Sprocket with laterally adjustable alignment elements
By setting a laterally adjustable alignment element in the sprocket tooth groove, the problems of precise meshing and high cost in existing sprocket manufacturing are solved, achieving a more efficient and lower-cost belt alignment effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- THE GATES CORP
- Filing Date
- 2024-11-06
- Publication Date
- 2026-07-21
AI Technical Summary
Existing sprocket manufacturing methods make it difficult to achieve precise meshing with side flanges, and existing belt alignment mechanisms suffer from high costs and long processing times.
A laterally adjustable internal alignment element is designed to achieve precise alignment between the sprocket and the belt by setting a movable alignment element in the sprocket tooth groove. The adjustable alignment element can be used to adapt to different application requirements.
It improves the alignment between the sprocket and the belt, reduces manufacturing costs and time, and enhances the stability and efficiency of the system.
Smart Images
Figure CN122439028A_ABST
Abstract
Description
[0001] Cross-referencing
[0002] This application claims priority to U.S. Provisional Application 63 / 599,297, filed November 15, 2023, the entire disclosure of which is incorporated herein by reference for various purposes. Background Technology
[0003] In conventional or manual mobility applications (such as pedal-powered bicycles) or power-driven mobility applications (such as electric bicycles or e-bikes, electric wheelchairs, scooters, etc.), toothed belts engaging with sprockets typically require some type of belt-tracking to prevent belt misalignment and / or derailment from the sprocket, which can adversely affect system performance. Some sprockets include side flanges as belt-tracking mechanisms, orthogonal to the teeth of the belt and the crossbars of the sprocket that engage with the teeth. Such side flanges laterally restrain the belt. Another belt-tracking mechanism is a center flange on the sprocket and a longitudinal cut along the centerline of the belt; in some belt designs, the center cut is discontinuous. The center flange also laterally restrains the belt.
[0004] Sprockets can be manufactured using various known methods and techniques. In one example, a sprocket is formed using a die-casting method. In such a method, a mold is used to form the specific shape and size of the sprocket, including its tooth profile and flanges. The die-casting process is economical and can produce very precise tooth meshing profiles. However, sprockets with side flanges are difficult to remove from the mold.
[0005] Other methods exist for forming flanged sprockets, including injection molding, insert molding, and overmolding; however, these techniques can be expensive, time-consuming, and may result in lower forming accuracy. Summary of the Invention
[0006] This disclosure relates to a sprocket having an internal alignment element for laterally constraining the belt, the alignment element being adjustable in the lateral direction. Such lateral adjustment achieves better alignment of the sprocket in the system and / or better alignment of the belt on the sprocket. The alignment element can be floating, capable of being laterally moved and repositioned as needed during the use of the sprocket. Alternatively, the alignment element can be fixed in place after the desired position has been determined.
[0007] This document describes an internally aligned sprocket, wherein the alignment element is laterally movable within a circumferential groove. In one particular embodiment, the sprocket has a body having a plurality of teeth longitudinally surrounding the periphery of the body, and a groove extending through the plurality of teeth, the groove having a width. The alignment element is positioned within the groove, the width of the alignment element being smaller than the width of the groove.
[0008] Another specific embodiment described herein is an internally aligned sprocket having a body having a plurality of teeth longitudinally surrounding the periphery of the body and a groove extending through the plurality of teeth having a width, the sprocket also having an alignment element positioned in the groove, the width of the alignment element not exceeding half the width of the groove.
[0009] Another specific embodiment described herein is an internally aligned sprocket having a body having a plurality of teeth longitudinally surrounding the periphery of the body and a groove extending through the plurality of teeth having a width, the sprocket also having an alignment element positioned in the groove having a width and being laterally movable within the groove by at least 1 mm, and in some embodiments at least 3 mm.
[0010] Another specific embodiment described herein is a method for manufacturing an internally aligned sprocket. The method includes forming a sprocket body and forming longitudinal grooves through the teeth. A ring is provided and optionally placed in the groove by expanding the ring and then releasing the ring into the groove. The width of the groove can be at least twice the width of the ring.
[0011] These and other sprockets can be part of a belt drive system comprising a belt (e.g., an annular belt with grooves) and sprockets. Some belt drive systems have a first sprocket associated with a crank and a second sprocket associated with a driven shaft, one or both of which have the features described herein. Thus, the embodiment described herein is a belt drive system having a belt and sprockets as described herein, the belt having a plurality of longitudinally spaced teeth and grooves extending through the teeth. Another embodiment described herein is a belt drive system having: a belt having a plurality of longitudinally spaced teeth and grooves extending through the teeth; a first sprocket as described herein associated with a crank; and a second sprocket associated with a driven shaft.
[0012] These and other aspects of the technology described herein will become apparent after taking into account the specific embodiments and accompanying drawings.
[0013] This summary is provided to introduce, in a simplified form, some concepts that will be further described in the detailed embodiments below. The summary and the foregoing background are not intended to identify key or essential aspects of the claimed subject matter. Furthermore, this summary is not intended to help determine the scope of the claimed subject matter. It should be understood that the scope of the claimed subject matter should be determined by the published claims, and not by whether the given subject matter solves any or all of the problems mentioned in the background or whether it includes any features or aspects listed in the summary. Attached Figure Description
[0014] Figure 1 This is a 3D view of the sprocket.
[0015] Figure 2 for Figure 1 Side view of the sprocket.
[0016] Figure 3A for Figure 1 An end view of the sprocket, wherein the alignment element is in the first end position; Figure 3B This is an end view of the sprocket, with the alignment element in the center position; and Figure 3C This is an end view of the sprocket, with the alignment element in the second end position.
[0017] Figure 4A , 4B 4C and 4D are enlarged cross-sectional views of an exemplary arrangement of sprocket teeth and adjustable alignment elements.
[0018] Figure 5 An exemplary step-by-step method for manufacturing a sprocket with a laterally adjustable internal alignment element.
[0019] Figure 6 This is an exemplary step-by-step method for using sprockets. Detailed Implementation
[0020] As described above, this disclosure relates to an internally aligned sprocket for a toothed belt system, suitable for applications such as mobility devices (e.g., bicycles, electric bicycles or e-bikes, electric wheelchairs, scooters, etc.). The alignment element is laterally movable or laterally adjustable.
[0021] The term "internal alignment element" or variations thereof refers to an alignment element that is axially or laterally positioned between a first outer wall, side, or surface of the sprocket and an opposing outer wall, side, or surface. The internal alignment element may be located at the center between the walls, sides, or surfaces, or may be offset to a position closer to one side or the other.
[0022] In the following description, reference is made to the accompanying drawings, which form part of the description and illustrate at least one specific embodiment by way of example. Additional specific embodiments are provided in the following description. It should be understood that other embodiments may be conceived and made without departing from the scope or spirit of this disclosure. Therefore, the following detailed description should not be considered limiting. While this disclosure is not limited thereto, an understanding of various aspects of this disclosure will be obtained through the discussion of the examples provided below, including the accompanying drawings. In some cases, reference numerals may have associated sublabels consisting of lowercase letters to indicate one of a plurality of similar components. When reference numerals are used without sublabels, the reference is intended to refer to all such plurality of similar components.
[0023] Figure 1 , 2 Figures 3A, 3B, and 3C illustrate various features of sprocket 100, which is suitable for, for example, mobile power systems with toothed belts (typically "annular" belts). The figures show that sprocket 100 has a body 102 having a generally disc-shaped or wheel-like structure, and the body 102 has a first side 104 (see Figure 3A). Figure 3B ) and second side 106 (see Figure 3B The sprocket 100 comprises a plurality of parallel teeth 110 surrounding the periphery or periphery of the body 102, each tooth 110 having a first end 114 at a first side 104 and a second end 116 at a second side 106, such that the tooth 110 extends from the first side 104 to the second side 106. The width of the sprocket 100 is defined from the first side 104 to the second side 106, the width being configured for the toothed belt and the belt system on which the sprocket will be mounted. The teeth 110 define the outer periphery and radial edges of the sprocket 100.
[0024] The position, size, and shape of the teeth 110 are configured to mesh with the teeth of the toothed band (particularly between adjacent teeth). There are grooves 115 between adjacent teeth 110, which are grooves between the sidewalls of adjacent teeth 110.
[0025] The distance between adjacent teeth 110 (typically the length of tooth groove 115 in the longitudinal or circumferential direction, the width of which is measured from side 104 to side 106) is equal to or substantially equal to (e.g., slightly less, e.g., slightly greater than) the pitch length of the belt the sprocket will engage (the approximate length of the tooth). The teeth 110 are evenly spaced around the periphery of the sprocket 100. The number of teeth 110 and the distance between adjacent teeth 110 can be adjusted based on the sprocket diameter and the dimensions of the teeth 110 (e.g., width measured in a direction orthogonal to the direction between the first end 114 and the second end 116).
[0026] The sprocket 100 includes an internal alignment element 120 extending circumferentially around the sprocket 100 and positioned between a first side 104 and a second side 106. The internal alignment element 120 engages with a groove, slot, or cut present in the belt meshing with the sprocket 100. The groove, slot, or cut may be continuous along the length of the belt or may be discontinuous, for example, present between belt teeth. The alignment element 120 facilitates belt alignment on the sprocket 100 during operation and prevents lateral movement of the belt relative to the sprocket 100.
[0027] Alignment element 120 is positioned in a groove 122 within teeth 110 between first side 104 and second side 106. Groove 122 is typically located centrally between first side 104 and second side 106, but in some embodiments, it may be desirable for groove 122 to be offset closer to one side 104, 106 than the other. Measured axially from side 104 to side 106, the width of groove 122 is greater than the width of alignment element 120. In some embodiments, the width of groove is at least twice the width of alignment element 120 (in other words, the width of alignment element does not exceed half the width of groove 122). Making the width of groove 122 greater than the width of alignment element 120 allows for lateral movement of alignment element 120 within groove 122.
[0028] The groove 122 has a first sidewall 124 ( Figure 3B ) and second sidewall 126 ( Figure 3B The width of the groove 122 from sidewall 124 to sidewall 126 can be at least 3 mm to 10 mm, but this width can be greater, as it depends largely on the overall width of the tooth 110 and sprocket 100 and the size of the alignment element 120. In some embodiments, for example, for very narrow sprockets and / or very narrow alignment elements, the width of the groove 122 can be less than 3 mm. The width of the groove 122 typically does not exceed 20% of the width of the sprocket 100, and in some embodiments does not exceed 10%. The width of the groove 122 is greater than the width of the alignment element 120, being twice (2x) in some embodiments and three, four, or five times in other embodiments.
[0029] In some embodiments, the total permissible lateral movement of the alignment element 120 within the slot 122 is at least 1 mm, in other embodiments at least 3 mm, and in still other embodiments at least 5 mm. In other embodiments, the total permissible lateral movement does not exceed 1 cm, in some embodiments not more than 8 mm, and in still other embodiments not more than 5 mm. For the purposes of discussion herein, the lateral movement is measured with respect to the center of the alignment element 120. Figure 3A , 3BThe diagram shows the alignment element 120 in three different positions within the slot 122; Figure 3A In the middle, the alignment element 120 is positioned against the first wall 124 of the groove 122, in Figure 3B In the middle, the alignment element 120 is located in the intermediate position between the two walls 124, 126 (e.g., in the center position of the groove 122), in Figure 3C In the middle, the alignment element 120 is positioned against the second wall 126 of the groove 122.
[0030] The depth of the groove 122, measured in the radial direction of the tooth 110, is typically at least 2 mm and depends largely on the dimensions (e.g., height or depth) of the tooth 110 and the alignment element 120. The groove 122 may extend through the depth of the tooth 110.
[0031] When positioned in the slot 122, the alignment element 120 may have the same height as the tooth 110 (e.g., the depth of the slot 122 is the same as the height of the alignment element 120), or may be larger, for example, extending above the top level of the tooth 110, or may be smaller, for example, extending below the top level of the tooth. In some embodiments, the alignment element 120 may not be located at the bottom of the slot 122.
[0032] Alignment element 120 and slot 122 can have any cross-sectional shape; Figures 4A to 4D Various alternative designs are illustrated. For example, if the alignment element 120 is formed of wire, the cross-sectional shape can be circular or elliptical / oblong. Other shapes of the alignment element 120 include rectangles, triangles, and trapezoids. The slot 122 can essentially be any shape in which the alignment element 120 is received and allows lateral movement of the alignment element 120 within the slot 122. For example, when the alignment element 120 is trapezoidal, the corresponding slot 122 can also be trapezoidal or dovetail-shaped; such a design prevents radial (outward) displacement of the alignment element from the slot. As another example, the slot 122 can include an undercut, having a greater width at the bottom of the slot 122 than at the exposed top of the slot 122, thereby allowing for greater lateral movement of the alignment element.
[0033] Go to Figures 4A to 4D Each of these examples has a tooth 210 with an alignment element 220 positioned in a groove 222 having a first wall 224 and a second wall 226.
[0034] exist Figure 4AIn the sprocket, tooth 210A has a thin rectangular alignment element 220A positioned within a rectangular groove 222A having a first wall 224A and a second wall 226A. The alignment element 220A is disposed on the bottom or bottom surface of the groove 222A and extends beyond the depth of the groove 222A. The width of the groove 222A is approximately three times the width of the alignment element 220A. For a sprocket with this design, the alignment element 220A will continuously engage longitudinally with the belt running on the sprocket.
[0035] exist Figure 4B In this design, tooth 210B has a wire alignment element 220B positioned within a rectangular groove 222B having a first wall 224B and a second wall 226B. The alignment element 220B does not extend beyond the depth of the groove 222B but is recessed into it; in this design, the alignment element 220B is not placed on the bottom or bottom surface of the groove 222B but is "floating". The width of the groove 222B is less than twice the width of the wire alignment element 220B. For a sprocket with this design, the alignment element 220B will engage discontinuously longitudinally with the belt running on the sprocket, engaging only between teeth 210B.
[0036] exist Figure 4C In the sprocket, tooth 210C has a rectangular alignment element 220C positioned within a rectangular groove 222C having a first wall 224C and a second wall 226C. The alignment element 220C, placed on the bottom or bottom surface of the groove 222C, is flush with the top of the groove 222C. The width of the groove 222C is approximately five to six times the width of the alignment element 220C. For a sprocket with this design, the alignment element 220C will engage discontinuously longitudinally with the belt running on the sprocket, engaging only between teeth 210C.
[0037] exist Figure 4D In this design, tooth 210D has a wire alignment element 220D positioned within a trapezoidal or dovetail groove 222D having a first wall 224D and a second wall 226D. The wire alignment element 220D is fully contained within the groove 222D and has a diameter greater than its top width, thus preventing it from being removed from the groove 222D. The wire alignment element 220D can move laterally between the first wall 224D and the second wall 226D. For a sprocket with this design, the wire alignment element 220D will engage discontinuously longitudinally with the belt running on the sprocket, engaging only between teeth 210D.
[0038] Alignment elements 120 and 220 can be single elements extending circumferentially around the sprocket, or they can be formed from multiple parts. As an example, alignment elements 120 and 220 can be wire placed around the sprocket body 102 in slots 122 and 222, and then joined to form a continuous loop; for example, the metal rings can be welded or brazed. Another example of alignment elements 120 and 220 is an open or single-turn clasp or open ring. Yet another example is a circular open ring with more than one turn, such as a "keychain" ring.
[0039] The choice between single-turn and multi-turn rings depends primarily on the ring size, the groove size, and the sprocket body size. For small rings, increasing the ring size is more difficult; therefore, double / multi-turn rings are advantageous. For larger rings, radial expansion is easier; therefore, single-turn rings are more economical. Another consideration when selecting the number of turns is the overall width of the ring along its axial dimension. Multi-turn rings with thinner cross-sections can achieve greater widths better than single-turn rings with thicker cross-sections.
[0040] Alignment elements 120 and 220 can float in slots 122 and 222, and can be laterally moved and repositioned in slots 122 and 222 as needed during the use of the sprocket. Alternatively, after the desired position of the alignment element has been determined and calibrated, the alignment element can be fixed in place.
[0041] Alignment elements 120, 220 may be glued, welded, brazed, or otherwise adhered to the desired position. Additionally or alternatively, alignment elements 120, 220 may be secured in the desired position via a locking mechanism (such as a spacer, washer, or set screw). The locking mechanism may be permanent or removable and replaceable, for example, to readjust the position or reuse the sprocket in a different system.
[0042] Figure 5 An exemplary method 300 is provided for forming a sprocket as described herein. In a first step 302 of method 300, a sprocket body is formed. The sprocket body comprises a wheel-like structure having a plurality of teeth extending around the outer periphery of the wheel. The sprocket can be formed by casting, molding, machining, 3D printing, waterjet cutting, plasma cutting, forging, or other suitable processes.
[0043] In step 304, a groove is formed in the tooth, the groove extending around the periphery of the sprocket body. The groove may extend as deep as the tooth or may be less than the tooth depth. The groove may be formed by machining, waterjet cutting, plasma cutting, or other suitable processes. The groove may or may not be located at the center of the sprocket body.
[0044] In some methods, the formation of the groove in step 304 can be carried out simultaneously with the formation of the sprocket itself in step 302.
[0045] In step 306, a ring is provided, and in step 308, the ring is expanded. The ring can be a circular open ring, such as a closed ring or an open-end ring. The ring can have one or more turns and can expand from a relaxed, stress-free state to an expanded state. The width of the ring is less than the width of the groove, and in some embodiments, does not exceed half the width of the groove.
[0046] In step 310, the expanded ring is placed onto the sprocket body and into the groove. In step 312, the ring is released so that it can be seated in the groove. The ring is capable of moving laterally within the groove.
[0047] Another suitable method of manufacturing a sprocket includes: providing a sprocket body having a periphery and a groove in the periphery; expanding a ring; positioning the ring above the groove; and releasing the ring into the groove. Yet another suitable method of manufacturing a sprocket includes: forming a sprocket body having a periphery; forming a circumferential groove in the periphery; expanding a circular open ring from a natural state to an open state; positioning the ring above the groove; and releasing the ring into the groove. In all methods, the lateral width of the groove is greater than the width of the ring.
[0048] Figure 6 An example method 400 is provided using a sprocket (such as sprocket 100 or a variation thereof, or a sprocket manufactured by method 300) with a laterally adjustable alignment element. In a first step 402 of method 400, the sprocket is mounted on a shaft; this mounting may use, for example, a bushing. The sprocket may be mounted as a driven sprocket, a drive sprocket, an idler sprocket, or a tensioner sprocket. In step 404, a corresponding toothed belt with a central longitudinal groove or cut is mounted on the sprocket.
[0049] In step 406, the aligning element is calibrated relative to the lateral position of the belt to achieve proper centering and alignment of the belt and sprocket. In some embodiments, this may require running the belt on the sprocket to bring the system to a stable state. After determining the desired position of the aligning element in the slot, in step 408, the aligning element is locked in that position by a suitable mechanism, such as by spot welding the aligning element to the sprocket, by inserting a shim or spacer into the slot adjacent to the aligning element, or by placing a set screw in a threaded hole.
[0050] In other methods, the alignment element is not locked in a specific position, but is allowed to float laterally within the slot.
[0051] The sprocket 100 or a variant thereof may include debris removal elements, such as chamfered areas in the tooth groove 115, which help remove dirt, dust, fluid, and other debris from the volume between adjacent teeth 110. In some embodiments, debris removal holes or channels may extend through the alignment element 120 to provide lateral fluid communication from one side of the alignment element 120 to the other.
[0052] Examples of suitable materials for alignment element 120 include metals (e.g., steel, stainless steel, nickel, iron, aluminum, alloys), composite materials, polymer fibers (such as Kevlar® aramid fibers and other polymer fibers), and thermoplastic and / or thermosetting polymers (e.g., polycarbonate, polyamide, polyethylene, polyphthalamide, including fiber-reinforced polymers).
[0053] Examples of suitable materials for sprocket 100 and its variations include thermoplastic and / or thermosetting polymers (e.g., polycarbonate, polyamide, polyethylene, polyphthalamide, including fiber-reinforced polymers), metals (e.g., steel, stainless steel, nickel, iron, aluminum, alloys), and composite materials.
[0054] The sprocket 100 and its variations described herein can generally be manufactured using any known and suitable technology. For example, the sprocket can be manufactured by machining, molding (e.g., injection molding), die casting, forging, 3D printing, gear hobbing, plasma cutting, waterjet cutting, or a combination of multiple processes.
[0055] The sprocket 100 and its variations described herein can be centrally mounted on a shaft (e.g., a rotatable shaft). The sprocket may have a central hub for mounting the sprocket to the shaft. In other embodiments, the center of the sprocket may be configured to receive a bushing therein, the bushing being used to secure the sprocket to the shaft. Any type of hub or bushing can be used, wherein the shape and size of the center of the sprocket are adjusted to accommodate any suitable type of hub or bushing, and the shape and size of any hub or bushing are set to accommodate any suitable shaft.
[0056] Therefore, at least one specific example of a sprocket having a laterally adjustable internal circumferential alignment element is described herein. The foregoing description and examples provide a complete description of the structure and use of exemplary embodiments of the invention. Therefore, the detailed description above should not be considered limiting. It should be understood that other embodiments can be conceived and constructed without departing from the scope or spirit of this disclosure. Furthermore, an element or feature of one example, design, embodiment, or implementation may be applied to any other example, design, embodiment, or implementation described herein to the extent that such content does not conflict. Therefore, the detailed description above should not be considered limiting.
[0057] Unless otherwise specified, all figures representing characteristic dimensions, quantities, and physical properties should be understood to be modified by the term "approximately," whether or not the term "approximately" is directly present. Therefore, unless the contrary is indicated, stated numerical parameters are approximations that can vary according to the desired performance sought by those skilled in the art using the teachings disclosed herein.
[0058] As used herein, the singular form “a” and “described” cover embodiments having plural referents, unless otherwise expressly indicated. As used in this specification and the appended claims, the term “or” is generally used in its meaning including “and / or”, unless otherwise expressly indicated.
[0059] When used herein, spatially related terms, including but not limited to “bottom,” “lower,” “top,” “upper,” “below,” “below,” “above,” “on top,” “above,” etc., are used for the convenience of describing the spatial relationship between one or more elements and another element. In addition to the specific orientations depicted in the figures and described herein, such spatially related terms also cover different orientations of the apparatus. For example, if the structure depicted in the figures is flipped or inverted, the portion previously described as being below or beneath other elements will be above or above those other elements.
Claims
1. A sprocket, comprising: A body having a plurality of teeth longitudinally surrounding the periphery of the body, and a groove extending through the plurality of teeth, the groove having a width; as well as An alignment element positioned in the groove, the width of the alignment element not exceeding half the width of the groove, or capable of laterally moving at least 1 mm or at least 3 mm within the groove.
2. The sprocket according to claim 1, wherein, The alignment element can move laterally to the ground within the groove by at least 1 mm.
3. The sprocket according to claim 2, wherein, The alignment element can move at least 3 mm within the slot.
4. The sprocket according to claim 2, wherein, The alignment element has a circular cross-section.
5. The sprocket according to claim 2, wherein, The alignment element has a rectangular cross-section.
6. The sprocket according to claim 2, wherein, The groove extends at least 2 mm into each of the plurality of teeth.
7. The sprocket according to claim 6, wherein, The groove extends the entire depth of the tooth.
8. The sprocket according to claim 2, wherein, The alignment element extends over the plurality of teeth.
9. The sprocket according to claim 2, wherein, The alignment element does not extend over the plurality of teeth.
10. The sprocket according to claim 1, wherein, The width of the alignment element is no more than half the width of the slot.
11. The sprocket according to claim 10, wherein, The width of the slot is at least three times the width of the alignment element.
12. The sprocket according to claim 11, wherein, The width of the slot is at least four times the width of the alignment element.
13. The sprocket according to claim 10, wherein, The alignment element is fixed to the groove to prevent lateral movement of the alignment element within the groove.
14. The sprocket according to claim 10, wherein, The alignment element has a circular cross-section.
15. The sprocket according to claim 10, wherein, The alignment element has a rectangular cross-section.
16. The sprocket according to claim 10, wherein, The groove extends at least 2 mm into each of the plurality of teeth.
17. The sprocket according to claim 16, wherein, The groove extends the entire depth of the tooth.
18. The sprocket according to claim 10, wherein, The alignment element extends over the plurality of teeth.
19. The sprocket according to claim 10, wherein, The alignment element does not extend over the plurality of teeth.
20. A drive system, comprising: A belt having a plurality of longitudinally spaced teeth and grooves extending through the teeth; as well as The sprocket according to any one of the preceding claims.
21. A drive system, comprising: A belt having a plurality of longitudinally spaced teeth and grooves extending through the teeth; A first sprocket associated with a crank, as described in any one of claims 1-19; as well as The second sprocket associated with the driven shaft.