Gear transmission mechanism of power-assisted bicycle and power-assisted bicycle

Abstract

The utility model discloses a gear transmission mechanism of a power-assisted bicycle and the power-assisted bicycle, and relates to the field of bicycles. The gear transmission mechanism comprises a plurality of transmission gears; a first gear and a second gear form a first-stage high-speed gear pair; the third gear and the fourth gear form a second-stage medium-speed gear pair; and a third-stage low-speed gear pair is formed by the fifth gear and the sixth gear. Gear teeth of the transmission gears are provided with working tooth surfaces and non-working tooth surfaces, and the pressure angle of the working tooth surface of each transmission gear is larger than that of the non-working tooth surface. The gear transmission mechanism adopts a three-stage speed reduction scheme, and is simple to process and assemble and low in cost. The gear teeth of the transmission gear are asymmetrically designed, so that the gear strength of the transmission gear can be improved, and the tooth surface pitting corrosion of the working tooth surface is effectively prevented. The reduction ratio of each stage of gear pair is relatively small, a gear with a large modulus can be adopted as a transmission gear, the strength of all gears can be improved, the stress balance is improved, and noise is reduced.

Description

Technical Field

[0001] The utility model relates to the field of power-assisted bicycles, in particular to a gear transmission mechanism of a power-assisted bicycle and the power-assisted bicycle. Background Art

[0002] Traditional power-assisted bicycles are equipped with a gear transmission module for speed reduction transmission. Since the gear transmission module is installed on the bicycle, it is required to be small in size and light in weight. In order to achieve this goal, designers often use small gears with small modules to meet the transmission requirements. However, due to the extreme miniaturization, the gears are prone to insufficient strength under the same load due to excessive surface pressure, which makes the life of the gear transmission module fail to meet the standards. At the same time, the gear transmission module will also produce a high noise problem when rotating at high speed. Some speed change mechanisms have been designed in the prior art, which use planetary gear solutions for speed reduction transmission. However, the planetary gear solution has a complex structure, and no other solutions for enhancing gear strength and reducing noise are mentioned. The overly complex structure of the whole machine also increases the difficulty of processing and manufacturing. Therefore, a better solution needs to be proposed to solve the above problems. Utility Model Content

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model provides a gear transmission mechanism for a power-assisted bicycle, which adopts a graded speed reduction, which is not only simple in structure and assembly, but also can improve the strength of the transmission gear.

[0004] The utility model also aims to provide a power-assisted bicycle with the gear transmission mechanism.

[0005] The gear transmission mechanism of the power-assisted bicycle according to the embodiment of the utility model comprises a plurality of transmission gears, which are respectively: a first gear and a second gear meshed with each other, used to form a first-stage high-speed gear pair, the first gear being used to connect a power source; a third gear and a fourth gear meshed with each other, used to form a second-stage medium-speed gear pair, the third gear being connected to the second gear; a fifth gear and a sixth gear meshed with each other, used to form a third-stage low-speed gear pair, the fifth gear being connected to the fourth gear. The gear teeth of the transmission gears have working tooth surfaces and non-working tooth surfaces, and the pressure angle of the working tooth surface of each transmission gear is greater than the pressure angle of the non-working tooth surface.

[0006] According to the gear transmission mechanism of the power-assisted bicycle of the embodiment of the utility model, a three-stage speed reduction gear transmission scheme is adopted, which is simple to process and assemble, and has low cost. By utilizing the pressure angle of the working tooth surface of each transmission gear to be greater than the pressure angle of the non-working tooth surface, the asymmetric design can improve the gear strength of the transmission gear and effectively prevent the pitting of the tooth surface of the working tooth surface. Moreover, compared with the one-stage speed reduction, the reduction ratio of each gear pair of the three-stage speed reduction is relatively small, and gears with larger modulus can be used as transmission gears, which is beneficial to increase the strength of all gears, improve the force balance, and reduce noise.

[0007] In some embodiments, the working tooth surface is an involute tooth surface, and the pressure angle of the working tooth surface ranges from 30° to 35°.

[0008] In some embodiments, the non-working tooth surface is an involute tooth surface, and the pressure angle of the non-working tooth surface ranges from 20° to 25°.

[0009] In some embodiments, the tooth direction trimming adopted by the working tooth surface is 3um-5um drum trimming, and the tooth shape trimming adopts 2um-4um upper pressure angle trimming.

[0010] In some embodiments, the module of the transmission gear is m, the tooth root of the transmission gear has a fillet, and the radius R of the fillet reaches 0.2-0.4 times of m.

[0011] In some embodiments, the overlap of the first-stage high-speed gear pair is at least 4.5, the overlap of the second-stage medium-speed gear pair is at least 3.5, and the overlap of the third-stage low-speed gear pair is at least 1.5.

[0012] In some embodiments, the number of teeth of the first gear and the number of teeth of the second gear are mutually prime.

[0013] In some embodiments, the first gear and the second gear are plastic parts.

[0014] In some embodiments, axes of the six transmission gears are arranged in parallel.

[0015] The power-assisted bicycle according to the embodiment of the utility model comprises: a motor; and the gear transmission mechanism of the power-assisted bicycle described in the above embodiment, wherein the first gear is connected to the motor shaft of the motor.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0018] Figure 1 is a distribution diagram of a motor and a gear transmission mechanism in one embodiment;

[0019] Figure 2 is a cross-sectional view of a motor and a gear transmission mechanism in one embodiment;

[0020] Figure 3 is a schematic diagram of the tooth profile of a transmission gear in an embodiment (the dotted line in the figure is a reference profile symmetrical to the non-working tooth surface profile);

[0021] Figure 4 It is a tooth surface contact surface pressure distribution diagram when the transmission gear of the gear pair in the gear transmission mechanism in a specific embodiment adopts a symmetrical gear without modification;

[0022] Figure 5 The diagram is a tooth contact surface pressure distribution diagram when the transmission gear of the gear pair in the gear transmission mechanism in a specific embodiment adopts an asymmetric gear with modified shape.

[0023] Reference numerals:

[0024] Power-assisted bicycles 100;

[0025] Gear transmission mechanism 1, transmission gear 10;

[0026] The first gear 11, the second gear 12, and the primary high-speed gear pair 1A;

[0027] The third gear 13, the fourth gear 14, and the secondary medium-speed gear pair 1B;

[0028] The fifth gear 15, the sixth gear 16, and the third-stage low-speed gear pair 1C;

[0029] Working tooth surface 101, non-working tooth surface 102;

[0030] The pressure angle of the working tooth surface is α1, and the pressure angle of the non-working tooth surface is α2;

[0031] Motor 3. DETAILED DESCRIPTION

[0032] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0033] In the description of the present utility model, it should be understood that the terms "center", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, unless otherwise specified, "multiple" means two or more.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] Reference below Figure 1-Figure 5 A gear transmission mechanism 1 according to an embodiment of the present invention is described.

[0036] According to the gear transmission mechanism 1 of the power-assisted bicycle 100 of the present utility model, Figure 1 and Figure 2 , including a plurality of transmission gears 10. The plurality of transmission gears 10 include a first gear 11, a second gear 12, a third gear 13, a fourth gear 14, a fifth gear 15, and a sixth gear 16.

[0037] The first gear 11 and the second gear 12 are meshed and constitute a first-stage high-speed gear pair 1A. It can be understood that the number of teeth of the first gear 11 is less than the number of teeth of the second gear 12. The third gear 13 and the fourth gear 14 are meshed and constitute a second-stage medium-speed gear pair 1B. It can be understood that the number of teeth of the third gear 13 is less than the number of teeth of the fourth gear 14. The fifth gear 15 and the sixth gear 16 are meshed and constitute a third-stage low-speed gear pair 1C. It can be understood that the number of teeth of the fifth gear 15 is less than the number of teeth of the sixth gear 16.

[0038] Among them, the first gear 11 is used to connect the power source, the third gear 13 is connected to the second gear 12, and the fifth gear 15 is connected to the fourth gear 14. That is to say, after the power source transmits the rotational motion to the first gear 11, the first gear 11 is decelerated and transmitted to the second gear 12. Then, after the second gear 12 transmits the rotational motion to the third gear 13, the third gear 13 is decelerated and transmitted to the fourth gear 14. After that, the fourth gear 14 transmits the rotational motion to the fifth gear 15, and the fifth gear 15 is decelerated and transmitted to the sixth gear 16. In this way, the gear transmission mechanism 1 realizes reduction transmission through three-stage deceleration.

[0039] It can be understood that, compared to modifying the same reduction ratio from one stage speed reduction to three stages speed reduction from the first gear 11 to the sixth gear 16 in this application, the reduction ratio of each stage gear pair speed reduction can be reduced. With this arrangement, the tooth number ratio between the two transmission gears 10 of the same gear pair does not need to be set too large, so that a gear with a larger module can be used as the transmission gear 10. In this way, under the same load, the pressure bearing capacity of the working tooth surface 101 of the transmission gear 10 is increased, the strength of the transmission gear 10 can be improved, and the service life can be extended. Moreover, the diameter difference between the two transmission gears 10 of the same gear pair will not be too large, and the forces acting on the two transmission gears 10 are more balanced, which is conducive to reducing transmission noise.

[0040] Reference Figure 3 The gear teeth of the transmission gear 10 have a working tooth surface 101 and a non-working tooth surface 102. The pressure angle α1 of the working tooth surface 101 of each transmission gear 10 is greater than the pressure angle α2 of the non-working tooth surface 102. That is to say, the gear teeth are asymmetric teeth, the pressure angle α1 of the working tooth surface 101 of the transmission gear 10 is larger, and the pressure angle α2 of the non-working tooth surface 102 is smaller.

[0041] Specifically, each gear tooth of the transmission gear 10 has two opposite tooth surfaces. When the gear pairs are meshed, the tooth surface of the gear teeth of the transmission gear 10 that contacts the gear teeth of another transmission gear 10 is the working tooth surface 101 , and the other tooth surface is the non-working tooth surface 102 .

[0042] As is well known to those skilled in the art, the pressure angle of a gear refers to the angle between the tooth profile line and the tangent line. It is an important geometric parameter in gear design and is used to describe the shape of the gear tooth surface. The pressure angle is the angle between the direction line of the driving force on the driven gear and the velocity direction line of the force action point when the gear pair moves. It is an important indicator for judging transmission performance.

[0043] In the present application, since the working tooth surface 101 of the gear teeth of the transmission gear 10 is the main load-bearing surface, the pressure angle α1 of the working tooth surface 101 of the transmission gear 10 is selected to be larger, which is beneficial to reducing the tooth surface contact normal stress and working shear stress of the working tooth surface 101, and at the same time improving the bending strength of the tooth root, thereby improving the gear strength of the transmission gear 10, which is beneficial to preventing pitting corrosion of the working tooth surface 101.

[0044] For example, in a specific example, when the gear transmission mechanism of the three-stage reduction transmission adopts a symmetrical design of the transmission gear, that is, the pressure angle of the working tooth surface is equal to the pressure angle of the non-working tooth surface, such as Figure 4 As shown in the figure, the contact surface pressure of the tooth surface of the symmetrical gear without modification can be as high as 2471MPa, while the contact surface pressure of the tooth surface of the asymmetrical gear with modification is reduced to 2153Mpa. After a before-and-after comparison, it was found that the contact surface pressure of the tooth surface of the transmission gear dropped by nearly 13%, which was a significant drop in the tooth surface contact surface pressure.

[0045] The pressure angle α2 of the non-working tooth surface 102 of the transmission gear 10 is selected to be relatively small, which can ensure that the thickness of the tooth tip is sufficient, which is beneficial to ensuring the meshing efficiency of the gears and reducing energy loss.

[0046] In this application, a three-stage speed reduction gear transmission scheme is adopted, which is simple to process and assemble, and has low cost. By utilizing the pressure angle α1 of the working tooth surface 101 of each transmission gear 10 to be greater than the pressure angle α2 of the non-working tooth surface 102, the asymmetric design can improve the gear strength of the transmission gear 10 and effectively prevent pitting of the working tooth surface 101. Moreover, compared with the one-stage speed reduction, the reduction ratio of each gear pair of the three-stage speed reduction is relatively small, and a gear with a larger modulus can be used as the transmission gear 10, which is beneficial to increase the strength of all gears, improve force balance, and reduce noise.

[0047] In some embodiments, Figure 3 As shown, the working tooth surface 101 is an involute tooth surface. Using an involute tooth surface as the working tooth surface 101 can ensure a fixed transmission ratio in the meshing transmission, which is conducive to ensuring the consistency of the force transmission direction in the rotation.

[0048] Specifically, the working tooth surface 101 is a modified standard involute tooth surface, and the pressure angle α1 of the working tooth surface 101 ranges from 30° to 35°. In this way, the gear teeth are thickened near the root, and although the radial force generated is large, the gear teeth have a large bending strength and can resist a large impact force.

[0049] In some embodiments, Figure 3 As shown, the non-working tooth surface 102 is an involute tooth surface. Using an involute tooth surface as the non-working tooth surface 102 can ensure a fixed transmission ratio in the meshing transmission, which is beneficial to ensuring the consistency of the force transmission direction in the rotation.

[0050] Specifically, the non-working tooth surface 102 is a standard involute tooth surface without modification, and the pressure angle α2 of the non-working tooth surface 102 ranges from 20° to 25°. The pressure angle α2 of the non-working tooth surface 102 is close to the standard pressure angle, and the force transmission efficiency is high.

[0051] In some embodiments, the tooth direction modification adopted by the working tooth surface 101 is 3um-5um drum modification, and the tooth shape modification adopts 2um-4um upper pressure angle modification.

[0052] It is known to those skilled in the art that tooth trimming refers to the conscious trimming of the tooth surface along the tooth line direction, which can reduce the tooth side load caused by manufacturing errors and elastic deformation of the gear mechanism shaft system parts, and can also improve the lubrication state of the gear pair. The appropriate drum shape processed along the tooth direction is called drum trimming. Since drum trimming will gradually thin the tooth thickness at both ends of the tooth from the center of the tooth to both sides, it can prevent the one-sided contact of the tooth caused by the manufacturing error and assembly error of the gear or shaft, and can achieve the purpose of concentrating the contact of the tooth near the center of the tooth width.

[0053] The different forms of slight changes to the involute cylinder or involute helix for specific applications are called gear modification. By fine-tuning the tooth surface shape, the pressure angle can be adjusted appropriately. Such tooth profile modification range can reduce the noise level by adjusting the contact range and transmission error.

[0054] By modifying the tooth direction and the tooth shape of the working tooth surface 101 , a composite modified tooth surface is formed, so that the load is evenly distributed, thereby avoiding load stress concentration and reducing noise.

[0055] In some embodiments, the module of the transmission gear 10 is m, and the tooth root of the transmission gear 10 has a fillet, and the radius R of the fillet reaches 0.2-0.4 times of m. It is well known to those skilled in the art that the module m=pitch circle diameter d / number of teeth z=pitch p / pi, and the module m reflects the size and load-bearing capacity of a single tooth. By optimizing the fillet radius of the tooth root of the transmission gear 10, tooth root interference can be avoided and the tooth root bending strength can be improved.

[0056] In some embodiments, the overlap of the first-stage high-speed gear pair 1A is at least 4.5, the overlap of the second-stage medium-speed gear pair 1B is at least 3.5, and the overlap of the third-stage low-speed gear pair 1C is at least 1.5.

[0057] It is well known to those skilled in the art that the ratio of the length of the actual meshing line to the base circle pitch is called the overlap. In order for the gear pair to be able to transmit continuously, it should be ensured that when the first pair of gears disengages, the second pair of gears will enter into meshing, so the overlap should be greater than 1. The greater the overlap, the better the transmission stability.

[0058] In this application, the overlap of the first-stage high-speed gear pair 1A, the second-stage medium-speed gear pair 1B, and the third-stage low-speed gear pair 1C are controlled separately. The higher the speed, the higher the overlap of the gear pair, and the higher the speed, the smaller the torque. Therefore, different requirements can be adapted to different speeds to achieve overall noise reduction.

[0059] In some embodiments, the number of teeth of the first gear 11 and the number of teeth of the second gear 12 are mutually prime, that is, the common divisor of the number of teeth of the first gear 11 and the number of teeth of the second gear 12 is only 1, thereby avoiding the occurrence of the resonance frequency of the first-stage high-speed gear pair 1A.

[0060] In some embodiments, the first gear 11 and the second gear 12 are plastic parts. Here, since the first-stage high-speed gear pair 1A has the highest speed, the higher the speed, the lower the torque. Therefore, the use of plastic parts can meet the torque requirements and reduce weight and noise.

[0061] Optionally, the third gear 13 and the fourth gear 14 are made of metal. Optionally, the fifth gear 15 and the sixth gear 16 are made of metal.

[0062] In some embodiments, the axes of the six transmission gears 10 are arranged in parallel, which makes assembly easier.

[0063] The power-assisted bicycle 100 according to the embodiment of the utility model comprises: a motor 3 and the gear transmission mechanism 1 of the power-assisted bicycle 100 of the above embodiment, the structure of the gear transmission mechanism 1 is not repeated, the first gear 11 is connected to the motor shaft of the motor 3, and the motor is the power source. With this arrangement, the overall reliability is enhanced and the noise is reduced.

[0064] Other structures of the power-assisted bicycle 100 according to the embodiment of the utility model are known to those skilled in the art and will not be described in detail here.

[0065] In the description of this specification, the description with reference to the terms "embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A gear transmission mechanism for a power-assisted bicycle, characterized in that: It includes multiple transmission gears and they are: The meshing first gear and the second gear are used to form a first-stage high-speed gear pair, and the first gear is used to connect to a power source; The meshing third gear and the fourth gear are used to form a two-stage medium-speed gear pair, and the third gear is connected to the second gear; The meshing fifth gear and the sixth gear are used to form a three-stage low-speed gear pair, and the fifth gear is connected to the fourth gear; The gear teeth of the transmission gear have a working tooth surface and a non-working tooth surface, and the pressure angle of the working tooth surface of each transmission gear is greater than the pressure angle of the non-working tooth surface.

2. The gear transmission mechanism of the power-assisted bicycle according to claim 1, characterized in that: The working tooth surface is an involute tooth surface, and the pressure angle of the working tooth surface ranges between 30° and 35°.

3. The gear transmission mechanism of the power-assisted bicycle according to claim 1, characterized in that: The non-working tooth surface is an involute tooth surface, and the pressure angle of the non-working tooth surface ranges between 20° and 25°.

4. The gear transmission mechanism of the power-assisted bicycle according to claim 1, characterized in that: The tooth direction modification adopted by the working tooth surface is 3um-5um drum modification, and the tooth shape modification adopts 2um-4um upper pressure angle modification.

5. The gear transmission mechanism of the power-assisted bicycle according to claim 1, characterized in that: The module of the transmission gear is m, and the tooth root of the transmission gear has a fillet, and the radius R of the fillet reaches 0.2-0.4 times of m.

6. The gear transmission mechanism of the power-assisted bicycle according to claim 1, characterized in that: The overlap of the first-stage high-speed gear pair is at least 4.5, the overlap of the second-stage medium-speed gear pair is at least 3.5, and the overlap of the third-stage low-speed gear pair is at least 1.

5.

7. The gear transmission mechanism of the power-assisted bicycle according to any one of claims 1 to 6, characterized in that: The number of teeth of the first gear and the number of teeth of the second gear are mutually prime.

8. The gear transmission mechanism of the power-assisted bicycle according to any one of claims 1 to 6, characterized in that: The first gear and the second gear are plastic parts.

9. The gear transmission mechanism of the power-assisted bicycle according to any one of claims 1 to 6, characterized in that: The axes of the six transmission gears are all arranged in parallel.

10. A power-assisted bicycle, characterized in that: include: Motor; According to the gear transmission mechanism of the power-assisted bicycle according to any one of claims 1 to 9, the first gear is connected to the motor shaft of the motor.

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