CN104929766B - Hydraulic free piston engine - Google Patents

Abstract

The invention discloses a hydraulic free piston engine. The power piston and the pump piston are rigidly connected through a piston rod to form a piston assembly. The power piston is installed in the cylinder body, and the pump piston is installed in the pump body. There are hydraulic passages with different diameters on the body, and the hydraulic passages are connected with the hydraulic system, and the hydraulic system is a pressure differential closed hydraulic system. By adopting the technical scheme of the invention, the structure of the hydraulic free-piston engine can be simplified, the manufacturability of actual manufacturing and processing can be reduced, and the structural compactness of the hydraulic free-piston engine can be further improved.

Description

A hydraulic free piston engine

technical field

The invention relates to the technical field of power and hydraulic pressure, in particular to a hydraulic free piston engine.

Background technique

The hydraulic free piston engine is a power machine that integrates a reciprocating piston internal combustion engine and a plunger hydraulic pump. The hydraulic free piston engine directly converts the heat energy of fuel combustion into hydraulic energy for external output through the reciprocating piston assembly. It has the advantages of simple structure, short transmission chain, variable compression ratio, and flexible medium for power transmission. It can be used as a power source for vehicles and other mobile equipment, especially for mobile devices that use hydraulic pressure as a power source.

At present, from the perspective of the structure type to realize the principle of the hydraulic free piston engine, there are two forms: one is to connect the three pistons of the power piston of the internal combustion engine, the pump piston of the hydraulic pump, and the compression piston to restore the piston in sequence through rigid rods It is a slender piston assembly; another way is to connect the pump piston and the compression piston to the power piston respectively to form a power piston that drives 2 or 3 hydraulic pistons as a piston assembly. Above-mentioned two forms all can realize the working principle of hydraulic free piston engine. In the above two schemes of hydraulic free piston engines, one or more hydraulic pistons are used to provide energy for the compression stroke of the power piston. Since the hydraulic free piston engine saves the crank connecting rod mechanism, the compression stroke of the power piston is gone. It is powered by an inertial element such as a flywheel, and a separate hydraulic system must be used to power its compression stroke. However, due to the need to increase the recovery system of the power piston, the axial dimension of the piston assembly in these two arrangements will be too large (at least more than twice the piston stroke) or the radial dimension of the pump body part will be too large, so that the hydraulic pressure is free. Piston engines are not compact in structure, the processing technology of piston components is deteriorated, and the coaxiality between the cylinder block and the corresponding cavity of the pump piston is too high, etc., which have seriously restricted and limited the further application and promotion of hydraulic free piston engines.

Contents of the invention

The object of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a hydraulic free-piston engine, which can simplify the structure of the hydraulic free-piston engine, reduce the manufacturability of actual manufacturing and processing, and further improve the structural compactness of the hydraulic free-piston engine.

The invention provides a hydraulic free piston engine. The power piston and the pump piston are rigidly connected through a piston rod to form a piston assembly. The power piston is installed in the cylinder body, and the pump piston is installed in the pump body. There are hydraulic passages with different diameters on the body, and the hydraulic passages are connected with the hydraulic system, and the hydraulic system is a pressure differential closed hydraulic system.

Preferably, the hydraulic system includes a high-pressure stage hydraulic oil circuit and a secondary high-pressure stage hydraulic oil circuit, and the hydraulic circuit of the hydraulic system is a closed circuit.

Preferably, the high-pressure stage hydraulic oil circuit further includes a high-pressure accumulator, the first hydraulic channel on the pump body is connected to the high-pressure accumulator through a first one-way valve, and the second hydraulic channel on the pump body is connected to the high-pressure accumulator through a second one-way valve It is connected with the high-pressure accumulator, and the third hydraulic passage on the pump body is connected with the second hydraulic passage and the second check valve through the damping valve, wherein the first hydraulic passage is the oil outlet hydraulic passage, and the second hydraulic passage is the oil outlet hydraulic passage. The hydraulic channel, the third hydraulic channel is a damping hole hydraulic channel, the diameter of the first hydraulic channel is larger than the diameter of the second hydraulic channel, the diameter of the second hydraulic channel is larger than the diameter of the third hydraulic channel, the first check valve and the second check valve Directional valves are all oil outlet check valves.

Preferably, the secondary high-pressure stage hydraulic oil circuit further includes a secondary high-pressure accumulator, the fourth hydraulic channel on the pump body is connected to the secondary high-pressure accumulator, and the fifth hydraulic channel on the pump body passes through the third check valve It is connected with the secondary high-pressure accumulator, the sixth hydraulic channel on the pump body is connected with the secondary high-pressure accumulator through the first solenoid valve, and the starting hydraulic pump is connected with the secondary high-pressure accumulator through the fourth one-way valve. A relief valve is connected between the outlet of the starting hydraulic pump and the fourth one-way valve, wherein the fifth hydraulic channel is the oil inlet hydraulic channel, the sixth hydraulic channel is the oil inlet solenoid valve channel, and the diameter of the fifth hydraulic channel is larger than that of the sixth hydraulic channel. The diameter of the hydraulic channel, the first solenoid valve is a frequency control solenoid valve, and the third one-way valve is a secondary high-pressure oil inlet one-way valve.

Preferably, the seventh hydraulic channel on the pump body is connected with the second solenoid valve.

Preferably, a third solenoid valve is connected between the high-pressure accumulator and the secondary high-pressure accumulator.

Preferably, the cylinder head is installed on one end of the cylinder block, the spark plug is installed on the cylinder head, an intake check valve is installed at the air inlet, the scavenging chamber communicates with the scavenging port through the scavenging channel, and the exhaust port is located at one side of the cylinder. side.

Preferably, the tail end surface of the pump piston is an annular acting surface, the head end surface is a circular acting surface, and the circular acting surface area of the head end surface is larger than the annular acting surface area of the tail end surface.

Preferably, a controller is also included, and the controller is respectively connected to the spark plug, the first solenoid valve, the second solenoid valve, the third solenoid valve and the overflow valve via circuits.

Preferably, the high-pressure accumulator is connected to the oil inlet end of the hydraulic motor, the secondary high-pressure accumulator is connected to the oil return end of the hydraulic motor, the high-pressure accumulator is connected to the oil inlet end of the hydraulic cylinder, and the secondary high-pressure accumulator Connect with the oil return port of the hydraulic cylinder.

In the technical solution of the present invention, since the pressure difference closed hydraulic system is used to provide energy for the compression stroke of the power piston, the piston recovery system in the traditional hydraulic free piston engine is omitted, and the piston assembly is only directly driven by a power piston. The structure of the pump piston, combined with the differential pressure closed hydraulic system, can complete the working cycle of the hydraulic free piston engine. Therefore, the structure of the hydraulic free-piston engine is greatly simplified, the manufacturability of actual manufacturing and processing is reduced, and the structural compactness of the hydraulic free-piston engine is further improved.

Description of drawings

Fig. 1 is a schematic structural diagram of a hydraulic free-piston engine in an embodiment of the present invention.

Fig. 2 is a schematic diagram of the left dead center position of the hydraulic free piston engine in the embodiment of the present invention.

Fig. 3 is a schematic diagram of the implementation and application of the hydraulic free piston engine in the embodiment of the present invention.

Fig. 4 is a schematic diagram of the control system of the hydraulic free piston engine in the embodiment of the present invention.

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, the embodiments of the present invention are not limited thereto.

Generally, the low-pressure end of the hydraulic system is atmospheric pressure, or in order to ensure that the pump piston does not appear cavitation when sucking oil, the pressure at the low-pressure end is increased to 0.5 MPa, and the output high-pressure oil pressure is a pressure of more than ten MPa or tens of MPa. The basic idea of the technical solution of the present invention is to increase the pressure at the low-pressure end of the hydraulic free-piston engine from the traditional atmospheric pressure or 0.5 MPa pressure to a pressure sufficient to drive the piston assembly to complete the compression stroke, such as a higher pressure of 5 MPa. This pressure is sufficient to push the piston assembly through the compression stroke of the power piston. When the piston assembly enters the expansion stroke under the action of the high-pressure gas pressure generated by fuel combustion, the pressure is further increased to a higher pressure, such as a high pressure of 10 MPa, and output to the outside. By increasing the pressure at the low-pressure end, the pressure at the low-pressure end can be fully utilized to drive the piston assembly into the compression stroke and at the same time complete the oil suction task of the pump piston. Since the pressure at the low-pressure end increases from low pressure to secondary high pressure (relative to the high-pressure oil at the output end), the oil suction process of the pump piston is changed into a secondary high-pressure active oil intake process. After the pressure at the low-pressure end is increased, the secondary high pressure acts on the pump piston to push the piston to complete the compression stroke of the power piston, which saves the huge mechanism such as the piston assembly recovery system that provides energy for the compression stroke of the power piston in the traditional hydraulic free piston engine , which greatly simplifies the structure of the engine and the complexity of the system. At the same time, the processing and installation process of parts is reduced.

The hydraulic free piston engine in the technical solution of the present invention not only shortens the transmission chain, but also saves the repeated conversion between different motion forms, realizes a high degree of simplification in structure, optimizes the energy transmission form of the engine and transmission system, and realizes Flexible adjustment of the power transmission. In particular, the present invention adopts the pressure difference to drive the closed hydraulic circuit system to provide energy for the compression stroke of the power piston, which saves the piston recovery system in the traditional hydraulic free piston engine, greatly simplifies the structure of the engine, and the piston assembly is only composed of the power piston It is composed of directly driving a differential hydraulic plunger, combined with differential pressure to drive a closed hydraulic closed circuit system to complete the working cycle of the hydraulic free piston engine. The technical scheme of the invention will greatly simplify the structure of the hydraulic free-piston engine, reduce the manufacturability of actual manufacturing and processing, and improve the structural compactness of the hydraulic free-piston engine. It provides a good foundation for the further popularization and application of the hydraulic free piston engine.

Fig. 1 is a schematic structural diagram of a hydraulic free-piston engine in an embodiment of the present invention. As shown in FIG. 1 , the power piston 5 and the pump piston 29 of the hydraulic free piston engine are rigidly connected by a piston rod 8 to form a piston assembly. The power piston 5 is installed in the cylinder body 3, and the pump piston 29 is installed in the pump body 9 through cooperation.

The internal combustion engine part adopts the working principle and structure of the backflow scavenging two-stroke engine: the cylinder head 2 is installed at one end of the cylinder block, and forms the cylinder working volume and combustion chamber with the cylinder block and the power piston. The spark plug 1 is installed on the cylinder head, and the air inlet An intake check valve 7 is installed, the scavenging cavity 6 communicates with the scavenging port 33 through the scavenging channel 32 , and the exhaust port 4 is arranged on one side of the cylinder.

The pump piston 29 is installed in the pump body 9. The pump piston adopts a differential pressure piston structure, that is, the left end face (tail end face) of the pump piston is a ring-shaped acting face, the right end face (head end face) is a circular acting face, and the right end face is a circular acting face. The shape action area is larger than the ring action area of the left end face. On the pump body from left to right, there are four hydraulic passages 31, fifth hydraulic passages 28, first hydraulic passages 10, sixth hydraulic passages 24, second hydraulic passages 11, third hydraulic passages 15, Seventh hydraulic channels 34, these hydraulic channels are connected with the hydraulic system.

The hydraulic system is a pressure differential closed hydraulic system. The hydraulic oil circuit where the high-pressure accumulator 17 is located is a high-pressure hydraulic oil circuit, and the hydraulic oil circuit where the secondary high-pressure accumulator 21 is located is a secondary high-pressure hydraulic oil circuit. The loop is a closed loop.

The fourth hydraulic passage 31 is directly connected to the secondary high-pressure accumulator 17, the fifth hydraulic passage 28 (a hydraulic passage with a larger diameter) is connected to the secondary high-pressure accumulator through the third check valve 27, and the sixth hydraulic passage 24 (smaller diameter hydraulic passage) is connected to the secondary high pressure accumulator through the first solenoid valve 25. The starting hydraulic pump 20 is connected to the secondary high-pressure accumulator through the fourth one-way valve 19, and a relief valve 26 is connected between the outlet of the starting hydraulic pump and the fourth one-way valve for adjusting the pressure of the starting hydraulic pump. Among them, the fifth hydraulic channel is the oil inlet hydraulic channel, the sixth hydraulic channel is the oil inlet electromagnetic valve channel, the diameter of the fifth hydraulic channel is larger than the diameter of the sixth hydraulic channel, the first electromagnetic valve is a frequency control electromagnetic valve, and the third one-way The valve is a secondary high pressure inlet check valve. The above constitutes the secondary high-pressure hydraulic oil circuit part.

The first hydraulic passage 10 (a hydraulic passage with a larger diameter) is connected to the high-pressure accumulator 17 through the first one-way valve 12, and the second hydraulic passage 11 (the hydraulic passage with a smaller diameter) is connected to the high-pressure accumulator through the second one-way valve 13. The accumulator 17 is connected, and the third hydraulic passage 15 (the hydraulic passage with the smallest diameter) is connected with the second hydraulic passage 11 and the second one-way valve 13 through the damping valve 14 . Wherein the first hydraulic passage is an oil outlet hydraulic passage, the second hydraulic passage is an oil outlet hydraulic passage, and the third hydraulic passage is a damping hole hydraulic passage, the diameter of the first hydraulic passage is larger than the diameter of the second hydraulic passage, and the diameter of the second hydraulic passage is The diameter is larger than that of the third hydraulic channel, and both the first check valve and the second check valve are oil outlet check valves. The high-pressure accumulator 17 is arranged in the high-pressure hydraulic oil circuit, and is used for stabilizing and storing the high-pressure hydraulic energy output by the hydraulic free-piston engine, so as to drive the hydraulic actuator. The above constitutes the high-pressure stage hydraulic oil circuit part.

The seventh hydraulic passage 34 is connected with the second solenoid valve 22 .

A third solenoid valve 16 is connected between the high-pressure accumulator 17 and the secondary high-pressure accumulator 21 .

Fig. 2 is a schematic diagram of the left dead center position of the hydraulic free piston engine in the embodiment of the present invention. Fig. 3 is a schematic diagram of the implementation and application of the hydraulic free piston engine in the embodiment of the present invention. As shown in Figures 2 and 3, the high-pressure accumulator is connected to the oil inlet end of the hydraulic motor 18, the secondary high-pressure accumulator is connected to the oil return end of the hydraulic motor 18, and the high-pressure accumulator is connected to the oil inlet of the hydraulic cylinder 35. The secondary high-pressure accumulator is connected to the oil return end of the hydraulic cylinder 35.

Fig. 4 is a schematic diagram of the control system of the hydraulic free piston engine in the embodiment of the present invention. As shown in Figure 4, the controller (ECU) is respectively connected to the spark plug, the first solenoid valve, the second solenoid valve, the third solenoid valve and the overflow valve through circuits.

The working process of the hydraulic free piston engine in the present embodiment is as follows:

When the hydraulic free-piston engine starts, the starting hydraulic pump 20 runs, and the pressure is adjusted to the secondary high-pressure stage pressure, such as 5 MPa, by adjusting the overflow valve 26, and the secondary high-pressure accumulator 21 is filled. During this process, the second solenoid valve 22 is in an open state, and other solenoid valves are in a closed state. The secondary high-pressure oil in the secondary high-pressure accumulator fills the secondary high-pressure chamber 30 through the fourth hydraulic passage 31, and the piston assembly pushes the piston assembly to the left end annular area of the pump piston 29 under the action of the secondary high-pressure hydraulic pressure Bottom dead center position as shown in Figure 1.

Afterwards, close the second electromagnetic valve 22, and close the starting hydraulic pump. When the first electromagnetic valve 25 is opened, the hydraulic oil in the secondary high-pressure accumulator enters the pump cavity 23 through the first electromagnetic valve 25, because the circular area of the right end surface of the pump piston is much larger than the annular area of the left end surface, and the secondary The high-pressure pressure is enough to overcome the compression resistance of the gas in the cylinder and the hydraulic pressure on the left-end annular surface of the pump piston, so the secondary high-pressure hydraulic oil will push the piston assembly to move in the direction of the upper dead center. When the pump piston moves to open the fifth hydraulic passage 28 , the first electromagnetic valve 25 can be closed. The hydraulic oil in the secondary high-pressure accumulator will directly enter the pump cavity through the third check valve 27 and the fifth hydraulic passage 28. Since the diameter of the fifth hydraulic passage 28 is greater than the diameter of the sixth hydraulic passage 24, the piston will Accelerate the movement towards the top dead center, and at the same time, the power piston 5 compresses the gas sealed in the cylinder to complete the compression stroke of the internal combustion engine. At the same time, the power piston pre-inhales fresh gas through the intake check valve 7 The scavenging cavity 6 is shown in FIG. 2 .

When the power piston reaches near the top dead center, the spark plug flashes to ignite the combustible mixture in the cylinder, and the high-temperature and high-pressure gas generated by fuel combustion pushes the piston assembly to move in the direction of the bottom dead center, and the power piston enters the expansion stroke. During this process, the pump The piston also moves to the right under the drive of the power piston. Due to the push of the pump piston, the hydraulic oil pressure in the pump chamber increases instantaneously, and the third check valve 27 is immediately closed, while the first check valve 12 and the second check valve The valve 13 will be opened, and the pump piston will output the high-pressure hydraulic oil in the pump cavity to the high-pressure end, such as 10MPa, during the rightward movement. When the power piston moves to the right to open the exhaust hole 4, the exhaust gas after combustion in the cylinder will be discharged from the exhaust hole; The fresh gas inside enters the cylinder through the scavenging channel 32 and the scavenging port 33, and the combustion exhaust gas is further discharged out of the cylinder under the push of the fresh gas to complete the exchange of exhaust gas and fresh gas.

When the piston assembly reaches the bottom dead center, the first solenoid valve 25 is opened again and repeats to enter the next cycle, and the heat energy of fuel combustion is converted into high-pressure hydraulic oil output through the reciprocating piston assembly to realize Conversion of thermal energy to hydraulic energy.

When the required power is small, the control of the engine output power can be realized by controlling the operating frequency of the piston assembly. The specific implementation method is: when the piston assembly completes a cycle, when the pump piston moves to the position where both the fifth hydraulic passage 28 and the first hydraulic passage 10 are closed, the first electromagnetic valve 25 is still in the closed state, as shown in Figure 1 In the position shown, due to the incompressibility of the liquid, the pump chamber will form an instantaneous high pressure, pushing the piston to rebound in the direction of the upward dead center (because the liquid is incompressible, the amount of rebound is very small, and the rebounded pump piston cannot open the fifth hydraulic channel 28), while The rebound of the pump piston causes the pressure in the pump chamber to decrease, and the piston assembly is pushed back to the bottom dead center by the secondary high-pressure hydraulic oil acting on the left-end annular surface of the pump piston. After several times of reciprocation, the piston assembly will Stop at bottom dead center. If the piston assembly still cannot stop at this time, the piston assembly will continue to move to the right until the second hydraulic passage 11 and the sixth hydraulic passage 24 are closed. Since the second solenoid valve 22 is in a closed state at this time, the piston assembly will continue to move to the right At this time, the outflow path of the high-pressure oil in the pump chamber only passes through the third hydraulic passage 15, and the damping effect of the damping valve 14 will force the piston assembly to stop. Until the first solenoid valve 25 is opened again to send the instruction of the next cycle. The opening frequency of the first electromagnetic valve 25 is the operating frequency of the piston assembly. Therefore, the engine can control the operating frequency by controlling the opening of the first electromagnetic valve 25, and then realize the control of engine power.

The pump piston 29 involved in this embodiment is a double-sided working piston, that is, both the front end face and the rear end face are working faces, the tail end face (left end face) is an annular working face, the head end face (right end face) is a circular working face, and the right end face The circular area of the face is larger than the annular area of the left end face.

During this process, if the pressure of the secondary high-pressure accumulator 21 decreases due to hydraulic loss, the third electromagnetic valve 16 can be opened for high-pressure replenishment, so that it can be stabilized within the working set pressure range.

In this process, if the engine is stalled due to some uncertain factors, the second electromagnetic valve 22 can be opened to adjust the position of the piston assembly and restart quickly.

The differential pressure drive involved in this embodiment means that the secondary high pressure is used to drive the piston assembly to complete the compression stroke of the power piston, the pump piston outputs a higher pressure, and the output power of the engine depends on the pressure difference between the high pressure and the secondary high pressure.

The control part of the hydraulic system realizes the control of the hydraulic system by controlling the opening and closing of the hydraulic channel and the solenoid valve during the movement of the pump piston, and connects the engine part and the hydraulic pump part through the reciprocating piston assembly to realize the differential pressure driven hydraulic free piston engine work. The specific implementation plan is as follows:

1. The basic composition and working process are as mentioned above.

2. The area of the power piston, the pump piston, and the annular piston at the end of the pump piston determines the output power of the engine.

3. The compression stroke of the piston is completed by the differential pressure drive method, and the differential pressure is determined by the power piston, the pump piston and the annular piston area at the end of the pump piston.

Differential pressure driven hydraulic free piston engines can be connected to several different hydraulic loads depending on the type of motion required by the load. For example, the hydraulic motor 18 load that needs to drive the rotary motion, the hydraulic cylinder 35 load that needs to drive the linear motion, etc. Different forms, wherein the rotary motion is like the driving wheel of the vehicle, etc., and the linear motion is like the steering system of the vehicle, the reciprocating motion mechanism of other walking machines, swing mechanism etc. As the hydraulic energy supply device, the pressure difference driven hydraulic free piston engine can provide high pressure hydraulic energy for the above hydraulic actuators, as shown in Figure 3.

According to the different power requirements of the vehicle or mobile device, the hydraulic free piston engine has the following states during the working process:

1. Starting state. Start the hydraulic pump 20 to run, adjust the pressure to the secondary high-pressure stage pressure by adjusting the relief valve 26, such as 5MPa, fill the secondary high-pressure accumulator 21, and fill the secondary high-pressure oil through the fourth hydraulic channel 31 at the same time High pressure chamber 30. During this process, the second solenoid valve 22 is in an open state, and other solenoid valves are in a closed state. Then the piston assembly pushes the piston assembly to the bottom dead center position shown in Figure 1 through the left end annular area of the pump piston 29 under the action of the secondary high-pressure hydraulic pressure in the secondary high-pressure chamber 30, and then closes the second solenoid valve 22 , turn off the starting hydraulic pump. When the first electromagnetic valve 25 is opened, the hydraulic oil in the secondary high-pressure accumulator enters the pump cavity 23 through the first electromagnetic valve 25, because the circular area of the right end surface of the pump piston is much larger than the annular area of the left end surface, and the secondary The high-pressure pressure is enough to overcome the compression resistance of the gas in the cylinder and the hydraulic pressure on the left-end annular surface of the pump piston, so the secondary high-pressure hydraulic oil will push the piston assembly to move in the direction of the upper dead center. When the pump piston moves to open the fifth hydraulic passage 28 , the first electromagnetic valve 25 can be closed. The hydraulic oil in the secondary high-pressure accumulator will directly enter the pump cavity through the third check valve 27 and the fifth hydraulic passage 28. Since the diameter of the fifth hydraulic passage 28 is greater than the diameter of the sixth hydraulic passage 24, the piston will Accelerate the movement towards the top dead center, and at the same time, the power piston 5 compresses the gas sealed in the cylinder to complete the compression stroke of the internal combustion engine. At the same time, the power piston pre-inhales fresh gas through the intake check valve 7 The scavenging cavity 6 is shown in FIG. 2 .

When the power piston reaches near the top dead center, the spark plug flashes to ignite the combustible mixture in the cylinder, and the high-temperature and high-pressure gas generated by fuel combustion pushes the piston assembly to move in the direction of the bottom dead center, and the power piston enters the expansion stroke. During this process, the pump The piston also moves to the right under the drive of the power piston. Due to the push of the pump piston, the hydraulic oil pressure in the pump chamber increases instantaneously, and the third check valve 27 is immediately closed, while the first check valve 12 and the second check valve The valve 13 will be opened, and the pump piston will output the high-pressure hydraulic oil in the pump cavity to the high-pressure end, such as 10MPa, during the rightward movement. When the power piston moves to the right to open the exhaust hole 4, the exhaust gas after combustion in the cylinder will be discharged from the exhaust hole; The fresh gas inside enters the cylinder through the scavenging channel 32 and the scavenging port 33, and the combustion exhaust gas is further discharged out of the cylinder under the push of the fresh gas to complete the exchange of exhaust gas and fresh gas. When the pump piston moves to the position where both the fifth hydraulic passage 28 and the first hydraulic passage 10 are closed, as shown in Figure 1, due to the incompressibility of the liquid, the pump chamber will form an instantaneous high pressure, pushing the piston to rebound in the direction of the upper dead center , and the rebound of the pump piston causes the pressure in the pump chamber to decrease, and the piston assembly is pushed back to the bottom dead center by the secondary high-pressure hydraulic oil acting on the left end annular surface of the pump piston. The assembly will stop at bottom dead center. If the piston assembly still cannot stop at this time, the piston assembly will continue to move to the right until the second hydraulic passage 11 is closed. Since the second solenoid valve 22 is in a closed state at this time, when the piston assembly continues to move to the right, the high pressure oil in the pump chamber will Only through the third hydraulic passage 15, the damping effect of the damping valve 14 will force the piston assembly to stop. Until the first solenoid valve 25 is opened again to send the instruction of the next cycle.

2. Continuous working status. When the vehicle or mobile device needs to provide full-load hydraulic energy, the first electromagnetic valve 25 controls the piston assembly to continuously reciprocate at the natural frequency during the running of the engine, so as to achieve the maximum capacity output of high-pressure hydraulic energy. The specific implementation method is: when the piston assembly completes a cycle and the pump piston reaches the bottom dead center, the first electromagnetic valve 25 is opened, and the secondary high pressure enters the pump chamber through the first electromagnetic valve 25, and the piston assembly is pushed into the bottom immediately. One cycle without stopping at the bottom dead center. The maximum operating frequency that the engine can achieve is the natural frequency of the reciprocating motion of the piston assembly, which depends on the mass of the piston assembly, the gas pressure and hydraulic pressure of fuel combustion and other parameters.

3. Low frequency working state. When loads such as vehicles or mobile devices require less high-pressure hydraulic energy, the engine can ensure that the piston assembly works at different operating frequencies under the control of the first electromagnetic valve 25, thereby realizing the adjustment of the output hydraulic energy. The specific implementation method is: after the piston assembly completes one cycle, when the pump piston moves to the position where both the fifth hydraulic passage 28 and the first hydraulic passage 10 are closed, the first electromagnetic valve 25 is still in the closed state, as described above As mentioned above, when the piston assembly will stop at the bottom dead center under the action of the hydraulic pressure, until the first solenoid valve 25 is opened again to issue a command for the next cycle, the piston assembly enters a new cycle. The opening time and opening time interval of the first electromagnetic valve 25 control the operating frequency of the piston assembly, therefore, the low-frequency operating state of the engine can be realized by controlling the opening frequency of the first electromagnetic valve 25 . The lowest frequency is 0 Hz and the highest frequency is the natural frequency of the piston assembly. In general, the frequency range is 0-40Hz.

4. Pressure regulation. When the engine is running, when the pressure of the secondary high-pressure accumulator 21 decreases due to pressure loss, the pressure can be supplemented by controlling the third solenoid valve 16, that is, when the pressure of the secondary high-pressure accumulator 21 decreases, the third solenoid valve 16 is opened. Solenoid valve 16, because the hydraulic oil pressure in the high-pressure accumulator 17 is higher than the hydraulic oil in the secondary high-pressure accumulator 21, therefore, the high-pressure oil in the high-pressure accumulator 17 is replenished to the secondary In the high-pressure accumulator 21, the third electromagnetic valve 16 is closed after the pressure of the secondary high-pressure accumulator rises to a set value to ensure normal operation of the engine.

5. Piston position adjustment. When the engine has occasional phenomena such as incomplete combustion during operation, it will cause the piston assembly to fail to return to the bottom dead center, which will cause the engine to shut down and other phenomena. After this phenomenon occurs, it is necessary to adjust the piston assembly to the bottom dead center in time. Click on the heavy line for a quick start. The specific implementation method is: after the controller 36 tests that the engine is turned off, it will control the second electromagnetic valve 22 to open, the pressure oil in the pump chamber 23 is connected to the fuel tank, and is in a low-pressure state, and the piston assembly is in the secondary high pressure chamber 30. The high-pressure hydraulic oil acts on the annular piston surface to push the piston assembly back to the bottom dead center, close the second solenoid valve 22, open the first solenoid valve 25 to enter the starting state, and start the engine to continue running. Due to the energy storage effect of the high-pressure accumulator 17 in the system, short-time flameout will not affect the normal operation of the system.

According to the above structure, the engine can also be expanded into a diesel engine form. Change the spark plug 1 to an injector, and change the fuel from gasoline to diesel.

The hydraulic free-piston engine in the embodiment of the present invention greatly simplifies the structure of the traditional hydraulic free-piston engine, especially the compression stroke of the piston assembly is completed by means of differential pressure drive, which saves the huge compression system of the traditional hydraulic free-piston engine . On the basis of ensuring the advantages of the hydraulic free piston engine, the structure is greatly simplified and compact. The flexible adjustment of the power unit is realized, and the engine power is adjusted by frequency modulation, which effectively solves the disadvantages of traditional engines such as economical deterioration and emission deterioration at low speed and low load. The differential-pressure driven hydraulic free-piston engine involved in the invention realizes a variable compression ratio, can adapt to various fuels, and effectively widens the dependence of traditional engines on petroleum fuels. The piston structure of the differential-pressure driven hydraulic free-piston engine of the present invention effectively shortens the axial and radial dimensions of the engine, makes the structure more compact, and improves the processability of parts and assembly.

The hydraulic free-piston engine in the embodiment of the present invention is suitable for use in a hydraulic system with constant pressure variable flow rate and energy recovery. Such as construction machinery, forklifts, cranes and other mobile machinery, as well as municipal tractors and hoists. It is especially suitable for the power of mobile devices such as robots that use hydraulic pressure as a power source. If higher power is required, it can be achieved by combining multiple hydraulic free piston engine units. In addition, this engine is also suitable for urban public transport vehicles with low maximum speed and frequent stops and starts, which can greatly improve its economy and power. At the same time, it can effectively Recover energy from frequent braking.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (8)

1. A hydraulic free piston engine, characterized in that, the power piston and the pump piston are rigidly connected into a piston assembly by a piston rod, the power piston is installed in the cylinder body, and the pump piston is installed in the pump body, and the pump piston is a differential pressure piston structure, There are hydraulic passages with different diameters on the pump body, the hydraulic passages are connected with the hydraulic system, the hydraulic system is a pressure differential closed hydraulic system, and the hydraulic system includes high-pressure hydraulic oil circuit and secondary high-pressure hydraulic oil Road, the hydraulic circuit of the hydraulic system is a closed circuit, Wherein, the high-pressure stage hydraulic oil circuit includes a high-pressure accumulator, the first hydraulic channel on the pump body is connected to the high-pressure accumulator through a first check valve, and the second hydraulic channel on the pump body is connected to the high-pressure accumulator through a first check valve. The second one-way valve is connected with the high-pressure accumulator, and the third hydraulic passage on the pump body is connected with the second hydraulic passage and the second one-way valve through a damping valve, wherein the first hydraulic passage is the outlet The oil hydraulic channel, the second hydraulic channel is an oil outlet hydraulic channel, the third hydraulic channel is a damping hole hydraulic channel, the diameter of the first hydraulic channel is larger than the diameter of the second hydraulic channel, and the second The diameter of the hydraulic channel is larger than that of the third hydraulic channel, and both the first check valve and the second check valve are oil outlet check valves. 2. A kind of hydraulic free piston engine according to claim 1, characterized in that, the secondary high-pressure stage hydraulic oil circuit comprises a secondary high-pressure accumulator, the fourth hydraulic channel on the pump body and the secondary The fifth hydraulic passage on the pump body is connected to the secondary high-pressure accumulator through the third check valve, and the sixth hydraulic passage on the pump body is connected to the secondary high-pressure accumulator through the first solenoid valve. The accumulator is connected, the starting hydraulic pump is connected with the secondary high-pressure accumulator through the fourth one-way valve, and a relief valve is connected between the outlet of the starting hydraulic pump and the fourth one-way valve, wherein the fifth hydraulic channel is the oil inlet hydraulic channel, the sixth hydraulic channel is the oil inlet solenoid valve channel, the diameter of the fifth hydraulic channel is larger than the diameter of the sixth hydraulic channel, the first solenoid valve is a frequency control solenoid valve, and the third one-way valve is a secondary high pressure Inlet check valve. 3. A hydraulic free piston engine according to claim 1, characterized in that the seventh hydraulic channel on the pump body is connected to the second solenoid valve. 4. A hydraulic free-piston engine according to claim 2, characterized in that a third solenoid valve is connected between the high-pressure accumulator and the secondary high-pressure accumulator. 5. A kind of hydraulic free-piston engine according to claim 1, characterized in that, the cylinder head is installed on one end of the cylinder block, the spark plug is installed on the cylinder head, and an air intake check valve is installed at the air inlet to scavenge air. The cavity communicates with the scavenging port through the scavenging channel, and the exhaust port is located on one side of the cylinder. 6. A hydraulic free-piston engine according to claim 1, characterized in that, the tail end face of the pump piston is an annular acting surface, the head end face is a circular acting face, and the circular acting face area of the head end face is larger than that of the tail end. The annular active surface area of the end face. 7. A kind of hydraulic free piston engine according to claim 1, is characterized in that, also comprises controller, and this controller communicates with spark plug, first solenoid valve, second solenoid valve, the 3rd solenoid valve and relief valve respectively connected through the circuit. 8. A hydraulic free piston engine according to claim 1, characterized in that the high-pressure accumulator is connected to the oil inlet end of the hydraulic motor, the secondary high-pressure accumulator is connected to the oil return end of the hydraulic motor, and the high-pressure accumulator The accumulator is connected to the oil inlet end of the hydraulic cylinder, and the secondary high-pressure accumulator is connected to the oil return end of the hydraulic cylinder.