Braking system comprising a ball screw device, and vehicle comprising this braking system

Abstract

The vehicle braking system comprises: - an electric actuator (8), - a clamping force application member (7), and - a ball screw device (10) intended to convert the rotational movement of an output shaft (9) of the electric actuator (8) into translational movement of the clamping force application member (7). The ball screw device comprises: a screw (11) cooperating with a nut (12) via balls, a channel (20) delimiting a ball recirculation path formed at least partly in the nut (12) and comprising a ball recovery end (20R) and a ball insertion end (20I). The recirculation channel (20) comprises a radially inner surface (24) for guiding the balls evolving along the entire recirculation path in accordance with the movement of a generating curve along this same recirculation path. Figure for abstract: Figure 3

Description

Title of the invention: Braking system comprising a ball screw device, and vehicle comprising this braking system Technical field of the invention

[0001] The invention relates to the field of vehicle braking systems, more particularly electromechanically controlled braking systems. Technical background

[0002] A braking system for a vehicle, in particular an automobile, of the disc type is already known in the prior art, i.e. comprising at least two friction elements intended to cooperate by friction respectively with two opposite faces of a disc integral in rotation with a wheel of the vehicle. The clamping of the friction elements against the disc causes the vehicle to brake. When the friction elements are separated from the faces of the disc, the braking ceases.

[0003] Usually, at least one of the friction elements is urged against a corresponding face of the disc by a clamping force application member, sometimes called a piston. It is known to control the clamping force application member by hydraulic means. More recently, it has been proposed to control the clamping force application member by electromechanical means. Indeed, the electromechanical control means have the particular advantage of being able to be controlled electronically and thus of making it possible to define by software means different operating modes according to different situations.

[0004] The electromechanical means for controlling the clamping force application member usually comprise an electric actuator intended to provide a clamping force. A ball screw device converts the rotational movement of an output shaft of the electric actuator into translational movement of the clamping force application member.

[0005] A ball screw device is already known in the prior art, of the type comprising a screw cooperating with a nut by means of balls guided along a helical path by complementary threads provided in the screw and the nut. Because the balls move along the helical path, it is appropriate to recirculate them from the end of this helical path to the beginning of this helical path. For this purpose, the ball screw device comprises a channel delimiting a path for recirculating the balls, this channel comprising an end for recovering the balls at the end of the helical path and an end for inserting the balls at the beginning of the helical path.

[0006] However, in an electromechanically controlled braking system, the size of the ball screw device must be as limited as possible. It has therefore been proposed in the state of the art to provide this recirculation channel at least partly in the nut.

[0007] Furthermore, it has been observed that the efficiency of a ball screw device is all the more efficient if the balls can roll rather than slide. Indeed, if the balls do not roll, in particular if the balls slide against their guide surfaces, the efficiency of the ball screw device is less good. However, it is observed in the prior art that, due to space constraints, the recirculation channel is relatively small and has a shape producing at least locally a sliding of the balls to the detriment of the rolling of the balls. Summary of the invention

[0008] The invention aims in particular to promote as much as possible the rolling of the balls in the ball recirculation channel, this by taking into account the constraints of limitation of the size specific to a ball screw device.

[0009] To this end, the invention relates to a ball screw device, of the type comprising: - a screw cooperating with a nut via balls, - the balls being guided along a helical path by complementary threads provided in the screw and the nut, - a channel delimiting a recirculation path for the balls, this recirculation channel being arranged at least partly in the nut and comprising a ball recovery end at the end of the helical path and a ball insertion end at the start of the helical path,

[0010] characterized in that the recirculation channel comprises a radially inner surface for guiding the balls moving along the entire recirculation path in accordance with the movement of a generating curve along this same recirculation path.

[0011] A radially inner surface of the recirculation channel is distinguished from a radially outer surface of this recirculation channel in that it is closer to the axis of the helical path of the balls than the radially outer surface.

[0012] The radially inner ball guide surface which, according to the invention, evolves along the entire recirculation path in accordance with the movement of a curve along this same recirculation path very effectively promotes the rolling of the balls in the recirculation channel, while making it possible to arrange this recirculation channel in a reduced space. As a result, the efficiency of the ball screw device is very high.

[0013] Other optional features of this ball screw device which can be taken alone or in combination will be specified below.

[0014] - The generating curve is formed by an arc of a circle or a complete circle. We thus optimizes the rolling of the balls in the recirculation channel. - The ball recovery and insertion ends delimit paths along curved parts of a neutral fiber of the channel called respectively ball recovery and insertion. The paths along curved parts of the neutral fiber of the channel optimize the rolling of the balls in the recirculation channel. - The curved parts of the neutral fiber for ball recovery and insertion are formed by circular arcs. This further optimizes the rolling of the balls in the recirculation channel. - The generating curve is formed by an arc of a circle or a complete circle of radius Rc between 105% and 115% of the radius Rb of a ball, preferably between 105% and 111% of the radius Rb of a ball, and at least one of the curved parts of neutral fiber for recovery and insertion of the balls, called the curved part of neutral fiber considered, has a minimal radius Rmin verifying the relation:

[0015] . ZM-lÆriœs / t Rmin-—^—

[0016] in which A is the angle between a first ray of the considered neutral fiber curved portion passing through a point of contact between first and second balls moving along the considered neutral fiber curved portion and a second ray of the considered neutral fiber curved portion passing through the center of the first ball.

[0017] This further optimizes the rolling of the balls in the recirculation channel.

[0018] - The curved parts of neutral fiber for recovery and insertion of the balls are parallel respectively to secant planes symmetrical with respect to a plane passing through an axis of the nut and a straight line of intersection of the symmetrical planes. This symmetry optimizes the rolling of the balls in the recirculation channel while homogenizing the manufacturing stages of the recirculation channel.

[0019] - The recirculation channel comprises a ball transfer part connecting the ball recovery and insertion ends, preferably delimiting a path along a rectilinear part of the ball transfer from the neutral fiber of the channel. This transfer part is simple to manufacture.

[0020] - The nut comprises a body in which at least part of the channel is formed recirculation, the recovery and insertion ends of this channel being arranged at least in part respectively in ball recovery and insertion elements fitted in respective radial housings arranged in the body of the nut. The ball recovery and insertion elements can be manufactured separately, which facilitates the production of the complete recirculation channel while ensuring great control over the shape of this channel.

[0021] - The ball screw device comprises a sleeve covering at least in part the nut body so as to retain the recovery and insertion elements in their respective radial housings. The sleeve, manufactured separately, also facilitates the creation of the complete recirculation channel.

[0022] - The sleeve has a radially internal surface participating in the delimitation of the transfer part of the recirculation channel. Thus, before mounting the sleeve, part of the surface of the channel can be produced by allowing access of machining tools in a relevant area of ​​the nut.

[0023] The invention also relates to a braking system for a vehicle, comprising: - an electric actuator intended to provide a clamping force, - a member for applying clamping force to at least one friction element, and - a ball screw device intended to convert the rotational movement of an output shaft of the electric actuator into translational movement of the clamping force application member,

[0024] characterized in that the ball screw device is as defined above.

[0025] The invention also relates to a vehicle, characterized in that it comprises a braking system as defined above. Brief description of the figures

[0026] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawings in which:

[0027] [Fig-1] [Fig.l] is a schematic top view of a vehicle in which a braking system according to the invention is arranged;

[0028] [Fig.2] [Fig.2] is a schematic view of a braking system to which the invention can be applied;

[0029] [Fig.3] [Fig.3] is an axial sectional view of a ball screw device according to the invention;

[0030] [Fig.4] [Fig.4] is a perspective view of a row of balls moving between their recirculation path and their helical path;

[0031] [Fig.5] [Fig.5] is a perspective view, partially exploded, of the device of ball screw of [Fig.3];

[0032] [Fig.6] [Fig.6] is a perspective view of a set of balls moving in the recirculation path and helical path;

[0033] [Fig.7] [Fig.7] is a perspective view, partially exploded, of part of the ball screw device of [Fig. 3], showing a ball insertion element and a housing in which it is intended to be fitted, provided in a body of the nut;

[0034] [Fig-8] [Fig.8] is a perspective view of an imaginary envelope representing guide surfaces of the balls in the recirculation channel;

[0035] [Fig.9] [Fig.9] is a perspective view of the imaginary envelope of [Fig.8] from a different point of view than that of [Fig.8];

[0036] [Fig. 10] [Fig. 10] is a diagram of geometric planes and axes useful for describing the shape of the ball recirculation channel;

[0037] [Fig. 11] [Fig. 11] is a diagram showing first and second balls moving along a curved neutral fiber in a ball retrieval or insertion end of the recirculation channel.

[0038] [Fig. 1] shows a motor vehicle 1 in which a braking system 2, of the electromechanical type, according to the invention, is arranged on each of the four wheels 3.

[0039] It will be noted that the invention applies to any type of braking system, in particular those intended to equip motor vehicles of the passenger car type, SUV (English acronym for "Sport Utility Vehicles"), two-wheelers (in particular motorcycles), airplanes, industrial vehicles such as vans, "heavy goods vehicles" - that is to say metros, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering vehicles -, or other transport or handling vehicles. The invention also applies to non-motorized vehicles such as trailers, semi-trailers or caravans.

[0040] [Fig. 2] shows a diagram of an example of a braking system 2 to which the invention, which will be described in more detail below, is applied. This braking system 2 is of the floating caliper disc type. It comprises at least two friction elements 4A, 4B intended to cooperate by friction respectively with two opposite faces FA, FB of a disc 5, integral in rotation with a wheel 3 of the vehicle.

[0041] The braking system 2 is of the electromechanical type. It comprises a clamping device D for clamping the two friction elements 4A, 4B on the two opposite faces FA, FB of the disc 5.

[0042] The clamping device D is provided with a floating caliper 6 carrying a member 7 for applying clamping force to one of the friction elements 4A. It will be noted that, according to a variant not shown, the invention also applies to a braking system with a fixed caliper. In this case, the clamping device D comprises two members 7 for applying force respectively to the two friction elements 4A, 4B.

[0043] Referring to Figures 3 to 6, it can be seen that the braking system 2 comprises an electric actuator 8 (shown schematically in [Fig. 3]) intended to provide a clamping force. The electric actuator 8 comprises a rotary output shaft 9. A ball screw device 10 according to the invention makes it possible to convert the rotational movement of the output shaft 9 of the actuator 8 in translational movement of the clamping force application member 7.

[0044] Indeed, the ball screw device 10 comprises a screw 11 cooperating with a nut 12 by means of balls 13 (see figures 4 to 6). These balls 13 are guided along a helical path 14 (shown diagrammatically by a helical line in [Fig. 6]) by complementary threads 15, 16 (see [Fig. 3]) formed in the screw 11 and a body 17 of the nut 12. More particularly, the shaft 9 is coupled with the nut 12 by gear coupling means 18 comprising for example epicyclic type gears forming a reducer (shown diagrammatically in [Fig. 3]). The nut 12 therefore receives the rotational movement of the shaft 9.

[0045] Furthermore, a connecting end 11E of the screw 11 is connected by coupling means 19 to the clamping force application member 7. Thus, the screw 11 delivers the translational movement of the clamping force application member 7.

[0046] In the ball screw device 10, the balls 13 move along the helical path 14 while being put back into circulation from the end of this helical path 14 to the beginning of this helical path 14 by a channel 20 delimiting a recirculation path of the balls 13. This recirculation channel 20, formed at least partly in the nut 12, is visible in particular in FIGS. 3 and 7.

[0047] The recirculation channel 20 coincides at least in part with an imaginary envelope which is shown in FIGS. 8 and 9 and which, in the following, will be designated by the same reference 20.

[0048] Referring in particular to these figures 8 and 9, it can be seen that the recirculation channel 20 comprises an end 20R for recovering the balls 13, at the end of the helical path, and an end 201 for inserting the balls 13, at the start of the helical path.

[0049] Referring to Figures 3 to 7, it can be seen that at least a portion of the recirculation channel 20 is formed in the body 17 of the nut 12. More particularly, it can be seen that the recovery 20R and insertion 201 ends of the channel 20 are formed, at least in part, respectively in recovery 21R and insertion 211 elements of the balls 13. Each of these elements 21R, 211 is fitted into a corresponding radial housing 22R, 221 formed in the body 17 of the nut 12. It will be noted that the recovery 21R and insertion 211 elements each comprise a shoulder E21 intended to cooperate with a complementary shoulder E22 formed in the corresponding radial housing 22R, 221 (see in particular Figures 6 and 7).

[0050] Referring in particular to Figures 3 and 5, it can be seen that the nut 12 comprises a sleeve 23 covering at least in part the body 17 of the nut 12 so as to retain the recovery 21R and insertion 211 elements in their corresponding radial housings 22R, 221.

[0051] In the description of the recirculation channel 20 which follows, an element will be described as radially internal or external depending on whether it is radially close to the axis H of the helical path 14 or radially distant from this axis H. It will be noted that the axis H of the helical path 14 coincides with the axis of the screw 11 and the nut 12.

[0052] Referring in particular to Figures 3 and 7 to 9, it can be seen that the recirculation channel 20 comprises a radially inner surface 24 for guiding the balls 13. This surface 24, part of which is clearly visible in [Fig. 7], evolves along the entire recirculation path in accordance with the movement of a generating curve along this same recirculation path.

[0053] Preferably, the generating curve is formed by an arc of a circle or, for example depending on the position in the recirculation path, a complete circle.

[0054] In the following, the imaginary line passing through the center of gravity of the straight sections of this channel 20 will be called the neutral fiber of the recirculation channel 20, this by imaginarily considering the recirculation channel 20 as a solid body. In Figures 6, 8 and 9, the neutral fiber of the recirculation channel 20 has been designated by the numerical reference 25.

[0055] Referring to these figures 6, 8 and 9, it can be seen that the recovery 20R and insertion 201 ends of the recirculation channel 20 of the balls 13 delimit paths along curved parts 25CR, 25CI of the neutral fiber 25, called respectively recovery and insertion parts of the balls 13. Preferably, the curved recovery 25CR and insertion 25CI parts of the neutral fiber 25 are formed by arcs of a circle.

[0056] Referring more particularly to Figures 8 to 10, it can be seen that the curved recovery 25CR and insertion 25CI parts of the neutral fiber 25 are parallel respectively to sequential planes PCR, PCI symmetrical with respect to a plane P passing through the axis H of the nut 12 and a straight line G of intersection of the symmetrical planes PCR, PCI.

[0057] Referring in particular to Figures 3, 5, 8 and 9, it can be seen that the recirculation channel 20 comprises a part 20T for transferring the balls 13 connecting the recovery ends 20R and insertion ends 201 of the balls. This transfer part 20T preferably delimits a path along a rectilinear part of the neutral fiber 25, called the transfer part 25T of the neutral fiber 25.

[0058] Referring in particular to [Fig. 3], it can be seen that the sleeve 23 has a radially internal surface 231 participating in the delimitation of the transfer part 20T of the recirculation channel 20.

[0059] In the recirculation channel 20, the radially inner surface 24 for guiding the balls 13 which evolves, all along the recirculation path in accordance with the movement of a generating curve along this same recirculation path, very effectively promotes the rolling of the balls 13 in the channel 20.

[0060] However, to further optimize the rolling of the balls in the channel 20, avoiding their jamming, the generating curve of the radially inner surface 24 is formed by an arc of a circle or a complete circle of radius Rc between 105% and 115% of the radius Rb of a ball 13, preferably between 105% and 111% of the radius RB of a ball 13 (see [Fig. 11]).

[0061] Furthermore, to further optimize the rolling of the balls in the channel 20, at least one of the parts chosen from:

[0062] - the curved part 25CI for inserting the balls 13 of the neutral fiber 25 of the channel of recirculation 20, and - the curved part 25CR for recovering the balls 13 of the neutral fiber 25 of the recirculation channel 20,

[0063] said curved part of neutral fiber considered, has a minimal radius Rmin verifying the relation:

[0064] . (I Rb-2RckosA Rmm = -“—

[0065] in which A (see [Fig.l 1]) is the angle between: - a first ray RI of the curved part of neutral fiber considered passing through a point 26 of contact between first and second balls 13 moving along the curved part of neutral fiber considered and - a second ray R2 of the curved part of neutral fiber considered passing through the center 27 of the first ball 13.

[0066] Preferably, the two curved parts of insertion 25CI and recovery 25CR of the balls 13 of the neutral fiber have a minimum radius Rmin verifying the above relationship.

[0067] It will be noted that because the channel 20 is formed in different elements (body 17 of the nut 12, recovery elements 21R and insertion 211 of the balls 13, sleeve 23 covering at least in part the body 17 of the nut 12 so as to retain the recovery elements 21R and insertion 211 in their radial housings 22R, 221) assembled together to form the nut 12, access for machining tools to these elements taken separately is easy, which facilitates the production of the overall surface of the channel 20 described above.

[0068] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. It is in particular possible to produce the various elements of the ball screw device in various materials, in particular metallic materials or other materials having resistances adapted to the usual forces undergone by these elements. Reference list#:

[0069] 1: motor vehicle 2: braking system D: clamping device 3: wheel 4A, 4B: friction element 5: disc 6: floating caliper 7: force application organ 8: electric actuator 9: output shaft 10: Ball screw device 11: screws 11E: screw connecting end 12: nut 13: marbles 14: helical path of the balls 15: screw thread 16: thread of the nut body 17: nut body 18: coupling means 19: coupling means 20: ball recirculation channel 201: insertion end of the recirculation channel balls 20R: recirculation channel ball recovery end 20T: ball transfer part of the recirculation channel 211: ball insertion element 21R: ball recovery element 221: corresponding radial housing 22R: corresponding radial housing 23: nut sleeve 231: radially internal surface of the sleeve 24: radially inner ball guide surface 25: neutral fiber of the recirculation channel 25CI: curved part for inserting the balls of the neutral fiber of the recirculation channel 25CR: curved part for recovering the balls of the neutral fiber of the recirculation channel 25T: neutral fiber transfer part 26: point of contact between first and second balls moving along a curved portion of the neutral fiber of the recirculation channel 27: center of a ball D: clamping device E21: shoulder E22: additional shoulder FA, FB: sides of the disc G: intersection line of the symmetrical planes PCR, PCI H: axis of the helical path coinciding with the axis of the screw and the nut PCR, PCI: sequential planes symmetrical with respect to a plane P passing through the H axis and the line G of intersection of the symmetrical PCR, PCI planes

Claims

Claims

1. Braking system for a vehicle, comprising: - an electric actuator (8) intended to provide a clamping force, - a member (7) for applying clamping force to at least one friction element (4A, 4B), and - a ball screw device (10) intended to convert the rotational movement of an output shaft (9) of the electric actuator (8) into translational movement of the clamping force application member (7), wherein the ball screw device (10) comprises: - a screw (11) cooperating with a nut (12) by means of balls (13), - the balls (13) being guided along a helical path (14) by complementary threads (15, 16) provided in the screw (11) and the nut (12), - a channel (20) delimiting a recirculation path for the balls (13), this recirculation channel (20) being arranged at least partly in the nut (12) and comprising an end (20R) for recovering the balls (13) at the end of the helical path (14), an end (201) for inserting the balls (13) at the start of the helical path (14) and a part (20T) for transferring the balls (13) connecting the recovery (20R) and insertion (201) ends of the balls (13), characterized in that the recirculation channel (20) comprises a radially inner surface (24) for guiding the balls (13) moving along the entire recirculation path in accordance with the movement of a generating curve along this same recirculation path, and in that the nut (12) comprises a body (17) in which at least part of the recirculation channel (20) is arranged, the ball screw device further comprising a sleeve (23) at least partly covering the body (17) of the nut (12) and comprising a radially internal surface (231) participating in the delimitation of the transfer part (20T) of the recirculation channel (20).

2. Braking system according to claim 1, in which the nut (12) receives the rotational movement of the output shaft (9) of the electric actuator (8) and the screw (11) delivers the translational movement of the clamping force application member (7).

3. Braking system according to claim 2, in which the output shaft (9) of the electric actuator (8) is coupled with the nut 12 by gear coupling means (18), comprising for example epicyclic type gears forming a reducer.

4. Braking system according to any one of the preceding claims, in which the transfer portion (20T) of the balls (13) delimits a path along a rectilinear portion (25T) of transfer of the balls (13) of a neutral fiber of the recirculation channel (20).

5. Braking system according to any one of the preceding claims, in which the recovery (20R) and insertion (201) ends of the recirculation channel (20) are provided at least in part respectively in recovery (20R) and insertion (201) elements of balls fitted in respective radial housings (22R, 221) provided in the body (17) of the nut (12).

6. Braking system according to claim 5, in which the sleeve (23) at least partly covers the body (17) of the nut (12) so as to retain the recovery (20R) and insertion (201) elements in their respective radial housings.

7. A braking system according to any preceding claim, wherein the generating curve is formed by an arc of a circle or a complete circle.

8. Braking system according to any one of the preceding claims, in which the recovery (20R) and insertion (201) ends of the balls (13) delimit paths along curved parts of a neutral fiber of the channel (20) called respectively recovery (25CR) and insertion (25CI) ends of the balls (13).

9. Braking system according to the preceding claim, in which the curved portions of the recovery neutral fiber (25CR) and insertion (25CI) of the balls (13) are formed by circular arcs.

10. A braking system according to claims 7 and 9 taken together, wherein the generating curve is formed by an arc of a circle or a complete circle of radius Rc between 105% and 115% of the radius Rb of a ball (13), preferably between 105% and 111% of the radius Rb of a ball (13), and at least one of the recovery (25CR) and insertion (25CI) neutral fiber curved parts of the balls (13), called the neutral fiber curved part considered, has a minimum radius Rmin verifying the relationship: . (4 Rb-2Rc)coüA Rmin- in which A is the angle between a first radius (RI) of the neutral fiber curved part considered passing through a point (26) of contact between first and second balls (13) moving along the neutral fiber curved part considered and a second radius (R2) of the neutral fiber curved part considered passing through the center (27) of the first ball.

11. Braking system according to any one of claims 8 to 10, in which the curved parts of the recovery (25CR) and insertion (25CI) neutral fiber of the balls (13) are parallel respectively to secant planes (PCR, PCI) symmetrical with respect to a plane (P) passing through an axis (H) of the nut (12) and a straight line (G) of intersection of the symmetrical planes (PCR, PCI).

12. Vehicle, characterized in that it comprises a braking system (2) according to any one of the preceding claims.

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