FR3052723A1 - BRAKE SYSTEM MECHANICALLY MAINTAINED - Google Patents

Abstract

The invention relates to a vehicle braking system comprising: a pressure source (1) configured to pressurize fluid, a supply line (10) connected to the source (1), a negative braking device (14); ) operable hydraulically, a braking line (12) connected to the braking device (14), a release valve (4) connected to the pressure source (1) by the supply line (10) and connected to the device (14). ) by the braking line (12), said valve comprising: a first position, connecting the supply line (10) to the braking line (12), a second position, connecting the braking line (12) to a vacuum outlet (16), at least one electrically controllable actuator (8), characterized in that: the system comprises at least one mechanical position holding device (18) of the brake release valve (4) to maintain mechanically the brake release valve (4) in first and second position, said actuator (8) is configured to move the valve (4) from the first position to the second position and from the second position to the first command position of an electronic control unit (2).

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to the field of machines comprising a hydraulic brake.

In particular, the machines concerned are agricultural tractors or other agricultural machines such as steamers or straddle-lifters.

More specifically, the invention relates to hydrauiiques machines comprising a braking system associated said "negative control", and comprising a command iadite negative control, said "release" by pressure of oil.

STATE OF THE ART

Braking devices with negative control, or brake release or negative brakes are known: the document FR 2 529 978 in the name of the Applicant gives a iiiustration of such braking device.

The negative-controlled braking device comprises a pressure chamber which, when pressurized, releases the braked element. Conversely, when no pressure is applied, rappeis means, typically one or more springs, keep the device in a tight position. More specifically, these devices generally comprise a cover in which a brake piston is moved in translation. The translation is controlled by the return means and by the pressure within the pressure chamber.

When a pressurized fluid is sent into the pressure chamber, the piston is moved to the brake release position, causing the disks to release: the brake therefore does not brake. On the other hand, in the absence of applied pressure or at least in the absence of sufficient pressure to overcome the effort of the return means, the piston is held in default position and compresses the discs, which, by rubbing, cause braking.

The brakes are supplied with oil pressure by a pressure source 1. The pressure source 1 is typically a hydraulic pump, which may be crimped or be compacted by unrepresented regulating and imitation devices. It may be a pump dedicated to braking, a machine accessory pump, an open-circuit transmission pump, or the booster pump of a closed circuit comprising another power pump, or a tapping on a hydraulic circuit of machine dedicated to other uses than ie braking.

As shown in FIG. 1, the negative braking device is piioted by a three-way two-position gateway B. One defines a rest position, maintained by default by means of rappeis C, and a position piiotée electrically. The vault B is connected to the pressure source A by a feed line D and is connected to the brakes F by a braking line E.

When the valve B is in the rest position, the supply line D is plugged and the braking line E is connected to a vacuum release output G, zero pressure: the pressure of the fluid in the device F is therefore zero or low and the device brakes. The output G is connected to a vacuum line which flows into a tank R at zero pressure, not shown.

When the valve B is electrically controlled, and the pressure source A is operating, the pressurized fluid is sent from the pressure source A to the negative brake device via the supply line D, the valve B and the pressure line. E. The device then no longer brakes. Because of the means of reminders C, the valve B must be maintained driven in this position, always sending a command (electrical in general) for holding in position.

This architecture has the defect that in case of interruption of the control of the valve B, due to a power failure or breakage of the electrical harness, the valve B mechanically switches to the rest position, which can cause instantaneous braking of the wheel : there is a risk of collision with the following vehicles and / or wheel lock with loss of directionality.

It also has the defect of not being able to perform emergency brake release to tow the machine out of a zone.

It is also not possible to use the parking brake as a controllable emergency brake.

It is also not possible to empty the brake circuit in the event of stopping the motors and pressure sources but keeping the electrical circuit energized.

Finally, it is not possible to warn if it is impossible to maintain pressure

PRESENTATION OF THE INVENTION The invention has a vehicle braking system comprising: a pressure source configured to put fluid under pressure, a supply line connected to the source, a braking device operable hydraulically and configured to brake a member rotatable when no hydraulic pressure is applied and for releasing the rotating member when a hydraulic pressure is applied, a braking line connected to the braking device, a brake release valve connected to the pressure source by the supply line and connected to the device by the braking line, said valve comprising: a first position, connecting the supply line to the braking line, a second position, connecting the braking line to a braking line output; vacuum, at least one actuator electrically controllable, characterized in that: the system comprises at least one holding device mec the position of the brake release valve to mechanically maintain the brake release valve in first and second positions, said actuator is configured to move the valve from the first position to the second position and from the second position to the first position to command an electronic control unit.

The first position of the brake release valve may close the brake release output, and the second position of the brake release valve may close the supply line.

The brake release valve may include two actuators, each of which is configured to switch from one position to the other; an electronic control unit can drive said actuators that can, and the mechanical holding devices can comprise two elements each configured to mechanically maintain one of the two positions.

The brake release valve may comprise a body inside which a slide is movably mounted in translation in a longitudinal direction between the first and second positions, and in which the mechanical holding devices comprise a rod mounted movable in translation integrally with the slide , said rod comprising a groove, and comprise two balls or locking fingers at different longitudinal positions, said balls being configured to be housed in the groove and then to oppose a resistance to the displacement of the slide, and in which the valve is in the first position, respectively the second, when the first ball, respectively the second, is in the groove

The one or more mechanical holding devices can be electrically controlled to release and activate a mechanical hold.

The system may advantageously comprise: a manual brake release pump, a manual control valve located on the braking line, which comprises a first passing position connecting the brake release valve to the braking device via the braking line and a second position connecting the braking circuit; brake release valve at the emptying outlet and connecting the braking device to the manual pump.

The system may also comprise a manually operated valve disposed on the braking line which comprises a mechanical control, said manual control valve makes it possible to control the pressure in the braking device according to a stroke of said mechanical control, said activation mechanical control for decreasing the pressure in the braking device to activate the braking.

The manually operated valve may include an inlet / outlet port connected to the respective pressure source, an inlet / outlet port connected to a reservoir, and an inlet / outlet port connected to the braking device, the valve with manual control being adapted to selectively connect the inlet / outlet port connected to the braking device to one or other of the other orifices, depending on the pressure in the braking device and the degree of actuation of the braking device. the command.

The manually operated valve may comprise: a plunger movable in translation in a cylinder, a thrust transfer member, adapted to exert a thrust on the plunger tending to put into communication the inlet-outlet orifice connected to the source of pressure with the inlet / outlet port connected to the braking device in response to actuation of the control, and a feedback chamber connected to the braking device through an inlet / outlet port of the valve, the chamber being disposed on a side opposite to the transfer member with respect to the plunger so that a fluid pressure in the chamber exerts a thrust on the plunger tending to put into communication the inlet / outlet port connected to the plunger. braking with the inlet / outlet port connected to the tank.

The manually controlled vaive is advantageously adapted to connect the inlet / outlet orifice connected to the chamber to the inlet / outlet port connected to the reservoir when the pressure in the braking device exceeds a pressure corresponding to a level of actuation of the command.

The manually actuated valve is advantageously adapted to connect the inlet / outlet port connected to the braking device to the inlet / outlet port connected to the reservoir when the pressure in the brake device exceeds a pressure corresponding to one level. operating the control.

The system may further comprise a safety nozzle connected to a sampling point on the supply or braking line, said nozzle being configured to allow by a pressure leak on the line, to lower the pressure in said lines.

The pressure source of the system may be an accumulator and the system may comprise an upstream circuit having: a charging circuit of the pressure source connected to the supply line, and warning means, configured to signal a fall of pressure in the supply line or the braking line, the charging circuit being configured to recharge the accumulator under pressure and the warning means being configured to block the accumulator and prevent it from emptying when a fall pressure is detected.

The system may further comprise a disengageable hydraulic motor, and a booster pump configured to engage said engine by pressurizing. In this case, the pressure source is the booster pump, so that the clutch of the engine is not possible if the manual valve is in second position.

The system may comprise an assembly further comprising an electronic control unit for controlling the actuator (s) of the brake release valve, and / or the mechanical holding devices according to the embodiment. In addition, the unit is advantageously configured to maintain the brake release valve in the first position based on data relating to the engine torque of the vehicle as the acceleration does not compensate for the slope, thus making it possible to start up hill .

The system may be included in an assembly with an electronic control unit that is configured to drive the system actuator (s). The invention thus also relates to such an assembly.

This set can be included in a vehicle. The invention also relates to a braking method of an assembly as described above, comprising a step of generation by the electronic control unit of a position change instruction of the brake release valve.

Advantageously, the electronic control unit sends a switching command of the valve in the first position in order to brake the vehicle, then sends a switching command of the valve in the second position once a threshold engine torque of the vehicle is detected, in order to start a hill climb.

PRESENTATION OF THE FIGURES Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which: FIG. has previously been described, presents an example of a hydraulic control braking system according to the state of the art; FIG. 2 illustrates an overall view of a hydraulically controlled braking system according to one aspect of the invention: maintaining a valve position in the event of an electrical power failure; FIG. 3 illustrates an overall view of a hydraulically controlled braking system according to the first aspect of the invention and two other aspects of the invention: manual release and pressure leakage; FIG. 4 illustrates an embodiment 5 illustrates a general view of a hydraulically controlled braking system according to the first aspect of the invention and a fourth aspect of the invention: progressive manual brake release, FIG. 6 illustrates a progressive actuating valve as used in one embodiment of the invention; FIG. 7 illustrates the relationship between the pressure in the braking device and the degree of actuation of the brake control allowed. 8 illustrates a general view of a hydraulically controlled braking system grouping together several of the aspects mentioned above, FIG. 9 illustrates an overall view of a braking system. FIG. e hydraulic control according to one aspect of the invention that can alert in case of hydraulic pressure drop.

DETAILED DESCRIPTION Now, in connection with FIG. 2, a hydraulically controlled braking system will be described.

This braking system is advantageously mounted on vehicles having hydraulic assistance in the form of a traction pump supplying hydraulic motors mounted on axles of the vehicle. Advantageously, the hydraulic motors are connected to the wheels, and comprise a braking device 14.

The system comprises a pressure source 1, a braking device 14 and a release valve 4. The pressure source 1 is connected to the valve 4 by a supply line 10 and the valve 4 is connected to the braking device 14 by a braking line 12.

The pressure source 1 is configured to supply pressurized oil to the supply line 10. The pressure source 1 can be a booster pump or an accumulator. More details will be given later.

The braking device 14 actuated hydraulically is configured to brake a rotating member when no pressure is applied, using biasing means, typically springs, which keep the device in position by default. Conversely, the braking device 14 is configured to release the mobile element in rotation when a pressure is applied. It will be understood that the rotational release depends on the value of the pressure and that this release can be continuous. This is a negative braking device as described in the introduction. More specifically, and as indicated in the introduction, the pressure source 1 feeds a pressure chamber which makes it possible to control the displacement of a brake piston, which makes it possible to tighten fittings on a disc or a drum. When talking about the pressure in the braking device 14, we are talking about the pressure in the pressure chamber. The movable member is typically a shaft or axle carrying a wheel.

The device further comprises an electronic control unit 2 for controlling the brake release valve 4.

In a first position, the release valve 4 makes it possible to connect the supply line 10 to the braking line 12. In other words, it makes it possible to connect the source of pressure 1 to the braking device 14 in order to allow its activation (and thus release the braking).

In a second position, the brake release valve 4 makes it possible to connect the braking line 12 to a vacuum outlet 16 of the brake release valve 4. In other words, it makes it possible to connect the braking device 14 to a empty to release the pressure and brake again.

In practice, in second position, the emptying outlet 16 of the brake release valve 4 is connected to a vacuum line which discharges into a tank R at zero pressure.

The release valve 4 is electrically controlled.

The system further comprises a mechanical position-holding device 18 of the release valve 4. This device 18 makes it possible to mechanically maintain the release valve 4 in the first position and in the second position: each position is maintained in its state of mechanical way. Advantageously, this device 18 is included in the brake release valve 4.

Due to this device 18, the release valve 4 is now controlled by the control unit 2 at each change of position, unlike the valves described in the introduction which are controlled only to be maintained in the piloted position.

In order to change the position, it is necessary for the control unit 2 to generate a position change command which causes switching between the first and the second position (or vice versa). The holding in this position is provided by the holding device 18, without it being necessary for the control unit 2 to maintain the position change instruction. The control unit 2 can thus locate the braking vault 4 by pulses.

Therefore, a power failure has no effect on the position of the vaive 4.

The brake release valve 4 comprises at least one controllable actuator 8, which can change the valve in one and in the other position (bidirectional actuator) or two controllable actuators (8, 8 '), each actuator making it possible to switch respectively from one position to the other.

The mechanical position holding devices 18 may take a number of forms.

In a first mode of realization, it is a purely mechanical system which decipates if an effort is greater than a threshold. The threshold is determined so that in use, the vaive 4 keeps its position, but under impotence of the actuator 8, the holding devices in one of the positions debunk and the holding devices in the other position are block.

In Figure 3 is shown schematically a valve 4 comprising two actuators 8, 8 'and holding devices in the form of two elements 18, 18'. The actuator 8 makes it possible to pass from the first to the second position and the element 18 'makes it possible to maintain mechanically in the second position. The actuator 8 'makes it possible to pass from the second to the first position and the element 18 makes it possible to maintain mechanically in the first position.

FIG. 4 shows a detail of the embodiment of the valve of FIG. 3. The valve 4 comprises a body 40 inside which a slide 41 is movable in translation in a longitudinal direction between the two positions explained previously to connect the line alternately. supply 10 to the braking line 12 and the supply line 10 to the emptying output 16 (the ports have the same references as the lines, the port of the line 12 is in another plane of section and is not represented). The valve 4 is driven in the first position, respectively the second, by a first solenoid 42a, respectively a second solenoid 42b, which act as actuators 8, 8 '. The solenoids 42a, 42b set in motion respectively plungers 43a, 43b which transmit the movement to the drawer 41. The holding devices 8, 18 take the form of a rod 81 movable in translation longitudinally solidarily of the drawer 41. The rod 81 is here mounted longitudinally between one of the two plungers 43b and the slide 41. The rod 81 comprises a groove 82 and two balls, 83a, 83b which can be housed within the groove 82. Equivalently, the two balls can be replaced by other means known stops, for example fingers, or locking men (cylinders end in half-sphere). The two balls 83a, 83b are housed at different longitudinal locations, so that depending on the longitudinal position of the slide 41, only one of the two balls can be engaged in the groove 82. Each ball 83a, 83b is mounted with a locking spring 84a, 84b which tends to push the ball 83a, 83b against the rod 81 and hold it in the groove 82. Thus, to change position, the solenoid 8, for example, must exert a force tending to overcome the resistance of the ball couple 83a / spring 84a, so that the spring compresses and the ball goes into the retracted position. It is thus understood that the balls make it possible to maintain the valve in position, without piloting by the solenoids, and that these are only required to induce a change of position. The springs and balls are housed in respective housings, each closed by a plug.

The valve further comprises a creepage line T, which leads to the tank R, and a purge plug BP. The valve also includes an internal leak collection channel connected to the creepage, and typically an LC connection line between the two chambers at the ends of the rod 81 to facilitate the reciprocating movement of the rod 81.

During the transition positions, no ball is in the groove. To change position, an actuator must be activated to overcome a mechanical holding means, until the other mechanical holding means is engaged. Then activate the other actuator to change the position of the valve again.

This valve 4 can be modified simply by incorporating for example a second groove, or by placing a second rod on the other side of the slide 41, each rod being associated with a ball and a spring, etc.

In another embodiment, it is a mechano-electric system which is released only on command of the control unit 2. In this case, the control unit 2 sends a setpoint at a time to the control unit. actuator 8 and the position holding devices.

The mechanical holding devices 18 can thus lock and unlock on command of the control unit 2, but mechanically maintain the locked position in the absence of control.

It is possible to integrate the holding devices 18 to the actuator itself or to the actuators themselves.

The release valve 4 as illustrated comprises at least two positions, but may include more, as needed. An intermediate position where all channels are cut can be considered for switching issues.

Voluntary flight

If the brake release valve 4 is defective and can no longer be switched to the first position (released device) even when the thermal supply of the vehicle is stopped, it is preferable that the system returns to a default position, which is the blocking of wheels.

For this, a leak is placed on the supply line 10 or the braking line 12, in order to gradually reduce the pressure.

The flow rate of this leak is lower than the flow rate that can be provided by the pressure source, so that when the pressure source 1 is operating, the leakage does not cause a pressure drop.

The leak is made for example in the form of a nozzle 24 (Figure 3). The leak is typically directed to a vacuum line which discharges into a tank R at zero pressure, not shown.

In addition, this leak ensures a renewal of the oil, for filtering and cooling. Manual defreinaoe

The system may be equipped with a manual brake release pump 22 and a manual brake release valve 20 (FIG. 3). They allow, in case of vehicle failure, to manually release the brake in order to tow the vehicle freely. It also allows you to temporarily move a vehicle when its engine is stopped. By "manually" is meant "by direct intervention of the man", whether with the hand or the foot for example.

The valve 20 is located on the braking line 12. The hand pump is equipped with non-return valves 26 such that the fluid can move only from the tank of the hand pump 22, to the valve 20 and not in the other way.

In a first position, the valve 20 connects the release valve 4 to the braking device 14 and connects the manual pump 22 to a vacuum outlet 21 of the manual control valve 20.

In a second position, the valve 20 connects the hand pump 22 to the braking device 14 and connects the release valve 4 to the emptying outlet. The evacuation output is generally connected to a vacuum line which flows into a reservoir. In the usual way, it is preferable that there is only one oil tank R on the hydraulic circuit of the machine, which is connected to all the draws, and all returns, including updates. empty.

Thus, in the first position, the manual control valve 20 allows the normal operation of the brake device, as has been explained previously. In the second position, the manual control valve 20 allows the braking device 14 to operate by means of the hand pump 22 while sending the flow, if it exists, from the pressure source 1 to the emptying.

When the source 1 is a booster pump, if the manual control valve 20 is in the second position, the source 1 flows into the emptying line and prevents the pressure rise in the booster circuit. Now, this booster circuit is generally used to control the displacement of the traction pump. Therefore, as the manual valve 20 is not returned to the first position, it is the entire hydraulic transmission of the vehicle that can be interrupted, or even all the hydraulic functions of the machine.

In the case of a disengageable hydraulic motor connected to the wheels whose disengaging means are hydraulically controlled by the booster pump, the manual control valve 20 thus allows a global manual control of the hydraulic assistance. The clutch is typically by pressurizing chamber (s) clutch which tends to engage a cylinder block with a shaft. In the absence of pressurization, the cylinder block rotates empty and the hydraulic assistance is inactive. The cylinder block comprises a plurality of pistons movable within the respective cylinder and arranged radially around the shaft. With the rotation, the pistons follow a lobed cam which cause their movement within the cylinder (or conversely in engine operation). The engine is typically a radial piston engine and multi-lobe cam, which advantageously and compact includes a multi-disc brake, and which can be disengaged.

Advantageously, the manual control valve is of "all or nothing" type, that is to say that there is either the entire flow that passes or no flow.

Additional order

As shown in FIGS. 5 and 6, a manually operated progressive valve 28 may also be provided on the braking line. The latter is controlled by the vehicle operator. To this end, the manual actuating progressive valve comprises a mechanical control 30. It may be a lever or lever or a pedal. By "manual", one means "by direct intervention of the man". When the operator needs to brake, he raises the lever 30 which gradually releases the pressure downstream of said valve. Pedal mounting may exist provided that it performs the same movement on the valve 28 when the pedal is depressed. The pressure downstream of said valve is discharged in the same proportion. The brake device 14, normally used as a parking brake, can be used as an emergency brake.

The manually operated progressive valve 28 is a valve comprising an inlet port and an outlet port and comprising a single mechanical control for controlling the fluidic relationship between the inlet and the outlet of the valve 28.

The progressive valve with manual actuation 28 allows a progressive dosage of the pressure between the upstream and the downstream. Between an idle position which blocks the flow rate and a maximum position which allows a maximum pressurization, an activation stroke of the mechanical control is defined. Preferably, the pressurization is proportional to this race.

In a preferred embodiment, the maximum pressure transmissible by the manually operated progressive valve 28 does not depend on the source of pressure, but only on the characteristics of said valve 28. Such a valve 28 also allows greater operability and greater flexibility. greater flexibility in the use of pressure sources.

The valve 28 is in accordance with a valve shown diagrammatically in section in FIG. 6 and comprises: an inlet / outlet orifice 33 connected to the pressure source 1 by a channel P, the channel P is therefore subjected to a flow rate at a certain pressure corresponding to the pressure delivered by the pressure source 1, the track P corresponds to the braking line 12, pressure source side 1, an inlet / outlet orifice 34 connected to the tank R at atmospheric pressure by a channel T , and an inlet / outlet port 35 connected to the braking device 14, by the braking line 12 also, on the braking device side 14.

The valve 28 comprises a line 36 for measuring the pressure in the braking device 14, making it possible to regulate the pressure in the channel F as a function of the degree of actuation of the brake control. This line 36 is shown schematically to illustrate a feedback of the pressure in the braking device 14 on the operation of the valve 28, the feedback being described in more detail below.

As can be seen in FIG. 6 each valve 28 comprises a plunger or drawer 320 mounted in translation in a cylinder 321 so as to selectively put in communication the orifice 35 of the channel F connected to the braking device 14 with the orifice 33 of the track P at the pressure of the pressure source 1 or with the orifice 34 of the track T at atmospheric pressure depending on a degree of actuation of the brake lever 310. In this regard, the valve 28 comprises a spring loading 322 put in compression by the mechanical control 310 such as a brake lever 310 (or more generally of the progressive mechanical control), tending to the displacement of the plunger 320 to put the P or T channel in communication with the channel F.

The valve 28 also comprises a feedback chamber 323 comprising a spring 324, the spring and the chamber being positioned on the opposite side of the loading spring 322 with respect to the plunger for exerting thrust that is opposite to that of the loading spring.

In the absence of actuation of the lever 310, the spring 322 exerts its maximum thrust on the plunger 320 to connect the track P with the track F and thus release the brake by pressurizing the brake device. At the same time, the pressure also increases in the feedback chamber 323 since it is connected to the braking device 14. The pressure in the feedback chamber 323 is equal to the pressure in the braking device 14, with any pressure drop around .

The pressure in the feedback chamber 323 exerts a thrust on the plunger 320 opposing the thrust of the loading spring 322, and tends to reduce the flow rate from the track P to the track F.

When there is a balance between the thrust of the loading spring 322 on the one hand and the thrust exerted by the fluid pressure in the feedback chamber 323 on the other hand, the plunger remains in equilibrium and maintains the pressure in the track F - and in the braking device 14 - at a constant value. The equilibrium depends on the geometric characteristics of the valve (plunger, cylinder) and the setting of the loading spring 322. Thus, the valve 28 delivers a pressure in the braking device 14 and in the track F which is proportional to a degree of Actuation of the lever, the coefficient of proportionality depending on the characteristics of the valve and the setting of the spring.

When the lever 31 is actuated upwards, the spring 324 exerts a thrust on the plunger 320 which puts the track T in communication with the track F and thus empties the braking device of the brakes and clamps the brakes. Depending on the new balance that is created in the valve 28, the braking pressure is progressive depending on the position of the lever. If the lever 310 is replaced by a pedal, connected so as to detach, that is to say, decompress the spring 322 when the pedal is depressed, it is possible to obtain a proportional brake pedal.

For the default position of the lever to compress the springs 322 and 324, a retaining spring 326 is provided on the other side of the point of rotation PR of the lever, and which opposes the actuation of the lever 31 The spring 326 has for this a stiffness greater than that of the springs 322 and 324.

FIG. 7 shows the relationship between the pressure obtained in the braking device 14 and the degree of actuation of the mechanical control unit 310. The proportional increase of the pressure as a function of the stroke of the mechanical control only begins when the race exceeds a race called "dead race" in which the compression exerted by the pedal on the loading spring 322 is not sufficient to transmit a force on the plunger 320.

When the pressure in the feedback chamber 323 of the brake exceeds the set pressure corresponding to the degree of actuation of the mechanical control, the additional pressure in the feedback chamber 323 pushes the plunger to put the channel T in communication with the channel F and decrease the pressure in the brake.

The pressure in the line F is therefore regulated regardless of the flow rate through F, as long as the flow capacity of the pump is not reached, that is to say as long as the pump can provide the flow rate consumed by the circuit connected to line F.

Thus the pressure in the track F and in the braking device 14 is regulated at any time as a function of the degree of actuation of the brake control. This regulation is understood when the brake lining is physically supported or not on its disk or on its drum, when there is a pressure on the mechanical control or when it is released, that the brake is in movement, it is that is to say dynamically moving, or static, that is to say without movement. Each position of the lever 30, 310 or the brake pedal therefore corresponds to a defined pressure.

In this embodiment, it is the very operation of the valve that makes it possible to obtain this pressure regulation by feedback shown schematically in the figures by line 36.

Alternatively, the operation of the valve 28 could be replaced by an electric feedback 36 controlling the valve as a function of a pressure value measured in the braking device by a dedicated sensor. Manual defreinaoe and additional order

In the case where the two previous variants are implemented, as illustrated in FIG. 8, the additional control is connected directly to the brake device 14 and the manually-controlled brake release valve 20 is connected directly to the brake release valve 4. Thus, from upstream to downstream, there is: the pressure source 1, the brake release valve 4, the manual brake release valve 20, the manually operated progressive valve 28, the brake device 14.

Accumulator

When the pressure source 1 is an accumulator, a recharging circuit is provided, for recharging the accumulator when the pressure is below a given threshold or for injecting oil into the circuit, following the losses related to the release of the device 14. The recharging circuit may include a circuit-breaker. The recharging circuit is connected to the supply line 10. This recharging circuit 32 may comprise pressure alert means, which indicate to the vehicle operator or to the electronic control unit (ECU) 2 whether the pressure in the supply line 10 is below a given threshold. Figure 9 schematizes this embodiment.

For example, if the manual brake release valve 20 is in the second position and the brake release valve 4 is in the first position, the accumulator 1 is sent directly to the vacuum, which causes a pressure drop.

Advantageously, the recharging circuit 32 can close the accumulator to prevent its discharge, for example if the warning means have detected a pressure drop. Therefore, the warning means thus advantageously make it possible to indicate to the operator or to an ECU 2 in which position is the manually controlled brake release valve 20.

The recharging circuit 32 is generally connected to the main circuit by a nonreturn valve 34.

Process

The device as presented can be used in the case of a hill start. To this end, a torque sensor, disposed either on the axle or at a motor mounted on the axle, to know the available torque. The processing unit 2 is then configured, when the vehicle is at a standstill, to transmit to the brake release valve 4 a passage control in the first position as soon as the available torque makes it possible to overcome the weight of the vehicle.

More generally, a method of using said device is defined, wherein the electronic control unit 2 generates a position change control of the brake release valve 4.

Claims (15)

claims A vehicle braking system comprising: a pressure source (1) configured to pressurize fluid, a supply line (10) connected to the source (1), a braking device (14) operable hydraulically and configured to brake a rotatable member when no hydraulic pressure is applied and to release the rotating member when hydraulic pressure is applied, a braking line (12) connected to the braking device (14), a release valve (4) connected to the pressure source (1) by the supply line (10) and connected to the device (14) by the braking line (12), said valve comprising: a first position, connecting the supply line (10) at the braking line (12), a second position, connecting the braking line (12) to a no-load output (16), at least one electrically-controllable actuator (8), characterized in that: the system comprises at least one di mechanical position holding spositive (18) of the brake release valve (4) for mechanically holding the brake release valve (4) in first and second positions, said actuator (8) is configured to move the valve (4) the first position at the second position and the second position at the first command position of an electronic control unit (2). 2. System according to claim 1, wherein the first position of the brake release valve (4) closes the unbraked release output (16), the second position of the brake release valve (4) closes the brake line. power supply (10). 3. System according to any one of the preceding claims, wherein the one or more mechanical holding devices (18) are electrically controlled to release and activate a mechanical support. 4. System according to any one of the preceding claims, wherein the brake release valve comprises two actuators (8, 8 '), each of which is configured to switch from one position to the other, said actuators being controllable by a unit. electronic control device (2), and wherein the at least one mechanical holding device (18) comprises two elements, each element being configured to mechanically maintain one of the two positions. 5. System according to any one of the preceding claims, comprising: a manual brake release pump (22), a manually operated valve (20) located on the braking line (12), said valve comprising: a first passing position connecting the release valve (4) to the braking device (14) via the braking line (12), a second position connecting the brake release valve (4) to a vacuum output (21) and connecting the braking device ( 14) to the hand pump (22). A system according to any one of the preceding claims comprising: a manually operated valve (28) disposed on the braking line (12) and comprising a mechanical control (30, 310), said manually operated valve for controlling the pressure in the braking device (14) according to a stroke of said mechanical control, said activation of the mechanical control (30, 310) for decreasing the pressure in the braking device to activate the braking. 7. System according to the preceding claim, wherein the manually operated valve (28) comprises an inlet / outlet port connected to the respective source of pressure, an inlet / outlet port connected to a reservoir, and a port d an inlet / outlet connected to the braking device (14), the manually operated valve (28) being adapted to selectively connect the inlet / outlet port connected to the braking device (14) to one or the other other ports, depending on the pressure in the braking device and the degree of actuation of the control. 8. System according to any one of the preceding claims comprising a safety nozzle (24) connected to a sampling point on the supply line (10) or braking (12). 9. System according to any one of the preceding claims wherein the pressure source (1) is an accumulator and comprising an upstream circuit (34) having: • a charging circuit of the pressure source (1) connected to the line power supply (10), • warning means (32), configured to signal a pressure drop in the supply line (10), the charging circuit being configured to recharge the accumulator under pressure and to block the accumulator and prevent it from emptying when a pressure drop is detected. 10. System according to claim 5, further comprising a disengageable hydraulic motor, a booster pump configured to engage said engine by pressurization, wherein the pressure source is the booster pump, so that the clutch of the engine is not possible if the manual valve is in second position. 11. An assembly comprising a system according to any one of the preceding claims and an electronic control unit (2) configured to control in particular the actuator (s) (8, 8 '). 12. An assembly according to the preceding claim wherein the electronic control unit (2) is configured to maintain the brake release valve (4) in the first position based on data relating to the engine torque of the vehicle as the acceleration does not allow to compensate for the slope, thus enabling a hill start. 13. Vehicle comprising an assembly according to claim 11 or 12. 14. A method of braking an assembly according to claim 11 or 12 or a vehicle according to claim 13, comprising a step of generating by the electronic control unit (2) a position change instruction of the brake release valve 4. 15. The method of claim 14 for performing a hill start by a vehicle, wherein the electronic control unit (2) sends a switching command of the valve (4) in the first position to brake the vehicle, then sends a valve switching instruction (4) in second position once a threshold vehicle engine torque is detected, in order to perform a hill start.