Ball screw drive with external circulation

Abstract

Ball screw with external circulation (10), comprising: a screw spindle (11) comprising an external thread groove (111) around the circumference; a nut (12) screwed onto the screw spindle (11) and movable axially along the screw spindle (11), the nut (12) comprising an internal thread groove (121) which, together with the external thread groove (111) of the screw spindle (11), forms a loading path (P1), a fastening groove (122) located in an opposite outer periphery thereof, two opposite return holes (123) which are respectively connected to the fastening groove (122) and the loading path (P1), a first step (124) located in the fastening groove (122) between the two return holes (123) and a first half return channel (125) formed in the first step (124); a cover (13) fixed to the nut (12) to cover the fixing groove (122), the cover (13) comprising a second step (131) located on an inner side thereof and a second half return passage (132) formed in the second step (131), the second half return passage (132) and the first half return passage (125) forming a return passage (P2); two return elements (14), each having a passage (141) therein, a first end (142) located at one end of the passage (141) and a second end (143) at an opposite end of the passage (141), the first end (142) of each return element (14) being inserted into a corresponding return hole (123) of the nut (12) to keep the passage (141) in communication with the loading path (P1), the second ends (143) of the two return elements (14) being arranged respectively on two opposite sides relative to the return channel (P2) to keep the passages (141) in communication with the return channel (P2), the loading path (P1), the return channel (P2), and the passages (141) of the two return elements (14), thus forming a return path (P3); and a plurality of rolling elements (15) movably arranged in the return flow path (P3), wherein the second end (143) of each return element (14) abuts against the first stage (124) and the second stage (131).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to the field of ball screws and, in particular, to a ball screw with external circulation. 2. Description of the state of the art

[0002] Conventional ball screws are divided into two types: internal circulation and external circulation. External circulation ball screws are typically used for high-load applications. DE 102016106986 B3 discloses a ball screw with a maintenance device, comprising a screw shaft with a spiral rolling groove; a nut with an outer peripheral surface in which at least two mounting holes are formed; two return elements mounted on the nut, each having a through hole with an open end spaced from the rolling groove; and a mounting cover mounted on the outer peripheral surface of the nut and having a collecting recess formed therein. The through hole has one end communicating with the collecting recess.Taiwan Patent I509169 discloses an external circulation ball screw in which the return channels of two return elements are connected in a mounting groove to allow circulation of the rolling balls, so that the ball screw can function smoothly.

[0003] However, the design of a ball screw with external circulation has the following disadvantages: 1. For nuts with different lengths (with different numbers of threads), different molds must be used to produce different sizes of the return elements so that the return channels of the return elements arranged in the nut can be connected to each other, which leads to increased manufacturing costs. 2. The return elements are manufactured using injection molding techniques, and longer return elements are more likely to deform. During assembly, the time required for reworking the return elements increases, which increases the assembly time. In addition, altering the return elements results in inaccurate connections between the return channels, which can lead to uneven ball circulation. SUMMARY OF THE INVENTION

[0004] The present invention was realized under the given circumstances. The primary object of the present invention is to provide an external circulation ball screw in which return elements of the same size can be used with nuts of different lengths, thus saving costs.

[0005] To achieve these and other objects of the present invention, an external circulation ball screw according to an embodiment of the present invention includes a screw shaft, a nut, a cover, two return elements, and a plurality of rolling elements. The screw shaft includes an external thread groove around a circumference thereof. The nut is threaded onto the screw shaft, is axially movable along the screw shaft, and includes an internal thread groove forming a loading path with the external thread groove of the screw shaft, a mounting groove located in an opposite outer circumference thereof, two opposite return holes respectively arranged in communication between the mounting groove and the loading path, and a first step located in the mounting groove between the two return holes and a first half return passage formed in the first step.The cover is arranged on the nut to cover the fastening groove and includes a second step located on an inner side thereof and a second half return channel formed in the second step. The second half return channel and the first half return channel form a return channel. Each of the two return elements includes a passage therein, with a first end located at one end of the passage and a second end at an opposite end of the passage. The first end of each return element is inserted into a corresponding return hole of the nut to keep the passage in communication with the charging path. The second ends of the two return elements are respectively arranged on two opposite sides relative to the return channel to keep the passages in communication with the return channel. Thus, the charging path, the return channel, and the passages of the two return elements form a return path.The rolling elements are movably arranged in the return flow path.

[0006] In this embodiment, the external circulation ball screw can still use the same-sized return elements even if the lengths of the nuts are different, by arranging the first half return passage and the second half return passage in the nut and the cover, respectively. By using the same-sized return elements with the different-length return passages, circulation of the rolling elements can be achieved. Since only one size of return elements is required, a single mold can be used, reducing molding costs. In addition, the return passage also shortens the length of the return elements, preventing deformation of the return elements during manufacturing, thus improving the assembly of the ball screw effectively and economically.

[0007] The second end of each reflux element abuts against the first stage and the second stage.

[0008] Preferably, each backflow element further comprises a flange extending around its second end. The cover further comprises two stop walls, respectively disposed on two opposite sides relative to the second stage, and a positioning groove located between each stop wall and the second stage. The flanges of the two backflow elements are respectively disposed in the positioning grooves. Thus, the backflow elements are stably disposed in the nut.

[0009] Preferably, the cover further includes a lubrication hole connected to the return channel. This allows the user to conveniently fill the cover with lubricating oil to directly lubricate the rolling elements.

[0010] According to an alternative form of the present invention, the external circulation ball screw comprises a screw shaft, a nut, a cover, two return elements, and a plurality of rolling elements. The screw shaft includes an external thread groove around its circumference. The nut is threaded onto the screw shaft, is axially movable along the screw shaft, and includes an internal thread groove that forms a loading path with the external thread groove of the screw shaft, a mounting groove located in an opposite outer periphery thereof, and two opposite return holes respectively arranged in communication between the mounting groove and the loading path. The cover is attached to the nut to cover the mounting groove.The cover or the nut includes a third step located on an inner side thereof between the two return holes and a return channel located at the third step. Each of the two return elements includes a passage therein, with a first end located at one end of the passage and a second end at an opposite end of the passage. The first end of each return element is inserted into a corresponding return hole of the nut to keep the passage in communication with the loading path. The second ends of the two return elements are respectively arranged on two opposite sides relative to the return channel to keep the passages in communication with the return channel. Thus, the loading path, the return channel, and the passages of the two return elements form a return path. The rolling elements are movably arranged in the return path.

[0011] Preferably, the second end of each reflux element abuts against the third step, which improves the positioning stability of the reflux elements in the nut.

[0012] Preferably, each backflow element further comprises a flange extending around a second end thereof. The cover further comprises two stop walls, respectively arranged on two opposite sides relative to the third stage, and a positioning groove located between each stop wall and the third stage. The flanges of the two backflow elements are respectively arranged in the positioning grooves. Thus, the backflow elements are stably positioned in the nut.

[0013] Preferably, the cover further includes a lubrication hole connected to the return channel. This allows the user to conveniently fill the cover with lubricating oil to directly lubricate the rolling elements.

[0014] Other advantages and features of the present invention will be better understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals designate like parts of the structure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an oblique plan view of an external circulation type ball screw according to a first embodiment of the present invention. Fig. 2 is an exploded view of a part of the external circulation type ball screw according to the first embodiment of the present invention. Fig. 3 is an exploded view of the external circulation type ball screw according to the first embodiment of the present invention. Fig. 4 is a sectional view taken along line 4-4 of Fig. 1. Fig. 5 is a sectional view taken along line 5-5 of the Fig. 1. Fig. 6 is an exploded view of the external circulation ball screw according to a second embodiment of the present invention, showing a third step formed in the nut fastening groove. Fig. 7 is an exploded view of the external circulation type ball screw according to a second embodiment of the present invention, showing a third step formed in the cover. DETAILED DESCRIPTION OF THE INVENTION

[0015] In the Fig. 1 to 5, an external circulation ball screw 10 according to a first embodiment of the present invention is shown. As shown, the external circulation ball screw 10 includes a screw shaft 11, a nut 12, a cover 13, two return elements 14, and a plurality of rolling elements 15.

[0016] The screw spindle 11 includes an external thread groove 111 around its circumference.

[0017] The nut 12 is screwed onto the screw spindle 11 for axial movement along the screw spindle 11. The nut 12 includes an internal thread groove 121 that spirals around an inner circumference thereof and forms a loading path P1 with the external thread groove 111 of the screw spindle 11. The nut 12 further includes a fastening groove 122 located in an opposite outer circumference thereof, and two opposite return holes 123 arranged in communication between the fastening groove 122 and the loading path P1, respectively. The nut 12 further includes a first step 124 located in the fastening groove 122 between the two return holes 123, and a first half return channel 125 formed in the first step 124.

[0018] The cover 13 is arranged on the nut 12 to cover the fastening groove 122 and includes a second step 131 located on an inner side thereof and a second half return channel 132 formed in the second step 131. The second half return channel 132 and the first half return channel 125 form a return channel P2.

[0019] Each of the two return elements 14 has a passage 141 therein. The passage 141 has two opposite ends, which terminate in a first end 142 and a second end 143, respectively. The first end 142 of each return element 14 is inserted into one of the return holes 123 of the nut 12, respectively, to keep the passage 141 in communication with the charging path P1. The second ends 143 of the return elements 14 are respectively arranged on two opposite sides relative to the return channel P2 and keep the passages 141 in communication with the return channel P2. The charging path P1, the return channel P2, and the passages 141 of the return elements 14 form a return path P3.

[0020] The rolling elements 15 are movably arranged in the return flow path P3.

[0021] Due to the above-described structure, the external circulation ball screw 10 of the present invention can utilize return elements 14 of the same size even if the length of the nut 12 differs. Circulation of the rolling elements 15 can be achieved with return elements 14 of the same size and return passages P2 of different lengths. Since only one size of return elements 14 is required, a single mold size can be used, reducing molding costs. In addition, with the return passage P2, the lengths of the return elements 14 can also be shortened, preventing deformation of the return elements 14 during manufacturing and effectively improving the structure of the ball screw.

[0022] It should be noted that according to this embodiment, the second end 143 of each reflux element 14 stops at the first step 124 or the second step 131. Thus, the reflux elements 14 can be stably arranged on the nut 12. Furthermore, a positioning flange 144 is formed on each reflux element 14 around the second end 143. The cover 13 further includes two stop walls 133 formed respectively on two opposite sides relative to the second step 131, and a positioning groove 134 formed between each stop wall 133 and the second step 131. The positioning flanges 144 of the reflux elements 14 are respectively arranged in the respective positioning grooves 134. Thus, the reflux elements 14 are stably arranged on the nut 12.

[0023] It should also be noted that although this embodiment has the technical features mentioned in the previous paragraph, it is also possible to use return elements 14 of the same size with nuts 12 of different lengths to save molding costs if it is decided not to implement the technical features mentioned in the previous paragraph. According to the present invention, the second end 143 of each return element 14 abuts against the first step 124 and the second step 131, respectively. The second end 143 of each return element 14 may include positioning grooves 134 and positioning flanges 144. Alternatively, the positioning grooves 134 and the positioning flanges 144 are not provided, provided that the rolling elements 15 are prevented from leaving the return path P3 through the passage 141 and the return channel P2, so that circulation of the rolling elements 15 can continue.

[0024] Additionally, according to this embodiment, it is possible for the cover 13 to have a lubrication hole 135. The lubrication hole 135 communicates with the return channel P2. It is convenient for the user to fill the cover 13 with lubricating oil to achieve direct lubrication of the rolling elements 15 with the lubricating oil.

[0025] In the Fig. 6 and Fig. Figure 7 shows an external circulation ball screw 10 according to a second embodiment of the present invention. This second embodiment is substantially identical to the aforementioned embodiment, except that a third step 161 is formed in the cover 13 or the mounting groove 122 of the nut 12. This third step 161 is located between the two return holes 123. The return channel P2 is located in the third step 161.

[0026] In this second embodiment, the second ends 143 of the reflux elements 14 abut the third step 161, respectively. Thus, the reflux elements 14 are stably disposed on the nut 12. Furthermore, a positioning flange 144 is formed on each reflux element 14 around its second end 143. The cover 13 further includes two stop walls 133, which are respectively formed on two opposite sides relative to the third step 161, and a positioning groove 134 formed between each stop wall 133 and the third step 161. The positioning flanges 144 of the reflux elements 14 are respectively disposed in the corresponding positioning groove 134. Thus, the reflux elements 14 are stably disposed on the nut 12.

[0027] Even if it is decided not to implement the technical features mentioned in the previous paragraph, it is still possible to use return flow elements 14 of the same size with nuts 12 of different lengths in order to save molding costs.

[0028] Additionally, with this embodiment, it is also possible to provide a lubrication hole 135 in the cover 13. The lubrication hole 135 communicates with the return channel P2. It is easy and convenient for the user to fill the cover 13 with lubricating oil to ensure that the lubricating oil directly lubricates the rolling elements 15.

Claims

[1] Ball screw with external circulation (10), comprising: a screw spindle (11) comprising an external thread groove (111) around the circumference; a nut (12) screwed onto the screw spindle (11) and movable axially along the screw spindle (11), the nut (12) comprising an internal thread groove (121) which, together with the external thread groove (111) of the screw spindle (11), forms a loading path (P1), a fastening groove (122) located in an opposite outer periphery thereof, two opposite return holes (123) which are respectively connected to the fastening groove (122) and the loading path (P1), a first step (124) located in the fastening groove (122) between the two return holes (123) and a first half return channel (125) formed in the first step (124); a cover (13) fixed to the nut (12) to cover the fixing groove (122), the cover (13) comprising a second step (131) located on an inner side thereof and a second half return passage (132) formed in the second step (131), the second half return passage (132) and the first half return passage (125) forming a return passage (P2); two return elements (14), each having a passage (141) therein, a first end (142) located at one end of the passage (141) and a second end (143) at an opposite end of the passage (141), the first end (142) of each return element (14) being inserted into a corresponding return hole (123) of the nut (12) to keep the passage (141) in communication with the loading path (P1), the second ends (143) of the two return elements (14) being arranged respectively on two opposite sides relative to the return channel (P2) to keep the passages (141) in communication with the return channel (P2), the loading path (P1), the return channel (P2), and the passages (141) of the two return elements (14), thus forming a return path (P3); and a plurality of rolling elements (15) movably arranged in the return flow path (P3), wherein the second end (143) of each return element (14) abuts against the first stage (124) and the second stage (131). [2] The external circulation ball screw (10) according to claim 1, wherein each return element (14) further comprises a flange (144) extending around the second end (143) thereof; wherein the cover (13) further comprises two stop walls (133) respectively disposed on two opposite sides relative to the second stage (131), and a positioning groove (134) disposed between each stop wall (133) and the second stage (131); wherein the flanges (144) of the two return elements (14) are respectively disposed in the positioning grooves (134). [3] The external circulation ball screw (10) according to claim 1, wherein the cover (13) further comprises a lubrication hole (135) in communication with the return passage (P2). [4] A ball screw with external circulation (10), comprising: a screw spindle (11) comprising an external thread groove (111) around the circumference thereof; a nut (12) which is screwed onto the screw spindle (11) and is axially movable along the screw spindle (11), the nut (12) comprising an internal thread groove (121) which forms a loading path (P1) with the external thread groove (121) of the screw spindle (11), a fastening groove (122) which is located on an opposite outer circumference thereof, two opposite return holes (123) which are respectively in communication with the fastening groove (122) and the loading path (P1); a cover (13) fixed to the nut (12) to cover the fixing groove (122), the cover (13) including a third step (161) located on an inner side thereof between the two return holes (123) and a return passage (P2) located in the third step (161); two return elements (14), each having a passage (141) therein, a first end (142) located at one end of the passage (141) and a second end (143) at an opposite end of the passage (141), the first end (142) of each return element (14) being inserted into a corresponding return hole (123) of the nut (12) to keep the passage (141) in communication with the loading path (P1), the second ends (143) of the two return elements (14) being arranged respectively on two opposite sides relative to the return channel (P2) to keep the passages (141) in communication with the return channel (P2), the loading path (P1), the return channel (P2), and the passages (141) of the two return elements (14) to form a return path (P3); and a plurality of rolling elements (15) movably arranged in the return flow path (P3), wherein the second end (143) of each return element (14) abuts against the third stage (161). [5] The external circulation ball screw (10) according to claim 4, wherein each return element (14) further comprises a flange (144) extending around its second end (143); wherein the cover (13) further comprises two stop walls (133) respectively disposed on two opposite sides relative to the third stage (161), and a positioning groove (134) formed between each stop wall (133) and the third stage (161); wherein the flanges (144) of the two return elements (14) are respectively disposed in the positioning grooves (134). [6] The external circulation ball screw (10) according to claim 4, wherein the cover (13) further comprises a lubrication hole (135) in communication with the return passage (P3). [7] A ball screw with external circulation (10), comprising: a screw spindle (11) comprising an external thread groove (111) around the circumference thereof; a nut (12) which is screwed onto the screw spindle (11) and is axially movable along the screw spindle (11), the nut (12) comprising an internal thread groove (121) which forms a loading path (P1) with the external thread groove (121) of the screw spindle (11), a fastening groove (122) which is located on an opposite outer circumference thereof, two opposite return holes (123) which are respectively in communication with the fastening groove (122) and the loading path (P1); a cover (13) attached to the nut (12) to cover the fastening groove (122), the nut (12) comprising a third step (161) located on an inner side of the fastening groove (122) between the two return holes (123) and a return channel (P2) located in the third step (161); two return elements (14), each having a passage (141) therein, a first end (142) located at one end of the passage (141) and a second end (143) at an opposite end of the passage (141), the first end (142) of each return element (14) being inserted into a corresponding return hole (123) of the nut (12) to keep the passage (141) in communication with the loading path (P1), the second ends (143) of the two return elements (14) being arranged respectively on two opposite sides relative to the return channel (P2) to keep the passages (141) in communication with the return channel (P2), the loading path (P1), the return channel (P2), and the passages (141) of the two return elements (14) to form a return path (P3); and a plurality of rolling elements (15) movably arranged in the return flow path (P3); wherein the second end (143) of each return element (14) abuts against the third stage (161). [8] The external circulation ball screw (10) according to claim 7, wherein each return element (14) further comprises a flange (144) extending around its second end (143); wherein the cover (13) further comprises two stop walls (133) respectively disposed on two opposite sides relative to the third stage (161), and a positioning groove (134) formed between each stop wall (133) and the third stage (161); wherein the flanges (144) of the two return elements (14) are respectively disposed in the positioning grooves (134). [9] The external circulation ball screw (10) according to claim 7, wherein the cover (13) further comprises a lubrication hole (135) in communication with the return passage (P3).

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