WO2004050444A1

WO2004050444A1 - Self-blocking and/or self-locking parking brake

Info

Publication number: WO2004050444A1
Application number: PCT/EP2003/013407
Authority: WO
Inventors: Riccardo Abbattista; Corrado Caruso; Nicola Tristano
Original assignee: Robert Bosch Sistemi Frenanti, S.P.A
Priority date: 2002-11-29
Filing date: 2003-11-28
Publication date: 2004-06-17
Also published as: AU2003294740A1; WO2004050443A1; AU2003302618A1; AU2003289908A1; WO2004050449A1

Abstract

The invention relates to a mechanically self-blocking and/or self-locking parking brake. The inventive parking brake comprises at least one piston which is driven by a pressurised fluid, typically brake fluid, and which is slidably mounted in a blind bore that is disposed in a brake calliper, said bore forming a cylinder. According to the invention, a pressurised fluid moves the piston towards the disc and, in this way, applies the shoes firmly against said disc, i.e. with a sufficient force such as to ensure that the vehicle is immobilised. The possible release of the parking brake owing to brake cooling is preferably taken into account. In said case, an actuator positions blocking and/or locking means comprising a part, typically a key, which immobilises the piston, thereby preventing same from retreating from the disc by a distance that could cause the release of the parking brakes.

Description

SELF-LOCKING AND / OR SELF-LOCKING PARKING BRAKE.

The present invention relates mainly to a self-locking and / or mechanically self-locking parking brake.

EP 0526 273 describes a disc brake provided with a parking brake actuated hydraulically by a pressure exerted by the driver on the brake pedal of the vehicle, ensuring the application of the pads on the opposite faces of the disc. While keeping the foot on the brake pedal, the driver operates an electric switch allowing to energize an electric motor driving in linear translation along the axis of the piston a sleeve coaxial with said piston, until the piston is locked in a position in which the pads are applied to the disc. The prior hydraulic application allows the implementation of a low-power electric locking motor.

The parking brake described in EP 0526 273 has many drawbacks. First of all, the driver is asked to muscularly generate the hydraulic pressure necessary for the application of the pads on the disc. On the other hand, the electric motor recommended by EP 0526273 does not make it possible to increase the force of application of the pads on the disc. As a result, if the driver does not apply the brake pedal at all or not strongly enough, the vehicle will not be immobilized properly, which can lead to an accident.

In addition, the axial arrangement of the sleeve and its drive motor increases the size of the brake as well as the unsprung mass, which degrades the dynamic performance of the vehicle equipped with such a brake.

EP 0995 659 and WO 99 48738 describe the architecture of a braking system comprising a parking brake activated by a pressurized fluid with mechanical locking by blocking a lever arm for applying friction elements to the disk. The mechanical parking brake locking devices of EP 0995 659 and WO 99 48738 do not seem to have sufficient reliability to allow their application to the automotive industry.

It is therefore an object of the present invention to provide a reliable parking brake and safe operation.

It is also an object of the present invention to offer a parking brake associated with a control system from the passenger compartment having a small footprint.

It is also an object of the present invention to provide a parking brake having a small footprint at the wheel to be immobilized.

It is also an object of the present invention to offer a parking brake having a low mass and in particular a low mass of the unsprung part. It is also an object of the present invention to offer a parking brake cooperating with the trajectory control (ESP), anti-skid (ASR), anti-lock braking (ABS), anti-roll and / or collision avoidance (ACC).

It is also an object of the present invention to provide a parking brake of simple construction.

It is also an object of the present invention to offer a parking brake at a moderate cost price.

It is also an object of the present invention to provide a parking brake that is easy to actuate without significant effort from the driver.

These goals are achieved by a parking disc brake comprising at least one piston capable of being driven by a pressurized fluid, typically brake fluid, slidably mounted in a blind bore formed in a brake caliper, the bore forming a cylinder. A source of pressurized fluid advances the piston towards the disc and thus firmly applies the pads on the latter, that is to say with sufficient force to ensure the immobilization of the vehicle. Preferably, account is taken of a possible release of the parking brake due to the cooling of the brake. At this time, an actuator sets up blocking and / or locking means comprising an immobilizing part, typically a key, of the piston preventing its recoil relative to the disc from a distance which would risk releasing the parking brakes according to the invention.

A partial or total release of the fluid pressure in the cylinder ensures a limited recoil of the piston with direct or indirect support of the latter on the immobilization part with a significant reaction force. According to the present invention, the recoil force of the piston applied to the immobilizing part ensures the blocking and / or locking of this part ensuring the stability of the brake applied to the pads ensuring the immobilization of the vehicle.

Advantageously, the actuator moves the key in rectilinear translation along an axis orthogonal or substantially orthogonal to the axis of the piston. However, a displacement in oblique translation, in rotation or parallel to the axis of the piston does not depart from the scope of the present invention. In the preferred embodiment, the key blocks the recoil of a device, preferably of screw-nut types, for compensating for wear of pads bearing on the piston. Advantageously, the trajectory of the locking key is located at the rear of the element to be blocked (piston or pad wear take-up device). However, the use of keys or the like entering a recess in the element to be blocked (piston or pad wear take-up device) does not depart from the scope of the present invention.

Advantageously, the actuator is an actuator displaced by a pressurized fluid. In the preferred embodiment, the key forms a hydraulic piston driven by the brake fluid. However, the implementation of other types of actuators, for example electrical or electromagnetic actuators does not depart from the scope of the present invention. Advantageously, the parking brake according to the present invention also performs the function of the main service brake.

Advantageously, the parking brake according to the present invention is a floating caliper brake, for example of the single piston type.

Advantageously, the source of fluid under pressure for actuation of the hydraulic actuator is a pump and / or an accumulator of a trajectory control system (ESP), of an electrohydraulic brake (EHB), of an anti -skating (ASR) and / or an anti-lock braking system (ABS).

The invention will be better understood by means of the description below and the appended figures given as nonlimiting examples and in which:

- Figure 1 is a sectional view of a first embodiment of a parking brake according to the present invention; Figure 2 is a sectional view of a second embodiment of a parking brake according to the present invention; Figure 3 is a sectional view of a third embodiment of a parking brake according to the present invention; Figure 4 is a sectional view of a fourth embodiment of a parking brake according to the present invention; Figure 5 is a sectional view of a fifth embodiment of a parking brake according to the present invention; - Figure 6 is a sectional view of a first alternative embodiment of a key capable of being implemented in the brake according to the present invention;

- Figure 7 is a sectional view of a second alternative embodiment of a key capable of being implemented in the brake according to the present invention;

- Figure 8 is a side view of the key of Figure 7; - Figure 9 is a sectional view of a third alternative embodiment of a key capable of being implemented in the brake according to the present invention;

- Figure 10 is a side view of the key of Figure 9.

- Figure 1 1 is a top view with partial cutaway of a sixth embodiment of a parking brake according to the invention at rest; - Figure 12 is a top view with partial cutaway of the parking brake of Figure 11 during a first step of the application process or activation of the parking brake;

- Figure 13 is a top view with partial cutaway of the parking brake of Figure 1 1 during a second step of the parking brake application process; - Figure 14 is a top view with partial cutaway of the parking brake of Figure 11 during a third step of the parking brake application process.

- Figure 15 is a top view with partial cutaway of a seventh alternative embodiment of a parking brake according to the present invention;

- Figure 16 is a top view with partial cutaway of an eighth alternative embodiment of a parking brake according to the present invention;

- Figure 17 is a sectional view of the rear part of the preferred embodiment of a parking brake according to the present invention. In FIGS. 1 to 17, the same references have been used to designate the same elements.

In Figures 1 to 5 and 11 to 17, there are shown 9 embodiments of the brake according to the present invention. These examples correspond to a floating caliper disc brake 1 also providing the main service brake function. In the example illustrated, a rear brake is shown, it being understood that the use of a parking brake according to the present invention on front wheels and / or a parking brake separate from the main service brake does not is not beyond the scope of the present invention.

The caliper 1 is provided with a blind bore 3 forming a hydraulic cylinder of a piston 5 provided with a device 7 for taking up wear on brake pads 8 comprising, in known manner, a nut 9 and a screw 11 unscrewing relative to the nut 9 as the brake pads wear. A rear part 13 of the caliper 1 comprises a housing of a key 15 for direct or indirect mechanical blocking of the piston.

In the example of the representation in FIG. 1, the parking brake is locked in the locked position with the pads firmly applied to the disc, 16 is effected by applying the key 15 to the rear face 19 'of the piston 5 in a first condition in which the pads are firmly applied to the disc.

In the example illustrated, the key 15 is mounted in translation along an axis Y perpendicular to the axis X of the hydraulic piston 5. The key 15 has a first support zone 17 for the rear face 19 'of the piston 5 and a second support zone 21, offset along the Y axis relative to the zone 17 and having a forward extension, along the X axis, in the direction of the hydraulic piston 5 greater than the extension along the X axis , in this same direction, of zone 17.

The locking illustrated in FIG. 1 is effected by a key, the zones 17 and 21 of which form slots making any accidental locking or unlocking impossible. In the unlocked condition, a first upper zone 21 takes place in a housing 22 located outside the cylinder 3 while a second lower zone 21 takes place in an opening 24 made in the rear face 19 'of the piston 5. In condition locked as illustrated in FIG. 1, the two zones 21 come to bear on the rear face 19 'of the piston 5.

The brake according to the invention of FIG. 2 differs from the brake according to FIG. 1 in that it maintains the parking brake in the applied position by a blocking and no longer by a locking. In the illustrated embodiment, the key 15 comprises a zone 21 having the shape of a spherical cap, the zone 17 being substantially planar. The opening 24 made in the rear face 19 ′ of the piston 5 lets pass the screw 11 which, in this way is capable of bearing, when it retreats on the protuberance 21 of the key 15.

In the example illustrated in FIG. 3, the brake according to the present invention comprises a continuous ramp without it being possible to clearly distinguish the passage from zone 17 to zone 21. In FIG. 4, an exemplary embodiment of a brake according to the present invention can be seen, the piston 5 of which is provided with one or more radial openings 55 arranged, under the condition of application of the parking brake, facing each other. screw of an opening 57, of the same diameter, formed in the wall of the cylinder 3. Pawns arranged in housings 61, driven, on command, by electric, hydraulic or other actuators penetrate into the openings 57 and 55. This penetration of one or more pins 59 prevent the piston 5 from retreating. Likewise, the shear forces between the piston 5 and the cylinder 3 exerted on the pins 59 prevent the withdrawal of said pins towards the housing 61 despite a return force exerted by springs 63. Three pins 59 are used, for example, 120 ° apart.

In Figure 5, we can see an embodiment of a brake according to the invention comprising a secondary nut 90 capable of being screwed or unscrewed on the screw 11 by a motor 92 for example electric.

In the example illustrated, the secondary nut 90 has at its periphery a straight toothing 91 meshed with a pinion 93 mounted on the axis 95 of the motor 92. On command 27, the motor 92 unscrews along the axis Y the nut 90 so that it takes support on a wall 97 preventing the recoil of the piston 5.

It is understood that the implementation of a secondary screw in place of the secondary nut 90 does not depart from the scope of the present invention.

In Figure 6, we can see a first alternative embodiment of a key 15 capable of being implemented in a brake according to the present invention provided with a variable depth groove into which penetrates the rear face 19 of the nut 9.

In FIGS. 7 and 8, one can see a second alternative embodiment of the key 15 according to the present invention comprising at its two axial ends of axis Y two cylinders 49 of a first diameter with in its center a third cylinder 51 d a second diameter smaller than said first diameter, the cylinders of larger diameter 49 being connected to the central cylinder 51 by frustoconical portions 53. The rear face 19 of the nut 9 comprises a spherical cap.

In Figures 9 and 10 we can see a third embodiment of a key according to the present invention associated with a nut 9 having two rear faces 19 diametrically opposite with respect to the axis X. The key 15 of Figures 9 and 10 also comprises cylinders of different diameters connected by frustoconical zones.

Figures 1 1 to 14, there is shown a sixth embodiment of the brake according to the present invention. This example corresponds to a floating caliper disc brake 1 also providing the main service brake function. In the example illustrated, a rear brake is shown, it being understood that the use of a parking brake according to the present invention on front wheels and / or a parking brake separate from the main service brake does not is not beyond the scope of the present invention.

The caliper 1 is provided with a blind bore forming a hydraulic cylinder of a piston 5 provided with a device 7 for taking up brake shoe wear comprising, in known manner, a nut 9 and a screw 11 unscrewing relative to the nut 9 as the brake pads wear. A rear part 13 of the stirrup has a housing for a key 15 for mechanical locking, direct or indirect. In the example shown, the blocking is carried out by means of the device 7 for compensating for the wear of the pads, of the piston 5 in a first condition in which the pads (not shown) are firmly applied to the disc (also not shown).

By firm application is meant an application making it possible to immobilize vehicles, in particular on a slope. It is commonly considered that such an application corresponds _. at a force of 10,000 N to 20,000 N.

In a second condition, the key 15 does not oppose the recoil of the piston 5. In the preferred example illustrated, the key 15 is mounted in translation along an axis Y perpendicular to the axis X of the hydraulic piston 5. The key 15 comprises a first support area 17 for the rear face 19 of the nut 9 and a second support area 21, offset along the axis Y relative to the area 17 and having a forward extension along the axis X, in the direction of the hydraulic piston 5 greater than the extension along the axis X, in this same direction, of zone 17.

In the preferred embodiment illustrated, the nut 9 is substantially cylindrical with axis X, the rear face 19 has two zones spaced along the axis Y capable of coming into contact with the key 15. The latter has a first first zone 17 followed by a first second zone 21 followed by a second first zone 17 followed by a second second zone 21.

Advantageously, the zone or zones 21 have a gentle slope forming a ramp whose orientation facilitates the movement of the key 15 in the eventual contact of the rear face 19, according to arrow 23. In the example illustrated, the extension according to l X axis of zones 21 increases from left to right.

The brake according to the present invention comprises an actuator making it possible to move, on command, for example when the driver presses a key, a switch, a lever, a pedal or the like, located in the passenger compartment, the key 15 along the axis Y, in the direction of arrow 23. This movement ensuring the parking brake lock can also be controlled by a computer, for example when the engine of the vehicle has been stopped and / or when the driver has left the vehicle. On the other hand, it is advantageous to use only hydraulic braking without mechanical blocking of the piston when stopping at a red light or when starting on a hill (Hill Holder in English terminology). In the preferred example illustrated, the actuation of the key 15 is hydraulic by means of a solenoid valve 25, of the type closed at rest connecting, on command 27, a pressure chamber 29 located at a first axial end of the key 15 at the pressure prevailing in the cylinder 3. The valve 25 is disposed at the hydraulic unit of the vehicle braking system or advantageously at the caliper 4. In the example illustrated, a chamber 29 is defined by an auxiliary piston 31 movable along the Y axis and pushed axially along arrow 23 by a spring 33 and by the face of the key 15, disposed opposite the auxiliary piston 31. The key 15 forms a hydraulic piston and is pushed axially along the Y axis in the direction opposite to the arrow 23 by a spring 35 exerting a force greater than that exerted by the spring 33. As a variant, the spring 35 is replaced by a stepped key 15, the diameter of application of the pressure on its two axial ends being different. The key 15 has seals 37 making it possible to isolate the chamber 29 relative to the cylinder 3 and to the housing of the spring 35. The piston 31 comprises a seal 39 making it possible to isolate the chamber 29 relative to the pressure prevailing in the housing of the spring 33.

The springs 33 and 35 are located in housings insulated from the brake fluid and for example filled with air. These housings can be connected to the atmosphere by channels not shown.

The operation of the preferred embodiment of the parking brake according to the present invention will be explained below.

The driver actuates the parking brake activation command, for example by pressing a button or a switch located in the passenger compartment. Advantageously, a computer (not shown), for example the brake system computer, checks that the driver's instructions correspond to satisfactory safety conditions. For example, if the vehicle speed is greater than 5 km / h, the order to apply the parking brake is not directly executed, but the driver is warned of the anomaly by a light and / or audible signal. The computer detects the change in state of the parking brake control button and checks the supply of

7 7 brake under high pressure, for example between 10 Pa and 1.7 10 Pa in the cylinder 3 from a pressure source not shown, such as a pneumatic brake booster (booster in English terminology -saxonne) active controlled by an electric valve, a pump or an accumulator. Advantageously, a source of pressurized brake fluid is already available in a modern vehicle such as ABS pumps or accumulators, ESP pumps or accumulators, EHB pumps or accumulators or others. The pressure difference between the high pressure of the brake fluid prevailing in the cylinder 3 and the atmospheric pressure prevailing in particular at the front face of the piston 5 ensures the advancement of the latter according to arrow 41, in the direction of the disc with clamping. pads on the disc ensuring the immobilization of the wheel. Insofar as at least one train of the vehicle is equipped with the brakes according to the present invention, the vehicle is immobilized. The play take-up device 7 also advances along arrow 41, as can be seen in FIG. 12, so as to avoid over-adjustment by rotationally blocking the screw 11 by applying the conical bearings 43 of the screws 11 and piston 5 and on the other hand, to provide a space 45 between the rear face 19 of the nut 9 and the first contact area 17 of the key 15.

In the example illustrated in FIG. 12, the space 45 has a thickness less than the difference between the extension along the axis X of the second zone 21 and of the first zone 17 of the key 15. However, it is of course, the implementation of a space 45 greater than this difference in extension along the axis X is not beyond the scope of the present invention. Indeed, the thickness of the rear space 45 facilitates the movement of the key 15 according to arrow 23.

The computer generates the signal 27 (FIG. 13) for controlling the opening of the valve 25, putting the cylinder 3 into communication with the chamber 29. The pressure in the chamber 29 is at this time sufficient to overcome the force opposed by the spring 35 and moves the key 15 in the direction of arrow 23 as illustrated in FIG. 13. The second bearing zones 21 of the key 15 are therefore opposite the rear face of the nut 9. Releasing the pressure in the cylinder allows the piston to retreat. The computer controls the pressure drop prevailing in the cylinder 3 causing a firm application of the rear faces 19 of the nut 9 on the second bearing zone 21 of the key 15. Simultaneously, the brake fluid flows from the chamber 29 towards the cylinder 3 via the valve 25, under the action of the auxiliary piston 31 driven by the spring 33 according to arrow 23 and the key 15 driven by the spring 35 in the opposite direction to arrow 23.

The firm support ensures the translational locking of the key 15. As a result, the key 15 and the piston 5 (by means of the device 7) lock and / or mutually lock preventing the translation of the key despite a significant drop in pressure in chamber 29. The parking brake is therefore applied in a perfectly stable condition even in the absence of hydraulic, electrical or other power.

The computer then closes the valve 25 isolating the chamber 29 from the cylinder 3 as illustrated in FIG. 14.

It should be noted that the application of the high pressure in the cylinder 3 ensures an elastic deformation of the caliper 1, called the opening of the caliper, which stores considerable elastic energy ensuring parking braking. The amount of stored energy can be optimized by a particular design of the stirrup or the choice of materials used favoring this deformation when it is subjected to significant stresses imposed by the high pressure of the hydraulic fluid. For example, a cast iron, steel, composite material caliper or an aluminum or cast iron caliper with steel inserts is used. Likewise, this energy can be stored in elastic elements external to the caliper, for example to improve the resistance of the parking brake when cooling a brake applied at high temperature. As a variant, the braking system according to the present invention comprises means for measuring the clamping force of the parking brake and ensures an increase in this force by the cycles explained above when necessary, for example as a result of cooling of a brake applied when hot after heavy service braking.

The parking brake deactivation according to the present invention is carried out according to the following steps:

The valve 25 is permanently closed. Initially, a pressure is applied greater than that which was used to ensure the locking of the parking brake, for example between 1.1 x 10 ⁷ Pa and 2 x 10 ⁷ Pa.

The piston 5 and the backlash take-up device 7 advances along the arrow 41 forming a space 45. In the absence of pressure in the chamber 29, the spring 35 brings the zones 17 opposite the faces 19 of the nut 9 (translation of the key 15 in the opposite direction to the arrow 23). The pressure in cylinder 3 is reduced and the parking brake is released. It is understood that the present invention is not limited to the implementation of a single valve 25 and a single pressure chamber 29. On the contrary, as for example illustrated in FIG. 5, it is possible to use a double valve 25 ′ supplying, on command 27 ′, a first chamber 29 ′ situated to the left of FIG. 5 allowing the parking brake to be released or a second chamber 29 "located on the right of the figure enabling the parking brake to be applied to a high pressure source, directly or indirectly, via the cylinder 3. In the example illustrated, the valve 25 'has three positions: a first position in which the cylinder 3 and the two chambers are isolated, a second position in which the chamber 29 'is supplied while the chamber 29 "is isolated and a third position in which the chamber 29" is supplied and the chamber 29' is It is understood that the single three-way valve 25 'can be replaced by two two-way valves, each controlling the supply of one of the two chambers 29' or 29 "

Similarly, as illustrated in FIG. 6, the key 15 can also be driven by an electric or electromechanical actuator such as a motor 47 illustrated in FIG. 6. The motor 47 receives a control signal 27 "coming from the computer of the vehicle braking system.

It is understood that the present invention is not limited to the implementation of a single valve 25 and a single pressure chamber 29. On the contrary, as for example illustrated in FIG. 15, it is possible to use a double valve 25 ′ supplying on command 27 ′, a first chamber 29 ′ situated to the left of FIG. 15 making it possible to release the parking brake or a second chamber 29 'located to the right of the figure allowing the parking brake to be applied to a high pressure source, directly or indirectly, via the cylinder 3. In the example illustrated, the valve 25' has three positions: a first position in which the cylinder 3 and the two chambers are isolated, a second position in which the chamber 29 'is supplied while the chamber 29 "is isolated and a third position in which the chamber 29" is supplied and the chamber 29' is isolated . It is understood that the single three-way valve 25 'can be replaced by two two-way valves, each controlling the supply of one of the two chambers 29' or 29 ".

Similarly, as illustrated in FIG. 16, the key 15 can also be driven by an electric or electromechanical actuator such as a motor 47 illustrated in FIG. 16. The motor 47 receives a control signal 27 "coming from the computer of the vehicle braking system.

As a variant, as illustrated in FIG. 17, the spring 35 is replaced by a stepped key 15, the diameter of application of the pressure on its two axial ends being different. The key 15 has seals 37 making it possible to isolate the chamber 29 relative to the cylinder 3 and to the housing of the spring 35. The piston 31 comprises a seal 39 making it possible to isolate the chamber 29 relative to the pressure prevailing in the housing of the spring 33.

It should be noted that in the event of a breakdown of the pressure generation system, the parking brake according to the present invention can still be released by exerting a very large force on the brake pedal. The parking brake according to the present invention can be associated or combined with an emergency brake without departing from the scope of the present invention.

The parking brake according to the present invention is particularly applicable to the automotive industry.

The parking brake according to the present invention mainly applies to the braking industry for motor vehicles, in particular passenger vehicles.

Claims

1. Disc parking brake comprising a piston for applying pads on the disc, means for supplying a fluid under sufficient pressure to be capable, on command, of firmly applying the pads on the disc, means blocking and / or locking the piston in a first condition in which the pads are firmly applied to the disc characterized in that it comprises means for advancing the piston (5) so as to create a rear space (45) between the blocking means (15) and a part bearing on these blocking means (15) and preventing the recoil of the piston (5), the rear space (45) facilitating the movement of these blocking means (15) between a first position in which the piston is free to move back and a second position in which the locking means (15) directly or indirectly block the recoil of the piston (5).

2. Parking brake according to claim 1 characterized in that the locking means comprise a key (15) and an actuator (25, 29, 31) for movement on command of said key (15) along an axis (Y) not parallel to the axis (X) of the piston (5) between a first position of the key (15) in which it does not oppose the recoil of the piston (5) along its axis (X) and a second position of the key (15) in which it ensures a blocking of the piston (5) in the condition in which said piston firmly applies the pads on the disc.

3. Parking brake according to claim 2 characterized in that the axis (Y) of movement of said key (15) is a straight axis orthogonal or substantially orthogonal to the axis (X) of the piston (5).

4. Parking brake according to claim 2 or 3 characterized in that it further comprises a mechanism (7) for taking up wear of pads (8) of brakes bearing on a rear face of the piston (5) opposite to the front face of the piston (5) bearing on the brake shoe (8) and in that the key bears on the side of the device (7) for taking up wear on the brake shoes opposite to the sides of this device ( 7) bearing on the piston (5).

5. Parking brake according to claim 3 or 4 characterized in that the key (15) has, along its axis (Y), a first bearing zone (17) having a first extension along the axis (X) of the piston (5) active in a first position where the key (15) does not oppose the recoil of the piston (5) along its axis (X) and a second support zone (21) having a second extension along the axis (X) of the cylinder, greater than said first extension along the axis (X) of the piston (5) of the first support zone (17) active in a second position of the key (15) in which the key s' opposes the recoil of the piston (5) along its axis (X) and in that the extension along the axis of the piston (X) of the second zone (21) varies with the position on the axis (Y) of the key so as to form a locking slope.

6. Parking brake according to any one of the preceding claims, characterized in that said brake is a floating caliper brake (1) in that said brake is also a service brake.

7. Hydraulic parking brake according to any one of the preceding claims, characterized in that the actuator for moving the key (15) comprises a hydraulic chamber (29) and a valve (25) capable of connecting, on command (27) ), said hydraulic chamber (29) to a source of brake fluid under high pressure so as to drive the key (15) between a first position in which the piston is free to move back and a second position in which the key (15) blocks the recoil of the piston (5).

8. Parking brake according to claim 7 characterized in that it comprises at a first axial end of the key (15) a first elastic return means (35) and at a second axial end of the key (15) a second elastic return means (33) and in that the elastic return force (35, 33) combines with the force exerted by the hydraulic pressure in the pressure chamber (29) and in that the return force of the return means located on the side of the pressure chamber 29 is less than the elastic return force exerted by the elastic return means (35) disposed at the other end of the key (15).

9. Braking system comprising a computer, brakes according to claim 7 or 8, and a source of pressurized brake fluid characterized in that the valve (25) is capable of connecting directly or via the cylinder (3 ), on command (27), the hydraulic chamber (29) at said pressure source.

10. Method for immobilizing a motor vehicle, characterized in that it comprises the steps consisting in:

- advancing a hydraulic piston (5) in the direction of a disc of a disc brake so as to create a space (45) at the rear of the piston;

- Bring a blocking piece (15) of the recoil of the piston in the space thus provided; and

- release the force exerted on the piston so that it moves back so as to bear firm support on the locking piece (15) for recoil of the piston (5).