Four-stroke free piston engine

Abstract

The utility model discloses a four-stroke free piston engine which comprises two groups of air cylinders which are oppositely arranged, and further comprises a swing gear, a first one-way clutch, a second one-way clutch, a first power output piece and a second power output piece, the swing gear is arranged in a fixed-axis rotating mode, and pistons of the two air cylinders in each group are connected through a push rod. The swing gear is meshed with racks on the two push rods, each air cylinder sequentially completes an air inlet stroke, a compression stroke, an acting stroke and an exhaust stroke, the four strokes form a working cycle, a piston of one air cylinder does work all the time, and the other three air cylinders are synchronously driven to complete the air inlet stroke, the compression stroke and the exhaust stroke respectively. In this way, complex parts such as a push rod, a crankshaft, a high-pressure oil bearing and a high-pressure oil pump in the prior art can be omitted, linear reciprocating motion of the piston is converted into rotating motion so as to output power in the rotating form, meanwhile, the efficiency of the engine is improved, and the engine is suitable for being used as an engine of vehicles such as HEV, PHEV and REEV.

Description

Technical Field

[0001] The utility model relates to the technical field of engines, in particular to a four-stroke free piston engine. Background Art

[0002] Hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) and range-extended electric vehicles (REEV) are the main technical routes for energy-saving and new energy vehicles. What the three 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 to the push rod through the piston, and the push rod is then transmitted to the crankshaft through the crank, which is then converted into rotational motion and output power. Due to the limitations of the push rod and crankshaft, the stroke of the piston is fixed, so it is impossible to adjust and optimize the compression ratio according to power requirements, and the thermal efficiency of the system is limited. In addition, when doing work, the push rod will exert a reaction force, and its lateral component will press the piston tightly against the cylinder wall, greatly increasing friction and increasing energy loss. And subject to the constraints of the working mode, most piston engines are two-stroke engines, including compression stroke and power stroke, and the compressed mixed gas in the cylinder is ignited at the end of the compression stroke (top dead center), and scavenging and ventilation are performed at the end of the power stroke (bottom dead center) to discharge exhaust gas and fill in air and gas, but the scavenging time is very short, and the air needs to be pressurized to forcibly discharge the exhaust gas in the cylinder; or during the gas exchange process, part of the exhaust gas will be retained in the cylinder, and some fresh air will easily be entrained in the exhaust flow. This situation is called short-circuit loss, which will also affect the efficiency of the entire power system.

[0004] At the beginning of the power stroke, the pressure in the cylinder is maximum, but the crank is near top dead center, and the push rod's moment arm on the crankshaft is small, resulting in less torque and, consequently, less power output. Simultaneously, the energy contained in the high-temperature, high-pressure gas is released more slowly, increasing energy losses due to gas leakage and heat loss. Near the end of the power stroke, the crank is near bottom dead center, and the push rod's moment arm on the crankshaft is smaller. Consequently, the pressure in the cylinder is lower, resulting in less power output. This reduces the engine's power density and increases power output fluctuations.

[0005] Furthermore, the loads between the pushrod and crankshaft, and between the crankshaft and the housing, are high, resulting in significant friction losses. These bearings require high-pressure oil bearings, which in turn require a high-pressure oil source and a high-pressure oil pump. This consumes additional energy to operate the high-pressure oil pump, reducing the engine's output power and efficiency. The high-pressure oil bearings of the pushrod and crank are both mobile, requiring complex high-pressure oil circuits to deliver the high-pressure lubricating oil to the bearings. These circuits must pass through moving parts such as the crankshaft, crank, and pushrod, making the manufacturing of these components more difficult and costly. Summary of the Invention

[0006] To this end, in order to solve the above-mentioned problems, the present invention provides a four-stroke free-piston engine that can eliminate complex components such as push rods, crankshafts, high-pressure oil bearings and high-pressure oil pumps in the prior art, and convert the linear reciprocating motion of the piston into rotational motion to output power in a rotational form, while improving engine efficiency and being suitable as an engine for vehicles such as HEVs, PHEVs and REEVs.

[0007] To achieve the above purpose, the technical solutions provided by the present invention are as follows:

[0008] The utility model provides a four-stroke free-piston engine, comprising two groups of cylinders, each group of cylinders comprising two cylinders arranged opposite to each other, the pistons of the two cylinders of each group being connected by a push rod, the two push rods being respectively provided with racks, and also comprising a transmission assembly; the transmission assembly comprising a swing gear, a first one-way clutch, a second one-way clutch, a first power output member and a second power output member, the swing gear being meshed with the racks on the two push rods, the swing gear being connected to the first one-way clutch, the first power output member being matched with the first one-way clutch, the swing gear being connected to the second one-way clutch, and the second power output member being matched with the second one-way clutch; the swing gear being arranged for fixed-axis rotation; each cylinder sequentially completes an intake stroke, a compression stroke, a power stroke and an exhaust stroke; every four strokes of the system form a working cycle, and in each stroke there is always a piston of a cylinder doing work, and synchronously drives the other three cylinders to respectively complete an intake stroke, a compression stroke and an exhaust stroke through the cooperation of the push rod, the rack and the swing gear. During the first stroke, only one working piston drives the rocking gear to rotate toward the first direction through the rack of the push rod; during the second stroke, only one working piston drives the rocking gear to rotate toward the second direction opposite to the first direction through the rack of the push rod; during the third stroke, only one working piston drives the rocking gear to rotate toward the first direction through the rack of the push rod; during the fourth stroke, only one working piston drives the rocking gear to rotate toward the second direction through the rack of the push rod; when the rocking gear rotates in the first direction, the first one-way clutch is engaged, the rocking gear transmits torque and outputs power through the first power output member, and the second one-way clutch is disengaged synchronously, and the second power output member idles in the same direction as the rotation direction of the previous stroke; when the rocking gear rotates in the second direction, the first one-way clutch is disengaged, the first power output member idles in the same direction as the rotation direction of the previous stroke, and the second one-way clutch is locked synchronously, and the rocking gear transmits torque and outputs power through the second power output member.

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

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

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

[0012] Furthermore, the two push rods are connected as one body and move synchronously in the same direction; the racks on the two push rods are arranged on the same side, and the rocking gear is engaged with the racks of the two push rods at the same time.

[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 swing gear is directly driven to connect to the first power output member via the first one-way clutch, and the swing gear is directly driven to connect to the second power output member via the second one-way clutch.

[0015] Furthermore, the first power output member 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 member 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 that are coaxially arranged. The first transmission gear is driven and connected to the first gear through the coupling gear, and the second transmission gear is driven and connected to the second gear.

[0017] In one embodiment, the first power output member and the second power output member are both output wheels, the first one-way clutch is provided between the first power output member and the shaft of the rocking gear, and the second one-way clutch is provided between the second power output member and the shaft of the rocking 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 and connected to the first power output member through the coupling gear, and the second transmission gear is driven and connected to the second power output member.

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

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

[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 member is a first gear, and the shaft of the rocking gear is directly driven and connected to the first gear through the first one-way clutch; the second power output member includes a second output shaft connected to the second one-way clutch and a second gear fixed on the second output shaft, and the transmission gear set is driven and connected to the second output shaft through the second one-way clutch; the first gear is driven and connected to the second gear through the coupling gear.

[0022] The technical solution provided by the utility model has the following beneficial effects:

[0023] 1. The present invention can eliminate complex components such as the push rod, crankshaft, high-pressure oil bearing and high-pressure oil pump in the prior art, which not only reduces the overall cost, but also realizes the conversion of the linear reciprocating motion of the piston into rotational motion by driving the push rod provided with a rack to drive the same rocking gear to rotate, so as to output power in the form of rotation, which is used to drive a rotating generator with stable power generation efficiency, thereby improving the conversion efficiency of mechanical energy into electrical energy, and at the same time improving the engine efficiency. It can also be used as a direct power for driving vehicles such as HEVs, PHEVs and REEVs.

[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 force arm of the push rod acting on the transmission shaft of the utility model is equal to the radius of the rocking gear. At the beginning of the power stroke, when the energy of the gas in the cylinder is maximum, the energy can be quickly transferred out, reducing leakage and heat loss, thereby improving engine efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Shown is a schematic diagram of a four-stroke free piston engine in the first stroke in Example 1;

[0027] Figure 2 Shown is a schematic diagram of a four-stroke free piston engine in the second stroke in Example 1;

[0028] Figure 3 Shown is a schematic diagram of a four-stroke free piston engine in the third stroke in Example 1;

[0029] Figure 4 Shown is a schematic diagram of a four-stroke free piston engine in the fourth stroke in Example 1;

[0030] Figure 5 Shown is a connection diagram of a four-stroke free piston engine in Example 1;

[0031] Figure 6 Shown is a connection diagram of a four-stroke free piston engine in Example 2;

[0032] Figure 7 Shown is a connection diagram of a four-stroke free piston engine in embodiment three;

[0033] Figure 8 Shown is a connection diagram of a four-stroke free piston engine in Example 4. DETAILED DESCRIPTION

[0034] To further illustrate various embodiments, the present invention is provided with accompanying drawings. These drawings form part of the disclosure of this invention and are primarily used to illustrate the embodiments and, in conjunction with the relevant description in the specification, to explain the operating principles of the embodiments. By referring to these drawings, those skilled in the art will understand other possible implementations and the advantages of this invention. The components in the figures are not drawn to scale, and similar reference numerals are generally used to represent similar components.

[0035] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[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), which includes two groups of cylinders, each group of cylinders including two cylinders arranged opposite to each other, and also includes a transmission assembly, such as Figure 5 The transmission assembly shown includes a swing gear 4, a first one-way clutch 5a, a second one-way clutch 5b, a first power output member and a second power output member, wherein the first power output member is matched with the first one-way clutch 5a, and the second power output member is matched with the second one-way clutch 5b; the first power output member and the second power output member are both used to transmit engine torque, and the swing gear 4 is set to rotate on a fixed axis so that the swing gear 4 can swing 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. The two push rods are respectively provided with racks, and the rocking gear 4 is meshed 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, there is always a cylinder's piston doing work and synchronously driving 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 rocking gear 4 is arranged between the racks of the two push rods.

[0041] The two groups of cylinders are respectively on the upper and lower sides of the swing gear 4. The two cylinders of the cylinder group on the upper side are the first cylinder 1a and the second cylinder 1b, which are spaced left and right respectively. The two cylinders of the cylinder group on the lower side are the third cylinder 1c and the fourth cylinder 1d, which are spaced left and right respectively. Specifically, the first cylinder 1a, the second cylinder 1b, the third cylinder 1c and the fourth cylinder 1d are all fixedly assembled on the casing of the four-stroke engine and are stationary.

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

[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 make a left and right reciprocating linear motion together. 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 make a left and right reciprocating linear motion together. At this time, the first direction is defined as the horizontal right direction of the first push rod, the second direction is the horizontal left direction of the first push rod, the first turn is the clockwise rotation direction, and the second turn is the counterclockwise rotation direction.

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

[0045] The first stroke 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 produce work. This is the power stroke. The high-pressure gas pushes the third piston 2c leftward, which in turn pushes the second push rod and the second rack 3b leftward, driving the rocking gear 4 clockwise, which in turn drives the first push rod and the first rack 3a rightward. Simultaneously, the first push rod drives the first piston 2a rightward, increasing the volume of the first cylinder 1a and drawing in gas (such as air). This is the intake stroke. The first push rod pushes the second piston 2b rightward, expelling the exhaust gas in the second cylinder 1b. This is the exhaust stroke. The second push rod pushes the fourth piston 2d leftward, compressing the gas in the fourth cylinder 1d. This 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 working, the third piston 2c pushes the second rack 3b of the second push rod to move left, thereby driving the rocking gear 4 to rotate clockwise.

[0047] The second stroke 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 produce work. This is the power stroke. The high-pressure gas pushes the fourth piston 2d to the right, which in turn pushes the second push rod and second rack 3b to the right, driving the rocking gear 4 to rotate counterclockwise, which in turn drives the first push rod and 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. This is the compression stroke. The first push rod and first rack 3a drive the second piston 2b to the left, increasing the volume of the second cylinder 1b and drawing gas in. This 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. This is the exhaust stroke.

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

[0049] The third stroke 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 produce work. This 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. This in turn drives the rocking 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. This is the compression stroke. The second push rod 3b drives the third piston 2c to the left, increasing the volume of the third cylinder 1c and drawing gas in. This 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. This is the exhaust stroke.

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

[0051] The fourth stroke Figure 4As shown, when first cylinder 1a is in the exhaust stroke, the driving force comes from second piston 2b in second cylinder 1b. The fuel in second cylinder 1b burns and expands, producing work (this is the power stroke). High-pressure gas pushes second piston 2b leftward, which in turn pushes first push rod and its rack 3a leftward, driving rocking gear 4 counterclockwise, which in turn drives second push rod and its rack 3b rightward. Simultaneously, the first push rod drives first piston 2a leftward, venting exhaust gas from first cylinder 1a (this is the exhaust stroke). Second push rod 3b drives third piston 2c rightward, compressing the gas in third cylinder 2c (this is the compression stroke). Second push rod 3b drives fourth piston 2d rightward, increasing the volume of second cylinder 1b and drawing gas in (this is the intake stroke).

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

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

[0054] The piston engine completes one working cycle, four strokes, and the push rod completes two round-trip linear motions. Accordingly, rocking gear 4 completes two rocking rotations: in the first stroke, the piston drives rocking gear 4 clockwise; in the second stroke, the piston drives rocking gear 4 counterclockwise; in the third stroke, the piston drives rocking gear 4 clockwise, and the behavior and function of rocking gear 4 and its downstream components are the same as in the first stroke; in the fourth stroke, the piston drives rocking gear 4 counterclockwise, and the behavior and function of rocking 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 detailed here.

[0055] The first stroke is a clockwise stroke in which the swing gear 4 swings clockwise, and the second stroke corresponds to a counterclockwise stroke in which the swing gear 4 swings counterclockwise. The swing gear 4 first rotates clockwise, then counterclockwise, then clockwise again, and then counterclockwise again, and so on, repeatedly and continuously swings back and forth.

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

[0057] The first one-way clutch 5a and the second one-way clutch 5b are arranged to engage in opposite directions. That is, when the swing gear 4 rotates clockwise, the first one-way clutch 5a engages and the second one-way clutch 5b disengages. When the swing gear 4 rotates counterclockwise, the first one-way clutch 5a disengages and the second one-way clutch 5b engages. In this way, regardless of whether the swing gear 4 rotates clockwise or counterclockwise, one power output member is always transmitting torque while the other is idling. This ensures that the two power output members alternately transmit torque and idle during each stroke of the four-stroke engine, and that the rotational direction of each power output member remains unchanged.

[0058] When the swing gear 4 rotates clockwise, the first one-way clutch 5a locks, and the swing gear 4 drives the first power output member to rotate and transmit torque via the first one-way clutch 5a. Next, when the swing gear 4 rotates counterclockwise, the first one-way clutch 5a disengages, separating the swing gear 4, which has reversed counterclockwise, from the first power output member. The first power output member can continue to rotate without load and its rotation direction remains unchanged. Simultaneously, when the swing gear 4 rotates clockwise, the second one-way clutch 5b disengages, separating the swing gear 4 from the second power output member. The second power output member rotates without load and its rotation direction remains unchanged. Next, when the swing gear 4 rotates counterclockwise, the second one-way clutch 5b locks, and the swing gear 4 drives the second power output member to rotate and transmit torque via the second one-way clutch 5b.

[0059] In short, when the swing gear 4 rotates clockwise, the swing gear 4 drives the first output member to rotate and transmit through the first one-way clutch 5a, and at the same time the second one-way clutch 5b cuts off the connection between the swing gear 4 and the second output member, so that the second output member can idle along the original direction; when the swing gear 4 rotates counterclockwise, the swing gear 4 outputs power through the second one-way clutch 5b and the second output member, and at the same time the first one-way clutch 5a cuts off the connection between the swing gear 4 and the first output member, so that the first output member can idle along the original direction.

[0060] In another preferred embodiment, Figure 5As shown, the swing gear 4 is directly driven to connect to the first power output member through the first one-way clutch 5a, and the swing gear 4 is directly driven to connect to the second power output member through the second one-way clutch 5b.

[0061] Of course, in other embodiments, other drive components including a driver may be used to replace the drive component consisting of the rocking gear 4, two push rods and two cylinder groups of this embodiment to provide a power source; other transmission components may also be used to replace the rocking gear 4 of this embodiment to achieve a transmission connection.

[0062] To be more specific, the four-stroke engine of 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 arranged coaxially; the first power output member includes a first output shaft 6a connected to the first one-way clutch 5a and a first gear 7a fixed on the first output shaft 6a; the second power output member includes a second output shaft 6b connected to the second one-way clutch 5b and a second gear 7b fixed on the second output shaft 6b; the first transmission gear 10 is driven by the first gear 7a connected to the first power output member through the coupling gear 8, and the second transmission gear 9 is driven by the second gear 7b connected to the second power output member, wherein the coupling gear 8 is engaged with the first gear 7a of the first power output member, the coupling gear 8 is engaged with the first transmission gear 10, the second transmission gear 9 is engaged with the second gear 7b of the second power output member, and the second transmission gear 9 and the first transmission gear 10 are coaxially fixedly connected.

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

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

[0065] In short, in the first stroke, the swing gear 4 rotates clockwise, the first power output member rotates clockwise and transmits, and the second power output member idles counterclockwise; in the second stroke, the swing gear 4 rotates counterclockwise, the first power output member idles clockwise, and the second power output member rotates counterclockwise and transmits.

[0066] The first power output member maintains a constant rotational direction (i.e., clockwise rotation), driving during the first stroke and idling during the second stroke. Similarly, the second power output member maintains a constant rotational direction (i.e., counterclockwise rotation), idling during the first stroke and driving during the second stroke. The first and second power output members alternate between driving and idling, with one output member driving and outputting power during each stroke of the engine.

[0067] The first power output member and the second power output member can be connected to a load (such as a generator) respectively to output power.

[0068] To convert the oscillating rotation of the oscillating gear 4 into a motion that maintains its direction of rotation and alternates between driving and idling, two one-way clutches are provided. When the oscillating gear 4 rotates clockwise, the first one-way clutch 5a locks, driving the first power output member, while the second one-way clutch 5b disengages, idling the second power output member. When the oscillating gear 4 rotates counterclockwise, the first one-way clutch 5a disengages, idling the first power output member, while the second one-way clutch 5b locks, driving the second power output member.

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

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

[0071] Therefore, the first power output member can output power independently, and the direction of rotation remains unchanged, and it alternates between transmission and idling; the second power output member can output power independently, and the direction of rotation remains unchanged, and it alternates between transmission and idling; and the transmission of the two power output members is complementary: there is always one power output member transmitting and the other power output member idling. This embodiment has two power output members, each with a constant direction of rotation, and alternately outputs power and idles (i.e., outputs intermittent torque). This can meet the needs of different drive systems, such as driving two generators to generate electricity as a range extender for a range-extended hybrid vehicle. However, the engine of a vehicle usually has a single output shaft and outputs continuous and stable power. Therefore, it is necessary to design an engine with a single output shaft and outputs continuous and uninterrupted power as in this embodiment.

[0072] When the swing gear 4 rotates clockwise, it drives the first power output member to rotate; when the swing gear 4 rotates counterclockwise, it drives the second power output member to rotate. The coupling mechanism can adjust the rotation direction and couple the two power output members together to form an output shaft.

[0073] The first output shaft 6a and the first gear 7a are fixedly connected and rotate coaxially and in the same direction. The first gear 7a is meshed with the coupling gear 8 and rotates in opposite directions, and the coupling gear 8 is meshed with the first transmission gear 10 and rotates in opposite directions.

[0074] The second output shaft 6b and the second gear 7b are fixedly connected and rotate coaxially and in the same direction. The second gear 7b is meshed with the first transmission gear 10 and rotates in opposite directions.

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

[0076] In the first stroke (clockwise stroke), the swing gear 4 rotates clockwise, the first one-way clutch 5a is locked, and the swing gear 4 drives the first output shaft 6a to rotate clockwise through the first one-way clutch 5a, and the synchronous first gear 7a follows the first output shaft 6a to transmit clockwise, the first gear 7a drives the coupling gear 8 to rotate counterclockwise, and the coupling gear 8 drives the first transmission gear 10 and the second transmission gear 9 to rotate and transmit clockwise together; at the same time, the second one-way clutch 5b is disengaged, and the second output shaft 6b can rotate counterclockwise idly without restraint, that is, the second transmission gear 9 drives the second gear 7b and the second output shaft 6b to rotate counterclockwise idly.

[0077] In the second stroke (counterclockwise stroke), the swing gear 4 rotates counterclockwise, the second one-way clutch 5b is locked, and the swing gear 4 drives the second output shaft 6b to rotate counterclockwise through the second one-way clutch 5b, and the synchronous second gear 7b follows the second output shaft 6b to transmit counterclockwise, and the second gear 7b drives the second transmission gear 9 and the first transmission gear 10 to rotate and transmit clockwise together; at the same time, the first one-way clutch 5a is disengaged, and the first output shaft 6a can idle 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 idle clockwise together.

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

[0079] Whether rotating clockwise or counterclockwise, the swing gear 4 always drives the shafts of the second transmission gear 9 and the first transmission gear 10 clockwise (through different paths). The common shaft of the second transmission gear 9 and the first transmission gear 10 can be used as the main output shaft to output power. In this way, the coupling mechanism couples the two separate power output components together to form a single output shaft, outputting continuous and stable power or torque.

[0080] Within 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 enhance the flexibility and adaptability of the engine, promotes HCCI combustion to ensure higher thermal efficiency (i.e., thermal efficiency can reach 60%), and improves the potential for SI-HCCI conversion through the variable compression ratio.

[0081] The four-stroke engine of this embodiment can eliminate complex components such as push rods, crankshafts, high-pressure oil bearings and high-pressure oil pumps in the prior art, which not only reduces the overall cost, but also promotes the rotation of the same rocking gear 4 through the push rod provided with a rack, thereby converting the linear reciprocating motion of the piston into rotational motion, outputting power in the form of rotation, and driving a rotating generator with stable power generation efficiency, thereby improving the conversion efficiency of mechanical energy into electrical energy, and at the same time improving the engine efficiency. It can also be used as a direct power for driving vehicles such as HEVs, PHEVs and REEVs.

[0082] The push rod of this embodiment 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.

[0083] Furthermore, the four cylinders of this embodiment work together and coordinate to achieve a sequential reciprocating cycle of four stroke stages. Two push rods are arranged in parallel, with a single rocking gear 4 positioned between them. This gear meshes with the racks of the two push rods, ensuring kinematic coupling of the two racks via the rocking gear 4. Compared to existing two-stroke engines, the four-stroke engine of 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 expel exhaust gases, leaving minimal residual exhaust gas. During the next stroke, the piston movement creates negative pressure within the cylinder, drawing air in and improving ventilation efficiency. Furthermore, fresh fuel-containing gas is prevented from being short-circuited, preventing fuel loss. This also allows for a higher effective compression ratio, making it more suitable for the HCCI combustion cycle and improving efficiency. It also allows for the reuse of existing four-stroke engine components, reducing manufacturing costs.

[0084] Of course, in other embodiments, if the transmission unit adopts a dual rocking gear design, and during operation, the two rocking gears need to withstand the huge thrust output by the piston and have large load fluctuations, the technical requirements and costs of the gears, gear shafts, and bearings are high. Arranging two rocking gears between the two cylinders requires more space and the rigidity of the push rod 3 must be increased. However, this embodiment uses a transmission unit with a single rocking gear, which can reduce costs, size and weight, and improve design flexibility.

[0085] The force arm of the push rod acting on the transmission shaft in this embodiment is equal to the radius of the rocking gear 4. At the beginning of the power stroke, the energy can be quickly transferred out when the fuel gas energy in the cylinder is at its maximum, thereby reducing leakage and heat loss, and thus improving engine efficiency.

[0086] When the piston of a four-stroke engine is around the top dead center, its acceleration is significantly higher, thereby reducing the residence time at high temperature and reducing heat transfer losses during combustion. When the piston of a four-stroke engine is around the bottom dead center, the push rod's lever arm does not decrease and the output power attenuation is small, thereby achieving small output power fluctuations.

[0087] In addition, compared with the four-stroke engine of the prior art, which has strong vibrations in three axes, namely the x-axis, y-axis and z-axis, the four-stroke engine of this embodiment has strong vibrations only in one direction (i.e., the left and right movement directions of the piston), and the NVH (NVH includes noise, vibration and harshness) characteristics are significantly improved.

[0088] Example 2

[0089] like Figure 6 As shown, embodiment 2 provides a four-stroke free-piston engine. The structures of embodiment 2 and embodiment 1 are substantially the same, except that: the first power output member and the second power output member are both output wheels, a first one-way clutch 5a is provided between the first power output member and the shaft of the rocking gear 4, and a second one-way clutch 5b is provided between the second power output member and the shaft of the rocking gear 4.

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

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

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

[0093] First stroke: the swing gear 4 rotates clockwise, the first one-way clutch 5a is locked, the swing 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, the coupling gear 8 drives the first transmission gear 10 and the first transmission gear 10 to rotate clockwise and transmit together. At the same time, the second one-way clutch 5b is disengaged. Since the second gear 7b can idle without restraint, the first transmission gear 10 can drive the second gear 7b to idle counterclockwise.

[0094] Second stroke: the swing gear 4 rotates counterclockwise, the second one-way clutch 5b is locked, the swing gear 4 drives the second gear 7b to rotate counterclockwise through the second one-way clutch 5b, and the second gear 7b drives the first transmission gear 10 and the first transmission gear 10 to rotate clockwise and transmit together. 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 is disengaged. Since the first gear 7a can idle without restraint, the coupling gear 8 can drive the first gear 7a to idle clockwise.

[0095] In summary, the first stroke: the swing gear 4 rotates clockwise, and drives the first transmission gear 10 and the shaft of the second transmission gear 9 to rotate clockwise and transmit through the first one-way clutch 5a, the first power output member and the coupling gear 8, and drives the second power output member to idle counterclockwise through the second transmission gear 9; the second stroke: the swing gear 4 rotates counterclockwise, and drives the second transmission gear 9 and the shaft of the first transmission gear 10 to rotate clockwise and transmit through the second one-way clutch 5b and the second power output member, and drives the first power output member to idle clockwise through the first transmission gear 10 and the coupling gear 8.

[0096] Whether rotating clockwise or counterclockwise, the swing gear 4 always drives the shafts of the second transmission gear 9 and the first transmission gear 10 clockwise (through different paths). The common shaft of the second transmission gear 9 and the first transmission gear 10 can be used as the main output shaft to output power. In this way, the coupling mechanism couples the two separate power output components together 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 substantially the same as that of embodiment 1, except that: the transmission assembly also includes a transmission gear set; the shaft of the rocking gear 4 is fixedly connected to the transmission gear set, and the transmission gear set is driven to connect the first power output member through a first one-way clutch 5a, and is driven to connect the second power output member through a second one-way clutch 5b, thereby forming an indirect drive arrangement.

[0099] In this specific embodiment, the first power output member includes a first output shaft 6a connected to the first one-way clutch 5a and a first gear 7a fixed on the first output shaft 6a; the second power output member includes a second output shaft 6b connected to the second one-way clutch 5b and a second gear 7b fixed on the second output shaft 6b, and the first gear 7a and the second gear 7b are engaged.

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

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

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

[0103] The swing gear 4 is drivingly connected to the second output shaft 6b through the transmission gear A, the transmission gear C and the second one-way clutch 5b to form a second torque transmission route of indirect drive.

[0104] First stroke: The swing gear 4 and the transmission gear A rotate clockwise together, and the transmission gear A drives the transmission gear B and the transmission gear C to rotate counterclockwise at the same time. The first one-way clutch 5a is locked, and 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 idly without restraint, the first gear 7a drives the second gear 7b and the second output shaft 6b to rotate idly clockwise.

[0105] Second stroke: The swing gear 4 and the transmission gear A rotate counterclockwise together, the transmission gear A drives the transmission gear B and the transmission gear C to rotate clockwise at the same time, the second one-way clutch 5b is locked, and 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 idly without restraint, the second gear 7b drives the first gear 7a and the first output shaft 6a to rotate idly counterclockwise.

[0106] In summary, in the first stroke, the swing gear 4 rotates clockwise, and drives the first power output member to rotate counterclockwise and transmit through the transmission gear A, the transmission gear B and the first one-way clutch 5a; in the second stroke, the swing gear 4 rotates counterclockwise, and drives the second power output member to rotate clockwise through the transmission gear A, the transmission gear C and the second one-way clutch 5b, thereby driving the first power output member to rotate counterclockwise and transmit; the first power output member serves as the total output shaft.

[0107] Whether rotating clockwise or counterclockwise, the rocking gear 4 always drives the second power output member clockwise (through different paths), and the second power output member can be used as a main output shaft to output power. In this way, the coupling mechanism couples the two separate output members together 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 substantially the same as that of embodiment 1, except that: the coupling mechanism further includes a transmission gear set, the first power output member is a first gear 7a, and the shaft of the rocking gear 4 is directly driven and connected to the first gear 7a through a first one-way clutch 5a; the second power output member 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 transmission gear set is driven and connected to the second output shaft 6b through the second one-way clutch 5b; the first gear 7a is driven and connected 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 rocking gear 4 .

[0111] The swing gear 4 is connected to the first one-way clutch 5a through its own shaft, and is connected to the second one-way clutch 5b through the transmission gear D and the transmission gear E; the swing gear 4 drives the first power output member to rotate clockwise through its own shaft and the first one-way clutch 5a, and drives the second power output member to rotate clockwise through the transmission gear D, the transmission gear 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 gear 7a are meshed through the coupling gear 8 to achieve power coupling.

[0113] First stroke: The swing 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 swing gear 4 drives the first gear 7a to rotate clockwise through the first one-way clutch 5a, and the first gear 7a drives the coupling gear 8 to rotate counterclockwise and transmit 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 idly without restraint, the coupling gear 8 drives the second gear 7b and the second output shaft 6b to rotate idly clockwise.

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

[0115] Second stroke: The swing 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, and 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 idly without restraint, the coupling gear 8 drives the first gear 7a to rotate idly clockwise.

[0116] It can be seen that the torque transmission route of the second stroke is: the swing 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 pistons and push rods of the cylinders move back and forth and complete a working cycle. In each working cycle, the coupling gear 8 continues to rotate counterclockwise and output power.

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

[0119] Whether rotating clockwise or counterclockwise, the rocking gear 4 always drives the second power output member clockwise (through different paths), and the second power output member can be used as a main output shaft to output power. In this way, the coupling mechanism couples the two separate power output members together to form a single output shaft, outputting continuous and stable power or torque.

[0120] Example 5

[0121] Embodiment 5 provides a four-stroke free-piston engine. The structure of embodiment 5 is substantially the same as that of embodiment 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 arranged on the same side, and the same rocking gear is engaged with the racks on the two push rods at the same time.

[0122] In this embodiment, the two push rods are connected as a whole to form an integral push rod, and then connected one by one through the gears of the two racks to form a new rack on the integral push rod. The new rack and the rocking gear are arranged on the same side of the two push rods, and the rocking gear is engaged with the new rack. In this way, it is also possible to ensure that the piston of one cylinder is always doing work, and synchronously drive 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 may be independent of each other, and the gear of the same swing gear may be wider to overcome the spacing between the two racks, thereby ensuring that the swing gear is engaged with the two racks at the same time.

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

Claims

1. A four-stroke free-piston engine comprising two cylinder groups, each cylinder group comprising two cylinders arranged opposite each other, the pistons of the two cylinders in each group being connected by a push rod, each push rod being provided with a rack, characterized in that: Also included are transmission components; The transmission assembly includes a swing gear, a first one-way clutch, a second one-way clutch, a first power output member and a second power output member. The swing gear is engaged with the racks on the two push rods. The swing gear is connected to the first one-way clutch. The first power output member is matched with the first one-way clutch. The swing gear is connected to the second one-way clutch. The second power output member is matched with the second one-way clutch. The swing gear is arranged to rotate on a fixed axis. Each cylinder completes the intake stroke, compression stroke, power stroke and exhaust stroke in sequence; every four strokes of the system form a working cycle, and in each stroke, the piston of one cylinder is always working, and synchronously drives the other three cylinders to complete the intake stroke, compression stroke and exhaust stroke respectively through the cooperation of the push rod, the rack and the rocking gear; In the first stroke, only one working piston drives the rocking gear to rotate toward the first direction through the rack of the push rod; In the second stroke, only one working piston drives the rocking gear to rotate in a second direction opposite to the first direction through the rack of the push rod; In the third stroke, only one working piston drives the rocking gear to rotate toward the first direction through the rack of the push rod; in the fourth stroke, only one working piston drives the rocking gear to rotate toward the second direction through the rack of the push rod; When the swing gear rotates in the first direction, the first one-way clutch is locked, the swing gear transmits torque and outputs power through the first power output member, and the second one-way clutch is disengaged synchronously, and the second power output member idles in the same direction as the rotation direction of the previous stroke; When the swing gear rotates in the second direction, the first one-way clutch is disengaged, the first power output member idles in the same direction as the rotation direction of the previous stroke, and the second one-way clutch is synchronously locked, and the swing gear transmits torque and outputs power through the second power output member.

2. The four-stroke free-piston engine according to claim 1, characterized in that: It also includes a coupling mechanism; the first power output member and the second power output member 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 a power stroke to push its piston to move in a first direction; and through the transmission assembly, drives the piston of another cylinder in the same group to move in the first direction and realize the compression stroke, and synchronously drives the pistons of the third cylinder and the fourth cylinder in the other group to move in a second direction opposite to the first direction, so that the third cylinder and the fourth cylinder in the other group respectively complete the intake stroke and the exhaust stroke; or drives the piston of another cylinder in the same group to move in the first direction and realize the exhaust stroke, and synchronously drives the pistons of the third cylinder and the fourth cylinder in the other group to move in the second direction opposite to the first direction, so that the third cylinder and the fourth cylinder in the other group respectively complete the intake stroke and the compression stroke.

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 rocking 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 one body and move synchronously in the same direction; the racks on the two push rods are arranged on the same side, and the rocking gear is engaged with the racks on the two push rods at the same time.

6. The four-stroke free-piston engine according to claim 5, characterized in that: The gears of the two racks are connected one by 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 swing gear is directly driven to connect to the first power output member through the first one-way clutch, and the swing gear is directly driven to connect to the second power output member through the second one-way clutch.

8. The four-stroke free-piston engine according to claim 7, characterized in that: The first power output member 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 member 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 that are coaxially arranged. The first transmission gear is driven and connected to the first gear through the coupling gear, and the second transmission gear is driven and connected to the second gear.

10. The four-stroke free-piston engine according to claim 2, characterized in that: The first power output member and the second power output member are both gears. The first one-way clutch is provided between the first power output member and the shaft of the swing gear. The second one-way clutch is provided between the second power output member and the shaft of the swing 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 that are coaxially arranged. The first transmission gear is driven and connected to the first power output member through the coupling gear, and the second transmission gear is driven and connected to the second power output member.

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 rocking gear is fixedly connected to the transmission gear set, and the transmission gear set is driven to connect to the first power output member through the first one-way clutch, and is driven to connect to the second power output member through the second one-way clutch, thereby forming an indirect drive setting.

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

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 swing gear is fixedly connected to the transmission gear set. The first power output member is a first gear. The shaft of the swing gear is directly driven and connected to the first gear through the first one-way clutch; the second power output member includes a second output shaft connected to the second one-way clutch and a second gear fixed on the second output shaft. The transmission gear set is driven and connected to the second output shaft through the second one-way clutch; the first gear is driven and connected to the second gear through the coupling gear.

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