WO2004072507A1

WO2004072507A1 - Hydraulically-activated parking brake with a mechanical locking device

Info

Publication number: WO2004072507A1
Application number: PCT/EP2004/001008
Authority: WO
Inventors: Nicola Tristano; Corrado Caruso; Martin Kirschner
Original assignee: Robert Bosch Gmbh
Priority date: 2003-02-07
Filing date: 2004-02-04
Publication date: 2004-08-26
Also published as: FR2850928B1; FR2850928A1

Abstract

The invention relates to a parking brake operated by means of a fluid, typically a hydraulic fluid, for application of the parking brake and means for mechanical locking and/or clamping of the brake in the activated state. Said parking brake is a disc parking brake comprising at least one piston, operated by a fluid under pressure, typically a brake fluid, arranged to slide in a blind drilling machined in a brake caliper, said drilling forming a cylinder. A fluid pressure source pushes the piston in the direction of the disc and thus securely applies the pads to the same with a force sufficient to guarantee the immobilisation of the vehicle. According to the invention, a possible release due to the cooling of the brake is preferably taken account of, whereby an actuator displaces a fixing wedge (15) for the piston, preferably in a direction non-parallel to the axis of the above, preventing the retraction thereof relative to the disc to a distance which would risk the release of the parking brake. The actuator preferably displaces the wedge (15) in a rectilinear movement along an orthogonal axis or essentially orthogonal to the axis of the piston. However, an oblique translation movement, a rotation or a movement parallel to the axis of the piston is not excluded from the invention. In a preferred embodiment the wedge is moved in translation by means of the pressure in the hydraulic chambers (29, 29') arranged a the axial ends thereof or by the pressure in a central part of the wedge (15), hermetically sealed with relation to the hydraulic chambers (29, 29').

Description

PARKING BRAKE WITH HYDRAULIC ACTINATION OF A MECHANICAL LOCKING MEANS

The present invention relates mainly to a parking brake activated by a fluid, typically hydraulic, of the application of the parking brake as well as mechanical locking and / or locking means of the brake in activated condition.

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.

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, typically a valve open at rest, advantageously moves a key for immobilizing the piston in a direction that is not parallel to the axis of the latter preventing, its retraction from the disc from a distance which would risk release the parking brakes according to the invention. 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.

The actuator used is moved by a pressurized fluid. In the preferred embodiment, the key forms a hydraulic piston driven by the brake fluid.

The use of a high hydraulic pressure source, already available on a modern vehicle, makes it possible to limit the cost of the parking brake according to the invention.

In addition, very large amplitude forces are thus available for operating the piston and the key.

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 actuating the hydraulic actuator is a pump and / or an accumulator of a trajectory control system. i

(ESP) of an electro-hydraulic brake (EHB) of a traction control system (ASR) and / or of 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 top view with partial cutaway of an embodiment of a parking brake according to the invention at rest;

- Figure 2 is a top view with partial cutaway of the parking brake of Figure 1 during a first step of the parking brake application process;

- Figure 3 is a top view with partial cutaway of the parking brake of Figure 1 during a second step of the parking brake application process;

- Figure 4 is a top view with partial cutaway of the parking brake of Figure 1 during a third step of the parking brake application process;

- Figure 5 is a top view with partial cutaway of a first alternative embodiment of a parking brake according to the present invention;

- Figure 6 is a sectional view of the rear part of a second alternative embodiment of a parking brake according to the invention;

- Figure 7 is a partial sectional view of the preferred embodiment of a parking brake according to the present invention;

- Figure 8 is an explanatory diagram illustrating a first step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 7;

- Figure 9 is an explanatory diagram illustrating a second step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 7;

- Figure 10 is an explanatory diagram illustrating a third step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 7;

- Figure 11 is an explanatory diagram illustrating a first step in a process, according to the invention, clamping that is to say, unlocking and / or unlocking the brake of Figure 7;

- Figure 12 is an explanatory diagram illustrating a second step of a process, according to the invention, for unlocking and / or unlocking the brake of Figure 7;

- Figure 13 is an explanatory diagram illustrating a third step of a process, according to the invention, for unlocking and / or unlocking the brake of Figure 7;

- Figure 14 is a sectional view of a detail of an alternative embodiment of the brake of Figure 7; - Figure 15 is an explanatory diagram illustrating a first step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 14;

- Figure 16 is an explanatory diagram illustrating a second step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 14;

- Figure 17 is an explanatory diagram illustrating a third step in a process, according to the invention, clamping that is to say blocking and / or locking the brake of Figure 14;

- Figure 18 is an explanatory diagram illustrating a first step in a process, according to the invention, for unlocking and / or unlocking the brake of Figure 14;

- Figure 19 is an explanatory diagram illustrating a second step in a process, according to the invention, for unlocking and / or unlocking the brake of Figure 14;

- Figure 20 is an explanatory diagram illustrating a third step of a process, according to the invention, for unlocking and / or unlocking the brake of Figure 14;

In FIGS. 1 to 20, the same references have been used to designate the same elements.

In Figures 1 to 4, there is shown an 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 3 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 1 comprises a housing of a key 15 for direct or indirect mechanical blocking. 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 to 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 includes 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 X axis, in the direction of the hydraulic piston 5 greater than the extension along the X axis, in this same direction, of the 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 lever, a pedal or the like, located in the passenger compartment, the key 15 along the Y axis, in the direction of the 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 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, as illustrated in FIG. 6, 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, for example elastomer O-rings for isolating the chamber 29 with respect to the cylinder 3 and the spring housing 35. The piston 31 has a seal 39 for isolating the chamber 29 with respect to the pressure prevailing in the spring housing 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 example of FIGS. 1 to 6 for producing the parking brake according to the present invention will be explained below. o

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 controls the supply of brake fluid under high pressure, for example between 10 ⁷ Pa and 1.7 10 ⁷ Pa in cylinder 3 from a pressure source not shown, such as a pneumatic brake booster (booster in English terminology) 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. 2, so as to prevent over-adjustment by rotationally blocking the screw 11 by applying the conical bearings 43 of the screws 11 and the 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. 2, 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. In fact, the thickness of the space 45 facilitates the movement of the key 15 according to the arrow 23.

The computer generates the signal 27 (FIG. 3) for controlling the opening of the valve 25, putting the cylinder 3 in 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 according to arrow 23 as illustrated in FIG. 3. The second bearing zones 21 of the key 15 are therefore opposite the rear face of the nut 9. A loosening 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.

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. 4.

It should be noted that the application of the high pressure in the cylinder 3 ensures an elastic deformation of the caliper 1, called opening of the caliper, which stores considerable elastic energy ensuring the maintenance of the 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.

It is understood that the present invention is not limited to the formation of a space 45 between the face 19 of the nut 9 and the key 15. It is perfectly possible without departing from the scope of the present invention the parking brakes directly by moving the key 15 according to arrow 23.

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 Pa and 2 x 10 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 making it possible to release the parking brake 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 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" .

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.

It is understood that the present invention is not limited to the use of a valve closed at rest. Advantageously, as illustrated in FIG. 7, a valve 25 which is open at rest connecting the cylinder 3 to the chamber 29 is used. Furthermore, the chamber 29 and a chamber 29 ′, arranged opposite each other at the two axial ends (of axis Y) of the key 15 are connected to the high pressure brake supply source, typically a master cylinder and / or a high pressure pump.

The brake of FIG. 7 comprises a stepped key 15 comprising a first seal 37 'between the chamber 29' and the cylinder 3 of a first diameter Dl and a second seal 37 "seal between the chamber 29 and the cylinder 3 of a second diameter D2 different from the first diameter Dl. For example, D2 is greater than Dl.

The seals 37 'and 37 "are advantageously O-rings, for example made of elastomer, each disposed in a groove, for example of square section. The seals 37' and 37" define the surface for applying the pressure prevailing in the hydraulic chamber 29 ' respectively 29 on the key 15.

The operation of the preferred embodiment of the parking brake according to the present invention, illustrated in FIG. 7, will be explained below preferably in FIGS. 8 to 13.

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 controls the supply of brake fluid under high pressure, for example between 10 ⁷ Pa and 1.7 10 ⁷ Pa in cylinder 3 and the chambers 29 and 29 'from a pressure source not shown, such as a pneumatic brake booster (booster in English terminology) 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 direction of the disc with clamping of 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 the arrow 41 so as, on the one hand, to avoid over-adjustment by rotationally locking the screw 11 by applying the conical surfaces 43 of the screw 11 and of the 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.

As illustrated in FIG. 8, the pressure is applied simultaneously to the cylinder 3 ensuring the advancement of the piston according to arrow 41, to the central part of the key 15 located between the seals 37 'and 37 ", and to the chambers 29 and 29 .

As illustrated in FIG. 9, the computer generates a signal 27 for closing the valve 25 as well as the generation of a second pressure greater than the pressure previously applied. The valve 25 being closed, this pressure is only applied to the chambers 29 and 29 '. Insofar as the seal 37 "has a diameter D2 greater than the diameter Dl of the seal 37 ', the key 15 moves according to the arrow 23 to the left of FIG. 9 so that the second support zones 21 are arranged opposite the rear face 19 of the nut 9.

As can be seen in FIG. 10, the computer ensures the generation of a signal 27 for opening the valve 25 and for a drop in pressure ensuring the retraction of the piston 5 according to an arrow 41 ′ in the opposite direction to that of the arrow 41 with support of the rear face 19 of the nut 9 on the support zones 21 of the key 15 ensuring the locking of the brake in the position in which the pads are firmly applied to the disc ensuring permanent immobilization of the vehicle.

The release of the parking brake in FIG. 7 is illustrated in FIGS. 11 to 13.

First of all, as illustrated in FIG. 11, the valve 25 being open, the computer ensures the application of pressure to the cylinder 3, to the central zone of the key 15 as well as to the chambers 29 and 29 ′. This pressure ensures the advancement of the piston 5 along arrow 41 freeing a space 45 between the rear face 19 of the screw 9 and the key 15.

Then, as illustrated in FIG. 12, the computer generates a signal 27 for closing the valve 25 and the drop in pressure applied by the pressure source. The residual pressure trapped at the central zone of the key 15 being applied to the joint 37 "ensures the displacement of the key 15 to the right of FIG. 12 according to an arrow 23 'whose direction is opposite to that of the arrow 23.

Finally, the computer generates a signal 27 for opening the valve 25 and ensuring the release of pressure and the retraction of the piston 5 in the direction of arrow 41 ′ in the opposite direction to that of arrow 41. However, the key 15 being in a position in which the bearing areas 17 are located vis-à-vis the rear face 19 of the nut 9 and, consequently, the parking brake is released.

The variant embodiment of the brake according to the invention illustrated in FIG. 14 differs mainly from that illustrated in FIG. 7 in that the diameter Dl of the seal 37 'is tu greater than the diameter D2 of the joint 37 ". The tightening cycle, that is to say locking and / or blocking of the resulting brake is illustrated in FIGS. 15 to 17.

The computer generates a pressure increase control signal for locking the parking brake according to the invention.

As illustrated in FIG. 15, the pressure is applied simultaneously to the cylinder 3 ensuring the advancement of the piston according to arrow 41, to the central part of the key 15 located between the seals 37 'and 37 ", and to the chambers 29 and 29 .

As illustrated in FIG. 16, the computer generates a signal 27 for closing the valve 25 as well as the setpoint for reducing the pressure previously applied. The valve 25 being closed, the pressure reduction only concerns the chambers 29 and 29 '.

The valve 25 being closed, the pressure prevailing in the central part of the key 15 located between the seals 37 'and 37 "ensures the displacement of the key 15 according to arrow 23, to the left of FIG. 16 so that the second support zones 21 are arranged opposite the rear face 19 of the nut 9. As can be seen in FIG. 17, the computer ensures the generation of a signal 27 for opening of the valve 25 and pressure drop prevailing in the cylinder 3 ensuring the recoil of the piston 5 in an arrow 41 'in the opposite direction to that of arrow 41 with support of the rear face 19 of the nut 9 on the areas of support 21 of the key 15 ensuring the locking of the brake in the position in which the pads are applied firmly to the disc ensuring permanent immobilization of the vehicle.

The release of the parking brake in FIG. 14 is illustrated in FIGS. 18 to 20.

First of all, as illustrated in FIG. 18, the valve 25 being open, the computer ensures the application of pressure to the cylinder 3, to the central zone of the key 15 as well as to the chambers 29 and 29 ′. This pressure ensures the advancement of the piston 5 along arrow 41 freeing a space 45 between the rear face 19 of the screw 9 and the key 15.

Then, as illustrated in FIG. 19, the computer generates a signal 27 for closing the valve 25 and generating a second pressure greater than the pressure previously applied by the pressure source. This second pressure is only applied to chambers 29 and 29 '. Insofar as the seal 37 'has a diameter D1 greater than the diameter D2 of the seal 37 ", the key moves in the direction of arrow 23' in the opposite direction to arrow 23, to the right of FIG. 19 so that the support zones 17 are located opposite the rear face 19 of the screw 9.

Finally, as illustrated in FIG. 20, the computer ensures that the pressure is released and generates a signal 27 for opening the valve 25 causing the piston 5 to retreat in the direction of arrow 41 'in the opposite direction to that of arrow 41. .

Advantageously, each wheel of a front and / or rear axle of a vehicle is provided with a brake according to the present invention. The equipment of four wheels with brakes according to the present invention is particularly advantageous in the case of vehicles with four wheel drive, in particular sport utility vehicles (SUN in English terminology).

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 for blocking the piston in a first condition in which the pads are firmly applied to the disc, characterized in that the blocking means comprise a key (15) and an actuator (25, 29, 29 ') for movement on command of said key (15), said key displacement actuator (15) comprises a first hydraulic chamber (29) and a second hydraulic chamber (29 ') opposite the first hydraulic chamber and a valve (25) capable of connecting, on command ( 27), said hydraulic chambers (29, 29 ') to a source of high pressure brake fluid so as to drive the key (15) between a first position in which the brake piston (5) is free to move back and a second position in which the key (15) blocks the recoil of the piston (5), and in that the surface of application on the key (15) of the pressure prevailing in the first hydraulic chamber (29) is different from the surface of application on the key

(15) of the pressure prevailing in the second hydraulic chamber (29 ').

2. Parking brake according to claim 1 characterized in that it comprises a means of hydraulic interconnection of the two hydraulic chambers (29, 29 ') to ensure equal pressures prevailing in these two hydraulic chambers

(29, 29 ').

3. Parking brake according to any one of the preceding claims, characterized in that a first hydraulic chamber (29) is arranged at a first axial end (of axis Y) of the key (15) and in that the second hydraulic chamber (29 ') is arranged at a second axial end (of axis Y) of the key (15) opposite to said first axial end.

4. Parking brake according to any one of the preceding claims, characterized in that the key (15) is provided with hermetic insulation means typically seals (37, 37 ', 37 ") ensuring hermetic insulation between, d 'firstly the first hydraulic chamber (29) and a central part of the key (15) hydraulically connected to the cylinder (3) of the brake piston (5) and, secondly said central part of the key (15) the second hydraulic chamber (29 ').

5. Parking brake according to any one of the preceding claims, characterized in that the valve (25) is an electrically controlled valve (27) open at rest.

6. Parking brake according to claim 5 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).

. Parking brake according to any one of the preceding claims, characterized in that it further comprises a mechanism (7) for taking up wear on the brake pads bearing on a rear face of the piston (5) opposite the front face of the piston (5) bearing on the brake shoe and in that the key bears on the side of the device (7) for taking up wear on the brake pads opposite to the sides of this device (7) resting on the piston (5).

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

advancing a hydraulic piston (5) towards a disc of a disc brake so as to create a space (45) at the rear of the piston; bring a blocking part (15) of the recoil of the piston into the space thus provided and in that the displacement of 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) is ensured by bringing the same hydraulic pressure into two hydraulic chambers arranged at the ends of the key (15); 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).

9. Method according to claim 8 characterized in that it comprises a step of establishing a hydraulic pressure in a central part of the key (15) hydraulically connected to the cylinder (3) of the piston (5) sufficient to move the key (15) between a first condition in which the piston is free to move back and a second condition in which the key (15) blocks the recoil of the piston (5).

10. Method according to any one of claims 8 or 9 characterized in that it comprises a first step of establishing a first hydraulic pressure in the central part of the key (15) and the hydraulic chambers (29, 29 '), a second step of hermetically isolating the central part of the key (15) from the hydraulic chambers (29) and a third step of establishing a second hydraulic pressure, higher than said first hydraulic pressure in the hydraulic chambers (29, 29 ').