A four-stroke free piston engine

Abstract

The application discloses a four-stroke free piston engine, which comprises two groups of oppositely arranged cylinders, a swing gear, a first one-way clutch, a second one-way clutch, a first power output and a second power output, wherein the swing gear is arranged in a fixed shaft rotation mode, the pistons of two cylinders in each group are connected through push rods, the swing gear is engaged with the racks on the two push rods, each cylinder sequentially completes an intake stroke, a compression stroke, a working stroke and an exhaust stroke, four strokes form one working cycle, and the piston of one cylinder is always working, and the other three cylinders are synchronously driven to complete an intake stroke, a compression stroke and an exhaust stroke respectively, so that the complicated parts such as the push rod, the crankshaft, the high-pressure oil bearing and the high-pressure oil pump in the prior art can be cancelled, the linear reciprocating motion of the piston is converted into rotary motion, the power in a rotary mode is output, the engine efficiency is improved, and the engine is suitable for being used as the engine of HEV, PHEV and REEV vehicles.

Description

Technical Field

[0001] This invention relates to the field of engine technology, and in particular to a four-stroke free piston engine. Background Technology

[0002] Hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and range-extended electric vehicles (REEV) are the main technological routes for energy-saving and new energy vehicles. What they have in common is that they all contain a piston engine with a crankshaft and convert fuel (such as gasoline, diesel, methanol, natural gas, hydrogen, etc.) into mechanical energy. Moreover, HEV, PHEV, and REEV all need to maximize the energy conversion efficiency of the engine.

[0003] The power generated by existing piston engines with crankshafts is transmitted from the piston to the pushrod, which then transmits the power to the crankshaft via the crank, thus converting it into rotational motion and outputting power. Due to the limitations of the pushrod and crankshaft, the piston stroke is fixed, so the compression ratio cannot be adjusted or optimized according to power requirements, which limits the system's thermal efficiency. Furthermore, when the piston is working, the pushrod applies a reaction force, the lateral component of which presses the piston tightly against the cylinder wall, greatly increasing friction and energy loss. Furthermore, constrained by their operating mode, most piston engines are two-stroke engines, including a compression stroke and a power stroke. At the end of the compression stroke (top dead center), the compressed gas mixture in the cylinder is ignited, and at the end of the power stroke (bottom dead center), scavenging occurs to expel exhaust gas and introduce air and gas. However, the scavenging time is very short, requiring air pressurization to force the exhaust gas out of the cylinder. Alternatively, during the gas exchange process, some exhaust gas may remain in the cylinder, while some fresh air may be entrained in the exhaust stream. This situation is called short-circuit loss, which also affects the efficiency of the entire power system.

[0004] At the beginning of the power stroke, the pressure inside the cylinder is at its highest, but the crankshaft is near top dead center, the pushrod lever arm on the crankshaft is very small, resulting in a smaller torque and therefore a smaller power output. Simultaneously, the energy contained in the high-temperature, high-pressure combustion gases is released more slowly, and energy losses due to gas leakage and heat loss also increase. Towards the end of the power stroke, the crankshaft is near bottom dead center, the pushrod lever arm on the crankshaft is also small, and the pressure inside the cylinder is lower, resulting in another lower power output. This reduces the engine's power density and increases power output fluctuations.

[0005] Furthermore, the loads between the pushrod and the crankshaft, and between the crankshaft and the housing, are substantial, resulting in significant frictional losses. High-pressure oil bearings are required, which in turn necessitate a high-pressure oil source and a high-pressure oil pump. This necessitates additional energy to drive the high-pressure oil pump, leading to a reduction in engine output power and efficiency. Since the high-pressure oil bearings of the pushrod and crankshaft are both moving parts, complex high-pressure oil circuits are needed to deliver high-pressure lubricating oil to them. These circuits must pass through moving components such as the crankshaft, crankshaft, and pushrod, increasing the manufacturing difficulty and cost of these components. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a four-stroke free piston engine that eliminates complex components such as pushrods, crankshafts, high-pressure oil bearings, and high-pressure oil pumps found in existing technologies. It also transforms the linear reciprocating motion of the piston into rotary motion to output rotational power, thereby improving engine efficiency and making it suitable as an engine for vehicles such as HEVs, PHEVs, and REEVs.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] This invention provides a four-stroke free piston engine, comprising two sets of cylinders, each set including two opposing cylinders, with the pistons of the two cylinders in each set connected by a push rod. Each push rod has a rack. The engine also includes a transmission assembly. The transmission assembly includes a rocker gear, a first one-way clutch, a second one-way clutch, a first power output component, and a second power output component. The rocker gear meshes with the racks on the two push rods. The rocker gear is connected to the first one-way clutch, the first power output component engages with the first one-way clutch, the rocker gear is connected to the second one-way clutch, and the second power output component engages with the second one-way clutch. The rocker gear is fixed-axis rotating. Each cylinder sequentially completes the intake stroke, compression stroke, power stroke, and exhaust stroke. The system forms a working cycle every four strokes. In each stroke, one cylinder's piston performs power stroke and simultaneously drives the other three cylinders to complete their respective intake, compression, and exhaust strokes through the combined action of the push rod, rack, and rocker gear. In the first stroke, only one power piston drives the rocker gear to rotate in the first direction via the rack of the push rod; in the second stroke, only one power piston drives the rocker gear to rotate in the second direction opposite to the first direction via the rack of the push rod; in the third stroke, only one power piston drives the rocker gear to rotate in the first direction via the rack of the push rod; in the fourth stroke, only one power piston drives the rocker gear to rotate in the second direction via the rack of the push rod. When the rocker gear rotates in the first direction, the first one-way clutch engages, and the rocker gear transmits torque and outputs power through the first power output component, while simultaneously disengaging the second one-way clutch. The second power output component idles in the same direction as the rotation direction of the previous stroke. When the rocker gear rotates in the second direction, the first one-way clutch disengages, and the first power output component idles in the same direction as the rotation direction of the previous stroke, while simultaneously engaging the second one-way clutch. The rocker gear transmits torque and outputs power through the second power output component.

[0009] Furthermore, it also includes a coupling mechanism; the first power output component and the second power output component are coupled through the coupling mechanism to output continuous power.

[0010] Furthermore, during the power stroke, one cylinder in one group generates a driving force to push its piston towards a first direction; and through the transmission assembly, it drives the piston of another cylinder in the same group to move towards the first direction to achieve the compression stroke, simultaneously driving the pistons of the third and fourth cylinders in another group to move towards a second direction opposite to the first direction, so that the third and fourth cylinders in the other group respectively complete the intake stroke and the exhaust stroke; or it drives the piston of another cylinder in the same group to move towards the first direction to achieve the exhaust stroke, simultaneously driving the pistons of the third and fourth cylinders in another group to move towards a second direction opposite to the first direction, so that the third and fourth cylinders in the other group respectively complete the intake stroke and the compression stroke.

[0011] Furthermore, the racks on the two push rods are single-sided racks and are arranged opposite to each other; the rocker gear is arranged between the racks of the two push rods.

[0012] Furthermore, the two push rods are integrally connected and move synchronously in the same direction; the racks on the two push rods are set on the same side, and the rocker gear meshes with the racks of the two push rods simultaneously.

[0013] Furthermore, the gears of the two racks are connected one-to-one; or the gears of the two racks are independent of each other.

[0014] In one embodiment, the rocker gear is directly driven to the first power output component via the first one-way clutch, and the rocker gear is directly driven to the second power output component via the second one-way clutch.

[0015] Furthermore, the first power output component includes a first output shaft connected to the first one-way clutch and a first output wheel fixed to the first output shaft; the second power output component includes a second output shaft connected to the second one-way clutch and a second output wheel fixed to the second output shaft.

[0016] Furthermore, the coupling mechanism includes a coupling gear and a first transmission gear and a second transmission gear arranged coaxially. The first transmission gear is driven to connect to the first gear through the coupling gear, and the second transmission gear is driven to connect to the second gear.

[0017] In one embodiment, both the first power output component and the second power output component are output wheels, a first one-way clutch is provided between the first power output component and the shaft of the rocker gear, and a second one-way clutch is provided between the second power output component and the shaft of the rocker gear.

[0018] Furthermore, the coupling mechanism includes a coupling gear and a first transmission gear and a second transmission gear arranged coaxially. The first transmission gear is driven to connect to the first power output component through the coupling gear, and the second transmission gear is driven to connect to the second power output component.

[0019] In one embodiment, the transmission assembly includes a transmission gear set; the shaft of the rocker gear is fixedly connected to the transmission gear set, the transmission gear set is driven to the first power output component through the first one-way clutch, and is driven to the second power output component through the second one-way clutch, thereby forming an indirect drive configuration.

[0020] Furthermore, the first power output component includes a first output shaft connected to the first one-way clutch and a first output wheel fixed to the first output shaft; the second power output component includes a second output shaft connected to the second one-way clutch and a second output wheel fixed to the second output shaft, and the first output wheel and the second output wheel are engaged.

[0021] In one embodiment, the coupling mechanism includes a coupling gear and a transmission gear set, the shaft of the rocking gear is fixedly connected to the transmission gear set, the first power output component is a first gear, and the shaft of the rocking gear is directly driven to the first gear through the first one-way clutch; the second power output component includes a second output shaft connected to the second one-way clutch and a second gear fixed to the second output shaft, the transmission gear set is driven to the second output shaft through the second one-way clutch; the first gear is driven to the second gear through the coupling gear.

[0022] The technical solution provided by this invention has the following beneficial effects:

[0023] 1. This invention eliminates the need for complex components such as push rods, crankshafts, high-pressure oil bearings, and high-pressure oil pumps found in existing technologies. This not only reduces overall costs but also transforms the linear reciprocating motion of the piston into rotary motion by using a push rod with a rack to drive the same rocker gear. This outputs rotational power to drive a rotary generator with stable power generation efficiency, thereby improving the conversion efficiency of mechanical energy into electrical energy. It also improves engine efficiency and can be used as a direct power source for driving HEV, PHEV, and REEV vehicles.

[0024] 2. The push rod of the present invention is arranged at the pressure center of the piston to ensure that the eccentric force generated by the push rod is very small and negligible, thereby reducing energy loss and improving engine efficiency.

[0025] 3. The lever arm of the push rod force of the present invention relative to the drive shaft is equal to the radius of the rocker gear. At the beginning of the power stroke, when the gas energy in the cylinder is at its maximum, the energy can be quickly transferred out, reducing leakage and heat loss, thereby improving engine efficiency. Attached Figure Description

[0026] Figure 1 The diagram shown is a schematic of a four-stroke free piston engine in the first stroke of Embodiment 1.

[0027] Figure 2 The diagram shown is a schematic of a four-stroke free piston engine in the second stroke of Embodiment 1.

[0028] Figure 3 The diagram shown is a schematic of a four-stroke free piston engine in the third stroke of Embodiment 1.

[0029] Figure 4 The diagram shown is a schematic of a four-stroke free piston engine in the fourth stroke of Embodiment 1.

[0030] Figure 5 The diagram shown is a connection diagram of the four-stroke free piston engine in Embodiment 1.

[0031] Figure 6 The diagram shown is a connection diagram of the four-stroke free piston engine in Embodiment 2;

[0032] Figure 7 The diagram shown is a connection diagram of the four-stroke free piston engine in Embodiment 3;

[0033] Figure 8 The diagram shown is a connection diagram of the four-stroke free piston engine in Embodiment 4. Detailed Implementation

[0034] To further illustrate the various embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention, primarily used to illustrate the embodiments and to explain the operating principles of the embodiments in conjunction with the relevant descriptions in the specification. With reference to these drawings, those skilled in the art should be able to understand other possible implementations and the advantages of the present invention. Components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0035] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] Reference Figure 1 and Figure 5As shown, this embodiment provides a four-stroke free piston engine (hereinafter referred to as a four-stroke engine). The four-stroke engine includes two sets of cylinders, each set of cylinders including two cylinders arranged opposite each other, and also includes a transmission assembly, such as... Figure 5 The transmission assembly shown includes a rocker gear 4, a first one-way clutch 5a, a second one-way clutch 5b, a first power output component, and a second power output component. The first power output component is engaged with the first one-way clutch 5a, and the second power output component is engaged with the second one-way clutch 5b. Both the first power output component and the second power output component are used to transmit engine torque. The rocker gear 4 is configured to rotate around a fixed axis, so that the rocker gear 4 can rock around its own axis.

[0038] The four cylinders are divided into two groups. The pistons of the two cylinders in each group are connected by a push rod. Each push rod is equipped with a rack, and the rocker gear 4 meshes with the racks on the two push rods.

[0039] Each cylinder completes the intake stroke, compression stroke, power stroke, and exhaust stroke in sequence. The system (i.e., a four-stroke engine) forms a working cycle every four strokes, and in each stroke, the piston of one cylinder is always doing power, and synchronously drives the other three cylinders to complete the intake stroke, compression stroke, and exhaust stroke respectively.

[0040] In this embodiment, the racks on the two push rods are single-sided racks and are arranged opposite to each other, and the rocker gear 4 is arranged between the racks of the two push rods.

[0041] The two sets of cylinders are located on the upper and lower sides of the rocker gear 4, respectively. The two cylinders in the upper cylinder set are the first cylinder 1a and the second cylinder 1b, which are spaced to the left and right. The two cylinders in the lower cylinder set are the third cylinder 1c and the fourth cylinder 1d, which are spaced to the left and right. Specifically, the first cylinder 1a, the second cylinder 1b, the third cylinder 1c, and the fourth cylinder 1d are all fixedly mounted on the housing of the four-stroke engine and are stationary.

[0042] The first cylinder 1a is equipped with a first piston 2a, the second cylinder 1b is equipped with a second piston 2b, the third cylinder 1c is equipped with a third piston 2c, and the fourth cylinder 1d is equipped with a fourth piston 2d. The two push rods are the first push rod and the second push rod, and the racks of the first push rod and the second push rod are the first rack 3a and the second rack 3b, respectively.

[0043] The first piston 2a and the second piston 2b are fixedly connected by the first push rod, so that the first piston 2a, the second piston 2b and the first push rod can move together in a left-right reciprocating linear motion. The third piston 2c and the fourth piston 2d are fixedly connected by the second push rod, so that the third piston 2c, the fourth piston 2d and the second push rod can move together in a left-right reciprocating linear motion. At this time, the first direction is defined as the horizontal rightward direction of the first push rod, the second direction is defined as the horizontal leftward direction of the first push rod, the first direction of rotation is the clockwise rotation direction, and the second direction of rotation is the counterclockwise rotation direction.

[0044] The specific working principle of the four-stroke engine in this embodiment is as follows, and includes the following: Figure 1 The first stroke shown, as Figure 2 The second stroke shown, as Figure 3 The third stroke shown and as Figure 4 The fourth stroke is shown.

[0045] The first stroke is as follows Figure 1 As shown, when the first cylinder 1a is in the intake stroke, the driving force comes from the third piston 2c of the third cylinder 1c, that is, the fuel in the third cylinder 1c burns and expands to do work, which is the power stroke; the high-pressure gas pushes the third piston 2c to the left, which in turn pushes the second push rod and the second rack 3b to the left, thereby driving the rocker gear 4 to rotate clockwise, which in turn drives the first push rod and the first rack 3a to move to the right. Simultaneously, the first push rod drives the first piston 2a to move to the right, the volume in the first cylinder 1a increases, and gas (such as air) is drawn in, which is the intake stroke; the first push rod pushes the second piston 2b to move to the right, expelling the exhaust gas in the second cylinder 1b, which is the exhaust stroke; the second push rod pushes the fourth piston 2d to the left, compressing the gas in the fourth cylinder 1d, which is the compression stroke.

[0046] In the first stroke, the first cylinder 1a is the intake stroke, the second cylinder 1b is the exhaust stroke, the third cylinder 1c is the power stroke, and the fourth cylinder 1d is the compression stroke. When the third cylinder 1c is doing power, the third piston 2c pushes the second rack 3b of the second push rod to move to the left, thereby driving the rocker gear 4 to rotate clockwise.

[0047] The second stroke is as follows Figure 2As shown, when the first cylinder 1a is in the compression stroke, the driving force comes from the fourth piston 2d of the fourth cylinder 1d, that is, the fuel in the fourth cylinder 1d burns and expands to do work, which is the power stroke; the high-pressure gas pushes the fourth piston 2d to the right, the fourth piston 2d pushes the second push rod and the second rack 3b to the right, which in turn drives the rocker gear 4 to rotate counterclockwise, which in turn drives the first push rod and the first rack 3a to the left. Simultaneously, the first push rod drives the first piston 2a to the left, compressing the gas in the first cylinder 1a, which is the compression stroke; the first push rod and the first rack 3a drive the second piston 2b to the left, the volume in the second cylinder 1b increases, and gas is drawn in, which is the intake stroke; the second push rod 3b drives the third piston 2c to the right, discharging the exhaust gas in the third cylinder 1c, which is the exhaust stroke.

[0048] In the second stroke, the first cylinder 1a is the compression stroke, the second cylinder 1b is the intake stroke, the third cylinder 1c is the exhaust stroke, and the fourth cylinder 1d is the power stroke. When the fourth cylinder 1d is performing power, the fourth piston 2d pushes the second rack 3b of the second push rod to move to the right, thereby driving the rocker gear 4 to rotate counterclockwise.

[0049] The third stroke, as Figure 3 As shown, when the first cylinder 1a is in the power stroke, the driving force comes from the first piston 2a of the first cylinder 1a, that is, the fuel in the first cylinder 1a burns and expands to do work, which is the power stroke. The high-pressure gas pushes the first piston 2a to the right, pushing the first push rod and the first rack 3a to the right, which in turn drives the rocker gear 4 to rotate clockwise, which in turn drives the second push rod and the second rack 3b to the left. Simultaneously, the first push rod drives the second piston 2b to the right, compressing the gas in the second cylinder 1b, which is the compression stroke; the second push rod 3b drives the third piston 2c to the left, increasing the volume in the third cylinder 1c and drawing in gas, which is the intake stroke; the second push rod 3b drives the fourth piston 2d to the left, expelling the exhaust gas in the fourth cylinder 1d, which is the exhaust stroke.

[0050] In the third stroke, the first cylinder 1a is the power stroke, the second cylinder 1b is the compression stroke, the third cylinder 1c is the intake stroke, and the fourth cylinder 1d is the exhaust stroke. When the first cylinder 1a is doing power, the first piston 2a pushes the first rack 3a of the first push rod to move to the right, thereby driving the rocker gear 4 to rotate clockwise.

[0051] The fourth stroke, as Figure 4As shown, when the first cylinder 1a is in the exhaust stroke, the driving force comes from the second piston 2b of the second cylinder 1b, that is, the fuel in the second cylinder 1b burns and expands to do work, which is the power stroke; the high-pressure gas pushes the second piston 2b to the left, the second piston 2b pushes the first push rod and its rack 3a to the left, driving the rocker gear 4 to rotate counterclockwise, which in turn drives the second push rod and its rack 3b to the right. Simultaneously, the first push rod drives the first piston 2a to the left, venting the exhaust gas in the first cylinder 1a, which is the exhaust stroke; the second push rod 3b drives the third piston 2c to the right, compressing the gas in the third cylinder 2c, which is the compression stroke; the second push rod 3b drives the fourth piston 2d to the right, increasing the volume in the second cylinder 1b and drawing in gas, which is the intake stroke.

[0052] In the fourth stroke, the first cylinder 1a is the exhaust stroke, the second cylinder 1b is the power stroke, the third cylinder 1c is the compression stroke, and the fourth cylinder 1d is the intake stroke. When the second cylinder 1b is doing power, the second piston 2b pushes the first push rod and its rack 3a to move to the left, thereby driving the rocker gear 4 to rotate counterclockwise.

[0053] In summary, a working cycle of a four-stroke piston engine consists of four strokes. In these four strokes, the first cylinder 1a sequentially performs intake, compression, power, and exhaust; the second cylinder 1b sequentially performs exhaust, intake, compression, and power; the third cylinder 1c sequentially performs power, exhaust, intake, and compression; and the fourth cylinder 1d sequentially performs compression, power, exhaust, and intake. In the first stroke, cylinder 1a is for intake, cylinder 1b is for exhaust, cylinder 1c is for power, and cylinder 1d is for compression; in the second stroke, cylinder 1a is for compression, cylinder 1b is for intake, cylinder 1c is for exhaust, and cylinder 1d is for power; in the third stroke, cylinder 1a is for power, cylinder 1b is for compression, cylinder 1c is for intake, and cylinder 1d is for exhaust; in the fourth stroke, cylinder 1a is for exhaust, cylinder 1b is for power, cylinder 1c is for compression, and cylinder 1d is for intake.

[0054] A piston engine completes one working cycle, consisting of four strokes, with the pushrod completing two reciprocating linear movements. Correspondingly, the rocker gear 4 completes two rocker rotations: in the first stroke, the piston drives the rocker gear 4 to rotate clockwise; in the second stroke, the piston drives the rocker gear 4 to rotate counterclockwise; in the third stroke, the piston drives the rocker gear 4 to rotate clockwise, and the behavior and function of the rocker gear 4 and its downstream components are the same as in the first stroke; in the fourth stroke, the piston drives the rocker gear 4 to rotate counterclockwise, and the behavior and function of the rocker gear 4 and its downstream components are the same as in the second stroke. Therefore, the working principles of the third and fourth strokes will not be described in detail.

[0055] The first stroke is the clockwise stroke of the rocker gear 4 rocking clockwise, and the second stroke corresponds to the counterclockwise stroke of the rocker gear 4 rocking counterclockwise. The rocker gear 4 first rotates clockwise, then counterclockwise, then clockwise again, and then counterclockwise again, repeating this back-and-forth rotation continuously.

[0056] The following describes how to convert the rocking rotation of the rocking gear 4 into a rotational motion with constant direction and alternating transmission and idling.

[0057] The locking directions of the first one-way clutch 5a and the second one-way clutch 5b are set to be opposite to each other. That is, when the rocker gear 4 rotates clockwise, the first one-way clutch 5a is locked and the second one-way clutch 5b is disengaged; when the rocker gear 4 rotates counterclockwise, the first one-way clutch 5a is disengaged and the second one-way clutch 5b is locked. In this way, regardless of whether the rocker gear 4 rotates clockwise or counterclockwise, there is always one power output component in transmission and the other power output component idling, so as to ensure that the two power output components alternately transmit torque and idle accordingly in each stroke stage of the four-stroke engine, and the rotation direction of each power output component remains unchanged.

[0058] When the rocker gear 4 rotates clockwise, the first one-way clutch 5a locks, and the rocker gear 4 drives the first power output component to rotate and transmit power through the first one-way clutch 5a. Next, when the rocker gear 4 rotates counterclockwise, the first one-way clutch 5a disengages, separating the counterclockwise rotating rocker gear 4 from the first power output component, allowing the first power output component to continue rotating without load and maintaining its rotation direction. Simultaneously, when the rocker gear 4 rotates clockwise, the second one-way clutch 5b disengages, separating the rocker gear 4 from the second power output component, allowing the second power output component to rotate without load and maintain its rotation direction. Next, when the rocker gear 4 rotates counterclockwise, the second one-way clutch 5b locks, and the rocker gear 4 drives the second power output component to rotate and transmit torque through the second one-way clutch 5b.

[0059] In summary, when the rocker gear 4 rotates clockwise, it drives the first output component to rotate and transmit power through the first one-way clutch 5a, while the second one-way clutch 5b disconnects the connection between the rocker gear 4 and the second output component, thus allowing the second output component to idle in its original direction. When the rocker gear 4 rotates counterclockwise, it outputs power through the second one-way clutch 5b and the second output component, while the first one-way clutch 5a disconnects the connection between the rocker gear 4 and the first output component, thus allowing the first output component to idle in its original direction.

[0060] In another preferred embodiment, such as Figure 5As shown, the rocker gear 4 is directly driven to the first power output component via the first one-way clutch 5a, and the rocker gear 4 is directly driven to the second power output component via the second one-way clutch 5b.

[0061] Of course, in other embodiments, the drive assembly consisting of the rocker gear 4, two push rods and two cylinder groups in this embodiment can be replaced with other drive components containing a driver to provide a power source; other transmission components can also be used to replace the rocker gear 4 in this embodiment to achieve a transmission connection.

[0062] More specifically, the four-stroke engine in this embodiment also includes a coupling mechanism, which includes a coupling gear 8 and a first transmission gear 10 and a second transmission gear 9 coaxially arranged; the first power output component includes a first output shaft 6a connected to a first one-way clutch 5a and a first gear 7a fixed to the first output shaft 6a; the second power output component includes a second output shaft 6b connected to a second one-way clutch 5b and a second gear 7b fixed to the second output shaft 6b; the first transmission gear 10 drives the first gear 7a connected to the first power output component through the coupling gear 8, and the second transmission gear 9 drives the second gear 7b connected to the second power output component, wherein the coupling gear 8 meshes with the first gear 7a of the first power output component, the coupling gear 8 meshes with the first transmission gear 10, the second transmission gear 9 meshes with the second gear 7b of the second power output component, and the second transmission gear 9 and the first transmission gear 10 are coaxially fixedly connected.

[0063] In the first stroke (i.e., the clockwise stroke), the rocker gear 4 rotates clockwise, the first one-way clutch 5a locks, and the rocker gear 4 drives the first output shaft 6a and the first gear 7a to rotate clockwise through the first one-way clutch 5a and outputs power; at the same time, the second one-way clutch 5b disengages, and the second output shaft 6b and the second gear 7b can rotate counterclockwise without restraint.

[0064] In the second stroke (i.e., the counterclockwise stroke), the rocker gear 4 rotates counterclockwise, the second one-way clutch 5b locks, and the rocker gear 4 drives the second output shaft 6b and the second gear 7b to rotate counterclockwise through the second one-way clutch 5b, and outputs power; at the same time, the first one-way clutch 5a disengages, and the first output shaft 6a and the first gear 7a can rotate clockwise without restraint.

[0065] In short, during the first stroke, the rocker gear 4 rotates clockwise, the first power output component rotates clockwise and drives the transmission, and the second power output component rotates counterclockwise and idles. During the second stroke, the rocker gear 4 rotates counterclockwise, the first power output component rotates clockwise and idles, and the second power output component rotates counterclockwise and drives the transmission.

[0066] The first power take-off component maintains a constant rotation direction (i.e., rotates clockwise), driving in the first stroke and idling in the second stroke; similarly, the second power take-off component maintains a constant rotation direction (i.e., rotates counterclockwise), idling in the first stroke and driving in the second stroke. The first and second power take-off components alternately drive and idle, with one output component driving and outputting power in each stroke of the engine.

[0067] The first and second power output components can be connected to loads (such as generators) respectively to output power.

[0068] To convert the rocking rotation of the rocker gear 4 into a motion with a constant rotation direction and alternating transmission and free rotation, two one-way clutches are used. When the rocker gear 4 rotates clockwise, the first one-way clutch 5a is locked, the first power output component is driven, and the second one-way clutch 5b is disengaged, allowing the second power output component to idle. When the rocker gear 4 rotates counterclockwise, the first one-way clutch 5a is disengaged, the first power output component is idle, and the second one-way clutch 5b is locked, allowing the second power output component to drive.

[0069] The rocker gear 4 can be directly connected to two one-way clutches, or it can be connected through several transmission components.

[0070] like Figure 5 As shown, the rocker gear 4 is directly connected to the first one-way clutch 5a and the second one-way clutch 5b; the rocker gear 4 drives the first power output component to rotate clockwise through the first one-way clutch 5a, and drives the second power output component to rotate counterclockwise through the second one-way clutch 5b.

[0071] Therefore, the first power output component can output power independently, with a constant rotation direction, alternating between transmission and idling; the second power output component can also output power independently, with a constant rotation direction, alternating between transmission and idling; and the transmission of the two power output components is complementary: one power output component is always in transmission while the other is idling. This embodiment has two power output components, each with a constant rotation direction, alternating between power output and idling (i.e., outputting intermittent torque). This can meet the needs of different drive systems, such as driving two generators to generate electricity as a range extender in a range-extended hybrid vehicle. However, vehicle engines typically have a single output shaft and output continuous and stable power. Therefore, it is necessary to design an engine with a single output shaft, as in this embodiment, that outputs continuous and uninterrupted power.

[0072] When the rocker gear 4 rotates clockwise, it drives the first power output component to rotate; when the rocker gear 4 rotates counterclockwise, it drives the second power output component to rotate. The direction of rotation can be adjusted by a coupling mechanism, which couples the two power output components together to form an output shaft.

[0073] The first output shaft 6a and the first gear 7a are fixedly connected and rotate in the same direction on the same axis. The first gear 7a meshes with the coupling gear 8 and rotates in opposite directions, as do the coupling gear 8 and the first transmission gear 10, which also rotate in opposite directions.

[0074] The second output shaft 6b and the second gear 7b are fixedly connected and rotate in the same direction on the same axis. The second gear 7b meshes with the first transmission gear 10, and they rotate in opposite directions.

[0075] The first transmission gear 10 and the second transmission gear 9 are coaxially fixedly connected to achieve rotation in the same direction.

[0076] In the first stroke (clockwise stroke), the rocker gear 4 rotates clockwise, the first one-way clutch 5a locks, and the rocker gear 4 drives the first output shaft 6a to rotate clockwise through the first one-way clutch 5a. The first gear 7a synchronously follows the first output shaft 6a clockwise. The first gear 7a drives the coupling gear 8 to rotate counterclockwise. The coupling gear 8 drives the first transmission gear 10 and the second transmission gear 9 to rotate clockwise together and transmit power. At the same time, the second one-way clutch 5b disengages, and the second output shaft 6b can rotate counterclockwise without restraint. That is, the second transmission gear 9 drives the second gear 7b and the second output shaft 6b to rotate counterclockwise.

[0077] In the second stroke (counterclockwise stroke), the rocker gear 4 rotates counterclockwise, the second one-way clutch 5b locks, and the rocker gear 4 drives the second output shaft 6b to rotate counterclockwise through the second one-way clutch 5b. The second gear 7b synchronously follows the second output shaft 6b in counterclockwise transmission. The second gear 7b drives the second transmission gear 9 and the first transmission gear 10 to rotate clockwise together and transmit power. At the same time, the first one-way clutch 5a disengages, and the first output shaft 6a can rotate clockwise without restraint. That is, the first transmission gear 10 drives the coupling gear 8 to rotate counterclockwise, and the coupling gear 8 drives the first gear 7a and the first output shaft 6a to rotate clockwise together.

[0078] As can be seen, in the first stroke, the rocker gear 4 rotates clockwise, and drives the shafts of the first transmission gear 10 and the second transmission gear 9 to rotate clockwise and transmit power through the first one-way clutch 5a, the first power output component and the coupling gear 8, and drives the second power output component to rotate counterclockwise through the second transmission gear 9; in the second stroke, the rocker gear 4 rotates counterclockwise, and drives the shafts of the second transmission gear 9 and the first transmission gear 10 to rotate clockwise and transmit power through the second one-way clutch 5b and the second power output component, and drives the first power output component to rotate clockwise through the first transmission gear 10 and the coupling gear 8.

[0079] Regardless of whether it rotates clockwise or counterclockwise, the rocker gear 4 always drives the shafts of the second transmission gear 9 and the first transmission gear 10 to rotate clockwise (through different paths). The common shaft of the second transmission gear 9 and the first transmission gear 10 can serve as the total output shaft to output power. In this way, the two separate power output components are coupled together by the coupling mechanism to form a single output shaft, outputting continuous and stable power or torque.

[0080] In one working cycle of the four-stroke engine of this embodiment, the four-stroke engine of this embodiment has a variable stroke and compression ratio. The variable compression ratio allows the use of different fuels to improve the flexibility and adaptability of the engine, and can also promote HCCI combustion to ensure higher thermal efficiency (i.e., thermal efficiency up to 60%). It can also improve the potential for SI-HCCI conversion through the variable compression ratio.

[0081] The four-stroke engine of this embodiment eliminates complex components such as pushrods, crankshafts, high-pressure oil bearings, and high-pressure oil pumps found in existing technologies. This not only reduces overall costs but also converts the linear reciprocating motion of the piston into rotary motion by using a pushrod with a rack to drive the same rocker gear 4. This outputs rotary power to drive a rotary generator with stable power generation efficiency, thereby improving the conversion efficiency of mechanical energy into electrical energy. It also improves engine efficiency and can be used as a direct power source for driving HEV, PHEV, and REEV vehicles.

[0082] In this embodiment, the push rod is positioned at the pressure center of the piston to ensure that the eccentric force generated by the push rod is very small and negligible, thereby reducing energy loss and improving engine efficiency.

[0083] Furthermore, in this embodiment, the four cylinders work together in a coordinated manner to achieve a sequential reciprocating cycle of four stroke stages. The two push rods are arranged in parallel, with only one rocker gear 4 positioned in the middle, meshing with the racks of the two push rods respectively, ensuring motion coupling between the two racks through the rocker gear 4. Compared to existing two-stroke engines, the four-stroke engine in this embodiment has exhaust and intake strokes to ensure high-quality exhaust and intake. The driving force generated by the power stroke drives the piston to compress and expel the exhaust gas, leaving very little residual exhaust gas. In the next stroke, the piston movement creates negative pressure inside the cylinder, drawing in air and improving scavenging efficiency. Additionally, fresh gas containing fuel is not short-circuited out, avoiding fuel loss, and a higher effective compression ratio can be achieved, making it more suitable for the HCCI combustion cycle, improving efficiency. It also allows for the use of existing four-stroke engine components, reducing manufacturing costs.

[0084] Of course, in other embodiments, if the transmission unit adopts a double rocker gear design, the two rocker gears need to withstand the huge thrust output by the piston during operation, and the load fluctuates greatly. The technical requirements for the gears, gear shafts, and bearings are high, and the cost is also high. Arranging two rocker gears between the two cylinders requires more space, and the stiffness of the push rod 3 needs to be enhanced. However, this embodiment uses a transmission unit with a single rocker gear, which can reduce costs, reduce size and weight, and improve design flexibility.

[0085] In this embodiment, the lever arm of the push rod force on the drive shaft is equal to the radius of the rocker gear 4. At the beginning of the power stroke, when the combustion energy in the cylinder is at its maximum, the energy can be quickly transferred out, reducing leakage and heat loss, thereby improving engine efficiency.

[0086] When the piston of a four-stroke engine is around top dead center, its acceleration is significantly higher, thereby reducing the residence time at high temperatures and reducing heat transfer losses during combustion. When the piston of a four-stroke engine is around bottom dead center, the pushrod lever arm does not decrease, and the output power decays less, so as to achieve small output power fluctuations.

[0087] In addition, compared with the existing four-stroke engines which have strong vibrations in the three axes of x, y and z, the four-stroke engine in this embodiment only has strong vibrations in one direction (i.e., the piston moves in the left and right directions), and the NVH (NVH includes noise, vibration and acoustic roughness) characteristics are significantly improved.

[0088] Example 2

[0089] like Figure 6 As shown, Embodiment 2 provides a four-stroke free piston engine. Embodiment 2 and Embodiment 1 have largely the same structure, except that: both the first power output component and the second power output component are output wheels; a first one-way clutch 5a is provided between the first power output component and the shaft of the rocker gear 4; and a second one-way clutch 5b is provided between the second power output component and the shaft of the rocker gear 4.

[0090] In this specific embodiment, the first power output component is the first gear 7a, and the second power output component is the second gear 7b.

[0091] The rocker gear 4 is connected to the first one-way clutch 5a and the second one-way clutch 5b via its own shaft; the rocker gear 4 drives the first power output component to rotate clockwise via its own shaft and the first one-way clutch 5a, and drives the second power output component to rotate counterclockwise via its own shaft and the second one-way clutch 5b.

[0092] The first one-way clutch 5a is arranged between the shaft of the rocker gear 4 and the first gear 7a, and the second one-way clutch 5b is arranged between the shaft of the rocker gear 4 and the second gear 7b. The first gear 7a meshes with the coupling gear 8 and rotates in opposite directions. The coupling gear 8 meshes with the first transmission gear 10 and rotates in opposite directions. The second gear 7b meshes with the first transmission gear 10 and rotates in opposite directions.

[0093] First stroke: The rocker gear 4 rotates clockwise, the first one-way clutch 5a locks, the rocker gear 4 drives the first gear 7a to rotate clockwise through the first one-way clutch 5a, the first gear 7a drives the coupling gear 8 to rotate counterclockwise and transmit power, the coupling gear 8 drives the first transmission gear 10 and the first transmission gear 10 together to rotate clockwise and transmit power. At the same time, the second one-way clutch 5b disengages. Since the second gear 7b can rotate freely without restraint, the first transmission gear 10 can drive the second gear 7b to rotate counterclockwise.

[0094] Second stroke: The rocker gear 4 rotates counterclockwise, the second one-way clutch 5b locks, and the rocker gear 4 drives the second gear 7b to rotate counterclockwise through the second one-way clutch 5b. The second gear 7b drives the first transmission gear 10 and the first transmission gear 10 to rotate clockwise together and transmit power. At this time, the first transmission gear 10 drives the coupling gear 8 to rotate counterclockwise. At the same time, the first one-way clutch 5a disengages. Since the first gear 7a can rotate freely without restraint, the coupling gear 8 can drive the first gear 7a to rotate clockwise freely.

[0095] In summary, during the first stroke: the rocker gear 4 rotates clockwise, and through the first one-way clutch 5a, the first power output component, and the coupling gear 8, drives the shafts of the first transmission gear 10 and the second transmission gear 9 to rotate clockwise and transmit power, while the second transmission gear 9 drives the second power output component to rotate counterclockwise. During the second stroke: the rocker gear 4 rotates counterclockwise, and through the second one-way clutch 5b and the second power output component, drives the shafts of the second transmission gear 9 and the first transmission gear 10 to rotate clockwise and transmit power, while the first transmission gear 10 and the coupling gear 8 drive the first power output component to rotate clockwise.

[0096] Regardless of whether it rotates clockwise or counterclockwise, the rocker gear 4 always drives the shafts of the second transmission gear 9 and the first transmission gear 10 to rotate clockwise (through different paths). The common shaft of the second transmission gear 9 and the first transmission gear 10 can serve as the total output shaft to output power. In this way, the two separate power output components are coupled together by the coupling mechanism to form a single output shaft, outputting continuous and stable power or torque.

[0097] Example 3

[0098] like Figure 7As shown, Embodiment 3 provides a four-stroke free piston engine. The structure of Embodiment 3 is generally the same as that of Embodiment 1, except that the transmission assembly further includes a transmission gear set; the shaft of the rocker gear 4 is fixedly connected to the transmission gear set, and the transmission gear set is driven to connect to the first power output component through the first one-way clutch 5a, and driven to connect to the second power output component through the second one-way clutch 5b, thereby forming an indirect drive configuration.

[0099] In this specific embodiment, the first power output component includes a first output shaft 6a connected to the first one-way clutch 5a and a first gear 7a fixed to the first output shaft 6a; the second power output component includes a second output shaft 6b connected to the second one-way clutch 5b and a second gear 7b fixed to the second output shaft 6b, and the first gear 7a and the second gear 7b mesh with each other.

[0100] The transmission gear set includes transmission gear A, transmission gear B and transmission gear C, wherein transmission gear A is fixed on the shaft of rocker gear 4, and transmission gear B and transmission gear C are respectively meshed with transmission gear A.

[0101] The rocker gear 4 is connected to the first one-way clutch 5a via transmission gear A and transmission gear B, and is also connected to the second one-way clutch 5b via transmission gear A and transmission gear C. The rocker gear 4 drives the first power output component to rotate counterclockwise via transmission gear A, transmission gear B and the first one-way clutch 5a, and drives the second power output component to rotate clockwise via transmission gear A, transmission gear C and the second one-way clutch 5b.

[0102] The rocker gear 4 is driven to connect with the first output shaft 6a through the transmission gear A, the transmission gear B and the first one-way clutch 5a to form the first torque transmission route of indirect drive.

[0103] The rocker gear 4 is driven to connect with the second output shaft 6b via the transmission gear A, the transmission gear C, and the second one-way clutch 5b, to form a second torque transmission route for indirect drive.

[0104] First stroke: The rocker gear 4 and the transmission gear A rotate clockwise together. The transmission gear A drives the transmission gears B and C to rotate counterclockwise simultaneously. The first one-way clutch 5a is locked. The transmission gear B drives the first output shaft 6a and the first gear 7a to rotate counterclockwise through the first one-way clutch 5a. At the same time, the second one-way clutch 5b is disengaged. Since the second output shaft 6b and the second gear 7b can rotate freely without restraint, the first gear 7a drives the second gear 7b and the second output shaft 6b to rotate clockwise freely.

[0105] Second stroke: The rocker gear 4 and the transmission gear A rotate counterclockwise together. The transmission gear A drives the transmission gears B and C to rotate clockwise simultaneously. The second one-way clutch 5b is locked. The transmission gear C drives the second output shaft 6b and the second gear 7b to rotate clockwise through the second one-way clutch 5b. At the same time, the first one-way clutch 5a is disengaged. Since the first output shaft 6a and the first gear 7a can rotate freely without restraint, the second gear 7b drives the first gear 7a and the first output shaft 6a to rotate counterclockwise.

[0106] In summary, during the first stroke: the rocker gear 4 rotates clockwise, and through transmission gear A, transmission gear B and the first one-way clutch 5a, drives the first power output component to rotate counterclockwise and transmit power; during the second stroke: the rocker gear 4 rotates counterclockwise, and through transmission gear A, transmission gear C and the second one-way clutch 5b, drives the second power output component to rotate clockwise, which in turn drives the first power output component to rotate counterclockwise and transmit power; the first power output component serves as the main output shaft.

[0107] Regardless of whether it rotates clockwise or counterclockwise, the rocker gear 4 always drives the second power output component to rotate clockwise (through different paths), and the second power output component can act as the main output shaft to output power. In this way, the two separate output components are coupled together by the coupling mechanism to form a single output shaft, outputting continuous and stable power or torque.

[0108] Example 4

[0109] like Figure 8 As shown, Embodiment 4 provides a four-stroke free piston engine. The structure of Embodiment 4 is largely the same as that of Embodiment 1, except that the coupling mechanism further includes a transmission gear set. The first power output component is a first gear 7a, and the shaft of the rocker gear 4 is directly driven to the first gear 7a through a first one-way clutch 5a. The second power output component includes a second output shaft 6b connected to a second one-way clutch 5b and a second gear 7b fixed to the second output shaft 6b. The transmission gear set is driven to the second output shaft 6b through the second one-way clutch 5b. The first gear 7a is driven to the second gear 7b through a coupling gear 8.

[0110] The transmission gear set includes a transmission gear D and a transmission gear E, wherein the transmission gear D is fixed on the shaft of the rocker gear 4.

[0111] The rocker gear 4 is connected to the first one-way clutch 5a via its own shaft, and to the second one-way clutch 5b via transmission gears D and E. The rocker gear 4 drives the first power output component to rotate clockwise via its own shaft and the first one-way clutch 5a, and drives the second power output component to rotate clockwise via transmission gears D, E and the second one-way clutch 5b.

[0112] The second output shaft 6b and the second gear 7b are coaxially fixedly connected, and the first gear 7a and the second output wheel 7a mesh through the coupling gear 8 to achieve power coupling.

[0113] First stroke: The rocker gear 4 and the transmission gear D rotate clockwise together. The transmission gear D drives the transmission gear E to rotate counterclockwise. The first one-way clutch 5a is locked. The rocker gear 4 drives the first gear 7a to rotate clockwise through the first one-way clutch 5a. The first gear 7a drives the coupling gear 8 to rotate counterclockwise and transmits power. At the same time, the second one-way clutch 5b is disengaged. Since the second output shaft 6b and the second gear 7b can rotate freely without restraint, the coupling gear 8 drives the second gear 7b and the second output shaft 6b to rotate clockwise.

[0114] It can be seen that the torque transmission route of the first stroke is as follows: the rocker gear 4, the first gear 7a and the coupling gear 8 transmit power in sequence.

[0115] Second stroke: The rocker gear 4 and the transmission gear D rotate counterclockwise together. The transmission gear D drives the transmission gear E to rotate clockwise. The second one-way clutch 5b is locked. The transmission gear E drives the second output shaft 6b and the second gear 7b to rotate clockwise through the second one-way clutch 5b. The second gear 7b drives the coupling gear 8 to rotate counterclockwise and transmit power. At the same time, the first one-way clutch 5a is disengaged. Since the first gear 7a can rotate freely without restraint, the coupling gear 8 drives the first gear 7a to rotate clockwise.

[0116] It can be seen that the torque transmission route of the second stroke is as follows: the rocker gear 4, the transmission gear D, the transmission gear E, the second output shaft 6b, the second gear 7b and the coupling gear 8 transmit power in sequence.

[0117] When the four-stroke engine is working, the four cylinders work in sequence to make the piston and push rod of the cylinder move back and forth and complete one working cycle. In each working cycle, the coupling gear 8 rotates counterclockwise continuously to output power.

[0118] In summary, during the first stroke, the rocker gear 4 rotates clockwise and drives the second power output component to rotate clockwise via its own shaft, the first one-way clutch 5a, the first power output component, and the coupling gear 8; during the second stroke, the rocker gear 4 rotates counterclockwise and drives the second power output component to rotate clockwise via its own shaft, the transmission gear D, the transmission gear E, and the second one-way clutch 5b; the second power output component outputs power or torque as the main output shaft.

[0119] Regardless of whether it rotates clockwise or counterclockwise, the rocker gear 4 always drives the second power output component to rotate clockwise (through different paths), and the second power output component can act as the main output shaft to output power. In this way, the two separate power output components are coupled together by the coupling mechanism to form a single output shaft, outputting continuous and stable power or torque.

[0120] Example 5

[0121] Example 5 provides a four-stroke free piston engine. The structure of Example 5 is generally the same as that of Example 1, except that the two push rods are integrally connected and move synchronously in the same direction. The racks on the two push rods are set on the same side, and the same rocker gear meshes with the racks on the two push rods at the same time.

[0122] In this embodiment, two push rods are integrally connected to form a single push rod, and then connected one by one by two rack gears to form a new rack on the integral push rod. The new rack and the rocker gear are arranged on the same side of the two push rods, and the rocker gear meshes with the new rack. In this way, it can be achieved that the piston of one cylinder is always doing work, and simultaneously driving the other three cylinders to complete the intake stroke, compression stroke and exhaust stroke respectively.

[0123] Of course, in other embodiments, the gears of the two racks can also be independent of each other, and the gear of the same rocker gear is wider to overcome the gap between the two racks, thereby ensuring that the rocker gear meshes with the two racks at the same time.

[0124] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A four-stroke free-piston engine, comprising two sets of cylinders, each set of cylinders including two opposing cylinders, the pistons of the two cylinders in each set being connected by a push rod, the two push rods being respectively provided with racks, characterized in that: It also includes transmission components; The transmission assembly includes a rocker gear, a first one-way clutch, a second one-way clutch, a first power output component, and a second power output component. The rocker gear meshes with racks on two push rods. The rocker gear is connected to the first one-way clutch. The first power output component is engaged with the first one-way clutch. The rocker gear is connected to the second one-way clutch. The second power output component is engaged with the second one-way clutch. The rocker gear is configured to rotate around a fixed axis. Each cylinder sequentially completes the intake stroke, compression stroke, power stroke, and exhaust stroke; the system forms a working cycle every four strokes, and in each stroke, the piston of one cylinder is always doing work, and simultaneously drives the other three cylinders to complete the intake stroke, compression stroke, and exhaust stroke through the joint cooperation of the push rod, the rack, and the rocker gear. In the first stroke, only one power piston drives the rocker gear to rotate in the first direction via the rack of the push rod; In the second stroke, only one power piston drives the rocker gear to rotate in a second direction opposite to the first direction via the rack of the push rod; In the third stroke, only one power piston drives the rocker gear to rotate in the first direction via the rack of the push rod; in the fourth stroke, only one power piston drives the rocker gear to rotate in the second direction via the rack of the push rod. When the rocker gear rotates in the first direction, the first one-way clutch engages, the rocker gear transmits torque and outputs power through the first power output component, and simultaneously the second one-way clutch disengages, and the second power output component idles in the same direction as the rotation direction of the previous stroke. When the rocker gear rotates in the second direction, the first one-way clutch disengages, the first power output component rotates freely in the same direction as the rotation direction of the previous stroke, and the second one-way clutch engages synchronously. The rocker gear transmits torque and outputs power through the second power output component.

2. The four-stroke free piston engine according to claim 1, characterized in that: It also includes a coupling mechanism; the first power output component and the second power output component are coupled through the coupling mechanism to output continuous power.

3. The four-stroke free-piston engine according to claim 1, characterized in that: One cylinder in one group generates a driving force during its power stroke to push its piston in a first direction; and through the transmission assembly, it drives the piston of another cylinder in the same group to move in the first direction to achieve the compression stroke, simultaneously driving the pistons of the third and fourth cylinders in another group to move in a second direction opposite to the first direction, so that the third and fourth cylinders in the other group complete the intake stroke and the exhaust stroke respectively; or it drives the piston of another cylinder in the same group to move in the first direction to achieve the exhaust stroke, simultaneously driving the pistons of the third and fourth cylinders in another group to move in a second direction opposite to the first direction, so that the third and fourth cylinders in the other group complete the intake stroke and the compression stroke respectively.

4. The four-stroke free-piston engine according to claim 1, characterized in that: The racks of the two push rods are single-sided racks and are arranged opposite to each other; the rocker gear is arranged between the racks of the two push rods.

5. The four-stroke free-piston engine according to claim 1, characterized in that: The two push rods are connected as a single unit and move synchronously in the same direction; the racks on the two push rods are located on the same side, and the rocker gear meshes with the racks on both push rods simultaneously.

6. The four-stroke free-piston engine according to claim 5, characterized in that: The gears of the two racks are connected one to one; or the gears of the two racks are independent of each other.

7. The four-stroke free-piston engine according to claim 2, characterized in that: The rocker gear is directly driven to the first power output component via the first one-way clutch, and the rocker gear is directly driven to the second power output component via the second one-way clutch.

8. The four-stroke free-piston engine according to claim 7, characterized in that: The first power output component includes a first output shaft connected to the first one-way clutch and a first gear fixed to the first output shaft; the second power output component includes a second output shaft connected to the second one-way clutch and a second gear fixed to the second output shaft.

9. The four-stroke free-piston engine according to claim 8, characterized in that: The coupling mechanism includes a coupling gear and a first transmission gear and a second transmission gear arranged coaxially. The first transmission gear is driven to connect to the first gear through the coupling gear, and the second transmission gear is driven to connect to the second gear.

10. The four-stroke free-piston engine according to claim 2, characterized in that: Both the first power output component and the second power output component are gears. A first one-way clutch is provided between the shaft of the first power output component and the shaft of the rocker gear, and a second one-way clutch is provided between the shaft of the second power output component and the shaft of the rocker gear.

11. The four-stroke free-piston engine according to claim 10, characterized in that: The coupling mechanism includes a coupling gear and a first transmission gear and a second transmission gear arranged coaxially. The first transmission gear is driven to connect to the first power output component through the coupling gear, and the second transmission gear is driven to connect to the second power output component.

12. The four-stroke free piston engine according to claim 2, characterized in that: The transmission assembly includes a transmission gear set; the shaft of the rocker gear is fixedly connected to the transmission gear set, and the transmission gear set is driven to the first power output component through the first one-way clutch and driven to the second power output component through the second one-way clutch, thereby forming an indirect drive configuration.

13. The four-stroke free-piston engine according to claim 12, characterized in that: The first power output component includes a first output shaft connected to the first one-way clutch and a first gear fixed to the first output shaft; the second power output component includes a second output shaft connected to the second one-way clutch and a second gear fixed to the second output shaft, wherein the first gear and the second gear mesh.

14. The four-stroke free-piston engine according to claim 2, characterized in that: The coupling mechanism includes a coupling gear and a transmission gear set. The shaft of the rocking gear is fixedly connected to the transmission gear set. The first power output component is a first gear. The shaft of the rocking gear is directly driven to the first gear through the first one-way clutch. The second power output component includes a second output shaft connected to the second one-way clutch and a second gear fixed to the second output shaft. The transmission gear set is driven to the second output shaft through the second one-way clutch. The first gear is driven to the second gear through the coupling gear.

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