FR3159999A1 - Braking system comprising a ball screw device, and vehicle comprising this braking system - Google Patents

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 partially 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, which surface moves 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

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

The invention relates to the field of vehicle braking systems, more particularly electromechanically controlled braking systems.

Technical background

A braking system for a vehicle, particularly an automobile, is already known in the prior art, of the disc type, 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, braking ceases.

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, electromechanical control means have the particular advantage of being able to be controlled electronically and thus making it possible to define different operating modes by software means depending on different situations.

The electromechanical means for controlling the clamping force application member usually comprise an electric actuator for providing 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.

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 ball recirculation path, this channel comprising a ball recovery end at the end of the helical path and a ball insertion end at the beginning of the helical path.

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

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 lower. However, it is observed in the state of the art that, due to space constraints, the recirculation channel is relatively narrow and has a shape producing at least locally a sliding of the balls to the detriment of the rolling of the balls.

The invention aims in particular to promote as much as possible the rolling of the balls in the ball recirculation channel, while taking into account the constraints of limiting the size specific to a ball screw device.

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,

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.

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.

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 allowing this recirculation channel to be arranged in a reduced space. As a result, the efficiency of the ball screw device is very high.

Other optional features of this ball screw drive that can be taken alone or in combination are specified below.

- The generating curve is formed by an arc of a circle or a complete circle. This 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:

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.

This further optimizes the rolling of the balls in the recirculation channel.

- The curved parts of the 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 steps of the recirculation channel.

- The recirculation channel comprises a ball transfer portion connecting the ball recovery and insertion ends, preferably delimiting a path along a straight ball transfer portion of the neutral fiber of the channel. This transfer portion is simple to manufacture.

- The nut comprises a body in which at least part of the recirculation channel is arranged, 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.

- The ball screw device comprises a sleeve covering at least partially the body of the nut 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.

- 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, allowing access for machining tools in a relevant area of the nut.

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,

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

The invention also relates to a vehicle, characterized in that it comprises a braking system as defined above.

Brief description of the figures

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:

FIG. 1 there FIG. 1 is a schematic top view of a vehicle in which a braking system according to the invention is arranged;

FIG. 2 there FIG. 2 is a schematic view of a braking system to which the invention can be applied;

FIG. 3 there FIG. 3 is an axial sectional view of a ball screw device according to the invention;

FIG. 4 there FIG. 4 is a perspective view of a row of balls moving between their recirculating path and their helical path;

FIG. 5 there FIG. 5 is a perspective view, partially exploded, of the ball screw device of the FIG. 3 ;

FIG. 6 there FIG. 6 is a perspective view of a set of balls moving in the recirculation path and the helical path;

FIG. 7 there FIG. 7 is a perspective view, partially exploded, of a portion of the ball screw arrangement of the FIG. 3 , showing a ball insertion element as well as a housing in which it is intended to be fitted, provided in a body of the nut;

FIG. 8 there FIG. 8 is a perspective view of an imaginary envelope representing guide surfaces for the balls in the recirculation channel;

FIG. 9 there FIG. 9 is a perspective view of the imaginary envelope of the FIG. 8 from a point of view other than that of the FIG. 8 ;

FIG. 10 there FIG. 10 is a diagram of geometric planes and axes useful for describing the shape of the ball recirculation channel;

FIG. 11 there 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.

It has been represented on the FIG. 1 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.

It should 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), aircraft, industrial vehicles such as vans, “heavy goods vehicles” - i.e. 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.

We have schematized on the FIG. 2 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.

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.

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.

Referring to Figures 3 to 6, it can be seen that the braking system 2 comprises an electric actuator 8 (shown schematically in the 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 into translational movement of the clamping force application member 7.

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 schematically by a helical line on the FIG. 6 ) by complementary nets 15, 16 (see FIG. 3 ) arranged 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 on the FIG. 3 ). Nut 12 therefore receives the rotational movement of shaft 9.

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.

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 start of this helical path 14 by a channel 20 delimiting a recirculation path for the balls 13. This recirculation channel 20, formed at least partly in the nut 12, is visible in particular in figures 3 and 7.

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

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 20I for inserting the balls 13, at the start of the helical path.

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

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 21I elements in their corresponding radial housings 22R, 22I.

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.

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 on the FIG. 7 , evolves along the entire recirculation path in accordance with the movement of a generating curve along this same recirculation path.

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.

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.

Referring to these figures 6, 8 and 9, it can be seen that the recovery 20R and insertion 20I 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.

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.

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 20I 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.

With particular reference to the FIG. 3 , we see that the sleeve 23 has a radially internal surface 23I participating in the delimitation of the transfer part 20T of the recirculation channel 20.

In the recirculation channel 20, the radially inner surface 24 for guiding the balls 13 which evolves, along the entire 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.

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 ).

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

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

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

in which A (see FIG. 11 ) is the angle between:
- a first ray R1 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.

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.

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 21I 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 21I in their radial housings 22R, 22I) 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.

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.

List of references:

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
20I: insertion end of the recirculation channel balls
20R: recirculation channel ball recovery end
20T: ball transfer part of the recirculation channel
21I: ball insertion element
21R: ball recovery element
22I: corresponding radial housing
22R: corresponding radial housing
23: nut sleeve
23I: radially internal surface of the sleeve
24: radially inner ball guide surface
25: neutral fiber of the recirculation channel
25CI: curved part of insertion of the balls of the neutral fiber of the recirculation channel
25CR: curved part of the recovery of 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 (12)

Braking system for 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 (20I) 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 (20I) ends of the balls (13),

characterized in thatthe 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 (23I) participating in the delimitation of the transfer part (20T) of the recirculation channel (20). 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). 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. Braking system according to any one of the preceding claims, in which the transfer part (20T) of the balls (13) delimits a path along a rectilinear part (25T) of transfer of the balls (13) of a neutral fiber of the recirculation channel (20). Braking system according to any one of the preceding claims, in which the recovery (20R) and insertion (20I) ends of the recirculation channel (20) are provided at least in part respectively in recovery (20R) and insertion (20I) elements of balls fitted in respective radial housings (22R, 22I) provided in the body (17) of the nut (12). Braking system according to claim 5, in which the sleeve (23) at least partially covers the body (17) of the nut (12) so as to retain the recovery (20R) and insertion (20I) elements in their respective radial housings. A braking system according to any preceding claim, wherein the generating curve is formed by an arc of a circle or a complete circle. Braking system according to any one of the preceding claims, in which the recovery (20R) and insertion (20I) 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). Braking system according to the preceding claim, in which the curved parts of the recovery neutral fiber (25CR) and insertion (25CI) of the balls (13) are formed by circular arcs. Braking system according to claims 7 and 9 taken together, in which 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 curved parts of the neutral fiber of recovery (25CR) and insertion (25CI) of the balls (13), called the curved part of the neutral fiber considered, has a minimum radius Rmin verifying the relation:

in which A is the angle between a first ray (R1) of the curved portion of neutral fiber considered passing through a point (26) of contact between first and second balls (13) moving along the curved portion of neutral fiber considered and a second ray (R2) of the curved portion of neutral fiber considered passing through the center (27) of the first ball. Braking system according to any one of claims 8 to 10, in which the curved parts of the recovery neutral fiber (25CR) and insertion (25CI) 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). Vehicle, characterized in that it comprises a braking system (2) according to any one of the preceding claims.