Variable speed adjusting device

Abstract

The invention provides a variable speed adjusting device which comprises a power input driving wheel and a power output driven shaft coaxially arranged with a driving shaft, and the driven shaft is provided with a change wheel in an idling mode and is provided with a mode switching assembly in an axially displaceable mode. When the mode switching assembly is arranged at the first axial position, a direct power transmission path from the driving wheel to the driven shaft is established, and the driven shaft is driven to rotate at a constant speed; at the second axial position, an indirect power transmission path from the change wheel to the driven shaft is established, and the driven shaft is driven to rotate at a variable speed. A power transmission path is directly switched through axial displacement of the mode switching assembly; at the first position, the mode switching assembly is meshed with the driving wheel to establish a constant-speed transmission chain with zero intermediate loss, so that the driven shaft obtains rotating speed output completely synchronous with the driving wheel; and at the second position, the transmission shaft is meshed with the change wheel to activate the variable-speed transmission chain with the preset speed ratio, so that the driven shaft outputs variable-speed power accurately modulated by the transmission shaft.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical transmission, and in particular to a speed-changing regulating device. Background Art

[0002] In the field of mechanical transmission, dynamic adjustment of the output speed of the driven shaft (such as switching between constant speed and variable speed modes) is a common requirement. Traditional solutions mostly rely on complex clutch mechanisms, multi-stage gearboxes or electronic frequency conversion devices. Although these solutions can achieve the speed change function, they generally have problems such as complex structure, large size, high manufacturing cost, inconvenient maintenance and reliability that is easily affected by wear. Especially for compact equipment that requires coaxial input and output (such as precision instruments, specific industrial machinery), how to achieve efficient, reliable and low-cost speed ratio switching in a limited space while maintaining the coaxiality of the input / output shaft has become a long-standing technical challenge. The existing technology lacks a simple mechanical structure that can maintain the coaxial layout of input and output and achieve fast and stable switching between constant speed and variable speed modes.

[0003] Furthermore, for coaxial transmission systems using belt drive, existing designs often struggle to coordinate the coexistence of direct and indirect variable speed drive modes. Common solutions either sacrifice the coaxial layout and adopt a complex bypass transmission chain, or only achieve fixed speed ratio output without dynamic switching. When attempting to integrate speed-changing functionality into a coaxial system, additional clutch elements or complex linkage mechanisms are often required. This not only increases system complexity and failure points, but also makes the overall structure bloated and the dynamic response sluggish, making it difficult to meet the requirements of application scenarios with demanding space utilization and switching efficiency. Summary of the Invention

[0004] The present invention provides a speed adjustment device which can realize rapid switching between constant speed and variable speed driving modes without adding a complex clutch mechanism.

[0005] The technical solution of the present invention is achieved as follows: A speed adjustment device includes a driving wheel for power input and a driven shaft for power output arranged coaxially with the driving shaft. The driven shaft is provided with a speed change wheel that can rotatably idle and a mode switching component that can be axially displaced. The mode switching component is configured to establish a direct power transmission path from the driving wheel to the driven shaft when in a first axial position, driving the driven shaft to rotate at a constant speed; and to establish an indirect power transmission path from the speed change wheel to the driven shaft when in a second axial position, driving the driven shaft to rotate at a variable speed.

[0006] Furthermore, it also includes a switching drive system configured to provide an axial displacement driving force to the mode switching assembly.

[0007] Furthermore, the switching drive system includes a linear drive and a force transmission frame connected to the output end of the linear drive, and the force transmission frame surrounds and drives the mode switching component to move axially.

[0008] Furthermore, the force transmission frame is a U-shaped frame, and the U-shaped frame is provided with a radially protruding engaging portion, which extends into a restraining groove provided on the outside of the mode switching assembly to achieve axial drive coupling.

[0009] Furthermore, the speed change wheel is rotatably mounted on the driven shaft via a bearing, and is configured to maintain an idling state when the mode switching assembly is in the first position.

[0010] Furthermore, the mode switching assembly is provided with a selective interlocking structure; the end of the driving wheel is provided with a first engaging portion corresponding to the interlocking structure; the speed change wheel is provided with a second engaging portion corresponding to the interlocking structure; the interlocking structure is configured to engage with the first engaging portion when in the axial first position or to engage with the second engaging portion when in the axial second position.

[0011] Furthermore, the interlocking structure is a radial positioning shaft; the first engaging portion is the socket a on the driving wheel; the second engaging portion is the socket b on the speed change wheel; and the end of the radial positioning shaft is adapted to the socket a or the socket b.

[0012] Furthermore, it also includes a transmission shaft, which is configured to receive the driving wheel power through the first constant speed transmission unit; and transmit the speed change power to the speed change wheel assembly through the second speed change transmission unit.

[0013] Furthermore, the first constant velocity transmission unit includes a driving wheel, a transmission wheel a provided on a transmission shaft, and an annular transmission belt a wrapped around the driving wheel and the transmission wheel a for power transmission.

[0014] Furthermore, the second constant speed transmission unit includes a speed change wheel, a transmission wheel b provided on the transmission shaft, and an endless transmission belt b wrapped around the speed change wheel and the transmission wheel b for power transmission.

[0015] The beneficial effects of the technical solution provided by this application are: 1. This speed adjustment device utilizes the axial displacement of a mode-switching assembly to directly switch the power transmission path: in the first position, it engages the driving wheel to establish a zero-intermediate-loss constant-speed transmission chain, allowing the driven shaft to achieve a fully synchronized speed output with the driving wheel; in the second position, it engages the speed-shifting wheel to activate a variable-speed transmission chain with a preset speed ratio, allowing the driven shaft to output variable power precisely modulated by the drive shaft. This design completely eliminates the complex structures of traditional clutches or multi-stage gearboxes, achieving efficient switching between two drive modes through the physical displacement of a single sliding assembly while maintaining strict coaxiality between the input and output. 2. This speed adjustment device solves the interference problem of dual power paths by utilizing the idling isolation mechanism of the speed change wheel and the bidirectional coupling capability of the mode switching assembly. In constant speed mode, the speed change wheel driven by the drive shaft rotates freely due to the idling design, eliminating parasitic drag on the driven shaft. In variable speed mode, the mode switching assembly simultaneously disengages the driving wheel and locks the speed change wheel, ensuring seamless power transfer to the variable speed path. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 is a schematic diagram of the speed adjustment device of the present invention; Figure 2 It is an exploded schematic diagram of the speed adjustment device of the present invention; Figure 3 Schematic cross-sectional view of the speed adjustment device of the present invention; Figure 4 This is an exploded schematic diagram of some components of the speed adjustment device of the present invention; Figure 5 is a schematic diagram of the frame assembly of the present invention; Figure 6 Schematic diagram of a transmission belt tension maintaining system of the present invention; Figure 7 Schematic diagram of the switching drive system of the present invention.

[0018] In the figure: 10 driving shaft, 11 driving wheel, 12 jack a; 20 transmission shaft, 21 transmission wheel a, 22 transmission wheel b; 30 driven shaft, 31 bearing, 32 socket b, 33 mode switching assembly, 34 radial positioning shaft, 35 speed change wheel; 40 annular transmission belt a, 50 annular transmission belt b; 60 frame assembly, 61 support plate, 62 rigid connector; 70 transmission belt tension maintaining system, 71 mounting base, 72 slide bar, 73 tension wheel, 74 guide member; 80 switching drive system, 81 linear drive, 82 U-shaped frame, 83 guide assembly. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] Reference Figure 1-7 , a speed change adjustment device includes a driving wheel 11 for power input and a driven shaft 30 for power output arranged coaxially with the driving shaft. The driven shaft 30 is provided with a speed change wheel 35 and an axially displaceable mode switching component 33. Through the axial displacement of the mode switching component 33 on the driven shaft 30, combined with the idling characteristics of the speed change wheel 35, a physical selection of a dual-mode power transmission path is realized: when the mode switching component 33 slides to the first position, it directly bridges the driving wheel 11 and the driven shaft 30, constructing a zero-speed loss rigid transmission chain, so that the driven shaft 30 strictly follows the speed of the driving wheel 11; when it slides to the second position, it switches to an indirect speed change path that conducts the speed change wheel 35 to the driven shaft 30. At this time, the power connection between the driving wheel 11 and the driven shaft 30 is physically cut off, and the speed change wheel 35 is converted from an idling state to a torque output state through the bearing 31, driving the driven shaft 30 to rotate according to a preset speed ratio. The essence of this design is to utilize the space occupation switching of a single sliding component, and to solve the mechanical logic problem of mutually exclusive switching between the constant speed / variable speed dual modes while maintaining the coaxial layout of the driving wheel 11 and the driven shaft 30.

[0021] Some embodiments further include a frame assembly 60, which is constructed as a rotational support structure that simultaneously supports the driving wheel 11, the driven shaft 30, and the driving wheel 11. The frame assembly 60 includes a plurality of rigid connectors 62 and support plates 61 connected to both ends of the rigid connectors 62. The driving wheel 11 is provided with a driving shaft 10, and the driving shaft 10 and the driven shaft 30 are coaxially connected to the support plates 61 on both sides via bearing blocks. The transmission shaft 20 is connected to the two support plates 61 at both ends via bearing blocks. The frame assembly 60 provides a high-precision coaxial positioning platform for the active shaft 10, the driven shaft 30 and the transmission shaft 20 through the coordinated construction of the support plates 61 and the rigid connectors 62: the support plates 61 on both sides serve as reference bearing surfaces, and a strict parallel spacing is maintained by the rigid connectors 62 to ensure that the active shaft 10 and the driven shaft 30 are physically coaxially aligned after being installed through the bearing seats; at the same time, the two ends of the transmission shaft 20 are fixed to the same pair of support plates 61 through the bearing seats, so that it forms a stable spatial relative posture with the active-driven shaft system, fundamentally eliminating the risk of axis deviation in the multi-axis transmission system, and laying a rigid foundation for the reliable switching of the direct power transmission path and the indirect speed change path.

[0022] In some embodiments, the speed wheel 35 is rotatably mounted on the driven shaft 30 via a bearing 31, providing the speed wheel 35 with an independent degree of rotational freedom. This effectively achieves "idle-motion isolation" when the mode switching assembly 33 is in the first position. In this state, although power from the drive shaft 20 drives the speed wheel 35 to rotate, the physical isolation provided by the bearing 31 restricts its rotation to the outer ring of the bearing 31, preventing its rotational power from being transmitted to the driven shaft 30 within its inner sleeve. This "idle-motion" mechanism is crucial. It ensures that in constant-speed mode, while power from the indirect speed-shifting path reaches the speed wheel 35, it is completely isolated from the core power flow, avoiding unnecessary energy loss, interference, or parasitic drag. This ensures the purity and efficiency of direct constant-speed path power transmission and provides the underlying mechanical foundation for the dual-mode operation, which allows for non-interference and physical selective conduction.

[0023] In some embodiments, the mode switching assembly 33 is provided with a selective interlocking structure; the end of the driving wheel 11 is provided with a first engaging portion 12 corresponding to the interlocking structure; and the speed change wheel 35 is provided with a second engaging portion 32 corresponding to the interlocking structure. The interlocking structure is a radial positioning shaft 34; the first engaging portion is the socket a12 on the driving wheel 11; the second engaging portion is the socket b32 on the speed change wheel 35. Through the physical adaptation relationship between the radial positioning shaft 34 and the dual sockets, the interlocking structure provides an absolutely mutually exclusive path coupling mechanism for the mode switching assembly 33: when the mode switching assembly 33 slides axially to the first position, the radial positioning shaft 34 precisely inserts into the socket a12 of the driving wheel 11, forming a rigid connection for torque transmission without relative slip, forcing the driving wheel 11 and the driven shaft 30 to rotate synchronously; when sliding to the second position, the radial positioning shaft 34 disengages from the socket a12 and inserts into the socket b32 of the speed change wheel 35, cutting off the power transmission from the driving wheel 11 while locking the rotational freedom of the speed change wheel 35 to the driven shaft 30. This plug-in design mechanically eliminates the risk of dual paths being simultaneously conductive, ensuring zero ambiguity in power switching.

[0024] Its core operating principle lies in the coordinated control of spatial coupling and motion decoupling: when the mode switching assembly 33 moves axially, its built-in interlocking structure, such as the positioning shaft 34, selectively inserts into the socket a12 of the driving wheel 11 or the socket b32 of the speed change wheel 35. When inserted into the socket a12, the rotational force of the driving wheel 11 is directly transmitted to the driven shaft 30 through the mode switching assembly 33. At this time, although the speed change wheel 35 is driven by the transmission belt, it remains idle due to the isolation effect of the bearing 31, avoiding interference with the constant speed transmission. When switched to inserting into the socket b32, the mode switching assembly 33 disengages from the driving wheel 11 and instead locks the speed change wheel 35 to the driven shaft 30, so that the speed change power received by the speed change wheel 35 drives the driven shaft 30 through the mode switching assembly 33. At the same time, the power of the driving wheel 11 no longer affects the driven shaft 30 due to physical disconnection. The entire process changes the power coupling point through axial displacement to achieve mechanical interlocking switching between the two transmission modes.

[0025] Some embodiments further include a transmission shaft 20 configured to receive power from the driving wheel 11 via a first constant-speed transmission unit and transmit variable-speed power to the variable-speed wheel assembly via a second variable-speed transmission unit. The first constant-speed transmission unit includes the driving wheel 11, a transmission wheel a21 disposed on the transmission shaft 20, and an annular transmission belt a40 that wraps around the driving wheel 11 and the transmission wheel a21 for power transmission. The second constant-speed transmission unit includes a variable-speed wheel 35, a transmission wheel b22 disposed on the transmission shaft 20, and an annular transmission belt b50 that wraps around the variable-speed wheel 35 and the transmission wheel b22 for power transmission. This creates an efficient power transfer and speed ratio conversion platform, enabling precise distribution and guidance of input power to the transmission links required for the two different operating modes. Specifically, drive shaft 20 acts as a transfer hub, receiving input power from driving wheel 11 at a 1:1 speed ratio without loss through the first constant speed transmission unit. Simultaneously, it converts this received power to a preset speed ratio through the second variable speed transmission unit, ultimately delivering the adjusted variable speed power to the variable speed wheel assembly 35. The fundamental function of this dual-belt system, connected in series by drive shaft 20, is to simultaneously and continuously supply a single input power source to two independent mechanical paths: one maintains its original speed as a backup for constant speed mode, while the other achieves speed ratio conversion as needed for variable speed mode activation. This provides the necessary and precise power source guarantee for the subsequent mode switching assembly 33 to physically select one of the two power paths.

[0026] It should be noted that to avoid frictional backlash during transmission, the exteriors of the driving pulley 11, transmission pulley a21, transmission pulley b22, and speed-changing pulley 35 are toothed, while the interiors of the endless transmission belts a40 and b50 are also toothed. Furthermore, the outer diameter of the transmission pulley b22 is smaller than that of the speed-changing pulley 35 to ensure consistent speed change.

[0027] The working principle of the above technical solution is that the input power of the driving wheel 11 is first transmitted to the meshing transmission wheel a21 via the annular transmission belt a40. Because the annular transmission belt a40 maintains a 1:1 speed ratio between the driving wheel 11 and the transmission wheel a21, the transmission shaft 20, which is fixed to the transmission wheel a21, receives input power that is completely consistent with the rotation speed of the driving wheel 11. When the transmission wheel b22 fixed to the transmission shaft 20 drives the other end of the transmission wheel b22 to rotate, the transmission wheel b22 transmits the power carried by the transmission shaft 20 to the speed change wheel 35 via the annular transmission belt b50 that surrounds it and the speed change wheel 35. The key point is that the transmission wheel b22 and the speed change wheel 35 form a speed change relationship with a preset speed ratio, which is set by the diameter difference of the annular transmission belt b50 or its own tooth number ratio. Therefore, the uniform rotation of the transmission wheel b22, after being transmitted via the annular transmission belt b50, is converted into an output speed adjusted according to the speed ratio at the speed change wheel 35. The entire process realizes the diversion, maintenance and speed conversion of the input power on the transmission shaft 20, ensuring that the speed wheel 35 component always obtains the power input required for its drive and adjusted by the speed ratio, regardless of whether it is currently selected as the effective drive source by the mode switching component 33.

[0028] In some embodiments, a switching drive system 80 is further included, which is configured to provide an axial displacement driving force to the mode switching assembly 33. The switching drive system 80 includes a linear drive 81 and a force transmission frame connected to the output end of the linear drive 81. The force transmission frame surrounds and drives the mode switching assembly 33 to move axially. The force transmission frame is a U-shaped frame 82. The U-shaped frame 82 is provided with a radially protruding snap-fit ​​portion, and the snap-fit ​​portion extends into a constraint groove provided on the outside of the mode switching assembly 33 to achieve axial drive coupling. The switching drive system 80 also includes a guide assembly 83 for constraining the movement direction of the U-shaped frame 82; the guide assembly 83 includes a plurality of parallel guide shafts, two support plates 61 are fixed at both ends of the guide shafts, and the guide shafts slide through the U-shaped frame 82. The linear drive 81 serves as a power source and is responsible for generating axial push / pull force; the U-shaped frame 82 rigidly connected to it acts as a force transmission medium, and its radially protruding engaging portion engages with the external constraint groove of the mode switching component 33, efficiently and without distortion, converting the linear motion of the linear drive 81 into the axial displacement of the mode switching component 33; at the same time, the additional guide component 83 passes through the U-shaped frame 82 through its guide shaft fixed to both ends of the support plate 61 and arranged in parallel, strictly constraining the output motion trajectory of the U-shaped frame 82 and even the entire switching drive system 80, ensuring that the driving force can only be accurately applied along the preset direction parallel to the axis of the master / slave shaft system, completely eliminating the risk of jamming or switching failure due to offset or skew.

[0029] When the transmission mode needs to be switched, the linear actuator 81 is activated and drives its output end to perform linear telescopic motion. This linear motion is directly transmitted to the U-shaped frame 82 via a rigid connection. The engaging portion provided on the inner side of the U-shaped frame 82 tightly fits into the prefabricated constraint groove on the mode switching assembly 33. This coupling ensures that the axial movement of the U-shaped frame 82 is forcibly applied to the mode switching assembly 33 through "rigid translation," forcing the mode switching assembly 33 to shift axially. During this entire displacement process, the multiple parallel guide shafts of the guide assembly 83 act as rigid rails, on which the corresponding parts of the U-shaped frame 82 slide and are strictly guided. The parallel arrangement of the guide shafts ensures that the U-shaped frame 82 is restricted to a single degree of freedom—that is, it is only allowed to slide parallel to the axis of the master / slave shaft. In this way, the driving force from the linear actuator 81 is ultimately coupled through the U-shaped frame 82 and, under the mandatory guidance of the guide assembly 83, converted into the required axial displacement of the mode switching assembly 33, precisely parallel to the axis, thus achieving the switching of the power transmission path.

[0030] Some embodiments further include a belt tension maintenance system 70, which acts on the first constant-speed transmission unit and / or the second variable-speed transmission unit to dynamically compensate for belt tension. The belt tension maintenance system 70 includes a mounting base 71 that spans the frame assembly 60 and a plurality of pressure-applying mechanisms displaceably disposed on the mounting base 71. The working ends of the pressure-applying mechanisms contact the endless belt a40 / endless belt b50 to maintain a preset tension. The pressure-applying mechanisms include a slide bar 72 that slides through the mounting base 71 and is secured by a plurality of fasteners, a tension pulley 73 pivotally mounted to the bottom of the slide bar 72, and a guide member 74 connected between the tension pulley 73 and the mounting base 71. Mounting base 71 is fixed across frame assembly 60, providing a stable support platform for the entire tension maintenance function. The slide bars 72 of the multiple pressure-applying mechanisms it carries can be adjusted along mounting base 71 and locked in a set position by fasteners. A tension pulley 73, mounted at the bottom of slide bar 72, directly acts on and contacts the non-meshing surface of either ring belt a40 or ring belt b50. A guide member 74 connecting tension pulley 73 to mounting base 71 ensures that tension pulley 73 moves only along a preset path during pressure adjustment. The entire system works in tandem, adjusting the initial compression of tension pulley 73 on the belt using the preset position of slide bar 72. If the belt undergoes slight length changes due to operational wear, thermal expansion, or other factors, the tension pulley 73's adjustable position compensates for belt slack in real time, maintaining a preset constant effective tension at all times, effectively preventing belt slippage, jerkiness, or misalignment.

[0031] The working principle of the transmission belt tension maintenance system 70 revolves around static preset adjustment and dynamic adaptive compensation: when the circular transmission belt a40 or the circular transmission belt b50 undergoes a slight elongation due to natural wear, temperature changes, or other reasons, its effective working tension will show a downward trend. At this time, by loosening the fasteners, the penetration depth of the slide bar 72 in the mounting base 71 is manually adjusted, thereby changing the effective depth of the tension wheel 73 pressing against its corresponding circular transmission belt. During this process, the guide member 74 slides on the bolts on the mounting base 71 through its internal strip groove to form a guiding effect, which improves the movement stability of the slide bar 72. Once the tension wheel 73 is adjusted into place to achieve the desired preset initial tension, the fasteners are then tightened to firmly lock the slide bar 72 on the mounting base 71.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A speed adjustment device, characterized in that: The invention comprises a driving wheel (11) for power input, a driven shaft (30) for power output arranged coaxially with the driving shaft, a speed change wheel (35) being idlingly provided on the driven shaft (30) and a mode switching assembly (33) being axially displaceable; the mode switching assembly (33) being configured to establish a direct power transmission path from the driving wheel (11) to the driven shaft (30) when in a first axial position, driving the driven shaft (30) to rotate at a constant speed; and to establish an indirect power transmission path from the speed change wheel (35) to the driven shaft (30) when in a second axial position, driving the driven shaft (30) to rotate at a variable speed.

2. The speed adjustment device according to claim 1, characterized in that: Also included is a switching drive system (80) configured to provide an axial displacement drive force to the mode switching assembly (33).

3. The speed adjustment device according to claim 2, characterized in that: The switching drive system (80) includes a linear drive (81) and a force transmission frame connected to the output end of the linear drive (81), and the force transmission frame surrounds and drives the mode switching component (33) to move axially.

4. The speed adjustment device according to claim 3, characterized in that: The force transmission frame is a U-shaped frame (82), and the U-shaped frame (82) is provided with a radially protruding engaging portion, which extends into a restraining groove provided on the outside of the mode switching assembly (33) to achieve axial drive coupling.

5. The speed adjustment device according to claim 1, wherein: The speed change wheel (35) is rotatably sleeved on the driven shaft (30) via a bearing (31), and is configured to maintain an idling state when the mode switching assembly (33) is in the first position.

6. The speed adjustment device according to claim 1, wherein: The mode switching assembly (33) is provided with a selective interlocking structure; the end of the driving wheel (11) is provided with a first engaging portion (12) corresponding to the interlocking structure; the speed change wheel (35) is provided with a second engaging portion (32) corresponding to the interlocking structure; the interlocking structure is configured to engage with the first engaging portion (12) when in an axial first position or to engage with the second engaging portion (32) when in an axial second position.

7. The speed adjustment device according to claim 6, characterized in that: The interlocking structure is a radial positioning shaft (34); the first engaging portion is a socket a (12) on the driving wheel (11); the second engaging portion is a socket b (32) on the speed-changing wheel (35); and the end of the radial positioning shaft (34) is adapted to the socket a (12) or the socket b (32).

8. The speed adjustment device according to claim 1, wherein: It also includes a transmission shaft (20) configured to receive power from the driving wheel (11) through a first constant speed transmission unit; and transmit speed-changing power to the speed-changing wheel assembly through a second speed-changing transmission unit.

9. The speed adjustment device according to claim 8, characterized in that: The first constant speed transmission unit comprises a driving wheel (11), a transmission wheel a (21) provided on a transmission shaft (20), and an annular transmission belt a (40) wrapped around the driving wheel (11) and the transmission wheel a (21) for power transmission.

10. The speed adjustment device according to claim 8, wherein: The second constant speed transmission unit comprises a speed change wheel (35), a transmission wheel b (22) provided on a transmission shaft (20), and an annular transmission belt b (50) wrapped around the speed change wheel (35) and the transmission wheel b (22) for power transmission.

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