FR2867243A1 - Disc brake caliper for braking system of motor vehicle, has return joint housed in groove arranged in hydraulic actuator body having groove tread which extends from hydraulic chamber, containing hydraulic oil, to groove - Google Patents

Abstract

The caliper has a piston (7) sliding in a hydraulic actuator (6), and a hydraulic chamber with variable volume, containing hydraulic oil and arranged between the bottom of the actuator and the piston. A groove (13) is arranged in the body of the actuator, and a return joint (12) is housed in the groove. The body of the actuator is equipped with a groove tread (14) which extends from the chamber to the groove.

Description

Disc brake caliper

  The invention relates to a disc brake caliper. It is more particularly a return ring of a brake piston, located in the caliper.

  The invention aims to improve the return, at the end of a braking, a brake piston housed in a disc brake caliper. It is also intended to allow play catching such that a dead stroke of a brake control is as short as possible. That is to say that the actuation of the brake pedal is followed, almost immediately, braking. Another object of the invention is to increase the service life of a brake pad.

  A motor vehicle braking system generally comprises a brake pedal which controls, directly or indirectly, brakes. The brakes, in contact with the wheels of a vehicle, will oppose the rotation of the wheels, that is to say, the progress of the vehicle, when the brake pedal is actuated. In general, the slowing of the wheels is obtained by friction of an element fixed to a frame, on an element secured to a rotating wheel.

  Two categories of brake systems are commonly used. Drum brakes, and disc brakes.

  The invention relates to disc brakes.

  A disc brake caliper is integral with a vehicle frame. The caliper is generally provided with a hydraulic cylinder, in which is mounted a sliding piston. A hydraulic chamber, filled with hydraulic fluid, and variable volume, is located between a bottom of the hydraulic cylinder and the piston. Increasing the volume of the hydraulic chamber pushes the piston towards brake pads.

  A seal makes it possible to avoid any leakage of the brake fluid from the hydraulic chamber to the outside.

  The brake piston is installed in a bore in the caliper. A space is provided between the brake piston and a nose of the stirrup.

  In this space are housed two plates: an outer plate and an inner plate. The two plates delimit a space in which is housed a disc. The disc is integral with a wheel. The pads are fixedly mounted, while the disk is rotatably mounted and rotates at the same time as the vehicle wheel.

  When the brake pedal of the vehicle is actuated, brake fluid is sent to the braking system. The brake fluid arrives in the hydraulic chamber. The volume of the hydraulic chamber increases. The brake piston is pushed in a direction opposite to the bottom of the hydraulic cylinder. Advancing the piston causes an advance of the inner and outer plates respectively against an inner face and an outer face of the disc. The disc is sandwiched between the two plates.

  The friction force exerted on the rotating disc comes to oppose the rotation of the disc and therefore the wheel. If the action on the brake pedal is maintained, the action of the pads on the disk results in a braking of the vehicle.

  When the brake pedal is released, so when the driver no longer intends to brake, it is necessary that the braking system returns to the rest position. That is to say, it is necessary that the brake pads return to a position such that they leave free the rotation of the disc and the wheel. For this, it is necessary that the release of the brake pedal is accompanied by a return of the brake piston in the rest position.

  If the return of the brake piston is not complete, residual braking forces continue to be exerted on the disk. Indeed, if the pads are not located at a minimum distance allowing the free rotation of the disc, a parasitic friction of the brake pads on the disc takes place, even though no braking is required. This results in significant wear of the brake pads.

  To allow a quick return of the brake piston, when the cessation of braking, it is known to use a return gasket. The return gasket undergoes deformation, inside a groove located in the bore, during the advance of the piston. The groove hosting the seal is such that a significant deformation of the seal is possible. The deformation of the seal is due on the one hand to the hydraulic pressure applied to the seal, and on the other hand to the translational movement of the piston.

  When the brake pedal is released, and the hydraulic pressure 35 decreases, the seal returns to its original shape. Returning to its original shape, the seal recalls the piston.

  The braking system then returns to its initial position.

  However, such a system has drawbacks. Indeed, given the adjustment of the piston in the bore, which must be very accurate, it is possible that the pressure applied to the seal during the advance of the piston is almost zero. This phenomenon results from a loss of load, which itself results from the low clearance between the bore and the piston. This results in insufficient deformation of the joint. The return of the piston, when the joint returns to its original shape, is then nonexistent, or at least insufficient.

  Moreover, it is also possible, when the increase in pressure is too sudden, that the piston slides relative to the seal. That is, the piston moves forward without the seal deforming. Again the piston return is almost nonexistent.

  Also, during a second braking, the advance of the piston is virtually zero. It is even necessary to carry out several rapid and successive actuations of the brake pedal, in order to gradually bring the piston back into the rest position, by successive and weak deformations of the seal.

  In the invention, it is sought to solve the problem of insufficient recall of a brake piston during a release of a brake pedal.

  It is also sought to promote the deformation of a seal at each movement of the brake piston.

  For this, the seal is housed in a particular groove. This groove, formed in a body of a hydraulic cylinder, is such that a hydraulic pressure exerted on the piston is also exerted on the seal, promoting its deformation. The shape of the groove, recommended by the invention, organizes the easy arrival of the brake fluid on the seal. Thus, the slightest hydraulic pressure sliding the piston, also deforms the seal. The return of the piston, by the return to the initial position of the seal, is always possible.

  The subject of the invention is therefore a disc brake caliper comprising: - a hydraulic cylinder, - a piston sliding in the hydraulic cylinder, - a hydraulic chamber of variable volume, formed between a bottom of the cylinder and the piston, - a groove in a body of the hydraulic cylinder, light side of the hydraulic cylinder, a seal housed in the groove, characterized in that the body of the hydraulic cylinder is provided with at least one groove which goes from the chamber to the groove.

  In a particular embodiment of the invention, the cylinder body is provided with six grooves. The six grooves are for example regularly distributed over the entire circumference of the groove.

  The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented only as an indication and in no way limitative of the invention. The figures show: FIG. 1: A general representation of a disk brake caliper of the state of the art, adaptable to the invention; - Figure 2: a sectional view of a groove of a joint according to the state of the art and the seal housed in the groove.

  - Figures 3a, b, c: A sectional view of a groove of a seal, according to the invention, and the seal housed in the groove, at different stages of braking.

  - Figure 4: A partial cross sectional view along an axis A-A of a hydraulic cylinder of the invention.

  - Figures 5a and 5b: A numerical modeling of a phenomenon of return of a brake piston by a seal respectively according to the state of the art and according to the invention.

  Figure 1 shows a stirrup 1 disc brake type sliding caliper. The invention also applies to disc brake callipers fixed stirrup type. A yoke 2 holds the stirrup 1 on the vehicle to be braked, at a wheel (not shown). An inner plate 3 and an outer plate 4 are housed at least partially inside the yoke 1. The two plates 3 and 4 define a space 5 in which is housed a disk (not shown). The disk is thus framed on one side by an inner face of the outer plate 4, and on the other side by an outer face of the inner plate 3. By internal is meant directed towards a piston 7, and external means directed towards a nose 10 of the stirrup 1. The disc is connected in rotation to a vehicle wheel (not shown). The stirrup 1 is provided with a hydraulic cylinder 6. The brake piston 7 slides in a bore formed in the hydraulic cylinder 6. A hydraulic chamber 8, with variable volume, is formed between a bottom 9 of the hydraulic cylinder 6 and the piston 7. The stirrup 1 ends at one of its ends, by a stirrup nose. A space 11 is formed between the nose 10 of the stirrup 1 and the piston 7. It is in this space 11 that are housed platelets. The nose 10 is thus in abutment against the outer plate 4, while the inner plate 3 bears against the piston 7.

  At rest, that is to say when the braking system is not actuated, the inner pad 3 and outer 4 are spaced from the disk by a distance such that the brake pads 3 and 4 do not rub on the disk.

  When a driver wishes to brake, he presses, for example, a brake pedal. The brake pedal actuates, directly or indirectly, the piston 7, by sending brake fluid into the hydraulic chamber 8. The volume of the hydraulic chamber 8 increases, pushing the piston 7 and the nose 10 towards the disc.

  A seal 12, housed in a groove 13, is deformed inside its groove 13 during the advancement of the piston 7. In the embodiment shown in Figure 1, the return gasket is square. In addition, the return gasket also serves as a seal. That is to say, the seal 12 prevents any leakage of the brake fluid, from the hydraulic chamber 8 to the disk and the plates 3 and 4. The seal 12 is not necessarily square. It can be rectangular. More generally, it has a shape conducive to its deformation in the groove 13 under the effect of the friction of the piston 7 and the hydraulic pressure that compresses it.

  It is also possible to provide an additional seal acting solely as a seal. This prevents any leakage of liquid. In this case, the seal is placed after the return seal 12. The return gasket 12 is in this case disposed between the seal and the bottom of the cylinder.

  Figure 2 shows a groove 22 of the state of the art. In the groove 22 is housed a seal 18. The groove 22 partially follows the contours of the seal 18 and is extended by a chamfer 19. The chamfer 19 is located on a side opposite a bottom of a cylinder 20. The chamfer 19 allows a deformation of the seal 18 in the same direction as an advance of the piston 21. During braking, a brake fluid is injected into the hydraulic chamber (not shown), pushing the piston 21 to the platelets.

  However, the seal 18 in the groove 22 is not subjected to sufficient hydraulic pressure to allow good deformation. Indeed, an adjustment of the piston 21 in the bore is such that insufficient space is provided between the piston 21 and an inner wall of the cylinder 20. A small amount of hydraulic fluid can infiltrate into this space. No part of the seal 18 is in contact with the brake fluid. The hydraulic pressure exerted on the seal 18 is therefore insufficient to allow good deformation. The deformation of the seal 18 in the groove 22 is mainly due to a friction of the piston 21. Thus, if the displacement of the piston 21 is such that a deformation of the seal 18 is low or zero, the return of the piston 21 is almost non-existent, causing the problems outlined above.

  In Figures 3a to 3c, one can see the deformation undergone by a seal 12 of the invention, during braking.

  FIG. 3a shows the seal 12, at rest in its groove 13. The groove 13 is formed in a body 17 of the hydraulic cylinder 6. The groove 13 partially follows the contours of the seal 12. However, the throat 13 has a volume slightly greater than a volume of the seal 12. Thus, the seal 12 can be deformed inside the groove 13.

  A groove 14 according to the invention is formed in the circumference of the bore 17. The groove 14 is oriented from the groove 13 to the bottom 9 of the cylinder 6. The groove 14 makes hydraulic communication, efficient and easy, the groove 13 with the chamber 8. The groove 14 in particular to guide the oil, or brake fluid, to the seal 12, to optimize the deformation of the seal (Figures 3b and 3c).

  Thus the deformation of the seal 12 is allowed by the pressure exerted by the hydraulic fluid on the seal 12, as well as by the displacement of the piston 7. The deformation, which begins in Figure 3b, is maximum in Figure 3c. That is to say that a form of seal 12 partially marries a contour of the groove 13. The deformation of the seal 12 is in the direction of advance of the piston 7. To this end, the groove 13 is provided a chamfer 15 on the opposite side to the bottom 9. The chamfer 15 allows the deformation of the seal 12 in a preferred manner in the direction of advance of the piston 7.

  When the brake pedal is released, and the pressure decreases, the seal 12 returns to its initial position, reminding the piston 7 in the rest position. The return of the piston 7 allows the return of the inner pad 3 and outer 4 in the rest position. That is to say that the plates 3 and 4 emerge from the disc 5, to allow it to rotate again.

  The disadvantage of a disk brake is in particular the existence of a residual braking torque. That is to say, during repeated use of the disc brake, a parasitic resistance continues to oppose the rotation of the wheel, even when the brake is not biased. This parasitic resistance is due, among other things, to a bad return of the brake pads, and therefore to a bad return of the piston.

  This residual braking torque, non-zero, causes energy expenditure which results in particular, for the vehicle, overconsumption of fuel, and early wear pads. The shape of the groove 13, as proposed in the invention, optimizes the return of the piston 7 in all cases. Thus the pads 3 and 4 of the brake, recalled by the return of the piston 7, will peel off the disk sufficiently to prevent any residual friction. Indeed, the groove 14 allows a good application of the hydraulic pressure on the seal 12. The deformation of the seal 12 is total at the time of braking.

  In Figure 4, we can see a particular embodiment of the invention. Figure 4 shows a cross section along an axis AA of a stirrup of Figure 1. Six grooves 14 are formed all around the groove 13 (not visible). The grooves 14 are regularly distributed in the circumference of the groove 13. Each groove 14 conducts the hydraulic fluid on the seal 12 during the advance of the piston 7. In addition, preferably, a width of the groove 13, measured in the direction of sliding of the piston, is greater than a width of the seal 12, a gap 16. This gap 16 allows a circulation of hydraulic fluid around the entire periphery of the seal 12. This good circular distribution promotes good subsequent recall. The presence of grooves 14 on the entire circumference of the groove 13 ensures a uniform application of the hydraulic pressure on the seal 12, and therefore a uniform deformation of the seal 12. Moreover, because of the presence of these grooves 14, an adjustment piston 7 in the bore is always good.

  In a particular embodiment of the invention, the seal 12 has dimensions of 3 mm by 3 mm. The groove 14 has, for example, a depth of 1.5 mm. The groove 14 thus has a depth equal to half a thickness of the seal 12. By acting in this way, it is ensured that a good part of the seal 12 (ie half of its thickness) contributes, by its deformation, to the return of the piston 7.

  It is possible, even though grooves 14 in the bore optimize the deformation of the seal 12, that the piston 7 slides relative to the seal 12, without any deformation thereof. This happens especially when braking too brutal. In this case, as in the state of the art, the return of the piston 7 is virtually zero.

  However, contrary to the state of the art, a single increase in pressure, subsequently, allows the piston 7 to return to its initial position.

  Indeed, during a second normal braking, the hydraulic pressure is exerted completely on the seal 12. The deformation of the seal 12 is again maximum. When the brake pedal is released from this second braking, the seal 12 returns to its original shape, recalling with it the piston 7.

  In Figure 5a, we can see a numerical modeling of a piston return by a joint according to the state of the art.

  In FIG. 5b, it is possible to see the same numerical modeling of a return of a piston by a seal, the seal being in a groove of the invention.

  On the abscissa, the time is represented in ms. In ordinate, is represented the displacement of the piston, in mm. In the modeling shown in FIG. 5a, as in the modeling shown in FIG. 5b, the pressure exerted on the piston is from 1 to 10 Mega Pascal.

  In Figure 5a, which represents the state of the art, no pressure is exerted on the seal. In Figure 5b, according to the invention, a pressure equivalent to a hydraulic pressure is exerted on the seal.

  The position 0, in the ordinate, represents a position of the piston such that the piston is glued to the plates. In the 0 mm position, there is therefore a residual braking torque.

  In Figure 5a, the initial rest position of the piston is -2mm. After four successive brakings, that is to say at t = 80 ms, the piston return does not go beyond 0 mm. The piston remains stuck to the pads. This results in significant wafer wear and over-consumption of fuel.

  In Figure 5b, the position 0 in the ordinate also represents a position of the piston as it is glued to the plates. The initial rest position of the piston is approximately -3 mm. It is noted that the return of the piston, even after several successive braking, is almost total. After four braking, the piston is approximately in position - 2.5 mm. At the end of the ninth braking, the return position of the piston is still - 2.5 mm. Thus, unlike the state of the art, the return of the piston according to the invention is almost total at the end of each braking. We have a catch of minimum game about constant.

  In a preferred embodiment, the seal 12 is made of rubber.

Claims (6)

  A disc brake caliper (1) comprising: - a hydraulic cylinder (6) - a piston (7) sliding in the hydraulic cylinder - a variable volume hydraulic chamber (8) arranged between a bottom (9) of the cylinder and the piston, - a groove (13) formed in a body (17) of the hydraulic cylinder, light side of the hydraulic cylinder, - a seal (12) housed in the groove, characterized in that the body of the hydraulic cylinder is provided with at least one groove (14) which extends from the chamber to the groove.   2- A stirrup according to claim 1, characterized in that the groove has a volume greater than that of the seal.   3- caliper according to one of claims 1 to 2, characterized in that the groove is provided with six grooves (14) in its circumference.   4- A stirrup according to one of claims 1 to 3, characterized in that the groove has a depth of approximately equal to a half thickness of the seal.   5. Caliper according to one of claims 1 to 4, characterized in that the seal is square.   6. A stirrup according to one of claims 1 to 5, characterized in that the seal is rubber.