阅读说明：本技术 交叉连杆双曲轴功率传输机构 (Cross connecting rod double-crankshaft power transmission mechanism ) 是由 张佰力 张健 张玉川 于 2020-07-17 设计创作，主要内容包括：交叉连杆双曲轴功率传输机构包括活塞,活塞上安装相互平行的第一活塞销和第二活塞销,第一活塞销与第一连杆的小头连接,第一连杆的大头与第一曲轴的连杆轴颈连接,第二活塞销与第二连杆的小头连接,第二连杆的大头与第二曲轴的连杆轴颈连接,第一连杆与第二连杆相互交叉。本发明的优点在于：本发明有效缩减了两个曲轴之间的间距、减小了两个同步齿轮的直径,有利于缩小双曲轴发动机功率传输机构的体积、降低自身重量,减少功率传输机构对双曲轴发动机自身动力的消耗,有利于显著提升发动机的有效热效率；还可降低对发动机功率传输机构中相应部件的加工和装配精度的要求,有利于降低发动机的生产成本等。(The crossed connecting rod double-crankshaft power transmission mechanism comprises a piston, wherein a first piston pin and a second piston pin which are parallel to each other are mounted on the piston, the first piston pin is connected with a small end of a first connecting rod, a large end of the first connecting rod is connected with a connecting rod journal of a first crankshaft, the second piston pin is connected with a small end of a second connecting rod, a large end of the second connecting rod is connected with a connecting rod journal of a second crankshaft, and the first connecting rod and the second connecting rod are crossed with each other. The invention has the advantages that: the invention effectively reduces the space between the two crankshafts, reduces the diameters of the two synchronous gears, is beneficial to reducing the volume of the power transmission mechanism of the double-crankshaft engine, reducing the self weight, reducing the consumption of the power transmission mechanism to the self power of the double-crankshaft engine and obviously improving the effective thermal efficiency of the engine; the requirements on the machining and assembling precision of corresponding parts in the engine power transmission mechanism can be reduced, and the production cost of the engine can be reduced.)

1. Cross connecting rod double-crankshaft power transmission mechanism, including piston (1), its characterized in that: a first piston pin (2) and a second piston pin (3) which are parallel to each other are mounted on a piston (1), the first piston pin (2) is connected with a small end of a first connecting rod (4), a large end of the first connecting rod (4) is connected with a connecting rod journal of a first crankshaft (5), the second piston pin (3) is connected with a small end of a second connecting rod (6), a large end of the second connecting rod (6) is connected with a connecting rod journal of a second crankshaft (7), the first connecting rod (4) and the second connecting rod (6) are crossed with each other, synchronizing gears (8) are mounted on the first crankshaft (5) and the second crankshaft (7), the synchronizing gears (8) on the first crankshaft (5) are meshed with the synchronizing gears (8) on the second crankshaft (7), and the connecting rods and the crankshafts are arranged in a negative deflection mode.

2. The cross-link dual crankshaft power transfer mechanism of claim 1, wherein: first bent axle (5) and second bent axle (7) structure are the same, all include multistage main shaft (11), synchronous gear (8) of one end installation of at least one section main shaft (11), main shaft (11) tip is connected with the centre of a circle of synchronous gear (8), eccentric setting connecting rod journal (18) between the crank of synchronous gear (8) and adjacent one section main shaft (11) tip, synchronous gear (8) of first bent axle (5) and synchronous gear (8) intermeshing of second bent axle (7), all set up balanced counter weight (14) on each synchronous gear (8).

3. The cross-link dual crankshaft power transfer mechanism of claim 1, wherein: the structure of the first crankshaft (5) is the same as that of the second crankshaft (7), the first crankshaft and the second crankshaft both comprise a plurality of sections of main shafts (11), one end, close to each other, of at least two sections of adjacent main shafts (11) is provided with one synchronous gear (8), the end part of each main shaft (11) is connected with the circle center of each synchronous gear (8), a connecting rod journal (18) is eccentrically arranged between the two synchronous gears (8), the synchronous gears (8) of the first crankshaft (5) are meshed with the synchronous gears (8) of the corresponding positions of the second crankshaft (7), and each synchronous gear (8) is provided with a balance weight (14).

4. The cross-link dual crankshaft power transmission mechanism of claim 2 or 3, wherein: each synchronous gear (8) is provided with a lightening groove (13), and the position of each synchronous gear (8) without the lightening groove (13) forms a balance weight (14) of the crankshaft.

5. The cross-link dual crankshaft power transmission mechanism of any of claims 1, 2 or 3, wherein: the first connecting rod (4) and the second connecting rod (6) are identical in shape and size and comprise a small connecting rod head (15) and a large connecting rod head (16), a connecting rod body (17) between the small connecting rod head (15) and the large connecting rod head (16) is located on one side of the axial central point of the small connecting rod head (15), the first connecting rod (4) and the second connecting rod (6) are installed in a forward-reverse mode during installation, and namely the connecting rod bodies (17) of the first connecting rod (4) and the second connecting rod (6) are located on two sides of the axial central point of the small connecting rod head respectively.

Technical Field

The invention relates to a piston engine, in particular to a crossed connecting rod double-crankshaft power transmission mechanism.

Background

The reciprocating piston engine refers to a piston which makes reciprocating linear motion in a cylinder, and the linear motion of the piston is converted into the rotation motion of a crankshaft through a connecting rod and a crankshaft mechanism to transmit the power of the engine. The piston mainly has the functions of bearing the combustion pressure in the cylinder and ensuring the reliable sealing of the working medium of the power generator. In the traditional engine structure, a piston is hinged with a small end of a connecting rod through a piston pin, a large end of the connecting rod is hinged with a connecting rod journal of a crankshaft, when the structure operates, a part of combustion pressure borne by the piston is converted into lateral force between the piston and a cylinder wall under the swinging action of the connecting rod, the lateral force exists all the time in the whole working process of the piston and does not work, the abrasion of the piston and the cylinder wall is accelerated, the noise and vibration of the engine during working are increased, and therefore the lateral force between the piston and the cylinder wall can bring power loss to the engine, influence the service life of the engine, and bring difficulty for suppressing the noise and vibration of a manufacturing enterprise, and is obviously a negative acting force. In order to eliminate the lateral force of the piston as much as possible, a person skilled in the art designs a double-crankshaft engine, a power transmission mechanism of the engine comprises two crankshafts which are parallel to each other, the two crankshafts are respectively connected with the same piston through two connecting rods, the two crankshafts rotate reversely and synchronously during operation, and the lateral force between the piston and the cylinder wall is eliminated by utilizing the lateral force which is generated by the two connecting rods and has opposite directions to realize the balance of the lateral force on the piston.

At present, two connecting rods of a double-crankshaft engine are generally connected with a piston in two modes, wherein one mode is that two piston pins are arranged on the piston from left to right, a left connecting rod is connected with a left piston pin, and a right connecting rod is connected with a right piston pin; the other is that only one piston pin is arranged on the piston, and the left connecting rod and the right connecting rod are connected with the same piston pin. Two kinds of connection structure above, for guaranteeing that the connecting rod has sufficient activity space, need leave sufficient interval between two bent axles, and the interval between the bent axle is big more, the diameter of synchronous gear between the bent axle is just big more, consequently current double-crankshaft engine compares with the ordinary engine of same discharge capacity, the ubiquitous power transmission mechanism volume is bigger, the heavier disadvantage of dead weight, although vibration and noise can be restrained, the dead weight of power transmission mechanism has consumed the power of engine by a wide margin, the effective thermal efficiency and the fuel economy of engine are not showing and are promoted, and need still occupy more spaces. Therefore, the double-crankshaft engine is not widely applied at present.

It is found by those skilled in the art that, in a double crankshaft power transmission mechanism with negative bias (the angle range through which the crankshaft rotates in the power stroke of the engine power output mechanism is less than 180 degrees), the power transmission efficiency of the engine power transmission mechanism (i.e. the effective thermal efficiency of the engine) is closely related to the coefficient of the bias mechanism (the quotient of the difference between the length L of the connecting rod and the radius R of the crankshaft divided by the eccentric distance e), and the larger the coefficient of the bias mechanism, the higher the power transmission efficiency of the engine power transmission mechanism (for example, the method for improving the effective thermal efficiency of the engine disclosed in chinese patent CN 108518279B). If the coefficient of the offset mechanism is further improved, the double-crankshaft engine inevitably brings further increase of the distance between the crankshafts, the size and the weight of the synchronous gear between the crankshafts are also greatly increased, the load of the engine is larger, the improvement effect on the effective heat efficiency of the engine is limited, the body volume and the weight of the engine are obviously increased, and the practicability is lower.

Disclosure of Invention

The invention aims to provide a crossed connecting rod double-crankshaft power transmission mechanism, which is characterized in that connecting rods are arranged in a crossed manner on the basis of a double-crankshaft engine power transmission mechanism, so that the distance between two crankshafts is effectively reduced, the diameters of two synchronous gears are reduced, the size and the weight of the double-crankshaft engine power transmission mechanism are favorably reduced, the consumption of the power transmission mechanism on the power of the double-crankshaft engine is reduced, favorable conditions are created for further improving the coefficient of a biasing mechanism of the engine power transmission mechanism, and the effective thermal efficiency of the engine is favorably and remarkably improved.

In order to achieve the purpose, the invention is realized by the following technical scheme: the piston is provided with a first piston pin and a second piston pin which are parallel to each other, the first piston pin is connected with a small end of a first connecting rod, a big end of the first connecting rod is connected with a connecting rod journal of a first crankshaft, the second piston pin is connected with a small end of a second connecting rod, a big end of the second connecting rod is connected with a connecting rod journal of a second crankshaft, the first connecting rod and the second connecting rod are crossed with each other, the first crankshaft and the second crankshaft are both provided with synchronous gears, the synchronous gears on the first crankshaft are meshed with the synchronous gears on the second crankshaft, and the connecting rods and the crankshafts are arranged in a negative offset mode. The first crankshaft and the second crankshaft are identical in structure and respectively comprise a plurality of sections of main shafts, one end, close to each other, of at least two sections of adjacent main shafts is provided with a synchronous gear, the end part of each main shaft is connected with the circle center of the corresponding synchronous gear, a connecting rod journal is eccentrically arranged between the two synchronous gears, the synchronous gears of the first crankshaft are meshed with the synchronous gears of the corresponding positions of the second crankshaft, and each synchronous gear is provided with a balance weight. Each synchronous gear is provided with a weight reduction groove, and a balance weight of the crankshaft is formed at the position where the weight reduction groove is not arranged on each synchronous gear. The first connecting rod and the second connecting rod are the same in shape and size and respectively comprise a small connecting rod head and a large connecting rod head, the rod body between the small connecting rod head and the large connecting rod head is positioned on one side of the axial central point of the small connecting rod head, and the first connecting rod and the second connecting rod are installed in a forward-backward mode during installation, namely the rod bodies of the first connecting rod and the second connecting rod are respectively positioned on two sides of the axial central point of the small connecting rod head. The connecting rod and crankshaft are arranged in a negatively biased manner.

The invention has the advantages that: on the basis of the power transmission mechanism of the double-crankshaft engine, the connecting rods are arranged in a crossed manner, so that the distance between the two crankshafts is effectively reduced, the diameters of the two synchronous gears are reduced, the size and the weight of the power transmission mechanism of the double-crankshaft engine are reduced, the consumption of the power transmission mechanism on the power of the double-crankshaft engine is reduced, favorable conditions are created for further improving the coefficient of a biasing mechanism of the power transmission mechanism of the engine, and the effective thermal efficiency of the engine is improved remarkably; when the engine crank connecting rod has assembly errors due to processing, installation and other problems, the piston offset generated by the invention is far smaller than the structure of the existing double-crankshaft engine, so that the invention can effectively reduce the occurrence probability of cylinder clamping phenomenon and reduce the abrasion degree of the piston and the cylinder body when the assembly errors are difficult to avoid, can also reduce the requirements on the processing and assembly precision of corresponding parts in the engine power transmission mechanism, and is beneficial to reducing the production cost of the engine and the like.

Drawings

FIG. 1 is a schematic diagram of the structure of the present invention;

FIG. 2 is one of the schematic diagrams of a prior art engine power transmission mechanism employing a non-intersecting double link configuration of two pins;

FIG. 3 is a second schematic diagram of a prior art engine power transmission mechanism employing a dual link structure sharing the same pin;

FIG. 4 is a screenshot of a dynamic representation of a non-intersecting double link configuration using two pins under assumed error conditions, illustrating primarily the piston excursion;

FIG. 5 is a screenshot of a dynamic representation of a dual link configuration using a common pin under assumed error conditions, illustrating primarily the piston excursion;

FIG. 6 is a screenshot of a dynamic representation of a crossed double link configuration using two pins under assumed error conditions, illustrating primarily the piston excursion;

FIG. 7 is a graph comparing piston excursion curves under assumed error conditions;

FIG. 8 is a schematic structural view of the present invention;

FIG. 9 is a schematic left side view of the structure of FIG. 8;

FIG. 10 is a schematic sectional view A-A of FIG. 8;

FIG. 11 is a schematic perspective view of the present invention;

FIG. 12 is a schematic view of the arrangement of FIG. 9 replaced with two sets of synchronizing gears;

FIG. 13 is a schematic view of the alternate arrangement of the two connecting rods and the two wrist pins according to the present invention.

Detailed Description

The invention relates to a crossed connecting rod double-crankshaft power transmission mechanism, which comprises a piston 1, wherein a first piston pin 2 and a second piston pin 3 which are parallel to each other are installed on the piston 1, the first piston pin 2 is connected with a small end of a first connecting rod 4, a large end of the first connecting rod 4 is connected with a connecting rod journal of a first crankshaft 5, the second piston pin 3 is connected with a small end of a second connecting rod 6, a large end of the second connecting rod 6 is connected with a connecting rod journal of a second crankshaft 7, the first connecting rod 4 and the second connecting rod 6 are crossed with each other, synchronous gears 8 are installed on the first crankshaft 5 and the second crankshaft 7, the synchronous gears 8 on the first crankshaft 5 are meshed with the synchronous gears 8 on the second crankshaft 7, and the connecting rods and the crankshafts are arranged in a negative deflection mode. The negative bias of the connecting rod and the crankshaft means that the angle range rotated by the crankshaft is less than 180 degrees in the whole working stroke of the engine power output mechanism. The invention adopts the mutually crossed connecting rod structure, can effectively increase the overlapping area of the swing range of the two connecting rods of the double-crankshaft engine, greatly reduce the distance between the two crankshafts, obviously reduce the diameters of the two synchronous gears, and is favorable for reducing the volume of the power transmission mechanism of the double-crankshaft engine, reducing the self weight of the power transmission mechanism of the double-crankshaft engine and the consumption of the power transmission mechanism on the self power of the double-crankshaft engine after the diameters of the synchronous gears are reduced, thereby creating favorable conditions for further improving the offset mechanism coefficient of the power transmission mechanism of the engine and being favorable for obviously improving the effective thermal efficiency of the engine.

Taking a power transmission mechanism used in a double-crankshaft engine with a certain type of non-crossed connecting rods as an example, the size data of the power transmission mechanism of the engine are as follows:

the length L of the connecting rod is 8.60 cm;

the radius R of the crankshaft is 2.00 cm;

eccentricity e is 4.85 cm;

the coefficient of the biasing mechanism of the power transmission mechanism is e/(L-R) ═ 0.735;

as shown in fig. 2, two piston pins are arranged on a piston of the power transmission mechanism, and the center distance k between the two piston pins and the center line of the piston is 1.15 cm;

the pitch circle diameter of the power transmission mechanism synchronizing gear is 2 × (e + k) ═ 12.0 cm.

If the power transmission mechanism of the above-described double crankshaft engine is changed to a structure in which two connecting rods share the same piston pin, as shown in fig. 3, the pitch circle diameter of the synchronizing gear is 2 × e, which is 9.7cm, while the coefficient of the biasing mechanism remains unchanged.

In the power transmission mechanism of the dual-crankshaft engine, if the cross connecting rod structure provided by the invention is adopted, as shown in fig. 1, the center distance k between the two piston pins and the center line of the piston is 1.15cm, and under the condition that the offset mechanism coefficient is kept unchanged, the pitch circle diameter of the synchronous gear of the power transmission mechanism is 2 x (e-k), which is 7.4 cm.

The comparison shows that under the same condition, the diameter of the synchronous gear can be obviously reduced by adopting the cross connecting rod structure provided by the invention, the consumption of the power transmission mechanism to the self power of the double-crankshaft engine is reduced, and favorable conditions are created for further improving the offset mechanism coefficient of the power transmission mechanism of the engine. The problem that the volume and the weight of a power transmission mechanism are greatly increased along with the increase of the offset coefficient of a conventional double-crankshaft engine and the effective thermal efficiency of the engine is not obviously improved due to the fact that a larger load is brought to the engine can be effectively solved.

Although the power transmission mechanism of the dual-crankshaft engine can theoretically eliminate the lateral force of the piston and enable the piston to reciprocate along a straight line, in the actual manufacturing and mounting process, the motion trail of the piston deviates from the central line of the cylinder during the working of the engine due to various reasons such as the deviation of the processing size of a connecting rod, the deviation of the non-perpendicularity of the cylinder axis and the connecting line of two crankshafts, the deviation of the position of a synchronous gear during the assembly, the inconsistency of gaps between pin holes and the like, and when the offset of the motion trail of the piston is large, the abrasion of the piston and the cylinder wall can be accelerated, the sealing performance of the piston is affected, the service life of the engine is shortened, the noise and vibration of the engine during the working can be increased, and. After the engine adopts the cross connecting rod structure provided by the invention, the offset of the motion trail of the piston caused by various reasons can be obviously reduced.

The diameter of a piston at a piston ring is set to be 6.78cm on the basis of the double-crankshaft engine of a certain model; the cylinder diameter is 6.80 cm. The pitch circle diameter of the synchronous gear is set to be 7.4cm, assuming that the accumulated error of processing and mounting of the engine crank connecting rod is that the crank of the crankshaft deviates 0.5 degrees from the theoretical angle (the deviation of the circle center of the connecting rod journal on the corresponding crank deviates 0.175mm from the arc length), a non-crossed double-connecting-rod structure dynamic representation diagram (figure 4) adopting two pin shafts, a double-connecting-rod structure dynamic representation diagram (figure 5) sharing the same pin shaft and a crossed connecting-rod structure dynamic representation diagram (figure 6) adopting two pin shafts of the engine are drawn according to the actual size of the double-crankshaft engine by using geometric drawing board software, the offset values of pistons in the 360-degree rotating process of the crankshaft of three structures are respectively recorded, and then a piston offset curve comparison diagram (figure 7) is drawn according to the offset of the pistons of the three.

From the values and the variation curves of the piston offset shown in fig. 7, it can be seen that: when the engine adopts a non-crossed double-connecting-rod structure with two pin shafts, under the assumed error condition, the piston is subjected to cylinder clamping due to overlarge offset just after descending from the upper dead center, so that the piston generates large-amplitude vibration, the maximum value of the offset of the piston reaches 0.376mm, the piston engine used in various fields generally requires that the maximum fit clearance between the piston and the cylinder wall is within 0.2mm, and the offset of the piston of the structure under the assumed error condition far exceeds the fit clearance between the piston and the cylinder wall, so that the cylinder clamping phenomenon is difficult to avoid in practical use, and the engine cannot work normally.

When the engine adopts a double-connecting-rod structure sharing the same pin shaft, the offset value and the variation curve of the piston shown in figure 7 can be seen: under the assumed error condition, the maximum offset of the piston reaches 0.438mm at a crank angle of 74 degrees from the top dead center in the compression stroke, although the piston inclines at a certain angle in a demonstration drawing to enable the stroke to run smoothly, the actual offset of the piston still far exceeds the normal fit clearance between the piston and the cylinder wall, the cylinder clamping phenomenon is difficult to avoid in actual use, and although the maximum deviation does not occur in the power stroke, the abrasion condition of the piston and the cylinder wall is aggravated in use, and the service life of the engine is influenced.

When the engine adopts the crossed connecting rod structure of two pin shafts provided by the invention, the numerical value and the variation curve of the offset of the piston shown in figure 7 can be seen: under the assumed error condition, the maximum offset of the piston is only 0.098mm, and the maximum fit clearance between the piston and the cylinder wall can work normally under the condition of 0.2 mm.

The analysis result shows that when the engine crank connecting rod has assembly errors due to processing, installation and other problems, the offset generated by the piston when the cross connecting rod structure provided by the invention is adopted is far smaller than that of a non-cross double connecting rod structure adopting two pin shafts and that of a double connecting rod structure sharing the same pin shaft, so that the cross connecting rod structure provided by the invention can effectively reduce the occurrence probability of cylinder clamping phenomenon and the abrasion degree of the piston and a cylinder body when the assembly errors are difficult to avoid, can also reduce the requirements on the processing and assembly precision of corresponding parts in an engine power transmission mechanism, and is beneficial to reducing the production cost of the engine.

In the operation process of the demonstration diagram, when the engine power transmission mechanism adopts the crossed connecting rod structure with two pin shafts provided by the invention, the radial offset of the piston is reduced, and the axial stroke of the piston is slightly increased, so that the crossed connecting rod structure can convert partial offset of the piston into the linear motion stroke of the piston compared with a non-crossed connecting rod structure.

Since the pitch circle diameter of the synchronous gears is uniformly set to be 7.4cm in fig. 4, 5 and 6, it can be seen that under the condition that the pitch circle size of the synchronous gears is uniform, the eccentric distances e of the crank connecting rods are different in different connecting rod cross connection modes, so that the coefficient of the biasing mechanism is changed accordingly; according to the calculation formula of the coefficient of the biasing mechanism, the coefficient of the biasing mechanism of the non-crossed double-link structure adopting the two pin shafts of the engine is 0.386, the coefficient of the biasing mechanism of the double-link structure adopting the same pin shaft is 0.561, and the coefficient of the biasing mechanism of the crossed link structure adopting the two pin shafts provided by the invention is 0.735. The comparison shows that under the condition that the sizes of the components of the engine power transmission mechanism are the same, the cross connecting rod structure provided by the invention can obviously improve the coefficient of the offset mechanism, so that the power transmission efficiency of the power transmission mechanism is greatly improved, and the effective thermal efficiency of the engine is further greatly improved.

Since the traditional non-cross connecting rod double-crankshaft engine is born till now, the problem of piston lateral force can be solved by the knowledge of the double-crankshaft engine in the industry, but the effective thermal efficiency of the engine is not improved, the requirements on component manufacturing and assembling precision are extremely high, and the production cost is difficult to be accepted by the market. The arrangement of the connecting rods has never been appreciated by those skilled in the art as having an effect on the thermal efficiency and accuracy requirements of the twin crankshaft engine, which has been known for many years to have formed a common understanding of those skilled in the art, and thus the twin crankshaft engine has not been widely used. The applicant of the invention deeply studies the structural principle of the double-crankshaft engine for many years, and repeatedly tries to improve the double-crankshaft engine in combination with tests, finally discovers that the cross-connecting rod double-crankshaft structure can obviously improve the effective thermal efficiency of the engine, further discovers that the cross-connecting rod double-crankshaft structure can reduce the offset of a piston in the tests, so that the precision of the double-crankshaft engine on component manufacturing and assembling is reduced, the production cost is effectively reduced, and then proves that the effect is really existing in combination with the tests and theoretical derivation, the effect greatly exceeds the expectation of people on the performance of the double-crankshaft engine, so that the common cognition of technicians in the field on the double-crankshaft engine can be covered, and the technical bias in the industry can be overcome.

The invention can be applied to various engine products such as small single-cylinder engines, multi-cylinder engines and the like, and in order to further reduce the volume of the engine power transmission mechanism and the weight of the engine power transmission mechanism, as shown in figures 8-11, the following structures are preferably adopted: the first crankshaft 5 and the second crankshaft 7 are identical in structure and respectively comprise a plurality of sections of main shafts 11, one end of at least one section of main shaft 11 is provided with a synchronous gear 8, the end part of the main shaft 11 is connected with the circle center of the synchronous gear 8, a connecting rod journal 18 is eccentrically arranged between the synchronous gear 8 and the crank at the end part of the adjacent section of main shaft 11, the synchronous gear 8 of the first crankshaft 5 is meshed with the synchronous gear 8 of the second crankshaft 7, and each synchronous gear 8 is provided with a balance weight 14. The structure integrates the synchronous gear of the double-crankshaft engine, the crank of the crankshaft and the balancing weight into a whole, further simplifies the structure of the power transmission mechanism of the engine, enables the size of the power transmission mechanism to be more compact and the self weight to be lighter, and further reduces the consumption of the power transmission mechanism to the self power of the double-crankshaft engine.

On the basis of the above scheme, in order to ensure the rotation stability of the two crankshafts, as shown in fig. 12, two groups of synchronous gears can be arranged between the two crankshafts, and the specific structure is as follows: the first crankshaft 5 and the second crankshaft 7 have the same structure and respectively comprise a plurality of sections of main shafts 11, wherein one end, close to each other, of each of the two sections of adjacent main shafts 11 is respectively provided with one synchronous gear 8, the end part of each main shaft 11 is connected with the circle center of the corresponding synchronous gear 8, a connecting rod journal 18 is eccentrically arranged between the two synchronous gears 8, the synchronous gear 8 of the first crankshaft 5 is meshed with the synchronous gear 8 at the corresponding position of the second crankshaft 7, and each synchronous gear 8 is provided with a balance weight 14. This structure ensures two bent axle synchronous revolution through two sets of synchronous gears that are adjacent, and two sets of synchronous gears have all replaced the crank portion of bent axle, and the counter weight part of bent axle is shared by two synchronous gears jointly, therefore the thickness of each synchronous gear can suitably reduce, can not cause obvious influence to the dead weight of power transmission mechanism, but the stability of two bent axles can be showing and is promoted.

In order to further reduce the volume of the engine power transmission mechanism and reduce the weight of the engine power transmission mechanism, weight reducing grooves 13 are formed in all the synchronous gears 8, and balance weights 14 of crankshafts are formed at positions where the weight reducing grooves 13 are not formed in all the synchronous gears 8. According to the structure, the balance weight 14 is hidden in the synchronous gear 8, so that the number of parts of the engine power transmission mechanism can be reduced, the processing and assembling difficulty is reduced, and the balance weight 14 can be prevented from interfering with other parts when the crankshaft rotates, so that the structure of the engine power transmission mechanism is more compact.

The double connecting rod in the invention can adopt various structures, wherein the preferable structure is as follows: the first connecting rod 4 and the second connecting rod 6 are the same in shape and size and both comprise a small connecting rod head 15 and a large connecting rod head 16, a connecting rod body 17 between the small connecting rod head 15 and the large connecting rod head 16 is located on one side of the axial central point of the small connecting rod head 15, and the first connecting rod 4 and the second connecting rod 6 are installed in a forward-reverse mode during installation, namely the connecting rod bodies 17 of the first connecting rod 4 and the second connecting rod 6 are located on two sides of the axial central point of the small connecting rod head 15 respectively. The shape and the size of the first crankshaft 5 and the second crankshaft 7 of the structure are completely the same, the directions are opposite when only the structure is installed, the two connecting rods can adopt the connecting rods of the same batch produced by the same set of production equipment, and the structure can avoid the problem that when the left connecting rod and the right connecting rod are designed into different shapes, the two sets of production equipment are adopted for processing to generate processing errors, thereby being beneficial to minimizing the errors generated when the two connecting rods are manufactured and assembled and reducing the offset generated in the piston stroke as much as possible. In addition, the double connecting rods of the present invention may also adopt other various structures, such as the structure shown in fig. 13, and the two connecting rods and the two piston pins are arranged in a staggered manner, so that although the two connecting rods may also adopt the connecting rods of the same batch produced by the same set of production equipment, the stressed positions of the pistons are staggered, and a synchronous gear cannot be used to replace the crank of the crankshaft, and a separate synchronous gear needs to be installed on the crankshaft. In addition, the connecting rod and the piston pin which are arranged in a staggered mode can cause the piston to be stressed and deviated, the piston is prone to torsion deviation in the range of fit clearance between the piston pin and the cylinder wall when the engine works actually, abrasion of the piston ring and the cylinder body is aggravated, and shaking is prone to occurring in the working process of the piston.