Safety clutch and power tool

Abstract

This application discloses a safety clutch and power tool, including a drive shaft. A bearing, a clutch gear, a clutch pressure plate, an elastic element, and a support seat are sequentially mounted on the drive shaft. The support seat is axially positioned and connected to the drive shaft. Both ends of the elastic element abut against the clutch pressure plate and the support seat, respectively. The clutch gear is rotatably connected to the drive shaft and has an axially extending through hole. A rolling element is disposed within the through hole. The clutch also includes a clutch disc, which is positioned between the bearing and the clutch gear and circumferentially fixed to the drive shaft. A groove is provided on the clutch disc facing the clutch gear. One end of the rolling element extends into the groove, and the other end abuts against the clutch pressure plate. Under the preload of the elastic element, the clutch pressure plate presses the rolling element into the groove. This constitutes a torque-responsive disengagement mechanism. The safety clutch and power tool of this application avoid direct contact between the clutch gear and the bearing, reducing energy loss and component wear caused by friction.

Description

Technical Field

[0001] This application relates to the field of power tool technology, and more specifically, to a safety clutch and a power tool. Background Technology

[0002] In the field of power tools, to prevent damage to the internal motor or transmission mechanism from overload operation, a safety clutch is usually installed in the drive train. In a common existing safety clutch structure, the clutch gear interacts with a clutch pressure plate or similar component through rolling elements (such as balls) within its grooves, thereby transmitting torque to the drive shaft. Disengagement is achieved by the displacement of the rolling elements when the torque exceeds the limit. However, for support and positioning, the clutch gear typically needs to be in direct contact with a bearing and generate relative rotation. This design results in continuous sliding friction between the clutch gear and the bearing throughout the entire operating process, whether the clutch is normally engaged and transmitting power or experiencing overload slippage.

[0003] This sliding friction introduces several technical drawbacks: First, it causes unnecessary energy loss and reduces transmission efficiency; second, friction leads to rapid wear at the contact points, shortening the clutch's lifespan and potentially affecting bearing precision; more critically, as wear intensifies, the clutch disengagement torque setting threshold drifts, making overload protection inaccurate and unreliable, thus impacting the safety performance of power tools. Furthermore, friction also causes heat generation and operating noise. Therefore, it is necessary to improve the existing structure to completely eliminate the direct friction pair between the clutch gear and the bearing. Utility Model Content

[0004] In view of this, this application provides a safety clutch and power tool. By adding an independent clutch disc that is circumferentially fixed to the drive shaft, the clutch gear transmits torque only through the rolling elements and the grooves of the clutch disc, thus structurally achieving complete isolation between the clutch gear and the bearing. This design fundamentally eliminates direct friction between the two, significantly reducing energy loss, improving transmission efficiency and component life, and making the clutch torque response more precise and the overload protection action more reliable and stable.

[0005] In a first aspect, this application provides a safety clutch for the safe disengagement of an electric tool. The safety clutch includes a drive shaft, on which a bearing, a clutch gear, a clutch pressure plate, an elastic element, and a support seat are sequentially mounted. The support seat is axially positioned and connected to the drive shaft, and both ends of the elastic element abut against the clutch pressure plate and the support seat, respectively. The clutch gear is rotatably connected to the drive shaft, and the clutch gear has a through hole extending along the axial direction, with a rolling element inside the through hole; The clutch further includes a clutch disc, which is disposed between the bearing and the clutch gear and is circumferentially fixedly connected to the drive shaft; the clutch disc has a groove on the side facing the clutch gear. One end of the rolling element extends into the groove, and the other end abuts against the clutch pressure plate. Under the pre-tightening force of the elastic element, the clutch pressure plate presses the rolling element into the groove. This constitutes a torque-responsive disengagement mechanism: when the resistance torque on the drive shaft is lower than a set threshold, the clutch gear drives the clutch disc and drive shaft to rotate synchronously through the cooperation of the rolling element and the groove; when the resistance torque on the drive shaft reaches or exceeds the set threshold, the rolling element is driven by the clutch gear to axially push the clutch pressure plate to compress the elastic element, causing the rolling element to disengage from the groove and cutting off the power transmission from the clutch gear to the drive shaft.

[0006] By adopting the above technical solution, the torque transmission path and the radial support structure are completely separated. The clutch gear is torque-coupled with the clutch disc only through rolling elements, without contacting the bearing. This eliminates the sliding friction between the clutch gear and the bearing in traditional structures, significantly reducing no-load loss and wear, and ensuring the accuracy of overload torque sensing and the consistency of clutch action. The clutch disc is formed by stamping, resulting in a simple structure, low manufacturing cost, and easy maintenance and replacement.

[0007] In some embodiments, the clutch disc includes a plurality of grooves spaced apart circumferentially, and adjacent grooves are connected by slides.

[0008] By adopting the above technical solution, a continuous path is provided for the circumferential movement of the rolling element between the grooves, ensuring that after overload release, when the torque decreases, the rolling element can smoothly slide back into the groove along the slide, realizing automatic power reset and re-engagement, and improving the cyclic reliability of clutch operation.

[0009] In some implementations, the slide is a groove with a gradually varying depth in the circumferential direction, having a uniform radius at its bottom profile, and being shallowest at the junction with an adjacent groove.

[0010] By adopting the above technical solution, the axial thrust experienced by the rolling element changes gradually when it moves in the slide, achieving a smooth transition during the clutch disengagement and engagement process and avoiding impact. At the same time, the shallowest connection point forms a clear positioning point, which is conducive to the accurate reset of the rolling element to the groove and ensures the stability of re-engagement.

[0011] In some embodiments, the clutch pressure plate has an annular groove on the side facing the rolling element for the end of the rolling element to contact.

[0012] By adopting the above technical solution, the contact between the rolling element and the clutch pressure plate is transformed from point contact or small area contact to line contact, and a guide surface is provided, which effectively reduces contact stress and frictional resistance, making the rolling element smoother when pushing the clutch pressure plate axially, and further improving the sensitivity and durability of the clutch action.

[0013] In some implementations, the elastic element is a conical spring, with its larger diameter end abutting against the clutch pressure plate and its smaller diameter end abutting against the support seat.

[0014] By adopting the above technical solution, the conical spring provides a nonlinear and more stable load-displacement characteristic during compression, which is beneficial for accurately setting and maintaining the required clutch pressure threshold within a compact axial space. Its conical structure offers better tolerance for different centering errors, ensuring that pressure is applied evenly to the clutch plate, thereby improving the consistency of torque sensing. The large end abutting against the pressure plate provides a stable bearing surface, while the connection between the small end and the support optimizes the spring's guidance and anti-instability capabilities, making the overall structure more reliable.

[0015] In some embodiments, the projections of the conical springs in the axial direction are non-overlapping.

[0016] By adopting the above technical solution, the phenomenon of spring coiling under maximum compression is effectively prevented, abrupt changes in spring stiffness are avoided, and the predictability and smoothness of elastic force are ensured throughout the entire working stroke, thereby making the clutch disengagement torque threshold more accurate and stable. Furthermore, this structure allows the spring to have a larger compressible stroke in the axial direction, achieving a longer effective working stroke within a limited space. This facilitates meeting different pressure and stroke design requirements in a compact layout, further optimizing the clutch's space utilization.

[0017] In some embodiments, a drive gear is provided at one end of the drive shaft located outside the bearing.

[0018] By adopting the above technical solution, the safety clutch can be integrated as an integrated module, directly meshing with other transmission components of power tools (such as intermediate gears, output shaft gears, etc.) through the drive gear, thus expanding its application range and adaptability.

[0019] In some implementations, the drive gear is a bevel gear.

[0020] By adopting the above technical solution, it is easy to realize the change of transmission direction, which is particularly suitable for the design of compact power tools that require spatial reversal, and enhances the practicality of this safety clutch in complex transmission layouts.

[0021] In some implementations, the rolling element is a ball, roller, or tapered roller.

[0022] By adopting the above technical solutions, a variety of options are provided, allowing the selection of the most suitable rolling element type based on specific torque capacity, space size, and cost requirements, thereby enhancing design flexibility.

[0023] Secondly, this application provides an electric tool including the safety clutch of the first aspect.

[0024] By adopting the above technical solution, a safety clutch with low friction and high precision overload protection can be integrated into the power tool, which can effectively protect the motor and transmission system from stall or overload damage, while reducing useless power loss and improving tool energy efficiency, service life and safety.

[0025] In summary, this application has at least one of the following beneficial technical effects: 1. Completely eliminate harmful friction and improve overall performance: Through the independent clutch disc design, the clutch gear and bearing are physically isolated, eliminating the sliding friction between them, thereby greatly reducing energy loss, wear and heat generation, and significantly improving transmission efficiency, component life and tool endurance.

[0026] 2. Achieve precise torque sensing and reliable protection: Based on the pure rolling torque transmission mechanism of rolling elements and grooves, combined with optimized elastic elements, the system responds to the output shaft resistance torque with extreme sensitivity and accuracy, ensuring that the power can be quickly and consistently cut off at the preset torque threshold when overloaded, and the safety protection performance is reliable.

[0027] 3. Ensure smooth disengagement and automatic reset: The unique groove design with a gradient slide makes the clutch move smoothly and without impact during overload disengagement and torque recovery engagement, and can automatically and accurately reset, ensuring the stability and durability of the clutch cycle operation.

[0028] 4. Offers a flexible and versatile modular design: The clutch has a compact structure and can be flexibly adapted to power tools with different torque specifications, spatial layouts, and transmission directions by changing the type of rolling elements, elastic element parameters, and drive gear form. It has wide applicability and good engineering potential. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the external structure of the safety clutch of this application; Figure 2 This is an exploded view of the safety clutch of this application; Figure 3 This is a cross-sectional schematic diagram of the safety clutch of this application; Figure 4 This is a schematic diagram of the drive shaft; Figure 5This is a schematic diagram of the front of the clutch disc; Figure 6 This is a schematic diagram of the structure on the back of the clutch disc.

[0030] Explanation of reference numerals in the attached drawings: 1. Drive shaft; 11. Bevel gear; 12. Keyway; 13. Slot; 2. Upper bearing; 3. Clutch gear; 31. Through hole; 4. Support seat; 5. Lower bearing; 6. Elastic element; 7. Clutch disc; 71. Irregular hole; 72. Groove; 73. Slide rail; 8. Rolling element; 9. Clutch pressure plate; 91. Annular groove; 10. Snap ring. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the utility model will be further described in detail below with reference to the accompanying drawings. The components of the embodiments of this utility model described and shown in the accompanying drawings can be arranged and designed in various different configurations. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0033] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0034] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0035] The embodiments of this utility model will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features in the following embodiments can be combined with each other.

[0036] Example 1: Please see Figures 1 to 6This application provides a safety clutch, which is particularly suitable for power tools such as electric drills, angle grinders, impact screwdrivers, and electric hammers. When the output end of the tool encounters abnormal stall or overload, it can quickly and reliably cut off the power transmission, thereby effectively protecting the motor and transmission system.

[0037] like Figures 1-3 As shown, the core transmission and actuation components of this safety clutch are arranged sequentially along the axial direction of a drive shaft 1. The drive shaft 1 is usually driven to rotate by a motor inside the tool through a transmission mechanism such as a gear set. It can itself serve as a power output shaft, connecting to working tools such as drill chucks and grinding wheels, or connecting to other transmission mechanisms for power transmission.

[0038] exist Figure 2 As shown, along the drive shaft 1, from top to bottom, are the following components: upper bearing 2, clutch disc 7, rolling element 8, clutch gear 3, clutch pressure plate 9, elastic element 6, support seat 4, retaining ring, and lower bearing 5. The upper bearing 2 and lower bearing 5 are fixedly mounted in the bearing housing of the power tool. Their main function is to provide radial support for the drive shaft 1, ensuring its rotational concentricity, while also bearing a certain axial force. Below the upper bearing 2 is a crucial torque transmission component—the clutch disc 7. The clutch disc 7 is circumferentially fixed to the drive shaft 1 via splines, flat keys, or interference fits, allowing the clutch disc 7 to rotate synchronously with the drive shaft 1, but permitting slight axial relative displacement when necessary.

[0039] Below the clutch disc 7, a clutch gear 3, a clutch pressure plate 9, an elastic element 6, and a support base 4 are arranged in sequence. The clutch gear 3 is mounted on the drive shaft 1 via a sliding bearing or bushing, or it can be directly rotatably connected to the drive shaft 1, meaning that the clutch gear 3 can rotate freely independently of the drive shaft 1. The external teeth of the clutch gear 3 are used to mesh with other gears in the power tool transmission system to receive power from the motor. On the disc body of the clutch gear 3, multiple axial through holes 31 are formed along its circumference, and the number and position of the through holes 31 correspond one-to-one with the grooves 72 on the clutch disc 7. A rolling element 8 is placed in each through hole 31. In this embodiment, the rolling element 8 is preferably a high-precision ball, but it can also be a roller or a tapered roller. Part of the ball protrudes from the through hole 31, with one side embedded in the corresponding groove 72 of the clutch disc 7, and the other side abutting against the end face of the clutch pressure plate 9.

[0040] The clutch pressure plate 9 is also sleeved on the drive shaft 1 and can slide within a small range along the axial direction of the drive shaft 1. An annular groove 91 is machined on the end face of the clutch pressure plate 9 facing the clutch gear 3. The ends of all the balls abut within this annular groove 91. The cross-sectional shape of the annular groove 91 is preferably an arc groove that matches the balls, which optimizes point contact into line contact, reduces contact stress, and guides the balls to roll.

[0041] Below the clutch pressure plate 9, the elastic element 6 is pre-compressed and installed. In this embodiment, the elastic element 6 is preferably a conical spring. The large-diameter end of the conical spring abuts against the lower end face of the clutch pressure plate 9, while the small-diameter end abuts against the support seat 4. The support seat 4 is axially positioned and connected to the drive shaft 1 by a snap ring 10, a shoulder, or a threaded fastener, meaning that the axial position of the support seat 4 relative to the drive shaft 1 is fixed. In this embodiment, the snap ring 10 is used for axial fixation. During installation, the conical spring is pre-compressed to continuously and evenly press a set of rolling elements 8 against the clutch disc 7 via the clutch pressure plate 9, making them stably embedded in the groove 72 of the clutch disc 7. The conical spring used in this embodiment has non-overlapping projections of its coils in the axial direction. This structure ensures that the spring will not "coil together" within its maximum compression stroke, thus providing a smooth and predictable elastic force-displacement characteristic curve.

[0042] In some embodiments, a drive gear is provided at the end of the drive shaft 1 to transmit power to the next stage mechanism. This drive gear can be a spur gear, but in this embodiment, a bevel gear is preferred to facilitate changing the transmission direction within a compact space.

[0043] Please see Figure 3 and Figure 4 One end of the drive shaft 1 is provided with a tapered tooth 11, and the other end is provided with a groove 13, in which a retaining spring 10 is fixed. A keyway 12 is provided axially on the drive shaft 1 for sliding connection with the clutch disc 7.

[0044] Please see Figures 4-6 The clutch disc 7 has a shaped hole 71 machined at its center, which slides and connects to the keyway 12 on the drive shaft 1, achieving circumferential fixation. One end face of the clutch disc 7 is precision machined to form multiple grooves 72 evenly spaced circumferentially. As shown, these grooves 72 are preferably spherical pits or arc-shaped grooves. Each pair of adjacent grooves 72 is interconnected by a slide 73. The bottom profile of the slide 73 smoothly connects to the bottom of the groove 72, i.e., having the same radius of rotation, but its depth gradually changes circumferentially. Specifically, the depth of the slide 73 gradually decreases circumferentially from its connection with a groove 72 until it reaches its shallowest point at the connection with the next groove 72, forming a gentle "slope" structure. The purpose of this design is to guide the rolling element 8 smoothly into and out of the groove 72.

[0045] Based on the above diagrams, the working principle can be briefly described as follows: Normal torque transmission state: When the power tool is working normally, the motor power drives the clutch gear 3 to rotate. The balls are firmly pressed into the groove 72 by the preload of the clutch pressure plate 9 and the conical spring, and are stuck between the groove 72 and the annular groove 91 of the clutch pressure plate 9. When the clutch gear 3 attempts to rotate relative to the clutch disc 7, the balls interact with the inclined surface of the groove 72. The axial component of this force attempts to push the clutch pressure plate 9 to the right to compress the spring, while the radial component drives the clutch disc 7 to rotate. When the output resistance torque is less than the spring's set threshold, the spring's preload is sufficient to overcome the axial component, and the balls cannot roll out of the groove 72. Therefore, the rotational motion of the clutch gear 3 is transmitted to the clutch disc 7 without slippage through the meshing of the balls and the groove 72, thereby driving the drive shaft 1, which is fixed to the clutch disc 7, to rotate synchronously and output working torque.

[0046] Overload Disengagement State: When the output suddenly jams or the resistance torque increases sharply and exceeds the set threshold, the drive shaft 1 and clutch disc 7 tend to stop rotating. However, the clutch gear 3 continues to attempt to rotate under the drive of the motor. At this time, the balls are subjected to a huge normal force from the inclined surface of the groove 72, and its axial component instantly exceeds the preset clamping force of the conical spring. This huge axial force pushes the clutch pressure plate 9 to move axially downward, further compressing the conical spring. At the same time, driven by the clutch gear 3, the balls roll upward along the inclined surface of the groove 72, eventually rolling completely out of the groove 72 and into the slide 73 between adjacent grooves 72. Once the balls enter the shallow slide 73, they no longer have reliable torque transmission capability with the clutch disc 7. At this time, the idle power of the clutch gear 3 can no longer be transmitted to the clutch disc 7 and drive shaft 1, realizing rapid power cut-off and protecting the motor and transmission components.

[0047] Automatic Reset State: When the overload is released, the resistance torque acting on drive shaft 1 decreases. At this time, the compressed conical spring begins to release its elasticity, pushing the clutch pressure plate 9 upward to reset. The clutch pressure plate 9 pushes all the balls upward through the annular groove 91. Under the combined action of the spring force and the rotational force of the clutch gear 3, the balls smoothly slide back to the bottom of the next groove 72 along the gradual ramp of the slide 73 and are pressed again. The clutch automatically restores its torque transmission capability, and the tool can continue to work normally without manual intervention.

[0048] Example 2: This embodiment applies the safety clutch structure of Embodiment 1 to a specific product—a handheld electric hammer—to demonstrate its integration method and working value in a real end product.

[0049] Referring to the figures above, this handheld electric drill mainly includes a housing, a motor, a gear reducer, the aforementioned safety clutch, an output spindle, and a chuck. A small-diameter drive gear is mounted on the motor's output shaft. In this embodiment, the safety clutch is integrated into the gear reducer as a separate modular assembly.

[0050] Specifically, the clutch gear 3 of the safety clutch is constantly meshed with the drive gear of the motor, receiving power from the motor. The bevel gear 11 of the drive shaft 1 of the safety clutch is connected to the final output spindle of the electric drill through another gear. When the user presses the switch and the electric drill is drilling normally, the power transmission path is: motor → motor gear → clutch gear 3 → rolling element 8 → clutch disc 7 → drive shaft 1 → subsequent gear → output spindle → tool head. At this time, the safety clutch is in the meshing transmission state.

[0051] When the tool head suddenly jams during operation, the resistance torque of the output spindle increases sharply and is instantly transmitted to the drive shaft 1 of the safety clutch. When this torque exceeds the threshold determined by the pressure preset by the elastic element 6, the clutch quickly disengages: the engagement between the clutch gear 3 and the clutch disc 7 via the ball bearings is broken, the clutch gear 3 begins to spin freely, and the drive shaft 1, the subsequent output spindle, and the tool head stop rotating. This process is completed within milliseconds, effectively preventing the motor from burning out due to stalling and also preventing gear damage due to overload impact.

[0052] Once the user releases the switch or lifts the hammer backward to disengage, the excessive resistance acting on the tool head disappears. The safety clutch automatically resets under the action of the elastic element 6, the balls slide back into the groove 72, power transmission is restored, and the user can immediately continue operation. The entire process is smooth and automatic, greatly improving tool safety and user experience.

[0053] As can be seen from this embodiment, the safety clutch provided by the present invention, with its zero-slip friction torque transmission path, precise overload threshold response, and rapid automatic disengagement and reset characteristics, can be perfectly integrated into various power tools, ensuring the safety of the core components of the tool while achieving efficient, reliable, and user-friendly overload protection functions.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments; the embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes, modifications, substitutions, and variations can be made to this utility model without departing from its spirit and scope, and all such changes, modifications, substitutions, and variations fall within the scope of the claimed utility model.

Claims

1. A safety clutch for safe engagement / disengagement of an electric tool, the safety clutch comprising a drive shaft, on which a bearing, a clutch gear, a clutch pressure plate, an elastic element, and a support seat are sequentially mounted, the support seat being axially positioned and connected to the drive shaft, and the elastic element abutting against the clutch pressure plate and the support seat at both ends, characterized in that... The clutch gear is rotatably connected to the drive shaft, and the clutch gear has a through hole extending along the axial direction, with a rolling element inside the through hole; The clutch further includes a clutch disc, which is disposed between the bearing and the clutch gear and is circumferentially fixedly connected to the drive shaft; the clutch disc has a groove on the side facing the clutch gear. One end of the rolling element extends into the groove, and the other end abuts against the clutch pressure plate. Under the pre-tightening force of the elastic element, the clutch pressure plate presses the rolling element into the groove. This constitutes a torque-responsive disengagement mechanism: when the resistance torque on the drive shaft is lower than a set threshold, the clutch gear drives the clutch disc and drive shaft to rotate synchronously through the cooperation of the rolling element and the groove; when the resistance torque on the drive shaft reaches or exceeds the set threshold, the rolling element is driven by the clutch gear to axially push the clutch pressure plate to compress the elastic element, causing the rolling element to disengage from the groove and cutting off the power transmission from the clutch gear to the drive shaft.

2. The safety clutch according to claim 1, characterized in that, The clutch disc includes a plurality of grooves spaced apart along the circumference, and adjacent grooves are connected by a slide rail.

3. The safety clutch according to claim 2, characterized in that, The slide is a groove with a gradually changing depth in the circumferential direction. Its bottom contour has the same radius, and the depth is shallowest at the connection with the adjacent groove.

4. The safety clutch according to claim 1, characterized in that, The clutch pressure plate has an annular groove on the side facing the rolling element for the end of the rolling element to contact.

5. The safety clutch according to claim 1, characterized in that, The elastic element is a conical spring, with its large-diameter end abutting against the clutch pressure plate and its small-diameter end abutting against the support base.

6. The safety clutch according to claim 5, characterized in that, The projections of the coils of the conical spring in the axial direction are non-overlapping.

7. The safety clutch according to claim 1, characterized in that, The drive shaft has a drive gear at one end located outside the bearing.

8. The safety clutch according to claim 7, characterized in that, The drive gear is a bevel gear.

9. The safety clutch according to claim 1, characterized in that, The rolling element is a ball, roller, or tapered roller.

10. A power tool, characterized in that, Includes the safety clutch as described in any one of claims 1-9.

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