FR3142228A1 - LIGHTWEIGHT PISTON FOR DISC BRAKE AND DISC BRAKE COMPRISING SUCH A PISTON - Google Patents

Abstract

Piston for a disc brake comprising a housing configured to receive at least one part of a device for transforming a rotational movement into a translational movement, said housing comprising a side wall (16), the interior surface (25) of the side wall (16) comprising n flat bearing faces (26, 28) and n connecting faces (30, 32) between the flat bearing faces (26, 28), each of the flat bearing faces (26 , 28) being intended to cooperate with a straight edge of a side face of said one piece, the flat support faces (26, 28) delimiting with the exterior surface of the side wall (16) portions of first average thickness e1 and the connecting faces (30, 32) delimiting with the exterior surface of the side wall (16) portions of a second average thickness e2, the second average thickness e2 being substantially weaker than the first average thickness e1. [Fig. 3]

Description

LIGHTWEIGHT PISTON FOR DISC BRAKE AND DISC BRAKE COMPRISING SUCH A PISTON TECHNICAL FIELD AND PRIOR ART

The present invention relates to a lightened piston for a disc brake for a motor vehicle and to a disc brake comprising such a piston.

A motor vehicle is equipped with a brake on each of its wheels. This can be a disc brake or a drum brake.

In the case of a floating caliper brake, it comprises a yoke intended to be fixed on the steering knuckle, a caliper mounted sliding on the yoke, a piston mounted in the caliper and at least two brake pads on either side of a disc fixed to the wheel.

When the piston is moved towards the disc, for example by pressurized hydraulic fluid, it applies the inner brake pad to one face of the brake disc and, in reaction, the caliper moves and applies the outer brake pad to the other face of the brake disc.

In the case of a fixed caliper brake, this comprises a caliper intended to be fixed on a stub axle, at least two pistons mounted sliding in the caliper and each associated with at least one brake pad, the brake pads being arranged on either side of the brake disc.

The parking brake function is increasingly activated by a gear motor that is mounted on the disc brake. There are also disc brakes whose service brake function is provided by a gear motor.

The geared motor comprises a rotating output shaft. The brake comprises a device for transforming the rotational movement of the output shaft of the geared motor into translational movement capable of being applied by the piston to the brake pad arranged between said piston and the disc. Such a transformation device comprises a rotating part blocked in translation, typically a screw, and a part blocked in rotation and capable of being moved in translation, typically a nut associated with said screw. It is usual to ensure the rotational blocking by the piston, itself blocked in rotation for example by a protrusion of the brake pad.

The rotation of the geared motor causes the screw to rotate, which causes the nut to translate into the piston, relative to which it is immobilized in rotation, the piston itself being immobilized in rotation relative to the caliper. The nut then pushes the piston outwards, which comes into contact with the inner pad, which itself comes into contact with the disc.

The nut has a square shape cooperating with a cavity whose internal cross-section is also square.

This brake is satisfactory. However, we are trying to reduce the mass of the brake and therefore of all or part of its components. In addition, depending on the vehicles on which the disc brakes are mounted, constraints on the dimensions of the piston appear, in particular a longer piston may be required, which implies an increase in the mass of the piston.

An example of such a disc brake is described in document EP2932131.

On the , an example of a cross-section of a piston 1010 implemented in such a brake can be seen, in which a square nut 1022 is mounted.

It is therefore an aim of the present invention to provide a piston for a disc brake comprising means for locking the rotation of the element capable of being moved in translation while having a mass lower than that of a piston of known type.

The aim stated above is achieved by a piston for a disc brake comprising a housing configured to receive a part of a device for transforming the rotational movement, said part being intended to be blocked in rotation by the piston, said housing comprising a lateral partition provided with an inner surface comprising n flat faces and n connecting faces, the n flat faces being intended to cooperate with n straight edges of a lateral surface of the part intended to be blocked in rotation. The flat faces define portions of the lateral partition of substantially greater thickness than that of the portions defined by the connecting faces.

The inventors realized that the transmission of the force between the part intended to be blocked in rotation, for example a nut, and the piston could be achieved by a reduced surface, unlike the pistons of the state of the art. Thus the other parts of the piston not participating in the transmission of the force can be substantially thinned in comparison with those carrying the bearing faces, and thus reduce the mass of the piston, and therefore that of the brake.

In an exemplary embodiment, n is equal to two and the planar faces are parallel and diametrically opposed.

In other words, a piston is produced whose side wall has an alternation of thick and thin portions, the thick portions ensuring the transmission of the force between the nut and the piston.

The part intended to be blocked in rotation is for example a nut comprising a collar whose shape cooperates with the internal shape of the piston housing so as to secure the nut and the piston in rotation.

The present invention then relates to a piston for a disc brake comprising a housing configured to receive at least one part of a device for transforming a rotational movement into a translational movement, said housing comprising a side wall, the inner surface of the side wall comprising n flat bearing faces and n connecting faces between the flat bearing faces, each of the flat bearing faces being intended to cooperate with a straight edge of a side face of said one part, the flat bearing faces delimiting with the outer surface of the side wall portions of first average thickness e1 and the connecting faces delimiting with the outer surface of the side wall portions of a second average thickness e2, the second average thickness e2 being substantially smaller than the first average thickness e1.

Preferably, the first average thickness e1 is between 5 mm and 12 mm and the second average thickness e2 is between 2.5 mm and 5 mm.

In an exemplary embodiment, n is equal to 2 and the flat support faces are parallel to each other and diametrically opposed.

Advantageously, the flat support faces are connected to the connection zones by concave portions.

Another subject of the present application is a disc brake comprising a caliper, at least one piston according to the invention slidably mounted in the caliper and immobilized in rotation in said caliper, at least one brake pad intended to be moved by the piston and to come into contact with a brake disc, at least one geared motor, a device for transforming the rotational movement of an output shaft of the geared motor into translational movement capable of being applied by the piston to the brake pad, the transformation device comprising a rotating part blocked in translation and a part blocked in rotation and capable of being moved in translation, said rotating part and said part blocked in rotation being received in the housing of the piston and the part blocked in rotation comprising at least one straight edge configured to cooperate with a flat bearing face of the side wall of the housing of the piston.

For example, said rotating part is a screw and the part blocked in rotation is a nut, the nut cooperating with the screw.

The nut may comprise a collar comprising said at least one straight edge. In an exemplary embodiment, the collar of the nut comprises four straight edges.

In an exemplary embodiment, the piston housing delimits with the caliper a hydraulic chamber intended to be connected to a pressurized hydraulic source for service braking and in which the geared motor forms a parking brake.

In an advantageous example, the disc brake has two brake pads and the caliper is of the floating type.

BRIEF DESCRIPTION OF THE FIGURES

The following description will be better understood with the help of the attached drawings, in which:
is a longitudinal sectional view of an example of a disc brake comprising a piston according to the invention,
is a front view of the open end of a state-of-the-art brake piston in which a nut is housed,
is a front view of the open end of a brake piston according to an exemplary embodiment,
is a perspective view of a brake piston according to an alternative embodiment of the ,
is a front view of the open end of the piston of the ,
is a front view of the open end of a brake piston according to another exemplary embodiment,
is a front view of the open end of a brake piston according to an exemplary embodiment,
is a front view of the open end of a brake piston according to another exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

On the , a longitudinal sectional view of an example of a disc brake to which the present invention applies can be seen.

In this example, the disc brake is a floating caliper brake. The disc brake comprises a caliper 2 comprising a body 4 and a caliper nose 6 connected to the body by an arch 7. The arch is intended to straddle the brake disc.

The brake also includes two brake pads P1, P2 arranged in the space defined between the body and the caliper nose. The brake pad P1 is called the “inner pad” and is arranged on the side of the caliper body, and the pad P2 is called the “outer pad” and is arranged on the side of the caliper nose.

The body 4 has a bore 8 opening opposite the caliper nose. The bore 8 houses a piston 10 intended to come into contact with the inner pad P1. The other end of the bore is closed by a bottom 11.

The bore extends along a longitudinal axis X, and the piston 10 is slidably mounted in the bore 8 along the axis X.

The piston 10 is tubular in shape and has a first longitudinal end closed by a base 12 intended to come into contact with the inner plate P1, and designated “piston nose”, and a second longitudinal end open towards the base 11 of the bore 8.

The piston is locked in rotation around the longitudinal axis X by cooperation between the piston nose and the inner plate P1.

The piston 10 comprises a housing 14 delimited at one longitudinal end by the bottom 12 and laterally by a side wall 16. The piston 10 has a cylindrical shape with a circular section.

The piston 10 and the bore 8 delimit a hydraulic chamber 9 intended to be supplied with brake fluid for actuating the brake during service braking. A seal, for example a square seal, is mounted in the wall of the bore and in contact with the outer face of the side wall of the piston, ensuring the sealing of the hydraulic chamber. In a known manner, the supply of the chamber 9 with pressurized hydraulic fluid produces hydraulic operation of the brake by axial thrust towards the front of the piston 10 relative to the housing of the caliper 2.

The disc brake also includes a motor-reducer group MG mounted on the body of the caliper on the rear face of the bottom 11 of the bore 8, and intended to actuate the brake to provide the parking brake function.

The MG geared motor group comprises an electric motor M and a reducer R.

The brake also includes a screw-nut block 18 intended to ensure the movement of the piston 10 for the parking brake function.

The screw-nut block consists of a screw 20 and a nut 22 screwed onto the screw.

The screw 20 comprises a rear longitudinal portion 20.1 mounted in a through-hole 23 made in the bottom 11 of the bore and coaxial with the axis X. This first longitudinal portion 20.1 is engaged with the reducer R, allowing the screw 20 to be rotated under the action of the motor-reducer group MG. In the example shown, it comprises a hexagonal cavity and the output shaft of the motor-reducer comprises a hexagonal section.

The screw 20 has a front longitudinal end 20.2 threaded cooperating with a tapping of the nut 22.

Advantageously, the screw 20 comprises, in an intermediate zone between the front longitudinal part 20.2 and the rear longitudinal part 20.1, a stop collar 20.3 having an inclined lateral face cooperating with the free end of the piston wall.

The nut 22 comprises a tubular body crossed by a tapped bore 22.1. The body is delimited longitudinally by a first rear end 22.2 and by a second front end 22.3 formed by a head of substantially hemispherical shape.

The head 22.3 is intended to come into contact with the bottom 12 of the housing 14 of the piston 10 to move the piston axially. The head 22.3 carries a thrust surface shaped to cooperate with the bottom of the housing.

The head also includes a collar 24 extending radially from the base of the head 22.3. The cross-section of the collar is intended to cooperate with the inner surface 25 of the side wall 16 of the housing 14.

The cooperation between the collar 24 and the inner surface 25 of the side wall 16 of the wall 14 of the piston ensures, on the one hand, sliding of the nut 22 in the piston 10 along the axis X, and on the other hand a rotational blocking of the nut 22 in the piston 10. Thus, when the screw 20 is driven in rotation by the motor-reducer group, the nut 22 moves in translation along the longitudinal axis X.

The front and rear are to be considered in the direction of movement of the piston 10 during a braking application during which the piston 10 comes out of the bore 8.

According to the invention, the inner surface 25 of the side wall 16 of the piston 10 is configured, on the one hand to support the torque applied by the nut to the piston due to the rotation of the screw, and on the other hand to reduce the mass of the piston compared to the pistons of the state of the art.

On the , we can see a view of the bottom of a piston according to an example embodiment.

The inner surface 25 comprises two flat faces 26, 28 parallel to each other connected by two curved connecting faces 30, 32.

The outer surface is bounded by a circle CC.

The invention differs from prior art pistons in that the surfaces of the bearing areas between the nut and the piston are reduced. Indeed, as shown in the , the cross-section of the inner surface 1025 of a piston 1010 of the state of the art is substantially square and the support between the nut 1022 and the piston is made by means of four large-surface support faces. The lateral partition 1016 then has a significant thickness and over its entire periphery.

In the example of the , the support between the nut 22 and the piston 10 is provided by two flat support faces 26, 28.

Reducing the surface area of the support faces and/or their number makes it possible to produce more thinned portions of the side wall.

The inventors realized that the transmission of the force between the nut and the piston could be achieved by flat faces of smaller dimensions and more or less numerous. In addition, they also discovered that the translational guidance of the screw-nut block was sufficient to not have to resort to the support surfaces to ensure the guidance. In the example of the , the support surfaces only ensure the transmission of the torque from the nut 22 to the piston 10, they do not ensure the maintenance of the nut 22 in the longitudinal direction.

In the example shown, the thinned portions have an average thickness e2 and the support zones have an average thickness e1, e1 being significantly greater than e2.

Preferably the average thickness e1 is between 5 mm and 12 mm and the average thickness e2 is between 2.5 mm and 5 mm.

Thus, the piston 10 requires a reduced quantity of material for its manufacture, compared to the pistons of the state of the art, it follows that for the same material the mass of the piston is reduced, as well as that of the brake integrating it.

The embodiment is particularly suitable for pistons of smaller diameter, for example of diameter of 40 mm and less.

The table below illustrates the mass gain for a piston of the compared to a state-of-the-art piston.

State-of-the-art piston with a length of 53 mm Figure 3 piston length 55 mm Diameter (mm) Mass (g) Mass (g) 40 265 258 38 216 207 State-of-the-art piston with a length of 52 mm Piston according to figure 3 of length 54 mm Diameter (mm) Mass (g) Mass (g) 36 161 157

It is noted that a piston according to the invention having a greater length than that of the prior art has a significantly lower mass.

In Figures 4A and 4B, we can see an alternative embodiment of a piston 110, in which the surfaces of the flat support zones 126, 128 connect to a connecting face 130, 132 by a concave face 134. This alternative embodiment is more suitable for pistons of larger diameter, for example 42 mm and more.

As an example, considering the shape of the piston in Figures 4A and 4B, the table below illustrates the mass gain obtained thanks to the invention compared to a piston of the state of the art.

State-of-the-art piston with a length of 53 mm Piston according to figure 4A of length 55 mm Diameter (mm) Mass (g) Mass (g) 48 492 393 45 396 330 42 316 282

It is noted that a piston according to the invention having a greater length than that of the prior art has a significantly lower mass.

On the , we can see another example of embodiment of a piston, in which the inner surface 225 of the piston comprises three flat bearing faces 226, 228, 229 intended to be in contact with flat edges of the collar of the nut, and connected by connecting faces 230, 232, 233 delimiting with the outer surface of the side wall 216 thinned zones. Preferably the three flat bearing faces 226, 228, 229 are distributed angularly in a regular manner, and advantageously all have the same dimensions.

On the , another exemplary embodiment of a piston 310 can be seen, in which the inner surface 325 of the piston comprises a single flat bearing surface 326 .

On the , we can see another exemplary embodiment in which the inner surface comprises four flat bearing faces 426 of reduced surface area relative to those of the pistons of the prior art, connected by connecting faces 430 delimiting with the outer surface of the side wall 416 thinned portions. Preferably, the four flat bearing faces are distributed angularly in a regular manner and advantageously all have the same dimensions.

It will be understood that the number of flat support faces may be greater than 4.

Thanks to the invention, it is possible to produce pistons of reduced mass which can replace the pistons of the state of the art with little or no modification of the caliper and the screw-nut system.

In fact, the pistons of figures 3, 4A, 4B and 7 can cooperate with a square nut 10.

The pistons in Figures 5 and 6 only require replacement of the nut with a three-flat edge or single-flat edge nut.

Furthermore, in certain applications it may be desirable to use longer pistons. The invention allows such lengthening without increasing the mass of the piston.

It will be understood that a brake comprising a piston of the or Figures 4A and 4B and a nut comprising only two straight edges does not depart from the scope of the present invention.

In the example described, the brake provides service braking by hydraulic power and parking braking electrically. It will be understood that a fully electrically actuated brake is not outside the scope of this application.

Furthermore, the invention applies to both floating caliper disc brakes and fixed disc brakes. In the case of fixed disc brakes, these comprise two pistons and two geared motors.

It is understood that the external shape of the nut is adapted and complementary to the internal shape of the piston.

Digital references

2: stirrup
4: body
6: caliper nose
7: vault
8: Bore
9: hydraulic chamber
10, 110, 310 1010: pistons
11: background
12: background
14: housing
16, 216, 416: side wall
18: screw-nut block
20: screw
20.1: rear longitudinal portion
20.2: front longitudinal end
20.3: stop collar
22: nut
22.1: Bore
22.2: first rear end
22.3: second front end or head
23: through drilling
24: collar
25, 225, 325: inner surface
26, 126, 226, 326, 426: flat support face
28, 128, 228: flat support face
30, 130, 230, 430: bonding face
32, 132, 232: bonding face
134: concave portion
233: bonding face
1016: side partition
1022: square nut
CC: circle
MG: motor-reducer group
M: electric motor
P1: brake pad
P2: brake pad
R: reducer
e1: first average thickness
e2: second average thickness

Claims (10)

Piston for a disc brake comprising a housing configured to receive at least one part of a device for transforming a rotational movement into a translational movement, said housing comprising a side wall (16), the inner surface (25) of the side wall (16) comprising n flat bearing faces (26, 28) and n connecting faces (30, 32) between the flat bearing faces (26, 28), each of the flat bearing faces (26, 28) being intended to cooperate with a straight edge of a side face of said one part, the flat bearing faces (26, 28) delimiting with the outer surface of the side wall (16) portions of first average thickness e1 and the connecting faces (30, 32) delimiting with the outer surface of the side wall (16) portions of a second average thickness e2, the second average thickness e2 being substantially less than the first average thickness e1. Piston according to claim 1, in which the first average thickness e1 is between 5 mm and 12 mm and the second average thickness e2 is between 2.5 mm and 5 mm. Piston according to claim 1 or 2, in which n is equal to 2 and in which the flat bearing faces (26, 28) are parallel to each other and diametrically opposed. Piston according to one of claims 1 to 3, in which the flat bearing faces are connected to the connecting zones by concave portions (134). Disc brake comprising a caliper (2), at least one piston (10) according to one of claims 1 to 4 slidably mounted in the caliper (2) and immobilized in rotation in said caliper, at least one brake pad (P1, P2) intended to be moved by the piston (10) and to come into contact with a brake disc, at least one geared motor (MG), a device for transforming the rotational movement of an output shaft of the geared motor into translational movement capable of being applied by the piston to the brake pad, the transformation device comprising a rotating part (20) blocked in translation and a part (22) blocked in rotation and capable of being moved in translation, said rotating part (20) and said part blocked in rotation (22) being received in the housing (14) of the piston (10) and the part blocked in rotation (22) comprising at least one straight edge configured to cooperate with a flat bearing face of the side wall of the housing (14) of the piston (10). Disc brake according to claim 5, wherein said rotating part (20) is a screw and the rotationally locked part (22) is a nut, the nut cooperating with the screw. Disc brake according to claim 6, wherein the nut (22) comprises a collar (24) comprising said at least one straight edge. A disc brake according to claim 7, wherein the collar (24) of the nut (22) has four straight edges. Disc brake according to one of claims 5 to 8, in which the housing (14) of the piston (10) delimits with the caliper a hydraulic chamber intended to be connected to a pressurized hydraulic source for service braking and in which the geared motor forms a parking brake. Disc brake according to one of claims 5 to 9, comprising two brake pads (P1, P2) and in which the caliper (2) is of the floating type.