Patent Description:
The present invention applies in particular to agricultural tractors and the like, which have dual brake pedals and can perform a "steer-by-braking function" (SBF).

The use of hydraulic braking systems comprising one or more master cylinders with a pump function, operated by a pedal or respective pedals, is known in the motor vehicle industry.

Many such braking systems also include hydraulic braking assistance devices or servo-devices, also referred to as hydroboosters, associated with each master cylinder.

An example of a braking system of this type is described in patent application <CIT>, in the name of the Applicant.

The use of hydraulic braking systems comprising two coupled master cylinders is also known in the field of agricultural tractors and the like.

Such braking systems typically use two pedals to control the braking of a rear right wheel and a rear left wheel, respectively, exerting respective braking pressures.

The two pedals can be actuated by an operator individually, thereby steering the vehicle, hence the name "steer-by-braking function" (SBF).

The two pedals can be actuated by an operator simultaneously, thus simultaneously braking at least both of the rear wheels of the vehicle. In this case, to ensure balanced braking, in other words braking of substantially equal intensity on both rear wheels, devices for balancing the braking pressures are used.

Electrohydraulic braking systems comprising two brake pedals and two or more solenoid valves for regulating the flow of liquid to a first and a second brake of the vehicle (right and left brake), as described in <CIT>, are also known. Such a system may further comprise a steering control system that can act on the brakes to facilitate steering of the vehicle. On the basis of a signal supplied by turning the steering wheel of the vehicle, the control unit acts on the solenoid valves of the braking system to actuate the brake corresponding to the direction in which the vehicle is to be steered.

The abovementioned electrohydraulic braking system has the drawback of requiring special actuators to allow steering by means of actuation of the brakes. The Applicant has thus observed that the abovementioned electrohydraulic system is difficult to implement in existing vehicles having purely hydraulic braking systems that are not controlled electronically.

The aim of the present invention is to overcome the problems and limitations of the prior art by providing a hydraulic braking device that is suitable for use in autonomous guidance and that can be implemented in existing vehicles equipped with hydraulic braking systems inexpensively and without requiring special actuators.

This and other aims are achieved with the braking device as claimed in the attached claims.

The hydraulic braking device of a vehicle according to the invention comprises a master cylinder and a servo-device. In the master cylinder, a hydraulic piston defines a pressure chamber which is adapted to contain a pressurized liquid and in which a control pressure is generated that is transmitted to one or more brake(s) of the vehicle. In the servo-device, a plunger defines a first chamber and a second chamber of the servo-device, said chambers being associated with communication means adapted to establish, when the braking device is in a rest condition, a hydraulic communication between the first chamber and the second chamber and to interrupt said communication when the braking device is actuated.

The braking device comprises a shuttle piston, which is connected to a thrusting rod associatable with a brake pedal and is mounted to be sealingly slidable in a plunging piston movably integral to the plunger of the servo-device.

According to the invention, the braking device comprises a solenoid valve and a hydraulic coupling connected in a movably integral manner to the thrusting rod and comprising an inlet aperture opening into a rear inner cavity of the hydraulic coupling. This inlet aperture is hydraulically connected to the solenoid valve, preferably supplied by a hydraulic power unit of the vehicle.

The braking device according to the invention further comprises a stem, which is associated, on the side of a first end thereof, to the hydraulic coupling and having, on the side of its second end, the shape of a spherical tip.

The braking device according to the invention also comprises a distributor block sealingly slidably received within the plunging piston and adapted to abut against the shuttle piston.

According to the invention, the spherical tip of the stem is associated, in an articulated manner, to the distributor block. Furthermore, the rear inner cavity of the hydraulic coupling is in hydraulic communication with a through-channel formed within the stem, which is in turn in hydraulic communication with a driving duct formed in the distributor block, said driving duct opening into a region comprised between the distributor block and the shuttle piston.

According to the invention, between the distributor block and the spherical tip of the stem there are preferably arranged two gaskets longitudinally stacked on each other and having inner surfaces suitably shaped so as to match the spherical shape of the spherical tip. Said gaskets are configured so as to ensure articulation of the spherical tip and to ensure hydraulic sealing with said spherical tip.

The braking device with the features described above makes it possible to incorporate, between the thrusting rod and the shuttle piston, a plurality of elements, described above, adapted to actuate the servo-device and, through these elements, hydraulically actuate the servo-device, said hydraulic actuation advantageously being managed by ordinary proportional valves and by the hydraulic power unit of the vehicle.

According to the invention, the braking device is the first braking device of a pair of braking devices (which are substantially the same) of a braking system, in which a first braking device is arranged to actuate a first brake, associated with a rear right wheel of the vehicle, and a second braking device is arranged to actuate a second brake associated to a rear left wheel of the vehicle.

Each braking device of such a braking system preferably has a balancing device, which comprises a balancing valve that is normally closed and adapted, when braking is actuated, to open a hydraulic connection between the pressure chamber of the respective braking device and a balancing duct of the braking system, to ensure balanced braking.

According to the invention, a method of operating the braking device provides for said device to be actuated both manually and automatically.

The manual actuation comprises the steps of:.

The automatic actuation comprises the steps of:.

According to the invention, a method of operating the braking system comprises the step of:.

In agricultural tractors and the like, a braking system according to the invention not only makes it possible to actuate braking autonomously, but also allows the vehicle to be steered autonomously, acting on only one of the two braking devices of the system (the "steer-by-braking function"). Again in this case, the system also offers the possibility of actuating the individual braking devices manually, by acting on the brake pedals.

The invention thus makes it possible to achieve autonomous guidance in agricultural tractors and the like at low cost, allowing the switch from autonomous guidance to manual guidance simply.

These and other features and advantages of the present invention will become clear from the following description of preferred embodiments, provided by way of non-limiting example, accompanied by the attached figures, in which elements designated using the same or similar reference numbers are elements with the same or similar operation and structure. In said figures:.

A braking device <NUM> according to an embodiment of the present invention, for controlling hydraulic brakes of a motor vehicle, is described below with reference to <FIG>; in particular, in <FIG> and <FIG> the device is depicted in a rest condition (i.e. a condition in which the brakes are not actuated), and in <FIG> and <FIG> the same device is depicted in a condition in which braking is actuated by means of automatic actuation.

The braking device <NUM> comprises a thrusting rod <NUM>, which can be actuated in a known manner by means of a brake pedal (not shown), and a master cylinder <NUM> adapted to convert the thrust exerted by means of the brake pedal into a hydraulic pressure for actuating the brakes of the vehicle. The thrusting rod <NUM> is connected to the brake pedal, for example by means of a fork <NUM>. The master cylinder <NUM> comprises a pressure chamber <NUM> inside which a hydraulic piston <NUM> operates, this hydraulic piston being adapted to transfer the hydraulic pressure to the brakes of the vehicle, and a spring <NUM>, adapted to act against the thrust exerted by the hydraulic piston <NUM>. Preferably, said elements extend longitudinally along an axis A of the braking device <NUM>.

In the remainder of the description, for the sake of simplicity, the term "front" will be used to designate elements closer to or facing the master cylinder <NUM> and the term
"rear" to designate elements closer to or facing the brake pedal.

The braking device <NUM> according to the present invention is equipped with a braking servo-device (also referred to as a hydrobooster), of known type, to assist braking of the vehicle by providing a predetermined servo pressure. The general structure of the servo-device included in the braking device <NUM> according to the present invention corresponds to that described in <CIT>, to which reference should be made for a detailed description of the structure and operation of this device. Only the main components of the servo-device and its operation will be described below, briefly, attention being focused on the aspects necessary to understand the present invention.

With particular reference to <FIG> and <FIG>, the servo-device comprises, in a known manner, a plunging piston <NUM> mounted slidingly in the longitudinal direction and movably integral to an annular plunger <NUM> that separates a front chamber <NUM> from a rear chamber <NUM> of the servo-device. A shuttle piston <NUM> is also housed inside the plunging piston <NUM>, slidingly with respect to the latter. Said shuttle piston <NUM> is associated with the hydraulic piston <NUM> of the master cylinder and is held in position, in a known manner, by internal springs <NUM> of the master cylinder <NUM>.

In a rest condition, the front chamber <NUM> and the rear chamber <NUM> are hydraulically connected, for example by means of first holes <NUM> and second holes <NUM> formed radially in the plunging piston <NUM>, which place the front chamber <NUM> and the rear chamber <NUM> in communication, respectively, with a channel <NUM>, which is annular, formed on the outer surface of the shuttle piston <NUM>. In said rest condition, the same pressure prevails in the front chamber <NUM> and in the rear chamber <NUM> of the servo-device, in particular a high pressure, by virtue of the fact that pressurized oil from a volumetric pump and/or from an accumulator external to the braking device <NUM> flows in the rear chamber <NUM>, in a known manner.

In an actuation condition of the braking device <NUM>, the shuttle piston <NUM> slides relative to the plunging piston <NUM>, advancing towards the master cylinder <NUM>. The shuttle piston <NUM> is configured in such a way that its advancement results, in a known manner, in an interruption of the hydraulic connection between the front chamber <NUM> and the rear chamber <NUM> of the servo-device. The braking device <NUM> is further configured such that the advancement of the shuttle piston <NUM> also causes, in a known manner, the opening of a hydraulic connection between the front chamber <NUM> of the servo-device and a discharge chamber <NUM>, for example by means of a discharge hole <NUM> formed in the plunging piston <NUM> and said channel <NUM> of the shuttle piston <NUM>.

Owing to the difference in pressure created between the front chamber <NUM> of the servo-device, at low pressure as it is in communication with the discharge chamber <NUM>, and the rear chamber <NUM> of the servo-device, at high pressure, the plunging piston <NUM> slides towards the hydraulic piston <NUM> of the master cylinder <NUM>. The plunging piston <NUM>, advancing, causes the closure of a hydraulic connection present, in rest conditions, between the pressure chamber <NUM> and the discharge chamber <NUM> and pushes the hydraulic piston <NUM> of the master cylinder <NUM>, which thus exerts the pressure necessary to actuate the brakes of the vehicle. The servo-device thus performs the function of assisting braking.

With particular reference to <FIG> and <FIG>, according to the present invention, the thrusting rod <NUM> of the braking device <NUM> is connected in a movably integral manner to a hydraulic coupling <NUM>, which is longitudinally hollow. For example, the thrust rod <NUM> has an externally threaded end part 21a screwed into a rear cavity 22a of the hydraulic coupling, which is threaded internally.

The hydraulic coupling <NUM> is in turn associated with a stem <NUM>, which is coaxial to the hydraulic coupling <NUM> and is partly housed therein, preferably with some clearance in the longitudinal direction and so that it cannot slip out of said coupling. For example, the stem <NUM> comprises a coupling portion 23d, which is threaded externally, and the hydraulic coupling <NUM> comprises a front inlet portion 22c, which is threaded internally and configured to be coupled with the coupling portion 23d of the stem <NUM> when the latter is inserted in the hydraulic coupling <NUM>, after which there is a recess <NUM>, configured to house, with clearance, the coupling portion 23d of the stem <NUM> after it has passed through the front inlet portion 22c of the hydraulic coupling <NUM>. This advantageously makes it possible to connect the stem <NUM> to the hydraulic coupling <NUM>, preventing them from coming apart, while at the same time making up for any misalignments.

The hydraulic coupling <NUM> comprises an inlet aperture <NUM>, preferably formed radially, opening into the rear cavity 22a and connected to a tube (not shown), preferably a flexible tube, associated with an electronically controlled proportional valve (not shown), supplied by a hydraulic power unit of the vehicle.

Inside the rear cavity 22a of the hydraulic coupling <NUM>, a first end 23a (rear end) of the stem <NUM> is in abutment, with clearance, against the end part 21a of the thrusting rod. This clearance, along with the abovementioned clearance between the coupling portion 23d of the stem <NUM> and the recess <NUM> of the hydraulic coupling <NUM>, helps make up for any misalignments. On the side from which the thrusting rod <NUM> is inserted in the hydraulic coupling <NUM>, i.e. on rear side of the hydraulic coupling <NUM>, the rear cavity 22a is fluid-tight, sealed by suitable connection means 21b. Moreover, on the side from which the stem <NUM> is inserted in the hydraulic coupling <NUM>, i.e. on the front side of the hydraulic coupling <NUM>, the rear cavity 22a is fluid-tight, sealed for example by means of an O-ring seal <NUM> housed in a groove 22b of the hydraulic coupling <NUM> and interacting with an outer surface 23c of the stem <NUM>.

The stem <NUM> comprises an internal through-channel <NUM>, formed coaxially with respect to said stem, which extends from the rear end 23a of the stem to a front end 23b of the stem. The inlet aperture <NUM> of the hydraulic coupling <NUM> is in hydraulic connection, through the rear cavity 22a, with the channel <NUM> of the stem <NUM> in correspondence with the rear end 23a thereof. Preferably, a radial score <NUM> is formed at the rear end 23a of the stem, adapted to ensure the hydraulic connection between the rear cavity 22a and the channel <NUM> when the rear end 23a of the stem is in abutment against the end part 21a of the thrusting rod <NUM>. The stem <NUM>, on the side of the its end front 23b, has the shape of a spherical tip <NUM>, located externally to the hydraulic coupling <NUM>. This spherical tip <NUM> is associated to a distributor block <NUM>, housed inside the plunging piston <NUM> of the servo-device. This distributor block <NUM> abuts, at the rear, against a circlip <NUM>, while at the front it is adapted to abut against the shuttle piston <NUM> of the servo-device.

Between the distributor block <NUM> and the spherical tip <NUM> of the stem <NUM>, in the radial direction, there are two circular gaskets <NUM>, <NUM>, with a longitudinal axis substantially coincident with the axis A of the braking device <NUM> and hence substantially coaxial to the stem <NUM>, arranged in contact with and next to one another. The inner surfaces 29a, 30a of the two circular gaskets are shaped appropriately so as to adapt to the spherical shape of the spherical tip <NUM> and interact sealingly with said spherical tip. Preferably, to facilitate insertion of the spherical tip <NUM> and the circular gaskets <NUM>, <NUM>, the distributor block <NUM> is divided in a main body 24a and a cap 24b, arranged at the side of the distributor block facing the hydraulic coupling <NUM>, or at the rear side of the distributor block <NUM>, from which, once the cap 24b has been removed, the spherical tip <NUM> and the associated gaskets <NUM>, <NUM> are inserted. This cap 24b is adapted to close, for example by screwing, onto the main body 24a, after the insertion of the spherical tip <NUM> and the gaskets <NUM>, <NUM>, whereby said gaskets <NUM>, <NUM> are retained, in a longitudinal direction, between the main body 24a and the cap 24b of the distributor block.

The gaskets <NUM>, <NUM> are preferably made of PTFE or another similar material and are configured so as to ensure articulation of the spherical tip <NUM> and to ensure hydraulic sealing.

A driving duct <NUM>, which is a through-duct, that hydraulically connects the second end 23b of the stem <NUM> to a region <NUM> at the front of the main body 24a, comprised between the latter and the shuttle piston <NUM> is formed, preferably in the longitudinal direction, in the main body 24a of the distributor block <NUM>.

Because there is clearance between the second end 23b of the stem and the main body 24a of the distributor block, the channel <NUM> of the stem <NUM> is in hydraulic connection with the driving duct <NUM> and hence with said region <NUM> at the front of the main body 24a. The region <NUM> is hydraulically sealed, by virtue of appropriate O-ring seals <NUM>, <NUM> arranged between the main body 24a of the distributor block and the plunging piston <NUM> and between the shuttle piston <NUM> and the plunging piston <NUM>, respectively.

In the embodiment shown, the braking device <NUM> is further equipped with a pre-filling device, i.e. a device adapted to supply pressurized liquid so as to take up the clearance existing in the braking circuit downstream of the master cylinder <NUM> before the start of braking proper. Pre-filling devices of known type are described, for example, in patents <CIT> and <CIT>, in the name of the Applicant. Only the main components of the pre-filling device and its operation will be described below, briefly, attention being focused on the aspects necessary to understand the present invention.

The pre-filling device according to the embodiment shown in <FIG> and <FIG> is housed in a cavity 25a, a longitudinal cavity, formed inside the shuttle piston <NUM>, and comprises a valve piston <NUM>, acting as hydraulic valve, in abutment against a front end of a spring <NUM>, the rear end of which is, conversely, secured to a seat <NUM> formed in the cavity 25a of the shuttle piston <NUM>, so as to be unable to slide longitudinally. The spring <NUM> is housed in a chamber <NUM> comprised between a front end 24c of the distributor block <NUM> and the valve piston <NUM> and tends to push the latter forward, in abutment against a shoulder <NUM> present in the cavity 25a of the shuttle piston <NUM>, for example formed Integrally with said shuttle piston <NUM>. The valve piston <NUM> is configured to close, at the front, in a fluid-tight manner, the chamber <NUM> in which the spring <NUM> is located, for example by means of an O-ring seal <NUM> housed in a seat of the valve piston <NUM> and adapted to interact with the walls of the cavity 25a of the shuttle piston <NUM>. The chamber <NUM>, on the other hand, is in communication, at the rear, with a region at atmospheric pressure, in such a way that the chamber <NUM> is also at atmospheric pressure. This communication is achieved, for example, by means of a duct <NUM> formed in the main body 24a of the distributor block <NUM>.

The valve piston <NUM> of the pre-filling device comprises a duct 50a, which is longitudinal, and which is open at the front towards a front portion of the cavity 25a (referred to hereinbelow as the pre-filling duct <NUM>) and blind at the rear, and a radial hole (hole in the valve piston) 50b communicating with this duct 50a. Furthermore, when the valve piston <NUM> is in abutment against the shoulder <NUM>, the radial hole 50b in the valve piston is in hydraulic communication with radial holes <NUM> formed in the shuttle piston <NUM> (holes in the shuttle piston) and communicating, in turn, with the second holes <NUM> in the plunging piston <NUM> and hence with the rear chamber <NUM> of the servo-device. In a rest condition of the braking device <NUM>, the radial holes <NUM> in the shuttle piston <NUM> are also in hydraulic communication with the channel <NUM> in the shuttle piston <NUM> and hence with the front chamber <NUM> of the servo-device.

According to the embodiment shown, the pre-filling device further comprises a valve unit positioned at the front with respect to the valve piston <NUM> and comprising a first sphere (front sphere) <NUM> and a second sphere (rear sphere) <NUM> between which there is a spring <NUM>. The spring <NUM> is configured to keep the front sphere <NUM> in abutment against a first shoulder <NUM> formed in the pre-filling duct <NUM> and the rear sphere <NUM> in abutment against a second shoulder <NUM> formed in the pre-filling duct <NUM>, thereby cutting off the hydraulic communication through the pre-filling duct <NUM>.

The pre-filling device further comprises a stem <NUM>, which is fixed, positioned in such a way that its rear end 63a can interact with the front sphere <NUM>, pushing same and opening the hydraulic communication between the pre-filling duct <NUM> and the pressure chamber <NUM> of the master cylinder <NUM> when the shuttle piston <NUM> starts to advance towards the master cylinder <NUM>.

The pre-filling device described above is only one example of a pre-filling device that can be used in the braking device <NUM> according to the present invention. Other pre-filling devices, such as those disclosed in the abovementioned documents, may just as easily be used without departing from the scope of the invention.

Briefly, the pre-filling device functions as follows. In the rest position, the servo pressure in the front <NUM> and rear <NUM> chambers of the servo-device, connected to one another as described above, supplies, by means of the channel <NUM> in the shuttle piston <NUM>, through the holes <NUM> in the shuttle piston <NUM> and the hole 50b in the valve piston <NUM>, the pre-filling duct <NUM>.

In the rest position, the front sphere <NUM> is closed and therefore the liquid coming from the rear chamber <NUM> increases in pressure in the pre-filling duct <NUM>, exerting a hydraulic thrust on the valve piston <NUM> until it overcomes the load of the spring <NUM> arranged in the chamber <NUM>, which, as stated above, is at atmospheric pressure. Once the "pre-filling pressure" has been reached, the valve piston <NUM> closes the hole 50b in the shuttle piston, blocking same.

The pre-filling device stays in said position while the pressure in the pre-filling duct <NUM> is the same as or greater than the pre-filling pressure.

When the braking device is actuated, following the advancement of the shuttle piston <NUM>, the front sphere <NUM> is pushed by the stem <NUM>, opening the hydraulic communication between the pre-filling duct <NUM> and the pressure chamber <NUM> of the master cylinder <NUM> and the consequent passage of pressurized liquid from the pre-filling duct <NUM> to the pressure chamber <NUM>, so as to take up the clearances present in the braking circuit downstream of the master cylinder <NUM> before the start of braking proper. The abovementioned opening of hydraulic communication between the pre-filling duct <NUM> and the pressure chamber <NUM> of the master cylinder <NUM> causes a fall in pressure in the pre-filling duct <NUM>, such that the valve piston <NUM> of the pre-filling device again advances against the shoulder <NUM> present in the cavity 25a in the shuttle piston <NUM>, reconnecting the rear chamber <NUM> of the servo-device to the pre-filling duct <NUM>. The pre-filling device thus acts in such a way as to keep the pressure in the pre-filling duct <NUM> substantially constant through a modulated continuous movement of the valve piston <NUM> which causes opening and closure of the hydraulic communication between the pre-filling duct <NUM> and the rear chamber <NUM> of the servo-device. This constant pressure value is determined by the thrust exerted by the spring <NUM>. According to other embodiments, the braking device according to the present invention does not have a pre-filling device.

According to the embodiment of the present invention described, the braking device <NUM> represents the first braking device of a pair of braking devices (which are substantially the same) of a braking system (not shown) of an agricultural tractor or the like. In such braking systems, as is known, each braking device is associated with a respective brake of a rear wheel of the agricultural tractor, so that it can act on a single rear brake and perform the function known as "steer-by-braking". In such braking systems, when normal braking is desired, rather than steer-by-braking, acting on the pedals of both braking devices, it is necessary to balance out the control pressures provided by the master cylinders of the pair of braking devices so as to ensure balanced braking, i.e. braking of substantially equal intensity on both rear wheels. To this end, the braking devices are equipped with balancing devices.

The braking device <NUM> according to the embodiment shown includes a balancing device with a general structure, described below only briefly, corresponding to that described in patent application <CIT>, in the name of the Applicant, to which reference should be made for a more detailed description. With particular reference to <FIG> and <FIG>, the balancing device comprises the abovementioned stem <NUM>, which is coaxial to the shuttle piston <NUM> and fixed in correspondence with a front end wall 71a of the pressure chamber <NUM> of the master cylinder <NUM>. A balancing channel <NUM> is formed inside the stem <NUM>. A front end of the balancing channel <NUM> is connected, by means of a hole <NUM>, to a balancing duct (not shown), which is in turn in communication with a front end of a balancing duct of the second braking device of the pair of braking devices. A rear end of the balancing channel <NUM> ends with at least one radial hole 64a. This radial hole 64a is blocked by a balancing valve <NUM>, which is normally closed, movably integral with the shuttle piston <NUM>. The balancing valve <NUM> opens when the shuttle piston <NUM>, as a result of the actuation of the braking device <NUM>, moves towards the front part of the braking device <NUM>. The radial hole 64a is thus uncovered, thereby placing the balancing channel <NUM> in hydraulic connection with the pre-filling duct <NUM> and hence with the pressure chamber <NUM> of the master cylinder <NUM>, through a radial hole <NUM> formed in the shuttle piston <NUM>.

Balancing between the control pressures prevailing inside the pressure chambers of the master cylinders of the two braking devices is thus actuated mechanically, after a predetermined stroke of the respective shuttle pistons.

According to another embodiment (not shown), the braking device does not form part of a braking system comprising a pair of braking devices but is a single device, and is therefore configured to control by itself the braking of the right and left wheels of the vehicle. In this embodiment, the braking device will therefore not have the balancing device. In this case, the stem <NUM> will only have the function of interacting with the front sphere <NUM> of the pre-filling device. The stem may therefore be a solid stem (not shown), without the balancing channel <NUM> and the related radial hole 64a.

The operation of the braking device <NUM> according to the present invention is described below.

Starting from the condition of rest described above and shown in <FIG> and <FIG>, the braking device <NUM> is actuated so as to generate the hydraulic pressure necessary for braking, by means of two alternative types of actuation, namely manual and automatic actuation.

In the case of manual actuation, braking is actuated by acting on the brake pedal. The thrust exerted by means of the brake pedal is transferred to the thrusting rod <NUM> and then, via the stem <NUM>, to the distributor block <NUM>, which, as it is in abutment against the shuttle piston <NUM>, causes advancement of the latter towards the front part of the braking device <NUM>.

The advancement of the shuttle piston <NUM> causes, in a known manner, actuation of the servo-device, by means of the intermittent interruption of the hydraulic connection between its front chamber <NUM> and its rear chamber <NUM>. The actuation of the servo-device in combination with the shuttle piston <NUM> causes actuation of the plunging piston <NUM> which engages the hydraulic piston <NUM> of the master cylinder <NUM>, causing it to advance. This advancement in turn generates a pressure in the pressure chamber <NUM> of the master cylinder <NUM> adapted to actuate one or more brakes of the vehicle connected to the braking device <NUM>. In the case of automatic actuation, shown in <FIG> and <FIG>, braking is actuated by supplying an appropriate pressure at the inlet aperture <NUM> of the hydraulic coupling <NUM>; this pressure, as described above, is regulated by a solenoid valve and supplied by the hydraulic power unit of the vehicle.

The pressure supplied at the inlet aperture <NUM> is transferred, via the channel <NUM> in the stem <NUM> and the driving duct <NUM> in the main body 24a of the distributor block <NUM>, to the region <NUM> comprised between the main body 24a and the shuttle piston <NUM>. The increase in pressure in the region <NUM> generates a thrust on the shuttle piston that causes the latter to advance towards the front part of the braking device <NUM>. The usable area for generating the thrust on the shuttle piston <NUM> is the area between the guide diameter of the distributor block <NUM> and the diameter of the chamber <NUM>.

As in the case of manual actuation, the advancement of the shuttle piston <NUM> causes actuation of the servo-device, by means of the intermittent interruption of the hydraulic connection between its front chamber <NUM> and its rear chamber <NUM>, and the actuation of the servo-device in combination with the shuttle piston <NUM> causes actuation of the plunging piston <NUM> and thus advancement of the hydraulic piston <NUM> and consequent generation of a pressure in the pressure chamber <NUM> adapted to actuate one or more brakes of the vehicle connected to the braking device <NUM>.

When braking is actuated by means of automatic actuation, the brake pedal of the braking device <NUM> itself also moves as if it was actuated manually, as it is connected, as described above, to the thrusting rod <NUM> which is brought towards the front part of the braking device <NUM> owing to the advancement of the plunging piston <NUM>, to which the thrusting rod <NUM> is connected via the distributor block <NUM>, the stem <NUM> and the hydraulic coupling <NUM>. Obviously, in the case of automatic actuation, it is also possible to disengage the brake pedal from the respective fork <NUM>.

When the braking device <NUM> has a pre-filling device, actuation of braking, whether manual or automatic, will include actuation of this pre-filling device, in the manner described above.

Advantageously, automatic actuation of the braking device makes it possible to control braking of the vehicle autonomously.

In the case of a braking system comprising a pair of braking devices <NUM>, both braking devices may be actuated simultaneously, causing simultaneous braking of at least both rear wheels of the vehicle, or just one of the two braking devices may be actuated, performing the "steer-by-braking" function.

As in the case of the single braking device, the pair of braking devices is actuated manually or automatically.

When the braking devices are actuated simultaneously, if the braking devices are equipped with a balancing device, this makes it possible to balance out the control pressures at the outlet of the pressure chambers of the two master cylinders, ensuring the same braking action on at least both rear wheels of the vehicle.

Claim 1:
Hydraulic braking device (<NUM>) for a vehicle, comprising a master cylinder (<NUM>) and a servo-device, wherein
- a hydraulic piston (<NUM>) of the master cylinder (<NUM>) defines a pressure chamber (<NUM>) which is adapted to contain a pressurized liquid and in which a control pressure is generated that is transmitted to one or more brake(s) of the vehicle;
- a plunger (<NUM>) of the servo-device defines a first chamber (<NUM>) and a second chamber (<NUM>) of the servo-device, said chambers being associated with communication means (<NUM>, <NUM>, <NUM>) adapted to establish, when the braking device (<NUM>) is in a rest condition, a hydraulic communication between the first chamber (<NUM>) and the second chamber (<NUM>) and to interrupt said communication when the braking device (<NUM>) is actuated;
- a shuttle piston (<NUM>), connected to a thrusting rod (<NUM>) associatable with a brake pedal, is mounted to be sealingly slidable in a plunging piston (<NUM>) movably integral to the plunger (<NUM>) of the servo-device,
characterized in that it comprises
- a hydraulic coupling (<NUM>) connected in a movably integral manner to the thrusting rod (<NUM>) and comprising an inlet aperture (<NUM>) opening into an rear inner cavity (22a) of the hydraulic coupling (<NUM>) and hydraulically connected to a solenoid valve,
- a stem (<NUM>) associated, on the side of a first end (23a) thereof, to the hydraulic coupling (<NUM>) and having, on the side of its second end (23b), the shape of a spherical tip (<NUM>);
- a distributor block (<NUM>) sealingly received within the plunging piston (<NUM>) and adapted to abut against the shuttle piston (<NUM>),
wherein the spherical tip (<NUM>) of the stem (<NUM>) is associated, in an articulated manner, to the distributor block (<NUM>), and wherein the rear inner cavity (22a) of the hydraulic coupling (<NUM>) is in hydraulic communication with a through-channel (<NUM>) formed within the stem (<NUM>), said through-channel (<NUM>) being in turn in hydraulic communication with a driving duct (<NUM>) formed in the distributor block (<NUM>), said driving duct opening into a region (<NUM>) comprised between the distributor block (<NUM>) and the shuttle piston (<NUM>).