Ball screw and gear combination transmission mechanism used in a brake

Abstract

The present invention relates to the technical field of braking systems, and in particular to a ball screw and gear combination transmission mechanism used in a brake. A ball screw and gear combination transmission mechanism used in a brake, characterized in that: a driving shaft of a motor is axially connected to a motor gear, the motor gear is meshed with an idler gear, and the idler gear is meshed with a planetary gear train; the planetary gear train is connected to a shaft end of a ball screw, a ball nut is sleeved on an outer side of a threaded section of the ball screw, an end of the ball nut is connected to an end cover, an outer side of the ball nut is connected to a boss, and the ball nut and the boss are an integrated structure; several closed circulation loops are provided on an outer edge of the threaded section of the ball screw; several steel balls are provided in the circulation loops; and the circulation loop is composed of a spiral raceway and a ball return channel, and both ends of the spiral raceway are seamlessly and smoothly communicated with both ends of the ball return channel. Compared with the prior art, the ball screw and gear combination transmission mechanism overcomes the shortcomings of the conventional ball screw and gear combination transmission mechanism, such as large space occupation and slow piston return response speed.

Description

2025P00172 BALL^SCREW^AND^GEAR^COMBINATION^TRANSMISSION^MECHANISM^USED^IN^A BRAKE Technical^Field

[0001] The present invention relates to the technical field of braking systems, and inparticular to a ball screw and gear combination transmission mechanism used in a brake. Background^Art

[0002] A conventional internal circulation ball screw realizes ball circulationthrough a ball returner. The ball returner is embedded in the wall of a ball nut and is floatable. A ball return channel is designed in the middle position of the ball returner. Both ends of the ball return channel are communicated with two adjacent spiral raceways on the ball nut, thereby forming a circulation loop.

[0003] A conventional ball screw and gear combination transmission mechanismrealizes vehicle braking by the following manner: a motor drives a gear, the gear drives a ball screw, the ball screw drives a ball nut, and the ball nut pushes a piston to clampa brake disc, thereby converting rotational motion into linear motion. Although thisbraking mechanism can meet the need of vehicle braking, it has the disadvantages of non-compact structure of the ball screw and gear, large space occupation, low efficiency,slow piston return response speed, etc.Summary^of^the^Invention

[0004] In order to overcome the deficiencies of the prior art, the presentinvention provides a ball screw and gear combination transmission mechanism used in a brake, which overcomes the shortcomings of the conventional ball screw and gear combination transmission mechanism, such as large space occupation, low efficiency, and slow piston return response speed.

[0005] In order to achieve the above objective, a ball screw and gear combinationtransmission mechanism used in a brake is designed, comprising a motor, a planetary gear train, and a ball screw assembly, characterized in that: a driving shaft of the motor is axially connected to a motor gear, the motor gear is meshed with an idler gear, and the idler gear is meshed with the planetary gear train; the planetary gear train is connected to a shaft end of the ball screw, a ball nut is sleeved on an outer side of a threaded section of the ball screw, an end of the ball nut is connected to an end cover, an outer side of the ball nut is connected to a boss, and the ball nut and the boss are an2025P00172 integrated structure; several closed circulation loops are provided on an outer edge of the threaded section of the ball screw; several steel balls are provided in the circulation loops; and the circulation loop is composed of a spiral raceway and a ball return channel, two adjacent circulation loops have the same pitch between the spiral raceways, the ball return channels of two adjacent circulation loops are arranged in a staggered manner, and both ends of the spiral raceways are seamlessly and smoothly communicated with both ends of the ball return channels.

[0006] Return grooves are provided on the threaded section of the ball screw, ballreturners are embedded in the return grooves, the circulation loop is composed of a spiral raceway and a ball return channel, the ball return channels are located in the ball returners, two adjacent circulation loops have the same pitch between the spiral raceways, the ball return channels of two adjacent circulation loops are arranged in a staggered manner, and the spiral raceways are all smoothly communicated with bothends of the ball return channels.

[0007] Plug plate grooves are provided on the threaded section of the ball screw,plug plates are embedded in the plug plate grooves, the circulation loop is composed of a spiral raceway and a ball return channel, the ball return channels are located on the plug plates, two adjacent circulation loops have the same pitch between the spiral raceways, the ball return channels of two adjacent circulation loops are arranged in parallel, and the spiral raceways are all smoothly communicated with both ends of the ball return channels.

[0008] The planetary gear train comprises a sun gear, a driving gear, planetarygears, bearings, a needle bearing, a planet carrier, an inner gear ring, and an MGU housing, wherein the idler gear is meshed with the sun gear, one side of the sun gear is axially connected to the driving gear, an outer edge of the driving gear is meshed with one side of several planetary gears, and the other side of the planetary gears is meshed with the inner gear ring; the planet carrier is located in the inner gear ring, and the inner gear ring is fixed to the MGU housing; the bearings are press-fitted on the planetary gears, and a planetary shaft passes through the bearings and the planetary gears and is connected to the planet carrier; a shaft end of the driving gear is in clearance fit with the needle bearing, and the needle bearing is located in the planet carrier.

[0009] The sun gear, the driving gear and the ball screw are coaxially connected.

[0010] The ball screw is axially supported by a bearing washer, a planar thrust2025P00172 bearing and a support washer, and the bearing washer, the planar thrust bearing and the support washer are located inside the ball nut.

[0011] The end cover and the ball nut are connected by means of an interferencefit, thread or welding; or the end cover and the ball nut are an integrated structure.

[0012] A ball return curve formed by the ball return channel is formed by theintersection of cylindrical surfaces Σ1 and Σ2, wherein a directrix of Σ1 is in an x0y plane, and a directrix of Σ2 is in a z0x plane.

[0013] The directrix of Σ1 is symmetrical with respect to an origin, an arc segmentis tangent to a straight line segment and a spiral line segment, and a directrix equation of Σ1 is as follows:straight line segment: ^1=^tanθ, where θ ranges from 15° to 60°;arc segment:range of 3.1^^~31^^;spiral line segment:where θ is an angle between the straight line segment and an ^-axis, ^ is a radius ofan arc, ^^ is a horizontal coordinate of a center of the arc, ^^ is a vertical coordinateof the center of the arc, ^ is a lead, ^^^ is a diameter of a pitch circle of the ball nut,and ^^is a radius of a ball.

[0014] An arc segment of the directrix of Σ2 coincides with the pitch circle of theball nut, and a tangent segment is tangent to the pitch circle of the ball nut, according to:^^=0.12^^~1.25^^, β=20°~60°, ^^=1.12^^~2.25^^, r=0.03^^~0.12^^; when the ball moves to point ^, ^^=(^^-^^)·(^^^^^-^^^^); when the ball moves to point ^, ^^=(^^+^^)^^^^^-(^^-^^)^^^^; when 0≤^≤^^,when ^^≤^≤^^,2025P00172^ ^ when ^^≤^≤ ^, ^= ^-^^;a boundary curve when the ball moves along a surface of the ball nut is z =^^^^ ^^+ ^^^^^^^ ^ ^ ^; a directrix equation of Σ2 is obtained as follows: ^=^;z =where ^ is the lead, ^^^ is the diameter of the pitch circle of the ball nut, ^^ is theradius of the ball, a is an endpoint of a double arc of a raceway profile, b is an endpointof a tooth top arc, c is a contact point when the ball moves in the raceway, β is a contactangle, ^^is a radius of a raceway arc, ^^is a diameter of the ball, ^^is a radius of atooth top arc of the ball nut, ^^ is a radius of a tooth top arc of the ball screw, ^ is anouter diameter of the ball screw, ^^is the diameter of the pitch circle of the ball screw, D is an inner diameter of the ball nut, e is a distance from the center of the double arc to a center of symmetry, ^^is a distance from a ball center to the center of symmetry when the ball moves to point ^, ^^is a distance from the ball center to the center ofsymmetry when the ball moves to point ^, ^ is a distance from the ball center to a y-axis, ^ is a distance from the ball center to a center line of symmetry, ^^ is an offsetbetween the ball center and a spiral line in an ^direction after the ball enters the ballreturn channel along the ball return curve in the x0y plane, given a ^ value, λ is ahelix angle of a ball screw pair, and ^ is a distance from the ball center to the y-axis.

[0015] Compared with the prior art, the present invention provides a ball screwand gear combination transmission mechanism used in a brake, which overcomes the shortcomings of the conventional ball screw and gear combination transmission mechanism, such as large space occupation, low efficiency, and slow piston return response speed. Brief^Description^of^the^Drawings

[0016] Fig. 1 is a schematic structural diagram of a first embodiment of thepresent invention.

[0017] Fig. 2 is a schematic structural diagram of a second embodiment of thepresent invention.

[0018] Fig. 3 is a schematic structural diagram of a third embodiment of the2025P00172 present invention.

[0019] Fig. 4 is a schematic diagram of a raceway spiral line of the presentinvention.

[0020] Fig. 5 is a schematic diagram of a directrix of Σ1 of the present invention.

[0021] Fig. 6 is a schematic diagram of a motion trajectory of the center of a steelball in a conventional ball screw.

[0022] Fig. 7 is a schematic diagram of a motion trajectory of the center of a steelball in a ball screw of the present invention.

[0023] Fig. 8 is a schematic diagram of a directrix of Σ2 of the present invention.

[0024] Referring to Figs. 1 to 3, 1 is a motor, 2 is a motor gear, 3 is an idler gear, 4is a sun gear, 5 is a driving gear, 6 is a planetary carrier, 7 is a planetary gear, 8 is aninner ring gear, 9 is a bearing, 10 is a planetary shaft, 11 is a needle bearing, 12 is a ballscrew, 13 is a bearing washer, 14 is a planar thrust bearing, 15 is a support washer, 16 is a steel ball, 17 is a ball nut, 18 is an end cover, 19 is a boss, 20 is an MGU housing, 21 is a ball returner, and 22 is a plug plate. Detailed^Description^of^the^Invention

[0025] The present invention will be further described below with reference tothe accompanying drawings.

[0026] Shown in Fig. 1 is a structure of a first embodiment of the presentinvention.

[0027] The structure includes a motor 1, a motor gear 2, an idler gear 3, a sun gear4, a driving gear 5, a planet carrier 6, planet gears 7, an inner gear ring 8, an MGU housing 20, bearings 9, a planet shaft 10, a needle bearing 11, a ball screw 12, a bearing washer 13, a planar thrust bearing 14, a support washer 15, steel balls 16, a ball nut 17 and an end cover 18. The motor gear 2 is press-fitted on a shaft of the motor and drives the idler gear 3. The idler gear 3 drives the sun gear 4. The driving gear 5 is press-fitted on the sun gear 4. The bearings 9 are press-fitted in the planet gears 7. The needle bearing 11 is press-fitted in the planet carrier 6. The planet shaft 10 passes through the planet carrier 6 and the bearings 9 in the planet gears 7, and both ends thereof are riveted or welded or interference-connected with the planet carrier 6. The driving gear 5 is installed in the planet carrier 6 and meshed with the planet gears 7. A shaft end of the driving gear 5 is in clearance fit with the needle bearing 11. The planet gears 7 are meshed with the inner ring gear 8, and the inner ring gear 8 is fixed to the MGU housing 20. The driving gear 5 drives several planet gears 7 to rotate and revolve, and the planet2025P00172 gears 7 revolve to drive the planet carrier 6 to rotate. The planet carrier 6 is splined to the ball screw 12 and drives the ball screw 12. The ball screw 12 is axially supportedby the support washer 15, the planar thrust bearing 14 and the bearing washer 13. Theball nut 17 is integrated with a boss 19 and guided by the boss 19. The end cover 18 is connected to the ball nut 17 by means of interference or thread or welding, or the endcover 18 is integrated with the ball nut 17, which can axially withstand the thrust of theball screw 12 without displacement.

[0028] When clamping, the motor 1 drives the motor gear 2, the motor gear 2drives the planetary gear train through the idler gear 3, the planetary gear train drives the ball screw 12, the ball screw 12 drives the ball nut 17, the steel ball 16 circulatesthrough a ball return channel on a threaded section of the ball screw 12, and the ballnut 17 is guided by the boss 19 to convert rotational motion into linear motion, thereby achieving the braking function. When releasing, the motor 1 reverses, the gears and the ball screw 12 reverse, and the ball nut 17 returns to its position in time and accurately under the drive of the threaded section of the ball screw 12. There are several spiral raceways and ball return channels on the threaded section of the ball screw 12. All the spiral raceways have the same pitch, and both ends of each spiral raceway are seamlessly and smoothly connected to both ends of one ball return channel, thereby forming a closed circulation loop. Several ball return channels are arranged in a staggered manner, and each set of spiral raceways and ball return channels is equipped with several steel balls 16. When working, the steel balls 16 return to starting positions through the ball return channels.

[0029] The ball screw and gear combination transmission mechanism used in thefirst embodiment of the present invention replaces the conventional ball screw and gear combination transmission mechanism, which reduces the weight, axial size and rotational inertia of the ball screw, and reduces the difficulty of software control; the ball return channels are designed on the threaded section of the ball screw, and are seamlessly and smoothly connected to both ends of the spiral raceways, which increases the flexibility of the ball return; the integral molding of the ball nut eliminates an original piston, and increases the rigidity of the ball nut after integration, and the support washer, the planar thrust bearing and the bearing washer can be hidden in the ball nut, which increases the overall envelope, saves space, improves the efficiency of the ball screw, increases the return response speed, reduces noise, and reduces the manufacturing cost of the ball screw, with a simple and practical structure.2025P00172

[0030] Shown in Fig. 2 is a structure of a second embodiment of the presentinvention.

[0031] The structure includes a motor 1, a motor gear 2, an idler gear 3, a sun gear4, a driving gear 5, a planet carrier 6, planet gears 7, an inner gear ring 8, an MGU housing 20, bearings 9, a planet shaft 10, a needle bearing 11, a ball screw 12, a bearing washer 13, a planar thrust bearing 14, a support washer 15, steel balls 16, a ball nut 17, an end cover 18 and ball returners 21. The motor gear 2 is press-fitted on a shaft of the motor and drives the idler gear 3. The idler gear 3 drives the sun gear 4. The driving gear 5 is press-fitted on the sun gear 4. The bearings 9 are press-fitted in the planet gears 7. The needle bearing 11 is press-fitted in the planet carrier 6. The planet shaft 10 passes through the planet carrier 6 and the bearings 9 in the planet gears 7, and both ends thereof are riveted or welded or interference-connected with the planet carrier 6. The driving gear 5 is installed in the planet carrier 6 and meshed with the planet gears 7. A shaft end of the driving gear 5 is in clearance fit with the needle bearing 11. The planet gears 7 are meshed with the inner ring gear 8, and the inner ring gear 8 is fixed to the MGU housing 20. The driving gear 5 drives several planet gears 7 to rotate and revolve, and the planet gears 7 revolve to drive the planet carrier 6 to rotate. The planet carrier 6 is splined to the ball screw 12 and drives the ball screw 12. The ball screw 12 is axially supported by the support washer 15, the planar thrust bearing 14 and the bearing washer 13. The ball nut 17 is integrated with a boss 19 and guided by the boss 19. The end cover 18 is connected to the ball nut 17 by means of interference or thread or welding, or the end cover 18 is integrated with the ball nut 17, which can axially withstand the thrust of the ball screw 12 without displacement.

[0032] When clamping, the motor 1 drives the motor gear 2, the motor gear 2drives the planetary gear train through the idler gear 3, the planetary gear train drives the ball screw 12, the ball screw 12 drives the ball nut 17, the steel ball 16 circulatesthrough the ball returners 21 on a threaded section of the ball screw 12, and the ballnut 17 is guided by the boss 19 to convert rotational motion into linear motion, thereby achieving the braking function. When releasing, the motor 1 reverses, the gears and the ball screw 12 reverse, and the ball nut 17 returns to its position in time and accurately under the drive of the threaded section of the ball screw 12. There are several spiralraceways and return grooves on the threaded section of the ball screw 12, each returngroove is embedded with one ball returner 21, and a ball return channel is designed in the middle of each ball returner 21. All the spiral raceways have the same pitch, and2025P00172 each spiral raceway is communicated with a ball return channel of one ball returner, thereby forming a circulation loop. Several ball returners 21 are arranged in a staggered manner. Several steel balls 16 are installed in each set of spiral raceways and ball returners 21. When working, the steel balls 16 return to starting positions through the ball returners 21.

[0033] The ball screw and gear combination transmission mechanism used in thesecond embodiment of the present invention replaces the conventional ball screw and gear combination transmission mechanism, which reduces the weight, axial size and rotational inertia of the ball screw, and reduces the difficulty of software control; the ball returners can be molded using a die, which reduces the processing cost of the ball return channels; the integral molding of the ball nut eliminates an original piston, and increases the rigidity of the ball nut after integration, and the support washer, the planar thrust bearing and the bearing washer can be hidden in the ball nut, which increases the overall envelope, saves space, improves the efficiency of the ball screw, increases the return response speed, and reduces the manufacturing cost of the ball screw, with a simple and practical structure.

[0034] Shown in Fig. 3 is the structure of a third embodiment of the presentinvention.

[0035] The structure includes a motor 1, a motor gear 2, an idler gear 3, a sun gear4, a driving gear 5, a planet carrier 6, planet gears 7, an inner gear ring 8, an MGU housing 20, bearings 9, a planet shaft 10, a needle bearing 11, a ball screw 12, a bearing washer 13, a planar thrust bearing 14, a support washer 15, steel balls 16, a ball nut 17, an end cover 18 and plug plates 22. The motor gear 2 is press-fitted on a shaft of the motor and drives the idler gear 3. The idler gear 3 drives the sun gear 4. The driving gear 5 is press-fitted on the sun gear 4. The bearings 9 are press-fitted in the planet gears 7. The needle bearing 11 is press-fitted in the planet carrier 6. The planet shaft10 passes through the planet carrier 6 and the bearings 9 in the planet gears 7, andboth ends thereof are riveted or welded or interference-connected with the planet carrier 6. The driving gear 5 is installed in the planet carrier 6 and meshed with the planet gears 7. A shaft end of the driving gear 5 is in clearance fit with the needle bearing 11. The planet gears 7 are meshed with the inner ring gear 8, and the inner ring gear 8 is fixed to the MGU housing 20. The driving gear 5 drives several planet gears 7to rotate and revolve, and the planet gears 7 revolve to drive the planet carrier 6 torotate. The planet carrier 6 is splined to the ball screw 12 and drives the ball screw 12.2025P00172 The ball screw 12 is axially supported by the support washer 15, the planar thrust bearing 14 and the bearing washer 13. The ball nut 17 is integrated with a boss 19 and guided by the boss 19. The end cover 18 is connected to the ball nut 17 by means of interference or thread or welding, or the end cover 18 is integrated with the ball nut 17, which can axially withstand the thrust of the ball screw 12 without displacement.

[0036] When clamping, the motor 1 drives the motor gear 2, the motor gear 2drives the planetary gear train through the idler gear 3, the planetary gear train drives the ball screw 12, the ball screw 12 drives the ball nut 17, the steel ball 16 circulatesthrough ball return channels on the plug plates 22, and the ball nut 17 is guided by theboss 19 to convert rotational motion into linear motion, thereby achieving the braking function. When releasing, the motor 1 reverses, the gears and the ball screw 12 reverse, and the ball nut 17 returns to its position in time and accurately under the drive of the threaded section of the ball screw 12. There are several spiral raceways and plug plate grooves on the threaded section of the ball screw 12, and one plug plate 22 is embedded in each plug plate groove. Several ball return channels are designed on each plug plate 22, and all the spiral raceways have the same pitch. Each spiral raceway is communicated with a ball return channel in the plug plate 22, thereby forming a circulation loop. Each set of spiral raceways and ball return channels in the plug plates 22 is equipped with several steel balls 16. When working, the steel balls 16 return to starting positions through the plug plates 22.

[0037] The ball screw and gear combination transmission mechanism used in thethird embodiment of the present invention replaces the conventional ball screw and gear combination transmission mechanism, which reduces the weight, axial size and rotational inertia of the ball screw, and reduces the difficulty of software control; the plug plates can be molded using a die, which reduces the processing cost of the ball return channels; the integral molding of the ball nut eliminates an original piston, and increases the rigidity of the ball nut after integration, and the support washer, the planar thrust bearing and the bearing washer can be hidden in the ball nut, which increases the overall envelope, saves space, improves the efficiency of the ball screw, increases the return response speed, and reduces the manufacturing cost of the ball screw, with a simple and practical structure.

[0038] The ball return curve of the circulation loop on the threaded section of theball screw of the present invention is designed as follows:

[0039] As shown in Fig. 4, a spiral equation is as follows:2025P00172 x=x;where ^^^is the diameter of a pitch circle of the ball nut and p is the lead.

[0040] The ball return curve is formed by the intersection of cylindrical surfacesΣ1 and Σ2. The directrix of Σ1 is in an xOy plane, and the directrix of Σ2 is in a zOx plane.

[0041] The directrix of Σ1 is symmetric with respect to an origin, and an arcsegment is tangent to a straight line segment and a spiral line segment.

[0042] As shown in 5, the directrix equation of Σ1 is as follows:straight line segment: ^1=^tanθ, where θ ranges from 15° to 60°;arc segment:range of 3.1^^~31^^;spiral line segment:where θ is an angle between the straight line segment and an ^ -axis, ^ is aradius of an arc, ^^ is a horizontal coordinate of a center of the arc, ^^ is a verticalcoordinate of the center of the arc, ^^^is the diameter of the pitch circle of the ball nut, and p is a lead.

[0043] A conventional ball return channel is located in the ball nut, the steel ballmoves along the surface of the ball screw, and the motion trajectory of the center of the steel ball is shown in Fig.6. The ball return channel of the present invention is locatedin the ball screw, the steel ball moves along the surface of the ball nut, and the motiontrajectory of the center of the steel ball is different from the conventional motion trajectory of the center of the steel ball.

[0044] As shown in Fig. 7,^^=0.12^^~1.25^^, β=20°~60°, ^^=1.12^^~2.25^^, r=0.03^^~0.12^^; R^The arc is tangent to the straight line segment and arc r; when the ball moves to point ^, ^^=(^^-^^)·(^^^^^-^^^^);2025P00172 when the ball moves to point ^, ^^=(^^+^^)^^^^^-(^^-^^)^^^^; when 0≤^≤^^,^ ^ when ^^≤^≤ ^, ^= ^-^^; aboundary curve when the ball moves along a surface of the ball nut is z =where p is the lead, D^^ is the diameter of the pitch circle of the ball nut, r^ isthe radius of the ball, a is an endpoint of a double arc of a raceway profile, b is an endpoint of a tooth top arc, c is a contact point when the ball moves in the raceway, β is a contact angle, ^^is the radius of a raceway arc, ^^is the diameter of the ball, ^^is the radius of a tooth top arc of the ball nut, ^^is the radius of a tooth top arc of theball screw, ^ is the outer diameter of the ball screw, ^^ is the diameter of the pitchcircle of the ball screw, D is an inner diameter of the ball nut, e is the distance from the center of the double arc to a center of symmetry, ^^is the distance from a ball center to the center of symmetry when the ball moves to point ^, ^^is the distance from theball center to the center of symmetry when the ball moves to point ^, ^ is the distancefrom the ball center to a y-axis, ^ is the distance from the ball center to a center lineof symmetry, ^^ is an offset between the ball center and a spiral line in an ^ directionafter the ball enters the ball return channel along the ball return curve in the x0y plane,given a ^ value, and λ is a helix angle of a ball screw pair.

[0045] As shown in Fig. 8, the arc segment of the Σ2 directrix coincides with thepitch circle of the ball nut, and the tangent segment is tangent to the pitch circle of the ball nut.

[0046] The curve segment of the Σ2 directrix is fitted according to the followingequation: ^=^; z= ρcos^^ ^+ ^^^^^^where ^ is the distance from the center of the ball to they-axis.

Claims

2025P00172 Claims 1. A ball screw and gear combination transmission mechanism used in a brake, comprising a motor, a planetary gear train, and a ball screw assembly, characterized in that: a driving shaft of the motor (1) is axially connected to a motor gear (2), the motor gear (2) is meshed with an idler gear (3), and the idler gear (3) is meshed with the planetary gear train; the planetary gear train is connected to a shaft end of the ball screw (12), a ball nut (17) is sleeved on an outer side of a threaded sectionof the ball screw (12), an end of the ball nut (17) is connected to an end cover (18),an outer side of the ball nut (17) is connected to a boss (19), and the ball nut (17) and the boss (19) are an integrated structure; several closed circulation loops are provided on an outer edge of the threaded section of the ball screw (12); several steel balls (16) are provided in the circulation loops; and the circulation loop is composed of a spiral raceway and a ball return channel, two adjacent circulationloops have the same pitch between the spiral raceways, the ball return channels oftwo adjacent circulation loops are arranged in a staggered manner, and both ends of the spiral raceways are seamlessly and smoothly communicated with both ends of the ball return channels.

2. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: return grooves are provided on the threaded section of the ball screw (12), ball returners (21) are embedded in the return grooves, the circulation loop is composed of a spiral raceway and a ball return channel, the ball return channels are located in the ball returners (21), two adjacent circulation loops have the same pitch between the spiral raceways, the ball return channels of two adjacent circulation loops are arranged in a staggered manner, and the spiral raceways are all smoothly communicated with both ends of the ball return channels.

3. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: plug plate grooves are provided on the threaded section of the ball screw (12), plug plates (22) are embedded in the plug plate grooves, the circulation loop is composed of a spiral raceway and a ball return channel, the ball return channels are located on the plug plates (22), two adjacent circulation loops have the same pitch between the spiral raceways, the ballreturn channels of two adjacent circulation loops are arranged in parallel, and the2025P00172 spiral raceways are all smoothly communicated with both ends of the ball return channels.

4. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: the planetary gear train comprises a sun gear, a driving gear, planetary gears, bearings, a needle bearing, a planet carrier, an inner gear ring, and an MGU housing, wherein the idler gear (3) is meshed with the sun gear (4), one side of the sun gear (4) is axially connected to the driving gear (5), an outer edge of the driving gear (5) is meshed with one side of several planetary gears (7), and the other side of the planetary gears (7) is meshed with the inner gear ring (8); the planet carrier (6) is located in the inner gear ring (8), and the inner gear ring (8) is fixed to the MGU housing (20); the bearings (9) are press-fitted on the planetary gears (7), and a planetary shaft (10)passes is connected to the planet carrier (6) through the bearings (9) and theplanetary gears (7) ; a shaft end of the driving gear (5) is in clearance fit with the needle bearing (11), and the needle bearing (11) is located in the planet carrier (6).

5. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 4, characterized in that: the sun gear (4), the driving gear (5) and the ball screw (12) are coaxially connected.

6. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: the ball screw (12) is axially supported by a bearing washer (13), a planar thrust bearing (14) and a supportwasher (15), and the bearing washer (13), the planar thrust bearing (14) and thesupport washer (15) are located inside the ball nut (17).

7. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: the end cover (18) and the ball nut (17) are connected by means of an interference fit, threading or welding; or the end cover (18) and the ball nut (17) are an integrated structure.

8. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 1, characterized in that: a ball return curve formed by the ball return channel is formed by the intersection of cylindrical surfaces Σ1 and Σ2, wherein a directrix of Σ1 is in an x0y plane, and a directrix of Σ2 is in a z0x plane.

9. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 8, characterized in that: the directrix of Σ1 is symmetricalwith respect to an origin, an arc segment is tangent to a straight-line segment and a2025P00172 spiral segment, and a directrix equation of Σ1 is as follows:straight line segment: ^1=^tanθ, where θ ranges from 15° to 60°;arc segment:range of 3.1^^~31^^;spiral line segment:where θ is an angle between the straight line segment and an ^-axis, ^ is a radius ofan arc, ^^ is a horizontal coordinate of a center of the arc, ^^ is a vertical coordinateof the center of the arc, ^ is a lead, ^^^ is a diameter of a pitch circle of the ball nut,and ^^is a radius of a ball.

10. The ball screw and gear combination transmission mechanism used in the brake as claimed in claim 8, characterized in that: an arc segment of the directrix of Σ2 coincides with the pitch circle of the ball nut, and a tangent segment is tangent to the pitch circle of the ball nut, according to:^^=0.12^^~1.25^^, β=20°~60°, ^^=1.12^^~2.25^^, r=0.03^^~0.12^^; when the ball moves to point ^, ^^=(^^-^^)·(^^^^^-^^^^); when the ball moves to point ^, ^^=(^^+^^)^^^^^-(^^-^^)^^^^; when 0≤^≤^^,^ ^ when ^^≤^≤ ^, ^= ^-^^;a boundary curve when the ball moves along a surface of the ball nut is z =a directrix equation of Σ2 is obtained as follows: ^=^;2025P00172where p is the lead, D^^ is the diameter of the pitch circle of the ball nut, r^ is theradius of the ball, a is an endpoint of a double arc of a raceway profile, b is an endpointof a tooth top arc, c is a contact point when the ball moves in the raceway, β is a contactangle, ^^is a radius of a raceway arc, ^^is a diameter of the ball, ^^is a radius of atooth top arc of the ball nut, ^^ is a radius of a tooth top arc of the ball screw, ^ is anouter diameter of the ball screw, ^^is the diameter of the pitch circle of the ball screw, D is an inner diameter of the ball nut, e is a distance from the center of the double arc to a center of symmetry, ^^is a distance from a ball center to the center of symmetry when the ball moves to point ^, ^^is a distance from the ball center to the center ofsymmetry when the ball moves to point ^, ^ is a distance from the ball center to a y-axis, ^ is a distance from the ball center to a center line of symmetry, ^^ is an offsetbetween the ball center and a spiral line in an ^ direction after the ball enters the ballreturn channel along the ball return curve in the x0y plane, given a ^ value, λ is ahelix angle of a ball screw pair, and ^ is a distance from the ball center to the y-axis.

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