and the expansion ratio is the sum of the maximum volume of the third chamber and the minimum volume of the first chamber divided by the minimum volume of the first chamber.

[0036] The maximum volume of the third air chamber is equal to the sum of the maximum volume of the second air chamber and the maximum volume of the first air chamber, minus the minimum volume of the first air chamber.

[0037] In a preferred embodiment, the linear reciprocating motion component includes:

[0038] flywheel;

[0039] A crank-connecting rod mechanism includes a crank and a connecting rod that are hinged to each other, wherein the crank shaft of the crank is rigidly connected to the flywheel;

[0040] The crosshead assembly includes:

[0041] The crosshead body is connected to one end of the piston rod;

[0042] A crosshead pin is provided on the crosshead body and is hinged to one end of the connecting rod of the crank-connecting rod mechanism;

[0043] The crosshead assembly is used to transmit the linear reciprocating motion of the piston rod to the crank-connecting rod mechanism and to prevent lateral forces from the crank-connecting rod mechanism from acting on the piston rod.

[0044] In a preferred embodiment, the linear reciprocating motion component is a linear motor.

[0045] In a preferred embodiment, the third valve is a one-way sealing ring, which includes:

[0046] An annular body is disposed within an annular groove on the second piston;

[0047] At least one ventilation groove is provided on one side of the annular groove;

[0048] Specifically, when the one-way sealing ring is close to the side of the annular groove with the vent groove, gas can leak through the vent groove, and a seal cannot be formed; when the one-way sealing ring is close to the side of the annular groove without the vent groove, a seal is formed between the one-way sealing ring, the annular groove, and the cylinder wall; thus achieving a one-way sealing function according to the piston movement direction.

[0049] In a preferred embodiment, the first cylinder and the second cylinder constitute a convex differential piston cylinder structure, wherein the first piston and the second piston form a convex differential piston;

[0050] The first air chamber and the third air chamber are connected by a vent hole that passes through the first piston and the second piston;

[0051] The third valve is an inertial force valve, which includes:

[0052] A valve is located at the top of the vent.

[0053] Valve stem, connected to the valve;

[0054] A connecting rod, the first end of which is hinged to the valve stem;

[0055] A lever, the first end of which is hinged to the second end of the connecting rod, the fulcrum of which is fixed on the second piston;

[0056] A counterweight is disposed at the second end of the lever, wherein the torque generated by the counterweight is greater than the torque generated by the valve weight;

[0057] When the first piston and the second piston reciprocate, due to the action of inertial force, the counterweight end of the lever rotates in the direction of inertial force, causing the valve to move in the opposite direction of inertial force, thereby realizing the opening or closing of the vent.

[0058] When the piston is below the center of reciprocating motion, the inertial force is downward, and the counterweight end of the lever rotates downward, lifting the valve and opening the vent.

[0059] When the piston is above the center of reciprocating motion, the inertial force is upward, the counterweight end of the lever rotates upward, driving the valve to move downward, thus closing the vent.

[0060] In the embodiments of this application, by adopting a dual-cylinder system with different sizes, a three-chamber structure, and a secondary expansion design, a highly efficient combustion and expansion process can be achieved, improving the efficiency of the internal combustion engine, reducing the impact force at the moment of combustion, and improving the stability and durability of the system.

[0061] Each stroke in the embodiments of this application includes a power-doping process, which improves the overall efficiency and power output of the system, while achieving smoother operation and more uniform output torque.

[0062] Furthermore, the design of the piston rod, guide bearing, and oil seal enables linear reciprocating motion support without lateral forces, while effectively isolating the lubricating oil. The guide bearing ensures that the piston assembly moves along the cylinder's central axis, avoiding contact and collision with the cylinder wall, thus improving system stability and lifespan. The oil seal, positioned between the guide bearing and the piston assembly, prevents lubricating oil from the guide bearing side from entering the piston assembly side, achieving oil-free operation of the piston-cylinder system. This design not only improves system reliability but also reduces oil consumption and emissions, while eliminating the cylinder cooling measures necessary for protecting the lubricating oil, creating conditions for adiabatic engines and significantly improving the energy efficiency of internal combustion engines.

[0063] By using a symmetrical double crank connecting rod mechanism and a dual-motor design, smooth reciprocating motion of the piston can be achieved, reducing vibration and noise, and improving the system's operational stability and efficiency.

[0064] Furthermore, by employing a symmetrical double-crank connecting rod mechanism, guide bearings to constrain piston rod movement, maintaining a uniform gap between the piston and the cylinder wall, connecting two identical motors in series, and using an oil seal isolation design, lateral forces on the piston can be eliminated, achieving frictionless motion, ensuring symmetrical driving force, and eliminating the need for lubrication in the piston-cylinder area. This design significantly reduces manufacturing difficulty and cost, improves operating efficiency, extends service life, and provides a foundation for oil-free pistons and adiabatic engines.

[0065] Furthermore, by designing an expansion ratio greater than the compression ratio, the Miller cycle can be achieved, significantly improving the system's thermal efficiency and reducing fuel consumption. Specifically, a smaller compression ratio reduces compression power consumption, while a larger expansion ratio allows for more efficient utilization of the gas expansion energy, thereby improving overall thermal efficiency. This design also lowers combustion temperature, reducing the formation of pollutants such as nitrogen oxides. Combined with the system's adiabatic design, the thermal efficiency can exceed 70%, far surpassing that of traditional internal combustion engines. At a speed of 6000 rpm, the power density can reach over 45 kW / L. In addition, this design gives the system excellent low-speed torque characteristics and allows it to adapt to various fuels (including hydrogen, natural gas, methanol, and other new energy fuels), which is beneficial for achieving the "dual carbon" goal. For hydrogen fuel, the system's efficiency can even exceed that of fuel cells, providing new possibilities for hydrogen energy utilization.

[0066] Optionally, the design of the crosshead assembly can effectively transmit linear reciprocating motion and eliminate lateral forces, thereby improving the system's operational stability and lifespan.

[0067] Alternatively, by using a linear motor as the linear reciprocating motion component, the system structure can be simplified and the energy conversion efficiency improved.

[0068] Optionally, by designing a one-way sealing ring, a one-way sealing function based on the piston's direction of movement can be achieved, simplifying the valve structure. This design enables valves requiring one-way sealing based on the piston's direction of movement to operate automatically, eliminating the need for complex gas distribution control mechanisms. It offers advantages such as simple structure, reliable operation, and no need for complex adjustments.

[0069] Optionally, by designing an inertial force valve, the opening and closing of the valve can be automatically controlled using the inertial force generated by the piston's motion, simplifying the control system. This design can shorten the working fluid transmission length, achieving advantages such as short transmission distance, reliable operation, large transmission flow rate, and small pressure difference. Attached Figure Description

[0070] Figure 1 is a schematic diagram of the basic structure of a two-stroke internal combustion engine piston cylinder system according to an embodiment of the present application;

[0071] Figure 2 is a schematic diagram of the partial arrangement of the large and small piston cylinder assembly of the two-stroke internal combustion engine piston cylinder system shown in Figure 1.

[0072] Figure 3 is a schematic diagram of the cooperation between the two-stroke internal combustion engine piston cylinder system shown in Figure 1 and the crosshead crank-connecting rod mechanism according to an embodiment of this application;

[0073] Figure 4 is a schematic diagram of the two-stroke internal combustion engine piston-cylinder system shown in Figure 1 and the symmetrical double crank connecting rod mechanism according to an embodiment of the present application;

[0074] Figure 5 is a schematic diagram of the two-stroke internal combustion engine piston cylinder system shown in Figure 1 and its cooperation with a linear motor according to an embodiment of this application;

[0075] Figure 6 is a comparative schematic diagram of a conventional piston ring and a one-way piston ring structure according to an embodiment of the present application;

[0076] Figure 7 is a schematic diagram of a two-stroke internal combustion engine with concave differential piston cylinder pair implemented using a one-way sealing ring according to an embodiment of the present application.

[0077] Figure 8 is a schematic diagram showing the piston positions of the two-stroke internal combustion engine with secondary expansion shown in Figure 7.

[0078] Figure 9 is a structural schematic diagram of an inertial force valve according to an embodiment of this application;

[0079] Figure 10 is a structural schematic diagram of a two-stroke internal combustion engine with secondary expansion achieved by using an inertial force valve according to an embodiment of this application;

[0080] Figure 11 is a screenshot of the output of a solver for optimizing the operating parameters of a two-stroke internal combustion engine with secondary expansion according to an embodiment of this application.

[0081] Figure 12 shows the optimization solution based on the combustion characteristics of hydrogen fuel according to an embodiment of this application.

[0082] The reference numerals used in the attached figures are as follows: Detailed Implementation

[0083] In the following description, many technical details are presented to help the reader better understand this application. However, those skilled in the art will understand that the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0084] Explanation of some concepts:

[0085] Piston effective area: refers to the effective cross-sectional area of ​​the piston under gas pressure inside the cylinder.

[0086] Secondary expansion: short for secondary expansion.

[0087] Secondary expansion chamber: a secondary expansion chamber.

[0088] Combustion expansion: a shorthand for the expansion caused by combustion.

[0089] Expansion chamber: The chamber for expanding combustion gases.

[0090] EGR stands for Exhaust Gas Recirculation. It is an emission control technology used in internal combustion engines.

[0091] This application provides an innovative two-stroke internal combustion engine with a secondary expansion mechanism. Employing a secondary expansion approach, the expansion and power-generating process is divided into two stages, effectively folding the combustion chamber and resolving the conflict between a high expansion ratio and an excessively flat combustion chamber and stroke length. By using two pistons of different sizes, the kinetic energy during the combustion process is rationally distributed, significantly reducing the mechanical shock at the moment of fuel ignition. Simultaneously, a design separating compression and expansion isolates cold air from the high-temperature combustion chamber. The cold air is compressed and heated before contacting the high-temperature materials, thus greatly reducing thermal shock. Thanks to these designs, the engine's energy efficiency exceeds 70% and possesses numerous advantages, such as high power density, stable operation, simple and reliable structure, long lifespan, low usage of high-temperature materials, and low manufacturing difficulty and cost. Furthermore, this embodiment can support various fuels, including hydrogen, natural gas, methanol, and other new energy fuels. With its ultra-high efficiency, it is expected to become a new force in achieving the "dual-carbon goal."

[0092] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0093] It should be noted that the piston-cylinder system described below is for a two-stroke internal combustion engine. Many conventional components of a two-stroke internal combustion engine that have been disclosed in the prior art, such as the fuel injection device, ignition device, timing mechanism, and control components, may not be explicitly shown or described in the drawings or embodiments. Those skilled in the art can readily conceive of how to construct the required two-stroke internal combustion engine based on the piston-cylinder system disclosed in this application and in conjunction with the prior art.

[0094] Figure 1 illustrates the basic structure of a two-stroke internal combustion engine piston-cylinder system according to an embodiment of this application. The system consists of two piston-cylinder pairs, a large and a small piston, fixedly connected to the same piston rod 14. The small piston-cylinder pair operates in a single-acting mode, while the large piston-cylinder pair operates in a double-acting mode, meaning there is a variable-volume chamber above and below the large piston 15. This forms a total of three chambers. The chamber formed by the small piston-cylinder pair is the combustion expansion chamber 10, or simply the "combustion expansion chamber." Of the two chambers formed by the large piston-cylinder pair, the one operating in the same direction as the combustion expansion chamber 10 is the compression chamber 5; and the one operating in the opposite direction is the secondary expansion chamber 6, or simply the "secondary expansion chamber."

[0095] Specifically, the center of the large piston 15 and the small piston 11 is fixedly connected to the piston rod 14. The piston rod 14 is equipped with a guide bearing 8 and an oil seal 7. The central axis of the guide bearing 8 coincides with the central axis of the cylinder 47. The piston rod 14 is connected to the reciprocating linear motion assembly 9. Under the transmission support of the reciprocating linear motion assembly 9, the large piston 15, the small piston 11, and the piston rod 14 reciprocate linearly along the central axis of the cylinder within the range from the top dead center 1 to the bottom dead center 3. The oil seal 7 isolates the lubricating oil within the reciprocating linear motion assembly 9 to prevent the lubricating oil from entering the cylinder. The external air intake 56 is connected to the compression chamber 5 through an intake valve 4. The compression chamber 5 is connected to the combustion chamber 10 through a compression transmission valve 12. The combustion chamber 10 is connected to the second expansion chamber 6 through a second expansion valve 2. The second expansion chamber 6 is connected to the exhaust 57 through an exhaust valve 17. The two expansion valves 2 and the exhaust valve 17 are controllable valves driven by the control mechanism; while the intake valve 4 and the compressed air transmission valve 12 are check valves (one-way valves).

[0096] This embodiment is a two-stroke system, with two strokes (upward stroke and downward stroke) in each cycle. The specific working process is explained below.

[0097] The upward stroke (second stroke): The stroke in which the piston (including the small piston 11 and the large piston 15) moves upward from the bottom dead center 3 to the top dead center 1, referred to as the upward stroke. This process begins at the bottom dead center 3, at which point the compression chamber 5 has completed intake, the combustion expansion chamber 10 has completed combustion and initial expansion, and the secondary expansion chamber 6 has completed exhaust.

[0098] As the piston moves upward, the following actions occur in sequence:

[0099] A. The space of the compression chamber 5 begins to shrink, the intake valve 4 closes, and the air pressure in the compression chamber 5 continues to increase; the space of the combustion expansion chamber 10 begins to shrink, the secondary expansion valve 2 opens, and the heated working fluid (hereinafter referred to as the old working fluid) that has completed ignition and initial expansion is transferred to the secondary expansion chamber 6 through the secondary expansion valve 2; the space of the secondary expansion chamber 6 begins to expand, and the secondary expansion chamber 6 is connected to the combustion expansion chamber 10. The air pressures of the combustion expansion chamber 10 and the secondary expansion chamber 6 are basically equal, and their total volume continues to increase. The old working fluid performs secondary expansion and does work, while the air pressure continues to decrease.

[0100] B. When the piston rises to a certain extent, and the pressure in the compression chamber 5 exceeds that in the combustion expansion chamber 10, the compression transfer valve 12 opens, and the new working fluid begins to enter the combustion expansion chamber 10. At this point, all three chambers are connected, and the pressures in the three chambers are basically equal. As the piston continues to rise, the total volume of the three chambers remains unchanged, and the pressure also remains unchanged. However, the new working fluid will continuously flow out of the compression chamber 5 and into the combustion expansion chamber 10, while the old working fluid in the combustion expansion chamber 10 will continuously flow into the secondary expansion chamber 6, thus achieving scavenging and gas exchange in the combustion expansion chamber 10.

[0101] C. After that, the piston continues to move upward, and the combustion chamber 10 is now filled with the new working fluid. At this point, the secondary expansion valve 2 closes, the volume of the secondary expansion chamber 6 continues to increase, and the old working fluid continues to expand and do work. The combustion chamber 10 begins to compress the new air, and at the same time, the compression chamber 5 continuously compresses the remaining new air and sends it to the combustion chamber 10 until it reaches the top dead center 1. At this point, all the gas in the compression chamber 5 enters the combustion chamber 10, and the compression transfer valve 12 closes. The combustion chamber 10 has completed the compression of the new working fluid, and the space has shrunk, leaving only the combustion space (i.e., the combustion chamber). At this point, the combustion chamber 10 begins to inject fuel, igniting or compressing the fuel, and a new stroke begins.

[0102] One detail worth noting is the improvement in ventilation effect in this embodiment. In ordinary two-stroke ventilation, all the working fluid is scavenged and ventilated simultaneously at bottom dead center 3. This results in a short ventilation time, a large ventilation volume, and a high degree of mixing between the new and old working fluids in the same chamber, leading to insufficient, unstable, and unreliable ventilation. However, in this embodiment, the secondary expansion ventilation occurs in the middle to late stages of the upward stroke. By this time, most of the working fluid has already been transferred to the secondary expansion chamber 6, and ventilation only applies to the small amount of remaining working fluid in the combustion expansion chamber 10. From the perspective of the combustion expansion chamber 10, this process can actually be divided into three sub-processes: exhaust, ventilation, and intake. From bottom dead center 3 until the pressure in compression chamber 5 exceeds that in expansion chamber 10, the process involves the exhaust of expansion chamber 10, during which most of the old working fluid is transferred to secondary expansion chamber 6. In the subsequent scavenging process, a small amount of new working fluid is forced from compression chamber 5 into expansion chamber 10, pushing the old working fluid out of expansion chamber 10 and into secondary expansion chamber 6. The secondary expansion chamber's transfer valve then closes, ending the scavenging process. In the subsequent intake process of expansion chamber 10, the new working fluid in compression chamber 5 is continuously transferred to expansion chamber 10 under the compression action of compression chamber 5 until it reaches top dead center 1, at which point it all enters expansion chamber 10. Clearly, most of the old and new working fluids reside separately in secondary expansion chamber 6 and compression chamber 5, without mixing; only a small amount of working fluid in expansion chamber 10 has the opportunity to mix. For expansion chamber 10, it is a process of "exhaust first, scavenging then intake." This fully ensures the stable and reliable replacement of old and new working fluids in the combustion expansion chamber 10, guaranteeing smooth operation.

[0103] It's important to note that there's a concept of air exchange rate here. This means that a reasonable air exchange rate can be set to allow a small portion of the old working fluid to remain in the combustion chamber 10 and participate in the next working cycle. Adjusting the timing of the closing of the secondary expansion valve 2 can change the air exchange rate. As a special case, if the secondary expansion valve 2 closes before the pressure transmission valve opens, the old working fluid in the combustion chamber 10 is retained, thus skipping the scavenging process. This method can be used when the air exchange rate is very low. A lower air exchange rate is equivalent to an exhaust gas recirculation (EGR) process. Some published research results indicate that EGR can improve exhaust gas emissions, increase compression ignition temperature, and improve efficiency to some extent.

[0104] Downward Stroke (First Stroke): The stroke in which the piston moves downward from top dead center (TDC) 1 to bottom dead center (BDC) 3, referred to as the downward stroke. This process begins at TDC 1. At this point, compression chamber 5 has completed compression, and all the new working fluid has entered combustion chamber 10; combustion chamber 10 has completed ignition; and secondary expansion chamber 6 has completed its second expansion and work. Next, the piston begins to descend, the space in compression chamber 5 begins to expand, intake valve 4 opens, and fresh air begins to enter compression chamber 5; the space in combustion chamber 10 expands, combustion continues, and the working fluid expands and does work; the space in secondary expansion chamber 6 begins to shrink, exhaust valve 17 opens, and the exhaust gas that has completed its second expansion begins to be discharged. This process continues until the piston reaches BDC. At this point, compression chamber 5 is full of fresh air, the old working fluid in combustion chamber 10 has completed its first expansion, and secondary expansion chamber 6 has discharged all exhaust gas. The aforementioned upward stroke then begins to repeat.

[0105] It is easy to see that in both the upward and downward strokes, all three chambers perform their functions fully and work in perfect harmony. Unlike ordinary internal combustion engines that only perform work in one stroke throughout the entire cycle, the dual-expansion internal combustion engine of this embodiment expands and performs work in all strokes of a cycle. Therefore, it runs more smoothly and the output torque is more uniform. It is easy to imagine that, since the effective piston area of ​​the combustion chamber 10 is much smaller than that of the dual-expansion chamber 6, the impact force on the piston during fuel combustion is reduced by several times. This dual-expansion internal combustion engine has the characteristics of quiet and stable operation, making it very suitable for range-extended electric vehicles.

[0106] It is easy to imagine that the above-mentioned large and small piston cylinder combination can be arranged in many specific ways. Figure 2 lists a few exemplary examples, and those skilled in the art can easily conceive of more combinations based on the description in this specification. Regardless of the form, they all have the same core characteristics: two pistons of different sizes that are rigidly connected. The small piston operates in a single-acting mode, while the large piston operates in a double-acting mode. The small piston and the corresponding cylinder form a combustion chamber. Of the two chambers formed by the large piston, the one that acts in the same direction as the combustion chamber is the compression chamber, while the one that acts in the opposite direction to the combustion chamber is the secondary expansion chamber.

[0107] The following section explains the principle of the scheme in Figure 1 and compares it with existing technologies.

[0108] Secondary expansion technology shortens the stroke length. For ordinary internal combustion engines, combustion expansion is completed in one cylinder. During the expansion process, the piston area remains unchanged, and the expansion ratio is the ratio of the total height of the air chamber to the height of the combustion chamber.

[0109] Let the height of the combustion chamber be L0, and the piston stroke be L1.

[0110] Then the expansion ratio N = (L1 + L0) / L0

[0111] Therefore, L1 / L0 = N-1

[0112] In other words, the piston stroke is (expansion ratio – 1) times the height of the combustion chamber. Therefore, under high expansion ratio conditions, the piston stroke becomes very long.

[0113] In the embodiments of this application, the expansion process occurs in two consecutive strokes of the folding mechanism. The initial ignition expansion occurs in the small cylinder, while the second expansion occurs in the large cylinder, and the piston areas corresponding to the two expansions are different. Assuming the area of ​​the large piston is M times that of the small piston, the height of the combustion chamber is L0, and the piston stroke length is L1, then the expansion ratio of the two expansions is N2 = M * L1 / (L1 + L0).

[0114] The expansion ratio of the first expansion is N1 = (L1 + L0) / L0.

[0115] Multiplying the two equations above, N1*N2=M*L1 / L0,

[0116] And N1*N2 is exactly the total expansion ratio N.

[0117] Therefore, L1 / L0 = N / M.

[0118] In other words, compared to a conventional internal combustion engine, the piston stroke length is reduced by approximately M times (M is the area ratio of the large and small pistons).

[0119] Compared to conventional internal combustion engines, the embodiments of this application can increase the expansion ratio while shortening the piston stroke by several times. With the stroke length shortened, the crank radius also shortens, which on the one hand greatly reduces the volume of the crankcase, and on the other hand further increases the rotational speed, thus significantly improving the engine's power density.

[0120] In this embodiment, the combustion chamber is located inside a small cylinder. Thanks to the smaller piston area, the combustion chamber is taller and more square in shape than that of a conventional internal combustion engine, for the same volume.

[0121] The piston thrust in this embodiment is more uniform. It is easy to understand that since the area of ​​the smaller piston is 1 / M of the area of ​​the larger piston, the pressure exerted on the piston at the moment of fuel ignition, under the same gas pressure conditions, is also reduced to 1 / M. Therefore, the mechanical impact intensity at the peak gas pressure is greatly reduced, protecting the cylinder block and piston.

[0122] During the secondary expansion, although the air pressure has dropped significantly, thanks to the piston area of ​​the large piston M times that of the large piston, a large piston thrust can still be provided. Therefore, the secondary expansion technology of this application embodiment can allow the piston rod to obtain a balanced thrust that covers the entire operating cycle, which is conducive to stable operation and reduces output fluctuations.

[0123] Fuel combustion is a continuous process, and the combustion delay varies depending on the fuel. The duration of combustion also limits the speed of an internal combustion engine. In the embodiments of this application, the combustion process can span two expansion processes, that is, cover both the downward and upward strokes. Therefore, under the same combustion delay conditions, the embodiments of this application can achieve twice the speed of a conventional internal combustion engine, and the power density is also doubled.

[0124] In this embodiment, the compressor chamber and the combustion chamber are separate. The high-temperature, high-pressure combustion process occurs in the combustion chamber, keeping it in a continuously high-temperature state. Fresh, cold air first enters the compressor chamber, where it is compressed and heated. Therefore, when the new working fluid enters the combustion chamber, its temperature is much higher than in a conventional internal combustion engine. This reduces the low-temperature thermal shock to the combustion chamber material and effectively protects the fragile, high-temperature resistant material.

[0125] The embodiments of this application employ a three-chamber separation design, which successfully isolates the combustion expansion chamber, which is under high temperature and high pressure, so that the components subjected to high temperature and high pressure are confined to the combustion expansion chamber, which is very small in size. Compared with ordinary internal combustion engines, this can save a lot of high temperature resistant materials.

[0126] In summary, the embodiments of this application have optimized the internal combustion engine in various aspects, resolved the various challenges faced in implementing an adiabatic engine, and achieved a technical platform for a high-efficiency, high-power-density, low-wear, and long-life high-quality internal combustion engine.

[0127] The embodiment of this application in Figure 1, due to its special structural form, is not suitable for use with the crankcase of a conventional internal combustion engine. The reciprocating linear motion assembly used with the embodiment of this application needs to provide linear reciprocating motion support without lateral forces. The solution in Figure 1 can be used with various reciprocating linear motion assemblies. Examples of several reciprocating linear motion assemblies are described below; these examples are illustrative and not limiting.

[0128] Figure 3 is a schematic diagram of an embodiment using a crosshead crank-connecting rod mechanism as a reciprocating linear motion component. Crosshead crank-connecting rod mechanisms 18 are commonly found in compressors and marine diesel engines, and are generally quite large. In this embodiment, the crosshead body can be directly connected to the piston rod 14 to achieve transmission. The crank-connecting rod mechanism 18 converts rotational motion into reciprocating linear motion, and the crosshead assembly 20 is used to counteract lateral forces. A guide bearing 8 and an oil seal 7 are provided on the piston rod 14, and an inertia flywheel 21 is located on the crankshaft 24, providing inertial energy storage support for piston movement and smoothing torque output fluctuations. The guide bearing 8 constrains the piston's movement along the cylinder's central axis, preventing contact and collision with the cylinder. The oil seal 7 isolates lubricating oil, preventing it from entering the cylinder. This embodiment can achieve a good connection and fit with the crosshead crank-connecting rod mechanism 18, and can be directly used in existing crosshead diesel engine bodies, thereby significantly improving energy efficiency and achieving significant energy-saving and consumption-reducing effects. It has the advantages of easy modification and significant results.

[0129] Figure 4 is a schematic diagram of an embodiment using a symmetrical double-crank connecting rod mechanism as a reciprocating linear motion component. This embodiment includes: two motors of identical specifications, with the stator windings of the two motors connected in series; a symmetrical double-crank connecting rod mechanism, which includes a horizontal connecting rod 66 rigidly connected to the lower end of the piston rod 14, two axisily symmetrically distributed connecting rods 67, and two cranks 68; one end of each of the two connecting rods 67 is hinged to both ends of the horizontal connecting rod 66, and the other end is hinged to one end of each of the two cranks 68, the other end of which is a crankshaft 69; the rotor shafts of the two motors are respectively connected to the two crankshafts 29; and two flywheels 21, rigidly connected to the two crankshafts 69. The flywheels 21 can provide inertial energy storage support for piston movement and smooth torque output fluctuations. By employing a symmetrical double-crank connecting rod mechanism, guide bearings to constrain piston rod movement, maintaining a uniform gap between the piston and the cylinder wall, connecting two identical motors in series, and using an oil seal isolation design, lateral forces on the piston can be eliminated, achieving frictionless motion, ensuring symmetrical driving force, and eliminating the need for lubrication in the piston-cylinder area. This design significantly reduces manufacturing difficulty and cost, improves operating efficiency, and extends service life. It provides more stable and lighter transmission support for the double-expansion two-stroke internal combustion engine 19, fully leveraging its high energy efficiency and high power density. The two motors are arranged axially symmetrically with the axis of the guide bearing 8 as the axis of symmetry, which further optimizes the overall structural balance, improves operational smoothness, helps reduce vibration and noise, and enhances system stability. Because the stator and rotor of the motor interact through electromagnetic force, they do not directly contact each other. Furthermore, the motor torque is mainly controlled by current; the slight phase difference between the rotor and stator does not affect the motor torque. In other words, the motor transmits torque without constraining the rotation phase. This embodiment cleverly utilizes this physical law, providing a stable transmission connection for the two crankshafts through a series of symmetrical motors, achieving the separation of torque transmission and phase constraint, thereby avoiding over-constraint introduced by the transmission mechanism.

[0130] Figure 5 is a schematic diagram of an embodiment using a linear motor as a reciprocating linear motion component. By cooperating with a linear motor, a high-power-density internal combustion generator can be formed. The piston rod 14 of the two-stroke internal combustion engine 19 is connected to the mover drive shaft of the linear motor 26. A guide bearing 8 and an oil seal 7 are provided on the piston rod 14. The guide bearing 8 constrains the piston's movement along the cylinder's central axis, preventing contact and collision with the cylinder. The oil seal 7 isolates the lubricating oil, preventing it from entering the upper cylinder. There are already many existing technologies that utilize a linear motor 26 to realize a free-piston internal combustion engine. However, most of these solutions are hampered by the enormous impact of the huge pressure fluctuation at the moment of fuel ignition on the linear motor 26, preventing the production of marketable products. This embodiment employs a secondary expansion method and uses expansion pistons of different sizes and areas, which reduces the peak thrust of the piston on the linear motor by several times at the moment of fuel ignition, greatly reducing the thrust requirements of the linear motor. On the other hand, long-stroke linear motors are very difficult to manufacture, while this embodiment uses secondary expansion to shorten the piston stroke by several times. Therefore, this embodiment and the linear motor can achieve excellent coordination, making it a perfect method for realizing a high-performance free-piston internal combustion engine.

[0131] In the scheme shown in Figure 1, the working fluid transfer channel from the combustion expansion chamber 10 to the secondary expansion chamber 6 and the secondary expansion valve 2 are the most difficult to manufacture. The following embodiment adopts a concave stepped piston structure and sets a transfer hole on the piston, thereby greatly shortening the working fluid transfer length; at the same time, it utilizes a one-way sealing ring to achieve a simplified structure that does not require an additional gas distribution control mechanism.

[0132] One-way piston rings are uncommon, used only occasionally in some compressors. For ease of understanding, Figure 6 uses piston rings as an example to compare ordinary piston rings and one-way piston rings. In Figure 6, the left side of the vertical dotted line represents an ordinary piston ring, and the right side represents a one-way piston ring. It can be understood that the piston ring 28 is installed in the piston ring groove 29 on the piston. Depending on the pressure difference, the upper or lower side of the piston ring 28 will be tightly against the side of the piston ring groove 29, forming a seal. That is, regardless of top or bottom, the piston ring 28 always has one sealing surface tightly against one side of the piston ring groove 29, forming a seal. However, the one-way piston ring 28 has several venting grooves 27 cut into one side of the piston ring groove 29. When the piston ring 28 is tightly against the side of the piston ring groove 29 with the venting grooves 27, gas will leak from the venting grooves 27, failing to seal; only when the piston ring 28 is tightly against another side of the piston ring groove 29 without venting grooves 27 can an effective seal be achieved. As shown in Figure 6, for a standard piston ring 28, a seal can be achieved regardless of whether the piston ring 28 is positioned above or below. However, for a one-way piston ring 28, when the piston ring 28 is below, it seals by fitting against the piston ring groove 29. But when the piston ring 28 is above, gas leaks from the vent groove 27 on the piston ring groove 29, failing to seal. It is easy to imagine that a one-way sealing ring can be used to achieve the function of a valve opening in one direction. It is also easy to imagine that similar one-way sealing rings can be installed not only on the piston sidewall but also on the cylinder sidewall.

[0133] Figure 7 is a schematic diagram of an embodiment of a two-stroke internal combustion engine with a concave stepped piston-cylinder assembly, utilizing a one-way sealing ring. This embodiment employs a concave stepped piston 25 (a modified stepped piston), similar to a conventional stepped piston, also a combination of two piston-cylinder assemblies of different sizes. However, the smaller piston and cylinder are reversed, essentially creating a blind hole in the center of the cylindrical larger piston, serving as the inner wall of the smaller piston-cylinder assembly. When the larger piston moves, the smaller piston-cylinder assembly can be understood as the smaller cylinder moving, while the smaller piston remains stationary. Corresponding to the outer and inner walls of piston 25, cylinder 47 can be considered as consisting of an outer cylinder, an inner cylinder, and upper and lower bottom surfaces. It is easy to imagine that the effect of the changing space of each chamber formed by cylinder 47 and piston 25 is consistent with that of a conventional stepped piston. This concave stepped piston structure allows piston 25 to have both long inner and outer walls, facilitating the placement of the one-way sealing ring.

[0134] An intake opening 43 and an exhaust opening 34 are provided on the outer wall of cylinder 47, with the intake opening 43 at the top and the exhaust opening 34 at the bottom. An isolation ring 33 is provided on the inner wall of the outer cylinder of cylinder 47, positioned between the intake opening 43 and the exhaust opening 34. An exhaust one-way ring 35 is provided below the isolation ring 33. When piston 25 is at top dead center 1, the exhaust one-way ring 35 is positioned just below the bottom of piston 25. An exhaust vent groove 36 is provided on the lower side of the mounting groove of the exhaust one-way ring 35. A combustion expansion ring 45 is provided on the outer wall of the inner cylinder of cylinder 47 near the bottom. A shaft seal ring 37 is provided at the center of the bottom of cylinder 47.

[0135] The piston 25 has an intake one-way ring 32 near the top on its outer wall; an intake vent groove 31 is provided above the mounting groove of the intake one-way ring 32. The piston 25 has a pressure ring 39 near the top on its inner wall, and below it are a secondary expansion transmission hole 46, a secondary expansion one-way ring 40, a secondary expansion vent groove 41, and a secondary expansion transmission groove 42.

[0136] The isolation ring 33, combustion expansion ring 45, compression ring 39, and shaft seal ring 37 are ordinary sealing rings. The isolation ring 33 is used to block the communication between the intake 56 and the exhaust 57; the combustion expansion ring 45 is used to seal the combustion expansion chamber 10; the compression ring 39 is used to seal the compression chamber 5; and the shaft seal ring 37 is used to seal the space between the secondary expansion chamber 6 and the piston rod 14.

[0137] The intake one-way ring 32, exhaust one-way ring 35, and secondary expansion one-way ring 40 are one-way sealing rings. As the piston 25 moves up or down, these one-way rings move up or down due to friction and pressure, thus sealing or connecting according to the corresponding ventilation grooves. Specifically, the intake one-way ring 32 and exhaust one-way ring 35 connect when the piston 25 moves down and seal when it moves up; while the secondary expansion one-way ring 40 does the opposite, connecting when the piston 25 moves up and sealing when it moves down. However, the secondary expansion working fluid transfer process is somewhat special; both the combustion expansion ring 45 and the secondary expansion one-way ring 40 need to be connected to achieve connection between the combustion expansion chamber 10 and the secondary expansion chamber 6.

[0138] The positions of piston 25 are detailed in Figure 8. First, consider the vertical relationship between the components: When piston 25 is at top dead center 1 (state B in the figure), the exhaust one-way ring 35 is positioned below the bottom of piston 25, leaving a small gap. When piston 25 is at bottom dead center 3 (state E in the figure), the intake port 43 is above the top of piston 25, close to the top of piston 25; the intake one-way ring 32 and the compression ring 39 are positioned close to the top of piston 25; an isolation ring 33 is positioned immediately below the intake one-way ring 32; immediately below the compression ring 39, the secondary expansion transfer hole 46 opening, the secondary expansion one-way ring 40, and the secondary expansion transfer groove 42 are sequentially positioned; a secondary expansion pressure relief groove 44 is positioned at the same horizontal level as the secondary expansion one-way ring 40; and a combustion expansion ring 45 is positioned immediately below the secondary expansion pressure relief groove 44. An exhaust port 34 is positioned between the isolation ring 33 and the exhaust one-way ring 35.

[0139] State E, viewed from top to bottom:

[0140] Minimum overall height of piston 25 = height of compressor ring 39 + opening height of secondary expansion transmission hole 46 + height of secondary expansion one-way ring 40 + height of combustion ring 45 + stroke length + bottom thickness of piston 25

[0141] Cylinder 47 minimum overall height = stroke length + piston 25 minimum overall height

[0142] The following describes the detailed states of piston 25 at each position:

[0143] In Figure 7, A is in the later stage of the upward stroke. The intake one-way ring 32 is in the sealed position, the compression chamber 5 continues to compress, the compression one-way valve 38 is open, and the remaining new working fluid is forced into the combustion expansion chamber 10; the secondary expansion one-way ring 40 is still in the connected position, but the secondary expansion transmission groove 42 is already higher than the combustion expansion ring 45, the combustion expansion ring 45 is in contact with the inner wall of the piston 25 and sealed, the secondary expansion transmission channel is closed, and the combustion expansion chamber 10 compresses the new working fluid; the exhaust one-way ring 35 is in the sealed position, and the hot working fluid in the secondary expansion chamber 6 continues to expand and do work.

[0144] B is at the end of the upward stroke and is about to switch to the downward stroke. The new working fluid in the compressor chamber 5 has been completely compressed into the combustion chamber 10, and the compressor check valve 38 is closed due to pressure equilibrium. At this time, the new working fluid in the combustion chamber 10 has been fully compressed, and the fuel injector 62 injects fuel. For compression ignition mode, the temperature has reached the compression ignition condition, while for spark ignition mode, the spark plug is triggered, and the fuel immediately burns. The bottom of piston 25 is higher than the exhaust check ring 35, and exhaust gas is discharged from the gap between the bottom of piston 25 and the exhaust check ring 35, achieving pressure equilibrium on both sides of the exhaust check ring 35. Piston 25 then enters the downward stroke.

[0145] C is in the early stage of the downward stroke. Piston 25 moves downward from top dead center 1, the space of the compression chamber 5 increases, the air pressure drops to below atmospheric pressure, and under the action of friction and air pressure, the intake one-way ring 32 moves upward to the connected position, and fresh air is drawn into the compression chamber 5 through the intake vent groove 31; the working fluid in the combustion expansion chamber 10 continues to burn and expand, and under the action of friction and air pressure, the secondary expansion one-way ring 40 moves upward to the sealing position, and the combustion expansion ring 45 contacts and seals with the inner wall of piston 25; under the action of friction and air pressure, the exhaust one-way ring 35 moves downward to the connected position, and the exhaust gas in the secondary expansion chamber 6 is continuously discharged through the exhaust vent groove 36.

[0146] During the later stages of the downward stroke, the compressor chamber 5 continues to draw in fresh air; the combustion expansion chamber 10 continues to burn and expand, and the combustion expansion ring 45 has reached the secondary expansion transfer groove 42, forming a connection. However, the secondary expansion one-way ring 40 is still in a sealed position, so the old working fluid still cannot be transferred to the secondary expansion chamber 6; the exhaust gas continues to be discharged from the secondary expansion chamber 6.

[0147] E is at the end of the downward stroke and is about to switch to the upward stroke. The intake one-way ring 32 moves below the intake opening 43, and the compressor chamber 5 is directly connected to the outside, fully drawing in fresh air; the secondary expansion one-way ring 40 moves to the position of the secondary expansion pressure relief groove 44, and the heat working fluid in the combustion expansion chamber 10 is transferred to the secondary expansion chamber 6 through the secondary expansion pressure relief groove 44 and the secondary expansion transmission hole 46, and the pressure on both sides of the secondary expansion one-way ring 40 reaches equilibrium; the exhaust gas in the secondary expansion chamber 6 has been completely discharged, and under the action of friction, when the piston 25 switches to the upward stroke, the exhaust one-way ring 35 moves up to the sealing position.

[0148] During the early upward stroke, under the influence of friction, the intake one-way ring 32 moves down to the sealing position, the compression chamber 5 continuously shrinks, and the air pressure continues to rise. Under the pressure, the intake one-way ring 32 maintains the sealing position. The combustion expansion ring 45 is in the area of ​​the secondary expansion transmission groove 42 and loses its seal. Under the influence of friction and pressure, the secondary expansion one-way ring 40 moves down to the connecting position, and the combustion expansion chamber 10 is connected to the secondary expansion chamber 6 through the secondary expansion transmission groove 42, the secondary expansion vent groove 41, and the secondary expansion transmission hole 46. As the piston 25 continues to move upward, the total volume of the combustion expansion chamber 10 and the secondary expansion chamber 6 continuously increases, the old working fluid continuously expands and does work, and the air pressure continuously decreases. When the pressure drops below that of the compression chamber 5, the compression transmission valve 12 opens, and the new working fluid in the compression chamber 5 begins to enter the combustion expansion chamber 10. At this point, the compression chamber 5, combustion expansion chamber 10, and secondary expansion chamber 6 are connected as a single unit, with a constant total volume. New working fluid continuously enters the combustion expansion chamber 10 from the compression chamber 5, pushing the existing old working fluid to the secondary expansion chamber 6, creating a scavenging and gas exchange effect. After the combustion expansion chamber 10 is filled with new working fluid, the piston 25 continues to move upwards, and the combustion expansion ring 45 contacts the inner wall of the piston 25, re-establishing a seal. The secondary expansion transmission path closes, and the system re-enters state A, continuing this cycle indefinitely.

[0149] Furthermore, based on the volume variation law of the double-acting differential piston 25 cylinder 47, it can be known that the maximum volume of each chamber satisfies:

[0150] Two expansion chambers = compression chamber + (fuel expansion chamber – combustion chamber)

[0151] That is, the maximum volume of the second expansion chamber 6 is greater than that of the compression chamber 5, which means the expansion ratio is greater than the compression ratio, thus realizing the Miller cycle and improving operating efficiency.

[0152] This embodiment cleverly utilizes a one-way sealing ring and a transmission hole 46 on the piston 25, combined with a one-way valve, enabling all valves and valves to operate automatically. This eliminates the need for a complex valve train control mechanism, offering advantages such as simple structure, reliable operation, and no need for complex adjustments. Such a complex secondary expansion internal combustion engine is achieved with such a simple structure, demonstrating the ingenuity of this embodiment.

[0153] The following is an embodiment based on another dual-expansion transmission control method. Those skilled in the art will know that when an internal combustion engine is running, the reciprocating linear motion of the piston is approximately a simple harmonic motion in the vertical direction. As a single non-inertial reference frame, all objects within the piston are subject to inertial forces. This inertial force is zero when the oscillator is at the center of vibration, and is maximum at the highest and lowest points. Furthermore, when the oscillator is above the center, the inertial force is upward, and when it is below the center line, the inertial force is downward. This embodiment utilizes this characteristic, employing levers and counterweights to control the valves mounted on the piston using inertial forces.

[0154] Figure 9 shows a convex stepped piston 52 with a vent hole 51 connecting its top and bottom. A valve 48 is located at the top of the vent hole 51, with its valve stem 49 hinged to a connecting rod 50 below. The other end of the connecting rod 50 is hinged to one end of a lever 54, whose fulcrum 55 is fixed to the piston 52. On either side of the fulcrum 55, the torque generated by the counterweight 53 is greater than the torque generated by the weight of the valve 48. Therefore, when this mechanism is subjected to inertial force, the counterweight 53 end of the lever 54 rotates in the same direction as the inertial force, thereby causing the valve 48 to move in the opposite direction to the inertial force. For the piston 52 undergoing high-speed simple harmonic motion, when the piston 52 is below the center of vibration, the inertial force it experiences is downward, and the counterweight 53 end of the lever 54 rotates downward, thereby lifting the valve 48 and separating the valve 48 from the vent hole 51, thus connecting the upper and lower surfaces of the piston 52; when the piston 52 is above the center of vibration, the inertial force it experiences is upward, and the counterweight 53 end of the lever 54 rotates upward, thereby driving the valve 48 to move downward and contact and seal with the top surface of the vent hole 51, thus closing the vent hole 51.

[0155] Figure 10 shows a schematic diagram of an embodiment of a two-stroke internal combustion engine with secondary expansion achieved by an inertial force valve 48. This embodiment uses a convex double-acting differential piston-cylinder assembly, in which the small piston-cylinder assembly constitutes a single-acting plunger cylinder, while the large piston-cylinder assembly operates in a double-acting mode. The chamber formed by the small piston cylinder is the combustion chamber 10, the chamber formed by the large piston cylinder on the same side is the compression chamber 5, and the chamber formed by the bottom surface of the large piston and cylinder 47 is the secondary expansion chamber 6. A combustion ring 64 is provided on the wall of the small piston, and a compression ring 65 is provided on the wall of the large piston. An intake valve 60 is provided above the compression chamber 5, through which fresh air can be drawn into the compression chamber 5. A compression transmission pipe 58 is also provided above the compression chamber 5, and the other end of the compression transmission pipe 58 is connected to the combustion chamber 10 via a compression transmission valve 12. An exhaust valve 17 is provided below the secondary expansion chamber 6, through which exhaust gas in the secondary expansion chamber 6 can be discharged. This stepped piston 52 is connected to the reciprocating linear motion assembly 9 by piston rod 14. A shaft sealing ring 61 is provided at the center of the bottom of cylinder 47, which contacts and seals with piston rod 14. A double expansion transmission hole 59 is provided inside piston 52, connecting the top and bottom surfaces of piston 52; a double expansion valve 2 is provided on the top surface of the double expansion transmission hole 59. The double expansion valve 2 adopts the aforementioned inertial force valve, which automatically controls the valve action by relying on inertial force.

[0156] The working process is basically the same as that of the aforementioned two-stroke internal combustion engine with secondary expansion. Only the differences are described here, specifically the parts related to the action of the valves due to inertia. At the beginning of the downward stroke, piston 52 is above the midpoint, with upward inertia, and the secondary expansion valve 2 is closed. After passing the midpoint, although the inertia is downward, the combustion chamber 10 is in a state of combustion and expansion. Under the enormous in-cylinder pressure, the secondary expansion valve 2 still cannot open. As piston 52 continues to descend, the space in the combustion chamber 10 increases. Although the pressure decreases, it is still greater than the torque generated by the inertia, and the secondary expansion valve 2 remains closed. On the other hand, during the downward stroke, the exhaust valve 17 opens, and the secondary expansion chamber is in the exhaust state. When the piston 52 moves close to the bottom dead center 3, the exhaust valve 17 closes in advance, and the residual exhaust gas in the secondary expansion chamber 6 begins to be compressed, and the gas pressure rises. At this time, the inertial force on the piston 52 reaches its maximum. On the other hand, the gas pressure in the combustion expansion chamber 10, which prevents the secondary expansion valve 2 from opening, has also decreased. As the exhaust gas pressure in the secondary expansion chamber 6 increases, it offsets most of the gas pressure in the combustion expansion chamber 10, causing the upward resultant force on the valve 48 to exceed the pressure from the combustion expansion chamber 10. The secondary expansion valve 2 opens, and the combustion expansion chamber 10 and the secondary expansion chamber 6 are connected through the secondary expansion transfer hole 59. The piston 52 begins to switch to the upward stroke, and the working fluid is continuously transferred to the secondary expansion chamber 6 to perform secondary expansion and work. As the upward stroke approaches the midpoint, the pressure in compression chamber 5 increases while the pressure in combustion chamber 10 and secondary expansion chamber 6 decreases. The compression transfer valve 12 automatically opens, allowing new working fluid to enter combustion chamber 10 for scavenging and gas exchange. After piston 52 continues upward past the midpoint, its inertial force shifts upward, driving secondary expansion valve 2 downward, at which point it closes. The timing of secondary expansion valve 2's closing can be adjusted by changing the size of counterweight 53 or its distance from fulcrum 55, or by adding a torsion spring to lever 54. In short, secondary expansion valve 2 opens after piston 52 reaches bottom dead center 3 and closes after piston 52 has moved past the midpoint of its stroke.

[0157] In this embodiment, the intake valve 60 and exhaust valve 17 are two valves that need to be controlled. These two valves can be implemented using valve timing control mechanisms commonly found in existing engines. The intake valve 60 can also be implemented using a one-way valve. It is easy to imagine that the intake valve 60 needs to remain closed during the upward stroke and open during the downward stroke; the exhaust valve 17 needs to remain closed during the upward stroke and open during the downward stroke, but it needs to close prematurely before the end of the downward stroke so that the residual exhaust gas pressure can control the inertial force to accurately open the valve.

[0158] Other operating details of this embodiment are the same as those of the two-stroke internal combustion engine with secondary expansion shown in Figure 7 of the previous embodiment, and will not be repeated here. This embodiment uses a convex stepped piston cylinder, and like the previous embodiment, it also has the characteristic that the expansion ratio is greater than the compression ratio, supporting the Miller cycle. This embodiment also has the advantages of high efficiency, high power density, and reliable scavenging.

[0159] The following operating parameters can be used to better understand the working process of this dual-expansion internal combustion engine. Figure 11 is a screenshot of the output of the operating parameter optimization solver for one embodiment. It shows the thermodynamic parameters of each chamber under key conditions to provide a detailed understanding of the engine's operation. These thermodynamic parameters are applicable to internal combustion engines employing a differential piston-cylinder structure.

[0160] These are the parameters of a diesel engine that have been repeatedly optimized and refined. Starting with the intake:

[0161] State S1: This is when the compressor chamber is filled with fresh air after the downward stroke. The pressure in the compressor chamber is atmospheric pressure, the temperature is ambient temperature, and the volume of the working fluid is the maximum volume of the compressor chamber. As mentioned earlier, the combustion expansion chamber has completed its initial expansion and is in State S5. The secondary expansion chamber has completed exhaust and its volume is 0. The upward stroke then begins. The intake valve is closed, the transfer valve is open, and the combustion expansion chamber and the secondary expansion chamber are connected. As the volume of the secondary expansion chamber continues to expand, the working fluid continuously enters through the transfer valve to expand and do work, causing the pressure to decrease. Simultaneously, the volume of the compressor chamber continuously decreases, and the pressure increases. When the pressure in the compressor chamber exceeds that of the combustion expansion chamber, the compressor valve opens, connecting the compressor chamber, combustion expansion chamber, and secondary expansion chamber. New working fluid enters the combustion expansion chamber, and old working fluid flows from the combustion expansion chamber to the secondary expansion chamber. The total volume of the three chambers remains unchanged. The decrease in volume of the compressor chamber and the combustion expansion chamber is exactly equal to the increase in volume of the secondary expansion chamber; therefore, the pressure also remains unchanged, and only the working fluid is transferred. After that, the transfer valve closes, and the process enters the next state.

[0162] States S2a, S2b, and S2c represent the moments when the aforementioned gas exchange process ends and the transfer valve closes. At this point, the pressures in the compression chamber, combustion expansion chamber, and secondary expansion chamber are approximately equal, at 0.312 MPa. The process of the compression chamber moving from S1 to S2a can be approximated as an isentropic compression process, with the compression chamber volume decreasing and the temperature and pressure increasing slightly. The process of the combustion expansion chamber moving from state S5 to S2b can be approximated as an isentropic expansion process. Although the volume of the combustion expansion chamber decreases from 8.1 to 3.40 (the combustion chamber volume is one volume unit), the volume of the secondary expansion chamber increases from 19.68, thus the total volume of the old working fluid increases. The pressure in the combustion expansion chamber decreases from 1.105 MPa in S5 to 0.312 MPa. At this point, all the old working fluid that needs to be discharged has entered the secondary expansion chamber, i.e., state S2c. It's important to note that there's a concept of air exchange rate involved here. This means that a reasonable air exchange rate can be set in the design to allow a small portion of the old working fluid to remain in the combustion chamber and participate in the next working cycle. This practice is generally called exhaust gas recirculation (EGR), which helps improve the combustion process and reduce pollutant emissions. In this example, the air exchange rate is set to 95%.

[0163] S3 state: The piston continues its upward movement to the top dead center. At this point, the volume of the compression chamber shrinks to 0, and all the new working fluid enters the combustion chamber; this process can be approximated as isentropic compression. The new working fluid in the combustion chamber S2b is further compressed to state S3: the volume of the combustion chamber shrinks to 1, the pressure reaches 8.357 Ma, and the temperature is 1053 K. This temperature meets the compression ignition conditions for diesel fuel. At this point, the fuel injector injects fuel, which then burns in the combustion chamber, entering state S4.

[0164] S4 state: The piston is still in the top dead center region, and the volume has not changed. The combustion heating from S3 to S4 is a constant volume heating process. The pressure in the combustion chamber reaches its maximum point of 16.9 MPa, and the temperature reaches its maximum point of 2100 K. It should be noted that due to the addition of fuel, the number of moles of working fluid in the combustion chamber increases after ignition.

[0165] S6 State: On the other hand, as the piston moves towards top dead center, after the aforementioned S2c state, the volume of the secondary expansion chamber continues to increase, and the old working fluid continues to expand and do work until it reaches top dead center. The secondary expansion chamber then completes its expansion and enters the S6 state. The process from S2c to S6 can be approximated as an isentropic expansion process. The volume of the secondary expansion chamber reaches its maximum value of 29.71 kJ, the pressure is 0.178 MPa, and the temperature is 691.7 K. It is easy to see that the maximum volume of the secondary expansion chamber is exactly equal to the sum of the maximum volumes of the compression chamber and the combustion chamber minus the volume of the combustion chamber. This is determined by the configuration of the staged double-acting piston.

[0166] S5 state: The cycle then enters a downward phase. The combustion chamber continues to burn and expand. Since combustion requires a certain amount of time, this process can be approximated as initial constant-pressure heating followed by adiabatic expansion. At this time, the compression chamber draws in air, and the secondary expansion chamber exhausts air. This continues until the piston reaches bottom dead center, at which point the combustion chamber completes its first expansion. The compression chamber then completes its intake phase and returns to S1, beginning a new cycle.

[0167] Based on the optimizer's results, expressed in units of combustion chamber volume, the maximum volume of the combustion expansion chamber is 8.1, the compressor chamber is 22.61, the dual expansion chamber is 29.71, and V... 二胀 =V 压气 +V 燃胀 The value -1 is determined by the volumetric characteristics of a double-acting differential piston, where V represents volume. The combustion chamber volume is 1, resulting in a compression ratio of 22.61 and an expansion ratio of 29.71. The expansion ratio is greater than the compression ratio, typical of the Miller cycle. The high expansion ratio and Miller cycle improve the efficiency of the internal combustion engine. This engine features an adiabatic design with no cylinder cooling losses, achieving an efficiency of 71.9%. At 6000 rpm, the power density reaches 67.41 kW / L, demonstrating exceptionally excellent performance.

[0168] Figure 12 shows the results of optimizing the design parameters for the combustion characteristics of hydrogen fuel. It's understandable that hydrogen, natural gas, or gasoline have very high ignition points, making compression ignition difficult, especially in low winter temperatures, which can easily lead to ignition failure. Here, a lower exchange rate is chosen, allowing more heated working fluid to remain in the combustion chamber and participate in the next cycle of combustion. This utilizes the old working fluid to heat the new working fluid, increasing the temperature of the compression ignition working fluid to be much higher than the fuel's ignition point, ensuring the reliability of compression ignition. On the other hand, a high expansion ratio, high compression ratio, and low combustion temperature are employed, achieving a maximum cylinder pressure of 21.7 MPa and a maximum cylinder temperature of only 1800 K. This improves efficiency and reduces the formation of pollutants such as nitrogen oxides. The efficiency reaches 76.7%, while the power density at 6000 RPM still exceeds 45 kW / L. In fact, hydrogen burns very quickly. Utilizing this characteristic, the engine speed can be significantly increased, thereby increasing the power density. Therefore, this example demonstrates remarkably excellent performance. It is sufficient to directly replace existing hydrogen fuel cells.

[0169] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, if it refers to performing an action according to an element, it means performing the action at least according to that element, including two cases: performing the action only according to that element, and performing the action according to that element and other elements. Expressions such as "multiple," "repeatedly," and "various" include two, two times, two kinds, and more than two, more than two times, and more than two kinds. The terms "up" and "down" used in this application are relative concepts used for ease of expression and are relative to the orientations shown in the attached drawings, not absolute orientations.

[0170] This specification includes combinations of various embodiments described herein. Individual references to embodiments (e.g., “one embodiment”, “some embodiments”, or “preferred embodiments”) do not necessarily refer to the same embodiment; however, these embodiments are not mutually exclusive unless indicated to be mutually exclusive or are readily apparent to those skilled in the art. It should be noted that the word “or” is used in a non-exclusive sense throughout this specification unless the context explicitly indicates or requires it.

[0171] All references to this application are considered to be incorporated in their entirety into the disclosure of this application so that they can serve as a basis for modifications if necessary. Furthermore, it should be understood that after reading the contents of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A piston-cylinder system for a two-stroke internal combustion engine, characterized in that, include: A first cylinder with one end closed and a second cylinder with both ends closed, wherein the inner diameter of the first cylinder is smaller than that of the second cylinder; A first piston is disposed in the first cylinder to form a first chamber; the fuel of the internal combustion engine is burned in the first chamber. A second piston is disposed in the second cylinder, dividing the second cylinder into a second chamber and a third chamber; the second chamber is provided with a first valve for air intake; the third chamber is provided with a second valve for air exhaust. The first piston and the second piston are rigidly connected and together perform linear reciprocating motion; The effective piston area of ​​the first piston in the first gas chamber is smaller than the effective piston area of ​​the second piston in the second gas chamber; A first air passage is provided between the first air chamber and the third air chamber, and a third valve for opening or closing the first air passage is provided in the first air passage; A second air passage is provided between the first air chamber and the second air chamber, and a fourth valve for opening or closing the second air passage is provided in the second air passage.

2. The two-stroke internal combustion engine piston-cylinder system as described in claim 1, characterized in that, The system's operation includes a first stroke and a second stroke, wherein... At the start of the first stroke, fuel burns and expands in the first chamber, pushing the first piston and the second piston away from the closed end of the first cylinder, thus increasing the volume of the first chamber. As the pistons move, the volume of the second chamber increases, at which point the first valve opens, allowing fresh air to enter the second chamber. Simultaneously, the volume of the third chamber decreases, the second valve opens, and exhaust gas is discharged from the third chamber. When the first piston reaches the position furthest from the closed end of the first cylinder, the second valve closes and the third valve opens, allowing the combustion products in the first chamber to enter the third chamber through the first air passage to begin secondary expansion. Subsequently, the first valve closes, and the first piston and the second piston begin to move toward the closed end of the first cylinder, entering the second stroke; As the piston continues to move, the volume of the first chamber decreases, continuously pushing combustion products into the third chamber; at the same time, the volume of the third chamber increases, receiving combustion products from the first chamber and achieving secondary expansion; simultaneously, the volume of the second chamber begins to decrease, compressing the air within it; when the pressure in the second chamber exceeds the pressure in the first chamber, the fourth valve opens, allowing compressed air to enter the first chamber from the second chamber through the second air passage; Once the combustion products have fully entered the third chamber, the third valve is closed; when the second stroke is about to end, the fourth valve is closed. When the first piston is closest to the closed end of the first cylinder, it enters the first stroke again.

3. The two-stroke internal combustion engine piston-cylinder system as described in claim 2, characterized in that, Also includes: A piston rod is rigidly connected to a piston assembly, which includes the first piston and the second piston. Guide bearing; The piston rod passes through the guide bearing and is constrained by the guide bearing to reciprocate linearly in a direction parallel to the central axis of the first cylinder. An oil seal is disposed between the guide bearing and the piston assembly, through which the piston rod passes to prevent... Prevent lubricating oil from entering the piston assembly from the guide bearing side; A linear reciprocating motion assembly is connected to the piston rod.

4. The two-stroke internal combustion engine piston-cylinder system as described in claim 3, characterized in that, The linear reciprocating motion component includes: Two motors of identical specifications, wherein the stator windings of the two motors are connected in series. A symmetrical double-crank connecting rod mechanism includes a transverse connecting rod rigidly connected to the second end of the piston rod, two connecting rods symmetrically distributed along an axis, and two cranks; one end of each of the two connecting rods is hinged to both ends of the transverse connecting rod, and the other end is hinged to the ends of the two cranks; the rotor shafts of the two motors are respectively connected to the crank shafts of the two cranks. Two flywheels are rigidly connected to the crankshafts of the two cranks, respectively.

5. The two-stroke internal combustion engine piston-cylinder system as described in claim 4, characterized in that, It also includes a crankcase, in which the symmetrical double crank connecting rod mechanism is disposed, and the crank shafts of the two cranks extend out of the crankcase as dual-path drive shafts.

6. The two-stroke internal combustion engine piston-cylinder system as described in claim 1, characterized in that, The expansion ratio of the system is greater than the compression ratio, wherein the compression ratio is the sum of the maximum volume of the second air chamber and the minimum volume of the first air chamber divided by the minimum volume of the first air chamber, and the expansion ratio is the sum of the maximum volume of the third air chamber and the minimum volume of the first air chamber divided by the minimum volume of the first air chamber. The maximum volume of the third air chamber is equal to the sum of the maximum volume of the second air chamber and the maximum volume of the first air chamber, minus the minimum volume of the first air chamber.

7. The two-stroke internal combustion engine piston-cylinder system as described in claim 1, characterized in that, The linear reciprocating motion component includes: flywheel; A crank-connecting rod mechanism includes a crank and a connecting rod that are hinged to each other, wherein the crank shaft of the crank is rigidly connected to the flywheel; Crosshead assembly, including: The crosshead body is connected to one end of the piston rod; A crosshead pin is provided on the crosshead body and is hinged to one end of the connecting rod of the crank-connecting rod mechanism; The crosshead assembly is used to transmit the linear reciprocating motion of the piston rod to the crank-connecting rod mechanism and to prevent lateral forces from the crank-connecting rod mechanism from acting on the piston rod.

8. The two-stroke internal combustion engine piston-cylinder system as described in claim 1, characterized in that, The linear reciprocating motion component is a linear motor.

9. The two-stroke internal combustion engine piston-cylinder system as described in any one of claims 1-8, characterized in that, The third valve is a one-way sealing ring, which includes: An annular body is disposed within an annular groove on the second piston; At least one ventilation groove is provided on one side of the annular groove; Specifically, when the one-way sealing ring is close to the side of the annular groove with the vent groove, gas can leak through the vent groove, and a seal cannot be formed; when the one-way sealing ring is close to the side of the annular groove without the vent groove, a seal is formed between the one-way sealing ring, the annular groove, and the cylinder wall; thus achieving a one-way sealing function according to the piston movement direction.

10. The two-stroke internal combustion engine piston-cylinder system as described in any one of claims 1-8, characterized in that, The first cylinder and the second cylinder constitute a convex differential piston cylinder structure, wherein the first piston and the second piston form a convex differential piston; The first air chamber and the third air chamber are connected by a vent hole that passes through the first piston and the second piston; The third valve is an inertial force valve, which includes: A valve is located at the top of the vent. Valve stem, connected to the valve; A connecting rod, the first end of which is hinged to the valve stem; A lever, the first end of which is hinged to the second end of the connecting rod, the fulcrum of which is fixed on the second piston; A counterweight is disposed at the second end of the lever, wherein the torque generated by the counterweight is greater than the torque generated by the valve weight; When the first piston and the second piston reciprocate, due to the action of inertial force, the counterweight end of the lever rotates in the direction of inertial force, causing the valve to move in the opposite direction of inertial force, thereby realizing the opening or closing of the vent. When the piston is below the center of reciprocating motion, the inertial force is downward, and the counterweight end of the lever rotates downward, lifting the valve and opening the vent. When the piston is above the center of reciprocating motion, the inertial force is upward, the counterweight end of the lever rotates upward, driving the valve to move downward, thus closing the vent.

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